JPH11110787A - Diffraction element and optical head device - Google Patents
Diffraction element and optical head deviceInfo
- Publication number
- JPH11110787A JPH11110787A JP9270124A JP27012497A JPH11110787A JP H11110787 A JPH11110787 A JP H11110787A JP 9270124 A JP9270124 A JP 9270124A JP 27012497 A JP27012497 A JP 27012497A JP H11110787 A JPH11110787 A JP H11110787A
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- Prior art keywords
- refractive index
- light
- diffraction
- efficiency
- optical material
- Prior art date
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、CDやDVDなど
の光記録媒体に光学的情報を書き込んだり、光学的情報
を読み取るための回折素子および光ヘッド装置に関す
る。[0001] 1. Field of the Invention [0002] The present invention relates to a diffraction element and an optical head device for writing optical information on an optical recording medium such as a CD and a DVD, and for reading optical information.
【0002】[0002]
【従来の技術】CDやDVDなどの光ディスクおよび光
磁気ディスクなどの光記録媒体に光学的情報を書き込ん
だり、光記録媒体から光学的情報を読み取ったりするの
に、回折素子などの光束制御素子を備えた光ヘッド装置
が用いられる。2. Description of the Related Art In order to write optical information on an optical recording medium such as an optical disk such as a CD or DVD and a magneto-optical disk or read optical information from an optical recording medium, a light flux controlling element such as a diffraction element is used. The optical head device provided is used.
【0003】図8は上記光ヘッド装置の概略を示す側面
図であり、光ヘッド装置では、半導体レーザなどの光源
1から出た出射光は、光束制御素子の一種であるホログ
ラムビームスプリッタなどの回折素子2を透過し、対物
レンズ3で光記録媒体であるCDやDVDなどの光ディ
スク4の上に集光される。FIG. 8 is a side view schematically showing the above-mentioned optical head device. In the optical head device, light emitted from a light source 1 such as a semiconductor laser is diffracted by a hologram beam splitter or the like which is a kind of light flux controlling element. The light passes through the element 2 and is focused by an objective lens 3 on an optical disc 4 such as a CD or DVD, which is an optical recording medium.
【0004】光ディスク4からの反射光は、再び対物レ
ンズ3を透過し、ホログラムビームスプリッタなどの回
折素子2により回折されて光検出器を構成する受光素子
5に到達する。受光素子5は、受光した反射光を電気信
号に変換し、電気信号はアンプ6で増幅され、さらに自
動ゲイン補正回路7でゲインが掛けられて信号レベルを
一定範囲に調整される。[0004] The reflected light from the optical disk 4 passes through the objective lens 3 again, is diffracted by the diffraction element 2 such as a hologram beam splitter, and reaches the light receiving element 5 constituting a photodetector. The light receiving element 5 converts the received reflected light into an electric signal, the electric signal is amplified by an amplifier 6, and the gain is multiplied by an automatic gain correction circuit 7, so that the signal level is adjusted to a certain range.
【0005】上記回折素子2などの光束制御素子として
は、従来、無偏光系のホログラムビームスプリッタが使
われていた。図9は無偏光系のホログラムビームスプリ
ッタの側方断面図であり、無偏光系のホログラムビーム
スプリッタは、たとえば、ガラス基板8の上面に、等方
性の光学材料からなる等方性回折格子9を形成したもの
である。なお、図中、10はホログラムビームスプリッ
タの両面に施された低反射コートである。As a light flux controlling element such as the diffractive element 2, a non-polarizing hologram beam splitter has been used. FIG. 9 is a side sectional view of a non-polarization hologram beam splitter. The non-polarization hologram beam splitter includes, for example, an isotropic diffraction grating 9 made of an isotropic optical material on an upper surface of a glass substrate 8. Is formed. In the drawing, reference numeral 10 denotes a low-reflection coat applied to both surfaces of the hologram beam splitter.
【0006】無偏光系のホログラムビームスプリッタの
場合、往路の0次透過効率が50%、復路の1次回折効
率が20%であるので、理論往復効率が、50%×20
%=10%となる。しかし、実際には、往復効率が10
%のホログラムビームスプリッタを作製するのは困難で
あり、6〜7%程度の往復効率が得られればよい方なの
で、無偏光系のホログラムビームスプリッタは往復効率
が低いという問題があった。そこで、光の往復効率を1
0%よりも上げるために、光の偏光方向によって回折効
率が変わるホログラムビームスプリッタを用いることが
提案されている。In the case of a non-polarizing hologram beam splitter, the zero-order transmission efficiency on the outward path is 50% and the first-order diffraction efficiency on the return path is 20%, so that the theoretical reciprocating efficiency is 50% × 20.
% = 10%. However, in practice, the round trip efficiency is 10
% Hologram beam splitter is difficult to produce, and it is only necessary to obtain a reciprocating efficiency of about 6 to 7%. Therefore, a non-polarizing hologram beam splitter has a problem that the reciprocating efficiency is low. Therefore, the light reciprocating efficiency is set to 1
It has been proposed to use a hologram beam splitter whose diffraction efficiency changes depending on the polarization direction of the light in order to raise it to more than 0%.
【0007】図10は偏光系のホログラムビームスプリ
ッタを示す側方断面図であり、偏光系のホログラムビー
ムスプリッタは、ガラス基板12の上に、後述する液晶
などの複屈折性光学材料13の常光屈折率nO または異
常光屈折率ne と等しい屈折率nS を有する等方性の光
学材料によって等方性回折格子14を形成し、等方性回
折格子14の上に配向膜15を塗布焼成して配向処理を
施した後、配向処理を実施した配向膜16を有する対向
基板17を向かい合わせるとともに、シール材18を介
在させて熱圧着し、内部に液晶などの複屈折性光学材料
13を液状のまま充填して封止するようにしたものであ
る。FIG. 10 is a side sectional view showing a polarization type hologram beam splitter. The polarization type hologram beam splitter is formed on a glass substrate 12 by ordinary light refraction of a birefringent optical material 13 such as a liquid crystal described later. isotropic diffraction grating 14 is formed by an optical material isotropic with the rate n O or the extraordinary refractive index n e is equal to the refractive index n S, coating baking an alignment film 15 on the isotropic diffraction grating 14 After the alignment process is performed, the opposing substrate 17 having the alignment film 16 on which the alignment process has been performed is opposed to each other, and is thermocompression-bonded with a sealing material 18 interposed therebetween, and the birefringent optical material 13 such as liquid crystal is placed inside. It is filled and sealed in a liquid state.
【0008】なお、偏光系のホログラムビームスプリッ
タを用いる場合には、このホログラムビームスプリッタ
と光ディスク4との間に、図8に示すような1/4波長
板19を挿入することにより、ホログラムビームスプリ
ッタを通過するときの光の偏光方向を往路と復路で90
度回転させる。When a hologram beam splitter of a polarization system is used, a 波長 wavelength plate 19 as shown in FIG. The polarization direction of the light when passing through
Rotate degrees.
【0009】偏光系のホログラムビームスプリッタで
は、たとえば、複屈折性光学材料13の常光屈折率nO
と等方性回折格子14の屈折率nS を等しくした場合
(nO =nS )、光源1からの出射光の往路における偏
光方向を複屈折性光学材料13の常光屈折率nO 方向に
一致させると、ホログラムビームスプリッタは機能しな
いため、0次透過効率を高くすることができ、復路で
は、1/4波長板19によって反射光の偏光方向が複屈
折性光学材料13の異常光屈折率ne 方向と等しくなる
ため、ホログラムビームスプリッタが機能し、1次回折
効率を高くすることができるので、結果として、無偏光
系のホログラムビームスプリッタの理論往復効率である
10%よりも高い往復効率が得られる。In a polarization type hologram beam splitter, for example, the ordinary refractive index n O of the birefringent optical material 13 is used.
When the refractive index n S of the isotropic diffraction grating 14 is equal to (n O = n S ), the polarization direction in the outward path of the light emitted from the light source 1 is changed to the direction of the ordinary light refractive index n O of the birefringent optical material 13. If they are matched, the hologram beam splitter does not function, so that the 0th-order transmission efficiency can be increased. On the return path, the polarization direction of the reflected light is changed by the quarter-wave plate 19 to the extraordinary refractive index of the birefringent optical material 13. since equal to n e direction, the hologram beam splitter functions, it is possible to increase the first-order diffraction efficiency, as a result, non-polarization-based high reciprocating efficiency than 10% the theoretical reciprocating efficiency of the hologram beam splitter Is obtained.
【0010】[0010]
【発明が解決しようとする課題】しかし、上記した偏光
系のホログラムビームスプリッタを用いた光ヘッド装置
には、以下のような問題があった。すなわち、光記録媒
体である光ディスク4は、一般に樹脂成形品であり、可
能な限り均質に成形することが要請されているが、実際
の光ディスクには、型に樹脂を注入する時などに樹脂の
流動に片寄りが生じるなどして歪を生じ、部分的な複屈
折性を1箇所以上持つものが含まれることがある。However, the optical head device using the above-mentioned polarizing hologram beam splitter has the following problems. In other words, the optical disc 4 as an optical recording medium is generally a resin molded product, and is required to be molded as homogeneously as possible. In some cases, the flow may be distorted due to, for example, a bias in the flow, and may have partial birefringence at one or more locations.
【0011】すると、光ディスク4は、高速回転される
ので、1箇所以上の部分的な複屈折性を持った光ディス
ク4からの反射光は、偏光方向が一定とならずに時々刻
々変動し、往路の光の偏光方向に対して復路の偏光方向
が90度よりもずれ、しかも、どの程度偏光方向がずれ
ているかがまったく不明な反射光が戻ってくることにな
る。Then, since the optical disk 4 is rotated at a high speed, the reflected light from the optical disk 4 having one or more partial birefringences is not constant in the polarization direction but fluctuates from time to time. In this case, reflected light whose direction of polarization on the return path is shifted by more than 90 degrees with respect to the direction of polarization of the light, and reflected light whose degree of polarization is completely unknown is returned.
【0012】そして、最悪の場合には、光ディスク4か
らの反射光が往路と同じ偏光方向で戻ることも起こる。
このよう場合には、偏光系のホログラムビームスプリッ
タは、ほとんど反射光を回折できず、光ディスク4の情
報を受光素子5で読み取ることができない。In the worst case, the reflected light from the optical disk 4 may return in the same polarization direction as the outward path.
In such a case, the hologram beam splitter of the polarization system can hardly diffract the reflected light, and the information on the optical disc 4 cannot be read by the light receiving element 5.
【0013】本発明は、上述の実情に鑑み、複屈折性を
持つ光記録媒体に対しても情報を読み取るようにした回
折素子および光ヘッド装置を提供することを目的とす
る。SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a diffraction element and an optical head device that can read information from an optical recording medium having birefringence.
【0014】[0014]
【課題を解決するための手段】本発明は、断面凹凸状の
回折格子を形成する光学材料と、回折格子の少なくとも
凸部間に充填される別の光学材料とからなる回折素子に
おいて、上記2種類の光学材料のうちの少なくとも一方
が複屈折性を示し、かつ、他方の光学材料が、複屈折性
を示す一方の光学材料の常光屈折率と異常光屈折率のど
ちらとも異なる屈折率を少なくとも一つ有することを特
徴とする回折素子を提供する。According to the present invention, there is provided a diffraction element comprising an optical material forming a diffraction grating having an uneven cross section and another optical material filled between at least convex portions of the diffraction grating. At least one of the types of optical materials exhibits birefringence, and the other optical material has at least a refractive index different from either the ordinary refractive index or the extraordinary refractive index of one of the birefringent optical materials. A diffractive element having one is provided.
【0015】さらに、2種類の光学材料のうちの一方
を、等方性の光学材料とした上記の回折素子を提供す
る。さらに、等方性の光学材料の屈折率が、複屈折性の
光学材料の常光屈折率および異常光屈折率のうちの小さ
い方よりも小さいか、または、大きい方よりも大きい上
記の回折素子を提供する。さらに、回折効率が最低とな
る偏光方向に対する1次回折効率が、回折効率が最高と
なる偏光方向に対する1次回折効率の10%以上とな
り、回折効率が最低となる偏光方向に対する0次透過効
率と回折効率が最高となる偏光方向に対する1次回折効
率との積が10%以上となる屈折率差を有する2種類の
光学材料を使用した上記の回折素子を提供する。Further, the present invention provides the above-described diffractive element in which one of the two types of optical materials is an isotropic optical material. Further, the refractive index of the isotropic optical material is smaller than the smaller one of the ordinary refractive index and the extraordinary refractive index of the birefringent optical material, or the above-described diffraction element larger than the larger one. provide. Further, the first-order diffraction efficiency in the polarization direction in which the diffraction efficiency is the lowest is 10% or more of the first-order diffraction efficiency in the polarization direction in which the diffraction efficiency is the highest, and the zero-order transmission efficiency in the polarization direction in which the diffraction efficiency is the lowest. The present invention provides the above-described diffraction element using two kinds of optical materials having a refractive index difference of which the product of the first-order diffraction efficiency and the polarization direction at which the diffraction efficiency is the highest is 10% or more.
【0016】さらに、光源と、光源からの出射光を通過
させるとともに光記録媒体で反射して戻ってきた反射光
の進行方向を変更する光束制御素子と、光束制御素子で
進行方向を変更された反射光の情報を検知する光検出器
とを備えた光ヘッド装置において、光束制御素子とし
て、上記の回折素子を用いたことを特徴とする光ヘッド
装置を提供する。Further, a light source, a light flux controlling element for passing the light emitted from the light source and changing the traveling direction of the reflected light reflected back from the optical recording medium, and the traveling direction changed by the light flux controlling element. An optical head device provided with a photodetector for detecting information of reflected light, wherein the above-described diffractive element is used as a light flux controlling element.
【0017】[0017]
【発明の実施の形態】以下、本発明の実施の形態を、図
示例とともに説明する。図1は本発明の第1の実施の形
態にかかる偏光系の回折素子の側方断面図、図2は本発
明の第1の実施の形態にかかる他の偏光系の回折素子の
側方断面図、図3は本発明の第1の実施の形態にかかる
別の偏光系の回折素子の側方断面図、図4は本発明の第
1の実施の形態にかかる、効率と、波長で規格化された
位相差Δn×d/λとの関係を示すグラフである。Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of a diffraction element of a polarization system according to the first embodiment of the present invention. FIG. 2 is a side cross section of another diffraction element of a polarization system according to the first embodiment of the present invention. FIG. 3 is a side cross-sectional view of a diffractive element of another polarization system according to the first embodiment of the present invention. FIG. 4 is a diagram showing the efficiency and the wavelength according to the first embodiment of the present invention. 6 is a graph showing a relationship with a converted phase difference Δn × d / λ.
【0018】また、光ヘッド装置の基本的な構成につい
ては、図8と同様であるため、必要に応じて図8を参照
する。本発明は、断面凹凸状の回折格子を形成する光学
材料と、回折格子の少なくとも凸部間に充填される別の
光学材料との2種類の光学材料のうちの少なくとも一方
が複屈折性を示し、かつ、他方の光学材料が、複屈折性
を示す一方の光学材料の常光屈折率と異常光屈折率のど
ちらとも異なる屈折率を少なくとも一つ有するようにし
たところにその特徴がある。The basic configuration of the optical head device is the same as that of FIG. 8, and therefore, FIG. 8 will be referred to as necessary. According to the present invention, at least one of two types of optical materials, that is, an optical material that forms a diffraction grating having an uneven cross section and another optical material that is filled between at least convex portions of the diffraction grating, exhibits birefringence. The feature is that the other optical material has at least one refractive index different from the ordinary light refractive index and the extraordinary light refractive index of the one optical material exhibiting birefringence.
【0019】そして、本実施の形態では、2種類の光学
材料のうちの一方を、等方性の光学材料としている。さ
らに、等方性の光学材料の屈折率は、複屈折性の光学材
料の常光屈折率と異常光屈折率の中間の値としてもよい
が、好ましくは、複屈折性の光学材料の常光屈折率およ
び異常光屈折率のうちの小さい方よりも小さくなるか、
または、大きい方よりも大きくなるようにする。In this embodiment, one of the two types of optical materials is an isotropic optical material. Further, the refractive index of the isotropic optical material may be an intermediate value between the ordinary refractive index and the extraordinary refractive index of the birefringent optical material, but is preferably the ordinary refractive index of the birefringent optical material. Or smaller than the smaller of the extraordinary refractive index,
Or, make it larger than the larger one.
【0020】そして、回折効率が最低となる偏光方向に
対する1次回折効率が、回折効率が最高となる偏光方向
に対する1次回折効率の10%以上となり、回折効率が
最低となる偏光方向に対する0次透過効率と回折効率が
最高となる偏光方向に対する1次回折効率との積が10
%以上となる屈折率差を有する2種類の光学材料を使用
する。The first-order diffraction efficiency for the polarization direction in which the diffraction efficiency is the lowest is 10% or more of the first-order diffraction efficiency for the polarization direction in which the diffraction efficiency is the highest, and the 0th-order diffraction efficiency for the polarization direction in which the diffraction efficiency is the lowest. The product of the first-order diffraction efficiency with respect to the polarization direction at which the transmission efficiency and the diffraction efficiency are highest is 10
% Of two types of optical materials having a refractive index difference of not less than%.
【0021】光源と、光源からの出射光を通過させると
ともに光記録媒体で反射して戻ってきた反射光の進行方
向を変更する光束制御素子と、光束制御素子で進行方向
を変更された反射光の情報を検知する光検出器とを備え
た光ヘッド装置において、光束制御素子として、上記の
回折素子を用いる。A light source, a light flux controlling element for passing the light emitted from the light source and changing the traveling direction of the reflected light reflected back from the optical recording medium, and the reflected light the traveling direction of which is changed by the light flux controlling element In the optical head device provided with a photodetector for detecting the above information, the above-described diffraction element is used as a light flux control element.
【0022】具体的な構造としては、たとえば、図1・
図2に示すように、ガラスなどの基板20の上に、フォ
トリソグラフィやエッチングなどにより断面矩形波状の
複屈折性回折格子21を形成し、複屈折性回折格子21
の少なくとも凸部間に等方性充填材22を充填して回折
素子23を構成し、この回折素子23を光ヘッド装置の
光源と光ディスクとの間に組み込む。As a specific structure, for example, FIG.
As shown in FIG. 2, a birefringent diffraction grating 21 having a rectangular cross section is formed on a substrate 20 such as glass by photolithography or etching.
A diffractive element 23 is formed by filling an isotropic filler 22 at least between the convex portions of the optical disc device, and the diffractive element 23 is incorporated between the light source of the optical head device and the optical disk.
【0023】なお、図1に示すように、基板20と複屈
折性光学材料とのエッチングレートの差を利用して凸部
間の複屈折性光学材料を完全に除去するようにしてもよ
いし、図2に示すように、複屈折性回折格子21の格子
深さdを調整するために、凸部間に複屈折性光学材料を
所要量残した構造としてもよい。As shown in FIG. 1, the birefringent optical material between the projections may be completely removed by utilizing the difference in the etching rate between the substrate 20 and the birefringent optical material. As shown in FIG. 2, in order to adjust the grating depth d of the birefringent diffraction grating 21, a structure may be employed in which a required amount of birefringent optical material is left between the convex portions.
【0024】この場合、複屈折性回折格子21を構成す
る複屈折性光学材料としては、たとえば、液晶材料を配
向させ重合して高分子化した高分子液晶や、1軸延伸し
た高分子のフィルムや複屈折性単結晶を使用できる。ま
た、等方性充填材22を構成する等方性光学材料として
は、たとえば、アクリル系樹脂やエポキシ系樹脂などを
使用できる。In this case, the birefringent optical material constituting the birefringent diffraction grating 21 is, for example, a polymer liquid crystal obtained by orienting and polymerizing a liquid crystal material or a uniaxially stretched polymer film. Or a birefringent single crystal. Further, as an isotropic optical material constituting the isotropic filler 22, for example, an acrylic resin or an epoxy resin can be used.
【0025】あるいは、図3に示すように、ガラスなど
の基板20の上に反応性スパッタ法で形成した等方性光
学材料の薄膜にフォトリソグラフィやエッチングなどを
施すことにより断面矩形波状の等方性回折格子24を形
成し、等方性回折格子24の凸部間に複屈折性充填材2
5を充填して回折素子23を構成し、回折素子23を光
ヘッド装置の光源と光ディスクとの間に組み込むように
してもよい。なお、ガラスなどの基板20に直接凹凸を
形成して等方性回折格子24とするようにしてもよい。Alternatively, as shown in FIG. 3, a thin film of an isotropic optical material formed on a substrate 20 such as glass by a reactive sputtering method is subjected to photolithography, etching, or the like, so as to form a rectangular isotropic wave. Birefringent filler 2 is formed between convex portions of isotropic diffraction grating 24.
5 to form the diffraction element 23, and the diffraction element 23 may be incorporated between the light source of the optical head device and the optical disk. Note that the isotropic diffraction grating 24 may be formed by directly forming irregularities on the substrate 20 such as glass.
【0026】この場合、等方性回折格子24を構成する
等方性光学材料としては、たとえば、ガラスやSiO−
N(SiO2 とSiNの混合物で、両者の比率を調整す
ることにより屈折率を調整可能とした物質)の薄膜やア
クリル系樹脂やエポキシ系樹脂などを使用できる。ま
た、複屈折性充填材25を構成する複屈折性光学材料と
しては、たとえば、液晶や、液晶材料を配向させ重合し
高分子化した高分子液晶を使用できる。なお、液晶を液
状のまま使用する場合には、図10の場合と同様に、対
向基板とシール材26を用いて液晶を封入する構造とす
る。In this case, as the isotropic optical material constituting the isotropic diffraction grating 24, for example, glass or SiO—
A thin film of N (a mixture of SiO 2 and SiN, the refractive index of which can be adjusted by adjusting the ratio of both) and an acrylic resin or an epoxy resin can be used. In addition, as the birefringent optical material constituting the birefringent filler 25, for example, a liquid crystal or a polymer liquid crystal in which a liquid crystal material is aligned and polymerized to polymerize can be used. When the liquid crystal is used in a liquid state, the liquid crystal is sealed using the counter substrate and the sealant 26 as in the case of FIG.
【0027】図1〜図3のいずれの場合にも、上面に1
/4波長板27を一体的に形成するようにしてもよい。
こうすることにより、部品点数を削減できるとともに、
小型軽量化を図れるので有利である。なお、図3では、
対向基板を1/4波長板27としているが、1/4波長
板27を対向基板とは別体に設けてもよい。In each case of FIGS. 1 to 3, 1
The 波長 wavelength plate 27 may be integrally formed.
By doing so, the number of parts can be reduced,
This is advantageous because the size and weight can be reduced. In FIG. 3,
Although the opposite substrate is a quarter-wave plate 27, the quarter-wave plate 27 may be provided separately from the opposite substrate.
【0028】そして、まず、複屈折性光学材料の常光屈
折率をnO 、異常光屈折率をne 、等方性材料の屈折率
をnS とすると、nS ≠ne で、かつ、nS ≠nO とな
るような複屈折性光学材料と等方性材料の組合せを選定
する。こうすることにより、複屈折性光学材料の常光屈
折率方向の偏光または異常光屈折率方向の偏光のいずれ
に対しても、等方性光学材料が複屈折性光学材料とは異
なる屈折率を示すため、この回折素子23は光の偏光方
向にかかわらず回折効率を持つようになる。[0028] Then, first, ordinary refractive index n O of the birefringent optical material, abnormal light refractive index n e, the refractive index of the isotropic material and n S, with n S ≠ n e, and, A combination of a birefringent optical material and an isotropic material such that n S ≠ n O is selected. By doing so, the isotropic optical material exhibits a different refractive index from the birefringent optical material for either polarized light in the ordinary refractive index direction or polarized light in the extraordinary refractive index direction of the birefringent optical material. Therefore, the diffraction element 23 has diffraction efficiency regardless of the polarization direction of light.
【0029】そして、回折素子23の回折効率や透過効
率は、2つの光学材料の屈折率差をΔn、格子深さを
d、光の波長をλとすると、効率と、波長で規格化され
た位相差Δn×d/λとの関係を示す図4のグラフなど
に基づいて求められる。このうち、光の波長λは、光源
の発振する波長として使途に応じて予め定められるの
で、屈折率差Δnと、格子深さdによって回折効率を決
めることになるが、格子深さdを深くすると回折素子製
造上の困難を伴うので、主として屈折率差Δnで決める
のがよい。The diffraction efficiency and transmission efficiency of the diffraction element 23 are standardized by the efficiency and the wavelength, where Δn is the refractive index difference between the two optical materials, d is the grating depth, and λ is the wavelength of light. It is determined based on the graph of FIG. 4 showing the relationship with the phase difference Δn × d / λ. Of these, the wavelength λ of light is predetermined as the wavelength at which the light source oscillates, so that the diffraction efficiency is determined by the refractive index difference Δn and the grating depth d. Then, it is difficult to manufacture the diffraction element. Therefore, it is preferable to mainly determine the refractive index difference Δn.
【0030】ここで、複屈折性光学材料の異常光屈折率
方向における、複屈折性光学材料と等方性光学材料との
屈折率差をΔn1 =|ne −nS |とし、複屈折性光学
材料の常光屈折率方向における、複屈折性光学材料と等
方性光学材料との屈折率差をΔn2 =|nO −nS |と
すると、等方性材料の屈折率nS を、複屈折性光学材料
の常光屈折率nO と異常光屈折率ne の中間の値(ne
<nS <nO 、または、nO <nS <ne )とした場合
には、屈折率差Δn1 とΔn2 が大差のない値となって
しまうため、回折効率などの設定に、格子深さdを深く
して対応せざるをえないので、構造上不利である。[0030] Here, in the extraordinary refractive index direction of the birefringent optical material, the refractive index difference between the birefringent optical material and an isotropic optical material Δn 1 = | n e -n S | and then, birefringence When the refractive index difference between the birefringent optical material and the isotropic optical material in the ordinary light refractive index direction of the isotropic optical material is Δn 2 = | n O −n S |, the refractive index n S of the isotropic material is , an intermediate value between the ordinary refractive index n O and the extraordinary refractive index n e of the birefringent optical material (n e
<N S <n O or, for the case of the n O <n S <n e ) , the refractive index difference [Delta] n 1 and [Delta] n 2 becomes a no great difference values, the settings such as diffraction efficiency, This is disadvantageous in terms of structure because it is inevitable to increase the lattice depth d.
【0031】そこで、等方性材料の屈折率nS を、複屈
折性光学材料の常光屈折率nO および異常光屈折率ne
のうちの小さい方よりも小さいか、または、大きい方よ
りも大きくなるようにする(nS <ne ,nO 、また
は、ne ,nO <nS )。こうすると、屈折率差Δn1
とΔn2 の値に大きな差を付けることができるので、格
子深さdを深くしなくとも、回折効率などの設定を容易
にでき、構造上、大きな利点が得られる。[0031] Therefore, the refractive index n S of the isotropic material, the ordinary refractive index of the birefringent optical material n O and the extraordinary refractive index n e
Is smaller than the smaller one or larger than the larger one (n S <n e , n O or n e , n O <n S ). Then, the refractive index difference Δn 1
And the value of Δn 2 , it is possible to easily set the diffraction efficiency and the like without increasing the grating depth d, thereby obtaining a great advantage in structure.
【0032】ここで、偏光系の回折素子23において、
最も回折効率の低い偏光方向をA方向とし、最も回折効
率の高い偏光方向をB方向とした場合、往路の0次透過
効率を高く(すなわち、1次回折効率を低く)し、復路
の1次回折効率を高くすると、往復効率が高くなるの
で、往路の光の偏光方向をA方向にし、復路の光の偏光
方向をB方向とするのが好ましい。そして、復路(B方
向)の偏光方向に対する1次回折効率は、できるだけ高
くした方が、光の往復効率を高くできるので好ましい。
B方向の偏光方向に対する1次回折効率は、図4によれ
ば、ほぼ40%程度を確保できる。Here, in the polarization type diffraction element 23,
When the polarization direction with the lowest diffraction efficiency is the A direction and the polarization direction with the highest diffraction efficiency is the B direction, the 0th-order transmission efficiency on the outward path is increased (that is, the 1st-order diffraction efficiency is reduced), and the first-order on the return path is reduced. When the folding efficiency is increased, the reciprocation efficiency is increased. Therefore, it is preferable that the polarization direction of the light on the outward path is set to the A direction and the polarization direction of the light on the return path is set to the B direction. It is preferable that the first-order diffraction efficiency with respect to the polarization direction of the return path (B direction) be as high as possible because the reciprocation efficiency of light can be increased.
According to FIG. 4, the first-order diffraction efficiency with respect to the polarization direction in the B direction can secure approximately 40%.
【0033】そして、無偏光系のホログラムビームスプ
リッタの理論往復効率である10%以上の往復効率を得
るには、復路の1次回折効率がほぼ40%(実際にはこ
れ以下となる)であるから、往路(A方向)の偏光に対
する0次透過効率は、多少の余裕を持たせてほぼ30%
以上とする必要がある。In order to obtain a reciprocating efficiency of 10% or more, which is the theoretical reciprocating efficiency of the non-polarizing hologram beam splitter, the first-order diffraction efficiency on the return path is almost 40% (actually less than this). Therefore, the zero-order transmission efficiency for the polarized light in the outward path (A direction) is approximately 30% with some allowance.
It is necessary to do above.
【0034】一方、光ディスクに複屈折があると、最悪
の場合、復路の偏光方向が往路と同じA方向の偏光方向
になることがある。この場合、A方向の偏光方向に対す
る1次回折効率によって回折されるが、往路と等しい偏
光方向に対する1次回折効率を余り低くしすぎると、受
光素子で光を有効に検知できない。On the other hand, if the optical disc has birefringence, in the worst case, the polarization direction on the return path may be the same as the polarization direction in the A direction on the outward path. In this case, the light is diffracted by the first-order diffraction efficiency with respect to the polarization direction in the A direction. However, if the first-order diffraction efficiency with respect to the polarization direction equal to the outward path is too low, the light receiving element cannot effectively detect light.
【0035】受光素子に接続された自動ゲイン補正回路
で信号を補正できる倍率は、ほぼ10倍程度までなの
で、A方向の偏光に対する1次回折効率をB方向の偏光
に対する1次回折効率の10%以上とすることにより、
受光素子で光を有効に検知できるようになる。なお、自
動ゲイン補正回路の構成を簡略化するためには、A方向
の偏光に対する1次回折効率をB方向の偏光に対する1
次回折効率の25%以上とするのが好ましい。Since the magnification at which a signal can be corrected by the automatic gain correction circuit connected to the light receiving element is approximately up to about 10 times, the first-order diffraction efficiency for polarized light in the A direction is 10% of the first-order diffraction efficiency for polarized light in the B direction. By doing the above,
Light can be effectively detected by the light receiving element. In order to simplify the configuration of the automatic gain correction circuit, the first-order diffraction efficiency with respect to the polarization in the A direction is set to be 1 to the polarization with respect to the polarization in the B direction.
It is preferable to set it to 25% or more of the next diffraction efficiency.
【0036】ここで、0次透過効率を高くすると、1次
回折効率が低くなり、反対に、0次透過効率を低くする
と、1次回折効率が高くなるという関係が成立している
ため、往路に対応するA方向の偏光方向における0次透
過効率と1次回折効率を、上記の両方の条件を満たす範
囲内に設定することにより、複屈折性を持った光ディス
クからでも情報を読み取らせることができる。Here, when the 0th-order transmission efficiency is increased, the first-order diffraction efficiency is reduced, and conversely, when the 0th-order transmission efficiency is reduced, the first-order diffraction efficiency is increased. By setting the zero-order transmission efficiency and the first-order diffraction efficiency in the polarization direction of the A direction corresponding to the above to be within a range that satisfies both of the above conditions, information can be read even from an optical disc having birefringence. it can.
【0037】なお、光ディスクには、必ず複屈折性を有
する部分があるとは限らないので、復路の偏光方向が往
路の偏光方向と直交した偏光方向になるように、回折素
子23と光ディスクとの間には1/4波長板を配置して
おくのが好ましい。Since the optical disk does not always have a portion having birefringence, the diffraction element 23 and the optical disk must be positioned so that the polarization direction of the return path is perpendicular to the polarization direction of the outward path. It is preferable to arrange a 波長 wavelength plate between them.
【0038】以上をさらに、常光屈折率nO が異常光屈
折率ne よりも小さい複屈折性光学材料と、屈折率nS
が複屈折性光学材料の常光屈折率nO よりも小さい等方
性材料を使用する場合、すなわち、nS <nO <ne で
ある場合で、かつ、凹部と凸部の幅寸法の比が1:1の
断面矩形波状の回折格子を用いる場合について、より具
体的に、屈折率nO 、ne 、nS の決め方を説明する。The above further includes a birefringent optical material smaller than the ordinary refractive index n O is the extraordinary refractive index n e, the refractive index n S
The ratio of but when using a small isotropic material than the ordinary refractive index n O of the birefringent optical material, i.e., in the case of n S <n O <n e , and the width dimension of the concave portion and the convex portion There 1: the case of using a cross-section rectangular wave diffraction grating, more specifically, the refractive index n O, n e, the method of determining n S will be described.
【0039】凹部と凸部の幅寸法の比が1:1の断面矩
形波状の回折格子を用いる場合、効率と、波長で規格化
された位相差Δn×d/λとの関係は、図4に示すよう
になり、図からΔn×d/λ=0.5のときに±1次回
折効率がそれぞれ40.5%と最も高くなるのがわか
る。In the case of using a diffraction grating having a rectangular cross section having a width ratio of the concave portion and the convex portion of 1: 1, the relationship between the efficiency and the phase difference Δn × d / λ normalized by the wavelength is shown in FIG. As can be seen from the figure, when Δn × d / λ = 0.5, the ± 1st-order diffraction efficiency is the highest at 40.5%, respectively.
【0040】この場合には、常光屈折率nO の方向が最
も回折効率の低いA方向となり、異常光屈折率ne の方
向が最も回折効率の高いB方向となるので、A方向を往
路の偏光方向に、B方向を復路の偏光方向に設定する。
そして、B方向の屈折率差をΔn1 =|ne −nS |と
すると、1次回折効率を最大値である40.5%とする
には、Δn1 ×dの値を最適化して、Δn1 ×d/λの
値が0.5もしくは、0.5付近となるようにする。[0040] In this case, becomes lower direction A direction most diffraction efficiency of the ordinary refractive index n O, since the direction of the extraordinary refractive index n e is higher B direction most diffraction efficiency, the A direction outward The direction B is set as the polarization direction, and the direction B is set as the return direction.
Then, the refractive index difference B direction Δn 1 = | n e -n S | if that, to the first-order diffraction efficiency 40.5% which is the maximum value, to optimize the value of [Delta] n 1 × d , Δn 1 × d / λ are set to 0.5 or around 0.5.
【0041】そして、無偏光系の回折素子の理論往復効
率である10%以上の往復効率を確保するためには、往
路の0次透過効率をほぼ30%以上とする必要があるの
で(復路の1次回折効率を40.5%とした場合には、
計算上は、往路の0次透過効率はほぼ25%以上でよい
ことになるが、実際には、復路の1次回折効率として4
0.5%という高い値は得られない)、往路の屈折率差
をΔn2 =|nO −nS |として、Δn2 ×d/λの値
をほぼ0.32以下とする。In order to secure the reciprocating efficiency of 10% or more, which is the theoretical reciprocating efficiency of the non-polarizing type diffraction element, it is necessary to make the 0th-order transmission efficiency of the outward path approximately 30% or more (return path). When the first-order diffraction efficiency is 40.5%,
Calculations show that the 0th-order transmission efficiency on the outward path may be approximately 25% or more, but in practice, the first-order diffraction efficiency on the return path is 4%.
A value as high as 0.5% cannot be obtained), and the value of Δn 2 × d / λ is approximately 0.32 or less, where Δn 2 = | n O −n S |
【0042】さらに、常光屈折率nO の方向(A方向)
の偏光に対する1次回折効率は、前述のように異常光屈
折率ne の方向(B方向)の偏光に対する1次回折効率
(=40.5%)の10%以上、好ましくは25%以上
が必要であるので、1次回折効率としては40.5%×
1/10≒4%以上、好ましくは40.5%×1/4≒
10%以上となり、この条件を満たすΔn2 ×d/λの
値は、ほぼ0.11以上、好ましくはほぼ0.17以上
とする。その結果、上記を合わせると、Δn2×d/λ
の値としては、ほぼ0.11以上、好ましくはほぼ0.
17以上で、ほぼ0.32以下という範囲が得られる。Further, the direction of the ordinary light refractive index n O (A direction)
The first-order diffraction efficiency for the polarized light, 1st-order diffraction efficiency with respect to the polarization direction (B direction) of the extraordinary refractive index n e, as described above (= 40.5 percent) of 10% or more, preferably 25% or more Since it is necessary, the first-order diffraction efficiency is 40.5% ×
1/10 {4% or more, preferably 40.5% × 1 /}
The value of Δn 2 × d / λ satisfying this condition is about 0.11 or more, and preferably about 0.17 or more. As a result, when the above is combined, Δn 2 × d / λ
Is about 0.11 or more, preferably about 0.1.
A range of about 0.32 or less can be obtained with a value of 17 or more.
【0043】図5は、本発明の第2の実施の形態にかか
る偏光系の回折素子の側方断面図であり、図6は、本発
明の第2の実施の形態にかかる、効率と、波長で規格化
された位相差Δn×d/λとの関係を示すグラフであ
る。FIG. 5 is a side sectional view of a polarization type diffraction element according to a second embodiment of the present invention, and FIG. 6 is a diagram showing efficiency and efficiency according to the second embodiment of the present invention. 9 is a graph showing a relationship with a phase difference Δn × d / λ normalized by wavelength.
【0044】本実施の形態では、上記第1の実施の形態
における、回折格子の断面形状を金型による熱間プレス
法などにより鋸歯状にしたところにその特徴がある。な
お、図5は、図3の等方性回折格子24を鋸歯状とした
場合を示すが、図1の複屈折性回折格子21を鋸歯状と
しても、図2の複屈折性回折格子21を鋸歯状としても
よい。The present embodiment is characterized in that the cross-sectional shape of the diffraction grating in the first embodiment is formed in a sawtooth shape by hot pressing using a mold or the like. FIG. 5 shows a case where the isotropic diffraction grating 24 of FIG. 3 has a sawtooth shape. However, even if the birefringent diffraction grating 21 of FIG. It may be in a sawtooth shape.
【0045】回折格子の断面形状を鋸歯状にすると、図
6に示すように、Δn×d/λ=1.0の時に、最も高
く、ほぼ100%という1次回折効率が得られる。した
がって、B方向の偏光に対する1次回折効率を100%
の近傍に設定することにより、無偏光系の回折素子の理
論往復効率である10%以上の往復効率を得るためのA
方向の偏光に対する0次透過効率はほぼ10%以上とな
り、この条件を満たすΔn2 ×d/λの値は、ほぼ0.
76以下となる。When the diffraction grating has a sawtooth cross section, as shown in FIG. 6, when Δn × d / λ = 1.0, the highest diffraction efficiency of about 100% is obtained. Therefore, the first-order diffraction efficiency for polarized light in the B direction is 100%.
Is set so as to obtain a reciprocating efficiency of 10% or more which is the theoretical reciprocating efficiency of the non-polarization type diffraction element.
The zero-order transmission efficiency for polarized light in the direction is approximately 10% or more, and the value of Δn 2 × d / λ satisfying this condition is approximately 0.
76 or less.
【0046】また、B方向の偏光に対する1次回折効率
(ほぼ100%)の10%以上、好ましくは25%以上
となるA方向の偏光に対する1次回折効率は、ほぼ10
%以上、好ましくはほぼ25%以上となり、この条件を
満たすΔn2 ×d/λの値は、ほぼ0.25以上、好ま
しくはほぼ0.4以上となる。その結果、上記を合せる
と、Δn2 ×d/λの値としては、ほぼ0.25以上、
好ましくはほぼ0.4以上、ほぼ0.74以下という範
囲が得られる。上記以外についても、前記実施の形態と
ほぼ同様の構成を備えており、同様の作用・効果が得ら
れる。The first-order diffraction efficiency for polarized light in the A direction, which is 10% or more, preferably 25% or more, of the first-order diffraction efficiency (approximately 100%) for polarized light in the B direction, is approximately 10%.
%, Preferably about 25% or more, and the value of Δn 2 × d / λ satisfying this condition is about 0.25 or more, preferably about 0.4 or more. As a result, when the above is combined, the value of Δn 2 × d / λ is approximately 0.25 or more,
Preferably, a range of about 0.4 or more and about 0.74 or less is obtained. Other than the above, the configuration is almost the same as that of the above embodiment, and the same operation and effect can be obtained.
【0047】図7の(1)、(2)、(3)は、本発明
の第3の実施の形態にかかる2つの複屈折性光学材料の
屈折率の関係を示す図である。本実施の形態は、2種類
の光学材料の両方を、複屈折性の光学材料としたところ
にその特徴がある。この場合において、2種類の複屈折
性の光学材料の常光屈折率および異常光屈折率のうちの
少なくとも3つが異なるようにする。FIGS. 7 (1), (2) and (3) show the relationship between the refractive indices of two birefringent optical materials according to the third embodiment of the present invention. This embodiment is characterized in that both of the two types of optical materials are birefringent optical materials. In this case, at least three of the ordinary light refractive index and the extraordinary light refractive index of the two types of birefringent optical materials are different.
【0048】たとえば、図7に示すように、2種類の複
屈折性の光学材料をそれぞれ光学材料(1)と光学材料
(2)とし、光学材料(1)の常光屈折率と異常光屈折
率のうち、A方向とする屈折率をna1、B方向とする屈
折率をnb1で表わし、光学材料(2)の常光屈折率と異
常光屈折率のうち、A方向とする屈折率をna2、B方向
とする屈折率をnb2で表わすとすると、光学材料(1)
と光学材料(2)の屈折率の方向を調整することによっ
て、常光屈折率と異常光屈折率を、na1、nb1、また
は、na2、nb2のどちらにでも設定できるので、たとえ
ば、図7(1)に示すように、光学材料(1)の常光屈
折率と異常光屈折率の間に、光学材料(2)の常光屈折
率と異常光屈折率の高い方があり、光学材料(1)の常
光屈折率と異常光屈折率の低い方よりも下に、光学材料
(2)の常光屈折率と異常光屈折率の低い方がある場合
に、光学材料(1)の常光屈折率と異常光屈折率のうち
屈折率の低い方をA方向にし、屈折率の高い方をB方向
にするとともに、光学材料(2)の常光屈折率と異常光
屈折率のうち屈折率の高い方をA方向にし、屈折率の低
い方をB方向にして、A方向の屈折率差Δn2 (=|n
a1−na2|)およびB方向の屈折率差Δn1 (=|nb1
−nb2|)を得るようにしたり、図7(2)に示すよう
に、光学材料(1)の常光屈折率と異常光屈折率のうち
屈折率の低い方をA方向にし、屈折率の高い方をB方向
にするとともに、光学材料(2)の常光屈折率と異常光
屈折率のうち屈折率の低い方をA方向にし、屈折率の高
い方をB方向にして、A方向の屈折率差Δn2 (=|n
a1−na2|)およびB方向の屈折率差Δn1 (=|nb1
−nb2|)を得るようにしたりして、屈折率差、また
は、波長で規格化された位相差Δn×d/λを選択し、
1次回折効率や0次透過効率を設定するようにする。For example, as shown in FIG. 7, two types of birefringent optical materials are referred to as an optical material (1) and an optical material (2), respectively. Among them, the refractive index in the A direction is represented by n a1 , the refractive index in the B direction is represented by n b1 , and the refractive index in the A direction of the ordinary light refractive index and the extraordinary light refractive index of the optical material (2) is n If the refractive index in the a2 and B directions is represented by n b2 , the optical material (1)
And the direction of the refractive index of the optical material (2), the ordinary refractive index and the extraordinary refractive index can be set to either n a1 , n b1 , or n a2 , n b2 . As shown in FIG. 7A, between the ordinary refractive index and the extraordinary refractive index of the optical material (1), there is a higher one of the ordinary refractive index and the extraordinary refractive index of the optical material (2). When the optical material (2) has a lower ordinary light refractive index and an extraordinary light refractive index below the lower ordinary light refractive index and the extraordinary light refractive index of (1), the ordinary light refraction of the optical material (1) is used. The lower one of the refractive index and the extraordinary light refractive index is set to the direction A, and the higher refractive index is set to the direction B, and the ordinary refractive index and the extraordinary refractive index of the optical material (2) are set to the higher refractive index. Is the direction A, and the one with the lower refractive index is the direction B, and the refractive index difference Δn 2 (= | n
a1 −n a2 |) and the refractive index difference Δn 1 in the B direction (= | n b1
−n b2 |), or as shown in FIG. 7 (2), the lower one of the ordinary refractive index and the extraordinary refractive index of the optical material (1) is set to the A direction, and the refractive index of the optical material (1) is changed to the A direction. The higher direction is set to the B direction, the lower one of the ordinary light refractive index and the extraordinary light refractive index of the optical material (2) is set to the A direction, and the higher refractive index is set to the B direction, and refraction in the A direction is performed. Rate difference Δn 2 (= | n
a1 −n a2 |) and the refractive index difference Δn 1 in the B direction (= | n b1
−n b2 |) to select a refractive index difference or a phase difference Δn × d / λ normalized by wavelength,
The first-order diffraction efficiency and the zero-order transmission efficiency are set.
【0049】また、図7(3)に示すように、光学材料
(1)の常光屈折率と異常光屈折率の低い方よりも下
に、光学材料(2)の常光屈折率と異常光屈折率の高い
方がある場合に、光学材料(1)の常光屈折率と異常光
屈折率のうち屈折率の低い方をA方向にし、屈折率の高
い方をB方向にするとともに、光学材料(2)の常光屈
折率と異常光屈折率のうち屈折率の高い方をA方向に
し、屈折率の低い方をB方向にして、A方向の屈折率差
Δn2 (=|na1−na2|)およびB方向の屈折率差Δ
n1 (=|nb1−nb2|)を得るようにしたり、図示し
ないが、光学材料(1)の常光屈折率と異常光屈折率の
うち屈折率の低い方をA方向にし、屈折率の高い方をB
方向にするとともに、光学材料(2)の常光屈折率と異
常光屈折率のうち屈折率の高い方をB方向にし、屈折率
の低い方をA方向にして、A方向の屈折率差Δn2 (=
|na1−na2|)およびB方向の屈折率差Δn1 (=|
nb1−nb2|)を得るようにしたりして、屈折率差、あ
るいは、波長で規格化された位相差Δn×d/λを選択
し、1次回折効率や0次透過効率を設定する。As shown in FIG. 7C, the ordinary refractive index and the extraordinary refractive index of the optical material (2) are lower than the lower of the ordinary refractive index and the extraordinary refractive index of the optical material (1). When there is a higher refractive index, the lower one of the ordinary refractive index and the extraordinary refractive index of the optical material (1) is set to the A direction, the higher refractive index is set to the B direction, and Of the ordinary light refractive index and the extraordinary light refractive index in 2), the higher refractive index is set to the A direction, and the lower refractive index is set to the B direction, and the refractive index difference Δn 2 in the A direction (= | n a1 −n a2). |) And the refractive index difference Δ in the B direction
Although n 1 (= | n b1 −n b2 |) is obtained or not shown, the lower one of the ordinary light refractive index and the extraordinary light refractive index of the optical material (1) is set in the A direction, and the refractive index is changed. The higher one is B
Direction, the higher refractive index of the ordinary light refractive index and the extraordinary light refractive index of the optical material (2) is set to the B direction, and the lower refractive index is set to the A direction, and the refractive index difference Δn 2 in the A direction. (=
| N a1 −n a2 |) and the refractive index difference Δn 1 in the B direction (= |
n b1 −n b2 |) to select the refractive index difference or the phase difference Δn × d / λ normalized by the wavelength, and set the first-order diffraction efficiency and zero-order transmission efficiency. .
【0050】また、光学材料(1)の常光屈折率と異常
光屈折率の間に、光学材料(2)の常光屈折率と異常光
屈折率の両方がある場合に対しても、同様に、屈折率
差、あるいは、波長で規格化された位相差Δn×d/λ
を選択し、1次回折効率や0次透過効率を設定できる。Similarly, when both the ordinary refractive index and the extraordinary refractive index of the optical material (2) are between the ordinary refractive index and the extraordinary refractive index of the optical material (1), Refractive index difference or phase difference Δn × d / λ normalized by wavelength
And the first-order diffraction efficiency and zero-order transmission efficiency can be set.
【0051】このように2種類の光学材料の両方を複屈
折性の光学材料とすることにより、屈折率差の選択範囲
が拡がるので、1次回折効率や0次透過効率を設定する
うえで自由度が増えて好ましい。上記以外についても、
前記実施の形態とほぼ同様の構成を備えており、同様の
作用・効果が得られる。By using both types of optical materials as birefringent optical materials as described above, the selection range of the refractive index difference is expanded, so that the first-order diffraction efficiency and the zero-order transmission efficiency can be freely set. The degree increases, which is preferable. In addition to the above,
It has almost the same configuration as the above-described embodiment, and the same operation and effect can be obtained.
【0052】[0052]
[実施例1]断面矩形波状の複屈折性回折格子21に等
方性充填材22を充填することにより図1のものとほぼ
同様の回折素子23を作製した。この場合に、複屈折性
回折格子21として常光屈折率nO =1.52、異常光
屈折率ne =1.64の高分子液晶を用い、等方性充填
材22として屈折率nS=1.43のアクリル系等方性
媒質を用いた。そして、格子深さdを約1.62μmに
設定し、波長λが650nmの光源を用いた。Example 1 A birefringent diffraction grating 21 having a rectangular wave cross section was filled with an isotropic filler 22 to produce a diffraction element 23 substantially similar to that shown in FIG. In this case, the ordinary refractive index n O = 1.52, the polymer liquid crystal of the extraordinary refractive index n e = 1.64 is used as the birefringent diffraction grating 21, refractive index n S as isotropic filler 22 = An acrylic isotropic medium of 1.43 was used. Then, a grating depth d was set to about 1.62 μm, and a light source having a wavelength λ of 650 nm was used.
【0053】この回折素子23の最も屈折率の高いB方
向の屈折率差Δn1 は、1.64−1.43=0.21
となり、格子の深さdが1.62μm、波長λが650
nmであることから、Δn1 ×d/λの値は、ほぼ0.
5となり、B方向の偏光の光に対する1次回折効率は、
理論限界であるほぼ38%という値が得られた。The refractive index difference Δn 1 in the B direction having the highest refractive index of the diffraction element 23 is 1.64-1.43 = 0.21.
Where the depth d of the grating is 1.62 μm and the wavelength λ is 650.
nm, the value of Δn 1 × d / λ is approximately 0.
5, and the first-order diffraction efficiency for the polarized light in the B direction is
A value of approximately 38%, the theoretical limit, was obtained.
【0054】また、この回折素子23の最も屈折率の低
いA方向の屈折率差Δn2 は、1.52−1.43=
0.09となり、格子の深さdが1.62μm、波長λ
が650nmであることから、Δn2 ×d/λの値はほ
ぼ0.22となり、A方向の偏光の光に対する0次透過
効率はほぼ58%、1次回折効率はほぼ15%という値
が得られた。Further, the refractive index difference Δn 2 in the A direction having the lowest refractive index of the diffraction element 23 is 1.52-1.43 =
0.09, the grating depth d is 1.62 μm, and the wavelength λ
Is 650 nm, the value of Δn 2 × d / λ is approximately 0.22, and the zero-order transmission efficiency for polarized light in the A direction is approximately 58%, and the first-order diffraction efficiency is approximately 15%. Was done.
【0055】したがって、複屈折のほとんどない光ディ
スクの場合には、A方向に偏光された出射光が58%の
0次透過効率で回折素子23を透過され、1/4波長板
で円偏光に変換され、光ディスクで反射されて、再び1
/4波長板でB方向の偏光に変化された後、回折素子2
3で38%の1次回折効率で回折され、受光素子に到達
した。この時の往復効率は、58%×38%≒22%で
あった。ただし、この値は、対物レンズの瞳径による開
口制限やディスクの反射損などはないと仮定したときの
換算値である。Therefore, in the case of an optical disk having almost no birefringence, the outgoing light polarized in the A direction is transmitted through the diffraction element 23 with a zero-order transmission efficiency of 58%, and is converted into circularly polarized light by a quarter-wave plate. Is reflected by the optical disk and
After being changed to B-direction polarized light by a 偏光 wavelength plate, the diffraction element 2
In No. 3, the light was diffracted with a first-order diffraction efficiency of 38% and reached the light receiving element. The reciprocating efficiency at this time was 58% × 38% ≒ 22%. However, this value is a converted value on the assumption that there is no aperture restriction due to the pupil diameter of the objective lens, and no reflection loss of the disk.
【0056】また、光ディスクに大きな複屈折性がある
場合を想定し、復路の偏光方向が往路と同じA方向にな
ったときの往復効率を調べると、58%×15%=8.
7%となった。Further, assuming that the optical disk has a large birefringence, the reciprocation efficiency when the polarization direction of the return path is the same as the A direction as the forward path is examined, and is 58% × 15% = 8.
It was 7%.
【0057】[実施例2]断面矩形波状の等方性回折格
子24に複屈折性充填材25を充填することにより図3
のものとほぼ同様の回折素子23を作製した。この場合
に、複屈折性充填材25として常光屈折率nO =1.5
2、異常光屈折率ne =1.77の液晶を用い、等方性
回折格子24として屈折率nS =1.58のSiO−N
を用いた。そして、格子深さdを約1.72μmに設定
し、波長λが650nmの光源を用いた。Embodiment 2 FIG. 3 shows that an isotropic diffraction grating 24 having a rectangular cross section is filled with a birefringent filler 25.
A diffraction element 23 substantially similar to that described above was produced. In this case, the ordinary refractive index n O = 1.5 as the birefringent filler 25.
2, using the liquid crystal of the extraordinary refractive index n e = 1.77, SiO-N in the refractive index n S = 1.58 as isotropic diffraction grating 24
Was used. Then, the grating depth d was set to about 1.72 μm, and a light source having a wavelength λ of 650 nm was used.
【0058】この回折素子23の最も屈折率の高いB方
向の屈折率差Δn1 は、1.77−1.58=0.19
となり、格子の深さdが1.72μm、波長λが650
nmであることから、Δn1 ×d/λの値は、ほぼ0.
5となり、B方向の偏光の光に対する1次回折効率は、
理論限界であるほぼ38%という値が得られた。The refractive index difference Δn 1 of the diffraction element 23 in the direction B having the highest refractive index is 1.77−1.58 = 0.19.
Where the depth d of the grating is 1.72 μm and the wavelength λ is 650.
nm, the value of Δn 1 × d / λ is approximately 0.
5, and the first-order diffraction efficiency for the polarized light in the B direction is
A value of approximately 38%, the theoretical limit, was obtained.
【0059】また、この回折素子23の最も屈折率の低
いA方向の屈折率差Δn2 は、1.52−1.58=−
0.06となり、格子の深さdが1.72μm、波長λ
が650nmであることから、Δn2 ×d/λの値はほ
ぼ0.16となり、A方向の偏光の光に対する0次透過
効率はほぼ74%、1次回折効率はほぼ9%という値が
得られた。The refractive index difference Δn 2 in the direction A having the lowest refractive index of the diffraction element 23 is 1.52 to 1.58 = −
0.06, the grating depth d is 1.72 μm, and the wavelength λ
Is 650 nm, the value of Δn 2 × d / λ is approximately 0.16, and the zero-order transmission efficiency for the polarized light in the A direction is approximately 74%, and the first-order diffraction efficiency is approximately 9%. Was done.
【0060】したがって、複屈折のほとんどない光ディ
スクの場合には、A方向に偏光された出射光が74%の
0次透過効率で回折素子23を透過され、1/4波長板
で円偏光に変換され、光ディスクで反射されて、再び1
/4波長板でB方向の偏光に変化された後、回折素子2
3で38%の1次回折効率で回折され、受光素子に到達
した。この時の往復効率は、74%×38%≒28%で
あった。ただし、この値は、対物レンズの瞳径による開
口制限やディスクの反射損などはないと仮定したときの
換算値である。Therefore, in the case of an optical disk having almost no birefringence, the outgoing light polarized in the A direction is transmitted through the diffractive element 23 with a zero-order transmission efficiency of 74%, and is converted into circularly polarized light by a quarter-wave plate. Is reflected by the optical disk and
After being changed to B-direction polarized light by a 偏光 wavelength plate, the diffraction element 2
In No. 3, the light was diffracted with a first-order diffraction efficiency of 38% and reached the light receiving element. The reciprocating efficiency at this time was 74% × 38% ≒ 28%. However, this value is a converted value on the assumption that there is no aperture restriction due to the pupil diameter of the objective lens, and no reflection loss of the disk.
【0061】また、光ディスクに大きな複屈折性がある
場合を想定し、復路の偏光方向が往路と同じA方向にな
ったときの往復効率を調べると、74%×9%≒6.6
%となった。Assuming that the optical disk has a large birefringence, the reciprocation efficiency when the polarization direction of the return path is the same as the A direction as the forward path is examined, and it is found that 74% × 9% ≒ 6.6.
%.
【0062】[実施例3]断面形状が鋸歯状の等方性回
折格子24に複屈折性充填材25を充填することにより
図5のものとほぼ同様の回折素子23を作製した。この
場合に、複屈折性充填材25として常光屈折率nO =
1.52、異常光屈折率ne =1.77の液晶を用い、
屈折率nS =1.59のガラス製の基板20に直接等方
性回折格子24を形成した。そして、格子深さdを約
3.6μmに設定し、波長λが650nmの光源を用い
た。Example 3 By filling a birefringent filler 25 into an isotropic diffraction grating 24 having a sawtooth cross section, a diffraction element 23 substantially similar to that shown in FIG. 5 was manufactured. In this case, the ordinary refractive index n O =
1.52, using the liquid crystal of the extraordinary refractive index n e = 1.77,
An isotropic diffraction grating 24 was formed directly on a glass substrate 20 having a refractive index n S = 1.59. Then, a grating depth d was set to about 3.6 μm, and a light source having a wavelength λ of 650 nm was used.
【0063】この回折素子23の最も屈折率の高いB方
向の屈折率差Δn1 は、1.77−1.59=0.18
となり、格子の深さdが3.6μm、波長λが650n
mであることから、Δn1 ×d/λの値は、ほぼ1.0
となり、B方向の偏光の光に対する1次回折効率は、理
論限界であるほぼ95%という値が得られた。The refractive index difference Δn 1 in the B direction having the highest refractive index of the diffraction element 23 is 1.77−1.59 = 0.18.
Where the depth d of the grating is 3.6 μm and the wavelength λ is 650 n
m, the value of Δn 1 × d / λ is approximately 1.0
Thus, the first-order diffraction efficiency with respect to the polarized light in the B direction was about 95%, which is the theoretical limit.
【0064】また、この回折素子23の最も屈折率の低
いA方向の屈折率差Δn2 は、1.52−1.59=−
0.07となり、格子の深さdが3.6μm、波長λが
650nmであることから、Δn2 ×d/λの値はほぼ
0.39となり、A方向の偏光の光に対する0次透過効
率はほぼ58%、1次回折効率はほぼ22%という値が
得られた。The refractive index difference Δn 2 in the direction A having the lowest refractive index of the diffraction element 23 is 1.52 to 1.59 = −
0.07, the depth d of the grating is 3.6 μm, and the wavelength λ is 650 nm. Therefore, the value of Δn 2 × d / λ is approximately 0.39, and the zero-order transmission efficiency for the polarized light in the A direction is 0. Was about 58%, and the first-order diffraction efficiency was about 22%.
【0065】したがって、複屈折のほとんどない光ディ
スクの場合には、A方向に偏光された出射光が58%の
0次透過効率で回折素子23を透過され、1/4波長板
で円偏光に変換され、光ディスクで反射されて、再び1
/4波長板でB方向の偏光に変化された後、回折素子2
3で95%の1次回折効率で回折され、受光素子に到達
した。この時の往復効率は、58%×95%≒55%で
あった。ただし、この値は、対物レンズの瞳径による開
口制限やディスクの反射損などはないと仮定したときの
換算値である。Therefore, in the case of an optical disk having almost no birefringence, the outgoing light polarized in the A direction is transmitted through the diffraction element 23 with a zero-order transmission efficiency of 58%, and is converted into circularly polarized light by a quarter-wave plate. Is reflected by the optical disk and
After being changed to B-direction polarized light by a 偏光 wavelength plate, the diffraction element 2
3 and was diffracted with a first-order diffraction efficiency of 95%, and reached the light receiving element. The reciprocating efficiency at this time was 58% × 95% ≒ 55%. However, this value is a converted value on the assumption that there is no aperture restriction due to the pupil diameter of the objective lens, and no reflection loss of the disk.
【0066】また、光ディスクに大きな複屈折性がある
場合を想定し、復路の偏光方向が往路と同じA方向にな
ったときの往復効率を調べると、58%×22%≒13
%となった。Assuming that the optical disk has a large birefringence, the reciprocation efficiency when the polarization direction of the return path is the same as the A direction as the forward path is examined, and is 58% × 22% ≒ 13
%.
【0067】なお、本発明は、上述の実施の形態にのみ
限定されず、本発明の要旨を逸脱しない範囲内において
種々変更を加えうる。It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.
【0068】[0068]
【発明の効果】以上説明したように、本発明の回折素子
および光ヘッド装置によれば、複屈折性を持つ光記録媒
体に対しても情報を読み取ることができるという優れた
効果を奏しうる。As described above, according to the diffraction element and the optical head device of the present invention, an excellent effect that information can be read from an optical recording medium having birefringence can be obtained.
【図1】本発明の第1の実施の形態にかかる偏光系の回
折素子の側方断面図。FIG. 1 is a side sectional view of a polarizing diffraction element according to a first embodiment of the present invention.
【図2】本発明の第1の実施の形態にかかる他の偏光系
の回折素子の側方断面図。FIG. 2 is a side cross-sectional view of another polarization type diffraction element according to the first embodiment of the present invention.
【図3】本発明の第1の実施の形態にかかる別の偏光系
の回折素子の側方断面図。FIG. 3 is a side cross-sectional view of another polarization type diffraction element according to the first embodiment of the present invention.
【図4】本発明の第1の実施の形態にかかる、効率と、
波長で規格化された位相差Δn×d/λとの関係を示す
グラフ。FIG. 4 is a diagram showing the efficiency and efficiency according to the first embodiment of the present invention;
9 is a graph showing a relationship with a phase difference Δn × d / λ normalized by wavelength.
【図5】本発明の第2の実施の形態にかかる偏光系の回
折素子の側方断面図。FIG. 5 is a side sectional view of a polarizing diffraction element according to a second embodiment of the present invention.
【図6】本発明の第2の実施の形態にかかる、効率と、
波長で規格化された位相差Δn×d/λとの関係を示す
グラフ。FIG. 6 shows the efficiency and the second embodiment according to the present invention;
9 is a graph showing a relationship with a phase difference Δn × d / λ normalized by wavelength.
【図7】(1)、(2)、(3)は、本発明の第3の実
施の形態にかかる2つの複屈折性光学材料の屈折率の関
係を示す図。FIGS. 7 (1), (2) and (3) are diagrams showing the relationship between the refractive indices of two birefringent optical materials according to a third embodiment of the present invention.
【図8】従来の光ヘッド装置の概略を示す側面図。FIG. 8 is a side view schematically showing a conventional optical head device.
【図9】無偏光系のホログラムビームスプリッタの側方
断面図。FIG. 9 is a side sectional view of a non-polarization hologram beam splitter.
【図10】偏光系のホログラムビームスプリッタを示す
側方断面図。FIG. 10 is a side sectional view showing a polarization type hologram beam splitter.
1:光源 4:光ディスク(光記録媒体) 5:受光素子(光検出器) 6:アンプ(光検出器) 7:自動ゲイン補正回路(光検出器) 20:基板 21:複屈折性回折格子(光学材料) 22:等方性充填材(光学材料) 23:回折素子(光束制御素子) 24:等方性回折格子(光学材料) 25:複屈折性充填材(光学材料) 1: light source 4: optical disk (optical recording medium) 5: light receiving element (photodetector) 6: amplifier (photodetector) 7: automatic gain correction circuit (photodetector) 20: substrate 21: birefringent diffraction grating ( 22: Isotropic filler (optical material) 23: Diffraction element (light flux controlling element) 24: Isotropic diffraction grating (optical material) 25: Birefringent filler (optical material)
Claims (5)
と、回折格子の少なくとも凸部間に充填される別の光学
材料とからなる回折素子において、上記2種類の光学材
料のうちの少なくとも一方が複屈折性を示し、かつ、他
方の光学材料が、複屈折性を示す一方の光学材料の常光
屈折率と異常光屈折率のどちらとも異なる屈折率を少な
くとも一つ有することを特徴とする回折素子。1. A diffraction element comprising an optical material forming a diffraction grating having an uneven cross section and another optical material filled between at least convex portions of the diffraction grating, wherein at least one of the two types of optical materials is used. One shows birefringence, and the other optical material has at least one refractive index different from both the ordinary light refractive index and the extraordinary light refractive index of the one optical material showing birefringence. Diffraction element.
の光学材料とした請求項1記載の回折素子。2. The diffraction element according to claim 1, wherein one of the two types of optical materials is an isotropic optical material.
光学材料の常光屈折率および異常光屈折率のうちの小さ
い方よりも小さいか、または、大きい方よりも大きい請
求項2記載の回折素子。3. The refractive index of the isotropic optical material is smaller than the smaller one of the ordinary light refractive index and the extraordinary light refractive index of the birefringent optical material, or larger than the larger one. 2. The diffraction element according to 2.
次回折効率が、回折効率が最高となる偏光方向に対する
1次回折効率の10%以上となり、回折効率が最低とな
る偏光方向に対する0次透過効率と回折効率が最高とな
る偏光方向に対する1次回折効率との積が10%以上と
なる屈折率差を有する2種類の光学材料を使用した請求
項1、2または3記載の回折素子。4. A method according to claim 1, wherein said light beam has a diffraction efficiency of 1.
The first-order diffraction efficiency is 10% or more of the first-order diffraction efficiency in the polarization direction in which the diffraction efficiency is the highest, and the zero-order transmission efficiency in the polarization direction in which the diffraction efficiency is the lowest and the first-order diffraction in the polarization direction in which the diffraction efficiency is the highest. 4. The diffractive element according to claim 1, wherein two types of optical materials having a difference in the refractive index such that the product of the efficiency and the efficiency is 10% or more are used.
ともに光記録媒体で反射して戻ってきた反射光の進行方
向を変更する光束制御素子と、光束制御素子で進行方向
を変更された反射光の情報を検知する光検出器とを備え
た光ヘッド装置において、光束制御素子として、請求項
1、2、3または4記載の回折素子を用いたことを特徴
とする光ヘッド装置。5. A light source, a light flux controlling element for passing the light emitted from the light source and changing the traveling direction of the reflected light reflected back by the optical recording medium, and the traveling direction changed by the light flux controlling element. 5. An optical head device comprising a photodetector for detecting information of reflected light, wherein the diffraction element according to claim 1, 2, 3 or 4 is used as a light flux controlling element.
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP9270124A JPH11110787A (en) | 1997-10-02 | 1997-10-02 | Diffraction element and optical head device |
US09/509,532 US6618116B1 (en) | 1997-10-02 | 1998-10-01 | Optical head device and a diffraction element suitable for the device, and a method of manufacturing the diffraction element and the optical head device |
PCT/JP1998/004445 WO1999018459A1 (en) | 1997-10-02 | 1998-10-01 | Optical head device and a diffraction element suitable for the device, and a method of manufacturing the diffraction element and the optical head device |
KR10-2000-7003571A KR100497586B1 (en) | 1997-10-02 | 1998-10-01 | Optical head device and a diffraction element suitable for the device, and a method of manufacturing the diffraction element and the optical head device |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP9270124A JPH11110787A (en) | 1997-10-02 | 1997-10-02 | Diffraction element and optical head device |
Publications (1)
Publication Number | Publication Date |
---|---|
JPH11110787A true JPH11110787A (en) | 1999-04-23 |
Family
ID=17481895
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP9270124A Pending JPH11110787A (en) | 1997-10-02 | 1997-10-02 | Diffraction element and optical head device |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH11110787A (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2006259132A (en) * | 2005-03-16 | 2006-09-28 | Asahi Glass Co Ltd | Stair-shaped diffraction element and optical head apparatus |
KR100697614B1 (en) | 2006-01-31 | 2007-03-22 | 주식회사 엘지에스 | Diffraction grating and method of fabrication thereof |
JP2007225905A (en) * | 2006-02-23 | 2007-09-06 | Asahi Glass Co Ltd | Optical isolator and bidirectional optical transmitting/receiving apparatus |
KR100779693B1 (en) | 2006-08-09 | 2007-11-26 | 주식회사 엘지에스 | Wave selection type diffractive optical elements and optical pickup device has them |
JP2011054273A (en) * | 2010-10-28 | 2011-03-17 | Asahi Glass Co Ltd | Polarization diffraction element |
-
1997
- 1997-10-02 JP JP9270124A patent/JPH11110787A/en active Pending
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2006259132A (en) * | 2005-03-16 | 2006-09-28 | Asahi Glass Co Ltd | Stair-shaped diffraction element and optical head apparatus |
JP4613651B2 (en) * | 2005-03-16 | 2011-01-19 | 旭硝子株式会社 | Staircase diffraction element and optical head device |
KR100697614B1 (en) | 2006-01-31 | 2007-03-22 | 주식회사 엘지에스 | Diffraction grating and method of fabrication thereof |
JP2007225905A (en) * | 2006-02-23 | 2007-09-06 | Asahi Glass Co Ltd | Optical isolator and bidirectional optical transmitting/receiving apparatus |
KR100779693B1 (en) | 2006-08-09 | 2007-11-26 | 주식회사 엘지에스 | Wave selection type diffractive optical elements and optical pickup device has them |
JP2011054273A (en) * | 2010-10-28 | 2011-03-17 | Asahi Glass Co Ltd | Polarization diffraction element |
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