Spatial Vortex Solitons In Electromagnetically Induced Transparent Media

Optical vortex solitons have become an active research topic because the topological charges (angular momenta) carried by the vortices enrich nonlinear dynamics with many new features and they also provide interesting possibilities for a variety of applications, such as optical data storage, processing and aiding laser cooling by optical trapping of particles in a vortex field. Up to the present, optical vortex solitons have been observed experimentally in different mediums including Kerr, saturable-atomic and photorefractive nonlinear media. Here spatial vortex solitons in Electromagnetically Induced Transparent (EIT) media have been investigated both analytically and numerically. The developments of spatial soliton and spatial vortex soliton are reviewed first, the soliton equations and basic properties of corresponding solutions are then introduced as well as the physical mechanism of EIT effect. Finally the formation mechanism, condition and stabilization of vortex soliton in EIT media are discussed.A lifetime-broadened three-state atomic system interacting with a strong control field and a probe field is analyzed in detail, where the control field is precisely resonant between two excitation states and the probe field couples the ground state and first excitation state with one-photon detuning. We demonstrate that spatial vortex soliton can exist in above three-state EIT medium because of the equilibrium between nonlinear effect and diffraction property, and different types of vortex solitons, such as dark and bright vortex solitons, can be obtained by choosing suitable control field Rabi frequency and detuning. In addition, the stability analysis for these soliton solutions shows that both dark and bright rings can exist stably in above system.The parameters we take here are all experimental parameters, so we believe that dark and bright vortex solitons can be observed experimentally in three-state EIT media. This work can provide other research opportunities in nonlinear optical experiments and may result in a substantial impact on technology.