JPH10289473A - Optical head and optical drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mount an objective lens for an optical storage medium (DVD) with a thin substrate and an objective lens for an optical storage medium (CD) with a thick substrate on an objective lens actuator, and to use the optical storage medium as an optical storage medium. An object of the present invention is to provide an optical head capable of performing recording by improving the light use efficiency of an optical system for an optical storage medium having a thick substrate in an optical head for performing compatible reproduction by switching an objective lens in response thereto. SOLUTION: By making the spot diameter on a light receiving element formed according to each objective lens substantially equal, it is possible to record and reproduce on and from optical recording media of various specifications such as CD and DVD. An optical head can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical head and an optical drive device for recording or reproducing information on an optical storage medium such as an optical disk or an optical card by using a laser beam.

[0002]

2. Description of the Related Art Currently available optical disks, for example, in the case of a compact disk (CD), have a disk substrate thickness of 1.2 mm and a track pitch for recording information of 1.6 μm. On the other hand, in recent years, optical disks of various specifications have been proposed as high-density and large-capacity optical storage media. Among them, for example, a digital video disk (DVD) has a disk substrate thickness of 0.6 m.
m, and a track pitch of 0.74 μm is standardized. A laser wavelength light source having a wavelength of 650 nm or 635 nm for the DVD, and a numerical aperture (NA) of 0.6
An optical head for reproducing or recording information using an objective lens has been developed. Further, as the optical head, an optical head having a function of reproducing or recording not only a high-density, large-capacity disc such as the DVD but also an optical disc such as a CD currently on the market, and an optical recording apparatus have been proposed. .

When an optical disk having a different substrate thickness is irradiated with a laser beam using an objective lens optimally designed for a certain substrate thickness, a diffraction-limited spot cannot be formed on an optical disk having a different substrate thickness. In other words, when laser light is irradiated onto a CD disk having a substrate thickness of 1.2 mm using an objective lens optimally designed for a DVD having a substrate thickness of 0.6 mm, spherical aberration increases due to the difference in substrate thickness. Therefore, a satisfactory reproduced signal cannot be obtained.

For this reason, there have been proposed various types of optical heads that can handle optical disks having different substrate thicknesses. As one of the methods, there is a twin lens method in which two objective lenses as shown in FIG. 8 are mounted and the objective lenses are switched according to the difference in substrate thickness. That is, two objective lenses optimally designed for optical disks having respective substrate thicknesses are used.

As shown in FIG. 8, a laser light source 101 and other optical systems (three-beam diffraction grating 102, beam splitter 104, collimator lens 103, mirror 105, concave lens 110, light receiving element 111) are common, and the objective Only the lens is switched and used according to the optical disk having a different substrate thickness. An optical disk 8 shown in FIG. 8 is an optical disk for a DVD having a small substrate thickness.
A state in which recording or reproduction is performed using the D objective lens 106 is illustrated. Also, a CD with a thick substrate
When the optical disk for CD is mounted, the objective lens 107 for CD is arranged on the laser optical axis instead of the objective lens 106.

The DVD objective lens 106 and the CD objective lens 107 are connected to the objective lens biaxial actuator 11.
The optical disk 108 is driven on the optical disk 108 in the surface deflection direction and the radial direction according to the surface deflection, eccentricity, and the like of the optical disk 108.

The specifications of the objective lens are, for example, those having a numerical aperture of 0.6 and a focal length of 3.3 mm for DVD and those having a numerical aperture of 0.38 and a focal length of 3.4 mm for CD.

FIGS. 9A and 9B show light receiving patterns 130a to 130d used for detecting a focus error of the light receiving element 111 and a light spot 117 on the light receiving element at the time of focusing.
FIG. 9A shows a light receiving spot 117 that has been reflected back from a DVD optical disk using a DVD objective lens. FIG. 9B shows a case where a CD objective lens is used and a CD is used.
Light receiving spot 11 reflected back from the optical disk
7 is shown. The ± first-order light diffracted by the three-beam diffraction grating and its light-receiving pattern are omitted in FIG.

[0009]

The optical head of the twin lens system described above has a PP (peak t) of an S-shaped curve of a focus error signal between disks having different substrate thicknesses.
o peak) is designed to have the same detection range (distance). For example, if the focal length of the detection lens is 45 mm, the above two types of objective lens specifications are used, and the focus error signal S-curve detection range for CD is 10 μm, for example. Character curve detection range is also about 10μm
Which is almost the same value. In this case, if the amount of light incident on the light receiving element is the same, the focus error signal sensitivity can be made the same for optical disks having different substrate thicknesses.

However, the effective diameter of the objective lens is about 4 mm for a DVD and 2.6 mm for a CD,
In the twin-lens type CD optical system, the laser light incident on the objective lens is partially kicked by the objective lens. Therefore, considering the coupling efficiency, C
There is a problem that the light use efficiency of the optical head for the CD is reduced because the use for the D becomes about 1/2 of that for the DVD.

[0011]

In order to solve the above-mentioned problems, an optical head and an optical drive device according to the present invention have the following features.

An optical head according to the present invention comprises a plurality of objective lenses having different numerical apertures, and uses a system in which the objective lenses are switched according to the thickness of a substrate to reproduce or record signals. The effective diameter of the objective lens is made substantially equal, and the spot diameter at the time of focusing on a light receiving element formed according to each of the objective lenses is made substantially equal.

An optical drive device according to the present invention is an optical head for switching between a plurality of objective lenses in accordance with the thickness of a substrate, wherein each objective lens has a different numerical aperture and each objective lens has a different numerical aperture. And an optical head having substantially equal spot diameters at the time of focusing on a light receiving element formed according to each of the objective lenses, and an optical head having a focus error signal output from the optical head. It is characterized by comprising means for correcting the signal amplitude.

Further, in this optical drive device, the focus error signal detection sensitivity when the objective lens having a large numerical aperture is used is H, and the focus error signal detection sensitivity when the objective lens having a small numerical aperture is used is L. When the correction constant of the focus error signal detection sensitivity is G, the above-mentioned means that satisfies G = H / L> 1 is provided.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Several embodiments of the present invention will be described below with reference to the accompanying drawings to explain the present invention in further detail. FIGS. 1 and 2 are diagrams showing a schematic configuration of an optical head according to the first embodiment of the present invention. In FIG. 1, a laser beam 15 emitted from a semiconductor laser 1 which is a laser beam emission source passes through a three-beam diffraction grating 2, is reflected by a beam splitter 4, and then passes through a collimator lens 3 to form a parallel beam. The light beam is bent by the mirror 5 in the direction of the optical disk 8, and is condensed by the objective lens 6 on the information track of the optical disk 8 having a small substrate thickness. Optical disk 8
The light reflected by the laser beam enters the beam splitter 4 again through an optical path opposite to that of the laser beam, and generates astigmatism by transmitting through the beam splitter 4.
The light passes through the concave lens 10 and is incident on the light receiving element 11, and a signal is detected. The optical disk 8 having a small substrate thickness is a DVD having a substrate thickness of 0.6 mm and a track pitch of 0.74 μm.
(Digital video disk).
The objective lens 6 is a lens optimally designed in a state where the light passes through the substrate having a thickness of 0.6 mm.

The optical head of the present embodiment is optimally designed with a substrate thickness of 1.2 mm so that a commercially available disk substrate such as a CD having a thickness of 1.2 mm and an optical disk 9 having a track pitch of 1.6 μm can be reproduced. Objective lens 7
It also has. As shown in FIG. 2, for an optical disk 9 with a thick substrate, an objective lens 7 is installed on the laser optical axis in place of the objective lens 6, and the objective lens 7 allows the laser light to be applied to the optical disk with a thick substrate. Light is condensed on nine information tracks. Also in FIG. 2, the laser light emitted from the semiconductor laser 1 follows the same optical path as that described in FIG. 1, and is condensed on the light receiving element 11 to detect a signal.

The objective lenses 6 and 7 include a head holder 13
It is mounted on and is movable by a magnetic two-axis actuator 13a. The head holder 13 is provided with a light receiving element 1 for the surface deflection and eccentricity of the optical disk 8 or 9.
The focus error signal and the track error signal obtained from the intensity of the light focused on the optical disk 8 or the optical disk 8 or 9 extend in the tangential direction of the optical disk 8 or 9 so that the recording surface is always in focus. Driven so as to always follow the track.

FIG. 3 shows a light receiving pattern of the light receiving element 11 as viewed from the concave lens 10 side of the optical head of this embodiment, and laser beams 17, 18, and 19 incident on the light receiving element 11. The optical disk 8 or 9 is placed on the semiconductor substrate 20 mounted on the light receiving element 11 with respect to the optical axis center of the incident laser beam 17.
-Shaped light-receiving pattern (diode element) 30a divided into four in the radial direction X and the tangential direction Y
30d and light-receiving patterns (diode elements) 30 at two positions symmetrical with respect to the tangential direction X outside thereof.
e to 30h are formed by a semiconductor process.
The reflected light 17 from the optical disk is received by the light receiving elements 30a to 30d.
, The reflected light 18 is incident on the light receiving elements 30e and 30f, and the reflected light 19 is incident on the light receiving elements 30g and 30h. 40 h are obtained. The focus error signal, the track error signal, and the information signal can be obtained by performing the calculation according to the following equation using the light receiving signals 40a to 40h. Here, the reflected lights 18 and 19 are laser spots where the ± 1st-order diffracted light generated by the three-beam diffraction grating 2 is reflected by the optical disk and returned.

First, the focus error signal uses an astigmatism method that detects the astigmatism generated by the beam splitter 4, and calculates the following equation (1) for the light receiving signals 40a to 40f. Output by

[0020]

(Equation 1)

The shape of the laser spot 17 condensed on the light receiving patterns 30a to 30d changes as 17a to 17b and 17a to 17c due to astigmatism according to the focus error, and is output from the light receiving patterns 30a to 30d. The intensity of the received light signals 40a to 40d changes. Therefore, the focus error signal 61 can be detected by performing the calculation of the equation (1) in the output circuit 51. Light receiving pattern 3
The laser spot 18 on the light receiving patterns 30a to 30d and the laser spot 18 on the light receiving patterns 30g and 30h are caused by astigmatism generated by transmitting through the beam splitter 4. Although it changes in the same manner as 17c, it is omitted in this figure.

Next, the optical head according to the present embodiment has two circuits 52 as a track error signal output circuit for detecting a tracking deviation for the light emitted from the objective lens to always follow one track with respect to the eccentricity of the optical disk. And 53, and the following equations (2) and (3) are performed in the respective output circuits 52 and 53, and the output signals 62 and 53 are output.
63 is output.

[0023]

(Equation 2)

The signal output by performing the operation of the equation (2) in the first output circuit 52 is a signal 62 used for obtaining a tracking error signal by the phase difference method. Since this calculation is described in the DVD standard or the like, its description is omitted. However, after addition of 40a and 40c and 40b and 40d, an error signal is detected by comparing the respective phases.

The signal output by performing the operation of equation (3) in the second output circuit 53 is
This is a signal 63 used when a tracking error signal is obtained by the differential push-pull method.

Next, an output circuit 54 for detecting information reproduced from the optical disk is configured to perform the operation of the following equation (4), and outputs an information signal 64.

[0027]

(Equation 3)

FIG. 4 shows a light receiving pattern of the light receiving element 11 as viewed from the concave lens 10 side of the optical head of this embodiment, similarly to FIG.
The state at the time of focusing of the laser beam incident on the light receiving element 11 is shown. In FIG. 4A, the ± first-order diffracted lights 18 and 19 and the light receiving patterns 30e to 30h are omitted. FIG. 4A shows a detection state of reflected light from the optical disc 8 having a substrate thickness of 0.6 mm and a track pitch of 0.74 μm shown in FIG. When reproducing or recording data on an optical disk having a small substrate thickness and a narrow track pitch, the tracking error detection method is performed using the phase difference method, and the calculation of the equation (2) is performed using the output circuit 52. A tracking error is detected using the signal 62 output by the control circuit. FIG. 4B is a view similar to FIG.
Substrate thickness 1.2 mm, track pitch 1.6 μ
The state of detection of reflected light from the optical disk 9 of m is shown. In the case of performing reproduction or recording on the optical disk in this case, the differential push-pull method is used as the tracking error detection method, and the output is obtained by performing the calculation of Expression (3) using the output circuit 53. Signal 6
3 to perform tracking error detection. Therefore,
The ± first-order diffracted light (sub-beam) generated by the three-beam diffraction grating 2 is focused on the center of the information track on both sides of the information track tracked by the zero-order light (main beam) on the CD optical disc. It has been adjusted as follows. Note that the phase difference method and the differential push-pull method are known techniques, and there are other detailed documents and the like, and therefore, the details are omitted here.

In the optical head of this embodiment, the laser beam spot diameter 17 formed on the light
The objective lens is designed so that both have the same size. The DVD objective lens 6 has a numerical aperture (NA) of 0.6, a focal length of 3.3 mm, and an effective aperture of about 4 mm. Also, C
The numerical aperture (NA) of the objective lens 7 for D is 0.3
8. The focal length is 5.2 mm and the effective aperture of the lens is about φ.
A 4 mm one is used. Further, the head holder 13
Apertures (diaphragms) 13b and 13c each having a diameter of 4 mm are provided below the objective lens mounting portion at a position where the laser beam passes. When the optical head shown in FIG. 1 or 2 is configured using the objective lens of the present specification, a light receiving spot 17a having substantially the same diameter is obtained on the light receiving element 11 when the optical disk is focused.

FIG. 5 shows an S-shaped curve of a focus error signal detected from the optical head of this embodiment. Coordinate origin O
Indicates a position where the focus of the objective lens is focused on the information track of the optical disc. Further, the distance D1 or D2 of the focus error signal with respect to the peak-to-peak (P-P) P1, Q1 or P2, Q2 indicates a detection distance indicating a range in which the optical head can detect a focus error generated due to a surface shake or the like of the optical disk. It is. Also, the signal amplitude h
Is defined as the focus error signal sensitivity. The focus error signal sensitivity of the DVD optical system is h / D2, and the focus error signal sensitivity of the CD optical system is h / D1. In the optical head of this configuration, when the specification of the objective lens and the detection distance of PP of one of the focus error signals of CD and DVD are determined, the other focus error signal P-
The P detection distance, the astigmatic difference on the light receiving element side, and the spot diameter on the light receiving element are determined. For example, if the combined focal length of the system constituted by the collimator lens 3 and the concave lens 10 is 55
mm, the detection distance D1 of the PP of the focus error signal for CD is 15 μm, the detection distance D2 of the PP of the focus error signal for DVD is 6 μm, and the spot diameter on the light receiving element is 120 μm.

Assuming that the same amount of laser light returns from the DVD and CD optical disks to the light receiving element, the detection sensitivity of the focus error signal has a difference of 1/6 to 1/15. That is, the ratio of DVD to CD is 1: 0.4, and the sensitivity of CD is 40% of the sensitivity of DVD.

Therefore, the optical drive equipped with the optical head according to the present embodiment is provided with a gain switching circuit 55 as a signal amplitude correction means at the subsequent stage of the focus error signal output circuit 51 as shown in FIG. The analog switch 55a is turned on / off by the disc discrimination signal 55b. The gain switching circuit is used to make correction so that the focus error detection sensitivities of CD and DVD become equal. That is, the detection sensitivity is corrected by multiplying the focus error signal amplitude of the CD by 2.5.

On the other hand, the depth of focus of the objective lens is inversely proportional to the square of the numerical aperture of the objective lens. In the case of this embodiment, DV
The D to CD ratio is 0.6 to the square of 1: 0.38 to the square and about 1: 2.5. The depth of focus of the objective lens is 2.5 for the CD optical system with respect to the DVD optical system 1.
According to an experiment, the correction gain of the detection sensitivity of the focus error signal for CD is 1 to 3.0, preferably 1.8 to 2.
8, more preferably from 2.2 to 2.8.

On the other hand, the loop gain of the focus servo system is determined in consideration of the reflectivity of the optical disk, the read power, the number of rotations of the optical disk, and the like. In the optical drive device of this embodiment, the numerical aperture of the objective lens is further increased. The determination is made in consideration of the correction of the detection sensitivity due to the difference.

Although the above optical head uses the differential push-pull method as a track error detection method for a CD, it is also possible to realize the mainstream three-beam method by performing the following calculation with a head that does not perform recording. Of course it is possible.

[0036]

(Equation 4)

In the optical head described above, since the effective diameters of the objective lenses are substantially equal, there is almost no light loss at the objective lens portion, and the light use efficiency of the optical system for CD can be improved.

The signal S / N ratio of the CD optical system is improved by improving the light use efficiency of the CD optical system.
An optical head capable of responding to higher-speed CD reproduction can be provided.

Further, when recording is performed on an optical disk by a CD optical system, it is possible to output a recording power with a higher light output from the objective lens. For example, a high-power laser having a wavelength of 650 nm or 635 nm is mounted as a semiconductor laser, and a numerical aperture of 0.42 is used as a CD objective lens.
By mounting a lens having a focal length of 4.7 mm on the objective lens actuator, a CD-E (Erasa) can be obtained.
ble-CD) disk, and by switching the objective lens to a DVD objective lens, it becomes possible to perform recording and reproduction on a DVD disk. That is, D
VD-RAM, CD-E disk recording / reproduction, and D
An optical head capable of reproducing a VD-ROM and a CD disc can be provided.

(Embodiment 2) FIG. 7 is a view showing a schematic configuration of an optical head according to Embodiment 2 of the present invention. In FIG. 7, a laser beam 15 emitted from a semiconductor laser 1 which is a laser beam emission source is converted into a parallel beam by transmitting through a three-beam diffraction grating 2 and then through a collimator lens 3, and is transmitted through a phase variable filter 12. The light passes through, is reflected by the beam splitter 14, is bent in the direction of the optical disk 8 by the mirror 5, and is condensed by the objective lens 26 on the information track of the optical disk 8 having a small substrate thickness. Optical disk 8
The light reflected by the laser beam enters the beam splitter 14 again through the optical path opposite to the laser beam, and the laser beam 16 transmitted through the beam splitter 14 transmits through the signal lens 21 and then transmits through the cylindrical lens 22. As a result, astigmatism is generated, the light passes through the slit 23, enters the light receiving element 11, and a signal is detected. The optical disk 8 having a small substrate thickness is a DVD (digital video disk) having a substrate thickness of 0.6 mm and a track pitch of 0.74 μm.
Optical disk. The objective lens 26 is a lens that is optimally designed in a state where the light passes through the substrate having a thickness of 0.6 mm.

The optical head of this embodiment is also optimally designed with a substrate thickness of 1.2 mm so that a commercially available disk substrate such as a CD having a thickness of 1.2 mm and a track pitch of 1.6 μm can be reproduced. Objective lens 2
7, the objective lens 27 is set on the laser optical axis instead of the objective lens 26 for the optical disc 9 having a large substrate thickness, as in the first embodiment. The laser beam is condensed on the information track of the optical disk 9 having a large substrate thickness (not shown in this example).

In the optical head of this embodiment, a high-power laser having a wavelength of 780 nm is mounted on the semiconductor laser 1. The objective lens 26 having a numerical aperture of 0.65 is mounted on the objective lens actuator and used as a DVD objective lens. Further, the phase variable filter 12 has a function of adding a phase to a part of the laser light, and is used for forming an optical super-resolution spot on the optical disc 8.
Laser light wavelength 780 nm, objective lens numerical aperture 0.6
Using the optical system of this example having five specifications, the wavelength 650 of the laser light
The above optical super-resolution is added so that a spot diameter of about 0.9 μm, which is equivalent to that of a DVD specification optical head having a nm and a numerical aperture of an objective lens of 0.6, is formed on a recording track of an optical disk. Further, the slit 23 is used for removing a component which is generated by adding the above-mentioned optical super-resolution and degrades the reproduction characteristics, and shields a part of the laser light incident on the light receiving element 11.

In the optical head of this embodiment, the objective lens is designed so that the laser beam spot formed on the light receiving element 11 has the same diameter for both DVD and CD. The DVD objective lens 26 has a numerical aperture (NA) of 0.65, a focal length of 3.1 mm, and an effective aperture of about 4 mm. Also, C
The numerical aperture (NA) of the objective lens 27 for D is 0.4
5. The focal length is 4.4 mm, and the effective aperture of the lens is about φ.
A 4 mm one is used. Further, the head holder 13
Apertures (diaphragms) 13b and 13c each having a diameter of 4 mm are provided below the objective lens mounting portion at a position where the laser beam passes. When the optical head shown in FIG. 7 is configured using the objective lens of this specification, when the optical disk is focused on the light receiving element 11, as in FIGS. 4A and 4B described in the first embodiment,
The light receiving spots 17a having the same diameter are obtained.

The CD objective lens 27 is set so as to satisfy the specification for recording on a recordable CD with the optical super-resolution added, and has a laser beam wavelength of 780 nm and a numerical aperture of 0. The spot diameter of about 1.3 μm, which is the same as that of the optical head constituted by No. 5, is set to be formed on the recording track of the optical disk.

In the optical head of this configuration, when the specification of the objective lens and the detection distance of the PP of one of the focus error signals of CD and DVD are determined, the other focus error signal PP is determined by the magnification of the optical system. The P detection distance, the astigmatic difference on the light receiving element side, and the spot diameter on the light receiving element are determined. For example, if the focal length of the signal lens 21 is 5
5 mm, the focus error signal P for CD shown in FIG.
Assuming that the detection distance D1 of −P is 15 μm, the detection distance D2 of PP of the focus error signal for DVD is 7 μm,
The spot diameter on the light receiving element is 170 μm.

Assuming that the same amount of laser light returns from the DVD and CD optical discs to the light receiving element, the detection sensitivity of the focus error signal will differ by a ratio of 1/7 to 1/15. That is, the ratio of DVD to CD is 1: 0.47, and the sensitivity of CD is 47% of the sensitivity of DVD.

Therefore, even in the optical drive equipped with the optical head of the present embodiment, a gain switching circuit 55 is provided as a signal amplitude correction means at the subsequent stage of the focus error signal output circuit 51 as shown in FIG. The analog switch 55a is turned on / off by the disc discrimination signal 55b. Using the above gain switching circuit, CD
And the focus error detection sensitivity of the DVD and the DVD are made equal. That is, the detection sensitivity is corrected by multiplying the CD focus error signal amplitude by 2.1 times.

On the other hand, the depth of focus of the objective lens is inversely proportional to the square of the numerical aperture of the objective lens. In the case of this embodiment, DV
The D to CD ratio is 0.6 to the square of 1: 0.45 to the square and about 1: 1.8. The depth of focus of the objective lens is 1.8 for the CD optical system with respect to the DVD optical system 1.
According to an experiment, the correction gain of the detection sensitivity of the focus error signal for CD is 1.0 to 3.0, preferably 1.8 to 3.0.
It turned out that it is better to set it to 2.8, more preferably 1.8 to 2.5.

On the other hand, the loop gain of the focus servo system is determined in consideration of the reflectivity of the optical disk, the read power, the number of rotations of the optical disk, and the like. In the optical drive device of this embodiment, the numerical aperture of the objective lens is further increased. The determination is made in consideration of the correction of the detection sensitivity due to the difference.

In the optical head described above, since the effective diameters of the objective lenses are substantially equal, there is almost no light loss at the objective lens portion, and the light use efficiency of the optical system for CD can be improved.

The signal S / N ratio of the CD optical system is improved by improving the light use efficiency of the CD optical system.
An optical head capable of responding to higher-speed CD reproduction can be provided.

Further, when recording is performed on an optical disk by a CD optical system, it is possible to output a recording power with a higher light output from the objective lens. In this example, by using the optical head having the above specification, the CD-R (Re
An optical head capable of recording and reproducing on a cordable-CD) disk is realized. CD-E (E
(recordable-CD) disk, and recording / reproduction on a DVD disk is also possible by switching the objective lens to a DVD objective lens.

That is, DVD-RAM, CD-R, CD
-E disk recording / reproduction, DVD-ROM, CD
An optical head capable of reproducing a system disk can be provided.

[0054]

As described above, the optical head of the present invention can be used for detecting signals from an optical disk having a small substrate thickness by using an objective lens optimally designed for an optical disk having a small substrate thickness. Using an objective lens optimally designed for an optical disc with a thick spot diameter and a thick substrate,
By making the spot diameters on the light receiving element for detecting signals from an optical disk having a thick substrate substantially equal to each other, the light use efficiency of the optical system for an optical disk having a thick substrate can be improved.

The signal S / N ratio of the CD optical system is improved by improving the light use efficiency of the CD optical system.
An optical head capable of responding to higher-speed CD reproduction can be provided.

Further, since the optical utilization efficiency of the optical disk optical system having a small substrate thickness of the optical head and the optical system for the optical disk having a large substrate thickness are substantially equal, by mounting a laser light source having a large optical output, either substrate can be mounted. Recording can be performed even on a disk having a large thickness. For this reason,
An optical head capable of recording and reproducing information on optical recording media of various specifications such as a CD and a DVD can be provided. Further, in the optical drive device equipped with the optical head of the present invention, it is possible to automatically switch and process optical disks having different specifications such as a difference in the substrate thickness of the optical disk. An optical drive device capable of recording and reproducing data on and from a recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an optical head according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of an optical head according to a first embodiment of the present invention.

FIG. 3 is a plan view showing a light receiving pattern of a light receiving element of the optical head according to the first embodiment of the present invention.

FIG. 4 is a plan view showing a light receiving pattern of a light receiving element of the optical head according to the first embodiment of the present invention.

FIG. 5 is a diagram showing an S-shaped curve of a focus error signal output from the optical head of the present invention.

FIG. 6 is a diagram showing a schematic circuit configuration for calculating a focus error signal of the optical head of the present invention.

FIG. 7 is a diagram illustrating a schematic configuration of an optical head according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a schematic configuration of a conventional optical head.

FIG. 9 is a plan view showing a light receiving pattern of a light receiving element of a conventional optical head.

[Explanation of symbols]

1, 101 semiconductor laser 2, 102 three-beam diffraction grating 3, 103 collimator lens 4, 14, 104 beam splitter 5, 105 mirror 6, 26, 106 objective lens for thin substrate 7, 27, 107 · · · Objective lens for thick substrate · · · Optical disk for DVD · · · Optical disk for CD 10, 110 · · · Concave lens 11, 111 · · · Light receiving element 12 · · · Phase variable filter 13, 113 · · · Head holder 13a, 113a ··· Biaxial actuator 13b, 113b ··· Aperture for DVD objective lens 13c, 113c ··· Aperture for CD objective lens 15, 16 ··· Laser light 17a, 117 ··· Laser spot at focusing on light receiving element 17b, 17c... Laser spot at the time of defocus on light receiving element 18, 19. Spot 20 Semiconductor substrate 21 Signal lens 22 Cylindrical lens 23 Slit 30a-h, 130a-d Light-receiving pattern 40a-h Light-receiving element output signal 51 Focus error signal output circuit 52 ··· First track error signal output circuit 53 ··· Second track error signal output circuit 54 ··· Information signal output circuit 55 ··· Gain switching circuit 55a ··· Analog switch 55b ··· Discrimination signal 61 ··· Focus error signal 61a Focus error signal after gain adjustment 62 First track error signal 63 Second track error signal 64 Information signal

Claims (3)

[Claims] 1. An optical head for reproducing or recording a signal, wherein a plurality of objective lenses having different numerical apertures are provided and the objective lenses are switched according to a substrate thickness. An optical head wherein the diameters are made substantially equal, and the spot diameters at the time of focusing on light receiving elements formed according to the respective objective lenses are made substantially equal. 2. An optical head for switching between a plurality of objective lenses according to a substrate thickness, wherein the numerical aperture of each of the objective lenses is made different, and the effective diameter of each of the objective lenses is made substantially equal; An optical head having a spot diameter substantially equal at the time of focusing on a light receiving element formed according to each of the objective lenses is mounted, and means for correcting a signal amplitude of a focus error signal output from the optical head is provided. An optical drive device. 3. The focus error signal detection sensitivity when using the objective lens with a large numerical aperture is H, the focus error signal detection sensitivity when using the objective lens with a small numerical aperture is L, and the focus error signal detection sensitivity. Wherein the correction means satisfies the following condition: G = H / L> 1.
An optical drive device according to claim 1.