JP2005158163A - Optical disk and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an optical disk drive which is compatible with a plurality of kinds of optical disks including an optical disk having a plurality of recording layers. <P>SOLUTION: A space t<SB>2</SB>between recording layers in an optical disk 15b having two recording layers (M0b, M1b)corresponding to a second luminous flux (wavelength λ<SB>2</SB>) is set to satisfy a relationship of a formula (1) by using; a refractive index n<SB>2</SB>of a interlayer MLb; a numerical aperture NA<SB>1</SB>to a first luminous flux (wavelength λ<SB>1</SB>) of an objective lens and a numerical aperture NA<SB>2</SB>to a second luminous flux; a minimum value t<SB>1min</SB>and a maximum value t<SB>1max</SB>of the space t<SB>1</SB>between the recording layers in the optical disk 15a having two recording layers corresponding to the first luminous flux; and the reflective index n<SB>1</SB>of the interlayer MLr. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disc and an optical disc apparatus, and more particularly, an optical disc device that performs at least reproduction of information recording, reproduction, and erasure on an optical disc having a plurality of recording layers and a plurality of types of optical discs including the optical disc. About.

  In recent years, with the advancement of digital technology and the improvement of data compression technology, DVD (digital versatile disc) and the like are used as media for recording information (hereinafter also referred to as “content”) such as music, movies, photos, and computer software. Optical discs have attracted attention, and along with the reduction in price, optical disc apparatuses that use optical discs as information recording media have become widespread.

  Incidentally, the amount of content information tends to increase year by year, and a further increase in the recording capacity of an optical disc is expected. As a means for increasing the recording capacity of the optical disk, it is conceivable to increase the recording density and the recording density.

  As for the multi-layered recording layer, an optical disc having a plurality of recording layers (hereinafter also referred to as “multi-layer disc”) and a device for accessing the multi-layer disc are being actively developed (for example, see Patent Document 1). ). For example, in a so-called single-sided multilayer disk that is irradiated with a light beam from one side, information can be recorded and reproduced without turning the disk upside down, but the transmission distance of the light beam in the disk is different for each recording layer. The wavefront aberration (especially spherical aberration component) of the light spot is different for each recording layer. Therefore, various devices for correcting the spherical aberration component have been proposed (see, for example, Patent Document 2 and Patent Document 3).

  As for the improvement of the recording density, it has been studied to shorten the wavelength of the light beam applied to the optical disk and to reduce the size (spot diameter) of the light spot formed on the recording layer, and the light beam having a wavelength of about 660 nm. Development and standardization of the next generation DVD (hereinafter also referred to as “blue DVD”) corresponding to a light flux of about 405 nm, which is shorter than the current DVD corresponding to DVD (hereinafter also referred to as “red DVD”) It is. Also for this blue DVD, a multilayered recording layer is being studied.

  By the way, information-related devices such as personal computers are progressing toward miniaturization, and accordingly, it will be essential in the future that the optical disc apparatus can support both the red DVD multilayer disc and the blue DVD multilayer disc. is expected. However, if the spherical aberration component is corrected in the same manner as the devices disclosed in Patent Document 2 and Patent Document 3, it is necessary to set correction conditions for each wavelength and for each recording layer, which complicates the correction circuit. At the same time, the memory capacity necessary for storing the processing program and the like increases, and it becomes difficult to reduce the size of the optical disk apparatus.

Japanese Patent Laid-Open No. 08-096406 JP 05-266511 A Japanese Patent Laid-Open No. 10-269611

  The present invention has been made under such circumstances, and a first object thereof is an optical disc that can promote downsizing of an optical disc apparatus that can handle a plurality of types of optical discs including an optical disc having a plurality of recording layers. Is to provide.

  A second object of the present invention is to provide an optical disc apparatus capable of accurately and stably accessing a plurality of types of optical discs including an optical disc having a plurality of recording layers without causing an increase in size. It is in.

According to the first aspect of the present invention, a light source that emits a first light flux having a wavelength λ ₁ , a light source that emits a second light flux having a wavelength λ ₂ , and a light flux emitted from each light source is collected on a recording layer of an optical disc. An optical disk having a first recording layer and a second recording layer corresponding to the second light beam, the distance t between the first recording layer and the second recording layer. ₂ is the numerical aperture NA _{1 of} the objective lens for the first luminous flux, the numerical aperture NA _{2 of} the objective lens for the second luminous flux, and recording on the first optical disc having two recording layers corresponding to the first luminous flux. The minimum spacing t _1min and the maximum spacing t _{1max of} the layers, the refractive index n ₁ of the intermediate layer sandwiched between two recording layers in the first optical disc, and the sandwiching between the first recording layer and the second recording layer Using the refractive index n ₂ of the intermediate layer,

の関係を満足する光ディスクである。

It is an optical disc that satisfies the above relationship.

  According to this, when used in an optical disc apparatus having the first optical disc as a target medium, spherical aberrations in the first recording layer and the second recording layer can be corrected under the same conditions as in the case of the first optical disc. Therefore, in the optical disc apparatus, it is possible to share the circuit and process for correcting the spherical aberration with the first optical disc. Therefore, it is possible to promote downsizing of the optical disk apparatus corresponding to a plurality of types of optical disks including an optical disk having a plurality of recording layers.

According to a second aspect of the present invention, a light source that emits a first light beam having a wavelength λ ₁ , a light source that emits a second light beam having a wavelength λ ₂ , and a light beam emitted from each light source is collected on a recording layer of an optical disc. An optical disk device including an objective lens that has a first recording layer and a second recording layer corresponding to the second light flux, and an average distance between the first recording layer and the second recording layer In the first optical disc having T ₂ , the numerical aperture NA _{1 of} the objective lens for the first light flux, the numerical aperture NA _{2 of} the objective lens for the second light flux, and two recording layers corresponding to the first light flux. The average interval T ₁ between the recording layers, the refractive index n ₁ of the intermediate layer sandwiched between two recording layers in the first optical disc, and the intermediate layer sandwiched between the first recording layer and the second recording layer Using the refractive index n ₂ ,

で示される光ディスクである。

It is an optical disc indicated by

  According to this, when used in an optical disc apparatus having the first optical disc as a target medium, spherical aberrations in the first recording layer and the second recording layer can be corrected under the same conditions as in the case of the first optical disc. Therefore, in the optical disc apparatus, it is possible to share the circuit and process for correcting the spherical aberration with the first optical disc. Therefore, it is possible to promote downsizing of the optical disk apparatus corresponding to a plurality of types of optical disks including an optical disk having a plurality of recording layers.

  In each of the optical disks according to claims 1 and 2, the average value of the distance from the first recording layer to the substrate surface and the distance from the second recording layer to the substrate surface is the same as the optical disk according to claim 3. The distance from the recording layer to the substrate surface in the second optical disk having one recording layer corresponding to the first light flux or the second light flux can be approximately equal.

According to a fourth aspect of the present invention, a light source that emits a first light beam having a wavelength λ ₁ , a light source that emits a second light beam having a wavelength λ ₂ , and a light beam emitted from each light source is collected on a recording layer of an optical disc. An optical disk having a first recording layer and a second recording layer corresponding to the second light beam, the distance t between the first recording layer and the second recording layer. ₂ is the numerical aperture NA _{1 of} the objective lens for the first luminous flux, the numerical aperture NA _{2 of} the objective lens for the second luminous flux, and recording on the first optical disc having two recording layers corresponding to the first luminous flux. The minimum spacing t _1min and the maximum spacing t _{1max of} the layers, the refractive index n ₁ of the intermediate layer sandwiched between two recording layers in the first optical disc, and the sandwiching between the first recording layer and the second recording layer Using the refractive index n ₂ of the intermediate layer,

の関係を満足し、前記第１記録層から基板表面までの距離又は前記第２記録層から基板表面までの距離が、前記第２光束に対応し１つの記録層を有する第２の光ディスクにおける記録層から基板表面までの距離とほぼ等しい光ディスクである。

And the distance from the first recording layer to the substrate surface or the distance from the second recording layer to the substrate surface corresponds to the second light flux and is recorded on the second optical disc having one recording layer. The optical disc is approximately equal to the distance from the layer to the substrate surface.

  According to this, when used in an optical disc apparatus that uses the first optical disc and the second optical disc as a target medium, the optical disc apparatus can add the first recording layer and the first recording layer without adding a circuit and a process for correcting spherical aberration. The spherical aberration in the second recording layer can be corrected in the same manner as in the first optical disk. Therefore, it is possible to promote downsizing of the optical disk apparatus corresponding to a plurality of types of optical disks including an optical disk having a plurality of recording layers.

According to a fifth aspect of the present invention, a light source that emits a first light flux having a wavelength λ ₁ , a light source that emits a second light flux having a wavelength λ ₂ , and a light flux emitted from each light source is collected on a recording layer of an optical disc. An optical disk device including an objective lens that has a first recording layer and a second recording layer corresponding to the second light flux, and an average distance between the first recording layer and the second recording layer In the first optical disc having T ₂ , the numerical aperture NA _{1 of} the objective lens for the first light flux, the numerical aperture NA _{2 of} the objective lens for the second light flux, and two recording layers corresponding to the first light flux. The average interval T ₁ between the recording layers, the refractive index n ₁ of the intermediate layer sandwiched between two recording layers in the first optical disc, and the intermediate layer sandwiched between the first recording layer and the second recording layer Using the refractive index n ₂ ,

で示され、前記第１記録層から基板表面までの距離又は前記第２記録層から基板表面までの距離が、前記第２光束に対応し１つの記録層を有する第２の光ディスクにおける記録層から基板表面までの距離とほぼ等しい光ディスクである。

The distance from the first recording layer to the substrate surface or the distance from the second recording layer to the substrate surface is from the recording layer in the second optical disc having one recording layer corresponding to the second light flux. The optical disk is approximately equal to the distance to the substrate surface.

  According to this, when used in an optical disc apparatus that uses the first optical disc and the second optical disc as a target medium, the optical disc apparatus can add the first recording layer and the first recording layer without adding a circuit and a process for correcting spherical aberration. The spherical aberration in the second recording layer can be corrected in the same manner as in the first optical disk. Therefore, it is possible to promote downsizing of the optical disk apparatus corresponding to a plurality of types of optical disks including an optical disk having a plurality of recording layers.

  A sixth aspect of the present invention is an optical disc apparatus that performs at least reproduction of information recording, reproduction and erasure on a plurality of types of optical discs including the optical disc according to any one of claims 1 to 5. A plurality of light sources provided individually corresponding to the plurality of types of optical discs, each of which emits a light beam having a wavelength corresponding to any one of the optical discs; and a light beam emitted from the light source is a target of the optical disc An optical system that includes an objective lens that focuses light on the layer and guides the return light beam reflected by the target recording layer to a predetermined light receiving position; and a photodetector that is disposed at the light receiving position and receives the return light beam; Switching means for switching a divergent state of a light beam incident on the objective lens in accordance with the type of the optical disk and the target recording layer; using the output signal of the photodetector Recording of the information, the processing unit performs at least reproduction of reproduction and erasure; an optical disc apparatus comprising a.

  According to this, prior to access to the optical disk for reproduction or the like, depending on the type of the optical disk and the target recording layer, the light beam incident on the objective lens so that the spherical aberration in the recording layer is within an allowable range. The divergence state is switched by the switching means. In this case, for example, when the target recording layer is the first recording layer or the second recording layer of the optical disc according to any one of claims 1 to 5, the divergence is performed in the same manner as in the case of the first optical disc. Since the state can be switched, it is possible to suppress complication of the switching unit. Therefore, it is possible to accurately and stably access a plurality of types of optical discs including an optical disc having a plurality of recording layers without causing an increase in size.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 6C. FIG. 1 shows a schematic configuration of an optical disc apparatus 20 according to an embodiment of the present invention.

  An optical disk apparatus 20 shown in FIG. 1 includes a spindle motor 22 that rotates and drives an optical disk 15, an optical pickup apparatus 23, a seek motor 21 that drives the optical pickup apparatus 23 in a sledge direction, a laser control circuit 24, an encoder 25, and a motor. A control circuit 26, a servo control circuit 27, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, a RAM 41, and the like are provided. In addition, the connection line in FIG. 1 shows the flow of a typical signal and information, and does not represent all the connection relationships of each block.

  In addition, as an example in the present embodiment, the optical disc device 20 includes a blue DVD having two recording layers as an optical disc according to an embodiment of the present invention (hereinafter also referred to as “single-sided dual-layer blue DVD”), the first A red DVD having two recording layers as an optical disc (hereinafter also referred to as “single-sided dual-layer red DVD”), a blue DVD having one recording layer as a second optical disc (hereinafter also referred to as “single-layer blue DVD”), And four types of optical disks of red DVD (hereinafter also referred to as “single-layer red DVD”) having one recording layer. That is, any one of the above four types of optical disks is mounted as the optical disk 15.

As shown in FIG. 2A, for example, the single-sided dual-layer red DVD (15a) has a first substrate L02r, a first recording layer M0r, and an intermediate layer MLr in order from the side closer to the optical pickup device 23. The second recording layer M1r, the second substrate L12r, and the like. A semi-transmissive film formed of silicon, silver, aluminum, or the like is provided between the first recording layer M0r and the intermediate layer MLr, and silver, aluminum is provided between the second recording layer M1r and the second substrate L12r. There is a metal reflective film formed by, for example. Hereinafter, the distance from the first recording layer M0r to the surface of the first substrate L02r (that is, the thickness of the first substrate L02r) is d01, and the distance between the first recording layer M0r and the second recording layer M1r ( That is, the thickness of the intermediate layer MLr is t ₁ and the distance from the second recording layer M1r to the surface of the first substrate L02r is d11.

For example, as shown in FIG. 2B, the single-sided dual-layer blue DVD (referred to as 15b) has a first substrate L02b, a first recording layer M0b, and an intermediate layer MLb in order from the side closest to the optical pickup device 23. The second recording layer M1b, the second substrate L12b, and the like. There is a semi-transmissive film formed of silicon, silver, aluminum, or the like between the first recording layer M0b and the intermediate layer MLb, and silver, aluminum is formed between the second recording layer M1b and the second substrate L12b. There is a metal reflective film formed by, for example. Hereinafter, the distance from the first recording layer M0b to the surface of the first substrate L02b (that is, the thickness of the first substrate L02b) is d02, and the distance between the first recording layer M0b and the second recording layer M1b ( that intermediate layer MLb thickness) t _2, and d12 of the distance to the surface of the first substrate L02b from the second recording layer M1b. Note that the thickness t ₂ of the intermediate layer MLb will be described later.

  For example, as shown in FIG. 3A, the single-layer red DVD (referred to as 15c) includes a first substrate L01r, a recording layer Mr, a second substrate L11r, and the like in order from the side closer to the optical pickup device 23. Have. In addition, there is a metal reflective film between the recording layer Mr and the second substrate L11r. Hereinafter, the distance from the recording layer Mr to the surface of the first substrate L01r (that is, the thickness of the first substrate L01r) is d1.

  For example, as shown in FIG. 3B, the single-layer blue DVD (referred to as 15d) includes a first substrate L01b, a recording layer Mb, a second substrate L11b, and the like in order from the side closer to the optical pickup device 23. Have. In addition, there is a metal reflective film between the recording layer Mb and the second substrate L11b. Hereinafter, the distance from the recording layer Mb to the surface of the first substrate L01b (that is, the thickness of the first substrate L01b) is d2.

  The optical pickup device 23 irradiates a recording layer (hereinafter abbreviated as “target recording layer”) to be accessed in the optical disc 15 with laser light and receives reflected light from the target recording layer. Device. As shown in FIG. 4 as an example, the optical pickup device 23 includes a light source LD1, a hologram unit HU, two coupling lenses (52a, 52b), two beam splitters (54a, 54b), a beam expander 56, A diaphragm 57, an objective lens 60, a detection lens 58, a light receiver PD1, a drive system (a focusing actuator and a tracking actuator (both not shown)) and the like are provided. In the present embodiment, as an example, an optical disc conforming to the DVD + R or DVD + RW standard is used for the single-layer red DVD 15c and the single-sided dual-layer red DVD 15a.

  The light source LD1 is a semiconductor laser that emits laser light having a wavelength of about 660 nm as a first light beam (hereinafter also referred to as “red DVD light beam”). This light source LD1 is used when the optical disk 15 is a single-sided double-layer red DVD 15a or a single-layer red DVD 15c. The maximum intensity emission direction of the red DVD light beam emitted from the light source LD1 is defined as the + X direction. The coupling lens 52a is disposed on the + X side of the light source LD1, and the red DVD light beam emitted from the light source LD1 is made substantially parallel light. The beam splitter 54a is disposed on the + X side of the coupling lens 52a. This beam splitter 54a transmits the red DVD light flux from the coupling lens 52a and returns the red DVD light flux reflected by the target recording layer of the optical disc 15 (single-sided dual-layer red DVD 15a or single-layer red DVD 15c) ( (Hereinafter also referred to as “red DVD return beam”) is branched in the −Z direction.

  The hologram unit HU includes a light source LD2, a light receiver PD2, a hologram 53, and the like that emit a laser beam having a wavelength of about 405 nm as a second light beam (hereinafter also referred to as a “blue DVD light beam”). The light source LD2 is used when the optical disk 15 is a single-sided dual-layer blue DVD 15b or a single-layer blue DVD 15d. The hologram unit HU is arranged such that the maximum intensity emission direction of the blue DVD light beam emitted from the light source LD2 is the + Z direction. The coupling lens 52b is disposed on the + Z side of the hologram unit HU, and the blue DVD light beam emitted from the light source LD2 and transmitted through the hologram 53 is set as substantially parallel light. The hologram 53 receives the return light beam of the blue DVD light beam (hereinafter also referred to as “blue DVD return light beam”) reflected by the target recording layer of the optical disk 15 (single-sided double-layer blue DVD 15b or single-layer blue DVD 15d) by the light receiver PD2. Diffracts in the plane direction.

  The beam splitter 54b is disposed on the + X side of the beam splitter 54a and on the + Z side of the coupling lens 52b. The beam splitter 54b transmits the red DVD light flux from the beam splitter 54a and branches the blue DVD light flux from the coupling lens 52b in the + X direction. The beam splitter 54b branches the blue DVD return beam in the -Z direction and transmits the red DVD return beam.

  The beam expander 56 is disposed on the + X side of the beam splitter 54b, and includes a concave lens 56a, a convex lens 56b, and a lens driving device (not shown) that drives at least one of both lenses and changes the distance between both lenses. Yes. When the distance between both lenses is reduced, the light beam from the convex lens 56b becomes divergent light, and when the distance between both lenses is increased, the light beam from the convex lens 56b becomes convergent light. Here, it is set so that the light beam from the convex lens 56b becomes substantially parallel light when the distance between both lenses is db (see FIG. 6B).

  The stop 57 is disposed on the + X side of the beam expander 56, and limits the beam diameter of the light beam from the beam expander 56. In this embodiment, as an example, the diaphragm 57 is set so that the numerical aperture of the objective lens 60 is 0.65 for both the red DVD light flux and the blue DVD light flux. The objective lens 60 is disposed on the + X side of the stop 57, and the light beam that has passed through the stop 57 is condensed on the target recording layer of the optical disc 15.

  The condensing lens 58 is disposed on the −Z side of the beam splitter 54a, and condenses the red DVD return light beam branched by the beam splitter 54a on the light receiving surface of the light receiver PD1.

  Each of the light receiver PD1 and the light receiver PD2 has a plurality of light receiving regions, and outputs a signal (photoelectric conversion signal) corresponding to the amount of received light for each light receiving region.

  That is, the red DVD light beam emitted from the light source LD1 passes through the coupling lens 52a, the beam splitter 54a, the beam splitter 54b, the beam expander 56, the stop 57, and the objective lens 60, and the optical disc 15 (single-sided, dual-layer red DVD 15a). Alternatively, the light is condensed on the target recording layer of the single-layer red DVD 15c). The red DVD light flux reflected by the target recording layer of the optical disc 15 is received as a red DVD return light flux through the objective lens 60, the aperture 57, the beam expander 56, the beam splitter 54b, the beam splitter 54a, and the detection lens 58. The light is received by the device PD1.

  On the other hand, the blue DVD luminous flux emitted from the light source LD2 is passed through the hologram 53, the coupling lens 52b, the beam splitter 54b, the beam expander 56, the stop 57, and the objective lens 60, and the optical disc 15 (single-sided dual-layer blue DVD 15b or The light is condensed on the target recording layer of the single-layer blue DVD 15d). The blue DVD light beam reflected by the target recording layer of the optical disc 15 is received as a blue DVD return light beam through the objective lens 60, the aperture 57, the beam expander 56, the beam splitter 54b, the coupling lens 52b, and the hologram 53. Light is received by PD2.

  The focusing actuator (not shown) is an actuator for minutely driving the objective lens 60 in the focus direction that is the optical axis direction of the objective lens 60. The tracking actuator (not shown) is an actuator for minutely driving the objective lens 60 in a tracking direction which is a direction orthogonal to the tangential direction of the track.

  Returning to FIG. 1, the reproduction signal processing circuit 28 includes an I / V amplifier 28a, a servo signal detection circuit 28b, a wobble signal detection circuit 28c, an RF signal detection circuit 28d, and a decoder 28e.

  The I / V amplifier 28a converts each output signal of the light receiver PD1 and the light receiver PD2 into a voltage signal, and amplifies it with a predetermined gain.

  The servo signal detection circuit 28b detects servo signals such as a focus error signal and a track error signal based on the output signal of the I / V amplifier 28a. The servo signal detected here is output to the servo control circuit 27.

  The wobble signal detection circuit 28c detects a wobble signal based on the output signal of the I / V amplifier 28a. The RF signal detection circuit 28d detects an RF signal based on the output signal of the I / V amplifier 28a. The decoder 28e extracts address information and a synchronization signal from the wobble signal. The address information extracted here is output to the CPU 40, and the synchronization signal is output to the encoder 25. The decoder 28e performs a decoding process and an error detection process on the RF signal. When an error is detected, the decoder 28e performs an error correction process, and then stores the reproduced data in the buffer RAM 34 via the buffer manager 37. To do.

  The servo control circuit 27 includes an FC controller 27a, a TR controller 27b, an ACT driver 27c, an SA controller 27d, an SA driver 27e, and the like.

  The FC controller 27a generates a focus control signal for correcting a focus shift based on the focus error signal. The TR controller 27b generates a tracking control signal for correcting a track deviation based on the track error signal. The focus control signal and tracking control signal generated here are each output to the ACT driver 27c.

  The ACT driver 27c outputs a driving signal for the focusing actuator to the optical pickup device 23 according to the focus control signal, and outputs a driving signal for the tracking actuator to the optical pickup device 23 according to the tracking control signal. Thereby, tracking control and focus control are performed.

  The SA controller 27d generates a lens interval control signal for controlling the interval between the two lenses constituting the expander 56 based on a switching signal described later from the CPU 40. The lens interval control signal generated here is output to the SA driver 27e.

  The SA driver 27e outputs a driving signal of a lens driving device (not shown) constituting the expander 56 to the optical pickup device 23 in accordance with the lens interval control signal. In the present embodiment, any one of three preset driving signals (referred to as a driving signal A, a driving signal B, and a driving signal C) is output as a driving signal for the lens driving device.

  Here, the relationship among the four types of optical disks (single-sided dual-layer red DVD 15a, single-sided double-layer blue DVD 15b, single-layer red DVD 15c, and single-layer blue DVD 15d) will be described.

  In the present embodiment, the substrates in the four types of optical disks are made of the same material (for example, polycarbonate). The thickness d1 of the first substrate L01r in the single-layer red DVD 15c and the thickness d2 of the first substrate L01b in the single-layer blue DVD 15d are substantially the same as each other (FIGS. 3A and 3B). )reference).

Further, it is assumed that each recording layer of the single-sided dual-layer red DVD 15a and the recording layer Mr of the single-layer red DVD 15c have a relationship represented by the following equation (1). As described above, d01 is the thickness of the first substrate L02r in single-sided, dual-layer red DVD15a, t ₁ is the thickness of the intermediate layer MLr in double layer red DVD15a. That is, the average value of the distance from the first recording layer M0r to the surface of the first substrate L02r and the distance from the second recording layer M1r to the surface of the first substrate L02r is the surface of the first substrate L01r from the recording layer Mr in the single-layer red DVD 15c. Is almost equal to the distance to
(D01 + d11) / 2≈d1 (1)

Furthermore, it is assumed that each recording layer of the single-sided dual-layer blue DVD 15b and the recording layer of the single-layer blue DVD 15d have a relationship represented by the following equation (2). As described above, d02 is the thickness of the first substrate L02b in single-sided, dual-layer blue DVD15b, t ₂ is the thickness of the intermediate layer MLb in double layer blue DVD15b. That is, the average value of the distance from the first recording layer M0b to the surface of the first substrate L02b and the distance from the second recording layer M1b to the surface of the first substrate L02b is the surface of the first substrate L01b from the recording layer Mb in the single-layer blue DVD 15d. Is almost equal to the distance to
(D02 + d12) / 2≈d2 (2)

  That is, with respect to the optical axis direction of the objective lens 60, the intermediate position between the first recording layer M0r and the second recording layer M1r in the single-sided dual-layer red DVD 15a substantially coincides with the position of the recording layer Mr in the single-layer red DVD 15c. Further, with respect to the optical axis direction of the objective lens 60, the intermediate position between the first recording layer M0b and the second recording layer M1b in the single-sided double-layer blue DVD 15b is substantially coincident with the position of the recording layer Mb in the single-layer blue DVD 15d.

Next, the thickness t ₂ of the intermediate layer MLb in the single-sided dual-layer blue DVD 15b will be described below.

For example, if the objective lens 60 is set so that the wavefront aberration at the position corresponding to the intermediate position is minimized, in the single-sided dual-layer red DVD 15a, the first recording layer M0r and the second recording layer M1r spherical aberration (a [Delta] W ₁₎ is represented by the following equation (3). Here, n ₁ is the refractive index of the intermediate layer MLr, and NA ₁ is the numerical aperture of the objective lens 60 for the red DVD light flux.

Similarly, in the single-sided dual-layer blue DVD 15b, the spherical aberration (referred to as ΔW ₂ ) in the first recording layer M0b and the second recording layer M1b is expressed by the following equation (4). Here, n ₂ is the refractive index of the intermediate layer MLb, and NA ₂ is the numerical aperture of the objective lens 60 for the blue DVD light flux.

Even if the distance between both lenses constituting the beam expander 56 is the same, the situation of spherical aberration varies depending on the wavelength of the light beam. Therefore, if the relationship of the following expression (5) is satisfied, the spherical aberration in the first recording layer M0r of the single-sided dual-layer red DVD 15a and the spherical aberration in the first recording layer M0b of the single-sided dual-layer blue DVD 15b have the same amount. In addition, the spherical aberration in the second recording layer M1r of the single-sided dual-layer red DVD 15a and the spherical aberration in the second recording layer M1b of the single-sided dual-layer blue DVD 15b can be made the same amount. Here, λ ₁ is the wavelength of the light beam applied to the single-sided double-layer red DVD 15a, and λ ₂ is the wavelength of the light beam applied to the single-sided double-layer blue DVD 15b.

(5) formula Substituting the expressions (3) and (4) the relationship of the intermediate layer MLr of the intermediate layer MLb single-sided dual-layer blue DVD15b thickness t ₂ and double layer red DVD15a thickness t _As a relational expression with ₁ , the following expression (6) is obtained.

Accordingly, there is a variation in the thickness of the intermediate layer MLr of the single-sided dual-layer red DVD 15a. If the minimum value is t _1min and the maximum value is t _1max , the thickness t ₂ of the intermediate layer MLb of the single-sided dual-layer blue DVD 15b is Is set so as to satisfy the expression (7).

For example, when the single-sided dual-layer red DVD 15a is an optical disc conforming to the DVD-ROM standard, λ ₁ = 650 nm, NA ₁ = 0.6, n ₁ = 1.5791, t _1min = 40 μm, t _1max = 70 μm, Substituting λ ₂ = 405 nm and n ₂ = 1.6202 into the above equation (7) results in 25 μm ≦ t ₂ ≦ 43 μm if the numerical aperture is the same as shown in FIG. For example, when the single-sided dual-layer red DVD 15a is an optical disc conforming to the DVD + R or DVD + RW standard, λ ₁ = 660 nm, NA ₁ = 0.65, n ₁ = 1.5791, t _1min = 40 μm, t _1max = When 60 μm, λ ₂ = 405 nm, and n ₂ = 1.6202 are substituted into the above equation (7), as shown in FIG. 5B, if the numerical aperture is the same, 24 μm ≦ t ₂ ≦ 37 μm. .

  The drive signal A is a drive signal output when the target recording layer is the second recording layer M1r of the single-sided dual-layer red DVD 15a or the second recording layer M1b of the single-sided dual-layer blue DVD 15b. In this case, as shown in FIG. 6A as an example, the distance between the concave lens 56a and the convex lens 56b is da (<db), and the light beam incident on the objective lens 60 is a slightly divergent light beam.

  The drive signal B is a drive signal output when the target recording layer is the recording layer Mr of the single red DVD 15c or the recording layer Mb of the single blue DVD 15d. In this case, as shown in FIG. 6B as an example, the distance between the concave lens 56a and the convex lens 56b is db, and the light beam incident on the objective lens 60 is substantially parallel light.

  The drive signal C is a drive signal output when the target recording layer is the first recording layer M0r of the single-sided dual-layer red DVD 15a or the first recording layer M0b of the single-sided dual-layer blue DVD 15b. In this case, as shown in FIG. 6C as an example, the distance between the concave lens 56a and the convex lens 56b is dc (> db), and the light beam incident on the objective lens 60 is a slightly converged light beam.

  The process of determining whether the optical disk 15 is one of the above four types of optical disks (single-sided double-layer red DVD 15a, single-sided double-layer blue DVD 15b, single-layer red DVD 15c, and single-layer blue DVD 15d) Sometimes done by CPU 40. In the single-sided dual-layer red DVD 15a and the single-sided dual-layer blue DVD 15b, the CPU 40 determines whether the target recording layer is the first recording layer or the second recording layer based on the designated address. Therefore, when there is a recording request or a reproduction request from the host, the CPU 40 selects one of three types of driving signals (the driving signal A, the driving signal B, and the driving signal C) according to the type of the optical disc 15 and the target recording layer. The switching signal designating either one is output to the SA controller 27d. Further, the CPU 40 notifies the FC controller 27a of information related to the target recording layer. Thereby, the focus of the objective lens 60 is controlled so as to focus on the target recording layer.

  Returning to FIG. 1, the motor control circuit 26 drives and controls the spindle motor 22 and the seek motor 21 based on instructions from the CPU 40.

  The buffer RAM 34 temporarily stores data to be recorded on the optical disc 15 (recording data), data reproduced from the optical disc 15 (reproduction data), and the like. Data input / output to / from the buffer RAM 34 is managed by the buffer manager 37.

  The encoder 25 takes out the recording data stored in the buffer RAM 34 based on an instruction from the CPU 40 via the buffer manager 37, modulates the data, adds an error correction code, and the like, and outputs a write signal to the optical disc 15. Generate. The write signal generated here is output to the laser control circuit 24.

  The laser control circuit 24 controls the power of the laser light emitted from the light source LD1 and the light source LD2. For example, at the time of recording, a drive signal for each light source is generated based on the write signal, recording conditions, light emission characteristics of each light source, and the like. The laser control circuit 24 determines a light source to be controlled based on information on the type of optical disk from the CPU 40.

  The interface 38 is a bidirectional communication interface with a host (for example, a personal computer), and conforms to standard interfaces such as ATAPI (AT Attachment Packet Interface) and SCSI (Small Computer System Interface).

  The flash memory 39 stores a program written in codes readable by the CPU 40, recording conditions, light emission characteristics of each light source, and the like.

  The CPU 40 controls the operation of each unit in accordance with the program stored in the flash memory 39 and stores data necessary for control in the RAM 41.

  As is clear from the above description, in the optical disc apparatus 20 according to the present embodiment, the switching means is provided by the CPU 40 and the program executed by the CPU 40, the SA controller 27d, the SA driver 27e, and the beam expander 56. It has been realized. A processing device is realized by the CPU 40 and a program executed by the CPU 40. Note that at least a part of the processing by the CPU 40 may be configured by hardware, or all may be configured by hardware.

  As described above, according to the optical disk apparatus 20 according to the present embodiment, when the single-sided dual-layer red DVD 15a or the single-sided dual-layer blue DVD 15b is mounted and a recording request or reproduction request is received from the host, the CPU 40 determines the target recording layer. When the target recording layer is the first recording layer, a driving signal C is output to a lens driving device (not shown) constituting the expander 56 via the SA controller 27d and the SA driver 27e. On the other hand, when the target recording layer is the second recording layer, the CPU 40 outputs a driving signal A to the lens driving device via the SA controller 27d and the SA driver 27e. When the single-layer red DVD 15c or the single-layer blue DVD 15d is mounted and there is a recording request or reproduction request from the host, the CPU 40 outputs a drive signal B to the lens driving device via the SA controller 27d and SA driver 27e. That is, spherical aberrations in six types of recording layers can be corrected by three types of drive signals. Therefore, it is possible to accurately and stably access a plurality of types of optical disks having a plurality of recording layers without causing an increase in size.

  Further, according to the single-sided dual-layer blue DVD 15b according to the present embodiment, when used in the optical disc device 20, the spherical aberration in each recording layer can be kept low as in the single-sided dual-layer red DVD 15a. That is, the circuit and process for correcting the spherical aberration in the optical disc apparatus 20 can be shared with the single-sided dual-layer red DVD 15a. Accordingly, as a result, it is possible to promote downsizing of the optical disc apparatus corresponding to a plurality of types of optical discs having a plurality of recording layers.

  In the above embodiment, instead of the beam expander 56, a liquid crystal element (liquid crystal panel) that imparts an optical phase difference to a transmitted light beam may be used. In this case, an optical phase difference that cancels out the spherical aberration in the target recording layer is given by the liquid crystal element.

  In the above embodiment, the case where the wavelength of the light beam emitted from the light source LD1 is about 660 nm and the wavelength of the light beam emitted from the light source LD2 is about 405 nm has been described. The wavelength of the light beam emitted from the LD2 may be about 660 nm, and the wavelength of the light beam emitted from the light source LD1 may be about 405 nm. That is, the wavelength of the light beam emitted from the hologram HU may be about 660 nm.

Further, in the above embodiment, when the thickness variation of each intermediate layer in the single-sided dual-layer red DVD 15a and the single-sided dual-layer blue DVD 15b has a substantially normal distribution, the following equation (8) is satisfied. by setting the average thickness T ₂ of the intermediate layer MLb of the dual-layer blue DVD15b so, it is possible to obtain the same effect as the above embodiment. Thereby, the productivity of the single-sided dual-layer blue DVD 15b can be improved. Here, T ₁ is the average thickness of the intermediate layer MLr of the single-sided dual-layer red DVD 15a.

For example, when the single-sided dual-layer red DVD 15a is an optical disc conforming to the DVD-ROM standard, λ ₁ = 650 nm, NA ₁ = 0.6, n ₁ = 1.5791, T ₁ = 55 μm, λ ₂ = 405 nm, When n ₂ = 1.6202 is substituted into the above equation (8), as shown in FIG. 5A, T ₂ ≈34 μm if the numerical aperture is the same. For example, when the single-sided dual-layer red DVD 15a is an optical disc conforming to the DVD + R or DVD + RW standard, λ ₁ = 660 nm, NA ₁ = 0.65, n ₁ = 1.5791, T ₁ = 50 μm, λ ₂ = Substituting 405 nm and n ₂ = 1.6202 into the above equation (8) results in T ₂ ≈30 μm if the numerical aperture is the same as shown in FIG. 5B.

Further, instead of the single-sided dual-layer blue DVD 15b, for example, as shown in FIG. 7A, the single-sided dual-layer blue DVD in which the second recording layer M1b is set so as to satisfy the following equation (9): (and 15b ₁₎ may be used. That is, the distance from the second recording layer M1b to the surface of the first substrate L02b may be substantially equal to the distance from the recording layer Mb to the surface of the first substrate L01b in the single-layer blue DVD 15d. Here, d12 ₁ is the distance from the second recording layer M1b in double layer blue DVD15b ₁ to the first substrate L02b surface. As in the above embodiment, d1≈d2≈ (d01 + d11) / 2.
d12 ₁ ≒ d2 (9)

Then, by setting the thickness t ₂₁ of the intermediate layer MLb of the single-sided dual-layer blue DVD 15b ₁ so that the following expression (10) is satisfied, the three types of drive signals are used as in the above embodiment. It becomes possible to correct spherical aberration in six types of recording layers. In this case, the drive signal A is selected when the target recording layer is the second recording layer M1r of the single-sided dual-layer red DVD 15a. The drive signal B is selected when the target recording layer is the recording layer Mr of the single red DVD 15c, the recording layer Mb of the single blue DVD 15d, or the second recording layer M1b of the single-sided dual blue DVD 15b ₁ . Further, the target recording layer is at a first recording layer M0r or the first recording layer M0b single-sided dual-layer blue DVD15b ₁ of the single-sided dual-layer red DVD15a, the driving signal C is selected.

Here, if the variation in the thickness of the intermediate layer of a single-sided dual-layer red DVD15a and double layer blue DVD15b ₁ is substantially normal distribution, respectively, as follows: (11) is satisfied, one surface 2 by setting the average thickness T ₂₁ of the intermediate layer MLb layer blue DVD15b _1, it is possible to obtain the same effect as the above embodiment.

Further, instead of the single-sided dual-layer blue DVD 15b, for example, as shown in FIG. 7B, the single-sided dual-layer blue DVD in which the first recording layer M0b is set so as to satisfy the following equation (12): (and 15b ₂₎ may be used. That is, the distance from the first recording layer M0b to the surface of the first substrate L02b may be substantially equal to the distance from the recording layer Mb to the surface of the first substrate L01b in the single-layer blue DVD 15d. Here, d02 ₁ is the thickness of the first substrate L02b in single-sided, dual-layer blue DVD15b _2. As in the above embodiment, d1≈d2≈ (d01 + d11) / 2.
d02 ₁ ≒ d2 (12)

Then, by setting the thickness t ₂₂ of the intermediate layer MLb of the single-sided dual-layer blue DVD 15b ₂ so that the following expression (13) is satisfied, the three types of drive signals are used as in the above embodiment. It becomes possible to correct spherical aberration in six types of recording layers. In this case, the target recording layer is at a second recording layer M1r or second recording layer M1b single-sided dual-layer blue DVD15b ₂ of the single-sided dual-layer red DVD15a, the drive signal A is selected. Further, the target recording layer is at a first recording layer M0b recording layer Mr or one layer blue DVD15d recording layer Mb, or single-sided two-layer blue DVD15b ₂ of one layer red DVD15c, the drive signal B is selected. Further, the drive signal C is selected when the target recording layer is the first recording layer M0r of the single-sided dual-layer red DVD 15a.

Here, if the variation in the thickness of the intermediate layer of a single-sided dual-layer red DVD15a and Double Layer blue DVD15b ₂ is substantially normal distribution, respectively, as follows: (14) is satisfied, one surface 2 by setting the average thickness T ₂₂ of the intermediate layer MLb layer blue DVD15b _2, it is possible to obtain the same effect as the above embodiment.

Moreover, although the said embodiment demonstrated the case where the thickness of each 1st board | substrate of 1 layer red DVD15c and 1 layer blue DVD15d was mutually substantially the same, it is not limited to this. As an example, instead of the single-layer blue DVD 15d, as shown in FIG. 8A, the thickness of the first substrate L01b (referred to as d2 ₁ ) is the thickness d1 of the first substrate L01r in the single-layer red DVD. it may be used a small one layer blue DVD than (and 15d _1). Then, instead of the single-sided dual-layer blue DVD 15b, as shown in FIG. 8B as an example, the single-sided dual-layer blue DVD (each recording layer is set so as to satisfy the following equation (15)) 15b ₃ to) using, as follows (16) is satisfied, by setting the thickness t ₂₃ of the intermediate layer MLb of this dual-layer blue DVD15b _3, similarly to the above embodiment, It is possible to correct spherical aberration in six types of recording layers by using three types of drive signals. In this case, the target recording layer is at a second recording layer M1b of the second recording layer M1r or double layer blue DVD15b ₃ of the single-sided dual-layer red DVD15a, the drive signal A is selected. Further, when the target recording layer is the recording layer Mr of the single-layer red DVD 15c, the drive signal B is selected. Further, when the target recording layer is the first recording layer M0r of the single-sided dual-layer red DVD 15a, the first recording layer M0b of the single-sided dual-layer blue DVD 15b ₃ , or the recording layer Mb of the single-layer blue DVD 15d ₁ , the drive signal C is selected. Is done.

d02 ₂ ≈d2 ₁ and (d02 ₂ + d12 ₂ ) / 2≈d1 (15)
d02 ₂ is the thickness of the first substrate L02b of the single-sided dual-layer blue DVD15b _3, d12 ₂ is the distance from the second recording layer M1b in double layer blue DVD15b ₃ to the first substrate L02b surface. As in the above embodiment, d1≈ (d01 + d11) / 2.

Here, if the variation in the thickness of the intermediate layer of a single-sided dual-layer red DVD15a and dual-layer blue DVD15b ₃ is substantially normal distribution, respectively, as follows: (17) is satisfied, one surface 2 by setting the average thickness T ₂₃ of the intermediate layer MLb layer blue DVD15b _3, it is possible to obtain the same effect as the above embodiment.

Furthermore, instead of the single-layer blue DVD 15d, as shown in FIG. 9A as an example, the thickness of the first substrate L01b (d2 ₂ ) is the thickness of the first substrate L01r in the single-layer red DVD. is one layer (and 15d ₂₎ blue DVD larger than d1 may also be used. Then, instead of the single-sided dual-layer blue DVD 15b, as shown in FIG. 9B as an example, the single-sided dual-layer blue DVD (each recording layer is set so as to satisfy the following equation (18)) 15b ₄ to) using, as follows (19) is satisfied, by setting the thickness t ₂₄ of the intermediate layer MLb of this dual-layer blue DVD15b _4, similarly to the above embodiment, It is possible to correct spherical aberration in six types of recording layers by using three types of drive signals. In this case, when the target recording layer is the second recording layer M1b or one layer blue DVD15d ₂ recording layer Mb of the second recording layer M1r or double layer blue DVD15b ₄ of the single-sided dual-layer red DVD15a, the drive signal A is selected. Further, when the target recording layer is the recording layer Mr of the single-layer red DVD 15c, the drive signal B is selected. Further, the target recording layer is at a first recording layer M0b the first recording layer M0r or double layer blue DVD15b ₄ of the single-sided dual-layer red DVD15a, the driving signal C is selected.

d12 ₃ ≈d2 ₂ and (d02 ₃ + d12 ₃ ) / 2≈d1 (18)
d02 ₃ is the thickness of the first substrate L02b in the single-sided dual-layer blue DVD 15b4, and d12 ₃ is the distance from the second recording layer M1b to the surface of the first substrate L02b in the single-sided dual-layer blue DVD 15b4. As in the above embodiment, d1≈ (d01 + d11) / 2.

Here, if the variation in the thickness of the intermediate layer of a single-sided dual-layer red DVD15a and dual-layer blue DVD15b ₄ is substantially normal distribution, respectively, as follows: (20) is satisfied, one surface 2 By setting the average thickness T ₂₄ of the intermediate layer MLb of the layer blue DVD 15b _4, the same effect as in the above embodiment can be obtained.

  Moreover, although the said embodiment demonstrated the case where the numerical aperture of the objective lens 60 with respect to the light beam for blue DVD was 0.65, it is not limited to this.

  In the above embodiment, the optical disk apparatus capable of recording and reproducing information has been described. However, the present invention is not limited to this, and any optical disk apparatus capable of reproducing at least information recording, reproduction, and erasure may be used.

  In the above-described embodiment, the case where the optical disk device 20 supports four types of optical disks has been described, but the present invention is not limited to this. For example, three types of optical disks (single-sided dual-layer red DVD 15a, single-sided dual-layer blue DVD 15b, and single-layer blue DVD 15d) may be supported. In this case, by making the distance from the recording layer of the single-layer blue DVD 15d to the substrate surface substantially equal to d02 or d12, two types of driving signals (driving signal A and driving signal) are used as driving signals for the lens driving device. Signal C) can be used. That is, spherical aberration in five types of recording layers can be corrected by two types of drive signals.

  Further, for example, three types of optical disks (single-sided dual-layer red DVD 15a, single-sided dual-layer blue DVD 15b, and single-layer red DVD 15c) may be supported. In this case, by making the distance from the recording layer of the single-layer red DVD 15c to the substrate surface substantially equal to d01 or d11, two types of drive signals (drive signal A and drive signal) are used as drive signals for the lens drive device. Signal C) can be used. That is, spherical aberration in five types of recording layers can be corrected by two types of drive signals.

  Also, for example, two types of optical disks (single-sided dual-layer red DVD 15a and single-sided dual-layer blue DVD 15b) may be supported. In this case, it is possible to deal with two types of drive signals (drive signal A and drive signal C) as drive signals of the lens drive device. That is, spherical aberrations in four types of recording layers can be corrected by two types of drive signals.

  In the above embodiment, the case where the optical disc apparatus 20 includes two light sources (the light source LD1 and the light source LD2) has been described. However, the present invention is not limited to this. good. As a result, it is possible to deal with an optical disc conforming to the CD standard.

  Further, in the case of an optical disc apparatus including only a light source that emits a light beam having a wavelength of about 405 nm, the distance from the first recording layer to the substrate surface or the distance from the second recording layer to the substrate surface in the single-sided dual-layer blue DVD is By setting the distance from the recording layer to the substrate surface in the single-layer blue DVD to be approximately equal, it is possible to correct spherical aberration in the three types of recording layers by using two types of drive signals.

1 is a block diagram showing a configuration of an optical disc device according to an embodiment of the present invention. 2A is a diagram for explaining the structure of a single-sided dual-layer red DVD, and FIG. 2B is a diagram for explaining the structure of a single-sided dual-layer blue DVD as an optical disc according to an embodiment of the present invention. FIG. 3A is a diagram for explaining the structure of a single-layer red DVD, and FIG. 3B is a diagram for explaining the structure of a single-layer blue DVD. It is a figure for demonstrating the structure of the optical pick-up apparatus in FIG. FIG. 5A shows the calculation result of the thickness of the intermediate layer in the single-sided dual-layer blue DVD when the single-sided dual-layer red DVD is a DVD-ROM, and FIG. 5B shows the single-sided dual-layer red DVD as DVD + R or DVD + RW. It is the calculation result of the thickness of the intermediate | middle layer in the single-sided double-layer blue DVD at the time. FIGS. 6A to 6C are diagrams for explaining the relationship between the lens interval in the beam expander and the divergence state of the light beam incident on the objective lens. FIG. 7A and FIG. 7B are diagrams for explaining another configuration example of a single-sided dual-layer blue DVD, respectively. 8A and 8B are diagrams for explaining the structure of a single-sided dual-layer blue DVD when the thickness of the single-layer blue DVD substrate is smaller than the thickness of the single-layer red DVD substrate, respectively. FIG. 9A and 9B are diagrams for explaining the structure of a single-sided dual-layer blue DVD when the thickness of the single-layer blue DVD substrate is larger than the thickness of the single-layer red DVD substrate, respectively. FIG.

Explanation of symbols

15 ... Optical disc, 15a ... Single-sided double-layer red DVD (first optical disc), 15b ... Single-sided double-layer blue DVD (optical disc), 15c ... Single-layer red DVD (second optical disc), 15d ... Single-layer blue DVD (first optical disc) 2 ... optical disk device, 20 ... optical disk device, 27d ... SA controller (part of switching means), 27e ... SA driver (part of switching means), 40 ... CPU (part of switching means, processing device), 56 ... Beam expander (part of switching means), 60 ... objective lens, LD1, LD2 ... light source, PD1, PD2 ... light receiver, M0b ... first recording layer, M1b ... second recording layer, MLb, MLr ... intermediate layer.

Claims (6)

An optical disc apparatus comprising: a light source that emits a first light flux having a wavelength λ ₁ ; a light source that emits a second light flux having a wavelength λ ₂ ; and an objective lens that focuses the light flux emitted from each light source on a recording layer of the optical disc. An optical disc having a first recording layer and a second recording layer corresponding to the second luminous flux,
The distance t ₂ between the first recording layer and the second recording layer is such that the numerical aperture NA _{1 of} the objective lens with respect to the first luminous flux, the numerical aperture NA _{2 of} the objective lens with respect to the second luminous flux, and the first luminous flux. , The minimum interval t _1min and the maximum interval t _1max of the recording layer in the first optical disc having two recording layers, the refractive index n ₁ of the intermediate layer sandwiched between the two recording layers in the first optical disc, and Using the refractive index n ₂ of the intermediate layer sandwiched between the first recording layer and the second recording layer,

An optical disc that satisfies this relationship. An optical disc apparatus comprising: a light source that emits a first light flux having a wavelength λ ₁ ; a light source that emits a second light flux having a wavelength λ ₂ ; and an objective lens that focuses the light flux emitted from each light source on a recording layer of the optical disc. An optical disc having a first recording layer and a second recording layer corresponding to the second luminous flux,
The average distance T ₂ between the first recording layer and the second recording layer is such that the numerical aperture NA _{1 of} the objective lens for the first light flux, the numerical aperture NA _{2 of} the objective lens for the second light flux, and the first The average interval T ₁ of the recording layers in the first optical disc corresponding to the light beam and having two recording layers, the refractive index n ₁ of the intermediate layer sandwiched between the two recording layers in the first optical disc, and the first recording Using the refractive index n ₂ of the intermediate layer sandwiched between the layer and the second recording layer,

An optical disc indicated by   A second optical disc having one recording layer in which an average value of the distance from the first recording layer to the substrate surface and the distance from the second recording layer to the substrate surface corresponds to the first light flux or the second light flux. The optical disk according to claim 1, wherein the distance is substantially equal to the distance from the recording layer to the substrate surface. An optical disc apparatus comprising: a light source that emits a first light flux having a wavelength λ ₁ ; a light source that emits a second light flux having a wavelength λ ₂ ; and an objective lens that focuses the light flux emitted from each light source on a recording layer of the optical disc. An optical disc having a first recording layer and a second recording layer corresponding to the second luminous flux,
The distance t ₂ between the first recording layer and the second recording layer is such that the numerical aperture NA _{1 of} the objective lens with respect to the first luminous flux, the numerical aperture NA _{2 of} the objective lens with respect to the second luminous flux, and the first luminous flux. , The minimum interval t _1min and the maximum interval t _1max of the recording layer in the first optical disc having two recording layers, the refractive index n ₁ of the intermediate layer sandwiched between the two recording layers in the first optical disc, and Using the refractive index n ₂ of the intermediate layer sandwiched between the first recording layer and the second recording layer,

And the distance from the first recording layer to the substrate surface or the distance from the second recording layer to the substrate surface corresponds to the second light flux and is recorded on the second optical disc having one recording layer. An optical disc approximately equal to the distance from the layer to the substrate surface. An optical disc apparatus comprising: a light source that emits a first light flux having a wavelength λ ₁ ; a light source that emits a second light flux having a wavelength λ ₂ ; and an objective lens that focuses the light flux emitted from each light source on a recording layer of the optical disc. An optical disc having a first recording layer and a second recording layer corresponding to the second luminous flux,
The average distance T ₂ between the first recording layer and the second recording layer is such that the numerical aperture NA _{1 of} the objective lens for the first light flux, the numerical aperture NA _{2 of} the objective lens for the second light flux, and the first The average interval T ₁ of the recording layers in the first optical disc corresponding to the light beam and having two recording layers, the refractive index n ₁ of the intermediate layer sandwiched between the two recording layers in the first optical disc, and the first recording Using the refractive index n ₂ of the intermediate layer sandwiched between the layer and the second recording layer,

The distance from the first recording layer to the substrate surface or the distance from the second recording layer to the substrate surface is from the recording layer in the second optical disc having one recording layer corresponding to the second light flux. An optical disc approximately equal to the distance to the substrate surface. An optical disc apparatus that performs at least reproduction of information recording, reproduction, and erasure on a plurality of types of optical discs including the optical disc according to any one of claims 1 to 5,
A plurality of light sources provided individually corresponding to the plurality of types of optical discs, each emitting a light beam having a wavelength corresponding to any one of the optical discs;
An optical system that includes an objective lens that condenses the light beam emitted from the light source onto the target recording layer of the optical disc, and guides the return light beam reflected by the target recording layer to a predetermined light receiving position;
A photodetector disposed at the light receiving position for receiving the return light beam;
Switching means for switching a divergence state of a light beam incident on the objective lens according to the type of the optical disk and the target recording layer;
An optical disk apparatus comprising: a processing device that performs at least reproduction among recording, reproduction, and erasure of the information using an output signal of the photodetector.

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