Compact Vectorial Transverse Force Sensor Based on Two-Modal Interference in a Few-Mode Seven-Core Fiber

A compact and highly sensitive optical fiber vectorial transverse force sensor is proposed to simultaneously measure the magnitude and direction of the transverse force based on two-modal interference. The sensor consists of a few-mode seven-core fiber (FM-SCF) connected to a fan-in/out coupler. The calculation model for predicting the performance characteristics of the proposed FM-SCF sensor under transverse forces has been developed, and the different spectral shifts of its each core are theoretically and experimentally analyzed. The magnitudes and direction angles are investigated by calculating the dip wavelength shifts and its difference. The sensitivity of the force sensor of 17.527 nm/N and the minimum resolved force of 0.005N were observed experimentally. Additionally, it is able to detect the direction angle of the transverse force with an accuracy of 1.15°. The effect of temperature on the response of FM-SCF sensor can be eliminated while measuring the direction angles. The presented results indicate a great potential of the FM-SCF sensor applications of microsurgery.