Long-Sensing-Length Strain Sensor Based on Optical Fiber Fabry-Perot Interferometer With HCF-SMF Structure

We proposed and demonstrated an optical fiber Fabry-Perot (F-P) sensor with long sensing length for strain measurement. The structure of the sensor was fabricated with a simple process by splicing a long single mode fiber (SMF) with a short section of hollow-core fiber (HCF). The end of the SMF was cleaved with smooth reflective surface which hence allows the sensing length of the proposed sensor can achieve several centimeters with good visibility. Sensors with different sensing lengths were fabricated and experimentally analyzed in this paper. The relationship between the optical path difference (OPD) of the sensor and strain is found to be linear. With the sensing length of ~10 mm and ~49 mm, the sensor can achieve the OPD strain sensitivity of 20.42 nm/με and 115.57 nm/με at 1550 nm over the range of 1000 με respectively. Besides, with the sensing length of ~10 mm, the OPD temperature sensitivity of the sensor was 187.64 nm/°C. With the advantages of easy making, low cost and long sensing length, it is anticipated that the proposed sensor has great potential in measuring the strain with a large distribution.