We demonstrate polarization-controlled switching of the orbital angular momentum (OAM) transfer in nonlinear wave mixing. By adjusting the input beam geometry, we are able to produce a three-channel orbital OAM, with arbitrary topological charges simultaneously generated and spatially resolved in the second-harmonic wavelength. The use of path and polarization degrees of freedom allows nearly perfect optical switching between different OAM operations. These results are supported by a theoretical model showing very good agreement with the experiments.

We present an experimental and theoretical study of type I, frequency-degenerate spontaneous parametric downconversion (SPDC) with a Bessel-Gauss pump in which we include, both, paraxial and non-paraxial pump beam configurations. We present measurements of the SPDC angular spectrum (AS), of the conditional angular spectrum (CAS) of signal-mode single photons as heralded by the detection of an idler photon, and of the transverse wavevector signal-idler correlations (TWC). We show that as the pump is made increasingly non-paraxial the AS acquires a non-concentric double-cone structure, with the CAS shape depending on the azimuthal location of the heralding detector, while the signal-idler wavevector correlation region splits into characteristic doublet stripes, representing as yet unexplored non-trivial, non-local quantum correlations between the signal and idler photons. Our work provides further understanding of SPDC with a particular class of structured pump beams, and we believe that the controlled presence of double wavevector correlations represents an interesting new resource for photon-pair quantum state engineering.

No abstract