Fiber Optic Sensor of Axial Strain and Dynamic Transverse Force Based on Intensity Demodulation

This paper presents a fiber-optic sensor with intensity demodulation for simultaneous measurement of dynamic transverse force and axial strain. The sensor uses a Sagnac loop filter with a polarization-maintaining photonic crystal fiber (PM-PCF) that is subjected to a dynamic transverse force. The Sagnac loop filter is illuminated by the reflected beam froma uniform fiber-optic Bragg grating (FBG), which is subjected to an axial strain. This way, intensity demodulation is performed in the sensor,enabling it to measure two quantities simultaneously: the dynamic force and the strain. Experimental results show that the sensor achieves a sensitivity to the dynamic transverse force of 38.1 mV/N and a sensitivity to the axial strain of 0.527 mV/με, while the nonlinearity errorsare 4.9% for the dynamic force and 0.9% for the strain. The sensor exhibits low temperature sensitivity due to partial self-compensation of the temperature coefficients of the Sagnac loop filter with the polarization-maintaining photonic crystal fiber and the fiber Bragg grating.