OADMs provide the functionality to drop and add a certain number of wavelengths at an intermediate location where access to all the propagating optical channels is not required between WDM transmission terminals. The conventional OADM is based on the cascaded demux/mux configuration
but it requires a lot of equipments
is difficult to manage
and is very costly. The AWG-based OADMs use one AWG as both multiplexer and demultiplexer. Two types of such configurations
loop-back configuration and fold-back configuration