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arXiv:0904.4577 · Applied Physics Letters

Experimental characterization of three-wave mixing in a multimode nonlinear KTiOPO4 waveguide

Michał Karpiński, Czesław Radzewicz, Konrad Banaszek

Published May 4, 2009• 38 citations
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Abstract

We report experimental determination of the phase-matching function for type-II three-wave mixing in a periodically poled KTiOPO4 waveguide in the 792–815 nm spectral region. The measurement was performed by sum-frequency generation of spectrally tuned fundamental components. Strong dependence of the observed signal on the excited spatial modes in the waveguide has been observed and fully interpreted. These results indicate a route to employ the waveguide for spontaneous parametric down-conversion producing photon pairs in well-defined spatial modes.

DOI
10.1063/1.3132086

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We report experimental determination of the phase-matching function for type-II three-wave mixing in a periodically poled KTiOPO4 waveguide in the 792–815 nm spectral region. The measurement was performed by sum-frequency generation of spectrally tuned fundamental components. Strong dependence of the observed signal on the excited spatial modes in the waveguide has been observed and fully interpreted. These results indicate a route to employ the waveguide for spontaneous parametric down-conversion producing photon pairs in well-defined spatial modes.
We have demonstrated recently the feasibility of controlling the spatial characteristics of photon pairs produced in a multimode waveguide through intermodal dispersion. Here we present experimental methods to characterise the spatial purity of the generated photons. Our sample was a 1 mm long periodically poled potassium titanyl phosphate (PPKTP) multimode waveguide suitable for type-II down-conversion producing photons in the 800 nm wavelength region. The phase matching function for these waveguides was characterized using the sum-frequency generation process, and the nonlinear process was carefully arranged to generate photons in fundamental spatial modes.
We present experimental realization of type-II spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate (KTiOPO4) nonlinear waveguide. We demonstrate that by careful exploitation of intermodal dispersion in the waveguide it is feasible to produce photon pairs in well defined transverse modes without any additional spatial filtering at the output. Spatial characteristics is verified by measurements of the M2 beam quality factors. We also prepared a postselected polarization-entangled two-photon state shown to violate Bell’s inequality. Similar techniques based on intermodal dispersion can be used to generate spatial entanglement and hyperentanglement.
We report generation of near-infrared photon pairs in fundamental spatial modes via type-II spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate (KTiOPO(4)) nonlinear waveguide supporting multiple transverse modes. This demonstrates experimentally a versatile scheme for controlling the spatial characteristics of the produced nonclassical light based on exploitation of intermodal dispersion. The down-converted photons are characterized by the measurement of the beam quality factors in the heralded regime.
Under extended phase-matching conditions, the first frequency derivative of the wave-vector mismatch is zero and the phase-matching bandwidth is greatly increased. We present extensive three-wave mixing measurements of the wave-vector mismatch and obtain improved Sellmeier equations for KTiOPO4. We observed a type-II extended phase-matching bandwidth of 100 nm for second-harmonic generation in periodically poled KTiOPO4, centered at the fundamental wavelength of 1584 nm. Applications in quantum entanglement and frequency metrology are discussed.
We present a scheme for generation and characterization of entangled spatial qubits based on type-II spontaneous parametric down-conversion (SPDC) in a periodically poled titanyl phosphate (PPKTP) multimode nonlinear waveguide [1]. Our scheme exploits intermodal dispersion which has been hitherto successfully employed to produce spatially pure SPDC photon pairs from a multimode waveguide without spatial filtering [2]. Production of discrete entanglement relies on driving simultaneously two SPDC processes that involve different combinations of transverse spatial modes for which phase matching bandwidths significantly overlap. We propose a procedure for experimental identification of the spatial qubit subspace based on a scan of the spatial Wigner function via the displaced parity measurement using an inverting Sagnac interferometer and photon counting. We numerically verified the robustness of the mode reconstruction procedure against experimental imperfections. We also propose an experimental method for detecting spatial entanglement in the position-wave vector phase space. Numerical simulations indicate that waveguide parameters required for experimental demonstrations are compatible with current manufacturing capabilities. Using simulated mode profiles we calculate the maximum attainable Clauser-Horne- Shimony-Holt combination value reaching 2.12, which clearly violates the classical limit and confirms the feasibility of observing non-classical features of the generated state. [1] M. Jachura et al. Physical Review A, 95, 032322 (2017). [2] M. Jachura, M. Karpiński, C. Radzewicz, K. Banaszek, Optics Express, 22, 8624-8632 (2014).