Nonlinear physical systems can have multiple output states compatible with a single input state. This enables them to be used to store, process, and transmit information. Applications typically require the selection of a particular desired state out of this multiplicity, for example, the Gaussian mode in a laser. Often the desired state is, or becomes, unstable—as when a laser passes from single- to multi-mode operation. In 1998, several experiments have shown how Fourier-space filtering can persuade optical systems to produce otherwise unstable patterns. Persuade, rather than force, because with appropriate design, the system self-organizes in such a way that little or no energy is lost in the filter. This is exciting because optical systems could, in principle, be similarly persuaded to display unstable states representing images or information rather than simple patterns.
by Graeme K. Harkness, Gian-Luca Oppo, and Willie J. Firth, Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow, Scotland, U.K.