  With the increasing need for large volumes of data processing, transport, and
storage, optimizing the trade-off between high-speed and energy consumption in
today's optoelectronic devices is getting increasingly difficult. Heterogeneous
material integration into Silicon- and Nitride-based photonics has showed
high-speed promise, albeit at the expense of millimeter- to centimeter-scale
footprints. The hunt for an electro-optic modulator that combines high speed,
energy efficiency, and compactness to support high component density on-chip
continues. Using a double-layer graphene optical modulator integrated on a
Silicon photonics platform, we are able to achieve 60 GHz speed (3 dB
roll-off), micrometer compactness, and efficiency of 2.25 fJ/bit in this paper.
The electro-optic response is boosted further by a vertical
distributed-Bragg-reflector cavity, which reduces the driving voltage by about
40 times while maintaining a sufficient modulation depth (5.2 dB/V). Modulators
that are small, efficient, and quick allow high photonic chip density and
performance, which is critical for signal processing, sensor platforms, and
analog- and neuromorphic photonic processors.
