Optical modulator

An optical modulator is a device which is used to modulate a beam of light. The beam may be carried over free space, or propagated through an optical waveguide (optical fibre). Depending on the parameter of a light beam which is manipulated, modulators may be categorized into amplitude modulators, phase modulators, polarization modulators etc. Often the easiest way to obtain modulation of intensity of a light beam, is to modulate the current driving the light source, e.g. a laser diode. This sort of modulation is called direct modulation, as opposed to the external modulation performed by a light modulator. For this reason light modulators are, e.g. in fiber optic communications, called external light modulators.According to the properties of the material that are used to modulate the light beam, modulators are divided into two groups: absorptive modulators and refractive modulators. In absorptive modulators the absorption coefficient of the material is changed, in refractive modulators the refractive index of the material is changed.