Mitigation of dynamical instabilities in laser arrays via non-Hermitian coupling

TL;DR

This paper demonstrates that non-Hermitian coupling in laser arrays can suppress dynamical instabilities, enabling stable phase locking and vortex beam emission, inspired by concepts from non-Hermitian photonics.

Contribution

It introduces non-Hermitian coupling engineering in laser arrays to mitigate instabilities, a novel approach inspired by $ ext{PT}$-symmetry and non-Hermitian photonics.

Findings

Non-Hermitian coupling suppresses laser dynamical instabilities.

Stable phase locking achieved with in-phase or $rac{ ext{pi}}{2}$ phase gradient.

Chirality in asymmetric coupling enables phase locking despite disorder.

Abstract

Arrays of coupled semiconductor lasers are systems possessing complex dynamical behavior that are of major interest in photonics and laser science. Dynamical instabilities, arising from supermode competition and slow carrier dynamics, are known to prevent stable phase locking in a wide range of parameter space, requiring special methods to realize stable laser operation. Inspired by recent concepts of parity-time ($\mathcal{PT}$) and non-Hermitian photonics, in this work we consider non-Hermitian coupling engineering in laser arrays in a ring geometry and show, both analytically and numerically, that non-Hermitian coupling can help to mitigate the onset of dynamical laser instabilities. In particular, we consider in details two kinds of nearest-neighbor non-Hermitian couplings: symmetric but complex mode coupling (type-I non-Hermitian coupling) and asymmetric mode coupling (type-II non-Hermitian coupling). Suppression of dynamical instabilities can be realized in both coupling schemes, resulting in stable phase-locking laser emission with the lasers emitting in phase (for type-I coupling) or with $\pi/2$ phase gradient (for type-II coupling), resulting in a vortex far-field beam. In type-II non-Hermitian coupling, chirality induced by asymmetric mode coupling enables laser phase locking even in presence of moderate disorder in the resonance frequencies of the lasers.