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

have been proposed in this paper.