66 research outputs found
Structured Optical Materials Controlled by Light
Materials of which the optical response is determined by their structure are
of much interest both for their fundamental properties and applications.
Examples range from simple gratings to photonic crystals. Obtaining control
over the optical properties is of crucial importance in this context, and it is
often attempted by electro-optical effect or by using magnetic fields. In this
paper, we introduce the use of light to switch and tune the optical response of
a structured material, exploiting a physical deformation induced by light
itself. In this new strategy, light drives an elastic reshaping, which leads to
different spectral properties and hence to a change in the optical response.
This is made possible by the use of liquid crystalline networks structured by
Direct Laser Writing. As a proof of concept, a grating structure with
sub-millisecond time-response is demonstrated for optical beam steering
exploiting an optically induced reversible shape-change. Experimental
observations are combined with finite-element modeling to understand the
actuation process dynamics and to obtain information on how to tune the time
and the power response of this technology. This optical beam steerer serves as
an example for achieving full optical control of light in broad range of
structured optical materials
Photonic Microhand with Autonomous Action
Grabbing and holding objects at the microscale is a complex function, even for microscopic living animals. Inspired by the hominid-type hand, a microscopic equivalent able to catch microelements is engineered. This microhand is light sensitive and can be either remotely controlled by optical illumination or can act autonomously and grab small particles on the basis of their optical properties. Since the energy is delivered optically, without the need for wires or batteries, the artificial hand can be shrunk down to the micrometer scale. Soft material is used, in particular, a custom-made liquid-crystal network that is patterned by a photolithographic technique. The elastic reshaping properties of this material allow finger movement, using environmental light as the only energy source. The hand can be either controlled externally (via the light field), or else the conditions in which it autonomously grabs a particle in its vicinity can be created. This microrobot has the unique feature that it can distinguish between particles of different colors and gray levels. The realization of this autonomous hand constitutes a crucial element in the development of microscopic creatures that can perform tasks without human intervention and self-organized automation at the micrometer scale
Opposite Self-Folding Behavior of Polymeric Photoresponsive Actuators Enabled by a Molecular Approach
Multichannel remote polarization control enabled by nanostructured Liquid Crystalline Networks
In this article we demonstrate that a grating fabricated through nanoscale
volumetric crosslinking of a liquid crystalline polymer enables remote
polarization control over the diffracted channels. This functionality is a
consequence of the responsivity of liquid crystal networks upon light stimuli.
Tuning the photonic response of the device is obtained thanks to both a
refractive index and a shape change of the grating elements induced by a
molecular rearrangement under irradiation. In particular, the material
anisotropy allows for nontrivial polarization state management over multiple
beams. Absence of any liquid component and a time response down to 0.2
milliseconds make our device appealing in the fields of polarimetry and optical
communications.Comment: 16 pages,8 figures, featured article in AL
Light‐Powered Microrobots: Challenges and Opportunities for Hard and Soft Responsive Microswimmers
Worldwide research in microrobotics has exploded in the past two decades,
leading to the development of microrobots propelled in various manners. Despite
significant advances in the field and successful demonstration of a wide range of
applications, microrobots have yet to become the preferred choice outside a
laboratory environment. After introducing available microrobotic propulsion and
control mechanisms, microrobots that are manufactured and powered by light
are focused herein. Referring to pioneering works and recent interesting
examples, light is presented not only as a fabrication tool, by means of twophoton
polymerization direct laser writing, but also as an actuator for microrobots
in both hard and soft stimuli–responsive polymers. In this scenario, a
number of challenges that yet prevent polymeric light-powered microrobots from
reaching their full potential are identified, whereas potential solutions to overcome
said challenges are suggested. As an outlook, a number of real-world
applications that light-powered microrobots should be particularly suited for are
mentioned, together with the advances needed for them to achieve such purposes.
An interdisciplinary approach combining materials science, microfabrication,
photonics, and data science should be conducive to the next generation of
microrobots and will ultimately foster the translation of microrobotic applications
into the real world
Cellular Contact Guidance on Liquid Crystalline Networks with Anisotropic Roughness
: Cell contact guidance is widely employed to manipulate cell alignment and differentiation in vitro. The use of nano- or micro-patterned substrates allows efficient control of cell organization, thus opening up to biological models that cannot be reproduced spontaneously on standard culture dishes. In this paper, we explore the concept of cell contact guidance by Liquid Crystalline Networks (LCNs) presenting different surface topographies obtained by self-assembly of the monomeric mixture. The materials are prepared by photopolymerization of a low amount of diacrylate monomer dissolved in a liquid crystalline solvent, not participating in the reaction. The alignment of the liquid crystals, obtained before polymerization, determines the scaffold morphology, characterized by a nanometric structure. Such materials are able to drive the organization of different cell lines, e.g., fibroblasts and myoblasts, allowing for the alignment of single cells or high-density cell cultures. These results demonstrate the capabilities of rough surfaces prepared from the spontaneous assembly of liquid crystals to control biological models without the need of lithographic patterning or complex fabrication procedures. Interestingly, during myoblast differentiation, also myotube structuring in linear arrays is observed along the LCN fiber orientation. The implementation of this technology will open up to the formation of muscular tissue with well-aligned fibers in vitro mimicking the structure of native tissues
Dynamically Tunable Optical Cavities with Embedded Nematic Liquid Crystalline Networks
Tunable metal–insulator–metal (MIM) Fabry–P\ue9rot (FP) cavities that can dynamically control light enable novel sensing, imaging\ua0and display applications. However, the realization of dynamic cavities incorporating stimuli-responsive materials poses a significant engineering challenge. Current approaches rely on refractive index modulation and suffer from low dynamic tunability, high losses, and limited spectral ranges, and require liquid and hazardous materials for operation. To overcome these challenges, a new tuning mechanism employing reversible mechanical adaptations of a polymer network is proposed, and dynamic tuning of optical resonances is demonstrated. Solid-state temperature-responsive optical coatings are developed by preparing a monodomain nematic liquid crystalline network (LCN) and are incorporated between metallic mirrors to form active optical microcavities. LCN microcavities offer large, reversible and highly linear spectral tuning of FP resonances reaching wavelength-shifts up to 40\ua0nm via thermomechanical actuation while featuring outstanding repeatability and precision over more than 100 heating–cooling cycles. This degree of tunability allows for reversible switching between the reflective and the absorbing states of the device over the entire visible and near-infrared spectral regions, reaching large changes in reflectance with modulation efficiency ΔR\ua0=\ua079%
Three-Dimensional Photonic Circuits in Rigid and Soft Polymers Tunable by Light
partially_open6Polymeric matrices offer a wide and powerful platform for integrated photonics, complementary to the well established silicon photonics technology. The possibility to integrate, on the same chip, different customized materials allows for many functionalities, like the ability to dynamically control the spectral properties of single optical components. Within this context, this Article reports on the fabrication and optical characterization of integrated photonic circuits for the telecom C-band, made of a combination of both rigid and tunable elastic polymers. By using a 3D photolithographic technique (direct laser writing), in a single-step process, every building block of the polymeric circuit is fabricated: straight and bent waveguides, grating couplers, and single and vertically coupled whispering gallery mode resonators designed in planar and vertical geometries. Using this platform, a new type of operation was introduced through true three-dimensional integration of tunable photonic components, made by liquid crystalline networks that can be actuated and controlled by a remote and non-invasive light stimulus. Depending on the architecture, it is possible to integrate them as elastic actuators or as constituents of the photonic cavity itself. The two strategies then exploit the optical induced deformation and variation of its refractive index, inducing a net red or blue shift of the cavity resonances, respectively. This work paves the way for light-tunable optical networks that combine different photonic components, made by glassy or shape-changing materials, in order to implement further photonic circuit requirements.openSara Nocentini; Francesco Riboli; Matteo Burresi; Daniele Martella; Camilla Parmeggiani; Diederik S. WiersmaNocentini, Sara; Riboli, Francesco; Burresi, Matteo; Martella, Daniele; Parmeggiani, Camilla; Wiersma, Diederik S
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