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

TL;DR

This paper presents a comprehensive study of multimode interference fiber sensors, demonstrating a strain-insensitive temperature sensor with stable performance and detailed analysis of how fiber parameters affect sensitivity.

Contribution

The study provides new insights into how core diameter, NA, and length influence temperature and strain sensitivities, enabling the design of strain-insensitive temperature sensors.

Findings

Larger core diameter increases temperature sensitivity but decreases strain sensitivity.

Higher NA results in higher strain sensitivity without affecting temperature sensitivity.

Longer MMF sections decrease temperature sensitivity but do not impact strain sensitivity.

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--multimode--single-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 $\mu\epsilon$ with steps of 100 $\mu\epsilon$. The measured results are consistent with the comprehensive study. The mean temperature sensitivity is 6.14 pm/$^{\circ}$C with a standard deviation of 0.39 pm/$^{\circ}$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.