Solid Rocket Motor Filling Glue Level Sensor Based on Annular Oxide-Doped Fiber Mach–Zehnder Interferometer

A novel optical fiber filling glue level sensor based on the oxide-doped optical fiber annular structure is designed and experimentally fabricated. As far as we know, this is the first time to measure the filling glue level with optical fiber sensor in which the core of the optical fiber is doped with hybrid oxide material and the refractive index (RI) of the core is linearly distributed. The sensor model is constructed and analyzed by a finite-element method. The fast Fourier transform (FFT) is used to explore the interference characteristics of transmission spectrum. The experimental results show that the filling glue level sensitivity of the sensor is as high as 0.282 nm/mm within the extremely wide liquid level range of 0–110 mm, in which the level resolution of the measuring system is as high as 0.075 mm and the linearity up to 0.999. The crosstalk of the heat released by the filling glue to the level measurement is insignificant compared to the sensitivity and measurement range of the level. Ultrafast time response characteristics and ultrahigh long-term stability are fully reflected. What is more, the sensor has the advantages of good robustness, simple structure, and tunable measurement range.