Nonlinear discrete systems are encountered in a wide variety of physical
systems, ranging from the localized modes in molecular systems, polarons in
a one-dimensional ionic lattice and coupled arrays of mechanical
oscillators. Such discrete systems are of fundamental interest, yet it is
difficult to experimentally study energy transport in such systems.
In this presentation recent results on the observation of discrete spatial
solitons in arrays of coupled AlGaAs waveguides will be presented. The
AlGaAs material system has an almost ideal Kerr nonlinearity which allows
controllable nonlinear experiments to be carried out. At low input intensity
levels the optical field spreads out as it couples to adjacent waveguides.
At high input intensities this coupling is broken and the wave propagates as
a discrete spatial soliton. The discrete nature of the sample results in a
number of novel effects which do not occur in the corresponding continuous
situation. For example the direction of propagation becomes power dependent,
the diffractive properties of the array can be controlled and defect states
can be engineered. The talk will introduce these effects and present
experimental results which illustrate how a discrete system differs from a
A more general approach to describing the periodic system formed by the
waveguide array is to use a one dimensional Floquet-Bloch description. Here
the spectrum of the propagation constants is divided into bands, separated
by bandgaps. The linear modes of the higher order bands can be excited by
appropriate choice of input coupling angle. At high intensity Floquet Bloch
solitons are formed and have been experimentally observed.