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与传统的金属或金属传输媒介(对称电缆、同轴电缆、无线中继系统)相比,光纤提供了更宽的传输频带和更长的中继段距离。然而,由于材料色散、模色散以及不可忽视的所用光源的谱宽,这些系统传送的毕特率是有限的。特别是使用发光二极管(LED)和多模光纤的传输系统,不能传送高的毕特率。这种系统可以用在地区网路中(连接用户和交换局)。为了增加地区网的传输容量,必须采用谱宽较窄的激光二极管作为光源。这样也将使它有可能将那些远离交换局的少量用户接入地区网。
Compared with traditional metal or metal transmission media (symmetric cable, coaxial cable, wireless relay system), optical fiber provides a wider transmission band and longer hop distance. However, the bit rates transmitted by these systems are limited due to material dispersion, mode dispersion, and non-negligible spectral width of the light sources used. In particular, transmission systems using light-emitting diodes (LEDs) and multi-mode fibers can not deliver high bit rates. This system can be used in regional networks (connecting users and exchanges). In order to increase the transmission capacity of the regional network, it is necessary to use a laser diode with a narrow spectral width as a light source. This will also make it possible to access a small number of users away from the exchange.