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本文根据光纤通信技术的近年进展动向,阐述长途光纤通信系统在设计时应考虑的主要问题。先介绍长途光纤系统的近期打算,说明我国应该尽快建立中距离(500km以下)、中容量(140Mb/s)的光纤数字通信的实验线路,文中扼要提出实验线路的一些主要参数,备供参考和讨论。实验线路将用长波长1.3μm的多模光纤。光源虽可利用长波长激光管,但文中详细阐述LED在长途光纤系统的作用。光检测可采用新型长波长PIN/FET,文中详细阐述长波长光纤系统对APD的要求。这就使我们对长波长、中距离、中容量光纤系统选择光源和光检测器件提供具体论证和根据。关于长期计划,本文先是详细阐述单模光纤系统性能的限制因素,这包括光纤的损耗和色散,激光管的谱宽,模式分隔噪声,模式跳跃的突发误码,以及接收机灵敏度。又说明如何获得最大码速容量和最长中继站间隔,以及利用波分多群复用WDM的条件。其次,本文提出光外差检测和相干通信的探讨。文中回顾数据通信的相干检测,从无线电外差检测谈到光外差检测,又谈到为什么光纤通信要考虑光外差检测,外差检测究竟提高灵敏度多少。最后概述外差检测对激光管频率稳定度和波谱纯度的要求,对光纤偏振的要求,光纤中的非线性,以及光放大器发展的可能性。
In this paper, according to the progress of optical fiber communication technology in recent years, the main problems that should be considered in the design of long-distance optical fiber communication system are expounded. This article first introduces the recent plan of long-distance optical fiber system, which shows that our country should set up the experimental line of optical fiber digital communication with middle distance (under 500km) and medium capacity (140Mb / s) as soon as possible. In this paper, some main parameters of the experimental line are briefly proposed for reference discuss. The experimental line will use long wavelength 1.3μm multimode fiber. Although long-wavelength laser tubes can be used as light sources, the role of LEDs in long-haul fiber systems is described in detail in the text. The new long wavelength PIN / FET can be used for light detection. The article elaborates on the APD requirements of long wavelength fiber systems. This allows us to provide specific proof and basis for the selection of light sources and optical detection devices for long-wavelength, medium-range, medium-capacity optical fiber systems. Regarding long-term planning, this article first details the limitations of single-mode fiber system performance, including fiber loss and dispersion, laser tube spectral width, mode separation noise, mode hop burst errors, and receiver sensitivity. It also shows how to get the maximum code rate capacity and the longest relay station interval, as well as the use of wavelength division multiplexing WDM conditions. Secondly, this paper presents the discussion of optical heterodyne detection and coherent communication. In this paper, we review the coherent detection of data communications, from the detection of radio heterodyne to the detection of optical heterodyne, and also talk about why optical heterodyne detection should be considered in optical fiber communication and how to increase the sensitivity of heterodyne detection. Finally, the requirements of heterodyne testing on the frequency stability and spectral purity of laser tubes, the requirements on optical fiber polarization, the nonlinearity in optical fibers and the development of optical amplifiers are summarized.