Photonics.com Feature Article 2007/07/19
Through a Lens, Wetly
The following is an excerpt from Photonics.com, for the the full article please click on the link below:
Photonics.com Feature Articles | June 2008
by Hank Hogan, Contributing Editor
Traditionally, varying focal length has been accomplished through the mechanical movement of static lenses. This approach, however, constrains the size, cost, reliability and speed of the system. In contrast, liquid lenses vary their focal length by borrowing techniques from a familiar imaging system. “Fluidic lenses really are inspired by the human eye. They generally all go back to the same principle, and the idea has been around for a very long time,” said Robert Batchko, president and CEO of Holochip Corp. in Albuquerque, N.M. The basic idea of his company’s liquid lenses, he explained, is that of a fluid confined by an elastic membrane. The application of hydrostatic pressure causes the membrane to bulge, changing from a flat surface to a curved one, for example. That transformation brings about an alteration in optical properties — including a shift in focal length — as the membrane transforms, for instance, from a flat to a concave surface. Varying the pressure adjusts the focal length, enabling the tuning of optical parameters. The resulting lenses are lighter, smaller, faster and more robust than those that use mechanical methods.
Turning the dial on the liquid lens system shown
here changes the focal length of the lens.
Holochip develops and manufactures adaptive lenses based on its proprietary adaptive polymer lens technology, which has been in development for several years. The company now offers an adaptive singlet lens for optical research and engineering. The product can be mounted in standard optics hardware, such as posts and lens holders. The minimum focal length is 20 mm and the maximum is more than 1 m, giving a range of focal power greater than 50 diopters. Static lenses can be stacked in the housing to bias the focal length. According to Batchko, the company’s adaptive lenses can be optimized for speed, diopter range, shock resistance or other parameters. The lenses use a proprietary fluid with what he characterized as excellent physical and optical qualities and are part of a blend of components, packaging and designs that are key to the devices’ success. One problem that such lenses faced in the past was gravity, which could induce a position-dependent deviation from the ideal in the membrane shape. However, Batchko said that such effects had been addressed. Various groups have investigated membrane-based liquid lenses. One such, at Louisiana Tech University in Ruston, placed a transparent flexible polymer, PDMS, atop a reservoir of the same material. Varying the pressure changed the shape of the membrane and, therefore, altered its optics. A similar approach was investigated by a team from the Institute of Materials Research and Engineering in Singapore. Building many or just one Holochip has licensed technology related to adaptive lenses from Louisiana Tech University and from the University of Central Florida in Orlando. Senior research scientist Hongwen Ren and optics professor Shin-Tson Wu, both of the latter institution have reported a demonstration, of a novel liquid lens technique that extends the idea into a microlens array.