Resonant-grating reflection extended to wide-band, large-aperture beams by waveguide-mode coalescence.

The resonant reflection of a free-space beam from a slab waveguide grating is rendered high bandwidth and angularly robust by using a bimodal high index waveguide. A deep double-sided corrugation gives rise to the coalescence of the resonant reflection peaks resulting in a top-hat reflection spectrum. A low-cost waveguide technology based on solar cell amorphous silicon is demonstrated in the near infrared in a polarizer application.