A multifunctional chiral metasurface based on an Au–Nb2O5–Au configuration is proposed to achieve strong circular and linear dichroism in the visible region. The incorporation of a high-index Nb2O5 dielectric spacer enhances plasmon–cavity coupling, leading to sharp resonances and improved polarization selectivity. The metasurface exhibits pronounced spin-dependent reflection, with a circular dichroism (CD) exceeding 0.7 at 670 nm and a linear dichroism (LD) of 0.84 at 490 nm, demonstrating simultaneous control over circular and linear polarization states. The sensing capability is further explored for enantiomeric detection of D- and L-phenylalanine, where distinct resonance shifts and opposite CD amplitude variations confirm visible-range chiral selectivity. The coexistence of strong CD and LD responses establishes the proposed metasurface as a compact and efficient platform for polarization-resolved biosensing, photonic polarization control, and secure optical communication applications.

In this paper, we numerically investigate the design of an all-dielectric terahertz metasurface sensor with an ultra-high Q-factor, utilizing the concept of bound states in the continuum (BIC). The proposed metasurface consists of silicon-based cylindrical disks arranged as metamolecules. It is observed that two resonant modes are formed at 3.79 THz and 4.19 THz under symmetric conditions. By introducing a local asymmetry parameter (α) to break the structural symmetry, a leaky channel emerges, converting the ideal BIC into a quasi-BIC (q-BIC). This results in a sharp resonance at 4.06 THz with a Q-factor of 1.5 × 10^4 . The numerically evaluated sensing performance demonstrates a high refractive index sensitivity of 1.0746 THz/RIU and a figure of merit (FOM) of 10854.56/RIU over a refractive index range of 1.00-1.15. Tuning the asymmetry further enhances the FOM up to 41330.77/RIU. The proposed metasurface finds strong potential for high-precision sensing, detection, and imaging in the terahertz frequency regime.

Chiral metasurfaces have emerged as powerful platforms for spin-selective light manipulation, enabling compact alternatives to bulky polarization optics. In this work, a reflective chiral metasurface based on a Au-SiO2-Au trilayer configuration is proposed and numerically demonstrated. The design employs a pair of enantiomeric Omega-shaped resonators, where each unit selectively converts one circular polarization into its opposite while strongly absorbing the other. This asymmetric response produces a high circular dichroism of 0.78. By arranging the two enantiomers in an alternating 40 x 40 array, a spin-multiplexed metalens is realized that focuses left- and right-circularly polarized beams to spatially separated foci, while suppressing unwanted background. Broadband analysis confirms stable diffraction efficiency across the mid-infrared spectrum, with peak efficiencies of 76.4% and 75.8% for LCP and RCP incidence. The metasurface further supports dual-beam operation under mixed polarization input, exhibiting simultaneous, well-resolved focal spots with minimal overlap. This multifunctional platform unifies polarization conversion, selective absorption, and spin-dependent focusing within a lithographycompatible reflective architecture, offering promising opportunities for polarization-multiplexed imaging, optical encryption, and spin-based information routing.

In this study a chiral metasurface based on three concentric asymmetrical semicircular rings (SCRs) made of gold is presented. Analysis shows that the number of SCRs extensively affects the value of circular dichroism (CD). Perfect absorption and a large CD covering the S and C bands is achieved. The bandwidth and the peak value of CD are tuned by varying the heights of the SCRs and their orientation angle, leading to strong Fano resonance. The structure also exhibits wide angular stability. Furthermore, a 4 x 4 periodic array of this metasurface is designed for dynamic modulation of the imaging state over the S and C bands for potential applications in optical communication encryption.

This paper presents a systematic analysis of temperature-dependent coupling characteristics in a photonic crystal waveguide (PCW) coupler. Unlike previous works that primarily rely on either numerical simulations or experimental studies, our approach integrates an analytical framework based on Coupled Mode Theory (CMT) with computational validation using COMSOL Multiphysics. The proposed PCW coupler, composed of silicon rods in air, exhibits a significant reduction in coupling length, enhancing its suitability for photonic integrated circuits (PICs). Through a combination of Plane Wave Expansion (PWE) simulations and wavelength-domain modelling, we demonstrate that the coupling length decreases with increasing temperature, indicating enhanced efficiency for thermally sensitive applications. The study not only provides theoretical insights into thermo-optic coupling in PCWs but also offers a practical design strategy for compact photonic devices operating at variable temperatures.

This research paper presents a novel photonic structure design to achieve an ultra-high spin-dependent shift associated with the Photonic Spin Hall Effect (PSHE) possessing high Q-factor. The high quality Q-factor is achieved through the merging of two distinct Bound States in the Continuum (BICs): the Friedrich-Wintgen BIC (FW-BIC) and the symmetry-protected BIC (SP-BIC). Mostly throughout the literature, PSHE shift has been enhanced for H-polarized light with only fewer studies carried out for the enhancement of PSHE shift for V-polarized light. The present structure, comprising periodic silicon steps on a silica substrate with an intercalated graphene layer, exhibits a PSHE shift of 20.83 lambda upon reflection of V-polarized light at 8.7 degrees. Tuning the unit cell's filling factor generates high Q-factor of 104 through the merging of BICs. Additionally, the influence of graphene's Fermi energy (Ef) on the PSHE shift is analyzed, demonstrating a sensitivity of 0.5 nm/eV. A theoretical framework is provided, showing that the Jones matrix for circularly polarized light aligns with the Pauli spin matrix, offering deeper insight into the spin-optical interaction.

The presented study proposed a metasurface design with an I-shaped structure for detecting biomolecules in the terahertz (THz) region. The proposed metasurface exhibits three sharp resonance modes f1, f2, and f3 appearing in the transmittance spectra at frequencies of 3.78, 4.32, and 5.00 THz, respectively. The modes f1 and f2 correspond to Fano resonance and mode f3 represents a toroidal dipole resonance. The toroidal dipole resonance arises in the structure as the displacement currents form interconnected loops. An exceptionally high Q-factor of 14 443 is achieved for the toroidal dipole resonance. A maximum figure of merit of 838/RIU was attained when the sensing performance was examined for biomolecules with refractive indices in the range of 1.0–1.4, where RIU is refractive index unit. Additionally, the metasurface demonstrates outstanding sensitivity, with a maximum value of 2163 GHz/RIU, in terms of detecting malaria-infected red blood cells (RBCs) from healthy RBCs. The proposed biosensor holds significant potential for applications in biosensing, enabling the detection and analysis of trace amounts of biomolecules.

Driven by the need for unified design and miniaturization across bands, this work presents a novel approach to overcoming the single-functionality and limited applications of traditional metasurfaces. Here, a cutting-edge structural chiral metasurface is proposed exhibiting circular dichroism efficiently across three distinct spectral regions: the visible, near infrared, and mid infrared (MIR) bands each offering unique biosensing applications. The engineered metasurface is designed to achieve strong circular dichroism of 0.72, 0.56 and 0.71 in three different bands, providing tailored functionality as a biosensor for different biochemical and medical applications. Also, the designed structure has been tested as haemoglobin sensor for the detection of higher and lower concentration in the visible region, glucose sensor in near infrared region and as a cancer cell detection sensor in the MIR region offering the very high sensitivity.

The current study proposes an air quality index (AQI) sensor based on the photonic spin Hall effect (PSHE). It senses the changes in AQI caused by the variations in the concentration of particulate matter (PM2.5). The layered structure utilizes the surface plasmon resonance (SPR) mechanism for PSHE shifting and enhancement. The present study reports an enhanced PSHE shift of 1888 mu m. The proposed AQI sensor possesses a sensitivity of 42.0349 degrees/RIU and a figure of merit (FOM) of 4.2 x 10(6) /RIU. The PSHE shift ( delta(H)(r +/-)) also shows a switching response upon change in AQI range, which may serve as an indicator of high pollution level.

We present a new design and study of metamaterial (MTM) structure for wide bandwidth for biosensor and wireless applications. The geometrical parameters were analyzed and optimized for a triple-band operation in the frequency range of 0.1-16 GHz. The propagation characteristics were obtained using Finite element method. The proposed MTM provides negative permittivity at 1.4 GHz and negative permeability in the 9-16 GHz region. The proposed design exhibits left-handed characteristics in L, C, and Ku microwave region's frequency band. The electric field (E), magnetic field (H), and surface current distribution of the proposed MTM unit cell have been studied at three different resonance frequencies. The proposed MTM design has a wide bandwidth of 2.2 GHz in C-band and a high effective medium ratio (EMR) of 13.37. The performance of the sensor is evaluated for different biomedical samples in the refractive index range of 1.00 to 1.39. The results indicate that the proposed biosensor has a high sensitivity in triple band of microwave region. The present research work can be highly suitable for Wi-Fi and satellite applications due to its overall performance, including wide bandwidth in the C-band, high EMR, and triple band operation.

We report a graded index chalcogenide glass (As2Se3)-based photonic crystal fiber having a solid core. The proposed PCF has ultra-high numerical aperture value reaching up to 1.82 for the explored wavelength range of 1.8–10 μm in the mid-infrared region. The value of numerical aperture increases as the pitch increase from 0.92 to 0.96 to 1 micrometer, at a particular value of wavelength. With this high value of numerical aperture, a PCF is capable of gathering a high amount of light in its core. With negative dispersion reaching up to −2000 ps/km/nm at 4.8 µm, the fiber acts as a dispersion-compensating fiber, with confinement loss being close to zero for higher values of wavelength. The confinement loss of the designed PCF is also significantly less and it decreases as the wavelength increases. Also, the value of dispersion is significantly less due to the regular variation in the size of the holes in the transverse direction, as compared to the design when there is no gradation. The design has been optimized with an appropriate value of the perfectly matched layer to achieve the best results.

Rising levels of heavy metal pollution in riverine ecosystems and their hazardous effects on fish species and human health are a globally recognised concern. The accumulation of toxic metals may not target different tissues of fish species in a similar pattern. In addition, it is widely accepted that heavy metals bio-accumulation differs significantly with size and feeding preferences. A recent study on size-dependent accumulation of heavy metals found contradictory findings, and also, limited studies have covered this across tissues of fish species with different ecological guilds. Therefore, the study aims to evaluate the tissue-specific and size-dependent accumulation of heavy metals. Five different species of fish of small and large size were collected from the River Ganga during 2022–2023. The tissues of the gills, liver, kidney, and muscles were excised and digested following standard protocols. The highest accumulation of Pb and Hg in most of the small-sized fish species was found in the liver tissues, while Cd was accumulated in the gills. Among the large-sized fishes, the highest concentration of Pb (25.73 mg kg-1), and Cd (7.33 mg kg-1) was found in the liver tissues of S. aor, whereas the maximum level of Hg was observed in the Kidney (6.21 mg kg-1) of the same. The Sankey diagram has revealed tissue-specific accumulation of the studied metal varies with the feeding behaviour of species in the river. A significant increase (p < 0.05) in mercury accumulation was noted in the tissues of all the studied fish species of larger size.

A highly sensitive Photonic Spin Hall Effect (PSHE)-based layered sensor is proposed which detects changes in refractive index of biological sample. A simple and elegant design measures haemoglobin concentrations using Surface Plasmon Resonance (SPR) effect. It consists of a BK7 prism, a thin gold layer, an analyte layer of haemoglobin and BK7 glass as the substrate. The average angle sensitivity (S-R) has been calculated and found to be 191 degrees/RIU, 208 degrees/RIU and 171 degrees/RIU respectively for low, normal and high haemoglobin concentrations. The Figure of Merit (FOM) for the proposed structure is found to be 896RIU(-1), 812RIU(-1) and 3166RIU(-1) respectively for low, normal and high concentrations of oxygenated haemoglobin.

Metalenses can potentially reduce the size and complexity of existing cameras, displays, and other optical devices, owing to their capability of flexible manipulation of the polarization, amplitude, and phase of light. However, a high meta-atom aspect ratio is still a drawback as it causes difficulty in fabrication of metalens. In this paper, we present the first demonstration of a human-eye inspired metalens with a much lower and constant meta-atom aspect ratio while maintaining the polarization under an arbitrarily polarized excitation in the near-infrared waveband.

We propose modeling and design of a low-loss all-dielectric metasurface (DM), comprised of Silicon on Insulator (SiO2) substrate to demonstrate a perfect reflector in the visible spectrum. The proposed metasurface unit cell consists of V and W shapes arranged in a mirror image configuration, with nanometre-sized gaps (g) between them. A narrow peak with a nearly 100% reflectance and a broad perfect reflectance spectrum is observed within the visible region (400-700 nm) of the electromagnetic spectrum. The effective electromagnetic parameters were also analyzed for electric and magnetic dipole resonance. The electric and magnetic field distributions at the resonant wavelength were also analyzed for the proposed structure. By altering the gap region 'g', the thickness of the dielectric Silica layer (ts ), and the Si resonator (t m), the proposed structure exhibits tunable characteristics. We have successfully illustrated the consistent position of the scattering parameter's response, regardless of the structure's rotation, concluding the homogeneity of the designed structure across the entire visible spectrum. The all-DM exhibits a unique combination of features, including a distinct and wide reflectance spectrum as well as a tuned and enhanced electric field which makes it an ideal platform for the applications in filters, color printing, low-loss slow-light devices, and nonlinear optics.

In this paper, design and fabrication of a dual-band near-zero index metamaterial (MTM) structure using copper on an epoxy resin fiber (FR-4) dielectric substrate is reported for refractive index sensing applications. The primary objective is to achieve dual-band operation spanning a 1–15 GHz frequency range, with a specific focus on achieving a broad bandwidth in the C-band. The resonance of the MTM structure was ascribed to the coupling of plane electromagnetic waves with surface plasmon polaritons on the structure, resulting in a quadrupole plasmon resonance mode. Furthermore, transmission characteristics of the fabricated MTM structure were experimentally measured and found to align closely with the simulated results obtained through the finite element method in COMSOL Multiphysics. The designed MTM structure demonstrates negative and near-zero permittivity at resonance frequencies, enabling left-handed and near-zero index behavior in dual microwave frequency bands. Under room temperature conditions, the MTM sensor exhibited sensitivities of 1 GHz/RIU and 3 GHz/RIU at resonance frequencies of 2.7 and 7.3 GHz, respectively. Consequently, the MTM structure exhibits significant potential for diverse applications, serving as a valuable component in sensors, detectors, and optoelectronic devices operating in the GHz region.

The present study elucidates a photonic crystal (PhC)-based pressure sensor exploiting the change in refractive index with pressure and the corresponding structural deformation of the dielectric material. The stress-sensitive refractive indices of the constituent materials of the PhC have been considered to study the effect of applied pressure on the photonic bandgap (PBG) characteristics of the structure. The designed pressure sensor, proposed using a two-dimensional hexagonal lattice arrangement of air holes in a dielectric slab, operates in the high-pressure range of 1-6 GPa. A comparative study of the PBG characteristics with the application of high pressure has been reported for three semiconducting materials-GaAs, Ge and Si, used for the dielectric slab in the proposed structure. GaAs is found to exhibit the highest sensitivity to pressure variations and shows more pronounced shifting of the midgap wavelength with pressure in comparison to Ge and Si. The largest PBG is seen in the Ge-based structure, closely followed by the GaAs and Si-based structures. The proposed structure is suitable for high-pressure sensing applications.