Tunable frequency conversion in doped photonic crystal fiber pumped near degeneracy

TL;DR

This paper presents a germanium-doped photonic crystal fiber enabling efficient, tunable frequency conversion between 920 nm and telecom wavelengths, facilitating quantum information transfer and frequency comb generation.

Contribution

Introduction of a specialized doped fiber with precise dispersion control for high-efficiency, tunable frequency conversion near 1550 nm and 920 nm wavelengths.

Findings

Achieved up to 79.4% internal conversion efficiency.

Enabled frequency conversion of weak classical signals.

Demonstrated cascaded frequency conversion for comb generation.

Abstract

Future quantum networks will rely on the ability to coherently transfer optically encoded quantum information between different wavelength bands. Bragg-scattering four-wave mixing in optical fiber is a promising route to achieving this, but requires fibers with precise dispersion control and broadband transmission at signal, target and pump wavelengths. Here we introduce a photonic crystal fiber with a germanium-doped core featuring group velocity matching at 1550 nm, the telecoms C-band, and 920 nm, within the emission range of efficient single photon sources based on InAs quantum dots. With low chromatic walk-off and good optical guidance even at long wavelengths, large lengths of this fiber are used to achieve nanometer-scale frequency shifts between wavelengths around 920 nm with up to 79.4\% internal conversion efficiency, allowing dissimilar InAs dots to be interfaced. We also show how cascading this frequency conversion can be used to generate a frequency comb away from telecoms wavelengths. Finally, we use the fiber to demonstrate tunable frequency conversion of weak classical signals around 918 nm to the telecoms C-band.