We present a consistent multimode theory that describes the coupling of single photons generated by collinear Type-I parametric down-conversion into single-mode optical fibers. We have calculated an analytic expression for the fiber diameter which maximizes the pair photon count rate. For a given focal length and wavelength, a lower limit of the fiber diameter for satisfactory coupling is obtained.
@article{arxiv.quant-ph/0412065,
title = {Optimal coupling of entangled photons into single-mode optical fibers},
author = {R. Andrews and E. R. Pike and Sarben Sarkar},
journal= {arXiv preprint arXiv:quant-ph/0412065},
year = {2009}
}