Comment on "numerical investigation of optically induced director oscillations in nematic liquid crystals"

A nonlinear optical system based on nematic liquid crystals film was numerically investigated by Demeter and Kramer in [Phys. Rev. E 64, 020701(R) (2001)]. They show that the uncommon route to chaos via a cascade of homoclinic gluing bifurcations predicted by a perturbative approach surprinsingly does not exist when the problem is solved exactly. On the other hand, the system still exhibits a secondary instability but its threshold is found to be much higher than previously reported. We clarify the reason for the failure of the perturbative approach and its limits of applicability. Moreover, the significant increase of the secondary instability threshold can be understood from a nonrealistic amplification of light intensity introduced by the perturbative model.