Large incident angle tolerance of guided-mode resonant gratings by light coupling via waveguide end faces

By designing and fabricating appropriate structures, guided-mode resonant gratings can be used as optical filters to attain extremely narrow bandwidths. This high performance makes it difficult to couple light into a waveguide via the grating, which demands extremely high mechanical accuracy to adjust the incident conditions. This paper shows both numerically and experimentally that the incident angle tolerance is significantly wider when the incident light is coupled into the waveguide through an end face rather than via the grating.