Polarization mode dispersion, decorrelation, and diffusion inoptical fibers with randomly varying birefringence

Polarization mode dispersion and the polarization decorrelation and diffusion lengths are calculated in fibers with randomly varying birefringence. Two different physical models in which the birefringence orientation varies arbitrarily are studied and are shown to yield nearly identical results. These models are appropriate for communication fibers. We show that both the length scales for polarization mode dispersion and polarization decorrelation measured with respect to the local axes of birefringence are equal to the fiber autocorrelation length. We also show that the coupled nonlinear Schrodinger equation which describes wave evolution over long length along a communication fiber can be reduced to the Manakov equation. The appropriate averaging length for the linear polarization mode dispersion is just the fiber autocorrelation length but the appropriate averaging length for the nonlinear terms is the diffusion length in the azimuthal direction along the Poincare sphere which can be different, The implications for the nonlinear evolution are discussed     

Linearly Single Polarization Fibers with Zero Polarization Mode Dispersion

The optimum waveguide structure for linearly single polarization fibers, which satisfies the large modal birefringence and the zero polarization mode dispersion simultaneously, has been investigated. The basic waveguide structure is the single-mode optical fiber that has an elliptical core and stress-applying parts with a different expansion coefficient from that of the cladding. Waveguide parameters, such as index difference, core ellipticity, and cutoff wavelength, are first determined to obtain highly birefringent fibers with B = 1 X 10/sup -5/ or B = 5 X 10/sup -5/. The structure of the stress-applying parts that provides zero polarization mode dispersion is then determined.     

双折射单模光纤的保圆耦合

提出了一种利用双折射单模光纤扭转时产生的圆双折射性获得保圆偏振的新方法，该法应用于光纤耦合器的基本思想是通过有效地改变扭转光纤在耦合区域的单位扭转度，从而达到光纤之间实现保圆耦合的目的。同时，用耦合模方程分析了利用该法构成的２×２单模光纤耦合器的耦合行为，结果表明光纤耦合器达到了较好的保圆耦合。     

Polarization distortion in birefringent fiber amplifiers

Numerical simulation of pulse amplification in birefringent optical fibers is reported with emphasis on the evolution of its polarization. We find a complex polarization state of the amplified pulse and stress the implications of our results for the operation of fiber lasers using a birefringent fiber amplifier mode locking element     

Polarization behavior in multiply perturbed single-mode fibers

A general theory is presented for polarization evolution characteristics in anisotropic single-mode optical fibers to which plural perturbations of different kinds are applied simultaneously. This treatment is based on modified coupled-mode theory. Polarization performance in the system can be described by a simple projection rule when the birefringence caused by individual perturbation is known. Several examples of applications are classified according to their mode coupling properties in fused silica fibers.     

A fully polarimetric optical time-domain reflectometer

We report the implementation of the first fully polarization sensitive optical time domain reflectometer (POTDR). This nondestructive measurement technique, requiring access to one fiber end only, enables the determination of both the linear and twist induced circular birefringence distribution along the fiber. This information, combined with a knowledge of the mode coupling length, enables the evaluation of the polarization mode dispersion (PMD) properties of fibers and optical cables exhibiting both types of birefringence, as well as identifying fiber sections with and without twist. The POTDR, which has a spatial resolution of 0.3 m, could also be used for monitoring the birefringence properties of fibers at the manufacturing stage, leading to optimization of fabrication techniques to minimize PMD     

光栅参数对线性啁啾光纤光栅偏振特性的影响

研究了单模线性啁啾光纤光栅的偏振相关损耗特性。运用耦合模理论和传输矩阵分析法推出了反射光的偏振相关损耗,并模拟了光栅的反射谱和偏振相关损耗随光栅参数和双折射量的变化曲线。模拟显示双折射值的变化对啁啾光栅偏振相关损耗的影响非常显著, 尤其是在带边比较陡峭时。啁啾光栅的偏振相关损耗也受光栅的啁啾系数和调制深度的影响。这表明线性啁啾光栅的偏振相关损耗不光依赖光栅双折射量,还依赖其啁啾系数等其他参数。实验结果与理论模拟基本吻合。     

Polarization analysis of Brillouin scattering in a circularlybirefringent fiber ring resonator

A complete analysis of the eigenstate of polarization (ESOP's) in a Brillouin fiber ring laser using fibers with a high circular birefringence is proposed in this paper. Conditions to obtain circular ESOP's for application in a Brillouin fiber optic current sensor are highlighted as well as conditions to have stable ESOP's for applications in other passive or active sensors. Measurements are performed on a Brillouin laser using a mechanically twisted fiber ring resonator confirming the theoretical predictions. Ring resonator configurations using linearly birefringent fibers are compared to configurations using circularly birefringent fibers     

Measure of twist-induced circular birefringence in long single-mode fibers: theory and experiments

Production defects and external perturbations cause standard telecommunication fibers to be randomly birefringent. Fiber birefringence is the origin of the well-known polarization mode dispersion (PMD), which degrades system performances. The knowledge of birefringence properties may be crucial, especially when problems like development of low-PMD fibers or PMD interaction with optical nonlinearities in very high-capacity systems are faced. Some techniques are known to measure birefringence, and useful results have been obtained for both installed and wound-on-drum fibers. However, measurement of the circular component of birefringence still presents difficulties. In this paper, a new method for circular birefringence measurement is proposed that applies to long single-mode twisted fibers. The technique is based on polarization-sensitive optical time-domain reflectometry. Experimental results are in good agreement with the theoretical analysis.     

波分复用系统中偏振模色散特性的研究

推导了双折射光纤中两个波长的光波所满足的耦合非线性薛定谔方程。建立了研究两信道波分复用(WDM)系统中偏振模色散效应的模型。基于这一模型,在考虑偏振模色散情况下,数值模拟了在两信道WDM系统中光信号的传输变化,并且分析了在此系统中偏振模色散的影响     

Depolarization of broadband radiation in optical fibers with the twisted structure of birefringence

The depolarization of broadband linearly polarized radiation that propagates in optical fibers with the twisted structure of birefringence is investigated. The basic relationships for calculating the degree of radiation polarization at the fiber output at arbitrary fiber lengths and arbitrary azimuths of the input linear polarization are obtained. The depolarization length (on the order of several meters) at which the degree of polarization decreases from unity to a certain residual level is found. It is shown that the depolarization length depends on the width of the spectrum of a radiation source, the magnitude of the fiber’s built-in linear birefringence, and the twist pitch. For long fibers (of a length exceeding 50 m), the residual degree of polarization depends on the azimuth of the input linear polarization.     

Polarization dispersion measurement on twisted single-mode optical fibers

A new method for measuring polarization dispersion between two eigen polarization modes is presented. It utilizes the measured phase shift corresponding to birefringence difference between two adjacent wavelengths. This method makes it possible to measure small polarization dispersion by using a short test piece even when eigen polarization modes are elliptically polarized. A polarization dispersion of 0.4 ps/km in twisted single-mode fibers can be measured in an approximately 4-m-long fiber by using 1.152- and 1.161-μm lines in a He-Ne laser. Experimental data that polarization dispersion decreases with an increase in fiber twist ate in very close agreement with theoretical results.     

折射率导模高双折射光子晶体光纤的偏振特性

本文应用全矢量模型,研究一种折射率导模高双折射光子晶体光纤的特性.重点研究了该种光纤的偏振特性,包括基模场的线偏振特性,模式的双折射及偏振模色散.研究表明,由于在包层中采用两种不同尺寸的空气孔,基模中两个正交偏振模简并被打破,呈现出较高的模式双折射,模式双折射比普通的保偏光纤高至少一个量级,在波长1540nm,其拍长可达0.4067mm.改变光子晶体光纤的结构参数,将获得更高的双折射和更大的群时延差.分析结果与实验测量结果相吻合.     

Polarization independent InP WDM multiplexer/demultiplexer module

We report the design, fabrication, packaging, and characterization of a polarization independent integrated optical InP multiplexer/demultiplexer module. The device is based on a vertically etched diffractive grating and separates four channels with 4 spacing in the 1.55 μm window. An n^-/n⁺-InP layer structure with very low birefringence results in a shift of the passbands between transverse electric (TE) and transverse magnetic (TM) polarization of less than 0.1 nm. With a self-aligned flip-chip mounting technique light is optically coupled from the input and output waveguides to an array of lensed single mode fibers with a coupling efficiency of more than 80%. The packaging includes temperature control that allows fine tuning of the channel passbands over 5 nm. Optical crosstalk is always better than -17 dB and fiber to fiber losses of 15 dB are achieved. The module has been successfully implemented in a 4×2.5 Gb/s WDM transmission system     

椭圆孔六角点阵聚合物光子晶体光纤的偏振特性研究

基于全矢量平面波方法,以聚甲基丙烯酸甲酯为基材,设计了一种高双折射光子晶体光纤,并对其传输性质和偏振特性进行了数值模拟。结果表明,椭圆孔六角点阵聚合物光子晶体光纤的双折射是由于包层的不对称性引起的全局双折射,通过调节椭圆率,发现该光纤可以以单模方式在一合适波段运行,该波段与聚合物光纤的低损耗通信窗口一致。并且在 时,其双折射最高可达 。该研究结果为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据。     

Polarization properties of randomly-birefringent spun fibers

The spinning of single-mode telecommunication fibers is a technique currently and widely used to reduce polarization mode dispersion. Yet, this technique was originally envisaged as a way to produce fibers with arbitrarily low birefringence, to be used in sensor applications. In spite of their applicative significance, spun fibers are still not completely understood. In this paper, we report an extensive analysis of the polarization properties of spun fiber. Both unidirectional and periodic spin profiles are considered. It is shown that very high polarization maintaining capabilities may be achieved by properly tuning the spin parameters.     

光纤偏振模色散测试仪

论述了测试仪所采用的光谱分析法光纤偏振模色散测试原理,介绍了弱导模光纤中偏振模色散的随机特性以及变化规律,并给出了光纤偏振模色散测试仪的测试结果。     

Spatially resolved PMD measurements

Spatially resolved measurements of polarization properties of fiber optic link-such as birefringence, polarization-mode dispersion (PMD) and polarization dependent loss (PDL)-may be effectively performed using polarization sensitive reflectometric techniques. In particular, this paper focuses on polarization-OTDR and reviews its theory and applications. Special emphasis is given to the use of optical reflectometry as a tool to characterize fiber birefringence. This allows to inspect the fiber while cabled and, consequently, to test and improve the cabling process. In addition, it also allows to define reliable mathematical models, which are essential for the design of low polarization mode dispersion fibers. The application of polarization-OTDR to polarization mode dispersion and polarization dependent loss measurements is also discussed.