Fully reconfigurable terahertz devices enabled by T-shaped graphene two-parallel-sheet

A tunable bifunctional terahertz (THz) metamaterial device based on Dirac semimetal films (DSFs) and VO2 is presented. The insulator-to-metal phase transition of VO2 enables bifunctional asymmetric transmission and dual-directional absorption to be switched in the THz range. When VO2 serves as a dielectric, tunable broadband asymmetric transmission of linearly polarized THz waves can be achieved. When VO2 is in a metallic state, the proposed device acts as a tunable dual-directional absorber with perfect absorption in both illumination directions. In each case, the response can be tuned by varying the Fermi energy of the DSFs. This offers a new pathway for the development of tunable multifunctional THz metamaterial devices.

In this paper, a nematic liquid crystal (NLC)-based tunable terahertz (THz) plasmonic metamaterials (MMs) with large modulation depth (MD) and low insertion loss (IL) is designed and experimentally verified at THz frequencies. The proposed structure includes two-layered MM that is immersed in LC. The metal MM is used directly as electrode. The tunable device with a 46×46 array of sub-wavelength circular air loops was fabricated on a quartz glass substrate, with 2×2 cm2 area and 220 µm thickness. The obtained results show that the amplitude MD and IL for normally incident electromagnetic (EM) waves are about 96% and 1.19 dB at 421.2 GHz, respectively, when the bias voltage applied to the NLC layer varies from 0 to 16 V. Meanwhile, the transmission peak frequency gradually decreases from 421.2 to 381.8 GHz, and the frequency tunability (FT) of the proposed structure is greater than 9.35%. This study provides a potential solution for THz modulators, filters, and switches.

Actively tunable ultrafast broadband terahertz (THz) polarimetry using a reconfigurable phase‐change material holds great potentials and prospects for the achievement of next‐generation versatile integrated THz components and systems in a variety of THz applications. Here, an optically tunable ultrafast broadband THz polarimetric device (THz‐PoD) composed of a phase‐change material Ge2Sb2Te5 (GST) and a thin mica substrate is demonstrated. This proposed novel THz‐PoD is verified for a frequency range of 0.1–2.5 THz, exhibiting broadband and ultrafast determination of polarization states for linearly polarized THz waves at polarization angles from −90° to 90°. It is shown that optical excitation with ns pulses allows easy and efficient control of the polarimetric properties of such THz‐PoD. The essential role of the GST film in switching the phase transition between the amorphous and crystalline phases is emphasized by the theoretical investigation of the optically tunable ultrafast polarimetric mechanism of the device. This phase transition allows optically changing the THz‐PoD's properties by ns‐pulsed laser in a controlled way to achieve THz polarimetry for linearly polarized THz waves. The combined advantages of this strategy can open up a new and promising way for realizing versatile reconfigurable and integrated THz devices, which may further promote the development of novel THz systems and applications.

Despite significant advancements in terahertz (THz) generation and detection technologies, the practical deployment of portable THz systems remains constrained by existing modulator limitations, particularly stringent temperature requirements, inefficient thermal management, and high power consumption. Here, we demonstrate a breakthrough in magnetically controlled THz modulation using a CoFe2O4/MgO/F-Mica composite structure. The tunable optical response and dielectric properties of the composite under varying magnetic fields were systematically investigated via THz time-domain spectroscopy. Experimental results revealed a magnetic field-dependent THz transmission attenuation, with systematic suppression of transmission spectra proportional to the applied magnetic field intensity. A theoretical model accounting for external magnetic field variations was proposed, which agrees well with the experimental results regarding the imaginary component. Remarkably, the composite material realizes phase modulation simultaneously under magnetic field. This exceptional magnetic responsiveness significantly broadens the application potential of ferrites in the THz regime. These findings provide critical insights for designing tunable multifunctional THz magnetic devices in 6G communications, medical diagnostics, and nondestructive testing applications.

In recent years, the limited tuning ranges and selections of active materials in tunable terahertz metamaterials severely restrict their wide applications in tunable terahertz devices. In this paper, we reported an in-plane reconfigurable terahertz metamaterial which consists of a couple of T-shape structures. One is fixed to the substrate while the other is patterned on a movable frame actuated though a micromachined actuator. By adjusting the distance between T-shapes, the terahertz metamaterial exhibits a large tuning range up to 43%. In addition, the terahertz metamaterial can also realize switching between the polarization dependent and polarization independent state. Therefore, the proposed terahertz metamaterial shows potential applications in designing tunable terahertz devices.

We proposed a polarization-insensitive absorber based on strontium titanate (STO) and bulk Dirac semimetal (BDS) in the terahertz (THz) region. The center frequency of the absorption peak can be independently regulated by temperature or Fermi energy level of STO or BDS, respectively. The numerical simulation result reveals that the peak absorptivity reaches to 99.98% at 2.16 THz when the temperature and Fermi energy were set at 300 K and 20 meV, respectively. Interestingly, by adjusting the temperature of STO from 250 to 400 K, the simulation results indicate that the center frequency can be tuned from 1.94 to 2.53 THz, and peak absorptivity can be maintained above 99% at normal incident. As the Fermi energy EF of Dirac semimetal increases from 10 to 60 meV, the center frequency can be changed from 2.14 to 2.44 THz and the amplitude of absorption peaks can be tuned from 99.9% to 82.8%. Impedance matching theory was used to understand the tunable performance. Furthermore, interference theory was employed to further explain the absorption mechanism of the proposed absorber. The absorber achieves bi-controlled absorptance via two independently controllable methods, which may provide guidance to research tunable, smart and multifunctional terahertz devices.

Metamaterial-based photonic components are driving significant scientific and technological advancements in the terahertz (THz) frequency range. In this study, we present a multilayered metamaterial based on toroidal excitation for ultra-broadband THz modulation. The toroidal resonance within the stacked resonators enables subwavelength coupling with individual resonators, significantly broadening the transmission bandwidth. Our multi-stacked metamaterial demonstrates a full width at half maximum (FWHM) of 370 GHz, which is approximately 137% of the 270 GHz bandwidth of a single-layer metamaterial. A detailed multipolar analysis reveals that the toroidal dipole dominates the electromagnetic response, confirming the enhanced performance of the stacked configuration over its planar counterpart. Furthermore, by integrating a temperature-responsive vanadium dioxide (VO2) layer into the multilayer structure, we enable tunable amplitude transmission through external thermal control. By varying the temperature of the VO2 layer from 30 °C to 120 °C, we achieve a transition from a band-reject filter to a broadband reflector, as verified by experimentally obtained THz-TDS spectral results. In addition, we investigate the temporal switching dynamics of the modulator using time-resolved transmission measurements under periodic electrical pulsing. The device exhibits efficient and reversible electro-thermal modulation, with rise and fall times in the range of a few seconds, making it suitable for practical applications requiring dynamic THz control. This tunable and switchable THz modulator holds significant promise for broadband communication systems and adaptive photonic platforms.

In this paper, we propose a novel structure of anisotropic graphene-based hyperbolic metamaterial (AGHMM) sandwiched as a defect between two one-dimensional photonic crystals (PCs) in the terahertz (THz) region. The proposed structure is numerically simulated and analyzed using the transfer matrix method, effective medium theory and three-dimensional finite-difference time-domain. The defect layer of AGHMM consists of graphene sheets separated by subwavelength dielectric spacers. According to the presented results, a sharp defect mode originated from the optical Tamm state (OTS) takes place at the interfaces between PCs and AGHMM. The platform is then applied as various THz devices with outstanding characteristics compared with their previous counterparts. The performance of all the proposed devices can be tuned by changing the incident angle and graphene chemical potential. Our designed electro-optical modulator exhibits a high extinction ratio of 24.75 dB. The required switching voltage and insertion loss are as low as 9.94 V and 0.05 dB, respectively. Owing to the anisotropy of graphene, a tunable polarizer over wide incident angles is attained. The highest polarization extinction ratios (PERs) for TE- and TM-pass polarizers are 42.4 dB and 76.8 dB, respectively, which are the highest PER ever reported. By introducing more AGHMM defects, multiband tunable filters with quality factors of as high as 75314 are realized. Finally, a narrowband perfect absorber is proposed so that a high absorption of 99.8% with an ultra-narrow FWHM of 0.00055 THz is achieved. Hence, the proposed structure is a promising platform that could have many potential THz applications.

With the fast development of terahertz (THz) techniques, THz absorbers have a variety of applications. However, current designs have a series of shortcomings, such as low absorption rate and a fixed and narrow absorption bandwidth. To solve such problems, in this paper, we design a tunable broadband THz absorber, which consists of two layers of graphene structures: the top layer is arrayed with the graphene concentric hexagonal rings and the bottom layer is arrayed with regular graphene hexagon rings; therefore, both layers support hybridization and stacking effects. The coexistence of both effects achieves the absorption rate of over 90% in a broad band from 0.93 THz to 1.80 THz. Moreover, the absorption spectrum can be tuned by adjusting the graphene chemical potential, which is insensitive to both incident angle and polarization. Considering advantages such as a tunable broad absorption band, a high absorption rate and insensitive incident angle and polarization, the proposed dual-layer graphene based tunable broadband THz absorber can be a useful reference for absorber design even in other electromagnetic wavebands.

Tunable broadband terahertz absorber based on graphene metamaterials and VO2

Terahertz (THz) technology is becoming a spotlight of scientific interest due to its promising myriad applications including imaging, spectroscopy, industry control and communication. However, one of the major bottlenecks for advancing this field is due to lack of well-developed solid-state sources and detectors operating at THz gap which serves to mark the boundary between electronics and photonics. Here, we demonstrate exceptionally wide tunable terahertz plasma-wave excitation can be realized in the channel of micrometer-level graphene field effect transistors (FET). Owing to the intrinsic high propagation velocity of plasma waves (>~108 cm/s) and Dirac band structure, the plasma-wave graphene-FETs yield promising prospects for fast sensing, THz detection, etc. The results indicate that the multiple guide-wave resonances in the graphene sheets can lead to the deep sub-wavelength confinement of terahertz wave and with Q-factor orders of magnitude higher than that of conventional 2DEG system at room temperature. Rooted in this understanding, the performance trade-off among signal attenuation, broadband operation, on-chip integrability can be avoided in future THz smart photonic network system by merging photonics and electronics. The unique properties presented can open up the exciting routes to compact solid state tunable THz detectors, filters, and wide band subwavelength imaging based on the graphene-FETs.

A tunable dual-band asymmetric transmission metasurface with strong circular dichroism in the terahertz communication band

The rapid evolution of terahertz (THz) technology has opened new frontiers in high-speed wireless communication, imaging, and sensing. However, the practical deployment of THz systems, particularly in remote or space-constrained environments, is often limited by power constraints and rigid antenna structures. A reconfigurable THz antenna system that is powered by solar energy is suggested. By leveraging real-time energy harvesting, the antenna system maintains operation without external power sources, making it ideal for deployment in remote IoT nodes, CubeSats, or energy-constrained sensor networks. Material used in antenna design is lead glass while gold is used as a radiator, the MIMO antenna loaded with graphene with chemical potential of graphene= 0 works from 2.4–2.5 THz, 3.87–3.98 THz, and 5.17–5.3 THz. The MIMO antenna with graphene chemical potential= 1 eV works from 2.54–2.63 THz, 3.96–4.1 THz, and 5.27–5.45 THz. The MIMO antenna with graphene chemical potential= 2 eV works from 2.6–2.68 THz, 4–4.2 THz, and 5.3–5.55 THz. Gain of antenna at 2.45, 3.95, and 5.3 THz maximum gain obtained at these frequencies is 6, 5 and 7 dBi, respectively. By integrating real-time solar energy harvesting with a tunable THz antenna structure, the design enables self-sustained, high-efficiency operation for remote IoT nodes, CubeSats, and energy-constrained sensor networks, merging green energy and next-generation THz communication in a compact platform. Advantages of the proposed design are self-powered operation, reconfigurable multi-band tuning, high gain, and suitability for diverse THz applications.OPEN ACCESS Received: 23/06/2025 Accepted: 17/09/2025 Published: 23/01/2026

We report a diffraction-limited photonic terahertz (THz) source with linewidth <10 MHz that can be used for nonlinear THz studies in the continuous wave (CW) regime with uninterrupted tunability in a broad range of THz frequencies. THz output is produced in orientation-patterned (OP) gallium arsenide (GaAs) via intracavity frequency mixing between the two closely spaced resonating signal and idler waves of an optical parametric oscillator (OPO) operating near λ = 2 μm. The doubly resonant type II OPO is based on a periodically poled lithium niobate (PPLN) pumped by a single-frequency Yb:YAG disc laser at 1030 nm. We take advantage of the enhancement of both optical fields inside a high-finesse OPO cavity: with 10 W of 1030 nm pump, 100 W of intracavity power near 2 μm was attained with GaAs inside cavity. This allows dramatic improvement in terms of generated THz power, as compared to the state-of-the art CW methods. We achieved >25 μW of single-frequency tunable CW THz output power scalable to >1 mW with proper choice of pump laser wavelength.

A theoretical investigation is presented on the generation of terahertz (THz) radiation through the nonlinear interaction of a cubic frequency chirped Hermite–Cosh–Gaussian (HChG) laser beam with an underdense plasma. The structured intensity profile of the HChG beam, characterized by its mode index, beam width parameter, decentered parameter, and Cosh envelope, enables enhanced spatial confinement and field gradients, which are very significant for efficient THz generation. The incorporation of a cubic frequency chirp modulates the temporal phase of the laser pulse, thereby increasing the interaction duration between the laser and plasma electrons. This leads to a stronger ponderomotive force, which drives a transient nonlinear current density at the beat frequency, resulting in the emission of THz radiation. Analytical expressions for the nonlinear current and THz field amplitude are derived, and parametric analysis reveals that the THz output is highly sensitive to the chirp coefficient, laser intensity, mode index, and plasma density profile. We found that higher-order spatial modes and carefully adjusted beam positioning (decentering) further enhance THz output. The best results were achieved at a lower chirp value ( b = 0.00099), which outperformed traditional linear and quadratic chirping. This study demonstrates that cubic chirping significantly enhances the THz conversion efficiency compared to linear and quadratic chirps, offering a tunable and high-intensity THz source for applications in spectroscopy, imaging, wireless communication, ultrafast material characterization, and medical diagnostics.