In this paper, we present a nonmechanical three-dimensional beam steering system using electrowetting based liquid lens and liquid prism. The optical design for the radius of curvature of the liquid lens and the tilting angle of the liquid prism was modeled with Zemax and three-dimensional beam steering was simulated. The liquid lens from Corning-Varioptic was used and the focal length of the lens was varied depending on the applied voltage. Cuboid-shaped chamber of the liquid prism was fabricated with glasses and two immiscible liquids whose densities are the same were injected into the fabricated chamber. The apex angle of the liquid prism and beam steering on the x-axis, y-axis, and xy-axis were measured by changing the applied voltages on the four sidewalls of the liquid prism. The light spot passing through the liquid lens and liquid prism was measured and the calculated beam steering angle was 11.6 º to 12.0 º. The effects of gravity on the shape and apex angle of the liquid prism were also measured by rotating the sample. Nonmechanical three-dimensional beam steering control including the z-axis direction was demonstrated by combining the electrowetting based liquid lens and liquid prism.
Electrowetting is a phenomenon that controls the surface tension of droplets by electricity and changes the wettability of the droplets. There are many applications of electrowetting, such as tunable liquid lenses, electronic paper and 3D display. Response time of electrowetting applications is important for them, but the relationship between response time and the physical parameters for electrowetting operation has not been deeply investigated. Therefore, we have investigated the effects of physical properties such as viscosity, interfacial tension and substrate roughness on the response time in AC electrowetting and found the optimal conditions for fast electrowetting. Also, an electrowetting circular lens was fabricated based on the optimal conditions and compared to a conventional electrowetting circular lens for response time. The experiment was conducted on a 0.4 mm thick aluminum plate with a 1μm thin parylene C film deposited with a 50 nm Teflon coating. The experiment results showed that the fastest response time is obtained at 5 mPa∙s conducting liquid (water-glycerol mixture) with 0 wt % SDS (sodium dodecyl sulfate) on default aluminum plate (RMS roughness 270 nm). Through this experiment, it was possible to control the spreading response pattern of electrowetting from under-damped response to over-damped response by changing the conditions of viscosity of conducting liquid, surface tension between two immiscible liquids, and substrate roughness. Also, a critical damping response was implemented using a hardware method by applying the optimum condition without voltage shape variation technology.
In this study, we propose light field 3D endoscope using the electro-wetting lens array. Compared to conventional light field endoscope technology, the electro-wetting micro lens array are not only switchable between 2D and 3D, but also adjusts the focal length to capture the varying images and control the diopter sufficiently fast (ms). The electro-wetting lens array has diameter 2.4mm and diopter -20D ~ 28D with 40ms of response time, which is an appropriate to get an endoscopic image. We also compare with light field 3D endoscope using a fixed focus lens array and our proposed light field 3D endoscope under the same condition. To achieve the electro-wetting lens array, parylene C layer are deposited on the silicon through hole substrate. In this study, we focus on the electro-wetting lens array fabrication and feasibility of a light field 3D system based on the electro-wetting micro lens array, accordingly we do not assemble the whole system in the real endoscope. Although it is performed on the optical stage, we successfully captured a light field images of several objects and reproduce a 3D image. Hereafter research, we will apply extended depth-of-field algorithm in our technology to improve the 3D image resolution and depth of field.