Design and fabrication tolerance analysis of multimode interference couplers

This paper examines the sensitivity of InP multimode interference couplers (MMIs) to fabrication errors caused by over or under exposure during device processing. MMIs are modelled using modal propagation analysis, which provides a rapid means of simulating the performance of such couplers across a large design space with varying structural parameters. We show for the first time that when MMIs are anlaysed with fabrication errors in mind, there exists an optimal set of design parameters for a given input waveguide width which offer the best tolerance to fabrication errors while maximising optical throughput and ensuring compact size. Such MMIs are ideally suited for use in photonic integrated circuits, where robust performance and smallest possible device footprint are required.