Magnetically controllable holographic encryption based on a magneto-optical metasurface.

As a flexible and compact nanophotonic device, the metasurface exhibits excellent potential in holographic display and optical information encryption. However, most metasurfaces are passive devices due to the limitations of fixed material properties and structural components. Magneto-optical metasurface is a hybrid device that integrates tunable functional material with elaborately designed nanostructures. It can realize dynamic modulation of the properties of light since the permittivity tensor for the magneto-optical material can be changed by applying an external magnetic field. Here, we propose a tunable metasurface composing metallic nanohole arrays with a bismuth-substituted yttrium iron garnet interleave layer and a metallic film underlayer placed on a glass substrate. The magneto-optical metasurface can achieve dynamic switchable holographic display in different polarization channels via magnetic field control based on the optical rotation of magnetic material and the complex amplitude modulation of the elaborately designed nanoholes. This feature provides a novel approach for the construction of an active tunable metasurface, which can improve the information storage capacity and security of the device. This concept is expected to be applied to various dynamic modulation fields, such as magnetically tunable lens, beam shaping, and optical information encryption.

Ultra-dense moving cascaded metasurface holography by using a physics-driven neural network.

Metasurfaces are promising platforms for integrated compact optical systems. Traditional metasurface holography design algorithms are limited to information capacity due to finite spatial bandwidth production, which is insufficient for the growing demand for big data storage and encryption. Here, we propose and demonstrate deep learning empowered ultra-dense complex-amplitude holography using step-moving cascaded metasurfaces. Using deep learning artificial intelligence optimization strategy, the barriers of traditional algorithms can be conquered to meet diverse practical requirements. Two metasurfaces are cascaded to form the desired holography. One of them can move to switch the reconstruction images due to diffraction propagation accumulated during the cascaded path. The diffraction pattern from the first metasurface propagates at a different distance and meets with the second metasurface, reconstructing the target holographic reconstructions in the far-field. Such a technique can provide a new solution for multi-dimensional beam shaping, optical encryption, camouflage, integrated on-chip ultra-high-density storage, etc.

Spectrum dispersion element based on the metasurface with parabolic phase.

New kinds of dispersion elements are required for the minimization of the spectrometers. Metasurfaces offer new methods for a novel type of spectrometers due to their ultra-thin property and great ability to manipulate the electromagnetic field. Here, we propose and demonstrate a spectral modulated metasurface as a miniaturized dispersion element that possesses parabolic phase profile. Different wavelengths of the incident light can be dispersed to different spatial positions due to the accumulation of the dynamic phase varies with the wavelengths from metasurface. Detailed theoretical spectrum dispersion ability is analyzed and experimental demonstration is achieved. The polarization conversion efficiency is high, which is promising to be used in practical applications. Such metasurface provides a new and simple way to design dispersion devices and has the potential to be used in spectrometers, variable filters, spectrum tomography, etc.

All-dielectric bifocal isotropic metalens for a single-shot hologram generation device.

Planar metalenses are regarded as promising functional nanodevices because of their lightweight, nano-resolution properties, and, therefore, they can serve as versatile platforms for imaging and Fourier transforming. Here, we demonstrate a meta-device that functions as an isotropic bifocal all-dielectric Huygens' metalens to realize nanoscale real-time coaxial digital hologram generation. We design an isotropic bifocal metalens for micro/nano hologram recording, and the metalens utilizes the complete region compared to a previously reported interleaved multifocal metalens scheme. In addition, the hologram generation does not depend on complex polarization conversion, thereby improving the practical efficiency. For high-fidelity reconstruction, compressive reconstruction is utilized to remove twin-image and zero-order items and to suppress noise. Such concept would be extended to white-light achromatic meta-holography and three-dimensional micro/nano in vivo incoherent super-resolution imaging under subwavelength modulation.

Basis function approach for diffractive pattern generation with Dammann vortex metasurfaces.

In mathematics, general functions can be decomposed into a linear combination of basis functions. This principle can be used for creating an infinite number of distinct geometric patterns based on a finite number of basis patterns. Here, we propose a Dammann vortex metasurface (DVM) for optically generating an array of diverse, diffraction-multiplexed vortex patterns, based on three custom-defined basis patterns. The proposed DVM, with its capability of quantitatively correlating phase and intensity distribution in different diffraction orders, opens up doors for various applications including orbital angular momentum encryptions and quantum entanglement.

Roadmap on Recent Progress in FINCH Technology.

Fresnel incoherent correlation holography (FINCH) was a milestone in incoherent holography. In this roadmap, two pathways, namely the development of FINCH and applications of FINCH explored by many prominent research groups, are discussed. The current state-of-the-art FINCH technology, challenges, and future perspectives of FINCH technology as recognized by a diverse group of researchers contributing to different facets of research in FINCH have been presented.

Polarization-Encrypted Orbital Angular Momentum Multiplexed Metasurface Holography.

Metasurface holography has the advantage of realizing complex wavefront modulation by thin layers together with the progressive technique of computer-generated holographic imaging. Despite the well-known light parameters, such as amplitude, phase, polarization, and frequency, the orbital angular momentum (OAM) of a beam can be regarded as another degree of freedom. Here, we propose and demonstrate orbital angular momentum multiplexing at different polarization channels using a birefringent metasurface for holographic encryption. The OAM selective holographic information can only be reconstructed with the exact topological charge and a specific polarization state. By using an incident beam with different topological charges as erasers, we mimic a super-resolution case for the reconstructed image, in analogy to the well-known STED technique in microscopy. The combination of multiple polarization channels together with the orbital angular momentum selectivity provides a higher security level for holographic encryption. Such a technique can be applied for beam shaping, optical camouflage, data storage, and dynamic displays.