Source of polarization entanglement in a single periodically poled KTiOPO4 crystal with overlapping emission cones.

We present a simple polarization entanglemenet source based on type-II phase-matched parametric down-conversion in periodically poled KTiOPO4. By use of noncritical phase matching in a noncollinear geometry the single-crystal source emits a cone of polarization-entangled photons. Two beams on opposite sides of the cone are selected for measurements to yield an observed flux of 820 pairs/s per mW of pump power with a two-photon fringe visibility of 96%. With this source we measure a violation of Bell's inequality of 140 standard deviations in 160 s.