利用非线性脉冲预整形实现脉冲快速自相似放大

Fast self-similar amplification through passive nonlinear pulse pre-shaping

报道了一种通过预先对信号光脉冲非线性整形,进而在光纤放大器中实现自相似演化的方法.利用透射光栅对和普通单模光纤组成被动脉冲整形装置,预先优化脉冲的时域宽度和光谱质量,使脉冲在光纤放大器中快速演化到自相似子.研究中首先通过数值模拟对比,说明了非线性整形对脉冲实现快速自相似放大的关键作用,提高了放大器输出脉冲质量,减小了去啁啾脉冲宽度.实验中,通过优化非线性整形输出,在2.2m长的掺Yb3+光纤中,在一定抽运功率范围内均实现了脉冲自相似放大,去啁啾后得到脉冲宽度60fs的变换极限脉冲输出.这种非线性脉冲预整形方法有效减小了自相似演化所需光纤长度,同时降低了自相似放大对种子源质量的要求,首次将全正色散光纤锁模激光器成功用于自相似放大,促进了当前自相似放大系统的全光纤化.

A nonlinear pre-shaper which optimizes initial pulses for self-similar evolution in a following short fiber amplifier is demon- strated. It consists of a pair of transmission gratings and a segment of single mode fiber, by which pulses are shaped temporally and spectrally before amplification. To confirm the benefit of nonlinear pre-shaping for the self-similar evolution, pulse amplifications with and without the nonlinear pre-shaper are simulated. From comparison, pulses optimized by nonlinear pre-shaper show a shorter pulse duration, less pedestal and broader spectrum after amplification and compensation. With this optimization, the self-similar amplification can be realized in a 2.2-meter Yb3＋ -doped fiber in a large range of pump power, generating 60 fs transform-limited pulses after compression. This nonlinear pre-shaping method can efficiently shorten the fiber length and release the seed quality required for self-similar amplification. An all-normal dispersion mode-locked fiber laser is employed as the seed of a self-similar amplifier for the first time, thus facilitating an all-fiber system.