Broadband-laser-diode pumped PPKTP-Sagnac polarization-entangled photon source

We experimentally demonstrate a polarization-entangled photon source at 810 nm using type-II phase-matched periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by low-cost, broadband laser diode with central wavelength of 405 and typical bandwidth 0.53 nm. The PPKTP is placed in Sagnac loop to realize the compact size high stability. downconverted biphotons, signal idler, have bandwidths 5.57 7.32 prepare two Bell states | ? + fence="false" stretchy="false">? ?<!-- ? fidelities <mml:mn>0.948 ±<!-- ± <mml:mn>0.004 0.963 0.002 . In polarization correlation measurement, visibilities are all higher than 96.2%, inequality test, S value can achieve 2.78 0.01 This high-quality low-cost entangled may many practical applications quantum information processing.