  Graphene is an ideal 2D material system bridging electronic and photonic
devices. It also breaks the fundamental speed and size limits by electronics
and photonics, respectively. Graphene offers multiple functions of signal
transmission, emission, modulation, and detection in a broad band, high speed,
compact size, and low loss. Here, we have a brief view of graphene based
functional devices at microwave, terahertz, and optical frequencies. Their
fundamental physics and computational models were discussed as well.
