High-performance silicon-on-insulator grating coupler with completely vertical emission

We study the physical concept of utilizing a critical coupling to obtain a high-performance grating coupler with completely vertical emission on a silicon-on-insulator substrate. Following our design strategy, we numerically show that when our grating coupler is coupled to a standard single-mode fiber operating at 1310 nm wavelength, a -1.46 dB coupling loss, a 20 nm spectral full-width-half-maximum, and a -24 dB back reflection can be achieved at the same time without full optimization. A practical design that largely relaxes the stringent lithography requirement is also proposed and presented.