Application of a curious waveform known as a soliton that maintains its shape over vast distances without the need for any amplification could increase the capacity of today’s fibre optic networks almost a hundred-fold, researchers at AT&T Bell Laboratories believe. The soliton wave was first observed in 1834 by a Scottish naval architect who followed a slow-moving, unchanging wave down a canal for almost two miles (it was no doubt caused by the Loch Ness Monster). Since then, the existence of the waves have been confirmed in electrical transmission, acoustics, ocean currents – and light. In a Bell Laboratories experiment last year a soliton wave retained its shape while travelling through 3,700 miles of fibre loops with no repeaters, reports the New York Times. The Bell boys believe that pulse code modulation of such a wave would enable fibre optic cables to run at up to 100Gbps, sufficient capacity for fast facsimile transmission of glossy colour photographs, and for two-way high definition television. The key to creating soliton waves, so that the pulses of light do not begin to disperse and merge without repeaters to reconstruct them at regular intervals is to inject a concurrent signal of continuous laser light: the pulses draw on the energy of the second stream to retain their conformation. As well as eliminating repeaters, which interrupt and slow transmission, although light-emitting diodes to amplify the continuous signal would be needed, soliton waves would enable much shorter duration pulses to be transmitted, the much higher frequency giving the vast increase in capacity that could be made available on present generation fibre optic cables. The task then would be to develop decoders to handle the new capacity.
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