Comparative Study on Large and Small Signal Theory for Intensity Modulation Response of Semiconductor Lasers Including Higher-Order Dispersion Terms

In this article, the comparison of large signal theory and small signal theory has been done with dispersive propagation of optical signal with IMDD (Intensity Modulation Direct Detection) systems for semiconductor lasers with higher-order dispersion terms. The expressions for an exact large signal theory and small signal theory including higher-order dispersion terms for propagation of an optical wave with sinusoidal amplitude and frequency modulation in a dispersive fiber have been derived. It is observed that small signal theory is more sensitive compared to large signal theory in terms of intensity modulation/direct detection systems. Also, it is reported that for large signal analysis the higher-order effects of dispersion can be ignored, whereas for small signal theory, the higher-order effects can be ignored for lower modulation frequencies only. The variation in the transfer function for various values of modulation indices are greater for small signal analysis than for large signal analysis. Also, as the intensity modulation index is increased, there is a decrease in the value of transfer function. The large signal model approximates the small signal model for lower values of the intensity modulation index.     

垂直腔激光器中弛豫振荡频率的优化控制

从垂直腔面发射的半导体激光器（VCSELs）的结构出发，利用增益与载流子密度的广义对数关系，借助小信号分析法，推出了直接调制情形下驰豫振荡频率的严格解析关系。分析指出，量子阱器件的光子寿命并非越短越好，欲提高VCSELs的驰豫振荡频率，除了增加注入电流，提高微分增益等基本途径外，控制器件的结构参数可使驰豫振荡频率达到极大值。同时，自发辐射因子的可控性，以及降低稳态载流子密度，也都是提高VCSELs驰豫振荡频率和拓宽调制带宽的有效措施。     

Optical modulation and digital demodulation of an in-plane moiré carrier

A rotational mismatch of gratings is used to generate a fringe carrier of an in-plane moiré pattern so that specimen deformation shows itself in the form of modulation of the carrier frequency. As both the unmodulated and modulated carriers are the patterns without fringe-loop or fringe-connection, they are automatically numbered with monotonical increasing orders by a digital image processing system without any ambiguity. The orders at every pixel of the image are determined by interpolation of the orders of the tracked fringes to establish two grey image files, from the difference of which, the orders of the in-plane displacement moiré are displayed with grey-level variation.     

调制脉冲声测量系统的原理及应用

本文介绍的调制脉冲声测量系统是TDS和数字测量技术的进一步发展,其特点是简化了TEF系统的实现条件,解决了全频带的测量动态问题。本系统曾在上海音像公司录音棚中进行过测量,取得了一定的效果。     

一种适于自适应光学的旋转软刀口波面传感器的研究

利用傅里叶光学理论,证明了一种新型波面传感器——旋转软刀口波面传感器的概念.在经典刀口法的刀口区,以渐变透过率代替突变透过率函数,在光瞳象面上可获得反映光瞳面位置待测波面位相梯度及位相梯度方向的调制信号.文中给出了实验结果和讨论.     

一种视频信号压缩编码方法的研究

文章采用自适应预测编码加熵编码的复合编码方法，对视频信号进行压缩编码。计算机模拟结果表明，压缩比为3.5：1（2.25bits／Pixel）时可获得良好的图像质量，因此，可实现在PCM三次群信道上传输一路彩色电视信号。     

广义准正则格形码距离谱的计算

本文讨论了格形码距离谱的计算问题，定义了度量空间意义下的广义准正则格形码，对具有Ｉｍａｉ与Ｈｉｒａｋａｗａ［２］和Ｕｎｇｅｒｂｏｅｃｋ［３］定义的典型的时不变网格结构的广义准正则格形码，证明了其距离谱可用全零信息序列对应的码字进行计算。在理论上推广了Ｍ．Ｒｏｕａｎｃｅ与Ｄ．Ｊ．Ｃｏｓｔｅｌｏ的结果，解决了非平方欧几里德度量意义下一类ＴＣＭ信号序列的距离谱计算问题     

Nd：YAG激光器中的自锁模

本文报道在Nd:YAG激光器中首次获得的自锁模脉冲序列.自锁模是由于Nd:YAG棒中的自相位调制引起的.在主被动对撞锁模运转情况下,自锁模对脉冲波形有较大的影响.     

国内外中短波调幅广播技术20年来的回顾和展望

文章回顾２０年来国内外调幅广播在调制制式，射频放大系统以及包括单边带，浮动载波和调幅多工等多种功能的发展状况。同时对今后调幅广播技术发展方向发表了几点看法。     

Turbo码综合性能分析与Turbo编码调制

对 Ｔｕｒｂｏ码的 ＲＳＣ分量码、交织器、调制方式、信道以及迭代译码算法进行了综合研究与性能分析，并给出了一种基于逐比特ＭＡＰ算法的Ｔｕｒｂｏ编码与多元调制相结合的编码调制方式。仿真结果表明，该方案将Ｔｕｒｂｏ码的高编码增益与多元调制的高频谱利用率有效地结合在一起，是一种功率和频谱高效的编码调制方式，比传统的ＴＣＭ方式有更好的性能。