JP2005285249A - Optical pickup and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which corrects chromatic aberration of an objective lens, a coupling lens, etc., simultaneously, while shaping a beam so as to fully demonstrate a recording/reproducing performance and which is made small-sized. <P>SOLUTION: This optical pickup is equipped with a semiconductor laser 1, a beam shaping lens 2 constituted of one or more lenses having different magnifications in the vertical and horizontal directions on an image plane, the coupling lens 3 for making a radial luminous flux to the nearly parallel luminous flux, and the objective lens 5 for converging the nearly parallel luminous flux on an information recording medium 6. The beam shaping lens 2 is arranged between the semiconductor laser 1 and the coupling lens 3, and between the beam shaping lens 2 and the information recording medium 6, a chromatic aberration correction means 4 is provided which is constituted of; a combined lens combining two or more lenses having the different refractive indexes or; a diffractive lens provided with a refraction surface and a diffraction surface for producing diffracted light of 1st order light or 2nd or more order light, for correcting the chromatic aberration of the coupling lens 3 and the chromatic aberration of the objective lens 5 by one optical element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup and an optical disc drive used for an optical disc, and is a technique for having a function of forming a minute spot and miniaturizing the configuration of an optical system.

  In recent years, the capacity of optical disks has increased with the increase in information capacity. Increasing the capacity of an optical disk increases the amount of information by increasing the recording density. In order to increase the recording density, the track width can be reduced and recording / reproduction can be performed with a minute spot. That is, in order to form a minute spot of the optical pickup, the wavelength of the light source of the optical pickup may be shortened or the aperture (NA) of the objective lens may be increased.

  For example, a CD with a recording capacity of 640 MB uses an optical pickup with a wavelength of 785 nm and NA of 0.45, and a 4.7 GB DVD with a wavelength of 660 nm and an NA of 0.65. At present, standardization of an optical disk using a blue laser having a wavelength of 405 nm is also in progress.

  In order to form a minute spot in the optical pickup, it is necessary to sufficiently reduce the wavefront aberration. However, it is known that when the wavelength of the light source is shortened, the chromatic aberration of the optical component (lens) of the optical pickup becomes remarkable. That is, the wavelength of the light source fluctuates slightly during recording / reproduction, thereby deteriorating the wavefront aberration and lowering the signal recording / reproduction quality. In order to avoid such a situation, the optical pickup having a wavelength of 405 nm requires sufficient chromatic aberration correction.

  Incidentally, a semiconductor laser is generally used as a light source of an optical pickup. The luminous flux emitted from the semiconductor laser is radial, and at the same time, the diameter in the direction perpendicular to the diameter parallel to the bonding surface of the semiconductor laser is different. For this reason, the optical pickup generally uses a beam shaping prism so that the diameters in each direction are substantially equal, and the rim intensity of the light beam incident on the objective lens is made uniform in each direction.

  Conventionally, there is a technique disclosed in Patent Document 1 as an optical pickup in consideration of these matters.

  FIG. 11 is an explanatory diagram showing an optical pickup described in Patent Document 1. Light source 50 that emits light, collimating lens 51, beam shaping prism 52, and light incident from the light source 50 side are shown. An objective lens 55 that converges to form a light spot on the recording medium 60, an optical path converter 54 that is disposed on the optical path between the light source 50 and the objective lens 55 and converts the traveling path of incident light, and the light source 50. A chromatic aberration correction lens 53 that is disposed on the optical path between the objective lens 55 and corrects chromatic aberration due to a change in wavelength and / or an increase in wavelength line width of the light emitted from the light source 50, and is reflected from the recording medium 60. Thereafter, a photodetector 56 that receives light incident through the optical path changer 54 is provided. The chromatic aberration correction lens 53 is formed by at least two lenses so that a lens having a positive power and a lens having a negative power are adjacent to each other, and the overall focal length thereof is relatively smaller than the focal length of the objective lens 55. Infinite focal length.

As described above, in Patent Document 1, a beam shaping prism is disposed between a coupling lens and an objective lens, and an achromatic coupling lens that corrects chromatic aberration of the coupling lens and a chromatic aberration correction lens that corrects chromatic aberration of the objective lens. Each optical pickup is described.
JP 2001-154153 A

  In recent years, along with the miniaturization and thinning of personal computers, optical disc drives have also been miniaturized. For this reason, downsizing of an optical pickup for an optical disk drive is also desired.

  In the configuration described in Patent Document 1, chromatic aberration correction means are required at two locations on the coupling lens side and the objective lens side with the beam shaping prism interposed therebetween, which makes the optical pickup excessive and difficult to downsize.

  The present invention is an optical pickup which solves such problems and simultaneously corrects chromatic aberrations such as an objective lens and a coupling lens while simultaneously performing beam shaping so that recording / reproduction characteristics can be sufficiently obtained. And an optical disk drive.

  In order to achieve the above object, the invention according to claim 1 is directed to a semiconductor laser that emits a radial light beam along the optical axis, and a diameter in a direction perpendicular to a diameter parallel to the bonding surface of the semiconductor laser. An optical pickup comprising beam shaping means for making substantially equal, a coupling lens for converting a radial light beam into a substantially parallel light beam, and an objective lens for condensing the substantially parallel light beam on an information recording medium. As a means, a beam shaping lens comprising one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane is provided, and the beam shaping lens is disposed between the semiconductor laser and the coupling lens, and the cup Chromatic aberration correction means for correcting the chromatic aberration of the ring lens and the chromatic aberration of the objective lens with one optical element is provided. In this way, by using the beam shaping lens, the semiconductor laser beam is circularized and the chromatic aberration correction means is provided, so that the wavefront aberration deterioration due to the wavelength fluctuation of the optical pickup is reduced, and the beam shaping lens is coupled with the semiconductor laser. By providing between the lenses and integrating the chromatic aberration correction means of the coupling lens and the objective lens, the optical pickup can be downsized, the cost can be reduced by reducing the number of parts, and the assembly can be simplified.

  According to a second aspect of the present invention, there is provided a semiconductor laser for emitting a radial light beam along the optical axis, and beam shaping means for making the diameter in a direction perpendicular to the direction parallel to the bonding surface of the semiconductor laser substantially equal. And a coupling lens for converting the radial light beam into a substantially parallel light beam, an objective lens for condensing the substantially parallel light beam on the information recording medium, and incident on the objective lens according to the substrate thickness error of the information recording medium In the optical pickup including a magnification correction lens for switching the magnification of the luminous flux to be emitted, the beam shaping means includes a beam shaping lens composed of one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane. The beam shaping lens is disposed between the semiconductor laser and the coupling lens or between the semiconductor laser and the magnification correction lens, and the coupling lens is disposed. And chromatic aberration of chromatic aberration and the objective lens's, characterized in that a chromatic aberration correcting means for correcting the one optical element and the chromatic aberration of the magnification correction lens. By using the beam shaping lens in this way, the beam of the semiconductor laser is circularized, and chromatic aberration correction means is provided to reduce the wavefront aberration deterioration due to wavelength fluctuation of the optical pickup, and the beam shaping lens is combined with the semiconductor laser and the coupling lens. By integrating the chromatic aberration correcting means of the coupling lens, the objective lens, and the magnification correcting lens, the optical pickup can be downsized, the cost can be reduced by reducing the number of parts, and the assembly can be simplified.

  The invention according to claim 3 is the invention according to claim 2, characterized in that the chromatic aberration correction means is provided in the magnification correction lens. With such a configuration, in addition to the effect of claim 2, by integrating the magnification correction lens and the chromatic aberration correction means, further downsizing of the optical pickup, cost reduction by reducing the number of parts, and simplification of assembly are realized. it can.

  According to a fourth aspect of the present invention, there is provided a semiconductor laser that emits a radial light beam along the optical axis, and beam shaping means for making the diameter in a direction perpendicular to the direction parallel to the bonding surface of the semiconductor laser substantially equal. And a coupling lens for converting the radial light beam into a substantially parallel light beam, an objective lens for condensing the substantially parallel light beam on the information recording medium, and incident on the objective lens according to the substrate thickness error of the information recording medium In the optical pickup provided with a liquid crystal element for switching the magnification of the luminous flux to be provided, the beam shaping means includes a beam shaping lens composed of one or more lenses having different magnifications in the vertical and horizontal directions on the image plane, The beam shaping lens is disposed between the semiconductor laser and the coupling lens, and the chromatic aberration of the coupling lens, the chromatic aberration of the objective lens, and the color collection of the liquid crystal element. Characterized in that a chromatic aberration correcting means for correcting the one optical element and. By using the beam shaping lens in this way, the beam of the semiconductor laser is circularized, and chromatic aberration correction means is provided to reduce the wavefront aberration deterioration due to wavelength fluctuation of the optical pickup, and the beam shaping lens is combined with the semiconductor laser and the coupling lens. By integrating the coupling lens, the objective lens, and the chromatic aberration correcting means of the liquid crystal element, the optical pickup can be miniaturized, the cost can be reduced by reducing the number of parts, and the assembly can be simplified.

  The invention according to claim 5 is the invention according to claim 1, 2, or 4, characterized in that the chromatic aberration correcting means is provided in the coupling lens. With such a configuration, in addition to the effects of claim 1, 2, or 4, by integrating the coupling lens and the chromatic aberration correcting means, the optical pickup can be further reduced in size and cost can be reduced by reducing the number of parts. Simplification can be realized.

  The invention according to claim 6 is the invention according to claim 1, 2, or 4, wherein the chromatic aberration correcting means is provided in the objective lens. With such a configuration, in addition to the effects of claim 1, 2, or 4, the objective lens and the chromatic aberration correction means are integrated, thereby further reducing the size of the optical pickup, reducing the number of parts, and simplifying the assembly. Can be realized.

  According to a seventh aspect of the present invention, in the optical disk drive, the optical pickup according to any one of the first to sixth aspects is mounted. As described above, by using the optical pickup according to any one of claims 1 to 6, it is possible to provide a small optical disk drive.

  The present invention uses a beam shaping lens to circularize the beam of the semiconductor laser and provide chromatic aberration correction means to reduce wavefront aberration deterioration due to wavelength fluctuations of the optical pickup, and to connect the beam shaping lens to the semiconductor laser. By providing the chromatic aberration correction means of the coupling lens and the objective lens between the ring lenses, the optical pickup can be downsized, the cost can be reduced by reducing the number of parts, and the assembly can be simplified.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram showing a main part of an optical pickup according to Embodiment 1 of the present invention. The optical pickup includes a semiconductor laser 1 that emits a radial light beam at least along the optical axis, and a beam shaping lens 2 for making the diameter in a direction parallel to the joint surface of the semiconductor laser 1 and the diameter in a direction perpendicular to the semiconductor laser 1 substantially equal. A coupling lens 3 for converting the radial light beam into a substantially parallel light beam, and an objective lens 4 for condensing the substantially parallel light beam on the information recording medium.

  The beam shaping lens 2 is disposed between the semiconductor laser 1 and the coupling lens 3 and is composed of one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane. The beam shaping lens 2 has an anamorphic surface, a toric surface, a cylinder surface, an incident surface, an exit surface, or both surfaces of the beam shaping lens 2 in order to change the magnification in the vertical direction and the horizontal direction on the image plane. An anamorphic shape such as an anamorphic aspherical surface, a toric aspherical surface, or a cylinder aspherical surface is used.

  Further, chromatic aberration correcting means 4 for correcting the chromatic aberration of the coupling lens 3 and the chromatic aberration of the objective lens 5 with one optical element is provided between the beam shaping lens 2 and the information recording medium 6. The chromatic aberration correcting means 4 is a diffraction lens provided with a laminated lens obtained by laminating two or more lenses having different refractive indexes, or a refracting surface and a diffractive surface that generates diffracted light of primary light or secondary light. It consists of a lens.

  Next, the difference between the conventional example and the first embodiment will be described using (Table 1).

従来例では、光源を出射した発散光束は、カップリングレンズにより略平行になり、ビーム整形プリズムにより半導体レーザの接合面に平行な方向での径と垂直な方向での径をほぼ等しくし、対物レンズにより略平行光を微小スポットに集光する。波長変動が生じた場合、カップリングレンズでは、光軸に対して回転対称な色収差が生じる。その色収差は、ビーム整形プリズムを介すると非対称な倍率の影響を受け、光軸に対して非回転対象な色収差に変わる。対物レンズでは、光軸に対して回転対称な色収差が生じる。このため、ビーム整形を介したカップリングレンズで発生する色収差と対物レンズで発生する色収差を合わせて補正することができない。

In the conventional example, the divergent light beam emitted from the light source is made substantially parallel by the coupling lens, and the diameter in the direction perpendicular to the direction parallel to the bonding surface of the semiconductor laser is made almost equal by the beam shaping prism. The lens collects substantially parallel light into a minute spot. When wavelength variation occurs, the coupling lens generates chromatic aberration that is rotationally symmetric with respect to the optical axis. The chromatic aberration is influenced by an asymmetric magnification through the beam shaping prism, and changes to chromatic aberration that is not rotated with respect to the optical axis. In the objective lens, chromatic aberration that is rotationally symmetric with respect to the optical axis occurs. For this reason, it is impossible to correct the chromatic aberration generated in the coupling lens through beam shaping and the chromatic aberration generated in the objective lens together.

  On the other hand, in the first embodiment, the divergent light beam emitted from the light source has a diameter in a direction perpendicular to a direction parallel to the bonding surface of the semiconductor laser 1 by the beam shaping lens 2 and is approximately equal to the coupling lens. 3 becomes substantially parallel, and the objective lens 5 collects substantially parallel light on a minute spot. When the wavelength variation occurs, the coupling lens 3 generates chromatic aberration that is rotationally symmetric with respect to the optical axis. Even in the objective lens 1, chromatic aberration that is rotationally symmetric with respect to the optical axis occurs. For this reason, it becomes possible to correct chromatic aberration generated in the coupling lens 3 and chromatic aberration generated in the objective lens 5 together.

  The present invention will be described in detail below.

  According to the first embodiment, the beam shaping lens is used instead of the beam shaping prism as means for shaping the beam from the semiconductor laser 1. This is because the light beam emitted from the semiconductor laser 1 is a divergent light beam, so that when the beam shaping prism is used, astigmatism occurs and the wavefront aberration increases, so that a minute spot cannot be formed. In the case of a beam shaping lens, it is possible to reduce astigmatism while performing beam shaping by optimally designing the radius of curvature of the entrance surface and the exit surface.

  (Table 2) is a design example of a beam shaping lens having a shaping magnification of 2.4 times when a semiconductor laser wavelength of 401 nm is used.

入射面ｓ２と、出射面ｓ３をそれぞれアナモルフィック非球面レンズを用いることで、非点収差を０．００６λｒｍｓにまで小さくすることが可能になる。

By using anamorphic aspherical lenses for the entrance surface s2 and the exit surface s3, astigmatism can be reduced to 0.006λrms.

  FIG. 10 is a cross-sectional view along the optical axis z in the beam shaping lens of (Table 2). The light beam that has passed through the beam shaping lens is shaped to the same diameter in both the xy and xz sections.

  The chromatic aberration correcting means 5 of the coupling lens 3 and the objective lens 5 is a bonded lens in which two or more lenses having different refractive indexes (= partial dispersion) are bonded, or a refractive surface and primary light or secondary light or higher. And a diffractive lens provided with a diffractive surface for generating diffracted light. By designing these lenses so as to satisfy the following equation (Equation 1), it becomes possible to correct the chromatic aberration of the coupling lens 3 and the objective lens 5.

ｆ_１：色収差補正手段の第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：色収差補正手段の第２レンズの焦点距離（回折面の焦点距離）
ｆ_ＣＬ：カップリングレンズの焦点距離
ｆ_ＯＬ：対物レンズの焦点距離
ν_１：色収差補正手段の第１レンズの部分分散（屈折面を含むレンズの部分分散）
ν_２：色収差補正手段の第２レンズの部分分散（回折面の部分分散）
ν_ＣＬ：カップリングレンズの部分分散
ν_ＯＬ：対物レンズの部分分散
図２は本発明の実施の形態２における光ピックアップの要部を示す説明図であり、１０はカップリングレンズを示す。このカップリングレンズ１０は、図１に示す実施の形態１における色収差補正手段４とカップリングレンズ３を一体化させた構成である。すなわち、カップリングレンズ１０は、２枚以上の屈折率が異なるレンズを貼り合せた構成であり、このような構成により、カップリングレンズ１０と、対物レンズ５との色収差を同時に補正することが可能になる。

f ₁ : focal length of the first lens of the chromatic aberration correcting means (focal length of the refractive surface)
f ₂ : focal length of the second lens of the chromatic aberration correcting means (focal length of the diffractive surface)
f _CL : focal length of coupling lens f _OL : focal length of objective lens ν ₁ : partial dispersion of first lens of chromatic aberration correction means (partial dispersion of lens including refractive surface)
ν ₂ : partial dispersion of the second lens of the chromatic aberration correction means (partial dispersion of the diffraction surface)
ν _CL : Partial dispersion of the coupling lens ν _OL : Partial dispersion of the objective lens FIG. 2 is an explanatory view showing the main part of the optical pickup according to the second embodiment of the present invention, and 10 shows the coupling lens. This coupling lens 10 has a configuration in which the chromatic aberration correcting means 4 and the coupling lens 3 in the first embodiment shown in FIG. 1 are integrated. That is, the coupling lens 10 has a configuration in which two or more lenses having different refractive indexes are bonded to each other. With such a configuration, it is possible to simultaneously correct chromatic aberrations of the coupling lens 10 and the objective lens 5. become.

  FIG. 3 is an explanatory view showing a modification of the second embodiment of the present invention, and 11 shows a coupling lens. This coupling lens 11 also has a configuration in which the chromatic aberration correcting means 4 and the coupling lens 3 in the first embodiment shown in FIG. In this modification, the first surface (or second surface) of the coupling lens 11 is a refracting surface, and a diffractive surface that generates first-order or second-order or higher-order diffracted light is formed on the second surface (or first surface). With such a configuration, the chromatic aberration of the coupling lens 11 and the objective lens 5 can be corrected simultaneously.

  As shown in FIGS. 2 and 3, when the chromatic aberration correcting means and the coupling lens are integrated, the chromatic aberration of the coupling lens and the objective lens is corrected by designing so as to satisfy the following equation (Equation 2). It becomes possible.

ｆ_１：カップリングレンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：カップリングレンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：カップリングレンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：カップリングレンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＣＬ：カップリングレンズのｆ_１、ｆ_２の合成焦点距離
図４は本発明の実施の形態３における光ピックアップの要部を示す説明図であり、１２は対物レンズを示す。この対物レンズ１２は、図１に示す実施の形態１における色収差補正手段４と対物レンズ５を一体化させた構成である。すなわち、対物レンズ１２は、２枚以上の屈折率が異なるレンズを貼り合せたものであり、このような構成により、カップリングレンズ３と、対物レンズ１２との色収差を同時に補正することが可能になる。

f ₁ : focal length of the first lens of the coupling lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the coupling lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the coupling lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the coupling lens (partial dispersion of the diffraction surface)
f _CL : _Combined focal length of f ₁ and f ₂ of the coupling lens FIG. 4 is an explanatory view showing a main part of the optical pickup according to Embodiment 3 of the present invention, and 12 shows an objective lens. The objective lens 12 has a configuration in which the chromatic aberration correcting means 4 and the objective lens 5 in the first embodiment shown in FIG. 1 are integrated. In other words, the objective lens 12 is formed by bonding two or more lenses having different refractive indexes, and this configuration makes it possible to simultaneously correct chromatic aberration between the coupling lens 3 and the objective lens 12. Become.

  FIG. 5 is an explanatory view showing a modification of the third embodiment of the present invention, and 13 shows an objective lens. This objective lens 13 also has a configuration in which the chromatic aberration correcting means 4 and the objective lens 5 in the first embodiment shown in FIG. 1 are integrated. In this modification, the first surface (or second surface) of the objective lens 13 is a refracting surface, and a diffractive surface that generates first-order or second-order diffracted light is provided on the second surface (or first surface). With such a configuration, it becomes possible to simultaneously correct chromatic aberrations of the coupling lens 3 and the objective lens 13.

  As shown in FIGS. 4 and 5, when the chromatic aberration correcting means and the objective lens are integrated, the chromatic aberration of the coupling lens and the objective lens is corrected by designing so as to satisfy the following formula (Equation 3). Is possible.

ｆ_１：対物レンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：対物レンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：対物レンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：対物レンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＯＬ：対物レンズのｆ_１、ｆ_２の合成焦点距離
図６は本発明の実施の形態４における光ピックアップの要部を示す説明図であり、１５は倍率補正レンズである。

f ₁ : focal length of the first lens of the objective lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the objective lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the objective lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the objective lens (partial dispersion of the diffraction surface)
f _OL : Composite focal length of f ₁ and f ₂ of the objective lens FIG. 6 is an explanatory view showing a main part of the optical pickup according to Embodiment 4 of the present invention, and 15 is a magnification correction lens.

  The optical pickup according to the fourth embodiment is for making the semiconductor laser 1 emitting a radial light beam at least along the optical axis and the diameter in a direction perpendicular to the direction parallel to the bonding surface of the semiconductor laser 1 substantially equal. A beam shaping lens 2, a coupling lens 3 for converting a radial light beam into a substantially parallel light beam, an objective lens 5 for condensing the substantially parallel light beam on the information recording medium 6, and a substrate thickness error of the information recording medium 6. Accordingly, a magnification correction lens 15 for switching the magnification of the light beam incident on the objective lens 5 is provided.

The beam shaping lens 2 is composed of one or more lenses having different magnifications in the vertical and horizontal directions on the image plane. To change the magnification in the vertical and horizontal directions on the image plane, the incident surface, the exit surface, or both surfaces of the beam shaping lens 2 are anamorphic surfaces, toric surfaces, cylinder surfaces, anamorphic aspheric surfaces, toric surfaces. It is configured by an aspherical shape or a cylindrical aspherical shape. Although the beam shaping lens 2 is disposed between the semiconductor laser 1 and the coupling lens 3 in FIG. 6, it may be disposed between the semiconductor laser 1 and the magnification correction lens 15.
Further, between the beam shaping lens 2 and the information recording medium 6, a chromatic aberration correction unit 4 that corrects the chromatic aberration of the coupling lens 3, the chromatic aberration of the objective lens 5, and the chromatic aberration of the magnification correction lens 15 with one optical element. Provided. The chromatic aberration correcting means 4 is a diffraction lens provided with a laminated lens obtained by laminating two or more lenses having different refractive indexes, or a refracting surface and a diffractive surface that generates diffracted light of primary light or secondary light. It consists of a lens.

  By the way, the magnification correction lens 15 for switching the magnification of the light beam incident on the objective lens 5 in accordance with the substrate thickness error of the information recording medium 6 also has a chromatic aberration that is rotationally symmetric with respect to the optical axis when wavelength variation occurs. Arise. Therefore, it is possible to correct the chromatic aberration generated in the coupling lens 3 and the chromatic aberration generated in the objective lens 5 together.

  According to the third embodiment, the chromatic aberration correction means 4 of the coupling lens 3, the objective lens 5, and the magnification correction lens 15 is a bonded lens in which two or more lenses having different refractive indexes (= partial dispersion) are bonded. And a diffractive lens provided with a refracting surface and a diffractive surface for generating diffracted light of primary light or secondary light or higher. By designing these lenses so as to satisfy the following equation (Equation 4), it becomes possible to correct the chromatic aberration of the coupling lens 3, the objective lens 5, and the magnification correction lens 15.

ｆ_ＰＷ１：倍率補正レンズの第１レンズの焦点距離
ｆ_ＰＷ２：倍率補正レンズの第２レンズの焦点距離
ν_ＰＷ１：倍率補正レンズの第１レンズの部分分散
ν_ＰＷ２：倍率補正レンズの第２レンズの部分分散
ｆ_１：色収差補正手段の第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：色収差補正手段の第２レンズの焦点距離（回折面の焦点距離）
ν_１：色収差補正手段の第１レンズの部分分散（屈折面を含むレンズの部分分散）
ν_２：色収差補正手段の第２レンズの部分分散（回折面の部分分散）
なお、実施の形態４においても、図２，図３に示すように、色収差補正手段とカップリングレンズを一体化させることにより、カップリングレンズ３と、対物レンズ５と、倍率補正レンズ１５との色収差を同時に補正することが可能になる。

f _PW1 : focal length of first lens of magnification correction lens f _PW2 : focal length of second lens of magnification correction lens ν _PW1 : partial dispersion of first lens of magnification correction lens ν _PW2 : second lens of magnification correction lens Partial dispersion f ₁ : focal length of the first lens of the chromatic aberration correcting means (focal length of the refractive surface)
f ₂ : focal length of the second lens of the chromatic aberration correcting means (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the chromatic aberration correcting means (partial dispersion of the lens including the refractive surface)
ν ₂ : partial dispersion of the second lens of the chromatic aberration correction means (partial dispersion of the diffraction surface)
Also in the fourth embodiment, as shown in FIGS. 2 and 3, the chromatic aberration correcting means and the coupling lens are integrated so that the coupling lens 3, the objective lens 5, and the magnification correcting lens 15 are integrated. Chromatic aberration can be corrected simultaneously.

  In the fourth embodiment, as shown in FIGS. 2 and 3, when the chromatic aberration correcting unit and the coupling lens are integrated, the coupling lens and the coupling lens are designed by satisfying the following formula (Equation 5). It becomes possible to correct the chromatic aberration of the objective lens and the magnification correction lens.

ｆ_ＰＷ１：倍率補正レンズの第１レンズの焦点距離
ｆ_ＰＷ２：倍率補正レンズの第２レンズの焦点距離
ν_ＰＷ１：倍率補正レンズの第１レンズの部分分散
ν_ＰＷ２：倍率補正レンズの第２レンズの部分分散
ｆ_１：カップリングレンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：カップリングレンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：カップリングレンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：カップリングレンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＣＬ：カップリングレンズのｆ_１、ｆ_２の合成焦点距離
また実施の形態４においても、図４，図５に示すように、前記色収差補正手段と対物レンズを一体化させる場合には、次式（数６）を満たすように設計することで、カップリングレンズおよび対物レンズおよび倍率補正レンズの色収差を補正することが可能になる。

f _PW1 : focal length of first lens of magnification correction lens f _PW2 : focal length of second lens of magnification correction lens ν _PW1 : partial dispersion of first lens of magnification correction lens ν _PW2 : second lens of magnification correction lens Partial dispersion f ₁ : focal length of the first lens of the coupling lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the coupling lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the coupling lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the coupling lens (partial dispersion of the diffraction surface)
f _CL : _Combined focal length of f ₁ and f ₂ of the coupling lens Also in the fourth embodiment, as shown in FIGS. 4 and 5, when the chromatic aberration correcting means and the objective lens are integrated, the following is performed. By designing so as to satisfy Expression (Equation 6), it becomes possible to correct chromatic aberration of the coupling lens, the objective lens, and the magnification correction lens.

ｆ_ＰＷ１：倍率補正レンズの第１レンズの焦点距離
ｆ_ＰＷ２：倍率補正レンズの第２レンズの焦点距離
ν_ＰＷ１：倍率補正レンズの第１レンズの部分分散
ν_ＰＷ２：倍率補正レンズの第２レンズの部分分散
ｆ_１：対物レンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：対物レンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：対物レンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：対物レンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＯＬ：対物レンズのｆ_１、ｆ_２の合成焦点距離
図７は本発明の実施の形態５における光ピックアップの要部を示す説明図であり、１６は倍率補正レンズを示す。この倍率補正レンズ１６は、図６に示す実施の形態４における色収差補正手段４と倍率補正レンズ１５を一体化させた構成である。すなわち、図６に示す倍率補正レンズ１５の少なくとも一つのレンズを、２枚以上の屈折率が異なるレンズを貼り合せて構成することで、カップリングレンズ３と、対物レンズ５と、倍率補正レンズ１６との色収差を同時に補正することが可能になる。

f _PW1 : focal length of first lens of magnification correction lens f _PW2 : focal length of second lens of magnification correction lens ν _PW1 : partial dispersion of first lens of magnification correction lens ν _PW2 : second lens of magnification correction lens Partial dispersion f ₁ : focal length of the first lens of the objective lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the objective lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the objective lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the objective lens (partial dispersion of the diffraction surface)
f _OL : Composite focal length of f ₁ and f ₂ of the objective lens FIG. 7 is an explanatory view showing the main part of the optical pickup according to the fifth embodiment of the present invention, and 16 shows a magnification correction lens. This magnification correction lens 16 has a configuration in which the chromatic aberration correction means 4 and the magnification correction lens 15 in Embodiment 4 shown in FIG. 6 are integrated. That is, at least one lens of the magnification correction lens 15 shown in FIG. 6 is configured by bonding two or more lenses having different refractive indexes, so that the coupling lens 3, the objective lens 5, and the magnification correction lens 16 are combined. And chromatic aberration can be corrected simultaneously.

  In addition, the first surface (or second surface) of the magnification correction lens 16 is provided with a refracting surface, and the second surface (or first surface) is provided with a diffractive surface that generates first-order or second-order or higher-order diffracted light. It is also possible to simultaneously correct chromatic aberrations of the ring lens, the objective lens, and the magnification correction lens.

  As shown in FIG. 7, when the chromatic aberration correcting means and the magnification correcting lens are integrated, the coupling lens, the objective lens, and the magnification are designed by satisfying the following equation (Equation 7) or Equation (Equation 8). It becomes possible to correct the chromatic aberration of the correction lens.

ｆ_１：倍率補正レンズの前側第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：倍率補正レンズの前側第２レンズの焦点距離（回折面の焦点距離）
ν_１：倍率補正レンズの前側第１レンズの部分分散（屈折面の部分分散）
ν_２：倍率補正レンズの前側第２レンズの部分分散（回折面の部分分散）
ｆ_ＯＬ：倍率補正レンズのｆ_１、ｆ_２の合成焦点距離

f ₁ : Focal length of the first lens on the front side of the magnification correction lens (focal length of the refractive surface)
f ₂ : Focal length of the second lens on the front side of the magnification correction lens (focal length of the diffractive surface)
ν ₁ : Partial dispersion of the first lens on the front side of the magnification correction lens (partial dispersion of the refractive surface)
ν ₂ : Partial dispersion of the second lens on the front side of the magnification correction lens (partial dispersion of the diffraction surface)
f _OL : Composite focal length of f ₁ and f ₂ of the magnification correction lens

ｆ_１：倍率補正レンズの後側第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：倍率補正レンズの後側第２レンズの焦点距離（回折面の焦点距離）
ν_１：倍率補正レンズの後側第１レンズの部分分散（屈折面の部分分散）
ν_２：倍率補正レンズの後側第２レンズの部分分散（回折面の部分分散）
ｆ_ＯＬ：倍率補正レンズのｆ_１、ｆ_２の合成焦点距離
図８は本発明の実施の形態６における光ピックアップの要部を示す説明図であり、１７は液晶素子を示す。

f ₁ : Focal length of the first lens behind the magnification correction lens (focal length of the refractive surface)
f ₂ : Focal length of the second lens behind the magnification correction lens (focal length of the diffraction surface)
ν ₁ : Partial dispersion of the first lens behind the magnification correction lens (partial dispersion of the refractive surface)
ν ₂ : Partial dispersion of the second lens behind the magnification correction lens (partial dispersion of the diffraction surface)
f _OL : Combined focal length of f ₁ and f ₂ of the magnification correction lens FIG. 8 is an explanatory view showing a main part of the optical pickup according to Embodiment 6 of the present invention, and 17 shows a liquid crystal element.

  The optical pickup includes a semiconductor laser 1 that emits a radial light beam at least along the optical axis, and a beam shaping lens 2 for making the diameter in a direction parallel to the joint surface of the semiconductor laser 1 and the diameter in a direction perpendicular to the semiconductor laser 1 substantially equal. In accordance with the substrate thickness error of the information recording medium 6, the coupling lens 3 that converts the radial light flux into a substantially parallel light flux, the objective lens 5 that collects the substantially parallel light flux on the information recording medium 6, and the objective lens And a liquid crystal element 17 for switching the magnification of the light beam incident on the light source 5.

  The beam shaping lens 2 is disposed between the semiconductor laser 1 and the coupling lens 3 and is composed of one or more lenses having different magnifications in the vertical and horizontal directions on the image plane. Since the magnification in the vertical and horizontal directions on the image plane is different, the incident surface, the exit surface, or both surfaces of the beam shaping lens 2 are anamorphic surfaces, toric surfaces, cylinder surfaces, anamorphic aspheric surfaces, toric surfaces. It has an anamorphic shape such as an aspherical surface or cylinder aspherical surface.

  Further, between the beam shaping lens 2 and the information recording medium 6, there is provided chromatic aberration correcting means 4 for correcting the chromatic aberration of the coupling lens 3, the chromatic aberration of the objective lens 5, and the chromatic aberration of the liquid crystal element 17 with one optical element. ing. The chromatic aberration correcting means 4 is a diffraction lens provided with a laminated lens obtained by laminating two or more lenses having different refractive indexes, or a refracting surface and a diffractive surface that generates diffracted light of primary light or secondary light. It consists of a lens.

  By the way, the liquid crystal element 17 for switching the magnification of the light beam incident on the objective lens 5 according to the substrate thickness error of the information recording medium 6 also causes chromatic aberration that is rotationally symmetric with respect to the optical axis when wavelength variation occurs. . Therefore, it is possible to correct the chromatic aberration generated in the coupling lens 3 and the chromatic aberration generated in the objective lens 5 together.

  In the sixth embodiment, the chromatic aberration correcting means 4 of the coupling lens 3, the objective lens 5, and the liquid crystal element 17 is a bonded lens obtained by bonding two or more lenses having different refractive indexes (= partial dispersion), or It consists of a diffractive lens provided with a refracting surface and a diffractive surface for generating diffracted light of primary light or secondary light. By designing these lenses so as to satisfy the following equation (Equation 9), it becomes possible to correct the chromatic aberration of the coupling lens 3, the objective lens 5, and the liquid crystal element 17.

ｆ_ＬＩＱ：液晶素子の駆動時焦点距離
ν_ＬＩＱ：液晶素子の部分分散
ｆ_１：色収差補正手段の第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：色収差補正手段の第２レンズの焦点距離（回折面の焦点距離）
ν_１：色収差補正手段の第１レンズの部分分散（屈折面を含むレンズの部分分散）
ν_２：色収差補正手段の第２レンズの部分分散（回折面の部分分散）
また、実施の形態６において、図２，図３に示すように、色収差補正手段とカップリングレンズを一体化する場合には、次式（数１０）を満たすように設計することで、カップリングレンズ、対物レンズおよび液晶素子の色収差を補正することが可能になる。

f _LIQ : focal length when driving the liquid crystal element ν _LIQ : partial dispersion of the liquid crystal element f ₁ : focal length of the first lens of the chromatic aberration correcting means (focal length of the refractive surface)
f ₂ : focal length of the second lens of the chromatic aberration correcting means (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the chromatic aberration correcting means (partial dispersion of the lens including the refractive surface)
ν ₂ : partial dispersion of the second lens of the chromatic aberration correction means (partial dispersion of the diffraction surface)
In the sixth embodiment, as shown in FIGS. 2 and 3, when the chromatic aberration correcting means and the coupling lens are integrated, the coupling is designed by satisfying the following equation (Equation 10). It becomes possible to correct chromatic aberration of the lens, the objective lens, and the liquid crystal element.

ｆ_１：カップリングレンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：カップリングレンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：カップリングレンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：カップリングレンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＣＬ：カップリングレンズのｆ_１、ｆ_２の合成焦点距離
また実施の形態６においても、図４，図５に示すように、前記色収差補正手段と対物レンズを一体化させる場合には、次式（数１１）を満たすように設計することで、カップリングレンズおよび対物レンズおよび倍率補正レンズの色収差を補正することが可能になる。

f ₁ : focal length of the first lens of the coupling lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the coupling lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the coupling lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the coupling lens (partial dispersion of the diffraction surface)
f _CL : _Combined focal length of f ₁ and f ₂ of the coupling lens Also in the sixth embodiment, as shown in FIGS. 4 and 5, when the chromatic aberration correcting means and the objective lens are integrated, By designing so as to satisfy the formula (Equation 11), it becomes possible to correct the chromatic aberration of the coupling lens, the objective lens, and the magnification correction lens.

ｆ_１：対物レンズの第１レンズの焦点距離（屈折面の焦点距離）
ｆ_２：対物レンズの第２レンズの焦点距離（回折面の焦点距離）
ν_１：対物レンズの第１レンズの部分分散（屈折面の部分分散）
ν_２：対物レンズの第２レンズの部分分散（回折面の部分分散）
ｆ_ＯＬ：対物レンズのｆ_１、ｆ_２の合成焦点距離
図９は本発明の光ディスクドライブの構成を示すブロック図であり、２５は図１〜図８に示した光ピックアップを示す。

f ₁ : focal length of the first lens of the objective lens (focal length of the refractive surface)
f ₂ : focal length of the second lens of the objective lens (focal length of the diffractive surface)
ν ₁ : partial dispersion of the first lens of the objective lens (partial dispersion of the refractive surface)
ν ₂ : partial dispersion of the second lens of the objective lens (partial dispersion of the diffraction surface)
f _OL : Composite focal length of f ₁ and f ₂ of the objective lens FIG. 9 is a block diagram showing the configuration of the optical disk drive of the present invention, and 25 shows the optical pickup shown in FIGS.

  The emitted light of the semiconductor laser mounted on the optical pickup 25 is detected by a front monitor photodiode mounted on the optical pickup 25 and controlled by the laser controller 37 via the signal processing circuit 30. Driven.

  The light beam reflected from the surface of the information recording medium 6 is detected by a divided light receiving element mounted on the optical pickup 25 and input to the signal processing circuit 30. The signal processing circuit 30 generates a focus error signal for focusing the objective lens and a track error signal for tracking the objective lens. The objective lens actuator mounted on the optical pickup 25 is controlled by the Fo controller 35 and the Tr controller 36 and driven by the ACT driver 39. A reproduction signal is output from the m signal processing circuit 30 according to the information recording surface.

  A spindle motor 42 that rotates the information recording medium 6 is controlled by a spindle controller 38 and driven by a spindle driver 41.

  As described above, according to the optical pickup of the present embodiment, the coupling lens and the objective lens, or the coupling lens, the objective lens and the magnification correction element, or the coupling lens, the objective lens and the liquid crystal element are used. Since the elements for correcting the generated chromatic aberration can be integrated, the size can be reduced, and the entire configuration of the optical disk drive can be reduced.

  INDUSTRIAL APPLICABILITY The present invention can be used in the fields of an optical pickup and an optical disk drive used for recording / reproducing information with respect to a large capacity optical disk.

Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 1 of this invention. Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 2 of this invention. Explanatory drawing which shows the modification of Embodiment 2 of this invention. Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 3 of this invention. Explanatory drawing which shows the modification of Embodiment 3 of this invention. Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 4 of this invention. Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 5 of this invention. Explanatory drawing which shows the principal part of the optical pick-up in Embodiment 6 of this invention. The block diagram which shows the structure of the optical disk drive of this invention Sectional view along the optical axis z of the beam shaping lens of Table 2 Explanatory drawing showing the main part of a conventional optical pickup

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Beam shaping lens 3 Coupling lens 4 Chromatic aberration correction means 5 Objective lens 6 Information recording medium 10, 11 Coupling lens 12, 13 Objective lens 15, 16 Magnification correction lens 17 Liquid crystal element

Claims (7)

A semiconductor laser that emits a radial light beam along the optical axis, beam shaping means for making the diameter in a direction perpendicular to the diameter parallel to the bonding surface of the semiconductor laser, and a radial light beam substantially parallel In an optical pickup comprising a coupling lens for making a light beam and an objective lens for condensing a substantially parallel light beam on an information recording medium,
The beam shaping means includes a beam shaping lens composed of one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane, and the beam shaping lens is disposed between the semiconductor laser and the coupling lens. An optical pickup comprising chromatic aberration correcting means for correcting chromatic aberration of the coupling lens and chromatic aberration of the objective lens by a single optical element. A semiconductor laser that emits a radial light beam along the optical axis, beam shaping means for making the diameter in a direction perpendicular to the diameter parallel to the bonding surface of the semiconductor laser, and a radial light beam substantially parallel A coupling lens for forming a light beam, an objective lens for condensing a substantially parallel light beam on the information recording medium, and a magnification for switching the light beam incident on the objective lens according to the substrate thickness error of the information recording medium. In an optical pickup equipped with a magnification correction lens,
The beam shaping means includes a beam shaping lens including one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane, and the beam shaping lens is provided between the semiconductor laser and the coupling lens, or Chromatic aberration correction means is provided between the semiconductor laser and the magnification correction lens, and corrects chromatic aberration of the coupling lens, chromatic aberration of the objective lens, and chromatic aberration of the magnification correction lens with a single optical element. Features an optical pickup.   3. The optical pickup according to claim 2, wherein the chromatic aberration correcting means is provided in the magnification correcting lens. A semiconductor laser that emits a radial light beam along the optical axis, beam shaping means for making the diameter in a direction perpendicular to the diameter parallel to the bonding surface of the semiconductor laser, and a radial light beam substantially parallel A coupling lens for forming a light beam, an objective lens for condensing a substantially parallel light beam on the information recording medium, and a magnification for switching the light beam incident on the objective lens according to the substrate thickness error of the information recording medium. In an optical pickup equipped with a liquid crystal element,
The beam shaping means includes a beam shaping lens composed of one or more lenses having different magnifications in the vertical direction and the horizontal direction on the image plane, and the beam shaping lens is disposed between the semiconductor laser and the coupling lens. An optical pickup comprising chromatic aberration correcting means for correcting chromatic aberration of the coupling lens, chromatic aberration of the objective lens, and chromatic aberration of the liquid crystal element with a single optical element.   5. The optical pickup according to claim 1, wherein the chromatic aberration correcting means is provided in the coupling lens.   5. The optical pickup according to claim 1, wherein the chromatic aberration correcting means is provided in the objective lens.   An optical disc drive comprising the optical pickup according to any one of claims 1 to 6.

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