Number Of Resonant Modes Research Articles

High-performance plasmonic band-pass / band-stop / cut-off filter using elliptical and rectangular ring resonators

A plasmonic filter including Metal-Insulator-Metal waveguides (MIM) with an elliptical ring resonator is proposed. Using the Finite Difference Time Domain (FDTD) method, we analyze the amount of transmittance in the structure. The results show the creation of five resonance modes with narrow FWHM and suitable transmittance at the resonance points of the spectrum. The resonance wavelength and transmittance at the resonance points are tuned by changing the device geometry. In this structure, preventing the transmittance of the spectrum creates a band-gap between the wavelengths 919 nm–1388 nm, which by changing the size of the structure, the band-gap width changes. This filter also cuts off the transmission of wavelengths greater than 1707 nm. By adding a rectangular ring resonator outside the elliptical ring resonator, the performance of the device was improved and the transmittance included very narrow resonance modes. Due to the number of resonance modes and their narrow FWHM, the introduced structures can be used as devices for filtering several wavelengths, which significantly reduces costs and enhances economic efficiency for the production of plasmonic band-pass filters. Also, this structure can be used as band-stop and cut-off filters. This multiplicity of functions makes it cost-effective to use the proposed device for making integrated optics devices.

Topologically protected multiple resonant modes in a one-dimensional photonic crystal heterostructure

This paper proposed and theoretically examined a double-interfaced one-dimensional photonic crystal heterostructure for strong localization of topologically protected resonant modes. It is challenging to achieve these modes for a range of wavelengths using a single photonic crystal. The design proposed in this study is a heterostructure of photonic crystals 1 (PC1) and 2 (PC2), and it provides distributed localized modes from the infrared to ultraviolet wavelength ranges. In addition, multiple resonant modes occur at certain photonic bandgaps due to the addition of the third photonic crystal (PC3), which is analytically modeled with the heterostructure of PC1 and PC2. The enhancement in the number of resonant modes depends on the PC2 number of unit-cells and the reflection phase of the proposed heterostructure. The reflection phase is abruptly changing from 0 to π for several wavelengths inside the bandgap. These resonance modes are also dependent on the topological behavior of each connected photonic crystal and are immune to small disorder and back-scattering within the crystal. The high-quality factor (Q-factor ∼107) shows strong light–matter interaction of these multiple resonant modes. The characterization was done in terms of the Zak phase, sign of the reflection phase, and bandgap overlapping. Consequently, this heterostructure may pave the way for new topological photonics and new applications in optoelectronics, frequency up-conversion, photonic devices, rainbow trapping, multiwavelength optical filters, and so on.

Multiport Pixel Antenna Optimization Using Characteristic Mode Analysis and Sequential Feeding Port Search

An optimization approach for multiport pixel antenna design using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -port characteristic mode analysis (CMA) and sequential feeding port selection is proposed. CMA is utilized to characterize the maximum number of independent or orthogonal resonant modes that can be formed in the limited space constrained by the size of the pixel antenna. Once the maximum number of orthogonal resonance modes is found sequential feeding port selection is proposed to find the optimum feed positions to independently excite each of the orthogonal resonance modes. The resulting design does not need additional complex feeding networks or impedance matching circuits, making the physical implementation of the design straightforward, compact and practical. Two examples are provided to verify the performance of the proposed approach, including a 3-port pixel antenna and a 4-port pixel antenna operating at 2.4 GHz. The performance of the optimized antennas is very good, and verifies the usefulness of the proposed approach.

Tunable kilohertz microwave photonic bandpass filter based on backscattering in a microresonator.

A tunable microwave photonic bandpass filter (MPBPF) with a kilohertz bandwidth based on the backscattering mode of a silica microsphere resonator is proposed and experimentally demonstrated. In this work, an ultrahigh-quality-factor microsphere resonator is used to generate a radio frequency bandpass response with a bandwidth of 600 kHz. Meanwhile, scattering-induced coupling between the clockwise mode and the counterclockwise mode is introduced to reduce the number of resonance modes, and a single backscattering mode which has a high extinction ratio is obtained. Therefore, an MPBPF with a tuning range of 40 GHz and a rejection ratio of 16.9 dB is realized. This MPBPF possesses advantages such as ultranarrow bandwidth, large tuning range, and compactness, and shows great potential for microwave photonic applications.

Bound states in the continuum supported by silicon oligomer metasurfaces.

Oligomer metasurfaces have attracted a lot of attention in recent years because of their ability to drive strong resonance effects. In this work, by perturbing the symmetry of the structure, we find that there are a large number of resonance modes in the oligomer metasurfaces associated with the optical bound states in the continuum (BICs) near the communication wavelength. When the positions of two nanodisks of the hexamer oligomers are moved along the x- or y-directions at the same time, the mirror symmetry is broken, and an electric quadrupole BIC and three magnetic dipole BICs are excited. The results of near-field distribution of three-dimensional nanodisks and far-field scattering of multiple dipoles in each quasi-BIC reveal that the four BICs present different optical characteristics. It is noted that the method of symmetry breaking by moving the position of nanodisks can accurately control the asymmetric parameter of symmetry-protected BICs, which provides a route for the realization of ultrahigh quality (Q)-factor oligomer metasurfaces in experiment.

Tunable enhanced Faraday rotation in a defected plasma photonic crystal under external magnetic field with different declinations

Magneto-optical responses and the potential for tunability when changing the variables of a one-dimensional defected magnetized plasma photonic crystal have been studied using a transfer matrix method for operation in the mm-range wavelength region. The effect of the number and dielectric defect layer thickness as well as the intensity and declination angle of magnetic field on transmittance, Faraday rotation, and its ellipticity has been investigated. The results demonstrate the ability to alter the resonant modes frequency at multiple levels of precision. The structures with four, six, and eight defect layers have been investigated. The number of defect dielectric layers changes the number of resonance modes. A single defect mode appears within the photonic bandgap with four defect dielectric layers while two defect modes were observed with six layers, and three modes with eight layers. An increase in magnetic field declination decreased the Faraday rotation intensity and width of Faraday resonance mode.

Characteristics of defect states in periodic railway track structure

To overcome the ill-conditioned matrix problem of the traditional transfer matrix method, the Floquet transform method and supercell technology are used to study the defect states of the periodic track structure. By solving the equations of the supercell directly, the propagation characteristics of elastic waves in the track structure with defects are analyzed. The existence of defects destroys the periodicity of track structure, thus resulting in the formation of defect states within the band gaps. Moreover, the elastic wave is localized near the defect position at the frequency of the defect state. The formation mechanism of the defect state in track structure can be explained by the local resonance at the defect. With the expansion of the defect range, the number of local resonance modes that can be formed near the defect increases, thus generating multiple defect states. Furthermore, the defect state enhances the vibration of the structure adjacent to the defect. Therefore, the vibration transmission coefficient in a finite-length range can be used to detect the defect characteristics in the track structure, and the defect degree can be evaluated by the peak frequency of the vibration transmission coefficient within the band gap.

A rational design of multimodal asymmetric nanoshells as efficient tunable absorbers within the biological optical window

In this work, the optical properties of asymmetric nanoshells with different geometries are comprehensively investigated in the quasi-static regime by applying the dipolar model and effective medium theory. The plasmonic behaviors of these nanostructures are explained by the plasmon hybridization model. Asymmetric hybrid nanoshells, composed of off-center core or nanorod core surrounded by a spherical metallic shell layer possess highly geometrically tunable optical resonances in the near-infrared regime. The plasmon modes of this nanostructures arise from the hybridization of the cavity and solid plasmon modes at the inner and outer surfaces of the shell. The results reveal that the symmetry breaking drastically affects the strength of hybridization between plasmon modes, which ultimately affects the absorption spectrum by altering the number of resonance modes, their wavelengths and absorption efficiencies. Therefore, offsetting the spherical core as well as changing the internal geometry of the nanoparticle to nanorod not only shift the resonance frequencies but can also strongly modify the relative magnitudes of the absorption efficiencies. Furthermore, higher order multipolar plasmon modes can appear in the spectrum of asymmetric nanoshell, especially in nanoegg configuration. The results also indicate that the strength of hybridization strongly depends on the metal of shell, material of core and the filling factor. Using Au-Ag alloy as a material of the shell can provide red-shifted narrow resonance peak in the near-infrared regime by combining the specific features of gold and silver. Moreover, inserting a high permittivity core in a nanoshell corresponds to a red-shift, while a core with small dielectric constant results in a blue-shift of spectrum. We envision that this research offers a novel perspective and provides a practical guideline in the fabrication of efficient tunable absorbers in the nanoscale regime.

A neural network for prediction of high intensity resonance modes in magnetic multilayers

The use of magnetic materials as building blocks for frequency applications makes it possible to fabricate micrometer and nanometer high frequency devices. Moreover, devices with multiple high intensity modes for multiband devices can be designed by using magnetic multilayers. However, as the number of layers increases the multilayer becomes more complex, making it very difficult to find optimal configurations due to a big number of possible configurations. Fortunately, over the past decade a surge in the applicability and accessibility of machine learning algorithms and neural networks has been observed, which allow to analyse big quantities of data in search of complex patterns not always evident to humans. In this work, a theoretical model is used to generate approximately 10 × 106 data points, which in turn are used to train a neural network to calculate the number of high intensity resonance modes of three ferromagnetically coupled magnetic layers with an accuracy of over 99.8%. The neural network is then used to identify a configuration of the multilayer which provides the maximum number of high-intensity modes, and comparisons with the theoretical model are presented. Finally, the correlations between parameter were calculated over 600 million of data points, and clear guidelines for obtention of two high intensity resonance modes were identified. These results provide a simple way to find a configuration of the trilayer that have a high number of high intensity modes, thus greatly simplifying the design process of magnetic multi-band frequency devices.

A new elastic characterization method for anisotropic bilayer specimens via Bayesian resonant ultrasound spectroscopy

A novel nondestructive method for complete elastic characterization of substrate-coating bilayer specimens with distinct anisotropic layers via resonant ultrasound spectroscopy (RUS) and Bayesian inversion is developed here. Bayesian formulations of the RUS inversion problem—of quantifying elastic properties given a measured list of resonance frequencies recorded from a single, typically small, precisely fabricated, macroscopically homogeneous, linear-elastic specimen—are a recent development. Here we report the first Bayesian formulation of the bilayer problem, and through a series of practical examples, demonstrate novel parameter estimation capabilities of our open-source CmdStan-RUS code. Finding specimen geometry and the number of resonance modes used for inversion strongly govern the ability to retrieve individual elastic moduli. The concept of “invertability” is explored for a range of relevant geometries using virtual specimens that resemble experimental bilayers of plasma sprayed ceramic coatings on single crystal metallic substrates. A range of Bayesian posterior evaluation methods are addressed, particularly considering the large computational cost of the bilayer forward model. Laplace approximation methods are thus developed and implemented for bilayer geometry design space modeling and expedient estimates of parameter uncertainties. Ideal specimen design, different noise models, the influence of prior distributions, dual-likelihood fits incorporating measurements of the bare substrate, and how Bayesian RUS methods differ from traditional RUS optimization are discussed.

Dual-band reflection polarization converter for circularly polarized waves based on a zigzag asymmetric split ring resonator

Polarization converters based on metasurfaces are one of the recently developed metadevices that can change the polarization state with designated modes, utilizing the sub-wavelength unit construction. In this paper, a kind of planar zigzag asymmetric split ring resonator (Z-ASRR) metasurface with dual bands is proposed to achieve nearly perfect polarization conversion for circularly polarized waves. Compared with the original prototype asymmetric resonant ring (ASRR), both magnitude and bandwidth have been remarkably improved for achieving a higher resonance, with the introduction of zigzag metallic wires. The reflection polarization conversion ratio possesses two peak values with 0.94 and 0.99 at 5.39 GHz and 9.65 GHz, respectively. It is also demonstrated that the introduction of extra gaps, which are closely linked with the multi-node standing wave characteristic, can control the number of resonant modes or modulate the relative bandwidth. Besides, an equivalent circuit model, the degree of zigzag bending, and the oblique incidence are further analyzed in detail. The experimental results agree well with the simulations, and this chiral metadevice could be applied for on-chip integration in an optical detection/laser, a chiral biosensor, and molecular spectroscopy.

Complex Permittivity Extraction of Planar Dielectrics Using a Noninvasive Microwave Transmission Line Resonant Technique

This article presents a novel planar resonant method for complex permittivity measurement of planar dielectric substrates. Conventional planar dielectric sensors are composed of resonant structures, such as metamaterials, annular rings, and patch coupled to transmission lines to generate resonance. Here, we demonstrate a simple microstrip line resonator for complex permittivity measurement, and the generated resonant modes in the microstrip line are much like in 3-D conventional microwave cavities. The proposed prototype is distinguished from regular planar resonators due to the presence of a number of distinct electric and magnetic perturbable resonant modes and the absence of additional resonating structures in the design. The use of test samples in the commercially available thickness eliminates extensive sample preparation and possible air gaps or errors introduced due to the stacking of multiple dielectric layers. The microstrip line resonator fabricated on the FR4 substrate shows good agreement in measured permittivity and loss tangent values compared with the manufacturer’s datasheets. The proposed technique is a simple, fast, compact, and cost-effective measurement method for dielectric characterization, and it could be extended for other microwave transmission lines also.

Third-harmonic generation enhancement in an ITO nanoparticle-coated microresonator.

We report a ∼3-fold enhancement of third-harmonic generation (THG) conversion efficiency using indium tin oxide (ITO) nanoparticles on the surface of an ultra-high-Q silica microsphere. This is one of the largest microcavity-based THG enhancements reported. Phase-matching and spatial mode overlap are explored numerically to determine the microsphere radius (∼29 µm) and resonant mode numbers that maximize THG. Furthermore, the ITO nanoparticles are uniformly bonded to the cavity surface by drop-casting, eliminating the need for complex fabrication. The significant improvement in THG conversion efficiency establishes functionalized ITO microcavities as a promising tool for broadband frequency conversion, nonlinear enhancement, and applications in integrated photonics.

Ultra-sensitive pressure sensor using double stage racetrack silicon micro resonator

Three layouts of add-drop double stage racetrack microring resonators (ADSRMRR) located on the centre of the flexible silicon diaphragm were introduced as microscale optomechanical pressure sensors. The light propagation through all of the proposed ADSRMRR layouts were simulated using the signal flow graph method and the variational finite difference time domain (varFDTD) analysis. To achieve optimum transmission, a formula was derived for a critical coupling coefficient in the presence of the coupling loss factor for each coupling region. The pressure was measured from a wavelength shift in the output drop port signals considering the change in the optical length of the ADSRMRR due to the diaphragm shear stress. The pressure sensitivity of 48.5 pm/kPa, 42.4 pm/kPa and 33.2 pm/kPa with the limit of detection of 4.1 × 10−2 kPa, 4.7 × 10−2 kPa and 6.0 × 10−2 kPa were measured for the symmetric-large layout, the asymmetric and the symmetric-small layout of ADSRMRR pressure sensor, respectively. We introduced the ratio of the total optical length rather the sum of the resonant mode numbers (R-ratio) as a key factor in designing of the microscale Vernier based-pressure sensors. It is found that, using an ADSRMRR layout with a higher R-ratio provides a higher sensitivity with a lower detection limit, which are required in altitude sensors in satellites, aircraft, and weather balloons.

Hydrostatic pressure effects on a one-dimensional defective phononic crystal comprising a polymer material

In this research, the hydrostatic pressure effects on the transmission spectra of a one-dimensional (1D) defective phononic crystal (PnC) are calculated and studied. The transmission spectra of the defective PnC are calculated based on the transfer matrix method (TMM). To measure the hydrostatic pressure efficiently, a pressure-sensitive material such as Poly (methyl methacrylate) (PMMA) is proposed as a defect layer. Thereby, the proposed PnC structure is designed from silicon (Si) and tungsten (W) according to the configuration [(Si/W)2 PMMA (Si/W)2]. The numerical results show the appearance of a localized resonant mode through the transmission spectra. A wide pressure range from 0 GPa to 10 GPa is considered on the PnC transmission spectra and the localized resonant mode as well. Remarkably, any increase in the hydrostatic pressure value resulted in the displacement of the resonant mode towards the higher frequencies with a significant increase in its intensity as well. The effect of the PMMA thickness on the number of resonant modes is studied as well. Moreover, the proposed PnC design showed high performance for hydrostatic pressure sensing represented by the high sensitivity and Q-factor values of 556,300 Hz/GPa and 3660, respectively. We expect this design to attract the researchers' attention to hydrostatic pressure influences that may affect different PnC designs and applications.

Exploiting Symmetries in the Variational Meshless Method for 3-D Inhomogeneous Cavities

The variational meshless method (VMM) is a novel numerical algorithm that combines the intrinsic advantages of the meshless method based on the use of radial basis functions (RBFs) with the reliability of the variational formulation of electromagnetic boundary problems. It has been originally proposed and demonstrated in the analysis of 2-D structures, both homogeneous and inhomogeneous, aiming at the determination of the mode spectrum and the dispersion diagram. In this article, the VMM is extended to the calculation of the resonant modes of 3-D inhomogeneous cavities. The full theory is presented with implementation details. Moreover, the exploitation of symmetries is also discussed, which significantly speedup the method. Some examples are reported, and the results of the VMM are compared against either analytical values (when available) or commercial numerical codes based on the finite element method (FEM). In all cases, the VMM provides a large number of resonant modes with a limited number of unknowns, exhibiting high accuracy in short computing time.

High-Sensitivity Detection of Hazardous Chemical by Special Featured Grating-Assisted Surface Plasmon Resonance Sensor Based on Bimetallic Layer

In this article, we present the analysis of a special featured grating-assisted surface plasmon resonance (SPR) phenomena by multiple stacked metamaterial and silver layers as one grating structure. The bimetallic layer of gold (Au) and silver (Ag) has been used with stacked multiple negative refractive index (NRI) metamaterial layers to explore the special featured sensing capability. NRI grating with Ag layer supports better coupling to excite the multimode for the proposed structure at the same excitation condition. Hence, the alternating layer of NRI material along with Ag is used as a grating structure that is an excellent combination of the grating layer through which the proposed structure supports better coupling to the adjacent sensing region. The grating parameters have been optimized in such a way to enhance the number of resonance modes in the sensing region. It is found that SPR sensor sensitivity using negative diffraction order has a larger dip, while the resonant angle became wider for positive diffraction order. The transfer matrix method is used for the calculation of various parameters. The special featured structure with corresponding response graphs is described along with discussing what happens when the metamaterial layer thickness varies (and vice versa). Sensitivity tunability is demonstrated with variable metamaterial layer thickness. A sensitivity study is a significant parameter in the design of any high-sensitive sensor to enhance the performance. Hence, the sensitivity slope property has been explored further for each case.

Controllable Growth of Aligned Monocrystalline CsPbBr3 Microwire Arrays for Piezoelectric-Induced Dynamic Modulation of Single-Mode Lasing.

CsPbBr3 shows great potential in laser applications due to its superior optoelectronic characteristics. The growth of CsPbBr3 wire arrays with well-controlled sizes and locations is beneficial for cost-effective and largely scalable integration into on-chip devices. Besides, dynamic modulation of perovskite lasers is vital for practical applications. Here, monocrystalline CsPbBr3 microwire (MW) arrays with tunable widths, lengths, and locations are successfully synthesized. These MWs could serve as high-quality whispering-gallery-mode lasers with high quality factors (>1500), low thresholds (<3 µJ cm-2 ), and long stability (>2 h). An increase of the width results in an increase of the laser quality and the resonant mode number. The dynamic modulation of lasing modes is achieved by a piezoelectric polarization-induced refractive index change. Single-mode lasing can be obtained by applying strain to CsPbBr3 MWs with widths between 2.3 and 3.5 µm, and the mode positions can be modulated dynamically up to ≈9 nm by changing the applied strain. Piezoelectric-induced dynamic modulation of single-mode lasing is convenient and repeatable. This method opens new horizons in understanding and utilizing the piezoelectric properties of lead halide perovskites in lasing applications and shows potential in other applications, such as on-chip strain sensing.

Temperature dependence of spin-wave modes and Gilbert damping in lanthanum-doped yttrium-iron-garnet films

In this work, we study the ferromagnetic resonance (FMR) spectra of lanthanum-doped yttrium-iron-garnet (La:YIG) film as a function of temperature and frequency. The experimental results show a significant increase in the number of spin-wave resonance modes with increasing temperature. The FMR linewidth is nonlinear as a function of frequency at low temperatures but linear at room temperature. This nonlinear behavior at low temperature indicates the relaxation of the magnetization by impurities (La3+ dopant) or defects at the surfaces. Most importantly, the results reveal that temperature-dependent Gilbert damping in La:YIG film originates from two-magnon scattering, whereas the enhanced Gilbert damping at low-temperature (≤100K) is due mainly to spin-lattice relaxation of La3+ dopants.

Regulation of spatial fields in wireless power transfer with artificial magnetic conductor

In order to improve the efficiency of wireless power transfer (WPT) system, the spatial fields are regulated on a two-non-resonant-coil WPT system by hexagon artificial magnetic conductors (AMC). In our configuration, the AMC is located by the side of the two-non-resonant-coil WPT system and close to the transmitter coil. The AMC structure consists of small hexagon copper patches periodically arranged on the dielectric substrate. Each patch is grounded by a via passing through its center hole. Chip capacitors are soldered in the gaps between the adjacent patches. We can design the working frequency of WPT system through the capacitance of these chip capacitors. The results show that the electromagnetic fields are changed between the transmitter coil and the receiver coil in WPT system due to the introducing of the AMC structure. There are two main reasons. First, many resonant modes are excited by near magnetic fields on the AMC structure. Second, near magnetic fields are shielded by the AMC structure. The variation of space electromagnetic field improves the transmission efficiency of WPT system. When the working frequency is 27 MHz and the transmission distance is 3 cm, the experiment verifies that the transmission efficiency increases by 22% in the WPT system with the AMC structure compared with the WPT system without the AMC structure. Simultaneously, the transmission efficiency is raised by 25% at different transmission distances. The simulation results are almost consistent with the experimental results. There is a little difference that the number of resonant modes is different between the simulation and the experiment due to the resistance loss of the chip capacitors in experiment. Therefore, we correct the simulation results under consideration of resistive loss. In addition, the excited multiple resonant modes can supply multiple and adjustable working frequencies in the WPT system with the AMC structure. In practical applications, AMC is low in cost and easy to implement.