Resonant Waveguide - Grating Structures

Abstract

Under certain conditions, a resonance phenomenon can occur in waveguide-grating structures. Such structures have multilayer configuration, the most basic of which is comprised of a substrate, a thin layer dielectric or semiconductor waveguide layer, and an additional transparent layer in which a grating is etched. The resonance phenomenon is based on the interaction of light diffracted by the grating and light propagating through the waveguide. Specifically, when such a structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is trapped in the waveguide layer. Some of the trapped light is then rescattered outwards, so that it interferes destructively with the transmitted part of the light beam. At a specific wavelength and angular orientation of the incident beam, the structure “resonates”; namely, complete interference occurs and no light is transmitted. The bandwidth of the resonance is based on several parameters, such as the grating depth and duty cycle, as well as the thickness of the waveguide layer.