  We report on the impact of realistic gain and loss models on the bistable
operation of nonlinear parity-time Bragg gratings. In our model we include both
dispersive and saturable gain and show that levels of gain/loss saturation can
have significant impact on the bistable operation of a nonlinear PT Bragg
grating based on GaAs material. The hysteresis of the nonlinear PT Bragg
grating is analyzed for different levels of gain and loss and different
saturation levels. We show that high saturation levels can improve the
nonlinear operation by reducing the intensity at which the bistability occurs.
However when the saturation intensity is low, saturation inhibits the PT
characteristics of the grating.
