Lightmatter, a company building computer chips that process information with light, has raised a $400 million Series D at a $4.4 billion valuation, highlighting investors’ appetite for novel solutions to AI’s computational demands. T. Rowe Price Associates led the round with additional backing from previous investors GV and Fidelity. The raise continues Boston-based Lightmatter’s remarkable growth. Founded in 2017, the company has raised $709 million in the past 18 months. With its Series D, Lightmatter has nearly quadrupled its previous valuation of $1.2 billion in a $155 million Series C-2 that closed in December 2023. In May 2023, it raised...