▎ 摘　　要

We design surface plasmon polariton (SPP) absorption modulators using monolayer graphene as the active layer in the 1.5 mu m telecommunication wavelength window. Modulation is achieved by electrically modulating the Fermi energy level in the graphene layer. We investigated a silver slab SPP waveguide on graphene and found that there are limitations on the modulation performance as the guided mode only weakly interacts with the graphene layer. To overcome these limitations, we propose a silver-air-silver SPP waveguide on graphene configuration. We show that the latter design can achieve a two times improvement in the figure of merit, defined by the ratio of the extinction ratio to the voltage-off propagation loss, compared to previous indium-tin oxide based SPP absorption modulators. (C) 2014 The Japan Society of Applied Physics