High sensitivity temperature sensor based on fiber air-microbubble Fabry-Perot interferometer with PDMS-filled hollow-core fiber

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.