Analogue gravity in hyperbolic metamaterials

TL;DR

This paper explains the sub-wavelength light confinement and soliton formation in hyperbolic metamaterials through an analogy with gravity, where nonlinear effects mimic gravitational forces in an effective spacetime.

Contribution

It introduces a novel interpretation of hyperbolic metamaterials' nonlinear optical behavior using analogue gravity, linking wave equations to Lorentz symmetry and effective gravitational interactions.

Findings

Wave propagation exhibits 2+1D Lorentz symmetry.

Nonlinear Kerr effects induce effective gravity between photons.

Potential for soliton collapse into black hole analogues.

Abstract

Sub-wavelength confinement of light in nonlinear hyperbolic metamaterials due to formation of spatial solitons has attracted much recent attention because of its seemingly counter-intuitive behavior. In order to achieve self-focusing in a hyperbolic wire medium, a nonlinear self-defocusing Kerr medium must be used as a dielectric host. Here we demonstrate that this behavior finds natural explanation in terms of analogue gravity. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. In order for the effective gravitational constant to be positive, negative self-defocusing Kerr medium must be used as a host. If gravitational self-interaction is strong enough, spatial soliton may collapse into a black hole analogue.