The optical properties of stacked graphene microribbons in the terahertz region were simulated by the finite element method. The microribbons, which couple with terahertz light through the excitation of plasmons, were stacked with micrometer-scale vertical spacing (∼0.1λ or larger). Reflection and absorption spectra were found to strongly depend on the direction of incident light (forward or backward incidence), when the stacking structure was made slightly asymmetric by changing the ribbon width or the chemical potentials in each layer. At a certain frequency, light reflection is almost completely suppressed only for one incidence direction. The high directivity is considered to be due to the phasing effects of electromagnetic waves emitted from each layer like in a Yagi-Uda antenna.
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