Simultaneous Measurement of Strain and Temperature Based on Dual Cross-Axis Interference Polarization-Maintaining Fiber Interferometer

Abstract

A dual cross-axis interference polarization-maintaining fiber interferometer (DCAI-PMFI) for simultaneous measurement of strain and temperature is proposed. By using the cross-interference of the fast and slow axes in the polarization-maintaining fiber interferometer with dual axis independent detection, common path dual cross-axis interferometers (DCAIs) are realized. Since the fast and slow axes are different in refractive index and thermo-optic coefficient, the DCAIs have different phase sensitivities to strain and temperature. A sensitivity matrix for simultaneous measurement of temperature and strain is constructed. The temperature phase sensitivities can be adjusted by changing the length ratio of two arms of the DCAI-PMFI to optimize the decoupling performance of temperature and strain. It is found that the temperature sensitivities are opposite signs when the length ratio of two arms is between the ratio of the temperature optical path coefficients of the fast and slow axis and its reciprocal, and the best measurement resolution can be obtained when two arms are equal in length. In the experimental setup of DCAI-PMFI with equal length of two arms, the strain sensitivities are 1.5648 rad/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μϵ</i> and 1.5790 rad/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μϵ</i> respectively at 0.35m strain sensing fiber, the temperature sensitivities are −25.4990 rad/°C and 24.6000 rad/°C respectively at 10m arm length, the resolutions are 2.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μϵ</i> in strain and 0.02°C in temperature. The experimental results show that the proposed sensor can solve the crosstalk between strain and temperature of interferometer, and can be applied to various interferometric fiber sensors without changing the topology.