Tunable Unidirectional Nonlinear Emission from Transition-Metal-Dichalcogenide Metasurfaces

TL;DR

This paper demonstrates a novel transition-metal-dichalcogenide metasurface that enables tunable, unidirectional second- and third-harmonic generation, overcoming diffraction limitations and opening new avenues for miniaturized nonlinear light sources.

Contribution

It introduces a crystalline transition-metal-dichalcogenide metasurface capable of tunable unidirectional nonlinear emission, a significant advancement over existing nonlinear metasurfaces.

Findings

Achieved highest refractive index for nonlinear metasurfaces.

Demonstrated tunable unidirectional second-harmonic emission.

Enabled potential applications in nonlinear mirrors and entangled-photon sources.

Abstract

Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale. In this quest, nonlinear metasurfaces hold a great promise, as they enhance nonlinear effects through their resonant photonic environment and high refractive index, such as in high-index dielectric metasurfaces. However, despite the sub-diffractive operation of dielectric metasurfaces at the fundamental wave, this condition is not fulfilled for the nonlinearly generated harmonic waves, thereby all nonlinear metasurfaces to date emit multiple diffractive beams. Here, we demonstrate the enhanced single-beam second- and third-harmonic generation in a metasurface of crystalline transition-metal-dichalcogenide material, offering the highest refractive index. We show that the interplay between the resonances of the metasurface allows for tuning of the unidirectional second-harmonic radiation in forward or backward direction, not possible in any bulk nonlinear crystal. Our results open new opportunities for metasurface-based nonlinear light-sources, including nonlinear mirrors and entangled-photon generation.