Optical fibre Bragg grating sensors inscribed in polymer optical fibre have been shown to be sensitive to the water content of the medium surrounding the fibre and this property has been applied, for example, to the monitoring of humidity and the water content of aviation fuel. In this work we assess the feasibility of using such sensors for monitoring the saturation of soils, which is important for civil engineering applications. We find a very non-linear response, with a rapid increase in Bragg wavelength as the water content increases from 0 to 0.5%, with a much more gradual, but still monotonic, increase thereafter. We speculate on the causes of this response.
A photonic crystal fiber (PCF) based on local surface plasmon resonance (LSPR) sensor with silver nanowires deposited in two microfluidic detection channels is designed. The coupling characteristics and sensing properties of the proposed sensor are analyzed numerically by finite-element method (FEM). The optical loss spectra of the proposed PCF-LSPR sensor can be effectively tuned by the parameters of the PCF structure and silver nanowires configuration. When the cylindrical silver nanowires number is 12 (single-detection channel), arranged in an even way, and the angle between adjacent cylindrical silver nanowires is 10 deg, an average wavelength sensitivity of 5507.1 nm / RIU is obtained in the refractive index (RI) range from 1.330 to 1.360, and a maximum wavelength sensitivity of 9000 nm / RIU is achieved in the RI sensing range from 1.355 to 1.360, corresponding to a maximum RI resolution of 1.11 × 10 − 5 RIU, which can be used to detect slight changes in the RI of an unknown analyte.
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