Polarization-independent guided-mode resonance filtering by all-dielectric gratings in the terahertz region.

Abstract

We propose an angular-dependent polarization-insensitive filter in the terahertz (THz) region, based on the guided-mode resonance of one-dimensional zero-contrast grating architectural design. Particle swarm optimization combined with the rigorous coupled-wave analysis method is used to design the filter and investigate the influences of the planes of incidence on the characteristics of the proposed all-dielectric THz filter. With the planes of incidence set at 0°, 30°, 45°, and 60°, the polarization-independent resonances occur at 0.458 THz, 0.459 THz, 0.461 THz, and 0.465 THz under oblique incidences of 9.3°, 10.8°, 13.3°, and 19.2°, respectively, which means the oblique incident angle of the polarization-independent THz filter increases with the rotation of the planes of incidence from classic mounting to fully conical mounting. In addition, for the fully conical mounting case, the resonance has high angular stability and is no longer split, compared with classic incidence; meanwhile, there is only a tiny blue shift in resonance of less than 3 GHz when changing the incident angle from 0° to 10°. The physical mechanism of the spectral characteristics is also analyzed in detail. The spectral properties proposed herein enable significant potential application in the fields of spectroscopy, image sensors, communication, etc., in the THz region.