Search Results (885)

We propose a silicon carbide (3C-SiC) periodic grating structure based on quasi-bound states in the continuum (q-BICs), which is used to significantly enhance the second-order optical nonlinear effect, including second-harmonic generation (SHG) and sum-frequency generation (SFG). By introducing a four-segment sub-wavelength grating on the SiC thin film and tailor the dimension, the structure successfully excites two q-BIC modes with ultra-high Q factor (resonant wavelengths at 1713.2 nm and 1804.6 nm respectively), realizing enhanced localization and nonlinear interaction of the strong light field. The simulation results show that under oblique incidence, the structure significantly enhances SFG efficiency and exhibits strong robustness to variations in key structural parameters. In addition, the study also reveals the coexistence of forward and backward SHG, and resonant wavelength tuning can be achieved by adjusting the structure dimension. This work not only provides a new path to enhance the nonlinear conversion efficiency of SiC thin films and solve the problem of difficult phase matching, but also lays the theoretical and technical foundation for the development of compact, efficient and integrated SiC-based nonlinear photonic devices. Full article

The technological promise of nonlinear optical (NLO) compounds has stimulated intense interest in optoelectronic devices, data storage, photonics, and anticancer therapy. Thiosemicarbazone ruthenium materials are of growing interest because of their tunable ligand framework and coordination sphere, allowing fine control over geometry, electronics, and functional properties. Here, we report an N-substituted salicylaldehyde thiosemicarbazone ligand and a series of octahedral Ru(III) complexes bearing triphenylphosphine or triphenylarsine and halide (Cl, Br) co-ligands. The complexes were characterized by elemental analysis, FT-IR, UV–Vis, EPR, mass spectrometry, and magnetic susceptibility measurements, which together confirm NS-chelation to a low-spin Ru(III) center in a distorted octahedral environment. Their photophysical and NLO responses were assessed by UV–Vis spectroscopy and powder second-harmonic generation measurements (Kurtz–Perry method), revealing promising NLO behavior. In parallel, antioxidant activity and in vitro anticancer effects against HeLa cells were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assays. These results provide insight into ligand-controlled structure–activity relationships, in which the halide (Cl/Br) and ancillary triarylphosphine co-ligands regulate electronic interactions and lipophilicity and ultimately increase biological performance, underscoring the dual materials and medicinal potential of these Ru(III) complexes. Full article

The cavity-less electro-optic combs (EOCs), recognized for exceptional tunability, stability and high power, are a crucial enabler for the fields such as optical communications, precision measurement and metrology, and microwave photonics. This work systematically investigates the fundamental physical factors that govern the spectral flatness via ultrafast measurements and modeling simulations. The ultrafast analysis results demonstrate that, the finite effective modulation extinction ratio of the electro-optic intensity modulators will result in generation of coherent spectral components with identical frequencies but varying phases and amplitudes in ultrashort temporal scale, finally lead to remarkable spectral interference and further intensity fluctuations across the combs spectrum. Furthermore, the established mathematical relationship between the spectral flatness and the modulation extinction ratio of the intensity modulators exhibits a nonlinear dependence up to the third order. Cascading intensity modulators has been exploited to mitigate the spectral interference and improve the modulation extinction ratio, which has been verified by using home-made high sensitive autocorrelator and frequency-resolved optical gating (FROG), and finely spectral flatness of 0.54 dB among 11 lines has been achieved, which recognized for the first time that modulation extinction ratio related spectral interference phenomenon play a subtle role in EOCs generation. Furthermore, photonic analog-to-digital converters (PADCs) have been investigated and an obvious enhancement in signal-to-noise-and-distortion (SINAD) is achieved, These findings will provide crucial theoretical and experimental support for optimizing EOCs performance, and advance the development and application. Full article

The constant growth of IP data traffic, driven by sustained annual increases surpassing 26%, is pushing current optical transport infrastructures towards their capacity limits. Since the deployment of new fiber cables is economically demanding, ultra-wideband transmission is emerging as a promising cost-effective solution, enabled by multi-band amplifiers and transceivers spanning the entire low-loss window of standard single-mode fibers. In this scenario, an accurate modeling of the frequency-dependent fiber parameters is essential to reliably model optical signal propagation. In particular, the combined impact of attenuation variations with frequency and inter-channel stimulated Raman scattering (SRS) fundamentally shapes the power evolution of wide wavelength division multiplexing (WDM) combs and directly affects nonlinear interference (NLI) generation, as well as the amount of ASE noise. In this work, we review a set of analytical approximations, based on phenomenological approaches, for frequency-dependent attenuation and Raman scattering gain, and analyze their impact on achieving an effective balance between computational efficiency and physical fidelity. Through extensive analyses performed with the open-source software GNPy (version 2.12, Telecom Infra Project) on an optical line system exploring multi-band scenarios spanning C+L+S, C+L+E, and U-to-E transmission, we demonstrate that the proposed approximations reproduce the reference SRS power evolution and NLI profiles with root mean square errors (RMSEs) consistently below 0.03 dB, and down to the 10⁻³–10⁻² dB range for the most accurate configurations. Although the current implementation does not yet provide a direct reduction in computational time, the proposed framework lays the groundwork for future developments toward closed-form or semi-analytical solutions, enabling more efficient modeling and optimization of ultra-wideband optical transmission. Full article

This study examines a nonlinear partial differential equation, namely the (3+1)-dimensional Boussinesq-type equation. To explore this model, three versatile analytical approaches are applied: the Exp-function method, the Kudryashov method, and the Riccati equation method. Using these techniques, a range of exact analytical solutions is derived, exhibiting diverse structural forms such as periodic, kink-type, rational, and trigonometric solutions. The analysis reveals the rich dynamical behavior of the equation and demonstrates its effectiveness in modeling a variety of nonlinear wave phenomena across different physical contexts. Several of the obtained solutions are illustrated through graphical representations for better interpretation. The results include hyperbolic, trigonometric, and rational function solutions, along with a sensitivity analysis. To highlight the physical relevance of the findings, suitable parameter values are selected, and the corresponding wave behaviors are visualized using three-dimensional and contour plots generated with Maple 2024. Overall, the study provides valuable insights into the mechanisms underlying the generation and propagation of complex nonlinear phenomena in fields such as fluid dynamics, optical fiber systems, plasma physics, and ocean wave transmission. Full article

Line-field spectral-domain optical coherence tomography (LF-SD-OCT) offers high-speed parallel imaging, but lateral beam expansion limits the photon budget per spatial channel, compromising sensitivity. Here, we demonstrate a high-speed LF-SD-OCT system driven by a gain-managed nonlinear (GMN) all-fiber source operating at a central wavelength of 1063.2 nm. Delivering 269 mW of average power with a smooth 98 nm (3 dB) bandwidth, the GMN source effectively fulfills the stringent photon budget and stability requirements of parallel detection. The system achieves a 5.68 μm axial resolution and a ~1.2 mm effective imaging range. Ex vivo porcine myocardial tissue ablation experiments validate its capability for high-contrast cross-sectional visualization of ablation crater morphology, showing excellent agreement with optical microscopy. These results establish GMN-enabled LF-SD-OCT as a robust solution for the precise intraoperative monitoring of laser-induced tissue damage. Full article

Accurate temperature control in ceramic roller kilns is critical for ensuring product quality; however, it remains challenging due to nonlinear thermal dynamics and the spatial lag inherent in traditional contact-based sensors. To address the limitations of sparse wall-mounted thermocouples and optical interference in kiln images, this paper presents a multimodal spatiotemporal fusion network (MST-FusionNet) for noncontact temperature detection of ceramic bodies on roller tracks. The proposed network integrates in-furnace combustion image sequences with distributed thermocouple measurements. First, a physics-informed pseudo-heatmap generation strategy based on Gaussian distributions is introduced to align discrete thermocouple readings with visual features, enabling effective early-stage multimodal fusion. Second, a residual compensation mechanism uses thermocouple data as a stable reference to learn local temperature deviations from visual and temporal features. In addition, an attention-enhanced LSTM module is employed to model combustion dynamics and suppress unreliable frames caused by smoke and flame fluctuations. Experimental results on a real industrial dataset show that the proposed method achieves a mean absolute error of 0.9164 °C and a root mean squared error of 1.2422 °C, demonstrating better performance than single-modal methods and simple fusion baselines. The proposed framework exhibits stable spatial characteristics across different roller positions and helps bridge the spatial discrepancy between boundary measurements and the actual thermal state of ceramic products, providing an effective solution for temperature detection in roller kilns. Full article

Transverse mode instability (TMI) in high-power ytterbium-doped double-clad fiber lasers is widely interpreted as being a consequence of a thermo-optic nonlinear phenomenon driven by stimulated thermal Rayleigh scattering. This work presents a coupled optical–thermal model for a continuous-wave forward-pumped (${\lambda }_p=976\mathrm{nm}$) fiber amplifier emitting at ${\lambda }_s=1064\mathrm{nm}$ over an optimal length of 12 m. The formulation explicitly resolves the three radial regions of a double-clad fiber, avoiding single-clad approximations. Modal fields are computed using the weakly guiding approximation (WGA) in the core combined with the semi-WGA at the cladding interfaces, enabling accurate calculation of higher-order modes of penetration into the inner cladding and of the transverse eigenvalues $U_{01}$ and $U_{mn}$ relevant to TMI. Within this framework, the nonlinear stimulated thermal Rayleigh scattering coupling coefficient is evaluated, including gain saturation and the thermal eigenmodes of the multi-layer geometry. The results show that the inner cladding modifies both the optical and thermal mode structures, altering the optical–thermal overlap between ${\mathrm{LP}}_{01}$ and higher-order modes and changing the effective strength of STRS, directly influencing the predicted TMI threshold. The proposed formulation provides a quantitative and physically consistent tool for analyzing thermo–optic dynamics in Yb-double-clad fiber amplifiers and supports the design of next-generation high-power fiber lasers with improved modal stability. Full article

This paper proposes a short-term photovoltaic (PV) power prediction method that integrates aerosol optical feature mining with a dual-channel attention mechanism to address the complex non-linear attenuation effects of atmospheric aerosols and the limitations of existing models in handling sudden meteorological changes and aerosol evolution. Using the optical properties of aerosols and clouds (OPAC) database, a high-dimensional aerosol optical feature set is constructed, which is subsequently optimized using the minimum redundancy maximum relevance (mRMR) algorithm. The prediction scenarios are categorized into polluted and clean regimes through K-means clustering. A dual-channel encoder–decoder network, combining bidirectional long short-term memory (BiLSTM) and iTransformer, is developed to capture high-frequency meteorological volatility and low-frequency aerosol evolution. A bidirectional cross-attention mechanism enables deep feature interaction between the optical and meteorological channels. The method is validated using in situ measurements from a PV station in Hebei, China, along with aerosol data from the Copernicus Atmosphere Monitoring Service (CAMS) and meteorological data from the ECMWF Reanalysis v5 (ERA5). Experimental results demonstrate an average reduction of approximately 29.83% in mean absolute error (MAE) on polluted days and 15.22% on clean days. Interpretability analysis reveals distinct physical mechanisms driving the predictions, emphasizing the role of extinction on polluted days and scattering on clean days. Full article

A focus-control mechanism is essential for maintaining the optical performance of spaceborne telescopes, the mirror alignment of which is degraded by gravity release, moisture desorption, and thermal distortion in orbit. Achieving submicrometer-level drive accuracy is challenging because bearing deformation and bolted-joint hysteresis introduce nonlinear behavior, which must be addressed in ultraprecision mechanisms. In this study, the 1D Computer-Aided Engineering (1DCAE) approach was applied to the early-phase design of a spaceborne focus-control mechanism for developing practical design equations that accurately represent the stiffness and deformation characteristics of key components. Modification functions derived from finite element analysis (FEA) and the indirect fictitious boundary integral method (IFBIM) were incorporated into the equations for a linear guide, rectangular spring, and bearing deformation. These equations showed excellent agreement with analytical solutions, numerical simulations, and experimental data, achieving accuracies within 3% and 2.5% for the linear guide and rectangular spring, respectively, and close correspondence with the IFBIM-based bearing deformation reference values. Integrating the equations into the 1DCAE model enabled accurate prediction of the nonlinear drive characteristics of the mechanism and improved the overall drive accuracy to one-fortieth that of the initial design. In conclusion, 1DCAE provides an effective and computationally efficient framework for optimizing ultraprecision mechanisms used in space applications. Full article

The thickness of silicon carbide (SiC) wafers is a crucial parameter that significantly affects the performance of devices, and its high-precision online measurement during chemical mechanical polishing (CMP) faces challenges from complex process-induced errors. To address this issue, this study develops a non-contact online thickness measurement system based on oblique-incidence laser triangulation and proposes a hierarchical hybrid error compensation method. Deterministic systematic errors caused by optical interference from polishing slurry are first compensated by combining an optical propagation physical model with experimental calibration. Subsequently, a Long Short-Term Memory (LSTM) network model is introduced to compensate for nonlinear, time-series-related dynamic random errors, primarily induced by temperature drift and associated thermal effects. Experimental results indicate that, after applying the proposed compensation method, the root mean square error (RMSE) of the online thickness measurement is 0.47471 $\mathsf{\mu }\mathrm{m}$, and the mean absolute percentage error (MAPE) is 0.1102%. The deviation from reference thickness values is maintained within ±1 $\mathsf{\mu }\mathrm{m}$. The proposed method provides an effective solution for high-precision online thickness measurement and error compensation in the SiC CMP process. Full article

This paper presents a comprehensive analysis and simulation of a cost-effective optical Intensity-Modulation/Direct-Detection (IM/DD) Orthogonal Frequency Division Multiplexing (OFDM) system. Implemented via a MATLABR2024a and OptiSystem 23 co-simulation environment, the study evaluates a 4-QAM modulated link over a 120 km transmission distance, providing detailed investigations into signal spectral properties and constellation characteristics. To address the critical performance limitation posed by high Peak-to-Average Power Ratio (PAPR), a novel Hybrid Whale Optimization Algorithm with Selective Mapping (HWOA-SLM) is proposed. Simulation results demonstrate that the proposed scheme significantly outperforms conventional reduction techniques; specifically, at a Complementary Cumulative Distribution Function (CCDF) of 10⁻² and a fixed computational budget of 256 evaluations, the HWOA-SLM achieves a PAPR reduction gain of 3.9 dB relative to the original OFDM signal. Furthermore, in terms of algorithmic efficiency, it outperforms standard Genetic Algorithm (GA) and WOA-based SLM techniques by approximately 0.4 dB under identical computational budgets. Parametric analysis further confirms that increasing population size and iteration numbers consistently improves convergence, thereby minimizing non-linear distortions and enhancing signal integrity. Moreover, the technique exhibits superior Bit Error Rate (BER) performance, delivering Optical Signal-to-Noise Ratio (OSNR) gains of 0.63 dB, 1.31 dB, and 2.0 dB over standard WOA-SLM, GA-SLM, and conventional SLM, respectively. Conclusively, the HWOA-SLM offers a favorable trade-off between computational complexity and reduction efficiency, validating its potential for reliable, high-speed optical communication networks. Full article

This paper investigates the optical solitons to the M-truncated fractional $(1+1)$-dimensional nonlinear generalized Bretherton model with arbitrary constants. It is employed to forecast the movement of liquid droplets or gas bubbles in microchannels, which is crucial for drug delivery systems, biomedical diagnostics, and lab-on-a-chip technologies. We obtain optical soliton solutions using the extended hyperbolic function method (EHFM) and the modified extended tanh method (METM). Numerous solutions, such as singular, periodic–singular, bright, and dark optical solitons, are obtained from our investigation. The $2D$ graphical depiction of the solutions shows a variety of wave patterns that change with varied values of $\alpha$ and t. The wave’s amplitude forms become more apparent as $\alpha$ and t increase. Using 2D plots, the comparison of fractional effects for the M-truncated fractional derivative is demonstrated by giving specific values to the fractional parameter. Full article

Laser-based manufacturing processes—including marking, hardening, cutting, and welding—demand the precise selection of processing parameters, as the resulting surface state is critically dependent on the delivered power density and beam–material interaction time. This study presents a unified predictive framework for estimating the critical surface power density thresholds for melting q_scm and evaporation q_scv as functions of scanning speed v for the following four technologically important metallic materials: titanium, C26000 brass, SS304 stainless steel, and 42CrMo4 alloy steel. The principal novelty of this work is twofold. First, it provides the first directly comparative analysis of these four materials under identical, standardized laser conditions (λ = 1064 nm, d = 40 μm, constant absorptivity A = 0.4), eliminating the confounding effects of variable beam geometries and optical assumptions that hinder cross-study comparisons. Second, it translates fundamental thermophysical principles into a practical engineering tool, such as a validated spreadsheet calculator that outputs material-specific threshold curves in real time, enabling rapid, physics-based parameter estimation without recourse to complex numerical simulations. The computed threshold curves exhibit a consistent non-linear increase with scanning speed for all materials, governed by the inverse relationship between interaction time and required power density. The following clear material hierarchy emerges: C26000 brass exhibits the highest thresholds (e.g., q_scm = 0.94 × 10¹⁰ W/m², q_scv = 10.74 × 10¹⁰ W/m² at v = 100 mm/s) due to its high thermal conductivity, while titanium shows the lowest (q_scm = 0.19 × 10¹⁰ W/m², q_scv = 0.48 × 10¹⁰ W/m² at v = 100 mm/s) as a consequence of strong heat confinement. SS304 and 42CrMo4 occupy intermediate positions, with 42CrMo4 demonstrating notably higher evaporation resistance than SS304 despite similar melting thresholds. The resulting dual-threshold framework delineates three distinct process regimes—sub-melting heating, melting-dominant processing, and evaporation—providing a quantitative basis for parameter selection in applications ranging from surface hardening to micromachining. By bridging the gap between theoretical material science and applied manufacturing, this work offers a robust, first-order reference for process design and establishes a methodological template for future comparative studies of laser–material interactions. Full article

Molybdenum tellurite compounds have attracted increasing interest as promising nonlinear optical (NLO) materials, yet their microscopic second-harmonic generation (SHG) mechanisms remain unclear. In this work, the electronic structures and SHG responses of ATeMoO₆ (ATM, A = Mg, Cd, Zn) are systematically investigated using first-principles calculations combined with atom response theory. The results show that the SHG responses are mainly governed by the occupied nonbonding O 2p states and the unoccupied Mo 4d and Te 5p states. Our atom response theory analysis reveals that a strong synergistic effect between stereochemically active lone pairs (SCALPs) on Te atoms and nonbonding O 2p states critically enhances the SHG response in ZnTM and MgTM. In contrast, the relative weaker Te SCALPs in CdTM fail to provide a comparable contribution, leading to its lower SHG performance. The structure group analysis reveals that MoO₄ units dominate the SHG response, while TeO₄ units provide secondary contributions. Moreover, group dipole moments are found to be insufficient to explain the SHG behavior. These findings provide microscopic insights into SHG origins and offer guidance for NLO material design. Full article