Narrowband heralded single photons via Bragg grating inscription in germanium-doped photonic crystal fiber

TL;DR

This paper reports a fiber-based method for generating narrowband heralded single photons in the telecom C-band using photonic crystal fiber with a Bragg grating, suitable for quantum memory interfacing.

Contribution

Introduction of a fiber-integrated, narrowband heralded single photon source using Bragg grating inscription in germanium-doped photonic crystal fiber.

Findings

Coincidence-to-accidental ratio up to 70

Narrowband photons with 0.2 nm bandwidth

Effective heralding at the fiber end

Abstract

We present a fiber-based source of narrowband heralded single photons in the telecoms C-band. Photon pairs were generated by spontaneous four-wave mixing in photonic crystal fiber (PCF) with a germanium-doped region incorporated into its core for enhanced photosensitivity. A fiber Bragg grating (FBG) with a bandwidth of 0.2 nm and contrast of 17.5 dB was UV-written into the PCF to reflect a sub-nanometre slice of the photon-pair spectrum. This allowed narrowband photons to be heralded at the proximal end of the fiber by detection events after the distal end. We present photon counting data with a coincidence-to-accidental ratio of up to 70. Our source demonstrates a viable route to fiber-integrated narrowband heralded single photon sources suitable for coupling to quantum memories and interfacing heterogeneous qubit types.