Electro-optic modulator (EOM) is an optical device in which a signal-controlled element displaying electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or polarization of the modulated beam. Modulation bandwidths extending into the gigahertz range are possible with the use of laser-controlled modulators.
Generally a nonlinear optical material (organic polymers have the fastest response rates, and thus are best for this application) with an incident static or low frequency optical field will see a modulation of its refractive index.
Certain materials change their optical properties when subjected to an electric field. This is caused by forces that distort the positions, orientations, or shape of the molecules constituting the material. The electro-optic effect is the change in the refractive index resulting from applications of a dc or low-frequency electric field.