The sign of the Kerr nonlinear coefficient, which determines the nonlinear propagation characteristics of high-power lasers, is usually only sensitive to the operating frequency. Here, we report a method to reverse the sign according to the polarization of the input beam. The sign reversal is realized in the first band of a two-dimensional Kerr photonic crystal (PhC) by using local-field effects. By appropriately adjusting the unit cell, we find that the effective nonlinear coefficient of the PhC is negative for the TM mode while positive for t...
