色散补偿型分布式光纤喇曼放大器的实验研究

在后向抽运和前向抽运方式下,采用光纤喇曼激光器作为抽运源,对S波段色散补偿型光纤喇曼放大器(FRA)进行了实验研究。在增益和噪声特性方面,后向抽运方式优于前向抽运方式。在后向抽运时,测量了5kmDCF-50kmG652光纤色散补偿型分布式FRA,分布式FRA和分立式FRA等三种FRA增益和噪声光谱特性,色散补偿型分布式FRA的增益和噪声特性均优于分布式FRA和分立式FRA。在后向抽运方式下,5kmDCF-50kmG652光纤色散补偿型分布式FRA的抽运功率增大时,其增益增大,噪声指数减小。在抽运功率为1.0W时,当信号功率为0dBm时,最大开关增益为21.4dB,增益光谱大于10dB的带宽超过50nm,噪声指数小于-0.05dB。在同样抽运条件下,色散补偿型FRA的增益与小信号功率无关。     

宽带光纤拉曼放大器的增益平坦化实验研究

本文采用波长为 1 455nm的大功率光纤拉曼激光器(FRL)作为泵浦源,啁啾布拉格光纤光栅作为增益平坦滤波器,用两种不同的光源组合作为信号源(宽带ASE光源) 波分复用模拟器(WDM-emulator)以及四通道外腔可谐调式激光器(ECL) 滤波器型波分复用器(FWDM))对光纤拉曼放大器的增益平坦化特性进行实验研究,获得了平坦增益带宽为55nm(1 519～1 574nm),平均开关增益大小为15.2dB,增益不平坦度为±0.8dBd的宽带光纤拉曼放大器.通过实验研究表明,该方案为带宽低于60nm的光纤拉曼放大器的增益平坦化设计提供了一种新的选择.     

分布式光纤拉曼放大器研制的进展

对分布式光纤拉曼放大器研究的历史、基本原理、优化设计以及现状和进展进行了讨论.对S波段的色散补偿型分布式光纤拉曼放大器以及采用光纤拉曼激光器作为抽运源,在前向抽运和后向抽运条件下,对5kmDCF-50kmG652光纤色散补偿型分布式光纤拉曼放大器增益光谱和噪声谱进行了研究.设计和制作了光纤光栅的增益平坦滤波器,取得了较好的增益平坦效果.FRA-1型分布式光纤拉曼放大器在校园网进行了应用试验,取得了较好的试验效果.     

理论研究垂直腔半导体光放大器脉冲放大特性

从速率方程和薄膜光学理论出发,对垂直腔半导体光放大器(Vertical Cavity Semiconductor Optical Amplifiers,简称VCSOAs)在脉冲工作情况下的动态增益进行了数值模拟.在计算中考虑了载流子和光强沿光轴方向的不均匀性,以及腔内介质折射率的不连续性对光波传输的影响.详细分析了反射模式下VCSOA在脉冲通过时载流子密度和瞬时增益的变化、输出光脉冲的畸变以及抽运光功率、分布布拉格反射镜(Distributed Bragger Reflector,简称DBR)周期数、输入脉冲能量以及脉冲宽度等参量对脉冲放大中的能量增益的影响.结果表明,能量增益随抽运光功率增大而增加;在峰值功率一定时输入脉冲宽度的增加将减小能量增益;输入脉冲能量的增加也会引起能量增益的下降,而适当减少顶部DBR的周期数可以改善这种脉冲放大的能量增益饱和特性.     

抽运光方向对染料激光放大器提取效率的影响

对抽运激光的提取效率是染料激光放大器的重要指标,染料激光放大器的提取效率受到泵浦激光抽运方向的影响.文章从纵向抽运的脉冲染料激光放大器的速率方程推导了抽运光顺向抽运和逆向抽运时放大器提取效率的表达式.采用倍频绿光(532nm)Nd:YAG固体激光器进行了不同方向抽运脉冲染料激光放大器的实验研究.理论计算和实验结果都表明了在纵向抽运的染料激光放大器中,随着放大器级间增益的增加,抽运光提取效率逐渐下降,而且采用逆向抽运方式比采用顺向抽运方式获得的抽运光提取效率要高.     

基于FPGA波形存储法合成大宽带DDS信号源设计与实现

本文研究利用直接数字波形合成法(DDWS)进行直接数字合成(DDS)的设计原理,提出高速率、大带宽下用DDWS产生宽带雷达线性调频信号(LFM)的设计方法,给出系统硬件框图和软件设计模块.设计采用单片高速FPGA作为控制核心,双路单通道DAC芯片进行数模转换,利用ISE软件进行硬件程序设计.设计的信号源可产生时钟频率400 MHz、时宽16μs以内、带宽320 MHz以下的任意LFM.本文对基带信号的带内平坦度,脉冲压缩结果,调频斜率线性度,I/Q正交性等指标进行了分析.分析结果表明,杂散可以通过适当带宽的低通滤波器滤除,基带信号带内平坦度在0.452 dB之内,脉冲压缩最大旁瓣电平低于-12.8 dB.正交圆图、时频分析结果和理想情况相差不大.同时本设计在具体实践应用中获得良好的效果.     

三自由度水平轴硅微机械陀螺结构设计与仿真

为了兼顾测量带宽和灵敏度的要求，提出了一种三自由度水平轴硅微陀螺系统，此系统由3个质量块组成。质量块2与质量块3组合后与质量块1构成了一个二自由度驱动方向的谐振器，再利用该谐振器进行动力学放大，得到非谐振状态下的大驱动振幅．陀螺驱动频率响应曲线有两个谐振尖峰，在两峰值之间存在一个较平坦的区域，当陀螺驱动工作在频率响应曲线的平坦区域时，机械增益虽然比工作在谐振尖峰处小，但机械增益受频率变化的影响减小，驱动频率的工作带宽增加，使得对驱动的控制要求相对宽松．文中给出了动力学放大原理及所设计的陀螺结构的理论计算和仿真值．     

L波段高增益低噪声放大器的设计

低噪声放大器(LNA)是接收机的重要组成部分,它的性能的好坏直接影响着接收机的灵敏度,增益和噪声系数是LNA的两个最重要的指标,所设计的低噪声放大器中心频段为1650MHz时,工作带宽为200M,噪声系数为1.3dB,增益大于35dB,带内平坦度小于±0.5dB,达到应用要求。     

L波段掺铒光纤超荧光光源和放大器研究

通过优化铒光纤长度,获得了平坦谱宽达30nm(0.7dB)的L波段超荧光光源,该光源具有7.21dBm的输出功率。在此基础上,研究L波段放大器增益特性,通过对铒光纤长度的进一步优化,用1480nm激光器作前向泵浦源,实验上获得了波长从1565nm~1595nm范围平坦的增益带宽,小信号增益可达22dB。     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

基于改进型匹配网络的宽带高效率E类功放的设计

为了解决E类功放工作带宽过窄的问题,对E类功放的输入、输出匹配网络提出了一种改进方案.该方案中输出匹配网络采用微带线结构与切比雪夫低通匹配网络相结合的方法,在较宽的工作带宽内有效地抑制了谐波;并采用阻抗变换方法设计了含闭式解的宽带带通输入匹配网络,明显增强了输入匹配网络设计的灵活性.利用该方案,同时采用多谐波双向牵引技术得到功率管的最佳源阻抗和负载阻抗,基于CGH40010F功率管设计了一款应用于L波段的宽带高效率E类功放.测试结果表明,在输入功率为28dBm,漏极偏置电压VDS=28V,栅极电压VGS=-3.3V时,在整个L波段频率范围内漏极工作效率大于65%,最高达到83%,输出功率为39~41.1dBm,增益为11~13.1dB,增益平坦度为±1dB.这一结果验证了该改进方案的有效性,使得E类功放具有宽带宽、高效率的性能.     

Wideband multilayered microstrip antennas fed by coplanar waveguide-loop with and without via combinations

Coplanar waveguide (CPW)-loop fed wideband multilayered microstrip antennas with and without via combinations are presented. The antenna consists of two dielectric substrates, CPW-loop on the ground plane layer, main patch on the middle layer and four asymmetric parasitic patches on the upper layer. The feed consists of a CPW, a loop on a ground plane and a via between main patch and feeding strip on the ground plane layer. Using via, the gain flatness over the impedance bandwidth and return loss are improved. The proposed antenna with four feeding structures is also studied. The 10 dB return loss bandwidths of the antenna with and without via are 34% (3.12? 4.41 GHz) and 33.7% (3.18 ?4.47 GHz), respectively. The measured gain is >5.0 dBi over the impedance bandwidth.     

Performance analysis of BER optimization in WDM systems using EDFA

Wavelength division multiplexing (WDM) systems, which are widely used in telecommunication, have the advantages of huge bandwidth support and reliability. A performance analysis is presented of a WDM system using an erbium-doped fiber amplifier (EDFA), with specific emphasis on bit error rate (BER) optimization. EDFA parameters, including doped fiber length and pump power, are optimized and performance evaluating parameters for different modulation schemes are observed. Simulation results provide optimized BER, noise figure, and gain flatness values. The WDM system is modeled from 1546 nm to 1558 nm bandwidth to obtain maximum gain uniformity, low noise figure, and low BER. This wavelength range is selected to investigate the 1550 nm wavelength commonly used in the telecommunication industry. Also, that we are using a WDM grid, so multiple channels can be accommodated in this range.     

Flat broadband wavelength conversion based on cascaded second-harmonic generation and difference frequency generation in segmented quasi-phase matched gratings

Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation were investigated in segmented quasi-phase matched (QPM) gratings. It is shown that the signal and pump bandwidths are both efficiently widened by increasing the segment number of the QPM grating and optimising the poling period of each segment. The ripple on the matching response is also very small. The conversion bandwidth in a 3-cm-long three-segment waveguide reaches 150–160?nm, which is over the whole conventional band and long-wavelength band. Larger signal bandwidth can be obtained with a little response flatness penalty and conversion efficiency penalty, which can be compensated by increasing the input pump power. Compared with a sinusoidally chirped optical superlattice device, a wavelength converter based on the segmented gratings has higher conversion efficiency, broader bandwidth and better pump-wavelength tolerance, and is easier to fabricate in practice.     

PSO-Gabor-CNN算法在印刷品套印缺陷的检测

目的二维Gabor滤波器含有多个参数,在印刷品套印缺陷检测中,二维Gabor滤波器使用不同参数增强图像特征的效果差别较大,为了获得二维Gabor在某印刷品套印缺陷检测下的优化参数。方法在印刷品套印缺陷检测中,提出一种PSO-Gabor-CNN算法,采用Sobel算子对印刷品图像进行边缘检测,以粒子群算法(PSO)对二维Gabor滤波器的中心最大频率kmax、带宽σ、模板窗口window进行参数寻优,处理后的图像与模板图像采用加权欧式距离进行评价。然后用优化后的Gabor滤波器对图像进行滤波,最后采用卷积神经网络(CNN)对印刷品套印缺陷进行检测和分类。结果通过粒子群算法,确定了二维Gabor中心最大频率kmax为6.0476、带宽σ为0.1444、模板窗口window为27×27取得最佳效果,此时加权欧式距离为1.1927×10-33。卷积神经网络经过70次训练的均方误差为0.0035,测试样本正确率为96.93%。该方法与无数据预处理的BP神经网络(BPNN)、Sobel预处理的BP神经网络(Sobel-BPNN)、无数据预处理的卷积神经网络(CNN)、Sobel预处理的卷积神经网络(Sobel-CNN)对比,表现出了较好的识别效果。结论该方法可以获取二维Gabor滤波器的较优参数,从而获得较好的滤波效果,将其应用于套印缺陷检测,具有一定的应用价值。     

宽带铋基掺铒光纤放大器增益及噪声特性研究

利用Er3 离子四能级结构速率方程组和光功率传输方程组,数值模拟了铋基掺铒光纤放大器(EDFA)的增益及噪声特性,模拟结果与实验报道结果取得了很好的一致。同时,详尽地分析了增益及噪声特性与光纤长度、泵浦功率和输入信号功率的关系,优化了放大器的性能,从理论上得出一个20dB增益带宽达76nm、噪声系数接近4dB的铋基EDFA。研究表明了铋基掺铒光纤放大器适合用作于现代DWDM系统中C L波段的光纤放大器。     

Adaptive noise filtering using an error-backpropagation neuralnetwork

A neural network of the feedforward-error backpropagation type proposed by D.E. Rumelhart et al. (1986) was applied to filter noise from spectral data commonly encountered in infrared absorption of molecular transitions. The purpose was to gain insight into the way a neural network can be trained to remove noise from a noise-corrupted signal with implications for signal processing in general. The neural network simulation was implemented in Fortran and run on a VAX 8800. Training of the neural network occurred on a set of spectral data with random transitions and line shape parameters. Preliminary results of the performance of the adopted neural network are reported and discussed along with observed limitations. Future improvements on noise filtering using a neural network are proposed     

宽带太赫兹非对称十字孔矩形波导定向耦合器的设计

根据波导定向耦合器原理,设计了一种太赫兹频段,采用非对称十字形孔耦合的矩形波导定向耦合器。通过优化波导结构和十字形耦合孔参数,在WR4波导频段内,实现了稳定的耦合平坦度、良好的方向性和工作带宽。仿真结果表明该型波导定向耦合器耦合度稳定在-19.9d B~-22.0d B之间,方向性优于32d B,相对工作带宽为40%。     

Scaling up of a high average power dye laser amplifier and its new pumping designs

Scaling up of a high average power dye laser amplifier is discussed. Differences in the characteristics between a high average power dye laser amplifier with transverse pumping and longitudinal pumping are presented by a simple theory and simulations. The simulation results for dye laser amplifiers of 10-kW average output power show that longitudinal pumping is as efficient as transverse pumping with the potential of orders of magnitude lower dye flow rate. New pumping designs are also proposed for a dye laser amplifier aimed to achieve high gain with high efficiency to reduce the number of amplifier stages. Simulation results suggest that the new designs, in comparison with a conventional amplifier, can produce several orders of magnitude higher gain without decreasing the conversion efficiency.