Spectral properties of photon pairs generated by spontaneous four wave mixing in inhomogeneous photonic crystal fibers

TL;DR

This paper investigates how inhomogeneity in photonic crystal fibers affects the spectral properties of photon pairs generated via spontaneous four wave mixing, combining theoretical modeling with experimental validation.

Contribution

It introduces a theoretical model describing the impact of inhomogeneity on photon pair spectra and demonstrates an experimental method to test fiber homogeneity.

Findings

Inhomogeneity causes spectral modulation that hinders spectral factorability.

Spectral measurements of individual photons reveal inhomogeneity effects.

Experimental results align with theoretical predictions.

Abstract

The photonic crystal fiber (PCF) is one of the excellent media for generating photon pairs via spontaneous four wave mixing. Here we study how the inhomogeneity of PCFs affect the spectral properties of photon pairs from both the theoretical and experimental aspects. The theoretical model shows that the photon pairs born in different place of the inhomogeneous PCF are coherently superposed, and a modulation in the broadened spectrum of phase matching function will appear, which prevents the realization of spectral factorable photon pairs. In particular, the inhomogeneity induced modulation can be examined by measuring the spectrum of individual signal or idler field when the asymmetric group velocity matching is approximately fulfilled. Our experiments are performed by tailoring the spectrum of pulsed pump to satisfy the specified phase matching condition. The observed spectra of individual signal photons, which are produced from different segments of the 1.9 m inhomogeneous PCF, agree with the theoretical predictions. The investigations are not only useful for fiber based quantum state engineering, but also provide a dependable method to test the homogeneity of PCF.