Number 39 (Story #1), July 1, 1991 by Phillip F. Schewe and Ben Stein THE FIRST ALL-OPTICAL SWITCH has been created by Alan Huang at AT&T Bell Labs. Previous optical switches involved a conversion between electricity and light at some point in the process. In Huang's device, which exploits the fact that the speed of light in certain (nonlinear) media depends on the light intensity, a laser beam enters a 100-meter loop of optical fiber, splits off into two directions, and reconverges, producing an interference pattern. By sending out an additional burst of light in parallel with one of the counter-propagating beams, the interference pattern can be altered and the exit of light from the switch can be controlled. The new switch, described by Huang at the recent Physics Computing '91 conference in San Jose, CA, can currently turn on and off in only 0.5 ps, whereas all-electronic switches take at least 10 ps. With the invention of the switch, Huang believes that scientists have all the fundamental components needed to create an all-optical computer. (Science News, 22 June 1991.)