Optical
fiber helped bring us the Internet, and silicon/germanium
devices brought us microelectronics. Now, a joint
team from Penn State University and the University
of Southampton has developed a new way to combine
these technologies. The team has made semiconductor
devices, including a transistor, inside microstructured
optical fibers. The resulting ability to generate
and manipulate signals inside optical fibers could
have applications in fields as diverse as medicine,
computing, and remote sensing devices.
Optical fiber has proved to be the ideal medium
for transmitting signals based on light, while crystalline
semiconductors are the best way to manipulate electrons.
One of the greatest current technological challenges
is exchanging information between optics and electronics
rapidly and efficiently. This new technique may provide
the tools to cross the divide. The results of this
research will be published in the 17 March edition
of the journal Science.
"This advance is the basis for a technology that
could build a large range of devices inside an optical
fiber," said John Badding, associate professor of
chemistry at Penn State University. While the optical
fiber transmits data, a semiconductor device allows
active manipulation of the light, including generating
and detecting, amplifying signals, and controlling
wavelengths. "If the signal never leaves the fiber,
then it is faster, cheaper and more efficient," said
Badding. "
"This fusion of two separate technologies opens
the possibility of true optoelectronic devices that
do not require conversion between optical and electronic
signals," said Pier Sazio, senior research fellow
in the Optoelectronics Research Centre at the University
of Southampton (UK). "If you think of the fiber as
a water main, this structure places the pumping station
inside the pipe. The glass fiber provides the transmission
and the semiconductor provides the function."
Beyond telecommunications, optical fibers are used
in a wide range of technologies that employ light. "For
example, in endoscopic surgery, by building a laser
inside the fiber you might be able to deliver a wavelength
that could not otherwise be used," said Badding.
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The
key breakthrough was the ability to form crystalline
semiconductors that nearly fill the entire inside
diameter, or pore, of very narrow glass capillaries.
These capillaries are optical fibers--long, clear
tubes that can carry light signals in many wavelengths
simultaneously. When the tube is filled with a crystalline
semiconductor, such as germanium, the semiconductor
forms a wire inside the optical fiber. The combination
of optical and electrical capabilities provides the
platform for development of new optoelectronic devices.
The crystals were formed using chemical vapor deposition
(CVD) to deposit germanium and other semiconductors
inside the long, narrow pores of the hollow optical
fiber. In the CVD process, a germanium compound is
vaporized and then forced through the pores of the
fiber at pressures as high as 1000 times atmospheric
pressure and temperatures up to 500°C. A chemical
reaction within the fiber allows germanium to coat
the interior walls of the hollow fiber and then form
crystals that grow inward. "The process works so
perfectly that you can get a germanium tube that
has an opening in the center of only 25 nanometers
through the length of the fiber," said Sazio. "This
is only a tiny fraction of the diameter of the fiber
pore, so it is essentially a wire." This is the first
demonstration of building crystalline structures,
which are best for semiconductor devices, inside
the pores of the capillaries.
The team has built a simple in-fiber transistor,
and they point to the success of the Erbium Doped
Fiber Amplifier, which was invented at Southampton
in the late 1980s, to illustrate the transformational
possibilities of this technology. By incorporating
the chemical element erbium into the fiber, the Erbium
Amplifier allows efficient transmission of data signals
in transoceanic optical fibers. "Without that kind
of device, it would be necessary to periodically
convert the light to an electronic signal, amplify
the signal, and convert it back to light, which is
expensive and inefficient" said Sazio. " Since its
inception, the Erbium Amplifier has made the internet
possible in its current form."
Beyond the simple devices that this research has
demonstrated, the research team sees the potential
for the embedded semiconductors to carry optoelectronic
applications to the next level. "At present you still
have electrical switching at both ends of the optical
fiber," says Badding. "If we can get to the point
where the signal never leaves the fiber, it will
be faster and more efficient. If we can actually
generate signals inside a fiber, a whole range of
optoelectronic applications become possible."
CONTACTS:
John Badding: (+1) 814-777-3054, jbadding@pearl.chem.psu.edu
Pier Sazio: (+44) (0)7884-444-429, pjas@soton.ac.uk
Barbara K. Kennedy (PIO at Penn State): (+1) 814-863-4682, science@psu.edu
David C. Evans (PIO at the University of Southampton: (+44) (0)2380-593-139, dce@orc.soton.ac.uk
FUNDING SOURCES:
This research was funded by the U.S. National Science Foundation, the Penn
State Center for Nanoscale Science (funded by the National Science Foundation's
Materials Research Science and Engineering Center program), the Penn State-Lehigh
Center for Optical Technologies, the U.K. Engineering and Physical Sciences
Research Council, and the Mexican Council for Science and Technology.
NOTES
The following information is provided by the University of Southampton.
The University of Southampton is one of the UK's top 10 research universities,
with a global reputation for excellence in both teaching and research. With
first-rate opportunities and facilities across a wide range of subjects in
science and engineering, health, arts and humanities, the University has around
20,000 students and 5000 staff at its campuses in Southampton and Winchester.
Its annual turnover is in the region of £274 million. Southampton is
recognised internationally for its leading-edge research in engineering, science,
computer science and medicine, and for its strong enterprise agenda. It is
home to world-leading research centres, including the National Oceanography
Centre, Southampton; the Institute of Sound and Vibration Research; the Optoelectronics
Research Centre; the Textile Conservation Centre and the Centre for the Developmental
Origins of Health and Disease.
The Optoelectronics Research Centre (ORC) is one
of the Schools in the Faculty of Engineering, Science
and Mathematics at the University of Southampton.
Its mission is to blend focused, application-led
research with fundamental studies on the generation,
transmission and control of light. This includes
work on optical fibres, lasers, optical circuits
and chemical/biological sensing. |
