Resonator Research Articles

Slow sound mode prediction and band structure calculation in 1D phononic crystal nanobeams using an artificial neural network.

Phononic crystals, which are artificial crystals formed by the periodic arrangement of materials with different elastic coefficients in space, can display modulated sound waves propagating within them. Similar to the natural crystals used in semiconductor research with electronic bandgaps, phononic crystals exhibit the characteristics of phononic bandgaps. A gap design can be utilized to create various resonant cavities, confining specific resonance modes within the defects of the structure. In studies on phononic crystals, phononic band structure diagrams are often used to investigate the variations in phononic bandgaps and elastic resonance modes. As the phononic band frequencies vary nonlinearly with the structural parameters, numerous calculations are required to analyze the gap or mode frequency shifts in phononic band structure diagrams. However, traditional calculation methods are time-consuming. Therefore, this study proposes the use of neural networks to replace the time-consuming calculation processes of traditional methods. Numerous band structure diagrams are initially obtained through the finite-element method and serve as the raw dataset, and a certain proportion of the data is randomly extracted from the dataset for neural network training. By treating each mode point in the band structure diagram as an independent data point, the training dataset for neural networks can be expanded from a small number to a large number of band structure diagrams. This study also introduces another network that effectively improves mode prediction accuracy by training neural networks to focus on specific modes. The proposed method effectively reduces the cost of repetitive calculations.

Cubical radiator for three‐dimensional flexible beam controller with multiple radiation beams and directions

AbstractA novel approach for generation of the multiple three‐directional and controllable beams from a cubical electromagnetic (EM) wave radiator is proposed in this paper. This cubical radiator is a multiple‐mode EM resonator, which is formed by a cubical metal cavity. Three resonant modes are excited in this cavity resonator by a feeding slot. Besides the feeding slot, a few additional slots are opened on the side wall(s) of the cavity to act as the EM wave radiation elements. Various combinations of radiation slots contribute to different beam directions, for example, side‐direction (single radiation slot), edge‐direction (two radiation slots), and vertex‐direction of the cavity (three radiation slots). More combinations of these slots are further studied in the cases of side + edge and edge + vertex to illustrate the diversity in the directions of the produced EM beams. To validate the predicted results, two prototypes are fabricated and measured to display their far‐field radiation patterns. The measured results agree well with the full‐wave simulated ones, thereby demonstrating the possibility of a large number of the flexible EM beams, as well as the capability of the controllable beam directions.

Multiple micro-cavity vibro-polaritons formation with different vibrational bands of the methylene group

We present an experimental technique to accurately predict the formation of vibro-polaritons from a molecular polymeric film embedded in a resonant mid-infrared cavity. Using simple Fourier-transform reflectance measurement, we extract the complex dielectric function of a polyethylene film using Kramers-Kronig relations. The fitted dielectric function can be plugged into a numerical code to predict the strength and dispersion of the strong light-matter coupling regime between the quantized electromagnetic modes of a microcavity and the vibrational bands of the molecules. As a demonstration, we experimentally resolve the simultaneous formation of multiple vibro-polariton modes issued from the strong coupling of some vibrational bands of the methylene group (CH2) in a 2.5-μm-thick polyethylene film embedded in a microcavity. We measure a Rabi splitting of 6.3 THz for the stretching doublet around 87.5 THz and a Rabi splitting of 1.1 THz for the scissoring doublet around 43.7 THz, in excellent agreement with numerical predictions.

3-D Printed Multiband Filtering Crossovers Based on Mixed Spherical Cavity Resonators

3-D Printed Multiband Filtering Crossovers Based on Mixed Spherical Cavity Resonators

Theoretical investigation of VO2 smart window with large-scale dynamic infrared emittance adjustment for adaptive thermal management

Thermochromic windows based on vanadium dioxide (VO2) are widely used in architectural windows due to its reversible phase change process. However, traditional VO2 windows only manage solar radiative transmittance and their emittance variation trend in the mid-infrared contradicts realistic requirements, which seriously hinders the further development of thermochromic windows. To address this issue, a VO2 full-spectrum smart window based on theoretical calculations is proposed for adaptive adjustment of solar spectral transmittance and thermal emittance. We cleverly utilize a thin Ag layer to construct a Fabry-Perot (FP) resonant cavity with the VO2 layer to achieve forward modulation of the emittance in the atmospheric window. Notably, the smart window has 83.8 % emittance modulated ability, which enables effective control of radiative cooling and has greatly exceeded the reported performance of the smart windows while maintaining 72.8 % high visible transparency. Energy consumption analysis indicates that the smart window has high energy-saving potential worldwide, achieving over 60 MJ/m2 energy-saving effect. This simple and easy-to-manufacture smart window expands the research scope of windows and broadens application prospects in thermal management, infrared camouflage, and building energy conservation.

Simulation and Analysis of a Near-Perfect Solar Absorber Based on SiO2-Ti Cascade Optical Cavity

The main development direction for current solar technology is to improve absorption efficiency and stability. To bridge this gap, we design in this paper a structure consisting of two multilayer disc stacks of different radii, one topped by a TiO2 disc and the other by a cascade disc stack composed of SiO2-Ti, for use in thermal emitters and solar absorbers. The innovation of our work is the exploitation of multiple Fabry–Perot resonances in SiO2-Ti cascade optical cavities to develop absorber bandwidths while investigating it in the field of thermal emission and many aspects affecting the efficiency of the absorber. The finite difference time domain method (FDTD) results show absorption averages as high as 96.68% with an absorption bandwidth of 2445 nm (A > 90%) at 280 nm–3000 nm solar incidence and even higher weighted averages as high as 98.48% at 1.5 solar air mass (AM) illumination. In order to investigate the physical mechanisms of our designed absorber in a high absorption state, we analyzed the electric field distributions of its four absorption peaks and concluded that its high absorption is mainly caused by the coupling of multiple Fabry–Perot resonance modes in the cascaded optical cavity. While considering this high efficiency, we also investigated the effect of complex environments such as extreme high temperatures and changes in the angle of incidence of the absorber, and the results show that the thermal radiation efficiency of the emitter is 96.79% at an operating temperature of 1700 K, which is higher than its thermal radiation efficiency of 96.38% at an operating temperature of 1500 K, which is a perfect result. On the other hand, we conclude that the designed structure is independent of polarization, while the absorber still has 88.22% absorption at incidence angles of up to 60°, both in transverse electric (TE) and transverse magnetic (TM) modes. The results of this study can help improve the performance of future solar absorbers and expand their application areas.

Measuring microwave dielectric properties of materials: Theory and applications

The knowledge of the microwave dielectric properties of materials has great significance for scientific and industrial applications. The measurement of the complex permittivity, ε*=ε′−iε″, in this frequency range, can be made using the small perturbation theory. In this method, the resonance frequency and the quality factor of a cavity, with and without a sample, can be used to calculate the complex dielectric permittivity of the material. The design of a cavity resonator implies solving the Maxwell equations inside that cavity, respecting the boundary conditions.This method was applied to characterize the dielectric properties of yttrium ferrites, that were prepared by solid state reaction, and exposed to different heat treatments. Structural and morphological characterizations were also performed. A correlation between these properties is presented. The best results, in terms of energy storage at microwave frequencies, are obtained for the sample heat treated at 1400 °C, with ε´=6.4, at 2.7 GHz, and with losses tangent lower than 10–4, at 300 K.

Bright Tripartite Quantum Steering Generated by Above‐Threshold Optical Parametric Oscillation

AbstractEinstein–Podolsky–Rosen (EPR) steering is the key resources in quantum information processing. EPR steering light sources typically obtained through spontaneous parametric down conversion below a threshold are relatively weak. Strong bright EPR steering light source can be obtained by operating the resonant cavity above the threshold. Here, the quantum steering correlations of the system above the threshold are analyzed using numerical simulations based on the quantum random trajectory method in Wigner representation. By employing the genuine multipartite EPR steering criterion, it is demonstrated that genuine bright tripartite EPR steering can be generated above the threshold, and investigate the influences of the nonlinear parameters on the genuine tripartite EPR steering. The scheme of bright EPR steering light source generated by cascaded nonlinear process can be used as a quantum repeater in quantum communication.

Microwave-Based State Diagnosis of Three-Way Catalysts: Impact Factors and Application Recommendations.

This study reassesses an overview of the potential of the radio frequency (RF)-based state diagnostics of three-way catalysts (TWC) based on a previous study with an emphasis on the defect chemistry of the catalyst material during reoxidation and reduction. Some data are based on the previous works but are newly processed, and the signal parameters resonant frequency and inverse quality factor are evaluated with respect to applicability. The RF-based method uses electromagnetic resonances in a cavity resonator to provide information on the storage level of the oxygen storage component. The analysis focuses on a holistic investigation and evaluation of the major effects influencing the RF signal during operation. On the one hand, the response to the oxygen storage behavior and the resolution of the measurement method are considered. Therefore, this study merges original data from multiple former publications to provide a comprehensive insight into important measurement effects and their defect chemistry background. On the other hand, the most important cross-sensitivities are discussed and their impact during operation is evaluated. Additionally, the effect of catalyst aging is analyzed. The effects are presented separately for the two resonant parameters: resonant frequency and (unloaded) quality factor. Overall, the data suggest that the quality factor has a way higher signal quality at low temperatures (<400 °C) and the resonant frequency is primarily suitable for high operating temperatures. At most operating points, the quality factor is even more robust against interferences such as exhaust gas stoichiometry and water content. Correctly estimating the catalyst temperature is the most important factor for reliable results, which can be achieved by combining the information of both resonant signals. In the end, the data indicate that microwave-based state diagnosis is a powerful system for evaluating the oxygen storage level over the entire operating range of a TWC. As a research tool and in its application, the system can therefore contribute to the improvement of the emission control of future gasoline vehicles.

Microstructure-Assisted Wafer-Scale Fabrication of Perovskite Microlaser Arrays.

All inorganic lead halide perovskites exhibit fascinating optical and optoelectronic characteristics for on-chip lasing, but the lack of precise control of wafer-scale fabrication for perovskite microstructure arrays restricts their potential applications in on-chip-integrated devices. In this work, a microstructure-template assisted crystallization method is demonstrated via a designed chemical vapor deposition process, achieving the controllable fabrication of homogeneous perovskite micro-hemispheroid (PeMH) arrays spanning the entire surface area of a 4-inch wafer. Benefiting from the low-loss whispering gallery resonance and plasmon-enhanced light-matter interactions in well-confined hybrid cavities, this CsPbX3/Ag (X = Cl, Br) plasmonic microlasers exhibit quite low thresholds below 10µJcm-2. Interestingly, these thresholds can be efficiently modulated through the manipulation of plasmonic resonance and electromagnetic field mode in PeMHs owning various diameters. This strategy not only provides a valuable methodology for the large-scale fabrication of perovskite microstructures but also endorses the potential of all-inorganic perovskite nanostructures as promising candidates for on-chip-integrated light sources.

Simulation of the synergistic effect of multiple operation parameters on cavity soliton in nonlinear fiber resonator

All optical soliton communication is a new generation of ultra-long distance and ultra-high speed optical fiber communication technology. Optical cavity solitons (CSs), whose pulse property is unique, have shown great potentials in optical soliton communication systems. Here, a theoretical model of nonlinear fiber resonator for CS generation is proposed. The effect of pump laser and resonant cavity parameters on the CS pulse performance is detailedly investigated and deeply analysed. Furthermore, the synergistic effect of continuous wave (CW) pump laser power and pump pulse peak power, and the synergistic effect of dispersion condition, fiber nonlinear coefficient and fiber length on the generation and property of CS pulse are respectively discussed and summarized. Finally, the launch conditions and parameter variation tolerances of cavity soliton in nonlinear fiber resonant cavity have been successfully generalized. These results can provide important instruction to the experimental generation and optimization of CS pulse.

MIM waveguide refractive index sensor with graphene enhanced three-ring nested resonator Fano resonance

In this paper, a metal-insulator-metal (MIM) waveguide featuring a three-ring nested cavity structure is proposed. We enhance and optimize this design by integrating graphene nanostructures into the ferrule resonance cavity, resulting in a hybrid graphene-MIM waveguide structure. The transmission spectra and electric fields generated by the structure are analyzed by using the finite element method (FEM), shedding light on the formation mechanism of various Fano resonance peaks. The validity of our theoretical analysis is confirmed using multimode interference coupled mode theory (MICMT), and the simulation results are largely aligning with the theoretical verification results. Next, by manipulating the chemical potential of graphene, the Fano resonance can be tuned across a wide range of wavelength bands. And this capability enables the realization of a dynamically tunable refractive index sensor for transmission spectroscopy. Under optimized parameter settings, the refractive index sensor achieves a maximum sensitivity of 1266.67nm/RIU, and a maximum figure of merit (FOM) value of 199.67RIU−1. Compared with conventional MIM waveguide devices, this design overcomes the difficulty of conventional MIM waveguide structures that cannot be dynamically tunable. Notably, the wavelength of the Fano resonance formed by the transmission spectrum can be dramatically altered when the refractive index of the medium in the surrounding environment is slightly changed. Therefore, this structure expands the repertoire of integrated optical devices with potential applications, particularly in the field of optical sensors.

Wavelength Tuning in Resonant Cavity Interband Cascade Light Emitting Diodes (RCICLEDs) via Post Growth Cavity Length Adjustment.

We demonstrate substrate-emitting resonant cavity interband cascade light emitting diodes (RCICLEDs) based on a single distributed Bragg reflector (DBR). These devices operate in continuous wave mode at room temperature. Compared to standard ICLEDs without a cavity, we achieved an 89% reduction in the emission spectrum width, as indicated by the Full Width Half Maximum (FWHM) of 70 nm. Furthermore, we observed far-field narrowing and improved thermal stability. A single DBR configuration allows the cavity length to be adjusted by adding refractive index-matched material to the top of the epitaxial structure after epitaxial growth. This modification effectively shifts the cavity response towards longer wavelengths. We fabricated emitters comprising two cavities of different lengths, resulting in the emission of two distinct spectral lines that can be independently controlled. This dual-color capability enables one of the emission lines to serve as a built-in reference channel, making these LEDs highly suitable for cost-effective gas-sensing applications.

Ultra-wideband solar perfect absorber for photothermal conversion with high manufacturing error tolerance

Solar energy is a key way to solve today's energy and environmental crises, and the full collection and utilization of solar energy requires a solar absorber with a broader spectrum and higher efficiency. Here, we present a solar metamaterial absorber, consisting of a Ti substrate, a Si3N4 dielectric spacer layer, and a Ti–SiO2 patterned layer. The results of the simulation show that the average absorption of the absorber is 98.16% in the range of 200–4200 nm under normal incidence. Its high absorption is attributed to the interaction of magnetic resonance (MR), cavity resonance (CR), guided mode resonance (GMR) and surface plasmon resonance (SPR). Moreover, the total absorption of the absorber in the AM1.5 standard solar radiation spectrum is 97.8% and the total absorption of blackbody radiation at 1500 K is 98.0%. In addition, the total photothermal conversion efficiency is still 92.2% at 1000 K. The proposed metamaterial absorber is also characterized by wide-angle incidence insensitivity, polarization-independence and a high tolerance of fabrication errors, which can be practically applied in the field of solar energy harvesting.

Insights into the mechanisms of optical cavity-modified ground-state chemical reactions

In this work, we systematically investigate the mechanisms underlying the rate modification of ground-state chemical reactions in an optical cavity under vibrational strong-coupling conditions. We employ a symmetric double-well description of the molecular potential energy surface and a numerically exact open quantum system approach—the hierarchical equations of motion in twin space with a matrix product state solver. Our results predict the existence of multiple peaks in the photon frequency-dependent rate profile for a strongly anharmonic molecular system with multiple vibrational transition energies. The emergence of a new peak in the rate profile is attributed to the opening of an intramolecular reaction pathway, energetically fueled by the cavity photon bath through a resonant cavity mode. The peak intensity is determined jointly by kinetic factors. Going beyond the single-molecule limit, we examine the effects of the collective coupling of two molecules to the cavity. We find that when two identical molecules are simultaneously coupled to the same resonant cavity mode, the reaction rate is further increased. This additional increase is associated with the activation of a cavity-induced intermolecular reaction channel. Furthermore, the rate modification due to these cavity-promoted reaction pathways remains unaffected, regardless of whether the molecular dipole moments are aligned in the same or opposite direction as the light polarization.

Broadband tunable resonance modes from multi-composition monolayer MoS2(1−x)Se2x with SiO2 microsphere cavity

Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDCs) that are compatible with Si-based substrates have already exhibited huge application potential in optoelectronics and photonics. The MoS2(1−x)Se2x ternary alloy consisting of two different chalcogens, as a class of lasing gain medium, enriches the family of 2D TMDC materials. Here, monolayer MoS2(1−x)Se2x ternary alloys with tunable composition have been synthesized via single-step chemical vapor deposition method. Raman and photoluminescence studies demonstrate that the bandgap of grown monolayer MoS2(1−x)Se2x alloys can be gradually tuned from 1.59 to 1.82 eV, indicating the continuous changes of the chemical composition x from 0.82 to 0. The oscillation characteristic is further investigated, where the MoS2(1−x)Se2x alloy provides optical gain for the SiO2 microsphere resonant cavity. The achieved resonance modes in a broadband range from 610 to 810 nm not only extend the range of potential TMDC-based lasers, but also drive the applications of alloy materials in various optoelectronics devices.

Polarization entanglement generation in silicon nitride waveguide-coupled dual microring resonators.

Polarization-entangled photon pair sources exhibiting nonlocal quantum correlations are crucial to developments of quantum computing, quantum communications, quantum cryptography, and quantum sensing technologies. On-chip polarization entanglement generation thus constitutes one enabling component for integrated quantum photonic circuits. Here, we present to our knowledge the first polarization-entangled photon pair sources in a silicon nitride platform for integrated quantum photonic circuits. We demonstrate the generation of a polarization-entangled state by adopting a configuration comprising dual microring resonators, with nearly degenerate transverse electric and transverse magnetic polarized cavity resonances for the two resonators coupled in series to a common bus waveguide. We measure two-photon interference and quantum state tomography to characterize the polarization entanglement of the generated state and to reconstruct the density matrix. Our experiments reveal a visibility of 96.4% ± 3.1% and of 86.7% ± 3.2% with the |H⟩ and |V⟩ bases, respectively (and a visibility of 89.4% ± 6.6% and 81.3% ± 7.3% with the |D⟩ and |A⟩ bases), and a fidelity of ∼75.7% from the tomographic reconstructed density matrix.

Near-field optomechanical transduction enhanced by Raman gain.

Raman-gain-enhanced near-field optomechanical transduction between a movable optical cavity and SiN-membrane resonator is demonstrated. The Raman gain compensates for the intrinsic loss of the cavity and amplifies the optomechanical transduction, through which the membrane vibration is sensed using a high-Q whispering-gallery-mode optical cavity evanescently. The optical Q of the cavity resonance is improved with respect to the optical pump power, which results in an increase in the optomechanically transduced vibration signals of the mechanical resonator. Our near-field optomechanical coupling approach with optical gain realizes highly sensitive displacement measurement in nano- and micro-mechanical resonators consisting of arbitrary materials and structures.

A Vacuum Waveguide Filter Bank Spectrometer for Far-Infrared Astrophysics

Traditional technologies for far-infrared (FIR) spectroscopy generally involve bulky dispersive optics. Integrated filter bank spectrometers promise more compact designs, but implementations using superconducting transmission line networks become lossy at terahertz frequencies. We describe a novel on-chip spectrometer architecture designed to extend this range. A filter bank spectrometer is implemented using vacuum waveguide etched into a silicon wafer stack. A single trunk line feeds an array of resonant cavities, each coupled to a kinetic inductance detector fabricated on an adjacent wafer. We discuss the design and fabrication of a prototype implementation, initial test results at ambient temperature, and prospects for future development.

Detection of Low-Concentration Biological Samples Based on a QBIC Terahertz Metamaterial Sensor.

Quasi-bound state in the continuum (QBIC) can effectively enhance the interaction of terahertz (THz) wave with matter due to the tunable high-Q property, which has a strong potential application in the detection of low-concentration biological samples in the THz band. In this paper, a novel THz metamaterial sensor with a double-chain-separated resonant cavity structure based on QBIC is designed and fabricated. The process of excitation of the QBIC mode is verified and the structural parameters are optimized after considering the ohmic loss by simulations. The simulated refractive index sensitivity of the sensor is up to 544 GHz/RIU, much higher than those of recently reported THz metamaterial sensors. The sensitivity of the proposed metamaterial sensor is confirmed in an experiment by detecting low-concentration lithium citrate (LC) and bovine serum albumin (BSA) solutions. The limits of detection (LoDs) are obtained to be 0.0025 mg/mL (12 μM) for LC and 0.03125 mg/mL (0.47 μM) for BSA, respectively, both of which excel over most of the reported results in previous studies. These results indicate that the proposed THz metamaterial sensor has excellent sensing performances and can well be applied to the detection of low-concentration biological samples.