Dan Petrescu was appointed CEO of Quantum Photonics Inc., producer of optoelectronic components, modules and subsystems for telecommunications applications.   . . .    Preston M. Adcox has retired as president and COO of DuPont Photomasks Inc. He will continue to be a director on DuPont Photomasks' board and will work on key projects. James R. Northup joins the company as executive vice president of worldwide sales. Craig W. Kokjohn, previously executive vice president of worldwide sales, assumes the newly created position of executive vice president of worldwide operations.