Anisotropic waveguides induced by photorefractive (2+1)D solitons

We present theoretical and experimental investigations of the anisotropic character of the refractive-index modulation that is induced by a light beam propagating in a photorefractive strontium barium niobate crystal. Such a structure creates a so-called spatial screening soliton that is able to carry a second wave of a different wavelength and therefore can act as a waveguide. We show in numerical simulations as well as in experimental investigations the anisotropic property of refractive-index modulation. Furthermore, the noncircular shape of the induced waveguide is justified by the excitation of higher-order modes, which were found to be asymmetric in both transverse directions. Whereas in the direction perpendicular to the applied electric field the TEM01 and TEM02 modes can easily be excited, excitement of the TEM10 mode in the direction of the applied field is rather difficult. This effect can be explained by the constricted extension of the waveguide in this direction.