Coupler-free surface polariton excitation and propagation with cold four-level atomic medium

The possibility of the direct excitation of surface polaritons (SPs) by the free-space laser fields at the interface of negative-index metamaterial (NIMM) layer and a bottom layer of cold double Lambda-type atomic medium is investigated. The giant field enhancement (up to jE∕E₀j² ≈ 4.1), together with suppressed ohmic loss of the NIMM layer in a wide transparency window of a double electromagnetically induced transparency, results in the SPs generation. The excitation efficiency of these SPs can be effectively enhanced by applying the unidirectional atomic motion, modulation of the coupling laser characteristics, and using a probe laser with proper incident angle. Based on the special modulation of the driven fields parameters, the group velocity switching of the SPs is observed. In the nonlinear propagation regime of the SPs, a giant Kerr nonlinearity is produced by applying a negative unidirectional atomic velocity. The controllable optical Kerr effect in this coupler-free scheme results in the lossless propagation of the nonlinear SPs. It is revealed that the electromagnetically induced transparency-based system can be used for stable propagation of one-dimensional (1 + 1)D bright and dark superluminal polaritonic solitons. It is also shown that the proposed scheme could be easily realized in an experiment and hence can be used for various ultrafast optical devices.