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Highly Uniform Photonic Crystal Fibres for Photon Pair Generation

Mateusz J. Olszewski, R.J. Mears, Leah R. Murphy, Alex O. C. Davis, Peter J. Mosley

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Longitudinal variations in photonic crystal fibres broaden four-wave mixing, limiting photon-pair source performance. We present precise characterisation of highly uniform PCF, where non-uniformities are minimised by tight tolerances and high drawing tension.
DOI
10.1364/cleo_si.2026.sm4e.3

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Pure state single photons are at the heart of optical quantum technologies. We have previously reported the generation of photon pairs by four-wave mixing in a single-mode photonic crystal fibre (PCF) and the use of a new birefringent phase matching scheme which results in the generation of narrowband signal photons, around 0.2 nm in bandwidth, and a factorizable photon pair state with no requirement for spectral filtering, leading to increased count rates. Our source is bright, polarized, and tuneable by variable laser wavelength and fibre parameters. Hong-Ou-Mandel (HOM) interference is observed between photons from two of these sources, a requirement for optical quantum information tasks.
In this paper, we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high-fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong–Ou–Mandel interference visibilities of 77% between photons from the same PCF and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities.
Photonic crystal fibers (PCFs) offer a high degree of design flexibility, particularly in terms of dispersion control, making them ideal for nonlinear optical processes. These fibers have found applications in various photonic fields, including fiber lasers [1] and single-photon generation [2]. Dispersion control allows for efficient four-wave mixing at desired wavelengths, which can be used in quantum optical sources. These processes require or are enhanced by the use of fiber Bragg gratings (FBGs) in the fiber. For example, in PCF-based FWM heralded single photon sources, FBGs can be used to filter out unwanted noise contributions, such as Raman noise. However, current filtering methods are lossy [3], making it desirable to integrate filters into the fibers themselves. Additionally, specially designed PCFs with FBGs can be used for in-fiber OPOs to generate squeezed light.
The paper reviews a new source of time-correlated photon pairs based on phase matched four-wave mixing in an optical fiber. This source has the potential to replace sources based on a non-linear birefringent crystals and waveguides. It generates linear polarised photon pairs in a narrow bandwidth, single circular mode which can be efficiently coupled into single mode fibres. We generate the parametric gain by pumping with a laser wavelength slightly below the zero dispersion wavelength, in the normal dispersion regime.