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Metalenses of adjustable power and ultrathin flat zoom lens system have emerged as a promising and key photonic device for integrated optics and advanced reconfigurable optical systems. Nevertheless, realizing an active metasurface retaining lensing functionality in the visible frequency regime has not been fully explored to design reconfigurable optical devices. Here, we present a focal tunable metalens and intensity tunable metalens in the visible frequency regime through the control of the hydrophilic and hydrophobic behavior of freestanding thermoresponsive hydrogel. The metasurface is comprised of plasmonic resonators embedded on the top of hydrogel which serves as dynamically reconfigurable metalens. It is shown that the focal length can be continuously tuned by adjusting the phase transition of hydrogel, the results reveal that the device is diffraction limited in different states of hydrogel. In addition, the versatility of hydrogel-based metasurfaces is further explored to design intensity tunable metalens, that can dynamically tailor the transmission intensity and confined it into the same focal spot under different states, i.e., swollen and collapsed. It is anticipated that the non-toxicity and biocompatibility make the hydrogel-based active metasurfaces suitable for active plasmonic devices with ubiquitous roles in biomedical imaging, sensing, and encryption systems.

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.

Metasurfaces offer diverse wavefront control by manipulating amplitude, phase, and polarization of light which is beneficial to design subwavelength scaled integrated photonic devices. Metasurfaces based tunable circular polarization (CP) beam splitting is one functionality of interest in polarization control. Here, we propose and numerically realize metasurface based spin tunable beam splitter which splits the incoming CP beam into two different directions and tune the splitting angles by switching the handedness of incident light polarization. The proposed design approach has potential in applications such as optical communication, multiplexing, and imaging.

Metasurfaces have drawn considerable attention in manipulation of electromagnetic waves due to their exotic subwavelength footprints. Regardless of immense progress of polarization-dependent flat optics, the realization of on-device switchable complete phase multiplication is still missing from design multifunctional devices. Here, by combining geometric and propagation phases, a generalized design principle is proposed that can achieve switchable integer or fractional multiple complete phase modulation in transmitted circularly cross-polarized light by switching the handedness of incident polarization. As a proof of concept, two types of spin-dependent bifunctional wavefront manipulating devices, including switchable beam splitter/beam deflector and spin-to-orbital angular momentum converter designs are numerically realized. It is believed that the proposed single-cell spin-switchable rational-multiple complete-phase-modulation design principle based on combined propagation and geometric phases has great potential to underpin the development of meta-optics-based multifunctional operations in the field of integrated optics, imaging, and optical communication.

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.