  Inverse design is a powerful tool in wave-physics and in particular in
photonics for compact, high-performance devices. To date, applications have
mostly been limited to linear systems and it has rarely been investigated or
demonstrated in the nonlinear regime. In addition, the "black box" nature of
inverse design techniques has hindered the understanding of optimized
inverse-designed structures. We propose an inverse design method with
interpretable results to enhance the efficiency of on-chip photon generation
rate through nonlinear processes by controlling the effective phase-matching
conditions. We fabricate and characterize a compact, inverse-designed device
using a silicon-on-insulator platform that allows a spontaneous four-wave
mixing process to generate photon pairs at 1.1MHz with a coincidence to
accidental ratio of 162. Our design method accounts for fabrication constraints
and can be used for scalable quantum light sources in large-scale communication
and computing applications.

Optics;Quantum Physics