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Condensed Matter Physics Seminar


Discrete Solitons in Waveguide Arrays.

Prof. Stewart Aitchison
Dept. of Electrical and Computer Engineering, University of Toronto

Time
 
Wed. December 3, 2003     10:30 AM     Stirling 501

Abstract
 
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 continuous system.

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.

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