Guided-mode resonance excitation of waveguide grating at oblique incidence in the non-subwavelength region

Abstract

Guided-mode resonance (GMR) excitation of a waveguide grating at oblique incidence in the non-subwavelength region is investigated using the equivalent homogeneous thin-film model. The nondegenerate resonance locations are obtained and the spectral properties are demonstrated by using the rigorous coupled-wave analysis (RCWA) method based on the calculated parameters. It is shown that the dispersion equation of the slab waveguide can provide a reliable approximation in estimating the GMR locations even in the non-subwavelength region. The nondegenerate resonance in the subwavelength region at oblique incidence can be used to tailor an optical filter with good filtering features. Counter-propagating higher-order evanescent waves in the waveguide layer are possible at oblique incidence in the non-subwavelength region. The energy of the electric-field in the waveguide tends to be concentrated as the resonance wavelength decreases, and the lateral enhancement of the standingwave electric-field (SWEF) can be available due to Bragg reflection in the vicinity of the resonance wavelength.

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“…If the angle of the diffracted mode matches that of the slab waveguide mode, then coupling and strong resonance occur. The condition to trigger GMR is given by the following equation , n 1 ≤ | n 1 sin ⁡ θ i − m λ p | < n avg where n 1 is the refractive index of the incident medium, sin θ i is the incident angle, m is the diffraction mode number, λ is the free space wavelength, p is the period of the filter, and n avg is the average refractive index of the filter. In this research, only the TE mode at normal incidence is considered (sin θ i = 0).…”

“…If the angle of the diffracted mode matches that of the slab waveguide mode, then coupling and strong resonance occur. The condition to trigger GMR is given by the following equation 34,35 n n m p n sin i…”