Spectral Phase Transitions in Optical Parametric Oscillators

TL;DR

This paper demonstrates that optical parametric oscillators can undergo second-order spectral phase transitions with high sensitivity, spontaneous symmetry breaking, and distinct noise properties, with implications for sensing and quantum technologies.

Contribution

It reveals the existence of second-order spectral phase transitions in OPOs, maps their dynamics to the Swift-Hohenberg equation, and extends the analysis to Kerr OPOs and coupled systems.

Findings

Spectral phase transitions exhibit square-root critical behavior.

Divergent susceptibility and spontaneous symmetry breaking occur at the transition.

Predicted first-order transitions in coupled OPOs.

Abstract

Spectral behaviors of photonic resonators have been the basis for a range of fundamental studies, with applications in classical and quantum technologies. Driven nonlinear resonators provide a fertile ground for phenomena related to phase transitions far from equilibrium, which can open opportunities unattainable in their linear counterparts. Here, we show that optical parametric oscillators (OPOs) can undergo second-order phase transitions in the spectral domain between degenerate and non-degenerate regimes. This abrupt change in the spectral response follows a square-root dependence around the critical point, exhibiting high sensitivity to parameter variation akin to systems around an exceptional point. We experimentally demonstrate such a phase transition in a quadratic OPO, map its dynamics to the universal Swift-Hohenberg equation, and extend it to Kerr OPOs. To emphasize the fundamental importance and consequences of this phase transition, we show that the divergent susceptibility of the critical point is accompanied by spontaneous symmetry breaking and distinct phase noise properties in the two regimes, indicating the importance of a beyond nonlinear bifurcation interpretation. We also predict the occurrence of first-order spectral phase transitions in coupled OPOs. Our results on non-equilibrium spectral behaviors can be utilized for enhanced sensing, advanced computing, and quantum information processing.