Linear wavelength sweep of a semiconductor laser and its consequence for dispersion measurements and interference noise in optical fibers

The wavelength shift of a semiconductor laser during triangular pulse modulation has been investigated, using both a Michelson interferometer and direct spectral measurements. This property is used to establish a method for high-resolution dispersion measurements limited to 10 ps, and not affected by material dispersion or detector rise time. A theoretical investigation shows under what conditions the method is equivalent to the standard dispersion measurement setup. The technique is applied to measure polar mode dispersion in single-mode fibers. Examples of polarization noise caused by polarization anisotropy and the variation of source wavelength are presented.     

含氟聚酰亚胺波导波长分离耦合器优化设计

提出并采用统计优化的设计方法解决含氟聚酰亚胺波导波长交叉分离耦合器的偏振态变动的影响.在实测了含氟聚酰亚胺的色散和双折射特性的基础上,优化设计了40路波长信道、1550 nm中心波长、0.8 nm波长间隔的抗偏振变动的波长交叉分离耦合器.数值模拟显示:波长周期偏移小于0.1 nm,1 dB带宽为0.5 nm,3 dB带宽为0.8 nm,串扰小于－30 dB,偏振变动导致的波长漂移小于0.08 nm.     

单模光纤中偏振模色散的仿真模型

利用琼斯矩阵法研究了长单模光纤中偏振模色散的仿真模型.考虑到偏振模色散的随机性,该模型中单模光纤被看作是一系列短双折射光纤段的级联,相邻两段之间耦合角是随机的.研究结果表明,当短双折射光纤段等长时,偏振模色散呈现随波长周期性变化的特点;不符合实际情况.当短双折射光纤段不等长且服从高斯分布时,周期性逐渐消失;当其长度均方差为均值的20%,周期性完全消失.最后比较了偏振模色散的时域统计特性.取短双折射光纤段的长度服从高斯分布且均方差为均值的20%,偏振模色散的统计特性接近于实际分布.因此得出结论:为了正确估计偏振模色散的影响,在单模光纤的级联模型中,短双折射光纤段的长度应服从高斯分布,均方差为其均值的20%.     

偏振模色散及非线性效应对40 Gbit/s密集波分复用系统的影响

高速率、大容量的密集波分复用系统是光纤通信系统的最终发展方向 ,单信道速率达到 4 0Gbit/s时 ,光纤的非线性效应、偏振模色散现象对系统的影响更加突出。在综合考虑群速度色散、自相位调制、交叉相位调制、四波混合、偏振模色散等因素的基础上 ,推导了密集波分复用系统中任意信道的耦合非线性薛定谔方程组。利用扩展的分步傅里叶方法对该方程进行了数值计算 ,通过对 8× 4 0Gbit/s密集波分复用系统的仿真 ,分别研究了非线性效应和偏振模色散对密集波分复用系统的影响。发现由于交叉相位调制和四波混合作用 ,多波长的密集波分复用系统比单波系统受非线性效应影响严重 ;系统受偏振模色散与非线性效应的影响程度与输入信号功率有关 ,在入射光单信道平均功率较低 0 .1mW时 ,偏振模色散是影响系统性能的主要因素 ;当入射光单信道平均功率较高1mW时 ,系统受非线性效应影响严重。而偏振模色散在使信号脉冲展宽的同时 ,类似于非零色散位移光纤中的微小色散 ,对非线性效应又有一定的抑制作用。     

Measurements of Key Parameters for Birefringent Single-Mode Optical Fibers by Optical Frequency-Domain Interferometry

This Letter describes measurements of modal birefringence (MB) and polarization mode dispersion (PMD) of a birefringent single-mode optical fiber for use at 1.5 #x03BC;m in optical wavelength. Optical frequency-domain interferometry based on a fixed analyzer method is applied to the measurement of orthogonal polarization components of light guided in the fiber. An amplified spontaneous emission source having an optical wavelength range between 1520 and 1560 nm is used. A channeled interference spectrum is obtained to measure MB and PMD in turn. These two parameters are not frequency-dependent in the above optical wavelength range and MB = 4.0 #x00D7; 10^#x2212;4 and PMD = 1.33 ps/m are obtained.     

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.     

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.     

A deeper analysis of the second order polarization mode dispersion in optical communications systems

This article presents a new approach to the combined analysis of the first and second-order polarization mode dispersion (SOPMD) and shows their importance in optical communication systems performance. How it affects the relation between second-order polarization mode dispersion (PMD) and the differential group delay (DGD) in a single mode fiber is discussed. The analysis is based on time or wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long term statistical characteristics of second-order PMD over a PMD emulator, and investigate the correlation between SOPMD, depolarization (DEP) and polarization dependent chromatic dispersion (PCD). Some authors calculate these modes from measurements obtained from the first order polarization mode dispersion, assuming a positive correlation between these effects, but this not the real relationship between them. A new interpretation of SOPMD was used to analyze the problem of the spectral stability in terms of the temperature. Actual techniques for determination SOPMD, consequently DEP and PCD, use the variation in time and/or wavelength. In some studies the results obtained for SOPMD are correlated to first-order PMD (FOPMD). This paper shows, based on measurements, that the correlation between first and second order Polarization Mode Dispersion (PMD) in the case where the last one is a function of the temperature can assume positive or negative values.     

双折射光纤中偏振复用技术的三阶色散抑制和补偿

针对三阶色散对零色散波长附近光脉冲偏振复用技术的破坏作用，提出了使用色散平坦光纤来抑制三阶色散的影响。然而用色散平坦光纤只能在脉冲短距离传输时有效，故提出用正负三阶色散交替的光纤补偿三阶色散对光脉冲偏振复用技术的影响。研究发现该补偿方案能有效地抵消线路的总三阶色散，实现了偏振脉冲长距离稳定传输。     

云母晶体双折射率色散特性的研究

针对云母晶体材料本身性质所决定的双折射率色散关系不一致性,给波片设计带来非常不利的影响,提出偏光干涉法研究云母的色散特性.即由分光光度计测量出云母晶体的偏光干涉谱,通过对干涉谱极值点所对应波长的精确判断,准确计算出极值点的最大双折射率,获得从紫外至近红外光波段云母晶体的双折射率色散曲线,经多项式拟合数据处理,得到任意波长的双折射率色散公式.为求解不同温度任意波长的云母晶体双折射率提供了一种精确简单的方法,对云母晶体器件的设计与使用有重要的理论依据和参考价值.     

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。     

Polarization and dispersion properties of elliptical hole golden spiral photonic crystal fiber

An elliptical air-hole golden spiral photonic crystal fiber (EGS-PCF) is analyzed with the full-vectorial finite element method. The air-holes in the EGS-PCF are arranged in a spiral pattern governed by the Golden Ratio, where the design has been inspired by the optimal arrangement of seeds found in nature. The EGS-PCF exhibits extremely high birefringence (～0.022 at operating wavelength 1550 nm) which is particularly useful for generating a polarization stable supercontinuum (SC). The fiber can also be designed to have a Zero Dispersion Wavelength (ZDW) at a suitable wavelength for only one polarization and large negative dispersion for the other, leading to a single-polarization SC. In addition, the fiber dispersion can be designed to obtain ZDWs at 800 nm and 1064 nm simultaneously, which can facilitate broadband supercontinuum generation (SCG) through multi-wavelength pumping.     

超短光脉冲在双折射光子晶体光纤中产生超连续谱的偏振特性数值分析

采用矢量耦合非线性薛定谔方程描述了超短光脉冲在双折射光子晶体光纤中的传输过程,并利用分步傅里叶方法求解该方程。数值模拟了中心波长为1550nm的超短光脉冲在不同色散参量的双折射光子晶体光纤中超连续谱的产生及其偏振特性。分析了光纤在不同色散区时,高阶色散和非线性效应对超连续谱及其偏振态的影响。结果表明,当超短光脉冲波长位于近光纤零色散点的反常色散区时,比其在光纤正常色散区和远离光纤零色散点的反常色散区更容易产生宽且平坦的超连续谱,所得到的光谱显示出了复杂的偏振态特性。     

Dispersion and polarization properties of elliptical air-hole-containing photonic crystal fibers

In this paper, we investigate the dispersion and polarization properties of photonic crystal fiber with one ring or more rings of elliptical air-holes using plane-wave expansion (PWE) method. By introducing three rings of elliptical air-holes, PCF with ultra-low and ultra-flattened dispersion is designed and a total dispersion curve between ±0.5 ps/nm/km from 1315 to 1855 nm wavelength range is demonstrated. Furthermore, the polarization property of these elliptical air-hole-containing PCFs is analyzed and the variation of the birefringence with the area and ellipticity of the elliptical air-holes are discussed.     

石英晶体双折射率紫外至近红外波段色散特性实验的研究

介绍了偏光干涉测量石英晶体双折射率色散特性及其相关数据处理方法。利用偏光干涉光谱极值点的精确判断,完成极值点波长对应的材料的双折射率的测量,获得了紫外至近红外光波段石英晶体的最大双折射率与波长关系离散的数据曲线,经多项式拟合数据处理,进而得到任意波长的双折射率函数关系式。此方法对其它各向异性晶体材料的双折射率色散特性的研究同样适应。     

单个波长到多个波长的变换实验

报道一种波长变换的新方法.采用此方法不需要任何泵浦光便能够直接将信号光变换成在特定谱宽内的任意多个任意波长的变换光,这对于将来的波分复用光网络提供了较大的方便.此波长变换的原理是利用色散位移光纤的非线性效应产生超连续光谱(SC)信号,由于这种SC信号携带有变换光信号,对这种连续谱进行滤波便能够得到所需要的任意频率的变换信号.此变换方式具有变换频带宽,偏振不敏感的优点。     

pi-shifted Sagnac interferometer for characterization of femtosecond first- and second-order polarization mode dispersion

A novel configuration for measuring femtosecond polarization mode dispersion (PMD) with a pi-shifted Sagnac interferometer is studied. The advantages of this configuration include a response that is independent of the orientation of the device under test. This independence allows characterization of the first-and second-order PMD by measurement of the wavelength dependence of the differential group delay and of the orientation of the device's principal states of polarization. The method provides an extension of the dynamic range of the Sagnac interferometer technique to few-femtosecond PMD measurement.     

Field-trial evaluation of the Q-factor penalty introduced by fiber four-wave mixing wavelength converters

The performance of tunable all-optical wavelength converters based on four-wave mixing in optical fibers is experimentally tested in a field-trial network. Two converters were built with two different fibers. The first one was made with a small variation in the zero-dispersion wavelength (ZDW) dispersion shifted fiber and the second one with a highly nonlinear fiber that presents great ZDW variations. In order to compare the tuning ranges obtained in both cases we present an experimental spectral analysis. Numerical simulations that consider the influence of both the dispersion slope and the long-scale ZDW variations of the fiber complement the experiments. The tuning bandwidth was larger in the highly nonlinear fiber case. For a set of different optical signal-to-noise ratios, the measurements of the Q-factor of the signal and those of the converted wave are our main results. These results show that the penalty imposed by the converters is different for each converted wavelength. The maximum penalty obtained for the Q-factor was ∼6 dB, but it was ?3 dB for most cases. In all experiments we used a technique based on a dynamic polarization controller in order to avoid power fluctuations in the converted wave caused by polarization induced variations in the signal.     

类矩形芯光子晶体光纤的色散与偏振特性

应用全矢量模型分析类矩形芯光子晶体光纤的色散和偏振特性，讨论了光纤结构参数对光纤特性的影响.研究表明：类矩形芯光子晶体光纤的模式双折射比普通椭圆保偏光纤至少高一个数量级.增大光纤的相对孔径，可获得更高的双折射.零走离点对应的波长也比普通椭圆保偏光纤长，随着孔距的增大，走离曲线将向长波长方向产生移位，零走离点发生红移，零走离点所对应的波长与孔距成正比.零走离点的出现，将有效地抑制一阶偏振模色散.通过调整光纤的结构参数，可以获得灵活的色散特性，在孔距Λ=2μm, 相对孔径d/Λ=03时，在波长155μm附近，获得近400nm的超平坦色散区.该光纤在偏振控制、色散控制和管理方面具有广泛的应用前景. 关键词： 导波光学 光子晶体光纤 类矩形芯 全矢量     

Polarization mode dispersion in WDM systems

The coupled nonlinear Schrodinger equations for two wavelength optical pulses in a birefringence fiber are given. The model for treating polarization mode dispersion in two channel (WDM) system is established. Based on this model, optical signal propagation behaviors in two channel WDM with polarization mode dispersion are numerically simulated. The influences of polarization mode dispersion on two channel WDM system are also analyzed.