ALTHOUGH fibre-optics has brought a revolution in the field of teleco nications, the stumbling blocks arel the switches in use. Though the move through the fibres at the spi light (300,000 krn per sec), the inter between the electronics and the filll by electronic switches which are extrei slow in comparison to the spea light. The problem has been part solved by using optical switches 4 are much faster for isolated signals need to be reset between two sic thereby slowing down the effective sl of communication.

Now a group working at the Hil research laboratory in Cambridg-4 has developed a new optical switch u a technique called 'coherent coc which is 10,000 times faster than optical switches currently in use (Sd L October 6,1995).

a admique uses a laser light pulse I* ekictrons in a sample of gallium do (a semiconductor) from a low bmw to a higher energy band. UAW in the lower energy band. d pulse, coherent with the first rat ow of phase with it, is then f i red Wople; every wave has a property ~. tf two waves are such that Om wW the troughs coincide, they pbAse and if they are exactly oppoh other, they are out of phase. If maintain their phase relationship Ow they are coherent.

The second pulse now 'deexcites' the excited electron. The advantage is that the speed of the switch is only limited by the ability to generate accurate pulses in rapid succession. Already, pulse sequences of a femto- second (a billionth millionth of a second) are in use. The Cambridge team has demonstrated an important principle in opto-electronics which could find many other applications as well. The researchers are now working on a commercial switch which could further boost the rapidly growing fibre-optic telecommunication industry.