Impact of fiber birefringence on correlated photon pair generation in highly nonlinear microstructure fibers

In this paper, correlated photon pair generation in a piece of highly nonlinear microstructure fiber with birefringence is investigated experimentally under different pump polarization directions. In the experimental condition, correlated photon pairs are generated by two independent scalar scattering processes along the two fiber polarization axes. Under linearly polarized pump light with a polarization direction of 45A degrees with respect to the fiber polarization axes, the polarization entangled characteristics of generated two-photon state is demonstrated. The two-photon interference fringes are measured with fringe visibilities of 96 +/- 3% and 87 +/- 4% under two non-orthogonal detecting polarization directions at signal side. The experimental results are discussed using the quantum theory of spontaneous parametric fluorescence in birefringent fibers, showing that the pump polarization dependence of correlated photon pair generation in the highly nonlinear microstructure fiber is due to its group birefringence. The experiment and theoretical analysis show that fiber birefringence has important impact on correlated photon pair generation, which provides a simple way to generate maximum polarization entanglement in fibers.