Spontaneous parametric down-conversion photon pair generation in small footprint X-cut periodically poled lithium niobate micro-resonator

Spontaneous parametric down-conversion (SPDC) has been crucial for producing non-classical light, such as correlated photon pairs and squeezed states, essential for optical quantum technologies. Recently, thin-film lithium niobate (TFLN)-based devices have enabled high-performance SPDC in on-chip integrated photonics platforms. Here, we developed an X-cut periodically poled lithium niobate (PPLN) racetrack micro-resonator with a compact footprint and demonstrated bright SPDC photon pair generation characterized by distinct resonances and high extraction efficiency. Particularly, we separately assessed the internal and loaded photon pair generation rates, measuring them at 4.525 MHz/μW and 62.73 kHz/μW, respectively. Integrated with maturing electro-/thermo-optic TFLN circuit elements, our platform holds meaningful potential for advancing active quantum photonic applications.