Theoretical Analysis and Design of a High Bandwidth SiNx on SOI Grating Coupler for Telecommunications Application
One fundamental building block of integrated photonics is the fiber-to-chip grating coupler. The grating coupling method is mainly hindered by the vast difference in mode areas between the fiber cable and the waveguide, which causes low coupling efficiency. Other challenges include limited bandwidth, backward scattered light, and mode mismatch. Couplers based on a silicon nitride (SiNx) material platform can achieve wider bandwidths and better coupling efficiency than silicon-based couplers. In this research, we identify methods to increase the 1dB optical bandwidth of a SiNx on silicon-on-insulator (SOI) grating coupler while maintaining a coupling efficiency greater than 40% in efforts to develop a high-capacity grating coupler for telecommunications applications. Methods such as asymmetric grating trenches for low back reflections and optimization of grating dimensions are examined. The optimized structures yielded results up to 28.57 nm for 1dB bandwidth and a maximum coupling efficiency of 49.77%.