Cavity-resonator-integrated guided-mode resonance filters

A cavity-resonator-integrated guided-mode-resonance filter (CRIGF) consisting of a grating coupler (GC) and a pair of distributed-Bragg-reflectors (DBRs) on a thin-film dielectric waveguide is reviewed. The CRIGF has been recently proposed by the authors to provide a narrow-band reflection spectrum for an incident wave of a small beam width from the free space. A newly developed analysis model for device design with performance simulation is introduced. Curved gratings are utilized to construct a resonator for a small-aperture CRIGF. Design, fabrication and characterization of CRIGFs of 10 mu m aperture are described with a resonance wavelength of 850 nm. A Ge:SiO2 guiding core layer was deposited on a SiO2 glass substrate, and GC and DBRs were formed by the electron-beam direct writing lithography. A normal polarization-dependent CRIGF is shown with a obtained narrowband reflection spectrum of 0.2 nm full width at half maximum. A crossed-CRIGF is also discussed to eliminate the polarization dependence. It is successfully demonstrated that measured reflection spectra for TE and TM incident beams were well coincident with each other.