Optical Data Storage Research Articles

A Review: Laser Interference Lithography for Diffraction Gratings and Their Applications in Encoders and Spectrometers

The unique diffractive properties of gratings have made them essential in a wide range of applications, including spectral analysis, precision measurement, optical data storage, laser technology, and biomedical imaging. With advancements in micro- and nanotechnologies, the demand for more precise and efficient grating fabrication has increased. This review discusses the latest advancements in grating manufacturing techniques, particularly highlighting laser interference lithography, which excels in sub-beam generation through wavefront and amplitude division. Techniques such as Lloyd’s mirror configurations produce stable interference fringe fields for grating patterning in a single exposure. Orthogonal and non-orthogonal, two-axis Lloyd’s mirror interferometers have advanced the fabrication of two-dimensional gratings and large-area gratings, respectively, while laser interference combined with concave lenses enables the creation of concave gratings. Grating interferometry, utilizing optical interference principles, allows for highly precise measurements of minute displacements at the nanometer to sub-nanometer scale. This review also examines the application of grating interferometry in high-precision, absolute, and multi-degree-of-freedom measurement systems. Progress in grating fabrication has significantly advanced spectrometer technology, with integrated structures such as concave gratings, Fresnel gratings, and grating–microlens arrays driving the miniaturization of spectrometers and expanding their use in compact analytical instruments.

Femtosecond optical vortex-induced flower-shaped surface relief structures in an azo-polymer film

We study the formation of surface relief structures in azo-polymers generated via two-photon induced photoisomerization using a femtosecond near-infrared optical vortex laser beam. These structures exhibit exotic flower-like shapes with petals along the azimuthal direction, and they are formed from spatial mode instability, which is associated with third-order nonlinear effects in the azo-polymer. This process is a unique and exotic interaction between light and matter, which may be applied to the development of advanced optical data storage technologies. Here, an additional degree of freedom is offered by the number of formed petals, which themselves are a function of the topological charge of the optical vortex beam.

Multiphoton‐And SHG‐Active Pyrimidine‐Based Liquid Crystalline Thin Films Toward 3D Optical Data Storage

AbstractAn original asymmetric achiral pyrimidine core molecule, with long carbon chains on one side and a coumarin fragment on the other, is designed. This advanced molecular structure enabled the spontaneous emergence of crystalline and liquid crystalline thin films with strong 2nd harmonic generation (SHG) without any corona polishing process or tedious deposition techniques. Moreover, pin‐pointed multiphoton absorption in the liquid crystalline phase effectively switches off the SHG signal locally and permanently, underlining its interest in 3D data storage. This prototypical material, which can be fully addressed by NLO processes, multiphoton writing, and SHG reading, paves the way for the development of efficient flexible materials for 3D optical data storage.

Programmable Persistent Room Temperature Phosphorescence Switches through Wavelength-Selective Photoactivation.

Controlling multicolor persistent room-temperature phosphorescence (RTP) through photoirradiation holds fundamental significance but remains a significant challenge. In this study, we engineered a wavelength-selective photoresponsive system utilizing the Förster resonance energy transfer strategy. This system integrates a photoactivated long-lived luminescent material as the energy donor with a fluorescent photoswitch as the energy acceptor, facilitating programmable persistent luminescence switches. Distinct afterglow color states, such as initial nonemissive, green, yellow, and orange, were achieved through irradiation at 400 nm, 365 nm, and 254 nm, respectively. Based on this capability, we established an interacting network for multistate afterglow color switching among these four emissive states. In addition, we demonstrate the potential of this wavelength-selective photoresponsive system in the photo-controlled rewritable printing of multicolor afterglow images on a single thin film. This work represents a substantial step towards the fabrication of sophisticated wavelength-selective photoresponsive systems, potentially revolutionizing applications in optical data storage, security labeling, and smart displays by enabling precise control over photoresponsive behaviors under various photoirradiation wavelengths.

Sn2+/Pb2+ Doping‐Induced Highly Transparent Boroaluminate Microcrystalline Glass With Deep Traps for Long‐Term Optical Storage and Time‐Lapse X‐ray Imaging

AbstractThe development of microcrystalline glass‐ceramics with high transparency and deep trap energy levels is crucial for the cost‐effective and large‐scale production of scintillators and optical data storage applications. In this study, the incorporation of highly electronegative divalent tin (Sn2+) plays a key role in modulating the network structure of borate glass. This leads to the successful synthesis of SrAl2O4:Eu2+ microcrystalline glass with high transparency, reaching up to 80%, and excellent crystallinity. Additionally, a series of non‐optically active ions with different valence states is co‐doped with Eu2+ to fine‐tune the trap levels of the SrAl2O4 microcrystals. All samples maintain high crystallinity and exhibit good transparency. In particular, the Pb2+ ion co‐doped samples achieve an increased trap energy level of 1.28 eV, significantly enhancing their capacity to capture X‐rays and ultraviolet light. Density functional theory calculations reveal that this enhancement is due to severe lattice distortion caused by Pb2+ ions occupying interstitial sites in SrAl2O4. Utilizing the SrAl2O4:Eu2+, Pb2+ glass‐ceramics materials, X‐ray imaging with a delay of up to 210 s and optical information storage for >60 d is achieved. This study provides valuable insights into the crystal growth and trap modulation of persistent luminescent materials within a three‐dimensional glass network structure.

Hydrogen Bond‐Induced Flexible and Twisted Self‐Assembly of Functionalized Carbon Dots with Customized‐Color Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) is widely applied in optical data storage, quantum computing and backlights in three‐dimensional (3D) displays. Carbon dots (CDs) exhibit competitive optical properties, in addition to excellent resistance to photo‐ and chemical‐bleaching after carbonization. Combining the superior optical performance with polarization peculiarities through hierarchical structure engineering is imperative for the development of CDs. Here, oriented assembly was driven by hydrophobic interactions of aromatic ligands, which participated in the surface‐ligand post‐modification process on ground‐state chiral carbon core. Furthermore, the residual chiral amides on CDs formed multi‐hydrogen bonds during gradual aggregation, causing the assembled materials to form asymmetric bending structure. Superficial ligands interfered with optical dynamics of exciton radiation transition and promoted the excited state of the assembled materials to achieve a circularly polarized signal. The linkage ligands successfully overcame the frequent phenomenon of aggregation‐induced quenching and contributed further to the formation of self‐supporting films by assembly and facilitated chiral optical expression. The full‐color and white CPL were manipulated by simply regulating the functional groups on the ligands. Finally, based on the stable chiral powder phosphors, large chiral flexible films and multicolor chiral light‐emitting diodes were constructed which provide feasible materials and technical support for flexible 3D displays.

Nanoscale Photonic Barcodes Based on Anodic Alumina Photonic Crystal Heterostructures: Implications for Optical Communications, Data Storage, and Sensing

Nanoscale Photonic Barcodes Based on Anodic Alumina Photonic Crystal Heterostructures: Implications for Optical Communications, Data Storage, and Sensing

A multi-dimensional anti-counterfeiting nanocomposite based on fluorescent CDs and Eu-MOFs with dual function for continuous detection of Cu2+ and Bacillus anthracis

Traditional luminescent materials for anti-counterfeiting usually adopt encryption of low-level systems with limited security, which seriously hinders their application in preventing counterfeiting and information leakage. Therefore, it is urgent to develop materials for higher-level anti-counterfeiting. In this work, a stimulus-responsive intelligent luminescent material (AC@CDs-Eu-MOFs) was prepared by co-loading green-fluorescence CDs and red-fluorescence Eu-MOFs on Amino clay (AC). 5D security barcodes, which were easy to observe while difficult to clone, were ulteriorly designed based on the nanocomposite owing to the tunable fluorescence by optical stimulation and chemical stimulus. Owing to the large capacity, low cost, and easy authentication, the 5D security barcodes possess enormous potential in optical data storage and multi-dimensional information encryption. In addition, the chemical stimulus-response enables the nanocomposite achievable in detection of Cu2+ and Bacillus anthracis. Particularly, quantitative determination of copper in environmental water samples could be realized with a detection limit as low as 10.67 nM. Therefore, the material shows potential for detection of environmental pollutants besides advanced anti-counterfeiting.

Decoupling of Phase and Amplitude Channels with a Terahertz Metasurface Toward High‐Security Image Hiding

AbstractSteganography technology which conceals a message in a carrier to make it invisible is critical for information security. Conventional optical image steganography using diffractive optical components or spatial light modulators suffers from less encoding channel and bulky volume. The emergence of multifunctional metasurface that can manipulate abundant physical dimensions of optical fields allows the multi‐channel image steganography in a compact volume. Here, the image hiding in a metasurface is demonstrated by modulating the amplitude, phase, and polarization states of terahertz (THz) waves completely. Especially, the phase channel can decouple from the amplitude channel based on a Fresnel‐diffraction‐based algorithm. By directly measuring the phase distribution using the homemade THz focal plane imaging system, the number of transmission channels can expand from N to 2N. As a proof of concept, it is shown that the secret images can encode in the phase channel and subsequently extract by using different keys, such as polarization states, detection distances, and its combinations. Moreover, different hiding strategies with different attacker behaviors are also demonstrated. The decoupling of the phase and amplitude channels with a single metasurface may open an avenue toward innovative optoelectronic devices for optical image steganography, data storage, and terahertz communication.

Multimodal anti-counterfeiting and optical storage application based on luminescence reversible modification and color change of photochromic phosphor

Reversible upconversion luminescence (RUCL) modification based on photochromism has received considerable interest due to its potential applications in optical storage and invisible optical anti-counterfeiting. Herein, white β-Ba2ScAlO5: Yb3+, Er3+ (β-BSAO-YE) phosphor was irradiated with 254 nm light, which caused the phosphor to turn blue due to the increase of oxygen vacancy. The blue β-BSAO-YE phosphor returns to its original color upon stimulation with 808 nm laser light or 125 °C, exhibiting a double photo-induced reversible photochromic change. The green and red upconversion luminescence (UCL) of the β-BSAO-YE were reversibly modified according to their photochromic properties. The UCL modification changes the luminescence color of the pattern, indicating that β-BSAO-YE phosphor is an ideal compound anti-counterfeit agent. The light information recorded on the β-BSAO-YE binary photochromic dot matrix can be read under ultraviolet (UV) and near-infrared (NIR) excitation, demonstrating the potential application of β-BSAO-YE phosphors as optical data storage media. In addition, the cyclic experiment showed good photochromic and UCL modulation repeatability. The new luminescent β-BSAO-YE not only proposes a new way to exploring upconversion red light materials, but also provides new materials for optical storage, optical information and optical anti-counterfeiting.

Efficient generation of octave-separating orbital angular momentum beams via forked grating array in lithium niobite crystal

Abstract The concept of orbital angular momentum (OAM) of light has not only advanced fundamental physics research but also yielded a plethora of practical applications, benefitting from the abundant methods for OAM generation based on linear, nonlinear and combined schemes. The combined scheme could generate octave-separating OAM beams, potentially increasing the channels for optical communication and data storage. However, this scheme faces a challenge in achieving high conversion efficiency. In this work, we have demonstrated the generation of multiple OAM beams at both fundamental frequency and second harmonic (SH) wavelengths using a three-dimensional forked grating array with both spatial χ (1) and χ (2) distributions in a lithium niobate nonlinear photonic crystal platform. The enhancements of the fundamental and SH OAM beams have been achieved by employing linear Bragg diffraction and nonlinear Bragg diffraction, respectively, i.e., quasi-phase matching. The experimental results show that OAM beams with variable topological charges can be enhanced at different diffraction orders via wavelength or angle tuning, achieving conversion efficiencies of 60.45 % for the linear OAM beams and 1.08 × 10−4 W −1 for the nonlinear ones. This work provides a promising approach for parallel detection of OAM states in optical communications, and extends beyond OAM towards the control of structured light via cascaded linear and nonlinear processes.

Self-Assembled Chiral Polymers Exhibiting Amplified Circularly Polarized Electroluminescence.

Circularly polarized electroluminescence (CPEL) is highly promising in realm of 3D display and optical data storage. However, designing a groundbreaking chiral material with high comprehensive CPEL performance remains a formidable challenge. In this work, a pair of chiral polymers with self-assembled behavior is designed by integrating a chiral BN-moiety into polyfluorene backbone, named R-PBN and S-PBN, respectively. The chiral polymers show narrowband emission centered at 490 nm with full-width half maximum (FWHM) of 29 nm and high photoluminescence quantum yield (PLQY) of 79 %. After thermal annealing treatment, the chiral polymers undergo self-assembly, exhibiting amplified circularly polarized luminescence (CPL) with asymmetry factor (|glum|) of up to 0.11. Moreover, the solution-processed nondoped CP-OLEDs based on the chiral polymers as emitting layers exhibit maximum external quantum efficiency (EQEmax) of 9.8 %, intense CPEL activities with |gEL| of up to 0.07, and small FWHM of 36 nm, simultaneously. This represents the first case of self-assembled chiral polymers that combines high EQE, large gEL value and narrowband emission.

Self‐Assembled Chiral Polymers Exhibiting Amplified Circularly Polarized Electroluminescence

Circularly polarized electroluminescence (CPEL) is highly promising in realm of 3D display and optical data storage. However, designing a groundbreaking chiral material with high comprehensive CPEL performance remains a formidable challenge. In this work, a pair of chiral polymers with self‐assembled behavior is designed by integrating a chiral BN‐moiety into polyfluorene backbone, named R‐PBN and S‐PBN, respectively. The chiral polymers show narrowband emission centered at 490 nm with full‐width half maximum (FWHM) of 29 nm and high photoluminescence quantum yield (PLQY) of 79%. After thermal annealing treatment, the chiral polymers undergo self‐assembly, exhibiting amplified circularly polarized luminescence (CPL) with asymmetry factor (|glum|) of up to 0.11. Moreover, the solution‐processed nondoped CP‐OLEDs based on the chiral polymers as emitting layers exhibit maximum external quantum efficiency (EQEmax) of 9.8%, intense CPEL activities with |gEL| of up to 0.07, and small FWHM of 36 nm, simultaneously. This represents the first case of self‐assembled chiral polymers that combines high EQE, large gEL value and narrowband emission.

Functionality Expansion of Guided Mode Radiation via On-Chip Metasurfaces.

On-chip metasurfaces play a crucial role in bridging the guided mode and free-space light, enabling full control over the wavefront of scattered free-space light in an optimally compact manner. Recently, researchers have introduced various methods and on-chip metasurfaces to engineer the radiation of guided modes, but the total functions that a single metasurface can achieve are still relatively limited. In this work, we propose a novel on-chip metasurface design that can multiplex up to four distinct functions. We can efficiently control the polarization state, phase, angular momentum, and beam profile of the radiated waves by tailoring the geometry of V-shaped nanoantennas integrated on a slab waveguide. We demonstrate several innovative on-chip metasurfaces for switchable focusing/defocusing and for multifunctional generators of orbital angular momentum beams. Our on-chip metasurface design is expected to advance modern integrated photonics, offering applications in optical data storage, optical interconnection, augmented reality, and virtual reality.

High-accuracy data readout in multi-dimensional optical data storage using convolutional neural networks

The escalating global volume of digital data poses a critical challenge for storage solutions. Optical data storage techniques have garnered lots of interests due to their excellent offline storage capabilities, including low energy consumption, high capacity, and long lifespan. However, despite the focus on data recording, minimal attention has been dedicated to the readout aspect. This study introduced femtosecond laser direct writing to perform multi-dimensional optical data storage and employed a specialized convolutional neural network to enhance voxel readout accuracy. The proposed network architecture achieved a remarkable voxel readout accuracy of 98.83%, surpassing support vector machine method (90.07%) and LeNet (96.85%). Furthermore, the proposed method yielded a substantial increase in actual user capacity, outperforming traditional approaches and presenting a novel solution for addressing readout challenges in multi-dimensional optical data storage.

Investigating the nonlinear optical response of virgin cherry kernel oil and its application to detecting adulteration

The nonlinear optical (NLO) response of materials is the basis for their use in various applications including optical switching, optical data storage, and optical limiting. Additionally, it can be used as an innovative authentication method. In this study, the NLO properties of virgin cherry kernel oil (VCKO) were investigated by observing of spatial self-phase modulation (SSPM) diffraction rings using a 532nm continuous-wave laser beam. Based on the intensity-dependent number of symmetric diffraction rings, the nonlinear refraction coefficient and thermo-optical coefficient of VCKO were estimated to be 3.81×10−6cm2/W and 5.34×10−4K−1, respectively, for the first time, according to the authors’ knowledge. Furthermore, we employed the SSPM technique for adulteration detection in the VCKO sample by analyzing its NLO properties. To accomplish this, we prepared different adulterated samples by mixing VCKO with cheaper commercial oils, such as virgin sunflower oil (VSFO) and virgin canola oil (VCO) at various concentration ratios. In the mixed VCKO adulterated samples, the measured NLO parameters were highly correlated with the amount of adulteration. The results confirmed the ability of the SSPM technique to determine the degree of adulteration in oil samples by measuring and comparing their NLO properties. In addition, our results indicate that cherry kernel oil can be a viable candidate as a nonlinear medium for optical applications.

NIR regeneration and visible luminescence modification in photochromic glass: A novel encryption and 3D optical storage medium

AbstractPhotochromic glass shows great promise for 3D optical information encryption and storage applications. The formation of Ag nanoclusters by light irradiation has been a significant development in the field of photochromic glass research. However, extending this approach to other metal nanoclusters remains a challenge. In this study, we present a pioneering method for crafting photochromic glass with reliably adjustable dual‐mode luminescence in both the NIR and visible spectra. This was achieved by leveraging bimetallic clusters of bismuth, resulting in a distinct and novel photochromic glass. When rare‐earth‐doped, bismuth‐based glass is irradiated with a 473 nm laser, and it undergoes a color transformation from yellow to red, accompanied by visible and broad NIR luminescence. This phenomenon is attributed to the formation of laser‐induced (Bi+, Bi0) nanoclusters. We achieved reversible manipulation of the NIR luminescence of these nanoclusters and visible rare‐earth luminescence by alternating exposure to a 473 nm laser and thermal stimulation. Information patterns can be inscribed and erased on a glass surface or in 3D space, and the readout is enabled by modulating visible and NIR luminescence. This study introduces a pioneering strategy for designing photochromic glasses with extensive NIR luminescence and significant potential for applications in high‐capacity information encryption, optical data storage, optical communication, and NIR imaging. The exploration of bimetallic cluster formation in Bi represents a vital contribution to the advancement of multifunctional glass systems with augmented optical functionalities and versatile applications.image

Color morphing surfaces with effective chemical shielding

Color morphing refers to color change in response to an environmental stimulus. Photochromic materials allow color morphing in response to light, but almost all photochromic materials suffer from degradation when exposed to moist/humid environments or harsh chemical environments. One way of overcoming this challenge is by imparting chemical shielding to the color morphing materials via superomniphobicity. However, simultaneously imparting color morphing and superomniphobicity, both surface properties, requires a rational design. In this work, we systematically design color morphing surfaces with superomniphobicity through an appropriate combination of a photochromic dye, a low surface energy material, and a polymer in a suitable solvent (for one-pot synthesis), applied through spray coating (for the desired texture). We also investigate the influence of polymer polarity and material composition on color morphing kinetics and superomniphobicity. Our color morphing surfaces with effective chemical shielding can be designed with a wide variety of photochromic and thermochromic pigments and applied on a wide variety of substrates. We envision that such surfaces will have a wide range of applications including camouflage soldier fabrics/apparel for chem-bio warfare, color morphing soft robots, rewritable color patterns, optical data storage, and ophthalmic sun screening.

High‐Capacity Photochromic Rotary Encoder for Information Encryption and Storage

AbstractPhotochromic materials are widely used in optical data storage, data encryption, and anti‐counterfeiting because of their ability to be written, erased, and read repeatedly. However, conventional information encryption and storage capabilities based on a “matrix” pattern in a 2D plane are limited to fewer storage dimensions, making information less secure. Here, a new concept of expanding the storage dimensions is presented by manipulating the rotation angle in 2D photochromic encoding disks based on the principle of the absolute encoder. For this purpose, a novel photochromic material, NaNbO3:xEu3+ is developed, with highly efficient red emission, a large luminescence switching contrast, and antithermal quenching behavior. The designed photochromic rotary encoder made with the NaNbO3‐based material exhibits higher‐level data encryption than that of conventional encoders and unlimited storage capability. This study presents exciting opportunities for information storage and encryption using luminescent photochromic materials.

Advanced Transparent Glass‐Ceramics via Laser Anisotropic Nanocrystallization

AbstractTransparent glass‐ceramics, merging the attributes of both glass and ceramics, have diverse applications in ballistic protection, armor materials, dentistry, light‐emitting diode, and optical domains. A limitation of conventional methods for glass‐ceramic fabrication is their inadequacy in precisely controlling the morphology of crystallization, consequently constraining their prospective advancements in diverse areas. Here, a method that facilitates precise control over the formation and growth of polarization‐dependent nonperiodic anisotropic nanocrystals, with a short axis ranging from 15 to 280 nm, in Li2O‐Al2O3‐SiO2 (LAS) glass is proposed. The method utilizes the principles of near‐field anisotropy between light and matter, building upon the classical nucleation‐growth model of glass crystallization. Notably, the glass‐ceramics possessing laser‐induced nanocrystals within the Rayleigh size regime showcase an impressive 99.7% transmittance in the visible and near‐infrared wavelengths. Additionally, the glass‐ceramics with non‐periodic anisotropic nanocrystals macroscopically exhibit form‐birefringence properties, thus enabling transparent optical applications, such as polarization elements, geometric phase elements, and multi‐dimensional optical data storage. This work opens up new avenues for morphological manipulation of nanocrystallization, with potential applications in optics, nanophotonics, functional glass‐ceramics, and high mechanical performance devices.