Abstract: A switch capable of switching an optical beam without employing conventional mechanical, electrical, or optical devices. The switch includes a switching medium which may be a solid, liquid, gas, or supercritical gas. A signal or switched beam is directed into and through the switching medium. In order to change the path of the signal beam as it travels through the switching medium, the refractive index of the switching medium is changed. This change in refractive index is caused by a control beam selectively directed into the switching medium. The control beam produces a transient refractive index gradient within the switching medium. This gradient may be a thermal gradient and may constitute a thermal lens. The switch of the current invention is capable of picosecond response times and may serve as a fiber optics communications switch as well as an element in an optical computer.