高阶模补偿单模光纤色散技术研究

在分析计算高阶模色散特性的基础上,论述了利用高阶模大的负色散系数和色散斜率实现了对单模光纤补偿的可行性,着重研究了LP02模作为高阶模色散补偿的性能,结果表明,高阶模色散补偿技术是一种高品质因素的补偿方案。最后设计了基于LP02模的高阶模色散补偿方案,并详细描述了模式转换器的工作原理。     

强双折射光纤中三阶色散对DGD的影响

依据强双折射光纤中两垂直偏振分量所满足的非线性耦合模方程,研究了三阶色散对偏振分量间的时延差的影响。结果表明,当二阶色散、三阶色散同时存在时,三阶色散可以减小时延差;当只有三阶色散时,除了产生较大时延差外,还会在两个偏振脉冲的前后沿产生较大的色散波。     

高速光通信偏振模色散补偿前馈信号提取方法

为了得到高阶偏振模色散的前馈信息,采用数值模拟的方法,通过一种实时提取1阶和2阶偏振模色散的模型,直接得到了偏振模色散的大小和方向。将模拟得到的偏振模色散大小与从琼斯矩阵理论中计算的结果进行比较,结果表明,采用该模型的模拟结果与理论计算值在差分群时延为一个比特周期内符合较好。从得到的偏振模色散矢量的大小和方向信息可以为高阶偏振模色散补偿提供前馈信息。这一结果对偏振模色散的前馈补偿系统的设计具有参考价值。     

光纤偏振模散随波长变化特性的研究

目前,偏振模散已经成为高速光纤通信系统发展的主要障碍,本文用琼斯传输矩阵法研究了偏振模散,通过数值模拟给出其统计特性,差分群时延服从麦克斯韦分布;PMD各阶项随波长随机变化;偏振主态在邦加球上的变化走向说明出现了PMD高阶项。     

光脉冲的初始啁啾对单模光纤的色散效应的影响

在光纤通信中已经有利用光脉冲的初始啁啾来进行色散补偿的运用。文中从理论上分析了光脉冲的初始啁啾与单模光纤的色散效应的关系，并用数值仿真的方法验证了分析结果：线性初始啁啾可以在一定程度上补偿一阶色数，但却加大了高阶色散对传输光脉冲的负面影响。     

偏振模色散补偿对脉冲展宽的影响

在高速光纤通信系统中,偏振模色散(PMD)已被认为是限制光纤通信系统性能的一个主要因素,而脉冲的均方根展宽是表征信号传输性能的一个重要的物理量.研究了偏振模色散对脉冲展宽的影响,推导出含有一阶偏振模色散补偿的光纤链路中偏振模色散矢量的自相关函数的分析表达式.在此表达式的基础上,推出了以高斯脉冲为例的一阶偏振模色散补偿系统中的均方根脉宽解析表达式.     

Highly birefringent photonic crystal fibers with flattened dispersion and low confinement loss

A highly birefringent index-guiding photonic crystal fiber (PCF) with flattened dispersion and low confinement loss is proposed by introducing two small air holes with the same diameter in the core area. The fundamental mode field, birefringence, confinement loss, effective mode area and dispersion characteristic of the fibers are studied by the full-vector finite element method (FEM). Simulation results show that a high birefringence with the order of 10 -3 and a low confinement loss of 0.001 dB/km are obtained at 1550 nm. Furthermore, flattened chromatic dispersion from 1450 nm to 1590 nm is obtained.     

高速光纤通信系统中高阶PMD补偿技术研究

随着光放大器和色度色散补偿技术的不断提高，光纤的偏振模色散（PMD）已经成为超高速、超长距离光纤通信系统发展的主要障碍，在40Gbit/s或更高速率的光纤通信系统中，PMD的影响已不可忽略，必须考虑PMD的补偿问题，从高阶PMD对40Gbit/s NRZ系统影响的数值模拟发现，当光纤中PMD高阶效应比较明显时，将严重劣化一阶PMD补偿的效果，另外，通过对两种高阶PMD补偿器的比较介绍，认为两段级联的高队PMD补偿系统是一种比较现实的补偿方法。     

材料色散对1维光子晶体缺陷模影响的研究

为了分析材料色散对缺陷模的影响,对色散材料采用洛伦兹振子模型,利用传输矩阵法计算了含缺陷1维光子晶体的透射谱,分析了各层的色散对该结构1维光子晶体缺陷模的影响。结果表明,无论是高、低折射率介质还是缺陷层的色散都可以引起缺陷模的频移或分裂;缺陷模的频移方向与考虑色散后光学厚度的变化有关,如果光学厚度增大,则发生红移,反之则发生蓝移;低折射率介质的色散使缺陷模频移的效果最显著。这一结果对光子晶体的设计和研究有一定的参考价值。     

Design and characterization of dispersion compensating fiber basedon the LP01 mode

The practical implementation of erbium-doped fiber amplifiers with gain at 1.55 μm allows long unrepeatered transmission distances. However, in order to realize high data rates over these distances with already installed standard single mode fiber, techniques must be found to overcome the pulse spreading due to the positive chromatic dispersion of the transmission fiber in this window, we review a compensation technique based on propagating the signals through a specially designed fiber with large negative dispersion for the LP₀₁ mode, thereby ending up with zero net pulse spreading. The basis of the concept are discussed and a key figure of merit for dispersion compensating devices is defined. The design and optimization of dispersion compensating (DC) fiber is described with special attention to practical concerns including packaging and manufacturability. We describe experimental fabrication results of DC fiber, results of using the fiber to make compact dispersion compensating modules, and the outcome of recent systems experiments incorporating the fiber     

Large Negative Dispersion in Dual-Core Photonic Crystal Fibers Based on Optional Mode Coupling

Chromatic dispersion of dual-concentric-core photonic crystal fibers (PCFs), which have an inner low-index core and an outer high-index core, is investigated based on a full vector finite-element method. Large negative dispersion can be obtained by introducing avoided crossing between modes of the two asymmetric cores. While increasing the negative dispersion, larger effective mode area is also possible by choosing a higher order mode in the outer core to couple with the fundamental inner core mode. During the analysis, a dual-core PCF with a dispersion peak value of -36 000 ps/(nmldrkm) and effective mode area of 34.8 mum² is presented.     

偏振模色散补偿的2种反馈控制信号特性比较

为了研究光纤通信系统中存在高阶偏振模色散时,采用偏振度和电带宽作反馈信号,偏振模色散的补偿效果,采用数值模拟方法比较了两种常用的反馈控制信号对偏振模色散性能的影响,由模拟结果可知,从性能上讲,两种反馈信号都随1阶偏振模色散变化而具有线性变化,当系统中有高阶偏振模色散时,二者均不具有线性的变化,但偏振度的性能要优于电带宽信号。结果表明,这对偏振模色散补偿具有一定的指导意义。     

Electrical spectrum measurements of dispersion in higher order mode fibers

We present a novel technique for measuring the chromatic dispersion of the higher order mode of an optical fiber. The measurement technique is simple, accurate, and capable of measuring the dispersion of kilometer lengths of fiber without the need for mode converters. The dispersion of the LP/sub 02/ mode is measured for several different fibers, and accuracies of better than 1%, compared with a measurement with the modulation phase shift method, are achieved.     

光纤色散效应对脉冲展宽的影响

为了研究光通信系统中光纤色散特性对通信系统传输性能的影响,基于单模光纤和多模光纤的色散特性,采用数值模拟计算的方法,对脉冲展宽、光纤内部的偏振模色散、色度色散、波导色散和模间色散的物理机制进行了分析,分别得到了折射率n=1.516和n=1.458的标准单模光纤经过10km传输距离后色散导致脉冲展宽的结果,比较了传输波长在850nm和1310nm时多模光纤的色散效应,通过对不同光源LD(Δλ=1nm)和LED(Δλ=70nm)的比较,分析了光谱宽度对脉冲展宽的影响。结果表明,纯石英光纤在系统传输波长为1.27μm处群速度色散等于0;折射率渐变多模光纤工作在常见的850nm以及1310nm通信窗口时,其模内色散表现为负色散;色度色散和模间色散引起的脉冲展宽随光纤的数值孔径、材料折射率和光源光谱线宽的增大而增大。     

1维方形掺杂光子晶体波导中缺陷模的色散特性

为了研究1维方形掺杂光子晶体波导中缺陷模的色散,采用特征矩阵的方法研究了1维方形掺杂光子晶体波导中TE波和TM波缺陷模的变化特征,得到了TE波和TM波的缺陷模随色散强度、色散厚度变化的结果。结果表明,色散强度和色散厚度都会对1维方形掺杂光子晶体波导中TE波和TM波的缺陷模产生明显的影响;利用TE波和TM波的缺陷模随色散强度、色散厚度的变化规律,可以有效地实现对1维方形掺杂光子晶体波导中TE波和TM波各传输模式的有效控制。     

Bending Effects on Highly Birefringent Photonic Crystal Fibers With Low Chromatic Dispersion and Low Confinement Losses

Photonic crystal fibers (PCFs) with elliptical air-holes located in the core area that exhibit high birefringence, low losses, enhanced effective mode area, and low chromatic dispersion across a wide wavelength range have been presented. The effects of bending on birefringence, confinement losses and chromatic dispersion of the fundamental mode of the proposed PCFs have been thoroughly investigated by employing the full vectorial finite element method (FEM). Additionally, localization of higher order modes is presented. Also, effects of angular orientation on bending loss have been reported. Significant improvement on key propagation characteristics of the proposed PCFs are demonstrated by carefully altering the desired air hole diameters and their geometries and the hole-to-hole spacing.     

Optical fiber-based dispersion compensation using higher ordermodes near cutoff

Higher order spatial modes in optical fibers exhibit large, negative chromatic dispersion when operated near their cutoff wavelength. By using a spatial mode-converter to selectively excite a higher order mode in specially designed multimode fiber, this dispersion can be used to compensate the positive dispersion in conventional single-mode fiber spans. In this paper, issues related to compensating fiber and mode-converter design are explored. Experimental measurements in specially designed two-mode fibers operated in LP₁₁ mode show negative dispersion as large as -70 ps/nm·km at 1555 nm. Pulse propagation and system experiments employing spatial mode-converters to excite LP₁₁ mode in a two-mode fiber demonstrate the feasibility of this technique for dispersion compensation in lightwave systems     

自适应比特分配光正交频分复用的实验研究

为解决塑料光纤(POF)带宽窄、模式色散大的缺陷,提高光接入网的带宽利用率和色散容限,本文在光接入网中使用自适应比特分配算法的正交频分复用(OFDM)调制方式,利用OFDM系统极佳的频带利用率特性,提高了光接入系统的带宽利用率,并降低了系统的误码率(BER)。在搭建的实验系统中,成功地在不足2.5GHz带宽的光信道中完成了10 Gb/s的光OFDM(OOFDM)系统,从而证明了自适应比特分配算法在OOFDM系统中的有效性和可行性。     

各向异性左手材料平面波导TE模的传输特性

对芯层为左手材料而覆盖层和衬底均为不同普通材料的三层平面波导进行了探讨。考虑损耗、色散和各向异性的左手材料,利用TE模的色散方程,结合模阶数、波导厚度以及电磁衰减系数的变化,画出了相关的色散曲线和损耗曲线。根据这些曲线,发现对于TE2模,在频率为4.03GHz附近,波导厚度为5mm,它有非常大的有效折射率(接近80);当频率从4.0GHz增加到6.0GHz,色散曲线的斜率为正、零和负。正斜率为正常色散,负斜率为反常色散,零斜率则群速为零。对于高阶TE模,当频率为4.03GHz时,它的损耗是最大的;当频率超过5.0GHz后,波导厚度以及电磁衰减常数的变化对TE模的损耗特性影响不大,这些新特性为制备小型化的波导器件提供了理论基础。     

初始啁啾对WDM系统中偏振模色散的影响

依据耦合非线性薛定谔方程,利用分步傅利叶方法求耦合方程的数值解,仿真分析了初始啁啾对波分复用系统中偏振模色散的影响。仿真结果表明：输人功率较小时,正啁啾与二阶色散共同作用对偏振模色散进行抑制;输入功率较大时,正啁啾与二阶色散、非线性效应共同作用部分补偿了偏振模色散所造成的脉冲展宽;啁啾不宜过大,存在最佳值。