Preferential input-waveguide grating couplers: rigorous analysis using the pseudospectral time-domain method

Preferential input-waveguide grating couplers are rigorously analyzed using the pseudospectral time-domain method in the total field/scattered field formulation for TE and TM polarizations in conjunction with the convolutional perfect matching layer approach. Four kinds of preferential input-waveguide grating couplers are studied: the volume holographic grating coupler, the slanted parallelogrammic surface-relief grating coupler, the double-corrugated surface-relief grating coupler, and the reflecting-stack surface-relief grating coupler. Coupler's input coupling efficiencies to various waveguide modes are calculated. In addition, a comparative study of performance is presented in terms of the main design parameters and the operational free-space wavelength.