The MZ modulator is the basic building block used in optical communication links for modulation; it is based on the principle of interference using the electro-optic crystal. It modulates the output intensity as a function of the externally applied voltage.
It is implemented using two 3 dB couplers, connected by two equal lengths’ waveguides. Because of the electro-optic effects the externally modulated applied voltage results in the change in the refractive indices in the waveguide section. The various signal paths can results in additive and subtractive interference at the output as a function of the applied voltage. This results in the modulation of the output intensity as a function of the voltage.