The English full name of WDM is Wavelength Division Multiplexing. WDM technology is a relatively advanced optical fiber communication technology, called optical wavelength division multiplexing technology. It is a technology that combines multiple optical signals with different wavelengths and different speeds in different optical channels through a combiner and couples them to the same optical fiber for data transmission.
Two-way WDM means that the optical path achieves transmission in two different directions on an optical fiber at the same time, and the wavelengths used are separated from each other to achieve full-duplex communication between the two parties. The WDM system generally consists of four parts: optical transmitter, optical relay amplifier, optical receiver, and optical monitoring channel. In the entire WDM system, the optical wavelength division multiplexer and demultiplexer are key components in the WDM technology, and their performance is decisive for the transmission quality of the system. The device that combines signals of different light source and different wavelengths and outputs them through a transmission fiber is called a multiplexer; conversely, the device that separates the multi-wavelength signals sent from the same transmission fiber into individual wavelengths and outputs them separately is called a demultiplexer. In principle, the device is bidirectional and reversible, that is, as long as the output and input ends of the demultiplexer are used in reverse, it is a multiplexer. The performance indicators of the optical wavelength division multiplexer mainly include access loss and crosstalk. The loss and frequency deviation are required to be small, and the access loss should be less than 1.0～2.5db. The crosstalk between channels is small, the isolation is large, and the influence between signals of different wavelengths is small.
Wavelength × frequency = speed of light (constant value), so wavelength division multiplexing is actually frequency division multiplexing. Optical wavelength division multiplexing includes frequency division multiplexing and wavelength division multiplexing. There is no obvious difference between optical frequency division multiplexing (FDM) technology and optical wavelength division multiplexing (WDM) technology, because light waves are part of electromagnetic waves, and the frequency and wavelength of light have a single correspondence relationship. At the receiving end, these combined signals of different wavelengths are separated, and further processed, and the original signals are recovered and sent to different terminals. Therefore, this technology is called optical wavelength division multiplexing, or WDM for short.