Heng-Ju Cheng received the B.S. and M.S. degrees from National Chao Tung University, Taiwan, in 1985 and 1987, respectively. He is currently working towards the Ph.D. degree at the University of Michigan, Ann Arbor. Upon completion of military service, he joined the kdustrial Technology Research Institute, Taiwan, between 1989 to 1990 as a Device Engineer for developing charge couple device. His research interests include high speed device characterization, high speed photodetectors, and ultrafast optically based measurement techniques in the submillimeter wave regime.