Springs simplify micromirror
Technology Research News
of tiny mirrors that can be precisely positioned are the key components
of adaptive optics used in astronomy, biomedical imaging, free-space communications
and satellite imaging systems.
Adaptive optics correct light waves that have been distorted, usually
by the atmosphere, by bouncing them off a mirror that rapidly changes shape
to produce clearer images or signals.
The mirrors in micromirror arrays are typically less than a fifth
of a millimeter square and are controlled individually using a mechanism
that converts a digital computer signal into a mechanical movement. Large
arrays of micromirrors are relatively expensive because they require a large
number of electrical digital-to-analog converters to individually address,
or control, each micromirror. This also limits the size of an array.
Researchers from the National University of Singapore have found
a way make simpler, less expensive mirror controls. At the heart of the
researchers' digital-deflection programmable micromirror array is a digital-to-analog
converter that works mechanically rather than electrically.
The device controls a large array of micromirrors by addressing
them via row and column lines rather than having separate circuits to each
mirror. This drastically reduces the number of routing wires needed and
allows an array of mirrors to be controlled by off-chip electronics. It
also makes it easier to manufacture.
The method promises to reduce the complexity and thus cost and size
of devices that use micromirror arrays.
The research could lead to a cost-effective, compact wavefront aberration
correction method that uses little power, said Guangya Zhou, a research
fellow at the National University of Singapore. "It is also inherently robust
and accurate, insensitive to voltage and temperature fluctuations, and suitable
for harsh-environment applications where conventional microelectronics might
fail," he said.
Each micromirror is moved vertically by a set of microactuators.
Each microactuator has two possible positions -- an unpowered, or off, position,
and a powered, or on, position. A set of springs of different stiffnesses
connect the microactuators to the micromirror. The differences in spring
stiffness determines how far the mirrors move.
The researchers' built a prototype 2-bit, 3-by-3 micromirror array
with 160- by 160-micron mirrors. Each bit in the control signal controls
a pair of actuators that move the mirror a specific amount. The on-off combinations
of two bits coupled with the two spring stiffnesses yield four mirror positions.
The mirror positions in the prototype are set to alter the phase of a 632.8-nanometer
wavelength laser beam by one quarter of the wavelength, three-eighths of
the wavelength, or leave it as is.
The micromechanical digital-to-analog converter positions the prototype's
micromirrors precisely, with a range of 261 nanometers in increments of
87 nanometers. A nanometer is one millionth of a millimeter.
The prototype changes mirror positions in less than 100 microseconds,
according to Zhou. A microsecond is one millionth of a second.
The researchers' next step is to build a 4-bit digital-deflection
micromirror array that contains 10 by 10 micromirrors. The ultimate goal
is to produce a 6-bit device that contains more than 100 by 100 micromirrors,
Such an array could be used as a deformable mobile mirror for eliminating
atmospheric blurring in astronomy and space surveillance applications, controlling
the quality of communications laser beams that travel through the air, and
correcting aberrations in retinal imaging, said Zhou. It could also be used
as the optical element in holographic optical tweezers, he said. Optical
tweezers use beams of light to trap and manipulate microscopic objects.
It will be 3 to 6 years before the device use ready for commercial
use said Zhou.
Zhou's research colleagues were Logeeswaran VJ, Fook Siong Chau,
and Francis E. H. Tay. The work appeared in the November 15, 2004 issue
of Optics Letters. The research was funded by the National University
Timeline: 3-6 years
TRN Categories: MicroElectroMechanical Systems (MEMS); Displays;
Optical Computing, Optoelectronics and Photonics; Telecommunications
Story Type: News
Related Elements: Technical paper, "Line-Addressable Digital-Deflection
Programmable Micromirror Array," Optics Letters, November 15, 2004
February 23/March 2, 2005
Humanoid robots walk
Roadside Eye Catchers
Rod arrays focus sound
make silicon magnetic
makes concept maps
color in heat
data in electrons
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link