# Orbital angular momentum bistability in a microlaser

## TL;DR

This paper demonstrates a bistable regime in a chiral microlaser where two modes with different orbital angular momentum and polarization states coexist, enabling potential ultrafast optical switching and exploration of vortex dynamics.

## Contribution

The study introduces a novel bistability involving OAM modes in a microlaser, driven by polarization-dependent gain saturation and engineered spin-orbit coupling.

## Key findings

- Bistability between OAM modes L=0 and L=2 was observed.
- Modes exhibit distinct polarization patterns due to spin-orbit coupling.
- The bistability is explained by a dynamical model of gain saturation.

## Abstract

Light's orbital angular momentum (OAM) is an unbounded degree of freedom emerging in helical beams that appears very advantageous technologically. Using a chiral microlaser, i.e. an integrated device that allows generating an emission carrying a net OAM, we demonstrate a regime of bistability involving two modes presenting distinct OAM (L = 0 and L = 2). Furthermore, thanks to an engineered spin-orbit coupling of light in the device, these modes also exhibit distinct polarization patterns, i.e. cirular and azimuthal polarizations. Using a dynamical model of rate euqations, we show that this bistability arises from polarization-dependent saturation of the gain medium. Such a bistable regime appears very promising for implementing ultrafast optical switches based on the OAM of light. As well, it paves the way to the exploration of dynamical processes involving phase and polarization vortices.