Nonclassical interferences with separate fibre sources of intrinsically time bandwidth limited photon pairs

Single photons are at the heart of optical quantum technologies such as quantum cryptography, quantum computing and quantum metrology. In this paper we report on the creation of photon pairs via four-wave-mixing (FWM) in birefringent photonic crystal fibres (PCF). It has recently been suggested that for thoroughly engineering the phase matching condition of a birefringent PCF, photon pairs can by created in an intrinsically pure state and narrow band. This can be achieved for cross-polarized phase matching, where two pump photons in the slow axis are converted into a pair of photons, polarized in the orthogonal fast axis. The aim is to produce such intrinsically pure and narrow-band photons and hence to achieve high non-classical interference visibility without any requirement for spectral filtering. In order to experimentally test the purity of our heralded single photons we performed a Hong-Ou-Mandel experiment using heralded signal photons generated in separate PCF sources.