Monomode fiber modulators: Frequency and polarization state control

Two experimental fiber components are described that exploit the properties of highly birefringent monomode optical fiber. In the first the generation of a traveling ultrasonic flexure wave on the fiber produces a frequency shift on the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarization eigenmodes to produce an arbitrary output polarization state from a linear input state (or vice versa) without loss of optical power.     

Least-squares analysis of the Mueller matrix

In a single-mode fiber excited by light with a fixed polarization state, the output polarizations obtained at two different optical frequencies are related by a Mueller matrix. We examine least-squares procedures for estimating this matrix from repeated measurements of the output Stokes vector for a random set of input polarization states. We then apply these methods to the determination of polarization mode dispersion and polarization-dependent loss in an optical fiber. We find that a relatively simple formalism leads to results that are comparable with those of far more involved techniques.     

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.     

Effect of polarization nonreciprocity in rotating fiber ring interferometers

The effect of polarization nonreciprocity in sensors of angular velocity of rotation—fiber ring interferometers (FRIs)—is considered for arbitrary polarization of eigenmodes of the single-mode optical fiber of an FRI loop and arbitrary polarization state of radiation at the FRI input. A new method for detecting the polarization nonreciprocity in an FRI is proposed. Numerical estimations are made.     

A tunable nonlinear optical loop mirror with feedback using linear highly birefringent fiber in the loop

The dynamics of a nonlinear optical loop mirror (NOLM) with feedback using a high birefringence fiber in the loop are investigated. The effect of rotating input polarization angle on the output power and polarization angle is numerically examined, illustrating the sensitivity of the NOLM with feedback to the input’s polarization state, as well as the polarization chaos present with sufficient input powers. The inclusion of a polarization-dependant loss in one or both arms of the coupler is also shown to change the output dynamical behaviour of the system.     

Research of an integrative technique with polarization modulation for generating high-quality multi-wavelength optical source

With the development of society, the need of fiber optical communication expansion and upgrades is increasing. Multi-wavelength optical source has been popularly researched as one of the key component of DWDM. A integrative technique with polarization modulation for high-quality multi-wavelength optical source has been proposed theoretically and experimentally. A comprehensive and systematic overview of how to get a high-quality multi-wavelength optical source, based on in-depth and detailed experiment research. It is found that the optical intensity of the sidebands are not only related to the microwave source and DC bias voltage loaded at EOIM, but also affected by the polarization state of the input light. Five perfect sidebands with equal peak value can be realized by regulating the polarization state of the input light, in addition to regulating the microwave source and DC bias voltage loaded at EOIM as well as. The peak–peak difference of intensity of sidebands can be down to 0.00 dBm in the best situation. Polarization state of the input light plays a good role in generating wonderful sidebands with equal space, balanced peak value, high signal-to-noise ratio. The number of sidebands can be selected according to specific application. The findings may have important implications for high-quality multi-wavelength optical source.     

Calculation of Birefringence Distribution in Optical Fiber Based on Analysis of Angle Between States of Polarization

A method of the calculation of spatial birefringence distribution in an optical fiber link is presented. This method is based on analysis of the polarization properties of the backscattered optical signal. The analytical results are compared with numerical results. This comparison gives excellent agreement. The spatial birefringence distribution is evaluated from the measurement of the round-trip Mueller matrices derived from calculation of the angles between the input and output state of polarization.     

基于法拉第旋镜的干涉型光纤传感系统偏振相位噪声特性研究

偏振诱导信号衰落现象的抑制是干涉型光纤传感系统的关键技术之一. 针对法拉第旋镜(FRM)法抑制偏振诱导信号衰落技术的残留偏振相位噪声问题进行了深入的理论和实验研究. 运用琼斯矩阵法建立了基于法拉第旋镜的干涉型光纤传感系统偏振相位噪声的理论模型; 分析了影响系统偏振相位噪声的主要原因: 法拉第旋镜的旋光角度偏差、入射光偏振态调制度、干涉仪两臂光纤双折射; 提出了相应的抑制偏振相位噪声的方法. 详细仿真分析了入射光偏振态调制度对干涉型光纤传感系统偏振相位噪声的影响, 仿真分析得出若法拉第旋镜旋光角度偏差为最大工艺制造误差1°, 当入射光偏振态调制度为1.84 rad时, 系统可能出现的最大偏振相位噪声为0.0815 rad. 最后, 搭建了基于M-Z型偏振态调制器的偏振相位噪声测试系统, 测试了在传输光纤受到外界偏振扰动的情况下, 干涉传感系统存在的偏振相位噪声, 实验测试结果与理论分析结果基本一致, 有力地证明了该偏振相位噪声理论分析模型的正确性.     

低双折射光纤中拉曼增益对光偏振态的影响

利用包含拉曼增益的耦合非线性薛定谔方程, 导出了斯托克斯参量表示的含拉曼增益的杜芬方程, 通过椭圆积分求出了杜芬方程的解析解, 重点分析了光波在低双折射光纤中传播时, 拉曼增益对其偏振态演化的影响结果表明当输入功率与运动常量满足一定关系时, 拉曼增益改变了光波传输时其偏振态演化周期.     

双折射光纤受激拉曼散射偏光特性的实验研究

对椭圆芯光纤受激拉曼散射偏光特性进行了系统的实验研究。实验巾观察到8级斯托克斯线和2级反斯托克斯线,对不同偏振态的抽运光激励下各级斯托克斯线的偏振特性、拉曼频移等参量进行了分析,并给出了经验公式。其结果与实验数据符合良好。实验表明,双折射光纤受激拉曼谱的各级斯托克斯线的偏振状态不但与拉曼介质有关还与抽运光的偏振态有关,入射抽运光偏振态对低阶次的斯托克斯线拉曼频移的影响较小,而对高级斯托克斯线拉曼频移影响较大。     

拉曼效应对低双折射光纤偏振特性的影响

在低双折射光纤中,利用线偏振光满足的包含拉曼效应的非线性耦合模传输方程,通过引入斯托克斯参量,导出了斯托克斯参量所满足的耦合模传输方程.利用庞加莱球图示法,描述了拉曼增益效应作用下光波偏振态的演化,研究分析了拉曼效应对低双折射光纤中光波偏振态演化规律的影响.结果表明,当输入功率与运动常量满足一定关系时,拉曼增益效应改变了光波传输时其偏振态演化周期和偏振态的椭圆率.     

On a two-pass scheme without a faraday mirror for free-space relativistic quantum cryptography

The stability of destructive interference independent of the input polarization and the state of a quantum communication channel in fiber optic systems used in quantum cryptography plays a principal role in providing the security of communicated keys. A novel optical scheme is proposed that can be used both in relativistic quantum cryptography for communicating keys in open space and for communicating them over fiber optic lines. The scheme ensures stability of destructive interference and admits simple automatic balancing of a fiber interferometer.     

Nonlinear repolarization in optical fibers: polarization attraction with copropagating beams

We propose a type of lossless nonlinear polarizer, novel to our knowledge, a device that transforms any input state of polarization (SOP) of a signal beam into one and the same well-defined SOP toward the output, and perform this without any polarization-dependent losses. At the polarizer output end, the signal SOP appears to be locked to the input pump SOP. The polarizer is based on the nonlinear Kerr interaction of copropagating signal and pump beams in a telecom or randomly birefringent optical fiber.     

Influence of the irregularity of twisting of the birefringence axes of single-mode optical fibers on the polarization nonreciprocity of fiber ring interferometers

A particular example of the so-called minimum-configuration fiber ring interferometer whose loop comprises two different-length segments of a single-mode optical fiber with the same linear birefringence but different twisting is used to show that even in the case where the birefringence axes at the loop input coincide with the polarizer transmission direction, the phenomenon of polarization nonreciprocity of the fiber ring interferometer can emerge. It is shown that polarization nonreciprocity can be eliminated by the proper adjustment of the axes of a single-mode optical fiber, but the above adjustment should be changed if the waveguide temperature is changed. It is also shown that polarization nonreciprocity is a function of the light wavelength and the polarization nonreciprocity value in a fiber ring interferometer varies quasiperiodically in response to the temperature change in an optical fiber with random irregularities.     

Polarization effects and performance of fiber optic recirculating loops

Polarization effects such as PMD and PDL in a straight-line optical fiber communication system are random due to the random birefringence of optical fiber. However, since there is periodicity in a fiber recirculating loop, the polarization effects are quite different than in a straight line. Theoretically and experimentally we analyze the polarization effects in a loop and their effect on performance and the evolution of the state of polarization of a channel. Using this analysis, we are able to better understand the physical impact of the evolution of the state of polarization of a channel on performance. We show that loop-synchronous polarization scrambling is an effective way of breaking this periodicity in an attempt to make the recirculating loop perform more like a straight-line system.     

一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法

提出和论述了一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法。基本思想是设计和采用一种全光学偏振态转换器 ,理论上能将随机偏振态的输入信号光转换为固定偏振方向且功率基本不变的线偏振光 ,利用它控制信号光的偏振态能够克服四波混频过程所固有的偏振敏感性。将这种方法与正交偏振双抽运方法结合起来 ,能较简单地实现偏振不敏感且具有近似常数转换效率的宽带四波混频光波长转换     

基于Sagnac/双Mach-Zehnder原理的分布式光纤传感系统的偏振态分析

运用琼斯矩阵分析法,建立了该分布式传感器系统在传感光纤双折射和外部事件共同作用下,传输光的偏振态对系统功率传输系数影响的数学模型.仿真分析了在传感光纤线性双折射和圆双折射共同作用下,传输光的偏振态对系统功率传输系数的影响,并提出了利用偏振控制器对输入偏振态进行控制,从而改善干涉信号输出的方法.     

单模光纤系统激光偏振传输特性的研究

本文运用激光偏振性矢量传输理论,分析了在单模光纤传输系统中激光偏振性的传输特性.得出了激光偏振状态与单模光纤的双折射、传输系数和拍长的关系.