A scalable quadratic nonlinear silicon photonics platform with printable entangled photon-pair sources

Abstract: The integration of second-order optical nonlinearities into scalable photonic platforms remains a key challenge due to their large sensitivity to fabrication variations. Here, we present a scalable quadratic nonlinear platform that harnesses the maturity and scalability of existing CMOS processes by heterogeneously integrating periodically poled lithium niobate (PPLN) onto a silicon photonics platform. A generic PPLN design enables frequency conversion on two distinct waveguide geometries with efficiencies comparable to LNOI rib waveguides. We achieve reproducible phase-matching across the full radius of a commercial 200 mm silicon photonics wafer, leveraging superior CMOS fabrication tolerances. Furthermore, we introduce a tuning mechanism for both blue- and red-shifting of the operating wavelength, fully compensating fabrication-induced offsets. This enables deterministic phase-matching over an entire wafer and yields a strategy for wafer-scale phase-matched quadratic nonlinearities. Finally, we realize printable photon-pair sources via spontaneous parametric down-conversion, highlighting the platform's potential for large-scale quantum optical circuits. These results pave the way for wafer-scale integration of second-order optical nonlinearities in large photonic systems.