High-Brightness Semiconductor Laser-Pumped $1.56~\mu$ m Polarization-Entangled Photon Pairs

In this paper, a semiconductor laser-pumped high-brightness 1.56 μm polarization-entangled photon pairs with a 30-mm-length PPKTP down-converter inside a Sagnac-type interferometer is firstly demonstrate. Large active-area InGaAs/InP-based single photon detectors and step-index multi-mode fiber collection are attempted to evaluate the brightness and entanglement quality. The maximum spectral brightness is about 1.33×105 pairs(s
_*
mW*nm)
^-1
with a pump power of 200 mW and a spectral bandwidth of 1.34 nm. Under the condition of maximum entanglement brightness, polarization visibility of 96.08%±1.62% is obtained in the diagonal orthogonal basis. The quantum state tomography also shows a high fidelity of 97% for the ideal Bell states. Meanwhile, the CHSH-type Bell inequality is violated with a value of 2.8196±0.0098 (96 σ). Both the performance in brightness and entanglement quality indicate that the current 1.56 μm polarization-entangled source has great potential in free-space quantum key distribution or quantum communication.