Suppressing meta-holographic artifacts by laser coherence tuning

Yaniv Eliezer,Yujie Wang,Qinghai Song,Shumin Xiao,Hasan Yılmaz,Wenhong Yang,Geyang Qu,Hui Cao

doi:10.1038/s41377-021-00547-0

Abstract

A metasurface hologram combines fine spatial resolution and large viewing angles with a planar form factor and compact size. However, it suffers coherent artifacts originating from electromagnetic cross-talk between closely packed meta-atoms and fabrication defects of nanoscale features. Here, we introduce an efficient method to suppress all artifacts by fine-tuning the spatial coherence of illumination. Our method is implemented with a degenerate cavity laser, which allows a precise and continuous tuning of the spatial coherence over a wide range, with little variation in the emission spectrum and total power. We find the optimal degree of spatial coherence to suppress the coherent artifacts of a meta-hologram while maintaining the image sharpness. This work paves the way to compact and dynamical holographic displays free of coherent defects.

Highlights

Artificial metasurfaces, comprised of a two-dimensional (2D) array of subwavelength scatterers, have shown unprecedented ability in controlling optical wavefront and converting conventional bulky optical elements into planar thin films[1,2,3]
In this work, we tune the spatial coherence of a degenerate cavity laser (DCL) to suppress strong coherent artifacts created by metasurface holograms
Compared to the conventional method of lowering the spatial coherence of a laser by a moving diffuser, our approach has several distinct advantages: (i) The precise, continuous tuning of the DCL spatial coherence allows to reach the maximal contrast to noise ratio (CNR) for any desired spatial resolution. (ii) The tuning is energy efficient, and does not introduce a significant power variation. (iii) The spectral width of the DCL emission remains constant during the spatial coherence tuning, which is important for metaholograms with strong dispersion. (iv) No pre- or postprocessing procedures are needed in our method for coherent artifacts suppression. (v) Fast lasing dynamics leads to rapid decoherence of the DCL emission, enabling high-speed meta-holography

Summary

Introduction

Artificial metasurfaces, comprised of a two-dimensional (2D) array of subwavelength scatterers, have shown unprecedented ability in controlling optical wavefront and converting conventional bulky optical elements into planar thin films[1,2,3]. Multi-color, multiplexed, and dynamic metaholograms have been proposed and demonstrated, illustrating a great potential in information processing, 3D display, high-density data storage, and optical image encoding[13,14,15,16,17,18,19,20] Despite of these remarkable advances, the road to practical applications of meta-holograms is hindered by coherent artifacts. While coherent artifacts and speckle noise are well-known issues for conventional holography, they are more significant in regard to meta-holography, as close packing of meta-atoms enhances the cross-talk and fabrication of nanoscale features is susceptible to error Such artifacts cause severe distortions of holographic images, which are extremely difficult to correct.

Methods

Results

Conclusion