Subwavelength Electro-Optical Half-Subtractor and Half-Adder Based on Graphene Plasmonic Waveguides

In this paper, we present subwavelength half-subtractor and half-adder circuits based on graphene plasmonic waveguides. Surface plasmon polaritons are stimulated by an incident TM wave with a wavelength of 13.8 μm in graphene-insulator-metal structures. Using graphene provides high confinement, low loss, and flexibility in controlling light propagation. Simulations show that the proposed half-subtractor has contrast ratios as high as 10.60 dB and 15.75 dB for difference and borrow bits, respectively. This structure calculates A–B and B–A, simultaneously. Also, the results indicate that the contrast ratios for sum and carry signals of the half-adder are 7.4 dB and 14.83 dB, respectively. The footprints of the half-subtractor and half-adder are 0.315 μm2 and 0.640 μm2, respectively, which denote the compact sizes of the structures. Owing to the high contrast ratio and ultra-compact size, the presented circuits are expected to be used widely in photonic combinational integrated circuits.