Thermally compensated optical diffraction gratings

Abstract

An optical diffraction grating includes a substantially transparent grating substrate which has substantially flat first and second surfaces, and a set of grating lines on the first surface characterized by a grating spacing Λ. The grating substrate has a temperature-dependent refractive index nand is immersed in a medium having a temperature-dependent refractive index n. The first and second substrate surfaces are non-parallel and form a dihedral angle α. The gratings lines are substantially perpendicular to a plane of incidence defined by surface-normal vectors of the first and second surfaces. Variation of a diffraction angle θwith temperature, exhibited by the optical diffraction grating at a design wavelength λ and at a design incidence angle θin the plane of incidence, is less than that variation exhibited by a reference diffraction grating that has parallel first and second substrate surfaces but is otherwise identical to the optical diffraction grating.