Fiber-to-chip grating coupler on 4H-silicon-carbide-on-insulator platform with high-efficiency

A fiber-to-chip grating coupler for transverse electric (TE) polarization was demonstrated on the emerging 4H-silicon-carbide-on-insulator (4H-SiCOI) platform, with the advantages of high coupling efficiency, low back-reflection to the waveguide, and fabrication simplicity. These performances are enabled by the design combining an apodized diffractive grating with subwavelength gratings and the optimization using an intelligent algorithm. The grating coupler was fabricated via a single-mask process with lithography and etching techniques, and the experimental results demonstrate a peak coupling efficiency of -1.79 dB (66.2%) at 1549.7 nm with a 1-dB bandwidth of 31 nm and a back reflectance below -17 dB (2%) across 1541-1564 nm.