Hello,
I want to mention that in conventional DQPSK receivers a pair of onebit delay asymmetric Mach-Zehnder interferometers (AMZI) are used: one for the in-phase (I), and one for the quadrature (Q) component. Similar to binary DPSK3, a narrow optical filter can be used instead of each AMZI 4. The frequency response the optical filters should approximate the main lobe of the frequency response of the constructive port of the AMZI. By tuning the central frequency of the filter either the I or Q component of the DQPSK signal can be demodulated. We will call such a receiver a narrow filter (NF) receiver. We experimentally demonstrate in this paper that a single arrayed waveguide grating (AWG) can be used
to simultaneously demodulate the in-phase (or quadrature) component of a comb of DQPSK signals. It can be seen how the AWG filter approximates the main lobe of the theoretical response of the AMZI. The use of AWGs for WDMDQPSK signals represents a big advantage in terms of component counts.
Hope this helps.
regards