Ambient index sensing technique using a Sagnac interferometer incorporating a tapered polarization-maintaining fiber

We propose a novel refractive index sensor using Sagnac loop interferometers configured by using tapered polarization-maintaining fibers (PMFs) with different tapered diameters. To make the PMF sensitive to external index change, a micro-tapering technique is exploited to fabricate the tapered PMF. The sensitivities of the PMFs to ambient index strongly depend on the tapered diameters. The reduction of the PMF diameter results in the enhancement of the ambient index sensitivity of the tapered-PMF-based Sagnac interferometer. However, the temperature sensitivities of the proposed Sagnac interferometers are not changed by reducing the tapered diameters of the PMFs.