While applauding AT&T Bell Laboratories’ demonstration last week of a simple working optical computer (CI No 1,354), Professor Desmond Smith of Edinburgh-based Heriot-Watt University, which has been a leader in the field of optronics for the past 10 years and sees optical computing as a milestone in technology, has said and published over the last three years as much as 70% of what AT&T was saying last week, and believes that the University is in the same league as Bell Labs in the technology. The scientists at Bell Laboratories in Holmdel, New Jersey, four of which are ex-Herriot-Watt, demonstrated a computer that uses pulses of light with a network of lasers, lenses and mirrors based on digital switches but with not a circuit board or Silicon chip in sight to transmit and process information. The Scottish University has also taken information and processed it optically, passing it on using using restoring logic; in addition to this the information was put into a loop to form a one channel optical computer. The processor uses 15 by 15 logical elements in an array, this is an improvement on the eight by eight elements used by AT&T which, though faster, prove more expensive. A simple explanation of how the optical processor works is that one optical device transmits light whilst another light beam is shone on the one transmitted to vary the strength of the beam to create levels that can stand for zeros and ones to create binary logic. Input-output functions may be accomplished via optical fibres or laser beams, and AT&T calls the optical switches it has designed Symmetric Self-Electro-optic Effective Devices. They are fabricated in Gallium Arsenide to achieve a faster switching speed than Silicon. They are combined with modulated laser diodes that emit near infra-red wavelengths. At present the box is under a foot high and about the size of a table top and although the prototype was able to show that most computing problems can be handled optically, significant research must be done before optical computers can be produced commercially.
Parallism
The machines have the potential to handle information in ways impossible for electronic computers such as performing millions of tasks simultaneously using the fact that many light beams may be handled at once and can pass through each other without causing interference. The AT&T team reckons it has the potential to achieve over 1,000 times the throughput of an electronic computer. The AT&T optical processor operates at 1MHz, slower than most personal computers, however the company scientists predict that several hundred million cycles per second, faster than most supercomputers can be achieved. Some believe the technology breakthrough could be nearly as large as that of the transistor and the researchers hope to develop chips with hundreds of thousands of optical switches. AT&T sees application in speech and vision recognition, switching and general computing. The researcher Alan Huang who led the research feels that of the first uses of the processor will probably involve problems requiring interconnection and parallel processing. This will lead towards using parallelism to achieve, for example, error free software. Professor Smith at Heriot-Watt believes that optical computers will be important where sequential devices are no good, such as reading two-dimensional data optically. On the other hand IBM did extensive research into photonics in the 1960s but its scientists concluded that computing with light uses more energy than computing with electricity and therefore photonics could never compete with electronics and conluded that light is good for transmission and connections but not much else: if AT&T and the Scots are right, that could prove a very expensive mistake. – Elvadia Tolputt
