A scattering matrix oriented CAD tool is presented for design and simulation of photonic integrated circuits. In a scattering matrix approach each component is represented by a scattering matrix which describes the signal transfer between the different ports of the component. These components are usually waveguides. As an example of a more complicated component simulation of an optical PHASAR demultiplexer will be described and the potential of the approach will be illustrated in simulating an integrated add-drop multiplexer and comparing the results with measurement data of a realized device.

A scattering matrix oriented CAD tool is presented for design and simulation of photonic integrated circuits. In a scattering matrix approach each component is represented by a scattering matrix which describes the signal transfer between the different ports of the component. These components are usually waveguides. As an example of a more complicated component simulation of an optical PHASAR demultiplexer will be described and the potential of the approach will be illustrated in simulating an integrated add-drop multiplexer and comparing the results with measurements data of a realized device.

A novel spectral method, which combines the advantages of two proven techniques, namely the spectral index and free space radiation mode methods, is presented for the analysis f a mode spot converter with air clad boundaries. The approach is very efficient and accurate, giving propagation constants and field profiles in a matter of seconds. Design curves and field profiles which can be used to optimize the spot converter are also given.

A method of solution of the scalar Helmholtz eigenproblem for dielectric waveguides is presented. The fundamental idea is the expansion of the electric field on a discrete basis of sine functions which go to zero at the calculation window boundaries, for both transverse directions. A matrix eigen problem is correspondingly built up from the Helmholtz polynomial functions defined over rectangular domains. The solution algorithm takes advantage of the well-known Lanczos reduction technique, allowing for the straightforward evaluation of discrete eigen values within any desired precision order. The Lanczos algorithm, here combined with the Fourier-analysis technique, allows to examine very large-sized cases without the problem of storage space lacing. In this work, a few examples of propagation analysis are shown referring to both step-index and graded-index integrated optical structures, and the calculation results are compared with those obtained by commercial BPM algorithms and the effective index method.

We present an extension of the equivalent optical waveguide method to analyze multimode optical waveguides with arbitrary refractive-index profiles. Effective indices, propagation constant and coupling/switching properties of multimode planar by means of an equivalent optical waveguide for each guide mode. The effective indices are evaluated by applying the asymptotic effective index method. Numerical values were obtained and compared with those presented by other authors. In all cases, a good convergence and accuracy was noticed.

BeamBox polymer based fiber-optic space switches have been submitted to a reliability qualification program. The results of this program show that these switches meet the requirements for telecommunication applications. Highly stable switches have been obtained by proper design, testing, and optimization of materials, parts, and production processes.

A novel hybrid structure for optical modulation and switching is presented. It consists of a thin film of electro-optic polymer spin-coated on passive waveguide made by ion exchange on glass substrate. Two structures corresponding to weak guiding and strong guiding conditions are considered. Design issues and modulation performances are studied for the two structures. Low half-wave voltages less than 10 volts are expected for an interaction length of 1 cm provided the electro-optic coefficient of the nonlinear polymer is 10 pm/V.

The characteristics of Al_0.3Ga_0.7As/GaAs QW acousto- absorption and acousto-optic modulators using the interaction between surface acoustic wave (SAW) and quantum well (QW) optical waveguide structures are analyzed here theoretically. The QW structures are optimized by maximizing the optical confinement of modal field in the active region and the piezoelectric effect of SAW and QWs. The electric field induced by SAW reduces non-uniformly in depth, which limits in the development of high efficiency modulators, especially for devices with a large number of QWs in the active region. For devices with thin active regions, the QW structures are designed so that at the top surface strong SAW effects can be obtained while for the 25 periods structure, the QWs located at a depth of 2/3 SAW wavelength in order to obtain an uniform SAW induced electric field. The results show that the single and five QW devices are suitable for absorptive modulation and optical modulation respectively while the 25-QW modulators can shorten the modulation interaction length and thus increase modulation bandwidth. The effective index change of these devices are at least 10 times larger than the conventional surface acoustic wave devices. These result make the quantum-well modulators more attractive for the development of acousto- optic device applications.

An integrated electro-optical switch based on a planar nematic liquid crystal waveguide has been realized and tested. To achieve this goal, we fabricated and measured a number of step-index waveguides, using RF sputtering and sol-gel deposition techniques. A summary of their characteristics is presented. The design of electro-optical switch is reported, together with the analysis of the problems met in order to optimize the manufacturing process. Finally, we present the experimental results obtained with a three-stages device, having as middle stage a thin nematic LC film and two glass waveguides as other stages. The electro-optical behavior and the response times have been studied for different configurations. The experimental findings show that an additional bias voltage can improve both the transmittivity and the response time of the device, leading to very promising results in the frame of new integrated electro-optical switches.

A low loss ultra wide bandwidth electro-optic polarization converter/modulator was realized on a GaAs/AlGaAs substrate. The device uses slow wave coplanar strip electrodes to match the phase velocity of optical and microwave signals to increase the modulation bandwidth. Microwave measurements show an electrical bandwidth in excess of 40 GHz. Microwave loss of the electrode is dB/cm at 40 GHz and the phase velocity of microwave signal is 8.6 cm/nsec and flat over the measured frequency range. The phase velocity mismatch between the optical and electrical signal is less than 5 percent. Electro-optic modulation was performed up to 22 GHz and no roll-off was observed in this frequency range.

The level of integration within standard waveguide devices is usually restricted to the use of a single plane per wafer containing waveguides. Recently, concepts for waveguide structures with several planes of waveguides gain some special interest. They are mainly due to intentions to increase the number of channels per chip, to reduce the chip size and to improve device characteristics. Dense vertical stacking of waveguides turns out to be an approach to 3D integrated optics, which is within the resolution limits of up-to-date waveguide technologies. Theoretical and experimental results for 3D directional couplers are reported in detail.

Reliable, low cost, compact optical components are essential to the continuing development of fiber-based communications systems. Polymers offer the potential for cheap, low temperature processing of optical components, coupled with low optical losses, and good size and index matching with optical fibers. This paper describes the use of polyimide materials for the fabrication of passive optical devices and on-chip integrated optical interconnections. A variety of basic waveguiding structures, including bends and splitters have been demonstrated, with dimensions suitable for both multimode and single mode applications. The polyimides were patterned by standard photolithography and losses were typically 0.5-1.0 dB/cm. Multimode polyimide ridge waveguides have been integrated with metal-semiconductor- metal photodetectors. Efficient coupling of the light from the guide into the detector was achieved via gaps in the underlying optical buffer layer. The integrated waveguide/detectors have been fabricated into hybrid and monolithic 4 X 4 optoelectronic switches, which offer high bandwidth and low cross-talk. This technology has also been applied to the fabrication of integrated optical/electrical transmit/receive modules for use in optically controlled phased array antenna systems.

All optical structures for signal processing in optical links are studied. Both theoretical and experimental aspects are considered. Two configurations corresponding to frequency selection and frequency rejection are analyzed. First, hybrid circuits based on single mode optical fibers are studied. Frequency rejection circuits are mainly based on unbalanced Mach-Zehnder interferometers, while frequency selection function uses ring resonators. These structures show good stability and are well suited for low frequency uses ring resonators. These structures show good stability and are well suited for low frequency signals up to 100MHz. To meet microwave and millimeter wave ranges, integrated structure are introduced. The design and the realization of a 1.5GHz frequency rejecting filter made on a glass substrate is presented. The realized integrated filter shows a rejection depth better than 30dBe in a 20GHz band.

Lithium fluoride thin films represent an innovative material for integrated optics. Passive waveguides may be produced by using a LiF/NaF two-layer structure deposited on any substrate material. On the other hand, low-energy electron beam irradiation of LiF polycrystalline films gives rise to the efficient formation of laser active lattice defects showing intense photoluminescence and sizable optical gain in the visible spectral range from green to red at room temperature. This irradiation at the same rime induces an increase of the real part of the refractive index, thus allowing one to exploit electron lithography technique to directly write integrated optical amplifiers and lasers in LiF films. Experimental results of the characterization of both passive and active waveguides are reported, demonstrating the feasibility of more complex circuits in this material.

A computer simulation based on a travelling-wave, distributed model of the ring laser has been sued to investigate the regimes of operation of passive mode-locked ring semiconductor lasers 2-3mm in circumference. Different configurations of intracavity saturable absorber have been employed and their relative merits determined. Experimental devices with similar configurations have been fabricated, and shown to exhibit mode-locked operation under similar conditions to those predicted by simulation.

Silicate and phosphate glass waveguide amplifiers doped with Er³⁺, and codoped with Er³⁺/Yb³⁺ are theoretically studied. Configurations for core and core- cladding doped waveguide amplifiers are considered. It is hon that gain int e core-cladding doped waveguide amplifiers are considered. It is shown that gain in the core-cladding doped amplifiers is considerably higher than core doped amplifiers. It is also shown that with input signal power up to 1 mW and 200 mW pump power, a 12.5 dB gain can be achieved in a 3 cm long waveguide amplifier, with a noise figure of 3.05 dB.

Polarization dependence is a major factor of consideration in the design of optical waveguide devices for applications in optical fiber transmission systems. In many cases, the polarization-dependence problem can be solved by using waveguides with zero modal birefringence. In this paper, theoretical results are presented to show how zero- birefringence waveguides can be designed from various waveguide geometries. The waveguides considered in this paper include strip waveguides, rib waveguides, waveguides, strip-loaded waveguides, and multiple-quantum-well waveguides, which are of particular importance in the construction of semiconductor-based photonic integrated circuits. The design of polarization-insensitive directional couplers with rib waveguides is also discussed.

Among the fabrication techniques of integrated optical devices, the sol-gel chemistry is now performant enough to make thin films of transparent materials with controlled purity and composition, at low temperature. Semi-mineral semi-organic solutions allow dip coating followed by low temperature baking to deposit vitreous films up to eight micrometers thick which are free from cracks. A local polymerization process through UV exposure enables hybrid components compatible with electronic planar silicon or III- V components. This UV imprinting method is used here to make index modulation gratings with use of a holographic equipment as an alternative to the use of a costly phase mask. Gratings have been imprinted on various sol-gel films; single layer, with a protective coating, and/or with an isolating buffer layer from the substrate, which is silicon and glass. Diffraction magnitude is measured in the various cases, as well as analysis and computer simulations are performed. Wavelength filters are experimented and studied. This shows the potential of this low cost technology in integrated optics, for application in telecommunications.

In this paper, we present the simulation, fabrication and measurement results of GaAs/Al_yGa_1-yAs waveguides having a cladding layer nearly 50 percent thinner than the conventional cladding layer thickness, while still achieving an equivalent optical performance. These waveguides are realized by inserting thin layers of Al_xGa_1-xAs in the Al_yGa_1-yAs bottom cladding layers. The waveguide layers are grown by standard organo-metallic vapor phase epitaxy with the ridge waveguides defined by reactive ion etching. The composition, thickness and the position f the inserted Al_xGa_1-xAs layers were optimized so as to maintain the original waveguide performance. The channel waveguide propagation losses are about 1 dB/cm, measured by the Fabry- Perot cavity and the cutback methods. These results were found to be consistent with simulations. The insertion of the thin layers of Al_xGa_1-xAs in the specific optimized device performance.

The length of NxN multimode interference-based devices scales as the square of the MMI region width, and as a result, the use of these structures for large-N applications can require large chip areas. We discuss the NxN applications of a recently proposed MMI structure which has smaller device dimensions than conventional multimode interference structures. Numerical simulations of such structures and design rules are presented.

In this paper several approaches to expand the field profile of a laser beam are studied. The power coupling efficiency and fiber coupling loss are discussed in detail. To achieve this, the rigorous vector finite element method is used to calculate the modal propagation properties and the least squares boundary residual method is employed to calculate the coupling loss, the reflection coefficient and the alignment tolerances of these devices.

An accurate model is presented for the analysis of ion- implanted AlGaAs/GaAs multi-quantum well symmetric and asymmetric twin waveguides. The modal propagation constants, modal indices and field profiles of the leading supermodes are solved numerically by using a quasi-vector method based on the finite difference method. Impurity induced disordering defined multi-quantum well twin waveguides are shown to have similar optical properties as conventional dielectric rib waveguides. They provide a more flexible control over the waveguiding and coupling characteristics by changing the diffusion time, the ion implant energy, the mask width, the waveguide separation, and the operating wavelength. By suitably varying these parameters, single- mode operation can be achieved, while the coupling length can be theoretically tuned from a few millimeters to a hundred meters, a difference in the order of 10⁵. Impurity induced disordering produced waveguide arrays are therefore highly recommended for integrated photonic IC realization.

In this report, an active PVC thin film waveguide sensor which can select a specific ion and measure its concentrations is proposed. In order to investigate the applicability of this sensor, we measured calcium ion. The waveguide layer was fabricated with plasticized poly (vinyl chloride) (PVC) co-polymer matrix containing a neutral ionophore for calcium dioctyl phthalate, and chromoionophore, which plays important roles both in incident light propagation and in selective ion sensing. For this purpose, we applied the sensor to the sample solution whose CaCl₂ was gradually altered. In this study, we found that this thin film waveguide possessed good light propagation. In addition, it showed enough chemical reaction to Ca²⁺ to select Ca²⁺ and to measure its concentration. These findings suggested that the proposed active PVC optical thin film waveguide sensor was very effective in selecting Ca²⁺ and measuring its concentration. Also, it will be expected that this sensor is applicable to various ions other than Ca²⁺.

Microoptic probes for gas absorption-measurement making use of single mode optical fibers and graded-index microlenses are considered. A model for a potentially rugged and low- cost probe is given, which minimizes the optical alignment problems, as well as offering intrinsic-loss less than 3 dB for absorption path-lengths up 20 cm, and less than 10 dB when path-lengths up to 40 cm are considered. Probe tests on a breadboard assembly are presented, together with the implementation of two demonstrator probes for methane alarm measurements.

Multimode optical fibers are used for evanescent-wave absorption spectroscopy ofliquids by replacing, to some extent, the normal cladding with the media being tested. Plastic-cladding silica-core fibers and all-plastic fibers are frequently used for evanescent-wave absorption-spectroscopy of liquids, since the plastic cladding can be easily removed. However, these fibers offer only limited efficiency. This paper presents tapered-core PCS and all-plastic fibers with enhanced sensitivitycompared to uniform-core fibers, and discusses how the enhancement of absorbance is influenced by the parameters characterizing the taper profile.

Significance and some potential applications of Strontium Barium Niobate Sr_xBa_1-xNb₂O₆ (SBN) crystals in the field of photonics are succinctly discussed. The very large electrooptic coefficients of SBN crystals reported thus far and in this study have been empowering its role as one of the most promising nominees amid ferroelectric materials for the production of photonic devices functioning on account of nonlinear optical phenomena.

We demonstrate a sixteen channel, GaAs/AlGaAs staring spectrum analyzer device based on a phased-array of sixteen electro-optic waveguide delay lines. The device is effectively a high resolution version of the widely reported optical wavelength division multiplexer phased-array devices, using electro-optic waveguides to adjust the optical phases across the array. The device comprises: a 1- to-16 way multimode interference coupler; 16 electro-optic phase controllers; 16 folded waveguide delay lines, from 0 to 1 nanosecond in equal steps; and a waveguide phased array output. By making use of novel waveguide and corner designs we demonstrate the device as a spectrum analyzer, the RF signal to be analyzed was superimposed on an optical carrier using a GaAs/AlGaAs electro-optic waveguide push-pull Mach Zehnder interferometer, and the intensity modulated light was then passed through the phased-array chip. The spectrum of the RF input signal was displayed in the far field of the phased-array as diffraction lines on either side of the main diffraction lines. By biasing the modulator to extinction, the CW carrier could be removed from the far field diffraction pattern so that only the RF spectrum was displayed. In this presentation we describe the device design, fabrication and testing including measurements of the dynamic range and resolution.

IR to visible light conversion in titanium dioxide sol-gel waveguides doped with charge transfer luminescent molecules is investigated. Second harmonic generation and two photon fluorescence are reported and potential uses of these samples for practical devices is discussed.

We present design considerations and fabrication results for a vertically integrated waveguide polarization splitter. Fabrication techniques of shadow reactive ion etching and variable photolithography exposure produced the required vertical waveguide structures. The fabricated vertical waveguide bends exhibit excess loss of only 0.2dB. By constructing this vertical bend with a birefringent polyimide, simulation results show the possibility of a polarization splitter wit an extinction ratio of over 15dB. We demonstrate preliminary waveguide experiments showing the practicality of these structures as 3D integrated optical devices.

Bandgap tailoring and lattice-matching in SiGeC/Si heterostructures has potential for improving the performance and capabilities of Si based optoelectronics. Although remarkable progress in the molecular beam epitaxy (MBE) of SiGeC/Si heterostructures has been achieved, important questions concerning growth kinetics and thermal stability are still not fully understood. One major obstacle during MBE growth of these heterostructures may be the high surface diffusivity of carbon, which leads to small fractions of substitutional carbon at temperatures necessary for device quality epitaxial growth. We report on the surface kinetic properties of Si_0.992C_0.008/Si and thermal stability of strained Si_0.992C_0.008/Si and strain compensated Si_0.892Ge_0.10C_0.008/Si alloys were shown to be more stable then the binary Si_0.992C_0.008/Si heterostructure alloys.

Power splitters with high performances in a very broad region of wavelengths are key components in Passive Optical Networks. To this end, we designed an 8 channel power divider that works in the range 1260 nm-1650 nm by cascading Y-junctions optimized for low loss operation. Several devices have been fabricated using the silicon technology and then fully characterized on a semi-automatic bench developed on purpose to evaluate the spectral response and polarization dependent losses. Preliminary measurements show that the devices are within ETSI and Bellcore specifications.

The present work reports on our recent achievements in the exploitation of a simple technology for the fabrication of hydrogenated amorphous silicon (a-Si:H) based low-loss rib waveguides. In particular, waveguides with various widths have been fabricated out of an a-SiC:H/a-Si:H stack deposited by plasma enhanced chemical vapor deposition at the relatively low temperature of 220 degrees C. The ribs were defined by an anisotropic, CH₄-based, reactive ion etching process. The devices have been subsequently characterized by cut-back technique. Even though a dependence of attenuation parameter on the waveguide width was observed, propagation losses as low as 0.7 dB/cm could be measured at λ=1.3 μm, in good agreement with he theoretical estimations based on the intrinsic absorption of the material. Starting from the same structure, a Fabry- Perot thermo optical modulator has been also fabricated and tested at the communication wavelength of 1.3 μm.

A new type of resonant enhanced photodetectors based on the 1D photonic bandgap is proposed. It can potentially overcome problems encountered in resonant-cavity-enhanced photodetectors. Resonating structures with very high quality factors and large free spectral ranges can be obtained by varying the optical parameters of the gratin overlay without the presence of rigid design constraints. The use of coupled-cavities with distributed resonances is discussed. In particular, we demonstrate that the exploitation of cascaded structures allows resonant-enhanced parallel detection of wavelength division multiplexed optical signals.

Photonic crystals or photonic bandgap (PBG) structures promise to revolutionize optoelectronics by making anew class of highly efficient, low noise light emitters possible. We present data to show that their properties, in particular 2D systems, have now been fully characterized in the relevant semiconductor material system and at near-IR wavelengths, so effort can be redirected towards making active light emitters. As a first example, we present a semiconductor laser with one output mirror designed according to PBG principles. From threshold and efficiency data, we derive a reflectivity of 95 +/- 10 percent for this mirror, which underlines the viability of the PBG approach for practical devices. In order to realize the full potential of photonic crystal light emitters, however, important material issues need to be considered. Non- radiative recombination, for example, is a big problem when the photonic crystal is an integral part of the active region because of the relatively large areas of exposed surface. Several possible solutions to this problem are presented.

We report room-temperature pulsed-mode operation of 8.5 micrometers quantum cascade lasers grown by gas-source molecular beam epitaxy. The theory necessary to understand the operation of the laser is presented and current problems are analyzed. Very good agreement is shown to exist between theoretical and experimental emission wavelengths. The high- temperature operation is achieved with 1 microsecond(s) pulses at a repetition rate of 200 Hz. Peak output power in these conditions is in excess of 700 mW per 2 facets at 79 K and 25 mW at 300 K. Threshold current as a function of temperature shows an exponential dependence with T₀ equals 188 K for a 1.5 mm cavity.

Low loss optical waveguides with extreme stability against pulsed optical intensity allowing for a nonlinear induced phase shift of >3π have been fabricated in a class of conjugated polymers, substituted poly(phenylene-vinylene) (PPV), which are promising candidates for demonstration of nonlinear switching in waveguide elements. The wavelength dependence of the nonlinear optical properties were measured with interferometer and spectral pulse broadening techniques. The nonresonant n₂ values are several times 10^-14 cm²/W for the two PPV derivatives measured. Ultrafast nonlinear switching is demonstrated exploring purely electronic effects by suing a semi- integrated nonlinear Mach-Zehnder interferometer and directional couplers.

Plasma enhanced chemical vapor deposited a-Si:H/a-SIN_x:H superlattices on silicon wafers were annealed by KrF excimer pulsed laser. Room temperature visible electroluminescence (EL) was successfully realized from these silicon-based superlattices structures with quite low threshold biased value 3.0V. It is a promising new way, in which all procedures are compatible with current silicon ULSI technology, to the realization of opto-electronic devices different from the porous silicon. Luminescent properties of samples with different laser annealing energy densities were compared and a preferred annealing condition was given.

The fiber optic sensors measuring accuracy depends on such destabilizing factors influence, as light emitter power variations, different research surface reflecting and scattering properties, photoreceiver parameters alterations and etc. Sometimes it is necessary to transform the measuring displacement into time interval, which duration is in proportionality to measurement value and is independent to destabilizing factors influence also. The mathematical model of the invariant transformation method of measuring displacement into time interval was elaborated for two channel fiber optic sensor. Using two measuring channels with mutual involuting adjustment permits to compensate the error components of the transfer functions and time dependences errors, gives the opportunity to becomes more simile, because frequency instability of excitation voltages doesn't influence at the transformation results. Considered method permits to increase of the device quick-action, to simplify of displacement analog-digital conversion and to decrease of the comparator's error on account of contrary changing voltages comparison. The two-channel fiber optic sensor with modulated emission for precision positioning was elaborated in which research object surface is illuminated by modulated emission with the help of semiconductor laser, laser pulses duration is chosen divisible to 1/50 Hz. The two-channel fiber optic sensor with modulated emission for precision positioning operates in the structure of laser microscope positioning system. The device output signal sign is defined identically by fiber optic guide face plane shift direction. Its value is in proportionality to deflection value. Schematic diagrams of method realized devices are shown and the main concerned to these method and devices correlations are discussed.

We present design considerations and fabrication results for a vertically integrated waveguide polarization splitter. Fabrication techniques of shadow reactive ion etching (RIE) and variable photolithography exposure produced the required vertical waveguide structures. The fabricated vertical waveguide bends exhibit excess loss of only 0.2dB. By constructing this vertical bend with a birefringent polyimide, simulation results show the possibility of a polarization splitter with an extinction ratio of over 15dB. We demonstrate preliminary waveguide experiments showing the practicality of these structures as three dimensionally integrated optical devices.