**5. Graphene use in Electro-Optical (EO) devices**

One of the interesting applications for graphene is its use in EO devices and lasers. Graphene can absorb wavelengths from the visible to the mid-IR with wavelength modulation enabled through electrostatic gating. [63–67] The electrostatic gating interacts with light either by modulating the band gap width up to a certain wavelength working as an absorption modu‐ lating element, or it modifies the graphene surface plasmon modes that interact with light. [63– 67] The last example is how graphene was utilized for mode locking a laser. [63–67] The problem with utilizing graphene for pure optical devices is due to its inherent thinness only absorbing 2.3% of the incident light per monolayer. [63–67] This makes it more desirable to integrate graphene with other electro-optical components such as photonic cavities or plasmonic waveguides with an example shown in Figure 26. [63–67]

**Figure 26.** Integration of a tunable graphene capacitor with an EO modulator [63].

The EO modulator pictured in Figure 26 was created through the coupling of Si plasmonic nanocavities to a tunable graphene capacitor made from stacked layers of graphene and BN dielectric film. [63] The top and bottom graphene layers are electrostatically doped differently from one another with varying voltages for optical modulation of absorbed light. [63] The modulator worked up to 1.2 GHz frequency, which was limited by the RC time constant of the capacitor. [63]

Although on its own graphene is not practical for use as a waveguide or modulator, it can be combined with already active materials to increase the performance of such devices.
