Compact and highly-efficient polarization independent vertical resonant couplers for active-passive monolithic integration

Compact low-loss polarization independent vertical coupling between a 1.55 µm InGaAsP bulk active waveguide and a passive waveguide based on bimodal interference is presented. Simulation results show low coupling loss (<0.1 dB) over coupler lengths more than 5 times shorter than using the adiabatic design. The concept avoids submicron photolithographic features and shows acceptable fabrication tolerances.