SAN JOSE, Calif.—The copper cables under the world’s data centers are running out of headroom, and a startup few people had heard of a year ago just raised a large pile of money to replace them. Lumilens, which makes optical interconnects for the inside of AI data centers, has raised more than $700 million at a valuation of $5.5 billion, according to people familiar with the matter. The round, first reported by The Wall Street Journal, is a bet that the next bottleneck in the AI buildout is not chips but the connections between them.
The problem Lumilens is trying to solve is physical. As AI clusters grow, the amount of data moving between accelerators grows even faster, and the copper cables that carry most of that traffic are hitting limits on bandwidth, power and physical space. Copper works well for short distances, but its capacity is finite, and the racks that hold AI accelerators are becoming too dense for the cables that connect them. Optical interconnects, which use light rather than electricity, offer far more bandwidth per cable and consume less power, but they have historically been expensive and complex to deploy at scale. Lumilens’s pitch is that it has solved the cost and packaging problems that kept optics out of the data center’s inner workings.
The timing is driven by the AI buildout’s scale. Training clusters now connect tens of thousands of accelerators, and the networking fabric that links them can cost as much as the chips themselves. The largest models require more interconnect bandwidth with each generation, and data center operators are spending billions on networking gear that will be obsolete within a few years. The market for the components that move data inside the data center has become one of the fastest-growing segments of the AI economy, and startups and incumbents alike are racing to capture it.
The precedent for Lumilens’s valuation is Marvell’s acquisition of Celestial AI, a deal that valued an optical interconnect startup at a price that made the sector’s investors sit up. That acquisition signaled that the biggest chip companies see interconnect technology as strategically essential, and it has drawn capital into the field. Lumilens’s $5.5 billion valuation, achieved without the kind of revenue that would justify it in a traditional market, is a measure of how much money is chasing the same thesis: that the data center’s internal plumbing is the next thing to be rebuilt.
The technical details matter. Lumilens’s products are designed to replace the copper cables that connect accelerators within racks and between racks, using light to move data at speeds that copper cannot match. The company says its technology can be deployed without redesigning the data center, a claim that matters to operators who are already struggling to build AI infrastructure fast enough. The products are aimed at the highest-volume part of the market, the short-distance connections where the bandwidth crunch is most acute.
The competitive field is crowded and getting more so. The traditional optical networking companies—Coherent, Lumentum and others—have deep expertise but have focused on longer-distance connections, and the incumbents are now pushing into the data center market as well. Nvidia, the largest buyer of interconnect hardware, has its own optical plans, and the company’s purchasing decisions will shape the market. Lumilens’s hope is that its technology is good enough to win orders from the hyperscalers who are building the biggest clusters, and that the valuation becomes the platform for the next round of growth.
The round’s size reflects the capital intensity of the business. Optical interconnect is a hardware business, and winning in it requires manufacturing capacity, engineering talent and the patience to qualify products with customers who are slow to adopt new technology. The more than $700 million raised will fund production, product development and the sales effort required to break into data centers where incumbents have decades of relationships. The company has said it is already shipping products to early customers, though it has not disclosed who they are.
The strategic logic is easy to state and hard to execute. The AI data center of the future will need dramatically more interconnect bandwidth, and the technology that delivers it will be worth billions. Whether that technology comes from a startup like Lumilens or from the incumbents and chipmakers is the question the round is betting on. Investors have concluded that the answer is not yet decided, and that a well-funded challenger with a differentiated product has a chance. The $5.5 billion valuation is the price of that uncertainty, and the more than $700 million in fresh capital is the fuel for the attempt.
The implications for the AI buildout are straightforward. If optical interconnects replace copper inside the data center, the cost of AI infrastructure will fall, and the scale of what can be built will rise. If the transition is delayed, the industry will keep spending on copper cables that are increasingly inadequate. The outcome will be decided by engineering, by customer qualification and by the billions of dollars now flowing into the sector. Lumilens is one of the largest single bets on the outcome, and its next few quarters will show whether the thesis holds.
