The synthesis of generalised Mach–Zehnder optical switches based on multimode interference (MMI) couplers

The space-division switching properties of a generalised Mach–Zehnder photonic switch are examined in this paper. It is shown for the first time that such an N × N switch can only produce N independent point-to-point switching states. A method that unambiguously identifies these states and thereby provides a synthesis technique for the design of these switches is presented.