Resonant Transmission Peak Research Articles

Exploring the tuning mechanism of multipolar quasi-continuous domain bound states in tetramer metasurface

High-quality factor (high-<i>Q</i>) resonance has broad prospects in applications such as in narrow-band filtering, slow-light devices, and nonlinear optics interaction enhanced to highly sensitive sensing. Previous methods of designing high-<i>Q</i> resonance suffered intrinsic drawbacks such as high-volume cavities or large-scale bending radii. However, recently, a new approach to designing high-<i>Q</i> resonances has begun to attract public attention on the basis of asymmetric metasurfaces that are related to the bound states in the continuum (BIC) phenomenon. Constructing BIC resonance in electromagnetic metasurface can generate sharp resonant transmission peak. Therefore, there is growing interest in utilizing BIC to achieve metasurface with high-<i>Q</i>. However, most of existing studies are based on single BIC, and few studies focusing on multiband BICs and multiple forms of symmetry breaking. In this work, we propose an all-dielectric metasurface composed of tetrameric cuboids. By etching two elliptical cylinders in each cuboid, the metasurface can simultaneously support in-plane symmetry breaking, displacement perturbations and periodic perturbations. We first use multipole calculations to analyze the physical mechanism by which the metasurface generates quasi-BIC under these three conditions. It is confirmed that the <i>Q</i> factor and resonant peak position of quasi-BIC can be controlled by adjusting the asymmetry parameters. Subsequently, we introduce the in-plane symmetry breaking, displacement perturbations and periodic perturbations into the metasurface simultaneously and generate five quasi-BIC modes, whose numbers and positions can be flexibly adjusted, and the largest <i>Q</i> factor is 58039. In summary, this work provides a new practical design concept for realizing high-<i>Q</i> all-dielectric metasurfaces, which can be used to improve the sensitivity of multi-parameter sensors.

Exploring Photonic Crystals: Band Structure and Topological Interface States

The physical mechanisms supporting the existence of topological interface modes in photonic structures, formed with the concatenation of two finite, N-period, one-dimensional photonic crystals, are investigated. It is shown that these mechanisms originate from a specific configuration of bands and bandgaps of topological origin in the band structure of the concatenated structure. Our analysis reveals that the characteristics of such a configuration depend on the structural parameters, including the number, N, of unit cells, and determine the properties of the corresponding resonant transmission peak. It was shown that the width and maximum value of the transmission peaks decrease with N. These results not only provide new physical insight into the origin and nature of such modes, but also can be used to control and manipulate the transmission peak properties, such as peak values, full width at half maximum (FWHM), and Q-factor, which are of special interest in the fields of optical sensing, filters, etc.

Microwave Polarization Sensing for Dielectric Materials Based on a Twisted Dual-Layer Meta-Surface.

A microwave sensor is proposed based on a chiral twisted dual-layer meta-surface. Elliptical angle and polarization rotation angle are used to characterize the different dielectric constants of materials. The dielectric films consisting of polydimethylsiloxane and barium titanate with volume fractions 0%, 10%, 15%, 20% are prepared and tested for a proof of concept. The measured results show that the Q factors of polarization rotation angle and elliptical angle peak are 11.85 when the volume fraction of barium titanate is 20%, which is 75.5% higher than 6.75 of the transmission resonance peak, and the figures of merit of the polarization rotation angle and elliptical angle peak are 0.99 and 0.86, which are 73.7% and 50.9% higher than the 0.57 of transmission resonance, respectively. Compared to the resonance sensing method, polarization sensing not only has a better Q factor and figure of merit while maintaining similar sensitivity, but also obtains more characterization information due to the double-parameter sensing, which provide a new idea for the development of high-sensitivity microwave sensors.

Optical limiter coatings towards reusable high irradiance shielding

Optical limiters (OLs) are systems designed to protect objects from high intensity irradiance above a set threshold. Often times, these OL systems are in the form of coatings and can be used to protect objects such as sensors, critical components, or human eyes. In this work, we report the successful development of a multilayer reflective OL coating system based on a non-linear Fabry-Perot resonator structure. The structure utilized distributed Bragg reflectors (DBRs) composed of silicon/silicon nitride and a boron nitride non-linear layer embedded in the resonant cavity. The coatings were fabricated via DC and RF magnetron sputtering and exhibited high reflectance (∼99%) over a 525 nm bandwidth with a single resonant transmission peak (∼7%). The optical limiters fabricated in this study exhibited a transmission drop-off when exposed to irradiances above ∼1000 kW/cm2 from a 1064 nm Nd:YAG laser, demonstrating an abrupt reduction in resonant transmission. Fabricated optical limiters also demonstrated multi-hit survivability, maintaining low transmittance (<0.4%) after numerous 3.6 ns laser pulse exposures. This multi-hit survivability and high reflectivity offers promising opportunities for improved protection against directed energy weapons. This study lays groundwork for future evaluation of the observed on/off mechanism, as well as further development of high laser damage threshold optical limiting thin films.

Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface.

Thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops, while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of VO2. For a y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO2. For an x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO2, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch.

Electro-optic properties of one-dimensional (1D) nonlinear perfect photonic crystals based on Lithium tantalate layer

Electro-optic properties of one-dimensional (1D) nonlinear perfect photonic crystals (PCs) based on Lithium tantalate (LiTaO3) layer and air were studied. Using transfer matrix method, we found that the resonance transmission peak induced by weak defocusing Kerr nonlinearity can be tuned to any wavelength when the 1D structure is subject to external electric field. We demonstrated numerically that the intensity of this localized mode either increases or decreases depending on both the magnitude and the direction of the applied electric field. In addition, the wavelength varies linearly with the applied external electrical field and depends on the incidence angle. For a critical nonlinearity strength |αc|, the single resonance peak splits into two resonances as the magnitude of the external electric field is increased. Moreover, the number of transmission resonance peaks with narrow FWHM, high Q factor and total transmission can be enhanced by increasing the intensity of the applied electric field. Results presented in the current study promote the application of our one-dimensional (1D) nonlinear perfect photonic crystal for electrically tunable narrow-band transmission multi-channel optical filters and some other optoelectronic applications.

Terphenylthiazole-based self-assembled monolayers on cobalt with high conductance photo-switching ratio for spintronics.

Two new photo-switchable terphenylthiazole molecules are synthesized and self-assembled as monolayers on Au and on ferromagnetic Co electrodes. The electron transport properties probed by conductive atomic force microscopy in ultra-high vacuum reveal a larger conductance of the light-induced closed (c) form than for the open (o) form. We report an unprecedented conductance ratio of up to 380 between the closed and open forms on Co for the molecule with the anchoring group (thiol) on the side of the two N atoms of the thiazole unit. This result is rationalized by Density Functional Theory (DFT) calculations coupled to the Non-Equilibrium Green's function (NEGF) formalism. These calculations show that the high conductance in the closed form is due to a strong electronic coupling between the terphenylthiazole molecules and the Co electrode that manifests by a resonant transmission peak at the Fermi energy of the Co electrode with a large broadening. This behavior is not observed for the same molecules self-assembled on gold electrodes. These high conductance ratios make these Co-based molecular junctions attractive candidates to develop and study switchable molecular spintronic devices.

Tunable terahertz metamaterial filter based on applying distributed load

A terahertz metamaterial filter with a tuning capability between the modes of single band and dual band is presented. The filter consists of two metal-array layers and three polymer layers, the latter of which can be tuned by mechanical loads. The proposed structure can afford three neighboring intrinsic resonant transmission peaks (0.59 THz, 0.70 THz and 0.84 THz), in which the first two peaks are different from the last one via the analysis of equivalent permittivity as well as the distributions of surface current and electric field. With the increase of distributed load within 30 N/mm2, the former resonant peaks of 0.59 THz and 0.70 THz approach and merge to form a new pass band, while the former resonant peak of 0.84 THz shows an obvious blue shift and departs from the former neighboring peaks to form a new narrow pass band with high transmittance of 0.95. The transmission characteristics of the structure are analyzed in detail by the distribution of electromagnetic fields and surface current. This work may provide a new tuning method which can realize the switch from single band to dual band.

High Sensitivity Terahertz Biosensor Based on Mode Coupling of a Graphene/Bragg Reflector Hybrid Structure.

In this work, a high-sensitivity terahertz (THz) biosensor is achieved by using a graphene/Bragg reflector hybrid structure. This high-sensitivity THz biosensor is developed from the sharp Fano resonance transmission peak created by coupling the graphene Tamm plasmons (GTPs) mode to a defect mode. It is found that the proposed THz biosensor is highly sensitive to the Fermi energy of graphene, as well as the thickness and refractive index of the sensing medium. Through specific parameter settings, the composite structure can achieve both a liquid biosensor and a gas biosensor. For the liquid biosensor, the maximum sensitivity of is obtained by selecting appropriate parameters. We believe the proposed layered hybrid structure has the potential to fabricate graphene-based high-sensitivity biosensors.

Carbon nanotube-based flexible metamaterials for THz sensing

The inherent limitations of metal-based metamaterials are the key factors limiting the rapid development of the field of flexible terahertz metamaterials. The advantages of carbon nanotube-based materials and devices in terms of weight, cost, and flexibility of free bending, make them of great use for flexible terahertz metamaterials and devices. Here, a flexible terahertz metamaterial sensor, based on a subwavelength periodic array structure of carbon nanotube thin films, is reported. The proposed flexible metamaterial can achieve the surface plasmon resonance to generate local field enhancement phenomenon, resulting in enhanced resonance transmission peaks. We observed that the resonant frequency and amplitude modulation can be continuously adjusted when the device is subjected to a small external strain. In addition, we found that the terahertz transmission spectrum changes significantly when analytes or dielectric layers, with different refractive indices, thicknesses, or carrying pore defects, are added on the surface of the carbon nanotubes film or below the polyimide substrate of the flexible metamaterials sensor in the bent state. Our results show that these materials and designed device strategies will aid in developing new terahertz functional devices, such as strain sensors, biochemical sensors, curved surface defect detectors, and wearable terahertz imagers.

Optimizing temperature-dependent molar volume fraction of biodiesel fuel in a pseudo-binary mixture through Bragg fiber waveguide sensor having defect layer

In the present communication, the temperature-dependent molar volume fraction of various kinds of renewable biodiesel fuel resources in a pseudo-binary mixture is theoretically optimized through the Bragg fiber waveguide (BFW) sensor with a geometrical defect in periodic cylindrical Bragg reflectors. BFW structure is modelled using a transfer matrix method (TMM) and Henkel formalism in a cylindrical coordinate system. The temperature dependence molar volume fraction is linked to the change in the refractive index of the pseudo-binary mixture, which is further predicted using the capacity of various models; Lorentz-Lorenz, Dale-Gladstone, Eykman, Newton, and Kay. In the presence of a geometric defect layer, a sharp transmission peak of 0.1nmfull width at half maxima (FWHM) is obtained in the considered photonic band gap (PBG), which is sensitive to the change in core refractive index. The temperature-dependent (due to different weather conditions) maximum sensitivity of the proposed sensor is found to be 1280 nm/RIU, which is further compared with the phoxonic crystal-based static temperature sensor having sensitivity 142 nm/RIU only. Along with improved sensitivity in the proposed sensor, other sensing performance parameters detection accuracy and quality parameter (which are inversely proportional to the FWHM) are also improved due to least FWHM of resonant transmission peak about 0.1 nm comparatively.

Optical transmission through MDM plasmonic tri-layer consisting of T and L shape periodic structures

Optical transmission properties of plasmonic MDM (metal–dielectric–metal) tri-layer consisting of T and L shape periodic slit structures are investigated by finite difference time domain method. The spectral transmission in the range of visible to NIR (near-infrared) frequencies greatly depends on the slit structure. For T shape structure, single resonant transmission peak is observed, while L shape structure shows double resonance behaviour. The present study shows how structural shapes and polarizations of incident light determine the resonant condition. Based on the observed transmission spectra, an LC circuit model is presented. The low-frequency resonant peak is observed to be sensitive to the structural shape. The presence of side channel oriented parallel to the polarization direction of the input beam is responsible for the origin of high-frequency band (visible-end) in “L” shape structure. The present plasmonic structure is useful in optical transmissive devices.

Excitation of Surface Plasmon Resonance on Multiwalled Carbon Nanotube Metasurfaces for Pesticide Sensors.

With the rapid advances in functional optoelectronics, the research on carbon-based materials and devices has become increasingly important at the terahertz frequency range owing to their advantages in terms of weight, cost, and freely bendable flexibility. Here, we report an effective material and device design for a terahertz plasmonic metasurface sensor (PMS) based on carbon nanotubes (CNTs). CNT metasurfaces based on silicon wafers have been prepared and obvious resonant transmission peaks are observed experimentally. The enhanced resonant peaks of transmission spectra are attributed to the surface plasmon polariton resonance, and the transmission peaks are further well explained by the Fano model. Furthermore, the different concentration gradients of pesticides (2,4-dichlorophenoxyacetic and chlorpyrifos solutions) have been detected by the designed PMSs, showing the lowest detection mass of 10 ng and the sensitivities of 1.38 × 10-2/ppm and 2.0 × 10-3/ppm, respectively. Good linear relationships between transmission amplitude and pesticide concentration and acceptable reliability and stability have been obtained. These materials and device strategies provide opportunities for novel terahertz functional devices such as sensors, detectors, and wearable terahertz imagers.

An atomic Fabry\u2013Perot interferometer using a pulsed interacting Bose\u2013Einstein condensate

We numerically demonstrate atomic Fabry–Perot resonances for a pulsed interacting Bose–Einstein condensate (BEC) source transmitting through double Gaussian barriers. These resonances are observable for an experimentally-feasible parameter choice, which we determined using a previously-developed analytical model for a plane matter-wave incident on a double rectangular barrier system. Through numerical simulations using the non-polynomial Schödinger equation—an effective one-dimensional Gross–Pitaevskii equation—we investigate the effect of atom number, scattering length, and BEC momentum width on the resonant transmission peaks. For ^{85}Rb atomic sources with the current experimentally-achievable momentum width of 0.02 hbar k_0 [k_0 = 2pi /(780~text {nm})], we show that reasonably high contrast Fabry–Perot resonant transmission peaks can be observed using (a) non-interacting BECs, (b) interacting BECs of 5 times 10^4 atoms with s-wave scattering lengths a_s=pm 0.1a_0 (a_0 is the Bohr radius), and (c) interacting BECs of 10^3 atoms with a_s=pm 1.0a_0. Our theoretical investigation impacts any future experimental realization of an atomic Fabry–Perot interferometer with an ultracold atomic source.

Doubly electrically tuned cylindrical Bragg fiber waveguide inline optical filter for multiwavelength LASER applications

In present communication, doubly tuned Bragg fiber waveguide low power inline optical filter with voltage tunable single crystal PMMA defect cavity is theoretically modeled and discussed using Henkel formalism in a cylindrical coordinate system for multiwavelength LASER applications. The structure provides photonic band gap (PBG) with a resonant transmission peak in the obtained PBG region. The defect cavity thickness is controlled by applying an external electric DC voltage. Initially, PBG of the proposed inline optical filter may tune-up to 828nm by modulating the incidence angle upto 80°. Thus, the resonant transmission peak also blue-shifted by 243nm, which can further tuned in presence of DC voltages and so-called doubly electrically tuned. Further, in doubly electrically tuned mode, the application range of such a device is very large up to 129nm for a small change in voltage range about 20V. Thus, the present device can be utilized as multiwavelength laser sources.

Maze-like acoustic metamaterial for low-frequency broadband noise suppression

We propose the maze-like acoustic metamaterial (MLAMM) unit suitable for regulating the transformer noise. The influence of the length and width of the acoustic waveguide on the sound transmission loss (TL) is studied, and the TL and resonance frequencies of the MLAMM unit are calculated. The visco-thermal effect weakens the resonance transmission peak of the MLAMM unit. Finally, experiments verify that the proposed MLAMM unit has low-frequency broadband sound insulation performance, and the TL is about 25 dB in the frequency band of 100 Hz–500 Hz. The research provides a reasonable and effective solution for noise suppression of transformers.

Asymmetric tunneling properties in a 2D anisotropic massless linear energy system

With the aid of the transfer matrix method, the carrier tunneling properties in a two-dimensional (2D) structure with an anisotropic linear energy dispersion are investigated. Several factors, the barrier structure, the incident energy, and the incident angle can be applied to modify the transmission characteristics. An impressive fact is that the anisotropic parameter and different potential directions can be used to tune the Klein tunneling. Therefore, the features of the normal incident transmission and the controllable side resonance transmission peaks can enrich the transport properties in a 2D system and are useful for the designing and utilization of electronic devices.

Resonant peak splitting in finite periodic superlattices with an unit cell of two barriers and two wells on monolayer graphene

The general expressions for transmission probability and resonant peaks in one-dimensional N-periods graphene superlattice with unit cell of two barriers and two wells are analytically derived, and two types of resonant peaks are obtained: (1) the periodicity induced resonant peaks splitting of (N − 1)-fold as N increases; and (2) the resonant peak through a unit cell unchanged as N varies. As the two-barriers in unit cell become asymmetric, the resonance transmission probability of unit cell becomes imperfect (T1 < 1), which drops quickly with the unit asymmetry increases. Thus, the unit cell related resonant peak could only be observed in superlattices with less unit cell asymmetry of a few of period numbers. With the period increases, the unit related resonant peak disappears and only periodicity induced (N − 1)-fold splitting remains. The splitting rule is further confirmed by the conductance and noise versus the incident energy and the misunderstandings in publication domain is cleared up.

An ab initio study on the transport characteristics of Si2C2 clusters

We have studied the transport properties of three different contact structures in Si2C2 clusters by using the first principles based on density functional theory (DFT) and non-equilibrium Green’s function (NEGF) in this paper. Both M1 and M2 show excellent transport properties and a weak negative differential resistance (NDR) phenomenon appears due to greater transferring charge between the central area and the electrodes. The intermediate barrier of M3 is very large, and the electrons are difficult to transmit. However, it also shows good conductivity after we add sulfur (S) atoms at both ends of the molecule. Through the molecular projected self-consistent Hamiltonian (MPSH) analysis, the molecular orbital is expanded with the addition of S atoms, thus showing good conductivity. With the addition of the bias, the conductance of Si2C2 clusters at the Fermi level is reduced due to the drift of the energy level. It is interesting to note that there is a high resonant transmission peak at −1.14 eV under 2 V bias of the M3 system, which shows a molecular switching behavior.

Transcendental equation calculated analytically obeyed by quasi-bound energy levels of quantum well and resonant transmission peaks

Transcendental equation calculated analytically obeyed by quasi-bound energy levels of quantum well and resonant transmission peaks