Fano Peak Research Articles

Scattering singularities in Fano-resonant multilayer grating structure with phase-change materials

In non-Hermitian systems, the singularities refer to poles or zeros of the scattering and transfer matrices. Here, we investigate the kinds of singularities in a non-parity-time-symmetric multilayer structure which mainly consists of double layers of silver grating and one layer of phase-change material Ge2Sb2Te5 (GST). When the GST is in its crystalline phase, a unidirectional zero-reflection singularity, i.e., exceptional point (EP) is achieved with the aid of Fano resonance. Interestingly, a coherent perfect absorber (CPA)-laser singularity adjacent to the EP is observed in the Fano peak. Meanwhile, a few CPA singularities exist at other wavelengths. By switching the GST from its crystalline to amorphous phase, the CPA-laser singularity will be absent, and the CPA singularity can be switched to a laser singularity. The scattering spectra near the singularities are sensitive to a tiny perturbation of the gain material and the environmental refractive index. The study is beneficial for making switchable active optical implementations.

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.

Active control of Fano resonance in side-coupled resonator-cavity systems

The study delves into actively controlling Fano resonance within a single-mode microstrip cavity, coupled with a split ring resonator (SRR) incorporating a varactor diode. This resonance arises from the interference between the SRR and a Fabry–Pérot cavity, resulting in a sharply asymmetric transmission spectrum. The varactor diode, situated within the SRR gap, is biased electrically via an external DC voltage source. Through manipulation of this bias voltage, both the transmission frequency and amplitude of the pronounced Fano resonance can be dynamically adjusted. Notably, a significant frequency shift of 345 MHz is achieved, accompanied by a transmission modulation depth of up to 34.2 dB. Moreover, at the Fano peak frequency of 2.65 GHz, the composite SRR-cavity structure exhibits a notable change in group delay, shifting by 21.3 ns with the bias voltage varying from 5 V to 2.6 V. These findings hold promise for the development of electrically controlled functional photonic devices, facilitating their adaptability and versatility in practical applications.

Giant enhancement of positive and negative Goos-Hänchen shifts in two-dimensional grating waveguide structures supporting Fano resonances

We propose a two-dimensional grating waveguide structure based on guided-mode resonance (GMR) to greatly enhance the Goos-Hänchen (GH) shift due to the asymmetric Fano peak. In addition, the enhancement of the GH shift is located at the peak of the reflectivity, which enables a more accessible measurement compared to the conventional GH shift enhancement based on Brewster angle or transmission-type resonance. In particular, such structure supports four channels for the GH shift enhancements, with a maximum value of 4.8×104λ0 for the positive one and -6000 λ0 for the negative one. Our results benefit the potential applications for optical sensors, optical filters, optical absorbers and surface plasmon resonators, etc.

Fano resonance based on a triangular resonator and its application on nanosensing

Fano resonance sensors based on metal–insulator–metal (MIM) waveguide have potential applications in fields such as biology, chemistry, and the environment. Here, a nanosensor based on Fano resonance in an MIM-based isosceles triangular resonator system is proposed and numerically studied by finite element method. Simulation results show that the Fano peak can be easily tuned by adjusting the scale factor and the refractive index within the resonator. Furthermore, we thoroughly analyze the impact of the apex angle, rotation angle, and vertical displacement of the resonator on the transmission spectrum. Finally, the sensing characteristics of the proposed structure are optimized and analyzed, and a high-performance plasmonic sensor with a sensitivity of 1100[Formula: see text]nm/RIU and the maximum figure of merit of [Formula: see text] is obtained. The distinctive attributes of our suggested structure are applicable in the realization of various integrated components for the development of multifunctional high-performance nanophotonics devices.

Sensing performance of Fano resonance induced by the coupling of two 1D topological photonic crystals

In this work, a realized Fano resonance due to the coupling between two 1DTPC is proposed for refractive index sensing with an ultra-high-quality factor of 106. The generated Fano can be assigned to the coupling between topological edge states of two 1D TPCs. The resulting Fano peak is characteristic with a high transmission value reach to 99% with high sensing performance parameters making the proposed sensor a novel detector for refractive index. The proposed coupling 1D TPCs show a high sensitivity value of 888.252 nm/RIU, ultra-high-quality factor and figure of merit value reach 106, and perfect detection limit value of 10−7. The proposed coupling 1D TPCs provides a straightforward platform for sensing refractive index applications with high performance.

Process-Gas-Influenced Anti-Site Disorder and Its Effects on Magnetic and Electronic Properties of Half-Metallic Sr2FeMoO6 Thin Films

Anti-site disorder, arising due to the similar size of Fe and Mo ions in Sr2FeMoO6 (SFMO) double perovskites, hampers spintronic applicability by deteriorating the magnetic response of this double perovskite system. A higher degree of anti-site disorder can also completely destroy the half-metallicity of the SFMO system. To study the effects of different process gas conditions on the anti-site disorder, we have prepared a series of SFMO thin films on SrTiO3 (001) single-crystal substrate using a pulsed laser deposition (PLD) technique. The films are grown either under vacuum or under N2/O2 partial gas pressures. The vacuum-grown SFMO film shows the maximum value of saturation magnetization (MS) and Curie temperature (TC), signaling the lowest anti-site disorder in this series. In other words, there is a long-range Fe/Mo-O-Mo/Fe ferrimagnetic exchange in the vacuum-grown thin film, thereby enhancing the magnetization. Further, all the SFMO films show a semiconducting state with a systematic increase in overall resistivity with the increased anti-site disorder. The electrical conduction mechanism is defined by the variable-range hopping model at low temperatures. Raman spectra show a weak Fano peak, suggesting the presence of electron–phonon coupling in SFMO thin films. These results show the significance of the process gas in causing anti-site disorder, tuning the degree of this disorder and therefore its influence on the structural, magnetic, electrical, and vibrational properties of SFMO thin films.

Interference effects in coupled triple quantum dot systems

Electronic transport through a coupled triple quantum dot (TQD) system is theoretically studied using Equilibrium Green’s function approach. The TQD system is systematically investigated for T-shape configuration and triangular shape configuration. T-shape (triangular shape) configuration corresponds to the TQD structure in which two quantum dots (QD)s are connected to the left and right leads in series and third one is side coupled to the right one (both) the QDs. In the electronic transmission spectrum of T-shape configuration, it is found that an antiresonance peak occurs at the QDs energy level and width of the peak increases with the increase in the tunnel coupling of the side coupled QD. Further, an asymmetric Fano lineshape is also observed while investigating transition from the T-shape to the triangular shape configuration. Interestingly, this Fano peak is found to occur when side coupled QD is weakly coupled to both the serially coupled QDs and its appearance becomes more prominent when the side coupled QD is symmetrically coupled to both the QDs. Both these effects reveal quantum interference effects that take place between discrete states and the continuum in electron transport through multiple channels in T-shape and triangular shape geometries.

Tunable terahertz hybrid metamaterials supported by 3D Dirac semimetals

By utilizing the three-dimensional Dirac semimetal (DSM)-strontium titanate (SrTiO3, STO) elliptical hybrid metamaterials, the tunable Fano resonances were systematically analyzed in the THz regime, for example, the effects of asymmetric degrees, DSM Fermi levels, and operation frequencies. Interestingly, an obvious Fano peak is observed by introducing a displacement (asymmetric degree) between STO and DSM resonators. In particular, the amplitude modulation depth (MD) of the Fano transmission peak (reflection dip) is 49.5% (86.65%) when the asymmetric degree ranges from 0 to 20 µm. Furthermore, on the condition that the asymmetric degree is larger than 10 µm, the LC resonance is also excited with an extraordinary Q–factor of more than 25. Additionally, by modifying the Fermi level of DSM layer, the amplitude MD of Fano transmission peak (reflection dip) is 32.86% (67.26%). The results facilitate our understanding of the tunable mechanisms of DSM metamaterials and potentially promote the development of novel plasmonic devices, including filters, modulators and sensors.

Quantum interference between dark-excitons and zone-edged acoustic phonons in few-layer WS2

Fano resonance which describes a quantum interference between continuum and discrete states, provides a unique method for studying strongly interacting physics. Here, we report a Fano resonance between dark excitons and zone-edged acoustic phonons in few-layer WS2 by using the resonant Raman technique. The discrete phonons with large momentum at the M-point of the Brillouin zone and the continuum dark exciton states related to the optically forbidden transition at K and Q valleys are coupled by the exciton-phonon interactions. We observe rich Fano resonance behaviors across layers and modes defined by an asymmetry-parameter q: including constructive interference with two mirrored asymmetry Fano peaks (weak coupling, q > 1 and q < − 1), and destructive interference with Fano dip (strong coupling, ∣q∣ < < 1). Our results provide new insight into the exciton-phonon quantum interference in two-dimensional semiconductors, where such interferences play a key role in their transport, optical, and thermodynamic properties.

Low-Loss Dual-Band Transparency Metamaterial with Toroidal Dipole.

In this paper, a low-loss toroidal dipole metamaterial composed of four metal split ring resonators is proposed and verified at microwave range. Dual-band Fano resonances could be excited by normal incident electromagnetic waves at 6 GHz and 7.23 GHz. Analysis of the current distribution at the resonance frequency and the scattered power of multipoles shows that both Fano resonances derive from the predominant novel toroidal dipole. The simulation results exhibit that the sensitivity to refractive index of the analyte is 1.56 GHz/RIU and 1.8 GHz/RIU. Meanwhile, the group delay at two Fano peaks can reach to 11.38 ns and 12.85 ns, which means the presented toroidal metamaterial has significant slow light effects. The proposed dual-band toroidal dipole metamaterial may offer a new path for designing ultra-sensitive sensors, filters, modulators, slow light devices, and so on.

Demonstration of Tunable Fano Resonances in a Meta-material Absorber Composed of Asymmetric Double Bars with Bent Arms

In this paper, a metal–insulator-metal (MIM) plasmonic absorber consisting of asymmetric double bars with bent arms located on top of a silica layer coated on a metal film is proposed, and its resonant features are analyzed. The suggested structure supports both Fano and dipole perfect absorption resonances at the near-infrared region (NIR). The asymmetry introduced into the structure can be induced by changing the bending angle or rotation angle of one of the antennas, while the other one remains fixed. Simulation results demonstrate that by applying both asymmetry factors to the structure, one can have two individual Fano peaks at the same time. It is shown that the magnitude, central wavelength, and line width of the Fano peaks are adjustable by controlling the geometrical parameters of the structure. It is also indicated that the quality factor (Q-factor) of the Fano resonance is inversely related to the degree of asymmetry introduced into the structure. According to the simulations, an ultra-narrow resonance peak with a bandwidth of 1.87 nm at the wavelength of 710 nm (corresponding to a Q-factor of 387) can be obtained by controlling the geometrical parameters. It is also discussed that the absorptivity of Fano and the dipole peaks can be adjusted inversely, by manipulating the grapheme chemical potential. The ratio of the absorptivity to the chemical potential of graphene about 275%/eV and 226%/eV is calculated for the Fano peak and dipole peak, respectively. Accordingly, the presented structure is an adjustable NIR absorber with a fully tunable absorption spectrum which can be utilized in various applications from tunable reflectors and photo-detectors to ultra-narrowband and broadband optical modulators.

Excitations of Multiple Fano Resonances Based on Permittivity-Asymmetric Dielectric Meta-Surfaces for Nano-Sensors

We have designed an all-dielectric device based on permittivity-asymmetric rectangular blocks on meta-surfaces, yielding multiple Fano resonances with high sensitivity and high figure of merit (FOM) in the near-infrared regime. By introducing different materials to break the permittivity-symmetry, three sharp Fano peaks are generated with high Q-factors arising from the interference between the sub-radiant modes and the magnetic dipole resonance modes. Combining the field distributions and the multipole decomposition in Cartesian coordinates, the resonance modes are analyzed to be magnetic quadrupoles (MQs) and magnetic dipoles (MDs). Furthermore, the dependence on materials and geometric parameters has been studied. The maximal sensitivity, FOM and Q-factor reach 394 nm&#x002F;RIU, 4925 and 14437, respectively. This proposed structure provides a good alternative to geometry-asymmetric meta-surface structures and may be used for multichannel sensing, nonlinear optical devices, and laser.

Ultranarrow and Tunable Fano Resonance in Ag Nanoshells and a Simple Ag Nanomatryushka.

We study theoretically the Fano resonances (FRs) produced by the near-field coupling between the lowest-order (dipolar) sphere plasmon resonance and the dipolar cavity plasmon mode supported by an Ag nanoshell or the hybrid mode in a simple three-layered Ag nanomatryushka constructed by incorporating a solid Ag nanosphere into the center of Ag nanoshell. We find that the linewidth of dipolar cavity plasmon resonance or hybrid mode induced FR is as narrow as 6.8 nm (corresponding to a high Q-factor of ~160 and a long dephasing time of ~200 fs) due to the highly localized feature of the electric-fields. In addition, we attribute the formation mechanisms of typical asymmetrical Fano line profiles in the extinction spectra to the constructive (Fano peak) and the destructive interferences (Fano dip) arising from the symmetric and asymmetric charge distributions between the dipolar sphere and cavity plasmon or hybrid modes. Interestingly, by simply adjusting the structural parameters, the dielectric refractive index required for the strongest FR in the Ag nanomatryushka can be reduced to be as small as 1.4, which largely reduces the restriction on materials, and the positions of FR can also be easily tuned across a broad spectral range. The ultranarrow linewidth, highly tunability together with the huge enhancement of electric fields at the FR may find important applications in sensing, slow light, and plasmon rulers.

Structure of Multiple Fano Resonances in Double-baffle MDM Waveguide Coupled Cascaded Square Cavity for Application of High Throughput Detection

A structure of double-baffle metal-dielectric-metal (MDM) waveguide coupled cascaded square cavity is designed based on the transmission characteristics of the surface plasmon polaritons. Combined with coupled mode theory (CMT), the mechanism of multiple Fano resonances generated by this structure is analyzed qualitatively. The wide-band spectrum mode generated by the F-P resonant cavity and the four narrow-band spectrum modes produced by the cascaded square resonant cavities interfere with each other. Moreover, an new scheme of introducing a semiconductor material InGaAsP into this structure is designed for improving the transmittance of the Fano peaks. Analyze the influence of refractive indexes of the test objects on sensing performance by finite element method (FEM) quantitatively, which shows the improved structure can achieve the independent tuning of multiple Fano resonances. Combining with 96-well microplate technology, the structure can achieve the detection of multiple different samples with high-performance simultaneously. It is believed that the proposed structure has a strong reference significance for the design of optical micro-nanostructures for high throughput detection.

Numerical investigation of an optimized plasmonic on-chip refractive index sensor for temperature and blood group detection

A highly sensitive sensor focused on two Metal-Insulator-Metal (MIM) waveguides and three quadrilateral cavities sandwiched perpendicularly in between the MIM waveguides is proposed. Fano resonance induced by the coherent superposition of the narrow band spectral response and broadband spectral response, excites the structural transmission characteristics. The Finite Element Method (FEM) is used to numerically investigate the transmission characteristics and sensitivity of the refractive index sensor for different configurations. The linear relationship between resonant wavelength and refractive index is used to sense the materials. By optimizing the structural parameters, a numerical evaluation of the refractive index sensitivity (S) up to 1556 nm/RIU, and associate figure of merit (FOM) of 14.83 is recorded. The device is also explored as a temperature sensor with 0.61 nm/°C sensitivity. Since ethanol is used as a sensing medium, the operating range of the sensor is between −114.3 °C and 78 °C, melting and boiling temperature of ethanol. To detect human blood groups using the proposed sensor, a mathematical model is developed, which shows impressive performance for the detection of human blood groups very precisely. Compact size, ultrafine sensitivity, and sharp Fano peak profile make the proposed sensor an ideal candidate for on-chip sensors.

Optical switching of terahertz wave based on asymmetric metamaterial structures

In recent years, research progress in terahertz devices has affected the development of terahertz communications. In this article, an asymmetric metamaterial coated with the GaAs layer is proposed and numerically demonstrated for terahertz wave optical switching. Based on the Fano resonance of the asymmetric metamaterial, the modulation depth of 80% for Fano peak can obtained by changing the conductivity of the GaAs layer via optical pump. In addition, the modulation mechanism is discussed in detail. Therefore, this work proves the feasibility of the structure and its potential application in ultrafast optical pump terahertz switching.

Subwavelength plasmonic liquid sensor using Fano resonance in a ring resonator structure

A plasmonic Metal-Dielectric-Metal waveguide-based sensor with a radius of 0.44 μm is designed by generating Fano resonance in the device which consist of a gap in the main waveguide which acts like a Fabry-Perot structure and a micro ring resonator coupled to the main waveguide. The increased sensitivity of 1200 nm/RIU is achieved by optimizing the device parameters for different kind of liquids. Finite Element Method is used for complete study of the design. For analyzing the transmission modes in plasmonic systems, the normalized Electric Field distributions are calculated. Effect of different gap sizes, different coupling distances between ring & main waveguide and effect of different radius of ring on transmission and sensitivity of device for different liquids is also investigated. A large tunability of 740 nm in Fano peaks is achieved by changing the radius of the ring. The device results are useful in designing nanoscale and highly sensitive sensors for different liquids.

Transmission phase read-out of a large quantum dot in a nanowire interferometer

Detecting the transmission phase of a quantum dot via interferometry can reveal the symmetry of the orbitals and details of electron transport. Crucially, interferometry will enable the read-out of topological qubits based on one-dimensional nanowires. However, measuring the transmission phase of a quantum dot in a nanowire has not yet been established. Here, we exploit recent breakthroughs in the growth of one-dimensional networks and demonstrate interferometric read-out in a nanowire-based architecture. In our two-path interferometer, we define a quantum dot in one branch and use the other path as a reference arm. We observe Fano resonances stemming from the interference between electrons that travel through the reference arm and undergo resonant tunnelling in the quantum dot. Between consecutive Fano peaks, the transmission phase exhibits phase lapses that are affected by the presence of multiple trajectories in the interferometer. These results provide critical insights for the design of future topological qubits.

Investigation of graphene supported terahertz elliptical metamaterials

Abstract Based on a graphene asymmetric sdouble ellipse (ADE) structure, the tunable Fano resonance characteristics in the terahertz range have been symmetrically studied, including the effects of graphene Fermi levels, asymmetrical degrees, operation frequencies and structural parameters. The results show that due to the strong coupling between the incident THz waves and graphene ADE structures, a strong Fano peak can be observed by arranging double ellipse asymmetrically. The maximum peak of Fano resonance reaches 0.918, and its Q-factor is about 20. As the asymmetrical degree of the ADE structure increases, the Fano peak value increases, and the amplitude modulation depth reaches about 75%. As graphene level increases, the amplitude and frequency modulation depths reaches more than 31% and 11%, respectively. These results are very helpful to design novel tunable graphene devices with high Q-factor devices in the future, such as sensors, modulators, and filters.