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FLUID LENSES: bringing things into focus At this year’s CeBIT Exhibition in Hannover, Germany, Philips Research demonstrated FluidFocus: a unique variable-focus optical lens system that has no mechanical moving parts. S uited to a wide range of optical wall and one of its end caps are coated focal length of the lens. By increasing the applied electric imaging applications including with a hydrophobic (water-repellent) such things as digital cameras, coating that causes the aqueous solu- field, the surface of the initially convex camera phones, endoscopes, home tion to form itself into a hemispherical lens can be made completely flat (no security systems and optical storage mass at the opposite end of the tube, lens effect) or even concave. As a result it is possible to make drives, the FluidFocus system mim- where it acts as a spherically curved lenses that transition smoothly from ics the action of the human eye using lens. The shape of the lens is adjusted being convergent to divergent and a fluid lens that alters its focal length by applying an electric field across back again. by changing its shape. In the FluidFocus technology demThe new lens, which lends itself the hydrophobic coating such that it to high-volume manufacturing, over- becomes less hydrophobic – a process onstrator exhibited at CeBIT 2004, the comes the fixed-focus disadvantages called ‘electro-wetting’ that results fluid lens measured 3mm in diameter of many of today’s low-cost imaging from an electrically induced change by 2.2mm in length, making it easy in surface-tension. to incorporate into miniature optical systems. As a result of this change in surface pathways. The FluidFocus lens consists of The focal range provided by the two immiscible (non-mixing) fluids tension, the aqueous solution begins to of different refractive index (optical wet the sidewalls of the tube, altering demonstrator extends from 5cm to inproperties). One is an electrically con- the radius of curvature of the meniscus finity and it is extremely fast: switching between the two fluids and hence the over the full focal range is obtained in ducting aqueous solution and the other less than 10ms. an electrically nonControlled conducting oil, both by a DC voltcontained in a short age and presenttube with transparing a capacitive ent end caps. load, the lens The internal surfaces of the tube Shapes of a 6-mm diameter lens taken at different applied voltages. Photo: Philips consumes virtu78  Silicon Chip siliconchip.com.au At left: researchers show the miniature variable lens along with the camera that contains the lens. Photo: Philips ally zero power, which for battery powered portable applications gives it a real advantage. The durability of the lens is also very high, Philips having already tested the lens with over one million 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, suiting it to mobile applications. Big Brother may soon be watching you . . . in focus! SC siliconchip.com.au A) Schematic cross section of the FluidFocus lens principle. (B) When a voltage is applied, charges accumulate in the glass wall electrode and opposite charges collect near the solid/liquid interface in the conducting liquid. The resulting electrostatic force lowers the solid/liquid interfacial tension and with that the contact angle and hence the focal distance of the lens. Diagrams: Philips. May 2004  79