An optical interferometer incorporating a signal strength modulated optical phase delay, such as a Kerr effect element in one of its arms is employed to improve the cross-talk isolation/extinction ratio of an optical switch, amplitude modulator, or amplitude modulated optical transmitter. The Kerr element is constructed so that its intensity dependent optical path length is such as to provide destructive interference at the interferometer output when the light input to the interferometer is low, and constructive interference when the input is high. The place of the Kerr effect element can alternatively be taken by an electro-optic modulator driven with an electrical version of the data modulation appearing on the optical signal.