Anisotropic guided-wave diffraction by interdigitated electrode-induced phase gratings

Abstract

The diffraction of a pure guided mode in a uniaxial anisotropic slab waveguide by a phase grating which is induced by a voltage applied to interdigitated electrodes over the waveguide is analyzed. A pure guided mode is decomposed into four plane wave components (two ordinary and two extraordinary), which are not phase matched on the boundary between the waveguide and the grating. Thus the diffraction of a pure guided mode may be decomposed into the diffraction of four plane waves. Three-dimensional vector rigorous coupled-wave diffraction analysis of anisotropic gratings with anisotopic external regions is used to treat the diffraction of each plane wave component of the pure guided mode. Geometrical and phase/amplitude requirements are identified for the diffracted waves to constitute a guided mode. Diffracted mode efficiencies and Bragg conditions are calculated. Optic axis orientations for efficient diffraction are identified. Example calculations are presented for lithium niobate waveguide Givens rotation devices, and herringbone multiplier structures including a favorable comparison with experimental results.