Peter Hark has joined Sunex Inc., of Carlsbad, Calif., as an optical sales engineer. He previously held positions with Melles Griot and JMAR Research. While at JMAR, he worked as a laser engineer to develop high-power, diode-pumped solid-state laser systems for advanced research and semiconductor x-ray lithography. Sunex is a supplier of digital imaging optics for CMOS and CCD applications.   . . .   Edward Alton Parrish, president of Worcester Polytechnic Institute, has announced he will retire at the end of this academic year.   . . .   Industry, Calif.-based DMG Technologies, a manufacturer of optical subassemblies used in telecommunications, data communications, CATV and instrumentation systems, has appointed Toshi Makino as CTO. Makino has worked on developing microwave and photonics technologies, particularly semiconductor lasers, with firms such as Nortel, Fujitsu, Furukawa and Matsushita.