Optimized Spectral Purity of Heralded Single Photons at the Telecom O-Band

TL;DR

This paper demonstrates the optimization of heralded single photon sources in the telecom O-band, achieving over 99.4% spectral purity through poling structure design and filtering, facilitating practical quantum communication applications.

Contribution

It introduces a numerical optimization method for poling structures in nonlinear crystals to enhance spectral purity of telecom-band single photons, with practical feasibility.

Findings

Achieved >99.4% spectral purity in the telecom O-band

Identified feasible configurations with off-the-shelf lasers

Showed spectral filtering enhances purity in practical setups

Abstract

We report on optimizing the spectral purity of heralded single photons in the telecom O-band, where single photons can be propagated with low loss and low dispersion in a standard telecom optical fiber. We numerically searched for various group-velocity-matching conditions and corresponding optimal poling structures of a potassium titanyl phosphate crystal for spontaneous parametric downconversion. Our poling optimization results using phase-matching coherence-length and sub-coherence-length modulation schemes show > 99.4% spectral purity with pump wavelengths ranging from 603.8 nm to 887.3 nm. Some optimized configurations are feasible with off-the-shelf lasers and single-photon detectors. Moreover, by investigating noise photon spectra for different poling optimization methods, we show that, in practice, appropriate, gentle spectral filtering helps achieve high purity. This study will pave the way for developing practical quantum sources for quantum information applications at the telecom O-band.