Difference between CWDM and DWDM modules

CWDM modules-Coarse Wavelength Division Multiplexer

The figure-1 depicts CWDM based fiber system. As shown it is used to transmit 4 different applications using single optical finer instead of pair of fiber cables. Different applications are using different light wavelengths which helps in multiplexing and de-multiplexing applications at transmit and receive end.

DWDM modules -Dense Wavelength Division Multiplexer


The figure-2 depicts DWDM system consisting of transmitter and receiver parts. Typically DWDM consists of MUX, DEMUX, isolators, circulators, EDFA (Erbium Doped Fiber Amplifier) etc. 
DWDM system basics 

Figure-3 depicts spectrum of CWDM and DWDM technologies. As shown DWDM spectrum will have tighter wavelength spacing between the channels compare to CWDM counterpart. Following table compares the two.

Specifications/Features CWDM DWDM
Full form Coarse Wavelength Division Multiplexing,WDM system having less than 8 active wavelengths per optical fiber Dense Wavelength Division Multiplexing, WDM system having more than 8 active wavelengths per optical fiber
characteristic Defined by wavelengths Defined by frequencies
capacity lower higher
cost low high
Distance short range communication long range communication
Frequencies uses wide range frequencies uses narrow range frequencies
Wavelength spacing more less, hence can pack 40+ channels compare to CWDM in the same frequency range
Amplification light signal is not amplified here light signal amplification can be used here
Drift Wavelength drift is possible Precision lasers are needed to keep channels on the target
Spectrum utilization Breaks the spectrum into big chunks dices the spectrum into small pieces
No. of active wavelengths per fiber Fewer than 8 More than 8