JP2010170693A - Recording/reproducing objective lens of optical information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens of an optical pickup that is integrally molded with a bobbin section to regulate the diameter of a condensed light flux. <P>SOLUTION: A step 3 is formed in a bent surface S1 on a light source side of an objective lens 1 integrally molded with a bobbin 2 at a location on the side of an optical information recoding medium, which corresponds to a numerical aperture NA to be required according to a laser light source wavelength and an information recording density, the bent surface having a discontinuous change in normal direction. Light passing outside the discontinuous section 3 of the bent surface is not focused on a light focusing point where the light passing through the inside thereof is focused. The light flux diameter effective for recording and reproducing is regulated by the discontinuous section 3 to form a condensed light beam with a predetermined numerical aperture NA. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique. The present invention relates to an objective lens for recording / reproduction of an optical pickup device for an optical information recording medium, particularly an optical information recording in which a portion for restricting the diameter of a condensed light beam is integrally provided at a position corresponding to a required numerical aperture NA on the optical information recording medium side. The present invention relates to a recording / reproducing objective lens for a medium.

  A laser light source, an objective lens having a positive refractive power for condensing an almost no-aberration light beam from the laser light source on the information recording surface via the transparent substrate of the optical information recording medium, and the objective lens reflected by the information recording surface In recent years, optical pickup devices for optical information recording media having a light receiving means for receiving a light beam that has passed through a lens are required to be particularly small, light, and low in cost. In order to meet such a demand, the objective lens is usually a single lens, and as shown in FIG. 5, the molded lens 11 also serves as a bobbin for a coil used for driving such as focusing. A structure that adheres to the member 12 is often used. The objective lens requires a certain numerical aperture NA on the optical information recording medium side in accordance with the wavelength of the laser light source and the information recording density, and in order to obtain a condensed light beam diameter corresponding to this numerical aperture, Is provided with a diaphragm 13 protruding so as to cover the surface of the objective lens 11 up to a necessary portion.

  In order to further reduce the size and weight of the objective lens, there has been proposed one in which the objective lens and a bobbin are integrally formed (for example, JP-A-61-148637). However, in such an objective lens, an attempt to integrally mold the diaphragm 13 as shown in FIG. 5 with the objective lens 11 is impossible because it cannot be removed from the mold. In addition, forming the diaphragm as a separate body and incorporating it in the objective lens complicates the process and goes against the object of cost reduction. In addition, when the diaphragm is incorporated separately, the gap between the diaphragm and the refracting surface of the lens is likely to be generated. However, when this gap is present, the incident light becomes more transmitted as a result of passing through the periphery of the lens. There is a problem.

Japanese Patent Laid-Open No. 61-148637 “Objective Lens Driving Device for Optical Information Processing Device” Published July 7, 1986

  The present invention is a function capable of obtaining a converged light beam necessary for recording / reproducing information recording on an optical information recording medium on an objective lens without any other member or additional process by integral molding with a transparent material. An objective lens for an optical pickup that gives

  The objective lens for recording / reproducing of the present invention has a positive refracting power for condensing a laser light source and a light beam substantially free of aberration from the laser light source onto an information recording surface via a transparent substrate of an optical information recording medium. And a recording / reproducing objective lens of an optical pickup device of an optical information recording medium having a light receiving means for receiving a light beam reflected by the information recording surface and passed through the objective lens, on the refractive surface on the light source side of the objective lens, Condensing light by providing a portion where the normal direction of the refractive surface changes discontinuously at a position corresponding to the numerical aperture NA on the optical information recording medium side required according to the wavelength of the laser light source and the information recording density. The light beam diameter is regulated. The objective lens is a single lens, and the portion where the normal direction of the refractive surface changes discontinuously is preferably formed on the surface on the light source side. More specifically, as shown in FIG. 1, the step 3 provided on the light source side refractive surface S1 of the objective lens 1 formed integrally with the bobbin 2 ensures the discontinuity in the normal direction. Can be taken greatly. As a result, the light beam that has passed through the refracting surface outside the discontinuous part 3 is not collected at the condensing point of the inner light beam, and the effective light beam diameter for recording and reproduction is regulated by the discontinuous part 3, The collected light has a numerical aperture NA. In the detailed description of the present invention, the discontinuous portion 3 is provided on the refracting surface S1. However, the restricting action of the condensed light beam diameter can be achieved even if the discontinuous portion 3 is provided on the diffraction surface or the reflecting surface. Similarly, in this specification, the “refractive surface” should be understood as including a diffractive surface or a reflective surface.

  The objective lens for an optical pickup according to the present invention is formed by integral molding with a transparent material, and does not require other members or additional steps, and the objective lens has a collection necessary for recording and reproducing information on an optical information recording medium. A function capable of obtaining a light beam is provided, and the optical pickup can be reduced in size, weight, and cost.

It is a conceptual diagram which shows the structure of one Example of the objective lens for recording / reproducing of the optical pick-up apparatus of this invention. It is the elements on larger scale which show the structure of the level | step-difference part of one Example of the objective single lens for recording / reproducing of the optical pick-up apparatus of this invention. FIG. 6 is a spherical aberration diagram of one example of a recording / reproducing objective single lens of the optical pickup device of the present invention. It is a spherical aberration diagram of another example of the objective single lens for recording / reproducing of the optical pickup device of the present invention. It is a conceptual diagram which shows the structure of the conventional optical pick-up apparatus.

Hereinafter, embodiments of the present invention will be described in detail.
More specifically, in the objective lens for recording / reproducing having the discontinuous portion 3, with reference to FIG. 2, when the discontinuous portion is a step 3, the height Δ of the step in the optical axis O direction is: When the light source wavelength is λ
△ / λ <200/8
It is desirable that If the height Δ is larger than that, the sagging of the refracting surface tends to occur at the transition from the refracting surface S1 to the step.
When the outer refracting surface S2 is displaced toward the optical information recording medium as shown in FIG. 2, it is desirable that the angle θ of the step surface with respect to the surface perpendicular to the optical axis O is greater than 90 °. . Thereby, a level | step difference becomes a shape without an undercut, and shaping | molding becomes easy. Conversely, when it is displaced to the optical axis side, it is smaller than 90 °.

In the recording / reproducing objective lens, when h is a height from the optical axis, the portion where the normal direction of the refractive surface changes discontinuously, that is, in the lens of FIG. When the function representing the shape of the side surface S1 is f (h) and the function representing the shape of the surface S2 outside the step is g (h), the differential functions f ′ (h) and g ′ (h) are
f ′ (h) ≠ g ′ (h)
It is necessary to be. If the surface shape is
f ′ (h) = g ′ (h)
If so, the light beam from the outer surface S2 and the light beam from the inner surface S1 are condensed at substantially the same point.

At this time, it is desirable that the spherical aberration caused by the surface shape g (h) is lower than the spherical aberration caused when the surface shape f (h) is extended to the peripheral portion.
In general, the focusing operation of the objective lens performs focusing by approaching from a distant position in order to prevent contact between the objective lens and the transparent substrate. At this time, if the spherical aberration caused by the surface shape g (h) is more over, the focus detection means detects the focus position of the light beam transmitted through the surface S2 before the true focus position. It becomes. However, when the signal processing circuit can avoid detection of this erroneous focus position, the spherical aberration caused by the surface shape g (h) is a spherical surface generated when the surface shape f (h) is extended to the peripheral portion. In many cases, it is desirable to be over in comparison with aberration.
This is because the surface shape that is more over is a surface with a smaller curvature than the surface shape f (h), which is advantageous for securing the peripheral thickness of the objective lens.

The objective lens is integrally formed of a single transparent material including a portion where the normal direction of the refractive surface changes discontinuously.
Needless to say, it is desirable that the objective lens 1 is formed integrally with the bobbin 2. However, even when only the objective lens 1 is molded, the objective lens 1 is superior to the conventional product shown in FIG. Not only does the diaphragm 13 become unnecessary when forming the bobbin, but also the restriction part of the light beam diameter is formed on the refracting surface itself, so that there is no deterioration of aberration even with respect to obliquely incident light.

ただし、ｘは光軸方向の軸、ｈは光軸と垂直方向の軸、光の進行方向を正とし、ｒは近軸曲率半径、κは円錐形数、Ａｊは非球面係数、Ｐｊは非球面のべき数（ただし、Ｐｊ≧３）である。 Examples of the objective lens of the present invention are shown below. In the table, i is a surface number, ri is a radius of curvature, di is a surface interval, and ni is a refractive index. In addition, the equation representing the aspheric shape is

Where x is an axis in the optical axis direction, h is an axis perpendicular to the optical axis, and the light traveling direction is positive, r is a paraxial radius of curvature, κ is a cone number, Aj is an aspheric coefficient, and Pj is non-spherical The power of the spherical surface (where Pj ≧ 3).

[Example 1]
Light source wavelength: 780 nm Focal length: 3.22 mm
Horizontal magnification: -1 / 5.0 Image side numerical aperture: 0.45
i ri di ni
1 (* 1, * 1 ') 2.360 2.55 1.53
2 (* 2) -3.848 1.88 1.0
3 ∞ 1.20
4 ∞
Aspheric data * 1 0 ≦ h ≦ 1.736 (where h is the lens surface height from the optical axis)
κ = −0.65899
A ₁ = −0.19126 × 10 ⁻² P ₁ = 4
A ₂ = −0.42737 × 10 ⁻³ P ₂ = 6
A ₃ = −0.14471 × 10 ⁻⁴ P ₃ = 8
A ₄ = −0.55726 × 10 ⁻⁵ P ₄ = 10
* 1 '1.736 <h (where h is the height of the lens surface from the optical axis)
d ₁ ′ = 2.55 (where d ₁ ′ is the light at the intersection of the optical axis and the surface of the i = 2 surface extending from the i = 1 ′ surface to the optical axis (h = 0) according to the aspherical shape formula) On-axis spacing)
κ = −0.65899
A ₁ = −0.19126 × 10 ⁻² P ₁ = 4
A ₂ = −0.20000 × 10 ⁻³ P ₂ = 6
A ₃ = −0.10000 × 10 ⁻⁴ P ₃ = 8
A ₄ = −0.30000 × 10 ⁻⁵ P ₄ = 10
* 2 κ = -0.9925 × 10
A ₁ = −0.28758 × 10 ⁻² P ₁ = 4
A ₂ = 0.42999 × 10 ⁻⁴ P ₂ = 6
A ₃ = −0.40216 × 10 ⁻⁴ P ₃ = 8
A ₄ = 0.33548 × 10 ⁻⁵ P ⁴ = 10
The spherical aberration diagram of this example is shown in FIG.

[Example 2]
Light source wavelength: 780 nm Focal length: 3.22 mm
Horizontal magnification: -1 / 5.0 Image side numerical aperture: 0.45
i ri di ni
1 (* 1, * 1 ') 2.360 2.55 1.53
2 (* 2) -3.848 1.88 1.0
3 ∞ 1.20
4 ∞
Aspheric data * 1 0 ≦ h ≦ 1.736 (where h is the lens surface height from the optical axis)
κ = −0.65899
A ₁ = −0.19126 × 10 ⁻² P ₁ = 4
A ₂ = −0.42737 × 10 ⁻³ P ₂ = 6
A ₃ = −0.14471 × 10 ⁻⁴ P ₃ = 8
A ₄ = −0.55726 × 10 ⁻⁵ P ₄ = 10
* 1 '1.736 <h (where h is the height of the lens surface from the optical axis)
d ₁ '= 2.557232
(Where d1 ′ is the distance on the optical axis between the intersection of the optical axis and the surface of the optical axis (h = 0) obtained by extending the i = 1 ′ surface up to the optical axis (h = 0) according to the aspherical shape)
κ = −0.65899
A ₁ = −0.19126 × 10 ⁻² P ₁ = 4
A ₂ = −0.20000 × 10 ⁻³ P ₂ = 6
A ₃ = −0.10000 × 10 ⁻⁴ P ₃ = 8
A ₄ = −0.30000 × 10 ⁻⁵ P ₄ = 10
* 2 κ = -0.9925 × 10
A ₁ = −0.28758 × 10 ⁻² P ₁ = 4
A ₂ = 0.42999 × 10 ⁻⁴ P ₂ = 6
A ₃ = −0.40216 × 10 ⁻⁴ P ₃ = 8
A ₄ = 0.33548 × 10 ⁻⁵ P ₄ = 10
The spherical aberration diagram of this example is shown in FIG.

1,11 Objective lens
2,12 Bobbin member 3 Step part 13 Aperture

Claims (9)

  A laser light source, an objective lens having a positive refractive power for condensing an almost no-aberration light beam from the laser light source on the information recording surface via the transparent substrate of the optical information recording medium, and the objective lens reflected by the information recording surface An objective lens for recording / reproduction of an optical pickup device for an optical information recording medium having a light receiving means for receiving a light beam that has passed through a lens, which is necessary according to the wavelength of the laser light source and the information recording density on the refractive surface of the objective lens Optical information recording, characterized in that the diameter of the condensed light beam is regulated by providing a portion where the normal direction of the refracting surface changes discontinuously at a position corresponding to the numerical aperture NA on the optical information recording medium side. Objective lens for recording / reproducing media.   2. The objective lens for recording and reproduction according to claim 1, wherein the objective lens is configured as a single lens, and a portion where the normal direction of the refractive surface changes discontinuously is provided on the light source side surface of the objective lens. An objective lens for recording / reproducing of an optical information recording medium.   3. The recording / reproducing objective lens according to claim 1, wherein the portion where the normal direction of the refracting surface changes discontinuously is a step provided on the refracting surface. Reproduction objective lens.   4. The objective lens for recording / reproducing of an optical information recording medium according to claim 3, wherein the stepped surface has a shape without undercut. 5. The recording / reproducing objective lens according to claim 3, wherein the height Δ of the step in the optical axis direction is set when the light source wavelength is λ.
Δ / λ <200/8
An objective lens for recording / reproducing of an optical information recording medium. 6. A recording / reproducing objective lens according to claim 1, wherein f (h) is a function representing a surface shape on the optical axis side of a portion where the normal direction of the refractive surface changes discontinuously. Where g (h) is the function representing the outer surface shape of
f ′ (h) ≠ g ′ (h)
An objective lens for recording / reproducing of an optical information recording medium.
However, h represents the height from the optical axis.   7. The recording / reproducing objective lens according to claim 1, wherein the spherical aberration caused by the surface shape g (h) is compared with the spherical aberration caused when the surface shape f (h) is extended to the peripheral portion. An objective lens for recording / reproducing an optical information recording medium, wherein the objective lens is under-under.   7. The recording / reproducing objective lens according to claim 1, wherein the spherical aberration caused by the surface shape g (h) is compared with the spherical aberration caused when the surface shape f (h) is extended to the peripheral portion. An objective lens for recording / reproducing of an optical information recording medium, characterized by being over.   9. The recording / reproducing objective lens according to claim 1, wherein the objective lens is integrally formed of a single transparent material including a portion where the normal direction of the refractive surface changes discontinuously. An objective lens for recording / reproducing an optical information recording medium.

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