Measurement of thermal binding energy of photodarkening-induced color centers in ytterbium-doped silica fibers

We report on thermal bleaching measurements of photodarkening-induced color centers in ytterbium-doped silica fibers. We make use of the similarity between UV and photodarkening-induced defects and apply a model, developed to describe and predict the performance of thermal decay of UV-induced fiber Bragg gratings [1], to study the thermal binding energy associated with photodarkening-induced color centers. This model assumes a broad distribution of trap sites, with the rate of thermal depopulation being an activated function of the trap depth [1]. Fraction of depopulated traps is uniquely defined by the demarcation energy Ed, with traps having energy greater than Ed remaining unchanged. Time t and temperature T are related through Ed = kBT·ln(v0t), where kB=8.62·10⁻⁵ eV/K is Boltzmann's constant and v0 is a frequency term (attempt frequency), obtained by acquiring datasets at different temperatures and fitting them together.