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Optical holography by using metasurfaces has attracted wide attention in three-dimensional imaging techniques. In particular, polarization encoded meta-holography have shown much interest to encode multiple images on a single metasurface. But these metasurfaces either use a separate array of pixels or use additional space on the image plane for encoding and decoding the optical information. Here, we propose a multichannel reflective encrypted metahologram which is aimed to reconstruct distinct holographic images by incident polarizations of light and polarization selectors at the output without any additional meta-atoms or space on the imaging plane. To have full control on our design, we used C-shaped antennas associated with an ultra-thin spacer of phase change material and a back reflector that stores the holographic images on both of output polarizations. This study chooses the extended 3D Gerchberg–Saxton (GS) algorithm to get the desired phase distribution of metasurface hologram. Two distinct holographic images are firstly calculated and then numerically realized by this approach on the same imaging plane. This work suggests a novel route to encrypt optical information, fast data transmission and compact data storage where the limited area is the primary concern.

Reconfigurable metalenses have received a significant amount of attention in recent years due to its versatility. In this paper, a reconfigurable graphene-integrated plasmonic metalens operating as a converging lens for linearly polarized terahertz (THz) plan waves is proposed and numerically investigated at 0.83 THz. The beam focusing is realized by the geometrical configuration of C-shaped ring resonators. Furthermore, focal tuning is realized by gate-controlled graphene, which locally changes the permittivity in response to external biasing. This design provides a simple route to electrically tunable optical and optoelectronic devices.

The development of new materials, having exceptional properties in comparison to existing materials is highly required for bringing advancement in electronic and optoelectronic technologies. Keeping this fact, we investigated structural, electronic, and optical properties of zincblende GaN doped with selected Zn concentrations (6.25%, 12.50%, and 18.70%), using the first-principle calculations based on density functional theory with GGA + U. We conducted the entire study using the WIEN2K code. In this study, we calculated various significant parametric quantities such as cohesive energies, formation energies, bulk moduli, and lattice constants along with the study of optical and electronic properties by substituting Ga atoms with Zn atoms in 1 × 2 × 2 supercell. The structural stability is confirmed by studying the phonon dispersion curves which suggest that Zn:GaN material is stable against the 6.25% and 18.70% Zn concentrations while for 12.50%, it shows instability. The Hubbard values U = 0, 2, 4, 6 eV were added to GGA and the electronic properties were improved with the U = 6 eV. Optical absorption was blue shifted while the refractive index and dielectric constant were increased with increasing the Zn concentrations. Electronic properties are enhanced due to the prime contribution of cations (Zn) 3d states. The optical and electronic properties are further discussed in detail in the entire study.

Current computational study is focused on calculation of optical properties of Cu doped zincblende GaN system where PBE-GGA approximation is employed in Wien2K code. We consider various Cu concentrations 6.25 %, 3.12 %, 1.56 % corresponding to 1 × 1 × 2 , 1 × 2 × 2 , 2 × 2 × 2 supercell configurations respectively. We substitute one Ga atom with one Cu atom in each concentration and we present a good comparison among optical properties of pure GaN and all Cu concentrations. TDOS and PDOS plots reveal contribution of Ga p-states, N p-states and Cu d-states. Optical absorption shows redshift in comparison to pure GaN and because of interactions of Cu and N atoms, we inspect localized d-states at minima of conduction band or Fermi level. Hence, electro-optical properties of zincblende GaN are enhanced upon addition of impurity (Cu) and the material may potentially be used in photonic, power electronics, solar cells, optoelectronics, UV photodetectors and LEDs.

Metasurfaces have proven their great application potentials in terahertz (THz) wave modulations. However, realizing an active metasurface retaining lensing functionality in the THz frequency regime is still highly desired. Here a metalens, featuring electrically tunable focal length, based on propagation phase delay, is proposed and demonstrated experimentally. To have full control over the designed lens functionality, a gold thin film etched with a C-shaped aperture antenna array covered by monolayer graphene is used. By applying a bias voltage to the graphene, the phase control of the antenna array is changed, and thus the focus of the linearly polarized THz beam can be flexibly tuned from 7.13mm to 8.25mm. The proposed approach has a promising perspective for a variety of applications in communication, reconfigurable flat optics and real-time imaging in THz regime.

Metamaterials have shown great promise for manipulating electromagnetic (EM) waves, thus opening new routes for the progression of flat optics. However, postfabrication fixed structures hinder the dynamic manipulation of light. Dynamic control of EM light has been realized through different mechanisms including electrical gating, optical pumping, mechanical actuation, and temperature stimulation. Here, we are first proposing the plasmonic-resonators-mounted thermoresponsive free-standing hydrogel for holographic display that swells and collapses laterally by temperature. By taking leverage of reversible switching of the hydrogel, we numerically examine the polarization-insensitive dynamic holographic switch by a plasmonic-rings/discs-loaded hydrogel in reflection as a primary application. Second, we observe the transmissive functionality of a plasmonic-sector-resonators-mounted hydrogel, which displays a persistent holographic image under swelling and collapsing conditions. This work demonstrates the potential of a resonators-loaded thermoresponsive hydrogel for EM wave manipulation including dynamic holography, active lensing, switching, and so on.

We propose and numerically demonstrate a dynamic beam deflector based on plasmonic resonator loaded thermoresponsive freestanding hydrogel that swells and collapses in water by temperature. For this purpose, we utilize four-step phase gradients mounted on freestanding hydrated hydrogel. For normal incidence, linearly orthogonal light deflects to 19.44° in the collapsed state and 14.40° in the swollen state of hydrogel. Furthermore, the light deflects at a third angle of 12.29° when the solvent changes from water to ethanol. It is expected that our metadesign will provide a platform for dynamic holography, active lensing, data storage, and anticounterfeiting.

Heavy computational complexity and imprecise reconstruction of objects are crucial problems in computer-generated holograms. In this paper, we propose a non-uniform sampling based on novel compressed look up table method to generate holograms. The method consists of two steps: in the first step, the non-uniform basic modulation factors are precalculated and stored in look-up-table. Secondly, fringe patterns for other points are obtained by simply shifting and multiplying the pre-calculated non-uniform basic modulation factors, and the final computer-generated hologram is obtained by adding them all together. The proposed method eliminates the redundant information properly and modulates the reconstructed images precisely. Numerical simulation results show proposed method reduces the memory usage, speeds up computation time and the quality of reconstructed images do not degrade evidently compared with uniform sampling method. Optical experiments results are in good agreement with numerical simulation results. The proposed method is simple, effective and could be applied in the holographic field in the future.