JP3584257B2

JP3584257B2 - Polarizing beam splitter

Info

Publication number: JP3584257B2
Application number: JP07062394A
Authority: JP
Inventors: 幹夫岡本
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 1994-04-08
Filing date: 1994-04-08
Publication date: 2004-11-04
Anticipated expiration: 2019-11-04
Also published as: JPH07281024A

Description

【０００１】
【産業上の利用分野】
本発明は、Ｓ及びＰ両偏光成分の分離合成に使用される偏光ビームスプリッタに関する。
【０００２】
【比較の技術】
一般に偏光ビームスプリッタは、２個の４５゜プリズムの間に高屈折率物質と低屈折率物質との誘電体薄膜を交互に積層した誘電体多層膜を介在させたものが使われている。誘電体多層膜の物質選択は、４５゜プリズムの光軸上から入射する入射光のＰ偏光成分の反射率がもっとも小さく、かつＳ偏光成分の反射率が最も高くなるような波長範囲内に入るよう行われる。
【０００３】
偏光ビームスプリッタは、入射光をＰとＳの両偏光成分を高効率に分離するために光ディスク装置や投射表示装置等に利用されている。比較から偏光ビームスプリッタの使用波長帯域幅を広げるために、誘電体多層膜構成について様々な提案がなされている。例えば、特開昭６１−１４１４０２号公報では、高屈折率物質と低屈折率物質との２層を基本周期とした誘電体多層膜に中間層を設け、この層の膜厚を調整することにより帯域幅を広げている。また、特開平３−２８４７０５号公報で示されている従来の偏光ビームスプリッタの構成例では、設計基準波長が異なる２つの誘電体多層膜でそれぞれ高屈折率物質と低屈折率物質の組み合わせが同一な組み合わせである。この構成により、使用波長の帯域幅を広げ、かつ偏光分離比向上がなされている。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来の誘電体多層膜構成を有する偏光ビームスプリッタでは、設計入射角に対しては帯域幅は広がるものの、光束の入射角が少しでもずれるとＰ／Ｓ偏光分離比が悪くなり、帯域幅が非常に狭くなるという問題がある。
本発明の目的は、偏光分離多層膜面に入射する光束の入射角依存性が少なくかつ偏光分離比が高い、使用帯域幅が広い偏光ビームスプリッタを提供しようとするものである。
【０００５】
【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では、透光性基板上に形成された誘電体多層膜を有する偏光ビームスプリッタにおいて、前記誘電体多層膜は２つの異なる設計基準波長λ1を有する第１の誘電体多層膜と、設計基準波長λ2を有する第２の誘電体多層膜とからなり、前記第１および第２の誘電体多層膜は、それぞれ高屈折率物質と低屈折率物質との交互層を有し、前記第１の誘電体多層膜の交互層のブリュースター条件を満足する入射角と、前記第２の誘電体多層膜の交互層のブリュースター条件を満足する入射角とが異なるように、前記第１の誘電体多層膜の交互層と、前記第２の誘電体多層膜の交互層とで、交互層を形成する高屈折率物質と低屈折率物質との屈折率の値の組み合わせを異ならせたことを特徴とする。
【０００６】
【作用】
本発明の偏光ビームスプリッタは、誘電体多層膜への光束の入射角が多少変化しても使用波長領域の帯域幅を狭めることのないような構成及び誘電体多層膜の交互層の高屈折率層、低屈折率層に用いる物質を選択するようにしたものである。広帯域にわたって偏光分離するためには、偏光分離膜に入射する光束の波長に対して、Ｐ偏光成分とＳ偏光成分とを分離している波長帯域を大きくする必要がある。そのためには、スネルの法則に従い、Ｐ偏光成分とＳ偏光成分との偏光分離が最も大きい角度であるブリュースター角近傍を設計入射角として、偏光分離膜に入射させるようにする。
【０００７】
本発明の誘電体多層膜構成では、設計基準波長が異なる第１及び第２の誘電体多層膜を有している。第１及び第２の誘電体多層膜のそれぞれに入射する光束の入射角が異なるように設定する。また第１及び第２の誘電体多層膜の高屈折率と低屈折率の物質は、下記ブリュースター条件（１）と（２）が異なるように選択した。例えば、一方の誘電体多層膜の交互層には高屈折率物質としてＴｉＯ_２、低屈折率物質ＳｉＯ_２とした組み合わせとし、他方の誘電体多層膜の交互層には高屈折率物質としてＴｉＯ_２、低屈折率物質としてＡｌ_２Ｏ_３とした組み合わせを用いれば良い。
【０００８】
各設計基準波長λ１、λ２（λ１≠λ２）、設計基準入射角θに対しそれぞれの入射角θ１、θ２とする。それぞれにおけるブリュースタ条件は、次式（１）（２）で表される。
λ１＞λ２
λ１、θ１；ｎＨ１／ＣＯＳθＨ１＝ｎＬ１／ＣＯＳθＬ１（１）
λ２、θ２；ｎＨ２／ＣＯＳθＨ２＝ｎＬ２／ＣＯＳθＬ２（２）
θ１；透光性基体１から第１の誘電体多層膜と透光性基体１との境界面に入射する角度
θ２；透光性基体２から第２の誘電体多層膜と透光性基体２との境界面に入射する角度
ｎＨ１、ｎＬ１；設計基準波長λ１での第１の誘電体多層膜の交互層における高屈折率層及び低屈折率層の屈折率
ｎＨ２、ｎＬ２；設計基準波長λ２での第２の誘電体多層膜の交互層における高屈折率層及び低屈折率層の屈折率
θＨ１、θＬ１；設計基準波長λ１での第１の誘電体多層膜の交互層において、高屈折率層及び低屈折率層の各層から境界面に入射する角度
θＨ２、θＬ２；設計基準波長λ２での第２の誘電体多層膜の交互層において、高屈折率層及び低屈折率層の各層から境界面に入射する角度
図３は、上記誘電体多層膜に入射する光束が、高屈折率層及び低屈折率層から境界面に入射する状態説明図である。図中θｉ、θＨｉ、θＬｉは、第１及び第２の誘電体多層膜ｉ＝１、２に対応している。
【０００９】
本発明の誘電体多層膜の交互層に用いられる高屈折率層、低屈折率層及び調整層の膜厚は、それぞれλ／４、λ／４、λ／８である。ただし、実際に形成される膜厚は、実験的に試行錯誤して決められ設計値から多少ずれることもある。
また、本発明の調整層はＰ偏光成分の透過率に発生するリップルを低減するために設けられている。大きなリップルがあると、偏光ビームスプリッタとして使用できる波長範囲は制限されるので好ましくない。
【００１０】
本発明の実施例と比較するために、偏光ビームスプリッタの構成は基本的に図１と同じで、第１及び第２の誘電体多層膜の交互層に用いる高屈折率層ＴｉＯ_２と低屈折率層ＳｉＯ_２との物質の組み合わせを同一とした透過率特性をみる。図１０は、その透過率特性の入射角依存性である。
設計基準入射角４５゜で、Ｐ／Ｓ偏光分離比が高い帯域は１６０ｎｍであるが、入射角が±２．５゜ずれると、その帯域幅は９０ｎｍとなる。１種類のみの組み合わせで構成された誘電体多層膜を用いた偏光ビームスプリッタは、Ｓ及びＰ偏光成分の分離可能な使用波長域を広く得ることができる。しかしながら、誘電体多層膜面への入射角がわずかにずれるだけで、所望の波長帯域幅が非常に狭くなってしまう。
【００１１】
それに反し、本発明の実施例の使用帯域幅は、光束が誘電体多層膜面に入射する角度が多少ずれてもＰ偏光成分とＳ偏光成分との分離比を維持しつつ非常に広くなる。また、偏光ビームスプリッタを組み込まれた光学系の配置の自由度も高くなる。
次に、本発明の偏光ビームスプリッタの誘電体多層膜の構成法について説明する。
【００１２】
図１は、本発明の第１及び第２の誘電体多層膜３、４のそれぞれが、各透光性基体であるプリズム１上に形成され、その各々を接着層５を介して接合されている構成である。
図８は、透光性基体１に第１の誘電体多層膜と第２の誘電体多層膜とを連続して形成する。さらに、その上に透光性基体１２を接着する構成である。
【００１３】
図９は、透光性基体が平板ガラス２の両面上に誘電体多層膜を施し、ガラスと同程度の屈折率を持つ液体媒質６中に浸した構成にしても同様な性能が得られる。
【００１４】
【実施例】
本発明の偏光ビームスプリッタの第１の実施例について説明する。
図１は、調整層１Ｃと第１の誘電体多層膜３の交互層１３とが積層されたプリズム１と調整層２Ｃと第２の誘電体多層膜４の交互層２３とが積層されているプリズム２とが光学接着剤５で接合されている偏光ビームスプリッタの構成である。プリズム１及びプリズム２は、屈折率ｎＳが１．８４である。また、光学接着剤の屈折率ｎｂ＝１．５２である。図には、光束が４５°で入射させた時の反射光Ｒと透過光Ｔとを記載してある。透過光Ｔには、Ｓ偏光成分ＴＳとＰ偏光成分ＴＰとがある。
【００１５】
第１の誘電体多層膜の交互層１３は、設計基準波長λ１＝６８０ｎｍで、高屈折率物質ｎＨ１＝２．３８のＴｉＯ_２１１と低屈折率物質ｎＬ１＝１．６５のＡｌ_２Ｏ_３１２とが光学的膜厚λ１／４で構成されている。
第２の誘電体多層膜の交互層２３は、設計基準波長λ２＝４２０ｎｍで高屈折率物質ｎＨ２＝２．３８のＴｉＯ_２２１と低屈折率物質ｎＬ２＝１．４７のＳｉＯ_２２２とがそれぞれ光学的膜厚λ２／４で構成されている。
また第１及び第２の誘電体多層膜の各交互層とプリズム１及びプリズム２との間には、それぞれ膜厚λ１／８、λ２／８の調整層が設けられている。
【００１６】
光束が設計基準入射角４５゜から入射角が±２．５゜ずれた場合を考える。高角度側に対応する（使用波長域では短波長側に相当する）第１の誘電体多層膜の交互層１３に用いている高屈折率物質１１及び低屈折率物質１２は、光束が透光性基体１から透光性基体１と第１の誘電体多層膜との境界面に入射する角度θ１＝４７．５゜でブリュースター条件（１）を満足するように選択する。本実施例では、第１の誘電体多層膜の交互層の物質組み合わせとして、高屈折率層１１にＴｉＯ_２、低屈折率層１２にＡｌ_２Ｏ_３を選択した。
【００１７】
また低角度側に対応する（使用波長域で長波長側に相当する）第２の誘電体多層膜の交互層２３に用いている高屈折率物質２１及び低屈折率物質２２は、光束が透光性基体２から透光性基体２と第２の誘電体多層膜との境界面に入射する角度θ２＝４２．５゜でブリュースター条件（２）を満足するように選択する。本実施例では、第２の誘電体多層膜の交互層の物質組み合わせとして、高屈折率層２１にＴｉＯ_２、低屈折率層２２にＳｉＯ_２を選択した。
【００１８】
図４は、第１実施例の誘電体多層膜構成のＰ及びＳ偏光成分の透過率特性Ｔｐ、ＴＳ及び入射角４２．５゜、４５゜、４７．５゜のそれぞれの透過率特性である。
本発明の第１実施例の誘電体多層膜構成を有する偏光ビームスプリッタのＰ及びＳ偏光成分の透過率の入射角依存性について図１０の比較例と比較する。
【００１９】
比較例の多層膜構成は、波長範囲が４８０ｎｍから５５０ｎｍにおいて、入射角を設計基準角度から数度ずれると帯域幅Ｘが７０ｎｍとなり、使用帯域は非常に狭くなってしまう。
それに対し、本発明の第１実施例は、波長範囲４６０ｎｍから６２０ｎｍにわたり、高い偏光分離（ＴＳ／ＴＰ）０．１％以下を示している。設計基準入射角から±２．５゜ずれても帯域幅Ｘは、１６０ｎｍと広い帯域を維持している。
【００２０】
図５は、本発明の実施例１の、長波長側λ＝６２０ｎｍにおけるＰ偏光成分の透過率の入射角依存性について示したものである。
本実施例は、第１の誘電体多層膜の交互層、第２の誘電体多層膜の交互層それぞれの組み合わせが同一な種類の物質ＴｉＯ_２とＳｉＯ_２を用いた図１０の比較例に比べ、入射角依存性を考慮に入れても、透過率特性の帯域幅を大幅に広げることができた。
【００２１】
これは長波長側のＰ偏光透過率の落ち込みの原因となっている第１の誘電体多層膜の交互層が４７．５゜でブリュースター条件（１）を満足し、短波長側の落ち込みの原因となっている第２の誘電体多層膜の交互層が４２．５゜でブリュースター条件（２）を満足するようにそれぞれの誘電体多層膜の膜物質を選択しているからである。
【００２２】
このように、本発明の構成の偏光ビームスプリッタを用いることにより、従来例より大幅に使用波長帯域が広げることができ、光の入射角に対し自由度の高い偏光ビームスプリッタが得ることができた。
次に本発明の第２の実施例について述べる。
第２の実施例の誘電体多層膜構成は、第１の実施例と基本的には同じであり、誘電体多層膜に用いる物質の組み合わせが異なる。その構成は、調整層１Ｃと第１の誘電体多層膜３の交互層１３とが積層された透光性基体１と調整層２Ｃと第２の誘電体多層膜４の交互層２３とが積層されている透光性基体２とが光学的接着剤５で接合されている偏光ビームスプリッタの構成である。透光性基体１及び透光性基体２は、屈折率ｎＳが１．５２である。
【００２３】
第１の誘電体多層膜の交互層は、設計基準波長λ１＝７００ｎｍで、高屈折率物質ｎＨ１＝２．３８のＴｉＯ_２と低屈折率物質ｎ１＝１．４７のＳｉＯ_２とが光学的膜厚λ１／４で構成されている。
第２の誘電体多層膜の交互層は、設計基準波長λ２＝４３０ｎｍで高屈折率物質ｎＨ２＝２．０２のＺｒＯ_２と低屈折率物質ｎＬ２＝１．３７のＭｇＦ_２とがそれぞれ光学的膜厚λ２／４で構成されている。
また第１及び第２の誘電体多層膜の各交互層とプリズム１及び２との間には、それぞれ膜厚λ１／８、λ２／８の調整層が設けられている。
【００２４】
光束が設計基準入射角５２゜近傍で入射角±４゜ずれた場合、高角度側に対応する（使用波長域では短波長側に相当する）第１の誘電体多層膜の交互層に用いている高屈折率物質及び低屈折率物質は、光束の膜面法線に対する入射角５６゜でブリュースター条件（１）を満足するように選択する。本実施例の第１の誘電体多層膜の物質組み合わせは、高屈折率層１１にＴｉＯ_２、低屈折率層１２にＳｉＯ_２を選択した。
【００２５】
また低角度側に対応する（使用波長域で長波長側に相当する）第２の誘電体多層膜の交互層に用いている高屈折率物質及び低屈折率物質は、光束が入射角４８゜でブリュースター条件（２）を満足するように選択する。本実施例の第２の誘電体多層膜の物質組み合わせは、高屈折率層２１にＺｒＯ_２、低屈折率層２２にＭｇＦ_２を選択した。
【００２６】
図６は、誘電体多層膜構成の第２実施例のＰ及びＳ偏光成分の透過率特性及び入射角４８゜、５２゜、５６゜のそれぞれの透過率特性である。
本発明の第２実施例の誘電体多層膜構成を有する偏光ビームスプリッタのＰ及びＳ偏光成分の透過率の入射角依存性について図１０の比較例と比較する。
比較例の多層膜構成は、波長範囲が４８０ｎｍから５５０ｎｍにおいて、入射角を設計基準角度から数度ずれると帯域幅が７０ｎｍとなり、使用帯域は非常に狭くなってしまう。
【００２７】
それに対し、本発明の第２実施例は、波長範囲４６０ｎｍから６２０ｎｍにわたり、Ｓ偏光成分とＰ偏光成分との高い偏光分離を示している。設計基準入射角から±４゜ずれても帯域幅Ｘは、１７０ｎｍと広い帯域を維持している。
このように、本発明の実施例は、第１の誘電体多層膜の交互層と第２の誘電体多層膜の交互層とが同一な種類の物質組み合わせであるＴｉＯ_２とＳｉＯ_２とを用いた比較例に比べ、入射角依存性を考慮に入れても、透過率特性の帯域幅を大幅に広げることができた。
【００２８】
これは長波長側のＰ偏光透過率の落ち込みの原因となっている第１の誘電体多層膜の交互層では５６゜でブリュースター条件（１）を満足し、短波長側の落ち込みの原因となっている第２の誘電体多層膜の交互層では４８゜でブリュースター条件（２）を満足するよう誘電体多層膜の膜物質を選択しているからである。
このように、第１の誘電体多層膜と第２の誘電体多層膜それぞれの設計基準波長や低屈折率物質と高屈折率物質との組み合わせを異ならせることにより、入射角に対し自由度が高く、かつ偏光分離比Ｓ／Ｐが高い、高帯域な偏光ビームスプリッタを得ることが可能である。
【００２９】
図７及び図８は、第３の実施例である。
本実施例は、本発明の偏光ビームスプリッタの配置に関する変形例である。
透光性基体１上に第１の誘電体多層膜３と第２の誘電体多層膜４とが連続して積層し、透光性基体２を接着層５を介して構成されている。
この構成によれば、低屈折率層及び高屈折率層の成膜が、１バッチですむ利点がある。
【００３０】
図９は、本発明の偏光ビームスプリッタの第４の実施例である。
本実施例の偏光ビームスプリッタは、透光性基体に透明平板基体２を用い、平板基体とほぼ同一な屈折率を有する液体媒質６で満たされた第１及び第２の誘電体多層膜とから構成されている。その第１の誘電体多層膜３と第２の誘電体多層膜４は、透明平板基体の両側に配置されている。液体媒質としては、例えばエチレングリコール（屈折率１．４３）、ベンゼン（屈折率１．５１）などがある。
【００３１】
一般に、透光性基体にプリズムを用いた場合、プリズム内の材料不均一により複屈折を生ずる。基体中を光束が通過する際、偏光状態が変化し直線偏光特性が悪くなることが知られている。この様な場合、液体媒質を用いた構成により、透光性基体の複屈折の問題を避けることができる。
第３実施例のような構成配置を有する偏光ビームスプリッタにより、誘電体多層膜層の成膜が１バッチで済み、生産性の向上が期待できる。
【００３２】
第４実施例の構成配置を有する偏光ビームスプリッタは、高価なプリズムを使用しなくて済むためコスト低減などが期待できる。
【００３３】
【発明の効果】
以上のように本発明の偏光ビームスプリッタによれば、低屈折率物質と高屈折率物質との組み合わせや設計基準波長が異なる第１及び第２の誘電体多層膜とを設けた構成を用いることにより、入射角に対し自由度が高く、かつ、広い波長域でＳ偏光成分とＰ偏光成分との高い分離または合成が可能となる。
【図面の簡単な説明】
【図１】本発明の偏光ビームスプリッタの構成を示す概略断面図。
【図２】本発明の第１及び第２の誘電体多層膜の構成断面図。
【図３】本発明の誘電体多層膜構成に入射する光束の状態説明図。
【図４】本発明第１実施例の誘電体多層膜構成の透過率特性図。
【図５】本発明第１実施例の誘電体多層膜構成の透過率特性の入射角依存性。
【図６】本発明第２実施例の誘電体多層膜構成のＰ偏光成分の透過率特性図。
【図７】本発明第３実施例の偏光ビームスプリッタの構成断面図。
【図８】本発明第３実施例の第１及び第２の誘電体多層膜の構成断面図。
【図９】本発明第４実施例の偏光ビームスプリッタの構成断面図。
【図１０】従来の偏光ビームスプリッタの構成に基づく透過率特性比較図。
【符号の説明】
１第１の透光性基体（プリズム）
２第２の透光性基体（プリズム）
３第１の誘電体多層膜
４第２の誘電体多層膜
５接着層
６液体媒質
１１光学的膜厚がλ１／４の高屈折率物質
１２光学的膜厚がλ１／４の低屈折率物質
１３光学的膜厚がそれぞれλ１／４の高屈折率物質と低屈折率物質とからなる交互層
１Ｃ光学的膜厚がλ１／８の調整層
２１光学的膜厚がλ２／４の高屈折率物質
２２光学的膜厚がλ２／４の低屈折率物質
２３光学的膜厚がそれぞれλ２／４の高屈折率物質と低屈折率物質とからなる交互層
２Ｃ光学的膜厚がλ２／８の調整層[0001]
[Industrial applications]
The present invention relates to a polarizing beam splitter used for separating and combining both S and P polarization components.
[0002]
[Comparison technology]
Generally, a polarizing beam splitter is used in which a dielectric multilayer film in which dielectric thin films of a high refractive index material and a low refractive index material are alternately stacked is interposed between two 45 ° prisms. The material selection of the dielectric multilayer film is within a wavelength range where the reflectance of the P-polarized light component of the incident light incident from the optical axis of the 45 ° prism is the smallest and the reflectance of the S-polarized light component is the highest. It is done as follows.
[0003]
2. Description of the Related Art A polarizing beam splitter is used in an optical disk device, a projection display device, and the like in order to efficiently separate incident light into P and S polarization components. From the comparison, various proposals have been made on the configuration of the dielectric multilayer film in order to widen the usable wavelength bandwidth of the polarizing beam splitter. For example, in JP-A-61-141402, an intermediate layer is provided on a dielectric multilayer film having a basic period of two layers of a high refractive index material and a low refractive index material, and the thickness of this layer is adjusted. Broadening the bandwidth. Further, in the configuration example of the conventional polarizing beam splitter disclosed in Japanese Patent Application Laid-Open No. 3-284705, a combination of a high refractive index material and a low refractive index material is the same in two dielectric multilayer films having different design reference wavelengths. It is a combination. With this configuration, the bandwidth of the used wavelength is widened and the polarization separation ratio is improved.
[0004]
[Problems to be solved by the invention]
However, in the conventional polarization beam splitter having a dielectric multilayer structure, although the bandwidth is widened with respect to the design incident angle, even if the incident angle of the light beam is slightly deviated, the P / S polarization separation ratio is deteriorated, and the bandwidth is reduced. Is very narrow.
SUMMARY OF THE INVENTION An object of the present invention is to provide a polarization beam splitter which has a small incident angle dependence of a light beam incident on a polarization separation multilayer film surface, a high polarization separation ratio, and a wide use bandwidth.
[0005]
[Means for Solving the Problems]
According to the present invention, there is provided a polarizing beam splitter having a dielectric multilayer film formed on a light-transmitting substrate, wherein the dielectric multilayer film has a first dielectric layer having two different design reference wavelengths λ1. And a second dielectric multilayer film having a design reference wavelength λ2, wherein the first and second dielectric multilayer films each include alternating layers of a high refractive index material and a low refractive index material. And the incident angle satisfying the Brewster condition of the alternate layer of the first dielectric multilayer film and the incident angle satisfying the Brewster condition of the alternate layer of the second dielectric multilayer film are different. A combination of the refractive index values of the high-refractive index material and the low-refractive index material forming the alternating layers in the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film Are characterized in that they differ from each other.
[0006]
[Action]
The polarizing beam splitter according to the present invention has a configuration in which the bandwidth of the used wavelength region is not narrowed even if the angle of incidence of the light beam on the dielectric multilayer film slightly changes, and a high refractive index of the alternating layers of the dielectric multilayer film. The material used for the layer and the low refractive index layer is selected. In order to separate the polarized light over a wide band, it is necessary to increase the wavelength band separating the P-polarized component and the S-polarized component from the wavelength of the light beam incident on the polarization separating film. To this end, according to Snell's law, the vicinity of the Brewster angle, at which the polarization separation of the P-polarized light component and the S-polarized light component is the largest, is set as the design incident angle and the light is incident on the polarization splitting film.
[0007]
The dielectric multilayer structure of the present invention includes first and second dielectric multilayer films having different design reference wavelengths. The incident angles of the light beams incident on the first and second dielectric multilayer films are set to be different. The high refractive index and low refractive index substances of the first and second dielectric multilayer films were selected so that the following Brewster conditions (1) and (2) were different. For example, one of the alternate layers of the dielectric multilayer film is a combination of TiO ₂ and a low-refractive-index material SiO ₂ as a high-refractive-index material, and the other alternating layer of the dielectric multilayer film is a combination of TiO _{2 and a} high-refractive-index material. Alternatively, a combination in which Al ₂ O ₃ is used as the low refractive index substance may be used.
[0008]
The design reference wavelengths λ1 and λ2 (λ1 ≠ λ2) and the design reference incident angle θ are the incident angles θ1 and θ2, respectively. The Brewster conditions in each case are represented by the following equations (1) and (2).
λ1> λ2
λ1, θ1; nH1 / COSθH1 = nL1 / COSθL1 (1)
λ2, θ2; nH2 / COSθH2 = nL2 / COSθL2 (2)
θ1; the angle θ2 from the light-transmitting substrate 1 to the boundary surface between the first dielectric multilayer film and the light-transmitting substrate 1; Angles nH1 and nL1 incident on the boundary surface with the refractive index nH2 and nL2 of the high refractive index layer and the low refractive index layer in the alternating layers of the first dielectric multilayer film at the design reference wavelength λ1; High refractive index layers and low refractive index layers in the alternate layers of the second dielectric multilayer film θH1 and θL1; high refractive index layers in the first dielectric multilayer film at the design reference wavelength λ1 ΘH2, θL2 incident on the interface from each layer of the low-refractive-index layer and the interface between the high-refractive-index layer and the low-refractive-index layer at the design reference wavelength λ2. FIG. 3 shows that the luminous flux incident on the dielectric multilayer film has a high refractive index layer and It is a state diagram enters the boundary surface from the refractive index layer. In the figure, θi, θHi, and θLi correspond to the first and second dielectric multilayer films i = 1 and 2, respectively.
[0009]
The thicknesses of the high refractive index layer, the low refractive index layer, and the adjustment layer used for the alternating layers of the dielectric multilayer film of the present invention are λ / 4, λ / 4, and λ / 8, respectively. However, the actually formed film thickness is determined experimentally through trial and error, and may slightly deviate from the designed value.
Further, the adjustment layer of the present invention is provided to reduce a ripple generated in the transmittance of the P-polarized light component. If there is a large ripple, the wavelength range that can be used as the polarizing beam splitter is limited, which is not preferable.
[0010]
For comparison with the embodiment of the present invention, the configuration of the polarizing beam splitter is basically the same as that of FIG. 1, and the high refractive index layer TiO ₂ and the low refractive index used for the alternating layers of the first and second dielectric multilayer films are used. The transmittance characteristics in which the combination of the substance with the rate layer SiO ₂ is the same will be examined. FIG. 10 shows the incident angle dependence of the transmittance characteristics.
At a design reference angle of incidence of 45 °, the band having a high P / S polarization separation ratio is 160 nm, but if the angle of incidence is shifted by ± 2.5 °, the bandwidth becomes 90 nm. A polarization beam splitter using a dielectric multilayer film composed of only one type can obtain a wide usable wavelength range in which S and P polarization components can be separated. However, even if the angle of incidence on the surface of the dielectric multilayer film is slightly shifted, the desired wavelength bandwidth becomes very narrow.
[0011]
On the other hand, the working bandwidth of the embodiment of the present invention is very wide while maintaining the separation ratio between the P-polarized light component and the S-polarized light component even if the angle at which the light beam enters the dielectric multilayer film is slightly shifted. Further, the degree of freedom in the arrangement of the optical system incorporating the polarizing beam splitter is increased.
Next, a method of forming the dielectric multilayer film of the polarizing beam splitter of the present invention will be described.
[0012]
FIG. 1 shows that first and second dielectric multilayer films 3 and 4 of the present invention are formed on a prism 1 which is a translucent substrate, and each of them is bonded via an adhesive layer 5. Configuration.
FIG. 8 shows that a first dielectric multilayer film and a second dielectric multilayer film are continuously formed on a transparent substrate 1. Further, the translucent base 12 is bonded thereon.
[0013]
In FIG. 9, the same performance can be obtained even when the transparent substrate is formed by applying a dielectric multilayer film on both sides of the flat glass 2 and immersing it in a liquid medium 6 having a refractive index similar to that of the glass.
[0014]
【Example】
A first embodiment of the polarizing beam splitter according to the present invention will be described.
FIG. 1 shows a prism 1 in which an adjustment layer 1C and an alternating layer 13 of the first dielectric multilayer film 3 are stacked, and an adjustment layer 2C and an alternating layer 23 of the second dielectric multilayer film 4 stacked. This is a configuration of a polarizing beam splitter in which a prism 2 and an optical adhesive 5 are joined. The prism 1 and the prism 2 have a refractive index nS of 1.84. The refractive index nb of the optical adhesive is 1.52. The drawing shows the reflected light R and the transmitted light T when the light beam is incident at 45 °. The transmitted light T has an S-polarized component TS and a P-polarized component TP.
[0015]
The alternating layers 13 of the first dielectric multilayer film are composed of TiO ₂ 11 having a high refractive index material nH1 = 2.38 and Al ₂ O ₃ 12 having a low refractive index material nL1 = 1.65 at a design reference wavelength λ1 = 680 nm. Are configured with an optical film thickness λ1 / 4.
The alternating layers 23 of the second dielectric multilayer film are composed of TiO ₂ 21 having a high refractive index material nH2 = 2.38 and SiO ₂ 22 having a low refractive index material nL2 = 1.47 at a design reference wavelength λ2 = 420 nm. It has an optical film thickness λ2 / 4.
Further, between each alternate layer of the first and second dielectric multilayer films and the prism 1 and the prism 2, adjustment layers having a film thickness of λ1 / 8 and λ2 / 8, respectively, are provided.
[0016]
Consider a case where the light beam has an incident angle shifted by ± 2.5 ° from the design reference incident angle of 45 °. The high-refractive-index material 11 and the low-refractive-index material 12 used for the alternating layers 13 of the first dielectric multilayer film corresponding to the high angle side (corresponding to the short wavelength side in the used wavelength region) transmit light. Is selected so as to satisfy the Brewster condition (1) at an angle θ1 = 47.5 ° from the transparent substrate 1 to the interface between the transparent substrate 1 and the first dielectric multilayer film. In this embodiment, TiO ₂ was selected for the high refractive index layer 11 and Al ₂ O ₃ was selected for the low refractive index layer 12 as a material combination of the alternating layers of the first dielectric multilayer film.
[0017]
The high-refractive-index substance 21 and the low-refractive-index substance 22 used for the alternating layer 23 of the second dielectric multilayer film corresponding to the low angle side (corresponding to the long wavelength side in the used wavelength range) transmit light. It is selected so as to satisfy the Brewster condition (2) at an angle θ2 = 42.5 ° at which the light enters the interface between the light-transmitting substrate 2 and the second dielectric multilayer film from the light-transmitting substrate 2. In this embodiment, as the substance a combination of alternating layers of the second dielectric multilayer film, TiO 2 in the high refractive index layer _21, was chosen SiO ₂ for the low refractive index layer 22.
[0018]
FIG. 4 shows the transmittance characteristics Tp and TS of the P and S polarization components and the respective transmittance characteristics of the incident angles 42.5 °, 45 °, and 47.5 ° of the dielectric multilayer structure of the first embodiment. .
The dependence of the transmittance of the P and S polarization components of the polarization beam splitter having the dielectric multilayer structure of the first embodiment of the present invention on the incident angle will be compared with the comparative example of FIG.
[0019]
In the multilayer film configuration of the comparative example, when the incident angle deviates from the design reference angle by several degrees in the wavelength range of 480 nm to 550 nm, the bandwidth X becomes 70 nm, and the used band becomes very narrow.
In contrast, the first embodiment of the present invention has a high polarization separation (TS / TP) of 0.1% or less over the wavelength range of 460 nm to 620 nm. Even if it deviates from the design standard incident angle by ± 2.5 °, the bandwidth X maintains a wide band of 160 nm.
[0020]
FIG. 5 shows the dependency of the transmittance of the P-polarized light component on the long wavelength side λ = 620 nm in the incident angle according to the first embodiment of the present invention.
This embodiment is different from the comparative example of FIG. 10 in which the combination of the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film uses the same type of substance TiO ₂ and SiO ₂ . The bandwidth of the transmittance characteristics could be greatly expanded even if the incident angle dependence was taken into consideration.
[0021]
This is because the alternating layer of the first dielectric multilayer film, which causes the drop of the P-polarized light transmittance on the long wavelength side, satisfies the Brewster condition (1) at 47.5 °, and the drop on the short wavelength side does not. This is because the film material of each dielectric multilayer film is selected so that the alternate layer of the second dielectric multilayer film which causes the problem satisfies the Brewster condition (2) at 42.5 °.
[0022]
As described above, by using the polarization beam splitter having the configuration of the present invention, the wavelength band to be used can be significantly widened as compared with the conventional example, and a polarization beam splitter having a high degree of freedom with respect to the incident angle of light can be obtained. .
Next, a second embodiment of the present invention will be described.
The structure of the dielectric multilayer film of the second embodiment is basically the same as that of the first embodiment, and the combination of substances used for the dielectric multilayer film is different. The structure is such that the light-transmitting substrate 1 in which the adjustment layer 1C and the alternating layer 13 of the first dielectric multilayer film 3 are stacked, the adjustment layer 2C and the alternating layer 23 of the second dielectric multilayer film 4 are stacked. This is a configuration of a polarization beam splitter in which a transparent substrate 2 is bonded with an optical adhesive 5. The translucent substrate 1 and the translucent substrate 2 have a refractive index nS of 1.52.
[0023]
Alternating layers of the first dielectric multilayer film is a design wavelength .lambda.1 = 700 nm, the high refractive index material nH1 = 2.38 TiO ₂ and the low refractive index material n1 = 1.47 SiO ₂ and an optical membrane of It has a thickness of λ1 / 4.
The alternate layers of the second dielectric multilayer film are optical films of ZrO ₂ having a high refractive index material nH2 = 2.02 and MgF ₂ having a low refractive index material nL2 = 1.37 at a design reference wavelength λ2 = 430 nm. It has a thickness of λ2 / 4.
Further, between the alternating layers of the first and second dielectric multilayer films and the prisms 1 and 2, adjustment layers having a film thickness of λ1 / 8 and λ2 / 8, respectively, are provided.
[0024]
When the luminous flux is deviated by ± 4 ° in the vicinity of the design reference incident angle of 52 °, the luminous flux is used as an alternate layer of the first dielectric multilayer film corresponding to the higher angle side (corresponding to the shorter wavelength side in the used wavelength range). The high-refractive-index substance and the low-refractive-index substance are selected so as to satisfy the Brewster condition (1) at an incident angle of 56 ° with respect to the normal to the film surface of the light beam. Substance combination of the first dielectric multilayer film of this example, TiO _2, the low refractive index layer 12 was selected SiO ₂ in the high refractive index layer 11.
[0025]
The high-refractive index material and the low-refractive index material used for the alternating layers of the second dielectric multilayer film corresponding to the low angle side (corresponding to the long wavelength side in the used wavelength range) have a light flux of an incident angle of 48 °. Is selected so as to satisfy the Brewster condition (2). Substance combination of the second dielectric multilayer film of this example, ZrO 2 in the high refractive index layer _21, was chosen MgF ₂ for the low refractive index layer 22.
[0026]
FIG. 6 shows the transmittance characteristics of the P and S polarization components and the transmittance characteristics at incident angles of 48 °, 52 ° and 56 ° in the second embodiment of the dielectric multilayer structure.
The incident angle dependence of the transmittance of the P and S polarization components of the polarizing beam splitter having the dielectric multilayer structure according to the second embodiment of the present invention will be compared with the comparative example of FIG.
In the multilayer structure of the comparative example, in the wavelength range of 480 nm to 550 nm, if the incident angle deviates from the design reference angle by several degrees, the bandwidth becomes 70 nm, and the used band becomes very narrow.
[0027]
On the other hand, the second embodiment of the present invention shows high polarization separation of the S-polarized component and the P-polarized component over the wavelength range of 460 nm to 620 nm. Even if it deviates from the design standard incident angle by ± 4 °, the bandwidth X maintains a wide band of 170 nm.
As described above, the embodiment of the present invention uses TiO ₂ and SiO _{2 in} which the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film are the same kind of substance combination. Compared with the comparative example, the bandwidth of the transmittance characteristics could be greatly increased even when the incident angle dependency was taken into consideration.
[0028]
This is because the alternating layers of the first dielectric multilayer film, which cause the drop in the transmittance of P-polarized light on the long wavelength side, satisfy the Brewster condition (1) at 56 °, and cause the drop on the short wavelength side. This is because the material of the dielectric multilayer film is selected so as to satisfy the Brewster condition (2) at 48 ° in the alternate layer of the second dielectric multilayer film.
As described above, by changing the design reference wavelength of each of the first dielectric multilayer film and the second dielectric multilayer film and the combination of the low refractive index material and the high refractive index material, the degree of freedom with respect to the incident angle is increased. It is possible to obtain a high-bandwidth polarization beam splitter having a high polarization separation ratio S / P.
[0029]
7 and 8 show a third embodiment.
This embodiment is a modified example regarding the arrangement of the polarizing beam splitter of the present invention.
A first dielectric multilayer film 3 and a second dielectric multilayer film 4 are continuously laminated on a light-transmitting substrate 1, and the light-transmitting substrate 2 is formed via an adhesive layer 5.
According to this configuration, there is an advantage that the deposition of the low refractive index layer and the high refractive index layer can be performed in one batch.
[0030]
FIG. 9 shows a fourth embodiment of the polarizing beam splitter according to the present invention.
The polarizing beam splitter of this embodiment uses a transparent flat substrate 2 as a light-transmitting substrate, and includes a first and a second dielectric multilayer film filled with a liquid medium 6 having substantially the same refractive index as the flat substrate. It is configured. The first dielectric multilayer film 3 and the second dielectric multilayer film 4 are arranged on both sides of the transparent flat substrate. Examples of the liquid medium include ethylene glycol (refractive index: 1.43) and benzene (refractive index: 1.51).
[0031]
In general, when a prism is used for a light-transmitting substrate, birefringence occurs due to unevenness of the material in the prism. It is known that when a light beam passes through a substrate, the state of polarization changes and linear polarization characteristics deteriorate. In such a case, the problem of birefringence of the light-transmitting substrate can be avoided by the structure using the liquid medium.
With the polarization beam splitter having the configuration and arrangement as in the third embodiment, the formation of the dielectric multilayer film is completed in one batch, and an improvement in productivity can be expected.
[0032]
The polarization beam splitter having the configuration and arrangement of the fourth embodiment does not need to use an expensive prism, so that cost reduction can be expected.
[0033]
【The invention's effect】
As described above, according to the polarizing beam splitter of the present invention, a configuration in which a combination of a low-refractive index substance and a high-refractive index substance and first and second dielectric multilayer films having different design reference wavelengths are used. Accordingly, the degree of freedom with respect to the incident angle is high, and the S-polarized component and the P-polarized component can be separated or synthesized in a wide wavelength range.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a configuration of a polarizing beam splitter according to the present invention.
FIG. 2 is a configuration sectional view of first and second dielectric multilayer films of the present invention.
FIG. 3 is an explanatory diagram of a state of a light beam incident on a dielectric multilayer structure of the present invention.
FIG. 4 is a transmittance characteristic diagram of a dielectric multilayer structure according to the first embodiment of the present invention.
FIG. 5 is an incident angle dependence of transmittance characteristics of the dielectric multilayer structure of the first embodiment of the present invention.
FIG. 6 is a transmittance characteristic diagram of a P-polarized light component having a dielectric multilayer structure according to a second embodiment of the present invention.
FIG. 7 is a configuration sectional view of a polarization beam splitter according to a third embodiment of the present invention.
FIG. 8 is a configuration sectional view of first and second dielectric multilayer films according to a third embodiment of the present invention.
FIG. 9 is a configuration sectional view of a polarization beam splitter according to a fourth embodiment of the present invention.
FIG. 10 is a graph showing a comparison of transmittance characteristics based on the configuration of a conventional polarizing beam splitter.
[Explanation of symbols]
1 First translucent substrate (prism)
2 Second translucent substrate (prism)
3 First Dielectric Multilayer Film 4 Second Dielectric Multilayer Film 5 Adhesive Layer 6 Liquid Medium 11 High Refractive Index Material with Optical Thickness λ1 / 4 Low Refractive Index Material with Optical Thickness λ1 / 4 13 Alternating layer 1C made of a high-refractive-index substance and a low-refractive-index substance each having an optical thickness of λ1 / 4 Adjusting layer 21 having an optical thickness of λ1 / 8 High-refractive index having an optical thickness of λ2 / 4 Substance 22 Low-refractive-index substance having an optical film thickness of λ2 / 4 23 Alternating layer 2C composed of high-refractive-index substance and low-refractive-index substance having an optical film thickness of λ2 / 4, respectively. Adjustment layer

Claims

In a polarizing beam splitter having a dielectric multilayer film formed on a transparent substrate,
The dielectric multilayer has two different design reference wavelengths λ. One A first dielectric multilayer film having Two And a second dielectric multilayer film having
The first and second dielectric multilayer films each include alternating layers of a high refractive index material and a low refractive index material,
The second dielectric multilayer film is formed such that the incident angle satisfying the Brewster condition of the alternating layer and the incident angle satisfying the Brewster condition of the alternating layer of the second dielectric multilayer film are different from each other. The combination of the refractive indices of the high-refractive index material and the low-refractive index material forming the alternating layer is made different between the alternating layer of the first dielectric multilayer film and the alternating layer of the second dielectric multilayer film. A polarizing beam splitter.

2. The polarization beam splitter according to claim 1, wherein the high refractive index material of the first dielectric multilayer film, the high refractive index material of the second dielectric multilayer film, and the first dielectric multilayer film. A polarizing beam splitter, wherein at least one set of the low refractive index material and the low refractive index material of the second dielectric multilayer film has different refractive indexes.

2. The polarization beam splitter according to claim 1, wherein the high refractive index material of the first dielectric multilayer film, the high refractive index material of the second dielectric multilayer film, and the first dielectric multilayer film. A polarizing beam splitter, wherein at least one pair of the low refractive index material and the low refractive index material of the second dielectric multilayer film is different from each other.

The high refractive index material TiO ₂ and the low refractive index material SiO ₂ are provided in the alternating layers of the first dielectric multilayer film, and the high refractive index material TiO ₂ and the low refractive index material Al are provided in the alternating layers of the second dielectric multilayer film. 4. The polarization beam splitter according to claim 3, wherein the polarization beam splitter is a combination using ₂ O ₃ .

A high refractive index material TiO ₂ and a low refractive index material SiO ₂ are provided in the alternate layers of the first dielectric multilayer film, and a high refractive index material ZrO ₂ and a low refractive index material MgF are provided in the alternate layers of the second dielectric multilayer film. polarization beam splitter according to claim 3, characterized in that a combination with the _2.

The first and second dielectric multilayer films have respective reference wavelengths λ One , Λ Two At the optical film thickness λ One / 4, λ Two 4. An alternating layer in which two layers composed of a high-refractive-index substance and a low-refractive-index substance of / 4 are stacked with n periods (n is an arbitrary integer) as a basic period. One The polarizing beam splitter according to 1.

The polarizing beam splitter according to claim 6, further comprising an optical thin film λ formed on both sides of the alternating layer. One / 8, λ Two / 8. A polarizing beam splitter comprising a thin film layer made of either the high refractive index material or the low refractive index material.