Multichannel vectorial holographic display and encryption

Zhao et al. Light: Science & Applications (2018)7:95 DOI 10.1038/s41377-018-0091-0 Official journal of the CIOMP 2047-7538 www.nature.com/lsa ARTICLE Open Access Multichannel vectorial holographic display and encryption Ruizhe Zhao1, Basudeb Sain 2, Qunshuo Wei1, Chengchun Tang3,4, Xiaowei Li Lingling Huang 1,2, Yongtian Wang1 and Thomas Zentgraf 2 5 , Thomas Weiss6, 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Abstract Since its invention, holography has emerged as a powerful tool to fully reconstruct the wavefronts of light including all the fundamental properties (amplitude, phase, polarization, wave vector, and frequency). For exploring the full capability for information storage/display and enhancing the encryption security of metasurface holograms, smart multiplexing techniques together with suitable metasurface designs are highly demanded. Here, we integrate multiple polarization manipulation channels for various spatial phase profiles into a single birefringent vectorial hologram by completely avoiding unwanted cross-talk. Multiple independent target phase profiles with quantified phase relations that can process significantly different information in different polarization states are realized within a single metasurface. For our metasurface holograms, we demonstrate high fidelity, large efficiency, broadband operation, and a total of twelve polarization channels. Such multichannel polarization multiplexing can be used for dynamic vectorial holographic display and can provide triple protection for optical security. The concept is appealing for applications of arbitrary spin to angular momentum conversion and various phase modulation/beam shaping elements. Introduction Holography based on metasurfaces has emerged as a promising candidate for applications in optical displays, optical storage and security by exhibiting unprecedented spatial resolution, enormous information capacity and a large field of view compared to traditional methods1–11. The practical realization of metasurface holograms relies on the encoding of holographic profiles on ultrathin nanostructures, which can possess strong light-matter interaction within an ultrashort distance12–18. Many efforts have been put into incorporating novel holographic-related functionalities such as beam shaping and ghost imaging into metasurfaces19–22. By utilizing the arbitrary design freedom of metasurfaces to Correspondence: Lingling Huang () or Yongtian Wang () or Thomas Zentgraf () 1 School of Optics and Photonics, Beijing Institute of Technology, 100081 Beijing, China 2 Department of Physics, University of Paderborn, Warburger Straße 100, 33098 Paderborn, Germany Full list of author information is available at the end of the article. simultaneously engineer the local wavelength, amplitude, phase, and polarization response, it might be possible to provide a flexible and compact platform to realize all types of vectorial holograms (with high-dimensional information) rather than scalar intensity information, which can surpass the limitations of natural materials such as liquid crystals or optical photoresists23–26. For the purpose of optimizing the tremendous information capability of metasurface holograms, multiplexing techniques are highly desired including color holograms27–29, polarization multiplexing30–34 and hybrid multiplexing35,36. Among the mentioned multiplexing techniques, polarization multiplexing is an attractive method due to polarization sensitivity of artificially tailored meta-atoms that can completely alter the polarization state of the interacting light. Polarization multiplexed metasurface holograms that support only two orthogonal states and based on spatial multiplexing with more than one meta-atom within a unit-cell have been described previously30,31. Such spatial multiplexing usually results in strong cross-talk between the information channels and © The Author(s) 2018 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Zhao et al. Light: Science & Applications (2018)7:95 lowers the space-bandwidth product. Furthermore, the increased space requirement for the larger unit cell reduces the information density, which might counterbalance the additional information capacity of the second polarization channel. By using birefringent metasurfaces composed of a single meta-atom per unit-cell that possess a variation in the phase shifts for the orthogonal polarization states, an alternative approach for realizing polarization multiplexing has been demonstrated32,33. Nevertheless, the full capacity of all polarization channels (input/output polarizations) has not yet been explored. This limits the improvement of the information capacity stored in metasurface holograms and restricts the versatile functionality of holographic-based optical devices. Here, we demonstrate a novel method for realizing multichannel vectorial holography and show its potential for obtaining dynamic displays and high-security applications. We explore birefringent metasurfaces for the complete control of polarization channels with the freedom of designing both the polarization-dependent phase shift and polarization rotation matrix. We show that although the target holographic phase profiles have quantified phase relations, they can process very different information within different polarization manipulation channels. The reconstructed vectorial images can be switched with negligible cross-talk by selecting the desired combination of input/output polarization states. A set of reconstructed images can conceive different meanings and therefore host unique merits for encryption. Our demonstrated multiplexing method may lead to a new frontier for applications related to dynamic holographic displays, switchable optical devices, data storage, and optical encryption/anti-counterfeiting, which are compatible with most optical systems that operate in transmission. Furthermore, our proposed method can also be adapted to arbitrary spin to orbital angular momentum conversion or other types of polarization/phase modulation and enhance the information capacity. Results We comparatively study two schemes of multiple polarization chan (...truncated)