Ultracompact amplitude modulator by coupling hyperbolic polaritons over a graphene-covered gap

TL;DR

This paper proposes a theoretical design for a broadband, ultra-compact amplitude modulator for hyperbolic phonon-polaritons in hBN, utilizing a graphene-covered nanogap to achieve low-loss and high-depth modulation.

Contribution

It introduces a novel, graphene-mediated coupling mechanism in a nanogap for efficient amplitude modulation of hyperbolic polaritons in hBN.

Findings

Achieves low insertion loss of 3 dB

Provides modulation depth between 14 and 20 dB

Operates effectively within the 1450-1550 cm$^{-1}$ frequency range

Abstract

The hyperbolic phonon-polaritons within the Reststrahlen band of hBN are of great interest for applications in nanophotonics as they are capable of propagating light signals with low losses over large distances. However, due to the phononic nature of the polaritons in hBN, amplitude modulation of its signal proves to be difficult and has been underexplored. In this paper, we propose theoretically a broadband efficient amplitude modulator for hyperbolic rays in hBN operating in the frequency range between 1450 cm$^{-1}$ and 1550 cm$^{-1}$. The modulating region comprises a few tens of nanometers wide gap carved within the hBN slab and covered by a graphene layer, where electrostatically gated graphene serves as a mediator that facilitates the coupling between phonon-polaritons on each side of the gap through plasmonic modes within graphene. We demonstrate that such an ultra compact modulator has insertion losses as low as 3 dB and provides modulation depth varying between 14 and 20 dB within the type-II hyperbolicity region of hBN.