high-Q Resonator Research Articles

Superbound state in photonic bandgap and its application to generate complete tunable SBS-EIT, SBS-EIR and SBS-Fano.

Bound states in continua (BICs) have high-quality factors that may approach infinity. However, the wide-band continua in BICs are noise to the bound states, limiting their applications. Therefore, this study designed fully controlled superbound state (SBS) modes in the bandgap with ultra-high-quality factors approaching infinity. The operating mechanism of the SBS is based on the interference of the fields of two phase-opposite dipole sources. Quasi-SBSs can be obtained by breaking the cavity symmetry. The SBSs can also be used to produce high-Q Fano resonance and electromagnetically-induced-reflection-like modes. The line shapes and the quality factor values of these modes could be controlled separately. Our findings provide useful guidelines for the design and manufacture of compact and high-performance sensors, nonlinear effects, and optical switches.

Toroidal dipole bound states in the continuum based on hybridization of surface lattice resonances.

Obtaining a high quality factor (Q factor) in applications based on metasurfaces is crucial for improving device performance. Therefore, bound states in the continuum (BICs) with ultra-high Q factors are expected to have many exciting applications in photonics. Breaking the structure symmetry has been viewed as an effective way of exciting quasi-bound states in the continuum (QBICs) and generating high-Q resonances. Among these, one exciting strategy is based on the hybridization of surface lattice resonances (SLRs). In this study, we investigated for the first time the Toroidal dipole bound states in the continuum (TD-BICs) based on the hybridization of Mie surface lattice resonances (SLRs) in an array. The unit cell of metasurface is made of a silicon nanorods dimer. The Q factor of QBICs can be precisely adjusted by changing the position of two nanorods, while the resonance wavelength remains quite stable against the change of position. Simultaneously, the far-field radiation and near-field distribution of the resonance are discussed. The results indicate that the toroidal dipole dominates this type of QBIC. Our results indicate that this quasi-BIC can be tuned by adjusting the size of the nanorods or the lattice period. Meanwhile, through the study of the shape variation, we found that this quasi-BIC exhibits excellent robustness, whether in the case of two symmetric or asymmetric nanoscale structures. This will also provide large fabrication tolerance for the fabrication of devices. Our research results will improve the mode analysis of surface lattice resonance hybridization, and may find promising applications in enhancing light-matter interaction, such as lasing, sensing, strong-coupling, and nonlinear harmonic generation.

A thermally controlled high-Q metasurface lens

Dynamic metasurface control is a promising yet challenging prospect for next generation optical components. Here, we design and characterize a thermally controllable metasurface lens, with a high-quality-factor (high-Q) resonance working as both the basis of the lensing behavior and method for efficient modulation. Our high-Q lens is constructed via a zone plate architecture comprised of alternating regions with and without resonant character. Non-resonant regions block transmission, while resonant regions—with measured Qs up to ∼1350—transmit only on resonance. By leveraging the thermo-optic effect, we dynamically control the spectral position of the high-Q resonance to achieve wavelength selectivity of the focusing behavior. Due to the sharp spectral linewidth and amplitude variation of the high-Q resonance, thermal tuning can further result in metasurface switching, where the lensing behavior is changed between on and off states. For a device utilizing only moderate Q-factors of ∼350, the resonance's FWHM can be shifted with temperature changes of only 50 °C, and the device can be fully switched off when operating at 100 °C. Our work provides an initial experimental demonstration of dynamic control of a local high-Q wavefront shaping metasurface.

High-Q Trampoline Resonators from Strained Crystalline InGaP for Integrated Free-Space Optomechanics.

Nanomechanical resonators realized from tensile-strained materials reach ultralow mechanical dissipation in the kHz to MHz frequency range. Tensile-strained crystalline materials that are compatible with epitaxial growth of heterostructures would thereby at the same time allow realizing monolithic free-space optomechanical devices, which benefit from stability, ultrasmall mode volumes, and scalability. In our work, we demonstrate nanomechanical string and trampoline resonators made from tensile-strained InGaP, which is a crystalline material that is epitaxially grown on an AlGaAs heterostructure. We characterize the mechanical properties of suspended InGaP nanostrings, such as anisotropic stress, yield strength, and intrinsic quality factor. We find that the latter degrades over time. We reach mechanical quality factors surpassing 107 at room temperature with a Q·f product as high as 7 × 1011Hz with trampoline-shaped resonators. The trampoline is patterned with a photonic crystal to engineer its out-of-plane reflectivity, desired for efficient signal transduction of mechanical motion to light.

Selectively exciting quasibound states in the continuum in open microwave resonators using dielectric scatters

Bound states in the continuum (BICs) are wave modes that remain in the continuous spectrum of radiating waves that carry energy; however, they remain perfectly localized and nonradiating. BICs, or embedded eigenmodes, exhibit high quality factors that have been observed in optical and acoustic waveguides, photonic structures, and other physical systems. However, there are limited means to manipulate these BICs in terms of the quality factor and their excitation. In this work, we show that quasi-BICs (QBICs) in open resonators can be tailored by introducing embedded scatters. Using microwave cavities and dielectric scatters as an example, QBICs are shown to be capable of being repeatedly manipulated by tuning the geometry of the structure and the specific locations of the dielectric scatters. Using coupled mode theory and numerical simulations, we demonstrate by altering dielectric and structural parameters that tuning the quality factor as well as selective excitation and suppressing of specific QBIC modes can be achieved. These results provide an alternative means to control BICs in open structures and may be beneficial to applications including sensors and high-Q resonators that need confined fields and selectivity in frequency.

A High-Sensitivity Magnetic Field Sensor Based on PDMS Flexible Resonator

High-sensitivity resonator magnetic sensing requires a significant magnetostrictive response, while the narrow linewidth mode of a high-Q resonator can provide a high-precision frequency resolution. Therefore, a polydimethylsiloxane (PDMS) flexible resonator with both a low Young’s modulus and high optical transmittance is an ideal platform for realizing high-sensitivity magnetic sensing. Based on the sandwich structure of the PDMS flexible resonator, the mechanism of the magnetic field sensitivity of the PDMS flexible resonator sandwich structure is studied, and the impact of changes in the refractive index and radius on the sensor device is analyzed. In order to optimize the sensitivity of the sensor, when an external magnetic field acts on the sandwich structure, the impacts of three aspects on the sensitivity of the sensor are simulated and analyzed: different coupling positions of PDMS flexible resonator, different radii, and PDMS mixing ratios. The trend of sensitivity change is obtained, and the physical explanation of the sensitivity trend is analyzed. By optimizing these three aspects, the magnetic field sensitivity is eventually calculated as 19.02 nm/mT. Based on the existing experimental conditions and the preparation technology of the PDMS flexible resonator, the measured magnetic field sensitivity is 4.23 nm/mT.

Integrated Reconfigurable Photon-Pair Source Based on High-Q Nonlinear Chalcogenide Glass Microring Resonators.

Chalcogenide glasses (ChGs) have recently emerged as enabling materials for building reconfigurable nanophotonic devices by employing their refractive index changes associated with photosensitive effects. In particular, the availability of low-loss thin-film ChGs and the realization of high-Q microresonators provide exciting opportunities for integrated photonics. So far, the ChG photonic devices are predominately operated in the classical optics regime. In this work, we present the realization on-chip bright photon-pair quantum light sources via spontaneous four-wave mixing in a high-Q microring resonator fabricated on the newly developed ChG Ge25Sb10S65 platform. The emission wavelength of the photon-pair source can be continuously tuned across a double-free spectral range in a reconfigurable manner. Our work serves as a starting point to fully unleash the potential of exploiting ChGs for developing reconfigurable integrated quantum photonic devices.

Morphology Engineering for High-Q Plasmonic Surface Lattice Resonances with Large Field Enhancement

Plasmonic surface lattice resonances (SLRs) have endowed plasmonic systems with unprecedently high quality (Q) factors, giving rise to great advantages for light–matter interactions and boosting the developments of nanolaser, photodetector, biosensor and so on. However, it still lacks exploration to develop a strategy for achieving large electric field enhancements (FEs) while maintaining high Q factors of SLRs. Here, we investigate and verify such a strategy by engineering morphologies of plasmonic lattice, in which the influences of geometrical shapes, cross-section areas and structural compositions of particles are investigated. Firstly, we found that the Q factor of a plasmonic SLR is inversely proportional to the square of the cross-section area of the cell particles in the studied cases. Secondly, larger FEs of SLRs appear when the separated cell particles support stronger FEs. By combining these effects of particle morphology, we achieve a plasmonic SLR with Q factor and FE up to 2100 and 592 times, respectively. Additionally, supported by the derived connections between the Q factors and FEs of SLRs and the properties of cell particles, the property optimizations of SLRs can be done by optimizing the separated particles, which are distinctly time-saving in simulations. These results provide a guideline for the design of high-performance optical nanocavities, and can benefit a variety of fields including biosensing, nonlinear optics and quantum information processing.

Machine learning-assisted high-accuracy and large dynamic range thermometer in high-Q microbubble resonators.

Whispering gallery mode (WGM) resonators provide an important platform for fine measurement thanks to their small size, high sensitivity, and fast response time. Nevertheless, traditional methods focus on tracking single-mode changes for measurement, and a great deal of information from other resonances is ignored and wasted. Here, we demonstrate that the proposed multimode sensing contains more Fisher information than single mode tracking and has great potential to achieve better performance. Based on a microbubble resonator, a temperature detection system has been built to systematically investigate the proposed multimode sensing method. After the multimode spectral signals are collected by the automated experimental setup, a machine learning algorithm is used to predict the unknown temperature by taking full advantage of multiple resonances. The results show the average error of 3.8 × 10-3°C within the range from 25.00°C to 40.00°C by employing a generalized regression neural network (GRNN). In addition, we have also discussed the influence of the consumed data resource on its predicted performance, such as the amount of training data and the case of different temperate ranges between the training and test data. With high accuracy and large dynamic range, this work paves the way for WGM resonator-based intelligent optical sensing.

Solitary high-Q resonance in a grating waveguide via parity symmetry breaking at mode crossing

A phenomenon of a solitary narrow high-Q resonance in a planar grating waveguide associated with a bound state in the continuum (BIC) is revealed analytically. BICs appear when dispersion curves of the leaking even-parity and non-leaking odd-parity infinite-grating eigenmodes intersect. These intersections engender a parity symmetry break of the leaking eigenmode, causing it to decouple from a spatial Fourier harmonic that is emitted out of the waveguide. As a result, the otherwise low-Q waveguide eigenmode, comprised of those two aforementioned and some other infinite-grating eigenmodes, acquires a very high quality factor in a narrow vicinity of the mode-crossing frequency. Implementation of such a mechanism can be instructive for designing BICs in other photonic crystals and structures.

Observation of terahertz transition from Fano resonances to bound states in the continuum.

Bound states in the continuum (BIC) in metamaterials have recently attracted attention for their promising applications in photonics. Here, we investigate the transition from Fano resonances to BIC, at terahertz (THz) frequencies, of a one-dimensional photonic crystal slab made of rectangular dielectric rods. Simulations performed by an analytical exact solution of the Maxwell equations showed that symmetry-protected, high-quality factor (Q), BIC emerge at normal incidence. For non-normal incidence, BIC couple with the freely propagating waves and appear in the scattering field as a Fano resonance. Simulations were verified by realizing the photonic crystal slab by 3D-printing technique. THz time-domain spectroscopy measurements as a function of the incidence angle matched the simulation to good accuracy and confirmed the evolution of Fano resonances to high-Q resonances typical of BIC. These results point out the design of highly sensitive and low-cost THz devices for sensing for a wide range of applications.

Single SiGe quantum dot emission deterministically enhanced in a high-Q photonic crystal resonator.

We report the resonantly enhanced radiative emission from a single SiGe quantum dot (QD), which is deterministically embedded into a bichromatic photonic crystal resonator (PhCR) at the position of its largest modal electric field by a scalable method. By optimizing our molecular beam epitaxy (MBE) growth technique, we were able to reduce the amount of Ge within the whole resonator to obtain an absolute minimum of exactly one QD, accurately positioned by lithographic methods relative to the PhCR, and an otherwise flat, a few monolayer thin, Ge wetting layer (WL). With this method, record quality (Q) factors for QD-loaded PhCRs up to Q ∼ 105 are achieved. A comparison with control PhCRs on samples containing a WL but no QDs is presented, as well as a detailed analysis of the dependence of the resonator-coupled emission on temperature, excitation intensity, and emission decay after pulsed excitation. Our findings undoubtedly confirm a single QD in the center of the resonator as a potentially novel photon source in the telecom spectral range.

High-Q guided-mode resonance of a crossed grating with near-flat dispersion

Guided-mode resonances in diffraction gratings are manifested as peaks (dips) in reflection (transmission) spectra. Resonances with smaller line widths, i.e., with higher Q-factors, ensure stronger light–matter interactions and are beneficial for field-dependent physical processes. However, these high-Q resonances often suffer from strong angular and spectral dispersions. We demonstrate that a class of resonant modes with extraordinarily weak dispersion and Q-factor ∼1000 can be excited in crossed gratings simultaneously with the modes with well-known linear dispersion. Furthermore, the polarization of the incoming light can be adjusted to engineer the dispersion of these modes, and strong to near-flat dispersion or vice versa can be achieved by switching between two mutually orthogonal linear polarization states. We introduce a semi-analytical model to explain the underlying physics behind these observations and perform full-wave numerical simulations and experiments to support our theoretical conjecture. The results presented here will benefit all applications that rely on resonances in free-space-coupled geometries.

Investigation of High-Q Lithium Niobate-Based Double Ring Resonator Used in RF Signal Modulation

In recent years, millimeter-wave communication has played a crucial role in satellite communication, 5G, and even 6G applications. The millimeter-wave electro-optic modulator is capable of receiving and processing millimeter-wave signals effectively. However, the large attenuation of millimeter waves in the air remains a primary limiting factor for their future applications. Therefore, finding a waveguide structure with a high quality factor (Q-factor) is critical for millimeter-wave electro-optic modulators. This manuscript presents the demonstration of a double ring modulator made of lithium niobate with the specific goal of modulating an RF signal at approximately 35 GHz. By optimizing the microring structure, the double ring resonator with high Q-factor is studied to obtain high sensitivity modulation of the RF signal. This manuscript employs the transfer matrix method to investigate the operational principles of the double ring structure and conducts simulations to explore the influence of structural parameters on its performance. Through a comparison with the traditional single ring structure, it is observed that the Q-factor of the double ring modulator can reach 7.05 × 108, which is two orders of magnitude greater than that of the single ring structure. Meanwhile, the electro-optical tunability of the double ring modulator is 6 pm/V with a bandwidth of 2.4 pm, which only needs 0.4 V driving voltage. The high Q double ring structure proposed in this study has potential applications not only in the field of communication but also as a promising candidate for a variety of chemical and biomedical sensing applications.

High-Q tunable Fano resonances in the curved waveguide resonator with mirrors with spatially variable reflectivity

High-Q Fano resonances are demonstrated, as well as effects similar to electromagnetically induced transparency arising in a curved Fabry-Perot waveguide resonator with variable-reflection mirrors. It is shown that these effects arise as a result of coupling the fundamental mode of the bent waveguide core with whispering gallery cladding modes. An influence of the main geometrical parameters of the resonator on the resonance features in its reflection and transmission spectra is studied. The results obtained can be used in the creation of new functional elements of photonics based on curved waveguides, in particular, highly sensitive portable refractometers for bio- and chemosensory systems, as well as optical sensors of mechanical effects.

High-Q Fano resonances in diamond nanopillars

We report on the optical behaviour of a nanostructured diamond surface on a glass substrate. The numerical model reveals that a simple geometrical pattern sustains Fano-like resonances with a Q-factor as high as 3.5 · 105 that can be excited by plane waves impinging normally on the surface. We show that the geometrical parameters of the nanopillars affect both the resonant frequency and the line shape. The nanostructured surface can be straightforwardly used as a refractive index sensor with high sensitivity and linearity. Our findings show that diamond-based meta-surfaces are a valuable nanophotonic platform to control light propagation at the nanoscale, enabling large field enhancement within the nanoresonators that can foster both linear and nonlinear effects.

High-Q chalcogenide racetrack resonators based on the multimode waveguide.

We propose and demonstrate a highquality (Q) factor racetrack resonator based on uniform multimode waveguides in high-index contrast chalcogenide glass film. Our design features two carefully designed multimode waveguide bends based on modified Euler curves, which enable a compact 180° bend and reduce the chip footprint. A multimode straight waveguide directional coupler is utilized to couple the fundamental mode without exciting higher-order modes in the racetrack. The fabricated micro-racetrack resonator shows a record-high intrinsic Q of 1.31×106 for selenide-based devices, with a relatively low waveguide propagation loss of only 0.38dB/cm. Our proposed design has potential applications in power-efficient nonlinear photonics.

Si-microring resonator with sidewall nanograting structures for high-Q resonance modes

Si-microring resonator with sidewall nanograting structures for high-Q resonance modes

Temperature-controlled optical switch metasurface with large local field enhancement based on FW-BIC

Introduction: Many researchers have explored the bound states in the continuum (BICs) as a particular bound wave state which can be used to achieve a very high Q-factor. High-Q factor devices, typically based on the bound states in the continuum (BICs), are well used in the fields of hypersensitive biochemical sensors, non-linear effects enhancement, plasmon lasers, and hi-performance filtering. However, symmetrical-protected BIC is difficult to achieve experimentally high-Q factor because it strongly depends on the geometry and can be destroyed by any slight disturbance in the potential well.Methods: Therefore, we proposed a parameter-adjusted Friedrich-Wintergen BIC based on the analysis model of time-coupled model theory, where the target system parameters can be tuned to achieve high-Q excitation.Results: Moreover, considering the tunability and flexibility of the components in various practical applications, we integrate active materials into metasurface arrays with the help of external stimuli to achieve modulation of high-Q resonances. Our results demonstrate that an optical resonator based on FW-BIC can modulate the BIC state by changing the intermediate gap.Discussion: The BIC state and the high-Q factor Fano resonance can be dynamically tuned by adding temperature-sensitive VO2 material.

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.