Coherent Faces a Cash Flow Reckoning as Marvell Consolidates AI Optics

The market gave Coherent an open-field scarcity bid on Monday morning, and then took it back before lunch. When Marvell agreed to buy rival Lumentum for $115 billion in stock, optical networking capacity suddenly carried a massive public price tag. Coherent jumped roughly 2% at the open and touched a 4% gain by late morning. Investors were pricing the transaction's real consequence: it leaves Coherent as the last large independent merchant supplier of artificial intelligence laser optics. Yet the euphoria evaporated within two hours. By midday, shares round-tripped into the red, trading roughly 1% below Friday's close as enthusiasm collided with balance-sheet reality.

To understand why optical capacity commands an eleven-figure valuation, look at the physical bottleneck inside artificial intelligence data centers. Thousands of processors must swap data at near-instant speeds. Copper wires run out of road here because electrical resistance generates crippling heat and signal decay.

Coherent manufactures the light engines that solve this problem. The company grows microscopic indium phosphide lasers on semiconductor wafers and packages them into high-speed optical transceivers. These parts convert electrical voltage into beams of light, shooting data between chips at up to 1.6 terabits per second. If AI processors are jet engines, Coherent builds the fuel lines.

Only a handful of companies on earth can manufacture these photonics chips at volume, which is why the sector is consolidating.

In March, Nvidia struck matching $2 billion non-exclusive equity deals with both Coherent and Lumentum, pairing capital with massive purchase commitments to guarantee dual-sourced optics. Marvell's buyout collapses that balance into a single independent supplier. Lumentum's optical capacity is already completely sold out into early 2029. Any chipmaker or cloud giant wanting advanced optics without buying from a direct competitor in Marvell now has exactly one phone call to make.

Yet public investors spent autumn dumping Coherent. Shares fell roughly 27% in October and sit roughly half off their June highs, even as earnings estimates moved higher.

The disconnect points directly to what must happen for this equity to re-rate: cash flow needs to catch up to demand. The business generated $7.1 billion in revenue across fiscal 2026, but it burned roughly $1 billion in free cash flow. Building foundries cost $1.1 billion in capital spending against just $80 million in operating cash. Trading near six times trailing sales and roughly 22 times fiscal 2027 earnings, the stock cannot expand its multiple until that spending crests. To prove the market is overshooting, management must lift gross margins toward its 42% target as six-inch wafers ramp. It also has to fund the promised $3 billion quarterly revenue run rate without blowing out capital intensity.

A dedicated short seller would argue that Coherent is trapped on an expensive capital treadmill. Management promises an eighteen-month payback on data center capacity, but that remains an assertion while free cash flow bleeds red and a crucial six-inch fab in Zurich stays dark until calendar 2027. If Wednesday's fiscal first-quarter report prints capex over $600 million alongside operating cash flow under $150 million, the bears will claim their prize. Structural integration worsens the threat. Marvell can bundle custom compute silicon with in-house optics at prices merchant suppliers cannot match. Add heavy customer concentration—two buyers each drive over 10% of revenue, with Nvidia doubling as a customer, shareholder, and contract counterparty—and Coherent looks dangerously tethered to a single ecosystem's wallet.

Still, the operational engine has not cracked. Coherent posted two consecutive earnings beats, with data center revenue up roughly 66% year-over-year in the June quarter. The October slide stemmed from a broader sector de-rating rather than an execution stumble. Its legacy industrial laser arm is shrinking, down nearly 16% year-over-year, but data center connectivity now generates nearly four-fifths of the enterprise.

What we are watching after Wednesday's closing bell is the second-quarter revenue guidance. Management promised a three-billion-dollar quarter before the end of fiscal 2027, which requires step-ups toward $2.7 billion in short order. Analysts will also press management on how a combined Marvell and Lumentum changes the customer map, and whether the merchant model can survive as the biggest AI silicon vendors internalize optics. Demand for optical bandwidth is guaranteed, but the stock only works if the lasers generate cash faster than the cleanrooms consume it.

Disclosure: The Signal holds no position in Coherent Corp (COHR). Positions may change. This is not financial advice.