Research on graphene has revealed its remarkable electro-optic properties, which promise to satisfy the needs of future electro-optic modulators. However, its ultrasmall thickness, compared with operating light wavelength, downplays its role in an optoelectronic device. The key to achieve efficient electro-optic modulation based on graphene is to enhance its interaction with light. To this end, some novel waveguides and platforms will be employed to enhance the interaction. Herein, we present our recent exploration of graphene electro-optic modulators based on graphene sandwiched in dielectric or plasmonic waveguides. With a suitable gate voltage, the dielectric constant of graphene can be tuned to be very small due to the effect of intraband electronic transition, resulting in “graphene-slot waveguides” and greatly enhanced absorption modes. Up to 3 dB modulation depth can be achieved within 800 nm long silicon waveguides, or 120 nm long plasmonic waveguides based on three-dimensional numerical simulations. They have the advantages of nanoscale footprints, small insertion loss, low power consumption, and potentially ultrahigh speed, as well as being CMOS-compatible.
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