Advanced Imaging

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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Making a Splash in Optics

Autofocus liquid lenses provide variable focal lengths with no moving parts
Liquid lens technology
© Varioptic
Liquid lens technology is characterized by a very wide range of focal lengths that enable very close focus, high optical quality, fast and consistent response, and are very robust with no moving parts to wear or break.
The liquid interface
© Varioptic
The liquid interface is in contact with a conical metallic part insulated by a thin film. When an electrical voltage is applied charges accumulate on both sides of the film applying a force to the place where the interface rests. This becomes deformed and assumes a convex shape. The effect is rapid but also very reversible because the system has a very weak hysteresis.
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By Nathalie Combrousse, Varioptic

The liquid lens response is highly repeatable and linear in the main operating range of -5 diopters to +13 diopters optical power, with the slope equal to 1 diopter per 1 Vrms (volts root-mean-square).

APPLICATIONS

Varioptic's Liquid Lens offers solutions for a wide range of consumer and industrial applications from webcams, barcode readers, security and machine vision devices, medical and many others. All liquid lens products share very high performance and quality levels on critical parameters, either optical, such as transmission and wave front error; or electrical, such as low dissipated power. The use of the liquid lens allows complete real-time and dynamic control over focus during operation with supplied software while in operation. Here is a look at a few applications:

Webcams: With the increase in pixel count, and given the typical use of webcams (in front of a laptop, with the distance varying from "showing" close-up objects to overviews of a room, autofocus soon becomes mandatory, typically from as early as 1.3MP, because of the physics for good quality images. With its fast response time, the liquid lens is the ideal solution for webcams maintaining good focus while the webcam is in video mode. Its silent operation also avoids any irritating background noise or electromagnetic interference every time the focusing system changes.

Barcode readers: With standard, fixed-focus lenses, handheld manufacturers usually develop several designs to cater for long- and short-range requirements. With autofocus, it becomes possible to have a single product cover both needs, enabling users to scan items from as close as 5cm to infinity. This is particularly useful, for example, to take photos of damaged goods and help resolve customer complaints. Critical factors for this application are response time and repeatability (as barcode readers work in open loop architecture), and, of course, reliability, with requirements in excess of 10M cycles for autofocus, for which the liquid lens is particularly well-suited.

Biometrics readers: Face, iris and fingerprint recognition systems are being marketed for law enforcement, immigration control, military and, increasingly, for consumer applications such as access control in hotels or private homes, and device security in place of PIN codes. Current fixed-focus imaging systems can be cumbersome, with the holder having to follow a series of instructions to move closer or back to "manually" adjust the focus, and sometimes failing. Using autofocus gives a much better user experience, provided the variable focus system has fast response time (in closed loop system), repeatability, ease of integration to take the installed base into account, and reliability and robustness.



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