JP2002203333A - Objective lens, beam-condensing optical system, and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a beam-condensing optical system and an optical pickup device that enable a plurality of types of optical information recording mediums to be recorded and reproduced. SOLUTION: An objective lens 3 is used in an optical pickup device for recording and reproducing information, a device that information can be recorded or reproduced on the optical information recording mediums 23, 24 having a transparent substrate of different thickness, by an optical flux from light sources 11, 12 of a different wavelength. The objective lens 3 consists of a first and second lenses 3a, 3b of positive refractive power which are arranged in order from the light source side; each lens is formed from a material with a specific gravity of 2.0 or below or a plastic material, and is provided with a loop-belt-like diffraction structure at least on one surface, the wavefront aberration is 0.07 λ1 rms or below with respect to the combination of a wavelength λ1, the thickness t1 of the transparent substrate, and an image-side numerical aperture NA1, and also the wavefront aberration is 0.07 λ2 rms or below with respect to the combination of wavelength λ2, the thickness t2 of the transparent substrate, and an image-side numerical aperture NA2. (assuming that t1<t2, λ1<λ2, and NA1>=NA2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an objective lens, a condensing optical system, and an optical pickup device capable of recording and / or reproducing information on and from a plurality of types of optical information recording media.

[0002]

2. Description of the Related Art In recent years, along with the practical use of a short-wavelength red semiconductor laser, a conventional optical disk (optical information recording medium) C
DVD (digital versatile disk), which is a high-density optical disk that is as large and has a large capacity as D (compact disk), has been developed and commercialized. It is expected that next generation optical disks will appear. In such an optical system of an optical information recording / reproducing apparatus using a next-generation optical disc as a medium, an information recording surface is passed through an objective lens in order to increase the density of a recording signal or reproduce a high-density recording signal. It is required to reduce the diameter of the spot to be focused. For that purpose, it is necessary to shorten the wavelength of a laser as a light source and increase the numerical aperture of an objective lens. A blue-violet semiconductor laser having an oscillation wavelength of about 400 nm is expected to be put to practical use as a short-wavelength laser light source.

When a higher density next generation optical disk as described above is put to practical use, a recording / reproducing apparatus / optical pickup apparatus for such a high density optical disk can record / reproduce even a conventional optical disk such as a DVD. Compatibility is required as follows.

By the way, when the wavelength of the laser light source is shortened and the numerical aperture of the objective lens is increased, a relatively long length of information such as recording or reproducing information on or from a conventional optical disc such as a CD or DVD is required. In an optical pickup device including a combination of a laser light source having a wavelength and an objective lens having a low numerical aperture, it is expected that even a problem that can be almost ignored will become more apparent.

[0005] One of the problems that becomes apparent in shortening the wavelength of a laser light source and increasing the numerical aperture of an objective lens is fluctuation of spherical aberration of an optical system due to changes in temperature and humidity. That is, a plastic lens generally used in an optical pickup device is easily deformed by a change in temperature or humidity, and has a large change in refractive index. Variations in spherical aberration due to refractive index changes, which were not so problematic in optical systems used in conventional optical pickup devices,
The amount is not negligible in shortening the wavelength of the laser light source and increasing the numerical aperture of the objective lens.

Another problem that becomes apparent in shortening the wavelength of a laser light source and increasing the numerical aperture of an objective lens is that the spherical error of the optical system due to the thickness error of the protective layer (also referred to as a "transparent substrate") of the optical disk. Aberration variation. It is known that the spherical aberration caused by the thickness error of the protective layer occurs in proportion to the fourth power of the numerical aperture of the objective lens. Therefore, as the numerical aperture of the objective lens increases, the influence of the thickness error of the protective layer increases, and there is a possibility that stable recording or reproduction of information cannot be performed.

Further, there is also a problem of axial chromatic aberration generated in the objective lens due to a minute fluctuation of the oscillation wavelength of the laser light source. The change in the refractive index of a general optical lens material due to a minute wavelength change becomes larger as the wavelength becomes shorter. Therefore, the defocus amount of the focal point caused by a minute wavelength fluctuation becomes large. However, the depth of focus of the objective lens is k · λ / NA
^As can be seen from ² (k is a proportional constant, λ is a wavelength, and NA is an image-side numerical aperture of the objective lens), the shorter the wavelength used, the smaller the focal depth and the slight defocus is not allowed. Therefore, in an optical system using a short wavelength light source such as a blue-violet semiconductor laser and a high numerical aperture objective lens,
It is important to correct axial chromatic aberration in order to prevent wavelength fluctuations due to the mode hop phenomenon and output change of the semiconductor laser, and deterioration of wavefront aberration due to high frequency superposition.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention has a high numerical aperture (N) of an objective lens.
A) It is an object of the present invention to provide an inexpensive and lightweight objective lens which is compatible with a plurality of types of optical information recording media having different thicknesses of the transparent substrate and which is a high-performance objective lens and which is the same as a conventional plastic single lens. And

Further, the optical information recording medium has compatibility so that recording and reproduction can be performed with respect to a plurality of types of optical information recording media having different thicknesses of the transparent substrate. A condensing optical system and an optical pickup device that can effectively correct the fluctuation of spherical aberration generated on each optical surface of the optical pickup device due to an error in the thickness of the transparent substrate and the like with a simple configuration. The purpose is to provide.

Also, the optical information recording medium has compatibility so that recording / reproduction can be performed with respect to a plurality of types of optical information recording media having different thicknesses of the transparent substrate. It is an object of the present invention to provide a condensing optical system and an optical pickup device that can effectively correct generated axial chromatic aberration.

[0011]

According to another aspect of the present invention, there is provided an objective lens for focusing light beams from light sources having different wavelengths on a recording surface of an optical information recording medium. And a light receiving means for detecting reflected light from the recording surface, and recording and / or reproducing information on and from a plurality of optical information recording media having different thicknesses of transparent substrates. The objective lens used in the optical pickup device for information recording / reproducing, which comprises: a first lens having a positive refractive power and a second lens having a positive refractive power arranged in order from the light source side; The second lens is formed of a material having a specific gravity of 2.0 or less, has a ring-shaped diffractive structure on at least one surface thereof, and includes a plurality of optical information recording media having different transparent substrate thicknesses.
The thickness of the transparent substrate of any two optical information recording media is t1,
t2 (t1 <t2), the wavelength at the time of recording or reproducing information on or from the optical information recording medium having the transparent substrate thickness t1 is λ1, and the optical information recording having the transparent substrate thickness t2. The wavelength at the time of recording or reproducing information on a medium is λ2 (λ1 <λ2), and a predetermined wavelength required for recording or reproducing on an optical information recording medium having a thickness t1 of a transparent substrate with a light beam of wavelength λ1. Let NA1 be the image side numerical aperture of
When a predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a thickness t2 of the transparent substrate with a light beam of the wavelength λ2 is NA2 (NA1 ≧ NA2), the wavelength λ1 and the thickness of the transparent substrate The wavefront aberration is 0.07λ1 rms or less, the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture N for the combination of the height t1 and the image-side numerical aperture NA1.
The wavefront aberration is 0.07 with respect to the combination with A2.
λ2 rms or less.

According to a second aspect of the present invention, there is provided an objective lens, comprising: a condensing optical system including an objective lens for condensing light beams from light sources having different wavelengths on a recording surface of an optical information recording medium; Light receiving means for detecting reflected light of
In an objective lens used in an information recording / reproducing optical pickup device capable of recording and / or reproducing information on a plurality of optical information recording media having different thicknesses of a transparent substrate, positive lenses arranged in order from a light source side. A first lens having a refractive power and a second lens having a positive refractive power, wherein the first lens and the second lens are each formed of a plastic material, and have a ring-shaped diffraction structure on at least one surface;
Of the plurality of optical information recording media having different transparent substrate thicknesses, the transparent substrates of any two optical information recording media have thicknesses t1 and t2 (t1 <t2), and the thickness t1 of the transparent substrate. The wavelength at the time of recording or reproducing information on or from the optical information recording medium having λ is λ1, and the wavelength at the time of recording or reproducing information on the optical information recording medium having the thickness t2 of the transparent substrate is λ1. λ2 (λ1 <λ2), and the wavelength λ
A predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a thickness t1 of a transparent substrate with a light flux of 1 is N.
A1, and a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t2 of a transparent substrate with a light beam of wavelength λ2 is NA2 (NA1 ≧ NA2).
For a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1, the wavefront aberration is 0.07λ1rm.
s or less, and the wavefront aberration is 0.07λ2 rms or less for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2.

The objective lens described in claim 3 is the one according to claim 1 or 2, wherein the wavelength λ2 and the thickness t2 of the transparent substrate.
The wavefront aberration is 0.07λ2 rms or less for a combination of the image side numerical aperture NA2 and the wavefront aberration for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image side numerical aperture NA1. Is 0.07λ2 rms or more.

According to a fourth aspect of the present invention, there is provided the objective lens according to the first, second or third aspect, wherein the object point at a predetermined position and the wavelength λ
1 and the thickness t1 of the transparent substrate and the image-side numerical aperture NA1, the wavefront aberration is 0.07λ1 rms or less, and the object point at a distance optically equal to the predetermined position and the wavelength λ2, Transparent substrate thickness t2 and image-side numerical aperture NA
2, the wavefront aberration is 0.07λ.
2 rms or less.

The objective lens according to claim 5 is the object lens according to claim 1, 2 or 3, wherein the object point at a predetermined position and the wavelength λ
1 and the thickness t1 of the transparent substrate and the image-side numerical aperture NA1, the wavefront aberration is 0.07λ1 rms or less and the object point and the wavelength λ2 are located at a distance that is not optically equal to the predetermined position. And the thickness t2 of the transparent substrate and the image-side numerical aperture NA2, the wavefront aberration is 0.0
It is not more than 7λ2 rms.

According to a sixth aspect of the present invention, in the objective lens of the first aspect, at least two of the first to third surfaces are aspherical. I do.

An objective lens according to a seventh aspect is characterized in that, in any one of the first to sixth aspects, the following expression is satisfied.

0.4 ≦ | (Ph / Pf) −2 | ≦ 25 (1) where Pf is a predetermined image side required for performing recording or reproduction on an optical information recording medium having a thickness t1 of a transparent substrate. Numerical aperture NA
Diffraction ring spacing at 1 Ph: Diffraction ring spacing at 1/2 numerical aperture of NA1

The objective lens described in claim 8 satisfies the following expression in any one of claims 1 to 7.

1.3 ≦ f1 / f2 ≦ 4.0 (2)

0.3 ≦ (r2 + r1) / (r2−r1) ≦ 3.2 (3) where, fi: focal length of the i-th lens (when the i-th lens has a diffractive structure, the refractive lens and the diffractive structure Ri: paraxial radius of curvature of each surface (i = 1 and 2)

According to a ninth aspect of the present invention, there is provided an objective lens according to any one of the first to eighth aspects, wherein the following expression is satisfied.

T1 ≦ 0.6 mm (4)

T2 ≧ 0.6 mm (5)

Λ1 ≦ 500 nm (6)

600 nm ≦ λ2 ≦ 800 nm (7)

NA1 ≧ 0.65 (8)

NA2 ≦ 0.65 (9)

Further, the objective lens according to claim 10 is:
The method according to any one of claims 1 to 9, wherein the material is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a used wavelength region.

Further, the objective lens according to claim 11 is
The method according to any one of claims 1 to 10, wherein the material is formed from a material having a saturated water absorption of 0.5% or less.

Further, the converging optical system according to claim 12 is:
A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of the optical information recording medium, and a plurality of optical information recordings having different thicknesses of the transparent substrate. A recording / reproducing optical system capable of recording and / or reproducing information on / from a medium, wherein the objective lens is the objective lens according to any one of claims 1 to 11, Among the different wavelengths, any two wavelengths are λ1, λ2 (λ1 <λ2), and the transparent substrate of any two optical information recording media among the plurality of optical information recording media having different transparent substrate thicknesses. T1, t
2 (t1 <t2), a predetermined image-side numerical aperture required for recording or reproducing on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a light beam of wavelength λ2 is transparent. A predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a substrate thickness t2 is set to NA2.
When (NA1 ≧ NA2), for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1,
The wavefront aberration is 0.07λ1 rms or less and the wavelength λ2
And the thickness t2 of the transparent substrate and the image-side numerical aperture NA2 can be focused so that the wavefront aberration is 0.07λ2 rms or less, and the focusing optics is provided between the light source and the objective lens. The present invention is characterized in that spherical aberration correcting means for correcting fluctuation of spherical aberration occurring on each optical surface of the system is provided.

Further, the light condensing optical system according to claim 13 is:
A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of the optical information recording medium, and a plurality of optical information recordings having different thicknesses of the transparent substrate. A recording and reproducing light collecting optical system capable of recording and / or reproducing information on and from a medium, wherein the objective lens is the objective lens according to any one of claims 1 to 11, Any two of the different wavelengths
Λ1, λ2 (λ1 <λ2), and among the plurality of optical information recording media having different transparent substrate thicknesses,
The thickness of the transparent substrate of any two optical information recording media is t1,
t2 (t1 <t2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a light beam of wavelength λ2 is transparent. A predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a substrate thickness t2 is set to NA2.
When (NA1 ≧ NA2), for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1,
The wavefront aberration is 0.07λ1 rms or less and the wavelength λ2
And the thickness t2 of the transparent substrate and the image-side numerical aperture N2, the light can be condensed so that its wavefront aberration is 0,07λ2 rms or less, and the temperature and humidity change between the light source and the objective lens. A spherical aberration corrector for correcting a variation in spherical aberration generated on each optical surface of the condensing optical system is provided.

Further, the condensing optical system according to claim 14 is:
A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium, and a plurality of optical information recordings having different thicknesses of the transparent substrate. A recording and reproducing light collecting optical system capable of recording and / or reproducing information on and from a medium, wherein the objective lens is the objective lens according to any one of claims 1 to 11, Any two of the different wavelengths
Λ1, λ2 (λ1 <λ2), and among the plurality of optical information recording media having different transparent substrate thicknesses,
The thickness of the transparent substrate of any two optical information recording media is t1,
t2 (t1 <t2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a light beam of wavelength λ2 is transparent. A predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a substrate thickness t2 is set to NA2.
When (NA1 ≧ NA2), for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1,
The wavefront aberration is 0.07λ1 rms or less and the wavelength λ2
And the thickness t2 of the transparent substrate and the image-side numerical aperture NA2, the light can be collected so that the wavefront aberration is 0.07λ2 rms or less, and the optical information recording medium is provided between the light source and the objective lens. And a spherical aberration correcting means for correcting a variation in spherical aberration generated on each optical surface of the condensing optical system due to a minute variation in the thickness of the transparent substrate.

Further, the light condensing optical system according to claim 15 is
A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of the optical information recording medium, and a plurality of optical information recordings having different thicknesses of the transparent substrate. A recording and reproducing light collecting optical system capable of recording and / or reproducing information on and from a medium, wherein the objective lens is the objective lens according to any one of claims 1 to 11, Any two of the different wavelengths
Λ1, λ2 (λ1 <λ2), and among the plurality of optical information recording media having different transparent substrate thicknesses,
The thickness of the transparent substrate of any two optical information recording media is t1,
t2 (t1 <t2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a light beam of wavelength λ2 is transparent. A predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a substrate thickness t2 is set to NA2.
When (NA1 ≧ NA2), for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1,
The wavefront aberration is 0.07λ1 rms or less and the wavelength λ2
And the thickness t2 of the transparent substrate and the image-side numerical aperture NA2, the light can be condensed so that the wavefront aberration is 0.07λ2 rms or less, and the oscillation wavelength of the light source is provided between the light source and the objective lens. And a spherical aberration correcting means for correcting a variation in spherical aberration generated on each optical surface of the condensing optical system due to the minute variation of the optical system.

Further, the converging optical system according to claim 16 is:
A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of the optical information recording medium, and a plurality of optical information recordings having different thicknesses of the transparent substrate. A recording and reproducing light collecting optical system capable of recording and / or reproducing information with respect to a medium, wherein the objective lens is the objective lens according to any one of claims 1 to 11, Of the different wavelengths, any two wavelengths are λ1 and λ2 (λ1 <λ2), and among the plurality of optical information recording media having different transparent substrate thicknesses, two arbitrary optical information recording media The thickness of the transparent substrate is t
1, t2 (t1 <t2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of a transparent substrate with a light beam of wavelength λ1 is NA1, and a wavelength λ
The predetermined image-side numerical aperture required for recording or reproducing information on or from the optical information recording medium having the thickness t2 of the transparent substrate with the light flux of N2 is N.
When A2 (NA1 ≧ NA2), the wavefront aberration is 0.07λ1 rms or less for the combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1, and the wavelength λ2 and the thickness of the transparent substrate. With respect to the combination of t2 and the image-side numerical aperture NA2, the light can be focused so that the wavefront aberration is 0.07λ2 rms or less. A spherical surface that corrects a variation in spherical aberration that occurs on each optical surface of the condensing optical system due to a combination of at least two of a small variation in the thickness of the transparent substrate and a small variation in the oscillation wavelength of the light source. It is characterized in that aberration correction means is provided.

Further, the converging optical system according to claim 17 is
17. The optical recording medium according to claim 12, wherein the spherical aberration correction unit is configured to control each optical information recording medium having a different transparent substrate thickness according to the thickness of each transparent substrate. And changing the divergence angle of the light beam incident on the objective lens.

Further, the light condensing optical system according to claim 18 is:
In any one of claims 12 to 16, the condensing optical system is characterized in that the spherical aberration correcting means has a variable refractive index distribution.

The converging optical system according to claim 19 is
The beam according to any one of claims 12 to 17, wherein the spherical aberration correction unit includes at least one positive lens and at least one negative lens, and emits a light beam that enters substantially parallel and emits light that is substantially parallel. An expander, and at least one of the positive lens and the negative lens
The two lenses are movable elements that can move along the optical axis direction.

Further, the converging optical system according to claim 20 is:
In claim 19, the positive lens and the negative lens satisfy the following expression.

ΝdP> νdN (10) where νdP is the average value of the Abbe number of the d-line of the positive lens included in the spherical aberration correcting unit, and νdN is the Abbe number of the d-line of the negative lens included in the spherical aberration correcting unit. The average of

Further, the converging optical system according to claim 21 is:
In claim 20, the positive lens and the negative lens satisfy the following expression.

ΝdP> 55.0 (11)

ΝdN <35.0 (12)

Further, the converging optical system according to claim 22 is:
22. The difference between the average value of the Abbe number of the d-line of the positive lens included in the spherical aberration correction unit and the average value of the Abbe number of the d-line of the negative lens included in the spherical aberration correction unit is △. The following conditional expression is satisfied as ν, and the movable element is formed of a material having a specific gravity of 2.0 or less.

30 ≦ △ ν ≦ 50 (13)

Further, the light converging optical system according to claim 23,
20. The Abbe number of all the positive lenses included in the spherical aberration correcting means according to claim 19, or the Abbe number of all the negative lenses included in the spherical aberration correcting means is 4 or less.
0.0 or more, and has a diffraction surface having at least one ring-shaped diffraction structure.

According to a twenty-fourth aspect of the present invention, the movable element has a specific gravity of 2.
It is characterized by being formed from a material of 0 or less.

The converging optical system according to claim 25 is
According to Claim 22, 23 or 24, the spherical aberration correcting means is made of a plastic material.

The converging optical system according to claim 26 is
According to a twenty-fifth aspect, the spherical aberration correcting means is formed of a material having a saturated water absorption of 0.5% or less.

The converging optical system according to claim 27 is
The spherical aberration correcting hand hit according to any one of claims 19 to 26, is characterized by being formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a used wavelength region.

The condensing optical system according to claim 28 is
28. The spherical aberration correction unit according to claim 19, wherein the spherical aberration correction unit includes one positive lens and one negative lens, has at least one aspheric surface, and includes a lens having a spherical surface. At least one of the lenses is a movable element that can move along the optical axis direction.

Further, the light converging optical system according to claim 29,
29. The movable element according to claim 28, wherein when the spherical aberration of the optical system fluctuates to the over side, the distance between the positive lens and the negative lens is reduced, and when the spherical aberration of the optical system fluctuates to the under side. Is shifted along the optical axis direction so as to increase the distance between the positive lens and the negative lens.

The converging optical system according to claim 30 is:
30. The optical information recording medium according to claim 28, wherein, among the plurality of optical information recording media having different transparent substrate thicknesses, the transparent substrate thicknesses of any two optical information recording media are t1, t2 (t1).
When <t2), the movable element increases the distance between the positive lens and the negative lens when recording or reproducing information on or from the optical information recording medium with a transparent substrate having a thickness of t1, When recording or reproducing information on or from an optical information recording medium having a transparent substrate having a thickness of t2, the information is shifted along the optical axis direction so as to reduce the distance between the positive lens and the negative lens. And

The converging optical system according to claim 31 is:
18. The spherical aberration correction unit according to claim 12, wherein the spherical aberration correction unit is a coupling lens that changes a divergence angle of divergent light emitted from the light source, and the coupling lens is displaceable along an optical axis direction. It is characterized by being a movable element.

Further, the converging optical system according to claim 32,
In a thirty-first aspect, the spherical aberration correcting means is a single lens having at least one surface as a diffraction surface having a ring-shaped diffraction structure.

According to a thirty-third aspect of the present invention, in the converging optical system according to the thirty-second aspect, the spherical aberration correcting means is configured such that at least one surface is an aspheric surface having a radius of curvature that increases as the distance from the optical axis increases; Is a diffraction surface having a ring-shaped diffraction structure.

The condensing optical system according to claim 34 is
34. The spherical aberration correcting means according to claim 33, wherein the surface on the light source side is a spherical diffractive surface when viewed macroscopically, and the surface farther from the light source is an aspheric surface having a larger radius of curvature as being away from the optical axis. It is characterized by the following.

Further, the converging optical system according to claim 35 is
According to a thirty-first aspect of the present invention, the spherical aberration correcting means has a two-group configuration in which a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are cemented.

A light collecting optical system according to a thirty-sixth aspect is characterized in that, in the thirty-fifth aspect, the positive lens and the negative lens satisfy the following expression and have at least one aspheric surface.

ΝdP> 55.0 (14)

ΝdN <35.0 (15) where νdP: Abbe number of the d-line of the positive lens νdN: Abbe number of the d-line of the negative lens

Further, the converging optical system according to claim 37,
The spherical aberration correcting means according to any one of claims 31 to 36, is formed of a material having a specific gravity of 2.0 or less.

The converging optical system according to claim 38 is
37. The method according to claim 37, wherein said spherical aberration correcting means is formed of a plastic material. A converging optical system according to a thirty-ninth aspect is characterized in that, in the thirty-eighth aspect, the spherical aberration correcting means is made of a material having a saturated water absorption of 0.5% or less.

Further, the converging optical system according to claim 40 is
The spherical aberration correcting means according to any one of claims 31 to 39, is characterized by being formed from a material having an internal transmittance of 85% or more at a thickness of 3 mm in a used wavelength region.

The light-collecting optical system according to claim 41 is
41. The spherical aberration correction unit according to claim 31, wherein the spherical aberration correction unit increases a distance between the objective lens and the spherical aberration of the converging optical system when the spherical aberration of the converging optical system fluctuates to an over side. When the aberration fluctuates toward the under side, the aberration fluctuates along the optical axis so as to decrease the distance from the objective lens.

Further, the light condensing optical system according to claim 42 is
The thickness of the transparent substrate of any two optical information recording media among the plurality of optical information recording media having different thicknesses of the transparent substrates according to any one of claims 31 to 41, is t1, t.
2 (t1 <t2), when recording or reproducing information on or from an optical information recording medium with a transparent substrate having a thickness of t1, the movable element reduces the distance from the objective lens and reduces the distance between the transparent lens and the objective lens. When recording or reproducing information on or from an optical information recording medium having a substrate thickness of t2, the information is shifted along the optical axis so as to increase the distance from the objective lens.

Further, the converging optical system according to claim 43 is
In any one of claims 12 to 42, the following expression is satisfied.

T1 ≦ 0.6 mm (16)

T2 ≧ 0.6 mm (17)

Λ1 ≦ 500 nm (18)

600 nm ≦ λ2 ≦ 800 nm (19)

NA1 ≧ 0.65 (20)

NA2 ≦ 0.65 (21)

Further, the light condensing optical system according to claim 44,
In any one of claims 12 to 43, an axial chromatic aberration of a combined system of the spherical aberration correction unit and the objective lens satisfies the following expression.

| ΔfBi · NAi ² | ≦ 0.25 μm (i = 1 and 2) (22) where δfBi: change in focal position of the combining system when wavelength λi of the light source changes by +1 nm (μm)

An optical pickup device according to claim 45, further comprising: a light source having a different wavelength; an objective lens for condensing a light beam from the light source on a recording surface of an optical information recording medium;
A condensing optical system including a spherical aberration correcting unit disposed between the light source and the objective lens, a light receiving unit for detecting reflected light from the recording surface, and detecting the reflected light. A first driving device for driving the objective lens so as to converge the light on the recording surface, and detecting a condensed state of a light beam condensed on the recording surface by detecting the reflected light; An optical pickup device for recording and / or reproducing information on and from a plurality of optical information recording media having different thicknesses of transparent substrates, comprising: a second driving device for operating the aberration correcting means. Wherein the light-collecting optical system is the light-collecting optical system according to any one of claims 12 to 44.

[0077]

According to a first aspect of the present invention, an objective lens suitable for an optical pickup device capable of recording or reproducing information at different wavelengths on an arbitrary optical information recording medium having a transparent substrate having a different thickness is provided. In addition, when the objective lens is composed of two positive lenses, the amount of aberration generated on each refraction surface is small, and various aberrations including spherical aberration can be satisfactorily corrected even in a light beam having an NA of, for example, 0.65 or more. Further, when each lens is formed from a material having a specific gravity of 2.0 or less, even an objective lens composed of two lenses having a large NA and a large volume of the lens becomes light,
It is possible to perform high-speed tracking without placing a burden on the actuator for focusing the objective lens, or it is possible to drive with a smaller actuator, and the optical pickup device can be downsized. Further, since the two lenses are used, even when the NA is as large as 0.65 or more, it is possible to obtain an objective lens which is easy to manufacture with little deterioration of various aberrations due to errors such as eccentricity of each refractive surface. Due to the function of the diffractive structure, the wavefront aberration is 0.07λ1 rms or less for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1,
And the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2
The wavefront aberration is 0.07λ2
Since a light beam can be focused on the information recording surface in a state of rms or less, information can be recorded and / or recorded on an optical information record medium having a different transparent substrate thickness using light sources having different wavelengths.
Or reproduction can be performed appropriately.

Further, the chromatic aberration generated in the objective lens can be effectively corrected by giving the diffraction structure a wavelength characteristic such that the back focus of the objective lens becomes shorter when the oscillation wavelength of the light source fluctuates to the longer wavelength side. can do.

Further, the first lens of the objective lens according to the present invention is a lens having a two-group structure in which a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are joined. Is also good. With the first lens having the above-described configuration, chromatic aberration generated in the entire objective lens system can be effectively corrected, and both the positive lens and the negative lens are formed of a material having a specific gravity of 2.0 or less. Thus, a lightweight lens can be obtained even with a two-group configuration. Also, the second
Similarly, the lens may have a two-group configuration in which a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are cemented. By using the second lens as described above, it is possible to effectively correct chromatic aberration generated in the entire objective lens system, and to form both the positive lens and the negative lens from a material having a specific gravity of 2.0 or less. And one group 2
Even with a single lens configuration, a lightweight lens can be obtained.

When each lens is made of a plastic material, an aspherical surface or a diffractive structure can be easily added, mass production can be performed by injection molding or the like, and an inexpensive objective lens can be obtained.

According to a third aspect of the present invention, there is provided an objective lens wherein spherical aberration is satisfactorily corrected for a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1.
For the combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2, spherical aberration up to the range of the required numerical aperture NA2 is corrected by the action of the diffraction structure, and the numerical aperture N
It is preferable to generate a large amount of spherical aberration as a flare component in the range from A2 to NA1. When a light beam having a wavelength λ2 is made to pass through all the apertures determined by the wavelength λ1 and the numerical aperture NA1, a light beam having a numerical aperture NA2 or more that does not contribute to spot imaging has a small spot diameter on the information recording surface. It is possible to prevent unnecessary signals from being detected by the light receiving means of the optical pickup device, and it is not necessary to provide a means for switching a school corresponding to each combination of the wavelength and the numerical aperture. A pickup device can be obtained.

According to a fourth aspect of the present invention, when the position of an object point on a recording medium having a thin transparent substrate is equal to the position of an object point on a recording medium having a thick transparent substrate,
For example, when collimated parallel light is incident on the objective lens in any case, the spherical aberration due to the difference in the thickness of the transparent substrate is corrected only by the action of the diffractive structure.
Further, since it is not necessary to provide a mechanism for changing the divergence of the light beam incident on the objective lens for each recording medium having a different thickness of the transparent substrate, an optical pickup device having a simple configuration can be obtained.

In the case where the position of the object point on the recording medium having a small thickness of the transparent substrate is different from the position of the object point on the recording medium having a large thickness of the transparent substrate,
For example, if parallel light enters the objective lens on a recording medium with a thin transparent substrate and divergent light enters the objective lens on a recording medium with a large transparent substrate, the transparent substrate Can be corrected to some extent by the difference in the object point position, so that the spherical aberration can be corrected more precisely. In addition, since the burden of spherical aberration correction of the diffraction structure can be reduced,
The shape of the diffraction structure can be made easy to manufacture,
In addition, diffraction efficiency can be increased. Furthermore, when divergent light is incident on the objective lens on a recording medium having a thick transparent substrate, a large working distance can be ensured. Contact can be prevented.

If at least two of the four refracting surfaces from the first surface to the third surface are aspherical, coma and astigmatism can be obtained in addition to spherical aberration. The aberration can be corrected favorably, and the deterioration of the light-collecting performance due to the tilt of the objective lens and the deviation of the optical axis from the light source can be reduced. If the lens is made of plastic, it is easy to make the refracting surface aspherical, and the manufacturing cost does not increase.

The conditional expression of claim 7 relates to the interval between the annular zones of the diffraction structure, that is, the interval between the annular zones in the direction perpendicular to the optical axis. Second-order optical path difference function coefficient (also referred to as diffraction surface coefficient)
(Ph / Pf) −2 = 0, but in the present invention, in order to better correct the difference in spherical aberration caused by the difference in the thickness of the transparent substrate than the effect of diffraction, the optical path difference function It is preferable to use a higher-order optical path difference function coefficient. At this time, it is preferable that (Ph / Pf) -2 take a value that is somewhat apart from 0. Since the effect of diffraction for correcting high-order spherical aberration above the lower limit in the conditional expression becomes stronger, the thickness of the transparent substrate thickness is reduced. The difference in spherical aberration between the two wavelengths caused by the difference can be satisfactorily corrected. Below the upper limit in the conditional expression, the annular zone interval of the diffractive structure does not become too small, and it is easy to manufacture a diffractive lens with high diffraction efficiency.

Conditional expression (2) of claim 8 is for making the refractive power distribution of the first lens and the second lens appropriate.
If the upper limit of conditional expression (2) is not exceeded, the third surface,
That is, the radius of curvature of the surface of the second lens on the light source side does not become too small, the aberration deterioration due to the optical axis shift between the first lens and the second lens can be suppressed small, and the lower limit of conditional expression (2) is not exceeded. Accordingly, image height characteristics such as coma aberration and astigmatism can be favorably corrected. If the upper limit of conditional expression (3) is not exceeded, the degree of meniscus of the first lens will not be too large, and
Aberration deterioration due to axis deviation between the first surface and the second surface of the lens does not become too large. If the lower limit is not exceeded, correction of spherical aberration will not be insufficient.

When the conditional expressions (4) to (9) are satisfied, it is possible to record / reproduce data on both an optical information recording medium such as a DVD and a higher density optical information recording medium. The thickness of the transparent substrate of the optical information recording medium is 0.6 mm.
In the following cases, the effect of correcting the spherical aberration by the transparent substrate is reduced. However, since the objective lens has two lenses, the spherical aberration can be sufficiently corrected, and the NA of the objective lens is 0.65.
Even with the above, coma aberration due to slight inclination or warpage of the optical information recording medium is small, and good light-collecting performance can be obtained.

When the material has an internal transmittance of 85% or more with respect to the thickness of 3 mm of the material in the wavelength range to be used, a sufficient light intensity for recording can be obtained, and a material for reproduction can be obtained. Even when the light passes back and forth through the objective lens during reading, a sufficient amount of light incident on the sensor can be obtained, and the S / N ratio of the reading signal can be improved. Also, 50
Degradation of the lens material due to absorption is not negligible at 0 nm or less, especially around 400 nm. However, if the objective lens is made of a material satisfying the above conditions, the effect of the degradation is small and semi-permanent use is possible.

When the material is selected as in the eleventh aspect, a refractive index distribution due to a difference in water absorption in the lens during the process of absorbing moisture in the air by each lens is less likely to occur, thereby reducing aberrations. . In particular, when the NA is large, the occurrence of aberration tends to be large. However, the above-described configuration can sufficiently reduce the aberration.

As described above, according to the first to eleventh aspects, a good objective lens can be obtained by applying to recording / reproducing for a plurality of types of optical information recording media, but using a light source having a large NA and a shorter wavelength. When trying to increase the recording density, the effects of various errors, especially fluctuations in spherical aberration, cannot be ignored. Therefore, if a spherical aberration correcting means for correcting a variation in spherical aberration is provided between the light source and the objective lens, a good light-collecting characteristic can be maintained even if there are various errors, and a plurality of types of spherical aberration correcting means can be maintained. It is possible to obtain a good light condensing optical system for recording / reproducing on the optical information recording medium.

If spherical aberration correcting means for correcting a spherical aberration variation caused by an objective lens, especially an objective lens made of a plastic lens, etc. due to a change in temperature / humidity according to the thirteenth aspect is provided, an environmental change is prevented. Also, a light-converging optical system having a good light-converging spot can be obtained.

When the spherical aberration correcting means for correcting the fluctuation of the spherical aberration caused by the fluctuation of the thickness of the transparent substrate of the optical information recording medium is provided, even if the optical information recording medium has a manufacturing error, etc. A condensing optical system with a good light spot can be obtained.

If the spherical aberration correcting means for correcting the fluctuation of the spherical aberration caused by the difference in the oscillation wavelength of the light source is provided, the light-converging optical system can provide a good light-condensing spot even if there is an error in the light source device. Can be obtained.

A spherical surface for correcting a change in spherical aberration caused by a combination of at least two of a change in temperature / humidity, a change in the thickness of the transparent substrate of the optical information recording medium, and a change in the oscillation wavelength of the light source. By providing the aberration correcting means, it is possible to always obtain a condensing optical system having good condensing characteristics. When such spherical aberration correction means is provided, the required accuracy of the objective lens, the light source, the optical information recording medium, and the like does not become too strict, and a condensing optical system with good performance can be obtained.

According to the seventeenth aspect, the spherical aberration correcting means changes the light beam incident on the objective lens from infinite light to finite light or vice versa depending on the type of the optical information recording medium. The divergence angle can be changed.

When the fluctuation of the spherical aberration is corrected by a device for generating a distribution of the refractive index by applying a voltage, for example, as in the eighteenth aspect, the light condensing has a mechanically simple structure without a movable part. An optical system can be obtained.

According to a nineteenth aspect, the spherical aberration correcting means is constituted by a beam expander including at least one positive lens and at least one negative lens.
If the two lenses can be displaced along the optical axis direction, the divergence of the light beam incident on the objective lens can be changed, and the spherical aberration can be changed. In addition, by including a positive lens and a negative lens, it becomes easier to correct chromatic aberration, and if the lens position is fixed, the divergence due to wavelength fluctuation, that is, the fluctuation of spherical aberration is suppressed, and the wavelength fluctuation that occurs instantaneously such as mode hop Therefore, even if the spherical aberration correcting means cannot follow, it is possible to obtain a condensing optical system having a good condensing spot.

When the Abbe numbers of the positive lens and the negative lens are selected so as to satisfy the conditional expression (10) of claim 20, it is possible to obtain a condensing optical system having spherical aberration correcting means in which chromatic aberration is corrected well. it can.

By satisfying conditional expressions (11) and (12) of claim 21, it is possible to obtain a converging optical system having spherical aberration correcting means in which chromatic aberration is more preferably corrected.

It is more preferable to select the difference between the Abbe numbers of the positive lens and the negative lens so as to satisfy the conditional expression (13). If the lower limit of conditional expression (13) is not exceeded, correction of chromatic aberration becomes easy, chromatic aberration can be corrected without excessively increasing the refractive power of the positive lens and the negative lens, and deterioration of image height characteristics such as coma aberration is reduced. A small light collecting optical system can be obtained. If the upper limit of conditional expression (13) is not exceeded, the material is easily available and does not become a material having problems in internal transmittance and workability. Further, when the material of the movable element is formed of a material having a specific gravity of 2.0 or less, the light is sufficiently lightweight, and the light-collecting device has a spherical aberration correcting means which can easily follow even when the variation of the spherical aberration occurs at high speed. An optical system can be obtained.

If the positive lens is made of a material having an Abbe number of 70 or less, a material excellent in acid resistance and weather resistance can be selected, and if the negative lens is made of a material having an Abbe number of 40 or more. A material having an excellent internal transmittance, particularly a transmittance at a short wavelength, can be selected, and chromatic aberration can be sufficiently corrected by providing an annular diffraction structure. Further, diffracted light of the same order due to at least two light beams of different wavelengths is applied to the diffractive structure by at least two light beams having different thicknesses of the transparent substrate.
By imparting wavelength characteristics to each type of optical information recording medium so as to form a good wavefront, recording and / or reproduction on a plurality of types of optical information recording media having different thicknesses of the transparent substrate can be performed. .

The movable element has a specific gravity of 2.
If it is formed of a material of 0 or less, the movable element is sufficiently lightweight,
It is possible to obtain a condensing optical system having a spherical aberration correction unit that can easily follow even when the fluctuation of the spherical aberration occurs at a high speed.

When each lens is made of a plastic material as described in claim 25, mass production can be further achieved by injection molding or the like, and inexpensive spherical aberration correction means can be obtained.

According to the twenty-sixth aspect, it is difficult for a refractive index distribution due to a difference in water absorption rate to occur in the lens during the process of absorbing moisture in the air by each lens, and the diffraction efficiency caused by aberration and phase change caused by the difference. Can be suppressed. In particular, when the NA is large, the occurrence of aberrations and the reduction in diffraction efficiency tend to be large, but the above can sufficiently reduce them.

When the material has an internal transmittance of 85% or more with respect to the thickness of 3 mm of the material within the wavelength range used, sufficient light intensity for recording can be obtained, and the material for reproduction can be obtained. A sufficient amount of light can be obtained even when the light passes through the spherical aberration correcting means in a reciprocating manner and enters the sensor at the time of reading, and the S / N ratio of the read signal can be improved. When the wavelength is 500 nm or less, especially about 400 nm, the deterioration of the lens material due to absorption cannot be ignored. However, if a spherical aberration correction unit using a material that satisfies the above conditions is used, the influence of the deterioration is small, and the lens is permanently used. It becomes possible.

The spherical aberration correcting means having the structure as described in claim 28 is a simple and inexpensive spherical aberration correcting means with good performance.

When the spherical aberration fluctuates in the over (correction excessive) direction in the condensing optical system as described in claim 29, the distance between the positive and negative lenses is reduced, that is, the light flux incident on the objective lens is reduced. When the divergence is increased, spherical aberration in the under lens (undercorrection) direction occurs in the objective lens, and the spherical aberration is corrected as a whole. Conversely, when the spherical aberration in the condensing optical system fluctuates in the direction of under (undercorrection), the interval between the positive and negative lenses is increased, that is, the divergence of the light beam incident on the objective lens decreases. By doing so, over (correction excessive) spherical aberration occurs in the objective lens, so that the spherical aberration in the entire system is corrected.

In the case where the objective lens is corrected so that the aberration becomes better with respect to the transparent substrate having the thickness t1, the thickness t2
When recording and / or reproducing information on or from an optical information recording medium having a transparent substrate, spherical aberration occurs in the transparent substrate in the over direction. At this time, if the distance between the positive and negative lenses is reduced as in claim 30, that is, if the divergence of the light beam incident on the objective lens is increased, spherical aberration in the under direction occurs in the objective lens. , The spherical aberration is corrected as a whole.
Further, when the objective lens is corrected so that the aberration becomes better with respect to the transparent substrate having the thickness t2, recording and / or reproducing information on and from the optical information recording medium having the transparent substrate having the thickness t1. When performing the above, spherical aberration in the under direction occurs in the transparent substrate, so if the interval between the positive and negative lenses is increased, that is, if the divergence of the light beam incident on the objective lens is reduced, the A spherical aberration occurs in the direction, and the spherical aberration is corrected as a whole.

According to the thirty-first aspect, a coupling lens as a movable element is disposed as a spherical aberration correcting means between the light source and the objective lens so as to be displaceable in the optical axis direction. Variations in spherical aberration occurring on the optical surface can be corrected by displacing the coupling lens, and the coupling lens changes the light beam incident on the objective lens from infinite light to finite light according to the type of optical information recording medium. The divergence angle can be changed to change or conversely change from finite light to infinite light.

According to the thirty-second aspect, the coupling lens makes it possible to correct axial chromatic aberration on the annular diffractive surface and provide a spherical aberration correcting means having a simple configuration. Further, the diffractive structure has wavelength characteristics such that diffracted lights of the same order by light beams of at least two different wavelengths form good wavefronts on at least two types of optical information recording media having different thicknesses of the transparent substrate. By having the transparent substrate, recording and / or reproduction on a plurality of types of optical information recording media having different thicknesses of the transparent substrate can be performed.

As described in claim 33, by forming at least one surface as an aspheric surface having a radius of curvature that increases as the distance from the optical axis increases, spherical aberration can be satisfactorily corrected even with a single coupling lens. Chromatic aberration can be excessively corrected by using one surface as an annular diffraction surface.

When the surface of the coupling lens farther from the light source is an aspheric surface whose radius of curvature increases as the distance from the optical axis increases, coma as well as spherical aberration can be satisfactorily corrected. If the surface on the light source side is a macroscopically spherical diffractive surface, chromatic aberration can be overcorrected as described above with a simple configuration.

As described in the thirty-fifth aspect, it is possible to obtain a spherical aberration correcting means in which the chromatic aberration is moderately excessively corrected even when the coupling lens is a cemented lens having one group and two lenses.

Since at least one surface is made aspherical as in claim 36, the spherical aberration can be corrected, so that it is not necessary to expect the effect of correcting the spherical aberration by the cemented surface, and the correction of chromatic aberration can be made preferable. it can. By satisfying conditional expressions (14) and (15), it is possible to obtain a spherical aberration correcting means having better performance.

If the coupling lens is made of a material having a specific gravity of 2.0 or less, the spherical aberration correcting means can be made sufficiently light, and even if the spherical aberration varies at high speed. A converging optical system having spherical aberration correction means that can be easily followed can be obtained.

When the coupling lens is made of a plastic material as described in claim 38, mass production is possible by injection molding or the like, and inexpensive spherical aberration correction means can be obtained.

According to the thirty-ninth aspect, in the process of absorbing moisture in the air, the coupling lens hardly generates a refractive index distribution due to a difference in water absorption, and diffraction caused by aberration and phase change caused thereby. A decrease in efficiency can be suppressed. In particular, when the NA is large, the occurrence of aberrations and the reduction in diffraction efficiency tend to be large, but the above can sufficiently reduce them.

When the coupling lens is made of a material having an internal transmittance of 85% or more with respect to a thickness of 3 mm of the material in the wavelength range used, a sufficient light intensity for recording can be obtained. At the time of reading for reproduction, a sufficient amount of light can be obtained even when the light passes through the spherical aberration correction means in a reciprocating manner and enters the sensor, and the S / N ratio of the read signal can be improved. When the wavelength is 500 nm or less, especially about 400 nm, the deterioration of the lens material due to absorption cannot be ignored. However, if a spherical aberration correction unit using a material that satisfies the above conditions is used, the influence of the deterioration is small, and the lens is permanently used. It becomes possible.

When the spherical aberration fluctuates in the over direction in the condensing optical system, the coupling lens is shifted so as to widen the distance from the objective lens, that is, the divergence of the light beam incident on the objective lens is reduced. If it is made larger, spherical aberration in the under direction occurs in the objective lens, and the spherical aberration is corrected as a whole. Conversely, when the spherical aberration fluctuates in the direction of under in the condensing optical system, if the coupling lens is shifted to narrow the distance from the objective lens,
That is, if the degree of divergence of the light beam incident on the objective lens is reduced, excessive spherical aberration occurs in the objective lens, so that the spherical aberration in the entire system is corrected.

In the case where the objective lens is corrected so that the aberration becomes better with respect to the transparent substrate having the thickness t1, the thickness t2
When recording and / or reproducing information on or from an optical information recording medium having a transparent substrate, spherical aberration occurs in the transparent substrate in the over direction. At this time, if the coupling lens is shifted so as to widen the distance from the objective lens, that is, if the divergence of the light beam incident on the objective lens is increased, spherical aberration in the under direction of the objective lens is reduced. And spherical aberration is corrected as a whole. Further, when the aberration is corrected so that the aberration becomes better with respect to the transparent substrate having the thickness t2 of the objective lens t1, information is recorded and / or recorded on the optical information recording medium having the transparent substrate having the thickness t1. When reproduction is attempted, spherical aberration in the under direction occurs on the transparent substrate, so if the coupling lens is shifted to narrow the distance from the objective lens, that is, if the divergence of the light beam incident on the objective lens is reduced. Spherical aberration in the over direction occurs in the objective lens, and the spherical aberration is corrected as a whole.

When the conditional expressions (16) to (21) of claim 43 are satisfied, for example, a light-collecting device capable of recording / reproducing both optical information recording media such as DVDs and higher-density optical information recording media. An optical system can be obtained.

When the chromatic aberration is corrected so as to satisfy the conditional expression (22), it is possible to sufficiently prevent the spread of the spot size due to a minute wavelength variation of the light source even when the NA is 0.65 or more. .

When the optical pickup device is constructed as in claim 45, both the optical information recording medium having a small recording pit size and a large recording density and the optical information recording medium having a relatively large recording pit size and a relatively small recording density can be used. On the other hand, it is possible to obtain a high-performance and inexpensive optical pickup device in which recording and / or reproduction is favorably performed. In addition, an optical pickup device having the above-described characteristics can be obtained by selecting a focusing optical system.

[0124]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments and examples of the lens according to the present invention will be described. The aspherical surface of the lens according to the present embodiment is represented by the following equation (1) when the optical axis direction is X axis, the height in the direction perpendicular to the optical axis is h, and the radius of curvature of the refraction surface is r. Here, K is a cone coefficient, and A2i is an aspheric coefficient.

[0125]

(Equation 1) The diffractive surface of the lens according to the present embodiment can be represented by the following equation 2 as an optical path difference function Φb. Here, h is the height perpendicular to the optical axis, and b2i is the coefficient of the optical path difference function.

[0126]

(Equation 2)

Examples (Examples 1 to 5)

Table 1 shows the conditions for Examples 1, 2, 3, 4, and 5, and values relating to the above-mentioned conditional expressions. Tables 2, 3, 4, 5, and 6 show lens data. In each embodiment, an objective lens having a NA of 0.85 for a light beam having a wavelength of 405 nm and an NA of 0.65 for a light beam having a wavelength of 655 nm is obtained by combining two aspheric plastic lenses. As shown in Tables 2 to 6, the first to third surfaces are aspherical, and the first surface is a diffractive surface. Polyolefin resin is used as the plastic material, and the specific gravity is about 1.
0, the saturated water absorption is 0.01% or less, and as a result, the weight can be reduced to less than half of the weight of the objective lens in which two glass lenses are combined, and the NA is as large as 0.85. It could be about 0.02 g (excluding the mirror frame). In addition, the chromatic aberration of the objective lens can be satisfactorily corrected by using the first surface as a diffraction surface having an annular step.

[0128]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

FIG. 1 shows an optical path diagram when the NA is 0.85 in Example 1, and FIG. 3 shows a spherical aberration diagram, FIG. 4 shows an optical path diagram when the NA is 0.65, and FIG. 4 shows a spherical aberration diagram. FIG. 5 shows an optical path diagram when the NA is 0.85 in Example 2, and FIG. 7 shows a spherical aberration diagram, and FIG. 6 shows an optical path diagram when the NA is 0.65 in FIG. NA for Example 3
An optical path diagram for 0.85 is shown in FIG. 9, a spherical aberration diagram is shown in FIG. 11, an optical path diagram for NA 0.65 is shown in FIG. 10, and a spherical aberration diagram is shown in FIG. FIG. 13 shows an optical path diagram and a spherical aberration diagram of Example 4 when NA is 0.85.
FIG. 14 shows an optical path diagram in the case of 0.65, and FIG. 16 shows a spherical aberration diagram.
Shown in FIG. 17 shows an optical path diagram and a spherical aberration diagram of Example 5 in the case of NA 0.85.
FIG. 18 shows an optical path diagram for 65, and FIG. 20 shows a spherical aberration diagram. As can be seen from each example, NA 0.85 and NA
In both cases of 0.65, spherical aberration can be satisfactorily corrected.
A0.65, optical information recording medium (DVD etc.) having a relatively thick transparent substrate under the condition of wavelength 655 nm and NA 0.8
5. A good objective lens could be obtained for both a higher density optical information recording medium with a relatively thin transparent substrate under the condition of a wavelength of 405 nm.

(Examples 6 to 10)

As shown in Table 7, Examples 6, 7, and 8
A condensing optical system in which an objective lens composed of two aspheric plastic lenses having one, two, and three aspheric surfaces and one surface as a diffractive surface is combined with a beam expander as spherical aberration correction means, , Examples 9 and 10 were
An objective lens composed of two aspherical plastic lenses, one surface and three surfaces of which are aspherical surfaces and one surface of which is a diffractive surface, combined with a single lens or a coupling lens having two lenses per group as spherical aberration correcting means. It is an optical system. Example 6-
Tables 8, 9, 10, 11, and
12 respectively. Each of the spherical aberration correcting means of Examples 7, 8, and 9 is made of plastic, and is made of a polyolefin resin, and has a specific gravity of about 1.0 and a saturated water absorption of 0.01% or less. As can be seen from Table 7, the axial chromatic aberration in each condensing optical system satisfies the conditional expression (22).
Corrected well.

In the tables of Examples 1 to 10, the diffractive surface is represented by giving the phase function coefficient represented by the above-mentioned equation 2 ignoring the step, and the actual shape of the diffractive surface is The annular shape is manufactured such that the optical path difference due to the step between the annular zones becomes 1 or 2 times the wavelength.

[0133]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

FIG. 21 shows an optical path diagram and a spherical aberration diagram of Example 6 in the case of NA 0.85, and FIG.
The optical path diagram for the case of No. 5 is shown in FIG. 22, and the spherical aberration diagram is shown in FIG. FIG. 25 shows an optical path diagram when the NA is 0.85, and FIG. 27 shows a spherical aberration diagram for Example 7. FIG. 26 shows an optical path diagram when the NA is 0.65, and FIG. 28 shows a spherical aberration diagram. FIG. 29 shows an optical path diagram for Example 8 when the NA is 0.85, and FIG. 31 shows a spherical aberration diagram. FIG. 30 shows an optical path diagram for the NA 0.65 and FIG. 32 shows a spherical aberration diagram. FIG. 33 shows an optical path diagram for Example 9 when the NA is 0.85, and FIG. 35 shows a spherical aberration diagram. FIG. 34 shows an optical path diagram for the NA 0.65 and FIG. 36 shows a spherical aberration diagram. Further, in Example 10, N
FIG. 37 shows an optical path diagram for A0.85, and FIG. 3 shows a spherical aberration diagram.
9 and FIG. 38 shows an optical path diagram in the case of NA 0.65, and FIG. 40 shows a spherical aberration diagram. As can be seen from each embodiment, N
In both cases of A0.85 and NA0.65, spherical aberration can be corrected well, and an optical information recording medium (DVD) having a relatively thick transparent substrate under the conditions of NA0.65 and wavelength 655 nm
Etc.), a good condensing optical system for both higher density optical information recording media having a relatively thin transparent substrate thickness under the conditions of NA of 0.85 and wavelength of 405 nm.

Further, in Examples 6, 7 and 8, the distance between the positive lens and the negative lens of the beam expander is made variable to correct the variation of the spherical aberration. By varying the distance from the lens, the fluctuation of spherical aberration is corrected. Tables 13, 14, 15, 16 and 17 show the results of correcting the fluctuation of the spherical aberration generated in the optical system due to various causes in each of Examples 6 to 10 as described above. As can be seen from the tables, the converging optical system of the present embodiment can satisfactorily correct the spherical aberration generated due to the wavelength fluctuation of the laser light source (LD), the temperature change, and the thickness error of the transparent substrate. .

[0136]

[Table 13]

[Table 14]

[Table 15]

[Table 16]

[Table 17]

Next, an optical pickup device according to an embodiment of the present invention will be described with reference to FIG.

In the optical pickup device shown in FIG. 41, the plastic lens 3a, 3b according to the present invention
(c) a first light source for a relatively low-density first optical disc 23 having a thick transparent substrate and a relatively large wavelength, and a first semiconductor having a relatively large wavelength; A laser 11 and a second, relatively thin, transparent substrate
A second semiconductor laser 12 having a relatively small wavelength, which is a second light source for the optical disk 24, and diverging the light flux from the first light source 11 or the second light source 12 toward the objective lens 3 and A beam expander 1 including a positive lens 4 and a negative lens 5 that change the divergence angle, a first photodetector 41 that receives light reflected from the first optical disc 23,
A second photodetector that receives reflected light from the second optical disc that enters the light receiving element via the hologram; The objective lens 3 forms a spot on the information recording surface of the first or second optical disc 23 or 24 as an optical information recording medium and condenses the light beam from the beam expander 1 for recording or reproduction.

The optical pickup device shown in FIG. 41 further comprises a stop 8 provided in front of the objective lens 3 and a second optical disc 2
A beam splitter 62 that separates the reflected light from the fourth light beam toward the second photodetector 42;
A quarter-wave plate 72 and a focusing lens 22 disposed between the photodetector 42 and the beam splitter 61 for separating reflected light from the first optical disc 23 toward the first photodetector 41. A lens 9, 16 disposed between the beam splitter 61 and the second photodetector 41, a quarter-wave plate 71 and a collimator lens 21 disposed between the beam splitters 61 and 62, A lens 15 disposed between the first light source 11 and the beam splitter 61;
A biaxial actuator 6 for driving the objective lens 3 for focus tracking as a first driving device, and a beam expander 1 for correcting spherical aberration of the condensing optical system
And a uniaxial actuator 7 as a second driving device for moving the negative lens 5 in the optical axis direction. That is, in the present embodiment, the condensing optical system has a beam expander, a beam splitter, an objective lens, and a stop. In the present embodiment, the beam splitter may be regarded as not being included in the condensing optical system.

As described above, according to the optical pickup device of the present embodiment, the light beam from the first light source 11 is passed through the beam expander 1 by the objective lens 3 to the first optical disk 23 having a relatively low density. And the reflected light modulated thereby is reflected by the first photodetector 4 in the reverse path.
By receiving light at 1, reproduction can be performed. Further, the light beam from the second light source 11 is transmitted to the beam expander 1.
Is focused on the information pits of the second optical disc 24 having a relatively high density by the objective lens 3 through the optical disc, and the reflected light modulated thereby is received by the second photodetector 42 through the reverse path, Playback can be performed. Similarly, the first
Alternatively, recording can be performed on the second optical disk.

At the time of the above-mentioned recording or reproduction, the divergence angle of the light beam is changed by moving the negative lens 4 of the beam expander 1 in the optical axis direction by the uniaxial actuator 7 to change the distance from the positive lens 5. However, spherical aberration can be corrected. As described above, it is possible to perform good recording or reproduction on a plurality of types of optical disks having different transparent substrate thicknesses and different recording densities while canceling fluctuations in spherical aberration caused by various causes in the condensing optical system.

Next, an optical pickup device according to another embodiment will be described with reference to FIG. When reproducing the first optical disk having a relatively thick and transparent substrate and a relatively low density with the optical pickup device shown in FIG. The unit 410 is unitized with the first photodetector 301 and the hologram 231, and the light beam emitted from the first semiconductor laser 111 passes through the hologram 231, and the beam splitter 190 and the collimator 130 are light combining means.
And becomes a parallel light flux. The first optical disc 200 is further stopped down by the stop 170 and is stopped by the objective lens 160.
Is focused on the information recording surface 210 via the transparent substrate. The objective lens 160 includes the above-described plastic lens 161,
This is a two-group, two-sheet configuration in which 162 is integrally held by a holding member 163.

The light flux modulated and reflected by the information pits on the information recording surface 210 is again reflected by the objective lens 160 and the diaphragm 1.
70, the collimator 130, the beam splitter 1
90, the light is diffracted by the hologram 231 and is incident on the first photodetector 301. Using the output signal, a read signal of information recorded on the first optical disk is obtained.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 302, focus detection and track detection are performed, and a two-dimensional actuator 150 is used for focusing and tracking. Lens 160
To move.

Next, when reproducing a second optical disk having a thin transparent substrate and a relatively high density, a second semiconductor laser 112 (second light source) having a relatively short oscillation wavelength is provided by a laser / detector integrated unit. The light beam emitted from the second semiconductor laser 112 passes through the hologram 232, is reflected by the beam splitter 190 as a light combining means, and passes through the collimator 130. Into a parallel light flux. Further, the light is focused on the information recording surface 220 via the transparent substrate of the second optical disc 200 via the stop 170 and the objective lens 160.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, transmitted through the collimator 130 through the aperture 170,
The hologram 232 is reflected by the beam splitter 190,
The light is diffracted by the light source and is incident on the second photodetector 302, and a read signal of information recorded on the second optical disc is obtained using the output signal.

Also, a change in the light amount due to a change in the shape or position of the spot on the photodetector 302 is detected to detect focusing and track detection. The objective lens 160 is moved for tracking.

Further, in the present embodiment, the photodetector 30
Information recording surface 220 or 2 on 1 or 302
The state of the spot converged on the optical system 10 is detected, and based on this detection, the collimator 130 is moved by the uniaxial actuator 151 along the optical axis direction, whereby the spherical aberration generated on each optical surface of the condensing optical system is obtained. Is corrected favorably. Further, the collimator 130 movable along the optical axis direction changes the divergence of the light beam incident on the objective lens 160 according to the thickness of the transparent substrate of the optical disk.

As described above, according to the optical pickup device shown in FIG. 42, fluctuations in spherical aberration caused by various causes in the condensing optical system for a plurality of types of optical disks having different transparent substrate thicknesses and different recording densities are canceled. Recording or reproduction can be performed favorably.

In the above tables and figures, E (or e) is used to express a power of 10, for example, E-02
(= 10 ⁻² ) in some cases.

[0151]

As described above, according to the first to eleventh aspects of the present invention, it is possible to cope with a plurality of types of optical information recording media having different numerical apertures (NA) of the objective lens and different thicknesses of the transparent substrate. It is possible to provide an inexpensive and lightweight objective lens which is a high-performance and high-performance objective lens, similar to a conventional plastic single lens.

Further, according to the inventions described in claims 12 to 45, the laser light source is compatible so that recording and reproduction can be performed on a plurality of types of optical information recording media having different transparent substrate thicknesses. Effect of simple configuration on fluctuations of spherical aberration generated on each optical surface of condensing optical system and optical pickup device due to oscillation wavelength change, temperature / humidity change, error of transparent substrate thickness of optical information recording medium, etc. It is possible to provide a condensing optical system and an optical pickup device that can be corrected. In addition, it has compatibility so that recording and reproduction can be performed on multiple types of optical information recording media with different thicknesses of the transparent substrate, and the axis generated by the objective lens due to the mode hop phenomenon of the laser light source and high frequency superposition. The upper chromatic aberration can be effectively corrected.

[Brief description of the drawings]

FIG. 1 is an optical path diagram (NA 0.85) according to a first embodiment.

FIG. 2 is an optical path diagram (NA 0.65) according to the first embodiment.

FIG. 3 is a spherical aberration diagram (NA 0.85) related to Example 1.
It is.

FIG. 4 is a spherical aberration diagram (NA 0.65) related to Example 1.
It is.

FIG. 5 is an optical path diagram (NA 0.85) according to the second embodiment.

FIG. 6 is an optical path diagram (NA 0.65) according to the second embodiment.

FIG. 7 is a spherical aberration diagram (NA 0.85) related to Example 2.
It is.

FIG. 8 is a spherical aberration diagram (NA 0.65) related to Example 2.
It is.

FIG. 9 is an optical path diagram (NA 0.85) according to the third embodiment.

FIG. 10 is an optical path diagram (NA 0.65) according to the third embodiment.

FIG. 11 is a spherical aberration diagram (NA 0.8) of the third embodiment.
5).

FIG. 12 is a spherical aberration diagram (NA 0.6) of the third embodiment.
5).

FIG. 13 is an optical path diagram (NA 0.85) relating to Example 4.

FIG. 14 is an optical path diagram (NA 0.65) relating to Example 4.

FIG. 15 is a spherical aberration diagram (NA 0.8) of Example 4.
5).

FIG. 16 is a spherical aberration diagram (NA 0.6) of Example 4.
5).

FIG. 17 is an optical path diagram (NA 0.85) relating to Example 5.

FIG. 18 is an optical path diagram (NA 0.65) relating to Example 5.

FIG. 19 is a diagram showing spherical aberration (NA 0.8) according to Example 5.
5).

FIG. 20 is a spherical aberration diagram (NA 0.6) of Example 5.
5).

FIG. 21 is an optical path diagram (NA 0.85) relating to Example 6.

FIG. 22 is an optical path diagram (NA 0.65) relating to Example 6.

FIG. 23 is a spherical aberration diagram (NA 0.8) of Example 6.
5).

FIG. 24 is a spherical aberration diagram (NA 0.6) of Example 6.
5).

FIG. 25 is an optical path diagram (NA 0.85) relating to Example 7.

FIG. 26 is an optical path diagram (NA 0.65) relating to Example 7.

FIG. 27 is a spherical aberration diagram (NA 0.8) of the seventh embodiment.
5).

FIG. 28 is a spherical aberration diagram (NA 0.6) of the seventh embodiment.
5).

FIG. 29 is an optical path diagram (NA 0.85) relating to Example 8.

FIG. 30 is an optical path diagram (NA 0.65) relating to Example 8.

FIG. 31 is a spherical aberration diagram (NA 0.8) of Example 8.
5).

FIG. 32 is a spherical aberration diagram (NA 0.6) of Example 8.
5).

FIG. 33 is an optical path diagram (NA 0.85) relating to Example 9;

FIG. 34 is an optical path diagram (NA 0.65) according to Example 9;

FIG. 35 is a spherical aberration diagram (NA 0.8) of the ninth embodiment.
5).

FIG. 36 is a spherical aberration diagram (NA 0.6) of Example 9;
5).

FIG. 37 is an optical path diagram relating to Example 10 (NA 0.85);
It is.

FIG. 38 is an optical path diagram (NA 0.65) relating to Example 10;
It is.

FIG. 39 is a diagram showing the spherical aberration of the tenth embodiment (NA 0.8);
5).

FIG. 40 is a spherical aberration diagram (NA 0.6) of Example 10.
5).

FIG. 41 is a drawing schematically showing an optical pickup device according to the present embodiment.

FIG. 42 is a drawing schematically showing an optical pickup device according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Beam expander 4 Negative lens 5 Positive lens 3,160 Objective lens 6,150 Biaxial actuator 7,151 Uniaxial actuator 8 Aperture 11,111 First light source 12,112 Second light source 23 First optical disk 24 First 2 optical disks 41,301 first detector 42,302 second detector 130 collimator 200 first and second optical disks 210 information recording surface of first optical disk 220 information recording surface of second optical disk

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 9/04 G02B 9/04 13/00 13/00 13/18 13/18 G11B 7/09 G11B 7 / 09 BF term (reference) 2G065 AB04 AB09 BA01 BB06 BB14 BB17 CA21 DA20 2H049 AA04 AA18 AA43 AA57 AA68 2H087 KA13 LA01 LA27 NA01 NA08 PA01 PA02 PA17 PA18 PB01 PB02 QA02 QA07 QA12 QA21 QA14 QA14 QA14 QA12 UA01 UA09 5D118 AA26 BA01 CA05 DC04 DC05 5D119 AA17 AA41 BA01 CA16 EC01 EC03 FA08 JA02 JA06 JA09 JA44 JA47 JA49 JB01 JB02 JB04 JB06 JC05

Claims (45)

[Claims] 1. A condensing optical system including an objective lens for condensing light beams from light sources having different wavelengths on a recording surface of an optical information recording medium, and a light receiving means for detecting reflected light from the recording surface. An objective lens used in an information recording / reproducing optical pickup device capable of recording and / or reproducing information on a plurality of optical information recording media having different thicknesses of transparent substrates; A first lens having a positive refracting power and a second lens having a positive refracting power arranged in order, wherein the first lens and the second lens are each formed of a material having a specific gravity of 2.0 or less, and have at least one surface. Among the plurality of optical information recording media having different transparent substrate thicknesses, the transparent substrate thicknesses of any two optical information recording media are t1, t2 (t1 <t2). ) And said transparent substrate The wavelength at the time of recording or reproducing information on the optical information recording medium having the thickness t1 is set to λ1, and the recording or reproduction of information is performed on the optical information recording medium having the thickness t2 of the transparent substrate. The wavelength at this time is λ2 (λ1 <λ
2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a thickness of the transparent substrate is determined by a light beam of wavelength λ2. Assuming that a predetermined image-side numerical aperture necessary for performing recording or reproduction on the optical information recording medium at t2 is NA2 (NA1 ≧ NA2), the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 For the combination, the wavefront aberration is 0.07λ1rm
s or less, and the wavefront aberration is 0.07λ2 rms or less for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2. 2. A condensing optical system including an objective lens for converging light beams from light sources having different wavelengths on a recording surface of an optical information recording medium, and a light receiving means for detecting reflected light from the recording surface. An objective lens used in an information recording / reproducing optical pickup device capable of recording and / or reproducing information on a plurality of optical information recording media having different thicknesses of transparent substrates; A first lens having a positive refractive power and a second lens having a positive refractive power, which are sequentially arranged, wherein the first lens and the second lens are each formed of a plastic material, and at least one surface has a ring-shaped diffraction structure. And wherein the transparent substrates of any two optical information recording media have thicknesses of t1 and t2 (t1 <t2) among the plurality of optical information recording media having different thicknesses of the transparent substrate; Thickness The wavelength at the time of recording or reproducing information on the optical information recording medium having t1 is λ1, and the wavelength at the time of recording or reproducing information on the optical information recording medium having the thickness t2 of the transparent substrate. To λ2 (λ1 <λ
2), a predetermined image-side numerical aperture required for performing recording or reproduction on an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is NA1, and a thickness of the transparent substrate is determined by a light beam of wavelength λ2. Assuming that a predetermined image-side numerical aperture necessary for performing recording or reproduction on the optical information recording medium at t2 is NA2 (NA1 ≧ NA2), the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 For the combination, the wavefront aberration is 0.07λ1rm
s or less, and the wavefront aberration is 0.07λ2 rms or less for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2. 3. The wavefront aberration of the combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2 is 0.07λ2 rms or less, and the wavelength λ2, the thickness t2 of the transparent substrate, and the image The objective lens according to claim 1, wherein the wavefront aberration is 0.07λ2 rms or more with respect to the combination with the side numerical aperture NA1. 4. A combination of an object point at a predetermined position, a wavelength λ1, a thickness t1 of a transparent substrate, and an image-side numerical aperture NA1.
An object point whose wavefront aberration is equal to or less than 0.07λ1 rms and at an optically equal distance to the predetermined position and a wavelength λ2
4. The objective lens according to claim 1, wherein the wavefront aberration is 0.07λ2 rms or less for a combination of the thickness t2 of the transparent substrate and the image-side numerical aperture NA2. 5. 5. A combination of an object point at a predetermined position, a wavelength λ1, a thickness t1 of a transparent substrate, and an image-side numerical aperture NA1.
The wavefront aberration is 0.07λ1 rms or less, and for a combination of the object point, the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2 at an optically unequal distance from the predetermined position, 4. The objective lens according to claim 1, wherein the wavefront aberration is 0.07λ2 rms or less. 6. At least two of the first to third surfaces.
The objective lens according to claim 1, wherein the two surfaces are aspherical. 7. The method according to claim 1, wherein the following expression is satisfied.
7. The objective lens according to any one of items 6 to 6. 0.4 ≦ | (Ph / Pf) −2 | ≦ 25, where Pf is a predetermined image-side numerical aperture NA required for recording or reproducing on or from an optical information recording medium having a thickness t1 of a transparent substrate.
Diffraction ring spacing at 1 Ph: Diffraction ring spacing at 1/2 numerical aperture of NA1 8. The method according to claim 1, wherein the following expression is satisfied.
8. The objective lens according to any one of items 7 to 7. 1.3 ≦ f1 / f2 ≦ 4.0 0.3 ≦ (r2 + r1) / (r2-r1) ≦ 3.2 where fi: focal length of the i-th lens (when the i-th lens has a diffractive structure, (Focal length of the entire ith lens system including the refractive lens and the diffractive structure) ri: paraxial radius of curvature of each surface (i = 1 and 2) 9. The method according to claim 1, wherein the following expression is satisfied.
9. The objective lens according to any one of items 8 to 8. t1 ≦ 0.6 mm t2 ≧ 0.6 mm λ1 ≦ 500 nm 600 nm ≦ λ2 ≦ 800 nm NA1 ≧ 0.65 NA2 ≦ 0.65 10. The objective lens according to claim 1, wherein the objective lens is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a used wavelength region. 11. The objective lens according to claim 1, wherein the objective lens is made of a material having a saturated water absorption of 0.5% or less. 12. A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, wherein the thicknesses of the transparent substrates are different. A recording and reproducing light collecting optical system capable of recording and / or reproducing information on and from a plurality of optical information recording media, wherein the objective lens is the objective lens according to any one of claims 1 to 11. Where λ1 and λ2 (λ1 <λ2) are arbitrary two wavelengths among the different wavelengths, and arbitrary two optical information among the plurality of optical information recording media having different transparent substrate thicknesses. The thickness of the transparent substrate of the recording medium is defined as t1 and t2 (t1 <t2), and a predetermined image-side opening necessary for performing recording or reproduction on the optical information recording medium having the thickness of the transparent substrate t1 with a light beam of wavelength λ1. The number is NA1 and the luminous flux of wavelength λ2 When a predetermined image-side numerical aperture necessary for recording or reproducing information on or from an optical information recording medium having a thickness t2 of a transparent substrate is NA2 (NA1 ≧ NA2), the wavelength λ1, the thickness t1 of the transparent substrate, and the image The wavefront aberration is 0.07λ1rm for the combination with the side numerical aperture NA1.
s or less, and for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2, the wavefront aberration is 0.1 mm.
07λ2 rms or less, and spherical aberration correcting means for correcting a variation in spherical aberration occurring on each optical surface of the light collecting optical system is provided between the light source and the objective lens. Focusing optics. 13. A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, wherein the thicknesses of the transparent substrates are different. A recording / reproducing condensing optical system capable of recording and / or reproducing information on and from a plurality of optical information recording media, wherein the objective lens is an objective according to any one of claims 1 to 11. A lens, wherein any two wavelengths among the different wavelengths are λ
1, λ2 (λ1 <λ2), and, among the plurality of optical information recording media having different transparent substrate thicknesses, the thicknesses of the transparent substrates of any two optical information recording media are t1, t2 (t1 <t2 ), A predetermined image-side numerical aperture required for recording or reproducing information on or from an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is defined as NA1, and a thickness t2 of the transparent substrate is determined with a light beam of wavelength λ2. When the predetermined image-side numerical aperture necessary for recording or reproducing on the optical information recording medium is NA2 (NA1 ≧ NA2), a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 , The wavefront aberration is 0.07λ1 rm
s or less, and for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture N2, the wavefront aberration is 0, 0
Spherical aberration correcting means which can collect light so as to be equal to or less than 7λ2 rms, and corrects a variation in spherical aberration generated on each optical surface of the condensing optical system between the light source and the objective lens due to a change in temperature and humidity. A condensing optical system comprising: 14. A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, wherein the thicknesses of the transparent substrates are different. A recording / reproducing condensing optical system capable of recording and / or reproducing information on and from a plurality of optical information recording media, wherein the objective lens is an objective according to any one of claims 1 to 11. A lens, wherein any two wavelengths among the different wavelengths are λ
1, λ2 (λ1 <λ2), and, among the plurality of optical information recording media having different transparent substrate thicknesses, the thicknesses of the transparent substrates of any two optical information recording media are t1, t2 (t1 <t2 ), A predetermined image-side numerical aperture required for recording or reproducing information on or from an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is defined as NA1, and a thickness t2 of the transparent substrate is determined with a light beam of wavelength λ2. When the predetermined image-side numerical aperture necessary for recording or reproducing on the optical information recording medium is NA2 (NA1 ≧ NA2), a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 , The wavefront aberration is 0.07λ1 rm
s or less, and for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2, the wavefront aberration is 0.1 mm.
07λ2 rms or less, and a spherical surface generated on each optical surface of the condensing optical system between the light source and the objective lens due to a slight change in the thickness of the transparent substrate of the optical information recording medium. A condensing optical system comprising a spherical aberration corrector for correcting a variation in aberration. 15. A light source having different wavelengths, and an objective lens for condensing a light beam emitted from the light source onto an information recording surface via a transparent substrate of an optical information recording medium, wherein the thicknesses of the transparent substrates are different. A recording / reproducing condensing optical system capable of recording and / or reproducing information on and from a plurality of optical information recording media, wherein the objective lens is an objective according to any one of claims 1 to 11. A lens, wherein any two wavelengths among the different wavelengths are λ
1, λ2 (λ1 <λ2), and, among the plurality of optical information recording media having different transparent substrate thicknesses, the thicknesses of the transparent substrates of any two optical information recording media are t1, t2 (t1 <t2 ), A predetermined image-side numerical aperture required for recording or reproducing information on or from an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is defined as NA1, and a thickness t2 of the transparent substrate is determined with a light beam of wavelength λ2. When the predetermined image-side numerical aperture necessary for recording or reproducing on the optical information recording medium is NA2 (NA1 ≧ NA2), a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 , The wavefront aberration is 0.07λ1 rm
s or less, and for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2, the wavefront aberration is 0.1 mm.
07λ2 rms or less, and corrects the fluctuation of the spherical aberration between the light source and the objective lens, which occurs on each optical surface of the condensing optical system due to the minute fluctuation of the oscillation wavelength of the light source. A converging optical system, comprising: 16. A light source having different wavelengths and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, wherein the thicknesses of the transparent substrates are different. 12. A recording / reproducing condensing optical system capable of recording and / or reproducing information with respect to a plurality of optical information recording media, wherein the objective lens is any one of claims 1 to 11. An objective lens, wherein any two wavelengths among the different wavelengths are λ
1, λ2 (λ1 <λ2), and, among the plurality of optical information recording media having different transparent substrate thicknesses, the thicknesses of the transparent substrates of any two optical information recording media are t1, t2 (t1 <t2 ), A predetermined image-side numerical aperture required for recording or reproducing information on or from an optical information recording medium having a thickness t1 of the transparent substrate with a light beam of wavelength λ1 is defined as NA1, and a thickness t2 of the transparent substrate is determined with a light beam of wavelength λ2. When the predetermined image-side numerical aperture necessary for recording or reproducing on the optical information recording medium is NA2 (NA1 ≧ NA2), a combination of the wavelength λ1, the thickness t1 of the transparent substrate, and the image-side numerical aperture NA1 , The wavefront aberration is 0.07λ1 rm
s or less, and for a combination of the wavelength λ2, the thickness t2 of the transparent substrate, and the image-side numerical aperture NA2, the wavefront aberration is 0.1 mm.
07λ2 rms or less, and between the light source and the objective lens, a change in temperature and humidity, a small change in the thickness of the transparent substrate of the optical information recording medium, and a small change in the oscillation wavelength of the light source. A condensing optical system, comprising: a spherical aberration correcting unit that corrects a variation in spherical aberration generated on each optical surface of the condensing optical system due to a combination of at least two or more. 17. The divergence of a light beam incident on the objective lens according to the thickness of each transparent substrate for each optical information recording medium having a different thickness of the transparent substrate. The condensing optical system according to any one of claims 12 to 16, wherein the angle is changed. 18. The condensing optical system according to claim 12, wherein said spherical aberration correcting means has a variable refractive index distribution. 19. The spherical aberration correcting means includes at least one positive lens and at least one negative lens, and has a configuration of a beam expander that outputs a light beam incident substantially parallel and emits the light beam substantially parallel. The collection according to any one of claims 12 to 17, wherein at least one of the positive lens and the negative lens is a movable element that is movable along an optical axis direction. Optical optics. 20. The condensing optical system according to claim 19, wherein the positive lens and the negative lens satisfy the following expression. νdP> νdN, where νdP: average value of the Abbe number of the d-line of the positive lens included in the spherical aberration correcting unit νdN: d of the negative lens included in the spherical aberration correcting unit
Average value of Abbe number of line 21. The condensing optical system according to claim 20, wherein the positive lens and the negative lens satisfy the following expression. νdP> 55.0 νdN <35.0 22. The difference between the average value of the Abbe number of the d-line of the positive lens included in the spherical aberration correcting unit and the average value of the Abbe number of the d-line of the negative lens included in the spherical aberration correcting unit. 22. The focusing optical system according to claim 21, wherein Δν satisfies the following conditional expression, and the movable element is formed of a material having a specific gravity of 2.0 or less. 30 ≦ △ ν ≦ 50 23. The Abbe number of all the positive lenses included in the spherical aberration correcting means is 70.0 or less, or the Abbe number of all the negative lenses included in the spherical aberration correcting means is 4
20. A diffractive surface having a diffraction area of at least 0.0 and having at least one annular diffractive structure.
3. The condensing optical system according to 1. 24. The movable element is made of a material having a specific gravity of 2.0 or less.
3. The condensing optical system according to 3. 25. The apparatus according to claim 22, wherein said spherical aberration correcting means is formed of a plastic material.
25. A condensing optical system according to 24. 26. The condensing optical system according to claim 25, wherein said spherical aberration correcting means is made of a material having a saturated water absorption of 0.5% or less. 27. The method according to claim 19, wherein the spherical aberration correcting hand is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a working wavelength region.
27. The condensing optical system according to any one of 26. 28. The spherical aberration correcting means comprises one positive lens and one negative lens, has at least one aspheric surface, and at least one of the positive lens and the negative lens is The condensing optical system according to any one of claims 19 to 27, wherein the condensing optical system is a movable element that can move along the optical axis direction. 29. The movable element reduces a distance between the positive lens and the negative lens when the spherical aberration of the optical system changes to an over side, and changes the spherical aberration of the optical system to an under side. 29. The light-converging optical system according to claim 28, wherein the optical system shifts along the optical axis so as to increase the distance between the positive lens and the negative lens. 30. When the thicknesses of the transparent substrates of any two optical information recording media are t1 and t2 (t1 <t2) among the plurality of optical information recording media having different transparent substrate thicknesses, The movable element increases the distance between the positive lens and the negative lens when recording or reproducing information on or from an optical information recording medium having a transparent substrate having a thickness of t1, and the transparent substrate has a thickness of t2. 30. When recording or reproducing information on or from the optical information recording medium, the optical information recording medium is shifted along the optical axis direction so as to reduce the distance between the positive lens and the negative lens. 3. The condensing optical system according to 1. 31. The spherical aberration correction means is a coupling lens that changes a divergence angle of divergent light emitted from the light source, and the coupling lens is a movable element that can move along an optical axis direction. The condensing optical system according to any one of claims 12 to 17, wherein: 32. The condensing optical system according to claim 31, wherein said spherical aberration correcting means is a single lens having at least one surface as a diffraction surface having a ring-shaped diffraction structure. 33. The spherical aberration correcting means, wherein at least one surface is an aspheric surface having a radius of curvature that increases with distance from the optical axis, and at least one surface is a diffraction surface having a ring-like diffraction structure. 33. The condensing optical system according to claim 32, wherein: 34. The spherical aberration correction means includes an aspheric surface whose surface on the light source side is a spherical diffraction surface when viewed macroscopically, and whose radius of curvature increases as the surface farther from the light source moves away from the optical axis. 34. The condensing optical system according to claim 33, wherein: 35. The spherical aberration correcting means has a two-group configuration in which a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are cemented. 31. The condensing optical system according to 31. 36. The condensing optical system according to claim 35, wherein the positive lens and the negative lens satisfy the following expression and have at least one aspheric surface. νdP> 55.0 νdN <35.0 where νdP: Abbe number of the d-line of the positive lens νdN: Abbe number of the d-line of the negative lens 37. The spherical aberration correcting means having a specific gravity of 2.0
32. A material made of the following material:
37. The condensing optical system according to any one of -36. 38. The condensing optical system according to claim 37, wherein said spherical aberration correcting means is formed from a plastic material. 39. The condensing optical system according to claim 38, wherein said spherical aberration correcting means is made of a material having a saturated water absorption of 0.5% or less. 40. A method according to claim 31, wherein said spherical aberration correcting means is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a wavelength region to be used.
40. The condensing optical system according to any one of the items 39. 41. The spherical aberration correction means increases the distance between the objective lens and the spherical aberration of the converging optical system when the spherical aberration of the converging optical system fluctuates to the over side, and fluctuates the spherical aberration of the converging optical system to the under side. The focusing optical system according to any one of claims 31 to 40, wherein when performing, the displacement is made along the optical axis direction so as to reduce the distance from the objective lens. 42. When the thicknesses of the transparent substrates of any two optical information recording media are t1 and t2 (t1 <t2) among the plurality of optical information recording media having different transparent substrate thicknesses, When recording or reproducing information on or from an optical information recording medium having a transparent substrate having a thickness of t1, the movable element reduces the distance between the objective lens and the transparent substrate and has a thickness of t2.
32. When recording or reproducing information on or from the optical information recording medium, the optical information recording medium is shifted along the optical axis direction so as to increase the distance from the objective lens.
42. The condensing optical system according to any one of items 41 to 41. 43. The condensing optical system according to claim 12, wherein the following expression is satisfied. t1 ≦ 0.6 mm t2 ≧ 0.6 mm λ1 ≦ 500 nm 600 nm ≦ λ2 ≦ 800 nm NA1 ≧ 0.65 NA2 ≦ 0.65 44. A condensing optical system according to claim 12, wherein an axial chromatic aberration of a combined system of said spherical aberration correcting means and said objective lens satisfies the following expression. . | ΔfBi · NAi ² | ≦ 0.25 μm (i = 1 and 2) where δfBi: change in the focal position of the combining system when the wavelength λi of the light source changes by +1 nm (μm) 45. Light sources having different wavelengths, an objective lens for condensing a light beam from the light source on a recording surface of an optical information recording medium, and spherical aberration correction disposed between the light source and the objective lens. Condensing optical system including means, light-receiving means for detecting reflected light from the recording surface, and driving the objective lens to condense the light on the recording surface by detecting the reflected light. 1 drive device, and a second drive device that detects the light-collected state of the light flux condensed on the recording surface by detecting the reflected light, and operates the spherical aberration correction unit. An optical pickup device for information recording and reproduction capable of recording and / or reproducing information on a plurality of optical information recording media having different thicknesses of a transparent substrate, wherein the light-collecting optical system is configured as described above. The light-collecting optical system according to any one of the preceding claims. Optical pickup device, characterized in that.