Generation of pulsed polarization entangled photon pair via a space   cascaded two-crystal geometry
  The generation of pulsed polarization entangled photon pair has been realized using type-I phase matching in the spontaneous parametirc downconversion process in a space cascaded two-crystal geometry. The optical axes of the crystal are aligned in such a way that the horizontal polarization photon pair is produced from up crystal, and the vertical polarization photon pair is produced from down crystal. These two processes are simultaneous, but are separable in space. We get the high entangled polarization photon pair by using the single mode fiber to erase the spatial information between these two processes. This photon pair exhibits more than 86% high-visibility quantum interference for polarization variable without the narrowband filter and temporal compensation. 
Bao-Sen Shi and Akihisa Tomita