Efficient single-mode generation of degenerate 1550 nm entanglement in type-II parametric downconversion

Summary form only given. The first experiment on a source based on type-II parametric downconversion for beam-like creation of a pair of degenerate, entangled photons at 1550 nm produced in a 12 mm long BBO crystal is reported. The crystal is pumped with a femtosecond pulsed Ti-sapphire laser operating at 775 nm. The coupling is optimized by focusing the pump so that the crystal emits each pair of photons into a mode which has a maximum possible overlap-integral with the collection mode of the single-mode fiber. Calculations of the single-mode emission efficiency are performed considering beamsize and wavevector spread for a long crystal with strong focusing. With this optimization we experimentally get high singles-rates even with the relatively poor performance of the single photon detectors available at near-infrared.