中文摘要：

将信号模场和增益离子横向分布函数引入功率传输方程,采用多环法计算少模光纤放大器中信号及ASE的传输放大。研究增益离子分布对模式竞争和信噪比（SNR）的影响。对照模型改进前后结果,给出两种模型各自适用范围。结果表明,信号填充因子是表征不同模式在竞争中强弱地位的有效指标。增益离子集中掺杂有利于基模的放大和高阶模的抑制;集中均匀掺杂60%～70%较利于基模选择;随着掺杂范围趋于集中,ASE显著降低,信噪比逐渐提高。

英文摘要：

Transverse mode distribution and dopant profile are introduced in propagation-rate equations. An approximate numerical algorithm by multilayer method is presented to calculate the power of amplified signal and amplified spontaneous emission （ASE） in multimode fiber amplifiers. Numerical results of the propagation-rate equations before and after the improvement are compared. It shows that power filling factor is the key indication to describe the transverse mode competition behavior. Dopant profile makes great effect in mode selection and 60% - 70% confinement of flat doping is more helpful in high-order mode suppression. ASE significantly drops and SNR increases when the ions are doped more concentrated in the fiber core.