Nanophotonic architectures for classical and quantum optical technology can
boost light-matter interaction via sculpturing the optical modes, forming
cavities and designing long-range propagation channels. Conventional photonic
schemes minimise multiple scattering to realise a miniaturised version of
macroscopic beam-splitters, interferometers and optical cavities for light
propagation and lasing. Here instead, we introduce a nanophotonic network built
from multiple paths and interference, to control and enhance light-matter
interaction via light localisation beyond single scattering. The network is
built from a mesh of subwavelength waveguides, and can sustain localised modes
and mirror-less light trapping stemming from interference over hundreds of
nodes. When optical gain is added, these modes can easily lase, reaching
$\sim$100 pm linewidths. We introduce a graph solution to the Maxwell's
equation which describes light on the network, and predicts lasing action. In
this framework, the network optical modes can be designed via the network
connectivity and topology, and lasing can be tailored and enhanced by the
network shape. Nanophotonic networks pave the way for new laser device
architectures, which can be used for sensitive biosensing and on-chip optical
information processing.