An 'origami lens' for your camera phone?
Your next camera phone might get a new kind of lens if researchers at the University of California at San Diego convince the cell phones makers. They have designed an 'origami lens' which will slim high resolution cameras. Today, their 5-millimeter thick, 8-fold imager delivers images comparable in quality with photos taken with a compact camera lens with a 38 millimeter focal length. In a few years, these bendable lenses could be used in high resolution miniature cameras for unmanned surveillance aircraft, cell phones and infrared night vision applications.
This research project has been conducted at the UCSD Jacobs School of Engineering and led by Eric Tremblay, an electrical and computer engineering Ph.D. candidate under the direction of Joseph Ford, a professor of electrical and computer engineering. Here is what Ford says about this new lens.
"This type of miniature camera is very promising for applications where you want high resolution images and a short exposure time. This describes what cell phone cameras want to be when they grow up," said Ford. "Today's cell phone cameras are pretty good for wide angle shots, but because space constraints require short focal length lenses, when you zoom them in, they're terrible. They're blurry, dark, and low contrast."
Before going further, below are three images of this 'origami' lens: the diamond-turned optic before coating (left), the silver-coated front surface with ring-shaped entrance pupil (center) and the coated back surface of the optic (right). (Credit: UC San Diego)
And below are two images of the UC San Diego 'imager': a cross section of an eightfold imager (top) and a cut-out view of the same imager (bottom). The blue lines illustrate the path the light follows as it moves from aperture to light sensor. (Credit: UC San Diego)
So how this 'origami lens' works?
Instead of bending and focusing light as it passes through a series of separate mirrors and lenses, the new folded system bends and focuses light while it is reflected back and forth inside a single 5 millimeter thick optical crystal. The light is focused as if it were moving through a traditional lens system that is at least seven times thicker.
But how this lens has been built physically?
On a disk of calcium fluoride – a transparent optical crystal – the engineers cut a series of concentric, reflective surfaces that bend and focus the light as it is bounced to a facing flat reflector. The two round surfaces with 60 millimeter diameters are separated by 5 millimeters of transparent calcium fluoride.
This design strategy forces light entering the ring-shaped aperture to bounce back-and-forth between the two reflective surfaces. The light follows a predetermined zigzag path as it moves from the largest of the four concentric optic surfaces to the smallest and then to the CMOS light sensor.
This research work has been published by Applied Optics under the name "Ultrathin cameras using annular folded optics" (Volume 46, Issue 4, Pages 463-471, February 1, 2007). Here is a link to the abstract.
But will these lenses be part of our cell phones anytime soon? Tremblay said, "I don't know, but I'm hopeful. I think it's a good possibility."
Sources: Daniel Kane, UC San Diego, January 30, 2007; and various other websites
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