Detailed study of Er:YAG-derived optical fiber

This thesis presents a characterization of four Er:YAG-derived fibers with similar geometries and increasing erbium concentrations. Fibers were fabricated from bulk Er:YAG glass rods with 1%, 2%, 4%, and 5% erbium weight percentages using MCM. Fiber segments from these draw with 10 μm core diameters and consistent concentrations of silica, yttria, and alumina were compared. These four fibers exhibited matching results including a core refractive index peak of 1.544, absorption cross-section peaks of 0.25 pm2 near 980 nm and 0.63 pm2 near 1530 nm, and an emission cross-section peak of 0.65 pm2 near 1530 nm. Fluorescence lifetimes of the 4I13/2 energy state were found to decrease with erbium concentration. Relative abundances of isolated and clustered Er3+ sites were identified from the radiative decay measurements. The maximum upper state lifetime was identified in the 1% Er:YAG fiber to be 8.3 ms. Lifetimes were also investigated in their relation to draw position, showing an increase in radiative lifetime towards either end of the draw. It was found that ion clusters increase in number later during the draw process despite more erbium being present at the beginning of the draw. This identifies the beginning of the draw as an ideal position for increased efficiency and shorter amplifier lengths. A three-stage EDFA was configured for efficiency and SBS measurements. Amplifier efficiency results were consistent with lifetime results with respect to erbium concentration. A maximum efficiency of 32.7% was observed in the 1% Er:YAG fiber and minimum efficiency of 18.7% in the 5% Er:YAG fiber. The Brillouin gain coefficient of the fibers was estimated to be 0.39 ×10^(-11) m/W, which is significantly lower than that of silica fiber. These results show the effectiveness of highly concentrated Er:YAG fibers in EDFAs as well as reveal trends in erbium concentration and MCM fiber draw parameters that merit further investigation