Loss analysis of a grating coupler for single-mode fiber coupling into an SOI waveguide.

Silicon-on-insulator (SOI) technology is widely used in silicon photonic integrated circuits. How to improve the coupling efficiency of the light coupling in free space and optical fibers into waveguides on SOI must be discussed. Grating coupling is a commonly used and highly efficient coupling method. This article discusses the causes of loss in grating couplers from three aspects: transmission, reflection, and mode mismatch, and proposes corresponding loss reduction solutions. The coupling efficiency of Si and SiN grating couplers optimized according to the loss reduction scheme has been improved by 25% and 45%, respectively.