Single photon sources are fundamental elements for quantum information science, mainly for quantum key distribution (QKD) applications. Nevertheless, on-demand single photon sources are difficult to obtain, and their implementation in a practical application, such as QKD, demands further developments. A different approach to a single photon source is based on the generation of quantum correlated photon-pairs. In that case, the detection of one photon of the pair heralds the presence of the second photon. In this work, we present a heralded single photon source based on the spontaneous four-wave mixing (FWM) process in optical fibers. We characterize theoretically the heralded photon source by means of the conditional second-order coherence function, $g^{(2)}_c$, with $g^{(2)}_c=0$ for a perfect single photon source. We observe the nonclassical nature of the source, with $g^{(2)}_c \ll 1$ far below the classical limit. Our results also show that the Raman scattering in general degrades the quality of the source, due to the generation of uncorrelated photons. However, our findings show that in some frequency regimes we are able to observe a $g^{(2)}_c \approx 10^{-3}$. Moreover, our analysis shows that the propagation of the photons in a standard single mode fiber (SSMF) does not change significantly the value of $g^{(2)}_c$, for distances of $L < 25/\alpha$, with $\alpha$ the loss coefficient of the SSMF. This results can help to guide the development of single photon sources for quantum information applications.