The proposed modulation scheme enables us to combine the advantages of the duobinary modulation, i.e., reduced transmission bandwidth compared to traditional intensity modulation, together with the advantages of prechirped modulation. Below, a theoretical investigation is presented where four different methods of modulating a double electrode Mach-Zehnder modulator is compared. It will be shown that the proposed prechirped duobinary modulation scheme will have the best performance in terms of power penalty.