Custom nonlinearity profile for integrated quantum light sources

TL;DR

This paper presents a novel method to design nonlinear waveguides with customizable effective nonlinearity profiles, enabling integrated, unfiltered quantum light sources with improved purity and simplified fabrication processes.

Contribution

The authors introduce a technique to shape the nonlinearity profile of waveguides by controlling propagation directions, eliminating the need for complex patterning methods.

Findings

Designed waveguides with Gaussian nonlinearity profiles

Achieved generation of highly pure heralded single photons

Simplified fabrication process by using single-crystal structures

Abstract

Heralded single-photon sources are a fundamental building block for optical quantum technologies. These sources need to be unfiltered and integrated to have good scalability and avoid unnecessary losses. To attain this goal, it is necessary to control the effective nonlinearity seen by the fields as they mix and propagate in a waveguide source. In this paper, we introduce a method to design nonlinear waveguides with arbitrarily shaped effective nonlinearity profiles. The method takes advantage of the fact that the second order nonlinear response is a tensor quantity and thus the local effective nonlinearity of a material depends on the propagation direction of the fields participating in the interaction. Thus, by locally changing the propagation direction of the fields we can modulate the wave-mixing process. Our methods allows for the waveguide fabrication process to be significantly simplified: The material structure of the waveguide is made by a single crystal, no longer needing oriented patterning (OP) or periodic poling (PP). We use our method to design waveguides with a nonlinearity profile that is Gaussian in the propagation length, allowing to generate perfectly pure heralded single photons.