A material which is capable of transforming electrical information into optical information or performing some optical function in response to an electric signal.

One example is lead lanthanum zirconte titanate, a transparent ferroelectric ceramic whose optical properties can be changed by an electric field.

In lasers, such materials can be used for beam deflection, beam modulation, and Q switching (Quality switch or an optical valve in a laser that prevents light from transmitting outside the resonating cavity).

The Q switch allows for the build-up of energy before it is switched open to allow light to move out.