改进的16-QAM相干光通信系统中载波相位估计算法

在相干光传输系统中,相位噪声是影响系统性能的一个重要因素,研究了16-QAM中基于QPSK分割的相位恢复算法原理,提出了一种加权重的QPSK分割相位估计改进算法。仿真结果表明,在BER=10-3,SNR灵敏度代价为1d B时,改进算法对激光器线宽的容忍度约有38.7%的提升。     

16-QAM相干光纤通信系统星座图的优化与选择

基于16-QAM的相干光纤通信系统其抗噪声能力与调制格式的星座图特征密切相关。文章分析了Star 16-QAM的星座图在各种圈比下受噪声影响的特性,通过数值计算获得了在不同噪声条件下星座图的最佳圈比。研究了Square和Star两种16-QAM对激光相位噪声的要求,分析结果表明,获得相同的BER性能时,Star 16-QAM由激光相位噪声引起的光信噪比代价更小。     

PDM-16QAM系统中几种相位估计算法的性能与复杂度比较以及改进

在偏分复用的高速相干光通信系统中,16进制正交幅度调制(PDM-16QAM)是最有前景的调制格式,且载波相位估计是补偿发射端与接收端激光器对信号造成的相位失真的重要技术。该领域最经常使用的算法为QPSK分区算法与盲相位搜索算法,但他们都有自己的缺点,如估计效果不够好,适用范围不够广,或者计算复杂度过高。本论文实验搭建了224Gb/s PDM-16QAM波分复用传输640km相干检测系统平台,首先利用几种基于前述两种算法的相位估计方法对接收到的信号进行了数据处理,分别给出了误码率曲线图、误差向量幅度曲线图、计算复杂度分析表。然后基于性能最优与计算复杂度的平衡,提出了针对16QAM信号星座图中间圈的点的省略两级处理算法。将该改进的算法用于实验系统相位估计单元进行数据处理,结果表明,改进的算法P1,3/ML其误码率性能和误差向量幅度性能基本保持不变,但是计算复杂度降低为原来的1/2。     

Square m-QAM相干光通信载波相位估计性能研究

基于前馈载波相位估计算法,研究了square 16-QAM调制相干光纤通信系统的载波相位估计性能,进一步证明了当存在相位噪声时square m-QAM调制并非QAM调制最佳星座图的原因。仿真计算结果显示,由于square 16-QAM调制星座图中星点之间相位距离分布不均匀,引起载波相位估计中出现连续相位跳变,导致载波估计性能劣化,系统误码率增大约2～3倍。     

射频六端口网络在软件无线电中的应用

对射频六端口网络在射频上直接解调各类调制信号的普遍适用性进行了理论分析,推导了射频六端口网络解调正交调制信号的一般表达式,并对QPSK、16QAM和π/4QPSK三种调制制式使用计算机仿真验证了表达式的正确性;此外,仿真研究了射频六端口性能指标对解调性能的影响,其结果表明对于QPSK调制信号正交电桥0.3dB的幅度不平衡度和3o的相位不平衡度带来的解调性能恶化小于0.5dB。     

基于高维调制的模分复用系统性能研究

为了提高系统的传输容量和传输性能,提出了基于高维调制的模分复用通信技术.通过搭建的基于高维调制的模分复用系统,仿真分析了4b-4D和8b-8D高维信号在不同光信噪比、传输距离和模式耦合系数条件下的传输性能,并与传统的谱效率相同的二维调制信号QPSK进行了对比.实验结果表明,在目标误码率下,4b-4D信号和8b-8D信号所需信噪比分别比QPSK信号降低了2和4 dB,传输距离分别比QPSK信号增加了20和40km.可见,随着信号维度的增大,信号的抗噪声性能及抗色散性能越好.此外,实验结果表明模式耦合对误码率的影响也随着信号维度的增加而减小.     

载波相位误差对解调性能的影响分析

对MPSK、QAM信号载波相位误差对于解调性能的影响进行了定量分析,推导给出了载波估计方差较小时BPSK、QPSK信号载波相位误差对解调性能影响的表达式。根据定量分析结果,载波估计方差较小时对BPSK、QPSK信号载波估计方差与误码率的关系进行了仿真,仿真结果和理论分析结果是一致的。结果表明在Es/N0为2、载波估计方差小于1×10-2的情况下,载波相位误差对于解调性能的影响小于0.2 dB。     

一种基于代价函数的相位估计算法

针对BPSK,QPSK,OQPSK信号的相位估计问题,提出了一种基于代价函数的相位估计算法。该算法不依赖符号同步信息,直接使用零中频信号进行相位估计。构造了一个代价函数并从理论上推导了代价函数与信号相位的关系,给出了基于代价函数的相位估计算法的实现方法,分析了算法的性能以及计算的复杂度。仿真结果表明,该算法能有效地估计BPSK,QPSK,OQPSK信号的相位,估计精度受搜索步长、信号长度和信噪比等参数的影响。     

相对相位噪声对相干光通信系统性能影响

在使用前向抽运喇曼放大器的相干光正交频分复用传输系统中,由于喇曼抽运的强度噪声和交叉相位调制之间相互作用产生相对相位噪声,导致系统性能大幅下降。为了研究此问题,采用数值分析方法进行了理论分析与实验验证,分析了不同的调制格式下,相对相位噪声对相干光正交频分复用系统的影响,并且比较了正交频分复用多载波系统与单载波系统在相同条件下的系统性能,取得了由相对相位噪声所导致的系统损伤程度数据。结果表明,抽运和信号之间相对较大的离散系数有助于抑制相对相位噪声引起的损伤,高阶调制信号比低阶信号对相对相位噪声耐受性低;频谱相同效率时,正交幅度调制格式比相移键控耐受性更好。     

QPSK信号非相干和相干解调算法的研究

本文主要分析了QPSK基带信号的非相干解调和相干解调算法。介绍了QPSK信号非相干解调算法和性能,对于相干解调,介绍了载波相位估计的V＆V算法。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

A rigorous proof of MIMO channel capacity’s increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output（MIMO） communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas. The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.