WDM is the acronym of Wavelength-Division Multiplexing, it is a technique to carry different wavelengths through a single optic fiber. The system uses one multiplexer at the transmitting end to combine several signals with each other, and a demultiplexer at the receiving end to split the signals apart. According to the differences of channel space, there are mainly two kinds of WDM techniques, one is DWDM (Dense Wavelength-Division Multiplexing), and the other is CWDM (Coarse Wavelength-Division Multiplexing). WDM makes bidirectional communication come ture, which greatly saves the cost of optical fiber.


Coarse Wavelength-Division Multiplexing (CWDM) is an economical technique to save fiber resources through transmitting multiple wavelengths on one optic fiber. Especially, CWDM has the benefit of low cost becuase of its uncooled modulating lazer which only consumes 0.5w power. The cost of CWDM system only takes up 30% of the DWDM expense. Thus, CWDM is suitable for the application in short distance, high bandwidth and areas with dense access points. However, the disadvantage of CWDM is that its supportable wavelengths are limited, usually for five or six different optic wavelengths between 1270nm and 1610nm with a 20nm interval.


Dense Wavelength Division Multiplexing(DWDM) is used for carrying multiple optic waves into one single optic fiber. Compared with CWDM, the CWDM possesses a much more dense wavelength intervals which can support up to 80 channels at present. And each channel can carry the 2.5Gbps light signal. Therefore, DWDM maintains a more stable wavelength than CWDM and is available for long diatance optical transmission. But the biggest shortage of DWDM is the high cost of device price and energy consumption, it is not suitable for the use among ordinary people.

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