Radiation related polarization instability of fast Kerr spatial solitons in slab waveguides

We report the observation of a power-dependent polarization conversion from a fast spatial soliton-like beam into the orthogonal polarization in an Al GaAs slab waveguide at power levels below which the nonlinear index change becomes comparable to the birefringence. The slow soliton, however, shows n o polarization conversion. We interpret these results in terms of the previ ously predicted polarization instability of a fast soliton into orthogonall y polarized radiation. The experimental results are in qualitative agreemen t with theory. (C) 2000 Published by Elsevier Science B.V.