# Laser Mode Bifurcations Induced by $\mathcal{PT}$-Breaking Exceptional Points

## TL;DR

This paper explores how exceptional points in a two-resonator laser system lead to mode bifurcations and abrupt changes in laser behavior, especially when gain saturation intensities differ, revealing new nonlinear phenomena related to $ ext{PT}$ symmetry breaking.

## Contribution

It demonstrates that nonlinear bifurcations from exceptional points influence laser modes and behaviors, highlighting the role of gain saturation differences in mode switching.

## Key findings

- Exceptional points induce mode bifurcations in the laser system.
- Gain saturation differences enable abrupt mode switching.
- Laser behavior can transition between below-threshold and $ ext{PT}$-broken modes.

## Abstract

A laser consisting of two independently-pumped resonators can exhibit mode bifurcations that evolve out of the exceptional points (EPs) of the linear system at threshold. The EPs are non-Hermitian degeneracies occurring at the parity/time-reversal ($\mathcal{PT}$) symmetry breaking points of the threshold system. Above threshold, the EPs become bifurcations of the nonlinear zero-detuned laser modes, which can be most easily observed by making the gain saturation intensities in the two resonators substantially different. Small pump variations can then switch abruptly between different laser behaviors, e.g. between below-threshold and $\mathcal{PT}$-broken single-mode operation.