  The modulation of the transmitted (reflected) radiation due to change of
interband transitions under variation of carriers concentration by the gate
voltage is studied theoretically. The calculations were performed for strongly
doped graphene on high-K (Al_2O_3, HfO_2, AlN, and ZrO_2) or SiO_2 substrates
under normal propagation of radiation. We have obtained the modulation depth
above 10% depending on wavelength, gate voltage (i.e. carriers concentration),
and parameters of substrate. The graphene - dielectric substrate - doped Si (as
gate) structures can be used as an effective electrooptical modulator of
near-IR and mid-IR radiation for the cases of high-K and SiO_2 substrates,
respectively.
