光纤通信在市内接入网的应用

先说明市内接入网的单位用户和住家用户两大类使用通信和电视、交互型和分配型业务的要求不相同，相应地对光纤传输的应用须作不同的考虑，文中认为；光纤从市内交换局直连办公大楼是合乎现实需要的，而对于居民住家，宜选用光纤连至路边或光纤与同轴结合和适当利用无源光网络等方案，俟将来时机成熟才实行光纤连至每一家，文末有概括总结，说明接入网不同于长途网，接入网的光纤系统可以使用常规单模光纤，工作于波长1．3μm，而光放大器和波分多路系统不是普遍需要，但光电子集成在光端机中是必要的。     

长途高速通信主干线的技术考虑

阐述我国长距离，高速率通信主干线在设计时应行考虑的主要技术问题，包括工作波长的选择，单模光纤的新设计，光纤放大器的应用，密集波分多路系统的应用，对光子器件和光子集成的要求，文末附带提及越洋海底光缆的技术趋向。     

Blind multiuser channel estimation in asynchronous CDMA systems

In asynchronous code division multiple access (A-CDMA) systems transmitting over multipath channels, both intersymbol interference (ISI) as a result of interchip interference (ICI) and multiple access interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired users' signature waveform. Recently, Liu and Xu (see Proc. 29th Asilomar Conf. Signals, Systems and Computers, 1996) introduced a blind estimation algorithm for synchronous CDMA (S-CDMA) systems to estimate the multiuser channels. However, this algorithm cannot be directly applied to an asynchronous CDMA (A-CDMA) system. In this paper, we study a similar blind estimation scheme that provides estimates of the multiuser channels by exploiting the structure information of the data output and the users' delays. In particular, we show that the subspace of the data matrix contains sufficient information for unique determination of channels and, hence, the signature waveforms. By utilizing antenna arrays, we extended our approach to overloaded systems, where the number of users may exceed the spreading factor     

Optimal PN sequence design for quasisynchronous CDMA communicationsystems

Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated     

超强激光场中H_2~ 的隧道离解和波包演化

利用超强激光脉冲中分子与场相互作用的多电子态模型，数值模拟了分子波包在高低频超强激光场中的演化过程。结果发现，高频场中分子波包的扩展是渐进的，直到脉冲作用结束，分子才完全离解；而在低频场中，分子波包迅速隧穿到离解态，仅在脉冲的前几个周期，波包便溢出相互作用区。另外还比较了高低频场作用下分子的离解几率和离解碎片的动量分布。     

邮电通信对信息化适应问题浅析

信息化是社会发展的必然要求，适应信息化的要注是邮电通信发展的一个基本目标。本文采取国际上较为通用的分析方法研究了中国邮电通信对信息化的适应程度，并结合通信发展中现存问题对今后发展提出应引以注意的方面。     

Nitrogen Doping Effect in a-Ge: H Films Due To High Hydrogen Dilution

ＮｉｔｒｏｇｅｎＤｏｐｉｎｇＥｆｅｃｔｉｎａＧｅ：ＨＦｉｌｍｓＤｕｅＴｏＨｉｇｈＨｙｄｒｏｇｅｎＤｉｌｕｔｉｏｎＪ．Ｘｕ１Ｋ．Ｊ．Ｃｈｅｎ１Ｄ．Ｆｅｎｇ１，ＳｅｉｃｈｉＭｉｙａｚａｋｉ２ＭａｓａｔａｋａＨｉｒｏｓｅ２（１．Ｄｅｐｔ．ｏｆＰｈｙｓｉｃ...     

全保偏光纤迈克尔逊干涉仪

报道了全保偏光纤迈克尔逊干涉仪的研究结果.实验中采用熊猫保偏光纤、磨抛型保偏光纤偏振器(消光比为35dB.损耗相似文献   

激光散斑多重全息图

将激光散斑技术和全息技术相结合.提出了一种通过两步记录制作多重全息图的方法.详细地描述了实验方法,讨论了记录和再现过程的原理并进行了实验验证.     

连续Nd:YAG激光器中Cr~(4 ):YAG被动调Q的稳定性和功率的提高

Ｃｒ４＋ＹＡＧ用于连续ＮｄＹＡＧ激光器被动调Ｑ，激光横模结构和纵模结构以及激光泵浦速率起伏等是引起调Ｑ不稳定的重要因素，运用一定的技术可以使调Ｑ稳定性得到根本性改善；此外应考虑Ｃｒ４＋ＹＡＧ热效应及光学薄膜的激光损伤