Ultracompact, high-extinction ratio XOR, OR, and Feynman logic gates based on plasmonic metal-insulator-metal directional couplers.

Three plasmonic logic gates including XOR, OR, and Feynman based on directional couplers operating in the optical communications band are proposed. First, a 3 dB directional coupler based on metal-insulator-metal waveguides is presented and its operation principles are investigated using the coupled mode theory method. Then, XOR and OR logic gates are implemented simultaneously in one structure. The simulations performed by the finite-difference time-domain method show that the extinction ratios for the OR and XOR gates are infinite and 29.3 dB, respectively. The Feynman gate is also implemented using two directional couplers placed parallel to each other. The ER values for outputs and are 7.26 dB and 34.23 dB, respectively. The footprints of the XOR/OR and Feynman structures are less than 8µ and 12µ , respectively. The presented gates have a high potential to be used in photonic integrated circuits.