SpecTran Corp. of Avon, Conn., has increased by $11 million the value of its contract to provide Corning Inc. of Corning, N.Y., with multimode fiber. The three-year agreement, which was signed last year, is now worth $28 million. SpecTran officials said that because fiber supplied under the contract will not be subject to the volume limitations for multimode fiber in the companies' patent license agreement, the increase will provide an opportunity for improved revenue growth. Corning will use the fiber to augment its own multimode fiber production.