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实验采用共振增强式非线性折射率调制技术实现了半导体可饱和吸收镜锁模全保偏掺镱光纤激光器重复频率的精确锁定。在掺镱光纤激光器的腔内加入一个980/1064nm的波分复用器(WDM)和一段掺铒增益光纤,通过反馈控制加载在该掺铒光纤上的976nm抽运光LD2功率调控掺铒光纤的非线性折射率,进而对激光器的光学腔长实施控制,最终实现重复频率的精确锁定。优化了不同掺铒光纤长度及抽运光初始功率对激光器重复频率控制范围和锁定精度的影响。结果表明:当掺铒光纤长度为1.75m时,通过调整抽运光功率能够实现180Hz的重复频率调整范围;而重复频率的锁定精度仅与抽运光的初始功率密切相关,并不受掺铒光纤长度的明显影响。当LD2抽运光强度为18mW时,重复频率峰-峰值的波动范围小于0.5mHz,相应的标准偏差为0.16mHz,输出功率的标准偏差为0.009mW。此外,通过反馈控制抽运源LD1的强度,并取掉了腔内的掺铒增益光纤及与其相连的WDM,发现由于共振增强非线性和克尔非线性对光纤折射率的叠加,在稳定的单脉冲锁模区间内,重复频率单调变化的范围增加至1kHz,而锁定精度略有降低。
In this experiment, the resonance-enhanced nonlinear refractive index modulation technique is used to achieve the exact locking of the repetition frequency of a fully saturable Ytterbium-doped fiber laser with a saturable absorption mirror. A 980 / 1064nm wavelength division multiplexer (WDM) and a section of erbium-doped gain fiber are added into the cavity of the ytterbium-doped fiber laser to control 976nm pumping light LD2 loaded on the erbium-doped fiber by feedback control. The power control erbium-doped fiber Of the nonlinear refractive index, and then the implementation of the optical cavity length control, and ultimately achieve the exact frequency of the lock. The effects of different erbium-doped fiber lengths and initial pumping power on the control range and locking accuracy of laser repetition rate are optimized. The results show that when the length of erbium-doped fiber is 1.75m, the adjustment range of 180Hz can be achieved by adjusting the pump power. The locking accuracy of repetition frequency is only closely related to the initial power of pumping light, Significant effect of fiber length. When LD2 pumping light intensity is 18mW, the repetition frequency peak-to-peak fluctuation range is less than 0.5mHz, the corresponding standard deviation is 0.16mHz and the output power standard deviation is 0.009mW. In addition, by controlling the intensity of the pumping source LD1 and removing the erbium-doped fiber in the cavity and the WDM connected thereto, it is found that due to the superposition of resonance-enhanced nonlinearity and Kerr nonlinearity on the refractive index of the fiber, Within the single-pulse mode-locked range, the range of monotonous changes in repetition frequency increases to 1 kHz, while the locking accuracy decreases slightly.