JP2004069859A - Method and apparatus for manufacturing hologram optical element, and image combiner and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration in optical performance by a fluctuation in a shrinkage rate of a hologram photosensitive material by simple adjustment even if this shrinkage rate fluctuates from the estimation of the time for designing. <P>SOLUTION: A reference optical system for irradiating the hologram photosensitive material with reference light and an object light optical system for irradiating the hologram photosensitive material with object light are used to cause the interference exposure of the hologram photosensitive material with the reference light and the object light. An operator inputs the actual shrinkage rate of the hologram photosensitive material from an input section 53. A control section 52 controls a position adjusting mechanism 51 so as to adjust the positions in an optical axis direction (G-direction) of a lens 47 and pinhole 48 which are portions of the object light optical system and the positions in a direction (H-direction) perpendicular to the optical axis thereof in accordance with the inputted shrinkage rate. <P>COPYRIGHT: (C)2004,JPO

Description

【００４８】
表１で用いた位相関数の定義は、ＨＯＥをＸＹ座標面上の位置と指定した点に入射する光線の受ける光路差を、使用する波長で規格化した値で表すもので、ｍ，ｎを整数とするとき、一般形の下記の数１で表される多項式の係数を指定することで決められる。ただし、この係数は６５個まで指定可能であって、順にＣ１，Ｃ２，Ｃ３，・・・，Ｃ６５と呼び、係数の順番をｊという整数で表すときに、Ｘ座標及びＹ座標の次数を示す整数ｍ，ｎとの間に下記の数２という関係が成り立つように対応付ける。すなわち、本例では、位相関数は、下記の数３の多項式で定義されている。このような位相関数の定義は、後述する表についても同様である。
【００４９】
【数１】

【００５０】
【数２】

【００５１】
【数３】

【００５２】
また、本設計例における各光学面の位置関係として、第１面（面番号１＝図１中の符号Ｐ）の中心を原点（Ｘ，Ｙ，Ｚ）＝（０，０，０）とした各光学面の中心の絶対位置とＸ軸の周りの回転量（反時計周りを正として測った値）を、下記の表２に示す。
【００５３】
【表２】

【００５４】
本設計例のＨＯＥ６の第１光源（再生時に観察者の眼の側となる光源）は、ＨＸ１：０，ＨＹ１：−．１７３２２８×１０^＋１０，ＨＺ１：−．１３５８３１×１０^＋１０より、図２のｙｚ座標の第３象現で、ＨＯＥ面の原点からの距離は２．２×１０^９ｍｍである。
【００５５】
本設計例の画像表示装置における表１中に定義された反射型ＨＯＥ６を実際に作製する際に用いる露光光学系を設計した。その露光光学系の要部の光路図を図３に示す。図４は、図３に示す光学系におけるプリズム２１の拡大図である。さらに、図４に示す光学系を用いた、反射型ＨＯＥ６の作製時に反射型ＨＯＥ６を露光する本発明の一実施の形態によるホログラム露光装置の概略構成図を、図５に示す。
【００５６】
図３に示す光学系は、１つのプリズム２１と単一の球面レンズ２２とで構成され、非常にシンプルにまとめられている。プリズム２１は、図４に示すように、前述した図１中の板状部５の一部を構成する小片５ｄと、小片５ｄと同一の屈折率を持ち小片５ｄを保持する保持部材（「雇い」と呼ばれる場合もある。）２４と、小片５ｄと保持部材２４との間の隙間に充填され小片５ｄ及び保持部材２４と同一の屈折率を持つ充填剤（図示せず）と、から構成されている。プリズム２１の小片５ｄ側の面には、反射型ＨＯＥ６（厳密に言えば、反射型ＨＯＥ６を形成するための感光材料層）が形成され、露光が完了し反射型ＨＯＥ６の作製が完了した後に、反射型ＨＯＥ６が形成された小片５ｄを保持部材２４から取り外して、前述した方法で反射型ＨＯＥ６を板状部５の内部に設けることができるようになっている。
【００５７】
図３及び図４において、射出瞳Ｐは、ＨＯＥ６の位置を基準として、図１中の射出瞳Ｐを空気に屈折率換算した位置に配置している。図３及び図４において、Ｂ１は反射型ＨＯＥ６の露光時の第１光源（射出瞳Ｐ側の光源）による露光光束（参照光）、Ｂ２は第２光源による露光光束（物体光）を形成するための平行光束（平面波）を示す。このように、図３に示す光学系は、アフォーカル光学系となっている。また、２２ａは球面レンズ２２のプリズム２１側の面、２２ｂは球面レンズ２２の第２光源側の面である。
【００５８】
図５に示すホログラム露光装置では、レーザ光源３１は、露光時間を制御するためのシャッタ３２が開かれているときに、ビームエキスパンダ・ビーム整形ユニット３３に入射する。このユニット３３は、入射した光を集光点に集光するレンズ３４と、前記集光点に配置されたピンホール３５と、ピンホール３５を通過した光をコリメートするコリメータレンズ３６とを有し、ノイズ光をカットするスペイシャルフィルタとしての機能と、ビーム径を拡大するビームエキスパンダとしての機能とを、併せ持つ。ユニット３３からの平行光束は、その偏光方向が１／２波長板３７により回転された後に、所定の偏光成分のみが偏光ビームスプリッタ３８を透過する。１／２波長板３７は適宜回転させ得るようになっており、１／２波長板３７及び偏光ビームスプリッタ３８が光量調整部を構成している。偏光ビームスプリッタ３８を透過した光は、ミラー３９で反射された後に、ビームスプリッタ４０で２光束に分割される。
【００５９】
ビームスプリッタ４０を透過した光束は、ミラー４１で反射され、レンズ４２及びレンズ４３を経由し、更に絞り４４で所望の径に絞られた後に、平行光束（平面波）として、第１光源（射出瞳Ｐ側の光源）による露光光束（参照光束）として、プリズム２１に塗布された反射型ＨＯＥ６となるべき乳剤等のホログラム感光材料に入射する。ここで、レンズ４２は、ミラー４１で反射された平行光束をその焦点に集光する。レンズ４３は、レンズ４３の焦平面がレンズ４２の焦点を含み、かつ、レンズ４３の光軸とレンズ４２の光軸とが平行になるように、配置されている。レンズ４３は、モータ等のアクチュエータ（図示せず）により作動する位置調整機構４５により、レンズ４３の光軸と垂直な図５中の矢印Ｆの方向の位置を調整し得るようになっている。したがって、レンズ４３から射出して反射型ＨＯＥ６となるべきホログラム感光材料に入射する参照光は、平行光束であるが、位置調整機構４５によりレンズ４３位置を調整することによって、その入射方向が変わる。例えば、露光光学系の設計状態は、レンズ４３の焦点がレンズ４２の焦点と一致している位置にレンズ４３が位置している状態であり、このとき参照光束は、レンズ４２に入射する際の方向と同一の方向でホログラム感光材料に入射する。
【００６０】
一方、ビームスプリッタ４０で反射された光束は、ミラー４６で反射され、集光レンズ４７でその焦点に集光され、この焦点に配置されたピンホール４８を通過した後、コリメータレンズ４９で平行光束にされかつ必要な光束径に拡大され、更に絞り５０で所定の径に絞られ、第２光源による露光光束（物体光束）を形成するための前記平行光束Ｂ２となる。この平行光束（平面波）Ｂ２は、レンズ２２及びプリズム２１により所望の非球面波となって、プリズム２１に塗布された反射型ＨＯＥ６となるべき乳剤等のホログラム感光材料に、参照光とは反対側から入射する。ただし、以上の説明は、当該露光光学系の設計状態、すなわち、レンズ４７の焦点及びピンホール４８がコリメータレンズ４９の焦点と一致している状態での動作である。レンズ４７及びピンホール４８は、モータ等のアクチュエータ（図示せず）により作動する位置調整機構５１により、レンズ４７の光軸方向の図５中の矢印Ｇの方向の位置、及び、レンズ４７の光軸と垂直な図５中の矢印Ｈの方向の位置を、調整し得るようになっている。レンズ４７の焦点及びピンホール４８が、レンズ４７の焦点及びピンホール４８がコリメータレンズ４９の焦点と一致している設計時の位置から図５中の矢印Ｈの方向にずれると、それに応じて光束Ｂ２の方向（チルト）が変わる。また、レンズ４７の焦点及びピンホール４８が、前記設計時の位置から図５中の矢印Ｇの方向にずれると、それに応じて光束Ｂ２のフォーカスが変わって光束Ｂ２は平行光束ではなくなる。
【００６１】
前述したようにして参照光束と物体光束とが乳剤等の感光材料に入射されることにより、それらが感光材料に干渉露光され、参照光と物体光の干渉縞が感光材料に、例えば屈折率の差として記録される。なお、この露光後に、必要に応じて感光材料が現像されることは、言うまでもない。
【００６２】
以上の説明からわかるように、図５に示す露光装置では、図５中の要素３１〜４０は、平面波の参照光をホログラム感光材料に照射する参照光光学系と非球面波の物体光を前記ホログラム感光材料に照射する物体光光学系との、共用部分を構成している。また、図５中の要素４１〜４４が参照光学系の残りの部分を構成し、図５中の要素４７〜５０，２２，２１が物体光光学系の残りの部分を構成している。
【００６３】
また、図５に示す露光装置は、キーボード等の入力部５３と、マイクロコンピュータ又はパーソナルコンピュータ等からなる制御部５２と、を更に備えている。オペレータは、入力部５３から、ホログラム感光材料の実際の収縮率に関する収縮率情報（例えば、収縮率そのもの）及び干渉露光により作製される反射型ＨＯＥ６の使用時に当該反射型ＨＯＥ６に照射される再生光を発する光源としてのＬＥＤ３の実際の発光スペクトルに関する光源発光スペクトル情報（例えば、ＬＥＤ３のピーク強度波長）を、制御部５２の内部メモリ（図示せず）に入力することができるようになっている。制御部５２の内部メモリ内には、収縮率情報及び光源発光スペクトル情報と、これらをパラメータとしてこれらに応じて露光される干渉縞を最適化するのに必要なレンズ４３の位置並びにレンズ４７及びピンホール４８の位置と、の対応関係を示すルックアップテーブルが、予め格納されている。その例については、後述する。制御部５２は、入力部５３から入力された収縮率情報及び光源発光スペクトル情報に基づいて、ルックアップテーブルを参照してそれらの情報に対応する各位置を求め、その各位置となるように位置調整機構４５，５１を制御する。
【００６４】
ところで、露光レンズの設計手法には色々あるが、図３に示す光学系の設計に際し、前述したＣＯＤＥ　Ｖを用いた。ＣＯＤＥ　Ｖでは、表１中に示す反射型ＨＯＥ６の第１光源から反射型ＨＯＥ６を透過して、第２光源へ光線追跡することで行う。ＨＯＥ６を透過した後に、図３に示す光学系を挿入して、反射型ＨＯＥ６での位相変換作用と等価な作用を施せば、波面はきれいな球面波となって無収差で第２光源に結像する。
【００６５】
表１及び表２に示す画像表示装置の光学系の設計値を基に、図３に示す光学系を設計する際、反射型ＨＯＥ６を透過の設定に変更するが、このとき非球面位相項の変換作用が等しくなければならない。そのためには、位相係数を等しく受け渡すことと、第１光源の座標を物点としてそこから光線追跡することが必要である。再生系で定義した第１光源と異なる距離から露光系を設計しても、正しい位相変換作用は得られない。ただし、図３に示す光学系の設計においては、第１光源のＨＯＥ面の原点からの距離２．２×１０^９ｍｍは非常に大きいので、第１光源とＨＯＥ６面との間の空気換算距離の値は、無限遠とみなしても差し支えなく、実際に、無限遠とみなし、図３に示す光学系の光線追跡は平行光を入射して設計した。
【００６６】
ここで、図３に示す光学系の光線追跡のための諸量を、下記の表３に提示する。光学面の順序（面番号の順序）は第１光源（＝イメージコンバイナ１の射出瞳Ｐ側の光源）から第２光源への順である。
【００６７】
表３において、面番号１の符号Ｓ１は第１光源を示している。面番号３のホログラム面の諸係数は前記表１と同じであるが、反射型ＨＯＥ６を透過型ＨＯＥとして光線追跡するために、２光束はＨＯＥ６の同じ側から入射しなければならない。したがって、第１光源位置をＲＥＡからＶＩＲに変更している。入射瞳径は、ホログラム面の有効径を満たす径が必要で、ここではφ４である。点光源（ここではその極限として平行光）からの光であるので、画角は必要ない。光線追跡のための波長は、露光波長の５３２ｎｍである。この光学系は、面番号６の面を射出した後に平行光となるアフォーカル光学系である。
【００６８】
【表３】

【００６９】
また、図３に示す光学系における各光学面の位置関係として、第３面（面番号３＝図３中の符号６、ホログラム面）の中心を原点（Ｘ，Ｙ，Ｚ）＝（０，０，０）とした各光学面の中心の絶対位置とＸ軸の周りの回転量（反時計周りを正として測った値）を、下記の表４に示す。
【００７０】
【表４】

【００７１】
この表３に示す設計値を持つ場合の図３に示す光学系の光線軌跡による射出瞳面（すなわち、図３中の面２３）上での波面収差図を、図６に示す。なお、この光線追跡を行う場合には、ＨＯＥ６の位相係数として表１中の位相係数を用いる。図６からわかるように、ＲＭＳ０．１４λとよく補正されている。
【００７２】
以上のように、収縮率が１％でＬＥＤのピーク波長が５１６ｎｍであると仮定した場合の、図１に示す画像表示装置の光学系の設計例を、表１に示した。そして、この設計例における反射型ＨＯＥ６の設計値に応じて設計した露光光学系の設計値を、表３に示した。
【００７３】
ここで、実際の収縮率が、見積の収縮率１％から外れて２％であったとする。このとき、再生主波長は５２１．４ｎｍとなる。そうすると、５２６．７ｎｍで最適化した再生系の位相関数を５２１．４ｎｍで使用することになり、収差が生じてしまう。
【００７４】
これでは具合が悪いので、予め収縮率が２％と仮定した再生系データ（図１に示す光学系の設計値）も作っておく。その設計値を、表５に提示する。表５において、反射型ＨＯＥ６の位相関数以外の値は、表１と同じである。
【００７５】
【表５】

【００７６】
表５に示す設計値の場合について、表３の設計値を持つ場合の図３に示す光学系を光線追跡したときの、射出瞳面（すなわち、図３中の面２３）上での波面収差図を、図７に示す。なお、この光線追跡を行う場合には、ＨＯＥ６の位相係数として表５中の位相係数を用いる。図７からわかるように、ＲＭＳ０．４１λと比較的大きい収差が発生している。
【００７７】
図７に示す波面収差を光学設計プログラムｃｏｄｅ　Ｖを用いて分析したところ、この波面の乱れはチルト成分とフォーカス成分とに分けられ、その二つの成分を除けば、ＲＭＳ０．１５λに補正できることがわかった。
【００７８】
図５に示す露光装置では、設計値の状態では、レンズ４７の焦点及びピンホール４８とコリメータレンズ４９の焦点とを一致させて配置しているので、いずれか一方を光軸と垂直にシフトすれば、光線としてはチルトの効果が得られる。そして、ここでは、レンズ４７の方がレンズ４９より焦点距離が短いので、少しの移動量で大きな効果が得られるため、レンズ４７及びピンホール４８をシフトさせるのが好ましい。そこで、図５に示す露光装置では、位置調整機構５１によりレンズ４７及びピンホール４８の図５中のＨ方向の位置を調整し得るようにしている。
【００７９】
また、レンズ４７の焦点及びピンホール４８とコリメータレンズ４９のいずれか一方を光軸方向にシフトすれば、フォーカスの効果が得られる。そこで、図５に示す露光装置では、位置調整機構５１によりレンズ４７及びピンホール４８の図５中のＧ方向の位置を調整し得るようにしている。
【００８０】
ここで、実際の収縮率が見積の収縮率１％から外れて２％である場合、レンズ４７及びピンホール４８を、レンズ４７の光軸と垂直な方向（Ｈ方向）に６μｍ，光軸方向（Ｇ方向）に０．４７７ｍｍ動かして調整すると、そのときの図３に示す光学系を光線追跡したときの、射出瞳面（すなわち、図３中の面２３）上での波面収差は、図８に示すように、ｒｍｓ０．１５λに補正できる。なお、この光線追跡を行う場合には、ＨＯＥ６の位相係数として表５中の位相係数を用いる。
【００８１】
以上のことから、ホログラム感光材料の収縮率を１％と見込んで設計しておいたＨＯＥ６を基に設計した表３の設計値に従った露光装置を用いて露光した場合、露光工程の条件等により収縮率が２％に変動しても、位置調整機構５１により前述した位置調整を行って再度露光することにより、再生系の性能を発揮するＨＯＥ６を露光することができる。
【００８２】
前述した例では、図５中の制御部５２の内部メモリ内のルックアップテーブルには、収縮率１％に対応してＨ方向位置０μｍ及びＧ方向位置０ｍｍ、収縮率２％に対応してＨ方向位置６μｍ及びＧ方向位置０．４７７ｍｍを格納しておけばよい。収縮率２％についてＨ方向位置６μｍ及びＧ方向位置０．４７７ｍｍを求めたのと同様の方法により、他の種々の収縮率についてもＨ方向位置及びＧ方向位置をそれぞれ求めておき、これらも前記ルックアップテーブルに格納しておけばよい。
【００８３】
そして、例えば、最初に、Ｈ方向位置０μｍ及びＧ方向位置０ｍｍに位置させた状態（すなわち、表３に示す設計値通りの状態）で、ホログラム感光材料を露光してＨＯＥ６を作製し、その作製したＨＯＥ６について回折効率の分光特性を測定し、その測定結果に基づいてホログラム感光材料の実際の収縮率を求め、この収縮率をオペレータが入力部５３から制御部５２に入力すればよい。制御部５２は、この入力された収縮率に応じて位置調整機構５１を制御して前述した位置調整を行う。したがって、次回以降の露光により作製された反射型ＨＯＥ６は、画像表示装置の性能を十分に発揮するものとなる。本実施の形態による画像表示装置では、この反射型ＨＯＥ６を用いたものである。
【００８４】
ところで、実際の収縮率が見積の収縮率１％から外れて２％である場合には、前述したように、再生主波長（回折効率が最大となる波長）が５２６．７ｎｍから５２１．４ｎｍとなるが、前述した説明では、このような収縮率の変動に伴う再生主波長の変動による収差変動のみ補正し、光源波長とのずれによる明るさの変動は無視した。また、ＬＥＤ３のピーク波長が見積の５１６ｎｍから変動し得る点も無視し、参照光Ｂ１は、設計値通りの方向からホログラム感光材料に入射するものとし、レンズ４３はその方向に対応する図５中のＦ方向位置にあるものとした。
【００８５】
本発明では、これらを無視したままとして必ずしも位置調整機構４５を設ける必要はないが、これらを無視しないことが好ましい。よって、本実施の形態では、実際には、前述したように、制御部５２の内部メモリ内のルックアップテーブルには、収縮率情報のみならず光源発光スペクトル情報（ここでは、ＬＥＤ３のピーク波長とする。）をもパラメータとして、レンズ４７及びピンホール４８の位置のみならずレンズ４３の位置も、格納している。そして、制御部２は、ルックアップテーブルを参照して、入力部５３から入力された収縮率及び実際のＬＥＤ３のピーク波長に対応するレンズ４７及びピンホール４８のＧ方向位置及びＨ方向位置のみならずレンズ４３のＦ方向位置も求め、求めた各位置となるように、位置調整機構４５，５１を制御する。
【００８６】
実際の収縮率が見積の収縮率からはずれた場合、それに応じて再生主波長が変動する。例えば、実際の収縮率が見積の収縮率１％から外れて２％である場合、前述したように、再生主波長（回折効率が最大となる波長）が５２６．７ｎｍから５２１．４ｎｍする。また、ＬＥＤ３のピーク波長が見積の波長から変動すると、光量の低下を招かないように再生主波長をＬＥＤ３の実際のピーク波長と一致させることが好ましいことから、再生主波長を一致させるべき波長が変動することになる。一方、レンズ４３をＦ方向へずらすと、それに応じて参照光Ｂ１のホログラム感光材料への入射角が変わるため、再生主波長を調整することができる。したがって、収縮率変動に伴う再生主波長の変動やＬＥＤ３のピーク波長の変動を考慮する場合、それに応じてレンズ４３のＦ方向位置を調整すればよい。収縮率やＬＥＤ３のピーク波長に応じて最適化するためのレンズ４３のＦ方向位置は、予め求めておくことができるので、その関係を前記ルックアップテーブルに格納しておけばよい。
【００８７】
ところで、再生主波長の変動に応じて、収差（露光光学系の収差、すなわち、図３に示す光学系を光線追跡したときの、射出瞳面（すなわち、図３中の面２３）上での波面収差）が生ずることになる。したがって、収縮率変動に伴う再生主波長の変動やＬＥＤ３のピーク波長の変動を考慮する場合、この点も考慮してその収差が最も小さくなるようなレンズ４７及びピンホール４８のＧ方向位置及びＨ方向位置を求めておけばよい。すなわち、収縮率及び実際のＬＥＤ３のピーク波長の両方をパラメータとして収差が最も小さくなるようなレンズ４７及びピンホール４８のＧ方向位置及びＨ方向位置を求め、その関係を前記ルックアップテーブルに格納しておけばよい。
【００８８】
以上、本発明の実施の形態について説明したが、本発明はこの実施の形態に限定されるものではない。
【００８９】
例えば、前記実施の形態では、図５中の位置調整機構４５，５１は制御部５２により自動的に制御されるようになっていたが、制御部５２及び入力部５３を取り除き、位置調整機構４５，５１として手動調整し得るものを用いてもよい。
【００９０】
また、前記実施の形態は、レンズ４７及びピンホール４８の位置を調整し得るように構成されていたが、その代わりに、コリメータレンズ４９の位置を調整し得るように構成してもよい。
【００９１】
さらに、前記実施の形態では、レンズ４３の位置を調整し得るように構成されていたが、その代わりに、レンズ４２の位置を調整し得るように構成してもよい。
【００９２】
また、前述した実施の形態は、本発明をシースルー型の頭部装着式画像表示装置に適用した例であったが、本発明は、シースルー型ではない画像表示装置に適用することもできる。この場合、前述した各実施の形態による画像表示装置において、外界からの光がイメージコンバイナ１に入射しないように構成すればよい。この場合、イメージコンバイナ１の部分は、２つの像を重ね合わせるものではないので、イメージコンバイナとは言えず、画像表示素子２からの光を使用者の眼に導く導光部となる。この場合、イメージコンバイナ１における板状部の下側部分（ＨＯＥ６から下側の部分）を除去してもよい。このようなシースルー型でない画像表示装置は、例えば、特開２００１−２６４６８２号の場合と同様に携帯電話機のフリッパー部に内蔵することができる。
【００９３】
【発明の効果】
以上説明したように、本発明によれば、ホログラム感光材料の収縮率が設計時の見積から変動してもその変動による光学性能の劣化を簡単な調整で抑制することができること、及び、再生光を発する光源のピーク波長等が設計時の波長から変動しても光学性能の劣化を簡単な調整で抑制することができること、のいずれか一方又は両方を同時に達成することができる。
【００９４】
また、本発明によれば、このような製造方法及び装置により露光することによって作製したホログラム光学素子を用いることにより、光学性能に優れかつコストダウンを図ることができるイメージコンバイナ及び画像表示装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態による画像表示装置の構成及びその光線の概略の経路を示す図である。
【図２】ホログラムを定義する２光源の座標系を示す図である。
【図３】図１に示す画像表示装置における反射型ホログラム光学素子を露光するための露光光学系の要部を示す光路図である。
【図４】図３に示す光学系におけるプリズムの拡大図である。
【図５】本発明の一実施の形態によるホログラム露光装置の概略構成図である。
【図６】ホログラム感光材料の収縮率が設計時の見込通りの場合の、図３に示す光学系の波面収差図である。
【図７】ホログラム感光材料の収縮率が設計時の見込と異なった場合の、図３に示す光学系の波面収差図である。
【図８】ホログラム感光材料の収縮率が設計時の見込と異なった場合において、収縮率変動を補正した後の、図３に示す光学系の波面収差図である。
【符号の説明】
１　イメージコンバイナ
２　画像表示素子
３　ＬＥＤ
４　反射鏡
５　板状部
６　反射型ホログラム光学素子
１１　導光部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a manufacturing method and an apparatus for exposing a hologram optical element, and an image combiner and an image display device.
[0002]
[Prior art]
Hitherto, hologram optical elements have been widely used in various applications.
[0003]
For example, as a device using a hologram optical element, a so-called see-through type head-mounted image display device (head), which allows a user to see a display image superimposed thereon while observing the outside world, has conventionally been used. For example, an image display device disclosed in JP-A-2000-352689, JP-A-2001-264682, and JP-A-2000-121989 is known as a mount display. Japanese Patent Application Laid-Open No. 2001-264682 discloses not only a see-through type head-mounted image display device but also a see-through type having substantially the same configuration as the see-through type (that is, light from an image display element is not used). There is also disclosed an image display device in which only light from an image display element is guided to a user's eyes without superimposing other light such as from the outside world, and an example in which this image display device is incorporated in a flipper portion of a mobile phone. Are also disclosed.
[0004]
In these image display devices, reduction in size and weight is achieved by using a reflection type hologram optical element. The reflection type hologram optical element has excellent wavelength selectivity and can selectively diffract and reflect only light in an extremely limited wavelength region. Therefore, when a see-through type image display device is configured, the loss of the amount of light transmitted from the outside or the like by the reflection hologram optical element can be significantly reduced.
[0005]
A hologram optical element such as a reflection hologram optical element is manufactured by causing two coherent light beams to interfere with each other and recording the interference fringes on a hologram photosensitive material such as an emulsion. When the reproduction illumination light is incident at the same wavelength from one of the light source positions of the two light beams, the recorded interference fringes are subjected to a diffraction effect such as a diffraction grating, and a wavefront equivalent to the other incident light is generated. Because
[0006]
That is, if one forms a free-form surface wavefront during exposure and the other forms a simple spherical wave to record interference fringes, a simple free-form illumination can generate a complex freeform surface wavefront. It is.
[0007]
Since the hologram optical element can have a free-form surface phase conversion effect as described above, for example, a hologram optical element having a third or higher order phase conversion effect depending on the position on the hologram surface is used. When used in an image combiner, an image with good image quality with various aberrations corrected can be obtained even if all other surfaces are configured as flat surfaces or spherical surfaces.
[0008]
[Problems to be solved by the invention]
However, it is generally known that a hologram photosensitive material (hologram recording material) shrinks during some processes of an exposure step, and is disclosed as quality information by a recording material maker.
[0009]
When the recording material contracts, the interval between the interference fringes fluctuates, so that the performance as an image display device is deteriorated, for example, the diffraction efficiency is lowered, the diffraction wavelength is shifted, and aberration occurs.
[0010]
However, since the shrinkage ratio of the recording material often fluctuates depending on various conditions of the exposure process, when designing an image display device, for example, an intermediate range of the change ratio of the shrinkage ratio is estimated in advance and the actual shrinkage ratio is designed. It was necessary to take measures such as accepting the estimation error as a manufacturing error, stabilizing the process and suppressing the shrinkage ratio fluctuation range, or redesigning according to the actual shrinkage ratio.
[0011]
Further, when the hologram optical element is used, an emission spectrum such as a peak wavelength of a light source that emits reproduction light irradiated to the hologram optical element may fluctuate due to a manufacturing error of the light source. For example, in a small and inexpensive LED, the peak wavelength variation is generally said to be about ± 10 nm.
[0012]
If the reproduction wavelength fluctuates, the diffraction efficiency also fluctuates, causing the same performance degradation as described above.However, conventionally, manufacturing errors are allowed, or a method of selecting LEDs with a small wavelength error by selecting chips is used. But that would be costly.
[0013]
The present invention has been made in view of such circumstances, and even if the contraction rate of the hologram photosensitive material fluctuates from the estimate at the time of design, it is possible to suppress the deterioration of optical performance due to the fluctuation with a simple adjustment, A hologram capable of simultaneously achieving one or both of the following: even if the peak wavelength of a light source that emits reproduction light fluctuates from the wavelength at the time of design, deterioration of optical performance can be suppressed by simple adjustment. An object of the present invention is to provide a method and an apparatus for manufacturing an optical element.
[0014]
Further, the present invention provides an image combiner and an image display device which are excellent in optical performance and can be reduced in cost by using a hologram optical element manufactured by exposing by such a manufacturing method and apparatus. With the goal.
[0015]
[Means for Solving the Problems]
As a result of the research of the present inventors, the reference light and the object light are irradiated on the hologram photosensitive material by using the reference light optical system for irradiating the reference light to the hologram photosensitive material and the object light optical system for irradiating the hologram photosensitive material with the object light. It has been found that when the material is subjected to interference exposure, the wavelength at which the diffraction efficiency is maximized can be adjusted by adjusting the position of a part of the reference optical system. This is because the incident angle of the reference light is changed by adjusting the position of a part of the reference optical system. Further, by adjusting the position of a part of the object light optical system, the aberration of the exposure optical system including the reference light optical system and the object light optical system can be adjusted.
[0016]
On the other hand, a change in the contraction rate of the hologram photosensitive material corresponds to a change in the wavelength at which the diffraction efficiency is maximized, and also corresponds to a change in the aberration of the exposure optical system. Further, when the hologram optical element is used, the fluctuation of the emission spectrum such as the peak wavelength of the light source that emits the reproduction light applied to the hologram optical element corresponds to the fluctuation of the wavelength at which the diffraction efficiency is maximized. Corresponds to the fluctuation of the aberration of the exposure optical system.
[0017]
Therefore, the shrinkage ratio of the hologram photosensitive material and the peak wavelength of the reproduction light from the light source are set to predetermined values, and the desired characteristics of the hologram optical element are designed and optimized so as to obtain the characteristics. In an exposure optical system including the reference light optical system and the object light optical system, position adjustment of a part of the object light optical system and a part of the reference light optical system is performed based on an actual contraction ratio and an actual peak wavelength. For example, even if the actual shrinkage or the actual peak wavelength fluctuates from the set value, the deterioration of the optical performance due to the fluctuation can be easily suppressed.
[0018]
The present invention has been made based on new findings obtained as a result of such research by the present inventors in order to solve the aforementioned problems. That is, the method for manufacturing a hologram optical element according to the first aspect of the present invention uses a reference light optical system that irradiates reference light to a hologram photosensitive material and an object light optical system that irradiates object light to the hologram photosensitive material. A method for manufacturing a hologram optical element manufactured by subjecting said hologram photosensitive material to interference exposure of reference light and said object light, wherein an actual shrinkage ratio of said hologram photosensitive material of said hologram optical element manufactured by said interference exposure Information, and, based on at least one of the information on the actual emission spectrum of the light source that emits the reproduction light emitted to the hologram optical element when using the hologram optical element produced by the interference exposure, The position of at least one of a part of the reference light optical system and a part of the object light optical system is adjusted. To, it is intended to exposure.
[0019]
An exposure apparatus for a hologram optical element according to a second aspect of the present invention includes a reference light optical system for irradiating reference light to a hologram photosensitive material and an object light optical system for irradiating object light to the hologram photosensitive material. An exposure apparatus for a hologram optical element that causes light and the object light to interfere with and expose the hologram photosensitive material, wherein at least one of a part of the reference light optical system and a part of the object light optical system is positioned. A position adjustment unit to be adjusted, information on the actual shrinkage of the hologram photosensitive material of the hologram optical element produced by the interference exposure, and the hologram optical element when the hologram optical element produced by the interference exposure is used. The position is determined based on at least one of information on an actual emission spectrum of a light source that emits a reproduction light to be irradiated. A control unit for controlling the adjustment unit, those having a.
[0020]
An image combiner according to a third aspect of the present invention is an image combiner provided with a reflection type hologram optical element and superimposing light from an image display unit and light from the outside, wherein the reflection type hologram optical element includes It is manufactured by the manufacturing method according to the first aspect or by exposure using the exposure apparatus according to the second aspect.
[0021]
An image display device according to a fourth aspect of the present invention includes the image combiner according to the third aspect and the image display means, and a part including at least the image combiner is worn by a user during use. .
[0022]
An image display device according to a fifth aspect of the present invention is an image display device comprising: an image display unit; and a light guide unit that guides light from the image display unit to a user's eye, wherein the light guide unit Has a reflection type hologram optical element manufactured by exposure by the manufacturing method according to the first aspect or by the exposure apparatus according to the second aspect.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method and an apparatus for manufacturing a hologram optical element, an image combiner, and an image display device according to the present invention will be described with reference to the drawings.
[0024]
FIG. 1 is a diagram showing a configuration of an image display device according to an embodiment of the present invention and schematic paths of light rays (only light rays from the image display element 2).
[0025]
Here, as shown in FIG. 1, an X axis, a Y axis, and a Z axis that are orthogonal to each other are defined. That is, the left-right direction in the paper of FIG. 1 is defined as the Z axis, and the direction in which the Z coordinate value increases is defined as the right. 1 is defined as the Y axis, and the direction in which the Y coordinate value increases is defined as upward. A direction perpendicular to the paper surface of FIG. 1 is defined as the X axis, and a right-handed system, that is, a direction deeper from the paper surface of FIG. 1 is defined as a direction in which the X coordinate value increases. Note that the Y-axis direction may coincide with the actual horizontal direction, or may be any other appropriate direction.
[0026]
The image display device according to the present embodiment includes an image combiner 1 and an image display element 2.
[0027]
In the present embodiment, a transmission type LCD is used as the image display element 2. The image display element 2 is illuminated from behind by a light source including a LED 3 and a reflecting mirror 4 such as a parabolic mirror, and spatially modulates the light from the light source to transmit light indicating a display image. It is needless to say that another element such as a reflective LCD may be used as the image display element 2 or a self-luminous element such as an organic EL element may be used.
[0028]
The image combiner 1 includes a plate-shaped portion 5 made of an optical material such as glass or plastic and formed in a parallel plate shape, and guides light from the image display element 2 made of an optical material such as glass or plastic to the plate-shaped portion 5. A light guide unit 11. The plate-shaped portion 5 is not limited to a parallel flat plate, and may have, for example, optical power for correcting visual acuity of a user. In this case, for example, at least one of the two surfaces 5a and 5b in the Z-axis direction of the plate-shaped portion 5 is formed of a curved surface. In addition, the plate-shaped portion 5 also extends downward in FIG. 1, but is not shown. The light guide portion 11 is formed in a substantially triangular prism shape, and includes an incident surface 11c having a curved surface on which light from the image display element 2 is incident, and a reflecting surface 11b having a flat surface for totally reflecting the light incident from the incident surface 11c. An emission surface 11a formed of a curved surface that emits light reflected by the reflection surface 11b and causes the light to enter near the upper portion of the surface 5a of the plate-shaped portion 5 in FIG.
[0029]
The plate-like portion 5 is mounted on the head of the user via a support member (not shown) such as a frame, like a spectacle lens, and is located in front of the user's eyes (not shown). . In FIG. 1, P indicates the exit pupil of the image combiner 1 with respect to the light from the image display element 2, and P0 indicates the center of the center P of the exit pupil. The image combiner 1 is mounted on the user such that the exit pupil P substantially matches the pupil of the user's eye. Therefore, the center P0 of the exit pupil P substantially coincides with the center of the pupil of the user's eye. In FIG. 1, the Z-axis direction matches the thickness direction of the plate portion 5. The eye-side surface 5a and the opposite surface 5b of the plate-shaped portion 5 are parallel to the XY plane. Although not shown in the drawings, the LED 3, the reflecting mirror 4, the image display element 2, and the light guide 11 are also supported by the support member. Thereby, the image display element 2 does not hinder the user from observing the outside world and does not hinder the user from wearing the image display device. It is arranged diagonally to the upper left in the paper.
[0030]
Of course, the image display element 2 may be arranged at another appropriate place, and a display image may be guided to the position of the image display element 2 in FIG. 1 by a relay optical system, or this position may be obtained by using a scan optical system. The aerial image may be formed at the same time.
[0031]
In FIG. 1, points A1 and A2 indicate the positions of both ends of the display unit of the image display element 2 in the plane of the drawing. Point A0 indicates the center of the display unit.
[0032]
The image combiner 1 transmits light through the plate-shaped portion 5 so as to pass through the thickness d of the plate-shaped portion 5 from the front of the plate-shaped portion 5 (that is, to enter from the surface 5b and exit from the surface 5a). Hereinafter, the light from the image display element 2 is superimposed on “external light”, and is guided to the user's eyes.
[0033]
In the present embodiment, a reflection type hologram optical element (reflection type HOE) 6 is provided inside the plate-like portion 5 near a position facing the user's eye in the plate-like portion 5. In the present embodiment, as shown in FIG. 1, the reflection type HOE 6 is inclined at a predetermined angle counterclockwise with respect to the surfaces 5a and 5b. Further, a reflection surface (mirror) 5c is provided inside the plate portion 5 near a position facing the surface 11a of the light guide portion 11 in the plate portion 5. As shown in FIG. 1, the reflection surface 5c is inclined at a predetermined angle clockwise with respect to the surfaces 5a and 5b. Note that the portion of the plate-like portion 5 obliquely above the reflection surface 5c in FIG. 1 does not pass light from the image display element 2, and may be cut. In this case, the reflection surface 5c is provided on the surface of the plate portion 5.
[0034]
In the present embodiment, a small piece of the same material as the plate portion 5 (a small portion on the right side of the reflection type HOE 6 in the plate portion 5 in FIG. 1) 5d is used as a base material, and a reflection type HOE 6 is formed thereon. The small piece 5d is placed in a mold forming the plate portion 5, and the material of the plate portion 5 is melted, poured into the mold, and then solidified, whereby the reflection type HOE 6 is attached to the plate portion. 5 is provided inside. However, the method of providing the reflection type HOE 6 inside the plate portion 5 is not limited to this.
[0035]
The wavelength of the light from the image display element 2 has a wavelength width including the wavelength of the diffraction efficiency peak of the reflection type HOE 6, and a maximum part of the wavelength width substantially coincides with the wavelength of the diffraction efficiency peak. The light from the image display element 2 is reflected by the mold HOE6. On the other hand, the reflection type HOE 6 transmits external light (not shown) without being deflected. It is preferable to use a reflection type HOE 6 having high wavelength selectivity so as not to hinder external light as much as possible. If a reflective HOE 6 having selectivity with respect to three wavelength light in a narrow wavelength range representing each of R, G, and B colors is used, it is possible to color a display image viewed by a user. .
[0036]
As shown in FIG. 1, the reflective HOE 6 has a characteristic of reflecting light from the image display element 2 in the direction of the pupil of the observer, and has an image forming action in which various aberrations are corrected. It has a third or higher order phase conversion action depending on the position on the hologram surface. The reflection type HOE 6 may be a flat type or a curved type. In the case where a curved HOE 6 is used, if the curvature H of the curved surface is located on the user's eye side, when the angle of view is large, the amount of aberration variation due to the angle of view generated by the reflective HOE 6 is small. It is smaller and preferable.
[0037]
Examples of the hologram photosensitive material for constituting the reflection type HOE 6 include a photopolymer, a photoresist, a photochromic, a photodichromic, a silver salt emulsion, a dichromated gelatin, a dichromated gelatin, a plastic, a ferroelectric material, and a magneto-optical material. , An electro-optic material, an amorphous semiconductor, a photorefractive material, and the like. In the present embodiment, the reflective HOE 6 is manufactured by exposing the material by simultaneously irradiating the light from two light sources with a hologram exposing apparatus shown in FIG. A reflective HOE is used.
[0038]
Light (light of a display image) that has passed through an arbitrary point on the display unit of the image display element 2 enters the light guide unit 11 from the incident surface 11c of the light guide unit 11, and the reflection surface 11b of the light guide unit 11 The light is totally reflected from the light guide 11, exits from the emission surface 11 a of the light guide 11, and enters the plate 5 from the region R <b> 0 of the surface 5 a of the plate 5. The light that has entered the plate-like portion 5 from the region R0 is reflected by the reflection surface 5c, and then enters the region R1 of the surface 5a of the plate-like portion 5 at an incident angle larger than the critical angle, and is totally reflected by the region R1. You. This light is incident on the region R2 of the surface 5b of the plate portion 5 at an incident angle larger than the critical angle, and is totally reflected by the region R2. This light further enters the region R3 of the surface 5a of the plate-shaped portion 5 at an incident angle larger than the critical angle, and is totally reflected by the region R3. This light further enters the region R4 of the surface 5b of the plate-shaped portion 5 at an incident angle larger than the critical angle, and is totally reflected by the region R4. This light further enters the region R5 of the surface 5a of the plate-shaped portion 5 at an incident angle larger than the critical angle, and is totally reflected by the region R5, and then enters the reflection type HOE 6. At this time, the light is subjected to the reflection-diffraction function and the image formation function by the third or higher order phase conversion function depending on the position on the hologram surface by the reflection type HOE 6. After that, this light is emitted from the region R <b> 6 of the surface 5 a of the plate portion 5 to the outside of the plate portion 5. At this time, the light emitted from the same portion of the image display element 2 is placed on the exit pupil P so as to form an enlarged virtual image at infinity or a predetermined distance (1 m in a design example described later) from the exit pupil P. The light enters the pupil of the user's eye.
[0039]
The light that is emitted from the image display element 2 and reaches the user's eye after being diffracted and reflected by the reflection type HOE 6 usually has one wavelength range according to the emission spectrum characteristics of the LED 3 and the wavelength selectivity of the reflection type HOE 6. In the case where a white LED is used as the LED 3 and a color reflective HOE is used as the reflective HOE 6, for example, the LED 3 has a plurality of discrete individual wavelength region components.
[0040]
Here, a specific design example of the optical system of the image display device according to the present embodiment will be described with reference to FIG. In designing this design example, code V (trade name) manufactured by Optical Research Associates of the United States, which is famous in the technical field, was used as a design program. At this time, the path of a light beam emitted from the center A0 of the display unit of the image display element 2 and passing through the center PO of the exit pupil P is defined as the optical axis of the entire optical device. In the present design example, the optical axis is not a single straight line, but has a shape obtained by connecting mutually inclined line segments.
[0041]
The optical quantities of this design example are as follows.
[0042]
The diameter of the exit pupil P is 3 mm. The view angle in the upward direction in the drawing is 5 °. The viewing angle in the downward direction in the drawing is −5 °. The viewing angle in the depth direction of the paper is ± 6.75 °. The screen size (the length between points A1 and A2) in the paper of the drawing is 3.6 mm. The screen size in the depth direction of the paper is 4.8 mm. The thickness d of the plate portion 5 is 3.5 mm. The used wavelength has a wavelength width of about 480 nm to about 540 nm. The peak wavelength of the LED 3 in the wavelength width is assumed to be 516 nm, and the wavelength at which the diffraction efficiency of the reflective HOE 6 is maximized matches the peak wavelength. The refractive index of the plate portion 5 at a wavelength of 587.56 nm (d-line) is nd = 1.596229, and the Abbe number is νd = 40.4.
[0043]
Regarding the definition of the HOE 6, a hologram can be uniquely defined by defining two light beams used for exposure. The definition of the two luminous fluxes is defined by the position of the light source and either convergence (VIR) or divergence (REA) of the beam emitted from each light source. The coordinates of the first point light source (HV1) are (HX1, HY1, HZ1), and the coordinates of the second point light source are (HX2, HY2, HZ2). As shown in FIG. 2, the coordinates have the origin at the point where the HOE plane intersects the optical axis, the Z axis in the optical axis direction, the Y axis in the HOE plane above the paper surface, and the X axis in the depth direction of the paper surface. , Different from the coordinates defined in connection with FIG.
[0044]
The hologram recording emulsion used had a thickness of 20 μm, a refractive index of 1.493, and a refractive index modulation of 0.03. It is assumed that the exposure wavelength is 532 nm and the shrinkage of the emulsion is 1%. Since the wavelength fluctuation of the reproduction light due to the contraction is in a proportional relationship, the wavelength is also shortened by 1%, and the central wavelength of reproduction is 526.7 nm. The plane of the HOE 6 is a plane whose center is 1.7 mm to the right of the plane 5a along the Z-axis in FIG. 1 and rotated 29.3 ° clockwise on the paper from the same direction as the Y-axis. The HOE 6 has a phase function component to optimize the imaging performance.
[0045]
The phase function will now be described. The phase function defines an aspherical phase conversion amount other than that defined by two pure point light sources of the HOE 6, and in the optical design program code V, X , Y-axis component, or the like.
[0046]
Table 1 below shows various quantities for ray tracing in this design example. The order of the optical surfaces (the order of the surface numbers) is from the pupil plane of the user's eye (= the plane of the exit pupil P of the image combiner 1) to the image display element 2. In Table 1, reference numerals in FIG. 1 corresponding to the respective surface numbers are shown as “signs” in parentheses. This applies to a table described later.
[0047]
[Table 1]

[0048]
The definition of the phase function used in Table 1 is a value obtained by standardizing the optical path difference of a light ray incident on a point designated as a position on the XY coordinate plane of the HOE with the wavelength to be used. When an integer is used, it is determined by designating a coefficient of a polynomial expressed by the following equation 1 in a general form. However, up to 65 coefficients can be specified, and are called C1, C2, C3,..., C65 in order, and when the order of the coefficients is represented by an integer j, the order of the X coordinate and the Y coordinate is indicated. The integers m and n are associated with each other so that the following relationship is established. That is, in the present example, the phase function is defined by the following polynomial of Expression 3. The definition of such a phase function is the same for a table described later.
[0049]
(Equation 1)

[0050]
(Equation 2)

[0051]
[Equation 3]

[0052]
In addition, as the positional relationship between the optical surfaces in the present design example, the center of the first surface (surface number 1 = code P in FIG. 1) is defined as the origin (X, Y, Z) = (0, 0, 0). Table 2 below shows the absolute position of the center of each optical surface and the amount of rotation about the X-axis (value measured when the counterclockwise direction is positive).
[0053]
[Table 2]

[0054]
The first light source of the HOE 6 of this design example (the light source that is on the side of the observer's eye during reproduction) is HX1: 0, HY1: −. 173228 × 10 ⁺¹⁰ , HZ1:-. 135831 × 10 ⁺¹⁰ Accordingly, in the third quadrant of the yz coordinates in FIG. 2, the distance from the origin of the HOE plane is 2.2 × 10 ⁹ mm.
[0055]
An exposure optical system used when actually manufacturing the reflection type HOE 6 defined in Table 1 in the image display device of this design example was designed. FIG. 3 shows an optical path diagram of a main part of the exposure optical system. FIG. 4 is an enlarged view of the prism 21 in the optical system shown in FIG. Further, FIG. 5 shows a schematic configuration diagram of a hologram exposure apparatus according to an embodiment of the present invention for exposing the reflective HOE 6 at the time of manufacturing the reflective HOE 6 using the optical system shown in FIG.
[0056]
The optical system shown in FIG. 3 includes one prism 21 and a single spherical lens 22, and is very simply arranged. As shown in FIG. 4, the prism 21 includes a small piece 5d that constitutes a part of the plate-like portion 5 in FIG. 1 described above, and a holding member that has the same refractive index as the small piece 5d and holds the small piece 5d (“hiring”). And a filler (not shown) filled in the gap between the small piece 5d and the holding member 24 and having the same refractive index as the small piece 5d and the holding member 24. ing. On the surface of the prism 21 on the small piece 5d side, a reflective HOE 6 (a strictly speaking, a photosensitive material layer for forming the reflective HOE 6) is formed. The small piece 5d on which the reflection type HOE 6 is formed is detached from the holding member 24, and the reflection type HOE 6 can be provided inside the plate portion 5 by the above-described method.
[0057]
3 and 4, the exit pupil P is arranged at a position obtained by converting the exit pupil P in FIG. 3 and 4, B1 forms an exposure light beam (reference light) from the first light source (light source on the exit pupil P side) during exposure of the reflective HOE 6, and B2 forms an exposure light beam (object light) from the second light source. Of a parallel light beam (plane wave) is shown. Thus, the optical system shown in FIG. 3 is an afocal optical system. Reference numeral 22a denotes a surface of the spherical lens 22 on the prism 21 side, and reference numeral 22b denotes a surface of the spherical lens 22 on the second light source side.
[0058]
In the hologram exposure apparatus shown in FIG. 5, the laser light source 31 enters the beam expander / beam shaping unit 33 when the shutter 32 for controlling the exposure time is opened. The unit 33 has a lens 34 for condensing the incident light at a converging point, a pinhole 35 disposed at the converging point, and a collimator lens 36 for collimating the light passing through the pinhole 35. It has both a function as a spatial filter for cutting noise light and a function as a beam expander for expanding a beam diameter. After the polarization direction of the parallel light beam from the unit 33 is rotated by the half-wave plate 37, only a predetermined polarization component passes through the polarization beam splitter 38. The half-wave plate 37 can be appropriately rotated, and the half-wave plate 37 and the polarization beam splitter 38 constitute a light amount adjustment unit. The light transmitted through the polarizing beam splitter 38 is reflected by a mirror 39 and then split by a beam splitter 40 into two light beams.
[0059]
The light beam transmitted through the beam splitter 40 is reflected by the mirror 41, passes through the lens 42 and the lens 43, is further narrowed down to a desired diameter by the diaphragm 44, and is converted into a parallel light beam (plane wave) as a first light source (exit pupil). As an exposure light beam (reference light beam) from the P-side light source), the light is incident on a hologram photosensitive material such as an emulsion to be a reflective HOE 6 applied to the prism 21. Here, the lens 42 focuses the parallel light flux reflected by the mirror 41 at its focal point. The lens 43 is disposed such that the focal plane of the lens 43 includes the focal point of the lens 42 and the optical axis of the lens 43 is parallel to the optical axis of the lens 42. The position of the lens 43 in the direction of the arrow F in FIG. 5 perpendicular to the optical axis of the lens 43 can be adjusted by a position adjusting mechanism 45 operated by an actuator (not shown) such as a motor. Therefore, the reference light emitted from the lens 43 and incident on the hologram photosensitive material to be the reflection type HOE 6 is a parallel light flux, but the incident direction changes by adjusting the position of the lens 43 by the position adjusting mechanism 45. For example, the design state of the exposure optical system is a state in which the lens 43 is located at a position where the focal point of the lens 43 matches the focal point of the lens 42. At this time, the reference light beam when entering the lens 42 The light enters the hologram photosensitive material in the same direction as the direction.
[0060]
On the other hand, the light beam reflected by the beam splitter 40 is reflected by a mirror 46, condensed at a focal point by a condenser lens 47, passes through a pinhole 48 arranged at the focal point, and then collimated by a collimator lens 49. The beam is expanded to a required light beam diameter and further reduced to a predetermined diameter by the stop 50 to become the parallel light beam B2 for forming an exposure light beam (object light beam) by the second light source. This parallel light beam (plane wave) B2 is converted into a desired aspherical wave by the lens 22 and the prism 21, and is applied to the hologram photosensitive material such as an emulsion to be the reflection type HOE 6 applied to the prism 21 on the side opposite to the reference light. Incident from However, the above description is an operation in a design state of the exposure optical system, that is, a state in which the focal point of the lens 47 and the pinhole 48 coincide with the focal point of the collimator lens 49. The position of the lens 47 and the pinhole 48 in the direction of the arrow G in FIG. 5 in the optical axis direction of the lens 47 and the light of the lens 47 are adjusted by a position adjusting mechanism 51 operated by an actuator (not shown) such as a motor. The position in the direction of arrow H in FIG. 5 perpendicular to the axis can be adjusted. When the focal point of the lens 47 and the pinhole 48 deviate from the designed position where the focal point of the lens 47 and the pinhole 48 coincide with the focal point of the collimator lens 49 in the direction of arrow H in FIG. The direction (tilt) of B2 changes. When the focus of the lens 47 and the pinhole 48 deviate from the position at the time of the design in the direction of the arrow G in FIG. 5, the focus of the light beam B2 is changed accordingly, and the light beam B2 is no longer a parallel light beam.
[0061]
As described above, when the reference light beam and the object light beam are incident on a photosensitive material such as an emulsion, they are interference-exposed to the photosensitive material, and interference fringes of the reference light and the object light are applied to the photosensitive material, for example, with a refractive index of Recorded as the difference. Needless to say, the photosensitive material is developed as required after this exposure.
[0062]
As can be understood from the above description, in the exposure apparatus shown in FIG. 5, the elements 31 to 40 in FIG. 5 include the reference light optical system for irradiating the hologram photosensitive material with the reference light of the plane wave and the object light of the aspherical wave. It forms a common part with the object light optical system that irradiates the hologram photosensitive material. Elements 41 to 44 in FIG. 5 constitute the rest of the reference optical system, and elements 47 to 50, 22, and 21 in FIG. 5 constitute the rest of the object light optical system.
[0063]
The exposure apparatus shown in FIG. 5 further includes an input unit 53 such as a keyboard, and a control unit 52 including a microcomputer or a personal computer. The operator uses the input unit 53 to input shrinkage ratio information (for example, the shrinkage ratio itself) relating to the actual shrinkage ratio of the hologram photosensitive material, and the reproduction light emitted to the reflection-type HOE 6 when using the reflection-type HOE 6 produced by interference exposure. The light source emission spectrum information (for example, the peak intensity wavelength of the LED 3) relating to the actual emission spectrum of the LED 3 as the light source that emits light is input to an internal memory (not shown) of the control unit 52. In the internal memory of the control unit 52, the shrinkage ratio information and the light source emission spectrum information, the position of the lens 43, the lens 47, and the A look-up table indicating the correspondence between the position of the hole 48 and the position is stored in advance. An example will be described later. The control unit 52 obtains each position corresponding to the information by referring to the look-up table based on the contraction ratio information and the light source emission spectrum information input from the input unit 53, and sets the position to be each position. The adjusting mechanisms 45 and 51 are controlled.
[0064]
By the way, although there are various methods for designing the exposure lens, the above-mentioned CODEV was used in designing the optical system shown in FIG. In CODE V, the light is traced from the first light source of the reflective HOE 6 shown in Table 1 through the reflective HOE 6 and traced to the second light source. If the optical system shown in FIG. 3 is inserted after passing through the HOE 6 and an operation equivalent to the phase conversion operation of the reflection type HOE 6 is performed, the wavefront becomes a clear spherical wave and forms an image with no aberration on the second light source. I do.
[0065]
When designing the optical system shown in FIG. 3 based on the design values of the optical system of the image display device shown in Tables 1 and 2, the reflection type HOE 6 is changed to the transmission setting. The transformation effects must be equal. For that purpose, it is necessary to transfer the phase coefficient equally and to trace the ray from the coordinate of the first light source as an object point. Even if the exposure system is designed from a distance different from the first light source defined in the reproduction system, a correct phase conversion operation cannot be obtained. However, in the design of the optical system shown in FIG. 3, the distance from the origin of the HOE surface of the first light source is 2.2 × 10 ⁹ Since mm is very large, the value of the air-equivalent distance between the first light source and the surface of the HOE 6 may be regarded as infinity. In fact, it is regarded as infinity, and the ray tracing of the optical system shown in FIG. Was designed with parallel light incident.
[0066]
Here, various quantities for ray tracing of the optical system shown in FIG. 3 are presented in Table 3 below. The order of the optical surfaces (the order of the surface numbers) is from the first light source (= the light source on the exit pupil P side of the image combiner 1) to the second light source.
[0067]
In Table 3, reference numeral S1 of the surface number 1 indicates a first light source. The coefficients of the hologram surface of surface number 3 are the same as those in Table 1 above, but two rays must enter from the same side of HOE 6 in order to perform ray tracing using reflection HOE 6 as transmission HOE. Therefore, the first light source position is changed from REA to VIR. The entrance pupil diameter needs to be a diameter that satisfies the effective diameter of the hologram surface, and is φ4 here. Since the light is emitted from a point light source (here, parallel light as its limit), an angle of view is not required. The wavelength for ray tracing is the exposure wavelength of 532 nm. This optical system is an afocal optical system that becomes parallel light after emitting the surface of surface number 6.
[0068]
[Table 3]

[0069]
Further, as the positional relationship between the respective optical surfaces in the optical system shown in FIG. 3, the center of the third surface (surface number 3 = symbol 6 in FIG. 3, the hologram surface) has the origin (X, Y, Z) = (0, 0). Table 4 below shows the absolute position of the center of each optical surface as (0, 0) and the amount of rotation around the X-axis (value measured as positive counterclockwise).
[0070]
[Table 4]

[0071]
FIG. 6 shows a wavefront aberration diagram on the exit pupil plane (that is, the plane 23 in FIG. 3) based on the ray trajectory of the optical system shown in FIG. 3 having the design values shown in Table 3. When performing this ray tracing, the phase coefficients in Table 1 are used as the phase coefficients of the HOE 6. As can be seen from FIG. 6, the RMS is well corrected to 0.14λ.
[0072]
As described above, Table 1 shows a design example of the optical system of the image display device shown in FIG. 1 on the assumption that the contraction rate is 1% and the peak wavelength of the LED is 516 nm. Table 3 shows the design values of the exposure optical system designed according to the design values of the reflective HOE 6 in this design example.
[0073]
Here, it is assumed that the actual shrinkage ratio is 2% which deviates from the estimated shrinkage ratio of 1%. At this time, the main reproduction wavelength is 521.4 nm. In this case, the phase function of the reproduction system optimized at 526.7 nm is used at 521.4 nm, and aberration occurs.
[0074]
Since this is not good, reproduction system data (design values of the optical system shown in FIG. 1) in which the contraction rate is assumed to be 2% is also created in advance. The design values are presented in Table 5. In Table 5, values other than the phase function of the reflection type HOE 6 are the same as those in Table 1.
[0075]
[Table 5]

[0076]
Waveform aberration on the exit pupil plane (that is, the surface 23 in FIG. 3) when the optical system shown in FIG. 3 is ray-traced with the design values shown in Table 3 for the design values shown in Table 5. The figure is shown in FIG. When performing this ray tracing, the phase coefficients in Table 5 are used as the phase coefficients of the HOE 6. As can be seen from FIG. 7, a relatively large aberration of RMS 0.41λ is generated.
[0077]
When the wavefront aberration shown in FIG. 7 was analyzed using the optical design program code V, it was found that this wavefront disturbance was divided into a tilt component and a focus component, and it was possible to correct the RMS to 0.15λ by excluding the two components. Was.
[0078]
In the exposure apparatus shown in FIG. 5, in the state of the design value, the focal point of the lens 47 and the focal point of the pinhole 48 and the collimator lens 49 are arranged so as to be coincident with each other. For example, a tilt effect can be obtained as a light beam. Since the focal length of the lens 47 is shorter than that of the lens 49, a great effect can be obtained with a small amount of movement. Therefore, it is preferable to shift the lens 47 and the pinhole 48. Therefore, in the exposure apparatus shown in FIG. 5, the position of the lens 47 and the pinhole 48 in the H direction in FIG. 5 can be adjusted by the position adjusting mechanism 51.
[0079]
In addition, if one of the focus of the lens 47 and the pinhole 48 or the collimator lens 49 is shifted in the optical axis direction, a focusing effect can be obtained. Therefore, in the exposure apparatus shown in FIG. 5, the position of the lens 47 and the pinhole 48 in the direction G in FIG. 5 can be adjusted by the position adjusting mechanism 51.
[0080]
Here, when the actual shrinkage ratio is 2% which deviates from the estimated shrinkage ratio of 1%, the lens 47 and the pinhole 48 are set at 6 μm in the direction (H direction) perpendicular to the optical axis of the lens 47 and in the optical axis direction. When adjusted by moving the optical system shown in FIG. 3 in the (G direction) by 0.477 mm, the wavefront aberration on the exit pupil plane (that is, the plane 23 in FIG. 3) when the optical system shown in FIG. As shown in FIG. 8, the rms can be corrected to 0.15λ. When performing this ray tracing, the phase coefficients in Table 5 are used as the phase coefficients of the HOE 6.
[0081]
From the above, when exposure was performed using an exposure apparatus according to the design values in Table 3 designed based on HOE6, which was designed based on the assumption that the shrinkage ratio of the hologram photosensitive material was 1%, the conditions of the exposure process, etc. Even if the shrinkage rate fluctuates to 2%, the HOE 6 exhibiting the performance of the reproducing system can be exposed by performing the above-described position adjustment by the position adjustment mechanism 51 and exposing again.
[0082]
In the example described above, the look-up table in the internal memory of the control unit 52 in FIG. 5 shows that the H-direction position 0 μm and the G-direction position 0 mm corresponding to the contraction ratio 1% and H corresponding to the contraction ratio 2% What is necessary is just to store the direction position 6 μm and the G direction position 0.477 mm. The H-direction position and the G-direction position were also obtained for the other various shrinkage ratios by the same method as that for the H-direction position of 6 μm and the G-direction position of 0.477 mm for the shrinkage ratio of 2%. What is necessary is just to store it in a lookup table.
[0083]
Then, for example, first, the hologram photosensitive material is exposed in the state where it is positioned at the H-direction position 0 μm and the G-direction position 0 mm (that is, the state according to the design values shown in Table 3), and the HOE 6 is manufactured. The spectral characteristics of the diffraction efficiency of the obtained HOE 6 are measured, the actual shrinkage of the hologram photosensitive material is obtained based on the measurement result, and the operator may input the shrinkage from the input unit 53 to the control unit 52. The control unit 52 controls the position adjusting mechanism 51 according to the input contraction rate to perform the above-described position adjustment. Therefore, the reflective HOE 6 manufactured by the subsequent exposure will exhibit the performance of the image display device sufficiently. The image display device according to the present embodiment uses the reflection type HOE 6.
[0084]
By the way, when the actual shrinkage ratio is 2%, which deviates from the estimated shrinkage ratio of 1%, as described above, the main reproduction wavelength (the wavelength at which the diffraction efficiency is maximized) is 526.7 nm to 521.4 nm. However, in the above description, only the aberration fluctuation due to the fluctuation of the main reproduction wavelength due to the fluctuation of the contraction rate is corrected, and the fluctuation of the brightness due to the deviation from the light source wavelength is ignored. Also, ignoring the fact that the peak wavelength of the LED 3 can vary from the estimated 516 nm, the reference light B1 is assumed to be incident on the hologram photosensitive material from the direction as designed, and the lens 43 corresponds to that direction in FIG. In the F direction.
[0085]
In the present invention, it is not always necessary to provide the position adjustment mechanism 45 while ignoring them, but it is preferable not to ignore them. Therefore, in the present embodiment, as described above, the lookup table in the internal memory of the control unit 52 actually stores not only the contraction rate information but also the light source emission spectrum information (here, the peak wavelength of the LED 3 and the peak wavelength of the LED 3). ) Is stored as the parameter, not only the position of the lens 47 and the pinhole 48 but also the position of the lens 43. Then, the control unit 2 refers to the look-up table, and if only the G direction position and the H direction position of the lens 47 and the pinhole 48 corresponding to the contraction rate input from the input unit 53 and the actual peak wavelength of the LED 3 are determined. First, the position of the lens 43 in the F direction is also obtained, and the position adjusting mechanisms 45 and 51 are controlled so as to be at the obtained positions.
[0086]
When the actual shrinkage ratio deviates from the estimated shrinkage ratio, the dominant reproduction wavelength changes accordingly. For example, when the actual shrinkage ratio is 2%, which deviates from the estimated shrinkage ratio of 1%, as described above, the main reproduction wavelength (the wavelength at which the diffraction efficiency is maximized) changes from 526.7 nm to 521.4 nm. Further, if the peak wavelength of the LED 3 fluctuates from the estimated wavelength, it is preferable to match the main reproduction wavelength with the actual peak wavelength of the LED 3 so as not to cause a decrease in the amount of light. Will fluctuate. On the other hand, when the lens 43 is shifted in the F direction, the incident angle of the reference beam B1 on the hologram photosensitive material changes accordingly, so that the main reproduction wavelength can be adjusted. Therefore, when considering the fluctuation of the main reproduction wavelength and the fluctuation of the peak wavelength of the LED 3 due to the fluctuation of the shrinkage, the position of the lens 43 in the F direction may be adjusted accordingly. Since the position in the F direction of the lens 43 for optimizing according to the contraction ratio and the peak wavelength of the LED 3 can be obtained in advance, the relationship may be stored in the lookup table.
[0087]
By the way, according to the fluctuation of the main reproduction wavelength, aberration (aberration of the exposure optical system, that is, on the exit pupil plane (that is, plane 23 in FIG. 3) when light ray tracing is performed on the optical system shown in FIG. 3). (Wavefront aberration). Therefore, when the fluctuation of the main reproduction wavelength and the fluctuation of the peak wavelength of the LED 3 due to the fluctuation of the contraction rate are taken into consideration, the positions of the lens 47 and the pinhole 48 in the G direction and H where the aberration is minimized are also taken into consideration. What is necessary is just to obtain the direction position. That is, the G-direction position and the H-direction position of the lens 47 and the pinhole 48 that minimize the aberration are obtained using both the contraction rate and the actual peak wavelength of the LED 3 as parameters, and the relationship is stored in the lookup table. You should leave it.
[0088]
The embodiment of the present invention has been described above, but the present invention is not limited to this embodiment.
[0089]
For example, in the above embodiment, the position adjustment mechanisms 45 and 51 in FIG. 5 are automatically controlled by the control unit 52. However, the control unit 52 and the input unit 53 are removed, and the position adjustment mechanisms 45 and 51 are removed. , 51 may be manually adjustable.
[0090]
In the above embodiment, the positions of the lens 47 and the pinhole 48 can be adjusted. However, the position of the collimator lens 49 may be adjusted instead.
[0091]
Furthermore, in the above-described embodiment, the position of the lens 43 is configured to be adjustable, but instead, the position of the lens 42 may be adjusted.
[0092]
Although the above-described embodiment is an example in which the present invention is applied to a see-through type head mounted image display device, the present invention can be applied to an image display device which is not a see-through type. In this case, the image display device according to each of the above-described embodiments may be configured so that light from the outside does not enter the image combiner 1. In this case, the portion of the image combiner 1 is not an image combiner because it does not superimpose two images, and serves as a light guide that guides light from the image display element 2 to the user's eyes. In this case, a lower portion (a lower portion from the HOE 6) of the plate-shaped portion in the image combiner 1 may be removed. Such an image display device that is not a see-through type can be built in a flipper unit of a mobile phone, for example, as in Japanese Patent Application Laid-Open No. 2001-264682.
[0093]
【The invention's effect】
As described above, according to the present invention, even if the shrinkage ratio of the hologram photosensitive material fluctuates from the estimate at the time of design, the deterioration of the optical performance due to the fluctuation can be suppressed with a simple adjustment. , Even if the peak wavelength or the like of the light source that emits light fluctuates from the wavelength at the time of design, it is possible to simultaneously suppress one or both of the degradation of the optical performance and the simple adjustment.
[0094]
Further, according to the present invention, there is provided an image combiner and an image display device which are excellent in optical performance and can achieve cost reduction by using a hologram optical element produced by exposure using such a production method and apparatus. can do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image display device according to an embodiment of the present invention and a schematic path of light rays.
FIG. 2 is a diagram showing a coordinate system of two light sources defining a hologram.
3 is an optical path diagram showing a main part of an exposure optical system for exposing a reflection hologram optical element in the image display device shown in FIG.
FIG. 4 is an enlarged view of a prism in the optical system shown in FIG.
FIG. 5 is a schematic configuration diagram of a hologram exposure apparatus according to one embodiment of the present invention.
6 is a wavefront aberration diagram of the optical system shown in FIG. 3 when the contraction rate of the hologram photosensitive material is as expected at the time of design.
FIG. 7 is a wavefront aberration diagram of the optical system shown in FIG. 3 when the contraction rate of the hologram photosensitive material is different from the expected value at the time of design.
8 is a wavefront aberration diagram of the optical system shown in FIG. 3 after correcting for a change in shrinkage when the shrinkage of the hologram photosensitive material is different from the expected value at the time of design.
[Explanation of symbols]
1 Image combiner
2 Image display device
3 LED
4 Reflector
5 plate part
6. Reflection type hologram optical element
11 Light guide

Claims (5)

Manufacture by subjecting the hologram photosensitive material to interference exposure of the reference light and the object light using a reference light optical system that irradiates reference light to the hologram photosensitive material and an object light optical system that irradiates the hologram photosensitive material with object light. A method for producing a hologram optical element,
The information regarding the actual shrinkage ratio of the hologram photosensitive material of the hologram optical element produced by the interference exposure and the reproduction light emitted to the hologram optical element when the hologram optical element produced by the interference exposure is used are emitted. After adjusting the position of at least one of the part of the reference light optical system and the part of the object light optical system based on at least one of the information on the actual emission spectrum of the light source. A method for manufacturing a hologram optical element, comprising exposing. Hologram optics having a reference light optical system for irradiating reference light to the hologram photosensitive material and an object light optical system for irradiating object light to the hologram photosensitive material, and performing interference exposure of the reference light and the object light to the hologram photosensitive material An element exposure apparatus,
A position adjustment unit that adjusts the position of at least one of a part of the reference light optical system and a part of the object light optical system,
The information regarding the actual shrinkage ratio of the hologram photosensitive material of the hologram optical element manufactured by the interference exposure and the reproduction light emitted to the hologram optical element when the hologram optical element manufactured by the interference exposure is used are emitted. A control unit that controls the position adjustment unit based on at least one of information on the actual emission spectrum of the light source,
An exposure apparatus for a hologram optical element, comprising: An image combiner provided with a reflection type hologram optical element and superimposing light from an image display unit and light from the outside, wherein the reflection type hologram optical element is manufactured by the manufacturing method according to claim 1 or according to claim 2. An image combiner produced by exposing with an exposure device. An image display device comprising: the image combiner according to claim 3; and the image display means, wherein at least a portion including the image combiner is worn by a user during use. An image display device comprising: an image display unit; and a light guide unit that guides light from the image display unit to a user's eye, wherein the light guide unit is formed by the manufacturing method according to claim 1 or claim 2. 3. An image display device comprising a reflection hologram optical element produced by exposing with the exposure device according to 2.

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