Nonlinear transmission and color-center dynamics in germanosilicate fibers at 420-540 nm

We report evidence in support of the view that induced loss and nonlinear transmission in pure germanosilicate fibers at blue-green wavelengths are governed by the formation (through two-photon absorption), spontaneous and stimulated transformation, and bleaching (through single-photon events) of Ge(1), Ge(2), and Ge(3) color centers. Using a tunable pulsed-dye laser, the excitation spectrum of the induced absorption, its spectral attenuation, and the effects of Ge concentration and thermal annealing are investigated.