Enhancement in sensitivity for fiber optic torsion sensors

We present a fiber optic sensor with enhanced sensitivity to changes in circular birefringence. The sensor is based on the combination of a Malus and a Fabry-Perot 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, known as the Mauls Fabry-Perot (MFP) interferometer (Vallet et al., 1999), is to enhance the sensitivity for the measurement of intra-cavity anisotropies due to multiple passes of the beam through the sensing area. Theoretical analysis based on Jones calculus for a fiber optic MFP interferometer (FOMFPI) shows that it is possible to measure variations in circular birefringence of the fiber upon registering changes in the transmission through this arrangement. Experimental results with a hybrid MFP arrangement of bulk optical components and optical fibers show that, compared to single-pass polarimeters measurements, an enhancement in sensitivity is effectively achieved.