MXPA98001544A - Optical disk compatible with two different reading systems - Google Patents

Abstract

The invention relates to an optical disc composed of two elementary discs (D1, D2) joined together by a layer (3) of transparent glue. The first elementary disk comprises an information surface (4b) according to the DVD standard and the second elementary disk comprises an information surface according to the CD standard. The optical disc can be read by a CD player for CD information, and by a DVD player for DVD information. Therefore, cost issues and other difficulties are solved for more compatibility of DVD players and at the same time ensures a simple and uniform transition from CDs to DVDs for consumers.

Description

OPTICAL DISK COMPATIBLE WITH TWO DIFFERENT READING SYSTEMS DESCRIPTION OF THE INVENTION The present invention relates to an optical disk composed of two elementary discs adhesively bonded together, each elementary disc contains at least one transparent substrate with an information face provided with microallocations on the surface distributed on a spiral track or concentric tracks and designed to be read optically with the help of a laser beam. Currently, a new standard of high density optical disc is being designed under the name DVD (digital video disc). A specifically developed technique allows this new type of optical disk to have a storage capacity greater than 4.7 Gigabytes per side of information, and in this way it becomes possible to store more than two hours of digital video compressed according to the MPEG2 video standard. . Applications in the information processing field are also made possible by the high density of the optical disc. The increase in storage density on the optical disc has required a change of technique compared to the technology of the compact disc (CD), especially with respect to the size of the microalterations in the disc, the wavelength of the reading laser, the Modulation system and error correction method. As a result of this, a disc reader DVD does not allow, a priori, the reading of conventional compact discs. The compact disc has a thickness of approximately 1. 2 mm and consists of a transparent substrate that includes an information face provided with micro-alterations in the form of microwells or microprotrusions distributed on a spiral track. The information face is covered with a reflective metal layer which is itself covered with a protective layer on the outer face of which a label indicating the content of the disc is fixed. The DVD disc is composed of two elementary discs each approximately 0.6 mm thick. The two elementary discs are adhesively joined between their rear parts, on the side of their respective information face, if present, by a thin layer of adhesive, resulting in a disc of approximately 1.2 mm in thickness. For optical reading, the thickness of the substrate traversed by the laser beam is 1.2 mm and 0.6 mm respectively for the compact disc and for the DVD disc. The compact disc techniques use EFM modulation, the CIRC error correction code and the read wavelength? = 780 nm, while the DVD technique uses 8/16 modulation, the RSPC error correction code and the reading length? = 650 nm or 635 nm. Therefore, a reader designed only for a DVD disc is not compatible with reading compact discs. To ensure more compatibility that allows a DVD player to read compact discs, a laser source which is dedicated to reading compact discs should be included in the DVD player, this substantially increases the price of such readers. In addition, although the greater compatibility of DVD players allows compact discs to be read, such is not the case for conventional CD players which can not, in any case, read DVD discs since such readers do not include an electronic unit. and a laser which is specific for reading DVDs. The aim of the present invention is to solve this compatibility problem with respect to the reading of compact discs and DVD discs and at the same time to propose a simple and inexpensive solution. The invention proposes a novel type of optical disc which combines the advantages of compact discs and DVD discs that can also be read by CD players and DVD players. The invention also proposes a method for manufacturing this novel type of optical disk. The optical disk according to the invention is composed of two elementary disks assembled by adhesive bonding between each other, each elementary disk contains a transparent substrate with at least one face of information provided with surface microallocations distributed on a spiral track or concentric tracks and designed to be read with the aid of a laser beam. The microalterations may be in the form of microwells, microprotrusions and / or continuous slots. The information face of the first elementary disk is covered with a semi-reflective layer adjacent to the adhesive assembly layer, which is transparent. The information face of the second elementary disk is coated with a reflective metal layer and positioned opposite the adhesive assembly layer. Subsequently, a protective layer covers the reflective metal layer of the second disk so as to hold a label for the disk. The semi-reflective layer has a transmission coefficient greater than or equal to a first predetermined value for a laser wavelength greater than or equal to a first threshold. In addition, the semi-reflective layer has a reflection coefficient greater than or equal to a second predetermined value for a laser wavelength less than or equal to a second threshold. Preferably, the first threshold is greater than the second threshold by at least 100 nm. Advantageously, the information face of the first elementary disk and the information side of the second elementary disk satisfy two different standards, for example, DVD and CD. Preferably, the first predetermined value for the transmission coefficient is equal to 95%. The second default value for the reflection coefficient is equal to 25%. For the application of the optical disc within the CD and DVD compatibility structure, the wavelengths used are in the order of 780 nm for the first threshold and in the order of 650 nm for the second threshold, and the total thickness of the disc is 1.2 mm. A secondary information face of the second elementary disk, adjacent to the adhesive assembly layer on the opposite side of the reflective metal layer, can be produced. The secondary information side is coated with a semitransparent layer which has characteristics similar to that of the semi-reflective layer of the first elemental disk versus the laser wavelength, and should not substantially impede the normal reading of the semi-reflective layer and the layer reflective The invention will be better understood with the aid of the detailed description of some modalities which are taken as non-limiting examples and which are illustrated by the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of an optical disk in accordance With the invention, Figure 2 is a detailed sectional view through the optical disc of Figure 1, according to a first embodiment of the invention, Figure 3 is a characteristic curve of a semi-reflective layer according to the invention, Figure 4 is a schematic diagram with respect to the manufacture of the disk according to the embodiment of Figure 2, Figure 5 is a detailed sectional view through the optical disk of Figure 1, according to a second embodiment of the invention, figure 6 are two characteristic curves of a semi-reflective layer and a semitransparent layer, according to the invention, and figure 7 is a schematic diagram co with respect to the manufacture of the disc according to the embodiment of Figure 5. As illustrated in Figure 1, the optical disc of the invention is composed of two elementary discs DI, and D2 assembled together with the help of a transparent adhesive layer 3. Next, the description will refer to the CD and DVD standards in a manner that facilitates the understanding of the invention without this constituting any limitation with respect to other applications or other standards of optical discs. In the particular application, in order to ensure disc compatibility with CD and DVD standards, each of the two elementary discs DI and D2 have a thickness of approximately 0.6 mm. The diameter of the optical disc is 8 cm or 12 cm. The total thickness of the disc is approximately 1.2 mm.

Figure 2 illustrates diagrammatically the structure of the disk according to a first embodiment of the invention. The first elementary disk DI and the second elementary disk D2 are assembled together by the transparent adhesive layer 3. The elementary disk DI consists of a layer 4 of transparent substrate of approximately 0.6 mm in thickness. The upper face 4a of the transparent substrate 4 receives a read laser beam 5a or 5b. The lower face 4b of the information face of the substrate 4 includes micro-alterations 6 in the form of microwells or microprotrusions and is coated with a semi-reflective layer 6a. The microallocations 6 are distributed on a spiral track or on concentric tracks. Likewise, the second elementary disk D2 includes a transparent substrate 7 whose upper face 7a is adhesively bonded to the information face 4b of the first elementary disk DI with the aid of the transparent adhesive layer 3. The lower face 7b or the information face of the transparent substrate 7 includes a second series of micro-alterations 8 coated with a reflective metallic layer 9. The reflective metallic layer 9 is subsequently coated with a protective layer 10 whose outer face 10a can serve to hold a label or other item printed or adhered in relation to the contents of the disc. The second elementary disk D2 has a thickness of approximately 0.6 mm. Given the small thickness of the adhesive layer 3, the total thickness of the optical disc is approximately 1.2 mm.

The information face 4b of the first elementary disk DI produced according to the DVD standard and coated with the semi-reflective layer 6a is proposed to be read optically by the laser beam 5a with a wavelength? = 650 nm or 635 nm. The laser beam 5a is brought into contact with the first elementary disk DI by means of the upper face 4a of the transparent substrate 4, and then passes through the thickness of the transparent substrate 4 and focuses on the information face 4b. Part of the laser beam 5a is reflected by the semireflective layer 6a so that it is read optically by the photodetectors (not shown) and to generate information by means of the reader (not shown). Another part of the laser beam 5a passes through the semi-reflective layer 6a. If the absorption of the laser beam by the semi-reflective layer 6a is eliminated, the sum of the transmission coefficient and the reflection coefficient of the layer 6a is equal to 1. The laser beam 5a transmitted by the semi-reflective layer 6a traverses the layer in its section 3 transparent adhesive and the transparent substrate 7 before being reflected by the information face 7b of the second elementary disk 2 coated with the reflective metallic face 9. Given the numerical aperture of the objective of the reader (not shown) with respect to the laser beam 5a, the point of light generated by the laser beam 5a on the information face 7b of the second elementary disk is relatively large and unfocused. Therefore, the beam of light reflected by the reflective layer 9 is strongly diffracted by the information face 7b before being filtered again by the semi-reflective layer 6a and then emerges again from the disk via the face 4a of the first elementary disk. Any alteration to the optical reading of the semireflective layer 6a is minimized in this way. A laser beam 5a which has a wavelength of 780 nm is used to read the information face 7b produced according to the CD standard. For this wavelength, the semireflective layer 6a has a large transmission coefficient so as to minimize the energy losses of the laser beam designed for reading the information face 7b of the second elementary disk D2. The laser beam 5b is focused on the information face 7b and reflected by the reflective metallic layer 9. The reflected beam again passes through the semirreflective layer 6a and travels towards the reader's objective (not shown). It is important that the presence of the semi-reflecting layer 6a does not damage the quality of the optical reading of the information face 7b. In practice, the semireflective layer 6a has a reflection coefficient of more than or equal to 25% of the wavelengths less than or equal to 650 nm, and a transmission coefficient greater than or equal to 95% for wavelengths of more than of, or equal to, 780 nm (see Figure 3). Figure 4 illustrates diagrammatically the process for manufacturing the optical disk according to the invention. He . first elementary disc DI and second elementary disc D2 are produced in two parallel production lines. The elementary disc DI is produced by pressing a transparent substrate with the help of a standard DVD mold so that it forms a substrate of approximately 0.6 mm in thickness which includes an information face according to the DVD standard. Then a semi-reflective layer is deposited on the information face produced in this way. Likewise, the second elementary disk D2 is obtained by processing a transparent substrate with the aid of a mold so that a substrate of approximately 0.6 mm thickness is formed and having an information face according to the CD standard. The information layer obtained in this way is then coated with a reflective metallic layer and a protective layer. The two elementary discs DI and D2 obtained in this way are assembled together. With the aid of a thin transparent adhesive layer, the semi-reflective layer is adjacent to the adhesive layer while the reflective layer is placed on the opposite side of the face which receives the adhesive. The disc obtained in this way includes a DVD information face with a depth of 0.6 mm and a CD information face with a depth of approximately 1.2 mm. In figure 5 a second embodiment of the disc is represented which differs from the first embodiment by the adhesion of a secondary information face 7a in the second elementary disk D2. The disk according to Figure 5 is, in all other aspects, comparable with the disc described above, which is referred to in Figure 2. Here, the same reference numbers are reused simply to designate the same elements of the disk . Only the difference in this second modality with respect to the first modality is described below. The secondary information side 7a is produced on this transparent substrate face 7 which is adjacent to the transparent adhesive layer 3 and is opposite the information face 7b of the second elementary disk D2. The secondary information side 7a also includes microalterations 11 similar to those of the information face 4b of the first elementary disk DI, in the sense in which they are designed to be read according to the DVD standard as opposed to the information face 7b of the second elemental disk D2 which is designed to be read in accordance with. the CD standard. The secondary information side 7a is covered with a semitransparent layer 12 which is practically transparent with respect to the wavelength of 780 nm and which has a reflection coefficient greater than or equal to 45% with respect to the wavelengths less than or equal to 650 nm. Therefore, if it is considered that the energy of the light beam arriving at the optical detectors of the reader (not shown) must be greater than or equal to 25% of the energy of the incident laser beam 5c, the reflection coefficient of the Information face 4b of the first elementary disk 4 with respect to lengths less than or equal to 650 nm must be greater than or equal to 25%. This implies that the transmission coefficient of the semi-reflective layer 6a is less than or equal to 75%. To compensate for this, the reflection coefficient of the semitransparent layer 12 must be greater than or equal to 45%. Therefore, the laser beam 5c is focused on the secondary information side 7a for reading it and has a part that has the semi-transparent layer 12 of lower energy crossed compared to the first modality, so that the alterations related to the return of the laser beam reflected by the reflecting metallic layer 9 of the second elementary disk D2 are minimized further. In figure 6, two characteristic curves of the semi-reflecting layer 6a and the semitransparent layer 12 are illustrated. Reference will be made to Figure 7, which shows the manufacturing steps, in order to produce the optical disc of Figure 5. Two parallel lines are considered to produce the elementary disks DI and D2. The manufacture of the elementary disk DI is identical to the process described with respect to figure 4. For the manufacture of the elementary disk D2, a transparent substrate is pressed by means of a mold so that two faces of information are produced according to the DVD standards and CD, respectively. Then a semitransparent layer is deposited on the DVD information side and a reflective metal layer on the CD information side. The reflecting layer is then covered with a protective layer. The DI and D2 elementary discs produced in this way are joined together with a transparent adhesive, the information faces produced according to the DVD standard are joined face to face. The optical disc produced in this manner includes two layers of DVD information and a CD information layer, and therefore the storage capacity of the disc is increased. Semi-reflective layer 6a and semitransparent layer 12 can be produced using materials such as polydiacetylene or cholesteric polymer (e.g., by thin layer deposition) whose spacing can be detected to change the reflection and transmission characteristics as a function of the length of wave of light. By virtue of the invention, existing hardware can be used to play CDs and DVDs to produce, at low cost, an optical disc which is equally compatible with DVD players as with CD players without that it is necessary to produce a DVD player compatible with CD. This new type of disc makes it possible to reconcile the practical concerns of consumers regarding the compatibility between CD and DVD discs, and also to generate new markets for the discs, for example: the notch of a film or a concert recorded in stereo on the face of information CD and recorded in the Dolby perimetric digital system AC-3 on the face of DVD information; an audio album on the face of CD information and the associated video images on the face or faces of DVD information; all the songs of a singer in the face or faces of information DVD and its 20 best songs in the face of information CD; a film on the face or faces of information DVD and the original track or musical extracts of the film on the face of information CD, etc. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers. Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. An optical disc composed of two elementary discs assembled by adhesive bonding to each other, each elementary disc has at least one transparent substrate with an information face provided with microallocations on the surface distributed over a spiral track or concentric tracks and designed to be read optically With the aid of a laser beam, the optical disk is characterized in that the information face of the first elementary disk is coated with a semi-reflective layer adjacent to the adhesive assembly layer, which is transparent, if because the information side of the second disk is transparent. Elemental is coated with a reflective metal layer and is positioned opposite the adhesive assembly layer.

2. The optical disk according to claim 1, characterized in that the information faces of the elementary disks are produced according to two mutually different standards.

3. The optical disk according to claim 1 or 2, characterized in that the semi-reflective layer has a transmission coefficient greater than or equal to the first predetermined value for a laser wavelength greater than or equal to the first threshold and a reflection coefficient greater than or equal to a second predetermined value for a laser wavelength greater than or equal to a second threshold, the first threshold is greater than the second threshold by at least 100 nm. 5

4. The optical disc in accordance with the claim 3, characterized in that the first predetermined value for the transmission coefficient is equal to 95% and because the second predetermined value for the reflection coefficient is equal to 10 25%.

5. The optical disk according to any of the preceding claims, characterized in that the information face of the first elementary disk produces in accordance with the 15 standard DVD and the information side of the second elementary disc is produced with the CD standard, and because the elementary discs each have a thickness of approximately 0.6 mm.

6. The optical disk according to one of the preceding claims, characterized in that the second elementary disk includes a secondary information face adjacent to the adhesive assembly layer and coated with a semitransparent layer.

7. The optical disk according to claim 6, characterized in that the semitransparent layer has a reflection coefficient greater than or equal to 45% for a laser wavelength less than or equal to the second threshold, and a transmission coefficient greater than or equal to 95% for a laser wavelength greater than or equal to the first threshold.

8. The optical disk according to any of the preceding claims, characterized in that the semi-reflective layer of the first elementary disk and / or the semitransparent layer of the second elementary disk is produced with the aid of a thin-layer deposition of polydiacetylene or cholesteric polymer.

9. A process for manufacturing the optical disk according to claim 1, characterized in that the first elementary disk is produced by pressing a transparent substrate so that an information face is formed according to a first standard, the face of information is covered with a semi-reflecting layer; a second elementary disk is produced by pressing a transparent substrate so that an information face is formed according to a second standard, the information face is coated with a reflective metal layer and then protected with a protective layer; and the two elementary discs are assembled by adhesively bonding the two discs together, the information side of the first elementary disc is adjacent to the transparent adhesive layer and the information side of the second disc is opposite the adhesive layer.

10. The process according to claim 9, characterized in that, for the production of the second elementary disk, a secondary information side of the transparent substrate is pressed according to the first standard, the secondary information side is coated with a semitransparent layer before the assembly operation with the first elementary disk DI.