The Prolog language provides the flexibility to implement many expert system approaches and exhibits high levels of parallelism. However, it is too slow to have wide applicability to real-world problems or for real-time problems. The most computationally demanding steps in Prolog are the search and substitution required in unification. An all-digital opto-electronic architecture is described in which optical symbolic substitution is used to significantly speed unification by using high levels of parallelism. A simulator is being developed for the system to verify operation and assist performance evaluation. Progress in spatial light modulators suggests that such architectures will soon be feasible and superior to all-electronic counterparts.