◇◇新语丝(www.xys.org)(xys.dxiong.com)(xys.3322.org)(xys.freedns.us)◇◇ 请教清华大学杨昌喜教授几个“简单”问题 作者:侍子文 问题内容: 1. 在“构建”(fabricated,引杨昌喜教授语)你的Compact first-order polarization mode dispersion compensator based on birefringent crystals一文时,你和你的合作者是否知道GP公司的Fast digitally variable differential group delay module using polarization switching一文? 2. 如果上面问题回答“是”,是什么原因使你决定把GP公司的相关文章排除 在参考文献(References)之外?你认为GP公司的文章“创新性”(引GP公司语) 如何? 3. 请杨昌喜教授解释一下PMD补偿器(PMD compensator)和DGD模块的关系是 什么?DGD技术是不是实现PMD补偿(PMD compensation)的重要组成部分? (注:对杨教授“PMD与DGD是两个不同的概念” 的准确论断,没有疑问。) 问题背景: 在阅读杨昌喜教授这篇有争议的文章时,发现一些有趣的现象: 尽管文章的技术细节部分(第四段至结尾)几乎全部在讨论DGD,但在文章开始的 综述部分(前3个段落),对DGD似乎惜墨如金。文章开始的综述部分(前3个段落), 颇有些科普文献的风范,也有顾左右而言它之嫌。 在文章的第一段(附),杨教授对研究PMD补偿器的业界同人们似乎洋洋洒洒, 但把GP公司曾经的同事们全部“遗忘”了,在参考文献(References) 里也找 不到他们的影子。 附:杨昌喜教授一文第一段: As the bit rate and distance of optical fibre transmission systems continue to increase, polarization mode dispersion (PMD) is becoming a major system impairment.[1_3] PMD compensation has been attracting great research interests. Various techniques for the first-order PMD compensation have been reported.[4_8] Heisman et al. reported a first-order PMD compensator based on differential polarization delay line technique.[4;5] Unfortunately, the mechanical movement of delay line hinders the response time of the compensator. Moreover, the interferometer configuration is sensitive to environment vibrations. Sobiski et al. reported a first-order PMD compensator based on polarization-maintaining fibres (PMFs) [6] with response time of 200 ms. Lee et al. realized a first-order PMD compensator based on the similar technique [7] with the insertion loss of 16 dB and the response time of 300 ms. The PMF has relatively small birefringence. The compensator based on the PMF thus needs a long length of PMFs to generate a certain amount of differential group delay (DGD). On the other hand, a long length of PMF may cause harmful nonlinear optical effects for the transmission systems. Willner et al. proposed a first-order PMD compensator based on high-birefringence nonlinearly-chirped fibre Bragg grating.[8] Circulators are needed for coupling the light out, which causes additional insertion loss and complexity of the compensator. Furthermore, the fibre gratings generate additional chromatic dispersion in the transmission system. (XYS20050406) ◇◇新语丝(www.xys.org)(xys.dxiong.com)(xys.3322.org)(xys.freedns.us)◇◇