title: Negative axial strain sensitivity in gold-coated eccentric fiber Bragg gratings.
abstract: New dual temperature and strain sensor has been designed using eccentric second-order fiber Bragg gratings produced in standard single-mode optical fiber by point-by-point direct writing technique with tight focusing of 800 nm femtosecond laser pulses. With thin gold coating at the grating location, we experimentally show that such gratings exhibit a transmitted amplitude spectrum composed by the Bragg and cladding modes resonances that extend in a wide spectral range exceeding one octave. An overlapping of the first order and second order spectrum is then observed. High-order cladding modes belonging to the first order Bragg resonance coupling are close to the second order Bragg resonance, they show a negative axial strain sensitivity (-0.55 pm/με) compared to the Bragg resonance (1.20 pm/με) and the same temperature sensitivity (10.6 pm/°C). With this well conditioned system, temperature and strain can be determined independently with high sensitivity, in a wavelength range limited to a few nanometers.
authors.affiliation: Electromagnetism and Telecommunication Department, University of Mons (UMONS), Boulevard Dolez, 31, 7000 Mons, Belgium.
authors.forename: Karima
authors.initials: K
authors.lastname: Chah
authors.affiliation: Electromagnetism and Telecommunication Department, University of Mons (UMONS), Boulevard Dolez, 31, 7000 Mons, Belgium.
authors.forename: Damien
authors.initials: D
authors.lastname: Kinet
authors.affiliation: Electromagnetism and Telecommunication Department, University of Mons (UMONS), Boulevard Dolez, 31, 7000 Mons, Belgium.
authors.forename: Christophe
authors.initials: C
authors.lastname: Caucheteur