Fiber devices using polarization- maintaining fibers

Fiber devices using polarization-maintaining fibers called PANDA fibers are presented. They are polarization-maintaining couplers and polarization-splitting couplers, optical isolators and optical circulators, and multi/demultiplexers designed for 1.3 μm wavelength. Crosstalk of-32 dB and excess loss of 0.03 dB for the polarization-maintaining coupler, and polarization-splitting ratio of 17 dB and excess loss of 0.5 dB for the polarization-splitting coupler have been fabricated by a fusion-elongation method. A fiber polarizer with the extinction ratio of more than 40 dB has been presented by using the difference of bending loss between the orthogonal modes in the PANDA fibers. Multi/demultiplexer with narrow band-pass of 1.4 nm utilizing combination of PANDA fiber polarization dispersion and the polarization-splitting coupler has been realized. An optical isolator consisting of fiber polarizers and a spherical YIG with a lens function and an optical circulator consisting of polarizing-splitting couplers and spherical YIGs have been achieved.     

Polarization maintaining large nonlinear coefficient photonic crystal fibers using rotational hybrid cladding

In this paper, we present and explore a new hybrid cladding design for improved birefringence and highly nonlinear photonic crystal fibers (PCFs) in a broad range of wavelength bands. The birefringence of the fundamental mode in such a PCF is numerically analyzed using the finite element method (FEM). It is demonstrated that it is possible to design a simple highly nonlinear hybrid PCF (HyPCF) with a nonlinear coefficient of the about 46 W⁻¹ km⁻¹ at a 1.55 μm wavelength. According to simulation, the highest modal birefringence and lowest confinement loss of our proposed structure at the excitation wavelength of λ = 1.55 μm can be achieved at a magnitude of 1.77 × 10⁻² and of the order less than 10² dB/km with only five rings of air-holes in the fiber cladding.     

Fiber optical communications devices

Both low attenuation silica optical fibers with peak transmission in the wavelength regions of 0.85 μm, and 1.05 μm, and improved lasers at both wavelengths are now available. In this review paper, the principal components for emission, modulation and detection are described. The characteristics of both semiconductor lasers, made of GaAs and related compounds, emitting at 0.85 μm or 1.05 μm and high neodymium-content lasers are discussed. For modulation, current modulation of GaAs lasers and external electro-optic modulation are considered. Concerning detection, the realisation of Si photodetectors suitable at 0.85 μm and the new photodetectors at 1.05 μm from Ga_1−x In _x As are reviewed.     

Polarization maintaining fibers for application in magnetic field measurements

Optical fibers may be applied in measurements of electrical current, particularly as so-called optical current transformers. Electric current sensors, in which optical fibers are used are small, light, cheap and safe. Their sensitivity is, however, due to the restricted magnetootpic properties of optical fibers, rather small. Moreover, these sensors are susceptible to deformations of the optical fiber. An increase of their sensitivity consists in lengthening the distance of optical fiber on which the magnetic field acts. However, this can lead to an increase of disturbances caused by changes of internal stresses. The negative effects can be reduced by applying optical fibers with a higher magnetooptic sensitivity and a lower susceptibility to mechanical stresses and deformations. The present paper deals with side-hole optical fibers with a decreased birefringence reducing the susceptibility to deformations. The optical fibers consist of a multicomponent glass with a higher value of the refractive index, thanks to which the sensitivity to the effect of the external magnetic field is increased. In future such optical fibers are planed to be applied in magnetooptic sensors.     

Birefringence sensitivity to temperature of polarization maintaining photonic crystal fibers

In this paper, we investigate the birefringence of polarization maintaining photonic crystal fibers (PM-PCFs) under thermal effect. Modeling and simulation of PM-PCFs under thermal effect are conducted. Birefringence in a PM-PCF as a function of the temperature is measured experimentally. The experimental results are in agreement with theoretical calculation, and show that the relative temperature dependent birefringence coefficient of the PM-PCF, dΔn/dT/Δn, is 2.93×10^?5/°C, which is typically ～35 times less than that of conventional panda fibers. The insensitivity of polarization properties in PM-PCFs to temperature is demonstrated. These findings have important benefits in fiber optic systems and sensors, especially in fiber optic gyroscopes (FOG) where it translates into a lower polarization error and thus a higher measurement precision.     

Analysis on Raman gain coefficients in polarization maintaining photonic crystal fibers

The Raman gain coefficients in polarization maintaining photonic crystal fibers (PM-PCFs) are analyzed in order to design fibers for linearly polarized Raman fiber laser with enhanced performances. The results show that a well designed germanium-doped PM-PCF can attain the value of Raman gain coefficient over 50 W-1·km-1, going with very high birefringence and single mode operation at 1.55-μm signal wavelength and 1.45-μm pump wavelength.     

Analysis on Raman gain coefficients in polarization maintaining photonic crystal fibers

The Raman gain coefficients in polarization maintaining photonic crystal fibers (PM-PCFs) are analyzed in order to design fibers for linearly polarized Raman fiber laser with enhanced performances.The results show that a well designed germanium-doped PM-PCF can attain the value of Raman gain coefficient over 50 W-1.km-1,going with very high birefringence and single mode operation at 1.55-μm signal wavelength and 1.45-μm pump wavelength.     

Analysis of thermal property in hollow-core polarization maintaining photonic crystal fibers

We study the thermal-induced variance of effective refractive indices (ERIs) and birefringence in several kinds of polarization maintaining fibers (PMF) and carry out numerical simulations by utilizing the finite element method (FEM). Responses under varying temperatures in these fibers are analyzed thoroughly. According to our computational results, hollow-core photonic crystal fibers (HC-PCFs) exhibit much more stable temperature-dependent ERIs and birefringence among these PMFs.     

Fiber fuse effect in hollow optical fibers

We examined nonlinear fiber fuse effect (FFE) in hollow optical fibers (HOFs) that consist of a central air hole surrounded by a high-index ring core and silica cladding. In contrast to conventional solid-core fibers, the HOF with a hole diameter of 4 μm showed high threshold power of 4 W, and resulted in unique tadpole-like voids in periodic arrays after the FFE. As the hole diameter increased to 6 μm, plasma propagation was suppressed within the distance of 1 mm inside of the HOF. Detailed comparisons were made in terms of threshold power, void formation, and penetration length.     

Doped photonic bandgap fibers for short-wavelength nonlinear devices

Microstructured photonic bandgap fibers with a doped honeycomb cladding structure and the guiding defect defined by the absence of doping are proposed as nonlinear optical fibers for short wavelengths. It is shown that zero-dispersion wavelengths below 500 nm and corresponding effective areas of 1-2 microm2 can be obtained if structures with interhole distances near 600 nm can be fabricated. The cutoff wavelength for guidance of second-order modes can be controlled by variation of the radius and index contrast of the doped regions.     

Integrating liquid crystal based optical devices in photonic crystal fibers

Liquid crystal photonic bandgap fibers form a versatile and robust platform for designing optical fiber devices, which are highly tunable and exhibit novel optical properties for manipulation of guided light. We present fiber devices for spectral filtering and polarization control/analysis.     

偏振保持光反馈下1550 nm垂直腔面发射激光器的非线性动力学特性研究

基于自旋反转模型,研究了1550 nm垂直腔面发射激光器(VCSELs)在偏振保持光反馈下的非线性动力学特性.结果表明:自由运行的1550 nm-VCSELs在电流增加的过程中,发生偏振转换所对应的电流值与内部参数的取值有关,随着有源介质线性色散效应系数γ_a的增大,偏振开关的转换点所对应的电流值将增加;偏振保持光反馈的引入将导致1550 nm-VCSELs中自由运行时的主导模(Y偏振模式)在不同电流下呈现不同动力学状态,引起另外一个模式(X模式)激射,两个模式的平均输出功率随电流的增加总体呈现增加的趋势,但伴随着起伏;反馈时间取不同值时,1550 nm-VCSELs的输出随着反馈强度的增大经历倍周期、准周期或阵发混沌等多种通向混沌的演化途径.     

Soliton interaction in birefringent optical fibers: Effects of nonlinear gain devices

This paper presents the influences of polarization mode dispersion (PMD) on the performance of soliton transmission system in birefringent fibers. Dispersive waves generated in single mode fibers due to PMD degrade the soliton transmission system in two aspects. First, solitons continuously lose their energy, thus cause enhancement in pulse width. Second, the dispersive waves interact with neighboring pulses and cause distortion in a sequence of pulses. Both these effects reduce the effective bit-rate and degrade the performance of high-speed optical transmission systems. Optical fibers with large group velocity dispersion (GVD) have less dispersive waves and are relatively robust to pulse broadening, but it enhances the interaction between the adjacent pulses. In this paper, we analyzed these effects of PMD on soliton propagation in birefringent fibers and introduced nonlinear gain devices with perturbation terms proportional to second and fourth power of amplitudes to reduce these effects. We proposed Symmetric Split-Step Fourier Method to solve the coupled nonlinear Schrödinger equations (CNLSE); which yields better results over the existing Split-Step Fourier Method.     

Fiber spin-profile designs for producing fibers with low polarization mode dispersion

Using coupled-mode theory, we develop a theoretical model to analyze the effects of fiber spin profiles on polarization mode dispersion (PMD). Constant, sinusoidal, and frequency-modulated spin profiles are examined, and phase-matching conditions are analyzed. Our analysis shows that PMD can be reduced effectively by use of frequency-modulated spin profiles.     

保偏光纤中在不同频率区域拉曼效应和参量放大增益谱

根据考虑拉曼效应后的双折射光纤所满足的非线性相干耦合薛定谔方程, 推导出了当沿两个偏振轴入射两束不同波长的激光脉冲时所产生的增益表达式. 通过与入射相同频率的光脉冲所产生增益的对比, 在考虑拉曼效应的情况下, 讨论了入射不同频率光脉冲对增益谱的影响. 结果表明, 在正常色散区和反常色散区, 当输入两束激光脉冲频率不同时, 增益谱较输入相同频率激光脉冲时产生了明显的变化, 其外侧的斯托克斯部分和反斯托克斯部分增益峰, 随着群速度失配的增加强度明显加强、偏离中心频率, 可以用于提取太赫兹脉冲.当两偏振模处于不同色散区时, 增益谱与不考虑拉曼效应时也存在明显的不同, 增益谱的对称性遭到破坏, 斯托克斯部分的增益峰强度要明显高于反斯托克斯部分. 关键词： 不同频率区域 保偏光纤 拉曼效应 参量放大     

Subwavelength-resolution direct writing using submicron-diameter fibers

<正>A novel direct writing technique using submicron-diameter fibers is presented.This technique adopts contact mode in the process of writing,and submicron lines with different widths have been obtained. Experimental results demonstrate that the resolution of this technique can be smaller than the exposure wavelength of 442 nm,and 380-nm-wide line is achieved.In addition,the distribution of light fields in the photoresist layer is analyzed by finite-difference time-domain method.     

Broadband dispersion compensation using microstructure fibers

Beijing University of Posts and Telecommunications, Beijing 100876Dispersion and dispersion slope compensation of 10-Gb/s pulses using microstructure fibers (MFs) is demonstrated experimentally. A 26-m MF is used to compensate the dispersion of 2-km standard singe mode fiber in a 20-nm range in C band. The experimental results show that a significant improvement can be achieved in the quality of the observed pulses with the dispersion compensation. Moreover, the further research shows that the MF can compensate the anomalous dispersion of a single mode fiber within ±0.27 ps/(nm·km) over a 50-nm wavelength range from 1520 to 1570 nm.     

Supercapacitor devices using porous silicon electrodes

Electrical double layer (EDL) supercapacitors have been constructed using gold coated porous silicon (PSi) electrodes in a 0.25 M TEABF₄/PC solution. As a comparison with the PSi, graphite paper, carbon cloth and ITO on glass electrodes have also been tested using the same electrolyte. The capacitors have been characterised using a.c. impedance spectroscopy and cyclic voltammetry (normal staircase mode). Devices using PSi electrodes showed a capacitance of approximately 0.2 mF cm⁻² (equivalent to 5 mF g⁻¹). In comparison, devices based on ITO on glass electrodes had a capacitance of 0.76 mF cm⁻². Those based on graphite-paper electrodes gave 10 mF cm⁻² (equivalent to 131 mF g⁻¹) and those using carbon cloth gave 600 mF cm⁻² (equivalent to 35 F g⁻¹). Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Optical signal processing using nonlinear fibers

Ultra-fast optical signal processing is a promising technology for future photonic networks. This paper describes possible applications of nonlinear fibers to optical signal processing. The third-order optical nonlinearities in a fiber are discussed by analyzing the interaction of co-propagating optical waves. The properties of a nonlinear fiber are then considered in terms of optimizing the dispersion for achieving phase matching and decreasing walk-off. A highly nonlinear fiber (HNLF) is a practical candidate for an ultra-high-speed signal processor. Using HNLF, the following experiments are successfully demonstated: ultra-broadband wavelength conversion/optical phase conjugation by four-wave mixing, 160 Gb/s optical 3R-regeneration, and optical switching up to 640 Gb/s using a parametric amplified fiber switch. Steps for further improvements are also discussed.     

Nonlinear optical laser devices using GaSe

Tunable second-harmonic generation of CO₂ laser radiation and tunable upconversion of infrared radiation from CO₂-laser radiation in a GaSe crystal are demonstrated. The capability of low infrared-signal detection in this crystal is also explored and compared with the AgGaS₂ crystal.