A multi-axis fiber optic interferometric system, including: - a shared light source adapted to emit a source beam having a constant intensity as a function of time; - a plurality of N optical-fiber coils (11, 12, 13), each coil forming a ring optical path about an axis; - a first optical separation means adapted to spatially separate the source beam into a first split beam and a second split beam; - shared phase modulation means adapted to apply a time-modulated phase shift at a period of modulation T m between the first and the second split beams (140, 240) and to form a first phase modulated beam and a second phase modulated beam; - a shared photodetector; and - a shared signal-processing system; the system being adapted in that: - the N optical-fiber coils (11, 12, 13) are connected in parallel, so as to inject simultaneously a fraction of the first phase modulated beam (151, 152, 153) at a first end of each coil (11, 12, 13) and a fraction of the second phase modulated beam (251, 252, 253) at a second end of each coil (11, 12, 13), said N optical-fiber coils (11, 12, 13) having respective transit times T1, T2,... TN that are all different from each other; - the shared phase modulation means being adapted to apply simultaneously at the first end of the N optical-fiber coils, a rectangular-wave time modulated phase shift consisting, at each period of modulation T m, of rising fronts at instants 0 and T m and of a falling front at the instant T m /2; - the first optical separation means being adapted to recombine said fractions of the first modulated beam (161, 162, 163) and said fractions of the second modulated beam (261, 262, 263) having travelled counter-propagatively through the N coils to form an interferometric beam (320, 330); - the photodetector being adapted to receive the interferometric beam and to trigger the acquisitions and record the instant of arrival and the height of each rising and/or falling front in the detected interferometric signal (720, 730), said detected interferometric signal (720, 730) comprising at least 2*N acquisitions per period of modulation, the time position of these acquisitions being triggered by the position of the rising and/or falling fronts in the detected interferometric signal; - and - the signal-processing system being adapted to process the interferometric signal (720, 730) detected by the photodetector, the step of processing of the at least 2*N acquisitions of the detected interferometric signal comprising operations of linear combination of said at least 2*N acquisitions to deduce therefrom at least a plurality of N measurements of Sagnac phase shift associated with each of the N optical-fiber coils (11, 12, 13), respectively, as a function of the respective transit times T1, T2,... TN in the different coils. - a shared light source adapted to emit a source beam having a constant intensity as a function of time; - a plurality of N optical-fiber coils (11, 12, 13), each coil forming a ring optical path about an axis; - a first optical separation means adapted to spatially separate the source beam into a first split beam and a second split beam; - shared phase modulation means adapted to apply a time-modulated phase shift at a period of modulation T m between the first and the second split beams (140, 240) and to form a first phase modulated beam and a second phase modulated beam; - a shared photodetector; and - a shared signal-processing system; - the N optical-fiber coils (11, 12, 13) are connected in parallel, so as to inject simultaneously a fraction of the first phase modulated beam (151, 152, 153) at a first end of each coil (11, 12, 13) and a fraction of the second phase modulated beam (251, 252, 253) at a second end of each coil (11, 12, 13), said N optical-fiber coils (11, 12, 13) having respective transit times T1, T2,... TN that are all different from each other; - the shared phase modulation means being adapted to apply simultaneously at the first end of the N optical-fiber coils, a rectangular-wave time modulated phase shift consisting, at each period of modulation T m, of rising fronts at instants 0 and T m and of a falling front at the instant T m /2; - the first optical separation means being adapted to recombine said fractions of the first modulated beam (161, 162, 163) and said fractions of the second modulated beam (261, 262, 263) having travelled counter-propagatively through the N coils to form an interferometric beam (320, 330); - the photodetector being adapted to receive the interferometric beam and to trigger the acquisitions and record the instant of arrival and the height of each rising and/or falling front in the detected interferometric signal (720, 730), said detected interferometric signal (720, 730) comprising at least 2*N acquisitions per period of modulation, the time position of these acquisitions being triggered by the position of the rising and/or falling fronts in the detected interferometric signal; - and - the signal-processing system being adapted to process the interferometric signal (720, 730) detected by the photodetector, the step of processing of the at least 2*N acquisitions of the detected interferometric signal comprising operations of linear combination of said at least 2*N acquisitions to deduce therefrom at least a plurality of N measurements of Sagnac phase shift associated with each of the N optical-fiber coils (11, 12, 13), respectively, as a function of the respective transit times T1, T2,... TN in the different coils.