The glass ceiling

WHAT is the theoretical limit to the rate at which information can be sent down an optical fibre? With telecoms firms' shares in the doldrums and widespread talk of a glut of capacity, this might seem an odd time to ask such a question. But that is what a group of researchers at Lucent Technologies' Bell Laboratories in Murray Hill, New Jersey, have done. And they have found that the limit is far beyond the reach of today's technology, which means that there is plenty of scope to increase capacity in future—or, to look at it the other way round, that the present glut is even bigger than it looks.