JPWO2001001408A1 - Optical recording medium and method for reading from optical recording medium - Google Patents

Abstract

(57) [Abstract] The present invention provides an optical disk having a plurality of stacked recording layers, comprising: a light-transmitting substrate, a first recording layer provided on one side of the substrate, a second recording layer provided on top of the first recording layer and having a lead-in area in which at least data required for data reading is recorded, and an intermediate layer provided between the first and second recording layers, wherein the first recording layer is provided from outside the lead-in area.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to an optical recording medium having multiple recording layers and a method for reading data recorded on the optical recording medium. BACKGROUND ART Optical discs, which are used to reproduce information recorded on the recording medium using a light beam, have been widely used as recording media for various types of information such as audio information and video information. For this type of optical disc, optical discs with multiple recording layers have been proposed in order to increase the amount of recordable information. As an optical disc with multiple recording layers, an optical disc has been proposed in which a light beam is irradiated from one side of a substrate to reproduce data recorded on each recording layer. This optical disc has a first recording layer provided on one side of a light-transmitting substrate,
A second recording layer is provided on this first recording layer via an intermediate layer having optical transparency. The first recording layer is formed as a semi-transparent film that transmits and reflects a certain amount of the light beam incident from the substrate side so that the light beam is incident on the second recording layer side. By making the first recording layer located on the light beam incident side a semi-transparent film and the second recording layer a high reflectivity layer, it is possible to obtain reflected light from each of the first and second recording layers, and to read out information signals recorded on each recording layer. Reproduction of data signals recorded on each recording layer of an optical disc having multiple recording layers is performed as follows:
This is done by controlling the focal position of the light beam irradiated onto the optical disk.
In other words, by focusing a light beam on a desired recording layer, data recorded on the desired recording layer can be reproduced. Conventionally proposed optical discs with multiple recording layers are provided such that each recording layer overlaps with the other in a common area extending from the inner periphery to the outer periphery of the optical disc.
In this way, if multiple recording layers are provided so as to completely overlap each other, the reflectivity of the other recording layers overlapping one recording layer will be limited to the transmittance of the one recording layer, and sufficient reflectivity will not be obtained. As a result, the signal level based on the reflected light from the other recording layers will be low,
This makes it impossible to reproduce data using conventional optical disc reproduction devices that require high reflectivity for the recording layer. Therefore, if an attempt is made to increase the light transmittance of one recording layer so as to increase the reflectivity of the other recording layers, the reflectivity of the first recording layer decreases, making it difficult to configure an optical disc reproduction device that can reproduce both the first and other recording layers. Furthermore, in conventional optical discs with multiple recording layers, each recording layer has the same structure from the inner periphery to the outer periphery. Each recording layer has a lead-in area on the inner periphery where control data required for reading data such as audio information and video information is recorded, and a data area on the outer periphery of this lead-in area where data such as audio information and video information is recorded. Here, the control data required for reading data includes address information indicating the recording position of data recorded in the data area. [0006] In this way, if each recording layer is formed overlapping almost the entire area on the substrate of an optical disc, and control data and the like are recorded in a similar structure, when the optical disc is loaded into an optical disc playback device and data such as audio information and video information recorded on each recording layer is to be reproduced, the control data recorded in the lead-in area of one recording layer that is read first may be mixed with the control data recorded in the lead-in area of the other recording layer as a noise component due to, for example, a component of a light beam irradiated on one recording layer that passes through that recording layer being reflected by another recording layer, which may result in the control data in the lead-in area being inaccurately read, making it impossible to select the desired recording layer or to reproduce the recording layer. [0007] Disclosure of the Invention [0008] Therefore, an object of the present invention is to provide an optical recording medium and a reading method thereof that can reliably select each recording layer and accurately reproduce data recorded on each recording layer while increasing the number of recording layers in order to increase recording capacity. Another object of the present invention is to provide an optical recording medium and a reading method thereof that can be used in a manner compatible with optical discs used in conventional optical disc players that require high reflectivity. The optical recording medium according to the present invention, which is proposed to achieve the above-mentioned object, comprises a substrate having optical transparency, a first recording layer provided on one side of the substrate, a second recording layer provided so as to be laminated with the first recording layer and having a lead-in area in which at least data required for reading data is recorded, and
and an intermediate layer provided between the first recording layer and the second recording layer. The first recording layer is provided from the outside of the lead-in area. The optical recording medium according to the present invention also comprises a light-transmitting substrate, a first recording layer provided on one side of the substrate, a second recording layer provided so as to be laminated with the first recording layer and having a lead-in area in which at least data required for reading data is recorded, and an intermediate layer provided between the first recording layer and the second recording layer. At least a part of the portion of the first recording layer facing the lead-in area of the optical recording medium is made a mirror surface. The optical recording medium according to the present invention also comprises a light-transmitting substrate, a first recording layer provided on one side of the substrate, a second recording layer provided so as to be laminated with the first recording layer and having a lead-in area in which at least data required for reading data is recorded, and an intermediate layer provided between the first recording layer and the second recording layer.
and a second recording layer, one of the first and second recording layers being provided on one side of a substrate, the other recording layer being stacked on the one recording layer via an intermediate layer, and a lead-in area in which at least data required for data reading is recorded. A method for reading an optical recording medium according to the present invention reads data from the lead-in area of the second recording layer of an optical recording medium having a light-transmitting substrate and at least the first and second recording layers, one of the first and second recording layers being provided on one side of the substrate, the other recording layer being stacked on the one recording layer via an intermediate layer, and a lead-in area in which at least data required for data reading is recorded, and then reads the data from the first recording layer after reading the data in the lead-in area. The method for reading an optical recording medium according to the present invention comprises a light-transmitting substrate, a first recording layer provided on one side of the substrate, a second recording layer provided so as to be laminated with the first recording layer and having a lead-in area in which at least data required for data reading is recorded, and an intermediate layer provided between the first and second recording layers, and the first recording layer is provided outside the lead-in area, and after reading the data in the lead-in area, the method reads data from the lead-in area of the second recording layer of the optical recording medium.
The optical recording medium according to the present invention comprises a first recording layer provided on one side of the substrate, a second recording layer provided so as to be laminated with the first recording layer and having a lead-in area in which at least data required for data reading is recorded, and an intermediate layer provided between the first and second recording layers, at least a part of the portion facing the lead-in area of the first recording layer being a mirror surface, and the data in the lead-in area of the second recording layer is read, and after reading the data in the lead-in area, the data in the first recording layer is read.
and an intermediate layer provided between the first recording layer and the second recording layer. The optical recording medium is provided so that the first recording layer and the second recording layer are biased relative to each other in the layer direction. A method for reading an optical recording medium according to the present invention reads data recorded in the lead-in area from an optical recording medium having a first recording layer with a lead-in area provided in a state where the first recording layer is laminated on a substrate, determines whether a second recording layer exists between the recording layer and the substrate based on the data read from the lead-in area, and, when it is determined that a second recording layer exists, reads the second recording layer based on control data recorded in the lead-in area. Further objects of the present invention and specific advantages obtained by the present invention will be more clearly understood from the following description of the embodiments. Best Mode for Carrying Out the Invention An optical recording medium and a method for reading an optical recording medium according to the present invention will now be described in detail. First, as shown in FIG. 1, an optical disc 1 as an optical recording medium according to the present invention is a substrate 2 made of a light-transmitting synthetic resin such as polycarbonate resin or glass.
On one side of this substrate 2, a pit pattern 3 is provided, which is a minute concave-convex pattern corresponding to, for example, audio information to be recorded. The pit pattern 3 is configured so that a plurality of pits based on the information to be recorded form a spiral or concentric recording track. When the substrate 2 is made of synthetic resin, this pit pattern 3 is formed when the substrate 2 is molded by being transferred from a stamper when the substrate 2 is injection molded. The pit pattern 3 is
When the substrate 2 is made of glass, 2P (Photo Poly
The 2P method involves filling the gap between the glass substrate and the disk stamper with a photo-curable resin such as an ultraviolet-curable resin, and curing the photo-curable resin by irradiating it with light from the glass substrate side, thereby transferring the concave-convex pattern of the stamper to the photo-curable resin. The substrate 2 used in the optical disk 1 according to the present invention is injection-molded from polycarbonate resin, and recording information is recorded on one side of this substrate 2 as a pit pattern 3. This substrate 2 has a diameter of 12 cm, similar to the substrate of a conventionally used optical disk having a diameter of 12 cm, that is, a so-called compact disk.
The thickness of the first recording layer 4 is approximately 1.2 mm. On one side of the substrate 2 on which the pit pattern 3 is formed, a first recording layer 4 is provided so as to cover the pit pattern 3, as shown in FIG. 1.
is a semi-transparent film that transmits a certain amount of the light beam irradiated from the substrate 2 side and reflects a certain amount. For example, the first recording layer 4 is made of a silicon-based material such as _{Si3N4 or SiO2} and is formed to a thickness of about 100 nm to 500 nm. In this case,
The first recording layer 4 is formed as a multilayer of _{Si3N4 films} and _SiO2 films. The _Si3N4 films and _SiO2 films that make up the first recording layer 4 are formed on the substrate 2 by vacuum deposition or _sputtering . A second recording layer 6 is formed on the first recording layer 4 via an intermediate layer 5 made of a light-transmitting ultraviolet-curable resin or the like. The intermediate layer 5 is formed between the first recording layer 4 and the second recording layer 6.
The recording layer 6 is optically separated from the recording layer 4 so that the recording layers 4 and 6 are not located within the focal depth of the objective lens that focuses the light beam onto the recording layers 4 and 6. For example,
The intermediate layer 5 is formed to a thickness of about 30 μm. If the intermediate layer 5 is too thin, the first and second recording layers 4 and 6 will be located within the focal depth of the objective lens, making it difficult to sufficiently separate the reflected light from the first recording layer 4 and the reflected light from the second recording layer 6, making it difficult to accurately detect each reflected light. Also, if the intermediate layer 5 is too thick, spherical aberrations and the like will occur in the light beam irradiated onto the recording layer 6. Therefore, an appropriate thickness for the intermediate layer 5 is selected taking these points into consideration. The intermediate layer 5 is formed by applying a photo-curable resin such as an ultraviolet-curable resin onto the first recording layer 4 by spin coating, and then irradiating it with ultraviolet light or the like to harden the applied resin. Alternatively, the intermediate layer 5 can be formed by applying a photo-curable resin such as an ultraviolet-curable resin to a thickness of 5 μm to 10 μm.
Alternatively, a laminate formed in multiple steps with a thickness of about μm may be used. Furthermore, the intermediate layer 5 may be formed by attaching a transparent sheet to the first recording layer 4. A pit pattern 7, which is a minute concave-convex pattern corresponding to, for example, audio information to be recorded on the second recording layer 6, is formed on one side of the intermediate layer 5. This pit pattern 7 is configured to form a spiral or concentric recording track with multiple pits based on the information to be recorded, similar to the pit pattern 3 described above. This pit pattern 7 can be formed using the 2P method described above, which is used when forming a pit pattern on the glass substrate described above. The second recording layer 6 is formed so as to cover the pit pattern 7 formed on one side of the intermediate layer 5 and to be laminated on the first recording layer 4. The second recording layer 6 is formed by depositing a film made of a metal material such as aluminum (Al), gold (Au), or silver (Ag) that can ensure high reflectivity on one side of the intermediate layer 5, in order to reflect the light beam irradiated through the first recording layer 4 to the optical pickup located on the substrate 2 side. On this second recording layer 6, a second recording layer 6
In order to protect the surface of the optical disc 1, a protective layer 8 made of an ultraviolet-curable resin or the like is provided to cover the second recording layer 6. This protective layer 8 is formed by applying an ultraviolet-curable resin or the like to the second recording layer 6 by spin coating, and then irradiating the applied resin with ultraviolet light or the like to harden it. As shown in FIG. 2, the optical disc 1 described above has a center hole 11 at its center, and a clamping area 12 around this center hole 11. The optical disc 1 is centered on the disc table by engaging the center hole 11 with a centering portion provided at the center of the disc table of the disc rotation drive mechanism on the optical disc playback device, and the clamping area 12 is placed on the disc table and clamped by a clamp member, so that the optical disc 1 is centered on the disc table and rotatably mounted integrally with the disc table. In this way, the optical disc 1 is provided with the clamping area 12 on its inner periphery, which is clamped to the disc rotation drive mechanism, and the first clamping area 12 on its outer periphery.
and second recording layers 4, 6. The second recording layer 6, which is provided so as to be stacked on the first recording layer 4, is provided so as to extend further inward from the portion where the first recording layer 4 is provided to an area in the vicinity of a clamping area 12 on the inner periphery side, as shown in Fig. 1. In an area on the inner periphery side of the second recording layer 6 that does not face the first recording layer 4, there is provided a lead-in area 13 in which at least a part of control data is recorded, which is read out prior to reproduction of data such as audio information previously recorded in the data recording areas 13, 14 of the first and second recording layers 4, 6 when the optical disc 1 is loaded into an optical disc reproduction device.
5 is provided. The control data recorded in this lead-in area 15 includes, for example, data indicating a focus offset amount for controlling the focusing position of the light beam on the second recording layer 6 and data for tracking control of the light beam, which constitute part of the control data required to read data recorded on the second recording layer 6, and data indicating a focus offset amount for controlling the focusing position of the light beam on the first recording layer 4 and data for tracking of the light beam, which are part of the control data required to read data recorded on the first recording layer 4. The focus offset amount referred to here refers to a DC signal component for moving the objective lens in the optical axis direction of the objective lens to move the focal position of the light beam focused by the objective lens to either the first recording layer 4 or the second recording layer 6. The lead-in area 15 also includes, for example, a DC signal component for moving the objective lens in the optical axis direction of the objective lens to move the focal position of the light beam focused by the objective lens to either the first recording layer 4 or the second recording layer 6, as control data for controlling the reading of data recorded on the second recording layer 6.
The control data recorded in the lead-in area 15 is also recorded in the data recording area 13. The control data recorded in the lead-in area 15 is also recorded in the data recording area 13.
, 14, the data is recorded by a pit pattern 7, which is a minute concave-convex pattern. Furthermore, in the optical disc 1 according to the present invention, the lead-in area 15 is provided only in the second recording layer 6. Therefore, when the optical disc 1 is loaded into an optical disc playback device, the control data recorded in the lead-in area 15 provided in the second recording layer 6 is read, and then the data recorded in the first recording layer 4 or the second recording layer 6 is played back. Therefore, in addition to address information or absolute time information indicating the start position of the data recording area 14 of the second recording layer 6, the lead-in area 15 also contains
The minimum information required to access the first recording layer 4, such as address information such as the innermost position of the first recording layer 4 and the start position of the data recording area 13, or absolute time information, is recorded. The lead-in area 15 is provided in an area that can be scanned by a light beam emitted from an optical pickup provided on the optical disc playback device when the optical disc 1 is loaded into the optical disc playback device. In other words, the lead-in area 15 is provided so as to start from a position that is outer than the innermost position at which data can be read from the optical disc 1 when the optical pickup is moved in the inner circumferential direction of the optical disc 1. In this way, the optical disc 1 according to the present invention has a structure in which the start end side of the second recording layer 6 is closer to the first recording layer 4 than the innermost position at which data can be read from the optical disc 1.
The lead-in area 15 is formed on the inner periphery of the first recording layer 4, and the lead-in area 15 is provided in the extended portion of the second recording layer 6, so that the first recording layer 4 is provided in an area outside the lead-in area 15, as shown in Figure 1. The portion of the second recording layer 6 of this optical disc 1 where the lead-in area 15 is provided is structured so that no layer that reflects the light beam is provided from the substrate 2 onto which the light beam is incident to the second recording layer 6. Therefore, the light beam is incident without being attenuated by the first recording layer 4 and reflected by the lead-in area 15, so that the control data recorded in the lead-in area 15 can be read with high accuracy without being affected by noise due to the first recording layer 4 as described in the prior art. When reading control data recorded in the lead-in area 15 provided on the second recording layer 6, the light beam reflected by the first recording layer 4 can be eliminated, and the component reflected by the first recording layer 4 is added to the light beam reflected by the lead-in area 15 of the second recording layer 6, allowing accurate reading without including noise components. Meanwhile, the optical disc 1 according to the present invention reproduces data recorded on the first and second recording layers 4, 6 by irradiating a light beam from the substrate 2 side and detecting the returning light beam reflected from the first and second recording layers 4, 6 with a photodetector arranged on the substrate 2 side. The first recording layer 4 reflects the light beam to the second recording layer 6.
The second recording layer 6 is formed as a semi-transparent film that allows a predetermined amount of light to pass through to the first recording layer 6.
is formed so as to reflect with high efficiency the light beam that is irradiated after passing through the first recording layer 4. In other words, the reflectance of the second recording layer 6 is made higher than that of the first recording layer 4. More specifically, the first recording layer 4 of the optical disc 1 according to the present invention has a reflectance of 1
The reflectance of the intermediate layer 5 is set to 1%, and the reflectance of the second recording layer 6 is set to 99%. If the diffusion and absorption rate of the light beam of the substrate 2 made of polycarbonate resin is 5%, as shown in Figure 3, when a light beam _L1 is incident from the substrate 2 side, 10% is reflected from the first recording layer 4 as a returning light beam _L2 , and 85% passes through the first recording layer 4 and enters the second recording layer 6. At this time, the diffusion and absorption rate of the light beam of the intermediate layer 5 is almost zero, so most of the light is incident on the second recording layer 6. The light beam _L3 incident on the second recording layer 6 is reflected by the second recording layer 6 which has a reflectance of 99%.
The light beam L1 is reflected by the first recording layer ₄ , becomes a returning light beam L4, passes through the first recording layer 4 with a reflectivity of 11% and the substrate 2 with a diffusion/absorption rate of 5%, and is output to the outside of the optical disc 1. The return rate of this returning light beam _L4 reflected from the second recording layer 6 is approximately 71% of the light beam _L1 that is initially incident on the substrate 2. In another example of the optical disc 1 according to the present invention, if the reflectivity of the first recording layer 4 is 20% and the reflectivity of the second recording layer 6 is 99%, 18% of the light beam _L1 that is initially incident on the substrate 2 from the first recording layer 4 is reflected as the returning light beam _L2 , and approximately 57% of the light beam _L1 that is initially incident on the substrate 2 from the second recording layer 6 is reflected as the returning light beam _L4 . In this way, by reducing the reflectivity of the first recording layer 4 and increasing the light transmittance to give the second recording layer 6 a high reflectivity, it is possible to ensure a sufficient amount of light for the returning light beam reflected from the second recording layer 6. The data recorded in the data recording area 14 of the second recording layer 6, which has a high reflectivity, can be sufficiently reproduced even by conventional optical disc reproduction devices for so-called compact discs, which require a high reflectivity. By increasing the reflectivity of the second recording layer 6 to a level that allows it to be sufficiently readable by conventional optical disc reproduction devices, which require a high reflectivity, even when a light beam is irradiated through the first recording layer 4, the control data recorded in the lead-in area 15 provided on the second recording layer 6 can be read with even greater accuracy. Furthermore, data regarding the reflectivity of the first recording layer 4 is recorded in the lead-in area 15 as control data that is read prior to reproduction of data such as audio information pre-recorded in the data recording areas 13 and 14 of the first and second recording layers 4 and 6. At least the data regarding the reflectivity of the first recording layer 4 is recorded in the lead-in area 15. The data relating to the reflectivity of the first recording layer 4 can be read out and the gain of the amplifier circuit that amplifies the read data and the loop gain of the servo circuit (described later) can be switched in advance, thereby enabling the data recorded on the first recording layer 4 to be read out accurately. Of course, data relating to the reflectivity of the second recording layer 6 can be recorded in the lead-in area 15, the data relating to the reflectivity of the second recording layer 6 can be read out, and the gain of the amplifier circuit and the loop gain of the servo circuit can be switched based on the read data relating to the reflectivity of the second recording layer 6. Furthermore, by recording type data indicating that the first recording layer 4 is provided in addition to the second recording layer 6 in the lead-in area 15, the data recorded on the second recording layer 6 can be read out accurately.
When the optical disc 1 is loaded into an optical disc playback device, it can be immediately identified as a multi-layer optical disc 1 by reading data indicating that the optical disc 1 has a first recording layer 4. If it can be immediately recognized that the optical disc 1 loaded into the optical disc playback device has a first recording layer 4 based on the read type data, the device can switch to a playback mode in which data recorded on each recording layer 4, 6 is played back, and playback can be performed. Note that in the above-mentioned optical disc 1, the reflectance of the second recording layer 6 is greater than that of the first recording layer 4, in terms of the ratio of the amount of returned light of the light beam incident on the optical disc 1. However, the return light from the first recording layer 4 may be made greater than the return light from the second recording layer 6. For example, the reflectance of the first recording layer 4 may be set to 6.
0%, and the reflectivity of the second recording layer 6 is 99%, approximately 54
% becomes return light from the first recording layer 4 and about 15% becomes return light from the second recording layer 6. When the first and second recording layers 4 and 6 are formed with such a proportion of return light,
Contrary to the above-mentioned example, the lead-in area is provided in the first recording layer 4, and the second recording layer 6 is not provided on one side of the intermediate layer 5 facing the lead-in area provided in this first recording layer 4. Therefore, the control data recorded in the lead-in area provided in the first recording layer 4 can be read with high reflectivity without being affected by the second recording layer 6, which has high reflectivity and low light transmittance. As shown in Figure 1, the above-mentioned optical disc 1 does not provide the first recording layer 4 itself in an area of the first recording layer 4 corresponding to the lead-in area 15 provided in the second recording layer 6, and the first recording layer 4 is provided only in an area outside the lead-in area 15. However, this is not limiting, and the substrate 2 may not be provided with a pit pattern corresponding to the control data, but may instead have a flat surface as shown in Figure 4, and a mirror-finished portion 21 formed on this flat surface by depositing only the first recording layer 4. 4, by not recording data such as control data in the area of the first recording layer 4 corresponding to the lead-in area 15 provided on the second recording layer 6, i.e., by not providing a pit pattern on the substrate 2, when reading the data recorded in the lead-in area 15, it is possible to prevent the signal component of the light beam irradiated on the optical disc 1 that is reflected by the first recording layer 4 from being added as a noise component to the read signal of the second recording layer 6, and to accurately read the data in the lead-in area 15. In the optical disc 1 according to the present invention, as described above, the lead-in area 1 has at least the data required for reading data recorded on the second recording layer 6.
By providing the lead-in area 15, data reading starts from the second recording layer 6 side where the lead-in area 15 is provided. By reading the data in the lead-in area 15 first, it is possible to easily control the start of reading data such as audio information recorded on the first and second recording layers 4 and 6. The first and second recording layers 4 and 6 can be easily selected based on the control data recorded in the lead-in area 15. At this time, the first recording layer 4 is not recorded in the lead-in area 15.
By recording the reflectivity of the first recording layer 4 and type data indicating that the first recording layer 4 is provided as data required for reading data recorded on the optical disc 1, the gain settings of the amplifier circuit and servo circuit on the optical disc playback device can be immediately switched according to the type of optical disc based on the data read from the lead-in area 15, and data recorded on the first recording layer 4 can be easily played back even on optical discs having a first recording layer 4. A method for reading data such as audio information recorded on the optical disc 1 configured as described above will be described below. As shown in FIG. 5, an optical disc playback device for playing back the optical disc 1 according to the present invention includes a spindle motor 31 that rotates the optical disc 1 and a disc table provided at the tip of the rotation shaft of the spindle motor 31, a disc rotation drive mechanism that rotates the optical disc 1 placed on the disc table using the spindle motor 31, and an optical pickup 32 that scans the first or second recording layer 4, 6 of the optical disc 1 with a light beam and reads data recorded on the first or second recording layer 4, 6. The optical pickup 32 is moved in the radial direction of the optical disc 1 by a feed mechanism 33. The optical pickup 32 includes a semiconductor laser 34 as a light source that emits a light beam to be irradiated onto the optical disc 1, optical elements such as an objective lens 35 that selectively focuses the light beam L emitted from the semiconductor laser 34 onto the first or second recording layer 4, 6 of the optical disc 1, and a photodetector 36 that detects the returning light beam reflected from the first or second recording layer 4, 6. The objective lens 35 is supported by an actuator 37 so as to be displaceable in two mutually perpendicular directions: a focusing direction parallel to the optical axis of the objective lens 35 and a tracking direction in a plane perpendicular to the optical axis of the objective lens 35, and is driven and displaced in the focusing direction and/or the tracking direction based on a focus error signal and/or a tracking error signal obtained by detecting the returning light beam. The objective lens 35 adjusts the focus position of the first or second objective lens 35 based on data indicating a focus offset amount for controlling the focusing position of the light beam, which data is included in the control data recorded in the lead-in area 15 provided on the second recording layer 6 of the optical disc 1.
In the optical disc reproducing device for reproducing the optical disc 1 according to the present invention, when the optical disc 1 is placed on the disc table of the disc rotation driving mechanism and starts to be driven, the optical pickup 32 is moved by the feed mechanism 33 to a position corresponding to the position where the lead-in area 15 of the optical disc 1 is provided, based on a control signal from the system controller 52, which will be described later. In this example, the lead-in area 15 is
As shown in Fig. 1, the optical pickup 32 is provided on the inner periphery side of the second recording layer 6 of the optical disc 1, so that the optical pickup 32 is moved to the inner periphery side of the optical disc 1 by the feed mechanism 33, and the lead-in area 15 is scanned with a light beam focused by an objective lens 35. When the lead-in area 15 is scanned, the returning light beam reflected by the lead-in area 15 is detected by a photodetector 36 via the objective lens 35. The photodetector 36 has a light receiving section 41 divided into first, second, third and fourth photodetection sections 41a to 41d as shown in Fig. 6.
The returning light beam reflected from the light receiving portion 5 is incident on the light receiving portion 41 of the light detector 36, and is detected by the first to fourth light detecting portions 41a to 41d of the light receiving portion 41.
Based on the detection outputs from the first to fourth photodetectors 41a to 41d, an RF amplifier 48 (described later) detects an RF signal RF, which is a read signal for data recorded in the lead-in area 15, and a focus error signal FE. The RF sum signal RF is output by the RF amplifier 48 to the first to fourth photodetectors 41a to 41d.
The RF signal RF is obtained as a sum signal obtained by adding together the detection signals A and C detected by the first and third photodetectors 41a and 41c of the light receiving section 41. That is, the detection output (A+C) output from the first adder circuit 42, which adds together the detection signals A and C from the first and third photodetectors 41a and 41c of the light receiving section 41, and the detection output (B+D) output from the second adder circuit 43, which adds together the detection signals B and D from the second and fourth photodetectors 41b and 41d, are added together by the third adder circuit 44 to obtain the RF signal RF (=A+B+C+D), and the RF signal RF is also an intensity signal of the light beam reflected from the lead-in area 15.
The second adder circuit 43 and the third adder circuit 44 constitute an RF amplifier 48, which will be described later. The focus error signal FE is detected by the astigmatism method.
When the focal point of the light beam irradiated from the objective lens 35 onto the lead-in area 15 is on the objective lens 35 side of the lead-in area 15 and is defocused,
The shape of the beam spot S of the returning light beam reflected from the lead-in area 15 is determined by the first and third light detecting sections 41a and 41c of the light receiving section 41, as shown in FIG. 7A.
The light beam is focused on the lead-in area 15.
When the beam spot S is in the up position, i.e., in the focused state, the shape of the beam spot S is as shown in FIG.
7B, the beam spot S is a circle that is evenly distributed over the first to fourth photodetector sections 41a to 41d, and when the objective lens 35 is positioned close to the lead-in area 15 and the focal point of the light beam is positioned on the protective layer 8 side, behind the lead-in area 15, the shape of the beam spot S is an ellipse with the major axis extending in the direction extending over the second and fourth photodetector sections 41b and 41d, as shown in FIG. 7C. In this way, the shape of the beam spot S changes depending on the focusing position of the light beam, and the focus error signal FE is detected by detecting the difference in the amount of light irradiated on the first to fourth photodetector sections 41a to 41d. That is, the focus error signal FE is generated by detecting the difference in the amount of light irradiated on the first and third photodetector sections 41a and 41d of the light receiving section 41.
The focus error signal FE is generated by subtracting, by a subtraction circuit 45, a detection output (A+C) output from a first adder circuit 42 that adds together the detection signals A and C of the second and fourth photodetectors 41b and 41c, and a detection output (B+D) output from a second adder circuit 43 that adds together the detection signals B and D of the second and fourth photodetectors 41b and 41d.
The result of the subtraction circuit 45 is supplied to the servo circuit 50. The servo circuit 50 controls the actuator 37 based on the focus error signal FE to drive and displace the objective lens 35 in the focus direction so that the light beam is focused on the lead-in area 15. The subtraction circuit 45 calculates the sum of the first, second and third adder circuits 42.
, 43 and 44 constitute an RF amplifier 48, which will be described later. In the optical disc reproducing device for reproducing the optical disc 1 according to the present invention, when the optical pickup 32 starts scanning the lead-in area 15 with a light beam, the objective lens 35 is driven and displaced from a position away from the lead-in area 15 in a direction approaching the lead-in area 15, and is controlled so that the focal point of the light beam irradiated onto the lead-in area 15 is positioned. Here, for example, in the lead-in area 1 provided on the second recording layer 6 as shown in FIG.
When an optical disc having a first recording layer 4 extending up to a position facing the first recording layer 5 is loaded, as shown in FIGS. 8A and 8B, the forward beam reflected from the first recording layer 4 is detected by the photodetector 36, and R
The F sum signal rf and the focus error signal fe are generated, and then the first recording layer 4
The light beam that passes through the first recording layer 4 and is reflected by the lead-in area 15 of the second recording layer 6 is detected by the photodetector 36, and an RF sum signal RF and a focus error signal FE based on the light beam reflected from the lead-in area 15 are detected. When the optical disc 1 shown in FIG. 1 is loaded into an optical disc playback device, the first recording layer 4 is configured to reflect the light beam at a position opposite to the lead-in area 15.
9A and 9B, only the light beam reflected from the lead-in area 15 of the second recording layer 6 is detected by the photodetector 36, and an RF sum signal RF and a focus error signal FE based on the light beam reflected from the lead-in area 15 are obtained.
Since only the RF sum signal RF and the focus error signal FE based on the light beam reflected from the lead-in area 15 of the first recording layer 6 can be detected, the light beam from the optical pickup 32 can be reliably focused on the second recording layer 6 on which the lead-in area 15 is provided, and the data recorded in the lead-in area 15 can be read with high precision without including noise components that are generated by passing through the first recording layer 4. 4, even in the optical disc 1 in which the portion of the first recording layer 4 facing the lead-in area 15 is made into a mirrored portion 21, as shown in Figures 8A and 8B, the amount of the light beam reflected from the mirrored portion 21 is extremely small, so the signal levels of the RF signal rf and focus error signal fe generated by the mirrored portion 21 are small compared to the RF sum signal RF and focus error signal FE based on the light beam reflected from the lead-in area 15. Therefore, the RF signal RF and focus error signal FE based on the light beam reflected by the lead-in area 15 are reliably detected, and the light beam from the optical pickup 32 can be reliably focused on the lead-in area 15, and the data recorded in the lead-in area 15 can be read with high precision.
Control data required for reading data such as audio information recorded on at least the first and second recording layers 4 and 6, which is recorded in the lead-in area 15, is read, and based on the control data read from the lead-in area 15, it is determined whether or not the first recording layer 4 is present in the optical disc 1 loaded in the optical disc playback device. Furthermore, the data indicating the reflectivities of the first and second recording layers 4 and 6 is used to select an amplifier circuit, such as the gain of an RF amplifier 48 or a loop gain of a servo circuit 50 (described later), for playing back data recorded on the first and second recording layers 4 and 6. After this switching, the objective lens 35 is moved in the optical axis direction of the objective lens 35 based on a control signal from the system controller 52, and the spot of the light beam focused by the objective lens 35 is moved to either the first recording layer 4 or the second recording layer 6. In this state, the focus servo and tracking servo loops of the servo circuit 50 are already closed, and the optical disc 1 is also rotated by the spindle motor 31 at a constant linear velocity. As described above, in the optical disc 1 according to the present invention, data recorded in the lead-in area 15 is read first, and therefore reading of data recorded in the first recording layer 4 begins after the data recorded in the lead-in area 15 has been read. By recording in the lead-in area 15 the minimum amount of data required for reading data recorded on the first and second recording layers 4, 6, it is possible to select the first or second recording layer 4, 6 and read the data recorded on these recording layers 4, 6. Furthermore, in the optical disc 1 according to the present invention, data recorded in the lead-in area 15 provided on the second recording layer 6 is read first. Therefore, by setting the reflectivity of the incident light beam on the second recording layer 6 to a reflectivity that enables reproduction by a conventional optical disc reproduction device that requires a high reflectivity, it is possible to read the data recorded on the second recording layer 6 after reading the lead-in area 15 using a conventional optical disc reproduction device, thereby ensuring compatibility with conventional optical discs. The data recorded in the lead-in area 15 is read out, and the first or second recording layer 4 or 6 is selected based on this data. When the light beam is focused on the first or second recording layer 4 or 6 and scanning is started, the first or second recording layer 4 or 6
The light beam returning from the optical disc 30 is detected by the photodetector 36 equipped with the four-division detector 41, as described above. The detection signal detected by the photodetector 36 is supplied to an RF amplifier 48. The RF amplifier 48 performs arithmetic processing on the supplied detection signal to extract a reproduction RF signal, a tracking error signal TE, a focus error signal FE, etc. The extracted reproduction RF signal is supplied to a demodulation circuit 53. The tracking error signal TE and the focus error signal FE are also supplied to a servo circuit 50. The servo circuit 50 converts the supplied focus error signal FE and push-pull signal P into a signal.
P, and various servo drive signals are generated based on track jump commands, access commands, rotational speed detection information of the spindle motor 31, etc. from a system controller 52 configured by a microcomputer, and a drive circuit 49 controls the actuator 37 and the feed mechanism 33 to perform focus and tracking control.
The spindle motor 31 is driven at a constant linear velocity (CLV).
The demodulation circuit 53 converts the reproduced RF signal supplied from the RF amplifier 48 into a binary signal,
For example, EFM (eight to fourteen modulation)
The signal is demodulated by the C
IRC (cross interleaved Read Solomon c
2. The optical recording medium according to the present invention performs error correction using a digital-to-analog (D/A) conversion method, and the error-corrected data is supplied to a D/A conversion circuit 55, which converts the data into analog data and outputs it to the outside. Furthermore, the system controller 52 supplies a control signal corresponding to the operation content when an operation unit 56 is operated, and also supplies a control signal to a display unit 57 that displays various operating conditions. When reproducing data recorded on one of the first and second recording layers 4 and 6, which has a lower reflectivity, it is desirable to perform control so as to increase the gain of the reproduced RF signal. INDUSTRIAL APPLICABILITY As described above, the optical recording medium according to the present invention has a lead-in area, in which at least data required for data reading is recorded, located in an area that does not attenuate the transmission amount of the light beam. Therefore, even if a plurality of recording layers are provided, the data recorded in the lead-in area can be accurately read, and data such as audio information and video information recorded on each recording layer can be accurately read and reproduced. Furthermore, the optical disc of the present invention reads data from each recording layer after reading data recorded in a lead-in area in which at least data required for reading data is recorded, the lead-in area being provided in an area that is not affected by other recording layers, so that the desired recording layer can be reliably selected and the desired data can be reliably read.

[Brief explanation of the drawings]

FIG. 1 is a cross-sectional view of an optical disc according to the present invention. FIG. 2 is a plan view of an optical disc according to the present invention. FIG. 3 is a diagram showing a state in which a light beam is irradiated onto first and second recording layers provided on an optical disc according to the present invention. FIG. 4 is a cross-sectional view of another example of an optical disc according to the present invention. FIG. 5 is a block circuit diagram of an optical disc playback device using an optical disc according to the present invention. FIG. 6 is a circuit diagram showing a light beam irradiated onto an optical disc according to the present invention and detecting a focus error signal. FIGS. 7A to 7C are plan views showing a state in which a light beam is irradiated onto a four-division detector that detects a focus error signal using an astigmatism method. FIGS. 8A and 8B are diagrams showing an RF sum signal and a focus error signal obtained when a light beam is irradiated onto an optical disc formed with first and second recording layers facing each other. FIGS. 9A and 9B are diagrams showing an RF signal and a focus error signal obtained when a light beam is irradiated onto an optical disc according to the present invention.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (30)

[Claims] [Claim 1] An optical recording medium comprising: a substrate having optical transparency; a first recording layer provided on one side of the substrate; a second recording layer provided so as to be stacked on the first recording layer and having a lead-in area in which at least data required for reading data is recorded; and an intermediate layer provided between the first recording layer and the second recording layer, wherein the first recording layer is provided from outside the lead-in area. 2. The optical recording medium according to claim 1, wherein said lead-in area records at least a part of the data necessary for reading out the data recorded on said first recording layer. 3. The optical recording medium according to claim 1, wherein data relating to the reflectance of said first recording layer is recorded in said lead-in area. 4. The optical recording medium according to claim 1, wherein data indicating that the first recording layer is provided is recorded in the lead-in area. 5. The optical recording medium according to claim 1, wherein the reflectance of either said first recording layer or said second recording layer is higher than the reflectance of the other recording layer. [Claim 6] An optical recording medium comprising: a substrate having optical transparency; a first recording layer provided on one surface of the substrate; a second recording layer provided so as to be stacked on the first recording layer and having a lead-in area in which at least data required for reading data is recorded; and an intermediate layer provided between the first recording layer and the second recording layer, wherein at least a portion of the portion of the first recording layer facing the lead-in area is a mirror surface. 7. The optical recording medium according to claim 6, wherein said lead-in area records at least a part of the data necessary for reading out the data recorded on said first recording layer. 8. The method according to claim 6, wherein the mirror surface of the first recording layer is disposed in the direction of the data read start position of the lead-in area provided on the second recording layer.
Item 1. An optical recording medium according to item 1. 9. The optical recording medium according to claim 6, wherein data is recorded on said first recording layer following said mirror surface portion. 10. The optical recording medium according to claim 6, wherein data relating to the reflectance of said first recording layer is recorded in said lead-in area. 11. The optical recording medium according to claim 6, wherein data indicating that the first recording layer is provided is recorded in the lead-in area. 12. The optical recording medium according to claim 6, wherein the reflectance of either said first recording layer or said second recording layer is higher than the reflectance of the other recording layer. [Claim 13] An optical recording medium having a light-transmitting substrate and at least a first recording layer and a second recording layer, one of the first recording layer and the second recording layer being provided on one side of the substrate, and the other recording layer being provided so as to be stacked on the one recording layer via an intermediate layer, and having a lead-in area in which at least data required for reading data is recorded. 14. The lead-in area of claim 13, wherein at least a part of data necessary for reading data recorded on the first recording layer is recorded.
Item 1. An optical recording medium according to item 1. 15. The optical recording medium according to claim 13, wherein data relating to the reflectance of said first recording layer is recorded in said lead-in area. 16. The optical recording medium according to claim 13, wherein data indicating that the first recording layer is provided is recorded in the lead-in area. 17. The optical recording medium according to claim 13, wherein the reflectance of said one recording layer is lower than the reflectance of the other recording layer. [Claim 18] A method for reading an optical recording medium, the method comprising: reading data from the lead-in area of the second recording layer of an optical recording medium having a light-transmitting substrate and at least a first recording layer and a second recording layer, one of the first recording layer and the second recording layer being provided on one side of the substrate, the other recording layer being provided so as to be stacked on the one recording layer via an intermediate layer, and having a lead-in area in which at least data required for reading data is recorded; and reading data from the first recording layer after reading the data in the lead-in area. 19. A light-transmitting substrate and a first light-transmitting layer provided on one surface of the substrate.
a second recording layer provided so as to be stacked on the first recording layer and having a lead-in area in which at least data required for reading data is recorded;
and an intermediate layer provided between the first recording layer and the second recording layer, wherein the first recording layer is provided outside the lead-in area, the method comprising: reading data from the lead-in area of the second recording layer of the optical recording medium; and reading data from the first recording layer after reading the data in the lead-in area. 20. A light-transmitting substrate and a first light-transmitting layer provided on one surface of the substrate.
a second recording layer provided so as to be stacked on the first recording layer and having a lead-in area in which at least data required for reading data is recorded;
and an intermediate layer provided between the first recording layer and the second recording layer, wherein at least a part of a portion of the first recording layer facing the lead-in area is a mirror surface, the method comprising: reading data from the lead-in area of the second recording layer of the optical recording medium; and reading data from the first recording layer after reading the data from the lead-in area. [Claim 21] An optical recording medium comprising: a substrate; a first recording layer provided on one surface of the substrate; a second recording layer provided so as to be stacked on the first recording layer; and an intermediate layer provided between the first recording layer and the second recording layer, wherein the first recording layer and the second recording layer are biased relative to each other in the layer direction. 22. The optical recording medium according to claim 21, wherein said second recording layer is stacked so as to be read out before said first recording layer. [Claim 23] An optical recording medium as described in claim 22, wherein the second recording layer is provided so that the recording start position of the second recording layer protrudes in the layer direction beyond the recording start position of the first recording layer. 24. The optical recording medium according to claim 23, wherein the other ends of said first recording layer and said second recording layer are aligned. [Claim 25] An optical recording medium as described in claim 21, wherein the second recording layer has a lead-in area in which at least data required for reading data is recorded, and a data recording area, and the lead-in area is located at a position where it is read before the data recording area. 26. The method according to claim 21, wherein at least a part of data necessary for reading data recorded on the first recording layer is recorded in the lead-in area.
Item 1. An optical recording medium according to item 1. 27. The optical recording medium according to claim 21, wherein data relating to the reflectance of said first recording layer is recorded in said lead-in area. 28. The optical recording medium according to claim 21, wherein data indicating that the first recording layer is provided is recorded in the lead-in area. 29. The optical recording medium according to claim 21, wherein the reflectance of either said first recording layer or said second recording layer is higher than the reflectance of the other recording layer. [Claim 30] A method for reading an optical recording medium, comprising: reading data recorded in a lead-in area from an optical recording medium having a first recording layer with a lead-in area stacked on a substrate; determining whether or not a second recording layer exists between the recording layer and the substrate based on the data read from the lead-in area; and, when it is determined that the second recording layer exists, reading the second recording layer based on control data recorded in the lead-in area.