JP3515712B2 - Objective lens for optical disk, optical head device and optical information recording / reproducing device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used in an optical head such as a digital video disc, a digital audio disc, an optical memory disc for a computer, and more particularly, it is composed of one lens and has different substrate thicknesses. The present invention relates to an optical disk objective lens capable of satisfying good condensing characteristics depending on the type of optical disk, an optical head device and an optical information recording / reproducing apparatus using the same.

[0002]

2. Description of the Related Art Generally, in an optical head device for an optical disk, a single lens having an aspherical surface is used as an objective lens for condensing a diffraction-limited point image on an information medium surface to record or reproduce information. Is often used. However, recently, there is an increasing need for compatible reproduction of optical discs having different thicknesses. For example, a CD having a disc thickness of 1.2 mm is used.
Or CD-ROM and D with a disc thickness of 0.6 mm
It is required to read VD or DVD-ROM with one optical head. In this case, there is a method of using two objective lenses, but in order to further simplify the optical system, it is advantageous that one lens can handle two types of optical disks having different thicknesses. Further, it is desired that the objective lens also has a simple structure as much as possible.

For example, JP-A-8-334690, JP-A-9-184975, JP-A-10-55564, and other publications propose lenses for achieving such an object. Hereinafter, a conventional objective lens will be described with reference to FIG. FIG. 20 is a layout diagram showing the relationship between a conventional objective lens and an optical disk.

FIG. 20A shows a double-sided aspherical objective lens 33 when it is focused on an optical disc 32 having a thickness of 0.6 mm.
3 is an optical path diagram of FIG. The surface of the objective lens 33 on the light source side is divided into an outer peripheral region 34 and an inner peripheral region 35. In the outer peripheral area 34, spherical aberration is corrected for the optical disk 32 having a thickness of 0.6 mm. On the other hand, the inner peripheral area 35
Has spherical aberration corrected for an optical disc having a thickness of 0.9 mm. The boundary between the inner peripheral region 35 and the outer peripheral region 34 is 1
It is determined by the NA required for reproducing a 1.2 mm thick disc with respect to the wavelength of 655 nm of one light source. For example, if an optical disc with a thickness of 1.2 mm has a wavelength of 780 nm and N
When reproducing at A0.45, NA is used with a 655 nm light source.
It will be about 0.37. The inner peripheral region 35 has a spherical aberration with respect to the optical disc having a thickness of 0.6 mm, but the total aberration is much smaller than 0.07λ which is said to be a diffraction limit, and the optical disc having a thickness of 0.6 mm is used. The aberration is sufficient for reproduction.

FIG. 20B shows an optical path diagram when the same objective lens 33 is used to focus light on an optical disc 36 having a thickness of 1.2 mm. Since the inner peripheral area 35 of the same objective lens 33 is optimized for an optical disk having a thickness of 0.9 mm, the aberration is small for the optical disk 36 having a thickness of 1.2 mm. However, the outer peripheral region 34 has a thickness of 0.
Since it is optimized for the 6 mm optical disc 32, the optical disc 36 having a thickness of 1.2 mm has a large aberration and does not contribute to focusing. Therefore, the outer peripheral region 34
Also works like an opening.

[0006]

When one light source is used, the performance can be satisfied for the two types of optical disks having the thicknesses of 0.6 mm and 1.2 mm under the above conditions. However, when it is necessary to reproduce an optical disc having a thickness of 1.2 mm with a light source having a wavelength of 780 nm like a CD-R, it is necessary to relatively increase the NA because the wavelength becomes long. The boundary with the area will have to be made larger. For this reason, there is a problem that the aberration generated in the optical disc having a thickness of 0.6 mm becomes large and the condensing characteristic is deteriorated.

The present invention has been made to solve the above-mentioned problems in the prior art, and is suitable for any of two types of optical discs having one substrate and different substrate thicknesses. An object of the present invention is to provide an objective lens for an optical disk which can satisfy good light condensing characteristics, an optical head device and an optical information recording / reproducing device using the same.

[0008]

In order to achieve the above object, the first structure of the objective lens for an optical disk according to the present invention comprises a single lens having an aspherical surface on both sides, and a first lens having a different thickness.
And an objective lens for an optical disc which collects a point image through a second optical disc substrate, wherein at least one aspherical surface has an inner peripheral region inside a circular aperture centered on the optical axis and an outer region outside the inner peripheral region. It consists of two areas,
Aspherical shape of the outer peripheral region, the spherical aberration is corrected for small the first optical disk substrate thicknesses of the first and second optical disk substrates different the thicknesses, the aspherical shape of the inner peripheral region , the spherical aberration corrected for the greater the second optical disc substrate thickness, the boundary between the peripheral region and the inner region is in contact with a step in the optical axis direction,
Satisfying the relationships of the following expressions (1) to (4) , and
Of the wavefront aberration when condensing through the optical disc substrate of
The next spherical aberration component S3 is substantially 0, and the first optical diopter is
5th-order spherical surface of wavefront aberration when condensing through a disc substrate
The aberration component S5 (unit: λ: rms) is related to the equation (5) below.
And the aspherical shape of the inner peripheral region is
Spherical aberration is corrected for the thickness t3 of the disk substrate
When t3 is optimized as follows, t3 satisfies the relationship of the following formula (6).
Characterized by foot.

T1 <t2 (1) 0.05 <TW <0.12 (2) 0.38 <NA1 <0.46 (3) 0.1 <p (n-1) / λ <0.6 ( 4) −0.03 <S5 <0.03 (5) 0.8 <t3 <1.2 (6) where, t1: thickness of the first optical disc substrate t2: thickness of the second optical disc substrate NA1: within NA TW of the objective lens in the aperture of the peripheral region: Wavefront aberration when converging through the first optical disc substrate (unit: λ: rms) n: Refraction of the objective lens at the wavelength of the light source when reproducing the first optical disc Ratio p: Step difference in the optical axis direction between the inner peripheral region and the outer peripheral region λ: Wavelength of the light source when reproducing the first optical disc According to the first configuration of the optical disc objective lens, 1
With a single lens, a good focused spot can be obtained for both the first optical disc and the second optical disc, and as a result, good recording / reproducing characteristics can be obtained. Also, when collecting light through the first optical disk substrate
The third-order spherical aberration component S3 of the wavefront aberration is about 0
Causes performance degradation due to optical disc substrate thickness error
Can be minimized. In addition, the first optical disc
5th-order spherical aberration of wavefront aberration when condensing through a substrate
The difference component S5 (unit: λ: rms) is the relationship of the above equation (5).
When the first optical disc is played back by satisfying
The light condensing characteristics, especially the peak intensity of airy ring is suppressed.
As a result, the reproduction characteristics of the optical disc are inferior.
Can be prevented. In addition, the aspherical shape of the inner peripheral area
Spherical aberration is compensated for with respect to the thickness t3 of the optical disk substrate.
When optimizing to be corrected, t3 in the above equation (6) is
By satisfying the relationship,
Suppresses the deterioration of the focused spot, and
To have a lower recording density than the first optical disc
Therefore, depending on the tilt of the second optical disk,
The effect of the aberration is reduced, and spots other than spherical aberration are inferior.
It is possible to suppress the factor of activation.

[0010]

[0011]

[0012]

[0013]

[0014]

In the first structure of the optical disk objective lens of the present invention, it is preferable that the step between the inner peripheral region and the outer peripheral region has an arcuate cross section. According to this preferable example, it can be easily processed using a cutting tool, a grindstone, or the like.

Further, in the first configuration of the objective lens for an optical disc of the present invention, it is preferable that the objective lens is manufactured by glass molding or resin molding. According to this preferable example, by processing the aspherical shape into a mold, it becomes possible to mass-produce lenses having the same shape and performance at low cost.

The second configuration of the objective lens for an optical disc according to the present invention is composed of a single lens having aspherical surfaces on both sides, and an objective for an optical disc for condensing point images through the first and second optical disc substrates having different thicknesses. A lens, wherein at least one aspherical surface is surrounded by an inner peripheral region inside a circular aperture centered on the optical axis and another circular aperture outside the inner peripheral region and outside the circular aperture. than the intermediate region and the intermediate region consists of three regions of the outer peripheral region, the aspherical shape of the inner peripheral region and the peripheral region is less thick of the first and second optical disk substrates different the thicknesses Previous
The spherical aberration is corrected with respect to the first optical disc substrate, and the aspherical shape of the intermediate region has a spherical aberration with respect to the optical disc substrate having a larger thickness than both the first and second optical disc substrates having different thicknesses. The following formula (7)
Satisfies the relationship of (8) and has an aspherical shape in the intermediate region.
Spherical aberration is compensated for with respect to the thickness t4 of the optical disk substrate.
When optimizing to be corrected, t4 in the following equation (9)
The relationship between the inner peripheral region and the intermediate region is satisfied while satisfying the relationship.
Either the boundary between the middle area and the outer area is a step.
Characterized that it is connected without a difference.

0.35 <NA2 <0.43 (7) 0.03 <NA3-NA2 <0.1 (8) 1.4 <t4 <2.0 (9) However, NA2: inner peripheral region and intermediate NA of Objective Lens at Boundary with Region NA3: NA of Objective Lens at Boundary between Intermediate Region and Peripheral Region According to the second configuration of the objective lens for optical disc, 1
With a single lens, a good focused spot can be obtained for both the first optical disc and the second optical disc, and as a result, good recording / reproducing characteristics can be obtained. In addition, the aspherical shape of the intermediate area is changed to the optical disk substrate.
Optimized to correct spherical aberration for thickness t4
When t4 satisfies the relation of the above equation (9),
Satisfactorily corrects the aberration for the second optical disc.
You can In addition, there is a boundary between the inner peripheral area and the intermediate area.
Has a step on either the boundary between the middle area and the outer area.
This occurs when processing the lens because it is connected to the
It is possible to reduce the number of ineffective areas and secure the light intensity.
In addition, it is possible to suppress the deterioration of the light collecting characteristic.

[0019]

[0020]

[0021]

In the second structure of the optical disk objective lens of the present invention, it is preferable that the step between the inner peripheral region and the intermediate region or the step between the intermediate region and the outer peripheral region has an arcuate cross section.

In the second structure of the objective lens for an optical disk of the present invention, it is preferable that the objective lens is manufactured by glass molding or resin molding.

The third structure of the objective lens for an optical disc according to the present invention is an objective for an optical disc which is composed of a single lens having an aspherical surface on both sides and focuses point images through first and second optical disc substrates having different thicknesses. A lens, wherein at least one aspherical surface is surrounded by an inner peripheral region inside a circular aperture centered on the optical axis and another circular aperture outside the inner peripheral region and outside the circular aperture. than the intermediate region and the intermediate region consists of three regions of the outer peripheral region, the aspherical shape of the inner peripheral region and the peripheral region is less thick of the first and second optical disk substrates different the thicknesses Previous
The spherical aberration corrected for the serial first optical disk substrate, a non-spherical shape of the intermediate region, the thickness of the optical disk substrate t5
When optimizing so that spherical aberration is corrected for
t5 satisfies the relationship of the following formula (10), and the outer peripheral region is formed with a step corresponding to the optical path length of an integral multiple of the wavelength in the optical axis direction with respect to the inner peripheral region.
1) to (13) are satisfied , and the second optical data is satisfied.
And the inner peripheral region when condensing light through a disk substrate
The focus position where the wavefront aberration in each of the intermediate regions is minimized
Equally, if the light is condensed through the second optical disk substrate,
Wave front convergence in the range of the inner peripheral region and the intermediate region of the mushroom
The third-order spherical aberration component S3 of the difference is substantially 0, and
Boundary between the region and the intermediate region and the intermediate region and the outer periphery
Both of the boundaries with the area are connected without steps,
The boundary between the intermediate region and the outer peripheral region is the intermediate region.
Characterized that you have been set to pass the intersection of the shape of the outer peripheral region.

1.0 <t5 <1.4 (10) t1 <t2 (11) 0.35 <NA2 <0.43 (12) 0.03 <NA3-NA2 <0.1 (13) where t1 : Thickness t2 of the first optical disk substrate: thickness NA2 of the second optical disk substrate NA2: NA of the objective lens at the boundary between the inner peripheral area and the intermediate area NA3: NA of the objective lens at the boundary between the intermediate area and the outer peripheral area This optical disk According to the third configuration of the objective lens for use,
With a single lens, a good focused spot can be obtained for both the first optical disc and the second optical disc, and as a result, good recording / reproducing characteristics can be obtained. Also, when collecting light through the second optical disk substrate
The wavefront aberrations in the inner and intermediate regions of
Reflected on the information medium surface due to the same focal position
When light is incident on the light receiving element, it is
Since it returns to the same position, it is possible to obtain accurate signal light.
Wear. Also, if the light is condensed through the second optical disk substrate,
3rd order of wavefront aberration in the range of inner circumference region and middle region
Since the spherical aberration component S3 of
The disc can be recorded and reproduced well.

[0026]

[0027]

[0028]

Further, in the third structure of the optical disk objective lens of the present invention, it is preferable that the boundary between the intermediate region and the outer peripheral region is set at the intersection of the shapes of the intermediate region and the outer peripheral region. Further, in the third configuration of the objective lens for an optical disc of the present invention, it is preferable that both the boundary between the inner peripheral region and the intermediate region and the boundary between the intermediate region and the outer peripheral region are connected without a step. In this way, the boundary between the intermediate region and the outer peripheral region is set at the intersection of the shapes of the intermediate region and the outer peripheral region, and both the boundary between the inner peripheral region and the intermediate region and the boundary between the intermediate region and the outer peripheral region are connected without steps. According to the preferable example described above, the step can be eliminated from the aspherical shape to facilitate the processing, and the ineffective portion can be eliminated from the surface shape to suppress the loss of the light amount.

In the third structure of the objective lens for an optical disk of the present invention, it is preferable that the objective lens is manufactured by glass molding or resin molding.

As described above, the objective lens for the optical disk of the present invention is designed so that the aberration correction of the single lens can obtain the necessary condensing performance with respect to the substrate thickness of the two optical disks. With respect to the aberration of the lens of the optical disc whose substrate thickness is small and whose NA is high, the total aberration is larger than that of the conventional one because it is necessary to consider the aberration in the optical disc whose substrate thickness is large. By changing the design shape in the peripheral area and providing a step in the optical axis direction at the boundary between the outer peripheral area and the inner peripheral area, it is possible to maintain a good shape of the spot on the side of the optical disc recorded with high density. . Further, regarding the aberration of the lens having the larger substrate thickness of the optical disc and the lower recording density and NA, the aberration in the required aperture is suppressed to be sufficiently small, and the aberration outside the required aperture is sharply deteriorated. The same effect as the case where the diaphragm is provided can be provided. As a result, information is recorded with stable performance,
Alternatively, the information can be reproduced.

Further, in the structure of the optical head device according to the present invention, the information medium surface is passed through the two light sources and the first and second optical disk substrates having the thicknesses corresponding to the respective light sources emitted from the two light sources. Light collecting means for collecting light on the top,
An optical head device comprising: a light beam separating unit for separating a light beam modulated by the information medium; and a light receiving unit for receiving light modulated by the information medium, wherein the light condensing unit is the present invention. Is an objective lens for optical discs.

Further, in the configuration of the optical information recording / reproducing apparatus according to the present invention, information is recorded on the information medium surfaces of the first and second optical disk substrates having different thicknesses by using the optical head device, or An optical information recording / reproducing apparatus for reproducing information recorded on an information medium surface, wherein the optical head apparatus of the present invention is used as the optical head apparatus.

According to the configurations of the optical head device and the optical information recording / reproducing device, recording / reproducing can be performed on two types of optical discs having different substrate thicknesses by one objective lens, so that the optical head device is inexpensive. Also, an optical information recording / reproducing device can be realized. Further, by giving the aberration content suitable for the state of each optical disk to any optical disk according to the aperture of the objective lens,
One objective lens for two different types of optical disks
Good recording, reproducing and erasing performance can be obtained.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to embodiments.

<First Embodiment> FIG. 1 shows a first embodiment of the present invention.
FIG. 11 shows an optical path diagram when light is focused on an optical disk using the optical disk objective lens in the embodiment.

As shown in FIG. 1, the objective lens 2 of the present embodiment is a single lens having aspherical surfaces on both sides, and the surface 3 on the light source side is a rotationally symmetric aspherical surface. The surface of the objective lens 2 on the optical disk 6 side is divided into an inner peripheral area 4 and an outer peripheral area 5. Then, the incident light ray 1 is incident on the objective lens 2, and then is condensed by the objective lens 2 on the information medium surface 6 a of the optical disc 6.

As the optical disk 6 to be reproduced or recorded, a first optical disk having a substrate thickness of 0.6 mm,
A second optical disc having a substrate thickness of 1.2 mm is prepared.

When the wavefront aberration (unit: mλ: rms) when converging through the first optical disk substrate is TW, it is desirable that TW satisfy the relation of the following expression (2).

0.05 <TW <0.12 (2) When TW is 0.05 or less, the aberration in the desired aperture when reproducing the second optical disk becomes too bad, which is satisfactory. It becomes impossible to obtain a good condensing characteristic. On the other hand, when the TW is 0.12 or more, the aberration on the first optical disc becomes too bad, and similarly, a satisfactory condensing characteristic cannot be obtained.

When NA of the objective lens 6 at the opening of the inner peripheral region 4 is NA1, NA1 is given by the following equation (3).
It is desirable to satisfy the relationship.

0.38 <NA1 <0.46 (3) If NA1 is 0.38 or less, the aperture for reproducing the second optical disc becomes too small, and the spot diameter becomes too large. . On the other hand, when NA1 is 0.46 or more, the aberration on the first optical disk is the above equation (2).
If the upper limit of is not exceeded, the aberration on the second optical disc cannot be satisfied, and as a result, the aberration on the first optical disc is deteriorated.

When the first optical disc is reproduced, the refractive index of the objective lens 2 at the wavelength of the light source when reproducing the first optical disc is n, the step in the optical axis direction between the inner peripheral region 4 and the outer peripheral region 5 is p, and the first optical disc is reproduced. When the wavelength of the light source is λ,
It is desirable that (n-1) / λ satisfy the relationship of the following expression (4).

0.1 <p (n-1) / λ <0.6 (4) When p (n-1) / λ is 0.1 or less or 0.6 or more, the first The condensing characteristics when reproducing the optical disk, especially the peak intensity of the airy ring becomes too high, and the reproducing characteristics of the optical disk 6 deteriorate.

When the fifth-order spherical aberration component of the wavefront aberration when converging through the first optical disk substrate is S5 (unit: λ: rms), S5 satisfies the relation of the following expression (5). Is desirable.

−0.03 <S5 <0.03 (5) When S5 is −0.03 or less or 0.03 or more, the first optical disc is the same as in the case of the above formula (4). The light condensing characteristics when reproducing data are reproduced, especially the peak intensity of airy ring becomes too high, and the reproduction characteristics of the optical disk 6 deteriorate.

Further, when the aspherical shape of the inner peripheral area 4 is optimized so that the spherical aberration is corrected with respect to the thickness t3 of the optical disk 6, t3 satisfies the relation of the following expression (6). desirable.

0.8 <t3 <1.2 (6) When t3 is 0.8 or less, the aberration correction for the second optical disc becomes insufficient. On the other hand, when t3 is 1.2 or more, the aberration with respect to the first optical disc deteriorates.

FIG. 2 is a structural diagram showing the shape of the surface of the objective lens on the optical disk side in the first embodiment of the present invention. As shown in FIG. 2, on the surface of the objective lens 2 on the optical disk 6 side, a step 7 (in the optical axis direction) substantially parallel to the optical axis is provided at the boundary between the inner peripheral region 4 and the outer peripheral region 5. . Figure 2
In the figure, the step 7 is drawn more emphasized than the actual step for the sake of clarity, but the actual step 7 is 0.3 μm.
Before and after. Such a shape is ideal, but for example, when the objective lens 2 is manufactured by glass molding, the mold is a very hard material such as cemented carbide, and grinding processing with a grindstone is necessary. Therefore, the step 7 at the boundary between the inner peripheral region 4 and the outer peripheral region 5 becomes a shape 8 such as an arc shape. However, the area where the actual shape 8 is different from the ideal shape 5 is, for example, about 35 μm in the radial direction when the radius of the grindstone is 2 mm, which is sufficient for the total effective diameter of the lens (about 4 mm). Very small and has little effect on lens performance.

Next, specific numerical examples of the optical disc objective lens 2 in the present embodiment will be shown. The following reference numerals are common to the following embodiments. However, the first surface of the objective lens 2 is the surface on the light source side, and the second surface is the surface on the optical disc 6 side. The optical disk 6 is a parallel plate. Further, the wavelength of the first light source that focuses on the first optical disk is 655 nm, and the wavelength of the second light source that focuses on the second optical disk is 800 nm. Further, the refractive index of the first light source of the first optical disk is 1.578353, and the refractive index of the second light source of the second optical disk is 1.57.
153.

F1: focal length WD of the objective lens in the first light source: working distance n of the objective lens with respect to the first optical disc n1: refractive index of the objective lens in the first light source d: lens thickness t1 of the objective lens: first Optical disc substrate thickness t2: second optical disc substrate thickness t3: optical disc substrate thickness when optimizing the aspherical shape of the inner peripheral region so that spherical aberration becomes 0: NA of objective lens NA NA1: within NA f2 of the objective lens in the aperture of the peripheral region: focal length WD2 of the objective lens in the second light source: working distance of the objective lens with respect to the second optical disc n2: refractive index TW of the objective lens in the second light source: first Wavefront aberration when focused on the first optical disc by the light source (unit: λ (wavelength): rms) p: step in the optical axis direction between the inner peripheral region and the outer peripheral region 3: Third-order spherical aberration component of wavefront aberration when focused on the first optical disc by the first light source (unit: λ (wavelength): rms) S5: Focused on the first optical disc by the first light source In this case, the fifth-order spherical aberration component of the wavefront aberration (unit is λ (wavelength): rms) and the aspherical shape is given by the following (Equation 1).

[0052]

[Equation 1]

However, the meaning of each symbol in the above (Equation 1) is as follows.

H: Height from the optical axis X: Distance from the tangent plane of the aspherical vertex of the point on the aspherical surface whose height from the optical axis is h C _j : Aspherical vertex of the j-th surface of the objective lens Curvature (C _j = 1
/ R _j ) K _j : Conical constant of the j-th surface of the objective lens A _{j, n} : n-th order aspherical coefficient of the j-th surface of the objective lens, where j = 1, 2 (Example 1) Specific numerical values of Example 1 are shown.

F1 = 3.3142 WD1 = 1.891 n1 = 1.602892 d = 1.8 t1 = 0.6 t2 = 1.2 t3 = 1.1 NA = 0.6 NA1 = 0.42 f2 = 3.3384 WD2 = 1.521 n2 = 1.59842 The lens shape parameters of the first surface are as follows.

R ₁ = 2.1700 K ₁ = -6.72993 × 10 ^-1 A _1,4 = 2.08530 × 10 ^-3 A _1,6 = 7.99922 × 10 ^-5 A _1,8 =- 7.97741 × 10 ⁻⁷ A _1,10 = −7.300341 × 10 ⁻⁶ The lens shape parameters in the inner peripheral area of the second surface are as follows.

R ₂ = −17.3537 K ₂ = −3.61277 × 10 A _2,4 = 4.06605 × 10 ⁻³ A _2,6 = −1.06794 × 10 ⁻³ A _2,8 = 9 _{^{.75688 × 10 -5 a 2,10 = -2.01568}} × 10 -6 lens shape parameters in the outer peripheral region of the second surface are as follows.

R ₂ = −16.46001 K ₂ = −7.90807 × 10 A _2,4 = 4.57207 × 10 ⁻³ A _2,6 = −1.35987 × 10 ⁻³ A _2,8 = 1 _{^{.72647 × 10 -4 a 2,10 = -8.80573}} × 10 -6 other lens parameters are as follows.

TW = 0.112 p = 0.00059274 p (n1-1) /λ=0.545 S3 = 0.0125 S5 = 0.0231 FIG. 3 shows an aberration diagram of this example. The first is shown in FIG.
3 shows the optical path length aberration with respect to the light source and the first optical disk, and FIG. 3B shows the optical path length aberration with respect to the second light source and the second optical disk. Further, FIG. 4 shows the cross-sectional intensity distribution of the spot focused on the first optical disc. Similarly, in the calculation of the cross-sectional intensity distribution of other spots, it was assumed that the light intensity distribution of the incident light was uniform. Incidentally, FIG.
The broken line in the figure shows an ideal point image intensity distribution on the wavefront with zero wavefront aberration. In addition, the maximum peak of the calculated point image is normalized to 1 and shown. In FIG. 4, the point image intensity distribution near the airy ring, which particularly affects the performance of the optical disk, is enlarged and shown. The above also applies to Examples 2 to 6 below.

The thickness of the first optical disk substrate is 0.6 mm
Therefore, it is desirable that the first optical disc is reproduced by using the objective lens 2 having NA of 0.6. As can be seen from FIG. 3A, the optical path length aberration with respect to the first light source and the first optical disc is about ± 0.25λ, and the wavefront aberration is 0.11.
It reaches 2λ: rms. However, as is clear from the cross-sectional intensity distribution of the spots shown in FIG. 4, there is almost no difference from the ideal spot shape without aberration, and reproduction or recording can be performed without any problem in terms of the performance of the optical disc 6.

The NA of the second optical disk is 0.4.
It is desirable to reproduce using the objective lens 2 of about 5, but as shown in FIG. 3B, the optical path length aberration with respect to the second light source and the second optical disc is very small within NA 0.42, It can be seen that at NA higher than that, it will increase rapidly. If the optical path length aberration is very large,
Since the light rays reflected on the information medium surface of the optical disc 6 do not return to the light receiving element, the result is the same as providing an aperture in the objective lens 2, and even for the optical disc 6 having a thickness of 1.2 mm, It is possible to satisfactorily perform reproduction or recording without newly providing an aperture in the objective lens 2.

(Example 2) Specific numerical values of Example 2 are shown below.

F1 = 3.3142 WD1 = 1.890 n1 = 1.602892 d = 1.8 t1 = 0.6 t2 = 1.2 t3 = 1.0 NA = 0.6 NA1 = 0.42 f2 = 3.3384 WD2 = 1.540 n2 = 1.59842 The lens shape parameter of the first surface and the lens shape parameters of the inner surface area and the outer surface area of the second surface are the same as those in the first embodiment.

Other lens parameters are as follows.

TW = 0.0743 p = 0.00030266 p (n1-1) /λ=0.279 S3 = 0.0025 S5 = −0.011 FIG. 5 shows an aberration diagram of this example. The first is shown in FIG.
Shows the optical path length aberration with respect to the light source and the first optical disc, and FIG. 5B shows the optical path length aberration with respect to the second light source and the second optical disc. Further, FIG. 6 shows the cross-sectional intensity distribution of the spot focused on the first optical disc.

The thickness of the first optical disk substrate is 0.6 mm
Therefore, it is desirable that the first optical disc is reproduced by using the objective lens 2 having NA of 0.6. As can be seen from FIG. 5A, the maximum optical path length aberration for the first light source and the first optical disc is about −0.4λ, and the wavefront aberration is 0.074λ: rms. However, as is clear from the cross-sectional intensity distribution of the spots shown in FIG. 6, there is almost no difference from the ideal spot shape without aberration, and reproduction or recording can be performed without any problem in the performance of the optical disc 6.

The NA of the second optical disc is 0.4.
It is desirable to reproduce by using the objective lens 2 of around 5, but as shown in FIG. 5B, the optical path length aberration with respect to the second light source and the second optical disk is very small within NA 0.42, It can be seen that at NA higher than that, it will increase rapidly. Therefore, as in Example 1, the objective lens 2 has the same aperture as the aperture, and the thickness is 1.
Even with respect to the 2 mm optical disk 6, it is possible to satisfactorily reproduce or record without providing a new opening in the objective lens 2.

(Embodiment 3) Specific numerical values of Embodiment 3 are shown below.

F1 = 3.3128 WD1 = 1.890 n1 = 1.602892 d = 1.8 t1 = 0.6 t2 = 1.2 t3 = 1.0 NA = 0.6 NA1 = 0.44 f2 = 3.3370 WD2 = 1.541 n2 = 1.59842 The lens shape parameters of the first surface are as follows.

R ₁ = 2.1700 K ₁ = -6.72993 × 10 ^-1 A _1,4 = 2.08530 × 10 ^-3 A _1,6 = 7.99922 × 10 ^-5 A _1,8 =- 7.97741 × 10 ⁻⁷ A _1,10 = −7.300341 × 10 ⁻⁶ The lens shape parameters in the inner peripheral area of the second surface are as follows.

R ₂ = −17.262666 K ₂ = −4.55689 × 10 A _2,4 = 4.13486 × 10 ⁻³ A _2,6 = −1.11949 × 10 ⁻³ A _2,8 = 1 _{^{.04423 × 10 -4 a 2,10 = -5.61508}} × 10 -7 lens shape parameters in the outer peripheral region of the second surface are as follows.

R ₂ = −16.46001 K ₂ = −7.90807 × 10 A _2,4 = 4.57207 × 10 ⁻³ A _2,6 = −1.35987 × 10 ⁻³ A _2,8 = 1 _{^{.72647 × 10 -4 a 2,10 = -8.80573}} × 10 -6 other lens parameters are as follows.

TW = 0.072 p = 0.00015135 p (n1-1) /λ=0.139 S3 = 0.0031 S5 = −0.028 FIG. 7 shows an aberration diagram of this example. The first is shown in FIG.
Shows the optical path length aberration with respect to the light source and the first optical disk, and FIG. 7B shows the optical path length aberration with respect to the second light source and the second optical disk. In addition, FIG. 8 shows the cross-sectional intensity distribution of the spot focused on the first optical disc.

The thickness of the first optical disk substrate is 0.6 mm
Therefore, it is desirable that the first optical disc is reproduced by using the objective lens 2 having NA of 0.6. As can be seen from FIG. 7A, the maximum optical path length aberration for the first light source and the first optical disc is about −0.5λ, and the wavefront aberration is 0.072λ: rms. However, as is clear from the cross-sectional intensity distribution of the spots shown in FIG. 8, there is almost no difference from the ideal spot shape without aberration, and reproduction or recording can be performed without any problem in the performance of the optical disc 6.

The NA of the second optical disc is 0.4.
It is desirable to reproduce by using the objective lens 2 of around 5, but as shown in FIG. 7B, the optical path length aberration with respect to the second light source and the second optical disc is very small within NA 0.44, It can be seen that at NA higher than that, it will increase rapidly. Therefore, as in Example 1, the objective lens 2 has the same aperture as the aperture, and the thickness is 1.
Even with respect to the 2 mm optical disk 6, it is possible to satisfactorily reproduce or record without providing a new opening in the objective lens 2.

(Example 4) Specific numerical values of Example 4 are shown below.

F1 = 3.3106 WD1 = 1.889 n1 = 1.602773 d = 1.805 t1 = 0.6 t2 = 1.2 t3 = 0.9 NA = 0.6 NA1 = 0.44 f2 = 3.3341 WD2 = 1.538 n2 = 1.59842 The lens shape parameters of the first surface are as follows.

R ₁ = 2.1700 K ₁ = -6.72993 × 10 ^-1 A _1,4 = 2.08530 × 10 ^-3 A _1,6 = 7.99922 × 10 ^-5 A _1,8 =- 7.97741 × 10 ⁻⁷ A _1,10 = −7.300341 × 10 ⁻⁶ The lens shape parameters in the inner peripheral area of the second surface are as follows.

R ₂ = −17.0574 K ₂ = −5.333838 × 10 A _2,4 = 4.25485 × 10 ⁻³ A _2,6 = −1.18514 × 10 ⁻³ A _2,8 = 1 _{^{.22997 × 10 -4 a 2,10 = -3.46201}} × 10 -6 lens shape parameters in the outer peripheral region of the second surface are as follows.

R ₂ = -16.46575 K ₂ = 0.0 A _2,4 = 6.772727 × 10 ^-3 A _2,6 = -1.61122 × 10 ^-3 A _2,8 = 1.965560 × _{^{10 -4 a 2,10 = -9.90970 × 10}} -6 other lens parameters are as follows.

TW = 0.0589 p = 0.00030266 p (n1-1) /λ=0.274 S3 = 0.018 S5 = -0.003 FIG. 9 shows an aberration diagram of this example. In FIG. 9A, the first
9 shows the optical path length aberration with respect to the light source and the first optical disc, and FIG. 9B shows the optical path length aberration with respect to the second light source and the second optical disc. In addition, in FIG.
3 shows a cross-sectional intensity distribution of spots focused on the optical disc of FIG.

The thickness of the first optical disk substrate is 0.6 mm
Therefore, it is desirable that the first optical disc is reproduced by using the objective lens 2 having NA of 0.6. As can be seen from FIG. 9A, the maximum optical path length aberration for the first light source and the first optical disc is about −0.3λ, and the wavefront aberration is 0.059λ: rms. However, as is clear from the cross-sectional intensity distribution of the spots shown in FIG. 10, there is almost no difference from the ideal spot shape without aberrations.
The peak intensity of the Airy ring is lower than the ideal point image intensity distribution, and reproduction or recording can be performed without any problem in the performance of the optical disc 6.

The NA of the second optical disk is 0.4.
It is desirable to reproduce by using the objective lens 2 of about 5, but as shown in FIG. 9B, the optical path length aberration with respect to the second light source and the second optical disc is very small within NA 0.44, It can be seen that at NA higher than that, it will increase rapidly. Therefore, as in Example 1, the objective lens 2 has the same aperture as the aperture, and the thickness is 1.
Even with respect to the 2 mm optical disk 6, it is possible to satisfactorily reproduce or record without providing a new opening in the objective lens 2.

<Second Embodiment> FIG. 11 shows an optical path diagram when light is focused on an optical disk by using an optical disk objective lens according to a second embodiment of the present invention.

As shown in FIG. 11, the objective lens 2 of the present embodiment is composed of a single lens having aspherical surfaces on both sides, and the surface 3 on the light source side is a rotationally symmetric aspherical surface. The surface of the objective lens 2 on the optical disk 6 side is divided into an inner peripheral area 9, an intermediate area 10, and an outer peripheral area 11. Then, the incident light ray 1 is incident on the objective lens 2, and then is condensed by the objective lens 2 on the information medium surface 6 a of the optical disc 6.

Here, NA of the objective lens 2 at the boundary between the inner peripheral region 9 and the intermediate region 10 is NA2, and the intermediate region 10 is
When NA of the objective lens 2 at the boundary between the outer peripheral region 11 and the outer peripheral region 11 is NA3, NA2 and NA3 are expressed by the following formula (7),
It is desirable to satisfy the relationship of (8).

0.35 <NA2 <0.43 (7) 0.03 <NA3-NA2 <0.1 (8) If NA2 is 0.35 or less or 0.43 or more, the second The desired spot diameter cannot be obtained for the optical disc. Further, when NA3-NA2 is 0.03 or less, the width of the intermediate region 10 becomes too narrow, and it becomes difficult to correct the aberration with respect to the second optical disc. On the other hand, N
On the contrary, when A3-NA2 is 0.1 or more, the intermediate region 1
The width of 0 becomes too wide, and the aberration with respect to the first optical disc deteriorates.

Further, when the aspherical shape of the intermediate region 10 is optimized so that the spherical aberration is corrected with respect to the thickness t4 of the optical disk 6, it is desirable that t4 satisfy the relation of the following expression (9). .

1.4 <t4 <2.0 (9) When t4 is 1.4 or less or 2.0 or more, the aberration with respect to the second optical disk is deteriorated.

FIG. 12 is a structural diagram showing the shape of the surface of the objective lens on the optical disk side in the second embodiment of the present invention. As shown in FIG. 12, on the surface of the objective lens 2 on the optical disk 6 side, a step 12 that is substantially parallel to the optical axis is provided at the boundary between the inner peripheral area 9 and the intermediate area 10. In FIG. 12, the step 12 is drawn more emphasized than the actual step for the sake of clarity, but the actual step 12 is 0.3 μm.
Before and after. Such a shape is ideal, but if grinding is performed with a grindstone in actual processing, the inner peripheral region 9
The step 12 at the boundary between the intermediate region 10 and the intermediate region 10 is, for example,
The shape 13 becomes an arc shape. However, the area where the actual shape 13 is different from the ideal shape 10 is, for example, about 35 μm in the radial direction when the radius of the grindstone is 2 mm, which is sufficient for the total effective diameter of the lens (about 4 mm). Very small and has little effect on lens performance. On the other hand, the shape of the intermediate region 10 is determined so that no step is formed at the boundary between the intermediate region 10 and the outer peripheral region 11.

Next, specific numerical examples of the objective lens 2 for an optical disk in the present embodiment will be shown. In addition to the common reference numerals shown in the first embodiment, the following reference numerals are added.

NA2: NA of the objective lens at the boundary between the inner peripheral region and the intermediate region NA3: NA of the objective lens at the boundary between the intermediate region and the outer peripheral region t4: The spherical aberration of the aspherical shape of the intermediate region becomes 0 Thickness of Optical Disc Substrate when Optimized for (Example 5) Hereinafter, specific numerical values of Example 5 will be shown.

F1 = 3.300 WD1 = 1.890 n1 = 1.602972 d = 1.8 t1 = 0.6 t2 = 1.2 t4 = 1.8 NA2 = 0.39 NA3 = 0.44 f2 = 3.3241 WD2 = 1.538 n2 = 1.59842 The lens shape parameters of the first surface are as follows.

R ₁ = 2.1700 K ₁ = -6.72993 × 10 ^-1 A _1,4 = 2.08530 × 10 ^-3 A _1,6 = 7.99922 × 10 ^-5 A _1,8 =- 7.97741 × 10 ⁻⁷ A _1,10 = −7.300341 × 10 ⁻⁶ The lens shape parameters in the inner peripheral region and the outer peripheral region of the second surface are as follows.

R ₂ = -16.46001 K ₂ = -7.90807 × 10 A _2,4 = 4.57207 × 10 ⁻³ A _2,6 = −1.35987 × 10 ⁻³ A _2,8 = 1 _{^{.72647 × 10 -4 a 2,10 = -8.80573}} × 10 -6 lens shape parameters in the intermediate region of the second surface are as follows.

R ₂ = -18.9318 K ₂ = 1.65803 × 10 A _2,4 = 2.81973 × 10 ⁻³ A _2,6 = −4.83241 × 10 ⁻⁴ A _2,8 = −3 .23374 × 10 ^-5 a _2,10 = 1.75251 in × 10 ^-5 13 shows an aberration diagram of the present embodiment. FIG. 13A shows the optical path length aberration with respect to the first light source and the first optical disk, and FIG. 13B shows the optical path length aberration with respect to the second light source and the second optical disk. In addition, FIG.
The cross-sectional intensity distribution of the spot focused on the first optical disk is shown in FIG.

The thickness of the first optical disk substrate is 0.6 mm
Therefore, it is desirable that the first optical disc is reproduced by using the objective lens 2 having NA of 0.6. As can be seen from FIG. 13A, the optical path length aberration for the first light source and the first optical disc is about −0.5λ near NA 0.4. However, as is apparent from the cross-sectional intensity distribution of the spots shown in FIG. 14, there is almost no difference from the ideal spot shape without aberration, and reproduction or recording can be performed without any problem in the performance of the optical disc 6.

The second optical disc has an NA of 0.4.
It is desirable to reproduce by using the objective lens 2 of around 5, but as shown in FIG. 13B, the optical path length aberration with respect to the second light source and the second optical disk is small within NA 0.44, and more than that. It can be seen that the NA increases rapidly. When the optical path length aberration is very large, the light beam reflected on the information medium surface of the optical disc 6 does not return to the light receiving element. As a result, the objective lens 2 is provided with an aperture and the thickness is reduced. Even with respect to the 1.2 mm optical disc 6, it is possible to satisfactorily perform reproduction or recording without providing a new aperture in the objective lens 2.

<Third Embodiment> FIG. 15 shows an optical path diagram when light is focused on an optical disk using an optical disk objective lens according to a third embodiment of the present invention.

As shown in FIG. 15, the objective lens 2 of the present embodiment is composed of a single lens having aspherical surfaces on both sides, and the light source side surface 3 is a rotationally symmetric aspherical surface. The surface of the objective lens 2 on the optical disk 6 side is divided into an inner peripheral area 14, an intermediate area 15, and an outer peripheral area 16. Then, the incident light ray 1 is incident on the objective lens 2, and then is condensed by the objective lens 2 on the information medium surface 6 a of the optical disc 6.

Here, when the aspherical shape of the intermediate region 15 is optimized so that the spherical aberration is corrected with respect to the substrate thickness t5 of the optical disk 6, t5 satisfies the relationship of the following expression (10). Is desirable.

1.0 <t5 <1.4 (10) When t5 is 1.0 or less, or 1.4 or more, from the boundary between the inner peripheral region 14 and the outer peripheral region 16 for the second optical disc. Also, the spherical aberration at the inner opening deteriorates.

The NA of the objective lens 2 at the boundary between the inner peripheral region 14 and the intermediate region 15 is NA2, and the intermediate region 15 is
When the NA of the objective lens 2 at the boundary between the outer peripheral region 16 and the outer peripheral region 16 is NA3, NA2 and NA3 are given by the following formula (12),
It is desirable to satisfy the relationship of (13).

0.35 <NA2 <0.43 (12) 0.03 <NA3-NA2 <0.1 (13) If NA2 is 0.35 or less or 0.43 or more, the second The desired spot diameter cannot be obtained for the optical disc. Further, when NA3-NA2 is 0.03 or less, the width of the intermediate region 15 becomes too narrow, and it becomes difficult to correct the aberration with respect to the second optical disc. On the other hand, N
On the contrary, when A3-NA2 is 0.1 or more, the intermediate region 1
The width of 5 becomes too wide, and the aberration with respect to the first optical disk deteriorates.

FIG. 16 is a structural diagram showing the shape of the surface of the objective lens on the optical disk side in the third embodiment of the present invention. As shown in FIG. 16, on the surface of the objective lens 2 on the optical disk 6 side, the boundary between the inner peripheral region 14 and the intermediate region 15 is connected without a step. The outer peripheral region 16 has a shape 1 whose optical path length is shifted by one wavelength from the inner peripheral region 14.
Is equal to 7. In addition, the boundary between the intermediate region 15 and the outer peripheral region 16 is set so that no step is formed at the boundary between the intermediate region 15 and the outer peripheral region 16.

As described above, in the objective lens 2 of the present embodiment, since the step is not provided between the inner peripheral region, the middle region, and the outer peripheral region, the processing is facilitated.

(Embodiment 6) Specific numerical values of Embodiment 6 are shown below.

F1 = 3.300 WD1 = 1.890 n1 = 1.602972 d = 1.8 t1 = 0.6 t2 = 1.2 t4 = 1.2 NA2 = 0.39 NA3 = 0.46 f2 = 3.3241 WD2 = 1.539 n2 = 1.59842 The lens shape parameters of the first surface are as follows.

R ₁ = 2.1700 K ₁ = -6.72993 × 10 ^-1 A _1,4 = 2.08530 × 10 ^-3 A _1,6 = 7.99922 × 10 ^-5 A _1,8 =- 7.97741 × 10 ⁻⁷ A _1,10 = −7.300341 × 10 ⁻⁶ The lens shape parameters in the inner peripheral region and the outer peripheral region of the second surface are as follows. However, the intersection of the shape of the outer peripheral region with the optical axis is translated to the first surface side by 0.00109 with respect to that of the inner peripheral region.

R ₂ = -16.46001 K ₂ = -7.90807 × 10 A _2,4 = 4.57207 × 10 ⁻³ A _2,6 = −1.35987 × 10 ⁻³ A _2,8 = 1 _{^{.72647 × 10 -4 a 2,10 = -8.80573}} × 10 -6 lens shape parameters in the intermediate region of the second surface are as follows. However, the intersection of the shape of the intermediate region with the optical axis is translated by 0.0003419 to the first surface side relative to that of the inner peripheral region.

R ₂ = −17.3870 K ₂ = −2.71760 × 10 A _2,4 = 3.98819 × 10 ⁻³ A _2,6 = −9.93390 × 10 ⁻⁴ A _2,8 = 6 to _{^{.64032 × 10 -5 a 2,10 = 6.11772}} × 10 -6 FIG. 17 shows an aberration diagram of the present embodiment. FIG. 17A shows the optical path length aberration with respect to the first light source and the first optical disc, and FIG. 17B shows the optical path length aberration with respect to the second light source and the second optical disc. In addition, FIG.
The cross-sectional intensity distribution of the spot focused on the first optical disk is shown in FIG. As can be seen from FIG. 17A, the optical path length aberration for the first light source and the first optical disc has an NA of 0.
One wavelength is shifted by 46 or more, but as is clear from the cross-sectional intensity distribution of the spot shown in FIG. 18, there is almost no difference from the ideal spot shape without aberration, and the optical disc 6
Playback or recording is possible without any problem in terms of performance.

The NA of the second optical disk is 0.4.
It is desirable to reproduce by using the objective lens 2 of about 5, but as shown in FIG. 17B, the optical path length aberration with respect to the second light source and the second optical disk is small within NA 0.46, and more than that. It can be seen that the NA increases rapidly. When the optical path length aberration is very large, the light beam reflected on the information medium surface of the optical disc 6 does not return to the light receiving element. As a result, the objective lens 2 is provided with an aperture and the thickness is reduced. Even with respect to the 1.2 mm optical disc 6, it is possible to satisfactorily perform reproduction or recording without newly providing an aperture in the objective lens 2.

Further, when the light is focused on the second optical disk, the intermediate region 1 is adjusted so that the focus positions at which the wavefront aberrations of the inner peripheral region 14 and the intermediate region 15 are minimized are equal to each other.
Five shapes are designed. Therefore, when the light beam reflected on the information medium surface of the optical disc 6 enters the light receiving element,
Since the inner peripheral region 14 and the intermediate region 15 return to the same position, accurate signal light can be obtained.

Furthermore, in this embodiment, the third-order spherical aberration component of the wavefront aberration in the range of the inner peripheral area 14 and the intermediate area 15 when focused on the second optical disk is -0.0019.
Since λ is very small, the second optical disk can be satisfactorily reproduced or recorded.

The objective lens 2 shown in each of Examples 1 to 6 is preferably manufactured by glass molding or resin molding. By processing the aspherical shape into a mold, it becomes possible to mass-produce lenses having the same shape and performance at low cost.

<Fourth Embodiment> Next, an optical head device and an optical information recording / reproducing device using the objective lens 2 for an optical disk in the first to third embodiments will be described.
This will be described with reference to FIG. FIG. 19 is a configuration diagram showing an optical head device and an optical information recording / reproducing device according to a fourth embodiment of the present invention.

As shown in FIG. 19, the luminous flux 19 emitted from the semiconductor laser 18 having a wavelength of 655 nm which is the first light source.
Is converted into substantially parallel light by the collimator lens 20. Light flux 19 that has been converted into substantially parallel light by the collimator lens 20
Passes through the beam splitter 21, and the first to third
With the objective lens 2 shown in the embodiment of
The light is focused on the information medium surface 23a of the first optical disc 23 having a size of mm. Further, the light flux 25 emitted from the semiconductor laser 24 having a wavelength of 800 nm, which is the second light source, becomes substantially parallel light by the collimator lens 26. The light beam 25, which has been converted into substantially parallel light by the collimator lens 26, is reflected by the beam splitter 21 and is also reflected by the same objective lens 2 on the information medium surface 27a of the second optical disk 27 having a thickness of 1.2 mm.
Focused on top. Here, the objective lens 2 is attached to a movable holder 28, and its focus is always on the information medium surface in accordance with the surface deviation of the optical disc, and also has the function of limiting the opening of the objective lens 2. To do. The focused spot is diffracted by the unevenness formed on the information medium surface 23a or 27a. Information medium surface 23a or 2
The laser light (light flux 19 or 25) diffracted by 7a and reflected is reflected by the beam splitter 21, refracted by the convex lens 29 and the cylindrical lens 30, and condensed on the light receiving element 31. Then, a change in the amount of light modulated by the information medium surface 23a or 27a is detected by the electric signal of the light receiving element 31, and the data is read.

When light is focused on the first optical disk 23 having a substrate thickness of 0.6 mm by using the first light source having a wavelength of 655 nm as described above, the objective lens 2 has a large wavefront aberration value but is focused. In particular, the spots have relatively low airy ring strength, which has a great influence on the recording / reproducing of the first optical disk 23, and therefore good recording / reproducing characteristics can be obtained.

In addition, as described above, the second wavelength of 800 nm is used.
When light is focused on the second optical disc 27 having a substrate thickness of 1.2 mm by using the light source of No. 2, the aperture of the lens holder 28 remains equivalent to NA 0.6, but the N of the objective lens 2 is N.
When A is 0.4 to 0.45 or more, the optical path length aberration is drastically increased, which is the same as when the objective lens 2 is provided with an aperture. Also on the light-receiving side, when the NA is 0.4 to 0.45 or more, the light beam comes to the outside of the light-receiving element 31 due to the large optical path length aberration. As a result, the objective lens 2 is masked ( It is the same as having the opening). Of course, NA is 0.4 to 0.4
Since the optical path length aberration is sufficiently corrected for the second light source within the range of 5, the second optical disc 2 having a thickness of 1.2 mm
7, good recording and reproducing characteristics can be obtained.

As described above, by providing the objective lens 2 with the aberration content suitable for the state of each optical disk, good recording and reproduction can be performed with one lens for two different kinds of optical disks. .

Although the wavelength of the light source is set to 655 nm and 800 nm in the above embodiment, other wavelengths such as 400 nm and 650 nm may be combined.

In the above embodiment, the substrate thicknesses of the two types of optical disks are set to 0.6 mm and 1.2 mm, but other thicknesses such as 0.3 mm and 0.6 mm are set.
It may be a combination such as mm.

In the above embodiment, the refractive index of the objective lens 2 is set to about 1.6, but within the range of usable glass materials and resin materials, for example, 1.
Those in the range of 45 to 2.0 may be used.

Although the NA for the first optical disk is set to 0.6 in the above embodiment, the NA may be higher or lower than this.

Further, in the above embodiment, a step or the like is formed on the surface (second surface) of the objective lens 2 on the side of the optical disk, but a step is formed on the surface (first surface) of the objective lens 2 on the light source side. Etc. may be formed. Further, the function shown in the above embodiment may be added to an optical element such as a parallel plate different from the conventional single lens.

Further, in the above embodiment, the aperture limit is not changed for the objective lens 2 depending on the substrate thickness of the optical disk, but the aperture limit may be added according to the different substrate thickness.

In the above embodiment, the case where substantially parallel light is made incident on the optical disc objective lens 2 has been described as an example, but the light emitted from the semiconductor laser is directly collected by one lens. It is also possible to use a lens having a finite magnification that emits light or diverges or converges light instead of making it substantially parallel light by a collimating lens.

[0128]

As described above, according to the present invention,
Objective lens for optical disc, which is composed of one lens and can satisfy good condensing characteristics according to the optical disc for both two types of optical discs having different substrate thicknesses, and an optical head using the same The device and the optical information recording / reproducing device can be realized.

[Brief description of drawings]

FIG. 1 is an optical path diagram when light is focused on an optical disk using an optical disk objective lens according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a shape of a surface of an objective lens for an optical disk on the optical disk side according to the first embodiment of the present invention.

FIG. 3 is an aberration diagram of Example 1 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 4 is a graph showing a point image intensity distribution of Example 1 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 5 is an aberration diagram of Example 2 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 6 is a graph showing a point image intensity distribution of Example 2 of the optical disk objective lens according to the first embodiment of the invention.

FIG. 7 is an aberration diagram of Example 3 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 8 is a graph showing a point image intensity distribution of Example 3 of the optical disk objective lens according to the first embodiment of the invention.

FIG. 9 is an aberration diagram of Example 4 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 10 is a graph showing a point image intensity distribution of Example 4 of the objective lens for the optical disk according to the first embodiment of the invention.

FIG. 11 is an optical path diagram when light is focused on an optical disk using the optical disk objective lens according to the second embodiment of the present invention.

FIG. 12 is a configuration diagram showing a shape of an optical disk side surface of an optical disk objective lens according to a second embodiment of the present invention.

FIG. 13 is an aberration diagram of Example 5 of the optical disk objective lens according to the second embodiment of the invention.

FIG. 14 is a graph showing a point image intensity distribution of Example 5 of the optical disk objective lens according to the second embodiment of the invention.

FIG. 15 is an optical path diagram when light is focused on an optical disk by using the optical disk objective lens according to the third embodiment of the present invention.

FIG. 16 is a configuration diagram showing a shape of an optical disk side surface of an optical disk objective lens according to a third embodiment of the present invention.

FIG. 17 is an aberration diagram of Example 6 of the optical disk objective lens according to the third embodiment of the invention.

FIG. 18 is a graph showing a point image intensity distribution of Example 6 of the objective lens for the optical disk according to the third embodiment of the invention.

FIG. 19 is a configuration diagram showing an optical head device and an optical information recording / reproducing device according to a fourth embodiment of the present invention.

FIG. 20 is an optical path diagram when light is focused on an optical disc using a conventional objective lens for optical discs.

[Explanation of symbols]

1 incident ray 2 Objective lens 3 Objective lens light source side surface 4 Inner peripheral area of the disk-side surface of the objective lens 5 Outer peripheral area of the disk-side surface of the objective lens 6 optical disks 6a Information medium side 7 steps 9 Inner peripheral area of the disk-side surface of the objective lens 10 Intermediate area of the disk-side surface of the objective lens 11 Outer peripheral area of the disk-side surface of the objective lens 14 Inner peripheral area of the disk-side surface of the objective lens 15 Intermediate area of the disk-side surface of the objective lens 16 Outer peripheral area of the disk-side surface of the objective lens 18 Semiconductor laser 19 luminous flux 20 Collimating lens 21 Beam splitter 23 First Optical Disk 23a Information medium surface 24 Semiconductor laser 25 luminous flux 26 Collimating lens 27 Second optical disc 27a Information medium surface 28 Holder 29 Convex lens 30 Cylindrical lens 31 Light receiving element

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-26726 (JP, A) JP-A-10-228667 (JP, A) JP-A-10-319316 (JP, A) JP-A-9- 184975 (JP, A) JP 9-230114 (JP, A) JP 9-197108 (JP, A) JP 10-255305 (JP, A) JP 11-96585 (JP, A) JP-A-11-2759 (JP, A) JP-A-10-143905 (JP, A) JP-A-9-145995 (JP, A) JP-A-9-145994 (JP, A) JP-A-2000-56216 ( JP, A) JP 2000-28918 (JP, A) JP 2003-50347 (JP, A) JP 2003-51135 (JP, A) JP 2000-231057 (JP, A) JP 2001-236686 ( JP, A) JP 2001-236687 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 13/00 G11B 7/135

Claims (10)

(57) [Claims] 1. An objective lens for an optical disc, which comprises a single lens having aspherical surfaces on both sides and focuses point images through first and second optical disc substrates having different thicknesses, wherein at least one aspherical surface has an optical axis. It is composed of two regions, an inner peripheral region inside the circular opening as the center and an outer peripheral region outside the inner peripheral region, and the aspherical shape of the outer peripheral region is
The spherical aberration is corrected for small the first optical disk substrate thicknesses of the first and second optical disk substrates different the thicknesses, the aspherical shape of the inner peripheral region, the thickness larger the second optical disk the spherical aberration is corrected with respect to the substrate, the boundary between the peripheral region and the inner region is in contact with a step in the optical axis direction, satisfies the following relationship formula (1) to (4), and the Wavefront when focused through the first optical disc substrate
The wavefront when the third-order spherical aberration component S3 of the aberration is substantially 0 and the light is focused through the first optical disk substrate.
The fifth-order spherical aberration component S5 of the aberration (unit: λ: rms) is
In addition to satisfying the relationship of the following formula (5),
The aspherical shape is spherical with respect to the thickness t3 of the optical disc substrate.
When optimizing so that the aberration is corrected, t3 is given by
An objective lens for an optical disc, which satisfies the relationship of (6) . t1 <t2 (1) 0.05 <TW <0.12 (2) 0.38 <NA1 <0.46 (3) 0.1 <p (n-1) / λ <0.6 (4) − 0.03 <S5 <0.03 (5) 0.8 <t3 <1.2 (6) where, t1: thickness of the first optical disc substrate t2: thickness of the second optical disc substrate NA1: inner peripheral area NA TW of the objective lens at the aperture: Wavefront aberration when condensed through the first optical disc substrate (unit: λ: rms) n: Refractive index p of the objective lens at the wavelength of the light source when reproducing the first optical disc: Step difference λ in the optical axis direction between the inner peripheral region and the outer peripheral region: wavelength of the light source when reproducing the first optical disc 2. The objective lens for an optical disk according to claim 1, wherein the step between the inner peripheral region and the outer peripheral region has an arcuate cross section. 3. The objective lens for an optical disk according to claim 1, which is produced by glass molding or resin molding. 4. An objective lens for an optical disc, which comprises a single lens having aspherical surfaces on both sides and focuses point images through first and second optical disc substrates having different thicknesses, at least one aspherical surface having an optical axis. Three of an inner peripheral area inside a circular opening which is the center, an intermediate area surrounded by another circular opening outside the inner peripheral area outside the inner peripheral area and an outer peripheral area outside the intermediate area. consists regions, non-spherical shape of the said inner region outer peripheral region, the spherical aberration is corrected for small the first optical disk substrate thicknesses of the first and second optical disk substrates different the thicknesses, The aspherical shape of the intermediate region has first and second different thicknesses.
Spherical aberration is corrected with respect to an optical disc substrate having a thickness larger than any of the optical disc substrates described above , the relations of the following expressions (7) and (8) are satisfied , and the aspherical shape of the intermediate region is set to Thickness t
4 is optimized so that spherical aberration is corrected
When t4 satisfies the relation of the following formula (9),
The boundary between the area and the intermediate area, or the intermediate area and the outer area
An objective lens for an optical disc, characterized in that one of the boundaries is connected without a step . 0.35 <NA2 <0.43 (7) 0.03 <NA3-NA2 <0.1 (8) 1.4 <t4 <2.0 (9) However, NA2: between the inner peripheral region and the intermediate region NA of Objective Lens at Boundary NA3: NA of Objective Lens at Boundary between Intermediate Region and Outer Region 5. The objective lens for an optical disk according to claim 4, wherein the step between the inner peripheral region and the intermediate region or the step between the intermediate region and the outer peripheral region has an arcuate cross section. 6. The objective lens for an optical disc according to claim 4, which is produced by glass molding or resin molding. 7. An optical disk objective lens comprising a single lens having aspherical surfaces on both sides and condensing point images through first and second optical disk substrates having different thicknesses, wherein at least one aspherical surface has an optical axis. Three of an inner peripheral area inside a circular opening which is the center, an intermediate area surrounded by another circular opening outside the inner peripheral area outside the inner peripheral area and an outer peripheral area outside the intermediate area. consists regions, non-spherical shape of the said inner region outer peripheral region, the spherical aberration is corrected for small the first optical disk substrate thicknesses of the first and second optical disk substrates different the thicknesses, When the aspherical shape of the intermediate region is optimized so that the spherical aberration is corrected with respect to the thickness t5 of the optical disc substrate, t5 satisfies the relationship of the following expression (10), and the outer peripheral region is the inner peripheral region. To the area Axially it is formed with a step corresponding to the optical path length of an integral multiple of the wavelength, satisfying a relationship represented by the following formula (11) to (13), and said time for focusing through the second optical disc substrate
Minimize the wavefront aberrations in the inner and intermediate regions
The same focus positions are obtained, and when the light is focused through the second optical disk substrate,
Third-order wavefront aberration in the range of the inner peripheral region and the intermediate region
Has a spherical aberration component S3 of substantially 0, and the boundary between the inner peripheral region and the intermediate region and the intermediate region
And the boundary between the outer peripheral region and
And the boundary between the intermediate area and the outer peripheral area is
Set at the intersection of the shapes of the intermediate area and the outer peripheral area
There objective lens for an optical disk according to claim Rukoto. 1.0 <t5 <1.4 (10) t1 <t2 (11) 0.35 <NA2 <0.43 (12) 0.03 <NA3-NA2 <0.1 (13) However, t1: 1st Of the optical disc substrate t2: the thickness of the second optical disc substrate NA2: NA of the objective lens at the boundary between the inner peripheral region and the intermediate region NA3: NA of the objective lens at the boundary between the intermediate region and the outer peripheral region 8. The objective lens for an optical disk according to claim 7, which is manufactured by glass molding or resin molding. 9. A light source, and a light condensing means for condensing light beams emitted from the two light sources onto an information medium surface through first and second optical disk substrates having thicknesses corresponding to the respective light sources. An optical head device comprising: a light beam separating means for separating a light beam modulated by an information medium; and a light receiving means for receiving a light beam modulated by the information medium, wherein the light condensing means is a light emitting device. 9. An optical head device, which is the objective lens for an optical disc according to any one of items 8. 10. An optical system for recording information on the information medium surface of the first and second optical disc substrates having different thicknesses or reproducing the information recorded on the information medium surface by using the optical head device. An optical information recording / reproducing apparatus, wherein the optical head apparatus according to claim 9 is used as the optical head apparatus.