Full-color enhanced second harmonic generation using rainbow trapping in ultrathin hyperbolic metamaterials

Junhao Li,Jian Wang,Huange Fu,Daqian Li,Guangwei Hu,Jianguo Guan,Sailing He,Linlin Zhou,Qing Zhang,Lina Shi,Wei Xiong,Nan He,Lin Chen,Qiuyu Shang

doi:10.1038/s41467-021-26818-3

Abstract

Metasurfaces have provided a promising approach to enhance the nonlinearity at subwavelength scale, but usually suffer from a narrow bandwidth as imposed by sharp resonant features. Here, we counterintuitively report a broadband, enhanced second-harmonic generation, in nanopatterned hyperbolic metamaterials. The nanopatterning allows the direct access of the mode with large momentum, rendering the rainbow light trapping, i.e. slow light in a broad frequency, and thus enhancing the local field intensity for boosted nonlinear light-matter interactions. For a proof-of-concept demonstration, we fabricated a nanostructured Au/ZnO multilayer, and enhanced second harmonic generation can be observed within the visible wavelength range (400-650 nm). The enhancement factor is over 50 within the wavelength range of 470-650 nm, and a maximum conversion efficiency of 1.13×10−6 is obtained with a pump power of only 8.80 mW. Our results herein offer an effective and robust approach towards the broadband metasurface-based nonlinear devices for various important technologies.

Highlights

Metasurfaces have provided a promising approach to enhance the nonlinearity at subwavelength scale, but usually suffer from a narrow bandwidth as imposed by sharp resonant features
We demonstrated the broadband, covering nearly full visible frequency, enhanced second harmonic generation (SHG) in patterned hyperbolic metamaterials (HMMs) arrays comprising metal/dielectric multilayer
The broadband field enhancement and broadband SHG are achieved by designing an array of HMMs pillars with the graded width, i.e., the taper-patterned HMM (TP-HMM) unit cells with the width from wb to wt as described in the inset of Fig. 1

Summary

Introduction

Metasurfaces have provided a promising approach to enhance the nonlinearity at subwavelength scale, but usually suffer from a narrow bandwidth as imposed by sharp resonant features. We demonstrated the broadband, covering nearly full visible frequency, enhanced second harmonic generation (SHG) in patterned HMM arrays comprising metal/dielectric multilayer (see Fig. 1).

Results

Conclusion