JDS Uniphase Corp. has entered into a definitive agreement to acquire the privately held Acterna Inc. of Germantown, Md., for $760 million, $450 million of that in cash and the remainder in JDS common stock. With this acquisition, the San Jose, Calif., company will add to its position as a leading provider of optical communications subsystems and broadband optical test and management systems. JDS expects that the transaction, to close by the end of September, will double its communications market to more than $5 billion.