Design of Silicon Nitride Edge Coupler for Monolithically Integrated Laser on Silicon Photonic Circuits With Relaxed Alignment Tolerance and High Efficiency

We propose a bi-layer 5-tip edge coupler in a multilayer silicon nitride-on-silicon (SiN-on-Si) waveguide platform. The coupler is used for the integration between a monolithic 1550 nm laser and a single-mode SiN waveguide. The simulated coupling efficiency is 92.8%. The vertical 1-dB-loss misalignment tolerance is as large as 0.5 μm. Broad 1-dB-drop bandwidth (1338 nm to 1700 nm) and small footprint (total length: 38.2 μm) are achieved simultaneously. A broadband bi-layer SiN-Si adiabatic transition cascaded to the edge coupler is designed to couple the laser power into a single-mode Si waveguide at an efficiency of 90.6%. Low-computation-cost electromagnetic numerical simulation and optimization strategies are applied to improve the reverse design of the complex couplers.