JP3977021B2

JP3977021B2 - Image display device and head mounted display using the same

Info

Publication number: JP3977021B2
Application number: JP2001041799A
Authority: JP
Inventors: 章市山崎
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2001-02-19
Filing date: 2001-02-19
Publication date: 2007-09-19
Anticipated expiration: 2021-02-19
Also published as: JP2002244076A

Description

【０００１】
【発明の属する技術分野】
本発明は画像表示装置に関し、例えば観察用の画像情報を表示する表示素子として反射型の液晶表示素子を用い、そこに表示された画像情報を適切に設定した光学素子を介して拡大して観察するようにしたヘッドマウントディスプレイ（ＨＭＤ）やメガネ型ディスプレイ等に好適なものである。
【０００２】
【従来の技術】
従来より、液晶等の画像表示素子に表示した画像情報を拡大した虚像として観察するようにした頭部装着型の画像観察装置（画像表示装置）、所謂ヘッドマウントディスプレイ（ＨＭＤ）が種々と提案されている。
【０００３】
このうち反射型の表示素子を用いたＨＭＤが、例えば、特開平０７−１２８６１４号公報、特開平１１−１２５７９１号公報、特開平１１−３３７８６３号公報、特開２０００−１００４１号公報等で提案されている。
【０００４】
これらで提案されているＨＭＤは照明光源から発せられた光が反射型液晶で反射され、眼球に導かれて液晶で表示された画像の拡大像を観察するものである。このとき光束は照明光源、照明光学系、反射型の液晶、表示光学系、眼球の順序で進む。特開平１１−１２５７９１号公報で提案されているＨＭＤで開示されている実施例では照明光学系がなく、照明光源からの光がダイレクトに反射型液晶を照明している。この場合は照明光学系と表示光学系の共有面は存在しない例もある。この場合は照明光源からの光束がけられないようにしなければならないため、照明光源と反射型液晶の間に大きなスペースが必要になり、大型化しやすい。他の提案されている公報の実施例では、ほとんど照明光学系と表示光学系の間で共有面を持っている。共有面があれば、照明光学系と表示光学系で光路がオーバーラップするため小型化しやすい。しかしこの共有面が多ければ多いほど光学系は複雑になり、光量ロスも多くなる。一方、ＨＭＤのコンパクトな表示光学系を本発明者は特開平７−３３３５５１号公報で提案している。同公報では自由曲面プリズムを用いて装置全体の小型化を図っている。又本発明者は、自由曲面プリズムと反射型の表示素子を組み合わせたＨＭＤを特開平１１−１２５７９１号公報、特開平１１−３３７８６３号公報、特開２０００−１００４１号公報で提案している。
【０００５】
【発明が解決しようとする課題】
従来よりＨＭＤ等の画像観察装置では、装置を観察者の頭部に装着するために装置全体の小型化、及び軽量化を図ることが重要な課題となっている。又、表示手段に表示した画像情報を良好に観察できることが重要な課題となっている。
【０００６】
画像表示装置として反射型の液晶表示素子を用いた場合で装置全体の小型化を図るには、それを照明するための照明装置を装置内に適切に組み込む必要がある。
【０００７】
例えば照明光源からの光が反射型液晶を照明する際、多くの反射面や透過面を介したり、光路長の長いプリズム体の中を通過したりすると、反射型液晶に到達する前にどうしても照明光源からの光量がロスされてしまう。従って光量ロス、が少なく、表示光学系、照明光学系ともコンパクトなＨＭＤが望まれている。
【０００８】
本発明は、液晶ディスプレイ等の表示手段に表示した画像情報を観察する際、光源手段から表示手段に至る照明光学系及び表示手段からの光束を観察者の眼球に導光するための表示光学系の構成を適切に設定することによって、装置全体の小型化を図りつつ光量のロスを減らし、該画像情報を良好なる画質で観察することができる画像観察装置及びそれを用いたヘッドマウントディスプレイの提供を目的とする。
【０００９】
【課題を解決するための手段】
請求項１の発明の画像表示装置は、反射型の表示手段と、該表示手段を照明する照明手段と、該照明手段からの光を該表示手段に導く照明光学系と、該表示手段からの光を観察者側に導く表示光学系を有した画像表示装置において、
該照明光学系と該表示光学系で互いに共有する透過兼反射の両作用を有する光学面Ａを有し、該光学面Ａはローカル母線断面（該照明手段から発せられ該表示手段の画像中心と瞳中心を通る基準光線の入射光と射出光を含む面）上で曲率を有し、該光学面Ａに対し該表示手段と反対側に配置された曲率を有する光学面Ｂを有し、該光学面Ａと光学面Ｂとでガラス部材で構成されるレンズ体を形成し、
該照明手段から発せられた光線は、該レンズ体の該光学面Ａで反射して該表示手段を照明し、該表示手段からの反射光は、該光学面Ａを透過し、該レンズ体に入射し、光学面Ｂを射出して、複数の反射面で反射した後、瞳に導かれて、表示手段に表示した画像の拡大像を形成し、
該表示光学系における該レンズ体の該光学面Ａのローカル母線断面曲率半径をlocal_ryＡ、該光学面Ｂのローカル母線断面曲率半径をlocal_ryＢとした時、local_ryＡとlocal_ryＢは同符号であり、
０．４＜ local_ryＡ／ local_ryＢ＜２．０・・・（１）
を満たすことを特徴としている。
【００１０】
請求項２の発明は、請求項１の発明において、前記照明光学系と前記表示光学系で共有する透過兼反射の両作用を有する光学面Ａが１面のみ存在することを特徴としている。
【００１１】
請求項３の発明は、請求項１の発明において、前記表示手段からの反射光は、前記レンズ体を射出した後、偏心曲率面である複数の反射面で反射し、瞳に導かれることを特徴としている。
【００１２】
請求項４の発明は、請求項１、２又は３の発明において、前記照明手段は複数の色光を時分割で放射する時分割光源であり、該表示手段は該時分割光源から放射される色光に合わせて各色光に基づく画像を時分割表示することを特徴としている。
【００１３】
請求項５の発明は、請求項１、２、３又は４の発明において、前記表示光学系はアジムス角度により屈折力が異なる面を２面以上含み、該表示光学系全体として正の屈折力を有することを特徴としている。
【００１４】
請求項６の発明の画像表示装置は、反射型の表示手段と、該表示手段を照明する照明手段と、該照明手段からの光を該表示手段に導く照明光学系と、該表示手段からの光を観察者側に導く表示光学系を有した画像表示装置において、
該照明光学系と該表示光学系で互いに共有する透過兼反射の両作用を有する曲率を有した光学面Ａと、該光学面Ａに対し該表示手段と反対側に配置され曲率を有する光学面Ｂを有し、該光学面Ａと該光学面Ｂとでレンズ体を形成し、
該照明手段から発せられた光線は、該レンズ体の光学面Ａで反射して該表示手段を照明し、該表示手段からの反射光は、該光学面Ａを透過し、該レンズ体に入射し、該光学面Ｂを射出して、複数の反射面で反射した後、瞳に導かれて表示手段に表示した画像の拡大像を形成し、
該表示手段のローカル母線断面上（該照明手段から発せられ該表示手段の画像中心と眼球中心を通る基準光線の入射光と射出光を含む面）での最周辺画像のうち、眼球より遠いほう側の最周像高Ｆ３と眼球中心とを通る光線をＦ３眼球中心光線、眼球より近いほう側の最周辺像高Ｆ２と眼球中心とを通る光線をＦ２眼球中心光線とした時、Ｆ３眼球中心光線のほうが、Ｆ２眼球中心光線より表示光学系における該レンズ体内の光路長が長いことを特徴としている。
【００１５】
請求項７の発明は、請求項６の発明において、前記表示光学系における前記レンズ体の前記曲率光学面Ａのローカル母線断面曲率が、前記曲面Ｂのローカル母線断面曲率より大きいことを特徴としている。
【００１６】
請求項８の発明は、請求項７の発明において、前記表示手段のローカル母線断面上での各像高と眼球中心とを通る各像高の眼球中心光線における表示光学系中の該レンズ体内の光路長が、前記Ｆ２眼球中心光線側から前記Ｆ３眼球中心光線側になるにつれて徐々に長くなることを特徴としている。
【００１７】
請求項９の発明の画像表示装置は、反射型の表示手段と、該表示手段を照明する照明手段と、該照明手段からの光を該表示手段に導く照明光学系と、該表示手段からの光を観察者側に導く表示光学系を有した画像表示装置において、
該照明光学系と該表示光学系で互いに共有する透過兼反射の両作用を有する光学面Ａと、該光学面Ａに対し該表示手段と反対側に光学面Ｂとでレンズ体を形成し、
該照明手段から発せられた光線は、該光学面Ａで反射して該表示手段を照明し、該表示手段からの反射光は、該光学面Ａを透過し、該レンズ体に入射し、光学面Ｂを射出して、複数の反射面で反射した後、瞳に導かれて、表示手段に表示した画像の拡大像を形成し、
該照明手段から発せられ該表示手段の画像中心と瞳中心を通る基準光線の入射光と射出光を含む面をローカル母線断面、基準光線と各面とのヒットポイントを含みローカル母線断面と垂直な面をローカル子線断面とし、該表示光学系における該レンズ体の該光学面Ａのローカル母線断面曲率半径をlocal_ryＡ、該光学面Ｂのローカル母線断面曲率半径をlocal_ryＢとするとき、local_ryＡとlocal_ryＢは同符号であり、
０．４＜ local_ryＡ／ local_ryＢ＜２．０
を満たし、且つ該光学面Ａと光学面Ｂとは、ローカル子線断面方向のパワーに比して、ローカル母線断面方向のパワーが強いことを特徴としている。
【００１８】
請求項１０の発明は、請求項９の発明において、前記光学面Ａと前記光学面Ｂはシリンドリカル面であることを特徴としている。
【００１９】
請求項１１の発明のヘッドマウントディスプレイは、請求項１から１０のいずれか1項の画像表示装置を有したことを特徴としている。
【００２１】
【発明の実施の形態】
図１〜図５は本発明の実施形態１〜５の要部断面図である。図中１は瞳位置であり、観察者の眼球Ｅが位置している。
【００２２】
２は自由曲面プリズム、３は反射型液晶、４は照明光源（照明手段）、５はハーフミラーより成る曲率を有した透過兼反射面（光学面）、７は光学面５と曲面１４を含むブーメラン型レンズ、８，９は偏光板、１２は第１の自由曲面ミラー、１３は第２の自由曲面ミラー（第２の光学部材）である。
【００２３】
符番４，５で示されるものは照明系の一要素を構成し、符番３，５，１４，２又は符番３，５，１４，１２，１３で示されるものは表示系の一要素を構成している。
符番５、１４、２又は符番５、１４、１２、１３は、表示光学系の一要素を構成している。
【００２４】
本実施形態では、照明光源４からの光量のロスをなるべく少なくするために、照明光源４をできるだけ反射型液晶３に近づけて、照明光学系の光路長を短くしている。例えば表示光学系に自由曲面プリズム２を使用した場合は、自由曲面プリズム２と反射型液晶３の間に照明光学系を構成する部材を設けている。また図５に示すように、表示光学系に２枚の自由曲面ミラー１２，１３を使用した場合は、自由曲面ミラー系（１２，１３）と反射型液晶３との間に照明光学系を構成する部材を設けている。
【００２５】
本発明の各実施形態の説明の前に、本発明で使用される母線断面、子線断面、ローカル母線断面、ローカル子線断面の定義について説明する。偏心系に対応していない従来系の定義では、各面頂点座標系でｚ軸を光軸とすると、ｙｚ断面が従来の母線断面（メリジオナル断面）、ｘｚ断面が子線断面（サジタル断面）となる。本発明は偏心系なので偏心系に対応したローカル母線断面、ローカル子線断面を新たに定義する。
【００２６】
表示手段の画像中心（外界を観察する為のシースルーのときは外界画像中心）と眼球中心を通る光線（以下、基準光線）と各面とのヒットポイント（入射点）上で、基準光線の入射光と射出光を含む面をローカル母線断面とし、ヒットポイントを含みローカル母線断面と垂直で、各面頂点座標系の子線断面（通常の子線断面）と平行な面をローカル子線断面として定義する。なお、表示手段が反射型の場合は、該基準光線を照明光学系、および照明光源まで延長して、各ヒットポイント上で、上記と同様にローカル母線断面、ローカル子線断面を定義する。ローカル母線断面焦点距離とローカル子線断面焦点距離については後述の項目で説明する。
【００２７】
次に本発明の各実施形態について説明する。図１〜５は本発明の実施形態１〜５の光路断面図（ローカル母線断面図）である。実施形態１〜２は反射型ＬＣＤ３が照明光源４からの光束でほぼ垂直入射照明されるタイプのものであり、本発明の実施形態３〜５は反射型ＬＣＤ３が照明光源４からの光束で斜入射照明されるタイプのものである。
【００２８】
一般的な液晶（ＴＮ液晶など）の特性として、液晶面とほぼ垂直に射出する光は、十分なコントラストを持っており画質は良いが、射出光が垂直から離れ傾いてくると、コントラストは低くなり画質が悪くなることが知られている。
【００２９】
実施形態１〜２はこれを解決するために、反射型ＬＣＤ３を垂直入射の光束で照明させている。照明光源４から発せられ、表示手段３の画像中心３ａと眼球中心１ａとを通る基準光線の反射型表示手段３への入射角度は０度±１０度としている。この範囲を超えるとコントラスト低下が目立ってしまう。また強誘電液晶（ＦＬＣ）などは特性が異なり、かなりの斜め射出光でもコントラストが落ちることはないため、ほとんどどの角度からでも良質な画質が観察される。そこで実施形態３〜５はこの液晶（ＦＬＣ）を想定し、反射型ＬＣＤ３を斜入射の光束で照明させて光学系全体を薄型化し、かつコントラスト落ちのない良質な画質を得ている。
【００３０】
図１、図２（実施形態１，２）は反射型ＬＣＤ３（裏面側が液晶面）と任意の曲面を含む自由曲面プリズム２との間に、ブーメラン型レンズ７を配置している（以下、ローカル母線断面上で図１、２の形状のレンズ７をブーメラン型レンズと呼ぶ）。ＲＧＢ（赤色、緑色、赤色）のＬＥＤをそれぞれ複数個持った平面照明光源４から発せられた光は、偏光板８で直線偏光化され、ブーメラン型レンズ７の液晶側の光学面Ａ（ハーフミラー）５で反射され、反射型ＬＣＤ３にほぼ垂直（０度±１０度）で入射する。そして反射型ＬＣＤ３で反射された光は、光学面５を今度は透過してブーメラン型レンズ７を射出後、偏光板９に入射する。
【００３１】
この時、偏光板８で直線偏光化された光の偏光方向が液晶内部で回転するため（液晶駆動電圧ＯＦＦまたはＯＮ）、偏光板９は偏光方向が回転した光を通す方向に設定する必要がある。偏光板９の直線偏光方向が偏光板８の直線偏光方向と約９０度ずれている場合は（液晶内部の偏光方向の回転が９０度）、偏光板８で直線偏光化された光が、光学面（ハーフミラー）５で反射せず透過して行く光（ゴースト光）があるが、偏光板９でこのゴースト光をカットできるため、眼球Ｅにゴースト光が入るのを防ぐ付加価値も生まれる。また反射型ＬＣＤ３が表示面側近傍に不図示の１枚偏光板で表示させるタイプでは、偏光板８と偏光板９は不要となる。偏光板９を射出後、光は自由曲面プリズム２の入射面１１に入射、全反射面（透過面Ｃ）６で全反射し、凹面鏡１０で反射、今度は全反射面（透過面Ｃ）６を透過して観察者の眼球が位置する瞳１に導かれる。これによって反射型ＬＣＤ３に基づく画像情報を拡大虚像として観察している。
【００３２】
実施形態１，２では、ローカル母線断面上で２面とも反射型ＬＣＤ３と反対方向を向いた曲率面からなるブーメラン型レンズ７を、反射型ＬＣＤ３と対向して置き、ブーメラン型レンズ７の反射型ＬＣＤ３側の面を光学面Ａ（ハーフミラー）５とすることにより、反射型ＬＣＤ３のローカル母線断面上での、下側最周辺画像（Ｆ３）側の反射型ＬＣＤ３と自由曲面プリズム２との間隔をできるだけ短くして、表示系（部材３，７，２）がコンパクトでしかも照明系（部材４，５）もコンパクトなものにしている。
【００３３】
実施形態１ではブーメラン型レンズ７の両面５，１４を、母線断面のみパワーを持つシリンドリカル面（自由曲面）にして、ローカル子線断面（紙面と垂直断面）上での収差発生を極力少なくし、かつ子線断面またはローカル子線断面方向のパワーがなくこの断面方向に面形状が湾曲しないため、反射型ＬＣＤ３と光学面５を近くすることができ、コンパクト化・広画角化を可能としている。またブーメラン型レンズ７の他方の曲面１４も光学面５に近い面形状にして、ブーメラン型レンズ７での収差発生をキャンセルさせている。もちろんブーメラン型レンズ７の両面に、ローカル子線断面方向のパワーが弱く、ローカル母線断面方向にパワーが強い自由曲面を使用すれば、同等の効果が得られ、さらに良好な光学系性能が得られる。
【００３４】
実施形態２ではブーメラン型レンズ７の両面５，１４に回転対称非球面を使用している。これは光学面５のローカル子線断面上でも正のパワーを持たせることにより、平面照明用の光源４のローカル子線断面方向で大きさを小さくしている。また他方の曲面１４も光学面５に近い面形状にして、ブーメラン型レンズ７での収差発生をキャンセルさせている。なお両面回転対称球面でも可能であるが、両面回転対称非球面のほうが光学系能はよい。
【００３５】
本発明に係る表示系に含まれる自由曲面プリズムは（実施形態１〜４共通）、自由曲面プリズムのメインパワーを持つ凹面鏡１０に自由曲面を採用して、メインパワー面での偏心収差の発生を少なくする。メインパワー面で補正しきれなかった偏心収差は、メインパワー面に近い全反射面（透過面Ｃ）６を自由曲面化して収差がキヤンセルするような面形状にして補正している。
【００３６】
これだけでもある程度の収差補正は可能であるが、更に全体収差をバランスさせる為に表示手段（反射型ＬＣＤ）３近傍の入射面１１を自由曲面化して全体収差のバランスをとっている。
【００３７】
全反射面（透過面Ｃ）６においては、光が臨界角以上の角度で入射した時は全反射し、臨界角以下の角度で入射した時は射出するように全反射面条件（臨界角条件）を設定しているため、原理的に光量ロスが全くなく明るい表示光学系を可能としている。
【００３８】
図３、図４（本発明の実施形態３，４）は反射型ＬＣＤ３と自由曲面プリズム２との間に、ブーメラン型レンズ７を配置している。実施形態１，２と構成的に違うのは反射型ＬＣＤ３への照明光線の入射角度が垂直でなく、斜入射照明になっていることである。
【００３９】
ＲＧＢのＬＥＤをそれぞれ複数個持った平面照明光源４から発せられた光は、偏光板８で直線偏光化され、ブーメラン型レンズ７の液晶側の光学面Ａ（ハーフミラー）５で反射され、反射型ＬＣＤ３に斜入射し、反射型ＬＣＤ３で斜め方向に反射された光は、光学面５を今度は透過してブーメラン型レンズ７の面１４から射出後、偏光板９に入射する。この時偏光板８で直線偏光化された光の偏光方向が液晶内部で回転するため（液晶駆動電圧ＯＦＦまたはＯＮ）、偏光板９は偏光方向が回転した光を通す方向に設定する必要がある。
【００４０】
偏光板９の直線偏光方向が偏光板８の直線偏光方向と約９０度ずれている場合（液晶内部の偏光方向の回転が９０度）は、偏光板８で直線偏光化された光が、光学面（ハーフミラー）５で反射せず透過していく光（ゴースト光）があるが、偏光板９でこのゴースト光をカットできるため、眼球Ｅにゴースト光が入るのを防ぐ付加価値も生まれる。また反射型ＬＣＤ３が表示面側近傍に不図示の１枚偏光板で表示させるタイプでは、偏光板８と偏光板９は不要となる。偏光板９を射出後、光は自由曲面プリズム２の入射面１１に入射、全反射面（透過面Ｃ）６で全反射し、凹面鏡１０で反射した後に全反射面（透過面Ｃ）６を透過して眼球の瞳Ｅに導かれる。
【００４１】
実施形態３，４では、ローカル母線断面上で２面とも反射型ＬＣＤ３と反対方向を向いた曲率面からなるブーメラン型レンズ７を、反射型ＬＣＤ３と対向して置き、ブーメラン型レンズ７の反射型ＬＣＤ３側の面を光学面Ａ（ハーフミラー）５とすることにより、実施形態１，２と同様に照明系と表示系をコンパクトなものにしている。また斜入射照明により、反射型ＬＣＤ３のローカル母線断面上での下側最周辺像高Ｆ３側の反射型ＬＣＤ３と自由曲面プリズム２との間隔を、実施形態１，２よりもさらに短くできるため、反射型ＬＣＤ３の出っ張りが少なくでき、光学系全体の薄型化及び表示系の広画角化を容易にしている。
【００４２】
実施形態３，４ではブーメラン型レンズ７の両面を、母線断面のみパワーを持つシリンドリカル面にして、ローカル子線断面上での収差発生を極力少なくし、かつ子線断面またはローカル子線断面方向のパワーがなくこの断面方向に面形状が湾曲しないため、反射型ＬＣＤ３と光学面５を近くすることができ、コンパクト化と広画角化の双方を容易にしている。また他方の曲面１４も光学面５に近い面形状にして、ブーメラン型レンズ７での収差発生をキャンセルさせている。もちろんローカル子線断面方向のパワーが弱く、ローカル母線断面方向にパワーが強い自由曲面を使用すれば、同等の効果が得られ、さらに良好な光学系性能が得られる。
【００４３】
また実施形態４では、ブーメラン型レンズ７の該光学面（シリンドリカル面）５のローカル母線断面上での曲率を、実施形態３よりもゆるめに設定して、反射型ＬＣＤ３と平面照明光源４が十分干渉しないようにしている。
【００４４】
図５（実施形態５）は２つの自由曲面ミラー１２，１３を用いている。そして反射型ＬＣＤ３と自由曲面ミラー１３との間の光路中に、ブーメラン型レンズ７を配置している。
【００４５】
実施形態３、４と同じように、反射型ＬＣＤ３への照明光線の入射角度は斜入射照明になっている。ＲＧＢのＬＥＤをそれぞれ複数個持った平面照明光源４から発せられた光は、偏光板８で直線偏光化され、ブーメラン型レンズ７の液晶側の光学面（ハーフミラー）５で反射され、反射型ＬＣＤ３に斜入射し、反射型ＬＣＤ３で斜め方向に反射された光は、光学面５を今度は透過してブーメラン型レンズ7の面１４を射出後、偏光板９に入射する。
【００４６】
この時偏光板８で直線偏光化された光の偏光方向が液晶内部で回転するため（液晶駆動電圧ＯＦＦまたはＯＮ）、偏光板９は偏光方向が回転した光を通す方向に設定する必要がある。偏光板９の直線偏光方向が偏光板８の直線偏光方向と約９０度ずれている場合（液晶内部の偏光方向の回転が９０度）は、偏光板８で直線偏光化された光が、光学面（ハーフミラー）５で反射せず透過していく光（ゴースト光）があるが、偏光板９でこのゴースト光をカットできるため、眼球の瞳Ｅにゴースト光が入るのを防ぐ付加価値も生まれる。また反射型ＬＣＤ３が表示面側近傍に不図示の１枚偏光板で表示させるタイプでは、偏光板８と偏光板９は不要となる。
【００４７】
偏光板９を射出後、光はハーフミラー面１３ａを有する自由曲面ミラー１３に入射反射し、もう一枚の自由曲面ミラー１２で反射、ハーフミラー面１３ａの自由曲面ミラー１３を透過して眼球の瞳Ｅに導かれる。
【００４８】
実施形態５では、ローカル母線断面上で２面とも反射型ＬＣＤ３と反対方向を向いた曲率面からなるブーメラン型レンズ７を、反射型ＬＣＤ３と対向して置き、ブーメラン型レンズ７の反射型ＬＣＤ３側の面を該光学面（ハーフミラー）５とすることにより、実施形態１，２と同様に照明系（４，７）と表示系（３，７，１２，１３）をコンパクトなものにしている。また斜入射照明により、反射型ＬＣＤ３のローカル母線断面上での、チルト偏心量（時計回転方向）を大きくできるため、反射型ＬＣＤ３の出っ張りが少なくでき、光学系全体の薄型化を容易にしている。
【００４９】
実施形態５ではブーメラン型レンズ７の両面５，１４を、母線断面のみパワーを持つシリンドリカル面にして、ローカル子線断面上での収差発生を極力少なくし、かつ子線断面またはローカル子線断面方向のパワーがなくこの断面方向に面形状が湾曲しないため、反射型ＬＣＤ３と光学面５を近くすることができ、コンパクト化を容易にしている。また他方の曲面１４も光学面５に近い面形状にして、ブーメラン型レンズ７での収差発生をキャンセルさせている。もちろんローカル子線断面方向のパワーが弱く、ローカル母線断面方向にパワーが強い自由曲面を使用すれば、同等の効果が得られ、さらに良好な光学系性能が得られる。
【００５０】
本発明の画像表示装置では、反射型の表示手段と、照明光学系と表示光学系で共有する透過兼反射の両作用を有する光学面Ａ（５）はローカル母線断面（該照明光源手段から発せられ該表示手段の画像中心と眼球中心を通る基準光線の入射光と射出光を含む面）上で曲率を有し、該光学面Ａの該表示手段と反対側に他方の曲面Ｂ（１４）を有するレンズ体が存在し、該照明光源手段から発せられた光線は、該レンズ体（ブーメラン型レンズ）の該光学面Ａで反射して該表示手段を照明し、該表示手段からの反射光は、該光学面Ａを今度は透過し、該レンズ体（ブーメラン型レンズ）を射出して、複数の反射面で反射した後、眼球に導かれ表示手段に表示した画像の拡大像を形成し、該表示光学系における該レンズ体（ブーメラン型レンズ）の該光学面Ａのローカル母線断面曲率半径を local_ryＡ、他方の曲面Ｂのローカル母線断面曲率半径をlocal_ryＢとした時、local_ryＡとlocal_ryＢは同符号であり、
０．４＜ local_ryＡ／ local_ryＢ＜２．０・・・（１）
を満たす。ここで表示光学系とは、表示手段である反射型液晶から眼球直前の面に至る光路中に配置した各部材より成っている。また照明光学系は、照明光源から表示手段（反射型液晶）直前の面に至るころ中に配置した各部材より成っている。なおローカル母線断面曲率半径の説明は、後述の項目に記す。
【００５１】
条件式（１）の下限値を下回ると、光学面Ａと曲面Ｂよりなる該レンズ体（ブーメラン型レンズ）の該表示手段のローカル母線断面上での最周辺画像のうち、眼球より遠いほう側の最周辺像高Ｆ３側でのコバ肉厚が厚くなり大型化する。上限値を上回った時は、実施形態３〜５のような斜入射照明系における、光学面Ａと曲面Ｂよりなる該レンズ体（ブーメラン型レンズ）の眼球側でのコバ肉厚が薄くなるため、レンズ体（ブーメラン型レンズ）の全体の肉厚を厚くしなければならず、大型化してしまう傾向がある。
【００５２】
また実施形態１〜２（垂直入射照明系）の該レンズ体（ブーメラン型レンズ）は、斜入射照明系よりも大きさが短いため、条件式（１）の上限値を（２）式のようにするのが良い。ここで上限値１．３を超えると眼球側でのコバ肉厚が足りなくなる。
【００５３】
０．４＜ local_ryＡ／ local_ryＢ＜１．３・・・（２）
本発明の画像表示装置はパワーを持った該光学面Ａが複数面あっても構わないが、１面のみとすることにより照明光源から反射型液晶までの光路長が短くできるため、コンパクト化が容易となる。
【００５４】
表示光学系に関しては、反射型液晶からの光はハーフミラーである光学面Ａと光学面Ｂを透過して、複数の反射面（６，１０）で光線を折り畳むことにより、表示光学系の水平方向の厚さを薄くしている。また該複数の反射面を偏心曲率面とすると、該複数の反射面自体がパワーを持つため、別体の屈折レンズ等を必要とせず、曲率反射面の偏心量を適切に設定することによりコンパクトな表示光学系を得ている。尚、レンズ体７はryＡ＝ryＢとし、ノンパワーであっても良い。
【００５５】
又、本発明の画像表示装置では反射型の表示手段と、照明光源手段と、該照明光学系と、該表示光学系を有し、該照明光学系と該表示光学系で共有する透過兼反射の両作用を有する曲率光学面Ａと、該曲率光学面Ａの該表示手段と反対側に他方の曲面Ｂを有するレンズ体が存在し、該照明光源手段から発せられた光線は、該レンズ体の曲率光学面Ａで反射して該表示手段を照明し、該表示手段からの反射光は、該曲率光学面Ａを今度は透過し、該レンズ体を射出して、複数の反射面で反射した後、眼球に導かれ拡大像を形成する。
【００５６】
このとき、該表示手段のローカル母線断面上（該照明光源手段から発せられ該表示手段の画像中心と眼球中心を通る基準光線の入射光と射出光を含む面）での最周辺画像のうち、眼球より遠いほう側の最周辺像高Ｆ３と眼球中心とを通る光線をＦ３眼球中心光線とし、眼球より近いほう側の最周辺像高Ｆ２と眼球中心とを通る光線をＦ２眼球中心光線とした時、Ｆ３眼球中心光線のほうが、Ｆ２眼球中心光線より表示光学系における該レンズ体内の光路長が長くなるようにしている。
【００５７】
一般的に、自由曲面プリズムと透過型ＬＣＤのみの表示光学系では、自由曲面プリズムが広画角になる程、Ｆ３像高側の自由曲面プリズムとＬＣＤの間隔（バックフォーカス）を十分確保するのが難しくなる。
【００５８】
そこで反射型ＬＣＤのため、該レンズ体（ブーメラン型レンズ）をこの間隔に挿入する必要があり、Ｆ３像高側の該レンズ体（ブーメラン型レンズ）の肉厚を、Ｆ２像高側の該レンズ体（ブーメラン型レンズ）の肉厚より厚くすると、自由曲面プリズムとＬＣＤの間隔のin airでの換算バックフォーカスが、Ｆ３像高側のバックフォーカスほうが短くなり、広画角で良好は光学性能が得られやすくなる。またこのような肉厚の該レンズ体とすることにより、反射ＬＣＤ面と自由曲面プリズムの入射面を平行配置にしやすくなり、反射型ＬＣＤに対しテレセントリック光学系が成り立ち（Ｆ３像高とＦ２像高に関して）、垂直入射照明の光学系に最適なものとしている。
【００５９】
尚、本発明の画像表示装置において、更に装置全体の小型化を図りつつ、画像情報を良好に観察するには次の条件のうちの１以上を満足させるのが良い。
◎ 該照明光源手段は赤色、緑色、青色等の多色光を時分割で放射するＲＧＢ時分割光源であり、該表示手段はＲＧＢ時分割光源のＲＧＢ色光の発光に合わせてＲＧＢの画像を時分割表示することである。
【００６０】
一般的にフィルター方式におけるカラー表示の際は、３色ＲＧＢのカラーフィルターを液晶の前に付けるため、総画素数の１／３画素分が実際のカラー表示画素数となる。しかし上記のような時分割表示反射型液晶と３種類色のＬＥＤ（ＲＧＢ）の組み合わせを使用すると、総画素数がカラーフィルター方式液晶の１／３ですむため、同カラー表示画素数なら液晶のサイズが小さくなり、それに合わせて照明光学系・表示光学系共に小さくすることできる。
◎ 偏心した曲率反射面を有する光学系では、画面内で回転非対称な偏心収差が発生する。そこで表示光学系はアジムス角度により屈折力が異なる面を２面以上含み、表示光学系全体として正の屈折力を有することである。
【００６１】
このアジムス角度により屈折力が異なる面（自由曲面）を採用することにより、回転非対称な偏心収差の補正を可能とし、自由曲面を２面以上使うことにより、表示光学系のローカル母線断面上とローカル子線断面上の正の全系焦点距離をほぼ等しくすることができ、液晶のアスペクト比と同じ比率で拡大投影が可能となる。
◎ レンズ体（ブーメラン型レンズ）をガラス部材で構成することである。現在の反射型液晶の使い方は、照明光学系中に１枚の偏光板１、表示光学系中に他の偏光板を２入れて使用することが多い。ただし表示光学系で、反射液晶から表示光学系中の偏光板までの間は、光学的に平行二コルの関係になるため、この間に複屈折性の強い材料を入れると、材料の光弾性が目で観察されてしまい好ましくない。
【００６２】
そこで、この間に該レンズ体（ブーメラン型レンズ）を入れるが、該レンズ体をガラス部材で構成することにより、該レンズ体が全く複屈折性を持たなくなり、材料の光弾性が目で観察されることがなく、良好な表示系の画像が得られる。
◎ レンズ体の光学面Ａに母線断面のみパワーを持つシリンドリカル面を採用するのが良い。これによれば子線断面またはローカル子線断面方向のパワーがないため、ローカル子線断面上での収差発生を極力少なくでき、かつ子線断面またはローカル子線断面方向に面形状が湾曲しないため、反射型ＬＣＤ３と光学面Ａを近くすることができ、コンパクト化と広画角化が容易となる。
【００６３】
そしてレンズ体の他方の曲面Ｂも該光学面Ａと同様にシリンドリカル面を採用するのが良い。これによれば表示光学系における該レンズ体（ブーメラン型レンズ）での収差発生を抑えることが容易となる。
◎ レンズ体の光学面Ａには金属のハーフミラーを採用することである。これは多層の誘電体膜によるハーフミラーだと、Ｐ偏光とＳ偏光の反射率が異なり、どちらかの位相遅れが生るため、照明光源からの光は該光学面Ａへの入射角度によっては、偏光板１によって直線偏光化された光が該光学面Ａでの反射で楕円偏光に変わってしまい、反射型ＬＣＤで反射した後の偏光板で不要光を十分カット出来ず、表示光学系のコントラスト落ちにつながる。しかしながら金属のハーフミラーならこのようなことがないので、良好は画質を得ることができる。
◎ 該表示光学系における該レンズ体の該曲率光学面Ａのローカル母線断面曲率が、他方の曲面Ｂのローカル母線断面曲率より強くすることである。即ち曲率光学面Ａの曲率半径が曲面Ｂの曲率半径よりも短くすることである。これによれば、Ｆ３像高側の肉厚も厚く、しかも照明光学系も小さくすることができる。
◎ 該表示手段のローカル母線断面上での、各像高と眼球中心とを通る各像高の眼球中心光線における表示光学系中の該レンズ体内の光路長が、該Ｆ２眼球中心光線側からＦ３眼球中心光線側になるにつれて徐々に長くすることである。これによれば、全ての像高に関してテレセントリック光学系が容易に成り立ち、垂直入射照明の光学系に更に最適なものとなる。
【００６４】
つぎに本発明で使っているローカル近軸について説明する。
【００６５】
図１〜図５は各々本発明の後述する数値実施形態１〜５の要部断面図（ローカル母線断面図、添え字がy）であり、第１面（眼球７）の面頂点座標系を図１に示した。本発明では各面の面頂点をy軸方向でのシフト偏心、ｘ軸回りのチルト偏心しかさせていないため、従来の母線断面とローカル母線断面は同一断面であるが、各面の従来の子線断面とローカル子線断面は異なる。
【００６６】
なお前述した従来の母線断面、子線断面は従来の近軸(general-paraxial axis)の定義であり、ローカル母線断面、ローカル子線断面はこれから述べるローカル近軸(local-paraxial axis)での定義である。さらにローカル近軸では偏心系に対応したローカル曲率半径・ローカル面間隔・ローカル焦点距離・ローカル屈折力の定義も以下に説明する。
【００６７】
本発明では、照明光源手段４から発せられ表示手段３の画像中心３ａと眼球７の中心１ａを通る光線を基準光線とし、従来の各面面頂点基準の曲率半径・面間隔・焦点距離・屈折力でなく、基準光線の各面でのヒットポイント点（入射点）を基準としたローカル曲率半径・ローカル面間隔・ローカル焦点距離・ローカル屈折力を用いている。
【００６８】
ここでローカル曲率半径は光学面のヒットポイント点上でのローカルな曲率半径（ローカル母線断面上の曲率半径、ローカル子線断面上の曲率半径）をいう。又ローカル面間隔は現在の面と次の面との、２つのヒットポイント間の距離（基準光線上の距離、空気換算なしの値）の値をいう。又ローカル焦点距離はローカル曲率半径・面の前後の屈折率・ローカル面間隔より、従来の焦点距離計算方法（近軸追跡）で計算した値である。ローカル屈折力はローカル焦点距離の逆数の値である。
【００６９】
なお本発明の各数値実施例では従来の曲率半径・面間隔・偏心量・屈折率・アッべ数と、ローカル曲率半径・面の屈折率・ローカル面間隔・ローカル焦点距離を示している。
【００７０】
本発明では５つの数値実施例をあげた。数値実施例１〜５の数値データを表−１〜表−５（表１〜１６）に示し、光路断面図を図１〜５に示した。
【００７１】
表−１〜表−５の従来の近軸では（general-paraxial axis）、母線断面曲率半径ｒｙ・子線断面曲率半径ｒｘ・面間隔ｄ（第１面の面頂点座標系と平行）・偏心量（母線断面上において、第１面の面頂点座標系に対する各面の面頂点の平行偏心量をshift、傾き偏心量をｔｉｌｔ度）・ｄ線の屈折率ｎｄ、アッべ数vdを示し、ＦＦＳは自由曲面、ＹＴＯは母線断面のみ屈折力をもつシリンドリカル面、ＡＬは非球面を表している。またＭがついたものは反射面であり、ｄ線の屈折率ｎｄは逆符号とした。なお表１〜表５は眼球１から液晶３側へおよび照明光源への逆トレースの数値データである。
【００７２】
ＦＦＳ（自由曲面）の定義式を以下に示す。（各面の面頂点座標系で）
ｚ = 1/2*(1/a+1/b)*(y²*cos(c)²+x²)/cos(c)/(1+1/2*(1/a-1/b)*y*sin(c)+
(1+(1/a-1/b)*y*sin(c)-(1/a/b+1/4*tan(c)²*(1/a+1/b)²)*x²)^(1/2))
+c20*x²+c11*x*y+c02*y²
+c30*x³+c21* +c03*y³
+c40*x⁴+c31*x³*y+c22*x²*y²+c13*x*y³+c04*y⁴
+c50*x⁵+c41*x⁴*y+c32*x³*y²+c23*x²*y³+c14*x*y⁴+c05*y⁵
+c60*x⁶+c51*x⁵*y+c42*x⁴*y²+c33*x³*y³+c24*x²*y⁴+c15*x*y⁵+c06*y⁶
各a、b、ｃ、ｃ20、c11、c02…・は各々自由曲面係数である。（注意：本自由曲面の場合、自由曲面係数の中に近軸に関与する係数があるため、従来近軸の母線断面曲率半径ｒｙ・子線断面曲率半径ｒｘの値が面頂点上での実際の母線断面曲率半径ｒｙ・子線断面曲率半径ｒｘと一致しない。そこでポイント(0,0)つまり面頂点上での実際の母線断面曲率半径ｒｙ・子線断面曲率半径ｒｘも示した。）
ＹＴＯの定義式は母線断面が下記の非球面式で（各面の面頂点座標系で）
【００７３】
【数１】

【００７４】
子線断面は平面（rx=∞）である。
【００７５】
ＡＬの定義式は回転対称非球面で（各面の面頂点座標系で）
【００７６】
【数２】

【００７７】
h² = x² + y², r = rx = ry である。
【００７８】
またローカル近軸(local-paraxial axis)ではローカル曲率半径local-ry,local-rx・ローカル面間隔local-d（反射面は逆符号）・ローカル焦点距離local-fy,local-fx ・面の屈折率ｎｄ（反射面は逆符号）を示している。また各面でのヒットポイント座標（面頂点を0,0）と表示光学系全系ローカル焦点距離・画角と照明光学系光学面Ａのローカル焦点距離も示した。
【００７９】
【表１】

【００８０】
【表２】

【００８１】
【表３】

【００８２】
【表４】

【００８３】
【表５】

【００８４】
本発明のヘッドマウントディスプレイは、図１〜図５に示す構成からなる装置を画像表示装置５１，５２を図６に示すように観察者５０の左右の眼にそれぞれ設け、固定手段５３により観察者の頭部に着脱可能に固定している。
【００８５】
【発明の効果】
本発明によれば、液晶ディスプレイ等の表示手段に表示した画像情報を観察する際、光源手段から表示手段に至る照明光学系及び表示手段からの光束を観察者の眼球に導光するための表示光学系の構成を適切に設定することによって、装置全体の小型化を図りつつ光量のロスを減らし、該画像情報を良好なる画質で観察することができる画像観察装置及びそれを用いたヘッドマウントディスプレイを達成することができる。
【００８６】
特に本発明によれば、照明光源からの光量ロスが少なく、十分なコントラストを持った画質を提供し、コンパクトな照明光学系と表示光学系が成り立つ反射型ＬＣＤを使ったＨＭＤを達成することができる。
【図面の簡単な説明】
【図１】本発明の実施形態１の要部断面図
【図２】本発明の実施形態２の要部断面図
【図３】本発明の実施形態３の要部断面図
【図４】本発明の実施形態４の要部断面図
【図５】本発明の実施形態５の要部断面図
【図６】本発明の画像表示装置をＨＭＤに適用したときの要部外略図
【符号の説明】
１眼球
２自由曲面プリズム
３反射型ＬＣＤ(図はＬＣＤの保護板を示しており、液晶面はピント面に存在する。)
４照明光源（平面光源）
５光学面Ａ
６透過面Ｃ（自由曲面プリズムの全反射面）
７ブーメラン型レンズ
８偏光板１
９偏光板２
１０自由曲面プリズムの凹面鏡
１１自由曲面プリズムの入射面
１２自由曲面ミラー１
１３自由曲面ミラー２
１４曲面Ｂ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display apparatus, for example, a reflective liquid crystal display element is used as a display element for displaying image information for observation, and the image information displayed there is enlarged and observed through an optical element appropriately set. It is suitable for a head-mounted display (HMD), a glasses-type display, or the like.
[0002]
[Prior art]
2. Description of the Related Art Various head-mounted image observation devices (image display devices), so-called head mounted displays (HMD), have been proposed in which image information displayed on an image display element such as a liquid crystal is observed as an enlarged virtual image. ing.
[0003]
Of these, HMDs using reflective display elements have been proposed in, for example, Japanese Patent Application Laid-Open Nos. 07-128614, 11-125791, 11-337863, 2000-10041, and the like. ing.
[0004]
In these proposed HMDs, light emitted from an illumination light source is reflected by a reflective liquid crystal and guided to an eyeball to observe an enlarged image of the image displayed on the liquid crystal. At this time, the light beam proceeds in the order of the illumination light source, the illumination optical system, the reflective liquid crystal, the display optical system, and the eyeball. In the embodiment disclosed in the HMD proposed in Japanese Patent Laid-Open No. 11-125791, there is no illumination optical system, and light from the illumination light source directly illuminates the reflective liquid crystal. In this case, there is an example where there is no shared surface between the illumination optical system and the display optical system. In this case, since it is necessary to prevent the luminous flux from the illumination light source from being lost, a large space is required between the illumination light source and the reflective liquid crystal, which tends to increase the size. In other embodiments of the publication, there is almost a common surface between the illumination optical system and the display optical system. If there is a shared surface, the optical path overlaps between the illumination optical system and the display optical system, so that the size can be easily reduced. However, the more shared surfaces, the more complicated the optical system and the more light loss. On the other hand, the present inventor has proposed a compact display optical system of HMD in Japanese Patent Laid-Open No. 7-333551. This publication uses a free-form surface prism to reduce the size of the entire apparatus. The present inventor has proposed an HMD in which a free-form surface prism and a reflective display element are combined in Japanese Patent Laid-Open Nos. 11-1257991, 11-337863, and 2000-10041.
[0005]
[Problems to be solved by the invention]
2. Description of the Related Art Conventionally, in an image observation apparatus such as an HMD, it is important to reduce the size and weight of the entire apparatus in order to mount the apparatus on the observer's head. Further, it is an important problem that image information displayed on the display means can be observed well.
[0006]
When a reflective liquid crystal display element is used as an image display device, in order to reduce the overall size of the device, it is necessary to appropriately incorporate an illumination device for illuminating the device.
[0007]
For example, when the light from the illumination light source illuminates the reflective liquid crystal, if it passes through many reflective surfaces or transmissive surfaces, or passes through a prism with a long optical path length, it must illuminate before reaching the reflective liquid crystal. The amount of light from the light source is lost. Accordingly, there is a demand for a compact HMD with little loss of light quantity and a compact display optical system and illumination optical system.
[0008]
The present invention relates to an illumination optical system from a light source unit to a display unit and a display optical system for guiding a light beam from the display unit to an observer's eyeball when observing image information displayed on a display unit such as a liquid crystal display. By appropriately setting the configuration, the image observation apparatus capable of observing the image information with good image quality while reducing the amount of light loss while reducing the size of the entire apparatus, and a head mounted display using the image observation apparatus With the goal.
[0009]
[Means for Solving the Problems]
  The image display device of the invention of claim 1 is a reflection type display means, an illumination means for illuminating the display means, an illumination optical system for guiding the light from the illumination means to the display means, and the display means In an image display apparatus having a display optical system that guides light to an observer side,
  The illumination optical system has an optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system, and the optical surface A is a cross section of a local bus (emitted from the illumination means and the image center of the display means) An optical surface B having a curvature on a surface including the incident light and the outgoing light of a reference ray passing through the center of the pupil, and having a curvature arranged on the opposite side of the display means with respect to the optical surface A, A lens body composed of a glass member is formed by the optical surface A and the optical surface B,
  Light rays emitted from the illuminating means are reflected by the optical surface A of the lens body to illuminate the display means, and reflected light from the display means passes through the optical surface A and is incident on the lens body. Incident, exiting the optical surface B, reflected by a plurality of reflecting surfaces, then guided to the pupil to form an enlarged image of the image displayed on the display means,
  In the display optical system, when the local bus section curvature radius of the optical surface A of the lens body in the display optical system is local_ryA and the local bus section curvature radius of the optical surface B is local_ryB, local_ryA and local_ryB have the same sign,
      0.4 <local_ryA / local_ryB <2.0 (1)
It is characterized by satisfying.
[0010]
  The invention of claim 2 is characterized in that, in the invention of claim 1, there is only one optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system.
[0011]
  According to a third aspect of the present invention, in the first aspect of the present invention, the reflected light from the display means is reflected by a plurality of reflective surfaces that are eccentric curvature surfaces after being emitted from the lens body and guided to the pupil. It is a feature.
[0012]
  According to a fourth aspect of the present invention, in the first, second, or third aspect, the illumination means is a time-division light source that emits a plurality of color lights in a time-division manner, and the display means is a color light emitted from the time-division light source. According to this, an image based on each color light is displayed in a time-sharing manner.
[0013]
  According to a fifth aspect of the present invention, in the first, second, third, or fourth aspect of the invention, the display optical system includes two or more surfaces having different refractive powers depending on an azimuth angle, and the display optical system as a whole has a positive refractive power. It is characterized by having.
[0014]
  An image display apparatus according to a sixth aspect of the present invention is a reflection type display means, an illumination means for illuminating the display means, an illumination optical system for guiding light from the illumination means to the display means, and In an image display apparatus having a display optical system that guides light to an observer side,
  An optical surface A having a curvature having both transmission and reflection functions shared by the illumination optical system and the display optical system, and an optical surface having a curvature disposed on the side opposite to the display means with respect to the optical surface A B, and the optical surface A and the optical surface B form a lens body,
  Light rays emitted from the illumination means are reflected by the optical surface A of the lens body to illuminate the display means, and reflected light from the display means passes through the optical surface A and enters the lens body. The optical surface B is emitted, reflected by a plurality of reflecting surfaces, and then an enlarged image of the image guided to the pupil and displayed on the display means is formed.
  Of the most peripheral image on the cross section of the local bus of the display means (the surface including the incident light and the emitted light of the reference light beam emitted from the illumination means and passing through the image center of the display means and the eyeball center), the one farthest from the eyeball F3 eyeball center ray when the ray passing through the most peripheral image height F3 on the side and the eyeball center ray is F3 eyeball center ray, and the ray passing through the most peripheral image height F2 and eyeball center closer to the eyeball is F2 eyeball center ray. The light beam is characterized in that the optical path length in the lens body in the display optical system is longer than the F2 eyeball center light beam.
[0015]
  A seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, a local generatrix curvature of the curvature optical surface A of the lens body in the display optical system is larger than a local generatrix curvature of the curved surface B. .
[0016]
  According to an eighth aspect of the present invention, in the seventh aspect of the present invention, in the lens body in the display optical system in the eyeball center ray of each image height passing through each image height and the eyeball center on the cross section of the local bus of the display means. The optical path length is gradually increased from the F2 eyeball central ray side toward the F3 eyeball central ray side.
[0017]
  An image display apparatus according to a ninth aspect of the present invention includes a reflective display unit, an illuminating unit that illuminates the display unit, an illumination optical system that guides light from the illuminating unit to the display unit, and the display unit. In an image display apparatus having a display optical system that guides light to an observer side,
  A lens body is formed of an optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system, and an optical surface B opposite to the display means with respect to the optical surface A,
  The light emitted from the illumination means is reflected by the optical surface A to illuminate the display means, and the reflected light from the display means is transmitted through the optical surface A and incident on the lens body. After exiting the surface B and reflected by a plurality of reflecting surfaces, it is guided to the pupil to form an enlarged image of the image displayed on the display means,
  A plane including incident light and outgoing light of a reference ray emitted from the illumination means and passing through the image center and pupil center of the display means is a local bus cross section, and includes a hit point between the reference ray and each surface and is perpendicular to the local bus cross section. When the surface is the local cross section, the local bus section curvature radius of the optical surface A of the lens body in the display optical system is local_ryA, and the local bus section curvature radius of the optical surface B is local_ryB, local_ryA and local_ryB are The same sign,
    0.4 <local_ryA / local_ryB <2.0
In addition, the optical surface A and the optical surface B are characterized in that the power in the cross section direction of the local bus is stronger than the power in the cross section direction of the local bus.
[0018]
  The invention of claim 10 is characterized in that, in the invention of claim 9, the optical surface A and the optical surface B are cylindrical surfaces.
[0019]
  A head mounted display according to an eleventh aspect of the invention includes the image display device according to any one of the first to tenth aspects.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
1-5 is principal part sectional drawing of Embodiment 1-5 of this invention. In the figure, 1 is the pupil position, and the eyeball E of the observer is located.
[0022]
  2 includes a free-form surface prism, 3 a reflective liquid crystal, 4 an illumination light source (illuminating means), 5 a transmission / reflection surface (optical surface) having a curvature made of a half mirror, and 7 an optical surface 5 and a curved surface 14. A boomerang lens, 8 and 9 are polarizing plates, 12 is a first free-form curved mirror, and 13 is a second free-form curved mirror (second optical member).
[0023]
  Those indicated by reference numerals 4 and 5 constitute one element of the illumination system, and those indicated by

reference numerals

3, 5, 14, and 2 or

reference numerals

3, 5, 14, 12, and 13 are one element of the display system. Is configured.
The

numbers

5, 14, 2 or the

numbers

5, 14, 12, 13 constitute an element of the display optical system.
[0024]
In this embodiment, in order to reduce the loss of the amount of light from the illumination light source 4 as much as possible, the illumination light source 4 is brought as close to the reflective liquid crystal 3 as possible to shorten the optical path length of the illumination optical system. For example, when the free-form surface prism 2 is used in the display optical system, a member constituting the illumination optical system is provided between the free-form surface prism 2 and the reflective liquid crystal 3. As shown in FIG. 5, when two free-form surface mirrors 12 and 13 are used in the display optical system, an illumination optical system is configured between the free-form surface mirror system (12 and 13) and the reflective liquid crystal 3. The member which performs is provided.
[0025]
Prior to the description of each embodiment of the present invention, definitions of a bus cross section, a bus cross section, a local bus cross section, and a local bus cross section used in the present invention will be described. In the definition of the conventional system that does not correspond to the eccentric system, if the z-axis is the optical axis in each surface vertex coordinate system, the yz section is the conventional generatrix section (meridional section), and the xz section is the child section (sagittal section). Become. Since the present invention is an eccentric system, a local bus bar cross section and a local child cross section corresponding to the eccentric system are newly defined.
[0026]
The incident of the reference beam on the hit point (incident point) between the image center of the display means (the center of the external image when see-through for observing the outside world) and the ray passing through the center of the eyeball (hereinafter referred to as the reference beam). The plane containing the light and the emitted light is taken as the local bus cross section, and the plane perpendicular to the local bus cross section containing the hit point and parallel to the child cross section (normal child cross section) of each face vertex coordinate system is taken as the local bus cross section. Define. In the case where the display means is a reflection type, the reference light beam is extended to the illumination optical system and the illumination light source, and the local bus line cross section and the local child line cross section are defined on each hit point in the same manner as described above. The local bus section cross-section focal length and the local sub-section cross-section focal length will be described later in the item.
[0027]
Next, each embodiment of the present invention will be described. 1 to 5 are optical path cross-sectional views (local busbar cross-sectional views) according to Embodiments 1 to 5 of the present invention. Embodiments 1 and 2 are of a type in which the reflective LCD 3 is illuminated by a light beam from the illumination light source 4 at substantially normal incidence, and in Embodiments 3 to 5 of the present invention, the reflective LCD 3 is inclined by the light beam from the illumination light source 4. It is of the type that is illuminated.
[0028]
As a characteristic of general liquid crystal (TN liquid crystal, etc.), the light emitted almost perpendicularly to the liquid crystal surface has sufficient contrast and good image quality, but the contrast is low when the emitted light is tilted away from the vertical. It is known that the image quality deteriorates.
[0029]
In the first and second embodiments, in order to solve this, the reflective LCD 3 is illuminated with a vertically incident light beam. The incident angle of the reference light beam emitted from the illumination light source 4 and passing through the image center 3a and the eyeball center 1a of the display means 3 to the reflective display means 3 is 0 ° ± 10 °. If this range is exceeded, a reduction in contrast will be noticeable. Ferroelectric liquid crystal (FLC) has different characteristics, and the contrast does not drop even with a large amount of obliquely emitted light, so that a high quality image can be observed from almost any angle. Therefore, Embodiments 3 to 5 assume this liquid crystal (FLC), and the reflective LCD 3 is illuminated with an obliquely incident light beam so that the entire optical system is thinned, and a high-quality image without a drop in contrast is obtained.
[0030]
1 and 2 (Embodiments 1 and 2), a boomerang lens 7 is disposed between a reflective LCD 3 (the back side is a liquid crystal surface) and a free-form surface prism 2 including an arbitrary curved surface (hereinafter referred to as local). The lens 7 having the shape shown in FIGS. 1 and 2 on the cross section of the bus is called a boomerang type lens). The light emitted from the flat illumination light source 4 having a plurality of RGB (red, green, red) LEDs is linearly polarized by the polarizing plate 8 and the optical surface A (half mirror) of the boomerang lens 7 on the liquid crystal side. ) And is incident on the reflective LCD 3 substantially perpendicularly (0 ° ± 10 °). The light reflected by the reflective LCD 3 is then transmitted through the optical surface 5, exits from the boomerang lens 7, and then enters the polarizing plate 9.
[0031]
At this time, since the polarization direction of the light linearly polarized by the polarizing plate 8 rotates inside the liquid crystal (liquid crystal driving voltage OFF or ON), it is necessary to set the polarizing plate 9 to a direction through which the light whose polarization direction is rotated passes. is there. When the linear polarization direction of the polarizing plate 9 is shifted from the linear polarization direction of the polarizing plate 8 by about 90 degrees (the rotation of the polarization direction inside the liquid crystal is 90 degrees), the light linearly polarized by the polarizing plate 8 is optical Although there is light (ghost light) that is transmitted without being reflected by the surface (half mirror) 5, the ghost light can be cut by the polarizing plate 9, so that an added value for preventing the ghost light from entering the eyeball E is also created. Further, in the type in which the reflective LCD 3 displays with a single polarizing plate (not shown) near the display surface side, the polarizing plate 8 and the polarizing plate 9 are unnecessary. After exiting the polarizing plate 9, the light is incident on the incident surface 11 of the free-form surface prism 2, totally reflected by the total reflection surface (transmission surface C) 6, reflected by the concave mirror 10, and this time the total reflection surface (transmission surface C) 6. And is guided to the pupil 1 where the observer's eyeball is located. As a result, the image information based on the reflective LCD 3 is observed as an enlarged virtual image.
[0032]
In the first and second embodiments, a boomerang lens 7 having a curvature surface facing the reflective LCD 3 in both directions on the cross section of the local generatrix is placed facing the reflective LCD 3 to reflect the boomerang lens 7. By setting the surface on the LCD 3 side to the optical surface A (half mirror) 5, the distance between the reflective LCD 3 on the lowermost peripheral image (F 3) side and the free-form curved prism 2 on the local bus cross section of the reflective LCD 3. The display system (

members

3, 7, 2) is compact and the illumination system (members 4, 5) is also compact.
[0033]
In the first embodiment, both surfaces 5 and 14 of the boomerang type lens 7 are made cylindrical surfaces (free curved surfaces) having power only in the generatrix cross section, so that the occurrence of aberrations on the local child line cross section (cross section perpendicular to the paper surface) is minimized. In addition, since there is no power in the direction of the cross section of the sub-wire or the cross section of the local sub-wire, and the surface shape does not curve in this cross-section direction, the reflective LCD 3 and the optical surface 5 can be close to each other. Further, the other curved surface 14 of the boomerang lens 7 is also formed into a surface shape close to the optical surface 5 so as to cancel the aberration generation in the boomerang lens 7. Of course, if a free curved surface having a weak power in the cross section direction of the local bus line and a strong power in the cross section direction of the local generatrix is used on both surfaces of the boomerang lens 7, the same effect can be obtained, and a better optical system performance can be obtained. .
[0034]
In the second embodiment, rotationally symmetric aspheric surfaces are used for both surfaces 5 and 14 of the boomerang lens 7. This reduces the size of the light source 4 for planar illumination in the direction of the local sub-line cross section by giving positive power even on the local sub-line cross section of the optical surface 5. In addition, the other curved surface 14 is also made a surface shape close to the optical surface 5 to cancel the occurrence of aberrations in the boomerang type lens 7. Although a double-sided rotationally symmetric spherical surface is possible, a double-sided rotationally symmetric aspherical surface has better optical system performance.
[0035]
The free-form surface prism included in the display system according to the present invention (common to the first to fourth embodiments) employs a free-form surface in the concave mirror 10 having the main power of the free-form surface prism, and generates decentration aberrations on the main power surface. Reduce. Decentration aberrations that could not be corrected on the main power surface are corrected by making the total reflection surface (transmission surface C) 6 close to the main power surface into a free-form surface so that the aberration is cancelled.
[0036]
This alone can correct aberrations to some extent, but in order to further balance the overall aberration, the incident surface 11 in the vicinity of the display means (reflection LCD) 3 is formed into a free-form surface to balance the overall aberration.
[0037]
In the total reflection surface (transmission surface C) 6, the total reflection surface condition (critical angle condition) is such that light is totally reflected when incident at an angle greater than the critical angle and emitted when incident at an angle less than the critical angle. In principle, there is no loss of light amount, and a bright display optical system is possible.
[0038]
3 and 4 (Embodiments 3 and 4 of the present invention), a boomerang lens 7 is disposed between the reflective LCD 3 and the free-form surface prism 2. The structural difference from the first and second embodiments is that the incident angle of the illumination light beam on the reflective LCD 3 is not vertical but is oblique incidence illumination.
[0039]
The light emitted from the flat illumination light source 4 having a plurality of RGB LEDs is linearly polarized by the polarizing plate 8 and reflected by the optical surface A (half mirror) 5 on the liquid crystal side of the boomerang lens 7 to be reflected. The light incident obliquely on the mold LCD 3 and reflected obliquely by the reflective LCD 3 is then transmitted through the optical surface 5, exits from the surface 14 of the boomerang lens 7, and then enters the polarizing plate 9. At this time, since the polarization direction of the light linearly polarized by the polarizing plate 8 rotates inside the liquid crystal (liquid crystal driving voltage OFF or ON), it is necessary to set the polarizing plate 9 to a direction in which the light whose polarization direction is rotated passes. .
[0040]
When the linear polarization direction of the polarizing plate 9 is shifted by about 90 degrees from the linear polarization direction of the polarizing plate 8 (the rotation of the polarization direction inside the liquid crystal is 90 degrees), the light linearly polarized by the polarizing plate 8 is optical Although there is light (ghost light) that is transmitted without being reflected by the surface (half mirror) 5, this ghost light can be cut by the polarizing plate 9, so that an added value for preventing the ghost light from entering the eyeball E is also created. Further, in the type in which the reflective LCD 3 displays with a single polarizing plate (not shown) near the display surface side, the polarizing plate 8 and the polarizing plate 9 are unnecessary. After exiting the polarizing plate 9, the light is incident on the incident surface 11 of the free-form surface prism 2, totally reflected by the total reflection surface (transmission surface C) 6, reflected by the concave mirror 10, and then reflected by the total reflection surface (transmission surface C) 6. The light is transmitted and guided to the pupil E of the eyeball.
[0041]
In the third and fourth embodiments, a boomerang lens 7 having a curvature surface facing both directions opposite to the reflective LCD 3 on the cross section of the local bus line is placed opposite to the reflective LCD 3 to reflect the boomerang lens 7. By making the surface on the LCD 3 side an optical surface A (half mirror) 5, the illumination system and the display system are made compact as in the first and second embodiments. Further, since the oblique incidence illumination can further reduce the distance between the reflective LCD 3 on the lowermost peripheral image height F3 side on the local bus cross section of the reflective LCD 3 and the free-form surface prism 2 as compared with the first and second embodiments, The protrusion of the reflective LCD 3 can be reduced, and the entire optical system can be made thinner and the display system can be easily widened.
[0042]
In the third and fourth embodiments, both surfaces of the boomerang lens 7 are cylindrical surfaces having power only in the generatrix cross section so that aberrations on the local ray cross section are reduced as much as possible, and power in the ray cross section or in the direction of the local ray cross section is minimized. Therefore, the reflective LCD 3 and the optical surface 5 can be close to each other because the surface shape is not curved in this cross-sectional direction, and both compactness and wide angle of view are facilitated. In addition, the other curved surface 14 is also made a surface shape close to the optical surface 5 to cancel the occurrence of aberrations in the boomerang type lens 7. Of course, if a free-form surface having a weak power in the cross section direction of the local bus and a strong power in the cross section direction of the local bus is used, the same effect can be obtained, and a better optical system performance can be obtained.
[0043]
In the fourth embodiment, the curvature of the optical surface (cylindrical surface) 5 of the boomerang lens 7 on the cross section of the local generatrix is set to be looser than that of the third embodiment, so that the reflective LCD 3 and the flat illumination light source 4 are sufficient. I try not to interfere.
[0044]
FIG. 5 (Embodiment 5) uses two free-form surface mirrors 12 and 13. A boomerang lens 7 is disposed in the optical path between the reflective LCD 3 and the free-form surface mirror 13.
[0045]
As in the third and fourth embodiments, the incident angle of the illumination light beam on the reflective LCD 3 is oblique incidence illumination. Light emitted from a flat illumination light source 4 having a plurality of RGB LEDs is linearly polarized by a polarizing plate 8, reflected by an optical surface (half mirror) 5 on the liquid crystal side of the boomerang lens 7, and reflected. The light incident obliquely on the LCD 3 and reflected in the oblique direction by the reflective LCD 3 is transmitted through the optical surface 5 and then exits the surface 14 of the boomerang lens 7 and then enters the polarizing plate 9.
[0046]
At this time, since the polarization direction of the light linearly polarized by the polarizing plate 8 rotates inside the liquid crystal (liquid crystal driving voltage OFF or ON), it is necessary to set the polarizing plate 9 to a direction in which the light whose polarization direction is rotated passes. . When the linear polarization direction of the polarizing plate 9 is shifted by about 90 degrees from the linear polarization direction of the polarizing plate 8 (the rotation of the polarization direction inside the liquid crystal is 90 degrees), the light linearly polarized by the polarizing plate 8 is optical Although there is light (ghost light) that is transmitted without being reflected by the surface (half mirror) 5, this ghost light can be cut by the polarizing plate 9, so that added value for preventing ghost light from entering the pupil E of the eyeball is also provided. to be born. Further, in the type in which the reflective LCD 3 displays with a single polarizing plate (not shown) near the display surface side, the polarizing plate 8 and the polarizing plate 9 are unnecessary.
[0047]
After exiting the polarizing plate 9, the light is incident and reflected on the free curved mirror 13 having the half mirror surface 13 a, reflected by another free curved mirror 12, and transmitted through the free curved mirror 13 on the half mirror surface 13 a. Guided to pupil E.
[0048]
In the fifth embodiment, a boomerang lens 7 having a curvature surface facing both directions opposite to the reflective LCD 3 on the cross section of the local bus line is placed facing the reflective LCD 3, and the boomerang lens 7 side of the reflective LCD 3 is placed. By making this surface the optical surface (half mirror) 5, the illumination system (4, 7) and the display system (3, 7, 12, 13) are made compact as in the first and second embodiments. . Further, since the tilt eccentricity (clockwise rotation direction) on the cross section of the local bus of the reflective LCD 3 can be increased by the oblique incident illumination, the protrusion of the reflective LCD 3 can be reduced and the entire optical system can be easily made thin. .
[0049]
In the fifth embodiment, both surfaces 5 and 14 of the boomerang lens 7 are made cylindrical surfaces having power only in the generatrix cross section so as to reduce the occurrence of aberrations on the local genera cross section as much as possible, and in the generatrix cross section or in the local axis cross section direction. Since there is no power and the surface shape does not curve in this cross-sectional direction, the reflective LCD 3 and the optical surface 5 can be brought close to each other, which facilitates downsizing. In addition, the other curved surface 14 is also made a surface shape close to the optical surface 5 to cancel the occurrence of aberrations in the boomerang type lens 7. Of course, if a free-form surface having a weak power in the cross section direction of the local bus and a strong power in the cross section direction of the local bus is used, the same effect can be obtained, and a better optical system performance can be obtained.
[0050]
In the image display device of the present invention, the reflection type display means and the optical surface A (5) having both the transmission and reflection functions shared by the illumination optical system and the display optical system are cross-sectioned from the local bus line (from the illumination light source means). And a curved surface B (14) on the opposite side of the optical surface A from the display means. A light beam emitted from the illumination light source means is reflected by the optical surface A of the lens body (boomerang type lens) to illuminate the display means, and the reflected light from the display means Passes through the optical surface A, emits the lens body (boomerang lens), reflects off the plurality of reflecting surfaces, and then forms an enlarged image of the image guided to the eyeball and displayed on the display means. The lens body (boomerang lens) in the display optical system When Local_ryA the local meridional cross section curvature radius of the optical surface A, the local meridional cross section radius of curvature of the other curved surface B and local_ryB, local_ryA and Local_ryB are the same sign,
0.4 <local_ryA / local_ryB <2.0 (1)
Meet. Here, the display optical system is composed of members arranged in an optical path from a reflective liquid crystal serving as a display means to a surface immediately before the eyeball. The illumination optical system is made up of members arranged in the roller from the illumination light source to the surface immediately before the display means (reflection type liquid crystal). The explanation of the radius of curvature of the local bus bar cross section will be given in the item described later.
[0051]
When the lower limit value of conditional expression (1) is not reached, the farthest image from the eyeball in the most peripheral image on the local bus section of the display means of the lens body (boomerang type lens) composed of the optical surface A and the curved surface B The edge thickness on the most peripheral image height F3 side becomes thicker and larger. When the upper limit is exceeded, the edge thickness on the eyeball side of the lens body (boomerang type lens) composed of the optical surface A and the curved surface B in the oblique incidence illumination system as in Embodiments 3 to 5 becomes thin. The overall thickness of the lens body (boomerang type lens) must be increased, which tends to increase the size.
[0052]
In addition, since the lens body (Boomerang lens) of Embodiments 1 and 2 (normal incidence illumination system) is shorter in size than the oblique incidence illumination system, the upper limit value of the conditional expression (1) is expressed by the expression (2). It is good to be. Here, if the upper limit value 1.3 is exceeded, the edge thickness on the eyeball side becomes insufficient.
[0053]
0.4 <local_ryA / local_ryB <1.3 (2)
The image display apparatus according to the present invention may have a plurality of optical surfaces A having power. However, by using only one surface, the optical path length from the illumination light source to the reflective liquid crystal can be shortened, so that the compactness can be achieved. It becomes easy.
[0054]
As for the display optical system, the light from the reflective liquid crystal passes through the optical surfaces A and B, which are half mirrors, and the light beams are folded at the plurality of reflective surfaces (6, 10), whereby the horizontal direction of the display optical system. The thickness in the direction is reduced. Further, when the plurality of reflecting surfaces are eccentric curvature surfaces, since the plurality of reflecting surfaces themselves have power, a separate refracting lens or the like is not required, and a compact amount can be obtained by appropriately setting the amount of eccentricity of the curvature reflecting surfaces. A good display optical system. The lens body 7 may be non-power with ryA = ryB.
[0055]
Further, the image display apparatus of the present invention has a reflection type display means, an illumination light source means, the illumination optical system, and the display optical system, and the transmission and reflection shared by the illumination optical system and the display optical system. And a lens body having the other curved surface B on the opposite side of the curvature optical surface A from the display means, and the light emitted from the illumination light source means The reflective optical surface A is reflected to illuminate the display means, and the reflected light from the display means is then transmitted through the curved optical surface A, exits the lens body, and is reflected by a plurality of reflective surfaces. After that, it is guided to the eyeball to form an enlarged image.
[0056]
At this time, among the most peripheral images on the local bus cross section of the display means (the surface including the incident light and the emitted light of the reference light beam emitted from the illumination light source means and passing through the image center and the eyeball center of the display means) A ray passing through the most peripheral image height F3 far from the eyeball and the center of the eyeball is defined as F3 eyeball center ray, and a ray passing through the most peripheral image height F2 and the eyeball center closer to the eyeball is defined as the F2 eyeball center ray. At this time, the optical path length in the lens body in the display optical system is longer for the F3 eyeball center ray than for the F2 eyeball center ray.
[0057]
In general, in a display optical system including only a free-form surface prism and a transmissive LCD, the distance (back focus) between the free-form surface prism on the F3 image height side and the LCD is sufficiently secured as the free-form surface prism has a wider angle of view. Becomes difficult.
[0058]
Therefore, for a reflective LCD, it is necessary to insert the lens body (boomerang lens) at this interval, and the thickness of the lens body (boomerang lens) on the F3 image height side is set to the lens on the F2 image height side. If it is thicker than the body (boomerang type lens), the converted back focus in air at the distance between the free-form surface prism and the LCD will be shorter, and the back focus on the F3 image height side will be shorter. It becomes easy to obtain. Further, by making the lens body with such a thickness, the reflective LCD surface and the incident surface of the free-form surface prism can be easily arranged in parallel, and a telecentric optical system is established for the reflective LCD (F3 image height and F2 image height). In terms of normal incidence illumination optics.
[0059]
In the image display apparatus of the present invention, it is preferable to satisfy one or more of the following conditions in order to observe image information satisfactorily while further reducing the size of the entire apparatus.
◎ The illumination light source means is an RGB time-division light source that radiates multicolor light such as red, green, and blue in a time-sharing manner, and the display means time-divides the RGB image in accordance with the light emission of the RGB color light of the RGB time-division light source. Is to display.
[0060]
In general, when performing color display in the filter method, a color filter of three colors RGB is attached in front of the liquid crystal, so that one third of the total number of pixels is the actual number of color display pixels. However, if the combination of the time-division display reflective liquid crystal and the three types of LEDs (RGB) is used, the total number of pixels is one third of that of the color filter type liquid crystal. The size is reduced, and both the illumination optical system and the display optical system can be reduced accordingly.
◎ In an optical system having an eccentric curvature reflecting surface, rotationally asymmetric decentration aberration occurs in the screen. Therefore, the display optical system includes two or more surfaces having different refractive powers depending on the azimuth angle, and the display optical system as a whole has a positive refractive power.
[0061]
By adopting a surface (free curved surface) with different refractive power depending on this azimuth angle, it is possible to correct rotationally asymmetric decentration aberrations, and by using two or more free curved surfaces, the local bus cross section of the display optical system The positive total focal length on the cross section of the child line can be made substantially equal, and enlargement projection can be performed at the same ratio as the aspect ratio of the liquid crystal.
A lens body (boomerang lens) is made of a glass member. In the current usage of the reflective liquid crystal, in many cases, one polarizing plate 1 is put in the illumination optical system and two other polarizing plates are put in the display optical system. However, between the reflective liquid crystal and the polarizing plate in the display optical system in the display optical system, there is an optically parallel relationship, so if a material with strong birefringence is inserted between them, the photoelasticity of the material will be reduced. It is not preferable because it is observed with the eyes.
[0062]
Therefore, the lens body (boomerang type lens) is inserted in the meantime, but when the lens body is made of a glass member, the lens body does not have birefringence at all, and the photoelasticity of the material is observed with the eyes. And a good display image can be obtained.
◎ It is preferable to adopt a cylindrical surface having power only on the cross section of the generating line on the optical surface A of the lens body. According to this, since there is no power in the cross section of the sub-wire or the cross section of the local sub-line, the occurrence of aberrations on the cross section of the local sub-wire can be reduced as much as possible, and the surface shape does not curve in the cross-section direction of the sub-line The reflective LCD 3 and the optical surface A can be brought close to each other, and compactness and a wide angle of view are facilitated.
[0063]
The other curved surface B of the lens body is preferably a cylindrical surface in the same manner as the optical surface A. According to this, it becomes easy to suppress the occurrence of aberrations in the lens body (boomerang lens) in the display optical system.
A metal half mirror is used for the optical surface A of the lens body. If this is a half mirror made of a multilayer dielectric film, the reflectivity of P-polarized light and S-polarized light is different, and phase lag of either occurs, so the light from the illumination light source depends on the incident angle to the optical surface A The light linearly polarized by the polarizing plate 1 is changed to elliptically polarized light by reflection on the optical surface A, and the unnecessary light cannot be sufficiently cut by the polarizing plate after being reflected by the reflective LCD. This leads to a loss of contrast. However, since this is not the case with a metal half mirror, good image quality can be obtained.
(4) The local generatrix curvature of the curvature optical surface A of the lens body in the display optical system is made stronger than the local generatrix curvature of the other curved surface B. That is, the curvature radius of the curvature optical surface A is made shorter than the curvature radius of the curved surface B. According to this, the thickness on the F3 image height side is thick, and the illumination optical system can be made small.
The optical path length in the lens body in the display optical system at the eyeball center ray at each image height passing through each image height and the eyeball center on the local bus cross section of the display means is F3 from the F2 eyeball center ray side. Increasing the length gradually toward the eyeball central ray side. According to this, a telecentric optical system can be easily established for all image heights, and is more optimal for an optical system for normal incidence illumination.
[0064]
Next, the local paraxial used in the present invention will be described.
[0065]
FIGS. 1 to 5 are cross-sectional views (local bus cross-sectional view, subscript y) of numerical embodiments 1 to 5 described later of the present invention, respectively, and the surface vertex coordinate system of the first surface (eyeball 7) is shown. It was shown in FIG. In the present invention, since the surface apex of each surface is only shifted in the y-axis direction and tilted about the x-axis, the conventional bus cross section and the local bus cross section are the same cross section. The line cross section is different from the local child cross section.
[0066]
The above-mentioned conventional bus cross section and child cross section are the definition of the conventional general-paraxial axis, and the local bus cross section and local sub cross section are the definitions of the local paraxial axis to be described later. It is. Further, in the local paraxial, the definitions of the local curvature radius, the local surface distance, the local focal length, and the local refractive power corresponding to the eccentric system will be described below.
[0067]
In the present invention, a light beam emitted from the illumination light source unit 4 and passing through the image center 3a of the display unit 3 and the center 1a of the eyeball 7 is used as a reference light beam, and the conventional curvature radii, surface intervals, focal lengths, refractions of each surface surface vertex are used. Instead of the force, the local curvature radius, the local surface interval, the local focal length, and the local refractive power based on the hit point (incident point) on each surface of the reference ray are used.
[0068]
Here, the local radius of curvature refers to the local radius of curvature on the hit point of the optical surface (the radius of curvature on the local bus section, the radius of curvature on the local subsection). The local surface interval is the value of the distance between two hit points between the current surface and the next surface (distance on the reference ray, value without air conversion). The local focal length is a value calculated by a conventional focal length calculation method (paraxial tracking) from the local curvature radius, the refractive index before and after the surface, and the local surface spacing. The local refractive power is a reciprocal value of the local focal length.
[0069]
In each numerical example of the present invention, the conventional radius of curvature, surface interval, eccentricity, refractive index, Abbe number, local radius of curvature, refractive index of the surface, local surface interval, and local focal length are shown.
[0070]
In the present invention, five numerical examples are given. Numerical data of Numerical Examples 1 to 5 are shown in Tables 1 to 5 (Tables 1 to 16), and optical path cross-sectional views are shown in FIGS.
[0071]
In the conventional paraxial axes of Table-1 to Table-5, the generatrix section radius of curvature ry, the subsection curvature radius rx, the surface interval d (parallel to the surface vertex coordinate system of the first surface), and eccentricity Amount (in the cross section of the generatrix, the amount of parallel decentering of the surface vertices of each surface with respect to the surface vertex coordinate system of the first surface is shifted, the amount of tilt eccentricity is tilt), the refractive index nd of the d line, and the Abbe number vd, FFS is a free-form surface, YTO is a cylindrical surface having refractive power only in the generatrix, and AL is an aspheric surface. The one with M is a reflecting surface, and the refractive index nd of d-line is reversed. Tables 1 to 5 show numerical data of reverse tracing from the eyeball 1 to the liquid crystal 3 side and to the illumination light source.
[0072]
The definition formula of FFS (free-form surface) is shown below. (In the surface vertex coordinate system of each surface)
z = 1/2 * (1 / a + 1 / b) * (y²* cos (c)²+ x²) / cos (c) / (1 + 1/2 * (1 / a-1 / b) * y * sin (c) +
(1+ (1 / a-1 / b) * y * sin (c)-(1 / a / b + 1/4 * tan (c)²* (1 / a + 1 / b)²) * x²)^(1/2))
+ c20 * x²+ c11 * x * y + c02 * y²
+ c30 * x^Three+ c21 * + c03 * y^Three
+ c40 * x^Four+ c31 * x^Three* y + c22 * x²* y²+ c13 * x * y^Three+ c04 * y^Four
+ c50 * x^Five+ c41 * x^Four* y + c32 * x^Three* y²+ c23 * x²* y^Three+ c14 * x * y^Four+ c05 * y^Five
+ c60 * x⁶+ c51 * x^Five* y + c42 * x^Four* y²+ c33 * x^Three* y^Three+ c24 * x²* y^Four+ c15 * x * y^Five+ c06 * y⁶
Each of a, b, c, c20, c11, c02... Is a free-form surface coefficient. (Note: In the case of this free-form surface, since there are coefficients related to paraxials in the free-form surface coefficients, the values of the conventional paraxial bus section radius of curvature ry and child-line section radius of curvature rx are actually measured on the surface vertex. This is not the same as the bus section radius of curvature ry and the core section radius of curvature rx of the line, so the actual bus section radius of curvature ry and the core section radius of curvature rx on the point (0, 0), that is, the surface vertex are also shown.
The definition of YTO is the following aspherical formula (in the surface vertex coordinate system of each surface):
[0073]
[Expression 1]

[0074]
The cross section of the child wire is a plane (rx = ∞).
[0075]
The definition of AL is a rotationally symmetric aspherical surface (in the surface vertex coordinate system of each surface)
[0076]
[Expression 2]

[0077]
h² = x² + y², r = rx = ry.
[0078]
In the local paraxial axis, local radii of curvature local-ry, local-rx, local surface spacing local-d (reflecting surface has opposite sign), local focal length local-fy, local-fx, surface refraction It shows the rate nd (the reflecting surface has the opposite sign). Also shown are the hit point coordinates (surface vertex 0,0) on each surface, the local focal length / field angle of the entire display optical system, and the local focal length of the optical surface A of the illumination optical system.
[0079]
[Table 1]

[0080]
[Table 2]

[0081]
[Table 3]

[0082]
[Table 4]

[0083]
[Table 5]

[0084]
The head-mounted display of the present invention is provided with

image display devices

51 and 52 on the left and right eyes of an observer 50 as shown in FIG. It is detachably fixed to the head.
[0085]
【The invention's effect】
According to the present invention, when observing image information displayed on a display means such as a liquid crystal display, an illumination optical system from the light source means to the display means and a display for guiding the light flux from the display means to the eyeball of the observer By appropriately setting the configuration of the optical system, the entire apparatus can be reduced in size while reducing the loss of light quantity, and the image information can be observed with good image quality, and the head mounted display using the image observation apparatus Can be achieved.
[0086]
In particular, according to the present invention, it is possible to achieve an HMD using a reflective LCD that has a small amount of light loss from the illumination light source, provides image quality with sufficient contrast, and has a compact illumination optical system and display optical system. it can.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of main parts of Embodiment 1 of the present invention.
FIG. 2 is a cross-sectional view of an essential part of Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view of main parts of Embodiment 3 of the present invention.
FIG. 4 is a cross-sectional view of an essential part of Embodiment 4 of the present invention.
FIG. 5 is a sectional view of an essential part of Embodiment 5 of the present invention.
FIG. 6 is a schematic view of the main part when the image display device of the present invention is applied to an HMD.
[Explanation of symbols]
1 eyeball
2 Free-form surface prism
3 Reflective LCD (The figure shows the LCD protective plate, and the liquid crystal surface is on the focus surface.)
4 Illumination light source (planar light source)
5 Optical surface A
6 Transmission surface C (total reflection surface of free-form surface prism)
7 Boomerang lens
8 Polarizing plate 1
9 Polarizing plate 2
10 Concave mirror of free-form surface prism
11 Entrance surface of free-form surface prism
12 Free-form surface mirror 1
13 Free-form mirror 2
14 Curved surface B

Claims

Reflective display means, illumination means for illuminating the display means, illumination optical system for guiding light from the illumination means to the display means, and display optical system for guiding light from the display means to the viewer side In the image display apparatus having
The illumination optical system has an optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system, and the optical surface A is a cross section of a local bus (emitted from the illumination means and the image center of the display means) has a curvature on a plane) including the emitted light and the incident light of the reference light beam passing through the pupil center has an optical surface B having a optical surface the display means and arranged curvature on the opposite side with respect to a, the A lens body composed of a glass member is formed by the optical surface A and the optical surface B,
Light rays emitted from the illuminating means are reflected by the optical surface A of the lens body to illuminate the display means, and reflected light from the display means passes through the optical surface A and is incident on the lens body. Incident, exiting the optical surface B, reflected by a plurality of reflecting surfaces, then guided to the pupil to form an enlarged image of the image displayed on the display means,
When Local_ryA the local meridional cross section curvature radius of the optical surface A of the lens body, the local meridional cross section curvature radius of the optical surface B and local_ryB in said display optical system, Local_ryA and local_ryB are the same sign,
0.4 <local_ryA / local_ryB <2.0 (1)
An image display device characterized by satisfying the above.

2. The image display apparatus according to claim 1, wherein there is only one optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system.

2. The image display device according to claim 1, wherein the reflected light from the display means is reflected by a plurality of reflecting surfaces which are eccentric curvature surfaces after being emitted from the lens body and guided to a pupil.

The illumination means is a time-division light source that emits a plurality of color lights in a time-division manner, and the display means displays an image based on each color light in a time-division manner in accordance with the color lights emitted from the time-division light source. The image display device according to claim 1, 2 or 3.

5. The image display device according to claim 1, wherein the display optical system includes two or more surfaces having different refractive powers depending on an azimuth angle, and the display optical system as a whole has a positive refractive power.

Reflective display means, illumination means for illuminating the display means, illumination optical system for guiding light from the illumination means to the display means, and display optical system for guiding light from the display means to the viewer side In the image display apparatus having
And the optical surface A having a curvature having both effects of transmission and reflection to be shared with each other in the illumination optical system and the display optical system, an optical surface having the display means and arranged opposite curvature to the optical surface A has a B, to form a lens body with the optical surface a and the optical surface B,
The emitted light from the illumination means reflected by the optical surface A of the lens body by illuminating the display means, the reflected light from said display means is transmitted through the optical surface A, incident on the lens body and, by injecting the optical surface B, after being reflected by the plurality of reflecting surfaces to form an enlarged image of the image displayed on the display means is guided to the pupil,
Of the most peripheral image on the cross section of the local bus of the display means (the surface including the incident light and the emitted light of the reference light beam emitted from the illumination means and passing through the image center of the display means and the eyeball center), the one farthest from the eyeball F3 eyeball center ray when the light beam passing through the most peripheral image height F3 and the eyeball center on the side is F3 eyeball center light beam, and the light beam passing through the most peripheral image height F2 and the eyeball center closer to the eyeball is F2 eyeball center light beam An image display device characterized in that the light beam has a longer optical path length in the lens body in the display optical system than the F2 eyeball central light beam.

The image display device according to claim 6 , wherein a local generatrix curvature of the curvature optical surface A of the lens body in the display optical system is larger than a local generatrix curvature of the curved surface B.

The optical path length in the lens body in the display optical system at the center of the eyeball passing through each image height and the center of the eyeball on the cross section of the local bus of the display means is the F3 eyeball from the F2 eyeball center ray side. 8. The image display device according to claim 7 , wherein the image display device gradually becomes longer toward the central ray side.

Reflective display means, illumination means for illuminating the display means, illumination optical system for guiding light from the illumination means to the display means, and display optical system for guiding light from the display means to the viewer side In the image display apparatus having
A lens body is formed of an optical surface A having both transmission and reflection functions shared by the illumination optical system and the display optical system, and an optical surface B opposite to the display means with respect to the optical surface A,
The light emitted from the illumination means is reflected by the optical surface A to illuminate the display means, and the reflected light from the display means is transmitted through the optical surface A and incident on the lens body. After exiting the surface B and reflected by a plurality of reflecting surfaces, it is guided to the pupil to form an enlarged image of the image displayed on the display means,
A plane including incident light and outgoing light of a reference ray emitted from the illumination means and passing through the image center and pupil center of the display means is a local bus cross section, and includes a hit point between the reference ray and each surface and is perpendicular to the local bus cross section. When the surface is the local cross section, the local bus section curvature radius of the optical surface A of the lens body in the display optical system is local_ryA, and the local bus section curvature radius of the optical surface B is local_ryB, local_ryA and local_ryB are The same sign,
0.4 <local_ryA / local_ryB <2.0
And the optical surface A and the optical surface B have a higher power in the local bus cross-sectional direction than the power in the local child cross-sectional direction.

The image display device according to claim 9 , wherein the optical surface A and the optical surface B are cylindrical surfaces.

A head-mounted display comprising the image display device according to claim 1 .