“…Therefore, for many WDM applications, a flat-top spectral response is desirable. Several flat-top techniques have been proposed, such as using a rectangle multi-mode interference (MMI) coupler [5,6] or a Mach-Zehnder interferometer (MZI) [7] in the input waveguide, parabolic waveguide horn or Y-junction [8], hyper-Gaussian [9], multiple gratings [10], triplexers [11] and so on. Introducing a MMI section at the end of input waveguide is a relatively simple and effective way to obtain a flat-top AWG.…”