Abstract: In order to increase the distance over which binary data can be transmitted over an optical fiber, the device compensates for fiber-generated chromatic dispersion by modulating the emitted light wave both in power and in phase, in such a manner as to ensure that there is a phase shift of close to 180.degree. within each binary cell for which the optical power is low but not zero. The device comprises a Mach-Zehnder type interferometer made on a substrate of III-V elements and designed so that in the absence of electrical voltages being applied to its electrodes it establishes destructive interference. A control circuit applies control voltages to the electrodes which voltages have DC components that are substantially equal, with at least one of the control voltages being the result of superposing a bias voltage on a filtered signal obtained by lowpass filtering an input electrical signal. The invention is applicable to long distance transmission over standard optical fibers.