  We investigate the polarization state dynamics of single photon pulse for
optical fiber quantum communication channels. On the basis of a birefringence
vector model in which amplitude and direction are both stochastic variables,
Jones vector is obtained by solving the frequency domain wave equation. The
fidelity of output quantum state and degree of polarization of the pulse are
also obtained from the density operators. It is shown that the fidelity of
quantum state decreases quickly and tends to a stable value along optical
fiber, and increases for larger mean fluctuation magnitude of the stochastic
fiber birefringence. Degree of polarization is nearly constant for small mean
fluctuation magnitude of the birefringence. The fidelity and degree of
polarization vary in the same way for Gaussian and rectangular frequency
spectrum envelope, while the value of Lorentzian spectrum is smaller.
