光纤通信系统中基于光学相位共轭和预啁啾的色散及非线性补偿研究

采用光学相位共轭补偿光纤通信系统的色散及非线性必须满足一个前提条件,即相位共轭器两边线路上的色散和非线性分布(或传输功率分布)必须严格对称,这在现有的一般传输线路（标准单模光纤加集总掺铒光纤放大器）难以实现。提出了预啁啾结合中距相位共轭的补偿方案,并进行了数值计算。结果表明,通过在发送端对输入脉冲进行预啁啾展宽,可有效地减轻非线性效应与色散的相互作用,获得理想的补偿效果;对于皮秒超短光脉冲传输,脉冲内拉曼散射相对于三阶色散对补偿结果的影响很小,因此,频域相位共轭相对于时域相位共轭具有更好的综合补偿性能。该方案简单易行,无需对已敷设好的线路作较大改动。     

光相位共轭色散补偿波分复用系统的传输带宽

导出了光相位共轭器（DPC）接于常规单模光纤链路中点的色散补偿波分复用（WDM）系统传输带宽的估算公式，并用数值仿真的结果验证了公式的正确性；采用不对称接入光相位共轭器提高传输带宽的方法，导出了光相位共轭器接入位置对传输带宽影响的估算公式，利用公式估算和数值仿真的结果表明，当光相位共轭器处于最佳接入位置时，色散补偿的波分复用系统的传输带可以提高近一倍。     

剩余三阶色散对相位共轭偏振孤子的影响及其补偿

光学相位共轭中剩余三阶色散不利于共轭孤子的稳定传输,导致孤子脉冲具有更大的时间抖动.本文提出在传输线末采用具有正三阶色散的色散位移光纤补偿光学相位共轭中的剩余正三阶色散.数值结果证明了其可行性.同时也分析其补偿的物理机制.     

基于频域相位共轭技术的交叉相位调制所致失真的复原

理论分析和讨论了基于频域相位共轭技术的交叉相位调制所致信号失真的复原和补偿机理，数值模拟了在交叉相位调制作用下，高斯脉冲在中距相位共轭光纤系统中的传输演化过程.结果表明，频域相位共轭技术能够抑制交叉相位调制对光纤系统中传输信号的损害，复原其所导致的信号失真，并能够同步补偿群速度色散和自相位调制非线性效应所导致的信号失真.合适的初始脉冲时延和初始脉冲啁啾有利于频域相位共轭技术对交叉相位调制所致信号失真的抑制. 关键词： 频域相位共轭 交叉相位调制 色散 自相位调制     

基于高阶色散管理和相位共轭技术的色散补偿

相位共轭技术能够同时且高效地补偿二阶色散及非线性效应，且该技术同信号比特率、调制方式无关，是最有前景的色散补偿技术之一。理论分析了在高阶色散作用下，超短高斯脉冲信号在中距相位共轭通信系统中的传输演化特性，数值模拟了在二阶、三阶和四阶色散作用下，飞秒高斯脉冲信号在基于中距相位共轭技术的光纤色散管理链中的动态传输过程。结果表明，相位共轭技术和高阶色散管理相结合，不仅可以补偿和复原包括奇数阶和偶数阶色散在内的全部色散和非线性所引入的信号失真和畸变，而且能够减弱时分复用系统中脉冲之间的相互作用，使得信号在传输一个周期后恢复波形，从而提高了相位共轭系统对失真信号的补偿性能。     

连续线性温度梯度场对啁啾脉冲放大系统中啁啾光纤光栅的色散调节效应

利用啁啾光纤光栅的温度可调谐效应,提出了一种新型的色散补偿方法.该方法使啁啾光纤光栅处于一个连续的线性温度梯度场中,通过调节啁啾光纤光栅两端的温度差,改变其色散量,实现在以啁啾光纤光栅为展宽器和以体光栅为压缩器的超快激光系统中对输出脉宽的连续精密调节,并通过实验验证这一方法的可行性.实验结果表明:沿着啁啾光纤光栅应用连续的温度梯度场,当温差从0℃到50℃变化时,可以连续地调节啁啾光纤光栅的色散参数.展宽器和压缩器之间的色散失配可以通过调节线性温度场的温度梯度得到补偿,避免了繁琐的脉宽优化步骤.本文是以啁啾体光栅为压缩器的光纤啁啾脉冲放大系统中通过调节施加在展宽器上的连续线性温度场的梯度,实现对啁啾脉冲系统中的色散失配进行精密调制的技术方案.     

基于光纤自相位调制多波长全光再生的色散管理优化

针对基于光纤自相位调制效应的多波长全光再生系统,分析了光纤平均色散对再生器品质因子改进量的影响,提出一种色散管理优化方法.由于波长间色散差异会导致再生系统性能的稳定性下降,通过选择色散补偿光纤和单模光纤的长度,使其合成的色散曲线与各波长分别达到最优再生性能时对应的色散曲线近似拟合,同时保证该色散曲线落在性能满意度高的色散区域,然后调整信号输入功率和滤波器的偏移量,可有效改善多波长再生性能的稳定性,实现再生器的色散管理优化.     

色散效应对光纤自相位调制全光再生器性能的影响

针对基于光纤自相位调制效应的全光再生技术,分析了色散效应对再生器转移函数和Q因子改进量的影响以及再生器中色散和自相位调制的相互作用,提出一种通过改变再生器光纤结构实现转移函数平坦区改善的方法。数值结果表明:全光再生器中色散会抑制自相位调制引起的频谱展宽,使Q因子改进量减小;对于色散,非线性系数和长度等参量不同的光纤介质,如果色散与长度的乘积与最大非线性相移的比值一定,再生器的性能基本不变;在两段高非线性光纤间增加适当长度色散补偿光纤,可以改善转移函数平坦区,使平坦区范围显著增加。     

基于多纵模拍频测量光纤色散

利用激光多纵模拍频频率与谐振腔色散系数的关系实现光纤的色散测量.测量系统采用可调光纤Fabry-Perot滤波器与光环行器构成窄带波长可调反射镜,作为光纤激光器的后腔镜,以光纤Sagnac干涉器作为前腔镜.将待测光纤置于谐振腔内,用频谱分析仪测量激光器拍频频率随激光输出波长的变化,得到待测光纤的色散系数.用该系统分别测量了色散补偿光纤和标准单模光纤的色散系数,实验结果表明该方法能够满足通信光纤的色散测量要求.该系统测量速度快、成本低、结构简单,具有良好的应用前景.     

低串扰的多波长光纤光栅色散补偿器

分析了光纤光栅色散补偿系统中的串扰，并比较了几种常用的多波长光纤光栅色散补偿器的串扰特性，结合串联的窄带光纤光栅和取样光纤光栅的优点，提出一种抑制光纤光栅色散补偿系统串扰的方法.它通过在邻近信道间引入随机时延差，既能改善取样光纤光栅的线性串扰特性，又能抑制交叉相位调制效应和四波混频等非线性串扰.使用该方法可以得到具有低串扰的多波长光纤光栅色散补偿器.     

Analytical description of cross-phase modulation in dispersive optical fibers

The effect of intensity distortion induced by cross-phase modulation in dispersive optical fibers is studied. It is shown that, in most configurations in which distortions that are due to cross-phase modulation can become significant to optical communications, the effect of cross-phase modulation can be described with excellent accuracy by simple analytical expressions. The presented analysis also suggests that intensity distortions owing to cross-phase modulation can be efficiently reduced by linear dispersion compensation.     

Continuous radio-frequency tuning of an optoelectronic oscillator with dispersive feedback

We describe and demonstrate a novel technique for continuously tuning the frequency of a dual-loop-configuration optoelectronic rf oscillator. The rf tunability is obtained from a tunable diode laser and dispersive optical fibers. Results are presented for three ranges of frequency, centered at 550 MHz, 3 GHz, and 9 GHz. The frequency can be tuned electrically with constant rf power within a range of 0.1-1.9 MHz, depending on the center oscillation frequency. The tuning range can be increased eightfold through the use of highly dispersive fibers.     

Influence of a holey cladding structure on spectral characteristics of side-polished endlessly single-mode photonic crystal fibers

We experimentally investigate the spectral characteristics of side-polished endlessly single-mode photonic crystal fibers of different polishing depths and radii of curvature that are important to mode field diameter, evanescent coupling, waveguide losses, higher-order mode excitation, and dispersion slopes of photonic crystal fiber components. A polished photonic crystal fiber with a greater polishing depth or a larger radius of curvature shows a more dispersive characteristic. In contrast to conventional single-mode fibers, in photonic crystal fibers the evanescent field is more strongly localized, and the propagating light can be more efficiently guided within the deformed core.     

Multi-soliton management by the integrable nonautonomous nonlinear integro-differential Schrödinger equation

We consider a wide class of integrable nonautonomous nonlinear integro-differential Schrödinger equation which contains the models for the soliton management in Bose–Einstein condensates, nonlinear optics, and inhomogeneous Heisenberg spin chain. With the help of the nonisospectral AKNS hierarchy, we obtain the N-fold Darboux transformation and the N-fold soliton-like solutions for the equation. The soliton management, especially the synchronized dispersive and nonlinear management in optical fibers is discussed. It is found that in the situation without external potential, the synchronized dispersive and nonlinear management can keep the integrability of the nonlinear Schrödinger equation; this suggests that in optical fibers, the synchronized dispersive and nonlinear management can control and maintain the propagation of a multi-soliton.     

Transmission of quasi-monochromatic light wave through dispersive medium and measurement of refractive index

Relations used in the measurements of the refractive index in a non-absorbing dispersive medium are discussed, taking into account the quasi-monochromaticity of the light wave. It is shown that when interference methods using compensation are employed, it is always necessary to allow for corrections for dispersion. Relations describing the diffraction of a ray at the boundary of vacuum and a non-absorbing dispersive medium can be obtained only from the continuity of the Poynting vector at the interface of these media. The stationary phase method may lead to erroneous conclusions. The group velocity vector, which for diffraction describes correctly not only the absolute magnitude but also the direction of this velocity in a dispersive non-absorbing medium, is of the form $$v_g = \frac{{k(\omega _0 )}}{{|k|}}|\upsilon _g |$$ whereω ₀ is the frequency belonging to the maximum amplitude of a given quasi-monochromatic wave.     

双零色散光子晶体光纤中超连续谱的产生及控制

 通过数值模拟飞秒脉冲在具有双零色散波长的光子晶体光纤中的传输过程,详细分析了超连续谱的产生和控制机制.结果表明：中心波长处于反常色散区的泵浦脉冲在高阶非线性和高阶色散等作用的调制下,将演化为基孤子和正常色散区的两个色散波|该色散波进而经与之相位匹配的基孤子相干加强而使频谱展宽形成超连续谱,同时两个色散波上出现了干涉引起的振荡现象.进一步对比三种结构的光子晶体光纤中超连续谱的特点,定量分析了两色散波对超连续谱的限制作用,阐述了结构参量对超连续谱的影响.基于上述结论,结合对色散波的中心波长与光子晶体光纤的色散曲线、结构参量之间关系的分析,提出了设计光子晶体光纤的结构来控制超连续谱的方法.作为例证,通过优化光子晶体光纤结构理论上实现了频谱分量覆盖可见光区的平坦超连续谱.     

改进型蜂巢晶格结构光子晶体光纤的色散与非线性特性

结合蜂巢晶格与不同空气孔直径晶格二者的优势,提出一种改进犁蜂巢晶格结构光子晶体光纤,采用矢量光束传输法对该光纤的色散与非线性特性进行了数值模拟,分析了色散、非线性系数与其晶格参量之间的关系.数值结果表明,该光纤在1.2～1.6 μm波段内可以实现大负色散、色散平坦、正色散等多种色散特性;此外,晶格结构中空气孔直径的减小...     

Passive nonlinear reshaping towards parabolic pulses in the steady-state regime in optical fibers

The passive nonlinear reshaping in normally dispersive optical fibers in the steady-state regime is studied numerically. It is found that normal dispersion and self-phase modulation are able to provide pulse reshaping towards a parabolic pulse profile at the distances exceeding the optical wave breaking length. However, as compared to the similariton formation in active fibers the resulted pulse shape in passive fibers is strongly depended on the initial pulse parameters and nonlinear and dispersive fiber properties as well. The influence of initial pulse shape, initial chirp, third-order dispersion and loss on the parabolic pulse formation is studied consistently, and estimation of practical conditions which are needed for parabolic pulses formation in a passive fiber is provided.     

一维对称光子晶体的简正耦合模

对一维对称光子晶体中的色散介质采用洛仑兹振子模型,通过考虑色散介质层两侧的边界条件,得到了表征色散介质层的转移矩阵.对线性层及色散δ层均采用传输矩阵的方法,研究了一维含色散介质的光子晶体微腔中的简正耦合模.由于光与色散介质的相互作用,纵腔模将分裂成简正耦合模.通过改变色散介质的相关参数,详细研究了简正耦合模频率的移动、均匀展宽效应和失谐效应.发现两个简正的耦合模的频率间距主要依赖于振子的耦合强度,与约化的振子的HWHM线宽无关.失谐效应则会使其中的一个峰降低,而另一个峰相对拉高,这一现象可以通过Fabry-Pérot腔得到很好的解释.     

Interaction of an optical soliton with a dispersive wave

Scattering of a dispersive wave by optical solitons is studied experimentally in photonic crystal fibers in cases when the soliton and the dispersive wave have either identical or orthogonal polarization states. Observations of new resonant frequencies are reported. The experimental results are compared to numerical simulations and predictions from the recently derived wave vector matching conditions.