  Photonic networks are considered a promising substrate for high-performance
future computing systems. Compared to electronics, photonics has significant
advantages for a fully parallel implementation of networks. A promising
approach for parallel large-scale photonic networks is realizing the
connections using diffraction. Here, we characterize the scalability of such
diffractive coupling in great detail. Based on experiments, analytically
obtained bounds and numerical simulations considering real-world optical
imaging setups, we find that the concept in principle enables networks hosting
over a million optical emitters. This would be a breakthrough in multiple
areas, illustrating a clear path toward future, large scale photonic networks.
