London, March 7 : Scientists have demonstrated that pulses of light traveling down an optical fibre can be made to affect other light waves in much the same way as a black hole, thus creating an artificial black hole.
According to a report in Nature News, Ulf Leonhardt of the University of St Andrews, UK, and his colleagues, conducted the experiment in a laboratory.
Laboratory analogues of black holes have been proposed before, including an exotic ultracold gas of metal atoms that might act as a 'sonic black hole', but none has previously been demonstrated.
Now, the research group has shown that light pulses provide not only optical black holes, but 'white holes' too.
Whereas no light can escape from within a region called the event horizon surrounding the centre of a black hole - so light hitting it always falls in and becomes trapped - incoming light is repelled by the event horizon of a white hole.
The laboratory analogy involves a special, 'non-linear' optical fibre, in which light actually changes the fibre's light-bearing properties. This mimics the way that a black hole's gravity warps the space around it, altering the way light travels through it.
Because of this property of the fibre, a stream of light behind but faster than the 'hole' pulse gets slowed down as it catches up, and then is reflected backwards. So light can never cross into the trailing edge of the pulse, making it like a white hole. Just as with a cosmic white hole, the light also has its wavelength shortened by this process.
The 'black horizon' at the pulse front is more complicated.
In a cosmic black hole, incoming light is also frequency-shifted as it approaches, until its wavelength is so small that it requires new and unknown physics to describe how the light behaves.
In the optical fibre, the alteration of wavelength is not so extreme. The result is that the light actually bounces away. That sounds as if it's the opposite behaviour to a real black hole, but in fact the maths governing the behaviour is the same.
According to the researchers, such pulses might be made to act like mirrors - which might then be used to trap light in a way that could lead to 'black-hole lasers'.