Method for improving the resolution and accuracy against birefringence dispersion in distributed polarization cross-talk measurements

We present a novel method for improving the spatial resolution and amplitude accuracy of distributed polarization cross-talk measurements in a polarization maintaining (PM) fiber against its birefringence dispersion. We show that the broadening of measured polarization cross-talk peaks caused by birefringence dispersion can be restored by simply multiplying the measurement data with a compensation function. The birefringence dispersion variable in the function can be obtained by finding the widths of measured cross-talk envelopes at known distances along the fiber. We demonstrate that this method can effectively improve spatial resolution and amplitude accuracy of the space-resolved polarization cross-talk measurements of long PM fibers.     

Accurate method for measuring the thermal coefficient of group birefringence of polarization-maintaining fibers

We present a method to accurately measure the group birefringence variation with temperature in high-birefringence polarization-maintaining (PM) fibers using a distributed polarization analyzer. By analyzing polarization cross-talk peaks purposely induced at both ends of a PM fiber, the temperature coefficient of group birefringence can be accurately obtained. We confirm the theoretical prediction that the group birefringence of PANDA and TIGER PM fibers decrease linearly with temperature from -40 °C to 80 °C, and find that the temperature coefficients are -5.93 × 10(-7) °C(-1) and -5.29 × 10(-7) °C(-1) for two types of PANDA fibers, and -5.36 × 10(-7) °C(-1) for a TIGER fiber.     

Reflectometric measurements of polarization properties in optical-fiber links

Polarization sensitive reflectometric techniques can be effectively used to perform spatially resolved measurements of polarization properties of fiber optic link — such as birefringence, polarization mode dispersion and polarization dependent loss. In particular, this contribution is focused on polarization sensitive OTDR and provides a survey of its theory and main applications. Special emphasis is given to the characterization of fiber birefringence, that allows to inspect the fiber while cabled and, consequently, to test and improve the cabling process. In addition, the analysis of the birefringence also allows to define reliable mathematical models, which are essential for the design of low polarization mode dispersion fibers. Reflectometric measurements of polarization mode dispersion and polarization dependent loss are also discussed.     

一种新型的基于四孔单元光子晶体光纤的设计与分析

设计了一种基于四孔单元的光子晶体光纤,它可以满足光通信系统中高双折射率、负色散和低限制损耗的要求,比起通常的三角结构光纤有着更高的双折射率,并且结构制作也较简单。采用全矢量有限元法和各项异性完美匹配层法对所设计的光纤进行了仿真研究。仿真结果表明:该光纤在1.55μm波长处可获得10~(-2)数量级的双折射率,在较宽广的波段范围具有大的负色散,限制损耗低于10~(-9)dB/m;该光纤在保偏光纤、单极化单模光纤、色散补偿光纤等方面具有重要的应用。     

Influence of the polarization mode dispersion on the propagation of ultrashort optical pulses in single-mode fiber lightguides with very weak linear birefringence and random inhomogeneities

We consider the influence of the polarization mode dispersion, which is stipulated by the presence of random inhomogeneities in single-mode fiber lightguides, on the propagation of ultrashort optical pulses in the fiber communication lines with very weak linear birefringence. Evolution of the envelope of ultrashort optical pulses and their spectra as functions of the length of a single-mode fiber lightguide with very weak linear birefringence and random inhomogeneities are obtained by the method of mathematical simulation. An increase in the pulse duration is shown to be proportional to the square root of the length of a single-mode fiber lightguide. The numerical-simulation results are compared with the results of experimental measurements of the polarization mode dispersion.     

布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.     

Periodic microbending-induced core-to-cladding mode coupling in polarization-maintaining fibers

We investigate codirectional mode coupling induced by periodic microbending in polarization-maintaining (PM) fibers by using both an acoustic flexural wave and a pair of corrugated fixtures. The measured filtering spectra are found to be strongly polarization dependent. In addition, the coupling strength depends on the angle between the birefringence axes and the bending direction. These characteristics can be utilized for a variety of applications, such as fiber polarizers, polarization-dependent-loss compensators, and on-line alignment of birefringence axes for the manufacture of PM fiber couplers.     

Tunable fiber ring laser with an intracavity high resolution filter employing two-dimensional dispersion and LCoS modulator

We demonstrate a tunable fiber ring laser employing a two-dimensional dispersion arrangement filter, with the lasing determined by a liquid crystal on silicon (LCoS) spatial light modulator. Lasing wavelengths can be tuned discontinuously across the communication C-band at an addressable resolution of less than 200 MHz. We introduce full characterization of the laser output including phase and amplitude stability and short and long-term bandwidth measurements.     

Measurement of pulse amplitude and phase using cross-phase modulation in microstructure fiber

Cross-phase modulation in a highly nonlinear microstructure optical fiber with low dispersion and high birefringence is used for the measurement of the pulse amplitude and phase of picosecond pulses by frequency-resolved optical gating. An alignment-free configuration including an optical amplifier is proposed and experimentally tested. The simulated annealing method is used for retrieving the amplitude and phase from cross-phase modulation spectrograms. It takes into account the birefringence of the measurement fiber and the resolution of the optical spectrum analyzer.     

Influence of the birefringence autocorrelation function on the polarization mode dispersion of constantly spun fibers

We show that the polarization mode dispersion of a constantly spun, single-mode fiber is strongly influenced by the autocorrelation function of its birefringence. In particular, under probable conditions, the mean square differential group delay of the spun fiber may even be higher than the delay that the same fiber would have if it were not spun.     

高数值孔径双芯光纤的双折射研究

具体分析了具有高数值孔径的双芯光纤的双折射特性。首先利用超格子正交函数法和耦合模理论分析了双芯光纤的几何双折射,并将两种方法计算的几何双折射进行了比较分析。数值计算结果表明双芯光纤在两纤芯非常接近的情况下,几何双折射仍较小,只能到10-5量级。利用超格子正交函数法计算了双椭圆芯光纤的双折射,改变结构参量可使几何双折射达到10-4量级。高的数值孔径需要高的掺锗量,理论上分析了高数值孔径时双芯光纤功率集中区域的应力双折射,应力双折射接近10-4量级。设计制作出了具有良好保偏性能的双芯掺铒光纤,测试、分析了它的几何参量和折射率分布;双芯光纤双折射系数达到了8.4×10-5。双芯掺铒光纤可以作为保偏掺铒光纤,应用到制作具有稳定的单一偏振态输出的光纤激光器。     

Spectral polarimetry with a differential group delay bias

We show that the addition of a polarization controller and bias differential group delay to a spectral polarimeter increases the amount of polarization information that can be extracted from a Stokes spectrum measurement. We use this biased spectral polarimetry on 40-Gbit/s signals to measure the polarization mode dispersion of the optical fiber through which they propagate. Our measurements do not require any control of the polarization at the fiber input. Averaging measurements from several settings of the polarization controller yields improved accuracy, and, after data rejection is applied, both the accuracy and the number of valid data points is increased when using several measurements.     

Characterization of specially designed polarization maintaining photonic crystal fiber from far field radiation patterns

We report the development of theory and experiment for the characterization of polarization maintaining photonic crystal fiber (PM PCF) from far field intensity measurements. In this specially designed photonic crystal fiber, the air hole diameters along orthogonal axes adjacent to the core region are different, and hence create an effective index difference between the two orthogonal polarization modes. From the experimental measurements of the far field radiation pattern, we obtain transmission characteristics of PM PCF in terms of mode field diameters (MFD), V-values along major and minor axes, mode field area, birefringence, core radius, effective refractive index of cladding and numerical apertures along major and minor axes of PM PCFs. It is shown that the experimentally obtained geometrical and wave guiding parameters of the PM PCF match with the manufacturer/simulation/scanning electron microscope (SEM) data within the experimental limits.     

一种新型高双折射光子晶体光纤

提出了一种新的高双折射光子晶体光纤结构.应用全矢量频域有限差分方法所做的数值分析表明：该结构光纤基模的两个正交偏振态不再简并，其模式呈现很强的线偏振特性,并且模式双折射与结构参数设置有密切关系.通过选择合适的结构参数，可以使之达到10^-2量级，比传统的D型和熊猫型保偏光纤高出2个数量级.合理设计光纤包层的几何结构，可以取得理想的色散效果.这种结构的光子晶体光纤可用于制作具有适当色散特性或偏振特性的保偏光纤及相关光纤器件. 关键词： 光子晶体光纤 模式双折射 偏振特性 频域有限差分法     

Polarization mode dispersion probability distribution for arbitrary distances

The probability distribution of the differential group delay (DGD) at any fiber length is determined by use of a physically reasonable model of the fiber birefringence. We show that if the fiber correlation length is of the same order as or larger than the beat length, the DGD distribution approaches a Maxwellian in roughly 30 fiber correlation lengths, corresponding to a couple of kilometers in realistic cases. We also find that the probability distribution function of the polarization dispersion vector at the output of the fiber depends on the angle between it and the local birefringence vector on the Poincaré sphere, showing that the DGD remains correlated with the orientation of the local birefringence axes over arbitrarily long distances.     

Performance Analysis of High-speed Optical Pulse Transmission in Dispersion-managed Nonlinear Birefringent Fiber Using Quantum Well Laser Diode Sources

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　ＳｉｎｃｅＣ .Ｄ .Ｐｏｏｌｅ ｐｒｏｐｏｓｅｄｐｈｅｎｏｍｅｎｏｌｏｇｉｃａｌａｐｐｒｏａｃｈｔｏａｎａｌｙｚｅｐｏｌａｒｉｚａｔｉｏｎｍｏｄｅｄｉｓｐｅｒｓｉｏｎ (ＰＭＤ) [1] ,ｍａｎｙｍｏｄｅｌｓａｎｄｃａｌｃｕｌａｔｉｏｎｓｏｆＰＭＤｗｅｒｅｄｅｖｅｌｏｐｅｄｉｎＲｅｆ.[2 ].Ｈｏｗｅｖｅｒ,ｍｏｓｔｏｆｔｈｅｍｆｏｃｕｓｅｄｏｎｔｈｅ ｐｕｌｓｅｔｒａｎｓｍｉｓｓｉｏｎｏｆｉｄｅａｌｐｕｌｓｅｓ,ｓｕｃｈａｓｃｏｎｖｅｎｔｉｏｎａｌＧａｕｓｓｉａｎｐｕｌｓｅ ,ｓｅ…     

Performance Analysis of High-speed Optical Pulse Transmission in Dispersion-managed Nonlinear Birefringent Fiber Using Quantum Well Laser Diode Sources

This paper analyzes the high bit-rate optical pulse trasmission in single mode optical fiber with chromatic dispersion, polarization mode dispersion (small random birefringence) and nonlinearity. Numerical method employed can precisely describe their interactive effect on transmission performance. Different dispersion maps and the related performance are analysed. Various simulation results and discussion are given. The results show that chromatic dispersion compensation should be carefully designed. Appropriate dispersion management can also alleviate the effect of polarization mode dispersion.     

高双折射光子晶体光纤偏振模色散测量

对一种高双折射光子晶体光纤的偏振模色散进行了测量.实验用26 m长光子晶体光纤使皮秒光脉冲的两个正交偏振模产生了108 ps时延.运用脉冲时延法和固定分析仪法对这种高双折射光子晶体光纤的偏振模色散进行了实验测量，测量得到其偏振模色散参量可达4154 ps/km，对应的模式双折射度为1.25×10－3.这种新型的高双折射光纤可用于补偿光纤通信系统中的偏振模色散.     

Modeling polarization-dependent gain in fiber Raman amplifiers with randomly varying birefringence

We report a new stochastic model for studying the polarization-dependent gain in Raman fiber amplifiers with randomly varying birefringence as a function of the pump state of polarization and the polarization mode dispersion parameter. Our theoretical results agree with the previously obtained experimental data.     

微结构聚合物光纤中高双折射可调效应研究

通过在纤芯附近引入两个直径较大的空气孔诱导纤芯局部双折射,在包层减小x方向的孔间隔诱导包层双折射,设计实现了一种高双折射随波长可调效应的微结构光纤.采用全矢量平面波方法,以聚合物甲基丙烯酸甲酯为基材,对其偏振特性和基模模场进行了研究.结果发现,该光纤基模双折射在光通信波段呈现两个最大值,且最大双折射大小和位置随光纤结构和波长的变化可以进行调节.通过调节光纤结构参数,模拟得到了该光纤具有高双折射和零偏振模色散的最佳设计参数. 关键词： 导波与光纤光学 双折射可调 聚合物 全矢量平面波法