在DCF光纤中放大的背向自发拉曼散射的增益特性

光脉冲沿色散补偿光纤（DCF）传输会产生背向自发拉曼散射,当入纤激光功率大于阈值时,出现放大的背向自发拉曼散射现象。实验发现,反斯托克斯（ASR）和斯托克斯（SR）自身脉冲光纤拉曼放大的阈值泵浦峰值脉冲功率是18．2W和14．5W．当入纤激光功率为52W时,背向SR和ASR散射的增益分别为12dB和7dB。放大的反斯托克斯和斯托克斯背向自发拉曼散射时域曲线上的阈值时间位置随激发功率的增大而前移并具有规律性。     

正常色散光纤消啁啾的孤子传输实验

利用正常色散光纤消啁啾成功地进行了１Ｇｂｉｔ／ｓ，２３公里的光弧子传输，观察到了一阶和高阶孤子传输现象，通过实验发现：采用适当长度的正常色散光纤消负啁啾，不仅能够压窄负啁啾的脉宽而且能够压窄频谱。     

基于线性啁啾光纤光栅色散补偿的2500km-10Gbps无电中继传输系统

全部利用线性啁啾光纤布拉格光栅(CBG)作色散补偿模块,在G.652光纤上实现2500km-10Gbps的超长距离无电中继传输系统。在2060km处,功率代价~2dBm(NRZ码,BER:10-12,PRBS:1023-1);在2530km处,较大功率代价下实现无误码传输,远超过相同条件下用色散补偿光纤(DCF)作色散补偿模块的传输系统的无误码传输距离。     

基于DDF构成的非线性环镜的光脉冲压缩研究

提出利用色散渐减光纤(DDF)构成的非线性光纤环镜(NOLM)来进行光脉冲压缩的方法并进行相关分析.数值结果表明:利用色散渐减光纤对脉冲的压缩及非线性光纤环形镜的脉冲整形作用,可以获得压缩比高且压缩质量较好的脉冲.     

光脉冲展宽的解析公式在高速WDM系统设计中的应用

给出了光脉冲在光纤群速度色散和自相位调制效应的共同作用下，均方奶宽度沿传播距离变化的近似解析公式，并重点讨论其在高速波分复用光纤通信系统设计中的应用。解析公式不仅能用于估计信道功率、光纤色散等参数的容限范围，还可为系统色散补偿或色散管理的优化设计提供指导。     

10Gbit/s色散补偿系统中自相位调制效应的研究

首先讨论了单模光纤中自相位调制对系统色散的影响。数值计算和实验结果表明。增加入纤功率能在一定程度上抑制色散效应 ,当入纤功率为 1 5dBm时 ,对于 4 0 .0km的单模光纤 ,自相位调制效应和色散恰好抵消 ,功率代价接近为零。然后比较了前、后置色散补偿系统的性能。理论分析和实验表明 ,在入纤光功率较大的情况下 ,采取前置、完全色散补偿系统具有较低的误码率。前置补偿最佳入纤功率比后置补偿最佳入纤功率高约 1 0 .0dB。这表明 ,采取前置、完全色散补偿 ,系统具有较长的中继距离和较高的接收端光信噪比 ,对 (1 6 0× 1 0Gbit/s)DWDM系统 30 0 0km超长距离传输中光放大和色散补偿问题的整体优化具有重要现实意义。     

WDM系统中利用色散补偿降低脉冲定时抖动的研究

本文对色散管理孤子系统中存在的影响脉冲传输的ASE(放大器自发辐射)致定时抖动进行了研究。利用微扰理论,通过半解析算法推导出ASE致定时抖动的算术表达式,从中得出ASE致定时抖动主要受放大器间距和色散图的影响。在此基础上对通常采用的二级色散图进行拓展,提出三级色散图方案并对色散管理系统进行计算机数值模拟,结果表明,通过选取适当的色散图参数,三级色散图方案比之二级色散图将能更好地减小因ASE噪声致定时扰动的影响。     

利用后置补偿法对10-Gbit/s长距离波分复用光纤传输系统进行色散均衡

通过系统仿真,对以常规单模光纤和色散补偿光纤(SMF+DCF)组成的16×10-Gb/s WDM色散补偿系统进行了分析,调制器啁啾为0,激光器静态线宽为5MHz.结果表明:(1)对于数百公里的传输距离,以DCF进行在线补偿就可以使各个信息达到较好的色散补偿效果(16×10-Gb/s,400km,眼图代价差别小于0.5dB);(2)由于SPM在SMF光纤中对脉冲的压缩效应,每一信道应保持略微偏正的残留色散量;(3)对于上千公里的传输距离,仅以DCF进行在线补偿无法同时均衡所有信道的色散(16×10-Gb/s, 1200km,眼图代价差别大于0.85dB).为此,本文以SMF或DCF在系统接收端再次对各信道逐个进行色散补偿(后置色散补偿),达到了良好的效果(16×10-Gb/s, 1200km, 眼图代价差别小于0.3dB).     

光孤子通信系统的色散控制研究

光纤色散特性是支撑光纤孤子通信的决定性因素。比较了目前的几种色散补偿方案后,着重对相位共轭控制的色散控制方式进行了分析研究,该方式利用光纤非线性四波混频产生与输入光脉冲信号相位共轭的输出光脉冲信号,光脉冲的频谱以泵浦光频为中心进行反转,构建成相位共轭器,实现了对放大自发辐射(ASE)噪声、孤子相互作用与色散波等的控制,达到提高系统传输速率、距离和通信容量的目的。     

2.5GHZ光孤子传输

报导了我国首次成功地实现了２．５ＧＨｚ光孤子传输。近变换极限的孤子脉冲源是带有Ｆ－Ｐ标准具的增益开关分布反馈激光二极管。孤子脉冲的功率通过分别由１４８０ｎｍ和９８０ｎｍ泵浦的两个掺饵光纤放大器放大，当入纤功率达到一阶孤子功率时，经过２１ｋｍ色散位移光纤传输后，孤子的输出脉宽保持不变。同时还观察到孤子脉冲压缩现象。     

Analytic study on soliton-effect pulse compression in dispersion-shifted fibers with symbolic computation

The soliton-effect pulse compression of ultrashort solitons in a dispersion-shifted fiber (DSF) is investigated based on solving the higher-order nonlinear Schrödinger equation with the effects of third-order dispersion (TOD), self-steepening (SS) and stimulated Raman scattering (SRS). By using Hirota's bilinear method with a set of parametric conditions, the analytic one-, two- and three-soliton solutions of this model are obtained. According to those solutions, the higher-order soliton is shown to be compressed in the DSF for the pulse with width in the range of a few picoseconds or less. An appealing feature of the soliton-effect pulse compression is that, in contrast to the second-order soliton compression due to the combined effects of negative TOD and SRS, the third-order soliton can significantly enhance the soliton compression in the DSF with small values of the group-velocity dispersion (GVD) at the operating wavelength.     

Phase jitter control of ultrashort soliton in high-speed communication systems with nonlinear gain

An expression is derived for soliton phase jitter in soliton transmission with higher-order effects in the presence of nonlinear gain and filters. It is demonstrated that soliton phase jitter can be suppressed efficiently by nonlinear gain in addition to filters not only for long duration solitons but also for ultrashort solitons provided that the nonlinear gain coefficients satisfy specific conditions. This scheme offers an alternative means for the development of ultralong distance soliton transmission systems using differential phase-shift keying (DPSK), and exploits a robust technique to achieve a higher-speed soliton communication system using DPSK.     

Review of low timing jitter mode-locked fiber lasers and applications in dual-comb absolute distance measurement

Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.     

基于光纤延迟线的时间抖动测量系统

对飞秒激光器时间抖动的准确测量是推动其高精度应用的重要前提。为实现时间抖动的高精度、无参考测量,设计并搭建了一套基于光纤延迟线的测量系统。基于非对称迈克尔逊干涉仪的结构,在其中一臂引入一段长光纤延迟线鉴别时间误差,提高时间抖动测量精度。测量了一台实验室自制的重复频率为82 MHz的锁模光纤激光器的时间抖动功率谱,其在100 Hz~10 kHz的积分范围内RMS时间抖动为10.1 fs。     

Soliton collisions for a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system for an erbium-doped optical fiber

In this paper, we construct soliton solutions for a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system, which can describe the ultrashort optical pulse propagation in a nonlinear, dispersive fiber doped with two-level resonant atoms. Under certain transformations and constraints, one- and two-soliton solutions are obtained via the Hirota method and symbolic computation, and soliton collisions are graphically presented and analyzed. One soliton is shown to maintain its amplitude and shape during the propagation. Soliton collision is elastic, while bright two-peak solitons and dark two-peak solitons are also observed. We discuss the influence of the coefficients for the group velocity, group-velocity dispersion (GVD), self-phase modulation, distribution of the dopant, and Stark shift on the soliton propagation and collision features, with those coefficients are set as some constants and functions, respectively. We find the group velocity and self-phase modulation can change the solitons’ amplitudes and widths, and the solitons become curved when the GVD and distribution of the dopant are chosen as some functions. When the Stark shift is chosen as a certain constant, the two peaks of bright two-peak solitons and dark two-peak solitons are not parallel. In addition, we observe the periodic collision of the two solitons.     

A direct perturbation method investigation of the interplay between self-frequency shift and cross-phase modulation for solitons

The self-frequency shift of solitons, mainly observed in femtosecond pulses and arising from the Raman effect, can be counteracted by the cross-phase modulation (XPM) arising from collisions between pulses of different frequency. The same could be said for the time displacement that follows the frequency shift. The current work is an analytical approach to the interplay between the Raman self-frequency shift and XPM with third-order dispersion (TOD) effects taken into account. By using coupled NLS equations, the effect of XPM between two channels is considered for the cases of complete and incomplete collision. The analysis is based on the direct perturbation method and provides quantitative and qualitative insight of the spectral and temporal evolution of ultra short soliton pulses.     

Analysis of a three-coil contactless power transfer system for high-power applications

Recently, contactless power transfer (CPT) has become very popular in various fields of applications such as electronic appliances, medical implant devices, electrical vehicles, etc. When air gap distance between the transmitting and receiving coils of a CPT system increases, coupling coefficient between the coils decreases. In a large-air-gap CPT system, by incorporating an additional coil between the transmitting and receiving coils, coupling coefficient can be enhanced. Consequently, efficiency of a large-air-gap CPT system is improved. In this study, a three-coil system has been compared with a two-coil system using basic circuit models. Thereafter, the basic circuit models of two-coil and three-coil systems have been studied to confirm energy efficiency differences between the two systems for high-power applications. Using simplified circuit models, conditions for higher energy efficiency of a three-coil system than a two-coil system have been derived and it has been established that power transfer efficiency of a three-coil system has improved significantly in comparison with a traditional two-coil system. To confirm the theory, a two-coil and a three-coil systems with an air gap distance of 18 cm and a lateral misalignment of 3.5 cm have been verified using Ansys simulation tool for an output power of 2 kW.     

高速飞行器气动光学传输效应的工程计算方法

气动光学传输效应对飞行器光学成像探测系统的性能有着十分重要的影响，它使探测器接受的图像产生偏移、抖动和模糊。文章分析了目标光线通过流场时的光学传输特性，建立了流场光学传输特性的工程计算模型，描述了气动光学传输效应对成像探测系统影响的经验模型。在此基础上，对气动光学传输效应产生的像偏移、抖动和模糊进行了数值仿真，仿真结果表明，气动光学传输效应对成像探测系统的影响与飞行器的飞行参数、成像探测系统参数和探测器积分时间等密切相关。     

On measurement noise in the European TWSTFT network

Two-way satellite time and frequency transfer (TWSTFT) using geostationary telecommunication satellites is widely used in the timing community today and has also been chosen as the primary means to effect synchronization of elements of the ground segment of the European satellite navigation system Galileo. We investigated the link performance in a multistation network based on operational parameters such as the number of simultaneously transmitting stations, transmit and receive power, and chip rates of the pseudorandom noise modulation of the transmitted signals. Our work revealed that TWSTFT through a "quiet" transponder channel (2 stations transmitting only) leads to a measurement noise, expressed by the 1 pps jitter, reduced by a factor of 1.4 compared with a busy transponder carrying signals of 12 stations. The frequency transfer capability expressed by the Allan deviation is reduced at short averaging times by the same amount. At averaging times of >1 d, no such reduction could be observed, which points to the fact that other noise sources dominate at such averaging times. We also found that higher transmit power increases the carrier-to-noise density ratio at the receive station and thus entails lower jitter but causes interference with other station's signals. In addition, the use of lower chip rates, which could be accommodated by a reduced assigned bandwidth on the satellite transponder, is not recommended. The 1 pps jitter would go up by a factor of 2.5 when going from 2.5 MCh/s to 1 MCh/s. The 2 Galileo precise timing facilities (PTFs) can be included in the currently operated network of 12 stations in Europe and all requirements on the TWSTFT performance can be met, provided that suitable ground equipment will be installed in the Galileo ground segment.