Diffraction-limited imaging with monolayer 2D material-based ultrathin flat lenses

Han Lin,Zheng Liu,Baohua Jia,Cheng-Wei Qiu,Zhichen Wan,Zai-Quan Xu,Yupeng Zhang,Ziyu Wang,Qiaoliang Bao,Guiyuan Cao,Kian Ping Loh,Jiadong Zhou

doi:10.1038/s41377-020-00374-9

Abstract

Ultrathin flat optics allow control of light at the subwavelength scale that is unmatched by traditional refractive optics. To approach the atomically thin limit, the use of 2D materials is an attractive possibility due to their high refractive indices. However, achievement of diffraction-limited focusing and imaging is challenged by their thickness-limited spatial resolution and focusing efficiency. Here we report a universal method to transform 2D monolayers into ultrathin flat lenses. Femtosecond laser direct writing was applied to generate local scattering media inside a monolayer, which overcomes the longstanding challenge of obtaining sufficient phase or amplitude modulation in atomically thin 2D materials. We achieved highly efficient 3D focusing with subwavelength resolution and diffraction-limited imaging. The high focusing performance even allows diffraction-limited imaging at different focal positions with varying magnifications. Our work paves the way for downscaling of optical devices using 2D materials and reports an unprecedented approach for fabricating ultrathin imaging devices.

Highlights

Ultrathin flat lenses with the ability to focus optical energy with minimal aberration have attracted great attention as essential optical components in nano-optics and on-chip photonic systems[1]
The monolayer transition metal dichalcogenides12 (TMDCs) (i.e. WSe2) lens structure consisting of concentric rings was constructed by a femtosecond laser writing process[18] (Fig. 1a), in which the femtosecond laser pulses were focused by a high numerical aperture (NA) objective lens (×100, 0.85 NA) onto the surface of an MX2 single crystal
A WSe2 single crystal was synthesized with an atmospheric pressure chemical vapour deposition (APCVD) system (Supplementary Section S1)[23]

Summary

Introduction

Ultrathin flat lenses with the ability to focus optical energy with minimal aberration have attracted great attention as essential optical components in nano-optics and on-chip photonic systems[1]. MOx nanoparticles c Optical microscope d Raman microscope. C, d Optical microscopic image and Raman E12g band intensity image of a monolayer TMDC (WSe2 in this case) lens. E AFM image of the monolayer TMDC (WSe2 in this case) lens and the cross-sectional profile their strong light–matter interactions resulting from 2D quantum confinement[13,14,15,16,17,18]. The unique optical properties of monolayer TMDCs, namely, the extraordinarily large refractive indices in the visible range, can be leveraged for making flat lenses[19]. Flat lenses based on 200-nm-thick graphene oxide (GO) films can achieve highly efficient (~32%) three-dimensional (3D) focusing with a high resolution[20] due to the significant refractive index and absorption modulation in laser-reduced GO

Methods

Results

Conclusion