Fig. 1. Schematic diagram of grating coupler. (a) Diagram of three-dimensional structure; (b) diagram of x-y cross section

Fig. 2. Light distribution. (a) In the free space; (b) in atmospheric turbulence

Fig. 3. Effect of grating period on coupling efficiency

Fig. 4. Effect of etching depth on coupling efficiency

Fig. 5. Effect of buried oxide thickness on coupling efficiency

Fig. 6. Electric field distribution of the grating coupler at 1550 nm. (a) Without DBR mirror; (b) with DBR mirror

Fig. 7. Comparison of grating coupling efficiency between without DBR mirror and with DBR mirror at different wavelengths

Fig. 8. Process tolerance analysis. (a) Effect of etching width on coupling efficiency; (b) effect of etching depth on coupling efficiency;(c) effect of tilt angle on coupling efficiency