Harnessing Light: Free Space Optical and Visible Light Communication for Next-Generation Outdoor Networks

As the radio-frequency spectrum below 10 GHz approaches exhaustion, the demands of next-generation (6G) networks call for a fundamentally new physical layer capable of terabit-class links, sub-millisecond latency, and connection densities exceeding 100 billion devices. This work examines Free Space Optical communication (FSO) and Visible Light Communication (VLC) as two complementary halves of a single outdoor optical architecture, partitioned by distance. FSO provides directed, kilometre-scale backbone links between fixed nodes, while VLC delivers broad, metre-scale access from existing lighting infrastructure to mobile users; the two meet at a shared handoff node such as a streetlight. Following each technology through its transmitter, channel, modulation, and receiver design, the presentation highlights the physical constraints that distinguish them: the multiplicative, turbulence-dominated FSO channel with its coherent-detection and beam-steering requirements, and the intensity-modulated, bandwidth-limited VLC channel shaped by broadcast geometry, sunlight interference, and mobility-driven handover. It then shows how machine learning serves as a unifying intelligence layer that shifts both systems from reactive to proactive operation. Together, FSO and VLC are presented not as laboratory curiosities but as a deployable, standards-backed foundation for the outdoor optical layer of 6G.