Computational Study of the Coupling Performances for a Long-Distance Vertical Grating Coupler

We present a high-efficiency silicon grating coupler design based on a left–right mirror-symmetric grating and a metal mirror. The coupler achieves nearly perfect 90-degree vertical coupling. When two SOI chips are placed face to face with a vertical working distance of 50 μm, the chip-to-chip interlayer coupling efficiency reaches as high as 96%. When the vertical working distance ranges from 45 μm to 55 μm, the coupling loss remains below 1 dB. We also verified the effectiveness of our designed vertical coupler through 3D FDTD full-model simulation. The results demonstrate that our proposed vertical coupling structure represents a high-efficiency solution for 3D optical interconnects. The integration of multiple photonic chips in a 3D package with vertical optical and electrical interconnects is also feasible in the foreseeable future.