JP2003084196A - Objective lens, optical pickup device and recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high NA objective lens, wherein a lens is constituted of three lens groups, and the curvature of the lens surface is mitigated by dispersing the power of the lens surface with reference to a high NA luminous flux, the eccentricity allowance between the lens groups, a viewing angle allowance and an operating distance are satisfactorily secured and to provide an optical pickup device and a recording/ reproducing device. SOLUTION: The objective lens is used for recording/reproducing optical information on/from an optical information recording medium, and the lens is constituted of three groups of a first lens group, a second lens group and a third lens group arranged in order from a light source side, and the numerical aperture NA on the optical information recording medium side satisfies 0.60<NA<0.99. Besides, the lens is constituted of three groups of the first lens group having a positive refractive power, the second lens group having a positive refractive power and the third lens group having a positive refractive power. Alternatively, the lens is constituted of three groups of the first lens group having a negative refractive power, the second lens group having the positive refractive power and the third lens group having the positive refractive power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens for recording and / or reproducing an optical information recording medium, an optical pickup device including the objective lens, and a recording / reproducing device.

[0002]

2. Description of the Related Art Recently, a new high-density recording using a light source such as a blue-violet semiconductor laser or a blue-violet SHG laser having an oscillation wavelength of about 400 nm and a two-group objective lens whose numerical aperture is increased to about 0.85. Research and development of optical pickup systems are in progress. The recording density of an optical recording medium such as an optical disk or a magneto-optical disk is determined by the area (= k · (λ / N) of the spot condensed on the information recording surface by the objective lens.
It is a well known fact that A) ² , where k is a proportional constant, λ is the wavelength of the light source, and NA is inversely proportional to the numerical aperture of the objective lens). In order to increase the density of the optical recording medium, there is a method of shortening the light source wavelength in addition to increasing the numerical aperture of the objective lens. However, in the wavelength region shorter than 350 nm, the light transmittance of the lens material sharply decreases. Therefore, there is a problem that practically sufficient light utilization efficiency cannot be obtained. Therefore, in the new high-density recording optical pickup system,
It is expected that a higher numerical aperture of the objective lens will be required for higher density.

The above-mentioned two-group objective lens is designed to increase the NA while dispersing the power of the lens and relaxing the curvature. However, when the NA is larger than 0.85, Since the curvature of the lens surface becomes tight and the prospective angle of the aspherical surface becomes large, it becomes difficult to process the mold used for lens molding. Further, the tolerance of decentering and the tolerance of the angle of view between the lens groups at the time of manufacturing the lens become small, and the production efficiency of the objective lens and the optical pickup device deteriorates. This tendency becomes more noticeable when an attempt is made to secure a sufficient working distance while maintaining a small diameter.

When the high NA objective lens or the single wavelength light source of about 400 nm is used, the axial chromatic aberration generated in the objective lens poses a problem. Laser light emitted from a semiconductor laser is generally considered to have a single wavelength (single mode), and it is considered that there is no axial chromatic aberration.
It may cause nm hopping or mode hopping. Mode hopping is a wavelength change that occurs instantaneously so that focusing of the objective lens cannot follow, so if the axial chromatic aberration of the objective lens is not corrected, a defocus component is added and the wavefront aberration is deteriorated. The deterioration of wavefront aberration during mode hopping becomes particularly large when an objective lens with a high NA or a short wavelength light source is used, as shown below. It is assumed that the spherical aberration does not fluctuate with the objective lens with respect to the wavelength fluctuation Δλ, but the back focus fb fluctuates by Δfb. The value Wrms is 0, but if focusing is not performed, Wrms becomes
It becomes like the following formula (1 '). Wrms = 0.145 · {(NA) ² / λ} / | Δfb | (1 ′)

For example, DVD (NA = 0.6, λ = 6
50 nm) and an optical disk with NA = 0.85 and λ = 400 nm, the wavefront aberration of the latter is degraded by 3.26 times even if Δfb is the same. That is, if the allowable values of the wavefront aberration are the same, the allowable value of | Δfb | becomes as small as 1 / 3.26, and the axial chromatic aberration of the wavefront condensed through the objective lens on the recording surface of the optical disc is Need to be small.

Further, in an objective lens for an optical pickup equipped with a light source having a wavelength shorter than 650 nm, it is necessary to correct chromatic aberration caused by poor monochromaticity of the light source. Therefore, it is conceivable that a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are arranged adjacent to each other to correct chromatic aberration.
Is higher than 0.75, the edge thickness of the positive lens tends to be small, so burrs are likely to occur during processing, and the positive lens is fixed to the lens frame. At that time, there is a problem that the edge is easily damaged.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has a lens configuration of three groups, and relaxes the curvature of the lens surface by dispersing the power of the lens surface with respect to a high NA light flux. Furthermore, the eccentricity tolerance between the lens groups, the field angle tolerance, and the working distance are sufficiently secured, and the NA is 0.
It is an object to provide an objective lens having a value of more than 60, more preferably NA of more than 0.85. Further, it is an object of the present invention to provide an objective lens having a simple configuration, in which axial chromatic aberration is satisfactorily corrected, an NA of more than 0.60, and more preferably an NA of more than 0.75. .

Further, in a three-lens objective lens for an optical pickup equipped with a light source having a wavelength shorter than 650 nm, a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are adjacent to each other. Even if the chromatic aberration is corrected by placing the
Was secured to such an extent that it would not be a problem in lens processing, and spherical aberration and sine conditions were well corrected, and NA was 0.
The aim is to provide an objective lens which is greater than 75.

It is another object of the present invention to provide an optical pickup device and a recording / reproducing device equipped with the above-mentioned objective lens.

[0010]

In order to achieve the above object, the first objective lens according to the present invention is an objective lens for recording and / or reproducing of an optical information recording medium, which is arranged in order from the light source side. It has a three-group structure in which a first lens group, a second lens group, and a third lens group are arranged, and the numerical aperture NA value on the optical information recording medium side satisfies the following expression (1). . 0.60 <NA <0.99 (1)

According to the first objective lens, the NA value is (1) when the first lens group, the second lens group, and the third lens group are arranged in this order from the light source side. )
Even if the lens has a high NA satisfying the formula, the refractive power of the lens surface with respect to a high NA ray can be dispersed, so that the curvature of each lens surface does not become too small, and the prospective angle of the aspherical surface can be increased. Therefore, the mold used for molding the lens can be easily processed. Further, since the refraction angle of the light ray on each lens surface is small, the amount of aberration generated on each lens surface is small, and various aberrations including spherical aberration can be favorably corrected even in a light ray with a high NA, In addition, the objective lens can be easily manufactured with little deterioration of various aberrations due to errors such as decentering of each lens surface and decentering between lens groups.

The second objective lens according to the present invention is
An objective lens for recording and / or reproduction of an optical information recording medium, which comprises, in order from a light source side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a first lens group having a positive refractive power. It has a three-group structure in which three lens groups are arranged,
It is characterized in that the value of the numerical aperture NA on the optical information recording medium side satisfies the following equation. 0.60 <NA <0.99 (2)

According to the second objective lens, when all three lens groups have positive refracting power, the refracting power of the lens surface with respect to a high NA ray is dispersed, and the effect of increasing the curvature of each lens surface is further enhanced. Can be made bigger. At this time, the sag amount (Xi (where i = 1, 2,
By satisfying the following expression (3), the spherical aberration can be satisfactorily corrected even for a high NA ray.

0.01 <(X1 ′ + X2 ′ + X3 ′) / (NA ⁴ · f · (1+ | m |)) <0.10 (3) X1 ′ = X1 · (n1-1) ³ / f1 X2 '= X2 · (n2-1) ³ / f2 X3' = X3 · (n3-1) ³ / f3 where Xi: a plane perpendicular to the optical axis and in contact with the vertex of the most light source side surface of the i-th lens group. And the difference in the optical axis direction from the most light source side surface of the i-th lens group at the outermost periphery of the effective diameter (the position on the most light source side surface of the i-th lens group where the marginal ray of NA is incident) ( mm), the direction of the optical information recording medium with respect to the tangential plane is positive, and the direction of the light source is negative (i = 1, 2, 3) ni: the light source of the i-th lens group Refractive index (i = 1, 2, 3) at the wavelength of f i: focal length (mm) of the i-th lens group (i = 1,
2, 3) f: focal length of the objective lens at an infinite object (mm) m: imaging magnification of the objective lens

In the first and second objective lenses described above, the paraxial radius of curvature r1 (mm) of the surface of the first lens group closest to the light source, and the paraxial radius of curvature of the surface of the second lens group closest to the light source. It is preferable that the radius of curvature r2 (mm) and the paraxial radius of curvature r3 (mm) of the surface closest to the light source of the third lens group satisfy the following expressions (4), (5), and (6), respectively. . 0.30 <r1 / ((n1-1) · f1) <1.40 (4) 0.20 <r2 / ((n2-1) · f2) <1.20 (5) 0.50 <r3 / ((n3-1) · f3) <1.50 (6)

In the above equations (4) to (6), when all the three lens groups have positive refracting power, the coma aberration generated when the oblique light beam enters the objective lens is corrected well. The so-called sine condition is a condition for obtaining an objective lens that is satisfactorily corrected.

The paraxial power P1 of the first lens group
(Mm ⁻¹ ), paraxial power P2 (m of the second lens group)
m ⁻¹ ), paraxial power P3 (mm) of the third lens group
⁻¹ ), and the paraxial power P (mm
It is preferable that the values of ( ^-1 ) satisfy the following expressions (7), (8), and (9), respectively. As described above, when all three lens groups have positive refractive power, when the paraxial power of each lens group and the paraxial power of the objective lens satisfy the expressions (7) to (9), sufficient operation is achieved. Even if the distance is secured, the prospective angle of the aspherical surface of each lens surface can be increased, and the eccentricity allowance and the view angle allowance between the lens groups at the time of lens production can be increased. 0.1 <P1 / P <0.5 (7) 0.1 <P2 / P <0.6 (8) 0.6 <P3 / P <1.4 (9)

The third objective lens according to the present invention is
An objective lens for recording and / or reproducing of an optical information recording medium, which comprises, in order from a light source side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a first lens group having a positive refractive power. It has a three-group structure in which three lens groups are arranged,
It is characterized in that the value of the numerical aperture NA on the optical information recording medium side satisfies the following expression (10). 0.60 <NA <0.99 (10)

In a high-NA objective lens having a three-group structure, the working distance tends to be small when trying to secure a large tolerance during lens manufacturing. In designing a high NA objective lens, ensuring a sufficient working distance is important in terms of preventing contact between the objective lens and the optical information recording medium. Therefore, if one of the three lens groups forming the objective lens is a negative lens group having a negative refracting power like the third objective lens, even if the objective lens has a high NA three-group configuration. , A sufficient working distance can be secured. This negative lens group is preferably the first lens group arranged closest to the light source, so that the prospective angle of the aspheric surface of the third lens group arranged closest to the optical information recording medium side does not become too large. You can At this time, since the other two lens groups are positive lens groups having a positive refractive power, the refractive power of the lens surface with respect to the ray of high NA is dispersed to the two lens groups, and each lens of the two positive lens groups is The curvature of the surface does not become too small, and the prospective angle of the aspherical surface does not become too large.

At this time, the sag amount (Xi (where i = 1, 2, 3)) of the surface on the most light source side of each lens group is expressed by the following equation (1)
By satisfying 1), spherical aberration can be favorably corrected even for a high NA ray.

0.02 <(X1 ′ + X2 ′ + X3 ′) / (NA ⁴ · f · (1+ | m |)) <0.12 (11) X1 ′ = X1 · (n1-1) ³ / f1 X2 '= X2 · (n2-1) ³ / f2 X3' = X3 · (n3-1) ³ / f3 where Xi: a plane perpendicular to the optical axis and in contact with the apex of the most light source side surface of the i-th lens group. And the difference in the optical axis direction from the most light source side surface of the i-th lens group at the outermost periphery of the effective diameter (the position on the most light source side surface of the i-th lens group where the marginal ray of NA is incident) ( mm), the case of measuring in the direction of the optical information recording medium with reference to the tangential plane is positive, and the case of measuring in the direction of the light source is negative (i = 1, 2, 3). ni: Refractive index of the i-th lens group at the wavelength of the light source (i = 1, 2, 3) fi: Focal length (mm) of the i-th lens group (i = 1,
2, 3) f: focal length of the objective lens at an infinite object (mm) m: imaging magnification of the objective lens

The paraxial radius of curvature r1 (mm) of the surface of the first lens group closest to the light source, the paraxial radius of curvature r2 (mm) of the surface of the second lens group closest to the light source, and the first The paraxial radius of curvature r3 (m
The values of m) are respectively expressed by the following equations (12), (13) and (14).
It is preferable to satisfy. -1.00 <r1 / ((n1-1) · f1) <0.00 (12)

[0023]   0.30 <r2 / ((n2-1) · f2) <1.70 (13)

[0024]   0.50 <r3 / ((n3-1) · f3) <1.50 (14)

In the above equations (12) to (14), when the first lens group has a negative refractive power and the second lens group and the third lens group have a positive refractive power, the objective lens is inclined. This is a condition for obtaining an objective lens in which the so-called sine condition in which the coma aberration generated when a light beam enters is corrected in a favorable manner.

The paraxial power P1 of the first lens group
(Mm ⁻¹ ), paraxial power P2 (m of the second lens group)
m ⁻¹ ), paraxial power P3 (mm) of the third lens group
⁻¹ ), and the paraxial power P (mm
⁻¹ ) values are respectively expressed by the following equations (15), (16), (1)
It is preferable to satisfy 7). -0.5 <P1 / P <0.0 (15)

[0027] 0.3 <P2 / P <1.2 (16)

[0028] 0.6 <P3 / P <1.4 (17)

As described above, when the first lens group has a negative refractive power and the second lens group and the third lens group have a positive refractive power, the paraxial power of each lens group and the objective lens When the paraxial powers satisfy the equations (15) to (17), the prospective angle of the aspherical surface of each lens surface can be increased even if a sufficient working distance is secured. The eccentricity tolerance and the angle of view tolerance between the lens groups can be increased.

The thickness d of the first lens group on the optical axis is
It is preferable that 1 (mm) satisfies the following expression (18).

[0031] 0.8 <d1 / f <1.7 (18)

This equation (18) shows that when the first lens group has a negative refractive power and the second lens group and the third lens group have a positive refractive power, the lens surfaces of the first lens group are deviated. This is a condition for suppressing coma aberration due to the core. If the thickness of the first lens group on the optical axis and the focal length of the objective lens satisfy the formula (18), the tolerance for the manufacturing error of the first lens group can be increased, and the first lens group is manufactured. It is possible to make the lens easy to play.

In the above-mentioned first to third objective lenses, it is preferable that the value of the numerical aperture NA on the optical information recording medium side satisfies the following expression (19). 0.85 <NA <0.99 (19)

Further, the above-mentioned first to third objective lenses are
At least two surfaces of the surface of the first lens group closest to the light source, the surface of the second lens group closest to the light source, and the surface of the third lens group closest to the light source may be aspherical. preferable.

As described above, at least two of the surface of the first lens group closest to the light source, the surface of the second lens group closest to the light source, and the surface of the third lens group closest to the light source are aspherical surfaces. Then, in addition to spherical aberration, it is possible to favorably correct decentering of each lens surface, decentering between lens groups, and coma aberration that occurs when an oblique light beam is incident on the objective lens.

Further, the above-mentioned first to third objective lenses are
It is preferable that spherical aberration correction is performed corresponding to the thickness of the protective layer that protects the information recording surface of the optical information recording medium, and the value of the thickness t (mm) of the protective layer satisfies the following expression (20). .

0.0 ≦ t ≦ 0.15 (20)

The expression (20) is a conditional expression regarding the optimum thickness of the protective layer of the optical information recording medium for suppressing the coma aberration caused by the skew of the optical information recording medium.
If the numerical aperture of the objective lens is larger than 0.85,
By making the thickness of the protective layer of the optical information recording medium smaller than 0.10 mm, it is possible to secure a skew margin that is the same as or more than that of the conventional optical information recording medium such as a CD and a DVD. If the thickness of the protective layer is zero, no coma will occur due to the disc skew. Therefore, the objective lens according to the present invention has the spherical aberration correction corresponding to the thickness of the protective layer of zero.
That is, the spherical aberration may be corrected only by the objective lens.

Further, the above-mentioned first to third objective lenses are
In an objective lens for an optical pickup device having a light source of wavelength λ, it is preferable that the value of wavelength λ satisfies the following expression (21).

[0040] 350nm <λ <650nm (21)

As described above, by setting the design reference wavelength when designing the objective lens of the present invention to a short wavelength that satisfies the expression (21), there is a light source that generates a wavelength that satisfies the expression (21). It can be applied to a high-density recording optical pickup device. When the design wavelength is a short wavelength, the allowable error at the time of manufacturing the lens is small, but the objective lens of the present invention has a three-group structure and the refracting power of the lens surface is dispersed, so that even if the design wavelength is a short wavelength. Tolerances during lens manufacturing are never too small.

Further, the above-mentioned first to third objective lenses are
At least one surface is preferably a diffractive surface having a ring-shaped diffractive structure.

Laser light emitted from a semiconductor laser is generally considered to have a single wavelength (single mode) and is considered to have no chromatic aberration. In reality, however, the center wavelength is momentarily several nm due to temperature change, output change, or the like. Jumping or mode hopping may occur. The depth of focus d of the objective lens is represented by d∝λ / (NA) ² as is well known. Therefore, the larger the NA, the smaller the depth of focus. Therefore, in an objective lens having an NA larger than 0.90, defocus due to chromatic aberration caused by mode hopping of a semiconductor laser becomes an unacceptable problem. Need to be corrected. Further, in a general optical material, the shorter the wavelength is, the larger the change in the refractive index due to the change in wavelength is. Therefore, when a short wavelength semiconductor laser is used, a large amount of chromatic aberration occurs in the objective lens due to mode hopping. The shorter the wavelength of the light source is, the smaller the depth of focus of the objective lens is. Therefore, even a slight defocus is not allowed, and when a short wavelength semiconductor laser is used, the need for chromatic aberration correction of the objective lens becomes even higher. As a method of correcting chromatic aberration, for example, there is a method of forming a doublet of a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number, but in this case, the weight of the objective lens becomes large. Therefore, it is not preferable from the viewpoint of a burden on the focusing actuator. Therefore, as described above, if a ring-shaped diffractive structure is provided on at least one surface, chromatic aberration can be corrected without increasing the number of lenses.

Further, the above-mentioned first to third objective lenses are
It is preferably formed from an optical plastic material.
As described above, when the objective lens of the present invention is made of a plastic material, even a high-NA objective lens with a large volume and a three-group structure has a small weight and inertia, so that the burden on the focusing actuator can be reduced. Further, it becomes possible to perform more precise position control of the objective lens by the actuator. As a result, reduction of focusing error, miniaturization of the actuator, power saving of the actuator, etc. can be achieved. Further, since the inertia is small, the optical information recording medium can be prevented from being damaged when it comes into contact with the optical information recording medium. Furthermore, mass production can be carried out inexpensively by an injection molding method using a mold. As the plastic material, a material having a light transmittance of 85% or more and a saturated water absorption rate of 0.5% or less in a used wavelength region in a thickness of 3 mm is preferable. As such a plastic material, a polyolefin resin is preferable, and a norbornene resin is more preferable among the polyolefin resins.

The fourth objective lens according to the present invention is
An objective lens for recording and / or reproducing of an optical information recording medium, which has a three-group structure in which a first lens group, a second lens group, and a third lens group are arranged in order from the light source side, The surface of the three lens groups closest to the light source is an aspherical surface, and the numerical aperture NA on the side of the optical information recording medium satisfies the following expression (22). 0.60 <NA <0.99 (22)

The fourth objective lens according to the present invention comprises:
The first lens group has a positive refractive power, the second lens group has a negative refractive power, the third lens group has a positive refractive power, and the Abbe number νd1 of the d-line of the first lens group and the It is characterized in that the Abbe number νd2 of the d-line of the two lens groups satisfies the following expression (23). νd1> νd2 (23)

The above equation (23) is a condition relating to the Abbe number of the first lens group and the second lens group for correcting the axial chromatic aberration with a simple structure. By satisfying the equation (23), Since it is possible to obtain an objective lens with well-corrected upper chromatic aberration, the defocus component of the wavefront aberration at the time of mode hopping can be suppressed to be small even with an objective lens with a high NA such as formula (22) having a small depth of focus. be able to.

Here, it is more preferable to satisfy the following equations (24) and (25) in order to achieve the above action. νd1> 55 (24) νd2 <40 (25)

Furthermore, by making the surface of the third lens group closest to the light source an aspherical surface, it is possible to favorably correct not only spherical aberration but also coma aberration.

Even when the first lens group has a negative refracting power, the second lens group has a positive refracting power, and the third lens group has a positive refracting power, the d of the first lens group is similarly changed. Abbe number ν, d1 of the line and Abbe number νd of the d line of the second lens group
If the value of 2 satisfies the following expression (23 ′), the axial chromatic aberration can be satisfactorily corrected. νd1 <νd2 (23 ')

More preferably, the following equations (24 ') and (2
5 ') is satisfied. νd1 <40 (24 ') νd2> 55 (25')

If both the first lens group and the second lens group are composed of a single lens, and the first lens group and the second lens group are doublet cemented, the non-bonded surface is not formed. Due to the spherical aberration correcting action, spherical aberration and coma can be corrected more precisely.

The numerical aperture NA on the optical information recording medium side is preferably 0.75 <NA <0.99.

The above-mentioned objective lens is the second lens group.
And the distance d between the third lens group and the optical axis ₂₃(mm) and most
From the top of the lens surface on the light source side to the optical information recording medium side
The distance on the optical axis to the top of the surface (lens total length) Σd (mm)
The value preferably satisfies the following formula. 0.05 <d₂₃/Σd<0.35 (26)

The above expression (26) is a conditional expression for balancing the allowable tolerance of the eccentricity between the lens surfaces of the first lens group and the allowable tolerance of the eccentricity between the lens groups. If the value of d ₂₃ becomes larger than the upper limit of the equation (26), the curvature of the surface of the first lens group that is closest to the light source is relaxed, so that the surface of the first lens group that is closest to the light source is eccentric. Although the deterioration of the wavefront aberration is small, the expected angle of the aspherical surface of the surface closest to the light source of the third lens group is large, so that the wavefront aberration of the optical axis between the second lens group and the third lens group is decentered. The deterioration becomes too large, the number of assembly and adjustment steps increases, and the production cost rises. Further, when the value of d ₂₃ becomes smaller than the lower limit of the expression (26), the expected angle of the aspherical surface of the surface closest to the light source of the third lens group becomes small, so that the second lens group and the third lens group Although the deterioration of the wavefront aberration due to the eccentricity of the optical axes of and is small, the curvature of the surface of the first lens group that is closest to the light source is small. Deteriorates too much, and the production efficiency of the first lens group deteriorates. d ₂₃ / Σ
When the value of d is within the range of Expression (26), it is possible to balance the tolerance of eccentricity between lens surfaces and the tolerance of eccentricity between lens groups. In order to achieve the above action, it is more preferable to satisfy the following expression (27). 0.10 <d ₂₃ /Σd<0.30 (27)

Further, the above-mentioned objective lens is characterized in that it is an objective lens for an optical pickup device having a light source in which the value of the wavelength λ satisfies the value of the following expression (28). The objective lens according to the present invention can satisfactorily correct axial chromatic aberration even with respect to light having a short wavelength as expressed by the formula (28). 350nm <λ <650nm (28)

As described above, in the three-lens objective lens, the first lens having a relatively large Abbe number and a positive refractive power and the negative lens having a relatively small Abbe number are provided. When the second lenses of the first lens are arranged adjacent to each other to correct the chromatic aberration, the edge thickness of the first lens tends to be small. As a means for ensuring the edge thickness of the first lens, it is conceivable to reduce the curvature of the optical surfaces of the first lens and the second lens which face each other. Since the aberration correction action on the surface becomes small, spherical aberration and sine conditions cannot be corrected well.

Therefore, the fifth objective lens according to the present invention is an objective lens for recording and / or reproducing of the optical information recording medium, and the first lens having a positive refractive power in order from the light source side, A light source side optical surface of the first lens, which has a three-lens structure in which a second lens provided adjacent to one lens and having a negative refractive power and a third lens having a positive refractive power are arranged; Also, both of the optical surfaces on the light source side of the third lens are aspherical surfaces.

As described above, when the optical surface of the first lens on the light source side is an aspherical surface, the objective lens has a three-lens structure in which the edge thickness of the first lens is secured to such a degree that does not pose a problem in lens processing. Also, it is possible to obtain the objective lens in which the spherical aberration and the sine condition are favorably corrected by the aberration correcting action of the aspherical surface. At this time, by making the optical surface of the third lens on the light source side also aspheric, spherical aberration generated on the optical surface of the third lens on the optical information recording medium side can be satisfactorily corrected, resulting in higher performance. Objective lens.

In the fifth objective lens, the d-line Abbe number νd1 of the first lens and the d-line Abbe number νd2 of the second lens are set so as to satisfy the following equations (29) and (30). Chromatic aberration can be satisfactorily corrected by selecting the materials of the first lens and the second lens. νd1> 55 (29) νd2 <40 (30)

In order to achieve the above action, it is more preferable to satisfy the following equations (31) and (32). νd1> 60 (31) νd2 <30 (32)

If the first lens and the second lens are doublet lenses cemented together, the spherical aberration and the sine condition can be more finely corrected by the aspherical aberration correcting action of the cemented surface.

In the fifth objective lens, it is preferable that the numerical aperture NA on the optical information recording medium side satisfies the following expression (33). 0.75 <NA <0.99 (33)

In a three-element objective lens having positive, negative, and positive configurations, when the NA is increased as in the above expression (33), the edge thickness of the first lens becomes too small, Although it is difficult to process one lens, in the fifth objective lens, since the optical surface on the light source side of the first lens is an aspherical surface, even if the edge thickness of the first lens is secured, aberration correction of the aspherical surface will be possible. By the action, it is possible to obtain an objective lens in which high-order spherical aberration and high-order coma aberration are well corrected.

Further, as shown in FIG. 18, the center thickness dc (mm) of the first lens and 0.2 m from the outermost periphery of the effective diameter.
The thickness dh (m of the first lens in the optical axis direction at a height of m
The value of m) preferably satisfies the following expression (34). 0.1 <dh / dc <0.8 (34)

Above the lower limit of equation (34), the edge thickness is sufficiently secured, which is advantageous in processing. Also, equation (34)
Below the upper limit of, spherical aberration is not overcorrected.

The outermost periphery of the effective diameter of the first lens means the optical information recording medium of the objective lens which is necessary for recording information on the information recording surface of the optical information recording medium or reproducing information from the information recording surface. On the optical surface on the light source side of the first lens on which the marginal ray of NA on the side enters.

In the above-mentioned objective lens, the value of wavelength λ is
Since the objective lens is for an optical pickup device having a light source that satisfies the value of the following expression (35), the fifth objective lens has a simple configuration even for light of a short wavelength as shown in the expression (35). Thus, it is possible to satisfactorily correct the axial chromatic aberration. 350nm <λ <650nm (35)

Further, in the fifth objective lens, the following expression (3
It is preferable to satisfy 6). 0.7 <r1 / f <1.8 (36)

The above equation (36) is a condition for achieving a good balance between the workability of the lens and the correction of chromatic aberration, and
Above the lower limit of Expression (36), the occurrence of coma aberration due to the optical axis shift of the optical surface of the first lens does not become too large.
Since the edge thickness of the lens does not become too small, the first lens can be a lens that can be easily processed. Formula (36)
Since the thickness of the first lens on the optical axis does not become too large when the value is less than or equal to the upper limit, it is possible to obtain a lightweight objective lens.
Since the projected angle of the aspherical surface of the optical surface on the light source side of the lens does not become too large, it is possible to accurately create an aspherical shape when cutting the molding die with a diamond tool. Further, since the coma aberration caused by the optical axis shift between the second lens and the third lens does not become too large, the objective lens can be easily assembled. Further, since the chromatic aberration is not undercorrected, the defocus does not become too large even when the wavelength of the light source changes instantaneously.

Further, in the fifth objective lens, it is preferable that the following expression (37) is further satisfied. 0.5 <f3 / f <1.2 (37)

The above expression (37) is a condition for obtaining good distribution of the refractive power of the third lens with respect to the entire objective lens system, and is an aspherical surface on the light source side of the third lens when the lower limit of the expression (37) is exceeded. Since the expected angle of 3 does not become too large and the edge thickness of the 3rd lens does not become too small, it is possible to make the 3rd lens easy to process. Further, the coma aberration due to the optical axis shift of the optical surface of the first lens does not become too large, and the thickness of the first lens on the optical axis does not become too large, so that the first lens can be easily processed. it can. Expression (3
Below the upper limit of 7), coma aberration due to the optical axis shift between the second lens and the third lens does not become too large, so that the objective lens can be easily assembled. further,
Since the chromatic aberration is not undercorrected, the defocus does not become too large even when the wavelength of the light source changes instantaneously.

As described above, in the three-lens objective lens, the first lens having a relatively small Abbe number and a negative refractive power and the positive lens having a relatively large Abbe number are provided. When the second lenses that the two lenses have are arranged adjacent to each other and the chromatic aberration is corrected, the edge thickness of the second lens tends to be small. As a means for ensuring the edge thickness of the second lens, it is conceivable to reduce the curvature of the optical surfaces of the first lens and the second lens that face each other. In this case, the optical surfaces of the first lens and the second lens that face each other may be relaxed. Since the aberration correction action on the surface becomes small, spherical aberration and sine conditions cannot be corrected well.

Therefore, a sixth objective lens according to the present invention is an objective lens for recording and / or reproducing of an optical information recording medium, and the first lens having a negative refracting power in order from the light source side, A light source side optical surface of the first lens, which has a three-lens structure in which a second lens provided adjacent to one lens and having a positive refractive power and a third lens having a positive refractive power are arranged; Also, both of the optical surfaces on the light source side of the third lens are aspherical surfaces.

As described above, when the optical surface of the first lens on the light source side is an aspherical surface, the objective lens has a three-lens structure in which the edge thickness of the second lens is secured to such a degree that does not pose a problem in lens processing. Also, it is possible to obtain the objective lens in which the spherical aberration and the sine condition are favorably corrected by the aberration correcting action of the aspherical surface. At this time, by making the optical surface of the third lens on the light source side also aspheric, spherical aberration generated on the optical surface of the third lens on the optical information recording medium side can be satisfactorily corrected, resulting in higher performance. Objective lens.

In the above sixth objective lens, the values of the Abbe number νd1 of the first lens on the d line and the Abbe number νd2 of the second lens on the d line satisfy the following equations (38) and (39). When the materials of the first lens and the second lens are selected,
The chromatic aberration can be corrected well. νd1 <40 (38) νd2> 55 (39)

To achieve the above action, the following equation (4
It is more preferable to satisfy 0) and (41). νd1 <35 (40) νd2> 60 (41)

If the sixth objective lens described above is a doublet lens in which the first lens and the second lens are cemented, the spherical aberration and the sine condition are more finely corrected by the aspherical aberration correcting action of the cemented surface. it can.

Further, the sixth objective lens is characterized in that the value of the numerical aperture NA on the optical information recording medium side satisfies the following expression (42). 0.75 <NA <0.99 (42)

In a three-element objective lens having negative, positive and positive configurations, if the NA is increased as in the above expression (42), the edge thickness of the second lens becomes too small, Although it is difficult to process the two lenses, in the sixth objective lens, since the optical surface on the light source side of the first lens is an aspherical surface, even if the edge thickness of the second lens is secured, the aberration correction of the aspherical surface is performed. By the action, it is possible to obtain an objective lens in which high-order spherical aberration and high-order coma aberration are well corrected.

Further, in the sixth objective lens, as shown in FIG. 18, the center thickness dc (mm) of the second lens and the optical axis direction of the second lens at a height of 0.2 mm from the outermost periphery of the effective diameter are taken. It is preferable that the value of the thickness dh (mm) satisfies the following expression (43). 0.1 <dh / dc <0.8 (43)

Above the lower limit of equation (43), a sufficient edge thickness is secured, which is advantageous in processing. Also, equation (43)
Below the upper limit of, spherical aberration is not overcorrected.

The outermost periphery of the effective diameter of the second lens means the information recording surface of the optical information recording medium in the optical surface having the largest effective diameter among the optical surface on the light source side and the optical surface on the optical information recording medium side. N on the optical information recording medium side of the objective lens necessary for recording information or reproducing information from the information recording surface
It indicates the position on the optical surface on which the marginal ray A enters.

The objective lens described above is an objective lens for an optical pickup device having a light source whose wavelength λ satisfies the value of the following expression (44). On the other hand, with the sixth objective lens, it is possible to satisfactorily correct the axial chromatic aberration with a simple configuration. 350nm <λ <650nm (44)

In the sixth objective lens, the following expression (4
It is preferable to satisfy 5). 0.15 <d ₂₃ /Σd<0.40 (45)

The above expression (45) is a condition for making the objective lens in which each lens is easy to process, and yet the assembling of each lens is easy, and is equal to or more than the lower limit of the expression (45). Since the occurrence of coma aberration due to the deviation of the optical axis of the first lens does not become too large, the first lens can be a lens that can be easily processed, and the thickness of the second lens on the optical axis does not become too large. It can be a lens. Since the thickness of the first lens on the optical axis does not become too small below the upper limit of Expression (45), the first lens can be easily processed. Further, since the thickness of the second lens on the optical axis does not become too small and the edge thickness of the second lens does not become too small, it is possible to make the second lens easy to process. Further, the coma aberration caused by the optical axis shift between the second lens and the third lens does not become too large, and the objective lens can be easily assembled.

Further, in the sixth objective lens, it is preferable that the following expression (46) is further satisfied. 0.5 <f3 / f <1.2 (46)

The above expression (46) is a condition for achieving good distribution of the refractive power of the third lens with respect to the entire objective lens system, and is an aspherical surface on the light source side of the third lens when the lower limit of the expression (46) is satisfied. Since the expected angle of 3 does not become too large and the edge thickness of the 3rd lens does not become too small, it is possible to make the 3rd lens easy to process. Further, the occurrence of coma aberration due to the optical axis shift of the optical surface of the first lens does not become too large,
Since the thickness of the first lens on the optical axis does not become too large,
The first lens can be a lens that can be easily processed.
Below the upper limit of Expression (46), coma aberration due to the optical axis deviation of the second lens and the third lens does not become too large,
The objective lens can be easily assembled. Further, since the chromatic aberration is not undercorrected, the defocus does not become too large even when the wavelength of the light source changes instantaneously.

Further, in the sixth objective lens, it is preferable that the following expression (47) is further satisfied. 0.1 <(r4 + r3) / (r4-r3) <1.2 (47)

The above formula (47) is a condition for making each lens easy to process and yet easy to assemble each lens, and the optical surface of the first lens is equal to or more than the lower limit of the formula (47). Since the occurrence of coma aberration due to the optical axis deviation of 1 does not become too large, it is possible to make the first lens easy to process. Moreover, since the thickness of the second lens on the optical axis does not become too large, a lightweight objective lens can be obtained. Furthermore, since the occurrence of coma aberration due to the deviation of the optical axes of the second lens and the third lens does not become too large,
The objective lens can be easily assembled. Since the paraxial radius of curvature of the first lens on the optical information recording medium side does not become too small below the upper limit of the expression (47), the first lens can be easily processed. Furthermore, the second
Since the thickness of the lens on the optical axis does not become too large, a lightweight objective lens can be obtained.

Further, the optical pickup device according to the present invention comprises a light source and a condensing optical system including an objective lens for condensing the light flux emitted from the light source on the information recording surface of the optical information recording medium. An optical pickup device for recording and / or reproducing information on the optical information recording medium by detecting reflected light from the information recording surface, wherein the first to sixth objective lenses are used as the objective lens. It is characterized by having either.

According to this optical pickup device, by using an objective lens having a larger numerical aperture and a lens structure of a three-group structure, high-density recording / reproducing is possible, and yet a sufficient working distance can be secured. Further, the wavefront aberration does not deteriorate even if mode hopping or the like occurs in the light source.

The recording / reproducing apparatus according to the present invention is equipped with the above-mentioned optical pickup device to record voice and / or images and / or reproduce voice and / or images. According to this recording / reproducing apparatus, high-density recording / reproducing is possible.

The objective lens of the present invention is not limited to a so-called infinite lens in which the object point is at infinity, but may be a finite lens in which the object point is at a finite distance. When aberration correction is performed so that the parallel light flux from an object at infinity is minimized, even if the objective lens is moved in order to reduce tracking error / focusing error, there is little change in the incident condition on the objective lens. , Aberration change is small. When the objective lens is subjected to aberration correction so that the aberration is minimized with respect to a divergent light beam from an object at a finite distance, a larger working distance can be secured, so that the objective lens and the optical information recording medium are Collisions can be prevented. Also,
When this objective lens is subjected to aberration correction so that the aberration is minimized with respect to the convergent light flux toward the image side object, the incident angle of the light beam to the objective lens becomes small, so that the aberration deterioration due to the eccentricity error during manufacturing. Can be suppressed, and the objective lens can be easily manufactured.

[0095]

BEST MODE FOR CARRYING OUT THE INVENTION An optical pickup device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing the optical pickup device of the present embodiment.

The optical pickup device shown in FIG. 1 has an objective lens 1 of 3 groups 3 elements, a semiconductor laser 3 as a light source, and a 1 group 1 element for converting a divergence angle of divergent light emitted from the light source 3. A coupling lens 2 and a photodetector 4 that receives reflected light from the information recording surface 5 of the optical information recording medium are provided. The semiconductor laser 3 generates laser light having a wavelength of 500 nm or less, reproduces information recorded on the information recording surface 5 at a higher density than a conventional optical information recording medium, and / or records information at a higher density than a conventional optical disc. Information can be recorded on the recording surface 5.

The objective lens 1 of FIG. 1 is composed of a first lens 1a, a second lens 1b and a third lens 1c, and the NA on the optical information recording medium side is set to be larger than 0.85.
The first lens 1a, the second lens 1b, and the third lens 1c are integrated by a holding member 1d. The objective lens 1 can be accurately attached to the optical pickup device by the flange portion 1e of the holding member 1d.

The optical pickup device shown in FIG. 1 is further arranged between a polarization beam splitter 6 for separating reflected light from the information recording surface 5 toward a photodetector 4, and a coupling lens 2 and an objective lens 1. 1/4 wavelength plate 7, a diaphragm 8 placed in front of the objective lens 1, a condenser lens 9, and a biaxial actuator 10 for focus and tracking. Further, in the present embodiment, the coupling lens 2 can be displaced along the optical axis direction by the uniaxial actuator 11, so that the spherical aberration generated in the focusing optical system can be corrected. In the present embodiment, the condensing optical system has a light source, a beam splitter, a coupling lens, a 1/4 wavelength plate, an objective lens, and a diaphragm. In the present embodiment, the beam splitter may be regarded as not included in the condensing optical system.

The reproduction of information from the information recording surface 5 of the optical information recording medium will be described. The divergent light emitted from the semiconductor laser 3 changes its divergence angle by the coupling lens 2 to 1/4.
The objective lens 1 focuses the light on the information recording surface 5 of the optical information recording medium through the wave plate 7 and the diaphragm 8, and the light flux modulated and reflected by the information pits on the information recording surface 5 is reflected by the objective lens 1, the diaphragm 8, and the diaphragm 8. 1/4 wave plate 7, coupling lens 2,
The information recorded on the information recording surface of the optical information recording medium can be reproduced by the output signal generated by incidence on the photodetector 4 via the polarization beam splitter 6 and the condenser lens 9. The same applies to the case of recording information on the information recording surface of the optical information recording medium.

At the time of reproducing information as described above, each optical element of the condensing optical system is affected by changes in temperature and humidity of the apparatus environment, fluctuations in the transparent substrate thickness of the optical information recording medium, or minute fluctuations in the oscillation wavelength of the semiconductor laser 3. When spherical aberration variation occurs on the surface, the coupling lens 2 is displaced by an appropriate amount along the optical axis direction by the uniaxial actuator 11 to change the divergence angle of the light beam incident on the objective lens 1 to collect light. It is possible to correct spherical aberration generated on each optical surface of the optical system. Also,
Also in the case of recording information on the information recording surface 5 of the optical information recording medium, the spherical aberration generated on each optical surface of the condensing optical system can be corrected similarly to the above description.

Next, another optical pickup device will be described with reference to FIG. The objective lens 1 shown in FIG. 2 has a three-group, three-element configuration as in FIG.
It is said to be larger than 5. Further, the optical pickup device of FIG. 2 has a beam expander 12 including a positive lens 12a and a negative lens 12b as spherical aberration correction means.
And a uniaxial actuator 11 capable of moving the negative lens 12b along the optical axis direction. In FIG. 2, the coupling lens 2 and the quarter-wave plate 7 are arranged between the semiconductor laser 3 and the polarization beam splitter 6.

According to the optical pickup device of FIG.
Similarly, the spherical aberration variation occurs on each optical surface of the condensing optical system due to the temperature / humidity variation of the apparatus environment, the variation of the transparent substrate thickness of the optical information recording medium, or the minute variation of the oscillation wavelength of the semiconductor laser 3. If the negative lens 1 of the beam expander 12
2b is displaced by an appropriate amount along the optical axis direction by the uniaxial actuator 11 to change the divergence angle of the light beam incident on the objective lens 1, thereby correcting the spherical aberration generated on each optical surface of the condensing optical system. can do.

Although not shown, the optical pickup device of FIGS. 1 and 2 detects the variation of the spherical aberration generated in the converging optical system by detecting the reflected light from the information recording surface 5 and detecting it. It has a spherical aberration detecting means for generating a spherical aberration error signal based on the result. The coupling lens 2 as the spherical aberration correcting means or the negative lens 12 of the beam expander 12 so that the spherical aberration error signal becomes zero.
drive b. The spherical aberration detecting means and the spherical aberration detecting method in the spherical aberration detecting means include:
For example, those described in Japanese Patent Application No. 2001-108378 by the same applicant can be used. The above-mentioned spherical aberration detecting means is arranged in the optical path between the spherical aberration correcting means and the light source.

Further, in the optical pickup device of FIGS. 1 and 2, in addition to the coupling lens 2 and the beam expander 12 described above, the refractive index distribution in the direction perpendicular to the optical axis is electrically used as the spherical aberration correction means. An element that changes to can be used. In this case, since the movable portion is unnecessary, the weight and cost of the optical pickup device can be reduced. An example of such a variable refractive index distribution element is shown in FIG. The variable refractive index distribution element shown in FIG. 3 includes a liquid crystal element 2a in which liquid crystal molecules are aligned in an arbitrary X direction in a plane perpendicular to the optical axis, and a liquid crystal molecule is arbitrary in a plane perpendicular to the optical axis. Liquid crystal elements 2b aligned in the Y direction perpendicular to the X direction
Are laminated alternately with the glass substrate 2c sandwiched therebetween, and the half-wave plate 2d is arranged between the inner glass substrates 2c. By applying a voltage from the drive unit 2e to each of the liquid crystal element 2a and the liquid crystal element 2b, the X-direction component of the phase of the wavefront emitted from the liquid crystal element serving as the refractive index distribution variable element,
By controlling the and Y direction components independently, it is possible to correct the fluctuation of the spherical aberration generated in the condensing optical system.
The variable refractive index distribution element is not limited to the configuration shown in FIG. 3 as long as it can form a refractive index distribution that is substantially symmetrical with respect to the optical axis.

In the optical pickup device of FIGS. 1 and 2, a blue-violet semiconductor laser having an oscillation wavelength of about 400 nm can be used as the semiconductor laser 3 which emits a laser beam having a wavelength of 500 nm. Furthermore, an SHG laser with an oscillation wavelength of about 400 nm can be used as the short wavelength light source.

[0106]

Next, the present invention will be described in more detail with reference to Examples 1 to 5.

In a high NA objective lens composed of a plurality of lens groups, if the deterioration of the wavefront aberration due to the eccentricity error between the lens groups is large, it becomes difficult to adjust each lens group when the objective lens is incorporated. Since the production efficiency of lenses deteriorates sharply, when designing a high NA objective lens composed of multiple lens groups, how to suppress deterioration of wavefront aberration due to decentering error between each lens group It is important to correct aberrations, improve image height characteristics, and secure a sufficient working distance. Keeping this in mind, the allowable value of the eccentricity error between the lens groups is ± 20 μm or more, the allowable value of the eccentricity error between the lens surfaces is ± 3 μm or more, and the angle of view allowance is 0.5 ° or more. The lens designs of the following Examples 1 to 4 were performed so that the prospective angle of the aspherical surface of the lens surface was 60 degrees or less and the working distance was 0.05 mm or more. Table 1 below shows a list of data relating to the objective lenses of Examples 1 to 5. Table 7 shows a list of data on the objective lenses of Examples 6 and 7.

[0108]

[Table 1]

The aspherical surface in the lens of this embodiment is represented by the following formula 1 when the optical axis direction is the X axis, the height in the direction perpendicular to the optical axis is h, and the radius of curvature of the refracting surface is r. However, κ is a cone coefficient and A2i is an aspherical surface coefficient.

[0110]

[Equation 1]

Further, the ring-shaped diffractive surface provided on the lens of this embodiment can be expressed by the following equation 2 as the optical path difference function Φb. Here, n is the diffraction order of the diffracted light having the maximum diffracted light amount among the diffracted light generated on the diffractive surface, and h
Is the height perpendicular to the optical axis, and b _2j is the coefficient of the optical path difference function.

[0112]

[Equation 2]

<Example 1>

In Example 1, f = 1.58 mm, NA0.
95, t = 0.01 mm, λ = 405 nm, m = 0, 3
This is an objective lens composed of three lenses. Lens data are shown in Table 2. An optical path diagram of Example 1 is shown in FIG. 4, and a spherical aberration diagram is shown in FIG. The lens material is a polyolefin-based norporne-based resin, and has an optical transmittance of 95% or more, a saturated water absorption rate of 0.01% or less, and a specific gravity of about 1.0 in a wavelength range of use at a thickness of 3 mm. It was plastic. By making the first lens a negative lens having a negative refracting power, a working distance of 0.07 mm was ensured even though it was an objective lens with a high NA3 group having a small aperture (3 mm entrance pupil). Further, by making all lens surfaces except the lens surface closest to the optical information recording medium aspherical surfaces, decentering of each lens surface, decentering between lens groups, and oblique light beam incidence on the objective lens occurred. The coma aberration that occurs in some cases was corrected well.

[0115]

[Table 2]

<Example 2>

In the second embodiment, f = 1.55 mm, NA0.
97, t = 0.02 mm, λ = 405 nm, m = 0, 3
This is an objective lens composed of three lenses. Lens data are shown in Table 3. An optical path diagram of Example 2 is shown in FIG. 6, and a spherical aberration diagram is shown in FIG. Since the lens material is the same optical plastic as the material of Example 1, the description is omitted. First
Although the lens, the second lens, and the third lens are all positive lenses having a positive refractive power, by dispersing the refractive power of the lens surface with respect to a ray of NA 0.97, the plastic lens has a relatively small refractive power. Since the aspherical angle of each lens surface is set to 60 degrees or less, it is possible to accurately perform lens die processing with a diamond tool. Further, by making all lens surfaces except the lens surface closest to the optical information recording medium aspherical surfaces, decentering of each lens surface, decentering between lens groups, and oblique light beam incidence on the objective lens occurred. The coma aberration that occurs in some cases was corrected well.

[0118]

[Table 3]

<Example 3>

In the third embodiment, f = 1.58 mm, NA0.
95, t = 0.05 mm, λ = 405 nm, m = −0.
No. 08 is an objective lens having a structure of 3 elements in 3 groups. Table 4 shows the lens data. 8 is an optical path diagram of the third embodiment.
9 shows a spherical aberration diagram. The lens material is the same as in Example 1.
The explanation is omitted because it is the same optical plastic as the material. A small aperture (3 mm entrance pupil) is achieved by the finite specification that converges the divergent light beam from the light source on the information recording surface of the optical recording medium.
The working distance was as large as 0.1 mm even though it was an objective lens with a high NA 3 group. The first lens, the second lens, and the third lens are all positive lenses having a positive refractive power, and by dispersing the refractive power of the lens surface with respect to a ray of NA 0.95, a plastic lens having a relatively small refractive power is obtained. However, since the prospective angle of the aspherical surface of each lens surface is set to 60 degrees or less, the die machining of the lens by the diamond tool can be accurately performed. Also,
When all lens surfaces except the lens surface closest to the optical information recording medium are aspherical surfaces, decentering of each lens surface, decentering between lens groups, and oblique light flux incidence on the objective lens occur. Corrected coma aberration that occurred.

[0121]

[Table 4]

<Example 4>

In Example 4, f = 1.55 mm, NA0.
97, t = 0.02 mm, λ = 405 nm, m = 0, 3
This is an objective lens composed of three lenses. Table 5 shows the lens data. An optical path diagram of Example 4 is shown in FIG. 10, and a spherical aberration diagram is shown in FIG. Since the lens material is the same optical plastic as the material of Example 1, the description is omitted.
The first lens, the second lens, and the third lens are all positive lenses having a positive refracting power, and by dispersing the refracting power of the lens surface with respect to a ray of NA 0.97, a plastic lens having a relatively small refracting power is obtained. However, since the prospective angle of the aspherical surface of each lens surface is set to 60 degrees or less, the die machining of the lens by the diamond tool can be accurately performed. Further, by making all lens surfaces except the lens surface closest to the optical information recording medium aspherical surfaces, decentering of each lens surface, decentering between lens groups, and oblique light beam incidence on the objective lens occurred. The coma aberration that occurs in some cases was corrected well. Furthermore, since the axial chromatic aberration is corrected by making the light source side surface of the first lens a diffractive surface, the defocus component of the wavefront aberration when mode hopping of +1 nm occurs is 0.001 λrms or less (calculated value). I was able to keep it small. At this time, the coefficient of the optical path difference function representing the optical path difference added to the transmitted wavefront by the diffractive structure is designed so that the third-order diffracted light has the maximum diffracted light amount.

[0124]

[Table 5]

<Example 5>

In the fifth embodiment, f = 2.35 mm, NA0.
The objective lens is composed of two groups and three elements of 85, t = 0.1 mm, λ = 405 nm, and m = 0. Table 6 shows the lens data. An optical path diagram of Example 5 is shown in FIG. 12, and a spherical aberration diagram is shown in FIG. FC5 (νd = 70.4, which is a low-dispersion material as the material of the first lens having positive refractive power,
HOYA Co., Ltd.), and FD4 (νd = 27.v) which is a high dispersion material as the material of the second lens having negative refractive power.
5, HOYA) was selected to correct the axial chromatic aberration, so the defocus component of the wavefront aberration when mode hopping of +1 nm occurred can be suppressed to a small value of 0.015 λrms or less (calculated value). It was Also, the first
The distance between the lens group and the second lens group on the optical axis is defined by the above (2
By determining so as to satisfy the expression (7), the tolerance of the eccentricity of the surface of the first lens group closest to the light source, the first lens group and the second lens group
Balanced tolerance of eccentricity with the lens group.

[0127]

[Table 6]

[0128]

[Table 7]

<Example 6>

In Example 6, f = 1.80 mm, NA0.
93, t = 0 mm, λ = 405 nm, and m = 0. Lens data are shown in Table 8.
Further, FIG. 14 shows an optical path diagram of Example 5, and FIG. 15 shows a spherical aberration diagram. As a material for the first lens having a positive refractive power, S-FPL51 (νd = 81.
0, made by OHARA), and has a negative refractive power
S-TIH6 (ν
d = 25.4, manufactured by OHARA Co., Ltd., the axial chromatic aberration is corrected, so that the defocus component of the wavefront aberration when +1 nm mode hopping occurs is 0.0.
The value was as small as 02λrms (calculated value).
Further, by making the surface of the first lens on the light source side aspherical,
Although the objective lens has been satisfactorily corrected for spherical aberration and sine conditions, the edge thickness (dh) of the first lens is 0.95.
mm was sufficiently secured. Furthermore, by making the surface of the third lens on the light source side aspherical, the aberrations were corrected more finely.

[0131]

[Table 8]

<Example 7>

In the seventh embodiment, f = 1.80 mm, NA0.
93, t = 0 mm, λ = 405 nm, and m = 0. Table 9 shows lens data.
Further, FIG. 16 shows an optical path diagram of Example 5, and FIG. 17 shows a spherical aberration diagram. As the material of the first lens having negative refractive power, S-TIH4 (νd = 27.
No. 5, manufactured by OHARA), and has a positive refractive power
Low dispersion material S-FSL5 (ν
The axial chromatic aberration was corrected by selecting (d = 70.1, manufactured by OHARA), so that the defocus component of the wavefront aberration in the case of mode hopping of +1 nm is 0.0.
It was possible to keep the value as small as 04λrms (calculated value).
Further, by making the surface of the first lens on the light source side aspherical,
Although the objective lens has been satisfactorily corrected for spherical aberration and sine condition, the edge thickness (dh) of the second lens is 0.98.
mm was sufficiently secured. Furthermore, by making the surface of the third lens on the light source side aspherical, the aberrations were corrected more finely.

[0134]

[Table 9]

In the above table or figure, E (or e) is used to express the power of 10, for example, E-02
It may be expressed as (= 10 ⁻² ).

[0136]

According to the present invention, the lens structure is made up of three groups, the power of the lens surface is dispersed with respect to a light beam having a high NA, the curvature of the lens surface is relaxed, and further the decentering between the lens groups is allowed. It is possible to provide an objective lens having a sufficient NA, an angle of view tolerance, and a working distance, and an NA of more than 0.60, more preferably an NA of more than 0.85. Further, it is possible to provide an objective lens having a simple structure but well-corrected axial chromatic aberration, an NA of more than 0.60, and more preferably an NA of more than 0.75.

Moreover, high density recording / reproducing is possible,
Nevertheless, it is possible to provide an optical pickup device and a recording / reproducing device that can secure a sufficient working distance.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an optical pickup device according to an embodiment of the present invention.

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

FIG. 3 is a diagram showing an example of a refractive index distribution variable element that can be used as spherical aberration correction means of the optical pickup device of FIGS.

FIG. 4 is an optical path diagram relating to Example 1.

5 is a spherical aberration diagram for Example 1. FIG.

FIG. 6 is an optical path diagram of Example 2.

7 is a spherical aberration diagram for Example 2. FIG.

FIG. 8 is an optical path diagram of Example 3.

9 is a spherical aberration diagram for Example 3. FIG.

FIG. 10 is an optical path diagram of Example 4.

FIG. 11 is a spherical aberration diagram for Example 4.

FIG. 12 is an optical path diagram of Example 5.

13 is a spherical aberration diagram for Example 5. FIG.

FIG. 14 is an optical path diagram of Example 6;

FIG. 15 is a spherical aberration diagram for Example 6;

16 is an optical path diagram of Example 7. FIG.

FIG. 17 is a spherical aberration diagram for Example 7.

FIG. 18 is a diagram illustrating the center thickness dc (mm) of the first lens and the thickness dh (mm) of the first lens in the optical axis direction at a height of 0.2 mm from the outermost periphery of the effective diameter.

[Explanation of symbols]

1 Objective lens 2 coupling lens 3 Semiconductor laser (light source) 4 Photodetector 5 Information recording surface of optical information recording medium 5'Protective layer for optical information recording medium 10 2-axis actuator 11 1-axis actuator 12 beam expander

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA13 LA01 PA02 PA03 PA17                       PA18 PB03 QA01 QA05 QA12                       QA14 QA17 QA21 QA22 QA25                       QA33 QA41 QA45 QA46 RA05                       RA12 RA13 UA01                 5D119 AA11 AA22 JA44 JB02 JB04                 5D789 AA11 AA22 JA44 JB02 JB04

Claims (42)

[Claims] 1. An objective lens for recording and / or reproducing of an optical information recording medium, comprising a first lens group, a second lens group, and a third lens group arranged in order from a light source side. And an objective lens having a numerical aperture NA on the optical information recording medium side that satisfies the following expression. 0.60 <NA <0.99 2. An objective lens for recording and / or reproducing of an optical information recording medium, comprising a first lens group having a positive refracting power, a second lens group having a positive refracting power, and a positive lens in order from the light source side. An objective lens having a three-group structure in which a third lens group having a refractive power is arranged, and a value of a numerical aperture NA on the optical information recording medium side satisfies the following expression. 0.60 <NA <0.99 3. The objective lens according to claim 2, wherein the objective lens satisfies the following equation. 0.01 <(X1 ′ + X2 ′ + X3 ′) / (NA ⁴ · f · (1
+ | M |)) <0.10 X1 '= X1 * (n1-1) ³ / f1 X2' = X2 * (n2-1) ³ / f2 X3 '= X3 * (n3-1) ³ / f3 where Xi: a plane that is perpendicular to the optical axis and is in contact with the apex of the surface of the i-th lens group that is closest to the light source, and the outermost periphery of the effective diameter (the surface of the i-th lens group that is closest to the light source on which the marginal ray of NA is incident). The position (upper position) is the difference (mm) in the optical axis direction from the surface of the i-th lens group closest to the light source, and is positive when measured in the direction of the optical information recording medium with the tangential plane as a reference. The case of measurement is negative (i = 1, 2, 3) ni: Refractive index at the wavelength of the light source of the i-th lens group (i = 1, 2, 3) fi: Focal length of the i-th lens group (mm ) (I = 1,
2, 3) f: focal length of the objective lens at an infinite object (mm) m: imaging magnification of the objective lens 4. A paraxial radius of curvature r1 (mm) of the surface of the first lens group closest to the light source, a paraxial radius of curvature r2 (mm) of the surface of the second lens group closest to the light source, and The objective lens according to claim 1 or 2, wherein the values of the paraxial radius of curvature r3 (mm) of the surface closest to the light source of the three lens groups satisfy the following expressions, respectively. 0.30 <r1 / ((n1-1) · f1) <1.40 0.20 <r2 / ((n2-1) · f2) <1.20 0.50 <r3 / ((n3-1)・ F3) <1.50 5. A paraxial power P1 (m of the first lens group
m ⁻¹ ), paraxial power P2 (mm) of the second lens group
⁻¹ ), paraxial power P3 (m of the third lens group)
m ⁻¹ ), and the paraxial power P (mm) of the objective lens
The objective lens according to any one of claims 2 to 4, wherein each value of ^-1 ) satisfies the following equation. 0.1 <P1 / P <0.5 0.1 <P2 / P <0.6 0.6 <P3 / P <1.4 6. An objective lens for recording and / or reproducing of an optical information recording medium, wherein a first lens group having a negative refracting power, a second lens group having a positive refracting power, and a positive lens in order from a light source side. An objective lens having a three-group structure in which a third lens group having a refractive power is arranged, and a value of a numerical aperture NA on the optical information recording medium side satisfies the following expression. 0.60 <NA <0.99 7. The objective lens according to claim 6, wherein the objective lens satisfies the following equation. 0.02 <(X1 ′ + X2 ′ + X3 ′) / (NA ⁴ · f · (1
+ | M |)) <0.12 X1 '= X1 * (n1-1) ³ / f1 X2' = X2 * (n2-1) ³ / f2 X3 '= X3 * (n3-1) ³ / f3 where Xi: a plane that is perpendicular to the optical axis and is in contact with the apex of the surface of the i-th lens group that is closest to the light source, and the outermost periphery of the effective diameter (the surface of the i-th lens group that is closest to the light source on which the marginal ray of NA is incident). The position (upper position) is the difference (mm) in the optical axis direction from the surface of the i-th lens group closest to the light source, and is positive when measured in the direction of the optical information recording medium with the tangential plane as a reference. The case of measurement is negative (i = 1, 2, 3). ni: Refractive index of the i-th lens group at the wavelength of the light source (i = 1, 2, 3) fi: Focal length (mm) of the i-th lens group (i = 1,
2, 3) f: focal length of the objective lens at an infinite object (mm) m: imaging magnification of the objective lens 8. A paraxial radius of curvature r1 (mm) of the surface of the first lens group closest to the light source, a paraxial radius of curvature r2 (mm) of the surface of the second lens group closest to the light source, and The objective lens according to claim 6 or 7, wherein the values of the paraxial radius of curvature r3 (mm) of the surface closest to the light source of the three lens groups satisfy the following expressions, respectively. −1.00 <r1 / ((n1-1) · f1) <0.00 0.30 <r2 / ((n2-1) · f2) <1.70 0.50 <r3 / ((n3-1 ) ・ F3) <1.50 9. The paraxial power P1 (m of the first lens group
m ⁻¹ ), paraxial power P2 (mm) of the second lens group
⁻¹ ), paraxial power P3 (m of the third lens group)
m ⁻¹ ), and the paraxial power P (mm) of the objective lens
The objective lens according to any one of claims 6 to 8, wherein the values of ( ^-1 ) satisfy the following expressions. -0.5 <P1 / P <0.0 0.3 <P2 / P <1.2 0.6 <P3 / P <1.4 10. The thickness d1 of the first lens group on the optical axis.
The objective lens according to claim 6, wherein (mm) satisfies the following equation. 0.8 <d1 / f <1.7 11. The objective lens according to claim 1, wherein a value of a numerical aperture NA on the optical information recording medium side of the objective lens satisfies the following expression. 0.85 <NA <0.99 12. The objective lens is at least 2 of a surface of the first lens group that is closest to the light source, a surface of the second lens group that is closest to the light source, and a surface of the third lens group that is closest to the light source. The objective lens according to any one of claims 1 to 11, wherein two surfaces are aspherical surfaces. 13. The objective lens is corrected for spherical aberration corresponding to the thickness of a protective layer that protects an information recording surface of an optical information recording medium, and the thickness t (mm) of the protective layer has a value The objective lens according to any one of claims 1 to 12, which satisfies the following expression. 0.0 ≦ t ≦ 0.15 14. The objective lens for an optical pickup device having a light source having a wavelength λ, wherein the value of the wavelength λ satisfies the following equation. Item 1. The objective lens according to item 1. 350 nm <λ <650 nm 15. The objective lens according to claim 1, wherein at least one surface of the objective lens is a diffractive surface having a ring-shaped diffractive structure. 16. The objective lens is formed of an optical plastic material.
The objective lens according to any one of 1. 17. An objective lens for recording and / or reproducing on an optical information recording medium, which is a three-group structure in which a first lens group, a second lens group, and a third lens group are arranged in order from the light source side. And the surface of the third lens group closest to the light source is an aspherical surface, and the numerical aperture NA on the side of the optical information recording medium satisfies the following expression. 0.60 <NA <0.99 18. The first lens group has a positive refractive power,
The second lens group has a negative refractive power, the third lens group has a positive refractive power, the Abbe number νd1 of the first lens group at the d-line and the Abbe number of the second lens group at the d-line. 18. The objective lens according to claim 17, wherein the value of the number νd2 satisfies the following equation. νd1> νd2 19. The objective lens according to claim 18, wherein the objective lens satisfies the following equation. νd1> 55 νd2 <40 20. The first lens group has a negative refractive power,
The second lens group has a positive refractive power, the third lens group has a positive refractive power, and the Abbe number νd1 of the first lens group at the d line and the Abbe number of the second lens group at the d line. 18. The objective lens according to claim 17, wherein the value of the number νd2 satisfies the following equation. νd1 <νd2 21. The objective lens according to claim 20, wherein the objective lens satisfies the following equation. νd1 <40 νd2> 55 22. The first lens group and the second lens group are both composed of a single lens, and the first lens group and the second lens group are cemented together. 22. The objective lens according to any one of 21 to 21. 23. The objective lens according to claim 17, wherein a value of a numerical aperture NA on the optical information recording medium side of the objective lens satisfies the following expression. 0.75 <NA <0.99 24. The objective lens comprises a distance d ₂₃ (mm) on the optical axis between the second lens group and the third lens group,
24. The value of the distance .SIGMA.d (mm) on the optical axis from the surface vertex of the lens surface closest to the light source to the surface vertex of the lens surface closest to the optical information recording medium satisfies the following expression.
The objective lens according to any one of 1. 0.05 <d ₂₃ /Σd<0.35 25. The objective lens according to claim 24, wherein the objective lens satisfies the following equation. 0.10 <d ₂₃ /Σd<0.30 26. The objective lens is an objective lens for an optical pickup device having a light source of wavelength λ, and the value of the wavelength λ satisfies the following equation.
26. The objective lens according to any one of items 25 to 25. 350 nm <λ <650 nm 27. An objective lens for recording and / or reproducing of an optical information recording medium, comprising: a first lens having a positive refractive power in order from a light source side, and a negative lens provided adjacent to the first lens. Second with refractive power
A three-lens structure in which a lens and a third lens having a positive refractive power are arranged is provided, and the optical surface on the light source side of the first lens and the optical surface on the light source side of the third lens are both aspherical surfaces. Objective lens characterized in that 28. Abbe number νd of d-line of said first lens
28. The objective lens according to claim 27, wherein the Abbe number νd2 of the first lens and the d-line of the second lens satisfy the following equation. νd1> 55 νd2 <40 29. The objective lens according to claim 27, wherein the first lens and the second lens are cemented together. 30. The objective lens according to claim 27, wherein the value of the numerical aperture NA of the objective lens on the optical information recording medium side satisfies the following expression. 0.75 <NA <0.99 31. A center thickness dc (m of the first lens
m) and the value of the thickness dh (mm) in the optical axis direction of the first lens at a height of 0.2 mm from the outermost periphery of the effective diameter satisfy the following expression. Item 1. The objective lens according to Item 1. 0.1 <dh / dc <0.8 32. The objective lens is an objective lens for an optical pickup device having a light source of wavelength λ, and the value of the wavelength λ satisfies the following expression. Item 1. The objective lens according to item 1. 350 nm <λ <650 nm 33. A paraxial radius of curvature r1 (mm) of an optical surface of the first lens on the light source side, and a focal length f of the third lens.
3 (mm), and the focal length f of the entire objective lens system
The value of (mm) satisfies the following equation:
33. The objective lens according to any one of 7 to 32. 0.7 <r1 / f <1.8 0.5 <f3 / f <1.2 34. An objective lens for recording and / or reproducing of an optical information recording medium, comprising: a first lens having a negative refracting power in order from a light source side, and a positive lens provided adjacent to the first lens. Second with refractive power
A three-lens structure in which a lens and a third lens having a positive refractive power are arranged is provided, and the optical surface on the light source side of the first lens and the optical surface on the light source side of the third lens are both aspherical surfaces. Objective lens characterized in that 35. Abbe number νd of d-line of the first lens
35. The objective lens according to claim 34, wherein the Abbe number νd2 of the first lens and the d-line of the second lens satisfy the following equation. νd1 <40 νd2> 55 36. The objective lens according to claim 34, wherein the first lens and the second lens are cemented together. 37. The objective lens according to claim 34, wherein the value of the numerical aperture NA of the objective lens on the optical information recording medium side satisfies the following expression. 0.75 <NA <0.99 38. The center thickness dc (m of the second lens
m), and the value of the thickness dh (mm) in the optical axis direction of the second lens at a height of 0.2 mm from the outermost periphery of the effective diameter satisfy the following expression. Item 1. The objective lens according to Item 1. 0.1 <dh / dc <0.8 39. The objective lens for an optical pickup device having a light source of wavelength λ, wherein the value of the wavelength λ satisfies the following expression. Item 1. The objective lens according to item 1. 350 nm <λ <650 nm 40. The distance d ₂₃ (mm) on the optical axis between the second lens and the third lens, the optical surface closest to the optical information recording medium from the surface vertex of the optical surface closest to the light source of the objective lens. On the optical axis to the surface apex of Σd (mm), the third
The focal length f3 (mm) of the lens, the focal length f (mm) of the entire objective lens system, the paraxial radius of curvature r3 (mm) of the optical surface of the second lens on the light source side, and the optical information of the second lens Paraxial radius of curvature r4 (mm) of the optical surface on the recording medium side
34 to 3 wherein the value of satisfies the following equation:
Item 9. The objective lens according to any one of Item 9. _{0.15 <d 23 /Σd<0.40 0.5 <f3} / f <1.2 0.1 <(r4 + r3) / (r4-r3) <1.2 41. A light source and a condensing optical system including an objective lens for condensing a light beam emitted from the light source onto an information recording surface of an optical information recording medium, An optical pickup device for recording and / or reproducing information on the optical information recording medium by detecting reflected light, comprising the objective lens according to any one of claims 1 to 40 as the objective lens. An optical pickup device characterized by the above. 42. An audio and / or image recording device, and / or an audio and / or image reproducing device, comprising the optical pickup device according to claim 41.