偏振效应损伤的光通信系统失效概率估算

采用多重重要抽样方法,研究了受偏振模式色散和偏振相关损耗损伤的10 Gbit/s光通信系统的功率代价和失效概率.仿真结果表明,光滤波器对功率代价有重要影响.采用法布里-珀罗滤波器的系统比采用四阶高斯型滤波器的系统有更好的性能表现;发现功率代价通常随着啁啾因子的增大而增大,但当啁啾因子为0.5左右时,系统性能达到最好.仿真结果也表明,即使偏振模式色散和偏振相关损耗同时存在,DPSK系统比OOK系统有更强的PMD和PDL耐受性.     

频移键控无线光通信系统的Optisystem实验仿真

调制技术是无线激光通信中的关键技术之一.目前国内外无线激光通信所采用的调制方式多为强度调制或相位调制.对研究较少的频率调制系统进行了研究,分析了多普勒效应对系统的影响,借鉴光纤通信领域的最新研究成果提出了高速频移键控(FSK)无线光通信系统的方案设计,并使用Optisystem软件实现系统仿真,对激光器线宽、滤波器带宽...     

用于5G通信的二维圆柱型光子晶体波导带通滤波器设计

波导带通滤波器是大功率微波滤波的重要器件,为5G通信基站大功率微波传输提供了可能.基于光子晶体的频率带隙特性,把二维圆柱型光子晶体引入矩形波导中,设计了一款应用于5G通信的二维圆柱型光子晶体波导带通滤波器,仿真研究了该滤波器的滤波特性,以及引入点缺陷、线缺陷时滤波器的性能变化.二维光子晶体结构在矩形波导中在3～7 GH...     

基于表面等离子激元的口径耦合多功能非对称半圆腔滤波器设计

采用口径耦合的方法构造了一种金属-介质-金属非对称结构滤波器,由两个半圆腔通过两个矩形口径与波导管相连形成.运用有限元法仿真计算获得了该结构的磁场、透射谱、带宽及边沿陡峭度分布曲线.研究结果表明,通过调节结构参数,滤波器的透射曲线出现明显的红移或蓝移现象,且曲线分布平滑,其通带透射比高达0.95,阻带则具有平坦特性且透射比低至0.001,通带、阻带均具有较宽的带宽.对滤波器进行结构参数优化,可以实现类似矩形滤波器的特性,在光通信波段的三个通信窗口能够实现通道选择的滤波功能.该滤波器在微纳光学器件集成尤其是光通信系统中有良好的应用前景.     

基于扩展卡尔曼的PDM-16QAM偏振态和载波相位快速跟踪

在偏振复用(PDM)高速光通信系统的相干检测中,需要实现信号偏振态和载波相位的快速跟踪。将扩展卡尔曼滤波器用在偏振复用16进制正交振幅调制(PDM-16QAM)光调制信号相干接收机中,成功实现了偏振态和载波相位的快速精确跟踪。在单信道112Gb/s PDM-16QAM传输系统中,数值仿真发现,扩展卡尔曼滤波器所能跟踪的最大偏振态旋转速率可达级联多模算法的100倍,而且具有很好的收敛精度,其收敛速度和精度可以通过调优参量控制。使用扩展卡尔曼滤波器跟踪100kHz线宽18 Mrad/s偏振态旋转信号时,10-3误码率(BER)对应的接收机灵敏度代价仅为0.2dB。研究了应用于长距离传输光通信系统的扩展卡尔曼相干接收的性能。     

空间光通信ATP系统设计中的基本概念及关键参数探讨

空间光捕获、跟踪、对准(ATP)技术的采用是为了保证空间光通信系统建立可取通信链路，它是实现空间光通信需要首先突破和解决的关键技术。空间光通信ATP子系统中的瞄准误差等关键参数直接影响系统总体性能以及对总体设计指标的确定，在一定程度上还决定了空间光通信系统的重量、体积以及系统制作的复杂程度。因此，开展对ATP技术的研究对实现空间光通信有着重要的现实意义。简单介绍ATP系统的典型结构，分析ATP系统瞄准误差的产生、计算以及ATP跟瞄精度对系统整体设计的影响，同时给出对ATP系统的部分仿真结果。     

室内可见光多维CAP空间调制

针对室内可见光通信（VLC）光链路发射源（LED器件）有限的调制带宽问题,基于多维无载波幅度相位调制（CAP）技术,提出一种频带利用率高效的光空间调制方案（OSM-CAP）。OSM-CAP系统将输入信息序列分成两部分,一部分进行空域映射即空间调制,其结果用来选择激活的LED;另一部分进行信号域映射,即CAP调制。其中,CAP调制采用序列二次规划算法求取的时域正交多维CAP滤波器组实现。对于采用强度调制/直接检测（IM/DD）的VLC系统,该CAP信号还将进行单极化处理,文中提出两种相应的解决方案,即采用添加直流偏置（OSM-DCO/CAP方案）和零值位置极性编码（OSM-U/CAP方案）。基于朗伯体辐射模型,且可见光背景噪声建模为加性高斯白噪声,推导了OSM-DCO/CAP、OSM-U/CAP调制方案的误码率理论解,仿真验证了其准确性。在5 m×5 m×3 m的室内场景下,探讨了无载波幅度相位调制维度以及接收机个数、发射机间距、收发平面距离以及链路遮挡情况等信道参数对系统性能的影响。结果表明,星座调制阶数相同时,CAP调制维度越高,误码性能越好;接收机个数增多、发射机间距加大以及收发平面距离减小与系统可靠性存在正相关关系;链路存在遮挡情况时,会提高信道间的差异性,改善系统性能。     

星间相干激光通信中反射镜面形畸变状态下通信性能的研究

单个激光波长受卫星相干光通信系统中反射镜的影响,其波前将会发生不可预期的变化。研究了波前在单个反射镜面形畸变下的变化,并分析了它对卫星相干光通信效率的影响。仿真结果表明,畸变位置处的峰谷值是影响激光波前的主要因数,而畸变的大小对链路性能的影响却有限。     

基于数字相位恢复算法的正交相移键控自由空间相干光通信系统

近年来,大气湍流所引起的信号相位扰动以及光强闪烁对自由空间相干光通信系统性能的影响逐渐成为研究人员关注的焦点。为了提高系统性能,本文对自由空间相干光通信系统进行了研究。在假设大气湍流所引入的光强闪烁以及相位抖动分别服从对数正态以及高斯分布的条件下,本文提出了基于数字相位恢复算法(CPR)的正交相移键控(QPSK)自由空间相干光通信系统,该系统采用了二阶联合的相位恢复算法结构。仿真结果表明:该结构可以极大地降低相位噪声对系统产生的影响,且其误符号率比只采用一阶M次方的相位恢复算法的系统低3个数量级。因此,该系统的提出对于自由空间光通信性能的提升有着较大意义。     

适用于3G移动通讯的高温超导窄带滤波器

研制了一种适用于3G移动通讯基站接收机的高温超导窄带带通滤波器.其中心频率为1949.85兆赫兹,带宽为9.7兆赫兹.为了实现极高性能,理论设计了12阶准椭圆(quasi-elliptic)函数型滤波器,引入了3对传输零点.滤波器的计算机仿真是用Sonnet软件完成的.此滤波器是在直径为2英寸、厚度约为0.5毫米的氧化镁双面超导薄膜上制作的.实测表明,达到了极高的性能要求:相对带宽0.49%,带边陡度>150dB/MHZ,带外抑制>60dB,插入损耗<0.2dB,反射损耗<-14dB.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.