JP3670682B2

JP3670682B2 - Manufacturing method of gradient index optical element

Info

Publication number: JP3670682B2
Application number: JP16627894A
Authority: JP
Inventors: 博章木下
Original assignee: Olympus Corp
Current assignee: Olympus Corp
Priority date: 1994-06-24
Filing date: 1994-06-24
Publication date: 2005-07-13
Anticipated expiration: 2020-07-13
Also published as: JPH0812343A

Description

【０００１】
【産業上の利用分野】
本発明は、カメラ、顕微鏡などの光学素子に応用可能な屈折率分布型光学素子の製造方法に関する。
【０００２】
【従来の技術】
屈折率分布型光学素子は、媒質に屈折率分布を付与することによって、媒質自体にパワー（屈折力）を持たせたものであり、優れた収差補正能力を持つために、レンズの構成枚数を減らすことができ、次世代の光学系に欠くことのできない光学素子として注目されている。
一般に、屈折率分布を有する屈折率分布型光学素子の製造方法としては、ゾルゲル法、イオン交換法、分子スタッフィング法等が用いられている。特に、ゾルゲル法は、大口径のガラス体が得られること、多価金属の酸化物に分布を持たせることが可能であり、得られる屈折率分布型光学素子の光学特性にバリエーションを持たせることができるなどの特徴を持つため、注目されている。
【０００３】
特公平５ー２７５７５号公報には、次のような方法が開示されている。シリコンのアルコキシドと金属塩Ａを主体とする溶液を加水分解して得られるゾルをゲル化させ、金属塩Ａの溶解度の低い溶液に浸漬してゲル中に金属塩Ａの微結晶を析出させる。このゲルを、前記金属塩Ａとは異なる金属塩Ｂを含む溶液に浸漬する。すると、溶液中に含まれる金属塩Ｂがゲルの表面から内部にむけて次第に拡散していく。この際所定の時間経過後であれば、ゲルの径方向に対して金属塩Ｂの濃度がゲルの中心部で低く、外周部で高い、いわゆる凹分布となる。これとは反対に、ゲル中に含まれる金属塩Ａの微結晶は、表面から外部にむけて次第に溶出するので、金属塩Ａの濃度がゲルの中心部で高く、外周部で低い、いわゆる凸分布となる。このゲルを乾燥・焼成することにより、中心部から外周部に向かって屈折率が減少する屈折率分布型光学素子を得ることができる。
また、特開平４−２６０６０９号公報には、分布付与を複数回行うことで屈折率差を大きくする方法が開示されている。
さらに、特開平５−２３８７５７号公報には、相対的に溶解度の低い第１の金属イオンと、高い第２の金属イオンに関して、第２の金属イオンは溶解するが第１の金属イオンは溶解しない溶液にゲルを浸漬して、第１イオンの固定と第２イオンの分布を行うという、溶解度の低い金属塩から順次分布付与・固定して、分布の多重化を行う方法が開示されている。
【０００４】
【発明が解決しようとする課題】
特公平５ー２７５７５号公報や特開平４−２６０６０９号公報記載の方法により分布付与を行った場合、金属種Ａの塩を含む円柱状のゲルを金属種Ｂの塩を含む分布付与溶液に浸漬すると、分布付与時における金属種Ａ、Ｂそれぞれの径方向の濃度分布の形成は拡散則に従うと考えられる。つまり、金属種Ａ濃度の高いゲル中から、金属種Ａ濃度の低い分布付与液中への金属イオンＡの拡散となり、逆に分布付与溶液中の金属種Ｂは、金属種Ｂ濃度の高い溶液中から金属種Ｂ濃度の低いゲル中へ拡散する。したがって、中心部から外周部へ向かっての濃度勾配は、金属種Ａが単調減少、金属種Ｂが単調増加と相関関係を持って拡散をすると考えられる。
【０００５】
しかし、実際には金属塩の種類によってはこの関係が崩れる場合がある。その一例として、酢酸バリウム（金属種がバリウム）を含んだシリカゲルを、酢酸カリウム（金属種がカリウム）をメタノールに溶解した溶液に浸漬して分布付与を行った場合について述べる。
屈折率への寄与が大きいバリウムの濃度が、ゲルの中心部から外周部に向かって減少する、いわゆる凸分布を付与することで屈折率分布型光学素子を得る時、バリウムの濃度分布にともない、ゲルの径方向に熱膨張の分布が付くため、ゲルを焼成すると応力のかかり方が一様でなくなり、割れを生じる。この割れを回避するために、屈折率への寄与が少なく熱膨張への寄与の大きなカリウムにバリウムと反対の分布を付与するが、バリウムの溶出速度がカリウムの浸入速度に比べ著しく遅いため、図１０に示すように、バリウムに所望の凸状の金属濃度分布ａを付与しようとすると、カリウムが所望の凹分布を持つ金属濃度分布ｂではなく、ゲル中に大量にしかもフラットに導入されて金属濃度分布ｃのようになってしまう。したがって、このゲルを焼成しようとしても、上述した熱膨張の分布によって割れを生じてしまった。
【０００６】
特に、ガラス中に含まれるアルカリ金属成分（上記説明中では、カリウム）が多くなると、仮に焼成時に割れなかったとしても別の問題が生じた。すなわち、アルカリ金属成分が多くなると、製造されたガラスの熱膨張係数が大きくなるため、熱衝撃に弱くなったり、耐酸性や耐水性が著しく悪くなるので、ガラスの使用範囲が限られるという問題があった。
【０００７】
つまり、ゲル中の金属種Ａの分布溶液中への溶出速度が、分布溶液中の金属種Ｂのゲル中への拡散速度に対して相対的に遅い場合、ゲル中の金属種Ａに凸、金属種Ｂに凹の所望の金属濃度分布を付与しようとすると、従来の技術では分布溶液中の金属種Ｂがゲル中に大量に拡散してしまうため、所望の金属濃度分布が得られないという問題点を有していた。
【０００８】
また、これとは逆に、ゲル中の金属種Ａの分布溶液中への溶出速度が、分布溶液中の金属種Ｂのゲル中への拡散速度に対して相対的に速い場合、ゲル中の金属種Ａに凸、金属種Ｂに凹の所望の金属濃度分布を付与しようとすると、分布溶液中の金属種Ａが溶液中に大量に溶解してしまうため、所望の金属濃度分布が得られないという問題点を有していた。
【０００９】
一方、特開平５−２３８７５７号公報記載の方法により分布付与を行おうとしても、金属塩の種類によって適当な溶解度を持つ溶媒の選定が難しく、かつ工程が多いために時間がかかり、実際の屈折率分布型光学素子の製造方法としてはコストが高くなるなどの問題点を有していた。
【００１０】
また、ゲル中に含まれる金属種Ａの種類によっては、分布付与溶液中に含まれる酸の濃度がある程度以上高くないと、金属種Ａのゲルからの溶出が起こらない場合があった。この場合、金属種Ａを含有したゲルを一度比較的高濃度の酸を含む分布付与溶液に浸漬しなければならなかった。この工程により、金属種Ａには所望の濃度分布を付与することが可能となるが、ゲルを酸濃度の高い溶液に長時間浸漬すると、酸やアルカリが特にゲルの表面においてシリカ骨格を破壊するため、表面があれてぼろぼろになったり、亀裂が生じるという問題点があった。
【００１１】
本発明は、かかる従来の問題点に鑑みてなされたもので、所望の金属濃度分布を有する屈折率分布型光学素子の製法に関するもので、酸やアルカリによるゲル骨格への影響を抑制でき、焼結時に割れがない屈折率分布型光学素子を得ることができ、かつこれにより所望の光学特性、および、適切な耐熱衝撃性、耐酸性、耐アルカリ性を持たせることができる屈折率分布型光学素子の製造方法を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上記課題を解決するために、本発明の屈折率分布型光学素子の製造方法は、
ゾルゲル法により作製したゲルを濃度分布付与液に浸漬してゲル内に金属成分の濃度分布を付与する分布付与工程の後に前記濃度分布を固定し、乾燥、焼成する屈折率分布型光学素子の製造方法であって、前記濃度分布付与液が、有機溶媒もしくは水から選ばれた溶媒または前記溶媒の混合溶媒に、前記金属成分を溶解した金属成分溶解溶液であり、前記分布付与工程で、前記ゲルを前記金属成分溶解溶液に浸漬した状態で該金属成分溶解溶液の金属成分の濃度を変化する工程を有することを特徴とする。
前記濃度分布付与液は、前記金属成分溶解溶液にさらに酸を溶解した金属成分溶解溶液であることを特徴とする。
前記金属成分の濃度を変化する工程は、前記分布付与工程で複数回連続的に行うことを特徴とする。
前記金属成分の濃度を変化する工程は、金属成分の濃度を徐々に高くすることを特徴とする。
前記金属成分の濃度を変化する工程は、金属成分の濃度を徐々に低くすることを特徴とする。
また、本発明の屈折率分布型光学素子の製造方法は、ゾルゲル法により作製したゲルを濃度分布付与液に浸漬してゲル内に金属成分の濃度分布を付与する分布付与工程の後に前記濃度分布を固定し、乾燥、焼成する屈折率分布型光学素子の製造方法であって、前記濃度分布付与液が、有機溶媒もしくは水から選ばれた溶媒または前記溶媒の混合溶媒に、前記金属成分を溶解した金属成分溶解溶液であり、前記分布付与工程が少なくとも第１の分布付与工程と第２の分布付与工程からなり、前記第１および第２の分布付与工程で用いる濃度分布付与液の溶媒と金属成分を同じにして該第１および第２の分布付与工程を順次行い、かつ、前記第１の分布付与工程の濃度分布付与液の金属成分の濃度と、前記第２の分布付与工程の濃度分布付与液の金属成分の濃度とを異ならせ、前記第２の分布付与工程の濃度分布付与液の金属成分の濃度を、前記第１の分布付与工程の実施中の濃度分布付与液に対し、該実施中の濃度分布付与液の金属成分の濃度と異なる濃度分布付与液を加えて異ならせることを特徴とする。
前記濃度分布付与液は、前記金属成分溶解溶液にさらに酸を溶解した金属成分溶解溶液であることを特徴とする。
前記第１の分布付与工程で用いる濃度分布付与液と前記第２の分布付与工程で用いる濃度分布付与液のそれぞれの金属成分の濃度を変えて、それぞれの濃度分布付与液を準備し、それぞれの濃度分布付与液に前記ゲルを浸漬することにより、前記金属成分の濃度を異ならせることを特徴とする。
前記第１の分布付与工程の濃度分布付与液の金属成分の濃度に対し、前記第２の分布付与工程の濃度分布付与液の金属成分の濃度を高くして、濃度を異ならせることを特徴とする。
前記第１の分布付与工程の濃度分布付与液の金属成分の濃度に対し、前記第２の分布付与工程の濃度分布付与液の金属成分の濃度を低くして、濃度を異ならせることを特徴とする。更に、前記金属成分がアルカリ金属を含むことを特徴とする。
【００１３】
【作用】
本発明の作用について、前述したバリウムとカリウムに金属濃度分布を付与する工程においてカリウムが多量にしかもフラットに入ってしまうという問題点を、本発明の分布溶液の金属塩濃度を連続的に増加させる工程により解決した例をもとに説明する。
分布溶液中のカリウム濃度変化プログラムと、ゲルの金属成分濃度の概念図をそれぞれ図２と、図１に示す。ここで、図２中の領域Ｃ、Ｄにおけるゲルの金属濃度分布の概念図はそれぞれ図１（ｂ）、（ｃ）に対応する。図１（ａ）の金属濃度を持ったゲルを、図２に示したように、分布溶液中のカリウム濃度を時間とともに増加させる分布付与溶液に浸漬する。最初は比較的カリウム濃度の低い分布付与溶液を調製しておいて、ゲルを浸漬する。次に、分布付与溶液中のカリウム濃度を徐々に高くしてゆく。この工程において、ゲル中の金属濃度は次のように変化すると考えられる。
【００１４】
初めに、カリウム濃度の低い領域（図２中のＣ領域）で比較的長時間ゲルを浸漬し、バリウムを放物線状になるようにある程度溶出させる。バリウムに適当な濃度分布を付与する時間だけゲルを浸漬すると、カリウムの拡散速度は速いので既にゲルの中心部分まで拡散しきっており、飽和するので溶液とほぼ同じ濃度となり、所望のカリウム濃度より少量ゲル中にフラットに存在する。この時のゲルの金属濃度分布の概念図を図１（ｂ）に示す。
【００１５】
次に、カリウム濃度を段々高くしてゆき、カリウム濃度の高い領域（図２中のＤ領域）で比較的短時間ゲルを浸漬する。この時のゲルの金属濃度分布の概念図を図１（ｃ）に示す。バリウムは更に少量溶出するが、短時間であるのでバリウムの分布はほとんど崩れない。一方、カリウムは溶液中の方がゲル中に比べて高濃度であるためゲルに速やかに拡散してゆき、カリウムに凹分布を付与することができる。つまり、これらの工程を経ることで所望の分布を得ることができるわけである。
【００１６】
一方、上記分布付与方法以外に、以下に述べる方法によっても所望の分布を得ることができる。バリウムの微結晶を固定したゲルを、所望のカリウム濃度より低い分布付与溶液に浸漬すると、バリウムがある程度溶出され、カリウムが所望のカリウム濃度より少量ゲル中にフラットに拡散する。次に、前記溶液よりカリウム濃度が高い溶液を調製しておき、この溶液に比較的短時間ゲルを浸漬する。バリウムは更に溶出し、カリウムは溶液中の方がゲル中に比べて高濃度であるためゲルに拡散してゆき、所望の金属濃度分布を得ることができる。
【００１７】
また、これとは逆に、ゲル中の金属種Ａの分布溶液中への溶出速度が、分布溶液中の金属種Ｂのゲル中への拡散速度に対して相対的に速い場合、ゲル中の金属種Ａに凸、金属種Ｂに凹の所望の金属濃度分布を付与する場合に本発明を用いたときの作用について説明する。
分布溶液中への溶出速度が相対的に速い金属塩Ａの微結晶を析出させたゲルを作製する。このゲル中の径方向の金属濃度を図３（ａ）に示す。ゲル中への拡散速度が相対的に遅い金属塩Ｂと、ゲル中の金属塩Ａと等しい濃度の金属塩Ａとを溶解した分布付与溶液にゲルを比較的長時間浸漬する。この時、金属塩Ａは、ゲル中と溶液中とで濃度勾配が無いため、長時間浸漬しても分布付与溶液には溶出しないが、金属塩Ｂは、ゆっくりゲル中に拡散し、金属種Ｂに所望の凹分布を得ることができる。この様子を図３（ｂ）に示す。次に、金属塩Ａの濃度を徐々に減少させてゆくと、分布付与溶液中の金属塩Ａの濃度の方がゲル中の金属塩Ａの濃度よりも低くなるために濃度勾配を生じ、ゲル中の金属塩Ａが分布付与溶液に溶出して、金属種Ａに所望の凸分布を得ることができるのである。この様子を図３（ｃ）に示す。
【００１８】
以上、本発明の作用について例を挙げて説明したが、ゲル中の金属成分の溶出と拡散を操作するという観点から、上記分布溶液中の金属成分濃度を変化させる以外に、分布付与溶液中の酸濃度、溶液（溶媒種、溶媒量）等のパラメーターを適宜変化させても良い。
次に、その一例として、前述したように分布付与溶液中に含まれる酸の濃度がある程度以上高くないと、ゲル中に含まれる金属種Ａのゲルからの溶出が起こらない場合に生じる表面のひび割れを、本発明の分布付与溶液の酸濃度を段階的に減少させる工程を経ることにより解決した例を挙げ、その作用について説明する。
【００１９】
金属種Ａと、シリコンアルコキシドとにより作製したゲルを、比較的高濃度の酸を含む分布付与溶液に適当な時間浸漬すると、金属種Ａには所望の濃度分布を付与することができる。次に、別の容器に酸濃度の低い溶液をあらかじめ作製しておき、その溶液にゲルを浸漬する。ゲル中には分布付与溶液より拡散してきた酸が存在するので、酸により溶かされた金属成分が徐々に溶出を続けるが、一方ゲル骨格であるシリコン成分は、酸との反応性が比較的低いのでシラノール基やシリカ骨格に戻ろうとする。したがって、高濃度の酸を含む分布溶液に長時間浸漬する場合に比べ、ゲル表面のひび割れを防止することができるのである。
【００２０】
分布付与溶液中の金属種濃度、濃度変化プログラム、ゲルの浸漬時間などのパラメーターは、ゲル中に含まれる金属種、溶媒、酸濃度、細孔径、分布付与溶液中の金属種、溶媒、酸濃度、液量などの性質と、所望の分布形状を鑑みて適宜選んで設定すればよい。また、分布付与溶液の組成を連続して変化させる工程は、例えば金属種濃度を変える図２のような変化プログラム以外に、図４〜図８に示すように設定してもよい。また、適当な分布付与溶液であれば、溶液組成を連続して変化させる工程と、異なった組成の分布溶液に浸漬する工程とを組み合わせてもよい。
【００２１】
また、一般的にアルカリ金属の拡散定数は大きく、拡散し易い成分であるため、分布付与溶液中の金属種Ｂにアルカリ金属を用いて屈折率分布型光学素子を製造する場合には、前述したようなゲル中の金属種Ａとの拡散スピードの差が著しく大きくなる場合が多く、本発明が極めて効果的に働く。
【００２５】
（比較例１）
実施例１と同様の方法でバリウム微結晶を析出したゲルを作製した。
酢酸カリウム４．７ｇとメタノール７００ｍｌとを混合して溶解した溶液を調製しておき、この溶液にゲル１０本を８時間浸漬し、ゲル中のバリウム成分に凸分布を、カリウム成分に凹分布を付与した。その後、再びゲルをエタノール４００ｍｌと乳酸７．２ｇとを混合させた溶液に２日間浸漬し、酢酸バリウムおよび酢酸カリウムの微結晶を固定し、乾燥、焼成したが、焼成中と徐冷中に８本が割れてしまった。
このガラス体について、ＥＤＸによりガラスの径方向に組成分析を行った結果、ガラス体中にカリウムが２０ｍｏｌ％と大量にほぼフラットに入っていた。
また、このガラス体の耐酸性、耐アルカリ性の試験を行ったところ、実施例１で得られたガラス体に比べて劣っていた。
【００２６】
【実施例１】
シリコン、チタン、バリウム、カリウム原料にそれぞれテトラメトキシシランＳｉ（ＯＣＨ 3 ） 4 、チタンブトキシドモノマーＴｉ（Ｏ n Ｃ 4 Ｈ 9 ） 4 、酢酸バリウムＢａ（ＯＣＯＣＨ 3 ） 2 、酢酸カリウムＫＯＣＯＣＨ 3 を使用した。Ｓｉ（ＯＣＨ 3 ） 4 ２０．９ｇにエタノール３５ｍｌと２規定塩酸４．８ｍｌを加えて室温で１時間撹拌し、その溶液にＴｉ（Ｏ n Ｃ 4 Ｈ 9 ） 4 ７．７ｇとエタノール３５ｍｌとを混合した溶液を添加して１時間撹拌した。この溶液に、１Ｍ−酢酸バリウム水溶液４０ｍｌと、１７規定酢酸１６ｍｌとを加えて１時間撹拌してゾルを得た。このゾルを直径１８ｍｍのポリプロピレン製容器１０本にキャスティングして、５０℃の恒温槽で放置しゲル化させた後、更に熟成した。得られたゲルを容器から取り出し、エタノール４００ｍｌと乳酸７．２ｇとを混合した溶液に、該ゲル１０本を２日間浸漬し、ゲル中に酢酸バリウムの微結晶を固定した。このようにしてバリウム微結晶を析出したゲルを作製し、有機溶媒であるメタノール８００ｍｌにゲル１０本を浸漬し、２時間毎に４．７ｇずつ、ゲル内でのその金属成分に濃度分布が付与される金属成分（カリウム）を含む酢酸カリウムを添加した。ゲルは８時間浸漬した。その後、分布付与溶液に３２．９ｇの酢酸カリウムを添加し、ゲル中のバリウム成分に凸分布を、カリウム成分に凹分布を付与した。その後、再びゲルをエタノール４００ｍｌと乳酸７．２ｇとを混合させた溶液に２日間浸漬し、酢酸バリウムおよび酢酸カリウムの微結晶を固定し、乾燥、焼成することにより、１０本とも直径５．０ｍｍの割れのない透明なガラス体を得た。
【００２８】
（比較例２）
実施例３と同様の方法でバリウム微結晶を析出したゲルを作製した。次に、得られたゲルを容器から取り出し、硝酸カリウム４ｇと１規定硝酸２ｇと水１００ｍｌの混合溶液に３時間浸漬して、ゲル中のバリウム濃度に凸分布を付与した後、イソプロパノールで洗浄し、乾燥したが、ドライゲル表面が荒れて亀裂が入ったり、表面が剥がれてしまった。このゲルを焼成したが、割れの無いガラス体を得ることはできなかった。
【００２９】
【実施例２】
シリコン、ストロンチウム、ナトリウム原料にそれぞれテトラエトキシシランＳｉ（ＯＣ2 Ｈ5 ）₄、酢酸ストロンチウム半水和物Ｓｒ（ＯＣＯＣＨ₃ ）2 ・０．５Ｈ₂ Ｏ、酢酸ナトリウムＮａＯＣＯＣＨ₃を使用した。Ｓｉ（ＯＣ₂ Ｈ₅）₄３０ｇにエタノール３５ｍｌと２規定塩酸４．８ｍｌを加えて室温で１時間撹拌した。この溶液に、１Ｍ−酢酸ストロンチウム水溶液４０ｍｌと、１７規定酢酸１６ｍｌとを加えて更に１時間撹拌してゾルを得た。このゾルを直径１８ｍｍのポリプロピレン製容器１０本にキャスティングして、３０℃の恒温槽で放置しゲル化させた後、更に熟成した。得られたゲルを容器から取り出し、エタノール４００ｍｌと酢酸１０ｇとを混合した溶液に、該ゲル１０本を２日間浸漬し、ゲル中に酢酸ストロンチウムの微結晶を固定した。
【００３０】
有機溶媒であるメタノール４００ｍｌと有機溶媒であるエタノール４００ｍｌとの混合溶媒にゲル内でのその金属成分に濃度分布が付与される金属成分（ナトリウム）を含む酢酸ナトリウム５０ｇを溶解し第１の溶液を調製しておき、この溶液にゲル１０本を８時間浸漬し、ゲル中のストロンチウム成分に凸分布を付与した。
このウェットゲルを有機溶媒であるメタノール８００ｍｌと酸である酢酸１０ｇとを混合した酸溶液であり、酢酸ナトリウムの濃度が第１の溶液とは異なる第２の溶液に２時間浸漬し、ゲル中のナトリウム成分の一部を溶出させ、ゲル中に含まれるナトリウム成分を減少させた。その後、再びゲルをメタノール２００ｍｌとエタノール２００ｍｌと酢酸１０ｇと酢酸ナトリウム１０ｇとを混合させた、酢酸ナトリウムの濃度が第２の溶液とは異なる第３の溶液に１時間浸漬し、ナトリウム成分に凹分布を付与した。さらに、ゲルをアセトンに１日間浸漬し、酢酸ナトリウムの微結晶を固定し、乾燥、焼成することにより、１０本とも直径４．８ｍｍの全く割れのない透明なガラス体を得た。
【００３１】
このガラス体について、ＥＤＸによりガラスの径方向に組成分析を行った結果、ガラス体の中心から外周方向に向かってストロンチウム濃度が減少し、ナトリウム濃度が増加する所望の金属濃度分布であった。
【００３２】
（比較例３）
実施例２と同様の方法で作製したゲルを、酢酸ナトリウム１０ｇとメタノール４００ｍｌとエタノール４００ｍｌとを混合して溶解した溶液を調製しておき、この溶液にゲル１０本を８時間浸漬し、ゲル中のストロンチウム成分に凸分布を付与した。このゲルを乾燥し、ＥＤＸによりゲルの径方向に組成分析を行った結果、ストロンチウム濃度がほとんど変化しておらず、ナトリウムは、ゲル中にほぼフラットに分布していた。これはストロンチウムの溶出が、ナトリウムが少なすぎると起こらないことによると考えられる。実施例４で作製したゲルを、酢酸ナトリウム５０ｇとメタノール４００ｍｌとエタノール４００ｍｌとを混合して溶解した溶液を調製しておき、この溶液にゲル１０本を８時間浸漬し、ゲル中のストロンチウム成分に凸分布を付与した。このゲルを乾燥し、焼成したが、加熱中および徐冷中に全てのガラスが割れてしまった。これは、ナトリウム成分がゲル中に過剰かつフラットに存在したためと考えられる。
【００３３】
【実施例３】
テトラメトキシシラン３０ｍｌにエタノールを５０ｍｌ加えて攪拌し、１／１００規定塩酸で部分加水分解し、ここに０．１ｍｏｌ／ｌの硝酸カリウム水溶液２０ｍｌを添加し、室温で撹拌後、直径１２ｍｍのポリプロピレン製の容器に分注した。ゾル総量は約１００ｍｌであった。ゲル化後、３０℃の恒温乾燥器中で５日間の熟成を行なった。このゲルの骨格中に硝酸カリウムの沈澱を析出させた後、溶媒を有機溶媒であるメタノールとした０．６ｍｏｌ／ｌの酢酸鉛、ゲル内での金属成分に濃度分布が付与される金属成分（カリウム）を含む０．０２ｍｏｌ／ｌの硝酸カリウム、酸である０．１５ｍｏｌ／ｌの酢酸のメタノール溶液中で１６時間の分布付与を行なった。この後、分布付与溶液中の硝酸カリウム濃度を徐々に３０分かけて０．０００２ｍｏｌ／ｌにまで減少させ、更に２時間攪拌し続けてカリウムに凸分布を付与した後、ゲルを乾燥・焼結することによって、直径４．３ｍｍの無色透明のガラス体を得た。なお、ガラス中の鉛成分には径方向に凹状の分布を有していた。このガラス体の径方向の屈折率の分布を測定したところ、所望の金属濃度分布を有しており、鉛によるゲルの径方向への熱膨張の分布を、カリウムにより打ち消すことができたため、割れなく焼成できたと考えられる。
【００３４】
【実施例４】
シリカ、ニオブ原料にそれぞれＳｉ（ＯＣＨ₃ ）₄、Ｎｂ（ＯＣ₂ Ｈ₅ ）₅ を使用した。Ｓｉ（ＯＣＨ₃ ）4 ２０ｇにエタノール１０ｇと１規定塩酸２．５ｇを加えて３０℃で１時間撹拌し、その溶液にＮｂ（ＯＣ₂Ｈ₅ ）₅ １０ｇとエタノール１５．０ｇを混合した溶液を添加して１時間撹拌した後、１規定硝酸３ｍｌと水２０ｍｌとエタノール２３．０ｇとを混合した溶液を滴下してゾルを得た。このゾルを直径１８ｍｍのポリプロピレンチューブ容器にキャスティングして、３０℃の恒温槽で放置しゲル化させた後、更に熟成した。得られたゲル１０本の１本ずつをそれぞれ酸である１規定硝酸３０ｍｌと有機溶媒であるエタノール７０ｍｌを混合した第１の酸溶液に６時間浸漬してニオブに凸分布を付与した。その後、第１の酸溶液と酸の濃度が異なる、１規定硝酸５ｍｌとエタノール９５ｍｌを混合した第２の酸溶液にゲルを６時間浸漬した。この後、このゲルを乾燥、焼成することにより、１０本とも全く割れの無い屈折率分布型光学素子を得ることができた。
【００３５】
（比較例４）
実施例３と同様の方法で作製したゲル１０本を、１本ずつそれぞれ１規定硝酸３０ｍｌとエタノール７０ｍｌを混合した第２の酸溶液に６時間浸漬してニオブに凸分布を付与した。このゲルを乾燥したが、表面が白く変色し、ぼろぼろになってしまった。また、このゲルを焼成したが、表面からひび割れが生じ、ガラス体を得ることができなかった。また、実施例３と同様の方法で作製したゲルに同様の分布付与を行った後、エタノール１００ｍｌに６時間浸漬したゲルを乾燥したが、４本のゲルが内部に結晶を生じ、割れてしまった。これは、硝酸により溶解していたニオブ成分が、エタノールに浸漬されたことにより急激な溶解度低下を起こし結晶化したためと考えられる。
【００３６】
【発明の効果】
以上のように、本発明の屈折率分布型光学素子の製造法によれば、ゲル中の金属種の分布溶液中への溶出速度や、分布溶液中の金属種のゲル中への拡散速度等のパラメーターにかかわらず、所望の金属濃度分布が得られる。また、酸やアルカリによるゲル骨格への影響を抑えることができる。これらのことより、ゲルを焼成する際に生じる割れを防ぐことができ、優れた屈折率分布型光学素子を得ることができる。
【図面の簡単な説明】
【図１】本発明により分布付与する際の各工程におけるゲルの半径と金属濃度との関係を示す概念図である。
【図２】本発明においてゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す図である。
【図３】本発明により分布付与する際の各工程におけるゲルの半径と金属濃度との関係を示す概念図である。
【図４】ゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す概念図である。
【図５】ゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す概念図である。
【図６】ゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す概念図である。
【図７】ゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す概念図である。
【図８】ゲルを溶液に浸漬する時間と溶液中のカリウム濃度との関係を示す概念図である。
【図９】実施例１で得られたガラス体の半径と金属濃度との関係を示す図である。
【図１０】 Si-Ba-Ti-K系ゲルにおいて、バリウムに所望の凸分布を付与した場合における所望のカリウム濃度と従来技術により得られたカリウム濃度の関係を示す概念図である。[0001]
[Industrial application fields]
The present invention relates to a method of manufacturing a gradient index optical element applicable to an optical element such as a camera or a microscope.
[0002]
[Prior art]
Gradient index optical elements are those in which the medium itself is given power (refractive power) by imparting a refractive index distribution to the medium. It can be reduced and attracts attention as an optical element that is indispensable for the next generation optical system.
In general, a sol-gel method, an ion exchange method, a molecular stuffing method, or the like is used as a method for manufacturing a gradient index optical element having a refractive index distribution. In particular, the sol-gel method is capable of obtaining a large-diameter glass body, allowing the polyvalent metal oxide to have a distribution, and providing variations in the optical characteristics of the resulting gradient index optical element. It has attracted attention because it has features such as
[0003]
Japanese Patent Publication No. 5-27575 discloses the following method. A sol obtained by hydrolyzing a solution mainly composed of silicon alkoxide and metal salt A is gelled, and immersed in a solution having a low solubility of metal salt A to precipitate fine crystals of metal salt A in the gel. This gel is immersed in a solution containing a metal salt B different from the metal salt A. Then, the metal salt B contained in the solution gradually diffuses from the surface of the gel toward the inside. At this time, if a predetermined time has elapsed, the concentration of the metal salt B in the gel radial direction is low at the center of the gel and high at the outer periphery, so-called a concave distribution. On the contrary, since the metal salt A microcrystals contained in the gel are gradually eluted from the surface toward the outside, the concentration of the metal salt A is high at the center of the gel and low at the outer periphery. Distribution. By drying and baking this gel, a gradient index optical element whose refractive index decreases from the center toward the outer periphery can be obtained.
Japanese Patent Application Laid-Open No. 4-260609 discloses a method of increasing the difference in refractive index by performing distribution application a plurality of times.
Furthermore, in Japanese Patent Laid-Open No. 5-238757, regarding the first metal ion having a relatively low solubility and the second metal ion having a high solubility, the second metal ion is dissolved but the first metal ion is not dissolved. A method is disclosed in which a gel is immersed in a solution to fix and distribute the first ions and distribute the second ions by sequentially applying and fixing the distribution from a metal salt having a low solubility.
[0004]
[Problems to be solved by the invention]
When distribution is imparted by the method described in JP-B-5-27575 and JP-A-4-260609, a cylindrical gel containing a salt of metal species A is immersed in a distribution imparting solution containing a salt of metal species B Then, it is considered that the formation of the concentration distribution in the radial direction of each of the metal species A and B when the distribution is given follows the diffusion law. That is, the metal ion A diffuses from the gel having a high metal species A concentration into the distribution imparting solution having a low metal species A concentration. Conversely, the metal species B in the distribution imparting solution is a solution having a high metal species B concentration. It diffuses from the inside into a gel with a low metal species B concentration. Therefore, it is considered that the concentration gradient from the central portion toward the outer peripheral portion diffuses in a manner that correlates with a monotone decrease in the metal species A and a monotone increase in the metal species B.
[0005]
However, this relationship may be broken depending on the type of metal salt. As an example, a case where distribution is imparted by immersing silica gel containing barium acetate (metal species is barium) in a solution of potassium acetate (metal species is potassium) in methanol will be described.
When the refractive index distribution type optical element is obtained by giving a so-called convex distribution in which the concentration of barium having a large contribution to the refractive index decreases from the center to the outer periphery of the gel, along with the concentration distribution of barium, Since the distribution of thermal expansion is attached in the radial direction of the gel, when the gel is baked, the stress is not uniform and cracking occurs. To avoid this crack, the distribution opposite to barium is given to potassium, which has a small contribution to the refractive index and a large contribution to thermal expansion, but the dissolution rate of barium is significantly slower than the penetration rate of potassium. As shown in FIG. 10, when a desired convex metal concentration distribution a is given to barium, potassium is introduced into the gel in a large amount and not flat, rather than the metal concentration distribution b having the desired concave distribution. It becomes like density distribution c. Therefore, even if it tried to bake this gel, the crack was produced by the distribution of the thermal expansion mentioned above.
[0006]
In particular, when the alkali metal component (potassium in the above description) contained in the glass is increased, another problem arises even if the glass is not cracked during firing. That is, if the alkali metal component is increased, the coefficient of thermal expansion of the produced glass is increased, so that it is weak against thermal shock, and acid resistance and water resistance are remarkably deteriorated. there were.
[0007]
That is, when the dissolution rate of the metal species A in the gel into the distribution solution is relatively slow relative to the diffusion rate of the metal species B in the distribution solution into the gel, the metal species A in the gel is convex. If it is intended to give a concave desired metal concentration distribution to the metal species B, the metal concentration B in the distribution solution diffuses in the gel in a large amount in the conventional technique, and thus the desired metal concentration distribution cannot be obtained. Had problems.
[0008]
On the contrary, when the dissolution rate of the metal species A in the gel into the distribution solution is relatively high with respect to the diffusion rate of the metal species B in the distribution solution into the gel, When trying to give a desired metal concentration distribution that is convex to the metal species A and concave to the metal species B, the metal species A in the distribution solution is dissolved in a large amount in the solution, so that the desired metal concentration distribution is obtained. Had the problem of not.
[0009]
On the other hand, even if distribution is given by the method described in JP-A-5-238757, it is difficult to select a solvent having an appropriate solubility depending on the type of metal salt, and there are many processes, so it takes time, and the actual refraction. The method for manufacturing the rate distribution type optical element has problems such as high cost.
[0010]
Further, depending on the type of metal species A contained in the gel, the metal species A may not be eluted from the gel unless the concentration of the acid contained in the distribution imparting solution is higher than a certain level. In this case, the gel containing the metal species A had to be once immersed in a distribution imparting solution containing a relatively high concentration of acid. This step makes it possible to impart a desired concentration distribution to the metal species A. However, when the gel is immersed in a solution having a high acid concentration for a long time, the acid or alkali destroys the silica skeleton particularly on the surface of the gel. For this reason, there are problems that the surface becomes rough and cracks occur.
[0011]
The present invention has been made in view of such conventional problems, and relates to a method for producing a gradient index optical element having a desired metal concentration distribution, which can suppress the influence of acid or alkali on the gel skeleton, Refractive index distribution type optical element capable of obtaining a refractive index distribution type optical element free from cracks at the time of conjugation and thereby having desired optical characteristics and appropriate thermal shock resistance, acid resistance and alkali resistance It aims at providing the manufacturing method of.
[0012]
[Means for Solving the Problems]
  In order to solve the above problems, the manufacturing method of the gradient index optical element of the present invention,
  Manufacturing of a refractive index distribution type optical element in which a gel produced by a sol-gel method is immersed in a concentration distribution imparting solution and the concentration distribution is fixed after the distribution imparting step of imparting the concentration distribution of the metal component in the gel, followed by drying and baking. In the method, the concentration distribution imparting liquid is a metal component-dissolved solution in which the metal component is dissolved in a solvent selected from an organic solvent or water, or a mixed solvent of the solvent. In the state which was immersed in the said metal component solution, it has the process of changing the density | concentration of the metal component of this metal component solution.
  The concentration distribution imparting solution is a metal component solution obtained by further dissolving an acid in the metal component solution.
  The step of changing the concentration of the metal component is continuously performed a plurality of times in the distribution applying step.
  The step of changing the concentration of the metal component is characterized by gradually increasing the concentration of the metal component.
  The step of changing the concentration of the metal component is characterized by gradually decreasing the concentration of the metal component.
  In addition, the method for producing a gradient index optical element according to the present invention includes the concentration distribution after a distribution providing step of immersing a gel prepared by a sol-gel method in a concentration distribution applying liquid to provide a concentration distribution of a metal component in the gel. Is a method of manufacturing a gradient index optical element in which the metal component is dissolved in a solvent selected from an organic solvent or water or a mixed solvent of the solvent. A metal component dissolving solution, wherein the distribution imparting step comprises at least a first distribution imparting step and a second distribution imparting step, and the solvent and metal of the concentration distribution imparting solution used in the first and second distribution imparting steps The first and second distribution application steps are sequentially performed with the same components, and the concentration of the metal component in the concentration distribution application liquid of the first distribution application step and the concentration distribution of the second distribution application step Application liquid Different from the concentration of the genus component, the concentration of the metal component of the concentration distribution imparting liquid in the second distribution imparting step is different from the concentration distribution imparting liquid during the implementation of the first distribution imparting step. A concentration distribution imparting liquid different from the concentration of the metal component of the concentration distribution imparting liquid is added to make it different.
  The concentration distribution imparting solution is a metal component solution obtained by further dissolving an acid in the metal component solution.
  The concentration distribution applying liquid used in the first distribution applying step and the concentration of the respective metal components of the concentration distribution applying liquid used in the second distribution applying step are changed to prepare respective concentration distribution applying liquids. The concentration of the metal component is varied by immersing the gel in a concentration distribution imparting solution.
  The concentration of the metal component of the concentration distribution application liquid of the second distribution application process is increased with respect to the concentration of the metal component of the concentration distribution application liquid of the first distribution application process, and the concentration is made different. To do.
  The concentration of the metal component of the concentration distribution imparting liquid in the second distribution imparting step is lowered with respect to the concentration of the metal component of the concentration distribution imparting liquid in the first distribution imparting step, and the concentration is varied. To do. Furthermore, the metal component contains an alkali metal.
[0013]
[Action]
Regarding the action of the present invention, the problem that the metal concentration distribution in the above-described step of imparting metal concentration to barium and potassium is a large amount, and the metal salt concentration of the distribution solution of the present invention is continuously increased. An explanation will be given based on an example solved by the process.
FIG. 2 and FIG. 1 show a conceptual diagram of the potassium concentration change program in the distribution solution and the metal component concentration of the gel, respectively. Here, the conceptual diagrams of the metal concentration distribution of the gel in the regions C and D in FIG. 2 correspond to FIGS. 1B and 1C, respectively. As shown in FIG. 2, the gel having the metal concentration in FIG. 1A is immersed in a distribution imparting solution that increases the potassium concentration in the distribution solution with time. First, a distribution imparting solution having a relatively low potassium concentration is prepared, and the gel is immersed. Next, the potassium concentration in the distribution imparting solution is gradually increased. In this step, the metal concentration in the gel is considered to change as follows.
[0014]
First, the gel is immersed for a relatively long time in a region having a low potassium concentration (C region in FIG. 2), and barium is eluted to some extent so as to be parabolic. When the gel is soaked for a time to give an appropriate concentration distribution to barium, the diffusion rate of potassium is so fast that it has already diffused all the way to the center of the gel and is saturated, so the concentration is almost the same as the solution, and less than the desired potassium concentration. Flat in the gel. A conceptual diagram of the metal concentration distribution of the gel at this time is shown in FIG.
[0015]
Next, the potassium concentration is gradually increased, and the gel is immersed in a region having a high potassium concentration (D region in FIG. 2) for a relatively short time. A conceptual diagram of the metal concentration distribution of the gel at this time is shown in FIG. Although a small amount of barium elutes, the distribution of barium is hardly disrupted because of the short time. On the other hand, potassium has a higher concentration in the solution than in the gel, so that it diffuses rapidly into the gel and can impart a concave distribution to the potassium. That is, a desired distribution can be obtained through these steps.
[0016]
On the other hand, a desired distribution can be obtained by a method described below in addition to the above distribution providing method. When a gel in which barium microcrystals are fixed is immersed in a distribution imparting solution having a concentration lower than the desired potassium concentration, barium is eluted to some extent, and a small amount of potassium is diffused flatly in the gel below the desired potassium concentration. Next, a solution having a higher potassium concentration than the above solution is prepared, and the gel is immersed in this solution for a relatively short time. Barium elutes further, and potassium is more concentrated in the solution than in the gel, so that it diffuses into the gel and a desired metal concentration distribution can be obtained.
[0017]
On the contrary, when the dissolution rate of the metal species A in the gel into the distribution solution is relatively high with respect to the diffusion rate of the metal species B in the distribution solution into the gel, The operation when the present invention is used in the case where a desired metal concentration distribution that is convex on the metal species A and concave on the metal species B is given will be described.
A gel is prepared in which fine crystals of metal salt A having a relatively high elution rate into the distribution solution are precipitated. The metal concentration in the radial direction in this gel is shown in FIG. The gel is immersed for a relatively long time in a distribution imparting solution in which the metal salt B having a relatively low diffusion rate into the gel and the metal salt A having the same concentration as the metal salt A in the gel are dissolved. At this time, since the metal salt A has no concentration gradient between the gel and the solution, it does not elute into the distribution imparting solution even if immersed for a long time, but the metal salt B slowly diffuses into the gel, A desired concave distribution can be obtained in B. This is shown in FIG. Next, when the concentration of the metal salt A is gradually decreased, a concentration gradient is generated because the concentration of the metal salt A in the distribution imparting solution is lower than the concentration of the metal salt A in the gel. The metal salt A contained therein is eluted into the distribution imparting solution, and a desired convex distribution can be obtained for the metal species A. This is shown in FIG.
[0018]
As described above, the operation of the present invention has been described with an example. From the viewpoint of manipulating the elution and diffusion of the metal component in the gel, in addition to changing the metal component concentration in the distribution solution, Parameters such as acid concentration, solution (solvent type, amount of solvent) and the like may be appropriately changed.
Next, as an example, as described above, if the concentration of the acid contained in the distribution imparting solution is not higher than a certain level, surface cracking occurs when the metal species A contained in the gel does not elute from the gel. An example of solving this problem by going through a step of gradually reducing the acid concentration of the distribution imparting solution of the present invention will be described.
[0019]
When a gel prepared from metal species A and silicon alkoxide is immersed in a distribution imparting solution containing a relatively high concentration of acid for an appropriate time, the metal species A can be imparted with a desired concentration distribution. Next, a solution having a low acid concentration is prepared in another container in advance, and the gel is immersed in the solution. Since there is an acid diffused from the distribution imparting solution in the gel, the metal component dissolved by the acid continues to elute gradually, whereas the silicon component that is the gel skeleton has a relatively low reactivity with the acid. So it tries to return to silanol group or silica skeleton. Therefore, cracking of the gel surface can be prevented as compared with the case of immersing in a distributed solution containing a high concentration of acid for a long time.
[0020]
Parameters such as the concentration of metal species in the distribution imparting solution, concentration change program, and gel immersion time are the metal species, solvent, acid concentration, pore size, and metal species, solvent, acid concentration in the distribution imparting solution. In view of the properties such as the liquid amount and the desired distribution shape, it may be appropriately selected and set. Further, the step of continuously changing the composition of the distribution imparting solution may be set as shown in FIGS. 4 to 8 in addition to the change program as shown in FIG. 2 for changing the metal species concentration, for example. Moreover, if it is a suitable distribution provision solution, you may combine the process of changing a solution composition continuously, and the process of immersing in the distribution solution of a different composition.
[0021]
Moreover, since the diffusion constant of alkali metal is generally large and easily diffused, the refractive index distribution type optical element is manufactured by using alkali metal as the metal species B in the distribution imparting solution. In many cases, the difference in diffusion speed with the metal species A in such a gel becomes remarkably large, and the present invention works extremely effectively.
[0025]
(Comparative Example 1)
A gel in which barium microcrystals were deposited was prepared in the same manner as in Example 1.
A solution in which 4.7 g of potassium acetate and 700 ml of methanol were mixed and dissolved was prepared, 10 gels were immersed in this solution for 8 hours, and a convex distribution was distributed in the barium component and a concave distribution in the potassium component. Granted. After that, the gel was again immersed in a solution in which 400 ml of ethanol and 7.2 g of lactic acid were mixed for 2 days to fix the microcrystals of barium acetate and potassium acetate, dried and fired. It broke.
This glass body was subjected to composition analysis in the radial direction of the glass by EDX. As a result, potassium was contained in a large amount of 20 mol% in a large amount in the glass body.
Moreover, when the acid resistance and alkali resistance tests of this glass body were performed, it was inferior to the glass body obtained in Example 1.
[0026]
[Example 1]
Tetramethoxysilane Si (OCH) for silicon, titanium, barium and potassium raw materials Three ) Four , Titanium butoxide monomer Ti (O n C Four H 9 ) Four , Barium acetate Ba (OCOCH Three ) 2 , Potassium acetate KOCOCH Three It was used. Si (OCH Three ) Four To 20.9 g, 35 ml of ethanol and 4.8 ml of 2N hydrochloric acid were added and stirred at room temperature for 1 hour, and Ti (O n C Four H 9 ) Four A solution prepared by mixing 7.7 g and ethanol 35 ml was added and stirred for 1 hour. To this solution, 40 ml of 1M-barium acetate aqueous solution and 16 ml of 17N acetic acid were added and stirred for 1 hour to obtain a sol. This sol was cast into 10 polypropylene containers having a diameter of 18 mm, left to gel in a constant temperature bath at 50 ° C., and further aged. The obtained gel was taken out from the container, and 10 gels were immersed in a solution obtained by mixing 400 ml of ethanol and 7.2 g of lactic acid for 2 days, and barium acetate microcrystals were fixed in the gel. In this way, a gel in which barium microcrystals are deposited is prepared,Ten gels were immersed in 800 ml of methanol, which is an organic solvent, and 4.7 g of potassium acetate containing a metal component (potassium) that imparts a concentration distribution to the metal component in the gel was added every 2 hours. The gel was immersed for 8 hours. Thereafter, 32.9 g of potassium acetate was added to the distribution imparting solution to impart a convex distribution to the barium component in the gel and a concave distribution to the potassium component. Thereafter, the gel was again immersed in a solution in which 400 ml of ethanol and 7.2 g of lactic acid were mixed for 2 days to fix the microcrystals of barium acetate and potassium acetate, and then dried and fired, so that all 10 pieces had a diameter of 5.0 mm. A transparent glass body without cracks was obtained.
[0028]
(Comparative Example 2)
A gel in which barium microcrystals were deposited was prepared in the same manner as in Example 3. Next, the obtained gel is taken out of the container, immersed in a mixed solution of 4 g of potassium nitrate, 2 g of 1N nitric acid and 100 ml of water for 3 hours to give a convex distribution to the barium concentration in the gel, and then washed with isopropanol. Although it dried, the dry gel surface was rough and cracked, or the surface was peeled off. Although this gel was baked, a glass body without cracks could not be obtained.
[0029]
[Example 2]
  Tetraethoxysilane Si (OC2 H5) for silicon, strontium and sodium raw materials_FourStrontium acetate hemihydrate Sr (OCOCH_Three 2) 0.5H₂ O, sodium acetate NaOCOCH_ThreeIt was used. Si (OC₂ H_Five)_FourTo 30 g, 35 ml of ethanol and 4.8 ml of 2N hydrochloric acid were added and stirred at room temperature for 1 hour. To this solution, 40 ml of 1M strontium acetate aqueous solution and 16 ml of 17 N acetic acid were added and stirred for another hour to obtain a sol. This sol was cast in 10 polypropylene containers having a diameter of 18 mm, and left to stand in a thermostatic bath at 30 ° C. to be gelled, and further aged. The obtained gel was taken out of the container, and 10 gels were immersed in a solution obtained by mixing 400 ml of ethanol and 10 g of acetic acid for 2 days to fix strontium acetate microcrystals in the gel.
[0030]
  50 g of sodium acetate containing a metal component (sodium) to which a concentration distribution is given to the metal component in the gel is dissolved in a mixed solvent of 400 ml of methanol which is an organic solvent and 400 ml of ethanol which is an organic solvent. It was prepared and 10 gels were immersed in this solution for 8 hours to give a convex distribution to the strontium component in the gel.
  This wet gel is an acid solution obtained by mixing 800 ml of methanol as an organic solvent and 10 g of acetic acid as an acid. The wet gel is immersed in a second solution having a sodium acetate concentration different from that of the first solution for 2 hours. A part of the sodium component was eluted to reduce the sodium component contained in the gel. After that, the gel was again immersed in a third solution in which 200 ml of methanol, 200 ml of ethanol, 10 g of acetic acid and 10 g of sodium acetate were mixed, and the concentration of sodium acetate was different from that of the second solution, and the sodium component was distributed concavely Was granted. Furthermore, the gel is immersed in acetone for 1 day,Sodium acetateBy fixing, drying and firing the microcrystals, 10 glass 4.8 mm diameter transparent glass bodies having no cracks were obtained.
[0031]
This glass body was subjected to composition analysis in the radial direction of the glass by EDX. As a result, the strontium concentration decreased from the center of the glass body toward the outer peripheral direction, and the sodium concentration increased.
[0032]
  (Comparative Example 3)
  Example 2A solution prepared by mixing 10 g of sodium acetate, 400 ml of methanol and 400 ml of ethanol was prepared, and 10 gels were immersed in this solution for 8 hours to obtain a strontium component in the gel. Convex distribution was given to. As a result of drying this gel and performing composition analysis in the radial direction of the gel by EDX, the strontium concentration hardly changed, and sodium was distributed almost flatly in the gel. This is thought to be because strontium elution does not occur when there is too little sodium. A solution prepared by mixing 50 g of sodium acetate, 400 ml of methanol, and 400 ml of ethanol was prepared in advance in Example 4, and 10 gels were immersed in this solution for 8 hours. Convex distribution was given. This gel was dried and baked, but all the glass broke during heating and slow cooling. This is probably because the sodium component was excessive and flat in the gel.
[0033]
[Example 3]
  50 ml of ethanol was added to 30 ml of tetramethoxysilane, stirred, and partially hydrolyzed with 1/100 N hydrochloric acid. 20 ml of 0.1 mol / l potassium nitrate aqueous solution was added thereto, stirred at room temperature, and then made of polypropylene having a diameter of 12 mm. Dispense into containers. The total amount of sol was about 100 ml. After gelation, aging was carried out for 5 days in a constant temperature dryer at 30 ° C. After precipitation of potassium nitrate in the skeleton of this gel, 0.6 mol / l lead acetate with methanol as the organic solvent, a metal component (potassium potassium) that gives concentration distribution to the metal component in the gel ) Was added in a methanol solution of 0.02 mol / l potassium nitrate containing 0.15 mol / l acetic acid, which was an acid, for 16 hours. Thereafter, the potassium nitrate concentration in the distribution imparting solution is gradually reduced to 0.0002 mol / l over 30 minutes, and further stirred for 2 hours to impart a convex distribution to the potassium, and then the gel is dried and sintered. As a result, a colorless and transparent glass body having a diameter of 4.3 mm was obtained. The lead component in the glass had a concave distribution in the radial direction. When the refractive index distribution in the radial direction of this glass body was measured, it had a desired metal concentration distribution, and the distribution of thermal expansion in the radial direction of the gel due to lead could be canceled out by potassium, so cracking occurred. It is thought that it was able to be fired.
[0034]
[Example 4]
  Silica and niobium raw materials are respectively Si (OCH_Three )_Four, Nb (OC₂ H_Five )_Five It was used. Si (OCH_Three 4) Add 20 g of ethanol and 2.5 g of 1N hydrochloric acid to 20 g, stir at 30 ° C. for 1 hour, and add Nb (OC₂H_Five )_Five A solution in which 10 g and 15.0 g of ethanol were mixed was added and stirred for 1 hour, and then a solution in which 3 ml of 1N nitric acid, 20 ml of water and 23.0 g of ethanol were mixed was dropped to obtain a sol. This sol was cast in a polypropylene tube container having a diameter of 18 mm, and left to stand in a thermostatic bath at 30 ° C. to be gelled, and further aged. Each of the 10 gels obtained was immersed in a first acid solution in which 30 ml of 1N nitric acid as an acid and 70 ml of ethanol as an organic solvent were mixed to give a convex distribution to niobium. Thereafter, the gel was immersed for 6 hours in a second acid solution in which 5 ml of 1N nitric acid and 95 ml of ethanol having different acid concentrations from the first acid solution were mixed. Thereafter, the gel was dried and baked to obtain a gradient index optical element having no cracks at all.
[0035]
  (Comparative Example 4)
  Example 3Ten gels prepared by the same method as above were immersed in a second acid solution in which 30 ml of 1N nitric acid and 70 ml of ethanol were mixed one by one for 6 hours to give a convex distribution to niobium. When this gel was dried, the surface turned white and raged. Moreover, although this gel was baked, the surface was cracked and a glass body could not be obtained. Also,Example 3After applying the same distribution to the gel produced by the same method as described above, the gel immersed in 100 ml of ethanol for 6 hours was dried, but the four gels were crystallized and cracked. This is presumably because the niobium component dissolved in nitric acid crystallized due to a rapid decrease in solubility due to immersion in ethanol.
[0036]
【The invention's effect】
As described above, according to the manufacturing method of the gradient index optical element of the present invention, the dissolution rate of the metal species in the gel into the distribution solution, the diffusion rate of the metal species in the distribution solution into the gel, etc. Regardless of the parameters, the desired metal concentration distribution is obtained. Moreover, the influence on the gel skeleton by an acid or an alkali can be suppressed. From these things, the crack which arises when baking a gel can be prevented, and the outstanding refractive index distribution type | mold optical element can be obtained.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the relationship between the radius of a gel and the metal concentration in each step when a distribution is applied according to the present invention.
FIG. 2 is a graph showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution in the present invention.
FIG. 3 is a conceptual diagram showing the relationship between the radius of the gel and the metal concentration in each step when distribution is imparted according to the present invention.
FIG. 4 is a conceptual diagram showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution.
FIG. 5 is a conceptual diagram showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution.
FIG. 6 is a conceptual diagram showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution.
FIG. 7 is a conceptual diagram showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution.
FIG. 8 is a conceptual diagram showing the relationship between the time for immersing the gel in the solution and the potassium concentration in the solution.
FIG. 9 is a diagram showing the relationship between the radius of the glass body obtained in Example 1 and the metal concentration.
FIG. 10 is a conceptual diagram showing a relationship between a desired potassium concentration and a potassium concentration obtained by a conventional technique when a desired convex distribution is imparted to barium in a Si—Ba—Ti—K-based gel.

Claims

Manufacturing of a refractive index distribution type optical element in which a gel produced by a sol-gel method is immersed in a concentration distribution imparting solution and the concentration distribution is fixed after the distribution imparting step of imparting the concentration distribution of the metal component in the gel, followed by drying and baking. A method,
The concentration distribution imparting solution is a metal component solution obtained by dissolving the metal component in a solvent selected from an organic solvent or water or a mixed solvent of the solvent,
The method for producing a gradient index optical element, comprising the step of changing the concentration of the metal component of the metal component dissolving solution in a state in which the gel is immersed in the metal component dissolving solution in the distribution imparting step.

2. The refractive index distribution type optical element manufacturing method according to claim 1, wherein the concentration distribution providing liquid is a metal component solution obtained by further dissolving an acid in the metal component solution.

3. The method of manufacturing a gradient index optical element according to claim 1, wherein the step of changing the concentration of the metal component is continuously performed a plurality of times in the distribution applying step.

4. The method of manufacturing a gradient index optical element according to claim 3, wherein the step of changing the concentration of the metal component gradually increases the concentration of the metal component.

4. The method of manufacturing a gradient index optical element according to claim 3, wherein the step of changing the concentration of the metal component gradually decreases the concentration of the metal component.

Manufacturing of a refractive index distribution type optical element in which a gel produced by a sol-gel method is immersed in a concentration distribution imparting solution and the concentration distribution is fixed after the distribution imparting step of imparting the concentration distribution of the metal component in the gel, followed by drying and baking. A method,
The concentration distribution imparting solution is a metal component solution obtained by dissolving the metal component in a solvent selected from an organic solvent or water or a mixed solvent of the solvent,
The distribution imparting step includes at least a first distribution imparting step and a second distribution imparting step, and the first and second concentration imparting liquids used in the first and second distribution imparting steps have the same solvent and metal component. And the second distribution imparting step are sequentially performed, and the concentration of the metal component of the concentration distribution imparting liquid in the first distribution imparting step, and the concentration of the metal component in the concentration distribution imparting solution of the second distribution imparting step, And the concentration of the metal component of the concentration distribution applying liquid in the second distribution applying step is different from that of the concentration distribution applying liquid in the execution of the first distribution applying step. A method for producing a gradient index optical element, wherein a concentration distribution imparting liquid different from the concentration of a metal component is added to make the difference.

7. The method of manufacturing a gradient index optical element according to claim 6, wherein the concentration distribution imparting solution is a metal component solution obtained by further dissolving an acid in the metal component solution.

The concentration distribution applying liquid used in the first distribution applying step and the concentration of the respective metal components of the concentration distribution applying liquid used in the second distribution applying step are changed to prepare respective concentration distribution applying liquids. The method for producing a gradient index optical element according to claim 6 or 7, wherein the concentration of the metal component is varied by immersing the gel in a concentration distribution imparting solution.

The concentration of the metal component of the concentration distribution application liquid of the second distribution application process is increased with respect to the concentration of the metal component of the concentration distribution application liquid of the first distribution application process, and the concentration is made different. The manufacturing method of the gradient index optical element according to any one of claims 6 to 8.

The concentration of the metal component of the concentration distribution imparting liquid in the second distribution imparting step is lowered with respect to the concentration of the metal component of the concentration distribution imparting liquid in the first distribution imparting step, and the concentration is varied. The manufacturing method of the gradient index optical element according to any one of claims 6 to 8.

The method for manufacturing a gradient index optical element according to any one of claims 1 to 10, wherein the metal component includes an alkali metal.