# Enhanced stability, bistability, and exceptional points in saturable active photonic couplers

## TL;DR

This paper investigates a photonic coupler with active, lossy, and asymmetric parts, demonstrating how saturation enhances stability, enables bistability, and reveals exceptional points, thus providing a comprehensive understanding of its nonlinear dynamics for optical applications.

## Contribution

It introduces a generic model of a saturable active photonic coupler, analyzing its stability, bistability, and exceptional points, which advances the understanding of nonlinear photonic systems.

## Key findings

- Saturable activity enhances stability of steady states.
- Bistable operation is achievable in specific parameter regions.
- Exceptional points are controllably identified through system regulation.

## Abstract

A generic photonic coupler with active and lossy parts, gain saturation and asymmetric characteristics is examined. Saturable activity is shown to be able to enhance the overall stability of the steady states, prevent evolution to undesirable unbounded modes and allow for bistable operation in specific regions of parametric space. Both stability and bistability are studied in the phase space of the system, where the basins of attraction of each state are identified, providing an accurate description of the dependence of the electric fields on the initial conditions. Continuous families of exceptional points are detected via suitable regulation of the coupling and asymmetry features of the configuration. In this way, a complete description of the nonlinear dynamics landscape is provided, which should be crucial for multiple application-driven designs incorporating such a ubiquitous optical component.