Fig. 1. Related energy-level system and geometric configuration. (a) Energy-level of cascade three-level system; (b) phase-matching configuration

Fig. 2. Simulation results of DFWM signal. (a) Δ1versus DFWM signal intensity; (b) energy-level diagram of DFWM signal system

Fig. 3. Simulation results of singly-dressed DFWM signal. (a) Δ1, Δ2 versus DFWM signal intensity; (b) Δ1 versus DFWM signal intensity at different Δ2; (c) energy-level diagrams of DFWM signal system for (c1) Δ2=-150 MHz, (c2) Δ2=0 MHz and (c3) Δ2=150 MHz

Fig. 4. Simulation results of doubly-dressed DFWM signal. (a) Δ1versus FWM signal intensity under different Δ3 at Δ2=0 MHz; (b) energy-level diagrams of FWM signal system at Δ2=0 MHz for (b1) Δ3=-100 MHz, (b2) Δ3=0 MHz and (b3) Δ3=100 MHz