An accurate analysis for two-mode interferometer based Mach-Zehnder interferometers interleaver

By using a more accurate analysis, we investigate the effect of the mode coupling and radiation loss of a two-mode interferometer (TMI) which is employed in the design of Mach-Zehnder interferometer interleaver by considering different branching angles and index contrasts. Based on our study, we find that the transmission characteristics of a TMI in the interleaver design cannot always be treated as a simple zero gap directional coupler (DC), called pure model. Under certain conditions, its characteristics should be treated as a zero gap DC combined with two variable gap DCs, and correspondently called integrated model. The conditions under which a TMI is treated as pure model or integrated model are defined in terms of branching angle and index contrast. Our findings are confirmed with the experimental results.