On The Physical Limits of Digital Optical Switching and Logic Elements

A number of recent developments have increased the interest in digital optical signal-processing devices and techniques. Laser technology has now advanced to the point that lasers are being used in consumer electronics. Optical fiber communication systems are being widely installed. Integrated-optics spectrum analyzers have been developed. In the research stage it has been shown that optical fibers can be used to transmit information at rates approaching 1 THz.1,2 This rate is much beyond the capabilities of any presently known electronic light detector. Thus, to utilize this information-handling capacity, some form of optical signal processing will have to be performed before the light signals are converted to electronic ones. Low-power integrated-optics light switches3 and low-energy integrated-optical bistable devices4 capable of performing optical logic have been demonstrated. It is tempting to propose that such digital 1975 optical switching elements be used to construct high-speed computers as well as repeaters and terminal equipment for optical communications systems. To examine these possibilities we need to understand: (i) What are realistic possibilities for speed, power dissipation, and size for optical switching elements? and (ii) What are the fundamental limits imposed by the physics of the nonlinear interactions, and by the available optical materials? Previous studies of these optical device limits have been made by several authors. The pioneering work of Keyes5 examined several nonlinear optical processes and concluded that thermal considerations imposed severe limits on the use of optical logic elements.