An ultra-broadband continuously-tunable polarization-entangled photon-pair source covering the C+L telecom bands based on a single type-II PPKTP crystal

摘要

The first experimental preparation is reported of an ultra-broadband continuously-tunable highly polarization-entangled photon-pair source via spontaneous parametric down-conversion in a single type-II phase-matched bulk periodically-poled KTiOPO4 (PPKTP) crystal. A tuning band of more than 60 nm for the down-converted photons is achieved experimentally, which covers the C+L telecom bands. The photon pair generation rate is about 1.63 × 10 ~4 (s mW nm)~(-1). The calculated S parameter values of CHSH inequality between 2.60 ± 0.04 (minimum) and 2.72 ± 0.07 (maximum) over the whole tunable range clearly demonstrate high entanglement of the source. In combination with the dense wavelength-division multiplexing (DWDM) technique, our source could be used to enhance the transmission capacity of a communication channel in the field of quantum communication.