The theory behind liquid lens is based on the properties of one or more fluids to create magnifications within a small amount of space. Liquid lens can be considered as "infinitely variables" lens with variable focus, and the focus is controlled without using any moving parts.
The focus of a liquid lens is controlled by the surface of the liquid. Water forms naturally a bubble shape when adhered to materials such as glass or plastics. This desirable property makes water a very suitable candidate for the production of a liquid lens.
To generate a liquid lens, a mixture of two liquids is sandwiched between two pieces of clear plastics or glass. The second liquid needs to encapsulate the water drop and to fill any free space or void. It is well known that water and oil do not mix, and oil is also inexpensive and safe to use. Therefore, oil is chosen to be used as the other liquid mixture for the liquid lens system.
The surface profiles of the liquids determine the focal length of the liquid lens system, and ultimately, how the liquid lens focuses light. In other words, by altering the surface profile of the liquids, the focal length can be adjusted. This is done by changing the shape and size of the drop of water within the liquid lens.
Consumer electronics such as mobile phone cameras and small digital cameras are using liquid lens technology. Due to their low-cost and lightweight, and the ability for water to generate a lens which is flawless, this makes liquid lens a very attractive technology.
Philips Research has developed a unique variable-focus lens system that has no mechanical moving parts. Suited to a wide range of optical imaging applications, including such things as digital cameras, camera phones, endoscopes, home security systems and optical storage drives, Philips' FluidFocus system mimics the action of the human eye using a fluid lens that alters its focal length by changing its shape. The new lens, which lends itself to high volume manufacturing, overcomes the fixed-focus disadvantages of many of today's low-cost imaging systems.
Figure 1. Philips FluidFocus lens. (A) Schematic cross section of the FluidFocus lens principle. (B) When a voltage is applied, charges accumulate in the glass wall electrode and opposite charges collect near the solid/liquid interface in the conducting liquid. The resulting electrostatic force lowers the solid/liquid interfacial tension and with that the contact angle and hence the focal distance of the lens. (C) to (E) Shapes of a 6-mm diameter lens taken at different applied voltages.