Interpretable inverse-designed cavity for nonlinear photon pair generation on-chip

Inverse design has become a powerful tool in photonics for creating compact, high-performance devices. However, its application has been mostly limited to linear systems, with minimal exploration in nonlinear regimes. Additionally, the ”black box” nature of these techniques limits understanding of the optimized structures. Here, We introduce an inverse design approach to enhance on-chip photon pair generation efficiency using the opensource package EMopt. Our method employs a multi-frequency co-optimization strategy and calculates gradients via the adjoint method. Efficiency improvements result from field intensification in high-quality factor triply-resonant cavity resonances and better phase-matching conditions. We validate our method by fabricating and characterizing an optimized device that efficiently generates photon pairs, adhering to fabrication constraints and suitable for scalable quantum light sources in large-scale computing and communication applications. The design’s shape can be explained using effective potential analysis. This optimization technique can extend to other nonlinear processes for compact on-chip frequency-mixing devices.