The invention relates to a laser device comprising a number of fiber amplifiers (3) delivering a number of optical waves, which is supplied by an oscillator (1) that delivers a signal wave, characterized in that said device comprises: a coherent source (4) emitting a coherent wave at a wavelength approximately equal to that of the signal wave and the propagation direction of which is inclined to the propagation direction of the optical waves output by the fiber amplifiers; means for making the coherent wave interfere with the optical waves output by the fiber amplifiers, and generating an interferogram consisting of an array of fringes; interferogram detection means (7), the relative positions of the fringes transcribing an inter-fiber phase law; a spatial phase modulator (2); and processing/display means (6) for processing the detected phase law and for displaying it on the spatial modulator, said spatial modulator being positioned so as to be able to be read by the signal wave and thus generate a phase-modulated signal wave selectively at each of the fiber amplifiers, compensating for the phase shifts induced by said fiber amplifiers.