JPH11134702A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device capable of interchangeably reproducing three kinds of optical disks different in a distance from a substrate surface to a signal recording surface and in recording density. SOLUTION: A laser beam generation means 1 containing a first element 1a generating a laser beam of a wavelength 780 nm, a second element 1b generating a laser beam of a wavelength 635 nm and a third element 1c generating a laser beam of a wavelength 430 nm is used for a light source, the first, second and third elements are selectively driven by a laser drive circuit 11 and the laser beam of the wavelength suited to a loaded optical disk is emitted onto signal recording surfaces 8a, 8b, 8c. Further, an optical means 6 diffracting the laser beam at a diffraction angle based on the wavelength of the laser beam and correcting the deviation in an optical axis of a reflected beam on the signal recording surfaces 8a, 8b, 8c is provided on this side of a photodetector 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device for reproducing a plurality of types of optical disks having different substrate thicknesses and recording densities.

[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 disk, focus servo and tracking servo are performed on a pickup objective lens to irradiate a pit row on a signal recording surface with a laser beam to reproduce a signal. Recently, the recording density for recording a long moving image has been increasing.

[0003] For example, the same 12 cm diameter as a CD-ROM
DVDs that record 4.7 Gbytes of information on one side of an optical disc are now on the market. The thickness of a DVD disk is about 0.6 mm, and by bonding both sides to each other, information of 9.4 Gbytes can be recorded by one sheet. Further, the wavelength of a laser beam used for signal reproduction has been shortened, and a blue laser having a wavelength of 400 to 480 nm, which is shorter than the currently used laser beam of a wavelength of 635 nm, has been developed. Therefore, in the future,
It is expected that a next-generation DVD having smaller pits and a narrower track pitch than the current DVD will be put into practical use, and the distance from the substrate surface to the signal recording surface will be 0.6 mm or less.

[0004] In view of these circumstances, CD, D
Obviously, an optical pickup for compatible playback of VD and next-generation DVD is required. In the case of the former, the distance from the substrate surface to the signal recording surface is 1.2 (allowable range: 1.1 to 1.3) mm between the CD and the DVD.
In the latter case, 0.6 (allowable range: 0.55 to 0.65)
mm. The patent applicant has reported that a substrate thickness of 1.2
Japanese Patent Application No. 8-170276 discloses a technology capable of compatible reproduction of an optical disk having a diameter of 0.6 mm and a diameter of 0.6 mm, which combines a liquid crystal that selectively rotates a polarization plane of a laser beam and a polarization filter that transmits only a laser beam polarized in a specific direction. A method is disclosed.

[0005]

However, Japanese Patent Application No. Hei 8-1
In the method disclosed in U.S. Pat.
Compatible reproduction between VD and CD is possible, but if one laser beam is used and the distance from the substrate surface to the signal recording surface is different for three types,
There is a problem that it is difficult to perform compatible reproduction. Also, since the pit length and the track pitch are greatly different from CD, DVD, and next-generation DVDs, Japanese Patent Application No. Hei.
In the technology disclosed in Japanese Patent No. 170276, CDs, DVDs,
It is difficult to focus the laser beam in conformity with the pit length and track pitch of the next generation DVD.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical pickup device capable of compatible reproduction of three types of optical disks having different distances from the substrate surface to the signal recording surface and different recording densities.

[0007]

According to a first aspect of the present invention, an optical pickup device guides a reflected light of a laser beam having a different wavelength on a signal recording surface to a photodetector after correcting an optical axis shift based on the wavelength. It is an optical pickup device including an optical element. According to the first aspect of the invention, since the optical axis shift of the laser beams having different wavelengths can be corrected, the reflected light of the laser beams having different wavelengths on the signal recording surface can be detected by one photodetector.

According to another aspect of the present invention, there is provided an optical pickup device, comprising: a laser beam generating means for selectively generating laser beams having different wavelengths; And an optical element that corrects the optical axis shift based on the wavelength and guides the corrected optical axis to the photodetector.

According to the second aspect of the present invention, laser light having different wavelengths can be selectively generated by the laser light generating means, and the reflected light of the generated laser light having different wavelengths on the signal recording surface can be generated. Since the optical axis shift can be corrected, the laser light selectively generated can be detected by one photodetector. An optical pickup device according to a third aspect is the optical pickup device according to the second aspect, wherein the laser light generating means includes a plurality of semiconductor elements.

According to the third aspect of the present invention, laser beams having different wavelengths can be selectively generated from a plurality of semiconductor elements, so that laser beams having different wavelengths can be generated with good controllability. Further, the optical pickup device according to claim 4 irradiates a laser beam to a signal recording surface with an objective lens according to a reproduction condition of a recording medium and guides reflected light from the signal recording surface to a photodetector. A first element for generating a first laser light having a first wavelength, a second element for generating a second laser light having a second wavelength different from the first wavelength, A laser light generating means including a third element for generating a third laser light having a third wavelength different from the wavelength and the second wavelength, and a first element and a second element in the laser light generating means And a laser driving means for selectively driving the third element, and receiving the first laser light, the second laser light, and the third laser light reflected on the signal recording surface, and receiving the reflected light. Light that corrects optical axis deviation based on wavelength and guides the light to a photodetector An optical pickup apparatus including the device.

According to the fourth aspect of the present invention, the three elements having different wavelengths from the three elements according to the reproduction condition of the recording medium.
Laser light is selectively generated, and the optical axis deviation of the reflected light of the three laser lights at the signal recording surface is corrected, so that the laser light having a wavelength suitable for reproducing the mounted recording medium can be controlled. The laser light can be generated well, and the reflected light of the generated laser light on the signal recording surface can be detected by one photodetector. As a result, compatible playback of recording media having different playback conditions becomes possible.

An optical pickup device according to a fifth aspect is the optical pickup device according to the fourth aspect, wherein the optical element corrects the optical axis shift of the reflected light by diffraction of light. According to the fifth aspect of the present invention, the deviation of the optical axis can be corrected by using the diffraction phenomenon of light, so that laser beams having different wavelengths can be detected with substantially the same intensity in consideration of diffraction efficiency.

An optical pickup device according to a sixth aspect is the optical pickup device according to the fifth aspect, wherein the optical element comprises a triangular lattice. According to the sixth aspect of the present invention, since the optical element can be formed by a triangular lattice, the production of the optical element is facilitated.

According to a seventh aspect of the present invention, in the optical pickup device according to the fifth or sixth aspect, the optical element is such that the wavelength of the laser beam is λ, the pitch of the grating is p, and the reflected light is An optical pickup device that satisfies the relationship of sin θ = λ / p, where θ is the angle diffracted by the optical element. According to the seventh aspect of the present invention, the diffraction angle can be set by the wavelength of the laser light and the pitch of the grating of the optical element, so that laser lights having different wavelengths can be focused on one point.

According to an eighth aspect of the present invention, in the optical pickup device according to the seventh aspect, the photodetector has a distance L in the optical axis direction between the optical element and the photodetector.
When the angle at which the reflected light is diffracted by the optical element is θ,
The optical pickup device is provided at a position shifted in a direction perpendicular to the optical axis by a distance determined by Ltan θ. According to the invention described in claim 8, since the photodetector is provided at a position separated from the optical axis by a predetermined distance in a direction perpendicular to the optical axis, a compact optical pickup device can be manufactured.

According to a ninth aspect of the present invention, in the optical pickup device according to any one of the fifth to eighth aspects, the distance between the first element and the second element is equal to or less than the first distance. The distance between the second element and the third element corresponds to the optical axis deviation between the first laser light and the second laser light, and the optical axis deviation between the second laser light and the third laser light. The optical pickup devices are provided correspondingly.

According to the ninth aspect of the present invention, the first, second, and third elements can be installed in accordance with the optical axis shift of the laser beams having different wavelengths, so that the laser beams having different wavelengths can be surely provided. Can be detected by one photodetector. The optical pickup device according to claim 10 is:
The optical pickup device according to claim 9, wherein:
In the optical pickup device, the light emitting points of the second and third elements are shifted from each other by a predetermined distance in the optical axis direction.

According to the tenth aspect of the invention, since the light emitting points of the first, second, and third elements are shifted in the optical axis direction, the shift of the optical path length can be corrected. According to an eleventh aspect of the present invention, in the optical pickup device according to any one of the fifth to tenth aspects, the laser driving unit is configured to control the first or the second type according to the substrate thickness or the recording density of the recording medium. An optical pickup device for selectively driving the second and third elements.

According to the eleventh aspect of the present invention, the first, second, and third recording media are selected according to the substrate thickness or recording density of the recording medium.
In addition, since the third element is selectively driven, compatible reproduction of recording media having different substrate thicknesses and recording densities is easy.

[0020]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a CD, DVD, and next-generation DVD (hereinafter, referred to as high-density
VD ". ) Shows the standard values and the reproduction conditions. The CD substrate thickness is 1.2 (allowable error ± 0.1) mm, the shortest pit length is 0.83 (allowable range: 0.80 to 0.90) μm, and the track pitch is 1.6 (allowable error ± 0). .1) μm, wavelength 780
The reflectance for a laser beam of 70 nm is 70% or more, the spot diameter of the laser beam during reproduction is 1.51 (allowable error ± 0.2) μm, and the numerical aperture of the objective lens is 0.45.
(Tolerance ± 0.05), reproduction laser beam wavelength is 78
0 (allowable error ± 15) nm. The substrate thickness of the DVD is 0.6 (tolerance ± 0.05) mm, the shortest pit length is 0.40 (tolerance ± 0.2) μm, and the track pitch is 0.74 (tolerance ± 0.05). ) The reflectivity with respect to a laser beam having a wavelength of 635 nm and a wavelength of 635 nm is 70% or more, and the spot diameter of the laser beam during reproduction is 0.92 (allowable error ±
0.2) μm, numerical aperture of the objective lens is 0.6 (tolerance ±
0.05), and the reproduction laser beam wavelength is 635 (allowable error ± 15) nm. Further, the substrate thickness of the high-density DVD is 0.3 (allowable range: 0.1 to 0.6) mm, the shortest pit length is 0.27 (allowable error ± 0.05) μm, and the track pitch is 0.50 ( Tolerance ± 0.08) μm, wavelength 43
The reflectance for a laser beam of 0 nm is 70% or more, the spot diameter of the laser beam during reproduction is 0.62 (allowable range: 0.48 to 0.75) μm, and the numerical aperture of the objective lens is 0.60 ( The tolerance is ± 0.05), and the reproducing laser beam wavelength is 430 (allowable range: 400 to 480) nm.

FIG. 2 shows the configuration of an optical pickup device 10 for performing compatible reproduction of a CD, DVD, and high-density DVD. The optical pickup device 10 is 780 (allowable error ± 1).
5, the same shall apply hereinafter. ) The first semiconductor lasers 1a and 635 that generate laser light of nm (tolerance ± 15, the same applies hereinafter).
a second semiconductor laser 1b for generating a laser beam of 1 nm, a laser beam generating means 1 including a third semiconductor laser 1c for generating a laser beam of 430 nm (tolerance ± 15, the same applies hereinafter), and a laser beam. A collimator lens 2 for converting the laser light generated by the generation means 1 into parallel light; a half mirror 3 for transmitting the laser light from the collimator lens 2 and reflecting the reflected light from the recording medium 8 in a right angle direction; An objective lens 4 for condensing the laser light, a condensing lens 5 for condensing the laser light reflected from the recording medium 8, a first semiconductor laser 1a, a second semiconductor laser 1b, and a third semiconductor laser 1c. The optical element 6 that corrects the deviation of the optical axis of the laser light generated by the reflection light on the recording medium 8 and guides the deviation to the photodetector 7, and the photodetector 7 that detects the reflection light on the recording medium 8 Prepare.

The first semiconductor laser 1a, the second semiconductor laser 1b, and the third semiconductor laser 1c in the laser beam generating means 1 are selectively driven by the laser drive circuit 11 according to the recording medium mounted. . That is, the substrate thickness is 1.2 m
When reproducing a CD of m, a semiconductor laser 1a for generating a laser beam having a wavelength of 780 nm
When reproducing VD, the semiconductor laser 1b that generates laser light having a wavelength of 635 nm is selectively driven, and when reproducing high-density DVD having a substrate thickness of 0.3 mm, the semiconductor laser 1c is selectively driven.

The objective lens 4 emits a laser beam having a wavelength of 430 nm at a distance of 0.3 mm from the substrate surface to the signal recording surface.
The numerical aperture is set to 0.65 (permissible error ± 0.05) so as to converge and irradiate the signal recording surface of a high-density DVD of mm. Wavelength 635 for objective lens with numerical aperture 0.65
0.6m from the substrate surface when laser light of nm
When a laser beam having a wavelength of 780 nm is focused on the position m, the laser beam is focused on a position 1.2 mm from the substrate surface. Therefore, in the optical pickup device 10, it is possible to perform compatible reproduction of recording media having different distances from the substrate surface to the signal recording surface by merely changing the wavelength of the laser light without shielding the outer peripheral portion of the laser light at all.

The details of the optical element 6 and the positional relationship between the optical element 6 and the photodetector 7 will be described with reference to FIG. The optical element 6 has a structure in which a triangular lattice 63 is formed in a cross section on one main surface 62 of a flat glass plate 61, and the incident laser light is formed at a predetermined angle in accordance with the wavelength. It has the function of diffracting and transmitting. That is, if the wavelengths of the laser light incident on the optical element 6 are λ1, λ2, λ3, and the angles at which the respective laser lights are diffracted by the optical element 6 are θ1, θ2, and θ3, the laser light of these three wavelengths Focuses on the focal point 70 of the photodetector 7. Further, referring to FIG. 4, the pitch p of the triangular grid 63 is about 10 μm, and the height t of the triangular grid is about 0.5 μm. Here, the wavelength of the laser light incident on the optical element 6 is λ, and the angle at which the laser light is diffracted by the optical element 6 (the normal direction of the optical element 6 and the direction in which the diffracted laser light travels). (Angle) is θ, a relationship of sin θ = λ / p is established. Therefore, the angle of diffraction by the optical element 6 is determined by the wavelength of the incident laser beam and the pitch of the grating 63 of the optical element 6. The wavelengths of the laser light incident on the optical element 6 are λ1, λ2, and λ.
3. The diffraction angles diffracted by the optical element 6 are:
θ1, θ2, θ3, focal point 7 of optical element 6 and photodetector 7
The distance between the laser beam having the wavelength λ1 and the converging point 70 is c1, the distance between the optical axis of the laser beam having the wavelength λ2 and the converging point 70 is c2, The distance between the optical axis of the laser light and the focal point 70 is c3, the deviation of the optical axis between the laser light of the wavelength λ1 and the laser light of the wavelength λ2 is a, and the light of the laser light of the wavelength λ2 and the laser light of the wavelength λ3. Axis shift b
Then, c1 = L × tan (sin ⁻¹ (λ1 / p)) (1) c2 = L × tan (sin ⁻¹ (λ2 / p)) (2) c3 = L × tan (Sin ^-1 (λ3 / p)) (3) a = c2-c1 (4) b = c3-c2 ... ... (5) holds. λ1 = 430 nm, λ2 = 635 nm, λ
Substituting 3 = 780 nm, L = 5000 μm, and p = 10 μm into the above equations (1), (2), and (3), c1 =
215.2 μm, c2 = 318.1 μm, c3 = 39
1.2 μm, and a = 10 from the above equations (4) and (5).
2.9 μm and b = 73.1 μm. Therefore, the wavelength 4
The emission point of the 30 nm laser light and the emission point of the 635 nm laser light are 102.9 μm, and the emission point of the 635 nm wavelength laser light and the emission point of the 780 nm wavelength are 73.1 μm.
By shifting, the laser beam having a wavelength of 430 nm, the laser beam having a wavelength of 635 nm, and the laser beam having a wavelength of 780 nm reflected by the recording medium can be detected at the converging point 70 of the photodetector 7.

The features of the optical element 6 according to the present invention are as follows.
The point is that the diffraction efficiency of the diffracted light by the optical element 6 can be determined by the height of the grating 63 of the optical element 6, the refractive index of the grating 63, and the wavelength of the laser light. In a normal diffraction grating, the laser light after passing through the diffraction grating has a predetermined intensity ratio between the zero-order light and the ± first-order light.
3, the height of the grating 63, the grating 63
By changing the refractive index of the light, diffracted light having a desired intensity can be extracted. Referring again to FIG. 4, the diffraction efficiency of laser light by the optical element 6 will be described. In the present invention, the primary light 65 is extracted from the incident light 64. Therefore, the diffraction efficiency shown here is the incident light 6
This means the diffraction efficiency of the primary light 65 with respect to 4. The wavelength of the laser beam is λ, the height of the grating 63 of the optical element 6 is t,
Assuming that the refractive index of the grating 63 is n, the diffraction efficiency k of the primary light 65 is as follows: k = [[sin (πa)] / πa] ² (6) Here, a = ((n−1) × t / λ−1). t = 0.489 μm, n = 2.3, wavelength λ = 4
When the diffraction efficiency is calculated by substituting 30 nm, 635 nm, and 780 nm into the equation (6), when the diffraction efficiency of the primary light of the laser light having the wavelength of 635 nm is set to be 100%, the diffraction efficiency of the laser light having the wavelength of 430 nm is 1%. The diffraction efficiency of the next light is 9
The diffraction efficiency of the primary light of the laser beam having a wavelength of 2.6% and a wavelength of 780 nm is 98.9%. Therefore, wavelength 430 nm, 63
Since the diffraction efficiency of the primary light by the optical element 6 for the laser light of 5 nm and 780 nm is 0.9 or more, there is no problem for the light detection.

With reference to FIG. 5, the arrangement of the first, second and third elements in the laser beam generating means 1 will be described. FIG. 5A is a diagram of the laser light generating means 1 as viewed from a direction perpendicular to the paper surface of FIG. 780nm wavelength
Element 1a that generates laser light of wavelength 635 nm
Element 1b that generates laser light of a wavelength of 43
The third element that generates the laser light of 0 nm is mounted on the base 50, and the distance between the elements is such that laser light having different wavelengths generated from each element is applied to the photodetector 7 by the optical element 6. The value corresponds to the amount of deviation of the optical axis of the laser light so that it can be focused on one point. That is, the first element 1
The distance between the light emitting point a and the light emitting point of the second element 1b is 73.1 μm, which is the shift amount of the optical axis between the laser light having the wavelength of 780 nm and the laser light having the wavelength of 635 nm.
The distance between the light emitting point of b and the light emitting point of the third element 1c is 102.9 μm, which is the shift amount of the optical axis between the laser light having the wavelength of 635 nm and the laser light having the wavelength of 430 nm. Although it is usually difficult to set the light emitting points of the two elements to such a small value, the first, second, and third elements 1a,
When 1b and 1c are created, the gap between the elements can be easily set small by shifting the light emitting point from the center of the element.

FIG. 5B shows the laser beam generating means 1 as viewed from the collimator lens 2 in FIG. Here, for example, an arrow 51 indicates a tracking direction, and an arrow 52 indicates a track direction. In FIG. 5B, the second element 1 that generates a laser beam having a wavelength of 635 nm
The light emitting point of b is set in the tracking direction 51 and the track direction 52
And a third element 1c that generates a laser beam with a wavelength of 430 nm on both sides of the second element 1b in the tracking direction 51 with the second element 1b as a center. Has been arranged. First,
Although the arrangement of the second and third elements has been described as being in the tracking direction, the arrangement is not limited to this, and they may be arranged in the track direction.

More preferably, the arrangement of the first, second and third elements is as shown in FIG. In the arrangement shown in FIG. 6, the arrangement positions of the first, second, and third elements are displaced in the traveling direction 53 of the laser light. Strictly speaking, since the focal lengths of the collimator lens 2 and the objective lens 4 differ depending on the wavelength of the laser light, the light reflected on the recording medium 8 is diffracted by the optical element 6 and is reflected on the photodetector 7. This is because, when light is focused on one point, the focal length is slightly shifted between laser lights having different wavelengths. Therefore, in the present invention,
The emission point of the third element 1c that generates the laser light of 430 nm is made coincident with the end face 54 of the laser light generation means 1, and the wavelength 6
The second element 1b that generates a laser beam of 35 nm is shifted from the end face 54 by a distance L2 in a direction opposite to the direction 53, and a first element that generates a laser beam of a wavelength of 780 nm.
Is displaced from the end face 54 by L1 in the direction opposite to the direction 53. The numerical aperture of the objective lens 4 is such that laser light having a wavelength of 430 nm is 0.3 mm from the substrate surface.
is designed so that it can focus on the signal recording surface at the position of mm, when a laser beam having a wavelength of 635 nm or 780 nm longer than the wavelength of 430 nm is incident on the objective lens 4, the focal length is Wavelength 430n
This is because the length is longer than that of the laser light of m.

Referring again to FIG. 2, the operation of the optical pickup device 10 will be described. The laser light having a wavelength of 780 nm (or 635 nm or 430 nm) generated by the laser light generating means 1 is
Is collimated by the objective lens 4 via the half mirror 3
After being incident on the signal recording surface 8a (or 8b or 8c), the light is condensed by the objective lens 4 and passes through the transparent substrate of the recording medium 8. Signal recording surface 8a (or 8b)
Alternatively, the laser beam reflected by 8c) returns to the half mirror 3 via the transparent substrate of the recording medium 8 and the objective lens 4, is reflected by the half mirror 3 in a right angle direction, is condensed by the condensing lens 5, and is optically reflected. The light enters the element 6. The laser light incident on the optical element 6 is diffracted at a predetermined angle based on the wavelength and is irradiated on the photodetector 7.

With reference to FIGS. 7 and 8, the operation of reproducing a CD which is an optical disk having a substrate thickness of 1.2 mm will be described. Referring to FIG. 7, when a CD is reproduced, first element 1a in laser light generating means 1 is driven by laser driving circuit 11.
Is selectively driven. As a result, laser light having a wavelength of 780 nm is emitted from the laser light generating means 1, converted into parallel light by the collimator lens 2, and incident on the objective lens 4 via the half mirror 3. The laser light incident on the objective lens 4 is condensed by the objective lens 4, passes through a transparent substrate 88a of an optical disc having a substrate thickness of 1.2 mm, and is condensed and irradiated on a signal recording surface 8a. The laser beam reflected by the signal recording surface 8a returns to the half mirror 3 via the transparent substrate 88a and the objective lens 4, is reflected by the half mirror 3 in a right angle direction, is collected by the condenser lens 5, and is collected by optical means. 6 is incident. Referring to FIG. 8, laser light 80 of wavelength 780 incident on optical means 6
Is diffracted by the angle θ3 based on the wavelength of the laser beam 80 by the triangular grating 63 of the optical unit 6 and the arrow 81
The light travels in the direction shown by the arrow and is irradiated on the focal point 70 of the photodetector 7.

Next, referring to FIGS.
A reproduction operation of a DVD which is a 6 mm optical disk will be described. Referring to FIG. 9, when a DVD is reproduced, the second element in laser light generating means 1 is selectively driven by laser driving circuit 11. As a result, laser light having a wavelength of 635 nm is emitted from the laser light generating means 1. The operation from the collimator lens 2 to the objective lens 4 is the same as that described with reference to FIG. The laser beam having a wavelength of 635 nm incident on the objective lens 4 is condensed by the objective lens 4, passes through a transparent substrate 88b of an optical disc having a substrate thickness of 0.6 mm, and is condensed and irradiated on a signal recording surface 8b. The laser beam reflected by the signal recording surface 8b returns to the half mirror 3 via the transparent substrate 88b and the objective lens 4, is reflected by the half mirror 3 in a right angle direction, is collected by the condenser lens 5, and is condensed by optical means. 6 is incident. Referring to FIG. 10, laser light 100 having a wavelength of 635 nm incident on optical means 6 is diffracted by angle θ2 based on the wavelength of laser light 100 by grating 63 of optical means 6, in the direction indicated by arrow 101. The light advances and is irradiated on the light condensing point 70 of the photodetector 7.

The reproducing operation of a high-density DVD which is an optical disk having a substrate thickness of 0.3 mm will be described with reference to FIGS. Referring to FIG. 11, m, high density DVD
Is reproduced, the third element 1c in the laser beam generating means 1 is selectively driven by the laser drive circuit 11.
As a result, laser light having a wavelength of 430 nm is emitted from the laser light generating means 1. The operation from the collimator lens 2 to the objective lens 4 is the same as that described with reference to FIG. Wavelength 43 incident on objective lens 4
The laser light of 0 nm is condensed by the objective lens 4, passes through the transparent substrate 88c of the optical disk having a thickness of 0.3 mm, and is condensed and irradiated on the signal recording surface 8c. The laser beam reflected by the signal recording surface 8c returns to the half mirror 3 via the transparent substrate 88c and the objective lens 4, is reflected by the half mirror 3 in a right angle direction, is collected by the condenser lens 5, and is condensed by optical means. 6
Incident on. Referring to FIG. 12, laser light 120 having a wavelength of 430 nm incident on optical means 6 is diffracted by angle θ1 based on the wavelength of laser light 120 by grating 63 of optical means 6 and directed in the direction indicated by arrow 121. The light advances and is irradiated on the light condensing point 70 of the photodetector 7.

As described above, the optical pickup device 1
0, the substrate thickness is 0.3 mm, 0.6 m
The reflected light from the signal recording surfaces of three types of optical disks different from m and 1.2 mm is detected at one point on the photodetector 7, and these three types of optical disks can be reproduced compatible. In the above description, the optical element 6 has a triangular lattice, but the portion corresponding to the triangular hypotenuse may be stepped, and the number of steps is designed for laser light having a wavelength of 635 nm. Sometimes four stages are preferred. In this case, the intensity of the laser light after diffraction becomes 80%, and this intensity is a value that can sufficiently withstand signal detection. The stepped shape in this manner facilitates the production of the optical element 6.

In the above description, an optical pickup device capable of interchangeably reproducing three types of optical discs having different substrate thicknesses of optical discs has been described. However, even if the substrate thicknesses are the same, the recording densities are different. The present invention can also be applied to a case where three types of optical disks are reproduced with three laser beams having different wavelengths. Further, in the above description, only the signal reproduction using the optical pickup device 10 has been described. However, a magneto-optical recording medium, a phase change disk, and a CD-R, which are optical disks recordable using the optical pickup device 10, are described. Of course is also possible.

[0035]

According to the present invention, three laser light sources can be used.
Even if laser beams of different wavelengths are emitted, it is possible to detect a signal at one point by correcting the deviation of the optical axis between the laser beams having each wavelength. Further, according to the present invention, an optical disc having three different substrate thicknesses can be reproduced by one optical pickup device by correcting the deviation of the optical axis of the reflected light from the signal recording surface.

Further, according to the present invention, the deviation of the optical axis of the reflected light on the signal recording surface is removed by the diffraction phenomenon of the triangular grating, so that the desired diffracted light is detected with the desired intensity. be able to. Further, according to the present invention, the optical element for correcting the deviation of the optical axis of the laser light having different wavelengths by the diffraction phenomenon can be manufactured by etching glass, so that the optical pickup device can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a table showing standard values and reproduction conditions of CD, DVD, and high-density DVD.

FIG. 2 is a diagram showing a configuration of an optical pickup device according to the present invention.

FIG. 3 is a diagram illustrating details of an optical element.

FIG. 4 is a diagram illustrating further details of an optical element.

FIG. 5 is a diagram for explaining the arrangement of first, second, and third elements in a laser light generating unit.

FIG. 6 is a diagram for explaining another arrangement of the first, second, and third elements in the laser light generating means.

FIG. 7 is a diagram for explaining a CD reproducing operation.

8 is a diagram for explaining the progress of laser light from the optical element of FIG. 7 to the photodetector when reproducing a CD.

FIG. 9 is a diagram for explaining a DVD reproducing operation.

10 is a diagram illustrating the progress of laser light from the optical element of FIG. 9 to the photodetector when reproducing a DVD.

FIG. 11 is a diagram for explaining a reproduction operation of a high-density DVD.

FIG. 12 is a diagram illustrating the progress of laser light from the optical element of FIG. 11 to the photodetector when reproducing a high-density DVD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser beam generation means 1a ... 1st element 1b ... 2nd element 1c ... 3rd element 2 ... Collimator lens 3 ... Half mirror 4 ... Objective lens 5 Condensing lens 6 Optical element 7 Photodetector 8 Recording medium 8a, 8b, 8c Signal recording surface 88a, 88b, 88c Transparent substrate 10・ Optical pickup device 11 ・ ・ ・ Laser drive circuit 50 ・ ・ ・ Base 51 ・ ・ ・ Tracking direction 52 ・ ・ ・ Track direction 54 ・ ・ ・ End face 61 ・ ・ ・ Glass 62 ・ ・ ・ Main face 63 ・ ・ ・ Grating 64 ... Incident laser light 65 ... First-order diffracted light

Claims (11)

[Claims] 1. An optical pickup device including an optical element that guides a reflected light of a laser beam having a different wavelength on a signal recording surface to an optical detector after correcting an optical axis shift based on the wavelength. 2. A laser light generating means for selectively generating laser lights having different wavelengths, and a laser light generated by the laser light generating means, which reflects a laser light reflected from a signal recording surface on an optical axis based on the wavelength. An optical element that corrects and guides the corrected light to a photodetector. 3. The optical pickup device according to claim 2, wherein said laser light generating means includes a plurality of semiconductor elements. 4. An optical pickup device which irradiates a laser beam onto a signal recording surface with an objective lens according to a reproduction condition of a recording medium and guides reflected light from the signal recording surface to a photodetector, wherein the optical pickup device has a first wavelength. A first element for generating a first laser light, a second element for generating a second laser light having a second wavelength different from the first wavelength,
A laser light generating unit including a third element that generates a third laser light having a third wavelength different from the wavelength of the first laser light, a first element, a second element, and a second element in the laser light generating means. Laser driving means for selectively driving the third element; and receiving the first laser light, the second laser light, and the third laser light reflected by the signal recording surface, and receiving the reflected light. An optical element that corrects an optical axis shift of the reflected light based on the wavelength and guides the reflected light to the photodetector. 5. The optical pickup device according to claim 4, wherein the optical element corrects an optical axis shift of the reflected light by diffraction of light. 6. The optical pickup device according to claim 5, wherein said optical element comprises a triangular lattice. 7. The optical element, wherein the wavelength of the laser light is λ,
6. An element satisfying a relationship of sin θ = λ / p, where p is a pitch of the grating and θ is an angle at which reflected light is diffracted by the optical element.
An optical pickup device according to claim 6. 8. The optical detector is determined by Ltanθ, where L is the distance between the optical element and the optical detector in the optical axis direction and θ is the angle at which the reflected light is diffracted by the optical element. The optical pickup device according to claim 7, wherein the optical pickup device is provided at a position shifted from the optical axis in a direction perpendicular to the optical axis by a predetermined distance. 9. The distance between the first element and the second element is determined by the optical axis deviation between the first laser light and the second laser light, and the distance between the second element and the third element. The distance from the element of the second
9. The optical pickup device according to claim 5, wherein the optical pickup device is provided so as to correspond to an optical axis shift between the laser light and the third laser light. 10. 10. The optical pickup device according to claim 9, wherein the light emitting points of the first, second, and third elements are respectively shifted by a predetermined distance in the optical axis direction. 11. The laser driving unit according to claim 5, wherein the laser driving unit selectively drives the first, second, and third elements according to a substrate thickness or a recording density of a recording medium. An optical pickup device according to item 1.