WO2014207911A1 - Optical storage medium, information recording device, and information recording method - Google Patents

Optical storage medium, information recording device, and information recording method Download PDF

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Publication number
WO2014207911A1
WO2014207911A1 PCT/JP2013/067856 JP2013067856W WO2014207911A1 WO 2014207911 A1 WO2014207911 A1 WO 2014207911A1 JP 2013067856 W JP2013067856 W JP 2013067856W WO 2014207911 A1 WO2014207911 A1 WO 2014207911A1
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WIPO (PCT)
Prior art keywords
layer
recording
thickness
guide
light
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PCT/JP2013/067856
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French (fr)
Japanese (ja)
Inventor
渡部　一雄
岡野　英明
小川　昭人
Original Assignee
株式会社 東芝
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Priority to PCT/JP2013/067856 priority Critical patent/WO2014207911A1/en
Publication of WO2014207911A1 publication Critical patent/WO2014207911A1/en

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24035—Recording layers
    • G11B7/24038—Multiple laminated recording layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24067—Combinations of two or more layers with specific interrelation

Definitions

  • Embodiments described herein relate generally to an optical storage medium, an information recording apparatus, and an information recording method.
  • interlayer crosstalk occurs during information reproduction of a multilayer optical disc having a plurality of recording layers.
  • a technique for reducing the occurrence of crosstalk of light rays (usually blue light) for reproducing information on a recording layer has been proposed.
  • a multilayer optical disc having a servo (dedicated) layer separately from the recording layer is known, and there is a demand to reduce the occurrence of crosstalk of servo dedicated light (usually red light) that reproduces information on the servo layer.
  • the servo signal is a signal that is the basis of information recording / reproduction, and it is required to have the same high reliability as the information reproduction signal not only in information recording but also in information reproduction.
  • the prior art documents do not mention interlayer crosstalk generated in the optical path of servo-dedicated light, and it is difficult to reduce interlayer crosstalk generated in the optical path of servo-dedicated light. Therefore, there is a possibility that sufficient performance as a multilayer optical disk cannot be exhibited.
  • the optical storage medium of the embodiment includes a cover layer, a recording layer group including a plurality of recording layers and a plurality of intermediate layers arranged between the plurality of recording layers.
  • the sum S1 of the thickness C1 of the cover layer and the layer thickness C2 between the first recording layer closest to the cover layer and the reflective recording layer where the laser beam that has passed through the cover layer is first reflected However, it does not coincide with the sum S2 of the thicknesses of one or more intermediate layers between the reflective recording layer and the target recording layer.
  • FIG. 1 is a diagram illustrating an example of an optical storage medium according to an embodiment.
  • the figure which shows an example of a structure of the information recording / reproducing apparatus of embodiment. 1 is a diagram illustrating an example of a configuration of an optical pickup according to an embodiment.
  • production The figure explaining an example of the 2nd conditions of guide light confocal crosstalk generation
  • the figure which shows an example of a mode that the confocal crosstalk was reduced.
  • the figure which shows an example of a mode that the confocal crosstalk of guide light was reduced.
  • FIG. 1 is a diagram illustrating a cross-sectional structure of an optical storage medium according to an embodiment.
  • the optical storage medium is an optical disc 10 having a plurality of recording / reproducing layers, and information is recorded on a recording film in the optical disc 10 by a laser beam emitted from an optical pickup (OPU) described later.
  • OPU optical pickup
  • the upper surface shape is, for example, a circle having a diameter of 120 mm.
  • the effect of the optical storage medium of the present embodiment does not depend on the shape of the upper surface, and may be, for example, an ellipse, a polygon, or a shape obtained by connecting them.
  • the optical disc 10 has a structure in which a guide layer 20 and a recording layer 21 (including recording layers 21A to 21L) in which guide grooves or pit rows for generating servo signals during recording and reproduction are formed are formed on a substrate 11. It has become.
  • the recording layer 21 is also referred to as a recording layer group, and the recording layer group includes 12 recording layers 21A to 21L and 11 intermediate layers 31A to 31K.
  • the recording layers 21A to 21L and the intermediate layers 31A to 31K are alternately arranged.
  • the guide layer 20 and the recording layer 21 are formed in the order of the guide layer 20 and the recording layer 21 from the substrate 11 side, and recording / reproducing laser beams 15 and 16 from the optical pickup enter from the opposite side of the substrate 11.
  • a cover layer 12 is formed on the side of the recording layer 21 opposite to the substrate 11.
  • the guide groove or pit row on the guide layer 20 has, for example, a helical structure with a depth of 60 nm and a track pitch of 0.64 ⁇ m, and the ratio of the concave and convex portions in the cross section is approximately 1: 1.
  • the groove depth (pit depth) and the track pitch are not limited to this, and may be a deep groove (deep pit) with a depth of about 100 nm or a shallow groove (shallow pit) with a thickness of about 20 nm, about 0.32 ⁇ m.
  • a narrow track pitch of about 0.74 ⁇ m, or a wide track pitch of about 1.2 ⁇ m may be used.
  • the track structure may be a concentric structure, a spiral structure, or a so-called single spiral structure in which the concave and convex portions are switched every round.
  • address information is applied to the guide groove by, for example, wobble.
  • the wobble is meandering in a direction perpendicular to the track extending direction of the guide groove in the surface of the optical disc 10.
  • An intermediate layer 30 having optical transparency is formed between the guide layer 20 and the recording layer 21A closest to the guide layer 20.
  • intermediate layers 31A to 31K having optical transparency are also formed between two adjacent recording layers of the recording layer 21. The thicknesses of the intermediate layer 30 and the intermediate layer 31 (including the intermediate layers 31A to 31K) will be described later.
  • the cover layer 12 is light transmissive and has a thickness of, for example, 53 ⁇ m.
  • the cover layer is not particularly limited as long as it is a transparent material, but synthetic resins such as polycarbonate and PMMA, glass, and the like can be used.
  • the recording layer 21 is a layer for recording information, and a change corresponding to the laser beam emitted from the optical pickup is generated, and a mark corresponding to the information is recorded.
  • a phase change recording film composed of a multilayer film containing a phase change material, a write-once recording film composed of an organic dye, and the like.
  • the thickness of one recording layer 21 is usually 0.2 ⁇ m or less, and the thickness of the recording layer 21 is very small with respect to the thickness of the cover layer and the intermediate layer.
  • the guide layer 20 and the recording layer 31 are irradiated with laser beams 15 and 16, respectively.
  • the laser beams 15 and 16 have different wavelengths for easy optical path separation in the optical pickup.
  • the laser beam 15 is a red laser beam and the laser beam 16 is a blue-violet laser beam.
  • FIG. 2 shows the configuration of the information recording / reproducing apparatus 300 according to the first embodiment.
  • Information recording / reproducing apparatus 300 includes interface (IF) 310, signal processing unit (DSP) 320, laser driver (LDD1) 330, (LDD2) 340, optical pickup head unit (OPU) 200, RF amplifier IC (RFRFAMP) 350 , A servo controller 360 and a spindle motor 60, and the multilayer optical disk 10 is set on the spindle motor 60.
  • IF interface
  • DSP signal processing unit
  • LDD1 laser driver
  • OPU optical pickup head unit
  • RFRFAMP RF amplifier IC
  • the interface 310 is a connection part for exchanging commands and data with an external host (not shown), and corresponds to a specific standard (for example, SATA).
  • the signal processing unit 320 transmits / receives commands and data to / from an external host via the interface 310, converts data, transmits data pulses and control signals to the laser driver, transmits control signals to the servo controller 360, RF amplifier IC 350 responsible for receiving data signals from
  • Laser drivers 330 and 340 receive data pulses from the signal processing unit 320, control signals, convert them into drive pulses, and transmit drive pulses to the optical pickup head unit 200.
  • the optical pickup head unit 200 irradiates the guide layer 20 and the recording layer 21 of the multilayer optical disc 10 with the laser beams 15 and 16 in response to the drive pulses from the laser drivers 330 and 340, receives the reflected light, and receives the reflected light.
  • a signal corresponding to the change in strength is transmitted to the RF amplifier IC 350.
  • the RF amplifier IC 350 amplifies the signal from the optical pickup head unit 200, generates a servo signal and a data signal, and transmits them to the servo controller 360 and the signal processing unit 320, respectively.
  • the servo controller 360 receives the servo signal from the RF amplifier IC 350, converts the servo signal into an actuator drive signal and a spindle motor drive signal, transmits the actuator drive signal to the optical pickup head unit 200, and drives the spindle motor 60. Transmit the signal.
  • the spindle motor 60 receives the spindle motor drive signal from the servo controller 360, and rotates the mounted optical disc 10 about an axis perpendicular to the extending direction.
  • FIG. 3 shows an example of a detailed configuration of the optical pickup head unit 200 of the information recording / reproducing apparatus 300 according to the embodiment.
  • the optical pickup head unit (OPU) 200 consists of a blue-violet laser (Blue LD), a red laser (Red LD), a polarizing beam splitter (PBS) 1 and 2, a quarter-wave plate (QWP) 1 and 2, a collimating lens (CL) 1, 2, objective lens (OL), hologram element (HOE), blue-violet detector IC (Blue PDIC), red detector IC (Red PDIC), diffraction element (GT), dichroic prism (DP), collimating lens actuator (CL-ACT), and objective lens actuator (OL-ACT).
  • Blue LD blue-violet laser
  • Red LD red laser
  • PBS polarizing beam splitter
  • QWP quarter-wave plate
  • the blue-violet laser is a semiconductor laser having a wavelength of 405 nm, for example, and emits laser light for recording and reproduction.
  • the blue-violet laser is connected to the laser driver 1 of the information recording / reproducing apparatus 300 in FIG.
  • PBS 1 transmits the incident light from the blue-violet laser and reflects the reflected light from the optical disk 10 of the blue-violet laser in which the incident light and the 90-degree polarization plane are rotated.
  • QWP1 transmits incident light from a blue-violet laser and converts linearly polarized light into circularly polarized light. Further, the reflected light from the optical disk 10 of the blue-violet laser is transmitted, and the circularly polarized light is converted into linearly polarized light. At this time, the incident light and the 90-degree polarization plane are linearly polarized light different from each other. For example, if the incident light is P-polarized light, the reflected light is S-polarized light.
  • the collimating lens 1 converts incident light from the blue-violet laser 1 into substantially parallel light.
  • the objective lens focuses the light emitted from the blue-violet laser on the recording layer 21 of the optical disc 10.
  • the objective lens has a wavelength selective aperture on the laser light source side so that the red laser beam 15 and the blue-violet laser beam 16 have different numerical apertures. For example, for the blue-violet laser beam 16, 0.85 and 0.65 for the red laser beam 15.
  • the dichroic prism transmits incident light from the blue-violet laser and reflects incident light from the red laser.
  • the red laser is a semiconductor laser having a wavelength of 655 nm, for example, and emits a tracking servo laser beam.
  • the red laser is connected to the laser driver 2 of the information recording / reproducing apparatus 300.
  • the diffraction element splits the red laser light into three beams by diffraction.
  • the three beams become one main beam and two sub beams on the optical disc 10.
  • PBS 2 transmits the incident light from the red laser and reflects the reflected light from the optical disk 10 of the red laser in which the incident light and the 90-degree polarization plane are rotated.
  • QWP2 transmits incident light from a red laser and converts linearly polarized light into circularly polarized light. Further, the reflected light from the optical disk 10 of the red laser is transmitted, and the circularly polarized light is converted into linearly polarized light. At this time, the incident light and the 90-degree polarization plane are linearly polarized light different from each other. For example, if the incident light is P-polarized light, the reflected light is S-polarized light.
  • the collimating lens 2 converts light emitted from the red laser into substantially parallel light.
  • the light beam emitted from the blue-violet laser 1 transmits the light beam reflected by the information recording layer of the optical disc 10, and diffracts a predetermined region of the light beam at a predetermined angle.
  • the blue-violet light detector IC receives the blue-violet laser light from the HOE, generates a current corresponding to the received light amount, converts the light into a voltage by an internal current-voltage conversion circuit, and outputs the voltage.
  • the red light detector IC receives the red laser light reflected by the PBS 2, generates a current corresponding to the received light amount, converts it into a voltage by an internal current-voltage conversion circuit, and outputs the voltage.
  • the collimating lens actuator drives the collimating lens 2 in the vertical direction in the drawing so that the red laser light emitted from the objective lens moves on the optical disk 10 in the optical axis direction (focus direction).
  • the objective lens actuator drives the objective lens in the left-right direction in the drawing so that the laser light emitted from the objective lens moves on the optical disc 10 along the optical axis (focus direction). Further, the laser beam emitted from the objective lens is driven in a direction perpendicular to the paper surface so that the laser beam moves in the vertical direction (radial direction) of the recording track on the optical disk 10.
  • a user data recording command and data to be recorded are sent from a host (not shown) and sent to the signal processing unit 320 via the interface 310.
  • the signal processing unit 320 starts the data recording process according to the received recording command.
  • the signal processing unit 320 transmits a drive signal to the laser driver 1 and the laser driver 2 to turn on the blue-violet laser and the red laser with the reproduction power.
  • the servo controller 360 transmits a rotation drive signal to the spindle motor 60 to drive the optical disk 10 to rotate at a predetermined rotation speed.
  • the signal processing unit 320 transmits a focus search control signal to the servo controller 360.
  • the servo controller 360 drives the collimating lens actuator with a single vibration in the focus direction in accordance with the transmitted control signal.
  • the focal point of the red laser light 15 emitted from the objective lens through the collimating lens driven by a single vibration reciprocates up and down repeatedly with the guide layer 20 of the optical disc 10 interposed therebetween.
  • the reflected light of the red laser light 15 on the guide layer 20 is condensed on the red photodetector IC.
  • the red photodetector IC converts a current based on the amount of reflected light into a voltage and sends it to the RF amplifier IC 350.
  • the RF amplifier IC 350 generates a focus error signal of the red laser light by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360.
  • the focus error signal is generated by, for example, a known astigmatism method using an astigmatism generation optical element (not shown).
  • the servo controller 360 switches the drive of the collimating lens actuator from the single vibration drive to the drive based on the focus error signal near the focus error signal becomes zero, and draws the focus of the red laser light into the guide groove layer. Subsequently, the servo controller 360 draws the focus of the blue-violet laser beam 16 into the target recording layer 21 on the optical disc 10. At this time, the blue-violet laser beam 16 is focused on the recording layer by driving the objective lens actuator based on the focus error signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC.
  • the servo controller 360 pulls the red laser light 15 into a track formed by a guide groove or the like on the guide layer 20 of the optical disc 10. At this time, the servo controller 360 drives the objective lens actuator based on the tracking error signal generated by the RF amplifier IC based on the voltage signal sent from the red light detector IC and pulls it into the track on the guide layer.
  • the tracking error signal is generated by a known differential push-pull method, for example.
  • the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the red photodetector IC, and reproduces the current address.
  • the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360.
  • the servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the red laser light 15 to a desired track. At this time, the blue-violet laser light 16 irradiated through the same objective lens also performs track movement.
  • the signal processing unit 320 transmits the recording data series to the laser driver 1.
  • the laser driver 1 generates a drive pulse corresponding to the received recording data series, sends it to a blue-violet laser, and performs pulse drive.
  • the pulse emitted by the blue-violet laser passes through the objective lens and is applied to the recording layer 21 of the optical disc 10 to form a recording mark corresponding to the recording data series.
  • the information recording / reproducing apparatus of this embodiment records the recording target data on the target recording layer 21 of the optical disc 10.
  • a user data reproduction command is sent from a host (not shown) and sent to the signal processing unit 320 via the interface 310.
  • the signal processing unit 320 starts the data reproduction process according to the received reproduction command.
  • the signal processing unit 320 transmits a drive signal to the laser driver 1 and the laser driver 2 to turn on the blue-violet laser and the red laser with the reproduction power.
  • the signal processing unit 320 transmits a focus search control signal to the servo controller 360.
  • the servo controller 360 drives the collimating lens actuator with a single vibration in the focus direction in accordance with the transmitted control signal.
  • the focal point of the red laser light 15 emitted from the objective lens through the collimating lens driven by a single vibration repeatedly reciprocates up and down across the guide layer 20 of the optical disc 10.
  • the reflected light of the red laser light 15 on the guide layer is condensed on the red photodetector IC.
  • the red photodetector IC converts a current based on the amount of reflected light into a voltage and sends it to the RF amplifier IC 350.
  • the RF amplifier IC 350 generates a focus error signal of the red laser light by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360.
  • the servo controller 360 switches the drive of the collimating lens actuator from the single vibration drive to the drive based on the focus error signal near the focus error signal becomes zero, and pulls the focus of the red laser light into the guide layer.
  • the servo controller 360 draws the focus of the blue-violet laser beam 16 into the target recording layer 21 on the optical disc 10.
  • the blue-violet laser beam 16 is focused on the recording layer by driving the objective lens actuator based on the focus error signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC. Pull the desired recording layer out of 21.
  • the servo controller 360 pulls the red laser light 15 into the track of the guide layer 20.
  • the servo controller 360 drives the objective lens actuator based on the tracking error signal generated by the RF amplifier IC based on the voltage signal sent from the red light detector IC and pulls it into the track of the guide layer 20.
  • the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the red photodetector IC, and reproduces the current address. If the target address is different, the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360.
  • the servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the red laser light 15 to a desired track. At this time, the blue-violet laser light 16 irradiated through the same objective lens also performs track movement.
  • the blue-violet photodetector IC converts a current based on the amount of reflected light reflected by the recording layer 21 of the optical disk 10 into the blue-violet laser light 16 into a voltage, and sends the voltage to the RF amplifier IC 350.
  • the RF amplifier IC 350 generates a tracking error signal of the blue-violet laser light 16 by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360.
  • the tracking error signal in this case is, for example, a DPD (Differential Pase Deciton) signal or a push-pull signal generated from a recorded mark string of the recording layer 21.
  • the signal processing unit 320 transmits a disconnection control signal from the guide layer servo to the servo controller 360 after determining that the track near the target address has been reached.
  • the servo controller 360 switches the driving of the objective lens actuator from driving based on the tracking error signal of the red laser beam 15 to driving based on the tracking error signal of the blue purple laser beam 16, and records the blue-violet laser beam 16. Pull into the recorded track of layer 21.
  • the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC, and the current of the recording layer 21 into which the blue-violet laser light 16 has been drawn. Play the address.
  • the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360.
  • the servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the blue-violet laser light 16 to a desired track.
  • the signal processing unit 320 confirms that the target address has been reached, and starts data reproduction from the recording layer 21.
  • the information recording / reproducing apparatus of this embodiment can reproduce information from the recording layer.
  • the red laser beam 15 for reproducing information from the guide layer 20 and the blue-violet laser beam 16 for recording information on the recording layer 21 or reproducing information from the recording layer 21 each play a necessary role.
  • the recording / reproduction of the optical disk 10 is established.
  • Interlayer crosstalk is a phenomenon that causes problems in optical discs having a plurality of recording layers.
  • Interlayer crosstalk includes interlayer crosstalk caused by reflection of adjacent recording layers and confocal crosstalk (see the prior art). Interlayer crosstalk due to reflection of adjacent recording layers can be avoided by setting the thickness of the intermediate layer 31 to 10 ⁇ m or more as in the prior art, and the minimum value of the thickness of the intermediate layer 31 is 10 ⁇ m. In consideration of the error, the thickness design value of the intermediate layer 31 may be used.
  • the recording / reproducing blue-violet laser light 16 irradiated on the target recording layer (the recording layer 21C in the figure) of the recording layer 21 of the optical disc 10 is branched into a plurality of light beams due to the semi-transmission of the recording layer.
  • a part of the laser beam 16 is reflected by the recording layer 21G, becomes a branched beam 17 and is focused on the recording layer 21K, and this reflected light is reflected again by the recording layer 21G and is reflected by the laser beam 16, that is, the recording It merges with the recording / reproducing light of the layer 21C, and is detected simultaneously and spatially at substantially the same position by the blue photodetector IC.
  • This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes.
  • the thickness of the intermediate layer 31 of the recording layer 21 is different from each other for reducing the confocal crosstalk of the recording / reproducing light (blue-violet laser light) in the recording layer.
  • the intermediate layer 31 may have a thickness in which the first and second intermediate layer thicknesses are alternately repeated.
  • the first intermediate layer thickness and the second intermediate layer thickness take a manufacturing margin into consideration, and the confocal crosstalk is reduced by providing a difference of 4 ⁇ m or more. Therefore, by setting the first intermediate layer thickness to 12 ⁇ m and the second intermediate layer thickness to 16 ⁇ m, it is possible to reduce confocal crosstalk and also reduce interlayer crosstalk due to reflection. . Further, the confocal crosstalk can be further reduced by setting the reflectance of all the recording layers 21 to 2% or less.
  • the countermeasure against the interlayer crosstalk of the guide light (red laser beam 15) is as important as the interlayer crosstalk of the recording / reproducing light.
  • FIG. 6 shows how the confocal crosstalk occurs in the guide light (red laser light 15).
  • the red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer.
  • a part of the laser beam 15 is reflected by the recording layer 21A, becomes a branched beam 40 and is focused by the recording layer 21F, and this reflected light is reflected again by the recording layer 21A and is reflected by the laser beam 15, that is, the guide It merges with the recording / reproducing light of the layer 20 and is detected simultaneously and spatially at substantially the same position by the red photodetector IC.
  • FIG. 7 shows another confocal crosstalk occurring in the guide light (red laser light 15).
  • the red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer. For example, a part of the laser beam 15 is reflected by the recording layer 21A, becomes a branched beam 42, and is reflected by the recording layer 21J.
  • the reflected light is reflected by the recording layer 21E and merges with the laser light 15, that is, the recording / reproducing light of the guide layer 20.
  • the crosstalk light is not focused on the recording layer 21 ⁇ / b> J.
  • the crosstalk light is substantially simultaneously and spatially reduced by the red photodetector IC. It will be detected at the same position. Therefore, in the present embodiment, this is also considered as a kind of confocal crosstalk.
  • the reflectance of the recording layer 21 is adjusted in accordance with the blue-violet wavelength band that is recording / reproducing light, the reflectance in the red wavelength band that is the guide light cannot be preferentially adjusted. Conversely, if priority is given to adjusting the reflectance in the red wavelength band so that confocal crosstalk does not occur, the material selection range and film thickness adjustment range of the recording layer will be extremely limited. As a result, the productivity of the optical disk 10 is extremely deteriorated and the cost is increased. Therefore, in order to reduce the confocal crosstalk of the guide light, it is desirable to take an approach independent of the confocal crosstalk (FIG. 5) in the recording layer of the recording / reproducing light. Therefore, in this embodiment, the confocal crosstalk of the guide light is reduced by suitably creating the thickness of the intermediate layer 30 between the guide layer 20 and the recording layer 21A and the intermediate layer 31 in the recording layer 21; did.
  • FIG. 8 is a diagram illustrating an example of a state in which the confocal crosstalk of the guide light is reduced.
  • a part of the guide red laser light 15 irradiated to the guide layer 20 of the optical disc 10 is reflected by the recording layer 21A, and becomes a branched beam 41 and reflected by the recording layer 21F.
  • the branched beam 41 does not have to be focused on the recording layer 21F, and even if this reflected light is reflected again by the recording layer 21A,
  • the laser beam 15, that is, the recording / reproducing light of the guide layer 20 does not merge in the same optical path, but is detected at a position that does not spatially coincide with the red photodetector IC. For this reason, the crosstalk light can be spatially separated from the guide light 15, and noise can be reduced.
  • an intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light will be described.
  • an intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light it is necessary to clarify the intermediate layer thickness condition in which the confocal crosstalk is generated, and to integrate the front and back. Therefore, conditions for generating confocal crosstalk of the guide light will be described below.
  • FIG. 9 shows how the confocal crosstalk occurs when the guide light is satisfied.
  • the thickness (SL0) of the intermediate layer 30 between the guide layer and the recording layer closest to the guide layer is the thickness of the intermediate layer 31H to the intermediate layer 31J between the recording layer 21H and the recording layer 21K. It is consistent with the sum. Therefore, the line segment AD and the line segment BC in FIG. 9 have the same length. At this time, the quadrangle ABCD in FIG.
  • the branched beam passing through the optical path IABCO merges with the guide light (optical path IADCO) to become confocal crosstalk light. If the thickness of the intermediate layer 30 matches the sum of the thicknesses of any successive intermediate layers including the intermediate layer 31A, the branched beam is a type of confocal crosstalk light that is focused on the recording layer. Become.
  • FIG. 10 shows how the confocal crosstalk occurs in the guide light when this condition is satisfied. In FIG. 10, the sum SL0 + SL1 of the thickness (SL0) of the intermediate layer 30 between the guide layer and the recording layer 21A closest to the guide layer and the thickness of the intermediate layer 31A between the recording layer 21A and the recording layer 21B.
  • the line segment A′D ′ and the line segment B′C ′ in FIG. 10 have the same length.
  • the quadrangle A′B′C′D ′ in FIG. 10 becomes a parallelogram, and the branched beam passing through the optical path IA′B′C′O merges with the guide light (optical path IA′D′C′O). It becomes confocal crosstalk light.
  • the branched beam is of a type that focuses on the recording layer. Confocal crosstalk light.
  • the branched beam is focused on the recording layer. Type of confocal crosstalk light.
  • the intermediate layer thickness configuration that can reduce the confocal crosstalk of the guide light means an intermediate layer thickness configuration that does not satisfy the first condition and the second condition at the same time or one of them.
  • the intermediate layer 31 of the recording layer 21 may have a structure in which the first and second intermediate layer thicknesses are alternately repeated in order to reduce the interlayer crosstalk of the recording / reproducing light (blue-violet laser light 16).
  • the optical disc 10 has a structure that can reduce the interlayer crosstalk of the guide light (red laser beam 15) and the interlayer crosstalk of the recording / reproducing light (blue-violet laser beam 16) at the same time. Is possible. Accordingly, it is preferable to apply the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light to a structure in which the first and second intermediate layer thicknesses are alternately repeated.
  • the conditions of the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light while reducing the interlayer crosstalk of the recording / reproducing light will be examined. It is assumed that the recording layer 21 has 12 layers. Generalizing the structure in which the first and second intermediate layer thicknesses are alternately repeated, the first intermediate layer thickness is expressed as m ( ⁇ m), and the second intermediate layer thickness is expressed as m + a ( ⁇ m). Can do. Here, the first intermediate layer thickness is assumed to be thinner than the second intermediate layer thickness. Note that the intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is considered to have the first intermediate layer thickness.
  • the thickness of the intermediate layer 30 satisfying the first condition is as follows. However, the case where the thickness of the intermediate layer 30 is equal to or smaller than the second intermediate layer thickness is excluded because the interlayer crosstalk due to the reflection of the recording layer adjacent to the guide layer increases.
  • the thickness of the intermediate layer 30 that satisfies the second condition is as follows.
  • the thickness of the intermediate layer 30 that satisfies either the first condition or the second condition is as follows (intermediate layer thickness condition group 1).
  • the difference between the first intermediate layer thickness and the second intermediate layer thickness that is, a ( ⁇ m) is better from the viewpoint of reducing the interlayer crosstalk. If it is too large, the thickness of the entire recording layer 21 is increased, and the aberration becomes large as a characteristic of the objective lens of the optical pickup unit 200.
  • a needs to be smaller than m. That is, m> a.
  • the thickness of the intermediate layer 30 preferably satisfies neither the first condition nor the second condition from the viewpoint of avoiding confocal crosstalk.
  • the thickness of the intermediate layer 30 is preferably set to a thickness far from any value of the intermediate layer thickness condition group 1 described above. For this reason, for example, one method is to make the thickness of the intermediate layer 30 sufficiently larger than 11 m + 6a. In this case, the confocal crosstalk of the guide light does not occur, but the total thickness of the intermediate layer 30, the intermediate layer 31, and the cover layer becomes too large, and the aberration is large as a characteristic of the objective lens of the optical pickup unit 200. turn into.
  • the first condition is 2m + a, 3m + a, 3m + 2a, 4m + 2a, 5m + 2a, 5m + 3a, 6m + 3a, 7m + 3a, 7m + 4a, 8m + 4a, 9m
  • the thickness of the intermediate layer 30 can be set to an intermediate value or a value close to the intermediate value among + 4a, 9m + 5a, 10m + 5a, 11m + 5a, and 11m + 6a.
  • the intermediate value between 2m + a and 3m + a is 2.5m + a.
  • the thickness of the intermediate layer 30 is preferably set to an intermediate value in the intermediate layer thickness condition group 1 or a value close to the intermediate value.
  • the interval of the continuous values in the intermediate layer thickness condition group 1 is any one of m, a, and m-a. When m> a is considered, the interval is the longest when the interval is m. That is, between 3m + 2a and 4m + 2a, 5m + 3a and 6m + 3a, 7m + 4a and 8m + 4a, and 9m + 5a and 10m + 5a.
  • the thickness of the intermediate layer 30 is a guide when formed as an intermediate value of these, 3.5 m + 2a, 5.5 m + 3a, 7.5 m + 4a, 9.5 m + 5a Interlayer crosstalk of recording / reproducing light can be reduced while reducing confocal crosstalk of light.
  • the optical disk 10 is a highly reliable optical disk in which the interlayer crosstalk of the guide light (red laser light 15) and the recording / reproducing light (blue-violet laser light 16) is reduced, and the defective product rate at the time of manufacturing the disk is low.
  • the intermediate layer 30 is preferably thin from the viewpoint of aberration of the objective lens of the optical pickup unit 200, it is preferably 57 ⁇ m or 89 ⁇ m among the above.
  • the first intermediate layer thickness may be larger than the second intermediate layer thickness.
  • the first intermediate layer thickness can be expressed as m + a ( ⁇ m)
  • the second intermediate layer thickness can be expressed as m ( ⁇ m).
  • the thickness of the intermediate layer 30 that satisfies the second condition is as follows.
  • the thickness of the intermediate layer 30 that satisfies either the first condition or the second condition is as follows (intermediate layer thickness condition group 2).
  • the first condition is 2m + a, 3m + a, 3m + 2a, 4m + 2a, 5m + 2a, 5m + 3a, 6m + 3a, 7m + 3a, 7m + 4a, 8m + 4a, 9m
  • the thickness of the intermediate layer 30 can be set to an intermediate value or a value close to the intermediate value among + 4a, 9m + 5a, 10m + 5a, 11m + 5a, and 11m + 6a.
  • the intermediate value between 2m + a and 3m + a is 2.5m + a.
  • the thickness of the intermediate layer 30 is preferably set to an intermediate value of the intermediate layer thickness condition group 2 or a value close to the intermediate value.
  • the interval between the continuous values of the intermediate layer thickness condition group 2 is any one of m, a, and ma. Considering m> a, the interval is the longest when the interval is m. That is, between 2m + a and 3m + a, 4m + 2a and 5m + 2a, 6m + 3a and 7m + 3a, and 8m + 4a and 9m + 4a.
  • the thickness of the intermediate layer 30 is a guide when it is formed as these intermediate values, 2.5m + a, 4.5m + 2a, 6.5m + 3a, 8.5m + 4a Interlayer crosstalk of recording / reproducing light can be reduced while reducing confocal crosstalk of light.
  • the optical disk 10 is a highly reliable optical disk in which the interlayer crosstalk of the guide light (red laser light 15) and the recording / reproducing light (blue-violet laser light 16) is reduced, and the defective product rate at the time of manufacturing the disk is low.
  • the intermediate layer 30 is preferably thin from the viewpoint of aberration of the objective lens of the optical pickup unit 200, it is preferably 39 ⁇ m or 71 ⁇ m among the above.
  • FIG. 11A, 11B, and 11C show the disk structure when the first intermediate layer is thinner than the second intermediate layer.
  • the thickness of the intermediate layer 30 is 57 ⁇ m or 89 ⁇ m so that the optical disk is highly reliable. Is obtained.
  • FIG. 11A shows an example of the structure of the optical disc 10 having 12 recording layers 21.
  • FIG. 11B and FIG. 11C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively.
  • the guide layer 20 is located 284 ⁇ m from the surface of the cover layer as in the case of the 12 layers.
  • An optical disk with high reliability can be obtained by setting the thickness of the intermediate layer 30 to 57 ⁇ m or 89 ⁇ m. However, in order to prevent the cover layer 12 from becoming extremely thick, the thickness is set to 89 ⁇ m. As a result, the distance of the recording layer 21A from the cover layer surface is 195 ⁇ m. As a result, the thickness of the cover layer 12 of the disc having eight recording layers is 85 ⁇ m (FIG. 11B), and the thickness of the cover layer 12 of the disc having six recording layers is 117 ⁇ m (FIG. 11C).
  • FIG. 12A, FIG. 12B, and FIG. 12C show examples of the disk structure when the first intermediate layer is thicker than the second intermediate layer.
  • the thickness of the intermediate layer 30 is 39 ⁇ m or 71 ⁇ m.
  • FIG. 12A is a structural example of the optical disc 10 having 12 recording layers 21.
  • the thickness of the cover layer 12 was 53 ⁇ m for the same reason as described above.
  • the distance from the cover layer surface of the guide layer 20 is 270 ⁇ m
  • the distance from the cover layer surface of the recording layer 21A is 231 ⁇ m.
  • the guide layer 20 is located 270 ⁇ m from the surface of the cover layer as in the example of 12 layers.
  • An optical disk with high reliability can be obtained by setting the thickness of the intermediate layer 30 to 39 ⁇ m or 71 ⁇ m.
  • the thickness is set to 71 ⁇ m.
  • the distance of the recording layer 21A from the cover layer surface is 199 ⁇ m.
  • the thickness of the cover layer 12 of the disc having 8 recording layers is 85 ⁇ m (FIG. 12B), and the thickness of the cover layer 12 of the disc having 6 recording layers is 117 ⁇ m (FIG. 12C).
  • Confocal crosstalk to be considered in this case includes (1) confocal crosstalk of recording / reproducing light (blue-violet laser light 16) and (2) confocal crosstalk of guide light (red laser light 15). .
  • the recording / reproducing blue-violet laser light 16 irradiated to the target recording layer (the recording layer 21F in the figure) of the recording layer 21 of the optical disc 10 is branched into a plurality of light beams due to the semi-transmission of the recording layer.
  • a part of the laser light 16 is reflected by the recording layer 21L, becomes a branched beam 51 and is focused from the inside of the cover layer on the surface of the cover layer 12, and this reflected light is reflected again by the recording layer 21L.
  • the laser light 16 that is, the recording / reproducing light of the recording layer 21F is merged and detected simultaneously and spatially at substantially the same position by the blue photodetector IC.
  • This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes.
  • the cover layer 12 is too thick, the tilt margin at the time of recording / reproducing of the recording layer is lowered. If the cover layer 12 is too thin, there is a problem that the recording layer 21L closest to the cover layer is not sufficiently protected. It is relatively gentle, and the confocal crosstalk of the recording / reproducing light can be reduced by making the thickness of the cover layer 12 more preferable in detail.
  • FIG. 16 is a diagram showing an example of a state in which confocal crosstalk of recording / reproducing light is reduced.
  • the recording / reproducing blue-violet laser light 16 irradiated on the target recording layer (in the figure, the recording layer 21F) is partially reflected by the recording layer 21L, and the branched beam 52 and
  • the surface of the cover layer 12 is reflected from the inside.
  • the cover layer 12 since the cover layer 12 is suitably formed, the branched beam 52 does not have to be focused on the surface of the cover layer 12, and even if this reflected light is reflected again by the recording layer 21L, it is bluish purple.
  • the laser beam 16 that is, the recording / reproducing light of the recording layer 21, does not merge in the same optical path, but is detected at a position not spatially matched by the blue-violet photodetector IC. Therefore, the crosstalk light can be spatially separated from the recording / reproducing light 16, and noise can be reduced.
  • the cover layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light will be described.
  • the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light it is necessary to clarify the cover layer thickness condition in which the confocal crosstalk is generated and to be integrated. Therefore, conditions for generating confocal crosstalk of recording / reproducing light will be described below.
  • the first reflective recording layer is a recording layer in which recording / reproducing light is first branched and reflected among the recording layers, and in the example of FIG. 15, is the recording layer 21L.
  • FIG. 17 shows the occurrence of confocal crosstalk of the recording / reproducing light when this condition is satisfied.
  • the sum of the thicknesses coincides with the sum of the thicknesses of the intermediate layers (intermediate layer 31C to intermediate layer 31I) between the first reflective recording layer (recording layer 21J) and the target recording layer (recording layer 21C).
  • the line segment AD and the line segment BC in FIG. 17 have the same length.
  • the quadrangle ABCD in FIG. 17 becomes a parallelogram, and the branched beam passing through the optical path IABCO merges with the recording / reproducing light (optical path IADCO) to become confocal crosstalk light.
  • the cover layer thickness configuration that can reduce the confocal crosstalk of the recording / reproducing light in consideration of the reflected light on the surface of the cover layer means a cover layer thickness configuration that does not satisfy the above conditions.
  • the thickness of the intermediate layer since the recording layer is extremely thin relative to the intermediate layer, the thickness of the intermediate layer can be designed without considering the thickness of the recording layer.
  • the thickness of the intermediate layer may be designed in consideration of the thickness.
  • the intermediate layer 31 of the recording layer 21 is preferably applied to a structure in which the first and second intermediate layer thicknesses are alternately repeated.
  • the conditions of the cover layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light will be examined.
  • the case where the number of recording layers 21 is 12 is considered.
  • the first intermediate layer thickness can be expressed as m ( ⁇ m)
  • the second intermediate layer thickness can be expressed as m + a ( ⁇ m). Note that the intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is considered to have the first intermediate layer thickness.
  • the thickness of the cover layer 12 satisfying the above conditions is as follows.
  • the thickness of the cover layer thickness 12 that satisfies the above conditions is as follows. .
  • the first intermediate layer thickness may be larger than the second intermediate layer thickness.
  • the first intermediate layer thickness can be expressed as m + a ( ⁇ m)
  • the second intermediate layer thickness can be expressed as m ( ⁇ m).
  • the thickness of the cover layer thickness 12 that satisfies the above conditions is as follows. .
  • the red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer.
  • a part of the laser beam 15 is reflected by the recording layer 21H, becomes a branched beam 43 and is focused from the inside of the cover layer on the surface of the cover layer 12, and this reflected light is reflected again by the recording layer 21H.
  • the laser beam 15, that is, the recording / reproducing light of the guide layer 20 is merged and detected simultaneously and spatially at substantially the same position by the red photodetector IC.
  • This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes.
  • the intermediate layer 30 between the guide layer 20 and the recording layer 21A and the thickness of the intermediate layer 31 in the recording layer 21 should be suitably created. Therefore, the confocal crosstalk of the guide light is reduced. Therefore, for the confocal crosstalk caused by the light beam reflected from the surface of the cover layer 12, it is desirable to reduce the confocal crosstalk of the guide light by suitably creating the thickness of the cover layer 12.
  • FIG. 19 is a diagram illustrating an example of a state in which the confocal crosstalk of the guide light is reduced.
  • a part of the guide red laser light 15 irradiated to the guide layer 20 of the optical disc 10 is reflected by the recording layer 21H, and becomes a branched beam 44 and reflected by the recording layer 21H.
  • the cover layer 12 is preferably formed, the branched beam 44 does not focus on the surface of the cover layer 12, and even if this reflected light is reflected again by the recording layer 21H, the laser beam 15, that is, the recording / reproducing light of the guide layer 20 does not merge in the same optical path, and is detected at a position that does not spatially coincide with the red photodetector IC. For this reason, the crosstalk light can be spatially separated from the guide light 15, and noise can be reduced.
  • the thickness of the cover layer 12 is determined in consideration of the confocal crosstalk of (1) recording / reproducing light and (2) guide light caused by the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12.
  • the thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be secured to 7 ⁇ m or more.
  • cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1), that is, a cover layer thickness range having a margin of 2 ⁇ m or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 ⁇ m or more. As described above, the cover layer thickness is required to be approximately 50 ⁇ m or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 ⁇ m or less in the case of 12 recording layers.
  • FIG. 21A, 21B, and 21C show examples of the disk structure when the first intermediate layer is thinner than the second intermediate layer.
  • the thickness of the cover layer is preferably 66 ⁇ m as an example.
  • An optical disk with high reliability can be obtained by setting the thickness of 30 to about 57 ⁇ m or 89 ⁇ m.
  • the preferable thickness is set to 58 ⁇ m.
  • FIG. 21A shows an example of the structure of the optical disc 10 having 12 recording layers 21.
  • the distance of the guide layer 20 from the cover layer surface is 298 ⁇ m
  • the distance of the recording layer 21A from the cover layer surface is 240 ⁇ m.
  • FIG. 21B and FIG. 21C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively.
  • the guide layer 20 is located at 298 ⁇ m from the cover layer surface as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same.
  • the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 21A, and the thickness of the intermediate layer 30 is 90 ⁇ m.
  • the distance of the recording layer 21A from the cover layer surface is 208 ⁇ m.
  • the thickness of the cover layer is 98 ⁇ m.
  • the disc having 6 recording layers in FIG. 21C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 90 ⁇ m, and the thickness of the cover layer is 130 ⁇ m. did.
  • the line graph in FIG. 22 is a diagram showing a reduced state of the confocal crosstalk of the guide light (2) when the first intermediate layer thickness is 18 ⁇ m and the second intermediate layer thickness is 14 ⁇ m.
  • the thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted.
  • the wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk it is possible to provide a multilayer optical disk having better characteristics. More preferably, as described above, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be ensured to be 7 ⁇ m or more.
  • the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 ⁇ m or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 ⁇ m or more. As described above, the cover layer thickness is required to be approximately 50 ⁇ m or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 ⁇ m or less in the case of 12 recording layers.
  • FIG. 23A, FIG. 23B, and FIG. 23C show the disk structure when the first intermediate layer is thicker than the second intermediate layer.
  • the thickness of the cover layer is preferably 75 ⁇ m as an example.
  • An optical disk with high reliability can be obtained by setting the thickness of 30 to about 39 ⁇ m or 71 ⁇ m.
  • the preferable thickness is set to 37.5 ⁇ m.
  • FIG. 23A shows an example of the structure of the optical disc 10 having 12 recording layers 21.
  • the distance of the guide layer 20 from the cover layer surface is 290.5 ⁇ m
  • the distance of the recording layer 21A from the cover layer surface is 253 ⁇ m.
  • FIG. 23B and FIG. 23C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively.
  • the guide layer 20 is located at 290.5 ⁇ m from the cover layer surface as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same.
  • the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 23A, and the thickness of the intermediate layer 30 is 69.5 ⁇ m.
  • the distance of the recording layer 21A from the cover layer surface is 221 ⁇ m.
  • the thickness of the cover layer is 107 ⁇ m.
  • the disc having 6 recording layers in FIG. 23C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 69.5 ⁇ m, and the thickness of the cover layer is 139 ⁇ m. It was.
  • the thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be secured to 7 ⁇ m or more.
  • the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 ⁇ m or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 ⁇ m or more. As described above, the cover layer thickness is required to be approximately 50 ⁇ m or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 ⁇ m or less in the case of 12 recording layers.
  • FIG. 25A, FIG. 25B, and FIG. 25C show examples of the disk structure when the first intermediate layer is thinner than the second intermediate layer.
  • the thickness of the cover layer is preferably 68 ⁇ m as an example.
  • a highly reliable optical disk can be obtained by setting the thickness of the intermediate layer 30 to about 58.75 ⁇ m or 91.75 ⁇ m.
  • FIG. 25A shows an example of the structure of the optical disc 10 having 12 recording layers 21.
  • the distance of the guide layer 20 from the cover layer surface is 307 ⁇ m, and the distance of the recording layer 21A from the cover layer surface is 247.5 ⁇ m.
  • 25B and 25C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively.
  • the guide layer 20 is located 307 ⁇ m from the surface of the cover layer as in the case of the 12 layers.
  • the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 25A, and the thickness of the intermediate layer 30 is 92.5 ⁇ m. As a result, the distance of the recording layer 21A from the cover layer surface is 214.5 ⁇ m.
  • the thickness of the cover layer is 101 ⁇ m.
  • the disc having 6 recording layers in FIG. 25C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 92.5 ⁇ m, and the thickness of the cover layer is 134 ⁇ m. It was.
  • the line graph of FIG. 26 is a diagram showing a reduced state of the confocal crosstalk of the guide light (2) when the first intermediate layer thickness is 18.5 ⁇ m and the second intermediate layer thickness is 14.5 ⁇ m. .
  • the thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted.
  • the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 ⁇ m or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 ⁇ m or more. As described above, the cover layer thickness is required to be approximately 50 ⁇ m or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 ⁇ m or less in the case of 12 recording layers.
  • FIG. 27A, 27B, and 27C show the disk structure in the case where the first intermediate layer is thicker than the second intermediate layer.
  • the cover layer thickness is preferably 77.5 ⁇ m as an example.
  • the thickness of the intermediate layer 30 is about 40.25 ⁇ m or 73.25 ⁇ m, a highly reliable optical disk can be obtained.
  • the preferable thickness is 39 ⁇ m. did.
  • FIG. 27A shows an example of the structure of the optical disc 10 having 12 recording layers 21.
  • the distance of the guide layer 20 from the cover layer surface is 300 ⁇ m
  • the distance of the recording layer 21A from the cover layer surface is 261 ⁇ m.
  • 27B and 27C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively.
  • the guide layer 20 is located 300 ⁇ m from the surface of the cover layer as in the example of 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same.
  • the 8-layer disc has a configuration in which two recording layers near the guide layer and two recording layers near the cover layer are deleted from the configuration in FIG. 27A, and the thickness of the intermediate layer 30 is 72 ⁇ m.
  • the distance of the recording layer 21A from the cover layer surface is 228 ⁇ m.
  • the thickness of the cover layer is 110.5 ⁇ m.
  • the disc having the 6 recording layers in FIG. 27C has a configuration in which two recording layers close to the cover layer are deleted, the intermediate layer 30 remains 72 ⁇ m, and the cover layer has a thickness of 143.5 ⁇ m. It was.
  • the cover layer thickness configuration that does not satisfy the confocal crosstalk generation condition of the recording / reproducing light is preferable. More specifically, 1) The cover layer thickness is as far as possible from the cover layer thickness that satisfies the above-mentioned generation conditions. 2) When the margin from the cover layer thickness that satisfies the above-mentioned generation conditions is the same, the intermediate between the first reflective layer and the target layer. It can be said that the smaller the number obtained by subtracting the number of intermediate layers between the first reflective layer and the reflective layer closest to the cover layer from the number of layers is better.
  • the manufacturing error of the optical storage medium is not taken into consideration.
  • the manufacturing error such as the intermediate layer thickness
  • the cover layer thickness can be selected.
  • thickness manufacturing errors do not occur unevenly in a plurality of intermediate layers, but thickness manufacturing errors tend to occur uniformly.
  • the first intermediate layer thickness is designed to be 18 ⁇ m and the second intermediate layer thickness is 14 ⁇ m
  • the first intermediate layer thickness is actually 18 ⁇ m + error ⁇
  • the second intermediate layer thickness is 14 ⁇ m + error ⁇ . May be.
  • a plurality of intermediate layer thicknesses including manufacturing errors can be examined. Thereby, a more suitable cover layer thickness can be selected from a plurality of cover layer thickness candidates described in the present embodiment.
  • the recording layer is formed by suitably creating the intermediate layer thickness configuration of the guide layer and the recording layer. Interlayer crosstalk in guide light for reproducing the guide layer as well as recording / reproduction light for recording / reproduction can be reduced, and a multilayer optical disc having high reliability in information recording / reproduction can be provided.
  • the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer does not match the sum of the thicknesses of any continuous intermediate layers in the recording layer group.
  • the intermediate layer of the recording layer group has a first intermediate layer that is the first film thickness and a second film thickness that is different from the first film thickness. Second intermediate layers are alternately stacked with the recording layer interposed therebetween.
  • the first film thickness is m
  • the second film thickness is m + a
  • the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer Is 3.5m + 2a, 5.5m + 3a, 7.5m + 4a, or 9.5m + 5a.
  • the first film thickness is m + a
  • the second film thickness is m
  • the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer Is 2.5m + a, 4.5m + 2a, 6.5m + 3a, 8.5m + 4a, or 10.5m + 5a.
  • the first film thickness is 14 ⁇ m
  • the second film thickness is 18 ⁇ m
  • the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer is 57 ⁇ m or 89 ⁇ m.
  • the first film thickness is 18 ⁇ m
  • the second film thickness is 14 ⁇ m
  • the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer is It is 39 ⁇ m or 71 ⁇ m.
  • the thickness of the cover layer and the layer thickness between the first recording layer closest to the cover layer and the reflective recording layer where the laser beam that has passed through the cover layer is first reflected. Is not the same as the sum of the thicknesses of one or more intermediate layers between the reflective recording layer and the target recording layer.
  • the recording layer group includes a first intermediate layer having a first film thickness that is alternately arranged with one recording layer interposed therebetween, and a second film that is different from the first film thickness.
  • the first film thickness is 18 ⁇ m
  • the second film thickness is 14 ⁇ m
  • the cover layer thickness is 62 ⁇ m, 66-68 ⁇ m, 74-76 ⁇ m, 80 ⁇ m, 94 ⁇ m, and It is a value included in any range of 98 to 100 ⁇ m or any value.
  • the first film thickness is 14.5 ⁇ m
  • the second film thickness is 18.5 ⁇ m
  • the cover layer thickness is 53.5 to 56 ⁇ m, 61 to 64 ⁇ m, 68 ⁇ m, 82.5 ⁇ m, And a value included in any one of 86.5 to 89 ⁇ m and 94 to 97 ⁇ m, or any value.
  • the first film thickness is 18.5 ⁇ m
  • the second film thickness is 14.5 ⁇ m
  • the cover layer thickness C1 is 64 ⁇ m, 68-71.5 ⁇ m, 75.5-78.5 ⁇ m.

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Abstract

An optical storage device capable of reducing interlayer crosstalk caused by a laser beam directed toward a servo layer (guide layer) is provided. An optical storage medium of an embodiment is equipped with: a cover layer; and a recording layer group which comprises multiple recording layers and multiple intermediate layer provided between the multiple recording layers. Sum (S1) of thickness (C1) of the cover layer and thickness (C2) of layers located between a first recording layer, which is closest to the cover layer, and a reflective recording layer, by which a laser beam passed through the cover layer is reflected first, does not match with sum (S2) of the thicknesses of one or more layers located between the reflective recording layer and a target recording layer.

Description

光記憶媒体、情報記録装置、及び情報記録方法Optical storage medium, information recording apparatus, and information recording method
　本発明の実施形態は、光記憶媒体、情報記録装置、及び情報記録方法に関する。 Embodiments described herein relate generally to an optical storage medium, an information recording apparatus, and an information recording method.
　複数の記録層を備えた多層光ディスクの情報再生時に層間クロストークが発生することが知られている。例えば、記録層の情報を再生する光線(通常青色光)のクロストークの発生を低減する技術が提案されている。 It is known that interlayer crosstalk occurs during information reproduction of a multilayer optical disc having a plurality of recording layers. For example, a technique for reducing the occurrence of crosstalk of light rays (usually blue light) for reproducing information on a recording layer has been proposed.
特開２０１１－１７０９３７号公報JP 2011-170937 A
　記録層とは別にサーボ(専用)層を持つ多層光ディスクが知られており、サーボ層の情報を再生するサーボ専用光(通常赤色光)のクロストークの発生を低減したいという要望がある。 A multilayer optical disc having a servo (dedicated) layer separately from the recording layer is known, and there is a demand to reduce the occurrence of crosstalk of servo dedicated light (usually red light) that reproduces information on the servo layer.
　サーボ信号は、情報記録再生の基礎となる信号であり、情報記録においては勿論のこと、情報再生においても、情報再生信号と同等に高い信頼性が要求されるものである。先行技術文献には、サーボ専用光の光路にて発生する層間クロストークについて言及が無く、サーボ専用光の光路にて発生する層間クロストークを低減することは難しい。よって、多層光ディスクとして十分な性能を発揮できない可能性がある。 The servo signal is a signal that is the basis of information recording / reproduction, and it is required to have the same high reliability as the information reproduction signal not only in information recording but also in information reproduction. The prior art documents do not mention interlayer crosstalk generated in the optical path of servo-dedicated light, and it is difficult to reduce interlayer crosstalk generated in the optical path of servo-dedicated light. Therefore, there is a possibility that sufficient performance as a multilayer optical disk cannot be exhibited.
　本発明の目的は、サーボ層（ガイド層）に向けたレーザ光による層間クロストークを低減可能な光記憶媒体を提供することである。また、このような光記憶媒体に対して情報を記録する情報記録装置及び情報記録方法を提供することである。 An object of the present invention is to provide an optical storage medium capable of reducing interlayer crosstalk due to laser light directed to a servo layer (guide layer). Another object of the present invention is to provide an information recording apparatus and an information recording method for recording information on such an optical storage medium.
　実施形態の光記憶媒体は、カバー層と、複数の記録層とこれら複数の記録層の間に配置された複数の中間層とにより構成される記録層群と、を備える。前記カバー層の厚さＣ１と、前記カバー層に最も近い第一の記録層と前記カバー層を通過したレーザ光が最初に反射する反射記録層との間の層の厚さＣ２との和Ｓ１が、前記反射記録層と目標記録層との間の１以上の中間層の厚さの和Ｓ２と一致しない。 The optical storage medium of the embodiment includes a cover layer, a recording layer group including a plurality of recording layers and a plurality of intermediate layers arranged between the plurality of recording layers. The sum S1 of the thickness C1 of the cover layer and the layer thickness C2 between the first recording layer closest to the cover layer and the reflective recording layer where the laser beam that has passed through the cover layer is first reflected However, it does not coincide with the sum S2 of the thicknesses of one or more intermediate layers between the reflective recording layer and the target recording layer.
実施形態の光記憶媒体の一例を示す図。1 is a diagram illustrating an example of an optical storage medium according to an embodiment. 実施形態の情報記録再生装置の構成の一例を示す図。The figure which shows an example of a structure of the information recording / reproducing apparatus of embodiment. 実施形態の光ピックアップの構成の一例を示す図。1 is a diagram illustrating an example of a configuration of an optical pickup according to an embodiment. 実施形態の記録再生の一例を示す図。The figure which shows an example of the recording / reproducing of embodiment. 青紫色レーザ光の共焦点クロストーク光の発生の一例を示す図。The figure which shows an example of generation | occurrence | production of the confocal crosstalk light of a blue-violet laser beam. 赤色レーザ光の共焦点クロストーク光の発生の一例を示す図。The figure which shows an example of generation | occurrence | production of the confocal crosstalk light of a red laser beam. 赤色レーザ光の別の共焦点クロストーク光の発生の一例を示す図。The figure which shows an example of generation | occurrence | production of another confocal crosstalk light of a red laser beam. 共焦点クロストーク光が発生しない場合の一例を示す図。The figure which shows an example when confocal crosstalk light does not generate | occur | produce. ガイド光共焦点クロストーク発生の第一条件の一例を説明する図。The figure explaining an example of the 1st conditions of guide light confocal crosstalk generation | occurrence | production. ガイド光共焦点クロストーク発生の第二条件の一例を説明する図。The figure explaining an example of the 2nd conditions of guide light confocal crosstalk generation | occurrence | production. 実施形態の多層光記憶媒体のディスク構造の第一例を説明する図（第一中間層＜第二中間層）。The figure explaining the 1st example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第二例を説明する図（第一中間層＜第二中間層）。The figure explaining the 2nd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第三例を説明する図（第一中間層＜第二中間層）。The figure explaining the 3rd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第一例を説明する図（第一中間層＞第二中間層）。The figure explaining the 1st example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第二例を説明する図（第一中間層＞第二中間層）。The figure explaining the 2nd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第三例を説明する図（第一中間層＞第二中間層）。The figure explaining the 3rd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 共焦点クロストークが発生する確率の一例を示す図である（第一中間層＜第二中間層）。It is a figure which shows an example of the probability that confocal crosstalk will generate | occur | produce (1st intermediate | middle layer <2nd intermediate | middle layer). 共焦点クロストークが発生する確率の一例を示す図である（第一中間層＞第二中間層）。It is a figure which shows an example of the probability that confocal crosstalk will generate | occur | produce (1st intermediate | middle layer> 2nd intermediate | middle layer). 青紫色レーザ光のカバー層の表面で反射した光線による共焦点クロストークの発生の一例を示す図。The figure which shows an example of generation | occurrence | production of the confocal crosstalk by the light ray reflected on the surface of the cover layer of a blue-violet laser beam. 共焦点クロストークの低減された様子の一例を示す図。The figure which shows an example of a mode that the confocal crosstalk was reduced. 所定条件下での共焦点クロストークの発生の様子の一例を示す図。The figure which shows an example of the mode of generation | occurrence | production of the confocal crosstalk on predetermined conditions. 赤色レーザ光のカバー層の表面で反射した光線による共焦点クロストークの発生の一例を示す図。The figure which shows an example of generation | occurrence | production of the confocal crosstalk by the light ray reflected on the surface of the cover layer of a red laser beam. ガイド光の共焦点クロストークが低減された様子の一例を示す図。The figure which shows an example of a mode that the confocal crosstalk of guide light was reduced. 共焦点クロストークが低減可能なカバー層厚範囲の一例を示す図。The figure which shows an example of the cover layer thickness range which can reduce confocal crosstalk. 実施形態の多層光記憶媒体のディスク構造の第一例を説明する図（第一中間層＜第二中間層）。The figure explaining the 1st example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第二例を説明する図（第一中間層＜第二中間層）。The figure explaining the 2nd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第三例を説明する図（第一中間層＜第二中間層）。The figure explaining the 3rd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 共焦点クロストークが低減可能なカバー層厚範囲の一例を示す図。The figure which shows an example of the cover layer thickness range which can reduce confocal crosstalk. 実施形態の多層光記憶媒体のディスク構造の第一例を説明する図（第一中間層＞第二中間層）。The figure explaining the 1st example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第二例を説明する図（第一中間層＞第二中間層）。The figure explaining the 2nd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第三例を説明する図（第一中間層＞第二中間層）。The figure explaining the 3rd example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 共焦点クロストークが低減可能なカバー層厚範囲の一例を示す図。The figure which shows an example of the cover layer thickness range which can reduce confocal crosstalk. 実施形態の多層光記憶媒体のディスク構造の第四例を説明する図（第一中間層＜第二中間層）。The figure explaining the 4th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第五例を説明する図（第一中間層＜第二中間層）。The figure explaining the 5th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第六例を説明する図（第一中間層＜第二中間層）。The figure explaining the 6th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer <2nd intermediate | middle layer). 共焦点クロストークが低減可能なカバー層厚範囲の一例を示す図。The figure which shows an example of the cover layer thickness range which can reduce confocal crosstalk. 実施形態の多層光記憶媒体のディスク構造の第四例を説明する図（第一中間層＞第二中間層）。The figure explaining the 4th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第五例を説明する図（第一中間層＞第二中間層）。The figure explaining the 5th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer). 実施形態の多層光記憶媒体のディスク構造の第六例を説明する図（第一中間層＞第二中間層）The figure explaining the 6th example of the disk structure of the multilayer optical storage medium of embodiment (1st intermediate | middle layer> 2nd intermediate | middle layer)
　以下、実施形態について図面を参照して説明する。 Hereinafter, embodiments will be described with reference to the drawings.
　図１は、実施形態にかかる光記憶媒体の断面構造を示す図である。実施形態において、光記憶媒体は複数の記録再生層を有する光ディスク10であって、後述する光ピックアップ(OPU)から発せられるレーザ光により情報が光ディスク10内の記録膜に記録される。その上面形状は例えば直径１２０ｍｍの円形である。本実施形態の光記憶媒体の効果はその上面形状には依存せず、たとえば、楕円、多角形、あるいはそれらを連結させた形状でも良い。 FIG. 1 is a diagram illustrating a cross-sectional structure of an optical storage medium according to an embodiment. In the embodiment, the optical storage medium is an optical disc 10 having a plurality of recording / reproducing layers, and information is recorded on a recording film in the optical disc 10 by a laser beam emitted from an optical pickup (OPU) described later. The upper surface shape is, for example, a circle having a diameter of 120 mm. The effect of the optical storage medium of the present embodiment does not depend on the shape of the upper surface, and may be, for example, an ellipse, a polygon, or a shape obtained by connecting them.
　光ディスク10は、記録再生時のサーボ信号生成のための案内溝、あるいはピット列が形成されたガイド層20と記録層21（記録層21A～21Lを含む）が基板11上に形成された構造となっている。記録層21は、記録層群とも称され、記録層群は、記録層21A～21Lの12層及び中間層31A～31Kの11層を含む。記録層21A～21Lと中間層31A～31Kとは交互に配置される。ガイド層20と記録層21は、基板11側からガイド層20、記録層21の順に形成され、光ピックアップからの記録再生用のレーザ光15,16は基板11と反対側から入射する。記録層21の基板11と反対側にはカバー層12が形成されている。 The optical disc 10 has a structure in which a guide layer 20 and a recording layer 21 (including recording layers 21A to 21L) in which guide grooves or pit rows for generating servo signals during recording and reproduction are formed are formed on a substrate 11. It has become. The recording layer 21 is also referred to as a recording layer group, and the recording layer group includes 12 recording layers 21A to 21L and 11 intermediate layers 31A to 31K. The recording layers 21A to 21L and the intermediate layers 31A to 31K are alternately arranged. The guide layer 20 and the recording layer 21 are formed in the order of the guide layer 20 and the recording layer 21 from the substrate 11 side, and recording / reproducing laser beams 15 and 16 from the optical pickup enter from the opposite side of the substrate 11. A cover layer 12 is formed on the side of the recording layer 21 opposite to the substrate 11.
　ガイド層20上の案内溝あるいはピット列は、例えば、深さ60ｎｍ、トラックピッチ0.64μｍのらせん構造であり、断面の凹部と凸部の比率は略1対1である。なお、溝深さ(ピット深さ)やトラックピッチはこれに限ったものではなく、深さ100ｎｍ程度の深溝（深ピット）、あるいは、20ｎｍ程度の浅溝（浅ピット）でも良く、0.32μｍ程度の狭トラックピッチや、0.74μｍ程度、あるいは1.2μｍ程度の広トラックピッチでも構わない。また、トラック構造も同心円構造でもよく、らせん構造でも凹部と凸部が一周毎に切り替わる、いわゆるシングルスパイラル構造でも良い。また、案内溝には、アドレス情報が例えばウォブルにより印加されている。ウォブルとは、光ディスク10面内での案内溝のトラック延伸方向に対して垂直な方向へ蛇行である。 The guide groove or pit row on the guide layer 20 has, for example, a helical structure with a depth of 60 nm and a track pitch of 0.64 μm, and the ratio of the concave and convex portions in the cross section is approximately 1: 1. Note that the groove depth (pit depth) and the track pitch are not limited to this, and may be a deep groove (deep pit) with a depth of about 100 nm or a shallow groove (shallow pit) with a thickness of about 20 nm, about 0.32 μm. A narrow track pitch of about 0.74 μm, or a wide track pitch of about 1.2 μm may be used. Also, the track structure may be a concentric structure, a spiral structure, or a so-called single spiral structure in which the concave and convex portions are switched every round. Further, address information is applied to the guide groove by, for example, wobble. The wobble is meandering in a direction perpendicular to the track extending direction of the guide groove in the surface of the optical disc 10.
　ガイド層20とガイド層20に最も近い記録層21Aの間には光透過性を有する中間層30が形成される。一方、記録層21のうち隣接する二つの記録層の間にも光透過性を有する中間層31A～31Kが形成される。中間層30および中間層31（中間層31A～31Kを含む）の厚さについては後述する。 An intermediate layer 30 having optical transparency is formed between the guide layer 20 and the recording layer 21A closest to the guide layer 20. On the other hand, intermediate layers 31A to 31K having optical transparency are also formed between two adjacent recording layers of the recording layer 21. The thicknesses of the intermediate layer 30 and the intermediate layer 31 (including the intermediate layers 31A to 31K) will be described later.
　カバー層12は光透過性を有し、その厚さは例えば53μｍである。カバー層は透明性を有する材料であれば特に限定はないが、ポリカーボネート、ＰＭＭＡなどの合成樹脂やガラスなどを用いることが可能である。記録層21は、情報を記録する層であり、光ピックアップから発せられるレーザ光により変化を生じ、情報に対応したマークが記録される。例えば、相変化材料を含む多層膜からなる相変化記録膜や、有機色素からなる追記型記録膜などである。一つの記録層21の厚さは、通常 0.2μｍ以下で、記録層21の厚さはカバー層や中間層の厚さに対して、非常に小さい。 The cover layer 12 is light transmissive and has a thickness of, for example, 53 μm. The cover layer is not particularly limited as long as it is a transparent material, but synthetic resins such as polycarbonate and PMMA, glass, and the like can be used. The recording layer 21 is a layer for recording information, and a change corresponding to the laser beam emitted from the optical pickup is generated, and a mark corresponding to the information is recorded. For example, a phase change recording film composed of a multilayer film containing a phase change material, a write-once recording film composed of an organic dye, and the like. The thickness of one recording layer 21 is usually 0.2 μm or less, and the thickness of the recording layer 21 is very small with respect to the thickness of the cover layer and the intermediate layer.
　光ディスク10の記録再生時には、ガイド層20と記録層31にはレーザ光15と16がそれぞれ照射される。レーザ光15と16は、光ピックアップ内での光路分離のし易さのため、異なる波長を持ち、たとえば、レーザ光15は赤色レーザ光であり、レーザ光16は青紫色レーザ光である。 During recording / reproduction of the optical disc 10, the guide layer 20 and the recording layer 31 are irradiated with laser beams 15 and 16, respectively. The laser beams 15 and 16 have different wavelengths for easy optical path separation in the optical pickup. For example, the laser beam 15 is a red laser beam and the laser beam 16 is a blue-violet laser beam.
　図２は、第一の実施形態に係る情報記録再生装置300の構成を示している。情報記録再生装置300は、インターフェース(IF)310、信号処理ユニット(DSP)320、レーザドライバ(LDD1)330、(LDD2)340、光ピックアップヘッドユニット(OPU)200、ＲＦアンプＩＣ(RF AMP)350、サーボコントローラ360、スピンドルモータ60で構成され、スピンドルモータ60には、多層光ディスク10がセットされる。 FIG. 2 shows the configuration of the information recording / reproducing apparatus 300 according to the first embodiment. Information recording / reproducing apparatus 300 includes interface (IF) 310, signal processing unit (DSP) 320, laser driver (LDD1) 330, (LDD2) 340, optical pickup head unit (OPU) 200, RF amplifier IC (RFＲＦAMP) 350 , A servo controller 360 and a spindle motor 60, and the multilayer optical disk 10 is set on the spindle motor 60.
　インターフェース310は、図示しない外部ホストとコマンドやデータのやり取りを行なう接続部分であり、特定の規格（例えばＳＡＴＡ）に対応している。 The interface 310 is a connection part for exchanging commands and data with an external host (not shown), and corresponds to a specific standard (for example, SATA).
　信号処理ユニット320は、インターフェース310を介して外部ホストとのコマンドおよびデータの送受信、データの変換、レーザドライバへのデータパルスおよび制御信号の送信、サーボコントローラ360への制御信号の送信、ＲＦアンプＩＣ350からのデータ信号の受信を担う。 The signal processing unit 320 transmits / receives commands and data to / from an external host via the interface 310, converts data, transmits data pulses and control signals to the laser driver, transmits control signals to the servo controller 360, RF amplifier IC 350 Responsible for receiving data signals from
　レーザドライバ330、340は、信号処理ユニット320からのデータパルス、制御信号の受信、駆動パルスへの変換、および光ピックアップヘッドユニット200への駆動パルスの送信を行なう。 Laser drivers 330 and 340 receive data pulses from the signal processing unit 320, control signals, convert them into drive pulses, and transmit drive pulses to the optical pickup head unit 200.
　光ピックアップヘッドユニット200は、レーザドライバ330、340からの駆動パルスの応じて、レーザ光15、16を多層光ディスク10のガイド層20と記録層21に照射し、その反射光を受光し、反射光の強弱変化に応じた信号をＲＦアンプＩＣ350に送信する。 The optical pickup head unit 200 irradiates the guide layer 20 and the recording layer 21 of the multilayer optical disc 10 with the laser beams 15 and 16 in response to the drive pulses from the laser drivers 330 and 340, receives the reflected light, and receives the reflected light. A signal corresponding to the change in strength is transmitted to the RF amplifier IC 350.
　ＲＦアンプＩＣ350は、光ピックアップヘッドユニット200からの信号を増幅し、サーボ信号、データ信号を生成し、それぞれ、サーボコントローラ360、および信号処理ユニット320に送信する。 The RF amplifier IC 350 amplifies the signal from the optical pickup head unit 200, generates a servo signal and a data signal, and transmits them to the servo controller 360 and the signal processing unit 320, respectively.
　サーボコントローラ360は、ＲＦアンプＩＣ350からのサーボ信号の受信、サーボ信号のアクチュエータ駆動信号およびスピンドルモータ駆動信号への変換、および光ピックアップヘッドユニット200へのアクチュエータ駆動信号の送信、スピンドルモータ60への駆動信号の送信を行なう。 The servo controller 360 receives the servo signal from the RF amplifier IC 350, converts the servo signal into an actuator drive signal and a spindle motor drive signal, transmits the actuator drive signal to the optical pickup head unit 200, and drives the spindle motor 60. Transmit the signal.
　スピンドルモータ60は、サーボコントローラ360からのスピンドルモータ駆動信号を受信し、装着された光ディスク10を、その延伸方向に対して垂直な軸を中心に回転させる。 The spindle motor 60 receives the spindle motor drive signal from the servo controller 360, and rotates the mounted optical disc 10 about an axis perpendicular to the extending direction.
　図３は、実施形態に係る情報記録再生装置300の光ピックアップヘッドユニット200の詳しい構成の一例を表している。光ピックアップヘッドユニット（ＯＰＵ）200は、青紫色レーザ(Blue LD)、赤色レーザ(Red LD)、偏光ビームスプリッタ(PBS)１、２、四分の１波長板(QWP)１、２、コリメートレンズ(CL)１、２、対物レンズ(OL)、ホログラム素子(HOE)、青紫色用光検出器ＩＣ(Blue PDIC)、赤色用光検出器ＩＣ(Red PDIC)、回折素子(GT)、ダイクロイックプリズム(DP)、コリメートレンズ用アクチュエータ(CL-ACT)、対物レンズアクチュエータ(OL-ACT)から構成される。 FIG. 3 shows an example of a detailed configuration of the optical pickup head unit 200 of the information recording / reproducing apparatus 300 according to the embodiment. The optical pickup head unit (OPU) 200 consists of a blue-violet laser (Blue LD), a red laser (Red LD), a polarizing beam splitter (PBS) 1 and 2, a quarter-wave plate (QWP) 1 and 2, a collimating lens (CL) 1, 2, objective lens (OL), hologram element (HOE), blue-violet detector IC (Blue PDIC), red detector IC (Red PDIC), diffraction element (GT), dichroic prism (DP), collimating lens actuator (CL-ACT), and objective lens actuator (OL-ACT).
　青紫色レーザは、例えば波長405ｎｍを有する半導体レーザであり、記録及び再生のためのレーザ光を放出する。青紫色レーザは、図２の情報記録再生装置300のレーザドライバ１に接続されている。 The blue-violet laser is a semiconductor laser having a wavelength of 405 nm, for example, and emits laser light for recording and reproduction. The blue-violet laser is connected to the laser driver 1 of the information recording / reproducing apparatus 300 in FIG.
　ＰＢＳ１は、青紫色レーザからの入射光を透過し、入射光と９０度偏光面が回転した、青紫色レーザの光ディスク10からの反射光を反射する。 PBS 1 transmits the incident light from the blue-violet laser and reflects the reflected light from the optical disk 10 of the blue-violet laser in which the incident light and the 90-degree polarization plane are rotated.
　ＱＷＰ１は、青紫色レーザからの入射光を透過し、直線偏光を円偏光に変換する。また、青紫色レーザの光ディスク10からの反射光を透過し、円偏光を直線偏光に変換する。このとき、入射光と９０度偏光面が異なる直線偏光になる。例えば、入射光がＰ偏光であれば、反射光はＳ偏光となる。 QWP1 transmits incident light from a blue-violet laser and converts linearly polarized light into circularly polarized light. Further, the reflected light from the optical disk 10 of the blue-violet laser is transmitted, and the circularly polarized light is converted into linearly polarized light. At this time, the incident light and the 90-degree polarization plane are linearly polarized light different from each other. For example, if the incident light is P-polarized light, the reflected light is S-polarized light.
　コリメートレンズ１は、青紫色レーザ１からの入射光を略平行光に変換する。 The collimating lens 1 converts incident light from the blue-violet laser 1 into substantially parallel light.
　対物レンズは、青紫色レーザから出射した光を光ディスク10の記録層21に集光する。なお、対物レンズは、レーザ光源側に波長選択制の開口を持つことにより、赤色レーザ光15と青紫色レーザ光16でそれぞれ異なる開口数を有し、たとえば、青紫色レーザ光16に対しては０．８５、赤色レーザ光15に対しては０．６５である。 The objective lens focuses the light emitted from the blue-violet laser on the recording layer 21 of the optical disc 10. The objective lens has a wavelength selective aperture on the laser light source side so that the red laser beam 15 and the blue-violet laser beam 16 have different numerical apertures. For example, for the blue-violet laser beam 16, 0.85 and 0.65 for the red laser beam 15.
　ダイクロイックプリズムは、青紫色レーザからの入射光を透過し、赤色レーザからの入射光を反射する。 The dichroic prism transmits incident light from the blue-violet laser and reflects incident light from the red laser.
　赤色レーザは、例えば波長655ｎｍを有する半導体レーザであり、トラッキングサーボ用のレーザ光を放出する。赤色レーザは、情報記録再生装置300のレーザドライバ２に接続されている。 The red laser is a semiconductor laser having a wavelength of 655 nm, for example, and emits a tracking servo laser beam. The red laser is connected to the laser driver 2 of the information recording / reproducing apparatus 300.
　回折素子は、赤色レーザ光を回折により３つのビームに分割する。３つのビームは光ディスク10上で１つのメインビームと２つのサブビームとなる。 The diffraction element splits the red laser light into three beams by diffraction. The three beams become one main beam and two sub beams on the optical disc 10.
　ＰＢＳ２は、赤色レーザからの入射光を透過し、入射光と９０度偏光面が回転した、赤色レーザの光ディスク10からの反射光を反射する。 PBS 2 transmits the incident light from the red laser and reflects the reflected light from the optical disk 10 of the red laser in which the incident light and the 90-degree polarization plane are rotated.
　ＱＷＰ２は、赤色レーザからの入射光を透過し、直線偏光を円偏光に変換する。また、赤色レーザの光ディスク10からの反射光を透過し、円偏光を直線偏光に変換する。このとき入射光と９０度偏光面が異なる直線偏光になる。例えば、入射光がＰ偏光であれば、反射光はＳ偏光となる。 QWP2 transmits incident light from a red laser and converts linearly polarized light into circularly polarized light. Further, the reflected light from the optical disk 10 of the red laser is transmitted, and the circularly polarized light is converted into linearly polarized light. At this time, the incident light and the 90-degree polarization plane are linearly polarized light different from each other. For example, if the incident light is P-polarized light, the reflected light is S-polarized light.
　コリメートレンズ２は、赤色レーザからの出射光を略平行光に変換する。 The collimating lens 2 converts light emitted from the red laser into substantially parallel light.
　ＨＯＥは、青紫色レーザ１を出射した光束が、光ディスク10の情報記録層で反射した光束を透過し、光束の所定の領域を所定の角度で回折させる。 In the HOE, the light beam emitted from the blue-violet laser 1 transmits the light beam reflected by the information recording layer of the optical disc 10, and diffracts a predetermined region of the light beam at a predetermined angle.
　青紫色用光検出器ＩＣは、ＨＯＥからの青紫色レーザ光を受光し、その受光光量に応じた電流を発生させ、その内部の電流－電圧変換回路にて電圧に変換した上で出力する。 The blue-violet light detector IC receives the blue-violet laser light from the HOE, generates a current corresponding to the received light amount, converts the light into a voltage by an internal current-voltage conversion circuit, and outputs the voltage.
　赤色用光検出器ＩＣは、ＰＢＳ２で反射した赤色レーザ光を受光し、その受光光量に応じた電流を発生させ、その内部の電流－電圧変換回路にて電圧に変換した上で出力する。 The red light detector IC receives the red laser light reflected by the PBS 2, generates a current corresponding to the received light amount, converts it into a voltage by an internal current-voltage conversion circuit, and outputs the voltage.
　コリメートレンズアクチュエータは、コリメートレンズ２を、対物レンズから出射した赤色レーザ光が光ディスク10上で光軸方向（フォーカス方向）に移動するように、紙面内上下方向に駆動する。 The collimating lens actuator drives the collimating lens 2 in the vertical direction in the drawing so that the red laser light emitted from the objective lens moves on the optical disk 10 in the optical axis direction (focus direction).
　対物レンズアクチュエータは、対物レンズから出射したレーザ光が光ディスク10上で光軸（フォーカス方向）に移動するように、紙面内左右方向に対物レンズを駆動する。また、対物レンズから出射したレーザ光が光ディスク10上の記録トラックの垂直方向（ラジアル方向）に移動するように、紙面に垂直な方向に駆動する。 The objective lens actuator drives the objective lens in the left-right direction in the drawing so that the laser light emitted from the objective lens moves on the optical disc 10 along the optical axis (focus direction). Further, the laser beam emitted from the objective lens is driven in a direction perpendicular to the paper surface so that the laser beam moves in the vertical direction (radial direction) of the recording track on the optical disk 10.
　次に、実施形態に係る情報記録再生装置の情報記録時の動作を図２および図４を用いて説明する。 Next, the operation during information recording of the information recording / reproducing apparatus according to the embodiment will be described with reference to FIGS.
　図示しないホストからユーザデータの記録命令と記録対象であるデータが送出され、インターフェース310を介して信号処理ユニット320に送られる。信号処理ユニット320は受信した記録コマンドに従い、データ記録プロセスを開始する。まず、信号処理ユニット320は、レーザドライバ１、およびレーザドライバ２に駆動信号を送信し、青紫色レーザ、および赤色レーザを再生パワーにて点灯させる。サーボコントローラ360は、スピンドルモータ60に回転駆動信号を送信し、光ディスク10を所定の回転数にて回転駆動する。信号処理ユニット320は、サーボコントローラ360にフォーカスサーチ制御信号を送信する。サーボコントローラ360は、送信された制御信号に従い、コリメートレンズアクチュエータをフォーカス方向に単振動駆動する。単振動駆動されたコリメートレンズを通り対物レンズから出射された赤色レーザ光15の焦点は、光ディスク10のガイド層20を挟んで上下に繰り返し往復運動する。赤色レーザ光15のガイド層20での反射光は、赤色用光検出器ＩＣに集光される。赤色用光検出器ＩＣは、反射光量に基づいた電流を電圧に変換し、ＲＦアンプＩＣ350に送出する。ＲＦアンプＩＣ350は、受信した電圧信号から所定の演算により、赤色レーザ光のフォーカスエラー信号を生成し、サーボコントローラ360に送出する。フォーカスエラー信号は例えば図示しない非点収差生成光学素子により公知の非点収差法により生成される。サーボコントローラ360は、このフォーカスエラー信号がゼロとなる付近で、コリメートレンズアクチュエータの駆動を単振動駆動からフォーカスエラー信号に基づいた駆動に切り替えて、赤色レーザ光のフォーカスを案内溝層に引き込む。引き続き、サーボコントローラ360は、青紫色レーザ光16のフォーカスを、光ディスク10上の目的とする記録層21に引き込む。このとき、青紫色レーザ光16のフォーカスは、青紫色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成したフォーカスエラー信号を元に、対物レンズアクチュエータを駆動して記録層21のうち目的の記録層に引き込む。全てのビームのフォーカス引き込みが完了した後、サーボコントローラ360は、赤色レーザ光15を光ディスク10のガイド層20上の案内溝等で形成されたトラックに引き込む。このとき、サーボコントローラ360は、赤色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成したトラッキングエラー信号を元に対物レンズアクチュエータを駆動してガイド層上のトラックに引き込む。トラッキングエラー信号は例えば公知の差動プッシュプル法により生成される。次に、信号処理ユニット320は、赤色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成されたデータ信号を読み取り、現在のアドレスを再生する。目的とするアドレスが異なる場合には、信号処理ユニット320は、現在アドレスと目的アドレスとの差異に相当するトラック分のトラックジャンプ制御信号をサーボコントローラ360に送出する。サーボコントローラ360は、トラックジャンプ制御信号に基づいて、対物レンズアクチュエータに駆動パルスを送信し、所望のトラックへ赤色レーザ光15を移動させる。このとき、同じ対物レンズを通って照射されている青紫色レーザ光16も同じくトラック移動を行なう。 A user data recording command and data to be recorded are sent from a host (not shown) and sent to the signal processing unit 320 via the interface 310. The signal processing unit 320 starts the data recording process according to the received recording command. First, the signal processing unit 320 transmits a drive signal to the laser driver 1 and the laser driver 2 to turn on the blue-violet laser and the red laser with the reproduction power. The servo controller 360 transmits a rotation drive signal to the spindle motor 60 to drive the optical disk 10 to rotate at a predetermined rotation speed. The signal processing unit 320 transmits a focus search control signal to the servo controller 360. The servo controller 360 drives the collimating lens actuator with a single vibration in the focus direction in accordance with the transmitted control signal. The focal point of the red laser light 15 emitted from the objective lens through the collimating lens driven by a single vibration reciprocates up and down repeatedly with the guide layer 20 of the optical disc 10 interposed therebetween. The reflected light of the red laser light 15 on the guide layer 20 is condensed on the red photodetector IC. The red photodetector IC converts a current based on the amount of reflected light into a voltage and sends it to the RF amplifier IC 350. The RF amplifier IC 350 generates a focus error signal of the red laser light by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360. The focus error signal is generated by, for example, a known astigmatism method using an astigmatism generation optical element (not shown). The servo controller 360 switches the drive of the collimating lens actuator from the single vibration drive to the drive based on the focus error signal near the focus error signal becomes zero, and draws the focus of the red laser light into the guide groove layer. Subsequently, the servo controller 360 draws the focus of the blue-violet laser beam 16 into the target recording layer 21 on the optical disc 10. At this time, the blue-violet laser beam 16 is focused on the recording layer by driving the objective lens actuator based on the focus error signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC. Pull the desired recording layer out of 21. After completing the focus pull-in of all the beams, the servo controller 360 pulls the red laser light 15 into a track formed by a guide groove or the like on the guide layer 20 of the optical disc 10. At this time, the servo controller 360 drives the objective lens actuator based on the tracking error signal generated by the RF amplifier IC based on the voltage signal sent from the red light detector IC and pulls it into the track on the guide layer. The tracking error signal is generated by a known differential push-pull method, for example. Next, the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the red photodetector IC, and reproduces the current address. If the target address is different, the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360. The servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the red laser light 15 to a desired track. At this time, the blue-violet laser light 16 irradiated through the same objective lens also performs track movement.
　目的のアドレスに到達したことを確認し、信号処理ユニット320は、記録データ系列をレーザドライバ１に送信する。レーザドライバ１は、受信した記録データ系列に応じた駆動パルスを生成し、青紫色レーザに送出して、パルス駆動する。青紫色レーザにより放出されたパルスは対物レンズを通って、光ディスク10の記録層21に照射され、記録データ系列に応じた記録マークを形成する。 After confirming that the target address has been reached, the signal processing unit 320 transmits the recording data series to the laser driver 1. The laser driver 1 generates a drive pulse corresponding to the received recording data series, sends it to a blue-violet laser, and performs pulse drive. The pulse emitted by the blue-violet laser passes through the objective lens and is applied to the recording layer 21 of the optical disc 10 to form a recording mark corresponding to the recording data series.
　こうして、本実施形態の情報記録再生装置は、記録対象データを光ディスク10の目的の記録層21に記録する。 Thus, the information recording / reproducing apparatus of this embodiment records the recording target data on the target recording layer 21 of the optical disc 10.
　次に、実施形態に係る情報記録再生装置の情報再生時の動作を図２を用いて説明する。 Next, an operation during information reproduction of the information recording / reproducing apparatus according to the embodiment will be described with reference to FIG.
　図示しないホストからユーザデータの再生命令が送出され、インターフェース310を介して信号処理ユニット320に送られる。信号処理ユニット320は受信した再生コマンドに従い、データ再生プロセスを開始する。まず、信号処理ユニット320は、レーザドライバ１、およびレーザドライバ２に駆動信号を送信し、青紫色レーザ、および赤色レーザを再生パワーにて点灯させる。信号処理ユニット320は、サーボコントローラ360にフォーカスサーチ制御信号を送信する。サーボコントローラ360は、送信された制御信号に従い、コリメートレンズアクチュエータをフォーカス方向に単振動駆動する。単振動駆動されたコリメートレンズを通って対物レンズから出射された赤色レーザ光15の焦点は、光ディスク10のガイド層20を挟んで上下に繰り返し往復運動する。赤色レーザ光15のガイド層での反射光は、赤色用光検出器ＩＣに集光される。赤色用光検出器ＩＣは、反射光量に基づいた電流を電圧に変換し、ＲＦアンプＩＣ350に送出する。ＲＦアンプＩＣ350は、受信した電圧信号から所定の演算により、赤色レーザ光のフォーカスエラー信号を生成し、サーボコントローラ360に送出する。サーボコントローラ360は、このフォーカスエラー信号がゼロとなる付近で、コリメートレンズアクチュエータの駆動を単振動駆動からフォーカスエラー信号に基づいた駆動に切り替えて、赤色レーザ光のフォーカスをガイド層に引き込む。引き続き、サーボコントローラ360は、青紫色レーザ光16のフォーカスを、光ディスク10上の目的とする記録層21に引き込む。このとき、青紫色レーザ光16のフォーカスは、青紫色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成したフォーカスエラー信号を元に、対物レンズアクチュエータを駆動して記録層21のうち目的の記録層に引き込む。全てのビームのフォーカス引き込みが完了した後、サーボコントローラ360は、赤色レーザ光15をガイド層20のトラックに引き込む。このとき、サーボコントローラ360は、赤色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成したトラッキングエラー信号を元に対物レンズアクチュエータを駆動してガイド層20のトラックに引き込む。次に、信号処理ユニット320は、赤色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成されたデータ信号を読み取り、現在のアドレスを再生する。目的とするアドレスが異なる場合には、信号処理ユニット320は、現在アドレスと目的アドレスとの差異に相当するトラック分のトラックジャンプ制御信号をサーボコントローラ360に送出する。サーボコントローラ360は、トラックジャンプ制御信号に基づいて、対物レンズアクチュエータに駆動パルスを送信し、所望のトラックへ赤色レーザ光15を移動させる。このとき、同じ対物レンズを通って照射されている青紫色レーザ光16も同じくトラック移動を行なう。 A user data reproduction command is sent from a host (not shown) and sent to the signal processing unit 320 via the interface 310. The signal processing unit 320 starts the data reproduction process according to the received reproduction command. First, the signal processing unit 320 transmits a drive signal to the laser driver 1 and the laser driver 2 to turn on the blue-violet laser and the red laser with the reproduction power. The signal processing unit 320 transmits a focus search control signal to the servo controller 360. The servo controller 360 drives the collimating lens actuator with a single vibration in the focus direction in accordance with the transmitted control signal. The focal point of the red laser light 15 emitted from the objective lens through the collimating lens driven by a single vibration repeatedly reciprocates up and down across the guide layer 20 of the optical disc 10. The reflected light of the red laser light 15 on the guide layer is condensed on the red photodetector IC. The red photodetector IC converts a current based on the amount of reflected light into a voltage and sends it to the RF amplifier IC 350. The RF amplifier IC 350 generates a focus error signal of the red laser light by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360. The servo controller 360 switches the drive of the collimating lens actuator from the single vibration drive to the drive based on the focus error signal near the focus error signal becomes zero, and pulls the focus of the red laser light into the guide layer. Subsequently, the servo controller 360 draws the focus of the blue-violet laser beam 16 into the target recording layer 21 on the optical disc 10. At this time, the blue-violet laser beam 16 is focused on the recording layer by driving the objective lens actuator based on the focus error signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC. Pull the desired recording layer out of 21. After completing the focus pull-in of all the beams, the servo controller 360 pulls the red laser light 15 into the track of the guide layer 20. At this time, the servo controller 360 drives the objective lens actuator based on the tracking error signal generated by the RF amplifier IC based on the voltage signal sent from the red light detector IC and pulls it into the track of the guide layer 20. Next, the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the red photodetector IC, and reproduces the current address. If the target address is different, the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360. The servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the red laser light 15 to a desired track. At this time, the blue-violet laser light 16 irradiated through the same objective lens also performs track movement.
青紫色用光検出器ＩＣは、青紫色レーザ光16が光ディスク10の記録層21で反射した反射光量に基づいた電流を電圧に変換し、ＲＦアンプＩＣ350に送出する。ＲＦアンプＩＣ350は、受信した電圧信号から所定の演算により、青紫色レーザ光16のトラッキングエラー信号を生成し、サーボコントローラ360に送出する。この場合のトラッキングエラー信号は、記録層21の記録済みマーク列から生成される、例えばＤＰＤ（Ｄｉｆｆｅｒｅｎｔｉａｌ　Ｐ　ａｓｅ　Ｄｅｔeciton）信号、あるいは、プッシュプル信号などである。 The blue-violet photodetector IC converts a current based on the amount of reflected light reflected by the recording layer 21 of the optical disk 10 into the blue-violet laser light 16 into a voltage, and sends the voltage to the RF amplifier IC 350. The RF amplifier IC 350 generates a tracking error signal of the blue-violet laser light 16 by a predetermined calculation from the received voltage signal, and sends it to the servo controller 360. The tracking error signal in this case is, for example, a DPD (Differential Pase Deciton) signal or a push-pull signal generated from a recorded mark string of the recording layer 21.
　信号処理ユニット320は、目的アドレス近傍のトラックに到達したと判断した後、サーボコントローラ360にガイド層サーボからの切り離し制御信号を送信する。サーボコントローラ360は、対物レンズアクチュエータの駆動を、赤色レーザ光15のトラッキングエラー信号に基づいた駆動から、青紫色レーザ光16のトラッキングエラー信号に基づいた駆動に切り替えて、青紫色レーザ光16を記録層21の記録済みトラックに引き込む。次に、信号処理ユニット320は、青紫色用光検出器ＩＣから送出された電圧信号を元にＲＦアンプＩＣで生成されたデータ信号を読み取り、青紫色レーザ光16が引き込んだ記録層21の現在のアドレスを再生する。目的とするアドレスが異なる場合には、信号処理ユニット320は、現在アドレスと目的アドレスとの差異に相当するトラック分のトラックジャンプ制御信号をサーボコントローラ360に送出する。サーボコントローラ360は、トラックジャンプ制御信号に基づいて、対物レンズアクチュエータに駆動パルスを送信し、所望のトラックへ青紫色レーザ光16を移動させる。 The signal processing unit 320 transmits a disconnection control signal from the guide layer servo to the servo controller 360 after determining that the track near the target address has been reached. The servo controller 360 switches the driving of the objective lens actuator from driving based on the tracking error signal of the red laser beam 15 to driving based on the tracking error signal of the blue purple laser beam 16, and records the blue-violet laser beam 16. Pull into the recorded track of layer 21. Next, the signal processing unit 320 reads the data signal generated by the RF amplifier IC based on the voltage signal transmitted from the blue-violet photodetector IC, and the current of the recording layer 21 into which the blue-violet laser light 16 has been drawn. Play the address. If the target address is different, the signal processing unit 320 sends a track jump control signal for the track corresponding to the difference between the current address and the target address to the servo controller 360. The servo controller 360 transmits a drive pulse to the objective lens actuator based on the track jump control signal, and moves the blue-violet laser light 16 to a desired track.
　信号処理ユニット320は、目的のアドレスに到達したことを確認し、記録層21からデータ再生を開始する。こうして、本実施形態の情報記録再生装置は、記録層から情報を再生することが出来る。 The signal processing unit 320 confirms that the target address has been reached, and starts data reproduction from the recording layer 21. Thus, the information recording / reproducing apparatus of this embodiment can reproduce information from the recording layer.
　上述のように、ガイド層20から情報を再生する赤色レーザ光15と、記録層21に情報を記録、あるいは記録層21から情報を再生する青紫色レーザ光16が、それぞれ必要な役割を果たすことで光ディスク10の記録再生が成り立つことが判る。 As described above, the red laser beam 15 for reproducing information from the guide layer 20 and the blue-violet laser beam 16 for recording information on the recording layer 21 or reproducing information from the recording layer 21 each play a necessary role. Thus, it can be seen that the recording / reproduction of the optical disk 10 is established.
　複数の記録層を持つ光ディスクにおいて問題となる現象として層間クロストークがある。層間クロストークには隣接する記録層の映り込みによる層間クロストークと、共焦点クロストークがある(先行技術参照)。隣接する記録層の映り込みによる層間クロストークについては、先行技術の如く、中間層31の厚みを10μｍ以上に設定することで回避可能であり、中間層31の厚みの最小値10μｍに製造上の誤差を見込んで中間層31の厚み設計値とすれば良い。 Interlayer crosstalk is a phenomenon that causes problems in optical discs having a plurality of recording layers. Interlayer crosstalk includes interlayer crosstalk caused by reflection of adjacent recording layers and confocal crosstalk (see the prior art). Interlayer crosstalk due to reflection of adjacent recording layers can be avoided by setting the thickness of the intermediate layer 31 to 10 μm or more as in the prior art, and the minimum value of the thickness of the intermediate layer 31 is 10 μm. In consideration of the error, the thickness design value of the intermediate layer 31 may be used.
　一方、記録再生光(青紫色レーザ光16)の共焦点クロストーク発生の様子を図５を用いて説明する。光ディスク10の記録層21のうち目的とする記録層(図では記録層21C)に照射された記録再生用の青紫色レーザ光16は、記録層の半透過性により複数の光ビームに分岐する。例えば、レーザ光16の一部は、記録層21Gで反射して、分岐ビーム17となって記録層21Kで焦点をむすび、この反射光が再び記録層21Gで反射してレーザ光16、すなわち記録層21Cの記録再生光と合流し、青色用光検出器ＩＣで同時かつ空間的に略同位置にて検出されてしまう。この共焦点クロストーク光は、記録再生光と同一波長でかつ略同一光路を通って検出されるため、空間的、帯域的分離手段が有効に働かず、強力なノイズとなって検出されることとなる。記録層における、記録再生光(青紫色レーザ光)の共焦点クロストークの低減には、記録層21の中間層31の厚さを互いに異なる厚さとすることが有効であることが知られており、たとえば、中間層31の厚さを第一および第二の中間層厚さが交互に繰り返す構造とするのが良い。このとき、第一の中間層厚さと第二の中間層厚さは製造上のマージンを考慮し、４μｍ以上の差を持たせることにより共焦点クロストークが低減される。したがって、第一の中間層厚さを１２μｍ、第二の中間層厚さを１６μｍとすることにより、共焦点クロストークが低減され、かつ、映り込みによる層間クロストークも低減することが可能である。また、記録層21のすべての層の反射率を2%以下とすることで共焦点クロストークをさらに低減することが可能である。 On the other hand, the occurrence of confocal crosstalk of the recording / reproducing light (blue-violet laser light 16) will be described with reference to FIG. The recording / reproducing blue-violet laser light 16 irradiated on the target recording layer (the recording layer 21C in the figure) of the recording layer 21 of the optical disc 10 is branched into a plurality of light beams due to the semi-transmission of the recording layer. For example, a part of the laser beam 16 is reflected by the recording layer 21G, becomes a branched beam 17 and is focused on the recording layer 21K, and this reflected light is reflected again by the recording layer 21G and is reflected by the laser beam 16, that is, the recording It merges with the recording / reproducing light of the layer 21C, and is detected simultaneously and spatially at substantially the same position by the blue photodetector IC. This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes. It is known that the thickness of the intermediate layer 31 of the recording layer 21 is different from each other for reducing the confocal crosstalk of the recording / reproducing light (blue-violet laser light) in the recording layer. For example, the intermediate layer 31 may have a thickness in which the first and second intermediate layer thicknesses are alternately repeated. At this time, the first intermediate layer thickness and the second intermediate layer thickness take a manufacturing margin into consideration, and the confocal crosstalk is reduced by providing a difference of 4 μm or more. Therefore, by setting the first intermediate layer thickness to 12 μm and the second intermediate layer thickness to 16 μm, it is possible to reduce confocal crosstalk and also reduce interlayer crosstalk due to reflection. . Further, the confocal crosstalk can be further reduced by setting the reflectance of all the recording layers 21 to 2% or less.
　ところで、記録層21への情報の記録あるいは記録層21からの情報の再生には、直接の記録層21の記録・再生に寄与する記録再生光(青紫色レーザ光16)はもとより、ガイド層20から情報を再生する赤色レーザ光15が必要な役割を果たすことが肝要であることは上述の通りである。したがって、記録再生光の層間クロストークと同等に、ガイド光(赤色レーザ光15)の層間クロストーク対策は重要である。図６は、ガイド光(赤色レーザ光15)の共焦点クロストーク発生の様子を示している。光ディスク10のガイド層20に照射されたガイド用の赤色レーザ光15は、記録層の半透過性により複数の光ビームに分岐する。例えば、レーザ光15の一部は、記録層21Aで反射して、分岐ビーム40となって記録層21Fで焦点をむすび、この反射光が再び記録層21Aで反射してレーザ光15、すなわちガイド層20の記録再生光と合流し、赤色用光検出器ＩＣで同時かつ空間的に略同位置にて検出されてしまう。この共焦点クロストーク光は、ガイド光と同一波長でかつ略同一光路を通って検出されるため、空間的、帯域的分離手段が有効に働かず、強力なノイズとなって検出されることとなる。一方、図７は、ガイド光(赤色レーザ光15)の別の共焦点クロストーク発生の様子を示している。光ディスク10のガイド層20に照射されたガイド用の赤色レーザ光15は、記録層の半透過性により複数の光ビームに分岐する。例えば、レーザ光15の一部は、記録層21Aで反射して、分岐ビーム42となって記録層21Jで反射する。この反射光が記録層21Eで反射してレーザ光15、すなわちガイド層20の記録再生光と合流する。このクロストーク光は、図６で説明したクロストーク光とは異なり、記録層21Jで焦点を結ばないが、赤色レーザ光15の周縁部において、赤色用光検出器ＩＣで同時かつ空間的に略同位置にて検出されてしまう。したがって、本実施形態ではこれも共焦点クロストークの一種として考えることとする。 By the way, for recording information on the recording layer 21 or reproducing information from the recording layer 21, not only recording / reproducing light (blue-violet laser beam 16) contributing to recording / reproducing of the direct recording layer 21, but also the guide layer 20 As described above, it is important that the red laser beam 15 for reproducing information from the above plays a necessary role. Therefore, the countermeasure against the interlayer crosstalk of the guide light (red laser beam 15) is as important as the interlayer crosstalk of the recording / reproducing light. FIG. 6 shows how the confocal crosstalk occurs in the guide light (red laser light 15). The red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer. For example, a part of the laser beam 15 is reflected by the recording layer 21A, becomes a branched beam 40 and is focused by the recording layer 21F, and this reflected light is reflected again by the recording layer 21A and is reflected by the laser beam 15, that is, the guide It merges with the recording / reproducing light of the layer 20 and is detected simultaneously and spatially at substantially the same position by the red photodetector IC. Since this confocal crosstalk light is detected through the same wavelength and substantially the same optical path as the guide light, the spatial and band separation means do not work effectively and are detected as powerful noise. Become. On the other hand, FIG. 7 shows another confocal crosstalk occurring in the guide light (red laser light 15). The red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer. For example, a part of the laser beam 15 is reflected by the recording layer 21A, becomes a branched beam 42, and is reflected by the recording layer 21J. The reflected light is reflected by the recording layer 21E and merges with the laser light 15, that is, the recording / reproducing light of the guide layer 20. Unlike the crosstalk light described with reference to FIG. 6, the crosstalk light is not focused on the recording layer 21 </ b> J. However, at the periphery of the red laser light 15, the crosstalk light is substantially simultaneously and spatially reduced by the red photodetector IC. It will be detected at the same position. Therefore, in the present embodiment, this is also considered as a kind of confocal crosstalk.
　一般に、記録層21の反射率は、記録再生光である青紫色波長帯に適合させて調整するため、ガイド光である赤色波長帯での反射率は優先的に調整することが出来ない。逆に言えば、赤色波長帯での反射率を、共焦点クロストークが生じないように調整することを優先させると記録層の材料選択範囲や膜厚調整範囲を極端に制限してしまうこととなり、光ディスク10の生産性を極端に悪化させ、コスト高となってしまう。したがって、ガイド光の共焦点クロストークの低減のためには、記録再生光の記録層における共焦点クロストーク（図５）とは独立したアプローチを採ることが望ましい。そこで、本実施形態では、ガイド層20と記録層21Aの間の中間層30と記録層21における中間層31の厚さを好適に作成することによりガイド光の共焦点クロストークを低減することとした。 Generally, since the reflectance of the recording layer 21 is adjusted in accordance with the blue-violet wavelength band that is recording / reproducing light, the reflectance in the red wavelength band that is the guide light cannot be preferentially adjusted. Conversely, if priority is given to adjusting the reflectance in the red wavelength band so that confocal crosstalk does not occur, the material selection range and film thickness adjustment range of the recording layer will be extremely limited. As a result, the productivity of the optical disk 10 is extremely deteriorated and the cost is increased. Therefore, in order to reduce the confocal crosstalk of the guide light, it is desirable to take an approach independent of the confocal crosstalk (FIG. 5) in the recording layer of the recording / reproducing light. Therefore, in this embodiment, the confocal crosstalk of the guide light is reduced by suitably creating the thickness of the intermediate layer 30 between the guide layer 20 and the recording layer 21A and the intermediate layer 31 in the recording layer 21; did.
　図８はガイド光の共焦点クロストークが低減された様子の一例を示す図である。光ディスク10のガイド層20に照射されたガイド用の赤色レーザ光15は、一部が記録層21Aで反射して、分岐ビーム41となって記録層21Fで反射する。しかし、この場合、中間層30と中間層31が好適に作成されているため、分岐ビーム41は記録層21Fで焦点をむすばず、かつ、この反射光が再び記録層21Aで反射しても、レーザ光15、すなわちガイド層20の記録再生光とは同一光路では合流せず、赤色用光検出器ＩＣで空間的に一致しない位置で検出される。このため、このクロストーク光は、ガイド光15と空間的な分離が可能であり、ノイズ低減が可能である。 FIG. 8 is a diagram illustrating an example of a state in which the confocal crosstalk of the guide light is reduced. A part of the guide red laser light 15 irradiated to the guide layer 20 of the optical disc 10 is reflected by the recording layer 21A, and becomes a branched beam 41 and reflected by the recording layer 21F. However, in this case, since the intermediate layer 30 and the intermediate layer 31 are suitably formed, the branched beam 41 does not have to be focused on the recording layer 21F, and even if this reflected light is reflected again by the recording layer 21A, The laser beam 15, that is, the recording / reproducing light of the guide layer 20, does not merge in the same optical path, but is detected at a position that does not spatially coincide with the red photodetector IC. For this reason, the crosstalk light can be spatially separated from the guide light 15, and noise can be reduced.
　ここで、ガイド光の共焦点クロストークを低減可能な中間層厚構成について述べる。ガイド光の共焦点クロストークを低減可能な中間層厚構成を導出するには、共焦点クロストークが発生する中間層厚条件を明らかにすることと表裏一体である。そこで、ガイド光の共焦点クロストークの発生条件を以下に述べる。 Here, an intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light will be described. In order to derive an intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light, it is necessary to clarify the intermediate layer thickness condition in which the confocal crosstalk is generated, and to integrate the front and back. Therefore, conditions for generating confocal crosstalk of the guide light will be described below.
　[第一条件]
「ガイド層とガイド層に最も近い記録層の間の中間層の厚さが、記録層群における任意の連続した中間層の厚さの和と一致する。」
　この条件を満たす場合のガイド光の共焦点クロストーク発生の様子を図９に示す。この図９では、ガイド層とガイド層に最も近い記録層の間の中間層30の厚さ(SL0)が、記録層21Hと記録層21Kの間の中間層31H～中間層31Jの厚さの和に一致している。したがって、図９の線分ADと線分BCが同じ長さとなる。このとき、図９の四角形ＡＢＣＤは平行四辺形となり、光路IABCOを通る分岐ビームは、ガイド光(光路IADCO)と合流し、共焦点クロストーク光となる。なお、中間層30の厚さが、中間層31Aを含む任意の連続した中間層の厚さの和と一致する場合は、分岐ビームは記録層上で焦点をむすぶタイプの共焦点クロストーク光となる。 [First condition]
“The thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer matches the sum of the thicknesses of any successive intermediate layers in the recording layer group.”
FIG. 9 shows how the confocal crosstalk occurs when the guide light is satisfied. In FIG. 9, the thickness (SL0) of the intermediate layer 30 between the guide layer and the recording layer closest to the guide layer is the thickness of the intermediate layer 31H to the intermediate layer 31J between the recording layer 21H and the recording layer 21K. It is consistent with the sum. Therefore, the line segment AD and the line segment BC in FIG. 9 have the same length. At this time, the quadrangle ABCD in FIG. 9 becomes a parallelogram, and the branched beam passing through the optical path IABCO merges with the guide light (optical path IADCO) to become confocal crosstalk light. If the thickness of the intermediate layer 30 matches the sum of the thicknesses of any successive intermediate layers including the intermediate layer 31A, the branched beam is a type of confocal crosstalk light that is focused on the recording layer. Become.
　[第二条件]
「ガイド層とガイド層に最も近い記録層の間の中間層と、ガイド層に最も近い記録層と任意の記録層の間の中間層との、厚さの和が記録層群における任意の連続した中間層の厚さの和と一致する。」
　この条件を満たす場合のガイド光の共焦点クロストーク発生の様子を図１０に示す。この図１０では、ガイド層とガイド層に最も近い記録層21Aの間の中間層30の厚さ(SL0)と記録層21Aと記録層21Bの間の中間層31Aの厚さの和SL0+SL1が、記録層21Dと記録層21Iの間の中間層31D～中間層31Hの厚さの和に一致している。したがって、図１０の線分A’D’と線分B’C’が同じ長さとなる。このとき、図１０の四角形Ａ’Ｂ’Ｃ’Ｄ’は平行四辺形となり、光路IA’B’C’Oを通る分岐ビームは、ガイド光(光路IA’D’C’O)と合流し、共焦点クロストーク光となる。なお、中間層30と中間層31Aの厚さの和が、中間層31Bを含む任意の連続した中間層の厚さの和と一致する場合は、分岐ビームは記録層上で焦点をむすぶタイプの共焦点クロストーク光となる。同様に中間層30と中間層31Aと31Bの厚さの和が、中間層31Cを含む任意の連続した中間層の厚さの和と一致する場合は、分岐ビームは記録層上で焦点をむすぶタイプの共焦点クロストーク光となる。 [Second condition]
“The sum of thicknesses of the intermediate layer between the guide layer and the recording layer closest to the guide layer and the intermediate layer between the recording layer closest to the guide layer and any recording layer is arbitrarily continuous in the recording layer group. This is consistent with the sum of the thickness of the intermediate layers. "
FIG. 10 shows how the confocal crosstalk occurs in the guide light when this condition is satisfied. In FIG. 10, the sum SL0 + SL1 of the thickness (SL0) of the intermediate layer 30 between the guide layer and the recording layer 21A closest to the guide layer and the thickness of the intermediate layer 31A between the recording layer 21A and the recording layer 21B. Is equal to the sum of the thicknesses of the intermediate layer 31D to the intermediate layer 31H between the recording layer 21D and the recording layer 21I. Therefore, the line segment A′D ′ and the line segment B′C ′ in FIG. 10 have the same length. At this time, the quadrangle A′B′C′D ′ in FIG. 10 becomes a parallelogram, and the branched beam passing through the optical path IA′B′C′O merges with the guide light (optical path IA′D′C′O). It becomes confocal crosstalk light. When the sum of the thicknesses of the intermediate layer 30 and the intermediate layer 31A matches the sum of the thicknesses of any continuous intermediate layers including the intermediate layer 31B, the branched beam is of a type that focuses on the recording layer. Confocal crosstalk light. Similarly, if the sum of the thicknesses of the intermediate layer 30 and the intermediate layers 31A and 31B matches the sum of the thicknesses of any successive intermediate layers including the intermediate layer 31C, the branched beam is focused on the recording layer. Type of confocal crosstalk light.
　したがって、ガイド光の共焦点クロストークを低減可能な中間層厚構成とは、上記第一条件と第二条件を同時に、あるいは一方を満たさない中間層厚構成を言うこととなる。 Therefore, the intermediate layer thickness configuration that can reduce the confocal crosstalk of the guide light means an intermediate layer thickness configuration that does not satisfy the first condition and the second condition at the same time or one of them.
　ところで、記録層21の中間層31は、記録再生光(青紫色レーザ光16)の層間クロストークを低減するため、第一および第二の中間層厚さが交互に繰り返す構造とするのが良いと述べた。光ディスク10は、ガイド光(赤色レーザ光15)の層間クロストークと記録再生光(青紫色レーザ光16)の層間クロストークが同時に低減可能な構造とすることで初めて信頼性の高い情報の記録再生が可能となる。したがって、ガイド光の共焦点クロストークを低減可能な中間層厚構成は、第一および第二の中間層厚さが交互に繰り返す構造に適用して考えるのが好ましい。以下、記録再生光の層間クロストークを低減しつつ、ガイド光の共焦点クロストークを低減可能な中間層厚構成の条件を検討する。なお、記録層21の層数が１２層の場合を考えることとする。第一および第二の中間層厚さが交互に繰り返す構造を一般化すると、第一の中間層厚さをm(μｍ)、第二の中間層厚さをm+a(μｍ)と表すことができる。ここで、第一の中間層厚さが第二の中間層厚さより薄いとした。なお、ガイド層に最も近い記録層とその次に近い記録層の間の中間層は、第一の中間層厚さを有するものと考える。 Incidentally, the intermediate layer 31 of the recording layer 21 may have a structure in which the first and second intermediate layer thicknesses are alternately repeated in order to reduce the interlayer crosstalk of the recording / reproducing light (blue-violet laser light 16). Said. The optical disc 10 has a structure that can reduce the interlayer crosstalk of the guide light (red laser beam 15) and the interlayer crosstalk of the recording / reproducing light (blue-violet laser beam 16) at the same time. Is possible. Accordingly, it is preferable to apply the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light to a structure in which the first and second intermediate layer thicknesses are alternately repeated. Hereinafter, the conditions of the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the guide light while reducing the interlayer crosstalk of the recording / reproducing light will be examined. It is assumed that the recording layer 21 has 12 layers. Generalizing the structure in which the first and second intermediate layer thicknesses are alternately repeated, the first intermediate layer thickness is expressed as m (μm), and the second intermediate layer thickness is expressed as m + a (μm). Can do. Here, the first intermediate layer thickness is assumed to be thinner than the second intermediate layer thickness. Note that the intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is considered to have the first intermediate layer thickness.
　このとき、上記の第一条件を満たす中間層30の厚さは、以下の通りである。但し、中間層30の厚さが第二の中間層厚さ以下となる場合は、ガイド層に隣接する記録層の映り込みによる層間クロストークが大きくなるため除外した。 At this time, the thickness of the intermediate layer 30 satisfying the first condition is as follows. However, the case where the thickness of the intermediate layer 30 is equal to or smaller than the second intermediate layer thickness is excluded because the interlayer crosstalk due to the reflection of the recording layer adjacent to the guide layer increases.
　2m+a
　3m+a
　3m+2a
　4m+2a
　5m+2a
　5m+3a
　6m+3a
　7m+3a
　7m+4a
　8m+4a
　9m+4a
　9m+5a
　10m+5a
　11m+5a
　11m+6a
　一方、上記の第二条件を満たす中間層30の厚さは、以下の通りである。 2m + a
3m + a
3m + 2a
4m + 2a
5m + 2a
5m + 3a
6m + 3a
7m + 3a
7m + 4a
8m + 4a
9m + 4a
9m + 5a
10m + 5a
11m + 5a
11m + 6a
On the other hand, the thickness of the intermediate layer 30 that satisfies the second condition is as follows.
　2m+2a
　4m+3a
　6m+4a
　8m+5a
　10m+6a
　但し、上記の第一条件を満たす中間層30の厚さと一致する場合は除外した。したがって、上記第一条件と第二条件のいずれかを満たす中間層30の厚さは、以下の通りである(中間層厚条件群１)。 2m + 2a
4m + 3a
6m + 4a
8m + 5a
10m + 6a
However, the case where it matches the thickness of the intermediate layer 30 that satisfies the above first condition was excluded. Therefore, the thickness of the intermediate layer 30 that satisfies either the first condition or the second condition is as follows (intermediate layer thickness condition group 1).
　2m+a
　2m+2a
　3m+a
　3m+2a
　4m+2a
　4m+3a
　5m+2a
　5m+3a
　6m+3a
　6m+4a
　7m+3a
　7m+4a
　8m+4a
　8m+5a
　9m+4a
　9m+5a
　10m+5a
　10m+6a
　11m+5a
　11m+6a
　記録層21の中間層31を形成する場合に、第一の中間層厚と第二の中間層厚の差、すなわち、a(μｍ)は、層間クロストークを低減する観点からは大きいほど良いが、あまり大きいと記録層21全体の厚さが厚くなり、光ピックアップユニット200の対物レンズの特性として収差が大きくなってしまう。したがって、aは、mより小さくする必要がある。すなわち、m>aである。さて、中間層30の厚さは上記第一条件と第二条件のいずれも満たさないことが共焦点クロストーク回避の観点から好ましい。このとき中間層30の厚さは上記の中間層厚条件群１のどの値からも遠い厚さに設定すると良い。このため、例えば、一つの方法は、中間層30の厚さを11m+6aよりも十分に大きくすることである。この場合は確かにガイド光の共焦点クロストークは発生しないが、中間層30、中間層31およびカバー層の合計の厚さが大きくなりすぎ、光ピックアップユニット200の対物レンズの特性として収差が大きくなってしまう。 2m + a
2m + 2a
3m + a
3m + 2a
4m + 2a
4m + 3a
5m + 2a
5m + 3a
6m + 3a
6m + 4a
7m + 3a
7m + 4a
8m + 4a
8m + 5a
9m + 4a
9m + 5a
10m + 5a
10m + 6a
11m + 5a
11m + 6a
When the intermediate layer 31 of the recording layer 21 is formed, the difference between the first intermediate layer thickness and the second intermediate layer thickness, that is, a (μm) is better from the viewpoint of reducing the interlayer crosstalk. If it is too large, the thickness of the entire recording layer 21 is increased, and the aberration becomes large as a characteristic of the objective lens of the optical pickup unit 200. Therefore, a needs to be smaller than m. That is, m> a. The thickness of the intermediate layer 30 preferably satisfies neither the first condition nor the second condition from the viewpoint of avoiding confocal crosstalk. At this time, the thickness of the intermediate layer 30 is preferably set to a thickness far from any value of the intermediate layer thickness condition group 1 described above. For this reason, for example, one method is to make the thickness of the intermediate layer 30 sufficiently larger than 11 m + 6a. In this case, the confocal crosstalk of the guide light does not occur, but the total thickness of the intermediate layer 30, the intermediate layer 31, and the cover layer becomes too large, and the aberration is large as a characteristic of the objective lens of the optical pickup unit 200. turn into.
　したがって、例えば、第一条件である2m+a、3m+a、3m+2a、4m+2a、5m+2a、5m+3a、6m+3a、7m+3a、7m+4a、8m+4a、9m+4a、9m+5a、10m+5a、11m+5a、11m+6aのうちの中間値又は中間値に近い値に中間層30の厚さを設定することができる。例えば、2m+a及び3m+aの中間値は、2.5m+aである。第一条件だけでなく、第二条件をも考慮することが好ましいので、中間層30の厚さは上記中間層厚条件群１の中間値又は中間値に近い値に設定するのが好ましい。中間層厚条件群１の連続した値の間隔は、m、a、m-aのいずれかであり、m>aを考慮すると、最も間隔が離れているのは、間隔がmの場合である。すなわち、3m+2aと4m+2a、5m+3aと6m+3a、7m+4aと8m+4a、9m+5aと10m+5aの間である。最も間隔が離れている場合を考慮するならば、中間層30の厚さは、これらの中間の値、3.5m+2a、5.5m+3a、7.5m+4a、9.5m+5aとして形成するとガイド光の共焦点クロストークを低減しつつ、記録再生光の層間クロストークが低減可能となる。 Thus, for example, the first condition is 2m + a, 3m + a, 3m + 2a, 4m + 2a, 5m + 2a, 5m + 3a, 6m + 3a, 7m + 3a, 7m + 4a, 8m + 4a, 9m The thickness of the intermediate layer 30 can be set to an intermediate value or a value close to the intermediate value among + 4a, 9m + 5a, 10m + 5a, 11m + 5a, and 11m + 6a. For example, the intermediate value between 2m + a and 3m + a is 2.5m + a. Since it is preferable to consider not only the first condition but also the second condition, the thickness of the intermediate layer 30 is preferably set to an intermediate value in the intermediate layer thickness condition group 1 or a value close to the intermediate value. The interval of the continuous values in the intermediate layer thickness condition group 1 is any one of m, a, and m-a. When m> a is considered, the interval is the longest when the interval is m. That is, between 3m + 2a and 4m + 2a, 5m + 3a and 6m + 3a, 7m + 4a and 8m + 4a, and 9m + 5a and 10m + 5a. Considering the case where the distances are the farthest, the thickness of the intermediate layer 30 is a guide when formed as an intermediate value of these, 3.5 m + 2a, 5.5 m + 3a, 7.5 m + 4a, 9.5 m + 5a Interlayer crosstalk of recording / reproducing light can be reduced while reducing confocal crosstalk of light.
　ところで、中間層31の値としては、例えば、m=12、a=4、すなわち、第一の中間層厚が12μｍ、第二の中間層厚が16μｍとすることが、記録再生光の層間クロストーク低減の観点から有効であると述べた。一方、ガイド光の共焦点クロストーク光の観点からは、mを大きくすることが好ましい。この両者を同時に満足し、中間層とカバー層の合計の厚さが大きくなりすぎない値の一例を求めた。 By the way, the values of the intermediate layer 31 are, for example, m = 12, a = 4, that is, the first intermediate layer thickness is 12 μm and the second intermediate layer thickness is 16 μm. It is said that it is effective from the viewpoint of talk reduction. On the other hand, it is preferable to increase m from the viewpoint of the confocal crosstalk light of the guide light. An example of a value that satisfies both of these requirements and does not cause the total thickness of the intermediate layer and the cover layer to be too large was determined.
　対物レンズの赤色レーザ光の開口数を０．６５、中間層30の厚さを3.5m+2aとした場合に、ガイド光の共焦点クロストークが発生する確率をモンテカルロシミュレーションで求めた結果を図１３に示す。結果として、m=14(μｍ)とすることで、m=12(μｍ)とくらべて、ガイド光の共焦点クロストークを生ずるディスクの発生確率(DPPM)が、180から0へと低減することが判明した（図１３参照）。 Fig. 6 shows the result of Monte Carlo simulation for the probability of confocal crosstalk in the guide light when the numerical aperture of the red laser light of the objective lens is 0.65 and the thickness of the intermediate layer 30 is 3.5 m + 2a. It is shown in FIG. As a result, by setting m = 14 (μm), the occurrence probability (DPPM) of the disc that causes the confocal crosstalk of the guide light is reduced from 180 to 0 compared to m = 12 (μm). Was found (see FIG. 13).
　したがって、例えば、m=14、a=4、すなわち第一の中間層厚が14μｍ、第二の中間層厚が18μｍとして形成され、中間層厚30が、57μｍ、89μｍ、121μｍ、153μｍとして形成された光ディスク10が、ガイド光(赤色レーザ光15)および記録再生光(青紫色レーザ光16)の層間クロストークが低減され、かつ、ディスク製造時の不良品率が低い、信頼性の高い光ディスクとなる。なお、中間層30は光ピックアップユニット200の対物レンズの収差の観点からは薄い方が好ましいため、上記のなかでも57μｍあるいは89μｍとすることが好ましい。 Therefore, for example, m = 14, a = 4, that is, the first intermediate layer thickness is 14 μm, the second intermediate layer thickness is 18 μm, and the intermediate layer thickness 30 is 57 μm, 89 μm, 121 μm, 153 μm. The optical disk 10 is a highly reliable optical disk in which the interlayer crosstalk of the guide light (red laser light 15) and the recording / reproducing light (blue-violet laser light 16) is reduced, and the defective product rate at the time of manufacturing the disk is low. Become. Since the intermediate layer 30 is preferably thin from the viewpoint of aberration of the objective lens of the optical pickup unit 200, it is preferably 57 μm or 89 μm among the above.
　第一および第二の中間層厚さが交互に繰り返す構造として、第一の中間層厚さが、第二の中間層厚さより厚い場合も考えられる。この場合、第一の中間層厚さをm+a(μｍ)、第二の中間層厚さをm(μｍ)と表すことができる。このとき、上記の第一条件を満たす中間層30の厚さは、以下の通りである。但し、中間層30の厚さが第二の中間層厚さ以下となる場合は、除外した。 As a structure in which the first and second intermediate layer thicknesses are alternately repeated, the first intermediate layer thickness may be larger than the second intermediate layer thickness. In this case, the first intermediate layer thickness can be expressed as m + a (μm), and the second intermediate layer thickness can be expressed as m (μm). At this time, the thickness of the intermediate layer 30 that satisfies the first condition is as follows. However, this was excluded when the thickness of the intermediate layer 30 was equal to or less than the second intermediate layer thickness.
　2m+a
　3m+a
　3m+2a
　4m+2a
　5m+2a
　5m+3a
　6m+3a
　7m+3a
　7m+4a
　8m+4a
　9m+4a
　9m+5a
　10m+5a
　11m+5a
　11m+6a
　一方、上記の第二条件を満たす中間層30の厚さは、以下の通りである。 2m + a
3m + a
3m + 2a
4m + 2a
5m + 2a
5m + 3a
6m + 3a
7m + 3a
7m + 4a
8m + 4a
9m + 4a
9m + 5a
10m + 5a
11m + 5a
11m + 6a
On the other hand, the thickness of the intermediate layer 30 that satisfies the second condition is as follows.
　2m
　4m+a
　6m+2a
　8m+3a
　10m+4a
　但し、上記の第一条件を満たす中間層30の厚さと一致する場合は除外した。したがって、上記第一条件と第二条件のいずれかを満たす中間層30の厚さは、以下の通りである(中間層厚条件群２)。 2m
4m + a
6m + 2a
8m + 3a
10m + 4a
However, the case where it matches the thickness of the intermediate layer 30 that satisfies the above first condition was excluded. Therefore, the thickness of the intermediate layer 30 that satisfies either the first condition or the second condition is as follows (intermediate layer thickness condition group 2).
　2m
　2m+a
　3m+a
　3m+2a
　4m+a
　4m+2a
　5m+2a
　5m+3a
　6m+2a
　6m+3a
　7m+3a
　7m+4a
　8m+3a
　8m+4a
　9m+4a
　9m+5a
　10m+4a
　10m+5a
　11m+5a
　11m+6a
　第一の中間層厚と第二の中間層厚の差、a(μｍ)は、m>aの関係を満たすことは前記と同様である。 2m
2m + a
3m + a
3m + 2a
4m + a
4m + 2a
5m + 2a
5m + 3a
6m + 2a
6m + 3a
7m + 3a
7m + 4a
8m + 3a
8m + 4a
9m + 4a
9m + 5a
10m + 4a
10m + 5a
11m + 5a
11m + 6a
The difference between the first intermediate layer thickness and the second intermediate layer thickness, a (μm), satisfies the relationship m> a as described above.
　したがって、例えば、第一条件である
　2m+a、3m+a、3m+2a、4m+2a、5m+2a、5m+3a、6m+3a、7m+3a、7m+4a、8m+4a、9m+4a、9m+5a、10m+5a、11m+5a、11m+6aのうちの中間値又は中間値に近い値に中間層30の厚さを設定することができる。例えば、2m+a及び3m+aの中間値は、2.5m+aである。第一条件だけでなく、第二条件をも考慮することが好ましいので、中間層30の厚さは上記中間層厚条件群２の中間値又は中間値に近い値に設定するのが好ましい。上記中間層厚条件群２の連続した値の間隔は、m、a、m-aのいずれかであり、m>aを考慮すると、最も間隔が離れているのは、間隔がmの場合である。すなわち、2m+aと3m+a、4m+2aと5m+2a、6m+3aと7m+3a、8m+4aと9m+4aの間である。最も間隔が離れている場合を考慮するならば、中間層30の厚さは、これらの中間の値、2.5m+a、4.5m+2a、6.5m+3a、8.5m+4aとして形成するとガイド光の共焦点クロストークを低減しつつ、記録再生光の層間クロストークが低減可能となる。 Thus, for example, the first condition is 2m + a, 3m + a, 3m + 2a, 4m + 2a, 5m + 2a, 5m + 3a, 6m + 3a, 7m + 3a, 7m + 4a, 8m + 4a, 9m The thickness of the intermediate layer 30 can be set to an intermediate value or a value close to the intermediate value among + 4a, 9m + 5a, 10m + 5a, 11m + 5a, and 11m + 6a. For example, the intermediate value between 2m + a and 3m + a is 2.5m + a. Since it is preferable to consider not only the first condition but also the second condition, the thickness of the intermediate layer 30 is preferably set to an intermediate value of the intermediate layer thickness condition group 2 or a value close to the intermediate value. The interval between the continuous values of the intermediate layer thickness condition group 2 is any one of m, a, and ma. Considering m> a, the interval is the longest when the interval is m. That is, between 2m + a and 3m + a, 4m + 2a and 5m + 2a, 6m + 3a and 7m + 3a, and 8m + 4a and 9m + 4a. Considering the case where the distance is the most apart, the thickness of the intermediate layer 30 is a guide when it is formed as these intermediate values, 2.5m + a, 4.5m + 2a, 6.5m + 3a, 8.5m + 4a Interlayer crosstalk of recording / reproducing light can be reduced while reducing confocal crosstalk of light.
　対物レンズの赤色レーザ光の開口数を０．６５、中間層30の厚さを2.5m+aとした場合に、ガイド光の共焦点クロストークが発生する確率をモンテカルロシミュレーションで求めた結果を図１４に示す。中間層30の厚さを上述の条件に基づいて形成することで、ガイド光の共焦点クロストークを生ずるディスクの発生確率(DPPM)が、0となることが確認された（図１４参照）。 When the numerical aperture of the red laser beam of the objective lens is 0.65 and the thickness of the intermediate layer 30 is 2.5 m + a, the result of obtaining the probability of the confocal crosstalk of the guide light by Monte Carlo simulation is shown in the figure 14 shows. By forming the thickness of the intermediate layer 30 based on the above-described conditions, it was confirmed that the occurrence probability (DPPM) of the disc causing the confocal crosstalk of the guide light becomes 0 (see FIG. 14).
　したがって、m=14、a=4、すなわち第一の中間層厚が18μｍ、第二の中間層厚が14μｍとして形成され、中間層厚30が、39μｍ、71μｍ、103μｍ、135μｍ、167μｍとして形成された光ディスク10が、ガイド光(赤色レーザ光15)および記録再生光(青紫色レーザ光16)の層間クロストークが低減され、かつ、ディスク製造時の不良品率が低い、信頼性の高い光ディスクとなる。なお、中間層30は光ピックアップユニット200の対物レンズの収差の観点からは薄い方が好ましいため、上記のなかでも39μｍあるいは71μｍとすることが好ましい。 Therefore, m = 14, a = 4, that is, the first intermediate layer thickness is 18 μm, the second intermediate layer thickness is 14 μm, and the intermediate layer thickness 30 is 39 μm, 71 μm, 103 μm, 135 μm, 167 μm. The optical disk 10 is a highly reliable optical disk in which the interlayer crosstalk of the guide light (red laser light 15) and the recording / reproducing light (blue-violet laser light 16) is reduced, and the defective product rate at the time of manufacturing the disk is low. Become. Since the intermediate layer 30 is preferably thin from the viewpoint of aberration of the objective lens of the optical pickup unit 200, it is preferably 39 μm or 71 μm among the above.
　[光ディスクの構造]
　上述のようにガイド層および記録層の中間層厚を構成した場合の光ディスク構造を図１１を用いて説明する。図１１Ａ、図１１Ｂ、図１１Ｃは第一の中間層が第二の中間層よりも薄い場合のディスク構造を示す。上記の実施形態にて述べたように第一の中間層厚を14μｍ、第二の中間層厚を18μｍとした場合、中間層30の厚さは57μｍあるいは89μｍとすることで信頼性の高い光ディスクが得られる。図１１Ａは、記録層21を12層備えた光ディスク10の構造例である。カバー層12の厚さは、厚すぎると記録層の記録再生時のチルトマージンが低下するが、薄すぎると最もカバー層に近い記録層21Lの保護が十分でなくなる。そこでカバー層12の厚さは、ブルーレイディスク等で実績のある53μｍとした。この結果、ガイド層20のカバー層表面からの距離は284μｍ、記録層21Aのカバー層表面からの距離は227μｍとなる。図１１Ｂ、図１１Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、ガイド層20は、12層の例と同じくカバー層表面から284μｍに位置する。これは、同一の光ピックアップユニット200でこれらのディスクを記録再生した場合にガイド光の品質、収差特性がほぼ同程度となることが期待できるからである。中間層30の厚さは57μｍあるいは89μｍとすることで信頼性の高い光ディスクが得られるが、カバー層12の厚さが極端に厚くならないようにするため、ここでは89μｍとした。この結果、記録層21Aのカバー層表面からの距離は195μｍとなる。結果として、8層の記録層を持つディスクのカバー層12の厚さは85μｍ（図１１Ｂ）、6層の記録層を持つディスクのカバー層12の厚さは117μｍ(図１１Ｃ)となる。 [Optical disk structure]
The optical disk structure when the intermediate layer thickness of the guide layer and the recording layer is configured as described above will be described with reference to FIG. 11A, 11B, and 11C show the disk structure when the first intermediate layer is thinner than the second intermediate layer. As described in the above embodiment, when the first intermediate layer thickness is 14 μm and the second intermediate layer thickness is 18 μm, the thickness of the intermediate layer 30 is 57 μm or 89 μm so that the optical disk is highly reliable. Is obtained. FIG. 11A shows an example of the structure of the optical disc 10 having 12 recording layers 21. If the cover layer 12 is too thick, the tilt margin at the time of recording / reproducing of the recording layer is reduced, but if it is too thin, the recording layer 21L closest to the cover layer is not sufficiently protected. Therefore, the thickness of the cover layer 12 was set to 53 μm, which has a proven record with Blu-ray discs. As a result, the distance of the guide layer 20 from the cover layer surface is 284 μm, and the distance of the recording layer 21A from the cover layer surface is 227 μm. FIG. 11B and FIG. 11C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, the guide layer 20 is located 284 μm from the surface of the cover layer as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same. An optical disk with high reliability can be obtained by setting the thickness of the intermediate layer 30 to 57 μm or 89 μm. However, in order to prevent the cover layer 12 from becoming extremely thick, the thickness is set to 89 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 195 μm. As a result, the thickness of the cover layer 12 of the disc having eight recording layers is 85 μm (FIG. 11B), and the thickness of the cover layer 12 of the disc having six recording layers is 117 μm (FIG. 11C).
一方、第一の中間層が第二の中間層よりも厚い場合のディスク構造例を図１２Ａ、図１２Ｂ、図１２Ｃに示す。この場合、上記の実施形態に記した通り、第一の中間層厚を18μｍ、第二の中間層厚を14μｍとした場合、中間層30の厚さは39μｍあるいは71μｍとすることで信頼性の高い光ディスクが得られる。図１２Ａは、記録層21を12層備えた光ディスク10の構造例である。ここでカバー層12の厚さは、上記と同じ理由で53μｍとした。この結果、ガイド層20のカバー層表面からの距離は270μｍ、記録層21Aのカバー層表面からの距離は231μｍとなる。図１２Ｂ、図１２Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、図１１Ａ、図１１Ｂ、図１１Ｃの例と同じ理由で、ガイド層20は、12層の例と同じくカバー層表面から270μｍに位置する。中間層30の厚さは39μｍあるいは71μｍとすることで信頼性の高い光ディスクが得られるが、カバー層12の厚さが極端に厚くならないようにするため、ここでは71μｍとした。この結果、記録層21Aのカバー層表面からの距離は199μｍとなる。結果として、8層の記録層を持つディスクのカバー層12の厚さは85μｍ（図１２Ｂ）、6層の記録層を持つディスクのカバー層12の厚さは117μｍ(図１２Ｃ)となる。 On the other hand, FIG. 12A, FIG. 12B, and FIG. 12C show examples of the disk structure when the first intermediate layer is thicker than the second intermediate layer. In this case, as described in the above embodiment, when the thickness of the first intermediate layer is 18 μm and the thickness of the second intermediate layer is 14 μm, the thickness of the intermediate layer 30 is 39 μm or 71 μm. A high optical disc can be obtained. FIG. 12A is a structural example of the optical disc 10 having 12 recording layers 21. Here, the thickness of the cover layer 12 was 53 μm for the same reason as described above. As a result, the distance from the cover layer surface of the guide layer 20 is 270 μm, and the distance from the cover layer surface of the recording layer 21A is 231 μm. 12B and 12C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, for the same reason as in the examples of FIGS. 11A, 11B, and 11C, the guide layer 20 is located 270 μm from the surface of the cover layer as in the example of 12 layers. An optical disk with high reliability can be obtained by setting the thickness of the intermediate layer 30 to 39 μm or 71 μm. However, in order to prevent the cover layer 12 from becoming extremely thick, the thickness is set to 71 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 199 μm. As a result, the thickness of the cover layer 12 of the disc having 8 recording layers is 85 μm (FIG. 12B), and the thickness of the cover layer 12 of the disc having 6 recording layers is 117 μm (FIG. 12C).
　ところで、カバー層12の厚さは、厚すぎると記録層の記録再生時のチルトマージンが低下するが、薄すぎると最もカバー層に近い記録層21Lの保護が十分でなくなるとして、ブルーレイディスク等で実績のある53μｍとした。しかし、カバー層12の表面でカバー層内部より反射した光線による共焦点クロストークを考慮した場合、より好適なカバー層12の厚さの作成が可能である。この場合考慮すべき共焦点クロストークには、（1）記録再生光(青紫色レーザ光16)の共焦点クロストークと、（2）ガイド光(赤色レーザ光15)の共焦点クロストークがある。 By the way, if the cover layer 12 is too thick, the tilt margin at the time of recording / reproducing of the recording layer is lowered, but if it is too thin, the recording layer 21L closest to the cover layer is not sufficiently protected. It was 53 μm with a proven track record. However, when confocal crosstalk due to light reflected from the inside of the cover layer on the surface of the cover layer 12 is taken into consideration, a more preferable thickness of the cover layer 12 can be created. Confocal crosstalk to be considered in this case includes (1) confocal crosstalk of recording / reproducing light (blue-violet laser light 16) and (2) confocal crosstalk of guide light (red laser light 15). .
　まず、（1）の記録再生光(青紫色レーザ光16)のカバー層12の表面で反射した光線による共焦点クロストークについて図１５を用いて説明する。光ディスク10の記録層21のうち目的とする記録層(図では記録層21F)に照射された記録再生用の青紫色レーザ光16は、記録層の半透過性により複数の光ビームに分岐する。例えば、レーザ光16の一部は、記録層21Lで反射して、分岐ビーム51となってカバー層12の表面でカバー層内部より焦点をむすび、この反射光が再び記録層21Lで反射してレーザ光16、すなわち記録層21Fの記録再生光と合流し、青色用光検出器ＩＣで同時かつ空間的に略同位置にて検出されてしまう。この共焦点クロストーク光は、記録再生光と同一波長でかつ略同一光路を通って検出されるため、空間的、帯域的分離手段が有効に働かず、強力なノイズとなって検出されることとなる。 First, the confocal crosstalk caused by the light beam reflected by the surface of the cover layer 12 of the recording / reproducing light (blue-violet laser light 16) of (1) will be described with reference to FIG. The recording / reproducing blue-violet laser light 16 irradiated to the target recording layer (the recording layer 21F in the figure) of the recording layer 21 of the optical disc 10 is branched into a plurality of light beams due to the semi-transmission of the recording layer. For example, a part of the laser light 16 is reflected by the recording layer 21L, becomes a branched beam 51 and is focused from the inside of the cover layer on the surface of the cover layer 12, and this reflected light is reflected again by the recording layer 21L. The laser light 16, that is, the recording / reproducing light of the recording layer 21F is merged and detected simultaneously and spatially at substantially the same position by the blue photodetector IC. This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes.
　カバー層12の厚さは、厚すぎると記録層の記録再生時のチルトマージンが低下し、薄すぎると最もカバー層に近い記録層21Lの保護が十分でなくなるという課題があるが、この制約は比較的緩やかなものであり、カバー層12の厚さをより詳細に好適に作成することにより記録再生光の共焦点クロストークを低減することが可能となる。 If the cover layer 12 is too thick, the tilt margin at the time of recording / reproducing of the recording layer is lowered.If the cover layer 12 is too thin, there is a problem that the recording layer 21L closest to the cover layer is not sufficiently protected. It is relatively gentle, and the confocal crosstalk of the recording / reproducing light can be reduced by making the thickness of the cover layer 12 more preferable in detail.
　図１６は記録再生光の共焦点クロストークが低減された様子の一例を示す図である。光ディスク10の記録層21のうち目的とする記録層(図では記録層21F)に照射された記録再生用の青紫色レーザ光16は、一部が記録層21Lで反射して、分岐ビーム52となってカバー層12の表面で内部より反射する。しかし、この場合、カバー層12が好適に作成されているため、分岐ビーム52はカバー層12の表面で焦点をむすばず、かつ、この反射光が再び記録層21Lで反射しても、青紫色レーザ光16、すなわち記録層21の記録再生光とは同一光路では合流せず、青紫用光検出器ＩＣで空間的に一致しない位置で検出される。このため、このクロストーク光は、記録再生光16と空間的な分離が可能であり、ノイズ低減が可能である。 FIG. 16 is a diagram showing an example of a state in which confocal crosstalk of recording / reproducing light is reduced. Of the recording layer 21 of the optical disc 10, the recording / reproducing blue-violet laser light 16 irradiated on the target recording layer (in the figure, the recording layer 21F) is partially reflected by the recording layer 21L, and the branched beam 52 and Thus, the surface of the cover layer 12 is reflected from the inside. However, in this case, since the cover layer 12 is suitably formed, the branched beam 52 does not have to be focused on the surface of the cover layer 12, and even if this reflected light is reflected again by the recording layer 21L, it is bluish purple. The laser beam 16, that is, the recording / reproducing light of the recording layer 21, does not merge in the same optical path, but is detected at a position not spatially matched by the blue-violet photodetector IC. Therefore, the crosstalk light can be spatially separated from the recording / reproducing light 16, and noise can be reduced.
　ここで、記録再生光の共焦点クロストークを低減可能なカバー層厚構成について述べる。記録再生光の共焦点クロストークを低減可能な中間層厚構成を導出するには、共焦点クロストークが発生するカバー層厚条件を明らかにすることと表裏一体である。そこで、記録再生光の共焦点クロストークの発生条件を以下に述べる。 Here, the cover layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light will be described. In order to derive the intermediate layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light, it is necessary to clarify the cover layer thickness condition in which the confocal crosstalk is generated and to be integrated. Therefore, conditions for generating confocal crosstalk of recording / reproducing light will be described below.
　「カバー層12の厚さと、カバー層12に最も近い記録層と第一反射記録層との間の中間層（群）の厚さとの和と、第一反射記録層と目標記録層との間の中間層（群）の厚さの和が一致する。」
　ここで第一反射記録層とは、記録再生光が記録層のうち最初に分岐、反射する記録層のことであり、図１５の例では、記録層21Lのことである。 “The sum of the thickness of the cover layer 12 and the thickness of the intermediate layer (group) between the recording layer closest to the cover layer 12 and the first reflective recording layer, and between the first reflective recording layer and the target recording layer The sum of the thickness of the intermediate layer (s) of the same. "
Here, the first reflective recording layer is a recording layer in which recording / reproducing light is first branched and reflected among the recording layers, and in the example of FIG. 15, is the recording layer 21L.
　この条件を満たす場合の記録再生光の共焦点クロストーク発生の様子を図１７に示す。この図１７では、カバー層厚さとカバー層の表面に最も近い記録層(記録層21L)と第一反射記録層(記録層21J)の間の中間層(中間層31Jと中間層31K)の厚さの和が、第一反射記録層(記録層21J)と目標記録層(記録層21C)との間の中間層(中間層31Cから中間層31I)の厚さの和に一致している。したがって、図１７の線分ADと線分BCが同じ長さとなる。このとき、図１７の四角形ＡＢＣＤは平行四辺形となり、光路IABCOを通る分岐ビームは、記録再生光(光路IADCO)と合流し、共焦点クロストーク光となる。 FIG. 17 shows the occurrence of confocal crosstalk of the recording / reproducing light when this condition is satisfied. In FIG. 17, the cover layer thickness and the thickness of the intermediate layer (intermediate layer 31J and intermediate layer 31K) between the recording layer (recording layer 21L) and the first reflective recording layer (recording layer 21J) closest to the surface of the cover layer. The sum of the thicknesses coincides with the sum of the thicknesses of the intermediate layers (intermediate layer 31C to intermediate layer 31I) between the first reflective recording layer (recording layer 21J) and the target recording layer (recording layer 21C). Accordingly, the line segment AD and the line segment BC in FIG. 17 have the same length. At this time, the quadrangle ABCD in FIG. 17 becomes a parallelogram, and the branched beam passing through the optical path IABCO merges with the recording / reproducing light (optical path IADCO) to become confocal crosstalk light.
　したがって、カバー層表面での反射光を考慮した、記録再生光の共焦点クロストークを低減可能なカバー層厚構成とは、上記条件を満たさないカバー層厚構成を言うこととなる。なお、中間層の厚さの設計において、中間層に対して記録層は極めて薄いので、記録層の厚さを考慮せずに、中間層の厚さを設計することができるが、記録層の厚さを考慮した上で中間層の厚さを設計してもい。 Therefore, the cover layer thickness configuration that can reduce the confocal crosstalk of the recording / reproducing light in consideration of the reflected light on the surface of the cover layer means a cover layer thickness configuration that does not satisfy the above conditions. In the design of the thickness of the intermediate layer, since the recording layer is extremely thin relative to the intermediate layer, the thickness of the intermediate layer can be designed without considering the thickness of the recording layer. The thickness of the intermediate layer may be designed in consideration of the thickness.
　記録層21の中間層31は、上述の通り、第一および第二の中間層厚さが交互に繰り返す構造に適用して考えるのが好ましい。以下、記録再生光の共焦点クロストークを低減可能なカバー層厚構成の条件を検討する。ここでも、記録層21の層数が１２層の場合を考えることとする。まず、第一の中間層厚さが第二の中間層厚さより薄い場合を考える。ここで、第一の中間層厚さをm(μｍ)、第二の中間層厚さをm+a(μｍ)と表すことができる。なお、ガイド層に最も近い記録層とその次に近い記録層の間の中間層は、第一の中間層厚さを有するものと考える。 As described above, the intermediate layer 31 of the recording layer 21 is preferably applied to a structure in which the first and second intermediate layer thicknesses are alternately repeated. Hereinafter, the conditions of the cover layer thickness configuration capable of reducing the confocal crosstalk of the recording / reproducing light will be examined. Here, the case where the number of recording layers 21 is 12 is considered. First, consider a case where the first intermediate layer thickness is thinner than the second intermediate layer thickness. Here, the first intermediate layer thickness can be expressed as m (μm), and the second intermediate layer thickness can be expressed as m + a (μm). Note that the intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is considered to have the first intermediate layer thickness.
　このとき、上記の条件を満たすカバー層12の厚さは、以下の通りである。 At this time, the thickness of the cover layer 12 satisfying the above conditions is as follows.
　m
　m+a
　2m+a
　2m+2a
　3m+a
　3m+2a
　4m+2a
　4m+3a
　5m+2a
　5m+3a
　6m+3a
　6m+4a
　7m+3a
　上記の実施形態にて述べたように第一の中間層厚を14μｍ、第二の中間層厚を18μｍとした場合、上記の条件を満たすカバー層厚12の厚さは、以下の通りである。 m
m + a
2m + a
2m + 2a
3m + a
3m + 2a
4m + 2a
4m + 3a
5m + 2a
5m + 3a
6m + 3a
6m + 4a
7m + 3a
As described in the above embodiment, when the first intermediate layer thickness is 14 μm and the second intermediate layer thickness is 18 μm, the thickness of the cover layer thickness 12 that satisfies the above conditions is as follows. .
　14μｍ
　18μｍ
　32μｍ
　36μｍ
　46μｍ
　50μｍ
　64μｍ
　68μｍ
　78μｍ
　82μｍ
　96μｍ
　100μｍ
　110μｍ
　第一および第二の中間層厚さが交互に繰り返す構造として、第一の中間層厚さが、第二の中間層厚さより厚い場合も考えられる。この場合、第一の中間層厚さをm+a(μｍ)、第二の中間層厚さをm(μｍ)と表すことができる。このとき、上記の条件を満たすカバー層12の厚さは、以下の通りである。 14μm
18μm
32μm
36μm
46μm
50μm
64μm
68μm
78μm
82μm
96μm
100μm
110μm
As a structure in which the first and second intermediate layer thicknesses are alternately repeated, the first intermediate layer thickness may be larger than the second intermediate layer thickness. In this case, the first intermediate layer thickness can be expressed as m + a (μm), and the second intermediate layer thickness can be expressed as m (μm). At this time, the thickness of the cover layer 12 satisfying the above conditions is as follows.
　m
　m+a
　2m
　2m+a
　3m+a
　3m+2a
　4m+a
　4m+2a
　5m+2a
　5m+3a
　6m+2a
　6m+3a
　7m+3a
　7m+4a
　上記の実施形態にて述べたように第一の中間層厚を18μｍ、第二の中間層厚を14μｍとした場合、上記の条件を満たすカバー層厚12の厚さは、以下の通りである。 m
m + a
2m
2m + a
3m + a
3m + 2a
4m + a
4m + 2a
5m + 2a
5m + 3a
6m + 2a
6m + 3a
7m + 3a
7m + 4a
As described in the above embodiment, when the first intermediate layer thickness is 18 μm and the second intermediate layer thickness is 14 μm, the thickness of the cover layer thickness 12 that satisfies the above conditions is as follows. .
　14μｍ
　18μｍ
　28μｍ
　32μｍ
　46μｍ
　50μｍ
　60μｍ
　64μｍ
　78μｍ
　82μｍ
　92μｍ
　96μｍ
　110μｍ
　114μｍ
　つづいて、（2）のガイド光(赤色レーザ光15)のカバー層12の表面で反射した光線による共焦点クロストークについて図１８を用いて説明する。光ディスク10のガイド層20に照射されたガイド用の赤色レーザ光15は、記録層の半透過性により複数の光ビームに分岐する。例えば、レーザ光15の一部は、記録層21Hで反射して、分岐ビーム43となってカバー層12の表面でカバー層内部より焦点をむすび、この反射光が再び記録層21Hで反射してレーザ光15、すなわちガイド層20の記録再生光と合流し、赤色用光検出器ＩＣで同時かつ空間的に略同位置にて検出されてしまう。この共焦点クロストーク光は、記録再生光と同一波長でかつ略同一光路を通って検出されるため、空間的、帯域的分離手段が有効に働かず、強力なノイズとなって検出されることとなる。 14μm
18μm
28μm
32μm
46μm
50μm
60μm
64μm
78μm
82μm
92μm
96μm
110μm
114μm
Next, the confocal crosstalk caused by the light beam reflected by the surface of the cover layer 12 of the guide light (red laser light 15) of (2) will be described with reference to FIG. The red laser light 15 for guide irradiated on the guide layer 20 of the optical disc 10 is branched into a plurality of light beams due to the semi-transparency of the recording layer. For example, a part of the laser beam 15 is reflected by the recording layer 21H, becomes a branched beam 43 and is focused from the inside of the cover layer on the surface of the cover layer 12, and this reflected light is reflected again by the recording layer 21H. The laser beam 15, that is, the recording / reproducing light of the guide layer 20 is merged and detected simultaneously and spatially at substantially the same position by the red photodetector IC. This confocal crosstalk light is detected at the same wavelength as the recording / reproducing light and through almost the same optical path, so that the spatial and band separation means do not work effectively and are detected as powerful noise. It becomes.
　ガイド光の共焦点クロストークの低減のためには、既に上述のように、ガイド層20と記録層21Aの間の中間層30と記録層21における中間層31の厚さを好適に作成することによりガイド光の共焦点クロストークを低減することとした。そこで、カバー層12の表面で反射した光線による共焦点クロストークについては、カバー層12の厚さを好適に作成することによりガイド光の共焦点クロストークを低減することが望ましい。 In order to reduce the confocal crosstalk of the guide light, as already described above, the intermediate layer 30 between the guide layer 20 and the recording layer 21A and the thickness of the intermediate layer 31 in the recording layer 21 should be suitably created. Therefore, the confocal crosstalk of the guide light is reduced. Therefore, for the confocal crosstalk caused by the light beam reflected from the surface of the cover layer 12, it is desirable to reduce the confocal crosstalk of the guide light by suitably creating the thickness of the cover layer 12.
　図１９はガイド光の共焦点クロストークが低減された様子の一例を示す図である。光ディスク10のガイド層20に照射されたガイド用の赤色レーザ光15は、一部が記録層21Hで反射して、分岐ビーム44となって記録層21Hで反射する。しかし、この場合、カバー層12が好適に作成されているため、分岐ビーム44はカバー層12の表面で焦点をむすばず、かつ、この反射光が再び記録層21Hで反射しても、レーザ光15、すなわちガイド層20の記録再生光とは同一光路では合流せず、赤色用光検出器ＩＣで空間的に一致しない位置で検出される。このため、このクロストーク光は、ガイド光15と空間的な分離が可能であり、ノイズ低減が可能である。 FIG. 19 is a diagram illustrating an example of a state in which the confocal crosstalk of the guide light is reduced. A part of the guide red laser light 15 irradiated to the guide layer 20 of the optical disc 10 is reflected by the recording layer 21H, and becomes a branched beam 44 and reflected by the recording layer 21H. However, in this case, since the cover layer 12 is preferably formed, the branched beam 44 does not focus on the surface of the cover layer 12, and even if this reflected light is reflected again by the recording layer 21H, the laser beam 15, that is, the recording / reproducing light of the guide layer 20 does not merge in the same optical path, and is detected at a position that does not spatially coincide with the red photodetector IC. For this reason, the crosstalk light can be spatially separated from the guide light 15, and noise can be reduced.
　以上のように、カバー層12の表面でカバー層内部より反射した光線による、（1）記録再生光および（2）ガイド光の共焦点クロストークを考慮した上で、カバー層12の厚さをより好適に作成することで、良好な特性を持つ、ガイド層と情報記録再生層を別個に持つ多層光ディスクを提供することが可能となる。 As described above, the thickness of the cover layer 12 is determined in consideration of the confocal crosstalk of (1) recording / reproducing light and (2) guide light caused by the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. By making it more suitable, it becomes possible to provide a multilayer optical disc having good characteristics and having a guide layer and an information recording / reproducing layer separately.
　図２０の折れ線グラフは、m=14、a=4、すなわち第一の中間層厚が14μｍ、第二の中間層厚が18μｍの場合の、上記（2）のガイド光の共焦点クロストークの低減状態を表す図である。カバー層厚さに応じた、共焦点クロストークが十分低減出来る中間層30の厚さ範囲（迷光ゼロゾーン幅）をプロットしている。共焦点クロストークが十分低減できる中間層30の厚さ範囲が広いほど、良好な特性をもつ多層光ディスクを提供することが出来る。より好適には、共焦点クロストークが十分低減できる中間層30の厚さ範囲が7μｍ以上確保出来ると良い。図２０の網掛けしたカバー層範囲は、上記（1）の記録再生光の共焦点クロストークが低減可能なカバー層厚、すなわち上記条件に対して、2μｍ以上のマージンを持つカバー層厚範囲を示している。したがって、カバー層12の表面でカバー層内部より反射した光線による、（1）記録再生光および（2）ガイド光の共焦点クロストークを低減可能な、カバー層厚は、図２０の網掛け範囲で、かつ、7μｍ以上の中間層30の厚さ範囲を持つ領域である。カバー層厚は、上に述べたように記録層保護の観点から概ね50μｍ以上は必要であり、一方、記録再生時のチルトマージンの観点から、12層の記録層の場合で概ね100μｍ以下には抑えるのが良い。従って、このケースでは、カバー層厚は52～54μｍ、60～62μｍ、66μｍ、80μｍ、84～86μｍ、92～94μｍ、98μｍとすることで良好な特性を持つ多層光ディスクを提供することが可能となる。 The line graph of FIG. 20 shows the confocal crosstalk of the guide light in (2) above when m = 14, a = 4, that is, the first intermediate layer thickness is 14 μm and the second intermediate layer thickness is 18 μm. It is a figure showing a reduction state. The thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be secured to 7 μm or more. The shaded cover layer range in FIG. 20 is a cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1), that is, a cover layer thickness range having a margin of 2 μm or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 μm or more. As described above, the cover layer thickness is required to be approximately 50 μm or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 μm or less in the case of 12 recording layers. It is good to suppress. Therefore, in this case, it is possible to provide a multilayer optical disk having good characteristics by setting the cover layer thickness to 52 to 54 μm, 60 to 62 μm, 66 μm, 80 μm, 84 to 86 μm, 92 to 94 μm, and 98 μm. .
　上述の説明をすべて踏まえてカバー層、ガイド層および記録層の中間層厚を構成した場合の光ディスク構造の例を図２１を用いて説明する。図２１Ａ、図２１Ｂ、図２１Ｃは第一の中間層が第二の中間層よりも薄い場合のディスク構造例を示す。上記の実施形態にて述べたように第一の中間層厚を14μｍ、第二の中間層厚を18μｍとした場合、カバー層の厚さは一例として66μｍとするのが好ましく、このとき中間層30の厚さは57μｍあるいは89μｍ程度とすることで信頼性の高い光ディスクが得られるが、共焦点クロストークを生ずるディスクの発生確率のシミュレーションの結果、好適な厚さとして58μｍとした。図２１Ａは、記録層21を12層備えた光ディスク10の構造例である。ガイド層20のカバー層表面からの距離は298μｍ、記録層21Aのカバー層表面からの距離は240μｍとなる。図２１Ｂ、図２１Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、ガイド層20は、12層の例と同じくカバー層表面から298μｍに位置する。これは、同一の光ピックアップユニット200でこれらのディスクを記録再生した場合にガイド光の品質、収差特性がほぼ同程度となることが期待できるからである。さらに共焦点クロストークは性質上、記録層、ガイド層のディスク表面からの位置関係が変わらなければ、記録層の数が減れば減少するため、8層および6層ディスクは、12層ディスクの構造から記録層を一部削除した構造とすると良い。このため、8層ディスクでは、図２１Ａの構成からガイド層に近い２つの記録層およびカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは90μｍとした。この結果、記録層21Aのカバー層表面からの距離は208μｍとなる。このとき、カバー層の厚さは98μｍとなる。一方、図２１Ｃの6層の記録層を持つディスクでは、さらにカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは90μｍのままで、カバー層の厚さを130μｍとした。 Based on all of the above description, an example of an optical disc structure in the case where the intermediate layer thickness of the cover layer, the guide layer, and the recording layer is configured will be described with reference to FIG. 21A, 21B, and 21C show examples of the disk structure when the first intermediate layer is thinner than the second intermediate layer. As described in the above embodiment, when the first intermediate layer thickness is 14 μm and the second intermediate layer thickness is 18 μm, the thickness of the cover layer is preferably 66 μm as an example. An optical disk with high reliability can be obtained by setting the thickness of 30 to about 57 μm or 89 μm. However, as a result of simulation of the occurrence probability of a disk that causes confocal crosstalk, the preferable thickness is set to 58 μm. FIG. 21A shows an example of the structure of the optical disc 10 having 12 recording layers 21. The distance of the guide layer 20 from the cover layer surface is 298 μm, and the distance of the recording layer 21A from the cover layer surface is 240 μm. FIG. 21B and FIG. 21C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, the guide layer 20 is located at 298 μm from the cover layer surface as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same. In addition, confocal crosstalk, by nature, decreases if the positional relationship from the disk surface of the recording layer and guide layer does not change and decreases if the number of recording layers decreases. A structure in which a part of the recording layer is deleted from is preferable. For this reason, the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 21A, and the thickness of the intermediate layer 30 is 90 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 208 μm. At this time, the thickness of the cover layer is 98 μm. On the other hand, the disc having 6 recording layers in FIG. 21C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 90 μm, and the thickness of the cover layer is 130 μm. did.
　図２２の折れ線グラフは、第一の中間層厚が18μｍ、第二の中間層厚が14μｍの場合の、上記（2）のガイド光の共焦点クロストークの低減状態を表す図である。カバー層厚さに応じた、共焦点クロストークが十分低減出来る中間層30の厚さ範囲（迷光ゼロゾーン幅）をプロットしている。共焦点クロストークが十分低減できる中間層30の厚さ範囲が広いほど、良好な特性をもつ多層光ディスクを提供することが出来る。より好適には、共焦点クロストークが十分低減できる中間層30の厚さ範囲が7μｍ以上確保出来ると良いのは上述の通りである。図２２の網掛けしたカバー層範囲は、上記（1）の記録再生光の共焦点クロストークが低減可能なカバー層厚、すなわち上記条件に対して、2μｍ以上のマージンを持つカバー層厚範囲を示している。したがって、カバー層12の表面でカバー層内部より反射した光線による、（1）記録再生光および（2）ガイド光の共焦点クロストークを低減可能な、カバー層厚は、図２０の網掛け範囲で、かつ、7μｍ以上の中間層30の厚さ範囲を持つ領域である。カバー層厚は、上に述べたように記録層保護の観点から概ね50μｍ以上は必要であり、一方、記録再生時のチルトマージンの観点から、12層の記録層の場合で概ね100μｍ以下には抑えるのが良い。従って、カバー層厚は62μｍ、66～68μｍ、74～76μｍ、80μｍ、94μｍ、98～100μｍとすることで良好な特性を持つ多層光ディスクを提供することが可能となる。 The line graph in FIG. 22 is a diagram showing a reduced state of the confocal crosstalk of the guide light (2) when the first intermediate layer thickness is 18 μm and the second intermediate layer thickness is 14 μm. The thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, as described above, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be ensured to be 7 μm or more. The shaded cover layer range in FIG. 22 is the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 μm or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 μm or more. As described above, the cover layer thickness is required to be approximately 50 μm or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 μm or less in the case of 12 recording layers. It is good to suppress. Therefore, it is possible to provide a multilayer optical disc having good characteristics by setting the cover layer thickness to 62 μm, 66 to 68 μm, 74 to 76 μm, 80 μm, 94 μm, and 98 to 100 μm.
　上述の説明をすべて踏まえてカバー層、ガイド層および記録層の中間層厚を構成した場合の光ディスク構造の例を図２３を用いて説明する。図２３Ａ、図２３Ｂ、図２３Ｃは第一の中間層が第二の中間層よりも厚い場合のディスク構造を示す。上記の実施形態にて述べたように第一の中間層厚を18μｍ、第二の中間層厚を14μｍとした場合、カバー層の厚さは一例として75μｍとするのが好ましく、このとき中間層30の厚さは39μｍあるいは71μｍ程度とすることで信頼性の高い光ディスクが得られるが、共焦点クロストークを生ずるディスクの発生確率のシミュレーションの結果、好適な厚さとして37.5μｍとした。図２３Ａは、記録層21を12層備えた光ディスク10の構造例である。ガイド層20のカバー層表面からの距離は290.5μｍ、記録層21Aのカバー層表面からの距離は253μｍとなる。図２３Ｂ、図２３Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、ガイド層20は、12層の例と同じくカバー層表面から290.5μｍに位置する。これは、同一の光ピックアップユニット200でこれらのディスクを記録再生した場合にガイド光の品質、収差特性がほぼ同程度となることが期待できるからである。さらに共焦点クロストークは性質上、記録層、ガイド層のディスク表面からの位置関係が変わらなければ、記録層の数が減れば減少するため、8層および6層ディスクは、12層ディスクの構造から記録層を一部削除した構造とすると良い。このため、8層ディスクでは、図２３Ａの構成からガイド層に近い２つの記録層およびカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは69.5μｍとした。この結果、記録層21Aのカバー層表面からの距離は221μｍとなる。このとき、カバー層の厚さは107μｍとなる。一方、図２３Ｃの6層の記録層を持つディスクでは、さらにカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは69.5μｍのままで、カバー層の厚さを139μｍとした。 Based on all of the above description, an example of an optical disk structure when the intermediate layer thickness of the cover layer, guide layer, and recording layer is configured will be described with reference to FIG. FIG. 23A, FIG. 23B, and FIG. 23C show the disk structure when the first intermediate layer is thicker than the second intermediate layer. As described in the above embodiment, when the first intermediate layer thickness is 18 μm and the second intermediate layer thickness is 14 μm, the thickness of the cover layer is preferably 75 μm as an example. An optical disk with high reliability can be obtained by setting the thickness of 30 to about 39 μm or 71 μm. However, as a result of simulation of the occurrence probability of a disk that causes confocal crosstalk, the preferable thickness is set to 37.5 μm. FIG. 23A shows an example of the structure of the optical disc 10 having 12 recording layers 21. The distance of the guide layer 20 from the cover layer surface is 290.5 μm, and the distance of the recording layer 21A from the cover layer surface is 253 μm. FIG. 23B and FIG. 23C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, the guide layer 20 is located at 290.5 μm from the cover layer surface as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same. In addition, confocal crosstalk, by nature, decreases if the positional relationship from the disk surface of the recording layer and guide layer does not change and decreases if the number of recording layers decreases. A structure in which a part of the recording layer is deleted from is preferable. For this reason, the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 23A, and the thickness of the intermediate layer 30 is 69.5 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 221 μm. At this time, the thickness of the cover layer is 107 μm. On the other hand, the disc having 6 recording layers in FIG. 23C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 69.5 μm, and the thickness of the cover layer is 139 μm. It was.
　図２４の折れ線グラフは、m=14.5、a=4、すなわち第一の中間層厚が14.5μｍ、第二の中間層厚が18.5μｍの場合の、上記（2）のガイド光の共焦点クロストークの低減状態を表す図である。カバー層厚さに応じた、共焦点クロストークが十分低減出来る中間層30の厚さ範囲（迷光ゼロゾーン幅）をプロットしている。共焦点クロストークが十分低減できる中間層30の厚さ範囲が広いほど、良好な特性をもつ多層光ディスクを提供することが出来る。より好適には、共焦点クロストークが十分低減できる中間層30の厚さ範囲が7μｍ以上確保出来ると良い。図２４の網掛けしたカバー層範囲は、上記（1）の記録再生光の共焦点クロストークが低減可能なカバー層厚、すなわち上記条件に対して、2μｍ以上のマージンを持つカバー層厚範囲を示している。したがって、カバー層12の表面でカバー層内部より反射した光線による、（1）記録再生光および（2）ガイド光の共焦点クロストークを低減可能な、カバー層厚は、図２４の網掛け範囲で、かつ、7μｍ以上の中間層30の厚さ範囲を持つ領域である。カバー層厚は、上に述べたように記録層保護の観点から概ね50μｍ以上は必要であり、一方、記録再生時のチルトマージンの観点から、12層の記録層の場合で概ね100μｍ以下には抑えるのが良い。従って、このケースでは、カバー層厚は53.5～56μｍ、61～64μｍ、68μｍ、82.5μｍ、86.5～89μｍ、94～97μｍとすることで良好な特性を持つ多層光ディスクを提供することが可能となる。 The line graph of FIG. 24 shows the confocal cross of the guide light of (2) above when m = 14.5, a = 4, that is, when the first intermediate layer thickness is 14.5 μm and the second intermediate layer thickness is 18.5 μm. It is a figure showing the reduction state of talk. The thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be secured to 7 μm or more. The shaded cover layer range in FIG. 24 is the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 μm or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 μm or more. As described above, the cover layer thickness is required to be approximately 50 μm or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 μm or less in the case of 12 recording layers. It is good to suppress. Therefore, in this case, it is possible to provide a multilayer optical disc having good characteristics by setting the cover layer thickness to 53.5 to 56 μm, 61 to 64 μm, 68 μm, 82.5 μm, 86.5 to 89 μm, and 94 to 97 μm.
　上述の説明をすべて踏まえてカバー層、ガイド層および記録層の中間層厚を構成した場合の光ディスク構造の例を図２５を用いて説明する。図２５Ａ、図２５Ｂ、図２５Ｃは第一の中間層が第二の中間層よりも薄い場合のディスク構造例を示す。上記の実施形態にて述べたように第一の中間層厚を14.5μｍ、第二の中間層厚を18.5μｍとした場合、カバー層の厚さは一例として68μｍとするのが好ましく、このとき中間層30の厚さは58.75μｍあるいは91.75μｍ程度とすることで信頼性の高い光ディスクが得られるが、共焦点クロストークを生ずるディスクの発生確率のシミュレーションの結果、好適な厚さとして59.5μｍとした。図２５Ａは、記録層21を12層備えた光ディスク10の構造例である。ガイド層20のカバー層表面からの距離は307μｍ、記録層21Aのカバー層表面からの距離は247.5μｍとなる。図２５Ｂ、図２５Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、ガイド層20は、12層の例と同じくカバー層表面から307μｍに位置する。これは、同一の光ピックアップユニット200でこれらのディスクを記録再生した場合にガイド光の品質、収差特性がほぼ同程度となることが期待できるからである。さらに共焦点クロストークは性質上、記録層、ガイド層のディスク表面からの位置関係が変わらなければ、記録層の数が減れば減少するため、8層および6層ディスクは、12層ディスクの構造から記録層を一部削除した構造とすると良い。このため、8層ディスクでは、図２５Ａの構成からガイド層に近い２つの記録層およびカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは92.5μｍとした。この結果、記録層21Aのカバー層表面からの距離は214.5μｍとなる。このとき、カバー層の厚さは101μｍとなる。一方、図２５Ｃの6層の記録層を持つディスクでは、さらにカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは92.5μｍのままで、カバー層の厚さを134μｍとした。 Based on all of the above description, an example of an optical disc structure when the intermediate layer thickness of the cover layer, guide layer, and recording layer is configured will be described with reference to FIG. FIG. 25A, FIG. 25B, and FIG. 25C show examples of the disk structure when the first intermediate layer is thinner than the second intermediate layer. As described in the above embodiment, when the first intermediate layer thickness is 14.5 μm and the second intermediate layer thickness is 18.5 μm, the thickness of the cover layer is preferably 68 μm as an example. A highly reliable optical disk can be obtained by setting the thickness of the intermediate layer 30 to about 58.75 μm or 91.75 μm. However, as a result of simulation of the probability of occurrence of a disk causing confocal crosstalk, a suitable thickness is 59.5 μm. did. FIG. 25A shows an example of the structure of the optical disc 10 having 12 recording layers 21. The distance of the guide layer 20 from the cover layer surface is 307 μm, and the distance of the recording layer 21A from the cover layer surface is 247.5 μm. 25B and 25C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, the guide layer 20 is located 307 μm from the surface of the cover layer as in the case of the 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same. In addition, confocal crosstalk, by nature, decreases if the positional relationship from the disk surface of the recording layer and guide layer does not change and decreases if the number of recording layers decreases. A structure in which a part of the recording layer is deleted from is preferable. For this reason, the 8-layer disc has a configuration in which the two recording layers near the guide layer and the two recording layers near the cover layer are deleted from the configuration in FIG. 25A, and the thickness of the intermediate layer 30 is 92.5 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 214.5 μm. At this time, the thickness of the cover layer is 101 μm. On the other hand, the disc having 6 recording layers in FIG. 25C has a configuration in which two recording layers close to the cover layer are deleted, the thickness of the intermediate layer 30 remains 92.5 μm, and the thickness of the cover layer is 134 μm. It was.
　図２６の折れ線グラフは、第一の中間層厚が18.5μｍ、第二の中間層厚が14.5μｍの場合の、上記（2）のガイド光の共焦点クロストークの低減状態を表す図である。カバー層厚さに応じた、共焦点クロストークが十分低減出来る中間層30の厚さ範囲（迷光ゼロゾーン幅）をプロットしている。共焦点クロストークが十分低減できる中間層30の厚さ範囲が広いほど、良好な特性をもつ多層光ディスクを提供することが出来る。より好適には、共焦点クロストークが十分低減できる中間層30の厚さ範囲が7μｍ以上確保出来ると良いのは上述の通りである。図２２の網掛けしたカバー層範囲は、上記（1）の記録再生光の共焦点クロストークが低減可能なカバー層厚、すなわち上記条件に対して、2μｍ以上のマージンを持つカバー層厚範囲を示している。したがって、カバー層12の表面でカバー層内部より反射した光線による、（1）記録再生光および（2）ガイド光の共焦点クロストークを低減可能な、カバー層厚は、図２０の網掛け範囲で、かつ、7μｍ以上の中間層30の厚さ範囲を持つ領域である。カバー層厚は、上に述べたように記録層保護の観点から概ね50μｍ以上は必要であり、一方、記録再生時のチルトマージンの観点から、12層の記録層の場合で概ね100μｍ以下には抑えるのが良い。従って、カバー層厚は64μｍ、68～71.5μｍ、75.5～78.5μｍ、82.5μｍ、97μｍとすることで良好な特性を持つ多層光ディスクを提供することが可能となる。 The line graph of FIG. 26 is a diagram showing a reduced state of the confocal crosstalk of the guide light (2) when the first intermediate layer thickness is 18.5 μm and the second intermediate layer thickness is 14.5 μm. . The thickness range (stray light zero zone width) of the intermediate layer 30 in which the confocal crosstalk can be sufficiently reduced according to the cover layer thickness is plotted. The wider the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk, it is possible to provide a multilayer optical disk having better characteristics. More preferably, as described above, the thickness range of the intermediate layer 30 that can sufficiently reduce the confocal crosstalk can be ensured to be 7 μm or more. The shaded cover layer range in FIG. 22 is the cover layer thickness that can reduce the confocal crosstalk of the recording / reproducing light of (1) above, that is, the cover layer thickness range having a margin of 2 μm or more with respect to the above conditions. Show. Therefore, the cover layer thickness can reduce the confocal crosstalk of (1) recording / reproducing light and (2) guide light due to the light reflected from the inside of the cover layer 12 on the surface of the cover layer 12. And an area having a thickness range of the intermediate layer 30 of 7 μm or more. As described above, the cover layer thickness is required to be approximately 50 μm or more from the viewpoint of recording layer protection. On the other hand, from the viewpoint of the tilt margin during recording and reproduction, the cover layer thickness is approximately 100 μm or less in the case of 12 recording layers. It is good to suppress. Accordingly, it is possible to provide a multilayer optical disc having good characteristics by setting the cover layer thickness to 64 μm, 68 to 71.5 μm, 75.5 to 78.5 μm, 82.5 μm, and 97 μm.
　上述の説明をすべて踏まえてカバー層、ガイド層および記録層の中間層厚を構成した場合の光ディスク構造の例を図２７を用いて説明する。図２７Ａ、図２７Ｂ、図２７Ｃは第一の中間層が第二の中間層よりも厚い場合のディスク構造を示す。上記の実施形態にて述べたように第一の中間層厚を18.5μｍ、第二の中間層厚を14.5μｍとした場合、カバー層の厚さは一例として77.5μｍとするのが好ましく、このとき中間層30の厚さは40.25μｍあるいは73.25μｍ程度とすることで信頼性の高い光ディスクが得られるが、共焦点クロストークを生ずるディスクの発生確率のシミュレーションの結果、好適な厚さとして39μｍとした。図２７Ａは、記録層21を12層備えた光ディスク10の構造例である。ガイド層20のカバー層表面からの距離は300μｍ、記録層21Aのカバー層表面からの距離は261μｍとなる。図２７Ｂ、図２７Ｃは、それぞれ記録層21を8層、および6層備えた光ディスク10の構造例である。まず、ガイド層20は、12層の例と同じくカバー層表面から300μｍに位置する。これは、同一の光ピックアップユニット200でこれらのディスクを記録再生した場合にガイド光の品質、収差特性がほぼ同程度となることが期待できるからである。さらに共焦点クロストークは性質上、記録層、ガイド層のディスク表面からの位置関係が変わらなければ、記録層の数が減れば減少するため、8層および6層ディスクは、12層ディスクの構造から記録層を一部削除した構造とすると良い。このため、8層ディスクでは、図２７Ａの構成からガイド層に近い２つの記録層およびカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは72μｍとした。この結果、記録層21Aのカバー層表面からの距離は228μｍとなる。このとき、カバー層の厚さは110.5μｍとなる。一方、図２７Ｃの6層の記録層を持つディスクでは、さらにカバー層に近い２つの記録層を削除した構成とし、中間層30の厚さは72μｍのままで、カバー層の厚さを143.5μｍとした。 Based on all of the above description, an example of an optical disc structure when the intermediate layer thickness of the cover layer, guide layer, and recording layer is configured will be described with reference to FIG. 27A, 27B, and 27C show the disk structure in the case where the first intermediate layer is thicker than the second intermediate layer. As described in the above embodiment, when the first intermediate layer thickness is 18.5 μm and the second intermediate layer thickness is 14.5 μm, the cover layer thickness is preferably 77.5 μm as an example. When the thickness of the intermediate layer 30 is about 40.25 μm or 73.25 μm, a highly reliable optical disk can be obtained. As a result of the simulation of the occurrence probability of a disk that causes confocal crosstalk, the preferable thickness is 39 μm. did. FIG. 27A shows an example of the structure of the optical disc 10 having 12 recording layers 21. The distance of the guide layer 20 from the cover layer surface is 300 μm, and the distance of the recording layer 21A from the cover layer surface is 261 μm. 27B and 27C are structural examples of the optical disc 10 provided with 8 and 6 recording layers 21, respectively. First, the guide layer 20 is located 300 μm from the surface of the cover layer as in the example of 12 layers. This is because when these discs are recorded and reproduced by the same optical pickup unit 200, it can be expected that the quality and aberration characteristics of the guide light are substantially the same. In addition, confocal crosstalk, by nature, decreases if the positional relationship from the disk surface of the recording layer and guide layer does not change and decreases if the number of recording layers decreases. A structure in which a part of the recording layer is deleted from is preferable. For this reason, the 8-layer disc has a configuration in which two recording layers near the guide layer and two recording layers near the cover layer are deleted from the configuration in FIG. 27A, and the thickness of the intermediate layer 30 is 72 μm. As a result, the distance of the recording layer 21A from the cover layer surface is 228 μm. At this time, the thickness of the cover layer is 110.5 μm. On the other hand, the disc having the 6 recording layers in FIG. 27C has a configuration in which two recording layers close to the cover layer are deleted, the intermediate layer 30 remains 72 μm, and the cover layer has a thickness of 143.5 μm. It was.
　なお、上記の記録再生光の共焦点クロストークの発生条件を満たさないカバー層厚構成が、好適であると述べた。より詳細には、
　１）カバー層厚が上記発生条件を満たすカバー層厚から出来るだけ離れていること
　２）上記発生条件を満たすカバー層厚からのマージンが同一の場合、第一反射層と目標層の間の中間層数から、第一反射層とカバー層に最も近い反射層の間の中間層数を引いた数が少ない方が良い
　ことが言える。 It has been stated that the cover layer thickness configuration that does not satisfy the confocal crosstalk generation condition of the recording / reproducing light is preferable. More specifically,
1) The cover layer thickness is as far as possible from the cover layer thickness that satisfies the above-mentioned generation conditions. 2) When the margin from the cover layer thickness that satisfies the above-mentioned generation conditions is the same, the intermediate between the first reflective layer and the target layer. It can be said that the smaller the number obtained by subtracting the number of intermediate layers between the first reflective layer and the reflective layer closest to the cover layer from the number of layers is better.
　上記説明では、光記憶媒体の製造誤差を考慮していないが、中間層厚等の製造誤差を考慮することにより、本実施形態で説明した好適な複数のカバー層厚の候補の中からより良いカバー層厚を選択することができる。例えば、複数の中間層において厚さの製造誤差は不均一に発生するのではなく、厚さの製造誤差は均一に発生し易い。第一の中間層厚を18μｍ、第二の中間層厚を14μｍで設計したが、実際には、第一の中間層厚が18μｍ+誤差α、第二の中間層厚が14μｍ+誤差αになることがある。誤差αの値を調べることにより、製造誤差を含む複数の中間層厚を調べることができる。これにより、本実施形態で説明した複数のカバー層厚の候補の中から、より好適なカバー層厚を選択することができる。 In the above description, the manufacturing error of the optical storage medium is not taken into consideration. However, by taking into account the manufacturing error such as the intermediate layer thickness, it is better to select from a plurality of suitable cover layer thickness candidates described in the present embodiment. The cover layer thickness can be selected. For example, thickness manufacturing errors do not occur unevenly in a plurality of intermediate layers, but thickness manufacturing errors tend to occur uniformly. Although the first intermediate layer thickness is designed to be 18 μm and the second intermediate layer thickness is 14 μm, the first intermediate layer thickness is actually 18 μm + error α, and the second intermediate layer thickness is 14 μm + error α. May be. By examining the value of the error α, a plurality of intermediate layer thicknesses including manufacturing errors can be examined. Thereby, a more suitable cover layer thickness can be selected from a plurality of cover layer thickness candidates described in the present embodiment.
　本実施形態の光記憶媒体では、サーボ専用層(ガイド層)と情報記録再生層を別個に持つ多層光ディスクにおいて、ガイド層および記録層の中間層厚構成を好適に作成することにより、記録層を記録再生する記録再生光のみならず、ガイド層を再生するガイド光における層間クロストークが低減可能となり、情報記録再生において、高い信頼性を有する多層光ディスクを提供することが可能となる。 In the optical storage medium of the present embodiment, in the multilayer optical disc having the servo dedicated layer (guide layer) and the information recording / reproducing layer separately, the recording layer is formed by suitably creating the intermediate layer thickness configuration of the guide layer and the recording layer. Interlayer crosstalk in guide light for reproducing the guide layer as well as recording / reproduction light for recording / reproduction can be reduced, and a multilayer optical disc having high reliability in information recording / reproduction can be provided.
　以下、本実施形態についてまとめる。 Hereinafter, this embodiment will be summarized.
　（１）実施形態の光記憶媒体において、ガイド層とガイド層に最も近い記録層の間の中間層の厚さが、記録層群における任意の連続した中間層の厚さの和と一致しない。 (1) In the optical storage medium of the embodiment, the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer does not match the sum of the thicknesses of any continuous intermediate layers in the recording layer group.
　（２）上記（１）を前提として、ガイド層とガイド層に最も近い記録層の間の中間層と、ガイド層に最も近い記録層と任意の記録層の間の中間層(群)との、厚さの和が、記録層群における任意の連続した中間層の厚さの和と一致しない。 (2) On the premise of (1) above, an intermediate layer between the guide layer and the recording layer closest to the guide layer, and an intermediate layer (group) between the recording layer closest to the guide layer and any recording layer The sum of the thicknesses does not match the sum of the thicknesses of any continuous intermediate layers in the recording layer group.
　（３）上記（１）又は（２）を前提として、記録層群の中間層が、第一の膜厚である第一中間層と、第一の膜厚と異なる第二の膜厚である第二中間層が、記録層を挟んで交互に積層される。 (3) On the premise of (1) or (2) above, the intermediate layer of the recording layer group has a first intermediate layer that is the first film thickness and a second film thickness that is different from the first film thickness. Second intermediate layers are alternately stacked with the recording layer interposed therebetween.
　（４）上記（３）を前提として、前記第一の膜厚をm、前記第二の膜厚をm+aとし、前記ガイド層とガイド層に最も近い記録層の間の中間層の厚さが3.5m+2a、5.5m+3a、7.5m+4a、9.5m+5aのいずれかである。 (4) On the premise of (3) above, the first film thickness is m, the second film thickness is m + a, and the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer Is 3.5m + 2a, 5.5m + 3a, 7.5m + 4a, or 9.5m + 5a.
　（５）上記（３）を前提として、前記第一の膜厚をm+a、前記第二の膜厚をmとし、前記ガイド層とガイド層に最も近い記録層の間の中間層の厚さが2.5m+a、4.5m+2a、6.5m+3a、8.5m+4a、10.5m+5aのいずれかである。 (5) On the premise of (3) above, the first film thickness is m + a, the second film thickness is m, and the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer Is 2.5m + a, 4.5m + 2a, 6.5m + 3a, 8.5m + 4a, or 10.5m + 5a.
　（６）上記（３）を前提として、前記第一の膜厚が１４μｍ、前記第二の膜厚が１８μｍで、前記ガイド層とガイド層に最も近い記録層の間の中間層の厚さが５７μｍあるいは８９μｍである。 (6) On the premise of (3) above, the first film thickness is 14 μm, the second film thickness is 18 μm, and the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer is 57 μm or 89 μm.
　（７）上記（３）を前提として、前記第一の膜厚が１８μｍ、前記第二の膜厚が１４μｍで、前記ガイド層とガイド層に最も近い記録層の間の中間層の厚さが３９μｍあるいは７１μｍである。 (7) On the premise of (3) above, the first film thickness is 18 μm, the second film thickness is 14 μm, and the thickness of the intermediate layer between the guide layer and the recording layer closest to the guide layer is It is 39 μm or 71 μm.
　（８）実施形態の光記憶媒体において、カバー層の厚さと、カバー層に最も近い第一の記録層とカバー層を通過したレーザ光が最初に反射する反射記録層との間の層の厚さとの和が、反射記録層と目標記録層との間の１以上の中間層の厚さの和と一致しない。 (8) In the optical storage medium of the embodiment, the thickness of the cover layer and the layer thickness between the first recording layer closest to the cover layer and the reflective recording layer where the laser beam that has passed through the cover layer is first reflected. Is not the same as the sum of the thicknesses of one or more intermediate layers between the reflective recording layer and the target recording layer.
　（９）上記（８）を前提として、記録層群は、一つの記録層を挟んで交互に配置された第一の膜厚の第一の中間層と前記第一の膜厚と異なる第二の膜厚の第二の中間層とを含み、第一の膜厚が14μｍ、第二の膜厚が18μｍであり、カバー層の厚さが52～54μｍ、60～62μｍ、66μｍ、80μｍ、84～86μｍ、92～94μｍ、及び98μｍのうちの何れかの範囲に含まれる値又は何れかの値である。 (9) On the premise of the above (8), the recording layer group includes a first intermediate layer having a first film thickness that is alternately arranged with one recording layer interposed therebetween, and a second film that is different from the first film thickness. A first intermediate film thickness of 14 μm, a second film thickness of 18 μm, and a cover layer thickness of 52-54 μm, 60-62 μm, 66 μm, 80 μm, 84 It is a value included in any one of -86 μm, 92-94 μm, and 98 μm, or any value.
　（１０）上記（８）を前提として、第一の膜厚が18μｍ、第二の膜厚が14μｍであり、カバー層の厚さが62μｍ、66～68μｍ、74～76μｍ、80μｍ、94μｍ、及び98～100μｍのうちの何れかの範囲に含まれる値又は何れかの値である。 (10) Based on (8) above, the first film thickness is 18 μm, the second film thickness is 14 μm, and the cover layer thickness is 62 μm, 66-68 μm, 74-76 μm, 80 μm, 94 μm, and It is a value included in any range of 98 to 100 μm or any value.
　（１１）上記（８）を前提として、第一の膜厚が14.5μｍ、第二の膜厚が18.5μｍであり、カバー層の厚さが53.5～56μｍ、61～64μｍ、68μｍ、82.5μｍ、及び86.5～89μｍ、94～97μｍのうちの何れかの範囲に含まれる値又は何れかの値である。 (11) Based on the above (8), the first film thickness is 14.5 μm, the second film thickness is 18.5 μm, and the cover layer thickness is 53.5 to 56 μm, 61 to 64 μm, 68 μm, 82.5 μm, And a value included in any one of 86.5 to 89 μm and 94 to 97 μm, or any value.
　（１２）上記（８）を前提として、第一の膜厚が18.5μｍ、前記第二の膜厚が14.5μｍであり、カバー層の厚さＣ１が64μｍ、68～71.5μｍ、75.5～78.5μｍ、及び82.5μｍ、97μｍのうちの何れかの範囲に含まれる値又は何れかの値である。 (12) Based on the above (8), the first film thickness is 18.5 μm, the second film thickness is 14.5 μm, and the cover layer thickness C1 is 64 μm, 68-71.5 μm, 75.5-78.5 μm. , And a value included in any range of 82.5 μm and 97 μm, or any value.
　また、上記（１）～（７）と、上記（８）～（１２）を組み合わせることも可能であり、組み合わせによりクロストークの軽減効果が増す。 It is also possible to combine the above (1) to (7) and the above (8) to (12), and the crosstalk reduction effect is increased by the combination.
　本発明のいくつかの実施形態を説明したが、これらの実施形態は、例として提示したものであり、発明の範囲を限定することは意図していない。これら実施形態は、その他の様々な形態で実施されることが可能であり、発明の要旨を逸脱しない範囲で、種々の省略、置き換え、変更を行うことができる。これら実施形態やその変形は、発明の範囲や要旨に含まれると同様に、特許請求の範囲に記載された発明とその均等の範囲に含まれるものである。 Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.
１０…光ディスク、１１…基板、２０…ガイド層、２１…記録層、３１…中間層 DESCRIPTION OF SYMBOLS 10 ... Optical disk, 11 ... Board | substrate, 20 ... Guide layer, 21 ... Recording layer, 31 ... Intermediate | middle layer

Claims (14)

  1. 　カバー層と、
    　複数の記録層とこれら複数の記録層の間に配置された複数の中間層とにより構成される記録層群と、
    　を備え、
    　前記カバー層の厚さＣ１と、前記カバー層に最も近い第一の記録層と前記カバー層を通過したレーザ光が最初に反射する反射記録層との間の層の厚さＣ２との和Ｓ１が、前記反射記録層と目標記録層との間の１以上の中間層の厚さの和Ｓ２と一致しない光記憶媒体。     A cover layer;
    A recording layer group composed of a plurality of recording layers and a plurality of intermediate layers arranged between the plurality of recording layers;
    With
    The sum S1 of the thickness C1 of the cover layer and the layer thickness C2 between the first recording layer closest to the cover layer and the reflective recording layer where the laser beam that has passed through the cover layer is first reflected Is not equal to the sum S2 of the thicknesses of one or more intermediate layers between the reflective recording layer and the target recording layer.
  2. 　前記記録層群は、一つの記録層を挟んで交互に配置された第一の膜厚の第一の中間層と前記第一の膜厚と異なる第二の膜厚の第二の中間層とを含み、
    　前記第一の膜厚が14μｍ、前記第二の膜厚が18μｍであり、前記カバー層の厚さＣ１が52～54μｍ、60～62μｍ、66μｍ、80μｍ、84～86μｍ、92～94μｍ、及び98μｍのうちの何れかの範囲に含まれる値又は何れかの値である請求項１の光記憶媒体。     The recording layer group includes a first intermediate layer having a first thickness and a second intermediate layer having a second thickness different from the first thickness, which are alternately arranged with one recording layer interposed therebetween. Including
    The first film thickness is 14 μm, the second film thickness is 18 μm, and the cover layer thickness C1 is 52 to 54 μm, 60 to 62 μm, 66 μm, 80 μm, 84 to 86 μm, 92 to 94 μm, and 98 μm. 2. The optical storage medium according to claim 1, wherein the optical storage medium is a value included in any one of the ranges.
  3. 　前記第一の膜厚が18μｍ、前記第二の膜厚が14μｍであり、カバー層の厚さＣ１が62μｍ、66～68μｍ、74～76μｍ、80μｍ、94μｍ、及び98～100μｍのうちの何れかの範囲に含まれる値又は何れかの値である請求項１の光記憶媒体。 The first film thickness is 18 μm, the second film thickness is 14 μm, and the cover layer thickness C1 is any one of 62 μm, 66 to 68 μm, 74 to 76 μm, 80 μm, 94 μm, and 98 to 100 μm. The optical storage medium according to claim 1, which is a value included in the range or any value.
  4. 　前記第一の膜厚が14.5μｍ、前記第二の膜厚が18.5μｍであり、カバー層の厚さＣ１が53.5～56μｍ、61～64μｍ、68μｍ、82.5μｍ、及び86.5～89μｍ、94～97μｍのうちの何れかの範囲に含まれる値又は何れかの値である請求項１の光記憶媒体。 The first film thickness is 14.5 μm, the second film thickness is 18.5 μm, and the cover layer thickness C1 is 53.5 to 56 μm, 61 to 64 μm, 68 μm, 82.5 μm, and 86.5 to 89 μm, 94 to 97 μm. 2. The optical storage medium according to claim 1, wherein the optical storage medium is a value included in any one of the ranges.
  5. 　前記第一の膜厚が18.5μｍ、前記第二の膜厚が14.5μｍであり、カバー層の厚さＣ１が64μｍ、68～71.5μｍ、75.5～78.5μｍ、及び82.5μｍ、97μｍのうちの何れかの範囲に含まれる値又は何れかの値である請求項１の光記憶媒体。 The first film thickness is 18.5 μm, the second film thickness is 14.5 μm, and the cover layer thickness C1 is 64 μm, 68-71.5 μm, 75.5-78.5 μm, 82.5 μm, 97 μm The optical storage medium according to claim 1, which is a value included in any one of the ranges or any value.
  6. 　ガイド層と、
    　前記複数の記録層のうちの前記ガイド層に最も近い第二の記録層と前記ガイド層との間のガイド層側中間層と、
    　を備え、
    　前記ガイド層側中間層の厚さＴ１が、前記記録層群に含まれた任意の連続した中間層の厚さの和Ｓ３と一致しない請求項１乃至５の何れか１つの光記憶媒体。     A guide layer,
    A guide layer side intermediate layer between the guide layer and the second recording layer closest to the guide layer of the plurality of recording layers;
    With
    6. The optical storage medium according to claim 1, wherein a thickness T1 of the guide layer side intermediate layer does not coincide with a sum S3 of thicknesses of arbitrary continuous intermediate layers included in the recording layer group.
  7. 　前記ガイド層側中間層の厚さＴ１と、前記記録層群に含まれた前記第二の記録層と第三の記録層との間の層の厚さＴ２との和Ｓ４が、前記和Ｓ３と一致しない請求項６の光記憶媒体。 The sum S4 of the thickness T1 of the intermediate layer on the guide layer side and the thickness T2 of the layer between the second recording layer and the third recording layer included in the recording layer group is the sum S3. The optical storage medium of claim 6 that does not match.
  8. 　前記ガイド層側中間層の厚さＴ１と前記和Ｓ３とが一致する複数の値を仮定し、前記複数の値のうちの第一の値と前記第一の値の次に大きい第２の値との間の中間値を定義し、
    　前記ガイド層側中間層の厚さＴ１が前記中間値に一致する請求項６又は７の光記憶媒体。     Assuming a plurality of values in which the thickness T1 of the intermediate layer on the guide layer side and the sum S3 coincide with each other, a first value out of the plurality of values and a second value that is the next larger than the first value Define an intermediate value between
    The optical storage medium according to claim 6 or 7, wherein a thickness T1 of the guide layer side intermediate layer coincides with the intermediate value.
  9. 　前記ガイド層側中間層の厚さＴ１と前記和Ｓ３とが一致する複数の値、及び前記和Ｓ４と前記和Ｓ３とが一致する複数の値を仮定し、これら全ての値のうちの第一の値と前記第一の値の次に大きい第２の値との間の中間値を定義し、
    　前記ガイド層側中間層の厚さＴ１が前記中間値に一致する請求項６又は７の光記憶媒体。     Assuming a plurality of values in which the thickness T1 of the guide layer side intermediate layer and the sum S3 match, and a plurality of values in which the sum S4 and the sum S3 match, the first of all these values is assumed. Defining an intermediate value between the value of and a second value next to the first value,
    The optical storage medium according to claim 6 or 7, wherein a thickness T1 of the guide layer side intermediate layer coincides with the intermediate value.
  10. 　前記記録層群は、一つの記録層を挟んで交互に配置された第一の膜厚の第一の中間層と前記第一の膜厚と異なる第二の膜厚の第二の中間層とを含む請求項６乃至９の何れか１つの光記憶媒体。 The recording layer group includes a first intermediate layer having a first thickness and a second intermediate layer having a second thickness different from the first thickness, which are alternately arranged with one recording layer interposed therebetween. An optical storage medium according to any one of claims 6 to 9.
  11. 　前記ガイド層に最も近い記録層とその次に近い記録層の間の中間層を第一の中間層とし、前記第一の膜厚m、前記第二の膜厚m+aを定義し、前記ガイド層側中間層の厚さＴ１が3.5m+2a、5.5m+3a、7.5m+4a、9.5m+5aのいずれかである請求項１０の光記憶媒体。 The intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is a first intermediate layer, and defines the first film thickness m and the second film thickness m + a, The optical storage medium according to claim 10, wherein the thickness T1 of the intermediate layer on the guide layer side is any one of 3.5m + 2a, 5.5m + 3a, 7.5m + 4a, and 9.5m + 5a.
  12. 　前記ガイド層に最も近い記録層とその次に近い記録層の間の中間層を第一の中間層とし、前記第一の膜厚m+a、前記第二の膜厚mを定義し、前記ガイド層側中間層の厚さＴ１が2.5m+a、4.5m+2a、6.5m+3a、8.5m+4a、10.5m+5aのいずれかである請求項１０の光記憶媒体。 The intermediate layer between the recording layer closest to the guide layer and the recording layer closest thereto is a first intermediate layer, and defines the first film thickness m + a, the second film thickness m, The optical storage medium according to claim 10, wherein the thickness T1 of the intermediate layer on the guide layer side is any one of 2.5m + a, 4.5m + 2a, 6.5m + 3a, 8.5m + 4a, and 10.5m + 5a.
  13. 　請求項６乃至１２の何れかの光記憶媒体に対してレーザ光により情報を記録する情報記録装置であって、
    　第一のレーザ光を前記ガイド層へ照射する第一の照射手段と、
    　前記第一のレーザ光に対応する第一の反射光を検出する検出手段と、
    　前記第一の反射光の検出結果に基づき前記ガイド層に記録された情報を再生する再生手段と、
    　記録情報に対応して制御される第二のレーザ光を前記複数の記録層のうちの指定された目的記録層へ照射する第二の照射手段と、
    　を備える情報記録装置。     An information recording apparatus for recording information with a laser beam on the optical storage medium according to any one of claims 6 to 12,
    First irradiation means for irradiating the guide layer with a first laser beam;
    Detecting means for detecting first reflected light corresponding to the first laser light;
    Reproducing means for reproducing information recorded on the guide layer based on the detection result of the first reflected light;
    A second irradiating means for irradiating a designated target recording layer among the plurality of recording layers with a second laser beam controlled corresponding to the recording information;
    An information recording apparatus comprising:
  14. 　請求項６乃至１２の何れかの光記憶媒体に対してレーザ光により情報を記録する情報記録方法であって、
    　第一のレーザ光を前記ガイド層へ照射し、
    　前記第一のレーザ光に対応する第一の反射光を検出し、
    　前記第一の反射光の検出結果に基づき前記ガイド層に記録された情報を再生し、
    　記録情報に対応して制御される第二のレーザ光を前記複数の記録層のうちの指定された目的記録層へ照射する、
    　を備える情報記録方法。     An information recording method for recording information by laser light on the optical storage medium according to any one of claims 6 to 12,
    Irradiating the guide layer with a first laser beam,
    Detecting a first reflected light corresponding to the first laser light;
    Reproducing information recorded on the guide layer based on the detection result of the first reflected light,
    Irradiating a designated target recording layer of the plurality of recording layers with a second laser beam controlled corresponding to the recording information;
    An information recording method comprising:
PCT/JP2013/067856 2013-06-28 2013-06-28 Optical storage medium, information recording device, and information recording method WO2014207911A1 (en)

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