Dynamic Tuning Research Articles

Dynamic tuning of optical absorbance and structural color of VO2-based metasurface

Abstract Vanadium dioxide (VO2) is an attractive thermal-control material exhibiting low thermal hysteresis and excellent temperature cycling performance. However, the deficiencies including weak spectral shift and narrow-band absorption during insulating-metallic transitions hinder its application in optoelectronics. The transition metal dichalcogenides (TMDs) can provide a promising solution with their high dielectric properties and robust optical coupling. Here, we report a MoS2/VO2/Au/Si metasurface and investigate the dynamic tunability of its optical absorbance and structural color upon heating via spectroscopic ellipsometry measurements and numerical simulations. The first-principles calculations reveal that the dielectric absorptions of metallic and insulating VO2 oppositely response to temperature, closely related to the difference in the transitions of O-2p states. Finite-element simulations reveal that the introduction of MoS2 nanostructure induces more absorption peaks by 2∼3 and achieves strong absorption in the full wavelength range of visible light. The Fabry–Perot (F–P) resonance is the critical factor for the optimized optical absorption. The structural color is sensitive to environmental perturbations at high-ε state of VO2, lower oblique incidence angles, and heights of MoS2. This work seeks to facilitate the spectral modulation of phase change metamaterials and can be extended to photoelectric detection and temperature sensing applications.

Experimental and numerical studies of the dynamic coupling effect in the primary-secondary system

Many complicated dynamic coupling effects(DCE) exist in the primary-secondary system(PS system) under earthquakes, among which the dynamic interaction and tuning effect have a more significant influence. However, the existing numerical analysis methods and experimental works are mostly based on the assumption of a small mass ratio, resulting in no significant interactions within the coupled system to be discussed. Therefore, a series of dynamic characteristics tests and shaking table tests were conducted to determine the working of the DCE works on the PS systems with appropriate mass ratios, and test results were used for the validation of an analysis method without the mass limitation and for the extended numerical analyses. According to the results, the dynamic interaction could reduce the responses of the secondary system(S system), and the reduction was positively related to the mass ratio, the tuning effect could cause a divergence of the natural frequencies and about 10–40% decrease in the primary system(P system) response and approximately 7–34 times increase in the S system response. The results of the extended analysis demonstrate the effectiveness of increasing the damping of connection, and decoupled analysis will yield more than double the security redundancy.

Numerical simulation of linewidth compression dynamics of external-cavity semiconductor laser

We theoretically simulate the linewidth compression dynamics of the semiconductor laser with a single external-cavity feedback. The evolution time from the periodic oscillation state to the equilibrium state is calculated by tracking the change of the intrinsic linewidth. The influences of the external-cavity length and feedback level are also explored. The linewidth evolution time of the external-cavity semiconductor laser can be extended with longer external cavity length and higher feedback level. Simultaneously, the intrinsic linewidth can be compressed while the side mode suppression ratio will be decreased. The simulation work show that the dynamic linewidth compression can be obtained by single external-cavity feedback, and nevertheless it is difficult to achieve the single-frequency output, which can instruct the design of the dynamical parameter tuning of the external-cavity semiconductor laser.

Graphene/Cholesteric Liquid-Crystal-Based Electro-Driven Thermochromic Light Modulators toward Wide-Gamut Dynamic Light Color-Tuning-Related Applications.

Light filters are ubiquitous in projection and display techniques, illumination engineering, image sensing, photography, etc., while those enabling wide-gamut dynamic light color tuning are still lacking. Herein, by combining the electro-heating capability of graphene and unique optical properties (thermochromism and circular dichroism) of small-molecule-weight cholesteric liquid crystal (ChLC), a brand-new thermochromic light modulator is constructed as actively tunable color filter. Transparent graphene/glass hybrid with reasonably high conductivity serves both as a high-performance heater for actuating the thermochromism of temperature-responsive ChLC and as neutral light attenuator for brightness control. Thanks to the temperature- and polarization-dependent spectral properties of the ChLC, widely tunable hue and saturation properties of transmission light color are achieved, respectively. Several intriguing applications, e.g., color-variable smart windows for backlight color tuning and color-variable filters for photography, are also demonstrated. This work hereby provides new paradigms for promoting the applications of graphene/ChLC-based light modulators in next-generation light-management-related scenarios.

Tunnel Junction Engineered Photocarrier Dynamics in Epitaxial Semiconductor Nanowires for Efficient and Ultrafast Photoelectrochemical Photodetectors

Photodetection using photoelectrochemical (PEC) principles is an emerging field in photonics. In recent years, using epitaxial III-nitride nanowires as photoelectrodes, high-performance PEC-type photodetectors (PDs) have been demonstrated, making the epitaxial III-nitride nanowires a scalable, high-performance PEC-PD architecture. Despite the progress, the photodetection performance improvement mainly occurs through incorporating photocatalysts into the nanowire photoelectrodes. In this study, we show that a semiconductor tunnel junction (TJ), which can be a natural component in the epitaxy process of semiconductor nanowires, can drastically improve the photodetection performance of such nanowire-based PEC-PDs. By using a three-electrode PEC cell configuration, we clearly show that an n++-GaN/InGaN/p++-GaN TJ can lead to a factor of 9× improvement on the responsivity of the InGaN nanowire photoelectrode in the blue band due to the TJ-induced photocarrier dynamics tuning, compared to the InGaN nanowire photoelectrode without the TJ. More drastically, the TJ also improves the photoresponse speed of the nanowire photoelectrode by 2 orders of magnitude, and for the electrode with the TJ an ultrafast response time of less than 10 ms is estimated. This TJ concept can also be applied to other TJ structures for other band photodetections. This study therefore sheds new light on further improving the performance of emerging epitaxial nanowire-based PEC-PDs for a wide range of applications from sensing to information processing.

Heterosynaptic MoS2 Memtransistors Emulating Biological Neuromodulation for Energy-Efficient Neuromorphic Electronics.

Heterosynaptic neuromodulation is a key enabler for energy-efficient and high-level biological neural processing. However, such manifold synaptic modulation cannot be emulated using conventional memristors and synaptic transistors. Thus, reported herein is a three-terminal heterosynaptic memtransistor using an intentional-defect-generated molybdenum disulfide channel. Particularly, the defect-mediated space-charge-limited conduction in the ultrathin channel results in memristive switching characteristics between the source and drain terminals, which are further modulated using a gate terminal according to the gate-tuned filling of trap states. The device acts as an artificial synapse controlled by sub-femtojoule impulses from both the source and gate terminals, consuming lower energy than its biological counterpart. In particular, electrostatic gate modulation, corresponding to biological neuromodulation, additionally regulates the dynamic range and tuning rate of the synaptic weight, independent of the programming (source) impulses. Notably, this heterosynaptic modulation not only improves the learning accuracy and efficiency but also reduces energy consumption in the pattern recognition. Thus, the study presents a new route leading toward the realization of highly networked and energy-efficient neuromorphic electronics.

Onboard train speed optimization for energy saving using the prediction of block clearing times under real-time rescheduling

Energy-saving driving is crucial during railway operation, especially in case of disturbances that require timetable rescheduling. This paper presents a method for the dynamic onboard tuning of energy-efficient speed profiles after the real-time train rescheduling process under a fixed block signaling system for mixed traffic. Similar to the idea of connected driver advisory systems, trains constantly communicate with a central traffic management system. After the rescheduling process, this system provides recommended time corridors for the passing of block signals that depend on the predicted clearing times of the block sections. These recommendations are then used for individual energy optimization of single train runs by avoiding unnecessary braking in front of block signals and maximizing cruising distances. The method is tested and evaluated on a representative line segment of the ELVA, the Railway Signaling Lab at RWTH Aachen University under realistic conditions. Energy consumptions are compared for different prediction time horizons at which the recommendations are available to the train's onboard system. In the examined test case of two trains, the energy-consumption could be decreased by up to 53% compared to operation without any rescheduling system. Thus, the proposed method is able to reduce energy consumption significantly.

Dynamic Control of Nonlinearly Generated Light Chirality with Nanostructured Graphene

The constant development of nanotechnology has facilitated significant improvements in the field of nonlinear optics. Metasurfaces and metamaterials, or nanostructured material systems, have allowed excellent control over a variety of linear and nonlinear optical processes, including manipulation of the amplitude, phase, and polarization of light. To facilitate this progress, there is an increasing demand for small footprint nonlinear material systems and metamaterial designs that offer diverse functionalities. Here, we demonstrate that this demand can be satisfied by utilizing the family of two-dimensional materials and more specifically graphene. In this work, we take advantage of the exceptionally large nonlinearity of graphene and demonstrate simultaneous dynamic control over the polarization state and nonlinear conversion efficiency of the third harmonic emission via the coherent excitation of localized surface plasmons in nanopatterned graphene rectangular arrays. Using finite-difference time-domain simulations and through electrostatic control over the Fermi level in graphene, we demonstrate broadband dynamic tuning between linear and circular polarization states for the third harmonic emission. The proposed method is not limited to third harmonic emission and is applicable to different nonlinear optical processes. As a result, the proposed metasurface constitutes an outstanding platform for commercially viable, CMOS-compatible, room-temperature devices for nonlinear conversion applications.

Paraventricular Thalamus Dynamically Modulates Aversive Memory via Tuning Prefrontal Inhibitory Circuitry.

The impact of stress on the formation and expression of memory is well studied, especially on the contributions of stress hormones. But how stress affects brain circuitry dynamically to modulate memory is far less understood. Here, we used male C57BL6/J mice in an auditory fear conditioning as a model system to examine this question and focused on the impact of stress on dorsomedial prefrontal cortex (dmPFC) neurons which play an important role in probabilistic fear memory. We found that paraventricular thalamus (PVT) neurons are robustly activated by acute restraining stress. Elevated PVT activity during probabilistic fear memory expression increases spiking in the dmPFC somatostatin neurons which in turn suppresses spiking of dmPFC parvalbumin (PV) neurons, and reverts the usual low fear responses associated with probabilistic fear memory to high fear. This dynamic and reversible modulation allows the original memory to be preserved and modulated during memory expression. In contrast, elevated PVT activity during fear conditioning impairs synaptic modifications in the dmPFC PV-neurons and abolishes the formation of probabilistic fear memory. Thus, PVT functions as a stress sensor to modulate the formation and expression of aversive memory by tuning inhibitory functions in the prefrontal circuitry.SIGNIFICANCE STATEMENT The impact of stress on cognitive functions, such as memory and executive functions, are well documented especially on the impact by stress hormone. However, the contributions of brain circuitry are far less understood. Here, we show that a circuitry-based mechanism can dynamically modulate memory formation and expression, namely, higher stress-induced activity in paraventricular thalamus (PVT) impairs the formation and expression of probabilistic fear memory by elevating the activity of somatostatin-neurons to suppress spiking in dorsomedial prefrontal parvalbumin (PV) neurons. This stress impact on memory via dynamic tuning of prefrontal inhibition preserves the formed memory but enables a dynamic expression of memory. These findings have implications for better stress coping strategies as well as treatment options including better drug targets/mechanisms.

Light-Triggered Reversible Tuning of Second-Harmonic Generation in a Photoactive Plasmonic Molecular Nanocavity.

The ultrasmall mode volume and ultralarge local field enhancement of compact plasmonic nanocavities have been widely explored to amplify a variety of optical phenomena at the nanoscale. Other than passively generating near-field enhancements, dynamic tuning of their intensity and associated nonlinear optical processes such as second-harmonic generation (SHG) play vital roles in the field of active nanophotonics. Here we apply a host-guest molecular complex to construct a photoswitchable molecule-sandwiched metallic particle-on-film nanocavity (MPoFN) and demonstrate both light-controlled linear and nonlinear optical tuning. Under alternating illumination of ultraviolet (UV) and visible light, the photoactive plasmonic molecular nanocavity shows reversible switching of both surface-enhanced Raman scattering (SERS) and plasmon resonance. Surprisingly, we observe more significant modulation of SHG from this photoactive MPoFN, which can be explained qualitatively by the quantum conductivity theory (QCT). Our study could pave the way for developing miniaturized integrated optical circuits for ultrafast all-optical information processing and communication.

Magnetotransport‐Induced Non‐Contact Terahertz Detection of Weak Magnetic Fields in Optically Thin Frequency‐Agile Superlattice Metasurfaces

AbstractMagnetotransport, the magnetic field induced electron transport phenomenon through metals and semiconductors, has proven to be a useful technique to tailor the properties of electromagnetic radiation upon interaction with suitable materials and structures. Very recently, magnetotransport has become an important tool to dynamically tailor terahertz (THz) radiation and response of different optical devices. Based on these backgrounds, optically thin, subwavelength superlattice (with alternate arrangement of four metallic films: two non‐magnetic aluminum [Al] and two ferromagnetic nickel [Ni] films, having thickness of each film as 10 nm) metasurfaces are demonstrated, consisting of periodic arrays of asymmetric cut‐wire pair metasurfaces, which have a unique ability to exhibit both frequency and intensity modulation at its hybridized resonances when low‐intensity magnetic fields are applied. Such dynamic tuning characteristics are attributed to the combined effects of spin‐dependent THz magnetotransport in superlattice films, near‐field electromagnetic coupling between the resonators, and lattice mode coupling. Such THz metasurface is further employed for non‐contact detection of external magnetic fields in the range of 0–30 mT, while operating at the optically thin regime. The demonstrated scheme can further be extended to realize THz magneto‐spectroscopy toward devising state‐of‐the‐art photonic and magnetic technologies.

Magnetic-field tuning of thermal conductivity via bionic nanochain and droplet deformation

Thermal conductivity of nanofluids has garnered widespread attention because of its potential applications in heat dissipation and insulation. There is a high need for advanced thermal management solutions on an urgent basis, which may rely on dynamic tuning of the thermal conductivity in liquid/solid system. Designing a controllable liquid/solid system has emerged as an effective strategy for achieving tunable heat transfer methods, which is a crucial problem for energy storage systems and electronic devices in energy conversions. In this study, magnetically dynamic tuning of liquid deformation and particle chains for heat transfer was explained. The particle movement in the droplet could be adjusted by an external magnetic intensity and direction, causing the liquid deformation and then altering the heat transfer. The dynamic tuning of heat transfer within different particle distributions was explained and verified. In particular, thermal conductivity of nanofluids within concentration gradient distribution and magnetic nano-chain was regulated by magnetic field. This work formed a magnetic-controlled nanofluid manipulation methodology and explained the heat transfer mechanism within magnetic nanoparticles movements, which can be utilized for thermal management of electronic devices by controlling the droplet and fluid.

Controllable electromagnetically induced transparency in an electrically tunable terahertz hybrid metasurface

Dynamic tuning of metasurfaces with active components is a prospective solution to improve their operation bandwidth. Here, we propose and experimentally demonstrate controllable electromagnetically induced transparency (EIT)-like response in a terahertz hybrid metasurface, where the classical EIT metallic pattern is coupled to the electrical biasing silicon carrier layer. Both the conductivity and thickness of the biased silicon layer can change significantly with increasing the external current. The electrically controllable hybrid metasurface shows complete electrical switching on the EIT-like response. The hybrid metasurface employing the state transition of the biased silicon layer between insulating and conductive states yields a substitute method to solve the narrowband operation bandwidth of photonic devices, which may inspire novel innovations on high-performance active terahertz applications.

Dynamic tuning of phase change interfacial thermal energy transport in hybrid nano-enhanced phase change materials by a non-uniform magnetic field

The present study aims to explore the synergistic enhanced phase change heat transfer behavior between magnetic field and hybrid nanoparticles under the consideration of non-Newtonian effects. The visualized experiments are conducted using thermochromic liquid crystal technology to extract the interconnection between dynamic phase change interface evolution and temperature change of hybrid nano-enhanced phase change material (HNEPCM), and thermocouples to measure temperature data inside the latent heat thermal energy storage unit. The magnetic field and hybrid nanoparticles synergistic mechanism is then further revealed based on the analysis of liquid phase fraction, Nusselt number, energy storage and energy storage efficiency. The results show that under magnetic field, the magnetic nanoparticles form a “thermal conductivity layer” at the solid-liquid interface, while the non-magnetic nanoparticles in the liquid phase region drive the phase change heat transfer to proceed. The non-Newtonian effect induced by high concentration of HNEPCM can weaken the convection intensity. The competition between natural convection and magnetic viscous effect under magnetic field is induced at different hybrid ratios of magnetic and non-magnetic nanoparticles. High hybrid ratios (R = 1.0, 1.5 and 2.0) will be more favorable to satisfy the high thermal conductivity requirement in the liquid phase region and the dynamic adjustment condition at the phase change interface. Under a non-uniform magnetic field, 1 wt.% HNEPCM with R = 1.0 is considered as the optimum strategy with better energy storage performance and higher magnetic field effect.

Laser polarization associated periodic oscillation of thermal response in silicon nanotip

The nanotip's thermal response and its regulation are essential to tip-assisted nanoscale manufacturing. Laser polarization provides a promising solution for the dynamic tuning of laser energy absorption. However, the thermal response of nanotip under laser irradiation has yet to be fully understood. Here, the temperature and stress response of silicon nanotip under laser heating at different polarization angles is studied by Raman thermometry technique. The temperature oscillates between ∼584 and ∼742 K, with the polarization angle changing from 90 to 0°, showing sound dependence with laser polarization. Finite element simulations indicate that such oscillation effect of high temperatures is caused by the electric enhancement induced by the lightning rod effect and the low thermal conductivity of ∼21 W/(m⋅K) due to the high temperature and the size effect of heat conduction. Meanwhile, polarization-dependent thermal stress occurs due to the large electric distribution gradient. The periodic oscillation of the temperature and stress with the polarization angle verifies the reversibility of the tuning process, which paves the way toward precise nano-manufacturing.

Self‐Adaptive and Electric Field‐Driven Protective Layer with Anchored Lithium Deposition Enable Stable Lithium Metal Anode

Lithium metal battery has great development potential because of its lowest electrochemical potential and highest theoretical capacity. However, the uneven deposition of Li+ flux in the process of deposition and stripping induces the vigorous growth of lithium dendrites, which results in severely battery performance degradation and serious safety hazards. Here, the tetragonal BaTiO3 polarized by high voltage corona was used to build an artificial protective layer with uniform positive polarization direction, which enables uniform Li+ flux. In contrast to traditional strategies of using protective layer, which can guide the uniform deposition of lithium metal. The ferroelectric protective layer can accurately anchor the Li+ and achieve bottom deposition of lithium due to the automatic adjustment of the electric field. Simultaneously, the huge volume changes caused by Li+ migration change of the lithium metal anode during charging and discharging is functioned to excite the piezoelectric effect of the protective layer, and achieve seamless dynamic tuning of lithium deposition/stripping. This dynamic effect can accurately anchor and capture Li+. Finally, the layer‐modified Li anode enables reversible Li plating/stripping over 1500 h at 1 mA cm−2 and 50 °C in symmetric cells. In addition, the assembled Li‐S full cell exhibits over 300 cycles with N/P ≈ 1.35. This work provides a new perspective on the uniform Li+ flux at the Li‐anode interface of the artificial protective layer.

Plasmon logic gates and dual-narrowband absorption switching effect in hybrid structure composed of silver and spaced dual graphene monolayers

We propose a hybrid structure composed of a silver mirror and two spaced graphene monolayers to enhance light absorption. A broad plasmon-induced reflection (PIR) window can be generated because of the destructive interference between the bright and dark modes, resulting in a dual-narrowband absorption switching effect. The dual-narrowband absorption switch is strongly dependent on the geometric structure parameters and dynamic tuning parameter of the hybrid structure, and each parameter has a wide tuning range for absorption state ‘on/on’. Especially, compared with the hybrid structure composed of a graphene monolayer and one-dimensional photonic crystal (1D PC), the proposed structure is simpler and easier to fabricate, and the dynamic tuning width of Fermi energy of graphene for light absorption state ‘on/on’ is significantly broadened (∼3 times). Compared with plasmon-induced transparency (PIT) systems, the absorption performance of graphene is greatly enhanced, and the absorption is increased from about 50% to higher than 97%. Moreover, by adjusting the widths of the graphene monolayers, NAND and NOR logic gates are realized, and the output contrast between logic states ‘1’ and ‘0’ is high up to 18.6 dB. This study may provide an approach to construct dual-narrowband absorption switches, perfect absorbers, and plasmon logic gates.

Dynamic Tuning of Plasmonic Hot‐Spot Generation through Cilia‐Inspired Magnetic Actuators

Soft actuators that draw inspiration from nature are powerful and versatile tools for both technological applications and fundamental research, yet their use in hot‐spot engineering is very limited. Conventional hot‐spot engineering methods still suffer from complexity, high process cost, and static generation of hot‐spots, thus, underperforming particularly in the application side. Herein, we demonstrate a strategy based on plasmonic nanoparticles decorated cilia‐inspired magnetic actuators that enable highly accessible millimeter‐sized hot‐spot generation via bending motion under a magnetic field. The hot‐spot formation is shown to be reversible and tunable, and leads to excellent Raman signal enhancements of up to ≈120 folds compared to the unactuated platforms. Accessible electromagnetic field magnification in the platforms can be manipulated by controlling magnetic field strength, which is further supported by finite difference time domain (FDTD) simulations. As a proof‐of‐concept demonstration, a centipede‐inspired robot is fabricated and used for sample collection/analysis in a target environment. Our results demonstrate an effective strategy in soft actuator platforms for reversible and tunable large‐area hot‐spot formation, which provides a promising guidance toward studying the fundamentals of hot‐spot generation and advancing real‐life plasmonic applications.

Dynamic chromatin accessibility tuning by the long noncoding RNA ELDR accelerates chondrocyte senescence and osteoarthritis

Epigenetic reprogramming plays a critical role in chondrocyte senescence during osteoarthritis (OA) pathology, but the underlying molecular mechanisms remain to be elucidated. Here, using large-scale individual datasets and genetically engineered (Col2a1-CreERT2;Eldrflox/flox and Col2a1-CreERT2;ROSA26-LSL-Eldr+/+ knockin) mouse models, we show that a novel transcript of long noncoding RNA ELDR is essential for the development of chondrocyte senescence. ELDR is highly expressed in chondrocytes and cartilage tissues of OA. Mechanistically, exon 4 of ELDR physically mediates a complex consisting of hnRNPL and KAT6A to regulate histone modifications of the promoter region of IHH, thereby activating hedgehog signaling and promoting chondrocyte senescence. Therapeutically, GapmeR-mediated silencing of ELDR in the OA model substantially attenuates chondrocyte senescence and cartilage degradation. Clinically, ELDR knockdown in cartilage explants from OA-affected individuals decreased the expression of senescence markers and catabolic mediators. Taken together, these findings uncover an lncRNA-dependent epigenetic driver in chondrocyte senescence, highlighting that ELDR could be a promising therapeutic avenue for OA.

Electrically programmable solid-state metasurfaces via flash localised heating

In the last decades, metasurfaces have attracted much attention because of their extraordinary light-scattering properties. However, their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required. Currently, there is a quest to enable dynamic tuning of metasurface properties, particularly with fast tuning rate, large modulation by small electrical signals, solid state and programmable across multiple pixels. Here, we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon. We show a 9-fold change in transmission by <5 V biasing voltage and the modulation rise-time of <625 µs. Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater. It allows for video frame rate optical switching over multiple pixels that can be electrically programmed. Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region, large modulation depth, working at transmission regime, exhibiting low optical loss, low input voltage requirement, and operating with higher than video-rate switching speed. The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays, virtual reality holography and light detection and ranging, where fast, solid-state and transparent optical switches are required.