What: Shares of Ciena Corporation (NYSE:CIEN) were down 17.2% as of 11:15 a.m. EST Thursday after the telecommunications networking equipment specialist reported solid fiscal fourth-quarter 2015 results, but followed with disappointing guidance.

So what: Quarterly revenue rose 17.1% year over year to $692 million, above the mid-point of Ciena's guidance for revenue of $665 million to $700 million. That translated to a GAAP net loss of $13.8 million, or $0.10 per share, compared to a $0.29 per share loss in the same year-ago period. On an adjusted basis -- which primarily means excluding things like share-based compensation and amortization of intangible assets -- Ciena achieved adjusted net income of $67.3 million, or $0.42 per share, compared to an $0.08 per-share loss in last year's fiscal fourth quarter. In addition, Ciena generated cash flow from operations of $84.6 million.

Analysts, on average, were anticipating adjusted earnings of $0.38 per share on revenue of $683.6 million.

For the current quarter, however, Ciena anticipates revenue of $555 million to $590 million, which is significantly below analysts' consensus estimates for fiscal first-quarter 2016 revenue of $637.9 million. Similarly, Ciena anticipates revenue growth in the range of 8% to 9% for the full fiscal year 2016, compared to Wall Street's models for 14% top-line growth.

Now what: Nonetheless, during the subsequent conference call Ciena management voiced optimism for its prospects, and insisted the company sees this as a "strong" fiscal 2016 outlook given sustained momentum across its business. Ciena CEO Gary Smith also elaborated that the company believes it will continue to take market share going forward, enabling it to grow revenue faster than operating expenses over the long term.

However, considering Ciena is currently not profitable on a GAAP basis, it's hard to blame investors for taking a step back as the company forecasts underwhelming growth. Though Ciena may be happy with where it stands going into the new fiscal year, and that's why I'm personally content watching its march toward sustained profitability from the sidelines.

Steve Symington has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. 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.