Hu Deng

Broadband nonreciprocal components are essential for suppressing unwanted backreflections in terahertz (THz) systems, yet practical THz isolators remain limited by narrow bandwidths, large insertion losses, or strong magnetic-bias requirements. Here, we demonstrate a broadband THz isolator based on an epoxy-engineered metasurface–rare-earth iron garnet magneto-optical element combined with two external linear polarizers. By optimizing the relative polarizer angle to 63°, the broadband Faraday rotation of the metasurface–rare-earth iron garnet structure is converted into strongly asymmetric forward and backward transmission. At room temperature under a magnetic field of 0.22 T, the device exhibits a reliable operating band of 0.40–1.00 THz, corresponding to a continuous bandwidth of 0.60 THz. The band-averaged isolation reaches approximately 30 dB, with a maximum of about 33 dB, while the favored-direction insertion loss remains approximately 5.3 dB. Magnetic field reversal switches the preferred transmission direction, and repeated reassembly measurements confirm stable device performance. These results establish a broadband, magnetically tunable THz isolation platform operating under moderate magnetic bias.

Lithium aluminosilicate (LAS) ultra-low-expansion glass ceramics are core materials for precision optical systems, whose quality and dimensional stability are critically constrained by the uniformity of the coefficient of thermal expansion (CTE). This work proposes a nondestructive ultrasonic immersion pulse reflection (UIPR) method for rapid and low-cost characterization of the CTE in LAS glass ceramics. Key parameters of the ultrasonic measurement system are optimized via finite element method (FEM) simulations and experimental validation. Employing the correlation method, the ultrasonic longitudinal wave velocity is measured in LAS glass ceramic samples with distinctly different CTE values. The proposed method achieves an ultrasonic longitudinal wave velocity measurement uncertainty of 0.49 m/s, contributing 4.78 ppb/°C to the overall uncertainty of ultrasonic CTE determination. Within the investigated sample set, a negative relationship is observed between ultrasonic longitudinal wave velocity and the mean CTE (0–50 °C). The linear fit yields a slope of −9.75736 (ppb/°C)/(m/s), with a Pearson correlation coefficient of −0.84303. Featuring noncontact and nondestructive capabilities, this method lays a solid methodological foundation for CTE evaluation and efficient iterative optimization of material fabrication processes. Meanwhile, it shows great potential for rapid full-aperture characterization of CTE uniformity in large-size LAS glass ceramics.

Efficient forward prediction and inverse design can bypass the complexity and computational cost of traditional full-wave simulations, accelerating the development of terahertz metamaterial absorbers. Most current machine-learning approaches for spectral prediction or inverse design are limited to absorbers with a single topology, requiring retraining whenever the topology changes. Simultaneous forward prediction and inverse design also require separate models that are trained independently. This study proposes a resonance-anchored residual surrogate framework for resonance-frequency prediction and goal-oriented inverse design across multiple absorber topologies. Unlike conventional spectral prediction, the proposed spectral representation consists of a resonance frequency and a continuous local absorption spectrum centered on the resonance peak. The residual network is trained using a physics-guided dynamic anchor loss to improve the accuracy of resonance-frequency prediction, local spectral reconstruction, peak alignment, and absorptivity estimation. On the test set, the model achieves a normalized resonance-frequency MSE of 6.64 × 10⁻⁵, a normalized spectral-waveform MSE of 3.58 × 10⁻³, and a physical-domain absorptivity RMSE of 0.0054. Ablation experiments verify the effectiveness of the residual connections and the dynamic anchor loss. The trained surrogate is then frozen and integrated into a projected gradient descent loop for inverse design. Full-wave simulations demonstrate that the optimized structures successfully reproduce the target resonance responses within the sampled design space.

To meet the demand for high-range and high-frequency impact acceleration measurements, a fiber Bragg grating (FBG) accelerometer with a double-sided symmetrical inclined cantilever beam structure is proposed. The sensing principle is analyzed based on inertial and FBG sensing theories, and theoretical models for sensitivity and resonant frequency are derived. Using PPA-CF material and parameter optimization, the structural dimensions of the cantilever beam, effective fiber length, and proof mass are determined through numerical simulation. Finite element modal analysis shows a first-order natural frequency of 1284 Hz, with the dominant mode being axial translation of the mass block, ensuring pure axial strain on the FBG. A drop-weight impact calibration system is established for experimental testing. Results demonstrate that the sensor achieves a resonant frequency exceeding 1333 Hz, a measurement range above 500 g, and a practical sensitivity of approximately 1.183 pm/g. The linear response exhibits a coefficient of determination, R², of 0.9875, confirming excellent linearity. The proposed accelerometer effectively balances high-frequency response and measurement accuracy, providing a reliable solution for high-frequency impact monitoring in aerospace and impact dynamics applications.

The practical development of non-reciprocal terahertz (THz) devices is severely hindered by the characteristically weak magneto-optical (MO) responses of conventional materials under room-temperature and low magnetic-field conditions. Herein, we demonstrate a dramatic enhancement of the MO effect in a rare-earth iron garnet (RIG) film by integrating it with an epoxy-engineered metasurface. The designed L-shaped boomerang configuration, combined with an anti-reflection coating, forms an artificial Fabry–Perot cavity that intensifies the light–matter interaction. Under a weak bias magnetic field of 0.22 T at room temperature, the hybrid metasurface-RIG structure achieves a stable Faraday rotation angle of 25°–28° over an ultra-broadband range of 0.2–1.0 THz—a threefold enhancement compared to a pristine RIG film under the same conditions. Simultaneously, the structure maintains a high transmission of 50%–60% with minimal ellipticity below 5°, preserving excellent linear polarization. The corresponding Verdet constant reaches 210−230     deg     mm ⁻¹     T ⁻¹ , nearly doubling the performance of our prior best RIG film. This work validates a practical metasurface-driven strategy for achieving high-performance THz MO devices operable under moderate conditions.

太赫兹超材料传感器的谐振频率是实际应用中影响传感器灵敏度的重要因素。目前的设计大多依赖于设计人员不断调整结构参数，不能精确调整结构，无法依据检测需求设计不同谐振频率超材料传感器。本文提出了一种基于带精英策略的非支配排序遗传算法的超材料传感器优化设计方法，结合不同光谱特征的表面结构，通过算法对谐振频率精确控制。以谐振频率及其吸收率和品质因子为设计目标，对超材料的结构参数进行多目标优化。仿真结果表明，该方法能够高效、准确地生成符合预期光谱特征的结构。所设计的三个传感器在目标频率处均有吸收峰，具有较高的传感灵敏度，最高可达351.43GHz/RIU。本文提出的设计方法显著提高了太赫兹超材料传感器的设计效率，为设计适合特定分子振动特性的多频传感器提供了新的途径，生物传感和材料检测等领域具有重要的应用潜力。

Terahertz metamaterial dual-band absorbers are used for multi-target detection and high-sensitivity sensing in complex environments by enhancing information that reflects differences in the measured substances. Traditional design processes are complex and time-consuming. Machine learning-based methods, such as neural networks and deep learning, require a large number of simulations to gather training samples. Existing design methods based on single-objective optimization often result in uneven multi-objective optimization, which restricts practical applications. In this study, we developed a metamaterial absorber featuring a circular split-ring resonator with four gaps nested in a “卍” structure and used the Multi-Objective Firefly Algorithm based on Multiple Cooperative Strategies to achieve fast optimization of the absorber’s structural parameters. A comparison revealed that our approach requires fewer iterations than the Multi-Objective Particle Swarm Optimization and reduces design time by nearly half. The absorber designed using this method exhibited two resonant peaks at 0.607 THz and 0.936 THz, with absorptivity exceeding 99%, indicating near-perfect absorption and quality factors of 31.42 and 30.08, respectively. Additionally, we validated the absorber’s wave-absorbing mechanism by applying impedance-matching theory. Finally, we elucidated the resonance-peak formation mechanism of the absorber based on the surface current and electric-field distribution at the resonance frequencies. These results confirmed that the proposed dual-band metamaterial absorber design is efficient, representing a significant step toward the development of metamaterial devices.

The existence of bubble defects in ultra-low expansion quartz glass will affect the optical properties and mechanical strength of the material. The present paper proposes a novel defect characterization method based on ultrasonic nondestructive testing. The simulation model of bubble defect detection in ultra-low expansion quartz glass was established using numerical simulation technology, and experimental verification was carried out. The propagation mechanism of the ultrasound and its interaction with bubble defects were then analyzed. The results showed that the shape of the reflected wave was similar to that of the corresponding defect, and the scattering of the reflected wave was different due to the different curvature radius of the defect interface. The acoustic scattering characteristics of the circular defect were more obvious than those of the elliptical defect. Finally, an analysis of the interaction between different depth defects and different size defects and the ultrasound was conducted, leading to the conclusion that the relative amplitude of the defect echo corresponding to a 6 mm probe diameter shows a monotonic decreasing relationship with the defect depth, and there is also a monotonic corresponding relationship between the relative amplitude of the defect echo and the size of bubble defect. Therefore, it can be concluded that the relative amplitude of the defect echo can be used to characterize the size of the bubble defect. This study not only analyses the interaction between defects and ultrasound but also provides a quantitative characterization of defects using the proposed method.

To address the high time cost and low efficiency of traditional terahertz (THz) metamaterial absorber (MMA) design, an adaptive method based on multi-objective particle swarm optimization (PSO) was proposed. First, we presented a symmetric absorber of a four-split-ring resonator with a cross-shaped top layer. The structural parameters were optimized by the PSO and multi-objective PSO (MOPSO) algorithms. The simulation results indicated that the MOPSO rapidly obtained geometric parameters that balance the high absorptivity and high quality factors. This method quickly identified a symmetric structure with absorptivity greater than 99% and quality factor of 377.45 at 1.584 THz. Additionally, the asymmetric structure achieved near-perfect absorption at 1.585 THz with a Q value of 281.32. By studying the electric field distribution and the surface current distribution, the physical mechanism of the absorber designed has been explained. This adaptive assisted method based on MOPSO can efficiently design MMAs and offer an artificial intelligence strategy for THz functional device design.

A novel 2D energetic MOF [Cu(ATRZ)(N₃)₂]_n was prepared by single-crystal-to-single-crystal transformation to encapsulating N₃⁻, which is a new copper azide variant with excellent safety and excellent laser initiation performance.