A tunable wideband terahertz absorber based on vanadium dioxide (VO2) has been proposed, and its optical characteristics have been studied. The absorber structure is comprised of three layers, which includes a VO2 metasurface layer, a silicon dioxide (SiO2) dielectric layer, and a gold substrate. The structure of this VO2 metasurface consists of symmetrically distributed square perforated VO2 resonators with circular holes, with a relative dielectric constant δ < 3.8 for the SiO2 dielectric layer and a conductivity 4.56 105 S/m 5 ≥ for the gold substrate. We studied the optical characteristics of the absorber through simulations and theoretical calculations employing the Finite-Difference Time-Domain (FDTD) technique. It was found that, while the VO2 is in the metallic phase, the absorber demonstrates a superior absorption spectrum, achieving a high absorptivity of 90% across a frequency range from 2.2 THz to 4.0 THz, with the absorption bandwidth reaching up to 1.8 THz. The absorptance for two peaks at 2.7 THz and 3.4 THz reaches 99% and 100%, respectively. When VO2 transitions to its dielectric state, its absorptance can be adjusted in a dynamic manner from 100% to 20%, achieving almost perfect amplitude modulation. The physical mechanism of wideband absorption is elucidated using electric field distribution and tunable absorption is verified using impedance matching theory. Besides, it displays insensitivity to variations in the angle of incident light polarization and maintains absorption stability under oblique incidence. This absorber exhibits excellent absorption performance, and the research and application of terahertz devices have opened up new frontiers.
Recent research in all-dielectric asymmetric metasurfaces has demonstrated the capability to generate highly sharp Fano resonances, offering bright prospects for applications in optical biosensing. This work proposed a Fano Resonance in Near-Infrared Metasurface based on Asymmetric All-Dielectric Cylindroids. Each unit of the metasurface consists of two all-dielectric Si elliptical cylinders with different short-axis lengths arranged on top of an MgF2 dielectric layer. By employing the Finite-Difference Time-Domain (FDTD) numerical analysis method, we investigate the optical characteristics of the metasurface. We found that when the semi-minor axis of the asymmetric cylindroids are 0.1μm(w1) and 0.094μm(w2), the metasurface exhibits a sharply narrow Fano resonance peak at λ=1.013μm, with a reflection intensity exceeding 92% and a Q-factor as high as 580. Which works at near-infrared region. The physical mechanism of the metasurface is the principle of electromagnetic coupling. The simulation results indicate that the Fano resonance arises from the interference of two distinct electric quadrupole modes. Moreover, the results demonstrate that the sensor exhibits a sensitivity of up to 85 nm/RIU, thereby validating its potential applications in areas such as biosensing and refractive index sensing.
In recent years, MXene materials have found great applications in fields such as photonics and nonlinear optics due to their special physical properties. Here, the non-linear absorption properties of vanadium carbide/silver (V2C/Ag) nanoparticle composites at different wavelengths (450-600 nm) are investigated using Z-scan techniques. Experimental and computational results show that the material has strong saturable absorption (SA) properties, and the SA intensity increases with decreasing wavelength. This research provides new applicable materials for laser technology.
In this paper, a dynamically tunable terahertz absorber is proposed. The absorber consists of a gold thin film, TOPAS and a graphene patterned structure. The absorption properties of the structure was investigated theoretically by using Time-Domain Finite-Difference (FDTD) method. The results show that the absorber can achieve a broadband and a narrowband absorption. Additionally, the amplitude of the two absorption bands can be adjusted. By adjusting the Fermi Energy (EF) of graphene from 0.1 eV to 1.2 eV, the absorbance of broadband absorption can change from 72% to 95%, and the absorbance of narrowband absorption changes from 40% to 97%. The design provides a new avenue for the development of terahertz absorption and modulation devices.
We propose a metal-insulator-metal (MIM) waveguide structure in which the plasma-induced transparency (PIT) effect is based. Using the finite-difference in time domain (FDTD) method, the designed structure was simulated in two dimensions. It obtains both narrowband PIT peaks, both with more than 90% absorption. In addition, we use the Kerr material filled in the cavity for tuning, and we can find that the transmission spectrum shifts with increasing pump light intensity. The proposed structure can be applied to filter. The proposed structure has important prospects for application in integrated optical devices.
A metasurface polarization conversion device is proposed by etching a specially shaped hole in the center of a single disk of graphene. The polarization converter can achieve the cross-polarization conversion function from x to y in the midinfrared band, with three polarization conversion rate peaks and a maximum conversion efficiency of more than 98%. By adjusting the chemical potential of graphene, the operating frequency can be dynamically adjusted to ensure that the conversion efficiency of two operating bands is above 90% and that of three operating bands is above 80%. Based on the above performance, the designed polarization conversion device can be potentially applied in the field of optical polarization control.
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