We consider a model of a nonlinear planar planar waveguide with a sinusoidal modulation of the refractive index in the transverse direction, which gives rise to a system of parallel troughs that may serve as channels that trap solitary beams (spatial solitons). The model can also be considered as an asymptotic one describing a dense planar array of parallel nonlinear optical fibers, with the modulation representing the corresponding effective Peierls-Nabarro potential. By means of the variational approximation and by direct simulations we demonstrate that the one-soliton state trapped in a channel has no existence threshold and is always stable. In contrast with this a stationary state of two beams trapped in two adjacent troughs has an existence border, which is found numerically. Depending on the values of the parameters, the two-soliton states are found to be dynamically stable over an indefinitely long or a finite but large distance. We consider the possibility of switching the beam from a channel where it was trapped into an adjacent one by a localized spot attracting the beam through the cross-phase modulation. The spot can be created between the troughs by a focused laser beam shone transversely to the waveguide. By means of the perturbation theory and numerical method we demonstrate that the switching is possible, provided that the spot's strength exceeds a certain threshold value.
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