Thin-Film Narrowband Retroreflector Based on Waveguide Grating Structure

A narrowband retroreflection is demonstrated by using a cavity-resonator-integrated guided-mode resonance filter (CRIGF) integrated on a high-reflection substrate for an oblique incidence. A CRIGF consists of a thin-film waveguide and three parts of surface-relief gratings. The middle part of the grating acts as a grating coupler, and both side parts act as distributed Bragg reflectors constructing a waveguide resonator. A CRIGF of 20-μm aperture on a multilayer dielectric mirror is designed and fabricated for the incidence angle of 9° and the operation wavelength of 1540 nm. A narrowband retroreflection of >85% efficiency with 2-nm bandwidth is obtained experimentally.