Direct Measurement of the Spatial-Spectral Structure of Waveguided Parametric Down-Conversion

TL;DR

This paper investigates the spatial and spectral properties of waveguided parametric down-conversion, demonstrating mode isolation, direct spatial measurement, and the potential for generating spatially entangled photon pairs.

Contribution

It provides the first direct measurement of the spatial distribution of modes in waveguided PDC and shows mode parity conservation during nonlinear interaction.

Findings

Individual spatial modes can be isolated via spectral properties.

Spatial distribution of photon pairs can be directly measured.

Waveguide sources can generate spatially entangled photon pairs.

Abstract

We present a study of the propagation of higher-order spatial modes in a waveguided parametric down-conversion photon pair source. Observing the multimode photon pair spectrum from a periodically poled KTiOPO$_4$ waveguide allowed us to isolate individual spatial modes through their distinctive spectral properties. We have measured directly the spatial distribution of each mode of the photon pairs, confirming the findings of our waveguide model, and demonstrated by coincidence measurements that the total parity of the modes is conserved in the nonlinear interaction. Furthermore, we show that we can combine the advantages of a waveguide source with the potential to generate spatially entangled photon pairs as in bulk crystal down-converters.