* Sees Q4 adj. rev $115-$120 mln vs est. $132.5 mln
* Sees Q4 adj. EPS $0.02-$0.05 vs est. $0.11
* Shares fall 20 pct after-mkt (Recasts; adds outlook, updates shares)
Oct 18 (Reuters) - Communications equipment maker Infinera Corp (INFN.O) posted a better-than-expected third-quarter profit, but forecast a weak fourth quarter, sending its shares down 20 percent in extended trade.
For the fourth quarter, the company sees adjusted revenue of $115-$120 million, saying customers have already completed significant network buildouts and are not expected to drive revenue for the rest of the year.
Analysts polled by Thomson Reuters I/B/E/S had estimated fourth-quarter revenue of $132.5 million.
Infinera sees gross margins of 45-47 percent for the fourth quarter, as against the 50 percent gross margin in the third quarter.
It sees adjusted earnings of 2-5 cents a share for the fourth quarter.
Infinera, which provides digital optical networking systems to telecom carriers, reported net earnings of $4.36 million, or 4 cents a share for the quarter ended Sept. 25, compared with a loss of $16.5 million, or 17 cents a share, a year ago.
Excluding items, the company posted earnings of 18 cents a share.
The company, which competes with Alcatel-Lucent ALUA.PA ALU.N and Cisco Systems Inc (CSCO.O), posted third-quarter revenue of $130.1 million, up 56 percent year-over-year.
Analysts on average were expecting the company to post earnings of 9 cents a share, excluding items, on revenue of $126.4 million.
Shares of the Sunnyvale, California-based company were down 20 percent at $9.90 in after-market trade, having closed at $12.33 Monday on Nasdaq. Shares of the company have fallen as much as 3 percent since touching a year-high in September. (Reporting by Siddharth Cavale in Bangalore; Editing by Unnikrishnan Nair)