Showing papers on "Q factor published in 2022"

Quasi-Static Modeling and Optimization of Two-Layer PCB Resonators in Wireless Power Transfer Systems for 110-kV Power Grid Online Monitoring Equipment

Abstract: The expanding functions of the emerging smart grid have posed new technical challenges on the power supplies for online monitoring systems in the transmission and distribution networks. A recent study has suggested that magnetic energy around the transmission line can be harvested and delivered wirelessly to the monitoring equipment through printed circuit board (PCB) resonators embedded inside an insulation rod. This article presents a rigorous analysis, modeling, and optimization of such PCB resonators. A new closed-form quasi-static model of the PCB resonators is derived. A fully automated simulation-driven optimization framework is constructed to enhance the quality factor of the resonator. Practical measurements show that the optimal design improves the quality factor ( $Q$ factor) from 52 to 132 as compared to the existing trial-and-error design. The corresponding wireless power transfer efficiency in a 20-W prototype across a 1.14-m distance improves significantly from 11 to 46%.

Beyond Q: The Importance of the Resonance Amplitude for Photonic Sensors

Abstract: Resonant photonic sensors are enjoying much attention based on the worldwide drive toward personalized healthcare diagnostics and the need to better monitor the environment. Recent developments exploiting novel concepts such as metasurfaces, bound states in the continuum, and topological sensing have added to the interest in this topic. The drive toward increasingly higher quality (Q)-factors, combined with the requirement for low costs, makes it critical to understand the impact of realistic limitations such as losses on photonic sensors. Traditionally, it is assumed that the reduction in the Q-factor sufficiently accounts for the presence of loss. Here, we highlight that this assumption is overly simplistic, and we show that losses have a stronger impact on the resonance amplitude than on the Q-factor. We note that the effect of the resonance amplitude has been largely ignored in the literature, and there is no physical model clearly describing the relationship between the limit of detection (LOD), Q-factor, and resonance amplitude. We have, therefore, developed a novel, ab initio analytical model, where we derive the complete figure of merit for resonant photonic sensors and determine their LOD. In addition to highlighting the importance of the optical losses and the resonance amplitude, we show that, counter-intuitively, optimization of the LOD is not achieved by maximization of the Q-factor but by counterbalancing the Q-factor and amplitude. We validate the model experimentally, put it into context, and show that it is essential for applying novel sensing concepts in realistic scenarios.

High Q-factor, ultrasensitivity slot microring resonator sensor based on chalcogenide glasses.

Abstract: In this article, the chalcogenide slot waveguide is theoretically studied, and the highest power confinement factors of the slot region and the cladding region are obtained to be 36.3% and 56.7%, respectively. A high-sensitivity chalcogenide slot microring resonator sensor is designed and fabricated by electron-beam lithography and dry etching. The structure increases the sensitivity of the sensor compared with the conventional evanescent field waveguide sensor. The cavity has achieved a quality factor of 1 × 104 by fitting the resonant peaks with the Lorentzian profile, one of the highest quality factors reported for chalcogenide slot microring resonators. The sensor sensitivity is measured to be 471 nm/RIU, which leads to an intrinsic limit of detection of 3.3 × 10--4 RIU.

Cascade Brillouin Lasing in a Tellurite-Glass Microsphere Resonator with Whispering Gallery Modes

Abstract: Brillouin microlasers based on microresonators with whispering gallery modes (WGMs) are in high demand for different applications including sensing and biosensing. We fabricated a microsphere resonator with WGMs from a synthesized high-quality tellurite glass with record high Q-factors for tellurite microresonators (Q ≥ 2.5 × 107), a high Brillouin gain coefficient (compared to standard materials, e.g., silica glasses), and a Brillouin frequency shift of 9 ± 0.5 GHz. The high density of excited resonance modes and high loaded Q-factors allowed us to achieve experimentally cascade Stokes-Brillouin lasing up to the 4th order inclusive. The experimental results are supported by the results of the theoretical analysis. We also theoretically obtained the dependences of the output Brillouin powers on the pump power and found the pump-power thresholds for the first five Brillouin orders at different values of pump frequency detuning and Q-factors, and showed a significant effect of these parameters on the processes under consideration.

Bound States in the Continuum in Asymmetric Dielectric Metasurfaces

Abstract: It is well established that for symmetry‐protected bound states in the continuum (BICs), introducing the broken geometry symmetry in a dielectric metasurface transforms such a BIC into a quasi‐BIC (QBIC) with high‐quality factor (Q‐factor). Typically, the smaller the asymmetry parameter, the larger the Q‐factor. However, it is very challenging to fabricate such nanostructures with an ultra‐small asymmetry parameter, thus limiting the measured Q‐factor of QBIC. In this work, the authors demonstrated that BICs can be sustained at Γ‐point in an asymmetric dielectric metasurface, whose unit cell is composed of a dielectric cuboid with an off‐centre hole inside it. Multipole decompositions and near‐field distributions indicate that the toroidal dipole dominates the nature of such a QBIC. Furthermore, the authors found that such a BIC is robust against the shape of the hole. Besides, two BICs at different wavelengths can be achieved by applying either a rectangular hole or a rectangular lattice. Finally, the authors presented experimental verifications of BIC types by fabricating asymmetric silicon metasurfaces. Measurement results show that the Q‐factor of QBIC can reach almost 5,000. The results may enrich the library of BICs and find exciting applications in developing high‐performance photonics devices, such as nanolasers, biosensors and enhanced nonlinear harmonic generation.

X-Band Multi-Frequency 30% Compound SCALN Microacustic Resonators and Filters for 5G-Advanced and 6G Applications

Abstract: SummaryThis paper reports on record-high resonance frequency-quality factor product (fs · Q) figure of merit 30% Sc-doped Aluminum Nitride (ScAlN) Cross-sectional Lamé Mode (CLM) microacustic resonators in the super high frequency (SHF) range, along with outstanding electromechanical coupling-quality factor products ($k_t^2 \cdot Q$). Moreover, for the first time above 5 GHz, ScAlN-based resonators have been arranged to produce first-order passband ladder filters, providing record-wide fractional bandwidth for the microacoustic technology in the same frequency range. The ScAlN piezoelectric material was deposited from a compound casted target on a 200 mm wafer, going into the direction of a foundry-standardized fabrication process for SHF resonators. This first-of-a-kind demonstration paves the way for the synthesis of high-performance commercial filters for communication in the 5G era and beyond, where SHF operation and wide carrier bandwidth are fundamental requirements.

Engineering Electromagnetic Field Distribution and Resonance Quality Factor Using Slotted Quasi-BIC Metasurfaces.

Abstract: Dielectric metasurfaces governed by bound states in the continuum (BIC) are actively investigated for achieving high-quality factors and strong electromagnetic field enhancements. Traditional approaches reported for tuning the performance of quasi-BIC metasurfaces include tuning the resonator size, period, and structure symmetry. Here we propose and experimentally demonstrate an alternative approach through engineering slots within a zigzag array of elliptical silicon resonators. Through analytical theory, three-dimensional electromagnetic modeling, and infrared spectroscopy, we systematically investigate the spectral responses and field distributions of the slotted metasurface in the mid-IR. Our results show that by introducing slots, the electric field intensity enhancement near the apex and the quality factor of the quasi-BIC resonance are increased by a factor of 2.1 and 3.3, respectively, in comparison to the metasurface without slots. Furthermore, the slotted metasurface also provides extra regions of electromagnetic enhancement and confinement, which holds enormous potential in particle trapping, sensing, and emission enhancement.

Thermal-optic tuning cascaded double ring optical sensor based on wavelength interrogation

Abstract: Based on the Vernier effect of the cascaded double ring resonator (CDRR) sensor, a sensor consisting of a microfluidic control system, a sensing ring, and a reference ring with a micro-heater for thermal tuning is proposed in this paper. In wavelength interrogation, a broadband spectrometer or a large tunable range laser is not required. The shift of the output spectrum caused by the refractive index change of the sample is converted into the change of the electric power by the thermal tuning heater. Due to the Vernier effect, the sensitivity of the sensor is 20 times higher than that of the single ring. The spectral envelope of the thermal-optic tuning of the sensor was fitted by a Gaussian function in the wavelength range of 8 nm. The experimental results showed that the sensitivity was 33.703 W/RIU, and the limit of detection was 1.34×10−5 RIU.

High Efficiency Wireless Power Transmission System That Uses HTS Transmitting and Copper Receiving Coils With a Large Difference in Quality Factor

Abstract: We developed an efficient wireless power transmission (WPT) system using a high-temperature superconductor (HTS) spiral coil with a high quality factor as the transmitting coil and a copper coil as the receiving coil. The HTS spiral coil was fabricated using double-sided HTS wire which we developed previously. The double-sided HTS wire consists of two conventional HTS coated conductor wires. The measured quality factor of the HTS spiral coil containing modified coil support was about 14 times higher than that of the copper coil. We designed the WPT system using the filter design theory. We measured the design parameters for a coupling coefficient and an external quality factor. We measured the power transmission efficiency (PTE) of the WPT in the facing direction, position misalignment, and angular misalignment. The PTE of the WPT system with the high quality factor HTS spiral coil showed significant improvements in all measurements compared to the system with copper coils.

A diamond-confined open microcavity featuring a high quality-factor and a small mode-volume

Abstract: With a highly coherent, optically addressable electron spin, the nitrogen-vacancy (NV) center in diamond is a promising candidate for a node in a quantum network. A resonant microcavity can boost the flux of coherent photons emerging from single NV centers. Here, we present an open Fabry–Pérot microcavity geometry containing a single-crystal diamond membrane, which operates in a regime where the vacuum electric field is strongly confined to the diamond membrane. There is a field anti-node at the diamond–air interface. Despite the presence of surface losses, a finesse of [Formula: see text] was observed. The quality ([Formula: see text]) factor for the lowest mode number is [Formula: see text]; the mode volume [Formula: see text] is estimated to be [Formula: see text], where [Formula: see text] is the free-space wavelength. We investigate the interplay between different loss mechanisms and the impact these loss channels have on the performance of the cavity. This analysis suggests that the surface waviness (roughness with a spatial frequency comparable to that of the microcavity mode) is the mechanism preventing the [Formula: see text] ratio from reaching even higher values. Finally, we apply the extracted cavity parameters to the NV center and calculate a predicted Purcell factor exceeding 150.

Bound states in the continuum in plasmonic metasurfaces

Abstract: Being inspired by the structure of butterfly wings, we design and demonstrate experimentally novel types of plasmonic metasurfaces supporting high-Q collective lattice resonances (Q~89) in the mid-IR region revealed by focused light beams with large apertures.

Mixed-Resolution High-Q Sensor Based on Hybridized Spoof Localized Surface Plasmons

Abstract: Spoof localized surface plasmons (LSPs) have proven significant advantages in sensing and detection. In this work, we propose a high-Q-factor and high-sensitivity hybridized spoof LSP sensor and a mixed-resolution algorithm. The sensor consists of two concentric inner and outer LSP structures with corrugated rings coupled to each other. The achieved Q-factor is up to 178, and the sensing figure of merit (FoM) is up to 30. Moreover, a mixed-resolution algorithm, combined with multiple resonant peaks, is proposed to enhance the Q-factor and sensing FoM. This algorithm doubles the Q-factor and sensing FoM effectively. This mixed-resolution sensor has a wide range of application prospects in the field of high-frequency on-chip resonators and sensors.

High-frequency traveling-wave phononic cavity with sub-micron wavelength

Abstract: Thin-film gallium nitride (GaN) as a proven piezoelectric material is a promising platform for the phononic integrated circuits, which hold great potential for scalable information processing processors. Here, an unsuspended traveling phononic resonator based on high-acoustic-index-contrast mechanism is realized in GaN-on-Sapphire with a frequency up to 5 GHz, which matches the typical superconducting qubit frequency. A sixfold increment in quality factor was found when temperature decreases from room temperature ($Q=5000$) to $7\,\mathrm{K}$ ($Q=30000$) and thus a frequency-quality factor product of $1.5\times10^{14}$ is obtained. Higher quality factors are available when the fabrication process is further optimized. Our system shows great potential in hybrid quantum devices via circuit quantum acoustodynamics.

Continuous-wave operation of electrically driven single mode microlaser

Abstract: Developing current-driven single-mode micro-/nanolasers is highly desirable for various practical applications, but still faces severe challenges. Herein, a continuous-wave operation of an electrically driven laser device using a Ga-incorporated n-type ZnO microwire, MgO nanofilm, and p-type GaAs substrate is demonstrated. The device can enable a single-mode lasing peaking at 820 nm and a narrow linewidth of about 0.4 nm, and the quality factor Q is evaluated to 2000. The presence of a distinct threshold, sharp linewidth reduction, and polarized coherent illumination provides conclusive evidence for achieving lasing oscillation. Relative polaritonic features are further proofed; thus, single-mode lasing feature should be ascribed to the exciton–polariton. The results can enable a workable avenue to realize near-infrared micro-/nanolaser diodes for high-efficiency coherent light sources, which are no longer limited by conventional narrow-bandgap semiconductors.

Quality factor control of mechanical resonators using variable phononic bandgap on periodic microstructures

Abstract: The quality factor (Q-factor) is an important parameter for mechanical resonant sensors, and the optimal values depend on its application. Therefore, Q-factor control is essential for microelectromechanical systems (MEMS). Conventional methods have some restrictions, such as additional and complicated equipment or nanoscale dimensions; thus, structural methods are one of the reasonable solutions for simplifying the system. In this study, we demonstrate Q-factor control using a variable phononic bandgap by changing the length of the periodic microstructure. For this, silicon microstructure is used because it has both periodicity and a spring structure. The bandgap change is experimentally confirmed by measuring the Q-factors of mechanical resonators with different resonant frequencies. The bandgap range varies depending on the extended structure length, followed by a change in the Q-factor value. In addition, the effects of the periodic structure on the Q-factor enhancement and the influence of stress on the structural length were evaluated. Although microstructures can improve the Q-factors irrespective of periodicity; the result of the periodic microstructure is found to be efficient. The proposed method is feasible as the novel Q-factor control technique has good compatibility with conventional MEMS.

Multiple toroidal dipole symmetry-protected bound states in the continuum in all-dielectric metasurfaces

Abstract: In nanophotonics, exciting multiple high quality factor (Q-factor) and high tunable Fano resonances is important for many applications. In this paper, an all-dielectric metasurface consists of Si layer and three Si rectangular bars with different widths and lengths is proposed. The triple high Q-factor and high tunable the quasi bound states in the continuum (quasi-BIC) modes with distinct Fano features can be achieved by breaking the C2 rotational symmetry of the unit cell. With adjusting the asymmetry parameter, the modulation depth, resonant frequency and linewidth of the sharp triple Fano resonances can be engineered, and the Q-factor can reach 107. In addition, the triple quasi-BIC are both mainly generated by the toroidal dipole oscillation through analyzing the result of electromagnetic distribution and the far-field scattering of Cartesian multipoles with asymmetric nanostructure. The proposed nanostructure has numerous potential applications on nonlinear optics, filters, and multi-channel biosensors.

Triple Mass Resonator for Electrostatic Quality Factor Tuning

Abstract: In this paper, a triple mass resonator (TMR) with a high capability to independently tune both resonant frequency and quality factor (Q-factor) is reported. An additive oscillating structure is designed into a conventional dual-mass resonator to control the modal shape. The theoretical studies revealed that the amplitude ratio between the outer masses, which mainly determine the Q-factor through the anchor loss, is sensitive to both suspension and inner springs because of mode coupling, while the resonant frequency is only sensitive to the suspension spring. Through this mechanism, the quality factor related to the anchor loss, $Q_{\mathrm {Anchor}}$ , can be adjusted by electrostatic tuning of the inner spring, while the resonant frequency keeps almost constant. On the other hand, the eigenfrequency could be significantly tuned by the electrostatic tuning of the suspension spring. The experimental results showed the Q-factor could be tuned as large as 19% by a DC bias of 15 V at the inner electrode, while the resonant frequency change was only as small as 162 ppm. In contrast, when the DC bias was applied to soften the suspension stiffness, the resonant frequency could be tuned as high as 7023 ppm with Q-factor change of 16%. [2021-0167]

Continuously tunable acoustic Fano resonance in side-coupled Helmholtz resonator array assisted by a surface phononic crystal

Abstract: Fano-like asymmetric line shape in a side-coupled series Helmholtz resonator array-waveguide system is continuously tuned by means of a one-dimensional surface phononic crystal, whose dispersion is exploited to adjust the phase factor appearing in indirectly coupled resonators. Finite-element method simulations reveal that the quality factor of the transmission spectrum can reach values on the order of 107, which can be finetuned by varying either waveguide width or phononic crystal groove depth. The Fano line shape dip, which appears around 25 kHz, red-shifts linearly with respect to the waveguide width at a rate of 308 Hz/mm. The quality factor exhibits a two order of magnitude drop for 0.01 mm waveguide width detuning from the optimal value. In comparison, three orders of magnitude decrease are observed for the same variation from the optimal value of the surface phononic crystal groove depth. Fano-like line shape is preserved when thermo-viscous losses are taken into account, where tunability with geometrical factors is still possible. Fine-tuning of either the dip frequency or quality factor can be utilized in demanding applications such as measurement of distance and concentrations of fluid mixtures with ultra high sensitivity.

High-Sensitivity Air-Coupled Megahertz-Frequency Ultrasound Detection Using On-Chip Microcavities

Abstract: Owing to their dual-resonance enhanced sensitivity, cavity optomechanical systems provide an ideal platform for ultrasound sensing. In this work, we realize high-sensitivity air-coupled ultrasound sensing from kilohertz to megahertz frequency range based on whispering gallery mode microcavities. Using a $57$-$\ensuremath{\mu}\mathrm{m}$-diameter microtoroid with high optical Q factor (approximately ${10}^{7}$) and mechanical Q factor (approximately $700$), we achieve sensitivities of $46\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{Pa}$ ${\mathrm{Hz}}^{\ensuremath{-}1/2}$--10 mPa ${\mathrm{Hz}}^{\ensuremath{-}1/2}$ in a frequency range of 0.25--3.2 MHz. Thermal-noise-limited sensitivity is realized around a mechanical resonance at 2.56 MHz, in a frequency range of 0.6 MHz. We also observe the second- and third-order mechanical sidebands, and quantitatively study the intensities of each mechanical sideband as a function of the mechanical displacement. Measuring the combination of signal-to-noise ratios at all sidebands has the potential to extend the dynamic range of ultrasound sensing.

Highly-twisted states of light from a high quality factor photonic crystal ring

Abstract: Abstract Twisted light with orbital angular momentum (OAM) has been extensively studied for applications in quantum and classical communications, microscopy, and optical micromanipulation. Ejecting high angular momentum states of a whispering gallery mode (WGM) microresonator through a grating-assisted mechanism provides a scalable, chip-integrated solution for OAM generation. However, demonstrated OAM microresonators have exhibited a much lower quality factor ( Q ) than conventional WGM resonators (by >100×), and an understanding of the limits on Q has been lacking. This is crucial given the importance of Q in enhancing light-matter interactions. Moreover, though high-OAM states are often desirable, the limits on what is achievable in a microresonator are not well understood. Here, we provide insight on these two questions, through understanding OAM from the perspective of mode coupling in a photonic crystal ring and linking it to coherent backscattering between counter-propagating WGMs. In addition to demonstrating high- Q (10 5 to 10 6 ), a high estimated upper bound on OAM ejection efficiency (up to 90%), and high-OAM number (up to l = 60), our empirical model is supported by experiments and provides a quantitative explanation for the behavior of Q and the upper bound of OAM ejection efficiency with l . The state-of-the-art performance and understanding of microresonator OAM generation opens opportunities for OAM applications using chip-integrated technologies.

Terahertz metasurface with multiple BICs/QBICs based on a split ring resonator.

Abstract: Bound state in the continuum (BIC) refers to the trapped state in the radiation continuum of a system. In the terahertz band, BIC provides a unique and feasible method to design devices with ultra-high quality factor (Q factor) and to achieve intense terahertz-matter interaction, which is of great value to terahertz science and technology. Here, multiple BICs protected by the resonance symmetry in the terahertz metasurface consisting of metallic split ring resonators (SRR) is demonstrated. The evolution from the BIC to the quasi-BIC (QBIC) is induced by changing the gap width of the SRRs. The proposed BICs are experimentally demonstrated and analyzed by the coupled mode theory along with the numerical simulation. It is found that the leakage behavior of these QBICs is strongly affected by the intrinsic Ohmic loss in the SRRs while it is quite robust to the tilted incidence.

Effect of Metallization on Fused Silica Dual-Shell Gyroscopes

Abstract: This paper reports the effect of metallization on performance of Fused Silica (FS) Micro-machined Hemispherical Resonator Gyroscopes (micro-HRGs). For capacitive detection of motion, a conductive coating of the sensing element is required, which results in a reduction of the mechanical quality factors as well as an introduction of the electrical resistance. We experimentally demonstrated the impact of metal coating on both the quality factor and the electrical resistance using a developed in-house FS Dual-Shell Gyroscope (DSG), a version of micro-HRG. We derived an electromechanical model, analytically predicted behavior, and experimentally confirmed the effect of electrical resistance on the motion detection sensitivity and the overall noise performance of the DSG. For the device under test, we identified an optimal thickness of Cr coating to achieve a low resistance for optimal noise performance with a minimal loss of the quality factor.

Fundamental Investigation of Subsurface Damage on the Quality Factor of Hemispherical Fused Silica Shell Resonator

Abstract: Hemispherical resonator gyroscope is an ultra-high precision and reliability solid-wave gyroscope. The quality factor (Q factor) is an important performance parameter of the resonator which is made of high purity fused silica. The subsurface damage (SSD) is generated due to brittle defects of fused silica during the grinding process. However, surface quality reduction caused by SSD significantly reduces the Q factor of the resonator. In this paper, the influence of SSD removal on the Q factor variation of the hemispherical fused silica resonator is investigated via the chemical etching method. The SSD depth of the hemispherical fused silica resonator fabricated by the precision grinding is measured. A device for Q factor measurement in high vacuum is built by employing the ring-down time method, which is composed of an impact exciter for excitation and a laser Doppler vibrometer for detection. The SSD is removed by chemical etching with several processing rounds. The Q factor and surface morphology of the resonator are evaluated after each round. The effect of residual subsurface damage depth on Q factor as etching processing is demonstrated. The experimental results indicated that the Q factor in the vacuum can be improved via chemical etching by 354% from the initial value of 1.84 × 105 into the final value of 8.36 × 105. The obtained results indicate that chemical etching can effectively remove the SSD on the subsurface of the fused silica resonator and significantly improve the Q factor.

Quality factor control of mechanical resonators using variable phononic bandgap on periodic microstructures

Abstract: The quality factor (Q-factor) is an important parameter for mechanical resonant sensors, and the optimal values depend on its application. Therefore, Q-factor control is essential for microelectromechanical systems (MEMS). Conventional methods have some restrictions, such as additional and complicated equipment or nanoscale dimensions; thus, structural methods are one of the reasonable solutions for simplifying the system. In this study, we demonstrate Q-factor control using a variable phononic bandgap by changing the length of the periodic microstructure. For this, silicon microstructure is used because it has both periodicity and a spring structure. The bandgap change is experimentally confirmed by measuring the Q-factors of mechanical resonators with different resonant frequencies. The bandgap range varies depending on the extended structure length, followed by a change in the Q-factor value. In addition, the effects of the periodic structure on the Q-factor enhancement and the influence of stress on the structural length were evaluated. Although microstructures can improve the Q-factors irrespective of periodicity; the result of the periodic microstructure is found to be efficient. The proposed method is feasible as the novel Q-factor control technique has good compatibility with conventional MEMS.

Unveiling the Enhancement of Spontaneous Emission at Exceptional Points

Abstract: Exceptional points (EPs), singularities of non-Hermitian physics where complex spectral resonances degenerate, are one of the most exotic features of nonequilibrium open systems with unique properties. For instance, the emission rate of quantum emitters placed near resonators with EPs is enhanced (compared to the free-space emission rate) by a factor that scales quadratically with the resonance quality factor. Here, we verify the theory of spontaneous emission at EPs by measuring photoluminescence from photonic-crystal slabs that are embedded with a high-quantum-yield active material. While our experimental results verify the theoretically predicted enhancement, it also highlights the practical limitations on the enhancement due to material loss. Our designed structures can be used in applications that require enhanced and controlled emission, such as quantum sensing and imaging.

Single-mode lasing in an AlGaInAs/InP dual-port square microresonator

Abstract: Mode selection is crucial to achieving stable single-mode lasing in microlasers. Here, we demonstrate experimentally a dual-port square microresonator for single-mode lasing with a side-mode-suppression ratio (SMSR) exceeding 40 dB. By connecting waveguides at two opposite vertices, the quality factor for the antisymmetric mode (ASM) is much higher than that of the symmetric mode (SM), enabling single-mode lasing. Furthermore, far-field interference patterns similar to Young's two-slit interference are observed. This microlaser is capable of providing two optical sources simultaneously for optical signal processing in high-density integrated photonic circuits.

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

Abstract: 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.

Scattering coefficients of superconducting microwave resonators. I. Transfer matrix approach

Abstract: We describe a unified classical approach for analyzing the scattering coefficients of superconducting microwave resonators with a variety of geometries. To fill the gap between experiment and theory, we also consider the influences of small circuit asymmetry and the finite length of the feedlines, and describe a procedure to correct their influences in typical experiments. We show that, similar to the transmission coefficient of a hanger-type resonator, the reflection coefficient of a necklace- or cross-type resonator also contains a so-called reference point that can be used to characterize the internal quality factor of the resonator. Our results provide a comprehensive understanding of superconducting microwave resonators from the design concepts to the characterization details.