Numerical Investigation of a Bidirectional Wave Coupler Based on Plasmonic Bragg Gratings in the Near Infrared Domain

In this paper, we present a theoretical discussion of the design of bidirectional wave couplers based on plasmonic Bragg gratings in the near infrared domain. A key feature in the design of the plasmonic Bragg gratings is the dependence of the effective refractive index on the thickness of the dielectric layer. These gratings, which function as band rejection filters, enable directional coupling of different SPP modes. By placing two gratings with different band gaps on opposite sides of a subwavelength metallic slit, a bidirectional plasmonic surface wave coupler can be realized. Two-dimensional (2-D) FDTD simulations were performed to elucidate the properties of the device, and were found to agree well with the theoretical predictions. Finally, the wave confinement properties of the plasmonic Bragg gratings are studied further by introducing the equivalent 1-D photonic crystal band structures.