# Long-range optical coupling with epsilon-near-zero materials

## TL;DR

This paper shows how epsilon-near-zero materials enable long-range optical interactions similar to quantum tunneling, with potential applications in photonic systems.

## Contribution

The paper introduces a new method for long-range optical coupling using epsilon-near-zero materials beyond evanescent coupling.

## Key findings

- Anti-correlated intensity oscillations were observed in electromagnetic fields up to hundreds of microns.
- Second harmonic generation confirmed the oscillatory behavior in indium tin oxide multilayers.
- The system supports subwavelength mode footprints and long-range radiative coupling.

## Abstract

Long-range resonant quantum tunneling of electrons happens across potential barriers when the wavefunction interferes constructively outside the barrier. Here we demonstrate an analogy in optical systems based on epsilon-near-zero materials, achieving phase-modulated, long-range optical interactions between transparent semiconducting oxide layers beyond the evanescent photonic coupling. Distinct from weak thin-film interference, intense electromagnetic fields confined within the epsilon-near-zero thin films show anti-correlated intensity oscillations as a function of interlayer separation up to hundreds of microns. The oscillatory, anti-correlated electromagnetic field intensities were probed by second harmonic generation from wedged indium tin oxide multilayers. Such a system that hosts subwavelength mode footprint and simultaneously long-range radiative coupling offers prospects for long-distance optical communication, large-scale photonic circuits, and hybrid quantum photonic systems.

Long-range resonant quantum tunnelling of electrons happens across potential barriers when the wavefunction interferes constructively. Here, authors demonstrate an analogy in optical systems based on epsilon-near-zero materials, achieving long-range optical interactions beyond evanescent coupling.