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Cyanide, a highly toxic chemical compound, presents severe risks to both human health and the environment. Its presence is particularly concerning in various industrial sectors, including mining, electroplating and chemical manufacturing, as well as in natural water bodies due to industrial discharge. This study introduces a graphene-based metasurface sensor designed for highly sensitive cyanide detection within the terahertz frequency range. The sensor's design was refined through comprehensive electromagnetic modelling and analysis. Performance characterization demonstrates optimal sensitivity of 929 GHz RIU−1, coupled with a figure of merit of 14.286 RIU−1 between 0.806 and 0.856 THz frequencies. The detection limit achieved is 0.053 RIU. Adjustments to graphene's chemical potential and structural dimensions demonstrated the device's adaptability. Additionally, the application of machine learning techniques, specifically 1D-CNN regression, proved effective in optimizing sensor performance. The predictive model demonstrated remarkable accuracy, with an optimal R2 score exceeding 95%, indicating that over 94.9% of the variance in the data was accounted for. This high precision enables accurate estimation of absorption values for wavelengths between measured points, underscoring the model's reliability in spectroscopic analysis. This work highlights a versatile platform for rapid, label-free cyanide detection, with significant potential for applications in environmental monitoring, industrial safety and public health protection. [ABSTRACT FROM AUTHOR]

This paper present graphene based metasurface circular resonator (MSCR) inspired optical sensors for detecting waterborne bacteria such as E. coli, Vibrio Cholera, and Shigella flexneri. The optimal design is achieved through simulating all possible combination of proposed structure and analysis based on evaluation metrices. In this study, we have investigated four different sensors and among these sensors other variations are also examined by varying the graphene chemical potential to finalize the structure. The sensor design also takes into account cost-effectiveness, ease of use, and scalability to ensure the widespread adoption of the technology. The proposed designs consist of one central circle surrounded by multiple circles that increase in number with each design. These designs provide a larger surface area for bacterial adhesion, leading to increased detection sensitivity. The MSCR designs can be easily fabricated using standard techniques and can be modified to detect other types of bacteria or contaminants by changing the surface chemistry. [ABSTRACT FROM AUTHOR]

In the present study, we report giant extra-ordinary transmission of near infrared (NIR) light, more than 90%, through a seemingly opaque plasmonic metasurface, which consists of two metal nano-slits arrays (MNSAs) with alternate opening arrangements. By using perfect coupling of the plasmonic modes formed between the sharp edges of the upper and lower MNSAs of silver, a giant, wavelength selective transmission could be obtained. The study is accompanied by optimization of electromagnetic (EM) field coupling for different interlayer spacings and lateral overlap between the two MNSAs to understand their significance in light transmission through the metasurface. The interlayer spacing between the MNSAs works as the transmitting channel for light. The optimization of performance with different fill factors and plasmonic metals was performed as well. Because of the excitation of extended surface plasmons (ESPs) generated at both the MNSAs, the metasurface can be used for refractive index (RI) sensing as one of its applications by using a transparent and flexible polymer, such as polydimethylsiloxane (PDMS), as substrate. The maximum sensitivity which could be achieved for the optimal configuration of the metasurface was 1435.71 nm/RIU, with a figure of merit (FOM) of 80 RIU−1 for 90.45% optical transmission of light for the refractive index variation of analyte medium from 1.33 to 1.38 RIU. The present study strengthens the concept of light funneling through subwavelength structures due to plasmons, which are responsible for light transmission through this seemingly opaque metasurface and finds use in highly sensitive, flexible, and cost-effective EOT-based sensors. [ABSTRACT FROM AUTHOR]

A new configuration for metasurface construction is presented to exhibit potential multi-functionalities including perfect absorption, bio/chem sensing, and enhancement of light–matter interaction. The reciprocal plasmonic metasurfaces discussed here are composed of two plasmonic surfaces of reciprocal geometries separated by a dielectric spacer. Compared to conventional metasurfaces this simple geometry exhibits an enhanced optical performance due to the hybrid plasmonic–photonic cavity. The discussed reciprocal metasurface design further enables effective structural optimization and allows for a simple and scalable fabrication. The physical principle and potential applications of the reciprocal plasmonic metasurfaces are demonstrated using numerical and analytical approaches. [ABSTRACT FROM AUTHOR]

Magnetooptical Faraday effect enables ultrafast photonic devices based on nonreciprocal polarization rotation; however, the intrinsic weakness of Faraday effect prevents miniaturization and practical applications of nonreciprocal photonic devices. Magnetoplasmonics offers new mechanisms for enhancing magnetooptical effects using surface plasmon resonances, which generally have narrow bandwidths. Using finite-difference time-domain modeling, we demonstrate a magnetoplasmonic metasurface, which remarkably enhances the Faraday effect in a wide spectral range. While Faraday rotation in a bare bismuth-substituted yttrium iron garnet film is below 0.02° in the studied range of 600–1600 nm, the proposed metasurface yields few degrees of rotation in a broad band with a maximum exceeding 6.5°, which indicates about three orders of magnitude enhancement. We also show that by optimizing the configuration of the system including the geometry and excitation parameters, the metasurface response and operation band can be tuned further, and rotation values higher than 20° can be achieved. Finally, we present guidelines for designing magnetoplasmonic metasurfaces. [ABSTRACT FROM AUTHOR]

We propose and numerically demonstrate a low-loss deep-subwavelength plasmonic metasurface that exhibits strong optical transmission at near-infrared wavelengths and concomitantly high electrical conductivity. The efficient realization of these two contrasting functionalities without a severe trade-off establishes the proposed metasurface as a potential alternative for conventional transparent electrodes. In contrast to conventional strategies of focusing on free carrier concentration management, the present design decouples the optical and electrical functionalities to a large extent. While the requirements of low electrical contact resistance are facilitated by the presence of an unstructured noble metal thin film, the optical requirements are fulfilled by achieving a transmission resonance through judicious structural and dispersion engineering. The genesis of transmission resonance in our impedance-matched metastructure lies in the excitation of structure derived magnetic plasmon resonance and its coupling to the radiative mode of the underlying planar plasmonic multilayer system. Furthermore, we develop a generalized theoretical framework where we analytically derive the modal dispersion for the plasmonic structure and investigate for the existence of the aforementioned radiative modes. The analysis establishes the fact that for asymmetric multilayer plasmonic systems, the evanescent plasmonic mode can exhibit a mode cut-off and becomes a propagating mode in the high refractive index medium, thereby materializing the possibility of resonant transmission. This theoretical model will be instrumental in gaining crucial physical insights into the operation of plasmonic devices and help in identifying their domain of operation. [ABSTRACT FROM AUTHOR]

A tunable terahertz filter based on graphene plasmonic all-dielectric metasurfaces is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Especially, hybrid all-dielectric metasurfaces are used to make a whole single-sheet graphene forms two different conductivity patterns with the same gate voltage. The simulated results show that resonance wavelength is shifted significantly with the change of gate voltage. Besides, the transmittance spectra are also shifted with the change of the width of SiC, and the filter shows a polarization-dependent modulation property for the length and the width of SiC being 480 and 320 nm, respectively. In addition, the filter can be applied for refractive sensing because the transmittance spectra are shifted with the change of the background refractive index. The study could provide availability for versatile tunable terahertz graphene plasmonic metasurfaces. [ABSTRACT FROM AUTHOR]

Patch-based metasurfaces as generic structures of the reflective flat optical devices, such as flat mirrors, waveplates, polarizer, and holograms, should fulfill two basic requirements of covering 0 to 2π phase shift range and providing a sufficiently high reflection amplitude. Under the current design paradigm, the design process has been based only on the width and length of the patch elements of the metasurfaces. The present study will exploit the potentials of the thickness of the patch elements as a design parameter. While for a metasurface based on patch elements with thickness of 50 nm, a phase shift coverage near 270°, corresponding to 90° phase steps, and reflection amplitude of 0.8 in the wavelength 775 nm are achievable, using just one additional value of 30 nm for thicknesses of the patches will increase the phase shift coverage to 320°, corresponding to 40° phase steps, with reflection amplitude higher than 0.85 in the same wavelength. In this way, the phase steps could be much smaller which means more closely approximating a targeted phase pattern. This would be evidently a remarkable performance improvement, which in the case of a polarization beam splitter, as shown, means reflecting more amount of energy in the desired angles. [ABSTRACT FROM AUTHOR]

Circular lens composed of annularly arranged metal nanoantennas is proposed to achieve far field superresolution focusing. Light illuminating on the nanoantennas' layer approximately acquires paraboloidal phase profile and then focuses into a spot. Lens constructed by monolayer nanoantennas achieve focusing with FWHM (full width at half maximum) of 924 nm and a focal length of 3385 nm, breaking the diffraction limit. Moreover, tri-layered lens realizes subwavelength focusing with FWHM of 320 nm (about 0.49 λ) and the field intensity of focus is optimized to 0.97 a.u. (arbitrary unit). Our proposal shows advances in focusing performance compared with previous work, making it promising in many applications, such as nanolithography, dense storage, and integrated optics. [ABSTRACT FROM AUTHOR]