New optics - new materials

The nature and applications of optical materials have evolved rapidly in recent years. Their role as passive optical elements in free space has been augmented by so-called photonic systems. These can have many active components-oscillators, amplifiers, frequency converters, modulators, switches, routers and so on-most of which rely, to some degree, on optical field confinement. The design of appropriate materials for this new technology involves progress on two separate levels. There is a need both for the optimisation of microscopic electronic properties and for the separate control of bulk optical parameters on the scale of optical wavelengths. This article uses several examples to illustrate selected areas of current activity under both these headings. It also emphasises the need for more general methods for creating optical scale microstructure.