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

Polarization division multiplex (PolDM) doubles the data rate in existing t runk lines without need for additional optical bandwidth. In the presence o f dispersion compensation, polarization mode dispersion (PMD) limits the ac hievable transmission length. PMD tolerance of standard binary intensity mo dulation or non-return-to-zero coding has already been published. Recently, the return-to-zero (RZ) transmission format has become of more interest; t herefore 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 inte nsity modulation. So, PolDM is an attractive multilevel modulation scheme t o solve capacity problems with low additional effort. (C) 2001 Optical Soci ety of America.