Rubidium-Doped KTiOPO$_4$ Waveguides as a Dual-Type Photon Pair Source

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 degree linearly polarized pump laser into the waveguide, both SPDC processes are concurrently excited: the type-0 SPDC process is facilitated via third-order quasi-phase matching (QPM) utilizing the nonlinear coefficient $d{33}$ , while the 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.