Temperature-independent fiber Bragg grating micro-displacement sensor

Temperature-independent micro-displacement measurement using a single fiber Bragg grating based on broadened reflection spectrum is proposed and experimentally demonstrated. The structure of specially designed bending cantilever beam (BCB) is proposed. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power correspond to micro-displacement changes, insensitive to spatially uniform temperature variations. For a displacement variation of 20mm and a temperature change from 20°C to 100°C, the micro-displacement measurement deviation error is ±0.12mm without any temperature compensation. Through optical power detecting by a pin photodiode (PD), the micro-displacement sensor avoids complex demodulation process and potentially costs little.