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Frontiers in Photonics

Generation of counterpropagating and spectrally uncorrelated photon-pair states by spontaneous four-wave mixing in photonic crystal waveguides

Sina Saravi, Yu Xin Zhang, Xiao Chen, Mina Afsharnia, Frank Setzpfandt, Thomas Pertsch

Published Aug 19, 2022• 1 citation
Publisher

Abstract

In this work, we propose and theoretically analyze a new scheme for generation of counterpropagating photon pairs in photonic crystal waveguides through the process of spontaneous four-wave mixing. Using the fundamental properties of periodic Bloch modes in a standard photonic crystal waveguide, we demonstrate how modal phase-matching can be reached between forward-propagating pump modes and counterpropagating signal and idler modes, for generation of degenerate and non-degenerate photon pairs. We then show how this scheme can be used for generation of photon pairs that are nearly uncorrelated in the spectral degree of freedom. Such a source will be highly interesting as a heralded source of single photons, especially as the spectrally separable signal and idler photons are also spatially separated directly at the source. We conduct our investigation based on a design in silicon, yet our design concept is general and can in principle be applied to any nanostructured material platform.

DOI
10.3389/fphot.2022.953105

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In this work, we propose and theoretically analyze a new scheme for generation of counterpropagating photon pairs in photonic crystal waveguides through the process of spontaneous four-wave mixing. Using the fundamental properties of periodic Bloch modes in a standard photonic crystal waveguide, we demonstrate how modal phase-matching can be reached between forward-propagating pump modes and counterpropagating signal and idler modes, for generation of degenerate and non-degenerate photon pairs. We then show how this scheme can be used for generation of photon pairs that are nearly uncorrelated in the spectral degree of freedom. Such a source will be highly interesting as a heralded source of single photons, especially as the spectrally separable signal and idler photons are also spatially separated directly at the source. We conduct our investigation based on a design in silicon, yet our design concept is general and can in principle be applied to any nanostructured material platform.
We demonstrate numerically that photonic crystal slab waveguides can generate spectrally unentangled biphoton states, highly desired for heralding of single photons. We achieve this by modally phase matching a counterpropagating spontaneous parametric down-conversion process, in a fully integrated scheme and without the need for periodic poling. Such a configuration is an ideal integrated source of heralded single photons, as it spatially separates the photons of a pair at the source without any extra components, while allowing for generation of spectrally narrow photons on a very short length scale.
In this thesis, I overcome the challenges and fill the gaps in knowledge for the design and analysis of photonic crystal slab waveguides (PCSWs) as spontaneous parametric down-conversion (SPDC) sources of photon-pairs, as well as to investigate their potential for engineering the properties of the photon-pair quantum state. I have developed the required formalism for analyzing both the quantum process of SPDC and its classical counterpart of second-harmonic generation (SHG). In studying SHG, I verified my formalism through comparing its results with direct nonlinear simulations. In these formulations, special attention was given to treating lossy modes, as they prove to be an inherent part of the SPDC designs in PCSWs. Moreover, I have found a practical set of PCSW designs, phase-matched for three-wave-mixing processes, while demonstrating that PCSWs can offer a strong control over the phase-matching configuration. This includes reaching phase-matching between modes of different propagation directions, reaching simultaneous phase-matching between multiple processes, and controlling the group velocity of the modes at the point of phase-matching. These capabilities proved to be the key to discovering the unique strength of PCSWs for the SPDC application. Through the use of various phase-matching configurations, I showed how compact SPDC sources can be designed using PCSWs that are capable of creating entanglement and tuning its extent in different degrees of freedom, with specific examples for path and spectral degrees of entanglement, all in a fully integrated way and directly at the generation step. This work also includes my experimental results on characterizing lithium niobate nanostructured ridge waveguides, demonstrating phase-matched SHG. Finally, I propose the concept of atom-mediated SPDC, for interfacing a single-emitter source with a photon-pair source, relying on the bandgap evanescent modes of a periodic waveguide.
We present a theoretical study of the generation of photon pairs by spontaneous four‐wave mixing (SFWM) in photonic crystal optical fiber. We show that it is possible to engineer two‐photon states with specific spectral entanglement properties suitable for quantum information processing applications. In this work, we concentrate on states exhibiting no spectral correlations in the two‐photon component of the state, which allow heralding of pure‐state, single‐photon wavepackets without the need for spectral post filtering. We present specific source designs which permit both symmetric and asymmetric factorable states, with signal and idler photons in the visible, and sufficiently removed from the pump to ensure suppression of background photons produced by spontaneous Raman scattering.
We study the generation of photon pairs by spontaneous four-wave mixing (SFWM) in photonic crystal optical fibers. We show that it is possible to engineer two-photon states with specific spectral entanglement properties suitable for quantum information processing applica- tions. In this work, we concentrate on inner-loop phasematching, for which signal and idler photons can be generated at a small spectral separation from the pump, while sufficiently removed from the pump to ensure the absence of background photons produced by spontaneous Raman scattering. We present specific source designs which permit both symmetric and asymmetric factorable states, which allow herald- ing of pure-state, single-photon wavepackets without the need for spectral post-filtering. Additionally, we present numerical results for the conversion efficiency, where we compare sources based on inner- and outer-loop phasematching.