A graphene optical device includes a base, a plurality of graphene transistors, and an electrical connection structure. Each of the graphene transistors includes a graphene layer, a metal nanoparticle layer, an insulation layer, a polymer electrolyte layer, and an electrode unit. The electrode unit includes a source electrode, a drain electrode, a first gate electrode component which includes a plurality of first gate electrodes, and a second gate electrode component which includes a plurality of second gate electrodes. The insulation layer has an opening. The polymer electrolyte layer is disposed between the metal nanoparticle layer exposed from the opening and the first gate electrodes, and between the metal nanoparticle layer exposed from the opening and the second gate electrodes. The electrical connection includes a source electrode connecting unit, a drain electrode connecting unit, a first gate electrode connecting unit, and a second gate electrode connecting unit.