Resonance Line Shape Research Articles

A comprehensive study of non-Lorentzian resonant lineshapes in nested ring resonators for quantum and photonic applications

Microring resonators are pivotal in photonic and quantum technologies. Enhancing their versatility for various applications often involves integrating additional elements to modify their resonant lineshapes. In this regard, Nested Ring Resonators (NRRs) offer a novel approach to generate a variety of lineshapes without the need for supplementary components. The coupled resonant architecture of NRRs can induce phenomena such as Electromagnetically Induced Absorption, Electromagnetically Induced Transparency, Fano resonance, and double Fano resonance. This study comprehensively analyzes the different resonant lineshapes achievable with NRRs, highlighting their broad applicability. We identify the specific conditions required for each resonant phenomenon and closely examine their characteristics. The theoretical insights from our research enable the autonomous design and realization of various resonance lineshapes within an NRR, eliminating the need for additional components while maintaining device compactness for a wide range of practical applications.

Ultrahigh-[formula omitted] Fano resonance in a cavity-waveguide coupled system based on second-order topological photonic crystals with elliptical holes

We present a novel configuration of second-order topological photonic crystal (SOTPC) comprising interconnected dielectric material with elliptical air holes. Based on this SOTPC design, we construct a topological corner state (TCS) cavity and a topological edge state (TES) waveguide. Through the coupling of the TCS cavity with the TES waveguide, we establish a topological cavity-waveguide coupled system (TCWCS) that exhibits an ultrasharp asymmetric topological Fano resonance. Numerical simulations demonstrate that the proposed TCWCS achieves an exceptionally high quality factor exceeding 108, surpassing previously reported results by several orders of magnitude. Moreover, the refractive index sensing application implemented with TCWCS shows a sensitivity of 278 nm/RIU and a figure of merit surpassing 107 1/RIU. Notably, our simulations reveal that the lineshape and quality factor of the Fano resonance, as well as the index sensing performance in the TCWCS, are highly robust against structural defects. The demonstrated capabilities of the TCWCS open up avenues for further exploration and development in the field of topological photonics based on our proposed SOTPC.

Unveiling the Influence of Line Shape of Surface Plasmon Resonances on Exciton–Plasmon Strong Coupling

AbstractStrong coupling between surface plasmon resonance (SPR) modes and excitons holds great potential for many chemical and physical applications. However, a clear understanding on how far‐field spectral characteristics of SPR (linewidths and intensity) affect the coupling strength remains unclear because these parameters are difficult to be individually tuned. These spectral characteristics are associated with the damping rate and field enhancement that depend on the morphology of the plasmonic nanostructure. In this work, the influence of the SPR line shape on exciton‐plasmon coupling is systematically investigated by delicately tuning the linewidths and resonance intensities of the plasmonic arrays. It is found that the SPR modes with narrow linewidths or large intensity are favorable for the exciton–plasmon system to achieve strong coupling. The obtained clear relationships between the SPR line shape and coupling strength provide guidance for the design and optimization of exciton‐plasmon coupling systems, favoring the highly efficient manipulation of exciton polaritons and enabling specific applications driven by strong coupling.

Spin-torque ferromagnetic resonance based on current-induced impedance

Spin-torque ferromagnetic resonance (ST-FMR) has been widely used for measuring damping-like spin–orbit torques in magnetic bilayers. Typically, the ratio between the damping-like and field-like spin–orbit torques are extrapolated based on the ferromagnetic resonance line shapes. However, when the field-like spin–orbit torque is unknown, the line shape analysis may lead to errors in extrapolating the damping-like spin–orbit torque. Here, we propose a modified version of the ST-FMR that allows extrapolation of both damping-like and field-like torques independently. By introducing an alternating current to the sample, the RF impedance is modulated, allowing detection via the reflected microwave. We show that the extrapolated field-like and damping-like torques in Py/Pt samples are consistent with the technique measuring current-induced linewidth and resonance field change but have much better signal-to-noise ratio. Our proposed method paves a way for more accurate measurement of spin–orbit torques.

Explainable AI to Facilitate Understanding of Neural Network-Based Metabolite Profiling Using NMR Spectroscopy.

Neural networks (NNs) are emerging as a rapid and scalable method for quantifying metabolites directly from nuclear magnetic resonance (NMR) spectra, but the nonlinear nature of NNs precludes understanding of how a model makes predictions. This study implements an explainable artificial intelligence algorithm called integrated gradients (IG) to elucidate which regions of input spectra are the most important for the quantification of specific analytes. The approach is first validated in simulated mixture spectra of eight aqueous metabolites and then investigated in experimentally acquired lipid spectra of a reference standard mixture and a murine hepatic extract. The IG method revealed that, like a human spectroscopist, NNs recognize and quantify analytes based on an analyte's respective resonance line-shapes, amplitudes, and frequencies. NNs can compensate for peak overlap and prioritize specific resonances most important for concentration determination. Further, we show how modifying a NN training dataset can affect how a model makes decisions, and we provide examples of how this approach can be used to de-bug issues with model performance. Overall, results show that the IG technique facilitates a visual and quantitative understanding of how model inputs relate to model outputs, potentially making NNs a more attractive option for targeted and automated NMR-based metabolomics.

Electroweak precision measurements of a nearly-degenerate Z′-Z system

In this paper, we discuss the possibility to probe a nearly-degenerate Z′-Z system by analyzing the Z-lineshape at an electron-positron collider. Compared with the usual Z′ in the literature well separated with the standard model (SM) Z boson in mass, the nearly-degenerate Z′-Z mixing affects the observed effective “oblique parameters” \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widetilde{S}$$\\end{document}, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widetilde{T}$$\\end{document}, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\widetilde{U}$$\\end{document}, and the effective deviation of “number of neutrino species” \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta {\\widetilde{N}}_{\ u }$$\\end{document} in a more complicated way and cannot be simply computed perturbatively up to a particular order. Aiming at solving this problem, we write down a general simplified effective Lagrangian and enumerate some parameter spaces corresponding to some typical models, and suggest a method to extract the constraints by looking into the line-shape of the Z-like resonance at an electron-positron collider.

Use of rational approximations for phonon density of states in evaluation of neutron thermal scattering law

We propose and explore a new analytical formulation for evaluation of Thermal Scattering Law (TSL) using continuous phonon spectra for neutron inelastic scattering. It involves approximating Phonon Density of States (PDOS) in terms of rational approximations in energy transfer. Debye Waller coefficient calculated with these forms are in reasonable agreement with LEAPR calculated values. TSL can be expanded as a power series, each term of which can be integrated analytically. The method leads to TSL being a series of exponential cosine integrals which again have closed rational forms in energy transfer. Their shapes are analogous to asymmetric resonance line shapes and show maxima for certain values of energy transfer which could correspond to phonon emission or absorption. The series is shown to be convergent and easy to compute as it does not involve any numerical integration. The approach is applied to Beryllium metal and Graphite which have vastly different PDOS shapes, and is shown to be capable of giving most of the trends shown by TSL and cross section results from NJOY nuclear code processing system, even with smaller number of power series terms. Since TSL can be calculated for both negative and positive energy transfer with equal ease, one can easily check for the validity of the approximation obeying Principle of Detailed Balance (PDB). The results overall have shown promise of our formulation in making a case for rapid calculations of TSL and also for using the rational forms in energy transfer for analysis of experimental/calculated PDOS data.

Tunable Fano resonance in a one-dimensional photonic crystal containing a Weyl semimetal

Fano resonances are widely utilized in the design of low-power all-optical switches, optical sensors and nonlinear optical devices. Although various nanostructures support Fano resonances, the lack of mechanisms for linear tuning of Fano resonance has become a limitation. In this paper, we propose a heterostructure consisting of a single layer of Weyl semimetal (WSM) and a one-dimensional photonic crystal (1DPC). Owing to the interference between the discrete state supported by the single layer of WSM and the continuous states supported by the 1DPC, a Fano resonance occurs. Besides, both the position and the line shape of the Fano resonance can be tuned by the Fermi energy, the distance between two Wely cones, and the tilt parameter of the WSM, the number of periods of the 1DPC, and the incident angle. With the assistance of the Fano resonance, a large Goos-Hänchen shift can be achieved. This work may offer greater possibilities to explore the applications of Fano resonances, including high-performance sensors and narrowband filters.

Interference effects in gg → H → Zγ beyond leading order

The ATLAS and CMS collaborations at the LHC have recently announced evidence for the rare Higgs boson decay into a Z boson and a photon. We analyze the interference between the process gg→H→Zγ induced by loops of heavy particles, which is by far the dominant contribution to the signal, and the continuum gg→Zγ QCD background process mediated by light quark loops. This interference modifies the event yield, the resonance line-shape and the apparent mass of the Higgs boson. We calculate the radiative corrections to this interference beyond the leading-order approximation in perturbative QCD and find that, while differing numerically from the corresponding effects on the more studied gg→γγ signal, they are generally rather small. As such, they do not impact significantly the interpretation of the present measurements of the H→Zγ decay mode.

GaN/AlN bilayers for integrated photonics

III-Nitride semiconductors offer a versatile platform for integrated photonic circuits operating from the ultra-violet to the near-infrared spectral range. Either pure AlN or pure GaN waveguiding layers have usually been investigated so far. In this work, we report on the study of GaN/AlN bilayers epitaxially-grown on a sapphire substrate for photonic circuits. Quality factors up to 410,000 are demonstrated with microring resonators in the near-infrared spectral range. We emphasize the peculiar advantages of these bilayers for nonlinear photonics: GaN offers a larger nonlinear susceptibility as compared to AlN. More importantly, both materials exhibit nonlinear susceptibilities with opposite signs that can be advantageous for nonlinear conversion. Thick epitaxial III-nitride bilayers are associated with the occurrence of cracks in the epi-layers and multimode waveguide propagation. We show that the multimode character can lead to peculiar resonance line shapes with the capacity to control full transmission and reflection by phase engineering.

Controlling Dual Fano Resonance Lineshapes Based on an Indirectly Coupled Double-Nanobeam-Cavity Photonic Molecule

Controlling Dual Fano Resonance Lineshapes Based on an Indirectly Coupled Double-Nanobeam-Cavity Photonic Molecule

Nuclear induction line shape: Non-Markovian diffusion with boundaries.

The dynamics of viscoelastic fluids are governed by a memory function, essential yet challenging to compute, especially when diffusion faces boundary restrictions. We propose a computational method that captures memory effects by analyzing the time-correlation function of the pressure tensor, a viscosity indicator, through the Stokes-Einstein equation's analytic continuation into the Laplace domain. We integrate this equation with molecular dynamics simulations to derive necessary parameters. Our approach computes nuclear magnetic resonance (NMR) line shapes using a generalized diffusion coefficient, accounting for temperature and confinement geometry. This method directly links the memory function with thermal transport parameters, facilitating accurate NMR signal computation for non-Markovian fluids in confined geometries.

Full optimization of dynamic nuclear polarization on a 1 tesla benchtop polarizer with hyperpolarizing solids.

Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) provides the opportunity to dramatically increase the weak nuclear magnetic resonance (NMR) signal of liquid molecular targets using the high polarization of electron radicals. Unfortunately, the solution-state hyperpolarization can only be accessed once since freezing and melting of the hyperpolarized sample happen in an irreversible fashion. A way to expand the application horizon of dDNP can therefore be to find a recyclable DNP alternative. To pursue this ambitious goal, we recently introduced the concept of recyclable hyperpolarized flow (HypFlow) DNP where hyperpolarization happens in porous hyperpolarizing solids placed in a compact benchtop DNP polarizer at a magnetic field of 1 T and a temperature of 77 K. Here we aim to optimize the radical concentrations immobilized in hyperpolarizing solids with the objective of generating as much polarization as possible in a timeframe (<1 s) compatible with future recyclable DNP applications. To do so, the solid-state DNP enhancement factors, build-up rates and DNP spectra of different hyperpolarizing solids containing various nitroxide radical loadings (20-74 μmol cm-3) are compared against the DNP performance of varying nitroxide concentrations (10-100 mM) solvated in a glassy frozen solution. We demonstrate that in <1 s, polarization enhancement goes up to 56 and 102 with surface-bound and solvated radicals, respectively, under the optimized conditions. For the range of nitroxide concentrations used cross effect DNP seems to be the dominant mechanism under benchtop conditions. This was deduced from the electron paramagnetic resonance (EPR) lineshape of TEMPOL investigated using Q-band EPR measurements.

A Highly Sensitive Biosensing Method Using Differential Detection of Fano Resonance Lineshape

A Highly Sensitive Biosensing Method Using Differential Detection of Fano Resonance Lineshape

LC-Photo-CIDNP hyperpolarization of biomolecules bearing a quasi-isolated spin pair: Magnetic-Field dependence via a rapid-shuttling device

Liquid-state low-concentration photochemically induced dynamic nuclear polarization (LC-photo-CIDNP) is an emerging technology tailored to enhance the sensitivity of NMR spectroscopy via LED- or laser-mediated optical irradiation. LC-photo-CIDNP is particularly useful to detect solvent-exposed aromatic residues (Trp, Tyr), either in isolation or within polypeptides and proteins. This study investigates the magnetic-field dependence of the LC-photo-CIDNP of Trp-α-13C-β,β,2,4,5,6,7-d7, a Trp isotopolog bearing a quasi-isolated 1Hα-13Cαspin pair (QISP). We employed a new rapid-shuttling side-illumination field-cycling device that enables ultra-fast (90–120 ms) vertical movements of NMR samples within the bore of a superconducting magnet. Thus, LC-photo-CIDNP hyperpolarization occurs at low field, while hyperpolarized signals are detected at high field (700 MHz). Resonance lineshapes were excellent, and the effect of several fields (1.18–7.08 T range) on hyperpolarization efficiency could be readily explored. Remarkably, unprecedented LC-photo-CIDNP enhancements ε ≅ 1,200 were obtained at 50 MHz (1.18 T), suggesting exciting avenues to hypersensitive LED-enhanced NMR in liquids at low field.

Measurement accuracy in silicon photonic ring resonator thermometers: identifying and mitigating intrinsic impairments.

Silicon photonic ring resonator thermometers have been shown to provide temperature measurements with a 10 mK accuracy. In this work we identify and quantify the intrinsic on-chip impairments that may limit further improvement in temperature measurement accuracy. The impairments arise from optically induced changes in the waveguide effective index, and from back-reflections and scattering at defects and interfaces inside the ring cavity and along the path between light source and detector. These impairments are characterized for 220 × 500 nm Si waveguide rings by experimental measurement in a calibrated temperature bath and by phenomenological models of ring response. At different optical power levels both positive and negative light induced resonance shifts are observed. For a ring with L = 100 µm cavity length, the self-heating induced resonance red shift can alter the temperature reading by 200 mK at 1 mW incident power, while a small blue shift is observed below 100 µW. The effect of self-heating is shown to be effectively suppressed by choosing longer ring cavities. Scattering and back-reflections often produce split and distorted resonance line shapes. Although these distortions can vary with resonance order, they are almost completely invariant with temperature for a given resonance and do not lead to measurement errors in themselves. The effect of line shape distortions can largely be mitigated by tracking only selected resonance orders with negligible shape distortion, and by measuring the resonance minimum wavelength directly, rather than attempting to fit the entire resonance line shape. The results demonstrate the temperature error due to these impairments can be limited to below the 3 mK level through appropriate design choices and measurement procedures.

Switchable optical differentiator using Fano resonance metasurface

Optical differentiation plays a pivotal role in analog computing and image processing, owing to its faster operating speeds and lower power consumption. However, the conventional differentiator encounters a common issue of single and fixed functions due to the lack of effective dynamic modulation means. Here, we proposed a polarization-sensitive differentiator based on a Fano resonance metasurface. The interference between transmitted light and a quasi-guided mode induces Fano resonance, resulting in the leakage of high-frequency component of the p-wave. By adjusting the asymmetry and line width of the Fano resonance line shape, the metasurface can function as a Fourier spatial filter to achieve the differential of an incident beam. Additionally, the direction of the s- and p-wave can be controlled to realize multiple differential functions. We demonstrate the simulation of switchable differential between arbitrary one-dimensional (1D) direction and two-dimensional (2D) directions, with a numerical aperture up to 0.26. It is expected that this switchable optical differentiator will have broad applications in areas such as bioimaging and computer vision.

Fano resonance in a microring resonator with a micro-reflective unit

Fano resonance is considered to be a promising approach for integrated sensing. However, achieving and controlling Fano resonance lineshapes on ultra-compact chips remains a challenge. In this article, we propose a theoretic model based on the transfer matrix method (TMM) to quantitatively interpret the impact of a micro-reflective unit (MRU) etched in the straight waveguide of a microring resonator (MRR). Numerical calculations and FDTD simulations indicate that the size and position of the MRU can be used to control the Fano resonance lineshape. Since the MRU is etched in the coupling region, the reflection caused by the MRU will significantly enhance the intensity of the counter-clockwise (CCW) mode in the microring. When applied to a single nanoparticle sensing, clockwise (CW) and CCW modes will couple due to a single nanoparticles or rough cavity walls, resulting in a sharp shift and split of the Fano lineshape. The proposed model for single nanoparticle sensing is described by the scattering matrix, and the calculations show a well matches with FDTD simulations. The results show that the model proposed in this paper provides a new theoretical basis for controlling Fano resonance lineshape and presents a new approach for the integrated sensing of silicon photonic devices with high sensitivity.

Plasmonic Refractive Index Sensor Including Two Waveguides, Rings and Two Cavities with Teeth Connected on Fano Resonances

A plasmonic refractive index sensor based on a metal-insulator-metal (MIM) waveguide coupled with rings and two cavities and interconnected teeth is proposed and investigated numerically. Transfer (T), sensitivity (S) and Figure of Merit (FOM) were calculated and analysed via Finite Difference Time Domain method (FDTD). The simulation results show the generation of double Fano resonances in the system that the resonance line-shapes and the resonance wavelength can be adjusted by changing the geometry of the device. By optimizing the structure in the initial configuration, the maximum sensitivity of 2832 nm / RIU and FOM of 15.1 is achieved. Then we change the structure parameters and the number of resonators. In this case, the maximum sensitivity and FOM are 2083nm / RIU and 18.9 respectively. Therefore two detection points can be used for the refractive index sensor. Such a plasmonic sensor with simple and optimal framework could be suitable and practical for sensing systems and integrated optical circuits.

Microwave-induced intersubband scattering and magneto-oscillation phenomena in an inhomogeneous 2D electron gas on liquid helium

The theoretical description of microwave-induced intersubband scattering in a 2D electron gas exposed to a magnetic field on liquid helium with the inhomogeneous distribution of subband excitation energies is presented. We demonstrate that the alignment of the staircases of Landau levels in the ground and the first excited subbands differently affects the microwave resonant absorption and in-plane magnetoconductivity. In contrast with previously used models, the microwave excitation rate is shown to have a strong dependence on the magnetic field with sharp minima at the Landau level alignment points even in a heavily inhomogeneous 2D electron system. The inhomogeneous distribution of transverse-quantization eigenfrequencies changes the lineshape of the intersubband resonance and substantially broadens conductivity magneto-oscillations. These results explain unexpected experimental observations reported previously.