Bath lights the way

Photonic crystal fibre’s ability to create broad spectra of light has been explained by researchers from Bath University, opening the way for developments in various technologies.

The fibre can create a supercontinuum, where a pulse of light with a narrow range of wavelengths is changed into a spectrum hundreds of times broader and ranging from visible light to the infra-red.

According to researchers, this effect could have potential in a range of technologies. In telecommunications optical systems could be hundreds of times more efficient as signals could be transmitted and processed at many wavelengths simultaneously.

Dr Dmitry Skryabin and Dr Andrey Gorbach, of the Centre for Photonics and Photonic Materials in the Department of Physics, found that this generation of light across the visible spectrum was caused by an interaction between conventional pulses of lights and special light waves, called solitons, that maintain their shape as they travel down the fibre.

Skryabin believes the interaction between light pulses and solitons has similarities with the effect of gravity. As the pulses of light and solitons travel down the fibre, the solitons slow down and the pulses of light get stuck behind them. This barrier forces the light pulses to shorten their wavelength and so become bluer, just as the solitons’ wavelength lengthens, becoming redder. This combined effect creates the broadened spectrum.

‘One of the most startling effects of the photonic fibre is its ability to create a strong bright spectrum of visible and infra red light from a very brief pulse of light,’ said 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.’

Despite the mechanism being previously unclear, supercotinua have already been used to create optical clocks, which are so accurate that they lose or gain only a second every million years.