Main features of WDM technology
1. Make full use of the huge bandwidth resources of optical fibers to increase the transmission capacity of one optical fiber several times to dozens of times compared with single-wavelength transmission, thereby increasing the transmission capacity of optical fibers and reducing costs, which has great application and economic value.
2. Since the wavelengths used in WDM technology are independent of each other, signals with completely different characteristics can be transmitted, the integration and separation of various signals can be completed, and the mixed transmission of multimedia signals can be realized.
3. Since many communications are in full-duplex mode, the use of WDM technology can save a lot of line investment.
4. According to needs, WDM technology can have many application forms, such as long-distance trunk network, broadcast distribution network, multi-channel and multi-location local area network, etc., so it is very important for network application.
5. Use WDM technology to select routes to realize network switching and recovery.
Application of EDFA in WDM System
EDFA can be used as preamplifier, line amplifier and power amplifier in WDM system. When EDFA is used as a preamplifier, it is placed before the optical receiver to improve the sensitivity of the optical receiver. Generally, it works in a small signal or linear state, and the signal input power is about -40dBm. The gain of the EDFA is required to be high enough, and the smaller the noise figure, the better. When EDFA is used as a line amplifier, it can be directly inserted into the optical fiber transmission link as an optical repeater amplifier, eliminating the optical/electrical/optical conversion process of the electrical repeater, and directly amplifying the optical signal to compensate for the loss of the transmission line and extend the Relay distance. Generally work in the near saturation region, the signal input power is about 20dBm. The EDFA is required to have high gain and output optical power at the same time, and it should also have real-time monitoring of its working status. When EDFA is used as a power amplifier, it is installed after the optical transmitter to amplify the optical signal emitted by the light source to compensate for the loss of passive optical components and improve the transmission optical power. Usually work in the deep saturation region, it is required that the EDFA can provide the highest possible output optical power while maintaining a moderate gain and noise figure, and double-pumping can be used if necessary.
Requirements of WDM system to EDFA
In order to ensure the transmission quality of the WDM system, the EDFA used in the WDM system should have sufficient bandwidth, flat gain, low noise figure and high output power. 5.1 EDFA Gain Bandwidth
At present, the available gain spectrum range of EDFA is 1530~1565nm, and the gain bandwidth is about 35nm, which can meet the WDM system of 4~32 channels. If it is desired to further increase the bandwidth to utilize wavelength resources, a new type of optical amplifier must be developed.