high-Q Resonator Research Articles

Wavelength-Tunable Narrow-Linewidth Laser Diode Based on Self-Injection Locking with a High-Q Lithium Niobate Microring Resonator.

We demonstrate a narrow linewidth 980 nm laser by self-injection locking of an electrically pumped distributed-feedback (DFB) laser diode to a high quality (Q) factor (>105) lithium niobate (LN) microring resonator. The lithium niobate microring resonator is fabricated by photolithography-assisted chemo-mechanical etching (PLACE) technique, and the Q factor of lithium niobate microring is measured as high as 6.91 × 105. The linewidth of the multimode 980 nm laser diode, which is ~2 nm measured from its output end, is narrowed down to 35 pm with a single-mode characteristic after coupling with the high-Q LN microring resonator. The output power of the narrow-linewidth microlaser is about 4.27 mW, and the wavelength tuning range reaches 2.57 nm. This work explores a hybrid integrated narrow linewidth 980 nm laser that has potential applications in high-efficient pump laser, optical tweezers, quantum information, as well as chip-based precision spectroscopy and metrology.

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.

Compact sub-hertz linewidth laser enabled by self-injection lock to a sub-milliliter FP cavity

A narrow linewidth laser (NLL) of high frequency stability and small form factor is essential to enable applications in long-range sensing, quantum information, and atomic clocks. Various high performance NLLs have been demonstrated by Pound-Drever-Hall (PDH) lock or self-injection lock (SIL) of a seed laser to a vacuum-stabilized Fabry-Perot (FP) cavity of ultrahigh quality (Q) factor. However, they are often complicated lab setups due to the sophisticated stabilizing system and locking electronics. Here we report a compact NLL of 67-mL volume, realized by SIL of a diode laser to a miniature FP cavity of 7.7 × 108 Q and 0.5-mL volume, bypassing table-size vacuum as well as thermal and vibration isolation. We characterized the NLL with a self-delayed heterodyne system, where the Lorentzian linewidth reaches 60 mHz and the integrated linewidth is ∼80 Hz. The frequency noise performance exceeds that of commercial NLLs and recently reported hybrid-integrated NLL realized by SIL to high-Q on-chip ring resonators. Our work marks a major step toward a field-deployable NLL of superior performance using an ultrahigh-Q FP cavity.

High-Q Nanophotonics over the Full Visible Spectrum Enabled by Hexagonal Boron Nitride Metasurfaces.

All-dielectric optical metasurfaces with high quality (Q) factors have been hampered by the lack of simultaneously lossless and high-refractive-index materials over the full visible spectrum. In fact, the use of low-refractive-index materials is unavoidable for extending the spectral coverage due to the inverse correlation between the bandgap energy (and therefore the optical losses) and the refractive index (n). However, for Mie resonant photonics, smaller refractive indicesare associated with reduced Q factors and low mode volume confinement. Here, symmetry-broken quasiboundstates in the continuum (qBICs) areleveragedto efficiently suppress radiation losses from the low-index (n≈2) van der Waals material hexagonal boron nitride (hBN), realizing metasurfaces with high-Q resonances over the complete visible spectrum. The rational use of low- and high-refractive-index materials as resonator components is analyzed and the insights are harnessed to experimentally demonstrate sharp qBIC resonances with Q factors above 300, spanning wavelengths between 400and 1000nm from a single hBN flake. Moreover, the enhanced electric near fields are utilized to demonstrate second-harmonic generation with enhancement factors above 102 . Theseresults provide a theoretical and experimental framework for the implementation of low-refractive-index materials as photonic media for metaoptics.

Bound states in the continuum in asymmetric one-dimensional photonic crystal systems guided by anisotropy.

Bound states in the continuum (BICs) have been widely observed in many symmetric geometries in the optical system during the last decade. Here, we consider a scenario in which the structure is designed asymmetrically with anisotropic birefringent material embedded in one-dimensional photonic crystals. This kind of new shape opens the possibility of obtaining symmetry-protected BICs (SP-BICs) and Friedrich-Wintgen BICs (FW-BICs) form in tunable anisotropy axis tilt. Interestingly, these BICs can be observed as high-Q resonances by variation of the system's parameters, such as the incident angle, which means the structure without being injected at Brewster's angle can also achieve BICs. Our findings might achieve active regulation and are easy to manufacture.

Extremely high-Q quasi-BICs induced by simultaneously broken out-of- and in-plane symmetries in dielectric metasurfaces of low-index materials

Generating high-Q resonances is a difficult task to realize with low-index materials as the building blocks of metasurfaces, despite of its significance. Up to date, various schemes for obtaining strong resonances with low-index materials have been reported, while the highest record of Q-factor still remains in the order of several thousands. This work shows that quasi-bound states in the continuum (quasi-BICs) with extremely high Q-factors in the orders of 105∼107 can be obtained in the low-index metasurfaces, taking lithium niobate (LN) metasurfaces supported by silica substrate as examples. In such metasurfaces, BICs with inversion symmetric distributions evolve to quasi-BICs with extremely high Q-factors by simultaneously breaking out-of- and in-plane symmetries due to multiple symmetry protectedness. Dramatically high enhancement of mode intensity in the order of 104∼106 due to the high Q-factor enables highly efficient nonlinear frequency conversion: the results based on the self-consistent approach show that the total efficiency of second-harmonic generation reaches around 9.4% for pump intensity of 0.5 W/cm2. As the first report on extremely high-Q quasi-BICs in low-index metasurfaces, the presented results pave the way towards broad applications for ultraviolet nanophotonics.

Biomarker detection using GST-based permittivity-asymmetric metasurface

Non-invasive detection of biomarkers can help in the early screening of lethal diseases, such as cancer and Alzheimer's. In this paper, we present a numerical study of a high-quality resonant permittivity-asymmetric metasurface that offers tunability in the mid-infrared range by employing the phase change property of Germanium Antimony Telluride, Ge3Sb2Te6 (GST326). In this approach, we used dissimilar materials of ellipse-shaped nanopillars, and shifted the nanopillars from their center positions to break the symmetry-protected bound state and generate a high-Q resonance sufficient for detecting trace amounts of analytes. The peak location of the resonance can be controlled by tuning the crystallization state of GST326 for broadband retrieval of analyte signatures. We performed a grid search to optimize the design parameters to obtain a tuning range that matches the absorption band of amide I and II groups. As a proof of concept, we demonstrate sensing of a thin protein layer using the proposed metasurface and we show how our structure is sensitive to the imaginary part of the analyte refractive index and how the permittivity-asymmetry resonance is robust against crystallization losses. We also propose a layout for a practical device that can be used for biomarker detection applications.

Magneto-optical detection of terahertz cavity magnon-polaritons in antiferromagnetic HoFeO3

An intense THz pulse excites a high-Q magnetic resonance mode in the antiferromagnetic insulator HoFeO3 by the THz Zeeman torque. By using magneto-optical detection and sweeping the temperature, we observed an anomalous beating in the magnon dynamics for certain temperatures. The beating originates from the formation of cavity magnon-polaritons upon the intersection of the antiferromagnetic resonance frequency with the frequencies of the Fabry–Pérot modes inside the etalon formed by the sample cavity in the weak coupling limit. The validity of this idea is demonstrated by simulations using Maxwell's equations. Furthermore, the observed beating pattern depends on the polarization of the probe pulse. This dependence can be reproduced in the simulations by considering an imaginary Verdet constant, which could be a result of an interplay between the magneto-optical Faraday effect and static linear birefringence.

Giant optical chirality in dielectric metasurfaces induced by toroidal dipole resonances.

Although toroidal dipole (TD) resonance is a highly localized mode with a high quality (Q) factor, in most chiral structures the TD resonance is much weaker than the electric or magnetic dipole resonances and contributes little to the chiral response. In this Letter, we theoretically propose a chiral all-dielectric TD metasurface that possesses giant optical chirality with a certain degree of incident-angle robustness induced by a strong TD resonance. Interestingly, the symmetry of the system can be broken simultaneously at oblique incidence to produce chiral quasi-bound states in the continuum. The nearly unchanged high-Q TD resonance within a certain range of incident angles can avoid the problem of a reduced image quality caused by the incident-angle sensitivity, as demonstrated by the polarization-multiplexed-field image displays. The giant chirality with a certain degree of incident-angle robustness induced by the TD mode would be useful in some applications, including high-quality optical imaging, high-performance asymmetric transmission, and sensing.

Dual-band tunable filter based on high-Q guided-mode resonance grating

A dual-band tunable filter with a 10.5 nm narrowband based on guided-mode resonance grating is demonstrated. The two filtering working bands around 1200 and 1550 nm can be switched by controlling the TE and TM polarization, respectively. And the Q factor as high as 146.7 at 1550 nm is experimentally realized by optimizing the grating parameters. At TE polarization, an asymmetrical line shape is obtained. In addition, the angle-dependent guided-mode resonance (GMR) effect is well studied in the designed GMR grating filter, in which the tunability and optical bistability based on the thermo-optic effect are first demonstrated.

Tunable optoelectronic oscillator based on a high-Q microring resonator

This paper proposes a tunable optoelectronic oscillator (OEO) by using a silicon nitride high-Q microring resonator (MRR) with a Q value of 4.36 × 105. Inserting the high-Q MRR into a phase-modulated link, an 8–38 GHz tunable microwave photonic filter (MPF) is realized with a 3-dB bandwidth of ∼610 MHz. Based on the tunable MPF, a tunable OEO is established. The frequency range of the OEO is 14.60 to 25.65 GHz, and the measured phase noise of the 25.65-GHz oscillation signal is -88 dBc/Hz@10 kHz.

Bound states in the continuum enabling ultra-narrowband perfect absorption

Resonant dielectric metasurfaces have been demonstrated to hold a great promise for manipulation of light-wave dispersion at the nanoscale due to their resonant photonic environment and high refractive index. However, the efficiency of devices based on dielectric nanostructures is usually limited by the quality (Q) factor of their resonant modes. The physics of the bound sates in the continuum (BICs) provide an elegant solution for control over the Q factor of resonant modes. Here, by engineering the substrate of Si-based metasurfaces, we demonstrate two eigenmodes that exhibit an intrinsic magnetic dipole (MD)character and have an infinite radiation lifetime. We reveal that they are characterized by in-plane and out-of-plane MD modes and respectively correspond to two groups of BICs, that is, Fabry–Pérot BICs and symmetry-protected BICs. Using temporal coupled-mode theory and numerical simulations, we show that these BIC modes can transform into high-Q quasi-BIC resonances with near-unity absorption under normal incidence through tuning structural parameters. Our work provides a promising route to use BIC-inspired metasurfaces for designing ultra-narrowband absorbers which can be used as absorption filters, photodetectors, and sensors.

Tuning magneto-electric coherent resonance with a deep-subwavelength localized spoof surface plasmonic structure.

It has been recently shown that an ultrathin corrugated spiral metal strip can simultaneously support electric and magnetic localized spoof plasmonic modes at lower frequencies. In this Letter, we report a mirror quasi-symmetrical corrugated spiral metal disk which can support coherent resonance of an orthogonal electric dipole and a magnetic dipole to achieve azimuthally symmetric unidirectional scattering. By tuning the geometric dimensions, reconfigurable magneto-electric (ME) coherent resonance enhancement is realized. Excellent agreement between numerical simulations and experimental results verifies the tunable ME coherent resonance phenomenon. Our finding could anticipate future sensitive and versatile functional devices based on high-Q coherent resonance from the microwave to the terahertz bands.

Plasmonic bound states in the continuum for unpolarized weak spatially coherent light

Plasmonic resonances empowered by bound states in the continuum (BICs) offer unprecedented opportunities to tailor light–matter interaction. However, excitation of high quality-factor ( Q -factor) quasi-BICs is often limited to collimated light at specific polarization and incident directions, rendering challenges for unpolarized focused light. The major hurdle is the lack of robustness against weak spatial coherence and poor polarization of incident light. Here, addressing this limitation, we demonstrate sharp resonances in symmetric plasmonic metasurfaces by exploiting BICs in the parameter space, offering ultraweak angular dispersion effect and polarization-independent performance. Specifically, a high- Q ( ≈ 71 ) resonance with near-perfect absorption ( > 90 % ) is obtained for the input of unpolarized focused light covering wide incident angles (from 0° to 30°). Also, giant electric and magnetic field enhancement simultaneously occurs in quasi-BICs. These results provide a way to achieve efficient near-field enhancement using focused light produced by high numerical aperture objectives.

High-Q multiple Fano resonances with near-unity modulation depth governed by nonradiative modes in all-dielectric terahertz metasurfaces.

Reducing radiative losses for a high quality factor resonance based on the concept of nonradiative states including anapole mode and bound states in the continuum mode has been attracting extensive attention. However, a high quality factor resonance is obtained at the expense of its modulation depth. Here, an asymmetric metasurfaces structure consisted of silicon double D-shaped resonator arrays that can support both an anapole mode and two bound states in the continuum modes in terahertz band is proposed, which has not only ultrahigh quality factor but also near-unity modulation depth. A resonance derived from anapole mode with stronger electromagnetic field enhancement and higher quality factor can be achieved by increasing the gap of resonator. Meanwhile, two Fano resonances governed by bound states in the continuum modes can be identified, and their quality factors can be easily tailored by controlling the asymmetry of resonator. Such an all-dielectric metasurfaces structure may give access to the development of the terahertz sensors, filters, and modulators.

Ultra-high-Q substrate-mode coupled resonances in complementary THz metamaterial.

Achieving high-Q resonances in the THz frequency range is significant for applications such as sensors, filters, and emitters. A promising approach for obtaining such resonances is by using metamaterials. However, high-Q resonances in THz metamaterials are usually limited by metallic radiation losses in the meta-atoms. In this Letter, we investigate both experimentally and numerically a complementary metallic disk-hole array (CMA) that uses the coupling between lattice resonances and Fabry-Pérot cavity resonances, and features in-substrate modes with experimentally obtained record breaking Q-factors of up to 750. To the best of our knowledge, this is the highest quality factor measured for free-space-coupled metallic metamaterial structure at THz frequencies.

Optical hydrogen sensing with high-Q guided-mode resonance of Al2O3/WO3/Pd nanostructure

Nanostructure based on a dielectric grating (Al2O3), gasochromic oxide (WO3) and catalyst (Pd) is proposed as a hydrogen sensor working at the room temperature. In the fabricated structure, the Pd catalyst film was as thin as 1 nm that allowed a significant decrease in the optical absorption. A high-Q guided-mode resonance was observed in a transmission spectrum at normal incidence and was utilized for hydrogen detection. The spectra were measured at 0–0.12% of hydrogen in a synthetic air (≈ 80% {text{N}}_{2} and 20% {text{O}}_{2}). The detection limit below 100 ppm of hydrogen was demonstrated. Hydrogen was detected in the presence of oxygen, which provides the sensor recovery but suppresses the sensor response. Sensor response was treated by the principal component analysis (PCA), which effectively performs noise averaging. Influence of temperature and humidity was measured and processed by PCA, and elimination of the humidity and temperature effects was performed. Square root dependence of the sensor response on the hydrogen concentration (Sievert’s law) was observed. Sensor calibration curve was built, and the sensor resolution of 40 ppm was found. Long term stability of the sensor was investigated. Particularly, it was shown that the sensor retains its functionality after 6 months and dozens of acts of response to gas.

Tunable high-Q resonance and abnormal phase-shift in P T-symmetric meta-molecules

We analyze the optical response of a parity-time ( P T ) symmetric diatomic meta-molecular array. We show that the P T symmetry can transform an initial dark antisymmetric mode of the diatomic meta-molecule into bright, featured by a high-Q peak in the scattering spectrum. The Q factor is tunable by managing the magnitudes of the gain and loss. Furthermore, around this high-Q resonance an abnormal phase-shift is obtained, which persists even at exceptional point. We also show that the effective dielectric constant of the P T -symmetric meta-molecular array can be modeled by an anomalous doubly-resonant Lorentz oscillator, which is different from that in electromagnetically induced transparency and Autler-Townes splitting. This study contributes to the advances of non-Hermitian optics and slow light.

High-Q resonances in terahertz all-silicon metasurface with imperforated air-hole array

High-Q resonances in terahertz all-silicon metasurface with imperforated air-hole array

Nonlinear Dynamics of the Primary Oscillation Circuit of a Mems Gyroscope Under the Action of Phase-locked Loop and Automatic Gain Control Systems

In this work, we study the dynamics of primary oscillations of a high-Q micromechanical resonator - a sensitive element of an RR-type MEMS gyroscope - under the action of various implementations of a phase-locked loop system operating in conjunction with an automatic gain control system for an electrostatic drive. The study of the dynamics of the object is carried out both numerically and analytically - using the averaging method. Conditions for the stability of a stationary regime in a linear approximation are obtained. The questions of accuracy of various methods of numerical solution of differential equations of the circuit of primary oscillations are considered. The influence of the mechanical nonlinearity of the resonator on the dynamics of the resonator and the control system has been studied. An implementation of a low-order PLL circuit that does not contain a double-frequency spurious signal at the output of the phase detector is proposed. The output characteristics of control systems (speed, capture bandwidth, etc.) are analyzed and qualitative conclusions are drawn about the features of the interaction between the dynamics of a mechanical oscillatory link and the PLL-ARC circuit.