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Quantum Computing, Communication, and Simulation

Fiber-coupled laser-written PPKTP nonlinear optical waveguides for enhanced pure heralded single-photon and polarization-entangled photon pair generation

Amit Nahor, Michael Schindler, Ziv Gefen, Ori Levin, Anatoly Shukhin

Published Mar 5, 2026• 0 citations
Publisher

Abstract

We report on fiber-coupled nonlinear optical waveguides in periodically poled potassium titanyl phosphate (PPKTP), fabricated via femtosecond laser direct writing for efficient quantum light generation through spontaneous parametric down-conversion. The platform achieves high nonlinear conversion efficiency with fiber integration for compact, alignment-free operation. We discuss applications including enhanced performance for low-efficiency parametric processes and high-visibility polarization-entangled photon pair generation. This work demonstrates laser-written PPKTP waveguides as promising building blocks for in-fiber integrated quantum photonic circuits and quantum technologies.

DOI
10.1117/12.3085389

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We report on fiber-coupled nonlinear optical waveguides in periodically poled potassium titanyl phosphate (PPKTP), fabricated via femtosecond laser direct writing for efficient quantum light generation through spontaneous parametric down-conversion. The platform achieves high nonlinear conversion efficiency with fiber integration for compact, alignment-free operation. We discuss applications including enhanced performance for low-efficiency parametric processes and high-visibility polarization-entangled photon pair generation. This work demonstrates laser-written PPKTP waveguides as promising building blocks for in-fiber integrated quantum photonic circuits and quantum technologies.
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We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
A scheme to generate multi-channel photon pairs is presented,based on a periodically poled(PP) Potassium Titanyl Phosphate(KTP) waveguide via spontaneous parametric downconversion(SPDC).Type-II and type-I phase matching cases with a pulsed and a cw pump laser are discussed respectively.It is analytically shown that several photon pairs could be generated in a single type-II PPKTP waveguide,and the wavelengths of all photon pairs are in the telecom band.In type-I case,several photon pairs can be prepared,but one photon of each pair is not in telecom band.And,a multi-channel photon pairs source could be realized.
A high generation rate photon-pair source using a dual element periodically-poled potassium titanyl phosphate (PP KTP) waveguide is described. The fully integrated photon-pair source consists of a 1064-nm pump diode laser, fiber-coupled to a dual element waveguide within which a pair of 1064-nm photons are up-converted to a single 532-nm photon in the first stage. In the second stage, the 532-nm photon is down-converted to an entangled photon-pair at 800 nm and 1600 nm which are fiber-coupled at the waveguide output. The photon-pair source features a high pair generation rate, a compact power-efficient package, and continuous wave (CW) or pulsed operation. This is a significant step towards the long term goal of developing sources for high-rate Quantum Key Distribution (QKD) to enable Earth-space secure communications. Characterization and test results are presented. Details and preliminary results of a laboratory free space QKD experiment with the B92 protocol are also presented.