Passive device for coherent combination of a plurality of optical amplifiers, characterised in that said device comprises an amplitude division interferometer having at least four arms (B1, B2, B3, B4), said interferometer comprising: - optical polarization splitting and combining means having four input/output ports (ES1, ES2, ES3, ES4), each input/output port (ES1, ES2, ES3, ES4) being connected to one of the four arms (B1, B2, B3, B4), respectively, - the first arm comprising a first polarizing means, a first bidirectional optical amplifier and a first mirror forming the end of said first arm, - the second arm comprising a second polarizing means, a second bidirectional optical amplifier and a second mirror forming the end of said second arm, - the third arm comprising a third polarizing means and a third mirror forming the end of said third arm, - said first, second and third polarizing means (R1, R2, R3) being configured so that a polarized optical beam entering into said first, second or third arm (B1, B2, B3), respectively, via the first, second or third input/output port, respectively, is reflected by the first, second or third mirror (M1, M2, M3), respectively, in order to form a polarized optical beam exiting from said arm, having a polarization orthogonal to the polarization of said polarized optical beam entering into said arm, - the fourth arm being an input/output arm of said interferometer, which arm is placed so as to receive and direct a polarized incident optical beam (S 0) toward the fourth input/output port, - the optical polarization splitting and combining means being configured so as to split component polarizations of the polarized incident beam (S 0) into a first secondary input beam (H 1 4i) and a second secondary input beam (H 2 4i), said first and second secondary input beams having mutually orthogonal polarizations; the first secondary input beam (H 1 4i) propagates through the first, second and third arms of the interferometer following a first optical path in order to form a first amplified output beam (H 1 4o), and the second secondary input beam (H 2 4i) propagates through the first, second and third arms of the interferometer following a second optical path that is the reciprocal of the first optical path in order to form a second amplified output beam (H 2 4o), said first and second amplified output beams (H 1 4o, H 2 4o) having mutually orthogonal polarizations, and - said splitting and recombining means being configured so as to receive and combine spatially, temporally and coherently said first amplified output beam (H 1 4o) and said second amplified output beam (H 2 4o), in order to form a coherent output beam (S 1) propagating through the fourth branch in the opposite direction to the polarized incident optical beam (S 0). - optical polarization splitting and combining means having four input/output ports (ES1, ES2, ES3, ES4), each input/output port (ES1, ES2, ES3, ES4) being connected to one of the four arms (B1, B2, B3, B4), respectively, - the first arm comprising a first polarizing means, a first bidirectional optical amplifier and a first mirror forming the end of said first arm, - the second arm comprising a second polarizing means, a second bidirectional optical amplifier and a second mirror forming the end of said second arm, - the third arm comprising a third polarizing means and a third mirror forming the end of said third arm, - said first, second and third polarizing means (R1, R2, R3) being configured so that a polarized optical beam entering into said first, second or third arm (B1, B2, B3), respectively, via the first, second or third input/output port, respectively, is reflected by the first, second or third mirror (M1, M2, M3), respectively, in order to form a polarized optical beam exiting from said arm, having a polarization orthogonal to the polarization of said polarized optical beam entering into said arm, - the fourth arm being an input/output arm of said interferometer, which arm is placed so as to receive and direct a polarized incident optical beam (S 0) toward the fourth input/output port, - the optical polarization splitting and combining means being configured so as to split component polarizations of the polarized incident beam (S 0) into a first secondary input beam (H 1 4i) and a second secondary input beam (H 2 4i), said first and second secondary input beams having mutually orthogonal polarizations; the first secondary input beam (H 1 4i) propagates through the first, second and third arms of the interferometer following a first optical path in order to form a first amplified output beam (H 1 4o), and the second secondary input beam (H 2 4i) propagates through the first, second and third arms of the interferometer following a second optical path that is the reciprocal of the first optical path in order to form a second amplified output beam (H 2 4o), said first and second amplified output beams (H 1 4o, H 2 4o) having mutually orthogonal polarizations, and - said splitting and recombining means being configured so as to receive and combine spatially, temporally and coherently said first amplified output beam (H 1 4o) and said second amplified output beam (H 2 4o), in order to form a coherent output beam (S 1) propagating through the fourth branch in the opposite direction to the polarized incident optical beam (S 0).