Fig. 5: Spectral phase transition in dual-pump four-wave mixing.

a Illustration of the two pump fields getting converted to the signal and idler. b The phase conjugation parametric instability gain (λ) (Eq. (3)) curve in the normal dispersion regime as the pump power is varied. The maximum of the gain where the signal/idler is supposed to oscillate is marked by the black lines. Degenerate and non-degenerate oscillations are both expected in this case. c The phase conjugation parametric process gain curve in the anomalous dispersion regime. Only non-degenerate oscillation is expected in this case. d Spectral phase transition (normal dispersion regime) as the pump separation (Δ) is varied. A degenerate to non-degenerate transition happens across the critical point. e The critical point is characterized to be a second-order which displays continuous behavior in order parameter but exhibits discontinuity in its derivative. Parameters used in the simulation are taken from ref. ⁴².