High efficiency wide band SiNx-on-SOI grating coupler with low fabrication complexity

The chip-fiber grating coupler is a fundamental building block in integrated photonics, providing convenient on-wafer testing and packaging. Couplers based on a silicon nitride(SiNx) material platform can achieve wider band widths than silicon-based couplers, but suffer from lower efficiency due to the relative low material refractive index. The efficiency of the SiNx grating coupler can be improved by using high-reflectivity silicon grating reflectors underneath. However, such as silicon grating reflector requires several fabrication steps, including lithography, etching, high precision alignment (HPA), and chemical mechanical polishing (CMP). In this Letter, we demonstrate an easy-to-fabricate SiNx-on-SOI transverse-electric mode grating coupler requiring only one patterning step (grating alone), and without the need for HPA and CMP. A coupling coefficient of −2.5 dBand1-dB-band width of 65 nm has been experimentally measured.