MZI/FPI Fiber Optic Dual- parameter Sensor Based on a Double Cone and Air Cavity Structure (Invited)

This paper proposes a Mach Zehnder/Fabry Perot Interferometer (MZI/FPI) fiber sensor based on Single-mode Fiber (SMF) and Hollow-core Fiber (HCF), which has high sensitivity to temperature and lateral loads. The proposed device consists of two single-mode fiber cones formed by manually controlling the fusion splicer and an air cavity formed by fusing a section of hollow-core fiber. The structure of the sensor is a double cone cascaded air cavity. At the beginning of the design, we compared the basic transmission spectra of single cone structure and double cone structure experimentally, and therefore chose to use double cone structure and air cavity cascade. Light undergoes its first reflection at the first interface between the single-mode fiber and the air cavity structure, and its second reflection at the second interface between the air cavity structure and the single-mode fiber. The two reflected light waves produced by the two reflections form FP interference, which can be used to measure lateral loads. The transmitted light is excited through the first cone, and a portion of the core mode light is excited to the cladding, while another portion of the core mode light continues to propagate in the core. The light couples at the second cone, and the cladding mode light couples back into the core, forming MZ interference with the core mode light, which can be used to measure temperature. The use of hollow-core fiber to form an air cavity has little effect on transmitted light, while avoiding the problem of crosstalk in dual parameter measurements. By designing temperature and lateral load experiments, this article verifies the sensitivity characteristics of this sensor to temperature and lateral loads. A significant redshift phenomenon was observed in the temperature experiment. A significant redshift phenomenon also occurred in the lateral load experiment. Through wavelength demodulation, the experimental results show that the wavelength sensitivity of the sensor to temperature is 56.29 pm/degrees C in the range of 30 degrees C to 80 degrees C. The wavelength sensitivity of the sensor to lateral loads is 1.123 nm/N in the range of 0 similar to 5 N. In addition, we have prepared multiple sets of fiber optic sensors with this structure and conducted repeated experiments to verify that the sensing performance of this structure of fiber optic sensors for temperature and lateral load is relatively stable. Also, the different waist diameters of cones will have a certain impact on the transmission spectrum of MZ, while the length of the air cavity will also have a certain impact on the reflection spectrum of FP. This article lists some fiber optic sensors for dual parameter measurement of temperature and lateral load. Compared with the listed sensors, the fiber optic sensor proposed in this article has better sensitivity to temperature and lateral load. And the fiber optic sensor proposed in this article has a simple manufacturing process, low production cost, and good performance, which has certain prospects in scientific research and industrial production.