Lightmatter

Founded in 2017 as an MIT spinout by Nicholas Harris and colleagues. Instead of transistors, the company's silicon performs matrix multiplies optically — light passing through photonic interferometers — which in theory offers computation near the speed of light with little heat. Its Passage product is an optical interconnect that lets hundreds of chips talk to each other without the electrical bottleneck that throttles large AI clusters.

Photonic computing was long a lab curiosity. Lightmatter is among the first to aim it squarely at transformer training, and was valued in 2024 at several billion dollars. The hard part isn't computing with light, but converting between optics and electronics cheaply enough for the gain to survive.