October 2007; Scientific American Magazine; by Steven Ashley; 1 Page(s)
Camera bugs love zoom lenses, but they tend to be too bulky for cell phones and many miniature digital cameras. A research team at the University of Central Florida (U.C.F.) led by optics professors Shin-Tson Wu and Hongwen Ren has developed zoom lenses that can be dramatically smaller than conventional zooms. Whereas traditional zoom lenses move sets of lens elements mechanically to adjust focal length (and therefore magnification), the group's adaptive lenses alter focal length nearly instantaneously without changing the position of the lenses.
The U.C.F. team has two ways to make adaptive lenses. The first class, Wu explains, is based on the ability of a liquid-crystal layer to alter the degree to which it can refract (or bend) light when subjected to an electric field. In one version of this approach, the researchers adjust the layer's refractive index by varying the strength of the electric field in a concentric and graduated fashion. A change in the low voltage applied to a clear electrode modifies the focal length of the lens. Makers of cell phone lenses like to have a zoom magnification ratio of at least three and low voltages to save battery power, he says.
The second approach "mimics the workings of the human eye," Wu states. It relies on a transparant fluid - water or oil - that is encapsulated between a see-through, flexible membrane and a flat glass substrate. When a tiny servo-motor compresses a circular periphery seal that acts like an iris diaphragm, the shape of the membrane grows convex, modifying the fluidic lens's focal length.
The U.C.F. team has licensed five of its patented technologies to Holochip, a start-up company based in Albuquerque and San Francisco. It hopes to place the adaptive zooms, which can have apertures as small as a millimeter, into products sometime during the next few years.