A novel scheme, using differential Mach-Zehnder modulator (DMZM) for generation of 80 Gbit/s return-to-zero differential phase-shift keyed (RZ-DPSK), carrier-suppressed (CS) RZ-DPSK, return-to-zero differential quadrature phase-shift keyed (RZ-DQPSK) and CSRZ-DQPSK, is proposed. To generate RZ/CSRZ-DQPSK, it needs only to add a dual-drive MZM based on the 80 Gbit/s RZ/CSRZ-DPSK signal which is generated by a two differential cascaded MZM. The proposed method of the generation of RZ/CSRZ-DPSK and RZ/CSRZ-DQPSK is of expansibility and simplicity. Simulation results show that CSRZ-DPSK has a more compact spectrum than that of RZ-DPSK, while the DQPSK has a similar spectral shape to that of DPSK, with its spectrum being compressed by a factor of two due to the halved symbol rate for transmission at a fixed bit rate.