Visible Frequency Range Research Articles

Compound spin Hall plasmonic lens

The propagation phase and the Pancharatnam–Berry phase are two primary strategies to control surface plasmon polaritons (SPPs) wave, however, hampered by the spatial conjugation and the spin conjugation, respectively. Combining these two approaches together, the conjugations are broken and a compound spin Hall plasmonic lens (SHPL) is proposed and demonstrated numerically and experimentally in the visible frequency range. The proposed strategy can be utilized to realize both transversal and longitudinal deviations of SPP focus. The positions of the SPP focus can be dynamically modulated by switching the spin states of excitation light and adjusting the phase gradient encoded onto the lens. Promising applications of the proposed SHPL include on-chip communication and polarization detection.

Sonoluminescence: Photon production in time-dependent analog systems

Sonoluminescence is a well-known laboratory phenomenon where an oscillating gas bubble in the appropriate environment periodically emits a flash of light in the visible frequency range. In this work, we study the system in the framework of analog gravity. We model the oscillating bubble in terms of analog geometry and propose a nonminimal coupling prescription of the electromagnetic field with the geometry. The geometry behaves as an analogous oscillating time-dependent background in which repeated flux of photons are produced in a wide frequency range through parametric resonance from quantum vacuum. Due to our numerical limitation, we could reach the frequency up to ∼105 m−1. However, we numerically fit the spectrum in a polynomial form including the observed frequency range around ∼107 m−1. Our current analysis seems to suggest that parametric resonance in analog background may play a fundamental role in explaining such phenomena in the quantum field theory framework. Published by the American Physical Society 2024

Optical Tellegen metamaterial with spontaneous magnetization

The nonreciprocal magnetoelectric effect, also known as the Tellegen effect, promises a number of groundbreaking phenomena connected to fundamental (e.g., electrodynamics of axion and relativistic matter) and applied physics (e.g., magnetless isolators). We propose a three-dimensional metamaterial with an isotropic and resonant Tellegen response in the visible frequency range. The metamaterial is formed by randomly oriented bi-material nanocylinders in a host medium. Each nanocylinder consists of a ferromagnet in a single-domain magnetic state and a high-permittivity dielectric operating near the magnetic Mie-type resonance. The proposed metamaterial requires no external magnetic bias and operates on the spontaneous magnetization of the nanocylinders. By leveraging the emerging magnetic Weyl semimetals, we further show how a giant bulk effective magnetoelectric effect can be achieved in a proposed metamaterial, exceeding that of natural materials by almost four orders of magnitude.

Meta-surface filter for visible frequency range based on meta-materials

To enhance the efficiency of exposure in greenhouses during specific cultivation periods, it is essential to design a meta-face that effectively filters the green part of visible light. This targeted filtering function will enable optimal control of the light spectrum, resulting in better cultivation conditions and increased productivity. Leveraging innovative concepts and advanced methods, a highly efficient meta-surface design aimed at filtering the green portion of the visible light spectrum is proposed. The proposed structure comprises periodic arrays of graphene disks and rings strategically positioned on both sides of a silicon oxide substrate. This straightforward coated layer configuration offers a practical solution for greenhouses and controlled agriculture applications, facilitating improved light management and tailored growth conditions. Through two separate simulation paths, the validity and accuracy of our proposed approach were investigated. Both theoretical analysis and simulation results demonstrate that the proposed structure attenuates the green part of visible light. Filtered output waves prove to be highly beneficial for indoor cultivation, during the flowering period, offering improved control over light conditions. The design methodology relies on an equivalent circuit model and impedance matching criteria. Additionally, full-wave simulation is performed to verify the effectiveness of the employed modeling. According to the simulation results, the proposed meta-surface effectively filters the green part of visible light, while allowing the transmission of the red spectrum.

Plasmon-induced magnetic anapole mode assisted strong field enhancement.

Optical metamaterials, sensing, nonlinear optics, and surface-enhanced spectroscopies have witnessed the remarkable potential of the anapole mode. While dielectric particles with a high refractive index have garnered significant attention in recent years, the exploration of plasmonic anapole modes with intense localized electric field enhancements in the visible frequency range remains limited. In this study, we present a theoretical investigation on the relationship between the strongest near-field response and magnetic anapole modes, along with their substantial enhancement of Raman signals from probing molecules. These captivating findings arise from the design of a practical metallic oblate spheroid-film plasmonic system that generates magnetic anapole resonances at frequencies within the visible-near-infrared range. This research not only sheds light on the underlying mechanisms in a wide range of plasmon-enhanced spectroscopies but also paves the way for innovative nano-device designs.

Synthesis of CoxZn1-x zeolitic imidazolate frameworks (ZIFs) as efficient photocatalyst with high stability

Sodalite-topology zeolitic imidazolate framework-8 (ZIF-8) composed of Zn2+ ions and organic linkers exhibit excellent physical and chemical properties such as high porosity, large surface area and abundant active sites. While it can only be excited by UV light due to the wide bandgap energy, which limits its application in photocatalysis. Herein, we synthesized Co-doped ZIF-8 with various ratio and systematically investigated its promotion effects on photocatalytic reaction. The as-synthesized CoxZn1-x-ZIF possessed homogeneous dodecahedron crystals and developed porous structure, together with obvious light absorption in visible frequency range. The photocatalytic performance of methylene blue (MB) had been improved with increasing of Co2+/Zn2+ ratio in ZIFs, while the reaction stability of Co0.75Zn0.25-ZIF and Co1.0-ZIF significantly decreased due to the apparent collapse in crystal phase. Taken together, Co0.5Zn0.5-ZIF was demonstrated to be a remarkable photocatalyst with high photocatalytic activity and strong stability. The photogenerated ·O2− and ·OH radicals were found to react as main oxygen species in photocatalytic reaction.

Metasurface enabled broadband all optical edge detection in visible frequencies

Image processing is of fundamental importance for numerous modern technologies. In recent years, due to increasing demand for real-time and continuous data processing, metamaterial and metasurface based all-optical computation techniques emerged as a promising alternative to digital computation. Most of the pioneer research focused on all-optical edge detection as a fundamental step of image processing. Metasurfaces have been shown to enable real time edge detection with low to no power consumption. However, the previous demonstrations were subjected to the several limitations such as need for oblique-incidence, polarization dependence, need for additional polarizers, narrow operation bandwidth, being limited with processing in 1D, operation with coherent light only, and requiring digital post-processing. Here, we propose and experimentally demonstrate 2D isotropic, polarization-independent, broadband edge detection with high transmission efficiency under both coherent and incoherent illumination along the visible frequency range using a metasurface based on Fourier optics principles.

The Broadband Optical Absorption Performance of Rod‐Based Hyperbolic Metamaterials in Cuboidal Patterns

AbstractThe development of metamaterials for advanced optical functions, especially optical metamaterials that can be synthesized through a colloidal assembly route, holds significance in nanophotonic research. A broadband absorber based on hyperbolic metamaterials (HMMs) with cuboidal patterns, constructed using 3D assembled nanorod arrays, is fabricated with the assistance of SU‐8 photoresist filling, photolithography, and atomic layer deposition (ALD) of Pt. The formation of cuboidal patterns creates a rod‐based metamaterial waveguide, enabling slow‐light dispersion in the visible frequency range. Slow light frequencies can be adjusted by varying the metal thickness and metal type, while they are minimally influenced by the width of each cuboidal framework. In addition to the absorption attributed to the rod metamaterial waveguides, the gap between the neighboring cuboidal frameworks induces a coupling effect that enhances light capture. The presence of curving morphologies on the side of each cuboidal framework further enhances optical absorption. The optimized broadband rod metamaterial absorber in cuboidal patterns can achieve an average absorptivity of 96.9% in the 400–1100 nm wavelength range.

A bendable wide oblique incident angle stable polarization insensitive metamaterials absorber for visible optical wavelength applications

In the visible frequency range, the most common application is for the transmission of electromagnetic signals over air and time to an aerial receiver. They are implemented to check tapped live powered components as well as identify defects, thermal leaking hot spots, or electrical failures. This study investigates the use of a compact nonagon-shaped metamaterial absorber (MMA) for wideband visible applications by employing a three-layer substrate material structure consisting of metal, dielectric, and metal. In comparison to the most current study, the presented MMA has a smaller size, which represents a noticeable novelty. Moreover, the proposed MMA has bendable properties and two numerical simulation software have been used to validate the proposed MMA. This demonstrates the successful acquisition of data from both the CST and HFSS simulations. The proposed metamaterial absorber attained above 80% absorption in the visible ranges from 400 nm to 750 nm wavelength for the simulation mode of TE and TM, respectively. An overall unit cell size of 930 × 930 × 202 nm3 which achieves an average absorption of 95.61% in its operating band 519–677 nm for visible optical wavelength when the performance of the proposed MMA was verified using the HFSS software. Moreover, the constant absorption feature is stable over a large range of oblique incidence angles. The quality of the MMA is verified by assessing the PCR value. Wide-angle incidence angle stability, polarization insensitivity, and absorption with 15⁰ bending effects can all be observed in both modes (TM and TE). In addition, the absorption property of MMA was investigated structurally by applying electric and magnetic fields. The presented MMA can be used in wide-angle stability, MRI, color imaging, solar cells, thermal imaging, and so on.

High-efficiency broadband polarisation converter via patterned multilayer twisted liquid crystal polymer

ABSTRACT We propose an ultra-compact polarisation converter based on liquid crystal (LC) material for effectively converting the obliquely incident unpolarised light into horizontal linearly polarised beam within the visible frequency range. Multilayer twisted configuration is introduced here to tackle the inherent dispersion issue from the LC itself and extended Jones matrix is employed to analyse the propagation of the electric field inside the LC medium under possible oblique illumination. Spatial angular separation of orthogonal polarised lights and polarisation conversion into the same polarisation direction are realised through specific patterned structure design, which effectively reduce the thickness of the device without sacrificing performance. Experimental results demonstrated that our fabricated LC-based device can deliver >80% polarisation conversion efficiency at normal illumination and 59%–80.5% efficiency for ±10° oblique incidence over the visible spectrum. Therefore, we envision that our presented device might find numerous potential applications associated with polarisation regulation such as vortex beam generator, augmented reality and optical computing.

Observation of Enhanced Generation of a Fifth Harmonic from Halide Perovskite Nonlocal Metasurfaces

Lead halide perovskites are widely employed in photonic and light-emitting devices because of their rich optoelectronic properties and simplicity of fabrication based on low-cost flexible technologies. Perovskite bulk crystals and films demonstrate outstanding nonlinear characteristics with large optical nonlinearities exceeding the nonlinear susceptibilities of conventional semiconductor materials by several orders of magnitude. One of the promising approaches for further enhancement of the nonlinear response of perovskites as dielectric photonic materials is to employ optical resonances of structured surfaces, or metasurfaces. Nonlocal metasurfaces supporting lattice modes over many unit cells provide a new approach to both spatial and spectral control of light fields, and they may deliver improved characteristics of nonlinear effects for a wide range of applications associated with broadband excitation of multiple high-quality resonances. Here we report on the first observation of enhanced fifth harmonic generation in MAPbBr3 halide perovskite nonlocal metasurfaces driven by high-quality resonances at the generated harmonic wavelength in the visible frequency range. The demonstrated enhancement is about 2 orders of magnitude compared to an unpatterned MAPbBr3 film of the same thickness, and is broadband by virtue of the excitation of multiple resonant modes in the highly nonlocal regime. Our work suggests a novel approach for achieving parametric processes in resonant dielectric structures with high efficiency.

Active Tunable Pulse Shaping Using MoS2‐Assisted All‐Dielectric Metasurface

While optical pulse shapers have important applications in classical and quantum communication regimes and laser resonant cavities, engineering of group delay dispersion (GDD) remains one of their greatest challenges. Herein, by taking advantage of the electrically tunable optical properties of 2D material and the low‐loss nature of dielectric material. This paper demonstrates how an active tunable all‐dielectric metasurface assisted by 2D material can be leveraged to shape the temporal profile of a pulse. The proposed metasurface consists of an array of nanobars covered by a 2D sheet and positioned on a distributed Bragg reflector (DBR) as a perfect mirror to design a phase‐only modulator. Upon introducing in‐plane asymmetries, the quasi‐bound state in the continuum (QBIC) resonance emerges under normal incidence, which subsequently leads to achieving both significant GDD and the two regimes of pulse stretching and compressing via boosting the effect of the permittivity variation of molybdenum disulfide (MoS2). The monolayer MoS2 proves to be an excellent substitute for other tunable materials with inherent dissipative loss in the visible frequency range. Following such an active tunable geometrically fixed configuration, various pulse‐shaping operations are achieved, including compression (peak intensity up to 350%), expansion (peak intensity from 60%), splitting, and higher‐order distortion.

Design and Parametric Analysis of a Wide-Angle and Polarization Insensitive Ultra-Broadband Metamaterial Absorber for Visible Optical Wavelength Applications

Researchers are trying to work out how to make a broadband response metamaterial absorber (MMA). Electromagnetic (EM) waves that can pass through the atmosphere and reach the ground are most commonly used in the visible frequency range. In addition, they are used to detect faults, inspect tapped live-powered components, electrical failures, and thermal leaking hot spots. This research provides a numerical analysis of a compact split ring resonator (SRR) and circular ring resonator (CRR) based metamaterial absorber (MMA) using a three-layer substrate material configuration for wideband visible optical wavelength applications. The proposed metamaterial absorber has an overall unit cell size of 800 nm × 800 nm × 175 nm in both TE and TM mode simulations and it achieved above 80% absorbance in the visible spectrums from 450 nm to 650 nm wavelength. The proposed MA performed a maximum absorptivity of 99.99% at 557 nm. In addition, the steady absorption property has a broad range of oblique incidence angle stability. The polarization conversion ratio (PCR) is evaluated to ensure that the MMA is perfect. Both TM and TE modes can observe polarization insensitivity and wide-angle incidence angle stability with 18° bending effects. Moreover, a structural study using electric and magnetic fields was carried out to better understand the MMA's absorption properties. The observable novelty of the proposed metamaterial is compact in size compared with reference paper, and it achieves an average absorbance of 91.82% for visible optical wavelength. The proposed MMA also has bendable properties. The proposed MMA validation has been done by two numerical simulation software. The MMA has diverse applications, such as color image, wide-angle stability, substantial absorption, absolute invisible layers, thermal imaging, and magnetic resonance imaging (MRI) applications.

Bichromatic four-wave mixing and quadrature-squeezing from biexcitons in atomically thin semiconductor microcavities

Nonlinear optical effects such as four-wave mixing and generation of squeezed light are ubiquitous in optical devices and light sources. For new devices operating at low optical power, the resonant nonlinearity arising from the two-photon sensitive bound biexciton in a semiconductor microcavity is an interesting prospective platform. Due to the particularly strong Coulomb interaction in atomically thin semiconductors, these materials have strongly bound biexcitons and operate in the visible frequency range of the electromagnetic spectrum. To remove the strong pump laser from the generated light in optical devices or to simultaneously excite non-degenerate polaritons, a bichromatic-pump configuration with two spectrally separated pump lasers is desirable. In this paper, we theoretically investigate spontanous four-wave mixing and quadrature-squeezing in a bichromatically pumped atomically thin semiconductor microcavity. We explore two different configurations that support degenerate and non-degenerate scattering from polaritons into bound biexcitons, respectively. We find that these configurations lead to the generation strongly single- and two-mode quadrature-squeezed light.

Langevin dynamics/Monte Carlo simulations method for calculating nanoscale dielectric functions of materials

We have developed a simulational methodology for calculating the nanoscale frequency-dependent complex dielectric function of a wide range of materials using a combination of Langevin dynamics and Metropolis Monte Carlo methods. The premise of such a scheme is to use the atomistic structure of materials and designate appropriate interatomic interactions as well as internal field couplings to accommodate correlated materials. We validate our model by recreating the dielectric functions of well-studied representative materials including insulator ${\text{SiO}}_{2}$ thin film that has phonon resonances in the midinfrared, and semiconductor monolayer ${\text{MoS}}_{2}$ that exhibits strong excitonic resonances in the visible frequency range. To further showcase the capability of the model in calculating nanoscale dielectric modulation of complex materials, we simulate the dielectric response of ${\text{SmNiO}}_{3}$, a correlated perovskite oxide, with respect to differing levels of hydrogenation, oxygen vacancy formation, and external fields. This is accomplished by inserting and tracking the movement of dopants at the nanoscale using Metropolis Monte Carlo methods that explicitly include interactions with each other as well as external fields. Simulated nanoscale dielectric spectra agree very well with high-resolution near-field experimental measurements based on scattering type scanning near-field microscopy. We find that this modeling scheme carries a broad utility in describing and predicting the nanoscale dielectric behavior of a broad range of materials exposed to changing local environments.

Extrinsic Chirality and Circular Dichroism at Visible Frequencies Enabled by Birefringent α-MoO3Nanoscale-Thick Films: Implications for Chiro-Optical Control

Nanophotonics community has shown great interest in 2D materials because of their unique properties of electromagnetic field manipulation. Many of these materials exhibit strong natural anisotropy, which further opens possibilities of polarization manipulation. Here, we show that α-MoO3, an emerging natural hyperbolic 2D material, can be combined with plasmonic nanostructures to provide strong extrinsic chirality in the visible range. A combination of biaxial anisotropy in α-MoO3 and Fabry–Perot cavities with nanoscale features leads to different absorption of left and right circularly polarized photons, hence exhibiting circular dichroism (CD). Our simulation results predict that multilayer nanoscale-thick films including α-MoO3 are potential candidates for achieving extrinsic chirality across the visible range. Furthermore, we show a significant CD increase when the α-MoO3 layer is coupled with plasmonic nanohole arrays or plasmonic nanocubes. Such designs are achiral in geometry and therefore easier to fabricate. Moreover, we optimize the CD dissymmetry factor gCD for the nanocube-based design at 780 nm, obtaining 84%. We believe that utilizing biaxially anisotropic α-MoO3 films to control and engineer chiro-optical properties in the visible frequency range will open research directions and enable enhanced functionalities in chiro-optical control at the nanoscale, further leading to applications in chiral sensing and CD.

Magnetic plasmon induced ultra-narrow perfect light absorption at visible frequency for gas sensing

We theoretically demonstrate an ultranarrow perfect light absorption (PIA) of a 3D metamaterial due to the strong coupling between the magnetic plasmon of the Au vertical split-ring resonator (VSRR) and the surface plasmon polariton propagating above the Au film. Through lifting the VSRRs above the metallic film to decrease the dielectric substrate effect, the linewidth of 1.9 nm of the PIA is obtained. Our proposed 3D metamaterial shows the high sensitivity (S = 711 nm RIU, S* = 13/RIU) and figure of merit (FoM = 374, FoM* = 1.3 × 105), which could be used for optical gas sensing in the visible frequency range.

Multifunctional metasurfaces enabled by simultaneous and independent control of phase and amplitude for orthogonal polarization states

Monochromatic light can be characterized by its three fundamental properties: amplitude, phase, and polarization. In this work, we propose a versatile, transmission-mode all-dielectric metasurface platform that can independently manipulate the phase and amplitude for two orthogonal states of polarization in the visible frequency range. For proof-of-concept experimental demonstration, various single-layer metasurfaces composed of subwavelength-spaced titanium-dioxide nanopillars are designed, fabricated, and characterized to exhibit the ability of polarization-switchable multidimensional light-field manipulation, including polarization-switchable grayscale nanoprinting, nonuniform cylindrical lensing, and complex-amplitude holography. We envision the metasurface platform demonstrated here to open new possibilities toward creating compact multifunctional optical devices for applications in polarization optics, information encoding, optical data storage, and security.

Numerical extrapolation method for complex conductivity of disordered metals

Recently, quantum corrections to optical conductivity of disordered metals up to the UV region were observed. Although this increase of conductivity with frequency, also called anti-Drude behaviour, should disappear at the electron collision frequency, such transition has never been observed or described theoretically. Thus, the knowledge of optical conductivity in a wide frequency range is of great interest. It is well known that the extrapolation of complex conductivity is ill-posed - a solution of the analytic continuation problem is not unique for data with finite accuracy. However, we show that assuming physically appropriate properties of the searched function $\sigma(\omega)$, such as: symmetry, smoothness, and asymptotic solution for low and high frequencies, one can significantly restrict the set of solutions. We present a simple numerical method utilizing the radial basis function approximation and simulated annealing, which reasonably extrapolates the optical conductivity from visible frequency range down to far infrared and up to ultraviolet region. Extrapolation obtained on MoC and NbN thin films was checked by transmission measurement across a wide frequency range.

Analysis of Photonic Bandgap Extension in One-Dimensional Quasiperiodic Superconducting Photonic Slabs

One-dimensional superconducting photonic slabs made of alternated layers of isotropic dielectric (SiO2) and a high-Tc superconductor (YBCO) are theoretically investigated by the Gorter Casimir two fluid model (GCTFM) and the transfer matrix method (TMM). The proposed photonic quasicrystals are built according to the inflation rule of quasiperiodic sequences. The enhancement of the photonic band gap is theoretically investigated. Extending photonic band gap (E-PBG) is achieved for suitable quasiperiodic chains. The bandwidth of the photonic band gap can be enhanced by changing the temperature of superconductor, parameter of quasiperiodic sequence. An overall photonic band gap is obtained in the visible frequency range and can be enhanced by applying a typical thickness’ deformation along the superconducting photonic sample.