High Quality Factor Research Articles

Dispersion-induced Q -factor enhancement in waveguide-coupled surface lattice resonances

Diffractively coupled nanoparticle arrays are promising candidates for helping to flatten many photonic devices such as lasers, lenses, and metrology instruments. Their performance, however, is directly linked with the size of the metasurfaces, limiting their applicability in nanophotonic applications. Here, we dramatically reduce array sizes of high-Q factor metasurfaces by utilizing strongly dispersive media. The effect is demonstrated by theoretically and numerically studying periodic arrays of plasmonic nanoparticles embedded inside Bragg-reflector waveguides. We demonstrate array dimensions reduction up to two orders of magnitude while still achieving ultrahigh-Q factors in excess of 104. Published by the American Physical Society 2024

On-chip deep subwavelength optomagnetic bistable memory based on inverse Faraday effect related nonlinearity in graphene waveguide ring resonators

Integrated optical devices that possess bistable characteristics are key elements for optical digital signal processing and all-optical computing. In this paper we report on an optomagnetic bistable memory based on the inverse Faraday effect related nonlinearity in graphene waveguide ring resonators. The effective magnetic field via the plasmon-induced inverse Faraday effect in the graphene resonator has two discrete stable states that represent logic one and logic zero and magnetic switching for memory operation can be achieved by injecting an optical pulse and momentarily blocking the bias input light. Our proposed optomagnetic bistable device based on a graphene magnetoplasmonic configuration has great potential for the development of next generation magnetic memory. It has benefits of ultrafast magnetization switching, simplicity of the considered structure, on-chip compatibility, and a deep subwavelength platform. It also enhances the nonlinear interaction due to strong confinement of the graphene plasmon modes and high-quality factor of traveling modes in the graphene ring resonator, and tunability and robustness by adjusting the gate voltages of the graphene sheets. These advantages will satisfy the demand for fast magnetization switching, low-energy consumption, and high-density recording required in future magnetic memories. Published by the American Physical Society 2024

Robust intrinsic chirality empowered by pair of off-Γ accidental BICs in triangular lattice metasurface

Abstract Optical chiral metasurfaces with high-quality factor enhance light-matter interactions. However, intrinsic chirality based on breaking the symmetry-protected BIC hardly reveals strong circular dichroism (CD) against structural perturbations. Here, we propose a design of the intrinsic chirality empowered by a pair of off-Γ accidental BICs and demonstrate a robust intrinsic chiroptical response continuously exhibiting strong and sign-controllable transmitted CD up to 0.98 and stable high-quality factors under a wide range of perturbations of geometrical parameters. A triangular lattice with slant T-shaped meta-atom is employed to break all mirror symmetries. The at-Γ quality factor of the chiral resonance is enhanced by four C points and maintains in the range of 105 to 106. Our work is beneficial for designing chiral metasurfaces with a strong intrinsic chirality.

Lithographically-defined cavities with high quality and purcell factors

Abstract We introduce and analyze a lithographically defined cavity (Li-cavity) incorporating a buried mesa defect in a planar vertical structure, which induces transverse photonic confinement while enabling compatibility with electrical injection. We systematically investigate the influence of key cavity parameters on optical behavior and fundamental properties using a comprehensive three-dimensional optical model. Our analysis reveals that the Li-cavity exhibits low optical scattering, resulting in high Q and Purcell factors, even at sub-wavelength dimensions. Furthermore, the Li-cavity supports single-mode operation within a broader aperture size range compared to conventional cavity designs, promising enhanced optical power of single-mode emission. Adequately designed structures demonstrate superior Q and Purcell factors at wavelength scale sizes,- outperforming conventional micropillar cavities. These improved properties and customizable device characteristics stem from a simple fabrication process that precisely controls the cavity size, shape, and optical mode. Superior characteristics, along with its adaptability to diverse materials, wavelengths, and photonic integration platforms, promise a broad range of applications and potential adaptation of this design to diverse photonic devices.

Open whispering gallery mode resonators.

There are some issues with traditional whispering gallery mode (WGM) resonators such as poor light extraction and a dense mode spectrum. In this paper, we introduce a solution to these limitations by proposing open WGM (OWGM) resonators that effectively reduce the mode density and enable directional radiation through a connected waveguide at the expense of some lowering in Q-factor. Numerical simulations of two-dimensional metallic and dielectric disk resonators with holes reveal a significant increase in intermode distance. The study also extends to three-dimensional dielectric OWGM resonators, demonstrating the formation of sparse spectra suitable for photonic applications. Additionally, the design of a cylindrical Bragg microresonator connected to a single-mode fiber via an optimized topology-based connector achieves near-unity transmission and efficient coupling. This approach enhances the development of new photonic devices, addressing the limitations of traditional high Q-factor WGM resonators and offering potential advancements in laser technology and optical communications.

SRPNet: stroke risk prediction based on two-level feature selection and deep fusion network

BackgroundStroke is one of the major chronic non-communicable diseases (NCDs) with high morbidity, disability and mortality. The key to preventing stroke lies in controlling risk factors. However, screening risk factors and quantifying stroke risk levels remain challenging.MethodsA novel prediction model for stroke risk based on two-level feature selection and deep fusion network (SRPNet) is proposed to solve the problem mentioned above. First, the two-level feature selection method is used to screen comprehensive features related to stroke risk, enabling accurate identification of significant risk factors while eliminating redundant information. Next, the deep fusion network integrating Transformer and fully connected neural network (FCN) is utilized to establish the risk prediction model SRPNet for stroke patients.ResultsWe evaluate the performance of the SRPNet using screening data from the China Stroke Data Center (CSDC), and further validate its effectiveness with census data on stroke collected in affiliated hospital of Jining Medical University. The experimental results demonstrate that the SRPNet model selects features closely related to stroke and achieves superior risk prediction performance over benchmark methods.ConclusionsSRPNet can rapidly identify high-quality stroke risk factors, improve the accuracy of stroke prediction, and provide a powerful tool for clinical diagnosis.

High Q-factor multi-Fano resonances in all-dielectric metasurface for high-performance optical switching and sensors

High Q-factor multi-Fano resonances in all-dielectric metasurface for high-performance optical switching and sensors

Whispering Gallery Mode Micro/Nanolasers for Intracellular Probing at Single Cell Resolution.

Intracellular probing at single cell resolution is key to revealing the heterogeneity of cells, learning new cell subtypes and functions, understanding the pathophysiology of disease, and ensuring precise diagnosis and treatment. Despite the best efforts, an enormous challenge remains due to the very small size, extremely low content, and dynamic microenvironment of a single cell. Whispering gallery mode (WGM) micro/nanolasers (active WGM) offer unique advantages of small mode volume, high quality factors, bright and low threshold laser emission, and narrow line width, particularly suitable for integration within a single cell. In this review, we provide a focused overview of WGM micro/nanolasers for intracellular probing. We deliver information on WGM micro/nanolaser concepts, sensing mechanism, and biocompatibility, as well as recent progress in intracellular probing applications mainly covering cellular-level sensing, molecular-level detection, and feasibility for cellular imaging. At the end, challenges and prospects of WGM micro/nanolasers for intracellular applications are discussed.

Coherent Acoustic Phonons in Plasmonic Nanoparticles: Elastic Properties and Dissipation at Low Temperatures.

We studied the frequency and quality factor of mechanical plasmonic nanoresonators as a function of temperature, ranging from ambient to 4 K. Our investigation focused on individual gold nanorods and nanodisks of various sizes. We observed that oscillation frequencies increase linearly as temperature decreases until saturation is reached at cryogenic temperatures. This behavior is explained by the temperature dependence of the elastic modulus, with a Debye temperature compatible with reported bulk values for gold. To describe the behavior of the quality factor, we developed a model considering the nanostructures as anelastic solids, identifying a dissipation peak around 150 K due to a thermally activated process, likely of the Niblett-Wilks mechanism type. Importantly, our findings suggest that external dissipation factors are more critical to improving quality factors than internal friction, which can be increased by modifying the nanoresonator's environment. Our results enable the future design of structures with high vibration frequencies and quality factors by effectively controlling external losses.

Multiple surface lattice resonances in symmetric nanocuboid dimer arrays

Abstract Surface lattice resonances based on nanoparticle arrays have significant characteristics such as localized field enhancement and high quality factor, and can be applied in fields such as optical sensors and lasers. In this work, we propose a symmetric Si/SiO2 nanocuboid dimer array that can generate and regulate two surface lattice resonances. One of the surface lattice resonances (named SLR1) is mainly due to the coupling between the electric dipole resonance of single Si/SiO2 nanocuboid dimers and the diffraction waves perpendicular to the applied electric field. Another surface lattice resonance (named SLR2) mainly originates from the coupling between the magnetic dipole resonance of single Si/SiO2 nanocuboid dimers and the diffraction waves parallel to the direction of the applied electric field. The research results indicate that the polarization direction of the incident field, the period of the array, the gap between the nanocuboids in the dimer, particle size, and the medium environment are all important for regulating the two surface lattice resonances. The sensing application of multiple surface lattice resonances is also investigated. The results show that under appropriate structural parameters, SLR1 can provide good stability for sensing applications, its sensitivity and figures of merit are 472 nm/RIU and 104, respectively. However, SLR2 is very weak or suppressed when the refractive index of the medium environment is greater than or equal to 1.2. This characteristic limits the application range of SLR2 in sensing. This work is of great significance for the design of micro-nano photonic devices based on multiple surface lattice resonances.

Chirality-controlled second-order nonlinear frequency conversion in lithium niobate film metasurfaces.

The high-quality factor resonant metasurfaces have extensive applications in enhancing nonlinear frequency conversion efficiency at the subwavelength scale. However, methods for actively modulating the frequency conversion process are limited. We design a chiral lithium niobate film metasurface and investigate the photonic spin as a new degree of freedom to dynamically control the second-order nonlinear frequency conversion, without reconfiguring the structure by using external stimuli. The chiral resonance with circular dichroism (CD) of 0.62 gives rise to a high nonlinear CD of 0.84 in second-harmonic generation efficiency. Interestingly, combining the chiral resonance and an achiral quasi-bound state in the continuum enables us to investigate the photonic-spin-controlled sum-frequency generation and the photon pair generation from the spontaneous parametric downconversion process. Owing to the ultrahigh quality factor exceeding 103 both for two resonances, the second-order nonlinear frequency conversion occurs at a wavelength region of 0.2 nm, suggesting good monochromaticity. Our work opens new, to our knowledge, avenues for practical implementation of dynamically controlled nonlinear optical devices and will find utility in holography, switchable light sources, and information processing.

Thermo-optic tuning of quasi bound state in continuum in lithium niobate thin film hetero-nanograting

Lithium niobate (LN) is difficult to etch precisely due to its stable physical and chemical properties. In recent years, more and more research has focused on etchless thin film lithium niobate (TFLN). Here, a one-dimensional SiO2 nanograting structure fabricated on lithium niobate on insulator (LNOI) platform is designed in this study. This nanograting can generate one-dimensional diffraction waves. Then quasi-bound state in the continuum (q-BIC) can be introduced by aligning with the waveguide mode supported by the TFLN, which can achieve a high-quality factor and strong field enhancement, thus improving the interaction between light and matter. Furthermore, we validate the polarization characteristics of the nanograting structure, and measure the thermo-optical tuning sensitivity of the device to be 26.67 pm/K. This finding opens up potential avenues for realizing multi-dimensional tunable and dynamic photonic devices.

High-Q terahertz chirality enhancement using elliptical hole metasurface

Circular dichroism (CD) technology has garnered significant attention due to its extensive applications in ultra-sensitive biosensing and spin-selective optical frequency conversion. However, existing terahertz chiral structures are constrained by linewidth, which limits their effectiveness in narrowband signal processing. In this study, we propose the notion of quasi-bound states in the continuum (quasi-BIC) within a planar elliptical hole all-silicon terahertz metasurface that exhibits broken mirror symmetry. This approach achieves a CD value as high as 0.97, with a linewidth below 0.5 GHz and a Quality (Q)-factor reaching up to 107 in the 1.3 THz to 1.55 THz band, thereby enabling ultra-narrowband terahertz chirality. This method significantly enhances the Q-factor of optical resonant systems, reduces linewidth, and achieves strong CD while addressing the trade-off between high Q-factor and high CD observed in existing structures. The theoretical foundations for achieving ultra-narrow linewidth are established through band structure calculations and far-field polarization analysis. Additionally, the Q-factor of quasi-BIC can be flexibly optimized through parameter tuning, rendering it more practical than perfect BIC in real-world applications. This study presents a novel solution for terahertz narrowband chirality and optical filters, potentially advancing technologies in related fields.© 2024 Optica Publishing Group under the terms of the Optica Publishing Group Open Access Publishing Agreement.

Magnetic force microscopy: High quality-factor two-pass mode.

Magnetic force microscopy (MFM) is a well-established technique in scanning probe microscopy that allows for the imaging of magnetic samples with a spatial resolution of tens of nm and stray fields down to the mT range. The spatial resolution and field sensitivity can be significantly improved by measuring in vacuum conditions. This improvement originates from the higher quality-factor (Q-factor) of the cantilever's oscillation in vacuum compared to ambient conditions. However, while high Q-factors are desirable as they directly enhance the magnetic measurement signal, they pose a challenge when performing standard MFM two-pass (lift) mode measurements. At high Q-factors, amplitude-based topography measurements become impossible, and the MFM phase response behaves non-linearly. Here, we present a modified two-pass mode implementation in a vacuum atomic force microscope that addresses these issues. By controlling the Q-factor in the first pass and using a phase-locked loop technique in the second pass, high Q-factor measurements in vacuum are enabled. Measuring the cantilever's frequency shift instead of the phase shift eliminates the issue of emerging nonlinearities. The improvements in MFM signal-to-noise ratio are demonstrated using a nano-patterned magnetic sample. The elimination of non-linear responses is highlighted through measurements performed on a well-characterized multilayer reference sample. Finally, we discuss a technique that avoids topography-induced artifacts by following the average sample slope. The newly developed, sensitive, and distortion-free high quality-factor two-pass mode has the potential to be widely implemented in commercial setups, facilitating high-resolution MFM measurements and advancing studies of modern magnetic materials.

Achieving low thermal conductivity and high quality factor in sextuple-doped TiS2

Transition-metal dichalcogenide TiS2 stands out as a sustainable candidate for room- and medium-temperature thermoelectric materials due to its affordability, non-toxicity, eco-friendly nature and use of non-critical elements. However, its light element compositional nature results in a large thermal conductivity, which is the main limitation of the thermoelectric performance of TiS2. Here, we report a multi-element doping strategy by incorporating equivalent (Se, Zr) elements and introducing higher-valence (Nb, Ta) and lower-valence (Y, La) elements in pairs to minimize its lattice thermal conductivity, κlat. The findings indicate a nearly 50% decrease in κlat across the entire temperature range, attributed to the presence of strong point-defect scattering after multi-element doping. Additionally, we observed a reduced dependency of κlat on temperature in multi-element doped TiS2, as point defects can effectively scatter phonons at room temperature. As a result, the multi-element doped TiS2 attained its highest ZT value of approximately 0.4 at 625 K. Incorporating higher-valence and lower-valence elements in pairs proves to be an effective method for decreasing lattice thermal conductivity without compromising too much of its large Seebeck coefficient.

Natural filter: Adjustable hydrophobicity from biodegradable zein nanofiber membrane for high efficiency air purification

Faced with the fact that air filtration materials prepared from traditional petroleum-based materials do not have good biodegradability and have the risk of causing secondary pollution to the environment, a kind of nanofiber membrane with biodegradable polylactic acid (PLA) and zein was prepared by electrospinning method. The morphology of as-prepared membrane was carried out along with filtration performance and degradation performance both experimentally and theoretically. The results showed that the hydrophobicity of nanofiber membrane can be adjusted by changing the ratio of PLA and zein. In addition, the highest filtration efficiency for PM2.5 and PM10 was achieved when the ratio of PLA to zein was 1:1, and it could be stabilized at 98.14 % and 97.39 %, and had the highest quality factor (QF) of 0.00738 Pa−1. Moreover, the fiber membrane has excellent adsorption effect on aqueous particles as well as oily particles. Notably, the as-prepared composite filter can be easily biodegraded thus contributing to green ecological environment.

A closed-loop sustainable method for the fabrication of electrospun nanofiber using food waste for filtration of particulate matters (PMs) and volatile organic matter (VOCs) from air

Indoor air pollution significantly impacts human health and the environment. Humans suffer the greatest health burden due to inefficient combustion technologies and polluted fuels. Therefore, air filtration is essential for a healthy and prosperous household. This study aims to develop a sustainable approach for the fabrication of biodegradable electrospun nanofibers (ENs) as air filters from food waste materials and offer a closed-loop circular solution and potential replacement for non-biodegradable HEPA air filters. We have tested banana peel extract (BPE), eggshell membrane, chitosan, and starch blended with polyvinyl alcohol (PVA) for fabricating ENs. Among the nanofibers investigated for air filtration application, BPE/PVA nanofiber shows the best performance in terms of maximum particulate matter (PM) removal efficiency and minimum pressure drop while incorporating > 50 % of the food waste into the electrospinning solution. Adding BPE into a 10 % PVA solution leads to a reduction in the hydrophilic behavior of the BPE/PVA nanofiber as compared to neat 10 % PVA ENs. The BPE/PVA nanofiber shows minimum pressure drop (156–160 Pa) and highest quality factor (Qf) in comparison with other waste-derived nanofibers with > 98 % filtration efficiency of PM2.5. Further, BPE/PVA nanofiber shows the highest adsorption of xylene vapor among other food waste derived nanofibers studied. Based on the above results, it can be concluded that BPE based nanofiber shows the best performance as air filter media among all other food waste-based ENs. The study demonstrates a successful regeneration and reuse of the BPE/PVA filter up to 3 cycles. The leftover material from banana peels after BPE extraction was utilized as a soil ameliorant. It showed 55 % soil water retention (SWR) capacity, making it possible to apply in arid regions or crops with high water requirements.

Characterization of temperature-dependent full-matrix constants of [001]c-poled Mn-doped 28PIN-43PMN-29PT single crystals using one sample

[001]c-poled Mn-doped xPb(In1/2Nb1/2)O3–(1–x–y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 (PIN–PMN–PT:Mn) single crystals (SCs) in the rhombohedral phase possess not only excellent piezoelectric properties but also a high mechanical quality factor, which make them suitable for fabricating high-performance piezoelectric devices. Characterizing the temperature dependence (TD) of full-matrix constants is indispensable for their use in device design. However, there is a significant lack of relevant data. In this study, the TD of the clamped dielectric properties of [001]c-poled 28PIN-43PMN-29PT:Mn SCs was characterized using a dielectric temperature spectroscopy measurement system from 0 to 60 °C. Their elastic and piezoelectric constants were measured using resonant ultrasound spectroscopy in the same temperature range. With an increase in the temperature, all the elastic stiffness constants decreased, whereas all the clamped dielectric constants and the absolute values of all the piezoelectric stress constants increased. The characterization process required only a single sample, which ensured the consistency of the results. Furthermore, the electrical impedance spectra of the sample at 30 and 50 °C were measured and compared with those simulated using the finite-element method with the characterization results. The close agreement between them confirmed the reliability of the characterization results.

Research on high-quality factor sensing characteristics of all-dielectric nanopore array metasurface based on POA-DELM

Abstract Based on the optical properties of symmetric structures independent of each other in the orthogonal direction, an all-dielectric nano-square hole array metasurface which is symmetric along the diagonal is proposed. By changing the size of square nanopores, the symmetry of the periodic unit structure is broken and the double Fano resonance can be excited. The influence of each structural parameter on the sensing performance of the metasurface is analyzed respectively. As the main structural parameters and performance index, the metasurface height and the lengths of the main and sub-diagonal square nanoholes are selected as the input parameters, and the figure of merit (FOM) value is used as the output value. Then the nonlinear mapping relationship between the input and the output is established through deep extreme learning machine (DELM). Different optimization algorithms are used to optimize the weighted FOM values globally. The four evaluation indicators including root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and model fit (R-squared, R2) are used to assess the training effectiveness of the model. It is shown that the indexes are 0.9986, 0.9725, 3.1612 and 0.9733 respectively, and the FOM values of the dual Fano resonance after pelican optimization algorithm ( POA ) optimization are as high as 9.88 × 103 and 1.28 × 105, which demonstrate the effectiveness of POA-DELM proposed in this paper.

High-Q triple-mode quasi-bound states in the continuum in an asymmetric dielectric metamaterial

Bound states in the continuum (BICs) in metamaterials have attracted much attention due to their high efficiency in field enhancing. In this paper, we numerically demonstrated the triple-mode symmetry-protected BICs (SP-BICs) in an all-dielectric microtube metamaterial. By moving the hollows transversely and longitudinally in microtubes, three SP-BICs are transformed into high quality-factor (Q-factor) quasi-BICs (q-BICs), which are supported by asymmetric magnetic toroidal dipole electric hexapolar resonances respectively. The maximum Q-factor of q-BICs enabled by asymmetric magnetic toroidal dipole reaches 67647. This high Q-factor triple-mode q-BICs in all-dielectric microtube metamaterial has great potential in the applications of sensing, laser generation, and nonlinear optics.