All-dielectric one-dimensional gratings exhibiting Fano resonances in the terahertz region

Transmittance spectra of an all-dielectric sub-wavelength grating exhibiting Fano resonances are studied both experimentally and theoretically for a frequency interval spanning several terahertz using both s- and p-polarized radiation. Modeled spectra based on the rigorous coupled wave analysis are shown to be in good agreement with the Fourier transform of measured time-domain transmission spectra for normal and angled incidence. Finally, a model is presented that explains Fano resonance frequencies by matching the propagation constant of a discrete set of guided modes to wavenumbers that both match diffraction orders in the grating and are in a range that allows propagation in the dielectric medium. (C) 2022 Optica Publishing Group