Search Results (265)

This study investigates trellis shaping (TS) for mitigating nonlinear impairments in photonic terahertz (THz) communication systems. A parallel shaping architecture integrating hierarchical modulation (HM) with adjustable power allocation is proposed. The scheme applies TS to structure the data stream hierarchically and employs superposition coding (SC) to generate non-uniformly distributed TS-16QAM signals, enhancing transmission performance. Experimental validation over a 5-m link at 320 GHz demonstrates that the proposed scheme achieves a 1.65 dB improvement in input power sensitivity and a 1.39 dB gain in Q-factor compared to the Maxwell–Boltzmann (MB) distribution. Furthermore, the system provides enhanced power allocation flexibility, expanding the tunable range of the hierarchical power ratio by a factor of 1.37. Full article

Accurate permittivity characterization at terahertz frequencies is important for material analysis and device design, yet it remains challenging for small-volume samples and compact test structures. In this work, a terahertz permittivity sensor based on a spoof surface plasmon polariton (SSPPs) transmission line coupled to a backside split-ring resonator (SRR) is proposed and numerically studied. The SSPPs line is patterned on the top side of the substrate, while the SRR is etched on the backside, with the sample loaded into the SRR gap. The SSPPs mode penetrates through the substrate and excites the SRR, producing a pronounced transmission notch. Changes in the sample permittivity modulate the effective capacitance of the resonator, resulting in a monotonic shift in the notch center frequency. For relative permittivities from 1 to 8, the notch center frequency decreases from 152.1 GHz to 117.8 GHz, corresponding to a total shift of 34.3 GHz and an average sensitivity of about 4.90 GHz/ε_r. The minimum S₂₁ remains within approximately −23.80 to −21.56 dB, while the Q-factor stays in the range of 94.33–108.23, indicating good spectral readability. Tolerance analysis further shows that the resonance frequency is sensitive to critical structural dimensions and layer alignment, and practical implementation is therefore more suitable for single-device calibrated frequency-shift sensing. These results demonstrate the feasibility of the proposed dual-layer SSPPs–SRR configuration for compact permittivity sensing in the terahertz regime. Full article

A graphene-based tunable broad-band terahertz (THz) metamaterial absorber is presented, exhibiting strong and stable absorption across a wide frequency range. The device employs an ultra-thin three-layer structure consisting of a metallic reflector, a dielectric spacer, and a patterned graphene metasurface with an asymmetric geometry. Through optimized structural parameters, the absorber achieves broad-band absorption exceeding 90% between 2.45 THz and 6.11 THz with a bandwidth of 3.66 THz, featuring three distinct resonant frequencies at 2.764 THz, 3.534 THz, and 5.41 THz, corresponding to peak absorption efficiencies of 97.26%, 96.96%, and 99.90%, respectively. Impedance matching and electric field analyses confirm that the enhanced absorption arises from the strong coupling of electric and magnetic resonances within the multilayer structure. Moreover, the absorber exhibits polarization-insensitive behavior under varying polarization angles and maintains high absorption stability for both TE and TM modes up to an incident angle of 60°, as verified by simulation results, and allows dynamic tunability through Fermi-level modulation. These characteristics highlight the absorber’s potential for advanced THz imaging, sensing, and stealth applications. Full article

The rapid development of 6G wireless networks requires ultra-high data rates that traditional microwave frequencies cannot support. Photonics-assisted terahertz (THz) technologies offer a promising solution by combining high-capacity optical fibers with wideband wireless transmission. However, as bandwidth expands, sampling frequency offset (SFO) becomes a critical issue that degrades signal quality in single-carrier systems. This paper evaluates the performance of two main compensation methods within a photonics-assisted THz system operating at 320 GHz. We compare the Gardner clock recovery algorithm and the Digital Interpolation Compensation Algorithm (DICA) across various modulation formats and offset levels. Our findings indicate that the Gardner algorithm is effective for low-order modulation when the SFO is below 100 ppm, but its performance fails outside this range. Conversely, the DICA provides robust compensation up to 1000 ppm regardless of the modulation format, provided that the exact offset value is known. Without proper compensation, the system BER increases significantly as the SFO grows. These results demonstrate the complementary nature of these two algorithms and provide a practical guide for selecting compensation strategies in future high-speed THz communication links. Full article

A terahertz multifunctional metasurface based on vanadium dioxide (VO₂) and graphene that can switch between waveplate and absorber functionalities is proposed. As the temperature is below 300 K, by electrically controlling the Femi energy of the graphene it can realize half-wave plate (HWP) and quarter-wave plate (QWP) functionalities in the operating bandwidths of both 1.39–2.34 THz and 0.92–2.68 THz, respectively. While the temperature is above 340 K, the dipole resonance between VO₂ and a gold reflector induces absorption. Furthermore, by applying the voltage to graphene, dual-parameter modulation of the amplitude of the transverse electric (TE) waves and the resonance frequency of the transverse magnetic (TM) waves is achieved, the absorption bandwidths of which are 3.65–3.78 THz and 1.41–3.12 THz, respectively. The operating frequencies for HWP, QWP, TE and TM waves can be tuned by changing the electrical field and working temperature. In addition, the incident angles are not sensitive to the performance of the metasurface, confirming its effectiveness even under large-angle incidence. The metasurface with simplicity in design, mature fabrication processes, and comprehensive functionality, has certain promising applications in terahertz optical switches, terahertz spectroscopy systems, modulators, and communication systems. Full article

With ongoing advancements toward 6G networks, the terahertz (THz) band is expected to serve as an essential platform for realizing integrated sensing and communication (ISAC). In particular, maintaining high-data-rate communication while ensuring highly responsive, real-time radar operation in dynamic environments is a critical requirement. This study presents a THz-band ISAC architecture that utilizes a high-speed wavelength-tunable laser for photomixing, enabling simultaneous generation of a fast frequency-swept frequency-modulated continuous-wave (FMCW) radar signal and amplitude-shift keying (ASK) communication. The wavelength-tunable laser enables sub-microsecond frequency sweeps and supports high repetition rates suitable for real-time operation. To address the limitations in waveform design efficiency in conventional time-division ISAC, we experimentally investigate two transmission strategies for simultaneous operation. The first is a frequency-division scheme that reduces mutual interference between radar and communication signals, and the second is a joint-waveform scheme in which both functions share the same THz carrier. Using a single THz transmitter, the proposed system achieves sub-centimeter ranging accuracy together with 15-Gbit/s data transmission. These findings demonstrate that the presented ISAC approach enables efficient integration of radar and communication functions while lowering overall system complexity and implementation cost, offering substantial potential for deployment in future 6G infrastructures. Full article

During the harvesting and storage of wheat, various impurities are often mixed in, which adversely affect the processing quality and food safety of wheat. Therefore, developing an efficient and accurate impurity detection method is of great importance. Terahertz (THz) imaging technology can acquire time-domain spectral transmission images of wheat impurities, providing more features and facilitating detection. However, due to the limitations of THz imaging system hardware and environmental factors, the acquired THz images are often contaminated with noise, resulting in blurred details and indistinct edges, which severely hinder the accurate identification of impurities. To improve the quality of THz images of wheat impurities, this study proposes an Edge-Enhanced and Feature-Fused Image Denoising Network (EEFDNet). The proposed network employs a dual-branch architecture: a denoising branch utilizing dilated convolutions to strengthen feature representation, and an edge enhancement branch designed to emphasize impurity contour information. The outputs of the two branches are integrated through a feature fusion module to effectively remove noise while preserving and enhancing structural details. Experimental results on a self-established THz image dataset of wheat impurities demonstrate that EEFDNet exhibits superior performance, with the PSNR (Peak Signal-to-Noise Ratio) and SSIM (Structural Similarity Index) reaching 32.59 dB and 0.9180, respectively, outperforming several mainstream denoising models. Moreover, the proposed method exhibits strong robustness under high-noise conditions. This study provides an effective image preprocessing approach for wheat impurity detection and establishes a solid foundation for subsequent high-precision impurity identification. Full article

Terahertz (THz) technology is finding increasingly widespread applications in biosensing, high-speed communication, and stealth materials. Meanwhile, graphene, as a quintessential two-dimensional material, has emerged as a core component of THz devices due to its unique optoelectronic properties. However, the precise and non-destructive characterization of the complex conductivity of graphene at the microscopic scale remains a formidable challenge. Conventional measurement methods often suffer from limitations associated with contact resistance or intricate sample preparation processes. In this paper, we propose a non-invasive parameter inversion method based on deep learning. We design a tri-layer graphene-silica-copper metasurface structure featuring a central cavity and establish a high-fidelity scattering model that incorporates physical effects such as edge diffraction and multi-mode resonance. Utilizing the Radar Cross Section (RCS) data generated by this model, we train a Deep Enhanced Conductivity Predictor (DECP) network integrated with a Convolutional Block Attention Module (CBAM). Experimental results demonstrate that the proposed network can accurately reconstruct the complex conductivity of graphene from far-field RCS data. The coefficients of determination (R²) for the prediction of both real and imaginary parts exceed 0.99, with a Root Mean Square Error (RMSE) as low as the order of 10⁻⁵. This study not only validates the effectiveness of data-driven approaches in material characterization but also provides a novel paradigm for the real-time monitoring and intelligent design of terahertz metasurfaces. Full article

Ceramic Matrix Composites (CMC) are widely used in critical applications such as leading edges of aircraft wings and thermal insulation layers of thermal protection systems due to their advantages of being lightweight, high-temperature resistant, and impact-resistant. However, influenced by manufacturing processes and service environments, internal defects such as pores and delamination are prone to occur, significantly compromising the mechanical properties and service reliability of the material. This paper primarily evaluates the feasibility and applicability of using Terahertz Frequency Modulated Continuous Wave (FMCW) technology for the non-contact detection of CMC. First, the measurement principle of FMCW is introduced, and the structure of the detection system, including a two-dimensional mechanical scanning platform, optical lenses, a control platform, and a data acquisition unit, is outlined. Subsequently, scanning imaging was performed on CMC specimens and their bonded thermal protection structure (TPS) specimens, demonstrating the feasibility of Terahertz FMCW technology as an advanced non-destructive testing tool for CMC inspection. The issues of diffraction and the Rayleigh limit inherent in real-aperture terahertz imaging were analyzed and discussed. A multi-scale fusion defect detection method incorporating background estimation is proposed to enable precise delineation of defect regions. Experimental results show that, after processing with the proposed algorithm, the minimum detectable pore diameter at the focal plane is 1 mm, with a regional error of approximately 3%. The detection error for pores and debonding areas in CMC is maintained within 6.44%. Analysis indicates that combining terahertz imaging technology with image processing algorithms enables the quantitative analysis of internal defects in composite materials, offering a new technical approach for defect detection in composite materials. Full article

A polarization-insensitive compact optical modulator based on a graphene-hybrid surface plasmon polariton waveguide is proposed. The inverted U-shaped structure enables the synchronous control of TE/TM modes via Fermi level tuning, achieving a maximum attenuation of 0.247 dB/μm (E_f = 0.3 eV) and a minimum attenuation of 0.026–0.028 dB/μm (E_f = 1.0 eV) at 3 THz, with a polarization-dependent modulation error of only 0.002 dB/μm. The 100 μm × 30 μm device operates effectively at 2.5 THz (120 μm), demonstrating its potential for integrated photonic circuits. Additionally, the proposed modulator is compatible with Complementary Metal-Oxide-Semiconductor (CMOS) technology. The excellent ultra-broadband modulation performance of the graphene-hybrid plasmonic waveguide (GHPW) thereby paves the way for high-speed communication, non-destructive testing, biomedical sensing and optical computing. Full article

Flatland metasurfaces provide a fundamentally distinct approach to optical gas sensing by confining light–matter interaction to planar, subwavelength interfaces, where resonant energy storage and near-field enhancement replace extended optical path lengths. This review presents a physics-driven perspective on metasurface-enabled gas sensing, focusing on how gaseous analytes perturb the complex eigenmodes of engineered planar resonators. Diverse sensing modalities, including enhanced molecular absorption, refractive index-induced resonance shifts, loss modulation, polarization conversion, and chemo-optical transduction, are unified within a common perturbative framework that links sensitivity to mode confinement, quality factor, and analyte overlap. The analysis highlights fundamental trade-offs imposed by material dispersion, intrinsic loss, and radiation balance across plasmonic, dielectric, polaritonic, and hybrid metasurface platforms operating from the visible to the terahertz regime. Attention is given to the limits of chemical selectivity in flatland architectures and to the role of functional materials, multimodal transduction, and computational inference in addressing these constraints. System-level considerations, including thermal stability, fabrication tolerance, and integration with detectors and electronics, are identified as critical determinants of real-world performance. By consolidating disparate approaches within a unified flatland framework, this review provides physical insight and design guidance for the development of compact, integrable, and application-specific optical gas sensing systems. Full article

This paper introduces a vanadium dioxide-integrated broadband metamaterial absorber designed for the terahertz frequency range. The simulation results for the proposed structure demonstrate a wide 90% absorption bandwidth of 8.23 THz, corresponding to a fractional bandwidth of 89.5%. By leveraging the phase-transition properties of VO₂, the absorber demonstrated dynamic adjustability by modulating the absorption from 3% to 98.74%. The absorption mechanism was analyzed through the impedance matching theory and electromagnetic field distributions, confirming the role of magnetic resonance and interference. Furthermore, machine learning algorithms, specifically Linear Regression, Support Vector Regression, and Random Forest (RF), were applied to accelerate the design process and optimize the structural parameters. Among these, the RF model demonstrated superior prediction accuracy. The machine learning-assisted optimization successfully extended the effective absorption bandwidth to 9 THz, representing an improvement by 9.4% compared to the traditional optimization methods. These results validate the efficacy of combining electromagnetic simulation with data-driven techniques for advanced metamaterial design. Full article

A terahertz (THz) metamaterial broadband perfect absorber featuring a simple sandwich structure with a top layer composed of a triangular-patterned graphene film is presented. The graphene pattern is designed to exhibit a pronounced surface plasmon resonance (SPR) effect, which locally enhances the internal electric field’s intensity, leading to broadband absorption of 2.8 THz above 90% and a peak absorption rate of 99.99% at 6.05 THz. The broadband tunability of the absorber was further investigated by modulating the Fermi level of the graphene, demonstrating an adjustment in the absorption rate from 6.18% to 99.99% via an external voltage. This study shows that the absorber demonstrates excellent angular tolerance by maintaining an absorption rate above 90% across incident angles ranging from 0° to 50°. The absorber’s broadband perfect absorption properties were examined using relative impedance theory. Additionally, to reveal the fundamental physics behind this absorption, detailed analyses of the electric field distributions were carried out. Consequently, the origin of the absorption peaks is elucidated. This absorber enables noise suppression for optoelectronic integration and THz communications. Full article

Sub-terahertz (sub-THz) frequencies are in the spotlight in the ongoing development of sixth-generation (6G) wireless communication systems, offering ultra-high data rates and low latency for rapidly emerging applications. However, employment of sub-THz frequencies introduces strict propagation challenges, including free-space path loss and atmospheric absorption, which limit coverage and reliability. To address these issues, highly directional links are required. The conventional beam-shaping solutions such as refractive lenses and parabolic mirrors are bulky, heavy, and costly, making them less attractive for compact systems. Diffractive optical elements (DOEs) offer a promising alternative by enabling precise wavefront control through phase modulation, resulting in thin, lightweight components with high focusing efficiency. Employing the fused deposition modelling (FDM) using high-impact polystyrene (HIPS) allows cost-effective fabrication of DOEs with minimal material waste and high diffraction efficiency. This work investigates the beam-shaping performance of the FDM-printed structures comparing DOEs and spherical refraction-based structures, wherein both are aiming for application in sub-THz communication systems. DOEs exhibit clear advantages over classically employed solutions. Full article

To address the phase noise issue in terahertz OFDM system, this paper proposes a dual-branch deep learning phase noise compensation network named AdaPhaseNet. The Transformer branch of this network leverages the powerful modeling capability of Transformers for long-range dependencies to achieve long-range phase noise estimation and compensation, while the CNN branch is employed for local signal enhancement. Finally, an optimized signal is output through a confidence-driven adaptive fusion module. For experimental validation of the algorithm, we constructed a photonic terahertz communication system comprising 10 km of fiber and 5 m of wireless transmission. Experimental results show that, compared with multiple baseline models, AdaPhaseNet achieves relative BER reductions ranging from 37.0% to 57.9% and EVM gains ranging from 1.4 dB to 3.2 dB. Full article