Wavelength division multiplexing (WDM) refers to the simultaneous transmission of signals of different wavelengths coupled on a single optical fiber. It usually has complex waves and partial waves. The main function of combiner MUX is to transmit multiple signal wavelengths in one optical fiber at the transmitter. The main function of the splitter DEMUX is to separate multiple wavelength signals transmitted in an optical fiber at the receiver. The main purpose of wavelength division multiplexing is to increase the available bandwidth of optical fiber. As a result, wavelength division multiplexing systems are widely used by telecom companies and can be expanded through WDM without the need to lay more optical fibers.
CWDM (Coarse Wavelength Division Multiplexer) is a sparse wavelength division multiplexer, also known as coarse wavelength division multiplexer. DWDM (Dense Wavelength Division Multiplexer) is a dense wavelength division multiplexer.
There is a big difference between CWDM and DWDM in their channel spacing. Channel interval (channel spacing) refers to the difference between the nominal carrier frequencies of two adjacent channels, which can be used to prevent inter-channel interference. The wavelength interval between the channels of CWDM is 20nm, while that of DWDM is 1.6, 0.8 and 0.4 nm (200GHz/100 GHz/50 GHz), which is much smaller than that of CWDM technology. The difference of channel spacing also leads to the difference of bandwidth and capacity that can be carried by CWDM and DWDM. The DWDM module can further improve the system bandwidth and capacity by using closely spaced wavelengths to carry more signals on the same optical fiber.
The biggest advantage of CWDM system lies in its low cost, and the device cost is mainly reflected in filters and lasers. The wide wavelength interval of 20nm also brings the advantages of low technical requirements for laser and simplified structure of optical multiplexer / demultiplexer for CWDM. The structure is simplified and the rate of finished products is increased, so the cost is reduced. The increase in the cost of DWDM is mainly due to the high cost of laser diodes and the cooling laser technology used to maintain wavelength stability.
How to choose the CWDM/DWDM scheme, we should comprehensively consider the needs and budget of the application scene construction according to their respective characteristics and differences to make the optimal scheme.