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arXiv:2505.14269 · Journal of the Optical Society of America B

Rubidium-doped KTiOPO 4 waveguides as a dual-type photon-pair source

Patrick Hendra, Josué Ricardo León-Torres, Valerio Flavio Gili, Markus Gräfe

Published Jul 24, 2025• 3 citations
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Abstract

We investigate the dual generation of type-0 and type-II spontaneous parametric down conversions (SPDCs) within a single periodically poled rubidium-doped KTiOPO 4 (PPRKTP) waveguide. By coupling a 45° linearly polarized pump laser into the waveguide, both SPDC processes are concurrently excited: type-0 SPDC process is facilitated via third-order quasi-phase matching (QPM) utilizing the nonlinear coefficient d 33 , while type-II SPDC process employs first-order QPM with the nonlinear coefficient d 24 . This dual-SPDC scheme holds potential for applications in quantum communication protocols targeting the telecommunication wavelength.

DOI
10.1364/josab.567775

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We investigate the dual generation of type-0 and type-II spontaneous parametric down conversions (SPDCs) within a single periodically poled rubidium-doped KTiOPO 4 (PPRKTP) waveguide. By coupling a 45° linearly polarized pump laser into the waveguide, both SPDC processes are concurrently excited: type-0 SPDC process is facilitated via third-order quasi-phase matching (QPM) utilizing the nonlinear coefficient d 33 , while type-II SPDC process employs first-order QPM with the nonlinear coefficient d 24 . This dual-SPDC scheme holds potential for applications in quantum communication protocols targeting the telecommunication wavelength.
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Ultrabright sources of entangled photon pairs with high heralding efficiency are an important step in the pursuit of high-bit-rate entanglement-base quantum key distribution, as well as an enabling tool for loss-sensitive quantum optics experiments. Here, we present a robust single-mode fiber-coupled source of polarization-entangled photons around 810 nm with both high brightness and heralding efficiency. Our approach is based on quasi-phase-matched spontaneous parametric downconversion (SPDC) from periodically poled KTiOPO4 in a Sagnac loop configuration. We demonstrate a high degree of two-photon polarization entanglement for single-frequency-pumped type-0 and type-II SPDC, and conduct a conclusive comparison in terms of efficiency and spectral characteristics. In light of applications outside a laboratory environment, we evaluate the feasibility of pumping nonlinear crystals with free-running laser diodes.
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.
We demonstrate a bright, bandwidth-tunable, quasi-phase-matched single-waveguide source generating photon pairs near 900 nm and 1300 nm. Two-photon coincidence spectra are measured at a range of operating temperatures of a periodically-poled KTiOPO(4) (PPKTP) waveguide, which supports both type-0 and type-II spontaneous parametric down-conversion. We map out relative contributions of two-photon to one-photon fluorescence for a range of operating parameters. Such a versatile device is highly promising for future chip-scale quantum information processing.