EP1214710A1

EP1214710A1 - Data memory

Info

Publication number: EP1214710A1
Application number: EP00956357A
Authority: EP
Inventors: Jörn LEIBER; Bernhard MÜSSIG; Stefan Stadler; Steffen Noehte
Original assignee: EML European Media Laborat GmbH; Tesa SE; Tesa Scribos GmbH
Current assignee: Scribos GmbH
Priority date: 1999-09-24
Filing date: 2000-07-31
Publication date: 2002-06-19
Also published as: DE19947782A1; JP2003510748A; WO2001024172A1

Abstract

The invention relates to a data memory comprising an optical information carrier which has several layers (10) of a polymer carrier (11) through which information can be read out of a preselected polymer carrier layer (10) and, optionally, can be written into a preselected polymer carrier layer (10). The information carrier is formed around an optically transparent core whose refractive index differs from the refractive index of the polymer carrier (11) by less than 0.08.

Description

data storage

The invention relates to a data storage device with an optical information carrier which has several layers of a polymer carrier.

DE 298 16 802 describes a data storage device with an optical information carrier which contains a polymer carrier in the form of a polymer film. Polymethyl methacrylate and a polymer film sold by Beiersdorf AG under the name "tesafilm crystal clear", which has biaxially oriented polypropylene, are mentioned as the material for the polymer film. The polymer film is spirally wound in several layers on a core, with an adhesive layer between each of the adjacent layers. Information can be written into this data memory by locally heating the polymer film with the aid of a write beam from a data drive, as a result of which the refractive index and thus the reflection (reflectivity) change locally at the interface of the polymer film. This can be detected with the aid of a read beam in the data drive. By focusing the writing beam or reading beam information can be specifically written into or read from a preselected position of the information carrier. The core can be optically transparent and have a cutout in its central area, which serves to accommodate the writing and reading device of a data drive. The read and write device is moved relative to the data memory while the data memory is at rest, so that the data memory does not have to be balanced with regard to a rapid rotational movement.

The core of the previously known data storage device is made of polystyrene. Polystyrene is not particularly scratch-resistant and has a refractive index (1.59 at the wavelength of the reading beam used), which differs significantly from that of the polymer film material (1.49 for biaxially oriented polypropylene at the wavelength of the reading beam). Since the wall of the core must be irradiated by the write beam and the read beam when the data storage device is used in a data drive, the write and read device of which is placed in the recess of the core (and even twice with each read operation), a bad one caused by scratches has an effect optical quality and especially the reflection losses associated with the large difference in refractive index.

It is an object of the invention to provide a data storage medium with an optical information carrier which has a plurality of layers of a polymer carrier, in which the disadvantages explained above which are due to an insufficient core do not occur.

This object is achieved by a data storage device having the features of claim 1. Claim 13 relates to the use of such a data storage device in a drive matched to it. Advantageous embodiments of the invention follow from the dependent claims. The data storage device according to the invention has an optical information carrier which has a plurality of layers of a polymer carrier, through which information can be read out from a preselected polymer carrier layer and optionally written into a preselected polymer carrier layer. The information carrier is formed around an optically transparent core, the refractive index of which differs from the refractive index of the polymer carrier by less than 0.08. The refractive indices are based on a light wavelength with which the optical reading device of a drive tuned to the data memory works.

Due to the relatively small difference in the refractive indices of the optically transparent core and the polymer carrier, it is achieved that a reading beam which is emitted by the reading device of a drive and which shines through the optically transparent core can penetrate into the polymer carrier without at the interfaces between the core and the polymer carrier to be reflected too strongly. Such reflections are disadvantageous because, on the one hand, they weaken the reading beam and, on the other hand, they cause a strong background level that overlaps the actual reading signal. The same applies to a write beam if the data store is optionally set up as a data store that can be written by the user. The smaller the difference in refractive index, the smaller the reflections. If the data memory has one or more additional layers between adjacent polymer carrier layers (see below), the refractive index of an additional layer should also differ only slightly from the refractive index of the polymer carrier.

The core is preferably sleeve-like or cylinder-like and has a cutout in its central region. This also includes configurations in which the cross section of the periphery of the core is not circular, but has a step so that the core is better adapted to the course of the layers of the polymer carrier adjacent to the core. This is explained in more detail below using an exemplary embodiment. The cutout in the central area of the core can be set up to accommodate a reading device and, optionally, a writing device of a drive matched to the data memory. It is particularly advantageous if the data memory is used in a drive which has a reading device and optionally a writing device, the reading device and the optional writing device being arranged in the cutout in the central region of the core and for reading or writing information relative to that Data storage are moved while the data storage is at rest. In this case, the data storage does not have to be balanced in order to enable high rotational speeds, which has a favorable effect on the production costs.

In an advantageous embodiment of the invention, the polymer carrier, which preferably has a polymer film, is wound spirally around the core. With such a multilayer structure of the data memory, a very high storage density can be achieved. For example, 10 to 30 layers of polymer film can be wound on top of one another, but also more or less. With a thickness of the polymer film between 10 μm and 100 μm, preferably less than 50 μm or around 35 μm, the information on different polymer film layers can be separated from one another in a readily resolvable manner with the aid of reading and writing devices known for example from DVD technology. However, it is also conceivable that the polymer carrier is not wound spirally around the core, but that, for example, several essentially concentric layers of the polymer carrier are arranged around the core.

The core can have a plastic. A plastic of optically high quality is preferably used as the core material. The refractive index of the plastic material must be in the range of the refractive index of the polymer carrier. For example, polymethyl methacrylate (PMMA) or a cycloolefinic sold by Nippon Zeon under the name "Zeonex" are suitable Copolymer, especially if a polymer film made of biaxially oriented polypropylene (BOPP; see below) is used for the polymer carrier.

If the core is made of plastic or consists entirely of plastic, the core is preferably provided with an anti-scratch coating. Anti-scratch coatings such as those e.g. are known from eyewear optics, at least largely prevent scratching of the surfaces of the core exposed to a reading beam or writing beam, which increases the operational reliability and service life of the data memory. It must be ensured that the anti-scratch coating does not lead to a large jump in the refractive index.

The core can also have a glass. Glasses generally have a better optical quality and a higher scratch resistance than plastics. A core made of glass also has mechanical advantages, because a data storage device with such a core is difficult to deform. A type of glass which is particularly suitable for use with a polymer carrier made of biaxially oriented polypropylene is the glass sold by Schott under the name "BK7".

An adhesive layer is preferably arranged in each case between adjacent polymer carrier layers in order to fix the polymer carrier layers to one another. For example, an adhesive layer can have a thickness in the range between 1 μm and 40 μm, preferably less than 25 μm or around 2 μm. A suitable adhesive is, for example, an air bubble-free acrylate adhesive that is crosslinked, for example, chemically or by UV or electron radiation. One or more layers with different or additional functions can also be located between adjacent polymer carrier layers, for example a layer with dye molecules of an absorber (see below). The refractive index of the adhesive layer preferably deviates only slightly from the refractive index of the polymer carrier in order to minimize disturbing reflections of the reading beam or the writing beam at a boundary layer between a polymer carrier layer and an adjacent adhesive layer. It is particularly advantageous if the difference in refractive indices is less than 0.005. An existing difference in refractive indices can, however, be used to format the data memory.

In a preferred embodiment of the data memory according to the invention, the refractive index of the polymer carrier can be changed locally by heating. For example, a polymer film made of biaxially oriented polypropylene (BOPP) can be considered as the material for the polymer carrier, but other materials can also be used. If polypropylene is pre-stressed on two levels after extrusion to the film, a high level of self-energy is stored in the material. Local heating, for example by means of a writing beam, then leads to a strong change in material due to reshaping, and indeed even with the deposition of a relatively small amount of energy per unit area. In this way, for example, a change in the refractive index of about 0.2 over an area for a stored information unit with a diameter or a side length of about 1 μ can be achieved, which can be easily detected with the aid of a reading beam.

An absorber can be assigned to the polymer carrier, which is set up to at least partially absorb a write beam and to at least partially emit the heat generated thereby locally to the polymer carrier. The absorber contains, for example, dye molecules, which are contained, for example, in the polymer carrier or in an adhesion layer adjacent to the polymer carrier, and enables local heating of the polymer carrier sufficient for changing the refractive index with a relatively low intensity of the writing beam. The invention is explained in more detail below on the basis of exemplary embodiments. The drawings show in

FIG. 1 shows a data memory according to the invention, which has a spiral-wound polymer film, in a schematic perspective illustration, parts of a drive which is matched to the data memory being arranged in a cutout in the central region of the data memory,

2 shows a schematic cross section through the data memory from FIG. 1 and

FIG. 3 shows a schematic cross section through the central area of a data memory, which has a core with a periphery differently than that in FIG. 2.

FIG. 1 shows a schematic representation of a data store 1 and a read and write device 2 of a drive that is matched to the data store 1. The data memory 1 has a number of layers 10 of a polymer carrier used for information storage in the form of a polymer film 11 which is wound spirally around an optically transparent core. The core is not shown in FIG. 1 for the sake of clarity; it is located within the innermost layer 10 and is explained in more detail with reference to FIG. 2. For better illustration, the individual layers 10 of the polymer film 11 are shown in FIG. 1 as concentric circular rings, although the layers 10 are formed by spiral winding the polymer film 11. An adhesive layer 12 is arranged between adjacent layers 10 of the polymer film 11. For reasons of clarity, the adhesive layers 12 are shown in FIG. 1 in a thickness that is not to scale.

In the exemplary embodiment, the polymer film 11 consists of biaxially oriented polypropylene and was used in both before winding Surface directions biased. In the exemplary embodiment, the polymer film 11 has a thickness of 35 μm; other thicknesses in the range from 10 μm to 100 μm or thicknesses outside this range are also conceivable. The adhesive layers 12 are free of gas bubbles and, in the exemplary embodiment, consist of acrylate adhesive to which an absorber dye is added, with a thickness of 23 μm, preferred layer thicknesses being between 1 μm and 40 μm. In the exemplary embodiment, the data memory 1 contains twenty layers 10 of the polymer film 11 and has an outside diameter of approximately 30 mm. Its height is 19 mm. A different number of layers 10 or other dimensions are also possible. The number of windings or layers 10 can be, for example, between ten and thirty, but can also be greater than thirty.

The read and write device 2 arranged in a recess in the central area of the core of the data memory 1 contains a read and write head 20 which can be rotated with the aid of a mechanism 21 in the directions of the arrows shown and moved axially back and forth. The write and read head 20 has optical elements, with the aid of which a light beam (for example of the wavelength 630 nm or 532 nm) generated by a laser not shown in FIG. 1 can be focused on the individual layers 10 of the polymer film 11. Since the read and write head 20 is moved by means of the mechanism 21, it can completely scan all layers 10 of the data memory 1. In the exemplary embodiment, the data memory 1 is at rest. It therefore does not need to be balanced with regard to a high rotational speed (and also does not have to be unwound or rewound), in contrast to the read and write head 20. For the sake of clarity, FIG the elements provided for balancing the read and write head 20 are not shown. The laser mentioned is located outside the read and write head 20 and is stationary; the laser beam is directed into the read and write head 20 via optical elements. In order to store or write information into the data memory 1, the laser in the exemplary embodiment is operated with a beam power of approximately 1 mW. The laser beam serves as a write beam and is focused on a preselected layer 10 of the polymer film 11, so that the beam spot is less than 1 μm, the light energy being introduced in the form of short pulses of approximately 10 μs duration. The energy of the write beam is absorbed in the beam spot, favored by the absorber in the adjacent adhesive layer 12, which leads to local heating of the polymer film 11 and thus to a local change in the refractive index and the reflectivity.

In order to read stored information from the data memory 1, the laser is operated in continuous wave mode (CW mode). Depending on the stored information, the reading beam focused on the desired location is reflected, and the intensity of the reflected beam is detected by a detector in the writing and reading device 2.

The data memory can also be of an embodiment that is not writable by the user. In this case, it contains information units registered by the manufacturer. A write function in the data drive of the user is then unnecessary.

In the polymer film 11, the information units are formed by changing the optical properties in a region with a preferred size of less than 1 μm. The information can be stored in binary form, ie the local reflectivity only takes two values at the location of an information unit. This means that if the reflectivity is above a defined threshold value, a "1" is stored, for example, at the position of the information carrier under consideration, and if it is below this threshold value or below another, lower threshold value, correspondingly a "0". However, it is also conceivable to display the information in several gray levels. save. This is possible if the reflectivity of the polymer film can be changed in a targeted manner at the location of an information unit by a defined setting of the refractive index, without saturation being achieved in the process.

FIG. 2 shows a schematic cross section through the data memory from FIG. 1. The core, which is designated here by 30, is sleeve-shaped or hollow-cylindrical and has a cutout 32 in its central region. The write and read device 2 of the drive can be received in the cutout 32, see FIG. 1. The optical information carrier with the spiral wound Polymer film 11 and the adhesive layers 12 extend from the outer periphery 34 of the core 30 to an outer periphery 36.

In the exemplary embodiment, the core 30 consists of polymethyl methacrylate (PMMA). It can be made by injection molding or extrusion. The surface of the core 30 delimiting the recess 32 is then preferably provided with an anti-scratch coating.

Examples of other materials for the core are a cycloolefinic copolymer marketed by Nippon Zeon under the name "Zeonex" or other plastics. Glasses are particularly advantageous, e.g. the glass with the designation "BK7" from Schott.

It is essential that the refractive index of the material for the core is matched to the refractive index of the polymer carrier. For example, at a light wavelength of 630 nm (ie a light wavelength that is suitable for a reading beam or writing beam), biaxially oriented polypropylene has a refractive index of 1.503, while the refractive indices of polymethyl methacrylate are 1.491, "Zeonex" 1.522 and the glass "BK7" 1.515 , In all cases, the difference between the refractive indices is small. The data memory, the central area of which is shown in a schematic cross section in FIG. 3, has a core 40, the shape of which is somewhat different from that of the data memory explained with reference to FIGS. 1 and 2. The core 40 has a cylindrical recess 41 for receiving a write and read device of a drive. However, the outer contour 42 of the core 40 is not circular, as in FIG. 2, but is shaped like a spiral and has a step 43. The height of the step 43, ie the size of the radial jump of the outer contour 42 at the step 43, is adapted to the thickness of the polymer film (including adjacent adhesive layer) designated here 44, which is wound onto the core 40.

FIG. 3 shows how the inner end 45 of the polymer film 44 (with an adhesive layer) is at the step 43. The innermost layer 46 of the polymer film 44 lies against the outer contour 42 of the core 40 via the adhesive layer. At the beginning of the following layer 47, the step 43 ensures that the polymer film 44 largely runs on an ideal spiral, as can be seen from FIG. In particular, an abrupt jump in the radial direction is prevented, as is the case with a core with a circular periphery, e.g. core 30, occurs when the polymer film hits the inner end at the beginning of the second turn, which marks the beginning of the first turn. In particular, the inner windings of the spiral arrangement of the polymer film 44 have a more even course, so that the focus of a reading or writing beam can be better tracked.

Claims

claims

1. Data memory with an optical information carrier which has a plurality of layers (10) of a polymer carrier (11) through which information can be read out from a preselected polymer carrier layer (10) and optionally can be written into a preselected polymer carrier layer (10), and which can be written by one optically transparent core (30) is formed, whose refractive index differs by less than 0.08 from the refractive index of the polymer carrier (11).

2. Data memory according to claim 1, characterized in that the core (30) is sleeve-like or cylinder-like and has a recess (32) in its central region.

3. Data memory according to claim 2, characterized in that the recess (32) for receiving a reading device (2) and optionally a writing device (2) is arranged on the data storage device (1) drive.

4. Data memory according to one of claims 1 to 3, characterized in that the polymer carrier (11), which preferably has a polymer film (11), is wound spirally around the core (30).

5. Data memory according to one of claims 1 to 4, characterized in that the core (30; 40) has a plastic.

Data memory according to claim 5, characterized in that the core (30; 40) comprises one or more of the following materials: polymethyl methacrylate, cyclo-olefinic copolymer.

7. Data memory according to claim 5 or 6, characterized in that the core (30; 40) is provided with an anti-scratch coating.

8. Data memory according to one of claims 1 to 4, characterized in that the core (30; 40) has a glass.

9. Data memory according to one of claims 1 to 8, characterized in that an adhesive layer (12) is arranged in each case between adjacent polymer carrier layers (10).

10. Data memory according to claim 9, characterized in that the refractive index of the adhesive layer (12) differs only slightly from the refractive index of the polymer carrier (11).

11. Data memory according to one of claims 1 to 10, characterized in that the refractive index of the polymer carrier (11) can be changed locally by heating.

12. Data memory according to claim 11, characterized in that the polymer carrier (11) is assigned an absorber which is set up to at least partially absorb a writing beam and at least partially emit the heat generated thereby locally to the polymer carrier (11).

13. Use of a data memory according to one of the preceding claims in conjunction with claim 3 in a drive which is matched thereto and has a reading device (2) and optionally a writing device (2), the reading device (2) and the optional writing device (2) in of the recess (32) are arranged in the central region of the core (30) and are moved relative to the data memory (1) for reading or writing information while the data memory (1) is at rest.