(a) Schematic of the proposed unidirectional plasmonic Bragg reflector. It is composed of N periodic triangle-shaped nanostructures with period p, width w, and height h. The input and output MIM waveguides have a width of D₀. ρ N ± and τ N ± are the reflectance and transmittance coefficients with “+” for the left-side incidence (right-going) and “-” for the right-side incidence (left-going). Each nanostructure is treated as a “black box” (indicated by a dashed box). (b) and (c) The reflectance and transmittance coefficients ρ 1 ± and τ 1 ± of a single nanostructure (the black box).