Optically switchable directional couplers can function as logically complete building blocks for constructing all-optical computational engines. Logically, such devices operate as all-optical five-terminal gates, where the two output signals are logical functions of two throughgoing input signals and a control input signal. Such an optically controlled exchange element is a promising functional unit for constructing general-purpose digital optical logic circuits. The implementation of such all-optical five-terminal gates using Ti:LiNbO3 electro-optic directional couplers is described. These optical logic gates utilize mature technology developed for the telecommunications industry, facilitating construction of robust optical logic hardware. Single-mode optical fiber is used for all logical interconnections. Effectively dc-coupled control circuitry converts optical pulses into electrical pulses capable of switching the transfer state of low-voltage lumped electrode directional couplers. The use of such Ti:LiNbO3 five-terminal optical logical gates in the construction of various simple circuits such as oscillators and divide-by-N circuits is shown. Such circuits demonstrate many of the issues arising in the construction of all- optical digital computing systems, and are fundamental subsections of an all-optical bit serial computer design currently under construction.
Alan F. Benner,
Harry F. Jordan,
Vincent P. Heuring,
"Digital optical computing with optically switched directional couplers," Optical Engineering 30(12), (1 December 1991). https://doi.org/10.1117/12.56031