Dual-frequency switchable bandpass filter in the terahertz range based on enhanced trapped-mode resonances

Abstract

We propose a high-quality and mechanically tunable dual-band narrow bandpass filter working in the THz range. Its high transmittance and modulation depth are verified both by simulations and experiments. The proposed design consists of two metasurfaces with concentric fabricated meta-atoms back-to-back on the two sides of a thin polyimide layer. When the polarization of the incident THz waves changes from y to × direction, the modulation depth of transmittance monotonically changes from 95.46% to a few percent at the resonance frequencies of 0.481 THz and inversely varies from a few percent to 97.62% at the resonance frequency of 0.931 THz. The analysis of in-plane and inter-planar distributions of induced surface current reveals that the narrow bandpass response is attributed to the excitation of “trapped mode”. The induced antiphase current excitation between the two metasurfaces not only lower the dipole moment but also weakly couple to external electromagnetic fields, consequently, leading to the high transmittance and narrow bandwidth. These features of such a simple device potentially can contribute to the design of much more advanced THz modulators and other THz applications in the future.