In a fixed delay optical communication system, rate adjustable differential phase shift key (DPSK) techniques eliminate the need for multiple comparing modules, each corresponding to a different data rate. Setting alternative data rates at integer multiples of the fundamental data rate of the optical communication system allows the system to process the respective integer number of symbols per period of the system, wherein the period of the system is the inverse of the fundamental data rate. Pulse carving techniques may be used to set the duty cycle of clock levels associated with a clock signal. The clock levels may be combined with respective symbols to provide optical symbols having a duty cycle less than 100%.