Fig. 1. Simulation model of grating coupler

Fig. 2. Design flowchart of double-layer etched grating coupler

Fig. 3. Schematic diagram of the change in update rate of cosine reduction attenuation strategy

Fig. 4. 100 sets of initial grating feature size distribution

Fig. 5. Effective grating group count versus iteration rounds relationship

Fig. 6. Final optimization model for double etch grating coupler raster area

Fig. 7. Internal optical field distribution of double etched grating

Fig. 8. Comparison of 2D and 3D simulation coupling efficiency and bandwidth characterization for grating couplers

Fig. 9. SEM image of double etched grating coupler

Fig. 10. Schematic diagram of experimental apparatus

Fig. 11. Experimental coupling efficiency and verification simulation of double-etched grating coupler

Fig. 12. Experimental coupling efficiency and depth error simulation

Fig. 13. Coupling efficiency and width error simulation