Optical switching using solitons

We are at the edge of another industrial revolution, namely, the information age.

Although some people may have not noticed, the amount of information produced by humanity is doubling every few months. Some clever countries now make more money from the information industry (computer hardware and software, movies, television, internet) than on anything else. The trend is still growing rapidly.

In order to respond to such a huge demand for information, the old analog metal cable communication devices are lagging behind, for they are slow and noisy. Modern communications relies on fast digital optical fiber systems. The idea of optical fiber communications is to inject laser pulses into a fiber. Information is coded within these pulses.

In order to increase the amount of information we can send in one second, we wish to make the pulses as short as possible, and inject many pulses per second. There is an end of any good thing, of course, and so there is also a limit of the width of laser pulses.

When a pulse propagates along a fiber, its width increase. The narrower the pulses, the more rapid the increase. This effect is called dispersion. One then can imagine that if we inject too many short pulses into a fiber, they will overlap after propagating over some distance. We then will not be able to distinguish between pulses - and information will have been lost.

If is fortunately that there is also another counter-effect which shortens the width of a pulse. This effect is called nonlinearity. If the intensity of a laser pulse is strong enough, this nonlinear effect can be in an active balance with the dispersion effect. The result is a pulse that can keep its shape for a long propagation distance, even including small disturbance. These steady pulses are called optical fiber solitons. Due to their short pulse duration and high stability, solitons could form the high-speed communications backbone' of tomorrow's information super-highway. These solitons have other interesting properties. They are composed of light but act more like particles.

There is however, a draw back to using fiber solitons. Current electronic amplifiers and switches just cannot operate quickly enough for the short pulses and high speeds that optical solitons can provide.

In recent years, an even newer type of optical soliton has been discovered. These solitons are created with a very strong nonlinear effect found in some crystals, in which two light fields can `shake hands' and cooperate by traveling together without dispersion. These are much more stable than any previously known soliton, because they are adapted to travel in many other types of environment rather than just inside optical fibers. For example, they can travel stably in the surface region of an optical integrated circuit. Because of the very strong nonlinear effect (which is several thousand times larger than the previous nonlinear effect), optical solitons of this type can also be produced with extremely low laser powers. Possible applications include optical information storage of enormous quantities of data (by using short wave-length light), and even the possibility of all-optical switches, much faster than any known electronic device.