"Hydroxyl ions are a common contaminant in optical fibers, and are responsible for strong absorption centered at 1380 nm that becomes significant over long optical path lengths. Recently, however, special fabrication methods have been developed that minimize the hydroxyl ion contamination, permitting use of the entire 1300-1700 nm spectral region for telecommunications. There is therefore interest in examining the Nd 4F3/2 to 4I13/2 transition for a potential optical amplifier at 1400 nm. In this thesis, the excited state absorption cross section and the overall gain/loss spectrum of neodymium in a silica glass fiber were determined for the 1200-1500 nm wavelength region using the pump-probe method. The ground state absorption cross section was also determined from transmission measurements, and the stimulated emission cross section was calculated using the fluorescence spectrum and the McCumber relation. Oscillator strengths for absorption and emission transitions were calculated in the 800-1600 nm wavelength range using the Judd-Ofelt method. The above procedures were followed for both the Nd-doped fiber, as well as an erbium-doped silica fiber. The shape of the Nd emission spectrum is also noteworthy, since the characteristic Nd peak at 1064 nm is not observed, although there is strong emission at 1092 nm. The pump-probe measurements revealed significant excited state absorption loss between 1200 and 1350 nm, due to excitation from the 4F3/2 to the higher 4G9/2 and 4G7/2 states. Between 1350 and 1475 nm, there was no net gain or loss that could be observed beyond the level of the noise. For the glass fibers studied, it appears that in the spectral region of interest for an optical amplifier, the stimulated emission and excited state absorption cancel one another out."