# Spectrally pure heralded single photons by spontaneous four-wave mixing in a fiber: reducing impact of dispersion fluctuations

## TL;DR

This paper models the spectral purity of heralded single photons generated via spontaneous four-wave mixing in fibers, demonstrating that optimized fiber design can mitigate dispersion fluctuations and Raman scattering effects to produce high-purity photons.

## Contribution

It introduces a model accounting for dispersion fluctuations in fiber-based photon sources and shows how fiber design optimization enhances photon purity despite these fluctuations.

## Key findings

- Fiber-core-radius fluctuations severely impact photon purity.
- Optimized fiber design can produce high-purity photons despite fluctuations.
- Separation of >32 THz from pump reduces Raman scattering contamination.

## Abstract

We model the spectral quantum-mechanical purity of heralded single photons from a photon-pair source based on nondegenerate spontaneous four-wave mixing taking the impact of distributed dispersion fluctuations into account. The considered photon-pair-generation scheme utilizes pump-pulse walk-off to produce pure heralded photons and phase matching is achieved through the dispersion properties of distinct spatial modes in a few-mode silica step-index fiber. We show that fiber-core-radius fluctuations in general severely impact the single-photon purity. Furthermore, by optimizing the fiber design we show that generation of single photons with very high spectral purity is feasible even in the presence of large core-radius fluctuations. At the same time, contamination from spontaneous Raman scattering is greatly mitigated by separating the single-photon frequency by more than 32 THz from the pump frequency.