To format a power modulated input optical signal, at the same time as improving its power dynamic range and the extinction rate of the output signal, a device for formatting binary optical signals includes a first stage for supplying a modulating signal having stabilized high levels as a function of the input signal and an interferometer structure second stage receiving the modulating signal and a probe wave power modulated in phase opposition to the modulation of the modulating signal. The low and high levels of the probe wave are stabilized. Applications include optical transmission.