Introduction

Abstract

Nonlinear optics is attracting increasing attention around the world because of its applications in telecommunications and possibilities for optical information storage and computing. Optical fibre communications show that optics is already the method of choice for many purposes, owing to its wide bandwidth and freedom from electromagnetic interference. This is certainly obvious to those of us whose cities have had their streets dug up to lay new fibre-optic cables! To the existing advantages of optics, nonlinear optics adds further improvements in efficiency and versatility. A simple example is in amplification of optical signals. Fibre-optic cables have such low absorption that they can transmit signals over many kilometres, but eventually the signals need to be amplified. At present, this is done by converting the weak optical signal to an electronic one, amplifying that electronically, and then converting the strong electronic signal into a strong optical signal again. It would obviously be more efficient if the light beam could be amplified directly, say by a laser beam in a suitable medium. Such a process comes into the realm of nonlinear optics.