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Mirrors Replace Lenses in UAVs

Photonics.com
Jan 2010
DRESDEN, Germany, Jan. 19, 2010 – Unmanned aerial vehicles (UAVs) carry optical measuring equipment that is required to operate free of chromatic aberrations across a wide spectral range – from ultraviolet to infrared. Conventional lens systems comprised of several lens elements are of limited use because when required to image a wide spectral range the image quality suffers from color fringing and becomes blurred.

Traditionally, specific lenses have been used for each different spectral band, but because UAVs can only carry a limited amount of weight this approach proves difficult.


A novel lens system produces images free from chromatic aberration in various spectral ranges. (© Fraunhofer IPMS)

Researchers from the Fraunhofer Institute for Photonic Microsystems IPMS have now designed an all-reflective zoom objective with deformable mirrors – making it possible to capture images free from chromatic aberration in a number of spectral ranges using this single system. This would have the advantage of prolonging the battery’s life and increasing the aircraft’s endurance.

“We’ve come up with a design for a new objective in which we’ve used mirrors instead of standard lens elements. The objective is comprised of four mirrors, carefully arranged to avoid obscuration – this produces a higher-contrast image,” said Dr. Heinrich Grüger, group manager of IPMS. “Two deformable mirrors take care of the triple zoom range – with no loss of image quality. The new design eliminates the need for elaborate mechanical guides within the lens barrel.”

Although IPMS scientists have already developed deformable mirrors, they have not yet managed to achieve the size and degree of variability required for the mirror zoom objective. Optical simulations have shown that the mirrors would need to be at least 12 millimeters in diameter in order to produce a zoom objective with a sufficient f-number.

Nevertheless, the researchers have already been able to demonstrate the optical performance of the objective: they built three identical setups with three different focal lengths in which the deformable mirrors were replaced by conventional rigid mirrors.

“Both the automation technology sector and the automobile and equipment engineering sector would profit from this type of objective,” Grüger said, noting that deformable mirrors will have to be created – conventional optical mirrors are rigid. “For the zoom function, we need mirrors that will permit flexible actuator control of the radius of curvature.”

For more information, visit: www.fraunhofer.de  


GLOSSARY
image quality
A measure of the closeness with which an optical image is capable of resembling the original object. The factors that affect image quality are lens aberrations, diffraction, dirt and stray light within the system, and atmospheric turbulence and haze outside it. If the image is recorded photographically, it can become further degraded by image motion during exposure and by light diffusion in the emulsion. At one time image quality was expressed by its resolving power, but today a more meaningful...
lens
A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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