Electro-optic modulator

In telecommunications, an electro-optic modulator is an optical device in which a signal-controlled element is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or direction of the modulated beam. Modulation bandwidths extending into the gigahertz range are possible with the use of laser-controlled modulators.

Source: Federal Standard 1037C and MIL-STD-188