Is PS-QPSK really an alternative to PDM-QPSK?

Inhalt:
In this contribution, we compare the performance of polarization-division multiplexing (PDM) quadrature phase-shift keying (QPSK) signals and polarization-switched (PS) QPSK signals in single-channel and wavelength-division multiplexing (WDM) transmission experiments over up to 15000 km ultra-large-effective-area fiber (ULAF). We discuss the influence of nonlinear intra-channel and inter-channel impairments on both modulation formats. Furthermore, we investigate the application of optical Nyquist pulse shaping and a reduced WDM channel spacing to increase the spectral efficiency of PS-QPSK signals. In particular, this could be an attractive option for future bandwidth-elastic optical networks using software-defined transponders. Finally, we try to answer the question whether PS-QPSK could be an alternative or complement to PDM-QPSK.