We propose a technique to design highly-efficient and -unidirectional DFB Raman fiber lasers based on the engineering of the grating’s coupling coefficient including a π -phase shift position in the fiber. For this purpose, first the ideal intra-cavity signal powers for different pump power levels are determined for given fiber lengths. Then, the sum and difference between the counter-propagating wave intensities at each small segment within fiber lengths are calculated resulting in determining the ideal grating’s coupling functions for co- and contra-directional-pumping. The steady-state behavior of the laser using realistic parameters is finally simulated for modified coupling functions considering the Kerr nonlinearity. For a 10 W co-directional-pumped, ∼1 m long single-mode super-efficient DFB, a ∼50% increase in the laser efficiency, more than 44 dB reduction in contra-directional lasing power, ∼15 times drop in the peak power of intra-cavity signal and ∼38% decrease ...

中文翻译：

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具有耦合系数纵向变化的光栅：分布式反馈拉曼光纤激光器的超效率和单向性

我们提出了一种基于光栅耦合系数（包括光纤中π相移位置）的工程设计高效单向DFB拉曼光纤激光器的技术。为此，首先针对给定的光纤长度确定不同泵浦功率水平的理想腔内信号功率。然后，计算光纤长度内每个小段的反向传播波强度之间的和与差，从而确定用于同向和反向泵浦的理想光栅的耦合函数。最后，考虑到Kerr非线性，使用修改后的耦合函数模拟了使用实际参数的激光器的稳态行为。对于10 W定向泵浦，〜1 m长的单模超高效DFB，激光效率提高了〜50％，