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We demonstrate tunable optical filters fabricated from metalized lithium niobate disk resonators and discuss further applications of the resonator chains for tunable photonic delay lines.
Hydrogels, exhibiting wide applications in soft robotics, tissue engineering, implantable electronics, etc., often require sophisticately tailoring of the hydrogel mechanical properties to meet specific demands. For examples, soft robotics necessitates tough hydrogels; stem cell culturing demands various tissue-matching modulus; and neuron probes desire dynamically tunable modulus. Herein, a strategy to broadly alter the mechanical properties of hydrogels reversibly via tuning the aggregation states of the polymer chains by ions based on the Hofmeister effect is reported. An ultratough poly(vinyl alcohol) (PVA) hydrogel as an exemplary material (toughness 150 ± 20 MJ m -3 ), which surpasses synthetic polymers like poly(dimethylsiloxane), synthetic rubber, and natural spider silk is fabricated. With various ions, the hydrogel's various mechanical properties are continuously and reversibly in situ modulated over a large window: tensile strength from 50 ± 9 kPa to 15 ± 1 MPa, toughness from 0.0167 ± 0.003 to 150 ± 20 MJ m -3 , elongation from 300 ± 100% to 2100 ± 300%, and modulus from 24 ± 2 to 2500 ± 140 kPa. Importantly, the ions serve as gelation triggers and property modulators only, not necessarily required to remain in the gel, maintaining the high biocompatibility of PVA without excess ions. Overall, this strategy, enabling high mechanical performance and broad dynamic tunability, presents a universal platform for broad applications from biomedicine to wearable electronics.
Abstract Metamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO 2 ‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO 2 matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm −3 , strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO 2 matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.
Despite remarkable progress in passive nonlinear nanophotonics, dynamically controlled ultracompact nonlinear optical sources with high efficiency remain elusive. Nonvolatility, large refractive index contrast between amorphous and crystalline phases, low thermal threshold for crystallization, and particularly high‐third‐order nonlinear optical susceptibility of phase‐change alloy Ge 2 Sb 2 Te 5 (GST) make it a promising candidate for active subwavelength metaphotonic structures for realization of third‐harmonic generation (THG) devices. Herein, a GST‐based asymmetric Fabry–Perot cavity is numerically designed and experimentally demonstrated to show a dynamically reconfigurable structure with a large shift of the THG resonant band. In addition, continuous resonant spectral shifting bridged by a precisely controlled semicrystalline phase of GST is realized. Tunable THG with the fundamental wavelength ranging from 1150 to 1400 nm is presented, which corresponds to a broadband THG source in the violet‐blue visible wavelength range. Herein, the potential of GST subwavelength structures as a reliable platform for realization of the broadband‐tunable frequency‐conversion sources for applications such as THG microscopy and optical communication is indicated.
Topology optimization is used to design phononic bandgap materials that are tunable by mechanical deformation. A periodic media is considered, which due to the assumption of length scale separation, allows the dispersion relations to be obtained by analyzing a single unit cell subjected to Floquet–Bloch boundary conditions. A finite macroscopic deformation is applied to the unit cell to affect its geometry and hence dispersion. We tune the dispersion–deformation relation to our liking by solving a topology optimization problem using nonlinear programming. The adjoint method is employed to compute the sensitivities, and the non-differentiability of degenerate eigenvalues is avoided using symmetric polynomials. Several tunable phononic crystal designs are presented. Also, a verification analysis is performed, wherein the optimized design is interpreted and analyzed using a conforming finite element mesh.
Phononic metamaterials offer unprecedented control over wave propagation, making them essential for applications such as vibration isolation, waveguiding, and acoustic filtering. However, achieving scalable and precisely tunable bandgap properties across different length scales remains challenging. This study presents a user-friendly design framework for phononic metamaterials, enabling ultra-wide bandgap tunability (B/ω c ratios up to 172 %) across multiple frequency ranges and scales. Using finite element simulations of a Yablonovite-inspired unit cell, we establish a comprehensive parametric design space that illustrates how geometric parameters, such as sphere size and beam diameter, controls bandgap width and frequency. The scalability and robustness of the framework are validated through experimental testing on additively manufactured structures at both macro (10 mm) and micro (80 µm) scales, fabricated using Stereolithography and Two-Photon Polymerization. Transmission loss measurements, conducted with piezoelectric transducers and laser vibrometry, closely match simulations in the kHz and MHz frequency ranges, confirming the reliability and consistency of the bandgap behavior across scales. This work bridges theory and experiments at multiple scales, offering a practical methodology for the rapid design of phononic metamaterials and expanding their potential for diverse applications across a broad range of frequencies.
Polymer based phase change materials (PCM) for thermal energy storage (TES) applications have gained some attention recently due to their high stability and potential solid to solid phase transition. In this work, we are the first to utilize a simple copolymerization strategy for static tunability transition temperature (T t ) of polymeric PCM. The copolymerization between short and long side chain polyethylene glycol based methacrylate polymers was designed to tune T t with minimum impact on their energy density. Polarized optical microscope and x-ray techniques were also used to understand the relationship between crystal structure and T t of different copolymer composition which was discussed in the context. The solid to solid transition polymeric PCM were successfully developed with tunable T t ranged from 18 °C to 35 °C which is suitable toward building envelop applications.
Self-healing elastomers provide extended longevity of functional materials, due to their unique adaptability and durability. However, a major scientific challenge remains in developing materials with a rapid healing process combined with decent mechanical properties, that can be prepared by a relatively simple synthesis approach. Herein, we report a versatile design approach on self-healing elastomers by incorporating two different hydrogen bonding containing monomers, i.e., 2-[[(butylamino)carbonyl]oxy]ethyl acrylate (BCOE) and 2-ureido-4[1H]pyrimidinone (UPy) functionalized ethyl methacrylate. Poly(BCOE-r-UPy)s are synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization, and controlling the ratio of two monomers enables well-tunable mechanical properties with tensile strength ranging from 0.04 to 6.3 MPa and tensile strain up to 3,000 %. The characteristic dissociation energy is calculated from a temperature dependence of terminal relaxation followed by subtracting the segmental relaxation. The rapid autonomous self-healing is achieved when the molar composition of Poly(BCOE-r-UPy) is tailored to BCOE/UPy = 99/1. The self-healing process is monitored in situ by a helium-ion microscope, and its macroscopic study using tensile tests indicates that Poly(BCOE-r-UPy1) with 1 % molar ratio of UPy recovers 70 % of its original toughness at ambient temperature within 10 mins. 3D printing of Poly(BCOE-r-UPy) affords a self-healable 3D structure, demonstrating the adaptability of Poly(BCOE-r-UPy) for on-demand fabrication. The simplicity of synthesis, well-tunable mechanical properties, unique self-healability, and 3D printing capability of Poly(BCOE-r-UPy)s indicate their potential for a range of applications.
Optical metasurfaces—planar nanostructured devices that can arbitrarily tailor the wavefront of light—may be reconfigured by changing their dielectric environment. The application of external stimuli to liquid crystals is a particularly promising means of tuning the optical properties of embedded metasurfaces because of liquid crystals' large and broadband optical anisotropy. However, the detailed behavior of liquid crystals immediately adjacent to the nanostructured meta-atoms elements is often overlooked, despite the optics of the device depending sensitively on this behavior (e.g., the spectral position of the meta-atom resonances). This is of increasing concern as the wavelength of operation further approaches the short-wavelength end of the visible spectrum and, therefore, the length scale of the inhomogeneities in the liquid crystal director field. In this manuscript, we undertake a fully comprehensive study, across the metasurface geometrical parameter space, of broadband (450-700 nm) all-dielectric liquid crystal tunable metasurfaces operating in the visible. Here, through combined experimental characterization, liquid crystal modeling, and optical simulations, we reveal and quantify the improved accuracy with which the optical properties of the liquid crystal tunable metasurfaces may be described, and identify the underlying physical mechanism: the three-dimensional spatial overlap of the liquid crystal director field and metasurface optical near fields in the vicinity of the meta-atoms.
Ultrafast optical frequency combs allow for both high spectral and temporal resolution in molecular spectroscopy and have become a powerful tool in many areas of chemistry and physics. Ultrafast lasers and frequency combs generated from ultrafast mode-locked lasers often need to be converted to other wavelengths. Commonly used wavelength conversions are optical parametric oscillators, which require an external optical cavity, and supercontinuum generation combined with optical parametric amplifiers. Whether commercial or home-built, these systems are complex and costly. Here, we investigate an alternative, simple, and easy-to-implement approach to tunable frequency comb ultrafast lasers enabled by new continuous-wave laser technology. Sum-frequency generation between an Nd:YAG continuous-wave laser and a Yb:fiber femtosecond frequency comb in a beta-barium borate (BBO) crystal is explored. The resulting sum-frequency beam is a pulsed frequency comb with the same repetition rate as the Yb:fiber source. SNLO simulation software is used to simulate the results and provide benchmarks for designing future systems to achieve wavelength conversion and tunability in otherwise difficult-to-reach spectral regions.
In this experimental study, we demonstrate the feasibility of a thermally tunable, resonant dielectric microwave metasurface based on sub-wavelength Mie resonances of ferroelectric dielectric cubes (Calcium titanate, CaTiO 3 ) in which the temperature of the meta-atoms can be locally and dynamically controlled by heating with an optical laser beam over a large range of temperatures and, consequently, values of the dielectric constant of the cube and corresponding resonance frequency of the meta-atoms. Further, this avoids any interference of otherwise necessary heating elements or power supply wires with the propagation of the microwave signal and can be made spatially addressable. The concept scales at least to the THz domain. This contactless approach opens up an alternative avenue to tunability and active control of metamaterials.
Abstract Metamaterials enable subwavelength tailoring of light–matter interactions, driving fundamental discoveries which fuel novel applications in areas ranging from compressed sensing to quantum engineering. Importantly, the metallic and dielectric resonators from which static metamaterials are comprised present an open architecture amenable to materials integration. Thus, incorporating responsive materials such as semiconductors, liquid crystals, phase-change materials, or quantum materials (e.g., superconductors, 2D materials, etc.) imbue metamaterials with dynamic properties, facilitating the development of active and tunable devices harboring enhanced or even entirely novel electromagnetic functionality. Ultimately, active control derives from the ability to craft the local electromagnetic fields; accomplished using a host of external stimuli to modify the electronic or optical properties of the responsive materials embedded into the active regions of the subwavelength resonators. We provide a broad overview of this frontier area of metamaterials research, introducing fundamental concepts and presenting control strategies that include electronic, optical, mechanical, thermal, and magnetic stimuli. The examples presented range from microwave to visible wavelengths, utilizing a wide range of materials to realize spatial light modulators, effective nonlinear media, on-demand optics, and polarimetric imaging as but a few examples. Often, active and tunable nanophotonic metamaterials yield an emergent electromagnetic response that is more than the sum of the parts, providing reconfigurable or real-time control of the amplitude, phase, wavevector, polarization, and frequency of light. The examples to date are impressive, setting the stage for future advances that are likely to impact holography, beyond 5G communications, imaging, and quantum sensing and transduction.
In this presentation a 2.4 GHz low profile (lambda45) tunable dipole antenna is evaluated in the presence of a human core model (HCM) body phantom. The antenna uses a frequency selective surface (FSS) with interdigital barium strontium titanate (BST) varactor-tuned unit cells and its performance is compared to a similar low profile antenna that uses an FSS with semiconductor varactor diodes. The measured data of the antenna demonstrate tunability from 2.2 GHz to 2.55 GHz in free space and impedance match improvement in the presence of a HCM at different distances. This antenna has smaller size, lower cost and less weight compared to the semiconductor varactor diode counterpart.
In this presentation, we introduce phase-change tunable filters (PCTFs), which are capable of actively tunable spectral filtering as well as continuous tuning (hyperspectral) across multiple IR wavebands (1–10 μm); several orders-of-magnitude faster switching speeds (GHz–MHz) than the state-of-the-art, and narrowband filtering (~50 nm passband). This technology subsystem is based on the unique electro-optics of non-volatile, phase-change materials (PCMs) such as GeSbTe and SbS. PCMs exhibit a large, reversible refractive index shift through applied energetic pulses. By integrating PCMs with established optical filter designs—whose optical properties are strongly dependent on the constituent materials’ refractive indices—we can rapidly and reversibly tune the PCTFs center wavelength (passband).
The middle-wavelength infrared (MWIR) waveband is considered the “spectral fingerprint”for many chemical species. MWIR: 3 –10 μm wavelength range. MWIR imaging devices are important for multispectral imaging, thermography, chemical spectroscopy, surveillance, automotive safety, and astronomy. Tunable optical properties are desired to increase the amount of information that is detectable. Ge2Sb2Te5(GST) is a chalcogenide phase change material (PCM) that has the potential to be used as a compact, solid-state, fast-switching tunable optical filter.
Phase change material (PCM)-based actively tunable mid-wave IR filters have broad imaging and sensing applications—from probing molecular vibrations in chemical species to detecting radiant thermal signatures. We introduce the Phase-change actively tunable filter (P-ACTIVE) project lead by NASA Langley Research Center with collaborators MIT and the University of Cambridge. It covers background science, experimental and theoretical device performance, as well as recent results obtained from a MISSE-14 mission for space qualification of active metasurface optics and constituent PCM. We conclude with a prospective view of the technology and discuss the potential for these filters to serve multiple NASA missions.
Abstract Antiferroelectrics, which undergo a field‐induced phase transition to ferroelectric order that manifests as double‐hysteresis polarization switching, exhibit great potential for dielectric, electromechanical, and electrothermal applications. Compared to their ferroelectric cousins, however, considerably fewer efforts have been made to understand and control antiferroelectrics. Here, it is demonstrated that the polarization switching behavior of an antiferroelectric can be strongly influenced and effectively regulated by point defects. In films of the canonical antiferroelectric PbZrO 3 , decreasing oxygen pressure during deposition (and thus increasing adatom kinetic energy) causes unexpected “ferroelectric‐like” polarization switching although the films remain in the expected antiferroelectric orthorhombic phase. This “ferroelectric‐like” switching is correlated with the creation of bombardment‐induced point‐defect complexes which pin the antiferroelectric–ferroelectric phase boundaries, and thus effectively delay the phase transition under changing field. The effective pinning energy is extracted via temperature‐dependent switching‐kinetics studies. In turn, by controlling the concentration of defect complexes, the dielectric tunability of the PbZrO 3 can be adjusted, including being able to convert between “positive” and “negative” tunability near zero field. This work reveals the important role and strong capability of defects to engineer antiferroelectrics for new performance and functionalities.
Effective membrane separation of Li + from Na + and Mg 2+ is crucial for lithium extraction from water yet challenging for conventional polymeric membranes. Two dimensional (2D) membranes with ordered laminar structures and tunable physicochemical properties offer distinctive ion-sieving capabilities promising for lithium extraction. Recently, phyllosilicates are introduced as abundant and cost-effective source materials for such membranes. However, their water instability and low inherent ion transport selectivity hinder practical applications. Herein, a new class of laminar membranes with excellent stability and tunable ion sieving is reported by incorporating inorganic alumina pillars into vermiculite interlayers. Crosslinking vermiculite flakes with alumina pillars significantly strengthens interlamellar interactions, resulting in robust water stability. Doping of Na + before the pillaring process reverses the membrane's surface charge, substantially boosting Li + separation from multivalent cations via electrostatic interactions. Lithium extraction is often complicated by the presence of co-existing monovalent cations (e.g., Na + ) at higher concentrations. Here, by introducing excess Na + into the membrane after the pillaring process, the separation of Li + from monovalent cations is enhanced through steric effects. This work realizes both monovalent/multivalent and monovalent/monovalent selective ion sieving with the same membrane platform. A separation mechanism is proposed based on Donnan exclusion and size exclusion, providing new insights for membrane design for resource recovery applications.