Interference in a Quantum Channel Due to Classical Four-Wave Mixing in Optical Fibers

The second-order coherence function for idler photons generated through stimulated four-wave mixing (FWM) is theoretically derived, considering both spontaneous and stimulated Raman contributions. Two distinct cases and two different power regimes are analyzed. First, we consider that the idler wave is fully generated inside the fiber. In a second scenario, we admit that at the fiber input there exist a quantum channel and idler photons will be created at that frequency through the combined processes of FWM and Raman scattering. Results show that for the first case, in a low power regime, the idler photons follow a thermal statistics. In a moderate power regime, the statistics of the generated idler wave presents a Poissonian distribution. Results also show that in the second case, in a low power regime, the statistics of the input quantum channel goes from a Poissonian statistics at the fiber input to a thermal statistics at the fiber output. Findings show that in a moderate power regime, the quantum channel maintains its Poissonian distribution through fiber propagation.