Compact and low loss 90° optical hybrid on a silicon-on-insulator platform

We present a compact and low loss 90° optical hybrid on a silicon-on-insulator (SOI) platform for coherent receiving systems. Our 90° optical hybrid uses a novel topology, comprising one Y-junction and three 2x2 multimode interference (MMI) couplers. The geometry of the 90° optical hybrid is fully optimized using particle swarm optimization (PSO). The fabricated 90° optical hybrid has a compact footprint of 21.6 μm x 27.9 μm, with an insertion loss less than 0.5 dB, a common mode rejection ratio (CMRR) larger than 30 dB, and phase error smaller than 3° in the C-band across 22 reticles on one wafer. The measured phase error (< 3°) in a packaged coherent receiver further confirms the excellent performance of the 90° optical hybrid.