A fiber-optic transmission system based on differential polarization-shift keying

A differential polarization-shift keying (DPolSK) scheme in which information is encoded as a differential polarization state with respect to the previous symbol is considered. A novel DPolSK demodulator consisting of optical delay interferometer and a pair of birefringence plates that do polarization rotation are proposed. Numerical simulations of the long haul fiber-optic systems based on differential phase-shift keying (DPSK) and DPolSK are carried out and it is found that DPolSK has a higher nonlinear tolerance than DPSK. This is because the ghost pulse generation due to intra-channel four-wave mixing (IFWM) is less efficient for DPolSK signals as compared to DPSK.