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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Third-order nonlinear optics in KTP ridge waveguides

Augustin Vernay, Véronique Boutou, C. Félix, David Jegouso, Florent Bassignot, Mathieu Chauvet, Benoı̂t Boulanger

Published Jun 21, 2021• 0 citations
Publisher

Abstract

Ridges waveguides carved in bulk nonlinear crystals such as LiNbO 3 [1] or KTiOPO 4 (KTP) [2] are a good alternative to reach a strong confinement of electromagnetic waves with large second-order or third-order non-linearity. We report here on our most recent experiments where we show the possibility to shape the birefringence phase-matching (BPM) conditions for direct Third-Harmonic Generation (THG: ω + ω + ω → 3ω) in micrometric KTP ridge waveguides by acting on their transverse dimensions. This study is the preliminary step for designing quantum optical experiments based on Triple Photons Generation (TPG: 3ω → ω + ω + ω) that is the reverse process of THG, thus exhibiting the same BPM conditions.

DOI
10.1109/cleo/europe-eqec52157.2021.9542186

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Ridges waveguides carved in bulk nonlinear crystals such as LiNbO 3 [1] or KTiOPO 4 (KTP) [2] are a good alternative to reach a strong confinement of electromagnetic waves with large second-order or third-order non-linearity. We report here on our most recent experiments where we show the possibility to shape the birefringence phase-matching (BPM) conditions for direct Third-Harmonic Generation (THG: ω + ω + ω → 3ω) in micrometric KTP ridge waveguides by acting on their transverse dimensions. This study is the preliminary step for designing quantum optical experiments based on Triple Photons Generation (TPG: 3ω → ω + ω + ω) that is the reverse process of THG, thus exhibiting the same BPM conditions.
Demonstrating quantum properties of triple photons generated by χ3\chi ^3χ3 processes
Abstract Triple-photon generation (TPG) is based on a third-order nonlinear optical interaction, which is the most direct way to produce pure quantum three-photon states. These states can exhibit three-body quantum correlations, and their statistics cannot be reproduced by any Gaussian statistics of coherent sources or optical parametric twin-photon generator, making them potentially useful for quantum information processing tasks such as quantum state distillation, quantum error-correction and universal quantum computing. Furthermore, the generation of entangled photon pairs heralded by the detection of a third photon can be used in advanced quantum communication protocols. We made the first experimental demonstration of TPG in 2004 using a bi-stimulation scheme in a bulk KTP crystal, followed by the quantum theory. The new challenges are now to achieve a spontaneous TPG and the corresponding quantum experiments and protocols using oriented ridge KTP waveguides, which ensures both birefringence phase-matching and light confinement. The waveguides are cut by a precision dicing saw. We recently performed their characterization using third-harmonic generation measurements, which showed their good quality. A rate of about 5 triplets per second is expected when pumping a 5-cm-long waveguide with a 5-W 532 nm beam in the CW regime. Such a spontaneous TPG exhibits low rate of triple photons, which makes the certification of quantum features hard. In this article, we review our theoretical and experimental work on TPG and the associated quantum modeling. We also develop theoretical tools for the certification of quantum features of spontaneous triple-photon states. Graphic abstract
Summary form only given. The experiments on quantum optical correlations partly depend on efficient optical frequency conversion: in the case of quadratic interactions, a second-harmonic generation efficiency of few percents is required to observe the correlations. Such conversion efficiencies are very difficult to reach for cubic processes because the associated /spl chi//sup (3)/ coefficients are weak. Consequently, the specific quantum optical effects linked to cubic parametric processes have never been studied. In the present work, we report the first experiments of efficient third harmonic generation (THG) phase-matched in KTiOPO/sub 4/ (KTP).
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In a photonic nanowire the strong optical confinement allows for the phase matching of nonlinear interactions that would not normally be phase matched, while the large longitudinal component of the electric field serves to further enhance the effective nonlinearity. Thus such waveguides are good choices for studying nonlinear effects such as third harmonic generation. In this paper we analyse third harmonic generation analytically and present the criteria for optimal harmonic generation. In addition we analyse the inverse process of 1/3 harmonic generation and show that efficient parametric amplifiers can be made which would be a high brightness source of entangled photons for producing GHZ states.