  We demonstrate a high-contrast electro-optic modulation of a photonic crystal
nanocavity integrated with an electrically gated monolayer graphene. A high
quality (Q) factor air-slot nanocavity design is employed for high overlap
between the optical field and graphene sheet. Tuning of graphene's Fermi level
up to 0.8 eV enables efficient control of its complex dielectric constant,
which allows modulation of the cavity reflection in excess of 10 dB for a swing
voltage of only 1.5 V. We also observe a controllable resonance wavelength
shift close to 2 nm around a wavelength of 1570 nm and a Q factor modulation in
excess of three. These observations allow cavity-enhanced measurements of the
graphene complex dielectric constant under different chemical potentials, in
agreement with a theoretical model of the graphene dielectric constant under
gating. This graphene-based nanocavity modulation demonstrates the feasibility
of high-contrast, low-power frequency-selective electro-optic nanocavity
modulators in graphene-integrated silicon photonic chips.
