The impact of channel occupancies on polarization division multiplexed quadrature phase-shift keying (PDM-QPSK)/on-off keying (OOK) hybrid systems is investigated numerically over a dispersion-managed transmission link. In addition to keep large residual dispersion per span, we find that suitable channel occupancy also help to improve the nonlinear tolerance of such hybrid systems significantly. About 2.4-dBm more nonlinear threshold (NLT) and 75% increase of transmission reach can be obtained u
