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 E d , with traps having energy greater than E d remaining unchanged. Time t and temperature T are related through E d = k B T·ln(v 0 t), where k B =8.62·10−5 eV/K is Boltzmann's constant and v 0 is a frequency term (attempt frequency), obtained by acquiring datasets at different temperatures and fitting them together.