source method, panel method, Fresnel diffraction method, and angular spectrum method. These algorithms can realize both 2D and 3D holography reconstruction at any distance between hologram and image plane. [6] In addition, there are also some adaptive methods for holographic-related technology of many specific functions. [7] Meanwhile, conventional CGHs based on spatial light modulators (SLM) inevitably generate reconstruction images with limited resolution and low field-of-view (FOV) because of large pixel size compared with wavelength. [8] Hence, sub-wavelength pixel size, high-resolution devices are highly demanded.Metasurfaces are ultrathin, artificial layered devices that are composed of nanoantenna or nanoresonator arrays, which have shown great promises for manipulating the phase, amplitude, polarization, angular momentum, and frequency of light with prior spatial resolution. [9][10][11][12][13][14] In previously reported works, phase-only metasurface holograms are employed most widely due to the excellent wavefront modulation properties. Abrupt phase discontinuities can be generated within ultrashort distance, and different phase modulation methods by means of resonance phase [15][16][17][18][19] or Pancharatnam-Berry (PB) phase [7,17,[19][20][21] have been revealed. In the phaseonly holographic algorithm, the amplitude distribution is usually uniform. However, as another important design freedom, the amplitude can also be applied to the reconstruction of the target image, known as amplitude holography. In particular, the transitivity or reflectivity of the local unit can be quantitatively divided to different amplitude levels. For simplicity, binary amplitude modulation, that is, 1 bit digital coding of 0 and 1, can also reproduce holographic images with satisfactory quality. For example, binary amplitude holography based on the scattering of carbon nanotubes array has been demonstrated. [22] Specially, photon sieves consisting of randomly distributed nanoholes are among the simplest and effective amplitude modulation schemes of all the metasurface devices. Such photon sieves can possess extraordinary transmission properties. One of its application is to replace the translucent bands of Fresnel zone plates to effectively enhance the focusing behavior. [23][24][25] In addition, the concept of photon sieves is also adopted to reconstruct the diffraction beams and vortex beams. [26][27][28] Because of the simple fabrication and polarization-independent properties, photon sieves can be used as an ideal medium for binary As an excellent holographic information carrier, metasurface holograms possess the advantages of subwavelength footprint, leading to large field of view and high resolution. Meanwhile, intelligent algorithms should be developed to fully exploit the flexible modulation properties provided by metasurfaces. Here, two amplitude holograms with quantitatively correlation are realized using the photon sieve as the amplitude modulation device. A new iterative algorithm is developed to obtain the ampl...

Optical security involving the use of light to achieve distinctive vision effects has become a widely used approach for anticounterfeiting. Holographic multiplexing has attracted considerable interest in multiplexing security due to its high degree of freedom for manipulating the optical parameters of incident laser beams. However, the complex and time-consuming fabrication process of metasurface-based holograms and the sophisticated nature of holographic imaging systems have hindered the practical application of holographic multiplexing in anticounterfeiting. Combining holography with shape memory polymers to construct reconfigurable holograms provides a simple and efficient way for holographic multiplexing. This paper proposes a reconfigurable fourlevel amplitude hologram fabricated on a heat-shrinkable shape memory polymer using spatially modulated femtosecond laser pulses. Simply by triggering the shape recovery of the polymer through heating, the amplitude modulation of light by the hologram is reconfigured through the shrinking of processed microcrater pixels with three diameters, which enables variation to be achieved in reconstructed holographic images. Examples of holographic multiplexing and data encryption are used to validate the proposed method. The proposed economic and simple approach for holographic multiplexing provides an integrated and single-material solution to packaging and optical security, which has extensive potential in anticounterfeiting and optical encryption.

No abstract

The ultimate goal of metasurface research in recent years is to apply metasurface to reality applications and improve the performance compared to its counterpart, namely conventional optical elements with the same function. Inspired by the application of electrically addressing spatial light modulator (EA-SLM) and based on the binary holographic algorithm, here we propose a reconfigurable metadevice integrated with the nematic liquid crystal (NLC). The smart metadevice directly uses the subwavelength antennas as the main contributor to the phase accumulation instead of the NLC layer. By applying different electrical modulation patterns on the NLC, the metadevice can realize the function of dynamic holographic display as traditional SLMs but features in smaller size, higher resolution and lager field of view. In addition, we improved the existing computer-generated hologram algorithm to generate three holograms with quantitative correlation and also propose a new optical encryption method based on our metadevice. The encryption method needs four elements in total to decrypt and can fully meets the requirements of the various encrypted content. We believe such metadevice paves the way for the new generation of micro-optical display and optical encryption devices.