非对称性对光子晶体光纤偏振相关滤波特性的影响

基于表面等离子共振效应,提出了三种不同非对称因素引入的金镀膜偏振相关滤波光子晶体光纤,利用全矢量有限元法研究了光子晶体光纤偏振相关滤波传输特性.当非对称纤芯模单独作用时,波长1.55μm处x与y偏振方向纤芯模损耗分别为5.58dB/cm和461.58dB/cm,两偏振方向损耗比为83;当非对称金属表面等离子模单独作用,且镀膜厚度为55nm时,其谐振波长1.31μm处x与y偏振方向纤芯模损耗分别为2.02dB/cm和412.91dB/cm,两偏振方向损耗比高达204,镀膜厚度19.5nm时其谐振波长1.55μm处x与y偏振方向纤芯模损耗分别为5.29dB/cm和536.25dB/cm,两偏振方向损耗比为101;当纤芯模和表面等离子模同时引入非对称因素时,通信波长1.55μm处y偏振纤芯模谐振强度高达802.08dB/cm,而x偏振纤芯模损耗仅为5.57dB/cm,两偏振方向损耗比为144.数值比较可知,在金属表面等离子模中或两种模式同时引入非对称因素,可获得两偏振方向偏振损耗比更高的强偏振相关滤波传输特性的光子晶体光纤,该研究对光子晶体光纤偏振相关滤波器及相关偏振器件的设计与应用具有一定参考意义.     

高精度偏振依赖损耗自动测试系统

光学器件的偏振依赖损耗(PDL)是发展光纤通信必须克服的关键技术之一。该文介绍了一种新型的高精度偏振依赖损耗自动测试系统，系统中采用耦合器和监测功率计，实现了单次接入即可完成偏振依赖损耗的测量，消除了系统光功率稳定性对测试结果的影响。在同一系统中，可实现多种方法测试偏振依赖损耗，采用偏振控制器的延迟补偿技术实现了全波段内的偏振依赖损耗高精度测试。系统工作波长范围为1200～1600nm，偏振依赖损耗测量范围0～5dB，测量不确定度高达0.005dB+PDL×4％，可满足各种光学器件偏振依赖损耗测试需要。     

基于光纤光栅的磁场测量新方法

提出了一种基于光纤光栅中法拉第效应和测量偏振相关损耗的直接测量磁场的新方法,给出了理论分析和实验结果.当有外加磁场时,光纤光栅中的法拉第效应使两个圆偏振光的传播常量改变,从而导致光纤光栅的偏振相关损耗的变化.仿真结果表明,外加磁场与偏振相关损耗峰值在一定的测量范围内存在线性关系,测量结果对温度变化不敏感.分析了光栅的参量对测量性能的影响.实验中得到该方案测量磁场的灵敏度为7.8e-6B/Gs,利用现有精度为10-6 dB的光矢量分析仪得到最小可测磁场为2 Gs.实验与理论吻合较好.     

双面曝光长周期光纤光栅偏振相关损耗

研究了采用高频CO2激光脉冲通过单面和双面曝光制作出的长周期光纤光栅(LPFG)的偏振相关损耗特性。单面曝光制作的长周期光纤光栅由于光纤横截面折射率改变不均匀,对入射光偏振态有较强的依赖性,主要表现为偏振相关损耗较大;为了降低偏振相关损耗,在制作长周期光纤光栅的过程中采用双面曝光的方法,以使其横截面折射率调制受高频CO2激光曝光改变均匀。实验数据显示,高频CO2激光脉冲制作的普通单面曝光长周期光纤光栅最大偏振相关损耗高达1.24 dB,而采用双面曝光的相同谐振峰值长周期光纤光栅的偏振相关损耗则可降至0.42 dB。因此,双面曝光制作的长周期光纤光栅能较好地克服入射光偏振态的不良影响,从而满足对偏振敏感的光纤通信和传感系统的应用要求。     

基于光子晶体光纤的弱压力传感器研究

利用有限元法仿真了光子晶体光纤的双折射与横向压力之间的关系,研究弱压力条件下光子晶体光栅的特性。虽然光子晶体光纤比传统的阶跃光纤对压力更为敏感,但弱压力导致的双折射变化很小,应用测量布拉格波长的变化测量压力的变化比较困难。采用偏振相关损耗来测量外界微弱压力导致的双折射变化。仿真结果表明：利用偏振相关损耗的方法,测量灵敏度可达0.75dB/MPa。     

两偏振态测量偏振相关损耗

基于具有偏振相关损耗和双折射的密勒矩阵洛伦兹变化特性,提出了一种测量偏振相关损耗的新方法.证实了测量偏振相关损耗取决于密勒矩阵的第一列元素.提出了一种实用的测量方法.新方法对于偏振相关损耗的测量只需要两个输入偏振态,因此具有测量速度快和测量误差小的优点,实验的测量结果证实了该方法的可靠性.     

可调光衰减器的光衰减量线性补偿

设计制成一种数字化电磁驱动微机械MOEMS可调光衰减器.与传统可调光衰减器相比,该器件不仅可实现光衰减量数字化电控调节,并且可通过器件结构的优化设计,对光衰减量的非线性进行补偿,最终得到线性衰减.器件性能测试表明,插入损耗IL＜0.3 dB,偏振相关损耗PDL＜0.1 dB,波长相关损耗WDL＜0.2 dB,衰减范围0～40 dB,回波损耗RL＞50 dB.     

特种非对称低损耗1×5光分路器

设计和优化了一种新型低损耗、低偏振的基于二氧化硅的特种非对称1×5光分路器.在设计Y分支结构时,输入端采用缓变展宽波导结构和直波导过渡波导相结合的结构,此结构可以使输入光场缓慢展宽,进行分束前的准备,大大减小分支结构的辐射损耗和模式转换损耗.非对称1×5光分路器第一个端口输出功率占50%,第二至五端口输出功率占50%.利用三维光束传播法模拟和优化了特种非对称1×5光分路器,模拟结果表明,该结构具有均匀性好、器件尺寸小、低损耗和低偏振等优点,1×5光分路器在1 250~1 650 nm波长范围内,第一个输出端口附加损耗小于0.07 dB,均匀性小于0.023 dB,偏振相关损耗小于0.009 dB,第二到五端口附加损耗小于0.45 dB,均匀性小于0.41 dB,偏振相关损耗小于0.06 dB.     

一种闭环控制的错位型MEMS可调光衰减器

针对一种错位型MEMS(Micro-Electro-Mechanical Systems)可调光衰减器,基于输入输出光纤间模场的交叠积分,数值分析了径向偏差和轴向间隙同时存在的情况下,光功率衰减量与错位量和波长的关系.演示了利用闭环反馈控制系统提高器件响应线性度的显著效果.研制出样机并测量得到器件的响应时间(约1.5 ms),动态范围(约35 dB),波长相关损耗(<0.4 dB),偏振相关损耗(<0.1 dB)等关键性能参量.     

线圈型全光纤偏振器的研究

本文采用等效电流法对线圈型全光纤偏振器进行了分析计算.对应于保偏光纤中两正交传输基模的消光比,提出了一种分析保偏光纤弯曲损耗的新方法,这种方法基于将保偏光纤两个不同偏振模式分别等效为两个普通圆光纤的基模,等效参数通过测量不同偏振模式的模场半径来确定.实验证明这种理论计算方法与实验结果一致.最终,我们研制出的线圈型光纤偏振器在1.31μm工作波长下,实测消光比达30dB以上,工作偏振模式插入损耗≤3dB.     

Novel Variable PDL Emulator Based on LiNbO3 Modulator

We propose and demonstrate a novel variable PDL emulator based on a LiNbO3 modulator. The proposed emulator could vary the PDL values simply by adjusting the bias voltage of modulator. The results show that the proposed PDL emulator could generate a wide range of PDL values (0 ～ 35 dB). The generated PDL value could be maintained within ± 0.02 dB for ＞70 minutes. The wavelength dependency was about 0.03 dB in the range of 1520nm ～ 1590 nm.     

Fault-tolerant polarization-insensitive photonic delay line architectures using two-dimensional digital micromirror devices

A binary multichannel photonic delay line (PDL) module is introduced that gives balanced loss switched states and a polarization-insensitive operation via the use of binary operation Digital Micromirror Devices (DMDs). Experimental demonstration of a DMD-based PDL architecture is performed for a 6.84-ns time delay design. Experimental results include a 25-beam feed interchannel crosstalk test indicating a <−60 dB optical interchannel crosstalk level for a 0.381 mm interchannel distance in the multichannel PDL. An average optical signal-to-leakage noise ratio of 35.33 dB is measured for this PDL. A butterfly design PDL optical architecture is proposed for minimizing loss and improving assembly accuracy. These DMD-based variable PDLs can be used in applications ranging from radio frequency (RF) fiber-optic signal processing systems to adaptive optics for astronomical and laser radar arrays.     

基于PLC的PMD补偿器中PDL效应的分析

应用穆勒（Müller）矩阵对硅基平面光波导线路（Planar lightwave circuit PLC）补偿器中PDL对差分群时延(Differential group delay DGD)分布的影响进行了分析，在不同的PDL值下对各种不同级次的PLC单元级联情况的DGD值分布进行了讨论，并与Maxwell分布进行了比较，得到了在特定PDL值情况下最为优化的PLC级次.     

Effect of Polarization Dependent Loss on Polarization-Multiplexed Transmission System

We report on the effects of the polarization-dependent loss (PDL) on the polarization-multiplexed system. The result shows that the PDL of 0.9 dB could cause 1-dB power penalty. Unlike PMD, the effect of PDL was not dependent on the transmission speed.     

Multi-Edge-Written Long-Period Fibre Gratings with Low PDL by Using High-Frequency CO2 Laser Pulses

A novel long-period fibre grating （LPFG） with low polarization-dependent loss （PDL） is fabricated by using a multi-edge exposure method with high frequency CO2 laser pulses. The experimental results show that the PDL of a triple-edge-written LPFG with a peak amplitude of-16.5 dB can be as low as 0.22 dB. These hovel LPFGs can find important applications in optical communication and sensing.     

A Pixelized Variable Optical Attenuator Using Liquid Crystal on Silicon Technology for Tunable Filters

We apply liquid crystal on silicon (LCOS) in 0.8-$mUm standard complementary metal-oxide semiconductor (CMOS) technology to demonstrate a low-cost, high-performance pixelized liquid crystal variable optical attenuator (VOA) with pulse width modulation. We then build a prototype tunable filter by using this VOA along with a grating in the Littrow configuration. With the application of 5-V pulse width modulation, the proposed VOA achieves a 5.6-dB insertion loss, a dynamic range of more than 20 dB, a 50-GHz channel spacing capability, and a polarization-dependent loss (PDL) of less than 0.6 dB at 15-dB attenuation. Our VOA is suitable for applications such as dynamic channel gain equalizers, channel-blocking filters, sub-components of re-configurable add-drop modules, and wavelength selectors.     

Mode field profile and polarization dependence of long period fiber gratings written by CO2 laser

Mode field profiles and polarization dependence in the CO₂-laser-notched long period fiber gratings (LPFGs) were investigated in detail. Asymmetric field profile was demonstrated in the 2- and 3-dimensional far field patterns of the CO₂-laser-notched LPFG, which experimentally verifies the previously-presented asymmetry of refractive index modulation within the cross section of the gratings. Polarization dependent loss (PDL) of the LPFG was measured via Mueller matrix method. The maximum PDL of 1.68 dB and the maximum polarization extinction ratio of 1.07 dB are observed in the LPFG.