Spatially single mode photon pair source at 800 nm in periodically poled Rubidium exchanged KTP waveguides

Photon pair sources in the visible to NIR wavelength region play a key role in quantum optics. The wavelength range around 800 nm provides an opportunity for using low cost detectors, which makes it highly interesting for practical, large scale quantum applications. Here, we report on the realization of single mode Rubidium (Rb) exchanged waveguides in periodically poled (PP) Potassium Titanyl Phosphate (Rb:KTiOPO₄ or Rb:KTP) for frequency-non-degenerate type II parametric down-conversion pumped at 400 nm and generating pairs of photons at around 800 nm. The source exhibits a nonlinear conversion efficiency of 2.0%/(Wcm²), estimated from SHG measurements. Characterisation of the generated two-photon state confirms nonclassical photon-number correlations, characterized by g^(1,1). The high nonlinear conversion efficiency and low temperature sensitivity make this source a promising candidate for operations in both classical and quantum integrated network applications.