主动拉曼增益介质中快光传播的非线性理论

Theory of Fast-Light Propagation in Active Raman Gain Media

介绍了最近发展的主动拉曼增益介质中快光传播的非线性理论。首先介绍了三能级Λ型和四能级N型主动拉曼增益介质中光的线性传播特性的研究结果,指出两者都可实现群速度为负值的快光传播,但在四能级体系中由于额外耦合光场的引入可导致量子干涉效应,使得信号光场的单峰增益谱线劈裂为双峰结构,利用该特性可实现共振点附近介质增益的有效抑制。其次介绍了在四能级体系中利用主动拉曼增益获得Kerr非线性效应的显著增强。再次介绍了主动拉曼增益体系中弱光的非线性传播。通过体系的色散与Kerr非线性效应的平衡可实现光学厚介质中非线性光脉冲的稳定传播,特别是形成弱光水平下的快光孤子。最后对主动拉曼增益体系中快光的进一步研究提出了展望。

Latest achievements in the theory of fast-light propagation in active Raman gain media are reviewed.Firstly,the linear propagation of light in three-level Λ-type and N-type active Raman gain media is introduced.Both of the systems are able to realize fast-light propagation with a negative group velocity.However,the N-type active Raman gain medium can exhibit a doublet structure in the gain spectrum based on the interference introduced by an additional coupling field.This feature can be used to effectively suppress the gain near the resonance.Secondly,the significant enhancement of Kerr nonlinearity in N-type active Raman gain medium is discussed.Thirdly,the nonlinear propagation of light in N-type active Raman gain media is introduced.Through a balance between the dispersion and nonlinearity of the system,it is possible to form a stable superluminal soliton at very low light level in such optically thick medium.A prospect is given in the end of the article.