All-optical 1-to-40 multicasting of 10-Gb/s intensity modulated nonreturn-to-zero data is experimentally demonstrated in an architecture based on a one-pump modulated wideband parametric optical amplifier. The unique combination encompassing a wideband multicasting function and a gain function resulted in less than 0.5-dB power penalty and a minimum of 11.5-dB conversion efficiency with less than 1.35 dB of gain ripple.