Linkage of oxygen deficiency defects and rare earth concentrations in silica glass optical fiber probed by ultraviolet absorption and laser excitation spectroscopy

Abstract

Ultraviolet absorption measurements and laser excitation spectroscopy in the vicinity of 248 nm provide compelling evidence for linkages between the oxygen deficiency center (ODC) and rare earth concentrations in Yb and Er-doped glass optical fibers. Investigations of YAG-derived and solution-doped glass fibers are described. For both Yb and Er-doped fibers, the dependence of Type II ODC absorption on the rare earth number density is approximately linear, but the magnitude of the effect is greater for Yb-doped fibers. Furthermore, laser excitation spectra demonstrate unambiguously the existence of an energy transfer mechanism coupling an ODC with Yb(3+). Photopumping glass fibers with a Ti:sapphire laser/optical parametric amplifier system, tunable over the 225-265 nm region, or with a KrF laser at 248.4 nm show: 1) emission features in the 200-1100 nm interval attributable only to the ODC (Type II) defect or Yb(3+), and 2) the excitation spectra for ODC (II) emission at ~280 nm and Yb(3+) fluorescence (λ ~1.03 μm) to be, within experimental uncertainty, identical. The latter demonstrates that, when irradiating Yb-doped silica fibers between ~240 and 255 nm, the ODC (II) defect is at least the primary precursor to Yb(3+) emission. Consistent with previous reports in the literature, the data show the ODC (II) absorption spectrum to have a peak wavelength and breadth of ~246 nm and ~19 nm (FWHM). Experiments also reveal that, in the absence of Yb, incorporating either Al(2)O(3) or Y(2)O(3) into glass fibers has a negligible impact on the ODC concentration. Not only do the data reported here demonstrate the relationship between the ODC (II) number density and the Yb doping concentration, but they also suggest that the appearance of ODC defects in the fiber is associated with the introduction of Yb and the process by which the fiber is formed.

The three-electron bond =Si<O_2:∙Yb absorption center of pre-darkened ytterbium-doped silica

“…In [1] a linear dependency for pristine Yb and Er-doped fibers between type II oxygen deficiency center (ODC(II)) absorption at 245 nm (5.06 eV) and rare earth number density is found. The direct ODC(II) to Yb emission excitation in these fibers is in [1] seen as either direct ODC(II) to Yb excitation transfer or that ODC(II) and Yb emission hold a common origin for UV excitation.…”

“…The difference between observed centers of [1,3] and [4] is in [1] proposed to be due to drawing induced ODC(II) measured on drawn fibers whereas [3,4] are for preform material. It is further in [1] hinted at that ODC(II), the E' center and non-bridging oxygen hole center (NBOHC) all are participants in UV-induced defect inter conversion processes [5] that provides one potential avenue for PD in Yb/Al fibers.…”

“…Several mechanisms and species potentially responsible for PD and the herewith associated PD color center (CC) have been proposed as discussed in [1,2] but a definitive explanation for the process remains a subject of debate.…”

“…The direct ODC(II) to Yb emission excitation in these fibers is in [1] seen as either direct ODC(II) to Yb excitation transfer or that ODC(II) and Yb emission hold a common origin for UV excitation. The growing Tm 3+ /Er 3+ trace impurity emission found to follow increase of PD in [2] collaborate this.…”

“…It is further in [1] hinted at that ODC(II), the E' center and non-bridging oxygen hole center (NBOHC) all are participants in UV-induced defect inter conversion processes [5] that provides one potential avenue for PD in Yb/Al fibers. The E' center and NBOHC hold, respectively, 5.6 -5.7 eV and ≈4.8 eV in center absorption [5].…”