DWDM is an optical multiplexing technology used to increase bandwidth over existing fiber networks. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. The operating window is in the 1600nm wavelength (L-band) which allows Dense Wave Division multiplexing (DWDM) Its is far more complex and expensive than CWDM but running perhaps 80 channels with 0.4nm spacing offers potentially many more depending on the complexity of the equipment.