الفهرس 
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Abstract
This work deals with the improvement of the performance of optical fiber arnplifie This is done by enhancing the performance of optical amplifiers, which are the maj component in optical communication systems. The main interest of the study is devoted rare earth doped optical amplifiers. This thesis provides a numeçical investigation of I performance of erbium and praseodymium doped optical amplifiers. The performar parameters that have been investigated are the gain coefficient, gain spectrum, minimi noise figure and the equivalent input noise factors.
First, the dependence of both the gain coefficient and the minimum noise figure the emission and absorption cross sections of the rare earth element doped in the fiber studied. These parameters are calculated for different values for the pump and sig. wavelengths. Then, the effect of changing the direction of the pumping signal, with respect the input signal, on the gain and noise performance of the amplifier is investigated. This carried out by calculating the equivalent input noise factor and noise figure for both forw and backward pumping schemes. The role of aluminum in improving the performance of I optical amplifier is also proved in this work through comparing the performance paramet of a germanosilicate host to an alumino-germanosilicate glass host. Finally, the performar of praseodymium doped fiber amplifiers in ZBLAN host material has been studied ir similar fashion and its results are compared to the reported results on EDFAs. To the best our knowledge, the studied materials have not been investigated before, although so experimental results are scattered, here and there, in the literature.