  The frequency domain equalizers (FDEs) employing two types of overlap-add
zero-padding (OLA-ZP) methods are applied to compensate the chromatic
dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed
quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission
system. Simulation results demonstrate that the OLA-ZP methods can achieve the
same acceptable performance as the overlap-save method. The required minimum
overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier
transform length to minimize the computational complexity is also analyzed.
