Unit 6： Evolution of Lightwave System.ppt

专 业 英 语 第一部分 专业英语基础知识 Unit 6： NEW WORDS AND PHRASES evolution n. 进展, 发展, 演变, 进化 dispersion n. 色散 drawback n. 缺点, 缺陷, 瑕疵, 障碍 sensitivity n. 灵敏度, 灵敏性 magnitude n. 量级,大小, 数量, 巨大, 广大, counteract vt. 抵消, 中和 nonlinearity n. 非线性 soliton n. 孤立子, 孤波 maturity n. 成热, 完备 TEXT The enormous progress over the 25-year period extending from 1975 to 2000 can be grouped into several distinct generations. extend from ... to ...:从……延续（一直）到 从1975年一直到2000年这25年期间的巨大发展可以划分为不同的几代。 In every generation, BL increases initially but then begins to saturate as the technology matures. initially:最初, 开头 saturate:饱和 BL：比特率和距离的乘积。表示传输容量。 在每一代（光波系统）中，BL最初总是增加的，但是随着技术的成熟，BL就开始饱和。 The larger repeater spacing compared with 1-km spacing of coaxial systems was an important motivation for system designers because it decreased the installation and maintenance costs associated with each repeater. repeater spacing :中继距离； repeater:中继器 coaxial systems:同轴（电缆）系统 motivation :动力，动力 与同轴系统1km的中继距离相比，这种更大的中继距离对系统设计者来说是一种很重要的动力，因为这降低了每一个中继器的安装和维护费用。 However, the introduction of third-generation lightwave systems operating at 1.55 μm was considerably delayed by a large fiber dispersion near 1.55 μm. 然而，1.55 μm附近大的光纤色散，严重的推迟了工作在该波段的第三代光波系统的引入。 Conventional InGaAsP semiconductor lasers could not be used because of pulse spreading occurring as a result of simultaneous oscillation of several longitudinal modes. semiconductor lasers：半导体激光器 pulse spreading ：脉冲展宽 longitudinal modes ：纵模 由于多纵同时模震荡导致的脉冲展宽，使得传统的InGaAsP半导体激光器不能使用。 The dispersion problem can be overcome either by using dispersion-shifted fibers designed to have minimum dispersion near 1.55 μm or by limiting the laser spectrum to a single longitudinal mode. dispersion-shifted fibers：色散位移光纤 spectrum ：光谱 通过使用在1.55 μm 附近色散最小的色散位移光纤，或者将激光器的光谱限制为单纵模， 来解决色散问题。 The repeater spacing can be increased by making use of a homodyne or heterodyne detection scheme be