粒子在基态和亚稳态之间的振荡会导致探测光吸收的降低,而探测光束在很窄的频率范围内吸收的降低, 会使介质的感生折射率在同样范围内迅速变化, 从而改变群折射率ng=n(ω)+ωdn/dω。本文利用光纤慢光理论, 对不同条件下的群折射率限定和群速度的变化特性展开讨论。群折射率随光纤长度的增加而降低, 不同离子浓度的掺铒光纤中慢光的感生群折射率均随调制频率的增加而降低, 同时在不同的调制频率条件下, 群折射率随入射信号光强度的增大均有一个饱和的过程。

The electron population oscillating between the ground and metastable level in the beat frequency between the pump and probe beam can result in the reduced absorption of the probe wave. The probe wave experiences the reduction of absorption in a narrow frequency band, which corresponds to rapid changes of the refractive index. According to the equation of ng=n(ω)+ωdn/dω, the group refractive index will increase. Utilizing the theory of slow light, the limitation of group refractive index in different environments and the change of group velocity were discussed. It is found that the group refractive index decreases with the increasing of the fiber length. The group refractive indices in the fibers with different Er3+ concentration decrease with the increasing of the modulation frequency, and the group refractive index has a saturation process with the increasing of the signal power under different modulation frequency.