Ultra-Compact Variable All-optical Attenuator Based on Multimode Interference Couplers on an SOI Platform

Abstract—In this paper, two methods for obtaining an ultra compact variable all-optical attenuator based on multimode interference (MMI) using silicon waveguides are proposed. The first method is to use two connected silicon waveguides. The second method is to use a multimode interference coupler. B forming a surface pattern on the top of the MMI region at special positions or on the top of linking waveguides, a variable attenuator is achieved. The device dimension is about 2 μm x30 μm that is the smallest length of an optical attenuator reported up-to-date. Designs of the proposed devices on silicon on insulator (SOI) platform are then verified and optimized using numerical simulation methods.