This paper presents an active tunable optical modulation system based on a silicon and silicon dioxide composite metamaterial surface. By rotating the nanorods, the bound states in the continuum is transformed into quasi-bound states in the continuum with high Q factor, and its magnetic dipole resonance dominant characteristic is confirmed. Further research reveal that bound states in the continuum are robust for geometric shapes, providing flexibility for device design.In particular, by integrating different materials other than silica and the angle of incident light, the broken structural symmetry, by using different refractive indices, produces different couplings, realizes the superposition of bound states in the continuum, thus generating new couplings, and enhances the control of the Goos–Hänchen (GH) shift under specific conditions,shift reaches -1414 λ0, far exceeding the optical interface.The GH shift occurs when light is fully reflected at the interface. The GH shift effect will cause the wave packet that should return along the original path to shift laterally, and the offset can reach tens to hundreds of nanometers.This study demonstrates a feasible approach to achieving high-performance reconfigurable photonic devices through control of structural symmetry and multi-parameter optimization of materials.
multispectral camouflage is important in modern military, particularly given the ongoing challenges in achieving synergistic control between high transmittance in visible range and spectrally selective emission in 3-14 μm. This paper proposes a practical inverse design strategy combining Bayesian optimization and genetic algorithms (Bayes-GA) for transparent multilayer films with infrared spectrally selective emissivity. The method operates in a four-dimensional space (material, number of layers, sequence, and thickness), automatically determining optimal hyperparameters as loss function weights. An optimized Ta₂O₅/ITO four-layer structure is designed, achieving a visible light transmittance of 72%, low emissivity in the atmospheric window (0.46 at 3–5 μm and 0.35 at 8–14 μm), and high emissivity (0.74) in the non-window band of 5–8 μm for radiative cooling. The structure exhibits insensitivity to variations in thickness (±10%) and incident angle (0°–60°), facilitating large-scale sputtering deposition fabrication. Furthermore, by coupling a color layer to the bottom layer, this film system enables multicolor visible light camouflage. This work provides an efficient and universal solution for the automated, high-degree-of-freedom design of multi-spectral compatible camouflage materials.
Compact ultraviolet varifocal components are highly desirable for miniaturized imaging, optical inspection, and integrated photonic systems. Here, we numerically demonstrate a bilayer Ta2O5 Moiré metalens operating at 325 nm that enables continuous focal-length tuning and varifocal imaging. The device comprises two cascaded propagation-phase metasurfaces with complementary rotational phase profiles. Relative in-plane rotation continuously modifies the effective quadratic phase curvature of the bilayer system, allowing the focal length to be tuned without axial displacement or active-material modulation. A polarization-insensitive library of Ta2O5 nanopillars with high transmittance and nearly complete 2π phase coverage is employed to realize the designed phase profiles. Cascaded full-wave simulations show that the focal length decreases from 122.25 to 29.90μm as the relative rotation angle increases from 30° to 120°, while the numerical aperture increases from 0.1218 to 0.4484. The extracted focal lengths differ from the prescribed analytical values by less than 3.1%, while the focal-spot full width at half maximum decreases from 1.49 to 0.35μm. Rotation-controlled imaging of the same binary letter “UV” provides a quantitative proof-of-concept demonstration of on-axis image-scale variation, with the relative image scale varying from 1.00× to 1.60×. These results provide a compact and mechanically simple route toward ultraviolet varifocal meta-optics for miniaturized imaging, optical inspection, and integrated photonic systems.
Depth-multiplexed metasurface holograms reconstruct different optical payloads at different propagation planes under single-wavelength illumination. However, many demonstrations rely on idealized continuous phase profiles, leaving insufficiently quantified whether depth selectivity can be preserved after implementation with a finite, fabricable meta-atom library. Here, we develop a finite-library-constrained numerical design and evaluation workflow for a TiO₂ nanopillar holographic metalens operating at 532nm. The workflow explicitly connects continuous multi-plane phase optimization, direct projection onto a 12-state FDTD-calibrated nanopillar library, and re-optimization under the same finite-library constraint. Correct-plane fidelity, wrong-plane crosstalk, axial selectivity, incident-power-normalized energy budget, fabrication tolerance, multiplexing capacity, and the validity of the local-periodic approximation are evaluated. The optimized four-channel device achieves correct-plane correlations of 0.84–0.86 while keeping all wrong-plane correlations at or below zero. It also reaches a mean incident-power-normalized ROI efficiency of 33.8%, with values ranging from 31.0% to 36.4% across the four reconstruction planes. Direct finite-library projection yields a mean correlation of 0.841, whereas the subsequent re-optimization increases it to 0.846 and reduces the inter-channel correlation range from 0.020 to 0.013, indicating that its primary role is to balance reconstruction quality among the four axial channels. Compared with a library-aware multi-plane Gerchberg–Saxton baseline that projects onto the same finite library at every iteration, the proposed route improves the mean correlation by 0.127 and maintains stronger wrong-plane suppression. A twelve-patch full-wave cross-check spanning low-, medium-, and high-gradient regions and aperture-edge positions gives a mean complex-field correlation of 0.86 ± 0.05 with the local-periodic model, while channel-count and depth-configuration tests identify four channels as the practical capacity of the present geometry. These results provide a numerically validated route for translating continuous multi-plane hologram designs into finite-library metasurface implementations while preserving depth-selective reconstruction and balanced channel performance.
A metamaterial absorber (MMA) using a cost-effective nickel material is proposed for infrared region applications. The resonating patch is composed of a metamaterial-based circular resonator with unique fourfold rotationally symmetric curved arms. The cost-effective nickel (Ni) material is utilized for both bottom and top conductive layers, and Rogers RT5880 is used as a dielectric material for the proposed absorber structure. The transmission of electromagnetic radiation is prevented by the bottom-side nickel-based layer. The overall physical size of the proposed unit cell is only 1.7 μm × 1.7 μm × 2.5µm, which corresponds to an ultra-compact electrical size of 0.0916λ0 × 0.0916λ0 × 0.1347λ0. The proposed absorber maintains a high absorptance of ≥90% over an ultra-wide absorption bandwidth of 25.36THz with polarization insensitivity and wide angular stability. It operates from 16.16THz to 41.52THz, corresponding to 7.22 μm to 18.55 μm wavelength range, covering the designated spectrum of the long-wave infrared (LWIR) atmospheric window (8–14 μm) and partly extending into adjacent infrared spectral regions. The absorption bandwidth of 25.36THz corresponds to a relative bandwidth (RBW) of 87.93%. The proposed thermal MMA shows Full Width at Half Maximum (FWHM) of 120%, which is 37.5THz, covering 12.5 to 50THz ultrawide spectrum. The proposed MMA effectively maintains a spectral emissivity of ≥0.90 across its entire functional band, confirming its applicability as an efficient ultra-wideband thermal emitter. Based on the results of this proposed study, the recommended nickel-based polarization-independent infrared metamaterial absorber (IR-MMA) could be an excellent option for thermal imaging, molecular spectroscopy, and stealth technology applications.
In this study, a one-dimensional photonic multilayer combining parity-time (PT) symmetry and the Thue-Morse sequence, with a highly nonlinear perovskite thin film inserted at its central region, is proposed to achieve nonlinear optical bistability. By numerically solving the theoretical model via the transfer matrix method, the results indicate that the response of optical bistability is highly sensitive to system parameters, including the thickness of each dielectric layer, the nonlinear Kerr coefficient of the perovskite layer, the incident angle, and the wavelength of the input light. When the incident wavelength is tuned over the 532–552nm spectral range, the first S-shaped bistable hysteresis loop attains its minimum width of 0.0022GW/m² at 532nm, whereas a maximum on/off ratio of 3.75dB is realized at the operating wavelength of 541nm. As the incident angle increases from 0° to 70°, substantial changes in both the bistable loop width and the associated on/off ratio are observed for TE and TM polarizations alike. The results demonstrate that the optical bistability with flexibly controllable width and greatly reduced switching threshold can be achieved by properly adjusting the corresponding parameters.
This theoretical study investigates the influence of incidence angle on coherent perfect absorption (CPA) in a symmetric thin-film metastructure (STMS). The STMS consists of two Si/SiO2 distributed Bragg reflectors and a central absorbing InSb-Ag-InSb defect. The dependence of the defect-mode resonance on incidence angle and relative phase is analyzed, together with its potential for spectral incidence-angle readout. Results indicate that the peak frequency shifts significantly as the incidence angle changes, exhibiting a distinct quasi-linear relationship. The angle-dependent CPA resonance exhibits a quasi-linear frequency shift over the range from 20° to 80°, with a fitted angular sensitivity of 0.0715 THz/° and a maximum quality factor exceeding 900. This response suggests a theoretical route for spectral readout of the common incidence angle of two symmetric coherent beams. This approach provides a new perspective for research in CPA and sensing technology, presenting potential utility across various fields.
Bound states in the continuum (BICs) offer a powerful route to high quality-factor (Q) resonances with exceptional light confinement. Here, we demonstrate multiple deterministic strategies to engineer tunable quasi-BICs in metasurfaces composed of bulk tungsten disulfide (WS₂) nanocylinders, leveraging geometric symmetry breaking without complex materials or external tuning. By introducing controlled asymmetry—via radial downsizing, elliptical deformation, or semicircular truncation of a single meta-atom within a 2×2 supercell—we activate high-Q quasi-BIC resonances with Q-factors 24800. Crucially, these resonances exhibit strong polarization and angular sensitivity: elliptical and semicircular designs enable continuous tuning of resonance wavelength and Q-factor through incident field rotation. The semicircular design, in particular, unveils a rich multi-resonant landscape under varying polarization, enabling multi-wavelength operation within a single unit cell. Our work establishes bulk WS₂ metasurfaces as a robust, CMOS-compatible platform for high-Q nanophotonics, with immediate applications in polarization-selective filtering, rotation sensing, nonlinear optics, and reconfigurable integrated photonic devices, all realized through simple, geometry-driven design.
Cross-fidelity transfer learning is widely used to accelerate neural-network (NN) surrogate modeling of nanophotonic structures, yet its benefit varies unpredictably across structures. We address this gap for physics-based transfer learning (PBTL) of metal–insulator–metal (MIM) absorber surrogates. First, we decompose PBTL into analytical physics features and transfer-matrix-method (TMM) pre-trained weights on three Cr-based absorbers: physics features yield a robust 4%–30% mean-absolute-error (MAE) reduction, while weight-level transfer is positive throughout but fidelity-graded—at matched n=350 the benefit tracks TMM–rigorous coupled-wave analysis (RCWA) spectral fidelity (＋31.3%, ＋13.5%, ＋9.7% for Structures A, B, C; peak ＋49.7% at n=50), and an Au/SiO2 check is positive on both structures tested. Second, we introduce a raw-output transferability indicator: a joint pilot-set diagnostic combining TMM–RCWA spectral correlation r (shape) and operating-band MAE (amplitude), with no principal-component projection or pre-trained model. Under controlled noise injection the benefit falls monotonically from ＋47% to −58% at zero fidelity (Spearman ρ=−1.0), and the amplitude MAE predicts the benefit markedly better than shape correlation (|Pearson|=0.98 vs. 0.81). Third, negative transfer arises only under controlled degradation—near zero fidelity for Structure A, at moderate noise (σ=0.10) for B and C. A 50-sample RCWA pilot (∼15–30 min) evaluates the diagnostic before the full pipeline (∼4–5h). The framework is solver-pair-agnostic pending broader validation.
This work demonstrates, for the first time, the use of calcined Zeolite Beta (BEA) nanoparticles as a high-performance optical modulator in a thulium-doped fibre laser (TDFL) cavity. As saturable absorbers (SAs), the BEA nanoparticles exhibit robust nonlinear properties, including a modulation depth of 4.2% at 1950 nm. Incorporating the BEA SA into the TDFL cavity enables the generation of stable mode-locked pulses with a 1.42 ps pulse duration and a 13.8 MHz repetition rate. The system has a high level of operational reliability, as evidenced by a signal-to-noise ratio (SNR) of ~58 dB and negligible fluctuations in output power over extended observation periods. The results of this work show that calcined BEA is a scalable and cost-effective alternative to traditional non-linear optical modulator materials, including 2D materials, and paves the way for a new frontier in ultrafast mid-infrared photonics.
Engineering the helicity of single photons is a central challenge in nanophotonics and quantum optics, with applications ranging from chiral light-matter interactions to quantum communication protocols. We investigate the effects produced by a chiral cavity consisting of two twisted anisotropic photonic crystal mirrors on the spontaneous emission of a quantum system. For a given vacuum wavelength, the considered mirrors can be engineered to concurrently exhibit high helicity-preserving reflectance for one circular polarization and high transmittance for the opposite one, for incidence angles up to 20◦ with respect to the optical axis. Considering an atomic two-level system within thecavity, we evaluate the total dyadic Green function, taking into account both inhomogeneous and scattering electromagnetic contributions. We demonstrate that optimal configurations can achieve a 3% imbalance between the spontaneous emission rates of right- and left-circularly polarized light when averaged over random dipole orientations. Remarkably, this imbalance increases to 20% under suitably tuned dipole orientations. Even larger values are expected for two-dimensional arrays of such dipoles that isolate the normal component of the emitted field, while the remaining contributions interfere destructively. We envision that the proposed system will expand the set of tools availablefor investigating chiral matter and support the development of compact sub-micrometer circularly polarized single-photon sources.
Metamaterials exhibit a diverse range of capabilities in electromagnetic manipulation. However, designing metamaterial structures for expected functions encounters an inverse problem. The advent of deep learning offers a data-driven approach to address this issue. To enhance the transparency of deep learning models, coupled mode theory (CMT) is incorporated into the design process. Despite this advancement, efficiently extracting coupled mode parameters for neural network training remains a significant challenge. To address this, we propose a simulation-free theory-driven pretraining neural network method for extracting coupled mode parameters. Using these extracted parameters, we perform both forward and inverse design of metamaterials, demonstrating the benefits of integrating CMT into intelligent design. By incorporating CMT, our approach transitions from a purely data-driven model to a "physics-driven" one, improving design accuracy. Compared to end-to-end data-driven methods, our CMT-based scheme offers superior design precision. The results, validated by simulation data, highlight that our method bridges the gap between intelligent and interpretable design.
Femtosecond laser irradiation of metal thin films can induce complex dynamics, such as protrusion, jetting, and nanoparticle formation. These are governed by both energy deposition and film-substrate mechanical coupling. In this study, we use coupled two-temperature molecular dynamics (TTM-MD) simulations to investigate the nonequilibrium thermomechanical response of a gold thin film in the paraxial region under laterally confined laser excitation. We systematically vary the electron diffusion coefficient, absorption depth, rear-side thermal and mechanical boundary conditions to identify how longitudinal energy deposition, electron-lattice coupling, and stress evolution control jet initiation and stability. Our results show that confined electron diffusion significantly enhances near-surface peak temperatures and transient tensile stresses, leading to stress-dominated local material separation. Implementing a dissipative rear-side boundary that mimics a substrate allows stress waves to be transmitted and attenuated, so that jetting is primarily driven by the release of near-surface nonequilibrium pressure and evolves into stable needles or liquid clusters. Spatiotemporal maps of atomic stress and stress rate reveal how localized mechanical stresses nucleate jets and clusters, thereby providing clear mechanical initial conditions for subsequent surface-tension-driven morphology evolution. This atomic-scale stress-based picture refines our understanding of laser-induced nanostructure formation in metal thin films and supplies physically grounded initial conditions for multiscale jetting models.
The excitation of surface plasmon polaritons (SPPs) by two-dimensional protrusions and depressions on a flat plasmonic metal surface illuminated by a normally incident plane wave is investigated. We employ an analytical approach treating SPPs as waveguide eigenmodes excited by a current source. A model is developed to describe the distribution of effective currents within Gaussian-profile protrusions and depressions responsible for SPP excitation. This approach extends beyond the classical Born approximation for the electromagnetic field intensity inside inhomogeneities by introducing corrections to account for polarization effects. This allows us to derive analytical expressions describing the dimensional (dependence on inhomogeneity size) and spectral (wavelength dependence) characteristics of the SPP response of such structures. The presented theory shows good agreement with the results of full-wave numerical simulations. The proposed approach also demonstrates the difference in SPP response between isolated protrusions/depressions and their arrays forming a periodic corrugation on the metal surface. It is shown that, in the case of sinusoidal gratings, polarization corrections—which are significant for individual inhomogeneities—are not required to quantify the resonant SPP response at the fundamental spatial frequency of the corrugation. The proposed analytical framework reduces computational costs and may serve as a useful tool for the design of nanophotonic devices and plasmonic metamaterials with desired optical properties.
The research compared a novel Ag@Cu@Ag core double-shelled composite to existing nanomaterials, including Ag NPs, Cu NPs, and Ag@Cu core shells. Using a pulsed laser technique in deionized water, the novel composite exhibited superior electrical and photoresponsive characteristics. Key parameters included 1200 mJ energy, 5Hz frequency, 500 light pulses, and a 1064nm wavelength. XRD analysis confirmed the presence of silver and copper, revealing crystal sizes of 15.56nm (Ag NPs), 70.96nm (Cu NPs), 22.29nm (Ag@Cu single shell), and 14.79nm (Ag@Cu@Ag double shell). The structure of the core shell was confirmed by TEM testing, and the particle form was spherical. The mean particle size of Ag -NPs, Cu- NPs, Ag@Cu core shell and Ag@Cu@Ag core double-layer shell had been 19.4, 17.4, 19.7 as well as 19.8nm, respectively. FESEM determined the nanoparticles' spherical shapes and sizes: 76nm (Ag), 66nm (Cu), 71nm (Ag@Cu CSNPs), and 98nm (Ag@Cu@Ag CSNPs). UV-visible spectroscopy showed minimal change in absorbance peaks for the novel composite, indicating enhanced optical efficiency. The Ag@Cu@Ag composite also demonstrated excellent photoresponse and electrical properties, suggesting its potential for light-sensitive applications.
GaN based lasers are pivotal in blue and visible semiconductor lasers. However, conventional GaN lasers face limitations in field confinement and modulation bandwidth. This study proposes a kind of blue-band photonic crystal laser cavity incorporating a porous-GaN/GaN distributed Bragg reflector (DBR) and a heterogeneous photonic crystal (PhC) structure. The porous-GaN DBR addresses challenges in epitaxial stress and low refractive index contrast by leveraging electrochemical etching to achieve high reflectivity (>99.9%) with fewer layers (10 pairs) due to its tunable refractive index. The combination of hetero-structure PhC and porous-GaN DBR reduces resonant mode volume and in-plane losses while enhancing quality factor (Q>9000), simultaneously improves optical confinement factor (Γact=9.1358%). Through systematic investigations, the optimized configuration demonstrates a 3-dB modulation bandwidth exceeding 46 GHz and energy consumption as low as 0.18 nJ/bit.
In this paper, a tunable dual-function terahertz absorber is proposed by integrating the phase-transition property of vanadium dioxide (VO₂) with the Fermi-level tunability of graphene. Here, the dual functionality specifically refers to broadband absorption switching over 3.0–4.25 THz, with the absorptance tunable from nearly 0 to nearly 98%, and narrowband-to-broadband mode conversion over 4.25–5.50 THz. Electromagnetic-field analyses indicate that the broadband absorption is associated with the Fabry–Pérot (FP) cavity resonance between the graphene and VO₂ layers, together with dipolar and higher-order multipolar resonances induced by localized surface plasmon resonance (LSPR) in graphene, whereas the narrowband absorption mainly originates from the LSPR in the graphene layer. Further investigations show that the tunable absorptance can be realized through the electrically tunable properties of graphene and the thermally tunable properties of vanadium dioxide. In addition, in the broadband mode, absorptance above 90% can be maintained for incident angles from 0° to 50°, and polarization insensitivity can be achieved under normal incidence. The proposed absorber provides both broadband switching and broadband–narrowband mode switching, showing potential for multifunctional terahertz dynamic devices.
