We present an analytical description and experimental demonstration of inter-polarization crosstalk caused by second-order polarization-mode dispersion (PMD). Even if the first-order PMD is completely compensated for, second-order PMD leads to large transmission impairments in ultrashort optical pulse transmissions through signal depolarization, which is caused by the frequency dependence of the principal state of polarization. In particular, depolarization in a polarization-multiplexed transmission inevitably prevents the complete separation of the two channels at the polarization demultiplexing. The analytical results show that the crosstalk increases in proportion to the fourth power of the signal bandwidth and grows by the square of distance as also verified by the experiments.
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