Compact source of polarization-entangled photon pairs

A compact source of polarization-entangled photon pairs is developed using a blue single-mode laser diode (λ = 402 nm, P = 30 mW) as the pump source of a beta-barium-borate (BBO) nonlinear optical crystal . Using the technique to optimize the collection efficiency, the created photon pairs are coupled into single-mode optical fibers, which are directly connected to quenched silicon avalanche photodiodes (Si APDs). The entanglement of the generated photon pairs was tested with the measurement of the polarization correlations in H/V and +45°/ -45° basis and by violating the Clauser-Horne-Shimony-Holt (CHSH)-type Bell inequality. This compact, robust and economic source can be employed in any application of quantum information and quantum communication, in particular in practicable entanglement based quantum key distribution.