Fig. 1. Structure and cross-section of SiGe grating coupler

Fig. 2. Relationship between coupling efficiency, etch depth, and operating wavelength

Fig. 3. Coupling efficiency spectra of SiGe grating with and without metal reflective layer

Fig. 4. Simulation results of SiGe grating with and without metal reflective layer. (a) Simulated electric field distribution; (b) simulated optical power distribution

Fig. 5. Coupling efficiency spectra of uniform SiGe gratings and two-step apodized SiGe grating

Fig. 6. Relationship between the coupling efficiency of SiGe grating and the thickness of silicon substrate

Fig. 7. Relationship between the etched groove width deviation and coupling efficiency of SiGe grating

Fig. 8. Relationship between the coupling efficiency and material effective refractive index deviation of SiGe grating

Fig. 9. Test results. (a) SEM image of SiGe grating; (b) partially enlarged SEM image of coupled grating; (c) metallographic microscope image of chip backside; (d) partially enlarged metallographic image of bottom metal reflective layer

Fig. 10. Schematic diagram of test device

Fig. 11. Comparison of experimental test and simulation results