Search Results (577)

We propose a 1D photonic crystal with nonlinear graphene–spacer–graphene truncation, which enables a tunable, non-monotonic, and intensity-dependent transmission response. By employing synthetic geometrical space to obtain Fermi arc states, the structure is designed to support a real-space topologically protected Tamm plasmon polariton, revealing an intensity-dependent transmission peak within the THz spectral range. As such, the proposed thin-film structure may serve as a nonlinear DBR element that can be integrated into a laser cavity to provide intensity-selective feedback, thereby facilitating controllable pulse shaping and enabling passive pulse formation mechanisms such as mode-locking or Q-switching. Due to its topological robustness, spectral scalability, and electrical tunability via graphene biasing, the platform provides a new route toward compact, reconfigurable nonlinear reflectors for efficient and controllable laser pulse generation, thereby extending the functionality of conventional saturable absorbers and semiconductor DBRs. Full article

In this paper, composite structures were fabricated by incorporating silver nanowires (AgNWs) with various metal oxides via the sol–gel method. This approach enhanced the electrical performance of AgNW-based transparent electrodes while simultaneously improving their stability under damp heat conditions and modifying the local medium environment surrounding the AgNW meshes. The randomly distributed AgNW meshes fabricated via drop-coating were treated with plasma to remove surface organic residues and reduce the inter-nanowire contact resistance. Subsequently, a zinc oxide (ZnO) coating was applied to further decrease the sheet resistance (R_sheet) value. The pristine AgNW mesh exhibits an R_sheet of 17.4 ohm/sq and an optical transmittance of 93.06% at a wavelength of 550 nm. After treatment, the composite structure achieves a reduced R_sheet of 8.7 ohm/sq while maintaining a high optical transmittance of 92.20%. The use of AgNW meshes as window electrodes enhances electron injection efficiency and facilitates the coupling mechanism between localized surface plasmon resonances and excitons. Compared with conventional ITO transparent electrodes, the incorporation of the AgNW mesh leads to a 17-fold enhancement in ZnO emission intensity under identical injection current conditions. Moreover, the unique scattering characteristics of the AgNW and metal oxide composite structure effectively reduce photon reflection at the device interface, thereby broadening the angular distribution of emitted light in electroluminescent devices. Full article

Surface plasmon resonance (SPR) sensors based on photonic crystal fibers (PCFs) hold significant promise for high-precision detection in biochemical and chemical sensing. However, achieving high sensitivity in low-refractive-index (RI) aqueous environments remains a formidable challenge due to weak light-matter interactions. To address this limitation, this paper designs and proposes a novel dual-channel D-shaped PCF-SPR sensor tailored for the refractive index range of 1.34–1.40. The sensor incorporates a dual-layer gold/titanium dioxide film, with gold nanoparticles deposited on the surface to synergistically enhance both propagating and localized surface plasmon resonance effects. Furthermore, a D-shaped polished structure integrated with double-sided microfluidic channels is employed to significantly strengthen the interaction between the guided-mode electric field and the analyte. Finite element method simulations demonstrate that the proposed sensor achieves an average wavelength sensitivity of 5733 nm/RIU and a peak sensitivity of 15,500 nm/RIU at a refractive index of 1.40. Notably, the introduction of gold nanoparticles contributes to an approximately 1.47-fold sensitivity enhancement over conventional structures. This work validates the efficacy of hybrid plasmonic nanostructures and optimized waveguide design in advancing RI sensing performance. Full article

Large-area metasurfaces were fabricated via a tunable pyramidal interference lithography (PIL) technique, which uses custom-built 2-faced, 3-faced, and 4-faced pyramidal prisms to create metasurfaces with customizable nano- and micro-scale surface feature periodicities. The 2-faced prism produced linear surface relief diffraction gratings, while the 3-faced prism produced metasurfaces with triangular lattices and the 4-faced prism produced metasurfaces with square lattices, all on azobenzene thin films. A double inline prism set-up enabled control over the metasurface feature periodicity, allowing systematic increase in the pattern size. Additional tunability was achieved by placing a prism inline with a lens, allowing precise control over the metasurface feature periodicity. A theoretical model was derived and successfully matched to the experimental results. The resulting metasurfaces were coated with gold and exhibited distinct surface plasmon resonance (SPR) and surface plasmon resonance imaging (SPRi) responses, confirming their functionality. Overall, this work establishes PIL as a cost-effective and highly adaptable metasurface fabrication method for producing customizable periodic metasurfaces for photonic, plasmonic, and sensing applications. Full article

The transition toward Industry 4.0 requires advanced sensing platforms capable of delivering real-time, high-fidelity data under extreme industrial conditions. Thin-film sensors, leveraging both photonic and functional approaches, are emerging as key enablers of this transformation. By exploiting optical phenomena such as Fabry–Pérot interference, guided-mode resonance, plasmonics, and photonic crystal effects, thin-film photonic devices provide highly sensitive, electromagnetic interference-immune, and remotely interrogated solutions for monitoring temperature, strain, and chemical environments. Complementarily, functional thin films including oxide-based chemiresistors, nanoparticle coatings, and flexible electronic skins extend sensing capabilities to diverse industrial contexts, from hazardous gas detection to structural health monitoring. This review surveys the fundamental optical principles, material platforms, and deposition strategies that underpin thin-film sensors, emphasizing advances in nanostructured oxides, 2D materials, hybrid perovskites, and additive manufacturing methods. Application-focused sections highlight their deployment in temperature and stress monitoring, chemical leakage detection, and industrial safety. Integration into Internet of Things (IoT) networks, cyber-physical systems, and photonic integrated circuits is examined, alongside challenges related to durability, reproducibility, and packaging. Future directions point to AI-driven signal processing, flexible and printable architectures, and autonomous self-calibration. Together, these developments position thin-film sensors as foundational technologies for intelligent, resilient, and adaptive manufacturing in Industry 4.0. Full article

Antibiotics are persistent organic pollutants that pose a serious problem for water resources, ultimately having a detrimental effect on human and animal health. The most important aspect of controlling and preventing the spread of antibiotics and their degradation products is continuous screening and monitoring of environmental samples. Optical sensing technologies represent a large group of sensors that allow short-term detection of antibiotics in non-laboratory settings. This article reviews the advances in optical sensing systems (colorimetric, fluorescent, surface-enhanced Raman spectra-based, surface plasmon resonance-based, localized surface plasmon resonance-based, photonic crystal-based, fiber optic, molecularly imprinted polymer-based and electro-optical platforms) for the detection of antibacterial drugs in water. Special attention is paid to the evaluation of the analytic characteristics of optical sensors for the analysis of antibiotics. Particular attention is paid to electro-optical sensing and to the unique possibility of its use in antibiotic determination. Potential strategies are considered for amplifying the recorded signals and improving the performance of sensor systems. The main trends in optical sensing for antibiotic analysis and the prospects for the commercial application of optical sensors are described. Full article

In this work, a quasi-D-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) biosensor is proposed and numerically investigated using the finite element method (FEM) implemented in COMSOL Multiphysics version 6.2 for the detection of cancer cells with different refractive indices. The biosensor has a coating of plasmonic material gold (Au) and a polymer coat of polymethyl methacrylate (PMMA). The effects of plasmonic material thickness and air hole dimensions on key sensing parameters, including confinement loss (CL), wavelength sensitivity (WS), and amplitude sensitivity (AS), are systematically analyzed. The results revealed that increasing plasmonic thickness beyond its optimum value significantly raises CL while reducing sensitivity due to reduced penetration depth of the evanescent field. Similarly, variations in the geometrical dimensions of the air holes (±10%) also affect the sensor response, emphasizing the importance of precise structural optimization. For the optimized design the proposed biosensor exhibits high performance with a maximum WS of 31,000 nm/RIU for MDA-MB-231 cells under x-polarization and 29,500 nm/RIU under y-polarization. The corresponding resolutions achieved are as low as 3.22 × 10⁻⁶ RIU and 3.38 × 10⁻⁶ RIU, respectively, with AS exceeding 9000 RIU⁻¹. The WS, AS, and other sensing parameters obtained from our sensor are relatively higher than some of the PCF–SPR sensors reported recently. These numerical results demonstrate that the optimized quasi-D-shaped PCF–SPR biosensor exhibits enhanced sensitivity to refractive index (RI) variations associated with cancerous cells, suggesting its suitability for early detection. Full article

Magnetooptics (MO) explores light—matter interactions in magnetized media and has advanced rapidly with progress in materials science, spectroscopy, and integrated photonics. This review highlights recent developments in fundamental principles, experimental techniques, and emerging applications. We revisit the canonical MO effects: Faraday, MO Kerr effect (MOKE), Voigt, Cotton—Mouton, Zeeman, and Magnetic Circular Dichroism (MCD), which underpin technologies ranging from optical isolators and high-resolution sensors to advanced spectroscopic and imaging systems. Ultrafast spectroscopy, particularly time-resolved MOKE, enables femtosecond-scale studies of spin dynamics and nonequilibrium processes. Hybrid magnetoplasmonic platforms that couple plasmonic resonances with MO activity offer enhanced sensitivity for environmental and biomedical sensing, while all-dielectric magnetooptical metasurfaces provide low-loss, high-efficiency alternatives. Maxwell-based modeling with permittivity tensor ($\epsilon$) and machine-learning approaches are accelerating materials discovery, inverse design, and performance optimization. Benchmark sensitivities and detection limits for surface plasmon resonance, SPR and MOSPR systems are summarized to provide quantitative context. Finally, we address key challenges in material quality, thermal stability, modeling, and fabrication. Overall, magnetooptics is evolving from fundamental science into diverse and expanding technologies with applications that extend far beyond current domains. Full article

Low-temperature Ag₂Se is a narrow-band semiconductor, with its transport and optical properties significantly influenced by the local coordination environment. This study investigates the effects of La and Gd incorporation using DFT+U calculations and Ag-K edge EXAFS analysis. Analysis of electron localization function (ELF) and charge density differences reveals increased electron localization at dopant sites. Additionally, k³χ(k) and wavelet transforms demonstrate that the first M-Se shell shifts from approximately 1.346 Å in Ag-Se to around 1.386 Å and 1.291 Å for La-Se and Gd-Se, respectively (phase-uncorrected), thereby confirming dopant-specific lattice distortions while maintaining the orthorhombic framework. The observed changes are associated with an increase in dielectric strength, with ε₂ increasing from approximately 30–40 in pristine Ag₂Se to around 50–60 for La and 70–80 for Gd at low photon energies, alongside enhanced absorption nearing 1.32–1.34 × 10⁵ cm⁻¹. The characteristic plasmon resonance in the range of 15–20 eV is maintained. Rare-earth substitution effectively adjusts local bonding and low-energy optical response in Ag₂Se, with Gd demonstrating the most significant impact among the examined dopants. Full article

This study presents an ultra-sensitive dual-core photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor for the detection of waterborne pathogens through refractive index (RI) variation. The proposed sensor integrates a bimetallic coating of silver and titanium dioxide (Ag–TiO₂). Silver ensures sharp plasmonic resonance, and TiO₂ enhances chemical stability and coupling efficiency. This dual-core configuration allows for increased interaction between the core-guided modes and the plasmonic interface. As a result, the sensor’s sensitivity improves significantly. The sensor can accurately detect analytes with an RI value of 1.28 to 1.43. It demonstrates a maximum wavelength sensitivity (WS) of 107,000 nm/RIU, an amplitude sensitivity (AS) of 2209.21 RIU⁻¹, a wavelength resolution of 9.35 × 10⁻⁷ RIU, and a figure of merit (FOM) of about 520. These results support the sensor’s ability to identify the presence of different pathogenic contaminants, such as E. coli, Vibrio cholerae, and Bacillus anthracis, based on their unique RI properties. This optimized design, high resolution, and potential for real-time detection enable this sensor to be a promising solution for environmental monitoring applications. Full article

Structural coloration arising from nanoscale light–matter interactions has emerged as a key research area in nanophotonics. Among the various materials investigated, noble metals—particularly gold—play a central role due to their well-defined plasmonic response and chemical stability, but their structural coloring typically requires complex and highly engineered nanostructures. However, modern photonic technologies demand scalable approaches to produce structural colors that can be finely tuned. In this contribution, we experimentally and numerically demonstrate the fine tunability of structural color in gold-based one-dimensional hyperbolic metamaterials (1D-HMMs) by varying their structural parameters: number of layers (N), period (T), and filling fraction (p). Our results show that variations in N lead to changes in luminance with minimal shifts in chromaticity, while variations in T introduce moderate color shifts without affecting luminance. In contrast, changes in p produce the largest modifications in chromaticity, though the trend is non-monotonic and less predictable. These findings highlight the potential of 1D-HMMs for achieving finely controlled gold-based coloration for advanced photonic technologies. Full article

Robust control over the coupling and propagation of surface plasmon polaritons (SPPs) is essential for advancing various plasmonic applications. Traditional planar structures, commonly used to design SPP directional couplers, face limitations such as low extinction ratios and design complexities. These issues frequently hinder the dense integration and miniaturisation of photonic systems. Recently, exceptional points (EPs)—unique degeneracies within the parameter space of non-Hermitian systems—have garnered significant attention for enabling a range of counterintuitive phenomena in non-conservative photonic systems, including the non-trivial control of light propagation. In this work, we develop a rigorous temporal coupled-mode theory (TCMT) description of a non-Hermitian metagrating composed of alternating silicon–germanium nanostrips and use it to explore the unidirectional excitation of SPPs at EPs in the visible spectrum. Within this framework, EPs, typically associated with the coalescence of eigenvalues and eigenstates, are leveraged to manipulate light propagation in nonconservative photonic systems, facilitating the refined control of SPPs. By spatially modulating the permittivity profile at a dielectric–metal interface, we induce a passive parity–time ($\mathcal{PT}$)-symmetry, which allows for refined tuning of the SPPs’ directional propagation by optimising the structure to operate at EPs. At these EPs, a unidirectional excitation of SPPs with a directional intensity extinction ratio as high as 40 dB between the left and right excited SPP modes can be reached, with potential applications in integrated optical circuits, visible communication technologies, and optical routing, where robust and flexible control of light at the nanoscale is crucial. Full article

This study explores the tunable characteristics of optical Tamm states (OTS) in a metal–distributed Bragg reflector (DBR) structure integrated with a monolayer of molybdenum disulfide (MoS₂). Through finite element simulations, we demonstrate that incorporating MoS₂ enhances electromagnetic field localization at the metal–DBR interface, facilitating enhanced exciton–photon interaction. As the number of DBR periods increases, the OTS resonance wavelength undergoes a blue shift and eventually stabilizes, which indicates a wavelength-locking behavior. Under external bias, the locking threshold is lowered, and the resonance wavelength exhibits a nearly linear blue shift of approximately ~1 nm/V. Moreover, absorptance varies non-monotonically with the metal thickness, reaching over 99% at a thickness of 25 nm, due to the combined effects of plasmonic confinement and MoS₂ excitonic enhancement. These findings demonstrate the potential of this structure for application in tunable photonic devices such as optical filters and modulators. Full article

To explore the potential of new information transmission windows, this work presents a broadband plasmonic filter based on gold-deposited silicon photonic crystal fiber (PCF) operating in mid-infrared regime numerically, using the finite element method (FEM). The simulation results indicate that the interaction between the high-refractive-index pure silicon material and the gold layer can cause a shift of the resonance central point to the mid-infrared band, which provides the prerequisite for mid-infrared filtering. When the cladding holes’ diameter is 1.3 µm, the inner holes’ diameter is 1.04 µm, the diameter of the holes located on both sides of the core region is 2.08 µm, the gold-coated holes’ diameter is 2.08 µm, the lattice constant is 2 µm, and the gold thickness is 50 nm, this PCF can operate in the mid-infrared band near the central wavelength of 3 µm. The 1 mm long PCF polarizer exhibits a maximum extinction ratio (ER) of −43.5 dB at 3 µm and a broad operating bandwidth of greater than 820 nm with ER better than −20 dB. Additionally, it also possesses high fabrication feasibility. This in-fiber polarization filter, characterized by its comprehensive performance and ease of fabrication, aids in exploring the development potential of high-speed and large-capacity modern communication networks within new optical bands and contributes to new photonic computing and sensing. Full article

Optical skyrmions, as topologically protected quasiparticles, hold great promise for on-chip photonic technologies. However, achieving programmable control over their properties through subtle structural changes remains challenging. This study introduces a minimal perturbation engineering strategy on a plasmonic metasurface. By applying controlled geometric perturbations (either continuous shortening or discrete segmentation) to a single edge of a hexagonal groove structure, combined with incident phase perturbations, we systematically manipulate the evolution of the skyrmion texture. These minimal perturbations induce reproducible shifts in the skyrmions’ center intensity and peak position, yielding up to ~32% center suppression, while the global topological charge remains conserved. This “geometry × phase” dual-perturbation approach provides a straightforward and efficient approach for engineering programmable topological light fields on a chip, with promising applications in integrated photonic devices. Full article