# Mid-Infrared Grayscale Metasurface Holograms

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

_{2}lens with a focal length of 5 cm was used to FT the reflected light field. The metasurface hologram was placed in the front foci plane of the lens and a mercury cadmium telluride (MCT) detector utilized in two dimensions to scan the back foci plane and collect the spatial field distribution. The size of the MCT detector was 25 μm, indicating that the minimal spatial resolution of the image was 25 μm. The phase-only hologram shown in Figure 2b was discretized to an eight-level hologram, meaning that 2π-phase variation was divided into 0, π/4, π/2, 3π/4, π, 5π/4, 3π/2 and 7π/4 modulation with pillar radii of 320, 420, 480, 560, 720, 820, 880 and 920 nm, respectively.

^{2}. The exposed resist films were developed in ZED-N50 developer for 60 s at 20 °C. After rinsing in isopropyl alcohol for 30 s and drying by nitrogen flow, the developed resist film with the desired pattern was transferred onto the α-Si using deep reactive-ion etching (RIE) Bosch process in an Oxford Estrelas system. Each cycle of the Bosch process comprised repetition of an etching (SF

_{6}) step of 2 s duration and a sidewall-passivation (C

_{4}F

_{8}) step of 1 s duration. In the etching step, SF

_{6}gas with the flow of 300 sccm was applied with an inductively coupled plasma (ICP) power of 3000 W in the applied pressure of 120 mTorr. For the passivation step, C

_{4}F

_{8}gas with the flow of 160 sccm was utilized with an ICP power of 1500 W in the same applied pressure of the etching step. This process cycle was then repeated 22 times until the α-Si was fully etched. The excess of resist was removed by flashing the device into a plasma etcher. The scanning electron microscope (SEM) (LEO 1550 Gemini FESEM) image shown in Figure 3b gives an oblique view of the fabricated hologram. Each pixel of hologram is 10 × 10 µm in size, containing 5 × 5 Si nanopillars. The total hologram contains 64 × 64 pixels. Figure 3c shows a top view of an enlarged area on the hologram. The unit of each scatter is isotropic, thus our present metasurface-based hologram is polarization-independent [28,29].

## 3. Results

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

- Yu, N.; Genevet, P.; Kats, M.A.; Aieta, F.; Tetienne, J.-P.; Capasso, F.; Gaburro, Z. Light propagation with phase discontinuities: Generalized laws of reflection and refraction. Science
**2011**, 334, 333. [Google Scholar] [CrossRef] [PubMed][Green Version] - Neshevand, D.; Aharonovich, I. Optical metasurfaces: New generation building blocks for multi-functional optics. Light Sci. Appl.
**2018**, 7, 58. [Google Scholar] [CrossRef] - Genevet, P.; Capasso, F.; Aieta, F.; Khorasaninejad, M.; Devlin, R. Recent advances in planar optics: From plasmonic to dielectric metasurfaces. Optica
**2017**, 4, 139. [Google Scholar] [CrossRef] - Parsons, J.; Hendry, E.; Burrows, C.P.; Auguie, B.; Sambles, J.R.; Barnes, W.L. Localized surface-plasmon resonances in periodic nondiffracting metallic nanoparticle and nanohole arrays. Phys. Rev. B
**2009**, 79, 073412. [Google Scholar] [CrossRef][Green Version] - de Abajo, F.J.G. Colloquium: Light scattering by particle and hole arrays. Rev. Mod. Phys.
**2007**, 79, 1267. [Google Scholar] [CrossRef][Green Version] - Lalanne, P.; Astilean, S.; Chavel, P.; Cambril, E.; Launois, H. Design and fabrication of blazed binary diffractive elements with sampling periods smaller than the structural cutoff. JOSA A
**1999**, 16, 1143. [Google Scholar] [CrossRef] - Huang, L.; Chen, X.; Muhlenbernd, H.; Li, G.; Bai, B.; Tan, Q.; Jin, G.; Zentgraf, T.; Zhang, S. Dispersionless Phase Discontinuities for Controlling Light Propagation. Nano Lett.
**2012**, 12, 5750. [Google Scholar] [CrossRef] [PubMed] - Yu, N.; Capasso, F. Flat optics with designer metasurfaces. Nat. Mater.
**2014**, 13, 139. [Google Scholar] [CrossRef] - Aieta, F.; Genevet, P.; Yu, N.; Kats, M.A.; Gaburro, Z.; Capasso, F. Out-of-Plane Reflection and Refraction of Light by Anisotropic Optical Antenna Metasurfaces with Phase Discontinuities. Nano Lett.
**2012**, 12, 1702. [Google Scholar] [CrossRef] - Jahani, S.; Jacob, Z. All-dielectric metamaterials. Nat. Nanotechnol.
**2016**, 11, 23. [Google Scholar] [CrossRef] - Lin, D.; Fan, P.; Hasman, E.; Brongersma, M.L. Dielectric gradient metasurface optical elements. Science
**2014**, 345, 298. [Google Scholar] [CrossRef] [PubMed] - Kuznetsov, A.I.; Miroshnichenko, A.E.; Fu, Y.H.; Zhang, J.; Luk’yanchuk, B. Magnetic light. Sci. Rep.
**2012**, 2, 492. [Google Scholar] [CrossRef] [PubMed][Green Version] - Decker, M.; Staude, I.; Falkner, M.; Dominguez, J.; Neshev, D.N.; Brener, I.; Pertsch, T.; Kivshar, Y.S. High-Efficiency Dielectric Huygens’ Surfaces. Adv. Opt. Mater.
**2015**, 3, 813. [Google Scholar] [CrossRef][Green Version] - Arbabi, A.; Horie, Y.; Bagheri, M.; Faraon, A. Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission. Nat. Nanotechnol.
**2015**, 10, 937. [Google Scholar] [CrossRef] - Kruk, S.; Hopkins, B.; Kravchenko, I.I.; Miroshnichenko, A.; Neshev, D.N.; Kivshar, Y.S. Invited Article: Broadband highly efficient dielectric metadevices for polarization control. APL Photonics
**2016**, 1, 030801. [Google Scholar] [CrossRef][Green Version] - Khorasaninejad, M.; Ambrosio, A.; Kanhaiya, P.; Capasso, F. Broadband and chiral binary dielectric meta-holograms. Sci. Adv.
**2016**, 2, e1501258. [Google Scholar] [CrossRef][Green Version] - Aieta, F.; Genevet, P.; Kats, M.A.; Yu, N.; Blanchard, R.; Gaburro, Z.; Capasso, F. Aberration-Free Ultrathin Flat Lenses and Axicons at Telecom Wavelengths Based on Plasmonic Metasurfaces. Nano Lett.
**2012**, 12, 4932. [Google Scholar] [CrossRef] - Lin, R.J.; Su, V.-C.; Wang, S.; Chen, M.K.; Chung, T.L.; Chen, Y.H.; Kuo, H.Y.; Chen, J.-W.; Chen, J.; Huang, Y.-T.; et al. Achromatic metalens array for full-colour light-field imaging. Nat. Nanotechnol.
**2019**, 14, 227. [Google Scholar] [CrossRef] - Cong, L.; Xu, N.; Gu, J.; Han, J.; Zhang, W. Highly flexible broadband terahertz metamaterial quarter-wave plate. Laser Photonics Rev.
**2014**, 8, 626. [Google Scholar] [CrossRef] - Yu, N.; Aieta, F.; Genevet, P.; Kats, M.A.; Gaburro, Z.; Broadband, F.C.A. Background-Free Quarter-Wave Plate Based on Plasmonic Metasurfaces. Nano Lett.
**2012**, 12, 6328. [Google Scholar] [CrossRef] - Huang, L.; Chen, X.; Muhlenbernd, H.; Zhang, H.; Chen, S.; Bai, B.; Tan, Q.; Jin, G.; Cheah, K.; Qiu, C.; et al. Three-dimensional optical holography using a plasmonic metasurface. Nat. Commun.
**2013**, 4, 2808. [Google Scholar] [CrossRef][Green Version] - Wang, L.; Kruk, S.; Tang, H.; Li, T.; Kravchenko, I.; Neshev, D.N.; Kivshar, Y.S. Grayscale transparent metasurface holograms. Optica
**2016**, 3, 1504. [Google Scholar] [CrossRef] - Wang, B.; Dong, F.; Li, Q.-T.; Yang, D.; Sun, C.; Chen, J.; Song, Z.; Xu, L.; Chu, W.; Xiao, Y.-F.; et al. Visible-Frequency Dielectric Metasurfaces for Multiwavelength Achromatic and Highly Dispersive Holograms. Nano Lett.
**2016**, 16, 5235. [Google Scholar] [CrossRef] - Genevet, P.; Capasso, F. Holographic optical metasurfaces: A review of current progress. Rep. Prog. Phys.
**2015**, 78, 024401. [Google Scholar] [CrossRef] - Brown, B.R.; Lohmann, A.W. Complex Spatial Filtering with Binary Masks. Appl. Opt.
**1966**, 5, 967. [Google Scholar] [CrossRef] - Bohren, C.F.; Huffman, D.R. Absorption and Scattering of Light by Small Particles; Wiley: New York, NY, USA, 1983. [Google Scholar]
- Taflove, A.; Hagness, S.C. Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed.; Artech House: Norwood, MA, USA, 2000. [Google Scholar]
- Helgert, C.; Menzel, C.; Rockstuhl, C.; Pshenay-Severin, E.; Kley, E.-B.; Chipouline, A.; Tünnermann, A.; Lederer, F.; Pertsch, T. Polarization-independent negative-index metamaterial in the near infrared. Opt. Lett.
**2009**, 34, 704. [Google Scholar] [CrossRef] - Li, T.; Wang, S.; Zhang, X.-L.; Deng, Z.-L.; Hang, Z.H.; Sun, H.-B.; Wang, G.P. Non-uniform annular rings-based metasurfaces for high-efficient and polarization-independent focusing. App. Phys. Lett.
**2015**, 107, 251107. [Google Scholar] [CrossRef] - Schmitt, N.; Georg, N.; Briere, G.; Loukrezis, D.; Heron, S.; Lanteri, S.; Klitis, C.; Sorel, M.; Romer, U.; Gersem, H.D.; et al. Optimization and uncertainty quantification of gradient index metasurfaces [Invited]. Opt. Mater. Express
**2019**, 9, 892. [Google Scholar] [CrossRef][Green Version] - So, S.; Rho, J. Designing nanophotonic structures using conditional deep convolutional generative adversarial networks. Nanophotonics
**2019**, 8, 12551261. [Google Scholar] [CrossRef][Green Version] - Ong, J.R.; Chu, H.S.; Chen, V.H.; Zhu, A.Y.; Genevet, P. Freestanding dielectric nanohole array metasurface for mid-infrared wavelength applications. Opt. Lett.
**2017**, 42, 2639. [Google Scholar] [CrossRef][Green Version] - Elsawy, M.M.R.; Lanteri, S.; Duvigneau, R.; Briere, G.; Mohamed, M.S.; Genevet, P. Global optimization of metasurface designs using statistical learning methods. Sci. Rep.
**2019**, 9, 17918. [Google Scholar] [CrossRef] - Peurifoy, J.; Shen, Y.; Jing, L.; Yang, Y.; Cano-Renteria, F.; DeLacy, B.G.; Joannopoulos, J.D.; Tegmark, M.; Soljacic, M. Nanophotonic particle simulation and inverse design using artificial neural networks. Sci. Adv.
**2018**, 4, eaar4206. [Google Scholar] [CrossRef][Green Version] - Jiang, J.; Fan, J.A. Global Optimization of Dielectric Metasurfaces Using a Physics-Driven Neural Network. Nano Lett.
**2019**, 19, 5366. [Google Scholar] [CrossRef][Green Version]

**Figure 1.**Schematic of the design of the hologram unit. (

**a**) Silicon nanopillar with variable radius R and constant period P = 2 μm and height H = 650 nm is placed on the gold substrate. (

**b**) Phase shift (red line) and amplitude (blue line) of the reflection light versus the radii of pillar at wavelength 4.7 μm.

**Figure 2.**(

**a**) Gray intensity distributions of an object $I\left(x,y\right)$ to be displayed. (

**b**) Calculated phase profile $B\left(u,v\right)$ of the phase-only hologram of the object in (a). (

**c**) Block diagram of the iterative Fourier transform algorithm used for calculating (b) from (a).

**Figure 3.**(

**a**) Sketch of the on-axis optical scanning experiment setup for demonstration of the hologram. (

**b**,

**c**) The SEM images of the fabricated hologram in oblique view and top view.

**Figure 4.**(

**a**) Simulation results of the image after light illuminated the hologram. (

**b**) Experimental results of the hologram image by using the on-axis optical setup. Note the presence of the zero order in the center of the image due to imperfect phase control.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Wu, K.; Kossowski, N.; Qiu, H.; Wang, H.; Wang, Q.; Genevet, P. Mid-Infrared Grayscale Metasurface Holograms. *Appl. Sci.* **2020**, *10*, 552.
https://doi.org/10.3390/app10020552

**AMA Style**

Wu K, Kossowski N, Qiu H, Wang H, Wang Q, Genevet P. Mid-Infrared Grayscale Metasurface Holograms. *Applied Sciences*. 2020; 10(2):552.
https://doi.org/10.3390/app10020552

**Chicago/Turabian Style**

Wu, Kedi, Nicolas Kossowski, Haodong Qiu, Hong Wang, Qijie Wang, and Patrice Genevet. 2020. "Mid-Infrared Grayscale Metasurface Holograms" *Applied Sciences* 10, no. 2: 552.
https://doi.org/10.3390/app10020552