Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Finisar (Nasdaq: FNSR) dropped 22% in intraday trading today after reporting weaker-than-expected revenue for its fiscal fourth quarter and issuing a disappointing outlook.

So what: Fourth-fiscal-quarter non-GAAP EPS of $0.33 met the consensus estimate and grew 50% year over year. Revenue of $237 million grew 25% year over year, but fell short of the consensus forecast of $243 million. Management blamed the revenue disappointment on soft demand from telecom customers, particularly Chinese OEMs.

Now what: For the current quarter, management said it expects revenue of $221 million to $236 million and non-GAAP EPS of $0.16 to $0.20. The consensus forecast called for revenue of $251 million and non-GAAP EPS of $0.36. Optical networking stocks have performed well recently on expectations of strong growth as networks expand to handle mobile data. Finisar's comment about soft demand suggests expectations were overdone and is causing weakness today in other optical networking stocks, including JDS Uniphase (Nasdaq: JDSU), Oplink (Nasdaq: OPLK), and Oclaro (Nasdaq: OCLR).

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.