Degenerate Resonant Modes Research Articles

Perfect Absorption and Reflection Modulation Based on Asymmetric Slot-Assisted Gratings without Mirrors.

As a perfect graphene absorber without any external mirrors, we proposed asymmetric slot-assisted grating structures supporting two degenerate resonant modes of the guided-mode resonances (GMR) and the quasi-bound states in the continuum (quasi-BIC). The GMR mode functions as an internal mirror in conjunction with the background scattering, while the quasi-BIC, which is responsible for perfect graphene absorption, stems from the horizontal symmetry breaking by an asymmetric slot. By properly shifting the slot center from the grating center, the leakage rate of quasi-BIC can be controlled in such a way as to satisfy the critical coupling condition. We provide a comprehensive study on the coupling mechanism of two degenerate resonant modes for a one-port system mimicking the resonance. We also numerically demonstrated that our proposed grating structures show an excellent reflection-type modulation performance at optical wavelength ranges when doped double-layer graphene is applied. Due to the perfect absorption at the OFF state, a high modulation depth of ~50 dB can be achieved via a small Fermi level variation of ~0.05 eV. To obtain the lower insertion loss at the ON state, the higher Fermi level is required to decrease the graphene absorption coefficient.

Ultraloop: Active Lateral Force Feedback Using Resonant Traveling Waves.

The sensation of touching virtual texture and shape can be provided to a touchscreen user by varying the friction force. Despite the saliency of the sensation, this modulated frictional force is purely passive and strictly opposes finger movement. Therefore, it is only possible to create forces along the direction of movement and this technology cannot stimulate a static fingertip or provide forces that are orthogonal to the direction of movement. The lack of orthogonal force limits the guidance to a target in an arbitrary direction and there is a need for active lateral forces to give directional cues to the fingertip. Here, we introduce a surface haptic interface that uses ultrasonic traveling waves to create an active lateral force on bare fingertips. The device is built around a ring shape cavity where two degenerate resonant modes around 40 kHz are excited with 90 ° phase shift. The interface provides active forces up to 0.3 N to a static bare finger uniformly over a 140×30 mm 2 surface. We report the model and design of the acoustic cavity, force measurements, and an application to create a key-click sensation. This work demonstrates a promising method for uniformly producing large lateral forces on a touch surface.

Mirror-Less Unidirectional Radiation in an Asymmetric Single Resonator

We propose a novel approach to realize unidirectional radiation in an asymmetric single resonator without using an external mirror, which is based on mutual coupling between two degenerate resonant modes through the background scattering of the asymmetric resonator. In the proposed approach, only one of the resonant modes experiences optical gain and the other works just as an internal reflector. So, our approach is conceptually to mimic a one-port system by introducing the internal reflector in a two-port system. Due to this intuitive and simple operation concept, the design of such devices is straightforward. We described the operation principle by using the temporal coupled-mode theory, from which a practical design method was derived. An example device of the proposed approach was designed based on guided-mode resonances in a slab waveguide grating and its performance was analyzed with the finite-difference time-domain simulation. A ratio of 4.6 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> between the upward and the downward radiations was numerically demonstrated.

General treatment of dielectric perturbations in optical rings

We introduce a formalism, inspired on the perturbation theory for nearly free electrons in a solid-state crystal, to describe the resonances in optical ring resonators subjected to a perturbation in their dielectric profile. We find that, for small perturbations, degenerate resonant modes are split with the splitting proportional to one specific coefficient of the Fourier expansion of the perturbation. We also find an expected asymmetry in the linewidths (and Q factors) of the split modes. Experimental transmission spectra from rings with specially designed perturbations show a qualitative match with the formalism predictions.

Graphene perfect absorber design based on an approach of mimicking a one-port system in an asymmetric single resonator.

We proposed a novel perfect absorber with an asymmetric single resonator supporting two degenerate resonant modes, whose operation concept is mimicking a one-port system by making only one of the modes experience loss while using the other for an internal 100% reflector in conjunction with the background scattering. We confirmed the operation principle and the design requirement from a theoretical study using the temporal coupled-mode theory. We also designed an example device based on the guided-mode resonances (GMRs) in a slab-waveguide grating and numerically demonstrated a high absorption of ∼ 99.95% in monolayer graphene with greatly enhanced fabrication error tolerance in comparison to the previously proposed scheme. Our proposed scheme will find various useful applications due to the intuitive design process and relatively easier fabrication, which is attributed to the one-port mimicking operation concept with a single GMR-based broadband flat-top reflector.

Degenerate quasi-normal mode theory for near-field radiation between plasmonic structures.

Near-field radiation can exceed the blackbody radiation limit due to the contributions from evanescent waves. One promising approach to further enhance near-field radiation beyond existing bulk materials is to utilize metamaterials or metasurfaces made from subwavelength plasmonic structures. In this work, we investigate the near-field thermal radiation between complex plasmonic structures with higher-order symmetry and degeneracy, which is crucial for understanding the radiative heat exchange between metamaterials or metasurfaces at extremely small gaps. We demonstrate that the introduction of degeneracy can drastically boost near-field thermal radiation between plasmonic structures. The enhancement of near-field thermal radiation originates from the emergence of degenerate resonance modes and the secondary emission of thermal photons due to the nonzero coupling between the degenerate modes. Our study provides new pathways for designing high-intensity near-field thermal emitters and absorbers for thermophotovoltaics, thermal management, and infrared spectroscopy.

Balanced‐to‐unbalanced filtering magic‐T based on circular patch resonator with high selectivity

This Letter presents a new design of balanced-to-unbalanced (B2U) filtering magic-T based on circular patch resonator. Without additional circuit, the prescribed in-phase and out-of-phase specifications of the magic-T are achieved by elaborately studying and exploring the electric field distributions of the degenerate resonant modes in the circular patch resonators. Meanwhile, the desired filtering responses are attained by virtue of the coupling extent between the two designed patch resonators in the back-to-back form. In the proposed design, a pair of TM11 modes at first make up passband. Meanwhile, nice common-mode suppression can be achieved at the balanced ports, and high isolation is achieved at the single-end ports, respectively. For demonstration, a prototype B2U filtering magic-T working at 4.3 GHz with 3 dB fractional bandwidth of 16.3% is implemented. Measured results coincide well with simulated ones, verifying the proposed design concept.

Compact Single- and Dual-Band Filtering 180° Hybrid Couplers on Circular Patch Resonator

In this article, an effective approach is proposed to design of compact single and dual-band patch filtering 180° hybrid couplers based on circular patch resonator. Without an additional circuit, the prescribed in-phase and out-of-phase specifications of the coupler are achieved by elaborately studying and utilizing the electric field distributions of the degenerate resonant modes in the unslotted/slotted patch resonators. Meanwhile, the desired single-/dual-band filtering responses are attained by virtue of the coupling extent between the two designed patch resonators in the back-to-back form. In our design, a pair of TM11-modes at first makeup a single passband for single-band operation, and a pair of TM11-like modes and a pair of TM12-like modes then construct the two separate passbands for dual-band operation, respectively. After the working principle is explained, the design procedure based on the coupling matrix is provided. For demonstration, two prototypes for single- and dual-band patch filtering 180° hybrid couplers are implemented, respectively. Measured results coincide well with simulated ones, verifying the proposed design concept.

Axion dark matter detection by superconducting resonant frequency conversion

We propose an approach to search for axion dark matter with a specially designed superconducting radio frequency cavity, targeting axions with masses ma ≲ 10−6 eV. Our approach exploits axion-induced transitions between nearly degenerate resonant modes of frequency ∼ GHz. A scan over axion mass is achieved by varying the frequency splitting between the two modes. Compared to traditional approaches, this allows for parametrically enhanced signal power for axions lighter than a GHz. The projected sensitivity covers unexplored parameter space for QCD axion dark matter for 10−8 eV ≲ ma ≲ 10−6 eV and axion-like particle dark matter as light as ma∼ 10−14 eV.

Highly degenerate photonic flat bands arising from complete graph configurations

Inspired by complete graph theory, we demonstrate that a metallic claw "meta-atom" structure can carry a high number of nearly degenerate resonant modes. A photonic meta-crystal composing of a lattice of such meta-atoms exhibits a large number of flat bands that are squeezed into a narrow frequency window, and these flat bands can be designed to locate in a wide complete 3D bandgap. The degeneracy dimension (Nf) of the flat bands is determined by the number of branches (Nb) of the metallic claw with Nf=Nb-3, which is geometrically related to the complete graph theory. Different from those flat bands emerging from special lattice arrangements (e.g., Kagome lattice), the isolated flat bands here are insensitive to lattice perturbations. The proposed mechanism offers a new platform for realizing various dispersion-less phenomena and a new paradigm to realize high density of states and spectra compressing.

Microstrip dual mode multi-bandpass filters based on tree fractal slotted resonator for wireless communication

Dual mode microstrip multi-bandpass filter is proposed with tree fractal slot on a square patch resonator. The tree fractal slotted resonators are generated from conventional square patch using an iterative tree fractal generator method. A single square patch is used for realizing both dual and tri-bandpass filters exploiting the dominant, higher order and its corresponding degenerate resonant modes by the tree fractal iteration on the diagonal unequal slots on the square patch.The resonant peaks, transmission zeros and bandwidth of the pass bands can be tuned by varying the length and width of the fractal slot. By optimizing various parameters dual mode dual and tri-band pass filters are simulated, fabricated and measured. The proposed filter finds application in wireless communication devices and falls in the bands of GSM, WLAN, Bluetooth, Zigbee, WiMax and WiFi.

Microstrip dual mode multi-bandpass filters based on tree fractal slotted resonator for wireless communication

Dual mode microstrip multi-bandpass filter is proposed with tree fractal slot on a square patch resonator. The tree fractal slotted resonators are generated from conventional square patch using an iterative tree fractal generator method. A single square patch is used for realizing both dual and tri-bandpass filters exploiting the dominant, higher order and its corresponding degenerate resonant modes by the tree fractal iteration on the diagonal unequal slots on the square patch.The resonant peaks, transmission zeros and bandwidth of the pass bands can be tuned by varying the length and width of the fractal slot. By optimizing various parameters dual mode dual and tri-band pass filters are simulated, fabricated and measured. The proposed filter finds application in wireless communication devices and falls in the bands of GSM, WLAN, Bluetooth, Zigbee, WiMax and WiFi.

Circularly polarized rectangular dielectric resonator antenna excited by an off-set conformal metal strip

&lt;p class="Abstract"&gt;A rectangular dielectric resonator antenna (DRA) has been excited by an off-set single conformal metal strip. By using such excitation technique two degenerate resonant modes, TExδ11 and TEy1δ1 of the rectangular DRA have been excited to achieve circular polarization (CP). A CP bandwidth of ~ 5.2% in conjunction with a wide impedance matching bandwidth of ~ 54% has been provided by the proposed DRA configuration. The antenna design has been simulated using computer simulation technology (CST). Antenna prototype has been built to verify the impedance matching bandwidth. Far field parameters have been optimized and verified using two simulation techniques in CST i.e. finite integration technique (FIT) and finite element method (FEM). A good agreement between the simulated and measured result has been observed for S11. Similarly a very good resemblance between the far field results from FIT and FEM have been demonstrated.&lt;/p&gt;

Photonic crystal double-coupled cavity waveguides and their application in design of slow-light delay lines

In this paper the idea of double-coupled cavity waveguides is introduced. The cavities used in this paper support two orthogonal degenerate resonance modes. These cavities are coupled together both horizontally and vertically. The obtained matrix of cavities introduces many interesting properties for design of photonic crystal devices such as phase shifters and gates. As an application, it is shown that the coupled matrix of cavities can be used for design of ultra-compact slow-light photonic crystal optical delay lines. Finite difference time domain method and plane wave expansion method are used to analyze the structures.

Flat-top narrowband filters enabled by guided-mode resonance in two-level waveguides.

Resonant nanogratings and periodic metasurfaces express diverse spectral and polarization properties on broadside illumination by incident light. Cooperative resonance interactions may yield shaped spectra for particular applications, in contrast to a multilayer dielectric mirror. Here, we provide guided-mode resonance filters with flat-top spectra suitable for wavelength division multiplexing systems. Applying a single one-dimensional grating layer sandwiched by two waveguides, we theoretically achieve high-efficiency flat-top spectra in the near-infrared region. This result is obtained by inducing simultaneous nearly degenerate resonant modes. The resonance separation under this condition controls the width of the flat-top spectrum. This means we can implement spectral widths ranging from a sub-nanometer to several nanometers applying fundamentally the same device architecture.

Impact of Synchronization in Micromechanical Gyroscopes

In this paper, we study the occurrence of synchronization between the two degenerate resonance modes of a microdisk resonator gyroscope. Recently, schemes involving the simultaneous actuation of the two vibration modes of the gyroscope have been implemented as a promising new method to increase their performance. However, this strategy might result in synchronization between the two modes, which would maintain frequency mode-matching but also may produce problems, such as degrading stability and sensitivity. Here, we demonstrate for the first time synchronization between the degenerate modes of a microgyroscope and show that synchronization arising from mutual coupling dramatically reduces frequency instability at the cost of increased amplitude instability. We present an alternative synchronization scheme that suppresses this drawback while still taking advantage of a passive frequency mode-match operation.

Center Frequency Stabilization in Planar Dual-Mode Resonators during Mode-Splitting Control

Shape symmetry in dual-mode planar electromagnetic resonators results in their ability to host two degenerate resonant modes. As the designer enforces a controllable break in the symmetry, the degeneracy is removed and the two modes couple, exchanging energy and elevating the resonator into its desirable second-order resonance operation. The amount of coupling is controlled by the degree of asymmetry introduced. However, this mode coupling (or splitting) usually comes at a price. The centre frequency of the perturbed resonator is inadvertently drifted from its original value prior to coupling. Maintaining centre frequency stability during mode splitting is a nontrivial geometric design problem. In this paper, we analyse the problem and propose a novel method to compensate for this frequency drift, based on field analysis and perturbation theory, and we validate the solution through a practical design example and measurements. The analytical method used works accurately within the perturbational limit. It may also be used as a starting point for further numerical optimization algorithms, reducing the required computational time during design, when larger perturbations are made to the resonator. In addition to enabling the novel design example presented, it is hoped that the findings will inspire akin designs for other resonator shapes, in different disciplines and applications.

Ultrahigh cooperativity interactions between magnons and resonant photons in a YIG sphere

Resonant photon modes of a 5-mm-diameter yttrium iron garnet (YIG) sphere loaded in a cylindrical cavity in the 10--30-GHz frequency range are characterized as a function of applied dc magnetic field at millikelvin temperatures. The photon modes are confined mainly to the sphere and exhibited large mode filling factors in comparison to previous experiments, allowing ultrastrong coupling with the magnon spin-wave resonances. The largest observed coupling between photons and magnons is $2g/2\ensuremath{\pi}=7.11$ GHz for a 15.5-GHz mode, corresponding to a cooperativity of $C=1.51\ifmmode\pm\else\textpm\fi{}0.47\ifmmode\times\else\texttimes\fi{}{10}^{7}$. Complex modifications, beyond a simple multioscillator model, of the photon mode frequencies were observed between 0 and 0.1 T. Between 0.4 and 1 T, degenerate resonant photon modes were observed to interact with magnon spin-wave resonances with different coupling strengths, indicating time-reversal symmetry breaking due to the gyrotropic permeability of YIG. Bare dielectric resonator mode frequencies were determined by detuning magnon modes to significantly higher frequencies with strong magnetic fields. By comparing measured mode frequencies at 7 T with finite element modeling, a bare dielectric permittivity of $15.96\ifmmode\pm\else\textpm\fi{}0.02$ of the YIG crystal has been determined at about 20 mK.

Design, fabrication and characterization of a piezoelectric MEMS diaphragm resonator mass sensor

This work reports on the design, fabrication and characterization of a piezoelectrically actuated mass sensor. The sensor utilizes degenerate resonant modes in which one mode is used as a reference to compensate for environmental effects. The project builds on a capacitively driven version of the sensor allowing improvements and challenges surrounding the new design to be assessed in relation to modeling and fabrication. The operational mode of interest showed an average resonant frequency of 7.8 MHz (quality factor of 490), at atmospheric pressure with an electrically recovered signal to noise ratio of 2400:1. The lead zirconate titanate performance yielded a central displacement sensitivity of 1.50 nm V−1, which is in good agreement with the levels predicted in modeling. A small initial split in the degenerate modes was recorded due to fabrication tolerances; however, the devices still exhibited good environmental stability, with a temperature sensitivity of only 11 Hz °C−1. Electroplating of gold onto the sensor surface demonstrated a device mass sensitivity of 12.0 Hz pg−1.

Circular Polarization in Defected Hexagonal Shaped Microstrip Antenna

A novel circular polarization (CP) design of a single-feed Hexagonal shaped microstrip antenna for enhanced antenna parameters is presented. The CP design is obtained by placing three isosceles triangular defects at proper locations in the hexagonal radiating patch as well as in the square ground plane. By adjusting one of the side lengths of the triangular defect, slightly longer or shorter than that of the others, two orthogonal near degenerate resonant modes for CP radiation are excited. Moreover, the 3 dB axial ratio bandwidth is surrounded by the 10 dB impedance bandwidth, to ensure that the antenna radiates CP waves in its impedance band. The antenna gain of the proposed antenna has increased by 5.34 dB (7.93 vs. 2.59 dB), as compared to the hexagonal microstrip antenna with triangular truncations in patch but without triangular defects in the ground plane having same substrate material, height and same radiating patch size and shape. Prototype antenna is fabricated for experimental evaluation. Simulated and measured results are in good agreement with each other.