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An optical fiber axial contact force sensor based on bubble-expanded Fabry–Pérot interferometer (FPI) is investigated in this paper. The FPI is packaged as a reflective sensing probe to measure the axial contact force which is applied on the end of sensing probe. To the best of the authors’ knowledge, this is the first time that intrinsic optical fiber FPI is used for axial contact force measurement, which has potential in application fields such as robotics. The sensing probe based on bubble-expanded FPI exhibits a high axial contact force measurement sensitivity of −750.17 pm/N, which is 3 times higher than that of the sensing probe based on traditional rectangular FPI fabricated in this work. This experimental results are well explained by the simulation analysis using Comsol software. The proposed optical fiber axial contact force sensor has advantages of compact size, simple structure and high sensitivity. [ABSTRACT FROM AUTHOR]

A miniature and highly sensitive optic fiber temperature sensor using a PDMS-filled air-microbubble Fabry-Perot (FP) interferometer (PAFPI) in a hollow-core fiber (HCF) is proposed. The sensor is fabricated by fusion splicing a single mode fiber (SMF) with a HCF, which is filled with polydimethylsiloxane (PDMS) by capillary effect, to form an air microbubble cavity. As far as we know, this is the first time that PDMS is applied to fill the hollow core fiber. There are three main reflected surfaces in the PAFPI sensor, and the superimposed interference spectrum of double FPI (a thin FPI and a thick FPI) is formed. Hence, the proposed sensor combines two advantages that are the large free spectral range (FSR) of the thin FPI and the high resolution of the thick FPI, which improve the resolution of spectral demodulation while ensuring a large dynamic range. Experimental results show that the sensor has the high temperature sensitivity of 2.7035 nm/℃ with a high linear response (R-square: 0.9962) in the range of 51.2–70.5 ℃, which is almost three orders larger than that of the conventional all-fiber air-cavity FP temperature sensors (about 10 pm/℃). The stability experiment is also carried out, and the maximal variations of the wavelength shift and the extinction ratio of the interference fringes are 20.3 pm and 0.1262 dB, respectively, for a long-term testing. Therefore, it may be applied to the surrounding temperature sensing. [ABSTRACT FROM AUTHOR]