High-sensitivity optical fiber seawater temperature and pressure sensor with a low-error demodulation method

Using a single optical microfiber (OM) sensor for multi-parameter sensing can lead to significant demodulation error due to ill-conditioned matrices and nonlinear response characteristics. To address these issues, this paper proposes a novel specially packaged optical microfiber coupler combined with a silver mirror (OMCM). OMCM is combined with a mechanically enhanced sensitivity fiber Bragg grating (FBG) to form a temperature-pressure sensor. The temperature sensitivity exceeds -1.7 nm/°C while the pressure sensitivity reaches 53.435 nm/MPa, with a depth resolution of 0.935 cm. According to the characteristics of the sensor spectrum, this paper proposes a new demodulation method, which combines machine learning methods with a traditional wavelength-tracking method to achieve low demodulation error. For temperature and pressure, the mean absolute percentage errors are 0.04% and 1.31%, respectively. This feature facilitates the detection of minute changes in shallow marine environments, lacustrine systems, and other aquatic habitats, thus making it highly suitable for applications such as underwater aquaculture and marine monitoring.