Ion-Gel-Gated Graphene Optical Modulator with Hysteretic Behavior

We propose a graphene-based optical modulator and comprehensively investigate its photonic characteristics by electrically controlling the device with an ion-gel top-gate dielectric. The density of the electrically driven charge carriers in the ion-gel gate dielectric plays a key role in tuning the optical output power of the device. The charge density at the ion-gel-graphene interface is tuned electrically, and the chemical potential of graphene is then changed to control its light absorption strength. The optical behavior of the ion-gel gate dielectric exhibits a large hysteresis which originates from the inherent nature of the ionic gel and the graphene ion-gel interface and a slow polarization response time of ions. The photonic device is applicable to both TE- and TM-polarized light waves, covering two entire optical communication bands, the O-band (1.26-1.36 mu m) and the C-band (1.52-1.565 mu m). The experimental results are in good agreement with theoretically simulated predictions. The temporal behavior of the ion-gel graphene-integrated optical modulator reveals a long-term modulation state because of the relatively low mobility of the ions in the ion-gel solution and formation of the electric double layer in the graphene ion-gel interface. Fast dynamic recovery is observed by applying an opposite voltage gate pulse. This study paves the way to the understanding of the operational principles and future applications of ion-gel-gated graphene optical devices in photonics.