Since the advent of optical fiber communications, it has brought a revolution to the entire communications field. It enables high-speed, high-capacity communications. Optical fiber communication has been favored by people in the industry due to its advantages of low loss, large transmission bandwidth, small size, light weight, anti-electromagnetic interference, and low crosstalk. The development is very rapid. The transmission capacity of optical fiber communication systems has increased nearly 10,000 times in the 20 years from 1980 to 2000, and the transmission speed has increased by about 100 times in the past 10 years. At present, the proportion of optical fiber for long-haul transmission networks in China has exceeded 80%. It is expected that by 2010 noon, the length of national cable construction will increase by about 105km, and there will be 11 large cities with large-capacity optical fiber communication networks with more than 10G. The development of optical fiber communication depends on the progress of optical fiber communication technology. At present, optical fiber communication technology has made considerable progress, and new technologies have also emerged, which has greatly improved the communication capabilities and has continuously expanded the application range of optical fiber communications. The fiber access network is the "last mile" of the information superhighway. To achieve high-speed information transmission to meet the needs of the public, not only must have a broadband backbone transmission network, the user access part is more critical, fiber access network is the key technology for high-speed information into millions of households. In optical fiber broadband access, because of the different arrival positions of optical fibers, there are different applications such as FTTB, FTTC, FTTCab, and FTTH, collectively referred to as FTTx. At present, the development of inline closure is still at an early stage, but it has shown good development prospects. Judging from the development trend, the formation of a true optical network layer based on WDM technology and optical switching technology, the establishment of a pure all-optical network, eliminating the electro-optical bottleneck has become an inevitable trend in the future development of optical communications, but also the future of information networks The core is also the highest level of communication technology development, and it is an ideal level.