(a) Schematic illustration of logic gate NOR built by cascaded OR and NOT gates. (b) Optical image of the designed Ag NW structure. (c) Schematics of experimental setup. BS, beamsplitter; OBJ, objective; PLR, polarizer; SBC, Soleil-Babinet compensator; λ/2 PL, half-wave plate.
Optical computing has been pursued for decades as a potential strategy for advancing beyond the fundamental performance limitations of semiconductor-based electronic devices, but feasible on-chip integrated logic units and cascade devices have not been reported. Here we demonstrate that a plasmonic binary NOR gate, a ‘universal logic gate’, can be realized through cascaded OR and NOT gates in four-terminal plasmonic nanowire networks. This finding provides a path for the development of novel nanophotonic on-chip processor architectures for future optical computing technologies.
We have demonstrated that cascaded plasmonic OR and NOT gates can be used to form a plasmonic NOR gate in a four-terminal nanowire network by multiple-beam plasmon interference. As cascading plasmonic devices are now possible, more complex functions can be realized by the precise design of complex plasmonic waveguide networks. NOR and NAND gates, the so-called universal logic gates, are the important elements of Boolean logics and are crucial to modern electronic circuits, because any Boolean logic gate can be constructed from a suitable network of NOR gates only, or NAND gates only. Similarly, plasmonic NOR gates demonstrated here could have key roles to constitute a logical formal system of Boolean logic in future optical computing. Moreover, plasmonic devices of the type discussed here can be further miniaturized and it is likely that improvement of the materials and wire interconnects will greatly reduce signal losses, thereby maintaining signal thresholds for the logic operations. This could allow for on-chip integration of a large number of cascaded subwavelength logic units for complex optical processing. Finally, our plasmonic structures allow for coherent control of optical quantum interferences and may therefore have a role in the development of future photonic quantum computation devices