Patent ID: 8593732

Claim:
A diffraction grating comprising: a substrate comprising a first dielectric or semiconductor material substantially transparent over a range of operational wavelengths λ with a refractive index n 1 , and having a first surface facing an optical medium with a refractive index n 2 that is less than n 1 ; a set of diffractive elements formed on the first surface of the substrate, wherein the diffractive elements comprise a set of protruding ridges separated by intervening trenches characterized by a ridge spacing Λ, a ridge width d, and a ridge height h; and a metal layer on a to surface of each ridge characterized by a thickness t, wherein: at least a portion of a bottom surface of each trench is substantially free of metal; λ/2n 1 <Λ<λ/(n 1 +n 2 ) over the operational wavelength range; and n 1 , n 2 , Λ, d, h, and t result in wavelength dependent diffraction efficiency over the operational wavelength range for s- and p-polarized optical signals wherein (i) a minimum of the p-polarized diffraction efficiency substantially coincides with a maximum of the s polarized diffraction efficiency or (ii) a maximum of the p-polarized diffraction efficiency substantially coincides with a minimum of the s-polarized diffraction efficiency, so that overall diffraction efficiency is polarization selective over the operational wavelength range for an optical signal incident on the diffractive elements from within the substrate at an incidence angle θ in that exceeds a critical angle θ c =sin −1 (n 2 /n 1 ).