Study Of Propagation Properties Of Ultrabroad-Bandwidth Pulse In Fiber Amplifiers

The fiber amplifier is widely used for pulse amplification owing to its intrinsically robust, good coupling efficiency, high reliability and compactness. So it becomes one of the most important devices in high-capacity, all-optical communication systems. In addition, the fiber amplifier offers a promising approach to generate high-power femtosecond laser pulses. The desirability of many current scientific and technological applications, such as highcapacity, long-distance, all-optical communication systems and ultrafast lasers, has motivated extensively studies of the ultrabroad bandwidth pulse amplification. In this thesis, we study the propagation properties of ultra-broad bandwidth pulse in fiber amplifiers. The main research results are listed below:Firstly, an extended version of the Ginzburg-Landau equation is derived based on the Maxwell-Bloch's equations, which describes the amplification of ultra-broad band pulse in the fiber amplifier. This equation beyond the limit of the conventional Ginzburg-Landau equation which is based on the assumption that the amplifier gain bandwidth is significantly larger than the signal's optical spectral bandwidth. So it can describes the amplification of ultra-broad band pulse in the fiber amplifier.Secondly, the computer program, which can simulate the process of linear and nonlinear propagation of optical pulses, has been independently developed based on the physical model of ultra-broad band pulse propagation in the fiber amplifier. Compared with the experimental and theoretical results reported in literatures, the validity of the computation results of our program is confirmed. The properties of propagation, especially the influence of gain bandwidth on propagation and amplification of ultra-short pulse, are investigated numerically. It is found that the narrow gain bandwidth delays the compression and dissociation of pulse, limits the efficiency of amplification in the anomalous dispersion regime, and in the normal dispersion regime it limits the stretching and amplification of pulse. In any dispersion domain, the narrow gain bandwidth deforms the pulse spectrum, slows down the spectral broadening, and decreases the saturation value of spectral broadening.