title: Heat-induced darkening and spectral broadening in photodarkened ytterbium-doped fiber under thermal cycling.
abstract: We study thermal bleaching of photodarkening-induced loss in a 20-microm core diameter, large-mode-area ytterbium-doped silica fiber. Pristine and photodarkened samples are subjected to thermal cycling pulses. Recovery of the photodarkened fiber absorption coefficient initiates at approximately 350 degrees C and complete recovery is reached at approximately 625 degrees C. However, prior to recovery, the photodarkened fiber exhibits further heat-induced increase of absorption loss. This increase of loss is attributed to both a permanent increase of loss-inducing color centers and a temperature-dependent broadening of the absorption spectrum. Post-irradiation heat-induced formation of color centers suggests the presence of an intermediate energy state in the near-infrared photochemical mechanism for photodarkening.
authors.affiliation: Helsinki University of Technology, Tietotie 3, FIN-02015 TKK, Finland. mikko.soderlund@tkk.fi
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Söderlund
authors.forename: Joan J
authors.initials: JJ
authors.lastname: Montiel i Ponsoda
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Koplow
authors.forename: Seppo
authors.initials: S
authors.lastname: Honkanen
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D055100:Optical Fibers; D017785:Photons; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012822:Silicon Dioxide / Q000737:chemistry*; D013057:Spectrum Analysis / Q000295:instrumentation*; D015018:Ytterbium / Q000737:chemistry*
chemical_list: D012822:Silicon Dioxide; D015018:Ytterbium