The chiral structures with strong circular dichroism (CD) response and narrow linewidth are desirable in chiral sensing, circularly-polarized light detection, and polarization imaging. Here, we theoretically proposed a hybrid chiral metasurface for differential absorption of circularly polarized light. Based on the multiple resonant modes coupling effect in a two-dimensional dielectric slab, it is realizable then to achieve a nearly perfect absorption for right circularly polarized light and simultaneously reflects 90% of left circularly polarized light, suggesting the generation of strong CD of 0.886 within a narrowly spectral linewidth of 4.53 nm. The multipole analysis reveals that the electric dipole, the magnetic dipole, and the electric quadrupole make dominant contributions to chiral absorption and the high CD response in this metsurface. The excitation of guided mode resonance enhances the ability of this metasurface to absorb electric field. Moreover, the optical chirality response can be further manipulated through the geometry features. These findings pave a powerful way to realize the narrowing and strong CD platform for single-band and multiband chirality behaviors.
We present a high-performance functional perfect absorber in a wide range of terahertz (THz) wave based on a hybrid structure of graphene and vanadium dioxide (VO2) resonators. Dynamically electrical and thermal tunable absorption is achieved due to the management on the resonant properties via the external surroundings. Multifunctional manipulations can be further realized within such absorber platform. For instance, a wide-frequency terahertz perfect absorber with the operation frequency range covering from 1.594 THz to 3.272 THz can be realized when the conductivity of VO2 is set to 100000 S/m (metal phase) and the Fermi level of graphene is 0.01 eV. The absorption can be dynamically changed from 0 to 99.98% and in verse by adjusting the conductivity of VO2. The impedance matching theory is introduced to analyze and elucidate the wideband absorption rate. In addition, the absorber can be changed from wideband absorption to dual-band absorption by adjusting the Fermi level of graphene from 0.01 eV to 0.7 eV when the conductivity of VO2 is fixed at 100000 S/m. Besides, the analysis of the chiral characteristics of the helical structure shows that the extinction cross-section has a circular dichroic response under the excitation of two different circularly polarized lights (CPL). Our study proposes approaches to manipulate the wide-band terahertz wave with multiple ways, paving the way for the development of technologies in the fields of switches, modulators, and imaging devices.
We successfully achieved high-Q dual-band quasi-bound states in the continuum (BICs) by introducing geometrical perturbations and thermally induced material perturbations into silicon half-disk nanodimers. Importantly, it is found that the Q factor obtained from the thermally induced material perturbations fits better with the inverse quadratic function of the asymmetry relation than that of the geometrical-perturbations-based system. Notably, we demonstrated that changes occurring at the sub-K scale can enable the simultaneous realization of the full width at half maximum offset distance for quasi-BICs and a maximum contrast ratio exceeding 44 dB. Our research provides novel, to the best of our knowledge, insights for potential applications in nano-lasers, temperature sensors, and infrared imaging.
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