JPH0922539A - Optical reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To interchangeably reproduce optical disks having different thicknesses of substrates by one optical pickup. SOLUTION: At the time of reproducing an optical disk 7 of a standard thickness, an aspherical aberration compensating means 50 for thin type is removed and an aperture 4 and an aspherical aberration compensating means 5 for standard thickness are inserted. At this time, a half of a laser beam of short wavelength emitted from a semiconductor laser 1 is reflected by a half mirror 2, made to be a parallel beam by a collimator lens 3, its outer peripheral side is shielded by the aperture 4, it is made incident on an objective lens 6 and converged on a signal recording surface 7a. At the time of reproducing a thin type optical disk, the aperture 4 and the aspherical aberration compensating means 5 for standard thickness are removed and the aspherical aberration compensating means 50 for thin type is inserted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing device for reproducing a plurality of types of optical disks having different substrate thicknesses.

[0002]

2. Description of the Related Art An optical disk having a thickness of about 1.2 mm, such as a CD-ROM, from which information is read using a semiconductor laser is provided. In this type of optical disc, a focus servo and a tracking servo are applied to the pickup objective lens to irradiate the laser beam to the pit train on the signal recording surface to reproduce the signal. In addition, recently, high density recording for recording a moving image for a long time is progressing.

[0003] For example, the same 12 cm diameter as a CD-ROM
SD, which records information of about 5 Gbytes on one side of the optical disc of, is proposed. SD disc thickness is about 0.6
mm, and by adhering these on both sides, information of about 10 Gbyte can be recorded with one sheet. Also, CD-
An MMCD has been proposed which records about 3.7 Gbytes of information on one layer on an optical disc having a diameter of 12 cm, which is the same as the ROM. The disk thickness of MMCD is about 1.2 mm,
Approximately 7.4 Gbyte on one side due to the two-layer structure
Can record information.

In an optical pickup for high density disc,
A laser beam with a short wavelength is used to narrow the spot diameter.
It is necessary to use an objective lens with a large numerical aperture. However, when the numerical aperture becomes large, the board tilts (when warped).
Coma becomes large. This is because the coma aberration increases in proportion to the cube of the numerical aperture. On the other hand, coma is also proportional to the thickness of the substrate of the optical disc. Therefore, SD
Then, by reducing the thickness of the substrate to about 0.6 mm, the coma aberration is reduced to 1/2, the deterioration of the signal when the substrate is tilted is suppressed, and the objective lens is The numerical aperture is increased.

On the other hand, the objective lens of the optical pickup is designed by incorporating the thickness of the substrate of the target disk and the laser beam wavelength, and when the thickness of the target substrate of recording / reproducing is different from the design time. Causes spherical aberration, and the spherical aberration increases in proportion to the fourth power of the numerical aperture of the objective lens. Therefore, in the case where the numerical aperture of the objective lens is increased and the spot diameter is narrowed down as described above, when an attempt is made to record / reproduce an optical disc having a thickness different from the design, the beam spot is focused on the information recording surface of the optical disc. No
Recording / playback becomes impossible. For example, in an objective lens designed for an optical disc with a substrate thickness of 1.2 mm,
The beam spot is not focused on the signal recording surface of the optical disc having a substrate thickness of 0.6 mm, and the signal cannot be reproduced.

Therefore, in Japanese Patent Laid-Open No. 5-303766, a high density optical disc having a thin substrate having a thickness of 0.6 mm and a standard density optical disc having a standard substrate having a thickness of 1.2 mm (CD, CD) are disclosed. -ROM) has been proposed to be reproducible by a single optical pickup. This device uses an objective lens with a numerical aperture of 0.6 designed to reproduce a high-density disc with a laser beam of a short wavelength, and when reproducing a standard-density optical disc, the outer periphery of the laser beam is used as an aberration correction means. This is a device in which an object having an aperture for reducing the effective numerical aperture by shielding the side is inserted in front of the objective lens.

[0007]

Problems to be Solved by the Invention
In the device disclosed in Japanese Patent No. 6, the objective lens is displaced in the tracking direction with respect to the optical axis of the laser beam by tracking control. However, the aperture is fixed with respect to the optical axis of the laser beam regardless of the tracking control. Therefore, when the objective lens having the aperture interposed therein is displaced in the same tracking range as when the aperture is not present, the degree of deformation of the beam spot irradiated on the signal recording surface increases. The reason is that the diameter of the laser beam is reduced by the aperture, and the beam spot changes greatly as if the displacement amount of the objective lens was relatively increased.

The irradiation spot is deformed in both the tracking direction and the track direction. The deformation in the tracking direction causes crosstalk noise, and the deformation in the track direction causes jitter deterioration. Therefore, when reproducing an optical disk having a substrate thickness of about 1.2 mm, a standard density optical disk can be reproduced, but a high density optical disk cannot be reproduced.

In the future, optical discs (CD, CD-ROM) with a current density and a substrate thickness of about 1.2 mm, optical discs with a high density and a substrate thickness of about 1.2 mm (MMCD), and a high density with a substrate thickness of about 1.2 mm will be used. It is expected that a 0.6 mm optical disk (SD) will coexist. Therefore, CD etc., MMCD and S
An optical reproducing device capable of reproducing all optical discs such as D is desired. According to the present invention, by selectively inserting the aspherical aberration correction means and the aperture, the CD and the like and the M
The purpose is to reproduce optical disks such as MCD and SD with a single optical pickup.

[0010]

According to the present invention, an objective lens designed to focus between a signal recording surface of a thin substrate and a signal recording surface of a standard thickness substrate, and a thin substrate for reproducing an optical disc of a thin substrate. The present invention is characterized in that it has means for inserting the aspherical aberration correcting means for the standard thickness and for inserting the aperture and the aspherical aberration correcting means for the standard thickness when reproducing the optical disk of the standard thickness substrate.

Further, according to the present invention, the objective lens designed so that the signal recording surface of the standard thickness substrate is focused and the aspherical aberration correcting means are inserted at the time of reproducing the optical disc of the thin substrate, and the optical disc of the standard thickness substrate is inserted. The feature is that it has a means for interposing an aperture during reproduction. Also,
The present invention is characterized in that the aperture and the aspherical aberration correcting means are inserted on the light source side of the objective lens.

Further, the present invention is characterized in that the aperture is mechanically or electrically inserted and the aspherical aberration correcting means is mechanically inserted. Further, in the present invention, the thin optical disc has a substrate thickness of about 0.6 mm, and the standard thickness optical disc has a substrate thickness of about 1.2 mm. Further, in the present invention, the wavelength of the laser beam is set to about 635
nm, the numerical aperture of the objective lens is about 0.6, and the effective numerical aperture in the track direction of the objective lens due to the aperture is 0.3.
It is characterized by being set to 2 to 0.54.

Further, in the present invention, the wavelength of the laser beam is about 650 nm, the numerical aperture of the objective lens is about 0.6, and the effective numerical aperture in the track direction of the objective lens due to the aperture is 0.32 to 0.54. It is characterized by doing. Also,
The present invention is characterized in that the effective numerical aperture in the track direction of the objective lens by the aperture is 0.50 to 0.54.

Further, according to the present invention, the effective numerical aperture in the track direction of the objective lens due to the aperture is 0.32 to 0.32.
It is characterized in that it is 0.38. In the present invention,
It is characterized in that the effective numerical aperture in the tracking direction of the objective lens due to the aperture is larger than the effective numerical aperture in the tracking direction. According to the present invention, the aberration of the laser beam is corrected at the time of reproducing a standard thickness optical disc and the outer peripheral side is shielded, and the aberration of the laser beam is corrected at the time of reproducing a thin optical disc.

Further, according to the present invention, the outer peripheral side of the laser beam is shielded when reproducing the standard thickness optical disc, and the aberration of the laser beam is corrected when reproducing the thin optical disc. Further, according to the present invention, the light beam shape of the laser beam is changed or the aberration is corrected on the light source side of the objective lens. Further, according to the present invention, the aperture is inserted by physical movement or is selectively inserted by an electrically formed light shield, and the aspherical aberration correction lens is inserted by physical movement. .

Further, according to the present invention, a thin optical disc of about 0.6 mm and a standard optical disc of about 1.2 mm are reproduced. Further, according to the present invention, a standard-thickness optical disk is used in a state where the effective numerical aperture of the objective lens having a numerical aperture of about 0.6 is changed to 0.32 to 0.54 by the laser beam of about 635 nm. Is played.

According to the present invention, the standard numerical aperture is changed to 0.32 to 0.54 by the laser beam of about 650 nm in the objective lens having the numerical aperture of about 0.6. A thick optical disc is reproduced. Further, according to the present invention, the effective numerical aperture of the objective lens is 0.50 to 0.50.
With the value changed to 0.54, a standard-thickness optical disc is reproduced.

Further, according to the present invention, with the effective numerical aperture of the objective lens changed to 0.32 to 0.38,
A standard-thickness optical disc is reproduced. According to the present invention, a laser beam long in the tracking direction is incident on the objective lens.

[0019]

[Embodiment]

First Embodiment FIGS. 1 and 2 show a standard thickness of 1.2 (tolerance ± 0.05) mm using an objective lens designed to be focused at a depth of 1.0 mm. Density optical disc having the substrate of MMCD, that is, MMCD (hereinafter referred to as the first optical disc)
And a standard density optical disk having a standard thickness of 1.2 mm (tolerance ± 0.1) mm, ie, CD, CD-R
OM (hereinafter referred to as the second optical disk) and high-density optical disk having a thin substrate with a thickness of 0.6 (tolerance ± 0.05) mm, that is, SD (hereinafter referred to as the third optical disk). The optical system of the optical reproducing apparatus of the first embodiment for reproducing a disc is shown.

First, the reproducing operation of the first optical disk and the second optical disk having a substrate thickness of 1.2 mm will be described. When the standard-thickness optical disk 7 is reproduced, as shown in FIG. 1, the thin aspherical aberration correcting means 50 is mechanically removed from the optical path, and the aperture 4 and the standard-thickness are provided on the light source side of the objective lens 6. The aspherical aberration correction means 5 is mechanically inserted. Although this mechanical insertion / removal mechanism is not shown, a normal slide mechanism that moves by a plunger or the like may be adopted and is not a special mechanism. The aperture is not necessarily mechanically inserted, and a liquid crystal shutter may be attached to the transparent plate and the aperture may be electrically formed by the liquid crystal shutter. In any case, the aperture 4 and the aspherical aberration correcting means 5 for standard thickness are fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation. In the case of an objective lens with a numerical aperture of 0.6 and an effective light beam diameter of 4 mm, the aperture has a diameter of 3.47 (permissible error ± 0.02) so that the effective numerical aperture is 0.52 (permissible error ± 0.02). ± 0.13) mm circular. In addition, when the effective light beam diameter is other than 4 mm, the size of the aperture through hole is proportionally set to a size such that the effective numerical aperture is 0.52.

In FIG. 1, a laser beam having a wavelength of 635 (tolerance of ± 15) nm output from the semiconductor laser 1 is half-reflected by the half mirror 2, collimated by the collimator lens 3, and collimated by the aperture 4. The side is shielded from light, the aberration is corrected by the standard thickness aspherical aberration correction means 5, and the light is incident on the objective lens 6. This objective lens 6
It is supported by a tracking control mechanism and a focus control mechanism (not shown) so as to be displaceable in the tracking direction and the focus direction. Therefore, the laser beam that has passed through the objective lens 6 is condensed, passes through the polycarbonate substrate 7 having a thickness of 1.2 mm, and passes through the signal recording surface 7a of the optical disc.
Is irradiated. The beam spot diameter formed on the signal recording surface 7a is 1.1 (permissible error ± 0.1) μm. Further, the reflected beam from the signal recording surface 7a is
It returns via the objective lens 6, the aspherical aberration correcting means 5 for standard thickness, and the aperture 4, and is condensed by the collimator lens 3 and half is transmitted by the half mirror 2.
The signal detecting portion of the light receiving sensor 8 is focused and irradiated.

As described above, when an objective lens designed to be focused at a depth of 1.0 mm is used, an objective lens designed to be focused at a depth of 0.6 mm is used. Compared with the case, spherical aberration is reduced when reproducing an optical disk having a substrate thickness of 1.2 mm. Next, the reproducing operation of the third optical disc having a substrate thickness of 0.6 mm will be described. When this thin optical disc 70 is reproduced,
As shown in FIG. 2, the aperture 4 and the standard thickness aspherical aberration correcting means 5 are mechanically removed from the optical path, and the thin aspherical aberration correcting means 50 is mechanically inserted on the light source side of the objective lens 6. . The mechanical insertion / removal mechanism is also not shown, but it is the same as when reproducing the standard-thickness optical disk 7. Moreover, the removal of the aperture is performed by the optical disc 7 having the standard thickness.
It may be electrically performed in the same manner as the aperture interposing means at the time of reproduction. In addition, this thin aspherical aberration correcting means 50
Is fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation.

In FIG. 2, the laser beam that has passed through the thin aspherical aberration correcting means 50 enters the objective lens 6,
The signal recording surface 70a of the optical disc is focused and irradiated through a polycarbonate substrate 70 having a thickness of 0.6 mm. The beam spot diameter formed on the recording surface is 0.9 (permissible error ± 0.1) μm. Further, the signal recording surface 7
The reflected beam 0a returns via the substrate 70, the objective lens 6, and the thin aspherical aberration correcting means 50,
The light is collected by the collimator lens 3, half of which is transmitted by the half mirror 2, and the signal detecting portion of the light receiving sensor 8 is condensed and irradiated.

As described above, when an objective lens designed to be focused at a depth of 1.0 mm is used, an objective lens designed to be focused at a depth of 1.2 mm is used. Compared with the case, spherical aberration is reduced when reproducing an optical disc having a substrate thickness of 0.6 mm. In the present embodiment, the aperture 4 and the standard thickness aspherical aberration correcting means 5 are shown separately, but the aperture 4 and the standard thickness aspherical aberration correcting means 5 may be integrated and inserted / removed. . Then, the insertion / removal mechanism becomes simple, and the size and weight can be reduced. It should be noted that upon integration, various methods such as adhesion, vapor deposition, coating, etc. are appropriately adopted.

In this embodiment, the half mirror 2 is used, but instead of this, a polarization beam splitter and 1 /
A four wave plate may be used. Polarizing beam splitter and 1
The use efficiency of the laser power is improved by using the / 4 wavelength plate. Further, the collimator lens 3 is included in the apparatus of this embodiment.
A reflection mirror (a rising mirror) for changing the optical path by 90 degrees is provided between the objective lens 6 and the objective lens 6, but the illustration is omitted for easy viewing. This raising mirror changes the optical path as described above, thereby making the optical pickup compact. When the polarization beam splitter and the quarter-wave plate are used as described above, the raising mirror may be a prism that also serves as the quarter-wave plate.

Further, in the present embodiment, the aperture 4, the aspherical aberration correcting means 5 for standard thickness, and the aspherical aberration correcting means 50 for thin type are inserted between the collimator lens 3 and the objective lens 6, but the semiconductor laser 1 Between the half mirror 2 and the half mirror 2, and between the half mirror 2 and the collimator lens 3. Further, in this embodiment, the laser beam wavelength is 635 nm, but the laser beam wavelength is 650 (allowable error ± 15) n.
In the case of m, the laser beam spot expands by about 0.1 μm, but it can be replaced sufficiently.

Further, in the present embodiment, the diameter value of the aperture hole of the aperture is determined so that the effective numerical aperture of the objective lens is 0.52 (permissible error ± 0.02). If it is not necessary to reproduce, the value of the diameter of the aperture hole of the aperture may be determined so that the effective numerical aperture of the objective lens is 0.32 to 0.50. In reproducing the second optical disc, the spot diameter may be larger, so that the effective numerical aperture of the objective lens can be reduced. For example, if the effective numerical aperture of the objective lens is 0.35
When (tolerance is ± 0.03), the aberration is smaller than that in the present embodiment, and stable reproduction is possible.

Further, in the present embodiment, the objective lens designed to focus at the position of 1.0 mm in depth was used, but 1.2 mm deeper than 0.6 mm except for 1.0 mm depth.
An objective lens designed to focus at a position shallower than mm may be used. When an objective lens designed to focus at a depth of 1.2 mm is used, reproduction of an optical disk having a substrate thickness of 1.2 mm becomes stable, and a depth of 0.
When an objective lens designed to be in focus near 6 mm is used, reproduction of an optical disc having a substrate thickness of 0.6 mm is stable.

Further, in this embodiment, the shape of the through hole of the aperture is circular, but the through hole may be longer in the tracking direction than in the track direction. Second Embodiment FIGS. 3 and 4 show a first optical disc and a second optical disc using an objective lens designed to be focused at a position of a depth of 1.2 mm, that is, a signal recording surface of an optical disc having a standard thickness. ,
The optical system of the optical reproducing apparatus of the second embodiment for reproducing three types of disks, that is, the third optical disk, is shown.

First, the reproducing operation of the first optical disk and the second optical disk having a substrate thickness of 1.2 mm will be described. When the standard-thickness optical disc 7 is reproduced, as shown in FIG. 3, the thin aspherical aberration correcting means 50 is mechanically removed from the optical path, and the aperture 4 is mechanically attached to the light source side of the objective lens 6. Be inserted into. Although this mechanical insertion / removal mechanism is not shown, a normal slide mechanism that moves by a plunger or the like may be adopted and is not a special mechanism. In addition,
The aperture is not necessarily mechanically inserted, and a liquid crystal shutter may be attached to the transparent plate and the aperture may be electrically formed by the liquid crystal shutter. In any case, the aperture 4 is fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation. The aperture of this aperture has an effective numerical aperture of 0. 0 in the case of an objective lens having a numerical aperture of 0.6 and an effective light beam diameter of 4 mm.
The diameter is 3.47 so that it is 52 (tolerance ± 0.02).
A circle with a tolerance of ± 0.13 mm is used. In addition, when the effective light beam diameter is other than 4 mm, the size of the aperture through hole is proportionally set to a size such that the effective numerical aperture is 0.52.

In FIG. 3, a laser beam having a wavelength of 635 (tolerance of ± 15) nm output from the semiconductor laser 1 is half-reflected by the half mirror 2, collimated by the collimator lens 3 and collimated by the aperture 4. The side is shielded from light and enters the objective lens 6. This objective lens 6
Are supported by a tracking control mechanism and a focus control mechanism (not shown) so as to be displaceable in the tracking direction and the focus direction. Therefore, the laser beam having passed through the objective lens 6 is condensed, passes through the polycarbonate substrate 7 having a thickness of 1.2 mm, and is irradiated onto the signal recording surface 7a of the optical disc. The beam spot diameter formed on the signal recording surface 7a is 1.1 (permissible error ± 0.1) μm.
Further, the reflected beam of the signal recording surface 7 a returns via the substrate 7, the objective lens 6, and the aperture 4, is condensed by the collimator lens 3, half is transmitted by the half mirror 2, and the light receiving sensor 8 The light is focused and irradiated onto the signal detection unit of.

Next, the reproducing operation of the third optical disk having a substrate thickness of 0.6 mm will be described. This thin optical disc 70
4 is reproduced, the aperture 4 is mechanically removed from the optical path, and the thin aspherical aberration correcting means 50 is mechanically inserted on the light source side of the objective lens 6, as shown in FIG. The mechanical insertion / removal mechanism is also not shown, but it is the same as when reproducing the standard-thickness optical disk 7. Further, the removal of the aperture may be performed electrically like the aperture interposing means at the time of reproducing the standard-thickness optical disc 7. The thin aspherical aberration correcting means 50 is also fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation.

In FIG. 4, the laser beam that has passed through the thin aspherical aberration correcting means 50 enters the objective lens 6,
The signal recording surface 70a of the optical disc is focused and irradiated through a polycarbonate substrate 70 having a thickness of 0.6 mm. The beam spot diameter formed on the recording surface is 0.9 (permissible error ± 0.1) μm. Further, the signal recording surface 7
The reflected beam 0a returns via the substrate 70, the objective lens 6, and the thin aspherical aberration correcting means 50,
The light is collected by the collimator lens 3, half of which is transmitted by the half mirror 2, and the signal detecting portion of the light receiving sensor 8 is condensed and irradiated.

Further, in this embodiment, the half mirror 2 is used, but instead of this, a polarization beam splitter and 1 /
A four wave plate may be used. Polarizing beam splitter and 1
The use efficiency of the laser power is improved by using the / 4 wavelength plate. Further, the collimator lens 3 is included in the apparatus of this embodiment.
A reflection mirror (a rising mirror) for changing the optical path by 90 degrees is provided between the objective lens 6 and the objective lens 6, but the illustration is omitted for easy viewing. This raising mirror changes the optical path as described above, thereby making the optical pickup compact. When the polarization beam splitter and the quarter-wave plate are used as described above, the raising mirror may be a prism that also serves as the quarter-wave plate.

Further, in the present embodiment, the aperture 4 and the thin aspherical aberration correcting means 50 are inserted between the collimator lens 3 and the objective lens 6, but between the semiconductor laser 1 and the half mirror 2, the half mirror 2 is provided. And the collimator lens 3 may be provided. Further, although the laser beam wavelength is set to 635 nm in this embodiment, the laser beam wavelength is set to 650 nm.
In the case of (allowable error ± 15) nm, the laser beam spot expands by about 0.1 μm, but it can be replaced sufficiently.

Further, in the present embodiment, the diameter value of the aperture hole of the aperture is determined so that the effective numerical aperture of the objective lens is 0.52 (tolerance ± 0.02). If it is not necessary to reproduce, the value of the diameter of the aperture hole of the aperture may be determined so that the effective numerical aperture of the objective lens is 0.32 to 0.50. In reproducing the second optical disc, the spot diameter may be larger, so that the effective numerical aperture of the objective lens can be reduced. For example, if the effective numerical aperture of the objective lens is 0.35
When (tolerance is ± 0.03), the aberration is smaller than that in the present embodiment, and stable reproduction is possible.

When an objective lens designed to focus at a depth of 1.2 mm as in this embodiment is used,
The reproduction of the optical disk having the substrate thickness of 1.2 mm is more stable than that of the first embodiment. Further, the standard thickness aspherical aberration correcting means 5 used in the first embodiment is also unnecessary. Further, in this embodiment, the shape of the through hole of the aperture is circular, but the through hole may be longer in the tracking direction than in the track direction. Third Embodiment FIG. 5 shows the reproduction of three types of discs of a first optical disc, a second optical disc, and a third optical disc by using an objective lens designed to focus at a position of 1.0 mm in depth. The optical system of the optical reproduction | regeneration apparatus of 3 Example is shown.

First, the reproducing operation of the first optical disk will be described. At the time of reproducing the first optical disc, as shown in FIG. 5, the high density aperture 41 and the standard thickness aspherical aberration correcting means 5 are mechanically inserted. Although this mechanical insertion mechanism is not shown, a normal slide mechanism that moves with a plunger or the like may be adopted, and it is not a special mechanism. The high-density aperture 41 and the standard-thickness aspherical aberration correction means 5 are fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation. Here, the through-hole of the high-density aperture 41 has an effective numerical aperture of 0.52 (tolerance ± ± in the case of an objective lens having a numerical aperture of 0.6 and an effective light beam diameter of 4 mm).
Diameter 3.47 (tolerance ± 0.
13) Make a circle of mm. The effective light beam diameter is 4 mm
In other cases, the size of the through hole of the aperture is set in proportion to this so that the effective numerical aperture is 0.52.

In FIG. 5, the laser beam having a wavelength of 635 (tolerance ± 15) nm output from the semiconductor laser 1 is half-reflected by the half mirror 2 and made into a parallel beam by the collimator lens 3, and the high-density aperture is formed. The outer peripheral side is shielded by 41, the aberration is corrected by the standard thickness aspherical aberration correction means 5, and the light is incident on the objective lens 6. The objective lens 6 is supported by a tracking control mechanism and a focus control mechanism (not shown) so as to be displaceable in the tracking direction and the focus direction. Therefore, the laser beam having passed through the objective lens 6 is condensed, passes through the polycarbonate substrate 71 having a thickness of 1.2 mm, and is irradiated onto the signal recording surface 71a of the optical disc. The beam spot diameter formed on the signal recording surface 71a is 1.1 (permissible error ± 0.1) μ
m. Further, the reflected beam of the signal recording surface 71 a returns via the substrate 71, the objective lens 6, the standard thickness aspherical aberration correcting means 5, and the high density aperture 41, and is condensed by the collimator lens 3. Then, half of the light is transmitted by the half mirror 2, and the signal detection portion of the light receiving sensor 8 is focused and irradiated.

Next, the reproducing operation of the second optical disk will be described. At the time of reproducing the second optical disc, the standard density aperture 42 and the standard thickness aspherical aberration correcting means 5 are mechanically inserted. This mechanical interposition mechanism is also not shown, but it is the same as when reproducing the first optical disc. Also,
The standard density aperture 42 and the standard thickness aspherical aberration correcting means 5 are also fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation. Here, the aperture of the standard density aperture 42 has a numerical aperture of 0.6 and an effective luminous flux diameter of 4
In the case of an objective lens of mm, the diameter is 2.3 (tolerance ± 0.2) mm so that the effective numerical aperture is 0.35 (tolerance ± 0.03). The effective light beam diameter is 4
In the case of other than mm, the size of the through hole of the aperture is set in proportion to this so that the effective numerical aperture becomes 0.35. The other reproducing operation is the same as that of the first optical disc,
The same reference numerals are given to the same portions, and the description of the operation principle and the like will be omitted. The beam spot diameter formed on the signal recording surface is 1.5 (permissible error ± 0.1) μm. As described above, the objective lens designed to focus at the position of 1.0 mm in depth. When using, the spherical aberration is reduced when reproducing an optical disk having a substrate thickness of 1.2 mm, as compared with the case of using an objective lens designed to focus at a position of a depth of 0.6 mm.

Next, the reproducing operation of the third optical disk will be described. When reproducing the third optical disc, the thin aspherical aberration correcting means 50 is mechanically inserted. This mechanical interposition mechanism is also not shown, but it is the same as when reproducing the first optical disc. The standard thickness aspherical aberration correcting means 50 is also fixedly positioned with respect to the optical axis of the laser beam with respect to the pickup body without interlocking with the tracking control operation. Other playback operations are the first
Since it is the same as the optical disc, the same reference numerals are given to the same portions, and the explanation of the operation principle and the like will be omitted. The beam spot diameter formed on the signal recording surface is 0.9 (allowable error ±
0.1) μm As described above, when an objective lens designed to be focused at a depth of 1.0 mm is used, it is designed to be focused at a depth of 1.2 mm. Spherical aberration is reduced when reproducing an optical disk having a substrate thickness of 0.6 mm, as compared with the case of using an objective lens.

In this embodiment, the aperture and the aspherical aberration correcting means are shown as an integrated unit, but the aperture and the aspherical aberration correcting means may be separately inserted / removed. Further, the aperture is not necessarily mechanically inserted, and a liquid crystal shutter may be attached to the transparent plate and the aperture may be electrically formed by the liquid crystal shutter.

Further, in this embodiment, the half mirror 2 is used, but instead of this, a polarization beam splitter and 1 /
A four wave plate may be used. Polarizing beam splitter and 1
The use efficiency of the laser power is improved by using the / 4 wavelength plate. Further, the collimator lens 3 is included in the apparatus of this embodiment.
A reflection mirror (a rising mirror) for changing the optical path by 90 degrees is provided between the objective lens 6 and the objective lens 6, but the illustration is omitted for easy viewing. This raising mirror changes the optical path as described above, thereby making the optical pickup compact. When the polarization beam splitter and the quarter-wave plate are used as described above, the raising mirror may be a prism that also serves as the quarter-wave plate.

Further, in this embodiment, the aperture and aspherical aberration correcting means are inserted between the collimator lens 3 and the objective lens 6, but between the semiconductor laser 1 and the half mirror 2.
It may be between the half mirror 2 and the collimator lens 3. Further, in this embodiment, the laser beam wavelength is set to 635n.
m, but the laser beam wavelength is 650 (tolerance ± 1
5) In the case of nm, the laser beam spot is 0.1
It is expanded by about μm, but it can be exchanged sufficiently.

Further, in this embodiment, the objective lens designed to focus at a position of 1.0 mm in depth was used, but other than 1.0 mm in depth, 1.2 mm deeper than 0.6 mm was used.
An objective lens designed to focus at a position shallower than mm may be used. When an objective lens designed to focus at a depth of 1.2 mm is used, reproduction of an optical disk having a substrate thickness of 1.2 mm becomes stable, and a depth of 0.
When an objective lens designed to be in focus near 6 mm is used, reproduction of an optical disc having a substrate thickness of 0.6 mm is stable.

Further, in this embodiment, the shape of the through hole of the aperture is circular, but the through hole may be longer in the tracking direction than in the track direction. With such a configuration, both the first optical disc and the third optical disc can be reproduced, and the second optical disc can be stably reproduced with little aberration.

[0047]

According to the present invention, the objective lens is designed so that the focus is at a position shallower than the standard thickness substrate and deeper than the thin thickness substrate, and the aperture and the standard thickness are used when reproducing the optical disc of the standard thickness substrate. If an aspherical aberration correcting means is interposed and a thin aspherical aberration correcting means is interposed during reproduction of an optical disc of a thin substrate, an objective designed to focus on the thin substrate during reproduction of an optical disc of standard thickness. Spherical aberration is less than using a lens.

Further, according to the present invention, the objective lens is designed according to the optical disc of the standard thickness substrate, the aperture is interposed when reproducing the optical disc of the standard thickness substrate, and the thin lens is used for reproducing the optical disc of the thin substrate. By interposing aspherical aberration correction means, when playing a standard thickness optical disc,
Less spherical aberration than using an objective designed to focus on a thin substrate.

According to the present invention, a thin high-density optical disc called SD, a standard-thickness high-density optical disc called MMCD, and a standard-thickness standard-density optical disc called CD. Can be played. Further, according to the present invention, SD and MMCD are emitted by a laser beam of about 635 nm.
And you can play the CD.

Further, according to the present invention, SD, MMCD and CD can be reproduced by a laser beam of about 650 nm. Further, according to the present invention, the aperture and the aspherical aberration correction means can be inserted / removed by effectively utilizing the space on the light source side of the objective lens. Further, according to the present invention, when the aperture is inserted by physical movement, the operation inspection is facilitated, and when the aperture is selectively inserted by the electrically formed light-shielding body, abrasion is caused. Assembled easily with few failures.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an optical system when reproducing an optical disc having a standard thickness in a first embodiment.

FIG. 2 is a diagram schematically showing an optical system when reproducing a thin optical disc in the first embodiment.

FIG. 3 is a diagram schematically showing an optical system when reproducing an optical disc having a standard thickness in the second embodiment.

FIG. 4 is a diagram schematically showing an optical system when reproducing a thin optical disc in a second embodiment.

FIG. 5 is a diagram schematically showing an optical system of an apparatus of Example 3;

[Explanation of symbols]

 4 Aperture 41 High Density Aperture 42 Standard Density Aperture 5 Standard Thickness Aspherical Aberration Correction Means 50 Thin Aspherical Aberration Correction Means 6 Objective Lens 7 Standard Thickness Optical Disk 70 Thin Optical Disk 71 Standard Thickness High Density Optical Disk

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shuichi Ichiura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (11)

[Claims] 1. A laser beam is irradiated onto a signal recording surface of an optical disc having a standard thickness substrate or a thin substrate by using an objective lens which is displaced by tracking control, and a laser beam reflected by the signal recording surface is emitted. It is an optical reproducing apparatus provided with an optical means for guiding to a detector, wherein the objective lens is focused at a position shallower than a signal recording surface of an optical disc of a standard thickness substrate and deeper than a signal recording surface of an optical disc of a thin substrate. Is designed to correct the aberration so that the laser beam passing through the objective lens is focused on the signal recording surface of the thin optical disk (hereinafter referred to as thin aspherical aberration correcting means). ), And an aspherical aberration correcting means for correcting the aberration so that the laser beam passing through the objective lens is focused on the signal recording surface of the optical disc of standard thickness. (Hereinafter, referred to as standard thickness aspherical aberration correction means), an aperture that shields the outer peripheral side of the laser beam to reduce the effective numerical aperture of the objective lens, and the aperture and the above-mentioned aperture when reproducing an optical disc of a thin substrate. The aspherical aberration correcting means for standard thickness is removed from the optical path of the laser beam, and the aspherical aberration correcting means for thin type is fixedly inserted in the optical path of the laser beam. An optical system, characterized in that: the aberration correction means is removed from the optical path of the laser beam, and the aperture and the aspherical aberration correction means for standard thickness are fixedly inserted in the optical path of the laser beam. Playback device. 2. A signal recording surface of an optical disc having a standard thickness substrate or a thin substrate is irradiated with a laser beam by using an objective lens that is displaced by tracking control, and a laser beam reflected by the signal recording surface is emitted. An optical reproducing device comprising optical means for guiding to a detector, wherein the objective lens is designed so as to be focused on a signal recording surface of an optical disc of a standard thickness substrate, and a laser beam passing through the objective lens. Is a thin aspherical aberration correcting means for correcting aberration so that the signal recording surface of a thin optical disc is focused, and an aperture for shielding the outer peripheral side of the laser beam to reduce the effective numerical aperture of the objective lens, At the time of reproducing the optical disk of the substrate, the aperture is removed from the optical path of the laser beam, and the thin aspherical aberration correcting means is used for the laser beam light. When the optical disc having the standard thickness is reproduced, the thin aspherical aberration correcting means is removed from the optical path of the laser beam and the aperture is fixedly inserted in the optical path of the laser beam. An optical regenerator characterized by comprising: 3. The optical reproducing device according to claim 1, wherein the aperture and the aspherical aberration correcting unit are inserted / removed on the light source side of the objective lens. 4. The optical reproducing device according to claim 3, wherein the interposing / removing means mechanically interposes / removes the aperture means and the aspherical aberration correcting means. 5. The interleaving / removing means according to claim 3, wherein the interposing / removing means electrically interposes / removes the aperture means, and mechanically interpolates / removes the aspherical aberration correcting means. Optical regenerator. 6. The thin optical disk according to claim 3, wherein the substrate has a thickness of about 0.6 mm.
In the standard thickness optical disc, the substrate thickness is about 1.2.
The optical regenerator is characterized in that it is mm. 7. The wavelength of the laser beam according to claim 6, the wavelength of the laser beam is about 635 nm, the numerical aperture of the objective lens is about 0.6, and the effective of the objective lens by inserting the aperture. A numerical aperture is 0.32 to 0.54, The optical regenerator characterized by the above-mentioned. 8. The wavelength of the laser beam according to claim 6, the wavelength of the laser beam is about 650 nm, the numerical aperture of the objective lens is about 0.6, and the effective of the objective lens by inserting the aperture. A numerical aperture is 0.32 to 0.54, The optical regenerator characterized by the above-mentioned. 9. The optical reproducing device according to claim 7, wherein the effective numerical aperture of the objective lens by inserting the aperture is 0.50 to 0.54. 10. The optical reproducing device according to claim 7, wherein an effective numerical aperture of the objective lens by inserting the aperture is 0.32 to 0.38. 11. The optical reproducing device according to claim 1, wherein the aperture is longer in the tracking direction than in the track direction.