Optical Solitons

A light pulse is a continuum of optical carriers of different frequencies. Optical media are dispersive, so these carriers in the light pulse travel at different velocities, causing the energy to spread over time and distance. In addition, there is the optical Kerr effect, which “instantaneously” increases the refractive index of the medium by an amount proportional to the optical power. Can one use these two effects dispersion and the Kerr effect to ensure that a light pulse retains its integrity while traveling thousands of kilometers through an optical fiber?

Answer

Under the right conditions, the two effects dispersion and the Kerr effect can be made to cancel exactly. The nonlinearity of the Kerr effect can delay the “fast” carriers relative to the “slow” carriers, bringing them together to counter the dispersion.

These pulses conserving their shape and integrity are exhibiting soliton behavior. Optical solitons were first observed in fibers in 1980 and are now fundamental components in optical transmission systems.