Issues

Mixing laser beams of different frequencies in a crystal with nonlinear polarizability can generate coherent output at sum and difference frequencies for which there are no convenient laser sources.

Electronic switching is a bottleneck that could limit single‐channel network speeds to about 5 gigabits per second. All‐optical switching and logic gates could repeal this speed limit on the information superhighway.

Optical signal processing in the future may use semiconductors in which the optical generation of electrons and holes controls the absorption and refractive index.

Exotic multiexciton strings, electron correlation effects and custom‐designed nonlinear optical molecules are some of the developments resulting from initial efforts toward active control of light‐matter interactions in nonlinear organic systems. The potential applications are equally diverse and exciting.