JP3545803B2 - Surface light source device with polarization function - Google Patents

Description

上式（１），（２）は各々いわゆる積分形及び微分形の表現であり、物理的な意味は等価である。なお、このＥは濁度と呼ばれることもある。
一方、媒体内に分布した不均一構造によって光散乱が起こる場合の散乱光強度は、縦偏光の入射光に対して出射光の大半が縦偏光である通常の場合（ＶV 散乱）には、次式（３）で表される。
【００１７】
【数２】

自然光を入射させた場合には、Ｈh 散乱を考慮して、式（３）の右辺に（１＋cos²Φ）／２を乗じた次式を考えれば良いことが知られている。
【００１８】
【数３】

ここで、λ0 は入射光の波長、ν＝（２πｎ）／λ0 、ｓ＝２sin （Φ／２）、ｎは媒体の屈折率、Φは散乱角、＜η² ＞は媒体中の誘電率ゆらぎ２乗平均（以下、＜η² ＞＝τとして、τを適宜使用する。）であり、γ（ｒ）は相関関数と呼ばれるものであり、次式（６）で表わされる。
【００１９】
Ｄｅｂｙｅの理論によれば、媒体の屈折率不均一構造が界面を持ってＡ相とＢ相に分かれて分散している場合には、誘電率のゆらぎに関して相関関数γ（ｒ）、相関距離ａ、誘電率ゆらぎ２乗平均τ等について、下記の関係式（７），（８）が成立する。
【００２０】
【数４】

不均一構造が半径Ｒの球状界面で構成されているとみなせば、相関距離ａは次式で表される。
【００２１】
【数５】

相関関数γ（ｒ）についての式（６）を用い、式（５）に基づいて自然光を媒体に入射させた時の有効散乱照射パラメータＥを計算すると結果は次のようになる。
【００２２】
【数６】

以上述べた諸関係から、相関距離ａ及び誘電率ゆらぎ２乗平均τを変化させることにより、散乱光強度、散乱光強度の角度依存性及び有効散乱照射パラメータＥを制御することが可能なことが判る。
図１は、横軸に相関距離ａ、縦軸に誘電率ゆらぎ２乗平均τをとり、有効散乱照射パラメータＥを一定にする条件を表わす曲線を、Ｅ＝５０［cm^-1］及びＥ＝１００［cm^-1］の場合について描いたものである。
Ｅの値は散乱導光媒体の散乱能の「強さ」を表わす指標であり、Ｅの値が大きければ散乱能が強く、Ｅの値が小さければ散乱能が弱い（透明に近い）ということになる。Ｅ＝０は無散乱状態に対応している。従って、大寸法で明るさが均一な面光源の用途にはＥの小さな光散乱導光体が適し、小寸法の面光源の用途にはＥの大きな光散乱導光体が適しているという一般論が成立する。
【００２３】
液晶表示装置のバックライト光源への適用時等に想定される通常サイズ（数ｃｍ〜数１０ｃｍの程度）の面光源を構成することを想定した場合、使用される光散乱導光体の有効散乱照射パラメータＥの実際的な値の範囲は、Ｅ＝０．５〜５０［cm^-1］の程度となる。
【００２４】
一方、相関距離ａは、光散乱導光体内部における個々の散乱現象における散乱光の方向特性に深く関わっている量である。即ち、上記（３）式乃至（５）式の形から推察されるように、光散乱導光体内部における光散乱は一般に前方散乱性を帯びているが、前方散乱性の強さが相関距離ａに依存して変化する。
【００２５】
図２は、これをａの２つの値について例示したグラフである。図において、横軸は散乱角度Φ（入射光線の進行方向をΦ＝０°とする。）を表わし、縦軸は自然光を仮定した場合の散乱光強度、即ち、上記（５）式をΦ＝０°に対して規格化した値、Ｖvh（Φ）／Ｖvh（０）を表わしている。
同図に併記されているように、ａ＝０．１３μｍ、上記（９）を用いて粒径に換算して２Ｒ＝０．２μｍの場合には、規格化散乱強度のグラフはΦに関する緩やかな減少関数となるが、ａ＝１．３μｍ、上記（９）式による粒径換算値で２Ｒ＝２．０μｍの場合には、規格化散乱強度のグラフはΦが小さい範囲で急激に減少する関数となる。
【００２６】
このように、光散乱導光体内の屈折率の不均一構造によって生ずる散乱は、基本的に前方散乱性を示し、相関距離ａの値が小さくなると前方散乱性が弱まり、１回の散乱における散乱角度範囲が広がる傾向を持つようになる。この事実自体は、実験的にも確認済みの事項である。
【００２７】
以上は光散乱導光体内部に分布した屈折率不均一構造による個々の散乱現象そのものに着目した議論であるが、光散乱導光体の光取出面から実際に出射される光の方向特性を評価する際には、光散乱導光体の内部側から光取出面に入射する光の全反射の現象と光出射時の界面透過率（光散乱導光体からの脱出率）を併せて考慮する必要がある。
【００２８】
基礎的な光学理論によって良く知られているように、外部の媒体（空気）に比して相対的に大きな屈折率を有する光散乱導光体の内部側から光取出面に光が入射した場合、光散乱導光体内外の媒体の屈折率によって決まる臨界角αc を入射角α（ここでは、光取出面に対して光散乱導光体内部に向けて立てた法線の方向をα＝０°とする。）が上回る場合には、外部（空気層）への出射（脱出）が起らない。
【００２９】
本願発明に使用される光散乱導光体の代表的な材料であるＰＭＭＡ（ポリメチルメタクリレート；屈折率１．４９２）では、αc ＝４２°となる。後述するように、本願発明で光散乱導光体のマトリックスとして好適に使用される樹脂材料の屈折率は、１．４〜１．７の範囲にあり、これに対応する臨界角αc の範囲は、３６．０°〜４５．６°となる。
【００３０】
従って、本願発明のように光取出面の側方に光入射面をとるケースでは（後述する各実施例参照）、光入射面から入射した光が不均一構造に遭遇して発生した１次散乱光が、直ちに上記臨界角条件を満たして光取出面から外部へ出射されることは極めて起り難いと考えられる。
【００３１】
即ち、本願発明が前提とする条件の下では、光散乱導光体内部における多重散乱の効果、光散乱導光体の光取出面側及び背面側の界面あるいはそれに面して配置された反射部材による反射の効果等が複合的に作用し合った結果、上記臨界角条件を満たすに至った光が外部に出射されるという現象が、光取出面からの光出射に大きく関与しているものと考えて良い。
【００３２】
そうだとすると、臨界角条件を満たした条件で光取出面方向に伝播する光について考えた場合、光入射面から入射した時点における光の伝播方向性を全体として保存するように作用する前記前方散乱性の効果は、上記複合的な効果によって相当程度薄められ、光の伝播方向分布にかなりの拡がりが生じている筈である。その結果、光散乱導光体から出射される光の方向特性は、臨界角条件を満たした光の光取出面における界面透過率（脱出率）の角度依存性に大きく左右されることになる。
【００３３】
一般に、臨界角条件（α＜αc ）をぎりぎりで満たすような条件における界面透過率は極めて低く（例えば、アクリル樹脂−空気界面の場合、Ｐ偏光成分４０％程度、Ｓ偏光成分２０％程度）、入射角αが臨界角αc を下回る量が増えれば界面透過率は急激に上昇し、５°乃至１０°以上下回った条件ではほぼ一定となる（アクリル樹脂−空気界面の場合、Ｐ偏光成分９０％以上、Ｓ偏光成分８５％以上）。
【００３４】
以上のことから、アクリル樹脂（αc ＝約４２°）の場合で言えば、光散乱導光体内部側から光取出面へ入射角α＝３５°〜４０°前後で入射した光が、光散乱導光体の光取出面からの光出射に最も寄与しているものと考えられる。このα＝３５°〜４０°の入射角で光取出面に入射した光は、スネルの法則に従って光取出面で屈折し、光取出面に外部に向けて立てた法線に対して６５°±１０°程度の範囲内に収まる方向（即ち、光取出面表面に対して１５°〜３５°程度立ち上がった方向）へ出射されることになる。
【００３５】
光散乱導光体にアクリル樹脂以外の材料を使用した場合でも、実際的な材料の屈折率の範囲は１．４〜１．７の程度であるから、上記角度に数度程度のずれを見込めば、同様の議論が成立する。
【００３６】
但し、ここで注意すべきことは、相関距離ａの値が余り小さくなると、個々の散乱における前方散乱性そのものが薄れてしまい、一次散乱のみで後方散乱を含む広角度範囲の散乱光が発生するようになる為に、この指向性がぼやけてしまうことである。本願発明では、このような指向性鈍化現象を顕著に示さないような特性を有する光散乱導光体を使用する。以下、このような光散乱導光体を「指向出射性」の光散乱導光体と呼ぶことにする。
【００３７】
本願発明が光散乱導光体の相関距離ａについて指定している範囲（０．０６μｍ≦ａ≦３５μｍ）には、この条件が考慮に入れられている。光散乱導光体として、ポリマーマトリックス中に異屈折率粒子を均一に分散させたものを使用する場合には、前記（９）式から、上記相関距離の範囲は異屈折率粒子径の範囲、０．１μｍ〜５４μｍに相当していることが判る。
【００３８】
次に、本願発明の偏光化機能付面光源装置に使用される指向出射性の光散乱導光体が楔形断面形状部分を有している意味について説明する。
図３は、本願発明の面光源装置に用いられる光散乱導光体の断面の基本形状を内部における繰り返し反射の様子と共に記したものである。
【００３９】
同図において、１は平行光束化素子を構成する指向出射性の光散乱導光体であり、Ｂ0 は光源Ｌから出射され、光入射面２から光散乱導光体１の内部に取り込まれる光を代表する代表光線の進路を示したものである。光源Ｌは楔形の相対的に断面積が大きい側端部にあたる光入射面２に面して配置されるから、代表光線Ｂ0 として図示した如く略水平方向に伝播するものを想定する。
【００４０】
この代表光線Ｂ0 の挙動を考察してみると、光線Ｂ0 は、一定割合で散乱による方向転換を受けながら、光取出面３及び該面に対して傾斜した裏面４で反射を繰り返しながら、光散乱導光体１の厚みの薄い末端部分へ近づいていく。面３，４の表面における内部反射は正反射であるから、個々の反射における入射角と反射角は当然等しい（θ1 ，θ2 ，θ3 ・・・・）。両面３，４の傾斜関係から、光取出面３における各反射について、θ2 ＞θ4 ＞θ6 ・・・の関係が成立する。
【００４１】
ここで、各反射時における界面透過率を考えてみると、光散乱導光体の指向出射性の説明中で述べたと同様の議論により、θi ＞αc （臨界角；ＰＭＭＡ−空気界面で４２°）の条件では全反射が起こり、θi がαc を下回ると透過率が急上昇し、θi が所定値（ＰＭＭＡ−空気界面で３５°前後）以下で透過率はほぼ一定となる。図では、θ2 ＞αc ＞θ4 ＞θ6 の関係によって、出射光Ｂ4 ，Ｂ6 が生じている様子が描かれている。
【００４２】
このような効果は、代表光線Ｂ0 （無散乱光）に限らず、１次散乱光や多重散乱光についても類似した形態で生じている筈であるから、全体としては、この効果によって光入射面２から遠ざかる程光取出面３からの光出射率が高められていることになる。この効果を、光入射面２からの距離ｘの関数ｆ（ｘ）で評価すると、ｆ（ｘ）はｘに関する増加関数である。一方、光入射面２に近い部分では光源Ｌに近いという効果が直接光、散乱光いずれについても働く。この近接効果をｇ（ｘ）で評価すれば、ｇ（ｘ）はｘに関して減少傾向を有する関数とみることが出来る。
【００４３】
従って、近接効果ｇ（ｘ）とｆ（ｘ）が相殺される関係にあり、光散乱導光体１の出射光強度（明るさ）が均一化される作用が生じることになる。また、光散乱導光体１内の光が光取出面３に入射する機会も、楔形状の効果によって入射面２から遠ざかるにつれて増大する傾向を持つと考えられるから、この傾向も上記増加関数ｆ（ｘ）で評価される効果を補強しているものと考えられる。
【００４４】
なお、両面３，４のなす角度ψに絶対的な制限は特にないが、明るさのレベル、均一度、指向特性等を考慮した実際的な範囲として、０．５°≦ψ≦６°という値が得られている。また、傾斜した裏面４（場合によっては光取出面３）を曲面とすることにより、反射角θ1 ，θ2 ，θ3 ・・・・の増大推移を制御し、より望ましい特性を実現することも可能である。また、楔形状の断面は必ずしも光散乱導光体１の全体に亙る必要はなく、光源の映り込みによる輝度むらを防止する為に、光入射面２の近傍の傾斜を緩めて平坦化したり、場合によっては逆傾斜部を形成する場合もある。
【００４５】
以上述べた断面楔形状の光散乱導光体を採用したことによる効果は、裏面４に沿って反射体５を配置した場合にも同様に成立することは明らかであり、入射面２から入射した光をより遠方まで導光させ、また、光散乱導光体１の指向出射性を乱さないという観点から、反射体５として正反射性を有する反射体を配置することがより好ましい。
【００４６】
本発明者は、このような楔形状断面部分を有する指向出射性の光散乱導光体と近似的なブリュースター角条件を利用した偏光分離手段を結合することにより、多重的な偏光化過程が発生し、高い光エネルギ利用効率で光束の偏光化が達成されるという原理を見い出した。本願発明は、この原理に基づいた偏光化機能付の面光源装置を提供したものであり、光散乱導光体とブリュースター角条件を利用した偏光分離手段の組合せ方、それによる多重的な偏光化過程の具体的内容については、次の実施例の中で述べることとする。
【００４７】
【実施例】
図４は、本願発明に係る偏光化機能付の面光源装置の第１の実施例を断面図で示したものである。同図中、図３と共通する要素については同じ符号が使用されている。符号１は楔形断面形状を有する指向出射性の光散乱導光体からなる平行光束化素子を表わしており、ここではその材料としてポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料粒子（径２μｍ、屈折率＝１．４３４５）を０．０７ｗｔ％の割合で一様に分散させたものが使用されている。平行光束化素子１のサイズは、図中左右方向の長さが６８ｍｍ、幅が８５ｍｍ、光入射面２側の端部で４．０ｍｍ、末端部６で０．２ｍｍとした。
【００４８】
Ｌは平行光束化素子１の入射面２から１ｍｍ離して配置された直径３ｍｍの蛍光ランプで、このランプＬから右方に向かって光を入射させ、光取出面３から平行化された光束を取り出す配置とした。また、Ｒは入射面２から入射する光量を可能な限り多く確保する為に適宜配置される反射体で、ここでは銀箔製シートでランプＬを取り囲むように配置した。
【００４９】
平行光束化素子１の裏面４には、光拡散インキパターンや凹凸拡散面等、強い光散乱を生じさせる為の処理は特に施されていない。符号５は裏面４に対向して配置された銀箔製シートからなる反射体で、裏面４から出射された光を平行光束化素子１内に復帰させるものである。また、空気層７を挟んで平行光束化素子１の光取出面３と対向する位置には、偏光分離手段としての偏光分離板８が配置され、更にその外側には空気層９を挟んで光出射方向修正素子１０が配置されている。符号１１は、光出射方向修正素子１０の光出射面であり、面光源装置としての光出射面でもある。この面光源装置を液晶表示装置のバックライト光源として使用する場合には、光出射方向修正素子１０の更に外側に液晶表示パネルが配置される。
【００５０】
偏光分離板８は、透明な光学材料からなる板状体で構成され、ここでは代表的な光学ガラスであるＢＫ−７（屈折率１．５１６３）からなる厚さ１ｍｍの平坦な板状部材を使用した。空気層７の屈折率ｎ0 ＝１として、ブリュースター角の値は５６．６０°となる。
【００５１】
以下、図５及び図６を順次参照図に加え、この偏光分離板８と平行光束化素子１を組み合わせた第１の実施例における偏光化機能の概要について説明する。 図４において、ランプＬの放射光及び反射体Ｒからの反射光は、光入射面２から平行光束化素子１の内部に進入し、平行光束化素子１内部の屈折率不均一構造（ここでは、異屈折率粒子）による散乱を受けながら、平行光束化素子１の末端部６に向けて導光される。その過程において光取出面３から徐々に光が出射されるが、「作用」の欄で述べた理由により、出射光は平行光束化されて明瞭な指向性を有するものとなっている。そこで、この平行光束を光線Ｃ0 で代表させ、平行光束化素子１から出射された光の挙動を光線追跡形式で記したものが図５である。
【００５２】
「作用」の欄で既述した通り、平行光束化素子１の基材にＰＭＭＡを使用したケースでは光取出面３に立てた法線Ｈ0 から測って６５°前後の方向へ強く光出射が起ることから、代表光線Ｃ0 の出射角は６５°とする。
【００５３】
平行光束化素子１の光取出面３から出射された代表光線Ｃ0 は、空気層７を直進して偏光分離板８の下面８ａに入射し、偏光分離板８内に進入する光線Ｃ1 と反射して再び平行光束化素子１に向かう光線Ｃ2 に分割される。光線Ｃ1 は面８ａで屈折し、偏光分離板８内を直進し、偏光分離板８の上面８ｂに至り、外部出射光線Ｃ3 と内部反射光線Ｃ4 に分割される。内部反射光線Ｃ4 は更に下面８ａに戻り、再度内部反射光線Ｃ7 と空気層７へ進む光線Ｃ8 に分割される。内部反射光線Ｃ7 は上面８ｂで、再度外部出射光線Ｃ9 と内部反射光線Ｃ10に分割される。以下、内部反射光線は同様の過程を繰り返す。
【００５４】
一方、空気層７を平行光束化素子１へ向かって直進する光線Ｃ2 及びＣ8 は、光取出面３で平行光束化素子１内に再入射する光線Ｃ11，Ｃ13と反射光線Ｃ12，Ｃ14 に分割される。反射光線Ｃ12，Ｃ14 は再度偏光分離板８へ向い、Ｃ0 と同様の経路を辿る。
【００５５】
このような多重反射／透過のプロセスを通して、光線Ｃ0 の光エネルギも各界面３，８ａ，８ｂにおいて反射光線と透過光線に分割・分配されるが、その分配割合はＰ偏光成分とＳ偏光成分とで大きく異なっている。また、偏光分離板８を構成する厚さ１ｍｍのＢＫ−７板の内部光透過率は９９．９％以上であり、その吸収損失は無視出来る程小さい。そこで、光線Ｃ0 をＰ偏光成分のエネルギとＳ偏光成分のエネルギを１００づつ等量に有する偏光度０の自然光とした場合の各光線Ｃ1 〜Ｃ14の偏光成分別エネルギ量を計算し、その結果を図中に併記した。
【００５６】
例えば、光線Ｃ0 がＣ1 とＣ2 と分割される際には、Ｐ偏光成分の透過率は極めて高く９８．８％を示すが、Ｓ偏光成分の透過率は７６．６％しかない。従って、光線Ｃ2 は殆どＳ偏光成分のみに偏光した光となっている。即ち、ＢＫ−７のブリュースター角５６．６０°から１０°程度ずれた範囲では、近似的にブリュースター角条件が満たされていると言うことができ、反射光線Ｃ2 のＳ偏光率は極めて高い（もし、Ｃ0 の入射角がブリュースター角５６．６０°に一致すれば、反射光線Ｃ2 のＳ偏光率は当然１００％となる）。
【００５７】
光線Ｃ1 が偏光分離板８の上面８ｂに入射した場合の偏光成分別反射率も、Ｐ偏光成分１．２％、Ｓ偏光成分２３．４％となる。従って、外部に出射される光線Ｃ3 の偏光成分別エネルギ量はＰ成分９７．６、Ｓ成分５８．７であり、相当程度の偏光度を有していることが判る。同様の計算をＣ4 以下について行なった値は図中に示されている。それらの数値から明かな如く、光線分割が繰り返されるにつれて、ＰＳ各偏光成分のエネルギ量が急激に減少するので、図５に示した光線Ｃ3 とＣ9 から近似的に外部出射光の偏光成分別エネルギ量を見積ると、Ｐ偏光成分＝９７．６、Ｓ偏光成分＝６１．９となる。
【００５８】
このように、図５に示された光線のみを考慮した場合でも、相当程度に偏光化された出射光束が得られていることが判るが、本願発明はこのようなプロセスのみに頼って偏光化機能を果たすものではない。本願発明は、平行光束化素子の光取出面に対向して配置される偏光分離手段（第１の実施例ではＢＫ−７板）から平行光束化素子に戻された光（以下、戻り光と言う。）を再利用し、最終的な出射光の偏光度を更に向上させるものである。
【００５９】
図５の例で言えば、光線Ｃ11とＣ13に付記された数値に示したように、戻り光はほぼ完全にＳ偏光となっている。この戻り光は、平行光束化素子１を構成する光散乱導光体内を伝播する過程で再び散乱、反射等のプロセスを経た上で、その大部分が光取出面３から出射される。その際の出射指向性を考察してみると、入射面２から入射した場合程ではないが、やはり全体として図５で右方に向かう前方散乱性は保存されているから、「作用」の欄で述べた原理により、やはり光線Ｃ0 の出射方向で代表し得る弱い指向性を有しているものと考えられる。
【００６０】
ところで、大半がＳ偏光成分からなる光線Ｃ11（Ｓ偏光成分１８．２）やＣ13（Ｓ偏光成分１０．６）は、平行光束化素子内で上記散乱、反射等のプロセスを経ることによってその偏光方向が乱されることになる。これを偏光スクランブル効果と呼ぶことにすると、この偏光スクランブル効果によって、Ｃ11あるいはＣ13に由来する光取出面３からの出射光のＳ偏光度はかなり低下しているものとみて良い。もし、偏光スクランブル効果が完全であり、無損失で光取出面３から再出射されると仮定すれば、そのエネルギ量は、Ｃ11由来分についてＰ偏光成分９．１、Ｓ偏光成分９．１であり、Ｃ13由来分については、Ｐ偏光成分５．３、Ｓ偏光成分５．３となる。
【００６１】
両者を加算すると、Ｐ偏光成分＝１４．４、Ｓ偏光成分＝１４．４となる。この光がＣ0 と同様の履歴を経るものとすれば、（１４．４／１００）×９７．６＝１４．１のエネルギ量が偏光分離板８の上面８ｂからの出射光束のＰ偏光成分に加算される。従って、このモデルから近似的に評価される最終的なＰ偏光成分エネルギ量は９７．６＋１４．１＝１１１．７となる。また、Ｓ偏光成分エネルギ量は６１．９＋（６１．９／１００）×１４．１＝７０．６となる。
【００６２】
即ち、本願発明では、平行光束化素子１の光取出面３から出射された光束の一部がＳ偏光化されて戻り光となり、その少なくとも一部が平行光束化素子１内で無偏光化されて平行光束化素子１の光取出面３から再出射され、再度偏光分離板によるＳ偏光排除作用を受けるという、リサイクル的な偏光化過程が取り入れられている。それ故、上記事例で説明した如く、少なくとも原理的には、自然光に含まれるＰ偏光成分を１００％以上に増幅する作用を果たさせることも可能である。このような特徴は、本願発明に固有のものであり、以下に述べる各実施例においても共通して備わっている特徴である。
【００６３】
なお、上記第１の実施例の説明では平行光束化素子１の（初回の）出射光を出射角６５°のＣ0 で代表させたが、出射角の条件が１０°程度変化したとしても現象の本質は殆ど変化しない。図６は、これを理解する為のグラフで、横軸にＢＫ−７板への入射角（＝光取出面３からの出射角）をとり、縦軸にＰ，Ｓ各偏光成分の１回透過の透過率（８ｂからの全出射エネルギ／８ａへの全入射エネルギ；戻り光の再入射は考えない。）をとったものである。グラフから判るように、５５°〜７５°のほぼ全域に亙ってＰ偏光成分の透過率は約８０％を越えており、Ｓ偏光成分の透過率はそれを約２０％以上下回っている。従って、光取出面３からの出射光束の伝播方向に多少の拡がりあるいはずれがあっても、上記説明の本質的な部分に変更を要しないことは明らかである。
【００６４】
第１の実施例に関してここまで述べたことから判るように、光源Ｌ、平行光束化素子１及び偏光分離手段（第１の実施例ではＢＫ−７からなる偏光分離板）８が、偏光化された光束を得る面光源装置を構成する為の基本的な構成要件となっている。しかし、上記偏光化のプロセスの説明からも判るように、代表光線Ｃ0 の大きな出射角（ここでは、６５°）で特徴付けられる指向性が偏光分離手段８からの出射光束についても強く残っており、通常の用途（液晶表示装置のバックライト光源等）で要求されることの多い正面方向あるいはこれに近い方向に光を出射する面光源装置を提供する上で好ましいとは言えない。
【００６５】
図４に示されているように、偏光分離板８の外側に配置される光出射方向修正素子１０は、このような要求に応えるもので、プリズム作用を通して偏光分離板８の光出射面８ｂから出射される指向性の光束の伝播方向を正面方向に修正する機能を有している。以下、図７（Ａ），（Ｂ）を参照図に加えて、この光出射方向修正素子の光出射方向修正機能について説明する。
【００６６】
図７（Ａ）は、光出射方向修正素子の典型的な構造と配置を説明する図、図７（Ｂ）は変形型の配置を示したものであり、両図は図４，図５に示した配置における偏光分離板及び光出射方向修正素子の周辺部分を抽出拡大した断面図に、光線Ｃ3 ，Ｃ9 の追跡経路を併記した形で提示されている。
両図において、光出射方向修正素子１０，１０’は、例えばポリカーボネート（ＰＣ；屈折率ｎpr＝１．５９）のような光学材料からなり、一方の面に多数のプリズム面１０ａ，１０ｂ（頂角θpr）あるいは１１ａ，１１ｂ（頂角θ'pr ）が形成されている。光出射方向修正素子１０，１０’は、そのプリズム形成面を図７（Ａ）のように光入射面とするか、逆に図７（Ｂ）のように光取出面として使用する。
【００６７】
先ず、図７（Ａ）では、前記の図５の関連説明から、偏光分離板８の光取出面８ｂに対して６５°の出射角で出射されるように描かれているＣ3 ，Ｃ9 は、前記代表光線Ｃ0 に由来して偏光分離板８から出射される光束をほぼ代表しているものと考えられる。これら代表光線Ｃ3 ，Ｃ9 は、空気層９（屈折率ｎ0 ＝１．０）を直進した後、光出射方向修正素子１０のプリズム面１０ａに垂直に近い角度で入射する。
【００６８】
プリズム面１０ａと相反する側のプリズム面１０ｂに入射する光量の割合は相対的に小さいと考えることが出来るから、代表光線Ｃ3 ，Ｃ9 はプリズム面１０ｂまでほぼ直進して正反射され、光出射方向修正素子１０の平坦な光取出面１１に対して垂直に近い角度で入射し、該面１１から垂直方向に近い角度で出射する光束Ｄとなる。
【００６９】
入射側のプリズム面１０ａの傾斜角θa を、光束Ｃ3 ，Ｃ9 がほぼ垂直に入射するように設定すると共に（ここではθa ＝２５°）、他方のプリズム面１０ｂの傾斜角θb を内部反射光が平坦な光取出面１１にほぼ垂直に入射するように設定（ここではθb ＝６５°／２=３２．５°）すれば、光束Ｄの方向を垂直方向により正確に一致させることが出来る。このように、プリズム面の形成角度を選択することを通して、光束Ｄの方向特性を調整することが可能である。
【００７０】
次に、図７（Ｂ）は、光出射方向修正素子１０’をそのプリズム面１１ａ，１１ｂが外側に向く配置とした場合について、代表光線Ｃ3 ，Ｃ9 の挙動を説明した断面図であり、図７（Ａ）の場合と同様に、代表光線Ｃ3 ，Ｃ9 は、空気層９（屈折率ｎ0 ＝１．０）を直進した後、光出射方向修正素子１０’の平坦面１０’ａに対して傾斜した角度で入射し、上方に向けて屈折され、その大半は反対側のプリズム面１１ａ から垂直に近い角度で光束Ｄ’として出射される。光出射方向修正素子１０’を構成する材料の屈折率やプリズム面１１ａ，１１ｂの傾斜角θ'a ，θ'bの値によっては、プリズム面１１ａから一旦空気中に出射された上で対向するプリズム面１１ｂで正反射されて正面方向へ向かう光路が利用される場合もある。
【００７１】
このように、図４の配置に、図７（Ａ），（Ｂ）いずれの配置を適用した場合にも、偏光分離板８からの出射光の方向特性や光出射方向修正素子を構成する材料と関連させて各プリズム面の傾斜角等を適当に選択することにより、相当程度の範囲に亙って光の出射方向を制御出来る。
【００７２】
なお、光出射方向修正素子１０，１０’は、図示したように列状にプリズム面が形成されたものに限らず、いかなる型のものを使用しても良い。例えば、三角錐状あるいはドーム状の突起群を分布させたフィルム、かまぼこ形断面を有する列状凸部を有する板状素子等が考えられる。また、複数枚重ねて使用することも考えられる。
【００７３】
次に、本願発明の第２の実施例について説明する。図８は、図４と同様の形式で本願発明に係る偏光化機能付の面光源装置の第２の実施例を表わしたものである。同図中、図４と共通する要素には同じ符号が使用されており、この第２の実施例は、偏光分離手段８，８’に関連した部分を除いて第１の実施例と全く同じ構成を備えている。そこで、この共通部分については説明を省き、偏光分離手段に関連した部分に絞って説明を行なうこととする。
【００７４】
第２の実施例において採用される偏光分離手段は、平行光束化素子１の光取出面３に沿って平行配置される２枚の偏光分離板８，８’を備えている。各偏光分離板８，８’は吸収損失の少ない光学材料からなるもので、ここでは、共に板厚１ｍｍのＰＭＭＡ（ポリメチルメタクリレート；屈折率１．４９２、ブリュースター角＝５６．１７°；内部透過の吸収損失は０．０１％以下で、ＢＫ−７の場合と同様、無視出来る。）の板状部材を用いた。
【００７５】
内側の偏光分離板８と外側の偏光分離板８’は適当なスペーサ（図示省略）によって互いに０．５ｍｍ離隔配置され、その間隙に空気層９が確保されている。
【００７６】
また、外側の偏光分離板８’の外側には、第１の実施例と同様な光出射方向修正素子１０が空気層９’を挟んで配置されている。
【００７７】
図９は、この２枚の偏光分離板８，８’と平行光束化素子１を組み合わせた第２の実施例における偏光化機能の概要について説明する図である。図５の場合と同様に、平行光束化素子１の光取出面３から出射される平行光束を出射角６５°の光線Ｃ0'で代表させ、平行光束化素子１から出射された光の挙動が光線追跡形式で記されている。また、各光線分岐時に伝播されるエネルギ量が、図５の場合と同じ表記法に従って併記されている（光線Ｃ0'のＰ偏光成分＝Ｓ偏光成分＝１００）。
【００７８】
代表光線Ｃ0'は、空気層７を直進して１枚目の偏光分離板８の下面８ａに入射し、偏光分離板８内に進入する光線Ｃ1'と、反射して再び平行光束化素子１に向かう光線Ｃ2'とに分割される。各光線Ｃ1'，Ｃ2'は、以後、図示したような種々の分岐経路を辿って、一部は空気層９を経て２枚目の偏光分離板８’の内側面８ａ’へ向い、一部は平行光束化素子１へ戻り光として入射する。
【００７９】
この間の経緯は、２枚目の偏光分離板８’が関与しない部分に関する限り、図５で示した第１の実施例の場合と全く同様であるから、詳しい説明は省略する。但し、ＰＭＭＡからなる偏光分離板８の屈折率がここでは第１の実施例の場合（ＢＫ−７）と若干異なる為に、各界面８ａ，８ｂの入出射時における屈折角がやや変化し、それに応じてＰ偏光成分とＳ偏光成分についての分岐割合が少量だけ変わっている。
【００８０】
１枚目の偏光分離板８から出射された光線Ｃ3'は、２枚目の偏光分離板８’の内側面８’ａに到達し、偏光分離板８’の内部へ進入する光線Ｃ2"とＣ1"に分割される。以後の経路は、１枚目の偏光分離板８の場合とほぼ同じであるが、偏光分離板８’の内部から内側面８’ａを通って空気層９へ出た光線の相当部分が１枚目の偏光分離板８の外側面８ｂへ入射し、一部がその内部へ戻り、一部が反射されて２枚目の偏光分離板８’へ再度向かうという経路が多重的に形成されることに注意することが必要である。この間に１枚目の偏光分離板８へ戻った光の一部が更に平行光束化素子１へ戻る現象も僅かではあるが生起されている筈である。
【００８１】
以上、述べたように、２枚（あるいはそれ以上の）偏光分離板８，８’を偏光分離手段として配置した場合には、光線経路は極めて複雑に分岐したものとなるから、最終的に２枚目の偏光分離板８’の外側面から出射されるＰ，Ｓ各偏光成分の量を厳密に計算することは困難である。
【００８２】
そこで、光線経路が分岐する度に伝播されるエネルギ量が逓減されることを利用して、図示された経路の範囲で近似計算を行なうと、光線Ｃ"3〜Ｃ"6の各数値の積算値から、Ｐ偏光成分＝９４．９、Ｓ偏光成分＝４６．７と評価される。
【００８３】
これを第１の実施例における対応数値、Ｐ偏光成分＝９７．６、Ｓ偏光成分＝６１．９と比較してみると（偏光分離板の材料の違いの影響は小さいことに注意。）、Ｐ偏光成分が抽出・保存状態はいずれの場合にも良好である一方、Ｓ偏光成分が大幅に低下していることが判る。
【００８４】
この事実からも判るように、平行光束化素子１から６５°前後で出射された光を１枚またはそれ以上の枚数の偏光分離板を介して取り出す場合には、１枚の偏光分離板の介在毎に、Ｐ偏光成分の大半を保存しながらＳ偏光成分の約３割〜４割程度が排除されて行く。
【００８５】
そして、本願発明における偏光分離板の偏光化作用は、実施例１に関連して既に述べたように、このＰ偏光保存／Ｓ偏光排除現象に加えて、Ｓ偏光成分に富んだ戻り光が平行光束化素子内に復帰して偏光状態がスクランブルされた後に偏光分離板（１枚あるいは２枚以上）のＰ偏光保存／Ｓ偏光排除作用を再度受けるというリサイクルプロセスを通して、Ｐ偏光成分がより富化されるという現象を巧妙に利用したものである。
【００８６】
第２の実施例における戻り光量（Ｓ偏光成分）を評価すると、図９に併記したデータから、１７．５＋１０．４＋７．４＋４．８＝４０．１となる。平行光束化素子１の偏光スクランブル作用が完全であれば、約２０のＰ偏光成分を有する平行光束化素子再出射光が得られる。その９４．９％が保存されて２枚目の偏光分離板８’から出射されれば、約１９の偏光成分が上乗せされる。これを戻り光除外評価分の９４．９に加算すれば、最終的に約１１４のＰ偏光成分を含む偏光出力が得られることになる。
【００８７】
なお、偏光分離板を２枚使用した程度では、光線Ｃ3"〜Ｃ6"等からなる出射光束の指向性が大きく崩れることは無い。従って、この第２の実施例においても、２枚目の偏光分離板８’の次段に配置された光出射方向修正素子１０によって、第１の実施例の場合とほぼ同等の光出射方向修正作用が発揮されることになり、光出射方向修正素子１０の光出射面１１から正面方向に伝播する偏光化光束を出射させることが出来る。
【００８８】
次に、上記各実施例で利用されている偏光分離板について、光入射時のブリュースター角条件の満足度をより向上させるよう更に工夫を加えた本願発明の第３の実施例について述べる。なお、この実施例の全体構成は偏光分離板自体の構造を除き、図４に示した第１の実施例と同様であるから、ここでは全体構成の説明は省略し、図４あるいは図５における平板型の偏光分離板８を図１０に示した波形の断面構造を有する偏光分離板８”（以下、「波形偏光分離板」と呼ぶ。）に読み換えると共に、同図に併記した如く、平行光束化素子１からの出射光束を出射角６５°の代表光線Ｃ0 で代表させて説明を行なう。
【００８９】
図１０（Ａ）には、波形偏光分離板８”の断面形状が示されており、図示された通り、比較的短い急斜面部分８１，８３と比較的長い緩斜面部分８２，８４の繰り返しからなる等厚の波型形状を呈している。この波形偏光分離板８”を構成する材料としては、適当な屈折率を有する透光性の素材が利用されるが、ここではＰＭＭＡ（ポリメチルメタクリレート；屈折率１．４９２、ブリュースター角５６．１７°）が使用されている。
【００９０】
図１０（Ｂ）は、図１０（Ａ）中に○印で囲まれた部分（繰り返し形状の１単位分）を拡大描示したもので、平行光束化素子１からの出射光束を代表する光線Ｃ0 の光線追跡図が併記されている。本実施例の本質的な特徴は、緩やかな斜面部分の入射側８２の傾斜が、代表光線Ｃ0 に対してブリュースター角条件を満たすように選択されていることである。ここでは、平行光束化素子１の光取出面３に立てた法線Ｎに対して６５°の出射角を持つ代表光線Ｃ0 が面８２に入射する際の入射角がブリュースター角５６°（概算）に合致するように、面８２の傾斜角が光取出面３と平行な面Ｍに対して９°に設定されている。
【００９１】
即ち、この角度条件の下では、代表光線Ｃ0 から分岐した反射光線Ｒ1 に含まれるＰ偏光成分は理論的には０であり、すべてのＰ偏光成分が面８２を透過することになる。特に、第１あるいは第２の実施例との比較で言えば、平行光束化素子１の光取出面３からの出射角が直角に近い（より寝た方向の）光に対してもＰ偏光成分の面８２，８４の透過率が高いという利点がある。
【００９２】
波形偏光分離板８”内部に進入したＰ偏光成分を多く含んだ光線Ｔ1 は、対向傾斜面８４で内部反射光線Ｔ2 と６５°の出射角を持った出射光線Ｔ3 に分岐するが、内部反射光線Ｔ2 にＰ偏光成分は殆ど含まれない（図５中の光線Ｃ2 あるいは図９中の光線Ｃ2'に付記されたデータ参照）。
【００９３】
内部反射光線Ｔ2 は、更に面８２で内部反射光線Ｔ4 と平行光束化素子１へ向かう光線Ｒ2 に分岐する。以下、多重的に繰り返される内部反射／出射のプロセスは、第１の実施例（特に、図５）で説明したものと類似したものであり、プロセスの進行に伴って運ばれるエネルギ量は急激に小さくなる。
【００９４】
従って、この実施例の構成によれば、偏光分離板８”を配置したことによるＰ偏光成分の損失量が極めて小さくなるという特徴があり、第１，第２の実施例で説明したと同様の戻り光に対する偏光スクランブル効果と平行光束化素子１からの再出射によるＰ偏光成分の更なる上乗せと相俟って、Ｐ偏光成分をより多く含む出射光を生成することが出来る。この面８４からの出射光に対して光出射方向修正素子１０を配置すれば、前記第１，第２の実施例と同様の光出射方向修正が行われることは言うまでもない。
【００９５】
急斜面８１，８３の傾斜角については、平行光束化素子１からの出射光が可能な限り光が入射しないよう代表光線Ｃ0 の方向に平行となるような角度に設定されることが望ましい。ここでは、９０°−６５°＝２５°とされている。急斜面８１，８３と緩斜面８２，８４の繰り返し周期について特に制限は無いが、一般には、稜線部８５，８６間で測った厚みを抑え、面光源として明かさの均一性を保つという観点から、短い周期とすることが好ましい。ここでは、稜線部８５，８６間で測った厚さが０．５ｍｍとなるような繰り返し周期が選ばれている。
【００９６】
次に、偏光分離手段として異屈折率材料からなる多層膜を備えた偏光分離板を利用した本願発明の第４の実施例について説明する。なお、この実施例の全体構成も、偏光分離板自体の構造を除き、図４に示した第１の実施例と同様であるから、ここでは全体構成の説明は省略し、図４あるいは図５における平板型の偏光分離板８を、図１１に示した多層膜型偏光分離板１８に読み換えた構成を想定するものとする。
【００９７】
また、図１１中に併記されているように、平行光束化素子１からの出射光束の出射角がやや高角度側（寝た方向）にずれた場合を想定し、７０°の出射角を持つ代表光線Ｄ0 で代表される状態にあるものとして説明を行なう。（「作用」のの欄で説明したように、平行光束化素子１の光取出面３からの出射光束の出射方向の中心は、平行光束化素子１を構成する光散乱導光体の屈折率や相関距離ａの値等によって、数度から１０度程度の変動幅がある。）
多層膜型偏光分離板は、各隣り合う層の材料に屈折率の異なる透明材料を使用するという条件で、数層（原理的には最低２層）〜数１０層の薄膜を積層形成した構造を有し、図１１にはその３層分の断面と代表光線Ｄ0 の主要光路が例示されている。多層膜型偏光分離板１８は、入射側から順に二酸化チタン（ＴｉＯ2 ；屈折率ｎ1 ＝２．３）層１８１、二酸化珪素（ＳｉＯ2 ；屈折率ｎ2 ＝１．４６）層１８２、二酸化チタン（ＴｉＯ2 ；屈折率ｎ3 ＝ｎ1 ＝２．３）層１８３で構成されており、以下、総層数に合わせて二酸化チタン層と二酸化珪素層が交互に積層された構造を有している。屈折率が更に異なる材料の層を積層させることもあり得る（例えば、二酸化ジルコニウムＺｒＯ2 、一般の酸化数を持った酸化チタンＴｉＯx の層）。
【００９８】
このような多層膜型の偏光分離板１８の偏光分離原理は、異屈折率材料間に形成される界面におけるＳ偏光成分とＰ偏光成分の反射特性の違いを利用したものであり、その点では、前述の第１〜第３の実施例における偏光分離板手段と共通した特徴を有していると言うことが出来る。
【００９９】
図１１に描かれているように、平行光束化素子１からの出射光束を代表する代表光線Ｄ0 が、空気層７（屈折率ｎ0 ＝１．０）からＳ偏光成分Ｉs ＝１００、Ｐ偏光成分Ｉp ＝１００の相対強度を以て第１層１８１に入射すると、層１８１の内部へ進入する光線Ｄ1 と反射光線Ｄ2 が生じる。
【０１００】
その際の反射率は、Ｓ偏光成分についてはＲs ＝５１．８％であるが、Ｐ偏光成分についてはＲp ＝０．５５％と極めて小さい。即ち、Ｓ偏光成分は半分程度しか第１層１８１内に進入出来ないが、Ｐ偏光成分についてはほぼその全量が界面を通過して第１層１８１内に進入する。
【０１０１】
この光線Ｄ2 が第２層との界面に到達すると、再び光線Ｄ3 とＤ4 に分岐する。その際の反射率は、Ｒs （Ｓ偏光成分）＝９．３％、Ｒp （Ｐ偏光成分）＝１．９％である。即ち、Ｓ偏光成分の９割程度が第２層１８２内に進入する一方、Ｐ偏光成分についてはその大半が界面を通過して第２層１８２内に進入することになる。
【０１０２】
同様に、第２層１８２と第３層１８３の界面においては、Ｄ5 とＤ6 の分岐が起こり、その際の反射率はＲs （Ｓ偏光成分）＝９．３％、Ｒp （Ｐ偏光成分）＝１．９％となる。
【０１０３】
このように、各界面に遭遇する度にＰ偏光成分の大部分が次層へ伝播されていくのに対し、Ｓ偏光成分の相当部分が排除されていくという現象が起る。多重反射及び吸収損失の効果は小さいとして、本事例における第３層進入時の偏光成分の見積りを行なうと、Ｓ成分；Ｉs ＝３９．７，Ｐ成分；Ｉp ＝９５．７という値が計算される。層数が更に増えれば、各数値Ｉs ，Ｉp は等比数列的に減少すると考えられる。
【０１０４】
その際の平均的な公比をｒs （Ｓ偏光成分），ｒp （Ｐ偏光成分）とすれば、ｒs ＜ｒp であり、ｒp は１を僅かに下回る程度となる。
従って、多層膜型偏光分離板１８を構成する層の総数が多い程Ｐ偏光成分の「純度」は高くなると考えられる。このような傾向は、代表光線Ｄ0 の出射角が７０°である場合に限らず、相当幅広い角度条件の下で成り立つものである。
【０１０５】
図１２〜図１４は、これを説明する為のグラフで、本実施例の層構成における各界面の光透過率がＰ偏光成分、Ｓ偏光成分に分けて記されている。これらのグラフから直ちに読み取れるように、代表光線Ｄ0 の層１８１への入射角が７０°から１０°程度ぶれたとしても、各界面におけるＰ偏光成分の透過率は１００％に近いままであり、且つ、Ｓ偏光成分の透過率はＰ偏光成分の透過率を一貫して下回っている。
【０１０６】
これは、上記多層膜型偏光分離板のＰ偏光成分純化機能が特殊な条件下だけで成立するものではないことを物語っている。
以上のことから、本実施例のような多層膜型の偏光分離板を利用した構成は、高い偏光度（Ｐ偏光成分の純度）の出射光を必要とするケースに適した特徴を備えていることが判る。
【０１０７】
参考の為に、図１５に実証データの１例を示した。これは厚さ１ｍｍの光学ガラス板ＢＫ−７（屈折率１．５１６３）上に、ＴｉＯx （屈折率２．３前後）、ＳｉＯ2 （屈折率１．４６）及びＺｒＯ2 （屈折率２．０）からなる多層膜を真空蒸着により形成した偏光分離板について、日立製作所製の分光光度計Ｕ−３２００を用いて、偏光分離機能を入射角度を５５°〜７０°まで変えながら測定した結果を示したものである。このグラフから容易に読み取れるように、可視光の全域に亙って高い偏光分離機能が発揮されていることが判る。また、入射角が大きい方が偏光分離機能が高いという傾向も読み取ることが出来る。
【０１０８】
なお、本実施例においても、第１，第２の実施例等で説明したと同様の戻り光に対する偏光スクランブル効果と平行光束化素子１からの再出射によるＰ偏光成分の増強作用が発揮されることや、多層膜型偏光分離板１８の後段に光出射方向修正素子１０を配置することによって光出射方向の修正を行えるということは言うまでもないことである。
【０１０９】
ここまでに説明した第１〜第４の実施例は、偏光分離手段の構成についてのバリエイションに関連したものであるが、次に説明する第５〜第７の実施例は偏光分離手段から平行光束化素子内に復帰した戻り光に対してＳ偏光成分をＰ偏光成分に変換する作用を強化する為の付加構成に関連したものである。即ち、第５〜第７の実施例の本質的な部分は、既述の第１〜第４のいずれの実施例とも組み合わせ得る性質を有しており、従って、各実施例に関する記述中の「偏光分離板８（第１の実施例に記載）」は、これを適宜他の第２〜第４の実施例に開示された型のものに置き換えても差し支えない。このような前提の下で、以下、各実施例について説明する。
【０１１０】
先ず、戻り光のＳ偏光成分をＰ偏光成分に変換する為の偏光スクランブル作用強化手段（以下、「補強スクランブラ」と言う。）として、高散乱能を有する平板状の光散乱導光体を用いた例として、第５の実施例について説明する。
【０１１１】
図１６は、本願発明に係る偏光化機能付の面光源装置の第５の実施例を断面図で示したものである。楔形断面形状を有する指向出射性の光散乱導光体からなる平行光束化素子１は、ポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料粒子（径２μｍ、屈折率＝１．４３４５）を０．０７ｗｔ％の割合で一様に分散させたもので構成されている。平行光束化素子１のサイズは、図中左右方向の長さが６８ｍｍ、幅が８５ｍｍ、光入射面２側の端部で４．０ｍｍ、末端部６で０．２ｍｍとした。
【０１１２】
Ｌは平行光束化素子１の入射面２から１ｍｍ離して配置された直径３ｍｍの蛍光ランプで、このランプＬから右方に向かって光を入射させ、光取出面３から平行化された光束を取り出す配置とした。また、Ｒは入射面２から入射する光量を可能な限り多く確保する為に適宜配置される反射手段で、ここでは銀箔製シートでランプＬを取り囲むように配置した。
【０１１３】
空気層７を挟んで平行光束化素子１の光取出面３と対向する位置には、偏光分離手段としての偏光分離板８が配置され、更にその外側には空気層９を挟んで光出射方向修正素子１０が配置されている。符号１１は、光出射方向修正素子１０の光出射面であり、面光源装置としての光出射面でもある。この面光源装置を液晶表示装置のバックライト光源として使用する場合には、光出射方向修正素子１０の更に外側に液晶表示パネルが配置される。
【０１１４】
偏光分離板８は、光学ガラスＢＫ−７からなる厚さ１ｍｍの平坦板状体で構成されている。以上の構成は、第１の実施例と同一であり、また、その作用も基本的には変わらないので、ここでは詳しい説明を省略する。
本実施例が第１の実施例と異なっているのは、平行光束化素子１の裏面４に沿って、偏光分離板８から平行光束化素子１内に復帰した戻り光に対する偏光スクランブル作用を強化する為の補強スクランブラＳＲが設けられている点である。この補強スクランブラＳＲは、平行光束化素子１の全体あるいは楔形状末端部６の近傍の厚みが、散乱能の強さとの関連で不十分な為に偏光スクランブル作用が不足することを防止する為の素子である。
【０１１５】
従って、平行光束化素子１を構成する光散乱導光体よりも強い散乱能が与えられた材料を使用する。ここでは、平行光束化素子１と同種の材料の散乱能を強化したものとして、ポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料粒子（径２μｍ、屈折率＝１．４３４５）を０．５ｗｔ％の割合で一様に分散させたものを使用した。補強スクランブラＳＲの大きさは、平行光束化素子１の裏面４に合わせたものとし、厚さは１ｍｍとした。
【０１１６】
このような構成により、平行光束化素子１から補強スクランブラＳＲ内に相当量の光が進入し、屈折率不均一構造（ここでは、異屈折率粒子材料）による異方性散乱作用を受けて、Ｓ偏光成分がＰ偏光成分に変換される。そして、この光はその強い散乱能に対応した充分な偏光スクランブル作用を受けた後に平行光束化素子１内に復帰するから、特に末端部６の近傍において不足しがちな偏光スクランブル作用を補強することが出来る。
【０１１７】
従って、戻り光が偏光分離板８へ向けて再出射される際のＰ偏光成分が５０％に近づくことになり、最終的な出射光束に含まれるＰ偏光成分量が富化される結果をもたらす。なお、符号５は補強スクランブラＳＲの外側に設けられた銀箔製の反射体であり、補強スクランブラＳＲの外側から光量が無駄に放散されるのを防止する。
【０１１８】
次に、第５の実施例における平板状の補強スクランブラＳＲを楔形の補強スクランブラＳＲ’として、平行光束化素子１に対して相補的な配置をとらせたのが図１７に示した第６の実施例である。この実施例では、平行光束化素子１の厚さの大小に対応した偏光スクランブル作用の強弱が、相補的に配置された楔形補強スクランブラＳＲ’の作用によって埋め合わされ、面光源装置の偏光機能がより均一化される。楔形の補強スクランブラＳＲ’の大きさは、平行光束化素子１の裏面４に合わせたものとし、厚さは最厚部で４ｍｍ、最薄部で０．２ｍｍとした。
【０１１９】
なお、この実施例の全体構成は、補強スクランブラＳＲ’の形状を除いて第５の実施例と同様であるから、ここでは説明を省略する。
【０１２０】
更に、図１８は、本願発明に係る偏光化機能付の面光源装置の第７の実施例を断面図で示したものである。楔形断面形状を有する指向出射性の光散乱導光体からなる平行光束化素子１は、ポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料粒子（径２μｍ、屈折率＝１．４３４５）を０．０７ｗｔ％の割合で一様に分散させたもので構成されている。平行光束化素子１のサイズは、図中左右方向の長さが６８ｍｍ、幅が８５ｍｍ、光入射面２側の端部で４．０ｍｍ、末端部６で０．２ｍｍである。
【０１２１】
Ｌは平行光束化素子１の入射面２から１ｍｍ離して配置された直径３ｍｍの蛍光ランプで、このランプＬから右方に向かって光を入射させ、光取出面３から平行化された光束を取り出す配置とした。また、Ｒは入射面２から入射する光量を可能な限り多く確保する為に適宜配置される反射手段で、ここでは銀箔製シートでランプＬを取り囲むように配置した。
【０１２２】
空気層７を挟んで平行光束化素子１の光取出面３と対向する位置には、偏光分離手段としての偏光分離板８が配置され、更にその外側には空気層９を挟んで光出射方向修正素子１０が配置されている。符号１１は、光出射方向修正素子１０の光出射面であり、面光源装置としての光出射面でもある。この面光源装置を液晶表示装置のバックライト光源として使用する場合には、光出射方向修正素子１０の更に外側に液晶表示パネルが配置される。
【０１２３】
偏光分離板８は、光学ガラスＢＫ−７からなる厚さ１ｍｍの平坦板状体で構成されている。以上の構成は、第５，第６の実施例の場合と同様に第１の実施例と同一であり、また、その作用も基本的には変わらないので、ここでは詳しい説明を省略する。
本実施例が第１の実施例と異なっているのは、平行光束化素子１の裏面４に沿って、可視光の全域に亙って２分の１波長板として作用する位相差板ＨＷを配置し、更にその外側に銀箔からなる反射体５を設けている点である。この位相差板の遅相軸方向は、平行光束化素子１の縦横稜線に対して４５°傾斜するように設定されている。また、その厚さは、偏光分離板８からの戻り光が平行光束化素子１内をほぼ直進して裏面４から透過した場合に、π／２の位相差（Δｎ・ｄ；ここで、Δｎは位相差板ＨＷの複屈折値、ｄは光路長）を与えるように調整されている。戻り光を図５の代表光線Ｃ0 （出射角６５°）に由来したものとすれば、位相差板ＨＷへの入射角を計算すると約６０°となるから、この６０°の入射角の光線について、上記位相差が与えられることになる。
【０１２４】
今、偏光分離板８からの戻り光の内偏光スクランブル作用を殆ど受けていない成分に注目すると、この成分は、上記前提にある直進性の戻り光に対応していると考えられるから、位相差板ＨＷはＳ偏光成分に対して特に有効な２分の１波長板として機能する。即ち、直進性の戻り光は、平行光束化素子１の裏面→位相差板ＨＷ→反射体５→位相差板ＨＷ→平行光束化素子１の裏面４、という経路を辿ることによってＰ偏光成分に富んだ光に変換される。
【０１２５】
この光は、平行光束化素子１の有する前方散乱性の効果（「作用」の説明の欄を参照）によって、その多くが平行光束化素子１から、再度６５°前後の出射角を以て出射される。この光のＰ偏光成分の大半は偏光分離板８で反射されることなく、偏光化された光として面光源装置から出射される。この偏光変換作用は、平行光束化素子１の持つ偏光スクランブル作用と同時に発揮されるから、全体としてＰ偏光成分のエネルギに富んだ偏光光束が得られることになる。
【０１２６】
なお、以上の各実施例においては光源Ｌとして棒状の蛍光灯を使用したが、本願発明における光源は広義には光供給手段であれば良く、必ずしも自身が発光能力を有する必要はなく、例えば、他の発光素子に結合された光ファイバ束の出射端などであっても構わない。その偏光特性についても特に制限はなく、レーザ発振に由来した光のように特定の偏光特性を有する光を供給した場合でも、本願発明の本質的な偏光化作用自体が損なわれることは無い。
【０１２７】
ところで、既に触れたように、本願発明の偏光化機能付面光源装置の特徴が極めて有効に生かされる代表的な事例として、液晶表示装置のバックライト光源手段への適用がある。即ち、従来の面光源装置には本願発明の偏光化機能付面光源装置のような偏光化機能が備わっていないために、液晶表示パネルの光入射側に設けられている偏光板によって面光源装置の出射光の光エネルギの約半分が遮断されて無駄になる現象が生じていたが、本願発明の偏光化機能付面光源装置を液晶表示装置のバックライト光源手段に採用すれば、バックライト光源出射光束の偏光方向と偏光板の偏光軸方向が平行となる配置をとるだけで、表示に有効に寄与する光エネルギの割合を格段に向上させることが出来る。
【０１２８】
図１９は、本願発明に係る偏光化機能付の面光源装置を液晶表示装置のバックライト光源手段として使用した場合の基本的な配置を要素分解斜視図で示したものである。この実施例では、バックライト光源手段として先に説明した本願発明の第１の実施例（図４参照）に示したものと同じ型の偏光化機能付面光源装置が使用されており、共通する要素については同じ符号で指示がなされている。
【０１２９】
即ち、符号１は楔形断面形状を有する指向出射性の光散乱導光体からなる平行光束化素子で、ここではポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料粒子（径２μｍ、屈折率＝１．４３４５）を０．０８ｗｔ％の割合で一様に分散させた材料からなるものが使用されている。この条件で有効散乱照射パラメータＥ及び相関距離ａを計算すると、Ｅ＝７．３９［cm^-1］，ａ＝１．３μｍとなる。また、平行光束化素子１のサイズは使用する液晶セルのサイズに合わせて、図中左右方向の長さが６８ｍｍ、幅が８５ｍｍ、光入射面側の端部で４．０ｍｍ、末端部で０．２ｍｍとした。
【０１３０】
Ｌは平行光束化素子１の入射面から１ｍｍ離して配置された直径３ｍｍの蛍光ランプで、このランプＬから右方に向かって入射した光は、光取出面３から平行化された光束として取り出される。Ｒは入射面から入射する光量を可能な限り多く確保する為に適宜配置される反射体で、銀箔製シートが使用されている。
【０１３１】
平行光束化素子１の裏面４には、光拡散インキパターンや凹凸拡散面等、強い光散乱を生じさせる為の処理は特に施されておらず、銀箔製シートからなる反射体５が配置されている。
【０１３２】
符号８は平行光束化素子１の光取出面３と対向する位置に配置された偏光分離板８であり、更にその外側には光出射方向修正素子１０が配置されている。偏光分離板８には、光学ガラスＢＫ−７（屈折率１．５１６３）からなる厚さ１ｍｍの平坦な板状部材を使用した。また、光出射方向修正素子１０はポリカーボネート（ＰＣ；屈折率１．５９）からなるものを使用し、そのプリズム形成面を偏光分離板８の方向に向けて配置した。
【０１３３】
これら要素からなる偏光化機能付面光源装置で構成されるバックライト光源部の光出射側には、２枚の偏光板１２，１４とその間に配置された液晶セル１３からなる液晶表示パネルが配置される。光入射側の偏光板１２の透過偏光軸の方向は図中で水平方向を向くように設定される一方、光出射側の偏光板１４の透過偏光軸の方向は図中で鉛直方向を向くように設定されている。
【０１３４】
既に詳しく説明したように、光源Ｌ、平行光束化素子１、反射体Ｒ，５、偏光分離板８及び光出射方向修正素子１０からなる偏光化機能付面光源装置から出射される光束は、高い偏光度を有しており、また、図中破線で示した方向に沿った指向性を有すると共に、平坦度の高い光強度プロファイルを有している。
【０１３５】
平行光束化素子１と偏光分離板８を利用した偏光化プロセスの説明部分で明らかにしたように、偏光化機能付面光源装置から出射される光束はＰ偏光化されているから、図示された配置条件では、その主たる偏光軸が図中水平方向を向くことになる。従って、バックライト光束として偏光板１２に入射した光の内、偏光板１２を透過する光量の割合が大きくなり、少なくとも原理的には、５０％を越える光透過率が確保される。
【０１３６】
このような特徴は、液晶パネル入射側の偏光板の透過偏光軸の方向をどのように選択しても光エネルギの少なくとも５０％が無駄になっていた従来の構成では全く期待出来なかったものである。
【０１３７】
なお、本実施例では、バックライト光源手段として第１の実施例の型の偏光化機能付面光源装置を使用した例を説明したが、他の実施例に示した型のものを使用しても、同様の液晶表示装置を構成出来ることは言うまでもない。
【０１３８】
また、使用される平行光束化素子の散乱特性について要求される基本的な条件は特許請求の範囲に記載した通りであるが、ビデオカメラ、パーソナルコンピュータ、ワープロ、テレビジョン等のディスプレイ用に需要度が高いパネルサイズ３インチ〜１０インチの液晶表示装置のバックライト光源手段としての用途を考えた場合には、有効散乱照射パラメータＥ及び相関距離ａが次の範囲にある時に特に好ましい結果がもたらされることが確かめられている。
・有効散乱照射パラメータＥ；２．７７［cm^-1］≦Ｅ≦９．２４［cm^-1］
・相関距離ａ；ａ≦７μｍ
最後に、本願発明において、平行光束化素子あるいは補強スクランブラとして使用される光散乱導光体の材料及び製造方法について説明する。
本願発明で使用する光散乱導光体のベースとしては、種々のポリマー材料が利用可能である。これらポリマーの代表的なものを下記の表１及び表２に示した。
【０１３９】
【表１】

【０１４０】
【表２】

このようなポリマー材料をベースとする光散乱導光体は、次のような方法によって製造することが可能である。
先ず、その１つは、２種類以上のポリマーを混練する工程を含む成形プロセスを利用する方法である。
即ち、２種類以上の屈折率の相互に異なるポリマー材料（任意形状で良い。工業的には、例えばペレット状のものが考えられる。）を混合加熱して、練り合わし（混練工程）、混練された液状材料を射出成形機の金型内に高圧で射出注入し、冷却固化することによって成形された平行光束化素子を金型から取り出せば金型形状に対応した形状の平行光束化素子を得ることが出来る。
【０１４１】
混練された２種類以上の異屈折率のポリマーは完全には混ざり合うことなく固化するので、それらの局所的濃度に不均一（ゆらぎ）が生まれて固定され、一様な散乱能が与えられる。
また、混練された材料を押し出し成形機のシリンダー内に注入し、通常のやり方で押し出せば目的とする成形物を得ることが出来る。
【０１４２】
これらポリマーブレンドの組合せや混合割合については、非常に幅広い選択が可能であり、屈折率差、成形プロセスで生成される屈折率不均一構造の強さや性質（散乱照射パラメータＥ、相関距離ａ、誘電率ゆらぎ２乗平均τ等）を考慮して決定すれば良い。なお、使用し得るポリマー材料の代表的なものは前記表１及び表２に示した通りである。
【０１４３】
光散乱導光体を構成する材料の製造法の別の１つは、ポリマー材料中に屈折率の異なる（０．００１以上の屈折率差）粒子状材料を一様に混入分散させるものである。
そして、粒子状材料の一様混入に利用可能な方法の１つにサスペンション重合法と呼ばれる方法がある。即ち、粒子状材料をモノマー中に混入し、湯中に懸濁させた状態で重合反応を行なわせると、粒子状材料が一様に混入されたポリマー材料を得ることが出来る。これを原材料に用いて成形を行なえば、所望の形状の光散乱導光体が製造される。
【０１４４】
また、サスペンション重合を種々の粒子状材料とモノマーの組合せ（粒子濃度、粒径、屈折率等の組合せ）について実行し、複数種類の材料を用意しておき、これを選択的にブレンドして成形を行なえば、多様な特性の光散乱導光体を製造することが出来る。また、粒子状材料を含まないポリマーをブレンドすれば、粒子濃度を簡単に制御することが出来る。
【０１４５】
粒子状材料の一様混入に利用可能な方法の他の１つは、ポリマー材料と粒子状材料を混練するものである。この場合も、種々の粒子状材料とポリマーの組合せ（粒子濃度、粒径、屈折率等の組合せ）で混練・成形（ペレット化）を行なっておき、これらを選択的にブレンドして光散乱導光体を成形製造することにより、多様な特性の光散乱導光体を得ることが出来る。
【０１４６】
また、上記のポリマーブレンド法と粒子状材料混入方法を組み合わせることも可能である。例えば、屈折率の異なるポリマーのブレンド・混練時に粒子状材料を混入させることが考えられる。
【０１４７】
以下、製造法の幾つかの実例を挙げておく。
＜製造例１＞
メタクリル樹脂のペレット（旭化成製、デルベット８０Ｎ）に粒径０．８μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１０８）を０．３ｗｔ％添加し、ミキサーで混合分散させた後、押し出し機でストランド状に押し出し、ペレタイザーでペレット化することにより、シリコーン系樹脂粉体が均一に分散されたペレットを調製した。
【０１４８】
このペレットを射出成形機を用い、シリンダー温度２３０゜Ｃ〜２６０゜Ｃ、型温度５０゜Ｃの条件で成形して、縦６８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の光散乱導光体を得た。
【０１４９】
製造された光散乱導光体の相関距離はａ＝０．５３μｍであり、有効散乱照射パラメータの前記（１１）式による見積計算値はＥ＝１２．６[cm^-1]であった。
【０１５０】
＜製造例２＞
ＭＭＡに粒径０．８μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１０８）を０．３ｗｔ％添加し、公知のサスペンション重合法により、該粉体が均一に分散した球状粒子を得た。これを製造例１と同様にペレタイザーでペレット化することにより、シリコーン系樹脂粉体が均一に分散されたペレットを調製した。
【０１５１】
以下、製造例１と同じ条件で同型の楔状光散乱導光体を得た。この光散乱導光体は、製造例１で作製された光散乱導光体と外観上全く区別がつかないものであった。そして、相関距離はａ＝０．５３μｍであり、有効散乱照射パラメータの前記（１１）式による見積値はＥ＝１２．６[cm^-1]であった。
【０１５２】
＜製造例３＞
ポリメチルメタクリレート（ＰＭＭＡ）にポリスチレン（ＰＳｔ）を０．５ｗｔ％添加し、Ｖ型タンブラーを用いて１０分間、次いでヘンシェルミキサーを用いて５分間混合した。これを径３０ｍｍの２軸押し出し機［ナカタニ機械（株）製］を使って、シリンダー温度２２０゜Ｃ〜２５０゜Ｃ、スクリュー回転数７５ｒｐｍ、吐出量６ｋｇ／ｈｒの条件で融解混合してペレットを作成した。
【０１５３】
このペレットを射出成形機を用い、シリンダー温度２２０゜Ｃ〜２５０゜Ｃ、型温度６５゜Ｃ、射出速度中速、射出圧力ショートショット圧プラス１０ｋｇ／ｃｍ² の条件で成形して、縦６８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の光散乱導光体を得た。
【０１５４】
＜製造例４＞
ＭＭＡ（メチルメタクリレート）に粒径２μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１２０）を各々０．０５ｗｔ％、０．０８ｗｔ％、０．１０ｗｔ％、０．１５ｗｔ％を加えて均一に分散した４種類の試料と粒子無添加のＭＭＡ試料を用意し、計５種類の試料の各々にラジカル重合開始剤としてベンゾイルパーオキサイド（ＢＰＯ）０．５ｗｔ％、連鎖移動剤としてｎ―ラウリルメルカプタン（ｎ−ＬＭ）を０．２ｗｔ％加え、７０℃で２４時間注型重合させて縦６８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の光散乱導光体を１枚づつ作製した。
【０１５５】
＜製造例５＞
ＭＭＡ（メチルメタクリレート）にシリコーンオイルを０．０２５ｗｔ％加えて均一に分散させ、ラジカル重合開始剤としてベンゾイルパーオキサイド（ＢＰＯ）を０．５ｗｔ％、連鎖移動剤としてｎ―ブチルメルカプタン（ｎ−ＢＭ）を０．２ｗｔ％、各々加え、７０℃で３０分間にわたりゾル化を行なった上で、更に６５℃で２４時間注型重合させて縦６８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍまで徐々に変化した楔型の光散乱導光体を作製した。
【０１５６】
＜製造例６＞
ＰＭＭＡ（ポリメチルメタクリレート）に粒径２μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１２０）を０．０８ｗｔ％加え、Ｖ型タンブラを用いて１０分間、次いでヘンシェルミキサを用いて５分間混合した。これを２軸押し出し機で溶融混合（シリンダ温度２２０℃〜２５０℃）・押出成形して、ペレットを作製した。
【０１５７】
このペレットを射出成形機を用いてシリンダ温度２２０℃〜２５０℃の条件で射出成形し、縦６８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍまで徐々に変化した楔型の光散乱導光体を作製した。
【０１５８】
【発明の効果】
本願発明の偏光化機能付面光源装置は、平行光束化素子と偏光成分に依存した反射特性を有する偏光分離手段を組み合わせる構成を基礎として、リサイクル的な偏光化プロセスを実現するものであるから、高いエネルギ利用効率を以て偏光化された光束を得ることが出来る。また、本願発明に係る偏光化機能付面光源装置によれば、その出射光束に平行光束化素子に由来する明瞭な指向性が保存されているから、プリズム作用を利用した平行光束化素子を付加的に利用することによって、所望の方向に伝播する偏光化光束を生成させることが出来る。
【０１５９】
このような特性は、本願発明の偏光化機能付面光源装置を液晶表示装置のバックライト光源手段として用いた際に極めて有利であり、液晶表示装置の表示品位を格段に向上させ、省電力性を大幅に改善させるに充分なものである。
【図面の簡単な説明】
【図１】横軸に相関距離ａ、縦軸に誘電率ゆらぎ２乗平均τをとり、有効散乱照射パラメータＥを一定にする条件を表わす曲線を、Ｅ＝５０［cm^-1］及びＥ＝１００［cm^-1］の場合について描いたものである。
【図２】相関距離ａによって光散乱導光体の前方散乱性の強さが変化することを説明するグラフである。
【図３】本願発明の面光源装置に用いられる光散乱導光体の断面の基本形状を内部における繰り返し反射の様子と共に記したものである。
【図４】本願発明に係る偏光化機能付の面光源装置の第１の実施例を断面図で示したものである。
【図５】平行光束化素子１から出射された光の挙動を代表光線に関する光線追跡形式で記したものである。
【図６】横軸にＢＫ−７板への入射角をとり、縦軸にＰ，Ｓ各偏光成分の１回透過の透過率をとってグラフ化したものである。
【図７】（Ａ）は、光出射方向修正素子の典型的な構造と配置を説明する図、（Ｂ）は変形型の配置を示した図である。両図は、図４，図５に示した配置における偏光分離板及び光出射方向修正素子の周辺部分を抽出拡大した断面図に、光線Ｃ3 ，Ｃ9 の追跡経路を併記した形で提示されている。
【図８】図４と同様の形式で本願発明に係る偏光化機能付の面光源装置の第２の実施例を表わしたものである。
【図９】２枚の偏光分離板と平行光束化素子を組み合わせた第２の実施例における偏光化機能の概要について説明する図である。
【図１０】（Ａ）は、波形偏光分離板の断面形状を表わした図であり、（Ｂ）は、（Ａ）中に○印で囲まれた部分（繰り返し形状の１単位分）を拡大描示したもので、平行光束化素子１からの出射光束を代表する光線Ｃ0 の光線追跡図が併記されている。
【図１１】多層膜型偏光分離板の構造と作用を説明する図であり、多層膜３層分の断面と代表光線Ｄ0 の主要光路が例示されている。
【図１２】図１１に示した構造における空気層と第１層の界面における各偏光成分の透過率を入射角の関数として表わしたグラフである。
【図１３】図１１に示した構造における第１層と第２層の界面における各偏光成分の透過率を入射角の関数として表わしたグラフである。
【図１４】図１１に示した構造における第２層と第３層の界面における各偏光成分の透過率を入射角の関数として表わしたグラフである。
【図１５】厚さ１ｍｍの光学ガラス板ＢＫ−７上に、ＴｉＯx 、ＳｉＯ2 及びＺｒＯ2 からなる多層膜を真空蒸着により形成した偏光分離板について、分光光度計を用いて、偏光分離機能を入射角度を５５°〜７０°まで変えながら測定した結果を示したグラフである。
【図１６】本願発明に係る偏光化機能付の面光源装置の第５の実施例を断面図で示したものである。
【図１７】本願発明に係る偏光化機能付の面光源装置の第６の実施例を断面図で示したものである。
【図１８】本願発明に係る偏光化機能付の面光源装置の第７の実施例を断面図で示したものである。
【図１９】本願発明を液晶表示装置のバックライト光源手段に適用した実施例の構成を要素分解斜視図で示したものである。
【符号の説明】
１ 平行光束化素子
２ 光入射面
３ 光取出面
４ 裏面
５ 反射体（銀箔）
６ 平行光束化素子の末端部
７，９ 空気層
８，８’ 偏光分離板（平板形）
８” 波形偏光分離板
１０ 光出射方向修正素子
１１ 光出射方向修正素子の光出射面
１８ 多層膜型偏光分離板
１８１〜１８３ 多層膜の第１〜第３層
Ｃ0 ，Ｃ'0，Ｄ0 代表光線
Ｌ 蛍光ランプ（光源）
Ｒ 反射体
ＳＲ，ＳＲ’ 補強スクランブラ
ＨＷ 位相差板[0001]
[Industrial applications]
The present invention provides a surface light source device having a function of generating a polarized light beam from unbiased light or a function of generating a highly polarized light beam from a light beam having a small polarization (hereinafter, referred to as a “polarization function”). About. The surface light source device according to the invention of the present application can be used for any application requiring a biased light beam, and is particularly advantageous for use as a backlight light source for a liquid crystal display device.
[0002]
[Prior art]
A surface light source device is configured by arranging a light source such as a fluorescent lamp on the side of a plate-shaped light guide having a light scattering function on the surface or inside, and is used for applications such as a backlight light source of a liquid crystal display device. Are well known in the art (for example, JP-A-2-221926, JP-A-4-145485 and JP-A-51-89888).
[0003]
These conventional surface light source devices ensure the amount of light emitted from the light extraction surface by making the traveling direction of light as random as possible by the light scattering action given inside the light guide or on the surface area. The light emitted from the light extraction surface has no clear directivity, and has no function of generating light exhibiting a bias in a specific direction.
[0004]
On the other hand, the present inventor has previously made a wedge-shaped light-scattering light guide in which characteristic parameters (effective scattering irradiation parameter E and correlation distance a; details will be described later) defining the scattering characteristics are set within a predetermined range. It has been proposed to construct a parallel beam forming device by utilizing the function of beam forming. When an improved surface light source device is configured by combining this parallel light beam forming device with light source means, the emitted light beam has a clear directivity, but the function of generating polarized light having a bias in a specific direction is not possible. Not equipped.
[0005]
By the way, as a means for obtaining a biased light from a non-biased light emitted from a general light source, a polarizing plate or a beam splitter type polarizer is known and used. Since an attempt is made to obtain polarized light by eliminating polarization components in orthogonal directions, about half of the light energy is wasted. Therefore, in a method of generating a polarized light beam by combining such a conventional or improved surface light source device with such a polarizing element, a polarized light beam that makes full use of the brightness of the used surface light source is used. It is difficult to get.
[0006]
For example, even when the above-mentioned conventional type or improved type surface light source device is disposed as a backlight light source means behind the liquid crystal display panel of the liquid crystal display device, light polarized in a predetermined direction is incident on the liquid crystal layer. The polarizing plate provided on the light incident side of the liquid crystal display panel causes a phenomenon that about half of the light energy of the light emitted from the surface light source device is wasted, which is one of the causes of deteriorating the display quality of the liquid crystal display device. Has become.
[0007]
If a surface light source device capable of generating a light beam polarized in a predetermined direction while suppressing a decrease in the utilization efficiency of light energy can be obtained, this is used as the backlight light source means of the liquid crystal display device. This makes it possible to reduce the loss when the liquid crystal display panel passes through the polarizing plate (the polarization direction of the light beam emitted from the backlight source and the polarizing axis of the polarizing plate may be parallel). Therefore, from such a viewpoint, realization of a surface light source device capable of generating a polarized light beam without greatly lowering the energy use efficiency has been awaited.
[0008]
[Problems to be solved by the invention]
The present invention is based on the background of the above-mentioned prior art, and it is a basic object of the present invention to provide a surface light source device with a polarization function capable of suppressing a decrease in utilization efficiency of light energy upon polarization and obtaining a bright polarized light beam. It was made for the purpose.
The invention of the present application also has a purpose of providing a surface light source device with a polarizing function, which is particularly suitable for use as a backlight source of a liquid crystal display device.
[0009]
[Means for Solving the Problems]
First, the invention of the present application provides, as a basic configuration for achieving the above object, "an effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a polarizing function-equipped surface light source device provided with a light-transmitting polarized light separating means that is disposed so as to extend along the axis and has a reflection characteristic depending on the polarization component.
[0010]
Then, as a configuration in which the polarization splitting means is specified in a more specific form, “an effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a light-transmitting polarized light separating means having a reflection characteristic depending on a polarized light component, wherein the polarized light separating means has a refractive index in a range of 1.3 to 2.0. Polarizing function-equipped surface light source device comprising a polarizing beam splitter made of a transparent optical material having
"Effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a light-transmitting polarization separation means having a reflection characteristic depending on a polarization component, wherein the polarization separation means has a refractive index in a range of 1.3 to 2.0. Polarizer comprising a plurality of polarization splitters having a refractive index and arranged in a stacked manner with an air layer interposed therebetween. With surface light source device "
"Effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a light-transmitting polarized light separating means having a reflection characteristic depending on a polarized light component, wherein the polarized light separating means has a refractive index in a range of 1.3 to 2.0. And a light incident surface of the polarized light separating plate having a parallel light exiting from a light exit surface of the parallel light beam forming element. Brewster's angle conditions corresponding to the emission direction of the bundle Full A surface light source device having a polarizing function, wherein a repetitive inclined surface is formed, and an effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a light-transmitting polarized light separating means having a reflection characteristic depending on a polarized light component, wherein the polarized light separating means has a refractive index in a range of 1.3 to 2.3. Characterized in that it includes a polarizing beam splitter having a multilayer film made of an optical material having a polarizing function. , In which was proposed.
[0011]
Further, after correcting the polarization state of the light re-entering the parallel beam forming element from the transmissive polarization splitting unit having the reflection characteristic depending on the polarization component in each of the above-described configurations, the light is directed to the polarization splitting unit again. As a configuration for obtaining light with a higher degree of polarization, the effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a translucent polarization separating means having a reflection characteristic depending on a polarization component, and disposed along a surface opposite to a light extraction surface of the parallel light beam generating element. Reinforced scrambler And a "polarizing function-equipped surface light source device," and "an effective scattering irradiation parameter E [cm ^-1 Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives light scattering ability is γ (r) = exp [−r / a] (where, (r is the distance between two points in the light-scattering light guide) and the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35. A parallel beam forming element made of a light body, light supply means arranged on the end face side having a relatively large cross-sectional area of the wedge-shaped cross section of the parallel beam forming element, and a light extraction surface of the parallel beam forming element And a translucent polarization separating means having a reflection characteristic depending on a polarization component, and disposed along a surface opposite to a light extraction surface of the parallel light beam generating element. Polarization conversion means, wherein the polarization conversion means is a retardation plate and a light reflection disposed facing the outside of the retardation plate. It is obtained by proposed polarization function with surface light source device "which is characterized in containing the stage.
[0012]
In addition, in order to prepare for the case where it is necessary to correct the propagation direction of the light beam emitted from the surface light source device, a requirement that a light emission direction correction element is disposed outside the polarization separation unit is further provided in each of the above configurations. This proposes a configuration of a surface light source device with a polarization function that imposes the following.
[0013]
[Action]
The present invention uses a combination of a parallel light flux conversion function of a light scattering light guide used in the improved surface light source device and a reflection / transmission characteristic of a polarization component related to an approximate Brewster angle condition. The present invention is based on a novel principle that a light beam containing a large amount of polarized light component in a predetermined direction can be generated with relatively high energy use efficiency.
[0014]
Therefore, first, the effective scattering irradiation parameter E and the correlation distance a describing the scattering characteristics of the light scattering light guide used in the present invention will be described with reference to Debye's theory. The parallel light beam conversion function described above will be described.
[0015]
Now, light of intensity I0 propagates in a light scattering / guiding body made of a medium in which a non-uniform refractive index structure is uniformly formed in a substrate having a constant refractive index. Considering the case where the intensity attenuates to I, the effective scattering irradiation parameter E is defined by the following equation (1) or (2).
[0016]
(Equation 1)

The above equations (1) and (2) are so-called integral and differential expressions, respectively, and their physical meanings are equivalent. In addition, this E may be called turbidity.
On the other hand, the scattered light intensity in the case where light scattering occurs due to the non-uniform structure distributed in the medium is as follows in a normal case (VV scattering) where most of outgoing light is vertically polarized light with respect to vertically polarized incident light. It is represented by equation (3).
[0017]
(Equation 2)

When natural light is incident, considering the Hh scattering, (1 + cos ^Two It is known that the following equation multiplied by (Φ) / 2 can be considered.
[0018]
[Equation 3]

Here, λ0 is the wavelength of the incident light, ν = (2πn) / λ0, s = 2sin (Φ / 2), n is the refractive index of the medium, Φ is the scattering angle, and <η ^Two > Is the mean square of the dielectric constant fluctuation in the medium (hereinafter, <η ^Two As ≧ = τ, τ is appropriately used. ), And γ (r) is called a correlation function, and is represented by the following equation (6).
[0019]
According to Debye's theory, when the non-uniform refractive index structure of the medium is dispersed and divided into A phase and B phase with an interface, the correlation function γ (r) and the correlation distance a The following relational expressions (7) and (8) hold for the dielectric constant fluctuation root mean square τ and the like.
[0020]
(Equation 4)

Assuming that the non-uniform structure is constituted by a spherical interface having a radius R, the correlation distance a is expressed by the following equation.
[0021]
(Equation 5)

Using the equation (6) for the correlation function γ (r) and calculating the effective scattering irradiation parameter E when natural light is incident on the medium based on the equation (5), the result is as follows.
[0022]
(Equation 6)

From the above-described relationships, it is possible to control the scattered light intensity, the angle dependence of the scattered light intensity, and the effective scattered irradiation parameter E by changing the correlation distance a and the mean square τ of the dielectric constant fluctuation. I understand.
FIG. 1 shows a curve representing the condition for keeping the effective scattering irradiation parameter E constant by taking the correlation distance a on the horizontal axis and the root mean square τ on the vertical axis. ^-1 ] And E = 100 [cm ^-1 ]].
The value of E is an index indicating the "strength" of the scattering power of the scattering light-guiding medium. The larger the value of E, the stronger the scattering power, and the smaller the value of E, the weaker the scattering power (close to transparent). become. E = 0 corresponds to the non-scattering state. Therefore, a light-scattering light guide with a small E is suitable for a large-sized surface light source with uniform brightness, and a light-scattering light-guide with a large E is suitable for a small-sized surface light source. The argument holds.
[0023]
When it is assumed that a surface light source of a normal size (approximately several cm to several tens of cm) assumed when the liquid crystal display device is applied to a backlight light source is used, the effective scattering of the light scattering light guide used is assumed. A practical range of the irradiation parameter E is E = 0.5 to 50 cm ^-1 ].
[0024]
On the other hand, the correlation distance a is an amount that is deeply related to the directional characteristics of scattered light in each scattering phenomenon inside the light scattering light guide. That is, as can be inferred from the expressions (3) to (5), the light scattering inside the light-scattering light guide generally has a forward scattering property. It changes depending on a.
[0025]
FIG. 2 is a graph illustrating this for two values of a. In the figure, the horizontal axis represents the scattering angle Φ (the traveling direction of the incident light is assumed to be Φ = 0 °), and the vertical axis represents the scattered light intensity assuming natural light, that is, Φ = Vvh (Φ) / Vvh (0) is a value normalized to 0 °.
As also shown in the figure, when a = 0.13 μm and the particle size is converted to 2R = 0.2 μm using the above (9), the graph of the normalized scattering intensity shows a gentle In the case of a = 1.3 μm and 2R = 2.0 μm in terms of the particle size converted by the above equation (9), the graph of the normalized scattering intensity shows a function in which Φ sharply decreases in a range where Φ is small. It becomes.
[0026]
As described above, the scattering caused by the non-uniform structure of the refractive index in the light-scattering light guide basically shows forward scattering, and when the value of the correlation distance a becomes smaller, the forward scattering becomes weaker, and the scattering in one scattering becomes smaller. The angle range tends to widen. This fact itself has been confirmed experimentally.
[0027]
The above discussion focuses on the individual scattering phenomena themselves due to the non-uniform refractive index structure distributed inside the light scattering guide, but the directional characteristics of the light actually emitted from the light extraction surface of the light scattering guide are In the evaluation, the phenomenon of total reflection of light entering the light extraction surface from the inside of the light scattering light guide and the interface transmittance at the time of light emission (escape rate from the light scattering light guide) are also considered. There is a need to.
[0028]
As is well known from basic optical theory, when light enters the light extraction surface from the inside of a light-scattering light guide having a relatively large refractive index compared to an external medium (air) The critical angle αc determined by the refractive index of the medium inside and outside the light-scattering light guide is defined as an incident angle α (here, the direction of a normal line directed toward the inside of the light-scattering lightguide with respect to the light extraction surface is α = 0). °)), the emission (escape) to the outside (air layer) does not occur.
[0029]
In PMMA (polymethyl methacrylate; refractive index: 1.492), which is a typical material of the light-scattering light guide used in the present invention, αc = 42 °. As will be described later, the refractive index of the resin material preferably used as the matrix of the light-scattering light guide in the present invention is in the range of 1.4 to 1.7, and the corresponding critical angle αc is in the range of , 36.0 ° to 45.6 °.
[0030]
Therefore, in the case where the light incident surface is formed on the side of the light extraction surface as in the present invention (see each embodiment described later), the primary scattering generated when the light incident from the light incident surface encounters the non-uniform structure. It is considered that it is extremely unlikely that the light is immediately emitted from the light extraction surface to the outside while satisfying the critical angle condition.
[0031]
That is, under the conditions presupposed by the present invention, the effect of multiple scattering inside the light-scattering light guide, the interface between the light-extraction surface side and the back surface side of the light-scattering light guide, or the reflecting member arranged facing the same As a result of the combined effect of the reflection effect and the like, the phenomenon that the light that has reached the critical angle condition is emitted to the outside is greatly involved in the light emission from the light extraction surface. You can think.
[0032]
If so, when considering light propagating in the direction of the light extraction surface under conditions satisfying the critical angle condition, the forward scattering property acts to preserve the propagation direction of light at the time of incidence from the light incidence surface as a whole. The effect of (1) should be considerably reduced by the above-described combined effect, and the distribution of the light propagation direction should be considerably widened. As a result, the directional characteristics of the light emitted from the light-scattering light guide greatly depend on the angle dependence of the interface transmittance (escape rate) on the light extraction surface of the light satisfying the critical angle condition.
[0033]
In general, the interface transmittance under a condition that barely meets the critical angle condition (α <αc) is extremely low (for example, in the case of an acrylic resin-air interface, a P-polarized component is about 40%, and an S-polarized component is about 20%). The interface transmittance increases sharply when the incident angle α falls below the critical angle αc, and becomes almost constant when the incident angle α falls below 5 ° to 10 ° (in the case of the acrylic resin-air interface, the P polarization component is 90% (S-polarized light component is 85% or more).
[0034]
From the above, in the case of acrylic resin (αc = about 42 °), light incident from the inside of the light scattering guide to the light extraction surface at an incident angle α = about 35 ° to 40 ° is light scattering. It is considered that this contributes most to light emission from the light extraction surface of the light guide. The light incident on the light extraction surface at an incident angle of α = 35 ° to 40 ° is refracted on the light extraction surface in accordance with Snell's law, and is 65 ° ± with respect to the normal set to the outside on the light extraction surface. The light is emitted in a direction falling within a range of about 10 ° (that is, a direction rising about 15 ° to 35 ° with respect to the surface of the light extraction surface).
[0035]
Even when a material other than acrylic resin is used for the light scattering light guide, since the practical range of the refractive index of the material is about 1.4 to 1.7, a deviation of about several degrees can be expected in the above angle. If so, a similar argument holds.
[0036]
However, what should be noted here is that if the value of the correlation distance a is too small, the forward scattering itself in individual scattering is weakened, and scattered light in a wide angle range including backscattering only in primary scattering is generated. This causes the directivity to be blurred. In the present invention, a light-scattering light guide having such characteristics as not to exhibit such a directivity weakening phenomenon is used. Hereinafter, such a light-scattering light guide will be referred to as a “directional light-emitting light-scattering light guide”.
[0037]
This condition is taken into account in the range (0.06 μm ≦ a ≦ 35 μm) in which the present invention specifies the correlation distance a of the light scattering guide. In the case where a light-scattering light guide is used in which different refractive index particles are uniformly dispersed in a polymer matrix, the range of the correlation distance is determined from the above equation (9), the range of the different refractive index particle diameter, It can be seen that it corresponds to 0.1 μm to 54 μm.
[0038]
Next, the meaning that the directional light-emitting light-scattering light guide used in the surface light source device with a polarizing function of the present invention has a wedge-shaped cross-sectional portion will be described.
FIG. 3 shows the basic shape of the cross section of the light scattering guide used in the surface light source device of the present invention, together with the state of repeated reflection inside.
[0039]
In FIG. 1, reference numeral 1 denotes a directional light-scattering light guide constituting a parallel light beam forming element, and B 0 denotes light emitted from the light source L and taken into the light scattering light guide 1 from the light incident surface 2. 2 shows the path of a representative light beam representing the above. Since the light source L is disposed so as to face the light incident surface 2 which is a wedge-shaped side end portion having a relatively large cross-sectional area, it is assumed that the representative light beam B0 propagates in a substantially horizontal direction as shown in the figure.
[0040]
Considering the behavior of the representative light beam B0, the light beam B0 undergoes light scattering while repeating reflection at the light extraction surface 3 and the back surface 4 inclined with respect to the light extraction surface 3 while undergoing a change in direction due to scattering at a constant rate. The light guide 1 approaches a thin end portion. Since the internal reflection on the surfaces 3 and 4 is specular reflection, the incident angles and the reflection angles in the individual reflections are naturally equal (θ1, θ2, θ3,...). From the inclination relationship between the two surfaces 3 and 4, the relationship of θ2>θ4> θ6 is established for each reflection on the light extraction surface 3.
[0041]
Here, considering the interface transmittance at each reflection, the same argument as described in the description of the directivity of the light scattering light guide reveals that θi> αc (critical angle; 42 ° at the PMMA-air interface). In the condition (1), total reflection occurs. When θi falls below αc, the transmittance sharply increases. When θi is equal to or less than a predetermined value (around 35 ° at the PMMA-air interface), the transmittance becomes substantially constant. In the drawing, a state in which the emitted lights B4 and B6 are generated is illustrated according to the relationship of θ2>αc>θ4> θ6.
[0042]
Such an effect should occur not only for the representative light beam B0 (non-scattered light) but also for the primary scattered light and the multiple scattered light in a similar manner. As the distance from the light extraction surface 2 increases, the light emission rate from the light extraction surface 3 increases. When this effect is evaluated by a function f (x) of a distance x from the light incident surface 2, f (x) is an increasing function related to x. On the other hand, the effect of being close to the light source L in the portion near the light incident surface 2 works for both direct light and scattered light. If this proximity effect is evaluated by g (x), g (x) can be regarded as a function having a decreasing tendency with respect to x.
[0043]
Accordingly, the proximity effects g (x) and f (x) are in a relationship of canceling each other, and an effect that the intensity (brightness) of the emitted light from the light scattering guide 1 is made uniform. Further, it is considered that the chance of the light in the light-scattering light guide 1 entering the light extraction surface 3 tends to increase as the distance from the incidence surface 2 increases due to the effect of the wedge shape. It is considered that the effect evaluated in (x) is reinforced.
[0044]
Although there is no absolute limitation on the angle ψ between the two surfaces 3 and 4, there is a practical range of 0.5 ° ≦ ψ ≦ 6 ° in consideration of the brightness level, uniformity, directivity and the like. Values have been obtained. Further, by making the inclined back surface 4 (or the light extraction surface 3 in some cases) a curved surface, it is possible to control the increase and transition of the reflection angles θ1, θ2, θ3,. is there. The wedge-shaped cross section does not necessarily have to cover the entire light scattering guide 1. In order to prevent uneven brightness due to the reflection of the light source, the inclination near the light incident surface 2 is relaxed and flattened. In some cases, a reverse inclined portion may be formed.
[0045]
It is clear that the effect obtained by employing the light-scattering light guide having the wedge-shaped cross section described above is similarly established when the reflector 5 is arranged along the back surface 4. It is more preferable to arrange a reflector having regular reflectivity as the reflector 5 from the viewpoint of guiding light to a farther distance and not disturbing the directivity of the light-scattering light guide 1.
[0046]
The inventor of the present invention combines a directional light-emitting light-scattering light guide having such a wedge-shaped cross-section with a polarization splitting means using an approximate Brewster angle condition, whereby multiple polarization processes can be performed. It has been found that the principle is that polarization of the luminous flux is achieved with high light energy utilization efficiency. The present invention provides a surface light source device having a polarizing function based on this principle, and a method of combining a light scattering light guide and polarization separation means using Brewster's angle condition, thereby multiplexing polarization. The specific contents of the conversion process will be described in the next embodiment.
[0047]
【Example】
FIG. 4 is a cross-sectional view showing a first embodiment of the surface light source device with a polarizing function according to the present invention. In the figure, the same reference numerals are used for elements common to FIG. Reference numeral 1 denotes a parallel light beam forming element made of a directional light-emitting light-scattering light guide having a wedge-shaped cross section. Here, as a material thereof, silicone-based resin material particles (diameter: 2 μm, 2 μm in polymethyl methacrylate (PMMA)) are used. (Refractive index = 1.4345) is uniformly dispersed at a rate of 0.07 wt%. The size of the parallel beam forming element 1 was 68 mm in length in the left-right direction in the figure, 85 mm in width, 4.0 mm at the end on the light incident surface 2 side, and 0.2 mm at the end 6.
[0048]
L is a fluorescent lamp having a diameter of 3 mm arranged at a distance of 1 mm from the incident surface 2 of the parallel light beam forming element 1. Light is incident rightward from the lamp L, and the light beam collimated from the light extraction surface 3 is emitted therefrom. The arrangement was taken out. Further, R is a reflector appropriately arranged to secure as much light quantity as possible from the incident surface 2, and is arranged here so as to surround the lamp L with a silver foil sheet.
[0049]
The back surface 4 of the parallel light beam forming element 1 is not particularly subjected to a process for generating strong light scattering, such as a light diffusion ink pattern or an uneven diffusion surface. Reference numeral 5 denotes a reflector made of a silver foil sheet disposed opposite to the back surface 4 to return the light emitted from the back surface 4 to the inside of the parallel light beam forming element 1. Further, a polarization separation plate 8 as polarization separation means is disposed at a position facing the light extraction surface 3 of the parallel light beam forming element 1 with the air layer 7 interposed therebetween. An emission direction correcting element 10 is provided. Reference numeral 11 denotes a light emitting surface of the light emitting direction correcting element 10, which is also a light emitting surface as a surface light source device. When this surface light source device is used as a backlight light source of a liquid crystal display device, a liquid crystal display panel is arranged further outside the light emitting direction correcting element 10.
[0050]
The polarization separation plate 8 is formed of a plate-shaped body made of a transparent optical material. In this case, a 1 mm-thick flat plate-shaped member made of BK-7 (refractive index 1.5163), which is a typical optical glass, is used. used. Assuming that the refractive index n0 of the air layer 7 is 1, the value of the Brewster angle is 56.60 °.
[0051]
Hereinafter, an outline of the polarization function in the first embodiment in which the polarization splitting plate 8 and the parallel light beam forming element 1 are combined will be described with reference to FIGS. In FIG. 4, the radiated light of the lamp L and the reflected light from the reflector R enter the inside of the parallel beam forming element 1 from the light incident surface 2 and have a non-uniform refractive index structure inside the parallel beam forming element 1 (here, the structure). The light is guided toward the end portion 6 of the parallel light beam forming element 1 while being scattered by the different refractive index particles. In the process, the light is gradually emitted from the light extraction surface 3, but the emitted light is converted into a parallel light flux and has a clear directivity for the reason described in the section of “action”. Therefore, FIG. 5 shows the behavior of the light emitted from the parallel light beam forming element 1 in a ray tracing format, with the parallel light beam represented by the light beam C0.
[0052]
As described above in the section of "action", in the case where PMMA is used as the base material of the parallel light beam generating element 1, light is strongly emitted in a direction of about 65 ° measured from the normal H0 erected on the light extraction surface 3. Therefore, the emission angle of the representative ray C0 is set to 65 °.
[0053]
The representative light beam C0 emitted from the light extraction surface 3 of the parallel light beam generating element 1 travels straight through the air layer 7, enters the lower surface 8a of the polarization separation plate 8, and is reflected as a light beam C1 entering the polarization separation plate 8. The light is again split into light rays C2 traveling toward the parallel beam forming element 1. The light ray C1 is refracted at the surface 8a, travels straight through the polarization splitter 8, reaches the upper surface 8b of the polarization splitter 8, and is split into an externally emitted light ray C3 and an internally reflected light ray C4. The internally reflected ray C4 further returns to the lower surface 8a and is again divided into the internally reflected ray C7 and the ray C8 traveling to the air layer 7. The internal reflection ray C7 is again split into an external emission ray C9 and an internal reflection ray C10 on the upper surface 8b. Hereinafter, the internally reflected light beam repeats the same process.
[0054]
On the other hand, the light rays C2 and C8 which travel straight through the air layer 7 toward the parallel light beam forming element 1 are split into light rays C11 and C13 and reflected light rays C12 and C14 which re-enter the parallel light beam forming element 1 on the light extraction surface 3. You. The reflected light rays C12 and C14 again go to the polarization separating plate 8 and follow the same path as C0.
[0055]
Through such a multiple reflection / transmission process, the light energy of the light beam C0 is also divided and distributed at each interface 3, 8a, 8b into a reflected light beam and a transmitted light beam. Are very different. The internal light transmittance of the BK-7 plate having a thickness of 1 mm constituting the polarization separation plate 8 is 99.9% or more, and the absorption loss is negligibly small. Therefore, when the light C0 is natural light having a degree of polarization of 0, in which the energy of the P-polarized light component and the energy of the S-polarized light component are equal to 100, the energy amounts of the respective polarized light components C1 to C14 are calculated. Also shown in the figure.
[0056]
For example, when the light ray C0 is split into C1 and C2, the transmittance of the P-polarized light component is extremely high, showing 98.8%, while the transmittance of the S-polarized light component is only 76.6%. Therefore, the light beam C2 is light polarized almost exclusively to the S-polarized light component. That is, it can be said that the Brewster angle condition is approximately satisfied in the range deviated from the Brewster angle of 56.60 ° of BK-7 by about 10 °, and the S-polarization rate of the reflected light beam C2 is extremely high. (If the incident angle of C0 coincides with the Brewster's angle of 56.60 °, the S-polarization of the reflected light beam C2 naturally becomes 100%.)
[0057]
When the light ray C1 is incident on the upper surface 8b of the polarized light separating plate 8, the reflectance for each polarized light component is 1.2% for the P-polarized light component and 23.4% for the S-polarized light component. Accordingly, the energy of the polarized light component of the light beam C3 emitted to the outside is 97.6 for the P component and 58.7 for the S component, indicating that it has a considerable degree of polarization. The values obtained by performing similar calculations for C4 and below are shown in the figure. As is apparent from these numerical values, the energy amount of each polarization component of the PS sharply decreases as the beam splitting is repeated, so that the energy for each polarization component of the externally emitted light is approximated from the rays C3 and C9 shown in FIG. When the amounts are estimated, P-polarized light component = 97.6 and S-polarized light component = 61.9.
[0058]
Thus, it can be seen that even when only the light beam shown in FIG. 5 is considered, a considerably polarized outgoing light beam is obtained, but the present invention relies only on such a process to obtain a polarized light beam. It does not function. The invention of the present application is directed to light returned from a polarization beam splitting means (a BK-7 plate in the first embodiment) disposed opposite to a light extraction surface of a parallel light beam generating element to a parallel light beam generating element (hereinafter referred to as return light). ) Is reused to further improve the degree of polarization of the final emitted light.
[0059]
In the example of FIG. 5, the return light is almost completely S-polarized light, as indicated by the numerical values added to the light rays C11 and C13. This return light undergoes processes such as scattering and reflection again in the process of propagating through the light-scattering light guide constituting the parallel light beam forming element 1, and most of the light is emitted from the light extraction surface 3. Considering the emission directivity at that time, although it is not as good as when the light is incident from the entrance surface 2, the forward scattering property toward the right in FIG. According to the principle described above, it is considered that the light beam has weak directivity which can be represented by the emission direction of the light beam C0.
[0060]
By the way, the light rays C11 (S-polarized light component 18.2) and C13 (S-polarized light component 10.6), which are mostly composed of S-polarized light components, are subjected to the above-mentioned processes such as scattering and reflection in the parallel beam forming element, so that they are polarized. The direction will be disturbed. If this is called the polarization scrambling effect, it can be considered that the degree of S-polarization of light emitted from the light extraction surface 3 derived from C11 or C13 is considerably reduced due to the polarization scrambling effect. If it is assumed that the polarization scrambling effect is perfect and the light is re-emitted from the light extraction surface 3 with no loss, the energy amounts of the P-polarized component 9.1 and the S-polarized component 9.1 for the component derived from C11. Yes, the C-derived component has a P-polarized component of 5.3 and an S-polarized component of 5.3.
[0061]
When both are added, P-polarized light component = 14.4 and S-polarized light component = 14.4. Assuming that this light goes through the same history as C0, the energy amount of (14.4 / 100) × 97.6 = 14.1 becomes the P-polarized light component of the light beam emitted from the upper surface 8b of the polarization separation plate 8. Is added. Therefore, the final amount of energy of the P-polarized light component approximately estimated from this model is 97.6 + 14.1 = 1111.7. The energy amount of the S-polarized light component is 61.9+ (61.9 / 100) × 14.1 = 70.6.
[0062]
That is, in the present invention, a part of the light beam emitted from the light extraction surface 3 of the parallel light beam-forming element 1 is S-polarized to return light, and at least a part of the light beam is depolarized in the parallel light beam-forming element 1. The light is re-emitted from the light extraction surface 3 of the parallel light beam generating element 1 and is again subjected to the S-polarized light elimination action by the polarization splitter. Therefore, as explained in the above case, at least in principle, it is also possible to achieve the effect of amplifying the P-polarized light component contained in natural light to 100% or more. Such a feature is unique to the present invention, and is a feature commonly provided in each embodiment described below.
[0063]
In the description of the first embodiment, the (first) emission light of the parallel beam forming element 1 is represented by C0 at an emission angle of 65 °. The essence hardly changes. FIG. 6 is a graph for understanding this, in which the horizontal axis represents the incident angle to the BK-7 plate (= the exit angle from the light extraction surface 3), and the vertical axis represents one time of each of the P and S polarization components. The transmittance of the transmission (total emission energy from 8b / 8 total incident energy to 8a; return light is not considered again). As can be seen from the graph, the transmittance of the P-polarized light component exceeds about 80% over almost the entire range of 55 ° to 75 °, and the transmittance of the S-polarized light component is about 20% or less. Therefore, even if there is some spread or deviation in the propagation direction of the light beam emitted from the light extraction surface 3, it is apparent that the essential part of the above description does not need to be changed.
[0064]
As can be seen from what has been described so far with respect to the first embodiment, the light source L, the parallel beam forming element 1 and the polarization separation means (the polarization separation plate made of BK-7 in the first embodiment) 8 are polarized. This is a basic configuration requirement for configuring a surface light source device that obtains a luminous flux. However, as can be seen from the description of the polarization process, the directivity characterized by the large exit angle (here, 65 °) of the representative ray C0 remains strong for the light beam emitted from the polarization separation means 8. However, this is not preferable in providing a surface light source device that emits light in a front direction or a direction close to the front direction, which is often required in ordinary applications (such as a backlight light source of a liquid crystal display device).
[0065]
As shown in FIG. 4, the light emitting direction correcting element 10 arranged outside the polarization separating plate 8 satisfies such a requirement. It has a function of correcting the propagation direction of the emitted directional light beam to the front direction. Hereinafter, the light emitting direction correcting function of the light emitting direction correcting element will be described with reference to FIGS. 7A and 7B.
[0066]
FIG. 7A is a view for explaining a typical structure and arrangement of a light emitting direction correcting element, and FIG. 7B is a view showing a modified arrangement. A cross-sectional view obtained by extracting and enlarging the peripheral portion of the polarization splitting plate and the light emitting direction correcting element in the arrangement shown is shown in a form in which the tracing paths of the light rays C3 and C9 are also shown.
In both figures, the light emitting direction correcting elements 10 and 10 'are made of an optical material such as polycarbonate (PC; refractive index npr = 1.59), and one surface has a large number of prism surfaces 10a and 10b (vertex angles). θpr) or 11a, 11b (vertex angle θ′pr). The light emitting direction correcting elements 10 and 10 'have their prism forming surfaces as light incident surfaces as shown in FIG. 7 (A) or conversely as light extracting surfaces as shown in FIG. 7 (B).
[0067]
First, in FIG. 7A, from the related description of FIG. 5, C3 and C9 drawn so as to be emitted at an emission angle of 65 ° with respect to the light extraction surface 8b of the polarization separation plate 8 are as follows: It is considered that the light beam emitted from the polarization splitting plate 8 originating from the representative light beam C0 substantially represents the light beam. These representative rays C3 and C9 go straight through the air layer 9 (refractive index n0 = 1.0) and then enter the prism surface 10a of the light emitting direction correcting element 10 at an angle close to perpendicular.
[0068]
Since the ratio of the amount of light incident on the prism surface 10b on the side opposite to the prism surface 10a can be considered to be relatively small, the representative light beams C3 and C9 travel almost straight to the prism surface 10b and are specularly reflected. The light flux D is incident on the flat light extraction surface 11 of the correction element 10 at an angle close to the vertical, and is emitted from the surface 11 at an angle close to the vertical direction.
[0069]
The angle of inclination .theta.a of the prism surface 10a on the incident side is set so that the light beams C3 and C9 are incident substantially perpendicularly (here, .theta.a = 25 DEG), and the internal reflected light is inclined at the angle of inclination .theta.b of the other prism surface 10b. If the setting is made such that the light is incident on the flat light extraction surface 11 almost perpendicularly (here, θb = 65 ° / 2 = 32.5 °), the direction of the light flux D can be made to more accurately coincide with the vertical direction. As described above, it is possible to adjust the directional characteristics of the light beam D by selecting the formation angle of the prism surface.
[0070]
Next, FIG. 7B is a cross-sectional view for explaining the behavior of the representative light rays C3 and C9 when the light emitting direction correcting element 10 'is arranged so that the prism surfaces 11a and 11b face outward. As in the case of FIG. 7 (A), the representative rays C3 and C9 travel straight through the air layer 9 (refractive index n0 = 1.0) and then strike the flat surface 10'a of the light emitting direction correcting element 10 '. The light enters at an oblique angle, is refracted upward, and most of the light is emitted as a light beam D 'from the opposite prism surface 11a at an angle close to vertical. Depending on the refractive index of the material constituting the light emitting direction correcting element 10 'and the values of the inclination angles θ'a and θ'b of the prism surfaces 11a and 11b, the light is once emitted into the air from the prism surface 11a and then opposed. An optical path that is specularly reflected by the prism surface 11b and heads in the front direction may be used.
[0071]
7A and 7B, the direction characteristics of the light emitted from the polarization splitting plate 8 and the materials constituting the light emission direction correcting element can be obtained. By appropriately selecting the inclination angle and the like of each prism surface in relation to the above, the light emitting direction can be controlled over a considerable range.
[0072]
The light emitting direction correcting elements 10 and 10 'are not limited to those having a prism surface formed in a row as shown in the figure, but may be of any type. For example, a film in which triangular pyramid-shaped or dome-shaped projection groups are distributed, a plate-shaped element having a row-shaped convex portion having a semicylindrical cross section, or the like can be considered. It is also conceivable to use a plurality of sheets in a stack.
[0073]
Next, a second embodiment of the present invention will be described. FIG. 8 shows a second embodiment of the surface light source device with a polarizing function according to the present invention in the same form as that of FIG. In the figure, the same reference numerals are used for the elements common to FIG. 4, and the second embodiment is exactly the same as the first embodiment except for the parts related to the polarization splitting means 8, 8 '. It has a configuration. Therefore, the description of the common part will be omitted, and the description will be focused on the part related to the polarization separating means.
[0074]
The polarization splitting means employed in the second embodiment includes two polarization splitters 8 and 8 ′ arranged in parallel along the light extraction surface 3 of the parallel light beam forming element 1. Each of the polarized light separating plates 8 and 8 'is made of an optical material having a small absorption loss. Here, PMMA (polymethyl methacrylate; refractive index: 1.492, Brewster's angle = 56.17 °) having a plate thickness of 1 mm is used. The transmission absorption loss is 0.01% or less and can be ignored as in the case of BK-7).
[0075]
The inner polarized light separating plate 8 and the outer polarized light separating plate 8 'are separated from each other by 0.5 mm by an appropriate spacer (not shown), and an air layer 9 is secured in a gap therebetween.
[0076]
Outside the outer polarization separation plate 8 ', a light emitting direction correcting element 10 similar to that of the first embodiment is arranged with an air layer 9' interposed therebetween.
[0077]
FIG. 9 is a diagram for explaining the outline of the polarization function in the second embodiment in which the two polarization splitters 8 and 8 'and the parallel light beam forming element 1 are combined. Similar to the case of FIG. 5, the parallel light beam emitted from the light extraction surface 3 of the parallel light beam generating element 1 is represented by a light ray C0 'having an emission angle of 65 °, and the behavior of the light emitted from the parallel light beam generating element 1 is It is written in ray tracing format. In addition, the amount of energy propagated at the time of each light beam branch is also described in accordance with the same notation as in FIG. 5 (P-polarized light component of light C0 '= S-polarized light component = 100).
[0078]
The representative light beam C0 'travels straight through the air layer 7 and is incident on the lower surface 8a of the first polarizing beam splitter 8; And a light beam C2 'traveling toward. Each of the light beams C1 'and C2' follows various branching paths as shown in the drawing, and a part thereof passes through the air layer 9 to the inner surface 8a 'of the second polarization separation plate 8'. Returns to the parallel beam forming element 1 and enters as a return light.
[0079]
The details during this period are exactly the same as in the case of the first embodiment shown in FIG. 5 as far as the portion where the second polarization separation plate 8 'is not involved, so that the detailed description is omitted. However, since the refractive index of the polarization separating plate 8 made of PMMA is slightly different from that of the first embodiment (BK-7), the refraction angle at the time of entering and exiting the interfaces 8a and 8b slightly changes. Accordingly, the branch ratio of the P-polarized light component and the S-polarized light component is changed by a small amount.
[0080]
The light beam C3 'emitted from the first polarization separation plate 8 reaches the inner surface 8'a of the second polarization separation plate 8', and the light beam C2 "enters the inside of the polarization separation plate 8 '. C1 ". Subsequent paths are almost the same as those of the first polarization separation plate 8, except that a substantial part of the light beam that has exited from the inside of the polarization separation plate 8 'to the air layer 9 through the inner side surface 8'a. A path is formed in a multiplex manner in which the light enters the outer side surface 8b of the second polarized light separating plate 8, a part of the light returns to the inside thereof, and a part of the reflected light is returned to the second polarized light separating plate 8 '. It is important to note that During this time, a phenomenon in which a part of the light returning to the first polarization separating plate 8 returns to the parallel light beam forming element 1 should have occurred, albeit slightly.
[0081]
As described above, when two (or more) polarization splitters 8 and 8 'are arranged as polarization splitters, the light path is extremely complicatedly branched. It is difficult to accurately calculate the amounts of the P and S polarization components emitted from the outer surface of the second polarization separation plate 8 '.
[0082]
Therefore, by making use of the fact that the amount of energy transmitted every time the light path branches, an approximate calculation is performed in the range of the illustrated path, and the numerical values of the light rays C "3 to C" 6 are integrated. From the values, it is estimated that the P-polarized light component = 94.9 and the S-polarized light component = 46.7.
[0083]
Comparing this with the corresponding numerical values in the first embodiment, P-polarized light component = 97.6 and S-polarized light component = 61.9 (note that the effect of the difference in the material of the polarization splitter is small). It can be seen that while the P-polarized component is well extracted and stored in each case, the S-polarized component is significantly reduced.
[0084]
As can be seen from this fact, when light emitted at about 65 ° from the parallel beam forming element 1 is taken out through one or more polarizing splitters, the interposition of one polarizing splitter is required. Each time, about 30 to 40% of the S-polarized component is eliminated while the majority of the P-polarized component is preserved.
[0085]
As described above with reference to the first embodiment, the polarization splitting plate of the present invention has a polarization-preserving effect that, in addition to the P-polarized light preservation / S-polarized light elimination phenomenon, returns light rich in S-polarized light components. The P-polarized light component is further enriched through a recycling process in which the polarization state is scrambled by returning to the inside of the light-flux-forming element, and then the polarization separation plate (one or more) undergoes the P-polarized light preservation / S-polarized light elimination action again. It is a clever use of the phenomenon of being done.
[0086]
When the return light amount (S-polarized light component) in the second embodiment is evaluated, it becomes 17.5 + 10.4 + 7.4 + 4.8 = 40.1 from the data also shown in FIG. If the polarization scrambling action of the parallel light beam generating element 1 is perfect, re-emitted light having about 20 P-polarized light components can be obtained. If 94.9% of the polarized light is stored and emitted from the second polarization separation plate 8 ', about 19 polarization components are added. If this is added to the return light exclusion evaluation of 94.9, a polarized light output including about 114 P-polarized light components is finally obtained.
[0087]
It should be noted that the directivity of the outgoing light beam composed of the light rays C3 "to C6" does not significantly deteriorate only when two polarization separation plates are used. Accordingly, also in the second embodiment, the light-emitting direction correcting element 10 disposed next to the second polarization separation plate 8 'can correct the light-emitting direction almost the same as in the first embodiment. As a result, the polarized light beam propagating in the front direction can be emitted from the light emitting surface 11 of the light emitting direction correcting element 10.
[0088]
Next, a description will be given of a third embodiment of the present invention in which the polarization separator used in each of the above embodiments is further devised so as to further improve the degree of satisfaction of the Brewster angle condition at the time of light incidence. Since the overall configuration of this embodiment is the same as that of the first embodiment shown in FIG. 4 except for the structure of the polarization separation plate itself, the description of the overall configuration is omitted here, and FIG. The flat-plate type polarized light separating plate 8 is replaced with a polarized light separating plate 8 ″ having a waveform cross-sectional structure shown in FIG. 10 (hereinafter, referred to as a “waveform polarized light separating plate”), and as shown in FIG. The light beam emitted from the light beam forming element 1 will be described as a representative light beam C0 having an emission angle of 65 °.
[0089]
FIG. 10 (A) shows the cross-sectional shape of the wave-form polarization splitting plate 8 ″, and as shown, is composed of repetitions of relatively short steep slope portions 81 and 83 and relatively long gentle slope portions 82 and 84. The wave-shaped polarization separating plate 8 ″ is made of a light-transmitting material having an appropriate refractive index. Here, PMMA (polymethyl methacrylate; Refractive index 1.492, Brewster angle 56.17 °) is used.
[0090]
FIG. 10B is an enlarged view of a portion surrounded by a circle (one unit of a repetitive shape) in FIG. 10A, and a light beam representing a light beam emitted from the parallel light beam forming element 1. A ray trace diagram of C0 is also shown. The essential feature of this embodiment is that the slope of the gentle side of the incident side 82 is selected so as to satisfy the Brewster angle condition with respect to the representative ray C0. Here, the incident angle when the representative ray C0 having an emission angle of 65 ° with respect to the normal N set on the light extraction surface 3 of the parallel light beam generating element 1 is incident on the surface 82 is assumed to be a Brewster angle of 56 ° (approximately ), The inclination angle of the surface 82 is set to 9 ° with respect to the surface M parallel to the light extraction surface 3.
[0091]
That is, under this angle condition, the P-polarized light component contained in the reflected light beam R1 branched from the representative light beam C0 is theoretically 0, and all the P-polarized light components pass through the surface 82. In particular, in comparison with the first or second embodiment, the P-polarized light component is also emitted with respect to light whose exit angle from the light extraction surface 3 of the parallel light beam forming element 1 is close to a right angle (in a more slanting direction). There is an advantage that the transmittance of the surfaces 82 and 84 is high.
[0092]
The light beam T1 containing a large amount of the P-polarized light component that has entered the inside of the wave form polarization separating plate 8 "is branched at the opposed inclined surface 84 into an outgoing light beam T3 having an outgoing angle of 65.degree. T2 contains almost no P-polarized component (see the data added to the ray C2 in FIG. 5 or the ray C2 'in FIG. 9).
[0093]
The internally reflected light beam T2 is further split at the surface 82 into an internally reflected light beam T4 and a light beam R2 traveling toward the parallel beam forming element 1. Hereinafter, the process of internal reflection / emission that is multiplexly repeated is similar to that described in the first embodiment (particularly, FIG. 5), and the amount of energy carried as the process proceeds is sharply increased. Become smaller.
[0094]
Therefore, according to the configuration of this embodiment, the amount of loss of the P-polarized light component due to the arrangement of the polarization separation plate 8 ″ is extremely small, and is the same as that described in the first and second embodiments. Combined with the polarization scrambling effect on the returning light and the additional addition of the P-polarized component due to the re-emission from the parallel beam forming element 1, it is possible to generate the emitted light containing more P-polarized components. It is needless to say that if the light emitting direction correcting element 10 is arranged for the emitted light, the same light emitting direction correction as in the first and second embodiments is performed.
[0095]
The inclination angles of the steep slopes 81 and 83 are desirably set so as to be parallel to the direction of the representative light beam C0 so that light emitted from the parallel light beam forming element 1 is not incident as much as possible. Here, 90 ° −65 ° = 25 °. The repetition period of the steep slopes 81 and 83 and the gentle slopes 82 and 84 is not particularly limited. However, in general, from the viewpoint of suppressing the thickness measured between the ridges 85 and 86 and maintaining uniformity of brightness as a surface light source, it is generally short. Preferably, it is a period. Here, a repetition period is selected such that the thickness measured between the ridge portions 85 and 86 is 0.5 mm.
[0096]
Next, a description will be given of a fourth embodiment of the present invention in which a polarization splitting plate having a multilayer film made of a different refractive index material is used as the polarization splitting means. The overall configuration of this embodiment is the same as that of the first embodiment shown in FIG. 4 except for the structure of the polarization splitting plate itself. Therefore, the description of the overall configuration is omitted here, and FIG. It is assumed that the configuration in which the flat-plate type polarization separating plate 8 in the above is replaced with the multilayer film-type polarization separating plate 18 shown in FIG. 11 is assumed.
[0097]
Further, as also shown in FIG. 11, it is assumed that the emission angle of the emitted light beam from the parallel light beam forming element 1 is slightly shifted to a higher angle side (the lying direction), and has an emission angle of 70 °. The description will be made assuming that the state is represented by the representative ray D0. (As described in the column of “Function”, the center of the light emitting direction of the light beam emitted from the light extraction surface 3 of the parallel light beam forming element 1 is the refractive index of the light scattering guide constituting the parallel light beam forming element 1. Depending on the value of the correlation distance a and the like, there is a variation range of several degrees to about 10 degrees.)
The multi-layered polarizing beam splitter has a structure in which several layers (in principle, at least two layers) to several tens of thin films are laminated under the condition that transparent materials having different refractive indices are used for materials of adjacent layers. FIG. 11 exemplifies a cross section of the three layers and a main optical path of the representative light beam D0. The multi-layer polarization separator 18 includes a titanium dioxide (TiO2; refractive index n1 = 2.3) layer 181, a silicon dioxide (SiO2; refractive index n2 = 1.46) layer 182, and a titanium dioxide (TiO2; Refractive index n3 = n1 = 2.3) The layer 183 has a structure in which a titanium dioxide layer and a silicon dioxide layer are alternately laminated according to the total number of layers. Layers of materials having further different refractive indices may be laminated (e.g. a layer of zirconium dioxide ZrO2, titanium oxide TiOx with a general oxidation number).
[0098]
The polarization separation principle of such a multilayer polarization separation plate 18 utilizes the difference in the reflection characteristics of the S-polarized light component and the P-polarized light component at the interface formed between the different refractive index materials. It can be said that it has features in common with the polarization separating plate means in the first to third embodiments.
[0099]
As shown in FIG. 11, the representative light beam D0 representing the light beam emitted from the parallel light beam forming element 1 is converted from the air layer 7 (refractive index n0 = 1.0) to the S-polarized light component Is = 100 and the P-polarized light component. When incident on the first layer 181 with a relative intensity of Ip = 100, a ray D1 and a reflected ray D2 that enter the interior of the layer 181 are produced.
[0100]
The reflectance at this time is Rs = 51.8% for the S-polarized component, but is extremely small, Rp = 0.55% for the P-polarized component. That is, only about half of the S-polarized light component can enter the first layer 181, but almost all of the P-polarized light component enters the first layer 181 through the interface.
[0101]
When this light beam D2 reaches the interface with the second layer, it is again split into light beams D3 and D4. The reflectance at that time is Rs (S-polarized component) = 9.3% and Rp (P-polarized component) = 1.9%. That is, about 90% of the S-polarized light component enters the second layer 182, while most of the P-polarized light component enters the second layer 182 through the interface.
[0102]
Similarly, at the interface between the second layer 182 and the third layer 183, branching of D5 and D6 occurs, and the reflectance at that time is Rs (S-polarized component) = 9.3% and Rp (P-polarized component) = 1.9%.
[0103]
As described above, a phenomenon occurs in which most of the P-polarized light component is propagated to the next layer each time it encounters each interface, while a considerable portion of the S-polarized light component is eliminated. Assuming that the effects of multiple reflection and absorption loss are small, when the polarization component at the time of entering the third layer in this case is estimated, values of S component; Is = 39.7, P component; Ip = 95.7 are calculated. You. When the number of layers further increases, it is considered that the numerical values Is and Ip decrease in geometric progression.
[0104]
Assuming that the average common ratio at that time is rs (S-polarized component) and rp (P-polarized component), rs <rp, and rp is slightly less than 1.
Therefore, it is considered that the “purity” of the P-polarized light component increases as the total number of layers constituting the multilayer polarizing plate 18 increases. Such a tendency is not limited to the case where the emission angle of the representative light beam D0 is 70 °, but is realized under a considerably wide angle condition.
[0105]
FIGS. 12 to 14 are graphs for explaining this, in which the light transmittance at each interface in the layer configuration of the present embodiment is shown separately for the P-polarized light component and the S-polarized light component. As can be immediately read from these graphs, even if the incident angle of the representative light beam D0 to the layer 181 is shifted by about 70 ° to 10 °, the transmittance of the P-polarized light component at each interface remains close to 100%, and , S-polarized light component is consistently lower than the P-polarized light component.
[0106]
This indicates that the function of purifying the P-polarized light component of the above-mentioned multilayer polarizing beam splitter cannot be realized only under special conditions.
As described above, the configuration using the multilayer-type polarization separation plate as in the present embodiment has a feature suitable for a case that requires outgoing light having a high degree of polarization (P polarization component purity). You can see that.
[0107]
For reference, FIG. 15 shows an example of the proof data. This is because TiOx (refractive index: around 2.3), SiO2 (refractive index: 1.46) and ZrO2 (refractive index: 2.0) are placed on a 1 mm thick optical glass plate BK-7 (refractive index: 1.5163). The results obtained by measuring the polarization separation function using a spectrophotometer U-3200 manufactured by Hitachi, Ltd. while changing the incident angle from 55 ° to 70 ° for a polarized light separating plate having a multilayer film formed by vacuum evaporation. It is. As can be easily read from this graph, it can be seen that a high polarization separation function is exhibited over the entire visible light range. It can also be seen that the larger the angle of incidence, the higher the polarization separation function.
[0108]
Also in this embodiment, the same polarization scrambling effect on the return light as described in the first and second embodiments and the like, and the effect of enhancing the P-polarized light component by re-emission from the parallel beam forming element 1 are exhibited. Needless to say, the light emission direction can be corrected by arranging the light emission direction correction element 10 at the subsequent stage of the multilayer polarization type separation plate 18.
[0109]
The first to fourth embodiments described so far relate to the variation of the configuration of the polarized light separating means, but the fifth to seventh embodiments to be described next are directed to parallel light beams from the polarized light separating means. The present invention relates to an additional configuration for enhancing the effect of converting an S-polarized component into a P-polarized component with respect to the return light that has returned into the optical element. That is, the essential parts of the fifth to seventh embodiments have properties that can be combined with any of the above-described first to fourth embodiments. The polarized light separating plate 8 (described in the first embodiment) "may be appropriately replaced with the type disclosed in the other second to fourth embodiments. The respective embodiments will be described below under such a premise.
[0110]
First, as a polarization scramble function enhancing means (hereinafter referred to as "reinforcement scrambler") for converting the S-polarized component of the return light into the P-polarized component, a plate-shaped light scattering guide having high scattering ability is used. A fifth embodiment will be described as an example of use.
[0111]
FIG. 16 is a sectional view showing a fifth embodiment of the surface light source device with a polarizing function according to the present invention. The parallel beam forming element 1 composed of a directional light-emitting light-scattering light guide having a wedge-shaped cross-section has a particle diameter of 2 μm and a refractive index of 1.4345 in polymethyl methacrylate (PMMA). It is composed of those uniformly dispersed at a rate of 07 wt%. The size of the parallel beam forming element 1 was 68 mm in length in the left-right direction in the figure, 85 mm in width, 4.0 mm at the end on the light incident surface 2 side, and 0.2 mm at the end 6.
[0112]
L is a fluorescent lamp having a diameter of 3 mm arranged at a distance of 1 mm from the incident surface 2 of the parallel light beam forming element 1. Light is incident rightward from the lamp L, and the light beam collimated from the light extraction surface 3 is emitted therefrom. The arrangement was taken out. Further, R is a reflecting means appropriately arranged to secure as much light quantity as possible from the incident surface 2, and is arranged here so as to surround the lamp L by a sheet made of silver foil.
[0113]
A polarization separation plate 8 as polarization separation means is disposed at a position facing the light extraction surface 3 of the parallel light beam forming element 1 with the air layer 7 interposed therebetween. A correction element 10 is arranged. Reference numeral 11 denotes a light emitting surface of the light emitting direction correcting element 10, which is also a light emitting surface as a surface light source device. When this surface light source device is used as a backlight light source of a liquid crystal display device, a liquid crystal display panel is arranged further outside the light emitting direction correcting element 10.
[0114]
The polarized light separating plate 8 is formed of a flat plate-like body having a thickness of 1 mm and made of the optical glass BK-7. The above configuration is the same as that of the first embodiment, and its operation is basically the same, so that the detailed description is omitted here.
This embodiment is different from the first embodiment in that the polarization scrambling effect on the return light returned from the polarization separation plate 8 into the parallel light beam forming element 1 along the back surface 4 of the parallel light beam generating element 1 is enhanced. Is provided with a reinforcing scrambler SR for performing the operation. This reinforcing scrambler SR prevents the polarization scrambling effect from being insufficient because the thickness of the entire parallel light beam forming element 1 or the vicinity of the wedge-shaped end portion 6 is insufficient in relation to the intensity of the scattering power. Device.
[0115]
Therefore, a material having a higher scattering power than that of the light scattering light guide constituting the parallel light beam forming element 1 is used. Here, assuming that the scattering ability of the same kind of material as the parallel beam forming element 1 is enhanced, 0.5 wt% of silicone-based resin material particles (diameter 2 μm, refractive index = 1.4345) in polymethyl methacrylate (PMMA). Used in a uniform dispersion. The size of the reinforcing scrambler SR was adjusted to the size of the back surface 4 of the parallel light beam forming element 1, and the thickness was 1 mm.
[0116]
With such a configuration, a considerable amount of light enters the reinforcing scrambler SR from the parallel beam forming element 1 and is subjected to an anisotropic scattering effect by a non-uniform refractive index structure (here, a particle material having a different refractive index). , S-polarized light components are converted to P-polarized light components. Then, since this light is subjected to a sufficient polarization scrambling action corresponding to its strong scattering power and returns to the inside of the parallel light beam generating element 1, the polarization scrambling action which tends to be insufficient particularly near the end portion 6 is reinforced. Can be done.
[0117]
Accordingly, the P-polarized light component when the return light is re-emitted toward the polarization separating plate 8 approaches 50%, and the amount of the P-polarized light component contained in the final emitted light beam is enriched. . Reference numeral 5 denotes a reflector made of silver foil provided outside the reinforcing scrambler SR, which prevents the amount of light from being wasted from the outside of the reinforcing scrambler SR.
[0118]
Next, the plate-shaped reinforcing scrambler SR in the fifth embodiment is replaced by a wedge-shaped reinforcing scrambler SR ′, which is arranged complementary to the parallel light beam generating element 1 as shown in FIG. 6 is an embodiment of FIG. In this embodiment, the strength of the polarization scrambling action corresponding to the thickness of the parallel light beam forming element 1 is compensated by the action of the complementary wedge-shaped reinforcing scrambler SR ′, and the polarization function of the surface light source device is improved. More uniform. The size of the wedge-shaped reinforcing scrambler SR ′ was adjusted to the size of the rear surface 4 of the parallel light beam generating element 1, and the thickness was 4 mm at the thickest portion and 0.2 mm at the thinnest portion.
[0119]
Note that the overall configuration of this embodiment is the same as that of the fifth embodiment except for the shape of the reinforcing scrambler SR ′, and thus the description is omitted here.
[0120]
FIG. 18 is a sectional view showing a seventh embodiment of the surface light source device with a polarizing function according to the present invention. The parallel beam forming element 1 composed of a directional light-emitting light-scattering light guide having a wedge-shaped cross-section has a particle diameter of 2 μm and a refractive index of 1.4345 in polymethyl methacrylate (PMMA). It is composed of those uniformly dispersed at a rate of 07 wt%. The size of the parallel beam forming element 1 is 68 mm in length in the left-right direction in the figure, 85 mm in width, 4.0 mm at the end on the light incident surface 2 side, and 0.2 mm at the end 6.
[0121]
L is a fluorescent lamp having a diameter of 3 mm arranged at a distance of 1 mm from the incident surface 2 of the parallel light beam forming element 1. Light is incident rightward from the lamp L, and the light beam collimated from the light extraction surface 3 is emitted therefrom. The arrangement was taken out. Further, R is a reflecting means appropriately arranged to secure as much light quantity as possible from the incident surface 2, and is arranged here so as to surround the lamp L by a sheet made of silver foil.
[0122]
A polarization separation plate 8 as polarization separation means is disposed at a position facing the light extraction surface 3 of the parallel light beam forming element 1 with the air layer 7 interposed therebetween. A correction element 10 is arranged. Reference numeral 11 denotes a light emitting surface of the light emitting direction correcting element 10, which is also a light emitting surface as a surface light source device. When this surface light source device is used as a backlight light source of a liquid crystal display device, a liquid crystal display panel is arranged further outside the light emitting direction correcting element 10.
[0123]
The polarized light separating plate 8 is formed of a flat plate-like body having a thickness of 1 mm and made of the optical glass BK-7. The above configuration is the same as that of the first embodiment as in the case of the fifth and sixth embodiments, and its operation is basically the same. Therefore, detailed description is omitted here.
This embodiment is different from the first embodiment in that a phase difference plate HW acting as a half-wave plate over the entire visible light range is provided along the back surface 4 of the parallel light beam forming element 1. And a reflector 5 made of silver foil is provided on the outside thereof. The slow axis direction of the phase difference plate is set so as to be inclined by 45 ° with respect to the vertical and horizontal ridge lines of the parallel light beam forming element 1. Further, when the return light from the polarization beam splitter 8 travels substantially straight in the parallel light beam forming element 1 and passes through the back surface 4, the phase difference of π / 2 (Δn · d; Is adjusted to give the birefringence value of the phase difference plate HW, and d is the optical path length). If the return light is derived from the representative light ray C0 (outgoing angle 65 °) in FIG. 5, the incident angle to the phase difference plate HW is calculated to be about 60 °. , The above phase difference is given.
[0124]
Attention is now directed to a component of the return light from the polarization separation plate 8 which has hardly undergone the polarization scrambling effect. Since this component is considered to correspond to the straight return light assumed above, the phase difference The plate HW functions as a half-wave plate particularly effective for the S-polarized light component. That is, the linearly returning light is converted into a P-polarized light component by following the path of the back surface of the parallel light beam forming element 1, the phase difference plate HW, the reflector 5, the phase difference plate HW, and the back surface 4 of the parallel light beam forming element 1. Converted to rich light.
[0125]
Most of this light is emitted again from the parallel light beam forming element 1 at an emission angle of about 65 ° due to the forward scattering effect of the parallel light beam forming element 1 (see the section of “Operation”). . Most of the P-polarized component of this light is emitted from the surface light source device as polarized light without being reflected by the polarization separation plate 8. This polarization conversion effect is exerted simultaneously with the polarization scrambling effect of the parallel light beam forming element 1, so that a polarized light beam having a high energy of the P-polarized component as a whole can be obtained.
[0126]
In each of the above embodiments, a rod-shaped fluorescent lamp was used as the light source L. However, the light source in the present invention may be a light supply unit in a broad sense, and does not necessarily have to have a light emitting capability. The output end of the optical fiber bundle coupled to another light emitting element may be used. There is no particular limitation on the polarization characteristics, and even when light having a specific polarization characteristic, such as light derived from laser oscillation, is supplied, the essential polarization function itself of the present invention is not impaired.
[0127]
By the way, as already mentioned, as a typical example in which the features of the surface light source device with a polarizing function of the present invention are very effectively utilized, there is application to a backlight light source means of a liquid crystal display device. That is, since the conventional surface light source device does not have a polarizing function like the surface light source device with the polarizing function of the present invention, the surface light source device is provided by the polarizing plate provided on the light incident side of the liquid crystal display panel. Although about half of the light energy of the outgoing light was cut off and wasted, the surface light source device with the polarization function of the present invention was adopted as the backlight light source means of the liquid crystal display device. By simply arranging the polarization direction of the emitted light beam and the polarization axis direction of the polarizing plate in parallel, the ratio of light energy that effectively contributes to display can be significantly improved.
[0128]
FIG. 19 is an element exploded perspective view showing a basic arrangement in a case where the surface light source device with a polarizing function according to the present invention is used as a backlight light source means of a liquid crystal display device. In this embodiment, the same type of surface light source device with a polarization function as that shown in the first embodiment of the present invention described above (see FIG. 4) is used as the backlight light source means. Elements are designated with the same reference numerals.
[0129]
That is, reference numeral 1 denotes a parallel beam forming element formed of a directional light-scattering light guide having a wedge-shaped cross-sectional shape. Here, silicone-based resin material particles (diameter 2 μm, refractive index = 1) in polymethyl methacrylate (PMMA) .4345) is uniformly dispersed at a rate of 0.08 wt%. When the effective scattering irradiation parameter E and the correlation distance a are calculated under these conditions, E = 7.39 [cm ^-1 ], A = 1.3 μm. The size of the parallel light beam generating element 1 is 68 mm in the left-right direction in the figure, 85 mm in width, 4.0 mm at the end on the light incident surface side, and 0 mm at the end according to the size of the liquid crystal cell used. 0.2 mm.
[0130]
L denotes a fluorescent lamp having a diameter of 3 mm arranged at a distance of 1 mm from the incident surface of the parallel light beam forming element 1. Light incident rightward from the lamp L is extracted from the light extraction surface 3 as a parallel light beam. It is. R is a reflector appropriately arranged to secure as much light quantity as possible from the incident surface, and a silver foil sheet is used.
[0131]
On the back surface 4 of the parallel light beam generating element 1, no treatment for generating strong light scattering, such as a light diffusion ink pattern or an uneven diffusion surface, is performed, and a reflector 5 made of a silver foil sheet is arranged. I have.
[0132]
Reference numeral 8 denotes a polarization separation plate 8 arranged at a position facing the light extraction surface 3 of the parallel light beam forming element 1, and further a light emission direction correcting element 10 is arranged outside the polarization separation plate 8. As the polarization separating plate 8, a flat plate-like member having a thickness of 1 mm and made of optical glass BK-7 (refractive index 1.5163) was used. The light emitting direction correcting element 10 was made of polycarbonate (PC; refractive index: 1.59), and was arranged with its prism-formed surface facing the polarization separating plate 8.
[0133]
A liquid crystal display panel comprising two polarizing plates 12, 14 and a liquid crystal cell 13 interposed therebetween is arranged on the light emission side of a backlight light source unit composed of a surface light source device with a polarizing function comprising these elements. Is done. The direction of the transmission polarization axis of the polarizing plate 12 on the light incident side is set to be horizontal in the figure, while the direction of the transmission polarization axis of the polarizing plate 14 on the light emission side is vertical in the figure. Is set to
[0134]
As already described in detail, the luminous flux emitted from the surface light source device with a polarizing function including the light source L, the parallel luminous flux converting element 1, the reflectors R and 5, the polarization separating plate 8, and the light emitting direction correcting element 10 is high. It has a degree of polarization, has directivity along the direction shown by the broken line in the figure, and has a light intensity profile with high flatness.
[0135]
As described in the description of the polarization process using the parallel light beam converting element 1 and the polarization splitting plate 8, the light beam emitted from the surface light source device with a polarization function is P-polarized, so that it is illustrated. Under the arrangement condition, the main polarization axis is in the horizontal direction in the figure. Therefore, the ratio of the amount of light transmitted through the polarizing plate 12 out of the light incident on the polarizing plate 12 as the backlight light flux increases, and at least in principle, a light transmittance exceeding 50% is secured.
[0136]
Such a feature cannot be expected at all in the conventional configuration in which at least 50% of the light energy is wasted no matter how the direction of the transmission polarization axis of the polarizing plate on the liquid crystal panel incident side is selected. is there.
[0137]
In this embodiment, the example in which the surface light source device with the polarization function of the first embodiment is used as the backlight light source means, but the type shown in other embodiments is used. Needless to say, a similar liquid crystal display device can be configured.
[0138]
Further, the basic conditions required for the scattering characteristics of the parallel beam forming element used are as described in the claims, but the degree of demand for displays for video cameras, personal computers, word processors, televisions, etc. When the application as a backlight light source means of a liquid crystal display device having a panel size of 3 inches to 10 inches with a high value is considered, a particularly preferable result is obtained when the effective scattering irradiation parameter E and the correlation distance a are in the following ranges. It has been confirmed that.
Effective scattering irradiation parameter E: 2.77 [cm ^-1 ] ≦ E ≦ 9.24 [cm ^-1 ]
・ Correlation distance a; a ≦ 7 μm
Finally, in the present invention, a material and a manufacturing method of the light-scattering light guide used as the parallel light beam forming element or the reinforcing scrambler will be described.
Various polymer materials can be used as the base of the light-scattering light guide used in the present invention. Representative examples of these polymers are shown in Tables 1 and 2 below.
[0139]
[Table 1]

[0140]
[Table 2]

The light scattering light guide based on such a polymer material can be manufactured by the following method.
First, one is a method using a molding process including a step of kneading two or more kinds of polymers.
That is, two or more types of polymer materials having different refractive indices mutually different (arbitrary shape may be used. Industrially, for example, pellets are considered), and they are mixed and kneaded (kneading step) and kneaded. The obtained liquid material is injected into a mold of an injection molding machine at a high pressure and cooled and solidified, and the molded parallel light beam forming element is removed from the mold to obtain a parallel light beam forming element having a shape corresponding to the mold shape. I can do it.
[0141]
Since the kneaded two or more kinds of polymers having different refractive indices solidify without being completely mixed, unevenness (fluctuation) is generated and fixed in their local concentration, and uniform scattering power is provided.
The kneaded material is poured into a cylinder of an extruder and extruded in a usual manner to obtain a desired molded product.
[0142]
A wide variety of combinations and mixing ratios of these polymer blends can be selected, and the refractive index difference, the strength and properties of the non-uniform refractive index structure generated in the molding process (scattering irradiation parameter E, correlation distance a, dielectric In this case, the ratio may be determined in consideration of the rate fluctuation square mean τ. Representative polymer materials that can be used are as shown in Tables 1 and 2.
[0143]
Another method of manufacturing a material constituting the light scattering light guide is to uniformly mix and disperse particulate materials having different refractive indices (a refractive index difference of 0.001 or more) in a polymer material. .
One of the methods that can be used for uniformly mixing the particulate material is a method called a suspension polymerization method. That is, when a particulate material is mixed in a monomer and a polymerization reaction is performed in a state of being suspended in hot water, a polymer material in which the particulate material is uniformly mixed can be obtained. If this is used as a raw material and molding is performed, a light-scattering light guide having a desired shape is manufactured.
[0144]
In addition, suspension polymerization is performed for various combinations of particulate materials and monomers (combinations of particle concentration, particle size, refractive index, etc.), and a plurality of types of materials are prepared, and these are selectively blended and molded. Is performed, light-scattering light guides having various characteristics can be manufactured. Further, if a polymer containing no particulate material is blended, the particle concentration can be easily controlled.
[0145]
Another method available for uniform incorporation of the particulate material is to knead the polymer material and the particulate material. Also in this case, kneading and molding (pelletization) are performed with various combinations of particulate materials and polymers (combinations of particle concentration, particle size, refractive index, etc.), and these are selectively blended to form a light scattering guide. By shaping and manufacturing the light body, light scattering light guides having various characteristics can be obtained.
[0146]
It is also possible to combine the above-mentioned polymer blending method and the method of mixing particulate materials. For example, it is conceivable to mix a particulate material when blending and kneading polymers having different refractive indices.
[0147]
Hereinafter, some examples of the manufacturing method will be given.
<Production Example 1>
To a methacrylic resin pellet (Asahi Kasei, Delvette 80N) was added 0.3 wt% of a silicone resin powder having a particle diameter of 0.8 μm (Toshiba Silicone, Tospearl 108), mixed and dispersed by a mixer, and then extruded by an extruder. By extruding into a strand and pelletizing with a pelletizer, a pellet in which the silicone resin powder was uniformly dispersed was prepared.
[0148]
The pellets are molded using an injection molding machine under the conditions of a cylinder temperature of 230 ° C. to 260 ° C. and a mold temperature of 50 ° C., and have a length of 68 mm, a width of 85 mm and a thickness of 3.8 mm to 0.8 mm in the long side direction. A wedge-shaped light-scattering light guide gradually changed to 2 mm was obtained.
[0149]
The correlation distance of the manufactured light scattering light guide is a = 0.53 μm, and the estimated calculated value of the effective scattering irradiation parameter by the above equation (11) is E = 12.6 [cm]. ^-1 ]Met.
[0150]
<Production Example 2>
0.3% by weight of a silicone resin powder (Tospearl 108, manufactured by Toshiba Silicone Co., Ltd.) having a particle size of 0.8 μm was added to MMA, and spherical particles in which the powder was uniformly dispersed were obtained by a known suspension polymerization method. This was pelletized with a pelletizer in the same manner as in Production Example 1 to prepare a pellet in which the silicone resin powder was uniformly dispersed.
[0151]
Hereinafter, the same type of wedge-shaped light scattering light guide was obtained under the same conditions as in Production Example 1. This light-scattering light guide was indistinguishable in appearance from the light-scattering light guide produced in Production Example 1. The correlation distance is a = 0.53 μm, and the estimated value of the effective scattering irradiation parameter according to the equation (11) is E = 12.6 [cm]. ^-1 ]Met.
[0152]
<Production Example 3>
0.5 wt% of polystyrene (PSt) was added to polymethyl methacrylate (PMMA), and mixed for 10 minutes using a V-type tumbler and then for 5 minutes using a Henschel mixer. This was melted and mixed using a 30 mm diameter twin screw extruder (manufactured by Nakatani Machinery Co., Ltd.) under the conditions of a cylinder temperature of 220 ° C. to 250 ° C., a screw rotation speed of 75 rpm, and a discharge rate of 6 kg / hr to pelletize. Created.
[0153]
Using an injection molding machine, these pellets are used at a cylinder temperature of 220 ° C. to 250 ° C., a mold temperature of 65 ° C., a medium injection speed, an injection pressure short shot pressure plus 10 kg / cm. ^Two To obtain a wedge-shaped light-scattering light guide having a length of 68 mm, a width of 85 mm and a thickness gradually changing from 3.8 mm to 0.2 mm in the long side direction.
[0154]
<Production Example 4>
To 0.05%, 0.08%, 0.10% and 0.15% by weight of MMA (methyl methacrylate) and 2 μm-size silicone resin powder (Toshiba Silicone, Tospearl 120) are added and dispersed uniformly. The four types of samples and the MMA sample without particles were prepared, and 0.5% by weight of benzoyl peroxide (BPO) was used as a radical polymerization initiator and n-lauryl mercaptan (n was used as a chain transfer agent) in each of the five types of samples. -LM) was added in an amount of 0.2 wt%, and the mixture was cast at 70 ° C. for 24 hours, and was subjected to casting polymerization at 68 mm in length and 85 mm in width, and the thickness gradually changed from 3.8 mm to 0.2 mm in the long side direction. Light guides were produced one by one.
[0155]
<Production Example 5>
0.025 wt% of silicone oil is added to MMA (methyl methacrylate) and uniformly dispersed, benzoyl peroxide (BPO) is 0.5 wt% as a radical polymerization initiator, and n-butyl mercaptan (n-BM) is used as a chain transfer agent. Sol at 70 ° C. for 30 minutes, and then cast and polymerized at 65 ° C. for 24 hours to be 68 mm long, 85 mm wide and 3.8 mm long in the long side direction. To produce a wedge-shaped light-scattering light guide gradually changing from 0.2 mm to 0.2 mm.
[0156]
<Production Example 6>
To PMMA (polymethyl methacrylate), 0.08 wt% of a silicone resin powder (Tospearl 120, manufactured by Toshiba Silicone Co., Ltd.) having a particle size of 2 μm was added, and mixed for 10 minutes using a V-type tumbler and then for 5 minutes using a Henschel mixer. . This was melt-mixed (cylinder temperature 220 ° C. to 250 ° C.) and extruded by a twin-screw extruder to produce pellets.
[0157]
The pellets are injection-molded using an injection molding machine at a cylinder temperature of 220 ° C. to 250 ° C., and a wedge shape having a length of 68 mm, a width of 85 mm and a thickness gradually changing from 3.8 mm to 0.2 mm in the long side direction. Was produced.
[0158]
【The invention's effect】
The surface light source device with a polarizing function of the present invention realizes a recyclable polarizing process based on a configuration in which a parallel beam forming element and a polarization separating unit having a reflection characteristic depending on a polarization component are combined. A polarized light beam can be obtained with high energy use efficiency. In addition, according to the surface light source device with a polarizing function according to the present invention, since a clear directivity derived from the parallel light emitting element is preserved in the emitted light beam, a parallel light emitting element utilizing a prism effect is added. By using such a method, a polarized light beam that propagates in a desired direction can be generated.
[0159]
Such characteristics are extremely advantageous when the surface light source device with a polarizing function of the present invention is used as a backlight light source means of a liquid crystal display device, which significantly improves the display quality of the liquid crystal display device and reduces power consumption. Is sufficient to greatly improve
[Brief description of the drawings]
FIG. 1 is a graph showing the condition for keeping the effective scattering irradiation parameter E constant by taking the correlation distance a on the horizontal axis and the root mean square τ of the dielectric constant fluctuation on the vertical axis, and E = 50 [cm]. ^-1 ] And E = 100 [cm ^-1 ]].
FIG. 2 is a graph illustrating that a forward scattering property of a light scattering light guide changes according to a correlation distance a.
FIG. 3 is a diagram illustrating a basic shape of a cross section of a light-scattering light guide used in the surface light source device of the present invention, together with a state of repeated reflection inside.
FIG. 4 is a cross-sectional view showing a first embodiment of the surface light source device with a polarizing function according to the present invention.
FIG. 5 shows the behavior of light emitted from the parallel light beam forming element 1 in a ray tracing format for a representative light ray.
FIG. 6 is a graph in which the horizontal axis represents the angle of incidence on the BK-7 plate, and the vertical axis represents the transmittance of the P and S polarization components for one transmission.
FIG. 7A is a diagram illustrating a typical structure and arrangement of a light emitting direction correction element, and FIG. 7B is a diagram illustrating a modified arrangement. Both figures are shown in a cross-sectional view in which the peripheral portions of the polarization separating plate and the light emitting direction correcting element in the arrangement shown in FIGS. 4 and 5 are extracted and enlarged, and the trace paths of the light rays C3 and C9 are also shown. .
FIG. 8 shows a second embodiment of the surface light source device with a polarizing function according to the present invention in the same form as in FIG.
FIG. 9 is a diagram for explaining an outline of a polarization function in a second embodiment in which two polarization splitters and a parallel beam forming element are combined.
10A is a diagram showing a cross-sectional shape of a wave-form polarization splitter, and FIG. 10B is an enlarged view of a portion surrounded by a circle (one unit of a repetitive shape) in FIG. In the drawing, a ray tracing diagram of a light ray C0 representing a light beam emitted from the parallel light beam forming element 1 is also shown.
FIG. 11 is a diagram for explaining the structure and operation of a multilayer polarizing beam splitter, illustrating a cross section of three multilayer films and a main optical path of a representative ray D0.
12 is a graph showing the transmittance of each polarized light component at the interface between the air layer and the first layer in the structure shown in FIG. 11 as a function of the incident angle.
13 is a graph showing the transmittance of each polarized light component at the interface between the first layer and the second layer in the structure shown in FIG. 11 as a function of the incident angle.
FIG. 14 is a graph showing the transmittance of each polarized light component at the interface between the second layer and the third layer in the structure shown in FIG. 11 as a function of the incident angle.
FIG. 15 shows a polarizing beam splitter having a multilayer film made of TiOx, SiO2 and ZrO2 formed on a 1 mm-thick optical glass plate BK-7 by vacuum evaporation. Is a graph showing the result of measurement while changing the angle from 55 ° to 70 °.
FIG. 16 is a sectional view showing a fifth embodiment of the surface light source device with a polarizing function according to the present invention.
FIG. 17 is a sectional view showing a sixth embodiment of the surface light source device with a polarizing function according to the present invention.
FIG. 18 is a sectional view showing a seventh embodiment of the surface light source device with a polarizing function according to the present invention.
FIG. 19 is an exploded perspective view showing a configuration of an embodiment in which the present invention is applied to a backlight light source means of a liquid crystal display device.
[Explanation of symbols]
1 Parallel beam forming element
2 Light incidence surface
3 Light extraction surface
4 Back
5 Reflector (silver foil)
6 Terminal part of parallel beam forming element
7,9 Air layer
8,8 'polarized light separator (flat plate)
8 "corrugated polarized light separator
10 Light emitting direction correction element
11 Light emitting surface of light emitting direction correction element
18 Multi-layered polarization separator
181 to 183 First to Third Layers of Multilayer Film
C0, C'0, D0 Representative rays
L Fluorescent lamp (light source)
R reflector
SR, SR 'Reinforced scrambler
HW retardation plate

Claims (8)

The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is expressed as The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, and a light-transmissive polarization separating means arranged along the light extraction surface of the parallel light beam generating element and having a reflection characteristic depending on a polarization component. Surface light source device with polarization function. The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, and a light-transmissive polarization separation means arranged to extend along the light extraction surface of the parallel light beam forming element and having a reflection characteristic depending on a polarization component. The means may include a polarization separator made of a transparent optical material having a refractive index in the range of 1.3 to 2.0. A surface light source device having a polarization function. The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is expressed as The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, and a light-transmissive polarization separation means arranged to extend along the light extraction surface of the parallel light beam forming element and having a reflection characteristic depending on a polarization component. The means are each stacked with an air layer in between, each having a refractive index in the range of 1.3 to 2.0. A surface light source device with a polarizing function, comprising: a plurality of polarized light separating plates. The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is expressed as The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, and a light-transmissive polarization separation means arranged to extend along the light extraction surface of the parallel light beam forming element and having a reflection characteristic depending on a polarization component. The means includes a polarization separator having a refractive index in the range of 1.3 to 2.0, and a light incident surface of the polarization separator. With polarization function, characterized in that it is repeatedly inclined surface as meet the Brewster angle condition corresponding to the emission direction of the parallel light flux emitted from the light output surface is formed of said collimated element in Surface light source device. The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is expressed as The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, and a light-transmissive polarization separation means arranged to extend along the light extraction surface of the parallel light beam forming element and having a reflection characteristic depending on a polarization component. A polarization separator having a multilayer film made of an optical material having a refractive index in a range of 1.3 to 2.3. A surface light source device with a polarizing function, comprising: The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is expressed as The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel light-flux forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range; Light supply means, light-transmitting polarized light separating means arranged to extend along the light extraction surface of the parallel light beam forming element, and having a reflection characteristic dependent on a polarization component; and A polarization scrambler arranged along a surface opposite to the light extraction surface. Surface light source device with optical function. The value of the effective scattering irradiation parameter E [cm ^-1 ] that defines the light scattering power is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the non-uniform refractive index structure that gives the light scattering power is The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering guide) is 0.06 ≦ a ≦ 35. A parallel light-flux-forming element comprising a light-scattering light guide including a volume region having a wedge-shaped cross-section in a range, and a cross-sectional area of the wedge-shaped cross-section of the parallel light-flux-forming element is disposed on an end face side having a relatively large size Light supply means, a light-transmitting polarized light separating means arranged to extend along a light extraction surface of the parallel light-fluxizing element, and having a reflection characteristic depending on a polarization component; and A polarization conversion unit arranged along a surface opposite to the light extraction surface, wherein the polarization conversion unit A surface light source device with a polarizing function, comprising: a retardation plate; and a light reflecting means disposed outside the retardation plate. The surface light source device with a polarization function according to any one of claims 1 to 7, wherein a light emission direction correcting element is disposed outside the polarization separation unit.

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