Light propagation along a helical waveguide: variational approach

We investigate numerically and analytically light propagation in a single spiral waveguide formed in a nonlinear dielectric medium, in the regime of low spatial frequency of the waveguide rotation. We present a general variational approach for computing soliton parameters analytically, which includes various types of nonlinearity. In the particular case of media with cubic-quintic nonlinearity, analytical expressions found are in very good agreement with the numerical findings.