Real-Time Optical Fiber Salinity Interrogator Based on Time-Domain Demodulation and TPMF Incorporated Sagnac Interferometer

• Published in: Sensors (Basel, Switzerland) Vol. 24; no. 16; p. 5339
• Main Authors: Lin, Weihao, Zhao, Fang, Hu, Jie, Liu, Yuhui, Xu, Renan, Chen, Xingwei, Shao, Liyang
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 18.08.2024; MDPI
• Subjects: Accuracy; Biodiversity; Climate change; Communication; dispersion compensation fiber; Economic activity; Environmental protection; Fiber optics; Lasers; Marine conservation; optical time stretching technology; Sagnac interferometer; Salinity; salinity monitoring; Sensors; Sound waves; Sustainable development; tapered polarization-maintaining fiber; dispersion compensation fiber; tapered polarization-maintaining fiber; salinity monitoring; Sagnac interferometer; optical time stretching technology
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s24165339

A novel demodulation scheme for a point-type fiber sensor is designed for salinity concentration monitoring based on a Sagnac interferometer (SI) composed of a tapered polarization-maintaining fiber (TPMF) and optical time stretching technology. The SI, constructed using a PMF with a taper region of 5.92 μm and an overall length of 30 cm, demonstrated a notable enhancement in the evanescent field, which intensifies the interaction between the light field and external salinity. This enhancement allows for a direct assessment of salinity concentration changes by analyzing the variations in the SI reflection spectra and the experimental results indicate that the sensitivity of the sensor is 0.151 nm/‱. In contrast to traditional fiber optic sensors that depend on spectral demodulation with slower response rates, this work introduces a new approach where the spectral shift is translated to the time domain, utilizing a dispersion compensation fiber (DCF) with the demodulation rate reaching up to 50 MHz. The experimental outcomes reveal that the sensor exhibits a sensitivity of -0.15 ns/‱ in the time domain. The designed sensor is anticipated to play a pivotal role in remote, real-time monitoring of ocean salinity.