Electrowetting


For centuries scientists have combined lenses of very different optical powers, from diverging lenses to highly converging ones, to design and manufacture complex optical instruments. Until now the optical properties of all these lenses, either made from glass or plastic and typically requiring months to be produced, were always fixed. Varioptic has now created a « smart lens » that can be reconfigured on demand with just a variation of voltage. The lens can adapt rapidly and continuously from diverging to converging and be modeled to support all key optical functions, starting with Auto-Focus and Optical Image Stabilization.

 

 

 

The technology uses the Electrowetting principle and a combination of transparent and optically defect-free liquids to create a lens and change its characteristics in real time. Liquids have been used since 40 years in optical systems for high-end products such as goggles or camcorders, but Varioptic’s innovation is to have created a real-time programmable platform that offers to change the shape of the liquids in a very fast, repeatable, precise and controlled way.


In the drawing below, Electrowetting is explained in a very basic configuration: a drop of oil is deposited on a planar surface , made of a flat electrode covered with a thin insulating and hydrophobic layer, all this being immersed in a water based conducting liquid. Voltage is applied between the flat substrate electrode and another electrode dipped in the conducting liquid (not shown on the photographs).


A basic experiment enables to measure very accurately the contact angle versus voltage shown on the curve below:

The curve shows the drop shape variation as a function of voltage during a voltage cycle. The dotted square shows the region of interest in a liquid lens. This basic experiment emphasizes two important characteristics of the Electrowetting fluid actuation: linearity (precision) and reversibility (or hysteresis free). Both are key for making a liquid lens, in addition to a number of other suitable design choices.