Enhancement of bandwidth-efficiency capability in apodized grating couplers by improving mode matching at multiwavelengths

Broadband-efficient grating couplers serve as the key bridge connecting fiber and the chip in silicon photonics. Apodized grating couplers (AGC) have already demonstrated with high coupling efficiency, but almost all of them have been designed by only considering of mode matching coupling at single-wavelength, which resulting in a limited coupling bandwidth. Here, a multi-wavelengths mode matching method by calculating the root mean square error of effective-index and leakage-factor is proposed to design AGCs with both an enhancement bandwidth and a high coupling efficiency. Our investigation shows that, compared with the conventional single-wavelength SOI AGC, in an optimized multi-wavelengths AGC, the 3 dB bandwidth could be extended from 60 nm to 88 nm and the coupling efficiency could be enhanced from 67 % to 74 %. Moreover, when a metal reflector at the bottom of the AGC was furtherly adopted, both the 3 dB bandwidth and the coupling efficiency could be enhanced to an even more higher value of 92 nm and 91 % in an optimized multi-wavelengths AGC. These results would provide a new pathway to achieve broadband grating couplers by considering of multi-wavelengths mode matching.