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基于非线性偏振旋转锁模原理、非线性薛定谔方程和色散波干涉理论,建立了被动锁模光纤激光器的光谱分析模型。采用此模型进行数值仿真,研究了腔体长度、增益光纤长度和耦合输出比对光谱边带的影响。并分别采用13 m、16 m和26 m的腔长,0.5 m,1.5 m和3 m的掺铒光纤以及不同的耦合输出比进行了实验,对比了上述情况下激光器的输出光谱。实验与仿真结果表明,要抑制光谱边带,应尽量缩短腔长,适当增加增益光纤的长度和采用较低的耦合输出比,并保证激光器处在基阶锁模状态。理论模型的仿真结果与实验现象吻合较好。取3 m增益光纤、13 m腔长和10%的输出比,获得了光谱边带抑制较好、谱宽20.4 nm的锁模脉冲激光,重复频率为15.87 MHz,单脉冲能量约0.52 nJ,脉冲幅值和光谱谱宽分别存在约4%和2%的波动。
Based on the theory of nonlinear polarization rotation mode-locking, nonlinear Schrödinger equation and the theory of dispersion wave interference, the spectral analysis model of passive mode-locked fiber laser was established. The model was used to simulate the effect of cavity length, gain fiber length and coupling output ratio on spectral sideband. The output spectra of lasers were compared with 13 m, 16 m and 26 m cavity lengths, 0.5 m, 1.5 m and 3 m erbium-doped fibers and different coupling output ratios respectively. Experimental and simulation results show that to suppress the spectral sideband, the cavity length should be shortened, the length of gain fiber should be increased properly, and the coupling output ratio should be lower, and the laser should be mode locked. The simulation results of the theoretical model are in good agreement with the experimental ones. Taking a 3 m gain fiber, 13 m cavity length and 10% output ratio, a mode-locked pulsed laser with a spectral band of 20.4 nm and a repetition frequency of 15.87 MHz was obtained. The pulse energy was about 0.52 nJ. The pulse There are about 4% and 2% fluctuations in amplitude and spectral width, respectively.