Ciena Corp., a maker of equipment that boosts phone-network capacity, agreed to buy closely held Lightera Networks Inc. and Omnia Communications Inc. for about $980 million in stock to expand the products it sells phone companies. Ciena will issue about 20.6 million shares, valued at $552 million, for Lightera, which makes equipment to direct traffic on phone networks. It will pay 16 million shares, or $429 million, for Omnia, whose gear delivers voice and data services. The acquisitions are a new tack for Linthicum, Md.-based Ciena, which saw suitor Tellabs Inc. scrap its planned purchase. Now, Ciena is forging ahead on its own, and as a larger company is less likely to be attractive to potential buyers, including Tellabs. Cupertino, Calif.-based Lightera and Marlborough, Mass.-based Omnia are still developing products, which will be shipped to customers by the end of the year. Ciena stock fell $2.06 to close at $24.75 on Nasdaq.