Fig. 1: Spectral phase transition in nonlinear photonic resonators.
From: Spectral phase transitions in optical parametric oscillators
a OPO with the resonant signal and idler in the cavity with variable detuning (Δϕ) and second-order group-velocity dispersion (β2). The nonlinearity can be provided by a quadratic \(({\chi }^{\left(2\right)})\) or a Kerr \(({\chi }^{\left(3\right)})\) medium. b A second-order phase transition occurs at the critical detuning that marks the transition between the degenerate and the non-degenerate spectrum. c This transition is characterized by a continuous order parameter, but a discontinuous derivative of the order parameter at the critical point (CP).
