Intrinsically narrowband pair photon generation in microstructured   fibres
  In this paper we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong-Ou-Mandel interference visibilities of 77% between photons from the same PCF, and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities. 
Alex Clark, Bryn Bell, Jeremie Fulconis, Matthaeus M. Halder, Ben   Cemlyn, Olivier Alibart, Chunle Xiong, William J. Wadswo...
quant-ph