Polarization-Independent Narrowband Terahertz Filter Based on All-Dielectric Metasurfaces

All-dielectric metasurfaces, which are periodic 2D gratings on slab waveguides, are designed to obtain angular-dependent polarization-insensitive guided-mode resonance filters operating in the terahertz region. The effect of the metasurface grating periods along the x- and y-axis on the filter's performance is systematically studied via the rigorous coupled-wave analysis method. When the grating periods along the x-axis are 380 mu m, 400 mu m, and 420 mu m, the polarization-independent resonances of the split bands occur at 0.517 THz, 0.498 THz, and 0.481 THz, respectively. When the grating periods along they-axis are adjusted to the above values, such polarization-independent resonances show good robustness, which means the polarization-independent resonance frequency of the split bands is mainly determined by the grating periods along the x-axis and is in an inverse proportion. Meanwhile, there are additional polarization-independent resonances formed by the intersection of the split and degenerate bands for the two unequal grating periods. This kind of component provides potential applications for narrowband filtering in emerging terahertz devices and systems for communication or sensing.