High-order modes in cavity-resonator-integrated guided-mode resonance filters (CRIGFs)

Abstract

Cavity-resonator-integrated guided-mode resonance filters (CRIGFs) are optical filters based on weak coupling by a grating between a free-space propagating optical mode and a guided mode, like guided-mode resonance filters (GMRFs). As compared to GMRFs they offer narrowband reflection with small aperture and high angular acceptance. We report experimental characterization and theoretical modeling of unexpected high-order reflected modes in such devices. Using coupled-mode modeling and moiré analysis we provide physical insight on key mechanisms ruling CRIGF properties. This model could serve as a simple and efficient framework to design new reflectors with tailored spatial and spectral modal reflectivities.

Thermally-tunable cavity resonator-integrated guided-mode resonance filters

“…To gain further insight into the characteristics of the device, the reflectivity was mapped as a function of the position along the grating lines with a slightly offset injection (with respect to the center of the CRIGF (y=0)). As in [3], Fig. 6.bottom reveals, on top of the substrate Fabry-Perot fringe pattern (with ~1-nm free spectral range), a multimode response i.e.…”

“…The CRIGFs were designed for operation at a wavelength of 1550 nm using a combination of rigorous coupled-wave analysis [18] and coupled-mode theory [3]. More specifically, the vertical planar waveguide is constituted of a 297-nm-thick X-cut LiNbO3 core surrounded by a [19] with refractive indices taken from references [20,21] and summarized in Table 1.…”

“…1). As such, the overall device operating principle is ruled by the excitation of and emission from supported localized Fabry-Perot modes [3]. The response is thus a fixed-wavelength(s) passband filter in reflection (and a notch filter in transmission) whose peak reflectivity and angular dependence are governed by the overlap between the excitation signal and the localized modes spatial and spectral properties.…”

Second-harmonic-generation enhancement in cavity resonator integrated grating filters

“…Since the mode field envelop is exponentially decreasing inside the DBRs, the electromagnetic energy is localized in the waveguide layer, under the GC. Contrary to the Resonant Waveguide Gratings (RWG), the resonance wavelength of the CRIGF is mainly determined by the modes localized between the DBRs [16]. The GC can be considered as a perturbative outcoupler for these modes and thus must be designed so that its resonant wavelength is close to the cavity mode resonance [17].…”

Tunable graded cavity resonator integrated grating filters

“…GMRFs and CRIGFs both rely on grating coupler (GC) to couple free-space waves to a guided mode inside a planar waveguide and exhibit Fano spectral resonance when Bragg coupling conditions are met. One striking difference is that GMRFs couple to a propagating guidedmode below a large area GC, while CRIGFs couple to a standing-wave guided mode [4,5], localized under a short GC by two side Distributed Bragg Reflectors (DBRs) (see Fig. 1).…”