Liquid optical system mimics human eye
The FluidFocus system has no mechanical moving parts, using a fluid lens that alters its focal length by changing its shape. The lens consists of two immiscible (non-mixing) fluids of different refractive index, one an electrically conducting aqueous solution and the other an electrically non-conducting oil, contained in a short tube with transparent end caps. The internal surfaces of the tube wall and one of its end caps are coated with a hydrophobic (water-repellent) coating that causes the aqueous solution to form itself into a hemispherical mass at the opposite end of the tube, where it acts as a spherically curved lens.
The shape of the lens is adjusted by applying an electric field across the hydrophobic coating such that it becomes less hydrophobic – a process called ‘electrowetting’ that results from an electrically induced change in surface-tension. As a result of this, the aqueous solution begins to wet the sidewalls of the tube, altering the radius of curvature of the meniscus between the two fluids and hence the focal length of the lens. By increasing the applied electric field, the surface of the initially convex lens can be made completely flat (no lens effect) or even concave. As a result it is possible to implement lenses that transition smoothly from being convergent to divergent and back again.
In the FluidFocus technology demonstrator to be exhibited at CeBIT, the fluid lens measures a mere 3mm in diameter and 2.2mm in length. The focal range extends from 5cm to infinity. Switching over the full focal range is obtained in less than 10ms. Control is by a dc voltage. The lens presents a capacitive load, consuming virtually zero power – a real advantage for battery powered portable applications. Philips is looking to a wide range of optical imaging applications - digital cameras, camera phones, endoscopes, home security systems and optical storage drives.
Philips has already tested the lens with over 1mn focusing operations without loss of optical performance. It also has the potential to be both shock-resistant and capable of operating over a wide temperature range. Its construction is regarded as compatible with high-volume manufacturing techniques.
