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arXiv:2309.00936

Fabrication of low-loss III-V Bragg-reflection waveguides for parametric down-conversion

Hannah Thiel, Marita Wagner, Bianca Nardi, Schlager, Alexander, Robert J. Chapman, Stefan Frick, Holger Suchomel, Martin Kamp, Sven Höfling, Christian Schneider, Gregor Weihs

Published Sep 2, 2023• 0 citations
arXivHTMLPDF

Abstract

Entangled photon pairs are an important resource for quantum cryptography schemes that go beyond point-to-point communication. Semiconductor Bragg-reflection waveguides are a promising photon-pair source due to mature fabrication, integrability, large transparency window in the telecom wavelength range, integration capabilities for electro-optical devices as well as a high second-order nonlinear coefficient. To increase performance we improved the fabrication of Bragg-reflection waveguides by employing fixed-beam-moving-stage optical lithography, low pressure and low chlorine concentration etching, and resist reflow. The reduction in sidewall roughness yields a low optical loss coefficient for telecom wavelength light of alpha_reflow = 0.08(6)mm^(-1). Owing to the decreased losses, we achieved a photon pair production rate of 8800(300)(mW*s*mm)^(-1) which is 15-fold higher than in previous samples.

DOI
10.48550/arxiv.2309.00936

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Entangled photon pairs are an important resource for quantum cryptography schemes that go beyond point-to-point communication. Semiconductor Bragg-reflection waveguides are a promising photon-pair source due to mature fabrication, integrability, large transparency window in the telecom wavelength range, integration capabilities for electro-optical devices as well as a high second-order nonlinear coefficient. To increase performance we improved the fabrication of Bragg-reflection waveguides by employing fixed-beam-moving-stage optical lithography, low pressure and low chlorine concentration etching, and resist reflow. The reduction in sidewall roughness yields a low optical loss coefficient for telecom wavelength light of alpha_reflow = 0.08(6)mm^(-1). Owing to the decreased losses, we achieved a photon pair production rate of 8800(300)(mWsmm)^(-1) which is 15-fold higher than in previous samples.
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Photon pairs generated via spontaneous parametric down-conversion (SPDC) are a crucial resource in the development of quantum protocols and quantum technologies, due to the strong correlation between two photons of the same pair. Efficient pair generation is necessary for protocols that require high signal-to-noise ratios when embedded in a lossy and noisy environment. Nonlinear waveguides are well-established platforms for photon pair generation. However, scattering and material absorption can inhibit the efficiency of the pair generation and require high pump powers. Here, we present an aluminum gallium arsenide Bragg-reflection waveguide, fabricated following an optimized recipe, that shows a record brightness compared to other samples with the same structure. When pumped with a sub-mW continuous wave laser, our waveguide generates photon pairs at a rate of340 kHz ⋅ mW−1340\,\rm {kHz}\,\cdot \, mW^{-1}340kHz⋅mW−1, and a spectral width of100 nm100\,\rm {nm}100nmin the telecom band. As a direct application, we investigate the operation of our waveguide in quantum rangefinding, a quantum protocol that employs time correlations between photon pairs to measure objects' distances, while camouflaging within background. This protocol was implemented with nonlinear crystals engineered for broadband emission. Supported by simulations of signal-to-noise ratio, we introduce our low-loss and broadband waveguide as a novel platform for telecom quantum rangefinding, robust against loss and noise.
Entangled photons are important for testing foundations of quantum physics and are at the heart of quantum technology. Integrated photonics has overwhelming dominance in terms of density and performance, making it a promise route for scalable quantum information processing. AlGaAs-based materials having large second-order non-linearities, direct bandgap and strong electro-optical effect can offer distinct advantages in quantum light source. Here we report a non-ideal quarter-wavelength Bragg reflection waveguide for generating three types of spontaneous parametric down-conversion processes. A general solution to the dispersion equation is derived and employed for designing high efficiency devices by taking into account the influence of core layer aluminium concentration. We further design and fabricate a Bragg reflection waveguide sample based on the analysis, and experimentally characterize its phase matching types and spectral brightness. Our work paves the path for the development of portable quantum light sources.
We demonstrate efficient photon pair generation for quantum communication using an all-semiconductor approach. In an AlGaAs Bragg-reflection waveguide we employ spontaneous parametric down-conversion to produce photon pairs at telecommunication wavelengths. The various phase-matching solutions present in our device can be used to create timebin or polarization entanglement. This approach can to lead to a fully integrated photon pair source with the pump laser, active and passive optical devices all on a single semiconductor chip.