Mode expansion and Bragg filtering for a high-fidelity fiber-based photon-pair Source

We report the development of a fiber-based single spatial-mode source of photon-pairs where the efficiency of extracting photon-pairs is increased through the use of fiber-end expansion and Bragg filters. This improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs s(-1)nm(-1)mW(-1). The source can be configured to generate entangled photon-pairs, characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without subtracting any background.