Lateral Force Sensing Based on Sagnac Interferometry Realized by a High-Birefringence Suspended-Core Fiber

In this paper, a directional lateral force sensor realized with a high-birefringence suspended-core fiber (HB-SCF)) based on a Sagnac interferometer (SI) is proposed and demonstrated experimentally. The two ends of a 40-cm long HB-SCF are spliced to the two arms of a 3-dB coupler to form the Sagnac interferometer. The lateral force leads to a change in refractive index, thus altering the birefringence of the HB-SCF. The output spectra show a wavelength shift which has a linear relationship with the lateral force. The relationship between the lateral force direction and the force sensitivity was investigated. A finite element analysis (FEA) is conducted to simulate the lateral force responses of the sensor, and the force sensitivities of various force directions are calculated theoretically. The results of both simulation and sensing experiment show that the lateral force sensitivity varied with the force-applied direction in a period of π, and the maximum lateral force sensitivity of 19.032 nm/(N/mm) was achieved. Such lateral force sensor has a good repeatability and low temperature sensitivity.Due to its simple fabrication, low cost, and high sensitivity, it is expected to be a competitive candidate in force sensing applications.