In the past 20 years, the development of optical fiber communication has exceeded people's imagination, and optical communication network has also become the basic platform of modern communication network. The optical fiber communication system has gone through several stages of development. From the PDH system in the late 1970s, the SDH system in the mid-90s, and the recent surging DWDM system, to the future intelligent optical network technology, the optical fiber communication system itself is rapidly being updated.
Wavelength division multiplexing technology has appeared since the emergence of optical fiber communication. In the late 1980s and early 1990s, Dr. Dingyi Li (TYLee) of AT&T Bell Labs strongly advocated the technology of wavelength division multiplexing (DWDM), two-wavelength WDM (1310/ 1550nm) The system was used in the American AT&T network in the 1980s at a rate of 2×1.7Gb/s. But by the mid-1990s, WDM system development speed was not fast, the main reasons are:
(1) TDM (time division multiplexing) technology development, 155Mb/s-622Mb/s-2.5Gb/s TDM technology is relatively simple. According to statistics, below 2.5Gb/s system (including 2.5Gb/s system), every time the system is upgraded, the transmission cost per bit drops by about 30%. Because of this, in the past system upgrades, people first thought of and adopted TDM technology.
(2) Wavelength division multiplexing devices are not yet fully mature. Wavelength division multiplexers/demultiplexers and optical amplifiers only began to be commercialized in the early 1990s.
The main reasons for the rapid development of DWDM are:
(1) TDM10Gb/s is facing the challenge of electronic components, and the use of TDM is increasingly approaching the limit of silicon and gallium arsenic technology. TDM has not much potential to tap, and the price of transmission equipment is also very high.
(2) The high dispersion of the G.652 fiber 1550nm window that has been laid has limited the transmission of the TDM10Gb/s system, and the influence of fiber chromatic dispersion and polarization mode dispersion is increasing. People are increasingly shifting their interest from electrical multiplexing to optical multiplexing, that is, using various multiplexing methods in the optical domain to improve transmission efficiency and increase multiplexing rates. WDM technology is currently the easiest to be commercialized. Optical multiplexing technology.
(3) The rapid development of optoelectronic devices. In 1985, the University of Southampton in the United Kingdom first developed a bait-doped fiber amplifier. In 1990, Pirelli developed the first commercial fiber amplifier (EDFA). The maturity and commercialization of EDFA made WDM technology long-distance transmission possible.
From a technical and economic point of view, DWDM technology is currently the most economical and feasible means of capacity expansion.
