Influence of fibre homogeneity on Four Wave Mixing pair generation

Abstract

Summary form only given. Optical fibre (either classical or microstructured) is a favourable medium for realization of sources of entangled photons for quantum communications. Indeed the photon pairs are generated through spontaneous Four Wave Mixing (FWM) directly in the fibre core and can thus be connected easily and without loss to the optical telecommunication network.We have realized such a source and characterized its performance. Our measurements showed a photon pair generation rate lower than expected in theory. Further characterization showed, as can be seen in Fig. 1A, a widened pair spectrum and a diminution of the generation rate compared to the prediction of our model (Fig. 1B) [2]. Such features can be explained by taking in account the intrinsic inhomogeneity of the fibre, i.e. the core and cladding dimensions fluctuation along the fibre. Indeed, a small variation of the fibre diameter implies a slightly different dispersion, hence shifted photon pair frequencies. To depict these uniformities, we extended our model through a similar approach as in Ref. [3], considering the fibre as an assembly of homogeneous sections, each one with its own length and phase mismatch. Consequently, the joint spectral intensity of pairs describing their generation probability for a given couple of frequencies is more complex. In Fig. 1B, we show the result of our numerical simulation for a purely uniform fibre with parameters corresponding to our source [1,2], and in the case of a linear variation of the zero dispersion wavelength along the fibre. In this specific case, a new analytical solution that will be presented, can be derived from our model, and is also shown in Fig. 1B as a comparison.