JP2004046053A - Objective and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective for high-density optical recording which comprises two lenses with low distortion and high precision. <P>SOLUTION: Disclosed is the objective for recording and reproducing information to and from an optical information recording medium 100 which has a ≥0.82 numerical aperture and comprises two lenses 2 and 3. The two lenses 2 and 3 are each obtained by throwing a resin preform, molded out of a resin material by injection, between top and bottom molds and performing heating and pressurization molding and the two lenses 2 and 3 are connected to a lens barrel 10 and united. <P>COPYRIGHT: (C)2004,JPO

Description

【００４７】
得られた第１レンズ２及び第２レンズ３の概略形状を図４（Ａ）、図４（Ｂ）に示す。各レンズの概略寸法は以下の通りである。第１レンズ２は、第１面の曲率半径Ｒ１＝２ｍｍ、第２面の曲率半径Ｒ２＝７ｍｍ、中心厚ｔ＝１．４ｍｍ、外径＝４．５ｍｍのメニスカス形状とした。また、第２レンズ３は、第１面の曲率半径Ｒ１＝１ｍｍ、第２面は平面（曲率半径Ｒ２＝∞）、中心厚ｔ＝１．１ｍｍ、外径＝４．５ｍｍの平凸形状とした。
【００４８】
得られた第１及び第２レンズ２，３にはバリがなく、光学性能に優れたものであった。
【００４９】
以上のように、本実施の形態では、射出成形によりプリフォームされた樹脂材料を成形用型に投入し、再加熱して所望の形状に成形した２枚の樹脂レンズを組み合わせて対物レンズを構成している。これにより、高開口数で歪みの少ない対物レンズを得ることができる。
【００５０】
（実施の形態２）
本実施の形態は、対物レンズを構成する第１レンズ２及び第２レンズ３の材料として非晶質ポリオレフィン樹脂を用いる以外は実施の形態１と同様である。従って、実施の形態１の説明はレンズ材料に関する部分を除いてそのまま本実施の形態にも適用される。
【００５１】
実施の形態１で説明した実施例と同様にして非晶質ポリオレフィン樹脂（ガラス転移点Ｔｇ＝１２３℃）を用いた対物レンズを作成した。但し、使用する樹脂材料が異なるために図３に示した成形装置８０の各ステージの設定温度と加圧力を表２のように変更した。
【００５２】
【表２】

【００５３】
得られた第１及び第２レンズ２，３には、実施の形態１の場合と同様にバリがなく、光学性能に優れたものであった。
【００５４】
更に、本実施例において使用した非晶質ポリオレフィン樹脂は、４０５ｎｍのレーザを照射した場合、その他の樹脂材料に比べて、光吸収率が小さいため、透過率が良い。また、光吸収による樹脂劣化がほとんどないため、４０５ｎｍのレーザ照射に対する長期間の信頼性についても問題が無い。表３に各樹脂材料で成形したレンズの評価結果を示す。
【００５５】
【表３】

【００５６】
表３に示すように、透過率の低い樹脂材料ほど、それを用いたレンズの光学特性は低下し、また、光吸収率が大きいために透過率が経時的に劣化しやすく、レンズの長期信頼性においても劣っていた。非晶質ポリオレフィン樹脂を用いた本実施の形態の対物レンズは、光学特性、長期信頼性共に良好であった。
【００５７】
（実施の形態３）
図５は本発明の実施の形態３に係る対物レンズの簡素化された光路図である。
【００５８】
図５に示すように、平行光束１は、第１レンズ２２に光源側の面である第１面２６から入射し、第２レンズ側の面である第２面２７から出射した後、第２レンズ２３に第１レンズ側の面である第１面２８から入射し、例えば情報記録面側の面である第２面２９から出射する。その後、例えば光ディスク１００の透明基板１０２を透過して、光ディスク１００の情報記録面１０４上に集光される。
【００５９】
第１レンズ２２及び第２レンズ２３は、いずれもレンズのレンズ有効面（入射光線に対して所望する光学的作用が発揮されるレンズの領域をいう）の外側に枠部２４，２５を有する。第１レンズ２２の枠部２４の第２レンズ側のフラット面と、第２レンズ２３の枠部２５の第１レンズ側のフラット面とを直接接合させることにより一体化されている。一体化は、例えば、両フラット面の間に接着剤を付与することで行なうことができる。
【００６０】
第１レンズ２２の枠部２４の上記フラット面には、光軸と略直交する方向の溝２１が形成されている。
【００６１】
このように構成された２枚組対物レンズの開口数は０．８２以上である。
【００６２】
このような第１，第２レンズ２２，２３は、図６に示す射出成形装置で樹脂材料を成形して得られる。あらかじめ乾燥してある樹脂材料６１がホッパー６０に供給される。シリンダー６２内のスクリュー６３により材料６１が移動されながら可塑化・計量される。材料６１はさらにノズル６４を通り、金型６９内のスプルー６５、ランナー６６、及びゲート６７を順に通り、所望するレンズ形状を有するキャビティ６８に射出される。キャビティ６８は上記の第１レンズ２２又は第２レンズ２３の形状に加工された金型により形成されている。材料がキャビティ６８に充填され、所定の冷却時間の経過後、型開きを行い成形品を取り出す。ゲートカットを行った後、第１レンズ２２及び第２レンズ２３が得られる。
【００６３】
一実施例の成形条件を示す。レンズ材料として非晶質ポリオレフィン樹脂（ガラス転移点Ｔｇ＝１２３℃）を用い、これをシリンダー６２及びスクリュー６３にて２６０℃に加熱し、溶融させて、１４０℃に加熱した金型内に射出した。保持力は８８．３ＭＰａとし、冷却時間は５０ｓｅｃとした。
【００６４】
本実施の形態の対物レンズによれば、２枚のレンズ２２，２３がレンズ外周の枠部２４，２５で直接接着されて一体化されているので、鏡筒が不要となるため、装置の簡素化、低コスト化を達成することができる。
【００６５】
また、実施の形態２で説明したように、レンズ材料として非晶質ポリオレフィン樹脂を用いることにより、光学特性と長期信頼性に優れた対物レンズを得ることができる。
【００６６】
また、溝２１を設けたことにより、第１レンズ２２と第２レンズ２３とを接着後、実使用状態において、第１レンズ２２と第２レンズ２３とで囲まれた空間内の気圧が空気の膨張によって上昇するのを防止することが可能となる。その結果、温度変化による気圧上昇でレンズが変形して、光学性能が変化するのを抑えることができる。なお、２枚のレンズが一体化された状態において、その内部空間と外界とを連通する貫通孔が確保できれば、内部空間の圧力変化を防止できる。従って、上記の例では、第１レンズ２２の枠部２４に溝２１を設けたが、第２レンズ２３の枠部２５に溝を設けても良い。あるいは溝を両者に設けても良い。また、両レンズ２２，２３の接合面に溝を形成するのではなく、少なくとも一方のレンズの枠部に貫通孔を形成しても良い。
【００６７】
（実施の形態４）
本実施の形態では、実施の形態３で示したような枠部を備えた２枚のレンズを、ガラス転移点が４５０℃以下の低融点ガラスを用いて成形し、実施の形態３と同様に、それぞれの枠部を接合して対物レンズを構成する。２枚組対物レンズの開口数は０．８２以上である。
【００６８】
具体的な製造方法を示す。低融点ガラス材料（ガラス転移点Ｔｇ＝３９８℃、屈伏点Ａｔ＝４０８℃）を研磨加工して略球形に前加工（プリフォーム）して光学素材１７ａ，１７ｂを得た。これを実施の形態１で説明した図２（Ａ）、図２（Ｂ）の金型と同様の構成の金型（但し、金型のレンズ成形部の形状は図（Ａ）、図２（Ｂ）の金型と異なる）にそれぞれ投入した。ここで、下型１３ａ，１３ｂ及び上型１４ａ，１４ｂは、ステンレス材料（たとえばＳＴＡＶＡＸ（ウッデホルム社の商標）にＮｉ−Ｐめっき膜を成膜した上で、バイト加工により所定のレンズ面形状に加工してある。
【００６９】
プリフォームしたガラス材料をセットした成形用型を実施の形態１で用いたのと同じ図３の成形装置８０を用いて、同様に加熱加圧後、冷却してレンズを得た。各ステージ８０ａ〜８０ｄの設定温度と加圧力を表４に示す。
【００７０】
【表４】

【００７１】
かくして、２枚のレンズを得た。得られたレンズにはバリがなく、光学性能に優れたものであった。
【００７２】
以上のように、本実施の形態では、プリフォームされた低融点ガラス材料を成形用型に投入し、加熱して所望の形状に成形した２枚のレンズを組み合わせて対物レンズを構成している。これにより、高開口数で歪みの少ない対物レンズを得ることができる。
【００７３】
また、２枚のレンズをレンズ外周の枠部を直接接着することにより一体化しているので、鏡筒が不要となるため、装置の簡素化、低コスト化を達成することができる。
【００７４】
なお、上記の例では、２枚のレンズを、その枠部を用いて相互に接着して一体化した例を示したが、実施の形態１と同様に、枠部（又はレンズのレンズ有効面の外側のコバ）を鏡筒に接着することにより、一体化しても良い。
【００７５】
また、実施の形態１〜３で説明したように、一体化したときの内部空間と外界とを連通する貫通孔を設けて、温度変化による内部空間の圧力変動を防止しても良い。
【００７６】
（実施の形態５）
図７は本発明の実施の形態５に係る対物レンズの側面断面図である。
【００７７】
本実施の形態５の対物レンズは、実施の形態３で説明した対物レンズ（図５参照）と同様に、樹脂材料を射出成形して得られた２枚のレンズ３２，３３が、それぞれの枠部３４，３５で接着剤を介して一体化されて構成される。２枚組対物レンズの開口数は０．８２以上である。
【００７８】
本実施の形態５の対物レンズは、更に、各レンズ３２，３３のレンズ有効面以外の面（図７の例では、枠部３４，３５の外周面）に、突起３７を少なくとも１つ以上形成している。
【００７９】
本実施の形態の対物レンズによれば、各レンズの外周面に突起３７を設けたことにより、レンズの表面積が拡大する。その結果、放熱性が顕著に向上する。実使用時における周辺温度の上昇に伴って、レンズ自身も温度上昇するが、突起３７を設けることにより、温度上昇が抑制される。その結果、温度上昇による光学特性の変化を抑えることができ、使用前の良好な光学特性を使用中も安定して維持することが可能となる。
【００８０】
突起３７の個数、設置位置、形状、大きさ等は、必要な放熱特性を考慮して決定できる。また、放熱特性は多少低下するものの、対物レンズを構成する２枚のレンズの一方のみに突起３７を設けても良い。
【００８１】
なお、上記の例では、２枚のレンズが実施の形態３と同様に接着により直接接合された対物レンズに突起３７を付与する例を示したが、実施の形態１に示した鏡筒により保持された対物レンズ（図１参照）において、各レンズの外部に露出した面（例えば、コバの表面）に突起を設けても良く、これにより上記と同様の効果を得ることができる。
【００８２】
また、実施の形態１〜３で説明したように、内部空間と外界とを連通する貫通孔を設けて、温度変化による内部空間の圧力変動を防止しても良い。
【００８３】
また、実施の形態２で説明したように、レンズ材料として非晶質ポリオレフィン樹脂を用いることにより、光学特性と長期信頼性に優れた対物レンズを得ることができる。
【００８４】
（実施の形態６）
図８（Ａ）は本発明の実施の形態６に係る対物レンズを構成する２枚のレンズの接合前の状態を示した側面断面図、図８（Ｂ）は本発明の実施の形態６に係る対物レンズを示した側面断面図である。
【００８５】
本実施の形態６の対物レンズは、実施の形態３で説明した対物レンズ（図５参照）と同様に、樹脂材料を射出成形して得られた２枚のレンズ４２，４３（図８（Ａ）参照）が、それぞれの枠部４４，４５で接着剤を介して一体化されて構成される（図８（Ｂ）参照）。２枚組対物レンズの開口数は０．８２以上である。
【００８６】
本実施の形態６の対物レンズでは、レンズ４３の枠部４５の、レンズ４２の枠部４４と接合するフラット面（突き合わせ面）に、光軸を中心とする略円状の溝４８を１つ以上形成している。
【００８７】
本実施の形態の対物レンズによれば、枠部４４と枠部４５とが接着接合される面に環状の溝４８を設けたことにより、対物レンズを構成する２枚のレンズ４２，４３を枠部４４，４５のフラット面同士で接着固定する際に、溝４８が接着剤溜まりとして機能して、枠部４４，４５より内側のレンズ有効面に接着剤が流入するのを防止することが出来る。その結果、対物レンズの組立作業性と歩留まりが向上する。さらに、これによりレンズのコストを低減できる。
【００８８】
上記の例では、溝４８はレンズ４３の枠部４５に設けたが、これに加えて又はこれに代えて、レンズ４２の枠部４４に設けることもできる。また、溝の数、太さ、深さなどは、使用する接着剤の量などを考慮して、適宜決定することができる。
【００８９】
なお、上記の例では、２枚のレンズが実施の形態３と同様に直接接合される対物レンズにおいて溝５８を設ける例を示したが、実施の形態１に示した鏡筒により保持された対物レンズ（図１参照）において、各レンズの鏡筒と接着されるコバの面に同様の溝を設けても良く、これにより上記と同様の効果を得ることができる。
【００９０】
また、実施の形態１〜３で説明したように、内部空間と外界とを連通する貫通孔を設けて、温度変化による内部空間の圧力変動を防止しても良い。
【００９１】
また、実施の形態５で説明したように、レンズ有効面以外の部分に、冷却のための１個以上の突起を形成してもよい。
【００９２】
また、実施の形態２で説明したように、レンズ材料として非晶質ポリオレフィン樹脂を用いることにより、光学特性と長期信頼性に優れた対物レンズを得ることができる。
【００９３】
（実施の形態７）
図９（Ａ）は本発明の実施の形態７に係る対物レンズを構成する２枚のレンズの接合前の状態を示した側面断面図、図９（Ｂ）は本発明の実施の形態７に係る対物レンズを示した側面断面図である。
【００９４】
本実施の形態７の対物レンズは、実施の形態３で説明した対物レンズ（図５参照）と同様に、樹脂材料を射出成形して得られた２枚のレンズ５２，５３（図９（Ａ）参照）が、それぞれの枠部５４，５５で接着剤を介して一体化されて構成される（図９（Ｂ）参照）。２枚組対物レンズの開口数は０．８２以上である。
【００９５】
本実施の形態７の対物レンズでは、レンズ５２の枠部５４のフラット面に２つの凹部５７を光軸に対して対称位置に設け、レンズ５３の枠部５５のフラット面に、上記凹部５７と嵌合する位置に２つの凸部５８を設けている。
【００９６】
本実施の形態の対物レンズによれば、枠部５４と枠部５５とが接着接合される面に相互に嵌合する凹部５７と凸部５８とを設けたので、レンズ５２，５３の相対的な位置決め（光軸に直交する方向及び光軸回りの位置決め）を容易に行なうことができ、対物レンズの製造工程が大幅に短縮でき、歩留まりが向上する。さらに、これによりレンズのコストを低減できる。
【００９７】
なお、接着剤は、接合前に、凹部５７及び／又は凸部５８に付与しておくことが好ましい。
【００９８】
上記の例では、枠部５４に凹部５７を、枠部５５に凸部５８を設けたが、両レンズ５２，５３の位置決めを行なうことができればこの形態に限定されず、相互に嵌合する任意の形状を枠部５４，５５の任意の場所に設ければよい。
【００９９】
また、上記の例では、２枚のレンズが実施の形態３と同様に直接接合される対物レンズにおいて２枚のレンズの接合面に嵌合形状を設ける例を示したが、実施の形態１に示した鏡筒により保持された対物レンズ（図１参照）において、各レンズと鏡筒との接合面に同様の嵌合形状を設けても良く、これにより上記と同様の効果を得ることができる。
【０１００】
また、実施の形態１〜で説明したように、内部空間と外界とを連通する貫通孔を設けて、温度変化による内部空間の圧力変動を防止しても良い。
【０１０１】
また、実施の形態５で説明したように、レンズ有効面以外の部分に、冷却のための１個以上の突起を形成してもよい。
【０１０２】
また、実施の形態６で説明したように、レンズ有効面以外の部分に、接着剤がレンズ有効面側に流入するのを防止するための溝を形成してもよい。
【０１０３】
また、実施の形態２で説明したように、レンズ材料として非晶質ポリオレフィン樹脂を用いることにより、光学特性と長期信頼性に優れた対物レンズを得ることができる。
【０１０４】
（実施の形態８）
図１０は本発明の実施の形態８に係る対物レンズの側面断面図である。
【０１０５】
本実施の形態８の対物レンズは、実施の形態７で説明した対物レンズにおいて、これを構成する２枚のレンズ５２，５３によって形成された空間内にゲル状物質５９を充填している。ゲル状物質５９の充填は、レンズ５２，５３を突き合わせ、凹部５７と凸部５８とを嵌合させる際に、両レンズのフラット面の隙間からゲル状物質５９を注入し、その後隙間を閉じ、固化させることで行なうことができる。ゲル状物質５９としては、例えば屈折率が１のシリコーンゲル状液体を例示できるが、屈折率が１の液体又はゲル状物質であればこれに限定されず用いることができる。
【０１０６】
本実施の形態の対物レンズによれば、レンズ５２，５３によって形成された空間内にゲル状物質５９が充填されているので、対物レンズの熱容量が増大する。従って、実使用状態において対物レンズの周囲温度が上昇しても、対物レンズの温度上昇が抑制され、その結果、温度変化に対して安定した光学性能が保証される。
【０１０７】
上記の例では、実施の形態７の対物レンズにゲル状物質を充填する例を説明したが、上述した他の実施の形態の対物レンズの内部空間にゲル状物質を充填しても良く、これにより上記と同様の効果を得ることができる。但し、この場合、ゲル状物質の漏洩を防止するために、実施の形態１〜３で説明したような、対物レンズ内の空間と外界とを連通する貫通孔を形成するのは好ましくない。
【０１０８】
また、実施の形態２で説明したように、レンズ材料として非晶質ポリオレフィン樹脂を用いることにより、光学特性と長期信頼性に優れた対物レンズを得ることができる。
【０１０９】
（実施の形態９）
図１１は本発明の実施の形態９に係る光ヘッド装置の一構成例を示した概略図である。
【０１１０】
図１１において、半導体レーザモジュール７１から出射した発散光束７２は、コリメートレンズ７３により略平行光束７４に変換される。平行光束７４は、折り曲げ（立ち上げ）ミラー７５により光路の向きを変えられ、対物レンズ７６の第１レンズ７７と第２レンズ７８とを順に透過して、光ディスク１００の透明基板１０２を透過して、光ディスク１００の情報記録面１０４上に集光される。情報記録面１０４に形成された反射率の違う信号により集光スポットの反射光強度は変調を受ける。情報記録面１０４で反射されたレーザ光は、もとの光路を辿って半導体レーザモジュール７１に戻る。ここで、半導体レーザモジュール７１は、異なる２つの波長の光を出射可能な光源、受光素子、及び往路の光と復路の光とを分離する光束分離手段を有する。また、対物レンズ７６は実施の形態１で説明した対物レンズであり、第１レンズ７７と第２レンズ７８は鏡筒７９により固定されている。
【０１１１】
上記の光ヘッド装置の構成によれば、温度変化による収差の劣化量が小さく抑えられる。
【０１１２】
上記の説明では、対物レンズ７６として、実施の形態１で説明した対物レンズを用いたが、実施の形態２〜８のいずれの対物レンズを用いてもよい。
【０１１３】
また、上記の説明では、光ディスクに直接記録及び／又は再生するための光ヘッド装置を例に説明したが、本発明の光ヘッド装置は、例えばＤＶＤなどの原盤を記録するためのレーザービームレコーダーの光ヘッド装置として用いても良い。
【０１１４】
【発明の効果】
以上説明したように、本発明によれば、低歪みで高精度の２枚組対物レンズ及びこれを備えた光ヘッド装置を提供できる。
【０１１５】
また、本発明によれば、光の吸収が少なく、光学特性が長期にわたって良好な２枚組対物レンズ及びこれを備えた光ヘッド装置を提供できる。
【０１１６】
また、本発明によれば、構造が簡単で低コストな２枚組対物レンズ及びこれを備えた光ヘッド装置を提供できる。
【０１１７】
また、本発明によれば、組立作業性が良好で、比較的安価に製造できる２枚組対物レンズ及びこれを備えた光ヘッド装置を提供できる。
【０１１８】
また、本発明によれば、温度変化による光学特性の変化が少ない２枚組対物レンズ及びこれを備えた光ヘッド装置を提供できる。
【図面の簡単な説明】
【図１】本発明の実施の形態１の対物レンズの側面断面図。
【図２】（Ａ）　本発明の実施の形態１の対物レンズを構成する第１レンズの成形に用いる成形用型の断面図。
（Ｂ）　本発明の実施の形態１の対物レンズを構成する第２レンズの成形に用いる成形用型の断面図。
【図３】本発明の実施の形態１の対物レンズを構成するレンズを成形するための成形装置の概略構成を示した断面図。
【図４】（Ａ）　本発明の実施の形態１の対物レンズを構成する第１レンズの側面断面図。
（Ｂ）　本発明の実施の形態１の対物レンズを構成する第２レンズの側面断面図。
【図５】本発明の実施の形態３の対物レンズの側面断面図。
【図６】本発明の実施の形態３の対物レンズを成形する成形装置の概略断面図。
【図７】本発明の実施の形態５の対物レンズの側面断面図。
【図８】（Ａ）　本発明の実施の形態６の対物レンズを構成する２枚のレンズの接合前の状態を示した側面断面図。
（Ｂ）　本発明の実施の形態６の対物レンズの側面断面図。
【図９】（Ａ）　本発明の実施の形態７の対物レンズを構成する２枚のレンズの接合前の状態を示した側面断面図。
（Ｂ）　本発明の実施の形態７の対物レンズの側面断面図。
【図１０】本発明の実施の形態８の対物レンズの側面断面図。
【図１１】本発明の実施の形態９の光ヘッド装置の構成図。
【符号の説明】
１　平行光束
２　第１レンズ
３　第２レンズ
６　第１レンズ第１面
７　第１レンズ第２面
８　第２レンズ第１面
９　第２レンズ第２面
１０　レンズ鏡筒
１１　貫通孔
１３ａ，１３ｂ　下型
１４ａ，１４ｂ　上型
１５ａ，１５ｂ　胴型
１７ａ、１７ｂ　光学素材
２１　溝
２２　第１レンズ
２３　第２レンズ
２６　第１レンズ第１面
２４，２５　枠部
２７　第１レンズ第２面
２８　第２レンズ第１面
２９　第２レンズ第２面
３２，３３　レンズ
３４，３５　枠部
３７　突起
４２，４３　レンズ
４４，４５　枠部
４８　溝
５２，５３　レンズ
５４，５５　枠部
５７　凹部
５８　凸部
５９　ゲル状物質
６０　ホッパー
６１　樹脂材料
６２　シリンダー
６３　スクリュー
６４　ノズル
６５　スプルー
６６　ランナー
６７　ゲート
６８　キャビティ
６９　金型
７１　半導体レーザモジュール
７２　発散光束
７３　コリメートレンズ
７４　平行光束
７５　立ち上げミラー
７６　対物レンズ
７７　第１レンズ
７８　第２レンズ
７９　鏡筒
８０　成形装置
８０ａ　予熱ステージ
８０ｂ　成形ステージ
８０ｃ　第１冷却ステージ
８０ｄ　第２冷却ステージ
８１　投入ステージ
８２　取り出しステージ
８５ａ，８５ｂ，８５ｃ，８５ｄ　下ステージ
８７ａ，８７ｂ，８７ｃ，８７ｄ　上ヘッド
１００　光ディスク
１０２　透明基板
１０４　情報記録面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an objective lens and an optical head device used for an optical head such as a DVD and an optical recording device for a computer.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, optical information recording media such as optical disks have been widely used for storing digital data such as storage of music information and video information or storage of computer data, as is known as CDs (compact disks) or DVDs. .
[0003]
In recent years, with the advent of the information society, increasing the capacity of these recording media has been strongly demanded.
[0004]
In order to improve the recording capacity (recording density) per unit area in the optical information recording medium, the diameter of a spot formed by the optical head on the information recording surface of the optical information recording medium may be reduced. The minimum diameter of this spot is generally proportional to λ / NA (where λ is the used wavelength and NA is the numerical aperture of the optical system) due to light diffraction. Therefore, it is known that the recording density and the capacity can be increased by shortening the wavelength of the light source used or increasing the numerical aperture of the optical system of the optical head. Actually, when achieving a large capacity from a CD to a DVD, the numerical aperture of the lens is increased, and the wavelength used is also shortened from 800 nm to 660 nm.
[0005]
In the short wavelength region, the dispersion of the lens material is very large, and the refractive index of the glass material changes greatly due to a slight difference in wavelength. Therefore, when it is attempted to further shorten the wavelength used by using the conventional single lens, chromatic aberration increases. At this time, when the spectrum width of the semiconductor laser is relatively large, a non-negligible aberration occurs, and the semiconductor laser cannot be used. Further, since the aberration performance changes depending on the wavelength of the semiconductor laser, it is necessary to design an objective lens for each wavelength, which is not suitable for mass production. Further, if a single lens having a relatively high NA of, for example, about 0.85 is to be realized, aberration caused by off-axis light or aberration caused by a deviation between the first surface and the second surface of the lens due to manufacturing will be reduced. Extremely large and unrealistic.
[0006]
[Problems to be solved by the invention]
Therefore, a two-lens lens group is being studied, but when resin is used as the two lenses for cost reduction, it is necessary to position the two lenses with high precision.
[0007]
Further, it is necessary to consider that when the used wavelength is changed to the shorter wavelength side, the light absorption characteristics of the lens material change accordingly. When the light absorptance is large, not only the efficiency of use of light from the light source is reduced and characteristics such as S / N ratio are deteriorated, but also the lens is deteriorated due to light absorption, and the optical characteristics change with time. , The long-term reliability decreases.
[0008]
A first object of the present invention is to provide a two-piece objective lens with low distortion and high accuracy. It is a second object of the present invention to provide a two-piece objective lens that absorbs less light and has good optical characteristics over a long period of time. A third object of the present invention is to provide a two-piece objective lens having a simple structure and low cost. A fourth object of the present invention is to provide a two-piece objective lens which has good assembling workability and can be manufactured relatively inexpensively. A fifth object of the present invention is to provide a two-piece objective lens in which changes in optical characteristics due to temperature changes are small. It is a sixth object of the present invention to provide an optical head device provided with these objective lenses.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following configuration.
[0010]
The first objective lens of the present invention is an objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The objective lens has a numerical aperture of 0.82 or more, and the objective lens is composed of two lenses. Each of the two lenses is a resin preform obtained by injection molding a resin material. It is obtained by being inserted between upper and lower molds and subjected to heat and pressure molding, and is characterized in that the two lenses are respectively joined and integrated into a lens barrel.
[0011]
Since the two lenses constituting the first objective lens are lenses obtained by putting resin preforms obtained by injection molding into upper and lower molds and performing heating and pressure molding, the two lenses have low distortion. And a highly accurate objective lens can be obtained.
[0012]
The second objective lens of the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The objective lens has a numerical aperture of 0.82 or more, the objective lens is composed of two lenses, and both the lenses are made of an amorphous polyolefin resin.
[0013]
Since both of the two lenses constituting the second objective lens are made of an amorphous polyolefin resin, the light absorptance in a short wavelength region is particularly small, and the efficiency of using light from a light source is improved. Further, it is possible to provide an objective lens which is less deteriorated by light absorption and has excellent long-term reliability.
[0014]
The third objective lens of the present invention is an objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The numerical aperture of the objective lens is 0.82 or more, the objective lens is composed of two lenses, each of the two lenses is made of a resin material, and each of the two lenses is It is obtained by injection molding a resin material, wherein each of the two lenses has a frame portion outside the lens effective surface, and the two lenses adhere each frame portion to each other. It is characterized by being integrated by doing.
[0015]
Since the two lenses constituting the third objective lens are made of resin, the molding temperature can be lowered in mass production of the lenses, so that mass productivity is improved and a low-cost objective lens can be obtained.
[0016]
Further, since the two lenses are integrated by bonding their respective frame parts to each other, a lens barrel is not required, and simplification of the apparatus and cost reduction can be achieved.
[0017]
The fourth objective lens of the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The objective lens has a numerical aperture of 0.82 or more, and the objective lens is composed of two lenses. Each of the two lenses is made of a low-melting glass material having a glass transition point of 450 ° C. or less. The preform formed into a predetermined shape is put between upper and lower molds, and is obtained by heating and pressing, and the two lenses are formed through portions other than the respective lens effective surfaces. An objective lens, which is connected and integrated.
[0018]
The two lenses constituting the fourth objective lens are lenses obtained by charging a preformed low-melting glass material into upper and lower molds and molding by heating and pressing. A highly accurate objective lens can be obtained.
[0019]
The fifth objective lens of the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The numerical aperture of the objective lens is 0.82 or more, the objective lens is composed of two lenses, each of the two lenses is made of a resin material, and each of the two lenses is It is obtained by injection molding a resin material, and at least one of the two lenses has at least one projection for cooling on a portion other than the lens effective surface. .
[0020]
Since at least one of the two lenses constituting the fifth objective lens has one or more projections for cooling, fluctuation of aberration due to temperature change is reduced, and good optical performance is maintained. Becomes possible.
[0021]
The sixth objective lens of the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The numerical aperture of the objective lens is 0.82 or more, the objective lens is composed of two lenses, each of the two lenses is made of a resin material, and each of the two lenses is The two lenses are obtained by injection molding of a resin material, and the two lenses are integrated via an adhesive at portions other than the respective lens effective surfaces, and at least one of the two lenses One is characterized in that at least one groove for preventing the adhesive from flowing into the lens effective surface side is provided in a portion other than the lens effective surface.
[0022]
At least one of the two lenses constituting the sixth objective has at least one groove for preventing the adhesive from flowing into the lens effective surface side. The workability of the bonding process is improved, and an inexpensive and highly accurate objective lens can be realized.
[0023]
The seventh objective lens of the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium. The numerical aperture of the objective lens is 0.82 or more, the objective lens is composed of two lenses, each of the two lenses is made of a resin material, and each of the two lenses is A fitting shape for performing relative positioning of the lens is provided on a surface other than the lens effective surface.
[0024]
Since the two lenses constituting the seventh objective lens are provided with a fitting shape for performing relative positioning, the workability of the assembling process of the two lenses is improved, and the cost is low and the precision is high. An objective lens can be realized.
[0025]
It is preferable that the first to seventh objective lenses have a through hole for communicating a space between the two lenses with the outside.
[0026]
With such a preferable configuration, it is possible to prevent a change in lens performance due to a change in the internal pressure between the two lenses caused by a temperature change.
[0027]
An eighth objective lens according to the present invention is an objective lens that forms incident light on an information recording surface of the optical information recording medium to record and / or reproduce information on the optical information recording medium. The numerical aperture of the objective lens is 0.82 or more, the objective lens is composed of two lenses, and both of the two lenses are made of a resin material and are sandwiched between the two lenses. The liquid or gel-like substance is filled in the space.
[0028]
According to the eighth objective lens, the liquid or gel-like substance can suppress the temperature change of the two lenses, and can maintain good lens performance.
[0029]
In the first, third, fifth to eighth objective lenses described above, it is preferable that the resin material is an amorphous polyolefin resin.
[0030]
According to such a preferred configuration, since both of the two lenses are made of an amorphous polyolefin resin, the light absorptance in a short wavelength region is particularly small, and the efficiency of using light from a light source is improved. Further, it is possible to provide an objective lens which is less deteriorated by light absorption and has excellent long-term reliability.
[0031]
Next, the optical head device of the present invention includes a light source, a light-condensing means for condensing a light beam emitted from the light source on an information recording surface of an optical information recording medium, and a light beam modulated by the information recording surface. A light beam separating unit that separates the light beam from the outward light beam, and a light receiving unit that receives the light beam modulated on the information recording surface, wherein the light collecting unit is any one of the first to eighth objective lenses. Features.
[0032]
According to the optical head device, since the optical head device includes any one of the first to eighth objective lenses of the present invention, it is possible to provide an optical head device having the features of each objective lens.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the objective lens and the optical head device of the present invention will be specifically described with reference to the drawings.
[0034]
(Embodiment 1)
FIG. 1 is a simplified optical path diagram of the objective lens according to Embodiment 1 of the present invention.
[0035]
As shown in FIG. 1, the parallel light flux 1 enters the first lens 2 from a first surface 6 which is a light source side surface, and exits from a second surface 7 which is a second lens side surface, and then a second light beam. The light enters the lens 3 from a first surface 8 which is a surface on the first lens side, and is emitted from, for example, a second surface 9 which is a surface on the information recording surface side. Thereafter, for example, the light passes through the transparent substrate 102 of the optical disc 100 and is focused on the information recording surface 104 of the optical disc 100.
[0036]
Each of the first lens 2 and the second lens 3 is bonded to the lens barrel 10 with an edge outside a lens effective surface of the lens (a region of the lens where a desired optical action is exhibited with respect to an incident light beam). Is maintained by doing so.
[0037]
The lens barrel 10 has one through hole 11. The through hole 11 penetrates between the outer peripheral wall and the inner peripheral wall of the lens barrel 10. The opening on the inner peripheral wall side of the through hole 11 is provided in a region between the first lens 2 and the second lens 3. By providing such a through-hole 11, even after the lenses 2 and 3 are bonded to the lens barrel 10 and the temperature of the objective lens increases in an actual use state, the lenses 2 and 3 are surrounded by the lenses 2 and 3 and the lens barrel 10. It is possible to prevent the air pressure in the closed space from rising due to the expansion of the air. As a result, it is possible to prevent the lens from being deformed due to an increase in the atmospheric pressure due to the temperature change and the optical performance from being changed.
[0038]
The numerical aperture of the two-piece objective lens thus configured is 0.82 or more.
[0039]
FIGS. 2A and 2B are cross-sectional views showing one embodiment of a mold for forming the first and second lenses 2 and 3, respectively. In these figures, 13a and 13b are lower dies, 14a and 14b are upper dies, and 15a and 15b are trunk dies.
[0040]
An example of a method for forming the lenses 2 and 3 of the first embodiment using the molding die will be described. Since the basic molding steps of the first and second lenses 2 and 3 are common, both molding steps will be described together.
[0041]
First, the optical materials 17a and 17b were set in a space surrounded by the lower dies 13a and 13b, the upper dies 14a and 14b, and the body dies 15a and 15b. The optical materials 17a and 17b are made of norbornene resin (glass transition point Tg = 167 ° C.), and are pre-processed (preformed) into a substantially spherical shape by cutting a block cut from a plate or the like obtained by injection molding. Using. The lower dies 13a and 13b and the upper dies 14a and 14b are made of a super hard material and are processed into a desired shape. The body dies 15a and 15b are made of stainless steel.
[0042]
FIG. 3 is a cross-sectional view showing a schematic configuration of the molding apparatus 80.
[0043]
The molding die set as shown in FIGS. 2 (A) and 2 (B) was transported by a robot to a loading stage 81 of a molding device 80. Next, the charging door (not shown) was opened, and the charging chamber was charged into the preheating stage 80a. The loading door was kept closed until the next mold was loaded. The molding die put into the preheating stage 80a further passes through the molding stage 80b, the first cooling stage 80c, and the second cooling stage 80d, and then opens an exit door (not shown) to take out the molding stage outside the molding device 80. Transferred to 82. Thereafter, the mold was disassembled by a robot, and the formed lens was taken out. The transfer in the molding apparatus was performed by a transfer arm.
[0044]
Each of the stages 80a to 80d includes a lower stage 85a, 85b, 85c, 85d on which a molding die is placed, and upper heads 87a, 87b, 87c, 87d for pressing the upper dies 14a, 14b downward. And Each lower stage 85a, 85b, 85c, 85d and each of the upper heads 87a, 87b, 87c, 87d have a built-in heater (not shown), and each heater is independently maintained at a predetermined temperature. After being transported to the individual stages 80a to 80d, the molding die is transported to the next stage after a predetermined time has elapsed. In this embodiment, the time during which the molding die stops at each of the stages 80a to 80d is set to 50 seconds.
[0045]
Table 1 shows the set temperatures and pressures of the stages 80a to 80d.
[0046]
[Table 1]

[0047]
FIGS. 4A and 4B show schematic shapes of the obtained first lens 2 and second lens 3. The approximate dimensions of each lens are as follows. The first lens 2 had a meniscus shape having a radius of curvature R1 of the first surface = 2 mm, a radius of curvature R2 of the second surface = 7 mm, a center thickness t = 1.4 mm, and an outer diameter of 4.5 mm. The second lens 3 has a plano-convex shape with a first surface having a radius of curvature R1 = 1 mm, a second surface having a flat surface (a radius of curvature R2 = ∞), a center thickness t = 1.1 mm, and an outer diameter of 4.5 mm. did.
[0048]
The obtained first and second lenses 2 and 3 had no burrs and were excellent in optical performance.
[0049]
As described above, in the present embodiment, an objective lens is formed by putting a resin material preformed by injection molding into a molding die, reheating and combining two resin lenses molded into a desired shape. are doing. Thus, an objective lens having a high numerical aperture and a small distortion can be obtained.
[0050]
(Embodiment 2)
This embodiment is the same as Embodiment 1 except that an amorphous polyolefin resin is used as the material of the first lens 2 and the second lens 3 constituting the objective lens. Therefore, the description of the first embodiment is applied to the present embodiment as it is, except for a portion related to the lens material.
[0051]
An objective lens using an amorphous polyolefin resin (glass transition point Tg = 123 ° C.) was prepared in the same manner as in the example described in the first embodiment. However, since the resin material used was different, the set temperature and pressure of each stage of the molding apparatus 80 shown in FIG. 3 were changed as shown in Table 2.
[0052]
[Table 2]

[0053]
The obtained first and second lenses 2 and 3 were free of burrs and excellent in optical performance as in the case of the first embodiment.
[0054]
Further, the amorphous polyolefin resin used in this example has a low light absorption when irradiated with a 405 nm laser compared to other resin materials, and thus has a good transmittance. Further, since there is almost no resin deterioration due to light absorption, there is no problem in long-term reliability with respect to laser irradiation at 405 nm. Table 3 shows the evaluation results of the lenses molded from each resin material.
[0055]
[Table 3]

[0056]
As shown in Table 3, the lower the transmittance of the resin material, the lower the optical characteristics of the lens using the resin material, and the higher the light absorption rate, the more the transmittance tends to deteriorate over time. He was also poor in sex. The objective lens of the present embodiment using the amorphous polyolefin resin had good optical characteristics and long-term reliability.
[0057]
(Embodiment 3)
FIG. 5 is a simplified optical path diagram of the objective lens according to Embodiment 3 of the present invention.
[0058]
As shown in FIG. 5, the parallel light flux 1 enters the first lens 22 from a first surface 26 which is a light source side surface, and exits from a second surface 27 which is a second lens side surface. The light enters the lens 23 from a first surface 28 which is a surface on the first lens side, and is emitted from a second surface 29 which is a surface on the information recording surface side, for example. Thereafter, for example, the light passes through the transparent substrate 102 of the optical disc 100 and is focused on the information recording surface 104 of the optical disc 100.
[0059]
Both the first lens 22 and the second lens 23 have frame portions 24 and 25 outside the lens effective surface of the lens (referred to as a region of the lens where a desired optical action is exerted on incident light). The flat surface of the frame portion 24 of the first lens 22 on the second lens side and the flat surface of the frame portion 25 of the second lens 23 on the first lens side are integrated by being directly joined. The integration can be performed, for example, by applying an adhesive between both flat surfaces.
[0060]
On the flat surface of the frame portion 24 of the first lens 22, a groove 21 is formed in a direction substantially perpendicular to the optical axis.
[0061]
The numerical aperture of the two-piece objective lens thus configured is 0.82 or more.
[0062]
Such first and second lenses 22 and 23 are obtained by molding a resin material using an injection molding apparatus shown in FIG. The previously dried resin material 61 is supplied to the hopper 60. The material 61 is plasticized and measured while being moved by the screw 63 in the cylinder 62. The material 61 further passes through a nozzle 64, a sprue 65, a runner 66, and a gate 67 in a mold 69, and is injected into a cavity 68 having a desired lens shape. The cavity 68 is formed by a mold processed into the shape of the first lens 22 or the second lens 23. After the material is filled in the cavity 68 and a predetermined cooling time has elapsed, the mold is opened and the molded product is taken out. After performing the gate cut, the first lens 22 and the second lens 23 are obtained.
[0063]
The molding conditions of one embodiment are shown. An amorphous polyolefin resin (glass transition point Tg = 123 ° C.) was used as a lens material, which was heated to 260 ° C. by a cylinder 62 and a screw 63, melted, and injected into a mold heated to 140 ° C. . The holding force was 88.3 MPa, and the cooling time was 50 seconds.
[0064]
According to the objective lens of the present embodiment, since the two lenses 22 and 23 are directly bonded and integrated at the frame portions 24 and 25 on the outer periphery of the lens, a lens barrel is not required, and thus the apparatus is simplified. And cost reduction can be achieved.
[0065]
Further, as described in Embodiment 2, by using an amorphous polyolefin resin as a lens material, an objective lens having excellent optical characteristics and long-term reliability can be obtained.
[0066]
In addition, by providing the groove 21, after the first lens 22 and the second lens 23 are bonded, the pressure in the space surrounded by the first lens 22 and the second lens 23 in an actual use state is reduced by air pressure. It is possible to prevent the rise due to the expansion. As a result, it is possible to prevent the lens from being deformed due to an increase in the atmospheric pressure due to the temperature change and the optical performance from being changed. In addition, in a state where the two lenses are integrated, if a through hole communicating the internal space and the outside world can be secured, a pressure change in the internal space can be prevented. Therefore, in the above example, the groove 21 is provided in the frame portion 24 of the first lens 22, but the groove may be provided in the frame portion 25 of the second lens 23. Alternatively, grooves may be provided on both. Instead of forming a groove on the joint surface between the two lenses 22 and 23, a through-hole may be formed in the frame portion of at least one of the lenses.
[0067]
(Embodiment 4)
In the present embodiment, two lenses having a frame portion as described in the third embodiment are formed using low-melting glass having a glass transition point of 450 ° C. or lower, and the same as in the third embodiment. Then, the respective frame portions are joined to form an objective lens. The numerical aperture of the two-piece objective lens is 0.82 or more.
[0068]
A specific manufacturing method will be described. The low melting point glass material (glass transition point Tg = 398 ° C., yield point At = 408 ° C.) was polished and pre-processed into a substantially spherical shape (preform) to obtain optical materials 17a and 17b. This is a mold having the same configuration as the molds of FIGS. 2A and 2B described in Embodiment 1 (however, the shape of the lens molding portion of the mold is shown in FIGS. 2A and 2B). (Different from the mold of B)). Here, the lower dies 13a and 13b and the upper dies 14a and 14b are formed into a predetermined lens surface shape by cutting a Ni-P plating film on a stainless material (for example, STAVAX (trademark of Wooddeholm Co.)). I have.
[0069]
Using the same molding apparatus 80 of FIG. 3 as used in the first embodiment for the molding die in which the preformed glass material was set, similarly heated and pressed, and then cooled to obtain a lens. Table 4 shows the set temperatures and pressures of the stages 80a to 80d.
[0070]
[Table 4]

[0071]
Thus, two lenses were obtained. The obtained lens had no burrs and was excellent in optical performance.
[0072]
As described above, in the present embodiment, an objective lens is formed by putting a preformed low-melting glass material into a molding die, heating and combining two lenses molded into a desired shape. . Thus, an objective lens having a high numerical aperture and a small distortion can be obtained.
[0073]
Further, since the two lenses are integrated by directly bonding the frame portion on the outer periphery of the lens, a lens barrel is not required, so that the apparatus can be simplified and the cost can be reduced.
[0074]
In the above example, an example in which the two lenses are bonded to each other and integrated using the frame portion has been described. However, similarly to the first embodiment, the frame portion (or the lens effective surface of the lens) is used. May be integrated by bonding the outer edge of the lens to the lens barrel.
[0075]
Further, as described in the first to third embodiments, a through-hole that communicates the internal space when integrated with the outside may be provided to prevent a pressure change in the internal space due to a temperature change.
[0076]
(Embodiment 5)
FIG. 7 is a side sectional view of an objective lens according to Embodiment 5 of the present invention.
[0077]
The objective lens according to the fifth embodiment includes, similarly to the objective lens described in the third embodiment (see FIG. 5), two lenses 32 and 33 obtained by injection molding a resin material, each having a frame. The parts 34 and 35 are configured to be integrated via an adhesive. The numerical aperture of the two-piece objective lens is 0.82 or more.
[0078]
The objective lens according to the fifth embodiment further has at least one projection 37 formed on a surface other than the lens effective surface of each of the lenses 32 and 33 (in the example of FIG. 7, the outer peripheral surfaces of the frame portions 34 and 35). are doing.
[0079]
According to the objective lens of the present embodiment, since the projections 37 are provided on the outer peripheral surface of each lens, the surface area of the lens increases. As a result, heat dissipation is significantly improved. Although the temperature of the lens itself rises as the ambient temperature rises during actual use, the provision of the projections 37 suppresses the temperature rise. As a result, a change in optical characteristics due to a temperature rise can be suppressed, and good optical characteristics before use can be stably maintained during use.
[0080]
The number, installation position, shape, size, and the like of the protrusions 37 can be determined in consideration of necessary heat radiation characteristics. Further, the projection 37 may be provided on only one of the two lenses constituting the objective lens, although the heat radiation characteristic is slightly lowered.
[0081]
Note that, in the above example, an example in which the projection 37 is provided to the objective lens in which the two lenses are directly bonded by bonding in the same manner as in the third embodiment, but is held by the lens barrel described in the first embodiment. In the objective lens described above (see FIG. 1), a projection may be provided on a surface (for example, a surface of the edge) exposed to the outside of each lens, whereby the same effect as described above can be obtained.
[0082]
Further, as described in the first to third embodiments, a through hole communicating the internal space with the outside world may be provided to prevent a pressure change in the internal space due to a temperature change.
[0083]
Further, as described in Embodiment 2, by using an amorphous polyolefin resin as a lens material, an objective lens having excellent optical characteristics and long-term reliability can be obtained.
[0084]
(Embodiment 6)
FIG. 8A is a side sectional view showing a state before two lenses constituting an objective lens according to Embodiment 6 of the present invention are joined, and FIG. 8B is a view showing Embodiment 6 of the present invention. It is a side sectional view showing such an objective lens.
[0085]
The objective lens according to the sixth embodiment is similar to the objective lens described in the third embodiment (see FIG. 5) in that two lenses 42 and 43 (FIG. 8A ) Is integrated with the respective frame portions 44 and 45 via an adhesive (see FIG. 8B). The numerical aperture of the two-piece objective lens is 0.82 or more.
[0086]
In the objective lens according to the sixth embodiment, one substantially circular groove 48 centered on the optical axis is formed on a flat surface (butting surface) of the frame portion 45 of the lens 43 that is joined to the frame portion 44 of the lens 42. The above is formed.
[0087]
According to the objective lens of the present embodiment, by providing the annular groove 48 on the surface where the frame portion 44 and the frame portion 45 are bonded and joined, the two lenses 42 and 43 constituting the objective lens can be framed. When the flat surfaces of the portions 44 and 45 are adhered and fixed to each other, the groove 48 functions as an adhesive reservoir, so that the adhesive can be prevented from flowing into the lens effective surface inside the frame portions 44 and 45. . As a result, the workability of assembling the objective lens and the yield are improved. Further, this can reduce the cost of the lens.
[0088]
In the above example, the groove 48 is provided in the frame portion 45 of the lens 43, but may be provided in the frame portion 44 of the lens 42 in addition to or instead of this. Further, the number, thickness, depth, and the like of the grooves can be appropriately determined in consideration of the amount of the adhesive to be used.
[0089]
In the above example, an example is shown in which the groove 58 is provided in the objective lens in which the two lenses are directly joined as in the third embodiment, but the objective held by the lens barrel described in the first embodiment is described. In the lens (see FIG. 1), a similar groove may be provided on the surface of the edge to be bonded to the lens barrel of each lens, whereby the same effect as described above can be obtained.
[0090]
Further, as described in the first to third embodiments, a through hole communicating the internal space with the outside world may be provided to prevent a pressure change in the internal space due to a temperature change.
[0091]
Further, as described in the fifth embodiment, one or more protrusions for cooling may be formed on a portion other than the lens effective surface.
[0092]
Further, as described in Embodiment 2, by using an amorphous polyolefin resin as a lens material, an objective lens having excellent optical characteristics and long-term reliability can be obtained.
[0093]
(Embodiment 7)
FIG. 9A is a side sectional view showing a state before two lenses constituting an objective lens according to Embodiment 7 of the present invention are joined, and FIG. 9B is a view showing Embodiment 7 of the present invention. It is a side sectional view showing such an objective lens.
[0094]
Similar to the objective lens described in Embodiment 3 (see FIG. 5), the objective lens of Embodiment 7 includes two lenses 52 and 53 (FIG. 9A) obtained by injection molding a resin material. )) Is integrated with the respective frame portions 54 and 55 via an adhesive (see FIG. 9B). The numerical aperture of the two-piece objective lens is 0.82 or more.
[0095]
In the objective lens according to the seventh embodiment, two concave portions 57 are provided on the flat surface of the frame portion 54 of the lens 52 at symmetrical positions with respect to the optical axis. Two protrusions 58 are provided at fitting positions.
[0096]
According to the objective lens of the present embodiment, since the concave portion 57 and the convex portion 58 that fit each other are provided on the surface where the frame portion 54 and the frame portion 55 are bonded and joined, the relative positions of the lenses 52 and 53 are relatively large. Positioning (direction perpendicular to the optical axis and positioning around the optical axis) can be easily performed, the manufacturing process of the objective lens can be greatly reduced, and the yield is improved. Further, this can reduce the cost of the lens.
[0097]
It is preferable that the adhesive is applied to the concave portions 57 and / or the convex portions 58 before joining.
[0098]
In the above example, the concave portion 57 is provided in the frame portion 54 and the convex portion 58 is provided in the frame portion 55. However, the present invention is not limited to this mode as long as the positioning of the lenses 52 and 53 can be performed. May be provided at arbitrary positions of the frame portions 54 and 55.
[0099]
Further, in the above example, an example is shown in which the fitting shape is provided on the joint surface of the two lenses in the objective lens in which the two lenses are directly joined in the same manner as in the third embodiment. In the objective lens (see FIG. 1) held by the illustrated lens barrel, a similar fitting shape may be provided at the joint surface between each lens and the lens barrel, whereby the same effect as described above can be obtained. .
[0100]
Further, as described in the first embodiment, a through hole communicating the internal space with the outside world may be provided to prevent a pressure change in the internal space due to a temperature change.
[0101]
Further, as described in the fifth embodiment, one or more protrusions for cooling may be formed on a portion other than the lens effective surface.
[0102]
Further, as described in the sixth embodiment, a groove for preventing the adhesive from flowing into the lens effective surface side may be formed in a portion other than the lens effective surface.
[0103]
Further, as described in Embodiment 2, by using an amorphous polyolefin resin as a lens material, an objective lens having excellent optical characteristics and long-term reliability can be obtained.
[0104]
(Embodiment 8)
FIG. 10 is a side sectional view of an objective lens according to Embodiment 8 of the present invention.
[0105]
The objective lens according to the eighth embodiment is the same as the objective lens described in the seventh embodiment, except that the space formed by the two lenses 52 and 53 constituting the objective lens is filled with a gel-like substance 59. The gel-like substance 59 is filled by injecting the gel-like substance 59 from the gap between the flat surfaces of both lenses when the lenses 52 and 53 are abutted and the concave part 57 and the convex part 58 are fitted to each other. It can be performed by solidifying. As the gel substance 59, for example, a silicone gel liquid having a refractive index of 1 can be exemplified, but any liquid or gel substance having a refractive index of 1 can be used without limitation.
[0106]
According to the objective lens of the present embodiment, since the space formed by the lenses 52 and 53 is filled with the gel-like substance 59, the heat capacity of the objective lens increases. Therefore, even if the ambient temperature of the objective lens increases in the actual use state, the increase in the temperature of the objective lens is suppressed, and as a result, stable optical performance against temperature changes is guaranteed.
[0107]
In the above example, the example in which the gel-like substance is filled in the objective lens according to the seventh embodiment has been described. However, the gel-like substance may be filled in the internal space of the objective lens according to the other embodiments described above. Thus, the same effect as described above can be obtained. However, in this case, it is not preferable to form a through hole that communicates the space inside the objective lens with the outside world as described in the first to third embodiments in order to prevent the gel-like substance from leaking.
[0108]
Further, as described in Embodiment 2, by using an amorphous polyolefin resin as a lens material, an objective lens having excellent optical characteristics and long-term reliability can be obtained.
[0109]
(Embodiment 9)
FIG. 11 is a schematic diagram showing one configuration example of the optical head device according to Embodiment 9 of the present invention.
[0110]
In FIG. 11, a divergent light beam 72 emitted from a semiconductor laser module 71 is converted into a substantially parallel light beam 74 by a collimating lens 73. The direction of the optical path of the parallel light beam 74 is changed by a bending (raising) mirror 75, the light beam passes through the first lens 77 and the second lens 78 of the objective lens 76 in order, and passes through the transparent substrate 102 of the optical disc 100. Is focused on the information recording surface 104 of the optical disc 100. The reflected light intensity of the condensed spot is modulated by signals having different reflectances formed on the information recording surface 104. The laser light reflected by the information recording surface 104 returns to the semiconductor laser module 71 along the original optical path. Here, the semiconductor laser module 71 has a light source capable of emitting light of two different wavelengths, a light receiving element, and a light beam separating unit that separates outgoing light and returning light. The objective lens 76 is the objective lens described in the first embodiment, and the first lens 77 and the second lens 78 are fixed by a lens barrel 79.
[0111]
According to the configuration of the optical head device described above, the amount of deterioration of aberration due to a change in temperature can be reduced.
[0112]
In the above description, the objective lens described in Embodiment 1 is used as the objective lens 76, but any of the objective lenses in Embodiments 2 to 8 may be used.
[0113]
In the above description, an optical head device for recording and / or reproducing directly on an optical disk has been described as an example. However, the optical head device of the present invention is, for example, a laser beam recorder for recording a master such as a DVD. It may be used as an optical head device.
[0114]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a low-distortion, high-precision two-lens objective lens and an optical head device including the same.
[0115]
Further, according to the present invention, it is possible to provide a two-piece objective lens which has low optical absorption and good optical characteristics over a long period of time, and an optical head device provided with the objective lens.
[0116]
Further, according to the present invention, it is possible to provide a two-piece objective lens having a simple structure and a low cost, and an optical head device including the objective lens.
[0117]
Further, according to the present invention, it is possible to provide a two-piece objective lens which has good assembling workability and can be manufactured relatively inexpensively and an optical head device provided with the objective lens.
[0118]
Further, according to the present invention, it is possible to provide a two-piece objective lens in which a change in optical characteristics due to a temperature change is small and an optical head device including the same.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an objective lens according to a first embodiment of the present invention.
FIG. 2A is a sectional view of a molding die used for molding a first lens constituting the objective lens according to the first embodiment of the present invention;
(B) A sectional view of a molding die used for molding a second lens constituting the objective lens according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a schematic configuration of a molding apparatus for molding a lens that forms the objective lens according to the first embodiment of the present invention.
FIG. 4A is a side sectional view of a first lens included in the objective lens according to the first embodiment of the present invention.
(B) A side sectional view of a second lens included in the objective lens according to the first embodiment of the present invention.
FIG. 5 is a side sectional view of an objective lens according to a third embodiment of the present invention.
FIG. 6 is a schematic sectional view of a molding apparatus for molding an objective lens according to a third embodiment of the present invention.
FIG. 7 is a side sectional view of an objective lens according to a fifth embodiment of the present invention.
FIG. 8A is a side cross-sectional view showing a state before two lenses constituting an objective lens according to a sixth embodiment of the present invention are joined;
(B) Side sectional view of the objective lens according to the sixth embodiment of the present invention.
FIG. 9A is a side cross-sectional view showing a state before joining two lenses constituting an objective lens according to a seventh embodiment of the present invention;
(B) Side sectional view of the objective lens according to the seventh embodiment of the present invention.
FIG. 10 is a side sectional view of an objective lens according to an eighth embodiment of the present invention.
FIG. 11 is a configuration diagram of an optical head device according to a ninth embodiment of the present invention.
[Explanation of symbols]
1 Parallel light flux
2 First lens
3 Second lens
6 First lens first surface
7 First lens second surface
8 First surface of second lens
9 Second lens second surface
10 Lens barrel
11 Through hole
13a, 13b Lower mold
14a, 14b Upper die
15a, 15b body type
17a, 17b Optical material
21 grooves
22 First lens
23 Second lens
26 First lens first surface
24, 25 frame part
27 First lens second surface
28 First surface of second lens
29 2nd lens 2nd surface
32,33 lens
34, 35 Frame
37 protrusion
42, 43 lenses
44, 45 Frame
48 grooves
52, 53 lenses
54, 55 Frame
57 recess
58 convex
59 Gel-like substance
60 Hopper
61 Resin material
62 cylinder
63 screw
64 nozzles
65 sprue
66 Runner
67 gate
68 cavities
69 mold
71 Semiconductor laser module
72 divergent luminous flux
73 collimating lens
74 parallel beam
75 Start-up mirror
76 Objective lens
77 First lens
78 Second lens
79 Barrel
80 Molding equipment
80a Preheating stage
80b molding stage
80c 1st cooling stage
80d 2nd cooling stage
81 Loading Stage
82 Removal Stage
85a, 85b, 85c, 85d Lower stage
87a, 87b, 87c, 87d Upper head
100 optical disk
102 Transparent substrate
104 Information recording surface

Claims (11)

An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is obtained by putting a resin preform obtained by injection molding a resin material between upper and lower molds and performing heating and pressure molding,
An objective lens, wherein the two lenses are respectively joined to a lens barrel to be integrated. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
The objective lens, wherein each of the two lenses is made of an amorphous polyolefin resin. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is made of a resin material,
Each of the two lenses is obtained by injection molding a resin material,
Each of the two lenses has a frame portion outside the lens effective surface,
The two lenses are integrated by bonding their respective frame parts to each other. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses was obtained by charging a preform formed of a low-melting glass material having a glass transition point of 450 ° C. or lower into a predetermined shape between upper and lower molds, and performing heating and pressure molding. Things,
The objective lens, wherein the two lenses are connected and integrated via portions other than the respective lens effective surfaces. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is made of a resin material,
Each of the two lenses is obtained by injection molding a resin material,
An objective lens, characterized in that at least one of the two lenses has one or more projections for cooling on a portion other than the lens effective surface. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is made of a resin material,
Each of the two lenses is obtained by injection molding a resin material,
The two lenses are integrated via an adhesive at portions other than the respective lens effective surfaces,
At least one of the two lenses has at least one groove in a portion other than the lens effective surface to prevent the adhesive from flowing into the lens effective surface side. Objective lens. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is made of a resin material,
An objective lens, wherein each of the two lenses has a fitting shape for performing relative positioning of the lens on a surface other than the lens effective surface. The objective lens according to any one of claims 1 to 7, further comprising a through-hole for communicating a space between the two lenses and the outside. An objective lens that forms an incident light on an information recording surface of the optical information recording medium in order to record and / or reproduce information on the optical information recording medium,
The numerical aperture of the objective lens is 0.82 or more,
The objective lens is composed of two lenses,
Each of the two lenses is made of a resin material,
An objective lens, characterized in that a space between the two lenses is filled with a liquid or gel-like substance. The objective lens according to any one of claims 1, 3, 5, 6, 7, and 9, wherein the resin material is an amorphous polyolefin resin. A light source, a light condensing unit that condenses a light beam emitted from the light source on an information recording surface of an optical information recording medium, and a light beam separating unit that separates a light beam modulated on the information recording surface from a forward light beam. An optical head device, comprising: a light receiving unit that receives a light beam modulated on the information recording surface, wherein the focusing unit is the objective lens according to claim 1.

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