Graphene-based TO modulators. (A) 3D illustration of a graphene-based TO microring modulator. (B) Transmission spectra of the ring resonator at different drive voltages [58]. (C) Microscope image of a graphene-based TO microdisk modulator. (D) Spectral responses of the thermally tunable microdisk resonator as a function of the heat power [60]. (E) Colour scanning electron microscope image of a TO modulator based on slow-light-enhanced graphene micro-heater. (F) Static response of the heating power [38]. (A) and (B) Adapted with permission from [58]. Copyright 2015, Royal Society of Chemistry. (C) and (D) Adapted with permission from [60]. Copyright 2016, Optica Publishing Group. (E) and (F) Adapted with permission from [38]. Copyright 2017, Springer Nature.