WDM is the acronym of Wavelength-Division Multiplexing, it is a technique to carry different wavelengths through a single optic fibre.
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While the two types of wavelength division multiplexing —CWDM and DWDM — are both effective methods to solve increasing bandwidth capacity needs, they are designed to tackle different network challenges.
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).
Coarse Wavelength-Division Multiplexing
Coarse Wavelength-Division Multiplexing (CWDM) is an economical technique to save fibre resources through transmitting multiple wavelengths on one optic fibre. Especially, CWDM has the benefit of low cost because of its uncooled modulating laser 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 CWDM are typically deployed on fibre spans up to 80km or less. Generally, CWDM is used for its lower cost, up to 10G and shorter distance applications where cost is an important factor.
Dense Wavelength Division Multiplexing
Dense Wavelength Division Multiplexing (DWDM) is used for carrying multiple optic waves into one single optic fibre. Compared with CWDM, the DWDM possesses a denser wavelength intervals which can support up to 96 channels. And each channel can carry the 2.5Gbps light signal. Therefore, DWDM maintains a more stable wavelength than CWDM and is available for long distance optical transmission up to 120km. However, typically DWDM has higher cost of device price and energy consumption compared to CDWM.
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CWDM |
DWDM |
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Defined by wavelengths |
Defined by frequencies |
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Short-range up to 80Km |
Long-range up to 120km |
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Uses wide-range frequencies |
Narrow frequencies |
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Wavelengths spread far apart |
Tightly packed wavelengths |
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Wavelength drift is possible |
Precision lasers required to keep channels on target |
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Light signal is not amplified |
Signal amplification may be used |
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Lower Price |
Higher Price |