WorldCom Japan Ltd., a subsidiary of U.S.-based WorldCom Inc., said Monday it will expand its presence in the Japanese telecommunications market by establishing its own fiber-optic network.As deregulation is slated to begin this month, WorldCom, which currently holds a Type II carrier license, will apply for a Type I carrier license as soon as the restriction is lifted, the company said. Under current regulations, foreign telecom firms, which hold only Type II carrier status in Japan, are only allowed to resell leased lines to customers.However, the planned deregulation measures are expected to allow those foreign carriers to provide services to customers independently, using their own lines, and enable less expensive services. Japan's telecommunications market for Type I carriers is believed to reach about 13 trillion yen, compared to the 1 trillion yen market for Type II carriers this year.WorldCom set up a firm in December to prepare for the new business opportunities. The company plans to offer telephone and data telecommunications services for major corporations.WorldCom has seen rapid growth in the U.S. through aggressive mergers and acquisitions in recent years, and many of its telecom rivals are keeping a keen eye on its expansion. Last year, WorldCom made a bold bid to take over MCI Communications Corp., the second largest carrier in the U.S.