0733-8724 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JLT.2019.2915012, Journal of Lightwave Technology > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract— thirteen different single-mode optical fibers have been experimentally and theoretically characterized highlighting the influence of the core and cladding dopants on their Brillouin signatures: Brillouin spectrum, temperature and strain coefficients. Tailoring the composition and the refractive index profile, optical fibers presenting Brillouin spectrum with multiple peaks have been designed, offering discrimination capabilities between the temperature and strain distributions along a single optical fiber. Index Terms—Optical fiber sensors, optical fiber, temperature, measurement, strain measurement I. INTRODUCTION ptical fiber sensors have attracted much attention due to their many advantages such as their light weight or their distributed capabilities [1],[2]. Among the various fiber sensor technologies, the one exploiting the Brillouin scattering phenomenon to monitor strain and/or temperature dependence has been deeply studied. Various architectures of distributed sensor exist such as BOTDR (Brillouin Optical Time-Domain Reflectometry) or BOTDA (Brillouin Optical Time-Domain Analysis) and fulfill the main requirements of the major applications in the civil engineering and oil and gas industry domains [3]. One of the remaining challenges to be overcome with this class of sensors concerns its capacity to discriminate between the strain and the temperature changes along a single optical fiber. Several solutions at the component level have been evaluated such as the use of photonic crystal fibers, sapphire-based or polarization maintaining fibers [4–6]. At the system level, suggested solutions usually combine two sensor technologies: Raman and Brillouin or Rayleigh and Brillouin [7–9], or imply to probe two identical optical fibers in the same cable one with a stress-free packaging [10]. C. Sabatier, S. Girard, Y. Ouerdane, A. Ladaci, A. Boukenter, and E. Marin, are with Univ Lyon, UJM, CNRS, IOGS, Laboratory Hubert Curien (LabHC), UMR 5516, 42000 Saint-Etienne, France, phone : (+33)469 663 269; email:, camille.sabatier@univ-st-etienne.fr; Emmanuel.marin@univ-st-etienne.fr C. Sabatier, A. Ladaci, T. Robin, and B. Cadier are with iXblue, Rue Paul Sabatier, 22300 Lannion, France email: camille.sabatier@ixblue.com C. Sabatier, A. Ladaci, and L. Mescia are with Politecnico di Bari, Via Amendola, 126/B, 70126 Bari, Italy Another approach was first presented in [11]: if a fiber presents a multi-peak Brillouin signature and if these peaks are characterized by different temperature and strain coefficients, the discrimination becomes possible along this fiber. The LEAF fiber by Corning presents such multi-peaks signature but the discrimination between the temperature and the strain was shown to be limited as these peaks present too close temperature and strain coefficients. Theoretical and experimental study have been presented in [12] to discriminate the temperature and the strain with multi-peak fibers. In this paper, we will investigate the Brillouin signature of numerous optical fibers, covering the main compositions used for Telecom and/or sensing applications. We first investigated the impact of the core dopant on the Brillouin scattering confronting our experimental measurements with simulations. In a second time the impact of the nature of the co-dopants (GeO2, P2O5, and F) incorporated in the silica-based cladding of a germanosilicate optical fiber on its Brillouin response is characterized. Obtained results provide evidence for the capacity of such fibers to discriminate between the strain and the temperature, the achieved performances are compared to the literature data. II. EXPERIMENTS AND SIMULATION DETAILS A. Experimental procedure To study the impact of the core dopant on the fiber Brillouin signature, seven very different optical fibers have been characterized. TABLE I reports all the sample core dopants: GeO2, P2O5, F, Ce and pure-silica-core (PSC) fiber. The second study concerns the impact of the cladding co- dopants and of the refractive index profile (RIP) on Brillouin signature. The used germanosilicate sample characteristics are reported in TABLE II. Fig 1 illustrates our experimental set-up. A BOTDA (Stimulated Brillouin Scattering – SBS) interrogator from OZ Optics operating at 1550 nm has been used to characterize the fibers. It’s well known that the Brillouin responses are probe power dependent. For a selected interrogator type (spontaneous or stimulated), their signatures can differ. Above the SBS threshold, the main resonance peak keeps increasing with the input power, while the other resonance peaks decrease in intensity and disappear eventually [13]. To determine their strain coefficients, a sample of each Combined Experimental and Simulation Study of the Fiber Composition Effects on its Brillouin Scattering Signature C. Sabatier, Student Member, IEEE, S. Girard, Senior Member, IEEE, L. Mescia, A. Ladaci, T. Robin, B. Cadier, A. Boukenter, Y. Ouerdane, and E. Marin O