Fiber-optic multimode interference sensing: comprehensive characterization and its potential for strain-insensitive temperature sensing

Abstract

A strain-insensitive temperature sensor based on multimode interference using standard multimode fibers (MMFs) is proposed according to the comprehensive study of the characteristics of the MMFs. The temperature and strain dependences on the core diameter, numerical aperture (NA), and the length of the MMF section in the single-mode-multimodesingle-mode (SMS) fiber structure are investigated experimentally. The results indicate that the larger core diameter of the MMF leads to higher temperature sensitivity but lower strain sensitivity (absolute values); the higher NA does not influence the temperature sensitivity but results in higher absolute value of strain sensitivity; the longer MMF section brings lower temperature sensitivity but does not have an impact on strain sensitivity. These findings also contribute to the theoretical analysis of the length dependence in the SMS fiber sensors. Besides, the results of the characterization study show that the strain sensitivity is relatively low, which brings a possibility to develop a strain-insensitive temperature sensor. The proposed sensor is used for temperature sensing while the strain is constantly applied from 0 to 1100 µε with steps of 100 µε. The measured results are consistent with the comprehensive study. The mean temperature sensitivity is 6.14 pm/ • C with a standard deviation of 0.39 pm/ • C, which proves that the proposed temperature sensor exhibits good stability and is insensitive to strain. We expect that these results will provide a profound guideline to fiber sensors based on multimode interference.

Strain-insensitive high-sensitivity temperature sensing based on multimode interference in a square-core fiber

“…The result shows that the temperature dependence is almost independent of the applied strain and that the mean temperature sensitivity is −22.35 pm °C−1 with a standard deviation of as small as 0.44 pm °C−1 . The absolute value of this sensitivity is approximately 3.5 times larger than that with a standard MMF-based SMS sensor, 25) which indicates that strain-insensitive highsensitivity temperature sensing is feasible with the SCF-based SMS sensor.…”

“…Our previous work demonstrated the temperature sensitivity of the strain-insensitive temperature sensor using a standard MMF with the same length (25 cm) is 6.32 pm °C−1 . 25) Therefore, the absolute value of the temperature sensitivity of the SCF-based sensor is ∼3.5 times that of a standard MMF. This result indicates that the temperature sensitivity exhibits remarkable stability with almost no influence of strain.…”