Gao Lei, Zhu Tao, Wabnitz Stefan, Liu Min, Huang Wei
Key Laboratory of Optoelectronic Technology &Systems (Ministry of Education), Chongqing University, Chongqing 400044, China.
Dipartimento di Ingegneria dell'Informazione, Università degli Studi di Brescia and INO-CNR, via Branze 38, 25123 Brescia, Italy.
Sci Rep. 2016 Apr 29;6:24995. doi: 10.1038/srep24995.
Stochastically driven nonlinear processes limit the number of amplified modes in a natural system due to competitive mode interaction, which is accompanied by loss of coherence when increasing the complexity of the system. Specifically, we find that modulation instability, which exhibits great fluctuations when it spontaneously grows from noise in conservative systems, may possess a high degree of coherence in dissipative laser system with gain. Nonlinear mode interactions can be competitive or cooperative: adjusting the intracavity polarization state controls the process of loss of coherence. Single-shot spectra reveal that, first, the fibre laser redistributes its energy from the center wavelength mode into sidebands through parametric instabilities. Subsequently, longitudinal modes are populated via cascaded four-wave-mixing. Parametric frequency conversion populates longitudinal modes with a random distribution of position, intensity and polarization, resulting in partially (rather than highly) coherent pulses. These dynamics unveil a new route towards complex pattern formation in nonlinear laser systems, and they may be also beneficial for the understanding of supercontinuum, Kerr-combs phenomena, and optical rogue waves.
由于竞争模式相互作用，随机驱动的非线性过程限制了自然系统中放大模式的数量，当系统复杂性增加时，这种相互作用伴随着相干性的丧失。具体而言，我们发现，调制不稳定性在保守系统中由噪声自发增长时表现出很大的波动，但在具有增益的耗散激光系统中可能具有高度的相干性。非线性模式相互作用可以是竞争性的或合作性的：调整腔内偏振态可控制相干性丧失的过程。单次光谱显示，首先，光纤激光器通过参量不稳定性将其能量从中心波长模式重新分配到边带。随后，纵向模式通过级联四波混频被填充。参量频率转换以随机分布的位置、强度和偏振填充纵向模式，从而产生部分（而非高度）相干脉冲。这些动力学揭示了非线性激光系统中复杂图案形成的一条新途径，它们可能也有助于理解超连续谱、克尔频率梳现象和光学 rogue 波。
