This PDF file contains the front matter associated with SPIE Proceedings Volume 6781, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Widely tunable All-optical wavelength conversion between picoseconds pulses based on Four-wave mixing is proposed and experimentally demonstrated in cascaded highly nonlinear fiber. The signal pulse with 40-GHz repetition rate and 1.57-ps pulse width is adopted. The converted idler wavelength can be tuned continuously from 1540.6 to 1594.8 nm as the CW laser wavelength is changed from 1514.5 to 1565.7 nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse.

In this paper, we investigate utilizing clock modulated signal as a pump to improve the efficiency of FWM in 26.5km dispersion shifted fiber. The experimental results show that, with the clock pumping, the conjugated FWM component has higher intensity than that with the CW pumping. The reason behind it is that SBS process is greatly quenched with the clock pumping, so most power of the pumping light contributes to nonlinear interaction with the probe signal during the propagation through DSF. But for CW pumping greater than Brillouin threshold, most power is depleted by SBS process and converted to backward Stokes light, so less power is left for other nonlinear process such as SPM, XPM and FWM to take place. As a result, the FWM components have lower intensity, and the pump and probe signal spectrum is also much less broadened. The measurement shows that, the improvement of FWM efficiency is negligible when the pump power is less than 10dBm. But when the pump power is greater than about 11dBm, the improvement becomes significant and increases with the increased pump power. When pump power reaches 17dBm, the improvement is increased to about 9dB.

In this paper, we studied SC generation in fiber lasers and in optical fibers pumped by different light sources which include fs and ps pulse sources, and continuous-wave (CW) amplified spontaneous emission (ASE) light sources. First, we demonstrated SC generation with a 10dB spectral bandwidth of 430nm in a fiber ring laser with conventional nonlinear fiber. Second, we proposed and demonstrated a new and efficient approach to generation of a CW SC in optical fibers pumped by a CW ASE light. A bandwidth of 268nm (at -15dB level) with an average spectral density of 2.7mW/nm was demonstrated. Various approaches to flattening the spectrum and increasing the spectral width were also studied. The application of this SC source in WDM passive optical access networks (WDM-PONs) was investigated. Third, the approach of SC generation in a fiber combination of standard SMF and nonlinear DSF pumped by an all-fiber fs pulse Master Oscillator Power Amplifier (MOPA) system was developed. A spectral bandwidth of over 1000nm was demonstrated. Finally, the generation of broad comb-like-spectral light based on the pulse compression of 40GHz optical pulses in a new nonlinear dispersion-decreasing fiber with high SBS threshold was studied. A continuum light source with over 125 channels and a channel spacing of 40 GHz was achieved. The use of this continuum light source as WDM source in WDM-PONs was investigated.

In this paper, we report on a method of developing a fiber pressure sensor using a conceptually new approach: optical clock recovery. This system consists of three parts: 10GHz RZ-modulated signal source, pressure sensor, and detection. The pressure sensor part consists of single-mode fiber resonator (SMFR) with stress pressure, birefringent resonator and a polarizer. The elementary theoretical results are given. It is demonstrated the validation of the proposed solution.

A passive homodyne Michelson interferometric fiber-optic hydrophone with a single-hole cylindrical Helmholtz resonator has been manufactured. To validate the theoretical results that the fluid coefficient of viscosity has great influence on the maximum sensitivity at the resonant frequency, the acoustic sensitivity frequency response of the fiber-optic hydrophone has been measured in a standing-wave tank filled with castor oil. The viscosity coefficient of castor oil will change with the variation of the temperature. Experimental Results show that the fiber-optic hydrophone frequency responses of different temperature have identical form except that the maximum sensitivities are different. The acoustic sensitivities of low frequency are about -159dB re 1rad/μPa. While the maximum sensitivities near the measured resonant frequency of 800Hz go down with the fall of the temperature, i.e. with the increase of the viscosity coefficient, which is agree with the theoretical conclusions. This fiber-optic hydrophone is a prototype device for a class of sensors that used to eliminate aliasing in the future sonar systems.

A dissolved oxygen sensor based on ruthenium(Ru) fluorescence and U-shape plastic optical fiber (POF) was described. Dichlorotris (1, 10-phenanthroline) ruthenium (II) was used as an oxygen indicator, which was coated on to the surface of a 1mm diameter U-shaped POF. Phase modulation technique is used to measure fluorescence lifetime. The phase difference between 100% and 0% dissolved oxygen is 1.78 degree. By using the nonlinear assumption, we also calculate that the there are only 20% thickness of the sensor material is affected by DO.

Experiments using high birefringence fiber Sagnac loop mirror as the temperature sensor are reported. We study the characteristics of this sensor based on intensity detection. The result is linear in the measurable range. The sensing sensitivities of temperature is 0.92nm/°C, which is nearly 89 times larger than the typical temperature sensitivities of fiber Bragg grating.

A novel high-birefringence fiber loop mirror(HBFLM) force sensor based on a freely supported beam(FSB) is demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the central surface of the FSB. The force is applied to the center of the FSB, which leads to the pre-demarcated wavelength shift of the transmission spectrum of the HBFLM. The sensitivity reaches 8.9N/nm, the resolution is 0.049N, and the linear measurement range is 0.049N~0.392N.There is a good linear relationship between the force and the wavelength shift. The advantages of the sensor include simple structure, high sensitivity, low cost, and good repeatability, etc.

The fiber-optic evanescent wave temperature sensor is investigated experimentally, for which the sensing probe consists of a fiber-optic coupler. The coupling visibility fluctuation of the fiber coupler probe was measured when the environmental temperature shifted center wavelength of the LD light source. From the experimental results, with the center wavelength of LD shift to longer wavelength, the transmission loss increased, and the wavelength shift of LD was about 0.5nm/°C. By using the supermode theory, the effect of wavelength shift of light source on the fiber coupler sensor was discussed.

As fibers with ever increasing mode area are used to enable high power fiber amplifiers and lasers, it important to use realistic models of bending in fiber design. The standard approach is to consider only the bend-induced losses and mode-coupling when designing an amplifier, even though changes in mode shape are well known in principle. But even coiling a fiber to fit into a reasonable package size produces large bend-induced distortion for fibers with large mode area. Here, several recent results are reviewed. Distortion significantly impacts amplifier performance by reducing the area, and can further degrade the interaction of light with the gain. Scaling rules for the distortion are derived from an intuitive sensitivity model. Bend distortion considerations lead to new strategies for large mode area fiber design, and cast existing strategies in a new light.

Four types of YDFs with different Al³⁺ concentration and mole content of GeO₂ were manufactured and the refractive index and absorption spectra of these fibers were explored. With the comparison of four YDFs and detailed analyze, it was found that higher Al³⁺ concentration leads to more GeO₂ volatilization, which results in the refractive index decrease. Therefore, mole content of GeO₂ should be increased when co-doping Al³⁺ in YDF to maintain numerical aperture. Meanwhile, the temperature of making porous layer should be controlled exactly to obtain good repetition of Al³⁺- codoped YDF as the little change of temperature has little effect on mole content of GeO₂ and SiO₂ but has great effect on compactness of porous layer. By drawing the fiber and testing the related parameters, the results show that the optimum temperature range for making soot layer should between 1440°C and 1480°C where the absorption coefficients were as high as 620dB/m with better repeatability. Finally, the ratio of GeO₂ to SiO₂ should be controlled to obtain long fluorescence lifetime for fabricating highly ytterbium-doped fiber with required numerical aperture.

Suppressing nonlinear effects such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) in high power fiber amplifiers and lasers is crucial for scaling up output power well beyond kW levels. The paper uses a sophisticated model to analyze many different fiber amplifier designs and compare their performance. The systematic modeling reveals many interesting results and shows that a co-pumped amplifier can be optimized by carefully choosing fiber lengths and applying additional heating to the fiber. It also explains why the amplifier configuration can make great impacts on SBS characteristics. In addition, a single-polarized fiber having an effective area of 206 μm² and cutoff wavelength of 1100 nm is designed to suppress SRS and provide better polarization properties. The systematic modeling concludes that in general a counter-pumped fiber amplifier has the lowest nonlinear effects and is less sensitive to the fiber length comparing with the co-pumped amplifiers. However, the co-pumped amplifier is easy to integrate with an all-fiber-based pump combiner without risking LD damage and it can be heated to increase SBS threshold by a factor of 1.7.

We propose the novel fiber devices with laser machining technique. one dimensional fiber end-surface grating was fabricated by inscribing micro-structure on the cleaved surface of a thermally expanded core fiber with femtosecond laser pulses. Diffraction beam patterns of the zeroth and the high order due to end-surface grating were observed. For the monitoring of signals in coarse wavelength division multiplexing wavelength, the measured diffraction beam patterns according to the wavelength of input light were investigated. Also, a structurally induced compact helicoidal long-period fiber grating (HLPFG) was fabricated by twisting a single mode fiber with CO₂ laser beam and its characteristics were experimentally investigated. The eccentricity between the core and the cladding of a fiber is introduced from the screw-type deformation. This helically induced significant periodic index change along the fiber produces a deep mode coupling between the core and the cladding of -20 dB with a short grating length of ~1 cm. The novel peak shift of a HLPFG was analyzed with co-directional or contra-directional torsion to the helix.

Based on the coupled mode theory by using the reversely recursive transmission matrix method, the switching characteristics of the λ/4 phase-shifted fiber grating and the influence of introducing chirp on the switching characteristics have been numerically studied when the reflection of the transmission facet is taken into consideration. The results show: for coherent superposition reflection strengthening, it can reduce the threshold switching energy of the λ/4 phase-shifted grating, but the switching contrast will decline; with the introduction of negative chirp in λ/4 phase-shifted grating, the switching contrast will be greatly improved, but the threshold switching energy will increase; with the introduction of positive chirp in λ/4 phase-shifted grating, the switching threshold can be further reduced, but the switching contrast will decline; and the hysteresis loop width will be influenced obviously by the introducing chirp.

The all-fiber, multi-cavity, Fabry-Perot passband filters based on fiber Bragg gratings, up to seven, are presented and modeled. The general formulas of the transfer function for the multiple-cavity Fabry-Perot filters are derived with the transfer matrix method. Transmission spectrum characteristics of the filters with different number of cavities are simulated, analyzed and compared. Numerical results show that near-rectangular bandpass shape can be realized by choosing the proper index modulation depths for every forming FBGs. And the simulations clearly demonstrate that the more we increase the number of cavities the more the shape of the central transmission peak is getting rectangular.

In this paper, special long period fiber gratings with Gauss envelope and rotary refractive index modulations, as well as ultra long period fiber grating are fabricated by using the high frequency CO₂ laser pulses exposure method. The characteristics of these LPFGs are investigated by experiment. It is anticipated that these novel LPFGs would find potential applications in optical fiber sensing and optical fiber communication due to their special optical waveguide structure.

This paper proposes a method of using fiber Bragg grating as optical filter in laser inter-satellites communication system. Effects of Doppler shift to SNR and band requirement of optical filter are researched in this paper. Given the wavelength is 1550nm, strong fiber and Blackman windows function are used in designing fiber grating to satisfy the need of the inter-satellites communication system. And the simulation and experiment results show that fiber Bragg grating can be used as optical filter in optical signal communication system of satellites communication.

The coupled-mode equations corresponding to a novel complex long-period-grating-assisted coupler (LPGAC), which consists of both the periodic refractive index modulation and gain/loss perturbation, is introduced and the close-form analytical solution is obtained, for the first time to our knowledge. And a unique unidirectional and nonreversible filtering characteristic is achieved by adjusting the gain/loss to match with the refractive index modulation. In addition, the impact of deviations in the grating profile is also evaluated, and the results show that the required device performance can be realized by controlling the amplitude and phase deviation <5%.

A novel design of M-Profile Ytterbium doped Fibers (YDFs) for high power fiber Lasers was given. The output power was two times higher than that in standard double-cladding fiber under the same threshold of damage.

Highly nonlinear fibers with nearly zero flattened dispersion over a wide band range has very wide applications in future high-capacity, all-optical networks. Because of its flexibility of structure design and much larger index contrast between the core and effective cladding than the conventional fibers, photonic crystal fibers (PCFs) are becoming to be an attractive candidate to form this kind of highly nonlinear fibers. Based on quantitative analysis on the effect of the difference of hole-sizes between the first ring and the other's, and the effect of Ge-doped concentration in the core region on the PCF's dispersion curve, a new way to design PCF with high nonlinear coefficient and nearly zero flattened dispersion is proposed. Based on this, a PCF is designed, which has dispersion values between ±0.8ps/nm/km over S+C+L wavelength bands, and the dispersion slope of 0.005ps/nm²/km, nonlinear coefficient of 46.6W^-1km^-1 at 1.55μm.

In this work the recent interest in waveguides for use in short optical links has motivated a study of the modal noise dependence on launch conditions in short-reach step-index multimode polymer waveguides. Short optical links, especially those with several connection interfaces and utilising a restricted launch are likely to be subject to a modal noise power penalty. We therefore experimentally study the modal noise impact of restricted launches for a short-reach optical link employing a 50 x 50 μm polymer multimode waveguide. Lens launches resulting in small diameter input spots are investigated as are restricted launches from an 8 μm core optical fibre. For a launch spot of 10 μm diameter no impairment is observed for up to 9 dBo of mode selective loss, and for a fibre launch with a dynamic input movement of 6 μm no impairment is seen for up to 8 dBo of mode selective loss.

We develop a new model to simulate and analyze sidelobes' influence on the pulses characteristics and performance of fiber Bragg grating-based Q-switched fiber laser. Our simulation results show that uniform fiber Bragg gratings with sidelobes negatively affect the Q-switched fiber laser performance. Their sidelobes introduce undesired multi-peaks and decrease the output pulses energy, while the apodized fiber Bragg grating with high sidelobe-suppression-ratio is able to eliminate the multi-peaks effectively and generate higher energy pulses with smoother profile. Experimental work has been conducted to validate the proposed model and verify the simulation results.

We demonstrate confinement of light in a submicron-diameter silica core by adding a Bragg multilayer cladding. Simulation results show that silica core Bragg fibers with Si/SiO₂ multilayer claddings exhibit stronger mode confinement than air cladding silica fiber. The optical properties of Bragg fiber taper can be fine tuned via controlling taper diameter and multilayer structures. In experiment, TE₀₁ mode-shaped spots with full-width at half-maximum (FWHM) of 1.2 μm are observed for the first time to our knowledge in solid-core Bragg fibers. By adjusting the refractive index of high index layer, HE₁₁ mode-shaped spots with FWHM of 0.75 μm are generated by 1.1 μm-core Bragg fiber tapers. The proposed devices will be good candidates as polarization selection and mode conversion devices for nano-optical applications.

Multi-wavelength optical buffer will be a key element in Wavelength Division Multiplexing (WDM) system and all-optical packet-switched networks. In this paper we have presented and demonstrated the dual-wavelength signal buffering in Dual-Loop Optical Buffer (DLOB) based on Semiconductor Optical Amplifier (SOA). The dual-wavelength packets are written in and read out of DLOB by single control signal. As the power of the control signal increasing, the output of the signals is better. In simulation confirmed by experiments, we obtained suitable control power, where the gain and phase-shift difference between "1" bit and "1+1" bit is minimum. More than 12 cycles' buffering results have been obtained and the power loss is lower than 4db.

Fundamental noise limitations of distributed quantum amplifiers are discussed. For Raman amplifier pumps to signals noise transfer, Rayleigh backscattering and polarization fluctuations of the pump are additional noise sources, which are discussed including their impact on system performances.

The relationship between the gain flatness performances with the pump wavelength spacing in single-stage backward-pumped distributed fiber Raman amplifiers (B-DFRAs) were demonstrated theoretically. It was shown that the gain spectrum of B-DFRA which pump wavelengths were arranged in a geometric proportion interval sequence were flatter than one which pump wavelengths were arranged in an equal interval sequence in the same conditions.

Dispersion compensating fiber (DCF) has seen considerable progress over the last decade and due to its well-controlled dispersion profile, high reliability and passive operation it has ecome the preferred method for compensating chromatic dispersion in today's optical communication systems. Raman amplification in fibers has found increased use in especially long-haul, high-capacity systems, mainly due to its low noise figure and versatile gain bandwidth. In this paper, we describe how Raman amplification can be used in DCF to realize discrete dispersion-compensating amplifiers, the so-called dispersion compensating Raman amplifier (DCRA). The main focus is on system applications and demonstrated results using DCRAs. These application include terminal compensation using DCRAs, hybrid amplifiers where the DCRA can be used to extend the dynamic range of existing erbium-doped fiber amplifiers (EDFAs), as well as hybrid EDFA/DCRAs with ultra wide gain bandwidth.

Raman fiber amplifiers (RFAs) have become increasingly important in optical communication systems and optical networks to compensate for the fiber loss and/or splitting loss. Comparing to the conventional rare-earth doped fiber amplifiers, RFAs have flexible signal gain band and low noise figure (NF) level [1]. Recently, we reported an RFA with signal/pump double-pass the gain medium scheme by utilizing an optical circulator (OC) as a signal/pump reflector [7]. The experiments have successfully confirmed that the pumping efficiency improvement for this kind of RFA is more efficiency than other types of RFAs. What's more, the pumping efficiency improvement and the NF suppression can be realized simultaneously. Although it is crucial to numerically predict the characteristics of RFA such as signal power and noise figure (NF) versus pump wavelength, pump power, gain medium characteristic and so on, the optimum design of RFA parameters has not yet been addressed. In this paper, we preliminary describe the numerical simulation method based on a set of coupled steady-state equations to estimate the characteristics of signal/pump double-pass RFA. First we assume that the ASE level combines other noises is 30 dB lower than that of the input signal [8], so only the forward and backward signal/pump are considered. This is a typical boundary condition problem and Newton method is used. As we get the distribution of pump power and signal power along the DCF, the noise item at different frequency can be found by the relaxation method. After several iterations, all WDM channel signals and noise are convergent as predict. In this paper, in order to optimize the length of the DCF to get the best performance, we suggest a proper definition of NF called effective NF. During the simulation, the length of SMF is kept constant, so DCF length becomes the only dominant variable parameter to affect the gain and NF of the RFA. To verify the algorithm above, the parameters are set equal to those in Ref. [7], and the simulation results are in very good agreement with those of experimental data. To show the optimum DCF length under a fixed pump power and pump wavelength, we calculate results of both the signal output power and NF versus DCF length at three signal wavelengths. We find that the largest signal output power may appear at the length of DCF is 3.6 km, and the lowest NF could be found as the DCF length is 4 km. In general, DCF has a larger gain coefficient than that of the SMF, but the attenuation coefficient of the former is also higher than that of SMF. So, there is a trade-off when selecting the length of DCF. From the simulation results, we conclude that the optimum length of DCF is 3.8 ± 0.2 km. DCF length of around 3.8 km is an ideal value to realize the best characteristics for the RFA.

We report an investigation of design, fabrication and measurement for photonic crystal fibers developed by YOFC in three years. The development status of PCFs and their applications are synoptically investigated. In the part of fabrication process, a technology route of PCF fabrication are reviewed, and the process principle, process control and realization method are introduced mainly, related to process bottlenecks. Based on different PCFs designed respectively by Beam-Propagation Method, Plane-Wave Expansion Method or FDTD and the above fabrication process, we probed into and realized some kinds of PCF samples. The structure parameters, cross-section morphologies, attenuation and dispersion properties for PCF samples are respectively investigated. We also debate upon the potential application of PCF field.

A highly birefringent polarization maintaining photonic crystal fiber based on organic macromolecule polymer material was fabricated. The fiber has an elliptical core and three ring square hexagonal structure, with the average hole-diameter, d=2.5 μm, and d/Λ=0.4. Polarization properties such as birefringence, beat length, polarization mode field were measured and numerically simulated. This research shows it is possible to fabricate high birefringence polarization maintaining photonic crystal fiber based on polymer at visible wavelength.

Two simple and low-cost methods for achieving selective filling of air-core photonic bandgap fibers (PBGFs) are proposed and demonstrated. In the first method, liquid paraffin was filled into a PBGF by capillary force. By a two-step filling-cleaving process, all cladding air-holes are finally blocked but the air-core remains open. In the second method, lateral erosion method by hydrofluoric acid was first used to make the cladding air-holes laterally open. Then, the laterally filled liquid paraffin made all cladding air-holes blocked and left only air-core open. With these two methods, the central hollow-core of the PBGF can be selectively filled, which allows for the fabrication of novel hybrid functional-material-silica PBGF for various applications.

The fabrication of a tunable all-solid photonic bandgap fiber coupler based on side-polishing technique is reported. The all-solid photonic bandgap fiber is set into a silica block and then polished to access the evanescent field. The photonic bandgap fiber coupler was assembled by mating two identical half-blocks with each other. By longitudinally adjusting the relative position between the mated pair, the tunable coupling ratio as much as 92.5% at 1550 nm is achieved. The investigation of the spectrum properties shows that the coupler has excellent tunability properties, for which the coupling ratio can be smoothly and continuously tuned.

We propose a novel design of dual-concentric-core all-solid photonic bandgap fiber (DCC-AS-PBGF). It is designed by introducing a ring of bigger high-index rods, a new defect, in the cladding of a conventional all-solid PBGF. Using plane wave expansion method (PWEM) and full-vector finite-element method (FEM), we study the effect of introducing such a ring of bigger high-index rods. The numerical results show that large dispersion is gained around the wavelength where the modes in the new defect couple with the modes in the core. More importantly, the confinement loss of the LP₀₁ modes around the wavelengths, where large dispersion is induced, could be decreased by increasing the rings of high-index rods for the fact that these waveband are within the bandgap.

A hybrid guiding liquid-crystal photonic crystal fiber is proposed, in which two polarization components (E_x and E_y) are confined by modified total internal reflection and bandgap guidance, respectively. With the aid of scalar wave approximation, the distinct features in band structures of liquid-crystal photonic bandgap fibers are successfully identified. This hybrid guiding feature makes it possible to achieve single-polarization single-mode guiding and high birefringence guiding effect in different wavelength ranges. Particularly, high birefringence in an order of 10^-2 can be easily obtained.

The current challenges facing the adoption of optical transmission in printed circuit applications will be discussed and our recent efforts establishing silicone polymers provide a viable route to manufacturable cost effective hybrid electric-optic printed circuit boards will be presented.

We investigate the influence of structure parameters to the band structures of one-dimensional photonic crystals stacking of alternating positive and negative refractive index materials. The refractive index of these two materials has the same given absolute value. We find that the layers' thickness of the photonic crystals determines the frequency and angle of the transmission peaks, and when the thickness is given, the permittivity and permeability of the negative index material determine the width of frequency peak and angular peak. For realizing ultra-narrow band frequency and sharp angular filer, we add a defect layer with positive refractive index in the middle of the photonic crystals. Setting its structure parameters satisfying some special conditions, there will be a narrow peak in the middle of the band gap. When electromagnetic wave incident on such PC, only those portions with special frequency and special angle can pass though, and the accuracy can be very high. Such filter will have wide applications in microwave and optical communications.

A theoretical model of wavelength division demultiplexer (WDD), which is based on an asymmetric Mach-Zehnder interferometer (AMZI) constructed in a two-dimensional photonic crystal (2D PhC), is proposed and numerically demonstrated. The 2D PhC consists of a square lattice of cylindric air holes in silicon. The AMZI includes two mirrors and two splitters. Lights propagate between them employing self-collimation effect. The two interferometer branches have different path lengths. By using the finite-difference time-domain method, the calculation results show that the transmission spectras at two AMZI output ports are in the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.26c/a to 0.27c/a. When the path length of the longer branch is increased and the shorter one is fixed, the peaks shift to the lower frequencies and the peak spacing decreases nonlinearly. Consequently, the transmission can be designed to meet various application demands by changing the length difference between the two branches. For the dimensions of the WDD are about tens of operating wavelengths, this PhC WDD may be applied in future photonic integrated circuits.

Based on a new metal-wire nano-grating which we suggested recently, a number of optical devices designs are discussed in this paper. The new metal-wire nano-grating consisted of a series of fine parallel metallic lines embedded in substrate. The unique property of this embedded grating is that it can be adhered with other optical elements arbitrarily and can endure any physical and chemical impact on trial due to the steady homogeneity upper cladding layer. The basic structure of these designs employs four pieces of the artificial material mentioned above. The two pieces at left side work as PBS. The other two pieces at right side work as PBC. When we insert one variable LC (liquid crystal) polarization rotator unit between the PBS and PBC. It could work as an essential 1x2 switch. If the voltage applied on the LC unit is not big enough for 90° rotation, It could work as an essential 1x2 VPS (variable power splitter). Obviously, when we only deploy one input and one output, this is an essential VOA (variable optical attenuator). When we insert one interleaver core between the PBS and PBC, plus two waveplates among the light path, it could works as an interleaver. When we insert one half waveplate and one Farady rotator, between the PBS and PBC, it could works as a circulator. We have actually built a prototype of 1x2 VPS (variable power splitter) device, and the performance meets most of the engineering application requirements.

A squeezed elliptical hole air-silica photonic crystal fibre is reported for all optical signal processing, which has some novel properties of high birefringence and high nonlinearity, according with tailorable dispersion at 1550nm.

A new near-elliptic cladding Polarization-maintaining photonic crystal fibre (PM-PCF) with four different hole diameters was proposed. Since the refractive index decreases gradually from x-axis to y-axis, less polarization coupling and high extinction ratio were obtained compared to the conventional PM-PCFs. Secondly, every hole diameter of near-elliptic cladding was optimized to get good performance, considering proper mode field diameter of x-axis and y-axis for better coupling to SLD and smaller confinement loss of the new PCF, high birefringence and high extinction ratio, especially the effects of disturbance on extinction ratio stability. According to series of comparison on different hole diameters and correlation between different holes, the optimum parameters of this new PCF of Λ=2.2μm, d₁=2μm, d₂=1.1μm, d₃=1.7μm and d₄=1.2μm were derived. The optimized near-elliptic cladding PCF can obtain both high extinction ratio (>29dB) and good extinction ratio stability (<2dB with ±10% transverse disturbance of d₃) which is useful for practical use.

A new near-elliptic inner cladding (NEIC) structure of polarization-stable highly birefringent photonic crystal fiber (HB-PCF) is proposed and analyzed by using a full-vector finite element method (FEM) with anisotropic perfectly matched layers. From the numerical results it is confirmed that, with the diameter of air hole A varied by ~10%, the modal birefringence degradations of the three proposed NEIC-PCFs are less than 4.2 × 10^-5, 6 × 10^-5 and 1.17 × 10^-4, respectively, while the average birefringence is of the order of 2 × 10^-3 at 1.55μm, which strongly proves that the proposed structure is highly polarization-stable. Especially, the MFDs in x-direction and y-direction of NEIC-PCF with three holes diminished in the center are measured as 5.8 μm and 2.6 μm, respectively, which are very attractive in the application field of fiber optic sensor, e.g. fiber optic gyros.

Through introducing two sizes of hole in the cladding of PCF, a kind of highly birefringent two-mode photonic crystal fiber (PCF) is proposed. Modal properties are analyzed numerically by the plane wave expansion method. Numerical results demonstrate that only two-mode, i.e. LP₀₁ and LP₁₁^even can propagate in the wavelength range from 500nm to 1890nm in the two-mode PCF which is nine times as wide as that in elliptical core fibers. The theory of highly birefringence two-mode PCF for constituting fiber sensor is also discussed. According to the structure proposed, we successfully fabricate the highly birefringent two-mode PCF with stack-drawing technique and gas-inert pressurization control at furnace temperature 1900°C and gas-inert pressure 900pa. They could extend significantly the application range of these two-mode devices and open up new possibilities.

A full-vectorial analysis of photonic crystal fibers based on a compact two-dimensional finite-difference time-domain method (C2D-FDTD) is presented. The model with material dispersion incorporation is formulated and validated. The Sellmeier equation is implicitly included into the model to account for the material dispersion of silica. In this paper we use a formulation of Maxwell's curl equations by electric flux density and magnetic field intensity, with auxiliary differential equations; and we demonstrate the flexibility and robustness of this approach in treating general material in PCF. We have good agreement with multipole method.

Photonic crystal fibers (PCFs) have attracted much interests recently mainly because of their unique properties. Based on the light confinement mechanisms, the photonic crystal fibers can be divided into tow classes: the index-guiding PCFs and the photonic bandgap (PBG) PCFs. The former, with multiple air holes periodically arranged around the core, possess numerous unusual properties, such as structure controllable chromatic dispersion, large mode areas, birefringence and stronger optical nonlinenarity.Based on the full vector, semi vector or even the approximate-scalar model, Lots of methods have been used to design the PCFs, such as the effective index approach, the localized function expansion method, the plane wave expansion method, the multipole method, the beam propagation method, the finite difference method, the finite difference time domain method, and the finite element method. Each of theses method mentioned above are accurate and efficient for ideal PCF, however, for the real fabricated PCFs, the geometry structure may not perfect, induced the base mode degeneracy may be destructive, and posses birefringence properties. Sometime the birefringence properties is necessary for special usefulness, such as polarization mode dispersion (PMD) compensation, and PCFs based polarized optical devices. In this paper, a full vector finite element is applied to investigate the mode birefringence, mainly focus on the rectangle lattice PCFs with elliptical or circular holes. It has been demonstrated from the calculated results that high birefringence to the order of 0.01 can be achieved by decreasing both the pitch and the x and y ratio of the elliptical hole. To increase the birefringence of the circular holes rectangle lattice, reduction of the width and height ratio of the lattice is necessary. Based on the simulation results, we conclude that both single polarization transmission and high birefringence polarization maintaining can be achieved by using the proposed structure with suitable parameters respectively. The available high birefringence at relative high frequency regime in the fibers and also the sufficiently broad single mode region would make the fabrication of highly birefringent photonic crystal fibers with novel properties possible.

We demonstrated an ultra-broadband wavelength converter based on co-polarized dual-pumping four-wave mixing technique in a dispersion-flattened photonic crystal fiber. Over 380-nm wavelength conversion range from 1260 nm to 1640 nm has been achieved. By sweeping the wavelengths of the second pump laser, we have obtained the relationship between the wavelength conversion efficiency and the converted data signals, which are consistant with our theoretical analysis. The OSNR of the converted data signals are up to 30 dB.

Liquid crystal (LC) devices for Photonics applications is a hot topic of research. Such elements begin to appear in Photonics market. Passive elements for fiber optical communication systems (DWDM components) based on LC cells can successfully compete with the other elements used for the purpose, such as micro electromechanical (MEM), thermo-optical, opto-mechanical or acousto-optical devices. Application of nematic and ferroelectric LC for high speed communication systems, producing elements that are extremely fast, stable, durable, of low loss, operable over a wide temperature range, and that require small operating voltages and extremely low power consumption. The known LC applications in fiber optics enable to produce switches, filters, attenuators, equalizers, polarization controllers, phase emulators and other fiber optical components. Good robustness due to the absence of moving parts and compatibility with VLSI technology, excellent parameters in a large photonic wavelength range, whereas the complexity of the design and the cost of the device are equivalent to regular passive matrix LC displays makes LC fiber optical devices very attractive for mass production. We have already successfully fabricated certain prototypes of the optical switches based on ferroelectric and nematic LC materials. The electrooptical modes used for the purpose included the light polarization rotation, voltage controllable diffraction and fast switching of the LC refractive index. We used the powerful software to optimize the LC modulation characteristics. Use of photo-alignment technique pioneered by us makes it possible to develop new LC fiber components. Almost all the criteria of perfect LC alignment are met in case of azo-dye layers. We have already used azo-dye materials to align LC in superthin photonic holes, curved and 3D surfaces and as cladding layers in microring silicon based resonators. The prototypes of new LC efficient Photonics devices are envisaged. Controllable photonic crystal / liquid crystal (PC/LC) devices became a "hot" topic of research. New PC/LC passive elements of fiber optical systems: electrically tunable LC photonic fibers, fiber optics tunable LC filters, tunable photonic crystal lasers are envisaged. A method for the formation of controllable PC/LC structures, based on photo-aligned LC is considered. Filling of the interstices of the photonic crystal with the photo-aligned LC material and subjecting the LC to a varying electric field can produce a tunable photonic crystal element. We have already used the photoaligning materials to align LC mixtures in small cavities, such as the holes and tubes of photonic crystals, having size of 1 μm and less and obtained excellent LC orientation inside the tubes by photoalignment.

There are two approaches to develop reliable photonic devices. One is by the process & materials optimization, and the other is the reliability assurance during the fabrication, packaging & operation period. These critical issues needed to be addressed in order to bring commercialization of these devices closer. The development of organic polymers with high optical quality & high performance has led to a maturing of the polymer photonic device field. The combination of structural flexibility and toughness in optical polymers also makes it more suitable for vertical integration to realize 3D and even for all-polymer integrated optics. Packages are usually an integral part of the device. Therefore, fabrication, packaging and reliability challenges are the well-known potential showstopper to the growth of photonic components. In this review, the suitability of optical polymer systems, the materials & process optimization issues in fabricating reliable planner lightwave circuit (PLC) devices, packaging of fiber array & splitter components to integrate fiber-to-waveguide devices for fiber-to-the-home (FTTH) networks are summarized.

A novel reflection-type filter composed of microring resonator array and MZI is presented and analyzed. Simulation results show that the devices can be used as reflection-type filters for DWDM system or wavelength-selective reflectors for fixed or tunable lasers by properly choosing the values of coupling ratios.

A compact wavelength division multiplexing (WDM) module is designed using discrete micro optics components assembled on silicon optical bench for multiple-channel transceivers. This design is optimized for a 4-channel multiplexer (MUX) plus a 4-channel demultiplexer (DEMUX). In this design, the micro optics components for the MUX and DEMUX are integrated, and the MUX and DEMUX share the same space. This helps to minimize the number of components required and hence reduce the cost and size. Therefore, the module is compact enough to be put in small standard packages (SFF/SFP).

Optical injection mode-locking of a weak-resonant-cavity Fabry-Perot laser diode based fiber ring with an intra-cavity power controlled wavelength shift and a reducing chirp linewidth at high intra-cavity coupling ratio condition is demonstrated. Both the strong dark-optical comb and strong feedback coupling contribute to the wavelength spectrum shift toward longer wavelength, a wavelength shift from 1356 nm to 1542 nm of the weak-resonant-cavity FPLD based fiber ring associated with its pulsewidth and linwidth also reduced from from 37.5 to 29.5 ps and from 10 to 6 nm, respectively, can be observed. Furthermore, the peak-to-peak frequency chirp reduced from 3.5 to 1.8 GHz was caused by the shrink of linewidth.

In this paper, we propose new types of dual microring resonators coupled via 3×3 couplers. By employing the transfer matrix method, a model for these four types is developed and analytical expressions for characterizing their transmissions are derived. The first two types show a coupled-resonator-induced-transparency-like transmission spectrum at the through port. The third type holds the same transmission spectrum, while the last type simultaneously realizes a first-order and a second-order filters at two drop ports. The effects of coupling coefficients on their transmission spectra are analyzed in more detail. These proposed types can be found applications in fields such as sensors and filters.

Solar blind ultraviolet communication systems can provide short to medium range non line-of-sight and line-of-sight links which are covert and insensitive to meteorological conditions. These unique properties endow solar blind ultraviolet communication systems increasing applications. While optical filters are key components of these solar blind ultraviolet communication systems. Although filters can be designed in different forms, thin-film interference narrow-band filters are widely adopted. In this paper, we make use of NCNBIF, which was so-called nonconventional narrow-band interference filters proposed by Jerzy Ciosek firstly, to design ultraviolet narrow-band interference filters. Generally, classical narrow-band interference dielectric filters, such as Fabry-Pérot filters, have a half-wave-thickness spacer layer. In contrast with a classical interference filter, the NCNBIF does not have a half-wave-thickness spacer layer. This spacer layer of NCNBIF consists of two different materials. This new kind of film system (NCNBIF) is synthesized by using needle optimization technique, and possesses desired spectral characteristics.

Polarization mode dispersion may be the optical impediment that prevents future system upgrades to higher transmission speeds or longer reach. In contrast to chromatic dispersion, PMD is a statistical quantity making it extremely difficult and expensive to compensate. Thus fibers with low PMD where no such compensation is needed is therefore of great interest. This paper discusses the levels of PMD that can be tolerated at future transmission speeds and relate these to the current ITU-T recommendations. The focus of this paper is the issues that have to be considered in order to manufacture fibers and cables with sufficiently low PMD levels. This includes process control, fiber spinning, and proper measurement of the PMD. A correct PMD measurement makes it possible to judge whether a specific step in the process introduces or changes PMD. We show that the proper process control and PMD measurements have facilitated production and installation of large volume of cables with PMD low enough to support future upgrades.

The impacts of polarization dependence loss (PDL) on the polarization mode dispersion (PMD) compensation in return-to-zero (RZ) and non-return-to-zero (NRZ) modulated systems are discussed in this paper. PDL affects the degree of polarization (DOP) feedback PMD compensation only in the presence of PMD. And in the presence of PMD and PDL, DOP relates not only to both the PMD and the PDL vectors, but also to the signal's polarization states. In the presence of PDL, DOP-feedback PMD compensation would be more effective in NRZ system than in RZ system.

A kind of voltage-controlled polarization controller made in electro-optic materials is studied in the experiment. By changing voltages added on the different plates, the corresponding out states of polarization are gotten which spread all over the Poincare. Results show that the phase retardation angle in each plate is a quadratic function of the applied voltages. And the degrees of polarization ellipsoids are obtained with the same the principal state of polarization. PC, a key element in the communication system, has great advantage for Polarization mode dispersion compensation and accurate controlling to the states of polarization.

The spatially and spectrally resolved polarization mode dispersion (PMD) measurement technique is proposed to measure PMD values of every fiber sections in an optical fiber link in the wavelength range interested. This technique is validated by comparing the results of reflectometric and forward measurements.

Generalized principal state of polarization (PSP) is proposed to analyse the piezoelectric polarization controller (PPC) and demonstrated by experiment. We find the generalized PSP is a constant in a given PPC unit and the output state of polarization (SOP) is expressed as a cosine function of driving voltage with its validity analysed. Then the polarization control system is established based on the PPC with three units and some of the its characteristics are investigated. Results show the PSPs of three PPC units are approximately orthogonal to each other, and the polarization response time of our PPC is about 40 μs, which will improve significantly the control speed of polarization control system.

Noise and quantum conversion efficiency(QCE) of ytterbium-doped fiber amplifier are researched theoretically in this paper. From the rate and propagation equations describing ytterbium-doped fiber amplifier system, the noise and QCE are calculated, and the effect of pump power, Yb doped concentration, and device length on noise and QCE is also discussed with 975nm pump wavelength.

The finite element method is applied for solving the modal field of erbium-doped hole-assisted lightguide fiber (EDHALF). The modified average population inversion iteration method is proposed for simulating the gain coefficients of EDHALF amplifiers. The relation between the structural parameters of EDHALFs and the gain coefficient of L band EDHALF amplifiers is investigated by means of the finite element method combined with the modified average population inversion method. Four structural parameters of EDHALF-core diameter, the refractive index difference between the core and silica cladding, the relative hole-to-core spacing and the relative size of air holes are optimized in terms of the design criteria of L band erbium-doped fiber, which take into account the cutoff wavelengths, the gain coefficients of L band fiber amplifiers and the splice loss between the EDHALF and the conventional single-mode fiber. At last, the comparisons between the EDHALF and the conventional erbium-doped fiber for L band applications are made.

A novel self-seeded multi-wavelength Brillouin-erbium fiber laser with a transmissive Sagnac loop filter is proposed. In the laser scheme, the Brillouin pump is self-excited within the cavity, which doesn't require injection from external cavity. 52 stokes lines are obtained by adjusting polarization controller (PC) in the Sagnac loop filter. The experiment also demonstrates that the pump power has an influence on the wavelength number and power distribution of the generated multi-wavelength comb. The multi-wavelength comb is tunable in a range of 6.5nm.

We have proposed and successfully demonstrated coherent polarization locking of two orthogonal-polarization beams in a Mach-Zehnder Erbium-doped fiber laser (MZEDFL) cavity based on the polarization-dependence losses of a polarizer. The two orthogonal polarizations are locked coherently to produce a resultant polarization state that sees maximal loss to the polarizer and minimal loss to the output port. High efficiency of coherent polarization locking of two orthogonal-polarization beams is realized, even when the powers of the two branch arms are highly imbalanced (19.3/14.8). The coherent output power can range from 45mW to 0.6mW by adjusting the PC with 120 degrees. This outcome shows the range from polarization locking to polarization unlocking occurring in the 50:50 fused fiber coupler.

The 7.1-magnitude earthquake on December 26, 2006 in the Strait of Luzon resulted in the failure of several submarine cable systems. Seven of the nine cables that pass through the strait were damaged, disrupting communications to China, Taiwan, Japan, Korea and Singapore. This recent event highlighted the dependence of international communications on submarine fiber optic transmission systems. This paper will review the evolution of optical fiber transmission line technology that has been deployed in the long haul undersea telecommunications network. It will start with a discussion of the chronological evolution of the optical fiber transmission line architecture in section one, then give more detail regarding the technology that is still being deployed today.

The mechanical reliability of single mode optical fiber is determined by the presence of surface flaws such as particles from the atmosphere during drawing or abrasion damage of the fiber surface by physical contact with any hard surface or drawing equipment and its size distribution, which are produced by normal fiber production methods. Proof testing is a common technique to ensure minimum strength of the fiber and eliminate the flaws whose sizes are dependent on the stress applied during proof testing. This paper describes the relation between the size and distribution of pre-and post-proof test flaws.

As the key of these optical devices which are widely used in the communication system, high nonlinear optical fibre will play an important role in the future optical fibre communication. With recent growth of nano-technology, researchers are hoping to obtain some kinds of optical fibre by combining the optical fibre with the nanotechnology. According to this current situation, the optical fibre doped with nano-material as InP (indium phosphide) is manufactured by using the MCVD (modified chemical vapor deposition) technology after our comprehensive consideration of many relative factors. Proved by experiments, this novel optical fibre has an excellent waveguide characteristic. After a consideration of the model of this novel optical fibre, its propagation constant β has been simulated by using the FEM (finite element method), and the graphs of presentation of magnetic field of the core are also obtained. In accordance with the results, the effective refractive index n_eff = 1.401 has be calculated. Both the calculated result and the simulated graphs are matching well with the test, and this result is a step-stone bridge for future research of nonlinear parameter on this novel optical fiber.

In this paper, we will briefly outline our contributions for the physical realization of coded OTDR, along with its principles and also highlight recent key results related with its applications. For the communication network application, we report a multi-port / multi-wavelength, high-speed supervisory system for the in-service monitoring of a bidirectional WDM-PON system transmission line up to 16 ports x 32 nodes (512 users) capacity. Monitoring of individual branch traces up to 60 km was achieved with the application of a 127-bit simplex code, corresponding to a 7.5dB SNR coding gain effectively reducing the measurement time about 30 times when compared to conventional average mode OTDR. Transmission experiments showed negligible penalty from the monitoring system to the transmission signal quality, at a 2.5Gbps / 125Mbps (down / up stream) data rate. As an application to sensor network, a Raman scattering based coded-OTDR distributed temperature sensor system will be presented. Utilizing a 255-bit Simplex coded OTDR together with optimized sensing link (composed of cascaded fibers with different Raman coefficients), significant enhancement in the interrogation distance (19.5km from coding gain, and 9.6km from link-combination optimization) was achieved to result a total sensing range of 37km (at 17m/3K spatial/temperature resolution), employing a conventional off-shelf low power (80mW) laser diode.

The dispersion properties of the index-step higher order mode dispersion-compensating fibers (HOM-DCFs) are simulated using an unequal interval finite difference method in this paper. Large negative dispersion of the first few higher order modes (HOMs) near cutoff are studied comparatively, which is helpful for designing the dispersion compensator based HOM-DCFs.

The formation mechanism of excess loss in LWP fiber after D₂ treatment was investigated. In drawing process, both the drawing tension and drawing speed have important effect on magnitude of excess loss. The origination of excess loss is related to the drawing-induced defects due to increasing on thermoelastic stress in glass fiber and it can be eliminated by optimization on viscosity match between core and cladding.

Surface plasmon poalriton (SPP) waveguides have the potential to bring technology revolutions in fields like photonic integration, optical sensing, and even deep sub-wavelength imaging. The peculiar guidance mechanism of such waveguides however imposes great challenges on our existing theoretical modeling tools. In this paper, the superiority of finite element method (FEM) is examined for deriving modes guided by realistic SPP waveguides. In consideration of the anisotropic field profiles of most SPP waveguides, we propose the deployment of anisotropic finite element mesh. The anisotropic finite mesh is found to be able to reduce the numerical problem size greatly. Among all SPP waveguides, we emphasis the importance of the metal-corner waveguides, including both V-channel and Λ-wedge waveguides. Such metal corners can be found in most SPP waveguides proposed or fabricated so far. The properties like dispersion and propagation loss etc are studied by using FEM. Subwavelength light guidance can be achieved by such corner waveguides when their angles are kept small enough. However their applicability in nanoscaled optical circuits is affected by high propagation loss. Loss reduction or introduction of metamaterial with gain is desired in order to obtain small mode field size as well as low loss.

The novel design of a silicon optical switch on the mechanism of a reverse p-n junction is proposed. The figuration of contact regions at slab waveguides and the ion implantation technology for creation of junctions are employed in the new design. The two-layer rib structure is helpful for reduction of optical absorption losses induced by metal and heavily-doped contact. And more, simulation results show that the index modulation efficiency of Mach-Zehnder interferometer enhances as the concentrations of dopants in junctions increase, while the trade-off of absorption loss is less than 3dB/μm. The phase shift reaches about 5×10^-4 π/μm at a reverse bias of 10V with the response time of about 0.2ns. The preliminary experimental results are presented. The frequency bandwidth of modulation operation can arrive in the range of GHz. However, heavily-doped contacts have an important effect on pulse response of these switches. While the contact region is not heavily-doped, that means metal electrodes have schottky contacts with p-n junctions, the operation bandwidth of the switch is limited to about 1GHz. For faster response, the heavily-doped contacts must be considered in the design.

A novel electro-optic integrated acceleration seismic geophone is presented in this paper and it is a new kind of micro-opto-electro-mechanical system (MOEMS). The optical waveguide polarizer, M-Z interferometer, harmonic oscillator system and waveguide phase modulator are integrated monolithically on silicon substrate with dimensions of 30mm×12mm×0.5mm. Mach-Zehnder waveguide interferometer of Si-based MOEMS acceleration seismic geophone is researched and its optimization structure design is accomplished. The material of buffer layer and coating layer is K9 glass. Two Bak7 glass Y-branching waveguides with width of 4μm and thickness of 0.4μm, and six guide mirrors are employed in interferometer. An S-shaped bend is used for the transition connecting two offset parallel waveguides in Y-branching. Because it is difficulty to make the branching angle large using conventional Y-branching, we designed 90º directional change by a vertical mirror facet to realize the special structure between measuring arm and reference arm. The inner dielectric film of the mirror facet is aluminum plating. To prevent polarization state of TE mode polarized light changed after passing through the aluminum film, 4 polarizers with length of 1mm have been used. The simulation results performed in BMP agrees with the theoretical analysis well.

Based on the Helmholtz's equation and energy conservation law for the travelling wave field, the actual wave function for the TE travelling wave in the inhomogeneous dielectric is recommended, the original field distribution functions of the TE mode in symmetrical planar waveguide core layer and cladding layers are suggested. Moreover, the virgin phase shift for total reflection effect at the turning point is proposed, the eigen equation of a new improved WKB method for the symmetrical planar waveguide is given. As the concept of phase delay for optical wave in the dielectric and the new improved WKB method are engaged, the multiple quantum wells planar waveguide is considered as an equivalent of the triplex layer waveguide, a new method for analyzing the symmetrical multiple quantum wells planar waveguide is put forward. Several approximate formulas for computing the effective refractive index, the normalized frequency and mode field distribution are presented. Then, found on the maximal matching efficiency method for the mode field distributions, the expression of Gaussian approximation for the mode field distribution of single mode symmetrical multiple quantum wells planar waveguide is present. As an example, the normalized field distributions of GaAs/GaAlAs symmetrical multiple quantum wells planar waveguide is referred.

LiNbO₃ films of 1-10μm thick were grown on z-cut LiTaO₃ substrates using vanadium and boron based fluxes by liquid phase epitaxy (LPE) growth. Characterization of these films using scanning electron microscopy (SEM), electron backscattering diffraction and high-resolution X-ray diffraction (HRXRD) show that they are single-crystal and epitaxial with the substrate. Subsequently, LiNbO₃ films were etched by SF₆/Ar inductively coupled plasma (ICP) in order to fabricate straight ridge waveguides. Effects of parameters including working pressure, RIE power and ICP power are investigated and analyzed by measurement of etching depth, selectivity, etched surface state and sidewall profile by means of focused ion beam (FIB) etching, energy dispersive X-ray (EDX) analysis, SEM and surface profilometry. Optimized processes with high etching rates, good mask selectivity and near vertical profile have been achieved.

Distributed sensors, based on Brillouin effect in the optical fiber, provide an excellent method for measuring temperature and strain over long distances. There are two types of such sensors. The first type is based on spontaneous Brillouin scattering, and is called Brillouin optical time domain reflectometer (BOTDR). It measures the Brillouin frequency shift or Brillouin power or Brillouin gain bandwidth to get the temperature and strain information. The second type of sensor is based on stimulated Brillouin amplification. It is called Brillouin optical time domain analyzer(BOTDA). Normally, it uses one laser at each fiber ends, one as pump and the other as a probe light. The probe light will experience Brillouin amplification. Through the analysis of Brillouin gain spectrum (BGS), we can get the temperature and strain information. Both the two types of sensors are attracting attention all over the world, and temperature resolution of less than 1 degree and strain resolution up to 5 με was reported. The fiber distances of up to 150km was presented while other papers reported a spatial resolution of the order of 1cm with frequency domain techniques or correlation techniques. We proposed and analyzed our design, it is an improvement of BOTDA with a single end laser, which make it easy to implement in field. Through simulations, optimized launch power has been found for a certain design.

20 ns-width pulses are modulated on a multi-wavelength fiber ring laser and transmit into two fiber Bragg grating based sensing heads with different wavelength. When the temperature exceeds the threshold at certain position, the light at corresponding time slot and wavelength will be reflected. Thus, the warning location of temperature increasing will be easily determined from OTDM (optical time division multiplexing) demodulation technique.

A novel design of linearly chirped fiber Bragg grating (LCFBG) based sensor, operating at a single optical wavelength and avoiding the complicated interrogation, is presented and demonstrated. The LCFBG exhibits a good linear relation between the group delay and the wavelength. When a pulsed optical signal goes through the LCFBG with a fixed wavelength within the grating bandwidth, it will be reflected at a particular spatial location along the grating and then will induce a particular time delay, which is direct proportional to the temperature applied on the grating. The time delay is an absolute parameter as well as the wavelength shift, resulting that it is insensitive to optical power fluctuation and loss. In order to measure the time delay accurately, the RF modulation technique is employed. The sensor setup is mainly composed of a narrowband laser source, a Mach-Zehnder electro-optic modulator driven by RF oscillator signal to provide an optical carrier, a 3dB fiber coupler to split the modulated signal into two parts, an optical circulator, a LCFBG with good linear behaviour of group delay spectrum as the sensor head, and two fast photo-detectors. The feasibility of the proposed sensor is demonstrated by numerical simulation, and the simulation result shows that the LCFBG can be used as a good temperature sensor.

The XPM technique is applied to the demodulation system for fiber grating sensor for the first time in this thesis. According to XPM principle, the intensity of accessorial light can be altered by feedback control and the phase of the light signal from the M-Z interferometer can be modulated in a phase-locked way, thus the system phase-difference can be locked at the point of the highest sensitivity. It resolves the precision non-linearity of interferometric demodulation, the limit of very small range for demodulating, the non-linearity of the demodulating sensitivity, the affect of backlight and undercurrent pair in the demodulating circuit, the delay-effect by PZT tune and the error from the machine.

A novel interrogation method with multi-switches channels for time-division multiplexing Fiber Bragg Grating (FBG) sensor system is introduced. An electric switches array controlled by a complex programmable logic device (CPLD) is used in this scheme to monitoring simultaneously each sensor of the FBG array according to the different transmition times of each sensor grating. In this paper, More than 10 FBG sensors are interrogated and demodulated simultaneously base on unbalanced Michelson interferometer. The sensing sensitivity of this system is 1.658 Deg per micro-strain, experimentally. The interrogation frequency of the system could reach 1 KHz.

An all-optical tunable delay line based on wavelength conversion in semiconductor optical amplifier (SOA), and group-velocity dispersion (GVD) in dispersion-compensating fiber (DCF) is theoretically analyzed and numerically demonstrated. By describing the basic theory, modeling and simulating the processes, we show that the scheme is feasible to produce large time delays. The system operates near 1550 nm, and with a nonreturn-to-zero (NRZ) pattern at 10 and 40 Gb/s, time delays from -3360 to 3360 ps are observed. The system achieves continuous control of a wide range of delays, wide signal bandwidth, nearly no pulse broadening, and very little spectral distortion.

We review our work done for topology optimization of passive photonic crystal component parts for broadband and wavelength dependent operations. We show examples of low-loss topology-optimized bends and splitters optimized for broadband transmission and demonstrate the applicability of topology optimization for designing slow-light and/or wavelength selective component parts. We also present how the dispersion of light in the slow-light regime of photonic crystal waveguides can be tailored to obtain filter functionalities in passive devices and/or to obtain semi-slow light having a group velocity in the range ~(c₀/15 - c₀/100); vanishing, positive, or negative group velocity dispersion (GVD); and low-loss propagation in a practical ~5-15 nm bandwidth.

The applications of microwave optoelectronics are extremely large since they extend from the Radio-over-Fibre to the Homeland security and defence systems. Then, the improved maturity of the optoelectronic components operating up to 40GHz permit to consider new optical processing functions (filtering, beamforming, ...) which can operate over very wideband microwave analogue signals. Specific performances are required which imply optical delay lines able to exhibit large Time-Bandwidth product values. It is proposed to evaluate slow light approach through highly dispersive structures based on either uniform or chirped Bragg Gratings. Therefore, we highlight the impact of the major parameters of such structures: index modulation depth, grating length, grating period, chirp coefficient and demonstrate the high potentiality of Bragg Grating for Large RF signals bandwidth processing under slow-light propagation.

In this paper, the Multi-wavelength fiber laser's polarization sensitivity is investigated in the experiment research, through adopting the polarization scrambler eliminate polarization sensitivity, Stabilizing output eight wavelengths with the 0.8nm or 1.6nm wavelength interval have been achieved.

We use improved fully vectorical effective index method (IFVEIM) to design a flattened-dispersion photonic crystal fiber (PCF). By using such 1.5-km-long photonic crystal fiber in the numerical simulation, we could obtain high pump depletion in a cw fiber optical parametric amplification (OPA) with a 1600-mW pump at 1560nm.

In this paper, multiwavelength erbium-doped fiber laser (EDFL) by use of fiber Bragg gratings (FBGs) with different tilt angles in single mode fibers (SMFs) is demonstrated. The offset spliced FBGs are employed as lasing wavelength selectors. FBGs with 2° and 8° tilt angles can produce dual- and multi-wavelength oscillations, respectively. A nonlinear optical loop mirror is incorporated in the laser cavity to stabilize the multiwavelength oscillation at room temperature. The difference in coupling characteristics when offset launched between tilted FBGs in SMFs and uniform/tilted FBGs in multimode fibers are discussed.

We report experimental results of wavelength dynamics in a soliton fiber ring laser passively mode locked by using the nonlinear polarization rotation technique. We find central wavelength of pulses can be tuned by adjusting the polarization controllers due to the fiber birefringence dependence on the light wavelength. The spectrum of pulses generated from that of continuous waves (CW) is also studied. We find the wavelength shifted between the CW and the mode-locked state exhibits hysteresis effect. The mechanism is investigated and it is found the wavelength tuning hysteresis is the combined effects of fiber birefringence and cavity propagation property.

A stable multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. Through carefully adjusting the state of the polarization controller, the stable two three-wavelength with a spacing of 0.8 nm and one four-wavelength with a spacing of 0.4 nm fiber laser have been obtained. A nonlinear optical loop mirror (NOLM) with 70-m long Photonic Crystal Fiber (PCF) is employed to ensure stable room-temperature multiwavelength operation. The measured power fluctuation of each wavelength is less than 0.2 dB and the peak power differences among the main oscillation wavelengths are less than 1.0 dB. Another desirable characteristic is that it needs a relatively low pump power of 100 mW. The signal-to-noise ratio is ~35 dB. And it is better than that inserting single-mode fiber (SMF) ever reported.

Based on the double-pass double-stage configuration, a better high erbium-doped (4000ppm) amplified spontaneous emission (ASE) configuration with an optical circulator and two (fiber loop mirror) FLMs first used together is experimentally presented, which provides us a output power of more than 0.79dBm and a 3dB line width of 85.3 nm ranging form 1526.017nm to 1611.317nm with the max-wave ripple reduced to 0.4dBm after 1530nm. A simulated profile flattened to 0.4dB is gained from Optisystem 3.0, where we even get a bandwidth of 110nm while the output power reach 3.5dBm

All-fiber magneto-optic switch is presented in this paper which contains both of optical route and high-speed magnetic field module. The optical route has a 1×2 Fiber Polarization Beam Splitter (FPBS) and a 2×2 Dual Fiber Polarization Beam Splitter (DFPBS). The high-speed magnetic field module is core of all-fiber magneto-optic switch which changes the electronic pulse into magnetic pulse to control the light polarization's plane based on Faraday Effect. The high-speed magnetic field module adopts Yttrium Iron Garnet (YIG) crystal fiber, nanosecond impulser and high-speed magnetic field, characterized by no moving parts, low transmission loss and polarization insensitive, low optical insertion loss etc. YIG crystal fiber, the magneto-optic material with high Verdet constant, used to rotate the polarization plane of the polarized light 90° in all-fiber magneto-optic switch, is grown by Laser Heated Pedestal Growth (LHPG). CMOS chip FMMT415 which has good avalanche effect is employed to generate the nanosecond pulse. The pulse we measured is about 10 ns of the rising time and 0~600V of the amplitude and the output current is used to create the magnetic field. The obtained results indicate that the switch has a potential of low cross-talk, low insertion-loss and high switching speed. The optical route will be easily and quickly controlled by the means of nanosecond impulser, therefore, and the switching time is expected to less than 1 μs.

The influence of the extinction ratio (ER) of the input signal on the copying optical signal are analyzed theoretically for the first time to our knowledge and the deterioration of the ER of the output signal result from continuous - wave (CW) is noticed. The relationship between the ER of the output and the input signals are given quantificationally. The experiment results are agree with the theory. The recopied optical signal using fiber ring cavity is realized in experiment by reducing CW. An Erbium-doped optical fiber amplifier (EDFA) is employed for compensating the round - trip loss of the fiber ring cavity and a semiconductor optical amplifier (SOA) is used for the power equalizing of the output signal, the tenth copied optical signal is implemented.

The performance and integrity of optical fiber based devices and systems are often critically dependent on the optical coupling between interconnected fibers. In this paper, we discuss the optical characteristics of the interconnected joint when two dissimilar fibers are fusion-spliced together, and compare different approaches to estimate the optical coupling loss. We treat the total optical splice loss as a combination of the mode-field (MF) mismatch loss and the transition taper loss. We describe the spectral characteristics of mode-field mismatch loss and the taper loss between an erbium-doped fiber (EDF) and SMF28 fiber both experimentally and analytically. In addition, we outline some advanced techniques for fusion-splicing of large mode area (LMA) fibers and microstructured fibers. Finally, we compare two types of splicers using arc-discharge fusion and filament fusion technologies, and describe an automated splicing system with some examples.

A feedback high birefringence fiber loop mirror is proposed and theoretically analyzed. Large effective free spectral range can be achieved by the intrinsic vernier effect between the fast and slow axes in the high birefringence fiber, which is independent of the input signal polarization.

All-optical switching based on cross-phase modulation using Bragg grating in the highly nonlinear photonic crystal fiber (PCF) is investigated numerically. Differential method is used in the simulation process. The numerical solutions of the coupled-mode equations which describe all-optical switching are presented. Switching characteristics influenced by different pump shape and pump power are analyzed. Furthermore, switching characters of using Bragg grating in a highly nonlinear photonic crystal fiber and in a conventional one are compared.

In this paper, we discuss the optimal design of line-tapered multimode interference (MMI) devices using a genetic algorithm (GA). A 1×4 MMI device is designed as a numerical example. Compared with the conventional design based on sel-image theory, the GA optimization demonstrates good performances such as a low insertion and small non-uniformity.

Directly modulated lasers (DML) have been widely used in data rate at 2.5 Gb/s and below. The advantages of its simplicity and cost effectiveness have attracted considerable amount of effort in developing DMLs for higher data rate optical transmission systems, especially for short reach applications. The major issue is semiconductor laser's intrinsic modulation bandwidth and the amplitude modulation induced frequency chirp at high speed of 10 Gb/s and beyond. In this paper, we first briefly review the advancement of directly modulated lasers at 10 Gb/s and above. We then present our work on the investigation of using 10 Gb/s directly modulated laser in multiple amplified spans of a typical metro system. The experimental results show that 10 Gb/s DML may have potential to be a cost-effective option for a typical 100GHz spacing DWDM, 6x80km metro link over standard single-mode fiber. The DML performance will also be compared to conventional Mach-Zehnder modulator-based transmitter.

An acousto-optic programmable ultrashort optical pulse shape modulator (AO-PPSM) is presented, which can compensate for large amounts of dispersion over large spectral bandwidths while at the same time provide amplitude shaping with high contrast. The analytical expression relating the group delay and amplitude at the output of the AO-PPSM to the input acoustic signal is obtained with coupled-wave theory in the case of collinear acousto-optic interactions. With these relations, the acoustic signal that will induce an arbitrary group-delay variation with frequency can be easily obtained.

A novel electro-optic integrated acceleration seismic geophone is presented in this paper. In order to modulate the phase of optical waveguide M-Z interferometer on silicon substrate, the method of acousto-optic phase modulation is proposed. The acousto-optic phase modulator realizes phase modulation by passing the reference beam through a surface acoustic wave (SAW) generated on a ZnO thin-film transducer driven by an interdigital transducer (IDT). The motivation and the transmission of the SAW is researched and the principle of IDT is discussed. The refractive index change, generated by the SAW is analyzed. On the basis of above analysis of acousto-optic phase modulation, considering the design demands of the electro-optic integrated acceleration seismic geophone, optimum dimension parameters of the acousto-optic modulation device, e.g., the number N of finger pairs, characteristic length L and interdigital period M is implemented. So optimization structure design of the ZnO thin film and the structure of IDT are designed. Lots of theoretical and experimental researches on preparation handicraft of ZnO thin film and IDT have been done and the acousto-optic phase modulator is fabricated.

For the next-generation ultra-high-speed TDM optical communication systems, we are developing a waveguide type digital optical pulse synthesizer based on the time-to-space conversion. Our digital optical synthesizer can produce arbitrary optical packets with high bit rate in the order of 100 Gbps and chirp-free pulses. In the early prototype, the signal for controlling the phase and the amplitude of optical signal was manually adjusted with trial and error. Recently, we have introduced a feedback system to this synthesizer for automatic generation of controlling signal, which makes it extremely easier to produce optical signal with arbitrary shape. In this paper, we demonstrate experimental generation of Fourier-transform limited optical pulses and arbitrary 8-bit RZ pulse packets with a bit rate of 100 Gbps.

Self similar mode locked fiber laser is studied based on a numerical model. By introducing a dimensionless factor k to characterize the pulse, the self similar pulse formation and its temporal and spectral changes are investigated throughout the cavity. The influences of all the elements inside the cavity on the pulse formation are also studied.

Based on the Maxwell-Bloch formalism, operation of a passively mode-locked fiber laser is numerically investigated. It is found that even with the effects of coherence stable solitary waves can still be obtained in the laser due to the cavity pulse peak clamping effect. And the discrepancies between the results obtained by the coupled GLEs and the Maxwell- Bloch formalism will increase as the linear phase delay bias increases.

In this paper, a nonlinear optical loop mirror (NOLM) based on photonic crystal fiber (PCF) is used for optical pulse compression. The transmission of optical pulses in the fiber loop can be described by the nonlinear Schrodinger equations. The crossing phase modulation (XPM) effect in NOLM is used for pulse compression. The theory of XPM effect in NOLM is analyzed and the process of pulse compression is simulated. Comparing three different shapes input pulses, it can be found that the Hyperbolic-Secant Pulses have the better compression quality than the other two shapes pulses. Due to the characteristics of PCF, especially high nonlinear properties, the high quality compressed pulses can be got. Compare with the self phase modulation (SPM) effect for optical pulse compression, it is shown that the input pulse with low power can be compressed and the compression of the input pulse can be controlled by the control pulse. By choosing the proper parameters of the NOLM, to some extent, the pedestal of the compressed pulse can be suppressed. Based on the analysis of the result, proper parameters and the crystal fiber of the NOLM will be selected.

In an intermediate asymptotic propagation distance, pulse's self similar evolution is influenced by the initial pulse width and chirp, as a result pulses can not completely evolve into a parabolic pulse, which can affect the compression of the evolved pulse. The self similar evolution results of ultra-short pulse with different width and initial chirp coefficient are studied by numerical simulation. The study shows the wider the pulse is, the worse the self similar evolution and compression are; it also shows the initial chirp can greatly hold out the self similar evolution and compression, the larger the chirp and the wider the pulse, the worse the self similar evolution, and the influence of the positive chirp on the evolution is bigger than that of negative chirp.

We propose a series method to analyze detuned active mode-locked lasers. Using this method, we can analyze not only noiseless lasers but also lasers modelled with amplified spontaneous emission (ASE) noise. Moreover, the method also helps to study the transient evolution of the pulse inside the cavity, which cannot be done using classical analysis.

In this paper, we focus on the properties of the complex modes in negative-refractive-index fibers. The characteristic equations for TE and TM modes in negative-refractive-index fibers are given. These solutions, termed complex surface waves, form another set of proper modes. We show that dispersion diagram for both TE and TM modes in negative-refractive-index fibers, including evanescent, ordinary, and complex surface modes. It is found that the complex surface modes have high cutoff frequencies which means they exist only when the frequency is lower than their respective cutoff frequencies. After a careful examination, we found that the total power flow turns out to be simply zero.

Microwave signals distributed over optical fibre are of great interest for many applications. There are many advantages of all-optical microwave filters for the direct processing of microwave signals in the optical domain, such as, large time-bandwidth products, insensitivity to electromagnetic interference, low loss, and lightweight. A number of low pass photonic microwave filters have been reported, where it is required to achieve optically incoherent summing of two light beams. To overcome the optical coherence problem, either a laser array is used, or the coherence length of the light source is kept smaller than the minimum delay time of the filter. Incoherent summing in bandpass filter has also been achieved; however, they require very long length of Hi-Bi fibre. We propose here all-optical low pass and bandpass microwave photonic filters configurations, together with their application in a 20 km radio-over-fibre (RoF) link. The key problem when using a narrow linewidth source is the coherent operation because of the narrow laser source. High differential group delay (DGD) will be induced by Hi-Bi linearly chirped fibre Bragg grating (LCFBG), the optical interference is avoided because the two orthogonal state of polarizations (SOPs). Meanwhile, the positive or negative chromatic dispersion (CD) will also be provided by the chirped Hi-Bi LCFBG. The bandpass resonance is eliminated by the use of phase modulation. The CD value also can be compensated or increased by the chirped LCFBG in the RoF link for both low pass and bandpass filters. Measured results agree well with the theoretical results.

A novel fibre Bragg grating (FBG) hydrophone system is introduced in the paper. The influence of the sound pressure on the FBG is transformed to light intensity measurement with tuned laser. Elastic material and matched FBGs are employed to enhance the sensitivity of the hydrophone system. The hydrophone system can operate in a wide acoustic frequency range from 100Hz to 3kHz and good linear relationship is observed between the output light intensity and the sound pressure.

The transmission characteristics of a nonuniform photonic fiber Bragg grating (PFBG) are studied in detail by FEM furnished with 1^st - order BGT - like TBC and transfer matrix method. The effects of the air hole size on PFBG's transmission properties such as effective index, Bragg reflective wavelength, normalized bandwidth and centre wavelength shift are investigated. It is believed the study can provide useful information for PFBG's design and optimization with a more effective and accurate method.

Ultraviolet (UV) communication is a new kind of communication method by realizing non line-of-sight transmission of information, which overcomes disadvantages of line-of sight communication in other free space optical communication, such as non-UV laser communication. It will have a bright prospect of application. At present, there are more and more studies on UV communication technology at home and abroad. As for the UV communication system of our studies, we have researched deeply on one of the key technologies of UV communication that is UV high reflectance coatings. Based on the traditional theories and arithmetic of design for quarter-wavelength multilayer high reflectance coatings, the Needle method is improved greatly for the coating design, thus a kind of solar blind UV high reflectance coatings is designed. Results of calculation shows that this solar blind UV high-reflecting coating's reflectance is more than 97% at the range of wavelength λ=250~280nm and the coating's reflectance is smaller than 3% at the range of wavelength λ>300nm. Compared with Al coating and quarter- wavelength high reflective multi-layers coating, the coating is more suitable to be used in the atmosphere UV communication system, so the communication distance and the sensitivity of receiving system can be improved greatly. This solar blind UV high-reflecting coating can also be used in other UV optical technology and application, such as UV image, UV reconnaissance.

A novel method of demodulation for fiber Bragg sensor is presented. An experimental system is built up in which HBF Sagnac LM is used as the edge filter. We achieve linear demodulation whith a bandwith of 3.6nm. We have also experimentally demonstrated that packaged HBF can compensate the temperature shift of the HBF Sagnac LM filter. The shift of wavelength for an uncompensated HBF Sagnac LM is approximately 2.3nm/°C,and that of the compensated HBF Sagnac LM is 0.005nm/°C,which is much less than that of the uncompensated HBF Sagnac LM filter.

A novel electro-optical modulator using GeO₂ doped silica waveguides based on silicon substrate is proposed. The modulator is analyzed and designed with the finite element method. The simulation results show that the designed modulator operates with a 3dB optical bandwidth of 56.6GHz, a half-wave voltage of 8.9V and a characteristic impedance of 51.8Ω at 1310nm wavelength. The presented modulator can be fabricated easily using Si-based very large-scale integrated technology and is very suitable for optoelectronic integrated circuits.

A novel optical switch based on silicon/kaolinite photonic-crystal line-defect waveguides is proposed. The optical switch is analyzed and simulated with the finite-difference time-domain (FDTD) method. The designed optic switch operates with high extinction ratio of 40 dB, and compact size of 10 μm at 1550 nm wavelength. Being a compact in size and silicon base photonic crystal, the device is very suitable for high-density integrated optics circuits.

Vector soliton is obtained in erbium-doped fiber laser via nonlinear polarization rotation techniques. In experiment, we observe the every 4- and 7-pulse sinusoidal peak modulation. Temporal pulse sinusoidal peak modulation owes to evolution behavior of vector solitons in multiple polarization states. The polarizer in the laser modulates the mode-locked pulses with different polarization states into periodical pulse train intensities modulation. Moreover, the increasing pumping power lead to the appearance of the harmonic pulses and change the equivalent beat length to accelerate the polarization rotation. When the laser cavity length is the n-th multiple ratios to the beat length to maintain the mode-locking, the mode-locked vector soliton is in n-th multiple polarization states, exhibiting every n-pulse sinusoidal peak modulation.

Transmission characteristics are studied for parallel-plate waveguide coupler. It is shown that the stable light field distribution and mode pattern are determined by its own geometric and dielectric parameters, but have nothing to do with the categories of incident sources. It is also found that the coupling effect would generate between waveguides through evanescent field. The calculated results indicate that the field amplitudes in both waveguides are changing with the change of propagation distances, simultaneously the transmitted powers are changing periodically between the two waveguides along the direction of wave propagation. According to the field distributions, the optimum coupling length and coupling efficiency can be obtained. Our numerical simulation is based on the finite difference time domain method without using special mathematical knowledge.

Chirped fiber Bragg gratings are supposed to be cascaded for multi-channel dispersion compensation in DWDM systems. The interaction between them restricts their employment. Gaussian and Super Gaussian apodization are used to reduce the out-of-band reflection so as to suppress the interaction of the cascaded gratings. The increase of the channel spacing can also diminish the interaction.

This paper has presented a design of dispersion compensating fiber with small core photonic crystal fiber (PCF) based on pure silica. The designed small core PCF can be controlled the dispersion properties in terms of the structural parameters, the pitch Λ and the air-filling fraction d/Λ. The negative chromatic dispersion coefficient can be achieved - 586.5ps/(nm·km) at λ=1550nm with Λ=0.9μm and d/Λ=0.9. This kind of PCF can be used for broadband dispersion compensation in S+C+L band (1460-1565nm) and the chromatic dispersion coefficient is lower than -450ps/(nm·km) in S+C+L band. It can realize the dispersion slope compensation because that it exhibits a negative dispersion slope.

A single-mode Er/Yb-codoped short cavity fiber laser was experimented on the basis of previous short cavity fiber laser. The single-mode operation is realized by using the FBG and a 10cm section of Er/Yb co-doped fiber as a short cavity. The output power exceeds 1.5mW for pump power of 80mW. The linewidth of output laser was measured as 2MHz at 1532.64nm, and the side mode suppression ratio was 55dB. The single-mode was observed by an interferometer with free spectrum range (FSR) of 7.5GHz, and the longitudinal-mode fabric is analyzed. Relative intensity noise was less than -100dB/Hz.

The reflectivity and the Bragg wavelength of a fiber Bragg grating formed in a photonic crystal fiber with central pure core defect and a regular hexagonal array of microscopical holes cladding were investigated by the improved effective index method, the calculated results indicate that the scalar approximation condition will not be satisfied when the filling factor is more than 0.45, the reflectivity increases from 86.6% to 93.9% with the filling factor increasing, and the Bragg wavelength decreases from 1550.347nm to 1549.236nm when f <0.53. This rules provided the theoretical basis for designing new fiber Bragg gratings formed in the PCF.

Normalized frequency, normalized propagation constant and asymmetry measure are introduced to the left-handed slab waveguides. The dispersion relations expressed by normalized parameters are then derived. All the possible waveguide configurations with the left handed materials as core, substrate, and cover are considered and divided into four cases. Universal dispersion curves, and dispersion properties have been obtained analytically. It is found that guided mode properties differ dramatically for these four cases. For some cases, fundamental mode does not exist. For some cases, double degeneracy of modes appears. In one case, the first order mode only exists in a small frequency range, while in another case the fundamental mode exists only in a small frequency range. Both TE and TM oscillating guided modes are discussed.

A novel polarization dependence loss (PDL) measurement approach using the degree of polarization (DOP) feedback signal has been introduced in this paper. Both the theoretical analysis and the experimental simulation show that, while maintaining a very acceptable level of measurement accuracy, this PDL measurement method could effectively reduce the measurement time. In comparison with the current PDL measurement technologies, the most prominent property of our method is that it could provide different PDL measurement accuracy and range by changing the value of polarization mode dispersion (PMD) element in the measurement setup.

This paper demonstrates the recent achievements in the field of distributed optical fiber sensor (DOFS). A novel type of distributed optic fiber vibration sensor is presented to detect and locate a time-varying disturbance along the whole fiber length. It measures the first simultaneous information by using Mach-Zehnder Interferometer(MZI). The sensor consists of a MZI where two directional optical signals are simultaneously traveling. We discuss the principles of distributed optic fiber vibration sensor based on long-length MZI, and present the preliminary results on the application of distributed optic fiber sensor for the measurements of distributed signals in long-distance region. The sensor is illuminated by one continuous-wave laser, which is different from the conventional scheme. The phase shift caused by any disturbance around the fiber is detected and converted to the information on the perturbation position and amplitude, which can be determined by combining two phase signals from the above device. In addition, we adopt a new technique by using optical delay effect to improve the spatial resolution of distributed optic fiber sensor. It is completely different from the spatial-resolution technique of optical time-domain reflectometry (OTDR). The system has capability for cross-correlation algorithm and fast Fourier transform (FFT) analysis of the detected disturbance signals. For the sake of determining the disturbance position and type, high speed digital processing (DSP) technology is used in the sensor system, which can carry out all operations in real time and promote the resolution of localization. The hardware design of the sensor is completed and the experimental results are obtained. This type of optic fiber sensor has better sensitivity and resolution than the others. It achieves a 100Hz-20KHz frequency of vibration resolution, with 100-m practical spatial resolution, over a sensing length of 8 km. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of distributed optical fiber sensor. The results mainly are presented in laboratory.

By using thin membrane plating technology in collimating lens, we successfully manufacture a 16×10Gbit/s multiplexer basing on the combination of fiber and space structure method. The multiplexer is flexible according to your practical need that can output 20, 40, 80, or 160Gbit/s signal. For 20, 40, 80 or 160Gbit/s multiplexer, insertion loss is 3.5dB, 7dB, 10.5dB and 14dB respectively. The low insertion loss provides maximum transmission power. It also has such features: high time-delay accuracy, polarization insensitivity, broadband, very short coherence length, high time-delay accuracy, and excellent temperature stability. It differs from the structure of general Mach-Zehnder interferometer. It has the structure of Michelson interferometer.

Long-period grating(LPG) which has a grating period of more than 100μm is a new kind of fiber gratting and its principle is that optical power is coupled from the forward transmission fundamental core mode to the forward transmission cladding modes and is attenuated after some distance. Transmission spectrum of LPG has a range close to linearity in both side of the peak. This range can be use as double edge filter on this property. Cascaded LPGs have special spectrum which is used as filters in multiple technology.

A compact all fiber Q-switched fiber laser based on an Er/Yb co-doped fiber (EYDF) is demonstrated. Two Bragg gratings (FBG1 and FBG2) were employed as the cavity mirrors. The Average output power, single pulse energy and pulse width of the fiber laser at different pumping powers and different repetition rates was studied. The output spectrum of the fiber laser is 0.5 nm. At maximum launched pump power of 558mW, pulse energy of about 50μJ and duration of 140ns was obtained at the repetition of 2 kHz.

In this paper, a novel 3D strain FBG sensor based on cylinder structure is reported. In our experiment, we used 3 FBGs as sensing element and fixed them on the side of the cylinder according to 120° angle intervals. Based on the physical and mathematics principle, theoretical derivations and experiment setup were also showed. In application, this sensor would have a good prospect.

A novel electric current sensor based on a high-birefringence fiber loop mirror(HBFLM) and a kind of magnetostrictive material rod(MMR) is demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The HBFLM is used as the sensor head and the linear filter simultaneously. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The rod will have elastic lengthening along the direction of the magnetic field when the uniform magnetic field changes, which will lead to a change of transmission intensity of the HBFLM filter, thus the variation of the electric current can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. The sensitivity reaches 0.0153/100mA, the resolution reaches 10mA. Comparing with the previous fiber-optic electric current sensor, it has nothing with the linear birefringence based on Faraday effects in the previous fiber-optic electric current sensor. Comparing with the expensive and complex FBG electric current, the sensing signal can be directly detected by a photodiode(PD) and complicated demodulation devices are avoidable. The advantages of the electric current include optical power detection, simple and smart structure, high sensitivity, low cost, and good repeatability, etc.

The depressed-index dual core PCF-based broadband directional coupler is designed by using semivectorial finite difference method. We study the influence of the structural parameters on the coupling characteristics in the dual core PCF. The results show that once the structural parameter of the cladding of the dual core PCF and the doping degree in the dual core region are optimised, the broadband coupling can be realised: in the wavelength range of 1.22~1.65μm, the value of the coupling length is stabilized at 26637nm±235nm and when the couplers are designed as two kinds of couple with coupling ratio of 50% and 10%, the coupling ratios of (50±0.702)% and (10±0.664)% are realized, respectively.

In this paper, a modified stacking method to fabricate photonic crystal fibers with squeezed lattice is presented, for the first time to our knowledge. This modified method can realize different structures of photonic crystal fibers with different expected squeezing ratios. The influences of the structural parameters on the squeezing ratio and birefringence are separately discussed in detail. Moreover, the birefringence characteristics of such photonic crystal fibers are simulated by using supercell lattice method.

A novel distributed fiber-optic vibration sensing system is proposed and demonstrated. By employing a ring Mach- Zehnder interferometer structure as the sensing section, which consists of one 3dB fiber coupler, two optical circulators, two symmetric 3×3 fiber couplers, and two fibers, one interferometer operates as double ones. The first one is defined by the CW directional path and the second one is represented by the CCW directional path. When a vibration occurs at certain point, the two interferometers will produce the same phase modulation simultaneously. Both position and frequency of the vibration can be determined by combining two phase signals from the ring Mach-Zehnder interferometer. With a piezo-electronic cylinder contained in the sensing cable to simulate a vibration, we select multiple test positions along the sensing fiber to demonstrate the theoretical analysis. The experimental results exhibit a good repeatability and agreement with the theoretical response. Hence, we conclude that the sensor can measure both the frequency and position of vibration in real time, with a spatial positional resolution better than 40 m in a long sensing distance prototype system.

Using the plane-wave expansion method and finite element method, we investigate the properties of all-solid square-lattice photonic bandgap fibers. The comparison of different r/Λ values in the proposed fiber is convenient to optimize the fiber design. The simulation results demonstrate that the effective mode area of all-solid square-lattice photonic bandgap fibers is 1.25 times larger than triangular-lattice ones and the confinement loss of the fibers is no more than 0.1dB/m within the selected bandgap.

A novel gain-clamped Long wavelength band erbium doped fiber amplifier (L-band EDFA) based on ring erbium-doped fiber laser cavity was demonstrated. By using a fiber Bragg grating (FBG) at the output end of the amplifier, a portion of forward conventional band (C-band) amplified spontaneous emission (ASE) was reflected back into the system, this new design provided a good gain clamping and decreased noise effectively. It used 1480nm laser diode (LD) to pump high Er³⁺ −concentration erbium-doped fiber for higher efficiency and lower noise figure (NF). The gain was clamped at 17.5dB with a variation of 0.3 dB from input signal power of -30dBm to -12dBm for a pump power of 180mW. By adjusting the intra-cavity loss, the gain reached 19.78dB with inputting small signal and NF below 5dB was obtained. At the longer wavelength (1614nm) of L-band 9.2dB gain was obtained.

We propose a novel broadband polarizing beam splitter with an embedded metal-wire nanograting structure that the metal wire is deposited in the grating trenches. This embedded structure makes the grating more firms in its applications. The design is based on Effective Medium Theory (EMT) and the structure is optimized with Rigorous Coupled Wave Theory (RCWA). The design results show that the polarizing beam splitter has uniform performance with wide variations in the angle of incidence and has low insertion loss, high polarization extinction ratio in a broad spectral range.

Some kinds of high birefringence photonic crystal fibers (PCFs) with elliptical inner cladding are analyzed by Galerkin finite element method with transparent boundary conditions (TBC). Several properties of them, such as the birefringence, confinement loss and dispersion are deduced and compared .It is shown that PCFs with different elliptical inner cladding formed by enlarging or diminishing air holes have different properties. High birefringence can be obtained through intruding the difference of air holes size along orthogonal direction. Enlarged air holes reduce the CL, and increase the dispersion and dispersion slope; but diminished air holes is reversed.

The variably coupled-mode equation in all-fiber polarization transformer (AFPT) is theoretically analyzed and an optimal profile of variably spun rate to get better performance for AFPT samples is proposed as Q(z) = 0.5tan{arcsin[(z/L)sin(arctan2Q(L))]} where Q(z) is the normalized spun rate by beat length L_B along the spinning section of AFPT with total length L. Then, in accordance with this specific intrinsic structure of AFPT, we found that there exists a set of strictly analytic solution for the variably coupled-mode equations of AFPT. It is also found that the linear polarized exact eigen-modes of AFPT at the un-spun end are not parallel but with a slight angle relative to the birefringence axes of the un-spun fiber. The difference of phase factor and amplitude between the exact analytic solution and the asymptotic solution is compared and discussed. The analysis has referential values to the design, fabrication and evaluation of AFPT samples.

Checking the great generator's vibration online is difficult because of its strong electric and magnetic field so it needs had better no metal in the sensor. We introduce a method of measuring vibration by using FBG and demodulating it by blazed grating and it doesn't use any metal. We present the design method and the theory of demodulation. The results of the experiment show that the vibration amplitude of the exciter matches the detected signal under the stable frequency. The experiment also successfully separated the temperature shift and vibration signal.

An all-fiber polarization transformer made of variably twisted holey birefringence fiber is proposed to decrease the temperature instability. After reviewing the beat length (or modal birefringence) variation of holey birefringence fiber with temperature and wavelength, the model for simulating the polarization transforming ability of the variably spun or twisted birefringence fiber is set up based on the mode-couple equation with variable coupled coefficients. Compared with the conventional polarization transformer made of variably spun stress birefringence fiber, the temperature instability from -20°C to +80°C and wavelength sensitivity from 1200nm to 1600nm of their polarization transforming performance are simulated and discussed.

We propose a novel scheme to generate return-to-zero differential phase-shift keyed (RZ-DPSK) and carrier-suppressed RZ-DPSK (CSRZ-DPSK) formats based on the differential Mach-Zehnder modulator (DMZM), which can adjust the operating point of the modulator and control chirp conditions easily. It is more cost-effective due to its simple configuration.

We calculated the errors of Chromatic dispersion (CD) in PCFs, under different air filling fraction f, that is under different refractive index difference ▵, by comparing the waveguide dispersion D_w between the formula of D_w, and that calculated from D_eff the chromatic dispersion of effective index and the fiber core material dispersion D_m.

By decreasing the arc power and choosing the optimal arc time, we use the FSM-20PM ARC Fusion Splicer for joining fluoride(ZBLAN) and silica fibers. The best results of the splice loss is 1.58dB, and the results can be improved if the Fusion Splicer with more stable arc power. Then glue connection is used to fix the splicing point, and the minimal loss we measured is 0.14dB. The above results show that it is possible to connect the fluoride and silica fibers by using Fusion Splicer with appropriate arc power and arc time, which will make the fabrication of these splices simpler and easier to be handled.

In a traditional weighing scale, the loadcells with strain gauges are widely used, however, as an electrical device, its performance is poor under the conditions of interference and corrosion. According to the stress distribution of a cantilever loadcell, two FBGs (fiber Bragg grating), were adhered to replace traditional strain gauges in a 0-20t cantilever loadcell. One of them was used as a tensive sensor and the other is as a compressive sensor. To subtract their measuring results, the response is doubled, meanwhile, the environmental interference is eliminated. The calibration showed that the repeatability in full scale achieved as high as 0.02%. In its application, FBG loadcells were used to do weighing of running vehicles in a weigh-in-motion (WIM) scale, the results showed that the FBG scale performed better than strain gauge scale under the same WIM processing program. Under the speed of 11km/h, the measuring accuracy could be kept within 1%.

A linear cavity photonics crystal fiber (PCF) laser has been fabricated. The home-made polarization-maintaining PCF is acted as active material, and polarization-maintaining fiber Bragg grating (PMF-FBG) is used as filter. The stabile two-wavelength laser, which has high degree of polarization (DOP), has been exported. The output power is 0.3mW, and DOP is about 98%. In this paper, we discuss the characteristics of PCF laser and PMF-FBG. in detail.