Search Results (741)

A hybrid metasurface absorber (MSA) based on a central-bar-coupled split-disk dimer is proposed and numerically investigated for high-resolution refractive-index sensing in the near-infrared spectral region. The metasurface consists of silicon nitride dielectric resonators integrated with a gold plasmonic layer, enabling strong electromagnetic confinement, enhanced light–matter interaction, and ultra-narrow resonant features within the 1000–1400 nm wavelength range. The optimized structure supports multiple resonant modes under both x- and y-polarized excitation, producing sharp reflection dips with full-width-at-half-maximum values as low as 0.58 nm and quality factors reaching 2007. Refractive-index sensing performance was evaluated by varying the aqueous superstrate refractive index from 1.33 to 1.35, resulting in bulk sensitivities up to 860 nm/RIU under normal incidence. The angular response was further analyzed for incidence angles up to 5°, revealing polarization-dependent resonance splitting and the emergence of additional high-Q resonant branches under oblique excitation. Several angularly induced resonances exhibit narrower linewidths than those observed at normal incidence while preserving high refractive-index sensitivity up to 870 nm/RIU. Electric-field distributions confirm strong field localization near the dielectric boundaries and coupling regions, validating the hybrid resonant mechanism responsible for the enhanced spectral selectivity and sensing performance. The proposed MSA provides a promising platform for compact and ultrasensitive biosensing applications. Full article

To address the critical thermal challenges in high-performance computing and three-dimensional integrated circuits, the doping-tunable control of near-field thermal radiation using CMOS-compatible materials offers a highly promising non-contact cooling strategy. In this work, radiative heat transfer between two parallel heavily phosphorus-doped silicon plates separated by a vacuum gap is studied using fluctuational electrodynamics. A doping-dependent Drude model is employed to describe the dielectric response of doped silicon, including carrier concentration, ionization, and mobility effects. The influences of gap width and doping concentration on the total and spectral heat transfer are systematically analyzed. The results show that the heat transfer increases sharply as the gap decreases and is mainly governed by TM-polarized evanescent modes. Under symmetric doping, the spectral peak shifts to higher frequencies as the doping concentration increases from ${10}^{18}$ to ${10}^{21} {\mathrm{cm}}^{-3}$, while the strongest transfer occurs at ${10}^{19} {\mathrm{cm}}^{-3}$ because of favorable surface-plasmon-polariton coupling and impedance matching. These findings provide a theoretical foundation for chip-scale thermal management and on-chip radiative cooling in CMOS-compatible silicon platforms, although practical implementation would require dynamic tuning mechanisms and device-level engineering in future work. Full article

Periodic grating structures allow for the excitation of surface plasmon resonance (SPR) by matching the momentum of incident light to the plasmon mode. Herein, we investigate Au-coated sinusoidal gratings with depths from 50 nm to 280 nm using transmission and reflection spectroscopy. For gratings with an 806 nm period, increasing the modulation depths results in an SPR red shift of more than 125 nm, spectral broadening, and branch separation in the SPR dispersion. Rigorous coupled-wave analysis simulations using Gsolver (v5.2) reproduced the experimentally observed depth-dependent spectral trends. These results suggest that the grating modulation depth is a key structural parameter for tuning the SPR wavelength, bandwidth, and dispersion characteristics of a grating-coupled SPR system. Full article

Surface plasmons are collective oscillations of electrons that can confine light within extremely tiny nanoscale spaces, acting to enhance the spectral signals (such as Raman and circular dichroism) of molecules. Borrowed from circular dichroism in chemistry, plasmonic local circular dichroism (CD) refers to the difference in electric field enhancement excited by left-handed (LCP) and right-handed (RCP) circularly polarized light in a nanogap. Nanosphere trimers have been employed to realize local CD. However, spherical nanoparticles exhibit a small gap area and poor structural stability. In this article, we propose asymmetric nanocylinder trimers on SiO₂/Si substrate to realize a strong local CD signal. In contrast to nanospheres, nanocylinder sidewalls increase effective gap areas and can be obtained by nanofabrication. We find that the asymmetric nanocylinder trimer achieves a local CD parameter 0.94 under the excitation of 782 nm. This strong local CD within the gaps mainly originates from the near-field interference between different modes generated by circularly polarized light. Furthermore, the gap distance and symmetry have a significant influence on the local CD. A giant local CD can be obtained for small gaps (1 nm) and right-angle trimers. These results provide a physical basis for the development of plasmonic CD and chirality, and they are of interest for the field of nanosensors, nanoantennas, solar energy conversion, and polarization-dependent photochemistry. Full article

This study addresses a major challenge in hyperthermia therapy: achieving fast and efficient heat generation in target tissues. A novel magneto-plasmonic nanostructure is developed by combining gold nanorods (GNRs) and iron oxide nanoparticles (IONPs), each synthesized independently to compare their individual and combined heating performance. A key innovation was the use of (3-mercaptopropyl)trimethoxysilane (MPTMS) as a covalent linker, enabling the stable integration of both components into a single hybrid system. Under simultaneous near-infrared (NIR) laser and alternating magnetic field exposure, the hybrid nanostructure exhibited a rapid and intense temperature rise, surpassing the effects of either material alone. A control sample consisting of a physical mixture of the two components (GNR + IONP) reached SAR values comparable to those of the covalently linked hybrid (GNR + MPTMS + IONP) under simultaneous excitation, the two being equal within experimental error. Although the chemical linkage modifies the optical absorbance of the GNRs and may partially restrict the Brownian relaxation of the magnetic nanoparticles, these effects do not translate into a measurable loss of heating efficiency under combined activation. Importantly, the covalent linkage yields a robust, structurally stable assembly whose components move together—an essential requirement for functionalities such as magnetic guidance and targeted delivery of the whole nanostructure, which a simple physical mixture cannot provide. As a physicochemical proof of concept, these results establish the dual-mode heating performance of the hybrid nanostructure in aqueous suspension and motivate the biological evaluation required for any future therapeutic use. Full article

To overcome the large size of conventional high-gain antennas and the structural complexity of typical photonic crystal antennas, this paper proposes a cavity-free photonic crystal (PC) antenna driven by microwave-band Tamm plasmon polaritons (TPPs), which eliminates the conventional half-wavelength resonant cavity while maintaining a moderate total height (38.4 mm, ~2.1λ₀). The core innovation of this work lies in shifting the gain-enhancement paradigm from traditional bulky, volume-based spatial resonances to a direct 2-D interface feeding strategy. By rigorously satisfying the phase-matching condition between a one-dimensional PC and a highly reflective substrate, a strong TPP mode is excited. Distinct from conventional designs, we embed a simple microstrip patch exactly at this phase-matched boundary to directly exploit the extreme electric field localization of TPPs. This novel mechanism enables a cavity-free architecture that achieves highly directional emission without complex feeding networks or metallic cavities. Simulations and measurements exhibit excellent agreement. At 16.43 GHz, the measured peak gain reaches 16.4 dBi, with 3-dB beamwidths of 13.5° and 18.5°. Ultimately, this TPP-driven paradigm offers a practical solution tailored for advanced wireless communications and radio astronomy. Full article

Continuous and noninvasive body fluid monitoring has attracted increasing attention in personalized healthcare, chronic disease management, and wearable point-of-care testing. Fiber-optic surface plasmon resonance (SPR) biosensors are particularly promising for this purpose because they combine label-free and real-time with miniaturization and low sample volume requirements. However, current body fluid sensing technologies and conventional bare metal SPR interfaces still face critical challenges, including insufficient analytical accuracy in complex biofluids, broad resonance linewidths, weak signal readability for trace biomarkers, and mechanical perturbations during wearable operation. These limitations highlight the need for nanomaterial-engineered fiber-optic SPR platforms that can convert interfacial molecular events into stable and sensitive signals. The review summarizes recent progress in nanomaterial-enabled fiber-optic SPR biosensors for continuous body fluid monitoring. Emphasis is first placed on nanomaterial mediated local electromagnetic field enhancement and plasmonic mode regulation. Subsequent discussion focuses on their functions in interfacial recognition, analyte enrichment, rapid mass transport, antifouling protection, and flexible integration for continuous operation. On this basis, representative sensing targets, material strategies, and device architectures for tears, urine, exhaled breath condensate, saliva and sweat are systematically analyzed. Finally, current challenges and future opportunities are discussed from the perspective of sensing reliability, wearable integration, and real sample validation. Full article

Plasmonic nanostructures offer a practical solution for solar-to-thermal conversion, yet simultaneously achieving ultra-broadband absorption, scalable fabrication, and long-term stability using earth-abundant aluminum remains difficult. In this work, we present a three-dimensional (3D) crown-like aluminum nanostructure absorber that achieves an experimental average absorption of 92% across the solar spectrum (200–2500 nm), with only 1.9% degradation in average absorption over 24 months. The structure is fabricated via a scalable anodic aluminum oxide (AAO) template-assisted method, enabling large-area production without costly lithography and exhibiting broad fabrication tolerance to deposition-thickness variations. Electromagnetic simulations and structure analysis reveal that the ultra-broadband absorption arises from three synergistic mechanisms: multi-mode electric resonances, magnetic resonance behavior within the metal–dielectric–metal architecture, and a graded-refractive-index profile. Proof-of-concept photothermal experiments under simulated sunlight offer experimental confirmation of the absorber’s solar-to-thermal conversion capability, showing substantially enhanced solar-to-thermal energy utilization compared to pure-water references. This work provides a scalable, durable, and cost-effective platform for ultra-broadband solar absorption and solar-to-thermal conversion, and offers a viable design strategy for plasmonic absorbers based on earth-abundant materials. Full article

To enable high-density multimode photonic integration, we propose and numerically demonstrate a plasmonic hybrid mode division multiplexer–demultiplexer with a sodium coating on a silicon-on-insulator (SOI) platform. The device enables simultaneous mode division multiplexing (MDM) and demultiplexing of the transverse magnetic modes TM₀ and TM₁ at λ = 1550 nm. Full-wave three-dimensional finite-difference time-domain (3D-FDTD) simulations confirm an insertion loss of 1.2 dB, an inter-modal crosstalk of −20.3 dB, and a compact footprint of 5 μm × 16 μm. Compared with representative SOI-based mode-selective couplers with longer conversion regions, the proposed design substantially reduces the coupling length and device footprint. This numerical study provides a potential route toward compact, high-density multimode photonic integration based on sodium-assisted hybrid plasmonics. Full article

Active control of multi-mode light–matter interactions is crucial for advancing quantum photonic technologies. Although triple-mode plasmon–exciton systems involving two distinct excitonic transitions offer a pathway to multi-level polaritonic states, achieving reversible electrical tuning at room temperature remains challenging. Here, we numerically investigate an electrically tunable triple-mode strong-coupling system comprising a J-aggregate-coated Au@Ag nanorod coupled with monolayer WS₂. The simulated spectra show a UPB–LPB energy separation of approximately 239 meV near the zero-detuning condition. A modest gate voltage (2.0 V to 3.8 V) selectively modulates the middle and lower polariton branches over ∼46 meV, while the upper branch remains largely unaffected. This selective control is elucidated via a triple-mode coupled-oscillator model and Hopfield coefficient analysis, linking the polariton response to the excitonic composition. These results establish a framework for electrically reconfigurable multi-level polaritonic devices, offering potential for ultracompact optical modulators, high-sensitivity multiplexed sensors, and programmable quantum photonic circuits. Full article

The interaction between light and chiral plasmonic metasurfaces provides a powerful mechanism for controlling polarization states at the nanoscale. Utilizing displacement Talbot lithography for large-area fabrication, we characterized the chiroptical response by measuring the evolution of Stokes parameters to quantify phase retardation between orthogonal polarization components. To elucidate the underlying physical mechanism, we employ a hybrid finite element method and rigorous coupled-wave analysis approach to investigate the behavior of the far-field and local-field configurations. Our results reveal that the phase shift is highly sensitive to symmetry-breaking features, where the interplay between different modes dictates the overall circular dichroism signal. Furthermore, the analysis of local field plots suggests specific contributions of plasmonic modes to the chiroptical response. We conclude that the phase shift effects, characterized via Stokes parameters and modal analysis, provide a robust metric for engineering chiroptical properties in these systems. This work establishes a fundamental framework for developing compact polarization-control elements and enhances the understanding of phase-modulated light-matter interactions in chiral plasmonic metasurfaces. Full article

We demonstrate a mechanism-oriented Surface-Enhanced Raman Scattering (SERS) platform based on a hybrid structure integrating monolayer molybdenum disulfide (MoS₂) and gold nanospheres (AuNSs) on an optical microfiber (MF). The microfiber serves as a whispering-gallery-mode (WGM) microcavity. Monolayer MoS₂, grown directly on the microfiber surface via chemical vapor deposition (CVD), provides a chemically active interface for molecular adsorption and charge-transfer-related chemical enhancement. Subsequently deposited AuNSs couple with the microfiber-supported WGM, leading to the formation of hybrid photonic–plasmonic modes. This coupling results in a narrowed scattering resonance and a localized electromagnetic hotspot near the AuNS–microfiber interface. The combined contribution of electromagnetic enhancement from the microfiber–AuNS hybrid cavity and chemical enhancement from the MoS₂ layer produces discernible Raman enhancement for Rhodamine 6G (R6G) molecules under proof-of-concept measurement conditions. This work provides a useful platform for studying SERS enhancement mediated by hybrid photonic–plasmonic modes and offers guidance for the future development of optimized fiber-based SERS sensors. Full article

A structurally simple three-layer optical absorber is proposed and systematically investigated, consisting of a continuous Ti ground plane, a SiO₂ dielectric spacer, and a Ti tetrahedral nanostructure. The absorber is constructed on a periodic square unit cell, where the lateral dimension directly determines the base width and sidewall inclination angle of the tetrahedral structure, thereby enabling effective modulation of the optical response. Full-wave electromagnetic simulations performed using COMSOL Multiphysics (version 6.0) are employed to evaluate the influence of geometric parameters on broadband absorption behavior. The optimized structure achieves a near-unity absorptivity of 0.9999 at 200 nm and maintains an effective absorption bandwidth (absorptivity > 0.9) spanning 200–3000 nm, covering the ultraviolet, visible, and near-infrared spectral regions. Parametric analysis reveals that the tetrahedral height primarily governs long-wavelength extension through enhanced optical path length, graded-index transition, and improved electromagnetic field confinement, while the unit cell width strongly influences impedance matching and localized field localization. In contrast, the Ti ground layer thickness exhibits minimal influence once it exceeds the optical skin depth, confirming its primary role as a transmission-blocking reflective substrate. Impedance retrieval analysis shows that the real part of the normalized impedance remains close to unity and the imaginary part approaches zero over most of the operating range, demonstrating that the ultrabroadband absorption behavior is dominated by effective impedance matching rather than isolated narrowband resonances. Furthermore, electric and magnetic field distribution analyses reveal that electromagnetic energy dissipation is concentrated near the tetrahedral apex and metal–dielectric interfaces, indicating the coexistence of localized plasmonic modes, cavity-assisted absorption, and multi-scale optical confinement. Full article

An optical sensor based on a polymethacrylate matrix (PMM) with immobilized gold nanoparticles (Au⁰ NPs) has been developed for the determination of pollutants in environmental samples. The nanoparticles are synthesized by chemical reduction of Au(III) to Au⁰ using sodium borohydride, which yields conglomerates of spherical particles with an absorption maximum at 530 nm. The time stability of the nanocomposite is demonstrated, as well as the ability to control the nanoparticle loading in the matrix by varying the concentration of the HAuCl₄ solution. The analytical capability of the PMM–Au⁰ system is demonstrated for the direct determination of tetracycline in river water in two linear concentration ranges: 0.001–0.010 mg/L and 0.025–0.100 mg/L, with detection limits of 0.0005 mg/L and 0.012 mg/L, respectively. The determination of tetracycline is based on the enhancement of its intrinsic fluorescence at 520 nm by gold nanoparticles in the solid phase following solid-phase extraction from water in the anionic form H₂TC⁻ using PMM–Au⁰. The colorimetric determination of thiocyanate anions is based on a color change of the PMM–Au⁰ nanocomposite from red to blue, corresponding to a shift in the plasmon absorption maximum from 530 nm to 630 nm. The sensor exhibits a linear response in the thiocyanate concentration range of 0.3–50.0 mg/L, with a detection limit of 0.1 mg/L. Thus, the multifunctional PMM–Au⁰ sensor has been used for the determination of various analytes employing different modes of analytical signal readout after minimal sample preparation. Full article

To meet the demand for highly sensitive temperature sensing in low-temperature environments, a surface plasmon resonance photonic crystal fiber (SPR-PCF) sensor with a central air hole and a dual-layer air-hole arrangement is designed and optimized. In this work, these air-hole features are used for mode-field regulation in a low-temperature sensing structure based on surface plasmon resonance (SPR), together with a polished gold film and an ethanol/chloroform (1:1) temperature-sensitive medium. The finite element method (FEM) was employed to analyze the resonance behavior and thermal response, and key structural parameters, including gold-film thickness, air-hole sizes, and radial positions, were optimized through cumulative parametric scanning. The optimized sensor shows good temperature response from −25 °C to 40 °C, with a maximum sensitivity of 36 nm/°C, a full width at half-maximum (FWHM) of 18.57 nm, and a figure of merit (FOM) of 1.2923. It is promising for cold-chain monitoring, low-temperature storage and transportation, and low-temperature sensing. Full article