In-Line Fiber-Integrated Photon-Pair Generation from van der Waals Crystals

TL;DR

This paper demonstrates a compact, fiber-integrated photon-pair source using van der Waals crystals, enabling efficient, alignment-free quantum light generation directly within optical fibers for quantum technologies.

Contribution

The work introduces a novel in-line, lens-free SPDC photon-pair source integrated with a van der Waals crystal on an optical fiber end, enhancing compactness and efficiency.

Findings

Achieved high purity photon pairs with a coincidence-to-accidental ratio of ~4600.

Demonstrated efficient photon collection into optical fibers without free-space optics.

Established van der Waals materials as a platform for fiber-integrated quantum light sources.

Abstract

Miniaturized quantum light sources that operate directly in optical fibers are an attractive platform for optical quantum technologies. However, most miniaturized spontaneous parametric down- conversion (SPDC) sources still rely on objective-lens-based free-space pumping and collection, which limits compactness, robustness, and direct compatibility with fiber-based systems. Here we demonstrate a lens-free in-line SPDC photon-pair source by integrating a van der Waals NbOI2 flake directly onto the end facet of an optical fiber. In this configuration, the generated photon- pairs are efficiently collected into optical fibers, eliminating the need for bulk free-space collection optics. Despite the limited numerical aperture of the single-mode fiber, efficient photon-pair collection with high purity, characterized by a coincidence-to-accidental ratio of up to ~4600, is achieved in an ultracompact configuration. These results establish van der Waals ferroelectric materials as a promising platform for fiber-integrated quantum light sources and provide a pathway toward compact, alignment-free quantum photonic devices.