Entangled photon generation in a phase-modulated, quasi-phasematched crystal

We propose a scheme to generate polarization-entangled photon pairs by spontaneous parametric downconversion in a phase-modulated, type-II, quasi-phasematched (QPM) crystal. Instead of using two distinct crystals to generate vertical bar HV> and vertical bar VH> states, the phase-modulated QPM grating allows both states to be generated simultaneously in a distributed fashion throughout the nonlinear crystal. Temporal compensation is still needed to correct for effects of birefringence in the crystal. The distributed generation of the polarization-entangled photons is compared to generation using two sequential crystals.