Ultra-enhanced Sensitivity in Nonlinear Exceptional-Point Lasers

In this work, we study a system of coupled resonators with saturable gain and/or saturable absorption. When biased at a nonlinear exceptional point, the steady-state lasing frequency demonstrates a cubed-root response to frequency/refractive index perturbation, despite using a binary configuration. The magnitude of this response can be further enhanced by tuning the passive losses and saturable absorption in the system. These findings are first described through a coupled mode formalism and then verified by Steady-state Ab-initial Laser Theory.