an inventive method for multi - symbol polarization switching for differential detection optical systems includes modulating a laser source by a dqpsk modulator , driving the dqpsk modulator with a data block configured for generating multi - symbol polarization - switched dqpsk differential - encoded signals , and polarizing the multi - symbol polarization - switched dqpsk signals with a polarizing modulator whose modulation speed is based on how often polarization states vary , wherein the data block provides a bits manipulation to provide the multi - symbol polarization switching thereby enabling differential detection for recovering correct original data by a receiver .