Adiabatic and Multimode Interference Couplers on Silicon-on-Insulator

Adiabatic and multimode interference (MMI) 3-dB couplers based on silicon-on-insulator rib waveguides were fabricated and measured. For testing purposes, pairs of identical couplers were cascaded to form Mach-Zehnder interferometers. The adiabatic couplers showed excess on-chip loss of ~0.5 dB, extinction ratio (ER) of 15-20 dB, and a wide spectral range. The MMI couplers processed on the same wafer showed similar loss per coupler, higher ER, and limited spectral characteristics