Reflective diffraction gratings employing efficiency enhancement or etch barrier layers

Abstract

A diffraction grating comprises a substrate (with index n) with a surface facing an optical medium (with index n<n), a dielectric or semiconductor layer of thickness t on the substrate surface (with index n≠n), and a set of diffractive elements on the layer (with index n≠n). The diffractive elements comprise a set of ridges protruding into the optical medium, which fills trenches between the ridges, and are characterized by a spacing Λ, a width d, and a height h. Over an operational wavelength range, λ/2n<Λ<λ/(n+n). An optical signal incident on the diffractive elements from within the substrate at an incidence angle exceeding the critical angle, n, n, n, n, Λ, d, h, and t result in wavelength-dependent, first-order diffraction efficiency of the grating greater than a prescribed level over the operational wavelength range for both s- and p-polarized optical signals.