Modulation instability of structured-light beams in negative-index metamaterials

TL;DR

This paper predicts and analyzes the azimuthal modulation instability of optical vortices in negative-index metamaterials, revealing unique rotation behaviors and conditions for instability due to their unusual electromagnetic properties.

Contribution

It provides the first analytical expression for modulation-instability gain in negative-index metamaterials with nonlinearities and explores the rotation dynamics of necklace beams.

Findings

Opposite rotation directions of necklace beams in positive- and negative-index materials.

Derived condition for azimuthal modulation instability based on diffraction and nonlinear lengths.

Analytical expression for instability gain in Kerr-type nonlinear negative-index metamaterials.

Abstract

One of the most fundamental properties of isotropic negative-index metamaterials, namely opposite directionality of the Poynting vector and the wavevector, enable many novel linear and nonlinear regimes of light-matter interactions. Here, we predict distinct characteristics of azimuthal modulation instability of optical vortices with different topological charges in negative-index metamaterials with Kerr-type and saturable nonlinearity. We derive an analytical expression for the spatial modulation-instability gain for the Kerr-nonlinearity case and show that a specific condition relating the diffraction and the nonlinear lengths must be fulfilled for the azimuthal modulation instability to occur. Finally, we investigate the rotation of the necklace beams due to the transfer of orbital angular momentum of the generating vortex on the movement of solitary necklace beams. We show that the direction of rotation is opposite in positive- and negative-index materials.