Photonic crystal fibre’s ability to create broad
spectra of light, which will be the basis for important developments in
technology, has been explained for the first time in an article in the
leading science journal Nature-Photonics.
The fibre can change a pulse of light with a narrow range of
wavelengths into a spectrum hundreds of times broader and ranging from
visible light to the infra-red. This is called a supercontinuum.
This supercontinuum is one of the most exciting areas of
applied physics today and the ability to create it easily will have a
significant effect on technology.
This includes telecommunications, where optical systems
hundreds of times more efficient than existing types will be created
because signals can be transmitted and processed at many wavelengths
simultaneously.
Supercontinua generated in photonic crystal fibres also help
to create optical clocks which are so accurate that they lose or gain
only a second every million years. Two physicists based in the US and
Germany shared the Nobel Prize for Physics in 2005 for work in this
area.
Despite these applications, the mechanism behind
supercontinuum generation has remained unclear, which has stopped
physicists from being even more precise in using it.
But researchers at the University of Bath have now
discovered the reason for much of the broadening of the spectrum.
Dr Dmitry Skryabin and Dr Andrey Gorbach, of the Centre for
Photonics and Photonic Materials in the Department of Physics, found
that the generation of light across the entire visible spectrum was
caused by an interaction between conventional pulse of lights and what
are called solitons, special light waves that maintain their shape as
they travel down the fibre.
The researchers found that the pulses of light sent down the
fibre get struck behind the solitons as both pass down the fibre,
because the solitons slow down as they move. This barrier caused by the
solitons forces the light pulses to shorten their wavelength and so
become bluer, just as the solitons’ wavelength lengthens,
becoming redder. This dual effect creates the broadened spectrum.
“One of the most startling effects of the photonic
crystal fibre is its ability to create a strong bright spectrum of
visible and infra red light from a very brief pulse of
light,” said Dr Skryabin.
“We have never fully understood exactly why this
happens until our research showed how the pulse of light is slowed down
and blocked by other activity in the fibre, forcing it to shorten its
wavelength.
“Until now the creation and manipulation of the
supercontinua in photonic crystal fibres have been done in an ad-hoc
way without knowing exactly why different effects are observed. But now
we should be able to be much more precise when using it.”
Dr Skryabin believes that the interaction between light pulses
and solitons has similarities with the way gravity acts on objects.
Posted 11th December 2007
