© 2006 Nature Physics

Solitary waves have fascinated scientists since the nineteenth century. Wherever there are waves, solitary oscillations can be created; be it in water waves (of which tidal bores are a common example), sound or light waves. With the advent of quantum mechanics and wave-particle duality, a term for solitary wave ‘particles’ was soon coined: the soliton. As with photons and phonons, the drive now is to understand and observe the particle-like properties of solitary waves. When it comes to optical solitons, the challenge is that the nonlinearities required for their creation tend to be localized, making it difficult to observe the interplay of two solitons separated by relatively large distances.

Now, an approach taken by a team in Israel and the USA has allowed them to investigate just that1. They generate the solitons in lead glass where optical nonlinearities can spread throughout the whole sample by thermal conduction, thus enabling the observation of soliton–soliton effects at separations of up to 600 µm, a distance ten times larger than previous experiments. Even at this range, two solitons are attracted to each other and, in three-dimensional experiments, each one spirals around the other as they propagate along the lead glass. The researchers have already taken this a step further by demonstrating a relationship between solitons in different samples. Here, the interaction is mediated by a thin copper film.

It has been suggested that solitons could be used in computational systems, with information being passed from one soliton to the next. The work here shows that such systems could possibly be connected — in this example, by copper films — to form soliton networks.