An interferometric system includes a polarization separation element (10), a first polarization conversion element (11), a Mach-Zehnder interferometer (2) including a first (4) and second (5) arms connected to one another by a first (6) and second (7) ends in order for a first and second beams (20, 21) having the same polarization to pass through the interferometer in a reciprocal manner in opposite directions of propagation, respectively, so as to form a first and second interferometric beam (22, 23), a second polarization conversion element (11) for obtaining an interferometric beam (24), the polarization of which is converted, a polarization-combining element (10), and a detection element (8) suitable for detecting an output beam (25).