JP2001034992A - Optical apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce a DVD(digital video disk) and CD(compact disk)-R by one objective lens. SOLUTION: A light from a light source 1 which emits the light of two wavelengths is focused by an objective lens 3 to a recording face 6b or 7b of a DVD 6 or a CD 7. The reflected light is guided through the objective lens 3 to a light-receiving element 8 and reproduced. At this time, given that a numerical aperture of the objective lens 3 is NA1 when the DVD 6 is reproduced and NA2 (<NA1) when the CD 7 is reproduced, a wave aberration of the objective lens 3 is set to be not larger than 0.055 λ at the time of NA1 and not larger than 0.07 λ at the time of NA2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device such as an optical pickup device for reproducing or recording optical information by condensing a laser beam on an information recording surface of an optical disk. The present invention relates to an optical device for realizing an optical pickup device or the like that can reproduce or record a plurality of optical disks having different wavelengths with laser beams having different wavelengths.

[0002]

2. Description of the Related Art D having a transparent substrate having a thickness of 0.6 mm
There has been proposed an optical pickup device for reproducing or recording a VD (digital video disc) and a CD (compact disc) having a transparent substrate having a thickness of 1.2 mm by one objective lens (Japanese Patent Application Laid-Open Nos. 9-81953 and 9-19553). 10-199023).

In the device disclosed in Japanese Patent Application Laid-Open No. 9-81953, the DV
Using a finite objective lens for both D and CD, DVD,
When reproducing or recording a CD, the laser light source and the objective lens are moved along the optical axis according to the thickness of the transparent substrate to correct aberration.

In the device disclosed in Japanese Patent Application Laid-Open No. Hei 10-199023,
When reproducing or recording a DVD or CD using an infinite or finite objective lens for both DVD and CD, the working distance (the distance between the lens and the transparent substrate) is adjusted according to the thickness of the transparent substrate. The aberration is corrected by changing the value on the axis.

[0005]

In the former device, the DV
When switching from reproduction or recording of D to reproduction or recording of CD, by changing the light source along the optical axis to change the distance between the object and the image, the axial aberration characteristics, particularly spherical aberration, are substantially zero.
(Zero). However, a moving mechanism for moving both the laser light source and the objective lens must be provided, and the correction of off-axis characteristics, particularly off-axis coma, is insufficient for reproduction or recording.

In the latter device, by changing the working distance between the reproduction or recording of a DVD and the reproduction or recording of a CD, the aberration characteristics, particularly the spherical aberration, are controlled to enable reproduction or recording. However, it is an optical pickup device having a light source of a single wavelength, and it has been impossible to reproduce or record a DVD and a CD-R (a CD that can be reproduced or recorded on a write-once compact disc).

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object to reproduce or record a plurality of optical discs having different thicknesses of a transparent substrate with one objective lens using different wavelengths. An object of the present invention is to provide an optical device which is simple and compact, and enables an optical pickup device or the like capable of reproducing or recording a CD and a DVD including a CD-R without moving the position of a light source.

[0008]

In order to achieve the above object, the present invention adopts the following configuration of an optical device.

(1) Light from a light source emitting at least two different wavelengths is condensed on the information recording surface of the first or second optical disk by an optical system including an objective lens, and reflected from the information recording surface. In an optical device for recording or reproducing data on an information recording surface by guiding light to a light receiving element via the objective lens, the recording density of the first optical disk is set to i ₁ ,
The wavelength for recording or reproduction of the second optical disk is λ ₁ , the recording density of the second optical disk is i ₂ (<i ₁ ), and the wavelength for recording or reproduction of the second optical disk is λ ₂ (≠ λ ₁ ).
The numerical aperture of the objective lens on the optical disk side when recording or reproducing the optical disk is NA ₁ , and the numerical aperture on the optical disk side of the objective lens when recording or reproducing the second optical disk is NA ₂ (<NA ₁ ). , The wavefront aberration of the optical system during recording or reproduction of the first optical disc is 0.055
λ or less, the wavefront aberration of the objective lens during recording or reproduction of the second optical disk is 0.07λ or less.

(2) In the case of (1), the wavefront aberration of the objective lens at the time of recording or reproduction of the first optical disk is W ₁ , the wavefront of the objective lens at the time of recording or reproduction of the second optical disk. When the aberration is W ₂ , the condition of 0.02λ <W ₁ <0.055λ 0.03λ <W ₂ <0.07λ is satisfied.

(3) In the case of (1) or (2), the light source
Wavelength λ₁Using the light of thickness t ₁First optical disc
The numerical aperture N on the first optical disk side through the transparent substrate
A₁At an image height of 0.1 mm when condensed in the range of
Coma aberration CM₁And the wavelength λ from the light source_TwoUsing the light of
And the thickness t_Two(> T₁) The transparent substrate of the second optical disc
, The numerical aperture NA on the second optical disk side_TwoIn the range
Coma at the image height of 0.1 mm when condensed is C
M_TwoAnd CM₁ <0.03λ CM_Two <0.02λ is satisfied.

(4) In the cases (1) to (3), the objective lens is configured as an infinite optical system for converging a parallel light beam from a laser light source on the information recording surface of the optical disk.

(5) In the cases (1) to (3), the objective lens is configured as a finite optical system for converging the divergent light beam from the laser light source on the information recording surface of the optical disk.

(6) In the cases of (1) to (3), the objective lens is a single lens having a smooth aspherical optical surface.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical device according to the present invention is used as an optical pickup device or the like, has a plurality of light sources, and reproduces or records data on a first optical disk and a first optical disk on a second optical disk. By changing the working distance between reproduction and recording at a wavelength different from the above, the aberration characteristics of the objective lens, particularly spherical aberration, are controlled to enable reproduction or recording.

For example, a high recording density optical disc D
This is an optical pickup device for reproduction of VD (recording density i ₁ , thickness t ₁ = 0.6 mm), and is a conventional CD or CD-R (recording density i ₂ <i) which is an optical disk having a lower recording density than DVD.
_1, when playing the optical disk of thickness t ₂ = 1.2 mm), using those having a wavelength for reproducing the CD or the like as a light source is to use a DVD playback the same objective lens. The aberration caused by the difference in the thickness of the transparent substrate of the optical disk during CD reproduction is determined by changing the distance between the objective lens and the optical disk (hereinafter referred to as the working distance) from d ₁ to DVD during DVD reproduction.
The design is performed so that the CD can be reproduced when it is changed to d ₂ during the D reproduction.

FIG. 1 is a block diagram showing one embodiment of the optical pickup device of the present invention. In FIG. 1, reference numeral 1 denotes a light source that simultaneously or selectively emits light of two wavelengths (λ ₁ , λ ₂ ), 2 denotes a half mirror surface, 3 denotes an objective lens, 5 denotes an auxiliary lens (for example, a collimator lens), 6 is a first optical disk, 6a is a transparent substrate of the first optical disk, 6b
Is an information recording surface of the first optical disk, 7 is a second optical disk, 7a is a transparent substrate of the second optical disk, 7b is an information recording surface of the second optical disk, 8 is a light receiving element, and 9 is a stop. d ₁ is the working distance on the first optical disk 6, d ₂ is the working distance on the second optical disk 7, t ₁ is the thickness of the first disk 6 (thickness of the transparent substrate), and t ₂ is the second disk 7
(The thickness of the transparent substrate), t ₃ is the first thickness of the objective lens 3
Plane and the axial distance of the second surface, t ₅ the axial distance between the first and second surfaces of the auxiliary lens 5, first S ₁ is a light source 1 and the auxiliary lens 5
S ₂ is the distance between the second surface of the auxiliary lens 5 and the first surface of the objective lens 3. In the following description, unless otherwise specified, the unit of dimensions such as distance, interval, and thickness is mm.

The light source 1 includes, for example, a laser light source, a laser light source having a wavelength of 780 nm (= λ ₂ ) for a CD, and a laser light source having a wavelength of 650 nm (= λ ₁ ) for a DVD. It is arranged close to the auxiliary lens 5 so as to have the same object distance S ₁ , and emits light of two wavelengths simultaneously or selectively from the position of the light source 1. As such an example, Japanese Patent Application Laid-Open No. 11-3
No. 9684 describes a light source module.

The first optical disk 6 is, for example, a DVD as described above, and the second optical disk 7
Examples include a CD and a CD-R.

In FIG. 1, the divergent luminous flux of the first wavelength λ ₁ or the second wavelength λ ₂ from the light source 1 is collimated by the auxiliary lens 5, converged by the diaphragm 9, and incident on the objective lens 3. The objective lens 3 forms an optical spot corrected to a predetermined aberration characteristic on the information recording surface 6b or 7b through the transparent substrate 6a or 7a having a predetermined thickness (t ₁ or t ₂ ). Is recorded, a mark representing a digital signal is recorded on the information recording surface 6b or 7b at recording densities i ₁ and i ₂ (<i ₁ ), respectively.

When reproducing the digital recording signal,
The reflected light from the information recording surface 6b or 7b illuminated with the first wavelength λ ₁ or the second wavelength λ ₂ from the light source 1 in the above arrangement is used for the objective lens 3, the aperture 9, and the auxiliary lens. 5, the light is reflected by the half mirror surface 2, and is photoelectrically converted by the light receiving element 8.
Read the digital signal recorded in b or 7b.

FIG. 2 is a block diagram showing another embodiment of the optical pickup device of the present invention. 2, 4 denotes an objective lens, S ₃ represents a distance on the optical axis between the first surface of the light source 1 and the objective lens 4, t ₄ is the axial distance of the first and second surfaces of the objective lens 4 .

FIG. 2 shows a finite optical system in which a divergent light beam having a _first wavelength λ ₁ or a second wavelength λ ₂ from a light source 1 is stopped by a stop 9 and enters an objective lens 4. A light spot corrected to a predetermined aberration characteristic is formed on the information recording surface 6b or 7b through the transparent substrate 6a or 7a of the optical disk 6 or 7 having a predetermined thickness (t ₁ or t ₂ ),
When optical information is recorded, marks representing digital signals are recorded on the information recording surface 6b or 7b at recording densities i ₁ and i ₂ (<i ₁ ), respectively.

When reproducing the digital recording signal,
In the above arrangement, the reflected light from the information recording surface 6b or 7b illuminated at the first wavelength λ ₁ or the second wavelength λ ₂ from the light source 1 is turned through the objective lens 4 and the aperture 9 this time. The digital signal recorded on the information recording surface 6b or 7b is read by guiding the light in the direction, reflecting the light on the half mirror surface 2, and performing photoelectric conversion by the light receiving element 8.

As described above, according to the present invention, the light from the light source 1 that emits at least two different wavelengths of light is provided by the objective lens 3 or 4 at the position of the different working distance d ₁ or d ₂ . Is focused on the information recording surface 6b or 7b of the optical disk 6 or the second optical disk 7, and the reflected light from the information recording surface is guided to the light receiving element 8 through the objective lens 3 to record data on the information recording surface 6b or 7b. Or to regenerate.

The wavelength of the light source 5 is not limited to 650 nm and 780 nm as described above, and for example, the following range can be used.

[0027] _{630nm ≦ λ 1 ≦ 670nm 750nm ≦} λ 2 ≦ 810nm and usually, the reproduction of the DVD is used at least 0.6 as NA _1, 0.35 ≦ NA ₂ ≦ the reproduction such as CD
0.45 is used.

The design of the objective lens was performed as follows.
The wavefront aberration when forming the light spot through the first optical disk and W _1, when the wave front aberration at the time of forming a light spot through a second optical disc was _{W 2, 0.02λ <W 1 <} 0.055λ The condition 0.03λ <W ₂ <0.07λ is satisfied.

If W ₁ <0.02λ, a spherical aberration occurs due to the thickness of the optical disk, and as a result, 0.07λ <W ₂ . Similarly, W ₂ <
If 0.03λ is set, 0.055λ <W ₁ results.

It is preferable that the above conditions regarding W ₁ and W ₂ satisfy 0.02λ <W ₁ <0.04λ 0.03λ <W ₂ <0.06λ.

An image height of 0.1 when a light spot is formed through the first optical disk while satisfying the above conditions.
coma in mm and CM _1, when a coma aberration in an image height 0.1mm when forming the light spot through the second optical disc was _{CM 2, CM 1 <0.03λ CM} 2 <0.02λ conditions It is desirable to configure so as to satisfy the following.

If this condition is satisfied, the allowable range for inclination or axis deviation from the optical axis of the light source, auxiliary lens, objective lens or optical disk is expanded.

In FIGS. 1 and 2, the stop 9 has a function of changing the numerical aperture. The reason for providing aperture 4 is
If the numerical aperture used for the first optical disk 6 is different from the numerical aperture used for the second optical disk 7 during recording or reproduction, the aperture 9 is used to adjust the numerical aperture.

The stop 9 includes a mechanical stop and an optical stop, and is not particularly limited. As an example of a mechanical diaphragm, prepare a plurality of plate-like bodies having holes with a diameter corresponding to the numerical aperture,
There is a method of selectively inserting and removing. As an example of the optical diaphragm, two kinds of optical thin films having a wavelength selectivity of a transparent plate are formed, and light of a first wavelength is transmitted through a first circle having a diameter corresponding to a first numerical aperture. , A light having a second wavelength transmitted through a second circle having a diameter corresponding to the second numerical aperture so that the first circle and the second circle are concentric circles.

When the objective lenses 3 and 4 are provided with means for switching the numerical aperture, the aperture 9 is unnecessary.

[0036]

(Example 1) In Example 1, a D-type optical disk was used as a first optical disk.
VD (t ₁ = 0.6 mm), CD (t ₂ = 1.2 mm) as the second optical disc, and C
The optical pickup device shown in FIG. 1 was manufactured on the premise of recording or reproduction of D and DVD.

For reproducing or recording a DVD, the wavelength is 650 nm.
Laser light source, wavelength 780 nm for reproduction or recording on CD
Was used. DVD has a refractive index of 1.580 at a wavelength of 650 nm, and CD has a wavelength of 78.
The design was performed assuming that the refractive index was 1.573 at 0 nm.

Table 1 shows numerical values and design values of the objective lens. In Table 1, f ₁ is the focal length of the objective lens at a wavelength of 650 nm, f ₂ is the focal length of the objective lens at a wavelength of 780 nm, R _j is the radius of curvature of the j-th surface, k _j is the conic constant of the j-th surface, a _{i, j} is the i-th aspherical coefficient of the j-th surface. n
₁ is the refractive index of the objective lens at the wavelength 650 nm, n ₂ is the refractive index of the objective lens at a wavelength of 780 nm.

The aspherical shape of the objective lens is shown by Equation 1. In Equation 1, z _j is a distance from the tangent plane of the vertex of the j-th surface aspheric surface to a point having a height r on the aspheric surface. i
Is 2, 4, 6, 8, 10, 12, and j is 1, 2.

Table 2 shows various numerical values and design values of the auxiliary lens used at that time. In Table 2, f ₁ is wavelength 6
Focal length of the auxiliary lens on the 50 nm, f ₂ is the wavelength 780
the focal length of the collimator in nm, f is the focal length, R _j
Is the radius of curvature of the j-th surface, k _j is the conic constant of the j-th surface, a _{i, j}
Is the i-th aspherical coefficient of the j-th surface. n ₁ is wavelength 650
The refractive index of the auxiliary lens in nm, n ₂ is the refractive index of the auxiliary lens at a wavelength of 780 nm. The aspherical shape of the auxiliary lens is shown by Equation 1. i is 2,4 and j is 1,2.

[0041]

Table 1 f ₁ = 2.426 f ₂ = 2.442 n ₁ = 1.591 n ₂ = 1.587 t ₃ = 1.2 d ₁ = 1.370 d ₂ = 1.012 R ₁ = 1.429173 R ₂ = -3.295592 k ₁ = -0.718702 k ₂ =- 13.94776 a _2,1 = -4.0250891 × 10 ^-2 a _2,2 = 9.7780128 × 10 ^-2 a _4,1 = 9.6158338 × 10 ^-3 a _4,2 = -5.6613831 × 10 ^-3 a _6,1 = -5.084959 _{^{× 10 -5 a 6,2 = -1.1070738 ×}} 10 -5 a 8,1 = -1.4644174 × 10 -5 a 8,2 = -1.4938422 × 10 -5 a 10,1 = 2.4156725 × 10 -5 a 10, ₂ = 2.7437866 x ^10-7 .

[0042]

Table 2 f ₁ = 25.00 f ₂ = 25.17 n ₁ = 1.5890 n ₂ = 1.5851 t ₅ = 2.20 S ₁ = 23 S ₂ = 5 R ₁ = -61.03815 R ₂ = -10.18929 k ₁ = -10 k ₂ = −1 a _2,1 = −9.9421684 × 10 ⁻³ a _2,2 = −1.5268838 × 10 ⁻³ a _4,1 = −5.2572908 × 10 ⁻⁴ a _4,2 = −4.4956909 × 10 ⁻⁴ .

[0043]

## EQU1 ## z _j = (1 / R _j ) r ² ÷ [1+ ｛1- (1+
_{k j) (1 / R j} ) 2 r 2} 0.5] + Σa i, j r i z j: j-th surface aspheric aspheric on the height r from the tangent plane of the vertex of
R _j : coefficient of the j-th surface, k _j : conical constant of the j-th surface, a _{i, j} : i-th aspherical coefficient of the j-th surface.

The effective diameter of the objective lens and the NA of the optical disk at the time of reproducing or recording a DVD in Example 1 are 2.94 mm and 0.606, respectively, and the diameter is 1.96 mm and 0.400 at the time of reproducing or recording a CD. .

FIG. 3 shows off-axis wavefront aberration characteristics during DVD reproduction. In FIG. 3, the solid line indicates the wavefront aberration, and the broken line indicates only the off-axis coma of the wavefront aberration. In FIG.
9 shows off-axis wavefront aberration characteristics during CD reproduction. In FIG.
The meaning of the solid and broken lines is the same as in FIG. In the following aberration characteristic diagrams, the meanings of the solid line and the broken line are the same as those in FIG. All aberration characteristic diagrams for each embodiment are calculated values.

(Example 2) An optical pickup device having the same configuration as in Example 1 was manufactured except that the specifications of the objective lens were changed to Table 3. Each numerical value in Table 3 is the same as in Table 1. i
Is 3,4,5,6,8,10, and j is 1,2.

[0047]

[Table 3] f ₁ = 2.446 f ₂ = 2.462 n ₁ = 1.591 n ₂ = 1.587 t ₃ = 1.2 d ₁ = 1.370 d ₂ = 1.012 R ₁ = 1.610235 R ₂ = -10.25083 k ₁ = -0.4871661 k ₂ =- 84.00661 a _3,1 = 5.4782288 × 10 ^-3 a _3,2 = -3.608225225 × 10 ^-2 a _4,1 = -3.0192404 × 10 ^-2 a _4,2 = 8.8697698 × 10 ^-2 a _5,1 = 4.8501647 × _{^{10 -2 a 5,2 = -5.0423421 × 10}} -2 a 6,1 = -2.2469126 × 10 -3 a 6,2 = 6.2459302 × 10 -3 a 8,1 = 1.3271973 × 10 -3 a 8,2 = _{^{7.2244733 × 10 -4 a 10,1 = 4.5311839}} × 10 -5 a 10,2 = 9.6207503 × 10 -5.

The effective diameter of the objective lens and the NA of the optical disk at the time of reproducing or recording a DVD in Example 2 are 2.96 mm and 0.608, respectively, and the diameter is 1.88 mm and 0.384 at the time of reproducing or recording a CD. . In FIG.
4 shows off-axis wavefront aberration characteristics during DVD reproduction. FIG. 6 shows the CD
9 shows off-axis wavefront aberration characteristics during reproduction.

(Example 3) In Example 3, a DVD is used as the first optical disk and a CD is used as the second optical disk.
The optical pickup device shown in FIG. A laser light source having a wavelength of 650 nm was used for reproducing or recording a DVD, and a laser light source having a wavelength of 780 nm was used for reproducing or recording a CD. The optical disk was designed as having a refractive index of 1.580.

Table 4 shows various numerical values and design values of the objective lens. In Table 4, each numerical value is the same as in Table 1. i is
3, 4, 5, 6, 8, 10, and j are 1, 2.

[0051]

Table 4 f ₁ = 2.040 f ₂ = 2.052 n ₁ = 1.591 n ₂ = 1.587 t ₄ = 1.2 S ₃ = 16 d ₁ = 1.370 d ₂ = 1.014 R ₁ = 1.555331 R ₂ = -3.824183 k ₁ = -0.9055811 k ₂ = -25.46314 a _3,1 = 4.8466083 × 10 ^-3 a _3,2 = 1.8656063 × 10 ^-2 a _4,1 = 1.3640323 × 10 ^-2 a _4,2 = -5.9653753 × 10 ^-3 a _5,1 = -2.5771612 × 10 ^-4 a _5,2 = 1.1398097 × 10 ^-3 a _6,1 = 4.9073079 × 10 ^-4 a _6,2 = -1.173922 × 10 ^-3 a _8,1 = -1.1113341 × 10 ^-3 a ^{_{8,2 = 1.5169942 × 10 -4 a 10,1}} = 3.1147917 × 10 -4 a 10,2 = 6.3928714 × 10 -5.

The effective diameter of the objective lens and the NA of the optical disk at the time of reproducing or recording a DVD in Example 3 are 2.86 mm and 0.612, respectively, and the same at the time of reproducing or recording a CD is 1.90 mm and 0.404, respectively. . Fig. 7 shows D
13 shows off-axis wavefront aberration characteristics during VD reproduction. FIG. 8 shows off-axis wavefront aberration characteristics during CD reproduction.

Example 4 In Example 4, a DVD was used as the first optical disk, and a CD was used as the second optical disk.
The optical pickup device shown in FIG. In Examples 1 and 2, the auxiliary lens 5 was a collimator lens, but here, the auxiliary lens 5 was not a collimator lens.

Table 5 shows various numerical values and design values of the objective lens. Table 6 shows various numerical values and design values of the auxiliary lens.
For both the objective lens and the auxiliary lens, i is 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, j is 1, 2,
It is.

[0055]

Table 5 f ₁ = 2.28 f ₂ = 2.29 n ₁ = 1.5911 n ₂ = 1.5872 t ₃ = 1.20 R ₁ = 1.553309 R ₂ = -5.723263 k ₁ = -0.7261543 k ₂ = -27.23872 a _1,1 = -2.9487244 × 10 ^-3 a _1,2 = -8.4112676 × 10 ^-4 a _2,1 = -6.4266728 × 10 ^-3 a _2,2 = 1.0400949 × 10 ^-2 a _3,1 = -5.1264045 × 10 ^-4 a _{3, 2} = 5.219831 x 10 ^-4 a _4,1 = 1.3036972 x 10 ^-3 a _4,2 = 1.4601097 x 10 ^-3 a _5,1 = 1.1942657 x 10 ^-5 a _5,2 = 5.5842235 x 10 ^-5 a _{6, ^{1 = -7.9836342 × 10 -6 a 6,2}} = 5.1194633 × 10 -5 a 7,1 = -5.4756284 × 10 -6 a 7,2 = 3.207899 × 10 -6 a 8,1 = 8.0609516 × 10 -6 a ^{_{8,2 = 1.3327667 × 10 -7 a 9,1}} = -2.4379619 × 10 -6 a 9,2 = -2.3528587 × 10 -5 a 10,1 = -1.6082235 × 10 -6 a 10,2 = -4.8520701 × _{^{10 -5 a 11,1 = -2.0481632 × 10}} -7 a 11,2 = -1.6393159 × 10 -6 a 12,1 = -1.6466929 × 10 -7 a 12,2 = -2.4433656 × 10 -6.

[0056]

[Table 6] _{f 1 = 332.32 f 2 = 334.65} n 1 = 1.5890 n 2 = 1.5851 t 5 = 2.20 R 1 = -129.4201 R 2 = -27.42091 k 1 = -11.08474 k 2 = -10.00419 a 1,1 = 4.6618285 × 10 ^-3 a _1,2 = 0.001122988 × 10 ^-3 a _2,1 = -6.1902943 × 10 ^-3 a _2,2 = 0.0058294072 × 10 ^-3 a _3,1 = 5.6759125 × 10 ^-3 a _3,2 = -6.0373022 × 10 ^-3 a _4,1 = -3.771356 × 10 ^-3 a _4,2 = 1.1013143 × 10 ^-5 a _5,1 = 9.535 0007 × 10 ^-6 a _5,2 = -5.8723505 × 10 ^-5 a _{6 ^{, 1 = -6.6536038 × 10 -5 a}} 6,2 = -6.7900812 × 10 -6 a 7,1 = -1.2122442 × 10 -6 a 7,2 = 2.170977 × 10 -6 a 8,1 = -5.256652 × 10 ^{_{-5 a 8,2 = 3.9443843 × 10 -5}} a 9,1 = 3.201221 × 10 -7 a 9,2 = 1.040815 × 10 -6 a 10,1 = -8.2908692 × 10 -6 a 10,2 = 2.9041342 × _{^{10 -5 a 11,1 = -1.1649685 × 10}} -8 a 11,2 = 2.2276493 × 10 -7 a 12,1 = 1.0440827 × 10 -7 a 12,2 = 1.3997998 × 10 -7.

S ₁ = 22.61, S ₂ = 5.0
0, d ₁ = 1.41 and d ₂ = 1.05.

The effective diameter of the objective lens and the NA of the optical disk at the time of reproducing or recording a DVD in Example 4 are 2.94 mm and 0.60, respectively, and the same at the time of reproducing or recording a CD is 2.22 mm and 0.45. . FIG.
13 shows off-axis wavefront aberration characteristics during D reproduction. FIG. 10 shows off-axis wavefront aberration characteristics during CD reproduction.

Although the optical device of the present invention has been described based on the embodiments of the objective lens particularly used in the optical pickup device, the present invention is not limited to these embodiments, and various modifications can be made.

[0060]

As described above, according to the optical apparatus of the present invention, the structure can be improved even when a plurality of optical disks having different thicknesses of the transparent substrate are reproduced or recorded by using one objective lens using different wavelengths. A simple and compact optical pickup device can be manufactured. That is, an optical pickup device that uses a light source that emits at least two wavelengths of light, does not require a light source moving mechanism, and can reproduce or record at least a DVD and a CD (including a CD-R) can be manufactured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an optical pickup device of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the optical pickup device of the present invention.

FIG. 3 is a DVD aberration characteristic diagram of the optical system of Example 1.

FIG. 4 is a CD aberration characteristic diagram of the optical system of Example 1.

FIG. 5 is a diagram showing DVD aberration characteristics of the optical system of Example 2.

FIG. 6 is a diagram showing CD aberration characteristics of the optical system of Example 2.

FIG. 7 is a DVD aberration characteristic diagram of the optical system of Example 3.

FIG. 8 is a CD aberration characteristic diagram of the optical system of Example 3.

FIG. 9 is a DVD aberration characteristic diagram of the optical system of Example 4.

FIG. 10 is an aberration diagram for CD of the optical system of Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Half mirror surface 3, 4 ... Objective lens 5 ... Auxiliary lens 6 ... First optical disk 6a ... Transparent substrate of 1st optical disk 6b ... Information recording surface of 1st optical disk 7 ... 2nd optical disk 7a ... Transparent substrate of second optical disk 7b ... Information recording surface of second optical disk 8 ... Light receiving element 9 ... Stop

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA13 LA01 NA03 PA01 PA02 PA17 PB01 PB02 QA03 QA07 QA12 QA14 QA21 QA34 QA41 RA05 RA12 RA13 RA32 RA34 RA42 5D119 AA41 BA01 CA16 DA05 EC01 JA44 JB02

Claims (3)

[Claims] An optical system including an objective lens receives light from a light source that emits light of at least two different wavelengths.
Or an optical device for condensing light on an information recording surface of a second optical disk and guiding reflected light from the information recording surface to a light receiving element through the objective lens to record or reproduce data on the information recording surface; recording density i _{1, 1} a recording or wavelength of reproducing the first optical disk lambda, the recording density of the second optical disc i ₂ (<i _1), a recording or wavelength of reproducing the second optical disk lambda ₂ (≠ λ ₁ ), the numerical aperture of the objective lens on the optical disc side when recording or reproducing the first optical disc is NA ₁ , and the aperture on the optical disc side of the objective lens when recording or reproducing the second optical disc. Number is NA ₂ (<
NA ₁ ), the wavefront aberration of the optical system at the time of recording or reproduction of the first optical disc is 0.055λ or less,
An optical device, wherein the wavefront aberration of the objective lens at the time of recording or reproduction of the optical disk is 0.07λ or less. Wherein when W ₁ the wavefront aberration of the objective lens when recording or reproducing the first optical disk, the wave front aberration of the objective lens when recording or reproducing of the second optical disk and W _2, The optical device according to claim 1, wherein a condition of 0.02λ <W ₁ <0.055λ 0.03λ <W ₂ <0.07λ is satisfied. 3. A light source having a wavelength of λ ₁ from a light source and condensed through a transparent substrate of a first optical disk having a thickness of t ₁ within a range of a numerical aperture NA ₁ on the first optical disk side. coma and CM ₁ at the image height 0.1mm when using light having a wavelength lambda ₂ from the light source through the transparent substrate of the second optical disk having a thickness of t ₂ (> t _1), second Height 0.1 mm when focused in the range of numerical aperture NA ₂ on the optical disk side of
3. The optical device according to claim 1, wherein a condition of CM ₁ <0.03λ CM ₂ <0.02λ is satisfied when a coma aberration is CM ₂ .