Tunable Resonance Research Articles

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

Non-volatile compact optical phase shifter based on Ge2Sb2Te5 operating at 2.3 µm

We investigate an optical phase shifter based on Ge2Sb2Te5 (GST) integrated with a Si waveguide at mid-infrared (MIR) wavelengths. Since the optical absorption of both amorphous and crystalline GST can be reduced at a longer wavelength, we demonstrate that the optical loss of the phase shifter can be reduced at MIR wavelengths. The measured optical loss per π phase shift of a phase-change material (PCM) phase shifter at 2.32 µm wavelength is 2.6 dB/π, which is more than 80 times smaller than that at 1.55 µm wavelength (21.7 dB/π) and more than 5 times smaller than that at 1.92 µm wavelength (9.7 dB/π). Moreover, resonance wavelength tuning of an add-drop micro-ring resonator using a PCM phase shifter at 2.32 µm wavelength is demonstrated owing to the low-loss optical phase shift. These findings reinforce the applicability of the approach toward a low-loss optical phase shifter based on PCMs operating at MIR wavelengths on a Si photonic platform for quantum computing, sensing, and optical communication.

Detection band expansion by independently tunable double resonances in a long-wavelength dual-color QWIP.

Multi-resonance light coupling management is a promising way to expand the operating spectral ranges of optoelectronic devices. The classical strategies are either lack of independent tunability for each resonance or involved with complex fabrication. Here, we propose a new scheme for expanding the operating spectral range of an optoelectronic device through a dual-color active material integrated with a simple resonant waveguide structure. The TM waveguide mode and the SPP mode of the resonant waveguide structure are regulated to match the two active regions of the dual-color material both spectrally and spatially. Applying this scheme to a long-wavelength infrared quantum well photodetector, the absorption efficiencies at the two peak detection wavelengths of the dual-color quantum wells are both enhanced by more than 10 times compared with the case of a standard 45° edge facet coupled device with the same detection material. The simple light coupling structure is easy to accomplish and compatible with focal plane arrays. For thermal radiation detection, the absorption efficiency of the 300 K blackbody radiation by our dual-color detector is 83.8% higher than that by a single-color detector with the optimized structural parameters. Moreover, either polarization sensitive or polarization insensitive detection could be achieved in this dual-color infrared quantum well photodetector by using anisotropic or isotropic gratings.

Tunable Topological Fano Resonances in Graphene-Based Nanomechanical Lattices

A topological Fano resonance with ultrasharp asymmetric line shape is sensitive to external parameters and is immune to structural disorder, and thus, acts as a robust sensor. Here, an ultracompact tunable on-chip integrated topological Fano resonance is designed based on graphene-based nanomechanical phononic crystals. The Fano resonance comes from the interference between topologically protected even and odd edge modes at the interface between trivial and nontrivial insulators. The two edge modes have different edge-mode widths, resulting in distinct resonant lifetimes. The resonant frequency can be adjusted by employing different gate voltages, which can vary the tension of the graphene membrane. Such tunable topological Fano resonances can be applied to design a wide variety of highly sensitive and accurate robust sensors, including extremely tiny forces, masses, and spatial positions.

Tunable stochastic resonance based on the optimization of centrifugal distance for rotation-induced energy harvesting

Energy harvesting from rotating systems has been developed into an important topic as a promising solution for realizing the powering applications of tire monitoring systems. Because of relatively narrow bandwidth of the efficiently operating response, this paper proposes a principle for optimizing the centrifugal distance for tuning frequency matching between stochastic resonance and the external rotation environments. It can minimize the negative effect of a low energy orbit owing to the optimally stabilized stochastic resonance, particularly over the low frequency range before high energy orbit oscillation. The centrifugal force caused by the behavior of rotation acting on the tip mass of the cantilever changes the equivalent stiffness of the cantilever and thus can tune the variation in the Kramers escape rate. Through the match-able relationship of a non-linear bitable system between the Kramers rate and the external rotation frequency, the expression of the optimally centrifugal distance can be solved by theoretical derivation and numerical analysis. The results of simulations and laboratory experiments simultaneously demonstrate that the centrifugal distance is tuned to be the optimal 6.45 cm as theoretically analyzed, and the effective bandwidth of energy harvesting can be stabilized from 30 rad s−1 to 50 rad s−1. While its maximum root mean square voltage can reach the value of 1.23 V corresponding to a harvesting average power of 45.55 μW, owing to the high matching relationship between stochastic resonance and external rotation frequencies. Thus, by the theoretical optimization of centrifugal distance, the frequency of stochastic resonance can be tuned for matching the externally rotating environments, and further improving the operating performance of rotating-induced energy harvesting.

High performance piezoelectric vibration energy harvesting by electrical resonant frequency tuning

Extending the frequency bandwidth (BW) of vibration energy harvesters (VEH) that power wireless sensor nodes is of scientific and industrial interest. In this aim, electrical methods to tune the resonant frequency of piezoelectric harvesters with strong electromechanical coupling coefficients have been developed. In this work, we provide guidelines for designing such strongly coupled VEH and present a broadband harvester with high normalized power density (NPD). Through an analytical model, we explain how the coupling coefficient and the quality factor of a cantilever can be jointly maximized, thereby maximizing the figure of merit . The proposed cantilever prototype made of PZN-5.5PT and aluminum offers one of the best coupling coefficients among the state-of-the-art (k 2= 49.8%) and a high quality factor (Qm = 140). Associated to an appropriate tunable electrical interface (short-circuit synchronous electric charge extraction (SECE) in our case), the prototype exhibits a NPD of 12.0 mW g−2 cm−3 and a frequency BW of 36.0% (56.5 Hz around 157 Hz) at 0.34 m s−2 with a tunable electrical interface: the short-circuit SECE. This represents the highest product NPW × BW from state of the art.

Projected sensitivity of DMRadio-m3 : A search for the QCD axion below 1 μeV

The QCD axion is one of the most compelling candidates to explain the dark matter abundance of the universe. With its extremely small mass ($\ll 1\,\mathrm{eV}/c^2$), axion dark matter interacts as a classical field rather than a particle. Its coupling to photons leads to a modification of Maxwell's equations that can be measured with extremely sensitive readout circuits. DMRadio-m$^3$ is a next-generation search for axion dark matter below $1\,\mu$eV using a $>4$ T static magnetic field, a coaxial inductive pickup, a tunable LC resonator, and a DC-SQUID readout. It is designed to search for QCD axion dark matter over the range $20\,\mathrm{neV}\lesssim m_ac^2\lesssim 800\,\mathrm{neV}$ ($5\,\mathrm{MHz}<\nu<200\,\mathrm{MHz}$). The primary science goal aims to achieve DFSZ sensitivity above $m_ac^2\approx 120$ neV (30 MHz), with a secondary science goal of probing KSVZ axions down to $m_ac^2\approx40\,\mathrm{neV}$ (10 MHz).

Ferrimagnet based spin Hall detector of subterahertz frequency signals

A concept of a subterahertz (sub-THz) frequency range signals detector based on a ferrimagnet/normal metal (FiM/NM) heterostructure is proposed. An external linearly polarized electromagnetic (EM) wave excites precession in the FiM and spin pumping at the FiM/NM interface. The excited spin current in the NM converts into a direct current via the inverse spin Hall effect. We show that non-zero uncompensation between magnetic spins in FiM gives a non-zero output rectified voltage for both “easy axis” and “easy plane” uniaxial anisotropies. The increase in the uncompensation parameter removes degeneracy from two normal resonance modes and changes the sensitivity to the EM wave. Namely, the sensitivity of the higher mode increases, and the lower mode decreases with increasing the uncompensation parameter. We believe that our results can be helpful for the practical development of sub-THz frequency tunable resonance detector based on the FiM.

Actively Tunable and Polarization-Independent Toroidal Resonance in Hybrid Metal-Vanadium Dioxide Metamaterial

A tunable toroidal resonance generated in hybrid metal-vanadium dioxide metamaterial, which is composed of rectangular aluminum split ring interconnected with VO2 strips, is proposed and illustrated in this paper. Simulation results show that the toroidal dipolar resonance is generated by two reversed closed-loop poloidal currents co-excited by aluminum and vanadium dioxide, and the toroidal dipolar resonance is insensitive to the polarization angle because of symmetrical structure. In addition, the calculated scattered powers show that the toroidal dipolar resonance is remarkable and plays a dominant role in the vicinity of transmission dip. Moreover, the amplitude of toroidal resonance can be actively tuned by conductivity of VO2, and theoretical fitting is carried out to further reveal the physical mechanism. The fitting results indicate that the physical mechanism can be attributed to the variation of overall damping rate caused by tuning conductivity of vanadium dioxide. This work can enrich the actively tunable toroidal dipolar metamaterial and have potential applications in terahertz high–Q-factor sensors.

1550 nm light activatable photothermal therapy on multifunctional CuBi2O4 bimetallic particles for treating drug resistance bacteria-infected skin in the NIR-III biological window

Nanomaterial mediated phototherapies are believed to be promising candidates to overcome the bacterial drug resistance crisis. However, due to the lack of nanomaterials able to absorb long NIR light, especially in the NIR-III (1500–1850 nm) and -IV (2100–2300 nm) regimes, it was never investigated the utilization of NIR-III and NIR-IV light for in vivo treatments of cancer or bacterial infections. To this end, plasmonic metal-doped transition metal oxides (TMO) are attracting a great attention due to their tunable surface plasmon resonance absorption to the NIR region. Unique features with extendable NIR light absorption of plasmonic metal-doped transition metal oxides make their applications very attractive in several fields, but their utilization for bacterial infection treatments was not yet reported. Moreover, up-to-date bacterial eradication was limited to phototherapies in the NIR-I (700–950 nm) and NIR-II (1000–1350 nm) biological windows (BWs) and has not yet been studied in the NIR-III (1500–1870 nm) BW. To overcome these literature limitations, we engineered NIR-III (1550 nm) light activatable multifunctional plasmonic CuBi2O4 bimetallic particles (i.e., CBO bMPs) with very high molar extinction coefficients (2.75 × 1011 M−1cm−1 @ 808 nm, 2.75 × 1011 M−1cm−1 @ 980 nm, and 3.5 × 1011 M−1cm−1 @1550 nm), able to absorb and convert long NIR (980 and 1550 nm) light energy to thermal heat and generate cytotoxic reactive oxygen species (ROS) for in vivo treatment of drug resistant bacterial infections. Our in vitro and in vivo results reveal that NIR-III (1550 nm) light irradiation of CBO bMPs exerts a remarkable in vivo antibacterial activity via NIR-III photothermal therapy (NIR-III PTT), which is superior than its corresponding NIR-I (808 nm) PTT and NIR-II photodynamic therapy (NIR-II PDT, 980 nm). We observed that hyperthermia-based photothermal therapy is more effective than ROS-based photodynamic therapy in killing multi-drug resistant bacteria. We also show that CBO bMPs also show an enzyme oxidase and peroxidase like activity, which is an additional asset to enhance the therapeutic efficiency.

Inverse Modeling and Optimization of CSRR-Based Microwave Sensors for Industrial Applications

Design optimization of multivariable resonators is a challenging topic in the area of microwave sensors for industrial applications. This article proposes a novel methodology for rapid redesign and parameter tuning of complementary split-ring resonators (CSRRs). Our approach involves inverse surrogate models established using preoptimized resonator data as well as analytical correction techniques to enable rapid adjustment of geometry parameters and CSRR optimization over broad ranges of operating frequencies. The tuning process is arranged to precisely allocate the operating frequency while maximizing the quality factor of the circuit. The procedure is generic and characterized by an extremely low computational cost of up to two electromagnetic (EM) analyses of the circuit at hand (not counting the inverse model setup). The presented technique is demonstrated using a circular CSRR coupled to a microstrip transmission line (MTL) and optimized to operate between 5 and 20 GHz. The design optimized for 15 GHz is fabricated and experimentally validated using a vector network analyzer. The sensor works in the transmission mode and senses the shift in resonance frequency determined by the properties of the material under test (MUT). Furthermore, an inverse regression model is developed that allows for directly finding the unknown permittivity of the MUT based on the measured resonant frequencies of the sensor. The obtained results corroborate the design utility of the proposed optimization method, as well as the practical usefulness of the specific CSRR structure developed with the aid thereof.

Nonlinear effects and applications for piezoelectric materials

The requirements of high quality factor, low power consumption, easy design techniques and compatibility with the main standard fabrication processes of integrated circuits (IC) make the tunable piezoelectric resonators a suitable option for the new technologies of fifth generation of telecommunication (5G) and Internet of Things (IoT). In this work the nonlinear state equations for piezoelectric effect are presented. From these equations we may deduce which materials can be used in applications where a hysteresis behavior or resonance frequency tunability are required, additionally, it is shown which crystals have the nonlinear tensor’s symmetry compatible with each application field. A novel model for the tunable piezoelectric devices is shown taking into account the consequences of voltage tuning. Finally, three different ways to design and implement the nonlinear behavior of piezoelectric materials to tune devices are introduced.

Switchable strong coupling between dual hyperbolic phonon polaritons and photons in hybrid structure of metasurfaces and h-BN slab

We propose an all-dielectric hybrid structure combined with hexagonal boron nitride slab and strontium titanate (STO) metasurfaces to excite dual hyperbolic phonon polaritons (HPhPs) and an additional optical (TO) phonon, and achieve their strong coupling with photons. The metasurfaces, supporting tunable guided-mode resonance via adjusting the external temperature, consists of STO two-dimensional grating and STO layer. Thus, the strong coupling can be switched and tuned actively between the dual HPhPs and TO phonon via adjusting the external temperature of metasurfaces. This work has numerous potential applications on multi-channel biosensors, filters and tunable source and detectors.

Miniaturized Broadband Dual-Polarized Dipole Antenna Based on Multiple Resonances and its Array for Base-Station Applications

A novel bandwidth enhancement method using loading multiple parasitic structures to realize broadband miniaturized antenna is proposed. Based on the proposed strategies, one miniaturized wideband dual-polarized dipole antenna covering LTE/CDMA/GSM bands (690–960 MHz) for base-station application is designed. The antenna consists of two folded bowtie-shaped dipoles fed with a pair of crossed baluns, and is further loaded on a ceramic block with high permittivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon$ </tex-math></inline-formula> ) for miniaturization. A parasitical square loop is loaded for bandwidth enhancement at a lower frequency. In addition, four split rings with a small square loop are firstly adopted for antenna resonance tuning, the impedance bandwidth is thus improved effectively. The antenna size is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18\,\times \,0.18\,\times \, 0.22\,\,\lambda _{0}$ </tex-math></inline-formula> at the center frequency. The measured result of the fabricated prototype exhibits a relatively large operation bandwidth of 32.73% (VSWR < 1.6) with stable radiation patterns and relatively flat broadside gains. Moreover, to verify the feasibility of the proposed miniaturized antenna element in the base-station application, an array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\,\times \, 4$ </tex-math></inline-formula> is further designed. The measured results of the array indicate isolation over 20 dB with an impedance bandwidth of 32%. Due to the good performance and compact feature, the proposed miniaturized broadband antenna element can find large application potential in multiband wireless communication base stations.

Amorphous and Porous Tungsten Oxide Films for Fast‐Switching Dual‐Band Electrochromic Smart Windows

AbstractDual‐band electrochromic smart windows with dynamic and independent control of near‐infrared (NIR) and visible (VIS) light transmittance can notably reduce the carbon footprint of buildings and improve the occupants’ visual and thermal comfort. The dual‐band response is often generated by the phase transition of crystalline electrochromic materials. However, the phase‐transition of crystalline materials is kinetically sluggish, resulting in a long response time. Herein, a fast‐switching dual‐band electrochromic smart window based on a single‐component amorphous and porous tungsten oxide (AP‐WO3) cathode without the slow phase‐transition process is demonstrated. The amorphous and porous structure of WO3 not only significantly improves the ion transport, but also provides a large surface area for Li+ adsorption that gives rise to a tunable surface plasmon resonance (SPR) in the NIR range. Consequently, the single‐component AP‐WO3 film can modulate the NIR and VIS light transmittance independently and effectively through three distinct modes with high optical modulation, fast switching speed, high bistability, and good cycling stability. The prototype dual‐band electrochromic device assembled by AP‐WO3 cathode also delivers an impressive dual‐band electrochromic performance with fast‐switching speed (6.4 s for coloration and 7.2 s for bleaching).

Optical Response of Periodic Arrays of Graphene Nanodisks

Doped graphene nanostructures are a promising platform for photonics due to their exceptionally strong and tunable plasmonic resonances. When placed in a periodic array configuration, the plasmons supported by the individual nanostructures interact with each other and, under the appropriate conditions, can give rise to a collective mode known as a lattice resonance. Here, we perform a comprehensive analysis of the response of periodic arrays of graphene nanodisks and identify the conditions under which the system is able to support lattice resonances. We find that the ratio between the period of the array and the wavelength of the plasmon completely determines the behavior of the system. As a consequence, strong lattice resonances are achieved for micron-size nanodisks in the terahertz regime. We develop a theoretical model valid beyond the electrostatic approximation and use it to derive closed analytical expressions for the strength, the wavelength, and the width of the optical resonance of the arrays. The theoretical framework developed in this work paves the way for facile design and discovery of emerging properties of periodic arrays of graphene nanostructures that could enable applications in photonics and plasmonics.

Perovskite/Hole Transport Layer Interfacial Engineering with Substoichiometric Tungsten Oxide Rich in Oxygen Vacancies to Boost the Photovoltaic Performance of Perovskite Solar Cells

The collaborative strategy of optical design and charge transport dynamics optimization can provide double guarantee to achieve high‐efficient planar perovskite solar cells (PSCs). Herein, WO3−X nanorods with tunable localized surface plasmon resonance (LSPR) effect are introduced at the interface between perovskite and hole transport layer (HTL) via antisolvent method during the preparation of perovskite films. The photocurrent of WO3−X nanorods‐based devices significantly increases due to the extension of absorption region caused by LSPR effect. The charge transfer at the perovskite/HTL interface is also accelerated due to the electromagnetic near‐field enhancement via the LSPR effect. The synchronized improvement in photocurrent and charge transfer by WO3−X nanorods leads to a power conversion efficiency of 21.14% in MAPbI3‐based PSCs. This work not only provides an effective approach to enhance the photovoltaic performance of PSCs, but also demonstrates the potential application of inorganic oxide semiconductors with LSPR in other optoelectronic devices.

Ultra-broadband natural frequency using automatic resonance tuning of energy harvester and deep learning algorithms

Previous broadband energy harvester techniques met many challenges like output power with a sharp peak, small enhancement in bandwidth, and large dimensions and weights. This paper introduces the Automatic Resonance Tuning (ART) technique of two piezoelectric beams to manage these challenges. The energy harvester of two clamped beams automatically adapts their natural frequencies corresponding to the ambient vibration using (sliding masses over the beams). The optimization using COMSOL was conducted to determine the frequency ranges of the low-frequency beam and high-frequency beam and maximize the output power. The bandwidth of the optimized ART harvester is broadened from 27 to 137Hz, ultra-broad bandwidth (110Hz). Our Finite Element Method (FEM) results were validated with experimental results that exhibited excellent convergence. Usually, the dataset of voltage and power is collected by the FEM. Voltages and power evaluated using FEM for some positions are used as the convolutional neural network (CNN) input. CNN predicts the most of masses' positions over the harvester due to the complexity of repetition implementation FEM in several positions. Then, the CNNs are trained for new wide masses position prediction. The mean square error (MSE) of the training dataset is 2.5601×10-7μw and the performance of the CNN training is 97.62% accuracy (P%), 95.38% regression rate (R%), and 93.78% F-score (F%), at epoch 1000, which shows the effectiveness of the proposed approach.

Tunable toroidal resonance based on hybrid graphene-metal metasurfaces

With the rise of artificial magnetism and metamaterials, toroidal resonance has gained much attention for its special properties. In this paper, we propose a novel hybrid graphene-metal metamolecule consisting of a square bracket-like resonator and two asymmetric U-shaped resonators. By applying various Fermi energies to graphene, the amplitude of electromagnetically induced transparency (EIT) can be efficiently manipulated, and the maximum amplitude modulation depth can attain 81% in the microwave region. Numerical simulations and theoretical analysis demonstrate that the dynamic manipulation is mainly induced by the active tuning toroidal resonance through the recombination effect of the conductive graphene. Also, the maximum group delay of 85 ps can be attained and controlled with the increasing Fermi energy. The proposed hybrid graphene-metal metamolecule and dynamically manipulating mode presents a novel modulating strategy of EIT-like analog based on the toroidal response, which has great application for the design of efficient tunable resonators, filters, and sensors.

Magnetically Tunable Micro-Ring Resonators for Massive Magneto-Optical Modulation in Dense Wavelength Division Multiplexing Systems.

We demonstrate, numerically, a new concept for on-chip magneto-optical (MO) modulation in dense wavelength division multiplexing (DWDM) applications. Our idea uses materials and mechanisms that are compatible with current silicon-on-insulator fabrication and CMOS technologies for monolithic integration. The physics behind our idea stems in the exploitation of the enhanced MO activity of a micro-ring, made of cerium substituted yttrium iron garnet (Ce:YIG) material, to actively manipulate the resonance wavelengths of an adjacent micro-ring resonator (MRR) of silicon (Si). This active manipulation of the latter MO-MRR structure is used to modulate the optical signal traveling through a side-coupled Si bus waveguide. Moreover, by proper tailoring multiple MO-MRRs (side-coupled to the single Si bus waveguide) to match wavelength channels in DWDM across the entire C-band optical communications spectrum, we extend our proposal to massive and dynamic MO modulation in DWDM applications. Significantly, we noticed that the active MO shifting of the resonant wavelength (used for MO modulation here) can be used for improvements in the spectrum utilization efficiency in future elastic optical networks (EONs).