Fig. 4: First-order spectral phase transition in coupled OPOs.
From: Spectral phase transitions in optical parametric oscillators
a Schematic configuration of a coupled OPO (coupling factor (κ)). Simulated spectrum (SP) as a function of the cavity detuning b in the normal dispersion regime, c in the anomalous dispersion regime. d Order parameter as a function of detuning showing the discontinuity at the location of the first-order transition point. The gain curve is also plotted alongside. The OPO selects the gain maximum and therefore doesn't follow the dashed portion of the gain curve. This gain competition between two second-order critical point gives rise to the first-order transition point. e The spectrum considering the wavelength experiencing the maximum gain around which the signal/idler is centered. At the first-order transition, there is a discontinuous jump from the non-degenerate spectrum to the degenerate spectrum.
