Tunable Liquid Optics: Electrowetting-Controlled Liquid Mirrors Based on Self-Assembled Janus Tiles
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In this paper, we describe a tunable, high-reflectivity optofluidic device based on self-assembly of anisotropically functionalized hexagonal micromirrors (Janus tiles) on the surface of an oil droplet to create a concave liquid mirror. The liquid mirror is deposited on a patterned transparent electrode that allows the focal length and axial position to be electrically controlled. The mirror is mechanically robust and retains its integrity even at high levels of vibrational excitation of the interface. The use of reflection instead of refraction overcomes the limited available refractive-index contrast between pairs of density-matched liquids, allowing stronger focusing than is possible for a liquid lens of the same geometry. This approach is compatible with optical instruments that could provide novel functionality-for example, a dynamic 3D projector, i.e., a light source which can scan an image onto a moving, nonplanar focal surface. Janus tiles with complex optical properties can be manufactured using our approach, thus potentially enabling a wide range of novel optical elements.Keywords:
Reflection
Curved mirror
In this paper, we describe a tunable, high-reflectivity optofluidic device based on self-assembly of anisotropically functionalized hexagonal micromirrors (Janus tiles) on the surface of an oil droplet to create a concave liquid mirror. The liquid mirror is deposited on a patterned transparent electrode that allows the focal length and axial position to be electrically controlled. The mirror is mechanically robust and retains its integrity even at high levels of vibrational excitation of the interface. The use of reflection instead of refraction overcomes the limited available refractive-index contrast between pairs of density-matched liquids, allowing stronger focusing than is possible for a liquid lens of the same geometry. This approach is compatible with optical instruments that could provide novel functionality-for example, a dynamic 3D projector, i.e., a light source which can scan an image onto a moving, nonplanar focal surface. Janus tiles with complex optical properties can be manufactured using our approach, thus potentially enabling a wide range of novel optical elements.
Reflection
Curved mirror
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Measurements of lens parameters such as focal length, radius of curvature, and refractive index are important. We describe a measurement method that utilizes a Michelson interferometer to determine parameters of thin, convex lenses. The real fringe system formed by a Michelson interferometer is used to determine the focal lengths and the radii of curvature of the lenses. The refractive index of the lens material is determined from the thin-lens formula. We were able to determine the refractive indices to an accuracy as great as 99.97%. A detailed theoretical and experimental analysis is given.
Radius of curvature
Gradient-index optics
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The technology of electrically adjustable optical interfaces has found applications in, e.g., camera lenses, where an adjustable focal length provides automatic focusing for the camera. In this paper, we will investigate a liquid lens, where both the focal length and the tilt of this lens can be adjusted electrically. Specifically, the tilting ability of this lens will be tested by combining the liquid lens with a projector in order to scan lines across a three-dimensional (3D) object. The linearity, reproducibility, hysteresis, and time response of its tilting functionality will be tested. Further, crosstalk between the two functionalities of the liquid lens is tested for the specific case, where the focal length is set to infinity. Finally, the liquid lens and the projector in combination with four stereo cameras will be demonstrated as a 3D imaging setup.
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Gradient-index optics
Simple lens
X-ray optics
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In this paper, we propose a method of chromatic aberration elimination in holographic display based on a zoomable liquid lens. The liquid lens is filled with two immiscible liquids and developed by using the principle of electrowetting. The shape at the liquid-liquid interface changes with the voltage applied to the liquid lens, so the focal length can be adjusted by changing the voltage. By using the liquid lens in the holographic display system, the position of the reconstructed image can be controlled. When three color lasers illuminate the corresponding holograms and the focal length of the liquid lens changes accordingly, three color images can coincide in the same location clearly. The experimental results verify its feasibility.
Chromatic aberration
Holographic display
Simple lens
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This paper is focused on the problem of determination of internal parameters of a fluidic lens composed of two immiscible liquids of different refractive index, which form a tunable refractive interface for changing the focal length of a lens. Formulas are derived for calculation of a radius of curvature of the internal interface between two liquids and refractive indices of liquids using the measurements of the focal length of the lens, positions of focal points, and transverse spherical aberration of the lens.
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The aberrations of a spherical mirror of moderate aperture (≈ f/5) can be corrected by a lens system near the focal plane. A four-element lens system is necessary to provide a satisfactory state of correction over a full field of 0.5 deg. The design of such a lens system is described with emphasis on the intrinsic properties of each component and the logic behind the choice of layout.
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A simple method of constructing 3-D gradient refractive-index profiles in crystalline lenses is proposed. The input data are derived from 2-D refraction measurements of rays in the equatorial plane of the lens. In this paper, the isoindicial contours within the lens are modeled as a family of concentric ellipses; however, other physically more appropriate models may also be constructed. This method is illustrated by using it to model the 3-D refractive-index profile of a bovine lens.
Gradient-index optics
Ellipse
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We present a novel design of an exclusively electrically controlled adaptive optofluidic lens that allows for manipulating both focal length and asphericity. The device is totally encapsulated and contains an aqueous lens with a clear aperture of 2mm immersed in ambient oil. The design is based on the combination of an electrowetting-driven pressure regulation to control the average curvature of the lens and a Maxwell stress-based correction of the local curvature to control spherical aberration. The performance of the lens is evaluated by a dedicated setup for the characterization of optical wavefronts using a Shack Hartmann Wavefront Sensor. The focal length of the device can be varied between 10 and 27mm. At the same time, the Zernike coefficient Z40, characterising spherical aberration, can be tuned reversibly between 0.059waves and 0.003waves at a wavelength of λ=532nm. Several possible extensions and applications of the device are discussed.
Aperture (computer memory)
Numerical aperture
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Characterization
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Gradient-index optics
Simple lens
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