Patent Application
20240265941
The present application claims priority from Australian Provisional Patent Application No. 2021901706 titled “IMPROVEMENTS IN OPTICAL DATA STORAGE” and filed on 8 Jun. 2021, the content of which is incorporated by reference in its entirety.
The following publication is referred to in the present application and its entire contents are incorporated by reference:
Xiang-lei Wang, Zhi-qiang Liu, Marion A. Stevens-Kalceff, and Hans Riesen, “Mechanochemical Preparation of Nanocrystalline BaFCl Doped with Samarium in the 2+ Oxidation State”, Inorganic Chemistry, 2014, 53 (17), 8839-8841.
The present disclosure relates to the storage of data. In a particular form, the present disclosure relates to a high density/high capacity optical based data storage medium.
In recent years worldwide data generation has grown at least 3-times faster than data storage capacities. This rapid growth has been driven by a massive increase in the use of the internet, social media and cloud computing. Traditional data storage technologies based on magnetic (eg, hard disk drives or tape) or solid-state (eg, solid state drives) have failed to address the growth in data storage demand.
Optical based storage arrangements have been one approach to the large scale storage of data and include implementations such as write-once-read-many times (WORM) storage media involving permanent ablation of a readable surface by a dye layer and rewritable implementations adopting the reversible change between amorphous and crystalline phases in thin metal, alloy or semiconductor films by laser heating. Optical data storage has some significant benefits over traditional hard drive technologies in terms of longer lifetime and significantly reduced operational energy requirements. Optical data storage could also offer much higher write and read speeds compared with commonly used magnetic tape and it is an attractive alternative to SSD technologies which can be prohibitively expensive for big data storage applications.
However, these optical based storage arrangements, including disc based arrangements such as CDs, DVDs and BDs, are ultimately restricted by the diffraction limited read/write area A of the laser as determined by the numerical aperture (NA) of the focussing lens and the wavelength of the laser that is employed. As an example, standard Blu-Ray™ arrangements with a typical NA of 0.85 and a 405 nm laser can only achieve a surface data density of approximately 2 Gb/cm2 resulting in a typical limit of around 25 GB per disc per layer. With requirements of petabyte to exabyte storage capacities, standard 25 GB (or 50 GB dual-layer) optical discs are not a viable solution for the large-scale storage demands of the future.
Against this background, it would be desirable to provide alternative optical based arrangements for data storage capable of increasing digital data storage capacities and/or to provide an alternative to current data storage methodologies.
In a first aspect, the present disclosure provides a data storage medium for storing digital data comprising:
In another form, the respective absorption/emission band is frequency selectively bleached to form a spectral hole in the combined optical transition profile to encode digital data.
In another form, the spectral hole in the combined optical transition profile is configured to have a predetermined depth level, the predetermined depth level selected from a plurality of depth levels to encode digital data in the spectral hole of the combined optical transition profile.
In another form, the respective wavelength ranges of the respective optical transition profiles of the different nano-sized materials have substantially the same width.
In another form, respective peak wavelengths of the respective optical transition profiles of the different nano-sized materials are substantially equally spaced with respect to each other.
In another form, the combined optical transition profile comprises a substantially flat portion over the extended wavelength range.
In another form, the mixture is distributed in a substantially two-dimensional (2D) configuration.
In another form, the mixture is distributed in a substantially three-dimensional (3D) configuration.
In another form, the different nano-sized materials comprise different BaxSryCazFClrBrsIt:Sm2+ nanocrystal materials where the values of x, y, z, r, s and t are selected from 0 to 1 and subject to the constraints that x+y+z=1 and r+s+t=1.
In another form, the different nano-sized materials comprise different Ba1-xSrxFCl: Sm2+ nanocrystal materials where x is selected from 0 to 1.
In another form, the data storage medium is operable to store and read digital data at cryogenic temperatures.
In another form, the data storage medium is operable to store and read digital data at substantially non-cryogenic temperatures.
In another form, the data storage medium is operable to store and read digital data at substantially room temperature.
In a second aspect, the present disclosure provides a method for storing digital data, comprising:
In a third aspect, the present disclosure provides a method for reading stored digital data, comprising:
In another form, determining whether the respective absorption/emission band has been selectively varied comprises measuring a reflection profile of the data storage medium.
In another form, determining whether the respective absorption/emission band has been selectively varied comprises measuring an absorption profile of the data storage medium.
In another form, determining whether the respective absorption/emission band has been selectively varied comprises measuring an emission profile of the data storage medium.
Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:
In the following description, like reference characters designate like or corresponding parts throughout the figures.
Referring now to
Throughout this specification the term “nano-sized material” is defined to mean a particle, compound, composition, structure or substance having a size or extent of less than 1 μm. In different embodiments, an individual nano-sized material may have a size in one or more of the following size ranges including, but not limited to, less than 25 nm, 25 nm-50 nm, 50 nm-75 nm, 75 nm-100 nm, 100 nm-125 nm, 125 nm-150 nm, 150 nm-175 nm, 175 nm-200 nm, 200 nm-225 nm, 225 nm-250 nm, 250 nm-300 nm, 300 nm-350 nm, 350 nm-400 nm, 400 nm-450 nm, 450 nm-500 nm, 500 nm-550 nm, 550 nm-600 nm, 600 nm-700 nm, 700 nm-800 nm, 800 nm-900 nm, and 900 nm-1000 nm.
In one example, the mixture may comprise different nano-sized materials all lying within the same size range, eg, 25 nm-50 nm. In another example, the different nano-sized materials may lie within different size ranges with respect to each other, eg, some of the different nano-sized material may be in the size range 25 nm-50 nm and others in the size range 100 nm-125 nm with the mixture together extending over a size range of 100 nm.
Referring now to
In this example, one or more of the different nano-sized materials is photo-reactive to selectively vary or bleach a respective absorption/emission band upon irradiation at the band wavelength to encode digital data in the combined optical transition profile 210 of mixture 110.
Referring now to
As an example, this variability could be caused by imperfection in the crystal lattice for a crystal based material. This may be caused by different bond lengths, proximity to impurity centres and isotope distributions resulting in an overall normal distribution over frequency for a given optical transition for the nano-sized material characterised by an inhomogeneous linewidth Γinh.
Referring now to
As will be appreciated, the number of holes that may be “burnt” or “bleached” into an optical transition profile of a given compound or material having an inhomogeneous linewidth is given by the ratio of the inhomogeneous to homogeneous linewidth (ie, Γinh/Γhom) which may be used as a figure-of-merit to characterise an optical transition profile. This ratio can be up to 108 at very low temperature and hence theoretically large data storage densities are potentially possible albeit at impractical liquid helium temperatures.
In most cases the homogeneous linewidth for a given material will be dominant at room temperature due to the rapid dynamic broadening of optical transitions which occur due to interactions with phonons. Natural (homogeneous) optical linewidths are governed by a range of dynamical processes such as two-phonon Raman scattering, direct one-phonon relaxation, etc, leading to dephasing of the wavefunctions. These processes are strongly temperature dependent becoming much more important at high temperatures, leading to relatively broad homogeneous linewidths at room temperature. This then results in large homogeneous linewidths that are typically wider than the inhomogeneous linewidth of the material at room temperature as a result preventing discernible individual spectral holes from being formed in the optical transition profile for most materials.
Referring back to
As such, the combined optical transition profile 210 may be “designed” to have a predetermined profile having at least the characteristic that the wavelength range covered by the combined optical transition profile is broader or broadened as compared to that of the optical transition profiles of individual nano-sized material forming the mixture. In one example, the optical transition profiles of each of the nano-sized materials have substantially the same width and their respective peak wavelengths are equally spaced with respect to each other as shown in
As would be appreciated, the combined optical transition profile 210 of the mixture of different nano-sized materials in accordance with the present disclosure has an effective combined inhomogeneous linewidth that exceeds any individual inhomogeneous line width of an individual nano-sized material. In this embodiment, one or more of nano-sized materials 111, 112, 113, 114, 115, 116 are chosen to be selectively photo-reactive so that on irradiation at the band wavelength, the emission/absorption band corresponding to that wavelength will be varied or bleached in effect producing a spectral hole or “gap” in the combined optical transition profile at this frequency.
Referring now to
In one example, the operable wavelengths where spectral holes may be formed lies substantially within the range of 400 nm-800 nm range, however, any wavelength is possible but as would be appreciated the diffraction limited spot becomes much smaller with decreasing wavelength. As such, any typical diffraction limited irradiation (or read) process will interact with large numbers of the different nano-sized materials and so it will be the combined optical transition profile of these different nano-sized materials that is “seen” by any irradiation or probe beam on interacting with a diffraction limited region of the data storage medium.
Referring now to
In this manner, the depth level of a given spectral hole or gap in the combined optical transition profile 210 may be selected from a number of set depth levels by choosing the degree of irradiation of data storage medium 100 in order to store additional digital information in a respective spectral hole.
This is shown in plot 600 where each of the spectral gaps 610, 620, 630 are selected from four depths, ie, where spectral gap 610 corresponds to depth I3, spectral gap 620 corresponds to depth I2 and spectral gap 630 corresponds to depth I4. Combined with the state where there is no spectral gap at a selected frequency or wavelength, ie depth I1, this corresponds to four depth levels or two bits of encoding in this example for each spectral hole 610, 620, 630.
Although in
As would be appreciated, there are other schemes for encoding digital data apart from the rudimentary binary encoding referred to above which may be implemented in accordance with the present disclosure especially appreciating that a spectral hole at a given wavelength location may be used to encode multiple bits of information.
The nano-sized materials that form the mixture may be any suitable material exhibiting the required optical transition characteristics, ie, having an isolated optical transition where a peak in the individual optical transition profile differs across the different nano-sized materials and further where one or more of the nano-sized materials have the characteristic that irradiation by specific wavelengths can result in an absorption/emission band corresponding to that wavelength being varied effectively leaving a spectral hole at the respective wavelength.
Referring now to
Read/write apparatus 700 comprises in this example an intensity detector 710, a configurable wavelength radiation source 720, a focusing arrangement comprising in this embodiment an objective lens 730 for focusing radiation onto, or into, an irradiation region 770 of the digital storage medium 100 and a beam splitter 740 for introducing the radiation into the optical path of the apparatus 700 and a pinhole arrangement 750.
In this example, detector 710 may comprise any suitable detector for measuring photon intensity in the wavelength range of interest such as by the use of one or more photomultiplier tubes or photodiodes including avalanche photodiodes, CCDs, CMOS or any other light sensitive device, or in another example using silicon photomultiplier (SiPM) detectors. In another example, an optical fibre arrangement may be used to collect or deliver light.
Configurable wavelength radiation source 720 may be any suitable optical arrangement capable of emitting an irradiation or probe beam at a selected wavelength and in one embodiment at a selectable intensity or duration for a given wavelength to vary the depth level of spectral holes being formed in the combined optical transition profile as referred to above. In one example, radiation source 720 may comprise multiple discrete lasers or LEDs operating at the relevant wavelengths. In other embodiments, radiation source 720 may be based on a single-frequency light source such as a tuneable laser. In another embodiment, the light of LEDs may be filtered or narrowed by the use of narrow bandpass filters or wavelength dispersive element to provide radiation at the required wavelengths.
In this example confocal configuration, the path length from wavelength radiation source 720 to the data storage medium 100 is equivalent to the path length from the data storage medium 100 to the detector 710. Read/write apparatus 700 also comprises a data processor 790 for controlling the writing process to write digital information onto digital storage medium 100 and processing the emission/absorption readings from detector 710 to decode any digital information stored in digital storage medium 100. In one example implementation, read/write apparatus 700 may be configured to measure a reflection profile from the data storage medium. In another embodiment, read/write apparatus 700 may be configured to measure an absorption profile of the data storage medium. In yet another embodiment, read/write apparatus 700 may be configured to measure an emission profile of the data storage medium. As would also be appreciated, read/write apparatus 700 may be configured as separate apparatus directed to read or writing individually.
As the read/write apparatus 700 is only sampling an irradiation region 770 at any instance defined by the diffraction limited spot size of the irradiation/probe beam, in order to read/write different regions the digital storage medium 100 must be translated with respect to the location of irradiation region 770. This may be achieved by either moving the read/write apparatus 700 or digital storage medium 100 or both with respect to each other. In another example, the irradiation region 770 may be moveable with respect to the read/write apparatus so that the probe beam may adopt a scanning pattern. As would be appreciated, where digital storage medium 100 has a 3D configuration this will also require translation in depth as well as within a plane of digital storage medium.
In one example, the digital storage medium 100 is formed as a 2D disc and the disc is rotated to present a different irradiation region 700 to the read/write apparatus. As would be appreciated, as the digital storage medium is being read or written at different wavelengths, different read/write schemes may elect to read/write the entire digital storage medium 100 at a first wavelength and then at a second wavelength or select a “track” of the digital storage medium that is read/written at a first wavelength and then a second wavelength before moving onto the next track.
Referring now to
In this example, data storage medium 100 is a thin film where even though the film has some thickness the mixture of different nano-sized materials is distributed in a substantially planar 2D-configuration so that the irradiation region is a planar region (eg, a “pixel”) located on the surface of data storage medium 100. In one example, the thin film is deposited on a suitable substrate. The data storage medium may be deposited in a homogeneous or patterned arrangement as required. Additionally, the substrate may be flexible or substantially rigid and the data storage medium 100 be deposited on one or both sides of the substrate.
This may be compared with where the data storage medium has a substantial thickness and the mixture of different nano-sized materials is distributed in substantially three-dimensional configurations in which case the irradiation region may be shifted to sample an irradiation region at a selected depth or discrete layer (eg, a “voxel”) within the data storage medium by virtue of focusing the beam at this selected depth or discrete layer. 3D configurations include, but are not limited to, multiple layer implementations deposited on a substrate in a homogeneous or patterned manner or in another medium, eg, formed in polymer, glass, sol-gel, soft glass or suitable material and could be formed into any geometric volume such as a cube, cylinder, or sphere. In addition, the nano-sized materials could be uniformly dispersed within the volume, or dispersed in accordance with a pattern or alternatively randomly distributed through the volume.
Referring now to
Referring now to
In one example, the nano-crystal materials are prepared by a mechanochemical method such as by ball milling where constituent compounds such as BaCl2 and BaF2 are mixed or milled together under an argon (or another inert gas) atmosphere and where the Sm2+ may be incorporated directly by using divalent Sm (as in SmI2) in the ball milling process. In this case the ball milling has to be undertaken with fully dried reagents and under an inert gas such as argon. Alternatively, in another example, the 2+ oxidation state may be achieved by exposing the formed materials to ionising radiation such as X-rays to reduce the incorporated Sm3+ to Sm2+.
Techniques for forming nanocrystal materials in accordance with the present disclosure are discussed in the paper by Xiang-lei Wang, Zhi-qiang Liu, Marion A. Stevens-Kalceff, and Hans Riesen titled “Mechanochemical Preparation of Nanocrystalline BaFCl Doped with Samarium in the 2+ Oxidation State” (Inorganic Chemistry, 2014, 53 (17), 8839-8841), whose entire disclosure is incorporated by reference.
Table 1 summarises the relevant lattice parameters and the average crystallite size for the different Ba1-xSrxFCl: Sm2+ nanocrystal materials for x ranging from 0 to 1 in accordance with an illustrative embodiment.
In this illustrative embodiment, the optical transition profile for each of the nanocrystal materials is based on the divalent Sm2+5D0→7F0 optical transition which shifts non-linearly both with mol-fraction x as well as the unit cell length a and c.
Referring now to
Referring now to
Referring now to
In this example, the mixture was irradiated initially at wavelengths 688.79 nm and 689.48 nm causing spectral holes at these two wavelengths resulting in a combined optical transition profile shown in solid line 1120 having holes 1121, 1122 with two subsequent irradiations or burn fluences at 689.48 nm resulting in the combined optical transition profile shown in solid line 1150 having holes 1151, 1152 with hole 1152 having the same depth as hole 1122. The respective dashed lines 1120a, 1150a show the corresponding different profiles for optical transition profiles 1120, 1150 respectively and the unmodified combined optical transition profile 1010 is also shown for reference purposes.
In this example, the 20% deep hole 1122, 1152 has a hole-width of about 5.8 cm−1 (ie, upper limit of homogenous linewidth of 2.9 cm−1). As can be seen from inspection of plot 1100, the data storage medium, comprising a mixture of different Ba1-xSrxFCl: Sm2+ nanocrystals, may be used to not only encode digital data by forming a gap or spectral hole at a specific wavelength location but that further data may be stored by the respective depth level of the spectral hole in the combined optical transition profile. Furthermore, the results presented in
Based on the above results, it is expected that a data storage medium comprising a mixture of different Ba1-xSrxFCl: Sm2+ nanocrystal materials could provide up to 10s if not 100s of bits/point data storage at the diffraction limit which then could potentially allow for data densities approaching the order of magnitude of Tbs/cm2 for a 2D configuration and potentially 10s or more Tbs/cm3. As would be appreciated a data storage medium in accordance with the present disclosure will result in significantly increased optical data storage densities.
By lowering the temperature, it is possible to reduce the homogeneous linewidths and therefore encode more spectral holes within the combined optical transition profile. Referring now to
Referring now to
Other nanocrystal materials and associated optical transitions that may be used in accordance with the present disclosure include, but are not limited to: Ba1-xSrxFBr:Sm2+, Ba1-xSrxFI:Sm2+. In another example, the mixture may comprise different BaxSryCazFClrBrsIt:Sm2+ nanocrystal materials where the values of x, y, z, r, s and t are selected from 0 to 1 and subject to the constraints that x+y+z=1 and r+s+t=1 potentially allowing the combined optical transition profile to have a flat region to 200 cm−1.
In one example, a mixture of different nanocrystal materials in accordance with the present disclosure may be formed in a substantially 2D configuration in a nano-crystalline film. In one embodiment, the nano-crystalline film is formed by casting the different nanocrystal materials with any suitable binder such as Kraton™ onto any suitable substrate such as poly(vinyl acetate). In one example, a nano-crystalline film may be formed using the “doctor's blade” technique. In one embodiment, a nano-crystalline film having a thickness of approximately 20 μm was formed by depositing a suspension of different nanocrystal materials with 5% weight of dissolved binder (Kraton™ stabilized with STANN™ in toluene: butyl acetate: methylcyclohexane 9:6:5), on a poly(vinyl acetate) substrate of 100 μm thickness with the mixture then being spread by a doctor's blade to form the resulting nano-crystalline film.
In another example, the different nanocrystal materials in accordance with the present disclosure may be formed in a 3D configuration by volume embedding of the nanocrystal materials into, in one embodiment, low temperature soft glasses (eg, tellurite, lead-silicate, ZBLAN or combinations of these materials). In another example, the nanocrystal materials may be embedded in a polymer media (eg, PMMA, Polystyrene). In another further embodiment, the nanocrystal materials may be embedded in a sol-gel type glass (eg, silica).
As would be appreciated, the composition of the glass or polymer employed will depend on for example optical transmission requirements. For example ZBLAN is more optically transparent at lower wavelengths than polymer for instance—so this material would be potentially indicated where this was the wavelength region of interest. In one example, a surfactant may be used in combination with the nanocrystals so that they disperse on synthesis of the 3D optical medium. In another embodiment, functional groups may be added to the nanocrystal materials to assist with dispersion. In another embodiment, the 3D optical medium may be 3D printed layer-by-layer with a suitable pattern.
Factors that influence the choice of material used to retain and disperse the nanocrystal mixture to form the 3D configuration include, but are not limited to, the materials influence on conversion efficiency, transparency in the UV and visible bands, any background fluorescence and the formation temperature. In one embodiment, low temperature soft glasses may be used to reduce the impact of damage to the nanocrystals on forming the 3D configuration.
In another example embodiment, the mixture comprises nano-sized materials comprising quantum dots. In one example, the nano-sized materials may comprise silver halide based quantum dots. In another example, the nano-sized materials may comprise lead halide based quantum dots.
In embodiments of the present disclosure, the data storage medium may be rewritable in the sense that the spectral holes formed in the combined optical transition profile may be removed by techniques such as laser illumination at the correct wavelength and/or suitable radiation (IR, visible, UV, X-ray) of the data storage medium to remove the encoded information.
A data storage medium formed in accordance with the present disclosure potentially allows for 100 bit/point data storage or more at room temperature that may be implemented in either 2D or 3D configurations representing a significant advance over current optical data storage methodologies. In example embodiments, this is achieved by significantly broadening the inhomogeneous line width of the data storage medium allowing spectral hole burning techniques to be used to encode a greater amount of digital data in the combined optical transition profile of the data storage medium. Furthermore, and in accordance with the present disclosure, spectral holes may be formed at different discrete depth levels allowing digital information to be encoded in the spectral hole itself.
In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
It will be understood that the terms “comprise” and “include” and any of their derivatives (eg, comprises, comprising, includes, including) as used in this specification are to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.
It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021901706 | Jun 2021 | AU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2022/050563 | 6/8/2022 | WO |
