Acoustic Assembly and Scanning of Superlens Arrays for High-Resolution and Large Field-of-View Bioimaging.

High-resolution and dynamic bioimaging is essential in life sciences and biomedical applications. In recent years, microspheres combined with optical microscopes have offered a low cost but promising solution for super-resolution imaging, by breaking the diffraction barrier. However, challenges still exist in precisely and parallelly superlens controlling using a noncontact manner, to meet the demands of large-area scanning imaging for desired targets. This study proposes an acoustic wavefield-based strategy for assembling and manipulating micrometer-scale superlens arrays, in addition to achieving on-demand scanning imaging through phase modulation. In experiments, acoustic pressure nodes are designed to be comparable in size to microspheres, allowing spatially dispersed microspheres to be arranged into arrays with one unit per node. Droplet microlenses with various diameters can be adapted in the array, allowing for a wide range of spacing periods by applying different frequencies. In addition, through the continuous phase shifting in the x and y directions, this acoustic superlens array achieves on-demand moving for the parallel high-resolution virtual image capturing and scanning of nanostructures and biological cell samples. As a comparison, this noncontact and cost-effective acoustic manner can obtain more than ∼100 times the acquisition efficiency of a single lens, holding promise in advancing super-resolution microscopy and subcellular-level bioimaging.

Geometric phase-encoded stimuli-responsive cholesteric liquid crystals for visualizing real-time remote monitoring: humidity sensing as a proof of concept.

Liquid crystals are a vital component of modern photonics, and recent studies have demonstrated the exceptional sensing properties of stimuli-responsive cholesteric liquid crystals. However, existing cholesteric liquid crystal-based sensors often rely on the naked eye perceptibility of structural color or the measurement of wavelength changes by spectrometric tools, which limits their practical applications. Therefore, developing a platform that produces recognizable sensing signals is critical. In this study, we present a visual sensing platform based on geometric phase encoding of stimuli-responsive cholesteric liquid crystal polymers that generates real-time visual patterns, rather than frequency changes. To demonstrate this platform's effectiveness, we used a humidity-responsive cholesteric liquid crystal polymer film encoded with a q-plate pattern, which revealed that humidity causes a shape change in the vortex beam reflected from the encoded cholesteric liquid crystal polymers. Moreover, we developed a prototype platform towards remote humidity monitoring benefiting from the high directionality and long-range transmission properties of laser beams carrying orbital angular momentum. Our approach provides a novel sensing platform for cholesteric liquid crystals-based sensors that offers promising practical applications. The ability to generate recognizable sensing signals through visual patterns offers a new level of practicality in the sensing field with stimuli-responsive cholesteric liquid crystals. This platform might have significant implications for a broad readership and will be of interest to researchers working in the field of photonics and sensing technology.

Electrical tuning of branched flow of light.

Branched flows occur ubiquitously in various wave systems, when the propagating waves encounter weak correlated scattering potentials. Here we report the experimental realization of electrical tuning of the branched flow of light using a nematic liquid crystal (NLC) system. We create the physical realization of the weakly correlated disordered potentials of light via the inhomogeneous orientations of the NLC. We demonstrate that the branched flow of light can be switched on and off as well as tuned continuously through the electro-optical properties of NLC film. We further show that the branched flow can be manipulated by the polarization of the incident light due to the optical anisotropy of the NLC film. The nature of the branched flow of light is revealed via the unconventional intensity statistics and the rapid fidelity decay along the light propagation. Our study unveils an excellent platform for the tuning of the branched flow of light which creates a testbed for fundamental physics and offers a new way for steering light.

Bioinspired Jumping Soft Actuators of the Liquid Crystal Elastomer Enabled by Photo-Mechanical Coupling.

Jumping, a fundamental survival behavior observed in organisms, serves as a vital mechanism for adapting to the surrounding environment and overcoming significant obstacles within a given terrain. Here, we present a light-controlled soft jumping actuator inspired by asphondylia, which employs a closed-loop structure and utilizes a liquid crystal elastomer (LCE). Photo-mechanical coupling highlights the significant influence of the light source on the actuator's jumping behavior. Manipulating the light intensity, the relative position of stimulus and light lock, and the concentration of disperse red 1 (DR1) allows precise control over both the maximum take-off velocity and jump height. Furthermore, tailoring the size of the LCE actuator offers a means of regulating jumping behavior. Upon exposure to 460 nm LED irradiation, our actuator achieves remarkable performance, with a maximum jumping height of 10 body length (BL) and take-off velocity of 62 BL/s. These actuators accumulate and rapidly release energy, enabling the effective transportation of microcargos across substantial distances. Our research yields valuable insights into the realm of soft robotics, underscoring the pivotal importance of photo-mechanical coupling in the field of soft robotics, thereby serving as a catalyst for inspiring continued exploration of agile and capable systems by prestoring elastic energy.

Trajectory engineering of directrons in liquid crystals via photoalignment.

As electrically generated solitons in liquid crystals, directrons represent intriguing structures promising extensive application prospects in the areas of microcargo vehicles, microreactors, and logic devices. However, manipulating directrons along elaborate predetermined trajectories still remains to be largely explored. In this work, the strategy of constructing high-resolution periodic alignment fields for directrons via the polarization holography photoalignment technique is presented. The optimum exposure dose for directrons to form over a broad range of electric fields is determined to be 32.4 J cm-2 for the alignment layers with 1 wt% azo dye SD1. Zigzag and fishhook-shaped trajectories of directrons are realized with two orthogonal polarized beams. The resolution for zigzag steering of directrons is evaluated to be approximately 56 µm to 80 µm, about three to four times the length of directrons. These results not only enrich the forms of motion of directrons, but also lay the foundations for customized trajectories of directrons in future developments.

Optofluidic tunable broadband distributed Bragg reflector based on liquid crystal polymer composites.

A dynamically reconfigurable liquid crystal (LC) photonic device is an important research field in modern LC photonics. We present a type of continuously tunable distributed Bragg reflector (DBR) based on LC polymer composites modulated via a novel optofluidic method. LC-templated DBR films are fabricated by photopolymerization under visible standing wave interference. The influences of the incident angle, incident light intensity, and content of ethanol as a pore-forming additive on the reflection behavior are discussed in detail. Then, the LC-templated DBR films are integrated into microfluidic channels and reversibly refilled by different organic solvents. The reconfigurable characteristics of optofluidic DBRs were demonstrated by changing the average refractive index (RI) of the mixed liquids and adjusting the flow rates, resulting in the dynamic and continuous variation of the reflection band within a specific visible light band. It is anticipated that the prototype optofluidic LC device will hopefully be applied to some specific scenarios where conventional means of regulation, such as electric, optical, and temperature fields, are unsuitable and possibly boost the development of microfluidic analysis techniques based on structural color.

Smart acoustic 3D cell construct assembly with high-resolution.

Precise and flexible three-dimensional (3D) cell construct assembly using external forces or fields can produce micro-scale cellular architectures with intercellular connections, which is an important prerequisite to reproducing the structures and functions of biological systems. Currently, it is also a substantial challenge in the bioengineering field. Here, we propose a smart acoustic 3D cell assembly strategy that utilizes a 3D printed module and hydrogel sheets. Digitally controlled six wave beams offer a high degree of freedom (including wave vector combination, frequency, phase, and amplitude) that enables versatile biomimetic micro cellular patterns in hydrogel sheets. Further, replaceable frames can be used to fix the acoustic-built micro-scale cellular structures in these sheets, enabling user-defined hierarchical or heterogeneous constructs through layer-by-layer assembly. This strategy can be employed to construct vasculature with different diameters and lengths, composed of human umbilical vein endothelial cells and smooth muscle cells. These constructs can also induce controllable vascular network formation. Overall, the findings of this work extend the capabilities of acoustic cell assembly into 3D space, offering advantages including innovative, flexible, and precise patterning, and displaying great potential for the manufacture of various artificial tissue structures that duplicatein vivofunctions.

Liquid Crystals in Curved Confined Geometries: Microfluidics Bring New Capabilities for Photonic Applications and Beyond.

The quest for interesting properties and phenomena in liquid crystals toward their employment in nondisplay application is an intense and vibrant endeavor. Remarkable progress has recently been achieved with regard to liquid crystals in curved confined geometries, typically represented as enclosed spherical geometries and cylindrical geometries with an infinitely extended axial-symmetrical space. Liquid-crystal emulsion droplets and fibers are intriguing examples from these fields and have attracted considerable attention. It is especially noteworthy that the rapid development of microfluidics brings about new capabilities to generate complex soft microstructures composed of both thermotropic and lyotropic liquid crystals. This review attempts to outline the recent developments related to the liquid crystals in curved confined geometries by focusing on microfluidics-mediated approaches. We highlight a wealth of novel photonic applications and beyond and also offer perspectives on the challenges, opportunities, and new directions for future development in this emerging research area.

Reconfigurable polymer-templated liquid crystal holographic gratings via visible-light recording.

Polymer-templated nematic liquid crystal (LC) holographic gratings via visible-light recording are presented in the presence of reactive mesogens (RMs) and rose bengal (RB)/N-phenylglycine (NPG) photoinitiation systems. By optimizing the concentration of RMs in the polymer-templated LC gratings, the template after being washed out can be refilled with suitable fluidic components. And the dependence of the first-order diffraction efficiency (DE) on the concentration of RB and NPG molecules was discussed in detail. The polarization-dependency of diffraction properties was also investigated. It is revealed that the diffractive behaviors of polymer-templated LC gratings can be dynamically reconfigured by varying temperature or refilling organic solutions with different refractive index (RI). Furthermore, the potential for recording holograms using green light is explored. We expect that the reconfigurable polymer-templated LC gratings fabricated via visible-light interference would provide a facile approach to regulate the diffraction properties of holographic gratings apart from electric field, thus paving a way towards a class of novel anti-counterfeiting devices.

Cu Nanowires Passivated with Hexagonal Boron Nitride: An Ultrastable, Selectively Transparent Conductor.

The copper nanowire (Cu NW) network is considered a promising alternative to indium tin oxide as transparent conductors for advanced optoelectronic devices. However, the fast degradation of copper in ambient conditions largely overshadows its practical applications. Here we demonstrate a facile method for epitaxial growth of hexagonal boron nitride (h-BN) of a few atomic layers on interlaced Cu NWs by low-pressure chemical vapor deposition, which exhibit excellent thermal and chemical stability under high temperature (900 °C in vacuum), high humidity (95% RH), and strong base/oxidizer solution (NaOH/H2O2). Meanwhile, their optical and electrical performances remain similar to those of the original Cu NWs (e.g., high optical transmittance (∼93%) and high conductivity (60.9 Ω/□)). A smart privacy glass is successfully fabricated based on a Cu@h-BN NW network and liquid crytal, which could rapidly control the visibility from transparent to opaque (0.26 s) and, at the same time, strongly block the mid-infrared light for energy saving by screening radiative heat. This precise engineering of epitaxial Cu@h-BN core-shell nanostructure offers broad applications in high-performance electronic and optoelectronic devices.

Microfluidic generation of cholesteric liquid crystal droplets with an integrative cavity for dual-gain and controllable lasing.

The integration of one more gain media in droplet microlasers with morphology-dependent modes, which can be employed in optofluidic systems as multi-wavelength lasing sources, is highly attractive and demands new cavity design and fabrication approaches. Here, cholesteric liquid crystal (CLC) droplets with an integrative triple-emulsion cavity are fabricated via glass-capillary-based microfluidic technologies and dual-gain lasing with variable modes, flexibly configured by the combination and incorporation of gain dyes and CLCs into both the core and shell. The distributed feedback (DFB) mode, formed by the feedback from the self-assembled helix periodic structure of CLCs, the whispering gallery (WG) mode, and the hybrid, is selectively excited by controlling the spatial coupling between the pump beam and the droplet with gain. With the merits of dual-gain and controllable lasing, a prototype dual-wavelength-ratiometric thermometer with self-calibration capability is expected to be developed. Furthermore, the anisotropic CLC core is substituted with an isotropic fluid and the gain from the CLC shell is additionally removed, DFB lasings in both shell and core are absent, and only Bragg-shell reflection-based hybrid modes are excited for lasing. The CLC droplet microlasers with an integrative cavity are expected to provide a new route to future lab-on-chip (LOC) applications.

Real-time generation of dynamically patterned cholesteric liquid crystal fingerprint textures based on photoconductive effect.

We present a convenient approach to facilitate the real-time generation of updatable dynamically patterned cholesteric liquid crystal (CLC) fingerprint textures based on photoconductive effect. The photoconductive Bi12SiO20 (BSO) substrate acts as virtual electrode to obtain the desired states of CLCs by both electric and light fields. Owing to different boundary conditions, the switching of four states; that is, planar, fingerprint, metastable, and homeotropic states, and the rotation of fingerprint stripes can be achieved in planar alignment (PA) cell and hybrid alignment (HA) cell, respectively. With the aid of a digital micro-mirror (DMD)-based exposure system, binary and gray-scale images were successfully written and updated by light upon suitable voltages. This work provides an alternative approach to photoaddress CLC fingerprint patterns, without needing special photoalignment agents or photoresponsitive chiral dopants. We expect that it could be employed in the manipulation of nano/micro-objects by light.

Photoalignment of dye-doped cholesteric liquid crystals for electrically tunable patterns with fingerprint textures.

We present a convenient photoalignment approach to fabricate rewritable fingerprint textures with designed geometrical patterns based on methyl red doped cholesteric liquid crystals (MDCLCs). MDCLC systems with/without nanoparticles of polyhedral oligomeric silsesquioxanes (POSS) were employed to realize two types of sophisticated binary patterns, respectively. Based on the understanding of involved mechanisms related to boundary conditions and middle-layer theory, we demonstrated the precise manipulation of fingerprint patterns by varying the fingerprint grating vectors in different domains. Notably, the hybrid-aligned liquid crystal configuration induced by POSS nanoparticles, which leads to the electrically rotatable grating, can be converted into the planar-aligned configuration by the adsorption of photoexcited methyl red molecules onto the indium-tin-oxide (ITO) surface. In this manner, the dynamic voltage-dependent behavior of fingerprint gratings is altered from the rotation mode (R-mode) to the on-off mode (O-mode).

Smectic Layer Origami via Preprogrammed Photoalignment.

Hierarchical architecture is of vital importance in soft materials. Focal conic domains (FCDs) of smectic liquid crystals, characterized by an ordered lamellar structure, attract intensive attention. Simultaneously tailoring the geometry and clustering characteristics of FCDs remains a challenge. Here, the 3D smectic layer origami via a 2D preprogrammed photoalignment film is accomplished. Full control of hierarchical superstructures is demonstrated, including the domain size, shape, and orientation, and the lattice symmetry of fragmented toric FCDs. The unique symmetry breaking of resultant superstructures combined with the optical anisotropy of the liquid crystals induces an intriguing polarization-dependent diffraction. This work broadens the scientific understanding of self-assembled soft materials and may inspire new opportunities for advanced functional materials and devices.

Demonstration of patterned polymer-stabilized cholesteric liquid crystal textures for anti-counterfeiting two-dimensional barcodes.

We evaluated the feasibility of embedding periodically arranged squares with planar and vertical texture into a background with a developable-modulation (DM) type cholesteric liquid crystal (CLC) fingerprint texture by a two-step ultraviolet-induced polymerization method. Checker-patterned optical diffractive elements, which can be seen as a variation of a two-dimensional (2D) barcode, were first realized and the dependence of diffraction behaviors on incident light polarization and applied voltage were investigated. Taking advantage of the natural randomness and uncontrollable variations of a DM-type fingerprint textures, a polymer-stabilized CLC (PSCLC) graphic symbol with a 2D barcode pattern was then implemented with enhanced anti-counterfeiting features that are difficult to falsify or duplicate. The results indicate that the multiplexing of nonuniform DM-type fingerprint gratings, cross-polarized light readout, and unique polarization diffraction characteristics can improve the level of security.

Light-Driven Rotation and Pitch Tuning of Self-Organized Cholesteric Gratings Formed in a Semi-Free Film.

Cholesteric liquid crystal (CLC) has attracted intensive attention due to its ability to form a periodic helical structure with broad tunability. CLC gratings in open systems are especially promising in sensing and micromanipulation. However, there is still much to learn about the inherent mechanism of such gratings. We investigate the light-driven rotation and pitch-tuning behaviors of CLC gratings in semi-free films which are formed by spin-coating the CLC mixtures onto planarly photoaligned substrates. The doped azobenzene chiral molecular switch supplies great flexibility to realize the continuous grating rotation. The maximum continuous rotational angle reaches 987.8°. Moreover, dependencies of light-driven rotation and pitch tuning on the dopant concentration and exposure are studied. The model of director configuration in the semi-free film is constructed. Precise beam steering and synchronous micromanipulation are also demonstrated. Our work may provide new opportunities for the CLC grating in applications of beam steering, micromanipulation, and sensing.

Microfluidic fabrication of cholesteric liquid crystal core-shell structures toward magnetically transportable microlasers.

We report a magnetically transportable microlaser with cholesteric liquid crystal (CLC) core-shell structure, operating in band-edge mode. The dye doped CLC shells as a water-in-oil-in-water (W/O/W) double emulsion were fabricated by microfluidics. Water-dispersible Fe3O4 magnetic nanoparticles were incorporated in the inner aqueous phase by taking advantage of the immiscibility with the middle CLC oil phase. The influence of temperature and shell thickness on laser properties was discussed in detail. The non-invasive manipulation of microlasers was realized under a magnetic field. The dependence of velocity on the viscosity of the carrying fluid and size of the core-shell structure was theoretically analyzed and experimentally investigated using a prototype electromagnetic platform. We also discussed the design principles for this type of DDCLC core-shell structure. Such magnetically transportable microlasers offer promise in in-channel illumination applications requiring active control inside micro-channels.

Metallically confined microdisks with in-plane multiple guided emissions.

We theoretically present in-plane multiple guided emissions of metallically confined microdisk lasers which can be applied to drive multiple elements in compact photonic integration at the same time. Two to four-port microdisks with transverse magnetic and electric polarizations are investigated based on finite difference time domain simulation and padé approximation. Modes filtering of coupling ports are verified by the calculated mode quality factors (Q) which are decided by the matching of coupling ports with the energy density distribution of corresponding modes. Single mode lasing operation of semiconductor microdisk with guided emissions is possibly realized by selectively pumping.