PMD tolerance of polarization division multiplex transmission using return-to-zero coding

Polarization division multiplex (PolDM) doubles the data rate in existing trunk lines without need for additional optical bandwidth. In the presence of dispersion compensation, polarization mode dispersion (PMD) limits the achievable transmission length. PMD tolerance of standard binary intensity modulation or non-return-to-zero coding has already been published. Recently, the return-to-zero (RZ) transmission format has become of more interest; therefore we assess the PMD tolerance of PolDM by numerical simulations and a transmission experiment. For a given total data rate per wavelength PolDM supports at least as much differential group delay as standard binary intensity modulation. So, PolDM is an attractive multilevel modulation scheme to solve capacity problems with low additional effort.