title: Optical sensor based on hybrid FBG/titanium dioxide coated LPFG for monitoring organic solvents in edible oils.
abstract: A hybrid optical sensing scheme based on a fiber Bragg grating (FBG) combined with a titanium dioxide coated long period fiber grating (LPFG) for monitoring organic solvents in high refractive index edible oils is reported. In order to investigate and optimize the sensor performance, two different FBG/LPFG interrogation systems were investigated. The readout of the sensor was implemented using either the wavelength shift of the LPFG resonance dip or the variation in the optical power level of the reflected/transmitted light at the FBG wavelength peak, which in turn depends on the wavelength position of the LPFG resonance. Hexane concentrations up to 20%V/V, corresponding to the refractive index range from 1.451 to 1.467, were considered. For the transmission mode of operation, sensitivities of 1.41 nm/%V/V and 0.11 dB/%V/V, with resolutions of 0.58%V/V and 0.29%V/V, were achieved when using the LPFG wavelength shift and the FBG transmitted optical power, respectively. For the FBG reflection mode of operation, a sensitivity of 0.07 dB/%V/V and a resolution better than 0.16%V/V were estimated.
authors.affiliation: CAP/INESC TEC, INESC Technology and Science (formerly INESC Porto), FCUP, Faculty of Sciences, University of Porto, Portugal; Department of Physics, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Porugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Coelho
authors.affiliation: INL - International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga 4175-330 Braga, Portugal.
authors.forename: Diana
authors.initials: D
authors.lastname: Viegas
authors.affiliation: CAP/INESC TEC, INESC Technology and Science (formerly INESC Porto), FCUP, Faculty of Sciences, University of Porto, Portugal; Department of Physics, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Porugal.
authors.forename: José Luís
authors.initials: JL
authors.lastname: Santos
authors.affiliation: CAP/INESC TEC, INESC Technology and Science (formerly INESC Porto), FCUP, Faculty of Sciences, University of Porto, Portugal; Department of Physics, School of Sciences and Technology, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal. Electronic address: jmmma@utad.pt.
authors.forename: José Manuel Marques Martins
authors.initials: JM
authors.lastname: de Almeida
mesh_terms: D004043:Dietary Fiber; D005336:Fiber Optic Technology / Q000379:methods*; D055100:Optical Fibers; D010938:Plant Oils / Q000032:analysis*; D012997:Solvents / Q000032:analysis*; D014025:Titanium / Q000737:chemistry*
chemical_list: D004043:Dietary Fiber; D010938:Plant Oils; D012997:Solvents; C009495:titanium dioxide; D014025:Titanium
keywords: Fiber Bragg grating; Long period fiber grating; Monitoring contamination of olive oil; Organic solvents in edible oils; Titanium dioxide coating