Fano Resonance Research Articles

Tunable Fano resonances at 2 μm waveband based on a single microring resonator

Abstract Development of silicon photonic devices for the 2 μm waveband is urgent since the 2 μm waveband has been considered as a potential communication window for next-generation optical communications. Asymmetric Fano resonances are very promising in the development of devices such as optical switches, sensors, and modulators for the 2 μm waveband. In this paper, a Fano resonance at the 2 μm waveband is theoretically realized by using a silicon-based microring resonator and the thermo-optic effect is employed to tune it. Utilizing this single microring resonator structure instead of the present coupled microring resonator structures, we achieve the Fano resonance with an extinction ratio of 30.5 dB and a slope ratio of 69.3 dB nm−1 at the 2 μm waveband. The metal heater and graphene heater are designed and optimized to achieve the Fano tuning. The thermal-optical tuning efficiencies are 0.46 nm mW−1, 0.61 nm mW−1 and 1 nm mW−1 for the metal heater, the metal heater with air adiabatic slots, and the graphene heater, respectively. This work provides an effective scheme for the formation and tuning of the Fano resonance at the 2 μm waveband, which is conducive to the development of devices and optical communication systems at the 2 μm waveband.

Multi-Cavity Nanorefractive Index Sensor Based on MIM Waveguide

Within this manuscript, we provide a novel Fano resonance-driven micro-nanosensor. Its primary structural components are a metal-insulator-metal (MIM) waveguide, a shield with three disks, and a T-shaped cavity (STDTC). The finite element approach was used to study the gadget in theory. It is found that the adjustment of the structure and the change of the dimensions are closely related to the sensitivity (S) and the quality factor (FOM). Different model structural parameters affect the Fano resonance, which in turn changes the transmission characteristics of the resonator. Through in-depth experimental analysis and selection of appropriate parameters, the sensor sensitivity finally reaches 3020 nm/RIU and the quality factor reaches 51.89. Furthermore, the installation of this microrefractive index sensor allows for the quick and sensitive measurement of glucose levels. It is a positive contribution to the field of optical devices and micro-nano sensors and meets the demand for efficient detection when applied in medical and environmental scenarios.

On the value of Fano resonance in wave energy converters

The article evaluates the potential of the Fano resonance operational principle in wave energy converters (WECs), using a 2-body loosely moored self-referenced WEC as an illustrative example. By leveraging Fano resonance, the point absorber buoy can remain relatively stationary with low loading on mooring lines, serving as an efficient wave energy transmitter while concurrently achieving resonance within the internal power take-off (PTO) system. This arrangement reduces the motion of the point absorber hull, thereby decreasing loads on the WEC structure, mooring lines, and anchors. As a result, operational and structural costs are minimised, further reducing the levelised costs of generated energy. Additionally, by ensuring minimal fluctuations in the WEC, confidence in using traditional linear mathematical models is increased, as commonly employed for WEC performance assessment and control design.The article presents a resonance study and introduces newly derived solutions in the frequency domain for the proposed operational concept. It analytically demonstrates the viability of employing the Fano resonance operational strategy for WECs, suggesting that this strategy has the potential to compete with traditional methods of wave energy transformation. Furthermore, the insights gained from the study contribute to identifying optimal parameters for a PTO system, as well as optimising the design of the heaving buoy.

Silicon-based double fano resonances photonic integrated gas sensor

The telecommunication wavelengths are crucial for developing a photonic integrated circuit (PIC). The absorption fingerprints of many gases lie within these spectral ranges, offering the potential to create a miniaturized gas sensor for PIC. This work presents novel double Fano resonances within the telecommunication band, based on silicon metasurfaces for selective gas sensing applications. Our proposed design comprises periodically coupled nanodisk and nanobar resonators mounted on a quartz substrate. Fano resonances can be engineered across the range from λ = 1.52 μm to λ = 1.7 μm by adjusting various geometrical parameters. A double detection sensor of carbon monoxide (CO) at λ = 1.566 μm and nitrous oxide (N2O) at λ = 1.674 μm is developed. The sensor exhibits exceptional refractometric sensitivity to CO of 1,735 nm/RIU with an outstanding FOM of 11,570 at the first Fano resonance (FR1). In addition, the sensor shows a sensitivity to N2O of 194 nm/RIU accompanied by an FOM of 510 at the second Fano resonance (FR2). The structure reveals absorption losses of 6.3% for CO at the FR1, indicating the sensor selectivity to CO. The sensor is less selective at FR2 and limited to spectral shifts induced by each gas type. Our proposed design holds significant promise for the development of a highly sensitive double-sensing refractometric photonic integrated gas sensor.

Femto-Laser Processed Metasurface With Fano Response: Applications to a High Performance Refractometric Sensor

The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs. We have engraved a split grating geometry on stainless steel using femtosecond laser processing. This structure serves as a template to fabricate efficient plasmonic sensors, where a thick gold layer is grown conformally on it. The scanning electron microscope (SEM) images confirm the generation of the split laser-induced periodic spatial structures. The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances (SPRs) at two different wavelengths. Furthermore, the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance. Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure. The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction. The parameters extracted from the fitting, such as the resonance wavelengths and line widths, are used to evaluate the performance of our device as a refractometric sensor for liquids. The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU−1, respectively. Besides the compact design of our sensing device, its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup.

Fano resonances in gated phosphorene junctions

Fano resonances appear in plenty of physical phenomena due to the interference phenomena of a continuum spectrum and discrete states. In gated bilayer graphene junctions, the chiral matching at oblique incidence between the spectrum of electron states outside the electrostatic barrier and hole bound states inside it gives rise to an asymmetric line shape in the transmission as a function of the energy or Fano resonance. Here, we show that Fano resonances are also possible in gated phosphorene junctions along the zigzag direction. The special pseudospin texture of the charge carriers in the zigzag direction allows at oblique incidence the interference phenomena of the spectrum of electron states outside the electrostatic barrier with hole bound states inside it, giving rise to an asymmetric Fano line shape in the transmission. Due to the energy scale of the electrostatic barriers in phosphorene ultra thin barriers are required to observe the Fano resonance phenomenon. The preservation of the pseudospin texture with the closing of the phosphorene band gap opens the possibility to observe Fano resonances in smaller and wider electrostatic barriers. The asymmetric Fano line shape is susceptible to the transverse wave vector, the strength and width of the electrostatic barrier. Additionally, the conductance shows a characteristic mark in the position where the Fano resonances take place. The similarities and differences with respect to Fano resonances in bilayer graphene are also addressed.

High order Fano resonance in the time domain for a freezing water microdroplet

Fog is a collection of micro drops of water suspended in the air, formed as a result of cooling of moist air. In supercooled air, water droplets freeze, forming ice fog at air temperatures below − 10–15° C. As the ice drop freezes, it forms a core-shell structure. In such a particle, a high-Q Fano resonance is possible, which entails the formation of a magnetic pulse. Our theoretical calculations have predicted the time-dependent formation of Fano resonances in a freezing the outside in water droplet. Time-varying unconventional Fano resonance with magnetic field enhancement yield new method to manipulate light–matter interactions in a freezing water droplet. To the best of our knowledge this mechanism was not discussed previously.

Engineering Fano resonances in plasmonic metasurfaces for colorimetric sensing and structural colors

In this paper, we present the design and fabrication of a plasmonic metasurface based on titanium dioxide (TiO2) nanowire arrays integrated with plasmonic layers. The structure is engineered to produce Fano resonances within the visible spectrum, resulting from the coupling of localized surface plasmon resonances, lattice modes, and nanowire's optical modes. Experimentally, we show that by tuning the geometrical features of the metasurface, such as the length, diameter, and period of the nanowires, a high-quality factor single peak can be achieved in the reflection spectra, resulting in vivid structural colors in bright field. To our knowledge, this is the first demonstration of such vivid colors with nanowire arrays in bright field reflections. When characterized by refractive index fluids around the refractive index of water, the plasmonic metasurface also showed great potential for biochemical colorimetric sensing. The best design demonstrated a bulk sensitivity of 183 nm/RIU with high Q resonance features and linear changes in color values using image processing.

Ultrafast, Fano resonant colorimetric sensor with high chromaticity beyond standard RGB

Fast-responsive colorimetric sensors with a wide color gamut have garnered significant attention for real-time atmospheric monitoring observable to the naked eye. Although swelling medium-based Fabry–Perot cavities, which enable linear resonance shifts with high Q-factors, have been widely suggested, they face limitations such as a restricted color gamut within standard RGB due to subtractive colors and slow response times caused by the top layer blocking, delaying the swelling medium’s equilibrium time. Here, we present two-dimensionally nanostructured Fano resonant colorimetric sensors using a swelling medium with significantly improved responsiveness and color representation beyond standard RGB. The nanostructured Fano resonator is elaborately designed to transform the spectral line shape into a Lorentz state in terms of reflectance, resulting in additive color through controlled coupling parameters of the resonator systems. In addition, the nanostructuring of the surface provides direct channels to water vapors, ensuring fast and strong interaction with the swelling medium. Consequently, the fabricated sensor exhibits a wide color gamut, covering 141% of standard RGB and 105% of Adobe RGB, and demonstrates rapid responsiveness with response and recovery times of 287 ms and 87 ms, respectively.

Transmission enhancement mechanism of PT symmetric photonic crystal coupled with grooved sub-wavelength grating

In order to enhance the sensing characteristics of the sensor, based on the periodic sub-wavelength grating(SWG), a groove structure is introduced to make the Fano resonance waveform sharper. At the same time, based on the Parity-Time(PT) symmetry principle, by making the periodic photonic crystal meet the PT symmetry condition, the structure can absorb the energy of the emitted light on the original basis, produce the transmission enhancement effect, and make the transmission peak of the structure exceed 1. The sensing is realized by using the property that the different refractive indices of the detected medium corresponds to different transmission. When the incident light is 1550 nm, the sensitivity and FOM (Figure of Merit) value of the proposed structure reach 5.702 × 105RIU−1and 1.9 × 107 respectively, which greatly improves the performance of the sensor.

Spectral prediction of all dielectric nanopore metasurface based on DBO-DNN model

Based on the optical properties of symmetric structures independent of each other in the orthogonal direction, a class of all-dielectric nanohole array metasurfaces symmetrical along the diagonal is designed. By adding nanopores of different shapes to break the symmetry of the periodic unit structure, the double Fano resonance is excited. The spectral characteristics of metasurfaces with the same structure type are studied by finitedifference timedomain (FDTD) method. The deep neural network (DNN) is used to establish the nonlinear mapping relationship between the input structural parameters and the transmission spectrum. The number of hidden layers in the DNN and the number of neurons in each layer are optimized by the dung beetle optimization (DBO) algorithm. Therefore, the number of hidden layers of the model is determined to be 5, and the number of neurons in each layer is 120, 30, 150, 60, 90, respectively. The mean square error (MSE) is used to evaluate the training effect of DNN after optimization search. After 35,000 epochs of training, MSE is reduced to 0.0003926. The influence of different gradient descent optimization algorithms on the prediction results is explored respectively, and it is found that Adamax is the most effective. The results show that the prediction model can predict the spectrum within 1 s. Compared with the traditional simulation method, the simulation time is effectively saved. Meet the requirements of efficient and rapid design of ultra-thin lenses. For the same type of metasurface structure, the transmission spectrum can be accurately predicted without multiple data sets.

Dynamic nonlocal metasurface for multifunctional integration via phase-change materials

Abstract Non-local metasurface supporting geometric phases at bound states in the continuum (BIC) simultaneously enables sharp spectral resonances and spatial wavefront shaping, thus providing a diversified optical platform for multifunctional devices. However, a static nonlocal metasurface cannot manipulate multiple degrees of freedom (DOFs), making it difficult to achieve multifunctional integration and be applied in different scenarios. Here, we presented and demonstrated phase-change non-local metasurfaces that can realize dynamic manipulation of multiple DOFs including resonant frequency, Q values, band, and spatial wavefront. Accordingly, a metasurface integrating multiple distinct functions is designed, as a proof-of-concept demonstration. Utilizing the geometry phase of quasi-BIC and the tunability of vanadium dioxide (VO2), a dynamic meta-lens is achieved by tailoring spatial light response at quasi-BIC in the temperature range from room temperature to 53 °C. Simultaneously, the sharp Fano resonance of quasi-BIC enables the metasurface to serve as an optical sensor in the mid-infrared band, yielding a sensitivity of 7.96 THz/RIU at room temperature. Furthermore, at the metallic state of VO2 (80 °C), the designed metasurface converts into a mid-infrared broadband absorber, achieving higher than 80 % absorptivity and an average absorption of 90 % from 28.62 THz to 37.56 THz. The proposed metasurface enabling multifunctional performances in different temperatures can effectively improve the availability of devices and find more new and complex scenarios in sensing, imaging, and communications.

Fano mode based plasmonic sensor for temperature and chemical pollutant detection

Plasmonic sensors provide great sensitivity to minute quantities of analytes and provide excellent detection. In present context of environmental monitoring, plasmonic sensor can prove to be an excellent choice in chemical pollutant and temperature detection. Plasmonic sensors can provide immediate results, allowing for monitoring temperature changes in ecosystems or climate studies and quick decision-making in emergency situations related chemical pollution incidents. They are compact and can be integrated into portable devices for on-site analysis. In this investigation, a plasmonic refractive index sensor based on key ring shaped resonator consisting of a microring resonator and two rectangular resonator is proposed. Finite-Difference Time-Domain (FDTD) method is used to study the transmittance characteristics of the sensor. The device exhibits quadruple Fano resonance with highest sensitivity of 2521.7 nm/RIU. Other performance parameters such as figure of Merit (FOM), Quality (Q) factor and Detection limit (DL) are also been calculated, with values 98.8 RIU−1, 99.6 and 0.01 respectively. Additionally, the effects of different geometrical configurations is also studied, providing insights into the design principles in context of potential fabrication complexities. Further, the simulated Fano characteristic is validated against the theoretical value. The application of the proposed sensor is investigated for different types of analyte such as chemical pollutants and temperature sensing.

Enhanced high-harmonic generation in a polarization-insensitive all-dielectric metasurface exploiting dual-Fano resonance

Nonlinear optics demands efficacious techniques for nonlinear properties engineering. Metasurfaces, as a flat technology with easy fabrication in various arrangements and without the need for phase-matching conditions, are suitable platforms for nonlinear optics. This study proposes a silicon metasurface with special geometry that provides high conversion efficiency by exploiting Fano resonances and the excitation of magnetic and toroidal dipoles. The results indicate the high efficiencies of third harmonic generation of 5.17×10−3 W−2 and fifth harmonic generation of 7.92×10−9 W−4 under 1 GW/cm2 pump intensity in the near-infrared regime. More specifically, linear and nonlinear optical responses of the structure are completely polarization-independent.

Tunable Fano-type resonance with quadrature squeezing in a double-cavity-waveguide structure of photonic crystals

We propose an optical approach to realizing Fano-type spectra of quadrature squeezing in a double-cavity-waveguide structure based on photonic crystals (PhCs). In this scheme, a partially transmitting element (PTE) in the waveguide creates the transmission and reflection light, which interferes with the outflow from the intracavity field and subsequently gives rise to Fano-type interference. Meanwhile, a degenerate parametric amplifier (DPA) embedded into the cavity is expected to yield quantum squeezed states in the interference process. After verifying the existence of the Fano resonance, we report that increasing the nonlinear gain of the DPA not only amplifies the transmitted intensity of the output field, but also improves its quadrature squeezing degree. More importantly, we illustrate that, when maintaining the high performance of quadrature squeezing, the linewidths and frequencies of the asymmetrical spectra can be modulated by adjusting the double-cavity coupling strength. This combination of Fano-type spectra and quadrature squeezing is beneficial for optimizing optical communications and signal processing with a low noise level.

High-Q fano resonance metasurface sensor for refractive index and methane gas concentration measurement

High-quality-factor Fano resonances excited by metasurfaces have been playing an important role in the field of optical sensing. A high-performance sensor for refractive index and methane concentration measurement is designed and prepared in this paper. The symmetry of the structure is broken by altering the size of the rectangular holes in the tetramer, resulting fano resonance Q-factor of 34176 and modulation depth of 100%. The finite-difference time-domain (FDTD) method is used to simulate the structure. The results show that the refractive index and methane concentration sensitivity are 325 nm/RIU and −1.44 nm/%, respectively. The FOM can achieve 10156 RIU−1. Furthermore, experiments are carried out on the gas application of the structure and the sensitivity of methane concentration is −1.03 nm/%. Therefore, the proposed metasurface has more practical and feasible significance in background refractive index and gas environment monitoring.

Low-frequency broadband acoustic ventilation meta-barrier based on consecutive multiple Fano resonances

Acoustic metamaterials utilizing Fano resonance provide the possibility of simultaneous airborne sound insulation and high-performance ventilation. However, the ultra-sharp line shape results in a narrow working frequency range, which is still insufficient for practical applications. In this work, we propose a low-frequency acoustic meta-barrier supporting consecutive multiple Fano resonances (CMFRs) with broadband (~75%) capability, efficient ventilation, and ultra-thin thickness, etc. The barrier features a binary metastructure, incorporating a chiral space coiling tunnel and a hollow pipe in a planar arrangement. This configuration offers discrete and continuous states within the composed Fano system, corresponding to the tunnel and the pipe, respectively. By means of superposition of multi-order Fano resonance modes, the destructive interference between the discrete and continuum states keeps effective in a broad frequency range, while simultaneously achieving high air permeability. Numerical results of transmission loss show significant attenuation of incident energy in the range of 479-1032 Hz. Our work lays the groundwork for next generation of Fano-based metamaterial applications, with far-reaching implications for noise control and related fields.

Enhanced sensor based on Fano resonance in a Al2O3/Ag hybrid metamaterial

Enhanced sensor based on Fano resonance in a Al2O3/Ag hybrid metamaterial

Optical Extinction-Based 3D Nano-Imaging of WS2 on Gold.

Broadband nanoextinction images recorded in tip-enhanced optical spectroscopy geometry track the 3D topography of a single layer of WS2 on Au substrate. The described nano-optical method is complementary to conventional atomic force microscopy and offers additional information about the buried material-metal interface that is not accessible using conventional topographic imaging. Beyond 3D optical imaging, we observe large variations in the junction plasmon resonance on the nanoscale. The latter is important to understand and account for in tip-enhanced Raman and photoluminescence studies that target low-dimensional materials specifically. Our observations and (coherent) optical scattering-based method are also relevant to emerging efforts aimed at exploring strong coupling and Fano interferences in hybrid plasmonic-low dimensional quantum material systems.

Boosting thermoelectric performance of molecular junction by utilizing edge branches and weak coupling

In this study, we investigated the thermoelectric properties of molecular junctions, created by trapping naphthacene (C18H12) and rubrene (C42H28) molecules between two graphene electrodes. It is found that the charge transport of naphthacene-based and rubrene-based graphene junctions is not sensitive to the introduction of edge side branches or the increase in molecular length and still maintains resonance transport at the Fermi level. Notably, the presence of pendant branches on the molecular trunk in rubrene-based graphene junctions leads to a suppression of phonon transport, attributed to multiple scattering at the branch attachment points or Fano resonance scattering. The phonon thermal conductance of the rubrene junctions can be reduced by nearly half compared to that of naphthalene junctions. Furthermore, the room-temperature figure of merit (ZT) is significantly enhanced from 0.2 to 1.1 upon constructing weak coupling junctions, representing an almost tenfold increase over covalent junctions. These findings mean that it is highly desirable to find a mechanism that can suppress the phonon thermal conductance of self-assembled molecular films, while preserving their power factor at optimal levels to obtain high-efficiency thermoelectric performance.