Terahertz graphene modulator based on hybrid plasmonic waveguide

Abstract

As a key component of on-chip interconnection, optical modulator with large modulation depth and tiny footprint has always been studied. Profiting by high carrier mobility and flexible adjustability of graphene, numerous graphene modulators at optical communication band are proposed to overcome inherent flaws of traditional semiconductor waveguide modulators. Here, a terahertz waveguide modulator combing noble metal and graphene is presented. When Fermi level changes from 0 eV to 1 eV, intensity distribution of electric field becomes dispersed. Interaction area of graphene and wave increases, which results in larger propagation loss. On the premise of the existence of the allowed mode, the size of metal and the thickness of dielectric should be small. Besides, modulation capability of this device can also be improved by multilayer graphene with relaxation time of 0.1 ps. After optimizing structure parameters, the designed graphene waveguide modulator obtains modulation depth of 6.1 dB μm−1 at the frequency of 5 THz, and keeps effective mode area below 10−5. With the increase of frequency, modulation depth decreases. Modulation depth of 1.5 dB μm−1 is achieved at 10 THz, but the corresponding effective mode area remains in an ideal range. Because the allowed mode is confined in a tiny room, cross-sectional area of device is less than 4 μm2.