High-performance photon-pair source using a two-photon-polymerized strip-loaded lithium niobate waveguide

Integrated photon-pair sources, providing scalability solutions, are crucial for large-scale realizations of quantum photonic technologies. Their traditional fabrication techniques, such as etching, are often complex, require long development cycles, and are resource inefficient in case of fabrication imperfections or failures. The two-photon polymerization (2PP) technique can offer a rapid, efficient, and reproducible alternative for the fabrication of integrated photonic devices. Here, we demonstrate an integrated photon-pair source based on a 2PP-defined strip-loaded waveguide on a periodically poled thin-film lithium niobate (TFLN) platform. The device generates photon pairs through type-II spontaneous parametric down-conversion (SPDC), employing first-order quasi-phase matching (QPM) with TM-polarized excitation light. The device achieves an on-chip pair generation rate of 4.357 MHz and a coincidence-to-accidental ratio (CAR) of ∼404. To prove the flexibility and versatility of the fabrication technique, the waveguides were erased from the LN substrate and reprinted, reaching comparable performance. This work demonstrates the potential of 2PP as a rapid production technique for high-performance integrated photon-pair sources, offering a practical solution to the limitations of traditional fabrication techniques and showcasing both reproducibility of the fabrication and the reusability of the substrate.