Angular dispersion suppression in deeply subwavelength phonon polariton bound states in the continuum metasurfaces

<sec>Refractive index sensors based on metal metasurfaces are commonly limited by their low quality factors due to significant Ohmic losses in the metal material. In contrast, sensors based on all-dielectric metasurfaces can overcome this disadvantage. Currently, all-dielectric metesurface sensors based on symmetry-protected bound states in the continuum (BIC) have aroused intense research interest due to their ability to achieve ultrahigh quality factors. Such a metasurface sensor is mainly based on single BIC and single form of symmetry breaking. There are few studies on metasurface sensors of multiple BICs and multiple forms of symmetry breaking. In additon, the refractive-index sensors commonly neglect the influence of temperature fluctuation and thus suffer the crosstalk between the refractive index and temperature of the environment.</sec><sec>In this work, an all-dielectric metasurface composed of a periodic array of asymmetric semicircular-cylinder pairs is designed and two quasi-bound states in the continuum (QBIC) with high quality factors are obtained. By choosing three different forms of symmetry breaking (two in-plane and one out-of-plane), two robust QBIC modes can be generated in the selected near-infrared frequency band, and their resonance wavelengths, quality factors and polarization dependences exhibit different characteristics. Full-wave simulation results show that by measuring the resonance wavelengths of the two QBICs (denoted by QBIC1 and QBIC2), two-parameter sensing of refractive index and temperature can be achieved, which then solves the problem of crosstalk between the refractive index and temperature of the environment in refractive-index sensing. The dependence of quality factor on asymmetric parameters follows an inverse quadratic relation for the two QBICs. By adjusting the asymmetric parameters, the quality factor can be theoretially increased to any value, so that the sensing performance can be improved and adjusted. For refractive-index sensing, the QBIC1 can achieve a sensitivity of 194.7 nm/RIU and a highest figure of merit (FOM) of 8197 (corresponding to a quality factor of 45829); the QBIC2 can achieve a sensitivity of 170 nm/RIU, and a highest FOM of 4970 (corresponding to a quality factor of 28097). For temperature sensing, the QBIC1 can achieve a sensitivity of 7.77 pm/℃, and the QBIC2 can achieve a sensitivity of 24 pm/℃.</sec>

Nonreciprocal devices are key technologies for modern photonic applications, and nonlinearly induced nonreciprocity based on metasurface platforms opens up the potential for compactness and miniaturization of such devices in free-space optical paths. In this work, a design of quasi-bound states in the continuum (QBICs) via scaled lattice constants is employed, featuring a plate-hole tetramer unit cell with single-step etching. Under normal incidence, QBICs exhibit polarization-insensitive excitation, with the scattering dominated by the combination term of magnetic dipoles, magnetic toroidal dipoles, electric quadrupoles as well as electric toroidal quadrupoles – rendering the vertical field distribution sensitive to parametric variations. Embedding Kerr nonlinearity yields nonreciprocal responses under upper and lower port excitation. The steep edges between peaks and valleys in the Fano-line-shaped transmission spectra facilitate balancing the nonreciprocal intensity range (NRIR) and isolation. The NRIR originates from electromagnetic asymmetry introduced by varying the substrate refractive index and can be flexibly tuned via structural parameters – validated by simulations of nonreciprocal responses with varying plate thickness alone. Additionally, Rabi splitting from varying hole depth induces abrupt electromagnetic asymmetry changes in the strong coupling region, offering a new NRIR tuning freedom. This design strategy provides fresh insights for nonreciprocal device research, with the structure holding promise for sensing and nonlinear applications.

As an emerging new material, graphene has aroused the great research interest. How to improve its absorption efficiency is one of the hot research topics. However, currently most of the studies concentrate in THz band or middle-to-far-infrared region: the research in the visible and near-infrared regions is rare, which greatly limits the applications of graphene in opto-electric fields. In order to improve the absorption efficiency of single-layered graphene in visible and near-infrared band and realize multi-channel optical absorption enhancement, we propose a hybrid structure consisting of graphene-metal grating-dielectric layer-metal substrate. The proposed structure can realize three-channel light absorption enhancement at wavelengths λ<sub>1</sub> = 0.553 μm, λ<sub>2</sub> = 0.769 μm, and λ<sub>3</sub> = 1.130 μm. The maximum absorption efficiency of graphene is 41%, which is 17.82 times that of single-layered graphene. The magnetic field distributions of the hybrid structure at three resonance wavelengths are calculated respectively. It can be found that for the resonance peak λ<sub>1</sub>, the energy of light field is distributed mainly on the surface of metal grating, which is the characteristic of surface plasmon polariton (SPP) resonance. Therefore, it can be judged that the enhancement of graphene absorption in this channel is due to the SPP resonance stimulated by metal grating. For the resonance peak λ<sub>2</sub>, the energy of the optical field is mainly confined into the metal grating groove, which is the remarkable resonance characteristic of the Fabry-Pérot (FP) cavity, it can be concluded that the enhancement of the optical absorption of graphene at the resonance peak λ<sub>2</sub> is due to the resonance of the FP cavity. When the resonance peak is λ<sub>3</sub>, the energy of the light field mainly concentrates on the upper and lower edges of the metal grating and permeates into the SiO<sub>2</sub> layer, and it can be observed that there are energy concentration points (reddish) at the left end and the right end of the metal grating edge, which is a typical magnetic polariton (MP) resonance feature. Therefore, the enhancement of absorption of graphene at the resonance peak λ<sub>3</sub> is caused by the MP resonance induced by the metal grating. We also analyze the absorption characteristic (resonance wavelength and absorption efficiency) dependence on structure parameters by using the finite-difference time-domain (FDTD) simulation. Our study reveals that by increasing grating width, all the three resonance wavelengths are red-shifted, and the absorption efficiency at λ<sub>2</sub> and λ<sub>3</sub> are both enhanced whereas the absorption efficiency at λ<sub>1</sub> almost keeps unchanged. By increasing dielectric layer thickness, λ<sub>2</sub> will be red-shifted and λ<sub>3</sub> will be blue-shifted, whereas the absorption efficiency at the three resonance wavelengths all remain constant. By increasing graphene chemical potential, none of the wavelengths of the three absorption peaks is shifted, and the absorption efficiency at λ<sub>3</sub> decreases. According to our findings, we optimize structure parameters and achieve the light absorption efficiency larger than 97% at the three channels simultaneously, which can make metamaterial absorbers.

This study proposes a tunable dual-band mid-infrared graphene-based one-dimensional photonic crystal absorber with strong surface phonon polaritons and Tamm phonon polariton coupling. We use an LC circuit, transfer matrices, and coupled harmonic oscillator models to theoretically analyze the different modes, and the theoretical results are consistent with the simulation results. The resonance wavelengths and absorption intensities of the coupled mode can be adjusted by the Fermi level and structure parameters. Moreover, because the perfect dual-band absorption peaks of the designed structure are sensitive to the air layer’s refractive index, we demonstrate the possibility of its application in the field of refractive index sensors and analyze its potential in the field of biomolecular layer sensors. The designed structure also has broad applications in absorbers, photodetectors, and energy harvesting devices due to the excellent performance of the tunable perfect absorption peaks.

The purpose of this research is to address a critical technology barrier to the deployment of next generation autonomous microsystems – the availability of efficient and reliable power sources. The vast majority of research on microsystems has been directed toward the development and miniaturization of sensors and other devices that enhance their intelligence, physical, and networking capabilities. However, the research into power generating and power storage technologies has not keep pace with this development. This research leveraged the capabilities of RIT’s NanoPower Research Laboratories (NPRL) in materials for advanced lithium ion batteries, nanostructured photovoltaics, and hybrid betavoltaics to develop reliable power sources for microsystems.

Recent optical time-resolved experiments on single supported nano-objects (gold nanodisks with various diameter over thickness ratios) have demonstrated a marked enhancement of their vibrational quality factors for specific nano-object morphologies, resulting from the near-suppression of radiative vibrational damping associated with the emission of acoustic waves in the nano-object environment. This paper clarifies the origin of this phenomenon, which is ascribed to the creation of a “quasi-bound state in the continuum” vibrational mode by radiative coupling between two nano-object modes whose frequencies become close for specific nano-object shapes. The symmetry breaking induced by the presence of a substrate, which limits nanodisk acoustic emission to a half-space, is shown to play an essential role in enabling such radiative coupling. The impact of the acoustic mismatch between the nano-object and the substrate is explored, and it is shown that a moderate acoustic mismatch can still enable the creation of near-localized vibrational modes with high radiative quality factors, while allowing radiative coupling effects to occur over a broad range of nano-object geometries. Although this paper focuses on the situation of a substrate-supported gold nanodisk, which has already been the object of experimental investigations, the effects that it describes are general and constitute a promising approach to enhance the vibrational quality factors of nano-objects.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTHigh-Q Optical Sensors for Chemical and Biological AnalysisMatthew S. Luchansky and Ryan C. Bailey*View Author Information Department of Chemistry, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States*E-mail: [email protected]. Address: 44 Roger Adams Lab 600 South Mathews Avenue, Urbana, IL, 61801. Phone: (217) 333-0676.Cite this: Anal. Chem. 2012, 84, 2, 793–821Publication Date (Web):November 23, 2011Publication History Published online23 November 2011Published inissue 17 January 2012https://pubs.acs.org/doi/10.1021/ac2029024https://doi.org/10.1021/ac2029024review-articleACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views6236Altmetric-Citations223LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Assays,Crystals,Nanoparticles,Quantum mechanics,Sensors Get e-Alerts

When developing methods for diagnosing pathologies and diseases in humans and animals using electronic noses, one of the important trends is the miniaturization of devices, while maintaining significant information for diagnostic purposes. A combination of several sorbents that have unique sorption features of volatile organic compounds (VOCs) on one transducer is a possible option for the miniaturization of sensors for gas analysis. This paper considers the principles of creating polycomposite coatings on the electrodes of piezoelectric quartz resonators, including the choice of sorbents for the formation of sensitive layers, determining the mass and geometry of the formation of sensitive layers in a polycomposite coating, as well as an algorithm for processing the output data of sensors to obtain maximum information about the qualitative and quantitative composition of the gas phase. A comparative analysis of the efficiency and kinetics of VOC vapor sorption by sensors with polycomposite coatings and a set of sensors with relevant single coatings has been carried out. Regression equations have been obtained to predict the molar-specific sensitivity of the microbalance of VOC vapors by a sensor with a polycomposite coating of three sorbents with an error of 5–15% based on the results of the microbalance of VOC vapors on single coatings. A method for creating “visual prints” of sensor signals with polycomposite coatings is shown, with results comparable to those from an array of sensors. The parameters Aij∑ are proposed for obtaining information on the qualitative composition of the gas phase when processing the output data of sensors with polycomposite coatings. A biochemical study of exhaled breath condensate (EBC) samples, a microbiological investigation of calf tracheal washes, and a clinical examination were conducted to assess the presence of bovine respiratory disease (BRD). An analysis of the gas phase over EBC samples with an array of sensors with polycomposite coatings was also carried out. The “visual prints” of the responses of sensors with polycomposite coatings and the results of the identification of VOCs in the gas phase over EBC samples were compared to the results of bacteriological studies of tracheal washes of the studied calves. A connection was found between the parameters Aij∑ of a group of sensors with polycomposite coatings and the biochemical parameters of biosamples. The adequacy of replacing an array of piezoelectric sensors with single coatings by the sensors with polycomposite coatings is shown.

This thesis will discuss and highlight the importance of the lattice mode in minimising the radiative losses and enhancing the quality factor in metamaterial resonances. The study of lattice modes has been done extensively in plasmonic arrays, and we would like to extend it into the field of terahertz metamaterials. It is particularly important to understand the role of lattices modes when they are coupled to the eigen-structural modes of the metamaterial systems that could be engineered to support, either uncoupled eigen-resonances or strongly coupled modes including Fano resonance at terahertz frequencies. Fano resonance is known for its asymmetric feature and high-quality factor that arises from breaking the symmetry of the constituent resonator in a unit cell. Subsequently, Fano resonance also known to be a consequence of a symmetry broken bound state in the continuum, which at low loss supports ultrahigh quality factors that are difficult to be measured. The lattice modes that are inherent in periodic structures play a pivotal role in mediating the coupling between constituent resonators and can also be utilized to resonantly couple to metamaterial resonance for quality factor enhancement. This mediative coupling is observed in an avoided crossing and can be modelled as two or more coupled oscillators. Likewise, resonant coupling with metamaterial resonance enhances the resonant fields with the help of the trapped surface fields of the lattice mode. Lattice mode coupling to narrow split resonances and Fano resonance was demonstrated and we achieved enhancement of quality factor up an order of magnitude. This proves that radiative losses can be further minimized through optimization of the lattice modes but still is significantly insufficient to achieve an ultrahigh quality factor known to quasi-bound state in the continuum. Quasi-bound state in the continuum known to be excited through structural symmetry breaking have piqued the interest of many, due to its ultrahigh quality factor resonant states. A new concept and model were developed to show that a subwavelength thin dielectric can be used to support and modulate such resonance in a symmetric and metallic split ring resonator. Additionally, we have shown that it could be used as an active ultrafast filter or a micro-fluidic sensor. The lattice mode could also directly excite and support a resonant mode and such modes requiring phase matching conditions, e.g. spoof surface plasmons and guided-mode resonances. These modes are very narrow and can be exploited for low loss application. Therefore, we hope that the lattice mode can be used as an optimising strategy for minimising the radiative loss in metamaterials and that the new proposed device could be used to support an active high quality resonance on any existing symmetric and metallic metamaterial. The development of low-loss THz devices is beneficial for the support of upcoming and future communication devices and technologies.

Wireless Body Area Networks (WBANs) are pivotal in health care and wearable technologies, enabling seamless communication between miniature sensors and devices on or within the human body. These biosensors capture critical physiological parameters, ranging from body temperature and blood oxygen levels to real-time electrocardiogram readings. However, WBANs face significant challenges during and after deployment, including energy conservation, security, reliability, and failure vulnerability. Sensor nodes, which are often battery-operated, expend considerable energy during sensing and transmission due to inherent spatiotemporal patterns in biomedical data streams. This paper provides a comprehensive survey of data-driven approaches that address these challenges, focusing on device placement and routing, sampling rate calibration, and the application of machine learning (ML) and statistical learning techniques to enhance network performance. Additionally, we validate three existing models (statistical, ML, and coding-based models) using two real datasets, namely the MIMIC clinical database and biomarkers collected from six subjects with a prototype biosensing device developed by our team. Our findings offer insights into strategies for optimizing energy efficiency while ensuring security and reliability in WBANs. We conclude by outlining future directions to leverage approaches to meet the evolving demands of healthcare applications.

We present IVN (In-Vivo Networking), a system that enables powering up and communicating with miniature sensors implanted or injected in deep tissues. IVN overcomes fundamental challenges which have prevented past systems from powering up miniature sensors beyond superficial depths. These challenges include the significant signal attenuation caused by bodily tissues and the miniature antennas of the implantable sensors. IVN's key contribution is a novel beamforming algorithm that can focus its energy toward an implantable device, despite its inability to estimate its channel or its location. We implement a multi-antenna prototype of IVN, and perform extensive evaluations via in-vitro, ex-vivo, and in-vivo tests in a pig. Our results demonstrate that it can power up and communicate with millimeter-sized sensors at over 10 cm depths in fluids, as well as battery-free tags placed in a central organ of a swine. The implications of our new beamforming technology extend beyond miniature implantables. In particular, our results demonstrate that IVN can power up off-the-shelf passive RFIDs at distances of 38 m, i.e., 7.6X larger than the operation range of the same RFIDs.

The miniaturization of magnetic sensors and storage devices down to the nano-scale leads to drastic changes in magnetic phenomena compared with the same devices with a larger size. Excited-nuclear-probe (radioactive probe) techniques are ideal for investigating these new magnetic nanostructures. By observing the magnetic hyperfine fields (and in some cases the electric-field-gradients (EFGs)) at the nuclei of radioactive probes, microscopic information about the magnetic environment of the probes is acquired. The magnetic hyperfine field is particularly sensitive to the s-spin polarization of the conduction electrons and to the orbital magnetic moment of the probe atom. Three methods of inserting radioactive probes into magnetic nanostructures are presented; neutron activation, recoil implantation and ‘soft-landing’, followed by descriptions of their application to selected examples. In some cases, these methods offer the simultaneous creation and observation of new magnetic materials at the atomic scale. This review focuses firstly on the induced magnetism in noble-metal spacer layers between either ferromagnetic (FM) or FM/antiferromagnetic (AFM) layers in a trilayer structure. Using the method of low-temperature nuclear orientation, the s-spin polarization of noble-metal probes was measured and was found to be very sensitive to the magnetic properties at both the FM and AFM interfaces. Secondly, the recoil implantation of radioactive Fe probes into rare-earth hosts and d-band alloys and subsequent measurement using time-differential perturbed angular distribution offer the possibility of controlling the chemical composition and number of nearest-neighbours. This method was used to prepare local 3d-magnetic clusters in a non-magnetic matrix and to observe their magnetic behaviour. Finally, non-magnetic radioactive probes were ‘soft-landed’ onto Ni surfaces and extremely lattice-expanded ultrathin Ni films. By measuring the magnetic hyperfine fields and EFGs at 111Cd probes using time-differential perturbed angular correlation (TDPAC), it was possible to distinguish the interaction of Cd probes located at various surface sites, i.e. atop terraces, within terraces, at steps and at corners. These experimental results are compared with the ground-state properties determined by ab initio density-functional theory.This article was invited by Professor S Washburn.

Quantum state engineering, the cornerstone of quantum photonic technologies, mainly relies on spontaneous parametric downconversion and four-wave mixing, where one or two pump photons spontaneously decay into a photon pair. Both of these nonlinear effects require momentum conservation for the participating photons, which strongly limits the versatility of the resulting quantum states. Nonlinear metasurfaces have subwavelength thickness and allow the relaxation of this constraint; when combined with resonances, they greatly expand the possibilities of quantum state engineering. Here, we generated entangled photons via spontaneous parametric downconversion in semiconductor metasurfaces with high-quality factor, quasi-bound state in the continuum resonances. By enhancing the quantum vacuum field, our metasurfaces boost the emission of nondegenerate entangled photons within multiple narrow resonance bands and over a wide spectral range. A single resonance or several resonances in the same sample, pumped at multiple wavelengths, can generate multifrequency quantum states, including cluster states. These features reveal metasurfaces as versatile sources of complex states for quantum information.

Ultranarrow and multiband perfect absorbers based on dual quasi-bound states in the continuum in near infrared

This paper presents the design and development of an optical pressure sensor based on a two-dimensional photonic crystal nanocavity, operating within the wavelength range of 1950.2-2091.4nm. The sensing mechanism is based on the linear relationship between the shift in resonance wavelength and the refractive index variation of the cavity induced by the external applied pressure. The refractive index variation is modeled using COMSOL Multiphysics, and the cavity design is thoroughly optimized by adjusting the size and number of air holes in and around the cavity to achieve a high-quality factor and enhanced sensitivity. The photonic band structure and sensing parameters are evaluated and analyzed using plane wave expansion and finite-difference time-domain techniques, respectively. The results indicate a red shift in the resonant wavelength with increasing pressure, achieving an extraordinary high-quality factor of 1.0443×106, and a pressure sensitivity of 20.17nm/GPa. Furthermore, the sensor exhibits a maximum refractive index sensitivity of 506.184nm/RIU, a high figure of merit of 2.4155×105RIU-1, and a low detection limit of 4.14×10-7RIU, collectively indicating excellent sensing performance. In addition, the sensor demonstrates stable operation in a wide temperature range (0°C-540°C), and a detailed investigation is conducted to evaluate the impact of fabrication-induced roughness on overall performance.