JP2003177312A - Objective lens for optical pickup, optical pickup and optical information processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an objective lens having a large numerical aperture (NA) with a single lens structure. <P>SOLUTION: The objective lens is for condensing a light beam emitted from a light source upon a recording face of an optical recording medium as a spot in an infinity type optical pickup in which one or more of recording, reproducing and deleting information are performed on the optical recording medium of which the used wavelength is 650±20 nm and the thickness of the substrate on the light-irradiated side is 0.1 mm and the lens is formed as a single lens, both sides of which are aspherical, and the aperture number NA is 0.65≤NA<0.75, the near axis curvature radius on the light source side R1, the working distance WD, the refractive index of material for d-line nd and the focal distance f satisfy respective subscribed conditions. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens for an optical pickup, an optical pickup and an optical information processing device.

[0002]

2. Description of the Related Art CD (Compact Disc) and DVD
In contrast to "optical recording media" represented by (digital video discs), "optical information processing devices" that record, reproduce, and erase information using optical pickups have become widespread and are indispensable in daily life. Is becoming. In such an optical information processing technique, a high density of information recording on an optical recording medium is constantly required.

The light spot formed on the recording surface of the optical recording medium is formed by the beam waist of the laser beam focused by the objective lens of the optical pickup, and the beam waist diameter is inversely proportional to the numerical aperture (NA) of the objective lens. However, since it is proportional to the wavelength of the laser light flux, it is required to increase the numerical aperture of the objective lens in the optical pickup and to shorten the wavelength of the laser light flux as a measure for realizing high density information recording.

For shortening the wavelength of the laser beam, DVD
A semiconductor laser having an "emission wavelength near 660 nm" for commercial use has already been put to practical use, and recently, a laser light source with a wavelength of about 400 nm is being put to practical use.

As an objective lens having a large numerical aperture, N
A: 0.7 or more have been proposed (for example, JP-A-10-123410). However, since all the objective lenses with a large numerical aperture proposed so far are “two-lens set”, the number of assembling steps is increased compared to the one-lens objective lens.
It is inevitable to improve the accuracy of assembly, and there is a problem such as difficulty in high-speed driving due to increased weight.

Further, in the two objective lenses, the working distance corresponding to the distance from the optical recording medium becomes small, and the possibility that the optical recording medium and the lens are damaged by the contact between the information recording medium and the objective lens increases. However, it is difficult to achieve high reliability.

On the other hand, although the objective lens having a single-lens structure does not have the above problem, it is difficult to increase the numerical aperture, and the currently known one has a numerical aperture of about 6.5. Is the maximum.

Conventionally, the "light irradiation side substrate thickness (the distance from the surface irradiated with light to the recording surface)" in an optical recording medium
Is 1.2 mm for CD and 0.6 m for DVD
m is the standard, but recently, the thickness of the substrate on the light irradiation side is 0.1 mm.
There is a trend toward standardization, and it is believed that this new standard will be realized sooner or later.

The emission wavelength of a semiconductor laser generally used as a light source of an optical pickup has "variation" among individuals, and the semiconductor laser has a phenomenon of mode hopping in which the center wavelength changes by several nm due to temperature change or the like. There is also.

In the optical pickup, the wavelength radiated from the semiconductor laser is "varied for each individual",
If it differs from the reference wavelength of the optical system design or if it changes due to mode hopping, chromatic aberration will occur in the optical pickup optical system, and the spot diameter of the optical spot on the recording surface will increase, which may interfere with the recording and reproducing operations. There is

In particular, when a short wavelength semiconductor laser having an emission wavelength of 440 nm or less is used as a light source, chromatic aberration caused in the objective lens due to wavelength fluctuation becomes an unacceptable problem. That is, in such a short wavelength region, the change in the refractive index with respect to a minute wavelength change becomes large, the chromatic aberration also becomes large, and the defocus amount which is the amount of movement of the focus becomes large. Therefore, when the diameter of the light spot is reduced, the depth of focus of the objective lens: d, wavelength: λ, numerical aperture: NA
And d = λ / (NA) ² , the shorter the wavelength: λ, the smaller the depth of focus: d, and the tolerance for defocus becomes stricter.

Light irradiation side substrate thickness of optical recording medium: 0.1 mm
On the other hand, a manufacturing error of about ± 10 nm is inevitable. Such a substrate thickness error may cause spherical aberration in the image formation of the objective lens designed according to the standard substrate thickness to expand the light spot diameter, which may hinder the operation of the optical pickup. As is well known, spherical aberration occurs in proportion to the numerical aperture of the objective lens: the fourth power of NA, so that the influence of the substrate thickness error increases as the numerical aperture of the objective lens increases.

As an optical recording medium, a so-called "multi-layer optical recording medium" in which recording surfaces are superposed on a plurality of layers has recently been put into practical use in order to increase the recording capacity. In the multilayer optical recording medium,
Since recording / reproducing / erasing of information is performed independently on multiple recording surfaces, recording surface spacing (spacer thickness) of several tens of μm or more
Since the distance from the objective lens is different for each recording surface, spherical aberration occurs on the recording surface deviated from the optimum position.

[0014]

In view of the above-mentioned circumstances, the present invention uses an objective lens for an optical pickup having a single lens structure and a large NA, which is effective for reducing the diameter of the light spot. Had an optical pickup,
The challenge is to realize an optical information processing device.

Another object of the present invention is to suppress chromatic aberration due to wavelength fluctuation and improve operation accuracy in an optical pickup using the above-mentioned objective lens for optical pickup.

Another object of the present invention is to improve the reliability of the optical pickup by correcting the spherical aberration caused by the substrate thickness error in the optical pickup using the above-mentioned optical pickup objective lens.

The present invention also makes it possible, in an optical pickup using the above-mentioned objective lens for an optical pickup, to perform one or more favorable recording / reproducing / erasing on each recording surface of a multilayer optical recording medium. Let's take another task.

[0018]

The objective lens for an optical pickup according to claim 1 has a "working wavelength: 650 ± 20 nm and a light irradiation side substrate thickness: 0.1 mm. It is an objective lens for converging the light flux from the light source side as a light spot on the recording surface of the optical recording medium in an infinite optical pickup that performs one or more erasures.

Performing one or more of recording / reproducing / erasing of information means that only recording of information or only reproducing of information is performed.
It is a general term for performing only erasing, performing recording and reproducing, performing recording and erasing, performing reproducing and erasing, and performing recording, reproducing and erasing. The “infinite optical pickup” is an optical pickup designed so that the designed object point (light source) with respect to the objective lens for the optical pickup is at infinity. The same applies to the following description.

The objective lens for an optical pickup according to claim 1 has the following features. That is, this objective lens is configured as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.65 ≦ NA <0.75.
Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd,
Focal length: f is the condition: (1) 1.2nd-1.1 <R1 / f ≦ 1.3nd-1.2 (2) 0.37nd-0.14 <WD / f ≦ 0.39nd-0 Satisfies 0.04.

The objective lens for an optical pickup according to a second aspect is the objective lens for an optical pickup according to the first aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (3) νd ≦ 60 (4) It is characterized by satisfying 1.5 ≦ nd. . The objective lens for an optical pickup according to claim 3 has a “working wavelength: 650 ± 20 nm.
At the light irradiation side substrate thickness: 0.1 mm, in an infinite optical pickup that records, reproduces, and erases information on an optical recording medium, the light flux from the light source side is recorded on the recording surface of the optical recording medium. Objective lens for focusing as a light spot "
And has the following features.

That is, this objective lens for an optical pickup is constructed as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.75 ≦ NA <0.85.
Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd,
Focal length: f is the condition: (5) 1.0nd-0.7 <R1 / f ≦ 1.2nd-1.1 (6) 0.33nd-0.18 <WD / f ≦ 0.37nd-0 .14 is satisfied.

The objective lens for an optical pickup according to a fourth aspect is the objective lens for an optical pickup according to the third aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (7) νd ≦ 60 (8) It is characterized by satisfying 1.6 ≦ nd. The objective lens for an optical pickup according to claim 5 is an infinite system that records / reproduces / erases information on / from an optical recording medium having a working wavelength of 650 ± 20 nm and a substrate thickness of a light irradiation side of 0.1 mm. In an optical pickup, it is an objective lens for converging a light beam from the light source side as a light spot on the recording surface of the optical recording medium, and has the following features.

That is, this objective lens for an optical pickup is constructed as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.85 ≦ NA. Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd, and the focal length: f are conditions: (9) R1 / f ≦ 1.0nd-0.7 ( 10) WD / f ≦ 0.33nd−0.18 is satisfied.

According to a sixth aspect of the present invention, there is provided the objective lens for an optical pickup according to the fifth aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (11) 30 ≦ νd ≦ 50 (12) 1.65 ≦ nd ≦ 1.80 is satisfied. The objective lens for an optical pickup according to any one of claims 1 to 6 can be a “meniscus lens having a convex surface facing the object side” (claim 7). The objective lens for an optical pickup according to claim 2 or 4 or 6 can be a "biconvex lens having a surface with a strong curvature facing the light source side" (claim 8). The objective lens for an optical pickup according to claim 9 has a “use wavelength: 407 ±
In an infinite optical pickup that records / reproduces / erases information on / from an optical recording medium having a substrate thickness of 0.1 mm at a light irradiation side of 10 nm, the light flux from the light source side is recorded on the recording surface of the optical recording medium. The objective lens for condensing the light spot as a light spot ”has the following features.

That is, this objective lens for optical pickup is constructed as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.65≤NA <0.75.
Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd,
Focal length: f is the condition: (13) 1.2nd-1.1 <R1 / f ≦ 1.3nd-1.2 (14) 0.37nd-0.14 <WD / f ≦ 0.39nd-0 Satisfies 0.04.

The objective lens for an optical pickup according to a tenth aspect is the objective lens for an optical pickup according to the ninth aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (15) νd ≦ 60 (16) It is characterized by satisfying 1.5 ≦ nd. The objective lens for an optical pickup according to claim 11 has a “working wavelength: 407 ± 10 nm.
At the light irradiation side substrate thickness: 0.1 mm, in an infinite optical pickup that records, reproduces, and erases information on an optical recording medium, the light flux from the light source side is recorded on the recording surface of the optical recording medium. Objective lens for focusing as a light spot "
And has the following features.

That is, this objective lens for optical pickup is constructed as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.75 ≦ NA <0.85.
Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd,
Focal length: f is the condition: (17) 1.0nd-0.7 <R1 / f ≦ 1.2nd-1.1 (18) 0.33nd-0.18 <WD / f ≦ 0.37nd-0 .14 is satisfied.

The objective lens for an optical pickup according to a twelfth aspect is the objective lens for an optical pickup according to the eleventh aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (19) νd ≦ 60 (20) 1.6 ≦ nd ≦ 1.8 is satisfied. The objective lens for an optical pickup according to claim 13 has a “working wavelength: 407 ± 10 nm.
At the light irradiation side substrate thickness: 0.1 mm, in an infinite optical pickup that records, reproduces, and erases information on an optical recording medium, the light flux from the light source side is recorded on the recording surface of the optical recording medium. Objective lens for focusing as a light spot "
And has the following features.

That is, this objective lens for an optical pickup is constructed as a single lens, both surfaces are aspherical surfaces, and the numerical aperture: NA is in the range of 0.85 ≦ NA. Then, the paraxial radius of curvature of the side surface of the light source: R1, the working distance: WD, the refractive index of the material with respect to the d-line: nd, and the focal length: f are the conditions: (21) R1 / f ≦ 1.0nd-0.7 ( 22) WD / f ≦ 0.33nd−0.18 is satisfied.

The objective lens for an optical pickup according to a fourteenth aspect is the objective lens for an optical pickup according to the first aspect, wherein the refractive index of the material with respect to the d-line: nd and the Abbe number: νd satisfy the condition: (23) 45 ≦ νd ≦ 55 (24) 1.65 ≦ nd ≦ 1.72 is satisfied. Claims 9 to 14
The objective lens for an optical pickup according to any one of 1,
It can be a “meniscus lens having a convex surface facing the light source side” (claim 15). In addition, claim 10 or 1 above
The objective lens for an optical pickup described in 2 or 14 can be "a biconvex lens with a surface having a strong curvature facing the light source side" (claim 16).

An optical pickup according to a seventeenth aspect of the present invention has a "working wavelength: 650 ± 20 nm and a light irradiation side substrate thickness: 0.1 mm.
Is an infinite optical pickup that performs at least one of recording, reproducing, and erasing of information on the optical recording medium, and is for converging the light flux from the light source as a light spot on the recording surface of the optical recording medium. As an objective lens, any one of claims 1 to 8
The objective lens for an optical pickup as described in 1. is used.

The optical pickup according to claim 18 has a "working wavelength: 407 ± 20 nm and a light irradiation side substrate thickness: 0.1 mm.
Is an infinite optical pickup that performs at least one of recording, reproducing, and erasing of information on the optical recording medium, and is for converging the light flux from the light source as a light spot on the recording surface of the optical recording medium. An objective lens for an optical pickup according to any one of claims 9 to 16 is used as the objective lens.

The optical pickup according to claim 17 or 18 can have "chromatic aberration correction means for correcting chromatic aberration due to wavelength fluctuation" (claim 19).
The chromatic aberration correcting means can be a "doublet lens", a "resin coat provided on the optical pickup objective lens", a "diffraction surface provided on the optical pickup objective lens", or the like (claim 20). The "wavelength fluctuation" is a general term for "individual deviation from the standard emission wavelength" of a semiconductor laser used as a light source and "wavelength fluctuation due to mode hopping".

The optical pickup according to any one of claims 17 to 20 can also have a substrate thickness error detecting means and a spherical aberration correcting means (claim 21). The "substrate thickness error detecting means" detects a substrate thickness error of the light irradiation side substrate of the optical recording medium.

The "spherical aberration correcting means" corrects the spherical aberration caused by the substrate thickness error based on the substrate thickness error detected by the substrate thickness error detecting means.

In the optical pickup of the twenty-first aspect, the spherical aberration correcting means may be a "positive / negative lens with variable lens spacing" or a "liquid crystal element having a concentric electrode pattern" (claim 22). ).

An optical pickup according to a twenty-third aspect is that "a recording surface is superposed in multiple layers, and a light irradiation side substrate thickness is 0.1 mm,
It is an infinite optical pickup that records / reproduces / erases information on / from an optical recording medium having a wavelength of 650 ± 20 nm ”and has a spherical aberration detecting means and a spherical aberration correcting means.

The "spherical aberration detecting means" is a means for detecting spherical aberration which changes according to the distance from the light irradiation side substrate surface to an arbitrary recording surface. The “spherical aberration correcting means” is a means for correcting the spherical aberration detected by the spherical aberration detecting means.

An objective lens for an optical pickup according to any one of claims 1 to 8 is used as an objective lens for converging a light beam from a light source as a light spot on a desired recording surface of an optical recording medium. Used.

An optical pickup according to a twenty-fourth aspect is that "a recording surface is laminated in multiple layers, and a light irradiation side substrate thickness is 0.1 mm,
It is an infinite optical pickup that records / reproduces / erases information on / from an optical recording medium having a working wavelength of 407 ± 10 nm ”and has a spherical aberration detecting means and a spherical aberration correcting means.

The "spherical aberration detecting means" is a means for detecting spherical aberration which changes according to the distance from the light-irradiating side substrate surface to an arbitrary recording surface. The “spherical aberration correcting means” is a means for correcting the spherical aberration detected by the spherical aberration detecting means.

An objective lens for an optical pickup according to any one of claims 9 to 16 is used as an objective lens for converging a light beam from a light source as a light spot on a desired recording surface of an optical recording medium. Used.

The optical pickup described in claim 23 or 24 can have "chromatic aberration correction means for correcting chromatic aberration due to wavelength fluctuation" (claim 25).
The optical pickup according to any one of claims 19 to 25 can have "the chromatic aberration correcting means and the spherical aberration correcting means as one body" (claim 26).

The optical information processing apparatus according to the present invention "records / reproduces / reproduces information on / from an optical recording medium using an optical pickup.
An optical information processing device for performing one or more erasures, wherein the optical pickup according to any one of claims 17 to 26 is used (claim 27).

In the above description, the "form of the optical recording medium" is generally disc-shaped. The light irradiation side substrate thickness of the optical recording medium: 0.1 mm is a standard value, and the "optical system of an infinite optical pickup" is designed based on this standard value. The objective lens for the optical pickup is designed as a part of this optical system. The substrate thickness on the light irradiation side in an actually used optical recording medium generally has an error with respect to the above standard value.

The conditions (9) to (6) in claims 5 and 6
(12), conditions (21) in claims 13 and 14 ~
(24) is the numerical aperture: NA = 9.5, practically NA =
Effective up to about 1.0.

The above conditions (1) to (24) are conditions for the objective lens for an optical pickup described in each claim to realize "a numerical aperture in a predetermined range and desired performance", and the condition (1) is satisfied. Meaning is the condition (5), (9), (13), (1
7) and (21) have the same meanings, and condition (2) has the same meaning as conditions (6), (10), (14), (18) and (2).
The meaning of condition (3) is the same as the meaning of condition (3), and the meaning of condition (4) is the same as that of conditions (7), (11), (15), (19), and (23). Condition (8), (1
It has the same meaning as 2), (16), (20) and (24).

The objective lens for an infinite optical pickup is
The objective lens for an optical pickup of the present invention is a positive lens that collects a parallel light flux incident from the light source side, and since both surfaces are aspherical surfaces in a single lens configuration, the lens form is a biconvex lens or a meniscus lens. It is possible.
In this case, from the viewpoint of aberration correction, in the case of a biconvex lens, "a surface having a strong curvature is preferably arranged on the light source side" (claims 8 and 16), and in the case of a meniscus lens, "a convex surface is directed to the light source side". Is preferable (claims 7 and 15).

Wavelength: 650 ± 20 nm and wavelength: 40
At irradiation wavelength of 7 ± 10 nm, substrate thickness on light irradiation side: 0.01
When forming a light spot with a “desired spot diameter” on a recording surface through a substrate of mm, the “upper limit of wavefront aberration allowed to form a good light spot” is 0.01
λ (λ: wavelength).

When the objective lens for an optical pickup according to the seventh or fifteenth aspect is formed as a “meniscus lens having a convex surface facing the light source side”, the above condition (1),
(2), (5), (6), (9), (10), (1
3), (14), (17), (18), (21), (2
If the condition (2) is not satisfied, it is not possible to achieve the required numerical aperture and the wavefront aberration of 0.01λ or less.

When the objective lens for an optical pickup is formed as a "biconvex lens with a surface having a strong curvature facing the light source side", the above condition (1),
(2), (5), (6), (9), (10), (1
3), (14), (17), (18), (21), (2
In addition to 2), conditions (3), (4), (7), (8),
(11), (12), (15), (16), (19),
It is preferable to satisfy (20), (23) and (24). These conditions (3), (4), ... (23), (2
It is preferable that 4) is also satisfied in the case of a meniscus lens having a convex surface facing the light source side.

As an example, looking at the conditions (1) and (13) in the objective lens for an optical pickup according to claims 1 and 9,
These are the same conditions. Conditions (1) and (13) are the paraxial radius of curvature R on the light source side of the objective lens for the optical pickup: R
1, the refractive index of the lens material with respect to the d-line: nd, and the focal length: f.

Taking the objective lens for an optical pickup described in claims 1 and 2, as an example, in this objective lens, the numerical aperture is N.
A is 0.65 ≦ NA <0.75. Therefore, consider the case where the numerical aperture: NA = 0.65 is realized, and the parameters R1 and nd are considered as parameters therefor.

Assuming that the surface of the objective lens for the optical pickup on the light source side is "convex toward the light source side", the paraxial radius of curvature: R1
A larger value means that the positive refractive power on this surface becomes smaller. In the present invention, it is an object to increase the numerical aperture of the objective lens for the optical pickup, but in order to increase the numerical aperture, the positive refractive power of the lens must be increased. Therefore, if the paraxial radius of curvature R1 is increased and the numerical aperture is increased as described above, the refractive index of the lens material must be increased, and "the refractive index of the lens material: nd is Radius of curvature: Increases as R1 increases. "

Under the condition that the above-mentioned "wavefront aberration: 0.01λ or less" can be achieved, the relationship that the paraxial radius of curvature R1 and the refractive index: nd satisfy is "the surface with a strong curvature is on the light source side. Effective diameter of objective lens for optical pickup formed as "biconvex lens toward": ψ = 3 mm, numerical aperture: NA
= 0.65, it looks like a black circle in Fig. 20. That is, the black circle is located on the straight line 14-1.
From this, the paraxial radius of curvature: R1 and the refractive index: nd are 1
It can be seen that they have the following proportional relationship.

On the other hand, the relation: f = (φ / 2) / NA holds between the numerical aperture: NA and the focal length: f. ψ = 3 mm,
Since NA = 0.65, f = 2.31 mm.
Using the value of this focal length, the straight line 14-1 in FIG.
When the equation (3) is obtained by using the parameters: R1 / f and nd as variables, R1 / f = 1.3nd-1.2. If the relationship between R1, nd, and f deviates from this expression, the wavefront aberration will be 0.65 even if the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness, and the material are adjusted. : 0.01 λ or less cannot be achieved.

As described above, numerical aperture: NA =
0.75 and wavefront aberration: 0.01λ or less, the relationship between the paraxial radius of curvature; R1 and the refractive index: nd is shown in FIG.
It becomes like a straight line 14-2 in which black triangles are arranged at 0, and when the equation of this straight line 14-2 is obtained by using the parameters: R1 / f and nd as variables, R1 / f = 1.2nd-1 It becomes 1. If the relationship between R1, nd, and f deviates from this expression, the wavefront aberration will be 0.75 even if the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness, or the material is adjusted. : 0.01 λ or less cannot be achieved.

Similarly, assuming that the numerical aperture is NA = 0.85 and the wavefront aberration is 0.01λ or less, the paraxial radius of curvature is R1.
20 and the refractive index: nd are as shown by a straight line 14-3 in which white squares are arranged in FIG. 20, and the equation of this straight line 14-3 is obtained by using the parameters: R1 / f and nd as variables. , R1 / f = 1.0nd-0.7. If the relationship between R1, nd, and f deviates from this equation, even if the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness, and the material are adjusted, the numerical aperture is 0.85 and the wavefront aberration is 0.85. : 0.01 λ or less cannot be achieved.

From this, it can be seen that the straight line representing the relationship between R1 and nd has a gentler gradient as the numerical aperture NA increases.

Therefore, in the objective lens for an optical pickup having a wavefront aberration of 0.01λ or less and a numerical aperture NA of 0.65 ≦ NA <0.75, the parameters: R1 / f and nd are: Wavelength used is 660 ± 20nm
Or 407 ± 10 nm, the conditions (1) and (13) must be satisfied.

Similarly, in the case of an objective lens for an optical pickup having a wavefront aberration of 0.01λ or less and a numerical aperture NA of 0.75 ≦ NA <0.85, a parameter R
1 / f and nd are conditions (5) regardless of whether the wavelength used is 660 ± 20 nm or 407 ± 10 nm.
(17) must be satisfied, and wavefront aberration: 0.01
In the objective lens for an optical pickup having a numerical aperture NA of 0.85 ≦ NA in the range of λ or less, the parameters are:
R1 / f and nd satisfy the condition (9) regardless of whether the used wavelength is 660 ± 20 nm or 407 ± 10 nm.
(21) must be satisfied.

Next, the objective lens for an optical pickup according to the present invention secures a working distance: WD necessary for improving the reliability of the optical pickup. Working Distance: To increase WD,
The back focus may be increased, and for that purpose, the refractive index of the objective lens for the optical pickup may be decreased to reduce the refractive power, but this leads to a decrease in the numerical aperture. Therefore, in order to secure the required working distance while securing the required numerical aperture, it is necessary to balance the numerical aperture and the refractive index.

The required numerical aperture is 0.65, 0.75,
0.85 to achieve these numerical apertures, and
The relationship between the working distance: WD and the refractive index of the lens material: nd, which is allowed under the condition that the wavefront aberration is suppressed to 0.01λ or less, is formed as “a biconvex lens with a surface having a strong curvature facing the light source side”. As shown in FIG. 21, the effective system of the objective lens for the optical pickup is ψ = 3 mm.
It becomes like. Straight line 15 in the arrangement of black circles in FIG.
-1 relates to the numerical aperture: 0.65, the straight line 15-2 in the arrangement of black triangles relates to the numerical aperture: 0.75, and the line 15-3 in the arrangement of the white squares relates to the numerical aperture: 0.85. is there.

When the straight lines 15-1 to 15-3 are obtained by using the parameters: WD / f and nd as variables, the straight line 15-1 for the numerical aperture: NA = 0.65 is WD / f = 0. .39nd-0.04, and if the relationship between WD, nd, and f deviates from this expression, the aperture will be adjusted even if the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness, or the material is adjusted. When the number is 0.65, the wavefront aberration: 0.01λ or less cannot be achieved.

Numerical aperture: Straight line 15 for NA = 0.75
-2 becomes WD / f = 0.37nd-0.14, and if the relationship between WD, nd and f deviates from this equation, the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness Even if the material is adjusted, the numerical aperture: 0.75 and the wavefront aberration: 0.01λ or less cannot be achieved.

Numerical aperture: Straight line 15 for NA = 0.85
-3 is WD / f = 0.33nd-0.18. If the relationship between WD, nd, and f deviates from this expression, the wavefront aberration will be 0.85 at the numerical aperture even if the aspherical shape of the lens surface on the light source side or the optical recording medium side, the lens thickness, and the material are adjusted. : 0.01 λ or less cannot be achieved.

From this, it can be seen that the straight line representing the relationship between WD and nd has a gentler gradient as the numerical aperture NA increases.

Therefore, in the objective lens for an optical pickup having a wavefront aberration of 0.01λ or less and a numerical aperture NA of 0.65 ≦ NA <0.75, the parameters: WD / f and nd are Wavelength used is 660 ± 20nm
Or 407 ± 10 nm, the conditions (2) and (14) must be satisfied.

Similarly, in the case of an optical pickup objective lens having a wavefront aberration of 0.01λ or less and a numerical aperture NA of 0.75 ≦ NA <0.85, the parameter: W
D / f and nd satisfy the condition (6) regardless of whether the used wavelength is 660 ± 20 nm or 407 ± 10 nm.
(18) must be satisfied, and wavefront aberration: 0.0
In an objective lens for an optical pickup having a numerical aperture: NA of 0.85 ≦ NA in a range of 1λ or less, parameters: WD / f and nd are used wavelengths of 660 ± 20 nm.
Condition or 407 ± 10 nm, the condition (1
0) and (22) must be satisfied.

Next, in the objective lens for an optical pickup formed as "a biconvex lens having a strong curvature toward the light source side", the above conditions (1), (2), (5),
(6), (9), (10), (13), (14), (1
7), (18), (21), and (22) are satisfied, the required numerical aperture is realized and the wavefront aberration is 0.01.
FIG. 22 shows a lens material that is allowed to achieve λ or less, as represented by a refractive index: nd and an Abbe number: νd.

22A to 22C show the wavelength used: 650
and the numerical aperture: NA is 0.
65, 0.75 in (b), 0.8 in (c)
It is 5. Further, FIGS. 22D to 22F show the used wavelength: 4
The numerical aperture NA is 0.65 in (d), 0.75 in (e), and 0.85 in (f).

In these figures, a lens material having a "combination of refractive index and Abbe number indicated by a black circle" is allowed. As a general tendency, the larger the numerical aperture, the narrower the range allowed for the refractive index / Abbe number, and this tendency is remarkable at the wavelength used: 407 nm.

Conditions (3), (4), (15), (16)
22 defines the allowable range of the refractive index and Abbe number in FIGS. 22 (a) and 22 (d). Conditions (7), (8),
(19) and (20) define the permissible range of the refractive index and Abbe number in FIGS. 22 (b) and 22 (e), and conditions (11), (12), (23), (24). Is shown in FIG.
It defines the allowable range of the refractive index and Abbe number in (c) and (f).

When the objective lens for the optical pickup is constructed as "a biconvex lens with a surface having a strong curvature facing the light source side", the conditions (4), (8), (1 for the refractive index: nd
When 2), (16), (20, (24) are not satisfied, the refractive index of the objective lens is too small, and when realizing a desired NA, the curvature of the lens surface on the light source side must be increased especially. However, it becomes difficult to form the objective lens surface with high precision, and the cost of the objective lens also increases.

Further, the conditions (3), (7), (11), (15), (19), and (2) for the Abbe number: νd
If 3) is not satisfied, chromatic aberration due to wavelength variation in the light source becomes too large. Abbe number of these: ν
It is preferable that the conditions regarding d and the refractive index: nd are satisfied particularly when the objective lens for the optical pickup is “a biconvex lens with a surface having a strong curvature facing the light source side”.

The case where the objective lens for the optical pickup is a "biconvex lens with a surface having a strong curvature facing the light source side" has been described above, but the objective lens for the optical pickup is described as "Example" below. Even when the convex surface is formed as a meniscus lens facing the light source side, the conditions (1), (2), (5), (6),
(9), (10), (13), (14), (17),
By satisfying (18), (21) and (22),
Wavefront aberration: Good performance of 0.01λ or less can be realized.

In the meniscus lens, since the surface on the optical recording medium side is a concave surface, the refractive power of the lens surface becomes weaker than in the case of a biconvex lens. Therefore, in order to compensate for this, the refractive index of the material is increased. Is good. Further, since the directions of chromatic aberrations are opposite between the surface on the light source side and the surface on the optical recording medium side, a material having a small Abbe number and a large dispersion can be used.
That is, in the meniscus-shaped objective lens for an optical pickup, a material having a “combination of high refractive index and low Abbe number” can be used as compared with a biconvex lens-shaped objective lens.

However, also in the case of an objective lens for an optical pickup using a “meniscus lens having a convex surface facing the light source side”, the above conditions (3), (7), (11), (15),
By satisfying (19) and (23), the conditions for the lens shape such as the lens surface shape are relaxed, and therefore it is preferable to satisfy these conditions.

In this way, by satisfying each of the conditions in claims 1 to 16, it is possible to realize an objective lens for an optical pickup having a numerical aperture of a required range and a wavefront aberration of 0.01λ or less. It is possible.

[0081]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples of an objective lens for an optical pickup will be given below. In order to avoid complication, the reference numerals are made common in each of FIGS. 1 to 12 (a), reference numeral 1 is "aperture", reference numeral 2 is "object lens for optical pickup", reference numeral 3 is "light irradiation of optical recording medium". Side substrate (thickness: 0.1 mm) ”.

The laser light flux from the light source side (the left side in each of FIGS. 1 to 12A) passes through the aperture (aperture diameter: ψ = 3 mm) of the aperture 1 as a “parallel light flux”, and the objective for the optical pickup is obtained. The light enters the lens 2, is made into a condensed light flux by the lens 2, passes through the light irradiation side substrate 3 of the optical recording medium, and forms a light spot on the recording surface (matching the right side surface of the light irradiation side substrate 3).

[0083]

[Examples] Twelve specific examples will be given below. Odd numbered embodiments, ie, embodiments 1, 3, 5, 7, 9, 11
Is an example in which the objective lens for the optical pickup is a “meniscus lens having a convex surface facing the light source side”, and examples with even numbers, that is, Examples 2, 4, 6, 8, 10,
Reference numeral 12 is an example in which the objective lens for the optical pickup is a “biconvex lens with a surface having a strong curvature facing the light source side”.

In each embodiment, the numerical aperture is NA, the focal length is f, the refractive index of the lens material with respect to the d-line and the Abbe number are nd and νd.

Further, the aspherical shape of the lens surface has a coordinate in the optical axis direction: X, a coordinate in the direction orthogonal to the optical axis: Y, a paraxial radius of curvature:
R, conic constant: K, higher coefficient: A, B, C, D, E,
Well-known aspherical expression using F, ...: X = (Y ² / R) / [1 + √ {1− (1 + K) (Y / R)
² } + AY ⁴ + BY ⁶ + CY ⁸ + DY ¹⁰ + EY ¹² + FY
¹⁴ + GY ¹⁶ + HY ¹⁸ + JY ²⁰ + ... Represents R, K, A, B, C, D ,.

Example 1 The objective lens for an optical pickup of Example 1 is defined by claim 1.
It is a specific example of those described in 2, 7 and used wavelength: 650n
m. NA: 0.65, f: 2.31 mm, nd =
1.74330, vd = 49.36 Table 1 shows specific data.

[0087]

[Table 1]

The symbols in the table are as follows.

"OBJ" means an object point (semiconductor laser as a light source), but the objective lens for the optical pickup is an "infinite system", and the radius of curvature is RDY and the thickness is THI.
“INFINITY” means that the light source is at infinity. Further, “STO” is the surface of the aperture 1, its radius of curvature is “INFINITY”, and its thickness is “0” in design. Also, unless otherwise specified, the unit of the quantity having the dimension of length is “mm”.

“S1” means the “light source side surface” of the optical pickup objective lens, and “S2” means the “optical recording medium side surface”. The lens thickness in Example 1 is 2.0000 mm.
And the thickness of 0.831223 mm described in the “right side of the radius of curvature” in the column S2 indicates the “working distance”.

"S3" is a light source side surface of the light irradiation side substrate 3 of the optical recording medium, and "S4" is a surface corresponding to the same recording surface. Is 0.1 mm, and the material: PC is polycarbonate with a refractive index: n = 1.58. "EPD: entrance pupil diameter" represents the aperture diameter (3 mm) of the aperture 1, and "WL: wavelength" represents the used wavelength (650 nm).

In the display of the aspherical surface coefficient, for example, "D:-. 625230E-04" means "D =
-0.625230 * 10 < ^-4 >"is meant. The same applies to the display of other examples.

FIG. 1A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the first embodiment. 1B and 1C, astigmatism and spherical aberration of the objective lens for the optical pickup of Example 1 (the ordinate scale is a value obtained by normalizing the entrance pupil radius to 1).
Indicates. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

As described above, in the first embodiment, R1 = 1.6
8376 mm, f = 2.31 mm, nd = 1.7333
0, Abbe number: νd = 49.36, working distance = 0.831223 mm, so the above R1,
f and nd are the conditions (1) and (2) in claim 1.
And the refractive index and the Abbe number are both within the ranges of the conditions (3) and (4).

Example 2 The objective lens for an optical pickup of Example 2 is the same as that of claim 2.
8 is a specific example described in 8 and the wavelength used is 650 nm. NA: 0.65, f: 2.31 mm, nd = 1.
58313, vd = 59.46 Table 2 shows specific data following Table 1.

[0096]

[Table 2]

FIG. 2A shows an arrangement state of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the second embodiment.

FIGS. 2B and 2C show astigmatism and spherical aberration of the objective lens for the optical pickup of Example 2 (the scale on the vertical axis is a value obtained by normalizing the entrance pupil radius to 1). Indicates.
Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

As described above, in the first embodiment, R1 = 1.4
7611 mm, f = 2.31 mm, nd = 1.5831
3, Abbe number: νd = 59.46, working distance = 1.096024 mm, so the above R1,
f and nd are the conditions (1) and (2) in claim 1.
Is satisfied, and both the refractive index and the Abbe number are within the ranges of the conditions (3) and (4).

Example 3 The objective lens for an optical pickup of Example 3 is the same as that of claim 3,
4 and 7 are specific examples, wavelength used: 650 nm
Is. NA: 0.75, f: 2.00 mm, nd =
1.74330, vd = 49.36 Table 3 shows specific data in the same manner as Table 1.

[0101]

[Table 3]

FIG. 3A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the third embodiment.

FIGS. 3B and 3C show astigmatism and spherical aberration of the objective lens for the optical pickup of the third embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 3, R1 = 1.45407 mm,
f = 2.00 mm, nd = 1.74330, Abbe number:
νd = 49.36, working distance = 0.58
Since it is 5206 mm, the above R1, f, nd are within the ranges of the conditions (5) and (6) in claim 3,
Both the refractive index and the Abbe number are within the ranges of the conditions (7) and (8).

Example 4 The objective lens for an optical pickup of Example 4 is the same as that of claim 4,
8 is a specific example, and the wavelength used is 650 nm. NA: 0.75, f: 2.00 mm, nd = 1.6
9330, νd = 53.17 Table 4 shows specific data in accordance with Table 1.

[0106]

[Table 4]

FIG. 4A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the fourth embodiment.

FIGS. 4B and 4C show astigmatism and spherical aberration of the objective lens for the optical pickup of the fourth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 4, R1 = 1.50153 mm,
f = 2.00 mm, nd = 1.69330, Abbe number:
νd = 53.17, working distance = 0.84
Since it is 9168 mm, the above R1, f, and nd satisfy the equal signs of the conditions (5) and (6) in claim 4,
Both the refractive index and the Abbe number are within the ranges of the conditions (7) and (8).

Example 5 The objective lens for an optical pickup of Example 3 is the same as that of claim 5,
6 and 7 are specific examples, wavelength used: 650n
m. NA: 0.85, f: 1.76 mm, nd =
1.74330, νd = 49.36 Table 5 shows specific data in the same manner as Table 1.

[0111]

[Table 5]

FIG. 5A shows the arrangement of the aperture 1, the objective lens 2 for the optical pickup, and the light irradiation side substrate 3 according to the fifth embodiment.

FIGS. 5B and 5C show astigmatism and spherical aberration of the objective lens for the optical pickup of Example 5, respectively. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 5, R1 = 1.2997 mm, f
= 1.76 mm, nd = 1.74330, Abbe number: ν
d = 49.36, working distance = 0.465
Since it is 294 mm, the above R1, f, and nd are within the ranges of the conditions (9) and (10) in claim 5, and the refractive index and Abbe number are both conditions (11) and (12).
Is within the range of.

Example 6 The objective lens for an optical pickup of Example 6 is the same as that of claim 6,
8 is a specific example, and the wavelength used is 650 nm. NA: 0.85, f: 1.76 mm, nd = 1.6
9330, vd = 53.17 Table 6 shows specific data in accordance with Table 1.

[0116]

[Table 6]

FIG. 6A shows an arrangement state of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the sixth embodiment.

6 (b) and 6 (c) show astigmatism and spherical aberration of the objective lens for the optical pickup of the sixth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 6, R1 = 1.297 mm, f
= 1.76 mm, nd = 1.69330, Abbe number: ν
d = 53.17, working distance = 0.591
Since it is 052 mm, the above R1, f, and nd satisfy the equal signs for the conditions (9) and (10) in claims 5 and 6, and the refractive index and the Abbe number are both the condition (11),
It is within the range of (12).

Example 7 The objective lens for an optical pickup of Example 7 is the same as that of claim 9.
This is a specific example of the ones in 10 and 15, wavelength used: 407
nm. NA: 0.65, f: 2.31 mm, nd
= 1.74330, vd = 49.36 Table 7 shows specific data in the same manner as Table 1.

[0121]

[Table 7]

FIG. 7A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the seventh embodiment.

7B and 7C show astigmatism and spherical aberration of the objective lens for the optical pickup of the seventh embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 7, R1 = 1.182
2 mm, f = 2.31 mm, nd = 1.74330, Abbe number: νd = 49.36, working distance =
Since it is 0.831223 mm, the above R1, f, nd
Is within the ranges of the conditions (13) and (14) in claim 9, and both the refractive index and the Abbe number are the conditions (15),
It is within the range of (16).

Example 8 The objective lens for an optical pickup of Example 8 is defined by claim 1.
0 and 16 are specific examples, wavelength used: 407
nm. NA: 0.65, f: 2.31 mm, nd
= 1.58313, vd = 59.46 Table 8 shows specific data in the same manner as Table 1.

[0126]

[Table 8]

FIG. 8A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the eighth embodiment.

8B and 8C show astigmatism and spherical aberration of the objective lens for the optical pickup of the eighth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 8, R1 = 1.5293
8 mm, f = 2.31 mm, nd = 1.58313, Abbe number: νd = 59.46, working distance =
Since it is 1.115081 mm, the above R1, f, nd
Satisfies the equal signs for the conditions (13) and (14) in claim 10, and both the refractive index and the Abbe number are within the ranges of the conditions (15) and (16).

Example 9 The objective lens for an optical pickup of Example 9 is defined in claim 1.
1, 12 and 15 are specific examples, wavelength used: 4
It is 07 nm. NA: 0.75, f: 2.00 mm,
nd = 1.74330, vd = 49.36 Table 9 shows specific data in the same manner as Table 1.

[0131]

[Table 9]

FIG. 9A shows an arrangement state of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the ninth embodiment.

9B and 9C show astigmatism and spherical aberration of the objective lens for the optical pickup of the ninth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 9, R1 = 1.48011 mm,
f = 2.00 mm, nd = 1.74330, Abbe number:
νd = 49.36, working distance = 0.58
Since it is 3068 mm, the above R1, f, and nd are within the ranges of the conditions (17) and (18) in claim 11, and the refractive index and Abbe number are both conditions (19) and (2).
It is within the range of 0).

Example 10 The objective lens for an optical pickup of Example 10 is defined by
2 and 16 are specific examples, wavelength used: 407
nm. NA: 0.75, f: 2.00 mm, nd
= 1.69330, νd = 53.17 Table 10 shows specific data in the same manner as Table 1.

[0136]

[Table 10]

FIG. 10A shows an arrangement state of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the tenth embodiment.

10B and 10C show astigmatism and spherical aberration of the objective lens for the optical pickup of the tenth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 10, R1 = 1.56813 m
m, f = 2.00 mm, nd = 1.69330, Abbe number: νd = 53.17, working distance = 0.
Since it is 874666 mm, the above R1, f, nd are
The conditions (17) and (18) in claim 12 satisfy the equal signs, and both the refractive index and the Abbe number satisfy the condition (1
9) and (20).

Example 11 The objective lens for an optical pickup of Example 11 is defined by claim 1.
3 and 15 are specific examples, wavelength used: 407
nm. NA: 0.85, f: 1.76 mm, nd
= 1.74330, vd = 49.36 Specific data are shown in Table 11 in the same manner as Table 1.

[0141]

[Table 11]

FIG. 11A shows an arrangement state of the aperture 1, the objective lens 2 for the optical pickup, and the light irradiation side substrate 3 according to the eleventh embodiment.

11 (b) and 11 (c) show astigmatism and spherical aberration of the objective lens for the optical pickup of the eleventh embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 11, R1 = 1.33386m
m, f = 1.76 mm, nd = 1.74330, Abbe number: νd = 49.36, working distance = 0.
It is 468034 mm, and R1, f, and nd are within the ranges of the conditions (21) and (22) in claim 13. The Abbe number is within the range of the condition (23), but the refractive index: nd is outside the range of the condition (24), and the condition (2
It is higher than the upper limit of 4).

As described above, in Example 11, since the lens form is the meniscus lens, the wavefront aberration:
It is possible to use a material having a refractive index higher than the upper limit of the condition (24) despite having good performance at 01λ or less.

Example 12 The objective lens for an optical pickup of Example 12 is the one according to claim 1.
4 and 16 are specific examples, wavelength used: 407
nm. NA: 0.85, f: 1.76 mm, nd
= 1.69330, vd = 53.17 Table 12 shows specific data in the same manner as Table 1.

[0147]

[Table 12]

FIG. 12A shows the arrangement of the aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 according to the twelfth embodiment.

12B and 12C show astigmatism and spherical aberration of the objective lens for the optical pickup of the twelfth embodiment. Both aberrations are corrected very well. Of course, the “wavefront aberration” is 0.01λ or less.

In Example 12, R1 = 1.35305m
m, f = 1.76 mm, nd = 1.69330, Abbe number: νd = 53.17, working distance = 0.
Since it is 615244 mm, the above R1, f, nd are
The conditions (21) and (22) in claim 13 satisfy the equal sign, and both the refractive index and the Abbe number satisfy the condition (2).
3) Within the range of (24).

The above Examples 1 to 6 are respectively defined by Claims 1 to 1.
It is an example of the objective lens for an optical pickup described in 8, but the objective lens for an optical pickup in each of these examples is a “meniscus lens having a convex surface facing the light source side” in Examples 1, 3 and 5. Item 7), Example 2,
Reference numerals 4 and 6 are "a biconvex lens with a surface having a strong curvature facing the light source side" (claim 8).

The above-mentioned Examples 7 to 12 are examples of the optical pickup objective lens according to claims 9 to 16, respectively. The optical pickup objective lenses in these Examples are Examples 7 and 9, respectively. , 11 is a “meniscus lens having a convex surface facing the light source side” (claim 1
5), "a biconvex lens with a surface having a strong curvature facing the light source side" in Examples 8, 10 and 12 (claim 16).

[Embodiment of the optical pickup] will be described below. FIG. 13 shows an embodiment of an optical pickup having "chromatic aberration correcting means for correcting chromatic aberration due to wavelength variation". The essential parts of the optical pickup shown in FIG. 13 are a semiconductor laser 4, a collimator lens 5, a polarization beam splitter 6, a deflection mirror 7, a quarter-wave plate 9, and an optical pickup objective lens 10 (hereinafter simply referred to as the objective lens 10). ), A detection lens 12, a light receiving element 13, and a chromatic aberration correcting means 14.

The laser light beam emitted from the semiconductor laser 4 is converted into a substantially parallel light beam by the collimator lens 5, transmitted through the polarization beam splitter 6, and the optical path is bent 90 degrees by the deflection mirror 7, and the chromatic aberration correcting means 14,
It is converted into a condensed light flux through the objective lens 10 and is irradiated onto the optical recording medium 11 having a light irradiation side substrate thickness of 0.1 mm and transmitted through the light irradiation side substrate to form a light spot on the recording surface.

A quarter-wave plate 9 is provided in front of the objective lens 10.
Are arranged to convert linearly polarized light from the light source side into circularly polarized light. The light flux reflected by the optical recording medium 11 becomes a "return light flux", and travels backward in the optical path at the time of irradiation, and the objective lens 1
The light enters the polarization beam splitter 6 through the 0, 1/4 wavelength plate 9 and the deflection mirror 7.

The return light beam incident on the quarter-wave plate 9 is circularly polarized light in the opposite direction to the outward path, and when transmitted through the quarter-wave plate 9, it becomes a linearly polarized light which is orthogonal to the polarization direction of the outward light and is polarized. It is reflected by the beam splitter 6. The return light flux reflected by the polarization beam splitter 6 is detected by the detection lens 12
It is incident on the light receiving element 13 via.

The light receiving element 13 has a "light receiving surface appropriately divided according to the servo signal generating method". A tracking signal / focusing signal is generated based on the photoelectric output from each light receiving surface, and a reproduction signal is generated together with these signals when reproducing information. These signals are output to a control circuit (not shown).

The emission wavelength of the semiconductor laser 4 is 65.
0 nm ± 20 nm or emission wavelength: 407 ±
10 nm is used, and as the objective lens 10, the objective lens according to any one of claims 1 to 8 or the objective lens according to any one of claims 9 to 16 is used depending on the emission wavelength and the aperture efficiency. Used.

If the emission wavelength of the semiconductor laser 4 deviates from the standard wavelength or there is "wavelength fluctuation" in which the emission wavelength changes due to mode hopping, this causes "chromatic aberration" as described above. The chromatic aberration corrector 14 corrects such chromatic aberration.

The chromatic aberration corrector 14 in the optical pickup of FIG. 13 is a doublet lens. The "normal achromatic doublet lens (achromat lens)" known as an achromatic lens combines a convex lens with a small dispersion of a crown glass and a concave lens of a flint glass with a large dispersion to suppress chromatic aberration with respect to wavelength fluctuation. The doublet lens 14 as "chromatic aberration correction means" mainly causes "chromatic aberration of the opposite polarity to the objective lens 10" in order to correct the chromatic aberration of the objective lens 10.
Therefore, there is a large difference (10 or more) in the Abbe number of the optical material forming the convex lens / concave lens of the doublet lens 14.
Is giving. Since the chromatic aberration generated in the doublet lens 14 can be increased, the chromatic aberration mainly generated in the objective lens 10 can be sufficiently corrected.

FIG. 14A shows an embodiment of an optical pickup using another chromatic aberration correcting means. FIG.
Since the parts denoted by the same reference numerals as in () are the same as those in FIG. 13, description thereof will be omitted. In this optical pickup, "the chromatic aberration correcting means is integrated with the objective lens 10".

In the example shown in FIG. 14B, the chromatic aberration corrector 14a is made of "a glass material or a resin having a chromatic aberration of the opposite polarity to that of the objective lens 10" which is closely attached to the surface of the objective lens 10 on the optical recording medium side. Is. Examples of the resin include photopolymers used as an ultraviolet curing agent.

Optical material to be adhered (glass material or resin)
By ensuring a “large difference in Abbe number (10 or more)” between the objective lens 10 and the objective lens 10, the light spot condensed on the optical recording medium 11 can be prevented from being affected by chromatic aberration.

In the example shown in FIG. 14C, the chromatic aberration corrector 14b is "a diffractive surface provided on the objective lens 10." The power of the diffractive surface 14b formed on the resin film integrated on the lens surface of the objective lens 10 (the side surface of the light source in the example shown in the figure) is proportional to the wavelength. It gets shorter. On the other hand, the refractive lens (objective lens 10) has an axial chromatic aberration characteristic in which the back focus extends on the long wavelength side because the refractive index of the material decreases as the wavelength increases. Due to the contradictory defocusing characteristics of the diffractive lens and the refraction lens, chromatic aberration can be compensated.

FIG. 15A shows an embodiment of an optical pickup having a substrate thickness error detecting means and a spherical aberration correcting means. In FIG. 15A, the parts denoted by the same reference numerals as those in FIG. 13 are the same as those in FIG.

The emission wavelength of the semiconductor laser 4 is 65.
0 nm ± 20 nm or emission wavelength: 407 ±
A 10 nm one is used, and as the objective lens 10,
The objective lens according to any one of claims 1 to 8 or the objective lens according to any one of claims 9 to 16 is used depending on the emission wavelength and the aperture efficiency.

In FIG. 15A, reference numeral 15 indicates "spherical aberration detecting means" as "substrate thickness error detecting means", and reference numeral 16 indicates "spherical aberration correcting means". The spherical aberration detecting means 15 is drawn by simplifying the actual configuration. As described above, the standard of the thickness of the light irradiation side substrate in the optical recording medium 11 is 0.1 mm, but in the actually manufactured optical recording medium, it is ± 10 n due to the manufacturing error.
There is a "substrate thickness error" of about m.

If there is a substrate thickness error, the “objective lens 10
Spherical aberration occurs in the combined system of "and the substrate on the light irradiation side", and the shape of the light spot formed on the recording surface deteriorates. The spherical aberration thus generated distorts the wavefront of the returning light flux, and spherical aberration is also generated in the light flux traveling toward the light receiving element 13 via the detection lens 12.

FIG. 15B shows this state. When spherical aberration occurs in the return light flux that enters the detection lens 12 from the left side of the drawing, there is a “wavefront delay” symmetrical to the reference wavefront of the return light flux, and the reference wavefront is condensed. The position where the wavefront that is delayed with respect to the focus point is focused is defocused.

Therefore, the "state of occurrence of wavefront aberration" can be known by extracting the difference between the delayed wavefront and the advanced wavefront to detect the focus state. For example, FIG. 15 (a)
As the spherical aberration detecting means 15 in FIG. 15, "a hologram, an optical path separating means such as a beam splitter, or an element for shifting the timing by a liquid crystal shutter, and FIG.
, The light receiving element 13A is formed by dividing the light receiving area such as the area: A and the area: B ", and the spherical aberration in the return light flux is detected by examining the light receiving output of each of the areas: A and B. be able to.

The spherical aberration detected by the spherical aberration detecting means as described above is “caused by the substrate thickness error of the light irradiation side substrate” if it is originally, so the detected spherical aberration and substrate thickness The error has a correspondence relationship with each other, and therefore the substrate thickness error can be known by detecting the spherical aberration of the returning light flux as described above.

Based on the thus-known substrate thickness error,
It becomes possible to correct the spherical aberration caused by the objective lens 10 and the light irradiation side substrate to form an appropriate light spot on the recording surface.

In the embodiment of FIG. 15, the spherical aberration detected by the spherical aberration detecting means 15 corresponding to the substrate thickness error of the light irradiation side substrate is photoelectric output from each region: A, B of the light receiving element 13A. It is given as a "spherical aberration signal" obtained by appropriately combining the signals.

The spherical aberration correction means 16 in the embodiment of FIG. 15 is composed of two lenses and an interval adjustment means (not shown) for adjusting the distance between these lenses. One of the two lenses is a positive lens and the other is a negative lens. In the example of the figure, the negative lens is arranged on the light source side.
A positive lens may be arranged on the light source side.

When the distance between the positive and negative lenses constituting the spherical aberration correcting means 16 is changed, a spherical aberration is generated in the light beam passing through the spherical aberration correcting means 16 toward the objective lens 10 side. It suffices to cancel the "spherical aberration generated between the lens and the substrate on the light irradiation side".

Specifically, the above-mentioned "spherical aberration signal" in "when spherical aberration does not occur between the objective lens and the light irradiation side substrate" is set with the distance between the two lenses in the spherical aberration correcting means 16 as a reference value. It is set to be 0, and when the spherical aberration actually occurs, the interval may be adjusted so that the spherical aberration signal becomes 0.

It should be noted that one or both of the positive lens and the negative lens which compose the spherical aberration correcting means may be composed of a plurality of lenses.

FIG. 16 is a diagram for explaining another embodiment of the optical pickup having the substrate thickness error detecting means and the spherical aberration correcting means. Also in FIG. 16A, FIG.
The parts denoted by the same reference numerals as those in FIG. 3 are the same as those in FIG.

The spherical aberration correction means 16A used in this embodiment is composed of "a liquid crystal element and a voltage control means (not shown) for driving the same". In the liquid crystal element, as shown in FIG. 16B, at least one transparent electrode is divided into concentric circles, and voltage can be independently applied to the electrode portions (between the common electrode) of each concentric zone. By controlling the above voltage, the refractive index: n of the liquid crystal in each electrode portion can be freely changed from n1 to n2.

When the refractive index: n is changed, the optical path difference: Δn · d (Δn is the change in the refractive index, d
Is the cell thickness of the liquid crystal), that is, where the wavelength is λ and the phase difference Δn
• d (2π / λ) can be given.

It is assumed that the "wavefront aberration giving spherical aberration generated between the objective lens 10 and the light irradiation side substrate" detected by the spherical aberration detecting means 15 is as shown in FIG. 16 (c), for example. The wavefront aberration is shown as a two-dimensional curve in the upper part of FIG. 16 (d).

For such wavefront aberration, the objective lens 1
If the voltage applied to each concentric band electrode of the liquid crystal element is adjusted so that the light flux entering from 0 to the light source side has a phase difference as shown in the lower part of FIG. The "wavefront aberration" can be canceled by the delay of the wavefront at each part of the light flux that is generated. FIG. 16E is the same as FIG.
6 (d) shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay due to the liquid crystal element), that is, the corrected wavefront aberration. It can be seen that the wavefront aberration is much smaller than the original wavefront aberration (the upper part of FIG. 16D).

As in the embodiment shown in FIGS. 15 and 16, the spherical aberration due to the substrate thickness error of the light irradiation side substrate of the optical recording medium is corrected by the spherical aberration correcting means, so that the recording surface is corrected. Therefore, a good light spot can be formed.

The spherical aberration correction means 16 and 16A are
The amount of change in wavefront aberration is ΔW, the numerical aperture of the objective lens is NA, and correction is performed to satisfy ΔW> | 200NA ² + 370NA−170 |, thereby improving the quality of the optical spot and recording high-quality information. Information can be reproduced.

The recording surface of the optical recording medium is not limited to one layer. Recently, a multi-layer optical recording medium in which recording surfaces are superposed in multiple layers and information can be recorded / reproduced / erased on / from each superposed recording surface is being put to practical use. The lens can also be used in such an “infinite optical pickup used in a multilayer optical recording medium”.

For a plurality of recording surfaces of a multilayer optical recording medium,
In order to write and read information independently, it is necessary to separate recording surfaces by several tens of μm or more, and the distance from the surface of the light irradiation side substrate to the “desired recording surface for recording” is the recording surface. Accordingly, a spherical aberration peculiar to each recording surface is generated.

According to the optical pickup of claims 23 and 24,
In order to record, reproduce, and erase information on the desired recording surface, the spherical aberration amount that occurs when the focus jumps to the desired surface is detected by the "spherical aberration detection means" and corrected by the "spherical aberration correction means". can do.

In FIG. 18, reference numeral 610 indicates an "optical recording medium having a multilayer recording surface". Reference numeral 601s indicates a “surface of the light irradiation side substrate”, and the first surface is sequentially arranged from this surface side.
The surface 601a, ..., The nth surface 601n are superposed. Reference numeral 602a indicates a focused light beam focused on the first surface 601a, and reference numeral 602b indicates a focused light flux focused on the nth surface 601n.

As a concrete embodiment of an optical pickup using such a multilayer optical recording medium, an optical pickup having the same structure as that shown in FIGS. 15 and 16 described above can be used. .

As described above, FIGS. 15 and 16
In the above, the optical recording medium 11 is “one recording surface”, and the spherical aberration detecting means 15 detects the spherical aberration generated by the substrate thickness error of the light irradiation side substrate in the optical recording medium 11, The spherical aberration detected in 1 was corrected by the spherical aberration correction means 16 (positive / negative lens etc.) or 16A (liquid crystal element etc.).

When the "multilayer optical recording medium" is used as the optical recording medium 11 in FIGS. 15 and 16, the spherical aberration correcting means 15 detects "a spherical aberration amount generated when a focus jump is made to a desired surface". The detected spherical aberration may be corrected by the spherical aberration correcting means 16 and 16A.

FIG. 17 shows another embodiment of the optical pickup using the multilayer optical recording medium. 13 that are the same as those in FIG. 13 are assigned the same reference numerals as those in FIG. 13 and description thereof is omitted. In FIG. 17, the optical recording medium 11
Is a "multilayer optical recording medium", and the objective lens 10 is such that "the wavefront aberration is minimized when a light spot is formed on the p-th surface farthest from the surface of the light irradiation side substrate in the optical recording medium 11". Is designed to. That is, the distance from the light irradiation side substrate surface to the p-th surface is 0.1 mm.

In this case, when a light spot is formed on the q-th surface which is different from the p-th surface, spherical aberration occurs, so this is detected by the spherical aberration detecting means 15 and corrected by the spherical aberration correcting means 16B.

In the spherical aberration correcting means 16B in this embodiment, a transparent parallel plate having a stepwise difference in thickness, and a portion of the transparent parallel plate having a desired thickness are provided between the objective lens 10 and the optical recording medium 11. It is composed of a driving means (not shown) for moving in and out.

The transparent parallel plate is made of the same material as that of the optical recording medium, and has "a stepwise change in thickness" with the interval: t between adjacent recording surfaces as a unit. At the time of performing, a portion having a thickness of (p−q) t is inserted between the objective lens 10 and the optical recording medium 11. As a result, when recording, reproducing, or erasing on the arbitrary q-th surface, the thickness of the transparent material between the objective lens 10 and the arbitrary recording surface does not change, so that the spot is blurred due to spherical aberration. The best recording and reproduction is possible without the occurrence of. Note that spherical aberration is corrected when information is recorded on an optical recording medium having a multi-layered recording surface, where ΔW> | (p is the numerical aperture of the objective lens is ΔW and the numerical aperture of the objective lens is NA. -1) t-200NA
By performing so as to satisfy ² + 370NA−170 |, it is possible to improve the quality of the light spot and perform high quality information recording / reproducing.

The optical pickup shown in the embodiments of FIGS. 13 to 17 is an infinite system for recording / reproducing / erasing information on / from an optical recording medium 11 having a light irradiation side substrate thickness of 0.1 mm. Is an optical pickup. And the used wavelength is 6
When it is 50 ± 20 nm, the objective lens for an optical pickup according to any one of claims 1 to 8 (specifically, as an objective lens for converging a light flux from a light source as a light spot on a recording surface of an optical recording medium). Specifically, those of Examples 1 to 6 are used (Claim 17), and the wavelength used is 407 ±
At 20 nm, an objective lens for optical pickup according to any one of claims 9 to 16 (specifically, one of Examples 7 to 12) is used as the objective lens (claim 1).
8).

The optical pickups of FIGS. 13 and 14 have chromatic aberration correcting means 14, 14a and 14b for correcting chromatic aberration due to wavelength fluctuation (claim 19), and the optical pickup of FIG. 13 has chromatic aberration correction. The means 14 is a “doublet lens by positive lens”, and in the optical pickup of FIG. 14, it is a “resin coat 14a provided on the objective lens for the optical pickup” or a “diffraction surface 14b” (claim 20).

The optical pickup shown in FIG. 15 to FIG.
Substrate thickness error detecting means 15 for detecting a substrate thickness error of the light irradiation side substrate of the optical recording medium, and spherical aberration caused by the substrate thickness error are corrected based on the substrate thickness error detected by the substrate thickness error detecting means 15. Spherical aberration correction means 16, 16A, 16B
In the optical pickup of FIG. 16, the spherical aberration correction means 16 is a “positive / negative lens with variable lens spacing”, and in the optical pickup of FIG. 17, “a concentric electrode pattern is provided”. Liquid crystal element "(claim 2)
2).

As described above, the optical pickups of FIGS. 16 and 17 can be applied even when the optical recording medium is a “multilayer optical recording medium having a substrate thickness of the light irradiation side: 0.1 mm”. , Spherical aberration detecting means 15 for detecting a spherical aberration that changes according to the distance from the light irradiation side substrate surface to an arbitrary recording surface, and spherical aberration correcting means 16 for correcting the spherical aberration detected by this spherical aberration detecting means. , 16A, and when the used wavelength is 650 ± 20 nm, it is an objective lens for condensing a light beam from a light source as a light spot on a desired recording surface of an optical recording medium. No. 1 (specifically, those of Examples 1 to 6) is used (claim 23), and the wavelength used is 407 ± 10 nm.
In this case, the objective lens according to any one of claims 9 to 16 as an objective lens for condensing a light beam from a light source as a light spot on a desired recording surface of an optical recording medium (specifically, Examples 7 to 12) are used (claim 2
4).

The optical pickups shown in FIGS. 15 to 18 also include “chromatic aberration correcting means 14, 14 for correcting chromatic aberration due to wavelength variation” as shown in FIGS. 13 and 14.
A and 14B can be added ”(claim 26).
Further, for example, by using "glass materials having different dispersions" for the two lens groups of the spherical aberration correction means 16 in FIG. 15, it is possible to have a function as a chromatic aberration correction means. That is, the chromatic aberration correcting means and the spherical aberration correcting means can be integrated (claim 26).

FIG. 19 is a diagram schematically showing an embodiment of an optical information processing apparatus. The optical information processing device 130 is a device for recording / reproducing / erasing information on / from an optical recording medium by using an optical pickup. In this embodiment, the optical recording medium 131 has a disk shape and is stored in the protective case 132. The optical recording medium 131, together with the protective case 132, is inserted and set in the optical information processing device 130 from the insertion port 136 in the direction of the "insertion" direction, is rotated by the spindle motor 133, and the optical pickup 135 records, reproduces, or erases information. Done.

As the optical pickup 135, the one described in each of the above embodiments can be appropriately used (claim 27).

A technique for correcting chromatic aberration in an optical pickup is conventionally known, for example, in Japanese Patent Laid-Open No. 2000-904.
No. 7, Japanese Patent Publication No. 6-14135, Japanese Patent Laid-Open No. 62-62
It is known from Japanese Patent No. 36621, Japanese Patent Laid-Open No. 9-138344, etc., and these known appropriate methods can be used.

Similarly, the spherical aberration correction means has been conventionally used in Japanese Patent Laid-Open No. 2000-13160 and Japanese Patent Laid-Open No. 10-2026.
No. 3, for example, is known, and conventionally known spherical aberration correcting means can be appropriately used.

[0205]

As described above, according to the present invention, a novel objective lens for an optical pickup, an optical pickup and an optical information processing apparatus can be realized. Since the objective lens for an optical pickup according to the present invention has a single lens structure, there is no problem that the number of parts is increased, the weight is increased, and the assembling accuracy is improved. Moreover, the conventional objective lens having a single lens structure is achieved. With a numerical aperture of 6.5 or more, which was not possible, the wavelength used:
In combination with the short wavelengths of 650 ± 20 nm and 407 ± 10 nm, a small-diameter light spot can be formed well.

Therefore, an optical pickup using such an objective lens for an optical pickup can handle high-density information processing. Further, by having a function of correcting chromatic aberration and spherical aberration, it is possible to cope with wavelength variation and substrate thickness error.

Therefore, the optical information processing apparatus using such an optical pickup can satisfactorily record, reproduce, and erase information on the optical recording medium having the above-mentioned used wavelength.

[Brief description of drawings]

FIG. 1 is a diagram showing a form of an objective lens for an optical pickup of Example 1, astigmatism, and spherical aberration.

FIG. 2 is a diagram showing a form of an objective lens for an optical pickup of Example 2, astigmatism, and spherical aberration.

FIG. 3 is a diagram showing a form of an objective lens for an optical pickup of Example 3, astigmatism, and spherical aberration.

FIG. 4 is a diagram showing the form of an objective lens for an optical pickup of Example 4, astigmatism, and spherical aberration.

5A and 5B are diagrams showing a form of an objective lens for an optical pickup of Example 5, astigmatism, and spherical aberration.

6A and 6B are diagrams showing the form of an objective lens for an optical pickup of Example 6, astigmatism, and spherical aberration.

FIG. 7 is a diagram showing a form of an objective lens for an optical pickup of Example 7, astigmatism, and spherical aberration.

8A and 8B are diagrams showing the form of an objective lens for an optical pickup of Example 8, astigmatism, and spherical aberration.

9A and 9B are diagrams showing the form of an objective lens for an optical pickup of Example 9, astigmatism, and spherical aberration.

FIG. 10 is a diagram showing the form of an objective lens for an optical pickup of Example 10, astigmatism, and spherical aberration.

FIG. 11 is a diagram showing the form of an objective lens for an optical pickup of Example 11, astigmatism, and spherical aberration.

FIG. 12 is a diagram showing the form of an objective lens for an optical pickup of Example 12, astigmatism, and spherical aberration.

FIG. 13 is a diagram for explaining the first embodiment of the optical pickup.

FIG. 14 is a diagram for explaining another embodiment of the optical pickup.

FIG. 15 is a diagram for explaining another embodiment of the optical pickup.

FIG. 16 is a diagram for explaining another embodiment of the optical pickup.

FIG. 17 is a diagram for explaining another embodiment of the optical pickup.

FIG. 18 is a diagram for explaining an optical recording medium in which recording surfaces are superposed in multiple layers.

FIG. 19 is a perspective view schematically showing only a main part of the first embodiment of the optical information processing apparatus.

FIG. 20 is a diagram for explaining a conditional expression of an objective lens for an optical pickup.

FIG. 21 is a diagram for explaining a conditional expression of an objective lens for an optical pickup.

FIG. 22 is a diagram for explaining a conditional expression of an objective lens for an optical pickup.

[Explanation of symbols]

1 aperture 2 Objective lens for optical pickup 3 Light irradiation side substrate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 7/125 G11B 7/125 B 5D789 7/135 7/135 AZ F term (reference) 2H049 AA04 AA16 AA57 AA65 2H087 KA13 LA01 LA21 NA01 NA14 PA01 PA02 PA17 PB01 PB02 QA02 QA06 QA07 QA12 QA14 QA32 QA34 RA05 RA12 RA13 RA42 RA44 RA45 RA46 UA09 2H088 EA42 EA62 5D090 AA01 BB12 CC16 DD03 FF11 KK01 LL01 5D119 AA01 AA04 AA11 AA21 AA22 AA39 BA01 BB13 EB02 EC01 EC03 JA09 JA43 JA46 JA64 JB01 JB02 JB03 JB04 JB06 5D789 AA01 AA04 AA11 AA21 AA22 AA39 BA01 BB13 EB02 EC01 EC03 JA09 JA43 JA46 JA64 JB01 JB02 JB03 JB04 JB06

Claims (27)

[Claims] 1. An infinite optical pickup for recording / reproducing / erasing information on / from an optical recording medium having a wavelength of 650 ± 20 nm and a substrate thickness of 0.1 mm on the light irradiation side. Is an objective lens for converging the light flux of the above as a light spot on the recording surface of the optical recording medium, and is configured as a single lens, both surfaces are aspherical surfaces, and numerical aperture: NA is 0.65 ≦ NA < Within the range of 0.75, the paraxial radius of curvature of the light source side surface is R1, the working distance is WD, the refractive index of the material with respect to the d-line is nd, and the focal length is f, the conditions are: (1) 1.2nd-1. 1 <R1 / f ≦ 1.3nd-1.2 (2) 0.37nd-0.14 <WD / f ≦ 0.39nd-0.04 The objective lens for an optical pickup characterized by the following. 2. The objective lens for an optical pickup according to claim 1, wherein the refractive index of the material with respect to d-line is nd and the Abbe number is vd.
However, the following conditions are satisfied: (3) νd ≦ 60 (4) 1.5 ≦ nd Objective lens for optical pickup characterized by the following: 3. An infinite optical pickup for recording / reproducing / erasing information on / from an optical recording medium having a wavelength of 650 ± 20 nm and a substrate thickness of 0.1 mm on the light irradiation side. Is an objective lens for condensing the light flux of the above as a light spot on the recording surface of the above optical recording medium, and is configured as a single lens, both surfaces are aspherical surfaces, and numerical aperture: NA is 0.75 ≦ NA < Within the range of 0.85, the paraxial radius of curvature of the light source side surface is R1, the working distance is WD, the refractive index of the material with respect to the d line is nd, and the focal length is f, the condition is: (5) 1.0nd-0. 7 <R1 / f ≦ 1.2nd-1.1 (6) 0.33nd−0.18 <WD / f ≦ 0.37nd−0.14 The objective lens for an optical pickup, characterized in that: 4. The objective lens for an optical pickup according to claim 3, wherein the refractive index of the material with respect to d line is nd and the Abbe number is vd.
However, the following conditions are satisfied: (7) νd ≦ 60 (8) 1.6 ≦ nd Objective lens for optical pickup characterized by the following: 5. An infinite optical pickup for recording / reproducing / erasing information on / from an optical recording medium having a working wavelength of 650 ± 20 nm and a light irradiation side substrate thickness of 0.1 mm. Is an objective lens for condensing the light flux of as a light spot on the recording surface of the optical recording medium, is configured as a single lens, has aspherical surfaces on both sides, and has a numerical aperture: NA of 0.85 ≦ NA. Within the range, the paraxial radius of curvature of the side surface of the light source is R1, the working distance is WD, the refractive index of the material for the d-line is nd, and the focal length is f, the conditions are: (9) R1 / f ≦ 1.0 nd-0. 7 (10) An objective lens for an optical pickup, which satisfies WD / f ≦ 0.33nd−0.18. 6. The objective lens for an optical pickup according to claim 5, wherein the refractive index of the material with respect to the d-line is nd and the Abbe number is vd.
However, the condition: (11) 30 ≦ νd ≦ 50 (12) 1.65 ≦ nd ≦ 1.80 is satisfied, and the objective lens for an optical pickup is characterized. 7. The objective lens for an optical pickup according to any one of claims 1 to 6, which is a meniscus lens having a convex surface facing a light source side. 8. The objective lens for an optical pickup according to claim 2, which is a biconvex lens with a surface having a strong curvature facing a light source side. 9. An infinite optical pickup for recording / reproducing / erasing information on / from an optical recording medium having a wavelength of 407 ± 10 nm and a light irradiation side substrate thickness of 0.1 mm. Is an objective lens for converging the light flux of the above as a light spot on the recording surface of the optical recording medium, and is configured as a single lens, both surfaces are aspherical surfaces, and numerical aperture: NA is 0.65 ≦ NA < Within the range of 0.75, the paraxial radius of curvature of the light source side surface is R1, the working distance is WD, the refractive index of the material for the d-line is nd, and the focal length is f, the conditions are: (13) 1.2nd-1. 1 <R1 / f ≦ 1.3nd−1.2 (14) 0.37nd−0.14 <WD / f ≦ 0.39nd−0.04 The objective lens for an optical pickup, characterized in that: 10. The objective lens for an optical pickup according to claim 9, wherein the refractive index of the material for d-line is nd and the Abbe number is vd.
However, the following conditions are satisfied: (15) νd ≦ 60 (16) 1.5 ≦ nd Objective lens for optical pickup. 11. Recording of information on an optical recording medium having a working wavelength of 407 ± 10 nm and a light irradiation side substrate thickness of 0.1 mm.
In an infinite optical pickup that performs one or more of reproduction and erasing, it is an objective lens for converging a light beam from the light source side as a light spot on the recording surface of the optical recording medium, and is configured as a single lens, Both surfaces are aspherical surfaces, numerical aperture: NA is in a range of 0.75 ≦ NA <0.85, paraxial radius of curvature of light source side surface: R1, working distance: WD, refractive index of material for d line: nd , Focal length: f, condition: (17) 1.0nd-0.7 <R1 / f ≦ 1.2nd-1.1 (18) 0.33nd-0.18 <WD / f ≦ 0.37nd- An objective lens for an optical pickup, which satisfies 0.14. 12. The objective lens for an optical pickup according to claim 11, wherein the refractive index of the material for d-line is nd and the Abbe number is vd.
However, the condition: (19) νd ≦ 60 (20) 1.6 ≦ nd ≦ 1.8 is satisfied, and an objective lens for an optical pickup is characterized. 13. Recording of information on an optical recording medium having a working wavelength of 407 ± 10 nm and a light irradiation side substrate thickness of 0.1 mm.
In an infinite optical pickup that performs one or more of reproduction and erasing, it is an objective lens for converging a light beam from the light source side as a light spot on the recording surface of the optical recording medium, and is configured as a single lens, Both surfaces are aspherical surfaces, numerical aperture: NA is in the range of 0.85 ≦ NA, paraxial radius of curvature of light source side surface: R1, working distance: WD, refractive index of material for d-line: nd, focal length: f satisfies the following condition: (21) R1 / f ≤ 1.0 nd-0.7 (22) WD / f ≤ 0.33 nd-0.18. 14. The objective lens for an optical pickup according to claim 13, wherein the refractive index of the material with respect to the d line is nd and the Abbe number is vd.
However, the condition: (23) 45 ≦ νd ≦ 55 (24) 1.65 ≦ nd ≦ 1.72 is satisfied, and the objective lens for an optical pickup is characterized. 15. The objective lens for an optical pickup according to any one of claims 9 to 14, which is a meniscus lens having a convex surface facing the light source side. 16. The objective lens for an optical pickup according to claim 10, which is a biconvex lens with a surface having a strong curvature facing a light source side. 17. Recording of information on an optical recording medium having a working wavelength of 650 ± 20 nm and a substrate thickness on the light irradiation side of 0.1 mm.
An infinite optical pickup that performs at least one of reproduction and erasing, and as an objective lens for converging a light flux from a light source as a light spot on a recording surface of the optical recording medium.
<8> An optical pickup using the objective lens for an optical pickup according to any one of <1> to <8>. 18. Recording of information on an optical recording medium having a working wavelength of 407 ± 20 nm and a light irradiation side substrate thickness of 0.1 mm.
10. An infinite optical pickup that performs at least one of reproduction and erasing, and as an objective lens for converging a light flux from a light source as a light spot on a recording surface of the optical recording medium.
An optical pickup using the objective lens for an optical pickup according to any one of 1 to 16. 19. The optical pickup according to claim 17 or 18, further comprising chromatic aberration correcting means for correcting chromatic aberration caused by wavelength fluctuation. 20. The optical pickup according to claim 19, wherein the chromatic aberration correcting means is a doublet lens, a resin coat provided on the objective lens for the optical pickup, or a diffractive surface provided on the objective lens for the optical pickup. An optical pickup characterized in that. 21. An optical pickup according to any one of claims 17 to 20, wherein a substrate thickness error detecting means for detecting a substrate thickness error of a light irradiation side substrate of an optical recording medium, and the substrate thickness error are caused. An optical pickup comprising: spherical aberration correcting means for correcting spherical aberration based on the substrate thickness error detected by the substrate thickness error detecting means. 22. The optical pickup according to claim 21, wherein the spherical aberration correcting means is a positive / negative second group lens having a variable lens spacing or a liquid crystal element having a concentric electrode pattern. Optical pickup. 23. Infinite recording / reproducing / erasing of information on / from an optical recording medium having recording surfaces laminated in multiple layers, a substrate thickness of light irradiation side: 0.1 mm, and a wavelength used: 650 ± 20 nm. A system optical pickup, including spherical aberration detecting means for detecting spherical aberration that changes according to the distance from the light-irradiating-side substrate surface to an arbitrary recording surface, and correcting spherical aberration detected by this spherical aberration detecting means. 9. A spherical aberration correction means for controlling the optical system according to claim 1, wherein the objective lens for condensing a light beam from the light source as a light spot on a desired recording surface of the optical recording medium is used. An optical pickup using an objective lens for an optical pickup. 24. Infinite recording / reproducing / erasing of information for an optical recording medium having a recording surface of a multi-layered structure, a substrate thickness of light irradiation side: 0.1 mm, and a wavelength used: 407 ± 10 nm. A system optical pickup, comprising: spherical aberration detecting means for detecting spherical aberration that changes according to the distance from the light irradiation side substrate surface to an arbitrary recording surface; and spherical aberration detected by this spherical aberration detecting means. 17. A spherical aberration correcting means for controlling the optical system according to claim 1, wherein the objective lens for condensing a light beam from a light source as a light spot on a desired recording surface of the optical recording medium. An optical pickup using an objective lens for an optical pickup. 25. The optical pickup according to claim 23, further comprising chromatic aberration correcting means for correcting chromatic aberration due to wavelength fluctuation. 26. An optical pickup according to any one of claims 19 to 25, characterized in that it has a chromatic aberration correction means and a spherical aberration correction means, and these two means are integrated. 27. An optical information processing apparatus for recording / reproducing / erasing information on / from an optical recording medium by using an optical pickup, the optical information processing apparatus being any one of claims 17 to 26 as an optical pickup. 1. An optical information processing device using the one described in 1.