Cavity-resonator-integrated guided-mode resonance mirror with high-confinement channel structure for improvement of reflectance

A cavity-resonator-integrated guided-mode resonance mirror (CRIGM) consists of a grating coupler integrated in a waveguide cavity formed by a pair of distributed Bragg reflectors (DBRs) on a high-reflectance substrate. It is theoretically predicted that a CRIGM can give interesting characteristics of not only a narrow band-stop reflection spectrum but also flat high reflectance with steep reflection-phase spectrum according to its structure, whereas only a CRIGM with a band-stop reflection spectrum has been confirmed experimentally so far. This time, the cause of undesirable reflectance drop in a CRIGM for flat high reflectance spectrum is investigated theoretically and experimentally. It is theoretically shown that the CRIGM reflectance at the resonance wavelength is affected considerably by a slight reduction of the DBR reflectance. A CRIGM with a rib-structured channel for high lateral confinement is designed and fabricated to keep the DBR reflectance high by suppressing a propagation loss of a guided wave. The improvement of the CRIGM reflection spectrum is confirmed experimentally by measurement of the reflection spectra of the fabricated devices.