Fano Resonance Research Articles

Controlling MMIT, Fano resonance, and slow/fast light in a magnomechanical system with an optical parametric amplifier

We study the slow-fast light effect and multi-transparency induced by magnomechanical systems. The system incorporates two magnons, which are collective magnetic excitations, placed alongside a degenerate optical parametric amplifier (OPA) within a cavity. The interaction between phonons, magnons, and light inside the cavity leads to two phenomena: magnomechanically induced transparency (MMIT) and magnon-induced transparency (MIT). We show how an OPA alters the absorption and dispersion characteristics of the light spectrum. The observation of the Fano resonance through magnon-mechanical coupling with the degenerate OPA is discussed. Through tuning vibration interactions and the OPA, we achieve the improvement of slow light. We hope that our findings can pave the way for advancements in quantum information processing.

Fano resonance and exceptional point enhanced sensing in a grating coupled heterostructure

Fano resonance line shape performs ultrasensitive sensing characteristics as its ultrahigh quality factor. Here, we theoretically investigate the sensitivity and figure of merit (FOM) of a novel, to our knowledge, multilayered heterostructure as a sensor. The heterostructure is non-Hermitian and composed of one layer of gold grating, multilayer polyethylene, and polymethyl methacrylate. The rigorous coupled wave analysis method (RCWA) is used to investigate the reflection characteristics of the structure. Interference between the “dark mode,” excited by the grating, and the “bright mode,” excited by the central layers, produces Fano resonance in the forward reflection spectra. Adjustment on the structure parameters can reduce the valley value of the Fano peak to zero, giving rise to scattering exceptional points (EPs). At the wavelength of the EP, the ambient temperature and mechanical stress fluctuations will lift the reflection, available for sensing signal. The sensitivity is higher than that of the structure without Fano peaks and EPs. Moreover, we use the spectral shift for refractive index sensing with a FOM exceeding 200RIU−1.

High FOM Fano Resonance Refractive-Index Sensor Based on a Baffled MIM Waveguide Coupled with an Inverted L-Shaped Resonator

Abstract A baffled metal-insulator-metal (MIM) waveguide coupled with an L-shaped resonator was developed and a double Fano resonance was excited in the structure. Using the optimal parameters, the sensing characteristics of the structure in a gas environment were studied. The maximum sensitivity was 682 nm/RIU and the maximum figure of merit (FOM) was 7587. Based on this structure, the influence of the resonators on the transmittance characteristics was studied for four different placement ways. A triple Fano resonance was obtained by simply inverting the L-shaped resonator. In this state, the maximum sensitivity and FOM reached 945 nm/RIU and 1.04×105, respectively. Compared with the L-shaped resonator structure, the sensitivity and FOM of the inverted L-shaped resonator structure were significantly improved. This study provides a new concept for designing a refractive-index sensor with high sensitivity, high FOM , and multichannel sensing.

Sound Mitigation by Metamaterials With Low-Transmission Flat Band

Abstract Space-coiling acoustic metamaterials dominated by the Fano resonance are being widely exploited for simultaneous control of sound isolation and air ventilation, and they usually achieve complete sound mitigation at multiple isolated frequencies. Here, we theoretically discover and experimentally demonstrate the low-transmission flat-band phenomenon in channeling-type acoustic metamaterials. The metamaterial is constructed with coupled coiling and straight channels, both working in acoustic resonant states. An analytic coupled-mode model is established to capture the coupling interaction between resonant states supported by two channels. A critical coupling condition is derived from the model, which can lead to sextremely low sound transmission in a finite band rather than at isolated frequencies, as validated by both numerical simulations and experiments. We then demonstrate the generality of the flat-band behavior of low transmission by a systematic survey of the coupling of different order resonant modes. Finally, the flat-band effect is also found to exist in the extended model with the side-loaded coiling channel as verified experimentally.

Quasi‐Bound States in the Continuum on Dislocated Bilayer Metal Gratings for Spatiotemporal Vortex Pulse Generation

AbstractSpatiotemporal vortex pulses (STVPs) with transverse orbital angular momentum (OAM) have recently stimulated great interest, influencing wide disciplines from classical to quantum optics. However, generating sophisticated STVPs in high‐efficiency and compact systems remains a challenge. This work outlines an ultra‐compact metasurface approach to efficiently generate STVPs through the coupling of free‐space plane waves with a quasi‐bound state in the continuum (quasi‐BIC). The approach leverages external excitation of the quasi‐BIC at the Γ‐point by slightly dislocating two sub‐layer gratings to break the mirror symmetries. This operation converts the incident wave into a unidirectional surface mode and induces a Fano resonance, resulting in STVPs in the frequency‐momentum domain. The method is demonstrated experimentally with a meta‐grating to produce an electromagnetic (EM) STVP with a topological charge of l = −1 with high fidelity and use the set‐up to unravel the hitherto unexplored diffraction and dispersive properties of near‐field STVPs. The present work can be extended from the microwave to the visible light regime by simply scaling the metasurface, and allowing high‐order OAM generation through cascaded elements, thereby paving a robust way to build up ultra‐compact STVP multiplexing devices for future applications.

Anti-resonance in the systems of nonlinear oscillators

The anti-resonance phenomenon analogous to the Fano resonance in the classical system of two oscillators with nonlinearity is observed. The focus of the work is on the effects of nonlinearity in the system. The explicit form of the solution for the full nonlinear problem is obtained for the arbitrary type of the nonlinearity and in a wide range of the parameters. The results of the analytical study show very good agreement with the data of the direct numerical simulations. The peculiarities resulted from the multiplicity of the solutions are discussed. The paper was presented at PhysCon2024.

Goos-Hänchen shifts around Fano resonances in superconducting photonic crystals embedded with graphene

Lateral Goos-Hänchen (GH) shifts at the Fano resonances are theoretically investigated in superconducting photonic crystals. The photonic system consists of superconductor layer pairs with embedded graphene and a dielectric layer. With an oblique incident light, multiple Fano resonances are realized in the transmission spectrum because of the embedded graphene. Large GH shifts of the reflected light, including positive (Δp) and negative (Δn) GH shifts, are obtained around the Fano resonances. The GH shifts almost keep stable for different chemical potentials of graphene. By decreasing hydrostatic pressure or incident angle, larger Δp and |Δn| are achieved and the corresponding frequency has a redshift. By increasing the ambient temperature, Δp and |Δn| first increase smoothly and then decrease sharply. Overall, Δp is more sensitive than Δn, while the reflectance corresponding to Δn is much larger than that corresponding to Δp. Large and tunable GH shifts in our study may have great potential for optical detectors and transducers.

Investigation of Machine Learning Algorithms and Plasmonic Waveguide-Based Fano Resonance Sensor for Diagnosis of Estrogen

Investigation of Machine Learning Algorithms and Plasmonic Waveguide-Based Fano Resonance Sensor for Diagnosis of Estrogen

Interferometric Near-field Fano Spectroscopy of Single Halide Perovskite Nanoparticles.

Semiconducting halide perovskite nanoparticles support Mie-type resonances that confine light on the nanoscale in localized modes with well-defined spatial field profiles yet unknown near-field dynamics. We introduce an interferometric scattering-type near-field microscopy technique to probe the local electric field dynamics at the surface of a single MAPbI3 nanoparticle. The amplitude and phase of the coherent light scattering from such modes are probed in a broad spectral range and with high spatial resolution. In the spectral domain, we uncover a Fano resonance with a 2π phase jump. In the near-field dynamics, this Fano resonance gives rise to a destructive interference dip after a few femtoseconds. Mie theory suggests that the interference between electric quadrupole and magnetic dipole modes of the particle, with spectra affected by resonant interband absorption of MAPbI3, lies at the origin of this effect. Our results open up a new approach for probing local near-field dynamics of single nanoparticles.

Elastic waves scattering by the schoty in microscopic system 2D

We investigate the scattering phenomenon at the non-uniform crystalline surface. Localized modes emerge in its vicinity due to the inhomogeneity-induced breakdown of translation symmetry. The phonon scattering mechanisms at the inhomogeneity are investigated by means of the Newton equation and matching approach. Numerical findings are presented across a wide range of scattering energies, together with the estimation of the transmission and reflection probabilities and the elastic wave average transmittance across the defect. This shows how the softening, homogeneity, and hardening characteristics of the perturbed defect vary in their scattering spectra. Fano resonances in the spectra are caused by the coherent coupling between the localized modes created by the defect and the propagating mode of the ideal waveguide. For a variety of values of the elastic constants in the bulk and inhomogeneous domain, a comprehensive explanation is given. The features of the system model and the stimulating dimensionless frequencies are used to calculate the conductance of the system.

Optimizing the chiral optical response in nanostructures using plasmonic Fano resonance

This study investigates the chiral enhancement effects of plasmonic Fano resonance modes in planar metallic nanostructures. The nanostructure consists of a central Z-shaped or 卍-shaped element surrounded by six clustered gold nanorods, focusing on the coupling between these doubly rotationally symmetric structures. This coupling induces plasmonic Fano resonance, which significantly enhances the chiral response. Under normal incidence of circularly polarized light, the maximum chiral response can reach up to 41%. Finite-difference time-domain simulation and multipole expansion analysis reveal the fundamental origin of this enhanced chiral response: the selective excitation of electric dipoles and toroidal dipoles in polarization. The study demonstrates that rotationally symmetric structures and coupling effects play a crucial role in modulating the chiral response of nanostructures.

Multiple Fano resonances in all-dielectric porous array structures

High Q metasurfaces play an important role in fields such as high-sensitivity sensing and nonlinear optics due to their strong localized electromagnetic field enhancement. Although ultra-high Q resonance has been developed in the field of optics, it is still a challenging task due to the loss of dielectric materials, design and fabrication of nanostructures. In this paper, we have designed an all-dielectric symmetric perforated array structure that supports multiple Fano resonances within the 0–1 THz range and realizes the anapole mode through this array perforation structure. By calculating the phase difference between different modes at the resonance frequencies, we explain the mechanism of the formation of resonance-coupled BIC. The Q-factors of the three modes have been calculated, where the highest Q-value can be up to 2703, it is excited by the MQ. Then, we analyzed the sensing performance and the highest sensitivity can reach 27,000 nm/RIU. Since the metasurface always maintains c_4v symmetry and mirror symmetry, all three resonances are polarization independent. The proposed metasurfaces can be applied to light-matter interactions, enhanced nonlinear response, and sensing.

Intertwined Fano resonances in sub-wavelength metallic gratings: omnidirectional and wideband optical transmission.

Metallic gratings can be used as infrared filters, but their performance is often limited by bandwidth restrictions due to metallic losses. In this work, we propose a metallic groove-slit-groove (GSG) structure that overcomes these limitations by exhibiting a large bandwidth, angularly independent, extraordinary optical transmission. Our design achieves high transmission efficiency in the longwave infrared range, driven by Fano-type resonances created through the interaction between the grooves and the central slit. This mechanism results in a tunable 2 µm transmission window with high rejection rate. We extend the concept to a two-dimensional GSG array, exhibiting a polarization-insensitive 80% transmission window for incident angles up to 50°, offering significant potential for infrared filtering applications.

Magnetic field sensor based on multiple Fano resonance in metal-insulator-metal waveguide coupled with cross-shape resonator

Abstract In this paper, an innovative plasmonic magnetic field sensor (MFS) that exploits a Metal-insulator-Metal (MIM) waveguide configuration with an asymmetric cross-shaped resonator is constructed. The design enables the observation of double Fano resonance in the transmission spectrum, resulting from the coupling between continuous spectrum and discrete spectrum. By incorporating magnetic fluid in the asymmetric cross-shape resonator, the Fano line shapes can be tuned by the external magnetic field. Finite-Difference Time-Domain (FDTD) is used to simulate the spectra response to external magnetic fields and geometrical sizes. The proposed structure exhibits remarkable magnetic field sensitivity of 12.1 p m / O e within the detection range of 15 O e to 199 O e . The resolution of MIM magnetic field sensors can reach 0.0826 O e . The optimal figure of merit (FOM) and maximum Q factor of the Fano dip are about 6.9 × 10 − 4 / O e and 66.74, respectively. Meanwhile, The proposed Fano resonance MFS has some advantages, including compact size, high sensitivity, and cost-effectiveness. A strong linear relationship between the magnetic field and resonance wavelength indicates that the proposed structure can find potential applications in diverse fields such as magnetic field sensors, aircraft navigation, and even nuclear energy generation.

Broadband surface enhanced infrared absorption with multiple Fano resonance by metallic oblique-wire-bundle metamaterial absorbers

Higher sensitivity with specific recognition of a sensor could ease the burden of sample purification or labelling procedure for specific testing and detection and there appear two methods including surface enhanced infrared absorption (SEIRA) and surface enhanced Raman scattering (SERS), promising better sensitivity and specificity, simultaneously, via detection of molecular footprints. Furthermore, researchers employ Fano resonance to further boost the detection limit of SEIRA by coupling between two absorption bands from molecules and metamaterials. Still, the current metamaterial absorbers are almost narrow band and require a specific design, only suitable for limited chemicals. Thus, in this work, we would like to design a broadband oblique-wire-bundle (OWB) metamaterial absorber (MA) which could interact with multiple functional groups’ absorption from a sample, thus easing the burden of custom-made resonators. In experiments, indeed, our designed OWB MA developed four Fano resonance responses with three PMMAs’ functional groups and one function group from carbon dioxide. The counterpart planar MA also performed SEIRA yet without occurrence of Fano resonance as a comparison. We believe this proposed OWB MA could facilitate the development of rapid detection in the field of food safety and chemical detection.

Photoconductance Induced by Excited-State Intramolecular Proton Transfer (ESIPT) in Single-Molecule Junctions.

Excited-state intramolecular Proton Transfer (ESIPT) molecules have been drawing considerable attention due to their unique photophysical properties and potential applications in optoelectronic devices. Although ground and excited-state tautomerism in various proton transfer systems associated with ESIPT has been extensively studied both experimentally and theoretically, the charge-transport characteristics of ESIPT molecules at the single-molecule level has been little investigated. In this work, scanning tunneling microscope-based fixed junction technique (STM-FJ) is employed with theoretical calculations to explore the electronic properties of SMe-PhOH (with ESIPT properties), together with its photoconductance induced by ESIPT photocycle processes under continuous light illumination (254/275/295/310nm). The conductance variation of SMe-PhOH with different UV wavelengths exhibits a continuous photoconductance distribution, which is highly consistent with the results of its UV-vis absorption spectrum. Theoretical calculations indicate that the interaction between localized HOMO and delocalized LUMO of SMe-PhOH K*-state gives rise to Fano resonance, thereby leading to enhanced conductance compared with its E-state. It reveals the microscopic mechanism of ESIPT process at the nanoscale and provides a constructive perspective for optimizing the photoresponsive properties of ESIPT-type molecules, as well as designing high-performance single-molecule devices.

Fully tunable Fano resonances in chiral electronic transport

Fully tunable Fano resonances in chiral electronic transport

Localized topological states beyond Fano resonances via counter-propagating wave mode conversion in piezoelectric microelectromechanical devices

A variety of scientific fields like proteomics and spintronics have created a new demand for on-chip devices capable of sensing parameters localized within a few tens of micrometers. Nano and microelectromechanical systems (NEMS/MEMS) are extensively employed for monitoring parameters that exert uniform forces over hundreds of micrometers or more, such as acceleration, pressure, and magnetic fields. However, they can show significantly degraded sensing performance when targeting more localized parameters, like the mass of a single cell. To address this challenge, we present a MEMS device that leverages the destructive interference of two topological radiofrequency (RF) counter-propagating wave modes along a piezoelectric Aluminum Scandium Nitride (AlScN) Su-Schrieffer-Heeger (SSH) interface. The reported MEMS device opens up opportunities for further purposes, including achieving more stable frequency sources for communication and timing applications.

Multi-scenario refractive index sensor based on merging BIC in an all-dielectric metasurface

In recent years, bound states in the continuum (BICs) in the all-dielectric metasurfaces have attracted considerable attention due to the low radiation loss and large quality factor (Q-factor). In this study, we design a highly sensitive refractive index sensor working in multi-scenario based on merging quasi-BIC in the silicon nitride metasurface. By adjusting the thickness of the metasurface and keeping the structural symmetry, nine BICs distributed in momentum space form the merging BIC at the Γ point with significantly enhanced Q-factor. The transmission spectra of the metasurface sensor disperse with the refractive index in multi-scenario. The modulation depth of the Fano resonance spectrum can exceed 99.9%. The sensitivity and figure of merit of the refractive index sensor based on the merging quasi-BIC can reach 41.35 nm/RIU and 13,389.1 RIU-1 for gas, 59.05 nm/RIU and 8,415.9 RIU-1 for blood, and 66.08 nm/RIU and 8,845.8 RIU-1 for cerebrospinal fluid, respectively. Furthermore, we investigate the influence of the structural deviations on the Q-factor, which of the merging quasi-BIC maintains higher than that of the isolated quasi-BIC. Our work offers a method for designing high-sensitivity sensors working in multi-scenarios, which may hold significant potential for enhancing device performance in gas and biological detection.

Extracting doubly excited state lifetimes in helium directly in the time domain with attosecond noncollinear four-wave-mixing spectroscopy

The helium atom, with one nucleus and two electrons, is a prototypical system to study quantum many-body dynamics. Doubly excited states, or quantum states in which both electrons are excited by one photon, showcase electronic-correlation mediated effects. In this paper, the natural lifetimes of the doubly excited 1Po2snp Rydberg series and the 1Se2p2 dark state in helium in the 60–65 eV region are measured directly in the time domain with extreme-ultraviolet/near-infrared noncollinear attosecond four-wave-mixing (FWM) spectroscopy. The measured lifetimes agree with lifetimes deduced from spectral linewidths and theoretical predictions, and the roles of specific decay mechanisms are considered. While complex spectral line shapes in the form of Fano resonances are common in absorption spectroscopy of autoionizing states, the background-free and thus homodyned character of noncollinear FWM results exclusively in Lorentzian spectral features in the absence of strong-field effects. The onset of strong-field effects that would affect the extraction of accurate natural lifetimes in helium by FWM is determined to be approximately 0.3 Rabi cycles. This study provides a systematic understanding of the FWM parameters necessary to enable accurate lifetime extractions, which can be utilized in more complex quantum systems in the future. Published by the American Physical Society 2024