High-efficiency fiber-chip coupler at 850 nm via an inverse-design-optimized multi-port waveguide structure

Silicon photonics is a key platform for realizing high-density integrated photonic chips for applications in optical interconnects, all-optical computing, and quantum information processing. However, it faces severe mode field mismatch and low coupling efficiency between the on-chip light source and the waveguide structure during integration, especially for short-wavelength light. This work demonstrates a high-efficiency silicon nitride ( Si 3 N 4 ) waveguide-based edge coupler (EC) operating at 850 nm by manipulating the light transmission-mode properties of multi-port waveguide structures and optimizing them via inverse design. Specifically, the simulation and experimental results indicated that the coupling losses were 0.56 and 1.76 dB, respectively, at 850 nm. They are much lower than those of a single waveguide and the traditional inverted-taper EC. This work provides a novel solution to achieve high-efficiency coupling between on-chip Si 3 N 4 waveguides and the light source with a small mode field, laying a solid foundation for increasing chip integration density to meet application requirements in high-precision measurement, high-speed computing, quantum information generation and processing, etc.