专业英语-光通信.pdf

Part 5 Optical Fiber Communications 光纤通信 Optical Communication System In an optical communication system, information is transmitted by light propagation inside an optical fiber in the form of a coded sequence of optical pulses. The signal weakens during propagation because of fiber loss. After some distance it becomes necessary to regenerate the signal through the use of a repeater (essentially a detector-amplifier-transmitter combination). System cost considerations require that the repeater spacing L, be as large as possible. 在光纤通信系统中，信息以编码光脉冲序列的形式在光纤中传 播。因为光纤中存在损耗，信号随着传播而逐渐变弱，所以传播一 定距离之后必须用中继器（本质上由探测器-放大器-发射器组成） 重建信号。出于对系统成本的考虑，这个中继间距L要求越大越好。 Optical Communication System Another consideration is related to the transmission capacity as determined by the bit rate, B (number of bits transmitted per second). The objective of many lightwave transmission systems is to maximize the bit rate-distance product, BL. The bit rate is limited inherently by chromatic dispersion in the fiber, which is responsible for the broadening of optical pulses during their propagation inside a single-mode fiber. The choice of the operating wavelength is therefore related to the loss and dispersion characteristics of the fiber. （光纤系统）另外一个要考虑的因素是其（信息的）传输能力，由 比特率B （每秒传输的比特数）决定。许多光传输系统的目标就是 最大化比特率-距离乘积，（即）BL 。（光纤的）比特率由光纤自 身的色散决定，这是因为色散乃是单模光纤中传输时光脉冲展宽现 象的起因。因此工作波长的选择是与光纤的损耗和色散特性紧密相 关的。 5.1 Development of Optical Communication System The first generation of lightwave transmission systems utilized GaAs lasers operating at a wavelength of about 0.85 m. Relatively high values of the loss and dispersion coefficients restricted the repeater spacing to ~10 km and the bit rate to ~100 Mb/s. 第一代光传输系统采用砷化镓激光器（作为光源），工作在 0.85微米波长，（该波长在光纤中的）损耗和色散系