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Liquid lens performs under pressure

14 Jan 2005

US researchers use photolithography to create a liquid-based integrated zoom lens.

Mobile phones, laptops and micro-surveillance applications could benefit from the integrated liquid zoom lenses being developed by scientists in the US. With a thickness of only 8 mm, applying pressure to the lens changes its shape and focal length. The authors believe that this is both a compact and cost effective alternative to traditional fixed focal length systems. (Optics Letters 29 2855)

Typically zoom lens systems work by varying the spacing of two fixed focal length lenses. However, with its liquid system the team from University of California at San Diego, US, is able tune the focal length of each lens by simply adjusting the fluidic pressure. This means that the device works at a fixed distance - a compact solution.

Manufactured using lithography, the researchers feel that their zoom lens device will be easy to mass produce. "The main body can be made into an integrated structure using a batch process similar to that for integrated circuits," say the authors in their paper. "We anticipate that the cost of fabricating zoom lenses can be greatly reduced and that zoom lens arrays will become feasible."

The body of the lens consists of two back-to-back fluidic adaptive lens chambers that sit either side of a glass substrate. Individual chambers measure 20 mm in diameter and are made from polydimethylsilioxane (PDMS). To create the lens, each chamber is filled with a 63% sodium chromate solution (refractive index = 1.5) and sealed with a flexible PDMS membrane. To control the pressure, the team uses a battery-powered miniature pump coupled to fluid inlet and outlet valves integrated within the chamber.

Putting their 20 mm system to the test, the scientists were able to demonstrate a zoom ratio (the ratio of the maximum and minimum focal lengths) of two. According to the team, zoom ratios of four and above could be achieved by reducing the diameter of the lens chambers.

A potentially attractive option for applications that are cost, weight and size sensitive, fluidic lenses are a breakthrough in-waiting. French firm VariOptic is also active in the area, but rather than using pressure to vary lens shape it applies a voltage to the lens substrate. This modifies the contact angle of the liquid drop.

James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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