Efficient Achromatic Broadband Focusing and Polarization Manipulation of a Novel Designed Multifunctional Metasurface Zone Plate.

Shaobo Ge,Weiguo Liu,Yechuan Zhu,Xinxin Pu,Yingxue Xi,Pengfei Yang,Jin Zhang,Xueping Sun,Shun Zhou

doi:10.3390/nano11123436

Shaobo Ge, Weiguo Liu + Show 7 more

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https://doi.org/10.3390/nano11123436

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Abstract

In this paper, comprehensively utilizing the diffraction theory and electromagnetic resonance effect is creatively employed to design a multifunctional metasurface zone plate (MMZP) and achieve the control of polarization states, while maintaining a broadband achromatic converging property in a near-IR region. The MMZP consists of several rings with fixed width and varying heights; each ring has a number of nanofins (usually called meta-atoms). The numerical simulation method is used to analyze the intensity distribution and polarization state of the emergent light, and the results show that the designed MMZP can realize the polarization manipulation while keeping the broadband in focus. For a specific design wavelength (0.7 μm), the incident light can be converted from left circularly polarized light to right circularly polarized light after passing through the MMZP, and the focusing efficiency reaches above 35%, which is more than twice as much as reported in the literature. Moreover, the achromatic broadband focusing property of the MMZP is independent with the polarization state of the incident light. This approach broadens degrees of freedom in micro-nano optical design, and is expected to find applications in multifunctional focusing devices and polarization imaging.

Highlights

To make optical components lightweight and multifunctional has always been one of the goals pursued in optics
Si is not selected because the refractive index difference between upper and lower materials is too large, which will produce strong interference effect to interfere with broadband focusing [39]
The SiO2 and SiNx used here have refractive index of 1.5 and 2.1, which can be prepared by plasma enhanced chemical vapor deposition (PECVD) [40]

Summary

Introduction

To make optical components lightweight and multifunctional has always been one of the goals pursued in optics. Developed on the basis of FZP, the multi-level diffraction lens (MDL) has achieved an achromatic imaging function range from visible to long-wave infrared bands via a globally optimized numerical iterative algorithm [9,10]. It can not modulate the polarization state of incident light while focusing with wide spectrum achromatic [11,12,13]. Many research studies devoted to the polarization transformation based on metasurface have appeared Some of these works are considered multifunctional optical elements which provide polarization transformation and focusing simultaneously [20,21,22,23]

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