JP4273606B2 - Dual wavelength light source device and optical head device - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、２波長光源装置および光ヘッド装置に関する。
【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光記録媒体の情報の記録・再生を行う光ヘッド装置において、半導体レーザからの出射光はレンズにより光記録媒体上に集光され、集光された光は光記録媒体に反射されて戻り光となる。そして、この戻り光はビームスプリッタを用いて光検出器である受光素子へ導かれ、光記録媒体上の情報が電気信号に変換される。
【０００３】
また、同一の光ヘッド装置を用いて規格の異なるＣＤおよびＤＶＤの光ディスクの情報を記録・再生するため、ＣＤ／ＤＶＤ互換の光ヘッド装置が製品化されている。特に、光記録媒体として波長依存性の高い媒体を用いるＣＤ−Ｒなどの再生を前提とした場合、ＣＤ用に波長７９０ｎｍの半導体レーザが用いられ、ＤＶＤ用に波長６５０ｎｍの半導体レーザが用いられている。
【０００４】
さらに、波長７９０ｎｍの半導体レーザと波長６５０ｎｍの半導体レーザをその発光点間隔を１００〜３００μｍ隔てて配置し構成した２波長用半導体レーザを、１つの光源ユニット内に用いることにより、発光点の位置精度が高く安定した光ヘッド装置が得られる。また、部品点数を削減して光ヘッド装置の小型化・軽量化が図られ、光学系の設計を簡略化できるなどの利点があるため、２波長用半導体レーザを用いた種々の光ヘッド装置の構成が提案されている。
【０００５】
例えば図５（ａ）、（ｂ）において、２波長用半導体レーザ１の波長６５０ｎｍの発光点１Ａおよび波長７９０ｎｍの発光点１Ｂからの出射光は、コリメートレンズ１１により平行光となり、対物レンズ１２により光記録媒体（ＣＤやＤＶＤなど）である光ディスク１３の上に集光される。
【０００６】
【発明が解決しようとする課題】
図５（ａ）に示すように、波長６５０ｎｍの半導体レーザの発光点１Ａをコリメートレンズ１１および対物レンズ１２の回転対称軸上（光軸上）に配置することにより、波面収差の少ない良好な光学特性が得られる。
一方、波長７９０ｎｍの半導体レーザ（図５（ｂ））は発光点１Ｂの位置が発光点１Ａとは異なり光軸上にないため、コリメートレンズ１１および対物レンズ１２に対して入射光は斜入射となり、それに伴って非点収差やコマ収差が発生し、光ディスク上への集光性が劣化する。その結果、情報の記録・再生が不安定となる問題があった。
【０００７】
【課題を解決するための手段】
本発明は、上記の課題を解決するためになされたものであり、波長λ１および波長λ２（λ１≠λ２）の互いに平行な振動面をもつ直線偏光でそれぞれ異なる発光点位置から出射する２波長用半導体レーザと、前記２波長用半導体レーザから出射した互いに平行な振動面をもつ前記波長λ １ と前記波長λ ２ の振動面を互いに直交させる効果があるリタデーション値を有する位相板と、前記波長λ１および前記波長λ２の直線偏光が透過する２波長用偏向光学素子と、をこの順に備えた２波長光源装置であって、前記２波長用偏向光学素子は、複屈折媒体を備え、常光となる前記波長λ１の直線偏光を偏向することなく透過させ、異常光となる前記波長λ２の直線偏光を前記波長λ１の透過光の光軸と一致するように偏向することを特徴とする２波長光源装置を提供する。
【０００８】
また、上記の２波長光源装置と、前記２波長光源装置からの出射光を光記録媒体に集光する対物レンズとを少なくとも備える、光記録媒体の情報の記録・再生を行う光ヘッド装置であって、前記２波長光源装置からの出射光の光軸が前記対物レンズの光軸と一致していることを特徴とする光ヘッド装置を提供する。
【０００９】
【発明の実施の形態】
図１の２波長光源装置は、２波長用半導体レーザ１と２波長用偏向光学素子２から構成され、２波長用偏向光学素子２は複屈折媒体４を備えている。
２波長用半導体レーザ１において、ＤＶＤ系の波長λ1＝６５０ｎｍの光を出射する発光点１ＡとＣＤ系の波長λ2＝７９０ｎｍの光を出射する発光点１Ｂとが間隔ｗで配置されている。発光点１Ａおよび１Ｂを出射した直線偏光は、振動面が互いに直交しており、複屈折媒体４上の点２Ａおよび２Ｂ（間隔ｗ離れている）にそれぞれ入射する。
【００１０】
２波長用偏向光学素子２は厚さがｔの平行平板状の複屈折媒体４からなり、この複屈折媒体４を、この表面に立てた法線と光学軸６との角がθとなり、波長λ1の直線偏光が常光、波長λ2の直線偏光が異常光になるように設置することにより、波長λ1の光は偏向することなく複屈折媒体４を透過し、波長λ2の光は式１の関係に従って、角度ψ偏向して複屈折媒体４中を進む。
【００１１】
【数１】
ここで、ｎoは波長λ1に対する複屈折媒体の常光屈折率、ｎeは波長λ2に対する複屈折媒体の異常光屈折率である。式１は鶴田匡夫著「応用光学ＩＩ」（培風館、第１５６頁）に記載されている（図６参照。図６中の符号で図１と同じものは同じ要素を表わす）。
【００１３】
複屈折媒体４を透過する波長λ1の光と波長λ2の光が、２波長用偏向光学素子２透過後に同一の光軸上を進むためには、複屈折媒体４の厚さｔが式２に従う必要がある。
ｔ＝ｗ／ｔａｎψ・・・（式２）
このとき、複屈折媒体４の表面に立てた法線と光学軸６とのなす角θを４５°にすることは、複屈折媒体の厚さｔを最小にすることができ望ましい。
【００１４】
複屈折媒体４として、常光屈折率ｎoと異常光屈折率ｎeとの差が大きい複屈折媒体、例えば、液晶、光学結晶の方解石などを利用することは、複屈折媒体の厚さｔを小さくでき望ましい。
図２の２波長光源装置は、２波長用半導体レーザ１と２波長用偏向光学素子２から構成され、特に２波長用偏向光学素子２は複屈折媒体４に位相板３を接着剤５で固定したものである。
【００１５】
２波長用半導体レーザ１において、ＤＶＤ系の波長λ1＝６５０ｎｍの光を出射する発光点１ＡとＣＤ系の波長λ2＝７９０ｎｍの光を出射する発光点１Ｂとが間隔ｗで配置されている。発光点１Ａおよび１Ｂを出射した直線偏光は、位相板３を透過することにより振動面が互いに直交する直線偏光になり、複屈折媒体４上の間隔がｗである点２Ａおよび２Ｂにそれぞれ入射する。
【００１６】
位相板３として、２波長用半導体レーザ１から出射する２つの直線偏光の振動面を互いに直交させる効果があるリタデーション値を有するものを選択することは、複屈折媒体４が上記の機能、すなわち波長λ1の常光と波長λ2の異常光との進む方向を異ならせることが効果的にでき望ましい。図２中図１の符号と同じ他の要素は、図１と同じ要素である。
【００１７】
２波長用半導体レーザ１を出射する２つの波長の光が互いに平行な振動面をもつ直線偏光である場合、位相板３として、波長λ1の直線偏光の振動面を９０°回転させ、波長λ2の直線偏光の振動面を回転させないリタデーション値を有するものを利用できる。例えば、リタデーション値が１６２５ｎｍの位相板は、波長λ1（６５０ｎｍ）の直線偏光の振動面を９０°回転させ、波長λ2（７９０ｎｍ）の直線偏光の振動面をほとんど回転させない。
【００１８】
また、波長λ1の直線偏光の振動面を回転させずに、波長λ2の直線偏光の振動面を９０°回転させるリタデーション値を有するものも利用できる。例えば、リタデーション値が１９５０ｎｍの位相板は、波長λ1（６５０ｎｍ）の直線偏光の振動面を回転させず、波長λ2（７９０ｎｍ）の直線偏光の振動面を約９０°回転させる。
【００１９】
位相板３の材料として、水晶やニオブ酸リチウムなどの複屈折性の光学結晶、ポリカボーネートなどを１軸延伸して複屈折性を発現させた有機物薄膜、または配向処理を施した透明基板に高分子液晶のモノマーを塗布し硬化させた高分子液晶薄膜などを使用できる。
【００２０】
接着剤５として、複屈折媒体４との屈折率差および位相板３との屈折率差が小さいものを選択することは、これらの材料の各界面での反射損失を低減できて望ましい。
図３の２波長光源装置は、２波長用半導体レーザ１とビームスプリッタ機能を有する２波長用偏向光学素子９から構成され、特にビームスプリッタ機能を有する２波長用偏向光学素子９は複屈折媒体４に位相板３を接着剤５で固定し、複屈折媒体４の位相板３とは反対側の面にビームスプリッタの機能を持たせている。
【００２１】
ビームスプリッタの機能を持たせる方法として、透明基板に直接断面が周期的な凹凸形状をした格子を形成または透明基板の表面に成膜した薄膜に断面が周期的な凹凸形状をした格子を形成する方法がある。またはホログラムを形成することによって作製された回折光学素子７を、複屈折媒体４に接着剤８で固定する方法がある。また、複屈折媒体４に直接、または複屈折媒体４の表面に形成した薄膜に、断面が周期的な凹凸の形状をした格子またはホログラムを形成することによっても、ビームスプリッタの機能を持たせることができる（図示せず）。図３中図１の符号と同じ他の要素は、図１と同じ要素である。
【００２２】
図４では２波長用偏向光学素子２を２波長用半導体レーザ１とコリメートレンズ１１との間に配置した光ヘッド装置としている。
発光点１Ａから出射された波長λ1の光は図４（ａ）に示すように２波長用偏向光学素子２を直進透過し、発光点１Ｂから出射された波長λ2の光は図４（ｂ）に示すように２波長用偏向光学素子２により、波長λ1の光と同じ光軸上に偏向され、コリメートレンズ１１および対物レンズ１２へと導かれる。
【００２３】
その結果、いずれの波長の光も対物レンズの収差が小さい良好な光学的状況が維持され、光記録媒体１３の情報の記録・再生が高精度で安定して行われる。
また、２波長用偏向光学素子２をコリメートレンズ１１と対物レンズ１２との間に配置してもよい。この場合、２波長用偏向光学素子２への入射光がほぼ平行光となり偏向特性の劣化、すなわち入射角度によって偏向方向が所定の方向からずれること、を低減できる。
【００２４】
【実施例】
まず本実施例の２波長光源装置を図２に基いて説明する。
２波長用半導体レーザ１として、発光点１ＡからＤＶＤ系の波長λ1＝６５０ｎｍの光を出射し、発光点１ＢからＣＤ系の波長λ2＝７９０ｎｍの光を出射するモノリシックな２波長用半導体レーザを用いた。発光点１Ａと１Ｂの間隔ｗは２００μｍであり、また２波長用半導体レーザ１を出射する波長λ1および波長λ2の光は紙面に垂直な方向に振動面を有する直線偏光であった。
【００２５】
２波長用偏向光学素子２を構成する複屈折媒体４として方解石の結晶を用い、その結晶表面に立てた法線と光学軸６とのなす角θが４５°であった。波長λ2に対する方解石の常光屈折率ｎoは１．６４９、異常光屈折率ｎeは１．４８２であり、式２に従って結晶の厚さを１．８９ｍｍに決定した。
【００２６】
位相板３としてリタデーション値が１９５０ｎｍの位相板を用い、この位相板は波長λ1の直線偏光の振動面を回転させず、波長λ2の直線偏光の振動面を約９０°回転させる効果がある。
上記の材料を用い、図２に示すように構成した２波長光源装置から出射する波長λ1と波長λ2の光は、同一軸を進むことができる。
【００２７】
次に、この２波長光源装置を図４に示した光ヘッド装置に搭載した。
その結果、波長λ1および波長λ2のいずれの光も光記録媒体１３の情報記録面に回折限界に相当するビーム径で集光され、使用波長の異なる２種類の光記録媒体の情報の記録・再生が高精度で安定して行われた。
【００２８】
【発明の効果】
以上説明したように、本発明の２波長光源装置によれば、２波長用偏向光学素子を用いて発光点と振動面の異なる２つの波長の光の光軸を一致させることができる。したがって、この２波長光源装置を光ヘッド装置に組み込むことにより、入射光は対物レンズ、コリメートレンズなどの同一の光軸に対して斜め入射することはなく、この入射光に基く収差は存在しない。
【００２９】
このため、使用波長の異なる光記録媒体の情報の記録・再生が高精度で安定して行える光ヘッド装置を構成できる。また、部品点数の少ない小型で軽量の光ヘッド装置も実現できる。
【図面の簡単な説明】
【図１】本発明の２波長光源装置の構成の１例を示す断面図。
【図２】本発明の２波長光源装置の構成の別の例を示す断面図。
【図３】本発明の２波長光源装置の構成の他の例を示す断面図。
【図４】本発明の２波長光源装置を用いた光ヘッド装置の１例を示す概念的側面図で、（ａ）発光点からの出射光が波長用偏向光学素子を直進透過する状況を示す概念的側面図、（ｂ）発光点からの出射光が波長用偏向光学素子により偏向する状況を示す概念的側面図。
【図５】従来の２波長用半導体レーザを用いた光ヘッド装置の１例を示す概念的側面図で、（ａ）発光点からの出射光が光軸上を直進する状況を示す概念的側面図、（ｂ）発光点からの出射光が光軸に対して斜めに入射する状況を示す概念的側面図。
【図６】複屈折媒体中で常光と異常光が進行する様子を示す概念図。
【符号の説明】
１：２波長用半導体レーザ
１Ａ、１Ｂ：発光点
２：２波長用偏向光学素子
３：位相板
４：複屈折媒体
５、８：接着剤
６：複屈折媒体４の光学軸
７：回折光学素子
９：ビームスプリッタ機能を有する２波長用偏向光学素子
１１：コリメートレンズ
１２：対物レンズ
１３：光記録媒体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a two-wavelength light source device and an optical head device.
[0002]
[Prior art]
In an optical head device for recording / reproducing information on an optical recording medium such as an optical disk such as a CD and a DVD and a magneto-optical disk, the light emitted from the semiconductor laser is condensed and condensed on the optical recording medium by a lens. The light is reflected by the optical recording medium and becomes return light. The return light is guided to a light receiving element which is a photodetector using a beam splitter, and information on the optical recording medium is converted into an electric signal.
[0003]
Also, CD / DVD compatible optical head devices have been commercialized in order to record / reproduce information on CD and DVD optical discs of different standards using the same optical head device. In particular, assuming reproduction of a CD-R using a wavelength-dependent medium as an optical recording medium, a semiconductor laser with a wavelength of 790 nm is used for CD, and a semiconductor laser with a wavelength of 650 nm is used for DVD. Yes.
[0004]
Further, by using a two-wavelength semiconductor laser in which a semiconductor laser having a wavelength of 790 nm and a semiconductor laser having a wavelength of 650 nm are arranged with a light-emitting point interval of 100 to 300 μm in one light source unit, the position accuracy of the light-emitting point is obtained. High and stable optical head device can be obtained. Further, since the number of components is reduced, the optical head device can be reduced in size and weight, and the design of the optical system can be simplified. Therefore, various optical head devices using two-wavelength semiconductor lasers can be used. A configuration is proposed.
[0005]
For example, in FIGS. 5 (a) and 5 (b), the light emitted from the light emission point 1 A having a wavelength of 650 nm and the light emission point 1 B having a wavelength of 790 nm of the two-wavelength semiconductor laser 1 is converted into parallel light by the collimator lens 11. The light is condensed on an optical disk 13 which is an optical recording medium (CD, DVD, etc.).
[0006]
[Problems to be solved by the invention]
As shown in FIG. 5A, by arranging the light emitting point 1A of the semiconductor laser having a wavelength of 650 nm on the rotational symmetry axis (on the optical axis) of the collimating lens 11 and the objective lens 12, a good optical with less wavefront aberration is obtained. Characteristics are obtained.
On the other hand, since the position of the light emitting point 1B is not on the optical axis unlike the light emitting point 1A, the incident light is obliquely incident on the collimating lens 11 and the objective lens 12 in the semiconductor laser having a wavelength of 790 nm (FIG. 5B). As a result, astigmatism and coma occur, and the light condensing performance on the optical disk deteriorates. As a result, there has been a problem that recording / reproduction of information becomes unstable.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, emitted from different light emitting points positions linearly polarized light having a wavelength lambda 1 and wavelength λ 2 (λ 1 ≠ λ 2 ) from one another parallel plane of vibration of A two-wavelength semiconductor laser, and a phase plate having a retardation value that has an effect of orthogonally crossing the vibration surfaces of the wavelength λ 1 and the wavelength λ 2 emitted from the two-wavelength semiconductor laser. , 2 and wavelength for the optical deflector to the wavelength lambda 1 and the wavelength lambda 2 of the linearly polarized light is transmitted, a a double-wavelength light source device provided in this order, the 2-wavelength optical deflector is a birefringent medium And transmitting the linearly polarized light having the wavelength λ 1 that becomes ordinary light without being deflected, and deflecting the linearly polarized light having the wavelength λ 2 that becomes abnormal light so as to coincide with the optical axis of the transmitted light having the wavelength λ 1. Features Providing two-wavelength light source unit.
[0008]
An optical head device for recording / reproducing information on an optical recording medium, comprising at least the above-mentioned two-wavelength light source device and an objective lens for condensing the light emitted from the two-wavelength light source device on the optical recording medium. The optical head device is characterized in that the optical axis of the light emitted from the two-wavelength light source device is coincident with the optical axis of the objective lens.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The two-wavelength light source device of FIG. 1 includes a two-wavelength semiconductor laser 1 and a two-wavelength deflecting optical element 2, and the two-wavelength deflecting optical element 2 includes a birefringent medium 4.
In the two-wavelength semiconductor laser 1, a light emitting point 1A that emits light with a wavelength of λ 1 = 650 nm for a DVD system and a light emitting point 1B that emits light with a wavelength of λ 2 = 790 nm for a CD system are arranged at an interval w. . The linearly polarized light beams emitted from the light emitting points 1A and 1B have vibration planes orthogonal to each other and are incident on the points 2A and 2B (separated by a distance w) on the birefringent medium 4, respectively.
[0010]
The two-wavelength deflecting optical element 2 is composed of a parallel flat birefringent medium 4 having a thickness t, and the angle between the normal line standing on the surface of the birefringent medium 4 and the optical axis 6 is θ, and the wavelength By setting the linearly polarized light of λ 1 to be ordinary light and the linearly polarized light of wavelength λ 2 to be extraordinary light, the light of wavelength λ 1 is transmitted through the birefringent medium 4 without being deflected, and the light of wavelength λ 2 is According to the relationship of Equation 1, the angle ψ is deflected and proceeds through the birefringent medium 4.
[0011]
[Expression 1]
Here, n o is the ordinary refractive index of the birefringent medium with respect to the wavelength lambda 1, n e is the extraordinary refractive index of the birefringent medium against wavelength lambda 2. Equation 1 is described in “Applied Optics II” by Yasio Tsuruta (see Baifukan, page 156) (see FIG. 6, the same reference numerals in FIG. 6 as those in FIG. 1 represent the same elements).
[0013]
Light of the wavelength lambda 1 of light and the wavelength lambda 2 passing through the birefringent medium 4, to advance the same optical axis in 2-wavelength optical deflector 2 transmission, the thickness t of the birefringent medium 4 wherein It is necessary to follow 2.
t = w / tanψ (Formula 2)
At this time, it is desirable that the angle θ formed by the normal line standing on the surface of the birefringent medium 4 and the optical axis 6 be 45 °, because the thickness t of the birefringent medium can be minimized.
[0014]
As the birefringent medium 4, the ordinary refractive index n o and the difference is greater birefringent medium of the extraordinary refractive index n e, for example, a liquid crystal, making use of such calcite optical crystal, the thickness t of the birefringent medium It can be small and desirable.
The two-wavelength light source device shown in FIG. 2 includes a two-wavelength semiconductor laser 1 and a two-wavelength deflecting optical element 2. In particular, the two-wavelength deflecting optical element 2 fixes a phase plate 3 to a birefringent medium 4 with an adhesive 5. It is a thing.
[0015]
In the two-wavelength semiconductor laser 1, a light emitting point 1A that emits light with a wavelength of λ 1 = 650 nm for a DVD system and a light emitting point 1B that emits light with a wavelength of λ 2 = 790 nm for a CD system are arranged at an interval w. . The linearly polarized light emitted from the light emitting points 1A and 1B is transmitted through the phase plate 3 to become linearly polarized light whose vibration planes are orthogonal to each other, and is incident on the points 2A and 2B where the distance on the birefringent medium 4 is w. .
[0016]
Selecting the phase plate 3 having a retardation value that has the effect of orthogonally oscillating the planes of vibration of two linearly polarized light emitted from the two-wavelength semiconductor laser 1 means that the birefringent medium 4 has the above function, that is, the wavelength. It is effective and desirable to make the traveling directions of the ordinary light of λ 1 and the extraordinary light of wavelength λ 2 different. Other elements in FIG. 2 that are the same as those in FIG. 1 are the same elements as in FIG.
[0017]
When the two wavelengths of light emitted from the two-wavelength semiconductor laser 1 are linearly polarized light having vibration surfaces parallel to each other, the vibration surface of the linearly polarized light having the wavelength λ 1 is rotated by 90 ° as the phase plate 3, and the wavelength λ Those having a retardation value that does not rotate the vibration plane of the linearly polarized light 2 can be used. For example, a phase plate having a retardation value of 1625 nm rotates the vibration plane of linearly polarized light with wavelength λ 1 (650 nm) by 90 ° and hardly rotates the vibration plane of linearly polarized light with wavelength λ 2 (790 nm).
[0018]
Further, it is also possible to use a material having a retardation value that rotates the vibration surface of the linearly polarized light having the wavelength λ 2 by 90 ° without rotating the vibration surface of the linearly polarized light having the wavelength λ 1 . For example, a phase plate having a retardation value of 1950 nm does not rotate the plane of vibration of linearly polarized light having the wavelength λ 1 (650 nm), but rotates the plane of vibration of linearly polarized light having the wavelength λ 2 (790 nm) by about 90 °.
[0019]
As a material for the phase plate 3, a birefringent optical crystal such as quartz or lithium niobate, an organic thin film obtained by uniaxial stretching of polycarbonate or the like, or a transparent substrate subjected to orientation treatment A polymer liquid crystal thin film coated with a polymer liquid crystal monomer and cured can be used.
[0020]
It is desirable to select an adhesive 5 that has a small difference in refractive index with the birefringent medium 4 and a small difference in refractive index with the phase plate 3 because reflection loss at each interface of these materials can be reduced.
3 includes a two-wavelength semiconductor laser 1 and a two-wavelength deflecting optical element 9 having a beam splitter function. In particular, the two-wavelength deflecting optical element 9 having a beam splitter function is a birefringent medium 4. The phase plate 3 is fixed with an adhesive 5 and the surface of the birefringent medium 4 opposite to the phase plate 3 has a beam splitter function.
[0021]
As a method of providing a beam splitter function, a grating having a periodic uneven shape with a periodic section is formed directly on a transparent substrate or a grating having a periodic uneven shape is formed on a thin film formed on the surface of a transparent substrate. There is a way. Or a diffractive optical element 7 which is made created by forming a hologram, a method of fixing with an adhesive 8 to the birefringent medium 4. Further, the beam splitter function can also be provided by forming a grating or a hologram having a concave-convex shape with a periodic section on the birefringent medium 4 directly or on a thin film formed on the surface of the birefringent medium 4. (Not shown). Other elements in FIG. 3 that are the same as those in FIG. 1 are the same elements as in FIG.
[0022]
In FIG. 4, an optical head device in which the two-wavelength deflecting optical element 2 is disposed between the two-wavelength semiconductor laser 1 and the collimating lens 11 is shown.
The light of wavelength λ 1 emitted from the light emitting point 1A passes straight through the two-wavelength deflecting optical element 2 as shown in FIG. 4A, and the light of wavelength λ 2 emitted from the light emitting point 1B is shown in FIG. As shown in b), the light is deflected by the two-wavelength deflecting optical element 2 on the same optical axis as the light of wavelength λ 1 and guided to the collimating lens 11 and the objective lens 12.
[0023]
As a result, a good optical situation in which the aberration of the objective lens is small is maintained for light of any wavelength, and information recording / reproduction on the optical recording medium 13 is performed stably with high accuracy.
Further, the two-wavelength deflecting optical element 2 may be disposed between the collimating lens 11 and the objective lens 12. In this case, the incident light to the two-wavelength deflecting optical element 2 becomes substantially parallel light, and it is possible to reduce the deterioration of the deflection characteristics, that is, the deviation of the deflection direction from a predetermined direction depending on the incident angle.
[0024]
【Example】
First, the two-wavelength light source device of this embodiment will be described with reference to FIG.
As the two-wavelength semiconductor laser 1, a monolithic two-wavelength semiconductor laser that emits light having a wavelength of λ 1 = 650 nm for a DVD system from the light emitting point 1A and light having a wavelength of λ 2 = 790 nm for a CD system is emitted from the light emitting point 1B. Was used. The distance w between the light emitting points 1A and 1B was 200 μm, and the light of wavelength λ 1 and wavelength λ 2 emitted from the two-wavelength semiconductor laser 1 was linearly polarized light having a vibration surface in a direction perpendicular to the paper surface.
[0025]
A calcite crystal was used as the birefringent medium 4 constituting the two-wavelength deflecting optical element 2, and the angle θ between the normal line standing on the crystal surface and the optical axis 6 was 45 °. Ordinary refractive index n o of calcite for the wavelength lambda 2 is 1.649, extraordinary refractive index n e is 1.482 to determine the thickness of the crystal in accordance with equation 2 to 1.89 mm.
[0026]
Retardation value using the phase plate of 1950nm as the phase plate 3, the phase plate has the effect without rotating the plane of vibration of linearly polarized light of wavelength lambda 1, is approximately 90 ° rotation of the plane of vibration of linearly polarized light having a wavelength lambda 2 .
The light of the wavelength λ 1 and the wavelength λ 2 emitted from the two-wavelength light source device configured as shown in FIG. 2 using the above materials can travel on the same axis.
[0027]
Next, this two-wavelength light source device was mounted on the optical head device shown in FIG.
As a result, both the light of wavelength λ 1 and wavelength λ 2 are condensed on the information recording surface of the optical recording medium 13 with a beam diameter corresponding to the diffraction limit, and information is recorded on two types of optical recording media having different working wavelengths. -Playback was performed with high accuracy and stability.
[0028]
【The invention's effect】
As described above, according to the two-wavelength light source device of the present invention, the optical axes of two wavelengths of light having different light emission points and vibration surfaces can be made coincident using the two-wavelength deflecting optical element. Therefore, by incorporating this two-wavelength light source device into the optical head device, incident light does not enter obliquely with respect to the same optical axis such as an objective lens and a collimating lens, and there is no aberration based on this incident light.
[0029]
Therefore, it is possible to configure an optical head device capable of stably recording and reproducing information on optical recording media having different use wavelengths with high accuracy. In addition, a small and lightweight optical head device with a small number of parts can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of the configuration of a two-wavelength light source device of the present invention.
FIG. 2 is a cross-sectional view showing another example of the configuration of the two-wavelength light source device of the present invention.
FIG. 3 is a cross-sectional view showing another example of the configuration of the two-wavelength light source device of the present invention.
FIG. 4 is a conceptual side view showing an example of an optical head device using the two-wavelength light source device of the present invention, and (a) shows a situation in which light emitted from a light emitting point goes straight through a wavelength deflecting optical element. The conceptual side view, (b) The conceptual side view which shows the condition where the emitted light from a light emission point deflect | deviates with the deflection optical element for wavelengths.
FIG. 5 is a conceptual side view showing an example of an optical head device using a conventional two-wavelength semiconductor laser; (a) a conceptual side view showing a situation where light emitted from a light emitting point goes straight on an optical axis; FIG. 4B is a conceptual side view showing a situation where light emitted from a light emitting point is incident obliquely with respect to the optical axis.
FIG. 6 is a conceptual diagram showing how ordinary light and extraordinary light travel in a birefringent medium.
[Explanation of symbols]
1: Semiconductor laser 1A for two wavelengths, 1B: Light emitting point 2: Deflection optical element for two wavelengths 3: Phase plate 4: Birefringent medium 5, 8: Adhesive 6: Optical axis 7 of birefringent medium 4: Diffraction optical element 9: Two-wavelength deflecting optical element 11 having a beam splitter function 11: Collimating lens 12: Objective lens 13: Optical recording medium
Claims (4)
前記２波長用半導体レーザから出射した互いに平行な振動面をもつ前記波長λ １ と前記波長λ ２ の振動面を互いに直交させる効果があるリタデーション値を有する位相板と、
前記波長λ１および前記波長λ２の直線偏光が透過する２波長用偏向光学素子と、をこの順に備えた２波長光源装置であって、
前記２波長用偏向光学素子は、複屈折媒体を備え、常光となる前記波長λ1の直線偏光を偏向することなく透過させ、異常光となる前記波長λ２の直線偏光を前記波長λ１の透過光の光軸と一致するように偏向することを特徴とする２波長光源装置。2 the wavelength semiconductor laser which emits different light emitting point position respectively linearly polarized light having mutually parallel plane of vibration of the wavelength lambda 1 and wavelength λ 2 (λ 1 ≠ λ 2 ),
A phase plate having a retardation value having an effect of orthogonally crossing the vibration surfaces of the wavelength λ 1 and the wavelength λ 2 having vibration surfaces parallel to each other emitted from the two-wavelength semiconductor laser ;
2 and the wavelength for the optical deflector, wherein the wavelength lambda 1 and the wavelength lambda 2 of the linearly polarized light is transmitted, a a double-wavelength light source device provided in this order,
The two-wavelength deflecting optical element includes a birefringent medium, transmits the linearly polarized light with the wavelength λ 1 that becomes ordinary light without being deflected, and transmits the linearly polarized light with the wavelength λ 2 that becomes abnormal light with the wavelength λ 1 . A two-wavelength light source device that deflects light to coincide with the optical axis of transmitted light.
前記２波長光源装置からの出射光の光軸が前記対物レンズの光軸と一致していることを特徴とする光ヘッド装置。Recording / reproducing information on an optical recording medium, comprising at least the two-wavelength light source device according to claim 1, 2 or 3 and an objective lens for condensing light emitted from the two-wavelength light source device onto the optical recording medium. An optical head device that performs
An optical head device, wherein an optical axis of light emitted from the two-wavelength light source device coincides with an optical axis of the objective lens.
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