IP: Working Photonic Lattice, A Dream For A Decade, Fabricated At Sandia

[Robert Hettinga <rah@shipwright.com>]

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Subject: IP: Working Photonic Lattice, A Dream For A Decade, Fabricated At
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Source:  EurekAlert!
http://www.eurekalert.org/releases/snl-wpladfad.html

For Immediate Release: 15 September 1998

 Contact: Neal Singer
 nsinger@sandia.gov
 (505) 845-7078
 Sandia National Laboratories

Working Photonic Lattice, A Dream For A Decade, Fabricated At Sandia:
Lincoln Log-Like Structure To Improve Infrared And Optical Communications,
Optical Computers

 ALBUQUERQUE, N.M. -- By interlocking tiny slivers of silicon into a
lattice that,
 under a microscope, appears to be formed by toy Lincoln logs, scientists
at the
 Department of Energy's Sandia National Laboratories believe they have
solved a
 major technical problem: how to bend light easily and cheaply without
leaking it, no
 matter how many twists or turns are needed for optical communications or
(potentially)
 optical computers.

 The lattice, dubbed a photonic crystal (crystals have regularly repeating
internal
 structures), now works in the infrared range (approximately 10-micron
wavelengths).
 This achievement is of military and commercial interest because the
technique can be
 used to enhance or better transmit infrared images. Sandia researchers
Shawn Lin and
 Jim Fleming now are preparing a 1.5 micron crystal -- the region in which
almost all
 the world?s optically transmitted information is passed.

 The improvement -- which bends far more light in far less space at
considerably less
 cost than current commercial methods -- will make possible tinier,
cheaper, more
 effective waveguides to combine or separate optical frequencies at the
beginning or
 end of information transmissions. It will find wide application in data
transmission and
 in more compact and efficient sensors. (See "Technique Perfected...."
backgrounder
 that follows.)

 Pierre Villeneuve, a research scientist at the Massachusetts Institute of
Technology
 (MIT), says, "With the structure [Sandia researcher] Shawn [Lin] is using
now, he'll be
 able to hit the 1.5 micron mark within the next 12 months. This shows how
'key' this
 work is: He's using a technique that lends itself to hitting the mark."

 A venture capitalist requesting anonymity has approached the researchers to
 commercialize the process. The achievement, for which Sandia has applied
for a
 patent, was reported in the July 16 issue of the journal Nature.

 The structure, in the regularity and spacing of its parts, is mirrorlike
in not permitting
 light of a particular frequency, caught within the cavity of the
structure, to escape.
 Instead, light must follow along any twists or turns designed into the log
structure.

 By designing the distance between logs carefully, a chosen wavelength is
reflected
 instead of passing out of the space, as longer or shorter wavelengths can.
With
 introduction of an impurity like air or much thicker polysilicon "logs" to
provide routes
 for preselected wavelengths introduced into the crystal, light travels
along the impurity
 as it twists or bends. No matter how sharp the turns, light of frequency
roughly in the
 middle of the band gap cannot escape.

 Funding for the project was provided by Sandia's Laboratory-Directed
Research and
 Development office, which funds speculative, defense-related research, and
by the
 DOE.

 A Photonic Band Gap

 What's "cool," in the eyes of some observers, is that Sandia researchers
Lin and
 Fleming have created the equivalent of a photonic "band gap" that forbids
certain
 frequencies of light from exiting the lattice. ("Band Gap" is a term
usually applied to
 electrons, not photons, and signifies a range of energies in which
electrons are absent
 because their presence would contradict quantum mechanical laws.)

 The nearly leak-proof lattices form a cage that trap and guide
approximately 95
 percent of the light sent within them, as compared with approximately 30
percent for
 conventional waveguides, and they take only one-tenth to one-fifth the
space to bend
 the light. (The Sandia photonic lattice's turning radius is currently in
the one-wavelength
 range, rather than the traditional waveguide bend of more than 10
wavelengths.)

 Standard, integrated-circuit manufacturing technology used to fabricate
micromachines
 -- machines nearly too small to see -- at Sandia's Microelctronics
Development
 Laboratory can create tens of thousands of waveguides from a single,
6-inch silicon
 wafer. This is a factor 10 to 100 times more dense than can be fabricated
using more
 expensive gallium arsenide with current commercial technology.

 Potential uses: low-energy lasers, photonic computers, communications
Because little
 light is lost in the three-dimensional mirroring that sends light back at
itself, a new type
 of microlaser requiring little start-up energy is theoretically
achievable. (Most
 conventional lasers require large jolts of energy to begin operating
because so much
 light is lost in the lasing start-up process.)

 The achievement also brings nearer the day when computers that transmit
information
 using photons rather than electrons become a practical reality. Currently,
desktop
 computers use electrons to pass information, but as more circuits are
included on new
 chips, they become more difficult to cool. Photons, the stuff of light,
are faster and
 cooler than electrons. The problem is that no one has been able to bend
useful
 frequencies of light around tight corners (as navigated by electrons
through a million
 turns on a computer chip the size of a postage stamp) without incurring
large losses in
 information; with previously used techniques, light leaks, and badly, the
more tightly it
 is turned.

 One principle of optical communications is that differing frequencies of
light are bent by
 different amounts. Waveguides first combine the frequencies of a number of
 information streams -- for example, telephone calls -- by bending them
into the
 combined "white" light passing through an optical cable; then other
waveguides
 separate the light into component frequencies by bending it at the end of
its journey.

 Photonic Band Gap Crystals -- A History

 The idea of a "photonic band gap structure" was first advanced in 1987 by Eli
 Yablonovitch, now a professor at the University of California at Los
Angeles. In 1990,
 he built the first photonic crystal, baseball-sized to channel microwaves
useful in
 antennae applications. In the mid 1990s, scientists at Ames Laboratory in
Iowa built
 crystals the size of ping pong balls, also for microwaves. The components
were of a
 size that could be put together by hand, using straight metal pins (of the
type that hold
 new shirts in place).

 The size reduction for current structures is a striking achievement that
researchers have
 been attempting to achieve for a decade, says Del Owyoung, Sandia manager
for the
 project. The difference in frequency is comparable to moving from masers
to lasers, he
 said ? from microwaves to optical waves.

 According to Rama Biswa, a researcher at Ames Lab, "We had built the same
 structure [as Sandia has] ourselves, but more than 100 times larger, in
the microwave
 frequency range. I think it is quite remarkable that Shawn Lin's group
could do it at
 these wavelengths in the infrared and at this size."

 Villeneuve, who has theorized about uses for photonic crystals for much of
the 1990s
 in a group led by MIT professor J. D. Joannopoulos, praised the Sandia
group for
 "showing that what we're doing is valid," he says. "[People would say,]
'It's wonderful
 that you're coming out with all these great devices [that make use of
photonic crystals],
 but your building block doesn't even exist!'" That is no longer the case.

 Sandia is a multiprogram DOE laboratory, operated by a subsidiary of Lockheed
 Martin Corp. With main facilities in Albuquerque, N.M., and Livermore,
Calif., Sandia
 has major research and development responsibilities in national security,
energy, and
 environmental technologies.

###

 BACKGROUND: Technique Perfected In Building Surface-Etched
 Micromachines

 Shawn Lin and Jim Fleming achieved the desired crystalline spacing using
techniques
 perfected in building surface-etched micromachines, at which Sandia is a
world leader.

 Gears that spin require spaces between parts; specifically, a silicon base
is covered
 with an expendable coating in which a part can be etched, and then the
expendable
 portion is removed by chemical and mechanical means, leaving the gear or axle
 unencumbered by surrounding material and thus able to spin freely
 [www.mdl.sandia.gov/micromachines].

 Using a variant on the same technique, Fleming made an artificial crystal
lattice. He
 took a silicon wafer, coated it with silicon dioxide, cut trenches into
the silicon dioxide
 and then bathed the chip in polysilicon till it filled the trenches. Then
he polished the
 surface until smooth and bathed the chip in another layer of silicon
dioxide, into which
 he cut the same number of trenches as before, but so they lay across the
trenches
 beneath them at right angles, and then filled these trenches with
polysilicon.

 After repeating this process a number of time, Jim removed the silicon
dioxide, using
 hydrofluoric acid, and got "micron layers of Lincoln logs, orthogonal to
each other, and
 joined where they touch."

 Center to center, the polysilicon logs were 1.2 microns wide, 1.5 microns
high, with a
 pitch of 4.8 microns -- child's play to achieve in the world of silicon
micromachines.
 The proportions were identical to that specified by Ames Laboratory and
Iowa State
 researchers as those necessary to make the photonic equivalent of an
electronic band
 gap.

 Media Contact:

Neal Singer
nsinger@sandia.gov
(505) 845-7078

 Technical Contact :

Shawn Lin
slin@sandia.gov
(505) 844-8097

Jim Fleming
fleminjg@sandia.gov
(505) 844-9158

Del Owyoung
aowyoun@sandia.gov
(505) 884-5481
-----------------------
NOTE: In accordance with Title 17 U.S.C. section 107, this material is
distributed without profit or payment to those who have expressed a prior
interest in receiving this information for non-profit research and
educational purposes only. For more information go to:
http://www.law.cornell.edu/uscode/17/107.shtml
-----------------------






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-----------------
Robert A. Hettinga <mailto: rah@philodox.com>
Philodox Financial Technology Evangelism <http://www.philodox.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'