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

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 standing-wave electric-field (SWEF) can be available due to Bragg reflection in the vicinity of the resonance wavelength.