Nanomembrane blazed grating coupler for vertical fiber-chip interface

Mid-infrared (mid-IR) silicon photonics holds promising applications for the Internet of Things, LiDAR, and optical communications. Perfectly vertical grating couplers are superior mid-IR light coupling techniques, featuring ease of packaging, positioning flexibility, and mass production scalability. However, high-efficiency mid-IR perfectly vertical grating couplers still need to be developed due to the difficulties of efficiently engineering grating directionality and diffracted light at long wavelengths. In this paper, we present a mid-IR nanomembrane blazed grating coupler with segmented structure engineering based on a standard multi-project wafer service. The method is based on exploring the improvement of the grating directionality and modal overlap by combining grating units with different structures and thicknesses. Experimental results showcase a maximum coupling efficiency of −4.4 dB with a 3-dB bandwidth of ∼70 nm at 2100 nm wavelengths. This study contributes to the strategy of designing exceptional grating couplers with multiple functional units, paving the way for developing mid-IR photonic integrated circuits based on silicon photonics foundries.