椭圆芯扁六角聚合物光子晶体光纤的偏振特性

采用全矢量定域基函数模型,以聚合物PMMA为基材,研究了椭圆芯三角点阵扁六角结构光子晶体光纤(Photonic crystal fibers,PCFs)的偏振特性,分析了其相位模双折射和群模双折射与相对孔间隔比的依赖关系,并与椭圆芯三角点阵正六角结构PCFs的研究结论进行比较;研究发现,椭圆芯扁六角结构PCF的偏振特性强烈的依赖于光纤的结构参数,由于色度色散的存在,在短波长段,群双折射远远高于相位模双折射,通过适当调节光纤的相对孔径和相对孔间隔比,有望在给定波长实现高双折射和零偏振模色散单模运行.该研究为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据.     

光纤光栅偏振模色散研究

对光纤光栅的偏振模色散特性进行了深入的研究，特别是啁啾光纤光栅色散补偿器的偏振模色散。研究表明啁啾光纤光栅色散补偿器的偏振模色散主要由光栅的双折射系数、色散量决定，提出了制作低偏振模色散的色散补偿器的方法。     

零模间色散三芯光子晶体光纤

为了研究纤芯掺杂低折射率材料后三芯光子晶体光纤中任意两超模之间的模间色散特性,采用全矢量有限元法进行了仿真,取得了模间色散系数、零模间色散波长随纤芯折射率和结构参量变化的数据。结果表明,通过调节纤芯折射率、纤芯直径、空气孔直径以及孔间距这4个结构参量,可以使任意两超模间的模间色散在两个常用波段1.31m和1.55m处为0。该结果对于消除基于模分复用的光纤不同模式间因为模间色散导致的脉冲失真和实现零模间色散的模分复用技术是有帮助的。     

温度对单模光纤偏振模色散的影响研究

随着光纤通信系统传输容量的不断发展 ,光纤中的偏振模色散 PMD成为限制高速光纤通信系统传输容量的极限因素。偏振模色散是由于光纤结构的不完善性或者受到外界应力的作用而产生的 ,因此偏振模色散受外界环境因素的影响较大。许多研究表明偏振模色散对温度具有较强的敏感性 ,是温度的函数。采用波长扫描法就温度对单模光纤偏振模色散的影响展开研究 ,研究结果表明 ,单模光纤偏振模色散将随着温度的升高而呈现减小的趋势     

12芯海底光缆的偏振模色散特性

由于光放大器的出现,人们正在积极研究传输距离离１０００ｋｍ以上的１Ｒ再生中继传输方式。偏振热色散,光纤色散可能限制如此长距离系统的传输。特别是偏振模色散,它是一个随周围温度,光缆构造和布设状态而变化的参数。而这些因素对海底光缆偏振模色散特性的影响还不十分清楚。本文为了明确采用光纤放大器的长距离传输系统中海底光缆和各种特性,试制了长约１０ｋｍ的１２芯海底光缆,对其偏振色散特性进行了研究。试验结果表明     

光纤光栅不同温度下偏振模色散的研究

光纤光栅的偏振模色散是由于在侧写入法写入光栅时,光敏光纤对紫外光的吸收不均匀造成的。分析了光纤光栅在不同温度下的偏振模色散,实验研究了光纤光栅的偏振模色散在-20~ 60℃的情况,统计结果表明,在不同温度下,光纤光栅的偏振模色散基本保持不变。     

单模光纤测量技术(之四)——单模光纤偏振特性的测量

一、单模光纤偏振特性及其表征单模光纤中一般存在着两个相互垂直的偏振态,即HE_(11)模的两个偏振态HE_(11x)和HE_(11y)。而对实际的单模光纤来说,由于其结构不完整性,如纤芯形变、弯曲、扭转,以及内应力或由于受到外力的作用等等原因,往往引起了双折射现象即:HE_(11x)模和HE_(11y)模间的相速差和群速差,从而产生模式色散;同时也引起了两个偏振态之间的模式能量耦合。这对于通信用单模光纤,特别是对于采用单频光源和零材料色散的高质量单模光纤的通信系统,常常会使其通信容量或中继距     

光纤和光缆的偏振模色散系数研究

综述了偏振模色散的概念、偏振模色散对光传输系统的影响、系统对单模光纤偏振模色散系数的要求,以及获得小的偏振模色散光纤和光缆的方法.     

浅谈波分系统的光纤色散及补偿

光纤色散(色度色散CD)是由于光纤所传送信号的不同频率成分或不同模式成分的群速度不同,而引起传输信号畸变的一种物理现象。所谓群速度就是光能在光纤中的传输速度。所谓光信号畸变,一般指脉冲展宽。偏振模色散PMD偏振模色散是由于光纤制造工艺造成纤芯截面一定程度的椭圆度,或者是由于材料的热涨系数的不均匀性造成光纤截面上各向异性的应力而导致光纤折射率的各向异性,这两者均能造成两个偏振模传播常数的差异,从而产生群时延的不同,形成了偏振模色散。当前,光纤通信正向超高速率、超长距离的方向发展。EDFA的出现为1550nm波长窗口实现大容量、长距离光通信创造了条件,并使光纤通信中衰耗的问题得到了一定的解决。然而光纤的色散影响仍然是制约因素之一。     

光纤偏振模色散测试仪

论述了测试仪所采用的光谱分析法光纤偏振模色散测试原理,介绍了弱导模光纤中偏振模色散的随机特性以及变化规律,并给出了光纤偏振模色散测试仪的测试结果。     

加权的基于多播节点的多播路由算法

在许多多播应用中,降低多播树网络费用非常重要.本文提出了加权的基于多播节点的多播路由算法（WDDMC算法）.由于改变了DDMC（Destination-Driven routing for low-cost Multicast ）算法中的指示函数,适当降低了多播节点作为中间节点的优先级,提高非多播节点作为中间节点的优先级,从而使得多播树更接近最小Steiner树.在随机网络上的仿真结果表明,WDDMC算法的多播树网络费用优于DDMC算法.该算法的复杂度与DDMC算法完全相同.     

A rigorous derivation of the relation between the effective areaand the directive gain and its extension to lossy antennas

It is well known that the effective area of a receiving antenna is linearly related to the directive gain of the same antenna in the transmitting mode. Conventionally, this relation is derived by constructing a two-port network involving the transfer impedance between a pair of antennas. Next, by use of the Thevenin theorem, the received power is related with the open-circuit voltage, which in turn is proportional to the transfer impedance. Alternatively, from field analysis, the received power is related to the effective area and the directive gain. Then, the reciprocity theorem is used to equate the transfer impedances between a pair of antennas. Based on these, the area-directivity relation is derived. However, it is indicated that the circuit model with the open-circuit voltage is not rigorous. In this investigation, the reciprocity theorem is used in a different way to directly derive the power absorbed at the load in terms of the radiated electric field in the transmitting mode. Thereby, the area-directivity relation is derived in a straightforward and rigorous manner. In the derivation of the relation, it is seen that the current in the terminal gap should be uniform. Thus, one limitation of this well-known relation is found. The effect of ohmic loss due to finite conductivity of the antenna material can be taken into consideration in the derivation. Thus, the area-directivity relation is extended such that it is applicable to lossy antennas     

A simple model for fatigue life

A simple model to handle fatigue-life length problems is discussed. The characteristic property of the model is that it combines the Palmgren-Miner rule with time invariance. The model is applied to situations with both random strength and random load. The randomness in the life is generated by the random strength and not by the random load. The only property of the random load that affects the life is its damage intensity, which is independent of the particular realization in the ergodic-load case. The damage intensity is even independent of the distribution of the random function, provided its level-crossing intensity is known. Particular attention is given to simple random strength models. In general, the exhaustion density is a random function, but in the simple models the only randomness that appears in the strength is either randomness in the time scale or randomness in the amplitude scale. The model is well-suited for comparative calculations under different load conditions, since it connects fatigue life for random loads to fatigue life for periodically oscillating loads, which is usually measured in experiments     

An example of a hybrid system: coherent optical system with Costasloop in receiver-system for transmission in baseband

The possibility of hybrid system construction is considered in this paper. The coherent optical system is the constituent part of this system. The first part of the system is constructed in passband (optical cable is transmission medium), and the second part of the system is constructed in baseband. The heterodyne optical receiver is used as optical receiver. Estimation is not done just after demodulation, but it is done at the end of the section in baseband. Taking into account shot noise of photodetectors, laser phase noise (transmitter laser and local laser) and noise which is generated during transmission by means of the section in baseband, we determine the performances of the proposed system     

双生物识别图象的光学加密方法研究

本文提出了一种将两幅生物识别图象通过一套光学系统进行同时加密的方法。该方法先将一幅图象转换为纯相位和进行纯相位编码,再对另一幅图象编码,然后经过4f光学系统作频率域纯相位编码,并利用与编码过程类似的方法进行解码。可以证明该方法的编码图象为恒定的白噪声。解码过程具有鲁棒性,相位部分图象加密的安全性要高于振幅部分图象的加密。并分析了加性高斯噪声对解码图象的影响     

A quantitative analysis of SNR in the short-time Fourier transformdomain for multicomponent signals

A quantitative analysis is given for the signal-to-noise ratio (SNR) in the short-time Fourier transform domain for multicomponent signals in additive white noise. It is shown that the SNR is increased on the order of O(N/K), where K is the number of components of a signal, N/T is the sampling rate, and T is the window size. The SNR increase rate is optimal for given K. For this result, the SNR definition is generalized, which is suitable for signals not only in the time domain but also in other domains. This theory is illustrated by one numerical example     

Throughput and delay analysis of free access tree algorithm withminislots

An analysis is made of the throughput and delay performance of two classes of free-access tree algorithms with minislots. In one class, binary feedback information is available in minislots, and in the other, ternary feedback information is available. It is shown that the highest maximum throughput 0.56714 is achieved in the limiting case where the number of minislots in a (large) slot is infinity and minislot overhead is zero. A lower bound of the average transmission delays in these algorithms is analytically derived. The obtained lower bound is also a lower bound of the average delay of the whole class of the free-access algorithms     

DDR3芯片基于XR8238A全地址全功能老炼过程测试

集成电路老炼的主要目的是模拟芯片的工作寿命,加偏压、加高温模拟产品最坏的工作条件,作为可靠性监控和从批次产品中剔除早期失效产品。取决于老炼时间的长短,早衰期或者损耗期的缺陷均可导致芯片的失效。第三代双倍数据率同步动态随机存储器目前还没有一套完整的老炼试验方法。基于设备XR8238A设计一套印制板,区别于传统的老炼试验模式,给芯片写入完整的数据,输出符合预期的波形,有效地完成了老炼过程测试,提供了第三代双倍数据率同步动态随机存储器产品出货平均故障间隔时间试验的一种方法,提升了集成电路老炼的效果。     

创新铸就高质量

该文回顾了质量管理发展的历史,探索了现代企业质量管理中提高产品质量的一种新实践模式,即将6sigma的分析方法与TRIZ的创新理论相结合,彻底地解决矛盾,而不是优化参数,最终达到满意的质量水平。并且通过企业的一个实际案例,来讲解具体的操作办法。     

大气折射率波动引起的SAR成像误差分析

合成孔径雷达(SAR)成像中通常默认大气折射率为1,即电磁(EM)波速率等于自由空间光速且忽略大气吸收特性,但实际存在的吸收会减弱入射功率,电磁波速率的变化会引起相位误差,从而影响图像重建。该文定量分析电磁波速率波动和大气吸收对雷达图像的影响,理论推导得出大气吸收会导致振幅误差,表现为散射点在图像中的重建幅度误差;电磁波速率波动会导致相位误差,表现为散射点在图像中的重建位置误差。仿真实验验证了误差分析的正确性。该分析进一步完备了SAR成像误差分析,有助于SAR图像正确解译。