五阶非线性光纤中连续谱相位扰动下的光传输与脉冲串产生

根据包含五阶非线性的扩展非线性薛定谔方程,数值研究了高斯型连续谱相位扰动而不是传统单色扰动下基于调制不稳定性的高重复率脉冲串产生.结果表明:脉冲串也能像传统情形那样形成,但却呈现出不同的特性.如脉冲数目有限,且各脉冲的高度、强度及间距不等.脉冲数目随传输距离增加而增加.而五阶非线性能使脉冲宽度和间距变小因而有利于高重复率脉冲串产生,负五阶非线性则相反.对脉冲串形成过程中演变啁啾的数值计算表明,啁啾及其随距离的变化都是高度非单调的,五阶非线性将改变啁啾的范围和量值.     

负五阶非线性下预啁啾高斯光脉冲的啁啾和频谱

为探究光纤负五阶非线性和光脉冲预啁啾对高斯光脉冲频率啁啾和频谱的综合影响,在忽略光纤色散的情况下,利用包含三五阶非线性的扩展非线性薛定谔方程,计算和分析了啁啾高斯脉冲的频谱和总啁啾。结果表明,脉冲无预啁啾时,负五阶非线性的存在可使脉冲频率啁啾的形状由单“S”形变为双“S”形,并使脉冲的中心附近由正啁啾变为负啁啾。此外,负五阶非线性的存在使预啁啾对脉冲频谱的影响发生了较大的变化。预啁啾与非线性所致啁啾叠加后对脉冲频谱的谱峰数目影响较小,而对能量在各个谱峰上的分布影响较大,在某些最大非线性相移下,甚至会出现总啁啾减小使谱峰值数目增加的情况。该研究对光开关、光脉冲压缩以及光纤通信系统等领域的深入发展具有一定的指导意义。     

三五阶非线性下啁啾超高斯脉冲的啁啾和频谱

利用三五阶非线性效应下的扩展非线性薛定谔方程,在忽略光纤色散的情况下,计算模拟了以二阶情形为例的啁啾超高斯光脉冲的啁啾和频谱。结果表明,脉冲无预啁啾时,正五阶非线性增大啁啾量,负五阶非线性在减小啁啾量的同时还改变啁啾曲线的形状。当预啁啾与五阶非线性系数同(异)号时,总啁啾增加(减小)。随着超高斯脉冲阶次的增大,总啁啾量增大,脉冲中心附近无啁啾的范围变宽,整个有啁啾的范围变小,总啁啾中预啁啾所占比重增大。脉冲无预啁啾时,正负五阶非线性分别可以增大和减小频谱展宽。预啁啾若增强非线性所致啁啾,则可能使频谱峰值结构加强,谱峰数目增多。当超高斯光脉冲的阶次或最大非线性相移增大时,在某些宽大的频谱峰上还可能出现许多精细谱峰。     

五阶非线性对啁啾超短脉冲间相互作用的影响

基于包含五次复系数的高阶Ginzburg Landau方程为模型,采用分步傅里叶方法数值研究了啁啾类超短脉冲间的相互作用。结果表明:相邻孤子之间的相互作用对五阶非线性效应非常敏感,即使参数改变很小的值,也会改变其传输特性。适当地选择五阶非线性参数值,能够很好地抑制孤子间的相互作用,提高光纤传输的比特率。当相邻孤子的初始间距为6.8,五阶非线性参数值取-0.001时,可以实现2个孤子长距离的保型传输。最后讨论了五阶非线性作用下多孤子之间的相互作用及抑制。     

四阶色散和五阶非线性对零色散附近交叉相位调制不稳定性的综合影响

从包含高阶色散和高阶非线性的广义非线性薛定谔方程出发,研究了零色散附近交叉相位调制不稳定性增益谱,分析了四阶色散和五阶非线性系数对增益谱的影响.结果表明：当光脉冲工作在零色散附近时,四阶色散对交叉相位调制不稳定性起决定作用,它使增益谱变宽.正（负）五阶非线性使增益谱的谱宽和峰值增大（减小）.随着二阶色散的增加,四阶色散对增益谱的影响越来越小.     

五阶克尔非线性光纤放大器中光脉冲的传输特性

以变系数高阶非线性薛定谔方程为理论模型,对光脉冲在具有五阶非线性克尔效应光纤放大器中的传输特性进行了研究.在加入振幅微扰、相位扰动、噪声微扰的情况下,数值模拟了亮孤波、灰孤波和黑孤波在光纤系统中的传输稳定性,并且讨论了孤子间的相互作用.数值模拟结果表明:在有限的微扰下,三种光脉冲具有良好的传输稳定性.     

用变分法研究高阶色散和五阶非线性对高斯脉冲在光纤中传输特性的影响

从修正的非线性薛定谔方程出发,采用变分法,导出了在高阶色散和五阶非线性共同作用情况下高斯型脉冲参量随传输距离的演化方程组;求出了振幅与脉宽、频率与啁啾、脉宽与啁啾之间的三个重要约束关系;并进一步得出了脉宽随传输距离演化的解析解和脉冲中心位置随传输距离的演化规律;描绘了高阶色散和五阶非线性下,脉宽随传输距离演化的图形.结果表明:光纤中的高阶色散和五阶非线性都会影响高斯型脉冲各个参量的演化,但脉宽和振幅间的绝热关系并未改变.高阶色散使高斯型脉冲的脉宽展宽,五阶非线性使高斯型脉冲的脉宽压缩,它们对脉宽或初始啁啾的影响可以在一定程度上抵消,从而有可能使脉冲近似实现保形传输.     

飞秒激光Z扫描技术研究CS_2的非线性特性

利用波长为800 nm的飞秒激光脉冲,通过Z扫描技术研究了CS2在不同光强下的非线性折射和非线性吸收特性发现,随着光强的增加,闭孔Z扫描透过率曲线发生了较大的轴向移位。分析结果表明:在低光强下,这种轴向移位源于双光子吸收的影响;而在高光强下,是双光子吸收和五阶非线性共同作用的结果。给出了决定五阶非线性存在与否的临界光强,以及非线性参量与轴向位移的关系。     

五阶非线性下零色散附近的调制不稳定性

在同时考虑光纤损耗、高阶色散以及高阶非线性情况下,从广义非线性薛定谔方程出发,研究了零色散附近的调制不稳定性,分析了四阶色散和五阶非线性对增益谱的影响.结果表明：当光脉冲工作在零色散附近时,四阶色散对调制不稳定性起决定作用,它使反常色散区的增益谱变宽.在光纤正常色散区,正（负）五阶非线性使增益谱的谱宽和峰值增大（减小）;但在反常色散区,五阶非线性仅改变增益谱的峰值,几乎不影响谱宽.     

五阶非线性克尔效应影响下光脉冲的传输

以变系数五次金兹堡-朗道方程为理论模型,在考虑和忽略五阶非线性克尔效应情况下,分别得到了精确的孤子解和耗散孤子解。数值模拟结果表明,这两类孤子解脉冲在非均匀光纤中都能以光孤子的形式传输。另外,考虑五阶非线性克尔效应时,分析了有微扰时光孤子的传输稳定性和双超短光脉冲相互作用。     

振镜扫描光学多道谱仪

以平面光栅单色仪和光学扫描振镜为基础研制一套具有高时间分辨能力的光学多道分析系统,并利用计算机进行实时控制与数据采集。实验表明：本系统在保持谱分辨的同时,时间分辨率达到１０ｍｓ以内。     

Ultra-High-Capacity Passive Optical Network Systems with Free-Space Optical Communications

Abstract

This article experimentally demonstrates a hybrid fiber–free-space passive optical network that enables high spectral density, aggregated capacity, and total throughput through ultra-dense wavelength-division multiplexing baseband and radio-over-fiber channels. Ultra-dense wavelength-division multiplexing 10-Gb/s Nyquist-shaped 16-ary quadrature amplitude modulation, 10-Gb/s radio-over-fiber orthogonal frequency-division multiplexing, and 8.75-Gb/s baseband orthogonal frequency-division multiplexing signals per user were transmitted through a maximum 40-km passive optical network, which includes a 6-m free-space optics link with acceptable performance.     

基于半导体光放大器进行光标签提取的性能分析

利用半导体光放大器增益饱和数学模型，第一次分析了基于单个半导体放大器进行光标签提取的节点性能.通过对半导体光放大器的参量分析和优化，仿真显示，对于标签速率2.5 Gb/ s 、净荷速率40 Gb/s 的光分组包，提取的标签消光比可达到13 dB.     

Optical pumping with laser-induced-fluorescence

We describe a new procedure for optical pumping that is based on laser-induced fluorescence (LIF). The procedure is demonstrated by optically exciting a sample of Rb⁸⁵ atoms, which then creates a population imbalance between the ground state hyperfine levels of Rb⁸⁷ by “LIF depopulation pumping”. Though optical pumping with this technique increases the intensity dependent light-shift coefficient (i.e., ac Stark shift) of the Rb⁸⁷ 0-0 hyperfine transition, it reduces the frequency dependent light-shift coefficient by at least an order of magnitude. Since the stabilization of the diode laser wavelength is a significant challenge in the development of laser-pumped gas-cell atomic clocks, it is anticipated that optical pumping with LIF will be of benefit to atomic clock technology.     

Comparison of Optical Transport Schemes for LMDS with Optical Fiber Backbone

We investigate and compare the performance of four optical transport schemes for distributing Local Multipoint Distribution Service (LMDS) signals using an optical fiber backbone.     

Controllable Optical Solitons in Optical Fiber System with Distributed Coefficients

We present how to control the dynamics of optical solitons in optical fibers under nonlinearity and dispersion management, together with the fiber loss or gain. We obtain a family of exact solutions for the nonlinear Schrödinger equation, which describes the propagation of optical pulses in optical fibers, and investigate the dynamical features of solitons by analyzing the exact analytical solutions in different physical situations. The results show that under the appropriate condition, not only the group velocity dispersion and the nonlinearity, but also the loss/gain can be used to manipulate the light pulse.     

任意波形输入脉冲光纤背向瑞利散射的研究

背向瑞利散射是光纤中一种重要的物理过程,利用该物理现象实现的光时域反射计是一种重要且常见的光纤测量设备.本文理论研究了任意波形的输入脉冲在光纤中的背向瑞利散射过程,导出了将瑞利散射看作为一种线性系统的冲激响应函数,讨论了方波与有振荡拖尾的注入脉冲的背向散射输出波形.对于方波注入,利用商用光时域反射仪表对理论进行了验证;对于有拖尾的脉冲,进行了实验研究,结果表明仿真与实验结果一致.     

任意波形输入脉冲光纤背向瑞利散射的研究

背向瑞利散射是光纤中一种重要的物理过程,利用该物理现象实现的光时域反射计是一种重要且常见的光纤测量设备.本文理论研究了任意波形的输入脉冲在光纤中的背向瑞利散射过程,导出了将瑞利散射看作为一种线性系统的冲激响应函数,讨论了方波与有振荡拖尾的注入脉冲的背向散射输出波形.对于方波注入,利用商用光时域反射仪表对理论进行了验证;对于有拖尾的脉冲,进行了实验研究,结果表明仿真与实验结果一致.     

High-Speed Optical Packet Switch with an Optical Digital-to-Analog Conversion-Type Header Processor

We describe a novel type of an optical packet switch with an optical header processor based on optical signal processing and wavelength routing architecture. It consists of an optical digital-to-analog conversion-type header processor, wavelength selection portion with an electrically tunable laser, a wavelength converter based on a semiconductor optical amplifier (SOA), and wavelength routing by use of an arrayed waveguide grating (AWG), which is called a wavelength label switch (WLS). Wavelength switching of an electrically tunable laser, and wavelength conversion were successfully achieved within a few nanoseconds after recognition of an optical header using a two-bit optical header processor and a FPGA-based wavelength table. High-speed transfer performance of less than a few tens of nanoseconds and BER of less than 10^-10 were verified in the wavelength routing operation among three assigned wavelengths.