Much of the AI conversation centers on chips, but there is a quieter bottleneck forming inside data centers, and it is all about how those chips talk to one another. As artificial intelligence clusters swell to tens and even hundreds of thousands of processors, the humble copper wiring that has connected computers for decades is running out of room.
The fix is silicon photonics, and investment in it is ramping quickly. Two companies look especially well placed to benefit.
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Why copper is hitting a wall in AI clusters
To train a modern AI model, thousands of chips must act like one enormous brain, constantly shuttling vast amounts of data among them. The more chips you add, the more traffic flows across the wires linking them, and that is where copper starts to break down. At the blistering signaling speeds these systems now demand, a passive copper cable can only carry a clean signal for less than a meter before it degrades. Push it further, and you have to pump in more and more electrical power just to keep the data intact, which generates heat and drives up the energy bill.
In a small server, that was never a problem. In a warehouse-sized cluster stretching across rows of racks, it becomes a hard physical ceiling that engineers now call the copper wall. When your bottleneck is measured in centimeters and watts, you cannot simply add more copper and hope for the best.
How silicon photonics breaks through
Silicon photonics solves the problem by sending information as pulses of light through fiber instead of electrons through metal. Light travels farther, carries far more data, and uses less power over distance, which is exactly what a giant AI cluster needs. The cutting edge of this shift is co-packaged optics, where the optical components are built right next to the switch chip rather than plugged in at the edge of the box. That tight integration slashes the power lost in translation and packs far more bandwidth into the same space.
Copper is not disappearing, but its job is shrinking to the shortest hops inside a package, while optics take over everything from board to rack scale. The money following this transition is real. The optical interconnect market for AI data centers is expected to grow several times over this decade, and the broader optical transceiver market is projected to jump about 60% in a single year to roughly $26 billion in 2026.
2 AI stocks that stand to win
The clearest beneficiaries are the companies that actually make the lasers, transceivers, and photonic components that this shift requires. Coherent (NYSE: COHR) is a global leader in the optical technology feeding AI data centers, and demand for its datacenter transceivers has surged as cloud giants build out. It has also deepened a partnership with Nvidia to pioneer next-generation silicon photonics, putting it close to the center of the build-out.
Lumentum (NASDAQ: LITE) is the other pure-play worth watching. It supplies the lasers and optical components that power data center networking, and it has been expanding capacity to meet demand that’s been outpacing supply. As roadmaps push toward lower-power optics and tighter silicon photonics integration, Lumentum sits right in the flow of that spending.
These are not sleepy blue chips. Optical component makers are cyclical and lumpy, with their fortunes closely tied to a handful of huge customers whose orders can swing hard from quarter to quarter. Both stocks have run up on AI enthusiasm, so valuations leave little room for disappointment, and competition in optics is fierce.
The takeaway for investors
The move from copper to light is not a maybe; it is a physical necessity as AI clusters keep growing, and silicon photonics is how the industry gets there. Coherent and Lumentum are two focused ways to invest in that transition. I would treat them as higher-risk, higher-reward plays on a durable trend, sizing positions with the optical business’s volatility firmly in mind.
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Micah Zimmerman has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Coherent, Lumentum, and Nvidia. The Motley Fool has a disclosure policy.
