Tuning Triangular Prism Dimer into Fano Resonance for Plasmonic Sensor

We theoretically investigate the plasmonic Fano resonance in a triangular nanoprism dimer. By adjusting the geometry parameters, we have observed a Fano line shape in the scattering spectra, which is induced by the competence of bonding and antibonding modes in the triangular nanoprism dimer. The Fano line shape can be well described by a theoretical model of two harmonic oscillators. A figure of merit value as high as 16.1 is achieved in the triangular nanoprism dimer, which is caused by the Fano resonance. The electric field at the corner of the triangular prisms is the highest among the circular cylinder dimer and square rod dimmers, which shows that the triangular prism dimer is more suitable for the detection of biomolecules. The triangular prism dimer may also used in plasmonic circuits.     

A High-Performance Refractive Index Sensor Based on Fano Resonance in Si Split-Ring Metasurface

We present a high-performance refractive index sensor based on Fano resonance with a figure of merit (FOM) about 56.5 in all-dielectric metasurface which consists of a periodically arranged silicon rings with two equal splits dividing them into pairs of arcs of different lengths. A Fano resonance with quality factor ~133 and spectral contrast ratio ~100% arises from destructive interference of two antiphase electric dipoles in the two arcs of the split-ring. We can turn on and/or off the Fano resonance with a modulation depth nearly 100% at the operating wavelength of 1067 nm by rotating the polarization of incident light. We believe that our results will open up avenues for the development of applications using Fano resonance with dynamically controllability such as biochemical sensors, optical switching, and modulator.     

Highly Sensitive Polarimetric Sensor Based on Fano Resonance for DNA Hybridization Detection

Plasmonics - Surface plasmon resonance (SPR) sensor based on reflectivity measurement has been widely studied for its convenient detection, high sensitivity, and real-time functions. However, the...     

Actively Tunable Fano Resonance in H-Like Metal-Graphene Hybrid Nanostructures

Actively tunable Fano resonance has obvious advantages in applications such as chemical or biological sensors, switches, modulators, and optical filters. In this paper, we studied theoretically the actively tunable Fano resonance in H-like metal-graphene hybrid nanostructures at visible and near-infrared wavelengths. We found that the absorption spectrum of H-like metal-graphene hybrid nanostructures has two resonance peaks, and the absorption spectrum has an obvious blue shift compared with that of the H-like metal nanostructures without graphene. The optical properties of different nanostructures are explained by the electric field distribution. Then, the dependence of the Fano resonance on the nanostructure parameters, refractive index of host materials, and graphene Fermi energy is studied. The wavelength and intensity of absorption spectrum can be manipulated by adjusting the structure parameters and host materials. In addition, the wavelength and intensity of absorption spectrum can be manipulated actively by changing the Fermi energy levels of graphene. This study provides a method for designing the actively tunable Fano resonance in H-like metal-graphene hybrid nanostructures.

     

Highly Sensitive Plasmonic Sensor Based on Fano Resonance from Silver Nanoparticle Heterodimer Array on a Thin Silver Film

We investigate the optical spectrum of a multilayer metallic slab using multiple-scattering formalism. A thin silver film is attached to a periodic array of heterodimers consisting of two vertically spaced silver nanoparticles of different radii. Depending on the radius of nanoparticles, heterodimer array presents a simple nanoscale geometry which gives rise to remarkable plasmonic properties of multipolar resonances. Due to the coherent interference of the localized nanoparticle plasmons (discrete mode) and surface plasmon polaritons of metallic film (continuous mode), the reflection spectrum represents a sharp asymmetric Fano resonance dip, which is strongly sensitive to the refractive index of the surrounding embedded dielectric host. The physical features contribute to a highly efficient plasmonic sensor for refractive index sensing with sensitivity of ～1.5?×?10^?3 RIU/nm.     

Tunable Fano Resonance Based Mode Interference in Waveguide-Cavity-Graphene Hybrid Structure

In this paper, a graphene strip is introduced into a metal-insulator-metal (MIM)-integrated square cavity hybrid structure; the transmission spectra are theoretically investigated by the finite different time domain (FDTD) methods. An asymmetric Fano resonance dip that has high figure of merit (FOM) value appears in the transmission band. According to the multimode interference coupled mode theory (MICMT) analytical method, the Fano resonance originates from the coherent coupling between TM₁₀ cavity magnetic mode and graphene plasmonic resonance electric mode. The center wavelength, full width at half maximum (FWHM), and FOM value of the Fano resonance can be tuned dynamically by altering the Fermi level of the graphene. Through breaking the symmetry of the hybrid structure or introducing double graphene strips with different Fermi level into hybrid structure, double Fano resonance are realized. This study can provide some theoretical basis and design reference for designing ultrahigh sensitivity plasmonic sensor.

     

Magnetic-Based Fano Resonance by a Trimer with Y-shaped Gap

We introduce a Y-shaped gap into a silver disk to break the structure symmetry which can be looked as a loop-linked structure. Magnetic resonances are excited by incident light when incident electric field is parallel to the trimer plane. Fano resonance is generated by the coupling between bright electric mode and dark magnetic mode. These resonances can be adjusted by tuning the gap size, the radius of trimer, and the position of Y-shaped gap. The extinction cross section of the structure is calculated with the finite element method (FEM). The maximum figure of merit (FOM) is 37.8. Both the magnetic and electric field are greatly enhanced at the Fano dip and the magnetic resonance peak.     

Fano Resonance Based on End-Coupled Cascaded-Ring MIM Waveguides Structure

Plasmonics - Though adding a groove to a plasmonic end-coupled perfect ring (PR) resonator, two additional resonance modes, which can be controlled by the length of the groove, will arise in this...     

Novel Crescent-Shaped Cavity Resonator Based on Fano Resonance Spectrum

Plasmonics - World is rich in unconventional oil and various alternatives to petroleum. However, conventional oil production declines so quickly that it is likely these unconventional oil resources...     

Double Directions Nanoscale Range Finding Using Fano Resonance in Coupled Gratings

In this paper, a theoretical demonstration is given of nanoscale range finding by exciting Fano resonance in coupled gratings. Metallic ridges induce oscillation mode, whose interference with surface plasmon polartions generate narrow Fano resonance. The concept of hybridization is employed to understand the coupling effect of surface plasmon polartions and the oscillation due to metallic ridges. Fano behavior in this structure is captured by using the temporal coupled-mode theory. The gained fundamental understanding opens up new ways to control nanoscale spacing distances and tailor Fano resonance, thus facilitating rational design of nanosensors to improve the performance of nanomotion control systems.

     

Actively Tunable Fano Resonance Based on a T-Shaped Graphene Nanodimer

We present the strength modulation and frequency tuning of Fano resonance by employing a graphene nanodimer formed by two coplanar perpendicular nanostrips with different dimensions. The Fano resonance is induced by destructive interference between the bright dipole mode of a short nanostrip and the dark quadrupole mode of a long nanostrip. The strength, line width, and resonance frequency of the Fano resonance can be actively modulated by changing the spatial separation of those two graphene nanostrips and the Fermi energy of the graphene nanodimer, respectively, without re-fabricating the nanostructures. The tuning of the strength and resonance frequency can be attributed to the coupling strength and optical properties of graphene, respectively. Importantly, a figure of merit value as high as 39 is achieved in the proposed nanostructures. Our results may provide potential applications in optical switching and bio-chemical sensing.     

High-Performance Magneto-Optic Surface Plasmon Resonance Sensor Design: An Optimization Approach

High-performance intensity-interrogated magneto-optic surface plasmon resonance (MOSPR) sensors are designed by a multi-objective optimization approach. Designed devices show bulk refractive index sensitivity 1 order of magnitude larger than the current state of the art, while the design procedure allows to chose an appropriate trade-off between sensor performance and ease of fabrication. Straightforward guidelines for the sensor design and fabrication emerge from the optimization process, indicating that minimization of the optical losses takes precedence on the maximization of the magneto-optical modulation.     

Ambiguous Refractive Index Sensitivity of Fano Resonance on an Array of Gold Nanoparticles

We investigate the optical response to refractive index changes of a Fano resonance occurring in a random array of gold nanoparticles supported on a glass substrate. The Fano resonance results from the interference between localized surface plasmon on a gold nanoparticle and the light reflected at the boundary of the glass substrate. We demonstrate that the sensitivity of the resonance to the refractive index of the surrounding medium is highly dependent on the excitation geometry and can assume either positive or negative values. We furthermore present a theoretical analysis explaining this behavior based on the rigorous coupled wave analysis (RCWA) as well as the island film theory.

     

Fano Resonance of Nanocrescent for the Detection of Single Molecules and Single Nanoparticles

This paper reports a theoretical study on the Fano resonance of a 3D nanocrescent and its application in single molecular detection. The resonance wavelength changes with the crescent radius, gap width and thickness. The Fano resonance is attributed to the interference between the quadrupolar mode supported by the horizontal crescent and the quadrupolar mode supported by the nanotip oscillating along the height direction. The Fano resonance is highly sensitive to a nanoparticle trapped by the nanocrescent. The wavelength shift is larger than 0.5 nm when a single protein nanoparticle with radius only of 1.25 nm is trapped. For a protein with radius of 0.3 nm, the wavelength shift is still larger than 0.03 nm, over the detection limit (10^?5 nm) by 3 orders in the magnitude, which indicates that the nanocrescent can be used to detect small molecule with several atoms.     

Ultra-High Sensitivity Nanosensor Based on Multiple Fano Resonance in the MIM Coupled Plasmonic Resonator

This paper proposes a compact plasmonic structure that is composed of a metal-insulator-metal (MIM) waveguide coupled with a groove and stub resonators, and then investigates it by utilizing the finite element method (FEM). Simulation results show that the interaction between the local discrete state caused by the stub resonator and the continuous spectrum caused by the groove resonator gives rise to one of the two Fano resonances, while the generation of the other resonance relies only on the groove. Meanwhile, the asymmetrical linear shape and the resonant wavelength can be easily tuned by changing the parameters of the structure. By adding stubs on the groove, we excited multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of 2000 nm/RIU and a figure of merit of about 3.04?×?10³, which can find extensive applications for nanosensors.     

Plasmonic Fano Resonance in Homotactic Aluminum Nanorod Trimer: the Key Role of Coupling Gap

Recently, the Fano effect of aluminum nanostructures has attracted a lot of attentions in several detector and sensor applications, but the role of coupling gap in it remains unintuitive. In this paper, a homotactic aluminum rod trimer (HART) is designed to form the plasmonic Fano resonances and visualize the important role of coupling gap size. The plasmon hybridization model and far field images were used to qualitatively describe the formation mechanism of Fano resonance. The simulation results intuitively show that the Fano dip of HART with a smaller coupling gap size has a higher red-shift speed when increasing the refractive index of surrounding environment or the length of HART with a fixed axial ratio (L_S/L_L = 0.6). Our study provides the insights to the key role of coupling gap in the performance of Fano structures.

     

Ultra-high Sensitivity Plasmonic Nanosensor Based on Multiple Fano Resonance in the MDM Side-Coupled Cavities

We propose a compact plasmonic structure comprising a metal-dielectric-metal (MDM) waveguide coupled with a side cavity and groove resonators. The proposed system is investigated by the finite element method. Simulation results show that the side-coupled cavity supports a local discrete state and the groove provides a continuous spectrum, the interaction between them, gives rise to the Fano resonance. The asymmetrical line shape and the resonant wavelength can be easily tuned by changing the geometrical parameters of the structure. Moreover, we can extend this plasmonic structure by the double side-coupled cavities to gain the multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of ～1900 nm/RIU and a figure of merit of about ～3.8?×?10⁴, which can find wide applications for nanosensors.     

Aluminum-Based Deep-Ultraviolet Surface Plasmon Resonance Sensor

Plasmonics - An aluminum-based deep-ultraviolet surface plasmon resonance (DUV-SPR) sensor is promising for biological applications. Design aspects of a DUV-SPR sensor are here considered by using...