Nonlocal quintic nonlinearity by cascaded THG in dispersive media

In this paper, the authors extend the theory of cascaded Kerr to the case of pulses propagating in a dispersion tuned optical fibre generating a strongly mismatched third harmonic wave. This model includes the nonlocal response due to group velocity mismatch and different levels of dispersion for the fundamental and the third harmonic. The nonlocal harmonic approximation was applied to the system of coupled equations and derive a perturbed nonlinear Schrodinger equation for the fundamental wave only. The perturbation was shown to have the functional structure of a 5th order Kerr effect with a phase shift dependent on the square of the intensity. The dispersion features of the system create a non-instantaneous response of the perturbation, which can act similarly to a higher order Raman response with a mean time delay of tuneable magnitude and sign.