JP2004101929A - Multi-viewpoint display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram screen for a multi-viewpoint display which prevents crosstalk and decrease in the diffraction efficiency of incoherent duplicate recording and to provide a multi-viewpoint display using the hologram screen. <P>SOLUTION: The multi-viewpoint display device includes the hologram screen as a volume hologram produced in such a manner that a development process is performed by irradiating a hologram recording material with the object light and reference light only once. In the multi-viewpoint display device, two dimensional images of different parallaxes are projected onto the hologram screen in duplicate from different directions with projectors so that Bragg conditions in the three dimensional space of the hologram screen are satisfied. The two-dimensional images are reproduced on the hologram screen in a multiple manner. However, the device is set so that by using the directionality of regenerated light caused by diffraction of the hologram, only specific parallax images corresponding to the positions of the left and right eyes of the observer of the hologram screen are recognized. <P>COPYRIGHT: (C)2004,JPO

Description

ここで、θはブラッグ角、λは光の波長、ｎはホログラムスクリーンの屈折率、Λは干渉縞層間隔を表す。
【００２８】
図３に示すように、第１の実施の形態に係る単一記録多重再生ホログラムスクリーン２によれば、干渉縞面層１４の方向がすべて同方向に揃っている。よって、クロストークを生じることが無く、更に単一記録なので回折効率の低下もない。
【００２９】
図１及び図２を利用して、図１３及び図１４と同様の２視点のホログラムスクリーン２の形成を説明する。まず記録時には、１回だけ物体光８と参照光１０とを矢印の方向に向けてホログラム記録材料１２に照射する。現像処理すると干渉縞面層１４が形成される。
【００３０】
ホログラム記録材料１２としては、銀塩感光材やフォトポリマが用いられ得る。
【００３１】
上記のように記録されたホログラムスクリーン２では、参照光１０と共役の方向からの照明光４により、物体光８と共役な方向に再生光６を生じる（図２）。ここで（図２）、ホログラム中心１８のブラッグ角θを維持するように、共役照明光４と共役再生光６を含む共役再生２光束光軸共有断面２０を回転させると、照明光４に対して方向４−１や４−２が、再生光６に対して方向６−１や６−２が得られる。このように、ホログラム中心１８を含む干渉縞面にてホログラム中心１８を通り干渉縞面に垂直な格子ベクトル２２を軸にして、ブラッグ角θを維持しつつ共役照明光４と共役再生光６とを回転すると、共通ブラッグ角円錐２４の円錐面が形成される。ここで格子ベクトル２２は、干渉縞面の方向を示す単位法線ベクトルである。
【００３２】
上記の方向４−１や４−２から２つの照明光（４−１、４−２）をホログラムスクリーン２に投影すると、再生光（６−１、６−２）を生じる。２つの再生光（６−１、６−２）は、夫々の像焦点１６−１、１６−２で、例えば、観察者の左右の目に別々に到達する。この時、照明光（４−１、４−２）として２台のプロジェクタから視差の異なる映像を供給すれば、左右の目に夫々が提供されるので、観察者は２つの視差画像を融像して立体像を認識できる。
【００３３】
上記と同様に、共通ブラッグ角円錐面２４に沿って、照明光４の方向を任意の数だけ増やせば、それに対応して任意の数の再生光６が生成される。よって、任意の視点数の多視点表示が可能になる。図３に、共通ブラッグ角円錐面２４に沿って照明光４の数を増やした（図では５個）場合の、再生光６の生成方向の例の模式図を示す。
【００３４】
ところで、ホログラムスクリーンを体積ホログラムとするために、ホログラムスクリーン中心１８と物焦点を結ぶ照明光の光軸と、ホログラムスクリーンと像焦点を結ぶ再生光の光軸の２つの光軸との交差角（ホログラムスクリーン内部ではブラッグ角θの２倍に相当）を、マグヌッソン・ゲイロード（Ｍａｇｎｕｓｓｏｎ　ａｎｄ　Ｇａｙｌｏａｄ）の判定式、
【数２】
Ｑ’＝Ｑ／ｃｏｓ（θ）＝（２πλｔ）／｛ｎΛ^２ｃｏｓ（θ）｝＞１０
を満たすように、一定の値よりも大きくする。なお、
θ；ホログラムスクリーン内部のブラッグ角
π；円周率
λ：光の波長
ｔ；ホログラムスクリーンの厚さ
ｎ；ホログラムスクリーンの屈折率
Λ；ホログラムの干渉縞層面の間隔
を意味する。
【００３５】
ホログラムが体積ホログラムであれば、照明光のプロジェクタと再生光の観察者とが、ホログラムスクリーンの反対側に配置される透過型ホログラムでもよく、照明光のプロジェクタと再生光の観察者とが、ホログラムスクリーンの同じ側に配置される反射型ホログラムでもよい。
【００３６】
≪第２の実施の形態≫
（２）マルチパネル大画面化
図４は、本発明の第２の実施の形態に係るマルチパネル形式多視点表示装置２６の概略斜視図である。共通ブラッグ角円錐面２４に沿う多視点表示が可能である第１の実施の形態に係る単一記録多重再生ホログラムスクリーン２を、４枚マルチパネル形式で配置している。ここでは、３台のプロジェクタで照明する場合（従って、３視点の場合）を示している。
【００３７】
図４から明らかなように、共通ブラッグ角円錐２４の形及び向きは、各要素ホログラムスクリーン２毎に異なるが、いずれの要素ホログラムスクリーン２の物焦点（図では、１５−０、１５−１、１５−２）、像焦点（図では、１６−０、１６−１、１６−２）もすべて一致しているところに特徴がある。
【００３８】
このようにすれば、４枚の要素ホログラムスクリーン２が、全体として１枚の大型ホログラムスクリーンの機能を実現できるようになり、例えば、等身大の多視点表示ホログラムスクリーンも製作可能である。要素ホログラムスクリーン２のサイズと個数は任意であり、プロジェクタの投影サイズ拡大が可能ならば、任意のサイズのマルチパネル形式の多視点表示装置２６が製作可能である。
【００３９】
例えば、縦横１ｍ×１ｍの大型ホログラムスクリーンを構成する場合、各要素ホログラムスクリーンサイズが縦横１ｍｍ×１ｍｍであってそれら計１００万個で構成してもよい。また、各要素ホログラムスクリーンサイズが縦横１０ｃｍ×１０ｃｍであってそれら計１００個で構成してもよく、結局同じ機能が実現される。但し、一般的傾向として、要素ホログラムスクリーンサイズが小さい程、ホログラムの収差が小さくなり回折効率が高く鮮明な映像が得られるが、要素数が増えるためホログラム記録時間が長くなる。
【００４０】
≪第３の実施の形態≫
（３）単一波長レーザ・カラー記録ホログラム
図５は、本発明の第３の実施の形態に係る単一波長レーザ・カラー記録ホログラム（スクリーン）の仕組みを示す模式図である。上記第１の実施の形態と同様に、ホログラム記録材料、即ちホログラムスクリーンの材料として、銀塩感光材やフォトポリマが用いられ得る。
【００４１】
第３の実施の形態に係る単一波長レーザ・カラー記録多視点表示装置１では、記録時に単一の波長の光を用いるが、再生時には異なる波長の光を再生し得る。
【００４２】
つまり、体積ホログラムのブラッグ条件式を利用し、以下の（記録時ブラッグ角が異なる）３回の撮影条件式により３回多重記録して、３色（各色の波長はλｃ_１、λｃ_２、λｃ_３）再生のカラーホログラムスクリーンを製作することができる。
【数３】
ｓｉｎ（Θｒ_１）／λｒ＝±ｓｉｎ（Θｃ）／λｃ_１＝１／（２ｎΛ_１）　　　　　　　（Ａ）
ｓｉｎ（Θｒ_２）／λｒ＝±ｓｉｎ（Θｃ）／λｃ_２＝１／（２ｎΛ_２）　　　　　　　（Ｂ）
ｓｉｎ（Θｒ_３）／λｒ＝±ｓｉｎ（Θｃ）／λｃ_３＝１／（２ｎΛ_３）　　　　　　　（Ｃ）
【００４３】
ここで、Θｒ（Θｒ_１、Θｒ_２、Θｒ_３）は、記録時のブラッグ角で、Θｃは、再生時のブラッグ角である。λｒは、記録時の光の波長で、λｃ（λｃ_１、λｃ_２、λｃ_３）は、再生時の光の波長である。Λ（Λ_１、Λ_２、Λ_３）は、干渉縞層面１４の間隔である。体積ホログラム２内には、λｃ_１に係る第１の干渉縞面層、λｃ_２に係る第２の干渉縞面層、及びλｃ_３に係る第３の干渉縞面層の、都合３種類の干渉縞層面が形成される。ｎはホログラムスクリーンの屈折率を示す。
【００４４】
ここで、上記３種類の干渉縞層面の方向が揃い、且つ再生時の物焦点と像焦点の位置が３色（λｃ_１、λｃ_２、λｃ_３）とも一致するように、上記の３回のホログラムスクリーンの撮影記録を通じて、全ての格子ベクトルの方向を同じにする。
【００４５】
（数３）の式において、３色に対応して変化しているのは、記録時のブラッグ角Θｒ（即ち、Θｒ_１、Θｒ_２、及びΘｒ_３）　、干渉縞層面の間隔Λ（即ち、Λ_１、Λ_２、及びΛ_３）、再生時の光の波長λｃ（即ち、λｃ_１、λｃ_２、及びλｃ_３）である。つまり、記録時に光の波長λｒを固定し一方でブラッグ角をΘｒ_１、Θｒ_２、Θｒ_３と変化させれば、再生時には同じブラッグ角Θｃの方向で異なる波長λｃ_１、λｃ_２、λｃ_３の光が再生できることになる。このことは、記録時にブラッグ角Θｒを再生時のブラッグ角Θｃに一致させた状態で、異なる波長λｃ_１、λｃ_２、λｃ_３の光（具体的には別々のレーザー光）で３回多重記録するのと同じ効果が得られることを示す。
【００４６】
具体的には、図５に示す構成において、記録時にブラッグ角円錐２４の余角であるブラッグ角を変化させる。つまり、再生光の波長を変えるにはブラッグ角円錐２４の「傘の開き具合」を変えるようにすればよいことになる。例えば、プロジェクタ１５−１の物焦点から、波長λｒの光をブラッグ角Θｒ_１で干渉縞層面１４に対してブラッグ角円錐面２４に沿って入射させた時に、ブラッグ角円錐面２４に沿ってブラッグ角Θｒ_１で波長λｒの再生光を回折させて、像焦点１６−１に集光させるように、波長λｒの光を用いて干渉縞間隔Λ_１の干渉縞層面１４を記録したとする。しかし、再生時において、干渉縞間隔Λ_１の干渉縞層面１４に対して、プロジェクタ１５−２の物焦点から、波長λｃ_１の光（あるいは波長λｃ_１の色を含む光）をブラッグ角Θｃでブラッグ角円錐面２４’に沿って入射させれば、ブラッグ角円錐面２４’に沿ってブラッグ角Θｃで波長λｃ_１の再生光を回折させて、像焦点１６−２に集光させることも可能になる。このようにすれば、共役再生２光束光軸共有断面２０内において、同一の干渉縞間隔Λ_１の干渉縞層面１４に対して、記録時の波長λｒを再生時の波長λｃ_１に変更することができる。さらに、このように記録された干渉縞間隔Λ_１の干渉縞層面１４に対して、共役再生２光束光軸共有断面２０を、格子ベクトル２２を軸にして任意の方向に回転すれば、再生時のブラッグ角円錐面２４’の面上で、再生波長λｃ_１に対応するプロジェクタの位置（物焦点）と観察位置（像焦点）の対が必ず一組存在する。同様に（数３）の式に基づいて、再生波長λｃ_１、λｃ_２、λｃ_３にそれぞれ対応する干渉縞間隔Λ_１、Λ_２、Λ_３の干渉縞層面１４を、格子ベクトル２２が一致するようにホログラム記録材料１２に記録すれば、共役再生２光束光軸共有断面２０を、格子ベクトル２２を軸にして任意の方向に回転すると、ブラッグ角円錐面２４’の面上で、３つの波長λｃ_１、λｃ_２、λｃ_３に対応する共通のプロジェクタ位置（共通物焦点）と共通の観察位置（共通像焦点）の対が必ず一組存在するようにできる。つまり、このように記録した多色ホログラムスクリーンを用いれば、図３の構成において、３つの波長λｃ_１、λｃ_２、λｃ_３を含む任意の数のカラー照明光４を用いて、それに対応して３つの波長λｃ_１、λｃ_２、λｃ_３を含む任意の数のカラー再生光６を生成することができる。
【００４７】
≪第４の実施の形態≫
（４）２枚組合せホログラムスクリーンにより集光位置を柔軟に変更
図６は、本発明の第４の実施の形態に係る２枚組合せホログラムスクリーンによる多視点表示装置２７の概略斜視図である。共通ブラッグ角円錐面２４に沿う多視点表示が可能である第１の実施の形態に係る単一記録多重再生ホログラムスクリーン２を、２枚重ねの組合せスクリーン（２−１、２−２）として配置している。ここでは、２台のプロジェクタ（１５−１、１５−２）で照明する場合（即ち、２視点の場合）を示している。
【００４８】
図６では、模式的な図解のために２枚のホログラムスクリーン（２−１、２−２）の間が離れているが、実際は密接している。通常は、ホログラム記録材料の厚みは数ミクロンのオーダーで、これを担持するためのガラス基板の厚みは２〜３ミリである。２枚重ねでせいぜい数ミリのオーダーは、ホログラムスクリーンからの照明光距離あるいは観察距離の５０ｃｍ〜５ｍに比較すれば、無視しうる厚みである。従って、３つの共通ブラッグ角円錐面（２４−０、２４−１、２４−２）の頂点は数ミリ程度のオーダーで近接していて、いずれもそれぞれのホログラムスクリーン２−１と２−２の中心近傍に存在すると見なして支障ない。とりわけ、ホログラムスクリーン２−２の２つの共通ブラッグ角円錐面（２４−１、２４−２）は近接しているので、それぞれの格子ベクトルの方向は等しく、ブラッグ角の大きさも等しいと考えてよい。
【００４９】
図６において、２台のプロジェクタ（１５−１、１５−２）から、視差の異なる２次元画像が、プロジェクタからの光軸が第１のホログラムスクリーン２−１の中心に向かうように重畳投影される。第１のホログラムスクリーン２−１の中心部における共通ブラッグ角円錐面２４−０に沿って入射された２つの照明光は、照明光の入射方向に応じて同じく共通ブラッグ角円錐面２４−０に沿う方向に２つの再生光を生成する。第１のホログラムスクリーン２−１の２つの再生光は第２のホログラムスクリーン２−２に対する２つの照明光となる。第２のホログラムスクリーン２−２に対する２つの照明光は、それぞれ第２のホログラムスクリーン２−２の中心近傍の共通ブラッグ角円錐面２４−１と２４−２に沿って入射される。共通ブラッグ角円錐面２４−１に沿う方向の照明光は、同じく共通ブラッグ角円錐面２４−１に沿う方向に再生光を生成し、像焦点１６−１に集光する。共通ブラッグ角円錐面２４−２に沿う方向の照明光は、同じく共通ブラッグ角円錐面２４−２に沿う方向に再生光を生成し、像焦点１６−２に集光する。このようにすると、２つの像焦点１６−１と１６−２において左右の視差画像が観察できて立体視可能になる。
【００５０】
本実施の形態の特徴は、２枚のホログラムスクリーン（２−１、２−２）により、２回の回折を受けるので、２台のプロジェクタ（１５−１、１５−２）の光軸の方向からの影響を少なくして、第２のホログラムスクリーン２−２からの再生光の光軸の方向すなわち観察位置が柔軟に変更できるというメリットがある。ホログラムスクリーン２が体積ホログラムとなるために、上記のマグヌッソン・ゲイロードの判定式を満足するようにするには、ブラッグ角の大きさに範囲制限が付く。よって、上述の第１の実施の形態においては、ホログラムスクリーン２に対する照明光の角度や再生光の角度に制約が伴う。本実施の形態によれば、照明光の角度や再生光の角度の制約が緩和されるので、装置のレイアウトや観察位置の柔軟な変更が可能になる。
【００５１】
なお、本実施の形態においては、２枚のホログラムスクリーンによる回折効率を高めるには、共通ブラッグ角円錐面２４−０の再生光の方向と共通ブラッグ角円錐面（２４−１、２４−２）の照明光の方向を一致させるように、２枚のホログラムスクリーン（２−１、２−２）を製作することが重要である。
【００５２】
≪第５の実施の形態≫
（５）再生光集光点となる像焦点のゾーン拡大
ホログラムスクリーン記録時の物体光源を点光源にすると、再生時の再生光集光点である像焦点が、３次元空間内で１点のみとなってしまう。そうすると、観察時に像焦点の位置を探すのが難しくなり、結局立体視が困難になる。
【００５３】
本発明に係る第５の実施の形態の多視点表示装置１では、記録時の物体光源として有限サイズの拡散板を利用する。例えば、記録時の板状物体光源として縦横１０ｃｍ×５ｃｍの拡散板を使用すると、再生時にはその拡散板の大きさに等しい像焦点ゾーン（縦横１０ｃｍ×５ｃｍ）が、観察可能エリアとして３次元空間内に形成される。この第５の実施の形態の多視点表示装置１を利用することで、特殊な専用メガネ無しの立体視がより容易になる。
【００５４】
なお、物体光源として用いる拡散板の横幅サイズが観察者の両眼距離よりも大きくなると、視差が異ならない画像が両目に提示される場合が生じる得る。よって、上記の拡散板の横幅サイズは、成人の平均的な眼間距離（例えば、約６．５ｃｍ）よりも相当分短くしておく（例えば、５ｃｍ以下にしておく）のが好ましい。
【００５５】
≪実証例≫
以下、本発明に係る多視点表示装置１に関して試行を幾つか行なったので、紹介する。
【００５６】
（１）装置の実施例
図１２に示す従来技術に類似させて４視点とし、更にホログラムスクリーン２を図４の装置のように４枚のマルチパネル形式とした、多視点表示装置に関して試作及び実証を行った。
【００５７】
ここで、各要素ホログラムスクリーン２のサイズは、縦横２０ｃｍ×２５ｃｍであり、ホログラムスクリーン全体のサイズは、縦横４０ｃｍ×５０ｃｍであった。物焦点は、ホログラムスクリーンの後面４５°下方２．５ｍの距離、像焦点は、ホログラムスクリーンの前面法線方向１ｍの距離であった。
【００５８】
（２）回折効率の測定例
図７は、照明光が仰角４５°方向であるとき、再生光がホログラム面の法線方向となるように製作されたホログラムスクリーンに対して、照明光の仰角と水平方向の経度とを変化させた場合の回折効率を測定した結果を示す。
【００５９】
グラフの横軸が照明光の仰角を、縦軸が回折効率を示す。多数の（上に凸な）曲線の夫々は、同一経度上（で照明光の仰角を変化させたとき）の回折効率の変化を示す。いずれの経度の場合も、仰角４５°近辺に極大値が存在する。経度の変化に従って極大点を結ぶと、図の下向き凸の鞍部状の曲線（「回折効率極大点の軌跡」）となっている。鞍部状の曲線の極小値点は、経度０°の極大点である。この経度０°の極大点が仰角４５°から２〜３°ずれているのは、観測装置の取り付けずれが理由である。
【００６０】
このように、照明光仰角がほぼ一定の状態で経度線を移動しても回折効率が低下しないことは、３次元空間内の共通ブラッグ角円錐面上で照明光、再生光を変化させても、ブラッグ条件を常に満足していることを立証している。
【００６１】
（３）多視点化による照明光の物焦点と再生光の像焦点の空間座標変化
図８は多視点化による照明光の物焦点の空間座標変化を表し、図９は多視点化による再生光の像焦点の空間座標変化を表した例である。
【００６２】
それぞれ、照明光仰角を３０°、４５°、６０°とした場合についての例を示す。ホログラムスクリーン中心から照明光の物焦点の距離は２ｍ、再生光の像焦点の距離は１ｍである。グラフの横軸は、格子ベクトルを軸に照明光あるいは再生光を、片方向に共通ブラッグ角円錐面上で変化（変位）させた場合の回転角ωを表す。
【００６３】
グラフの縦軸は、（ａ）ｘ座標では、ホログラム面に平行な鉛直方向の座標（変化）である。（ｂ）ｙ座標では、ホログラム面に平行な水平方向の座標（変化）である。（ｃ）ｚ座標では、ホログラム面に対して法線方向の座標（変化）である。
【００６４】
回転角ωとｙ座標の変化とは、照明光と再生光のいずれにおいても、略、比例関係にある。更に、プロジェクタの横方向間隔と観察者の観測可能位置の横方向間隔との関係がほぼ２：１になっていることもわかる。これは物焦点距離と像焦点距離の比率に比例している。
【００６５】
とりわけ、図９の再生光の（ａ）ｘ座標の変化が小さいことから、観察者の観察可能位置の高さは、横方向に変化してもあまり影響を受けないことがわかる。また、図９の再生光の（ｃ）ｚ座標の変化から、像焦点が周辺部（回転角１６°付近）では１０ｃｍ程度ホログラムスクリーンに接近することになるが、この「１０ｃｍ程度」というのは、観察者が同じ場所に立って身体を傾けたり、首を振ったりして得られる位置の移動の範囲内と考えられるため、実際に問題とすべきほどに大きな変化量ではない。
【００６６】
（４）大画面化による照明光の物焦点と再生光の像焦点の空間座標変化
図１０は大画面化による照明光の物焦点の空間座標変化を表し、図１１は大画面化による再生光の像焦点の空間座標変化を表した例である。
【００６７】
それぞれ、照明光仰角を４５°とした。ホログラムスクリーン中心から照明光の物焦点の距離は２ｍ、ホログラムスクリーン中心から再生光の像焦点の距離は１ｍである。各図では、ホログラムスクリーンの中央、左右２０ｃｍ、左右４０ｃｍそれぞれの位置からの物焦点の座標の変化、像焦点の座標の変化を示す。グラフの横軸は、格子ベクトルを軸に照明光あるいは再生光を、片方向にブラッグ角円錐面上で変化（変位）させた場合の回転角ωを表す。
【００６８】
グラフの縦軸は、（ａ）ｘ座標では、ホログラム面に平行な鉛直方向の座標（変化）である。（ｂ）ｙ座標では、ホログラム面に平行な水平方向の座標（変化）である。（ｃ）ｚ座標では、ホログラム面に対して法線方向の座標（変化）である。
【００６９】
再生光のｙ座標に関しては、ホログラムスクリーンの左右２０ｃｍの位置では回転角１６°でも中央部との差は略４ｃｍである。即ち、人間の左右の眼間距離の平均値６．５ｃｍの範囲に収まっており、依然立体視が可能である。ホログラムスクリーンの左右４０ｃｍの位置では回転角が１０°になると中央部との差が６ｃｍに達しており、ほぼ立体視の限界である。回転角１０°は、図９によれば観察位置を３０ｃｍ横にずらせた場合に相当し、左右４０ｃｍすなわち８０ｃｍ幅のホログラムスクリーンでは、観察位置の横移動は６０ｃｍ幅が限界となる。なお、回転角１６°は図９から５０ｃｍ弱に相当し、左右２０ｃｍすなわち４０ｃｍ幅のホログラムスクリーンでは、左右５０ｃｍ弱すなわち１ｍ弱の幅まで観察位置を横移動しても立体視に支障が無い。
【００７０】
再生光のｘ座標の変化量から、像焦点を拡大するための拡散板の縦方向サイズは、上下２０ｃｍすなわち４０ｃｍの長さが必要となる。再生光のｚ座標の変化量は左右４０ｃｍ幅では、回転角１０°では両端で２０ｃｍの差に達するが、同時に照明光側の物焦点が逆方向に４０ｃｍの差が生じている。この差の変化を吸収できるように、角度選択性の範囲が大体１０°なので、物焦点と像焦点のｚ座標を補正することが可能である。ただし、ホログラムスクリーンの周辺部の回折効率が低下するのはやむを得ないと思われる。
【００７１】
【発明の効果】
以上の説明から明白なように、本発明を利用することにより以下のような効果を得ることができる。
【００７２】
従来、立体表示装置で必要とされることが多かった立体視専用の特殊メガネが、不要である。
【００７３】
プロジェクタ台数の追加により視点数を増加させることが容易である。このとき、ホログラムスクリーン側の変更は必要ない。それら複数視点においてはブラッグ条件を常に満たしているので、どの方向（視点）から見ても画面が明るい。
【００７４】
本発明は原画投影方式なので、視点数を増やしても画素分配型の多視点表示スクリーンのように画像解像度が低下することが無い。
【００７５】
パネル数の増加により画面サイズを拡張することが容易である。
【００７６】
ホログラムスクリーンを、２枚重ねの組合せスクリーンとして配置することにより、照明光の角度や再生光の角度の制約が緩和され、装置のレイアウトや観察位置の柔軟な変更が可能になる。
【００７７】
本発明では、透視可能なホログラムスクリーンを用いているので、現実環境との複合表示も可能である。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る単一記録多重再生ホログラムスクリーンの概略の斜視図（１）である。
【図２】本発明の第１の実施の形態に係る単一記録多重再生ホログラムスクリーンの概略の斜視図（２）である。
【図３】本発明の第１の実施の形態に係る単一記録多重再生ホログラムスクリーンにおいて、共通ブラッグ角円錐面に沿って照明光の数を増やした場合の、再生光の生成方向の例の模式図である。
【図４】本発明の第２の実施の形態に係るマルチパネル形式多視点表示装置の概略の斜視図である。
【図５】本発明の第３の実施の形態に係る単一波長レーザ・カラー記録ホログラム（スクリーン）の仕組みを示す模式図である。
【図６】本発明の第４の実施の形態に係る２枚組合せホログラムスクリーンによる多視点表示装置の概略斜視図である。
【図７】照明光が仰角４５°方向であるとき、再生光がホログラム面の法線方向となるように製作された、本発明に係るホログラムスクリーンの一つの実証例において、照明光の仰角と水平方向の経度とを変化させた場合の回折効率を測定して、その結果を示すグラフである。
【図８】本発明に係るホログラムスクリーンの一つの実証例において、多視点化による照明光の物焦点の空間座標変化を表すグラフである。
【図９】本発明に係るホログラムスクリーンの一つの実証例において、多視点化による再生光の像焦点の空間座標変化を表すグラフである。
【図１０】本発明に係るホログラムスクリーンの一つの実証例において、大画面化による照明光の物焦点の空間座標変化を表すグラフである。
【図１１】本発明に係るホログラムスクリーンの一つの実証例において、大画面化による再生光の像焦点の空間座標変化を表すグラフである。
【図１２】従来技術である、ホログラムスクリーンの回折による再生光の指向性コントロール機能を利用した多視点立体表示の多視点表示装置の構成である。
【図１３】図１２の従来技術の構成で利用される多視点表示用ホログラムスクリーンの概略の斜視図（１）である。
【図１４】図１２の従来技術の構成で利用される多視点表示用ホログラムスクリーンの概略の斜視図（２）である。
【図１５】図１２の従来技術の構成で利用される多視点表示用ホログラムスクリーンの概略の斜視図（３）である。
【符号の説明】
１、１’・・・多視点表示装置、２・・・ホログラムスクリーン、４・・・照明光、６・・・再生光、８・・・物体光、１０・・・参照光、１２・・・ホログラム記録材料、１４・・・干渉縞面層、１５・・・物焦点、１６・・・像焦点、１８・・・ホログラム中心、２０・・・共役再生２光束光軸共有断面、２２・・・格子ベクトル、２４・・・共通ブラッグ角円錐、２６・・・マルチパネル形式多視点表示装置、２７・・・２枚組合せホログラムスクリーンによる多視点表示装置。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hologram screen for multi-view display and a multi-view display device using the same.
[0002]
[Prior art]
A multi-viewpoint display device 1 'for multi-viewpoint stereoscopic display using special directional glasses and utilizing a directivity control function of reproduction light by diffraction of the hologram screen 2 is known as a configuration shown in FIG. FIG. 12 shows (a) a bird's-eye view, (b) a plan view, and (c) a side view.
[0003]
In the configuration of FIG. 12, two-dimensional images having different parallaxes are projected onto the hologram screen 2 from a plurality of projector groups A1, A2,. The light projected from each projector becomes the illumination light 4 of the hologram screen 2 and generates the reproduction light 6 diffracted in a predetermined direction. The diffracted reproduction light 6 forms an image focus (convergent point) at each of the positions a1, a2,..., Am. When the observer places the left and right eyes at any two adjacent image focal points (light converging points), images having parallax corresponding to each can be seen. The observer can recognize the stereoscopic image fused by the two parallax images.
[0004]
In order to manufacture the hologram screen 2 having directivity, it is necessary to use a volume hologram (or a thick hologram). This is because a planar hologram (or a thin hologram) cannot generate a higher-order diffraction image and cause the reproduction light 6 to travel in one specific direction. Further, in order to obtain a high diffraction efficiency in the volume hologram, the recorded interference fringe layer is irradiated with the illumination light 4 so as to satisfy the Bragg condition, and the diffracted reproduction light 6 is directed in a direction suitable for the Bragg condition. Need to be designed to proceed.
[0005]
Therefore, when the hologram screen 2 for multi-viewpoint display used in the configuration of FIG. 12 is manufactured, the recording is conventionally performed as shown in FIG. FIG. 13 shows a case of two viewpoints for simplicity. First, the hologram recording material 12 is irradiated with the object light of (8-1) and the reference light of (10-1) in the directions of the arrows, respectively. The development process forms an interference fringe surface layer (14-1).
[0006]
In FIG. 13, one interference fringe surface (14-1) is shown (for convenience), but in actuality, as shown in FIG. 15, the interference fringe surface layer (14-1) is literally composed of a plurality of surfaces. A "layer".
[0007]
The irradiation direction is changed once again, and the hologram recording material 12 is irradiated with the object light (8-2) and the reference light (10-2) in the directions of the arrows, respectively. At this time, the interference fringe layer (14-2) is formed (see FIGS. 13 and 15).
[0008]
As shown in FIG. 14, when the two illuminating lights 4-1 and 4-2 are illuminated on the hologram screen 2 recorded in this manner from the direction conjugate with the reference light, the hologram screen 2 is conjugated with the object light. The reproduction light 6-1 and 6-2 are generated. The two reproduction lights 6-1 and 6-2 separately reach the left and right eyes of the observer at the respective image focal points 16-1 and 16-2. At this time, if images having different parallaxes are supplied from the two projectors A1 and A2 as the illumination lights 4-1 and 4-2, the images are separately provided to the left and right eyes, so that the observer can display the two parallax images. The three-dimensional image can be recognized by fusing.
[0009]
If the number of pairs of the object light 8 and the reference light 10 at the time of recording is increased based on the above operation, the number of pairs of the illuminating light 4 and the reproduction light 6 to be conjugate-reproduced can be increased. Any number of hologram screens 2 for multi-view display should be able to be manufactured.
[0010]
However, since the following two important obstacle factors ((1) and (2)) actually exist, it is impossible to manufacture the multi-viewpoint display hologram screen 2 by the above method.
[0011]
(1) Generation of crosstalk
First, there is a problem of occurrence of crosstalk due to multiplex recording. The distance between the human eyes is about 6.5 cm on average, but the distance of 6.5 cm from the screen 1 m away is only 4 °. However, in a volume hologram, diffraction occurs even if it is slightly deviated from the direction of the Bragg angle within the range of angle selectivity. Since the width of the angle selectivity is at least about 10 °, the hologram screen 2 recorded in FIG. 13 generates unintended reproduction light 6 even by the illumination light 4 from a direction different from the direction at the time of recording. As a result, crosstalk occurs. That is, in reality, the observer receives an overlapped image with many shifts due to crosstalk.
[0012]
In order to set the reproduction condition of the adjacent reproduction light to be equal to or more than the width of the angle selectivity, a measure to increase the angular interval of the reference light (conjugate illumination light at the time of reproduction) can be considered. However, in this case, the recording multiplicity decreases, and the number of multi-viewpoints cannot be increased.
[0013]
(2) Reduction of diffraction efficiency of incoherent duplicate recording
The multiplex recording of the above-mentioned method is called incoherent overlapping recording, and the intensity of the diffraction reproduction light decreases in inverse proportion to the square of the overlapping number. That is, the efficiency is reduced to 1/4 in the case of two viewpoints, and reduced to 1/16 in the case of four viewpoints. In FIG. 13 as well, since the directions of the two interference fringe surface layers 14-1 and 14-2 are different, mutual destruction of the interference fringe surface layers and generation of scattered light inside are expected, and abruptly accompanying an increase in the number of viewpoints. It is understood that the diffraction efficiency is greatly reduced.
[0014]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a hologram screen for multi-view display in which crosstalk does not occur and the diffraction efficiency of incoherent overlapping recording does not decrease, and a multi-view display device using the same.
[0015]
[Means for Solving the Problems]
The present invention has been made to achieve the above object. The multi-view display device according to claim 1 according to the present invention,
A multi-viewpoint display device including a hologram screen, which is a volume hologram having a single object focus and a single image focus, which is developed by irradiating the hologram recording material with object light and reference light only once. In the multi-view display device,
In order to satisfy the Bragg condition in the three-dimensional space of the hologram screen, a plurality of two-dimensional images having different parallaxes are superimposed and projected on the hologram screen surface from different directions using a plurality of projectors,
The plurality of two-dimensional images are multiplexed and reproduced on the hologram screen,
Utilizing the directivity of the reproduction light generated by the diffraction of the hologram screen, the parallax image group multiplexed and reproduced on the hologram screen corresponding to the positions of the left and right eyes of the observer observing the hologram screen. It is set that only a specific parallax image is recognized from the inside.
[0016]
The multi-view display device according to claim 2 according to the present invention,
A plurality of element hologram screens, which are volume holograms having a single object focus and a single image focus, which are developed by irradiating the hologram recording material only once with object light and reference light, are arranged in a multi-panel shape. ,
In this arrangement, the object focal point of the element hologram screen, that is, the light source position in the three-dimensional space of the illumination light, and the image focus, that is, the condensing position of the reproduction light in the three-dimensional space, match for each element hologram screen. As a result, as a result, the entire multi-panel shape hologram screen was made to be equivalent to a single object focus, a single image focus single hologram screen,
The entire multi-panel hologram screen is used in place of a single hologram screen,
A multi-view display device according to claim 1.
[0017]
The multi-view display device according to claim 3 according to the present invention,
At the time of recording, the wavelengths of the object light and the reference light are fixed with respect to the center of the hologram recording material, and the Bragg angle of each light is changed up to a predetermined number of times. Irradiate and record the hologram recording material with the object light and the reference light so that they all match,
Alternatively, with respect to the center of the hologram recording material, the wavelength of each light is changed up to a predetermined number of times while keeping the Bragg angles of the object light and the reference light constant. Irradiate and record the hologram recording material with the object light and the reference light so that they match,
At the time of reproduction, under the condition of one Bragg angle, the object focal points and the image focal points for light of a predetermined number of different colors coincide with each other, and the above-mentioned predetermined number of different colors from the object focal point are used as components. Forming a multicolor hologram screen having a single common object focal point and a single common image focal point so as to focus the reproduction light including the predetermined number of different colors in the image focal point at the image focal point. hand,
The above multicolor hologram screen,
Used as an alternative to a hologram screen, which is a volume hologram that irradiates the hologram recording material with object light and reference light and develops it.
A multi-view display device according to claim 1.
[0018]
The multi-view display device according to claim 4 according to the present invention,
At the time of recording, the wavelengths of the object light and the reference light are fixed with respect to the center of the hologram recording material, and the Bragg angle of each light is changed up to a predetermined number of times. Irradiate and record the hologram recording material with the object light and the reference light so that they all match,
Alternatively, with respect to the center of the hologram recording material, the wavelength of each light is changed up to a predetermined number of times while keeping the Bragg angles of the object light and the reference light constant. Irradiate and record the hologram recording material with the object light and the reference light so that they match,
At the time of reproduction, under the condition of one Bragg angle, the object focal points and the image focal points for light of a predetermined number of different colors coincide with each other, and the above-mentioned predetermined number of different colors from the object focal point are used as components. Forming a multicolor element hologram screen having a single common object focal point and a single common image focal point, wherein the reproduction light including the predetermined number of different colors in the components is focused on the image focal point. do it,
Using the multicolor element hologram screen as an alternative to the element hologram screen,
A multi-view display device according to claim 2.
[0019]
The multi-view display device according to claim 5 according to the present invention,
A combination hologram in which the two hologram screens are stacked to form a single object focus and a single image focus as a set of two hologram screens, and the positions of the object focus and the image focus are different from each hologram screen. Form the screen,
Using the combination hologram screen as a substitute for the hologram screen,
A multi-view display device according to claim 1.
[0020]
The multi-view display device according to claim 6 according to the present invention,
The two element hologram screens are stacked to form a single object focal point and a single image focal point as a set of two, and the positions of the object focal point and the image focal point are different from those of each element hologram screen. Form a combination element hologram screen,
Using the combination element hologram screen as an alternative to the element hologram screen,
A multi-view display device according to claim 2.
[0021]
The multi-view display device according to claim 7 according to the present invention,
The two multicolor hologram screens are stacked to form a single common object focus and a single common image focus as a set of two, and each single multicolor hologram screen is a single common object focus and a single common focus. Form a combined multicolor hologram screen with different common image focus positions,
Using the combination multicolor hologram screen as an alternative to the multicolor hologram screen,
A multi-viewpoint display device according to claim 3.
[0022]
The multi-view display device according to claim 8 according to the present invention,
The two multicolor element hologram screens are stacked to form a single common object focus and a single common image focus as a set of two, and each single multicolor element hologram screen is a single common object focus. Form a combined multicolor element hologram screen with a single common image focus position different,
Using the combination multicolor element hologram screen as an alternative to the multicolor element hologram screen,
A multi-view display device according to claim 4.
[0023]
The multi-view display device according to claim 9 according to the present invention,
At the time of recording, using a diffuser of a predetermined size as an object light source,
Therefore, at the time of reproduction, an image focal zone corresponding to the size of the diffusion plate is obtained.
A multi-view display device according to any one of claims 1 to 8.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0025]
<< 1st Embodiment >>
(1) Single-record multiple-play multi-view display device
FIGS. 1 and 2 show schematic perspective views of a single-recording-multiplex-reproduction hologram screen 2 according to a first embodiment of the present invention.
[0026]
In the first embodiment, the Bragg condition in the three-dimensional space of the hologram screen in the hologram screen 2 (screen of a volume hologram having a single object focus and a single image focus) recorded once (see below). Are superimposed and projected (multiple reproduction as a hologram screen) using a plurality of projectors to superimpose a plurality of two-dimensional images having different parallaxes from many directions. By moving the position where the hologram screen 2 is observed, only a specific parallax image can be selectively viewed from the parallax image group superimposed and projected on the hologram screen 2. Here, the directivity of the reproduction light generated by the diffraction of the hologram screen 2 is used. This makes it possible to display a multi-view stereoscopic video without using special glasses.
[0027]
As is well known, the above Bragg condition is generally expressed by the following equation.
(Equation 1)

Here, θ is the Bragg angle, λ is the light wavelength, n is the refractive index of the hologram screen, and Λ is the interference fringe layer interval.
[0028]
As shown in FIG. 3, according to the single recording / multiplex reproduction hologram screen 2 according to the first embodiment, the directions of the interference fringe surface layers 14 are all aligned in the same direction. Therefore, there is no occurrence of crosstalk, and there is no reduction in diffraction efficiency because of single recording.
[0029]
The formation of the two-viewpoint hologram screen 2 similar to FIGS. 13 and 14 will be described with reference to FIGS. First, at the time of recording, the hologram recording material 12 is irradiated only once with the object light 8 and the reference light 10 in the direction of the arrow. When the development processing is performed, the interference fringe surface layer 14 is formed.
[0030]
As the hologram recording material 12, a silver salt photosensitive material or a photopolymer can be used.
[0031]
In the hologram screen 2 recorded as described above, the reproduction light 6 is generated in the direction conjugate with the object light 8 by the illumination light 4 from the direction conjugate with the reference light 10 (FIG. 2). Here (FIG. 2), when the conjugate reproduction 2 light beam optical axis shared cross section 20 including the conjugate illumination light 4 and the conjugate reproduction light 6 is rotated so as to maintain the Bragg angle θ of the hologram center 18, the illumination light 4 Thus, the directions 4-1 and 4-2 are obtained, and the directions 6-1 and 6-2 are obtained with respect to the reproduction light 6. As described above, the conjugate illumination light 4 and the conjugate reproduction light 6 are combined with the conjugate illumination light 4 while maintaining the Bragg angle θ on the axis of the lattice vector 22 passing through the hologram center 18 and perpendicular to the interference fringe plane at the interference fringe plane including the hologram center 18. Is rotated, a conical surface of the common Bragg angle cone 24 is formed. Here, the lattice vector 22 is a unit normal vector indicating the direction of the interference fringe surface.
[0032]
When the two illumination lights (4-1, 4-2) are projected onto the hologram screen 2 from the above directions 4-1 and 4-2, reproduction lights (6-1, 6-2) are generated. The two reproduction lights (6-1, 6-2) separately reach, for example, the left and right eyes of the observer at the respective image focal points 16-1, 16-2. At this time, if images having different parallaxes are supplied from the two projectors as the illumination light (4-1, 4-2), the left and right eyes are provided, so that the observer can fuse the two parallax images. To recognize a stereoscopic image.
[0033]
Similarly to the above, if the direction of the illumination light 4 is increased by an arbitrary number along the common Bragg angle conical surface 24, an arbitrary number of reproduction lights 6 are generated correspondingly. Therefore, multi-view display with an arbitrary number of viewpoints becomes possible. FIG. 3 is a schematic diagram showing an example of the generation direction of the reproduction light 6 when the number of the illumination lights 4 is increased along the common Bragg angle conical surface 24 (five in the figure).
[0034]
By the way, in order to make the hologram screen a volume hologram, the intersection angle between the two optical axes of the illumination light that connects the center of the hologram screen to the object and the reproduction light that connects the hologram screen and the image focus ( The inside of the hologram screen is equivalent to twice the Bragg angle θ) by the Magnusson and Gayload determination formula,
(Equation 2)
Q ′ = Q / cos (θ) = (2πλt) / {n} ² cos (θ)｝> 10
Is larger than a certain value so that In addition,
θ: Bragg angle inside hologram screen
π: Pi
λ: wavelength of light
t: hologram screen thickness
n: Refractive index of hologram screen
Λ; hologram interference fringe layer spacing
Means
[0035]
If the hologram is a volume hologram, the illumination light projector and the observer of the reproduction light may be a transmission hologram arranged on the opposite side of the hologram screen. It may be a reflection hologram arranged on the same side of the screen.
[0036]
<< 2nd Embodiment >>
(2) Multi-panel large screen
FIG. 4 is a schematic perspective view of a multi-panel multi-view display device 26 according to the second embodiment of the present invention. The single-recording-multiplex-reproduction hologram screen 2 according to the first embodiment capable of multi-view display along the common Bragg angle conical surface 24 is arranged in a four-panel multi-panel format. Here, a case where illumination is performed by three projectors (accordingly, a case of three viewpoints) is shown.
[0037]
As is clear from FIG. 4, the shape and orientation of the common Bragg angle cone 24 are different for each element hologram screen 2, but the object focal point (15-0, 15-1, 15-2) and the image focus (16-0, 16-1, 16-2 in the figure) are all coincident.
[0038]
In this way, the four element hologram screens 2 can realize the function of one large hologram screen as a whole, and for example, a life-size multi-view display hologram screen can be manufactured. The size and number of element hologram screens 2 are arbitrary, and if the projection size of the projector can be increased, a multi-panel multi-viewpoint display device 26 of any size can be manufactured.
[0039]
For example, when forming a large hologram screen of 1 m × 1 m in length and width, the size of each element hologram screen is 1 mm × 1 mm in length and 1 million in total. Further, each element hologram screen size is 10 cm × 10 cm in length and width, and may be constituted by a total of 100 pieces, and the same function is eventually realized. However, as a general tendency, the smaller the element hologram screen size, the smaller the hologram aberration and the higher the diffraction efficiency, and a clearer image can be obtained. However, the hologram recording time becomes longer because the number of elements increases.
[0040]
<< 3rd Embodiment >>
(3) Single wavelength laser color recording hologram
FIG. 5 is a schematic diagram showing a mechanism of a single wavelength laser color recording hologram (screen) according to the third embodiment of the present invention. As in the first embodiment, a silver salt photosensitive material or a photopolymer can be used as the hologram recording material, that is, the material of the hologram screen.
[0041]
In the single-wavelength laser color recording multi-viewpoint display device 1 according to the third embodiment, light of a single wavelength is used at the time of recording, but light of a different wavelength can be reproduced at the time of reproduction.
[0042]
In other words, using the Bragg conditional expression of the volume hologram, multiplex recording is performed three times by the following three imaging conditional expressions (the Bragg angle during recording is different), and three colors (the wavelength of each color is λc ₁ , Λc ₂ , Λc ₃ 2.) A reproducible color hologram screen can be manufactured.
[Equation 3]
sin (Θr ₁ ) / Λr = ± sin (Θc) / λc ₁ = 1 / (2nΛ ₁ (A)
sin (Θr ₂ ) / Λr = ± sin (Θc) / λc ₂ = 1 / (2nΛ ₂ (B)
sin (Θr ₃ ) / Λr = ± sin (Θc) / λc ₃ = 1 / (2nΛ ₃ ) (C)
[0043]
Here, Θr (Θr ₁ , Θr ₂ , Θr ₃ ) Is the Bragg angle during recording, and Δc is the Bragg angle during reproduction. λr is the wavelength of light at the time of recording, and λc (λc ₁ , Λc ₂ , Λc ₃ ) Is the wavelength of light at the time of reproduction. Λ (Λ ₁ , Λ ₂ , Λ ₃ ) Is the interval between the interference fringe layer surfaces 14. In the volume hologram 2, λc ₁ The first interference fringe surface layer according to ₂ A second interference fringe surface layer according to ₃ Of the third interference fringe surface layer according to (1), three types of interference fringe layer surfaces are formed. n indicates the refractive index of the hologram screen.
[0044]
Here, the directions of the three types of interference fringe layer surfaces are aligned, and the positions of the object focal point and the image focal point during reproduction are three colors (λc ₁ , Λc ₂ , Λc ₃ ), The directions of all the lattice vectors are made the same through the above-mentioned three recordings of the hologram screen.
[0045]
In the equation (Equation 3), what changes corresponding to the three colors is the Bragg angle 記録 r (ie, Θr ₁ , Θr ₂ , And Δr ₃ ), The distance between the interference fringe layer surfaces Λ (that is, Λ ₁ , Λ ₂ , And Λ ₃ ), The wavelength λc of light during reproduction (ie, λc ₁ , Λc ₂ , And λc ₃ ). That is, the wavelength λr of the light is fixed during recording, while the Bragg angle is set to Θr ₁ , Θr ₂ , Θr ₃ When reproducing, different wavelengths λc in the direction of the same Bragg angle Θc during reproduction ₁ , Λc ₂ , Λc ₃ Light can be reproduced. This means that when the Bragg angle Θr during recording matches the Bragg angle Θc during reproduction, different wavelengths λc ₁ , Λc ₂ , Λc ₃ (Specifically, separate laser beams) can achieve the same effect as multiplexed recording three times.
[0046]
Specifically, in the configuration shown in FIG. 5, the Bragg angle, which is the complementary angle of the Bragg angle cone 24, is changed during recording. In other words, the wavelength of the reproduction light can be changed by changing the "degree of opening of the umbrella" of the Bragg angle cone 24. For example, from the object focal point of the projector 15-1, light having a wavelength λr is converted into a Bragg angle Θr ₁ When the light is incident on the interference fringe layer surface 14 along the Bragg angle conical surface 24, the Bragg angle Θr along the Bragg angle conical surface 24 ₁ The light having the wavelength λr is used to diffract the reproduction light having the wavelength λr and to condense it at the image focal point 16-1. ₁ It is assumed that the interference fringe layer surface 14 is recorded. However, during reproduction, the interference fringe interval Λ ₁ From the object focal point of the projector 15-2 with respect to the interference fringe layer surface 14 of FIG. ₁ Light (or wavelength λc ₁ Is incident along the Bragg angle conical surface 24 'at the Bragg angle Θc, the wavelength λc at the Bragg angle Θc along the Bragg angle conical surface 24'. ₁ Can be diffracted and focused on the image focal point 16-2. In this way, the same interference fringe interval Λ ₁ The wavelength λr at the time of recording is changed to the wavelength λc at the time of reproduction with respect to the interference fringe layer surface 14. ₁ Can be changed to Further, the interference fringe interval Λ thus recorded ₁ Is rotated in an arbitrary direction about the grating vector 22 with respect to the interference fringe layer surface 14 in the direction of the Bragg angle conical surface 24 'during reproduction. Wavelength λc ₁ , There always exists one set of a pair of a projector position (object focus) and an observation position (image focus). Similarly, based on the equation (Equation 3), the reproduction wavelength λc ₁ , Λc ₂ , Λc ₃ The corresponding fringe spacing ₁ , Λ ₂ , Λ ₃ When the interference fringe layer surface 14 is recorded on the hologram recording material 12 so that the lattice vectors 22 coincide with each other, when the conjugated reproduction two-beam optical axis shared section 20 is rotated in an arbitrary direction about the lattice vector 22, Bragg On the surface of the angular conical surface 24 ', three wavelengths λc ₁ , Λc ₂ , Λc ₃ , A pair of a common projector position (common object focal point) and a common observation position (common image focal point) corresponding to each pair can always exist. In other words, if a multicolor hologram screen recorded in this manner is used, three wavelengths λc ₁ , Λc ₂ , Λc ₃ , And correspondingly three wavelengths λc ₁ , Λc ₂ , Λc ₃ Any number of color reproduction lights 6 can be generated.
[0047]
<< 4th Embodiment >>
(4) Flexible change of the focusing position using a two-piece hologram screen
FIG. 6 is a schematic perspective view of a multi-viewpoint display device 27 using a two-piece hologram screen according to the fourth embodiment of the present invention. The single recording / multiplex reproduction hologram screen 2 according to the first embodiment capable of multi-view display along the common Bragg angle conical surface 24 is arranged as a two-layer combination screen (2-1, 2-2). are doing. Here, a case where illumination is performed by two projectors (15-1 and 15-2) (that is, a case of two viewpoints) is shown.
[0048]
In FIG. 6, the two hologram screens (2-1, 2-2) are separated for schematic illustration, but are actually close. Normally, the thickness of the hologram recording material is on the order of several microns, and the thickness of the glass substrate for supporting it is 2 to 3 mm. The order of several millimeters at the most when two sheets are stacked is a thickness that can be ignored when compared with the illumination light distance from the hologram screen or the observation distance of 50 cm to 5 m. Therefore, the vertices of the three common Bragg angle conical surfaces (24-0, 24-1, 24-2) are close to each other on the order of several millimeters, and all of the hologram screens 2-1 and 2-2 have respective vertices. There is no problem assuming that it exists near the center. In particular, since the two common Bragg angle conical surfaces (24-1, 24-2) of the hologram screen 2-2 are close to each other, the directions of the respective lattice vectors are equal, and the magnitudes of the Bragg angles may be equal. .
[0049]
In FIG. 6, two projectors (15-1 and 15-2) are superimposed and projected from the two projectors (15-1 and 15-2) such that the optical axes from the projectors are directed to the center of the first hologram screen 2-1. You. The two illuminating lights incident along the common Bragg angle conical surface 24-0 at the center of the first hologram screen 2-1 are also changed to the common Bragg angle conical surface 24-0 according to the incident direction of the illuminating light. Two reproduction lights are generated along the directions. The two reproduction lights of the first hologram screen 2-1 become two illumination lights for the second hologram screen 2-2. The two illumination lights for the second hologram screen 2-2 are respectively incident along common Bragg angle conical surfaces 24-1 and 24-2 near the center of the second hologram screen 2-2. The illumination light in the direction along the common Bragg angle conical surface 24-1 also generates reproduction light in the direction along the common Bragg angle conical surface 24-1 and converges on the image focal point 16-1. The illumination light in the direction along the common Bragg angle conical surface 24-2 also generates reproduction light in the direction along the common Bragg angle conical surface 24-2, and is converged on the image focal point 16-2. In this way, the left and right parallax images can be observed at the two image focal points 16-1 and 16-2, and stereoscopic viewing becomes possible.
[0050]
The feature of this embodiment is that two hologram screens (2-1, 2-2) receive two diffractions, and thus the directions of the optical axes of the two projectors (15-1, 15-2). There is an advantage that the direction of the optical axis of the reproduction light from the second hologram screen 2-2, that is, the observation position can be flexibly changed by reducing the influence of the hologram screen 2-2. Since the hologram screen 2 becomes a volume hologram, the range of the Bragg angle is limited in order to satisfy the above-mentioned Magnusson and Gaylord determination formula. Therefore, in the first embodiment, the angle of the illumination light and the angle of the reproduction light with respect to the hologram screen 2 are restricted. According to the present embodiment, since the restrictions on the angle of the illumination light and the angle of the reproduction light are relaxed, the layout of the apparatus and the observation position can be flexibly changed.
[0051]
In the present embodiment, in order to enhance the diffraction efficiency by the two hologram screens, the direction of the reproduction light of the common Bragg angle cone surface 24-0 and the common Bragg angle cone surfaces (24-1, 24-2) It is important to manufacture the two hologram screens (2-1, 2-2) so that the directions of the illumination light are the same.
[0052]
<< 5th Embodiment >>
(5) Enlargement of the image focal point zone that becomes the focal point of the reproduction light
If the object light source at the time of hologram screen recording is a point light source, the image focus, which is the focal point of the reproduction light at the time of reproduction, is only one point in the three-dimensional space. Then, it is difficult to find the position of the image focus at the time of observation, and eventually, it is difficult to perform stereoscopic viewing.
[0053]
In the multi-viewpoint display device 1 according to the fifth embodiment of the present invention, a finite-size diffuser is used as an object light source during recording. For example, if a diffusion plate of 10 cm × 5 cm in length and width is used as a plate-like object light source during recording, an image focal zone (10 cm × 5 cm in length and width) equal to the size of the diffusion plate during reproduction will be used as an observable area in a three-dimensional space. Formed. By using the multi-viewpoint display device 1 of the fifth embodiment, stereoscopic viewing without special glasses is easier.
[0054]
If the width of the diffuser plate used as the object light source is larger than the distance between both eyes of the observer, there may be a case where an image having the same parallax is presented to both eyes. Therefore, it is preferable that the width of the diffusion plate is considerably shorter (for example, 5 cm or less) than the average interocular distance of adults (for example, about 6.5 cm).
[0055]
<< demonstration example >>
Hereinafter, several trials of the multi-view display device 1 according to the present invention will be described.
[0056]
(1) Example of device
A prototype and demonstration were performed on a multi-view display device having four viewpoints similar to the conventional technology shown in FIG. 12 and a hologram screen 2 having four multi-panel types as in the device of FIG.
[0057]
Here, the size of each element hologram screen 2 was 20 cm × 25 cm in height and width, and the size of the entire hologram screen was 40 cm × 50 cm in length and width. The object focus was at a distance of 2.5 m below the rear surface of the hologram screen by 45 °, and the image focus was at a distance of 1 m in the direction normal to the front surface of the hologram screen.
[0058]
(2) Example of measuring diffraction efficiency
FIG. 7 shows that the elevation angle of the illumination light and the longitude in the horizontal direction are changed with respect to the hologram screen manufactured such that the reproduction light is in the normal direction of the hologram surface when the illumination light is in the elevation angle of 45 °. The result of measuring the diffraction efficiency in the case of the above is shown.
[0059]
The horizontal axis of the graph indicates the elevation angle of the illumination light, and the vertical axis indicates the diffraction efficiency. Each of a number of (upwardly convex) curves indicates a change in diffraction efficiency on the same longitude (when the elevation angle of the illumination light is changed). In each case of the longitude, the local maximum value exists near the elevation angle of 45 °. When the maximum points are connected according to the change in the longitude, a saddle-shaped curve (“trajectory of the diffraction efficiency maximum point”) having a downward convex in the figure is obtained. The local minimum point of the saddle-shaped curve is the local maximum point at longitude 0 °. The reason why the maximum point at the longitude of 0 ° deviates from the elevation angle of 45 ° by 2 to 3 ° is due to the mounting displacement of the observation device.
[0060]
Thus, the fact that the diffraction efficiency does not decrease even if the longitude line is moved in a state where the illumination light elevation angle is almost constant can be obtained by changing the illumination light and the reproduction light on the common Bragg angle cone surface in the three-dimensional space. , Has proven that he always satisfies the Bragg condition.
[0061]
(3) Changes in spatial coordinates between object focus of illumination light and image focus of reproduction light due to multi-viewpoint
FIG. 8 shows an example of the spatial coordinate change of the object focal point of the illumination light due to the multi-viewpoint, and FIG. 9 shows an example of the spatial coordinate change of the image focal point of the reproduction light due to the multi-viewpoint.
[0062]
Examples in the case where the illumination light elevation angles are 30 °, 45 °, and 60 °, respectively, will be described. The distance of the object focus of the illumination light from the center of the hologram screen is 2 m, and the distance of the image focus of the reproduction light is 1 m. The horizontal axis of the graph represents the rotation angle ω when the illumination light or the reproduction light is changed (displaced) in one direction on the common Bragg angle cone surface around the lattice vector.
[0063]
The vertical axis of the graph indicates (a) the x-coordinate (change) in the vertical direction parallel to the hologram surface. (B) The y-coordinate is a horizontal coordinate (change) parallel to the hologram surface. (C) The z coordinate is a coordinate (change) in a direction normal to the hologram surface.
[0064]
The rotation angle ω and the change in the y-coordinate are substantially proportional to both the illumination light and the reproduction light. Further, it can be seen that the relationship between the horizontal distance between the projectors and the horizontal distance between observable positions of the observer is approximately 2: 1. This is proportional to the ratio between the object focal length and the image focal length.
[0065]
In particular, since the change in the (a) x-coordinate of the reproduction light in FIG. 9 is small, it can be seen that the height of the observable position of the observer is not significantly affected even if it changes in the horizontal direction. Also, from the change of the (c) z coordinate of the reproduction light in FIG. 9, the image focal point approaches the hologram screen by about 10 cm in the peripheral portion (around the rotation angle of 16 °). However, since it is considered to be within the range of the movement of the position obtained by the observer standing in the same place and tilting the body or shaking the head, the amount of change is not so large as to actually be a problem.
[0066]
(4) Changes in spatial coordinates between object focus of illumination light and image focus of reproduction light due to enlargement of screen
FIG. 10 shows an example of the spatial coordinate change of the object focal point of the illumination light due to the enlargement of the screen, and FIG.
[0067]
In each case, the illumination light elevation angle was 45 °. The distance from the center of the hologram screen to the object focal point of the illumination light is 2 m, and the distance from the center of the hologram screen to the image focal point of the reproduction light is 1 m. In each figure, a change in the coordinates of the object focal point and a change in the coordinates of the image focal point from the center of the hologram screen, 20 cm left and right, and 40 cm right and left are shown. The horizontal axis of the graph represents the rotation angle ω when the illumination light or the reproduction light is changed (displaced) in one direction on the Bragg angle cone surface around the lattice vector.
[0068]
The vertical axis of the graph indicates (a) the x-coordinate (change) in the vertical direction parallel to the hologram surface. (B) The y-coordinate is a horizontal coordinate (change) parallel to the hologram surface. (C) The z coordinate is a coordinate (change) in a direction normal to the hologram surface.
[0069]
Regarding the y-coordinate of the reproduction light, the difference from the center at a rotation angle of 16 ° is approximately 4 cm at a position 20 cm left and right of the hologram screen. That is, the average value of the distance between the left and right eyes of a human is within a range of 6.5 cm, and stereoscopic vision is still possible. At a position 40 cm left and right of the hologram screen, the difference from the center reaches 6 cm at a rotation angle of 10 °, which is almost the limit of stereoscopic vision. According to FIG. 9, a rotation angle of 10 ° corresponds to a case where the observation position is shifted laterally by 30 cm. In the case of a hologram screen having a width of 40 cm, that is, an 80 cm width, the lateral movement of the observation position is limited to a width of 60 cm. It should be noted that the rotation angle of 16 ° corresponds to less than 50 cm from FIG. 9, and with a hologram screen having a width of 20 cm left and right, ie, a width of 40 cm, even if the observation position is laterally moved to a width of less than 50 cm left or right, ie, a little less than 1 m, there is no problem in stereoscopic vision.
[0070]
From the amount of change in the x-coordinate of the reproduction light, the vertical size of the diffuser for expanding the image focus needs to be 20 cm vertically, that is, 40 cm long. The amount of change in the z coordinate of the reproduction light reaches a difference of 20 cm at both ends at a rotation angle of 10 ° in a width of 40 cm left and right, but at the same time, a difference of 40 cm occurs in the object focus on the illumination light side in the opposite direction. Since the range of the angle selectivity is approximately 10 ° so as to absorb the change in the difference, it is possible to correct the z-coordinate between the object focal point and the image focal point. However, it seems unavoidable that the diffraction efficiency at the periphery of the hologram screen is reduced.
[0071]
【The invention's effect】
As is clear from the above description, the following effects can be obtained by utilizing the present invention.
[0072]
Conventionally, special glasses dedicated to stereoscopic vision, which are often required in a stereoscopic display device, are not required.
[0073]
It is easy to increase the number of viewpoints by adding the number of projectors. At this time, there is no need to change the hologram screen. Since the Bragg condition is always satisfied in these multiple viewpoints, the screen is bright from any direction (viewpoint).
[0074]
Since the present invention is an original image projection system, even if the number of viewpoints is increased, the image resolution does not decrease unlike a multi-view display screen of a pixel distribution type.
[0075]
It is easy to expand the screen size by increasing the number of panels.
[0076]
By arranging the hologram screen as a combination screen in which two holograms are stacked, restrictions on the angle of the illumination light and the angle of the reproduction light are relaxed, and the layout of the apparatus and the observation position can be flexibly changed.
[0077]
In the present invention, since a hologram screen that can be seen through is used, a composite display with a real environment is also possible.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view (1) of a single-recording-multiplex-reproduction hologram screen according to a first embodiment of the present invention.
FIG. 2 is a schematic perspective view (2) of the single-recording-multiplex-reproduction hologram screen according to the first embodiment of the present invention.
FIG. 3 shows an example of a reproduction light generation direction when the number of illumination lights is increased along a common Bragg angle conical surface in the single recording / multiplex reproduction hologram screen according to the first embodiment of the present invention. It is a schematic diagram.
FIG. 4 is a schematic perspective view of a multi-panel type multi-view display device according to a second embodiment of the present invention.
FIG. 5 is a schematic diagram showing a mechanism of a single wavelength laser color recording hologram (screen) according to a third embodiment of the present invention.
FIG. 6 is a schematic perspective view of a multi-viewpoint display device using a two-piece combination hologram screen according to a fourth embodiment of the present invention.
FIG. 7 shows an example of the hologram screen according to the present invention, in which the reproduction light is made to be in the direction normal to the hologram surface when the illumination light is in the 45 ° elevation direction. It is a graph which shows the result of measuring the diffraction efficiency when changing the longitude in the horizontal direction.
FIG. 8 is a graph showing a change in spatial coordinates of an object focal point of illumination light due to multiple viewpoints in one verification example of the hologram screen according to the present invention.
FIG. 9 is a graph showing changes in the spatial coordinates of the image focus of the reproduction light due to multi-viewpoints in one verification example of the hologram screen according to the present invention.
FIG. 10 is a graph showing a change in spatial coordinates of an object focal point of illumination light due to enlargement of a screen in one demonstration example of the hologram screen according to the present invention.
FIG. 11 is a graph showing a change in the spatial coordinates of the image focus of the reproduction light due to the enlargement of the screen in one demonstration example of the hologram screen according to the present invention.
FIG. 12 shows a configuration of a conventional multi-viewpoint display apparatus for multi-viewpoint stereoscopic display using a directional control function of reproduction light by diffraction of a hologram screen.
13 is a schematic perspective view (1) of a hologram screen for multi-viewpoint display used in the configuration of the prior art shown in FIG.
14 is a schematic perspective view (2) of a hologram screen for multi-viewpoint display used in the configuration of the prior art in FIG.
15 is a schematic perspective view (3) of a multi-viewpoint display hologram screen used in the configuration of the related art in FIG.
[Explanation of symbols]
1, 1 ': multi-view display device, 2: hologram screen, 4: illumination light, 6: reproduction light, 8: object light, 10: reference light, 12 ... Hologram recording material, 14: interference fringe surface layer, 15: object focal point, 16: image focal point, 18: hologram center, 20: conjugate reproduction 2 light beam optical axis shared cross section, 22. ··· Lattice vector, 24: Common Bragg angle cone, 26: Multi-panel type multi-view display device, 27: Multi-view display device using two-piece combination hologram screen.

Claims (9)

A multi-viewpoint display device including a hologram screen as a volume hologram having a single object focus and a single image focus, which is developed by irradiating the hologram recording material only once with an object light and a reference light,
In order to satisfy the Bragg condition in the three-dimensional space of the hologram screen, a plurality of two-dimensional images having different parallaxes are superimposed and projected on the hologram screen surface from different directions using a plurality of projectors,
The plurality of two-dimensional images are multiplexed and reproduced on the hologram screen,
Utilizing the directivity of the reproduction light generated by the diffraction of the hologram screen, the parallax image group multiplexed and reproduced on the hologram screen corresponding to the positions of the left and right eyes of the observer observing the hologram screen. From within, it is set so that only a specific parallax image is recognized,
Multi-view display device. A plurality of element hologram screens, which are volume holograms having a single object focus and a single image focus, which are developed by irradiating the hologram recording material only once with object light and reference light, are arranged in a multi-panel shape. ,
In this arrangement, the object focal point of the element hologram screen, that is, the light source position in the three-dimensional space of the illumination light, and the image focus, that is, the condensing position of the reproduction light in the three-dimensional space, match for each element hologram screen. As a result, as a result, the entire multi-panel shape hologram screen was made to be equivalent to a single object focus, a single image focus single hologram screen,
The entire multi-panel hologram screen is used in place of a single hologram screen,
The multi-view display device according to claim 1. At the time of recording, the wavelengths of the object light and the reference light are fixed with respect to the center of the hologram recording material, and the Bragg angle of each light is changed up to a predetermined number of times. Irradiate and record the hologram recording material with the object light and the reference light so that they all match,
Alternatively, with respect to the center of the hologram recording material, the wavelength of each light is changed up to a predetermined number of times while keeping the Bragg angles of the object light and the reference light constant. Irradiate and record the hologram recording material with the object light and the reference light so that they match,
At the time of reproduction, under the condition of one Bragg angle, the object focal points and the image focal points for light of a predetermined number of different colors coincide with each other, and the above-mentioned predetermined number of different colors from the object focal point are used as components. Forming a multicolor hologram screen having a single common object focal point and a single common image focal point so as to focus the reproduction light including the predetermined number of different colors in the image focal point at the image focal point. hand,
The above multicolor hologram screen,
Used as an alternative to a hologram screen, which is a volume hologram that irradiates the hologram recording material with object light and reference light and develops it.
The multi-view display device according to claim 1. At the time of recording, the wavelengths of the object light and the reference light are fixed with respect to the center of the hologram recording material, and the Bragg angle of each light is changed up to a predetermined number of times. Irradiate and record the hologram recording material with the object light and the reference light so that they all match,
Alternatively, with respect to the center of the hologram recording material, the wavelength of each light is changed up to a predetermined number of times while keeping the Bragg angles of the object light and the reference light constant. Irradiate and record the hologram recording material with the object light and the reference light so that they match,
At the time of reproduction, under the condition of one Bragg angle, the object focal points and the image focal points for light of a predetermined number of different colors coincide with each other, and the above-mentioned predetermined number of different colors from the object focal point are used as components. Forming a multicolor element hologram screen having a single common object focal point and a single common image focal point, wherein the reproduction light including the predetermined number of different colors in the components is focused on the image focal point. do it,
Using the multicolor element hologram screen as an alternative to the element hologram screen,
The multi-view display device according to claim 2. A combination hologram in which the two hologram screens are stacked to form a single object focus and a single image focus as a set of two hologram screens, and the positions of the object focus and the image focus are different from each hologram screen. Form the screen,
Using the combination hologram screen as a substitute for the hologram screen,
The multi-view display device according to claim 1. The two element hologram screens are stacked to form a single object focal point and a single image focal point as a set of two, and the positions of the object focal point and the image focal point are different from those of each element hologram screen. Form a combination element hologram screen,
Using the combination element hologram screen as an alternative to the element hologram screen,
The multi-view display device according to claim 2. The two multicolor hologram screens are stacked to form a single common object focus and a single common image focus as a set of two, and each single multicolor hologram screen is a single common object focus and a single common focus. Form a combined multicolor hologram screen with different common image focus positions,
Using the combination multicolor hologram screen as an alternative to the multicolor hologram screen,
The multi-view display device according to claim 3. The two multicolor element hologram screens are stacked to form a single common object focus and a single common image focus as a set of two, and each single multicolor element hologram screen is a single common object focus. Form a combined multicolor element hologram screen with a single common image focus position different,
Using the combination multicolor element hologram screen as an alternative to the multicolor element hologram screen,
The multi-view display device according to claim 4. At the time of recording, a diffuser of a predetermined size is used as an object light source, and thus, at the time of reproduction, an image focal zone corresponding to the size of the diffuser is obtained.
The multi-view display device according to claim 1.

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