This paper reports results of an extensive Monte Carlo simulation analysis on the impact of DP-QPSK pulse shape in high-spectral efficiency WDM transmission at 112 Gb/s per channel. The pulse shapes studied include NRZ, 50% duty cycle RZ and 67% duty cycle RZ. Both symbol-aligned and symbol-interleaved formats are investigated and compared for nonlinear transmission tolerance on common dispersion maps used in terrestrial long-haul systems. The RZ pulse shape shows the greatest improvement in nonlinear tolerance with symbol-interleaving. However, symbol-interleaving only provides significant benefit in optical line systems designed to preserve the pulse shape during transmission, such as systems based on distributed dispersion compensating fiber (DCF). The duty cycle of the RZ pulse has only a minor impact on nonlinear performance, and even systems based on the NRZ pulse shape can gain significant benefit from symbol-interleaving.
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