JP2005156719A - Objective lens for optical pickup device, optical pickup device, optical information recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens for an optical pickup device which can easily be manufactured in spite of a short focal distance and can record and/or reproduce information with high density, and to provide an optical pickup device and an optical information recording/reproducing apparatus. <P>SOLUTION: If the focal distance f of the objective lens is the upper limit of formula (1), that is, shorter than 1.3 mm, the optical pickup device can be downsized. If it is the lower limit, that is, longer than 0.41 mm, molding can be facilitated. In addition, if a value d/f is the upper limit of formula (2), that is, less than 2.1, the objective lens can obtain a sufficient operation distance (working distance), which does not interfere with the protective layer protecting the information recording face of an optical information recording medium. On the other hand, if the value d/f is the lower limit, that is, more than 1.0, the thickness of the peripheral part around the effective diameter of the objective lens in the axial direction is not too thin. Accordingly, molding can be facilitated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device, and more particularly to an objective lens, an optical pickup device, and an optical information recording / reproducing device for an optical pickup device that can be reduced in size.

  With the recent increase in the density of optical disks, objective lenses used for recording / reproducing on these high-density optical disks are likely to have a high numerical aperture (NA) due to the demand for a smaller focused spot. It has become. For example, in a so-called BD (Bul-One Ray Disk) using a blue-violet semiconductor laser light source with a wavelength (λ) of 405 nm, NA 0.85 is used in order to achieve high-density information recording of the same size as a CD and 20 GB or more. Objective lens is needed.

By the way, a portable information recording / reproducing apparatus that can use a BD or the like as an optical disk has been developed. Such an information recording / reproducing apparatus is required to have a thinner body on the assumption that it is carried. Therefore, it is desirable that the optical pickup device mounted on the information recording / reproducing apparatus is further downsized. In such a case, if the focal length of the objective lens of the optical pickup device can be shortened, the distance from the optical disk can be reduced. On the other hand, Patent Document 1 describes an objective lens having a short focal length.
JP 2003-85806 A

  However, as the focal length of the objective lens decreases, the radius of curvature of the optical surface tends to decrease, and the effective diameter outer peripheral portion (also referred to as the edge thickness or edge thickness) tends to decrease. This tendency becomes more prominent because the radius of curvature of the optical surface on the laser light source side decreases as the numerical aperture NA of the objective lens increases. When the outer peripheral portion of the effective diameter is thinned, the flange portion provided at the peripheral portion of the optical function region is thinned, so that it may be difficult to manufacture particularly with a glass lens or the like. However, Patent Document 1 does not disclose or suggest any demerit that the outer peripheral portion of the effective diameter is thin and countermeasures thereof.

  The present invention has been made in view of the above problems, and the thickness of the outer peripheral portion of the effective diameter in the direction of the optical axis is such that the focal length is short and the numerical aperture NA is large and can be easily manufactured. It is an object of the present invention to provide an objective lens, an optical pickup device, and an optical information recording / reproducing device for an optical pickup device capable of recording and / or reproducing high-density information.

The objective lens according to claim 1 includes a light source and a condensing optical system including the objective lens, and the condensing optical system collects a light beam from the light source on an information recording surface of an optical information recording medium. In an objective lens for an optical pickup device capable of recording and / or reproducing information by making it light,
When it has at least one aspherical surface, the focal length is f (mm), and the distance on the optical axis of the optical surface is d (mm), the equations (1) and (2) are satisfied, and the one-group configuration is used. It is characterized by being.
0.41 <f <1.3 (1)
1.0 <d / f <2.1 (2)

  If the focal length f of the objective lens is set to the upper limit of the formula (1), that is, less than 1.3 mm, the optical pickup device can be miniaturized, and if the lower limit, that is, greater than 0.41 mm, the molding can be easily performed. . Further, if the value d / f is set to the upper limit of the expression (2), that is, less than 2.1, a sufficient working distance (working distance) is provided so that the objective lens does not interfere with the protective layer protecting the information recording surface of the optical information recording medium. On the other hand, if it is larger than the lower limit, that is, 1.0, the thickness in the optical axis direction at the outer peripheral portion of the objective lens is not excessively thin and can be easily molded.

The objective lens for an optical pickup device according to claim 2 is characterized in that, in the invention according to claim 1, the objective lens further satisfies the expression (3). This is preferable because the thickness of the outer peripheral portion in the optical axis direction can be made thinner than the effective diameter at a higher level.
1.28 <d / f <1.60 (3)

The objective lens for an optical pickup device according to claim 3 is characterized in that, in the invention according to claim 1 or 2, when the refractive index at the d-line of the objective lens is nd, equation (4) is satisfied. And
1.50 <nd <1.73 (4)

  In general, when the focal length and the numerical aperture NA are equal, the larger the refractive index, the larger the paraxial radius of curvature of the optical surface. When the refractive index nd of the objective lens is larger than the lower limit of the expression (4), the paraxial radius of curvature can be increased, so that the distance in the optical axis direction at the outer peripheral portion having the same effective diameter can be increased. In general, when the refractive index is large, the dispersion tends to increase. In a high-density optical information recording / reproducing apparatus using a blue-violet semiconductor laser light source having a wavelength of 450 nm or less, the wavelength dependency of the refractive index of the optical component increases, but the refractive index nd is smaller than the upper limit of the expression (4). In this case, there is a merit that chromatic aberration does not become too large because dispersion does not become too large.

According to a fourth aspect of the present invention, there is provided an objective lens for an optical pickup device according to the third aspect of the present invention, wherein the paraxial radius of curvature of the optical surface on the light source side of the objective lens is r1 and the optical surface on the optical information recording medium side. When the paraxial radius of curvature is r2, Equation (5) is satisfied.
0.2 <(r2 + r1) / (r2-r1) <0.4 (5)

  The optical surface shape that optimally corrects the spherical aberration is determined by the refractive index nd of the objective lens. When the refractive index nd exists in a range that satisfies the equation (4), the paraxial curvature radius of the two optical surfaces satisfies the equation (5), so that the spherical aberration can be optimally corrected.

  An objective lens for an optical pickup device according to a fifth aspect of the present invention is the optical system according to any one of the first to fourth aspects, wherein the objective lens is made of glass. In general, glass has a higher refractive index than plastic, and glass objective lenses have a larger absolute value of the radius of curvature of the optical surface than plastic objective lenses. The thickness in the axial direction is increased, facilitating manufacturing.

The objective lens for an optical pickup device according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein a wavelength of a light source of the optical pickup device on which the objective lens is mounted is λ (nm), When the numerical aperture of the objective lens is NA, the expression (6) and the expression (7) are satisfied. Therefore, light that can record and / or reproduce high-density information by using the objective lens. An optical pickup device mounted on the information recording / reproducing apparatus can be realized.
λ ≦ 450nm (6)
0.80 ≤ NA ≤ 0.95 (7)

  An objective lens for an optical pickup device according to a seventh aspect of the present invention is the optical lens according to any one of the first to sixth aspects, wherein the optical functional region (a region through which a high bundle used for recording and / or reproducing information passes). A flange portion extending in a direction substantially perpendicular to the optical axis is formed at the peripheral portion, and the minimum value of the thickness of the flange portion in the optical axis direction is 0.20 mm or more. An easy objective lens can be realized.

The optical pickup device according to claim 8 includes a light source and a condensing optical system including an objective lens, and the condensing optical system transmits a light beam from the light source to an information recording surface of an optical information recording medium. In an optical pickup device capable of recording and / or reproducing information by condensing,
The objective lens has at least one aspherical surface, satisfies a formula (1) and a formula (2) when the focal length is f (mm) and the distance on the optical axis of the optical surface is d (mm). 1 group structure. The effect of the present invention is the same as that of the invention described in claim 1.
0.41 <f <1.3 (1)
1.0 <d / f <2.1 (2)

According to a ninth aspect of the present invention, in the invention according to the eighth aspect, the objective lens further satisfies the expression (3). The effect of the present invention is the same as that of the invention described in claim 2.
1.28 <d / f <1.60 (3)

An optical pickup device according to a tenth aspect is characterized in that, in the invention according to the eighth or ninth aspect, when the refractive index at the d-line of the objective lens is nd, the expression (4) is satisfied. The effect of the present invention is the same as that of the invention described in claim 3.
1.50 <nd <1.73 (4)

The optical pickup device according to an eleventh aspect is the optical pickup device according to the tenth aspect, wherein the paraxial radius of curvature of the optical surface on the light source side of the objective lens is r1, and the paraxial radius of curvature of the optical surface on the optical information recording medium side. When r is r2, the expression (5) is satisfied. The effect of the present invention is the same as that of the invention described in claim 4.
0.2 <(r2 + r1) / (r2-r1) <0.4 (5)

  According to a twelfth aspect of the present invention, in the invention according to any one of the eighth to eleventh aspects, the objective lens is made of glass. The effect of the present invention is the same as that of the invention described in claim 5.

An optical pickup device according to a thirteenth aspect is the invention according to any one of the eighth to twelfth aspects, wherein the wavelength of the light source of the optical pickup device on which the objective lens is mounted is λ (nm), and the aperture of the objective lens When the number is NA, the expression (6) and the expression (7) are satisfied. The effect of the present invention is the same as that of the invention described in claim 6.
λ ≦ 450nm (6)
0.80 ≤ NA ≤ 0.95 (7)

  The optical pickup device according to a fourteenth aspect is the invention according to any one of the eighth to thirteenth aspects, wherein the objective lens has a flange portion extending in a direction substantially perpendicular to the optical axis at a peripheral portion of the optical function region. The minimum thickness of the flange portion in the optical axis direction is 0.20 mm or more. The effect of the present invention is the same as that of the invention described in claim 7.

  An optical information recording / reproducing apparatus according to a fifteenth aspect is equipped with the optical pickup apparatus according to any one of the eighth to fourteenth aspects, and records information on the optical information recording medium and is recorded on the optical information recording medium. It is characterized in that at least one of the reproduced information can be executed.

  In this specification, the objective lens is a lens having a condensing function that is disposed so as to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. As expected. Accordingly, in this specification, the numerical aperture NA on the optical information recording medium side (image side) of the objective lens refers to the numerical aperture NA of the surface of the objective lens located closest to the optical information recording medium.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an optical pickup apparatus (optical information recording / reproducing apparatus) 10 according to an embodiment of the present invention, which can record / reproduce information with respect to an optical disc (also referred to as an optical information recording medium) such as a BD. It is. In FIG. 1, the optical axis is L.

  In FIG. 1, a light beam emitted from a semiconductor laser 11 (wavelength λ = 380 nm to 450 nm) as a light source passes through a beam splitter 12, passes through a quarter wavelength plate 16, and is collimated by a collimator 13. After that, the light passes through the diaphragm 18 and enters the objective lens 50 which is a single glass lens. The light beam that has passed through the objective lens 50 passes through the protective layer 22 of the optical disc 20 and is condensed on the information recording surface 21 to form a condensing spot.

  The light beam modulated and reflected by the information pits on the information recording surface is transmitted again through the objective lens 50, the diaphragm 18, the collimator 13, and the quarter wavelength plate 16, reflected by the beam splitter 12, and non-reflected by the cylindrical lens 17. A point aberration is given, and the light passes through the sensor lens 14 and enters the light receiving surface of the photodetector 15. Therefore, a read signal of information recorded on the optical disk 20 is obtained using the output signal of the photodetector 15.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape of the spot and a change in position on the photodetector 15. Based on this detection, the objective lens 50 is moved so that the biaxial actuator 19 appropriately forms an image of the light beam from the semiconductor laser 11 on the information recording surface 21 of the optical disk 20. The objective lens 50 has a flange 53 to be attached to the bobbin at a peripheral portion outside the effective diameter.

  Since the objective lens 50 is an objective lens having an NA of 0.85 with a small focal length by satisfying the above-mentioned expressions (1) to (4), the edge thickness is sufficiently secured. The thickness in the direction is 0.2 mm or more and can be easily manufactured.

  Hereinafter, Example 1 and Example 2 of the objective lens that can be used in the above-described embodiment will be described. Both surfaces of the objective lens are aspherical surfaces represented by [Equation 1]. Here, Z is an axis in the optical axis direction, h is an axis perpendicular to the optical axis, r is a paraxial radius of curvature, κ is a conical coefficient, A is an aspheric coefficient, and P is an aspheric power.

3 and 4 are sectional views of the objective lenses according to the first and second embodiments. Both examples are glass lenses. Tables 1 and 2 show the lens data of Example 1 and Example 2, respectively. NA is the numerical aperture, m is the magnification, f is the focal length, λ is the design wavelength, and Nλ is the refractive index at the design wavelength. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).

Table 3 shows the values of the equations in the claims of Examples 1 and 2. Here, the objective lens of Example 1 that satisfies the expressions (1), (2), and (3) has a sufficiently large edge thickness even though it has a small focal length of NA 0.85. The thickness d _FL of the flange portion is sufficiently thick as 0.51 mm and can be easily manufactured. Similarly, the objective lens of Example 2 that satisfies the expressions (1), (2), and (3) has a sufficiently large edge thickness while being an objective lens with a small focal length of NA 0.85. The thickness d _FL of the flange portion is sufficiently thick as 0.25 mm and can be easily manufactured. Therefore, since the objective lens of this embodiment has a sufficient flange thickness and a high numerical aperture NA, it is suitable for an optical pickup device capable of recording and / or reproducing compact and high-density information.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is a schematic block diagram of the optical pick-up apparatus concerning this Embodiment. FIG. 3 is a cross-sectional view of the objective lens of Example 1. 6 is a cross-sectional view of an objective lens according to Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up apparatus 11 Light source 12 Beam splitter 13 Collimator 14 Sensor lens 15 Photo detector 16 1/4 wavelength plate 17 Cylindrical lens 18 Aperture 19 Actuator 20 Optical disk 50 Objective lens

Claims (15)

A light source and a condensing optical system including an objective lens, and the condensing optical system condenses the light beam from the light source on the information recording surface of the optical information recording medium, thereby recording and / or recording information. Or, in an objective lens for an optical pickup device that can be reproduced,
When it has at least one aspherical surface, the focal length is f (mm), and the distance on the optical axis of the optical surface is d (mm), the equations (1) and (2) are satisfied, and the one-group configuration is used. An objective lens for an optical pickup device, comprising:
0.41 <f <1.3 (1)
1.0 <d / f <2.1 (2) Furthermore, (3) Formula is satisfy | filled, The objective lens for optical pick-up apparatuses of Claim 1 characterized by the above-mentioned.
1.28 <d / f <1.60 (3) 3. The objective lens for an optical pickup device according to claim 1, wherein when the refractive index at the d-line of the objective lens is nd, the expression (4) is satisfied.
1.50 <nd <1.73 (4) 4. The expression (5) is satisfied, where r1 is a paraxial curvature radius of an optical surface on the light source side of the objective lens and r2 is a paraxial curvature radius of an optical surface on the optical information recording medium side. Objective lens for the optical pickup device as described in 1.
0.2 <(r2 + r1) / (r2-r1) <0.4 (5)   The objective lens for an optical pickup device according to any one of claims 1 to 4, wherein the objective lens is made of glass. The expression (6) and the expression (7) are satisfied, where λ (nm) is a wavelength of a light source of an optical pickup device on which the objective lens is mounted, and NA is a numerical aperture of the objective lens. The objective lens for optical pick-up apparatuses as described in any one of 1-5.
λ ≦ 450nm (6)
0.80 ≤ NA ≤ 0.95 (7)   The objective lens has a flange portion extending in a direction substantially perpendicular to the optical axis at the periphery of the optical function region, and the minimum thickness of the flange portion in the optical axis direction is 0.20 mm or more. An objective lens for an optical pickup device according to any one of claims 1 to 6. A light source and a condensing optical system including an objective lens, and the condensing optical system condenses the light beam from the light source on the information recording surface of the optical information recording medium, thereby recording and / or recording information. Alternatively, in an optical pickup device that can perform reproduction,
The objective lens has at least one aspherical surface, satisfies a formula (1) and a formula (2) when the focal length is f (mm) and the distance on the optical axis of the optical surface is d (mm). An optical pickup device having a one-group configuration.
0.41 <f <1.3 (1)
1.0 <d / f <2.1 (2) The optical pickup device according to claim 8, wherein the objective lens satisfies Formula (3).
1.28 <d / f <1.60 (3) 10. The optical pickup device according to claim 8, wherein when the refractive index at the d-line of the objective lens is nd, the expression (4) is satisfied.
1.50 <nd <1.73 (4) 11. The expression (5) is satisfied, where r1 is a paraxial radius of curvature of the optical surface on the light source side of the objective lens, and r2 is a paraxial radius of curvature of the optical surface on the optical information recording medium side. The optical pickup device described in 1.
0.2 <(r2 + r1) / (r2-r1) <0.4 (5)   The optical pickup device according to claim 8, wherein the objective lens is made of glass. The expression (6) and the expression (7) are satisfied, where λ (nm) is a wavelength of a light source of an optical pickup device on which the objective lens is mounted, and NA is a numerical aperture of the objective lens. The optical pick-up apparatus as described in any one of 8-12.
λ ≦ 450nm (6)
0.80 ≤ NA ≤ 0.95 (7)   The objective lens has a flange portion extending in a direction substantially perpendicular to the optical axis at the periphery of the optical function region, and the minimum thickness of the flange portion in the optical axis direction is 0.20 mm or more. The optical pickup device according to claim 8, wherein: The optical pickup device according to any one of claims 8 to 14 is mounted, and at least one of recording of information on the optical information recording medium and reproduction of information recorded on the optical information recording medium can be executed. An optical information recording / reproducing apparatus.

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