Hengli Feng

This work investigates a switchable terahertz metasurface based on vanadium dioxide (VO ₂ ). Through temperature-induced modulation of the VO ₂ conductivity, reversible switching between broadband absorption and polarization conversion was achieved. The properties of the designed metasurface were analyzed using CST simulations. When VO ₂ is in the metallic phase, the proposed metasurface achieves an absorptivity above 90% over 1.80–4.40 THz, with a corresponding relative bandwidth of 83.9%. Moreover, stable absorption is maintained over wide ranges of polarization angles and incident angles. In the insulating phase, over 1.51–3.86 THz the metasurface achieves a polarization conversion ratio (PCR) above 90%, and a relative bandwidth of 87.5%. The physical mechanism was clarified through equivalent circuit modeling, impedance matching analysis, electric-field distributions, phase responses, and surface current characteristics. Owing to its simple configuration and excellent electromagnetic performance, the proposed metasurface provides a promising platform for tunable terahertz absorption, polarization manipulation, and multifunctional integrated devices.

In this work, we propose a novel transformer-based deep learning model for the design of electromagnetically induced transparency (EIT) metasurfaces, which consists of a forward network to predict transmission spectra from structural parameters and an inverse network to retrieve structural parameters from target spectra. To train the model, we generated a dataset of 23,500 samples by automating CST simulations. The well-trained model can predict all seven structural parameters of an EIT metasurface from a given target spectrum within milliseconds, achieving a mean square error (MSE) of 8.49 × 10⁻⁴ at convergence. The mean errors between the predicted data and target parameters remain below 0.25 μm. The relative spectral error (RSE) is employed to evaluate the discrepancy between the spectra from predicted structures and the targets, with a maximum RSE of 0.57%. Benchmarking against two other neural networks confirms the superior predictive capability and accuracy of our model. Furthermore, the method not only streamlines EIT metasurface design but is readily adaptable to diverse metasurface devices across the electromagnetic spectrum, establishing a versatile platform for metasurface inverse design.

In this paper, we propose a dual-channel mid-infrared toroidal metasurface that consists of split equilateral triangular rings. The electromagnetic responses are analyzed by the finite-difference-time-domain (FDTD) method and temporal coupled-mode theory (TCMT). The results show that one channel of the metasurface is insensitive to the polarization angle of the incident light and temperature, while the other channel is sensitive. The reflectance and resonance wavelength can be manipulated by the polarization angle and temperature independently. Based on such a mechanism, we propose metasurfaces for two-bit programmable imaging and thermal imaging. The metasurfaces are believed to have potential applications in information processing and thermal radiation manipulation.

In this paper, a side-coupled triangle cavity in a plasmonic waveguide structure is proposed and numerically analyzed by the finite-difference time-domain (FDTD) method and coupled mode theory (CMT). Triple plasmonically induced transparency (PIT) was achieved when an extra triangle was added into the structure, and the transmission characteristics were investigated. This novel structure has a maximal sensitivity of 933 nm/RIU when used as a sensor and a contrast ratio of 4 dB. Moreover, the tunability of PIT can be realized by filling the nematic liquid crystal (NLC) E7 into the triangles. The refractive index of E7 changes with the applied electric field. Given that E7 is also sensitive to temperature, this structure can be used as a temperature sensor with a sensitivity of 0.29 nm/°C. It is believed that this tunable structure with PIT may have potential applications in highly integrated optical circuits.

A kind of plasmonic structure consisted of an equilateral triangle-shaped cavity (ETSC) and a metal-insulator-metal (MIM) waveguide is proposed to realize triple Fano resonances. Numerically simulated by the finite difference time domain (FDTD) method, Fano resonances inside the structure are also explained by the coupled mode theory (CMT) and standing wave theory. For further research, inverting ETSC could dramatically increase quality factor to enhance resonance wavelength selectivity. After that, a bar is introduced into the ETSC and the inverted ETSC to increase resonance wavelengths through changing the structural parameters of the bar. In addition, working as a highly efficient narrowband filter, this structure owes a good sensitivity (S = 923 nm/RIU) and a pretty high-quality factor (Q = 322) along with a figure of merit (FOM = 710). Additionally, a narrowband peak with 1.25 nm Full-Width-Half-Maximum (FWHM) can be obtained. This structure will be used in highly integrated optical circuits in future.