JP2007213624A - Optical information recording medium and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording medium and device which can recognize the information of a recording medium written on it for the thickness of its base and shorten the time required to correct the spherical aberration by setting up the initial conditions for learning. <P>SOLUTION: The base thickness information of the optical information recording medium can be detected even if a spherical aberration is produced by the thickness difference of the base of which the thickness is unknown, and the method can shorten the time required to correct the spherical aberration. Recording the thickness information of the base by using a method capable of detecting the spherical aberration even if misaligned, the information is used as a guide for the recording and reproducing device to correct the spherical aberration, and the time before optimization can be shortened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc having at least one information recording layer, and relates to a disc for recording or reproduction.

  The present invention also relates to an apparatus for recording / reproducing information using the disc.

  Conventionally, in a CD or DVD, the numerical aperture of a lens when irradiating recording / reproducing light is small, and even a DVD larger than a CD is 0.6. Thus, the accuracy of the thickness of the base material on which the recording / reproducing light is incident is designed, and in DVD, it is defined as 0.6 ± 0.03 mm for a single layer disc. Conversely, if the thickness of the base material up to the information recording layer where information is to be recorded exceeds this range, the signal deteriorates, and the accuracy of recording and reproduction decreases.

  Recently, optical discs with higher density than DVD have been developed, and the thickness of the base material through which light passes has been studied from 0.6 mm for DVD to about 0.1 mm, which is thinner than recording DVD. -Ray Disc (BD) is on the market.

By reducing the thickness of the base material to 0.1 mm, the numerical aperture of the lens is set to 0.85, which is larger than that of the DVD. Thus, the occurrence of aberration with respect to tilt is suppressed, and a margin for tilt that is almost the same as that of DVD is secured.
JP 2000-76705 A

  However, when the substrate thickness is reduced to 0.1 mm, the influence of spherical aberration that occurs due to the change in thickness increases.

  For this reason, a mechanism for correcting spherical aberration is employed in an optical head that performs recording and reproduction. As a result, even if the substrate thickness changes, the optical head can ensure a good recording / reproducing function by correcting the spherical aberration.

  It is not easy to follow dynamically within one rotation of the disk, but in particular, for the deviation of the average thickness between the disks, it is necessary to correct the spherical aberration in the initial stage so that it is within the disk surface. Can be recorded and reproduced.

  However, in order to correct the spherical aberration, it is necessary to learn while detecting the tracking error signal and the recording / reproducing signal in order to detect the optimum value. There is a problem that it takes a long time to start after being inserted into.

  Therefore, in the present invention, the substrate thickness information is stored in the medium. In particular, by reducing the density of the recording means for the substrate thickness information, the information can be recognized even when the spherical aberration is not in the substrate thickness.

  As an example of such means, there is means called BCA (burst cutting area) which has been used in conventional DVDs. In BCA, a barcode-like mark is processed by burning a reflection film or a recording film in an information recording layer with, for example, a laser, and information such as a serial number of a medium can be additionally recorded. For example, Patent Document 1 described above describes an example of the processing method. By recording the substrate thickness information in the BCA mark, the recording / reproducing means can read the substrate thickness information even for an information recording medium in which the substrate thickness is unknown and the spherical aberration correction is shifted. Can do.

  According to the present invention, the information recording / reproducing means can recognize the substrate thickness information written on the information recording medium, and can set the initial value of learning to reduce the time required for correcting the spherical aberration.

  In particular, when the BCA mark has a sufficiently low recording density, information can be easily read even when the spherical aberration does not match.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram showing the structure of an optical disc according to an embodiment of the present invention. A reflective film 102 made of an Al alloy of an information recording layer is laminated on a 1.1 mm thick polycarbonate substrate 101 having information on one side with pits, and a cover layer 103 is laminated, from the cover layer 103 side. Play information.

  Recording is performed on this optical disk by irradiating light from a YAG laser (wavelength 1064 nm) shaped into a rectangle to the reflection film (information recording layer) 102 from the substrate 101 side and rotating the disk by a rotation mechanism in synchronization therewith. A barcode-like BCA mark 104 whose interval was modulated by the signal to be formed was formed on the reflective film (information recording layer) 102. The BCA mark 104 is read out with the optical head focused on the information recording layer.

  FIG. 2 is a schematic diagram of the BCA mark 104 formed on the reflective film (information recording layer) 102, which is formed in a stripe shape with a width of about 8 μm. Each mark has a basic interval of 28.6 μm and is formed at intervals of 1, 2, 3, and 4 times, and information is recorded by changing the interval.

  By this method, a disk A having a cover layer of 100 μm and a disk B having a thickness of 75 μm were prepared.

  In order to reproduce this disc, the built-in optical head has a built-in beam expander consisting of two lenses, and the spherical aberration of the light emitted from the objective lens is corrected by changing the distance. it can.

  For both discs, an objective lens having a wavelength of 405 nm and a numerical aperture (NA) of 0.85 is used, and the spherical aberration is focused in the best condition when the thickness of the cover layer is 100 μm, and the reflective film (information signal recording layer) FIG. 3 shows respective waveforms reproduced by passing the BCA mark 104 of 102 through the cover layer 103.

  Random data having a shortest pit length of 0.149 μm is recorded at a track pitch of 0.35 μm on the base subjected to BCA processing.

  The BCA mark portion is reproduced as a portion having a low reflectance because the reflective film 102 is burned.

  Since the spherical aberration of the optical head to be reproduced is adjusted so as to be optimal when the substrate thickness is 100 μm, when the disk A is reproduced, the light can be reduced to the smallest on the reflective film 102. Therefore, the amount of reflected light is modulated by the pits on the ground, and the pit information is reproduced as a large intensity change except for the BCA mark portion. Also, since the BCA signal has a lower recording density than the underlying pit signal and is recorded with a long mark, it is reproduced as a long low-reflectance part and can be sufficiently detected.

  However, in the disk B having a substrate thickness of 75 μm, the light on the reflection film 102 is blurred and enlarged due to spherical aberration. Therefore, the pits on the ground appear relatively small with respect to the reproduction light, and many pits enter the spot, so that the spatial frequency characteristic is lowered and the intensity modulation is reduced.

  However, it can be seen that the BCA mark portion is a sufficiently long mark, so that it is reproduced with a sufficient degree of modulation even in a state where the light is blurred and concentrated largely, and can be detected well.

  By including the cover layer thickness information as the BCA mark signal, the drive for reproducing the optical disk detects the base material thickness information from the BCA mark and corrects the spherical aberration correction value suitable for the disk. Can be known from the setting value built in itself. Then, conditions such as focus, spherical aberration, and tilt are optimized so that the reproduction quality of the recorded signal is optimized. At this time, by setting the spherical aberration setting value obtained from the base material thickness information of the disk as an initial value at the time of learning, the time required to optimize the spherical aberration can be shortened.

  In particular, since the BCA processing can be recorded after the cover layer 103 is formed, the optimum value can be recorded on each disk by measuring the thickness of the cover layer 103 and processing the thickness into BCA.

  In the embodiment of the present invention, the thickness of the cover layer 103 is reduced to 75 μm. However, even a thinner cover layer can be detected, and the BCA mark can be detected even without the cover layer.

  However, since the working distance of an objective lens having a large numerical aperture is shortened, the working distance becomes insufficient when the cover layer is thick. Therefore, the present invention is effective for an optical disc system having a thin cover layer 103 and a large numerical aperture. For example, it is particularly effective for a system such as a Blu-ray Disc having a cover layer of about 0.1 mm and a numerical aperture of 0.85.

  In the embodiment of the present invention, a read-only disc is used, but the same effect can be obtained by forming a mark such as BCA in the information recording layer in the recording / playback type and write once type discs as well. Obtainable.

  Furthermore, if the mark such as BCA is not on the information recording layer, on the cover layer, or in the cover layer, but can be detected by the reproducing head in the same way as BCA, the place where the mark is formed is Not limited.

  In the embodiment of the present invention, a single-layer disc having only one information recording layer has been described. However, the present invention is also useful for an information recording medium having a plurality of information recording methods. In this case, the thickness information of the base material is preferably placed in the information recording layer that is the farthest from the recording / reproducing surface side or the information recording layer that is closest to the focus servo. Further, the recorded thickness information is preferably thickness information from the recording / reproducing side surface to the information recording layer on which the information is recorded.

  Furthermore, by using the present invention, since the substrate thickness can be changed within the range where the substrate thickness information can be read out, the substrate thickness can be reduced to reduce the material cost and the effect of reducing the cost of the disk. It is done.

  The present invention is an information recording medium such as an optical disk, and an information recording medium in which the thickness of a base material on which information is recorded and reproduced through light is thin, and the light to be reproduced is condensed with a large numerical aperture, and the information is recorded and reproduced. The recording / reproducing apparatus can be used for a recording / reproducing apparatus that corrects spherical aberration and the like. In particular, it can be used effectively when the thickness of the substrate is different between the disks.

Schematic diagram of the optical disk of the present invention Schematic diagram of BCA mark in the present invention Schematic diagram of reproduction signal of BCA mark in the present invention

Explanation of symbols

101 Substrate 102 Reflective film 103 Cover layer 104 BCA mark

Claims (9)

An optical information recording medium having at least one information recording layer for recording or reproducing information through a substantially transparent base material at a wavelength of light for recording / reproducing information, wherein information indicating the thickness of the base material is recorded and An optical information recording medium having an information recording layer. 2. The optical information recording medium according to claim 1, wherein the information recording layer on which information indicating the thickness of the base material is recorded is an information recording layer farthest or closest to the surface of the base material. The optical information recording medium according to claim 1, wherein the information indicating the thickness of the base material is a thickness from the surface of the base material to the information recording layer on which information indicating the thickness of the base material is recorded. The optical information recording medium according to any one of claims 1 to 3, wherein an information recording density of the means for recording the thickness of the base material is lower than that of the other region of the information recording layer. The optical information recording medium according to any one of claims 1 to 4, wherein the information recording layer is recorded with a barcode mark as means for recording the thickness of the substrate. The optical information recording medium according to any one of claims 1 to 5, wherein the base material has a thickness of 0.1 mm or less. The information is recorded / reproduced by irradiating the information recording / reproducing light through a lens having a numerical aperture of 0.8 or more when irradiating the information recording / reproducing light through the substrate. The optical information recording medium according to one item. An information recording / reproducing apparatus for knowing a spherical aberration correction value of a recording / reproducing means according to information on a substrate thickness recorded on an information recording medium. 9. The optimum value of spherical aberration correction is obtained by setting an initial value of spherical aberration correction of the recording / reproducing means based on information on the substrate thickness recorded on the optical information recording medium, and performing learning by recording / reproducing. Information recording / reproducing apparatus.

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