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掺杂半径的选择是部分掺杂光纤能够有效选模的关键。从模式的归一化模场分布出发,通过对模式场分布的比较,确定采用较小或较大的掺杂半径均不利于基模的选取。从饱和增益和功率分配两个角度详细分析了掺杂半径的变化对各模式的增益获取能力和功率提取能力的影响。纤芯掺杂半径的变化改变了模式场与增益粒子的相互作用机会,因而改变了各模式的增益获取能力及模式功率的输出大小。当掺杂分布与基模场分布达到最佳重叠并使得基模在强度上占据优势时,则基模获得的增益超过其他模式,输出功率达到最大。定量计算结果说明,阶跃光纤采用0.6左右的相对掺杂半径可以有利于提取基模。
The choice of doping radius is the key to the effective selection of partially doped optical fiber. Starting from the normalized mode field distribution of the mode, it is not conducive to the selection of the fundamental mode that the smaller or larger doping radius is determined by comparing the mode field distribution. From the two aspects of saturation gain and power distribution, the influence of the change of doping radius on gain gain and power extraction ability of each mode is analyzed in detail. The variation of the core doping radius changes the chances of interaction between the mode field and the gain particles, thus changing the gain gain of each mode and the output power of the mode power. When the doping profile and the fundamental mode field reach the best overlap and make the fundamental mode dominant in strength, the gain obtained by the fundamental mode exceeds that of the other modes and the output power reaches the maximum. Quantitative calculation results show that step fiber with a relative doping radius of about 0.6 can be helpful to extract the fundamental mode.