Numerical analysis of pulse amplitude in harmonic mode locked ring fiber laser
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摘要: 为了研究马赫-曾德尔型调制器的调制特性及锁模脉冲振幅均衡条件,采用调节直流偏置电压和调制深度的方法,来控制调制器透射曲线。通过时域分析,在5GHz调制频率下对锁模脉冲序列和调制曲线进行数值研究。用MATLAB软件模拟分析了2阶～7阶锁模光脉冲序列和调制曲线的时域分布图。数值分析结果表明,锁模脉冲振幅均衡的条件是光脉冲序列经过调制器后经历相同的透射系数。线性调制区与非线性调制区均可获得振幅均衡的锁模脉冲;当有理数谐波锁模阶数p4时,调制深度β变化对脉冲振幅均衡程度影响剧烈。该结果对获得功率均衡的谐波锁模脉冲的实验研究有一定的参考意义。Abstract: The modulating characteristics of Mach-Zehnder modulator and pulse-amplitude equalization condition were demonstrated in detail.By adjusting the direct-current bias voltage and modulation depth,the shape of transmission curve can be controlled.Mode locking pulse train and the modulator transmission curve were numerically studied in time domain at 5GHz of modulation frequency.The pulse train and modulation curves for mode-locking pulse in the second to seventh order were simulated and analyzed with MATLAB software.The numerical result shows that: equalization of pulse-amplitude occurs only when the transmission coefficient in the modulator is uniform; amplitude-equalized pulses can be obtained both in the linear region and the nonlinear region; when the rational harmonic mode-locking order p is larger than 4, the value of modulation depth affects the pulse-amplitude equalization severely.The figure in the paper is laconic and the result is helpful to get amplitude equalized mode-locked pulses in experiments.
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