Yaguang Zeng

Superluminal optical solitons in a four-level tripod atomic system

With one weak probe field and two strong pumping fields, superluminal optical solitons are formed in a lifetime-broadened four-level tripod atomic medium. With proper parameters, both dark and bright solitons can occur in the highly resonant medium. The corresponding group velocity of the solitons can be superluminal. Meanwhile, the conditions for superluminal solitons occurrence are given.

Phase effects on group velocity propagation in a V-type system with spontaneously generated coherence

The effects of the relative phase between two laser beams on the propagation of a weak electromagnetic pulse are investigated in a V-type system with spontaneously generated coherence (SGC). Due to the relative phase, the subluminal and superluminal group velocity can be unified. Meanwhile, SGC can be regarded as a knob to manipulate light propagation between subluminal and superluminal.

Superluminal solitons in a Λ-type atomic system with two-folded levels

With one weak pulsed probe field, one strong pumping field, and one coupling field, superluminal optical solitons are formed in a lifetime-broadened Λ-type atomic medium with two-folded levels. The corresponding group velocity of the solitons can be larger than the vacuum light speed c; i.e., superluminal solitons can be presented.

Knob of the group velocity by the external field coupling two upper levels

We investigate how the external field coupling the two upper levels produces a variety of effects on the propagation of a weak electromagnetic pulse in a V-type atomic system. Due to the upper level (UL) coupling field, the dispersion of the system has been influenced by the relative phase. Then, subluminal and superluminal phenomena can be unified. Thus, the external field and the relative phase can be regarded as switches to manipulate light propagation between subluminal and superluminal.

Sub- and superluminance with gain in a three-level ladder-type atomic system with spontaneously generated coherence

The effects of spontaneously generated coherence (SGC) on the propagation of a weak probe pulse are investigated in a ladder-type atomic system. Due to SGC, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The effects of the incoherent pumping and the relative phase on the group velocity are also studied. They all can be used as switches to manipulate the group velocity of the weak probe field from gain-assisted sub- to superluminance.

Exhibition of subluminal solitons in a four-level atomic system with two-folded levels

With one weak probe, one strong pumping and one control field, the group velocity dispersion can be balanced by the Kerr effects in a lifetime-broadened four-level atomic medium with two folded levels with proper parameters. This results from the subluminal optical solitons that are formed. Additionally, the conditions for which subluminal solitons occur are given.