Holograms enable pocket projectors
Technology Research News
Video projectors can make entire walls
into television or computer screens. But video projection equipment is
relatively bulky, which has confined video projection to lecture halls,
conference rooms and home theaters.
Researchers from the University of Cambridge in England and Light
Blue Optics Ltd. have found a way to leverage holographic technology to
produce a small, laser-driven video projector.
The method could lead to pocket-sized, battery-powered video projectors
that produce images whose quality matches that of today's full-sized projectors,
according to Adrian Cable, a researcher at the University of Cambridge
in England and director of Light Blue Optics Ltd. This type of projector
could also be built into a laptop computer, said Cable.
Key to the device's diminutive size is the lack of lenses and
high-power light bulbs. Conventional digital video projectors form images
by generating a small picture on a transparent microdisplay inside the
projector, then shining a high-power light through the microdisplay to
a large magnifying lens.
In the researchers' design, a two-dimensional hologram is shown
on the microdisplay rather than an image, and the projected image is formed
by shining a laser beam through the microdisplay, which scatters the light
into a particular pattern. "No lenses are required -- the projected image
is formed entirely by diffraction," said Cable.
The challenge was producing a high-resolution hologram that can
be changed quickly enough to project video images. "The relationship between
images and the corresponding holograms is mathematically complex," said
The holographic projection of computer-generated images was first
demonstrated in the 1970s, but has not been practical because the algorithms
that generate the holograms have been too slow to use in real-time, said
Cable. Faster algorithms exist, but they can only produce the simple light
patterns used for optical communications, he said.
The researchers' algorithm solves the problem, said Cable. The
key was studying how noise, or the distortion of an image, affects people's
perception of video. The researchers showed test subjects 300 pairs of
video images and asked them to rate which, if either, was higher quality.
The images were the same but contained different levels of noise. The
researchers found that variation in noise levels affected people's perception
of video quality more than the actual level of the noise.
Most conventional two-dimensional hologram algorithms are designed
to minimize noise levels, according to Cable. The researchers' one-step
phase retrieval algorithm, in contrast, is designed to minimize noise
The researchers' algorithm generates holograms about one million
times faster than the standard direct binary search algorithm running
on a 2 gigahertz Athlon personal computer, according to Cable.
The researchers' prototype is black and white. They are working
on configuring two or more of the devices in parallel to generate full-color
The researchers aim to produce practical pocket-sized video projectors
in two to five years, said Cable.
Cable's research colleagues were Edward Buckley, T. Wilkinson,
Peter Mash, and N. Lawrence. The researchers presented the work at the
Society for Information Display (SID) International Symposium 2004 in
Seattle, Washington, May 23 to 28.
Timeline: 2-5 years
TRN Categories: Displays; Optical Computing, Optoelectronics
and Photonics; Data Structures and Algorithms
Story Type: News
Related Elements: Technical paper, "Real-Time Binary Hologram
Generation for High-quality Video Projection Applications," Society for
Information Display (SID) International Symposium 2004 May 23-28, Seattle,
June 30/July 7, 2004
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