High-density Optical Data Storage Research Articles

Design and analysis of a group-III nitride superlattice structure based semiconductor laser diode for blue region emission

The demand for high-power blue laser diodes (LDs) in the range above 2 W has been steadily increasing due to their applications in solid-state lighting, projection displays, high-density optical data storage and underwater communication. However, current designs face limitations in terms of achieving both high power output and efficiency. This work focuses on the design, development and numerical analysis of a blue LD utilizing group-III nitride superlattice structures. The present study aims to overcome design challenges by investigating the fundamental factors affecting the performance of blue LDs based on superlattice InGaN structures through careful device parameter optimization. The results show that our device successfully emits at around 430 nm wavelength and is capable of achieving a differential quantum efficiency of 46.91%, with a maximal optical power output of 2.18 W for 1.71 A of current for a strip width of 15 µm. However, when the strip width is increased to 20 µm, 4.6 W optical power is achieved with 3 A of injection current. Numerical studies are performed with several calibrated physics models and finite-difference time-domain techniques. Our results provide an insight into the potential of using superlattice group-III nitride structures to enhance the performance of blue LDs, opening up new possibilities for high-power and high-efficiency devices in the future.

Pressure-induced physical properties in topological semi-metals [formula omitted]

The present study employs first-principles DFT-based calculations within the generalized gradient approximation (GGA) to reveal various physical feature (including structural, elastic, mechanical, electronic, optical, as well as Debye temperature) of the topological semimetal MAs2M=Hf,Ti under stress up to 50GPa. Mechanical and thermodynamic stability of the investigated materials are supported by Born stability criteria and formation energy. To learn more about the mechanical features of MAs2M=Hf,Ti materials, we investigated at a variety of metrics such elastic constants, elastic moduli, Vickers hardness, machinability index, Kleinman parameter, and anisotropy factor. Interestingly, both Pugh’s ratio and Poisson’s ratio reveal that studied materials go through a brittle-to-ductile transition at different applied pressures. Due to the increase in elastic constants with increasing pressure, materials become more rigid and resistant to deformation, making them useful in various engineering fields. The studied materials are anisotropic, and their anisotropy factor changes significantly with rising pressure. The band structure analysis confirms that both materials are Weyl semi-metals, and the density of states reveals that the d orbital of Hf and Ti contributes significantly to DOS at EF. The electrical characteristics are strongly supported by the optical function. As external pressure increases, there is a corresponding increase in both the absorption coefficient and reflectivity. Their refractive index value falls and becomes flat at high energy, making them a high-density optical data storage media when exposed to the right light source. For both the material, pressure increases density, sound velocity, and Debye temperature, indicating that covalent bonds become stronger. The higher value of Debye temperature indicates the higher melting point of the studied compounds.

Generation of ultrafast tunable super-oscillation light fields

In this paper, we conceptually propose and numerically demonstrate the generation of ultrafast tunable super-oscillation (SO) light fields by tightly focusing a radially polarized Gaussian femtosecond pulse laser. It is shown that, as the fleeting time goes on within one-half cycle (0 fs < t < 200 fs), the light fields in the focal region can be converted from an Airy spot (>0.61λ/NA, where λ is the wavelength of incident beam and NA is the numerical aperture of objective lens), via a SO spot (<0.36λ/NA), to a super-resolved spot (<0.5λ/NA). We further uncover the rapid evolutions on the full width at half maximum, the normalized central intensity, and the side lobe of focused superoscillatory spots, thus supporting ultrafast adjustable SO light fields. In addition, the effect of primary spherical aberration on the focusing properties of SO spots is examined. The associated mechanism to yield such time-varying SO light fields is elucidated as well. The results presented here expand the flexibility of ultrafast light field manipulation and hold extensive applications in ultrafast and super-resolved imaging, high-density optical data storage, and high-efficiency particle trapping.

Dual-modulation of micro-photoluminescence in rare-earth-doped crystals by femtosecond laser irradiation for 5D optical data storage

In transparent dielectric materials, the property modulation induced by femtosecond laser irradiation (FLI) holds great promise for optical storage due to the advantages of high resolution, material flexibility and 3D recording capability. However, the benefits are often mitigated by its incapability of information multiplexing or stringent requirements on fabrication conditions. Here, based on the dual-modulation of micro-photoluminescence (μ-PL) in Pr:YLF crystals by applying FLI, a novel strategy for optical data storage (ODS) is proposed and experimentally demonstrated. Multiple laser parameters within broad ranges can be used to fine-tune the μ-PL emission bands of Pr3+ ions to create storage voxels, which makes the information recording more feasible and flexible from a perspective of practical application. Remarkably, the dual modulation of spectral features at around 638 and 641 nm, in combination with the innovative design of voxels, make it possible to realize both emission-intensity-multiplexing and emission-wavelength-multiplexing, meeting the requirements for large memory capacity and high encryption of new generation ODS. Furthermore, the spatially selective control of μ-PL signals through secondary FLI allows for rewriting and erasure of the encoded information. This work opens new opportunities for rare-earth-doped materials in the applications of multidimensional rewritable/erasable high-density optical data storage and optical information encryption.

Pressure-induced physical properties in topological semi-metal TaM2 (M = As, Sb).

In this study, DFT based first principles calculations are used for measuring the structural, elastic, mechanical, electronic, optical and thermodynamic features of topological semimetal TaM2 (M = As, Sb) under various pressures. We conducted the first investigation into the physical properties of the topological semimetal TaM2 (M = As, Sb) under pressure. Formation energy and Born stability criteria justify the compound's thermodynamic and mechanical stability. We used elastic constants, elastic moduli, Kleinman parameter, machinability index, and Vickers hardness to investigate the mechanical properties of topological semimetal TaM2. Poisson's and Pugh's ratios reveal that both compounds change from brittle to ductile in response to pressure. The increasing nature of elastic moduli suggests that TaM2 becomes stiffer under stress. The pressure has a significant effect on the anisotropy factor for both materials. Band structure analysis shows that both compounds are Weyl semi-metals and the d orbital contributes significantly to the formation of the Fermi level, as shown by the density of states (DOS) analysis. Investigation of electronic characteristics provides important support for dissecting optical performance. Both the reflectivity and absorption spectra shift upwards in energy when pressure is increased. The refractive index value decreases and becomes flat in the higher energy region. Based on their refractive indices, both of these materials demonstrate as a high-density optical data storage medium when exposed to the right light source. The thermodynamic properties including sound velocity, and Debye temperature all exhibit an increasing nature with applied pressure. Due to their high Debye temperatures, the components under study have a rather high melting point.

High performance two-way full colors of transmission and reflection generated by hybrid Mg–TiO2 metasurfaces

Colors are carriers of information, and two-way structural colors of transmission and reflection can be used to convey significantly more information. Herein, using numerical analysis, we demonstrate metasurfaces capable of simultaneously transmitting and reflecting different colors. The low-loss hybrid Mg–TiO2 structures and transparent substrate result high saturation and wide gamut transmitted colors and complementary reflected colors. Besides, the dynamic display is possible with the hydrogen-storage metal Mg. Through simulations, we studied the potential of the proposed metasurfaces for applications, such as nanoprintings and encrypted watermarks. We expect the results of this work to be applicable to double-sided displays, anti-counterfeiting, information coding, and high-density optical data storage.

Polymer-Based High Diffraction Efficiency and High Resolution Volume Holographic Transmission Gratings

We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security.

Alkaline-Earth Metal Effects on Physical Properties of Ferromagnetic AVO3 (A = Ba, Sr, Ca, and Mg): Density Functional Theory Insights.

The effects of alkaline-earth metals on electronic, optical, thermodynamic, and physical properties of ferromagnetic AVO3 (A = Ba, Sr, Ca, and Mg) have been investigated by first-principles calculations within the GGA+U formalism based on density functional theory. The optimized structural parameters are in good agreement with the available experimental results that evaluate the reliability of our calculations. The cell and mechanical stability is discussed using the formation energy and Born stability criteria, respectively. The mechanical behaviors of AVO3 are discussed on the basis of the results of elastic constants, elastic moduli, Peierls stress, and Vickers hardness. The nature of the ductile–brittle transition of AVO3 compounds was confirmed by the values of Pugh’s ratio, Poisson’s ratio, and Cauchy pressure. The electronic band structures, as well as density of states, reveal the half-metallic behavior of BaVO3 and SrVO3. However, CaVO3 and MgVO3 exhibit spin-gapless and magnetic semiconductor characteristics, respectively. The microscopic origin of the transition from the half-metallic to semiconductor nature of AVO3 is rationalized using electronic properties. The presence of covalent, ionic, and metallic bonds in AVO3 compounds is found by the analysis of bonding properties. The single-band nature of half-metallic AVO3 is seen by observing hole-like Fermi surfaces in this study. Furthermore, the various thermodynamic and optical properties are calculated and analyzed. The refractive index suggests that AVO3 could be a potential candidate for applications to high-density optical data storage devices.

Single-Pulse Laser-Induced Ag Nanoclustering in Silver-Doped Glass for High-Density 3D-Rewritable Optical Data Storage

Single-Pulse Laser-Induced Ag Nanoclustering in Silver-Doped Glass for High-Density 3D-Rewritable Optical Data Storage

Ultraviolet C random lasing at 230–280 nm from Pr3+ doped bulk crystal resonators by two-photon absorption

Ultraviolet solid-state light sources, especially in the short-wave ultraviolet band, are attracting great attention for potential applications in high-density optical data storage, biomedical research, and water and air purification and sterilization. As one of the means to generate solid-state short-wavelength lasers, upconversion technology, which can transform a low-energy photon to a high-energy photon, has a simple structure and does not require strict phase-matching conditions. However, because of the high non-radiative decay rate during multiphoton absorption process, the short-wave upconversion ultraviolet lasing is still difficult to achieve. Here, under 450 nm blue laser excitation, we have successfully obtained ultraviolet C random lasing from a Pr3+ doped YPO4 single crystal via two-photon absorption. Presently, ultraviolet C random lasing with the wavelength range of 230–280 nm is the shortest wavelength for upconversion lasing emission.

Defect-induced nonlinearity in 2D nanoparticles.

Optical nonlinearity depends on symmetry and symmetries vanish in the presence of defects. Vacancy defects in centrosymmetric crystals and thin films are a well-known source of even-order optical nonlinearity, e.g. causing second harmonic generation. The emerging ability to manipulate defects in two-dimensional materials and nanoparticles provides an opportunity for engineering of optical nonlinearity. Here, we demonstrate the effect of defects on the nonlinear optical response of two-dimensional dielectric nanoparticles. Using a toy model, where bound optical electrons of linear atoms are coupled by nonlinear Coulomb interactions, we model defect-induced nonlinearity. We find that defects at particle edges contribute strongly to even-order optical nonlinearity and that unique nonlinear signatures of different defect states could provide the smallest conceivable QR-codes and extremely high density optical data storage, in principle approaching 1 bit per atom.

Phototriggered color modulation of perovskite nanoparticles for high density optical data storage.

Photoresponsive luminescent materials (PLMs) have attracted much attention in various optoelectronic fields, especially in optical data storage. Multi-wavelength (N-wavelength) based optical storage is a promising approach to increase the data storage density, but its current application is limited by the fact that most PLMs have only two-wavelength emissive states after certain light excitation, which requires simultaneous use of several PLMs and different irradiation light sources. In this study, we discovered that the wavelength of perovskite nanocrystals (PNCs) in the presence of dichloromethane (DCM) could be continuously and precisely tuned over a very wide color range (from red to violet) with the help of a single UV light source. The changes in crystal structures and optical properties of PNCs during UV irradiation were investigated in detail; the effects of capping ligand, solvent, UV irradiation power and time were evaluated, and the mechanism of UV triggered PNC fluorescence change was studied and is discussed. Finally, the applicability of PNCs/DCM film in N-wavelength-based high-density optical data storage was verified.

Two-dimensional closely-packed gold nanoislands: A platform for optical data storage and carbon dot generation

Polymer films doped with gold (Au) nanoparticles have been successfully employed to realize optical data storage and carbon dot generation. However, such nanomaterials are not expected to have a long lifetime because polymers are not stable against humidity and heat. Here, we propose the use of two-dimensional closely-packed Au nanoparticles deposited on a silica substrate as the platform for realizing simultaneously high-density optical data storage and efficient carbon dot storage. The hot spots formed by plasmonic coupling between Au nanoparticles enable the realization of polarization and wavelength multiplexing in optical data storage with high quality and low energy. In addition, strongly localized temperature distribution can be achieved in closely-packed Au nanoparticles exploited to produce luminescent carbon quantum dots by using direct laser writing. Our findings indicate the potential applications of this new nanomaterial in the fabrication of novel photonic devices for optical data storage, optical display, and optical sensing in the future.

A new class of upconversion luminescence tuning materials based on non-photochromic reaction: Er3+-activated Ba0.7Sr0.3Nb2O6 ferroelectrics

The upconversion (UC) luminescence tuning of phosphors has attracted increasing interest as optical switches, optical sensing, and high-density optical data storage devices. However, the design and synthesis of photo-switchable inorganic luminescent materials were still at primary stage. In this work, a new type of UC luminescence regulation materials, Er3+-activated tetragonal tungsten bronze Ba0.7Sr0.3Nb2O6 ferroelectrics, showing strong susceptibility to visible light irradiation, was reported based on non-photochromic (N-PC) effect. Under visible light irradiation, the maximum luminescent modulation ability reached up to 79.4%. The tuning of UC luminescence was disclosed to tightly rely on the irradiation time and thermal treatment processes. Meanwhile, excellent reproducibility was also demonstrated. Besides, the luminescent readout almost had no any influence on the UC emission, indicating the extremely low destruction to the stored luminescent states. The mechanisms related to the UC luminescence and manipulation were also discussed. In contrast to the previous tuning way based on PC reaction, it is believed that this work shed new light for the understanding of UC modulation fundamentals.

Reversible photoluminescence modulation in praseodymium-doped bismuth titanate ceramics for information storage based on photochromic reaction

Photoluminescence materials with reversible luminescence regulation properties have great potential for applications in photoswitches, optical sensing, and high-density optical data storage devices. In this work, a series of Pr3+-doped Bi4Ti3O12 (BiT) ceramics were synthesized by a high-temperature solid-phase reaction method. It is well known that BiT is the most famous one within the Aurivillius ferroelectric (FE) system. Previous works routinely focused on the FE-related properties of BiT-based compounds, but little attention has been devoted to the luminescence, especially the luminescence modulation performance. Here, a large and reversible photoluminescence modulation by alternating visible light irradiation and thermal stimulus based on photochromic (PC) process was achieved. Meanwhile, the influence of sintering temperature on the luminescence modulation behavior was also illustrated. The luminescence regulation properties of the Pr3+-doped BiT ceramics prepared at optimized sintering temperature were investigated in detail. The mechanisms connected to the luminescence, luminescence manipulation, and PC effect were discussed. It is believed that Pr3+-doped BiT materials can be utilized as a kind of ideal optical medium for future information storage device.

Investigation of the null reconstruction effect of an orthogonal elliptical polarization hologram at a large recording angle

We report on the null reconstruction effect (NRE) of an elliptical polarization volume hologram with orthogonal elliptically, circularly, and linearly polarized waves, respectively. The NRE is a special phenomenon in polarization holography, which means the diffraction efficiency declines to zero when the hologram is reconstructed by an orthogonally polarized reading wave. In our previous work [Opt. Express24, 1641 (2016)OPEXFF1094-408710.1364/OE.24.001641; Opt. Lett.42, 1377 (2017)OPLEDP0146-959210.1364/OL.42.001377; Opt. Express23, 8880 (2015)OPEXFF1094-408710.1364/OE.23.008880], the NRE of polarization holography recorded by linear and circular polarization waves has been investigated. Compared with linear and circular polarization holography, elliptical polarization holography represents a more general and unified recording hologram. However, no work on the NRE of elliptical polarization holography, as far as we know, has been reported until now. In this paper, the NRE of elliptical polarization holography is investigated and demonstrated theoretically and experimentally. First, the conditions of achieving NRE in elliptical polarization holography are studied based on vector holography theory. The results indicate that the NRE is a common phenomenon in polarization holography written by linear, circular, and elliptical polarization waves. Then, a series of experiments of NRE in a polarization hologram written by orthogonal elliptically, circularly, and linearly polarized waves is carried out. The NRE of elliptical polarization holography is experimentally observed, and the results are in nice agreement with the theoretical analysis. The NRE of elliptical polarization holography is expected to be applied in high-density optical data storage and polarization-controlled holographic elements.

Atomically Thin Nonlinear Transition Metal Dichalcogenide Holograms.

Nonlinear holography enables optical beam generation and holographic image reconstruction at new frequencies other than the excitation fundamental frequency, providing pathways toward unprecedented applications in optical information processing and data security. So far, plasmonic metasurfaces with the thickness of tens of nanometers have been mostly adopted for realizing nonlinear holograms with the potential of on-chip integration but suffering from low conversion efficiency and high absorption loss. Here, we report a nonlinear transition metal dichalcogenide (TMD) hologram with high conversion efficiency and atomic thickness made of only single nanopatterned tungsten disulfide (WS2) monolayer, for producing optical vortex beams and Airy beams as well as reconstructing complex holographic images at the second harmonic (SH) frequency. Our concept of nonlinear TMD holograms paves the way toward not only the understanding of light-matter interactions at the atomic level but the integration of functional TMD-based devices with atomic thickness into the next-generation photonic circuits for optical communication, high-density optical data storage, and information security.

Femtosecond laser micro-patterning of optical properties and functionalities in novel photosensitive silver-containing fluorophosphate glasses

Silver-containing glasses are promising candidates for photonic applications, due to the potentiality of spectroscopic properties of silver nanoclusters (NC's) and/or silver metallic nanoparticles. In this framework, silver-containing fluorophosphate glasses are candidates with a strong potential. Indeed, combined with femtosecond laser irradiation, silver NC's may be tailored in three-dimensional fluorescent micro-structures, whose spectroscopic properties have been investigated, revealing the creation of silver NC's but also of NP's during laser irradiation in the studied fluorophosphate glass. Additionally, the photo-inscription of silver NC's is correlatively accompanied by a positive index change, which has led to the demonstration of optical waveguiding behavior. Finally, the management of the reservoir of available silvers for laser inscription is investigated. Unlike previous observations made in standard oxide phosphate glasses, the considered silver-containing fluorophosphate glass exhibes an intriguing ability to be re-written when subjected to successive overlapping laser irradiations. Upon the optimization of compositions with tailored photo-sensitivity, the re-writable ability of fluorophosphate glasses paves the way to the design of advanced photonic devices such as photonic optical circuits, evanescent sensors or 3D high-density optical data storage.

Super-resolution longitudinally polarized light needle achieved by tightly focusing radially polarized beams

Based on the vector diffraction theory, a super-resolution longitudinally polarized optical needle with ultra-long depth of focus (DOF) is generated by tightly focusing a radially polarized beam that is modulated by a self-designed ternary hybrid (phase/amplitude) filter (THF). Both the phase and the amplitude patterns of THF are judiciously optimized by the versatile particle swarm optimization (PSO) searching algorithm. For the focusing configuration with a combination of a high numerical aperture (NA) and the optimized sine-shaped THFs, an optical needle with the full width at half maximum (FWHM) of 0.414λ and the DOF of 7.58λ is accessed, which corresponds to an aspect ratio of 18.3. The demonstrated longitudinally polarized super-resolution light needle with high aspect ratio opens up broad applications in high-density optical data storage, nano-photolithography, super-resolution imaging and high-efficiency particle trapping.

Improved lateral resolution with an annular vortex depletion beam in STED microscopy.

We report on the experimental demonstration of improved lateral resolution in stimulated emission depletion (STED) microscopy using an annular depletion beam configuration. A tight and finely tuned doughnut focal spot can be created by annular vortex illumination. Its application in STED microscopy for enhanced lateral resolution is systematically investigated by imaging 40nm fluorescent beads. An improved resolution with more than 20% reduced effective point spread function of the imaging system determined by the full width at half-maximum compared to that of the conventional STED is achieved. The proposed scheme also demonstrates its resolving capability for biological samples. The principle holds great potential in the research fields of biological superresolution imaging as well as STED-based nanolithography and high-density optical data storage.