The primary difference between DWDM and CWDM is the channel spacing (CWDM has almost 100 times wider channel spacing) and the required frequency stability. Due to wider CWDM channels, the number of channels (lambdas) available on the same link is significantly reduced, but the optical interface components do not have to be as precise as DWDM components. CWDM equipment is thus significantly cheaper than DWDM equipment.
Please note that relaxed frequency stability might preclude the use of optical amplifiers, limiting the total CWDM optical span to tens of kilometers.
This was first published in March 2010