Coherent's 12% slide was not a vote against AI optics. It was a warning about what happens when a stock priced for perfection reaches earnings week.
Coherent stock fell 12% to $333.83 on August 10, its sharpest one-day drop in months. You don't need a conspiracy theory to explain it. The company was trading near 160 times trailing earnings heading into its August 12 results. No room there for a weak quarter, or a cautious sentence on the call.
Lumentum, its closest rival in building optical components used inside AI data centers, fell with it. The stock dropped 7% to $830.05 the same day. Applied Optoelectronics, a smaller name in the same trade, dropped as much as 12.8%. MarketWatch noted that the Roundhill Photonics and Optics ETF fell 7.4% on August 10, with Coherent leading the weakness in the group.
All three stocks had already done the hard running. Coherent was up 105% for the year before the slide. Lumentum had gained 142%. That kind of move turns a stock into its own trigger for profit-taking. Sell before the number lands, not after. That's the trade.
Lumentum made the selloff look too nervous #
Lumentum reported fiscal fourth-quarter results after the close on August 11, and the numbers were better than the market had been bracing for. Revenue came in at $1.01 billion, up 109% from a year earlier, ahead of the roughly $988 million analysts had expected, according to reports from MarketWatch and Investor's Business Daily. Adjusted earnings of $3.23 a share also beat estimates near $2.97 to $2.99.
The margin line mattered too. Lumentum reported non-GAAP gross margin of 50.4%, and the company guided fiscal first-quarter 2027 revenue to $1.225 billion to $1.275 billion. That was comfortably above where Wall Street had been sitting. One number looked ugly at first glance: a GAAP net loss of $7.16 billion, or $84.65 a share. That was tied to a one-time debt extinguishment charge, not a collapse in the operating business. Not a real loss.
The stock bounced the next morning. Not by the 13% figure that had been circulating in the earlier version of this story, though. Barron's put Lumentum's premarket gain at about 7.9%, while MarketWatch reported a smaller after-hours move right after the release. Either way, the message was plain. The demand scare did not show up in Lumentum's numbers.
Coherent is next. The company is due to report its fiscal fourth-quarter results after the New York Stock Exchange closes on August 12, with its call scheduled for 4:30 p.m. ET, according to Coherent's own investor notice. Barchart said analysts expected adjusted earnings of $1.43 a share, up from $0.74 a year earlier. Benzinga listed a higher consensus figure of $1.58 on revenue of $1.98 billion, which tells you the exact bar depends on whose survey you use. The revenue bar is not mysterious, though. It sits around $2 billion.
Coherent's own guidance from last quarter called for fiscal fourth-quarter revenue of $1.91 billion to $2.05 billion and non-GAAP earnings of $1.52 to $1.72 a share. That is the range investors have to judge now. Frankly, a stock doesn't lose 12% in a day because Wall Street has decided AI data-center demand is fake. It loses that because a 160-times multiple gives shareholders no cushion.
A China rule could help the US optics names #
There is a second story under the valuation nerves. Reuters reported that the Trump administration was preparing an FCC rule to bar imports of Chinese-made optical transceivers into US data centers, citing concerns over data theft and malware. Investopedia also cited the Reuters report when it noted that Coherent, Lumentum, Corning and Applied Optoelectronics rallied on the possibility of tighter restrictions.
That is not obviously bad news for Coherent and Lumentum. A ban on Chinese-made transceivers would hit suppliers such as Zhongji Innolight first, and could push more AI data-center spending toward US-based optics makers. It would also raise hard questions for cloud operators that have relied on cheaper Chinese components. Amazon Web Services, Microsoft Azure, Google Cloud, you name it. All of them have to care about cost when the AI buildout already eats capital at a brutal pace.
For Coherent and Lumentum, the policy risk cuts more like a tailwind than a headwind. The harder part is valuation. Investors are paying as if optical demand will stay tight, AI infrastructure budgets will keep expanding, and earnings will catch up quickly enough to justify the run. Lumentum gave that argument fresh support on August 11. Coherent still has to do its part. The next answer lands after the closing bell. If Coherent clears its own guidance and talks confidently about AI data-center demand, the August 10 selloff will look like nerves. If it doesn't, the stock has already shown you how little patience is left at 160 times earnings.
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