A Ring Core Fiber Sensor Based on Mach–Zehnder Interferometer for Transversal Force Sensing With Solvable Temperature Cross Sensitivity

In this work, we proposed a ring core fiber (RCF)-based all-fiber sensor used for transverse force sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then, the coreless (CL)-ring core (RC) fiber structure is connected to two segments of single-mode fibers to form a Mach–Zehnder interferometer (MZI). The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with a free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for force sensing at different temperatures. The different values of forces are applied on the fiber sensor, which are tuned from around 0.26 to 1.5 N/mm. With the increase of transverse force, the spectra of output signals show a linear redshift. The force sensitivity of the proposed MZI sensor reaches up to 4.109 nm/(N/mm) with a good linearity of 0.9824. By using a $2\times2$ matrix, the temperature cross sensitivity can be extracted. The proposed force sensor based on the MZI fiber structure shows great potential applications in the field of structural health monitoring and supercapacitor safety detection.