Angle- and polarization-dependent spectral characteristics of circular grating filters

Polarization-independent all-dielectric guided-mode resonance filter according to binary grating and slab waveguide dimensions

All-dielectric binary gratings, with and without slab waveguides, are designed to generate polarization-independent guided-mode resonance filters (GMRFs) operating in the THz frequency region using the rigorous coupled-wave analysis (RCWA) method. The filling factor and thickness of the grating were adjusted to have equal resonance frequencies of transverse electric (TE)- and transverse magnetic (TM)-polarized THz beams. The single polarization-independent resonance for a binary grating without a slab waveguide was obtained at 0.459 THz with full width at half maximum (FWHM) values of 8.3 and 8.5 GHz for the TE and TM modes, respectively. Moreover, double-layered polarization-independent resonances for binary gratings with slab waveguides were obtained at 0.369 and 0.442 THz with very high Q-factors of up to 284. This is the first study to propose a polarization-independent GMRF with two resonant frequencies.

THz guided-mode resonance notch filter with variable filtering strength

In this paper, we propose a terahertz (THz) guided-mode resonance (GMR) notch filter made of a monolithic polyethylene terephthalate (PET) film, which has a monolayer grating structure. The proposed configuration shows both polarization-dependent and polarization-independent notch filter characteristics for the incident THz wave depending on the rotation angle of the second grating film. When the rotation angle is 0°, the filtering strength (transmittance) at resonance frequency changes from 0.4 (0.996) to 99.0% (0.010) according to the incident polarization. The transmittance continuously decreases with increasing rotation angle until 90°. When the rotation angle is 90°, the transmittance converges to 0.065 (± 0.015) independent of the incident wave polarization. When the incident polarization angle ranges from 90° to 180°, paradoxically, the transmittance through the two GMR grating films is greater than the transmittance through only the first GMR grating film due to the enhancement of the vertical component of the THz wave. These results agree well with a calculation using a polar coordinate system.