Symmetric Resonator Research Articles

Atomic dephasing and coherence controlled tuning of the triple color scattering light using Autler–Townes triplet emission spectroscopy

This study shows atomic dephasing and coherence controlled tuning of a triple color scattering light from a four-level atomic system into the ones of single and double color when the system is cyclically coupled with one microwave field and two optical fields. The scattering light with the symmetric double resonance in the latter case tunes into two distinct features of the asymmetric Fano-like resonance using relative phase of the coupling fields and vice versa. The asymmetric resonance, in each case, agrees excellently with the original formulation of Fano (1961 Phys. Rev. 124 1866). The coherence tuning of the resonances, caused by the constructive interference effect in the spectrum, is analyzed analytically. Distinct in the technique, we further show atomic dephasing-induced tuning of the symmetric double and asymmetric single Fano-like resonance into a Lorentzian like statistical behavior. Upon adjusting the relative amplitude of the coupling fields in favor of the resonance tuning, the triple color scattered light is controlled from a sharpened central single and broadened sides double line through central broadened single and sides sharpened double line.

High absorbance performance of symmetrical split ring resonator (SRR) terahertz metamaterial based on paper as spacer

Paper is a fascinating material for electronic platform devices due to being an inexpensive and environment friendly material. Terahertz wave is able to penetrate paper, thus paper-based terahertz metamaterial will be great terahertz devices. Creating multiple symmetrical Split Ring Resonator (SRR) on upper side paper and depositing metallic plane on back side paper yield terahertz metamaterial absorber. The maximum of absorbance peak for numerical and analytical results are 98% at 0.92 THz and 99% at 0.92 THz, respectively. The superposition of multiple reflections of terahertz wave generated on paper and yielding destructive interference phenomenon. Numerical and analytical works have been carried out in this works and showed good agreement.

Design of microstrip bandpass filters based on stair-step patch resonator

ABSTRACTIn this research article, single pole bandpass filter using stair-step patch topology based on symmetrical and asymmetrical step impedance resonators has been designed for industrial, scientific and medical (ISM) band application. This filter has been modelled by Microwave Office simulator using RT/Duroid substrate constant of 10.8, the substrate thickness of 1.27 mm, loss tangent of 0.0023 and copper metallisation thickness of 0.035 mm. To enhance the stopband levels of filter response, two microstrip bandpass filters have been designed as two-pole configurations based on edge, and cross-coupled stair-step patch resonators using the same simulator tool and substrate specifications. The proposed filters have compact sizes of (0.311 x 0.233 for single pole filter, (0.578 x 0.24) for two-pole edge coupled filter and (0.566 x 0.234for two-pole cross-coupled filter designed at centre frequencies of 2.4, 2.46 and 2.41 GHz, respectively. These filters have interesting insertion loss and return loss magnitudes, narrow band frequency responses, second harmonic suppression and good stopband levels. Apart from ISM band applications, the proposed filters can be adopted in WLAN systems and Bluetooth applications for short-range devices. The experimental results for designed filters are of good consistency with the simulations.

Subwavelength Metamaterial Unit Cell for Low-Frequency Electromagnetic Absorber Applications

In this paper, we propose a subwavelength metamaterial unit cell for low-frequency electromagnetic absorber applications. To realize a periodic array for a metamaterial absorber, the footprint size and thickness of a unit cell must be miniaturized to a subwavelength. We achieved the electrical size of the unit cell as 0.027λ × 0.027λ × 0.043λ at 2.4 GHz by introducing the inductive lump elements to a symmetric square-loop resonator. The performance of the proposed absorber was demonstrated by full-wave simulations and measurements. An inductance tolerance of 2% yielded errors of 1.2% and 1.25% in the absorptivity and absorption frequency, respectively. A prototype with 13 × 27 unit cells was fabricated and its absorptivity was measured to be 99.6% at 2.4 GHz.

Study of cross-sensitivity of whispering gallery modes in bottle resonators to rotation

In recent years, the optical resonators of whispering gallery modes (WGMs) have attracted increasing interest in the scientific community. These are the axially symmetric dielectric resonators (spherical, disk, torus, bottle-shaped, etc.) with smooth edges that support the existence of WGMs due to the total internal reflection from the surface of the resonator. The rotation of the WGM resonators with respect to the inertial space causes changes in their radii. This, in turn, leads to the reciprocal (the same for light beams travelling in opposite directions) spectral shift of the WGMs. Thus, the rotation of such resonators causes a spectral shift, by which it is possible to calculate the motion parameters. Earlier the prospects of creation of the angular velocity sensor on the basis of this effect were discussed. Spherical, torus, and disk-shaped resonators were considered as possible sensitive elements. This work is devoted to the analysis of the influence of rotation on the mutual shift of the WGM of bottle-shaped resonators. An important part of the work is the study of cross-sensitivity of bottle resonators to rotation.

Fluctuations and noise-limited sensing near the exceptional point of parity-time-symmetric resonator systems

We theoretically explore the role of mesoscopic fluctuations and noise on the spectral and temporal properties of systems of $\mathcal{PT}$-symmetric coupled gain-loss resonators operating near the exceptional point, where eigenvalues and eigenvectors coalesce. We show that the inevitable detuning in the frequencies of the uncoupled resonators leads to an unavoidable modification of the conditions for reaching the exceptional point, while, as this point is approached in ensembles of resonator pairs, statistical averaging significantly smears the spectral features. We also discuss how these fluctuations affect the sensitivity of sensors based on coupled $\mathcal{PT}$-symmetric resonators. Finally, we show that temporal fluctuations in the detuning and gain of these sensors lead to a quadratic growth of the optical power in time, thus implying that maintaining operation at the exceptional point over a long period can be rather challenging. Our theoretical analysis clarifies issues central to the realization of $\mathcal{PT}$-symmetric devices, and should facilitate future experimental work in the field.

Multi-Band Sensing for Dielectric Property of Chemicals Using Metamaterial Integrated Microfluidic Sensor

The growth of the chemical industry has brought tremendous challenges to chemical sensing technology. Chemical sensors based on metamaterials have great potential because of their label-free and non-destructive characteristics. However, metamaterials applied in chemical sensing have mainly been investigated from the measurement of sample concentration or the determination of the dielectric properties at a fixed frequency. Here we present a metamaterial integrated microfluidic (MIM) sensor for the multi-band sensing for dielectric property of chemicals, which is promising for the identification of chemicals. The MIM sensor mainly consists of multiple pair of high sensitive symmetrical double split-ring resonators (DSRRs) and meandering microfluidic channels with a capacity of only 4 μL. A dielectric model has been innovatively established and experimentally verified to accurately estimate the complex permittivity and thus realize the multi-band sensing of dielectric property of chemicals. With the increase in the number of resonators in the sensor, a dielectric spectrum like curve could be obtained for more detailed dielectric information. This work delivers a miniaturized, reusable, label-free and non-destructive metamaterial-microfluidic solution and paves a way of the multi-band sensing for dielectric property of chemicals.

Parity-time symmetry in periodically curved optical waveguides.

The coupling strength between two parity-time (PT) symmetric resonators determines whether the PT phase is broken or not. Here we investigate the scenario that two optical waveguides are spatially curved so that they switch periodically between unbroken and broken PT phases. We show that the existence of locally broken PT phase does not necessarily render a broken phase to waves propagating inside. Criteria are proposed to characterize the collective dynamics of wave near the Brillouin zone (BZ) edge, toward the cases of a totally broken phase, a partially broken phase, or a totally unbroken phase. We also discuss the characteristics of two special kinds of exceptional points (EPs) at the BZ edge, and show that their field patterns are displaced by half a period with each other. Full-wave numerical simulation proves our analysis. Potential applications especially these associated with EPs are discussed. This study helps us to understand how the locally PT-symmetric related eigenstate influences the globally collective dynamics of wave in spatially periodic configuration.

Symmetry breaking in high frequency, symmetric capacitively coupled plasmas

Two radially propagating surface wave modes, “symmetric,” in which the upper and lower axial sheath fields (Ez) are aligned, and “anti-symmetric,” in which they are opposed, can exist in capacitively coupled plasma (CCP) discharges. For a symmetric (equal electrode areas) CCP driven symmetrically, we expected to observe only the symmetric mode. Instead, we find that when the applied rf frequency f is above or near an anti-symmetric spatial resonance, both modes can exist in combination and lead to unexpected non-symmetric equilibria. We use a fast 2D axisymmetric fluid-analytical code to study a symmetric CCP reactor at low pressure (7.5 mTorr argon) and low density (∼3 × 1015 m−3) in the frequency range of f = 55 to 100 MHz which encompasses the first anti-symmetric spatial resonance frequency fa but is far below the first symmetric spatial resonance fs. For lower frequencies such that f is well below fa, the symmetric CCP is in a stable symmetric equilibrium, as expected, but at higher frequencies such that f is near or greater than fa, a non-symmetric equilibrium appears which may be stable or unstable. We develop a nonlinear lumped circuit model of the symmetric CCP to better understand these unexpected results, indicating that the proximity to the anti-symmetric spatial resonance allows self-exciting of the anti-symmetric mode even in a symmetric system. The circuit model results agree well with the fluid simulations. A linear stability analysis of the symmetric equilibrium describes a transition with increasing frequency from stable to unstable.

The structural and dynamical role of water in natural organic matter: A 2H NMR and XRD study

Natural organic matter (NOM) is an important component in many near-surface geochemical environments, and its properties are greatly affected by the incorporation of water. Because of its importance, the macroscopic behavior and effects of water in NOM and soil organic matter (SOM) have been extensively studied using a wide range of experimental and computational methods. The molecular scale structural and dynamical behavior of water in these materials, however, is less well understood. This paper presents a variable temperature 2H NMR and XRD study of water in Suwannee River NOM and its fulvic acid (FA) and humic acid (HA) fractions that provides new insight into the dynamical behavior of structurally different types of water and exchangeable hydrogen environments in NOM. The results provide a basis for future studies of more complex natural organic materials and the interaction of organic materials with mineral surfaces. Room temperature 2H NMR spectra of samples hydrated in 2H2O and then dehydrated, distinguish 2H2O molecules that are in rapid reorientational motion (correlation times, νc, > 105 Hz), 2H exchanged onto carboxylic sites of the NOM that do not undergo rapid reorientation at frequencies >∼103 Hz, and 2H exchanged onto phenolic and possibly other alcohol sites of the NOM that undergoes rapid, but anisotropic, dynamical reorientation. For samples exposed to water and not dried, the XRD results collected at temperatures from 173 to 298 K show the formation of ice-1h in samples exposed to 100% relative humidity (R.H.) but not in samples exposed to 43% R.H. 2H NMR of those samples collected at temperatures from 313 K to 173 K show the presence of multiple sites. Near room temperature, the spectra contain a narrow resonance for mobile water undergoing rapid isotropic motion, and a broader symmetrical resonance probably due to a combination of more dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups undergoing rapid anisotropic motion. The 43% R.H. samples also yield a broader, quadrupole-dominated, resonance for 2H exchanged onto functional groups of the NOM. With decreasing temperature the resonances for dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups become broader, reflecting a decreasing rate of exchange between the water molecules and functional groups and a decreasing rate of reorientation of the 2H2O molecules. The formation of ice-1h is directly reflected in the 2H spectra of the 100% R.H. samples as a resonance with a quadrupole coupling constant (QCC) of ∼180 kHz. For the 43% R.H. samples, there is also a broad, poorly resolved resonance with typical QCCs of ∼180 kHz for which the relative signal intensity increases with decreasing temperature. This signal represents 2H2O molecules that are not crystallized in ice-1h but have greatly reduced reorientation frequencies at low temperature and a hydrogen bonding network with hydrogen bond strengths similar to, but somewhat weaker than, ice-1h. Such molecules are also likely to be present in the 100% R.H. samples. At both R.H.s, some of the 2H2O molecules do not freeze and retain their isotropic motion down to 173 K, the lowest temperature investigated.

Fano resonance in a U-shaped tunnel assisted graphene-based nanoring resonator waveguide system

A U-shaped tunnel connected side coupled nanoring resonator waveguide system is proposed to generate Fano interference in a novel mechanism. By mutually coupling the infrared light through the artificially introduced U-tunnel to the two nanorings with the same resonant wavelength, single symmetric Lorentzian resonance transforms to asymmetric Fano resonance within the original resonant spectral range. The transparency window bridges the distinct constructive interferences in either rings instead of the canceling the bright mode resonance compared to former conceptions. The sensitivity of the system reaches 167 μm∕RIU far higher than the level of hundreds nanometers and is highly tunable. The light at resonance is successfully trapped and slowed down to 1/144 times the speed in vacuum, which is also flexible to release by tuning the Fermi energy of graphene rings. Overall, our ideas may pave new avenues to the design of classical analogy of Fano resonance metastructures, sensors or light storage devices.

Semianalytical model for the electromagnetic enhancement by a rectangular nanowire optical antenna on metallic substrate.

The electromagnetic enhancement by a metallic nanowire optical antenna on metallic substrate is investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons in the nanogap between the antenna and the substrate, we build up an intuitive and comprehensive model that provides semianalytical expressions for the electromagnetic field in the nanogap to achieve an understanding of the mechanism of electromagnetic enhancement. Our results show that antennas with short lengths that support the lowest order of resonance can achieve a high electric-field enhancement factor over a large range of incidence angles. Two phase-matching conditions are derived from the model for predicting the antenna lengths at resonance. Excitation of symmetric or antisymmetric localized surface plasmon resonance is further explained with the model. The model also shows superior computational efficiency compared to the full-wave numerical method when scanning the antenna length, the incidence angle, or the wavelength.

Complex symmetric operators and semiclassical resonances

Unbounded complex symmetric operators on Hilbert space are discussed and various spectral results on these operators are presented in this paper. In addition, we show that the technique of complex scaling allows one to identify the quantum resonances of complex self-adjoint Schrödinger Hamiltonians.

Defining cylindrical space optical resonators through supported mode properties: inverse numerical process.

Faraday's and Ampere's laws are converted to matrix operator form and rearranged such that the unknown relative permittivity and relative permeability tensors can be determined. The material and geometry of cylindrically symmetric optical resonator structures are determined through the electric and magnetic field component profiles and complex angular frequency of a proposed localized state. This differs from the usual utilization of the electromagnetic wave equations, solving for states given the material properties and geometry. Thus the technique presented here is an inverse numerical process. The theoretical expressions are provided based on a Fourier-Bessel numerical approach which is highly suitable for cylindrical geometry resonators. Without loss of the generality of the technique, examples of resonant structure determination are presented for non-magnetic and diagonal relative permittivity tensor. Axial field propagation is included to demonstrate the design capabilities related to optical fiber and photonic crystal fiber structures.

In-Line Fiber Michelson Interferometer for Enhancing the Q Factor of Cone-Shaped Inwall Capillary Coupled Resonators

An in-line fiber Michelson interferometer in a cone-shaped inwall capillary with the whispering gallery mode microsphere resonator integrated inside is demonstrated for enhancing the Q factor, which is fabricated on the etched capillary by the femtosecond laser micromachining to decrease the coupling paths. The modulated symmetric WGM resonances and asymmetric Fano resonances induced by the Michelson interferometer are observed in the reflection spectra, with a slope of 91.87 dB/nm and Q factor as 3.85 × 104 achieved. Numerical simulations with the transfer matrix method also validate the resonator spectra modulated by the Michelson interference. This method shows a perspective potential for the enhancement of the Q factor by tailoring interacting paths through the femtosecond laser micromachining.

Design and Characterization of a Novel Bio-inspired Hair Flow Sensor Based on Resonant Sensing

Flow sensors inspired by the natural hair sensing mechanism have great prospect in the research of micro-autonomous system and technology (MAST) for the three-dimensional structure characteristics with high spatial and quality utilization. A novel bio-inspired hair flow sensor (BHFS) based on resonant sensing with a unique asymmetric design is presented in this paper. A hair transducer and a signal detector which is constituted of a two-stage micro-leverage mechanism and two symmetrical resonators (double ended tuning fork, DETF) are adopted to realize the high sensitivity to air flow. The sensitivity of the proposed BHFS is improved significantly than the published ones due to the high sensitivity of resonators and the higher amplification factor possessed by the two-stage micro-leverage mechanism. The standard deep dry silicon on glass (DDSOG) process is chosen to fabricate the proposed BHFS. The experiment result demonstrates that the fabricated BHFS has a mechanical sensitivity of 5.26 Hz/(m/s)2 at a resonant frequency of 22 kHz with the hair height of 6 mm.

Design of compact frequency agile filter-antenna using reconfigurable ring resonator bandpass filter for future cognitive radios

AbstractIn this paper, a new miniaturized frequency agile filter-antenna with a wide reconfigurable frequency band is proposed for interweave cognitive radios (CRs). A tunable bandpass filter (BPF) composed of a symmetrical ring resonator is cascaded to the feed line of an ultra-wideband planar antenna. The structure of the proposed ring resonator BPF is simple and compact so that the total size of the proposed filter-antenna is smaller than that of a conventional system made of a separate antenna and BPF. The reconfigurability of the proposed filter-antenna is achieved by changing the operating frequency of the BPF by loading the ring resonator with a single varactor diode at its center. The fabricated prototype has successfully achieved a wide operational bandwidth of 1.43 GHz which covers continuous narrow bands from 4.65 to 6.08 GHz. Moreover, the operating tunable narrow bands have stable radiation characteristics. Good agreement between measurement and simulation results is demonstrated.

UHR RFID ring resonator-based tag antenna with photonic bandgap structure for metallic objects

Several recent works highlighted that metamaterial-based antennas are capable to function similar to large printed antennas. This paper presents a novel split-ring resonator-based UHF RFID tag antenna with photonic bandgap structure on metallic objects for high gain, which consists of two symmetrical C-shaped resonators with outer strip lines to feed split-ring resonator structure through implementing an inductively coupled feed approach placed on the top surface of Polytetrafluoroethylene substrate. The simulation results were verified by the presented method via enhancing the performance of tag antennas for metallic object.

Influence of the whispering-gallery mode resonators shape on its inertial movement sensitivity

The optical whispering-gallery mode (WGM) resonators are axially symmetrical resonators with smooth edges, supporting the existence of the WGMs by the total internal reflection on the surface of the resonator. As of today, various types of such resonators have been developed, namely the ball shaped, tor shaped, bottle shaped, disk shaped, etc. The movement of WGM resonators in inertial space causes the changes in their shape. The result is a spectral shift of the WGMs. Optical methods allow to register this shift with high precision. It can be used in particular for the measurement of angular velocities in inertial orientation and navigation systems. However, different types of resonators react to the movement in different manners. In addition, their sensitivity to movement can be changed when changing the geometric parameters of these resonators. The work is devoted to investigation of these aspects.

Angle- and polarization-insensitive broadband metamaterial absorber using resistive fan-shaped resonators

In this paper, we propose an angle- and polarization-insensitive broadband metamaterial absorber with a resistive fan-shaped resonator. First, the symmetric fan-shaped resonator is designed, and four lumped resistors are loaded in the gap between each fan-shaped circular sector on the top layer to increase the bandwidth. Based on the circuit parameters, the periodic structure of the fan-shaped resonator is designed using full-wave analysis. The proposed absorber is fabricated using a printed circuit board process in a single layer. The experimental results indicate that an absorptivity value greater than 96% was achieved in the frequency range of 7–12.8 GHz for all polarization angles at normal incidence. Under oblique incidence, the measured absorptivity was greater than 90% in the range of 7–12.1 GHz when the incident angle varied from 0° to 45° in the transverse electric mode. In the transverse magnetic mode, the measured absorptivity was greater than 90% between 7.1 and 9.3 GHz when the incident angle varied from 0° to 45°.