Ultrahigh Sensitivity Sensor for Temperature and Strain Measurement Based on Solc-Sagnac Interferometer

An ultrahigh sensitivity sensor for temperature and strain measurement based on Solc-Sagnac interferometer is demonstrated, which is fabricated by fusing two segments of polarization maintaining fiber (PMF) with a rotation angle. As the lengths of the two PMFs are close to each other, a vernier effect is generated. Through theoretical and simulation analysis, it is found that as the fusion angle is 90°, the envelope can be eliminated and the waveform similar to that of ordinary single-ring Sagnac interferometer is realized. The longer PMF serves as the sensing part, and the changes in temperature and strain cause variations in the birefringence of the sensing fiber which leads to the shift of the interference signal. Three sets of temperature sensing experiments are carried out to demonstrate the influences of the length parameters of the two PMFs on the sensitivity. We find the temperature sensitivities are 16.9, 32.6, and 43.8 nm/°C, respectively, which is improved by 11.3, 21.9, and 29.4 times compared to the ordinary single-ring Sagnac interferometer. Meanwhile, the optimal fiber structure is used for strain sensing experiments whose sensitivity is 785 pm/
$\mu \varepsilon $
which increases by 28.8 times compared with ordinary single-loop interferometer. Then, the dual parameter measurement of temperature and strain is realized by using coefficient matrix. From the experimental results, it can be seen that the fiber structure with a fusion angle of 90° has the vernier effect to achieve the amplification of sensitivity and the corresponding interferometer possesses the advantages of easy demodulation and high accuracy due to the simple waveform.