Large phase shift of nonlocal optical spatial solitons.

In this paper, we discuss the evolution of the optical beam in nonlocal cubic nonlinear media, modeled by the nonlocal nonlinear Schrödinger equation (NNLSE). A different approximate model to the NNLSE is presented for the strongly nonlocal media with arbitrary response functions. An exact analytical solution of the model is obtained, and a spatial soliton is found to exist. A different phenomenon is revealed that the phase shift of such a nonlocal optical spatial soliton can be very large comparable to its local counterpart. The stability of the solution is rigorously proved. The comparisons of our analytical solution with the numerical simulation of the NNLSE, as well as with Snyder-Mitchell (linear) model [A. W. Snyder and D. J. Mitchell, Science 276, 1538 (1997)] are given.