Tunable unidirectional nonlinear emission from transition-metal-dichalcogenide metasurfaces

Mudassar Nauman,Dragomir N Neshev,Jingshi Yan,Domenico De Ceglia,Andrey E Miroshnichenko,Yuerui Lu,Mohsen Rahmani,Costantino De Angelis,Khosro Zangeneh Kamali

doi:10.1038/s41467-021-25717-x

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.

Highlights

Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale
While metasurfaces made of inversion-symmetry-broken nanoresonators[28,29] and individual nanoantennas[30,31] have been proposed to direct the emission at the normal direction, to date they operate in the diffractive regime[12,13,14], with multiple diffractive orders being emitted at the harmonic waves[27,32]
The ability to operate in the zero-order second-harmonic generation (SHG) and third-harmonic generation (THG), as well as to be able to tune the directionality of such unidirectional nonlinear emission from forward to backward direction remains elusive

Summary

Introduction

Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale. Full-wave nonlinear simulations have been performed in order to investigate the tapering angle effect of the following three meta-atom shapes: (i) cone, (ii) truncated cone, (iii) vertical cylinder, on the THG conversion efficiency (in either direction forward and backward) and the results are presented in Supplementary Fig. 5 of Supplementary Information.

Results

Conclusion