Ultra-high Density Optical Data Storage Research Articles

Pressure-induced tuning of physical properties in high-throughput metal halide MSn2Br5 (M = K, Cs) perovskites for optoelectronic applications.

The physical properties of the ferromagnetic oxide perovskites MSn2Br5 (M = K, Cs) were thoroughly examined using the GGA + PBE formalism of density functional theory. The investigation includes a comprehensive characterization of these materials under hydrostatic pressures ranging up to 25 GPa. Our work represents the first theoretical framework for exploring the behavior of MSn2Br5 (M = K, Cs) under pressure, providing valuable insights into their properties. To ensure the thermodynamic and mechanical stability of the studied compounds, we justified their stability through the analysis of formation energy and Born stability criteria. Furthermore, we conducted a thorough examination of the mechanical features of MSn2Br5 (M = K, Cs) based on various parameters, such as elastic constants, elastic moduli, the Kleinman parameter, the machinability index, and the Vickers hardness. Pugh's ratio and Poisson's ratio data show a ductile behavior for both compounds under stress. Moreover, our analysis of the refractive index suggests that both materials hold significant potential as candidates for ultrahigh-density optical data storage devices, particularly when subjected to appropriate laser irradiation. This finding opens up exciting possibilities for utilizing MSn2Br5 (M = K, Cs) in advanced optical technologies.

2D Hierarchical Microbarcodes with Expanded Storage Capacity for Optical Multiplex and Information Encryption.

The design of nanosegregated fluorescent tags/barcodes by geometrical patterning with precise dimensions and hierarchies could integrate multilevel optical information within one carrier and enhance microsized barcoding techniques for ultrahigh-density optical data storage and encryption. However, precise control of the spatial distribution in micro/nanosized matrices intrinsically limits the accessible barcoding applications in terms of material design and construction. Here, crystallization forces are leveraged to enable a rapid, programmable molecular packing and rapid epitaxial growth of fluorescent units in 2D via crystallization-driven self-assembly. The fluorescence encoding density, scalability, information storage capacity, and decoding techniques of the robust 2D polymeric barcoding platform are explored systematically. These results provide both a theoretical and an experimental foundation for expanding the fluorescence storage capacity, which is a longstanding challenge in state-of-the-art microbarcoding techniques and establish a generalized and adaptable coding platform for high-throughput analysis and optical multiplexing.

Creation of galaxy-shaped vortex relief structures in azo-polymers with petal-like beams.

We demonstrate the formation of surface relief structures in azo-polymers which exhibit multiple spiral arms, through irradiation of a rotating petal-like beam formed by the coherent superposition of Laguerre-Gaussian modes with opposite handedness. Intriguingly, the fabricated relief structures reflect full geometric parameters of the irradiated petal beam, such as handedness, topological charge, initial azimuthal phase and even ellipticity, corresponding to azimuthal and polar angles along equator and meridian planes of an orbital Poincaré sphere. The handedness, or direction of rotation, of the fabricated structures with multiple spiral arms could be controlled via the rotation and polarization directions of the irradiating laser field. This effect highlights an exotic coupling between the optical intensity gradient induced mass transport of the irradiated material and the spin angular momentum characteristics of the irradiating optical field. The azimuthal orientation of the surface relief structures could also be tuned by altering the initial relative phase between the coherently superposed Laguerre-Gaussian modes with opposite handedness, constituting the irradiating petal laser field. This work offers new insights into fundamental interactions which occur between light and matter, and we believe, will pave the way towards advanced technologies, such as ultrahigh density optical data storage.

An atomistic modeling study of high-throughput RVO3(R=La, Nd) perovskites for efficient solar energy conversion materials

For the first time, density functional theory-based first-principles calculations are used to study oxide perovskites RVO3(R=La,Nd) under pressure. Structural parameters match experimental and theoretical data. The d orbital significantly contributes to the density of states (DOS) near EF for all phases. At 0 GPa, the La, V, and O PDOS at EF are ∼0.27, ∼2.18, and ∼0.44 states/eV/f.u. With increasing pressure, reflectivity and absorption spectra shift to higher energy regions. Reflectivity is nearly flat and significant for both compounds between ∼4 eV and ∼12 eV of photon energy, showing that RVO3(R=La,Nd) can be used as a UV radiation reflector. Pressure stiffens RVO3(R=La,Nd) as elastic moduli increase. Pugh's ratio, Poisson's ratio, and Cauchy's pressure show that both compounds are ductile under pressure. With laser irradiation, both materials could be ultrahigh-density optical data storage devices due to their refractive index.

Ultra-high density optical data storage in common transparent plastics

The ever-increasing demand for high data storage capacity has spurred research on development of innovative technologies and new storage materials. Conventional GByte optical discs (DVDs and Bluray) can be transformed into ultrahigh capacity storage media by encoding multi-level and multiplexed information within the three dimensional volume of a recording medium. However, in most cases the recording medium had to be photosensitive requiring doping with photochromic molecules or nanoparticles in a multilayer stack or in the bulk material. Here, we show high-density data storage in commonly available plastics without any special material preparation. A pulsed laser was used to record data in micron-sized modified regions. Upon excitation by the read laser, each modified region emits fluorescence whose intensity represents 32 grey levels corresponding to 5 bits. We demonstrate up to 20 layers of embedded data. Adjusting the read laser power and detector sensitivity storage capacities up to 0.2 TBytes can be achieved in a standard 120 mm disc.

Synthesis and super-resolution imaging performance of a refractive-index-controllable microsphere superlens

Microspheres can function as optical superlenses for nanoscale super-resolution imaging. The imaging performance is mainly affected by the size and refractive index of the microsphere. Precise control of these parameters is a challenging task but of fundamental importance to the further development of the technique. In this study, we demonstrate for the first time a nanoparticle-hybrid suspension polymerization approach to chemically synthesize high-quality microspheres (ZrO2/polystyrene) with optical properties that are highly controllable. Microspheres of different sizes (d: 2–20 μm) and refractive indexes (np: 1.590–1.685) were synthesized and their super-resolution imaging performances were evaluated and compared. Our results show that continuously increasing the refractive index of microspheres can enhance the imaging resolution and quality. A 60 nm resolution has been obtained in the wide-field imaging mode and a 50 nm resolution has been obtained in the confocal mode imaging of semiconductor chip samples. The obtained 50–60 nm resolutions have significantly gone beyond the conventional 200 nm resolution limit for visible light optical microscopes; the super-resolution mechanism has been discussed. The synthesized microsphere superlenses may find applications in many other areas as well, including nanolithography, nano-sensing, nano-diagnosis, nano-spectroscopy and ultra-high density optical data storage.

Multistate electrically controlled photoluminescence switching

Reversibly fluorescent switchable materials have important applications in the fields of ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optical/electronic devices, sensors, bioimaging and so on. Some systems have been developed based on smart luminescent polymers and organic photoswitchable molecules. However, the use of such materials for practical applications is dramatically restricted by their intrinsic drawbacks such as low ON/OFF ratios, irreversibility and poor environmental resistance. An imperative challenge toward real applications is to design and fabricate photoluminescence switching devices with high on/off contrast and fast response time, and especially to obtain multicolored systems, in which the photoluminescence wavelength can be easily tuned in the visible region. Here we report the first inorganic example of a multicolored photoluminescence switching system by controlling the organization of crown-type polyoxometalates (POMs) and CdSe@CdS core–shell quantum dots (QDs) into the layer-by-layer (LBL) nanostructures. The photoluminescence of this system can be switched on and off reversibly upon application of step potentials for different redox states, owing to the energy transfer between reduced POMs and QDs. This system displays a quick response (off 17 s, on 38 s), high on/off contrast (∼91%), good cycling performance (the modulation ratio is only decreased by 19% after 200 cycles) and also has the advantage of low power consumption. Furthermore, reversible four-state fluorescence switching is realized by integrating different-sized QDs in one multifunctional system.

Photochromic Materials: More Than Meets The Eye

Photochromic materials are a family of compounds which can undergo reversible photo-switches between two different states or isomers with remarkably different properties. Inspired by their smart photo-switchable characteristics, a variety of light-driven functional materials have been exploited, such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optic/electronic devices, sensors, bio-imaging and so on. This review commences with a brief description of exciting progress in this field, from systems in solution to modified functional surfaces. Further development of these photo-switchable systems into practical applications as well as existing challenges are also discussed and put in prospect.

Direct measurement of the near-field super resolved focused spot in InSb

Under appropriate laser exposure, a thin film of InSb exhibits a sub-wavelength thermally modified area that can be used to focus light beyond the diffraction limit. This technique, called Super-Resolution Near-Field Structure, is a potential candidate for ultrahigh density optical data storage and many other high-resolution applications. We combined near field microscopy, confocal microscopy and time resolved pump-probe technique to directly measure the induced sub-diffraction limited spot in the near-field regime. The measured spot size was found to be dependent on the laser power and a decrease of 25% (100 nm) was observed. Experimental evidences that support a threshold-like simulation model to describe the effect are also provided. The experimental data are in excellent agreement with rigorous simulations obtained with a three dimensional Finite Element Method code.

Study of the optical response of phase‐change recording layer with zinc oxide nanostructured thin film

Recently, use of nanostructured materials as a near-field optical active layer has attracted a lot of interest. The non-linear optical properties and strong enhancements of metallic oxide nanostructured thin films are key functions in applications of promising nanophotonics. For the importance of ultra-high density optical data storage, we continue investigating the ultra-high density recording property of near-field optical disk consisting of zinc oxide (ZnO(x)) nanostructured thin film. A carrier-to-noise ratio above 38 dB at a recording mark size of 100 nm can be obtained in the ZnO(x) near-field optical disk by a DVD driver tester directly. In this article, we use an optical pump-probe system (static media tester) to measure the optical response of a phase-change recording layer (Ge(2)Sb(2)Te(5)) and demonstrate the high contrast of optical recording with a ZnO(x) nanostructured thin film in short pulse durations. Also, we investigate the dependence of writing power and the optical response in conventional re-writable recording layers and the phase-change material with ZnO(x) nanostructured thin film.

Photochromic bisthienylethene as multi-function switches

Bisthienylethenes (BTEs) are one of the most promising families of photochromic compounds because of their fatigue resistance and thermally irreversible properties for use in optoelectronic devices such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, sensors, and so on. This article describes recent development of switchable photochromic bisthienylethene materials, especially multi-switchable bisthienylethene materials including multi-color photochromic materials, multi-switchable organogelators and liquid crystals. We also highlight our recent contributions in this field.

Dynamic readout of subdiffraction-limited pit arrays with a silver superlens

Recent theoretical and experimental results suggested that the silver superlens could be constructed through controlling silver thin film thickness and preparation conditions, and applied in subdiffraction-limited optical imaging and optical lithography. In this work, we report another significant application of silver superlens—ultrahigh density optical data storage. With the silver superlens the subdiffraction-limited pit arrays on an optical disk are dynamically read out and the carrier-to-noise ratio can reach 25dB for the thin film thickness of 46nm. The readout laser power and readout velocity have little effect on the carrier-to-noise ratio. Additionally, in our experiment the silver thin film thickness needs to be controlled in the range from 20to80nm.

Carbocyanine Dyes as Efficient Reversible Single-Molecule Optical Switch

We demonstrate that commercially available unmodified carbocyanine dyes such as Cy5 (usually excited at 633 nm) can be used as efficient reversible single-molecule optical switch, whose fluorescent state after apparent photobleaching can be restored at room temperature upon irradiation at shorter wavelengths. Ensemble photobleaching and recovery experiments of Cy5 in aqueous solution irradiating first at 633 nm, then at 337, 488, or 532 nm, demonstrate that restoration of absorption and fluorescence strongly depends on efficient oxygen removal and the addition of the triplet quencher beta-mercaptoethylamine. Single-molecule fluorescence experiments show that individual immobilized Cy5 molecules can be switched optically in milliseconds by applying alternating excitation at 633 and 488 nm between a fluorescent and nonfluorescent state up to 100 times with a reliability of >90% at room temperature. Because of their intriguing performance, carbocyanine dyes volunteer as a simple alternative for ultrahigh-density optical data storage. Measurements on single donor/acceptor (tetramethylrhodamine/Cy5) labeled oligonucleotides point out that the described light-driven switching behavior imposes fundamental limitations on the use of carbocyanine dyes as energy transfer acceptors for the study of biological processes.

A semiconducting thermooptic material for potential application to super-resolution optical data storage

To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated read/write. Thermoelectric materials are proposed as candidates capable of yielding solid state SR effects in the absence of phase changes that are detrimental to durability. As a prototype material, PbTe is selected due to a large thermoelectric Seebeck coefficient and a high stability of a crystalline single phase state up to its melting temperature of 924 °C. A preliminary study of Pb 51Te 49 thin films was carried out with the following findings: Firstly, under exposure to pulsed light, completely reversible changes in transmittance take place regardless of power. Secondly, light transmittance grows with increasing laser power and this is not due to melting except at relatively high powers. By way of optical calculations using the measured reflectance and transmittance values combined with thermal calculations, a temperature variation of effective optical constants ( n, k) was also estimated to find that both of them decrease with increasing temperature.

Thermoelectric PbTe thin film for superresolution optical data storage

To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated readout and write. Thermoelectric materials appear to be promising candidates due to their capability of yielding phase-change-free thermo-optic changes. A feasibility study was carried out with PbTe for its large thermoelectric coefficient and high stability over a wide temperature range as a crystalline single phase. Under exposure to pulsed red light, the material was found to display positive, yet completely reversible changes of optical transmittance regardless of laser power, fulfilling basic requirements for SR readout and write. The material was also shown to have a high endurance against repeated static laser heating of up to 106–107 cycles tested. A read only memory disk with a PbTe SR layer led to the carrier to noise ratio value of 47dB at 3.5mW for 0.25μm pit; below the optical resolution limit (∼0.27μm) of the tester.

Optical Super-Resolution Technology for Application to Ultra-High Density Optical Storage

Super-resolution technologies for ultrahigh-density optical data storage are described. Applying optical nonlinear thin films, super-resolution readout is attained in less than the optical diffraction limit. In combination with near-field principle, it is further improved in less than 100 nm. In this paper, we discuss the basic principle of near-field optic and related surface and localized surface plasmon polaritons at first, and discribe several applications with metallic nanoparticles and wires to future optical disk technology.

Study on the Mechanism of Super-Resolution Near-Field Structure High-Density Optical Data Storage

The super-resolution near-field structure (Super-RENS), glass/SiN/Sb/SiN, which is promising for near-field ultrahigh-density optical data storage (ODS), has been proposed and investigated in recent years. The recording mark size is a few tens of nanometers, far beyond the diffraction limit of traditional optics. The mechanism of this Super-RENS, including the working principle of the nonlinear optical layers and the size reduction of the recording marks, has not been clearly understood. In this study, the action of sandwich multilayer films in Super-RENS is mainly investigated. The behavior of the optical wave at the boundary between two dielectric media is discussed in detail, and the resonance characteristic of the surface plasmon wave (SPW) is analyzed. The mechanism of ultrahigh-density ODS using Super-RENS is explained quantitatively. It is demonstrated that the wave effect is larger than the thermal effect in Super-RENS.

A virtual optical probe based on evanescent wave interference

A virtual probe is a novel immaterial tip based on the near-field evanescent wave interference and small aperture diffraction, which can be used in near-field high-density optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation of nano-scale specimen, etc. In this paper, the formation mechanism of the virtual probe is analysed, the evanescent wave interference discussed theoretically and the sidelobe suppression by small aperture is simulated by the three-dimensional finite-difference time-domain method. The simulation results of the optical distribution of the near-field virtual probe reveal that the transmission efficiency of the virtual probe is 102-104 times higher than that of the nano-aperture metal-coated fibre probe widely used in near-field optical systems. The full width at half maximum of the peak, in other words, the size of virtual probe, is constant whatever the distance in a certain range so that the critical nano-separation control in the near-field system can be relaxed. We give an example of the application of the virtual probe in ultrahigh-density optical data storage.

The Application of Silver Oxide Thin Films to Plasmon Photonic Devices

AbstractRF-magnetron sputtered thin films of silver oxide (AgOx) were recently applied to ultra-high density optical data storage. It has been elucidated that the AgOx film sandwiched by protection layers shows very attractive characteristics in strong light-scattering, local plasmon generation and super-resolution by focussing a laser beam on it. Especially, the combination with an active recording film (optical phase change or magneto-optical) used in the currently recordable optical disks improves the storage density and overcomes the diffraction limit. In this paper, we describe the basic characteristics of nano-scale light scattering centers generated in the AgOx films and the interaction with ultra-high density recorded mark patterns in a near-field region. In addition, we provide the structural transition of the AgOx film by thermal and laser annealing treatment.

Near-field images of the AgOx-type super-resolution near-field structure

As a promising disk structure for ultrahigh density optical data storage, super-resolution near-field structure of AgOx type has been studied by the tapping-mode tuning-fork near-field scanning optical microscope as well as the transmission electron microscope. This structure presents strong near-field intensity enhancement and nonlinear optical effect, compared with the ordinary material. Numerical calculations confirm that the localized surface plasmon and the nonuniform material structures are the main causes for these unusual characteristics.