The proposed work has the aim to investigate a full analog electrical circuitry to convert the wavelength-encoded signal coming from a pair of Fiber Bragg Grating (FBG) sensors into a single monotonic electrical signal. The latter can be used either to be read from a PLC system (or directly by a switch) if a 4-20 mA signal is needed (e.g. for safety application) or to have an instantly conversion without employing the classical interrogation system with a post-processing by means of a digital unit. Since its peculiarities (robust, reliable and completely free from any digital processing section) the proposed system has the aim to overcome the classical interrogator, with the aim to pave the way to a wider employment of FGB sensor in that environment where the reliability given by the interrogator based on multiple digital processing unit, handled by an operative system, may be subjected to failure. In the proposed manuscript, the system was studied analytically and numerically, taking advantage of its characteristic to behaves linearly in a range of 200pm Bragg wavelength shifting, due to the Arrayed Waveguide Grating (AWG) device, used as optical filter. As results, the capability to perform compensated measurement, by means of 2 FBG subjected to different physical quantities, was investigated. The obtained formula comprises FBGs linear coefficient in function of the physical phenomenon to measure and the system output.
We report on a innovative Lab on Fiber (LOF) dosimeter for ionizing radiation monitoring at ultra-high doses. The new dosimeter consists in a metallo-dielectric resonator at sub-wavelength scale supporting localized surface plasmon resonances realized on the optical fiber (OF) tip. The resonating structure involves two gold gratings separated by a templated dielectric layer of poly(methyl methacrylate) (PMMA). Two LOF prototypes have been manufactured and exposed, at the IRRAD Proton Facility at CERN in Geneva, to 23 GeV protons for a total fluence of 0.67x1016 protons/cm2 , corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrate the "radiation resistance" feature of the LOF devices and a clear dependence of the reflected spectrum on the total dose, expressed by a cumulative blue-shift of ~1.4 nm of the resonance combined with a slight increase of 0.16 dBm in the reflected spectrum. According to the numerical analysis and the literature, the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for High Energy Physics (HEP) experiments.
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