* Second-quarter adj earnings $0.02/share vs est loss $0.01/share
* Revenue $507.7 mln vs est $483.6 mln
* Expects third-quarter revenue $515-$545 mln vs est $509.5 mln
* Shares rise 10 pct before the bell
June 6 (Reuters) - Network equipment maker Ciena Corp reported a surprise second-quarter profit on an adjusted basis, helped by a 3 percentage-point rise in its gross margin, and forecast stronger-than-expected revenue for the current quarter.
Ciena shares jumped 10 percent before the bell.
The company said it expected third-quarter revenue of $515 million to $545 million. Analysts on average expected $509.5 million, according to Thomson Reuters I/B/E/S.
Ciena and rivals such as Cisco Systems Inc and Infinera Corp are likely to benefit as North American telecom companies, particularly AT&T Inc and Verizon Communications Inc, expand their 4G services.
"Our checks suggest stronger-than-expected demand for 100G because it is more economical to deploy 100G," Northland Capital Markets analysts Catharine Trebnick said in a pre-earnings note, referring to the deployment of 100 gigabit ethernet services.
Ethernet services are used by telecommunications companies to provide high-speed networks for corporate customers.
The global 100G market is expected to grow to $4.8 billion by 2016 from $892 million in 2012, according to market research firm Frost & Sullivan.
Cisco, which reported strong third-quarter results last month, also said it expected current-quarter revenue to increase.
Ciena's net loss narrowed to $27.1 million, or 27 cents per share, in the second quarter, from $27.8 million, or 28 cents per share, a year earlier. The company earned 2 cents per share before items.
Revenue rose 6.3 percent to $507.7 million.
Analysts expected an adjusted loss of 1 cent per share on revenue of $483.6 million.
Ciena's earnings quality score fell to 63 from 84 out of 100 after its first-quarter results, according to Thomson Reuters StarMine. This compares with a sector median of 64.
The model ranks companies according to the sustainability of their earnings - the closer a company is to 100, the more predictable its results are.
Ciena shares, which have gained 11 percent in the last month, closed at $16.31 on the Nasdaq on Wednesday.