Bound modes gain in microstructured optical fibers

Using of the model with a complex refraction index, amplification in microstructured optical fibers is investigated. The effect of the gain on the properties of high-order modes is considered. It is shown, that the variation of the radius of active core of the fiber allows to optimize the excitation of fundamental mode in few-mode fibers. Special arrangement of active elements in cross-section section of the fiber allows to excite high-order mode selectively.