Fabrication-friendly high-efficiency silicon nitride grating coupler

Grating coupler, as one of the key components can provide convenient on-wafer testing and packaging for integrated photonics. Silicon nitride (SiNx) grating coupler suffers from lower efficiency due to the relative low material refractive index. The efficiency of SiNx grating coupler can be improved by using high reflectivity silicon grating reflectors underneath. However, such silicon grating reflector requires several fabrication steps, including lithography, etching, high precision alignment (HPA), and chemical mechanical polishing (CMP). In this work, we demonstrate an easy-to-fabricate SiNx grating coupler only requiring a single patterning step without the need of HPA and CMP. A coupling coefficient of −2.5 dB and 1-dB-bandwidth of 65 nm have been experimentally measured.