Fig. 1. Schematic diagram of initialized structure of vertical coupler with metal mirror. (a) Diagram of three-dimensional rendering; (b) diagram of cross section

Fig. 2. Structural change diagrams of vertical coupler in process of optimization. (a) Global optimization; (b) local optimization; (c) binarizated optimization

Fig. 3. Effect of thickness of SiO₂ on coupling efficiency of vertical coupler when central wavelength is 1550 nm

Fig. 4. Final 3D-structure diagram of vertical coupler. (a) without Al mirror; (b) with Al mirror

Fig. 5. Simulation results of vertical coupler in FDTD module. (a) Intensity distributions of optimized layer and output waveguide without Al mirror; (b) intensity distributions of optimized layer and output waveguide with Al mirror

Fig. 6. Loss diagram of vertical coupler

Fig. 7. Loss analysis results of vertical coupler. (a) Loss analysis result of vertical coupler without Al mirror; (b) loss analysis result of vertical coupler with Al mirror

Fig. 8. Simulation result of bandwidth performance of vertical coupler with Al reflected mirror

Fig. 9. Comparison of insert losses of X-polarized and Y-polarized Gaussian beams based on the same device structure

Fig. 10. Fabricated process of vertical coupler with Al mirror

Fig. 11. Tolerance analysis of process errors. (a) Coupling efficiency versus etch depth; (b) Coupling efficiency versus SOI thickness

Fig. 12. Tolerance analysis of test errors. (a) Coupling efficiency versus tilt angle; (b) coupling efficiency versus alignment error