Innovative hybrid optical sensing design to simultaneously discriminate pressure and temperature

Abstract

In this work, hybrid optical fiber sensors based on Fabry-Perot (FP) interferometer and Fiber Bragg Grating (FBG) sensors were developed to simultaneously measure two external parameters, pressure, and temperature. The proposed sensor consists of a photosensitive Single-Mode Fiber (SMF), where the FBG is recorded, and spliced to a small section of a Hollow-Core Fiber (HCF). After that, the HCF tip is submerged in a UV-photosensitive polymer (RI = 1.46), creating three cavities, which will create two observable light interferences, allowing the observation of two FP responses in the spectral response. Two sensors with different HCF lengths were created to compare their sensitivities. After curing, the sensors were calibrated to both parameters in the ranges of 0.0 to 4.0 bar (steps of 1.0 bar) and 22.0 to 30.0 °C (steps of 2.0 °C), respectively. By tracking the peak shifts of the FP, it achieved higher sensitivities for the sensor with the shorter HCF tip (182.30 µm of HCF and 28.56 µm of UV-polymer lengths) of around 31.65 nm/bar and 1.53 nm/°C. On the other side, the sensor with the longer HCF tip (318.56 µm of HCF and with 52.17 µm of UV-polymer lengths) achieved 15.65 nm/bar and 1.02 nm/°C. Regarding the FBGs, they achieved 9.65 and 7.86 pm/°C for the longer and shorter sensor, respectively, while presenting insensitivity to pressure. Therefore, the shorter FP cavity produces the more sensitive sensor because, since its length is shorter and possesses a concave shape, it is more susceptible to external changes. Thus, variations of pressure and temperature could be discriminated by using the matrixial method with the FP and FBG sensitivities, given that the determinant of the coefficient matrix results is -0.31, a non-zero value. The developed sensor has the potential to integrate specific applications, such as LiBs to measure and decouple both parameters.

Internal monitorization and evaluation of specific 18650 Li-ion cells parameters by using tailored optical fiber sensors

“…Traditional methods for monitoring the performance and health of LiBs often rely on electrical measurements, which may lack spatial resolution and struggle to provide comprehensive insights into the intricate processes occurring within the battery [7]. In recent years, the integration of optical fiber sensors (OFS) has emerged as a promising approach to address these limitations [8][9][10][11]. From their advantages, high sensitivity, immunity to electromagnetic interference, and compatibility with harsh environments are the more relevant for their usability for this type of application [7,12].…”