Basic Structure of WDM System
The WDM system mainly consists of five parts: optical transmitter, optical receiver, optical relay amplifier, optical supervisory channel and network management system. WDM system total structure diagram
Optical transmitter is the core of the WDM system, according to the ITU-T recommendations and standards in addition to the WDM system transmitting laser central wavelength of special requirements, but also based on the WDM system for different applications (mainly the transmission fiber types and transmission distance) to select certain dispersion capacity transmitter. At the sending end will first from the terminal equipment ( such as SDH terminal ) to output optical signals, using optical transponder ( OTU ) to meet the ITU-TG.957 suggest a specific wavelength of light signal is converted into a stable optical signal of the particular wavelength; synthesis using multiplexer optical signal, the optical power amplifier ( BA ) amplified output optical signal.
After long distance transmission ( 80 ～ 120km), the need for light signal light amplifying relay. Current use of optical amplifier for erbium doped fiber amplifier ( EDFA ), in the WDM system must use the gain flattening technology, make EDFA at different wavelengths of the optical signal having the same amplification gain. At the same time, also need to take into account the different number of optical channel while working in a variety of circumstances, can ensure the optical channel gain competition does not affect the transmission performance. In application, according to the specific circumstances, will be used for EDFA line amplifier ( LA ), power amplifier ( BA ) and preamplifier ( PA ).
At the receiving end, the optical preamplifier amplified transmission and attenuation of the main optical signal, the divider from the main optical signal into optical signal of the particular wavelength. The receiver should not only satisfy the general optical receiver sensitivity of optical signals, the parameters such as overload power requirements, but also can withstand a certain noise signal, by enough power bandwidth performance.
Optical supervisory channel is the main function of monitoring system in each channel transmission. At the sending end, is inserted into the node generates a wavelengthλ s ( 1510nm ) of the optical supervisory signals, and the main channel of the optical signal output; at the receiving end, the received optical signal wave, respectively output aλ s (1510nm ) wavelength of the optical monitoring signal and traffic channel signal. Frame sync byte, byte and the official network overhead bytes are transmitted through the optical supervisory channel.
The network management system through the optical supervisory channel transport overhead bytes to other nodes or from other nodes receive the overhead bytes for WDM system management. Realization of configuration management, fault management, performance management, security management and other functions, and the upper layer management system interconnection.