Q-factor Of Resonator Research Articles

Asymmetric tetramer metasurface sensor governed by quasi-bound states in the continuum

Abstract Asymmetric metasurfaces supporting quasi-bound states in the continuum (BICs) with high Q-factors and strong light–matter interaction properties are attractive platforms for label-free biosensing applications. Recently, various meta-atom geometries have been exploited to support sharp high-Q quasi-BIC resonance. However, which meta-atom design may be a better practical choice remains unclear. Here, we compared several established meta-atom designs to address this issue by conducting an extensive theoretical discussion on sensing capability and fabrication difficulty. We theoretically revealed that the tetramer meta-atom geometry produces a higher surface sensitivity and exhibits a larger size-to-wavelength ratio than other meta-atom schemes. Furthermore, we found that metasurfaces with a higher depth considerably enhance surface sensitivity. The performance of two asymmetric tetramer metasurfaces (ATMs) with different heights was demonstrated experimentally. Both shallow and thick ATM structures exhibit sharp high Q-factor resonances with polarization-insensitive features. Notably, the surface sensitivity is 1.62 times for thick ATM compared to that for shallow ones. The combination of properties opens new opportunities for developing biosensing or chemical-sensing applications with high performance.

Quasi-guided modes resulting from the band folding effect in a photonic crystal slab for enhanced interactions of matters with free-space radiations.

We elucidate that guided modes supported by a regular photonic crystal slab structure composed of a square lattice of air holes in a silicon slab will transition into quasi-guided (leaky) modes when the radius of every second column of air holes is changed slightly. This intentional geometric perturbation will lead to a doubling of the period in one direction and the corresponding shrinkage of the first Brillouin zone. Because of the translational symmetry in the k-space, leaky waves inheriting the spatial dispersion of the original guided modes, which do not interact with external radiation, will appear with the dispersion curves above the light cone. Our results show that ultrahigh Q-factor resonances with large operating bandwidth can be achieved. Interestingly, the perturbation in only one direction of the photonic lattice will lead to an in-plane wave number-dependent resonance characteristic in both directions. Our numerical results demonstrate a local enhancement of the electric field magnitude by the order of 102, which is even more significant than those in most plasmonic structures. These quasi-guided modes with superior properties will provide a new platform for efficient light-matter interactions.

Polarization multiplexing multichannel high-Q terahertz sensing system

Terahertz functional devices with high-Q factor play an important role in spectral sensing, security imaging, and wireless communication. The reported terahertz devices based on the electromagnetic induction transparency (EIT) effect cannot meet the needs of high-Q in practical applications due to the low-Q factor. Therefore, to increase the Q-factor of resonance, researchers introduced the concept of bound state in the continuum (BIC). In the quasi-BIC state, the metasurface can be excited by the incident wave and provide resonance with a high-Q factor because the condition that the resonant state of the BIC state is orthogonal is not satisfied. The split ring resonator (SRR) is one of the most representative artificial microstructures in the metasurface field, and it shows great potential in BIC. In this paper, based on the classical single-SRR array structure, we combine the large and small SRR and change the resonance mode of the inner and outer SRR by changing the outer radius of the inner SRR. The metasurface based on parameter-tuned BIC verified that the continuous modulation of parameters in a system could make a pair of resonant states strongly coupled, and the coherent cancellation of the resonant states will cause the linewidth of one of the resonant states to disappear, thus forming BIC. Compared with the single-SRR array metasurface based on symmetry-protected BIC, the dual-SRR array metasurface designed in this paper has multiple accidental BICs and realizes multichannel multiplexing of X-polarization and Y-polarization. It provides a brilliant platform for high-sensitivity optical sensor array, low threshold laser and efficient optical harmonic generation.

Development of a continuous operation hop-kiln with power supply

Introduction.Hop production in the Russian Federation averages 116 thousand tons from 54 thousand hectares. The HS-400 hop-kiln used in the hop drying process line is energy-intensive. The concept of hop growing development in the Chuvash Republic for 2020–2025, approved by the decree of the Cabinet of Ministers of the Chuvash Republic (dated 20.08.2020 No. 738-r), provides for the development of up to 45–50 hectares of new areas for hop, at the rate of 15–17 hectares per one hop-kiln HS-400. To expand the production of hop, it is necessary to effectively master innovative technologies and installations for drying freshly harvested hop that are not inferior in technical and economic parameters of foreign analogues. The development of a hop-kiln that provides dehydration and disinfection of freshly harvested hop, pre-servs consumer properties with reduced operating costs, is currently relevant.Methodology.The electrophysical parameters of hop cones (according to the Rogov method) were analyzed depending on the frequency of the electromagnetic field, humidity and temperature, heat and mass transfer processes during the supply of convective heat to the volumetric resonator of the microwave installation were theoretically investigated, and the effective technological parameters of the hop-kiln were determined. Studies of the electromagnetic field strength, current density, and intrinsic Q-factor of resonators were carried out in the CST Studio Suite 2017 three-dimensional computer modeling program and its CST Microwave Studio subprogram.Results.A multi-resonator hop-kiln with an energy supply in an electromagnetic field has been developed. The proposed hop-kiln contains resonators sequentially arranged in a horizontal plane with curved surfaces, docked through ceramic biconvex perforated plates. The design and technological scheme of the hop-kiln has been developed. The intrinsic Q-factor of elliptical toroidal resonator is 14600, of triangular prismatic resonator — in the range of 9000–1200, depending on the degree of concavity of the upper face. The calculation of the installation productivity amounts to 180–200 kg/h with a power of 15.66 kW, which made it possible to determine energy costs — to 0.1 kWh/kg.

High Sensitivity Detection Method for Liquid Concentrations Based on Coupled Microwave Resonators

This paper presents a new measurement method for liquid concentrations based on two inductively coupled resonators with enhanced sensitivity compared with traditional methods in microwave frequency ranges. The equivalent circuit of the coupled resonators is proposed with its eigenequation having three eigenfrequencies derived. We demonstrate that, compared to a single resonator, the sensitivity of the center eigenfrequency shift to the changed capacitance increases by an order of magnitude if the product of the coupling coefficient and Q-factor of the second resonator is close to unity. In addition, that the reflection magnitude changes with the varied capacitance is also giant under impedance matching condition at the down and up eigenfrequencies. Based on the proposed method, a sensor composed of an open quarter-wavelength microstrip-line resonator (OQMR) and a split ring resonator (SRR) for detecting concentrations of water-glucose solutions is designed. By adjusting the sample volume and the distance between two resonators, different coupling coefficients and Q-factors can be attained, enabling marked increases in the sensitivity. Experimental and simulated results show that the sensitivity of the center eigenfrequency shift and of the reflection magnitude change to the concentration are as high as 9.4 MHz/(mg/mL) and 5.41 dB/(mg/mL), respectively, both of which are excellent compared to other sensors.

High Spectral Sensitivity of Strongly Coupled Hybrid Tamm-Plasmonic Resonances for Biosensing Application

In this study, the sensitivity to the refractive index changes of the ambient was studied on the uniform gold film (~50 nm) with a 1D photonic crystal (PC) from periodic five TiO2 (~110 nm)/SiO2 (~200 nm) bilayers and gold nano-bumps array produced by direct laser writing on the same sample. The optical signal sensitivity of hybrid plasmonic resonances was compared with traditional surface plasmon resonance (SPR) on a single gold layer. The influence of the strong coupling regime between Tamm plasmon polariton (TPP) and propagated plasmon polaritons in the hybrid plasmonic modes on the sensitivity of the optical was discussed. Recent studies have shown very high hybrid plasmonic mode sensitivity SHSPP ≈ 26,000 nm/RIU to the refractive index on the uniform gold layer; meanwhile, the introduction of gold lattice reduces the signal sensitivity, but increases the Q-factor of the plasmonic resonances. Despite this, the sensitivity to the ellipsometric parameters Ψ and Δ on the gold lattice was rather high due to the increased Q-factor of the resonances. The comparison of plasmonic resonance sensitivity to the refractive index changes of hybrid TPP-SPP mode on the uniform gold layer and traditional SPR have shown that hybrid plasmonic mode, due to a strong coupling effect, overcomes the SPR by about 27%.

Topological surface plasmon resonance in deep subwavelength structure

We propose a plasmonic topological junction structure that combines topological robustness and subwavelength localization properties. The proposed structure is a junction of two topologically distinguished metal-insulator-metal waveguide gratings. Assuming Au–SiO2–Au waveguide gratings, we theoretically demonstrate a plasmonic Jackiw-Rebbi-state resonance which has substantially small effective mode-field area in the order of 0.1 μm2 at 1560 nm wavelength and requires only 10 periods for fully sustaining the ideal resonance Q-factor of the infinitely large array. Therefore, our proposed approach provides an efficient scheme for creating various plasmonic leaky-mode resonance components that can take advantages of spectral robustness and strong localization properties.

Terahertz high-Q magnetic dipole resonance induced by coherent Fano interactions

High Q-factor resonance holds great promise for bio-chemical sensing and enhanced light–matter interaction. However, terahertz (THz) magnetic resonances usually demonstrate low Q-factors, resulting in huge energy radiation loss particularly in high frequency bands. Here, we show that high Q-factor magnetic dipole resonance at THz frequencies can be achieved by exploiting the coherent Fano interactions with strong field enhancements in an array composed of single metallic split-ring resonators, working at Wood–Rayleigh anomalies. It can give rise to ultrahigh Q-factor beyond 104 in the THz regime. Experimentally, the measured Q-factor of dominant magnetic dipole resonance can achieve no less than a level of ∼261 by Lorentzian fitting to the experimental data. In addition, a high Q-factor of the fundamental-order magnetic dipole resonance is demonstrated beyond 30. High-Q magnetic dipole resonance is closely associated with ultralow-damping and negative permeability in the THz band. The measurements of magnetic dipole resonances are in good agreement with the theoretical analyses. Our scheme suggests a feasible route to suppress radiative loss for enhanced THz field-matter interaction.

Electromagnetically induced transparency for efficient optical modulation in a graphene-dielectric metasurface with surface roughness

A high-performance optical modulator is proposed using a double-layer graphene-based metasurface. A theoretical study of the surface roughness in the proposed modulator is presented for the first time. The metasurface is constructed by a periodic array of double-slit ring resonators adjacent to silicon bars which can support a high quality factor (Q-factor) resonance based on the electromagnetically induced transparency (EIT). The dielectric nano-resonators are deposited on two graphene sheets spaced by a silicon dioxide layer. The modulation voltage is applied across the graphene sheets so that the graphene interband absorption can be adjusted. The proposed modulator is optimized and simulated using the finite-difference time-domain (FDTD) method. According to the presented results, a very high modulation depth of 18.49 dB for a gate voltage of 6.68 V is achieved that is attributed to the strong light-graphene interaction provided by the high Q-factor EIT resonance. To the best of our knowledge, this is the highest modulation depth ever reported for a free-space optical modulator. The 3dB bandwidth of the device is also calculated to be as high as 17.78 GHz. For the sake of completeness, the effect of surface roughness as one of the important fabrication errors is investigated. The performance of the modulator is weakly degraded by surface roughness so that the modulation depth remains higher than 17.1 dB which makes the proposed structure promising for practical realization of free-space optical systems.

Miniaturized ultrasound detector arrays in silicon photonics using pulse transmission amplitude monitoring.

Silicon photonics holds promise for a new generation of ultrasound-detection technology, based on optical resonators, with unparalleled miniaturization levels, sensitivities, and bandwidths, creating new possibilities for minimally invasive medical devices. While existing fabrication technologies are capable of producing dense resonator arrays whose resonance frequency is pressure sensitive, simultaneously monitoring the ultrasound-induced frequency modulation of numerous resonators has remained a challenge. Conventional techniques, which are based on tuning a continuous wave laser to the resonator wavelength, are not scalable due to the wavelength disparity between the resonators, requiring a separate laser for each resonator. In this work, we show that the Q-factor and transmission peak of silicon-based resonators can also be pressure sensitive, exploit this phenomenon to develop a readout scheme based on monitoring the amplitude, rather than frequency, at the output of the resonators using a single-pulse source, and demonstrate its compatibility with optoacoustic tomography.

E-shaped split ring resonator used for metasurface-based structure with an ultra-high Q-factor for terahertz application

Plasmonic devices based on split ring resonator (SRR) of ultra-low-loss performance (high Q-factor) are significant for a broad range of applications and studies. However, due to the inevitable ohmic and radiation losses, it has always been a challenge to design various types of plasmonic devices with high Q-factor. Here, we theoretically present a unique E-shaped SRR that can destructively suppress dipole radiation by adjusting the grating-arm position to produce asymmetry. Meanwhile, the proposed terahertz metasurface structure formed by periodically arranged E-shaped SRRs can give rise to high Q-factor resonances. The results show that an ultra-high Q-factor beyond 104 can be obtained in the terahertz frequency region by optimizing the structural parameters. The sensing characteristics of such a metasurface-based structure served as a refractive-index sensor are investigated as well, demonstrating its advantage of high sensitivity. Unique radiation properties of the metasurface-based structure enable it to use in the design of novel low-loss, ultra-sensitive sensors, narrowband filters, and other plasmonic devices.

Ultrathin Piezoelectric Resonators Based on Graphene and Free-Standing Single-Crystal BaTiO3.

Suspended piezoelectric thin films are key elements enabling high-frequency filtering in telecommunication devices. To meet the requirements of next-generation electronics, it is essential to reduce device thickness for reaching higher resonance frequencies. Here, the high-quality mechanical and electrical properties of graphene electrodes are combined with the strong piezoelectric performance of the free-standing complex oxide, BaTiO3 (BTO), to create ultrathin piezoelectric resonators. It is demonstrated that the device can be brought into mechanical resonance by piezoelectric actuation. By sweeping the DC bias voltage on the top graphene electrode, the BTO membrane is switched between the two poled ferroelectric states. Remarkably, ferroelectric hysteresis is also observed in the resonance frequency, magnitude and Q-factor of the first membrane mode. In the bulk acoustic mode, the device vibrates at 233 GHz. This work demonstrates the potential of combining van der Waals materials with complex oxides for next-generation electronics, which not only opens up opportunities for increasing filter frequencies, but also enables reconfiguration by poling, via ferroelectric memory effect.

High-quality resonances in terahertz composite slabs based on metal gratings

In this study, a terahertz (THz) composite slab (TCS) based on metal grating and dielectric films is experimentally and numerically investigated in the THz region. By combining a dielectric film, the TCS exhibits different sharp resonances for varied polarization waves. A sharp Fano resonance is excited for transverse magnetic (TM) waves, which originates from the introduced asymmetric factor by dielectric films. The film thickness and refractive index can be used for the Fano resonance tuning. The resonant Q-factor can be improved using thinner and lower refractive index films. For transverse electric (TE) modes, a resonance termed guided modes can also be induced when the dielectric film is thick enough. The effects of film thickness and refractive index on these resonances are analyzed in detail. These results demonstrated that this TCS with high Q-factors or narrow resonances for both TM and TE waves is a promising component for THz filter and sensor applications.

Superior terahertz sensing metasurface based on ultrahigh-Q toroidal dipole governed by quasi-BIC

Sharp quasi-bound states in the continuum (quasi-BIC) in all-dielectric metasurfaces with high quality-factor (Q-factor) resonance provide an important platform for terahertz (THz) sensing technology because of its ability to enhance the strong light-matter interaction between THz waves and analytes. In this paper, we propose an ultrasensitive sensing substrate based on an all-dielectric metasurface consisting of an array of stacked high-index structures. By introducing a geometry asymmetry along the horizontal direction in the unit cell, a toroidal-dipole–dominated quasi-BIC transitioned from a distorted symmetry-protected BIC is excited with a Q-factor as high as , which could maintain at a high level as the structure geometry varies. After characterizing the surface sensing performance, an ultrahigh surface sensitivity is achieved to be 263GHz per refractive index unit, while the resultant figure of merit reaches , which outperforms the existing designs. The proposed metasurface is promising for superior label-free sensing performance at THz regime.

Stress Analysis and Q-Factor of Free-Standing (La,Sr)MnO3 Oxide Resonators.

High-sensitivity nanomechanical sensors are mostly based on silicon technology and related materials. The use of functional materials, such as complex oxides having strong interplay between structural, electronic, and magnetic properties, may open possibilities for developing new mechanical transduction schemes and for further enhancement of the device performances. The integration of these materials into micro/nano-electro-mechanical systems (MEMS/NEMS) is still at its very beginning and critical basic aspects related to the stress state and the quality factors of mechanical resonators made from epitaxial oxide thin films need to be investigated. Here, suspended micro-bridges are realized from single-crystal thin films of (La0.7 ,Sr0.3 )MnO3 (LSMO), a prototypical complex oxide showing ferromagnetic ground state at room temperature. These devices are characterized in terms of resonance frequency, stress state, and Q-factor. LSMO resonators are highly stressed, with a maximum value of ≈260 MPa. The temperature dependence of their mechanical resonance is discussed considering both thermal strain and the temperature-dependent Young's modulus. The measured Q-factors reach few tens of thousands at room temperature, with indications of further improvements by optimizing the fabrication protocols. These results demonstrate that complex oxides are suitable to realize high Q-factor mechanical resonators, paving the way toward the development of full-oxide MEMS/NEMS sensors.

Reduced material loss in thin-film lithium niobate waveguides

Thin-film lithium niobate has shown promise for scalable applications ranging from single-photon sources to high-bandwidth data communication systems. Realization of the next generation high-performance classical and quantum devices, however, requires much lower optical losses than the current state of the art resonator (Q-factor of ∼10 million). Yet the material limitations of ion-sliced thin film lithium niobate have not been explored; therefore, it is unclear how high the quality factor can be achieved in this platform. Here, using our newly developed characterization method, we find out that the material limited quality factor of thin film lithium niobate photonic platform can be improved using post-fabrication annealing and can be as high as Q ≈ 1.6 × 108 at telecommunication wavelengths, corresponding to a propagation loss of 0.2 dB/m.

Guiding-mode-assisted double-BICs in an all-dielectric metasurface.

The electromagnetically induced transparency (EIT) effect realized in a metasurface is potential for slow light applications for its extreme dispersion variation in the transparency window. Herein, we propose an all-dielectric metasurface to generate a double resonance-trapped quasi bound states in the continuum (BICs) in the form of EIT or Fano resonance through selectively exciting the guiding modes with the grating. The group delay of the EIT is effectively improved up to 2113 ps attributing to the ultrahigh Q-factor resonance carried by the resonance-trapped quasi-BIC. The coupled harmonic oscillator model and a full multipole decomposition are utilized to analyze the physical mechanism of EIT-based quasi-BIC. In addition, the BIC based on Fano and EIT resonance can simultaneously exist at different wavelengths. These findings provide a new feasible platform for slow light devices in the near-infrared region.

Theoretical and Experimental Investigations on Differential Aperture-Coupled Rectangular Laminated Resonator Antenna

This letter studies differential aperture-coupled rectangular laminated resonator antenna (LRA) theoretically and experimentally. A theoretical model is proposed to analyze the resonance and radiation characteristics of the differential aperture-coupled rectangular LRA based on mode matching method. Analytical expressions for the resonant frequencies, Q-factor, impedance bandwidth (BW), radiation fields, directivity, radiation efficiency and gain are first derived. For verification, three prototypes of rectangular LRA with different length-to-height ratios differentially fed by a coupling slot are simulated, fabricated, and measured. Acceptable agreements among the calculated, simulated, and measured results are achieved. The proposed theoretical model provides physical insight into the operating principle of aperture-coupled LRA, which can be applied to predict the performances of rectangular LRAs and to instruct the design of rectangular LRAs.

Spectrally tunable liquid resonator based on electrowetting.

We present a tunable on-chip liquid resonator in conjunction with a tapered fiber coupling scheme. The resonator consists of a glycerol droplet submerged within an immiscible liquid bath, which mitigates the effects of environmental fluctuations. The platform is fabricated using standard semiconductor techniques, which enable the future integration of photonic components for an on-chip liquid resonator device. The liquid resonator maintains its high Q-factor on chip (105) due to surface tension forming an atomically smooth liquid-liquid interface. Higher Q-factor resonance modes experienced linewidth broadening due to the random excitation of thermal capillary vibrations. Spectral tuning is demonstrated using the electrowetting effect, increasing the surface's wettability and an expansion in the droplet diameter. A maximum spectral tuning of 1.44 nm ± 5 pm is observed by applying 35 V. The tuning range is twice the free spectral range (FSR) of 0.679 nm measured at a pumping wavelength range of 770-775 nm. A 2D axisymmetric finite-element simulation shows resonance modes in good agreement with experimentally measured spectra and with predicted tuning speeds of 20 nm/s.

Demonstration of Tunable Fano Resonances in a Meta-material Absorber Composed of Asymmetric Double Bars with Bent Arms

In this paper, a metal–insulator-metal (MIM) plasmonic absorber consisting of asymmetric double bars with bent arms located on top of a silica layer coated on a metal film is proposed, and its resonant features are analyzed. The suggested structure supports both Fano and dipole perfect absorption resonances at the near-infrared region (NIR). The asymmetry introduced into the structure can be induced by changing the bending angle or rotation angle of one of the antennas, while the other one remains fixed. Simulation results demonstrate that by applying both asymmetry factors to the structure, one can have two individual Fano peaks at the same time. It is shown that the magnitude, central wavelength, and line width of the Fano peaks are adjustable by controlling the geometrical parameters of the structure. It is also indicated that the quality factor (Q-factor) of the Fano resonance is inversely related to the degree of asymmetry introduced into the structure. According to the simulations, an ultra-narrow resonance peak with a bandwidth of 1.87 nm at the wavelength of 710 nm (corresponding to a Q-factor of 387) can be obtained by controlling the geometrical parameters. It is also discussed that the absorptivity of Fano and the dipole peaks can be adjusted inversely, by manipulating the grapheme chemical potential. The ratio of the absorptivity to the chemical potential of graphene about 275%/eV and 226%/eV is calculated for the Fano peak and dipole peak, respectively. Accordingly, the presented structure is an adjustable NIR absorber with a fully tunable absorption spectrum which can be utilized in various applications from tunable reflectors and photo-detectors to ultra-narrowband and broadband optical modulators.