$\pi$-phase-shifted distributed feedback, ultralong fiber Bragg gratings (FBGs) with Raman gain have been shown to be excellent ultranarrow single-frequency lasers that can be operated at any wavelength. However, these lasers have shown unusually low slope efficiency (1%–10%), while theoretical simulations predict a much higher (30%–60%) number. We believe this poor performance is due to a thermally induced phase shift inside the FBG due to absorption of the high intensity of the signal oscillating in the cavity. To compensate for this, a thermally controlled dynamic phase shift is proposed to increase efficiency after lasing first occurs. We show here an increase in the slope efficiency of a factor of 4 and an increase in the total output efficiency by a factor of 6.5 with 6 W of pump power by reducing the phase shift once the laser begins oscillating.

中文翻译：

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通过动态控制相移提高分布式反馈拉曼光纤激光器的效率

$\pi$相移分布反馈，具有拉曼增益的超长光纤布拉格光栅（FBG）被证明是出色的超窄单频激光器，可以在任何波长下工作。但是，这些激光器显示出异常低的斜率效率（1％–10％），而理论模拟预测该数字会更高（30％–60％）。我们认为，这种较差的性能是由于吸收了在腔中振荡的高强度信号而在FBG内部产生的热感应相移所致。为了对此进行补偿，提出了一种热控制的动态相移，以在首次发射激光之后提高效率。我们在这里展示了一旦​​激光器开始振荡，通过减小相移，斜率效率将增加4倍，总输出效率将增加6.5倍（泵浦功率为6 W）。