Optical recording medium and method of recording and reproducing information thereon

Abstract: An optical tape including an optical recording layer for permitting information to be optically recorded thereon and a light-reflective magnetic layer. The light-reflective magnetic layer which reflects light projected onto the recording layer, also permits magnetic recording or magneto-optical recording to be performed thereon, thereby increasing a storage capacity of the optical tape remarkably. Further, the optical tape is provided with a layer to form guiding grooves for tracking control. The layer to form guiding grooves is made up of ultraviolet-hardening resin, photo-resist, or a photochromic material. For example, in the case of using ultraviolet-hardening resin, after a guiding groove pattern has been exposed by projecting an ultraviolet ray on a layer made up of ultraviolet-hardening resin, the exposed areas harden to form areas corresponding to guiding grooves between those exposed areas. The guiding grooves are formed by-removing the areas corresponding to guiding grooves from the layer made up of the ultraviolet-hardening resin. Additionally, along with a guiding groove pattern, an index pattern can also be exposed. The guiding grooves thus formed do not reduce the recording density for information of the optical tape.

Description: FIELD OF THE INVENTION The present invention relates to an optical recording medium such as an optical disk, optical card, or optical tape on or from which optical recording/reproduction is performed and more-particularly to an optical recording medium having an increased storage capacity. BACKGROUND OF THE INVENTION Conventionally, various optical disks for providing optical recording and/or reproduction such as those of read-only type, that is, so-called compact disks and the like, of DRAW type capable of writing desired information only once and of rewritable type have been known. Among those optical disks, in those of the type such as read-only type, which record information by the use of pits physically provided thereon, so-called tracking control is performed by directing a light beam onto the center of a pit row. On the other hand, in magneto-optical disks and the like which record information without using such pits physically recorded, tracking control is provided, in general, by installing guiding grooves with a rectangular shape in their cross-section, indicating a recording path of information, preliminarily formed on a substrate. In those optical disks described above, detection of information is performed based on a reproduced light transmitted through a recording layer or on a reflected light obtained by allowing a reproduced light transmitted through a recording layer to reflect from a reflective layer suitably disposed. For example, a metal film made of A1 or the like is employed as the reflective layer in a magneto-optical disk where reflection-type detection is performed. In the meantime, recently studies on optical cards and so-called optical tapes have been carried out to provide an optical memory medium other than optical disks. In those optical cards and optical tapes, recording and/or reproduction is performed by utilizing the same principle as the optical disks. For example, an optical tape is basically composed of an elongated film substrate, an optical recording layer provided on the film substrate, on which recording of information is performed by utilizing the magneto-optical effect, photochromism, etc. and a protective layer for protecting the optical recording layer For those optical tapes, the following arrangement is suggested as in the case of magnetic tapes for VTR (Video Tape Recorder): an optical tape is stored in a cassette case; a portion thereof is taken out from the cassette case to be brought into an operative position for recording or reproduction; tracks as paths for information recording are predeterminately set in a direction slanting to the longitudinal direction of the optical tape so as to permit recording and/or reproduction. Meanwhile, in those optical tapes, since a substrate thereof is generally thin as well as flexible, it is extremely difficult to form on the substrate guiding grooves for providing tracking control. Hence, a method for providing tracking control for optical tapes is disclosed, for example, in Japanese Patent Laid-Open Publication No. 63-117326 (117326/1988). The system described therein provides straight guiding patterns which are optically recorded on a recording layer prior to recording operation, being predeterminately disposed in positions parallel to and adjacent to actual tracks, and performs recording and reproduction in parallel with the guiding patterns while reproducing the guiding patterns. In the meantime, the above-mentioned optical recording medium generally enables high recording density for information, and therefore has a comparatively large storage capacity, yet it is desired to further increase the storage capacity with the thought of using the medium for long-time recording of music information and video information or enabling, for example, double recording etc. of information in order to prevent the loss of information due to external causes. However, for the above-mentioned method, it is necessary to additionally install a light source for recording the guiding patterns, another light source for reproducing the guiding patterns, a photodetector and so on in addition to a light source, a photodetector, etc. for recording or reproducing information on or from the optical tape. Therefore, the arrangement presents problems that the number of parts of an optical head for the optical tape is increased, the cost becomes high, and the recording density of information is lowered due to the fact that the guiding patterns are recorded on the recording layer in addition to information. JP-A-60-70543 discloses an information recording carrier with an increased recording capacity comprising in this order, a substrate, an optical recording layer of the phase change type for optically recording information and a magnetic layer for magnetically recording information. JP-A-59-223967 discloses an optical disk having a photomagnetic layer and an optical layer in which separate writing on the two layers is performed. SUMMARY OF THE INVENTION The present invention is defined by claim 1 whose preamble relates to the disclosure of JP-A-60-70543. A method of recording and reproducing information on and from the recording medium of claim 1 is defined by claim 12. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 3 illustrate respective embodiments of the present invention in detail. Fig. 1 is a schematic vertical sectional view showing an optical tape of a first embodiment of the present invention. Fig. 2 is a schematic vertical sectional view showing an optical tape of a second embodiment of the present invention. Fig. 3 is a schematic vertical sectional view showing an optical tape of a third embodiment of the present invention. DESCRIPTION OF THE EMBODIMENTS The following description will discuss one embodiment of the present invention referring to Fig. 1. An optical tape 1 as one example of optical recording media is provided thereon with a film substrate 2 (with a thickness of substantially 5µm to 100µm) made of flexible polymeric resin with light transmission and heatproof characteristics, such as polyethylene terephthalate. On the substrate 2 is formed an optical recording layer 3 made of a photochromic material such as spiropyrane or fulgide by means of spattering, vapor deposition, or coating. Further, on the optical recording layer 3 is formed a light-reflective magnetic layer 4 made of CoCr or the like. With the above structure, in recording on the optical recording layer 3, desired information can be recorded thereon by allowing a light beam projected from a laser (not shown) to be converged onto the optical recording layer 3 from the substrate 2 side through a converging lens 5 and thus by changing refractive index of the light-converged portion. Moreover, in reproducing information recorded on the optical recording layer 3, reproduction can be performed by receiving a light reflected from the light-reflective magnetic layer 4 by a photodetector (not shown) after applying a light beam with a wavelength or a luminous intensity by which no information can be recorded onto the optical recording layer 3. On the other hand, magnetic recording and reproduction to be applied to the light-reflective magnetic layer 4 are performed by a magnetic head 6 disposed at the side of the light-reflective magnetic layer 4. As described above, by recording information individually on the optical recording layer 3 and the light-reflective magnetic layer 4, a storage capacity of the optical tape 1 can be increased. Here, the following description will discuss an example of effective use of the optical tape 1 with the above-mentioned structure. For example, such an application of the optical tape 1 is preferable that data for computers are recorded on the optical recording layer 3 of the optical tape 1 while music information, video information, or the like is recorded on the light-reflective magnetic layer 4. With the application, although a recording/reproduction device for use with a photochromic medium is necessary in recording or reproduction of data for computers, magnetic recording/ reproduction devices such as magnetic tape cassette units that the users already have can be used in recording or reproduction of music information, video information or the like. Another example of its application is proposed, wherein, for example, secret codes are preliminarily recorded on both of the respective optical recording layer 3 and light-reflective magnetic layer 4, and unless those secret codes are decoded, recorded information can not be read out. Thus, the application can increase reliability against stealing data. As still another example of its application, it is suggested that the same information should be recorded on both the optical recording layer 3 and the light-reflective magnetic layer 4. In that case, if information recorded on the optical recording layer 3 should be lost by light mistakenly applied on the optical recording layer 3 due to an external cause, the information still remains on the light-reflective magnetic layer 4, while if information recorded on the light-reflective magnetic layer 4 should be lost by a magnetic field mistakenly applied on the light-reflective magnetic layer 4, the information still remains on the optical recording layer 3. Thus, reliability for preserving information can be increased. Additionally, besides the above-mentioned applications, it is obvious that data for computers may be recorded on both the optical recording layer 3 and the light-reflective magnetic layer 4, or music information, video information or the like may be recorded on both the optical recording layer 3 and the light-reflective magnetic layer 4. In the first embodiment, the optical recording layer 3 is formed of a photochromic material, yet in lieu of the structure, the optical recording layer 3 may be made up of a material such as that of the so-called phase change type, DRAW type, or other type. Moreover, in the first embodiment, the optical tape 1 is used as the optical recording medium, yet in a like manner, an optical disk or optical card composed of a substrate 2, an optical recording layer 3 and a light-reflective magnetic layer 4 may be employed. For example, in the case of fabricating the optical disk, the substrate 2 as a base plate may be formed of PC [Polycarbonate], APO [Amorphous Polyolefin], or PMMA [Polymethyl Methacrylate], having a thickness of substantially 0.3mm to 1.5mm. Next, the following description will discuss a second embodiment referring to Fig. 2. The second embodiment provides an optical tape 8 wherein another optical recording layer 7 is formed on the light-reflective magnetic layer 4 of the first embodiment. In addition, those of the members having the same functions and described in the first embodiment are indicated by the same reference numerals and the description thereof is omitted. The optical recording layer 3 or 7 may be formed of photochromic material. Moreover, it is preferable to make a thickness of the optical recording layer 7 as thin as possible, for example, not more than 1µm. With the above structure, recording of information onto the optical recording layer 3 is performed by projecting a light beam emitted from a laser (not shown) onto the optical recording layer 3 from a substrate 2 side through an objective lens (not shown), while reproduction of information from the optical recording layer 3 is performed by projecting on the optical recording layer 3 a light beam with a luminous intensity and a wavelength by which no information can be recorded on the optical recording layer 3 and by utilizing a resulting light reflected from a light-reflective magnetic layer 4. Further, in a like manner, recording and/or reproduction of information on or from the optical recording layer 7 is performed by projecting a light beam suitable for a recording or reproducing operation onto the optical recording layer 7 from above in the drawing. Furthermore, recording and/or reproduction of information onto a light-reflective magnetic layer 4 is performed by a magnetic head (not shown) through an optical recording layer 7 which is comparatively thin. With the structure of the second embodiment wherein two optical recording layers (optical recording layers 3, 7) are employed, a storage capacity thereof can be further increased compared with that of the first embodiment. Next, the following description will discuss a third embodiment referring to Fig. 3. An optical tape 10 of the third embodiment comprises a film substrate 2 having light transmission characteristic, and an optical recording layer 3 made of photochromic material is installed on the substrate 2 by means of sputtering or other processes. Further, a light-reflective magnetic layer 11 made of Pt/Co multi-layer film is disposed on the optical recording layer 3. The light-reflective magnetic layer 11, on the one hand functions as a reflective layer in the case of performing recording or reproduction on or from the optical recording layer 3, and on the other hand, serves itself as a medium on which information is recorded by magneto-optical recording method. Additionally, in the present specification, magneto-optical recording method is considered as one of magnetic recording methods. On the light-reflective magnetic layer 11, is formed a protective layer 12 which is made of ultraviolet-hardening type resin which hardened after having been coated, and thereby the optical recording layer 3 and the light-reflective magnetic layer 11 are protected in a sealed state by the protective layer 12 and the substrate 2. With the above structure, recording of information onto the optical recording layer 3 is performed by projecting a light beam for recording onto the optical recording layer 3 through the substrate 2, while reproduction of information from the optical recording layer 3 is performed by projecting through the substrate 2 a light beam with a luminous intensity or a wavelength by which no information can be recorded on the optical recording layer 3 and by utilizing a resulting light reflected from the light-reflective magnetic layer 11. On the other hand, magneto-optical recording of information onto the light-reflective magnetic layer 11 is performed by applying a magnetic field through the protective layer 12 while projecting onto the light-reflective magnetic layer 11 from the protective layer 12 side or the material base 2 side a light beam by which no information can be recorded on the optical recording layer 3. As to reproduction of information recorded on the light-reflective magnetic layer 11, it is performed by projecting a light beam from the protective layer 12 side or the material base 2 side and by detecting a reflected light back from the light-reflective magnetic layer 11 or a transmitted light through the light-reflective magnetic layer 11. Additionally, in the second and third embodiments, the description was given of an optical tape, yet it is obvious that the principles of the embodiments are applicable to other optical recording media such as optical disks or optical cards. As described above, the optical recording medium of the present invention comprises a substrate, an optical recording layer formed on the substrate, whereon recording is optically performed, and a light-reflective magnetic layer from which a light beam projected onto the recording layer is reflected and on which magnetic recording is performed. Therefore, since a light-reflective layer for use in reflection type optical recording is modified to form a light-reflective magnetic layer so as to add another function as a magnetic layer, the arrangement permits magnetic recording independently on the light-reflective layer of an optical recording medium, while permitting optical recording on the the optical recording layer thereof. Accordingly, a storage capacity of the optical recording medium can be increased compared with that of a conventional type having only an optical recording layer formed thereon. Having an increased recording capacity is advantageous, for example, in performing long-time recording of video information, music information or the like or duplicated recording of information.

Claims: An information recording medium (1,8,10) comprising, in this order, a substrate (2), an optical recording layer (3) for optically recording information, and a magnetic layer (4,11) for magnetically recording information, characterised in that the magnetic layer has a light-reflecting function with respect to recording and reproduction of information in the recording layer, and in that information is recorded and reproduced in the optical recording layer using light transmitted to the optical recording layer through the substrate and light reflected back to the optical recording layer from the magnetic layer. An information recording medium according to claim 1, wherein the optical recording layer (3) is made of photochromic material. An information recording medium according to claim 1 or claim 2, wherein the magnetic layer (4,11) enables information to be recorded therein magnetooptically. An information recording medium according to claim 3, wherein the magnetic layer is a multi-layer film (11). An information recording medium according to any of claims 1 to 4, further comprising a protective layer (12) formed on the magnetic layer such that the optical recording layer and the magnetic layer are protected in a sealed state by the protective layer and the substrate (2). An information recording medium according to any of claims 1 to 4, further comprising a second optical recording layer (7) for optically recording information, the first (3) and second (7) optical recording layers sandwiching the magnetic layer (4). An information recording medium according to claim 6, wherein the second optical recording layer (7) is made of photochromic material. An information recording medium according to any of claims 1 to 7, in the form of a tape and wherein said substrate comprises a film substrate. An information recording medium according to claim 8, as appendant to claim 6 or claim 7, wherein the second optical recording layer has a thickness of no more that 1 µm. An information recording medium according to any of claims 1 to 7, in the form of a disk. An information recording medium according to any of claims 1 to 7, in the form of a card. A method of recording and reproducing information on and from the information recording medium defined by claim 1, the method comprising: performing optical recording and reproduction of information using, in each case, both light transmitted to said optical recording layer of the medium through said substrate thereof and light reflected back to said optical recording layer of the medium from said magnetic layer thereof; and performing magnetic recording and reproduction of information on said magnetic layer of the medium by using a magnetic head. A method according to claim 12, wherein digital signals are recorded on the optical recording layer and analogue signals are recorded on the magnetic layer. A method according to claim 12, wherein the same information is recorded on the optical recording layer and the magnetic layer. A method according to claim 12, wherein secret codes are predeterminately recorded on the optical recording layer and the magnetic layer respectively, thereby preventing information from being read unless both of the secret codes are decoded.

Inventors: KATAYAMA HIROYUKI, NAKAYAMA JUNICHIRO, OHTA KENJI, TAKAHASHI AKIRA, VAN KAZUO, KATAYAMA, HIROYUKI, NAKAYAMA, JUNICHIRO, OHTA, KENJI, TAKAHASHI, AKIRA, VAN, KAZUO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G11B13
IPC codes: G11B20, G11B7, G11B23, G11B5, G11B11, G11B13