JPS6355745A - Double-face type optical recording medium - Google Patents

Abstract

PURPOSE:To permit recording and reproduction of both faces with a piece of optical head without turning over an optical recording medium by providing optical recording films having the optical characteristics different from each other respectively to both faces of a transparent substrate. CONSTITUTION:The magneto-optical recording films 2, 3 are respectively formed on both the front and rear faces of the transparent substrate 1. The recording films 2, 3 are so formed as to have the characteristics different from each other. For example, these films are so formed that the optical rotatory angle of the film 2 is different from the optical rotary angle of the film 3. Since the optical recording medium is formed in the above-mentioned manner, the recording and reproduction of the recording surfaces 2, 3 is permitted by projecting laser light 8 to the medium from one side. The recording and reproduction of both faces are thus permitted with a piece of the optical head without turning over the optical recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a double-sided optical recording medium, and more specifically, a double-sided optical recording medium that can be rewritten and read from one side of the optical recording medium. This relates to the recording medium 1 thick.

A typical optical recording medium for conventional projection is an optical disk. In order to make it possible to record information on both sides of an optical disc, conventionally two substrates with a recording film formed on only one side have been fabricated, and these have been integrated into one structure. Examples of such optical discs are shown in FIGS. 3 and 4.

FIG. 3 is a sectional view of an example of an optical disk having an air sandwich structure. A transparent material with relatively low birefringence, such as polycarbonate (PC) or polymethyl methacrylate (PMMA), is used as the substrate 21,22.

A recording film 23 is formed on one side of the substrate 21 . An anti-oxidation film 27 is formed on the recording film 23 for the purpose of preventing oxidation of the recording film. On the other hand, the other surface of the M plate 21 is coated for the purpose of protecting the substrate 21. This covering is made of a hard transparent material 25 so that laser light used for information recording and reproduction can pass therethrough. The structure of the substrate 22 is similar to that described above, with a recording film 24 and an anti-oxidation film 28 formed on one surface, and a hard transparent material 26 covering the other surface.

The substrates 21 and 22 having the above-described configuration are bonded together with spacers (not shown) sandwiched between the inner and outer peripheries, with the recording films 23 and 24 facing inside. Antioxidant film 27
．． A portion surrounded by 28 and a spacer is a hollow portion 29 in which air, an inert gas, or the like exists.

The optical disc shown in FIG. 4 also has substantially the same configuration as the optical disc shown in FIG. 3. The difference is that the hollow portion 29 is filled with an adhesive film 30. Therefore, a spacer is not required in this case.

In order to record and reproduce information on both sides of these optical discs, laser light is incident from the outside of the optical disc through the substrate and focused on the recording film. It is operationally convenient to pass the laser beam through the substrate in this way when focusing the laser beam. The thickness of the substrate is approximately 1 mm. Since laser light is incident from two opposing directions, it is necessary to prepare one optical head on each side of the optical disk. If there is only one optical head, the optical disc must be taken out and turned over.

Problems to be Solved by the Invention As described above, conventional double-sided optical discs have a structure in which two independent substrates are bonded together, so they are more than twice as thick as single-sided recording optical discs. As a result, there are major drawbacks such as poor usability and large storage volume.

Furthermore, when two optical heads are provided, there is a problem that the recording and reproducing apparatus becomes large-scale. If only one optical head is used, the recording/reproducing apparatus may be made smaller, but an extra operation of once taking out the optical disk itself and turning it over is required.

Regarding the optical disk of the air sandwich structure shown in FIG. 3, the structure is relatively complicated, especially since it is necessary to provide holes in order to prevent a pressure difference between the hollow portion 9 and the outside of the optical disk.

In addition, in the case of a structure with an adhesive film, such as the optical disc shown in Figure 4, an additional intermediate layer is added to match the difference in physical properties such as the coefficient of thermal expansion between the adhesive film and the recording film. There are some things that need to be set up.

Therefore, the present invention provides recording and recording from either one side or both sides.
To provide a thin double-sided optical recording medium that can be reproduced and is easy to use.

Means for Solving the Problems In order to solve the above problems, the double-sided optical recording medium of the present invention comprises one transparent substrate and a first optical recording film formed on one side of the substrate. and a second optical recording film formed on the other surface of the substrate and having optical characteristics different from those of the first optical recording film.
and an optical recording film.

According to a preferred embodiment, the first and second optical recording films are magneto-optical effect films, and the angle of optical rotation of the first optical recording film and the angle of optical rotation of the second optical recording film are different.

According to another preferred embodiment, the first optical recording film is a rewritable magneto-optical film, and the second optical recording film is a write-once type.

Furthermore, the surface of each of the above-mentioned optical recording films can have an anti-oxidation film, and can also have a hard transparent material. According to a more preferred embodiment, an antioxidant film is provided on the surface of each of the recording films, and a hard transparent material is further provided on the surface of the polyoxidant film.

Function As described above, according to the present invention, a double-sided optical recording medium is constructed by forming recording films on both sides of one substrate. Therefore, the thickness can be reduced compared to conventional double-sided recording optical recording media that require two substrates. In particular, the double-sided optical recording medium of the present invention is characterized in that it has approximately the same thickness as a conventional single-sided optical recording medium. Therefore, it can be applied to single-sided recording and reproducing devices, and can also be applied to double-sided recording and reproducing devices. In addition, by using only one side, it can be used as a single-sided optical recording medium.

Furthermore, since the substrate is transparent, it is possible to record and reproduce information on the recording films on both sides of the substrate by simply irradiating laser light from one direction. Therefore, by using a recording and reproducing device that can adjust the focus of the laser beam, double-sided recording and reproducing can be performed without the need to turn over the optical recording medium, unlike conventional methods.

In particular, since the optical properties of the optical recording films provided on both sides of the substrate are different from each other, when detecting light from one optical recording film during reproduction, it is easy to separate the light from the other optical recording film. , or the effect of light can be eliminated.

Example The present invention will be explained below using the drawings.

FIG. 1 is a sectional view of an embodiment of a magneto-optical disk embodying the present invention. As the substrate 1, transparent PC, PMMA, etc. are used. Magneto-optical recording films 2.3 are formed on both the front and back surfaces of this substrate 1, respectively. A magnetic material that produces the Faraday effect is used as the magneto-optical recording film. For example, polycrystalline materials! , InB1. ! , InCuB1
．． Or amorphous TbFe, GdCo, GdTbF
e etc. are used. An anti-oxidation film 4.5 is formed on each magneto-optical recording film 2.3 for the purpose of preventing oxidation and the like. Each anti-oxidation film 4.5 is further covered with a hard transparent material 6.7 for protection purposes.

Furthermore, the magneto-optical recording films 2.3 are made to have different characteristics from each other. For example, the angle of optical rotation of the recording film 2 is set to be different from the angle of optical rotation of the recording film 3.

Typically, it is possible to have the optical rotation angles in opposite directions in both recording films 2.3. For this purpose, when adding a rare earth element to the material constituting the recording film 2.3, the amount added is increased to provide right-handed rotation, and the addition amount is decreased to provide left-handed rotation.

FIG. 2 is a cross-sectional view of another embodiment of the optical disc according to the invention. Although it has the same structure as the embodiment shown in FIG. 1, the recording film 2 is a rewritable type magneto-optical recording film, but the recording film 3 is a write-once type. In this case, since the write-once type is not rewritable, information such as the medium name that does not need to be erased or that should not be erased is written on the recording film 3.

Next, information recording and reproduction will be explained using the optical disc shown in FIG. 2 as an example.

Information is recorded by thermomagnetic recording. The magnetization of the recording film is aligned in one direction using a strong magnetic field.

Next, as shown in FIG. 2, incident light 8 from a laser is incident on the recording film surface from below. In this case, the incident light 8 is made to converge on the recording film on which recording is desired. For example, when focusing on the recording film 2, the laser beam passes through the substrate 1, which makes it relatively easy to focus the laser beam, but when focusing on the recording film 3, a separate magneto-optical disc is used that corresponds to the substrate. and the laser light source. In this way, the recording section is heated by laser beam irradiation and at the same time a bias magnetic field is applied. As a result, recording can be performed by reversing the magnetization of the recording section with a small bias magnetic field.

The Faraday effect is used to reproduce recorded information.

The linearly polarized liquid incident light 8 is focused on the recording film whose recording is to be reproduced. The transmitted light 9 rotates corresponding to the magnetization state of the portion where the incident light 8 is focused on the recording) [support]. By detecting the rotation of the polarization plane of this transmitted light 9,
Read recorded information. In this case, if the optical rotation angles of the magneto-optical recording films on both sides of the magneto-optical disk are different, especially if there is a relationship between 10 and 1 θ, there is a difference of 20 between the two.

Therefore, if the direction of the analyzer of the light-receiving element is set so that the light that has been optically rotated after passing through one magneto-optical recording film is detected at maximum output, the light that has been optically rotated when passing through the other magneto-optical recording film will be substantially detected. can be excluded. Therefore, for example, if the light-receiving element is divided into two parts, the analyzer attached to the negative divided light-receiving element is positioned according to the optical rotation characteristics of one of the magneto-optical recording films, and the analyzer attached to the other divided light-receiving element is positioned according to the optical rotation characteristics of the other magneto-optical recording film.

Furthermore, when performing recording by irradiating light onto an optical recording medium for double-sided recording, consider the case where the focus is set on the recording film 2 located on the back side when viewed from the incident side. The incident light naturally passes through the recording film 3 in the front, but if the thickness of the substrate 1 is about 1 mm, the influence of the recording film 3 in the front on the recording film 2 in the back is 0.1% in terms of power. That's about it. The same can be said for playback.

Therefore, the influence of one recording film on the other recording film is
The size is large enough to cause no problem in either recording or reproduction.

Note that when handling an optical recording medium in a special cartridge, there is usually no danger of humans touching the optical recording medium directly, so the hard transparent material 6.7 can be made extremely thin or may not be provided. It is.

Furthermore, if the recording film 2.3 is made of a material that does not easily deteriorate due to oxidation, it is not necessary to provide the anti-oxidation film 4.5. Further, in the above embodiment, only one substrate was used, but two sets of substrates each having a recording film provided on only one side may be directly bonded back to back.

In the above embodiments, the present invention has been described with reference to a disk-shaped optical recording medium, but it is obvious that the present invention can be applied to any other shape such as a card, tape, etc.

Furthermore, in the above embodiments, an optical recording medium using the Faraday effect has been described, but the present invention is applicable not only to an optical recording medium using the Kerr effect in the same way, but also to other rewritable optical recording media and various types of optical recording media. It is obvious that the present invention can also be applied to read-only optical recording media and write-once optical recording media.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, one
The two-sided optical head enables recording and playback on both sides of the optical recording medium without flipping it over, so the configuration and dimensions of the device can be exactly the same as those for single-sided recording, and the reversing operation of the optical recording medium is This has the advantage of being unnecessary.

Further, according to the present invention, since the thickness of the double-sided optical recording medium can be made almost the same as that of the single-sided recording medium, the double-sided optical recording medium according to the present invention can be used as both a single-sided optical recording medium and a double-sided optical recording medium. .

Therefore, there is an advantage that the dimensions of the cartridge and the device can be exactly the same.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a double-sided magneto-optical disk according to the present invention, FIG. 2 is a sectional view of another embodiment of a double-sided optical disk according to the present invention, and FIG. 3 is a sectional view of a conventional double-sided optical disk. FIG. 4 is a sectional view of another embodiment of a conventional double-sided optical disc. (Main reference numbers) 1.21.22... Substrate, 2, 3.23.24... Recording film, 4, 5, 27.28... Antioxidant film, 6, 7, 25.26... Hard Transparent material, 8...Incoming light, 9...Transmitted light,

Claims (6)

[Claims] (1) One transparent substrate, a first optical recording film formed on one surface of the substrate, and optical characteristics of the first optical recording film formed on the other surface of the substrate. The second of different characteristics
What is claimed is: 1. A double-sided optical recording medium comprising: an optical recording film; (2) A patent characterized in that the first and second optical recording films are magneto-optical effect films, and the optical rotation angle of the first optical recording film and the optical rotation angle of the second optical recording film are different. A double-sided optical recording medium according to claim 1. (3) The double-sided structure according to claim 1, wherein the first optical recording film is a rewritable magneto-optical effect film, and the second optical recording film is a write-once type. type optical recording medium. (4) The double-sided optical recording medium according to any one of claims 1 to 3, wherein the surface of each optical recording film is coated with an antioxidant film. (5) The double-sided optical recording medium according to any one of claims 1 to 3, wherein the surface of each optical recording film is coated with a hard transparent material. (6) The surface of each of the above optical recording films is coated with an antioxidant film,
The optical recording medium according to any one of claims 1 to 3, wherein the surface of each antioxidant film is further coated with a hard transparent material.