JP3189616B2 - Two-layer optical disk and optical disk reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical disk widely used for music, computer data, etc., in which a signal is recorded at a higher density than the recording density of a so-called compact disk (hereinafter abbreviated as CD). Related to high-density optical discs, and more particularly to a dual-layer optical disc having two recording surfaces in one optical disc substrate.

[0002]

2. Description of the Related Art In an optical disk device such as an optical disk represented by a CD or a CD reproducing device, a laser beam emitted from a laser diode is narrowed down to its diffraction limit, and a narrowed light spot is irradiated on a phase pit array on the optical disk. The signal recorded on the optical disk is reproduced by detecting a change in the amount of reflected light. This CD is 120m in diameter
m, the material of the transparent substrate is generally a polycarbonate resin, and its thickness is 1.2 mm. An optical reproducing apparatus for reproducing a CD uses a laser diode of near-infrared light of 770 to 780 nm as a light source, and a numerical aperture (NA) of an objective lens for condensing laser light on an optical disk is generally 0.45.
It is about.

On the other hand, the progress of laser diodes in recent years has been remarkable, and a laser diode for red light having a wavelength of 630 to 690 nm has been put to practical use. 3 ~
A high-density optical disk having a recording density four times as large has been proposed (for example, 1993 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, lecture number C-364, "Study of high-density CD-ROM using red laser pickup").

Further, in order to double the recording capacity, C
A bonded optical disk in which the recording surfaces of an optical disk having a thickness of half of D are bonded to each other, and a two-layer optical disk in which two recording surfaces are provided in one optical disk are also proposed.

[0005]

In the case of a two-layer optical disk, in order to reproduce signals recorded on two different recording surfaces, a lead-in and a lead-out must be provided on each recording surface. Providing a lead-in at the innermost periphery and a lead-out at the outermost periphery, like a CD, is equivalent to reproducing two different optical disks for the optical disk device. Therefore, after the reproduction of one recording surface is completed,
It is necessary to once remove the tracking and focus control, move the optical pickup to the innermost circumference, perform focus and tracking control again, and perform PLL control of the rotation speed of the spindle motor. Therefore, there is a problem that it takes time to change the reproduction surface.

Further, when the focused light emitted from the optical disk device passes through the optical disk substrate, spherical aberration occurs. In order to prevent this, the optical pickup usually generates in advance a spherical aberration that cancels out the spherical aberration generated in the optical disk substrate. The magnitude of this spherical aberration is
It is related to the thickness of the optical disk substrate. Therefore, when designing the optical pickup of the optical disk device, the optimum substrate thickness must be assumed. However, in the case of a two-layer type optical disk, it is equivalent to having two optical disks having different substrate thicknesses, and there is also a problem that an optical pickup assuming this has to be used.

[0007]

Means for Solving the Problems On one recording surface of a two-layer type optical disk, a lead-in is provided on the innermost periphery and a lead-out is provided on the outermost periphery, similarly to a CD, and the other recording surface is provided. In contrast, the lead-in is provided on the outermost periphery and the lead-out is provided on the innermost periphery, which is opposite to the CD, so that the path of movement of the optical pickup is continuous.

Further, the optimum substrate thickness when viewed from the objective lens determined when designing the optical pickup is as follows: a <t <(a + b) where a: thickness of the first substrate b: second substrate T: Determined as the optimum substrate thickness when viewed from the objective lens.

[0009]

A lead-in is provided on the innermost circumference and a lead-out is provided on the outermost circumference with respect to one recording surface of the two-layer type optical disk, and the lead-in and the lead-out are performed with respect to the other recording surface. With this arrangement, after the reproduction on one recording surface is completed, the focus and tracking control operations can be performed on the other recording surface with almost no movement of the optical pickup. Since the linear velocity hardly changes even when the recording surface changes, the rotation speed of the spindle motor only needs to maintain the state before the change of the recording surface.

By setting the optimum substrate thickness when viewed from the objective lens in the optical pickup near the middle between the two different thicknesses, an optical pickup showing sufficient performance for two recording surfaces can be constructed. If the thickness of the thinner substrate is set to be substantially the same as that of a CD, the most widely used CD can be reproduced by the optical pickup for a two-layer optical disk.

[0011]

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of a two-layer optical disk and an optical disk apparatus according to the present invention will be described below.

FIG. 1 shows a two-layer type optical disk according to a first embodiment of the present invention. 1A is a cross-sectional view of the right half of the optical disk, and FIG. 1B is a partially enlarged view thereof. The optical disc 1 includes a substrate 2, a substrate 3, and a protective film. However, the protective film is omitted here. Let the thickness of the substrate 2 be a and the thickness of the substrate 3 be b. FIG.
Has two recording surfaces A and B,
Lead-ins 101 and 111 and lead-outs 102 and 112 are provided for each recording surface. Usually C
On an optical disk such as D, data is spirally recorded from the inner circumference to the outer circumference, and lead-in, data (sound, video, etc.), and lead-out are configured from the inner circumference. On the other hand, in the optical disc of the present invention, when playing back two different recording surfaces continuously, the lead-in of the recording surface B is moved to the outer periphery and the lead-out is moved to the inner periphery so that the optical pickup moves along a closed path. It is provided on the side. Here, light enters from the substrate 2 side.

FIG. 2 shows the shape of the phase pit row viewed from the recording surface B side. FIG. 2 (a) shows the recording surface A, and FIG. 2 (b) shows the recording surface B. The phase pit row 21 on the recording surface A is
While it is formed in a clockwise spiral shape from the same inner circumference as the CD, the phase pit row 22 on the recording surface B is
Contrary to the recording surface A, it is formed in a clockwise spiral shape from the outside. By forming the phase pit array as shown in FIG. 2, a series of reproduction from the inner peripheral side of the recording surface A to the outer peripheral side and from the outer peripheral side of the recording surface B to the inner peripheral side without changing the rotation direction of the spindle motor. Becomes possible.

FIG. 3 shows a state in which the dual-layer optical disk of the present invention is being reproduced. The two-layer optical disk shown in FIG.
Lead-in 1 on the inner peripheral side of the recording surface A and the outer peripheral side of the recording surface B
Lead-ins 102 and 112 are provided on the outer peripheral side of the recording surface A and the inner peripheral side of the recording surface B. When the optical disk 1 is inserted into the optical disk device and signal reproduction is started, the optical pickup 31 moves so as to draw a locus T1. First, focus control is performed so that laser light emitted from the optical pickup 31 is focused on the recording surface A, and tracking control and reading of the lead-in 101 proceed. The optical pickup 31 reproduces the data area 121 on the recording surface A, and proceeds to the lead-out 102. After the reproduction of the recording surface A is completed, the control of tracking and focus is removed, and the focus control of the optical pickup 31 is performed on the recording surface B. At this time, the control circuit needs to have a mechanism for passing control at the first control point and performing control at the second control point.

FIG. 4 is a block diagram of a control system in the optical disk device of the present invention. FIG. 4A is a block diagram,
(B) shows a jump pulse waveform. In FIG. 4, components constituting a circuit and the like are given the names thereof, and numerals 60 to 78 indicate signal lines. The overall configuration is similar to a commonly used optical disk device. The details of the control system in the present invention will be described below.

When the recording surface to be reproduced is changed from the recording surface A to the recording surface B during the reproduction, the actuator is moved upward from the jump pulse generation circuit 54 to the drive circuit 55 as shown in FIG. Apply pulse and -pulse to apply brake. The zero cross point in the S curve of the focus error signal near the recording surface B is detected by the zero cross detection circuit 49, and the focus control loop is closed. On the other hand, when changing from the recording surface B to the recording surface A,
A jump pulse shown in the lower part of FIG.

Further, when the recording surface is changed, the PLL control of the rotation speed of the motor 41 may be lost while the focus and tracking controls are being removed. To prevent this, a hold circuit 46 is provided. The hold circuit 46 holds the number of revolutions before changing the recording surface, and uses the number of revolutions held in the hold circuit 46 until the optical pickup 31 moves onto the recording surface B and performs focus and tracking control. The motor 41 is controlled.

Further, it is necessary that the optical disc apparatus can distinguish between a two-layer type optical disc and an existing CD. In the case of a two-layer type optical disk, the recording surface B must be reproduced through the recording surface A, so that the total amount of light returning to the optical pickup 31 is less than half of that of a CD. Therefore, C
D and a threshold value are provided for each of the two-layer type optical discs,
By comparing the total light amount detected by the total light amount detection circuit 52 with a threshold value determined for each disk in the comparator 53, it is determined which optical disk is inserted.

In an optical disk, a laser beam is focused through a transparent substrate, and recording pits are read by a light spot on a signal surface of the optical disk. However, spherical aberration occurs when the focused light passes through the substrate (eg, WJSmit
h: Modern Optical Engineering, McGraw-Hill Book
Company, New York, 1966, Chap.4.8). Therefore,
A spherical aberration opposite to the spherical aberration generated on the substrate is given to the objective lens for condensing the laser light in advance so that the spherical aberrations cancel each other when the laser beam passes through the substrate. For this reason, the substrate of the optical disk can be regarded as a part of the objective lens.

Generally, an optical disk substrate is manufactured by injection molding of a polycarbonate resin, so that an error in thickness cannot be avoided. If the thickness of the substrate deviates from the substrate thickness assumed by the objective lens (the optimum thickness as viewed from the objective lens), spherical aberration occurs for the above-described reason. The mean square value (W) of the third-order spherical aberration that accounts for most of the generated spherical aberration is

[0022]

(Equation 1)

Δt: thickness error of disk substrate n: refractive index of disk substrate NA: numerical aperture of objective lens λ: wavelength of laser light.

Here, the refractive index n of the polycarbonate resin as the disk substrate is 1.58, and the numerical aperture N of the objective lens is
FIG. 5 shows the relationship between the thickness error of the disk substrate and the third-order spherical aberration generated in the light spot when A is 0.52 and the wavelength λ of the laser beam is 0.635 μm. Generally, in order to obtain an accurate reproduction signal, the spherical aberration should be 0 . 0 3λrms
Under the above conditions, the thickness error of the disk substrate is desirably 70 μm or less from FIG.

The center value of the thickness a of the substrate 2 of the two-layer optical disk shown in FIG. 1 is 1.2 mm, which is the same as that of the CD, the thickness error of the substrate 2 is ± 30 μm, and the distance b between the recording surface A and the recording surface B (Substantially equal to the thickness of the substrate 3) is set to 40 μm. Here, assuming that the thickness of the disk substrate assumed by the objective lens (the optimal substrate thickness when viewed from the objective lens) is a (= 1.2 mm), when reproducing the recording surface B, The thickness error is up to 70 μm. Further, the optimum substrate thickness as viewed from the objective lens is a + b (= 1.2
4 mm), the thickness error of the substrate viewed from the objective lens when reproducing the recording surface A is also 70 μm at the maximum,
In both cases, the third-order spherical aberration is within an allowable value. From the above description, if the optimum substrate thickness of the objective lens satisfies the following expression, the third-order spherical aberration is within the allowable value.

A <optimal substrate thickness as viewed from the objective lens <(a + b) (2) Further, in order to make the amounts of tertiary spherical aberration generated on the recording surface A and the recording surface B substantially equal, The optimum substrate thickness when viewed ≒ a + b / 2 (3)

Further, when the thickness error of the substrate 2 is ± 40 μm and the interval b between the recording surface A and the recording surface B is 40 μm, (a + b / 4) <optimal substrate thickness when viewed from the objective lens <( a + 3b / 4) (4) As described above, the range of the optimum substrate thickness t when viewed from the objective lens differs depending on the thickness error of the substrate 2, the thickness of the substrate 3, and the allowable values of the third-order spherical aberration. In the range of Expression (2).

In order to know the actual optimum substrate thickness of the objective lens, the spherical aberration of the objective lens may be measured by a laser interferometer (for example, a Twyman-Green interferometer).
At this time, parallel plates having different thicknesses are inserted into the light beam focused by the objective lens, and the thickness of the parallel plate that minimizes the spherical aberration is the optimum substrate thickness when viewed from the objective lens.

Next, the thickness of each substrate of a two-layer type optical disk when a compact disk (hereinafter abbreviated as CD) in which the optical disk device of the present invention is widely used is reproduced will be described. CD is a single-layer optical disk, and the center value of the thickness of the disk substrate is 1.2 mm. For this reason, the optimum substrate thickness of the objective lens is generally set to 1.2 mm.
Therefore, the thickness a of the substrate 2 of the two-layer type optical disc shown in FIG.
And the thickness b of the substrate 3 may be set to be a + b / 2 ≒ 1.2 mm. When b = 40 μm, a =
1.18 mm.

FIG. 6 shows a state in which a two-layer optical disk according to the second embodiment of the present invention is being reproduced. The two-layer type optical disc shown in FIG. 6 has lead-ins 101 and 111 on the outer peripheral side of the recording surface A and the inner peripheral side of the recording surface B, and lead-outs 102 and 111 on the inner peripheral side of the recording surface A and the outer peripheral side of the recording surface B. 112 are provided. The phase pit sequence recorded on the dual-layer optical disc of the second embodiment of the present invention shown in FIG.
The shape is reversed. That is, the recording surface B corresponds to FIG.
(A), the recording surface A is the same as that shown in FIG.
→ It is a specification to reproduce in the order of A. Therefore, the optical pickup 31 of the optical disk device moves so as to draw a locus of T2. With such a configuration, the recording surface B to the recording surface A
Since the optical pickup 31 moves downward, the focus control may be started at the next appearing control point without counting the focus control points.

FIG. 7 is a diagram for explaining a third embodiment of the present invention. FIG. 7 shows only the shape of the phase pit row on the second recording surface. Here, the first recording surface is the same as that in FIG. 2A, and the lead-in and lead-out of each recording surface are as shown in FIG. That is, in the third embodiment, there is a lead-in at the innermost periphery of one recording surface and an outermost periphery of the other recording surface, and a lead- out at the innermost periphery of one recording surface and the innermost periphery of the other recording surface. The feature is that the spiral shape formed by the phase pit row is in the same direction on both recording surfaces.

On the recording surface 2 in the above embodiment, first, S
The signal for one round is reproduced from 2 to S1. Thereafter, the track jump is performed only twice on the inner circumference side, the optical pickup is moved to S4, and the signal for one round is reproduced until S3.
A similar operation is repeated for each round of reproduction. In other words, in a broad sense, reproduction is performed from the outermost circumference toward the inner circumference, but is performed to the outer circumference side in the same manner as the recording surface 1 with a track jump to the inner circumference side every round.

[0033]

The dual-layer optical disk of the present invention has a lead-in at the innermost periphery of one recording surface and a lead-out at the outermost periphery, and a lead-in at the outermost periphery of the other recording surface and a lead-in at the innermost periphery. When the recording surface is provided, the optical pickup in the optical disk device hardly moves even when the recording surface is changed, and the rotation speed of the spindle motor can be maintained at the state before the recording surface was changed.

Further, by giving an allowable range to the optimum substrate thickness of the optical pickup used in the optical disk device,
Substrates of two different thicknesses can be regenerated. Furthermore, CD
If the substrate thickness is within this allowable range, a CD can be reproduced by an optical pickup for a two-layer optical disk.

[0035]

[Brief description of the drawings]

FIG. 1 is a two-layer optical disk showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a shape of a phase pit row recorded on an optical disc;

FIG. 3 is a diagram showing a state where a two-layer type optical disc is being reproduced.

FIG. 4 is a block diagram of a control system in the optical disk device.

FIG. 5 is a diagram illustrating a relationship between a disk substrate thickness and a third-order spherical aberration.

FIG. 6 is a two-layer optical disc showing a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a third embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshio Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Hitachi, Ltd. Multimedia System Development Division (56) References A) JP-A-8-212583 (JP, A) JP-A-8-249707 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/00-7/013 G11B 7 / 08-7/085 G11B 7/12-7/22 G11B 7/24

Claims (2)

(57) [Claims] A first substrate comprising a first recording surface, a first substrate comprising a second surface, a third surface comprising a second recording surface, and a fourth surface; A second thinner than the first substrate;
An optical disc reproducing apparatus for reproducing a two-layer type optical disc arranged such that the substrate is arranged in the order of the second surface, the first surface, the fourth surface, and the third surface. A laser light source for selectively reproducing a signal recorded on the first or second recording surface by irradiating a laser from the surface of the optical disk, an objective lens for condensing a light beam emitted from the laser light source, and the optical disk Detecting means for detecting light reflected from any one of the recording surfaces, wherein the objective lens is
The focused light emitted from the
An optical disc device characterized by minimizing spherical aberration caused by passing through a disc. a <t <(a + b ) where, a: the thickness of the first substrate b: thickness of the second substrate 2. A two-layer type optical disc including a first recording surface at a distance a from the laser light incident surface and a second recording surface at a distance (a + b) from the laser light incident surface is irradiated with laser light. And
An optical disc reproducing apparatus for reproducing a signal, a laser light source for selectively reproducing a signal recorded on the first or second recording surface, an objective lens for condensing a light beam emitted from the laser light source, Detecting means for detecting light reflected from any of the recording surfaces of the optical disc, wherein the objective lens is configured such that the converged light emitted from the objective lens is expressed by the following equation:
<T <(a + b)
An optical disk device characterized by minimizing spherical aberration caused by the optical disk .