Optimization of Ultracompact Polarization-Insensitive Multimode Interference Couplers Based on Si Nanowire Waveguides

An ultracompact multimode interference (MMI) coupler based on Si nanowire waveguides is optimized to achieve polarization-insensitive performances. According to numerical simulations, an optimal width of the MMI section to achieve a polarization-insensitive performance is obtained for a fixed thickness of the core layer. A polarization-insensitive 1times2 MMI coupler with a size of about 3.8 mum times15.3 mum is designed as an example. Numerical simulations show that this optimized MMI coupler has a good fabrication tolerance (about plusmn45 and plusmn330nm for the MMI width and length, respectively) and the 0.5-dB bandwidth is more than 60 nm for both polarizations