Cascaded logic gates in nanophotonic plasmon networks

Abstract

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.

Figure 1. Cascaded logic gates for NOR gate and the experimental setup.

(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.

Figure 2. Output intensity at the O end for different inputs versus the time sequence as the incident phases are changed.

(a–d) The output intensity for the inputs from terminals (C, I1), (C, I1, I2), (C, I2) and (I1, I2). The red lines emphasize the output intensity for the NOR operation. The green line emphasizes the corresponding output intensity for (I1, I2). (e–g) The scattering images showing the OR operations. (h) The scattering image when only C was enabled. (i, j) The scattering images for the NOR operations, corresponding to a NOT function acting on (f, g). The red arrows show the incident laser polarization. The green and yellow circles mark the C-branch junction and the O terminal, respectively.

Figure 3. Dependence of plasmon interference on incident polarizations.

(a) QD fluorescence image by wide-field illumination. Dashed white lines show the outline of the branch NWs. (b–e) QD fluorescence images with excitation at different terminals with polarization indicated by the white arrows. (f) The output intensity at terminal O as a function of the phase difference between two laser beams. Green: the output intensity when only one input (I1, I2, or C) is applied. Black: the output intensity resulting from two incident beams (I1 and I2). Red: the output intensity resulting from two incident beams (I1 and C). The incident polarizations at I1 and I2 terminals used for this set of measurement corresponds to the polarizations shown in (e, c). The incident polarization at C terminal is the same as in Figure 2. (g) Interference depth of (I1, I2) and (I1, C) as a function of polarization angle θ of the input laser at the I1 terminal. The definition of θ is shown in (a). The polarizations of I2 and C are kept the same as those in Figure 2.