Optical Actuator Research Articles

Experimental and analytical analysis of tapered optical fiber tweezers

This paper presents the experimental development and analytical modeling of cost-effective Optical Fiber Tweezers fabricated from tapered optical fibers. The optical fiber tweezers use a 976 nm pump laser to obtain the multimode effect in conventional silica optical fibers (since it is below the cutoff wavelength). In addition, the taper is performed in the optical fiber using a conventional optical fiber splicing machine, where the diameter of the taper can be controlled by simply changing the taper parameters. The simplified analytical model is performed for the analysis of the intensity and optical power variations of the fiber tip as a function of the axial distance and angle between the fiber tip and the region of interest as well as the attractive (or repulsive) force on the optical field. In this case, 3 optical fiber tweezers were fabricated with different tip diameters and tested as a function of two set of particle specimens, one using polystyrene with 17 μm diameter and the other with glass particles of 3.2 μm. Results show that the repulsive forces presented in the force estimation model do not occur as expected, where all optical fiber tweezers presented higher attractive forces than the expected by the analytical model. Such differences can be related to the photothermal effect, which may have led to an unbalanced relation between its sub-effects known as thermophoresis and negative photophoresis. The results also indicated a high dependency of the attractive forces as a function of the optical fiber tip diameter, where the fiber tweezer with smallest diameter presented a fivefold and fourfold increase in the optical force when compared with the fiber tweezer with highest diameter for polymer and glass particles, respectively. Therefore, the proposed approach is a cost-effective method with relatively large control of the optical fiber tip for the optical actuator of micro-scale particles.

Plasmonic Nanocomposite for Visible Light‐Modulated Bimorph‐Actuator

AbstractSoft actuators have great potential applications in sophisticated movement and sensitive devices due to their flexible nature, good interaction, and precise control. However, existing carbon‐based optical actuators are limited in their response under visible light irradiation. The limited visible light absorbance of the carbon nanostructure brought the metallic nanoparticle into the soft actuators that can absorb visible light. This study introduces a new type of plasmonic photothermal‐bimorph actuator, using graphene oxide (GO), reduced graphene oxide (rGO), and silver nanorods (Ag NRs) to overcome the limitations of traditional optical actuators. The bimorph film is actuated by visible and near‐infrared light stimuli with various power densities showing reversible deformation behavior. The actuator shows significant bending associated with a ≈50° change in bending angle under visible light irradiation with a response time of ≈5 ± 1 sec. Furthermore, a smart photo‐controlled non‐contact switch is fabricated based on photo‐thermal conversion properties, demonstrating perfect integration of plasmonic bimorph actuators. The density functional theory based molecular dynamics calculations provide an additional understanding of the bending of actuators under external stimulus. Using illustrative demonstrations of actuators, these results hint at a method for generating multipurpose visible light‐based soft robots, supporting a new approach to developing an optical locking system.

Revealing the Impact of Composition on Oil Monitoring Performance of Ni-Ti-Cu Coated Optical Fiber

Shape Memory Alloy-coated optical fiber provides an economical, Smart, and real-time monitoring technological solution for Industry 4.0. In this work, the compositional influence of Ni-Ti-Cu coating on optical signal actuation has been studied. Morphological studies showed improvement in the grain size, surface roughness, and a better shape memory effect. Thermal characteristics revealed an increase in the phase transformation temperature of NiTiCu with higher copper content. Experimental analysis of optical fiber sensors in Mineral Oil resulted in a gradual shift in the actuation temperature range. A sensitivity of ∼52 mV/°C was recorded in the actuation window, showcasing the improved response time for copper-rich composition. A comparison of coated-uncoated optical fiber performance in oil has also been presented, and delamination studies were conducted by continuously exposing the samples to hot oil. The work can be referred for requirement-based composition selection for real-time and smart monitoring capability in the Oil industries.

Photoinduced bending in bimorph optical fibers

Optomechanical materials directly generate work from light through physical deformation upon illumination. Here, we report an optical fiber-based optomechanical actuator that undergoes bending when illuminated by actinic light. A model for light-induced bending curvature as a function of geometrical and material properties was developed to aid in design. Polymer fibers were fabricated and filled directly during the draw with a molten azobenzene derivative. Upon illumination, photoactivated motion is observed and quantified with an optical lever beam approach.

Ultra-high spatial resolutions in photopatterning molecular orientations.

Accurately aligning liquid crystal molecules into predetermined spatially variant orientations is crucial for fabricating devices such as flat optical elements, soft actuators and robots. Despite the developments of various photopatterning techniques for this purpose, the limits of their spatial resolutions have been rarely addressed. In this study, we delve into the physical constraints governing the spatial resolutions of two prominent photopatterning methods: single exposure to light fields with structured polarizations and multi-exposures to light fields with structured intensities. Theoretical analyses show that the minimal grating period of the first method is only half of the Abbe limit of an intensity imaging system, and that the minimal grating period for the second system can surpass the Rayleigh limit. Experimental studies demonstrate unprecedent high spatial resolution with minimal grating periods of 1 µm. We further establish that the minimal core size in photopatterned singular topological defects is linearly proportional to the minimal grating period and the topological charge and that these photopatterning techniques can yield less than 1 µm defect cores that are in high demand for applications such as coronagraphs.

TWISP: a transgenic worm for interrogating signal propagation in Caenorhabditis elegans.

Genetically encoded optical indicators and actuators of neural activity allow for all-optical investigations of signaling in the nervous system. But commonly used indicators, actuators, and expression strategies are poorly suited for systematic measurements of signal propagation at brain scale and cellular resolution. Large-scale measurements of the brain require indicators and actuators with compatible excitation spectra to avoid optical crosstalk. They must be highly expressed in every neuron but at the same time avoid lethality and permit the animal to reach adulthood. Their expression must also be compatible with additional fluorescent labels to locate and identify neurons, such as those in the NeuroPAL cell identification system. We present TWISP, a transgenic worm for interrogating signal propagation, that addresses these needs and enables optical measurements of evoked calcium activity at brain scale and cellular resolution in the nervous system of the nematode Caenorhabditis elegans. In every neuron we express a nonconventional optical actuator, the gustatory receptor homolog GUR-3 + PRDX-2, under the control of a drug-inducible system QF + hGR, and a calcium indicator GCAMP6s, in a background with additional fluorophores from the NeuroPAL cell ID system. We show that this combination, but not others tested, avoids optical crosstalk, creates strong expression in the adult, and generates stable transgenic lines for systematic measurements of signal propagation in the worm brain.

A MXene Hydrogel-Based Versatile Microrobot for Controllable Water Pollution Management.

The urgent demand for addressing dye contaminants in water necessitates the development of microrobots that exhibit remote navigation, rapid removal, and molecular identification capabilities. The progress of microrobot development is currently hindered by the scarcity of multifunctional materials. In this study, a plasmonic MXene hydrogel (PM-Gel) is synthesized by combining bimetallic nanocubes and Ti3C2Tx MXene through the rapid gelation of degradable alginate. The hydrogel can efficiently adsorb over 60% of dye contaminants within 2 min, ultimately achieving a removal rate of >90%. Meanwhile, the hydrogel exhibits excellent sensitivity in surface enhanced Raman scattering (SERS) detection, with a limit of detection (LOD) as low as 3.76 am. The properties of the plasmonic hydrogel can be further adjusted for various applications. As a proof-of-concept experiment, thermosensitive polymers and superparamagnetic particles are successfully integrated into this hydrogel to construct a versatile, light-responsive microrobot for dye contaminants. With magnetic and optical actuation, the robot can remotely sample, identify, and remove pollutants in maze-like channels. Moreover, light-driven hydrophilic-hydrophobic switch of the microrobots through photothermal effect can further enhance the adsorption capacity and reduced the dye residue by up to 58%. These findings indicate of a broad application potential in complex real-world environments.

Liquid Crystal Elastomer Actuators Enhanced by Tapered Optical Fibers for Controllable Bending Directions and Amplitudes

AbstractLiquid crystal elastomer (LCE) photoactuators offer a versatile platform for executing complicated tasks through precisely controlled bending directions and amplitudes. Optical waveguides assist photoactuators to perform tasks unimpededly. While most existing optical waveguide actuators are limited to unidirectional bending, limiting their versatility. Here, a LCE actuator integrated with a tapered optical fiber with controllable bending directions and amplitudes is presented. The LCE actuator displays bending motions induced by uneven shrinkage due to the off‐center fiber. The bending directions are parallel to the previous uniaxial alignment of the LCE film, which can be adjusted to an arbitrary angle with the tapered optical fiber. The LCE actuators exhibit adaptable bending directions at 0°, 45°, and 90°, representing the possible bending motions. The bending amplitudes are regulated by infrared laser power. A hook‐like LCE actuator with 0° bending direction carried the handle of a basket. In addition, a 90° bending direction LCE actuator displays the shrinkage behavior, showing a special bending motion control. Moreover, a bionic hand, comprising five LCE actuators with various bending directions, exhibited diverse gestures with precise control. The controllable bending motions in optical waveguide actuators expand the promising applications in complicated scenarios, such as catheters or other medical devices.

Light-Responsive Soft Robot Integrating Actuation and Function Based on Laser Cutting.

Soft robots with good deformability and adaptability have important prospects in the bionics and intelligence field. However, current research into soft robots is primarily limited to the study of actuators and ignores the integrated use of functional devices and actuators. To enrich the functions of soft robots and expand their application fields, it is necessary to integrate various functional electronic devices into soft robots to perform diverse functions during dynamic deformation. Therefore, this paper discusses methods and strategies to manufacture optical stimuli-responsive soft actuators and integrate them into functional devices for soft robots. Specifically, laser cutting allows us to fabricate an optically responsive actuator structure, e.g., the curling direction can be controlled by adjusting the direction of the cutting line. Actuators with different bending curvatures, including nonbending, can be obtained by adjusting the cutting depth, cutting width, and the spacing of the cutting line, which makes it easy to obtain a folded structure. Thus, various actuators with complex shape patterns can be obtained. In addition, we demonstrate a fabrication scheme for a worm-like soft robot integrated with functional devices (LEDs are used in this paper). The local nonbending design provides an asymmetric structure that provides driving power and avoids damage to the functional circuit caused by the large deformation during movement. The integration of drive and function provides a new path for the application of soft robots in the intelligence and bionics field.

An integrated microfluidic platform for on-demand single droplet dispenser with high accuracy by electrohydrodynamic (EHD) printing technique

Droplet microfluidics has revolutionized single-cell analysis, allowing for ultra-high-throughput sorting of droplets to meet the demands of single-cell sorting. However, accurately and efficiently dispensing target droplets into specific containers for downstream analysis has remained a challenge. Here, we present an integrated microfluidic droplet dispenser based on the electrohydrodynamic (EHD) principle, capable of on-demand single droplet dispensing with high accuracy. Our system uses optical signal activation and EHD actuation to isolate and dispense droplets. The microfluidic droplet auto dispenser consists of four main modules: a pump-drive chip module, an optical automatic signal recognition module, a high voltage control module, and an automated X-Y translation stage module. By optimizing the chip structure and voltage parameter, this platform successfully isolates single Escherichia coli (E. coli) cells onto a Petri dish for downstream cultivation and heterogeneity analysis. In addition, the dispenser microfluidic system dispenses the sorted droplets in a "one droplet, one well" manner, providing an automated method for droplet interface from the micro- to macro- platform. This dispenser system provides a platform for phenotypic screening of single colony pick and single cell analysis

Optimizing Optical Dielectrophoretic (ODEP) Performance: Position- and Size-Dependent Droplet Manipulation in an Open-Chamber Oil Medium.

An optimization study is presented to enhance optical dielectrophoretic (ODEP) performance for effective manipulation of an oil-immersed droplet in the floating electrode optoelectronic tweezers (FEOET) device. This study focuses on understanding how the droplet's position and size, relative to light illumination, affect the maximum ODEP force. Numerical simulations identified the characteristic length (Lc) of the electric field as a pivotal factor, representing the location of peak field strength. Utilizing 3D finite element simulations, the ODEP force is calculated through the Maxwell stress tensor by integrating the electric field strength over the droplet's surface and then analyzed as a function of the droplet's position and size normalized to Lc. Our findings reveal that the optimal position is xopt= Lc+ r, (with r being the droplet radius), while the optimal droplet size is ropt = 5Lc, maximizing light-induced field perturbation around the droplet. Experimental validations involving the tracking of droplet dynamics corroborated these findings. Especially, a droplet sized at r = 5Lc demonstrated the greatest optical actuation by performing the longest travel distance of 13.5 mm with its highest moving speed of 6.15 mm/s, when it was initially positioned at x0= Lc+ r = 6Lc from the light's center. These results align well with our simulations, confirming the criticality of both the position (xopt) and size (ropt) for maximizing ODEP force. This study not only provides a deeper understanding of the position- and size-dependent parameters for effective droplet manipulation in FEOET systems, but also advances the development of low-cost, disposable, lab-on-a-chip (LOC) devices for multiplexed biological and biochemical analyses.

Photomechanical properties in metal-organic crystals.

The emergence of materials that can effectively convert photon energy (light) into motion (mechanical work) and change their shapes on command is of great interest for their potential in the fabrication of devices (powered by light) that will revolutionize the technologies of optical actuators, smart medical devices, soft robotics, artificial muscles and flexible electronics. Recently, metal-organic crystals have emerged as desirable smart hybrid materials that can hop, split and jump. Thus, their incorporation into polymer host objects can control movement from molecules to millimetres, opening up a new world of light-switching smart materials. This feature article briefly summarizes the recent part of the fast-growing literature on photomechanical properties in metal-organic crystals, such as coordination compounds, coordination polymers (CPs), and metal-organic frameworks (MOFs). The article highlights the contributions of our group along with others in this area and aims to provide a consolidated idea of the engineering strategies and structure-property relationships of these hybrid materials for such rare phenomena with diverse potential applications.

Optogenetic demonstration of the involvement of SMA-negative mural cells in the regulation of cerebral blood flow.

Mural cells are critical components of the cerebral vasculature. They are categorized into three primary subsets: arteriole smooth muscle cells (aSMCs), pericytes (PCs) and venule smooth muscle cells (vSMCs). It is well known that aSMCs can directly regulate cerebral blood flow (CBF) with their own contraction and dilation mechanisms. On the other hand, the direct involvement of PCs or vSMCs in CBF regulation is controversial. This ambiguity is largely due to the lack of specifically manipulable tools to isolate their function. To address this issue, we employed a set-subtraction approach by using a combination of tTA-mediated gene induction and Cre-mediated gene excision. We developed transgenic mice expressing optical actuators, channelrhodopsin-2 (ChR2) and photoactivated adenylyl cyclase (PAC) in smooth muscle actin (SMA)-negative mural cells that lack the machinery for SMA-mediated vasoregulation. Using these mouse models, we assessed CBF alterations in response to optical stimulation using laser Doppler techniques. Our results showed that optical stimulation induced notable CBF changes in both models. This study provides evidence for the potential regulatory role of PCs and vSMCs in cerebral hemodynamics and introduces powerful tools to specifically manipulate these cell types in vascular neurobiology.

Nanofiber-based flexible actuator with high transparency and large-scale deformation for biomimetic and intelligent control

In this study, a novel flexible PVP/PVA-co-PE composite film with excellent transparency and large-scale bending deformation capability was prepared by a simple impregnation process. Due to the similar refractive index between the filling phase of PVP and PVA-co-PE nanofibers, the pore layer of the nanofibrous was replaced by PVP after impregnation, thus endowing the composite film with excellent optical transparency. In addition, the excellent hygroscopic response of PVP promoted the rapid hygroscopic swelling behavior in response to external moisture, and thus achieved complex bending deformation of the PVP/PVA-co-PE composite film. Experimental results show that the optimum optical transparency of the composite film can reach 82.53%, and the maximum bending angle of the composite film can reach 180° within 1.2 s of contact with moisture stimulation. Based on the excellent optical transparency and actuation performance, the PVP/PVA-co-PE composite film was prepared into smart windows, Venus flytrap and bionic reptiles, which promoted its application and development in the field of intelligent bionic and smart control systems.

Autonomous nanorobots with powerful thrust under dry solid-contact conditions by photothermal shock

Nanorobotic motion on solid substrates is greatly hindered by strong nanofriction, and powerful nanomotors‒the core components for nanorobotic motion‒are still lacking. Optical actuation addresses power and motion control issues simultaneously, while conventional technologies with small thrust usually apply to fluid environments. Here, we demonstrate micronewton-thrust nanomotors that enable the autonomous nanorobots working like conventional robots with precise motion control on dry surfaces by a photothermal-shock technique. We build a pulsed laser-based actuation and trapping platform, termed photothermal-shock tweezers, for general motion control of metallic nanomaterials and assembled nanorobots with nanoscale precision. The thrust-to-weight ratios up to 107 enable nanomotors output forces to interact with external micro/nano-objects. Leveraging machine vision and deep learning technologies, we assemble the nanomotors into autonomous nanorobots with complex structures, and demonstrate multi-degree-of-freedom motion and sophisticated functions. Our photothermal shock-actuation concept fundamentally addresses the nanotribology challenges and expands the nanorobotic horizon from fluids to dry solid surfaces.

Solid-State Cholesteric Liquid Crystals as an Emerging Platform for the Development of Optical Photonic Sensors.

Over the past decade, solid-state cholesteric liquid crystals (CLCsolid ) have emerged as a promising photonic material, heralding new opportunities for the advancement of optical photonic biosensors and actuators. The periodic helical structure of CLCsolid s gives rise to their distinctive capability of selectively reflecting incident radiation, rendering them highly promising contenders for a wide spectrum of photonic applications. Extensive research is conducted on utilizing CLCsolid 's optical characteristics to create optical sensors for bioassays, diagnostics, and environmental monitoring. This review provides an overview of emerging technologies in the field of interpenetrating polymeric network-CLCsolid (IPN) and CLCsolid -based optical sensors, including their structural designs, processing, essential materials, working principles, and fabrication methodologies. The review concludes with a forward-looking perspective, addressing current challenges and potential trajectories for future research.

A Modified Low-Cost Surface Plasmonic Sensor with Tunable Optical Actuation Angle Based on Micromachining Techniques Used by Microfluidics

A Modified Low-Cost Surface Plasmonic Sensor with Tunable Optical Actuation Angle Based on Micromachining Techniques Used by Microfluidics

Optical readout and actuation of plasmonic nano-optomechanical drum resonators

We demonstrate optical readout and actuation of nanomechanical motion using plasmonic fields in a nanoscale gap waveguide. The top gold layer of the waveguide is free to vibrate like a drumhead, and patterned with an optical grating to facilitate efficient coupling to free-space radiation. The change of the plasmonic gap mode with the top layer position couples the plasmonic resonance to the mechanical displacement of the drum. We characterize optical and mechanical resonances of the system, and demonstrate sensing of nanomechanical vibrations with ∼10−14 m/Hz sensitivity. The mechanical resonators are actuated through plasmonic forces. Quantifying their magnitude shows that plasmonic forces can significantly exceed pure radiation pressure, indicating that their nature is dominated by a photothermoelastic effect. This work opens avenues to the use of plasmonic readout and control in nanomechanical sensing applications.

Coherent control of mid-infrared frequency comb by optical injection of near-infrared light

We demonstrate the use of a low power near-infrared laser illuminating the front facet of a quantum cascade laser (QCL) as an optical actuator for the coherent control of a mid-infrared frequency comb. We show that with appropriate current control of the QCL comb and intensity modulation of the near-infrared laser, a tight phase lock of a comb line to a distributed feedback laser is possible with 2 MHz of locking bandwidth and 200 mrad of residual phase noise. A characterization of the whole scheme is provided, showing the limits of the electrical actuation, which we bypassed using the optical actuation. Both comb degrees of freedom can be locked by performing electrical injection locking of the repetition rate in parallel. However, we show that the QCL acts as a fast near-infrared light detector such that injection locking can also be achieved through modulation of the near-infrared light. These results on the coherent control of a QCL frequency comb are particularly interesting for coherent averaging in dual-comb spectroscopy and for mid-infrared frequency comb applications requiring high spectral purity.

Actuation of Mobile Microbots: A Review

Maturation of robotics research and advances in the miniaturization of machines have contributed to the development of microbots and enabled new technological possibilities and applications. Microbots have a wide range of applications, including the navigation of confined spaces, environmental monitoring, micro‐assembly and manipulation of small objects, and in vivo micro‐surgeries and drug delivery. Actuators are among the most critical components that define the performance of robots. A comprehensive review of the actuation mechanisms that have been employed in mobile microbots is provided, including piezoelectric, magnetic, electrostatic, thermal, acoustic, biological, chemical, and optical actuation, with a focus on the most recent development and methodologies.