Researchers from Glasgow University have produced an optical switch capable of operating at least 2,000 times as fast as the best device on show at Telecom ’91 in Geneva. At the show Hitachi displayed its large capacity switching system capable of switching at around 5ns (five thousandths of a millionths of a second). The new Glasgow device, however has been tested at 10 picoseconds (10 millionths of a millionth of a second) at which speed, says Dr Charles Ironside, lecturer in the department of electrical engineering, switching was instantaneous. Ironside and co-researcher Dr Stuart Aitchison therefore believe that the technology is capable of switching a thousand times faster again – if they could just find a way of measuring light pulses which are only 10 femtoseconds long. The higher speeds have been achieved only by a fundamental change in the design of the switching element. In more conventional systems, light entering the switch hits a semi-conductor with a refractive index which is controlled by an electrical charge: changing the voltage applied to the semiconductor alters the way in which the light is bent and et voila – an optical switch. The trouble is that the speed of switching is determined by the speed at which the voltage can be changed. The Glasgow team, however is building its switches using Aluminum Gallium Arsenide, which changes its refractive properties when subjected to light, instead of an electrical signal. It is by cutting out the electronic components and using a totally optical switch that the gains have been made. Ironside has been working on the technology for five years, but has been hampered by the Aluminium compound’s inefficient response to the switch-pulse. A recent paper from the University of Central Florida provided the answer to that particular problem, but the switch still needs a very intense light to get the substance to change its properties says Ironside who added that this problem should be solved within three years.
