Integrated Optical Coupler With an Arbitrary Splitting Ratio Based on a Mode Converter

Optical couplers with different power splitting ratios are essential building blocks in photonic integrated circuits. We theoretically and experimentally demonstrate a broadband and fabrication-tolerant 1×2 integrated optical coupler with an arbitrary splitting ratio, based on a mode converter (MC). The MC converts the input mode into a targeted output mode with a desired power distribution, which determines the power splitting ratio at outputs. The geometry of the MC is engineered and optimized by using the particle swarm optimization algorithm combined with the finite-difference timedomain method. Couplers with 10/90, 20/80, 30/70, 40/60, and 50/50 splitting ratios are designed and fabricated on the siliconon-insulator platform as representatives, with footprints smaller than 2.75μ m ×18.41μ m. The experimental results show that the ±1 dB bandwidths of these devices are greater than 42 nm around 1550 nm, and the average insertion losses are less than 0.65 dB.