Plasmonics最新文献

In recent years, quantum wire infrared photodetectors have attracted extensive attention due to their high optoelectronic conversion efficiency arising from quantum confinement effects. Although metal gratings are widely employed to enhance light absorption, the influence mechanism of their parasitic absorption on device performance upon the introduction of a Cr adhesion layer to ensure mechanical stability remains unclear. In this work, a Cr adhesion layer is introduced into an Ag grating/InAs quantum wire multilayer heterostructure. Through frequency-domain simulations, the optical absorption characteristics are analyzed, and the energy redistribution mechanism of the Cr layer is revealed. The results show that after introducing a 10 nm Cr layer, the total absorptance of the device increases by 3.07% and 9.22% at 1.9 μm and 3.6 μm, respectively. However, the Cr layer dissipates 85.49% and 52.83% of the incident energy, compressing the effective absorption of the quantum wire active region to below 1%. This "increase in total absorption, yet loss in active-region absorption" effect originates from the interception and absorption of reflected energy by the Cr layer, which shifts the primary site of energy dissipation from the Ag grating to the Cr layer. This study provides quantitative criteria and theoretical guidance for the design of adhesion layers in quantum wire infrared photodetectors and similar multilayer plasmonic optoelectronic devices.

Atomic-scale control of bimetallic nanogaps provides a powerful route for engineering plasmonic hotspots and energy dissipation. Here, we employ an atomistically resolved electrodynamic framework to systematically investigate Au–Au, Ag–Ag, Au@Ag–Au@Ag, and Ag@Au–Ag@Au nanodimers separated by sub-nanometer gaps. By analyzing absorption spectra, induced charge distributions, near-field localization, and a spatially resolved dissipation-based hot-carrier proxy P(r,ω) ∝ ωIm[ε(ω)]|E(r,ω)|², we identify a termination-controlled regime in which the metal forming the nanogap interface governs plasmon coherence and hotspot confinement more strongly than overall stoichiometry. In particular, Ag-terminated junctions exhibit sharper resonances, stronger gap fields, and enhanced localized dissipation, whereas Au termination suppresses confinement despite higher intrinsic losses. This behavior originates from the interplay between material-dependent damping and nanoscale field localization, which is maximized when low-loss metals define the hotspot interface. These results establish a general nanoscale design principle for bimetallic plasmonic nanojunctions: surface termination at the optical hotspot acts as the dominant control parameter for plasmon-mediated energy localization within the classical, non-conductive coupling regime.

Manipulating light polarization at the subwavelength scale is critical for high-density photonic integration. Here, broadband and arbitrary linear polarization rotation is demonstrated in a subwavelength plasmonic nano-scatterer (0.22λ² at λ = 600 nm), consisting of two orthogonal metallic nanogroove antennas. This rotation is achieved by varying the phase difference between two counter-propagating surface plasmon polaritons (SPPs). The proposed approach exploits the intrinsic binary-phase and cosine-amplitude distributions of the SPP standing waves. The binary-phase distribution restricts the relative phase of orthogonal scattering components radiated from the two nanogrooves to 0 or π, ensuring high-purity linear polarization. The cosine-amplitude distribution modulates their power ratio to rotate the polarization angle of the total scattered light. Therefore, the linear polarization of the total scattered light is arbitrarily rotated (Δα = 180°) by only changing the phase difference between two incident SPPs with parallel linear polarization. Experimentally, an ultrasmall nano-scatterer (0.22λ² at λ = 600 nm) is fabricated. At λ = 550 nm, 600 nm, and 650 nm, it is demonstrated that the polarization angle α is arbitrarily rotated from 90° to − 90° with a degree of linear polarization (D_p > 0.82).

This work presents the design and numerical investigation of a fully graphene-based, tunable ultra-wideband (UWB) electromagnetic absorber for terahertz (THz) applications. The proposed metal-free device consists of an upper patterned graphene rectangular-ring resonator (GRRR) and a lower continuous graphene layer, separated by a silicon dioxide spacer. Ultra-wideband absorption is achieved through a sequential mode-merging method. In this approach, rotated rectangular resonators are systematically integrated to excite multiple plasmonic resonances. These resonances progressively merge into a continuous absorption spectrum through enhanced electromagnetic coupling and spectral overlap. The proposed absorber achieves an absorption bandwidth of 17.9 THz, corresponding to a fractional bandwidth of 197.79%, with absorptivity exceeding 95% over the frequency band of 0.1 to 18 THz. Owing to its high structural symmetry, the absorber demonstrates polarization-insensitive characteristics under normal incidence, and sustains consistent absorption performance for both transverse-electric and transverse-magnetic polarizations under oblique incidence. Additionally, the absorption response can be dynamically adjusted by modulating the graphene chemical potential, without any structural changes. The combination of an exceptionally wide operating bandwidth, compact configuration, polarization insensitivity, and electrical tunability makes the proposed absorber promising for applications in THz sensing, imaging, stealth, and adaptive optoelectronic devices.

In this research, we report on the analysis and optimization of the detection performance of an original nanodesign for a surface plasmon resonance (SPR) sensor, with a view to several applications in the fields of processing and diagnostics. Our enhanced SPR nanodesign is built on a Kretschmann hybrid configuration, consisting of a BK7 prism, a Cu film interleaved with a WO(_{3}) layer, and covered with a hybrid multilayer of perovskite oxide combined with a monolayer of graphene or black phosphorus, as well as the sensing medium. The finite element method (FEM), associated with an excitation at 633 nm, is used to analyze the plasmonic properties of the nanodesign. We analyze performance parameters such as detection sensitivity, sensitivity enhancement, figure of merit (FoM), and electric field distribution. Firstly, the study focuses on optimizing the effect of different layers of nanomaterials and their thicknesses on surface plasmon resonance and SPR biosensor performance. A detection sensitivity of around 576 deg/RIU and a FoM of 175.07 RIU(^{-1}) were found. These performance values are enhanced by 500% and 13.06% respectively, relative to those of a conventional SPR sensor (BK7/WO(_{3})/Cu/SM). Subsequently, we modeled the SPR biosensor optimized in this work to show how plasmon resonance and detection performance are affected by the refractive index of infected and normal blood samples containing plasma. The current SPR design can be used in highly sensitive biomedical and environmental detection and diagnostic applications.

Surface-enhanced Raman spectroscopy (SERS) relies on strong amplification of the local electromagnetic field within plasmonic hotspots formed around metallic nanostructures. In this study, we present a computational framework that models a silver nanoparticle (AgNP) dimer placed on a ZnO dielectric spacer, supported by a base substrate, to investigate hotspot-enhancement mechanisms. Finite-difference time-domain (FDTD) simulations were employed to systematically examine the combined influence of ZnO layer thickness, base substrate, interparticle gap, and nanoparticle (NP) radius on the plasmonic response and the enhancement factor (EF) arising from the local electric field. The simulations reveal two distinct plasmonic modes, the single-particle (SP) mode and the gap mode, whose resonance wavelengths and enhancement strengths are highly sensitive to the dielectric spacer, base substrate, and NP configuration. The EF for both modes varies non-monotonically with the ZnO layer thickness, initially increasing, reaching a maximum at intermediate thicknesses, and then decreasing, highlighting the tunability of EF through the dielectric layer. Further analysis confirms that interparticle separation and NP size play dominant roles in governing hotspot intensity and spectral position. Validation of the model against SERS experiments performed at an excitation wavelength of 785 nm shows good agreement, confirming the reliability of the simulations. These findings provide useful design guidelines for hybrid spacer-base substrate architectures and underscore the critical role of ZnO-base substrate synergy in optimizing plasmonic hotspots to improve SERS performance.

In the present work, a symmetric one-dimensional (1D) Silicon/Silicon Dioxide double-defect photonic crystal biosensor for high-resolution blood component screening in the near-infrared (NIR) regime has been proposed. The proposed structure, optimized for a central design wavelength of 1550 nm, is represented as (mathrm{Air}/left(mathrm{BA}right)^N-mathrm B-mathrm D-mathrm B-mathrm Dleft(mathrm{BA}right)^N-mathrm B/mathrm{Air}), where A and B represent Silicon Dioxide and Silicon layers, respectively, and D denotes identical microfluidic defect cavities containing blood analytes. The transmission spectra and localized electric field confinement profiles are rigorously modelled and validated using the Transfer Matrix Method (TMM) and a 1D Finite Element Method (FEM) Helmholtz solver. Due to electromagnetic state hybridization in the coupled defect cavities, the transmission spectrum exhibits split resonance modes (Peak 1 and Peak 2) inside the photonic bandgap. Under normal incidence θ = 0⁰ with a period N = 7, the sensor achieves a high refractive index sensitivity of up to 544.14 nm/RIU for Hemoglobin, extremely narrow linewidths (FWHM down to 5.08 pm), and Quality Factors (Q) up to 2.76 × 10⁵ for Plasma, resulting in a Limit of Detection (LoD) in the order of 10^− 6 RIU. The transition to extreme oblique angles of incidence (up to 80⁰) significantly elongates the optical path length through the cavity defects, enhancing the peak sensitivity to 784.18 nm/RIU and narrowing the resonance FWHM to sub-picometer levels 0.25 pm, which yields an ultra-high-Quality Factor of 5.32 × 10⁶ and a Figure of Merit ((:text{FoM})) of 3.12 × 10⁶ RIU^− 1 for the Plasma component. The comparative analysis shows perfect agreement between TMM and FEM calculations, with minor resonance peak shifts (+ 50 to + 90 pm) arising from finite-element discretization grid rounding, and peak shift discrepancies of less than 5 pm, validating the numerical consistency of the model. These results demonstrate that the proposed symmetric double-defect configuration represents a highly sensitive, and stable optical platform for rapid NIR blood diagnostics.

Absorption losses in plasmonic nanoparticles limit their performance in many optical and photonic applications by dissipating energy as heat and damping resonance strength. Using finite-difference time-domain simulations, we demonstrate that near-field coupling in dense, periodic nanoparticle arrays can significantly mitigate these losses. When interparticle distances are small, for the free carriers inside a given particle, the field enhancement of neighbouring particles reduces the effect of the field enhancement at the tip of the particle under study. As a result, the internal electric field – and thus the associated Ohmic losses – are substantially reduced, despite intense field enhancement in the narrow interparticle gaps. By comparing our results to the analytical theory of electric dipole arrays, we show that engineering the gaps in periodic arrays allows fine-tuning of the non-radiative to radiative losses ratio. This interplay between the near-field enhancement and the electric field within the nanoparticles suggests a route to exploit densely packed plasmonic arrays for optical devices, achieving high resonance strength and field enhancement while minimising thermal losses and associated damping. Furthermore, our results indicate the potential for decoupled control of hot-electron injection and thermal heating, offering new opportunities for the design of efficient plasmonic systems.

By adjusting composite films with different refractive indices, the coupling conditions of surface plasmon resonance (SPR) can be precisely controlled, thereby inducing a controllable redshift in the sensing bandwidth of the sensor. This feature provides a reliable means for effectively separating the dual-channel sensing bandwidths. In this study, we propose a sensor modulated by composite films for the simultaneous and independent measurement of refractive index (RI) and temperature. The RI sensing channel is realized by depositing Ag/MgF₂ films onto the surface of the no-core fiber (NCF), while the temperature sensing channel is implemented by coating the NCF with the Ag/MoS₂/ polydimethylsiloxane (PDMS) films. Experimental results show that the sensor achieves a maximum sensitivity of 7300 nm/RIU in the RI range of 1.33–1.39, and a maximum sensitivity within the temperature range of 30–100 ℃ can reach 4.4 nm/℃. The sensing bandwidth are effectively separated around 800 nm. Through rational design of the film structure, this study provides a feasible solution for achieving high-performance multi-parameter sensing.

A highly sensitive photonic crystal fiber surface plasmon resonance (PCF-SPR) magnetic sensor assisted by statistical optimization and machine learning is proposed and numerically investigated. The sensor consists of a silica-based PCF incorporating two gold-coated elliptical channels filled with magnetic fluid, enabling efficient coupling between the guided core mode and surface plasmon polaritons. Finite element method (FEM) simulations were performed over a magnetic-field range of 30–300 Oe. The air-hole diameter, pitch, and gold layer thickness were optimized using the Taguchi method and analysis of variance (ANOVA), identifying the pitch as the dominant design parameter. The optimized sensor achieves a wavelength sensitivity of 500 pm/Oe, an amplitude sensitivity of 0.0361 Oe^− 1, and a resolution of 2 × 10^− 2 Oe within the 30–90 Oe operating range. To accelerate sensor analysis, a multilayer perceptron (MLP) model was developed to predict the complete confinement-loss spectrum directly from the wavelength and magnetic-field intensity. The model was trained using a FEM-generated dataset and rigorously validated through a Leave-One-H-Configuration-Out (LOCO) cross-validation strategy. The MLP achieved an average R² of 0.9878 ± 0.0101, outperforming Support Vector Regression and Random Forest models under the same validation protocol. Furthermore, robustness analysis considering ± 5% variations in the air-hole diameter, pitch, and gold-layer thickness, together with partial magnetic-fluid infiltration, confirms the stability of the sensor response under realistic fabrication and implementation deviations. The proposed hybrid Taguchi-ML framework provides an efficient, accurate, and robust approach for the design and rapid evaluation of PCF-SPR magnetic sensors.