What happened

Shares of Applied Optoelectronics (NASDAQ:AAOI) fell 37% in October, according to data from S&P Global Market Intelligence. The maker of fiber-optic networking products for enterprise and service providers saw one major client's orders coming in slower than expected, so guidance for the third quarter was lowered across the board. 

A bundle of fiber optic wires set against a backdrop of dark clouds and a large lightning flash.

Image source: Getty Images.

So what

In the middle of October, Applied Optoelectronics took a look at its preliminary Q3 results and decided to issue a warning to its investors. One of the company's largest data center customers had ordered fewer high-speed transceivers than expected, and the shortfall was large enough to lower AOI's Q3 guidance targets by approximately 20%.

Now what

AOI's final report for the third quarter was released on Nov. 7. In the end, adjusted earnings landed at $1.08 per diluted share on sales of $88.9 million. That was near the top end of the revised guidance, though far below the original projection ranges. Share prices bounced nearly 18% higher on the news, but the chart starting in early October still looks like this:

AAOI Chart

AAOI data by YCharts

At this point, Applied Optoelectronics stock is still up 88% year over year, but the price has also plunged 57% from the all-time high it hit in late July. This is not a stock for risk-averse or faint-hearted investors.

The identity of the company behind those missing data center orders has not been officially confirmed, but it's likely Amazon.com (NASDAQ:AMZN). It's the only data center customer that has provided a large enough share of AOI's revenue in recent years to create a 20% plunge in sales simply by slowing down its orders. However, Amazon is likely to put its purchasing pedal back to the metal after AOI's newer and faster transceivers have been put through their paces in quality control tests, because the e-tailer's data center needs are growing quickly thanks to the success of the Amazon Web Services cloud computing platform.