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

In this work, we report on the preparation of an ultra-broadbandcontinuously-tunable, highly polarization-entangled photon-pair source coveringthe C+L telecom bands using a single type-II phase-matched bulk PPKTP crystal.Over 60 nm turning band of the down-converted photons is achievedexperimentally. The broad tuning ability is due to operating near an extendedphase match point in this crystal. The S parameter value of CHSH inequality isin the range between 2.60+/-0.04 (minimum) and 2.72+/-0.07 (maximum), whichclearly demonstrates the high entanglement of the source over the whole tunablerange. This is the first realization of such a broadband tunable degeneratepolarization entanglement pair source in the telecom band. Combined with densewavelength-division multiplexing technique, our source could be used to improvethe transmission capacity of a single communication channel in the field ofquantum communication.