JPH0981963A - Optical information recording and reproducing medium and optical information recording and reproducing device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording/reproducing medium and an optical information recording/reproducing device using the relevant optical information recording/reproducing medium capable of reducing the effect of aberration due to the warpage of a transparent protection substrate and suppressing the effect of dirt and flaw of the transparent protection substrate as in the conventional manner. SOLUTION: A first information recording layer 104, an air layer 107 and a protection substrate 103 comprising having a second information recording layer 105 on the front surface under the layer 107, is arranged on the rear of the transparent protection substrate 101 of an optical information recording/ reproducing medium. The image of the converged light spot of luminous flux is formed in the first information recording layer by focusing servo operation of an objective lens, the luminous flux is transmitted through the transparent protection substrate through the air layer and the image of the converged light spot is formed on the second information recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording and reproducing information by an irradiated light beam, and more particularly to an optical information recording / reproducing medium having an air sandwich structure and an optical information recording. Reproduction device

[0002]

2. Description of the Related Art A transparent substrate having a predetermined thickness, which has been conventionally used, is irradiated with a light beam from its surface to write information on the information recording layer. In the optical information recording / reproducing apparatus that reproduces information based on the reflected light, the one having the configuration shown in FIGS. 3 to 7 is generally adopted. The three types of conventional optical information recording / reproducing apparatuses will be sequentially described below.

(Prior Art 1) FIG. 3 is a schematic diagram showing the configuration of a conventional general optical information recording / reproducing apparatus. In the figure, reference numeral 301 indicates a transparent protective substrate, 302.
Is a transparent protective substrate thickness, 303 is a protective substrate, 304 is an information recording layer, 306 is recorded information (phase pits) or guide grooves,
313 is an objective lens, 314 is a light flux, and 316 is a substrate surface light flux diameter. As a general configuration of the optical information recording / reproducing medium of the optical information recording / reproducing apparatus, a light flux 314 for writing / reproducing information on / from the information recording layer 304.
A transparent protective substrate 301, which is a protective substrate made of a member transparent to the wavelength of the light flux, is arranged on the side irradiated with. In the manufacturing process of the optical information recording / reproducing medium, a transparent protective substrate 301 is used by using a mold in which a phase structure such as a guide groove 306 to be arranged on the information recording layer 304 is formed.
The resin material to be the member is poured and molded. The information recording layer 3 is formed by forming a film with various thin film materials on the side on which the phase structure of the completed resin transparent protective substrate 301 is transferred.
It is common to form 04 (often composed of multiple layers). Further, a functional layer (such as a protective layer) other than recording is formed on the information recording layer 304, and information is recorded / reproduced by irradiating light rays from the side of the transparent protective substrate 301 opposite to the side on which the thin film is attached. To implement.

A typical optical information recording / reproducing medium of the related art is a CD or a magneto-optical disk, which is widely used as a product in the market. Both of these two products are 1.2 mm thick transparent resin substrates, and are manufactured by injection molding using a resin such as polycarbonate as a material, using a stamper in which phase structures such as guide grooves and information pits are formed in advance.

The recording or reproducing light beam 314 is emitted from the side opposite to the side on which the phase structure of the above-mentioned substrate is transferred and the recording film is formed, and the transparent protective substrate thickness 30 of 1.2 mm is obtained.
The light propagates through the second transparent protective substrate 301 and reaches the information recording layer 304 on the opposite surface of the transparent protective substrate 301.
In the transparent protective substrate 301, the light flux 314 is reflected by the information recording layer 304.
Information is recorded or reproduced by being irradiated with the laser beam to heat the magneto-optical recording film formed thereon or by being affected by the phase structure formed therein. That is, the light beam 314 converged through the objective lens 313 passes through the transparent protective substrate 301 of the medium and forms a focused spot on the information recording layer 304 formed on the back surface side thereof.

As is well known, the unit length of information recording of an optical medium such as a CD is in the order of submicron in the information recording layer 304. Therefore, if this surface is directly exposed to the air, Even if dust or dust of a size of several to ten and several microns is attached, the recorded information 306 over a considerable area is blocked from the light flux 314 and becomes unreadable. However, in an actual optical disc, the information recording layer 304 is sealed in the transparent protective substrate 301. Therefore, dust adheres only to the surface of the transparent protective substrate 301.

As a general example, consider the case where the effective diameter of the light beam at the entrance pupil of the objective lens is 4.0 mm and the numerical aperture is 0.45, that is, the transparent protective substrate thickness 302 in FIG.
The substrate surface light beam diameter 316, which is the diameter of the irradiation light beam on the surface of the transparent protective substrate 301 of 2 mm, is about 1.1 mm. Therefore, even if the surface of the transparent protective substrate 301 is slightly scratched or dust is attached, if it is smaller than the substrate surface luminous flux diameter 316, the effect on the entire luminous flux 314 that passes therethrough Is relatively small. Therefore, the light flux 314 reaching the information recording layer 304, which is the recording / reproducing surface inside the transparent protective substrate 301, can reproduce information without being affected by dust on the surface of the transparent protective substrate 301. This is because, as is well known, the optical information recording / reproducing medium is said to be resistant to scratches and dirt.

Further, the details will be described in the section of the problem to be solved by the invention.
In recent years, it has been proposed to thin 02 from a typical 1.2 mm thickness to 0.8 mm or 0.6 mm.

(Prior Art 2) FIGS. 4 to 6 are schematic structural views of a conventional optical information recording / reproducing apparatus having an air sandwich structure. FIG. 4 shows an example in which the information recording layer is set on the surface of the protective substrate. Reference numeral 40 in the figure
Reference numeral 1 indicates a transparent protective substrate, 402 a transparent protective substrate thickness, 403 a protective substrate, 404 an information recording layer, 407.
Is an air layer, 408 is an air layer thickness, 409 is a recording film, 410
Is recording information, 413 is an objective lens, 414 is a luminous flux, 41
6 is the light flux diameter on the substrate surface. In the general optical information recording / reproducing apparatus shown in FIG. 3, the light beam 314 irradiated on the information recording layer 304 propagates inside the transparent protective substrate 301, and the information recording layer 304 is transparent when viewed from the light beam 314. It is configured on the back surface side of the protective base 301. On the other hand, in the air sandwich structure shown in FIG. 4, the information recording layer 404 is set on the surface of the protective substrate 403, and the light beam 414 transmits the air layer 40.
7 (or a predetermined gas) to propagate through the information recording layer 404.
Is irradiated. However, in this state, there is a problem that recording and reproduction cannot be performed due to the adhesion of dust to the surface, but the transparent protective substrate 401 made of a transparent member is arranged slightly apart from the information recording layer 404. Therefore, the recording / reproducing light beam 414 is transmitted through the transparent protective substrate 401 and the air layer 407.
To reach the information recording layer 404. That is, the optical information recording / reproducing medium of FIG. 4 may be called an air sandwich because the air layer 407 is sandwiched between the transparent protective substrate 401 and the information recording layer 404.

FIG. 5 is an example disclosed as a schematic configuration diagram of an optical information recording / reproducing medium having an air sandwich structure. This example is based on Japanese Patent Application Laid-Open No. 52-156605. In the figure, reference numeral 501 is a protective plate, 503 is a carrier plate, 504 is an information recording layer, and 507 is an air layer. Since the above publication describes that either the protective plate 501 or the carrier plate 503 is transparent, when the protective plate 501 is transparent, it is the same as the example shown in FIG. (Note to the author: However, in the example shown in FIG. 5, only an example of irradiating and reading the light flux from the side of the carrier plate 503 is disclosed.) FIG. 6 shows a case where the information recording layer is set on the back surface of the transparent protective substrate. Is an example of. In the figure, reference numeral 601 is a transparent protective substrate, 602 is a transparent protective substrate thickness, 603 is a protective substrate, 604 is an information recording layer, 607 is an air layer, 609 is a recording film, 610 is recorded information, and 614 is a luminous flux. , 616 are the light flux diameters on the substrate surface. In the example of FIG. 4, a transparent protective substrate 401,
While the light beam 414 is irradiated to the recording film 409 through the air layer 407, in the example of FIG. 6, since the recording film 609 is attached to the back surface side of the transparent protective substrate 601, the light beam 614 is generated inside the transparent protective substrate 601. Converged.

Another example disclosed regarding the air sandwich structure is disclosed in Japanese Patent Laid-Open No. 53-1002. The optical information recording / reproducing medium of this example has the same structure as that shown in FIGS. 4 and 6.

In these examples, the purpose of adopting the air sandwich structure is to prevent the harmful gas emitted from the recording material at the time of writing from being contained in the medium so as not to go out. The recording material in this example is not the magneto-optical system but the irradiated light beam 41.
This is a method in which the recording material undergoes changes such as sublimation due to heat generated by Nos. 4 and 614.

(Prior Art 3) FIG. 7 is a schematic structural view of a conventional optical information recording / reproducing apparatus having a two-layer structure of a transparent protective substrate. In the figure, reference numeral 701 indicates a transparent protective substrate, 702 a transparent protective substrate thickness, 703 a protective substrate, 704 a first information recording layer, 705 a second information recording layer, and 706a a first recording layer. Information (phase pit), 706b is second recording information (phase pit), 71
1 is a transparent layer, 712 is a transparent layer thickness, 713 is an objective lens,
714 and 715 are luminous fluxes. In recent years, in response to a demand for a large capacity of an optical information recording / reproducing medium, a transparent protective substrate 701
It has been proposed to increase the capacity by using a two-layer structure. This is a first information recording layer 7 in a read-only optical disc, in which a base of an optical information recording / reproducing medium is molded and manufactured as in the past and information is recorded and formed by a phase structure or the like.
The second information recording layer 705 is formed by further stacking a thin transparent resin layer or the like on 04, and forming another information signal on the surface of the new transparent layer 711 to form a phase structure. . As shown in FIG. 7, the convergent light beam 714 is made incident from the side opposite to the side having the two-layered phase structure of the transparent protective substrate 701. First, a semi-transmissive reflective film is attached to the surface (first information recording layer 704) on which the light beam 714 strikes, and then a film having a high reflectance is applied to the surface (second information recording layer 705) on which the light beam 715 strikes. Attach. The first information recording layer 704 is directly connected to the second information recording layer 705 and the first information recording layer 705 is connected to the first information recording layer 705.
The first recording information 706a recorded on the surface of the first information recording layer 704 and the first recording information 706a recorded on the surface of the second information recording layer 705 by focusing on the surface to be reproduced respectively through Second record information 706
This is a method that makes it possible to read b separately.

[0014]

One of the major problems in producing an optical information recording / reproducing medium is the warpage of the substrate. The base of the optical information recording / reproducing medium is manufactured by a method such as injection molding a resin material into a mold using a master stamper, and further requires steps such as annealing treatment and film formation. In the final product, it is required to suppress the warpage of the substrate to some extent, and there are many factors that affect the warpage such as the stress of the thin film on the substrate.Therefore, various technical measures must be taken to control these. Needed.

The warp of the substrate is the amount by which the substrate tilts from the state in which the substrate is perpendicular to the optical axis of the recording / reproducing light flux converged by the objective lens. The reason why suppression is required is that if the medium substrate, which is a plane-parallel plate placed in the convergent light beam emitted from the objective lens, is placed inclined with respect to the optical axis, the convergent light beam has coma aberration. This is because an aberration component such as or astigmatism is generated, and the condensed spot on the recording / reproducing surface of the medium cannot be ideally narrowed down, which hinders recording / reproducing. For example, when the optical information recording / reproducing medium is a disc and it is curved like an umbrella around the spindle hub, the outer peripheral side of the disc is always close to the objective lens and the inner peripheral side is always closer to the objective lens. The base will tilt away from the objective lens. This always brings about a constant inclination regardless of the rotating state of the disk.

The magnitudes of coma and astigmatism caused by the tilting of the flat plate in the convergent light beam include the numerical aperture of the objective lens, the tilt of the plane-parallel plate, and the thickness of the plane-parallel plate. Thickness), and the magnitude of the refractive index of the plane-parallel plate. For example, the magnitudes of the coefficients of third-order coma aberration and astigmatism are both proportional to the substrate thickness itself, and are also proportional to the cube and square of the numerical aperture, respectively.

Therefore, conventionally, it has been a cause of lowering the yield of the medium because it cannot be used in performance unless it has a substrate with a small warpage.

The problems to be solved by the invention with respect to the conventional three types of optical information recording / reproducing apparatuses will be described below.

(Problem with Prior Art 1) The difficulty of suppressing the warpage of the substrate is an obstacle to improving the yield of the medium manufacturing. If this can be alleviated, the cost of the medium can be reduced. Become. Therefore, in consideration of the factor of the aberration generated by the inclination of the substrate, it is considered that the numerical aperture of the objective lens is reduced, the thickness of the substrate is reduced, and the substrate material has a low refractive index. However, reducing the numerical aperture of the objective lens
Since the size of the focused spot on the information recording layer is increased, the information recording density is reduced (the performance of the optical information recording / reproducing system is reduced), which is unacceptable. In addition, the base material is made of a resin material having a low refractive index even at present, and there is no material having a refractive index low enough to reduce the required accuracy of the warp of the base. Therefore, it is conceivable to reduce the accuracy required for the warp of the substrate by reducing the thickness of the substrate as the remaining method.

Recently, the proposed transparent protective substrate thickness is reduced to 0.
An optical disk device with a size of 8 mm to 0.6 mm is a measure against the fact that the manufacturing yield of the medium cannot be increased due to the warp of this substrate.

However, if the thickness of the substrate is reduced,
That is, the distance from the information recording layer of the medium to the surface of the base becomes short. As a result, the diameter of the light flux on the substrate surface, which is the diameter of the light flux when passing through the substrate surface, becomes smaller than that when the substrate thickness is large. This impairs the above-mentioned characteristic of the optical information recording / reproducing medium that is resistant to scratches and dust on the substrate surface. This is because, as described above, the larger the diameter of the light flux on the substrate surface with respect to the size of scratches and dust on the substrate surface, the less the influence of the light flux upon passing through the surface will be. Therefore, there is a problem in simply making the transparent protective substrate thin.

(Problem with Prior Art 2) In the example of Prior Art 2, an optical information recording / reproducing apparatus for recording information by thermal deformation (drilling) such as melting or sublimation of a recording material originally caused by irradiation of a light beam is described. Has been done. The most important reason for adopting the air sandwich structure in these examples is that it is necessary to contain a toxic substance such as gas generated when the recording material is deformed by receiving heat inside the medium. Also, it is to protect the information recording surface from dust.

In this example, two kinds of structures shown in FIGS. 4 and 6 are disclosed. For example, in the structure shown in FIG. 4, the transparent protective base is a thin disk, and in the structure shown in FIG. The substrate is described as a thick disk only because its main purpose is to secure a large light flux diameter on the substrate surface so that dirt on the surface does not affect the recording / reproducing light flux. However, in these documents, there is no description relating the thickness and warpage of the transparent protective substrate to the aberration of the reading optical system.

(Problem with Prior Art 3) A light beam which is emitted and converged from an objective lens of an optical head has a minimum aberration when passing through a plane parallel plate (transparent protective substrate) having a certain thickness. Designed. In the case of an optical head for reproducing an information medium having only a single information recording layer, the first
It is designed by adjusting the aberration of the objective lens so that the optimum focused spot can be obtained for the substrate thickness of two sizes. Spherical aberration is proportional to the thickness of the transparent protective substrate, but the lens can be designed to be minimum for one substrate thickness, but not for two thicknesses.

The coma aberration and the astigmatism caused by the inclination of the transparent protective substrate also differ depending on the thickness of the substrate, and this is the same. In the information medium having the two-layer structure of the example of the related art 3, if the transparent layer between the first information recording layer and the second information recording layer is thick and the distance is too large, each information recording is performed. When the layers are reproduced, the distances through which the light flux passes through the substrate are different, that is, the substrate thicknesses when reproducing the respective information recording layers are far apart. Therefore, when the aberration of the objective lens is designed according to the substrate thickness of the first information recording layer,
Aberrations increase due to the substrate thickness of the second information recording layer, and the converging spot increases, which hinders information reproduction. If the transparent layer between the first information recording layer and the second information recording layer is too thin and the distance between the first information recording layer and the second information recording layer is too short, which of There is a problem that the information recorded in the other overlapping information recording layer, which is irradiated with light at the same time when the information recording layer is reproduced, leaks out and the information is mixed and reproduced. Get off.

In reality, in order to avoid signal interference between the two information recording layers, the transparent layer separating the two information recording layers must have a certain thickness, and there is an objective lens.
Only the optimum design can be made for one thickness base. Therefore, when actually designing this as a product, a compromise between the two is found.
That is, in reproducing either of the two information recording layers, for example, in order to obtain substantially the same focused spots, instead, the focused spots are not in the best states, respectively. You will be forced to do that.

The object of the present invention is to record information by irradiating the transparent protective substrate with a light beam from its surface, or to reproduce information based on the reflected light from the surface on which the information is recorded. An optical information recording / reproducing medium for optical information recording / reproducing medium to be performed, which can reduce the influence of aberration caused by the warp of the transparent protective substrate and also suppress the influence of dirt and scratches on the transparent protective substrate as much as before. An object of the present invention is to provide an optical information recording / reproducing apparatus using a recording / reproducing medium.

[0028]

In the optical information recording / reproducing medium of the present invention, a transparent protective substrate having a predetermined thickness is irradiated with a light beam from its surface, and recording is performed by light reflected from a recording layer inside the light beam. In an optical information recording / reproducing medium on which information is reproduced, a first information recording layer capable of reproducing recorded information by a light flux is provided on the back surface of a transparent protective substrate, and the first information recording layer is formed on the first information recording layer. Next, there is an air layer, a second protective substrate follows the air layer, and the surface of the second protective substrate is a first layer capable of reproducing recorded information by the light flux transmitted through the first information recording layer. Two information recording layers are provided.

In the optical information recording / reproducing medium of the present invention, a transparent protective substrate having a predetermined thickness is irradiated with a light flux from its surface, and the light flux records information on an internal recording layer and a light flux from the recording layer. In an optical information recording / reproducing medium in which recorded information is reproduced by reflected light, a first information recording layer capable of recording information by a light beam and reproducing recorded information is provided on a back surface of a transparent protective substrate. , The first information recording layer is followed by an air layer, the air layer is followed by a second protective substrate, and the surface of the second protective substrate is provided with the information of the light flux transmitted through the first information recording layer. A second information recording layer capable of recording and reproducing recorded information is provided.

Further, a first information recording layer capable of reproducing recorded information by a light flux is provided on the back surface of the transparent protective substrate, and an air layer is provided following the first information recording layer. Then, there is a second protective substrate, and a second information recording layer capable of recording information and reproducing the recorded information by the light flux transmitted through the first information recording layer on the surface of the second protective substrate. May be provided.

Further, a first information recording layer capable of recording information by a light beam and reproducing the recorded information is provided on the back surface of the transparent protective substrate, and an air layer follows the first information recording layer. Yes, there is a second protective base following the air layer, second
A second information recording layer capable of reproducing recorded information by a light flux transmitted through the first information recording layer may be provided on the surface of the protective substrate.

In addition, the transparent protective substrate on which the first information recording layer is arranged and the second protective substrate on which the second information recording layer facing each other with the air layer in between are arranged at the outer edge portions. Alternatively, they may be joined together via a support that keeps the air layer at a constant thickness.

The radiated light flux is a convergent light flux, and when the light flux is recording and reproducing on the second information recording layer, the diameter of the light flux becomes a predetermined value on the surface of the transparent protective substrate. The support may be designed to be retained.

Further, the transparent protective substrate provided with the first information recording layer may have a thickness of 0.4 mm to 1.0 mm.

In the optical information recording / reproducing apparatus using the optical information recording / reproducing medium of the present invention, a transparent protective substrate having a predetermined thickness is irradiated with a light beam from its surface, and the light beam causes information on an internal recording layer. In the optical information recording / reproducing apparatus in which the recording information and the reproduction of the recorded information by the reflected light of the light flux from the recording layer are performed, recording and reproduction are performed using the above-mentioned optical information recording / reproducing medium.

Further, the image forming position of the condensed spot of the light flux may be switchable between the first information recording layer and the second information recording layer by the focus servo of the objective lens.

[0037]

Next, embodiments of the present invention will be described with reference to the drawings. The first to fourth embodiments will be sequentially described below.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a schematic schematic configuration diagram of the optical information recording / reproducing apparatus of the embodiment of the present invention, in which reference numeral 101 indicates a transparent protective substrate, 102 indicates a transparent protective substrate thickness, 103 indicates a protective substrate,
104 is a first information recording layer, 105 is a second information recording layer, 106a is first recording information (phase pits), 106
b is the second recording information (phase pit), 107 is an air layer,
108 is an air layer thickness, 113 is an objective lens, 114 and 115 are luminous fluxes, and 116 and 117 are substrate surface luminous flux diameters.

In FIG. 1, this form is assumed to be a read-only optical information recording / reproducing medium. Therefore, the first information recording layer 104 and the second information recording layer 105 have the first recording information 106a and the second recording information 106b, which are read-only information recorded using the pits having the phase structure. Each is recorded. In addition, the first information recording layer 104 partially transmits the light beams 114 and 115,
A semi-transparent reflective film capable of partially reflecting is attached (not shown), and a reflective film having a high reflectance is attached to the second information recording layer 105 (not shown).

The objective lens 113 applies focus servo to the first information recording layer 104 formed on the back surface of the transparent protective substrate 101, and forms a focused spot of the light flux 114 on the first information recording layer 104. At another time, the light beam 115 that has been converged through the same objective lens 113 passes through the transparent protective substrate 101, passes through the air layer 107 below the transparent protective substrate 101, and is condensed on the second information recording layer 105. It is also possible to image the spot. Therefore, the first record information 106a and the second record information 1 recorded on the first information recording layer 104 and the second information recording layer 105, respectively.
06b can be read separately.

FIG. 2 is a graph showing a focus error signal when the focus is pulled in. (A) shows the case where the transparent protective substrate 101 and the objective lens 113 are far from each other, and (b) shows the case where the transparent protective substrate 101 and the objective lens 113 are close to each other. In the figure, reference numeral 218 denotes a focal point on the first information recording layer 104,
Reference numeral 219 indicates the focal point on the second information recording layer 105, and 220 and 221 indicate the S-curve amplitude. The method of focusing on the respective surfaces of the first information recording layer 104 or the second information recording layer 105 is as follows.
For example, when the focus is pulled in, the objective lens 113 is moved closer to or farther from the transparent protective substrate 101.
At this time, as shown in FIG. 2, two S-shaped curves appear in the focus error signal. Each zero cross of this S-shaped curve corresponds to the first information recording layer 104 or the second information recording layer 105. The zero cross that appears on the side where the objective lens 113 is far from the transparent protective substrate 101 is the focal point 218 to the first information recording layer 104, and the zero cross that appears on the near side is the focal point 219 to the second information recording layer 105.
It should be. Therefore, by utilizing this, it is possible to distinguish the two information recording layers and focus on each.

When the above method cannot be used, for example, in the case of a device in which it is not known whether the objective lens 113 is approaching or moving away from the medium, the amplitude of the S-curve differs depending on the difference in reflectance between the two information recording layers. There is also a way to use that. When the reflectance is set to reduce the amount of light returning from the first information recording layer 104, for example, the amplitudes of the two S-shaped curves 220 and 221 are different as shown in FIG. There is a method of detecting the difference in the amplitude and determining which surface corresponds to the zero cross.

Here, the transparent protective substrate thickness 1 shown in FIG.
02 and the air layer thickness 108 are determined so that the substrate surface light flux diameter 116 becomes substantially equal to the substrate surface light flux system 316 in the case of the example of the conventional technique 1 shown in FIG. 3, for example. That is, the transparent protective substrate thickness 102 and the air layer thickness 108 shown in FIG. 1 are D _S and D _Air , respectively, and the refractive indices of the transparent protective substrate 101 and the air layer 107 are N _S and N _Air , respectively.
(= 1.0) and the transparent protective substrate thickness 302 of the example of the conventional technique 1 is set.
1.2 mm, where N is the refractive index, (D _S / N _S ) + (D
It may be set such that _{Air /} 1.0) = 1.2 / N.

In addition, when there is a difference in reproduction performance between the first information recording layer 104 and the second information recording layer 105,
Making the first information recording layer 104 and the second information recording layer 105 have different recording densities is effective as a countermeasure. Specifically, the substrate surface luminous flux diameter 117 when the first information recording layer 104 is focused is compared with the substrate surface luminous flux diameter 116 when the second information recording layer 105 is focused. Therefore, the strength of the surface of the transparent protective substrate 101 against dirt is relatively thinned. Therefore, the first information recording layer 104 and the second information recording layer 104
There may be a case where there is a difference in recording / reproducing performance between the information recording layers 105. In addition, as a result of satisfying a predetermined condition when designing the reflective film on the reproducing surface, there are cases in which absorption of the film is large or the transmittance cannot be increased so much. In such a case, the attenuation of the light amount when passing through the first information recording layer 104 becomes large. Therefore, when trying to reproduce the second information recording layer 105, the reproduction light flux 11
Since No. 5 passes through the first information recording layer 104 twice, the total amount of signal light decreases. Therefore, there may be a case where there is a difference in recording / reproducing performance between the first information recording layer 104 and the second information recording layer 105.

In such a case, the first information recording layer 104 and the second information recording layer 105 are made to have different recording densities, that is, the recording density of the information recording layer on the side where the reproduction condition is more severe is slightly relaxed. By doing so, the problem can be suppressed.

(Second Embodiment) A second embodiment of the present invention is also shown with the same FIG. In FIG. 1, this form is assumed to be a recordable / erasable optical information recording / reproducing medium. Therefore, the first guide groove 106 having a phase structure is formed in the first information recording layer 104 and the second information recording layer 105.
The a and the second guide groove 106b are respectively formed to form a recordable and reproducible magneto-optical film. In addition, the first information recording layer 104 partially transmits the light beams 114 and 115,
A magneto-optical film having a semi-transparent reflection characteristic capable of partial reflection is attached, and a magneto-optical film having a high reflection characteristic is attached to the second information recording layer 105.

The objective lens 113 applies focus servo to the first information recording layer 104 formed on the back surface of the transparent protective substrate 101 to form a focused spot of the light flux 114 on the first information recording layer 104. At another time, the light beam 115 that has been converged through the same objective lens 113 passes through the transparent protective substrate 101, passes through the air layer 107 below the transparent protective substrate 101, and is condensed on the second information recording layer 105. It is also possible to image the spot. Therefore, information is separately recorded in the first information recording layer 104 and the second information recording layer 105, and the recorded first recording information 106a and second recorded information 106b are separately read out. be able to.

The method of focusing on the respective surfaces of the first information recording layer 104 or the second information recording layer 105 is the same as in the above-described first embodiment of the present invention.

When there is a difference in reproduction performance between the first information recording layer 104 and the second information recording layer 105, the recording densities of the first information recording layer 104 and the second information recording layer 105 are changed. The measure for making them different is the first aspect of the present invention described above.
This is the same as the embodiment.

(Third Embodiment) A third embodiment of the present invention is also shown with the same FIG. In FIG. 1, this form is an optical information recording / reproducing medium having both a read-only information recording surface and a record-erasable information recording surface. For example, the first information recording layer 104 is a read-only information recording surface, and the second information recording layer 105 is an information recording surface on which information can be recorded and reproduced. Therefore, the first information recording layer 104 has the first recording information 106a, which is read-only information recorded using the pits having the phase structure. A second guide groove 106b having a phase structure is formed in the second information recording layer 105 to form a recordable / reproducible magneto-optical film. Further, the first information recording layer 104 is provided with a reflective film having a semitransparent reflection characteristic capable of partially transmitting and partially reflecting the light fluxes 114 and 115, and the second information recording layer 105 has a high reflection characteristic. A magneto-optical film is attached.

The objective lens 113 applies focus servo to the first information recording layer 104 formed on the back surface of the transparent protective substrate 101 to form a focused spot of the light flux 114 on the first information recording layer 104. At another time, the light beam 115 that has been converged through the same objective lens 113 passes through the transparent protective substrate 101, passes through the air layer 107 below the transparent protective substrate 101, and is condensed on the second information recording layer 105. It is also possible to image the spot. Therefore, information is recorded on the second information recording layer 105, and the recorded first record information 106a and second record information 106 are recorded.
b can be read separately.

The method of focusing on the respective surfaces of the first information recording layer 104 or the second information recording layer 105 is the same as in the above-described first embodiment of the present invention.

When there is a difference in reproduction performance between the first information recording layer 104 and the second information recording layer 105, the recording densities of the first information recording layer 104 and the second information recording layer 105 are changed. The measure for making them different is the first aspect of the present invention described above.
This is the same as the embodiment. (Fourth Embodiment) A fourth embodiment of the present invention will also be described with reference to the same FIG. In FIG. 1, it is assumed that this embodiment is an optical information recording / reproducing medium having both a read-only information recording surface and a recordable / erasable information recording surface, as in the third embodiment.
However, the first information recording layer 104 and the second information recording layer 10
The role of 5 is opposite to that of the third embodiment. For example, assume that the first information recording layer 104 is an information recording surface on which information can be recorded and reproduced, and the second information recording layer 105 is a read-only information recording surface. Therefore, the first information recording layer 1
A first guide groove 106a having a phase structure is formed at 04 to constitute a recordable / reproducible magneto-optical film. Further, the second information recording layer 105 has second recording information 106b recorded therein which is read-only information recorded by using pits having a phase structure. Further, the first information recording layer 104 is provided with a magneto-optical film having a semitransparent reflection characteristic capable of partially transmitting and partially reflecting the light fluxes 114 and 115, and the second information recording layer 105 has a reflection characteristic. A high reflection film is attached.

The objective lens 113 applies focus servo to the first information recording layer 104 formed on the back surface of the transparent protective substrate 101, and forms a focused spot of the light flux 114 on the first information recording layer 104. At another time, the light beam 115 that has been converged through the same objective lens 113 passes through the transparent protective substrate 101, passes through the air layer 107 below the transparent protective substrate 101, and is condensed on the second information recording layer 105. It is also possible to image the spot. Therefore, information is recorded on the first information recording layer 104, and the recorded first record information 106a and second record information 106 are recorded.
b can be read separately.

The method of focusing on the respective surfaces of the first information recording layer 104 or the second information recording layer 105 is the same as in the above-described first embodiment of the present invention.

When there is a difference in reproduction performance between the first information recording layer 104 and the second information recording layer 105, the recording densities of the first information recording layer 104 and the second information recording layer 105 are changed. The measure for making them different is the first aspect of the present invention described above.
This is the same as the embodiment.

[0057]

As described above, according to the present invention, by reducing the thickness of the transparent protective substrate, it is possible to reduce the influence of aberration caused by the warp of the transparent protective substrate.
Moreover, there is an effect that the influence of dirt and scratches on the transparent protective substrate can be suppressed as much as before.

Further, since this technique can realize a medium provided with two information recording layers as a medium having one type of transparent protective substrate thickness, the objective lens is optimized only for one type of transparent protective substrate thickness. The greatest effect is that it is possible to design such a structure. Furthermore, for this reason, the convergence precision of the focused spot can always be kept high, and recording and reproduction can be performed with the focused spot that is sharply narrowed, so that high performance can be realized.

Further, since the distance between the two information recording layers can be made larger than in the conventional case, there is an effect that it is possible to greatly reduce the leakage of the signal from the layer which is not the recording / reproducing layer. Furthermore, in this case, even if the distance between the two information recording layers is large, the transparent protective substrate thickness is one, so that there is an effect that the occurrence of spherical aberration does not affect the recording / reproducing characteristics.

Further, the effects of the invention possessed by each claim will be described.

(Claim 1) Since the reproduction layers of the recorded information for two layers can be obtained, there is an effect that the capacity is approximately doubled and a large capacity ROM medium can be realized with one sheet.

(Claim 2) Since the recording / reproducing layer for recording information of two layers can be obtained, there is an effect that the capacity is approximately doubled and a large capacity recording / reproducing medium can be realized with one sheet. .

(Claim 3) When the first information recording layer is focused, the light flux diameter on the surface of the substrate is smaller than that when the second information recording layer is focused. The resistance to dirt on the surface is relatively reduced. However, when the first information recording layer is read-only by the pre-pits and the second information recording layer is for recording / reproducing by, for example, magneto-optical as in claim 3, generally, the modulation degree of the read-only phase pit reproduction signal is Has a much larger amplitude than the reproduction signal modulation of the magneto-optical signal. Therefore, this large amplitude is less likely to be affected by the dirt on the surface of the substrate to some extent, so that there is an effect that it can be used as a partial ROM medium capable of stably reproducing the first information recording layer.

(Claim 4) As a result of satisfying a predetermined condition when designing the magneto-optical film, whether absorption of the film is large,
Alternatively, the transmittance may not be increased so much in some cases. In such a case, the attenuation of the light amount when passing through the first information recording layer becomes large. Therefore, when an attempt is made to reproduce the second information recording layer, the reproduction light beam passes through the first information recording layer twice, so that the total amount of signal light is reduced. However, in the case where the first information recording layer is for recording / reproducing by magneto-optical recording and the second information recording layer is for reading only by pre-pits as in claim 4, in general, the degree of modulation of the read signal of the read-only phase pit is generally used. Has a much larger amplitude than the reproduction signal modulation of the magneto-optical signal. Therefore, this large amplitude is less likely to be affected by a slight decrease in the total amount of signal light, so that there is an effect that it can be used as a partial ROM medium capable of stably reproducing the second information recording layer.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical information recording / reproducing apparatus according to first to fourth embodiments of the present invention.

FIG. 2 is a graph showing a focus error signal when a focus is pulled in. (A) A case where the transparent protective substrate and the objective lens are far from each other is shown. (B) A case where the transparent protective substrate and the objective lens are close to each other is shown.

FIG. 3 is a schematic block diagram of a conventional general optical information recording / reproducing apparatus.

FIG. 4 is a schematic diagram of a conventional optical information recording / reproducing device having an air sandwich structure,
This is an example of the case where the information recording layer is set on the surface of the protective base.

FIG. 5 is an example disclosed as a schematic schematic configuration diagram of an optical information recording / reproducing medium having an air sandwich structure.

FIG. 6 is a schematic diagram of a conventional optical information recording / reproducing apparatus having an air sandwich structure,
This is an example of the case where the information recording layer is set on the back surface of the transparent protective substrate.

FIG. 7 is a schematic diagram showing the structure of a conventional optical information recording / reproducing device having a two-layer structure of a transparent protective substrate.

[Explanation of reference numerals] 101, 301, 401, 601, 701 Transparent protective substrate 102, 302, 402, 602, 702 Transparent protective substrate thickness 103, 303, 403, 603, 703 Protective substrate 104, 704 First information recording layer 105, 705 Second information recording layer 106 Recording information (phase pit) or guide groove 106a First recording information (phase pit) or guide groove 106b Second recording information (phase pit) or guide groove 107, 407, 507 , 607 Air layer 108, 408 Air layer thickness 113, 313, 413, 613, 713 Objective lens 114, 115, 314, 414, 614, 714, 7
15 Luminous flux 116, 117, 316, 416, 616 Base surface luminous flux diameter 218 Focus point on first information recording layer 219 Focus point on second information recording layer 220, 221 S-curve amplitude 304, 404, 504, 604 information recording layer 306 recording information (phase pit) or guide groove 409, 609 recording film 410, 610 recording information 501 protective plate 503 carrier plate 706 recording information (phase pit) 706a first recording information (phase pit) 706b second Recording information (phase pit) 711 Transparent layer 712 Transparent layer thickness

Claims (9)

[Claims] 1. An optical information recording / reproducing medium in which a transparent protective substrate having a predetermined thickness is irradiated with a light beam from its surface, and recorded information is reproduced by reflected light from a recording layer inside the light beam, A first information recording layer capable of reproducing the recorded information by the light flux is provided on the back surface of the transparent protective substrate, and an air layer is provided following the first information recording layer. Subsequently, there is a second protective substrate, and a second information recording layer capable of reproducing recorded information by the light flux transmitted through the first information recording layer is arranged on the surface of the second protective substrate. An optical information recording / reproducing medium characterized by being provided. 2. A transparent protective substrate having a predetermined thickness is irradiated with a light flux from its surface, information is recorded on an internal recording layer by the light flux, and recording information is recorded by reflected light of the light flux from the recording layer. In an optical information recording / reproducing medium for reproduction, a first information recording layer capable of recording information by the light flux and reproducing the recorded information is provided on the back surface of the transparent protective substrate, Information recording layer is followed by an air layer, the air layer is followed by a second protective substrate, and the surface of the second protective substrate is provided with information by the light flux transmitted through the first information recording layer. 2. An optical information recording / reproducing medium having a second information recording layer capable of recording and reproducing recorded information. 3. A transparent protective substrate having a predetermined thickness is irradiated with a light flux from its surface, the information is recorded on an internal recording layer by the light flux and the recorded information is recorded by the reflected light of the light flux from the recording layer. In an optical information recording / reproducing medium for reproduction, a first information recording layer capable of reproducing recorded information by the light flux is disposed on the back surface of the transparent protective substrate, and the first information recording layer Is followed by an air layer, and the air layer is followed by a second protective substrate, and the recording and recording of information by the light flux transmitted through the first information recording layer on the surface of the second protective substrate. An optical information recording / reproducing medium having a second information recording layer capable of reproducing the recorded information. 4. A transparent protective substrate having a predetermined thickness is irradiated with a light flux from its surface, and information is recorded on an internal recording layer by the light flux and recorded information by reflected light of the light flux from the recording layer. In an optical information recording / reproducing medium for reproduction, a first information recording layer capable of recording information by the light flux and reproducing the recorded information is provided on the back surface of the transparent protective substrate, The information recording layer is followed by an air layer, the air layer is followed by a second protective substrate, and the surface of the second protective substrate is recorded by the light flux transmitted through the first information recording layer. An optical information recording / reproducing medium having a second information recording layer capable of reproducing the recorded information. 5. The optical information recording / reproducing medium according to claim 1, wherein the transparent protective substrate on which the first information recording layer is provided and the air layer are provided. The second protective base on which the second information recording layer is sandwiched and is opposed to the second protective base, is joined at the outer edge portion thereof via a support that holds the air layer at a constant thickness. An optical information recording / reproducing medium characterized in that 6. The optical information recording / reproducing medium according to claim 5, wherein the irradiated light flux is a convergent light flux, and the light flux performs recording and reproduction on the second information recording layer. The optical information recording / reproducing medium is characterized in that the support is set so that the diameter of the light flux is maintained at a predetermined value on the surface of the transparent protective substrate. 7. The optical information recording / reproducing medium according to claim 1, wherein the transparent protective substrate provided with the first information recording layer has a thickness of An optical information recording / reproducing medium characterized by being 0.4 mm to 1.0 mm. 8. A transparent protective substrate having a predetermined thickness is irradiated with a light flux from its surface, and information is recorded on an internal recording layer by the light flux and recorded information by reflected light of the light flux from the recording layer. An optical information recording / reproducing apparatus for reproducing, wherein recording and reproducing are performed using the optical information recording / reproducing medium according to any one of claims 1 to 7. Type information recording / reproducing apparatus. 9. The optical information recording / reproducing apparatus according to claim 8, wherein the image formation position of the focused spot of the light flux is on the first information recording layer and the second information recording layer. An optical information recording / reproducing apparatus, which can be switched by a focus servo of an objective lens.