Theoretical analysis of simultaneously improving the light coupling efficiency and bandwidth between two separated grating couplers using integrated distributed Bragg reflectors

Abstract

A pair of identical grating couplers can be used to transmit/receive optical signals between vertically separated optical waveguides. We propose a silicon-based grating coupler with an integrated distributed Bragg reflector (DBR) to improve the light coupling bandwidth and efficiency. The optimized grating coupler structure and DBR position were developed using the finite-difference time-domain method. We numerically analyzed the coupling efficiency and bandwidth performance, and the proposed grating coupler structure achieved a theoretical peak coupling efficiency of 0.824 and a 1 dB bandwidth of 157.2 nm at close to 1550 nm, both of which represent improvements of more than two-fold compared with those of conventional grating couplers without a DBR layer.