Opto Speed, a developer, manufacturer and marketer of indium phosphide-based optoelectronic components, announced it has signed a distribution agreement with Unistand Technology Co. Inc. to sell and support Opto Speed's suite of products in the Taiwan market.   . . .    Martin O'Donoghue was appointed vice president, Analytical Instruments, at Varian Inc. He will be responsible for the company's optical spectroscopy, dissolution testing, chromatography and analytical supplies product lines. He will continue to be responsible for operations in Walnut Creek, Lake Forest, and Harbor City, Calif.; Wakefield, R.I., Grenoble, France; and Middelburg, The Netherlands, in addition to operations in Cary, N.C., and Melbourne, Australia.