Recent research progress on cavity-resonator-integrated guided-mode resonance devices

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) consists of a grating coupler (GC) integrated in a pair of distributed Bragg reflectors (DBRs) on a waveguide and can provide a narrow-band reflection spectrum for an incident wave of a small beam diameter from the free space. The DBRs form a cavity resonator. The GC is the reflection aperture for the incident beam. Effects of grating patterns on the reflection efficiency are discussed. One topic is an improvement of profile matching between the field of an incident beam and the coupling coefficient of GC. A GC with nonuniform fill factors was designed and integrated in order to obtain the profile matching with an incident Gaussian beam of about 10-μm diameter. An efficiency improvement was successfully demonstrated. Another is an investigation of a dependence of the reflection efficiency on a phase-adjusting gap between GC and DBR. The gap is determined to give the maximum reflection efficiency. CRIGFs with different gaps were fabricated and the dependence was experimentally measured to show no serious dependence.