JP4232188B2

JP4232188B2 - Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device

Info

Publication number: JP4232188B2
Application number: JP2002110354A
Authority: JP
Inventors: 真一郎斉藤
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2001-04-26
Filing date: 2002-04-12
Publication date: 2009-03-04
Anticipated expiration: 2022-04-12
Also published as: JP2003015031A

Description

【０００１】
【発明の属する技術分野】
本発明は、光ピックアップ装置に使用される対物レンズ、光ピックアップ装置及び光情報記録再生装置、特に単玉である対物レンズを有限倍率で用いることにより光情報記録媒体の記録及び／又は再生を行なうことができる光ピックアップ装置用の対物レンズ、光ピックアップ装置及び光情報記録再生装置に関する。
【０００２】
【従来の技術】
ＤＶＤなどの光情報記録媒体に対して高密度に情報を記録し、又再生することができる光ピックアップ装置が開発され、様々な用途で用いられている。このような光ピックアップ装置においては、構成のコンパクト化、環境温度変化時の信頼性など種々の要求がある。
【０００３】
ところで、光ピックアップ装置において、光情報記録媒体の情報記録面に情報記録光を集光させる対物レンズは、大量生産に有利であることから、プラスチック材料を素材とするものが多く用いられている。しかるに、その屈折率の温度変化において、プラスチック材料はガラス材料に比べて２桁程度大きい事が知られている。
【０００４】
ここで、プラスチック材料から形成された対物レンズを有する光ピックアップ装置の環境温度が上昇して、その対物レンズの屈折率が変化すると、集光光学系としては球面収差が劣化することが知られている。例えば、現状のＤＶＤ用の光ピックアップ装置においては、開口数ＮＡ０．６０、結像倍率ｍ＝０のプラスチック材料の対物レンズが多く普及しているが、その焦点距離を３ｍｍ、プラスチック材料の屈折率の温度変化をｄｎ／ｄＴ＝−０．０００１２（／℃）、光源波長λ＝６５０ｎｍでのプラスチック材料の屈折率をｎ＝１．５３で無収差となるように対物レンズを設計しても、光ピックアップ装置の温度が室温から３０℃上昇した時には、対物レンズの屈折率が１．５２６４となり、それにより計算上約０．０３３λｒｍｓの残留収差が発生してしまうこととなる。
【０００５】
一般的には、光学の回折限界（マレシャルの限界値０．０７λｒｍｓ）以下に光学系全体で抑えておく必要があるとされ、又対物レンズ以外にも、収差を発生させる様々な要因が存在するので、上記の環境温度変化により発生する収差を極力抑えることが、まず重要であるといえる。
【０００６】
この、環境温度変化によって屈折率が変化した場合の球面収差劣化δＳＡ／δＴは、次式で表される。
δＳＡ／δＴ∝ｆ（１−ｍ）^４ＮＡ^４・（ｄｎ／ｄＴ）／λ （２６）
但し、対物レンズの無限物体での焦点距離をｆ、光情報記録媒体側の開口数をＮＡ、光源の波長をλ、温度１℃上昇時の対物レンズ屈折率の変化量をｄｎ／ｄＴ、結像倍率をｍとする。
【０００７】
【発明が解決しようとする課題】
近年におけるＤＶＤなどの高密度な光情報記録媒体に対して、情報の記録又は再生を行う光ピックアップ装置において、開口数ＮＡをより増大する傾向にある。また、光ピックアップ装置のコンパクト化を確保するために、有限倍率で使用し且つ有限度合いを高める試みもなされている。しかるに、（２６）式によれば、対物レンズの開口数ＮＡが大きくなるほど、また光学系の有限度合いが強くなるスペックで使用される対物レンズほど、球面収差劣化が顕著となることが理解できる。例えば、上述したようにｆ＝３ｍｍ、ｍ＝０で、開口数ＮＡを０．６０から０．８５に増大させたとすると、ＮＡの４乗に比例して収差が劣化し、室温（例えば２５℃）から３０℃温度上昇時の球面収差概算値は０．１２λｒｍｓとなり、マレシャルの限界値を大きく越えることが予想される。更に、近年開発された青色レーザのごとき光源を用いることで、更なる情報の高密度化も期待できるが、それにより光源波長λがより短波長化し、温度変化に対する球面収差劣化の問題は、益々厳しくなる方向にあるといえる。
【０００８】
かかる問題に対し、同じく（２６）式から、焦点距離ｆを小さくすることにより、温度変化に対しての球面収差劣化をある程度抑えることができることが判る。例えば、開口数をＮＡ０．６０からＮＡ０．８５に増大させたとしても、焦点距離を１／４にすれば、開口数増大前と同等の温度特性を得ることがことが可能となる。
【０００９】
しかしながら、焦点距離ｆを小さくすると、像高特性としては不利となる。これは、同じ像高を得ようとすると、対物レンズへの入射角度が大きくなるためである。入射角度が大きくなるほど非点収差やコマ収差が劣化する。従って、像高特性的には焦点距離が大きい方が好ましい。
【００１０】
本発明は、上記問題点に鑑みてなされたものであり、開口数ＮＡの増大、光源波長の短波長化がなされた光ピックアップ装置においても、温度特性の優れた単玉対物レンズであって、像高特性とのバランスのとれた光学系全体をコンパクトとすることが可能な対物レンズ、その対物レンズを用いた光ピックアップ装置及び光情報記録再生装置を提供することを目的とする。また本発明は、小径の対物レンズで、ふち厚を厚くして成形性を向上させた対物レンズ、その対物レンズを用いた光ピックアップ装置及び光情報記録再生装置を提供することを目的とする。
【００１１】
【課題を解決するための手段】
請求項１に記載の光ピックアップ装置用の対物レンズは、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行なうようになっている対物レンズと、を有する光ピックアップ装置用の対物レンズにおいて、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１）
０．５０＜ＮＡ＜０．９０（２）
３５０ｎｍ＜λ＜８５０ｎｍ（３）
１／１０＜｜ｍ｜＜１／３（４）
０．０２９＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．２（５）
前記光ピックアップ装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．０２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜ δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（６）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。
【００１２】
請求項１に記載の対物レンズによれば、開口数ＮＡの増大、光源波長λの短波長化に応じて、焦点距離ｆを小さくすることにより、温度変化に対する球面収差の劣化を抑えることができるが、あまり焦点距離ｆを小さくすると、像高特性が劣化するので、（１）〜（６）式を満たすような範囲で、各値を定めることによって、温度特性、像高特性とのバランスのとれた対物レンズを提供することが可能となる。更に、高開口数ＮＡであっても有限倍率とすることが可能であり、それにより光源からの光束を、単一の前記対物レンズを用いて前記光情報記録媒体の情報記録面に集光させるといったコンパクトで簡素な構成の光ピックアップ装置とすることも可能となる。
【００１３】
請求項２に記載の光ピックアップ装置用の対物レンズによれば、前記対物レンズはプラスチック材料で構成されると、かかるプラスチック材料がガラス材料に比べて軽量であるため、前記対物レンズを光軸方向に移動させるフォーカシング動作の高速化を図れる。また、プラスチック材料は射出成形が容易であるため、安定した品質での前記対物レンズの大量生産が可能である。
【００１４】
請求項３に記載の光ピックアップ装置用の対物レンズによれば、前記対物レンズは両面非球面で構成されると好ましい。屈折面で構成すると、色収差に強い対物レンズが可能となる。特に、分散値の大きな材料を使うと、光源のモードホップに伴う対物レンズの近軸像点位置の変化をおさえることが可能となる。
【００１５】
請求項４に記載の光ピックアップ装置用の対物レンズによれば、前記対物レンズにおいて、光情報記録媒体側の前記開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすことを特徴とする。
０．５０＜ＮＡ＜０．７５（７）
４５０ｎｍ＜λ＜８５０ｎｍ（８）
０．０２９＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．０６（９）
前記開口数ＮＡが０．５０より大きく、前記光源波長λが８５０ｎｍ未満であれば、比較的高密度の光情報記録媒体に対応でき、一方、前記開口数ＮＡが０．７５未満であり、かつ前記光源波長λが４５０ｎｍより大きければ、温度変化に対する球面収差の劣化を、（９）式に示す範囲に抑えることができる。
【００１６】
請求項５に記載の光ピックアップ装置用の対物レンズによれば、前記対物レンズの軸上厚さｄが、
０．４＜ｄ／ｆ＜１．５（１０）
を満たすことを特徴とする。値ｄ／ｆが、（１０）式の下限値を上回ると、設計上、像高特性の制御が容易となり、一方、上限値を下回ると、前記対物レンズと前記光情報記録媒体とを離すことで十分なワーキングディスタンスを確保することが可能となる。
【００１７】
請求項６に記載の光ピックアップ装置用の対物レンズは、
０．１ｍｍ＜ｆ≦０．６ｍｍ（１１）
を満たすことを特徴とする。
【００１８】
請求項６に記載の対物レンズは、温度特性、像高特性とのバランスをとりつつ、請求項１に記載の対物レンズに対し、より高開口数ＮＡを高く且つ球面収差を低く抑えても有限倍率とすることが可能であり、それにより光源からの光束を、単一の前記対物レンズを用いて前記光情報記録媒体の情報記録面に集光させるといったコンパクトで簡素な構成の光ピックアップ装置を提供することができる。
【００１９】
請求項７に記載の光ピックアップ装置用の対物レンズは、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行うようになっている対物レンズと、を有する光ピックアップ装置用の対物レンズにおいて、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、前記対物レンズの軸上厚さｄ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１９）
０．７０＜ＮＡ＜０．９０（２０）
３５０ｎｍ＜λ＜８５０ｎｍ（２１）
−１／５＜ｍ＜−１／１０（２２）
０．０１≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２３）
１．２＜ｄ／ｆ＜１．７（２４）
前記光ピックアップ装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．００２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（２５）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。
【００２０】
請求項７に記載の対物レンズは、温度特性、像高特性とのバランスをとりつつ、請求項１に記載の対物レンズに対し、より高開口数ＮＡを高く且つ球面収差を低く抑えても有限倍率とすることが可能であり、それにより光源からの光束を、単一の前記対物レンズを用いて前記光情報記録媒体の情報記録面に集光させるといったコンパクトで簡素な構成の光ピックアップ装置を提供することができる。
【００２２】
「アンダーな球面収差もしくは／オーバーな球面収差」については、図８に示すように、近軸像点位置を原点とする球面収差において、近軸像点よりも手前側で光軸と交わる場合を「アンダー」、近軸像点よりも遠い位置で光軸と交わる場合を「オーバー」とする。
【００２３】
請求項８に記載の光ピックアップ装置用の対物レンズは、以下の式を満足することを特徴とする。
０．０８≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２７）
【００２４】
尚、前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たす効果について説明する。本発明は、特に像高特性のコマ収差成分に関するものである。（２８）式を満たすことで、前記対物レンズに対して光束が斜入射する時におけるコマ収差が補正される条件としての、いわゆる正弦条件の補正が容易となる。
【００２５】
（２８）式から明らかであるが、前記対物レンズでは、両凸レンズで前記光源側の近軸曲率半径ｒ１を小さくする方が収差補正上好ましいといえる。しかしながら、それにより前記光源側の非球面の見込み角度の変化は周辺に行くほど大きくなり、この光源側の面の非球面がふち厚を制限する大きな要因となっている。これを具体的に説明する。
【００２６】
図１は、本発明の対物レンズの一部を模式的に示す断面図である。ここで、従来は、前記対物レンズの両面非球面形状を、前記対物レンズのフランジ部に接続する位置まで延長させることが行われている。しかしながら、請求項１０に記載の本発明のごとく、（２８）式を満たすように近軸曲率半径ｒ１を小さく設定すると、図１に点線で示すごとく、見込み角θ１（光源側非球面の断面におけるフランジ部との交点Ｐ３の接線と、かかる交点Ｐ３におけるフランジ部の接線とのなす角度）が大きくなるため、フランジ厚ｔ１が薄くなる傾向にある。フランジ厚ｔ１が薄くなると、前記対物レンズの成形時に、素材の流れが悪くなることによる成形不良が生じやすくなるという問題がある。以下の発明によれば、かかる問題を解消もしくは緩和することができる。
【００２７】
請求項９に記載の光ピックアップ装置用の対物レンズは、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線（ここでは図１に示すＬＢ１）が交わる位置（ここでは図１に示すＰ１）において、前記対物レンズのふち厚が厚くなるような繋ぎ領域（図１に示すＡ）を設けたことを特徴とする。かかる発明によれば、前記対物レンズは、図１の実線で示すような面形状となり、それにより見込み角θ２は、従来の見込み角θ１より小さくなり、フランジ厚ｔ２をより厚くすることができ、前記対物レンズの成形性を向上させることができる。尚、前記繋ぎ領域の形状を最適化することにより、例えば前記繋ぎ領域を通過した光束を結像に関与しないフレア光に変換することで、絞り効果を持たせることもできる。
【００２８】
請求項１０に記載の光ピックアップ装置用の対物レンズは、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線（ここでは図１に示すＬＢ２）が交わる位置（ここでは図１に示すＰ２）の光軸に交差する方向の外側部において、前記対物レンズのふち厚が厚くなるような繋ぎ領域（図１に示すＡ）を設けたことを特徴とする。前記開口数ＮＡの最外光線が交わる位置の光軸に交差する方向の外側部を通過する光束は、前記光情報記録媒体の情報記録面に対して結像に関与しないものであるので、設計上は、請求項１１に記載の発明のごとく、前記最外光線の交わる位置Ｐ１から外側に向かって直に前記繋ぎ領域を形成すれば良いが、実際的には、部品の精度、組み付け誤差などにより、最外光線の通過する位置は設計位置に対して変動する。そこで、本発明のごとく、前記開口数ＮＡの最外光線（ＬＢ２）が交わる位置（Ｐ２）の光軸に交差する方向の外側部において、前記対物レンズのふち厚が厚くなるような繋ぎ領域を設けることにより、交わる位置が変動した場合でも、最外光線が通過する位置の内側を通過する光束は、常に結像に関与させることで、透過光量を効率的に確保できるようになっている。
【００２９】
請求項１１に記載の光ピックアップ装置用の対物レンズは、前記繋ぎ領域は、光軸方向に段差を設けたことを特徴とする。図２は、本発明の対物レンズの一部を示す図１と同様な断面図である。図２において、前記開口数ＮＡの最外光線（ここでは図２に示すＬＢ１）が交わる位置（ここでは図２に示すＰ１）から光軸直交方向の外側において、かかる対物レンズの光源側の面（即ち繋ぎ領域）は、光軸方向の光源側に突出した段差（図２に示すＡ'）となっている。このようにすることで、対物レンズのふち厚ｔ３をより大きく確保することができる。尚、前記段差の形状を最適化することにより、例えば前記段差を通過した光束を結像に関与しないフレア光に変換することで、絞り効果を持たせることもできる。かかる場合、段差は、図２に点線で示すように、光軸方向の光情報記録媒体側にくぼんだ形状となっていても良い。
【００３０】
請求項１２に記載の光ピックアップ装置用の対物レンズは、前記繋ぎ領域の光軸に直交する面に対する角度と、前記繋ぎ領域を設けない場合における非球面形状の光軸に直交する面に対する角度との差（図１で点Ｐ１における有効径内のレンズ表面との接線と、点Ｐ３における繋ぎ領域の接線とのなす角度、即ち（θ１−θ２）が２０度以内であると好ましい。前記繋ぎ領域の見込み角が大きすぎると、金型加工時のバイトの先端部分への負荷が大きくなりすぎ好ましくないからであり、また前記繋ぎ領域の外側と内側とで金型を別部材として前記対物レンズを成形すると、レンズ面内にバリを生じるので好ましくないからである。
【００３１】
請求項１３に記載の光ピックアップ装置は、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行なうようになっている対物レンズと、を有する光ピックアップ装置において、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１）
０．５０＜ＮＡ＜０．９０（２）
３５０ｎｍ＜λ＜８５０ｎｍ（３）
１／１０＜｜ｍ｜＜１／３（４）
０．０２９＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．２（５）
前記光ピックアップ装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．０２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜ δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（６）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。本発明の光ピックアップ装置は、請求項１に記載の発明と同様な作用効果を奏する。
【００３２】
請求項１４に記載の光ピックアップ装置は、前記対物レンズはプラスチック材料で構成されることを特徴とする。本発明の光ピックアップ装置は、請求項２に記載の発明と同様な作用効果を奏する。
【００３３】
請求項１５に記載の光ピックアップ装置は、前記対物レンズは両面非球面で構成されることを特徴とする。本発明の光ピックアップ装置は、請求項３に記載の発明と同様な作用効果を奏する。
【００３４】
請求項１６に記載の光ピックアップ装置は、前記対物レンズにおいて、光情報記録媒体側の前記開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすことを特徴とする。本発明の光ピックアップ装置は、請求項４に記載の発明と同様な作用効果を奏する。
０．５０＜ＮＡ＜０．７５（７）
４５０ｎｍ＜λ＜８５０ｎｍ（８）
０．０＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．０６（９）
【００３５】
請求項１７に記載の光ピックアップ装置は、前記対物レンズの軸上厚さｄが、
０．４＜ｄ／ｆ＜１．５（１０）
を満たすことを特徴とする。本発明の光ピックアップ装置は、請求項５に記載の発明と同様な作用効果を奏する。
【００３６】
請求項１８に記載の光ピックアップ装置は、
０．１ｍｍ＜ｆ≦０．６ｍｍ（１１）
を満たすことを特徴とする。
【００３７】
請求項１９に記載の光ピックアップ装置は、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行うようになっている対物レンズと、を有する光ピックアップ装置において、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、前記対物レンズの軸上厚さｄ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１９）
０．７０＜ＮＡ＜０．９０（２０）
３５０ｎｍ＜λ＜８５０ｎｍ（２１）
−１／５＜ｍ＜−１／１０（２２）
０．０１≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２３）
１．２＜ｄ／ｆ＜１．７（２４）
前記光ピックアップ装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．００２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（２５）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。本発明の光ピックアップ装置は、請求項７に記載の発明と同様な作用効果を奏する。
【００３９】
請求項２０に記載の光ピックアップ装置は、以下の式を満足することを特徴とする。本発明の光ピックアップ装置は、請求項８に記載の発明と同様な作用効果を奏する。
０．０８≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２７）
【００４１】
請求項２１に記載の光ピックアップ装置は、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線が交わる位置から光軸に対して外方に、前記対物レンズのふち厚が厚くなるような繋ぎ領域を設けたことを特徴とする。本発明の光ピックアップ装置は、請求項９に記載の発明と同様な作用効果を奏する。
【００４２】
請求項２２に記載の光ピックアップ装置は、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線が交わる位置よりも光軸に対して外方の位置の更に外側に、前記対物レンズのふち厚が厚くなるような繋ぎ領域を設けたことを特徴とする。本発明の光ピックアップ装置は、請求項１０に記載の発明と同様な作用効果を奏する。
【００４３】
請求項２３に記載の光ピックアップ装置は、前記繋ぎ領域は、光軸方向に段差を設けたことを特徴とする。本発明の光ピックアップ装置は、請求項１１に記載の発明と同様な作用効果を奏する。
【００４４】
請求項２４に記載の光ピックアップ装置は、前記繋ぎ領域の光軸に直交する面に対する角度と、前記繋ぎ領域を設けない場合における非球面形状の光軸に直交する面に対する角度との差が２０度以内であることを特徴とする。本発明の光ピックアップ装置は、請求項１２に記載の発明と同様な作用効果を奏する。
【００４５】
請求項２５に記載の光情報記録再生装置は、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行なうようになっている対物レンズと、を有する光情報記録再生装置において、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１）
０．５０＜ＮＡ＜０．９０（２）
３５０ｎｍ＜λ＜８５０ｎｍ（３）
１／１０＜｜ｍ｜＜１／３（４）
０．０２９＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．２（５）
前記光情報記録再生装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．０２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜ δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（６）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。本発明の光情報記録再生装置は、請求項１に記載の発明と同様な作用効果を奏する。
【００４６】
請求項２６に記載の光情報記録再生装置は、前記対物レンズはプラスチック材料で構成されることを特徴とする。本発明の光情報記録再生装置は、請求項２に記載の発明と同様な作用効果を奏する。
【００４７】
請求項２７に記載の光情報記録再生装置は、前記対物レンズは両面非球面で構成されることを特徴とする。本発明の光情報記録再生装置は、請求項３に記載の発明と同様な作用効果を奏する。
【００４８】
請求項２８に記載の光情報記録再生装置は、前記対物レンズにおいて、光情報記録媒体側の前記開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすことを特徴とする。本発明の光情報記録再生装置は、請求項４に記載の発明と同様な作用効果を奏する。
０．５０＜ＮＡ＜０．７５（７）
４５０ｎｍ＜λ＜８５０ｎｍ（８）
０．０＜（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ ＜０．０６（９）
【００４９】
請求項２９に記載の光情報記録再生装置は、前記対物レンズの軸上厚さｄが、
０．４＜ｄ／ｆ＜１．５（１０）
を満たすことを特徴とする。本発明の光情報記録再生装置は、請求項５に記載の発明と同様な作用効果を奏する。
【００５０】
請求項３０に記載の光情報記録再生装置は、
０．１ｍｍ＜ｆ≦０．６ｍｍ（１１）
を満たすことを特徴とする。
【００５１】
請求項３１に記載の光情報記録再生装置は、波長λの光源と、前記光源からの光束を光情報記録媒体に結像することで情報の記録及び／又は再生を行うようになっている対物レンズと、を有する光情報記録再生装置において、前記対物レンズは回折構造を有しない単玉レンズであり、前記対物レンズの無限物体での焦点距離ｆ、前記対物レンズの軸上厚さｄ、光情報記録媒体側の開口数ＮＡ、前記光源の波長λ、温度１℃上昇時の対物レンズ屈折率の変化量ｄｎ／ｄＴ、及び結像倍率ｍの値が、それぞれ以下の式を満たすと共に、
０．１ｍｍ＜ｆ＜１ｍｍ（１９）
０．７０＜ＮＡ＜０．９０（２０）
３５０ｎｍ＜λ＜８５０ｎｍ（２１）
−１／５＜ｍ＜−１／１０（２２）
０．０１≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２３）
１．２＜ｄ／ｆ＜１．７（２４）
前記光情報記録再生装置全体が室温から３０℃温度上昇した時の前記対物レンズの収差をδＷｔｅｍｐ、対物レンズの像高Ｙ＝０．００２ｍｍにおける収差をδＷｈｅｉｇｈｔとした場合に、
０．０λｒｍｓ＜δＷｔｅｍｐ＋δＷｈｅｉｇｈｔ＜０．０７λｒｍｓ（２５）
であり、
前記対物レンズの光源側の面の近軸曲率半径をｒ１、前記対物レンズの波長λにおける屈折率をｎとすると、
０．３＜ｒ１／（ｎ（１−ｍ）ｆ）＜０．５（２８）
を満たすことを特徴とする。本発明の光情報記録再生装置は、請求項７に記載の発明と同様な作用効果を奏する。
【００５３】
請求項３２に記載の光情報記録再生装置は、以下の式を満足することを特徴とする。本発明の光情報記録再生装置は、請求項８に記載の発明と同様な作用効果を奏する。
０．０８≦（（１−ｍ）ＮＡ）⁴・ｆ・｜ｄｎ／ｄＴ｜／λ＜０．１１（２７）
【００５５】
請求項３３に記載の光情報記録再生装置は、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線が交わる位置から光軸に対して外方に、前記対物レンズのふち厚が厚くなるような繋ぎ領域を設けたことを特徴とする。本発明の光情報記録再生装置は、請求項９に記載の発明と同様な作用効果を奏する。
【００５６】
請求項３４に記載の光情報記録再生装置は、前記対物レンズの光源側の面は、前記開口数ＮＡの最外光線が交わる位置よりも光軸に対して外方の位置の更に外側に、前記対物レンズのふち厚が厚くなるような繋ぎ領域を設けたことを特徴とする。本発明の光情報記録再生装置は、請求項１０に記載の発明と同様な作用効果を奏する。
【００５７】
請求項３５に記載の光情報記録再生装置は、前記繋ぎ領域は、光軸方向に段差を設けたことを特徴とする。本発明の光情報記録再生装置は、請求項１１に記載の発明と同様な作用効果を奏する。
【００５８】
請求項３６に記載の光情報記録再生装置は、前記繋ぎ領域の光軸に直交する面に対する角度と、前記繋ぎ領域を設けない場合における非球面形状の光軸に直交する面に対する角度との差が２０度以内であることを特徴とする。本発明の光情報記録再生装置は、請求項１２に記載の発明と同様な作用効果を奏する。
【００５９】
本明細書中において、対物レンズとは、狭義には光ピックアップ装置に光情報記録媒体を装填した状態において、最も光情報記録媒体側の位置で、これと対向すべく配置される集光作用を有するレンズを指す。従って、本明細書中において、対物レンズの光情報記録媒体側（像側）の開口数ＮＡとは、対物レンズの最も光情報記録媒体側に位置するレンズ面の開口数ＮＡを指すものである。また、本明細書中では必要開口数ＮＡは、それぞれの光情報記録媒体の規格で規定されている開口数、あるいはそれぞれの光情報記録媒体に対して、使用する光源の波長に応じ、情報の記録または再生をするために必要なスポット径を得ることができる回折限界性能の対物レンズの開口数を示すものとする。
【００６０】
本明細書中で用いる「回折構造」とは、対物レンズの表面に、レリーフを設けて、回折によって光束を集光あるいは発散させる作用を持たせた部分のことをいう。レリーフの形状としては、例えば、対物レンズの表面に、光軸を中心とする略同心円状の輪帯として形成され、光軸を含む平面でその断面をみれば各輪帯は鋸歯のような形状が知られているが、そのような形状を含むものであり、そのような形状を特に「回折輪帯」という。
【００６１】
【発明の実施の形態】
以下図面を参照して、本発明をさらに詳細に説明する。
（第１の実施の形態）
第１の実施の形態について説明する。図３は、本実施の形態の対物レンズを含む光ピックアップ装置（光情報記録再生装置）の概略構成図である。この光ピックアップ装置は、波長λの光源としての赤色レーザー１と、対物レンズ２と、光情報記録媒体３とから構成される。赤色レーザー１と対物レンズ２との間にはビームスプリッタ４が存在し、光情報記録媒体３からの反射光を検出器５の方向に偏向するようになっている。
【００６２】
対物レンズ２へは、赤色レーザー１からの発散光束が入射し、その光束径は絞り６によって制限される。このように、結像倍率を有限とすることで、光学系全体の部品点数が少なく簡素な構成とすることができる。対物レンズ２は、両面非球面でありプラスチック材料で構成される。本実施の形態では、プラスチック製の対物レンズの温度変化による球面収差劣化を小さくするために、焦点距離を小さくしている。
【００６３】
ただし、像高特性とのバランスを考慮して焦点距離ｆを決定する。ここで軸外補正のためには、軸上厚さを厚くする方が好ましい。軸上厚さを厚くすると、対物レンズ２のふち厚は厚くなり、対物レンズ２の開口数ＮＡが大きい場合にも、面交差が生じる恐れが減少し光学設計上で有利である。また対物レンズ２に発散光束を入射させた方が、無限光を入射させる場合に比べて、ワーキングディスタンスの確保という観点からも有利である。
【００６４】
また、対物レンズ２の光源側の面の近軸曲率半径ｒ１（図１参照）を０．３×（ｎ（１−ｍ）ｆ）＜ｒ１＜０．５×（ｎ（１−ｍ）ｆ）の範囲にすることが、正弦条件を満足させる上で好ましく、より好ましくは０．３６×（ｎ（１−ｍ）ｆ）＜ｒ１＜０．３９×（ｎ（１−ｍ）ｆ）とするのが良い。正弦条件を満足させておくと、軸外のコマ収差補正が容易となる。
【００６５】
尚、本発明は上記実施の形態（ＮＡ、λ、ｍなど）には制限されない。また、光情報記録媒体として情報記録面上に保護層が存在している場合には、各請求項を満足させつつ、保護層の厚みに応じて対物レンズの球面収差設計を行なえばよい。
【００６６】
（第２の実施の形態）
第２の実施の形態について説明する。本実施の形態においては、図３に示す第１の実施の形態と異なる点は、対物レンズの光源側の面の有効径外の面形状処理であり、同一の構成についての説明は省略する。
【００６７】
対物レンズ２の焦点距離を短くすると、近軸曲率半径ｒ１（図１）の絶対値および軸上厚さが小さくなる。従って、同じ開口数ＮＡであれば、レンズ形状は相似であるので、対物レンズ２のふち厚／軸上厚はほぼ同一になるが、絶対値でみると焦点距離ｆが小さくなるほどふち厚は小さくなる。後の実施例で述べるが、開口数ＮＡ０．６０の対物レンズにおいて、軸上厚さを０．４ｍｍとすると、ふち厚は０．１ｍｍを割り、流動性のよいプラスチック材料であっても対物レンズの成形性が悪化する。そこで、少しでもふち厚を厚くするために、有効径（ここでは最外光線が通過する径）外において、有効径内とは別非球面（或いは球面）を形成する。これを繋ぎ領域（図１のＡ、図２のＡ’）と呼ぶ。
【００６８】
有効径の外側から、すぐに光軸に垂直な繋ぎ領域を設けることは、金型加工上では可能である。しかし、成形性を考えると次のような理由から好ましくない。すなわち、通常、対物レンズを射出成形で作る場合にはゲート部を、ふちの外側に設けることとなる。この時、ゲート部から対物レンズの有効径内部に樹脂が射出されるが、樹脂の流れを考えると粘性抵抗の変化が大きいと転写性にムラが生じ複屈折などの影響が出やすい。
【００６９】
これに対し、図１のような繋ぎ領域Ａを設けると、成形的にも複屈折などの影響も少なく、ふち厚ｔ２を厚くすることが出来る。また光学的にも、繋ぎ領域Ａの外側では面のパワーが弱まるため、オーバーフレアが発生する。この場合、絞りを用いなくとも、光情報記録媒体面上で当初の開口数内を通過する光束は光スポットを形成し、繋ぎ領域を通過する光束はフレアとなり、結像への寄与は少ないので、所望のスポット形状を達成することが可能であり、より光学系の簡素化が図れる。なお、本発明も上記実施の形態に制限されない。
【００７０】
（実施例１）
実施例１は、上記第１の実施の形態に適用可能な対物レンズに関するものである。表１に、実施例１の対物レンズにかかるレンズデータを示す。光源を第０面とし、第１、２面はビームスプリッタで、第３面が絞り、第４、５面が対物レンズであり、第６面が光情報記録媒体の情報記録面を示す。尚、これ以降（表のレンズデータ含む）において、１０のべき乗数（例えば２．５×１０^−３）を、Ｅ（例えば２．５×Ｅ―３）を用いて表すものとする。
【表１】

【００７１】
実施例１の対物レンズは、両面非球面のプラスチックレンズで構成され、各々の非球面は数１で表される非球面形状を有している。
【数１】

ただし、Ｚは光軸方向の軸で、ｈは光軸と垂直方向の軸、ｒは近軸曲率半径、κは円錐係数、Ａは非球面係数、Ｐは非球面のべき数である。
【００７２】
実施例１の対物レンズはプラスチック材料から形成され、温度変化時の屈折率変化は、ｄｎ／ｄＴ＝−０．０００１２（／℃）である。室温（２５℃）から３０℃温度上昇時の球面収差の残留分は０．０２４λｒｍｓであり、像高０．０２ｍｍにおける残留収差が０．０３１λｒｍｓである。ＤＶＤにおけるトラックピッチは、約０．７４μｍであることから、対物レンズとして回折限界までのマージンとしては、像高特性的にも温度変化的にも余裕があることがわかる。これらのことから、対物レンズにプラスチック材料を用いても、温度特性と像高特性とのバランスのとれた対物レンズとなっていることが理解できる。図４は、実施例１の対物レンズにおける像高特性を示すグラフであり、図５は、実施例１の対物レンズにおける温度特性を示すグラフである。
【００７３】
（実施例２）
実施例２も、上記第１の実施の形態に適用可能な対物レンズに関するものである。実施例１との違いは対物レンズのスペックが異なるものであり、光ピックアップ装置としての構成は同じであり、同一箇所についての説明は省略する。
【００７４】
表２に、実施例１の対物レンズにかかるレンズデータを示す。光源を第０面とし、第１、２面はビームスプリッタで、第３面が絞り、第４、５面が対物レンズであり、第６面が光情報記録媒体の情報記録面を示す。
【表２】

【００７５】
実施例２の対物レンズは、両面非球面のプラスチックレンズで構成される。開口数ＮＡは０．７２と、第１の実施例よりも大きくなっているが、使用波長、焦点距離、倍率の設定を最適化することで、従来のｆ＝３ｍｍのＤＶＤ対物レンズよりも温度特性を良くすることが可能となった。
【００７６】
また、軸外補正のために、対物レンズの軸上厚さおよび正弦条件を満足するように、第１面の近軸曲率半径を決定した。表２にもあるように、対物レンズとして回折限界までのマージンとしては、像高特性的にも温度変化的にも余裕があることがわかる。これらのことから、実施例１と同様に、対物レンズにプラスチック材料を用いても、温度特性と像高特性とのバランスのとれた対物レンズとなっていることが理解できる。図６は、実施例２の対物レンズにおける像高特性を示すグラフであり、図７は、実施例２の対物レンズにおける温度特性を示すグラフである。尚、図６，７の特性は、以下の実施例３の対物レンズにも当てはまる。
【００７７】
（実施例３）
実施例３は、上記第２の実施の形態に適用可能な対物レンズに関するものである。なお、実施例３の対物レンズは、有効径内においては実施例２の対物レンズと同一のものとした。表３にレンズデータを示す。対物レンズの光源側の面を、繋ぎ領域を境にして別の非球面としている。繋ぎ領域の非球面を第４’面とする。開口数ＮＡ＝０．６０の最外光線は、第４面で光軸から０．５１２９ｍｍの位置を通過する。
【表３】

【００７８】
レンズ面を、光軸から０．６ｍｍの位置まで設ける場合を考える。光軸から０．５１２９ｍｍの位置と０．６ｍｍの位置との間に、第４面と同一の非球面を設ける場合と、第４’面のような繋ぎ領域を設ける場合では、後者の方が約０．０４８ｍｍふち厚が厚くなる。この増加量の絶対値は僅かではあるが、元々のふち厚が０．１ｍｍ程であるので、増加率としては約５０％あり効果としては顕著である。なお、第４’面を非球面としたが、これ以外にも断面図上でストレートとなるような形状としても、成形上の複屈折の影響が少なくふち厚を確保することが可能である。
【００７９】
（実施例４）
実施例４は、上記第１、第２の何れの実施の形態にも含まれない対物レンズに関する。この対物レンズを含む光ピックアップ装置（光情報記録再生装置）は、波長λの光源として赤色レーザーと対物レンズと検出器とを有しており、光情報記録媒体の情報記録面に光源からの光束を集光し、その反射光を検出器で検出するように構成されている。光源から出射された発散光束は、その光束径が絞りによって制限され、対物レンズを透過した後、光情報記録媒体の情報記録面上に集光される。この様な光ピックアップ装置に適用可能な対物レンズのデータを表４に示す。光源を第０面とし、第１面が絞り、第２、第３面が対物レンズであり、第４面が光情報記銀媒体の情報記録面を示す。尚、実施例４の対物レンズは、両面非球面のガラスレンズである。
【表４】

実施例４では、対物レンズに図１または図２に示した繋ぎ領域を設けていないが、それを設けても構わない。
【００８０】
（実施例５）
実施例５も、上記第１、第２の何れの実施の形態にも含まれない対物レンズに関する。実施例４の対物レンズを含む光ピックアップ装置では、光源に赤色レーザーが用いられていたが、実施例５の対物レンズを含む光ピックアップ装置では青紫色レーザーが用いられている。その他、光ピックアップ装置の構成は、実施例４と同じである。本実施例にかかる対物レンズのデータを表５に示す。光源を第０面とし、第１面が絞り、第２、第３面が対物レンズ、第４面が光情報記録媒体の情報記録面を示す。尚、実施例５の対物レンズは、両面非球面のガラスレンズである。
【表５】

実施例５では、対物レンズに図１または図２に示した繋ぎ領域を設けていないが、それを設けても構わない。
【００８１】
（実施例６）
実施例６も、上記第１、第２の何れの実施の形態にも含まれない対物レンズに関する。実施例６の対物レンズを含む光ピックアップ装置では、対物レンズとして回折面を有する非球面プラスチックレンズが用いられており、その他の構成は、実施例４の対物レンズを含む光ピックアップ装置と同じである。実施例６における回折面とは次の通りである。
【００８２】
対物レンズの光源側非球面の表面には回折構造が一体で形成されている。この回折構造は、ブレーズ化波長（基準波長）λＢに対する光路差関数Фにより単位をｍｍとして数２で表される。ｈが光軸と垂直方向の距離、ｃ２ｉが光路差関数の係数である。この２次係数が回折構造の近軸的なパワーである。また２次以外の４次、６次係数等で球面収差を制御できる。ここで制御出来るとは、対物レンズの屈折部分が有する球面収差を、回折構造で逆特性の球面収差を持たせ、対物レンズトータルとして球面収差を補正したりすることを意味する。この場合、温度変化時の球面収差も、屈折部分の球面収差の温度変化と、回折構造の球面収差の温度変化とのトータルと考えることが出来る。
【数２】

【００８３】
本実施例にかかる対物レンズのデータを表６に示す。光源を第０面とし、第１面が絞り、第２、第３面が対物レンズ、第４面が光情報記録媒体の情報記録面である。
【表６】

尚、実施例６では、対物レンズに図１または図２に示した繋ぎ領域を設けていないが、それを設けても構わない。以上の実施例４〜６においては、開口数ＮＡが比較的大きいので、それに応じてｄ／ｆを大きくすることで、対物レンズの縁厚を確保している。
【００８４】
【発明の効果】
本発明によれば、開口数ＮＡの増大、光源波長の短波長化がなされた光ピックアップ装置においても、温度特性の優れた単玉対物レンズであって、像高特性とのバランスのとれた光学系全体をコンパクトとすることが可能な対物レンズ、その対物レンズを用いた光ピックアップ装置及び光情報記録再生装置を提供することができる。また本発明によれば、小径の対物レンズで、ふち厚を厚くして成形性を向上させた対物レンズ、その対物レンズを用いた光ピックアップ装置及び光情報記録再生装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の一例にかかる対物レンズの一部を示す断面図である。
【図２】本発明の別な例にかかる対物レンズの一部を示す断面図である。
【図３】本発明の実施の形態にかかる光ピックアップ装置の概略構成図である。
【図４】実施例１の対物レンズにおける像高特性を示すグラフである。
【図５】実施例１の対物レンズにおける温度特性を示すグラフである。
【図６】実施例２の対物レンズにおける像高特性を示すグラフである。
【図７】実施例２の対物レンズにおける温度特性を示すグラフである。
【図８】球面収差がアンダーかオーバーかを説明するための図である。
【符号の説明】
１赤色レーザー
２対物レンズ
３光情報記録媒体
４ビームスプリッタ
５検出器
６絞り[0001]
BACKGROUND OF THE INVENTION
The present invention performs recording and / or reproduction of an optical information recording medium by using an objective lens used in an optical pickup device, an optical pickup device and an optical information recording / reproducing apparatus, in particular, a single objective lens at a finite magnification. The present invention relates to an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device.
[0002]
[Prior art]
An optical pickup device capable of recording and reproducing information with high density on an optical information recording medium such as a DVD has been developed and used in various applications. In such an optical pickup device, there are various demands such as a compact configuration and reliability when the environmental temperature changes.
[0003]
By the way, in an optical pickup device, an objective lens that condenses information recording light on an information recording surface of an optical information recording medium is advantageous for mass production. However, it is known that the plastic material is about two orders of magnitude larger than the glass material in the temperature change of the refractive index.
[0004]
Here, when the environmental temperature of an optical pickup device having an objective lens formed of a plastic material rises and the refractive index of the objective lens changes, it is known that spherical aberration deteriorates as a condensing optical system. Yes. For example, in an optical pickup device for a current DVD, an objective lens made of a plastic material having a numerical aperture NA of 0.60 and an imaging magnification of m = 0 is widely used, but its focal length is 3 mm, and the refractive index of the plastic material. Even if the objective lens is designed so that there is no aberration when the refractive index of the plastic material at the light source wavelength λ = 650 nm is n = 1.53, the temperature change is dn / dT = −0.00012 (/ ° C.) When the temperature of the optical pickup device rises by 30 ° C. from room temperature, the refractive index of the objective lens becomes 1.5264, which causes a residual aberration of about 0.033λrms in calculation.
[0005]
In general, it is necessary to keep the entire optical system below the optical diffraction limit (Maretial limit value 0.07λrms), and there are various factors that cause aberrations in addition to the objective lens. Therefore, it can be said that it is first important to suppress as much as possible the aberration that occurs due to the environmental temperature change.
[0006]
The spherical aberration deterioration δSA / δT when the refractive index changes due to the environmental temperature change is expressed by the following equation.
δSA / δT∝f (1-m)⁴NA⁴・ (Dn / dT) / λ (26)
However, the focal length of the objective lens at an infinite object is f, the numerical aperture on the optical information recording medium side is NA, the wavelength of the light source is λ, and the amount of change in the refractive index of the objective lens when the temperature rises by 1 ° C. is dn / dT. Let the image magnification be m.
[0007]
[Problems to be solved by the invention]
In recent optical pickup devices that record or reproduce information on a high-density optical information recording medium such as a DVD, the numerical aperture NA tends to increase. In addition, in order to ensure the compactness of the optical pickup device, attempts have been made to use the optical pickup device at a finite magnification and to increase the finite degree. However, according to the equation (26), it can be understood that the spherical aberration deterioration becomes more remarkable as the numerical aperture NA of the objective lens increases and as the objective lens is used in the specification in which the finite degree of the optical system becomes stronger. For example, if f = 3 mm and m = 0 as described above and the numerical aperture NA is increased from 0.60 to 0.85, the aberration is deteriorated in proportion to the fourth power of NA, and the room temperature (for example, 25 ° C.) ), The estimated spherical aberration when the temperature rises by 30 ° C. is 0.12 λrms, which is expected to greatly exceed the Marechal limit. Furthermore, the use of a light source such as a blue laser developed in recent years can be expected to further increase the density of information. However, the light source wavelength λ is further shortened, and the problem of spherical aberration deterioration due to temperature changes is increasing. It can be said that it is in a stricter direction.
[0008]
Similarly, from the equation (26), it can be seen that spherical aberration deterioration with respect to temperature change can be suppressed to some extent by reducing the focal length f. For example, even if the numerical aperture is increased from NA 0.60 to NA 0.85, if the focal length is reduced to ¼, it is possible to obtain temperature characteristics equivalent to those before the numerical aperture is increased.
[0009]
However, if the focal length f is reduced, the image height characteristics are disadvantageous. This is because the angle of incidence on the objective lens increases when trying to obtain the same image height. Astigmatism and coma deteriorate as the incident angle increases. Therefore, it is preferable that the focal length is large in terms of image height characteristics.
[0010]
The present invention has been made in view of the above problems, and in an optical pickup device in which the numerical aperture NA is increased and the light source wavelength is shortened, a single objective lens having excellent temperature characteristics, It is an object of the present invention to provide an objective lens capable of making the entire optical system balanced with image height characteristics compact, an optical pickup apparatus using the objective lens, and an optical information recording / reproducing apparatus. Another object of the present invention is to provide an objective lens having a small-diameter objective lens that has an increased thickness and improved moldability, and an optical pickup device and an optical information recording / reproducing apparatus using the objective lens.
[0011]
[Means for Solving the Problems]
  The objective lens for an optical pickup device according to claim 1 records and / or reproduces information by imaging a light source of wavelength λ and a light beam from the light source on an optical information recording medium. An objective lens for an optical pickup device having the objective lens, wherein the objective lens isDoes not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C. , And the value of the imaging magnification m satisfy the following expressions,
  0.1 mm <f <1 mm (1)
  0.50 <NA <0.90 (2)
  350 nm <λ <850 nm (3)
  1/10 <| m | <1/3 (4)
  0.029 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.2 (5)
  When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.02 mm of the objective lens is δWheight,
  0.0λrms <δWtemp + δWheight <0.07λrms (6)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that.
[0012]
According to the objective lens of the first aspect, it is possible to suppress the deterioration of the spherical aberration with respect to the temperature change by reducing the focal length f in accordance with the increase of the numerical aperture NA and the shortening of the light source wavelength λ. However, if the focal length f is too small, the image height characteristics deteriorate. Therefore, by setting each value within a range that satisfies the expressions (1) to (6), the balance between the temperature characteristics and the image height characteristics can be reduced. It is possible to provide a superior objective lens. Furthermore, even if the numerical aperture NA is high, it is possible to obtain a finite magnification, whereby the light beam from the light source is condensed on the information recording surface of the optical information recording medium using the single objective lens. It is also possible to provide an optical pickup device having a compact and simple configuration.
[0013]
According to the objective lens for an optical pickup device according to claim 2, when the objective lens is made of a plastic material, the plastic material is lighter than a glass material. It is possible to increase the speed of the focusing operation to be moved. Further, since the plastic material is easy to be injection-molded, the objective lens can be mass-produced with a stable quality.
[0014]
According to the objective lens for an optical pickup device of the third aspect, it is preferable that the objective lens is composed of a double-sided aspheric surface. If it is constituted by a refracting surface, an objective lens resistant to chromatic aberration can be realized. In particular, when a material having a large dispersion value is used, it is possible to suppress the change in the paraxial image point position of the objective lens accompanying the mode hop of the light source.
[0015]
  According to the objective lens for an optical pickup device according to claim 4, in the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the refractive index of the objective lens when the temperature is increased by 1 ° C. The values of the change amount dn / dT and the imaging magnification m satisfy the following expressions, respectively.
  0.50 <NA <0.75 (7)
  450nm <λ <850nm (8)
  0.029 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.06 (9)
  If the numerical aperture NA is larger than 0.50 and the light source wavelength λ is smaller than 850 nm, it can correspond to a relatively high density optical information recording medium, while the numerical aperture NA is smaller than 0.75, and If the light source wavelength λ is larger than 450 nm, the deterioration of the spherical aberration with respect to the temperature change can be suppressed within the range shown in the equation (9).
[0016]
According to the objective lens for an optical pickup device according to claim 5, the axial thickness d of the objective lens is:
0.4 <d / f <1.5 (10)
It is characterized by satisfying. If the value d / f exceeds the lower limit value of the expression (10), the control of the image height characteristic becomes easy by design. On the other hand, if the value d / f falls below the upper limit value, the objective lens and the optical information recording medium are separated. It is possible to secure a sufficient working distance.
[0017]
  The objective lens for an optical pickup device according to claim 6,
  0.1 mm <f≦ 0.6mm (11)
It is characterized by satisfying.
[0018]
The objective lens according to claim 6 is finite even if the numerical aperture NA is higher and the spherical aberration is kept lower than that of the objective lens according to claim 1 while maintaining a balance between temperature characteristics and image height characteristics. An optical pickup device having a compact and simple configuration in which the light beam from the light source is condensed on the information recording surface of the optical information recording medium using the single objective lens. Can be provided.
[0019]
  The objective lens for an optical pickup device according to claim 7 records and / or reproduces information by imaging a light source of wavelength λ and a light beam from the light source on an optical information recording medium. An objective lens for an optical pickup device having the objective lens, wherein the objective lens isDoes not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the temperature at 1 ° C. The values of the objective lens refractive index change amount dn / dT and the imaging magnification m satisfy the following expressions, respectively:
  0.1 mm <f <1 mm (19)
  0.70 <NA <0.90 (20)
  350 nm <λ <850 nm (21)
  -1/5 <m <-1/10 (22)
  0.01 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (23)
  1.2 <d / f <1.7 (24)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
  0.0λrms <δWtemp + δWheight <0.07λrms (25)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that.
[0020]
The objective lens according to claim 7 is finite even if the numerical aperture NA is higher and the spherical aberration is kept lower than that of the objective lens according to claim 1 while maintaining a balance between temperature characteristics and image height characteristics. An optical pickup device having a compact and simple configuration in which the light beam from the light source is condensed on the information recording surface of the optical information recording medium using the single objective lens. Can be provided.
[0022]
As for “under spherical aberration or / over spherical aberration”, as shown in FIG. 8, in the spherical aberration with the paraxial image point position as the origin, the case where the optical axis intersects the optical axis on the near side of the paraxial image point. “Under” is defined as “over” when it intersects the optical axis at a position far from the paraxial image point.
[0023]
  Claim8The objective lens for an optical pickup device described in 1) satisfies the following expression.
  0.08 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (27)
[0024]
  still,When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
  0.3 <r1 / (n (1-m) f) <0.5 (28)
MeetThe effect will be described.The present invention particularly relates to a coma component of image height characteristics. By satisfying the equation (28), correction of a so-called sine condition as a condition for correcting coma aberration when a light beam is obliquely incident on the objective lens is facilitated.
[0025]
As apparent from the equation (28), in the objective lens, it is preferable to reduce the paraxial radius of curvature r1 on the light source side with a biconvex lens in terms of aberration correction. However, as a result, the change in the expected angle of the aspheric surface on the light source side increases toward the periphery, and this aspheric surface on the light source side is a major factor that limits the edge thickness. This will be specifically described.
[0026]
FIG. 1 is a cross-sectional view schematically showing a part of the objective lens of the present invention. Here, conventionally, the double-sided aspheric shape of the objective lens is extended to a position where it is connected to the flange portion of the objective lens. However, when the paraxial radius of curvature r1 is set to be small so as to satisfy the expression (28) as in the present invention described in claim 10, as shown by a dotted line in FIG. Since the angle formed by the tangent of the intersection P3 with the flange and the tangent of the flange at the intersection P3 increases, the flange thickness t1 tends to decrease. When the flange thickness t1 is reduced, there is a problem in that a molding defect is likely to occur due to a poor material flow when the objective lens is molded. According to the following invention, this problem can be solved or alleviated.
[0027]
  Claim9In the objective lens for an optical pickup device described in (1), the surface on the light source side of the objective lens has a position (here P1 shown in FIG. 1) where the outermost light beam (LB1 shown in FIG. 1) of the numerical aperture NA intersects. ), A connecting region (A shown in FIG. 1) is provided so that the edge of the objective lens becomes thick. According to this invention, the objective lens has a surface shape as shown by a solid line in FIG. 1, whereby the expected angle θ2 can be smaller than the conventional expected angle θ1, and the flange thickness t2 can be made thicker. The moldability of the objective lens can be improved. In addition, by optimizing the shape of the connection area, for example, by converting the light beam that has passed through the connection area into flare light that does not participate in image formation, an aperture effect can be provided.
[0028]
  Claim10In the objective lens for the optical pickup apparatus described in the above, the surface on the light source side of the objective lens has a position (here, P2 shown in FIG. 1) where the outermost ray (LB2 shown in FIG. 1) of the numerical aperture NA intersects. In the outer portion in the direction crossing the optical axis of), a connecting region (A shown in FIG. 1) is provided so that the edge of the objective lens becomes thicker. The light beam passing through the outer portion in the direction intersecting the optical axis at the position where the outermost rays of the numerical aperture NA intersect does not participate in image formation with respect to the information recording surface of the optical information recording medium. In the above, as in the invention described in claim 11, the connecting region may be formed directly from the position P1 where the outermost rays intersect to the outside. In practice, however, accuracy of parts, assembly error, etc. Thus, the position through which the outermost ray passes varies with respect to the design position. Therefore, as in the present invention, a connecting region where the edge of the objective lens becomes thicker is formed on the outer side in the direction intersecting the optical axis at the position (P2) where the outermost light beam (LB2) having the numerical aperture NA intersects. Thus, even when the intersecting position fluctuates, the light flux that passes through the inside of the position through which the outermost ray passes always participates in image formation, so that the amount of transmitted light can be efficiently secured.
[0029]
  Claim11The objective lens for an optical pickup device described in 1 is characterized in that the connecting region has a step in the optical axis direction. FIG. 2 is a sectional view similar to FIG. 1 showing a part of the objective lens of the present invention. In FIG. 2, the surface on the light source side of the objective lens on the outer side in the direction perpendicular to the optical axis from the position (here, P1 shown in FIG. 2) where the outermost light beam having the numerical aperture NA intersects (here, LB1 shown in FIG. 2). (That is, the connecting region) is a step (A ′ shown in FIG. 2) protruding toward the light source in the optical axis direction. By doing so, it is possible to secure a larger edge thickness t3 of the objective lens. In addition, by optimizing the shape of the step, for example, by converting the light beam that has passed through the step into flare light that does not participate in image formation, it is possible to provide a diaphragm effect. In such a case, the step may have a shape recessed toward the optical information recording medium in the optical axis direction, as indicated by a dotted line in FIG.
[0030]
  Claim12The objective lens for an optical pickup device described in the above item has a difference between an angle with respect to a surface orthogonal to the optical axis of the connecting region and an angle with respect to a surface orthogonal to the aspherical optical axis when the connecting region is not provided ( 1, the angle formed by the tangent to the lens surface within the effective diameter at the point P1 and the tangent of the connecting region at the point P3, that is, (θ1-θ2) is preferably within 20 degrees. Is too large, it is not preferable because the load on the tip portion of the tool at the time of mold processing becomes too large, and when the objective lens is molded as a separate member on the outside and inside of the connecting region, This is because burrs are generated in the lens surface, which is not preferable.
[0031]
  Claim13The optical pickup device described in 1 includes a light source having a wavelength λ and an objective lens configured to record and / or reproduce information by forming an image of a light beam from the light source on an optical information recording medium. In the optical pickup device, the objective lens isDoes not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C. , And the value of the imaging magnification m satisfy the following expressions,
  0.1 mm <f <1 mm (1)
  0.50 <NA <0.90 (2)
  350 nm <λ <850 nm (3)
  1/10 <| m | <1/3 (4)
  0.029 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.2 (5)
  When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.02 mm of the objective lens is δWheight,
  0.0λrms <δWtemp + δWheight <0.07λrms (6)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that. The optical pickup device of the present invention has the same effect as that of the first aspect of the invention.
[0032]
  Claim14In the optical pickup device described in (1), the objective lens is made of a plastic material. The optical pickup device of the present invention has the same effects as the invention of the second aspect.
[0033]
  Claim15In the optical pickup device described in (1), the objective lens is composed of a double-sided aspheric surface. The optical pickup device of the present invention has the same effects as the invention of the third aspect.
[0034]
  Claim16The optical pickup device described in 1) includes, in the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, the amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C., and imaging The value of the magnification m satisfies the following formula, respectively. The optical pickup device of the present invention has the same effects as the invention of the fourth aspect.
  0.50 <NA <0.75 (7)
  450nm <λ <850nm (8)
  0.0 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.06 (9)
[0035]
  The optical pickup device according to claim 17, wherein an on-axis thickness d of the objective lens is
  0.4 <d / f <1.5 (10)
It is characterized by satisfying. The optical pickup device of the present invention has the same effect as that of the fifth aspect of the invention.
[0036]
  The optical pickup device according to claim 18,
0.1mm <f ≦ 0.6mm (11)
It is characterized by satisfying.
[0037]
  Claim19The optical pickup device described in 1 includes a light source having a wavelength λ and an objective lens configured to record and / or reproduce information by forming an image of a light beam from the light source on an optical information recording medium. In the optical pickup device, the objective lens isDoes not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the temperature at 1 ° C. The values of the objective lens refractive index change amount dn / dT and the imaging magnification m satisfy the following expressions, respectively:
  0.1 mm <f <1 mm (19)
  0.70 <NA <0.90 (20)
  350 nm <λ <850 nm (21)
  -1/5 <m <-1/10 (22)
  0.01 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (23)
  1.2 <d / f <1.7 (24)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
  0.0λrms <δWtemp + δWheight <0.07λrms (25)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that. The optical pickup device of the present invention is as follows.7The same effects as those of the invention described in 1) are exhibited.
[0039]
  Claim20The optical pickup device described in (1) satisfies the following expression. The optical pickup device of the present invention is as follows.8The same effects as those of the invention described in 1) are exhibited.
0.08 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (27)
[0041]
  Claim21The surface of the objective lens on the light source side is such that the thickness of the objective lens becomes thicker outward from the optical axis from the position where the outermost ray of the numerical aperture NA intersects. A connection area is provided. The optical pickup device of the present invention is as follows.9The same effects as those of the invention described in 1) are exhibited.
[0042]
  Claim22The surface of the objective lens on the light source side is located on the outer edge of the objective lens further outside the position outside the optical axis than the position where the outermost rays of the numerical aperture NA intersect. It is characterized in that a connecting region that increases the thickness is provided. The optical pickup device of the present invention is as follows.10The same effects as those of the invention described in 1) are exhibited.
[0043]
  Claim23The optical pickup device described in 1 is characterized in that the connecting region has a step in the optical axis direction. The optical pickup device of the present invention is as follows.11The same effects as those of the invention described in 1) are exhibited.
[0044]
  Claim24In the optical pickup device according to the above, a difference between an angle of the connecting region with respect to a surface orthogonal to the optical axis and an angle with respect to a surface orthogonal to the aspherical optical axis when the connecting region is not provided is within 20 degrees. It is characterized by being. The optical pickup device of the present invention is as follows.12The same effects as those of the invention described in 1) are exhibited.
[0045]
  Claim25An optical information recording / reproducing apparatus described in (1), a light source having a wavelength λ, and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium; In the optical information recording / reproducing apparatus having the objective lens,Does not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C. , And the value of the imaging magnification m satisfy the following expressions,
  0.1 mm <f <1 mm (1)
  0.50 <NA <0.90 (2)
  350 nm <λ <850 nm (3)
  1/10 <| m | <1/3 (4)
  0.029 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.2 (5)
  When the aberration of the objective lens is δWtemp and the aberration of the objective lens at the image height Y = 0.02 mm is δWheight when the temperature of the optical information recording / reproducing apparatus is increased by 30 ° C. from room temperature,
  0.0λrms <δWtemp + δWheight <0.07λrms (6)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that. The optical information recording / reproducing apparatus of the present invention has the same effect as that of the first aspect of the present invention.
[0046]
  Claim26In the optical information recording / reproducing apparatus described in (1), the objective lens is made of a plastic material. The optical information recording / reproducing apparatus of the present invention has the same effects as the invention of the second aspect.
[0047]
  Claim27The optical information recording / reproducing apparatus described in 1) is characterized in that the objective lens is constituted by a double-sided aspheric surface. The optical information recording / reproducing apparatus of the present invention has the same effect as that of the third aspect of the present invention.
[0048]
  Claim28In the optical information recording / reproducing apparatus described in the above, in the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, the amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C., and The value of the imaging magnification m satisfies the following formula, respectively. The optical information recording / reproducing apparatus of the present invention has the same effects as the invention of the fourth aspect.
  0.50 <NA <0.75 (7)
  450nm <λ <850nm (8)
  0.0 <((1-m) NA)^Four.F. | Dn / dT | / λ <0.06 (9)
[0049]
  Claim29The optical information recording / reproducing apparatus described in the above item has an on-axis thickness d of the objective lens,
  0.4 <d / f <1.5 (10)
It is characterized by satisfying. The optical information recording / reproducing apparatus of the present invention has the same effect as that of the fifth aspect of the present invention.
[0050]
  Claim30The optical information recording / reproducing apparatus described in
  0.1 mm <f ≦ 0.6 mm (11)
It is characterized by satisfying.
[0051]
  Claim31An optical information recording / reproducing apparatus described in the above, a light source having a wavelength λ, and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium; In the optical information recording / reproducing apparatus having the objective lens,Does not have a diffractive structureA single lens, the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the temperature at 1 ° C. The values of the objective lens refractive index change amount dn / dT and the imaging magnification m satisfy the following expressions, respectively:
  0.1 mm <f <1 mm (19)
  0.70 <NA <0.90 (20)
  350 nm <λ <850 nm (21)
  -1/5 <m <-1/10 (22)
  0.01 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (23)
  1.2 <d / f <1.7 (24)
  When the aberration of the objective lens is δWtemp when the temperature of the entire optical information recording / reproducing apparatus is increased by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
  0.0λrms <δWtemp + δWheight <0.07λrms (25)
InThe
  When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
MeetIt is characterized by that. The optical information recording / reproducing apparatus of the present invention has the same effect as that of the seventh aspect of the invention.
[0053]
  Claim32The optical information recording / reproducing apparatus described in 1) satisfies the following expression. The optical information recording / reproducing apparatus of the present invention is as follows.8The same effects as those of the invention described in 1) are exhibited.
0.08 ≦ ((1-m) NA)^Four.F. | Dn / dT | / λ <0.11 (27)
[0055]
  Claim33In the optical information recording / reproducing apparatus according to the above, the surface of the objective lens on the light source side is thicker at the edge of the objective lens outward from the optical axis from the position where the outermost ray of the numerical aperture NA intersects. Such a connection region is provided. The optical information recording / reproducing apparatus of the present invention is as follows.9The same effects as those of the invention described in 1) are exhibited.
[0056]
  Claim34In the optical information recording / reproducing apparatus according to the above, the surface of the objective lens on the light source side is further outside the position outside the optical axis than the position where the outermost rays of the numerical aperture NA intersect. A connecting region is provided so that the thickness of the edge is increased. The optical information recording / reproducing apparatus of the present invention is as follows.10The same effects as those of the invention described in 1) are exhibited.
[0057]
  Claim35The optical information recording / reproducing apparatus described in (1) is characterized in that the connection region has a step in the optical axis direction. The optical information recording / reproducing apparatus of the present invention is as follows.11The same effects as those of the invention described in 1) are exhibited.
[0058]
  The optical information recording / reproducing apparatus according to claim 36, wherein a difference between an angle of the connecting region with respect to a surface orthogonal to the optical axis and an angle with respect to a surface orthogonal to the aspherical optical axis when the connecting region is not provided. Is within 20 degrees. The optical information recording / reproducing apparatus of the present invention is as follows.12The same effects as those of the invention described in 1) are exhibited.
[0059]
In this specification, the objective lens is, in a narrow sense, a light collecting action that is arranged to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. The lens which has. Therefore, in this specification, the numerical aperture NA on the optical information recording medium side (image side) of the objective lens refers to the numerical aperture NA of the lens surface closest to the optical information recording medium side of the objective lens. . Further, in this specification, the required numerical aperture NA is the numerical aperture specified by the standard of each optical information recording medium, or the information of the information depending on the wavelength of the light source used for each optical information recording medium. It is assumed that the numerical aperture of an objective lens having a diffraction limit performance capable of obtaining a spot diameter necessary for recording or reproduction is shown.
[0060]
The “diffractive structure” used in the present specification refers to a portion provided with a relief on the surface of the objective lens so as to condense or diverge a light beam by diffraction. As the shape of the relief, for example, the surface of the objective lens is formed as a substantially concentric annular zone centered on the optical axis, and each annular zone is shaped like a sawtooth if the cross section is viewed in a plane including the optical axis. Is known, but includes such a shape, and such a shape is particularly referred to as a “diffraction ring zone”.
[0061]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
(First embodiment)
A first embodiment will be described. FIG. 3 is a schematic configuration diagram of an optical pickup device (optical information recording / reproducing device) including the objective lens according to the present embodiment. This optical pickup device includes a red laser 1 as a light source having a wavelength λ, an objective lens 2, and an optical information recording medium 3. A beam splitter 4 exists between the red laser 1 and the objective lens 2, and deflects reflected light from the optical information recording medium 3 in the direction of the detector 5.
[0062]
A divergent light beam from the red laser 1 is incident on the objective lens 2, and the diameter of the light beam is limited by the diaphragm 6. Thus, by making the imaging magnification finite, the number of parts of the entire optical system can be reduced and a simple configuration can be achieved. The objective lens 2 is a double-sided aspheric surface and is made of a plastic material. In the present embodiment, the focal length is reduced in order to reduce the spherical aberration deterioration due to the temperature change of the plastic objective lens.
[0063]
However, the focal length f is determined in consideration of the balance with the image height characteristics. For off-axis correction, it is preferable to increase the on-axis thickness. When the axial thickness is increased, the edge of the objective lens 2 is increased, and even when the numerical aperture NA of the objective lens 2 is large, the possibility of crossing the plane is reduced, which is advantageous in optical design. In addition, it is more advantageous from the viewpoint of ensuring a working distance that the divergent light beam is incident on the objective lens 2 than the case where infinite light is incident.
[0064]
Further, the paraxial radius of curvature r1 (see FIG. 1) of the surface of the objective lens 2 on the light source side is set to 0.3 × (n (1-m) f) <r1 <0.5 × (n (1-m) f. ) Is preferable in order to satisfy the sine condition, and more preferably 0.36 × (n (1-m) f) <r1 <0.39 × (n (1-m) f). Good to do. If the sine condition is satisfied, off-axis coma aberration correction becomes easy.
[0065]
The present invention is not limited to the above embodiments (NA, λ, m, etc.). When a protective layer is present on the information recording surface as an optical information recording medium, the spherical aberration of the objective lens may be designed according to the thickness of the protective layer while satisfying the claims.
[0066]
(Second Embodiment)
A second embodiment will be described. In the present embodiment, the difference from the first embodiment shown in FIG. 3 is the surface shape processing outside the effective diameter of the surface on the light source side of the objective lens, and the description of the same configuration is omitted.
[0067]
When the focal length of the objective lens 2 is shortened, the absolute value of the paraxial radius of curvature r1 (FIG. 1) and the axial thickness are reduced. Accordingly, since the lens shapes are similar if the numerical aperture NA is the same, the edge thickness / axial thickness of the objective lens 2 is substantially the same, but the edge thickness becomes smaller as the focal length f becomes smaller in terms of absolute value. Become. As will be described later, in an objective lens with a numerical aperture NA of 0.60, if the axial thickness is 0.4 mm, the edge thickness is divided by 0.1 mm, and even if the plastic material has good fluidity, the objective lens The moldability of the deteriorates. Therefore, in order to increase the thickness as much as possible, an aspherical surface (or spherical surface) different from the effective diameter is formed outside the effective diameter (the diameter through which the outermost light beam passes). This is referred to as a connecting region (A in FIG. 1, A ′ in FIG. 2).
[0068]
From the outside of the effective diameter, it is possible to provide a connecting region immediately perpendicular to the optical axis in terms of mold processing. However, considering moldability, it is not preferable for the following reasons. That is, normally, when the objective lens is made by injection molding, the gate portion is provided outside the edge. At this time, the resin is injected from the gate portion into the effective diameter of the objective lens. However, considering the flow of the resin, if the change in the viscous resistance is large, the transfer property is uneven and the influence of birefringence or the like tends to occur.
[0069]
On the other hand, when the connecting region A as shown in FIG. 1 is provided, the influence of birefringence and the like is small in terms of molding, and the edge thickness t2 can be increased. Also, optically, since the surface power is weakened outside the connection region A, overflare occurs. In this case, the light beam that passes through the original numerical aperture on the surface of the optical information recording medium forms a light spot without using a stop, and the light beam that passes through the connecting region becomes a flare, which contributes little to imaging. Therefore, it is possible to achieve a desired spot shape and further simplify the optical system. The present invention is not limited to the above embodiment.
[0070]
Example 1
Example 1 relates to an objective lens applicable to the first embodiment. Table 1 shows lens data concerning the objective lens of Example 1. The light source is the 0th surface, the first and second surfaces are beam splitters, the third surface is a stop, the fourth and fifth surfaces are objective lenses, and the sixth surface is the information recording surface of the optical information recording medium. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10^-3) Is expressed using E (for example, 2.5 × E-3).
[Table 1]

[0071]
The objective lens of Example 1 is composed of a double-sided aspheric plastic lens, and each aspherical surface has an aspherical shape expressed by Formula 1.
[Expression 1]

Here, Z is an axis in the optical axis direction, h is an axis perpendicular to the optical axis, r is a paraxial radius of curvature, κ is a conical coefficient, A is an aspheric coefficient, and P is an aspheric power.
[0072]
The objective lens of Example 1 is made of a plastic material, and the refractive index change at the time of temperature change is dn / dT = −0.00012 (/ ° C.). The residual spherical aberration when the temperature rises from room temperature (25 ° C.) to 30 ° C. is 0.024 λrms, and the residual aberration at an image height of 0.02 mm is 0.031 λrms. Since the track pitch in the DVD is about 0.74 μm, it can be seen that the objective lens has a margin up to the diffraction limit in terms of image height characteristics and temperature change. From these facts, it can be understood that even if a plastic material is used for the objective lens, the objective lens has a balance between temperature characteristics and image height characteristics. FIG. 4 is a graph showing image height characteristics of the objective lens of Example 1, and FIG. 5 is a graph showing temperature characteristics of the objective lens of Example 1. In FIG.
[0073]
(Example 2)
Example 2 also relates to an objective lens applicable to the first embodiment. The difference from the first embodiment is that the specs of the objective lens are different, the configuration as the optical pickup device is the same, and the description of the same portion is omitted.
[0074]
Table 2 shows lens data relating to the objective lens of Example 1. The light source is the 0th surface, the first and second surfaces are beam splitters, the third surface is a stop, the fourth and fifth surfaces are objective lenses, and the sixth surface is the information recording surface of the optical information recording medium.
[Table 2]

[0075]
The objective lens of Example 2 is composed of a double-sided aspheric plastic lens. The numerical aperture NA is 0.72, which is larger than that of the first embodiment. However, by optimizing the setting of the wavelength used, the focal length, and the magnification, the temperature is higher than that of the conventional DVD objective lens with f = 3 mm. It became possible to improve the characteristics.
[0076]
For off-axis correction, the paraxial radius of curvature of the first surface was determined so as to satisfy the on-axis thickness of the objective lens and the sine condition. As shown in Table 2, it can be seen that the objective lens has a margin up to the diffraction limit both in terms of image height characteristics and temperature change. From these facts, it can be understood that, similarly to the first embodiment, even if a plastic material is used for the objective lens, the objective lens has a balanced temperature characteristic and image height characteristic. FIG. 6 is a graph showing image height characteristics of the objective lens of Example 2, and FIG. 7 is a graph showing temperature characteristics of the objective lens of Example 2. In FIG. The characteristics shown in FIGS. 6 and 7 also apply to the objective lens of Example 3 below.
[0077]
(Example 3)
Example 3 relates to an objective lens applicable to the second embodiment. The objective lens of Example 3 was the same as the objective lens of Example 2 within the effective diameter. Table 3 shows lens data. The surface of the objective lens on the light source side is another aspherical surface with the connecting region as a boundary. The aspherical surface of the connection area is defined as the 4 'surface. The outermost ray having a numerical aperture NA = 0.60 passes through the fourth surface at a position 0.50.5 mm from the optical axis.
[Table 3]

[0078]
Consider a case where the lens surface is provided at a position 0.6 mm from the optical axis. In the case where the same aspherical surface as the fourth surface is provided between the position of 0.5129 mm and the position of 0.6 mm from the optical axis, and in the case where a connecting region such as the 4 ′ surface is provided, the latter is preferred. About 0.048mm edge becomes thick. Although the absolute value of the increase amount is small, the original edge thickness is about 0.1 mm, so the increase rate is about 50%, and the effect is remarkable. Although the 4 'surface is an aspherical surface, it is possible to secure the edge thickness with little influence of birefringence on molding even if the shape is straight in the cross-sectional view.
[0079]
(Example 4)
Example 4 relates to an objective lens that is not included in any of the first and second embodiments. The optical pickup device (optical information recording / reproducing device) including the objective lens has a red laser, an objective lens, and a detector as a light source having a wavelength λ, and a light beam from the light source on the information recording surface of the optical information recording medium. And the reflected light is detected by a detector. The divergent light beam emitted from the light source has its light beam diameter limited by the stop, passes through the objective lens, and is then condensed on the information recording surface of the optical information recording medium. Table 4 shows data of objective lenses applicable to such an optical pickup device. The light source is the 0th surface, the first surface is a stop, the second and third surfaces are objective lenses, and the fourth surface is the information recording surface of the optical information recording medium. The objective lens of Example 4 is a double-sided aspheric glass lens.
[Table 4]

In the fourth embodiment, the connection region shown in FIG. 1 or 2 is not provided in the objective lens, but it may be provided.
[0080]
(Example 5)
Example 5 also relates to an objective lens that is not included in any of the first and second embodiments. In the optical pickup device including the objective lens according to the fourth embodiment, a red laser is used as the light source. However, in the optical pickup device including the objective lens according to the fifth embodiment, a blue-violet laser is used. In addition, the configuration of the optical pickup device is the same as that of the fourth embodiment. Table 5 shows data of the objective lens according to this example. The light source is the 0th surface, the first surface is the stop, the second and third surfaces are the objective lens, and the fourth surface is the information recording surface of the optical information recording medium. The objective lens of Example 5 is a double-sided aspheric glass lens.
[Table 5]

In the fifth embodiment, the connection region shown in FIG. 1 or 2 is not provided in the objective lens, but it may be provided.
[0081]
(Example 6)
Example 6 also relates to an objective lens that is not included in any of the first and second embodiments. In the optical pickup device including the objective lens according to the sixth embodiment, an aspheric plastic lens having a diffractive surface is used as the objective lens, and other configurations are the same as those of the optical pickup device including the objective lens according to the fourth embodiment. . The diffraction surface in Example 6 is as follows.
[0082]
A diffractive structure is integrally formed on the light source side aspheric surface of the objective lens. This diffractive structure is expressed by the following equation (2) where the unit is mm by the optical path difference function Ф with respect to the blazed wavelength (reference wavelength) λB. h is a distance in a direction perpendicular to the optical axis, and c2i is a coefficient of an optical path difference function. This second order coefficient is the paraxial power of the diffractive structure. Further, spherical aberration can be controlled by a fourth-order or sixth-order coefficient other than the second order. Controllable here means that the spherical aberration of the refractive part of the objective lens is given a spherical aberration having a reverse characteristic with a diffractive structure, and the spherical aberration is corrected as a total objective lens. In this case, the spherical aberration at the time of temperature change can also be considered as the total of the temperature change of the spherical aberration of the refractive part and the temperature change of the spherical aberration of the diffractive structure.
[Expression 2]

[0083]
Table 6 shows data of the objective lens according to this example. The light source is the 0th surface, the first surface is the stop, the second and third surfaces are the objective lens, and the fourth surface is the information recording surface of the optical information recording medium.
[Table 6]

In Example 6, the objective lens is not provided with the connecting region shown in FIG. 1 or FIG. 2, but it may be provided. In Examples 4 to 6 described above, since the numerical aperture NA is relatively large, the edge thickness of the objective lens is secured by increasing d / f accordingly.
[0084]
【The invention's effect】
According to the present invention, even in an optical pickup device in which the numerical aperture NA is increased and the light source wavelength is shortened, a single objective lens having excellent temperature characteristics, which is optically balanced with image height characteristics. An objective lens capable of making the entire system compact, an optical pickup device using the objective lens, and an optical information recording / reproducing apparatus can be provided. In addition, according to the present invention, it is possible to provide an objective lens having a small-diameter objective lens that has an increased thickness and improved moldability, and an optical pickup device and an optical information recording / reproducing apparatus using the objective lens.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a part of an objective lens according to an example of the present invention.
FIG. 2 is a cross-sectional view showing a part of an objective lens according to another example of the present invention.
FIG. 3 is a schematic configuration diagram of an optical pickup device according to an embodiment of the present invention.
4 is a graph showing image height characteristics of the objective lens of Example 1. FIG.
5 is a graph showing temperature characteristics of the objective lens of Example 1. FIG.
6 is a graph showing image height characteristics in the objective lens of Example 2. FIG.
7 is a graph showing temperature characteristics of the objective lens of Example 2. FIG.
FIG. 8 is a diagram for explaining whether spherical aberration is under or over.
[Explanation of symbols]
1 Red laser
2 Objective lens
3 Optical information recording media
4 Beam splitter
5 Detector
6 Aperture

Claims

An objective lens for an optical pickup apparatus, comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by forming an image of a light beam from the light source on an optical information recording medium The objective lens is a single lens having no diffractive structure, and the focal length f of the objective lens at an infinite object, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the temperature at 1 ° C. rise. The values of the objective lens refractive index change amount dn / dT and the imaging magnification m satisfy the following expressions, respectively:
0.1 mm <f <1 mm (1)
0.50 <NA <0.90 (2)
350 nm <λ <850 nm (3)
1/10 <| m | <1/3 (4)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.2 (5)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.02 mm of the objective lens is δWheight,
0.0λrms <δWtemp + δWheight <0.07λrms (6)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An objective lens for the optical pickup device characterized by satisfying.

The objective lens for an optical pickup device according to claim 1, wherein the objective lens is made of a plastic material.

The objective lens for an optical pickup device according to claim 1, wherein the objective lens is formed of a double-sided aspheric surface.

In the objective lens, values of the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, the amount of change dn / dT in the objective lens refractive index when the temperature rises by 1 ° C., and the imaging magnification m are as follows: The objective lens for an optical pickup device according to claim 1, wherein the objective lens is satisfied.
0.50 <NA <0.75 (7)
450nm <λ <850nm (8)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.06 (9)

The axial thickness d of the objective lens is
0.4 <d / f <1.5 (10)
5. The objective lens for an optical pickup device according to claim 1, wherein:

0.1 mm <f ≦ 0.6 mm (11)
The objective lens for an optical pickup device according to claim 1, wherein:

An objective lens for an optical pickup device, comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by forming an image of a light beam from the light source on an optical information recording medium The objective lens is a single lens without a diffractive structure , the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the light source The value of the objective lens refractive index change dn / dT when the temperature rises by 1 ° C. and the imaging magnification m satisfy the following expressions, respectively:
0.1 mm <f <1 mm (19)
0.70 <NA <0.90 (20)
350 nm <λ <850 nm (21)
-1/5 <m <-1/10 (22)
0.01 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (23)
1.2 <d / f <1.7 (24)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
0.0λrms <δWtemp + δWheight <0.07λrms (25)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An objective lens for the optical pickup device characterized by satisfying.

The objective lens for an optical pickup device according to claim 7 , wherein the following expression is satisfied.
0.08 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (27)

The surface on the light source side of the objective lens is provided with a connecting region that increases the thickness of the objective lens on the outer side with respect to the optical axis from the position where the outermost rays of the numerical aperture NA intersect. An objective lens for an optical pickup device according to any one of claims 1 to 8 .

The surface on the light source side of the objective lens is a connecting region where the thickness of the objective lens is thicker on the outer side of the position outside the optical axis than the position where the outermost rays of the numerical aperture NA intersect. the objective lens for the optical pickup device written in any one of claims 1 to 9, characterized in that provided.

The objective lens for an optical pickup device according to claim 9 or 10 , wherein the connection region has a step in the optical axis direction.

The difference between an angle with respect to a surface orthogonal to the optical axis of the connecting region and an angle with respect to a surface orthogonal to the optical axis of the aspherical shape when the connecting region is not provided is within 20 degrees. An objective lens for an optical pickup device according to any one of 9 to 11 .

In the optical pickup device, comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium. Is a single lens without a diffractive structure , the focal length f of the objective lens at an infinite object, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, and the refractive index of the objective lens when the temperature rises by 1 ° C. The change amount dn / dT and the imaging magnification m satisfy the following expressions respectively:
0.1 mm <f <1 mm (1)
0.50 <NA <0.90 (2)
350 nm <λ <850 nm (3)
1/10 <| m | <1/3 (4)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.2 (5)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.02 mm of the objective lens is δWheight,
0.0λrms <δWtemp + δWheight <0.07λrms (6)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An optical pickup device satisfying the requirements .

The optical pickup device according to claim 13 , wherein the objective lens is made of a plastic material.

The optical pickup device according to claim 13 or 14 , wherein the objective lens is constituted by a double-sided aspheric surface.

In the objective lens, values of the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, the amount of change dn / dT in the objective lens refractive index when the temperature rises by 1 ° C., and the imaging magnification m are as follows: the optical pickup device according to any one of claims 13 to 15, characterized by satisfying the equation.
0.50 <NA <0.75 (7)
450nm <λ <850nm (8)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.06 (9)

The axial thickness d of the objective lens is
0.4 <d / f <1.5 (10)
The optical pickup device according to any one of claims 13 to 16, characterized in that meet.

0.1 mm <f ≦ 0.6 mm (11)
The optical pickup device according to any one of claims 13 to 17, characterized in that meet.

In the optical pickup device, comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium. Is a single lens having no diffractive structure , the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, The amount of change dn / dT in the refractive index of the objective lens when the temperature rises by 1 ° C. and the value of the imaging magnification m satisfy the following expressions, respectively:
0.1 mm <f <1 mm (19)
0.70 <NA <0.90 (20)
350 nm <λ <850 nm (21)
-1/5 <m <-1/10 (22)
0.01 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (23)
1.2 <d / f <1.7 (24)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical pickup device is raised by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
0.0λrms <δWtemp + δWheight <0.07λrms (25)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An optical pickup device satisfying the requirements .

The optical pickup device according to claim 19 , wherein the following expression is satisfied.
0.08 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (27)

The surface on the light source side of the objective lens is provided with a connecting region that increases the thickness of the objective lens on the outer side with respect to the optical axis from the position where the outermost rays of the numerical aperture NA intersect. the optical pickup device according to any one of claims 13 to 20,.

The surface on the light source side of the objective lens is a connecting region where the thickness of the objective lens is thicker on the outer side of the position outside the optical axis than the position where the outermost rays of the numerical aperture NA intersect. the optical pickup device according to any one of claims 13 to 21, characterized in that the provided.

The optical pickup device according to claim 21 or 22 , wherein the connection region has a step in the optical axis direction.

The difference between an angle with respect to a surface orthogonal to the optical axis of the connecting region and an angle with respect to a surface orthogonal to the optical axis of the aspherical shape when the connecting region is not provided is within 20 degrees. The optical pickup device according to any one of 21 to 23 .

An optical information recording / reproducing apparatus comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium. The objective lens is a single lens that does not have a diffractive structure, and the objective lens has a focal length f at an infinite object, a numerical aperture NA on the optical information recording medium side, a wavelength λ of the light source, and a temperature of 1 ° C. The values of the refractive index change amount dn / dT and the imaging magnification m satisfy the following equations, respectively.
0.1 mm <f <1 mm (1)
0.50 <NA <0.90 (2)
350 nm <λ <850 nm (3)
1/10 <| m | <1/3 (4)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.2 (5)
When the aberration of the objective lens is δWtemp and the aberration of the objective lens at the image height Y = 0.02 mm is δWheight when the temperature of the optical information recording / reproducing apparatus is increased by 30 ° C. from room temperature,
0.0λrms <δWtemp + δWheight <0.07λrms (6)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An optical information recording / reproducing apparatus characterized by satisfying the above.

The optical information recording / reproducing apparatus according to claim 25 , wherein the objective lens is made of a plastic material.

The objective lens optical information recording reproducing apparatus according to claim 25 or 26, characterized in that it is constituted by a bi-aspherical.

In the objective lens, values of the numerical aperture NA on the optical information recording medium side, the wavelength λ of the light source, the amount of change dn / dT in the objective lens refractive index when the temperature rises by 1 ° C., and the imaging magnification m are as follows: The optical information recording / reproducing apparatus according to any one of claims 25 to 27 , wherein:
0.50 <NA <0.75 (7)
450nm <λ <850nm (8)
0.029 <((1-m) NA) ⁴ · f · | dn / dT | / λ <0.06 (9)

The axial thickness d of the objective lens is
0.4 <d / f <1.5 (10)
The optical information recording reproducing apparatus according to any one of claims 25 to 28, characterized in that meet.

0.1 mm <f ≦ 0.6 mm (11)
The optical information recording reproducing apparatus according to any one of claims 25 to 29, characterized in that meet.

An optical information recording / reproducing apparatus comprising: a light source having a wavelength λ; and an objective lens configured to record and / or reproduce information by imaging a light beam from the light source on an optical information recording medium. The objective lens is a single lens having no diffractive structure , the focal length f of the objective lens at an infinite object, the axial thickness d of the objective lens, the numerical aperture NA on the optical information recording medium side, the wavelength of the light source The values of λ, the objective lens refractive index change dn / dT when the temperature rises by 1 ° C., and the imaging magnification m satisfy the following expressions, respectively:
0.1 mm <f <1 mm (19)
0.70 <NA <0.90 (20)
350 nm <λ <850 nm (21)
-1/5 <m <-1/10 (22)
0.01 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (23)
1.2 <d / f <1.7 (24)
When the aberration of the objective lens is δWtemp when the temperature of the entire optical information recording / reproducing apparatus is increased by 30 ° C. from room temperature, and the aberration at the image height Y = 0.002 mm of the objective lens is δWheight,
0.0λrms <δWtemp + δWheight <0.07λrms (25)
Der is,
When the paraxial radius of curvature of the light source side surface of the objective lens is r1, and the refractive index at the wavelength λ of the objective lens is n,
0.3 < r1 / (n (1-m) f) < 0.5 (28)
An optical information recording / reproducing apparatus characterized by satisfying the above.

32. The optical information recording / reproducing apparatus according to claim 31 , wherein the following expression is satisfied.
0.08 ≦ ((1-m) NA) ⁴ · f · | dn / dT | / λ <0.11 (27)

The surface on the light source side of the objective lens is provided with a connecting region that increases the thickness of the objective lens on the outer side with respect to the optical axis from the position where the outermost rays of the numerical aperture NA intersect. the optical information recording reproducing apparatus according to any one of claims 25 to 32 and.

The surface on the light source side of the objective lens is a connecting region where the thickness of the objective lens is thicker on the outer side of the position outside the optical axis than the position where the outermost rays of the numerical aperture NA intersect. 34. The optical information recording / reproducing apparatus according to any one of claims 25 to 33 , wherein:

35. The optical information recording / reproducing apparatus according to claim 33 or 34 , wherein the connection region has a step in the optical axis direction.

The difference between an angle with respect to a surface orthogonal to the optical axis of the connecting region and an angle with respect to a surface orthogonal to the optical axis of the aspherical shape when the connecting region is not provided is within 20 degrees. 36. The optical information recording / reproducing apparatus according to any one of 33 to 35 .