Long-Propagating Ghost Phonon Polaritons Enabled by Selective Mode Excitation

TL;DR

This paper demonstrates how shaping micro/nano antennas enables selective, directional excitation of ghost hyperbolic phonon polaritons with long propagation distances, advancing control in mid-IR nanophotonics.

Contribution

It introduces a method to control ghost hyperbolic phonon polaritons using asymmetric antennas, achieving selective, directional excitation and longer propagation lengths.

Findings

Achieved highly directional g-HP excitation with asymmetric triangular gold antennas.

Controlled g-HP modes by tuning excitation wavelength and antenna orientation.

Demonstrated g-HP propagation over distances exceeding 35 micrometers.

Abstract

The precise control of phonon polaritons(PhPs) is essential for advancements in nanophotonic applications like on-chip optical communication and quantum information processing. Ghost hyperbolic phonon polaritons (g-HPs), which have been recently discovered, feature in-plane hyperbolic dispersion and oblique wavefronts, enabling long-range propagation. Despite their potential, controlling the directionality and selective excitation of g-HPs remains challenging. Our research demonstrates that modifying the shape of the launching micro/nano antenna can achieve this control. Using an asymmetric triangular gold antenna on a calcite crystal surface, we achieve highly directional g-HP excitation by selectively targeting specific polariton modes. Additionally, the mode of g-HPs can be adjusted by changing the excitation wavelength or rotating the antenna. Remarkably, our near-field imaging experiments show g-HP propagation over distances exceeding 35 micrometers, more than twice the length reported in previous studies. This work merges g-HP theory with structural engineering, enhancing the control over g-HPs and paving the way for innovative applications in mid-IR optoelectronics.