Terahertz high-Q quasi-bound states in the continuum in laser-fabricated metallic double-slit arrays

Abstract

A laser-fabricated metallic resonator based on a double-slit array (DSA) is numerically and experimentally demonstrated at terahertz frequencies. Such free-standing resonators achieve a sharp resonance with high quality (Q) factor, arising from a distortion of symmetry-protected bound states in the continuum (BIC). By breaking the structural symmetry of DSAs, the BIC with infinite Q-factor can be transformed into quasi-BICs, and the Q-factors decrease gradually as the asymmetry parameter increases. We analyzed the influence of the imperfection in experimental samples such as the round edge and the trapezoid shape on the transmission properties of DSAs. Different from the DSAs composed of ideal perfect electrical conductors, copper DSAs show lower Q-factor because of the Ohmic loss. The effect of metal thickness on the quasi-BICs for DSAs is also investigated. Results exhibit that thinner resonators can achieve sharper quasi-BICs. These findings suggest that such metallic resonators with high Q-factors have great potential for practical applications in electromagnetic wave filtering and biomolecular sensing.

Terahertz high-Q magnetic dipole resonance induced by coherent Fano interactions

“…[23][24][25]27,28 Note that Liu et al presented a measured Q-factor of 44 lower than the simulated 60.9 due to manufacturing differences, which is under the electrical resonance rather than magnetic resonance. 52 The necessary experimental evidences reasonably support the THz high-Q magnetic dipole resonances induced by coherent Fano interactions, by measuring the fundamental-order magnetic dipole resonance and dominant magnetic dipole response of sample. This would trigger much interest to the THz community on the new approach.…”

Recent Progress of Terahertz Spatial Light Modulators: Materials, Principles and Applications

“…Additionally, researchers are actively exploring new tunable materials and modulation effects. The recent progress of metasurface high-Q resonators governed by the quasi-bound states in the continuum offers a fascinating platform for developing THz SLMs [ 117 , 118 ]. At the same time, the physical mechanism of improving the efficiency [ 119 ] and bandwidth [ 120 , 121 ] of metasurfaces in other applications can be used as a guidance to reduce insertion loss and increase the modulation bandwidth of THz SLMs.…”

High-quality resonances in terahertz composite slabs based on metal gratings

“…TE and TM waves are normal incidents onto the TCSs, whose electric fields are perpendicular to X-and Y-directions, respectively. Figure 1(b) shows the experimental sample of singlelayer metal (copper) gratings with a thickness of 50 µm, which are fabricated by laser processing [26,27]. The sectional view of unit-cell TCSs is depicted in figure 1(c), a MG covered on a dielectric film.…”

“…The resonant mode shows an asymmetric line shape, which is a typical feature of Fano resonance. According to the temporal coupled-mode theory, such Fano resonance results from the radiative coupling between localized SPPs and the waveguide mode can be fitted by [26]…”