In this paper, in order to improve the sensitivity of tactile sensor, we proposed and demonstrated a fiber in-line Mach-Zehnder interferometer (MZI) sensor for the measurement of grasp force. The sensor was fabricated by splicing a section of few-mode fiber (FMF) between two single mode fibers (SMFs). The simulation using Rsoft software shows that the sensor has the best performance with the FMF length is 10mm and the core offset is 5um. The mechanical strength of the sensor is improved by using heat shrink tube at the point of optical fiber fusion splicing. The MZI sensor is embedded in the gripper and the force calibration is carried out by using the piezoresistive sensor. The experiment shows that the sensitivity of the sensor is about 6nm/N. The sensor has many advantages including simple fabrication, low cost, and high sensitivity, demonstrating its great application potential in the fields of Human Machine Interface.
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