Computational Properties of Nonlinear Optical Devices

To design an optical digital computer it is essential to have a cascadable logic gate with a fanin and fanout of at least two. For a complete logical coverage it is necessary to have either a NAND or a NOR gate or have an AND and an OR gate and use dual rail logic to perform a spatial inversion. To built a general purpose computer without a ridiculous number of gates we must have loops in the system. That is the data must flow through the same gates more than once. This means one gate must be able to drive any other identical ones.