Unidirectional suppresion of Bragg reflection in grated PT-symmetric media

We study the scattering properties of light through optical fibers with grating that involves gain/loss modulation that respect Parity-Time (PT) symmetry. We derive analytical expressions for transmission and reflection coefficients both in the presence and absence of Kerr non-linearity. At the spontaneous PT-symmetric point we have found that Bragg reflection is suppressed once the light is injected from the left, while it is amplified (with respect to the passive medium) if the fiber is illuminated from the right. Our results are robust for a large interval of the detuning parameter away from the Bragg wavelength.