Fig. 1. Energy level structure diagram of a five-level M-type three-quantum-dot electromagnetically induced transparent medium. Here is the ground state, and are the direct exciton state, and represent the indirect exciton state, and and represent the strength of tunneling coupling between the intermediate quantum dot and the left and right quantum dot, respectively.

Fig. 2. The ratio of the imaginary part to the real part of (a) dispersion coefficient and (b) nonlinear coefficient as a function of tunneling strength of the quantum inter-dot. The parameters used are given in the text.

Fig. 3. The propagation behaviors of two polarized components (a) and (b) of the linear probe field under the different time. The parameters used are , . Other parameters used are given in the text.

Fig. 4. The collision behaviors of two solitons with the different initial phase differences under the condition that both tunneling strengths are 2.16 meV: (a) ; (b) ; (c) ; (d) .

Fig. 5. The amplitude of the left-handed polarized light as a function of the tunneling strength of the inter-dot. The parameters used are given in the text.

Fig. 6. When the tunneling strength is 4.32 meV, the collision behaviors of two solitons with the different initial phase: (a) ; (b) ; (c) ; (d) .