Three approaches that allow the tailoring of long period gratings based refractometric sensors for concentration measurement in fuel blends are employed to assess the fuel quality in biodiesel and biodiesel-petrodiesel blend. To allow the analysis of fuel samples with refractive index higher than fiber cladding one, the samples refractive indices were changed by thermo-optic effect and by dilution in a standard substance with low refractive index. The obtained results show the sensor can detect oil concentration in biodiesel samples with resolution as better as 0.07% and biodiesel concentration in biodiesel-petrodiesel samples with average resolution of 0.09%.
In this work, we demonstrate a refractometric fiber sensor with improved sensitivity for refractive indices ranging from 1.3629 to 1.4479. The device relies on the coupling between a long period grating (LPG) transducer and a localized surface plasmon resonance (LSPR). Sensor operation is based on the transference of energy from LPG cladding modes at the visible spectral range to the LSPR. The transducer consists of a long period grating 3.15-mm-long covered with 2-7 nm gold nanoparticles. The sensor is intensity coded at a 568 nm wavelength, presenting sensitivity of 208%/unit of refractive index for a refractive index of 1.39 and resolution better than 0.0003 for the dynamic range of refractive indices from 1.3629 to 1.4479.
The sensitivity and dynamical range of an optical-fiber transducer consisting of a long-period grating coated with gold nanoparticles is investigated. For a grating with an 80 μm spatial periodicity, the resonances close to the turning point lie within the 450-900 nm spectral range. Employing a bottom-up production route, the localized surface plasmon resonance of gold nanoparticles is matched to the grating resonances; it is shown that this results in an increase in the refractive index sensitivity of the device. The device also shows increased dynamic range and enhanced refractive index sensitivity in water.
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