High sensitivity, low temperature-crosstalk strain sensor based on a microsphere embedded Fabry–Perot interferometer

In this article, a high sensitivity, low temperature-crosstalk strain sensor based on a microsphere embedded Fabry–Perot interferometer (FPI) is reported and experimentally demonstrated. The sensor is fabricated by embedding a microsphere inside a tapered hollow-core fiber (HCF) whose ends are enclosed by two standard single-mode fibers (SMFs). The reflections occurring at the SMF/HCF interface and the surfaces of the microsphere, result in a three-beam interference. The cavity length of the formed FPI can be flexibly changed by controlling the diameter of the tapered HCF and the size of the embedded microsphere, and the maximum extinction ratio (ER) of the reflection spectrum is greater than 11 dB. This novel microsphere embedded FPI structure significantly enhances the sensing performance of traditional FPIs for strain measurement, providing a high strain sensitivity of 16.2 pm/με with a resolution of 1.3 με. Moreover, it is demonstrated that this strain sensor has a very low temperature-strain cross-sensitivity of 0.086 με/^oC, which greatly enhances the potential for applications in the field of precision strain measurement.