WDM and DWDM
DWDM (dense WDM) is often talked about when people talk about WDM system. Is WDM the same as DWDM? What are the differences between them? In fact, WDM and DWDM are the same technology. They are the names of WDM system in different development periods, which have close relationship with the development history of WDM technology.
In the early 1980s, at the beginning of optical fiber communication, people thought and first adopted one optical wavelength signal transmission in the two low loss windows 1310nm and 1550nm window, that is, the WDM system with 1310nm/1550nm two wave division, which has practical application in China. The system is simple, generally using the fused WDM device, with small insertion loss; without optical amplifier, on each relay station, both wavelengths are demultiplexed and optical / electrical / optical regeneration relay is carried out, and then reused to the next station. For a long time, WDM system is a system with wavelength interval of tens of nm, such as 1310nm/1550nm two wavelength system (with an interval of more than 200 nm). Because under the condition of that time, it is not possible to realize several nm wavelength intervals.
commercial
With the commercialization of 1550nm window EDFA, WDM system has entered a new period. Instead of using 1310nm window, people only transmit multi-channel optical carrier signal in 1550nm window. Because the adjacent wavelength intervals of these WDM systems are relatively narrow (generally 1.6nm), and EDFA optical amplifiers are shared in a window. In order to distinguish from traditional WDM systems, people call the WDM system with more close wavelength interval as dense WDM system. The so-called density is for the phase to side wavelength interval. In the past, WDM system was a few decades of wavelength interval, which was much smaller, only (0.8-2) nm, even < 0.8nm. In fact, the dense WDM technology is a concrete form of WDM. Because the optical carrier spacing of DWDM is very close, we must choose high resolution WDM devices, such as planar waveguide or fiber grating, instead of using the fused WDM devices.
In DWDM long-distance optical cable system, the multi-channel optical signals with small wavelength interval can share EDFA optical amplifiers. Between the two WDM terminals, one EDFA is used instead of many traditional electrical regeneration repeaters, and the multi-channel optical signal is amplified to extend the optical transmission distance. In DWDM system, EDFA optical amplifier and ordinary optical / electrical / optical regeneration repeater will exist together. EDFA will compensate for the loss of optical fiber, while conventional optical / electrical / optical regeneration repeater is used to compensate for the signal distortion caused by dispersion and noise accumulation.
Essential editor
People like to call DWDM system WDM. In essence, DWDM is only a form of WDM, WDM is more universal, DWDM lacks clear and accurate definition. With the development of technology, it is thought that the so-called dense wavelength interval is also more and more easy to realize in technology, and it has become less "intensive". Generally, if we don't specifically refer to 1310nm/1550nm WDM system, people talk about WDM system as DWDM system.
