WO2025229467A1

WO2025229467A1 - A method of recording data on an optical data carrier and an optical data carrier

Info

Publication number: WO2025229467A1
Application number: PCT/IB2025/054291
Authority: WO
Inventors: Lukasz Szostkiewicz; Marcin STRAGOWSKI; Napierala MAREK; Tenderenda TADEUSZ
Original assignee: Tachyotec Spolka Z Ograniczona Odpowiedzialnoscia
Current assignee: Tachyotec Spolka Z Ograniczona Odpowiedzialnoscia
Priority date: 2024-04-30
Filing date: 2025-04-24
Publication date: 2025-11-06
Anticipated expiration: 2026-10-30

Abstract

A method of recording data on an optical data carrier in the form of a rewindable tape containing a recordable layer, comprising a step of applying data symbols to the recordable layer by creating voxels with a locally changed refractive index by subjecting the recordable layer to the impact of electromagnetic radiation pulses from a pulsed focused source of radiation directed to the tape being rewound. The step of applying comprises focusing radiation within the volume of the recordable layer of the tape (100, 600, 800, 900), in voxels (110), located entirely below the surface of the recordable layer, having a size less than or equal to 1 μm a tape (100, 600, 800, 900). An optical data carrier according to the invention has a form of a tape (100, 600, 800, 900) having a recordable layer made of a material containing glass. The recordable layer also is a substrate layer. The tape and has thickness (H) ranging from 5 μm to 100 μm, width (W) ranging from 5 mm to 50 mm and length (L) of at least 100 m.

Description

A method of recording data on an optical data carrier and an optical data carrier

Field of the invention

[0001] The invention concerns a method of recording data on an optical data carrier having the form of an optical tape, an optical data carrier having the form of a tape, and a system for recording data on an optical data carrier.

State of the art

[0002] In the state of the art, LTO (Linear Tape-Open) tapes are known and used for archiving large volumes of data. These tapes are relatively unstable and require frequent copying to protect the data. The expected lifespan of an LTO tape is usually 15-30 years under controlled environmental conditions, while under uncontrolled temperature and humidity the lifespan decreases dramatically.

[0003] In the state of the art, optical tapes operating on a similar principle to optical discs, i.e. having a recordable layer and additional substrate layers to provide protection or mechanical stabilization are also known. These layers may contain glass. The recordable layer is usually very thin and changes its properties under the influence of radiation - especially laser radiation. As a result of a phase change, part of the layer is removed or its physical parameter is changed - for example, the refractive index. The substrate layer provides the mechanical properties necessary to ensure the integrity of the carrier during rewinding, as well as resistance to mechanical stress. Recordable layers are susceptible to erosion and environmental stress, so the durability of optical tapes is even lower than that of LTO tapes. Multiple attempts were made to replace LTO tapes with three-dimensional solid optical data storage in glass such as disclosed in Mitsuru Watanabe et al 1998 Jpn. J. Appt. Phys. 37 L1527, “Documented in Three- Dimensional Optical Data Storage in Vitreous Silica”. Despite extensive efforts and foundational breakthroughs, projects like Microsoft’s SILICA have not yet succeeded in replacing LTO tapes. Although SILICA has achieved significant milestones — particularly in data durability and long-term archival potential — its writing speed is still insufficient to serve as a practical alternative to current LTO technology. Generally there are two approaches to write on glass: writing on surface of thin plates e.g. CERABYTE or attempt to use whole volume in solid bodies e.g. SILICA project and 5D optical data storage. During surface recording, thin materials are used because only the surface serves as the information carrier, while the rest of the material is redundant. In the case of volume recording (not on the surface), carriers in the form of thick material (glass blocks) are used to increase the capacity of the carrier (data is recorded in volume). In the proposed solution, a non-functional modification was used contrary to this (volume recording combined with a very thin carrier), resulting in unexpected advantages, i.e. , a high mechanical strength of the flexible glass tape (not altered by defects on glass surface, which occurs in a case of recording on surface), which can be wound in large quantities, thus increasing the capacity of the carrier. Certain disadvantages of LTO tapes are well recognized for a long time and use of glass surface or volume for recording is since a long time considered a promising alternative in the literature: J. Zhang, A. Cerkauskaite, R. Drevinskas, A. Patel, M. Beresna, and P. G. Kazansky "Eternal 5D data storage by ultrafast laser writing in glass", Proc. SPIE 9736, Laser-based Micro- and Nanoprocessing X, 97360U (4 March 2016); https://doi.org/10.1117/12.2220600, Ken Anderson, Mark Ayres, Brad Sissom, and Fred Askham "Holographic data storage: rebirthing a commercialization effort", Proc. SPIE 9006, Practical Holography XXVIII: Materials and Applications, 90060C (25 February 2014); https://d0i.0rg/l 0.1117/12.2037429. Nevertheless so far attempt to replace LTO tapes with recording on glass were unsuccessful.

[0004] An example of an optical tape is disclosed in US5459018. Glass is used as a substrate layer. A thin (100 nm) coating constituting a recordable layer is provided on the glass substrate layer. The recordable layer can be made of a mixture of metal and oxide, which undergoes a thermal transformation when exposed to a laser, resulting in a change in the refractive index.

[0005] US2005117493A1 discloses an optical tape having a plurality of servo data tracks on which payload data is recorded and which are arranged longitudinally and adjacent to each other over the entire width or part of the width of the optical tape. The tape further contains servo address tracks indicating the appropriate location of the corresponding one of the servo tracks on which the payload data is recorded. This allows payload data to be recorded simultaneously on multiple tracks of different widths. The recording method disclosed in US2005117493A1 comprises using a laser to make the tracks on the recordable layer, which, under the influence of radiation, changes from a crystalline phase to an amorphous phase due to melting resulting from thermal action. The use of thermal transformations limits the recording density because they are imprecise and must occur on a relatively large area of the carrier (in this case, the surface of the recordable layer). US2005117493A1 discloses an apparatus for recording data on a tape comprising means for rewinding the tape and two lasers adapted to record servo data tracks and servo address tracks and a verification unit.

[0006] US9208813 discloses a method for reading a rewindable optical tape using a camera directed at it and image processing techniques.

[0007] US5321683 discloses a method and apparatus for reading digital data recorded on an optical tape in an optical tape reading system comprising an optical tape and an illumination system. The optical tape contains data that is recorded along multiple tracks of symbols referred to as bit cells in US5321683. Each path contains a line of bit cells, and each bit cell has either a first point power reflection coefficient representing the first binary value or a second point power reflection coefficient representing the second binary value. The illumination system is used to illuminate a selected area of the optical tape including a plurality of bit cells with incident light. A method of illuminating and reading data recorded on an optical tape includes a first step of generating a collimated coherent beam of light directed/guided into the optical tape, and a second step of imaging the coherent beam of light into a selected area of the optical tape including a plurality of bit cells. Reading both in the reflection configuration, in which the light reflected from the selected area of the optical tape is analyzed for reading, and in the transmission configuration, in which the light passing through the selected area of the optical tape is analyzed for reading is provided. EP4044182A1 , discloses glass data carrier recorded with data engraved with lasers on its surface. It also discloses embodiment of woundable tape. Such data carriers are prone to mechanical damage when being bent or wound. Acceptable radius of curvature of recorded carrier is significantly higher than the empty one. It is because glass breakage depends on defects located on edges and/or surfaces of glass substrates.

[0008] EP1494229 discloses recording in the volume of a transparent optical tape in which several recordable layers made of semiconductor material are used. The refractive index of these layers can be changed by exposing them to a pulsed laser, e.g. a femtosecond laser.

[0009] There are known solutions in the state of the art that use writing directly on glass. Glass is a promising data carrier due to its durability, corrosion resistance and the fact that it combines good optical and mechanical properties. EP3544936 discloses a method for etching data symbols on the surface of a glass plate produced by the Float method using a pulsed laser. A two-dimensional pattern of data symbols is created on the surface of the glass plate using the pulsed laser. It is indicated that a variety of lasers can be used to create data symbols on the edge or surface of the plate. Due to the use of etching, the size of the symbols produced is of the order of 100 pm. This technique does not allow recording dense enough for application in large data carriers such as LTO tapes. EP3544936 discloses that numerous different types of lasers can be used, including argon, ion (such as xenon or krypton), dye, FEL, GaN, or laser diodes. Picosecond and femtosecond lasers are mentioned as options. A similar solution is disclosed in JP3521221 , which proposes recording with the use of a femtosecond laser resulting in the change in the refractive index through thermal transformation.

Problem to be solved

[0010] The applications of optical tapes are limited by their relatively low durability and multi-layer structure, in which the recordable layer must be protected with additional layers, which results in an increase in the thickness of the tape. The lifespan of existing solutions is (depending on storage conditions) several, a dozen or a maximum of 30 years (in the case of LTO tapes stored in controlled conditions). This is at least an order of magnitude shorter than the real demand. The short lifespan of existing solutions means that all data must be periodically transferred to a new carrier, which involves significant financial and environmental costs. On the other hand, optical recording mechanisms based on thermal phase changes are imprecise, which translates into limitations in recording density. Additionally attempts to write durable information in volume of glass known in the art suffer from limited recording speed. The aim of the invention is to solve these problems.

Summary of the invention

[0011] The method of recording data on an optical data carrier in the form of a rewindable tape having a recordable layer susceptible to recording according to the invention comprises a step of applying data symbols to the recordable layer by creating voxels with a locally changed refractive index by subjecting the recordable layer to the impact of electromagnetic radiation pulses from a pulsed source of focused radiation directed/guided to the tape being rewound. The step of applying uses a tape that is transparent along its thickness to electromagnetic radiation with a wavelength of 2000 nm or less, allowing for convenient reading. The material of the recordable layer includes glass, and the recordable layer has a thickness ranging from 5 pm to 100 pm and a width ranging from 5 mm to 50 mm. Thanks to this, the recordable layer has sufficiently good mechanical parameters, constitutes also a substrate layer, and ensures extremely durable recording. This range of width is important for ease of re-wounding and read out from tape being rewound. Simultaneously width of the tapes up to 50 mm can be relatively easily handled by recording device. Higher widths are challenging to record with a method according to the invention. The invention requires high focus of the electromagnetic radiation beam used for recording and simultaneously close proximity of the electromagnetic radiation source as the lens applied need to have relatively short focal length. Accordingly sweeping across wide tape requires shifting position of the lens and that in turn results in reduction of recording speed. The invention provides a reasonable tradeoff of this constrains. The step of applying uses a beam of pulsed electromagnetic radiation with a pulse duration of less than 1 ps and a wavelength of less than or equal to 2000 nm. The both limitations determine the recording precision and voxel size. Short pulses are necessary to achieve the ionization of the medium and a change in the refractive index within a volume of the tape (not on its surface) without thermal melting of the medium by heating. This has an effect of highly localized change of optical parameter e.g. refractive index without significant change of mechanical parameters of glass tape. Additionally, it does not cause any defects on the surface of the glass (such defects have a significant impact on the tape's bending strength and longevity, as these defects are initiators of glass breakage). This contributes to very long durability of the recording and reduced risk of damage from bending during winding and rewinding of the tape. Using radiation with a wavelength less than or equal to 2000 nm allows for sufficiently small voxel sizes. The electromagnetic radiation is focused inside the volume of the recordable layer of the tape in order to obtain in at least one voxel the peak intensity of the radiation beam, to obtain a local change in the refractive index due to the temporary ionization of the material of the recordable layer. Causing this phenomenon requires a sufficiently high peak intensity of the radiation beam. The electromagnetic radiation beam is moved during the successive pulses relative to the tape being rewound to obtain at least a two-dimensional pattern of voxels. In the case of multi-voxel recording, this effect can be achieved by just rewinding, but when recording one voxel in a pulse, it is also necessary to move the beam perpendicular to the length of the tape.

[0012] The tape used has a length greater than 100 m, and preferably it has a length ranging from 500 m to 800 m. Tapes of this length provide a large capacity, and they can also fit into containers with dimensions similar to LTOs.

[0013] Preferably, the beam of pulsed electromagnetic radiation is Gaussian beam and has a quality parameter M² of less than or equal to 1 .3.

[0014] Preferably, the beam of pulsed electromagnetic radiation is focused in a voxel area of 1 pm or less in size.

[0015] Preferably, the phase front of the beam of pulsed electromagnetic radiation is shaped using a spatial modulator with one pulse to record data in many voxels at the same time. Thanks to such solutions, the number of mechanical elements in recording devices can be reduced. [0016] Preferably, after recording, the carrier is covered with a damp-proof layer improving its durability.

[0017] It should be noted that applying data symbols in the process of creating voxels with a changed refractive index can be done in various ways. Conceptually, it is simplest to encode symbols by introducing distinguishable levels of change in the refractive index within a voxel. However, other voxel parameters, like shape, size, or anisotropy of the change, can be used to encode data symbols. One can also encode data symbols in the spaces between adjacent voxels. Typically, N distinguishable data symbols are used. N is chosen as a power of two so that a single symbol represents log2N bits of recorded data. Preferably the intensity of the beam of pulsed electromagnetic radiation is tuned to provide multiple levels of change of refractive index e.g. 4 or 16 optionally combined with changes in other degrees of freedom such as shape or anisotropy. [0018] The optical data carrier according to the invention is a tape having a recordable layer with encoded data symbols. The recordable layer is made of a material containing glass, which ensures durability and sufficient mechanical properties for the recordable layer to also constitute a substrate layer. This layer has a thickness ranging from 5 pm to 100 pm and a width ranging from 5 mm to 50 mm. Such glass tape can be safely rewound and stored. Data symbols are encoded in voxels having a size of 1 pm or less, distributed throughout the volume of the recordable layer. The width of the tape directly affects its capacity. Reducing the tape width below 5 mm makes it insufficient for data archiving (cold storage) applications. On the other hand, using tapes wider than 50 mm makes it difficult to apply high-speed recording. This is because the recording method requires a strong focus of the optical beam, which involves high focusing power and a short focal length. Short focal lengths limit the ability to precisely adjust the position of the beam. To ensure fast recording, the beam must be controlled along the width of the tape, rather than moving the tape relative to the optical system. A width of 50 mm is the maximum range at which recording can occur without mechanically shifting the tape relative to the optical system. The tape is wound along its length, but lateral movement is not allowed as it would significantly reduce the recording speed. Voxels written within the volume of the tape are less susceptible to damage resulting in distorted data symbols.

[0019] Preferably, the recordable layer is made of a material containing boronsilica glass, which is resistant to erosion and chemical attacks.

[0020] Preferably, the carrier is covered with a damp-proof layer increasing its durability.

[0021] Advantageously change in refractive index has more than two intensity levels. Preferably change in refractive index has 4 intensity levels or 16 intensity levels. For encoding reasons it is preferred if number of distinguishable states of voxels is power of two.

[0022] Distinguishing voxels by intensity is a straightforward approach, but not the only one. Voxels, however can be distinguished also by size. Furthermore the change of the refractive index can be birefringent. Birefringence results in change of polarization of incident light and thus adds another dimension for distinguishing voxels. Information can also be encoded in spaces between voxels.

[0023] The invention can be implemented with a device for optically recording data symbols on a tape according which comprises a pulsed radiation source generating an electromagnetic radiation beam and a beam forming and guiding system. The pulsed radiation source is adapted to generate electromagnetic radiation with a length of 2000 nm or less in pulses with a duration of 1 ps or less. The power parameters of the radiation source and the beam forming and guiding system are selected so that they are adapted to focus the radiation beam in at least one voxel to obtain a peak intensity in the pulse greater than or equal to 29 MW/cm². The beam forming and guiding system preferably comprises an amplitude modulator and an objective (lens) with an adjustable mirror.

[0024] The beam forming and guiding system preferably comprises a polarizer and an adjustable polarization rotating system.

[0025] The beam forming and guiding system preferably comprises a spatial phase modulator. The spatial phase modulator can be more conveniently used when a beam-expanding objective is used first. The beam forming and guiding system preferably comprises an objective with a variable imaging plane enabling recording at several different depths. Problem solution

[0026] According to the invention, recording is achieved by introducing changes in the refractive index not on the surface but inside the volume of the glass layer of the recordable tape. This change occurs under the impact of a light pulse with a duration equal to or shorter than a picosecond. Glass subjected to such a pulse does not undergo a phase transformation to the liquid state, but due to ionization it changes its refractive index locally. Such a change in the refractive index can be made much more precisely than changes in the refractive index due to thermal impact, but a continuous servo path cannot be obtained in this way. The precision of making changes increases the recording density and, as a result, the volume of data that fits on a carrier of the same length.

[0027] The phenomenon of temporary and local ionization of the medium used to obtain a change in the refractive index, instead of the thermal phase transformation known in the state of the art, completely changes the achievable recording density.

[0028] The advantage of such a recording is that the entire carrier can have the form of a single glass tape, the mechanical properties of which enable rewinding. The lack of the need for a separate recordable layer and a separate substrate layer allows the tape thickness to be reduced and longer tapes to be used in the same cassettes, thus further increasing the achievable data capacity. [0029] Glass, as a recordable layer, also has the advantage of being stable, durable and resistant to corrosion. It has the mechanical properties required for a substrate layer, so an additional substrate layer is not needed. The recordable glass layer itself is also a substrate layer. Data symbols located inside the tape, not on the surface, are protected against distortion or blurring. If the surface is damaged, the data symbols remain intact and the damaged area of the tape can be repaired by polishing the surface.

[0030] Surprisingly, it also turned out that changes in the refractive index resulting from ionization with very short pulses of high-energy electromagnetic radiation focused in a small area are more persistent than changes in the refractive index resulting from a thermally forced phase change (melting). The recorded data symbols are difficult to erase without melting the glass and are resistant to common means used to attack data such as electromagnetic pulses. Additionally change of refractive index in the volume of the glass tape without mechanical change in the surface of the tape reduced risk of breaking during multiple rewinding. On the other hand focusing the beam in small range of depths and rewinding the tape allowed much faster recording than in case of known methods for spatial encoding of information within glass. Thus long-felt need has been satisfied and reliable replacement of LTO tape by durable recording in glass has been provided.

Description of the drawing

[0031] The subject of the invention is shown in embodiments in the drawing, in which

Fig. 1 shows schematically (not to scale) the carrier according to the invention in the form of a glass tape, in a cross-section;

Fig. 2 shows schematically (not to scale) this carrier in a longitudinal section;

Fig. 3 shows schematically a system for recording data on a carrier according to the invention;

Fig. 4 shows a block diagram of a system for recording data on a carrier,

Fig. 5 shows schematically, in perspective, the spatial arrangement of elements in the data recording system;

Fig. 6 shows a block diagram of a another data recording system according;

Fig. 7 shows schematically, in perspective, the spatial arrangement of elements in the data recording system;

Fig. 8 shows a block diagram of a system for recording data on a carrier according to another embodiment of the invention;

Fig. 9 shows a block diagram of a system for recording data on a carrier according to further embodiment of the invention.

Description of the embodiments

[0032] An embodiment of a recorded data carrier 100 according to the invention, in the form of a tape made of silica glass, is shown schematically in Fig. 1 in a cross-section, and in Fig. 2 in a longitudinal section with marked voxels 110 representing data symbols. In this embodiment, each voxel 110 has an intensity of one of 16 levels and therefore represents a 4-bit data symbol.

[0033] The dimensions of the data carrier 100 are W x L x H, where W = 30 mm, L = 500 m, H = 20 urn. Such thin glass tape can be freely wound on reels and rewound. The voxels 110 in which the data symbols are encoded are located in the volume of the glass, not on its surface, and are therefore not exposed to the influence of the environment. The size of a single voxel 110 is less than 1 pm. Voxels 110 are spaced from each other at a distance of 1 pm measured from their centers. As a result, a carrier is obtained that could hold 30000 data symbols along the W dimension and 500 000 000 data symbols along the L dimension. Each symbol represents 4 bits. The total capacity of the carrier is approximately 6.8 TB.

[0034] Voxel 110 is a spatial area with a modified refractive index, and its size is defined as its largest dimension in the W x L reading plane of the tape 100. It was found that recording can be carried out effectively and advantageous capacities can be obtained with the size of voxel 110 at the level of 1 pm or smaller. It should be noted that the voxel 110 can extend along the H dimension by up to several pm, which is much larger than the size in the reading plane defining the voxel size for the purposes of this description.

[0035] When focusing an electromagnetic radiation beam to a size of 1 pm in the transverse plane, it is focused in a different way than it results from the principles of geometric optics. The beam narrows to a certain point when it reaches its minimum diameter in the so-called beam waist. At the point of this narrowing, the beam has an essentially constant diameter over a length defined as the confocal parameter. The beginning of the narrowing is set at the tape surface. Thanks to this, it is possible to record in the volume of the glass and not only on its surface. The ionization effect causes a sharp increase in the absorption of the medium, which limits the penetration depth of the beam. The peak intensity of the radiation beam at the end of the narrowing therefore drops rapidly. The ionization effect occurs mainly in the narrowing of the beam, where the power is highest. Obtaining narrowing of a low-diameter beam is easier if the beam quality parameter M² is sufficiently low, i.e. with a value of 1.4 or less. Further narrowing the beam is beneficial for the invention thus a person skilled in the art after learning the teaching of the present invention can apply using vector, Bessel or super oscillatory beams to obtain more narrow beam top.

[0036] It was determined that the capacities provided by tapes of 100 m or longer can be useful, although in most archiving applications the required capacities can be obtained with tapes of 500 m to 800 m in length.

[0037] The glass serves as both a substrate layer and a recordable layer, and the tape thickness H of 20 pm ensures both convenient recording in the manner described below and required mechanical parameters. Data recorded in voxels 110 in the volume of glass have many times greater durability compared to recording on optical tapes known in the state of the art. The data carrier recorded according to the invention proved to be considerably less prone to being worn out during multiple rewinds than the carriers with data engraved on the surface. This was only partly expected by the inventors. Apparently recording on the surface results in surface/edge defects which contribute to reduced resistance to bending stress while change of refractive index below the surface does not. Respective information can be found in 28^th Edition of “Electronic Glass Materials Technical Reference Guide” by Nippon Electric Glass - page 5: glass breakage depends on defects located on edges and/or surfaces of glass substrates. 50MPa is considered to be the boundary between "broken" and "not broken" conditions.

[0038] This carrier 100 is recorded with data in the manner described below in a recording system shown schematically in Figs. 3, 4 and 5.

[0039] Data on the data carrier 100 is recorded using an electromagnetic radiation beam 333 generated in a beam forming and guiding system 310 in the form of radiation from a femtosecond laser. The data carrier 100 is being unwound from the reel 321 and wound onto the reel 322 so that the electromagnetic radiation beam 333 falls on the unwound section. Single-reel mechanisms are also known in the state of the art and can also be used here.

[0040] The source of electromagnetic radiation in the beam forming and guiding system 310 is a pulsed femtosecond laser 430 operating at a wavelength of 210 nm obtained by means of 4th harmonic generation and laser operation at a wavelength of 840 nm, a repetition frequency of 100 MHz, a pulse duration of 800 fs, a pulse energy of 10 pJ and a beam quality parameter M² equal to 1 .2. It is important that the beam quality parameter M² is below 1.3 to allow determination of the shape of the recorded voxel 110.

[0041] Using the objective 450, the electromagnetic radiation beam 333 from the laser 430 can be focused to obtain a maximum peak intensity of the radiation beam in the voxel area of 2.9 GW/cm².

[0042] Between the laser 430 and the objective 450 there is an amplitude modulator 440. The radiation beam 333 originating from the laser 430 passes through the amplitude modulator 440, which is adapted to change the amplitude of each pulse, with a dynamic range of at least 20 dB.

[0043] Using the amplitude modulator, the pulse energy is set, which determines the change in the refractive index in the voxel 110, where the beam is focused. As a result, the peak intensity values of the beam 333 used to record voxels 110 range from 29 MW/cm² to 2.9 GW/cm². Using a wavelength corresponding to deep UV facilitates the ionization of the medium.

[0044] The objective 450 has a focal length of 4 mm and is equipped with a movable mirror 451 inclined at an angle of X° relative to the beam and deflectable so as to allow the beam to be moved within an angular range of Y°. Thanks to this, the position of the beam focusing point can be adjusted within the entire range of a width W of the tape 100.

[0045] During recording, the tape 100 is being rewound from the reel 321 to the reel 322. The tape 100 in the present embodiment is made entirely of silica glass, so it contains only one layer that is both a recordable layer and a substrate layer. During rewinding, the step of applying data symbols to the tape 100 is performed by creating voxels 110 with a locally changed refractive index.

[0046] The change is achieved by exposing the glass tape 100 to pulses of radiation in the form of the electromagnetic radiation beam 333 originating from the laser 430. The exposure to the beam 333 with a sufficient peak intensity for a short time results in the temporary ionization of the medium. The area of voxel 110 subjected to such action does not melt, but is temporarily ionized, turning into plasma in the absence of significant heat exchange with the environment, which ensures the precision of the interaction. As a result, the glass fictive temperature of the material of the tape 100 changes in the local area of the voxel 110. As a consequence, the refractive index also changes. The amount of change in the refractive index depends on the peak intensity of the beam in the area affected by the electromagnetic radiation beam 333. Thus, by adjusting the beam power using the amplitude modulator 440, it is possible to record multi-bit data symbols differing in the value of the refractive index. It was experimentally verified that modulation in the dynamic range of 20 dB allows one to obtain 16 distinguishable levels of the refractive index within voxel 110 and therefore enables simple encoding of 4-bit data symbols.

[0047] The amplitude modulator 440 introduces attenuation in the range of 0 to 20 dB to the electromagnetic radiation beam 333 originating from the laser 430. At the output of the amplitude modulator 440, the pulse energy is in the range from 0.1 to 10 pJ. The electromagnetic radiation beam 333 is focused in a voxel 110, the cross-section of which has the shape of a circle at its widest point with a radius of 0.5 pm and an effective area of 0.78 (pm)². The pulse lasts 800 fs. As a result, in the Gaussian-shaped electromagnetic radiation beam focused in the voxel area 110, the peak intensity is in the range of 29 MW/cm² to 2.93 GW/cm² [0048] The refractive index of the pure tape is no = 1 .5384 for a wavelength of A = 210 nm. Exposing the material in the voxel area to the electromagnetic radiation beam 333 with a peak intensity ranging from 29 MW/cm² to 2.93 GW/cm² leads to a change An ranging from 0.000001 to 0.06.

[0049] It should be noted that when recording with fewer bits per symbol, the dynamic range may be smaller. In particular, when using dedicated coding and NRZ encoders, a binary notation can be used, in which a change means "1", no change means "0", and the peak intensity is the same for each pulse. For this recording method, even a peak intensity of the beam of 29 MW/cm² is sufficient. In the case of encoding data symbols by changing the An value, especially at longer wavelengths, higher intensities of 1 GW/cm² are more convenient. By using peak intensities of the beam above 0.1 TW/cm², it is possible to simplify the data reading system.

[0050] The wavelength of the radiation translates into how easy it is to focus the beam in an area of the voxel. In practice, this is achieved by using a pulse of electromagnetic radiation affecting the glass with a wavelength of less than 2000 nm. The use of pulses with a duration shorter than 1 ps ensures that there is no melting of the material and that the change in the refractive index is the result of temporary ionization.

[0051] Deflecting the electromagnetic radiation beam 333 with the mirror 451 allows it to be moved across the width W of the tape 100 and to apply a row of voxels 110. By rewinding the tape 100, subsequent rows are added. By using beam sweeping with a mirror, the movement of the beam across the tape 100 is much faster than the movement of the tape 100.

[0052] The bottleneck of the system is the pulse repetition frequency. In the present embodiment, a laser with a pulse repetition frequency of 100 MHz is used. This means that the recording symbol rate is limited to 100 Mbd, which translates to a write speed of 50 MB/s.

[0053] Although speed is secondary to durability in some applications, for practical purposes the use of radiation sources with a pulse repetition frequency of less than 1 MHz does not make sense for recording techniques that produce one point per pulse. According to the invention, multi-point recording techniques are also postulated in which lower repetition frequencies can be used.

[0054] The beam forming and guiding system in the present embodiment consists of the radiation source 430, the amplitude modulator 440, and the objective 450 with the movable mirror 451.

[0055] The pulse duration and its energy are parameters of the radiation source 430, while the size and effective area of a voxel and the energy changes introduced by the amplitude modulator 440 are determined by the beam forming and guiding system. By selecting these parameters, one can adjust the peak intensity of the beam in the voxel 110 during recording, as well as the size and effective area of the recorded voxel 110.

[0056] It is important that the tape 100 is transparent to radiation of 2000 nm or less. Thanks to this, the tape 100 can be easily read by rewinding it under the camera of the transmission microscope.

[0057] The choice of tape dimensions depends on the application. Generally, one can easily obtain capacities similar in range to LTO tapes by using glass tapes with a length of L ranging from 500 to 800 m. In some applications, one can use tapes as long as 1.5 km, but this translates into the size of the entire carrier and the rewinding time. The thickness of the tape determines its mechanical parameters, susceptibility to winding and tearing resistance. It was found that tapes with a thickness H of less than 5 pm are difficult to produce and are inconvenient to rewind. In turn, tapes with a thickness H above 100 pm bend less easily and take up a relatively large volume. Tapes with widths ranging from 5 mm to 50 mm wind well. Using wider tapes is problematic due to the risk of waving and bending, while narrower tapes accommodate few data symbols.

[0058] It should be noted that data symbols can be encoded not only using the amount of change in the refractive index in the voxel 110 but also using the size of voxel 110, the shape of the changed voxel 110, and the distance between voxels 110. This is possible using optical systems which are able to form and sweep the electromagnetic radiation beam 333 known in the state of the art. Using several of these options allows for more bits per symbol.

[0059] In another embodiment, the recording system illustrated in Fig. 6 and 7 is used, comprising a pulsed femtosecond laser 630 with a central wavelength of 500 nm obtained using the second harmonic, a repetition frequency of 200 MHz, a pulse energy of 1000 pJ, and a beam quality parameter M² = 1.02. The pulse duration is 8 fs. The maximum peak intensity of the beam achieved in the recording area is 117 TW/cm² As in the previous embodiment, the electromagnetic radiation beam is subjected to amplitude modulation, but the amplitude modulator 640 with greater dynamics of 30 dB is used here.

[0060] Then, the electromagnetic radiation beam 633 passes through a polarization control system comprising a polarizer 660 and an adjustable (controlled) polarization rotating element 670, e.g. a half-wave plate with electronically adjustable setting, operating at a wavelength of the laser 630.

[0061] The electromagnetic radiation beam is guided to an objective 650 with a focal length of 0.5 cm equipped in a movable mirror 651.

[0062] The system works analogously to the one discussed in the previous embodiment. The electromagnetic radiation beam 633 falls on the mirror 651 having a galvomechanism enabling the beam trajectory to be changed within a range of 5 degrees. The electromagnetic radiation beam 633 is guided to the data carrier - a glass tape 600 with dimensions W x L x H = 20 mm x 1000 m x 10 pm, which is being rewound in the focusing area of the electromagnetic radiation beam 633 so that the maximum of the peak intensity of the beam falls on the depth H/2 in the tape 600, and the change in the incidence angle Y of the beam caused by the galvomechanism runs along the W dimension in a plane substantially perpendicular to the direction of rewinding L of the tape 600. The tape 600 is made of boron-silica glass. Such glass is chemically more resistant than conventional silica glass, which allows for increased recording durability and insensitivity to chemical degradation of the material.

[0063] The recording of data symbols is performed by inducing permanent phase changes in the area of voxel 110 in the structure of the glass recordable layer, i.e. changes in the refractive index due to modification of the glass fictive temperature, as a result of exposure to electromagnetic radiation causing temporary ionization with different intensity. This is done by changing the energy of the incident laser pulse and changing the polarization state of the light at the data recording location in voxel 110.

[0064] The amplitude modulator 640 introduces attenuation in the range of 0 to 30 dB to the electromagnetic radiation beam 633 originating from the laser 630. At the output of the amplitude modulator 640, the pulse energy in the beam 633 is in the range from 1 to 1000 pJ. The pulse lasts 8 fs. The beam is focused in a voxel 110, the cross-section of which has the shape of a circle at its widest point with a radius of 0.25 pm and an effective area is 0.2 (pm)². As a result, when using a Gaussian beam, the peak intensity in the voxel area ranges from 0.1 TW/cm² to 117 TW/cm². Small voxel effective area enables high recording density and obtaining the required peak intensity of the beam.

[0065] The refractive index of the pure tape at a wavelength of A = 500 nm is no = 1.5214. This tape in a voxel area of 0.25 pm was exposed to the electromagnetic radiation beam 633 with the peak intensity ranging from 0.1 TW/cm² to 117 TW/cm². [0066] Using the amplitude modulator 640 and the polarization control system allows one to obtain at least 16 levels of the peak intensity of the radiation beam 633 and 4 directions of its polarization.

[0067] Adjusting the peak intensity of the radiation beam 633 translates into the amount of change in the refractive index in a voxel 110 in the glass of the tape 600.

[0068] Exposing glass to polarized light induces birefringence. It was found that the 4 directions of birefringence can be easily distinguished using fast and known measurement techniques.

[0069] As a result, in the present embodiment, a 16-state modulation of the amount of change in the refractive index and a 4-state modulation of the birefringence direction are obtained. Thus, 64 distinguishable states and an encoding of 6 bits per voxel 110 are obtained. The distance between data symbols measured from center to center in the L x W plane is 500 nm.

[0070] The reading is performed by illuminating the tape 600 with monochromatic coherent light with adjustable polarization, and then recording and analyzing the image resulting from interference on the linear array of detectors. It should be noted that the reading of data recorded in this way on the carrier can be performed using any technique suitable for measuring the birefringence and phase of light.

[0071] The beam forming and guiding system in the present embodiment consists of the amplitude modulator 640, the polarizer 660, the adjustable polarization rotating element 670, and the objective 650 with the movable mirror 651. In general, the beam forming and guiding system does not need to sweep the electromagnetic radiation beam in a plane perpendicular to the direction of translational movement of the tape. The beam sweep plane can be rotated slightly relative to the direction of movement of the tape to compensate for the "skew" of the voxel pattern due to translational movement. One can also, by design, use an arbitrary "skew" of the voxel pattern.

[0072] The pulse duration and its energy are parameters of the radiation source 630, while the size and effective area of a voxel and energy change (introduced by the amplitude modulator 640) are determined by the beam forming and guiding system 633. By selecting these parameters, one can adjust the peak intensity of the radiation beam in a voxel 110 during recording, as well as the size and effective area of the recorded voxel.

[0073] In another embodiment, a recording system comprising a pulsed femtosecond laser 830 with a pulse repetition frequency of 1 GHz, a maximum pulse energy of at least 2 mJ, a beam quality parameter of M² = 1 .4, and a pulse duration of 200 fs is used. A beam originating from the laser 830 passes through an objective 880 and is expanded therein, and then hits a spatial phase modulator 890. The spatial phase modulator 890 encodes data in the phase of the wave front of the electromagnetic radiation beam 833. As a result, the spatial Fourier transform of the wavefront of the electromagnetic radiation beam 833 forms encoded information at the focal point of the objective 850, which allows recording multiple points in one pulse and also guiding the electromagnetic radiation beam 833. Focusing with an objective implements the spatial Fourier transform of the incident beam. Preparing the wavefront of the beam and shaping the inverse transform of the desired symbol pattern on it results in the reproduction of this pattern at the focal point. The spatial phase modulator allows one to shape the wavefront according to the objective or lens used. The spatial phase modulator can also be used without a beam-expanding objective, but expanding of the beam facilitates proper illumination of the tape.

[0074] The electromagnetic radiation beam 833 originating from the laser 830 is guided to the objective 850 with focal length = 5 mm. The objective 850 preferably has a variable imaging plane 852 with a range of 20 pm and a resolution of 5 pm, which provides the ability to spatially record in three layers or use the third dimension to increase the number of bits per symbol. Such an objective can also be used in the previous embodiments.

[0075] The tape 800 is made of silica glass. Data is recorded by inducing permanent phase changes in the glass structure, i.e. changes in the refractive index as a result of modification of the glass fictive temperature, as a result of exposure to electromagnetic radiation causing temporary ionization with various intensity. [0076] Modification of the recorded information patterns is carried out by controlling the shape of the beam in the focal point using the spatial phase modulator 890. In this way, it is possible to both control the electromagnetic radiation beam and record 1000 or more points with different refractive index change amplitude in one pulse with resolution of 200 nm. Spatial modulation is implemented using the technique disclosed in: Satoshi Hasegawa and Yoshio Hayasaki, "Polarization distribution control of parallel femtosecond pulses with spatial light modulators," Opt. Express 21 , 12987-12995 (2013).

[0077] The beam forming and guiding system in the present embodiment consists of the objective 880, the spatial phase modulator 890, and the objective 850

[0078] The pulse duration and pulse energy are the parameters of the radiation source 830, while the energy distribution in the beam, including the size and effective area of a voxel, are determined by the beam forming and guiding system. By selecting these parameters, one can adjust the peak intensity of the radiation beam in voxels 110 during recording, as well as the size and effective area of a voxel.

[0079] To read the data, the tape is illuminated with monochromatic coherent light. The reading is then performed by analyzing the image resulting from interference using an array of detectors.

[0080] To extend the lifespan of the carrier according to the invention, it can be coated with a layer of a damp-proof material, e.g. acrylate. Covering can be applied to an empty data carrier before it is recorded, or the data carrier can be covered after recording. In the latter case, it is easier to avoid damaging the protective layer during recording.

[0081] The invention is applicable in data archiving techniques, in particular data requiring a high level of protection against destruction as a result of environmental exposures or intentional electromagnetic attacks.

[0082] In another embodiment discussed below with reference to Fig. 9, a recording system comprising a pulsed femtosecond laser 930 with a pulse repetition frequency of 100 MHz, a maximum pulse energy of at least 2 mJ, and a pulse duration of 800 fs. An output beam is structured into super-oscilatory beam using super-oscillatory lens 930 and is expanded therein, and then hits a acousto-optic deflector 990. The acousto-optic deflector 990 changes the angle of the beam 950 incident into telecentric scan lens 952. Small incident angle change of the wavefront 950 is translated into over 2 cm lateral movement of a focal spot 900. As a result, the super focused spot of the electromagnetic radiation beam 933 forms encoded information at the focal point of the telecentric scan lens 950. Focusing using super oscilatory lens allows to obtain voxels of size below diffraction limit in the glass tape 322. Thus, voxels of crossectional dimensions below 0.25 pm can be obtained.

[0083] The electromagnetic radiation beam 933 originating from the laser 930 is guided to the super-oscillatory lens 950 with focal length = 10 mm. The telecentric scan lens 950 preferably has a scanning range of 2 cm. Such lenses can also be used in the previous embodiments.

[0084] The tape 322 is made of silica glass. Data is recorded by inducing permanent phase changes in the glass structure, i.e. changes in the refractive index as a result of modification of the glass fictive temperature, as a result of exposure to electromagnetic radiation causing temporary ionization with various intensity.

[0085] Modification of the recorded information patterns is carried out by controlling the position of the beam in the focal point using the acousto-optic deflector 990. In this way, it is possible to control the position of focal point with resolution of 100 nm.

[0086] The beam forming and guiding system in the present embodiment consists of the super-oscilatory lens 980, the acousto-optic deflector 990, and the telecentric lens 950.

[0087] The pulse duration and pulse energy are the parameters of the radiation source 930, while the energy distribution in the beam, including the size and effective area of a voxel, are determined by the beam forming and guiding system. By selecting these parameters, one can adjust the peak intensity of the radiation beam in voxels 110 during recording, as well as the size and effective area of a voxel.

[0088] To read the data, the structured illumination microscope is used. [0089] Accordingly, while specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications, substitutions, and changes can be made without departing from the scope of the invention as defined by the appended claims. [0090] The present invention, by enabling volumetric data encoding within a flexible glass carrier, not only departs from conventional paradigms of surfacebased or rigid-volume recording, but also provides a novel and advantageous balance between mechanical flexibility and data storage integrity. This combination enhances both the speed and durability of the recording process, marking a significant advancement in the field of data storage technologies.

Person skilled in the art is able to suggest various schemes of encoding based on various parameters of produces voxels and gaps between the voxels without departing from the scope of protection as defined in the claims.

Claims

1 . A method of recording data on an optical data carrier in a form of a rewindable tape having a recordable layer, comprising a step of applying data symbols to the recordable layer in a process of creating voxels with a locally changed refractive index including subjecting the recordable layer to electromagnetic radiation pulses from a pulsed source of focused radiation, directed to the tape as it is being rewound, characterized in that in the step of applying the tape (100, 600, 800, 900) being used is transparent along its thickness to electromagnetic radiation having a wavelength of 2000 nm or lower, has a recordable layer made of a material comprising glass, and the recordable layer has a thickness (H) ranging from 5 pm to 100 pm a width (W) ranging from 5 mm to 50 mm, and a length (L) greater than 100 m, wherein the recordable layer is also a substrate layer, and further in the step of applying there is used a beam (333, 633, 833, 933) of the pulsed electromagnetic radiation having: a pulse duration of less than 1 ps and a wavelength of less than or equal to 2000 nm, said radiation being focused within the volume of the recordable layer of the tape (100, 600, 800, 900), in at least one voxel (110), located entirely below the surface of the recordable layer, having a size less than or equal to 1 pm, wherein the said focused radiation reaches the peak intensity greater than or equal to 29 MW/cm², for obtaining a local change in the refractive index of the material of the recordable layer, wherein the beam (333, 633, 833, 933) of electromagnetic radiation is directed in successive pulses into the tape (100, 600, 800, 900) being rewound to obtain at least a two-dimensional pattern of voxels (110).

2. The method according to claim 1 , wherein the tape used (100, 600, 800, 900) has a length ranging from 500 m to 800 m.

3. The method according to claim 2, wherein the beam of pulsed electromagnetic radiation used (333, 633, 833) is a Gaussian beam and has a beam quality parameter M² of less than or equal to 1 .3.

4. The method according to any one of claims from 1 to 3, wherein the beam of pulsed electromagnetic radiation (333, 633, 833, 933) is focused in a voxel area (110) of 0.5 pm or less in size.

5. The method according to any one of claims from 1 to 4, wherein the intensity of the beam of pulsed electromagnetic radiation (333, 633, 833) is tuned to provide multiple levels of change of refractive index.

6. The method according to any one of claims from 1 to 5, wherein the phase front of the beam of pulsed electromagnetic radiation (833) is shaped using a spatial modulator (890) to record many voxels (110) simultaneously.

7. The method according to any one of claims from 1 to 6, wherein after recording, the optical data carrier is coated with a damp-proof layer.

8. An optical data carrier comprising a recordable layer encoded with symbols, characterized in that it is a tape (100, 600, 800) with a recordable layer made of a material containing glass, the recordable layer is also a substrate layer and having a thickness (H) ranging from 5 pm to 100 pm and a width (W) ranging from 5 mm to 50 mm and a length (L) of at least 100 m, wherein the symbols are encoded in voxels (110) having a size of 1 pm or less, wherein the voxels (110) are located in the volume of the recordable layer entirely below its surface, the voxels (110) being represented as change in refractive index in solid glass.

9. The optical data carrier according to claim 8, wherein the recordable layer is made of a material containing boron-silica glass.

10. The optical data carrier according to claim 9, wherein it is coated with a damp-proof layer.

11 . The optical data carrier according to any of claim 8-10, wherein the change in refractive index within voxels has more than two intensity levels.

12. The optical data carrier according to any of claim 8-11 , wherein the change in refractive index within voxels has at least 4 intensity levels.

13. The optical data carrier according to any of claim 8-12, wherein the change in refractive index within voxels has 16 intensity levels.

14. The optical data carrier according to any of claim 8-13, wherein the change in refractive index within voxels is birefringent.