Interferometer with a fiber optic having a high PMD in coupled mode, fiber optic gyroscope (FOG), and inertial navigation system including such a gyroscope

A fiber-optic interferometer, including:

• a wideband optical source (1) capable of emitting an incident optical beam with a central wavelength λ and a spectral width ΔλFWHM, having a decoherence time τDC=λ2/(c·ΔλFWHM),
• a coil with N turns of a single-mode optical fiber (5) of total length L, said fiber (5) having a first and a second ends,
• optical means capable of splitting the incident beam into a first and a second beam and of coupling the first beam to the first end and the second beam to the second end of the optical fiber (5), respectively, so that the first beam travels through the optical fiber (5) in a first direction and the second beam travels through the optical fiber (5) in a counter-propagating direction, said optical means being capable of combining into an output beam the two beams emerging respectively from the two ends after propagation through the fiber (5),
• a detector capable of detecting the interference of the output beam,
• characterized in that
• the optical fiber (5) is a high polarization mode dispersion (PMD) optical fiber,
• the length L of the optical fiber coil (5) is higher than twice the correlation length of the fiber (5), L>2·Lc, so that the fiber (5) operates in coupled PMD regime and
• the group propagation time differential (DGD) between two orthogonal polarization states cumulated over the length L of the fiber (5) is higher that the decoherence time of the source:
• DGD>τDC.