Reflection optical notch filtering behavior of cavity-resonator-integrated guided-mode resonance mirror

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) consists of a grating coupler (GC) with two distributed Bragg reflectors (DBRs) in an optical waveguide and shows a narrow-band reflection spectrum with a reflection phase variation for a vertically incident wave. A CRIGF integrated on a high-reflection layer (CRIGM) was studied. It is theoretically predicted that a CRIGM shows a notch filtering behavior with a phase variation in the reflection under the condition of the appropriate optical-buffer-layer thickness between the guiding core and the high-reflection layer. A CRIGM of 6-μm aperture was designed with a resonance wavelength of 1540 nm. Eleven CRIGMs with different buffer-layer thicknesses from 5.2 to 5.7 μm were fabricated and their reflection spectra were measured. The reflection phase variation of 2π was observed as expected. A deep drop in reflection spectrum, namely reflection notch filtering, was observed for a CRIGM with a certain buffer-layer thickness.