Abstract: MFB twist distribution data is calculated along a multi-fiber shape sensor bundle (MFB) using optical frequency domain reflectometry (OFDR) phase interrogation data. Phase data is extracted from OFDR interferometric interrogation data acquired from an MFB having single core radially offset fibers with fiber Bragg gratings (FBGs) helically wrapped about and rigidly adhered to a central single core fiber with BRFs. A change in phase between current and previously acquired phase signals is calculated for the fibers. The change in phase is unwrapped and FBG gap-induced unwrapping discontinuities are accounted for in the change in phase. The FBG gap-mitigated phase differences are determined for each of the offset fibers and then averaged. The center fiber gap-mitigated phase difference is subtracted from the average to yield a twist-phase difference.

Abstract: Birefringence in optical fibers is mitigated using optical frequency domain reflectometry (OFDR) having a coupling point optically connected to a reference arm with a first, single mode fiber segment and optically connected to a measurement arm having single mode optical segments and polarization maintaining optical segments. The measurement arm has a first optical circulator connected to the coupling point via a second, single mode fiber segment; a second optical circulator for sending optical radiation to a sensor; a single mode optical segment between the first optical circulator and the second optical circulator including a third, single mode fiber segment. The measurement arm has an outbound path including a first polarization maintaining optical segment between the first and second optical circulator for rotating a polarization of the optical radiation once relative to a second polarization maintaining optical segment between the first and second optical circulator.