Axially Tailored Light Field by Means of a Dielectric Metalens

Xinhao Fan, Peng Li, Xuyue Guo, Bingjie Li, Yu Li, Sheng Liu, Yi Zhang, and Jianlin Zhao

Phys. Rev. Applied 14, 024035 – Published 13 August 2020

Abstract

Metasurfaces that enable wave-front manipulation within the subwavelength range exhibit fascinating capabilities and application potentials in ultrathin functional devices. Therein, various metasurfaces to realize delicate transverse and even three-dimensional structured light fields have been proposed for applications such as holographic displays, imaging, optical manipulation, etc. However, a metasurface with the capability of tailoring the axial structure of a light field has not been reported so far. Here, we propose and experimentally demonstrate a dielectric metalens to tailor the axial intensity distribution of a light field, based on the independent control of amplitude and phase. The metalens is designed according to an optimized Fourier spectrum encoding method, which allows construction of an ultrasmall nondiffractive light field with any arbitrary preestablished axial structure. This axial modulation scenario enriches the three-dimensional wave-front modulation functionality of the metasurface, and can be implemented for other waves beyond optics, from acoustic and elastic waves to matter waves.

Received 24 March 2020
Revised 25 May 2020
Accepted 10 July 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.024035

Physics Subject Headings (PhySH)

Dielectric properties Interference & diffraction of light Mechanical effects of light on material media Nanophotonics Polarization of light Spatial profiles of optical beams

Metamaterials Optical materials & elements

Atomic, Molecular & Optical

Authors & Affiliations

Xinhao Fan¹, Peng Li ^1,*, Xuyue Guo¹, Bingjie Li¹, Yu Li¹, Sheng Liu¹, Yi Zhang², and Jianlin Zhao^1,†

¹MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China
²School of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, Singapore, 637457, Singapore

^*pengli@nwpu.edu.cn
^†jlzhao@nwpu.edu.cn

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Vol. 14, Iss. 2 — August 2020

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Images

Figure 1
Design of dielectric metalens with independent control of amplitude and phase. (a) Schematic of axial tailoring of light field via a single-layer dielectric metalens. Inset: sketch of the illumination details. For the normal incidence of a circularly polarized beam, the metalens transforms it into an oppositely polarized beam with radially varying transmission amplitude (denoted by rectangles with different brightness) and phase, then generates an axially tailored field. (b) Top: meta-atom of poly- $Si$ nanopillar deposited on ${Si O}_{2}$ substrate with geometric parameters of L (length), W (width), h (height), and P (period). Bottom: top view of the meta-atom. θ is the rotation angle of the rectangular nanopillar relative to the reference coordinate system. (c) Transmission amplitudes of 17 selected geometries. (d) Normalized electric fields and phase distributions when x- and y-polarized light beams illuminate the 1st (N₁) and 17th (N₁₇) geometries. The red arrows and crosses depict the polarization orientations of incident light beams.
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Figure 2
Assembling a dielectric metalens for axially tailoring a light field. (a) Schematic of generating Bessel beam based on Durnin ring. Inset: Durnin ring mask with a sharp transparent ring and the corresponding normalized intensity profile on the z axis. (b) Preestablished intensity profile I(r = 0,z) (top) on the axis and amplitude distribution of the corresponding spatial spectrum U(k_r) (bottom). (c) Transmission distribution of the Fourier spectrum mask. The mask sizes are 1.08 × 1.08 mm². (d) Phase and (e) amplitude distribution of the optimized mask calculated from the spatial spectrum, according to Eq. (5). (f) Assembly diagram of metalens from the Fourier transform lens and optimized mask.
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Figure 3
(a) SEM image of the metalens and (b) its locally enlarged image. This metalens is fabricated for generating a nondiffractive light field with rectangular intensity profile along the z axis. (c) Experimental setup. QWP: quarter-wave plate. The microscopic measurement system consisting of objective and tube lenses and CMOS camera is placed on a linear translation stage that moves along the z direction.
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Figure 4
Normalized intensity distributions of a rectangle-profiled light field. (a) Numerically reconstructed light field in the y-z plane. (b) Calculated on-axis intensity distribution. (c) Measured 3D intensity distribution in a longitudinal interval of 2.6 mm. (d) Measured on-axis intensity distribution. Red points: z₁= 1.6 mm, z₂= 2.1 mm, z₃= 2.7 mm, and z₄= 3.9 mm. (e) Measured intensity distributions at the planes of z₁, z₂, z₃, and z₄.
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Figure 5
Measurement of oscillating field constructed from metalens. (a) Transmission distribution of the mask corresponding to a cosinusoidal profile. (b) Local SEM image of the metalens. (c) Measured 3D intensity distribution in a longitudinal interval from z = 2.52 to 4.68 mm. (d) Measured on-axis intensity and the corresponding fitted curve. (e) Transverse intensity distributions at four planes corresponding to the points shown in (d). Insets: top-view intensity patterns. These intensity distributions are normalized.
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