A Scalable Quadratic Nonlinear Silicon Photonics Platform With Printable Entangled Photon‐Pair Sources

The integration of second‐order optical nonlinearities into scalable photonic platforms remains a key challenge due to their large sensitivity to fabrication variations. Here, a scalable quadratic nonlinear platform is presented 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 reported lithium niobate on insulator (LNOI) rib waveguides. Reproducible phase‐matching is achieved across the full radius of a commercial 200 mm silicon photonics wafer, leveraging superior CMOS fabrication tolerances. Furthermore, a tuning mechanism is introduced 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, printable photon‐pair sources are realized via spontaneous parametric down‐conversion (SPDC), 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.