Polychromatic and polarized multilevel optical data storage

Nanostructure-based orbital angular momentum encryption and multiplexing

The orthogonality among the OAM modes provides a new degree of freedom for optical multiplexing communications. So far, traditional Dammann gratings and spatial light modulators (SLMs) have been widely used to generate OAM beams by modulating electromagnetic waves at each pixel. However, such architectures suffer from limitations in terms of having a resolution of only a few microns and the bulkiness of the entire optical system. With the rapid development of the electromagnetic theory and advanced nanofabrication methods, artificial nanostructures, especially optical metasurfaces, have been introduced which greatly shrink the size of OAM multiplexing devices while increasing the level of integration. This review focuses on the study of encryption, multiplexing and demultiplexing of OAM beams based on nanostructure platforms. After introducing the focusing characteristics of OAM beams, the interaction mechanism between OAM beams and nanostructures is discussed. The physical phenomena of helical dichroism response and spatial separation of OAM beams achieved through nanostructures, setting the stage for OAM encryption and multiplexing, are reviewed. Afterward, the further advancements and potential applications of nanophotonics-based OAM multiplexing are deliberated. Finally, the challenges of conventional design methods and dynamic tunable techniques for nanostructure-based OAM multiplexing technology are addressed.

Systematic design method for generation, storage, and reconstruction of holographic images

Metasurface has extraordinary capability in the wavefront manipulation of electromagnetic waves, which provides an effective method for meta-holographic technology. However, holographic technology mostly focuses on the generation of the single-plane image, which lacks a systematic design method to generate, store, and reconstruct multi-plane holographic images. In this paper, the Pancharatnam-Berry phase meta-atom is designed as electromagnetic controller with the characteristics of the full phase range and high reflection amplitude. Different from the single-plane holography method, a novel multi-plane retrieval algorithm is proposed for the computation of the phase distribution. The metasurface, containing only 24 × 24 (30 × 30) elements, can produce high-quality single-(double-) plane image(s) with fewer elements. Meanwhile, the implementation of the compressed sensing approach stores almost all the holographic image information under a 25% compression ratio and reconstructs the image by the compressed data. The experimental measurements of the samples are consistent with the theoretical and simulated results. This systematic scheme provides an innovative and effective way for designing miniaturized meta-devices to generate high-quality images, which relate to practical applications including high-density data storage, information security, and imaging.

Fluctuation of Plasmonically Induced Transparency Peaks within Multi-Rectangle Resonators

Numerical investigations were conducted of the plasmonically induced transparency (PIT) effect observed in a metal-insulator-metal waveguide coupled to asymmetric three-rectangle resonators, wherein, of the two PIT peaks that were generated, one PIT peak fell while the other PIT peak rose. PIT has been widely studied due to its sensing, slow light, and nonlinear effects, and it has a high potential for use in optical communication systems. To gain a better understanding of the PIT effect in multi-rectangle resonators, its corresponding properties, effects, and performance were numerically investigated based on PIT peak fluctuations. By modifying geometric parameters and filling dielectrics, we not only realized the off-to-on PIT optical response within single or double peaks but also obtained the peak fluctuation. Furthermore, our findings were found to be consistent with those of finite element simulations. These proposed structures have wide potential for use in sensing applications.

Decision-free downsampling method assisted via channel-transfer information to improve the reliability of holographic data storage systems

A decision-free downsampling method (DFDS) assisted by channel-transfer information for phase-modulated holographic data storage is proposed. DFDS is used to address the issue of the accumulation of decision errors induced by traditional downsampling. The issue degrades the downsampling accuracy. DFDS comprises two functional segments: acquiring the channel-transfer information offline and performing decision-free downsampling online. With the assistance of the channel-transfer information, DFDS uses Bayesian posterior probabilities instead of traditional decision results to avoid the accumulation of decision errors and achieve more accurate downsampling. The simulation and experimental results show that DFDS reduces the phase error rate, thereby improving the reliability of the holographic data storage system.

Femtosecond laser nanoprinting of anisotropic plasmonic surfaces: coloration and anticounterfeiting

An anisotropic plasmonic surface of nanoellipsoid arrays is successfully fabricated on an Au film using slit-shaping-based femtosecond laser nanoprinting. The size and orientation of the nanoellipsoid can be exquisitely and flexibly controlled by adjusting the width and direction of the slit and the laser pulse energy. By dark-field optical micro-spectroscopy, anisotropic plasmonic color rendering as well as resonant light scattering from the lateral and vertical modes are experimentally and theoretically investigated in the visible spectral range. In addition, prospective use in the fields of steganographic encryption and multidimensional optical multiplexing is also proposed.

Reversible Mn valence state switching in submicron α-Al2O3:Mn by soft X-rays and blue light - a potential pathway towards multilevel optical data storage

The generation of Mn⁴⁺ in α-Al₂O₃:Mn³⁺ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn⁴⁺ luminescence signal, indicating the potential use of α-Al₂O₃:Mn³⁺ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R-lines (²E → ⁴A₂) under ∼470 nm (⁴A₂ → ⁴T₂), or ∼630 nm (⁴A₂ → ²T₁) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn⁴⁺ valence state can be fully switched back to Mn³⁺ by blue light exposure (e.g., 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.

Titanium content influence on the optical response characteristics of TiO2/ormosils composite films doped with azobenzene

TiO₂-based organic-inorganic composite films doped with azobenzene and photosensitive groups were prepared by combining a low-temperature solgel technique and a spin-coating method. The influence of TiO₂ content on the optical and structural properties of the composite films including the film thickness, the refractive index, the transmission loss, the thermal gravity analysis, and Fourier transform infrared spectroscopy spectra was studied. Photoisomerization and optical switching characteristics of the composite film were investigated under the irradiation of 365 nm ultraviolet light and 450 nm visible light. Results indicate that several micrometer thick films can be easily obtained at room temperature and there is a proportional relationship between the refractive index value and the TiO₂ content. In addition, the composite films have a low optical propagation loss of about 0.1 dB/cm. The composite films with 0.2 M TiO₂ content have an obvious photoisomerization and good optical switching properties. Finally, the hexagonal microlens array was fabricated in the composite films by using an ultraviolet nanoimprint technology. All these results above indicate that the as-prepared TiO₂-based organic-inorganic composite film has potential applications in optical switching devices and photonic elements.

Polarization improvement of CsPbClBr2 quantum dot film by laser direct writing technology

Inorganic halogen perovskite quantum dots not only have high fluorescence quantum efficiency, but also can emit polarized light in solution or thin film. These excellent performances make perovskite quantum dots promising to be used in next-generation displays. In this study, we develop laser direct writing technology to improve the emitted light polarization of CsPbClBr₂ quantum dot film. Without using an additional polarizer, we prove that the polarization degree is maximumly increased by about 56%, and the reasons are analyzed from three perspectives: laser scanning space, laser power, and film thickness. In addition, the lifetime of the fluorescence is also greatly improved after laser treatment. The results we obtain provide the possibility for production of a new generation of displays.

Segmented cylindrical vector beams for massively-encoded optical data storage

The possibility to achieve unprecedented multiplexing of light-matter interaction in nanoscale is of virtue importance from both fundamental science and practical application points of view. Cylindrical vector beams (CVBs) manifested as polarization vortices represent a robust and emerging degree of freedom for information multiplexing with increased capacities. Here, we propose and demonstrate massively-encoded optical data storage (ODS) by harnessing spatially variant electric fields mediated by segmented CVBs. By tight focusing polychromatic segmented CVBs to plasmonic nanoparticle aggregates, record-high multiplexing channels of ODS through different combinations of polarization states and wavelengths have been experimentally demonstrated with a low error rate. Our result not only casts new perceptions for tailoring light-matter interactions utilizing structured light but also enables a new prospective for ultra-high capacity optical memory with minimalist system complexity by combining CVB's compatibility with fiber optics.

Five-Dimensional Optical Data Storage Based on Ellipse Orientation and Fluorescence Intensity in a Silver-Sensitized Commercial Glass

Five-dimensional (5D) recording and decoding is demonstrated by using femtosecond direct laser writing in a silver-containing commercial glass. In particular, laser intensities and ellipse orientations generated by anamorphic focusing are employed to produce 5D data storage unit (3D for XYZ, 1D for the orientation of the elliptically-shaped data storage unit and 1D for its fluorescence intensity). In the recording process, two different images of a 4-bit bitmap format were simultaneously embedded in the medium by multiplexing the elliptical orientation of the laser focus and its intensity so as to access oriented elliptical patterns with independent fluorescence intensity. In the decoding process, two merged original images were successfully reconstructed by comparing each data storage unit with a fabricated calibration matrix of 16 × 16 levels for elliptic orientations and fluorescence intensities. We believe this technique can be applied to semi-permanent high-density data storage device.

Macroscopic two-dimensional monolayer films of gold nanoparticles: fabrication strategies, surface engineering and functional applications

In the last few decades, two-dimensional monolayer films of gold nanoparticles (2D MFGS) have attracted increasing attention in various fields, due to their superior attributes of macroscopic size and accessible fabrication, controllable electromagnetic enhancement, distinctive optical harvesting and electron transport capabilities. This review will focus on the recent progress of 2D monolayer films of gold nanoparticles in construction approaches, surface engineering strategies and functional applications in the optical and electric fields. The research challenges and prospective directions of 2D MFGS are also discussed. This review would promote a better understanding of 2D MFGS and establish a necessary bridge among the multidisciplinary research fields.