Multiple Fano Resonances Research Articles

All-dielectric metasurface with multiple Fano resonances supporting high-performance refractive index sensing

All-dielectric metasurface has important application value in many fields, especially in refractive index sensing. In this paper, an all-dielectric metasurface composed of a silicon triangular-hole nanodisk array is designed and studied numerically. Through introducing asymmetry in the proposed metasurface and transforming the bound states in the continuum (BIC) into the quasi-BIC, three sharp Fano resonances with almost 100% modulation depth can be achieved, and the highest quality factor (Q-factor) can reach 49,915. Further, the three Fano resonances can be regulated and controlled by adjusting the structural parameters. Moreover, the sensing performance of the structure is researched by changing the ambient refractive index. The maximum sensitivity obtained is 248 nm/RIU, and the best figure of merit is 3815RIU−1. The proposed structure provides a scheme for the design of optical devices, especially refractive index sensors.

Refractive index sensor based on a D-shaped resonator and a stub resonator and its slow light characteristics

In this paper, a metal–insulator–metal waveguide structure is proposed based on a D-shaped resonator and a stub resonator, and it can generate multiple Fano resonances. The magnetic field (Z-direction) distribution and transmission spectrum of the structure are analyzed by the finite element method (FEM). The theory results are performed with the multimode interference coupled mode theory (MICMT), and they show high agreement with the simulation outcomes. The calculations also discuss the effect of structural parameters on the transmission spectrum. Moreover, the structure’s sensing characteristics are analyzed in detail, achieving a maximum sensitivity and FOM* of 1300 nm/RIU and 181.44, respectively. In addition, the slow light properties of the structure are also investigated, whose group delay and group index can reach 0.24 ps and 48.93, respectively. The group delay time is dynamically regulated by controlling the number of D-shaped resonators to achieve the effect of a delay line. It can provide some reference value for multifunctional on-chip optical integrated devices based on MIM waveguide structure.

On-chip plasmonic nanosensor based on multiple Fano resonances in rectangular coupled systems

The transmission characteristics of coupled multi-resonators integrated in metal-insulator-metal (MIM) waveguide systems are studied and used to design refractive nanosensors. The symmetry of this nanostructure can be easily broken by changing the relative distance between the multi-resonators, and the transmission spectrum for the system will exhibit double sharp Fano profiles. Simulation results show that the Fano profiles can be used for high-sensitivity refractive sensing with a sensitivity reaching ∼800nm/RIU and figure of merit (FOM) of ∼1.845×104. Moreover, the structure can be easily extended by adding another slender rectangular resonator, and multiple Fano resonances will appear in the spectrum. The new formed nanostructure can achieve a higher sensor sensitivity about ∼875 nm/RIU, and the FOM is 1.861×104. The proposed nanostructures will have great application prospects in on-chip information processing, biosensors and analytical chemistry.

Optical Properties of Multiple Fano Resonance in MIM Waveguide System Coupled with a Semi-Elliptical Ring Resonator

Optical Properties of Multiple Fano Resonance in MIM Waveguide System Coupled with a Semi-Elliptical Ring Resonator

Exploring the influence of nanocavity alignment on slow light generation via multiple EIT and Fano resonances in square lattice plasmonic silver nanostructures

In this paper, we present a comprehensive investigation of multiple electromagnetic induced transparency (EIT) and Fano resonances in a square lattice plasmonic nanostructure, which is composed of four silver slabs arranged in a square configuration, with each slab featuring a cylindrical nanocavity at its center. Initially, symmetric structures were analyzed to explore the potential for achieving EIT effects. Subsequently, we introduce deliberate symmetry breaking by precisely aligning the nanocavity in a controlled manner, first within a single slab, then in combinations of two, three, and all four slabs simultaneously. This controlled alignment strategy enabled the relaxation of dipole coupling selection rules, leading to the mixing of dipole and higher-order modes. The interaction between these modes resulted in the generation of multiple EITs and Fano resonances in the optical spectrum. Furthermore, the effective group index was evaluated for the optimal results obtained in the single, double, triple, and four symmetry reduced structures. High group index values were observed in the vicinity of the EIT and Fano resonances, with a remarkable maximum group index value of 6900 achieved within the EIT window. These findings highlight the significant potential of these structures in the design of slow light devices and sensitive sensors.

Achiral nanoparticle trapping and chiral nanoparticle separating with quasi-BIC metasurface.

Dielectric metasurfaces based on quasi-bound states in the continuum (quasi-BICs) are a promising approach for manipulating light-matter interactions. In this study, we numerically demonstrate the potential of silicon elliptical tetramer dielectric metasurfaces for achirality nanoparticle trapping and chiral nanoparticle separation. We first analyze a symmetric tetramer metasurface, which exhibits dual resonances (P1 and P2) with high electromagnetic field intensity enhancement and a high-quality factor (Q-factor). This metasurface can trap achiral nanoparticles with a maximum optical trapping force of 35 pN for 20 nm particles at an input intensity of 100 mW. We then investigate an asymmetric tetramer metasurface, which can identify and separate enantiomers under the excitation of left-handed circularly polarized (LCP) light. Results show that the chiral optical force can push one enantiomer towards regions of the quasi-BIC system while removing the other. In addition, the proposed asymmetric tetramer metasurface can provide multiple Fano resonances (ranging from R1 to R5) and high trap potential wells of up to 33 kBT. Our results demonstrate that the proposed all-dielectric metasurface has high performance in nanoparticle detection, with potential applications in biology, life science, and applied physics.

Near-infrared electromagnetic excitations in Si1-xGex alloy semiconductor based permittivity-asymmetric metasurface

As one of the promising and extensively studied alloy semiconductors, the optoelectronic properties of Si1-xGex alloys have been well studied, but fundamental electromagnetic (EM) properties are rarely explored and discussed. In this work, the EM excitations of magnetic multipoles and toroidal dipoles in Si1-xGex based permittivity-asymmetric metasurface at near-infrared spectral region are investigated. Multiple Fano resonances (FRs) occur in the structure, and the formation mechanisms of resonance excitations are analyzed in detail combining theory with EM field distributions. In addition, the proposed metasurface is also investigated for its potential as a refractive index sensor due to its finer spectral property. It is hoped that our work will help to understand the EM properties of Si1-xGex alloys and find its potential applications in optics, such as refractive index sensing. The results obtained here provide fundamental insights into the exploration of EM excitations of Si1-xGex alloys.

Multiple Fano Resonances in Plasmonic Waveguide-Based Cavity and Detection of Pathogenic Virus

Multiple Fano Resonances in Plasmonic Waveguide-Based Cavity and Detection of Pathogenic Virus

Refractive index sensor based on multiple Fano resonances excited by MIM waveguide couplessd hexagonal nut and square ring resonators

This study proposed a micro-nano structure capable of generating multiple Fano resonances for refractive index sensing of gases and liquids. The structure consists of a metal-insulator-metal waveguide with a baffle and two resonators, one of hexagonal nut and one of square ring. The transmission spectrum shows that the designed structure can generate up to five Fano resonances tuned by different resonators. The data obtained are fitted by multi-mode interferometric coupling mode theory, and the results are in good agreement. The sensing performance of the structure is investigated in the refractive index ranges of 1.00–1.10 and 1.30–1.40. The corresponding maximum sensitivity and maximum figure of merit are up to 998 nm/RIU and 49016, 1026 nm/RIU and 14890, respectively. The designed structure can be used as gas and liquid sensors and have great potential for micro-nasno sensing and biochemical medicine applications.

Multiple Fano Resonances in a Metal–Insulator–Metal Waveguide for Nano-Sensing of Multiple Biological Parameters and Tunable Slow Light

A surface plasmonic waveguide made of metal–insulator–metal (MIM) capable of generating triple Fano resonances is proposed and numerically investigated for multi-biological parameter sensing as well as tunable slow light. The waveguide is made up of a bus waveguide with a silver baffle, a square split-ring cavity with a square center (SSRCSC), and a circular ring cavity with a square center (CRCSC). Based on the triple Fano resonances, human blood temperature and plasma concentration are measured simultaneously at different locations in the waveguide, and the maximum sensitivities were 0.25 nm/°C and 0.2 nm·L/g, respectively. Furthermore, the two biological parameters can be used to achieve tunable slow light, and it was found that the group delay responses to human blood temperature and plasma concentration all conformed to cubic functions. The MIM waveguide may have great applications in future nano-sensing of multiple biological parameters and information processing of optical chips or bio-optical chips.

Multiple Fano resonance modes in an ultra-compact plasmonic waveguide-cavity system for temperature sensing

Multiple Fano resonance modes in an ultra-compact plasmonic waveguide-cavity system for temperature sensing

Multiple Fano Resonances in Dynamic Resonant Tunneling Processes

The existence of Fano resonances in dynamic resonant tunneling (RT) systems has been investigated. Fano resonances are characterized by the appearance of a 100% reflection coefficient in proximity to a high transmission coefficient. For a Fano resonance to appear, a bound state must exist. On the other hand, a resonant tunneling process is characterized by a high transmission and the existence of a quasi-bound state (QBS) instead of a bound one. It has been shown that, by narrowing the width of the barrier, the resonance energy of the QBS gradually decreases and eventually turns into a bound state. Consequently, in a dynamic RT process, there are two scenarios: either a bound state exists, in which case, Fano resonances exist for any barrier width, or a QBS exists, and the barrier should be narrow enough for the Fano resonance to appear. In both cases, the incoming particle’s frequency must be lower than the oscillating well’s frequency. In this work, these resonances are investigated in detail, and both exactly numerically and approximated analytical expressions are derived for both the weak and strong oscillating amplitude regimes. One of the conclusions is that, when the oscillating frequency is low enough, multiple Fano resonances can appear by varying the barrier’s width. Since these resonances are very sharp and zero transmission can easily be detected, this property can be used as a very accurate method for measuring the barrier’s width, even when the particle’s de-Broglie wavelength is much larger than the barrier’s width.

Digital coding Fano resonance based on active plasmonic metamaterials.

A novel approach that employs active plasmonic metamaterials to create a digital coding Fano resonator is proposed, to the best of our knowledge. The meta-device consists of three concentric spoof localized surface plasmon (LSP) resonators and three positive-intrinsic-negative (PIN) diodes positioned at three slits located in the middle and inner LSP resonators. Four Fano resonant modes can be independently switched by controlling the biased voltage applied to the three diodes. This provides a means for encoded modulation of multiple Fano resonances in metamaterials, which could have broad applications in fields such as multiway sensing, plasmonic circuits, and switching. We experimentally demonstrate the effectiveness of the proposed approach, which offers promising potential for practical implementation.

Ultra-High Quality Factor Resonances in a Pinwheel-Shaped All-Dielectric Metasurface Based on Bound States in the Continuum

Combining with the bound states in the continuum (BICs) theory in all-dielectric metasurfaces has become an extensively used method to excite multiple high quality(Q) factor Fano resonances, which remarkably enhance the performance of structures to be applied to refractive index sensors. In this article, a novel silicon pinwheel-shaped all-dielectric metasurface in the near-infrared region is designed and numerically investigated. Two Fano resonances are excited in the original structures. After breaking the symmetry of the original structures in combination with the BIC theory, four sharp Fano resonances are excited and the maximum Q-factor exceeds 3.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δ</i> = 10 nm. With the asymmetric parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δ</i> = 80 nm, multiple Fano resonances could be turned on and off by turning the polarization of the incident light, which performs excellent characteristics in optical switches. Both in the original structures and in the asymmetric state it offers outstanding sensing characteristics. Furthermore, with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δ</i> = 80 nm and the polarization angle 90 degrees, the sensitivity and the figure of merit (FOM) could respectively reach up to 355 nm/RIU and 1375.97 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The designed structures may provide a way to enhance the performance of bio-chemical sensors, optical switches, and nonlinear optics.

Dynamic Regulation of Multiple Fano Resonances Based on Liquid Crystal

A coupled structure, consisting of two perpendicular cavities coupled with a waveguide, has been proposed and researched numerically and theoretically. It is found that the lateral displacement <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> plays a key role in transmission spectrum. Whether the first- or the second-order mode can exist in the horizontal cavity has been well explained. Owing to the interaction among two discrete and a continuous states, four Fano resonance can be achieved to set appropriate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> . When the coupled structure is filled with liquid crystal (LC), the refractive index can be regulated dynamically by external voltage. The coupled structure can be act as a filter which filters arbitrary wavelength within the scope of certain wavelength. At the same time, in a certain wavelength range, an optical switch can be achieved with different voltage at any wavelength. This structure has the advantages of simple, easy fabrication and tunability, which has potential applications in integrated optical devices.

Tunable Multiple Fano Resonance Plasmonic Nanosensor with an Oblique Path in a Pentagonal-Ring-Shaped Resonator

Tunable Multiple Fano Resonance Plasmonic Nanosensor with an Oblique Path in a Pentagonal-Ring-Shaped Resonator

Highly sensitive multiple fano resonances excitation on all-dielectric metastructure

Highly sensitive multiple fano resonances excitation on all-dielectric metastructure

Asymmetric Cross Metasurfaces with Multiple Resonances Governed by Bound States in the Continuum.

The bound state in the continuum (BIC) has paved a new way to achieve excellent localization of the resonant mode coexisting with a continuous spectrum in the metasurface. Here, we propose an all-dielectric metasurface consisting of periodic pairs of asymmetric crosses that supports multiple Fano resonances. Due to the sufficient degrees of freedom in the unit cell, we displaced the vertical bars horizontally to introduce in-plane perturbation, doubling the unit cell structure. Dimerization directly resulted in the folding of the Brillouin zone in k space and transformed the BIC modes into quasi-BIC resonances. Then, simultaneous in-plane symmetry breaking was introduced in both the x and y directions to excite two more resonances. The physical mechanisms of these BIC modes were investigated by multipole decomposition of the scattering cross section and electromagnetic near-field analysis, confirming that they are governed by toroidal dipole (TD) modes and magnetic dipole (MD) modes. We also investigated the flexible tunability and evaluated the sensing performance of our proposed metasurface. Our work is promising for different applications requiring stable and tunable resonances, such as optical switching and biomolecule sensing.

Excitation of multiple Fano resonances on all-dielectric nanoparticle arrays.

In this paper, an all-dielectric metasurface consisting of a unit cell containing a nanocube array and organized periodically on a silicon dioxide substrate is designed and analyzed. By introducing asymmetric parameters that can excite the quasi-bound states in the continuum, three Fano resonances with high Q-factor and high modulation depth may be produced in the near-infrared range. Three Fano resonance peaks are excited by magnetic dipole and toroidal dipole, respectively, in conjunction with the distributive features of electromagnetism. The simulation results indicate that the discussed structure can be utilized as a refractive index sensor with a sensitivity of around 434 nm/RIU, a maximum Q factor of 3327, and a modulation depth equal to 100%. The proposed structure has been designed and experimentally investigated, and its maximum sensitivity is 227 nm/RIU. At the same time, the modulation depth of the resonance peak at λ = 1185.81 nm is nearly 100% when the polarization angle of the incident light is 0 °. Therefore, the suggested metasurface has applications in optical switches, nonlinear optics, and biological sensors.

Multiple Fano resonances driven by bound states in the continuum in an all-dielectric nanoarrays system

Fano resonance with high Q-factor can greatly enhance the light–matter interaction in all-dielectric metasurface, which is an important condition for developing high-performance micro-/nano-photonics devices. In this paper, we present an all-dielectric metasurface structure composed of nanoarrays to investigate the properties of BIC realization and Fano resonance in the near-infrared spectral region. Four Fano profiles are generated, and two quasi-BIC resonance modes excited by MD appear when the structural symmetry is broken. All the Fano resonances modulation depth close to 100%. The spectral response of the proposed structure is also highly tunable by adjusting the polarization of the incident light and the geometric parameters of the structure. This work may provide a reference for the design of devices, such as biochemical sensing, optical switches, and optical modulators.