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University of Southampton - New process builds electronic function into optical fibre
Published Mar 17 2006 [Printer friendly version] [Email article to a friend] [More Design & Manufacture articles]
Optical fibre helped bring us the Internet, and silicon/germanium devices
brought us microelectronics. Now, a joint team from the University of
Southampton and Penn State University has developed a new way to combine
these technologies. They have made semiconductor devices, including a
transistor, inside micro-structured optical fibres. The resulting ability
to generate and manipulate signals inside optical fibres could have
applications in fields as diverse as medicine, computing, and remote sensing
devices, says the team.
Optical fibre 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.
"This advance is the basis for a technology that could build a large range
of devices inside an optical fibre," said John Badding, associate professor
of chemistry, Penn State University. "While the optical fibre 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 fibre, then it is faster,
cheaper and more efficient."
Dr Pier Sazio, senior research fellow in the Optoelectronics Research
Centre, University of Southampton," said: "This fusion of two separate
technologies opens the possibility of true optoelectronic devices that do
not require conversion between optical and electronic signals. If you think
of the fibre as a water main, this structure places the pumping station
inside the pipe. The glass fibre provides the transmission and the
semiconductor provides the function."
Beyond telecommunications, optical fibres are used in a wide range of
technologies that employ light. "For example, in endoscopic surgery, by
building a laser inside the fibre you might be able to deliver a wavelength
that could not otherwise be used," added Badding.
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 fibres - 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 fibre. The combination of
optical and electrical capabilities provides the platform for development of
new optoelectronic devices.
The crystals were formed using chemical vapour deposition (CVD) to deposit
germanium and other semiconductors inside the long, narrow pores of the
hollow optical fibre. In the CVD process, a germanium compound is vaporized
and then forced through the pores of the fibre at pressures as high as 1000
times atmospheric pressure and temperatures up to 500C. A chemical reaction
within the fibre allows germanium to coat the interior walls of the hollow
fibre 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 centre of only 25 nanometres through the length of the
fibre," said Sazio. "This is only a tiny fraction of the diameter of the
fibre 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-fibre transistor, and they point to the
success of the Erbium Doped Fibre 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 fibre, the Erbium Amplifier allows efficient transmission of
data signals in transoceanic optical fibres.
"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
fibre," says Badding. "If we can get to the point where the signal never
leaves the fibre, it will be faster and more efficient. If we can actually
generate signals inside a fibre, a whole range of optoelectronic
applications become possible."
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