An optical modulator in which a Kerr cell, an electro-optical crystal, or other signal-controlled electro-optical device is used to modulate the amplitude, phase, frequency, or direction of a light beam.

With a laser beam, modulating frequencies well into the gigahertz range are possible.

A Kerr cell is an optical device consisting of a transparent cell with two electrodes between two polarizing media which passes light only if the two planes of polarization are parallel and it is used as a high-speed shutter or to modulate a laser beam.