The current research on optical computers is focused on three aspects: execution speed, twodimensional parallel processing, and system performance. Hot topics and difficult problems in these aspects are introduced. By comparison, it is concluded that the ternary optical computer (TOC) which seeks overall system performance is the most feasible. Advantages of ternary optical computers include availability of a large number of data bits, lower energy consumption, and easy reconfiguration and expansibility of the optical processor. Based on these advantages, new ideas and algorithms for solving highly complicated problems can be created. An experimental kilobit ternary optical computer is now under construction at the School of Computer Engineering and Science, Shanghai University, to be used for applications research. Related to the new machine, the advantages, possible applications, userviewable architectures, online operation, program operation, and hardware expansion of optical computers are discussed.