Heralded telecom single photons from a visible–telecom pair source on a hybrid PPKTP–PIC platform

We present a heralded photon-pair source using periodically poled potassium titanyl phosphate (PPKTP) waveguides coupled with photonic integrated circuits (PICs). The PPKTP generates correlated visible–telecom photon pairs, processed by the dual-band silicon and silicon nitride PIC. Heralding at visible wavelengths removes the need for large superconducting nanowire single-photon detectors (SNSPDs). Silicon Mach–Zehnder interferometers (MZIs) on the PIC modulate the telecom single photons and also serve as pump-rejection filters. We demonstrate an insertion loss of 2.37 ± 1.03 dB (4.46 ± 1.32 dB) at the visible (telecom) wavelength between the PPKTP waveguides and PIC edge couplers, and an on-chip pump suppression of 92.5 ± 2.5 dB. This platform will enable remote quantum nodes to securely communicate over telecom fiber-optic networks.