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Philips demonstrates fluid lens

10 Mar 2004

Consumer electronics giant Philips says it will be mass-producing liquid lenses within two years.

Philips Research has developed a variable-focus fluid lens that is just a few millimeters in size. Targeted at high-volume products such as digital cameras and mobile phones, Philips says that the lens will overcome the fixed-focus limitations of many of today’s low-cost imaging systems.

This announcement sees Philips following in the footsteps of French start-up Varioptic and Bell Labs in the US, both of which have demonstrated prototype liquid lenses.

Philips Research will unveil its prototype at this month’s CeBIT exhibition in Hannover, Germany. Stein Kuiper, a researcher from Philips Research, estimates that these devices could be in mass production within two years. “The quality of the lens is so good and its potential so high that commercialization has a high priority now,” he told Optics.org.

The lens consists of an electrically conducting aqueous solution and a non-conductive oil that are housed in a short tube with transparent end caps. The internal surface of the tube and one of the end caps are coated with a water repellent coating.

The aqueous solution collects in a hemisphere at the uncoated end of the tube. This creates a spherical curved lens because the two liquids have different refractive indices. “Typically the conductive liquid is a salt solution and the non-conductive liquid is a silicone oil,” said Kuiper. “For zoom applications we have liquids with a large difference in refractive index in order to obtain a high zoom factor. For autofocus applications the difference in refractive index is smaller in order to obtain a more sensitive focus action.”

The shape of the lens can be adjusted by changing the DC voltage that is applied across the coating, which changes the degree to which it repels water. By increasing the applied electric field, the lens can change from being convex to completely flat or even concave. The prototype device can allegedly change its focal length from 5 cm to infinity in less than 10 ms.

Philips’ prototype lens has a diameter of 3 mm and a length of 2.2 mm and is expected to be well-suited to high-volume manufacturing. “Simply drilling holes in a plate and covering them with two thin glass plates on both sides is possible,” said Kuiper. “In this way arrays of thousands of lenses can be made and the plates can be diced to obtain individual lenses”.

The FluidFocus prototype is said to consume very little power so could provide benefits for small, battery-powered devices. Philips also claims that the lens has performed over 1 million focusing operations with no loss of optical performance. “We have made lenses that can perform the focus function below 25 V by using thin insulating coatings and low surface tensions. But generally we prefer to use thicker insulating coatings and high surface tensions as this improves reliability, lens quality and switching speed,” said Kuiper.

Siân Harris is features editor of Opto & Laser Europe magazine.

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