Chaos under control
optoelectronics has revolutionised the field of communications. With lasers, optical switches and fibber optics, the data-transfer rates routinely achieved now on optical networks are thousands of time those of their conventional counterparts.
In the last few years, there have been many advances in optoelectronics which have made this possible. Now G D VanWiggeren and Rajarshi Roy of Georgia Institute of Technology, usa , have demonstrated the use of chaotic lasers in data communication.
This work could potentially have far reaching effects on he whole field. The use of chaos in communication was first suggested by Pecora and Carroll in 1991. They considered the possibility of using synchronised electronic circuits to code and decode the message ( Science , Vol 279).
Soon after their suggestion, several groups implemented the scheme using electronic circuits for transmission and reception. Though the bandwidth (the information carrying capacity of any network or channel) was very small, some tens of kilohertz, the demonstration showed conclusively that the scheme was feasible.
What VanWiggeren and Roy have now shown is that it is possible to transmit data at the rate of about 10 megabits per second with the use of optical circuits. Their transmitter is a ring laser which produces chaotic light with a broad spectrum, centred on a wavelength of about 1.5 micrometers. The laser itself consists of an optical fibber amplifier doped with erbium ions. The message is in the form of a square wave which is encoded in the chaotic light beam produced by the transmitter. The decoding of the message is again done by erbium-doped optical fibber amplifier, whose properties precisely match the receiver.
This identical receiver then unfolds the message from the chaotic carrier and a very high fidelity copy of the original message is obtained. With this scheme of things, it is possible to achieve even higher data transmission rates if the speed of the optical detectors is improved. The researchers are now claiming to have improved the speeds up to 150 Megabits per second. The use of a chaotic carrier offers several advantages over conventional transmission, since the risk of eavesdropping is less. Though the principle has been demonstrated by VanWiggeren and Roy, there will have to be a lot of work done before the scheme finds commercial applications.