This paper demonstrates bandwidth requirement for optical DPQSK transmitter using one Dual-drive Mach Zehnder
Modulator (DDMZM) for 100Gb/s physical transmission. The result shows that at receiver bandwidth of 40GHz, NRZDQPSK
signal requires 60GHz modulation bandwidth at least, while RZ-DQPSK scheme demands less bandwidth,
about 40GHz for 50% duty cycle RZ-DQPSK signal.