JP4535212B2 - Objective lens for recording / reproducing optical information recording media - Google Patents

Description

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。
【００１１】

【００１２】

【００１３】
【発明の効果】
この発明の光ピックアップ用の対物レンズは、透明材料による一体成形により、他の部材又は追加の工程を必要とせずに、対物レンズに、段差を形成することで光情報記録媒体上の情報記録の記録再生に必要な集光光束を得ることが出来る絞り機能を備えており、光ピックアップの小型化、軽量化、低コスト化を実現することが出来たものである。
【図面の簡単な説明】
【図１】本発明の光ピックアップ装置の記録再生用対物単レンズの１実施例の構成を示す概念図である。
【図２】本発明の光ピックアップ装置の記録再生用対物単レンズの１実施例の段差部の構成を示す部分拡大図である。
【図３】本発明の光ピックアップ装置の記録再生用対物単レンズの１実施例の球面収差図である。
【図４】本発明の光ピックアップ装置の記録再生用対物単レンズの他の実施例の球面収差図である。
【図５】従来の光ピックアップ装置の構成を示す概念図である。
【符号の説明】
１，１１ 対物レンズ ２，１２ ボビン部材
３ 段差部 １３ 絞り[0001]
[Industrial application fields]
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.
[0002]
[Prior art]
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.
[0003]
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. Further, 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.
[0004]
[Problems to be solved by the invention]
The present invention provides a diaphragm that can obtain a condensed light beam necessary for recording / reproducing information 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 provides a function is to be obtained.
[0005]
[Means for Solving the Problems]
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 The step 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 is provided with a step which is a portion where the normal direction of the refractive surface changes discontinuously, As the light beam which has passed through the refractive surface outside of the above step in the direction perpendicular to the optical axis by the step is not condensing on the information recording surface of all of the optical information recording medium used in the optical pickup device, an effective recording Flux diameter by being restricted to the boundary of the step, characterized in that the information recording on the optical information recording medium even without squeezing the bobbin is recordable reproduction. 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.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
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: Δ / λ <200/8 where λ is the wavelength of the light source
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 °.
[0007]
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.
[0008]
At this time, it is desirable that the spherical aberration caused by the surface shape g (h) is lower than the spherical aberration caused by the surface shape f (h). 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 the detection of the erroneous focus position, the spherical aberration caused by the surface shape g (h) is more than the spherical aberration of the surface shape f (h). Is often desirable. 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.
[0009]
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.
[0010]
【Example】
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 expression that expresses the aspherical 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).
[0011]

[0012]

[0013]
【The invention's effect】
The objective lens for an optical pickup according to the present invention is capable of recording information on an optical information recording medium by forming a step in the objective lens by integral molding with a transparent material without requiring other members or additional steps. It has a diaphragm function that can obtain the condensed light flux necessary for recording and reproduction, and the optical pickup can be reduced in size, weight, and cost.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a configuration of one embodiment of a recording / reproducing objective single lens of an optical pickup device of the present invention.
FIG. 2 is a partially enlarged view showing a configuration of a step portion of one embodiment of a recording / reproducing objective single lens of the optical pickup device of the present invention.
FIG. 3 is a spherical aberration diagram of one example of a recording / reproducing objective single lens of the optical pickup device of the present invention.
FIG. 4 is a spherical aberration diagram of another example of the recording / reproducing objective single lens of the optical pickup device of the present invention.
FIG. 5 is a conceptual diagram showing a configuration of a conventional optical pickup device.
[Explanation of symbols]
1,11 Objective lens 2,12 Bobbin member 3 Stepped portion 13 Aperture

Claims (8)

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 of 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 Is provided at a position corresponding to the numerical aperture NA on the optical information recording medium side where the normal direction of the refractive surface changes discontinuously, and the refractive surface outside the step in the direction perpendicular to the optical axis. The light beam that has passed through is not condensed on the information recording surface of all the optical information recording media used in the optical pickup device, and the effective light beam diameter for recording and reproduction is restricted at the step, thereby restricting it to the bobbin. But An objective lens for recording / reproducing an optical information recording medium, wherein the information recording on the optical information recording medium can be recorded / reproduced without the need .   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 stepped surface has a shape without undercut. 4. 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 wavelength of the light source is λ.
Δ / λ <200/8
An objective lens for recording / reproducing of an optical information recording medium. 5. The recording / reproducing objective lens according to claim 1, wherein a function representing a surface shape of the optical axis is expressed by f (h) and a step of the step relative to a portion where the normal direction of the refractive surface changes discontinuously. When the function representing the outer surface shape is g (h),
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.   6. In the recording / reproducing objective lens according to claim 1, the spherical aberration caused by the surface shape g (h) is lower than the spherical aberration caused by the surface shape f (h). An objective lens for recording / reproducing optical information recording media.   6. The recording / reproducing objective lens according to claim 1, wherein the spherical aberration caused by the surface shape g (h) is more than the spherical aberration caused by the surface shape f (h). An objective lens for recording / reproducing optical information recording media.   8. 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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