Optical Storage Applications Research Articles

Hierarchical Surface Structures and Large-Area Nanoscale Gratings in As2S3 and As2Se3 Films Irradiated with Femtosecond Laser Pulses.

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170-490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe-Drude approach. A good agreement of the calculations with the experimental data was achieved.

Multi‐Channel Image Encryption Based on an All‐Dielectric Metasurface Incorporating Near‐Field Nanoprinting and Far‐Field Holography

AbstractMetasurfaces that can efficiently control the light‐field characteristics have shown many advantages in ultra‐compact, high‐resolution, and high‐concealment optical imaging such as nanoprinting and holography. The development of metasurfaces with multiple functions operating at multiple wavelengths can promote the progress of optical imaging with high information storage and encryption densities. Here, an all‐dielectric metasurface is proposed for multi‐channel image encryption in the near field by controlling the amplitude distribution based on Marius’ law and for holographic imaging in the far field by controlling the phase distribution based on the Pancharatnam–Berry phase. This metasurface can realize the pattern imaging of 12 channels by independently regulating the three‐wavelength channel and different polarization modes. The metasurface achieves independent control of the amplitude, phase, polarization, and wavelength of the incident light wave, improving the storage capacity of information and its encryption security level. The proposed multichannel metasurface provides an effective solution for high‐capacity optical encryption and information storage applications.

Spatial modulation of refractive index in a dense atomic ensemble using Laguerre–Gaussian beams

We propose a scheme to investigate the spatial modulation of the refractive index in a dense atomic ensemble under the action of the Laguerre–Gaussian (LG) beams. Theoretical derivations based on a density-matrix approach associated with numerical simulations are utilized to study the behaviors of the index of refraction, showing that the azimuthal and radial mode indices (i.e., l 2 and p 2) of the LG beams significantly affect the real and imaginary parts of the refractive index. To be specific, the number of the dispersive peaks is determined by ( p 2 + 1 ) | l 2 |, and there are 2 | l 2 | lossless petals in conjunction with p 2 concentric absorption rings centered on the vortex center. Furthermore, by tuning the phase values of the electric and magnetic components of the electromagnetic field, the index of refraction can be drastically tuned from negative to zero to positive and accompanied by periodic absorption and amplification. This investigation provides a powerful tool for manipulating the index of refraction through a nonlinear interaction between atoms and the vortex beams and suggests potential applications in optical switching, logic gates, and optical storage with spatially varying refractive indices.

Enhancement of pattern quality in maskless plasmonic lithography via spatial loss modulation

Plasmonic lithography, which uses the evanescent electromagnetic (EM) fields to generate image beyond the diffraction limit, has been successfully demonstrated as an alternative lithographic technology for creating sub-10 nm patterns. However, the obtained photoresist pattern contour in general exhibits a very poor fidelity due to the near-field optical proximity effect (OPE), which is far below the minimum requirement for nanofabrication. Understanding the near-field OPE formation mechanism is important to minimize its impact on nanodevice fabrication and improve its lithographic performance. In this work, a point-spread function (PSF) generated by a plasmonic bowtie-shaped nanoaperture (BNA) is employed to quantify the photon-beam deposited energy in the near-field patterning process. The achievable resolution of plasmonic lithography has successfully been enhanced to approximately 4 nm with numerical simulations. A field enhancement factor (F) as a function of gap size is defined to quantitatively evaluate the strong near-field enhancement effect excited by a plasmonic BNA, which also reveals that the high enhancement of the evanescent field is due to the strong resonant coupling between the plasmonic waveguide and the surface plasmon waves (SPWs). However, based on an investigation of the physical origin of the near-field OPE, and the theoretical calculations and simulation results indicate that the evanescent-field-induced rapid loss of high-k information is one of the main optical contributors to the near-field OPE. Furthermore, an analytic formula is introduced to quantitatively analyze the effect of the rapidly decaying feature of the evanescent field on the final exposure pattern profile. Notably, a fast and effective optimization method based on the compensation principle of the exposure dose is proposed to reduce the pattern distortion by modulating the exposure map with dose leveling. The proposed pattern quality enhancement method can open new possibilities in the manufacture of nanostructures with ultrahigh pattern quality via plasmonic lithography, which would find potentially promising applications in high density optical storage, biosensors, and plasmonic nanofocusing.

Multicolor and 3D Holography Generated by Inverse-Designed Single-Cell Metasurfaces.

Metasurface-generated holography has emerged as a promising route for fully reproducing vivid scenes by manipulating the optical properties of light using ultra-compact devices. However, achieving multiple holographic images using a single metasurface is still difficult due to the capacity limit of a single meta-atom. In this work, an inverse design method based on gradient-descent optimization is presented to encode multiple pieces of holographic information into a single metasurface. The proposed method allows the inverse design of single-cell metasurfaces without the need for complex meta-atom design strategies, facilitating high-throughput fabrication using broadband low-loss materials. By exploiting the proposed design method, both multiplane red-green-blue(RGB)colorand three-dimensional(3D) holograms are designed and experimentally demonstrated. Multiplane RGB color holograms with nine distinct holograms are achieved, which demonstrate the state-of-the-art data capacity of a phase-only metasurface. The first experimental demonstration of metasurface-generated 3D holograms with completely independent and distinct images in each plane is also presented. The current research findings provide a viable route for practical metasurface-generated holography by demonstrating the high-density holography produced by a single metasurface. It is expected to ultimately lead to optical storage, display, and full-color imagingapplications.

Pyrene-dithienylethene-tetra(tri)phenylethylene triads: Photocontrolled intramolecular energy transfer and photochromic fluorescence switching

Photochromic fluorescence switching with aggregation-induced emission (AIE) property has attracted great research interest due to their wide application potential in optical electronics and biomaterials. In this work, three novel pyrene-dithienylethene-tetra(tri)phenylethylene triads were synthesized by connecting triphenylethene (TrPE) or tetraphenylethylene (TPE) and pyrene unit via dithienlethene (DTE) bridge. Efficient photochromism and fluorescence switching were demonstrated in solution, aggregates, solid powder, and poly(methyl methacrylate) (PMMA) films under alternating irradiation with UV/visible light. The photocyclization yield of DTE-Py-3 was examined by 1H NMR spectra and calculated as 59%. Moreover, these three compounds exhibited typical AIE character in THF/water mixture, the photochromic and fluorescent switching behavior were explored in aggregated state with 90% water fraction. Furthermore, they could be utilized in application of optical information storage and ink with naked-eye color and fluorescence double channel, indicating the promising potential in anti-counterfeiting. Interestingly, DTE-Py-3 could be reversibly switched by visible light in both directions, which endowed it with the application in biological filed.

Polarization-selective narrow band dual-toroidal-dipole resonances in a symmetry-broken dielectric tetramer metamaterial.

Here we propose a metasurface consisting of symmetry-broken dielectric tetramer arrays, which can generate polarization-selective dual-band toroidal dipole resonances (TDR) with ultra-narrow linewidth in the near-infrared region. We found, by breaking the C4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth reaching ∼ 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the nature of TDRs. A 100% modulation depth in light absorption and selective field confinement has been demonstrated theoretically by simply changing the polarization orientation of the exciting light. Intriguingly, it is also found that absorption responses of TDRs on polarization angle follow the equation of Malus' law in this metasurface. Furthermore, the dual-band toroidal resonances are proposed to sense the birefringence of an anisotropic medium. Such polarization-tunable dual toroidal dipole resonances with ultra-narrow bandwidth offered by this structure may find potential applications in optical switching, storage, polarization detection, and light emitting devices.

Polyimide-Derived Supramolecular Systems Containing Various Amounts of Azochromophore for Optical Storage Uses.

The progress of digital technologies demands more speed and larger storage capacity. Optical storage systems have the advantage of being cheap, fast and capacious. This article explores the potential use of polyimide-based films as a recording medium for optical storage devices. The materials were designed through a host-guest approach that involves a cyano-containing polyimide precursor and an azochromophore combined in the following ratios: 1:0.25, 1:0.5, 1:0.75 and 1:1. After thermal treatment up to 200 °C, polyimide systems were formed with supramolecular structures constructed via hydrogen bonding as shown by molecular modeling and FTIR at around 3350 cm-1. The aspects arising from the variation of the azo-dye content in the polyimide samples and their impact on the vitrification temperature, colorimetric features, refractive index, band gap, non-linear optical susceptibility and birefringence were investigated for the first time. The thermal analysis indicated a slight decrease in the vitrification temperature from 190.84 °C for the sample without azo dye to 163.91 °C for the film containing the highest leading of azo dye. The morphology images revealed the occurrence of periodic structures in azo-derived materials exposed to a UV laser, which is accentuated by the addition of more azo dye molecules. Optical tests allowed observation of the increase in the dominant wavelength, refractivity and optical conductivity of the samples, produced by the incorporation of azochromophore and laser irradiation. The photo-generated birefringence increased from 0.014 (sample with 1:0.25) to 0.036 (sample with 1:1), which in combination with the created regular topography pattern, is essential for the use of these materials as recording media in optical storage applications.

Photonic Pseudospin Skyrmion in Momentum Space

Magnetic Skyrmions are topologically protected spin structures with sophisticated swirls of electron spins. In recent times, photonic counterparts of the magnetic Skyrmions have been discovered with new deep-subwavelength characteristics promising for future applications in optical information storage and transfer. While the photonic Skyrmions in real space have been observed in diverse photonic systems, studies on the photonic Skyrmions in momentum space have rarely been done. Here we show different forms of pseudospin Skyrmion around the Dirac point in momentum space of photonic crystals with the Kagome and honeycomb lattice. The pseudospin Skyrmions in momentum space are directly related to the topologically nontrivial states and manipulated by the inter-cell and intra-cell interactions between cylinders of the photonic crystal. The observation of the pseudospin Skyrmion in momentum space is expected to be valuable for manipulation of the flows and polarizations of light in topologically robust ways.

Enhancement of the photoluminescence modulation ratio in highly transparent KNN-based ceramics for optical information storage

The combination of high transmittance and large switching contrast in transmittance and photoluminescence intensity make the K0.5Na0.5NbO3–xPr ceramics promising for optical information storage and optical switch applications.

A novel triple-network hydrogel based on borate ester groups: from structural modulation to rapid wound hemostasis.

Supramolecular hydrogels have received widespread attention due to their soft texture, strong hygroscopicity, and good biocompatibility. These materials have become particularly attractive for sensing, tissue engineering, fluorescence encoding, wound healing, etc. Inspired by the assembly of G-quadruplexes, we choose the boric acid/polyvinyl alcohol/guanosine system to construct a novel triple-network supramolecular hydrogel "tri-BA@PVA/G" via non-covalent cross-linking, and the effect of the concentration of each component on the hydrogel stability was systematically revealed at the same time. Then, the biocompatibility, shape adaption and optical information storage capacity, the rapid hemostatic ability and the ability of the hydrogel to promote wound healing were confirmed both in vitro and in vivo. These results that predict the properties and reveal prospective applications in the field of wound hemostasis have a certain guiding significance for the subsequent preparation of borate-based triple network hydrogels which can be used as wound hemostatic materials.

Generation of second-order sideband and slow-fast light effects in a PT-symmetric optomechanical system

We theoretically study the second-order sideband generation and slow-fast light effects in a parity-time (PT) symmetric optomechanical system, which consists of an active cavity and a passive cavity containing optical parametric amplifier (OPA). Compared to the double-passive nonlinear system, we find that the second-order sideband efficiency can be significantly enhanced by the tunneling strength in the PT-symmetric system with OPA. The flexible manipulation of the second-order generation also can be realized by modulating OPA gain and phase. Moreover, the fast and slow light effects in the optomechanical system are discussed. When the tunneling strength J=3κ1, the time of the second-order sideband group delay can be effectively prolonged in a PT-symmetric cavity in the presence of OPA. The results may have some guidance for the enhancement of second-order sideband efficiency, which has potential applications in optical communication and storage.

To Luminesce or to Change Valence? Insight into the Wavelength Dependency of the Reversible Valence Switching of Europium in Sr3SiO5

A good control over the valence state of dopants in luminescent materials or phosphors is important for the development of highly efficient phosphors for white light-emitting diodes (LEDs). Detailed spectroscopic studies allow us to reveal optically induced charge transfer processes and elucidate the underlying mechanisms in phosphors with additional functionalities such as photochromism or persistent luminescence. However, the spectroscopic study of the valence switching of europium has scarcely been reported. Here, we report on the Sr3SiO5:Eu phosphor, in which photo-reduction (Eu3+ → Eu2+) and photo- or thermal-oxidation (Eu2+ → Eu3+) reactions are demonstrated. The variation of the illumination wavelength influences the efficiency of both the photo-reduction/oxidation and the accompanying dynamic process, especially when the two opposite reactions occur simultaneously. Temperature-dependent annealing indicates a large trap depth for the electron trapped by Eu3+. The good stability of Eu2+ obtained by photo-reduction and the repeatability of the Eu2+/Eu3+ valence switching are confirmed as well. Furthermore, the application of optical information storage is demonstrated based on this phosphor. The results of this work may not only improve the understanding of Eu2+/Eu3+ valence change during illumination but also allow the development of new functional luminescent materials.

Dynamically Switchable Sub-THz Absorber Using VO2 Metamaterial Suitable in Optoelectronic Applications

Temperature-sensitive materials are known as phase change materials (PCMs) which has transition between two different states. Dynamically tunable devices can be designed utilizing these materials. Vanadium dioxide (VO2) considered as a PCM material which transits from the insulator state to the metal one by increasing the temperature. VO2 has recently been utilized to design tunable absorbers. In this article, we presented a dual-band absorber structure design which consist of double arrays of VO2 ring-based placed on top of a dielectric buffer/spacer terminated with a conducting layer acting as a back reflector. Each ring acts as a resonator producing a surface plasmon resonance (SPR). Having a proper unit cell design with an appropriate dimension, a dual-band absorber with an absorption amplitude above 95% (ON state) can be achieved at terahertz (THz) frequency range in the metallic state; whereas the absorption value is 0.6% (OFF state) in the insulator state of VO2. Therefore, the proposed structure design has the possibility to switch between these two ON/OFF states by changing the material’s temperature. The interference theory and the equivalent circuit model are investigated to verify the achieved result using high-frequency structure simulator (HFSS) software which works based on finite element method (FEM). This structure has the potential optoelectronic applications such as refractive index (RI) optical sensing and biomedical detection, photonics detectors, and optical storage applications.

BaMg0·28Zr0·16Ta0·56O3: Dy3+ an reversible inorganic photochromic material with large photochromic efficiency and high luminescence modulation

Inorganic photochromic (PC) materials are increasingly being considered potential candidates for security and optical storage applications. Although great progress has been made in inorganic photochromic materials, it is still challenging to reach both strong photochromic efficiency and large luminescence modulation in inorganic materials. In this work, an effective method is proposed to simultaneously achieve strong photochromic efficiency and large luminescence modulation in ferroelectric oxides BaMg0·28Zr0·16Ta0·56O3: Dy3+ (BZMT: Dy3+) via inducing a large number of oxygen vacancies. The obtained BZMT: Dy3+ ceramics exhibits a reversible white-black color change (∼59.5%) upon alternating illumination at 365 nm and 450 nm (or thermal stimulus 300 °C). Meanwhile, a large luminescence modulation (∼87.6%) had been achieved in BZMT: Dy3+ due to the well overlap between the absorb peak of BZMT and the emission peaks of Dy3+. Benefiting from these excellent properties, the obtained BZMT: Dy3+ ceramics can be used as electronic devices, security, and information storage multifunctional materials. Moreover, this study provides an effective method for developing other inorganic photochromic materials.

Highly Efficient and Ultralong Afterglow Emission with Anti-Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals.

Triplet exciton-based long-lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self-trapped excitons to Mn2+ dopants in solution-processed perovskite CsCdCl3 . It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti-thermal quenching from 300 to 400 K. In-depth charge-carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6 ]4- ) is responsible for the afterglow emission with anti-thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

Highly Efficient and Ultralong Afterglow Emission with Anti‐Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals

AbstractTriplet exciton‐based long‐lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self‐trapped excitons to Mn2+ dopants in solution‐processed perovskite CsCdCl3. It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti‐thermal quenching from 300 to 400 K. In‐depth charge‐carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6]4−) is responsible for the afterglow emission with anti‐thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

A novel modification strategy for photochromic KSr2Nb5O15-based ceramics by establishing a heterojunction band structure

Because of their rapid response, high sensitivity, and excellent thermal and chemical stabilities, photochromic ceramics have attracted great potential for optical applications in anti-counterfeiting and optical information storage. However, the inferior photochromic contrast restricted the further development of photochromic ceramics. Herein, a novel modification strategy for photochromic behavior is proposed in a KSr2Nb5O15-based system. A new heterojunction band structure was established at the interfaces in ceramics by compositing with transition metal oxides and generated novel transition paths for the excited carriers. After compositing with the Nb2O5 second phase, the photochromic contrast △Rdec was almost doubled by additional color centers from the heterojunction structure. The related mechanism was confirmed by the photochromic behavior, thermoluminescence spectra and band structure features. Moreover, rapid, convenient and reversible laser bleaching behaviors was explored, and a more flexible anti-counterfeiting method was attempted through secondary laser adjustment of the photochromic pattern. This work aims to present a new modification viewpoint into photochromic ceramics by building a heterojunction structure.

Switchable fast-slow light in a cavity-magnon system by adding a squeezed drive field

We theoretically discuss the influence of a squeezed drive on the fast and slow light effect at different temperatures by focusing on two main factors: the nonlinear gain coefficient of optical parametric amplification and the phase of the pumping field. We show that the nonlinear gain coefficient and the phase of the pump field will affect the coupling strength between photon and magnon, which provides a way to achieve more obvious fast and slow light effects and good potential to realize the fast-slow light conversion. Moreover, by comparing two different temperatures, we find that the low temperature environment is more conducive to the production of fast light and slow light. With the addition of the squeezing drive field, the group delay of the system will get a larger value and the symmetry of the system will be destroyed, leading to asymmetric absorption. Our results provide more freedom for the realization and conversion of fast and slow light and is expected to find applications in optical communication and optical storage.

Silicon metasurface embedded Fabry-Perot cavity enables the high-quality transmission structural color.

While nanoscale color generations have been studied for years, the high-performance transmission structural color, simultaneously equipped with large gamut, high resolution, and optical multiplexing abilities, still remains as a hanging issue. Here, a silicon metasurface embedded Fabry-Perot cavity is demonstrated to address this problem. By changing the planar geometries of meta-atoms, the cavities provide transmission colors with 194% sRGB gamut coverage and 141,111 DPI resolution, along with more than 300% enhanced angular tolerance. Such high density allows two-dimensional color mixing at the diffraction limit scale. Benefitting from the polarization manipulation capacity of the metasurface, arbitrary color arrangements between cyan and red for two orthogonal linear polarizations are also realized. Our proposed cavities can be used in filters, printings, optical storage, and many other applications in need of high quality and density colors.