Photonic integrated circuits (PIC) manipulate light at microscopic scales on the surface of a chip. These PICs are used for special functions like optical fiber communication or sensors. A new class of PICs, called programmable photonic circuits, are designed to be generic. Like an electronic computer processor, the functionality can be programmed in software. This new class of optical processors is especially interesting for new applications of light such as quantum computing and artificial intelligence. But unlike electronic processors, programmable photonics need completely new programming algorithms, as they behave more similar to road networks, pipeline distributions or some biological systems. Effectively, these chips are composed of a dense mesh of connected optical waveguides that route the light across the chip. In the GRAPHSPAY project, the NetModel group and the Photonics Research Group at Ghent University join forces to develop these programming strategies for programmable PICs. Using advanced optimization strategies and heuristics, new abstract graph representations will be composed, enabling new algorithms for the routing of light on such a chip, and implementing complex filter functions. This will form the basis to design and fabricate the next generation of programmable photonic chips in silicon, defining new architectures for scaling up the complexity of programmable PICs.