As AWGs operate reversibly, one device can be used to multiplex a set of inputs or, in reverse, demultiplex a single input. However, in practice, one device cannot be used for both actions at the same time: the wavelengths for upstream and downstream signals are the same and their direction cannot be differentiated. So standard AWGs have to be used unidirectionally, either multiplexing or demultiplexing their designed set of wavelengths, depending on their location within the network.
Another key property of AWGs is that each channel is an image with multiple adjacent diffraction orders that have spacings according to the free spectral range (FSR) of the AWG. In a standard AWG, the FSR is designed to be much larger than the channel envelope, to avoid crosstalk and keep the signal-to-noise ratio high.
We have developed a bidirectional AWG that can exploit the reversible nature of AWGs by using adjacent diffraction orders to carry both upstream and downstream information simultaneously. By reducing the device FSR in a way that enables much closer spacing of the adjacent orders without overlapping, one FSR can be used for downstream and one for upstream. The cyclical nature of the diffraction orders in this class of AWGs lends it the name ‘cyclic’. It enables a single AWG to be used bidirectionally, dramatically reducing the amount of fiber needed for a network and cutting in half the number of AWGs required.