JP4300914B2 - Optical pickup device and optical element - Google Patents

Description

【０１６４】
表１に示すように、本実施例の対物レンズは、波長λ１＝４０７ｎｍのときの焦点距離ｆ＝３．１ｍｍ、像側開口数ＮＡ１＝０．６５に設定されており、波長λ２＝６５５ｎｍのときの焦点距離ｆ２＝３．２６ｍｍ、像側開口数ＮＡ２＝０．６２に設定されており、波長λ３＝７８５ｎｍのときの焦点距離ｆ３＝３．５７ｍｍ、像側開口数ＮＡ３＝０．４０に設定されている。
【０１６５】
また、光束λ１〜λ３に対する倍率ｍ１〜ｍ３はほぼ０であり、対物レンズに平行光が入射する無限系の構成となっている。
表１中の面Ｎｏ．２、２´、２´´は、上述のように、それぞれ対物レンズの入射面のうち、１．４５ｍｍ≦ｈの第２面、１．１ｍｍ≦ｈ＜１．４５ｍｍの第２´面、ｈ＜１．１ｍｍの２´´面を示しており、面番号３、４はそれぞれ、光情報記録媒体の保護基板の表面、記録層を表している。また、Ｒｉは曲率半径、ｄｉは第ｉ面から第ｉ＋１面までの光軸方向の変位、ｎｉは各面の屈折率を表している。
【０１６６】
対物レンズの第２面、第２´面、第２´´面、第３面は、それぞれ次式（数１）に表１及び表２に示す係数を代入した数式で規定される、光軸Ｌの周りに軸対称な非球面に形成されている。
【０１６７】
【数１】

【０１６８】
ここで、Ｘ（ｈ）は光軸方向の軸（光の進行方向を正とする）、κは円錐係数、Ａ_2iは非球面係数である。
【表２】

【０１６９】
また、回折輪帯のピッチは数２の光路差関数に、表２に示す係数を代入した数式で規定される。
【０１７０】
【数２】

ここで、Ｂ_2iは光路差関数の係数、ｍＤは光路差付与構造が無いと仮定した場合（回折構造のみを備えるものと仮定した場合）の各光束の回折次数、λは使用波長、λＢは回折のブレーズ化波長（第１及び第２の実施例においてはλＢ＝１ｍｍ）である。
【０１７１】
図１３は、高密度光ディスク（ＡＯＤ）に用いられる波長λ１（４０７ｎｍ）の光束の波長が、４０７ｎｍから±１ｎｍ変動した場合における縦球面収差の変動量と開口数（ＮＡ）を示すグラフである。
通常、モードホップ等に起因した波長の変動量は１μｍ程度であるから、この範囲内において、縦球面収差の変動量は実用上支障が無い範囲に抑えられており、十分な色補正機能を有することが分かる。
【０１７２】
図１４は、波長λ１（ＡＯＤ）、波長λ２（ＤＶＤ）、波長λ３（ＣＤ）の各光束の波面収差及び回折効率を示すものであり、図１５〜図１７は、波長λ１〜λ３の各光束の集光位置ｆＢと開口数を示すグラフである。
図１４〜図１７より、各光束の波面収差は回折限界の０．０７λｒｍｓ以下に抑えられており、十分な色補正機能を有することが分かる。また、各光情報記録媒体に対する情報の記録及び／又は再生に用いるために十分な回折効率を有していることが分かる。
【０１７３】
次に、上記実施の形態で示した光ピックアップ装置及び光学素子の第２の実施例について説明する。
本実施例においても、図６に示したような、Ｓ１面とＳ２面とを入射面側で組み合わせた対物レンズを用いるものとする。
具体的に説明すると、両面非球面の単レンズである対物レンズの入射面が、光軸Ｌからの高さｈが１．４５ｍｍ以上の第２面、１．１ｍｍ以上で１．４５ｍｍ未満の第２´面（領域Ａ１）、１．１ｍｍ未満の２´´面（領域Ａ２）に区分されている。
【０１７４】
そして、領域Ａ１には第１回折構造としての複数の回折輪帯が形成され、領域Ａ２には第２回折構造としての回折輪帯が形成されている。また、第２面にも回折輪帯が形成されている。
そして、第２面、第２´面及び第２´´面を通過する波長λ１、λ２、λ３の各光束は、最大の回折効率となる回折次数ｍ＝３、ｎ＝２、ｋ＝２の回折光が得られるように、上記第１回折構造及び第２回折構造から回折作用を受けて出射されるようになっている。
表３、表４に対物レンズのレンズデータを示す。
【０１７５】
【表３】

【０１７６】
表３に示すように、本実施例の対物レンズは、波長λ１＝４０７ｎｍのときの焦点距離ｆ１＝３．１ｍｍ、像側開口数ＮＡ１＝０．６５に設定されており、波長λ２＝６５５ｎｍのときの焦点距離ｆ２＝３．１９ｍｍ、像側開口数ＮＡ２＝０．６３に設定されており、波長λ３＝７８５ｎｍのときの焦点距離ｆ３＝３．１８ｍｍ、像側開口数ＮＡ３＝０．４５に設定されている。
また、光束λ１〜λ３に対する倍率ｍ１〜ｍ３はほぼ０であり、対物レンズに平行光が入射する無限系の構成となっている。
【０１７７】
対物レンズの第２面、第２´面、第２´´面、第３面は、それぞれ上記数１に表３及び表４に示す係数を代入した数式で規定される、光軸Ｌの周りに軸対称な非球面に形成されている。
【表４】

【０１７８】
また、回折輪帯のピッチは上記数２の光路差関数に、表４に示す係数を代入した数式で規定される。
【０１７９】
図１８は、高密度光ディスク（ＡＯＤ）に用いられる波長λ１（４０７ｎｍ）の光束の波長が、４０７ｎｍから±１ｎｍ変動した場合における球面収差の変動量と開口数（ＮＡ）を示すグラフである。
通常、モードホップ等に起因した波長の変動量は１μｍ程度であるから、この範囲内において、縦球面収差の変動量は実用上支障が無い範囲に抑えられており、十分な色補正機能を有することが分かる。
【０１８０】
図１９は、波長λ１（ＡＯＤ）、波長λ２（ＤＶＤ）、波長λ３（ＣＤ）の各光束の波面収差及び回折効率を示すものであり、図２０〜図２２は、波長λ１〜λ３の各光束の集光位置ｆＢと開口数を示すグラフである。
図１９〜図２２より、波面収差は回折限界の０．０７λｒｍｓ以下に抑えられており、十分な色補正機能を有することが分かる。また、各光情報記録媒体に対する情報の記録及び／又は再生に用いるために十分な回折効率を有していることが分かる。
【０１８１】
【発明の効果】
以上、本発明に係る光ピックアップ装置及び光学素子によれば、第１光源、第２光源及び第３光源の共通光路に配置され、第１回折構造を有する回折光学素子を備え、第１光情報記録媒体、第２光情報記録媒体及び第３光情報記録媒体に対して情報の再生及び／又は記録を行う場合、回折光学素子に全ての前記光束をほぼ無限平行光として入射させる。
従って、例えば、第１〜第３の波長の光の光路がほぼ等しくなるので、光ピックアップ装置を構成する各種光学素子をこの共通光路に対応して配置すればよく、光ピックアップ装置の構造を簡略化できると共に、装置の部品点数を削減できる。
また、情報の再生及び／又は記録を行なう際に対物光学素子を光情報記録媒体に対して移動させるトラッキング時の像高特性の悪化を防止でき、コマ収差や非点収差等の各種収差の発生を抑えることができる。
また、温度変化により発生する球面収差も抑えることができる。
【図面の簡単な説明】
【図１】本発明に関わる光ピックアップ装置の図である。
【図２】本発明に関わる、別の態様の光ピックアップ装置の図である。
【図３】対物光学素子の構造を示す要部縦断面図である。
【図４】縦球面収差図（ａ）〜（ｃ）である。
【図５】縦球面収差図（ａ）〜（ｃ）である。
【図６】対物光学素子の構造を示す要部縦断面図である。
【図７】対物光学素子の構造を示す要部縦断面図である。
【図８】縦球面収差図（ａ）〜（ｃ）である。
【図９】対物光学素子の構造を示す要部縦断面図である。
【図１０】縦球面収差図（ａ）〜（ｃ）である。
【図１１】対物光学素子の構造を示す要部縦断面図である。
【図１２】対物光学素子の構造を示す要部縦断面図である。
【図１３】波長変動時の縦球面収差の変動量と開口数（ＮＡ）を示すグラフである。
【図１４】各光束の波面収差及び回折効率を示す表である。
【図１５】波長λ１の光束の集光位置ｆＢと開口数を示すグラフである
【図１６】波長λ２の光束の集光位置ｆＢと開口数を示すグラフである
【図１７】波長λ３の光束の集光位置ｆＢと開口数を示すグラフである
【図１８】波長変動時の縦球面収差の変動量と開口数（ＮＡ）を示すグラフである。
【図１９】各光束の波面収差及び回折効率を示す表である。
【図２０】波長λ１の光束の集光位置ｆＢと開口数を示すグラフである
【図２１】波長λ２の光束の集光位置ｆＢと開口数を示すグラフである
【図２２】波長λ３の光束の集光位置ｆＢと開口数を示すグラフである
【符号の説明】
ＬＤ１ 第１光源
ＬＤ２ 第２光源
ＬＤ３ 第３光源
ＬＤ２' 第２光源（２波長１パッケージ）
Ｓ１ センサー
Ｓ２ センサー
Ｓ３ センサー
Ｓ２' センサー
ＳＬ１ センサーレンズ
ＳＬ２ センサーレンズ
ＳＬ３ センサーレンズ
ＤＰ 回折板
ＢＳ１ ビームスプリッタ
ＢＳ２ ビームスプリッタ
ＢＳ３ ビームスプリッタ
ＢＳ４ ビームスプリッタ
ＣＬ１ コリメータ
ＣＬ２ コリメータ
ＣＬ３ コリメータ
ＩＲ 絞り
ＯＢＬ 対物光学素子
Ｄ１ 光ディスク（「高密度な光ディスク」）
Ｄ２ 光ディスク（ＤＶＤ）
Ｄ３ 光ディスク（ＣＤ）
Ｌ 光軸
Ｒｓ 輪帯状光学面
Ｒｌ 輪帯状光学面
１０ 対物光学素子
１１ 光学面（出射面）
１２ 光学面（入射面）
２０ 段差面
３０ 第１回折構造
４０ 第２回折構造
５０ 屈折面
６０ 輪帯状光学面
７０ 段差面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device that can meet the standards of three types of optical information recording media (optical discs) and an optical element used in the optical pickup device.
[0002]
[Prior art]
In recent years, with the practical use of short-wavelength red lasers, DVDs (digital video discs), which are high-density optical information recording media (also referred to as optical discs) with the same size and capacity as CDs (compact discs), Various optical discs with different operating wavelengths and protective substrate thickness, such as CD-R, RW (write-once compact disc), VD (video disc), MD (mini disc), MO (magneto-optical disc), etc. Has been.
Further, a high-density optical disk (hereinafter referred to as “high-density”) having a protective substrate thickness of about 0.1 mm using a blue-violet semiconductor laser light source having a wavelength of about 400 nm and an objective lens having an image-side numerical aperture (NA) increased to about 0.85. Research and development of a high-density optical disk having a protective substrate thickness of about 0.6 mm using an objective lens having an image-side numerical aperture (NA) of about 0.65.
[0003]
Various kinds of information can be reproduced and / or recorded by condensing light beams of three different wavelengths using one objective lens on the information recording surfaces of three types of optical discs having different working wavelengths and protective substrate thicknesses. Various compatible optical pickup devices (also referred to as optical disk devices) have been proposed. (For example, refer to Patent Document 1).
[0004]
Patent Document 1 discloses a first to third light source that emits light of first to third wavelengths and an object that receives light of first to third wavelengths and focuses the light on a predetermined optical information recording medium. An optical disc apparatus schematically constituted by a lens, a collimator lens and the like is disclosed.
The light having the first and second wavelengths emitted from the first and second light sources passes through the collimator lens. At this time, the light having the first wavelength is converted into parallel light by the collimator lens and the objective lens. The second wavelength light is incident on the objective lens as divergent light without being collimated. In addition, the light of the third wavelength from the third light source does not pass through the collimator lens and enters the objective lens directly as divergent light.
Then, the light of the first to third wavelengths emitted from the objective lens is condensed on three types of optical information recording media having different working wavelengths and protective substrate thicknesses such as high-density optical discs, DVDs, CDs, etc. Recording and / or reproduction is performed.
[0005]
[Patent Document 1]
JP 2001-43559 A
[0006]
[Problems to be solved by the invention]
By the way, as described above, in the apparatus disclosed in Patent Document 1, light having the first wavelength enters the objective lens as parallel light, and light having the second and third wavelengths enters the objective lens as divergent light. Therefore, the optical system magnification of the condensing optical system including the objective lens is different for the three types of optical information recording media.
Therefore, for example, since the optical paths of the first to third wavelengths of light are different from each other, it becomes necessary to arrange a plurality of optical elements corresponding to the respective optical paths, and the structure of the optical disc apparatus becomes complicated. There was a problem and a problem that the number of parts of the apparatus increased.
[0007]
In addition, since divergent light is incident on the objective lens, the image height characteristics deteriorate during tracking when the objective lens is moved relative to the optical disk during reproduction / recording of the optical disk, and various aberrations such as coma and astigmatism occur. There was a problem to do.
In addition, there is a problem that spherical aberration generated due to a temperature change is increased as compared with a so-called infinite system in which parallel light is incident on an objective lens.
[0008]
An object of the present invention is to take the above-mentioned problems into consideration, and is used for reproducing and / or recording information on three types of optical information recording media having different operating wavelengths and protective substrate thicknesses, thereby suppressing the occurrence of various aberrations. An optical pickup device and an optical element that can reduce the number of components are provided.
[0009]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, the invention according to claim 1 is directed to reproducing and reproducing information using a light beam emitted from a first light source having a wavelength λ1 with respect to a first optical information recording medium having a protective substrate thickness t1. Recording is performed, and information is reproduced and / or reproduced from a second optical information recording medium having a protective substrate thickness t2 (t1 ≦ t2) using a light beam emitted from a second light source having a wavelength λ2 (λ1 <λ2). Alternatively, recording is performed, and information is reproduced and / or reproduced from a third optical information recording medium having a protective substrate thickness t3 (t2 <t3) using a light beam emitted from a third light source having a wavelength λ3 (λ2 <λ3). An optical pickup device that performs recording, the optical pickup device including a diffractive optical element that is disposed in a common optical path of the first light source, the second light source, and the third light source and has a first diffractive structure, First optical information recording medium, second optical information recording medium And when the reproducing and / or recording information for the third optical information recording medium, almost all of the light flux in the diffractive optical element included in the optical pickup deviceAs infinite parallel lightIncident,The light beam having the wavelength λ3 is configured to obtain diffracted light of different orders when passing through the central portion of the diffractive optical element and when passing through the peripheral portion of the diffractive optical element,A condensing spot is formed by the diffracted light of m (m is a natural number) generated by the diffractive optical element with respect to the first optical information recording medium, and generated by the diffractive optical element with respect to the second optical information recording medium. n (n is a natural number where n.noteq.m) is formed so as to form a focused spot by the diffracted light of the order.The numerical aperture of the condensing spot formed on the first optical information recording medium by the light beam having the wavelength λ1 is NA1, and the condensing spot formed on the second optical information recording medium by the light beam having the wavelength λ2. Is NA2, and NA3 is the numerical aperture of the condensing spot formed on the third optical information recording medium by the light flux having the wavelength λ3,
  NA3 <NA1
  NA3 <NA2
MeetIt is characterized by that.
[0010]
  According to the first aspect of the present invention, the first optical information recording medium, the second optical information recording medium, and the second optical information recording medium are provided, including the diffractive optical element disposed in the common optical path of the first light source, the second light source, and the third light source and having the first diffractive structure. When information is reproduced and / or recorded on the optical information recording medium and the third optical information recording medium, almost all the luminous fluxes are applied to the diffractive optical element.As infinite parallel lightMake it incident.
  Therefore, for example, since the optical paths of the first to third wavelengths of light are substantially equal, various optical elements constituting the optical pickup device may be arranged corresponding to the common optical path, and the structure of the optical pickup device is simplified. And the number of parts of the device can be reduced.
  In addition, when reproducing and / or recording information, the objective optical element is moved relative to the optical information recording medium to prevent deterioration in image height characteristics during tracking, and various aberrations such as coma and astigmatism are generated. Can be suppressed.
  In addition, spherical aberration caused by temperature change can be suppressed.
[0011]
A second aspect of the present invention is the optical pickup device according to the first aspect, wherein the diffractive optical element is an objective optical element.
[0021]
  Claim 3The invention described isClaim 1 or 2The temperature pickup and / or chromatic aberration compensation is performed on at least one of the focused spots formed on the first, second, and third optical information recording media. It has an optical correction element for performing.
[0022]
  Claim 4The invention described isAny one of Claims 1-3An optical pickup device according to claim 1,When reproducing and / or recording information on the third optical information recording medium, the spherical aberration has a discontinuous portion.It is characterized by that.
[0023]
  Claim 5The invention described isAny one of Claims 1-4An optical pickup device according to claim 1,The first diffractive structure of the diffractive optical element includes a plurality of diffractive annular zones that are sawtooth-like discontinuous surfaces, and a step-like discontinuous surface that is formed on the optical surface of the diffractive annular zone along the optical axis. And an optical path difference providing structure consisting ofIt is characterized by that.
[0024]
  Claim 6The invention described isAny one of Claims 1-5An optical pickup device according to claim 1,The combination (m, n) of the diffraction orders of the m-th order diffracted light and the n-th order diffracted light is:
  (M, n) = any one of (8, 5), (6, 4), (2, 1), (5, 3), (2, 2), (3, 2), (10, 6) IsIt is characterized by that.
[0025]
  Claim 7The invention described isAny one of Claims 1-6An optical pickup device according to claim 1,The diffractive optical element generates a phase difference before and after passing through the diffractive optical element among the light beams having the wavelengths λ1, λ2, and λ3, and the light beams having the wavelengths λ1 and λ2. At least one is configured not to cause a phase difference before and after passing through the diffractive optical element.It is characterized by that.
[0046]
  Claim 8In the described invention, information is reproduced and / or recorded on the first optical information recording medium having the protective substrate thickness t1 using the light beam emitted from the first light source having the wavelength λ1, and the protective substrate thickness t2 (t1 With respect to the second optical information recording medium of ≦ t2), information is reproduced and / or recorded using a light beam emitted from the second light source having the wavelength λ2 (λ1 <λ2), and the protective substrate thickness t3 (t2 < Included in an optical pickup device that reproduces and / or records information using a light beam emitted from a third light source having a wavelength λ3 (λ2 <λ3) with respect to a third optical information recording medium at t3).LightAcademic elements,The optical element isA diffractive optical element disposed in a common optical path of the first light source, the second light source, and the third light source and having a first diffractive structureAndIn the case of reproducing and / or recording information on the first optical information recording medium, the second optical information recording medium, and the third optical information recording medium, the diffractive optical element included in the optical pickup device Almost all of the luminous fluxAs infinite parallel lightIncident,The light beam having the wavelength λ3 is configured so that diffracted light of different orders is obtained when passing through the central part of the diffractive optical element and when passing through the peripheral part of the diffractive optical element,A condensing spot is formed by the diffracted light of m (m is a natural number) generated by the diffractive optical element with respect to the first optical information recording medium, and generated by the diffractive optical element with respect to the second optical information recording medium. n (n is a natural number where n.noteq.m) is formed so as to form a focused spot by the diffracted light of the order.The numerical aperture of the condensing spot formed on the first optical information recording medium by the light beam having the wavelength λ1 is NA1, and the condensing spot formed on the second optical information recording medium by the light beam having the wavelength λ2. Is NA2, and NA3 is the numerical aperture of the condensing spot formed on the third optical information recording medium by the light flux having the wavelength λ3,
  NA3 <NA1
  NA3 <NA2
MeetIt is characterized by that.
  The invention according to claim 9 is the optical element according to claim 8, wherein the diffractive optical element is an objective optical element.
  The invention according to claim 10 is the optical element according to claim 8 or 9, wherein
  In reproducing and / or recording information on the third optical information recording medium, the spherical aberration has a discontinuous portion.
  Invention of Claim 11 is an optical element as described in any one of Claims 8-10, Comprising:
  The first diffractive structure of the diffractive optical element includes a plurality of diffracting ring zones that are serrated discontinuous surfaces;
  It is formed on the optical surface of the diffraction ring zone, and is formed of an optical path difference providing structure including a step-like discontinuous surface along the optical axis.
  Invention of Claim 12 is an optical element as described in any one of Claims 8-11, Comprising:
  The combinations (m, n) of the diffraction orders of the m-th order diffracted light and the n-th order diffracted light are (m, n) = (8, 5), (6, 4), (2, 1), ( 5, 3), (2, 2), (3, 2), (10, 6).
  Invention of Claim 13 is an optical element as described in any one of Claims 8-12,
  The diffractive optical element generates a phase difference before and after passing through the diffractive optical element among the light beams having the wavelengths λ1, λ2, and λ3, and the light beams having the wavelengths λ1 and λ2. At least one of them is configured so as not to cause a phase difference before and after passing through the diffractive optical element.
[0070]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the content of the present invention will be described in detail with reference to the drawings. However, embodiments of the present invention are not limited thereto.
(First embodiment)
The invention of claim 1 will be described with reference to FIG.
[0071]
In this embodiment, a “high-density optical disk” using a so-called blue-violet laser light source with a used wavelength of 405 nm is targeted, and a “high-density” protective substrate thickness t1 is 0.6 mm as the first optical information recording medium. It is assumed that the optical disk is a DVD having a protective substrate thickness t2 of 0.6 mm as the second optical information recording medium, and a CD having a protective substrate thickness t3 of 1.2 mm as the third optical information recording medium.
[0072]
FIG. 1 is a schematic diagram showing an optical pickup device according to the present invention.
[0073]
The laser diode LD1 is a first light source, and a blue-violet laser having a wavelength λ1 of 405 nm is used. However, a laser diode having a wavelength in the range of 390 nm to 420 nm can be appropriately employed. LD2 is a second light source, and a red laser having a wavelength λ2 of 655 nm is used, but a laser having a wavelength in the range of 630 nm to 680 nm can be appropriately employed. LD3 is a third light source, and an infrared laser having a wavelength λ3 of 780 nm is used, but one having a wavelength in the range of 750 nm to 800 nm can be appropriately employed.
[0074]
The beam splitter BS1 transmits the light source incident from the LD1 in the direction of the objective optical element OBL. The reflected light (returned light) from the optical disk (first optical information recording medium) passes through the sensor lens group SL1 to receive light. It has a function of condensing on S1. The function of BS2 is the same.
[0075]
BS3 is arranged to place the light flux from LD1 and the light flux from LD2 on the same optical path. BS4 is arranged to place the light flux from LD3 and the light flux from BS3 on the same optical path.
[0076]
The light beam projected from LD1 is incident on collimator CL1 via BS1, collimated into infinite parallel light, and then incident on objective lens OBL which is an objective optical element via BS3 and BS4. Then, a condensing spot is formed on the information recording surface via the protective substrate of the first optical information recording medium. After reflecting on the information recording surface, it follows the same path, passes through the collimator CL1, and then converges on the sensor S1 via the sensor lens SL1 by BS1. This sensor photoelectrically converts it into an electrical signal.
[0077]
Similarly, the light beam projected from the LD 2 forms a condensing spot on the optical disc (second optical information recording medium), is reflected, and finally converges on the sensor S2.
[0078]
Incidentally, the same applies to the light beam projected from the LD 3, but in this example, by providing a diffractive plate DP instead of the beam splitter, the return light is condensed to the sensor S 3. When reproducing information from a CD, the amount of light received may be less than that of a DVD or “high density optical disk”, and thus such a configuration can be employed.
Further, as described above, the light beams of the wavelengths λ1 to λ3 projected from the LD1 to LD3 are infinitely parallel to the objective optical element OBL serving as the diffractive optical element having the first diffractive structure, that is, substantially. Incident at the same angle.
The “same angle” means the same divergence angle or the same convergence angle. In the case of infinite parallel light, the divergence angle (or convergence angle) is zero.
[0079]
Note that the objective optical element OBL is a single lens in this figure, but may be composed of a plurality of optical elements as necessary. The material may be plastic resin or glass.
[0080]
The state where the light beam projected from LD1 and the light beam projected from LD2 are condensed on the information recording surface via the protective substrates of optical disks D1 and D2 are depicted on the left side of the optical axis of OBL. A state in which the projected light beam is condensed on the information recording surface via the protective substrate of the optical disc D3 is depicted on the right side of the optical axis of the OBL. In this way, the basic position is switched by an actuator (not shown) depending on the optical disk to be reproduced / recorded, and focusing is performed from the reference position.
[0081]
The numerical aperture required for the objective optical element OBL differs depending on the thickness of the protective substrate of each optical information recording medium and the size of the pits. Here, the numerical aperture NA3 for CD is 0.45, and the numerical apertures NA2 and NA1 of DVD and “high density optical disk” are both 0.65. However, it can be appropriately selected within the range of 0.43 to 0.50 for CD and 0.58 to 0.68 for DVD.
[0082]
IR is an aperture for cutting unnecessary light.
[0083]
In the present embodiment, as described above, the role of the “diffractive optical element disposed in the common optical path of the first light source, the second light source, and the third light source and having the first diffractive structure” is the objective optical element. It is given to OBL. Therefore, the objective optical element is provided with a sawtooth diffraction structure.
[0084]
Then, by setting the pitch (diffraction power) and depth (blazed wavelength) of the saw blade, the light beam from the first light source is formed as a condensed spot by the second-order diffracted light for the “high-density optical disk”. For a DVD, the light beam from the second light source is formed as a condensing spot by the first-order diffracted light.
[0085]
Thus, by using light having different diffraction orders depending on the relationship between the wavelengths λ1 and λ2, the diffraction efficiency in each case can be increased, and the amount of light can be secured.
[0086]
For CD, the k-th order (m / 2 when the diffraction order for wavelength λ1 is m) is desirable due to the relationship between wavelengths λ1 and λ3.
In this example, a condensing spot is formed as the same first-order diffracted light as DVD.
[0087]
In this example, the example in which the diffractive structure is provided in the objective optical element has been described as the diffractive optical element. However, as in claims 4 and 6, a diffractive structure that generates such different-order diffracted light may be provided in the collimator. However, another optical element can be provided in the optical path.
[0088]
Also for the switching of the apertures described above, known techniques including diffractive optical elements can be applied.
[0089]
In the above embodiment, the reproduction of information has been described. However, the basic configuration and optical action are not changed even in the recording of information, and a condensed spot is formed on the recording surface of the optical information recording medium. Recording is performed by causing a thermochemical change in the recording layer.
[0090]
It goes without saying that an optical element having an optical correction structure for performing temperature compensation and / or chromatic aberration compensation can be provided in the optical path as necessary. These optical correction structures can be realized by a diffractive structure or a phase difference providing structure, and can be provided in an objective optical element, a collimator, and other elements.
[0091]
(Second Embodiment)
The invention of claim 7 will be described with reference to FIG.
For each optical element, the description of the same function as in the first embodiment is omitted. In this embodiment, the objective optical element OBL has the role of the first compatible optical element. The collimator CL3 has the role of the second compatible optical element.
That is, the objective optical element OBL that is the first compatible optical element is disposed in the optical path through which all the light sources pass, and the collimator CL3 that is the second compatible optical element is disposed in the optical path through which only the third light source passes. The
[0092]
The objective optical element OBL, which is the first compatible optical element, has a diffractive structure, thereby achieving compatibility between the “high-density optical disk” and the DVD (first compatible function).
Specifically, spherical aberration based on the wavelength difference between the first light source and the second light source is corrected. Further, even if the phase difference providing structure is used instead of the diffractive structure, the same optical action can be obtained.
[0093]
For optical information recording media, if the thickness of the protective substrate is different, spherical aberration occurs due to the difference. Here, both the “high density optical disc” and the DVD use the same protective substrate of 0.6 mm. Therefore, such spherical aberration based on the substrate thickness difference does not occur.
[0094]
The collimator CL3, which is the second compatible optical element, is also provided with a diffractive structure. This is combined with the diffractive structure of the objective optical element OBL to achieve compatibility between the “high-density optical disk” and the CD, and further compatibility between the DVD and the CD (second compatibility function).
Specifically, regarding compatibility between “high-density optical disc” and CD, since the wavelength used and the thickness of the protective substrate are different, the spherical aberration based on the wavelength difference between the first light source and the third light source can be reduced. Both spherical aberrations based on the protective substrate thickness difference (0.1 mm and 1.2 mm) are corrected.
[0095]
The same applies to compatibility between DVD and CD. Both spherical aberration based on the wavelength difference between the second light source and the third light source and spherical aberration based on the difference in thickness of the protective substrate (0.6 mm and 1.2 mm) are obtained. to correct.
Thereby, a suitable condensing spot can be formed for each optical information recording medium.
In addition, as in the previous embodiment, a condensing spot is formed by diffracted light of different diffraction orders. Therefore, for a “high-density optical disc” or DVD, a sufficient amount of light is ensured and reliable information is obtained. Recording and / or playback is possible.
[0096]
In this embodiment, an example in which a diffractive optical element is provided in the collimator CL3 as the second compatible optical element is shown (claim 11). However, for example, an optical path difference providing structure that provides only a phase is provided. Even if an optical element (Claim 9) or a liquid crystal element capable of electrically switching the optical action is used, the same optical action can be obtained (Claim 10). In particular, the liquid crystal element can be dynamically controlled because it has an effect of changing the refractive index. Further, interchange may be performed between the first compatible optical element and the diffractive structure, and a dichroic filter that serves only as a diaphragm on the CD side may be used.
In addition, both the first compatible function and the second compatible function can be achieved by providing a phase difference providing structure.
[0097]
(Third embodiment)
This embodiment corresponds to the inventions of claims 1 and 2 and is an optical pickup device in which a coupling lens is provided in place of a predetermined collimator from the configuration of FIG. Specifically, coupling lenses Co1 to Co3 (not shown) are provided instead of the collimators CL1 to CL3.
Since a collimator that collimates incident light from the light source into parallel light is not provided, finite divergent light enters the objective optical element. Since the coupling lens does not have as much power as the collimator, the coupling lens is small. With such a configuration, the pickup device can be miniaturized.
[0098]
In this way, by using finite divergent light instead of infinite parallel light, the magnification of the condensing optical system with respect to the light beam incident on the objective optical element OBL is changed, so that the spherical aberration and the substrate thickness difference based on the wavelength difference are thereby changed. Although it is known that spherical aberration based can be corrected, there is still a case where sufficient correction cannot be performed.
Further, the use of finite light causes a problem that the temperature characteristics and tracking characteristics deteriorate.
[0099]
Therefore, in this embodiment, light beams having different magnifications are made incident on the objective optical element OBL for each wavelength. However, the first compatible optical element and the second compatible optical element allow the spherical aberration based on the wavelength difference and the protective substrate thickness difference. And spherical aberration based on the difference in magnification of the luminous flux are corrected.
[0100]
As in the second embodiment, the first compatible element is an objective optical element provided with a diffractive structure, and the second compatible optical element is provided with a coupling lens Co3 provided with a diffractive structure.
[0101]
Thereby, all the light beams from the first light source to the third light source are incident on the objective optical element OBL with finite divergent light, but all the spherical aberration is corrected and a suitable condensing spot is formed.
[0102]
Here, since the coupling lenses Co1 to C3 are used instead of the collimators CL1 to C3, diverging light is incident on the objective optical element for all light sources, but one of them is a collimator, and the objective lens is infinite. Parallel light may be incident.
[0103]
(Fourth embodiment)
Another embodiment of the invention of claim 1 will be described with reference to FIG. Components having the same reference numerals have basically the same functions as those in the first embodiment, but different components will be described. The optical action is almost the same.
[0104]
In this example, the light source is composed of two units. Specifically, the LD 2 ′ in FIG. 2 is a so-called two-laser one-package light source unit in which the second light source (DVD light source) and the third light source (CD light source) are housed in the same package. Is used.
[0105]
In this package, the second light source is adjusted so as to be positioned on the optical axis. Therefore, the third light source is located at a position slightly away from the optical axis. Techniques for improving the characteristics are already known, and these techniques can be applied as necessary. Here, the correction is performed by using the correction plate DP. A grating is formed on the correction plate DP, thereby correcting the deviation from the optical axis and contributing to the condensing on the sensor S2.
[0106]
Note that a light source beam for DVD is drawn from the LD 2 ′ by a solid line, and a light source beam for CD is drawn by a dotted line.
[0107]
BS2 is arranged to place the light beam from LD1 and the light beam from LD2 'on the same optical path. BS3 is arranged to cause the light beam from LD2 ′ to enter sensor lens SL2.
[0108]
The light beam projected from the LD1 is incident on the collimator CL1 via the BS1, collimated into infinite parallel light, and then incident on the objective lens OBL, which is an objective optical element, via the BS2. Then, a condensing spot is formed on the information recording surface via the protective substrate of the first optical information recording medium. After reflecting on the information recording surface, it follows the same path, passes through the collimator CL1, and then converges on the sensor S1 via the sensor lens SL1 by BS1. This sensor photoelectrically converts it into an electrical signal.
[0109]
Similarly, the light beam projected from the LD 2 ′ forms a condensing spot on the optical disc (second optical information recording medium or third optical information recording medium), reflects, and finally condenses on the sensor S 2.
[0110]
In the present embodiment, the objective optical element OBL has a role of “a diffractive optical element disposed in a common optical path of the first light source, the second light source, and the third light source and having a diffractive structure”. Therefore, the objective optical element is provided with a sawtooth diffraction structure.
[0111]
Then, by setting the pitch (diffraction power) and depth (blazed wavelength) of the saw blade, the light beam from the first light source is formed as a condensed spot by the second-order diffracted light for the “high-density optical disk”. For a DVD, the light beam from the second light source is formed as a condensing spot by the first-order diffracted light.
[0112]
Thus, by using light having different diffraction orders depending on the relationship between the wavelengths λ1 and λ2, the diffraction efficiency in each case can be increased, and the amount of light can be secured.
[0113]
For CD, the k-th order (m / 2 when the diffraction order for wavelength λ1 is m) is desirable due to the relationship between wavelengths λ1 and λ3.
In this example, a condensing spot is formed as the same first-order diffracted light as DVD.
[0114]
In this example, the example in which the diffractive structure is provided in the objective optical element has been described as the diffractive optical element. However, the collimator CL1 may be provided with a diffractive structure that generates such different-order diffracted light as in claims 4 and 6. It is also possible to provide another optical element in the optical path.
[0115]
Also for the switching of the apertures described above, known techniques including diffractive optical elements can be applied.
[0116]
In the above embodiment, the reproduction of information has been described. However, the basic configuration and optical action are not changed even in the recording of information, and a condensed spot is formed on the recording surface of the optical information recording medium. Recording is performed by causing a thermochemical change in the recording layer.
[0117]
It goes without saying that an optical element having an optical correction structure for performing temperature compensation and / or chromatic aberration compensation can be provided in the optical path as necessary. These optical correction structures can be realized by a diffractive structure or a phase difference providing structure, and can be provided in an objective optical element, a collimator, and other elements.
[0118]
(Fifth embodiment)
Similarly, another embodiment of the invention of claim 7 will be described with reference to FIG. For each optical element, the description of the same function as that of the fourth embodiment is omitted. In this embodiment, the objective optical element OBL has the role of the first compatible optical element. The collimator CL2 has the role of the second compatible optical element.
In other words, the objective optical element OBL that is the first compatible optical element is disposed in the optical path through which all the light sources pass, and the second light source and the third light source pass through the collimator CL2 that is the second compatible optical element. Located in the optical path.
[0119]
The objective optical element OBL, which is the first compatible optical element, has a diffractive structure, thereby contributing to the formation of a condensing spot necessary for a “high-density optical disk”. Specifically, compatibility between the first optical information recording medium and the second optical information recording medium is performed.
Further, even if the phase difference providing structure is used instead of the diffractive structure, the same optical action can be obtained.
[0120]
For optical information recording media, if the thickness of the protective substrate is different, spherical aberration occurs due to the difference. Here, both the “high density optical disc” and the DVD use the same protective substrate of 0.6 mm. Therefore, spherical aberration based on the substrate thickness difference does not occur.
The collimator CL2, which is the second compatible optical element, is also provided with a diffractive structure. This is combined with the diffractive structure of the objective optical element OBL to achieve compatibility between the DVD and the CD (second compatibility function).
[0121]
Regarding compatibility between DVD and CD, since the wavelength used and the thickness of the protective substrate are different, spherical aberration based on the wavelength difference between the second light source and the third light source and the protective substrate thickness difference (0.6 mm) 1.2 mm) to correct both spherical aberrations.
Thereby, a suitable condensing spot can be formed for each optical information recording medium.
In addition, as in the previous embodiment, a condensing spot is formed by diffracted light of different diffraction orders. Therefore, for a “high-density optical disc” or DVD, a sufficient amount of light is ensured and reliable information is obtained. Recording and / or playback is possible.
[0122]
In this embodiment, an example in which a diffractive optical element is provided in the collimator CL2 as the second compatible optical element is shown (claim 11). However, for example, an optical path difference providing structure that provides only a phase is provided. Even if an optical element (Claim 9) or a liquid crystal element capable of electrically switching the optical action is used, the same optical action can be obtained (Claim 10). In particular, the liquid crystal element can be dynamically controlled because it has an effect of changing the refractive index. Further, interchange may be performed between the first compatible optical element and the diffractive structure, and a dichroic filter that serves only as a diaphragm on the CD side may be used.
[0123]
(Sixth embodiment)
This embodiment is another embodiment corresponding to the first and second aspects of the present invention, and is an optical pickup device in which a coupling lens is provided instead of the predetermined collimator from the configuration of FIG. Specifically, coupling lenses Co1 and 2 are provided instead of the collimators CL1 and CL2.
Since a collimator that collimates incident light from the light source into parallel light is not provided, finite divergent light is incident on the objective optical element, and the incident angles of all the lights are substantially the same. Since the coupling lens does not have as much power as the collimator, the coupling lens is small. With such a configuration, the pickup device can be miniaturized.
[0124]
In this way, by using finite divergent light instead of infinite parallel light, the magnification of the condensing optical system with respect to the light beam incident on the objective optical element OBL is changed, so that the spherical aberration and the substrate thickness difference based on the wavelength difference are thereby changed. Although it is known that spherical aberration based can be corrected, there is still a case where sufficient correction cannot be performed.
Further, the use of finite light causes a problem that the temperature characteristics and tracking characteristics deteriorate.
[0125]
Therefore, in this embodiment, light beams having different magnifications are made incident on the objective optical element OBL for each wavelength. However, the first compatible optical element and the second compatible optical element allow the spherical aberration based on the wavelength difference and the protective substrate thickness difference. And spherical aberration based on the difference in magnification of the luminous flux are corrected.
[0126]
As in the fifth embodiment, the first compatible element is a diffractive structure provided on the objective optical element, and the second compatible optical element is a diffractive structure provided on the coupling lens Co3.
[0127]
Thereby, all the light beams from the first light source to the third light source are incident on the objective optical element OBL with finite divergent light, but all the spherical aberration is corrected and a suitable condensing spot is formed.
[0128]
Here, since the coupling lenses Co1 to C3 are used instead of the collimators CL1 to C3, diverging light is incident on the objective optical element for all light sources, but one of them is a collimator, and the objective lens is infinite. Parallel light may be incident.
[0129]
(Seventh embodiment)
In this embodiment, as shown in FIG. 3, the numerical aperture NA3 is formed on one optical surface 11 (emission surface) of the objective optical element 10 and on the information recording surface of the CD as the third optical information recording medium. A plurality of (two) ring-shaped optical surfaces (Rs, Rl) with the optical axis L as the center are continuously formed through the step surface 20 in a region where a light beam of wavelength λ3 that forms a condensing spot is passed. Has been. In the following description, the entire optical surface on which the annular optical surface is formed may be referred to as “S1 surface”.
The number of these annular optical surfaces is preferably 2 to 10.
[0130]
Here, of the two annular optical surfaces, the annular optical surface including the optical axis L is Rs, and the annular optical surface farthest from the optical axis is Rl.
Note that the annular optical surface Rs including the optical axis L includes not only the “annular zone” but also a substantially circular shape centered on the optical axis L, for example, as viewed from the optical axis L direction. The shape of the annular optical surface Rs shown in the present embodiment is substantially circular when viewed from the optical axis L direction.
Of the two step surfaces 20 continuous to the annular optical surface Rl, the distance parallel to the optical axis L of the step surface 20 closer to the optical axis L is compared with the distance parallel to the optical axis L of the other step surface 20. And it is preferable that it is short.
[0131]
The annular optical surface Rs is composed of a refractive surface, and light fluxes having wavelengths λ1, λ2, and λ3 that have passed through the annular optical surface Rs are transmitted to respective optical information recording media (“high-density optical disk”, DVD, and CD). ) Is formed on the information recording surface.
The annular optical surface Rl is similarly formed of a refracting surface, but is formed at a position shifted from the annular optical surface Rs by a predetermined distance to the light source side.
The light beam having the wavelength λ3 that has passed through the annular optical surface Rl also forms a condensed spot on the information recording surface of the third optical information recording medium.
[0132]
On the other optical surface 12 (incident surface) of the objective optical element 10, a diffraction ring zone as the first diffraction structure 30 is formed. In the following description, the entire optical surface on which the first diffractive structure 30 is formed may be referred to as “S2 surface”.
The first diffractive structure 30 is formed on the incident surface 12 in a region (hereinafter also referred to as a region A1) through which a light beam having a wavelength λ3 that forms a condensed spot having a numerical aperture NA3 passes through the third optical information recording medium. Has been.
The region A1 where the first diffractive structure is formed corresponds to a region through which light fluxes of wavelengths λ1, λ2, and λ3 that form a condensed spot on each optical information recording medium pass through the annular optical surface Rs. To do.
[0133]
In the present embodiment, it is an area farther from the optical axis L than the area A1, and has wavelengths λ1, λ2, and λ3 that form a condensed spot on each optical information recording medium after passing through the annular optical surface Rl. A diffraction zone as the second diffraction structure 40 is formed in a region through which the light beam passes (hereinafter also referred to as a region A2).
Further, the structure of the region farther from the optical axis than the region A2 is not limited, but a diffraction ring zone is formed in the present embodiment. Since the structure of these diffraction ring zones is well known, a description thereof will be omitted.
Then, by reproducing the m-th order, n-th order and k-th order diffracted light of wavelengths λ1, λ2 and λ3 by the first diffractive structure on the information recording surface of each optical information recording medium, information reproduction and / or recording is performed. Is supposed to do.
[0134]
Here, the light beams having the wavelengths λ1 and λ2 are incident on the objective optical element 10 with the same divergence angle or the same infinite light, and the first diffractive structure 30 has the light beams having the wavelengths λ1 and λ2 on the optical surface 10 of the objective optical element 10, It is preferable that the spherical aberration generated when passing through 12 is corrected by the difference between the wavelength λ1 and the wavelength λ2.
Also, the combinations of the diffraction orders of the diffracted lights are (m, n) = (8, 5), (6, 4), (2, 1), (5, 3), (2, 2), (3 2), (10, 6) is preferable, and (m, n, k) = (2, 1, 1,), (2, 1, 0), (5, 3, 2), (2, 2, 1), or any combination of (3, 2, 2).
In addition, when a light beam having wavelengths λ1, λ2, and λ3 is incident, a combination of diffracted light having the maximum diffracted light ratio among the diffracted light of each light beam generated by the first diffractive structure 30 and the second diffractive structure 40 are generated. It is preferable that the combination of diffracted light with the maximum diffracted light ratio among the diffracted light of each light flux is different.
[0135]
Moreover, although it is preferable that the combination of the diffracted light which becomes the maximum diffracted light rate among the diffracted light of each light beam produced by the 2nd diffraction structure 40 is 1, 1, 1, it is not specified to this.
Further, it is preferable that k = m / 2 is satisfied under the conditions of 370 nm ≦ λ1 ≦ 430 nm and 760 nm ≦ λ3 ≦ 810 nm.
The diffraction efficiencies of the m-th order diffracted light and the n-th order diffracted light are both preferably 80% or more.
The diffraction efficiency of the k-th order diffracted light is preferably 40% or more.
[0136]
FIG. 4 shows an example of a longitudinal spherical aberration diagram on each information recording surface of a high-density optical disc, DVD, or CD when the objective optical element 10 thus configured is used in an optical pickup device. is there. In FIGS. 4, 5, 8 and 10 below, the vertical axis represents the numerical aperture and the horizontal axis represents the spherical aberration.
As shown in FIG. 4A, the light beam having the wavelength λ1 used for the high-density optical disc has no change in spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ1 that has passed through the annular optical surface Rs is collected on the information recording surface of the first optical information recording medium with almost no aberration.
On the other hand, the spherical aberration becomes discontinuous on the underside within the numerical aperture corresponding to the location where the annular optical surface Rl is formed.
When the shape of the second diffractive structure is changed and the combination of the orders of diffracted light that gives the maximum diffraction efficiency when light of wavelengths λ1, λ2, and λ3 is incident, the spherical aberration is discontinuous on the over side. It can also be.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA1.
[0137]
Further, as shown in FIG. 4B, the light beam having the wavelength λ2 used for DVD does not change the spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ2 that has passed through the annular optical surface Rs is collected on the information recording surface of the second optical information recording medium with almost no aberration.
In addition, the spherical aberration does not change even within the numerical aperture corresponding to the location where the annular optical surface Rl is formed, that is, the light beam having the wavelength λ2 that has passed through the annular optical surface Rl is the second optical information recording medium. The light is condensed almost without aberration on the information recording surface.
Therefore, when viewed in the entire region corresponding to the numerical aperture NA2, spherical aberration can be almost eliminated.
[0138]
Further, as shown in FIG. 4C, the light beam having the wavelength λ3 used for CD is gradually increased in the spherical aberration toward the over side within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. growing.
On the other hand, the spherical aberration becomes discontinuous on the underside within the numerical aperture corresponding to the location where the annular optical surface Rl is formed.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA3. Note that the light beam having the wavelength λ3 that passes through the position away from the optical axis from the portion where the annular optical surface Rl is formed becomes flare light, and the spot diameter corresponds to the required numerical aperture.
[0139]
The wavefront aberration of the focused spot formed on the third optical information recording medium by the light beam having the wavelength λ3 is preferably 0.050 [λ3 rms] or less.
Further, the paraxial ray of the light beam having the wavelength λ3 with respect to the position in the optical axis direction (best image plane position) at which the wavefront aberration of the condensed spot formed on the third optical information recording medium by the light beam having the wavelength λ3 is minimized. Is preferably condensed on the light source side.
In addition, it is preferable that the light beam having the wavelength λ3 that has passed through the annular optical surface Rs and the light beam having the wavelength λ3 that has passed through the annular optical surface Rl are condensed at a distance of 10 μm or more in the optical axis direction.
In addition, it is preferable that the light beam with the wavelength λ2 that has passed through the annular optical surface Rs and the light beam with the wavelength λ2 that has passed through the annular optical surface Rl are condensed at a distance of 5 μm or more in the optical axis direction.
Further, the length D in the optical axis direction of the step surface between two adjacent annular optical surfaces is 1.5 μm ≦ D ≦ 2.0 μm, 2.0 μm ≦ D ≦ 3.0 μm, or 3.0 μm ≦ D ≦. It is preferable to satisfy 4.5 μm.
[0140]
In addition, the phase difference φ at the condensing spot between the light beam with the wavelength λ3 that has passed through the annular optical surface Rs and the light beam with the wavelength λ3 that has passed through the annular optical surface other than the annular optical surface Rs is −0.1π. It is preferable to satisfy ≦ φ ≦ 0.1π.
Further, after passing through the ring-shaped optical surface Rl, the condensing position fB3 of the light beam having the wavelength λ3 that forms the condensing spot is the best image surface of the condensing spot formed on the third optical information recording medium by the light beam having the wavelength λ3. It is preferable to satisfy | fB3 | ≦ 5 μm with respect to the position in the optical axis direction.
As described above, according to the objective optical element and the optical pickup device using the objective optical element shown in the present embodiment, compatibility with three types of optical information recording media can be achieved.
[0141]
FIG. 5 shows a longitudinal spherical aberration diagram of the objective optical element in which the S1 surface and the S2 surface are configured as shown in FIG. 3 by changing the surface shape of the second diffractive structure and the annular optical surface Rl. It may be.
As shown in FIG. 5A, the light beam having the wavelength λ1 used for a high-density optical disc has no change in spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ1 that has passed through the annular optical surface Rs is collected on the information recording surface of the first optical information recording medium with almost no aberration.
Also, the spherical aberration does not change even within the numerical aperture corresponding to the location where the annular optical surface Rl is formed, that is, the light beam having the wavelength λ1 that has passed through the annular optical surface Rl is the first optical information recording medium. The light is condensed almost without aberration on the information recording surface.
Accordingly, spherical aberration can be almost eliminated when viewed in the entire region below the numerical aperture NA1.
[0142]
Further, as shown in FIG. 5B, the light beam having the wavelength λ2 used for DVD does not change the spherical aberration at the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ2 that has passed through the band-shaped optical surface Rs is condensed on the information recording surface of the second optical information recording medium with almost no aberration.
On the other hand, the spherical aberration becomes discontinuous on the under side at the numerical aperture corresponding to the portion where the annular optical surface Rl is formed.
When the shape of the second diffractive structure is changed and the combination of the orders of diffracted light that gives the maximum diffraction efficiency when light of wavelengths λ1, λ2, and λ3 is incident, the spherical aberration is discontinuous on the over side. It can also be.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA2.
In this case, the longitudinal spherical aberration diagram of the light beam with the wavelength λ3 used for CD shown in FIG. 5C is the same as FIG. 4C.
[0143]
Moreover, as shown in FIG. 6, the objective optical element which combined the S1 surface and S2 surface which were shown in the said 7th Embodiment on the incident surface side may be sufficient.
More specifically, the entire second diffractive structure in the A2 region is formed at a position shifted by a predetermined distance toward the optical information recording medium side.
Even with such a configuration, the longitudinal spherical aberration diagram has substantially the same shape as that shown in FIG. 4 or FIG. 5, and an optical pickup device compatible with three types of optical information recording media and An objective optical element can be obtained.
In addition, although illustration is abbreviate | omitted, the objective optical element with which S1 surface and S2 surface were combined by the output surface side may be sufficient.
[0144]
(Eighth embodiment)
The objective optical element shown in the present embodiment is different from the seventh embodiment only in that the region A2 is composed of a refracting surface 50 as shown in FIG.
[0145]
FIG. 8 shows an example of a longitudinal spherical aberration diagram on each information recording surface of a high-density optical disc, DVD, and CD when the objective optical element configured as described above is used.
As shown in FIG. 8A, the light beam having the wavelength λ1 used for a high-density optical disc has no change in spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ1 that has passed through the annular optical surface Rs is collected on the information recording surface of the first optical information recording medium with almost no aberration.
On the other hand, the spherical aberration becomes discontinuous on the underside within the numerical aperture corresponding to the location where the annular optical surface Rl is formed.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA1.
[0146]
Further, as shown in FIG. 8B, the light beam having the wavelength λ2 used for DVD does not change the spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ2 that has passed through the annular optical surface Rs is collected on the information recording surface of the second optical information recording medium with almost no aberration.
On the other hand, the spherical aberration becomes discontinuous on the underside within the numerical aperture corresponding to the location where the annular optical surface Rl is formed.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA2.
In this case, the longitudinal spherical aberration diagram of the light beam with the wavelength λ3 used for the CD shown in FIG. 8C is the same as FIG. 4C.
As described above, according to the objective optical element and the optical pickup device using the objective optical element shown in the present embodiment, compatibility can be provided for three types of optical information recording media.
[0147]
(Ninth embodiment)
The objective optical element shown in the present embodiment is one optical surface 11 (emission surface) of the objective optical element as shown in FIG. A plurality of annular optical surfaces 60 centering on the optical axis are formed in a region where a light beam having a wavelength λ3 that forms a condensing spot having a numerical aperture NA3 passes on an information recording surface of a CD as an information recording medium. The difference is that a diffraction ring zone as the first diffraction structure 30 is formed in both the areas A1 and A2 of the incident surface 12.
[0148]
More specifically, a plurality of annular optical surfaces 60 centering on the optical axis are formed continuously in a stepped manner via the step surface 70.
Of the light beams having the wavelengths λ1, λ2, and λ3, the light beam having the wavelength λ3 is given a predetermined optical path difference when passing through each annular optical surface 60, thereby causing a phase difference before and after the passage. In addition, for at least one of the light beams having the wavelengths λ1 and λ2 (both in the present embodiment), a predetermined optical path difference is not given when passing through each annular optical surface 60, and the position is changed before and after the passage. It does not cause a phase difference.
[0149]
Here, among the plurality of annular optical surfaces 60, the annular optical surface including the optical axis L is Rs, and the annular optical surface farthest from the optical axis L is Rl.
The annular optical surface Rs is composed of a refractive surface, and light fluxes having wavelengths λ1, λ2, and λ3 that have passed through the annular optical surface Rs are transmitted to respective optical information recording media (“high-density optical disk”, DVD, and CD). ) Is formed on the information recording surface.
Similarly, the annular optical surface Rl is formed of a refracting surface, and the light beam having the wavelength λ3 that has passed through the annular optical surface Rl also forms a condensed spot on the information recording surface of the third optical information recording medium. It has become.
[0150]
FIG. 10 shows an example of a longitudinal spherical aberration diagram on each information recording surface of a high-density optical disc, DVD, and CD when the objective optical element configured as described above is used.
As shown in FIG. 10A, the light beam having the wavelength λ1 used for a high-density optical disc has no change in spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ1 that has passed through the annular optical surface Rs is collected on the information recording surface of the first optical information recording medium with almost no aberration.
Further, even at the numerical aperture corresponding to the portion where the annular optical surface Rl is formed, the spherical aberration does not change, that is, the light flux having the wavelength λ1 that has passed through the annular optical surface Rl is the first optical information recording medium. Condensed on the information recording surface with almost no aberration.
Accordingly, when viewed in the entire region corresponding to the numerical aperture NA1, substantially spherical aberration can be eliminated.
In some cases, due to the ring-shaped structure on the S1 surface, a slight deviation of the light collecting position due to the light flux that has passed through each ring-shaped optical surface as shown in FIG. Although it may appear in (b), it is schematically shown here as a longitudinal spherical aberration diagram that is completely free of aberrations.
[0151]
Further, as shown in FIG. 10B, the light beam having the wavelength λ2 used for DVD does not change the spherical aberration within the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. The light beam having the wavelength λ2 that has passed through the annular optical surface Rs is collected on the information recording surface of the second optical information recording medium with almost no aberration.
In addition, the spherical aberration does not change even within the numerical aperture corresponding to the location where the annular optical surface Rl is formed, that is, the light beam having the wavelength λ2 that has passed through the annular optical surface Rl is the second optical information recording medium. The light is condensed almost without aberration on the information recording surface.
Accordingly, when viewed in the entire region corresponding to the numerical aperture NA2, substantially spherical aberration can be eliminated.
[0152]
Further, as shown in FIG. 10C, the light beam having the wavelength λ3 used for the CD gradually has spherical aberration over the numerical aperture corresponding to the portion where the annular optical surface Rs is formed. It gets bigger.
On the other hand, the spherical aberration is discontinuous on the underside within the numerical aperture corresponding to the portion where the annular optical surface Rl is formed.
Then, it is relatively easy to design the shapes of the S1 surface and the S2 surface so that the spherical aberration is within a practically unobstructed range when viewed in the entire region corresponding to the numerical aperture NA3. Note that the light flux having the wavelength λ3 that passes through the position away from the optical axis from the portion where the annular optical surface Rl is formed becomes flare light.
For this reason, it is not necessary to provide a separate diaphragm for the light beam having the wavelength λ3.
As described above, according to the objective optical element and the optical pickup device using the objective optical element shown in the present embodiment, compatibility can be provided for three types of optical information recording media.
[0153]
Moreover, you may form the diffraction zone 80 and the optical path difference providing structure 90 as shown to FIG. 11 (a), (b) in one optical surface 12 of the objective lens 10. FIG.
Specifically, the objective lens 10 includes a plurality of diffraction ring zones 80 that are serrated discontinuous surfaces having a substantial inclination with respect to a predetermined aspherical optical surface with the optical axis L as the center. In addition, on the optical surface of each diffraction ring zone 80, a step-like irregularity along the optical axis that gives a predetermined optical path difference to the light beam passing through these diffraction ring zones 80 is formed. An optical path difference providing structure 90 including a continuous surface (step) 91 is formed.
[0154]
11 (a) and 11 (b), the line indicated by the alternate long and short dash line is an optical surface (having a predetermined aspherical shape) having a virtual aspherical shape formed by connecting the starting points of the diffraction ring zones 80 as described above. The line indicated by a two-dot chain line is a concentric saw-tooth shape that has been formed so as to increase in thickness with increasing distance from the optical axis L with the optical axis L as the center. This represents the outer shape of the diffraction zone 80.
A solid line indicates an actual lens including an outer shape of a step 91 that is formed on the optical surface of each diffraction ring zone 80 and gives a predetermined optical path difference to a light beam passing through each diffraction ring zone 80. It represents the shape.
[0155]
The depth d1 (length in the optical axis L direction) of the step 91 is substantially equal to the value represented by λ2 / (n−1), for example, where n is the refractive index of the objective lens with respect to the wavelength λ2. An optical path difference corresponding to approximately one wavelength λ2 occurs between the light beam having the wavelength λ2 that passes through one step and the light beam having the wavelength λ2 that passes through the adjacent step, and the wavefront does not shift. It is set to length.
In addition, the shape of the surface 91a (optical functional surface) of each step is divided by the section corresponding to each step 91, by dividing the shape of the surface of the sawtooth diffraction ring zone 80 indicated by a two-dot chain line in the figure, The shape approximates the shape translated in the optical axis L direction.
[0156]
As described above, the optical path difference providing structure 90 having the optical surface provided with the step 91 having a predetermined depth has a function of giving a predetermined optical path difference to the light beam passing through the objective lens 10. The shape of the surface 91a of the step is divided into sections corresponding to the respective steps 91 and is translated in the direction of the optical axis L, so that the maximum luminous flux of each of the wavelengths λ1 to λ3 is obtained. Thus, it has a function of extracting diffracted light of the diffraction order that gives a diffraction efficiency of.
For example, when a light beam with a wavelength λ1 (650 nm) is incident on the objective lens, the light beam with a wavelength λ1 is diffracted by the diffraction ring zone 80 and passes through the regions A to E in FIG. Each of the luminous fluxes is substantially given a phase difference of 780 nm−650 nm = 130 nm, that is, 2 / 5π radians, and as a result, is subjected to a diffractive action due to a change in the phase of the luminous flux of wavelength λ1. It has become.
[0157]
On the other hand, when a light beam having the wavelength λ2 (780 nm) is incident, the light beam having the wavelength λ2 is diffracted by the diffraction ring zone 80 and passes through the areas A to E in FIG. A phase difference corresponding to λ2 is given, and the phase difference generated between the light beams that have passed through the areas A to E is almost zero. Therefore, the light beam having the wavelength λ <b> 2 is transmitted as it is without being substantially diffracted by the optical path difference providing structure 90.
As described above, since the diffraction orders of the light beams of the respective wavelengths can be substantially changed in two stages of the diffraction ring zone 80 formed on the objective lens 10 and the optical path difference providing structure 90, the diffraction orders of the light beams are appropriately set. By changing it, it is possible to obtain diffracted light having a sufficient amount of light according to the type of the optical information recording medium. In addition, the degree of freedom in design with respect to diffraction efficiency and diffraction order can be increased.
[0158]
【Example】
Next, a first example of the optical pickup device and the optical element shown in the above embodiment will be described.
In this embodiment, an objective lens in which the S1 surface and the S2 surface are combined on the incident surface side as shown in FIG. 6 is used.
More specifically, as shown in FIG. 12, the incident surface of the objective lens, which is a double-sided aspheric single lens, is a second surface having a height h from the optical axis L of 1.45 mm or more, 1.1 mm or more. Are divided into a 2 ′ surface of less than 1.45 mm and a 2 ″ surface of less than 1.1 mm.
[0159]
Further, the second 'surface and the second' surface have a plurality of diffraction ring zones 80 that are sawtooth-like discontinuous surfaces having a substantial inclination with respect to a predetermined aspherical optical surface, and On the optical surface of each diffracting ring zone 80, an optical path difference consisting of a step-like discontinuous surface 91 (step) along the optical axis that gives a predetermined optical path difference to the light beam passing through these diffracting ring zones 80. An imparting structure 90 is formed, and each step 91 formed in one diffraction ring zone 80 has a shape that protrudes toward the light source as the distance from the optical axis L increases.
Moreover, only the sawtooth-shaped diffraction zone is formed on the second surface.
The light beams of wavelengths λ1, λ2, and λ3 that pass through the second ′ surface and the second ″ surface are obtained as diffracted light beams having diffraction orders m = 2, n = 1, and k = 0 that provide the maximum diffraction efficiency. As shown, the diffraction ring zone 80 and the optical path difference providing structure 90 are diffracted and emitted.
[0160]
More specifically, when it is assumed that the optical path difference providing structure 90 is not provided, the optical surface of the diffracting ring zone 80 is diffracted so that the 2 (= mB1) order diffracted light of the light beam having the wavelength λ1 has the maximum diffraction efficiency, The 1 (= mB2) order diffracted light of the light beam with wavelength λ2 is diffracted so as to have the maximum diffraction efficiency, and the 1 (= mB3) order diffracted light of the light beam with wavelength λ3 is diffracted so as to have the maximum diffraction efficiency.
Further, the optical path difference providing structure 90 gives an optical path difference in which the 2 (= m) order diffracted light of the light beam having the wavelength λ1 has the maximum diffraction efficiency to the diffracted light, and 1 (= n) of the light beam having the wavelength λ2. ) The order diffracted light gives an optical path difference having the maximum diffraction efficiency, and the 0 (= k) order diffracted light of the light flux of wavelength λ3 gives the optical path difference having the maximum diffraction efficiency.
[0161]
That is, in the following formulas (1) to (3),
m = mB1-mD (1)
n = mB2-mD + (-1, 0 or 1) (2)
k = mB3-mD + (-1, 0 or 1) (3)
As mB1 = 2, mB2 = 1, mB3 = 1, mD = 0,
m = 2-0 = 0
n = 1-0 + 0 = 1
k = 1-0-1 = 0
An optical path difference is given to each light flux so that
[0162]
In addition, the light beams of wavelengths λ1, λ2, and λ3 that pass through the second surface are diffracted from the diffraction ring zone 80 so that diffracted light of diffraction orders m = 2, n = 1, and k = 1 can be obtained. Received and emitted.
As described above, for the light beams having the wavelengths λ1 and λ2, diffracted light beams having diffraction orders m = 2 and n = 1 are obtained when passing through the second surface, the second ′ surface, and the second ″ surface, respectively. On the other hand, with respect to the light beam having the wavelength λ3, different orders of diffracted light are obtained when passing through the second surface and the second surface and when passing through the second surface. By applying a diffractive action in this manner, the light beam having the wavelength λ3 (first-order diffracted light) that has passed through the second surface can be formed into a so-called flare without being condensed on the information recording surface of the CD.
Tables 1 and 2 show the lens data of the objective lens.
[0163]
[Table 1]

[0164]
As shown in Table 1, the objective lens of this example has a focal length f = 3.1 mm when the wavelength λ1 = 407 nm, an image-side numerical aperture NA1 = 0.65, and a wavelength λ2 = 655 nm. Focal length f2 = 3.26 mm, image-side numerical aperture NA2 = 0.62, focal length f3 = 3.57 mm and wavelength-side numerical aperture NA3 = 0.40 when wavelength λ3 = 785 nm. Is set.
[0165]
Further, the magnifications m1 to m3 with respect to the light beams λ1 to λ3 are almost 0, and the structure is an infinite system in which parallel light enters the objective lens.
Surface No. 1 in Table 1 2, 2 ′, 2 ″ are the second surface of 1.45 mm ≦ h, the second surface of 1.1 mm ≦ h <1.45 mm, and h of the incident surface of the objective lens, respectively, as described above. <2 mm surface of 1.1 mm is shown, and surface numbers 3 and 4 represent the surface of the protective substrate of the optical information recording medium and the recording layer, respectively. Ri represents the radius of curvature, di represents the displacement in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni represents the refractive index of each surface.
[0166]
The second surface, the second 'surface, the second' surface, and the third surface of the objective lens are respectively defined by mathematical formulas obtained by substituting the coefficients shown in Tables 1 and 2 into the following formula (Equation 1). An aspherical surface that is axisymmetric about L is formed.
[0167]
[Expression 1]

[0168]
Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A_2iIs the aspheric coefficient.
[Table 2]

[0169]
Further, the pitch of the diffraction zone is defined by a mathematical formula in which the coefficients shown in Table 2 are substituted into the optical path difference function of Formula 2.
[0170]
[Expression 2]

Where B_2iIs the coefficient of the optical path difference function, mD is the diffraction order of each light beam assuming that there is no optical path difference providing structure (assuming that it has only a diffractive structure), λ is the wavelength used, λB is the blazed wavelength of diffraction (ΛB = 1 mm in the first and second embodiments).
[0171]
FIG. 13 is a graph showing the amount of variation and numerical aperture (NA) of longitudinal spherical aberration when the wavelength of the light beam having the wavelength λ1 (407 nm) used in the high-density optical disc (AOD) varies ± 1 nm from 407 nm.
Normally, the amount of fluctuation in wavelength due to mode hops and the like is about 1 μm. Therefore, within this range, the amount of fluctuation in longitudinal spherical aberration is suppressed to a practically unaffected range and has a sufficient color correction function. I understand that.
[0172]
FIG. 14 shows the wavefront aberration and diffraction efficiency of each light beam of wavelength λ1 (AOD), wavelength λ2 (DVD), and wavelength λ3 (CD). FIGS. 15 to 17 show the light beams of wavelengths λ1 to λ3. It is a graph which shows the condensing position fB and numerical aperture.
14 to 17, it can be seen that the wavefront aberration of each light flux is suppressed to 0.07 λrms or less, which is the diffraction limit, and has a sufficient color correction function. It can also be seen that the diffraction efficiency is sufficient for use in recording and / or reproducing information on each optical information recording medium.
[0173]
Next, a second example of the optical pickup device and the optical element shown in the above embodiment will be described.
Also in this embodiment, an objective lens in which the S1 surface and the S2 surface are combined on the incident surface side as shown in FIG. 6 is used.
Specifically, the incident surface of the objective lens, which is a single lens with double aspheric surfaces, is a second surface having a height h from the optical axis L of 1.45 mm or more, and a first surface having a height of 1.1 mm or more and less than 1.45 mm. It is divided into a 2 ′ surface (region A1) and a 2 ″ surface (region A2) of less than 1.1 mm.
[0174]
A plurality of diffraction ring zones as the first diffraction structure are formed in the region A1, and a diffraction ring zone as the second diffraction structure is formed in the region A2. A diffraction ring zone is also formed on the second surface.
The light beams having wavelengths λ1, λ2, and λ3 that pass through the second surface, the second ′ surface, and the second ″ surface have diffraction orders m = 3, n = 2, and k = 2 that provide the maximum diffraction efficiency. In order to obtain diffracted light, the first diffractive structure and the second diffractive structure are diffracted and emitted.
Tables 3 and 4 show the lens data of the objective lens.
[0175]
[Table 3]

[0176]
As shown in Table 3, the objective lens of the present example is set to have a focal length f1 = 3.1 mm when the wavelength λ1 = 407 nm, an image-side numerical aperture NA1 = 0.65, and a wavelength λ2 = 655 nm. Focal length f2 = 3.19 mm, image-side numerical aperture NA2 = 0.63, focal length f3 = 3.18 mm and wavelength-side numerical aperture NA3 = 0.45 when wavelength λ3 = 785 nm. Is set.
Further, the magnifications m1 to m3 with respect to the light beams λ1 to λ3 are almost 0, and the structure is an infinite system in which parallel light enters the objective lens.
[0177]
The second surface, the second 'surface, the second' surface, and the third surface of the objective lens are each defined around the optical axis L, which is defined by the mathematical formula obtained by substituting the coefficients shown in Tables 3 and 4 into Equation 1 above. It is formed in an aspherical surface that is axially symmetric.
[Table 4]

[0178]
Further, the pitch of the diffraction zone is defined by an equation in which the coefficients shown in Table 4 are substituted into the optical path difference function of the above formula 2.
[0179]
FIG. 18 is a graph showing the amount of change in spherical aberration and the numerical aperture (NA) when the wavelength of a light beam having a wavelength λ1 (407 nm) used for a high-density optical disc (AOD) varies ± 1 nm from 407 nm.
Normally, the amount of fluctuation in wavelength due to mode hops and the like is about 1 μm. Therefore, within this range, the amount of fluctuation in longitudinal spherical aberration is suppressed to a practically unaffected range and has a sufficient color correction function. I understand that.
[0180]
FIG. 19 shows the wavefront aberration and diffraction efficiency of each light beam of wavelength λ1 (AOD), wavelength λ2 (DVD), and wavelength λ3 (CD). FIGS. 20 to 22 show the light beams of wavelengths λ1 to λ3. It is a graph which shows the condensing position fB and numerical aperture.
19 to 22, it can be seen that the wavefront aberration is suppressed to 0.07 λrms or less, which is the diffraction limit, and has a sufficient color correction function. It can also be seen that the diffraction efficiency is sufficient for use in recording and / or reproducing information on each optical information recording medium.
[0181]
【The invention's effect】
  As described above, according to the optical pickup device and the optical element according to the present invention, the first optical information includes the diffractive optical element disposed in the common optical path of the first light source, the second light source, and the third light source and having the first diffractive structure. When information is reproduced and / or recorded on the recording medium, the second optical information recording medium, and the third optical information recording medium, almost all the light beams are applied to the diffractive optical element.As infinite parallel lightMake it incident.
  Therefore, for example, since the optical paths of the first to third wavelengths of light are substantially equal, various optical elements constituting the optical pickup device may be arranged corresponding to the common optical path, and the structure of the optical pickup device is simplified. And the number of parts of the device can be reduced.
  Also, EmotionWhen the information is reproduced and / or recorded, the objective optical element is moved with respect to the optical information recording medium, thereby preventing deterioration in image height characteristics during tracking and suppressing occurrence of various aberrations such as coma and astigmatism. be able to.
  In addition, spherical aberration caused by temperature change can be suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram of an optical pickup device according to the present invention.
FIG. 2 is a diagram of another embodiment of an optical pickup device according to the present invention.
FIG. 3 is a longitudinal sectional view of a main part showing a structure of an objective optical element.
FIG. 4 is longitudinal spherical aberration diagrams (a) to (c).
FIG. 5 is longitudinal spherical aberration diagrams (a) to (c).
FIG. 6 is a longitudinal sectional view of a main part showing the structure of an objective optical element.
FIG. 7 is a longitudinal sectional view of a main part showing the structure of an objective optical element.
FIG. 8 is longitudinal spherical aberration diagrams (a) to (c).
FIG. 9 is a longitudinal sectional view of a main part showing the structure of an objective optical element.
FIG. 10 is longitudinal spherical aberration diagrams (a) to (c).
FIG. 11 is a longitudinal sectional view of a main part showing the structure of an objective optical element.
FIG. 12 is a longitudinal sectional view of a main part showing the structure of an objective optical element.
FIG. 13 is a graph showing the amount of longitudinal spherical aberration variation and numerical aperture (NA) when the wavelength varies.
FIG. 14 is a table showing wavefront aberration and diffraction efficiency of each light beam.
FIG. 15 is a graph showing a condensing position fB and a numerical aperture of a light beam having a wavelength λ1.
FIG. 16 is a graph showing a condensing position fB and a numerical aperture of a light beam having a wavelength λ2.
FIG. 17 is a graph showing a condensing position fB and a numerical aperture of a light beam with a wavelength λ3.
FIG. 18 is a graph showing the amount of longitudinal spherical aberration variation and numerical aperture (NA) when the wavelength varies.
FIG. 19 is a table showing wavefront aberration and diffraction efficiency of each light beam.
FIG. 20 is a graph showing a condensing position fB and a numerical aperture of a light beam having a wavelength λ1.
FIG. 21 is a graph showing a condensing position fB and a numerical aperture of a light beam having a wavelength λ2.
FIG. 22 is a graph showing a condensing position fB and a numerical aperture of a light beam having a wavelength of λ3.
[Explanation of symbols]
LD1 first light source
LD2 Second light source
LD3 Third light source
LD2 '2nd light source (2 wavelength 1 package)
S1 sensor
S2 sensor
S3 sensor
S2 'sensor
SL1 sensor lens
SL2 sensor lens
SL3 sensor lens
DP diffraction plate
BS1 Beam splitter
BS2 Beam splitter
BS3 Beam splitter
BS4 beam splitter
CL1 collimator
CL2 collimator
CL3 collimator
IR aperture
OBL objective optical element
D1 optical disc ("high density optical disc")
D2 Optical disc (DVD)
D3 Optical disc (CD)
L Optical axis
Rs annular optical surface
Rl Annular optical surface
10 Objective optical elements
11 Optical surface (outgoing surface)
12 Optical surface (incident surface)
20 Step surface
30 First diffraction structure
40 Second diffraction structure
50 Refractive surface
60 Annular optical surface
70 Step surface

Claims (13)

Information is reproduced and / or recorded on the first optical information recording medium having the protective substrate thickness t1 using the light beam emitted from the first light source having the wavelength λ1, and the first optical information recording medium having the protective substrate thickness t2 (t1 ≦ t2) is obtained. Information is reproduced and / or recorded on a two-optical information recording medium using a light beam emitted from a second light source having a wavelength λ2 (λ1 <λ2), and a third thickness of the protective substrate t3 (t2 <t3) is obtained. An optical pickup device that reproduces and / or records information on an optical information recording medium using a light beam emitted from a third light source having a wavelength of λ3 (λ2 <λ3),
The optical pickup device includes a diffractive optical element disposed in a common optical path of the first light source, the second light source, and the third light source and having a first diffractive structure,
When reproducing and / or recording information on the first optical information recording medium, the second optical information recording medium, and the third optical information recording medium, all of the diffractive optical elements included in the optical pickup device are used. Is incident as almost infinite parallel light ,
The light beam having the wavelength λ3 is configured to obtain diffracted light of different orders when passing through the central portion of the diffractive optical element and when passing through the peripheral portion of the diffractive optical element,
A condensing spot is formed by the diffracted light of m (m is a natural number) generated by the diffractive optical element with respect to the first optical information recording medium, and generated by the diffractive optical element with respect to the second optical information recording medium. n (n is a natural number where n ≠ m) is configured to form a focused spot by the diffracted light of the order,
The numerical aperture of the condensing spot formed on the first optical information recording medium by the light beam having the wavelength λ1 is NA1, and the condensing spot formed on the second optical information recording medium by the light beam having the wavelength λ2. Is NA2, and NA3 is the numerical aperture of the condensing spot formed on the third optical information recording medium by the light flux having the wavelength λ3,
NA3 <NA1
NA3 <NA2
An optical pickup device satisfying the requirements .   The optical pickup device according to claim 1, wherein the diffractive optical element is an objective optical element. An optical correction element for performing temperature compensation and / or chromatic aberration compensation on at least one of the focused spots formed on the first, second, and third optical information recording media; The optical pickup device according to claim 1 or 2 . 4. The optical pickup device according to claim 1, wherein a spherical aberration has a discontinuous portion in reproducing and / or recording information on the third optical information recording medium. 5. The first diffractive structure of the diffractive optical element is:
A plurality of diffraction zones that are serrated discontinuous surfaces;
5. The optical path difference providing structure formed on the optical surface of the diffracting ring zone and including a step-like discontinuous surface along the optical axis. 5. The optical pickup device according to Item. The combination (m, n) of the diffraction orders of the m-th order diffracted light and the n-th order diffracted light is:
(M, n) = any one of (8, 5), (6, 4), (2, 1), (5, 3), (2, 2), (3, 2), (10, 6) The optical pickup device according to claim 1, wherein the optical pickup device is an optical pickup device. The diffractive optical element is
Among the light beams having the wavelengths λ1, λ2, and λ3, the light beam having the wavelength λ3 is caused to have a phase difference before and after passing through the diffractive optical element, and at least one of the light beams having the wavelengths λ1 and λ2. The optical pickup device according to claim 1, wherein the optical pickup device is configured not to cause a phase difference before and after passing through the diffractive optical element. Information is reproduced and / or recorded on the first optical information recording medium having the protective substrate thickness t1 using the light beam emitted from the first light source having the wavelength λ1, and the first optical information recording medium having the protective substrate thickness t2 (t1 ≦ t2) is obtained. Information is reproduced and / or recorded on a two-optical information recording medium using a light beam emitted from a second light source having a wavelength λ2 (λ1 <λ2), and a third thickness of the protective substrate t3 (t2 <t3) is obtained. with respect to the optical information recording medium, an optical optical element that is part of an optical pickup apparatus for reproducing and / or recording information by using a light flux emitted from the third light source of the wavelength λ3 (λ2 <λ3),
The optical element is a diffractive optical element that is disposed in a common optical path of the first light source, the second light source, and the third light source and has a first diffractive structure,
When reproducing and / or recording information on the first optical information recording medium, the second optical information recording medium, and the third optical information recording medium, all of the diffractive optical elements included in the optical pickup device are used. Is incident as almost infinite parallel light ,
The light beam having the wavelength λ3 is configured so that diffracted light of different orders is obtained when passing through the central part of the diffractive optical element and when passing through the peripheral part of the diffractive optical element,
A condensing spot is formed by the diffracted light of m (m is a natural number) generated by the diffractive optical element with respect to the first optical information recording medium, and generated by the diffractive optical element with respect to the second optical information recording medium. n (n is a natural number where n ≠ m) is configured to form a focused spot by the diffracted light of the order,
The numerical aperture of the condensing spot formed on the first optical information recording medium by the light beam having the wavelength λ1 is NA1, and the condensing spot formed on the second optical information recording medium by the light beam having the wavelength λ2. Is NA2, and NA3 is the numerical aperture of the condensing spot formed on the third optical information recording medium by the light flux having the wavelength λ3,
NA3 <NA1
NA3 <NA2
An optical element characterized by satisfying: The optical element according to claim 8, wherein the diffractive optical element is an objective optical element. 10. The optical element according to claim 8, wherein a spherical aberration has a discontinuous portion in reproducing and / or recording information on the third optical information recording medium. The first diffractive structure of the diffractive optical element is:
A plurality of diffraction zones that are serrated discontinuous surfaces;
The optical path difference providing structure which is formed on the optical surface of the diffractive ring zone and is formed of a step-like discontinuous surface along the optical axis. The optical element according to item. The combination (m, n) of the diffraction orders of the m-th order diffracted light and the n-th order diffracted light is:
(M, n) = any one of (8, 5), (6, 4), (2, 1), (5, 3), (2, 2), (3, 2), (10, 6) The optical element according to claim 8, wherein the optical element is an optical element. The diffractive optical element is
Among the light beams having the wavelengths λ1, λ2, and λ3, the light beam having the wavelength λ3 is caused to have a phase difference before and after passing through the diffractive optical element, and at least one of the light beams having the wavelengths λ1 and λ2. The optical element according to any one of claims 8 to 12, wherein the optical element is configured so as not to cause a phase difference before and after passing through the diffractive optical element.

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