Disk-shaped optical memory and method of making same

The subject of the invention is an optical data carrier in the form of a disc and a method for producing a glass pattern for producing matrices for producing an optical data carrier in the form of a disc.

Optical data carriers in the form of a plate for binary information, recorded in the form of a series of grooves and flat areas, successively along a spiral path in a smooth optical reference surface, are known, while the mutually independent groove lengths and flat areas embody the recorded binary values ​​read on interference principle using a focused and guided laser beam.

One of the best known data carriers of the above type is a compact disc whose essential properties are the subject of the IEC 908 standard and the Compact Disc Digital Audio System Description publication, June 1989, publisher Sony Corp. and NV Philips. The compact disc has, among other things, the following features: the information is serially recorded in the form of a spiral path on a smooth reference surface and read by reflection using a focused laser beam. In the smooth plane of the reference surface, the diameter of the focus is equal to the width of the path and is about 1 gm. Within the path there are successively hollow grooves, which in the direction of the path and in the radial direction are separated from each other by areas of a smooth reference surface. Areas of reference surface that lie in the direction of the path between adjacent grooves are called flat areas. The width of the grooves is less than half the width of the path. The lengths of the grooves and flat areas embody the binary values ​​recorded on the data carrier, namely every transition in the direction of the path between the groove and the flat area, or between the flat area and the groove is read as logical one, while the remaining areas of both the grooves and flat areas are read as logical zero. The principle of destructive interference, known from German Patent No. 22 08 379, is used to read passages. With a uniformly reflecting surface of the plate, this interference shows an optimum if, on the one hand, the depth of the groove corresponds exactly to a quarter of the wavelength of the reading light beam, on the other hand, one half of the incident light is reflected on the surrounding groove areas of the smooth reference surface (including areas flat) and the other half is reflected from the bottom of the groove. Subsequent succession of grooves and flat areas would then give maximum modulation of the reflected beam amplitude. An indispensable assumption for contactless reading of the optical data carrier is also to obtain the path tracking signal from the reflected part of the reading light beam. However, the track tracking signal is equal to 0 at the groove depth λ / 4, while it reaches the maximum when the groove depth is λ / 8.

Therefore, neither in the compact disc, nor in any other optical data carrier working on the same principle can be made use of the groove depth λ / 4, optimal for retrieving the information signal. The depth of the grooves is rather about 0.225 λ. In a compact disc made of transparent polycarbonate with a refractive index n = 1.46, which is known to be read through through transparent polycarbonate, and with a commonly accepted laser beam wavelength of 780 nm, i.e. with a wavelength in polycarbonate of 534 nm, the groove depth is 120 nm.

Further development of the optical data carrier of the type described above is known from German Laid-Open Publication No. 41 21 505, the purpose of which is to simplify the production of the support by allowing greater tolerances for the depth of the grooves, and in particular to enable shortening the operation time of the injection molding machine used to form the support, without compromising its compatibility data relative to the carriers of the kind described at the beginning. To this end, in the improved data carrier, instead of consecutive grooves and flat areas, a continuous groove with a modulated depth is used, which includes the first areas of greater depth corresponding to the grooves, and the second areas of smaller depth corresponding to flat areas, and located between them with stepped passages. The depth of the first areas is exactly equal to the said optimal value, which is one quarter of the wavelength of the reading light beam, while the depth of the second areas is about one-sixteenth of this wavelength.

From British Patent Application No. 2 250 626 A, an optical data carrier in the form of a disc is known, containing pre-formatted tracks in which grooves embodying information are recorded. To obtain a macroscopic pattern, the pre-formatted paths can be shifted a small dimension in a radial direction from the given direction of the path, according to the intended pattern.

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The optical storage medium in the form of a disc, containing pre-formatted paths in which grooves embodying information are stored, is also known from European Patent Application No. 0 520 251 A. The depth of the grooves is a quarter of the wavelength of the reading light, and the depth of the remaining area of ​​the pre-formatted path , that is, the depth of the flat areas, is one-sixteenth of the wavelength of the reading light.

Among the data carriers of this kind, compact discs have gained great popularity, and thus economic significance. Disc producers are increasingly facing the problem of illegal copies and pirated goods. In the meantime, the method of producing such optical data carriers has become a general state of the art and has been well mastered, so that neither trade nor the user is able to distinguish pirated products from original products.

The object of the invention is therefore to provide the above-described data carrier in the form of a disc with very difficult to forge, durable marking (of essentially any form and size) that would be clearly recognizable by means of optical means. The object of the invention is also to develop a method of producing a glass pattern for the production of matrices, enabling the production of such an optical data carrier in the form of a disc.

An optical storage medium in the form of a disc for recording binary information, recorded in the form of a series of grooves and flat areas, successively along a spiral path in a smooth optical reference surface, with each other independent lengths of grooves and flat areas embody the recorded binary values, read on the principle of interference by means of a focused and guided laser beam, according to the invention is characterized by that the selected number of flat areas is shaped as shallow, compared to the depth of the grooves, the recesses in the optical reference surface.

Preferably, the flat regions shaped in the form of recesses, successively along the path and / or radially adjacent to each other, form a macroscopic pattern.

Preferably, the flat areas shaped in the form of recesses have a U-shaped cross section and their width approximately corresponds to the width of the grooves.

Preferably, the flat areas shaped in the form of recesses have a V-shaped cross-section profile and their width is smaller than the width of the grooves.

Preferably, the depth of the recessed flat areas is less than 30% of the depth of the grooves.

A method for producing a glass pattern for producing matrices for the production of an optical data carrier in the form of a disc for recording binary information, recorded in the form of a series of grooves and flat areas, successively along a spiral path in a smooth optical reference surface, with mutually independent groove lengths and areas flat embody written binary values, read by interference using a focused and guided laser beam, in which way the photosensitive varnish layer on the glass pattern is irradiated in the area of ​​the produced grooves along the path with the laser beam, after which it develops the glass pattern, receiving grooves in the exposed places of the photosensitive varnish layer . and then the known duplication technique is used to produce an optical data carrier in the form of a plate as a replica of a glass pattern, according to the invention it is characterized in that the photosensitive varnish layer is irradiated with a laser beam also in a part of selected flat areas, shaping these flat areas in the form of shallow depressions in optical reference surface, where the intensity of the laser beam in selected flat areas decreases to a value, which, within the data storage surface necessary for reading, is at most 50% of the value of the groove production intensity, and outside this surface lies between the technically determined minimum value and the value of the groove production intensity.

Surprisingly, it turned out that regardless of the number of flat areas transferred in this way from the optical reference surface, the compatibility of such a data carrier will remain intact even when the groove depth is 0.225 λ instead of 0.25 λ. The invention therefore gives the manufacturer the opportunity to dress any data carrier

173 341 marking in the form of a number of flat areas in the shape of flat recesses, without any additional investment during the production process. This marking can in extreme cases be so small, and thus cover so few flat areas, that it is visible only by means of electron microscopy, and even then, if the control is not to be excessively time-consuming, the location of the marking must be known.

Of course, the flat areas, embedded in the optical reference surface and used for marking the data carrier, do not have to be directly in succession in the direction of the path, so they can also be separated by more than one groove and the normal flat area located between these grooves. In addition, not all depressed flat areas need to be of equal depth. On the contrary, these depths may be irregular or varied according to a given pattern.

Another unexpected advantage is that the recessed flat regions shaped according to the invention, although they enter the optical reference surface only at a fraction of the wavelength of the reading light beam, result in effects that are perceived visually even under illumination of white light (e.g. light) day), and with a sufficiently large number of flat areas shaped in such a way, also with the naked eye. Hence, in one embodiment of the invention, the depressed planar areas successively in the direction of the path and / or adjacent in the radial direction form a macroscopic pattern. This pattern stands out from the rest of the data carrier surface, depending on the angle of incidence of light and the angle of observation, with a different shade of gray similar to the so-called watermark. It goes without saying that the visual pattern thus created may have any shape, and thus may reproduce, for example, the name or mark of the manufacturer, the title of the registered program material or the like.

The principle of shallowness of recessed flat areas used for marking, and the limitation of their depth apply to the situation when the marking made in this way lies within the surface of the data carrier, necessary for its reading. In addition to the so-called program area, this surface includes, for example on a compact disc, an additional delivery area and an additional output area. The surfaces of the data carrier outside these areas are irrelevant to the reading process and thus to the proper functioning of the reproduction apparatus. Therefore, the above depth restrictions used for marking, special flat areas, recessed into the optical reference surface, do not apply. This means that in the case of grooves and flat areas located outside the surface of the medium needed for reading, the depth of the flat areas, depressed in the optical reference surface, is arbitrary, which allows it to be optimized in such a way that the marking strongly contrasts with the remaining surface of the storage medium, thanks to why it can be easily seen with the naked eye.

The method according to the invention makes it possible, by means of typical intermediate operations, to produce an optical data carrier with the labeling proposed.

The subject of the invention is shown in the embodiment of the drawing, in which fig. 1 shows a compact disc, provided with a CD marking, in a top view, and fig. 2 - a topography of a surface, for example in place X in fig. 1, in a perspective view at 600x magnification.

The compact disc, shown in Fig. 1 only as an example of an optical storage medium, has, in three places, also an exemplary, watermark-like CD marking, which on a generally mirrored surface appears as a different (darker) shade of gray. Depending on the viewing angle, all three markings are visible simultaneously, or only one or two.

Figure 2 shows the topography of the surface in perspective view from the embossed side. Visible paths are numbered (arbitrarily) along the left edge. Track fragments 1 to 6, which appear linear due to significant enlargement, but macroscopically follow one another in a spiral pattern, show the order of grooves 21 and flat regions 22 of varying lengths according to the binary information recorded in the fragment shown. The flat areas 22 are, in other words, the areas of the optical reference surface that belong to a given path.

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On tracks 7 to 10, however - in the fragment shown here - the flat areas are, compared to the depth of the unchanged grooves 21, shaped as shallow recesses 23 in the optical reference surface. It can be seen here that the flat areas thus shaped have a U-shaped cross-section profile and are only slightly narrower than the grooves 21. If the grooves 2l and the flat areas 22 or 23 are not made by the known laser / photographic method, but are cut in the pattern by a stylus, then both the grooves 21 and the flat areas 23 are negative in the shape of the stylus in cross-section, so they have a corresponding cross-section the letter V. Due to their shallow depth, typically less than 20% of the depth of the grooves, the flat areas are necessarily much narrower in width than the (not shown) grooves.

In the present embodiment of the compact disc according to Fig. 1, in the surface areas on which the watermark-like CD marking is placed, the flat areas 23 are shaped as shallow recesses, while in all other surface areas the usual flat areas 22 are preserved. If, instead of the CD macroscopic marking chosen here, the optical data carrier in the form of a disc would be provided with a hidden marking that cannot be detected with the naked eye or even with the help of a light microscope, it is sufficient here to reduce the number of flat areas 23 according to the invention and place them in a place known only to the media manufacturer. In addition, conventional flat areas 22 and flat areas 23 formed according to the invention may follow each other within the same path, the order in which they follow embodies binary information.

The starting point for the production of the above-mentioned optical data carrier in the form of a disc is usually a glass pattern, which is coated with a photosensitive varnish and irradiated with a laser beam along a spiral path. Where the layer of photosensitive lacquer has been exposed, grooves form after the glass pattern is developed. If the flat areas 23 according to the invention are now to be recorded, then the intensity of the irradiating laser beam decreases not to zero, but to a value of several dozen percent of the value of the groove production intensity in appropriate places.

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UP Department of Publications. Circulation of 90 copies

Price PLN 2.00