Vittorio Fossati-Bellani, Ph.D., has been appointed chief marketing officer at Coherent Inc.   . . .   Larry Schwartz has rejoined L-3 Communications as vice president of homeland security and president of the Navigation Products Group, which encompasses L-3's Interstate Electronics Corp. and Space and Navigation Divisions. Schwartz had previously served with the company for more than 30 years, most recently as vice president of business development.   . . .    Ian Butcher has been named CFO of Cambridge Display Technology, developer of light-emitting polymer and dendrimer organic light-emitting diode technology. Butcher became interim CFO at the company last summer.