Optical vortex harmonic generation facilitated by photonic spin-orbit entanglement

TL;DR

This paper demonstrates how photonic spin-orbit entanglement can facilitate nonlinear optical frequency conversion, enabling efficient vortex generation at the third harmonic using a simple Gaussian pump in a nanofiber.

Contribution

It provides the first experimental evidence of spin-orbit entanglement enabling nonlinear optical processes, specifically third harmonic vortex generation in isotropic media.

Findings

Successful generation of third harmonic optical vortex via spin-orbit entanglement

Demonstration of spin-to-orbit transfer among different optical frequencies

Efficient vortex generation with a single Gaussian pump beam

Abstract

Photons can undergo spin-orbit coupling, by which the polarization (spin) and spatial profile (orbit) of the electromagnetic field interact and mix. Strong photonic spin-orbit coupling may reportedly arise from light propagation confined in a small cross-section, where the optical modes feature spin-orbit entanglement. However, while photonic Hamiltonians generally exhibit nonlinearity, the role and implication of spin-orbit entanglement in nonlinear optics have received little attention and are still elusive. Here, we report the first experimental demonstration of nonlinear optical frequency conversion, where spin-orbit entanglement facilitates spin-to-orbit transfer among different optical frequencies. By pumping a multimode optical nanofiber with a spin-polarized Gaussian pump beam, we produce an optical vortex at the third harmonic, which has long been regarded as a forbidden process in isotropic media. Our findings offer a unique and powerful means for efficient optical vortex generation that only incorporates a single Gaussian pump beam, in sharp contrast to any other approaches employing structured pump fields or sophisticatedly designed media. Our work opens up new possibilities of spin-orbit-coupling subwavelength waveguides, inspiring fundamental studies of nonlinear optics involving various types of structured light, as well as paving the way for the realization of hybrid quantum systems comprised of telecom photonic networks and long-lived quantum memories.