Enhancement in sensitivity for fiber-optic torsion sensors

We demonstrate a simple fiber-optic torsion sensor with enhanced sensitivity. The sensor is based on the combination of a Malus and a Fabry-Perot (MFP) interferometer and allows for the sensitive detection of changes in the polarization of the guided beam due to torsion applied to the fiber. The basic idea behind this optical arrangement is to enhance the sensitivity for the measurements of intracavity anisotropies due to multiple passes of the beam through the sensing area. Theoretical analysis based on Jones calculus for a fiber-optic MFP interferometer shows that small twists in the fiber can be monitored through variations on the transmission of the arrangement. Experimental results with a hybrid MFP arrangement of bulk optical components and optical fibers show that, compared to single-pass polarimeter measurements, an enhancement in sensitivity up to 116 can be effectively achieved.