How does WDM work?
A WDM system uses a multiplexer at the transmitter to join the several signals together and a demultiplexer at the receiver to split them apart. There are multiplexer(MUX) and demultiplexer(DEMUX). The main function of MUX is to combine multiple signal wavelengths in one fiber for transmission at the sending end. And the main function of the demultiplexer DEMUX is to separate multiple wavelength signals transmitted in an optical fiber at the receiving end.
The main purpose of wavelength division multiplexing(WDM) is to increase the available bandwidth of the fiber. Therefore, wavelength division multiplexing systems are widely used by telecom companies to expand capacity through WDM without laying more fibers.
CWDM, DWDM, CCWDM, How to choose?
CWDM is sparse wavelength division multiplexer, also known as coarse wavelength division multiplexer. CWDM is being used in cable television networks, where different wavelengths are used for the downstream and upstream signals. In these systems, the wavelengths used are often widely separated.
DWDM is dense wavelength division multiplexer. Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities (and cost) of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565nm (C band), or 1570–1610nm (L band).
CCWDM is a mini wavelength division multiplexer, which is a mini version of CWDM. A wavelength division multiplexing technology based on TFF (Thin Film Filter), which works in the same way as CWDM. The difference is that CCWDM uses free space technology, its package size is smaller and the insertion loss is lower. It can replace CWDM products in telecom, enterprise networks, PON networks, TV and other applications.
The main advantage of the CWDM system is the low cost. The device cost is mainly manifested in filters and lasers. The wide wavelength spacing of 20nm also makes CWDM the advantage of low specification of the laser and simplified structure of the optical multiplexer/demultiplexer. The simplified structure and high yield will reduce the cost. The increased cost of DWDM is mainly due to the high cost of laser diodes and the cooling laser technology used to maintain wavelength stability.
CWDM, DWDM and CCWDM are kinds of effective methods to solve the increasing bandwidth capacity needs; but they are designed to meet different network needs.