Design and demonstration of high efficiency perfectly vertical grating couplers with a random structure.

Utilizing an automated optimization method, we propose a perfectly vertical grating coupler (PVGC) characterized by random structure, superior performance, simplified fabrication process, and increased minimum feature size (MFS). Within the range of MFS from 60 to 180 nm, the optimized PVGC exhibited a simulated coupling efficiency of approximately -2.0 dB at 1550 nm with a 34 nm 1-dB bandwidth.