具有高阶耦合色散系数三芯光纤耦合器非线性光开关特性的研究

利用两种方法研究了高速光脉冲在具有交叉相位调制的等边三角形排列结构的非线性三芯光纤耦合器中传输和开关特性.首先利用变分原理得到三纤芯中传输转移系数随距离变化的方程,然后利用分裂步长傅里叶方法求得了光脉冲的数值解.变分法和数值模拟的结果表明：当一阶模间色散系数较小时,光脉冲仍能在三芯之间周期性耦合传输,并且表现出良好的开关特性,但是随着一阶模间色散系数的增大,脉冲耦合传输的周期性和陡峭的开关特性都遭到破坏,光脉冲在传输中发生分裂;二阶耦合色散系数和初始啁啾都能使光脉冲传输时的耦合长度变短、光脉冲在三纤芯之间 关键词： 三芯光纤耦合器 模间色散系数 耦合长度 开关阈值功率     

Numerical simulation of solitons switching and propagating in asymmetric directional couplers

A numerical investigation, based on the use of split step Fourier transformation algorithm, of all-optical solitons switching in asymmetric directional couplers is presented. The numerical algorithm is described in details. The analysis highlights the influence of the different effective mode area, the phase- and group–velocity mismatch, the different dispersion between two cores on the switching and propagation of short pulses. The investigation indicates that the phase velocity mismatch and the different effective mode area can reduce the coupling length while the different group velocity and the different dispersion between two cores do not change the coupling length. We have also found that the increase of effective mode area ratio can lead to an increase of the switching threshold power but improve significantly the switching steepness, the increase of the phase velocity mismatch can cause a decrease of the switching threshold power but degrade the switching steepness, the increase of the ratio of dispersion can result in a decrease of the switching threshold power and vary the switching steepness, the increase of group velocity mismatch can give rise to an increase of the switching threshold power but improve obviously the switching steepness. Furthermore, the group velocity mismatch can induce solitons pulse to walk off or stretch in the asymmetric directional coupler.     

Optical Fiber Impulse Propagation: An Interaction Between the Third-Order Dispersion and Nonlinear Chirp

This article investigates the interaction between the third-order dispersion in optical fiber and the nonlinear (quadratic) chirp of Gaussian impulses. A formula is obtained for the impulse form at the fiber far end. The impulse propagation in nonlinear fiber is also examined by means of a computer simulation. The obtained results indicate that the interaction may lead to significant distortion of optical impulses at the fiber output even when the second-order dispersion is entirely canceled and the input impulse has no linear chirp. This distortion is more pronounced when the dispersion slope, fiber length, and nonlinear chirp parameter increase.     

Optical solitons switching in asymmetric dual-core nonlinear fiber couplers

With study on the switching characteristics in a asymmetric dual-core nonlinear fiber coupler, it is found the switch efficiencies when the dispersion values of two fibers have opposite signs are much higher than those when they have same signs. Meanwhile, when the dispersion values of two fibers have same signs, the switch efficiencies become much higher if the dispersion value of one core is decreased. In addition, the switch threshold power becomes lower than the one with the same sign if the nonlinearity coefficient of two fibers is opposite. The result shows that asymmetric coupler has much higher switch efficiencies and lower switch threshold power than symmetric coupler.     

基于SFRL的FWM型可调谐波长转换器啁啾特性分析

基于半导体光纤环形腔激光器的四波混频型可调谐全光波长转换器的宽带理论模型,从理论上研究了输入信号光功率、注入电流、两个耦合器的耦合比、激射光波长和半导体光放大器有源区长度对转换光频率啁啾的影响.结果表明:转换光的频率啁啾随着输入信号光峰值功率、注入电流以及SOA有源区长度的增大而增大,随两个耦合器耦合比的增大而减小.     

Chirped Bragg光纤光栅的优化设计与优化指数

根据线性ChirpedBragg光纤光栅的一般原理 ,探讨了不同啁啾系数 ,准高斯耦合函数对Bragg反射光栅的反射率及色散补偿特性的响应。结果表明 :增大啁啾系数以及选取适当的准高斯耦合函数 ,在保证反射率较大的情况下 ,能有效地改善色散补偿特性。通过引入微波领域的“优化指数”这一概念 ,量化了色散补偿器的补偿能力。     

色散平坦渐减光纤中非线性啁啾脉冲的传输及超连续谱的产生

基于非线性薛定谔方程,数值研究了色散平坦渐减光纤中非线性啁啾脉冲的传输及超连续谱的产生。研究结果表明,初始啁啾对脉冲传输及超连续谱产生的影响与泵浦条件和光纤参量的选取有很大关系。当色散平坦渐减光纤具有小的归一化二次色散系数时,适当的正啁啾能显著增强超连续谱的带宽,而负啁啾和太大的正啁啾抑制超连续谱的带宽。能增强超连续谱带宽的正啁啾有一个较宽的范围,但随着输入脉冲孤子阶数的降低,该范围将变窄。当色散平坦渐减光纤具有大的归一化二次色散系数同时输入脉冲为低阶孤子时,初始啁啾对超连续谱带宽的增强效果不明显,初始啁啾接近为0时可产生最宽的超连续谱。     

初始啁啾补偿光纤色散效应的适用范围

以啁啾高斯脉冲在单模光纤中的传输为例,分别就线性初始啁啾对光纤二阶和三阶色散的补偿进行了系统的理论分析和数值计算,结果表明：线性初始啁啾对光纤的二阶色散（线性色散）有一定的补偿作用,但不能有效地用于三阶色散的补偿.     

水的衰减系数及有效增益长度对受激布里渊散射输出能量的影响

本文从理论和实验上分析了水的衰减系数及有效增益长度对受激布里渊散射(SBS)输出能量的影响。实验结果表明,衰减系数越小,SBS输出能量越高。由于脉宽压缩效应,当入射光能量足够高并且有效增益长度相对较长时,SBS易获得高能量而形成极高的峰值功率。一旦这种峰值功率超过受激拉曼散射(SRS)或者二阶SBS阈值,SBS就会作为一个新的激发源去激发SRS或者二阶SBS,从而消耗掉部分SBS的能量,所以会出现后向有效增益长度越长,SBS的输出能量越低的现象。 关键词： 受激布里渊散射 衰减系数 有效增益长度 脉宽压缩     

级联单模光纤中初始啁啾对高阶孤子脉冲压缩的影响

采用两段级联单模光纤对高阶孤子脉冲进行压缩。两段光纤具有不同的反常色散值,当高阶孤子脉冲在第一段光纤中获得最大程度压缩时,通过转换色散值不同的光纤,使压缩脉冲继续以高阶孤子的形式在第二段光纤中再次被压缩。每段光纤的长度都进行了优化,使得脉冲在每段光纤中都获得最大程度的压缩。基于非线性薛定谔方程,数值研究了初始啁啾对高阶孤子脉冲压缩的影响。研究结果表明,初始啁啾对高阶孤子脉冲的压缩有重要影响。与无初始啁啾时的情形相比,正的初始啁啾能增强每段光纤中脉冲的压缩效果,降低压缩脉冲的基座能量,而负初始啁啾的影响则相反。随着初始啁啾参量Cp的增大,脉冲在每段光纤中的压缩因子均增加,而基座能量、最优光纤长度均减小。     

Investigation on the bistability of linearly chirped nonlinear Bragg gratings

Based on the nonlinear coupled mode theory, by using the reversely recursive transmission matrix method, the switching characteristics of linearly chirped nonlinear Bragg gratings (LC-NLBG) have been investigated numerically. The results show that, introducing spatial chirp in fiber gratings is helpful to widen the bistable wavelength range, and the influence of the chirp on the switching-on threshold and the on-off ratio of the bistable switching are obvious, the chirp-dependent bistability is due to the difference of the axial distribution of forward wave intensity in the gratings.     

Wave-coupling theory of linear electro-optic effect for ultrashort laser pulses

A wave-coupling theory of linear electro-optic (EO) effect for ultrashort laser pulses has been developed. As one of its applications, the linear EO effect of ultrashort Gaussian pulses propagating in LiNbO₃ crystal is demonstrated, with the intensity lower than the damage threshold. It is found that the EO effect is sensitive to both the azimuth angle and the polar angle of wave vector of light. And the larger the applied electric field, the shorter the crystal used for optimization of EO coupling is. The numerical results show that, with the duration of input pulse changing from 150 fs to 5 fs, the durations of output pulses are broadened due to the group-velocity dispersion, as well as the first- and second-order refractive dispersion. In addition, when input pulse duration is larger than 20 fs, in contrast with zero chirp, the output durations can be slightly compressed if a positive chirp input pulse is used. The validities of slowly varying amplitude approximation and continuous wave approximation are also discussed. The influence of self-phase modulation and cross-phase modulation on the EO effect is also discussed briefly.     

LD泵浦掺铥(Tm3+)光纤激光器的数值分析

首先从掺铥光纤激光器的速率方程和光传输方程出发,建立数学模型,通过Matlab软件进行数值计算,分析了泵浦光和激光沿光纤的分布以及各能级离子数的变化.在不同掺杂浓度下,研究了小信号增益与入纤泵浦功率的关系以及泵浦光和激光功率与增益介质长度的关系.在不同泵浦功率下,研究了输出功率与输出耦合镜反射率的关系.进一步对不同泵浦吸收系数,研究了斜率效率和泵浦阈值与光纤长度的关系.分析结果表明存在最佳光纤长度和最佳耦合输出透过率,使得激光输出功率达到最佳值.     

Impacts of polarization mode dispersion on the pulse-width with considering initial pulse chirp and fiber GVD

The impacts of polarization mode dispersion (PMD) on the pulse-width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp and group velocity dispersion (GVD), are derived. Analyses show that the pulse broadening effects induced by the second-order PMD depend on GVD and chirp parameter, which are different from those induced by the first-order PMD. An initially chirped Gaussian pulse is taken as an example, upon which analytical solutions of rms pulse-width are derived before and after the first-order PMD compensation. The first-order PMD compensator is also evaluated based on these solutions. The results show that the pulse broadening effects will be resisted efficiently by choosing appropriate GVD and chirp parameter; in general, the post-transmission compensation method will be less efficient than the PSP-transmission method.     

双带通啁啾光纤光栅光谱特性仿真及分析

针对啁啾光纤光栅的带通滤波特性,设计了纤芯/包层复合结构的啁啾光纤光栅滤波器.基于光纤耦合模和传输矩阵理论及坐标变换方法,对其光谱特性进行仿真分析,验证了该光栅的双带通滤波特性;对周期为536、537、538nm,长度为8、10、12mm,折射率调试深度为0.0002、0.0003、0.0004,啁啾系数为0.05、0...     

有限元分析法在SOI基微环谐振器设计中的应用

利用有限元法(FEM)分析了大横截面SOI(Silicon-on-insulator)脊型波导的本征模式分布,确定了脊型波导的单模条件。在保证单模传输的情况下,模拟了SOI微环谐振器中波导耦合器的耦合长度、功率耦合系数与波导尺寸和间距的关系。模拟结果表明:对于W=1μm,H=2μm的SOI脊型波导耦合器,耦合长度LC随波导间距d的增加而增大,功率耦合系数随之减小。在波导间距d0.8μm的情况下,耦合长度LC随着归一化脊高r的增加而增大,当d0.8μm时,耦合长度LC随r的增加而减小。模拟结果为SOI微环谐振器的设计和应用提供了理论依据。     

压缩平稳重调脉冲的色散渐减光纤的设计

文章根据平稳重调脉冲(SRP)在梳状光纤(CPF)结构中的压缩原理,对色散渐减光纤(DDF)的色散特性进行设计,结果发现该色散渐减光纤的色散特性呈线性递减.对于平稳重调脉冲其压缩比与功率比等于光纤始末两端二阶色散系数的比值.当色散渐减光纤的斜率足够小时,无啁啾基阶孤子可以近似为平稳重调脉冲,当色散渐减光纤的色散斜率较大时,无啁啾基阶孤子不能近似为平稳重调脉冲.当基阶孤子带有与光纤色散斜率成正比的线性啁啾时,脉冲的压缩比与功率比更接近于光纤始末两端二阶色散系数的比值.说明带有线性啁啾的基阶孤子比不带啁啾的基阶孤子更接近于平稳重调脉冲. 关键词： 平稳重调脉冲(SRP) 梳状光纤(CPF) 色散渐减光纤(DDF) 色散递减表达式     

影响光孤子传输的因素分析和可能的解决方案

从光孤子传输所满足的非线性薛定谔方程出发,通过对方程中参数的分析和选择,对影响孤子传输的各种因素采用单独分析和综合分析对比方法得到了两个新的结论:(1)二阶色散参数在不太大的范围内变化只会影响脉冲的幅值,对脉冲形状影响不大,而输入脉冲的啁啾则是使脉冲发生畸变的主要原因;(2)在啁啾、三阶色散和五阶非线性同时存在的情况下,它们对脉冲都会产生很大的影响,且存在相互影响和制约关系,三者在某一参数值附近,对脉冲却存在着增益效应和"整容"作用。针对分析结果从理论上提出了改进光孤子传输特性的解决方案,这对光孤子通信的实践过程是有一定实际意义的。     

Femtosecond pulse switching in a fiber coupler with third order dispersion and self-steepening effects

A numerical study of femtosecond pulse propagation and switching in a dual-core nonlinear directional coupler with the consideration of third order dispersion and self-steepening effects is reported. The Split Step Fourier Method (SSFM) is used to investigate the switching characteristics of nonlinear directional couplers. It is observed that the energy transfer from core to core is not affected by changing the input pulse shapes except super-Gaussian. While the normalized coupling co-efficient and the input peak power dominate the coupling characteristics, the effects of third order dispersion (TOD) and self-steepening (SS) are also reported.     

色散和非线性效应对高斯脉冲综合影响的理论分析

从光孤子传输所满足的非线性薛定谔方程出发,采用单独分析和综合分析对比,分析了影响高斯脉冲传输的色散、非线性等因素,结果表明：二阶色散参量只会影响脉冲的幅值,对脉冲形状影响不大,而输入脉冲的啁啾则是使脉冲发生形变的主要原因|在啁啾、三阶色散和五阶非线性的共同作用下,它们对脉冲都会产生较大的影响,且存在相互影响和制约作用,在某一临界值,对脉冲存在着较高的压缩增益效应和“整形”作用.从理论上提出了改善高斯光脉冲在光纤中传输特性的解决方案,这对光纤孤子通信的实践过程具有一定的理论借鉴意义.