Search Results (59)

Two-dimensional (2D) antiferromagnets are highly promising for next-generation spintronics due to their ultrafast dynamics and robustness against stray fields; however, their practical application is severely hindered by the vanishing magneto-optic effects restricted by strict crystal symmetries. In this work, we propose a universal physical mechanism to activate and manipulate the magneto-optic Faraday effect in 2D fully compensated bilayer antiferromagnets using an external vertical electric field. By constructing a comprehensive tight-binding model and performing first-principles calculations on bilayer ${\mathrm{VSe}}_2$, we demonstrate that the applied electric field explicitly breaks the spatial inversion and combined $\mathcal{PT}$ symmetries. This symmetry breaking lifts the Kramers degeneracy, inducing a pronounced spin splitting that, in conjunction with intrinsic spin–orbit coupling, generates non-vanishing Berry curvature. Consequently, the previously forbidden Faraday rotation angle is activated from zero to a significant non-zero value, and its rotation direction can be deterministically reversed by switching the electric field polarity. Our findings provide profound physical insights into the symmetry-modulated light–matter interactions and pave the way for designing fully electrically controllable, energy-efficient antiferromagnetic opto-spintronic devices. Full article

We demonstrate an underwater visible light communication system using a circularly polarized 520 nm laser transmitter, 32APSK modulation, and a polarization-diverse dual-aperture receiver. An end-to-end post-equalization network, DirectDemodNet, directly maps dual-polarization received waveforms to 32APSK symbol logits, replacing conventional Least Mean Square (LMS) + Volterra equalization. By combining waveform-difference features, dual-scale dilated temporal convolutions, and multi-period positional encoding, DirectDemodNet improves nonlinear compensation and branch fusion. Extensive evaluations are conducted across data rates from 7.5 to 13.75 Gbps over a 1.2 m static underwater channel. Experiments show that DirectDemodNet broadens the forward error correction compliant operating range and provides a maximum net transmission rate gain of 4.095 Gbps over LMS + Volterra at the 7% Hard-decision Forward Error Correction (HD-FEC) threshold. Full article

Metalenses based on optical metasurfaces enable wavefront manipulation using subwavelength nanostructures and provide a promising route toward compact and integrated optical systems. However, strong chromatic aberration caused by wavelength-dependent phase responses remains a major obstacle for practical metalens applications in the visible regime. In this work, we present the design and analysis of an achromatic metalens operating in the visible spectrum using silicon nitride (Si₃N₄) dielectric metasurfaces. The metalens employs a phase-engineering strategy based on propagation-phase modulation of polarization-independent nanostructures. By constructing a unit-cell phase library through systematic parameter scanning, the phase responses at different wavelengths are accurately mapped. An interleaved arrangement strategy is introduced, where meta-atoms designed for different target wavelengths are alternately distributed within a single metalens aperture, enabling multi-wavelength phase compensation without increasing the structural complexity. Numerical simulations demonstrate that the proposed metalens achieves near-coincident focal positions across a broad visible-wavelength range. The focal length variation is significantly suppressed compared with conventional single-wavelength metalenses. The metalens exhibits stable focusing behavior with symmetric focal spots, consistent focal sizes, and improved chromatic tolerance. The results confirm that the interleaved design effectively mitigates chromatic focal shift while maintaining high transmission efficiency. This study provides a practical and scalable approach to achieving achromatic focusing in visible-wavelength metalenses. The proposed Si₃N₄-based interleaved design offers strong potential for compact imaging systems, integrated photonics, and visible-light optical devices. Full article

This paper proposes a hybrid Vector Radiative Transfer Shooting (VRT-S)-Bouncing Ray (BR) method, referred to as the VRT-S-BR method, for predicting composite electromagnetic scattering from targets above vegetation-covered rough surfaces. In this proposed framework, the vegetation layer is modeled as a stratified random medium and incorporated into the BR solver through VRT-S-derived amplitude modulation and deterministic phase compensation. Specifically, an offline database of vegetation-induced complex reflection coefficients is first generated using the VRT-S model over a set of incidence angles. During the BR ray-tracing process, these coefficients are used to replace the conventional Fresnel reflection terms on a per-interaction basis, thereby accounting for vegetation-induced attenuation and coherent scattering effects. In addition, a facet-dependent phase compensation scheme is introduced to describe propagation-path variations of individual rays through the vegetation canopy, avoiding the empirical random phase perturbation used in previous hybrid models. The proposed method is validated against field-measured backscattering data over natural grassland, achieving root mean square height (RMSE) values of 1.82 dB and 3.10 dB for horizontal-horizontal (HH) and vertical-vertical (VV) polarizations, respectively. Numerical results further demonstrate the capability of the method to characterize target–vegetation coupled scattering under different percentages of vegetation cover, vegetation heights, terrain backgrounds, and bistatic observation geometries. Full article

The built-in electric field induced by polarization in ZnO/Mg_0.2Zn_0.8O quantum wells can be screened to modulate the conduction-band potential profile and intersubband energy levels. To optimize the screening of the built-in electric field, we analyze the influence of an external electric field, temperature, and modulation doping. The position of the doped layer is varied within the heterostructure to improve field compensation, providing additional control over electron localization and intersubband energy separation. In this work, within the effective mass approximation and by self-consistently solving the Poisson and Schrödinger equations using the finite-difference method, we calculate the electronic structure and nonlinear optical response of an n-type doped ZnO/Mg_0.2Zn_0.8O quantum well heterostructure. Our results indicate a strong dependence of the confinement potential on the applied external electric field and the electrostatic potential arising from the doped layer. We demonstrate electronic Raman gain values on the order of ${10}^3$–${10}^4$ cm⁻¹ for specific values of field strength, temperature, and doped-layer position. This approach enables fine-tuning of the nonlinear optical response, which is crucial for the development of ZnO-based optoelectronic devices. Full article

As the modulation rate in high-speed optical communication systems continues to increase and modulation formats become increasingly complex, conventional electrical-domain sampling techniques, limited by the “electronic bottleneck,” are unable to meet the time-domain analysis requirements of optical vector signals with bandwidths exceeding 100 GHz. In this paper, a system based on linear optical sampling (LOS) is implemented for time-domain analysis of high-speed polarization-division-multiplexed (PDM) optical vector signals. An unbalanced input method is proposed to ensure the integrity of the sampling clock when the power of the signal under test is zero; a resampling method combined with soft integration is proposed to replace the conventional peak detection method, improving the accuracy of sampling point position and amplitude information extraction; and an adaptive frequency offset estimation algorithm is proposed to compensate for the continuously varying frequency offset caused by the use of low-repetition-rate sampling pulses. We constructed a signal acquisition system for optical vector signal measurement based on LOS. Using the above methods, the eye diagrams and constellation diagrams of 50 Gbaud PDM-QPSK (quadrature phase-shift keying), PDM-16QAM (quadrature amplitude modulation), and PDM-32QAM signals are successfully measured, and related parameters, including error vector magnitude (EVM) and signal-to-noise ratio (SNR), are calculated. The experimental results show that the proposed system achieves quasi-real-time measurement of 500 Gbps optical vector signals, and the measured performance parameters are on the same order of magnitude as those obtained from a commercial high-speed oscilloscope. Full article

This study investigates the modulation of coercivity and magnetodielectric coupling in heat-treated, nickel-substituted lanthanum ferrite. LaFe_0.7Ni_0.3O₃ samples were synthesized by high-energy ball milling and sintered at temperatures between 1073 and 1473 K. Chemical composition, crystalline structural evolution, surface morphology, magnetic, dielectric, and electrical properties, as well as magnetodielectric coupling, were analyzed. The XPS spectra revealed the presence of adsorbed oxygen, associated with the high oxygen affinity of the material. This behavior is interpreted as a charge-compensation mechanism, related both to the formation of oxygen vacancies and to the partial oxidation of Fe³⁺ to Fe⁴⁺. XRD and Rietveld refinement confirmed a single-phase orthorhombic Pnma structure, and structural simulations revealed progressive octahedral distortions with increasing temperature, affecting the octahedral tilting and electronic bandwidth. Magnetic characterization revealed that thermal processing modifies the magnetic behavior, inducing weak ferromagnetism and a significant increase in coercivity, correlating with progressive densification, greater domain stability, and reduced microstrain. Impedance measurements revealed magnetodielectric coupling, the Maxwell–Wagner interfacial polarization mechanism, and reduced dielectric losses. These findings demonstrate that the coercivity and magnetodielectric response in cationic nickel-substituted lanthanum ferrite can be tuned through thermal processing. A semi-empirical magnetocrystalline anisotropy model is proposed to explain the coercivity evolution and associated multiferroic behaviors, thus contributing to the study of functional ferrites as sustainable alternatives to rare-earth magnetic materials with potential in sensors and memory devices. Full article

To address limitations in the modulation-quality analysis of high-order Quadrature Amplitude Modulation (QAM) signals, including insufficient timing synchronization accuracy, challenges in carrier recovery, and coupling between synchronization errors and parameter estimation, a cascaded digital baseband processing framework tailored for measurement scenarios is proposed. The proposed framework is designed to integrate synchronization recovery and parameter measurement. In the timing synchronization stage, a feedforward open-loop structure based on the Oerder–Meyr (OM) algorithm is employed to estimate the optimal sampling instants rapidly. In the carrier synchronization stage, a two-stage recovery structure is constructed, comprising coarse frequency offset estimation based on polarity decision and fine synchronization using an improved frequency–phase detector (FPD), thereby achieving both robust acquisition of large frequency offsets and high-precision compensation of residual errors. On this basis, a unified modulation quality evaluation model is established, enabling the joint estimation of the Error Vector Magnitude (EVM) and the Modulation Error Ratio (MER), as well as amplitude, phase, and frequency errors, within a consistent analytical framework. System-level validation of 256 QAM and 1024 QAM signals is conducted using a MATLAB R2021b-based simulation platform. The results demonstrate that stable synchronization recovery can be achieved under timing, frequency, and phase perturbations, yielding well-defined constellation diagrams. In terms of parameter estimation, the relative errors of all evaluated metrics are maintained within 2%, which is significantly below the conventional 5% measurement criterion. Further analysis indicates that the proposed method maintains strong robustness across varying signal-to-noise ratios (SNRs) and sampling rates. The results confirm that the proposed cascaded processing framework effectively unifies synchronization recovery and modulation quality analysis, significantly improving parameter estimation accuracy while maintaining high synchronization precision. This approach provides a practical and efficient solution for high-order QAM signal testing and measurement systems. Full article

The unique nature of polarization information can provide a reliable physical prior for underwater multimodal image fusion. Existing methods mainly employ the integration of linearly polarized images from multiple directions, which is essentially an intensity fusion process of images. To solve this problem, we propose an underwater polarization imaging technology based on multi-polarization modality fusion. This method employs the total intensity S₀ to provide the basic scene brightness, uses the degree of linear polarization (DoLP) as a physical prior, fully exploits the rich texture features in DoLP to compensate for S₀, and integrates color information channels to better preserve the color characteristics of the scene. In addition, we develop a Polarization Feature Enhancement Module (PFEM) tailored for polarization data, which embeds a customized gating mechanism to select features and adaptively fuse feature vectors from different channels. Finally, we construct and publicly release an underwater polarization image dataset with multiple turbidity levels and materials, and systematically verify the robustness of the proposed method. Full article

In this paper, we propose and demonstrate a sensitivity-enhanced sensing interrogation scheme based on an Optoelectronic oscillator (OEO), in which a switchable dual-passband microwave photonic filter (MPF) is introduced into the loop. The switchable dual-passband MPF is a combination of a modified fiber Mach–Zehnder interferometer (FMZI), an electro-optical modulator (EOM), a roll of dispersion compensating fiber (DCF), and a photodetector (PD). The dual-passband switching of the MPF can be achieved by simply adjusting the polarization state via rotating a polarization controller (PC) in the FMZI. The sensitivity can be improved by a factor of two by tracking the frequency corresponding to the central frequency of the high-frequency passband relative to the low-frequency passband. Temperature-sensing experiments were conducted to verify the concept of enhanced sensitivity. Experimental results on temperature sensing show that tracking low- and high-frequency OEO signals yields sensitivities of 5.23 MHz/°C and 10.84 MHz/°C, respectively, and temperature resolutions of 0.009 °C and 0.004 °C, thereby increasing sensitivity and resolution. Full article

We propose a terahertz achromatic polarization-multiplexed structured light metasurface based on the particle swarm optimization (PSO) algorithm, operating from 0.8 to 0.95 THz. A dielectric silicon meta-atom array combined with propagation phase modulation is employed to achieve broadband wavefront control under two orthogonal linear polarizations. By constructing a phase-response database and using PSO for global optimization of phase compensation factors at multiple frequencies, the metasurface simultaneously satisfies different target phase profiles while suppressing chromatic aberration. Two multifunctional devices are designed. The first generates a conventional focused spot under x-polarized incidence and a first-order Bessel beam under y-polarized incidence. The second produces a focused vortex beam with topological charge l = 1 under x polarization and a focused vortex beam with l = 2 under y polarization. Full-wave simulations demonstrate stable focal positions, low inter-channel crosstalk, and good achromatic performance across the operating band. The Bessel beam preserves its nondiffracting core, while both vortex channels exhibit clear phase singularities and well-defined orbital angular momentum states. Most operating frequencies maintain relatively high focusing efficiency. Compared with conventional cascaded optical components, our design provides a compact and stable platform for terahertz structured light generation, orbital angular momentum multiplexing, nondiffracting imaging, and multidimensional polarization information processing. Full article

Hyperspectral images (HSIs) from the lunar polar regions are frequently compromised by low signal-to-noise ratio (SNR) under adverse illumination, limiting their utility for scientific analysis. Existing spectral-only compensation approaches operate without spatial context, leading to speckle-like artifacts that degrade spatial consistency and constrain subsequent applications. To address this limitation, we propose SSF-3DSC, a spatial–spectral fusion 3D signal-compensation framework tailored for lunar HSIs to simultaneously restore spectral fidelity and spatial consistency under extreme low-illumination conditions. To the best of our knowledge, this represents the first deep learning framework specifically engineered for joint spatial–spectral restoration in the photon-starved regime. SSF-3DSC integrates three specialized components: a spectral compensation module (SCM) for restoring spectral fidelity, a multi-scale spatial attention (MSA) module for capturing hierarchical spatial patterns, and a cascaded 3D residual convolutional module (C3D-RCM) for refining spatial–spectral representations. Trained on paired low- and high-SNR Moon Mineralogy Mapper (M3) data cubes from the lunar south polar region, SSF-3DSC employs synergistic spatial–spectral fusion to achieve high-fidelity reconstruction, significantly outperforming a spectral-only lunar baseline (Paired-CycleGAN). Regional-scale experiments demonstrate its ability to recover both spatially coherent geological structures and spectrally reliable mineral abundance maps. By establishing a new benchmark for lunar HSI restoration under low-illumination conditions, this work enhances the scientific utility of low-signal M3 data and enables robust quantitative investigations into the Moon’s challenging polar regions. Full article

The simultaneous measurement of strain and temperature using Fiber Bragg Grating (FBG) sensors presents a significant challenge due to the intrinsic cross-sensitivity of the Bragg wavelength. While recent studies have increasingly employed “black-box” machine learning algorithms to address this ambiguity, such approaches often overlook the physical limitations of the sensor’s spectral response. This paper challenges the assumption that advanced algorithms alone can compensate for data that is physically ambiguous. We propose a “Sensor-Algorithm Co-Design” methodology, demonstrating that robust discrimination is achievable only when the sensor architecture exhibits a unique, orthogonal physical signature. Using a rigorous Transfer Matrix Method (TMM) and 4 × 4 polarization analysis, we evaluate three distinct architectures. Quantitative analysis reveals that a standard Quadratically Chirped FBG (QC-FBG) functions as an “ill-conditioned baseline” failing to distinguish measurands due to feature space collapse ($K_{cond}>4600$). Conversely, we validate two robust co-designs: (1) An Amplitude-Modulated Superstructure FBG (S-FBG) paired with an Artificial Neural Network (ANN), utilizing thermally induced duty-cycle variations to achieve high accuracy ($~3.4 °\mathrm{C}$ error) under noise; and (2) A Polarization-Diverse Inverse-Gaussian FBG (IG-FBG) paired with a 4 × 4 K-matrix, exploiting strain-induced birefringence ($K_{cond}\approx 64$). Furthermore, we address the data scarcity issue in AI-driven sensing by introducing a Physics-Informed Neural Network (PINN) strategy. By embedding TMM physics directly into the loss function, the PINN improves data efficiency by 2.2× compared to standard models, effectively bridging the gap between physical modeling and data-driven inference, addressing the critical data scarcity bottleneck identified in recent optical sensing roadmaps. Full article

This paper presents a hybrid architecture for automatic sentiment analysis of Kazakh-language political discourse. The Kazakh language is characterized by an agglutinative structure, a complex word-formation system, and the limited availability of digital resources, which significantly complicates the application of standard neural network approaches. To account for these characteristics, a multi-level system was developed that combines morphological and syntactic analysis rules, ontological relationships between political concepts, and multilingual representations of the XLM-R model, used in zero-shot mode. A corpus of 12,000 sentences was annotated for sentiment polarity and used for training and evaluation, while Universal Dependencies annotation was applied for morpho-syntactic analysis. Rule-based components compensate for errors related to affixation variability, modality, and directive constructions. An ontology comprising over 300 domain concepts ensures the correct interpretation of set expressions, terms, and political actors. Experimental results show that the proposed hybrid architecture outperforms both neural network baseline models and purely rule-based solutions, achieving Macro-F1 = 0.81. Ablation revealed that the contribution of modules is unevenly distributed: the ontology provides +0.04 to Macro-F1, the UD syntax +0.08, and the rule-based module +0.11. The developed system forms an interpretable and robust assessment of tonality, emotions, and discursive strategies in political discourse, and also creates a basis for further expansion of the corpus, additional training of models, and the application of hybrid methods to other tasks of analyzing low-resource languages. Full article

We begin by theoretically analyzing the relationship between the rotation rates of the rotation of state of polarization (RSOP) and the principal state of polarization (PSP) in a fiber link where both polarization mode dispersion (PMD) and time-varying RSOP are present. The theoretical analysis is validated through numerical simulations. Our findings reveal that the rotation rates of both the input and output PSPs significantly differ from the channel’s RSOP rate in most scenarios. Moreover, under varying RSOP distribution scenarios within the channel, the relationships among the rotation rates of input PSP, output PSP and RSOP also differ, and therefore rotation rates of input or output PSPs can reflect the changes of RSOP, indicating that monitoring PSP rotation rate can enable a better understanding of RSOP. Furthermore, we propose a DSP-based algorithm for monitoring PSPs and their rotation rates. By jointly applying a sliding-window median filter and a modulus judgment procedure, the algorithm yields more accurate PSP trajectories and rotation rate estimates than the existing approaches in literature, while relying solely on the existing DSP module without requiring any additional hardware. The recovered PSP orientation and rotation rate information can then be fed into the CMA equalizer, enhancing its compensation performance and thereby improving the overall stability and performance of the coherent optical system. Full article