IMRE, Singapore has developed a zoom liquid lens which uses pressure instead of electrowetting to change shape.
Another limitation, particularly with electrowetting lenses, is that to ensure that the two liquids do not mix, they must be immiscible with matched densities and responses to thermal changes. "This is what makes them so robust," says Hendriks. "It's practically impossible to mix the liquids," he says. However, such matching restricts the number of liquids available and so limits the range of their optical properties.
According to Dharmatilleke this restriction is less of a problem for the pressure lens approach. Using a single liquid means there is a much broader range of liquids to choose from. As a result, IMRE has been able to create a lens with an optical transmittance as good as Carl Zeiss glass lenses. "Electrowetting approaches are not far behind," says Barber. "Their transmittance is still very good," he says, "as high as 95%", and Barber is confident that it won't take long before this can be increased to 98% to match the quality of glass.
With conventional lenses, one way to increase the amount of available light is to increase the size of the lens; with liquid lenses, however, this could become a problem. Provided the lenses are small enough it is possible to achieve a curvature and smoothness of the meniscus that rivals polished glass — with aberrations occurring almost at the molecular level. However, as Benno Hendriks from Philips points out, as liquid lenses become larger gravity starts to have an effect, deforming this perfect curvature.
Varioptic - The Liquid Lens Company-electrowetting/double liquid
Philips Fluid Focus -electrowetting/double liquid
Variable Focus Zoom Lenses-pressure/single liquid/zoom
Holochip USA-pressure/single liquid/zoom
Rensselaer Polytechnic Institute -sound/single liquid
The last two seem to have the most potential for larger lens. By using teflon, silicone or some other super hydrophobic coated membrane for containing the liquid, the droplets would simply re-form if they were disrupted.