title: Analysis of color-center-related contribution to Bragg grating formation in Ge:SiO 2 fiber based on a local Kramers -Kronig transformation of excess loss spectra.
abstract: UV-induced excess losses have been measured at various pulse energy densities and exposure times in germanosilicate optical fiber preform cores. The corresponding refractive-index changes have been determined through a Kramers -Kronig analysis. Because of the nonlinear behavior of the excess losses as a function of both exposure time and fluence per pulse, one should be careful when comparing the refractive-index modulation deduced from such measurements with that obtained from Bragg grating reflectivity. Indeed nonlinear effects such as saturation imply that it is necessary to take into account the local character of the change in absorption to calculate the evolution of the refractive-index modulation accurately as a function of the exposure time. Implications of these results are discussed.
authors.forename: B
authors.initials: B
authors.lastname: Leconte
authors.forename: W X
authors.initials: WX
authors.lastname: Xie
authors.forename: M
authors.initials: M
authors.lastname: Douay
authors.forename: P
authors.initials: P
authors.lastname: Bernage
authors.forename: P
authors.initials: P
authors.lastname: Niay
authors.forename: J F
authors.initials: JF
authors.lastname: Bayon
authors.forename: E
authors.initials: E
authors.lastname: Delevaque
authors.forename: H
authors.initials: H
authors.lastname: Poignant