Experimental study on a parallel optical fiber Sagnac loops-based sensor with the advantages of both high sensitivity and ultra-wide measurement range

• Published in: Infrared physics & technology Vol. 137; p. 105174
• Main Authors: Liu, Chaoyi, Chen, Hailiang, Gu, Mingqi, Li, Lida, Shi, Ruyue, Zhang, Sa, Ullah, Sajid, Gao, Zhigang, Ma, Mingjian, Yang, Sigang, Ping Shum, Perry
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-03-2024
• Subjects: Fiber Bragg grating; Sagnac interferometer; Strain sensor; Temperature sensor; Vernier effect; Vernier effect; Temperature sensor; Fiber Bragg grating; Sagnac interferometer; Strain sensor
• ISSN: 1350-4495; 1879-0275
• DOI: 10.1016/j.infrared.2024.105174

•A high sensitivity strain and temperature sensor with large measurement range based on Vernier effect in two parallel optical fiber Sagnac loops was proposed and experimentally investigated.•The average strain sensitivity reached −104.4 pm/µε in a large measurement range of 0–5440 µε. The measurement range were enlarged 6 times contrasted to the measurement range limited by a free spectral range (FSR).•The average temperature sensitivity of 6.12 nm/°C was achieved in the temperature range of 2–58 °C. The measurement range were enlarged 4 times contrasted to the range limited by FSR.•The sensor can be used in many industries, including medical equipment, automotive and aerospace to make accurate strain and temperature measurements that allow better control of various systems.
The Vernier effect (VE) in optical interferometers has been used to improve the sensitivity in the measurements of strain, temperature, refractive index, etc. However, as the wavelength shifts beyond a free spectral range (FSR), it is difficult to determine the magnitude of the physical quantity and the measurement range is usually narrow. To overcome this problem, we constructed a fiber optic sensor combining two parallel Sagnac interferometers (PSIs) with a fiber Bragg grating (FBG). The sensitivity of temperature and strain measurements were enhanced about 5 times due to the VE effect in PSIs. FBG spectrum, which showed a monotonic and linear variation trend along with the variation of strain and temperature, was used to estimate the magnitude of the physical quantity beyond the FSR. Finally, an average strain sensitivity of −104.4 pm/µε was obtained in a wide measuring range of 0–5440 µε, while an average temperature sensitivity of 6.12 nm/°C was obtained in the temperature range of 2–58 °C. The measurement range has been extended 6 times and 4 times respectively compared to a single FSR. The integration of PSIs and FBG sensors offers not only high sensitivity, but also a wide measuring range. It can be used in many areas including medical equipment, automotive, and aerospace to make accurate strain and temperature measurements.