JP2012033267A - Multilayer optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer optical disk having three or more recording layers for easily performing focus drawing to a desired recording layer in which a BCA is disposed.SOLUTION: Among a desired recording layer and recording layers adjacent to the desired recording layer, an interlayer distance between the desired recording layer and a recording layer in which a laser spot crosses earlier than the desired recording layer at the time of focus drawing operation is set larger than the other interlayer distances.

Description

  The present invention relates to a multilayer optical disc having three or more recording layers.

  As a method for increasing the recording capacity of an optical disc, there are a method of shortening the wavelength of laser light for recording / reproducing data, miniaturization of a laser spot by increasing the NA of an objective lens, and multilayering of a plurality of recording layers. As a multilayer optical disc, a dual-layer disc has been put into practical use in DVD and Blu-ray Disc (hereinafter referred to as BD).

  In recent years, optical discs having three or more recording layers have been proposed. For example, Non-Patent Document 1 proposes a BD having six recording layers.

ODS2006 Technical digest (2006) 041

  Here, in the multilayer optical disc, a recording layer to be focused first is considered.

  In the two-layer BD, the recording layer at a depth of 100 μm from the disc surface on which the laser beam for recording / reproducing information is incident is called L0, and the recording layer at a depth of 75 μm is called L1, but the disc type information A BCA (Burst Cutting Area) code including DI (Disc Information) in which etc. are recorded is arranged in the recording layer L0.

  FIG. 2 shows a schematic diagram of an optical disc having BCA.

  In FIG. 2, a hole 202 for mounting a disk is provided at the center of the optical disk 201, and a BCA 203 is disposed around the hole. When the optical disc 201 is rotated and focusing servo is performed on the recording layer L0 at the radial position of the BCA, the reflected light level from the optical disc 201 becomes barcode data that repeats strength. This bar code data is a BCA code including DI.

  In order to read out the BCA code, only the focusing servo needs to be performed, and the tracking servo is unnecessary. The optical disc apparatus determines which of the media types, such as BD-ROM and BD-R, the mounted optical disc corresponds to by using the level of the reflected signal. Is performed with reference to the DI recorded in advance. In order to determine the type of the medium in a short time, it is necessary to focus the recording layer on which the BCA 203 that is the recording layer on which the information to be reproduced first is recorded. It is desirable for the optical disc apparatus to first draw the focus into the recording layer L0.

  The 6-layer BD has not been standardized yet, so it is not determined in which layer the BCA or its equivalent will be placed. However, considering the conventional technology, it is described in Non-Patent Document 1 described above. It is expected to be arranged in the innermost recording layer L0 in the 6-layer BD. In that case, for an optical disc apparatus that supports 6-layer BD, it is desirable to first draw the focus into the innermost recording layer L0, which is the recording layer on which information to be reproduced first is recorded.

  An object of the present invention is to provide a multilayer optical disc having three or more recording layers, which can be easily brought into the recording layer on which information to be reproduced first is recorded.

  For example, the object of the present invention can be achieved by adjusting the interlayer relationship between a recording layer in which information to be reproduced first is recorded and another recording layer adjacent thereto.

  According to the present invention, it is a multilayer optical disc having three or more recording layers, and the focus can be easily drawn into the recording layer on which information to be reproduced first is recorded.

1 is a cross-sectional view of a six-layer optical disk showing Example 1 of the present invention. It is a schematic diagram of the optical disk which has BCA. It is a schematic diagram which shows the focus error signal waveform at the time of raising an objective lens. It is a schematic diagram which shows the relationship between spherical aberration correction amount and focus S-shaped signal amplitude. It is sectional drawing of the 6 layer optical disk which shows Example 2 of this invention. It is a schematic diagram showing a focus error signal waveform when the objective lens is raised and lowered.

  Hereinafter, embodiments of the present invention will be described.

  Hereinafter, Example 1 in the present invention will be described.

  The operation of drawing the focus and the signal waveform in the 6-layer BD will be described with reference to the schematic diagram of FIG. In FIG. 3, the spherical aberration correction mechanism provided in the optical disc apparatus is adjusted in advance so as to be optimal for the recording layer L0.

  FIG. 3A is a cross-sectional view of a 6-layer BD disc. The arrow in the figure indicates the locus of a laser spot when the objective lens is raised when the focus is pulled. FIG. 3B is a conceptual diagram of a focus error (hereinafter referred to as FE) signal, and a known S-shaped signal that crosses zero at time T0 when the laser spot crosses the surface of the disk appears. As the objective lens continues to rise, an S-shaped signal that crosses zero at time T1 when the laser spot crosses the recording layer L5 appears in the FE signal. Hereinafter, recording layers L4, An S-shaped signal also appears in the FE signal when crossing L3, L2, L1, and L0.

  In a multilayer optical disc, spherical aberration occurs due to a difference in distance from the disc surface on which a laser for recording / reproducing information is incident to each recording layer. For this reason, the amplitude of the S-shaped signal in each recording layer is reduced. It is known to be different. For example, in FIG. 3, since the spherical aberration correction amount is set to be optimal in the recording layer L0, the S-shaped signal amplitude in the recording layer L0 is larger than the other S-shaped signal amplitudes. Further, since the spherical aberration correction amount is deviated from the optimum value in the recording layer L1, the S-shaped signal amplitude in the recording layer L1 is smaller than the S-shaped signal amplitude in the recording layer L0. Similarly, the S-shaped signal amplitude of the FE signal decreases as the distance from the recording layers L2, L3, L4, and L5 and the recording layer L0 decreases.

  Accordingly, as shown in FIG. 3, after the detection level Vth is provided between the bottom peak levels B1 and B0 of the S-shaped signals in the recording layer L1 and the recording layer L0, and the FE signal exceeds the detection level Vth. By using a method of detecting the timing at which the FE signal crosses zero, it is possible to accurately focus the recording layer L0.

  In order to use the above method, the S-shaped signal amplitude in the recording layer L0 where the BCA is arranged needs to be the largest. However, the S-shaped signal amplitude changes due to the reflectance of each recording layer and the correction error of spherical aberration correction, and the bottom level of the S-shaped signal in the other recording layer exceeds the detection level Vth, or in the recording layer L0. There arises a problem that the bottom level of the S-shaped signal does not exceed the detection level Vth. Therefore, in order to solve this problem, it is necessary to provide an optical disc having the largest S-shaped signal amplitude in the recording layer L0.

  FIG. 1 is a schematic cross-sectional view of a six-layer optical disk in Example 1 of the present invention.

  Reference numeral 100 denotes a cover layer having a thickness of 40 μm and is made of a transparent resin or the like.

  Reference numerals 101 to 106 denote recording layers L5, L4, L3, L2, L1, and L0, respectively. All the recording layers have the same reflectance. Each recording layer has a laminated structure using a phase change material or an organic material. However, the structure does not constitute the structure of this embodiment, so that the description thereof is omitted.

  Reference numerals 107 to 111 denote space layers. The thickness of the space layers 107 to 110 is 15 μm, and the thickness of the space layer 111 is 20 μm. Each space layer is made of a transparent resin.

  Reference numeral 112 denotes a base, which is made of polycarbonate or the like.

  Note that the thickness of the entire optical disk including the cover layer 100 and the base 112 is 1.2 mm.

  A laser beam for recording / reproducing information is incident from the cover layer 100 side.

  A feature of the optical disk of this embodiment is that the thickness of the space layer 111 is larger than that of other space layers. Hereinafter, the effect will be described with reference to FIG.

  FIG. 4 is a schematic diagram showing the relationship between the spherical aberration correction amount and the S-shaped signal amplitude of the FE signal.

Curve (a) in FIG. 4 is a plot of the S-shaped signal amplitude in the recording layer L5 when the spherical aberration correction amount is changed. Since the distance from the disk surface to the recording layer L5 is 40 μm, the optimum value of the spherical aberration correction amount is 40 μm, and the S-shaped signal amplitude is maximized at that time. Similarly, curve (b) plots the S-shaped signal amplitude in the recording layer L4 when the spherical aberration correction amount is changed. Since the distance from the disc surface to the recording layer L4 is 55 μm including the cover layer 100 and the space layer 107, 55 μm is the optimum value for the spherical aberration correction, and the S-shaped signal amplitude is maximized at that time. Similarly, curves (c), (d), (e), and (f) are plots of S-shaped signal amplitudes in the respective recording layers L3, L2, L1, and L0, and the respective spherical aberration correction amounts. Is equal to the distance from the disk surface to each recording layer, and the S-shaped signal amplitude is maximized at 70 μm, 85 μm, 100 μm, and 120 μm.

  As described above, the reflectance of each recording layer is the same, and the maximum value of each S-shaped signal amplitude is the same, so the maximum amplitude value is set to 100%.

  When the spherical aberration correction amount is 120 μm which is the optimum value for the recording layer L0, the S-shaped signal amplitude difference between the recording layer L0 and the recording layer L1 corresponds to D1 in FIG. Therefore, the level difference between the bottom levels B1 and B0 of the S-shaped signal in FIG. 3 corresponds to approximately half of D1.

  Here, the effect of this embodiment is compared with the case where this embodiment is not applied. As an example of the case where the present embodiment is not applied, consider a case where the thickness of the space layer 111 between the recording surfaces L1 and L0 is 15 μm, which is the same as other space layers. The relationship between the spherical aberration correction amount and the S-shaped signal amplitude at this time is plotted as a curve (g) indicated by a dotted line in FIG. When the thickness of the space layer 111 is 15 μm, the thickness from the disk surface to the recording layer L0 is 115 μm, and therefore the curve (g) becomes maximum when the spherical aberration correction amount is 115 μm. In this case, the S-shaped signal amplitude difference between the recording layer L0 and the recording layer L1 corresponds to D2 in FIG.

As is apparent from FIG. 4, the amplitude difference D1 of the S-shaped signal when the present embodiment is applied is larger than the amplitude difference D2 of the S-shaped signal when the present embodiment is not applied. This means that the level difference between the bottom levels B1 and B0 in FIG. 3 becomes large, so that the margin of the threshold level Vth for each of the bottom levels B0 and B1 can be increased. Therefore, even when the S-shaped signal amplitude of the FE signal changes due to the reflectance error of the recording layers L0 and L1 and the thickness error of the space layer 111, the bottom level B0 of the S-shaped signal in FIG. It does not occur that Vth is exceeded or the bottom level B1 is less than the threshold level Vth. For this reason, since the S-shaped signal in the recording layer L0 can be accurately detected by the threshold level Vth, the focus can be correctly drawn into the desired recording layer L0.

  In the first embodiment of the present invention described above, the thickness of the space layer 111 between the desired recording layer L0 and the recording layer L1 to be focused is made larger than the thicknesses of the other space layers. The bottom level difference of the focus S-shaped signal in the layer L0 and the recording layer L1 is enlarged. As a result, the optical disk apparatus can accurately detect the S-shaped signal in the recording layer L0, so that the focus can be correctly drawn into the target recording layer L0.

  In the first embodiment described above, the BCA is arranged in the recording layer L0. However, the recording layer in which the BCA is arranged is not necessarily limited to L0. For example, when the BCA is arranged in the recording layer L2, the target layer for focus pulling is L2. In this case, if the thickness of the space layer 109 between the recording layer L2 and the recording layer L3 is larger than the thicknesses of the other space layers, the focus is accurately drawn into the recording layer L2 in the same manner as the above-described operation. Can do.

  The six-layer optical disk in the first embodiment is configured such that the BCA is arranged in the recording layer L0, but the BCA may be arranged in the recording layer L5.

  Further, in the first embodiment, the case where the objective lens is raised to perform the focus pull-in has been described. However, in order to avoid the collision between the objective lens and the optical disk surface when the focus pull-in fails, the laser spot is formed on all the recording layers. A method is known in which the objective lens is once raised until the value exceeds, and then the lens is lowered to perform focus pull-in.

  Thus, as a second embodiment, a multilayer optical disc that allows the focus to be accurately drawn into the recording layer L5 when the above-described downward focus pull-in is performed on the six-layer optical disc in which the BCA is arranged in the recording layer L5 will be described.

  FIG. 5 is a schematic cross-sectional view of a six-layer optical disk in Example 2 of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  Reference numerals 113 and 114 are space layers. The thickness of the space layer 113 is 15 μm, and the thickness of the space layer 114 is 20 μm.

  As in the first embodiment, the total thickness of the optical disk including the base layer 112 from the cover layer 100 is 1.2 mm, and laser light for recording / reproducing information is incident from the cover layer 100 side.

  A feature of the optical disk of this embodiment is that the thickness of the space layer 114 is larger than that of other space layers. Hereinafter, the effect will be described with reference to FIG. Each schematic diagram of FIG. 6 is the same as FIG.

  The optical disc apparatus adjusts in advance the spherical aberration correction amount so as to be optimal for the recording layer L5 in order to focus the recording layer L5. In this state, when the objective lens is raised, the disk surface is crossed at time T0 in FIG. 6, and the recording layers L5, L4, L3, L2, L1, and L0 are crossed at times T1, T2, T3, T4, T5, and T6. . Then, the optical disk device switches the objective lens to the lowering operation at time T7 after the laser spot exceeds the recording layer L0. Thereafter, the descending objective lens crosses the recording layers L0, L1, L2, L3, L4, and L5 at times T8, T9, T10, T11, T12, and T13.

  When the laser spot crosses each recording layer in accordance with the operation of the objective lens described above, an S-shaped signal appears in the FE signal. Here, since the spherical aberration correction amount is set so as to be optimal for the recording layer L5 that is the target of focus pull-in, the S-shaped signal amplitude when traversing the recording layer L5 is maximized at times T1 and T13.

Here, in the second embodiment, the thickness of the space layer 114 between the recording layer L5 and the recording layer L4 is larger than the thickness of the other space layers, so the first embodiment will be described with reference to FIG. As a result, the difference in level between the top level B3 of the S-shaped signal in the recording layer L4 that appears near time T12 and the top level B2 of the S-shaped signal in the recording layer L5 that appears near time T13 increases. Therefore, the margin of the threshold level Vth for each of the top levels B2 and B3 can be increased. For this reason, even when the S-shaped signal amplitude of the FE signal changes due to the reflectance error of the recording layers L5 and L4 and the thickness error of the space layer 114, the top level B2 of the S-shaped signal in FIG. Below Vth, or the top level B3 is the threshold level V
No more than th. Therefore, since the S-shaped signal in the recording layer L5 can be accurately detected based on the threshold level Vth, if the focus servo loop is closed at the time T13 when the FE signal crosses 0 after detecting the S-shaped signal in the recording layer L5, the desired value can be obtained. It is possible to correctly focus the recording layer L5.

  In the second embodiment of the present invention described above, the thickness of the space layer 114 between the desired recording layer L5 and the recording layer L4 to be focused is made larger than the thicknesses of the other space layers. The bottom level difference of the focus S-shaped signal in the layer L5 and the recording layer L4 is enlarged. As a result, the optical disk apparatus can accurately detect the S-shaped signal in the recording layer L5, so that the focus can be correctly drawn into the target recording layer L5.

  In the second embodiment described above, the BCA is disposed in the recording layer L5. However, the recording layer in which the BCA is disposed is not necessarily limited to L5. For example, when the BCA is arranged in the recording layer L3, the target layer for drawing in the focus is L3. In this case, if the thickness of the space layer 109 between the recording layer L2 and the recording layer L3 is made larger than the thicknesses of the other space layers, the focus can be accurately drawn into the recording layer L3 as in the above-described operation. Can do.

  Further, in Example 1 and Example 2, the thickness of the cover layer is 40 μm and the thickness of each space layer is 15 μm or 20 μm. However, these thicknesses are not limited to the above values, The recording / reproducing characteristics may be set as appropriate so as to obtain desired characteristics.

  Furthermore, in the first and second embodiments, the description has been given by taking the six-layer optical disk as an example, but it goes without saying that the present invention may be applied to a multilayer optical disk having three or more layers.

  In the first and second embodiments, the recordable multilayer optical disc has been described. However, the present invention may be applied to a read-only multilayer optical disc.

  In the first and second embodiments, the optical disc type information is included in the BCA code. However, the optical disc type information is not limited to the BCA as long as the optical disc type information is included.

100 ... Cover layer, 101, 102, 103, 104, 105, 106 ... Recording layer, 107, 108, 109, 110, 111, 113, 114 ... Space layer, 112 ... Base

Claims (6)

A multilayer optical disc having three or more recording layers,
A first recording layer on which information to be reproduced first is recorded, and a second recording layer adjacent to the first recording layer, which is close to a disk surface on which a laser beam for recording / reproducing information is incident. The distance between the recording layers is larger than the distance between other layers.
Multi-layer optical disc. The multilayer optical disc according to claim 1,
The first recording layer is a recording layer farthest from a disk surface on which a laser beam for recording / reproducing information is incident,
Multi-layer optical disc. The multilayer optical disc according to claim 1 or 2,
The first recording layer is a recording layer having BCA;
Multi-layer optical disc. A multilayer optical disc having three or more recording layers,
A first recording layer on which information to be reproduced first is recorded, and a second recording layer adjacent to the first recording layer, which is far from a disk surface on which a laser beam for recording / reproducing information is incident. The distance between the recording layers is larger than the distance between other layers.
Multi-layer optical disc. The multilayer optical disc according to claim 4, wherein
The first recording layer is a recording layer closest to a disk surface on which a laser beam for recording / reproducing information is incident,
Multi-layer optical disc. The multilayer optical disc according to claim 4 or 5,
The first recording layer is a recording layer having BCA;
Multi-layer optical disc.

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