JP2006318520A - Optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk wherein inclination of an optical axis azimuth of double refraction of a transparent protective layer in one direction can be prevented and a stable reproducing signal with high recording density can be obtained. <P>SOLUTION: The optical disk wherein information which can be optically read out is recorded or wherein information can be optically recorded and information can be optically read out is provided with a substrate 1 having an information recording surface and the transparent protective layer including a plurality of transparent resin sheets laminated on the information recording surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc provided with a transparent protective sheet that enables high-density recording of information.

  An optical disc is composed of a substrate on which pits indicating information signals are formed and a transparent protective layer for protecting the information signals. The optical disc apparatus irradiates the information signals with light through the transparent protective layer of the optical disc and detects return light. Thus, an information signal is recorded and / or reproduced.

  Conventionally, the numerical aperture of an objective lens used for irradiating light to an optical disc is about 0.6 in a DVD (Digital Versatile Disc) or the like.

  In recent years, a technique for reducing the spot diameter of irradiated light by increasing the numerical aperture of an objective lens to 0.7 or more has been proposed in order to cope with higher recording density.

If the numerical aperture of the objective lens is increased, it becomes more susceptible to aberrations and birefringence due to the transparent protective layer, and the allowable tilt of the optical disk surface to keep the spot diameter of the irradiated light small, so the optical disk transparent protection It is necessary to make the layer thin. For example, in a DVD or the like, the transparent protective layer is composed of a substrate in which a transparent resin having a thickness of about 0.6 mm is injection-molded, but it is difficult to mold to a thickness thinner than this by an injection molding method. For optical disk devices with a large numerical aperture of 0.7 or more, transparent protection is achieved by sticking a transparent protective sheet made of resin with a thickness of about 0.1 mm to the substrate surface by roller pressing using an adhesive. Techniques for forming layers are used.
JP 2004-103141 A

  However, the birefringence having the azimuth of the optical axis in the transparent protective layer is caused by the molecular orientation caused by the shearing force when producing the transparent resin sheet, the tension applied when the transparent resin sheet is pressure-bonded to the optical disk surface, and the like. When the optical axis direction of the birefringence rotates with the rotation of the optical disk in the optical disk apparatus, a phenomenon that the detection signal intensity greatly fluctuates occurs and the reproduced signal deteriorates.

  FIG. 4 is a schematic diagram showing an optical disc and an optical disc apparatus not using the present invention. In the figure, 1 denotes an optical disk substrate, 2 denotes an information surface on which recorded information is formed, and 10 denotes a transparent resin sheet. The transparent resin sheet 10 has a thickness of 0.1 mm and constitutes a transparent protective layer. 11 shows the optical axis direction of a transparent resin sheet.

  FIG. 5 is a schematic diagram showing a reproduction signal of a conventional optical disc. In the figure, the horizontal axis represents the amount of rotation of the optical disk, and the vertical axis represents the reproduction signal voltage. The reproduction signal undergoes a phenomenon that varies greatly depending on the optical axis orientation of the birefringence of the transparent protective layer accompanying the rotation of the optical disk.

  In order to achieve the above object, the first aspect of the present invention records information that can be optically read, or records information optically and optically reads the information. An optical disc that can be used includes a substrate having an information recording surface and a transparent protective layer made of a plurality of transparent resin sheets laminated on the information recording surface.

  Further, when the transparent protective layer is formed by laminating a plurality of transparent resin sheets having substantially the same thickness, it becomes easy to cancel the direction of birefringence of the transparent resin sheet.

  Further, when the transparent protective layer is composed of n layers of the transparent resin sheet and the transparent resin sheet is arranged so that the optical axis directions of birefringence are different by π / n, the birefringence of the transparent resin sheet is effectively obtained. Offset.

  In addition, the transparent protective layer is composed of n layers of transparent resin sheets, and the transparent resin sheets are arranged on the information recording surface in different directions by π / n, and are pressed and laminated so as not to have birefringence directionality. Can be realized.

  According to the optical disc of the first aspect of the present invention, the birefringent optical axis direction of the transparent protective layer can be prevented from being biased in one direction, so that an optical disc with a high recording density and a stable reproduction signal can be obtained. Is possible.

(Embodiment 1)
FIG. 1 is a schematic view showing an example of an optical disk according to the present invention. In the figure, 1 is an optical disk substrate, 2 is an information surface on which recorded information is formed, 3 is a first transparent resin sheet having a thickness of 0.05 mm, and 4 is a second having a thickness of 0.05 mm. Each of the transparent resin sheets is shown. The first transparent resin sheet 3 and the second transparent resin sheet 4 are laminated to form a transparent protective layer having a thickness of 0.1 mm. 5 indicates the optical axis direction of the first transparent resin sheet, and 6 indicates the optical axis direction of the second transparent resin sheet.

  FIG. 2 is a schematic view showing an example of an optical disk according to the present invention. In FIG. 2, the first transparent resin sheet 3 supplied from the roll is pulled out from the roll and overlaid on the information surface 2 of the substrate 1 of the optical disk. The first transparent resin sheet 3 is pressure-pressed by a roller (not shown) to form a protective layer on the information surface 2. The thickness of this protective layer is half of the predetermined thickness. Thereafter, the second transparent resin sheet 4 supplied from another roll is pulled out from the roll, and the first optical disc is rotated in the direction in which the first transparent resin sheet 3 is formed and the sheet direction is rotated by π / 2. The protective layer is overlaid on the protective layer made of the transparent resin sheet 3 and press-pressed with a roller (not shown) to form the protective layer. The thickness of the protective layer is half of the desired thickness, and the total thickness of the protective layer is a predetermined thickness. Thereafter, the sheet is cut along the outer periphery of the optical disk. Thus, the two transparent resin sheets 3 and 4 are laminated in the direction rotated by π / 2, and thereafter, the transparent resin sheet is cut out along the inner diameter shape and the outer shape of the optical disk to thereby form a transparent protective layer. Configure. The birefringent optical axis orientation associated with the material of the two transparent resin sheets and the direction of pressure bonding can be rotated by π / 2.

  According to the transparent protective layer configured as described above, it is possible to reduce a phenomenon in which the reproduction signal fluctuates in two cycles with respect to one rotation of the disk due to the birefringence of the transparent resin sheet.

  FIG. 3 is a schematic diagram showing the operation of the optical disc. In the figure, 7 indicates a motor for rotating the optical disk, 8 indicates an optical pickup, and 9 indicates an objective lens. The optical disc apparatus irradiates the information surface 2 with light through the transparent protective layer by the objective lens 9 of the optical pickup 8 and records and / or reproduces information on the optical disc rotated by the motor 7. A light beam having a predetermined polarization direction is irradiated from the optical pickup 8 to the signal on the information surface 2 through the transparent protective layer of the optical disk, and the reflected light returns to the optical pickup 8 again and is converted into an electric signal by a photodetector (not shown). Read information. When the optical disk rotates, the relative direction of the protective layer with respect to the optical pickup rotates. However, in the conventional protective layer having a birefringent optical axis orientation in one direction, the optical pickup has a relationship with the polarization direction of the light beam. In contrast to the phenomenon that the light intensity of the light flux returning to the light detector fluctuates, the optical disc of the present invention has a small variation in light intensity because the birefringence optical axis orientation is dispersed, and stable signal reproduction is possible. It becomes.

  In this embodiment, the protective layer of the optical disk is formed by adhering two transparent resin sheets having substantially the same thickness in the direction of π / 2, but the number of transparent resin sheets is further increased and the thickness of the transparent resin sheet is increased. As a thin transparent resin sheet, the affixing direction may be dispersed to have a predetermined protective layer thickness. In this case, the fluctuation of the signal due to the rotation of the optical disk can be made uniform and constant.

  The optical disk of the present invention is industrially useful because high-capacity information can be recorded and reproduced with high density even with a small device.

Schematic showing an optical disc according to the invention Schematic showing an optical disc according to the invention Schematic showing the operation of the optical disc Schematic showing an optical disc and an optical disc apparatus not using the present invention Schematic showing the playback signal of a conventional optical disc

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Information surface 3 1st transparent resin sheet 4 2nd transparent resin sheet 5 Optical axis direction of 1st transparent resin sheet 6 Optical axis direction of 2nd transparent resin sheet 7 Motor 8 Optical pick-up 9 Objective lens 10 Transparent resin sheet 11 Optical axis orientation of transparent resin sheet

Claims (5)

An optical disc on which information is recorded or on which information can be recorded, comprising an information recording surface and a plurality of transparent resin sheets laminated on the information recording surface. The optical disk according to claim 1, wherein each of the transparent resin sheets has substantially the same thickness. 3. The optical disk according to claim 1, wherein the optical disk includes n layers of the transparent resin sheet, and the transparent resin sheet is laminated so that the orientations of the birefringence optical axes are different by π / n. optical disk. 4. The optical disc according to claim 1, wherein the optical disc includes n layers of the transparent resin sheet, and the transparent resin sheet is disposed on the information recording surface in a direction different by π / n and is pressed and laminated. An optical disc according to any one of the above. 5. The optical disk according to claim 1, wherein the thickness of the n-layer transparent resin sheet is approximately 0.1 mm.

Images