一、引言国际上,光纤通信技术的发展十分迅速,正处于广泛普及应用阶段。近几年来,光纤通信在国内也得到了很大的重视和一定的发展,我国铁路不久将在长途通信网中采用这一新技术。铁路是国民经济的大动脉,是遍及全国的巨型联动机,具有高度集中、半军事性、各个工作环节紧密联系并协同动作的特点。为使各部门、各单位、各工种安全、准确、迅速、协调地进行生产活动,铁路长途通信 I. INTRODUCTION In the world, the development of optical fiber communication technology is very rapid and it is in the stage of widespread popularization and application. In recent years, optical fiber communications in the country have also received great attention and some development, our railways will soon adopt this new technology in long-distance communications networks. The railway is the main artery of the national economy and a giant linkage engine all over the country. It is highly centralized and semi-military and closely linked and coordinated in all aspects of its work. In order to enable all departments, units and all kinds of work to carry out safety, accurate, prompt and coordinated production activities, long-distance railway communications