We report a new nearly degenerate two‐wave mixing interaction in photorefractive Bi12SiO20crystals in which the signal beam is time modulated at high frequency. The beam coupling phenomena and the time integration properties of the crystal allow us to achieve a differential gain &ggr;diffon the transmitted signal beam. The dependence of &ggr;diffversus the duty cycle of the modulated signal is analyzed. Amplification and regeneration of periodic, or random sequences of information bits are experimentally demonstrated.