Abstract
Through graphics-processing-unit-based simulations with different numbers
of copropagating channels (1--81), the dependence of the nonlinear threshold
on channel count, as well as on the fiber polarization mode dispersion (PMD)
coefficient, is investigated for both dispersion-managed and DCM-free 40 and
100 Gb/s coherent-detected polarization-multiplexed quadrature phase-shift
keying (CP-QPSK) transmission systems. Different fiber types including standard
single-mode fiber (SSMF), large effective area fiber (LEAF), and truewave
classic fiber (TWC) are considered and compared. Our investigations show that
the required number of simulated copropagating channels to correctly simulate
the nonlinear penalty caused by interchannel nonlinearities on CP-QSPK modulation
is strongly dependent on the fiber type. The generally used assumption of
around ten channels for simulating interchannel nonlinearities is only valid
for the SSMF with relative low channel input power. For transmission links
consisting of fiber types with low dispersion or high nonlinear coefficients,
such as the LEAF or TWC, ten copropagating channels are clearly not sufficient.
In dispersion-managed systems with DCMs, the required number of simulated
copropagating channels is not only dependent on fiber types and data rates
but also strongly on PMD present in the links. Our investigations have indicated
that for transmission over fibers with very low PMD (this is the case of most
new fibers), ten copropagating channels are not sufficient to correctly characterize
the interchannel nonlinearities even for high-dispersion fiber types, such
as the SSMF, and hence causes a clear underestimation of the nonlinearity
penalty. Finally, synchronized and interleaved CP-QPSK is compared. We show
that despite the depolarization effect of PMD, there are still some benefits
of using interleaved RZ-CP-QPSK systems.
© 2011 IEEE
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