Optical lenses with electrically controllable focal length are of growing interest, in order to reduce the complexity, size, weight, response time and power consumption of conventional focusing/zooming systems, based on glass lenses displaced by motors. They might become especially relevant for diverse robotic and machine vision-based devices, including cameras not only for portable consumer electronics (e.g. smart phones) and advanced optical instrumentation (e.g. microscopes, endoscopes, etc.), but also for emerging applications like small/micro-payload drones and wearable virtual/augmented-reality systems. This paper reviews the most widely studied strategies to obtain such varifocal “smart lenses”, which can electrically be tuned, either directly or via electro-mechanical or electro-thermal coupling. Only technologies that ensure controllable focusing of multi-chromatic light, with spatial continuity (i.e. continuous tunability) in wavefronts and focal lengths, as required for visible-range imaging, are considered. Both encapsulated fluid-based lenses and fully elastomeric lenses are reviewed, ranging from proof-of-concept prototypes to commercially available products. They are classified according to the focus-changing principles of operation, and they are described and compared in terms of advantages and drawbacks. This systematic overview should help to stimulate further developments in the field.
The possibility of electrically tuning the scattering of light from surfaces by dynamically varying their properties is desirable for controllable transparency devices and diffusion filters. As a difference from state-of-the-art approaches where scattering is changed isotropically, this paper presents the first smart-material-based technology enabling electrical modulations in a single or multiple directions, which can be selected dynamically. The effect is achieved from thin soft membranes with transparent PEDOT:PSS coatings, which are electrically deformed along a single or multiple axes, using dielectric elastomer actuation. Anisotropic scattering is induced by electrically tuning the formation of directional surface wrinkles. As a proof of concept, a bi-directional device is obtained by overlapping two 90°-shifted mono-directional layers that can be controlled independently. According to the activation of the layers, light can be scattered along either direction, as well as both of them. Prototypes made of an acrylic elastomer were demonstrated with mono-and bi-directional operations. Devices with a window-to-total area ratio of 1:4 also showed a maximum electrical reduction of optical transmittance from 75% to 4%. This functionality and possible extensions to more than two controllable directions suggest applicability as electrically controllable anisotropic light diffusers for dynamic light shaping, as well as tunable transparency surfaces.
The possibility to electrically tune the optical transparency of thin membranes is of significant interest for a number of possible applications, such as controllable light diffusers and smart windows, both for residential and mobile use. As a difference from state-of-the-art approaches, where with an applied voltage the transparency can only increase or decrease, this paper presents the first concept to make it electrically tuneable to both higher and lower values, within the same device. The concept is applicable to any soft insulating membrane, by coating both of its surfaces with a circular transparent stretchable conductor, surrounded by a stretchable annular conductor. The two conductors are used as independently addressable electrodes to generate a dielectric elastomer-based actuation of the membrane, so as to electrically control its surface topography. We show that the optical transmittance can electrically be modulated within a broad range, between 25% and 83%. This approach could be especially advantageous for systems that require such a broad tuning range within structures that have to be thin, lightweight and acoustically silent in operation.
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