(a) Modulation index-dependent peak amplitude of FWM lines at ν = Δ / 2 ; (b) FWM lines varying with ν for A = 0.5 (square), 0.8 (solid circle), 1 (upward triangle), 1.95 (downward triangle), 2.5 (rhombus), and 3 (leftward triangle), respectively. Other parameters are Δ 1 / Δ = 0.5 , g 2 = g 2 ′ = 0.3 γ 10 .