Jiuxing Jiang

Currently, vortex beams are extensively utilized in the information transmission and storage of communication systems due to their additional degree of freedom. However, traditional terahertz metasurfaces only focus on the generation of narrowband vortex beams in reflection or transmission mode, which is unbeneficial for practical applications. Here, we propose and design terahertz metasurface unit cells composed of anisotropic Z-shaped metal structures, two dielectric layers, and a VO₂ film layer. By utilizing the Pancharatnam–Berry phase theory, independent control of a full 2π phase over a wide frequency range can be achieved by rotating the unit cell. Moreover, the full-space mode (transmission and reflection) can also be implemented by utilizing the phase transition of VO₂ film. Based on the convolution operation, three different terahertz metasurfaces are created to generate vortex beams with different wavefronts in full-space, such as deflected vortex beams, focused vortex beams, and non-diffraction vortex beams. Additionally, the divergences of these vortex beams are also analyzed. Therefore, our designed metasurfaces are capable of efficiently shaping the wavefronts of broadband vortex beams in full-space, making them promising applications for long-distance transmission, high integration, and large capacity in 6G terahertz communications.

In recent years, two-dimensional (2D) halide perovskites have been widely used in solar cells and photoelectric devices due to their excellent photoelectric properties and high environmental stability. However, the terahertz (THz) and ultrafast responses of the 2D halide perovskites are seldom studied, limiting the developments and applications of tunable terahertz devices based on 2D perovskites. Here, 2D R-P type (PEA)₂(MA)₂Pb₃I₁₀ perovskite films are fabricated on quartz substrates by a one-step spin-coating process to study their THz and ultrafast characteristics. Based on our homemade ultrafast optical pump–THz probe (OPTP) system, the 2D perovskite film shows an intensity modulation depth of about 10% and an ultrafast relaxation time of about 3 ps at a pump power of 100 mW due to the quantum confinement effect. To further analyze the recombination mechanisms of the photogenerated carriers, a three-exponential function is used to fit the carrier decay processes, obtaining three different decay channels, originating from free carrier recombination, exciton recombination, and trap-assisted recombination, respectively. In addition, the photoconductor changes (∆σ) at different pump–probe delay times are also investigated using the Drude-Smith model, and a maximum difference of 600 S/m is obtained at τ_p = 0 ps for a pump power of 100 mW. Therefore, these results show that the 2D (PEA)₂(MA)₂Pb₃I₁₀ film has potential applications in high-performance tunable and ultrafast THz devices.

Currently, metasurfaces (MSs) integrating with different active materials have been widely explored to actively manipulate the resonance intensity of multi-band electromagnetic induced transparency (EIT) windows. Unfortunately, these hybrid MSs can only realize the global control of multi-EIT windows rather than selective control. Here, a graphene-functionalized complementary terahertz MS, composed of a dipole slot and two graphene-integrated quadrupole slots with different sizes, is proposed to execute selective and active control of dual-band electromagnetic induced reflection (EIR) windows. In this structure, dual-band EIR windows arise from the destructive interference caused by the near field coupling between the bright dipole slot and dark quadrupole slot. By embedding graphene ribbons beneath two quadrupole slots, the resonance intensity of two windows can be selectively and actively modulated by adjusting Fermi energy of the corresponding graphene ribbons via electrostatic doping. The theoretical model and field distributions demonstrate that the active tuning behavior can be ascribed to the change in the damper factor of the corresponding dark mode. In addition, the active control of the group delay is further investigated to develop compact slow light devices. Therefore, the selective and active control scheme introduced here can offer new opportunities and platforms for designing multifunctional terahertz devices.

We theoretically investigate the active control of electromagnetic induced transparency (EIT) in a terahertz graphene-based metamaterial, whose unit cell structure is composed two perpendicularly connected graphene cut-wires. The theoretical investigations and field distributions reveal that the EIT window arises from the destructive interference caused by asymmetric coupling between two cut-wire structures. Moreover, the strength and frequency of the EIT peak, the associated group delay and delay bandwidth product can be actively controlled. Therefore, the work presents a novel modulation strategy for controlling EIT behavior and exhibits potential applications for switching, modulation, and slow-light devices.

In this article, we fabricated two different graphene structure samples, composed of single-layer graphene and multilayer graphene/PMMA structures. When w samples are pumped by the 980 nm laser with different powers, we measure the time-domain and frequency domain spectra of the terahertz transmission using the terahertz time domain spectroscopy system. The measured results show that the average terahertz transmission can be actively controlled by changing the pump power or the layer number of graphene, which exhibits potential applications in the terahertz absorption devices.

In this paper, we proposed a multi-band metamaterial absorber for sensing thin film, which consists of tri-layer structure: patterned multi-split electric ring resonators layer, dielectric spacer layer, and continuous metal ground layer. The calculated results demonstrated that the absorber can exhibit three distinctive absorption peaks with narrow bandwidth. As the surface of the absorber was coated with the analyte layer, moreover, the locations of three absorption peaks appear obvious redshift, and the corresponding maximal sensitivities are 0.119 THz/RIU, 0.248 THz/RIU, and 0.662 THz/RIU, respectively. Therefore, the proposed absorber has significant potential applications in detecting and sensing.

A novel graphene-based metamaterial absorber with actively tunable bandwidth, intensity and frequency, working at the terahertz (THz) spectral region, was designed and numerically investigated in this paper. The actively controlled absorption characteristics in the graphene absorber were achieved by integrating two identical-sized graphene disc elements to construct a supercell, in which two elements of all unit cells were connected respectively by the electrical isolation graphene wires to form selectively electrostatic doping. The surface current distributions and the circuit model analysis were conducted to reveal the absorption mechanism and predict the tuning mechanism. Moreover, by selectively tuning two gate voltages to change the Fermi energy reconfiguration state of two graphene elements, the absorption bandwidth, intensity and frequency of the metamaterial absorber could be actively controlled. In addition, a striking switching contrast was obtained by switching the reconfiguration state of the two discs. Therefore, this work paves a pathway for the realization of actively controlled terahertz waves based on electrically reconfigured graphene metamaterials.

The colloidal carbon spheres were used as “transitional carriers” for the first time to obtain V₂O₅/ZnO nanocomposites. Each component was prepared by hydrothermal method, and the final product V₂O₅/ZnO nanocomposites were obtained after sintering in air to remove the colloidal carbon spheres completely. The XRD, TEM and XPS analyses showed the as-prepared samples were composed by wurtzite ZnO and orthorhombic V₂O₅. Meanwhile, the optical properties of samples were investigated in detail comparing with those of bare ZnO: UV-vis absorption spectra of V₂O₅/ZnO composites showed their stronger absorption in the visible region, in addition, a significant decrease on emission intensity was observed in the photoluminescence (PL) spectra, which revealed a low combination rate of photogenerated carriers of V₂O₅/ZnO nanocomposites in this work. Finally, the photocatalytic activities of samples were detected by photodegrading methylene blue (MB) under the simulated solar-driven irradiation. As a result, V₂O₅/ZnO nanocomposites showed an excellent photocatalytic behavior with a photodegradation rate over 2 times higher than that of bare ZnO, because of its extended visible response and enhanced charge separation efficiency.