Fano Resonance Research Articles

Enhanced detection limit in an exceptional surface-based fiber resonator by manipulating Fano interference.

An exceptional surface (ES) has advantages in improving sensing robustness and enhancing frequency splitting. Typically, the eigenvalue splitting must exceed the mode linewidth in order to be clearly visible in the spectrum, which limits the precision of the ES-based sensing structure. In this paper, a strategy for manipulating spectral line shape in an ES-based structure is experimentally realized. In addition, the limit of the minimum detectable displacement can be further reduced by monitoring the peak intensity of the Fano interference line shape. The demonstration of Fano interference in an ES-based system opens the way for a new class of ultrasensitive optical sensors.

Modular Assembly of Metamaterials Using Light Gradients.

This is a report on a pilot study that tests the feasibility of assembling photonic metamaterials (PMs) using light gradient forces. Following a strategy that works like modular construction, light gradient forces, produced by a tightly focused, 1D standing wave optical trap, time-multiplexed across a 2D lattice are used to assemble voxels consisting of prefabricated, monodispersed nanoparticles (NPs) with radii ranging from 30 to 500nm into 3D structures on a hydrogel scaffold. Hundreds of NPs can be manipulated concurrently into a complex heterogeneous voxel this way, and then the process can be repeated by stitching together voxels to form a metamaterial of any size, shape, and constituency although imperfectly. Imperfections introduce random phase shifts and amplitude variations that can have an adverse effect on the band structure. Regardless, PMs are created this way using two different dielectric NPs, polystyrene and rutile, and then the near-infrared performance for each is analyzed with angle-, wavelength-, and polarization-dependent reflection spectroscopy. The cross-polarized spectra show evidence of a resonance peak. Interestingly, whereas the line shape from the polystyrene array is symmetric, the rutile array is not, which may be indicative of Fano resonance. So, even with the structural defects, reflection spectroscopy reveals a resonance.

Double tunable Fano resonance based on a metal–insulator–metal waveguide with double coupled cavities and its application

A metal–insulator–metal (MIM) waveguide with a ring cavity (RC) and a half ring cavity (HRC) is proposed to realize the detection of two mediums simultaneously based on independently tunable double Fano resonances. Utilizing numerical simulation of the finite element method, the transmission characteristics and magnetic field distribution are investigated. The simulation findings indicate that the structure is capable of generating double Fano resonances, and the two Fano resonances are tuning independently. The maximum sensitivity and figure of merit (FOM) are 2385 nm/RIU (refractive index unit) and 31886RIU−1, respectively, and these values are achieved by changing the structural parameters and the refractive index of the insulator. Moreover, the sugar content in flavor and the concentration of ethanol solution can be detected at the same time, which indicates the high efficiency of the sensor. Therefore, these performances demonstrate that the tunable double Fano resonance based on a MIM waveguide is a hopeful method for chemical detection.

Fano resonances in tilted Weyl semimetals in an oscillating quantum well

Considering the low-energy model of tilted Weyl semimetal, we study the electronic transmission through a periodically driven quantum well, oriented in the transverse direction with respect to the tilt. We adopt the formalism of Floquet scattering theory and investigate the emergence of Fano resonances as an outcome of matching between the Floquet sidebands and quasi-bound states. The Fano resonance energy changes linearly with the tilt strength suggesting the fact that tilt-mediated part of quasi-bound states energies depends on the above factor. Given a value of momentum parallel (perpendicular) to the tilt, we find that the energy gap between two Fano resonances, appearing for two adjacent values of transverse (collinear) momentum with respect to the tilt direction, is insensitive (sensitive) to the change in the tilt strength. Such a coupled (decoupled) behavior of tilt strength and the collinear (transverse) momentum can be understood from the tilt-mediated and normal parts of the quasi-bound state energies inside the potential well. We vary the other tilt parameters and chirality of the Weyl points to conclusively verify the exact form of the tilt-mediated part of the quasi-bound state energy that is the same as the tilt term in the static dispersion. The tilt orientation can significantly alter the transport in terms of evolution of Fano resoance energy with tilt momentum. We analytically find the explicit form of the bound state energy that further supports all our numerical findings. Our work paves the way to probe the tilt-mediated part of quasi-bound state energy to understand the complex interplay between the tilt and Fano resonance.

Enhanced cation ordering, electron-spin-phonon interactions and Fano resonance in half-metallic Sr2FeMoO6 thin films

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials.

Optical terahertz metamaterial switch controlled via high-stability CsPbBr3 microcrystals.

Dynamic control of terahertz metamaterials using thin organic perovskite active layers has been extensively researched. However, the preparation of organic perovskite devices requires strict environmental conditions, and the devices are prone to hydrolysis in air, which reduces performance. Herein, we report an optical terahertz metamaterial switch controlled via hybridization with high-stability CsPbBr3 microcrystals prepared through precipitation from a water-dimethylformamide (DMF) mixed-solution. Under light excitation, a modulation factor of 24% was achieved based on the photoelectric and photothermal effects of the CsPbBr3 microcrystals. After exposure to air for four months, the modulation factor remained essentially unchanged, demonstrating the exceptional stability of the system generated. Following the integration of CsPbBr3 microcrystals with the metamaterial, a frequency-shift of its dipole resonance and switching of Fano resonance was achieved, providing a novel approach to dynamic control of terahertz waves.

Dynamically Tunable Half‐Ring Fano Resonator Based on Black Phosphorus

A tunable material black phosphorus (BP) terahertz (THz) half‐ring Fano resonator is proposed, exhibiting enhanced sensitivity, tunable frequency parameters, and the flexible sensing range. A half‐ring is positioned above the main channel, while a groove is excavated beneath it to produce the Fano resonance. The discrete mode of the half‐ring is coupled with the continuous mode of the groove, leading to a significantly enhanced sensitivity. This sensor can pick up subtle changes in the surrounding environment. Additionally, the incorporation of BP into the half‐ring positioned above the channel enables the flexible adjustment of the Fano resonator's resonant frequency. This adjustment is achieved through the manipulation of the electron doping concentration of the BP material. At the third‐order resonance around 5.81 THz, the frequency shift margin can reach 160 GHz. Adjusting the structural parameters of the Fano resonator, such as the radius of its outer ring, the distance of this ring to the main channel, and the groove's height, significantly affects its transmission spectrum. The Fano resonator demonstrates its considerable potential for applications in the field of integrated electronics. It not only provides an innovative design perspective, but also lays the foundation for the study of THz systems.

Combined acoustic metamaterial design based on multi-channel Fano resonance effect

In response to the increasing traffic noise problem, we designed a combined acoustic metamaterial (CAM) based on the multi-channel Fano resonance principle. By utilizing the Fano resonance coupling between the acoustic spiral structure and the hollow structure, efficient sound insulation under effective ventilation conditions is achieved. Simulation results of acoustic transmission loss show that the acoustic transmission loss of CAM is more than 13 dB in the frequency band of 520–989 Hz. The broadband sound insulation characteristic can block the oblique angle incident sound waves from different angles. Simulation results of the elastic strain energy and acoustic pressure field validate the sound insulation mechanism of the Fano resonance of the combined acoustic metamaterial. The experimental results in the impedance tube generally agree with the simulation results. To explore the possibility of wider engineering applications of CAM, we propose a combined CAM and CAM0.7 structure. The results show that a series structure of acoustic metamaterials can be selected to further realize broadband sound insulation within 500–1574 Hz.

Frequency‐Space Selective Fano Resonance Based on a Micro‐Ring Resonator on Lithium Niobate on Insulator

AbstractCorresponding to the different phase‐shifts of the interference modes, the whispering gallery mode resonator‐based Fano resonance exhibits a variety of unique spectral lineshapes that can be applied to sensing, optical signal processing, and so on. However, most approaches to lineshape tuning aim to alter the propagation phase‐shift or coupling strength, and generally suffer from relatively low efficiency and limited tuning range. In this paper, with a carefully designed waveguide‐taper coupled micro‐ring resonator structure and the assistance with the grating‐coupler, for the first time a near full‐lineshape selectivity of the Fano resonance is demonstrated in two isolated tuning dimensions of the frequency and transverse space, which means arbitrary lineshapes including the Lorentzian‐dip, asymmetric Fano peak or electromagnetically‐induced‐transparency (EIT)‐like peak can be obtained at a specific resonance wavelength in the whole C‐band. In addition to the different types of line shapes, the extinction ratio can also be enhanced by dynamically tuning the coupling position. This research provides an efficient approach to manipulate the transmission spectra of the Fano resonance, which is of great importance in promoting its further applications on integrated photonics platforms.

Excitation of Multiple Fano Resonances in a Plasmonic Device and Carcinoma Detection

Excitation of Multiple Fano Resonances in a Plasmonic Device and Carcinoma Detection

High-Q magnetic toroidal dipole resonance in all-dielectric metasurfaces

High quality (Q) factor toroidal dipole (TD) resonances have played an increasingly important role in enhancing light–matter interactions. Interestingly, TDs share a similar far-field distribution as the conventional electric/magnetic dipoles but have distinct near-field profiles from them. While most reported works focused on the electric TD, magnetic TDs (MTDs), particularly high-Q MTD, have not been fully explored yet. Here, we successfully realized a high-Q MTD by effectively harnessing the ultrahigh Q-factor guided mode resonances supported in an all-dielectric metasurface, that is, changing the interspacing between silicon nanobar dimers. Other salient properties include the stable resonance wavelength but a precisely tailored Q-factor by interspacing distance. A multipole decomposition analysis indicates that this mode is dominated by the MTD, where the electric fields are mainly confined within the dielectric nanostructures, while the induced magnetic dipole loops are connected head-to-tail. Finally, we experimentally demonstrated such high-Q MTD resonance by fabricating a series of silicon metasurfaces and measuring their transmission spectra. The MTD resonance is characterized by a sharp Fano resonance in the transmission spectrum. The maximum measured Q-factor is up to 5079. Our results provide useful guidance for realizing high-Q MTD and may find exciting applications in boosting light–matter interactions.

Phenomenology of Intermediate Molecular Dynamics at Metal-Oxide Interfaces.

Reaction intermediates buried within a solid-liquid interface are difficult targets for physiochemical measurements. They are inherently molecular and locally dynamic, while their surroundings are extended by a periodic lattice on one side and the solvent dielectric on the other. Challenges compound on a metal-oxide surface of varied sites and especially so at its aqueous interface of many prominent reactions. Recently, phenomenological theory coupled with optical spectroscopy has become a more prominent tool for isolating the intermediates and their molecular dynamics. The following article reviews three examples of the SrTiO3-aqueous interface subject to the oxygen evolution from water: reaction-dependent component analyses of time-resolved intermediates, a Fano resonance of a mode at the metal-oxide-water interface, and reaction isotherms of metastable intermediates. The phenomenology uses parameters to encase what is unknown at a microscopic level to then circumscribe the clear and macroscopically tuned trends seen in the spectroscopic data.

Multiple Fano Resonances Enabled by the Interference between an Out‐of‐Plane Plasmon Mode and Fabry–Pérot Cavity Modes

AbstractMultiple Fano resonances (mFRs) are arising as a promising optical platform to achieve precise sensing and detection. However, experimentally achieving mFRs by simple structures has remained challenging, which impedes the widespread applications of mFRs. Herein a simple structure composed of a single colloidal metal nanoparticle and a transition metal dichalcogenide flake to simultaneously achieve up to 8 FRs in experiments is demonstrated. Combining theoretical and experimental techniques, that an out‐of‐plane plasmon mode of the metal nanoparticle interferes with the Fabry–Pérot cavity modes from the WS2 flake to form mFRs in the visible region is proved. The simplicity and generality of the method further allow us to systematically study the tunability of the mFRs, in terms of the peak/dip positions and the number of FRs, by changing the structural parameters, which include the thickness of the WS2 flake, size and shape of the plasmonic nanoparticle. In addition, the quality of the mFRs is proved to be adjustable by tuning the reflectivity of the substrate in the system. The highest quality factor and spectral contrast of the achieved resonances are up to ≈180 and ≈0.95, respectively. The simple structure and high‐quality optical modes will prosper applications in precise sensing and light modulation.

Stretchable Metamaterials with Tamm/Fano Resonances for Tunable, Efficient Mechanochromic Color Shifting

AbstractNext‐generation wearable and optoelectronic technologies requires highly adaptable light manipulation capabilities for applications in sensors, displays, and optical switches on flexible substrates. Here, a cost‐effective approach is presented for realizing a Tamm Plasmon (TP) resonant device on a flexible platform by combining nanoimprint lithography with layer‐by‐layer assembly. The TP device incorporates a stretchable, 1D bragg (BRG) stack coupled with a gold (Au) and aluminum (Al) metasurface, whose dimensions are designed to enable tunability in the visible and near‐infrared (NIR) regions of the spectrum. The device exhibits substantial reflected intensities (≈75%) and a well‐defined, narrow TP minimum of approximately 30 nm. Both TP and Fano resonances can be clearly observed by incorporating symmetry‐broken metasurface features with the BRG stack. The integrated system is subjected to both uniaxial (up to 37% strain) and biaxial (up to 25% strain) stretching, demonstrating dynamic chromatic responses in both the visible and near‐infrared regimes with sensitivities of ≈6.2 nm/%. This work clearly demonstrates a cost‐effective route for the fabrication of multi‐plasmon resonant devices with tunable colors on a flexible platform.

Electrical field-induced Fano resonance tunability in photonic crystal slabs

The creation of tunable Fano resonances in a photonic crystal structure with a side-coupled nanocavity and a waveguide with a partially transmitting element is investigated in this paper. In the proposed structure, the nanocavity’s central hole is made up of two cylinders with different radii that are nested inside each other. The outer and inner cylinders are made of quartz and liquid crystal, respectively. The performance of this device is analyzed using the three-dimensional finite-difference time-domain. The transmission spectrum, resonance wavelength, and quality factor of the proposed structure are calculated for various applied voltages. It is demonstrated that as the applied voltage increases, the quality factor changes and the Fano resonance wavelength shifts. Based on the findings, a tuning range of 5.2 nm is achievable with an excellent transmission contrast within this range. The presented structure is appropriate for applications such as tunable switches and filters.

High-Performance Refractive Index and Temperature Sensing Based on Toroidal Dipole in All-Dielectric Metasurface.

This article shows an all-dielectric metasurface consisting of "H"-shaped silicon disks with tilted splitting gaps, which can detect the temperature and refractive index (RI). By introducing asymmetry parameters that excite the quasi-BIC, there are three distinct Fano resonances with nearly 100% modulation depth, and the maximal quality factor (Q-factor) is over 104. The predominant roles of different electromagnetic excitations in three distinct modes are demonstrated through near-field analysis and multipole decomposition. A numerical analysis of resonance response based on different refractive indices reveals a RI sensitivity of 262 nm/RIU and figure of merit (FOM) of 2183 RIU-1. This sensor can detect temperature fluctuations with a temperature sensitivity of 59.5 pm/k. The proposed metasurface provides a novel method to induce powerful TD resonances and offers possibilities for the design of high-performance sensors.

Nanosensor Based on the Circular Ring with External Rectangular Ring Structure

This paper presents a novel nanoscale refractive index sensor, which is produced by using a metal–insulator–metal (MIM) waveguide structure coupled with the circular ring with an external rectangular ring (CRERR) structure with the Fano resonance phenomenon. In this study, COMSOL software was used to model and simulate the structure, paired with an analysis of the output spectra to detail the effect of constructional factors on the output Fano curve as measured from a finite element method. After a series of studies, it was shown that an external rectangular ring is the linchpin of the unsymmetrical Fano resonance, while the circular ring’s radius strongly influences the transducer’s capability to achieve a maximum for 3180 nm/RIU sensitivity and a FOM of 54.8. The sensor is capable of achieving sensitivities of 0.495 nm/mgdL−1 and 0.6375 nm/mgdL−1 when detecting the concentration of the electrolyte sodium and potassium ions in human blood and is expected to play an important role in human health monitoring.

Majorana Modes and Fano Resonances in Aharonov–Bohm Ring with Topologically Nontrivial Superconducting Bridge

Majorana Modes and Fano Resonances in Aharonov–Bohm Ring with Topologically Nontrivial Superconducting Bridge

MIM waveguide refractive index sensor with graphene enhanced three-ring nested resonator Fano resonance

In this paper, a metal-insulator-metal (MIM) waveguide featuring a three-ring nested cavity structure is proposed. We enhance and optimize this design by integrating graphene nanostructures into the ferrule resonance cavity, resulting in a hybrid graphene-MIM waveguide structure. The transmission spectra and electric fields generated by the structure are analyzed by using the finite element method (FEM), shedding light on the formation mechanism of various Fano resonance peaks. The validity of our theoretical analysis is confirmed using multimode interference coupled mode theory (MICMT), and the simulation results are largely aligning with the theoretical verification results. Next, by manipulating the chemical potential of graphene, the Fano resonance can be tuned across a wide range of wavelength bands. And this capability enables the realization of a dynamically tunable refractive index sensor for transmission spectroscopy. Under optimized parameter settings, the refractive index sensor achieves a maximum sensitivity of 1266.67nm/RIU, and a maximum figure of merit (FOM) value of 199.67RIU−1. Compared with conventional MIM waveguide devices, this design overcomes the difficulty of conventional MIM waveguide structures that cannot be dynamically tunable. Notably, the wavelength of the Fano resonance formed by the transmission spectrum can be dramatically altered when the refractive index of the medium in the surrounding environment is slightly changed. Therefore, this structure expands the repertoire of integrated optical devices with potential applications, particularly in the field of optical sensors.

Inverse design of nanohole all-dielectric metasurface based on deep convolutional neural network

Compared with the traditional micro-nano device design method, the data-driven neural network model method can greatly improve the inverse design efficiency of micro-nano structures with tiny design errors. Micro-nano structures based on the Fano resonance effect are widely used and have various functions. In recent years, researchers have attached great importance to its inverse design. This paper addresses the application requirements of the Fano resonance effect and develops a Gramian angular field-Convolutional Neural Network-Long Short Term Memory (GAF–CNN–LSTM) hybrid model based on the Gramian angular field transition. The model takes the designed nanohole all-dielectric metasurface structure as an example. This structure can produce different types of Fano resonance effects under different parameter combinations, implement different types of Fano resonances relative to multiple structures,the proposed structure can be realized by dynamic tuning of a single structure to obtain multi-Fano resonances, thus better application to different sensors.Through the ablation experiments and the contrast experiments, the results indicate that the proposed hybrid model can achieve high-precision inverse prediction of multifunctional Fano resonance effects, with a model accuracy of up to 95%. This study provides a new perspective on the inverse design of array-type multifunctional Fano resonance effect micro-nano devices.