Concentric Ring Resonators Research Articles

Asymmetric χ(2)-translated optical frequency combs assisted by avoided mode crossing in concentric ring resonators.

χ(2)-translated microcomb generation in microresonators that possess both χ(2) and χ(3) nonlinear responses opens the door for ultra-broadband integrated comb sources. The interplay between the second- and third-order nonlinearities within a fixed coupling coefficient fertilizes complicated cavity dynamics which is of paramount scientific and technological potential. However, this coupling coefficient can be drastically wavelength-dependent, which is lack of consideration in previous studies. Here, we extend the range of coupling strengths to a full description and propose a new approach to delineate the spectral response of the interactions between the χ(2) and χ(3) nonlinearities. Critically, the underpinned physics is enabled by avoided mode crossing (AMX) in concentric double-ring microresonators. We demonstrate that the evolution of the anti-symmetric mode at fundamental wavelengths disrupts spectral symmetry, leading to asymmetric χ(2)-translated optical frequency combs at second-harmonic wavelengths. Simultaneous generation of skewed two-color optical frequency combs is numerically realized in an exemplary gallium phosphide-on-insulator platform with a coupling constant from 133.3 m-1W-1/2 to 7.4 m-1W-1/2, showing reasonable agreement with our theoretical model. Our findings provide a novel approach to shaping the optical frequency comb, which may facilitate potential applications in self-referencing and frequency metrology with desired comb spectral shapes.

Design of ultra-thin multi-band sub-terahertz metamaterial absorber using three concentric ring resonators with same opening direction

In this paper, an ultra-thin sub-terahertz multi-band terahertz metamaterial absorber is proposed, its cell consists of three concentric ring resonators with the same opening direction, which can realize three discrete absorption peaks in the sub-terahertz frequency domain. The absorption peaks are mainly formed when the three open circular resonators interact with each other, and the superposition of the three discrete peaks creates a three-band absorption. The physical mechanisms of three-band absorption are illustrated by the electric fields and surface current distributions of three absorption peaks. Adjustment of the absorption effect could be obtained by altering the dimensions of the cleft circular resonator. By fixing the dimensions and changing the opening direction, these resonators will couple to each other and play an important role in regulating the frequency, intensity, and number of absorption peaks. Moreover, the multi-band metamaterial structure could be combined with vanadium dioxide, a phase change material, to actively modulate the absorption. In addition, the three-band metamaterial absorber has the characteristics of polarization-sensitive and wide-angle, which has extensive applications in the domains of security detection, biomedicine and communication.

A SIMPLE STRUCTURED MULTIBAND TERAHERTZ METAMATERIAL ABSORBER WITH A HIGH Q FACTOR

A terahertz Eight-/Nine-/Twelve-/Fourteen-/Sixteen-Band Metamaterial Absorber (MMA) for sensing applications is built and simulated. The substrate is sandwiched between the bottom ground plane and the top patch structure of this primitive MMA. The top patch is made up of two concentric circular ring resonators. This structure generates a multiple number of multi bands without utilising stacked layers, multiple resonators, or overlapping in a single unit cell by altering the radius of the top patch structure within the shorter frequency range of 0.8 THz to 1.2 THz. The polarisation and angle insensitivity properties are investigated by shifting the angle values from 0 to 90 degrees. To learn about the inside mechanism of the planned structure, the magnetic field distribution, electric field distribution and surface current distribution plots are explained. For the sixteen-band MMA, the Q-Factor and full width half maximum are also determined. This proposed MMA will be used in biosensing applications, sensors and wireless communications.

Multi-band terahertz metamaterial absorber composed of concentric square patch and ring resonator array

An equivalent circuit model (ECM) to analyze a single-layered graphene multi-band metamaterial absorber was developed. This absorber consists of concentric square patch and ring resonator arrays and operates in the terahertz (THz) region. To validate our analysis based on the ECM, we also conducted numerical simulations using the finite element method (FEM) within CST software. Additionally, we have explained the absorption behavior of the metamaterial using the coupled mode theory (CMT). This absorber design, with its single-layer structure, tunability, and triple absorption bands, offers promise for applications in THz devices and systems. Notably, it achieves an average absorption of 99% for three bands and the absorption reaches 100% in the frequency range of 4 to 6.5 THz. The correlation of ECM and CMT analyses with the FEM simulations validate the accuracy and the effectiveness of these simplified approaches in comprehending the resonant characteristics of the metamaterial absorber.

An optically transparent dual-band frequency selective surface for polarization independent RF shielding

This article reports on a compact dual band, Frequency Selective Surface (FSS) based spatial filter for Wi-Fi and WLAN shielding applications on a transparent glass surface with optical transparency of 70%. The unit cell comprises an outer square loop resonator with a disconnected and concentric annular ring resonator. To introduce frequency tuning and compactness T shape stubs are strategically loaded on these resonators and it is ensured that the mutual coupling remains minimal. The outer square resonator suppresses the 2.4 GHz band, and the inner circular ring resonator stops the 5.4 GHz band. The unit element is four-fold symmetric thus it offers complete polarization independence. A detailed parametric and electromagnetic field analysis has been conducted to elucidate the significance of different sections of the unit element. An equivalent lumped circuit model is also derived for the proposed unit element to better explain the underlying working mechanism. A finite prototype of 15 × 11 elements is fabricated on a soda lime float glass by using ordinary adhesive copper foils with a standard chemical etching process. Polarization independence and angular stability up to 45° are measured and compared with the simulated responses. The FSS shield offers frequency suppression up to 45 dB and 43 dB for 2.4 GHz and 5.4 GHz bands respectively. With high optical transparency, the design allows maximum light through it and causes no extra burden on energy consumption for indoor applications. The compact dual band design and the possibility of direct application on host surfaces like glass windows and doors make this design an excellent candidate for data security and privacy applications in secure installations with an esthetically pleasing outlook.

Metamaterial physical property utilized antenna radiation pattern deflection for angular coverage and isolation enhancement of mm-wave 5G MIMO antenna system

This paper proposed metamaterials (MMs) inspired radiation pattern deflected multiple input multiple outputs (MIMO) antenna systems for 5G applications. The MMs structure achieves high gain and wide angular coverage to overcome attenuation in electromagnetic (EM) wave propagation paths. Besides, the MMs structure provides high isolation in the MIMO antenna system. The deflection mechanism is attained using two different MMs unit cells of circular splits ring resonator (CSRR) and concentric circular ring resonator (CCRR). The MMs unit cells are configured in three different arrangements to achieve negative, normal and positive deflection radiation patterns. The −10 dB impedance bandwidth of 3.4 GHz (27.5–30.9 GHz) with a gain improvement of 2–3 dBi is obtained for all three deflection configurations. The noticeable novelties of the proposed MIMO antenna system are achieving both negative and positive deflection of 30° and significant isolation enhancement at the entire operating frequency.

Nanosensor and slow light based on quintuple Fano resonances in a metal–insulator–metal waveguide coupled with a concentric-ring resonator

In this paper, quintuple Fano resonances are produced and numerically analyzed based on a plasmonic resonator system. The system is composed of an optical metal–insulator–metal (MIM) waveguide, a side-coupled disk, and a concentric-ring resonator. Five Fano resonances can be seen, which originate from the interaction of the cavity mode between the disk resonator and the concentric-ring resonator. The transmission spectrum shows that the Fano resonance can be independently tuned by changing different geometrical parameters, such as the outer radius or inner radius of the concentric-ring resonator. The refractive index sensitivity is 1250nm/RIU for FR5, and the figure of merit is 138.9 (RIU is a refractive index unit). It can also serve as a temperature sensor with a maximum sensitivity of about 0.4nm/∘C. Moreover, for slow light, the maximum delay time is about 0.12 ps at FR3. The proposed nano-scale structure has a sharp Fano line shape and effective ways of tuning independently, which may have applications in slow light and nano-biosensing; for example, we show the application of the detection of different human blood types.

Numerical Analysis and Structure Optimization of Concentric GST Ring Resonator Mounted over SiO2 Substrate and Cr Ground Layer

Since the introduction of Metal-Insulator-Metal (MIM) absorbers, most of the structures demonstrated a narrowband absorption response which is not suitable for potential applications in photovoltaic systems, as it requires higher energy to enhance its performance. Very little research is being conducted in this direction; to address this issue, we exhibit a broadband solar absorber designed using a concentric GST ring resonator placed upon a silicon dioxide substrate layer with chromium used as a ground plane. It was analyzed using the finite element method. The design is also optimized by using a nonlinear parametric optimization algorithm. Comparatively less work has been focused on solar absorbers designed with the help of GST material, and here we have compared the effect of two different phases of GST, i.e., amorphous (aGST) and crystalline (cGST); the results indicate the higher performance of aGST phase. Parametric optimization has been adapted to identify the optimal design to attain high performance at minimal resources. The absorption response is angle insensitive for 0 to 60 degrees, and at the same time for both TE and TM modes, the design provides identical results, indicating the polarization-insensitive properties. The electric field intensity changes at the six peak wavelengths are also demonstrated for the authentication of the high performance. Thus, the proposed concentric GST ring resonator solar absorber can present a higher solar energy absorption rate than other solar structure designs. This design can be applied for improving the performance of photovoltaic systems.

Dispersion-flattened concentric structure for microcomb bandwidth broadening in GaP-OI resonators

We propose and theoretically investigate the coupled concentric ring resonators on a thickness-constrained GaP on insulator (GaP-OI) integrated photonic platform. Achieving anomalous dispersion is fulfilled by mode hybridization in the coupled structure on a 200 nm thick GaP-OI resonator which originally only exhibits normal dispersion for the fundamental mode. The anomalous dispersion profile for the anti-symmetric mode is flattened and broadened in favor of Kerr frequency comb generation by optimizing the waveguide width and the coupling gap size synergistically. We show the flexibility of this design methodology by simultaneously flattening the dispersion profile while anchoring the dispersion peak location at 1550 nm. The optimized design has a flat anomalous dispersion span of 460 nm with a small peak of 160 ps/km/nm, 1.69 times lower than a traditional rectangular waveguide. The engineered dispersion profile enables a broadband Kerr frequency comb generation that has a 3 dB bandwidth of 67 nm and a 20 dB bandwidth of over 250 nm at both 1550 and 1650 nm pump wavelengths. The proposed design proves useful to achieve broad and flat anomalous dispersion on thickness-constrained materials, paving the way towards low-loss GaP-OI frequency comb resonators.

Independently tunable concentric graphene ring resonators based ultrathin broadband THz absorber

An ultrathin structure of graphene-based absorber is implemented and numerically analyzed. The absorber is designed with the usage of graphene ring resonators and graphene reflector in the lower terahertz (THz) frequency ranges. The geometry of the absorber can be implemented with the thickness as small as λ/193; (λ: free space wavelength). A number of resonances is generated using concentric graphene ring resonators which can individually tuned over frequency using chemical potential of graphene for merging and achieving the broad absorption band. An absorption of more than 90% is achieved over the frequency range of 10.34–16.23 THz and more than 80% in the frequency range of 9.89–16.77 THz. The proposed absorber provides the polarization independent geometry with the allowed incident angle up to 50°. The ultrathin geometry of the proposed absorber can provide a way to implement the absorber with broad absorption bandwidth.

Ultrawideband Polarization-Independent Nanoarchitectonics: A Perfect Metamaterial Absorber for Visible and Infrared Optical Window Applications.

This article presents numerical analysis of an ultrathin concentric hexagonal ring resonator (CHRR) metamaterial absorber (MMA) for ultrawideband visible and infrared optical window applications. The proposed MMA exhibits an absorption of above 90% from 380 to 2500 nm and an average absorbance of 96.64% at entire operational bandwidth with a compact unit cell size of 66 × 66 nm2. The designed MMA shows maximum absorption of 99% at 618 nm. The absorption bandwidth of the MMA covers the entire visible and infrared optical windows. The nickel material has been used to design the top and bottom layer of MMA, where aluminium nitride (AlN) has been used as the substrate. The designed hexagonal MMA shows polarization-independent properties due to the symmetry of the design and a stable absorption label is also achieved for oblique incident angles up to 70 °C. The absorption property of hexagonal ring resonator MMA has been analyzed by design evaluation, parametric and various material investigations. The metamaterial property, surface current allocation, magnetic field and electric field have also been analyzed to explore the absorption properties. The proposed MMA has promising prospects in numerous applications like infrared detection, solar cells, gas detection sensors, imaging, etc.

A high Q terahertz metamaterial absorber using concentric elliptical ring resonators for harmful gas sensing applications

A nearly perfect metamaterial absorber is proposed that can find utility in terahertz sensing applications. The design consists of two concentric elliptical ring resonators (ERRs) whose parameters are appropriately set to achieve dual band absorption with near perfect absorption. The first absorption band at 3.62 THz having a Q-factor of 51.7 was caused due to the currents in the outer and inner ERR. The second absorption peak at 3.814 THz having a Q factor of 1411.11 was a consequence of currents flowing across the gap between the two concentric resonators. Furthermore, it is observed that the absorption bands are sensitive to the variation in refractive index of the surrounding medium. The sensitivity’s in the absorption bands are 3 THz/RIU and 3.59 THz/RIU respectively. A sensor is proposed based on this design to detect harmful gases, which is demonstrated for detection of Methane and Chloroform. High Q-factor and high sensitivity of the narrow band makes the design an excellent sensor for detecting variations in the refractive index.

Ultra-high figure of merit refractive index sensor based on concentric ring and disk resonator

Ultra-high figure of merit refractive index sensor based on concentric ring and disk resonator

A highly sensitive plasmonic refractive index sensor based on concentric triple ring resonator for cancer biomarker and chemical concentration detection

A refractive index nanosensor with Metal–Insulator–Metal (MIM) waveguide setup, incorporating a concentric triple ring resonator (CTRR), is presented in this article. The proposed sensor identifies unknown materials by exploiting the linear interrelation between the refractive index and the corresponding shift of the resonant wavelength, aided by the Finite Element Method (FEM). Optimization of the initial structural parameters is performed one by one to increase the sensitivity of the designed sensor to the utmost. As a result, a maximum sensitivity of 3639.79 nm/RIU is obtained for gas sensing, with a FOM (Figure of Merit), FOM*, and Q-factor of 91.02, 0.26 × 106, and 99.75, respectively. Furthermore, the proposed optimized CTRR sensor displays a maximum sensitivity of 7530.49 nm/RIU for the biologically and chemically important refractive index range 1.30 to 1.40 and can also function as a plasmonic filter. Therefore, the numerous possible applications make the proposed sensor a promising contender in the field of refractive index sensing.

Ultranarrow dual-band metamaterial perfect absorber and its sensing application

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and high absorptivity is proposed. The MMA consists of two silver layers separated by a dielectric layer. Its top resonant element is constituted by two concentric ring resonators connected with four strips. Based on electromagnetic field simulation, the proposed MMA has two narrow absorption peaks with an absorption rate of 99.9% at 711 nm and 99.8% at 830 nm, and the corresponding line width of the two absorption peaks are only 9.7 and 9.8 nm. The dual-band MMA shows high absorptivity under wide incident angles. The simulated field pattern shows that dual-band perfect absorption is the combined result of the interaction of two concentric ring resonators and unit cell coupling. In addition, the hexapole plasmon mode can be observed at the outer ring at one absorption peak. The narrow plasmon resonance has a potential application in optical sensing, and can be used to measure the concentration of aqueous glucose with two frequency channels. The proposed MMA with high absorptivity is simple to manufacture, and has other potential applications, such as narrow-band filters, energy storage device, and so on.

Comparison of single and concentric split-ring resonator generated microplasmas

Microplasmas generated by a single split-ring resonator and a dual concentric split-ring resonator operating at the same frequency are compared. Argon is used as the working gas and held at a pressure of 0.5 Torr. The surface electric fields in the resonators were simulated to gain insight into the behavior of the fields in each device. Double Langmuir probes were used to measure the plasma density and electron temperature in a 2D plane 2 mm above the surface of the resonators. The single and the concentric ring resonators both had a maximum electron temperature in the discharge gap of 2.5 eV. The single and concentric split-ring resonators had the same maximum measured plasma density of 1.19 × 1017 m−3. Plots of the measured properties and comparisons with electric field simulations show the field coupling to the concentric ring and ignition produced in the secondary discharge gap. The concentric ring resonator has more spatially uniform temperature and density distributions relative to the single split-ring resonator.

Intracavity field dynamics near avoided mode crossing in a concentric silicon-nitride ring resonator

Understanding the intra-cavity field dynamics in passive microresonator systems has already been intriguing. It becomes fascinating when the system is complex, such as a concentric dual microring resonator that exhibit avoided mode crossing (AMC). In this work, we present a systematic study of intra-cavity oscillatory field dynamics near AMC in a concentric silicon nitride microring resonator with the help of the coupled Lugiato-Lefever equation (LLE). We identify two regions viz. weakly coupled region (WCR) and strongly coupled region (SCR) based on eigenfrequency separation of the two-hybrid modes, which originate from mode coupling near AMC. In WCR, the mode coupling effect is dominant, leading to intra-cavity power oscillation between these two modes in a periodic manner and non-identical variation of their phases. In SCR, the mode coupling effect reduces gradually with nearly identical characteristics of both the modes. We further verify our numerical findings with the semi-analytical variational method, leading to an in-depth understanding of the mode coupling induced dynamics. We finally analyze the polarization evolving state, and the polarization locked state with the help of Stokes parameters and Jones vectors in WCR and SCR, respectively.

Electrically tunable electromagnetically induced transparency in superconducting terahertz metamaterials

We present an electrically tunable superconducting metamaterial capable of modulating terahertz (THz) waves. The device consists of two concentric ring resonators, which exhibits the electromagnetically induced transparency-like spectral response. A relatively high modulation depth of 86.8% and a group delay of 25.4 ps were achieved at the transmission window. The experimental and simulated transmission spectra show good agreement. The hybrid coupling model could well explain the physical mechanism. The tuning of group delay of THz waves is of great significance to the applications of THz technology.

Single-Mode Lasing in Polymer Circular Gratings.

In recent years, conjugated polymers have become the materials of choice to fabricate optoelectronic devices, owing to their properties of high absorbance, high quantum efficiency, and wide luminescence tuning ranges. The efficient feedback mechanism in the concentric ring resonator and its circularly symmetric periodic geometry combined with the broadband photoluminescence spectrum of the conjugated polymer can generate a highly coherent output beam. Here, the detailed design of the ultralow-threshold single-mode circular distributed feedback polymer laser is presented with combined fabrication processes such as electron beam lithography and the spin-coating technique. We observe from the extinction spectra of the circular gratings that the transverse electric mode shows no change with the increase of incident beam angle. The strong enhancement of the conjugated polymer photoluminescence spectra with the circular periodic resonator can reduce the lasing threshold about 19 µJ/cm2. A very thin polymer film of about 110 nm is achieved with the spin-coating technique. The thickness of the gain medium can support only the zero-order transverse electric lasing mode. We expect that such a low threshold lasing device can find application in optoelectronic devices.

Influence of a split double concentric ring resonator elements axial rotation on the microwave transmission line frequency-selective characteristics

The work is dedicated toward studying the methods for correcting the frequency characteristics of a passive transmission path of a strip-line or coplanar microwave transmission line, equipped by a split double concentric ring resonator on the transmission section reverse side of the printed circuit board (plate). This correction is carried out by rotation around the center of the concentric rings (or an axis passing through this point and perpendicular to the plane of the substrate) of both constituent elements of the resonator separately and of the whole resonant structure.