1. What is WDM technology?
In the same optical fiber, two or more optical wavelength signals transmit information through different optical channels at the same time, which is called optical wavelength division multiplexing technology, or WDM for short.
2. the working principle of WDM
WDM combines optical signals carrying information but different wavelengths into one beam and transmits them along a single optical fiber; at the transmitting end, they are combined by a multiplexer (also called a multiplexer, MulTIplexer) and coupled to the same optical line. The technology of transmission in a root optical fiber; at the receiving end, the optical signal of various wavelengths is separated by a demultiplexer (also called a demultiplexer or demultiplexer, DemulTIplexer), and then further processed by the optical receiver To restore the original signal.
To put it simply, we can also think of WDM as a road-different types of vehicles flood into this road, and then go on their own after reaching the destination.
The function of WDM is to increase the transmission capacity of optical fiber and improve the utilization efficiency of optical fiber resources.
3. Classification of WDM
Commonly used WDM technologies include CWDM and DWDM
1) CWDM technology
For a WDM system, if you want it to work normally, you obviously need to control the wavelength of each optical signal. If the wavelength interval is too short, it is easy to "crash". If the wavelength interval is too long, the utilization rate is very low.
In the early days, the technical conditions were limited, and the wavelength interval would be controlled within tens of nm. This kind of relatively dispersed wavelength division multiplexing is called sparse wavelength division multiplexing, also called coarse wavelength division multiplexing, which is CWDM (Coarse WDM)
The initial wavelength range of CWDM is 1270nm to 1610nm, the wavelength interval is 20nm, and there are 18 bands. In order to distinguish between CWDM wavelength and conventional wavelength, the International Telecommunications Union changed it and shifted the channel center by 1nm, so the center wavelength is 1271nm to 1611nm. Because there is a significant increase in attenuation in the 1270-1470nm band, many old-type optical fibers cannot be used normally, so the preferred wavelength of CWDM is only 1471nm-1611nm, with 8 bands.
2) DWDM technology
The technology is more and more advanced, and the wavelength interval is getting shorter and shorter. When it reaches the level of a few nm, it becomes a compact WDM, called dense wavelength division multiplexing, also called subdivided wave multiplexing, which is DWDM (Dense WDM).
The wavelength interval of DWDM can be 1.6nm, 0.8nm, 0.4nm, 0.2nm and can accommodate 40, 80, 160 waves.
The wavelength range of DWDM is 1525nm to 1565nm (C band) and 1570nm to 1610nm (L band). DMDM is commonly used in the C band, with a wavelength interval of 0.4nm.
4. the difference between CWDM and DWDM
1) Wavelength interval:
CWDM 20nm
DWDM 0.2nm 0.4nm 0.8nm 1.6nm
2) Wavelength range:
CWDM 1270nm-1610nm commonly used 1470nm-1610nm
DWDM 1525nm-1565nm (C band) 1570nm-1610nm (L band) commonly used 1525nm-1565nm (C band) wavelength interval 0.4nm
3) Number of bands:
CWDM 18
DWDM 40 pieces 80 pieces 160 pieces
4) Application difference:
In long-distance optical transmission networks, the application of wavelength division transmission equipment is particularly important. DWDM wavelength division multiplexing equipment can complete the transmission task of long-distance, large-capacity long-distance backbone network, some large-capacity metropolitan area network core nodes, telecom 5G, metropolitan area network, backbone network, and some data centers will also apply DWDM technology And equipment. Compared with DWDM, the cost of CWDM will be much lower, mainly used in the access layer of the metropolitan area network, enterprise network, campus network, etc. The CWDM technology has a wide range of applications for upgrading the existing network architecture, which greatly saves users the cost of upgrading the network.
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