We show the formation of tunneling-induced ultraslow bright and dark solitons in an asymmetric double-quantum- well structure based on the tunneling induced transparency. In this semiconductor structure, the pump field is replaced by the electron-tunneling coupling, which can be modulated by a static electric field. With appropriate conditions, we demonstrate by modulating the intensity of the static electric field that the interplay between the group velocity dispersion and the self-Kerr nonlinearity results in the generation of dark and bright solitons with ultraslow group velocity.
Bistability behaviors in an optical ring cavity filled with a dense V-type four-level atomic medium are theoretically investigated. It is found that the optical bistability can appear in the negative refraction frequency band, while both the bistability and multi-stability can occur in the positive refraction frequency bands. Therefore, optical bistability can be realized from conventional material to negative index material due to quantum coherence in our scheme.
