One of the most interested aspects in the development of optical coherence tomography (OCT) is to construct a stable and easy fabricated optical delay line that can perform real-time imaging for clinical applications. There are many methods that have been used for fast scanning in OCT. However, most of the configurations are difficult to construct or variational intensity loss exists during the scanning because of the walk-off of different wavelength components and different tilted angle of the scanner. We proposed and constructed an optical delay line with all reflective components that is compact, easy to fabricate and can avoid the intensity loss during the scanning. The optical delay line was constructed of a retro-reflector fabricated with two right-angled prisms assembled on an aluminum jig, a reflection mirror and a galvoscanner. The size of the optical delay line is within 2 cm x 2 cm and the system can provide a scanning rate in the kilohertz range. The achieved imaging depth is 3.3 mm when the vibration angle of the scanning mirror is ±9°. This system can perform a real-time scanning and thus is supposed suitable for clinical applications.

Optical Coherence Tomography (OCT) is a fundamentally new type of optical imaging technology. OCT performs high resolution, cross-sectional tomographic imaging of the internal structure in materials and biological systems. The biomedical applications of the OCT imaging systems have been developed for diagnostics of ophthalmology, dermatology, dentistry and cardiology. Most of existing OCT systems use point-scanning based technology, however, the 3-axis scanning makes the system slow and cumbersome. A few OCT systems working directly on 2D full-field images were reported, however, they are designed to work in a relatively small area, around couple of hundred microns square. In this paper, we present a design and implementation of a full-field OCT imaging system for acquiring tomography and with a working area around 15mm by 15 mm. The problems rising from full-field OCT are addressed and analyzed. The algorithms to extract the tomography are proposed. Two applications of multilayer information retrieval and 3D object imaging using full-field OCT are described.

Incipient dental caries lesions appear as white spots on the tooth surface; however, accurate detection of early approximal lesions is difficult due to limited sensitivity of dental radiography and other traditional diagnostic tools. A new fibre-optic coupled spectroscopic method based on polarized Raman spectroscopy (P-RS) with near-IR laser excitation is introduced which provides contrast for detecting and characterizing incipient caries. Changes in polarized Raman spectra are observed in PO₄ ^3- vibrations arising from hydroxyapatite of mineralized tooth tissue. Demineralization-induced morphological/orientational alteration of enamel crystallites is believed to be responsible for the reduction of Raman polarization anisotropy observed in the polarized Raman spectra of caries lesions. Supporting evidence obtained by polarized Raman spectral imaging is presented. A specially designed fibre-optic coupled setup for simultaneous measurement of parallel- and cross-polarized tooth Raman spectra is demonstrated in this study.

Determining the viability of damaged or surgically reconstructed tissue is critical in most plastic and reconstructive surgery procedures. Information about tissue blood flow in the region in question can make this determination much easier. Laser speckle imaging (LSI) is one technique that could potentially aid in making this determination. LSI is a non-contact full-field imaging technique with simultaneous high spatial and temporal resolution. Tissue is illuminated with diffuse red laser light and the spatial and/or temporal statistics of the resulting speckle pattern can be used to calculate relative flow velocities. We have developed a LSI system that produces relative velocity blood flow images. Bench tests of the system indicate that it may be used to distinguish between normal, decreased, and increased blood flow states of a human finger. The system has also been used to take some initial laboratory measurements using an animal model - an epigastric free flap on a rat. Preliminary results indicate that the method may be used to distinguish states of venous or arterial occlusion from unoccluded states of the skin flap. While further experimentation is necessary, these initial results indicate that LSI could be a useful aid to the plastic surgeon for assessing tissue viability.

Photodynamic Therapy (PDT) is a relatively novel oncological treatment modality, in which a patient is administered a photosensitive drug, called a photosensitizer. After allowing sufficient time for biodistribution, the cancerous area is irradiated with light of the appropriate wavelength, activating the photosensitizer to produce highly reactive singlet oxygen, which produces a highly localized cell kill. The efficacy of PDT is determined by a) the intensity of the light b) the local concentration of the photosensitizer, and c) the availability of oxygen. However, with the clinical application of PDT, the patient is simply administered a body mass dependent quantity of photosensitizer, and then the target area is administered a prescribed amount of radiant energy (joules per cubic centimetre). For treatment of superficial malignancies, PDT has many successes; however, interstitial PDT (PDT of solid, internal malignancies) has inconsistent outcomes mostly due to the inability to predict, calculate or measure the variables that affect PDT: the radiation dose, oxygen concentration, and the photosensitizer concentration. We have developed sophisticated methods to determine the behaviour of light in homogeneous biological tissues. Tissue oxygen levels can be replenished by fractionating the light dose - allowing areas of your target tissue to go through a "dark" cycle during PDT. However, to date, there has not been an accurate method of determining tissue photosensitizer concentrations in-vivo. We are researching the efficacy of a novel hypocrellin derivative, SL-052. Like other photosensitizers available, SL-052 shows strong therapeutic photodynamic activity when irradiated by 635 nm light. Like most photosensitizers, SL-052 exhibits fluorescent activity, but SL-052 also shows strong fluorescent emission at 725nm when excited by 635 nm. The intensity of the fluorescent emission can been correlated with the local concentration of the photosenstizer. However, many clinically available photosensitizers require that fluorescence is excited using a wavelength of light much shorter than the therapeutic wavelength. This characteristic allows us to monitor the availability of the photosensitizer during PDT and to correlate the outcome of PDT to the observed fluorescence. In this paper, we monitor the temporal distribution of SL-052 in the Dunning R3327-AT cell line grown on the flank of a Fisher Copenhangen rats.

Age related macular degeneration (AMD) is a major cause of severe vision loss in the older population, due to ingrowth of new leaky blood vessels (neovasculature) from the choriocapillaris, which results in destruction of photoreceptors in the fovea and loss of central vision. "Standard" one-photon (1-γ) photodynamic therapy (PDT) using Visudyne^(R) is an approved method of AMD treatment but has the potential to damage healthy tissues lying above and below the neovasculature due to photosensitizer accumulation and its wide-beam 1-γ excitation. Highly-targeted two-photon (2-γ) excitation may avoid this, since, due to its non-linear intensity dependence, the probability of 2-γ excitation is greatest in the focal plane, which intrinsically avoids out-of-focus damage to healthy tissues. The aim of the present study is to evaluate the 2-γ efficiency of Visudyne and to compare it to the archetypal photosensitizer Photofrin^(R). Since neovascular endothelium is targeted in AMD, an endothelial cell line (YPEN-1) was selected as the in vitro model. 2-γ PDT was delivered using tightly focused ~300 fs laser pulses from a Ti:sapphire laser operating at 850 nm with 90 MHz pulse repetition rate. An assay was developed for quantification of the cellular damage using the permeability stain Hoechst 33258 and the viability stain SYTOX. Visudyne (LD₅₀= dose to kill 50% of cells: 500 J/cm², 10 M, 7.2 μg/ml) was about an order of magnitude more effective than Photofrin (LD50 : 7500 J/cm², ~42 μM, 25 μg/ml). We also demonstrate for the first time the quadratic dependence of the cellular response to 2-γ PDT. This in vitro work will lead to the design of optimized in vivo studies in animal models of AMD.

Nonlinear microscopy is a very attractive tool for studying photosynthetic organisms on cellular and subcellular levels. The multimodal microscope can be employed to image photosynthetic structures simultaneously with multiphoton excitation fluorescence (MPF), second harmonic generation (SHG), and third harmonic generation (THG) contrast mechanisms. Although the multimodal nonlinear microscope delivers invaluable information about the structure, spectroscopic properties, and functional dynamics of photosynthetic systems, the prompt light-induced changes of highly light sensitive pigment-protein complexes complicate the extensive study of photosynthetic organisms. In this work, we investigated the extent of light-induced changes in chloroplasts from higher plants by imaging with a Ti:Sapphire femtosecond laser and a Yb-ion doped potassium gadolinium tungstate (Yb:KGW) femtosecond laser. The Ti:Sapphire laser delivered 800 nm wavelength and ~25 fs duration pulses at a 26.7 MHz repetition rate. In comparison, the Yb:KGW laser provided a 1042 nm wavelength, ~200 fs pulses at a repetition rate of 14.6 MHz. The 800 nm pulses predominantly excited chlorophyll pigments via two-photon excitation, while 1042 nm excitation resulted in two-photon absorption of carotenoids. The induced fluorescence quenching, and decrease in SHG and THG signal was much stronger when imaged with a Ti:Sapphire laser. Prolonged imaging of up to tenths of minutes with the Yb:KGW laser did not result in appreciable changes of all three nonlinear signals. The difference in the light-induced changes most probably appears due to the difference in excited state dynamics following chlorophyll or carotenoid excitation. The slow component of MPF and THG changes as well as change in SHG reflects the light-induced macroorganization of the grana, while the fast MPF and THG component is tentatively attributed to the generation of quenchers from chlorophyll molecules. The success in imaging photosynthetic samples for prolonged periods of time with a Yb:KGW laser opens a new window of opportunity for thorough in vivo investigations of photosynthetic structures.

The functional dynamics and structure of both larval and adult Drosophila melanogaster muscle were investigated with a nonlinear multimodal microscope. Imaging was carried out using a home built microscope capable of recording the multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation signals simultaneously at a scanning rate of up to ~12 frames/sec. The sample was excited by a home built femtosecond Ti:Sapphire laser at 840 nm, or by a Yb-ion doped potassium gadolinium tungstate (Yb:KGW) crystal based oscillator at 1042 nm. There was no observable damage detected in the myocyte after prolonged scanning with either of the lasers. Microscopic second harmonic generation (SHG) appears particularly strong in the myocytes. This allows the fast contraction dynamics of the myocytes to be followed. The larger sarcomere size observed in the larvae myocytes is especially well suited for studying the contraction dynamics. Microscopic imaging of muscle contractions showed different relaxation and contraction rates. The SHG intensities were significantly higher in the relaxed state of the myocyte compared to the contracted state. The imaging also revealed disappearance of SHG signal in highly stretched sarcomeres, indicating that SHG diminishes in the disordered structures. The study illustrates that SHG microscopy, combined with other nonlinear contrast mechanisms, can help to elucidate physiological mechanisms of contraction. This study also provides further insight into the mechanisms of harmonic generation in biological tissue and shows that crystalline arrangement of macromolecules has a determining factor for the high efficiency second harmonic generation from the bulk structures.

We wish to deliver Two-Photon Excitation (TPE) to the in vivo retina and to image its effects in order to understand and treat eye disease. A schematic model of the rat eye with a gradient refractive index in the crystalline lens is reconstructed in ZEMAX^TM. This model predicts the monochromatic aberrations as a function of pupil size and field angle and the change in the Point Spread Function (PSF) at best focus. A simple water model of the nonlinear pulse broadening effect has been used to predict the minimal temporal pulse width that will propagate to the retina. In a rat eye uncorrected for monochromatic aberrations, a pupil between 1mm and 1.8mm diameter delivers a peak intensity acceptable for two-photon effects. A somewhat larger diameter pupil (1.35-2.0mm) gives an optimum optical quality for imaging on the optical axis. Correction of the monochromatic aberrations with adaptive optics would improve both imaging and peak intensity. The effect of second order dispersion is dependent on the form of the dispersion relation used. Based on experimental results of second order dispersion, the minimum pulse width to reach the retina is approximately 30fs for the rat eye and approximately 60fs for the human eye.

The ability of cells to sustain mechanical stress is essential. It is however not very well understood how tension is expressed from the inside of the cell to the exterior. Here we show that these forces can be measured by photonic force microscopy (PFM), which is able to apply a force to cells and to probe their response to the physical stress. Our setup consists of an inverted microscope coupled with an optical trap from a 5W ND:YVO₄ fiber laser. Forces are applied to the cell by the trap through a 5μm polystyrene bead coated with fibronectin, pre-incubated with cells to allow bead attachment and creation of focal adhesions. The reaction of the cell is monitored by sensing the position of the bead relative to the trap center by a quadrant photodiode, when the bead is in an equilibrium state between the photonics forces and the membrane elasticity and cell stiffness. The detection system is calibrated using a piezo nano-positioner and thermal noise analysis. We observed increased deformation of H4 cells treated with cytocholasin D, which disrupts the actin microfilaments. This observation is correlated to an overall decrease in the force by the photonics force microscope. Our results suggest that cell stiffness can be assessed by the PFM, which allows quantification of a tension within cells with sufficient precision.

The various ions present in the extra- and intracellular mediums, such as potassium, occupy an important role for many biological phenomena. So far, biologists and electrophysiologists have been working hard to understand the role of several ions in cellular behaviors. Our objective is to measure ionic concentration fluctuations using a tapered optical (fiber) guide and an ionic indicator. The optical cylindrical waveguides are tapered to a final diameter of 10 micrometers. The resulting probes are first used to transmit excitation light (349 nm wavelength) into the solution, and then, they are used to collect a potassium indicator (PBFI) fluorescence. The indicator emission depends on the potassium concentration and, by monitoring this fluorescence, a correlation can be made with the potassium current. Two types of optical waveguides have been studied: a multimode fiber optic (Thorlabs FG-200-UCR) and a borosilicate capillary (generally used as an electrophysiological electrode). Results show that concentration fluctuations in the order of 10 mM can be monitored using tapered optical guides. However the signal to noise ratio and the sensing repeatability are requiring further improvements. Thus, tapered optical waveguides can be used as ionic sensors. It has been demonstrated that sensors as small as 10 micrometers are sensitive to concentration fluctuations. Optical indicators are widely used in microscopy and they offer many possibilities in terms of their specificity (for ions as well as for other particles). Thus optical fibers, by guiding the light into deep regions, allow for the use of optical indicators in vivo.

Thermal lens microscope (TLM) is a kind of absorption spectrophotometry based on photothermal phenomena of non-fluorescent molecules. TLM has high sensitivity (single molecule concentration in fL detection volume) and wide applicability (non-fluorescent molecules). TLM was successfully applied to detection on microchip in clinical diagnosis, environmental analysis, single cell analysis and so on. The basic function of TLM is concentration determination in microspace. In addition, we have realized various functions on TLM for sensitive chiral analysis, individual nanoparticle counting and in situ flow sensing. In this presentation, we explain these functional TLMs for microchip chemistry.

In this paper, we present a compressive and complete mathematical description of the photonics force distribution on a spherical cell surface in optical stretcher. Using the ray tracing model, we demonstrate that the forces are always perpendicular to the surface and describe the apparition of a peak and a discontinuity in the force distribution that was not previously revealed. Besides, we present a better approximate fitting of the stress distribution by polynomials of powers of cosines as a function of physical parameters and the ratio between the FWHM of the Gaussian beam and the cell's radius. The fitting of the force distribution is required for analyzing the cell's deformation.

We constructed a dynamic spectroscopy system that can simultaneously measure the intensity and spectral distributions of samples with multi-fluorophores in a single scan. The system was used to monitor the fluorescence distribution of cells infected by the virus, which is constructed by a recombinant baculoviruses, vAcD-Rhir-E, containing the red and green fluorescent protein gene that can simultaneously produce dual fluorescence in recombinant virus-infected Spodoptera frugiperda 21 cells (Sf21) under the control of a polyhedrin promoter. The system was composed of an excitation light source, a scanning system and a spectrometer. We also developed an algorithm and fitting process to analyze the pattern of fluorescence distribution of the dual fluorescence produced in the recombinant virus-infected cells. All the algorithm and calculation are automatically processed in a visualized scanning program and can monitor the specific region of sample by calculating its intensity distribution. The spectral measurement of each pixel was performed at millisecond range and the two dimensional distribution of full spectrum was recorded within several seconds. We have constructed a dynamic spectroscopy system to monitor the process of virus-infection of cells. The distributions of the dual fluorescence were simultaneously measured at micrometer resolution.

We model the photocurrent of an A-scan in time-domain optical coherence tomography (OCT) as a non-stationary random process and obtain its statistics. We use this model to obtain a maximum likelihood estimate of the reflectivity at different depths of an object. We also present an expression for the Fisher information matrix in time-domain OCT.

Optical Coherence Tomography is an imaging technique for capturing three-dimensional images of weakly scattering sample¹. At the core of this technique are an interferometer with low temporal coherence and an optical delay line for in depth movement of the coherent gate. The interferometeric setup has to be robust and with high signal-to-noise ratio. Fiber-optic implementation of the interferometer has the advantages of being rugged, compact and by using SM fiber yields minimal scattering into higher-order modes. On the other hand large bandwidth required for light sources cannot be accommodated by the fiber optic components usually design for a smaller bandwidth. The Michelson configuration is widely used as an interferometric platform with OCT application.

Bacterial and viral pathogens are implicated in many severe autoimmune diseases, acting through such mechanisms as molecular mimicry, and superantigen activation of T-cells. For example, Helicobacter pylori, well known cause of stomach ulcers and cancers, is also identified in ischaemic heart disease (mimicry of heat shock protein 65), autoimmune pancreatitis, systemic sclerosis, autoimmune thyroiditis (HLA DRB1*0301 allele susceptibility), and Crohn's disease. Successful antibiotic eradication of H.pylori often accompanies their remission. Yet current diagnostic devices, and test-limiting cost containment, impede recognition of the linkage, delaying both diagnosis and therapeutic intervention until the chronic debilitating stage. We designed a 15 minute low cost 39 antigen microarray assay, combining autoimmune, viral and bacterial antigens¹. This enables point-of-care serodiagnosis and cost-effective narrowly targeted concurrent antibiotic and monoclonal anti-T-cell and anti-cytokine immunotherapy. Arrays of 26 pathogen and 13 autoimmune antigens with IgG and IgM dilution series were printed in triplicate on epoxysilane covalent binding slides with Teflon well masks. Sera diluted 1:20 were incubated 10 minutes, washed off, anti-IgG-Cy3 (green) and anti-IgM-Dy647 (red) were incubated for 5 minutes, washed off and the slide was read in an ArrayWoRx(e) scanning CCD imager (Applied Precision, Issaquah, WA). As a preliminary model for the combined infectious disease-autoimmune diagnostic microarray we surveyed 98 unidentified, outdated sera that were discarded after Hepatitis B antibody testing. In these, significant IgG or IgM autoantibody levels were found: dsDNA 5, ssDNA 11, Ro 2, RNP 7, SSB 4, gliadin 2, thyroglobulin 13 cases. Since control sera showed no autoantibodies, the high frequency of anti-DNA and anti-thyroglobulin antibodies found in infected sera lend increased support for linkage of infection to subsequent autoimmune disease. Expansion of the antigen set with synthetic peptide sequences should reveal the shared bacterial/human epitopes involved.

Optical coherence tomography (OCT) is an emerging medical diagnostic technology for noninvasive in situ and in vivo cross-sectional morphological imaging of transparent or nontransparent biological tissues and materials on a micrometer scale. The technique uses low coherence interferometry to extract the intensity of the reflected signal as a function of penetration depth in the sample and is analogous to ultrasound except that much shorter wavelength infrared radiation is used rather than sound waves. Among the key enabling technologies for OCT systems are high-power, broadband optical sources (BBS). Such sources are required to provide large dynamic range and sensitivity, as well as very high axial resolution. In this paper, we present our ongoing work on developing BBS based on the amplified spontaneous emission (ASE) from semiconductor optical amplifiers (SOAs) and erbium-doped fiber amplifiers (EDFAs). We target sources spanning the S, C, and L bands, with milliwatts of output power and smoothly shaped output spectra. In terms of shaping the output spectra, we consider different designs of gain flattening filters based on side-tapped fiber Bragg gratings (FBGs) as well as specially apodized FBGs operating in transmission. In terms of the source development, we have developed strained multiple-quantum well SOAs and hybrid SOA-EDFA structures. In the hybrid structures, we have also investigated the possibility of exploiting the unused ASE from the SOA as a secondary input to the L-band EDFA. We have also explored techniques such as double-passing to enhance efficiency as well as gain-clamping to provide some inherent spectral flattening.

Energy absorption and heat transfer are important factors for regulating the effects of ablation of biological tissues. Heat transfer to surrounding material may be desirable when ablating hard tissue, such as teeth or bone, since melting can produce helpful material modifications. However, when ablating soft tissue it is important to minimize heat transfer to avoid damage to healthy tissue - for example, in eye refractive surgery (e.g., Lasik), nanosecond pulses produce gross absorption and heating in tissue, leading to shockwaves, which kill and thin the non-replicating epithelial cells on the inside of the cornea; ultrafast pulses are recognized to reduce this effect. Using a laser system that delivers 1ps pulses in 10μs pulsetrains at 133MHz we have studied a range of heat- and energy-transfer effects on hard and soft tissue. We describe the ablation of tooth dentin and enamel under various conditions to determine the ablation rate and chemical changes that occur. Furthermore, we characterize the impact of pulsetrain-burst treatment of collagen-based tissue to determine more efficient methods of energy transfer to soft tissues. By studying the optical science of laser tissue interaction we hope to be able to make qualitative improvements to medical treatments using lasers.

We report on the experimental demonstration of a fiber-based chirped-pulse amplification system using a dispersion shifted fiber as stretcher, an electro-optic modulator for frequency division, two erbium-doped fiber amplifiers (a single mode and a large mode area) and a grating pair pulse compressor. We obtained 500-nJ pulses at a repetition rate of 1 MHz. Pulse duration was under 500 fs, which is in part due to the fine control of the beam polarization maintained throughout the system.

We developed a model that accurately predicts the performances of high power double cladding erbium ytterbium fibre amplifiers. We experimentally validate the model in co- and counter-propagation configuration for different pump wavelengths and fibre lengths. By adjusting the ytterbium to erbium cross-relaxation rate with a simple amplifier experiment, we obtained a complete agreement between the model predictions and the experimental data regarding the output signal. We measured that the McCumber relationship considerably overestimates the ytterbium emission crosssection; with a correction of this parameter, we obtained an excellent prediction of the ytterbium spontaneous emission at 1.0 μm. The model is valid for high power singlemode amplifiers as we obtained a full agreement for a 4W output power amplifier from a seed signal of 8 mW at 1556nm. The output was diffraction limited with a measured M² parameter of 1.03 without doing any mode selection from a slightly multimode fibre with a core diameter of 10 μm and a numerical aperture of 0.18.

We present current work developed at INO on phosphate glass optical fiber for laser and amplifier applications at 1.54 microns. Core and cladding glasses were fabricated by a multi-components melting process which gave an uniform refractive index core profile. Rod-in-tube method under Argon atmosphere was used to fabricate optical fibers. The effect of nitrogen atmosphere on hydroxyl groups OH^- during glass melting was studied. The absorption coefficient calculated at 3.42 μm was found to be lower than 0.5 cm^-1 which corresponds to less than 70 ppm OH^-. Absorption and emission cross sections were calculated at 1534 nm. Fabrication process allowed us to decrease background losses of core Er³⁺ - Yb³⁺ co-doped fiber between 0.02 and 0.04 dB/cm. Laser power was measured at 1563 nm and a 26% slope efficiency was achieved with a 22 cm-long single-clad fiber co-doped with 1.1 wt% in Er³⁺ and 11.1 wt% in Yb³⁺. For the same fiber, an internal gain was found to be 20 dB at 1536 nm for a 5-cm-long fiber.

Steady ultrashort bit pulses, originating in single-mode erbium-doped fiber amplifiers, are analytically investigated. This type of steady bit carriers can be grown in real time scale due to resculpturing external optical pulses incoherently by fiber amplifier in the traveling-wave regime. The analysis performed is related to the regimes without and with the gain saturation in a doped fiber and demonstrates that single-mode fiber amplifiers can form and support in these regimes steady bit pulses in the form of bright solitons. For both the regimes, the amplitude and frequency distributions are estimated, and the impact of the gain saturation is revealed.

This paper presents an analysis of how to calculate bit error ratio (BER) with physical explanation for optically pre-amplified DPSK receivers using optical Mach-Zehnder interferometer (MZI) demodulation and balanced detection. It is shown that BER calculation method for this kind of receivers is different from the conventional calculation method used widely for IM/DD receivers. An analytical relationship in receiver sensitivity between DPSK receivers using MZI demodulation with balanced detection and IM/DD receivers (or DPSK receivers using MZI demodulation and single-port detection) is given based on the Gaussian noise approximation. Our calculation method correctly predicts the 3-dB improvement of receiver sensitivity by using balanced detection over single-port detection or IM/DD receivers. This predicted 3-dB improvement by using balanced detection converges with the interpretation of the 3-dB improvement by signal constellation. Furthermore, quantum-limited DPSK receivers with MZI demodulation are also analyzed in Appendix B.

We have developed and prototyped C+L band erbium-doped fiber ASE source by making use of both forward and backward ASEs with double-pass configuration. Simulations and experiments are performed for different pump powers and fiber lengths to optimize the design. The spectrum bandwidth of 80.6nm (1526.7~1607.3nm) with flatness of 5.22dB is realized. Pumping-conversion efficiency of about 18.9% is reached. This C+L band light source will be used to extend illuminating bandwidth of the high-speed interrogator which has been prototyped and been used by different clients. The sampling rate can be up to 5 kHz. The broadband light source allows the interrogator no moving part that enables high-speed FBG sensor interrogation.

A novel SOA based fibre ring laser is presented. An S-band optimized SOA is added to the cavity of a C-band SOA fibre ring laser resulting in significant improvements in the ring laser characteristics. Three main linewidth control parameters are identified: 1) Bias current of C-band SOA, 2) Bias current of S-band SOA, and 3) SOP of lasing light in ring's cavity. Experimental measurements suggest the SOP of the lasing light to be the dominant control parameter for reduction or enhancement of the laser's linewidth. An output power level of 5.27 dBm (corresponding to 10.54 dBm cavity power) and less than 20 kHz FWHM (limited by equipment resolution) and 190 kHz 20-dB linewidth at 1558 nm is demonstrated. The measured 20-dB linewidths displayed stronger variations to changes in the bias currents of the ring lasers compared to variations in the FWHM. This suggests that the optical spectrum of the ring lasers becomes asymmetric at high bias currents and is no longer pure Lorentzian.

Modeling of a hybrid semiconductor external-cavity laser with an intra-cavity saturable absorber is presented. In this paper the simulations are based on a modified transmission line laser model for an external fiber grating laser. The designed model of a DFECL takes into account time-domain evolution of the dynamic grating due to the standing wave in the external cavity and high-power bleaching of the doped-fiber absorption. In contrast to the previous models of such a hybrid laser, here the properties of the dynamic grating strongly depend on the internal power inside the cavity, which causes the absorption bleaching. Modeling results of lasers at 980 nm and 1490 nm are presented.

Chirped Pulse Amplification (CPA) is widely used for generating high-energy femtosecond pulses. This is most commonly done with a solid-state Ti:Sapphire crystal through a free-space optical path. The high energy density in the crystal and the precise optical path required with the use of bulk optics make it difficult to design a simple system with good stability and beam quality over the environmental conditions typically encountered in the manufacturing environment. A CPA system using fiber architecture reduces the need for precise beam guiding since the light follows the fiber. The pump energy is more evenly distributed along the length of the amplifier fiber, reducing the thermal dissipation that is required (no water chiller is required) and improving the overall efficiency. The fiber architecture also produces a superior quality beam that does not require great care to maintain. IMRA's latest FCPA μJewel uses the inherent advantages of the FCPA architecture, along with extensive engineering, to produce a compact and stable femtosecond fiber laser system. Its high repetition rate and stable performance enables applications that were difficult to achieve previously. This paper will review the general design architecture of the FCPA μJewel and discuss several applications.

It is shown that the introduction of an adiabatic taper at the output end of a large-mode-area fiber amplifier can greatly improve the beam quality factor of the single-mode output beam when the core refractive index profile departs from an ideal step-index distribution. The deleterious impact of higher-order modes is also analyzed.

We have developed optical fibers with a very thin Lithium Niobate Layer at the glass core glass cladding boundary it is observed that the Lithium Niobate Cylinder Fibers have a large strain induced light loss of about 2.12784 x 10^-5 per kg per m. These fiber can be used as strain sensors operating in an amplitude mode rather than in the phase detection mode as is the case for strain sensors using standard Single Mode Fibers.

In this work, the problem of propagation of ultrashort optical solitons through a non-linear optical fiber is investigated in the joint Time-Frequency (TF) domain using optimized representations [i.e. Wigner-Ville (WV) Distribution or WV-Spectrograms with reduced cross-term interferences]. Based on these optimized representations, complete numerical simulations for nonlinear propagation of solitons were carried out. In particular we have analyzed the evolution of second and third order solitons and soliton interaction in optical fibers using joint TF representations.

The stimulated Brillouin scattering (SBS) is a major limitation of maximum output power extracted from a high-power fiber laser. Compared with the SBS in passive optical fibers, the formation and evolution of the Brillouin-Stokes waves in Q-switched fiber lasers are more complicated. In this work, the stochastic characteristics of the SBS pulses generated in Q-switching processes were investigated experimentally and theoretically. In the experiments, we measured the temporal and spectral outputs of a Q-switched ytterbium-doped double-clad fiber laser; while in the theory, using the proposed theoretical model of the Q-switched fiber laser in conjunction with the SBS, we investigated the stochastic characteristics of the signal and Stokes pulses and showed their mutual conversions in Q-switching processes. The experimental and theoretical results are consistent with each other.

The ytterbium-doped large mode area triple-clad fiber design allows for a high concentration of ytterbium in the fiber core which is difficult to achieve with a standard double-clad design. The novelty of the triple-clad fiber design consists in adding to the double-clad fiber design, a first clad next to its core. This first clad offers a better control of the core effective area. With this design a low numerical aperture is achievable (~0.06) for highly rare earth doped large mode area fiber. A 33-μm core ytterbium doped fiber has been fabricated using MCVD and solution doping processes. Selective doping and optimized first clad thickness have been used in the triple-clad design to obtain a nearly bending insensitive and nearly diffraction-limited fiber output. The fiber has been tested in a free-running laser configuration and its slope efficiency is 84% with a laser threshold of 1.4 W. A maximum output power of 26 W at 1070 nm has been achieved for a launched pump power of 34 W at 976 nm. The mode-field diameter has been measured at 18 μm and the output beam M² quality factor is below 1.1. Both output power and beam quality were not significantly affected by fiber bending with loops diameter as small as 2.5 cm. The optical performance of the triple-clad fiber design is robust to mechanical stress and well suited for building very compact high power fiber lasers and amplifier sources.

A highly efficient and high power Raman fiber laser was developed based on the use of broadband Fiber Bragg gratings as optical couplers. The broadening of the Stokes signal is analyzed in both cases where the laser emission is restricted or not by the FBGs bandwidth. Since broadband fiber Bragg gratings are involved, the effects of cladding mode losses have to be considered. In order to reduce overall losses in the cavity, an optimal cavity configuration has been determined based on the physical orientation of the fiber Bragg gratings.

Lumped fiber Raman amplifiers (LFRAs) using highly nonlinear fiber (HNLF) are investigated and compared to using dispersion compensating fiber (DCF). It is shown that both the signal and amplified spontaneous emission induced multiple-path interferences are reduced in HNLF, thus for a same Raman gain a better noise performance of LFRAs using HNLF can be achieved compared to using DCF. It is found that noise figure over the C+L band can be improved by ~6.7 dB for a Raman gain of ~15 dB for a LFRA using HNLF compared to DCF with counter-pumping.

In this work, the influences of stimulated Raman scattering (SRS) on Q-switched fiber lasers are studied experimentally and theoretically. In the experiments, the SRS was investigated in the temporal and spectral domains based on an actively Q-switched ytterbium-doped double-clad fiber laser. In the theory, the dynamic characteristics of SRS in Q-switching processes were analyzed by solving a set of laser rate equations in combination with the SRS. With the aid of numerical simulation, the evolution of Raman pulses together with the laser pulses was traced in the fiber laser cavity. The SRS in Q-switched fiber lasers exhibits a few distinct features from those in high-power continuous-wave fiber lasers. A quantitative analysis of the SRS influences on Q-switched lasers is given in this paper, which is important to the design and optimization of Q-switched fiber lasers.

A 2.4 μm room-temperature continuous-wave Cr²⁺:ZnSe laser pumped by a Thulium Fiber Laser is experimentally investigated. The laser delivers up to 720 mW of output power with absorbed power slope efficiency of 52%. The laser is tunable from 2294 to 2678 nm. Gain-switching is also demonstrated by using a Pulsed Erbium Fiber Laser pump source. A maximum pulse energy of 0.36 μJ is achieved with an absorbed threshold of 0.28 μJ and an absorbed power slope efficiency of 41%.

This invited talk presents the most recent work undertaken in our laboratory in the fields of direct laser writing of planar optical integrated circuits, laser written micro fluidics circuits, laser machining of v-grooves and laser machining in diffraction gratings.

Deposition of a high refractive index (RI) overlay on long-period grating (LPG) was recently studied to enhance the sensitivity of LPG sensor to the surrounding ambient RI changes and offset the sensitive operational range of LPG RI sensor to low ambient RI. The enhancement mechanism relies on cladding mode reorganization due to the existence of the overlay. In this paper, the reorganization of the cladding mode in a cladding radius reduced LPG coated with high RI overlay is studied with full vector transfer matrix method. The dependence of the cladding modes effective indices on the fiber parameters and ambient RI is systematically investigated. Based on the simulation result, an LPG refractive index sensor optimization procedure is proposed, in which the grating period is set as an adaptive parameter and the cladding radius of the LPG is reduced. It is found that by using the proposed optimization method, the notch band corresponding to low order cladding mode resonance has higher sensitivity to the ambient refractive index. It is shown that an ambient refractive index sensitivity as large as 4012nm/RI can be achieved, representing a 3-fold sensitivity enhancement as compared to the best result obtained from the reported structure in which the high order cladding mode resonate notch wavelength was employed in sensing.

In this paper we describe and evaluate three novel types of fiber-optic sensors based on Photonic Crystal Fibers (PCFs) which have been developed recently at our Photonics Research Center at Universite du Quebec en Outaouais (UQO). Three different sensing mechanisms and, correspondingly, three different types of PCFs were employed to fabricate these devices. All three sensors displayed superior performance than similar sensors developed using standard optical fibers.

Multimode PMMA optical fibres with a cladding made from ion-selective membrane were designed, prepared, and investigated. Some were prepared by direct drawing of membrane-coated preforms and others were overcoated. Results obtained indicate loss of membrane sensitivity that is attributed to decrease of its ionic permeability. Absorbance of the fibre follows a modified Beer law as confirmed by rank analysis of series of spectra and explained by significant mode coupling within the fibre.

In this paper we report on the development of an optical biochip to control both the excitation and resultant fluorescence using grating coupled surface plasmons. Electron beam lithography is used to fabricate line gratings in thin layers of gold on the surface of 150μm thick coverslips. Laser diodes operating at 630nm are close coupled to the coverslip resulting in the excitation of surface plasmons. In the region of the grating light can radiate into the far-field, and both the angle of emission and beam divergence can be controlled by the grating pitch and the number of lines included in the pattern. A model is presented which treats the grating as an optical antenna array which shows how these characteristics can be explained in terms of the wave vector matching between the surface plasmons and the grating. Fluorescence has also been excited in standard organic dyes on-chip. When placed in close proximity to the surface of the sample strong quenching of the fluorescence is seen in the region of the grating. In contrast an enhancement of the signal is seen when the fluorophores are placed on a 200nm thick spacer layer.

Optical electric field sensors have been used for the measurement of high-voltages found in power substations. Typical sensors are based on electro-optic crystals and hence require the coupling of light into and out of the crystals from optical fibers. This coupling is difficult and costly. The objective of the work presented here is the design and implementation of an optical electric field sensor that uses an entirely fiber-based sensor-head. The sensor-head is comprised of a D-shaped optical fiber with its flat side coated with liquid crystals. D-fibers allow easy access to the evanescent optical field and replacement of part of the cladding with an external medium allows for modulation of this optical field. We are investigating the use of chiral Smectic A liquid crystals, which respond linearly to electric fields through the electroclinic effect. The propagation characteristics of the D-fiber for various distances between the fiber core edge and flat and for various refractive indices of the external medium are theoretically investigated and experimentally verified. Preliminary experimental results for a prototype electric field sensor are presented. The sensor responds in a linear fashion to an applied electric field.

In this paper, we show a whispering gallery mode coupler utilizing a side-tap structure. Here we choose a microsphere as the resonator. We fabricate this device by standard photolithography. Therefore, it is a on-chip optical device. The coupling efficiency can be as high as 26% by simulation. We fabricate the waveguide by photolithography to increase the stability and mechanical strength. In the end, we also check the physical tolerance and wavelength selectivity.

The linear electrooptical effect can be induced in silica fibers with the application of high voltage at a temperature 280°C. Active fiber devices can thus be constructed such as phase or amplitude modulators, polarization rotators and 2x2 switches. Progress on electrooptical fiber devices and applications will be reviewed in this paper.

A reflectance measurement technique was used to determine the refractive index distribution of optical waveguides fabricated by a CW CO₂ direct writing technique. The uniformity of refractive index has been verified along the waveguides structure and used as input for accurate beam propagation method (BPM) calculations of waveguide devices.

A new design of vertical coupler (VC) based on only a single mesa is presented. The newly proposed vertical coupler has the potential of improving the fabrication yield, as it requires much simpler fabrication process. The vertical coupler comprises a large underlying rib waveguide to which light is coupled. The lower waveguide is formed by the loading effect provided by the smaller upper ridge waveguide. The upper ridge waveguide contains the actual device (e.g. modulator or photodetector) and is tapered in a way to maximize the vertical transfer of light from the lower waveguide, and thus the vertical coupler can be used as a spot-size converter (SSC) between a single-mode fiber and the actual device. We investigate the transfer efficiency of the single-mesa vertical coupler with different configurations. The single-mesa design is found to give a lower total loss (i.e., fiber coupling loss plus transfer loss) compared with direct coupling to the actual device. The transfer efficiencies obtained are more than 90% for both TE and TM polarizations, and are polarization independent.

A highly efficient and accurate full-vector finite-difference mode solver is developed for calculation of both guided and leaky modes of circular symmetric optical fibers with high index contrast. To demonstrate and validate the mode solver, several examples, such as the guided modes of a silicon wire with a large index difference, the vector properties of guided modes in step-index fibers, as well as the quasi-guided and leaky modes in a Bragg fiber, are simulated.

In this paper, modulation crosstalk from 1310nm Distributed Feedback laser (DFB) upstream signals to 1490nm downstream signals in the monolithic integrated DFB-PD (Distributed Feedback laser-Photodiode) optical transceiver structure was simulated by the time-domain traveling wave (TDTW) rate equations numerically. It was found that high differential gain coefficient at 1490nm can contribute to the modulation crosstalk at about -25 to -30 dB. It was also found that the modulation crosstalk is modulation frequency dependent which will be enhanced about 3 dB at the relaxation oscillation frequency compared with low modulation frequency. Increasing modulation extinction ratio of the 1310nm DFB section from 10 to 18 dB, the crosstalk increases 3 dB. Such a higher modulation crosstalk (larger than -30 dB) should be considered since such crosstalk will degrade strongly the sensitivity of the 1490nm photo-detector.

We describe a planar waveguide structure with an air core and a slightly tapered silica etalon that accomplishes periodic chromatic dispersion compensation by using the properties of an antiresonant reflecting optical waveguide (ARROW) [3]. Theory predicts resonance peaks in the dispersion spectrum. With a 40-micron air core diameter and a cladding thickness tapering from 215.0 to 216.25 microns, a free spectral range of 4.93 nm was measured, in agreement with a 4.95 nm calculation. Dispersion measurements with an optical network analyser gave a dispersion of -24 ps/nm.cm, which is about five orders of magnitude higher than the dispersion of standard communications fibres. This result is in excellent agreement with the value -27 ps/nm.cm calculated with the help of the RSoft© simulation software.

We have designed and studied the fabrication limitations for a new type of optical waveguide filter based on the concept of a "Segmented Waveguide Array Grating" (SWAG, see refs. 1,2). The idea is to make an optical waveguide consisting of a large number of segments which differ from each other by their precise length and by a precise change in one of their transverse dimensions. The transitions between different segments are abrupt in the transverse dimension on the scale of one tenth the wavelength of light in the medium and are positioned with nanometer precision along the propagation axis of light. Reflections from a given subset of these transitions add up coherently and can give a grating-like reflection spectrum. By precisely positioning the segment transitions and by setting the variable transverse dimension at precise values one can design a large variety of filtering functions. As an example we have designed a filtering function that has a nearly rectangular profile, something that would be very useful in applications of WDM optical communications. The light scattering losses at segment transitions can be minimized by choosing average transverse dimensions such that the waveguide operates near the diffraction minimum. The lithography step of simple planar SWAG devices has been carried out by means of electron beam direct writing. The waveguide materials used were 6-micron thick silica/germania layers (index 1.454) spaced from a silicon substrate by a 14-micron thick pure silica layer. Trapped electron phenomena in the silica layer were eliminated by depositing metal layers on top of the silica in order to stop electrons traversing the photoresist. SWAG patterns with sharp features were obtained and are expected to give the expected spectral filtering functions.

In this paper, we demonstrate that three-dimensional integrated optical devices can be realized using the mirroring properties of multimode interference. Using numerical simulations, the minimum optical loss between 3μm singlemode waveguides in adjacent vertical layers is found to be 0.12 dB at an image distance of 211μm. An optical bridge is also demonstrated with an optical power loss of 0.24 dB in a total device length of 725μm.

This paper presents recent scheme based of direct dual wavelength laser writing of lightwave circuits developed in our laboratories. The system allows the fabrication of features of the order of ~1 micron by using a short wavelength laser to ablate a region preheated by a second laser.

We consider physical principles of realizing the Bragg regime of three-order scattering of light by acoustic phonons in birefringent media in specially elaborated case, when direct transitions between all the orders of scattering are allowed and, moreover, the probabilities of these transitions can be electronically controlled. The exact and closed analytical model with slightly mismatched wave numbers predicts sculpturing multi-pulse four-wave coupled states. Computer simulations for the spatial-frequency distributions of their optical components are performed. Thus, multi-pulse four-wave Bragg solitons, originating with a two-phonon non-collinear light scattering, are uncovered in periodic birefringent media providing direct transitions between all the light modes. The performed analysis is confirmed by the experimental studies.

The wavelength conversion technique based on the cascaded sum-frequency generation/difference-frequency generation (SFG/DFG) process has an advantage of no pump occupation in the communication band, compared to the mostly adopted second-harmonic generation (SHG)/DFG process. In the SFG/DFG-based wavelength conversion, two pump waves and a signal wave are required. The pulsed wave, as a carrier of information, can be applied to the signal or one of the two pump waves. Though the converted wave has the form of pulses, its temporal and spectral characteristics are dependent on the arrangement of the input pulsed wave. Based on numerical simulation, the temporal and spectral characteristics of the pump, signal, converted and sum-frequency waves during their propagations in PPLN waveguides are systematically investigated in this work. In particular, temporal pulse shapes, optical spectra and conversion efficiency are emphasized and compared when picosecond pulse trains are used as the signal and pump waves, respectively.

A novel wavelength converter using LiNbO₃ waveguide ring resonator is proposed and simulated. In the design, a new wavelength is generated by combining the second harmonic generation (SHG) and the difference frequency generation (DFG). The quasi-phase-matched condition is achieved by periodically domain inverted lithium niobate crystal. A waveguide ring and four 1x2 beam splitters/combiners are used to link the SHG and SFG structures. The 1x2 beam splitter/combiners are carefully designed so that only the SHG signal at λ=0.77μm can stay inside the ring while the pumping signal at λ=1.54μm, idler signal at λ=1.55μm, and the converted signal at λ=1.53μm can coupled into and out of the ring. Therefore, the SHG signal, served as intermediate pumping source for the DFG, keeps circulating inside the ring and form resonance to gain higher power and to achieve higher conversion rate. The detail design is described and the design concept is proved by the simulation results.

Periodically Poled Lithium Niobate (PPLN) components are very promising for the development of active photonic devices. Most of the PPLN devices currently fabricated are based on the use of z-cut wafers. We report on the fabrication of Periodically Poled Lithium Niobate on x-cut substrates by the application of a high electric pulse. The technique is taking advantage of the use of high voltage amplifier to generate the needed high voltage waveform. The shape of the pulse is controlled by feedback to maintain the poling charge constant. This approach makes the total charge independent from the electric field amplitude and the pulse duration. Using this system we show evidence that a long poling pulse improves the domains wall propagation in the forward direction e.g. from Z+ to the Z- side. We also observed an improvement of the quality of the inverted domains when controlling the poling current to a low constant value. High nucleation spike was also critical to obtain uniform inversion and repeatable poling curves for different samples. Using adequate pulse duration, nucleation spike and charges amount, uniform 1 micrometer deep PPLN were successfully fabricated on x-cut substrates.

The implementation of wavelength conversion around 1.55 μm in quasi-phase-matched (QPM) periodically poled LiNbO₃ (PPLN) waveguides is mostly based on the cascaded second-harmonic generation/difference-frequency generation (SHG/DFG) process. As usual, a continuous wave (CW) and a pulsed wave are injected into a PPLN waveguide. Of them, the pulsed wave is regarded as the information carrier, and the CW is taken as the control. To transfer the information of optical codes from one wavelength to another, the codes can be applied to either the signal (CW-pumped scheme) or the pump (pulse-pumped scheme). In this work, the temporal and spectral properties of wavelength conversions during pulse propagation as well as the conversion efficiency in the two pumping schemes were compared experimentally and theoretically under different conditions of input pulse width, pump power and pump central wavelength. In the experiments, we adopted an MgO-doped PPLN waveguide, and a 40-GHz tunable picosecond-pulse source. The conversion characteristics were systematically investigated when the CW and the pulsed wave were alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In the theory, we solved the coupled-mode equations and explained the physical insights for the numerical results and experimental observations. The conversion properties of the two pumping schemes were quantitatively compared. The simulated results agree well with the experimental data, and the obtained results provide some guidelines for the design and application of QPM waveguides in wavelength conversion.

We study surface states of 1D photonic crystals using a semiclassical coupled wave theory. Both TE and TM modes are treated. We derive analytic approximations that clarify the systematics of the dispersion relations, and the roles of the various parameters defining the crystal.

In this paper we present our study of all optical label encoding and ultrafast processing to route packets through optical networks. Our investigations include new network topologies, novel photonic components and performance analysis. We propose a label stacked packet switching system using spectral amplitude codes (SAC) as labels. We have developed enabling technologies to realize key photonic components for generation, correlation (identification) and conversion (swapping) of SAC-labels. We generate and identify the labels with fibre Bragg gratings (FBGs) encoders used in transmission. Furthermore, we demonstrate a static, all-photonic code-label converter based on a semiconductor fiber ring laser that can be used for label swapping of SAC-labels. We also address the design of dedicated receivers for optical burst detection. For this, we propose a novel architecture for a burst mode receiver module. In the system studies, we have shown by simulations that the throughput of standard Ethernet passive optical networks (E-PONs) can be substantially increased by the use of data encoded with SACs to achieve optical code division multiple access over passive optical networks (OCDMA-PONs). In the paper, we present recent results for all of these photonic technologies and we discuss how they can enable flexible packet switched networks.

A combination of radial basis function (RBF) and multilayer perceptron neural networks (MLPNN) is employed for extracting the parameters of a non-uniform fiber Bragg grating (FBG) from its reflection spectra. The identification process is carried out in two stages; First, the type of the nonuniformity (Gaussian, Apodized, Chirped, or mixed) is identified by using RBF. Then, the parameters of the identified grating are extracted via MLPNN. In contrast to conventional reconstruction methods, which usually require a priori knowledge of the type of grating, here the grating type of nonuniformity is automatically identified. The required number of neurons for obtaining accurate results is 10 for MLPNN and 312 for RBFNN, and therefore the network can be trained fast. The proposed method is applied to different test cases and accurate results are obtained within a very short computation time.

We report on experimental measurements of the radiation effects on COTS laser-optimized graded-index multimode fibers exposed to intense gamma radiation fields. Measurements at room and cold temperatures of the radiation-induced attenuation losses at 850 nm for two dose rates (450 Gy/h and 157 Gy/h) and for a total dose of 1000 Gy are presented for several fibers from different manufacturers.

This paper presents the principles and experimental results of an optical fiber QKD system operating at 1550 nm, and using the BB84 protocol with QPSK signals. Our experimental setup consists of a time-multiplexed super-homodyne configuration using P.I.N detectors in a differential scheme as an alternative to avalanche photon counting. Transmission over 11km of optical fiber has been done using this detection scheme and major relevant characteristics such as noise, quantum efficiency and bit error rate (BER) are reported.

This document shows the presence of photonic band gaps on the dispersion curves of the TE and TM modes of a two concentric core optical fiber. Such a fiber presents two concentric cores where it is assumed that guided modes exist.

We report the experimental synchronous pulse generation in a multicavity fiber laser system with two Erbium-doped fiber laser cavities. We have demonstrated that through the evanescent fields interaction between one cavity with active modulation and other one in continuous wave it is possible to generate more intense pulses in both cavities. Moreover, the synchronous pulse generation between cavities is achieved with an appropriate selection of pump intensity, modulation frequency and coupling ratio. We found that the pulse intensity is 2.5 times greater and the pulse duration lowers than a single Erbium-doper fiber laser. Furthermore, by means of the synchronous diagram we determined the synchronization strength in temporal pulse emission between cavities.

Waveguide gratings used in laser technology, optical sensing or optical communications have to serve different specific purposes and, hence, have to have specific optical properties which can be tailored to a large extent. Characterization methods are required not only to measure the actual effect of a Bragg grating or long period grating under consideration but also to unveil the cause, i.e. to determine its spatial structure. This paper reviews the present status of the respective experimental characterization techniques. The methods emphasized rely on phase sensitive reflectometry together with advanced inverse scattering evaluation algorithms.

We have investigated tunable fiber Bragg gratings (TFBGs) for single channel and for dual channels drop applications. The TFBGs are cable of dropping single DWDM channel or two consecutives DWDM channels in 8 nm bandwidth in the C-band. This feature is desirable in metro-edge network applications where low channel count (up to eight) dominates. Extensive stability, reproducibility and system characterization in addition to numerical simulations were conducted to investigate the feasibility of TFBG in optical communication networks.

The Bragg reflection waveguide (BRW), or one-dimensional photonic bandgap waveguide, has recently received much interest for applications such as nonlinear frequency conversion, mechanically tunable air-core filters, and electron accelerators. One variation of this waveguide is the quarter-wave BRW (QtW-BRW), in which all cladding layers have a phase thickness of π/2. This places the mode in the center of the cladding stopband, ensuring the strongest possible confinement for a given pair of cladding materials. In addition, operating at the quarter-wave point permits the effective index of the guided modes to be given by a simple closed-form expression. For many applications of BRWs, the dispersion of effective index with frequency is of primary concern. In this work, we use a perturbation approach to derive analytical expressions for the dispersion of a QtW-BRW, and compare the results to numerical simulations to demonstrate accuracy. Several interesting properties of these waveguides are developed. The birefringence of the guides changes sign at the quarter-wave point. For fundamental modes of even symmetry, the first-order dispersion is always normal if the material dispersion is normal. It is shown that for certain QtW-BRW designs, group index and group velocity dispersion (GVD) can be orders of magnitude higher than is the case for their constituent materials, or on the other hand, very small or zero values of GVD can be attained. We will conclude with a discussion of the applications of such waveguides.

We report on an original calibration technique of tunable in-fiber Bragg grating chromatic dispersion compensators. The technique allows easy detection and monitoring, in the optical domain, of the dispersion characteristics of the tunable compensator for simple control of its dispersion level. The method requires only a broadband optical source like an LED such that the dispersion level can be determined in an easy manner.

We report on an original detection technique for the design of sensing apparatus, based on the measurement of the total reflectivity of a uniform Bragg grating, which spectral response is modified by an induced linear chirp under strain. The relationship between the total reflectivity and the chirp level is presented for several reflectivities and lengths of the fiber Bragg grating and the influence of the key parameters is analyzed.

Optical inspection tools based on low-coherence interferometry and specialized for hard to reach industrial parts are presented. A common path configuration using optical fiber components is described. Small diameter probes originally developed for biomedical applications have been specialized for industrial inspection. Probes that can be used with a Cartesian surface scanning system or a cylindrical scanning system are presented. The probes include a reference that makes absolute accuracy measurements easier. Characterization of the internal surface of a worn plasma torch electrode has been realized using that technique. Surface profiling of the barrel of a gun was also performed.

We proposed and developed a low-cost system for profilometry and thin film measurement at nanometer resolution. The system is based on the concept of a dual interferometer. The sample was measured while a simultaneous compensation of the phase deviation due to the instability of piezoelectric transducer served as an optical delay component was performed. In the application of profilometry, the information of the surface profile of a material was obtained from the phase shift of the interference signal. By using the proposed compensation mechanism, an axial resolution of 1.09 nm was achieved. For the measurement of a thin film or membrane, the probe beam was prepared to polarize at 45° and was oblique incident on the sample. The system can perform a simultaneous measurement of the refractive index and the geometrical thickness as well as the position when the thin film is suspended. In order to calculate the refractive index and thickness of the thin film, the phase shifts and intensities of the interferograms of TE and TM waves were measured independently. By comparing the ratio of intensities and the phase shifts of the interferograms, the refractive index and the thickness of the thin film can then be obtained simultaneously.

A promising way of improving the sensitivity of the LIBS (Laser-Induced Breakdown Spectroscopy) technique consists in using basically two successive laser pulses instead of only one as in conventional LIBS: the first pulse generates the plasma and the second pulse selectively excites a specific quantum level of a given trace atomic species inside the plasma. The effect of this second laser pulse is to increase the emission of the atomic species of interest and therefore enhance the signal-to-noise ratio, leading to an improved detection. As a first step toward the detection of Pb in various materials, we present in this work a study of the resonant excitation and decay paths of Pb atoms in a laser-produced plasma. The ablation was performed using a Nd:YAG laser and the 2^nd pulse provided by an Optical Parametric Oscillator (OPO) laser was launched several μs afterwards.

A requirement to advance consistency and predictability of Micro-Electro Mechanical System (MEMS) device has triggered research to have precise measurements and visual means to characterize dynamic parameters. Time resolved measurements of entire surface in a microdevice to nanometer level accuracy are difficult using conventional metrology system such as optical interferometer and optical microscopy. Laser Doppler Vibrometer (LDV) has found their applications to some extent. Due to Single point technique, scanning is a must in LDV which sets drawback for characterization in Microsystems. In this paper we propose the use of Acousto Optic Modulator (AOM) as a strobing device with a continuous wave laser to develop a stroboscopic interferometer for static and dynamic characterization of out of plane motion. Due to high random access time (typical 150 nanoseconds) AOM improves the capability of the tool to test MEMS devices of higher frequencies. Detail study is done on the strobe frequency to correlate the pulsating frequency of the laser by the AOM and the driven frequency of the microdevice. Theoretical modeling of the stroboscopic interferometer is carried out by formulating the understanding between strobe frequency and the MEMS device.

A cubic-phase distribution is applied in the design, fabrication and characterization of inexpensive Fresnel lens arrays for passive infrared motion sensors. The resulting lens array produces a point spread function (PSF) capable of distinguish the presence of humans from pets by the employment of the so-called wavefront coding method. The cubic phase distribution used in the design can also reduce the optical aberrations present in the system. This aberration control allows a high tolerance in the fabrication of the lenses and in the alignment errors of the sensor. In order to proof the principle, a lens was manufactured on amorphous hydrogenated carbon thin film, by well-known micro fabrication process steps. The optical results demonstrates that the optical power falling onto the detector surface is attenuated for targets that present a mass that is horizontally distributed in space (e.g. pets) while the optical power is enhanced for targets that present a mass vertically distributed in space (e.g. humans). Then a mould on steel was fabricated by laser engraving, allowing large-scale production of the lens array in polymeric material. A polymeric lens was injected and its optical transmittance was characterized by Fourier Transform Infrared Spectrometry technique, which has shown an adequate optical transmittance in the 8-14 μm wavelength range. Finally the performance of the sensor was measured in a climate-controlled test laboratory constructed for this purpose. The results show that the sensor operates normally with a human target, with a 12 meter detection zone and within an angle of 100 degrees. On the other hand, when a small pet runs through a total of 22 different trajectories no sensor trips are observed. The novelty of this work is the fact that the so-called pet immunity function was implemented in a purely optical filtering. As a result, this approach allows the reduction of some hardware parts as well as decreasing the software complexity, once the information about the intruder is optically processed before it is transduced by the pyroelectric sensor.

Laser peening without coating (LPwC) is an innovative surface enhancement technology to mitigate fatigue and stress corrosion of metallic materials by imparting a compressive residual stress. Toshiba has established a process without coating, whereas the coating is inevitably required in conventional process of laser peening to protect the surface from melting. Since the energy of laser pulses in LPwC is significantly small compared to that in the conventional process, a commercially available Nd:YAG laser can be used, and moreover, an optical fiber can be utilized to deliver the laser pulses. Compressive residual stress nearly equal to the yield strength of the materials was introduced on the surface after LPwC. The depth of the compressive residual stress reaches 1 mm or more from the surface. High-cycle fatigue tests proved that LPwC significantly prolonged the fatigue lives despite the increase in surface roughness due to ablative interaction of laser pulses with material surface. Accelerating stress corrosion cracking (SCC) tests showed that LPwC completely prevents SCC of sensitized austenitic stainless steels, nickel-base alloys and their weld metals. LPwC has been used since 1999 to prevent SCC of core shrouds or nozzle welds of ten nuclear power reactors of both boiling water reactor (BWR) and pressurized water reactor (PWR) types, already covering nearly one fifth of the existing nuclear power plants (NPPs) in Japan.

This paper presents recent research undertaken in our laboratory in the field of direct laser writing of microfluidics circuits. Our novel technology allows the rapid fabrication of complex fluidic circuits. The fabricated channel have smooth walls and surfaces enabling the encapsulation of the circuits.

Three-dimensional (3D) microstructure writing using the two photon absorption (TPA) process has potential applications in the fabrication of photonic crystals and micromechanical devices. Ormocore and SU-8, two commercially available photoresists, were used to produce 3D structures and compare their writing performances. A 40X objective (NA 0.65) was used to produce high aspect ratio structures with high resolution. The resultant widths and heights of the lines written in the resists were measured for various exposure conditions. Walls with ~320 nm width and aspect ratios of ~40 were produced in Ormocore. Other standing 3D structures were also written to demonstrate the capability of the resists.

An original experimental setup for shearography with metrological applications is presented herein. The simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM polarization modes with a coating and a thin glass plate attached on its face. The temporal phase shifting method is applied through the use of a liquid crystal variable retarder. The use of this shearing device enables an in-line and almostcommon path configuration for the shearing interferometer, a path that leads to high stability of the interferometer and a low sensitivity to external disturbances. In order to prove the efficiency and the accuracy of this speckle shearing interferometer, the out-of-plane displacement derivative relative to the shearing interferometry direction of a centrally loaded steel plate has been measured by the shearographic interferometer and then compared with the out-of-plane displacement derivative computed from the displacement field provided by the finite element method. The results are in good agreement.

Throughout all this paper we are going to analyze one application of the optical beam deflection method (OBDM), the procedure for its development, as well as its ideal implementation to reach measurements of displacements that could be the most accurate and of the smaller scale possible, this condition is essential for the magnitude of the results to evaluate. We also give an application of the OBDM such as a fine particle densimeter principally in solids. This present work will analyze the laser beam deflection technique, the procedure to apply, as well as its ideal implementation in order to obtain measures of displacements that can sense to the most exact and the smaller possible scale, obtaining results from microns, micrometers and even, until nanometers. Our objectives that are considered in this investigation are two: the first one is to build a device based on this technique, make accurate measures on a very low scale, which could be reliable and in the order of scale of microns until nanometers. The second objective that we are searching is to obtain an alternative method for verify the values of density that some substances that are hard to get like titanium oxide.

Most of the investigations that exist about the interferometer of Sagnac in our days, are made through fiber optic, which has the great advantage of having a big area size in very little space wound in a nucleus. The first interferometers of Sagnac, were used for very big angular speeds measures, it didn't have the advances to carry out detections of small signs, because the measurements systems like photo-detectors, amplifiers, filters, etc. didn't have the capacity of the systems that now exist. That is one reason that our experiments are based on the electronic advances, to make detections of phase changes of until less than 0.1 nm with area of 0.025 m². Besides we proposed changes in the original interferometer diagram, adding some elements that can helps to achieve a bigger sensibility, accuracy and reduction of noise. Another of the advantages of use an interferometer of Sagnac, is work directly with the beams that travel through it, because we can observe the behavior from the optic road to external physical effects, like angular velocity or speed and little movements. Finally the acquisition devises and the software were used for calculate the angular frequency of the sensor directly from the experiment and know the parameters of the movement.

Pulsetrain-burst machining has been shown to have advantages over single-pulse laser processing of materials and biological tissues. Ultrafast lasers are often able to drill holes in brittle and other difficult materials without cracking or swelling the target material, as is sometimes the case for nanosecond-pulse ablation; further, pulsetrain-bursts of ultrafast pulses are able to recondition the material during processing for instance, making brittle materials more ductile and striking advantages can result. In the work we report, we have investigated hole-drilling characteristics in metal and glass, using a Nd:glass pulsetrain-burst laser (1054 nm) delivering 1-10 ps pulses at 133 MHz, with trains 3-15 μs long. We show that as the beam propagates down the channel being drilled, the beam loses transverse coherence, and that this affects the etch-rate and characteristics of channel shape: as the original Gaussian beam travels into the channel, new boundary conditions are imposed on the propagating beam principally the boundary conditions of a cylindrical channel, and also the effects of plasma generated at the walls as the aluminum is ablated. As a result, the beam will decompose over the dispersive waveguide modes, and this will affect the transverse coherence of the beam as it propagates, ultimately limiting the maximum depth that laser-etching can reach. To measure transverse beam coherence, we use a Youngs two-slit interference setup. By measuring the fringe visibility for various slit separations, we can extract the transverse coherence as a function of displacement across the beam. However, this requires many data runs for different slit separations. Our solution to this problem is a novel approach to transverse coherence measurements: a modified Michelson interferometer. Flipping the beam left-right on one arm, we can interfere the beam with its own mirror-image and characterise the transverse coherence across the beam in a single shot.

We report the formation of optically tunable, smooth, hollow beams by reflection of a TEM00 Gaussian beam off a metal thin film. Hollow (doughnut-like) beams (HB) with controllable profiles are created by a phase distortion at the surface. Two regimes of operation are observed: below a certain power threshold, the hollow beam formation is reversible and optically tunable on a time scale of milliseconds; above that threshold, alterations on the film surface make the effect permanent. Optical control of the hollow beam shape is demonstrated by tuning the power of a second beam. High stability in the radial intensity profile and the possibility of adjusting the spatial distribution and aspect ratios make this technique promising for applications such as atom trapping and manipulation of Bose-Einstein condensates.

This paper addresses various "Microwave Photonics" techniques developed for biomedical applications. The first application is using RF photonics technique for calibration of ultrasound transducers operating at high-frequencies without spatial field averaging compromise. In particular a broadband fiber-optic based hydrophone probe is reported for measurements of acoustic fields at the frequencies up to 100 MHz. The fiber probe with a tip diameter of about 8 microns provides a desirable measurement tool eliminating the need for spatial averaging corrections. Power budget calculation of the fiber sensor set-up indicated that high power (200 mW) laser source is essential to achieve adequate signal-to-noise ratio. The results of the preliminary measurements allowed the probe sensitivity to be determined. Improvements to the measurement arrangements are discussed to bring this sensitivity (about 1.7mV/MPa) in line with that theoretically calculated (4.3mV/MPa). On the other hand the second application of microwave photonics is in the diffused photon near infra-red spectroscopy. A custom designed broadband NIR spectroscopy system is reported. A high-speed high power optical transmitter is designed over the frequency range from 100MHz up to 3GHz Phantom experiments are performed to extract optical parameters of a turbid media simulating a breast tissue. Both broadband and single-frequency extraction methods are used to extract optical parameters of the phantom model. The comparison shows that the achieved extraction accuracy of optical parameter (μ_a, μ_s') using broadband extraction method is better than the single frequency technique.

Photonic true-time delay (TTD) beamforming has been considered a promising technique for wideband phased-array antenna (PAA) systems. An efficient way to achieve optical TTD beamforming is through the use of fiber Bragg grating (FBG) delay lines. In an FBG-based TTD beamforming system, a microwave signal carried by an optical carrier is required, which is usually obtained by modulating the microwave signal on the optical carrier using an external modulator. In this paper, we propose a novel approach to economically generate high-frequency microwave signals using two wavelengths from two phase-locked laser diodes through optical heterodyning. Since no optical modulator is required, the cost is significantly reduced. In addition, since the system uses only two wavelengths, the power-penalty problem caused by chromatic dispersion is minimized. In the proposed approach, the two phase-locked wavelengths are generated using an optical phase-locked loop (OPLL). A TTD beamforming system using an OPLL in combination with FBG-based delay lines to achieve tunable time delays is investigated. Experimental results are provided.

The paper addresses two microwave photonics functionalities based on device potentialities. The first one is related to the specific use of a mode locked (multi-section) laser diode in the analog domain where different modulation functions can be achieved. The second one deals with the specific design of a photodetector aiming to separately detect multiple modulated input beams and to group the resulting photocurrents into a single one. This leads to build an optoelectronic "add" function that can be used, for example, in microwave photonics signal processing applications such as optical beamforming networks for phased array antennas.

An interesting method for broadband arbitrary waveform generation is based on frequency upshifting of a narrowband microwave signal. In this technique, the original microwave signal is imaged into a temporally compressed replica using a simple and practical fiber-based system. Recently, it has been shown that the conventional limitations of this approach (e.g. bandwidth limitations) can be overcome by exploiting a temporal self-imaging (Talbot) effect in fiber. This effect can be used whenever the signal to be imaged is a quasi-periodic waveform (e.g. microwave tones or any arbitrary periodic waveform). This work provides a comprehensive review of the microwave frequency upshifting technique for broadband arbitrary waveform generation, with a special focus on the Talbot-based approach. The design specifications, and the associated practical capabilities and constraints, of fiber-based microwave frequency upshifting systems will be examined. The influence of higher-order effects, in particular second-order dispersion terms in the employed fibers, on the system performance will be evaluated and some additional design rules to minimize the associated detrimental effects will be given. Experimental evidence of our findings has been also provided. Our results show that microwave frequencies up to a few hundreds of GHz over nanosecond temporal windows can be easily obtained with the described technique using readily available (sub-)picosecond pulsed optical sources.

A single sideband (SSB) modulation scheme using a superstructure fiber Bragg grating (FBG) for a remotely controlled photonic true time-delay (TTD) beamforming system is presented in this paper. Photonic true time-delay (TTD) is considered a promising technique for wideband phased array antennas, as it allows beam steering of the antenna without the beam squint problem. For remotely controlled phased array antennas, the dispersive properties of a single mode fiber induce a power penalty at discrete RF frequencies when a double sideband (DSB) modulation scheme is used. The SSB modulation scheme is an effective way to eliminate this power penalty as only one sideband is transmitted and thus no beating is possible upon the recovery of the electrical signal by a photodetector. This paper presents for the first time a theoretical model as well as experimental results of a SSB modulation scheme based on a superstructure grating with two phase shifts. The true-time delay system considered utilizes a discrete uniform Bragg prism which allows discrete beam steering capabilities for the phased array antenna.

In this paper, we present two approaches to generating and distributing FCC-regulated UltraWideBand (UWB) pulse signals in the optical domain, based on optical phase modulation. In the first approach, an electrical Gaussian pulse train is applied to modulate the phase of an optical carrier using an electrooptic phase modulator. A 25-km single-mode fiber link is then used to realize PM-IM conversion which has a frequency response equivalent to a microwave bandpass filter. When the Gaussian pulse train is distributed over the 25-km fiber, the Gaussian pulses are then shaped into doublet pulses at the receiver front-end. Therefore, the UWB pulses are not generated but also distributed over optical fiber. In the second approach, instead of using an electrooptic phase modulator, optical phase modulation is implemented in the optical domain based on cross phase modulation in a nonlinear fiber. The PM-IM conversion is then achieved by use of a fiber Bragg grating that serves as a frequency discriminator. Electrical monocycle and doublet pulses are obtained at the output of the photodetector. Experimental results for both approaches are presented and discussed. The use of the second configuration to implement pulse on-off, polarity and shape modulation in the optical domain is also discussed.

We present a simplified radio over fiber balanced system that uses only one wavelength, optical modulator and fiber. In this balanced system the upper and lower sidebands produced by subcarrier modulation along with its optical carrier are separated before balanced photodetection. Optical time delays are introduced to one of the sidebands by means of two cascaded tunable nonlinearly chirped fiber Bragg gratings. The first nonlinearly chirped fiber Bragg grating produces relative time delay that has the following relationship τ_delay ∝ 1/2f, while the second produces a relative time delay of τ _delay ∝ 1/f. The first nonlinearly chirped fiber Bragg grating will have a large enough bandwidth and group velocity dispersion to introduce a relative time delay for the subcarrier and second order distortion, while the second will have the bandwidth and group velocity dispersion to introduce a different relative time delay for the third order distortion. The net effect of the relative time delays is to provide a phase shift of π for the subcarrier, second order distortion currents and a phase shift of 2π for the third order distortion current. Simulated results show a suppression of 2nd and 3rd harmonic distortion of 25.4 dB and 2.6 dB, respectively. In the case of 2^nd and 3^rd intermodulation distortion suppression of 33 dB and 20 dB, respectively have been reported. Simulation also shows that the power penalty improvement is approximately 2.5 dB for bit error rate of 10-9 for subcarrier at 10 and 35 GHz and relative intensity noise is suppressed by 3 dB.

Measurements and analysis of electrical and temperature tuning characteristics of a 1490 nm erbium doped fiber external cavity semiconductor laser (DFECL) are presented. The laser has a long piece of doped fiber in the external cavity. The standing wave in the external cavity causes spatial hole-burning and absorption modulation in the saturable absorber, and forms a long dynamic grating. In this paper, we show that the wavelength of DFECL can be tuned within the bandwidth of the FBG (~100 pm), by tuning the semiconductor laser temperature. The wavelength of the laser can also be tuned smoothly and continuously over 60 pm by controlling the current over 160 mA; the equivalent optical frequency tuning rate is ~50MHz/mA. The results indicate that the peak wavelength of the dynamic grating can be tuned with the dominant mode within the bandwidth of the fiber Bragg grating. This fine tuning characteristic is very attractive for microwave optical generation in Radio over Fiber applications.

Microwave photonics contributes through ultrafast devices to the processing of high data rates. In this area, microwave photoconductive switches (MPCSs) in integrated technology have proved their performances to control the transmission of high frequency signals in complex systems. Their ability to switch microwave signal phase and magnitude is fully defined by a complex frequency-dependant ON/OFF ratio R_ON/OFF determined from S-Parameters measurements in microwave frequency domain. This paper reports on a new design of MPCSs to be used, after realization and evaluation, as a basic block in optically controlled MMIC devices for application in high frequency samplers or phase shifters.

A large signal theory is performed to analyze linear fibre dispersion effect on the intensity modulated dual-electrode Mach-Zehnder Modulators (DE-MZMs) when used for millimetre-wave harmonic up-conversion (MWHU) through photonic mixing in Radio over Fiber (RoF) systems. Closed form expressions are derived for the directly detected photocurrent spectrum in general case of MWHU and for general operating conditions of DE-MZM such as biasing, driving level, phase shifted and unbalanced drives. The analytical expressions derived here are much more useful than just numerical simulations or measurements. They provide fast and accurate analysis and better insight into harmonic up-conversion in terms of dispersive fading, amplitude and phase ripples. Harmonic up-conversion products are given in the case of any local oscillator (LO) order. Harmonic up-conversion is analysed in terms of dispersion induced power penalty (DIPP) and intensity modulation depth (IMD) of the up-converted signal. The special cases of double sideband (DSB) and single sideband (SSB) modulation of balanced drives of DE-MZM are studied in detail. The DIPP and IMD are expressed for different bias point configurations. Optimum LO modulation index that maximizes the IMD and reduces the DIPP is also calculated. The obtained new results are compared to previously published works.

The probability distribution function (pdf) used to model Synthetic Aperture Radar (SAR) clutter is an important design element in Constant False Alarm Rate (CFAR) detection; the mean of the local CFAR window is taken as the first moment of the pdf. This study presents research examining the relationship between clutter statistics and radar resolution cell size in the Convair-580 (CV-580) C-SAR and RADARSAT-2 systems. The experiment consisted of decreasing the resolution of a HV polarized, high-resolution, CV-580 sea SAR image and determining the best fit pdf for the corresponding clutter. The same methodology was used on standard- and fine-beam-mode RADARSAT-2 HV images. It was found that the GΓ pdf could be fitted very well to the experimental data for all CV-580 and RADARSAT-2 resolutions. Furthermore, the highest resolution SAR data was Weibull distributed, and decidedly non-Gaussian, in all cases. The medium resolution CV-580 image was very closely modelled by the Lognormal distribution while the Rayleigh distribution (Gaussian statistics) proved highly suitable for modelling the lowest resolution SAR data. The test results presented in this paper may be useful to SAR researchers.

A Quantum-dot saturable absorber mirror (QD-SAM) has been fabricated by the molecular beam epiiaxy (MBE) technique. Preliminary measurements show that our QD-SAM is a very promising candidate for passive mode-locking a fiber laser or a solid state laser with wavelength in the range of 970-1090nm. The 22%-33% dips in the reflectivity spectrum are observed, which are attributed to quantum dot absorption, indicating the potential for a large modulation depth and hence generation of ultra-short laser pulses through mode-locking.

This paper presents a wideband optical semiconductor Photonic Transistor (PT) and computer simulation results. The PT can be used to construct either N-valued digital photonic logic gates or binary Boolean logic gates. Digital photonic circuits can then be built using these logic gates. We used a buried stripe wave guide heterojunction microstructure for the PT. The objective of this paper is to report the results of computer simulations with different active region dimensions for the same design. Numerical experiments have shown that the same logic function can be achieved with different sizes of the PT, by setting the appropriate signal powers. However, smaller size designs have the advantage of higher speeds and low power consumptions.

We have produced Si nanocrystals by implanting Si ions at 90 keV into 430 nm thick SiO₂ films, to fluences from 6 x 10¹⁶ to 1.4 x 10¹⁷ ions/cm² (or 9 - 20 at. % excess Si). High temperature anneals at 1100°C and 1200°C in an N₂ ambient followed, to coalesce the excess silicon into nanocrystalline precipitates. Samples were further annealed for 1 hr at 450°C in a 5% H2 95% N₂ ambient to passivate dangling bonds and reduce non-radiative electron-hole recombinations. The films were then characterized by Photoluminescence (PL), and the PL intensity is maximized at 17 at. % excess silicon. This suggests that quantum confinement and/or the total number of nanocrystals is optimized at a Si excess of 17 at. % for high temperature annealing conditions. Annealing at 1100°C results in a greater number of smaller nanocrystals than annealing at 1200°C, and consequently a greater PL intensity. The peak wavelength of light emission reaches equilibrium after a much shorter annealing time than does the PL intensity, suggesting that the nanocrystals attain their final size before the film reaches equilibrium. Positron Annihilation Spectroscopy (PAS) was used to investigate defects in the film. The majority of defects introduced by ion implantation annealed away very quickly, in correlation with the rapid equilibration of the peak wavelength of PL emission.

The spaced metal nanoparticles arranged along a chain can interact through the near-field of surface plasmon-polariton modes of adjacent particles. The advantage of such propagation is that the mode confinement is below the diffraction limit of light, which is impossible with classical wave guides. The guiding of the electromagnetic wave along the chain becomes consequently possible. In this paper, we present the Finite Element Method (FEM) with adaptive mesh to investigate the plasmon resonaces of interracting metallic nanoparticles and describe the propagation of electromagnetic energy through functional structures. We propose, a general simulation tool to determine the various transmission coefficients through plasmonic discrete structures using multiple scattering computations based on a tight-binding Green function approach. We apply our theoretical and numerical approaches to investigate plasmonic discrete waveguides.

One technological challenge in microfluidic system design has been controlling the directional flow of minute amounts of fluid through various narrow channels. Stimuli-responsive polymers can be used as micro control devices such as valves because these materials significantly change their volumetric properties in response to small environmental changes in pH, temperature, solvent composition, or electric field. In this paper, a bi-layered hydrogel structure is introduced as a light activated microactuator. The first layer of the device is a light sensitive polymer network containing poly(vinyl alcohol) (PVA) and the retinal protein bacteriorhodopsin (bR). The second layer is a blend of PVA hydrogel and a pH sensitive polymer polyethylenimine (PEI). When exposed to a light source with a peak response at 568 nm, the bR molecules in the first layer undergo a multistage photocycle that cause protons to be pumped into the surrounding medium. The diffusion of these similarly charged ions through the adjoining pH responsive hydrogel generates electrostatic repulsive and attractive forces which alter the osmotic pressure within the cross-linked polymer network. Depending upon the type of electrostatic forces generated, the pH sensitive hydrogel layer will swell or, alternatively, collapse. The multi-layered structure can be fabricated and inserted into the microchannel. The expanding volume of the actuating hydrogel is used to regulate flow or control leakage. Preliminary experiments on a 625mm³ optical actuating device are presented to identify key response characteristics and illustrate the mechanism for actuation

At the present work we study the optical properties of spherical nanometals by Lindhard's quantum theory for the electron gas and then there is a theoretical study aiming at understanding the role of the electronic temperature on the optical response of simple metal clusters as the nanoparticles. The electronic temperature dependence of the optical response of simple metal clusters is investigated by many different quantum mechanical theories. The longitudinal and transverse dielectric functions are the most important quantities of a quantum many- electron system which are calculated at the present work.

The Yb³⁺-Er³⁺ co-doped YAG nanocrystal powders have been successfully prepared by the simple sol-gel method at a low temperature. The gel was prepared from nitrates of yttrium, aluminum, ytterbium, erbium and citric acid, and was heat-treated at temperatures from 800 to 1000°C. The phase purity and microstructural features of the materials were analyzed by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM result shows that the YAG nanocrystal particle size is about 20-50nm. The luminescence spectra for different Yb³⁺ and Er³⁺ dopant concentration was obtained at about 1.52um which is in the eyesafe regime where significantly higher pulse energies can be used without damaging human eyes.

Agar is a natural polysaccharide which, when doped with dichromate ammonium, can be considered as a promising light sensitive material used for real time hologram recording. The volume transmission gratings were recorded with a Kypton laser at 413 nm and they were read in real-time with a He/Ne laser at 632.8 nm contrary to dichromated gelatin. The so obtained holograms formed were phase holograms due to a refraction index modulation. The optimisation of chemical and physical parameters was investigated in order to form high quality holograms. It was demonstrated the crucial role played by the remaining water in the final film on the value of the diffraction efficiency. In the optimal conditions, a maximum diffraction efficiency of 37 % was attained. Both on-off experiments and the storage of the exposed materials at room temperature and in the dark reveal that the holograms were stable. An attempt to rationalize the set of results in terms of chemical structure of the polymeric matrix and of its ability to stabilize chromium (V) is presented.

In this paper, photorefractive performances in polymeric and molecular glass composites are presented for optical memories. Oxidation potential equivalent to ionization potential of each component is sensitive to the photorefractive performances. The combination of poly(diphenylamino)styrene (PDAS) as host photoconductive matrix and aminostyrene derivative of 4-azacycloheptylbenzylidene-malononitrile (7-DCST) as a NLO dye gave the better and faster photorefractive responses compared to that of poly(N-vinylcarbazole) (PVCz) and 7-DCST. This is ascribed to the fact that oxidation potential of PDAS and 7-DCST are close to each other, whereas 7-DCST with lower oxidation potential works as hole trap in the composites of PVCz with higher oxidation potential. Grating geometry is also important. Two types of grating geometry of transmission and reflection was employed for photorefractive performances of composites of molecular glasses endcapped with carbazole moieties. Reflection grating can be used for weak absorption film or no absorption film. Large net optical gain was obtained in reflection grating geometry due to the introduction of 7-DCST as an effective trap sites. Another interesting results were large asymmetric energy transfer and optical diffraction without applying electric field. Using the same type of composites, large optical gain up to 224 cm^-1 and diffraction efficiency of ca. 90 % were measured. Glass transition temperature of composite was sensitive to the diffraction efficiency and grating buildup speed. Long lived TNF anion radical and carbazole or triphenylamine cation radicals were responsible for the photorefractive performances in non-electric field condition. Thermally diffused cation radical is trapped in the dark region and leads to the asymmetric energy transfer and diffraction grating.

Holographic Versatile Disc (HVD^TM) using Collinear^TM Technologies is proposed by OPTWARE Corporation, in which the information and reference beams are displayed co-axially by the same SLM. With this unique configuration the optical pickup can be designed as small as the DVD's, and can be placed on one side of the recording disc. In HVD^TM structure, the pre-formatted meta-data reflective layer is used for the focus/tracking servo and reading address information, and the dichroic mirror layer is used for detecting holographic recording information without interfering with the preformatted information. A 2-dimensional digital page data format is used and the shift-multiplexing method is employed to increased recording density of HVD^TM. Experimental and theoretical studies suggest that the holographic material is very effective to increased recording density of the system. As the servo technology is being introduced to control the objective lens to be maintained precisely to the disc in the recording and the reconstructing process, a vibration isolator is no longer necessary. HVD^TM will be compatible with existing disc storage systems, like CD and DVD, and enable us to expand its applications into other optical information storage systems.

A bendable photocell array that exploits bioelectronic photoreceptors based on bacteriorhodopsin (bR) is described in this paper. Fabricating such a sensor array on a flexible plastic substrate introduces a new design approach that enables lightweight and durable non-planar sensing devices to be created with curved or spherical geometries. In this research, purple membrane patches obtained from wild-type bR are deposited onto a polyethylene terephthalate (PET) substrate coated with a patterned ITO layer using Electrophoretic Sedimentation (EPS) technique. The current prototype consists of a flexible 4x4 pixel array and an amplification circuit that magnifies the small electrical signal arising from the charge displacement and recombination within the dried bR film. Each individual pixel is a 2mm x 2mm square separated by a 1mm distance between neighboring elements. The measured photoelectric response of an individual pixel is approximately linear over the light power range between 200μW and 12mW. These bR photocells respond primarily to visible light with a spectral peak response at 568nm. The response times of the photoelectric signals can reach up to the microsecond range. Preliminary tests have demonstrated that photoresponse characteristics are maintained while the flexible substrate is deformed up to a 10mm bending radius. Unfortunately, dried bR photocells are inherently susceptible to electrical noise because of their extremely high film resistance, necessitating the employment of a noise-filtering amplifier. The image processing capabilities of bR are demonstrated in a motion detection application. Specifically, Reichardt's delay-and-correlate algorithm is implemented and is used to detect both the speed and direction of a moving light spot.

A comprehensive model of holographic lithography is used to predict the final structure of a phasemask-formed photonic crystal in SU-8 photoresist. It includes optical imperfections in the phase mask, beam attenuation in the resist, and resist reaction kinetics such as acid diffusion, resist shrinkage and developer diffusion. By comparing simulations with the laser-formed PC templates in our lab, we can identify the origin of various crystal lattice distortions, and more accurately predict the template geometry and crystal motif.

A diarylethene derivative, 1,2-bis[2-methyl-5-(3-fluorophenyl)-3-thienyl] perfluorocylcopentene, is synthesized and dispersed into PMMA to prepare a polymeric film. The film shows good color recycling between switching of irradiation of UV light and red light. Under the excitation of linear polarized light, an apparent characteristic of photoinduced anisotropy is observed in the diarylethene/PMMA film, which implies polarization modulation gratings can be recorded in this holographic medium apart from recording of intensity modulation gratings. We experimentally make a comparison among four types of polorization holograms recording for their reconstruction images, which shows that the orthogonal circular polarization hologram has both high signal-to-noise ratio and high diffraction efficiency. Based on the polarization gratings scheme, we demonstrate the polarization multiplexing holograms reocording and retrieval in the diarylethene/PMMA film and the combination with the angular multiplexing scheme.

We recorded reflection holographic gratings in thick photopolymeric films composed of Eosin (as sensitizer) mixed with acrylamide (as monomer), N,N'-methylenebisacrylamide as cross-linking monomer and Triethanolamine (as coinitiator), all dissolved in a polyvinylalcohol host matrix. The gratings were recorded using argon-ion laser at 514.5 nm. By optimization of all photopolymer compositions, we obtained diffraction efficiency as high as 17 % at high spatial frequency of 4800 lines/mm. A comparison was made by replacing Eosin with Rose Bengal in the photopolymer. 10 % shrinkage was measured in both systems.

We review our recent works on nanocomposite holographic photopolymers doped with inorganic or organic nanoparticles that act as secondary mobile species and play an important role both in the refractive index modulation enhancement and in the suppression of polymerization shrinkage. Diffraction properties of volume holograms formed in several types of nanocomposite photopolymers are described. Experimental verification of the mutual diffusion of monomer molecules and nanoparticles during grating buildup is also described.

The Nonlocal Polymerization Driven Diffusion model, NPDD, is can be used to describe holographic grating formation in Acrylamide-based photopolymer. The free radical chain polymerization process results in polymer being generated nonlocal both in space and time to the point of chain initiation. Temporal nonlocality can be used to describepost exposure dark effects. Nonlinear response and the effects of dye bleaching have been examined. Both primary and bimolecular chain termination mechanisms have been included and examined. Recently 3-D, and inhibition effects have also been included. In this paper we review of our recent work. It is shown that temporal effects become most notable for short exposres and the inclusion of the nonlocal temporal response function is shown to be necessary to accurately describe the process. In particular, brief post exposure self-amplification of the refractive index modulation is noted. This is attributed to continued chain growth for a brief period after exposure. Following this a slight decay in the grating amplitude also occurs. This we believe is due to the continued diffusion of monomer after exposure. Since the sinusoidal recording pattern generates a monomer concentration gradient during the recording process monomer diffusion occurs both during and after exposure. The evolution of the refractive index modulation is determined by the respective refractive index values of the recording material components. From independent measurements it is noted that the refractive index value of the monomer is slightly less than that of the background material. Therefore as monomer diffuses back into the dark regions, a reduction in overall refractive index modulation occurs. Volume changes occurring within the material also affect the nature of grating evolution. To model these effects we employ a free volume concept. Due to the fact that the covalent single carbon bond in the polymer is up to 50% shorter than the van der Waals bond in the liquid monomer state, free volume is created when monomer is converted to polymer. For each bond conversion we assume a hole is generated which then collapses at some characteristic rate constant. The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). Inhibition is typically observed at the start of grating growth during which the formation of polymer chains is suppressed. In this paper experiments are reported, carried out with the specific aim of understanding of these processes. The results support our description of the inhibition process in an PVA/Acrylamide based photopolymer and can be used to predict behaviour under certain conditions.

In this paper we report an experimental method to optimize diffraction efficiency and sensitivity of the grating in a photopolymer system using Real Time Infrared (RTIR) spectroscopy. Polymerization profiles were directly recorded, allowing a precise evaluation of the polymerization rate and the photosensitivity. The optimum chemical composition of the photopolymer system for recording high diffraction efficiency transmission gratings is experimentally obtained. Using the RTIR results and a photopolymerization-diffusion model we have further determined the basic kinetic and diffusion parameters of the photopolymer system.

Using electronic isolators as substrates for organic thin films one has to take care of long living surface charges which might influence or even control the film deposition. Unknown charges may be the origin of poor reproducibility. On the other side these charges may be used for controlled patterning as we will demonstrate in this paper. The described phenomenon might be of interest for electronic displays or patterned OLED's. Presented are different methods to deposit surface charges. The molecular orientation is investigated by measuring the angular dependence of the absorption coefficient.

Two processes explain radioluminescence of organic and inorganic materials. Exposition of organic materials to ionizing particles leads to the excitation of the molecules of the matrix. The relaxation leads to photon emission. In the case of the inorganic materials a self-trapped exciton (STE) propagates in the crystal until it reaches and excites an impurity; the relaxation of this impurity may be radiative. We observed that lanthanides (ErIV or NdIV) doped materials (porous or ED2 glasses) show some characteristic emission rays. The spectra are quite similar to the expected ones for inorganic materials, while these materials are organic. We developed a model explaining how the radioluminescence of the organic materials excites the lanthanide ions, and then the observed radioluminescence emission spectra can be explained by the Judd-Ofelt theory. Several materials have been studied: erbium doped porous glass (ErIV:PG), neodymium doped ED2 glass (NdIV:ED2), and also a sample of titan sapphire (Ti:Sa) as a comparison sample for inorganic materials. These samples have been exposed to H₂⁺, ⁴He⁺⁺, ¹²C⁺⁺ ions accelerated up to 4.1 MeV with a Van de Graaff accelerator. The emission spectra have been measured and a study of the luminescence lifetime of the material has been made. Luminescence lifetime of the characteristic rays is dependent on the radiation dose. These observations allow us to conclude that the lanthanide ions are well excited by the standard radioluminescence of the undoped material. Also, studies have been made as a function of the deposited energy to investigate the potential applications. All these results will be presented and discuted.

Polycrystalline layers of organic azo-dyes like DR1 (Disperse Red) have been prepared from the vapor phase. Due to their large electric dipole moment the orientation of the molecules may be changed or controlled by electric fields. Furthermore the capability of an optically induced TRANS-CIS transition allows an optical reorientation. In this study we will report on the optical recording of stable 2D-patterns in as grown and in electrically or optically preoriented films in the thickness range of 200-500nm.

Surface relief gratings (SRG) made from azobenzene polymer films by holographic exposure with actinic light show remarkable density modifications in addition to the surface relief. The origin of the huge material transport is attributed to cooperative phenomena associated with the light induced trans-cis and cis-trans isomerization of azobenzene moieties and the subsequent changing of viscoelastic properties during illumination. In case of polydisperse red 1 methacrylate (pDR1m) films and using particular illumination conditions the amplitude of the density grating (DG) can be maximized whereas the amplitude of surface undulations keeps small. The capability of DG formation makes it possible to induce grating formation in the azobenzene polymer film through a thick polymer cover layer which is not affected by the actinic light. Using PMMA as cover layer the grating is located at the PMMA - pDR1m interface (interface grating) while the sample surface stayed almost flat. This concept can be used to prepare 3D mesoscopic crystals by stacking several PMMA/pDR1m bi-layers on top of each other. The interface grating is created in each bi-layer before it becomes covered by the next bi-layer. Patterning of the upper bi-layer takes place after careful positioning of the writing position with respect to the underlying one. These 3D multilayer gratings can be used as dispersive elements for optical light. Their structural performance can be probed by means of light diffraction similar to the x-ray Laue experiment.

Surface relief gratings are optically inscribed on azobenzene polymer films. Multiple gratings can be inscribed on the same spot either simultaneously or sequentially by projecting a holographic pattern onto the surface. The grating pitch can range from 350 nm to 1.5 μm and depths can easily reach 400 nm. The inscription is done at room temperature, in air using a 100 mW/cm² beam for 1 to 5 minutes. In the present study we inscribe two sinusoidal gratings and coat the surface with a 20 nm thin film of gold. Light incident onto this structured surface is coupled into a surface plasmon when the appropriate angle of incidence and wavelength are selected. The coupling condition can be observed in the reflection spectrum from the surface. A dispersion curve for the plasmon propagation can then be produced by studying the reflection spectrum as a function of the angle of incidence. By using two gratings as couplers, a surface plasmon standing wave can be produced for a selected incident light wavelength.

We present a technical processing to fabricate substrates (fused silica) for 3-D photonic bandgap material. The potential surface was modified to improve the colloidal method for nanoparticles assembly. This method allows orientating the growth of the colloidal crystals in a specific way; the crystalline plans growth is parallel to the surface of the substrate, and we can eliminate stacking defects and polycrystallinity. The substrate is obtained with ions beam engraving, according to the following process: A layer of photoresist is deposited on the substrate; we write two identical holographic gratings on the photoresist with 90° angle; After the development of photoresist, we obtain a profile which corresponds to one of the crystalline plans of the face centered cubic lattice; This profile will be transferred on the substrate by RIE (reactive ion etching). This substrate has many advantages: it is reusable because it is easily cleaned with solvents like acetone; the same substrate will be easy to use in order to make several growth tests and to optimize physicochemical parameters during artificial opals fabrication.

Recently, interaction of electromagnetic waves with conducting interfaces has been studied and several applications have been proposed. For instance, new type of photonic crystals similar to Kronig-Penny electronic crystals has been implemented by using these structures. In these structures a free two dimensional interface charge layer is generated at the dielectric interfaces and interesting phenomena are observed. In this manuscript, the effect of finite charge layer thickness and its asymptotic behavior toward conducting interface, where the thin charge layer is modelled via a surface conductivity σ_s, is numerically studied for the first time. Two different regimes are considered: first, propagation of optical waves through sub-wavelength free charge layers and its corresponding reflection and transmission coefficients for both major polarizations TE and TM; second, propagation of optical slow waves localized at the interface of two dielectrics with interface conducting layer between them..

A new organic nonlinear optical (NLO) chalcone derivative viz.1- ( 4- methoxyphenyl )-3- (3,4 - dimethoxy phenyl ) - 2 - propene-1-one, has been synthesized by Claisen-Schmidt condensation method. The synthesized compound was purified by repeated recrystallization process. To confirm the identity of the synthesized compound, FTIR spectra was recorded and various functional groups present were identified. NMR spectra were recorded for structural identity and purity confirmation of the synthesized compound. Good quality single crystals were grown by solvent evaporation and slow cooling technique using acetone as solvent. The grown crystals were characterized by UV-Visible , differential thermal analysis and linear refractive index measurement. The hardness of the crystal was determined using Vicker's indentation method. The single crystal structure analysis of the crystal was performed and it is found that the crystal belongs to monoclinic system with space group P2₁. The powder second harmonic generation(SHG)frequency conversion efficiency of the crystal was determined using Nd: YAG laser(λ = 1064nm)and it is 15 times that of Urea.

In this paper the recent results of our studies of linear and nonlinear optical properties of a selected rotaxane are presented and discussed. The studied rotaxane can be processed into good optical quality thin films by vacuum evaporation. The linear optical properties of rotaxane solutions were studied by the UV-VIS spectroscopy and the nonlinear optical properties by the picosecond degenerate four wave mixing and Z-scan methods. The results show important rotational contribution to the nonlinear index of refraction.

Two new photochromic diarylethene compounds, {[1-(2-methyl-5-(4-(2-(1,3-dioxolane))phenyl)),2-(2-methyl-5-(p-methylphenyl))]thien-3-yl}perfluorocyclopentene (1a) and {[1-(2-methyl-5-(4-(2-(1,3-dioxolane))phenyl)),2-(2-methyl-5-(4-formyl- phenyl))]thien-3-yl}perfluorocyclopentene (2a), were synthesized. Their spectra properties, such as UV-Vis absorption spectra, fluorescence and kinetics properties in solution were also investigated. Diarylethene 1a shows relatively strong fluorescence at 353 nm when excited at 295 nm, and 2a shows no fluorescence under the same experimental condition. The cyclization/cycloreversion processes of the two diarylethenes were determined to be zeroth/first order reaction, respectively. In addition, photo-mode multi-step optical storage using 2a as recording medium was performed successfully.

A collective overview and review is presented on the original work conducted on the theory, design, fabrication, and in-tegration of micro/nano-scale optical wires and photonic devices for applications in a newly-conceived photonic systems called "optical printed circuit board" (O-PCBs) and "VLSI photonic integrated circuits" (VLSI-PIC). These are aimed for compact, high-speed, multi-functional, intelligent, light-weight, low-energy and environmentally friendly, low-cost, and high-volume applications to complement or surpass the capabilities of electrical PCBs (E-PCBs) and/or VLSI electronic integrated circuit (VLSI-IC) systems. These consist of 2-dimensional or 3-dimensional planar arrays of micro/nano-optical wires and circuits to perform the functions of all-optical sensing, storing, transporting, processing, switching, routing and distributing optical signals on flat modular boards or substrates. The integrated optical devices include micro/nano-scale waveguides, lasers, detectors, switches, sensors, directional couplers, multi-mode interference devices, ring-resonators, photonic crystal devices, plasmonic devices, and quantum devices, made of polymer, silicon and other semiconductor materials. For VLSI photonic integration, photonic crystals and plasmonic structures have been used. Scientific and technological issues concerning the processes of miniaturization, interconnection and integration of these systems as applicable to board-to-board, chip-to-chip, and intra-chip integration, are discussed along with applications for future computers, telecommunications, and sensor-systems. Visions and challenges toward these goals are also discussed.

Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are going to change the landscape for future metro optical networks. In this paper, we present the detailed design layouts for next generation metro optical network equipped with the most advanced 3rd generation ROADM modules. Mathematical equations have been developed to design complex network architecture based on traffic demand and the characteristics of network equipments. Our proposed design layout for next generation network alleviates some conventional design concepts that will ultimately reduce the capital- and operational-expenditure for the overall network.

Higher data throughput in optical packet switched interconnection networks can be achieved by minimizing the guard times through faster transition of the switching element. A hybrid integration of a semiconductor optical amplifier with its current driver is presented, which exhibits over 40% faster transition time compared to current commercial devices.

The stable two-mode operation of a 4-sections semiconductor laser emitting at 1.55 μm is experimentally demonstrated and analysed. An interpretation of the two-mode regime involving a saturable absorber is theoretically developed and the characteristic parameters of this saturable absorber deduced. This work exhibits the possibility of terahertz wave generation by photomixing using this device.

Resonant cavities are key components in photonic circuits which provide feedback, wavelength selectivity and energy storage. Microspheres^[1], in particular, support ultrahigh-Q whispering gallery modes (WGMs) that may lead to large delays and enhanced optical nonlinearity within several tens of microns length scale. Most of the demonstrated devices to date utilize a tapered fiber to excite the WGMs, however this coupling architecture not only lacks of rigid stability but inhibits dense integration to form more sophisticated planar lightwave circuits (PLCs). Here we report an alternative approach based on evanescent coupling between the microsphere and a S-bend waveguide structure. This approach provides better mechanical stability and is capable for on-chip integration.

In this paper optical filters based on photonic resonant tunneling effect are analyzed by using the polynomial expansion method. Amplitude and phase response together with their dependency on the physical parameters of the filters are also investigated. These steep-edge filters show low insertion loss amplitude response, and linear phase variation in their passband, a suitable feature for WDM and DWDM applications where constant time delay and dispersion free devices are needed. Two kinds of filters, namely discrete level and continuous profile filters are introduced. These structures can be analyzed and designed by using Transfer Matrix Method. However, this approach suffers from inaccuracy and numerical instability when narrow linewidth filters are desired. Moreover, analyzing the continuous profile filters using this method calls for breaking the structure into many homogeneous sublayers. Here, a method based on Legendre expansion of electromagnetic fields is adopted to design and analyze the proposed filters. Not only the method relieves some numerical problems peculiar to conventional methods, but also can be applied for holistic analysis of filters having continuous refractive index profile and therefore eliminates the need for cumbersome multilayer analysis.

Rapid advances in photonic and electro-optic technologies have given rise to sophisticated spaceborne optical instruments with important applications ranging from remote sensing to high-resolution hyperspectral imaging systems. This paper reviews past, present and future space missions employing Canadian optical instruments, discusses required detector technologies and their key performance parameters.

Rocket detection over a wide field of view is an important issue in the protection of light armored vehicle. Traditionally, the detection occurs in UV band, but recent studies have shown the existence of significant emission peaks in the visible and near infrared at rocket launch time. The use of the visible region is interesting in order to reduce the weight and cost of systems. Current methods to detect those specific peaks involve use of interferometric filters. However, they fail to combine wide angle with wavelength selectivity. A linear array of volume holographic elements combined with a curved exit slit is proposed for the development of a wide field of view sensor for the detection of solid propellant motor launch flash. The sensor is envisaged to trigger an active protection system. On the basis of geometric theory, a system has been designed. It consists of a collector, a linear array of holographic elements, a curved slit and a detector. The collector is an off-axis parabolic mirror. Holographic elements are recorded subdividing a hologram film in regions, each individually exposed with a different incidence angle. All regions have a common diffraction angle. The incident angle determines the instantaneous field of view of the elements. The volume hologram performs the function of separating and focusing the diffracted beam on an image plane to achieve wavelength filtering. Conical diffraction property is used to enlarge the field of view in elevation. A curved slit was designed to correspond to oblique incidence of the holographic linear array. It is situated at the image plane and filters the diffracted spectrum toward the sensor. The field of view of the design was calculated to be 34 degrees. This was validated by a prototype tested during a field trial. Results are presented and analyzed. The system succeeded in detecting the rocket launch flash at desired fields of view.

Photonic crystals (PhCs) exhibiting negative refraction have attracted much attention in recent years, with a vast majority of this research focusing on subwavelength imaging. Although the possibility of an open cavity using such a PhC is mentioned in Notomi's pioneering work, fewer researchers have addressed this issue except one study of an open cavity using three 60-degree PhC wedges of the hexagonal lattice. This paper reports our study of several different open cavity configurations in hexagonal and square lattices. To form an open cavity using PhC with negative refraction, there are many parameters to optimize, such as the lattice type, lattice period, the diameter of the hole or rod, materials, and the geometrical configurations. We first propose several configurations for open cavities in general, including two square slabs, two or more prism slabs, and one slab with two reflectors; Then we demonstrate some results obtained from photonic crystals with square and hexagonal lattices, simulated by the use of the finite-difference time-domain (FDTD) method. It is shown that resonance can occur at the first band and higher bands. The Q-factor obtained is about 280 to 400, which can be improved by optimizing the surface terminations of the photonic crystal prisms.

In this paper we present an encoding/decoding device for OCDMA communications. The device uses a single reflecting element to perform both the encoding of outgoing signal and the decoding of incoming signal. A directional optical assembly allows differentiating the origin of the signals to forward the outgoing signals after encoding to the network and the incoming signals after decoding to a receiver.

Optical Packet Switched (OPS) networks employing Optical Label Switching (OLS) techniques have the potential to enable an all-optical internet. In these networks, data remains in optical format throughout the entire network and routing is performed using a separate optical label. The label information is used to control fast tunable lasers that will transfer data packets to different wavelengths for routing and contention resolution. In this paper we investigate interference between subcarrier multiplexed (SCM) labels in such a network, due to switching events in the tunable laser transmitter. This interference may place a limitation on the channel spacing and subcarrier frequency used. Two 50GHz spaced optical carriers were modulated with 2.5Gbit/s SCM labels at 20GHz. Bit error rate measurements were taken with two lasers fixed 50 GHz apart, and also with one of the lasers (an SG-DBR) switching between this channel and another one 800GHz away. When the SG-DBR laser is not switching, a power penalty of approximately 0.25 dB is introduced due to interference through the optical filter. However, when the SG-DBR laser is switching between wavelengths an error floor of 1x10-5 is introduced due to the time it takes the tunable laser to settle to its target channel. In a systems application, this would result in packets being incorrectly routed.

Phase matching of the signal paths between input and drop ports significantly improves filter characteristics and results in a box-like passband and a deeply suppressed, flat stopband. As a result add/drop multiplexers built with only two filter elements, each consisting of a chain of one, two, or three series coupled microrings exhibit satisfactory filter characteristics and very moderate degradation due to resonator loss. Accurate phase matching however requires thermooptic or electrooptic tuning, usually embedded in one arm of the multiplexer. Analytical and simulated results are presented covering transmission and group delay characteristics, sensitivity to waveguide loss and free spectral range (FSR) extension techniques. A temperature/stress sensor application is also proposed.

Slab-coupled waveguide laser was theoretically analyzed by E. A. J. Marcatili [1] in the 1970's, based on which, we recently demonstrated a high power slab-coupled waveguide laser with buried hetero-structure. The laser lases around 1525.5 nm, with 3.4 μm*4.4 μm (FWHM) spatial mode shape. With improved current blocking mechanism, the output power reaches 326mW per facet, the coupling efficiency to the single mode fiber (SMF) is 80%, the horizontal and vertical far field angles are 10°, 18° respectively. Electron blocking layer will be implemented to improve internal quantum efficiency. Epi-side down bonding will be used to improve heat dissipation and output power.

In this paper, detailed analyses of the conversion efficiency in high-speed clock recovery based on Mach-Zehnder (MZ) modulator has been carried out. The theoretical results show the conversion efficiency changes with RF driving power and the mixing order. For high order clock recovery, the cascaded MZ modulator provides higher conversion efficiency. A study of clock recovery at 160 Gb/s using the cascaded MZ modulator has been carried out. The experimental results agree with the results of the analysis.

Monolithic integration of silicon micro-photonic devices with silicon microelectronics presents one potential solution to the interconnect bottleneck in deep submicron CMOS microprocessors. However, an inability to develop a robust silicon based electroluminescent (EL) technology continues to severely limit the feasibility of such a structure. Despite its promising photoluminescent (PL) properties, the erbium doped silicon rich silicon oxide material system has been only partly successful in EL devices owing to dielectric breakdown resulting from high field excitation requirements. However, PL data indicate that quantum confinement effects in this system enable it to overcome many of the luminescence quenching properties of bulk silicon based materials, while simultaneously offering the structural and chemical resilience which luminescent forms of silicon (eg. porous silicon) lack. However, it is now clear that the resolution of the current injection problem will require a detailed understanding of all known and especially potential luminescence excitation mechanisms. The present study compares PL measurements made for SiO_x:Er (x less than or equal to 2) thin films grown by electron cyclotron resonance plasma enhanced chemical vapour deposition. Various compositions, containing erbium concentration below 1 atomic %, have been annealed over a range of temperatures between 600-1100 °C. The presence of excess silicon relative to SiO₂ is found to result in a 100 fold increase of the PL emission near 1540 nm, resulting from the ⁴I_13/2 to ⁴I_15/2 transition of the trivalent erbium ion, relative to a sample containing no silicon excess. It has been found that luminescent silicon nano-clusters can be formed throughout the range of anneal temperatures studied. A dense array of extremely small amorphous silicon clusters is found to result in an optimized sensitization of the PL at 1540 nm for annealing at 800°C. It is proposed that in some cases, silicon nano-clusters coupled to erbium ions do not emit their intrinsic luminescence. Various oxygen-based luminescent defects are identified in this study, and they seem to exhibit a coupling to silicon nano-cluster and erbium-related centres. Possible application of these films to recently developed field-effect EL devices is discussed.

The results of studying the steady states for bright ultrashort optical pulses, developing in single-mode semiconductor amplifiers structured in a direction of passing those pulses, are presented. These steady states occur due to reshaping the incoming optical pulses via the passive mode-locking process in traveling-wave regime. The relations between the pulse parameters and the amplifier's properties are chosen in such a way that the mode-locking process is incoherent in behavior that leads to the phase decay of the incoming pulses. The analysis performed demonstrates the effect of the gain non-locality manifests itself in asymmetry of the issuing bright optical pulses with various shapes of envelopes.

Thin films of vanadium oxide were prepared and studied for the electro-optical properties of semiconductor-metal transition. Vanadium oxide films with thickness of ~ 0.15μm were deposited on SiO₂/Si substrates by reactive RF magnetron sputtering using a pure vanadium target under various ratios of argon and oxygen gases. The oxygen content in the mixed atmosphere has a significant influence on the semiconductor-metal transition characteristics. Both thermochromic and electrochromic modes were studied. In thermochromic mode, the oxide film deposited in an O₂/Ar ratio of 1.2% exhibits 90% optical transmission in semiconducting state at room temperatures, while very low transmission at 5% in metallic state at 65°C, in the wavelength region of 8 to 12μm. In the near infrared region of 1 to 2μm, the transmission is about 60% in the semiconducting state and a few percents in the metal state. A corresponding three-order variation of resistivity was observed over the transition. The refractive indices (n and k) of the vanadium oxide films were measured using an ellipsometer in the near infrared region between 1 and 2 μm in both states. The index n decreases in metal state while k increases. The electrochromic phase transition of vanadium oxide was investigated by applying a pulsed voltage to minimize the heating effect. The required charge density for the phase transition is consistence with the Mott metal-insulator model. Longwave IR switching and modulation were demonstrated by electrically induced semiconductor-metal transition.

Differential-phase-shift-keyed optical modulation (DPSK) has generated a lot of attention in fiber optic transmission over the past few years mainly because of its 3dB optical signal-to-noise ratio (OSNR) improvement over standard intensity modulated transmission [1] offering high receiver sensitivity, high tolerance to major nonlinear effects in high-speed transmissions [2], and high tolerance to coherent crosstalk [3]. To demodulate DPSK, a delay-line interferometer is usually employed to provide a one-bit delay such that a bit interferes on the following bit to provide constructive or destructive interference depending on the phase difference [4]. However, with the use of logical pre-coding a multi-bit delay can be used instead of a single-bit delay. It was recently reported that a two- or four-bit delay might be advantageous in allowing polarization interleaving between bits to lessen the detrimental effects of fiber nonlinearities in fiber optic transmission [5-7]. Multi-bit delay was also proposed as a method to correct errors from amplified spontaneous emission (ASE) noise-limited transmission [8-9]. We present here simulation and experimental results on the penalty of using multi-bit delay demodulation for DPSK detection. We present Q-factor degradation as a function of delay and find that the Q penalty scales with 0.5 x delay for integer delays. We also present results of the detrimental effect of spectral filtering from the reduced free-spectral-range (FSR) in a multi-bit delay interferometer. We also find that it exhibits reduced dispersion tolerance. If not taken into account, these important limitations and more stringent tolerance on the frequency offset may reduce the effectiveness of multi-bit delay methods and prohibit practical implementation.

In this paper we study the properties of polycrystalline yttrium iron garnet Y₃Fe₅O₁₂ (YIG) thin films deposited by means of a Pulsed Laser Deposition technique (PLD). The films were grown at a substrate temperature of 700-800°C and at various oxygen pressures. Annealing was performed for all the samples and the role of ambient gas as well as of temperature was investigated. The influence of structure and of phase purity was also studied through X-Ray Diffraction (XRD). In addition, compositional analysis was carried out via Rutherford Back Scattering (RBS). Finally, optical transmittance was tested for both amorphous and polycrystalline structures in view of their potential use in the fabrication of magneto-optic integrated devices.

Advanced optomechanical modeling, coupling FEA modeling and optical ray tracing, has led to ROADMs exhibiting superior performance and reliability, while accelerating design convergence and lowering prototyping cost. A methodology description and illustrative example are presented.

This paper presents modeling, design, and prototyping of a z-axis micro-platform actuator fabricated by MicraGEM (Micralyne GEneralized MEMS) process. With 4 crossly arranged rotational serpentine springs and 12 μm of gap between the circular disk and the bottom electrode underneath it, this platform demonstrates its simple actuation, easy control and capability of fine tuning the vertical displacement in the range of 0.5 μm to 3.0 μm through varying the applied electrical bias. Positioning sensitivity and repeatability of the platform with respect to the applied voltage have been estimated and verified by mathematical model. With proper selection of springs and their geometric parameters, high sensitivity of the z-axis platform actuators can be obtained. The proposed electrostatically actuated micro-platform will gain importance in micro-positioning for optical MEMS and microphotonic devices.