Tunable Resonance Research Articles

Highly sensitive CH4, C2H2 and CO simultaneous measurement LITES sensor based on multi-pass cell with overlapped spots pattern and QTFs with low resonant frequency.

This paper presents a simultaneous measurement light-induced thermoelectric spectroscopy (LITES) sensor with high sensitivity for detecting methane (CH4), carbon monoxide (CO) and acetylene (C2H2). It employs a multi-pass cell (MPC) with an overlapped spots pattern and low resonant frequency circle-head quartz tuning forks (QTFs) for the first time. The fiber-coupled MPC with an optical length (OPL) of 40 m was combined with a thin-film filter (TFF) to improve the laser absorption and enable light spots multiplexing on mirrors. Three self-designed circle-head QTFs with low resonant frequencies of less than 10 kHz and a quality factor of ∼ 11500 were adopted to improve the detection ability. The LITES sensor detected multi-gas signals based on their unique absorption spectrum, enabling real-simultaneous measurement of CH4, CO, and C2H2. After optimization, the minimum detection limits (MDLs) of 0.5 ppm, 126.9 ppm and 0.4 ppm for these gases were obtained, respectively. With integration times of 300 s for CH4 and 200 s each for CO and C2H2, the MDLs could be further reduced to 0.09 ppm, 57.1 ppm, and 0.07 ppm, correspondingly. The paper concludes with a discussion of potential strategies for further improving the performance of such LITES sensors.

Distributed Bragg reflector based ASE noise removal pump wavelength filters for futuristic chip-scale quantum photonic circuits.

This article reports a novel design of a compact tunable resonance filter with a highly extinguished and ultra-broad out-of-band rejection for on-chip amplified spontaneous noise suppression from pump lasers highly demanding for generating pure/entangled photon pairs via χ(3) process in a CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Perot resonant transmissions in a silicon-on-insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength. We observed that a device length of as low as ∼ 35 µm exhibits a rejection band as large as ∼ 60 nm with an extinction of ∼ 40 dB with respect to the resonant wavelength peak at λr ∼ 1550 nm (FWHM ∼ 80 pm, IL ∼ 2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modeling results in terms of its stop bandwidth and resonance wavelength for noise suppressed pump laser wavelength filtering. As expected from the theoretical prediction, the trend pertaining to the trade-off between passive insertion loss and Q-value of the resonances has been observed depending on the device parameters. The thermo-optic tuning characteristics of resonant wavelengths have been obtained by integrating microheaters. The resonance peak could be tuned at a rate of 96 pm per mW of consumed thermal power. Noise associated with an amplified pump wavelength (λP ∼ 1550 nm) has been shown to be suppressed (∼ 40-dB), up to the detector noise floor.

Tunable plasmonic resonance by photothermal deformation in Ag-SiO2 semi-shell nanostructures and enlargement of the controllable spectral region by UV-curable resin

Tunable plasmonic resonance by photothermal deformation in Ag-SiO2 semi-shell nanostructures and enlargement of the controllable spectral region by UV-curable resin

Quad-band circularly polarized graphene tunable SIW-dielectric resonator antenna for 6G THz applications

Quad-band circularly polarized graphene tunable SIW-dielectric resonator antenna for 6G THz applications

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.

Frequency tunable mid-infrared split ring resonators on a phase change material

Meta-surfaces arrays are 2D meta-materials with a periodicity below the diffraction limit that permits to obtain homogeneous layers of resonant effective refractive index. In this work we present an analytical model that describes the electromagnetic behavior of meta-surfaces constituted by split-ring resonators (SRR). SRR resonance frequency can be adjusted by choosing their geometric parameters and the materials they are made of. Their deposition on a phase change material enables an optical modulation of resonance peak during the phase transition. We demonstrate a mid-infrared tunable SRR meta-surface using Vanadium dioxide (VO2) as phase change material deposited on III-V semiconductors by low temperature pulsed laser ablation technique. The presented measurements exhibit a maximum of 100 cm−1 resonance shift. This result is very promising for the conception of monolithic, robust, compact, frequency tunable III-V based devices in the mid-infrared.

Tunable elastic wave transmission and resonance in a periodically aligned tube-block structure

A tube-block structure is proposed to realize tunable elastic wave transmission and resonance, consisting of periodically aligned circular tubes sandwiched and joined by two blocks. Finite element simulations for a unit structure are carried out to reveal the frequency dependence of the transmission behavior for the normal incidence of longitudinal and transverse waves in the tube-block structure. As a result, the transmission ratios are found to take multiple local maxima at different peak frequencies. Eigenfrequency analysis shows that the local resonances of the tube and the block surfaces occur at the peak frequencies in the transmission ratios. The peak frequencies originating from the local resonance of the tube depend on its radius and thickness, while those from the resonance on the block surfaces are in good agreement with the theoretical relation between the interval of the periodically aligned tubes and the wavelength of the Rayleigh wave. Furthermore, when the tube-block structure is subjected to compressive loading, the deformation shifts the peak frequencies of the transmission ratio corresponding to the local resonance of the tube. This result implies that the proposed structure has the potential to serve as a tunable meta-interface between solid blocks.

Ultra-high precision comb-locked terahertz frequency-domain spectroscopy of whispering-gallery modes

We demonstrate the capabilities of a novel frequency-domain terahertz spectrometer based on a comb-locked frequency synthesizer, which provides absolute frequency calibration. The inherent stability and repeatability of the scans allow for the combination of fast data acquisition with an average time-limited signal-to-noise ratio. We demonstrate kilohertz level frequency resolution in terahertz precision spectroscopy of ultra-high quality whispering-gallery-mode resonators. Spectra covering multiple free spectral ranges (>36 GHz) with sub-20 kHz resolution are acquired in 5 s. We analyze the coupling behavior and temperature tuning of single resonances and, for the first time, observe minute red and blue shifts of different mode families. The experimental results are supported with finite element simulations.

PCB-Based Electrically Tunable Resonator for VHF Band Rydberg Atomic Enhancement Sensing

PCB-Based Electrically Tunable Resonator for VHF Band Rydberg Atomic Enhancement Sensing

Versatile Nanoring Fabrication Assisted by Hole-mask Colloidal Lithography.

Nanomaterials shaped as rings are interesting nanostructures with control of the materials properties at the nanoscale. Nanoring plasmonic resonators provide tunable optical resonances in the near-infrared with application in sensing. Fabrication of nanorings can be carried out via top-down approaches based on electron beam lithography with high control of the ring size parameters but at high cost. Alternatively, fabrication via self-assembly approaches has a higher speed/lower cost but at the cost of control of ring parameters. Current colloidal lithography approaches can provide nanoring fabrication over large areas but only of specific materials and a select set of rings (large ring diameters or small rings with ultrathin walls). We extend Hole-mask Colloidal Lithography to use ring shaped holes, allow the deposition of arbitrary materials, and allow the independent tuning of ring-wall thickness over a large range of values. We present a generic approach for the fabrication of nanorings formed from a range of materials including low cost (e.g., Cu, Al) and nonplasmonic (e.g., W) materials and with control of ring wall thickness and diameter allowing tuning of ring parameters and materials for applications in nanooptics and beyond.

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.

Tunable high-Q resonances based on the asymmetric nanohole array of phase-change material

Dielectric metasurfaces have made great progress over the past decade to enhance light-matter interaction. Recently, dielectric nanohole structures have been employed for the creation of dielectric metasurfaces. However, the optical characteristics of most dielectric nanohole structures remain fixed once they are manufactured. This study investigates the optical properties of Ge2Sb2Te5 (GST) film perforated with a periodic dual nanohole array. The GST dual nanohole array is capable of supporting multiple guided resonances and bound states in the continuum (BICs). By introducing asymmetry in the radius, BICs can be transformed into quasi-BICs with high-Q resonances. The wavelengths of guided resonances and quasi-BICs can be dynamically controlled through the phase transition of GST. Furthermore, modifying the gap allows for the achievement of active high-Q electromagnetically induced transparency, resulting from the interaction between one guided resonance and one quasi-BIC mode. The GST asymmetric nanohole array holds potential for applications in optical modulators, slow-light devices, and nonlinear optical devices.

On the Photothermal Response of DNA–Au Core/Shell Nanotoroids as Potential Agents for Photothermal Therapies

Plasmonic nanoparticles play a pivotal role in various research areas due to their exceptional optical and thermo‐optical properties, like high spectral tunability and efficient light‐to‐heat conversion. Gold, with its biocompatibility, low cytotoxicity, and tunable resonances , makes gold nanoparticles ideal for photothermal therapies. Geometries, including spheres, core–shells, rods, disks, stars, nanocages, and nanotoroids, are extensively studied, with the gold nanodoughnut emerging as one of the most promising ones due to its ability to produce high temperatures and rotational stability. Nevertheless, the fabrication of metallic toroidal shapes remains a challenge. Recent advances in DNA‐based nanotechnology, especially DNA‐origami techniques, provide feasible route for the fabrication of this geometry through metallization reactions or attachment of metal nanoparticles. However, particles manufactured using this method possess a DNA core that influences their thermoplasmonic performance. In this work, a theoretical investigation is conducted on the thermoplasmonic response of DNA‐origami‐based core/shell toroids (CSTs) for photothermal applications. Key parameters that optimize the CST thermoplasmonic response are identified, and compared with their solid counterparts and discrete metallic coatings. Additionally, the CSTs tolerance to random rotations is assessed, providing insights into their behavior in fluidic environments and implications for its practical consideration.

Random lasing using laser generated and modified silver nanoparticles

The authors report incoherent random laser action in systems where the optical feedback is provided by multiple scattering generated by different classes of silver nanoparticles in the colloidal state, having plasmon resonances at different frequencies. They found improved performance of triangular silver nanoplates as compared to nanospheres, with a threshold as low as 1 mJ/cm2 and a 5 times lower optimal silver concentration, due to plasmonic enhancement effects and tuning of the plasmon resonance. The nanoparticles were also tested for stability against illumination by the pump laser, as the onset of pulsed laser melting is comparable to random laser threshold in terms of pump fluence, severely limiting the range of operation of nanoparticles with main plasmon resonance close to the pump wavelength. The optimal approach to choose plasmonic nanoparticles for random lasing must, therefore, take the stability aspect into serious consideration as well as the plasmonic enhancement of random lasing.

Ultrathin absorber with independently tunable dual-resonances for terahertz sensing

A technique is implemented for the generation and alteration of two independently tunable resonance peaks in a graphene based ultrathin absorber structure designed for the terahertz spectrum. The proposed structure is a multi-layered stacked arrangement of two resonator layers of graphene grown over the top of two isolated dielectric (SiO2) substrate layers shielded by a gold metal reflector at the bottom. The structure exhibits very low thickness profile and can be implemented with a thickness equivalent to λ/19.6 where λ is the free space wavelength. Two patterned graphene layers contributes to two independently tunable narrowband/near-perfect absorption peaks at 9.56 THz and 10.96 THz. This polarisation insensitive absorber structure also exhibits frequency ratio tunability of higher order mode with respect to lower order mode by distinctly/separately varying the Fermi level of graphene layers. The response is stable for a wider angle of wave incidence up to 70°. Its narrowband response makes it a suitable candidate to be utilized as biosensor for refractive index sensing.

Quasi-BICs enhanced second harmonic generation from WSe2 monolayer

Abstract Quasi-bound states in the continuum (quasi-BICs) offer unique advantages in enhancing nonlinear optical processes and advancing the development of active optical devices. Here, the tunable robust quasi-BICs resonances are experimentally achieved through the engineering of multiple-hole Si-metasurface. Notably, the quasi-BICs mode exhibits flat bands with minimal dispersion at a wide range of incident angles, as demonstrated by the angle-resolved spectroscopy measurements. Furthermore, we demonstrate a giant second-harmonic generation (SHG) enhancement by coupling a WSe2 monolayer to the quasi-BICs hosted in the metasurface. Leveraging the strong local electric field and high state density of the observed quasi-BICs, the SHG from the WSe2 monolayer can be enhanced by more than two orders of magnitude. Our work paves the way for effectively enhancing nonlinear optical processes in two dimensional (2D) materials within the framework of silicon photonics and is expected to be applied in nonlinear optical devices.

Tunable Fano resonance in mid-infrared region based on asymmetric graphene nanoribbon arrays

Tunable Fano resonance in mid-infrared region based on asymmetric graphene nanoribbon arrays

Wirelessly Powered and Bi-Directional Data Communication System With Adaptive Conversion Chain for Multisite Biomedical Implants Over Single Inductive Link.

A wirelessly powered and data communication system is presented which is implemented as a full system, designed for multisite implanted biomedical applications. The system is capable of receiving wireless power and data communication for each implant separately, using inductive links with different resonance frequencies. To achieve this, dual-band coils are presented in the system. In addition, the system supports bi-directional half-duplex data communication, utilizing amplitude and load shift keying (ASK and LSK) modulation schemes over a single inductive link. The system employs a digitally assisted active rectifier and an automatic resonance tuning system, to improve the power transfer efficiency (PTE) through various coupling coefficients, while minimizing the reverse current and power dissipation. The power control unit enables closed-loop monitoring to prevent high or low power delivery, and it can detect inefficient or excessive wireless power transmission or prevent temperature elevation by limiting the voltage to a safe level. A new structure of self-sampling separated- Vb ASK demodulator is proposed in the paper which is utilized within the data conversion chain, serving both the external and implanted units. The whole system is fabricated using a standard 180-nm 1.8/3.3 V CMOS process with a core area of 0.82 mm[Formula: see text]. The system is tested with coupled multisite inductive links and offers the maximum overall PTE of 31.2%, from the Tx coil to the implant load.

Observing S-Matrix Pole Flow in Resonance Interplay

We provide an overview of experiments exploring resonances in the collision of ultracold clouds of atoms. Using a laser-based accelerator that capitalises on the energy resolution provided by the ultracold atomic setting, we unveil resonance phenomena such as Feshbach and shape resonances in their quintessential form by literally photographing the halo of outgoing scattered atoms. We exploit the tunability of magnetic Feshbach resonances to instigate an interplay between scattering resonances. By experimentally recording the scattering in a parameter space spanned by collision energy and magnetic field, we capture the imprint of the S-matrix pole flow in the complex energy plane. After revisiting experiments that place a Feshbach resonance in the proximity of a shape resonance and an anti-bound state, respectively, we discuss the possibility of using S-matrix pole interplay between two Feshbach resonances to create a bound-state-in-the-continuum.

Tunable Fano resonance in a novel compact metal–insulator–metal structure

A novel compact scheme to realize tunable Fano resonance is proposed and investigated theoretically and numerically. The scheme is based on two slot cavities in a metal–insulator–metal structure. The model and formation mechanism of Fano resonance in this structure are studied. A new method based on four-mode temporal coupled-mode theory is used to analyze model of the structure with two slot cavities. Compared with previous studies, this method only considers the interaction between modes within two cavities rather than considering the energy coupling between them. The tunability and slow light phenomenon in the new structure are also studied. It is believed that research in this article can provide a new method to achieve Fano resonance. Furthermore, it is helpful to establish the Fano resonance model and reveal the formation mechanism of Fano resonance.