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

Imaging systems have undergone many changes over recent years driven primarily by the requirements of the mobile phone industry for smaller and cheaper camera systems with increasing performance. These changes, such as miniature variable focus optics, have brought in very different technologies that can be used in many other imaging system applications. This article describes the advantages of liquid lens solutions to meet the demand of high-performance variable-focus imaging applications.

WHAT IS IT?

A liquid lens is a watertight cell containing two non-miscible liquids. The shape of the liquid interface is controlled by a voltage to change the power of the lens. The liquid interface is in contact with a conical metallic part insulated by a thin film (several microns thick). The interface is represented in cross-section on the figure (see page 28) by a continuous line, which shows its concave shape. When an electrical voltage is applied between electrodes A and B, charges accumulate on both sides of the insulating film applying a force to the place where the interface rests, which becomes deformed and assumes the convex shape represented by the dotted line on the figure. The effect is rapid but also very reversible because the system has a very weak hysteresis. In addition it is relatively rapid.

In this configuration, the technology allows the manufacture of an extremely robust module that enables a rapid autofocus lens response time of 10ms, and system response (<500ms), using very little energy (<15mW) for the lens and driver circuit which can be manufactured at low cost in very large numbers.

ADVANTAGES

The liquid lens solution developed by Varioptic (Lyon, France), uses electrowetting technology to produce variable focal length lenses with no moving parts. These lenses have been available on the market for more than two years for mobile phones and other applications such as webcams, machine vision, security and medical devices. The 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.

Autofocus systems are a standard feature in digital cameras today, mainly with electro-mechanical technologies (such as stepper motor, voice-coil motor, piezzo motor) that rely on the precise translation of lenses relative to each other. These systems work well but are expensive, difficult to miniaturize, have a limited number of cycles, and the tight optical tolerances required suffer because of friction from the mechanical guides.

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