MULTIBAND RESONANT GRATINGS

An optical combiner includes a first layer with a periodic arrangement of structures of a material with a first refractive index. A second layer overlies the structures on the first layer, and the second layer includes a material with a second refractive index. A difference between the first refractive index and the second refractive index, measured at 587.5 nm, is less than 1.5. The periodic arrangement of structures is configured such that the optical combiner produces, for an input signal incident on the first layer from air at an oblique elevation angle of greater than 20°, an output signal with three reflection peaks, each reflection peak having an average reflection of greater than 50% within a ± 3° range of the elevation angle.