Optical wavelength division multiplexing (WDM) technology is one of the effective ways to expand optical fiber communication lines. It entered commercial use in 1997 and is now being widely promoted and vigorously developed. Optical wavelength division multiplexing (WDM) technology uses many other lengths of light as information carriers in a single optical fiber to expand the transmission capacity of the optical fiber. If the transmission rate of one wavelength is 2.5 Gb/s, the capacity of one optical fiber will be increased by 8 times if eight wavelengths are used, and its capacity will be 20 Gb/s. It can be seen that the use of optical wavelength division multiplexing technology can greatly improve the communication transmission rate. The trial phase of point-to-point WDM large-capacity systems has passed, and the phase of large-scale or full-scale adoption of WDM systems has now begun. Developed countries and large companies are planning how to build WDM networks? How many wavelengths to use? What rates to use? How to access and downlink channels? How to protect? How to manage and so on. ITU-T of ITU is also discussing and formulating standards for these issues, which is not perfect.
Development Trends of Optical Fiber Communication:
Since the 21st century, on the one hand, WDM equipment and optical components have become more and more mature, and the technology of WDM+EDFA has gradually penetrated from backbone network to MAN and access network; on the other hand, the development and application of optical cross-over technology (OXC) and optical add-drop multiplexing (OADM) equipment, point-to-point WDM systems are transferring differently to complex optical networks. Evolution of optical networks with wavelength channel, user-oriented and optical routing. However, in order to build a practical high-speed and large-capacity all-optical communication network, three problems need to be solved:
(1) Dispersion accumulation and nonlinearity of optical fibers, crosstalk and noise accumulation of optical signals caused by optical devices in optical fibers, etc.
(2) The problems of high stability integrated light source, integrated detector with adjustable wavelength in WDM equipment, wavelength converter, tunable optical tunable filter and optical cross-connection matrix in OXC and OADM equipment, etc.
(3) Standardization of equipment, interoperability, network management and expensive issues.
2. Wavelength Division Multiplexing Technology
1. Basic concepts and principles of WDM Technology
Wavelength Division Multiplexer (WDM) is a technology that combines two or more optical carrier signals of different wavelengths at the transmitting end with multiplexer (also called multiplexer) and couples them to the same optical fiber of the optical path for transmission. At the receiving end, demultiplexer (also called demultiplexer) combines the two or more optical carrier signals. The optical carriers of various wavelengths are separated and further processed by the optical receiver to restore the original signal. The technology of transmitting two or more different wavelength optical signals simultaneously in the same optical fiber is called wavelength division multiplexing technology. So WDM technology can multiply the transmission capacity without increasing the fiber core. Especially the application of dense wavelength division multiplexing makes the transmission capacity of optical fiber further improved. In principle, wavelength division multiplexing (WDM) can be implemented in low loss windows of optical fibers. However, the current EDFA bandwidth is flat in the range of 1530 nm to 1565 nm, so most of the multiplexing wavelengths are about 1550 nm. ITU-T classifies the available band resources of optical fibers in detail based on the attenuation spectrum of optical fibers