A method and apparatus for controlling operation of an electro-optic modulator is disclosed. A first intensity of light is obtained at an input to the electro-optic modulator. A second intensity of light is obtained at an output of the electro-optic modulator. A difference between the obtained first intensity and the obtained second intensity is used to control a biasing of a modulator transfer function of the electro-optic modulator to control the electro-optic modulator.