Intrabit polarization diversity modulation for the mitigation of PMD effects

The authors propose and demonstrate a novel modulation format called intrabit polarization diversity modulation (IPDM) that helps to mitigate the deleterious effects of PMD on system performance. IPDM is a format in which the optical power in the first half of a nonreturn-to-zero (NRZ) bit time is transmitted in an orthogonal state-of-polarization (SOP) to the optical power in the second half of the bit time. At the receiver, a tunable polarizer is used to recover only one SOP. Given that both SOPs are launched at the transmitter, the probability of network outage due to PMD is considerably smaller. The use of this format limits the power penalty induced by first-order PMD to 3 dB, and the system sensitivity is independent of the fiber link´s instantaneous differential group delay. In the presence of higher order PMD, the authors show a 4- and a 1-dB improvement in the average receiver sensitivity over conventional NRZ and RZ format, respectively, in terms of the 2% tail of the received optical power.