Regensburg 2007 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 10: Dielectric and Ferroelectric Thin Films and Nanostructures III

DF 10.6: Talk

Thursday, March 29, 2007, 16:10–16:30, H48

Observation of modulational instability in the 1st and 2nd band of a self-defocusing one-dimensional nonlinear waveguide array — Jürgen Wisniewski, •Christian Rüter, and Detlef Kip — Institut für Physik und Physikalische Technologien, Technische Universität Clausthal, 38678 Clausthal-Zellerfeld

Modulational instability (MI) is a universal phenomenon common to many nonlinear systems. Due to the interplay between nonlinearity and dispersion a propagating plane wave can become unstable to amplitude or phase modulations of certain frequencies which grow exponentially. MI has been investigated in various physical systems ranging from fluids to Bose-Einstein condensates, optical fibers, and electrical circuits, to mention a few. Here we explore this phenomenon in a discrete periodic nonlinear waveguide array consisting of parallel channel waveguides which are close enough to allow for tunneling of energy from one channel to its neighbours. The linear modes in such periodic lattices are extended Floquet-Bloch modes with a transmission spectrum consisting of allowed bands and forbidden gaps. In the nonlinear case, these modes experience instabilities, and break up into spatially modulated patterns of high regularity. As proposed by Kivshar it has already been observed at the edge of the first Brillouin zone of the first band of a waveguide array with a defocusing nonlinearity. We will present experimental results showing MI at the edge of the 1st band and the center of the 2nd band. The experimental results are confirmed by numerical simulations.