JP2004001396A - Optical writing device and image forming device - Google Patents

Abstract

A high-resolution image exposure can be performed even when a low-resolution illuminant array is used.
An optical path of light emitted from each light emitting body of a light emitting body array is shifted by an optical path shift unit, so that light irradiation in which pixel pitches are complemented is performed on a recording body. The optical path shifting means 301 is formed by filling a liquid crystal layer 305 made of a chiral smectic C phase having homeotropic alignment between a pair of transparent substrates 303 each having a vertical alignment film 304 formed on an inner surface thereof. A voltage is applied to the electrode pair 307 disposed along the liquid crystal layer 305 to such an optical path shift means 301, whereby the normal direction of the substrate surface and the arrangement direction of the luminous bodies 101 are arranged in the liquid crystal layer 305. An electric field is generated in a direction substantially orthogonal. As a result, the optical path shifting means 301 exhibits an optical path shifting function.
[Selection] Figure 2

Description

同様に、電極対３０７への印加電圧を反転して紙面奥側への電界が印加された場合、図６に示すように、液晶分子の自発分極が正ならば液晶ダイレクタは図６中右下に傾斜し、光学軸が下側に角度θで傾斜した複屈折板として機能する。異常光として左側から入射した直線偏光は、図６中下側に平行シフトする。したがって、電界方向の反転によって、２Ｓ分の光路偏向量が得られる。
【００７８】
したがって、電極対３０７を介して液晶層３０５に印加する電界の極性をスイッチング動作することで、液晶層３０５は光路シフト機能を発揮する。これにより、画素ピッチ間が補完された光照射を記録体２０１に対して行なうことが可能となり、低い解像度の発光体アレイ１０２を使用しても、高解像度の画像露光が可能である。
【００７９】
ここで、図５及び図６からも明確なように、発光体アレイ１０２が放射した光の光路は、対称にシフトする。したがって、光路シフト手段３０１では、光路をシフトする場合に光路長の変化をもたらさないという利点がある。
【００８０】
また、液晶層３０５においてキラルスメクチックＣ相の螺旋構造が解ける閾値電界以下でも、液晶ダイレクタの平均的な方向を液晶層３０５の光学軸として扱うことで、キラルスメクチックＣ相の螺旋構造が解ける閾値電界以上の場合と同様に扱うことが可能である。このようなキラルスメクチックＣ相の螺旋構造が解ける閾値電界以下の領域でも、電界強度に対して光学軸の傾斜方向が変化するため、シフト量を制御することが可能となる。
【００８１】
また、電界反転時のシフト量２Ｓは、液晶層３０５の液晶材料の光学特性や液晶層３０５の厚みに依存する。例えば、液晶層３０５の厚みが数十μｍから百μｍ程度の厚みの場合には、数μｍから数十μｍのシフト量が可能である。これにより、本実施の形態の光路シフト手段３０１は、数百ｄｐｉから数千ｄｐｉに対応する構造として適している。
【００８２】
さらに、本実施の形態では、水平電界を印加するために、図３１に例示した光書込み装置のような透明電極を光路中に設ける必要がないため、透明電極による透過率の低下の影響がないという構造上の利点がある。
【００８３】
加えて、光路シフト手段３０１における光学軸の切換え時間は、液晶層３０５における液晶材料の自発分極、チルト角、螺旋ピッチ、粘弾性や、電界強度、温度などによって変化するが、数百Ｖ／ｍｍの電界強度で数百μｓｅｃ程度、数千Ｖ／ｍｍ（数Ｖ／μｍ）の電界強度で数十μｓｅｃ程度の高速応答が可能である。
【００８４】
図７は、発光体１０１のピッチと光路シフト手段３０１による光路シフト量と画素ピッチと解像度との関係を例示する模式図である。
【００８５】
ここで、発光体１０１のピッチと光路シフト手段３０１による光路シフト量と画素ピッチと解像度との関係について具体例を挙げて説明する。
【００８６】
例えば、図７に示すように、６００ｄｐｉの一次元の発光体アレイ１０２（発光体ピッチ４２．３μｍ）を用い、解像度１２００ｄｐｉ（画素ピッチ２１．１μｍ）、記録体移動速度２０ｍｍ／ｓｅｃの速さで画像を書込む場合、必要なシフト量は２１．１μｍであり、上記の光路シフト手段を用いることができる。１ライン分の書込み時間は約１０６０μｓｅｃである。その間にシフト位置二ヶ所での印字が必要なので、一ヶ所の時間は半分の約５３０μｓｅｃであり、数百μｓｅｃの光路切換え時間でも十分に露光が可能な時間が確保できる。記録体２０１の移動が一定速度の場合、シフト位置での露光時には記録体２０１が僅かに進んでいるため、一つの発光体１０１による露光部の軌跡は図７に例示するようにジグザグ状になる。このような交互配置の画素位置に対応して書込む画像のデータを処理しても良い。あるいは、ステッピングモータなどを用いて記録体２０１の移動をステップ的に行ない、光路シフトの間は記録体２０１の移動を止め、シフト時の画素を同一ライン上に露光するようにしても良い。
【００８７】
［光書込み装置の第二の実施の形態］
本発明の光書込み装置の第二の実施の形態を図８に基づいて説明する。第一の実施の形態と同一部分は同一符号で示し説明も省略する。
【００８８】
図８（ａ）は、光書込み装置の縦断側面図、図８（ｂ）は、その縦断正面図である。
【００８９】
本実施の形態では、複数（本実施の形態では二個）の光路シフト手段３０１を、各光路シフト手段３０１による光の移動方向が略平行となる向きとなるように光路に対して直列に配置し、各光路シフト手段３０１に対して独立して電圧印加可能に電源３０８を設けた。本実施の形態では、一方の光路シフト手段３０１に電圧を印加する第一電源３０８ａと、もう一方の光路シフト手段３０１に電圧を印加する第二電源３０８ｂとを設けている。
【００９０】
そして、それぞれの光路シフト手段３０１における光路シフト量としては、発光体アレイ１０２のピッチＰに対して、発光体アレイ１０２側の光路シフト手段３０１のシフト量はＰ／２に、記録体２０１側の光路シフト手段３０１のシフト量はＰ／４に設定されている。
【００９１】
このような構成において、第一及び第二電源３０８ａ、３０８ｂの動作を制御することで、２倍×２倍の４倍の画素密度での光書込みが可能となる。したがって、２倍以上に画素密度を増加させることができる。しかも、このような画素密度の増加は、単純に光路シフト手段３０１を多段に重ねることで実現可能である。これは、光路シフト手段３０１の直線偏光面が一定だからである。
【００９２】
なお、光路シフト手段３０１の数や各光路シフト手段３０１における光路のシフト量などは、上記例に限定されない。
【００９３】
［光書込み装置の第三の実施の形態］
本発明の光書込み装置の第三の実施の形態を図９に基づいて説明する。第一の実施の形態と同一部分は同一符号で示し説明も省略する。
【００９４】
図９は、光書込み装置の縦断正面図である。
【００９５】
発光体１０１の間隔が比較的大きな安価な発光体アレイ１０２を用いる場合、光路シフト量も大きく設定する必要がある。そのために液晶層３０５の厚みを厚く設定すると、液晶層３０５中に垂直配向状態が崩れた配向欠陥が発生する恐れがある。この配向欠陥は、液晶層３０５が厚いほど発生し易い。そして、このような配向欠陥が生ずると、液晶層３０５が白濁して光散乱や透過率減少の原因となる。
【００９６】
そこで、本実施の形態では、このような配向欠陥の発生を防止するために、図９に示すように、一つの光路シフト手段３０１の液晶層３０５を中間層３０９によって厚み方向に分割し、中間層３０９の少なくとも一方の表面には基板３０３に形成されているのと同様な垂直配向膜３０４を形成する。そして、分割された両液晶層３０５の内部に均一に印加されるように電極対３０７を配置する。図９に示す例では、液晶層３０５の部分全体を挟みこむように電極対３０７が配置されている。あるいは、各液晶層３０５のスペーサ３０２を金属電極で形成して電極対として兼用しても良い。
【００９７】
中間層３０９としては屈折率異方性が少なく透明なフィルム状あるいは板状の材料を用いることができるが、垂直配向膜作成プロセスでの温度や溶剤の使用に対して耐性があることが好ましく、数十μｍから数百μｍ程度の厚みのガラス板が特に好ましい。
【００９８】
このような構成において、中間層３０９は、スメクチック層の配向規制力が弱くなる液晶層３０５の中央部において配向規制力を生じさせる。このため、それぞれの液晶層３０５についてその厚みを厚く設定することなく、光路シフト手段３０１による光路シフト量が増大する。したがって、液晶層３０５の各層の厚みを比較的薄くすることにより配向欠陥の発生を防止しつつ、液晶全体の厚みを厚く設定することができるので、光路シフト手段３０１による光路シフト量を増大させることが可能となる。
【００９９】
［光書込み装置の第四の実施の形態］
本発明の光書込み装置の第四の実施の形態を図１０に基づいて説明する。
【０１００】
図１０は、光書込み装置の一態様の縦断正面図、図１１は、光書込み装置の別の態様の縦断正面図である。
【０１０１】
前述した第一ないし第三の実施の形態では、スペーサ３０２で液晶層３０５の厚みを規制し、光路シフト手段３０１の側面に電極対３０７を設けていた。この構成では、電極対３０７の間に液晶層３０５とスペーサ３０２とを挟んでいるので、液晶層３０５の内部に電界を発生させる場合に、スペーサ３０２の幅の分だけ余分な電圧を印加する必要がある。
【０１０２】
そこで、本実施の形態では、図１０又は図１１に例示するように、電極対３０７が液晶層３０５とスペーサ３０２との間に位置付けられるようにスペーサ３０２の内側にシート状の電極対３０７を設けた。したがって、電極対３０７の間隔は、液晶層３０５の厚みと等しくなる。
【０１０３】
図ではスペーサ３０２の内側の側面にシート状の電極を設けているが、スペーサ３０２の側面上に金属材料をスパッタリング法により付着させて作成しても良いし、スペーサ材料固まりの一面に金属層を貼り合わせた後、金属層が側面となるようにスペーサ材料をスライスして作成することができる。また、スペーサ自体が金属材料からなり、スペーサと電極を兼用しても良い。
【０１０４】
このような構成において、液晶層３０５の内部に効率的に水平電界を発生させることができ、これによって、液晶層３０５に対する印加電圧の値を低減することができる。
【０１０５】
また、電極対３０７がスペーサ３０２を兼用しているので、部品点数を減らすことができると共に、液晶層３０５の厚みを確実に均一化することができる。
【０１０６】
なお、図１０に例示する光書込み装置は、図８に例示する第二の実施の形態の光書込み装置の構成を基本とする。よって、第二の実施の形態と同一部分は同一符号で示し説明も省略する。また、図１１に例示する光書込み装置は、図９に例示する第三の実施の形態の光書込み装置の構成を基本とする。よって、第三の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１０７】
［光書込み装置の第五の実施の形態］
本発明の光書込み装置の第五の実施の形態を図１２ないし図１４に基づいて説明する。第一の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１０８】
図１２は、第一の実施の形態における光書込み装置で発生する現象を説明するための光書込み装置の縦断側面図、図１３は、本実施の形態の光書込み装置の一態様を例示する光書込み装置の縦断側面図、図１４は、本実施の形態の光書込み装置の別の一態様を例示する光書込み装置の縦断側面図である。
【０１０９】
前述した第一ないし第四の各実施の形態では、発光体アレイ１０２からの放射光が光路シフト方向に平行な直線偏光である場合を想定して動作を説明した。しかしながら、実際には、発光体アレイ１０２からの放射光が所望の直線偏光であるとは限らない。そこで、光路シフト方向に平行、すなわち液晶ダイレクタの傾斜方向に平行な直線偏光成分は図５（ａ）と図５（ｂ）とに例示するようにシフトされるが、それ以外の光はシフトされず、図１２に例示するようなノイズ光となる。このようなノイズ光は、解像度の低下やコントラスト比の低下をもたらす。
【０１１０】
そこで、本実施の形態では、所望のシフトされた光のみが記録体２０１上に露光されるように、光路の移動方向に平行な偏光面の光のみを透過する直線偏光板４０１を設けている。このような直線偏光板４０１の設置位置は、光路シフト手段３０１の入射側あるいは出射側のいずれでも良い。図１３に例示する一態様では、光路シフト手段３０１の入射側に直線偏光板４０１を配置した一例を示し、図１４に例示する別の一態様では、光路シフト手段３０１の出射側に直線偏光板４０１を配置した一例を示す。
【０１１１】
このような構成において、記録体２０１に露光される光は、直線偏光板４０１によって、確実に光路の移動方向に平行な直線偏光だけとなるので、記録体２０１に不要な光が露光されることが防止され、これによって、高精細で高コントラストの光書込みを実施することが可能となる。
【０１１２】
［光書込み装置の第六の実施の形態］
本発明の光書込み装置の第六の実施の形態を図１５及び図１６に基づいて説明する。第一の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１１３】
図１５は、光書込み装置の縦断側面図、図１６は、本実施の形態の光書込み装置の動作を説明するための模式図である。
【０１１４】
前述した第一ないし第五の実施の形態では、光路シフト方向の直線偏光成分のみを記録体２０１に露光するため、発光体１０１自体が直線偏光を放射する場合以外は、余分な偏光成分を反射又は透過させて露光には利用しない。その分、発光体１０１から記録体２０１に露光されるまでの光利用効率が低下する。
【０１１５】
そこで、本実施の形態では、図１５に例示するように、液晶層３０５の厚みが略等しい二つの光路シフト手段３０１を、互いの光のシフト方向が略平行となる向きに向けて光路中に直列に配置し、両光路シフト手段３０１の間に直線偏光面を略９０度回転させる偏光面回転素子５０１を配置した。図１５及び図１６では、一方向の電界により一方向に液晶分子が傾斜している状態を示している。
【０１１６】
図１５に示すように、発光体１０１からの無偏光の放射光が最初の光路シフト手段３０１を透過すると、光路シフト方向に平行な偏光成分は液晶層３０５の厚みｄに対応して図１５中右側にシフトされ、紙面に垂直な偏光成分は偏向されずに直進する。これらの出射光が偏光面回転素子５０１を透過して各偏光面が略９０度回転すると、続く光路シフト手段３０１では、先にシフトした偏光成分は直進し、先に直進した偏光成分は液晶層３０５の厚みｄに対応して図１５中右側にシフトされる。図１６は、このような光のシフト状態を各液晶層３０５に生ずる電界の方向との関係で模式的に示している。
【０１１７】
この際、二つの液晶層３０５の液晶材料と液晶厚み、そのような液晶層３０５に印加する印加電界を等しく設定しておけば、各液晶層３０５で発生する偏光成分のシフト量が一致することになる。これにより、発光体１０１から放射される光の全ての偏光成分を利用することができ、一方向の直線偏光を用いる場合に比べて光の利用効率が略２倍になる。
【０１１８】
ここで、偏光面回転素子５０１としては、半波長板、ツイストネマチック液晶セル、ツイストネマチック液晶フィルムなどを用いることができる。
【０１１９】
［光書込み装置の第七の実施の形態］
本発明の光書込み装置の第七の実施の形態を図１７に基づいて説明する。図９に基づいて説明した第三の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１２０】
図１７は、光書込み装置の縦断側面図である。
【０１２１】
本実施の形態では、前述の中間層３０９に相当する部材が直線偏光面を略９０度回転させる偏光面回転素子５０１からなり、この偏光面回転素子５０１の位置に対して光路の上流側と下流側とに位置する液晶層３０５の厚みがそれぞれ略等しく設定されている。
【０１２２】
これによって、中間層３０９が偏光面回転素子５０１を兼用しているので、光路シフト手段３０１を構成する基板枚数を減少することできる。
【０１２３】
また、界面反射の影響を少なくできるので、光路シフト手段３０１全体の透過率が向上する。
【０１２４】
さらに、液晶層３０５の配向性が向上すると共に、光路シフト手段３０１に入射する全ての偏光成分の光をシフトできるので、光の利用効率が向上する。
【０１２５】
ここで、偏光面回転素子５０１としては、半波長板、ツイストネマチック液晶セル、ツイストネマチック液晶フィルムなどを用いることができる。
【０１２６】
また、実施に際しては、上流側と下流側との液晶層３０５中に更に中間層３０９を設けても良い。この場合、中間層３０９で分割された液晶層３０５の厚みの合計がそれぞれ略等しくなるように各液晶層３０５の厚みを設定してもよい。
【０１２７】
［光書込み装置の第八の実施の形態］
本発明の光書込み装置の第八の実施の形態を図１８及び図１９に基づいて説明する。第一ないし第七の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１２８】
図１８は、光路シフト手段の配置例を示す光書込み装置の縦断正面図、図１９は、本実施の形態の光路シフト手段の配置例を示す光書込み装置の縦断正面図である。
【０１２９】
発光体１０１から放射した光は光路シフト手段３０１を透過してレンズ５１０に入射し、記録体２０１上に集光する。発光体１０１は紙面に垂直方向に配列したアレイ状となっている。この図１８では、光路シフト手段３０１の一対の基板３０３の厚みが略等しく、金属電極対２０７がスペーサを兼用したタイプを示している。また、実際には光が透過する媒体の屈折率差に応じて界面で角度が変化するが、ここでは図示の簡単化のため屈折率差による各媒体中での角度変化などは表現していない（以下同様とする）。ここで、発光体１０１から液晶層３０５までの距離をＴとした場合、距離Ｔが大きいほど液晶層３０５を通過する光路の面積が大きくなる。したがって、光利用効率を低下させないように電極対２０７を設置する場合、電極間隔ｄを比較的大きくせざるを得ない。電極間隔を広げると高電界を印加するために高電圧の印加が必要となり、電源容量や放電対策などの規制が多くなり好ましくない。そのため、Ｔを小さく設定することが好ましいが、Ｔは基板の厚みで制限されてしまう。
【０１３０】
そこで、本実施の形態では、図１９に示すように発光体アレイ１０２と光路シフト手段３０１とを近接させて配置し、一対の基板３０３の内、発光体アレイ１０２側の基板３０３の厚みがレンズ５１０側の基板３０３の厚みよりも薄く設定する。例えば、光路シフト手段３０１を発光体アレイ１０２に近接させて配置し、発光体アレイ１０２側の基板３０３のみを数十μｍから数百μｍ程度の厚みとし、他方の基板３０３は剛性確保のために数ミリ程度の厚みとすると、発光体１０１から液晶層３０５までの距離を数十μｍから数百μｍ程度の位置に設定することができる。したがって、発光体アレイ１０２から出射した放射光の広がりが小さい領域に、光路シフト手段３０１の液晶層３０５を配置できるので、光路シフトに必要な液晶層３０５の有効面積を小さくすることができる。液晶層３０５の有効面積が小さいと電極間隔ｄを狭く設定できるので、比較的低電圧でも高電界を印加することができる。高電界の印加により高速な光路偏向動作が可能となり、高速な光書込み装置が得られる。また、液晶材料の使用量が低減するためコストダウンも図れる。
【０１３１】
［光書込み装置の第九の実施の形態］
本発明の光書込み装置の第九の実施の形態を図２０に基づいて説明する。図１８及び図１９に基づいて説明した第八の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１３２】
図２０は、本実施の形態の光路シフト手段の配置例を示す光書込み装置の縦断正面図である。
【０１３３】
本実施の形態では、図２０に示すように光路シフト手段３０１と記録体２０１とを近接させて配置し、一対の基板３０３の内、記録体２０１側の基板３０３の厚みがレンズ５１０側の基板３０３の厚みよりも薄く設定されている。
【０１３４】
このような構成によれば、放射光が記録体２０１上に集光する直前の光の広がりが小さい領域に、光路シフト手段３０１の液晶層３０５を配置することができるので、光路シフトに必要な液晶層３０５の有効面積が小さくできる。液晶層３０５の有効面積が小さいと電極間隔を狭く設定できるので、比較的低電圧でも高電界を印加することができる。よって、高電界の印加により高速な光路偏向動作が可能となり、高速な光書込み装置が得られる。また、液晶材料の使用量が低減するためコストダウンも図れる。
【０１３５】
［光書込み装置の第十の実施の形態］
本発明の光書込み装置の第十の実施の形態を図２１に基づいて説明する。図１８ないし図２０に基づいて説明した第八、第九の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１３６】
本実施の形態では、図１８ないし図２０に示したような光学系構成を考えたとき、レンズ５１０の開口数（ＮＡ）をＡ、光路シフト手段３０１の基板３０３の屈折率をｎ、レンズ５１０の焦点位置から光路シフト手段３０１内の液晶層３０５までの最大距離をＴとしたときに、電極対３０７の間隔ｄを以下の関係式
２Ｔ×Ａ／ｎ　≦　ｄ　≦　２Ｔ×Ａ
を満たすように設定する。
【０１３７】
図２１に、レンズ５１０の光の取込角度θと、焦点位置からの距離Ｔと、光路の径ｄの関係を示す。ここで、レンズ５１０の焦点距離をｆ、口径をＤ、とするとレンズ５１０の開口数（ＮＡ値）は、
ＮＡ＝ｎ×ｓｉｎθ＝ｎ×２ｆ／Ｄ
と表せる。ここで、ｎはレンズ５１０と焦点までの間の屈折率を表す。光路の広がり範囲が光路シフト手段３０１の電極対３０７で遮られない範囲で電極間隔を狭く設定するためには、電極間隔の開口幅ｄと焦点距離から液晶層３０５までの距離の関係を開口数（ＮＡ）に合わせれば良い。すなわち、図２１中の相似関係からＮＡ＝ｎ×２Ｔ／ｄとなれば良い。実際には、レンズ５１０と焦点位置までの間、あるいは、液晶層３０５から焦点位置までの間には比較的大きな屈折率を有する基板３０３と液晶層３０５とが存在する。仮にガラス基板の厚みがゼロの場合、液晶層３０５と焦点位置の間は空気で屈折率ｎ＝１であり、ｄ＝２Ｔ×Ａとなる。逆に、液晶層３０５と焦点位置の間が全て屈折率がｎの基板で満たされた場合は、ｄ＝２Ｔ×Ａ／ｎとなる。
【０１３８】
したがって、電極間隔ｄをこの間に設定することで、光利用効率と電界印加効率とを両立させた最適の設定が可能となる。この結果、光学系の光利用効率を低下させることなく、同じ印加電圧でも比較的高電界を印加することができ、高速な光書込み動作が可能となる。
【０１３９】
［光書込み装置の第十一の実施の形態］
本発明の光書込み装置の第十一の実施の形態を図２２に基づいて説明する。図１９に基づいて説明した第八の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１４０】
図２２は、本実施の形態の光書込み装置の縦断正面図である。
【０１４１】
本実施の形態では、図２２に示すように発光体アレイ１０２の発光体１０１近傍に、マイクロレンズアレイ５２０が設けられている。図２２では発光体１０１とマイクロレンズ５２１とが紙面に垂直方向にアレイ状に配列しており、個々の発光体１０１とマイクロレンズ５２１とのピッチと位置は対応している。
【０１４２】
このような構成によれば、発光体１０１からの放射光をマイクロレンズアレイ５２０の対応するマイクロレンズ５２１で一旦集光し、その集光点を記録体２０１上に投影することで、記録スポットサイズが小さくでき、光路シフトによる記録密度の増加が効果的になる。
【０１４３】
［光書込み装置の第十二の実施の形態］
本発明の光書込み装置の第十二の実施の形態を図２３に基づいて説明する。図２２に基づいて説明した第十一の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１４４】
図２３は、本実施の形態のマイクロレンズアレイのマイクロレンズを示す断面図である。
【０１４５】
マイクロレンズ５２１は、少なくとも液晶層５２２と、この液晶層５２２に電界を印加可能な電極とからなり、電界強度に応じて特定の偏光方向の光に対する当該マイクロレンズ５２１の焦点距離を変化させる構成とされている。図２３に示す例では、マイクロレンズ形状の凹部を持つレンズ基板５２３と平行基板５２４の間に液晶層５２２が設けられている。また、基板５２３，５２４と液晶層５２２との界面には図示しない透明電極層と図示しない配向膜とが設けられている。透明電極層としてはＩＴＯ電極などを用いることができ、基板表面の有効領域に形成されている。配向膜としては例えば水平配向用のものを用い、紙面の上下方向にラビングなどの配向処理を施している。
【０１４６】
したがって、図２３（ａ）に示すように電界を印加しない状態では液晶分子は紙面の上下方向に配向している。ここで、各基板５２３，５２４の屈折率よりも液晶分子長軸方向の屈折率（異常光屈折率）を十分に大きくする材料を選定することで、図中の直線偏光の入射光に対して大きなレンズ効果を発生する。
【０１４７】
一方、透明電極間に電界を印加すると、例えば液晶分子が正の誘電異方性を持つ場合は、図２３（ｂ）に示すように、基板５２３，５２４に対して液晶分子が垂直に配向する。ここで、各基板５２３，５２４の屈折率と液晶分子の常光屈折率の差が比較的小さくなるので、レンズ効果が小さくなる。
【０１４８】
したがって、マイクロレンズアレイ５２０の集光機能の有無または大小を制御することができる。光路シフト動作による高密度書込みを行なう場合は、マイクロレンズアレイ５２０の集光機能を発生させて発光体スポットを小さくすることで、画素サイズを小さく設定することができる。一方、光路シフト動作を必要としない場合には、マイクロレンズアレイ５２０の集光機能を無くして発光体スポットを大きくすることで、低密度書込みに対応した画素サイズに設定することができる。
【０１４９】
なお、液晶分子の誘電異方性の正負や、配向処理の方向、電界印加の有無とレンズ効果の大小の関係などは上記の例に限らず、同様な効果を得る組み合わせならば良い。
【０１５０】
［光書込み装置の第十三の実施の形態］
本発明の光書込み装置の第十三の実施の形態を図２４に基づいて説明する。図２３に基づいて説明した第十二の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１５１】
前述した第十二の実施の形態では、入射光が直線偏光の場合にしか対応できず、発光体１０１からの光が無偏光の場合は直線偏光板と組み合わせて使用する必要があり、光の利用効率が低下してしまう。
【０１５２】
そこで、本実施の形態では、マイクロレンズアレイが、図２４に示すように光軸方向に直列に配置された二つの液晶マイクロレンズアレイ５２０からなり、電界印加時あるいは無電界時における各マイクロレンズアレイ５２０内の液晶分子の配向方向が、互いに直交するように配向処理方向あるいは電界印加方向を設定する。各液晶マイクロレンズ５２１の構成は第十二の実施の形態の場合と同様である。
【０１５３】
図２４（ａ）では、左側の液晶マイクロレンズ５２１内の液晶配向方向は紙面内の上下方向で、右側の液晶マイクロレンズ５２１内の液晶配向方向は紙面に垂直な方向に設定している。無電界時に無偏光の光を入射すると、左側の液晶マイクロレンズ５２１において、紙面内上下方向の偏光成分は液晶層５２２の異常光屈折率を感じてレンズ効果を受けるが、紙面に垂直方向の偏光成分は液晶層５２２の常光屈折率を感じて略そのまま透過する。しかし、その後の右側の液晶マイクロレンズ５２１では、紙面内上下方向の偏光成分は液晶層５２２の常光屈折率を感じて略そのまま透過し、紙面に垂直方向の偏光成分が液晶層５２２の異常光屈折率を感じてレンズ効果を受けて集光される。二枚の液晶マイクロレンズアレイ５２０の焦点位置が一致するようにレンズ形状や液晶材料を最適化することで、無偏光の入射光に対して可変焦点機能を実現でき、無偏光に対応する光路シフト手段３０１と組み合わせることで、高い光利用効率で、書込み密度の切替えができる。
【０１５４】
なお、液晶マイクロレンズとして、基板がレンズ形状を有し液晶層の厚み分布によるレンズ効果を発生させる例を示したが、基板が平行で液晶層の厚みは一定で、液晶層内に電界分布を与えて空間的に屈折率分布を形成してレンズ効果を発生させても良い。この場合、電極を複数に分割して各電極の電圧値を変化させても良いし、高抵抗値の電極材料を用いて電極内に電位分布を形成することで電界分布を形成しても良い。電極形状はストライプ形状やリング形状でも良く、所望の電界強度分布の形状に合わせて適宜設計される。
【０１５５】
［光書込み装置の第十四の実施の形態］
本発明の光書込み装置の第十四の実施の形態を説明する。
【０１５６】
前述の例では、発光体１０１に近接させて液晶マイクロレンズアレイ５２０を設けて可変焦点とし、記録体２０１上での露光スポットサイズを可変としたが、本実施の形態では、特に図示しないが、発光体１０１が放射した光を記録体２０１上に集束させるレンズ５１０自体が、少なくとも液晶層と、この液晶層に電界を印加可能な電極とを有し、電界強度に応じて特定の偏光方向の光に対するレンズの焦点距離を変化させるように構成する。
【０１５７】
液晶マイクロレンズによる可変焦点の原理と基本構成は図２３の液晶マイクロレンズ５２１の場合と同様である。液晶による可変焦点レンズ部分の設計は、固定部分の球面レンズあるいは非球面レンズや屈折率分布型レンズの設計に応じて最適化される。
【０１５８】
光路シフト動作による高密度書込みを行なう場合は、レンズ５１０の焦点距離を制御して記録体２０１上の集光スポットサイズを小さくすれば、画素サイズを小さく設定することができる。一方、光路シフト動作を必要としない場合には、レンズ５１０の焦点距離を制御して記録体２０１上の集光スポットサイズを大きくすれば、低密度書込みに対応した画素サイズに設定することができる。
【０１５９】
［光書込み装置の第十五の実施の形態］
本発明の光書込み装置の第十五の実施の形態を説明する。
【０１６０】
前述の第十四の実施の形態では、入射光が直線偏光の場合にしか対応できず、発光体１０１からの光が無偏光の場合は直線偏光板と組み合わせて使用する必要があり、光の利用効率が低下してしまう。
【０１６１】
そこで、本実施の形態では、発光体１０１が放射した光を記録体２０１上に集束させるレンズ５１０が、少なくとも二つの液晶層と、各液晶層に電界を印加可能な電極とを有し、電界印加時あるいは無電界時における各液晶層の液晶分子の配向方向が、互いに直交するように配向処理方向あるいは電界印加方向を設定する構成とされている。
【０１６２】
配向方向が直交する二つの液晶マイクロレンズによる可変焦点の原理と基本構成は図２４に示した液晶マイクロレンズ５２１の場合と同様である。液晶による可変焦点レンズ部分の設計は、固定部分の球面レンズあるいは非球面レンズや屈折率分布型レンズの設計に応じて最適化される。
【０１６３】
したがって、無偏光の入射光に対して可変焦点機能を実現でき、無偏光に対応する光路シフト手段３０１と組み合わせることで、高い光利用効率で、書込み密度の切替えができる。
【０１６４】
［光書込み装置の第十六の実施の形態］
本発明の光書込み装置の第十六の実施の形態を図２５に基づいて説明する。第一ないし第十五の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１６５】
図２５は、発光体アレイ１０２の縦断側面図である。
【０１６６】
第一ないし第十五の実施の形態では、発光体アレイ１０２の種類を特に特定していない。
【０１６７】
これに対して、発光体アレイ１０２として、例えば、光源とネマチック液晶ライトバルブアレイとを組み合わせた方式のものを用いた場合には、液晶ライトバルブの応答性が比較的遅いため、高速書込みに対応できない。しかし、光源と強誘電性液晶ライトバルブとを組み合わせた方式では１ドットが数十マイクロ秒程度の高速書込みが可能であり、高速記録用の発光体アレイとして好ましい。しかし、また、液晶でスイッチングする光は直線偏光である必要があるため、無偏光の光源を用いる場合には光の利用効率が半減してしまうという問題がある。
【０１６８】
そこで、本実施の形態では、発光体アレイ１０２としてＬＥＤアレイを用いている。例えば、図２５に例示するように、ＬＥＤアレイの母材であるガリウム・アルミ・ヒ素のウェハ１１１の上にフォトリソ工程により、酸化アルミなどの拡散防止膜１１２を形成する。この場合、拡散防止膜１１２が無い部分、すなわち発光体１０１の中心のピッチをＰ、拡散防止膜１１２の間の幅をＬとする。次に、亜鉛雰囲気中に上記ウェハ１１１を入れ、拡散防止膜１１２の開口部に選択的にリンを拡散させ、発光部１１３を形成する。この際、発光部１１３の発光出力を最大にするために、発光部１１３の形成深さＤを１０μｍ程度とする。これにより、発光部１１３が実際に発光する幅Ｗは、Ｌ＋２Ｄとなる。ここでフォトリソ工程の精度から拡散防止膜の幅を５μｍ、拡散防止膜１１２の間の幅Ｌを２μｍ以上とすると、発光部１１３の幅Ｗはおよそ２２μｍ以上、発光部のピッチは２７μｍ以上必要となる。
【０１６９】
このようなことから、１２００ｄｐｉの書込みに必要な２１μｍピッチを一列の発光体アレイ１０２で実現することは困難であるのに対して、作成が容易な６００ｄｐｉの発光体アレイ１０２を作成し、これを前述した第一から第七の実施の形態における光路シフト手段３０１と組み合わせることによって、１２００ｄｐｉ相当の高精細な書込みを実現することができる。
【０１７０】
ここで、ＬＥＤアレイは、図２５に例示するように、基板であるウェハ１１１上に直接発光部１１３を形成するので、小型化が可能である。
【０１７１】
なお、実施に際しては、ＬＥＤからの放射光の指向性を高めるために発光部１１３の近傍に図示しないマイクロレンズアレイを設けても良い。
【０１７２】
［光書込み装置の第十七の実施の形態］
本発明の光書込み装置の第十七の実施の形態を説明する。
【０１７３】
本実施の形態では、図示しないが、発光体アレイ１０２としてレーザダイオードアレイを用いている。レーザダイオードは高効率で高出力が可能であり、露光部の画素を小さく絞ることによって、記録体２０１がヒートモードの光記録体であったとしても、これを十分に加熱し記録することができる。
【０１７４】
なお、実施に際しては、レーザダイオードからの放射光の指向性を高めるために、発光体１０１の近傍に図示しないマイクロレンズアレイを設けても良い。
【０１７５】
［画像形成装置の第一の実施の形態］
本発明の画像形成装置の第一の実施の形態を図２６に基づいて説明する。光書込み装置の第一ないし第十七の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１７６】
記録体２０１としては、露光によって潜像あるいは顕像を形成可能なものであるならば、本発明の光書込み装置を適用することが可能である。そこで、ここでは、記録体２０１として電子写真用の感光体６０１を用いた発光体アレイ１０２及び光路シフト手段３０１を有する画像形成装置の一例を図２６に基づいて説明する。
【０１７７】
ドラム状あるいはベルト状の感光体６０１の周囲には、帯電装置６０２、発光体アレイ１０２と光路シフト手段３０１を含む光書込み装置６０３、現像装置６０４、転写装置６０５、及びクリーニング装置６０６が配置されている。また、感光体６０１と転写装置６０５との間に転写紙６０７を案内搬送する転写紙搬送路６０８が形成され、この転写紙搬送路６０８中には、感光体６０１の上流側に位置させて給紙装置６０９が配置され、感光体６０１の下流側に位置させて定着装置６１０が配置されている。
【０１７８】
ここで、感光体６０１の表面には、無機材料あるいは有機材料からなる図示しない感光層が形成されている。無機材料からなる感光層が形成された感光体６０１を無機感光体、有機材料からなる感光層が形成された感光体６０１を有機感光体という。
【０１７９】
無機感光体としては、アモルファスセレン系やアモルファスシリコン系材料が用いられる。
【０１８０】
有機感光体は、電荷発生層と電荷輸送層との機能分離型とすることが好ましい（いずれも図示せず）。電界発生層は、数μｍ程度の厚みであり、フタロシアニン系顔料、ビスアゾ系顔料、ペリレン系顔料などの電荷発生剤の蒸着膜やポリカーボネートなどのバインダー樹脂中に前記顔料を分散した樹脂分散膜として形成される。電荷輸送層は、数十μｍ程度の厚みであり、ポリカーボネートなどのバインダー樹脂中に正孔輸送能を有するドナー材料あるいは電子輸送能力を有するアクセプター材料を分散した膜として形成される。一般的な機能分離型有機感光体では、感光体基体上に下地層、電界発生層、電荷輸送層が順に形成されている。
【０１８１】
また、無機感光体にしても有機感光体にしても、必要に応じて機械的強度に優れた図示しない表面保護層を設けても良い。一般的には、感光体表面はマイナス極性に帯電されるため、電荷輸送層はプラス電荷を輸送するドナー材料が分散される。ドナー材料としては、トリフェニルメタン系、トリフェニルアミン二量体系、ヒドラゾン系、ピラゾリン系などが用いられる。
【０１８２】
帯電装置６０２としては、接触帯電型の帯電ローラが用いられる。帯電ローラにマイナス電圧を印加することで、感光体６０１の表面をマイナスに帯電する。帯電装置６０２を形成するには、帯電ローラに限らず、コロナチャージャやブラシ部材を用いることもできる。帯電装置６０２によりマイナス数百Ｖ程度に帯電された感光体６０１上に前述の光書込み装置６０３を用いて露光すると、露光部位のマイナス電位が小さくなって静電潜像が形成される。この場合、発光体１０１からの放射光の波長は、感光体６０１の分光感度の大きな波長に合わせておくことが好ましい。
【０１８３】
現像装置６０４は、静電潜像にトナーを選択的に付着させ、トナー画像として顕像化する。つまり、現像装置６０４は、図示しない現像ローラを有し、この現像ローラにマイナス数百Ｖの現像バイアス電位を印加することで、感光体６０１上の露光部である低電位部にマイナス極性のトナー粒子を付着させ、これによって静電潜像をトナー画像として顕像化する。
【０１８４】
このような現像装置６０４の現像方式としては、一成分現像剤を用いる一成分現像方式と二成分現像剤を用いる二成分現像方式とのいずれも用いることができるが、トナーの帯電極性はマイナス極性とすることが好ましい。
【０１８５】
さらに、転写装置６０５としては、ローラ部材やベルト部材、コロナチャージャなどを用いることができる。このような転写装置６０５は、感光体６０１との間に電界を発生させる。
【０１８６】
このような構成の画像形成装置では、感光体６０１上にトナー画像が形成されるタイミングで図示しない給紙装置により転写紙６０７の搬送を開始する。そして、感光体６０１上のトナー画像と転写紙６０７の印刷開始位置とが同期して接触した所で、感光体６０１との間に電界を発生させる転写装置６０５にトナー画像が吸引され、吸引されたトナー画像が転写紙６０７上に静電的に転写される。そして、トナー画像が付着した転写紙６０７は、定着装置６１０に搬送され、ここでトナー画像が転写紙６０７に加熱融着される。一方、転写工程後の感光体６０１の表面に残留するトナー粒子は、クリーニング装置６０６によって除去される。
【０１８７】
このようにして電子写真プロセスを用いた画像形成が実行される。このような電子写真プロセスを利用した画像形成動作では、露光エネルギーが比較的小さくても感光体６０１上に静電潜像を形成することが可能であるため、高速で高精細な光書込みが可能である。
【０１８８】
［画像形成装置の第二の実施の形態］
本発明の画像形成装置の第二の実施の形態を説明する。光書込み装置の第一ないし第十七の実施の形態と同一部分は同一符号で示し説明も省略する。
【０１８９】
記録体２０１の別の一例としては、外部エネルギーが付与されることにより画像形成がなされる材料、例えば、感光性の画像形成材料又は感熱性の画像形成材料によって形成された記録体２０１を用いることができる。
【０１９０】
感光性の画像形成材料としては、ジアゾ、フォトクロミズム材料などを用いることができる。この場合、記録体２０１が直接発色する。このため、画像形成装置自体を小型化できるという利点がある。しかも、第一ないし第九の実施の形態で例示した光書込み装置を用いることで、高精細記録が可能である。
【０１９１】
感熱性の発色材料としては、従来のロイコ染料系材料などを用いることができる。この場合、光を吸収して熱に変換する材料を併用することが好ましい。光を熱に変換して記録するためには、レーザ光のように高出力の光を用いることが好ましい。しかし、高速に高密度な記録を行なうためには、レーザ光源をアレイ化する必要がある。前述のＬＥＤの場合と同様に、レーザダイオードの場合でも高密度にアレイ化することは困難であるが、第一ないし第九の実施の形態で例示した光書込み装置を用いることで、高精細な画像記録が可能となる。
【０１９２】
【実施例】
［第一の実施例］
以下、図２７ないし図２９に基づいて本発明の第一の実施例について説明する。
【０１９３】
［光路シフト手段の作成］
図２７は、本発明の発明者が作成した光路シフト手段１００１であり、（ａ）はその平面図、（ｂ）はその側面図である。
【０１９４】
幅１０ｍｍ、長さ１００ｍｍ、厚さ１ｍｍのガラス基板１００２の表面に厚み０．０６μｍの市販の垂直（ホメオトロピック）配向膜１００３を形成した。厚み１００μｍ、幅２ｍｍ、長さ１１０ｍｍのアルミの電極シート１００４をスペーサ兼電極として、有効領域の幅が１ｍｍとなるように、配向膜１００３を内側にした二枚のガラス基板１００２の間に２つの電極シート１００４を平行に配置した。一部を除いた周囲を紫外線硬化接着剤１００５で固定してセル１００６を作成した。このセル１００６を約９０度に加熱した状態で、ガラス基板１００２の間の空間に液晶層１００７となる強誘電性液晶（チッソ製ＣＳ１０２９：複屈折Δｎ＝０．１６、チルト角θ＝２５度、自発分極Ｐｓ＝−４０ｎＣ／ｃｍ^２）を毛管法にて注入した。冷却後、注入口も接着剤で封止し、厚み１００μｍ、有効幅１ｍｍ、長さ約９５ｍｍの液晶層１００７を形成した。そして、各電極対となる電極シート１００４にパルスジェネレータと高速アンプとからなる電源１００８を接続し、これによって図２７に示すような光路シフト手段１００１を作成した。
【０１９５】
このようにして作成された光路シフト手段１００１は、その透過率が８５％以上と高い値を示した。
【０１９６】
［光学軸の観察］
無電界の状態で、作成した光路シフト手段１００１における有効領域内にある液晶層１００７のコノスコープ像を観察したところ、十字形と円環の画像が中心部に観察された。したがって、無電界下では光学軸が液晶層１００７に垂直であることを確認できた。この状態では液晶分子のチルト方向がガラス基板１００２の面に垂直方向に対して回転する螺旋構造を取っており、平均的な光学軸は螺旋軸の方向であるガラス基板１００２の面に垂直な方向として観察される。次に、電源１００８から電極対をなす電極シート１００４に±１５０Ｖ、１Ｈｚの矩形波電圧を印加したところ、コノスコープ像の十字と円環の位置とが上下方向に１Ｈｚで往復シフトした。顕微鏡の対物レンズのＮＡ値と液晶の屈折率と十字位置のシフト量から光学軸の傾斜角度を計算すると、約２５度となり、液晶材料固有のチルト角θと一致していることが確かめられた。そして、１５０Ｖ／ｍｍ程度の電界強度では、螺旋構造が解けて一様な方向に液晶分子が配向し、液晶層１００７の光学軸の方向が±２５度で切換え可能となった。
【０１９７】
［光路シフト量の電界依存性］
光路シフト量の電界依存性を確かめた。図２８を参照しながら説明する。
【０１９８】
図２８は、印加電界と光路シフト量との関係を示すグラフである。
【０１９９】
実験では、開口部が４μｍ角のマスクパターンを裏面から直線偏光の光で照明し、光路シフト手段１００１を通してその透過光を観察した。つまり、光路シフト手段１００１を動作させることでマスクパターンの位置がシフトする様子を顕微鏡付きビデオカメラで観察し、この時の光路シフト量を測定した。光路シフト手段１００１の温度は約３０℃とした。また、電源１００８から電極対をなす電極シート１００４に０〜±１７５Ｖ、１Ｈｚの矩形波電圧を印加した。その結果、入射光の偏光面が電界方向と垂直、すなわち光路シフト方向と平行の場合には、図２８に示すような光路シフト量の特性が得られた。
【０２００】
図２８に示すように、±１２５Ｖ／ｍｍ程度の電界強度で、シフト量が約２１μｍとなり、この値で飽和した。同様に、光路シフト手段１００１の長手方向に数ヶ所の測定を行ったが、いずれも同様なシフト特性が得られた。また、両シフト位置でのピントズレは見られなかった。
【０２０１】
さらに、光路シフト手段１００１が無い時の開口部の輝度分布と光路シフト時の開口部の輝度分布との変化から、解像度の劣化度合い（コントラスト・トランスファー・ファンクション：ＣＴＦ）を調べたところ、ＣＴＦ値は８０％以上であり、実用上問題ないと判断した。
【０２０２】
加えて、入射光の偏光面を電界方向と水平にすると、光路シフトは観察されなかった。
【０２０３】
［光路シフトの応答時間の測定］
光路シフトの応答時間の測定を確かめた。図２９を参照しながら説明する。
【０２０４】
図２９は、印加電界と応答時間との関係を示すグラフである。
【０２０５】
光路シフト量の電界依存性を確かめた際と同様なシフトの様子を顕微鏡付き高速度カメラで観察することで、光路シフト量とその移動に要する時間、すなわち光路シフトの応答時間を測定した。この際、光路シフト手段１００１の温度は約３０℃とした。
【０２０６】
実験では、電源１００８から電極対をなす電極シート１００４に±１００Ｖ〜±４００Ｖ、１００Ｈｚの矩形波電圧を印加し、高速度カメラによる観察（時間分解能４０５００フレーム／秒）を行なった。その結果、図２９に示すような応答時間の特性が得られた。±４００Ｖ／ｍｍでは、応答時間は０．５ｍｓｅｃ以下であった。
【０２０７】
［第二の実施例］
以下、図３０に基づいて本発明の第二の実施例について説明する。
【０２０８】
図３０は、本発明の発明者が作成した光路シフト手段であり、（ａ）はその平面図、（ｂ）はその側面図である。
【０２０９】
幅１０ｍｍ、長さ１００ｍｍ、厚さ０．１５ｍｍの薄いガラス基板１００２と、幅１０ｍｍ、長さ１００ｍｍ、厚さ２ｍｍの厚いガラス基板１００２の表面に厚み０．０６μｍの市販の垂直（ホメオトロピック）配向膜１００３を形成した。厚み１００μｍ、幅２ｍｍ、長さ１１０ｍｍのアルミの電極シート１００４をスペーサ兼電極として、有効領域の幅が０．１５ｍｍとなるように、配向膜１００３を内側にした二枚のガラス基板１００２の間に２つの電極シート１００４を平行に配置した。一部を除いた周囲を紫外線硬化接着剤１００５で固定して基板１００２の厚みが非対称なセル１００６を作成した。このセル１００６に第１の実施例と同じ液晶材料を封入し、厚み１００μｍ、有効幅０．１５ｍｍ、長さ約９５ｍｍの液晶層を形成した。そして、各電極対となる電極シート１００４にパルスジェネレータと高速アンプとからなる電源１００８を接続し、これによって図３０に示すような光路シフト手段１００１を作成した。
【０２１０】
このようにして作成された光路シフト手段１００１は、その透過率が８５％以上と高い値を示した。第一の実施例と同様に各電極対となる電極シート１００４間に４００Ｖ印加して高速度カメラで応答時間を測定したところ、応答時間は３０μｓｅｃと非常に高速な応答性を示した。
【０２１１】
【発明の効果】
請求項１記載の発明は、複数個の発光部を予め決められた画素ピッチで配列する発光体アレイと、前記発光部が放射した光を記録体上に集束させるレンズと、前記発光部から放射された光を前記発光部の配列方向に電気的にシフト可能な光路シフト手段とを有し、前記光路シフト手段を駆動制御することにより前記発光部から放射された光をシフトさせ、これによって前記画素ピッチ間が補完された光照射を前記記録体に対して行なうようにした光書込み装置において、前記光路シフト手段は、前記発光体アレイから前記記録体に向かう光路上に配置されてスペーサにより対向間隔が規制される一対の透明な基板と、前記基板の内面側に設けられた垂直配向膜と、前記基板間に垂直配向膜を介して充填され、前記垂直配向膜によってホメオトロピック配向をなすキラルスメクチックＣ相よりなる液晶層と、前記光路を挾む位置に配置された電極対に電圧を印加することにより、前記液晶層内に前記基板面法線方向及び前記発光部の配列方向と略直交する方向に電界を発生させる電界発生手段と、を具備するので、
（１）液晶の自発分極による高速応答が可能であり、
（２）光路中に透明電極が無いため光利用効率が高く、
（３）電界強度に応じてシフト量が調整可能であり、更に、
（４）シフト時の光路長の変化が無い、
という優れた効果を有しつつ、高速で高精細な光書込みが可能となる。
【０２１２】
請求項２記載の発明は、請求項１記載の光書込み装置において、光路のシフト方向が平行となるように前記光路シフト手段を複数層重ね、前記電界発生手段は、それぞれの前記光路シフト手段を独立して駆動するので、画素位置を例えば４倍などの多値に増倍することができる。
【０２１３】
請求項３記載の発明は、請求項１または２記載の光書込み装置において、前記液晶層をその厚み方向に分割する中間層を設け、この中間層の少なくとも一面には垂直配向膜が形成されているので、中間層の存在により光路シフト量が大きくなるため、液晶層の厚みを薄く設定しながら光路シフト量を大きく設定することが可能となり、これにより、液晶層の垂直配向性を向上させ、垂直配向性の不良による透過率の低下を防止することができる。
【０２１４】
請求項４記載の発明は、請求項１ないし３の何れか一記載の光書込み装置において、前記スペーサの内側に前記電極対が設けられているので、電極対がスペーサを兼用することになり、これによって部品点数を減らすことができると共に、液晶層厚みを確実に均一化することができ、これによって液晶層内に均一な水平電界を印加することができる。したがって、比較的簡単な構成で、光路シフトの位置精度が高い光書込み装置を得ることができる。
【０２１５】
請求項５記載の発明は、請求項１ないし４の何れか一記載の光書込み装置において、前記発光体アレイから前記記録体に向かう光路上に、前記光路シフト手段による光路のシフト方向と平行な偏光面の光のみを透過する直線偏光板を介在させたので、光路シフト手段に入射する光に不要な偏光面の光が混ざっている場合、光路シフトされない光の成分が記録体上の不要な位置に露光され、コントラスト比の低下をもたらすのに対して、本発明では、直線偏光板の作用によって、光路シフト手段に入射する光が確実に光路の移動方向に平行な直線偏光のみとなることから、不要な光の発生を防止し、高精細で高コントラストの光書込み装置を得ることができる。
【０２１６】
請求項６記載の発明は、請求項１ないし４の何れか一記載の光書込み装置において、前記発光体アレイから前記記録体に向かう光路上に光シフト方向が平行となるように、少なくとも二つの前記光路シフト手段を配置し、これらの光路シフト手段の間に直線偏光面を略９０度回転させる偏光面回転素子を配置したので、両光路シフト手段のシフト量が同一となるように設定しておけば、全ての偏光成分を同一方向にシフトすることができ、したがって、一方向の直線偏光を用いる場合に比べて、光の利用効率を略２倍とすることができる。
【０２１７】
請求項７記載の発明は、請求項１ないし４の何れか一記載の光書込み装置において、前記液晶層をその厚み方向に略均しい厚みに分割し直線偏光面を略９０度回転させる偏光面回転素子からなる中間層を設け、この中間層の少なくとも一面には垂直配向膜が形成されているので、光路シフト量を大きく設定するために液晶層部分の厚みを厚く構成する場合でも、中間層の存在により液晶層中央部付近の配向安定性を向上させることができ、垂直配向性の不良による透過率の低下を防止することができる。しかも、液晶層中の中間層に偏光面回転素子が設けられているので、光路シフト手段を構成する基板枚数を減少させることができ、さらに、偏光面回転素子により界面反射の影響が少なくなるため、素子全体の透過率を向させることもできる。
【０２１８】
請求項８記載の発明は、請求項１ないし７の何れか一記載の光書込み装置において、前記一対の透明な基板の内、発光体アレイ側の基板の厚みがレンズ側の基板の厚みよりも薄いので、光路シフト手段を発光体アレイに近接させて配置させること、即ち、発光体アレイから出射した放射光の広がりが小さい領域に光路シフト手段の液晶層を配置させることができ、光路シフトに必要な液晶層の有効面積を小さくすることができる。また、液晶層の有効面積が小さいと電極間隔を狭く設定することができるので、比較的低電圧でも高電界を印加することができ、このような高電界の印加により高速な光路偏向動作が可能となり、高速な光書込み装置を得ることができ、さらには、液晶材料の使用量が低減するためコストダウンも図ることができる。
【０２１９】
請求項９記載の発明は、請求項１ないし７の何れか一記載の光書込み装置において、前記一対の透明な基板の内、記録体側の基板の厚みがレンズ側の基板の厚みよりも薄いので、光路シフト手段を記録体に近接させて配置させること、即ち、放射光が記録体上に集光する直前の光の広がりが小さい領域に光路シフト手段の液晶層を配置させることができ、光路シフトに必要な液晶層の有効面積を小さくすることができる。また、液晶層の有効面積が小さいと電極間隔を狭く設定することができるので、比較的低電圧でも高電界を印加することができ、このような高電界の印加により高速な光路偏向動作が可能となり、高速な光書込み装置を得ることができ、さらには、液晶材料の使用量が低減するためコストダウンも図ることができる。
【０２２０】
請求項１０記載の発明は、請求項１ないし９の何れか一記載の光書込み装置において、前記レンズの開口数（ＮＡ）をＡ、前記光路シフト手段の基板の屈折率をｎ、前記レンズの焦点位置から前記光路シフト手段の液晶層までの最大距離をＴとしたときに、前記電極対の間隔ｄが以下の関係式
２Ｔ×Ａ／ｎ　≦　ｄ　≦　２Ｔ×Ａ
を満たすように、レンズの光の取込角度を表す開口数Ａと、基板の屈折率ｎと、焦点位置から液晶層までの最大距離Ｔと、電極対の間隔ｄとの関係を一定範囲に設定したので、光路の広がり範囲が光路シフト手段の電極間隔で遮られない範囲で、電極間隔を狭く設定することができ、光利用効率と電界印加効率とを両立させた最適な設定が可能となり、したがって、光学系の光利用効率を低下させることなく、同じ印加電圧でも比較的高電界を印加することができ、高速な光書込み動作を可能にすることができる。
【０２２１】
請求項１１記載の発明は、請求項１ないし１０の何れか一記載の光書込み装置において、前記発光体アレイの発光体近傍に、個々の発光体に対応するマイクロレンズを有するマイクロレンズアレイを設けたので、記録スポットサイズが大きい状態で光路シフトを行っても、露光した画素が重なってしまうが、各発光体からの放射光をマイクロレンズアレイで一旦集光し、その集光点を記録体上に投影することで記録スポットサイズを小さくすることができ、光路シフトによる記録密度の増加を効果的に行なうことができる。
【０２２２】
請求項１２記載の発明は、請求項１１記載の光書込み装置において、前記マイクロレンズアレイが、少なくとも液晶層と、この液晶層に電界を印加可能な電極とからなり、電界強度に応じて特定の偏光方向の光に対する当該マイクロレンズの焦点距離を変化させることにより、発光体アレイからの放射光を集光するマイクロレンズアレイ中に電界印加可能な液晶層を有することで、マイクロレンズアレイの集光機能の有無を制御することができ、よって、光路シフト動作による高密度書込みを行なう場合は、マイクロレンズアレイの集光機能を発生させて発光体スポットを小さくすることで、画素サイズを小さく設定することができる一方、光路シフト動作を必要としない場合には、マイクロレンズアレイの集光機能を無くして発光体スポットを大きくすることで、低密度書込みに対応した画素サイズに設定することができ、書込み密度を切替えることができる。
【０２２３】
請求項１３記載の発明は、請求項１２記載の光書込み装置において、二つの前記液晶マイクロレンズアレイを、光軸方向に直列に配置させ、電界印加時あるいは無電界時における各液晶マイクロレンズアレイ内の液晶分子の配向方向が、互いに直交するように配向処理方向あるいは電界印加方向を設定したしたので、可変焦点機能を持つ二つの液晶マイクロレンズアレイの液晶配向方向を直交させて配置することで、特定の偏光方向の入射光成分に対しては一方の液晶マイクロレンズアレイが可変レンズとして機能し、直交する偏光方向の入射光成分に対しては他方の液晶マイクロレンズアレイが可変レンズとして機能させることができ、これにより、無偏光の入射光に対して可変焦点機能を実現でき、無偏光に対応する光路シフト手段と組み合わせることで、高い光利用効率で、書込み密度を切替えることができる。
【０２２４】
請求項１４記載の発明は、請求項１ないし１０の何れか一記載の光書込み装置において、前記発光部が放射した光を前記記録体上に集束させる前記レンズが、少なくとも液晶層と、この液晶層に電界を印加可能な電極とを有し、電界強度に応じて特定の偏光方向の光に対する前記レンズの焦点距離を変化させることにより、発光体アレイからの放射光を記録体上に集光するレンズ中に電界印加可能な液晶層を有することで、レンズの焦点距離を制御することができ、よって、光路シフト動作による高密度書込みを行なう場合は、レンズの焦点距離を制御して記録体上の集光スポットサイズを小さくすることで、画素サイズを小さく設定することができる一方、光路シフト動作を必要としない場合には、レンズの焦点距離を制御して記録体上の集光スポットサイズを大きくすることで、低密度書込みに対応した画素サイズに設定することができ、書込み密度を切替えることができる。
【０２２５】
請求項１５記載の発明は、請求項１４記載の光書込み装置において、前記発光部が放射した光を前記記録体上に集束させる前記レンズが、少なくとも二つの液晶層と、各液晶層に電界を印加可能な電極とを有し、電界印加時あるいは無電界時における各液晶層の液晶分子の配向方向が、互いに直交するように配向処理方向あるいは電界印加方向を設定することにより、レンズ内の二つの液晶層の液晶配向方向を直交させて配置することで、特定の偏光方向の入射光成分に対しては一方の液晶層により可変焦点レンズとして機能し、直交する偏光方向の入射光成分に対しては他方の液晶層により可変焦点レンズとして機能させることができ、したがって、無偏光の入射光に対して可変焦点機能を実現でき、無偏光に対応する光路シフト手段と組み合わせることで、高い光利用効率で、書込み密度を切替えることができる。
【０２２６】
請求項１６記載の発明は、請求項１ないし１５の何れか一記載の光書込み装置において、前記発光体アレイはＬＥＤアレイであるので、光源部の小型化を実現させることができる。
【０２２７】
請求項１７記載の発明は、請求項１ないし１５の何れか一記載の光書込み装置において、前記発光体アレイはレーザダイオードアレイであるので、光源部の高効率化と小型化とを実現させることができる。
【０２２８】
請求項１８記載の画像形成装置の発明は、前記記録体としての電子写真プロセスが実行される感光体と、この感光体を一様帯電する帯電装置と、光照射によって一様帯電された前記感光体に静電潜像を形成する請求項１ないし１７の何れか一記載の光書込み装置と、前記静電潜像を現像する現像装置と、前記感光体上の現像画像を転写紙に転写する転写装置と、を具備するので、請求項１ないし１７の何れか一記載の光書込み装置の効果を有すると共に、比較的低い光強度による書込みでもコントラストの高い画像形成を行なうことができる。
【０２２９】
請求項１９記載の画像形成装置の発明は、請求項１ないし１７の何れか一記載の光書込み装置を用いて、外部エネルギーが付与されることにより画像形成がなされる材料からなる前記記録体に直接画像形成を行なうので、請求項１ないし１７の何れか一記載の光書込み装置の効果を有すると共に、記録体に直接画像が形成されることから画像形成装置を小型化することができる。
【図面の簡単な説明】
【図１】本発明の光書込み装置の第一の実施の形態を示す光書込み装置の縦断側面図である。
【図２】その縦断正面図である。
【図３】光路シフト手段の液晶層に生ずる電界の方向と液晶分子の傾斜方向とを示す模式図である。
【図４】図３に示す状態とは電界方向が反転した場合の光路シフト手段の液晶層に生ずる電界の方向と液晶分子の傾斜方向とを示す模式図である。
【図５】液晶層における液晶分子の配向状態を示す模式図である。
【図６】図６に示す状態とは電界方向が反転した場合の液晶層における液晶分子の配向状態を示す模式図である。
【図７】発光体のピッチと光路シフト手段による光路シフト量と画素ピッチと解像度との関係を例示する模式図である。
【図８】本発明の光書込み装置の第二の実施の形態を示し、（ａ）は光書込み装置の縦断側面図、（ｂ）はその縦断正面図である。
【図９】本発明の光書込み装置の第三の実施の形態を示す光書込み装置の縦断正面図である。
【図１０】本発明の光書込み装置の第四の実施の形態として、光書込み装置の一態様を示す縦断正面図である。
【図１１】本発明の光書込み装置の第四の実施の形態として、光書込み装置の別の態様を示す縦断正面図である。
【図１２】第一の実施の形態における光書込み装置で発生する現象を説明するための光書込み装置の縦断側面図である。
【図１３】本発明の光書込み装置の第五の実施の形態として、光書込み装置の一態様を示す縦断側面図である。
【図１４】本発明の光書込み装置の第五の実施の形態として、光書込み装置の別の態様を示す縦断側面図である。
【図１５】本発明の光書込み装置の第六の実施の形態を示す光書込み装置の縦断側面図である。
【図１６】その動作を説明するための模式図である。
【図１７】本発明の光書込み装置の第七の実施の形態を示す光書込み装置の縦断側面図である。
【図１８】光路シフト手段の配置例を示す光書込み装置の縦断正面図である。
【図１９】本発明の光書込み装置の第八の実施の形態を示す光路シフト手段の配置例の縦断正面図である。
【図２０】本発明の光書込み装置の第九の実施の形態を示す光路シフト手段の配置例の縦断正面図である。
【図２１】本発明の光書込み装置の第十の実施の形態を示すレンズの光の取込角度と焦点位置からの距離と光路の径との関係を示す説明図である。
【図２２】本発明の光書込み装置の第十一の実施の形態を示す光書込み装置の縦断正面図である。
【図２３】本発明の光書込み装置の第十二の実施の形態を示すマイクロレンズアレイのマイクロレンズを示す断面図である。
【図２４】本発明の光書込み装置の第十三の実施の形態を示すマイクロレンズアレイのマイクロレンズを示す断面図である。
【図２５】本発明の光書込み装置の第十六の実施の形態を示す発光体アレイの縦断側面図である。
【図２６】本発明の画像形成装置の第一の実施の形態を示す模式図である。
【図２７】本発明の発明者が実験用に作成した第一の実施例の光路シフト手段の一例であり、（ａ）はその平面図、（ｂ）はその側面図である。
【図２８】印加電界と光路シフト量との関係を示すグラフである。
【図２９】印加電界と応答時間との関係を示すグラフである。
【図３０】本発明の発明者が実験用に作成した第二の実施例の光路シフト手段の一例であり、（ａ）はその平面図、（ｂ）はその側面図である。
【図３１】液晶層を用いた従来の光書込み装置の一例を示す縦断側面図である。
【符号の説明】
１０１　発光部
１０２　発光体アレイ
１１３　発光部
２０１　記録体
３０１　光路シフト手段
３０２　スペーサ
３０３　基板
３０４　垂直配向膜
３０５　液晶層
３０６　電界発生手段
３０７　電極対
３０９　中間層
４０１　直線偏光板
５０１　偏光面回転素子
５１０　レンズ
５２０　マイクロレンズアレイ
５２１　マイクロレンズ
５２２　液晶層
６０１　感光体
６０２　帯電装置
６０３　光書込み装置
６０４　現像装置
６０５　転写装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical writing device using a light emitting array and an image forming apparatus using the optical writing device.
[0002]
[Prior art]
An image forming engine is used in an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile, or a multifunction peripheral (MFP) thereof, a photographic exposure machine or a printer using a photosensitive material, a printer or a facsimile using a thermosensitive material. In some cases, an optical writing device using a light emitting array is used.
[0003]
In an optical writing device using such an illuminant array, the interval between a plurality of illuminants included in the illuminant array must be reduced in order to increase the resolution of a printed image. For example, when manufacturing a light emitting array having a pixel pitch of 1200 dpi, the light emitting pitch is about 21 μm. However, in this case, the mounting technology such as wire bonding must be increased in density, which increases the cost.
[0004]
Therefore, conventionally, while using a light-emitting element array with a low resolution, an imaging position control that changes the exposure position electro-optically by combining a ferroelectric liquid crystal cell that rotates the polarization plane by 90 degrees and a birefringent plate. There has been proposed an optical writing device capable of printing at a high resolution by using means (for example, see Patent Document 1).
[0005]
FIG. 31 is a vertical sectional side view showing an example of a conventional optical writing device described in Patent Document 1. Hereinafter, such an optical writing device will be briefly described.
[0006]
A pair of transparent electrodes 2 and a horizontal alignment film 3 are formed on a pair of transparent substrates 1, and a liquid crystal layer 4 made of a ferroelectric liquid crystal composed of a chiral smectic C phase is sandwiched between the two substrates 1. ing. The thickness of the liquid crystal layer 4 is smaller than the helical pitch of the chiral smectic C phase. Thus, the liquid crystal layer 4 is a surface-stabilized ferroelectric liquid crystal cell.
[0007]
Here, as the liquid crystal layer 4, a liquid crystal material is used such that the change in the orientation direction of the liquid crystal director at the time of electric field switching is 45 degrees. Therefore, by switching the direction of the liquid crystal director so as to be parallel to the linear polarization plane of the incident light or to have a relation of 45 degrees, the polarization plane can be rotated by 90 degrees.
[0008]
Further, if the birefringent plate 5 is provided after the liquid crystal cell constituting the liquid crystal layer 4, the light goes straight to the birefringent plate 5 when the plane of polarization becomes the ordinary light component, and the polarization plane becomes the extraordinary light component. Sometimes light shifts parallel. At this time, the shift amount of the optical path is determined by the direction and the thickness of the optical axis of the birefringent plate 5.
[0009]
Therefore, an optical writing device is configured by interposing the optical path shifting means 6 configured as described above between the light emitting body array 7 and the recording medium 8. In such an optical writing device, light emitted from a plurality of light emitters 9 provided on the light emitter array 7 is focused by a lens (not shown), and then irradiated onto the recording body 8 via an optical path shift unit 6. At this time, the direction of the spontaneous polarization of the liquid crystal layer 4 is switched by performing the switching operation of the polarity of the electric field applied to the liquid crystal layer 4 via the transparent electrode 2 (in FIG. 31, the direction of the symbol ● in FIG. (Indicated by the direction of the symbol x in ○). As a result, the recording body 8 is exposed to the light emitted from the luminous body array 7 at a pitch of 配 列 of the arrangement pitch of the luminous bodies 9 according to the switching operation of the spontaneous polarization direction in the optical path shifting means 6. That is, assuming that the light-emitting members 9 are arranged at intervals of N μm, it is possible to expose the recording body 8 with a shift of N / 2 μm in the arrangement direction.
[0010]
Therefore, by using the optical writing device configured as described above for an image forming apparatus, printing can be performed at a high resolution even when a light emitting array having a low resolution is used. Moreover, the surface-stabilized ferroelectric liquid crystal cell introduced as the liquid crystal layer 4 has an advantage that high-speed switching is possible and a high-speed optical path shift can be realized.
[0011]
[Patent Document 1]
JP-A-8-118726
[0012]
[Problems to be solved by the invention]
However, the optical writing device illustrated in FIG. 31 has the following problems.
(1) The surface-stable ferroelectric liquid crystal cell is required to control the cell gap with high precision, and therefore, it is difficult to manufacture the cell in an area corresponding to the size of the light emitting array.
(2) A surface-stable ferroelectric liquid crystal cell requires a pair of transparent electrodes in the optical path, and the transmittance of the cell is reduced.
(3) An optical crystal that functions as a birefringent plate is generally expensive, and using an optical crystal having an area corresponding to the size of the light emitting array increases the cost.
(4) Since the optical path that travels straight through the optical birefringent plate and the optical path that travels obliquely are switched, a difference in optical path length occurs between both optical paths, and the focal position is shifted.
(5) Since the moving amount of the optical path is determined by the birefringence and the thickness of the optical crystal, the moving amount of the optical path is fixed.
[0013]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical writing device capable of performing high-resolution image exposure even when a low-resolution illuminant array is used, while solving the problems described in (1) to (5) above. .
[0014]
[Means for Solving the Problems]
The invention according to claim 1 is a light-emitting array in which a plurality of light-emitting units are arranged at a predetermined pixel pitch, a lens that focuses light emitted by the light-emitting units on a recording medium, and light emitted from the light-emitting unit. Optical path shifting means capable of electrically shifting the light emitted in the arrangement direction of the light emitting section, and light emitted from the light emitting section is shifted by driving and controlling the optical path shifting means, whereby the light In an optical writing apparatus in which light irradiation in which pixel pitches are complemented is performed on the recording medium, the optical path shift means is disposed on an optical path from the light emitting element array to the recording medium and is opposed by a spacer. A pair of transparent substrates whose spacing is regulated, a vertical alignment film provided on the inner surface side of the substrate, and a space between the substrates filled with a vertical alignment film interposed therebetween, and the vertical alignment film By applying a voltage to a liquid crystal layer made of a chiral smectic C phase forming a pick alignment and an electrode pair disposed at a position sandwiching the optical path, a normal direction of the substrate surface and the light emitting portion in the liquid crystal layer are formed. Electric field generating means for generating an electric field in a direction substantially orthogonal to the arrangement direction.
[0015]
Therefore, by performing a switching operation of the polarity of the electric field applied to the liquid crystal layer through the electrode pair, the liquid crystal layer exhibits an optical path shift function, and the recording medium can be irradiated with light in which pixel pitches are complemented. It becomes possible. This allows high-resolution image exposure even when a low-resolution illuminant array is used. At this time, since a horizontal electric field is applied to the liquid crystal layer of the vertically aligned chiral smectic C phase,
(1) High-speed response by spontaneous polarization of liquid crystal is possible,
(2) Since there is no transparent electrode in the optical path, the light use efficiency is high,
(3) The shift amount can be adjusted according to the electric field strength.
(4) there is no change in the optical path length during shifting;
Thus, high-speed, high-definition optical writing can be performed.
[0016]
According to a second aspect of the present invention, in the optical writing apparatus according to the first aspect, the optical path shifting means is stacked in a plurality of layers so that the optical path shift direction is parallel, and the electric field generating means sets each of the optical path shifting means. Drive independently.
[0017]
Therefore, it is possible to multiply the pixel position to a multi-value such as four times.
[0018]
According to a third aspect of the present invention, in the optical writing device according to the first or second aspect, an intermediate layer that divides the liquid crystal layer in a thickness direction is provided, and a vertical alignment film is formed on at least one surface of the intermediate layer. I have.
[0019]
Therefore, even when the thickness of the liquid crystal layer portion is increased to set the optical path shift amount large, the presence of the intermediate layer improves the alignment stability near the center of the liquid crystal layer. Thereby, the vertical alignment of the entire liquid crystal layer is improved, and a decrease in transmittance due to poor vertical alignment is prevented.
[0020]
According to a fourth aspect of the present invention, in the optical writing device according to any one of the first to third aspects, the electrode pair is provided inside the spacer.
[0021]
Therefore, since the interval between the electrode pairs can be set to be small, an electric field can be efficiently applied in the liquid crystal layer. When the electrode pair also serves as a spacer, the number of components can be reduced. Further, since the thickness of the liquid crystal layer can be reliably made uniform, a uniform horizontal electric field can be applied to the inside of the liquid crystal layer. Thus, an optical writing device with a relatively simple configuration and high optical path shift position accuracy can be obtained.
[0022]
According to a fifth aspect of the present invention, in the optical writing apparatus according to any one of the first to fourth aspects, an optical path parallel to a shift direction of the optical path by the optical path shift means is provided on an optical path from the luminous body array to the recording medium. A linear polarizing plate that transmits only the light on the polarization plane was interposed.
[0023]
Therefore, when the light incident on the optical path shifting means is mixed with the light of the unnecessary polarization plane, the component of the light that is not optical path shifted is exposed at an unnecessary position on the recording medium, thereby lowering the contrast ratio. On the other hand, in the present invention, since the light incident on the optical path shifting means is only linearly polarized light parallel to the moving direction of the optical path by the action of the linear polarizing plate, generation of unnecessary light is prevented, A fine and high-contrast optical writing device can be obtained.
[0024]
According to a sixth aspect of the present invention, in the optical writing device according to any one of the first to fourth aspects, at least two light shifting directions are parallel to each other on an optical path from the luminous body array to the recording medium. The optical path shift means was arranged, and a polarization plane rotating element for rotating the linear polarization plane by about 90 degrees was arranged between the optical path shift means.
[0025]
Therefore, when non-polarized light is incident on the optical path shifting means, of the light incident on one of the optical path shifting means, the optical path of the extraordinary light component is shifted, and the ordinary light component goes straight and exits as it is. Next, when the polarization plane is rotated by 90 degrees by the polarization plane rotation element, the light shifted by the one optical path shift means travels straight as the ordinary light component of the other optical path shift means, and travels straight through the one optical path shift means. The light shifts as an extraordinary light component of the other optical path shifting means. Therefore, if the shift amounts of the two optical path shift means are set to be the same, all the polarization components can be shifted in the same direction, and the use of light can be reduced as compared with the case where linear polarization in one direction is used. The efficiency can be approximately doubled.
[0026]
According to a seventh aspect of the present invention, in the optical writing device according to any one of the first to fourth aspects, the liquid crystal layer is divided into substantially uniform thicknesses in a thickness direction thereof, and a linear polarization plane is rotated by approximately 90 degrees. An intermediate layer comprising a rotating element is provided, and a vertical alignment film is formed on at least one surface of the intermediate layer.
[0027]
Therefore, even when the thickness of the liquid crystal layer portion is increased to set the optical path shift amount large, the presence of the intermediate layer improves the alignment stability near the center of the liquid crystal layer. Therefore, a decrease in transmittance due to poor vertical alignment is prevented. Moreover, since the polarization plane rotation element is provided in the intermediate layer in the liquid crystal layer, it is possible to reduce the number of substrates constituting the optical path shift means. Further, the influence of interface reflection is reduced by the polarization plane rotation element, so that the transmittance of the entire element is improved.
[0028]
According to an eighth aspect of the present invention, in the optical writing device according to any one of the first to seventh aspects, the thickness of the substrate on the light emitting array side of the pair of transparent substrates is greater than the thickness of the substrate on the lens side. thin.
[0029]
Therefore, by making the thickness of the substrate on the illuminant array side smaller than the thickness of the substrate on the lens side, the optical path shift means is arranged close to the illuminant array, that is, the emission light emitted from the illuminant array Since the liquid crystal layer of the optical path shifting means can be arranged in a region where the spread is small, the effective area of the liquid crystal layer required for the optical path shift can be reduced. Also, if the effective area of the liquid crystal layer is small, the electrode spacing can be set small, so that a high electric field can be applied even at a relatively low voltage, and a high-speed optical path deflection operation is possible by applying such a high electric field. Thus, a high-speed optical writing device can be obtained. Further, the cost can be reduced because the amount of the liquid crystal material used is reduced.
[0030]
According to a ninth aspect of the present invention, in the optical writing device according to any one of the first to seventh aspects, the thickness of the recording medium-side substrate of the pair of transparent substrates is smaller than the thickness of the lens-side substrate.
[0031]
Therefore, the liquid crystal layer of the light path shifting means can be arranged in a region where the spread of the light immediately before the radiated light is condensed on the recording medium can be arranged by placing the light path shifting means close to the recording medium. The effective area of the liquid crystal layer required for the above can be reduced. Also, if the effective area of the liquid crystal layer is small, the electrode spacing can be set small, so that a high electric field can be applied even at a relatively low voltage, and a high-speed optical path deflection operation is possible by applying such a high electric field. Thus, a high-speed optical writing device can be obtained. Further, the cost can be reduced because the amount of the liquid crystal material used is reduced.
[0032]
According to a tenth aspect of the present invention, in the optical writing apparatus according to any one of the first to ninth aspects, the numerical aperture (NA) of the lens is A, the refractive index of the substrate of the optical path shifting means is n, and the lens is When the maximum distance from the focal position to the liquid crystal layer of the optical path shifting means is T, the distance d between the electrode pairs is expressed by the following relational expression.
2T × A / n ≦ d ≦ 2T × A
Meet.
[0033]
Therefore, the relationship among the numerical aperture A representing the light take-in angle of the lens, the refractive index n of the substrate, the maximum distance T from the focal position to the liquid crystal layer, and the distance d between the electrode pairs is set within a certain range. Therefore, the distance between the electrodes can be set to be small within a range in which the spread of the optical path is not blocked by the distance between the electrodes of the optical path shift means, and the optimum setting can be achieved in which both the light use efficiency and the electric field application efficiency are compatible. Therefore, a relatively high electric field can be applied even at the same applied voltage without lowering the light use efficiency of the optical system, and a high-speed optical writing operation can be performed.
[0034]
According to an eleventh aspect of the present invention, in the optical writing device according to any one of the first to tenth aspects, a microlens array having microlenses corresponding to individual light emitting units is provided near a light emitting unit of the light emitting unit array. Was.
[0035]
Therefore, even if the optical path is shifted in a state where the recording spot size is large, the exposed pixels overlap, but the emitted light from each light emitting unit is once condensed by the microlens array, and the condensing point is set on the recording medium. In this case, the recording spot size can be reduced, and the recording density can be effectively increased by shifting the optical path.
[0036]
According to a twelfth aspect of the present invention, in the optical writing device according to the eleventh aspect, the microlens array includes a liquid crystal microlens array having at least a liquid crystal layer and an electrode capable of applying an electric field to the liquid crystal layer. The focal length of the microlens for light in a specific polarization direction is changed according to the intensity.
[0037]
Therefore, the presence of the liquid crystal layer capable of applying an electric field in the microlens array for condensing the light emitted from the light emitter array makes it possible to control the presence or absence of the condensing function of the microlens array. Therefore, when performing high-density writing by the optical path shift operation, the pixel size can be set small by generating the light condensing function of the microlens array to reduce the light emitting spot, but the optical path shift operation is required. Otherwise, the pixel size corresponding to low-density writing can be set by switching the writing density by eliminating the light-collecting function of the microlens array and enlarging the light-emitting spot.
[0038]
According to a thirteenth aspect of the present invention, in the optical writing device according to the twelfth aspect, the two liquid crystal microlens arrays are arranged in series in an optical axis direction, and each liquid crystal microlens array is provided when an electric field is applied or when no electric field is applied. The direction of the alignment treatment or the direction of the electric field application was set such that the alignment directions of the liquid crystal molecules were orthogonal to each other.
[0039]
Therefore, by arranging two liquid crystal microlens arrays having a variable focus function with the liquid crystal alignment directions orthogonal to each other, one of the liquid crystal microlens arrays functions as a variable lens for incident light components in a specific polarization direction. The other liquid crystal microlens array functions as a variable lens for the incident light component in the orthogonal polarization direction. As a result, a variable focus function can be realized for non-polarized incident light, and the writing density can be switched with high light use efficiency by combining with an optical path shift unit corresponding to non-polarized light.
[0040]
According to a fourteenth aspect of the present invention, in the optical writing device according to any one of the first to tenth aspects, the lens that focuses the light emitted by the light emitting unit on the recording medium includes at least a liquid crystal layer and a liquid crystal. An electrode capable of applying an electric field to the layer, wherein a focal length of the lens with respect to light in a specific polarization direction is changed according to the electric field intensity.
[0041]
Therefore, the focal length of the lens can be controlled by providing the liquid crystal layer capable of applying an electric field in the lens for condensing the light emitted from the light emitting array on the recording medium. Therefore, when performing high-density writing by the optical path shifting operation, the pixel size can be set small by controlling the focal length of the lens to reduce the size of the condensed spot on the recording medium. If the pixel density is not required, the focal length of the lens can be controlled to increase the size of the focused spot on the recording medium, so that the pixel size can be set to correspond to low-density writing. it can.
[0042]
According to a fifteenth aspect of the present invention, in the optical writing device according to the fourteenth aspect, the lens that focuses the light emitted by the light emitting unit on the recording medium includes at least two liquid crystal layers and an electric field applied to each liquid crystal layer. An alignment process direction or an electric field application direction was set so that the liquid crystal molecules had an electrode capable of applying the electric field and the liquid crystal molecules in each liquid crystal layer were perpendicular to each other when an electric field was applied or when no electric field was applied.
[0043]
Therefore, by arranging the liquid crystal alignment directions of the two liquid crystal layers in the lens at right angles, one of the liquid crystal layers functions as a variable focus lens for the incident light component of a specific polarization direction, and the orthogonal polarization directions are used. Function as a varifocal lens with respect to the incident light component by the other liquid crystal layer. Therefore, a variable focus function can be realized for non-polarized incident light, and the writing density can be switched with high light use efficiency by combining with a non-polarized light path shifting means.
[0044]
According to a sixteenth aspect of the present invention, in the optical writing device according to any one of the first to fifteenth aspects, the illuminant array is an LED array.
[0045]
Therefore, downsizing of the light source unit is realized.
[0046]
According to a seventeenth aspect of the present invention, in the optical writing device according to any one of the first to fifteenth aspects, the illuminant array is a laser diode array.
[0047]
Therefore, high efficiency and downsizing of the light source unit are realized.
[0048]
The invention of an image forming apparatus according to claim 18, wherein the photosensitive member on which the electrophotographic process is performed as the recording member, a charging device for uniformly charging the photosensitive member, and the photosensitive member uniformly charged by light irradiation 18. The optical writing device according to claim 1, which forms an electrostatic latent image on a body, a developing device for developing the electrostatic latent image, and transferring a developed image on the photoconductor to a transfer paper. A transfer device.
[0049]
Therefore, the operation and effect of the optical writing device according to any one of claims 1 to 17 can be obtained. Further, an image with high contrast can be formed even with writing with a relatively low light intensity.
[0050]
The invention of an image forming apparatus according to claim 19 uses the optical writing device according to any one of claims 1 to 17, wherein the recording medium is made of a material on which an image is formed by applying external energy. Image formation is performed directly.
[0051]
Therefore, the operation and effect of the optical writing device according to any one of claims 1 to 17 can be obtained. Further, since the image is formed directly on the recording medium, the size of the image forming apparatus can be reduced.
[0052]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment of Optical Writing Device]
A first embodiment of the optical writing device according to the present invention will be described with reference to FIGS.
[0053]
FIG. 1 is a vertical side view of the optical writing device, and FIG. 2 is a vertical front view thereof.
[0054]
The optical writing device according to the present embodiment includes a light emitter array 102 in which a plurality of light emitters 101 are arranged at a predetermined pixel pitch, and a light emitted by the light emitter 101 is focused on a recording medium 201. And a light path shifter 301 that can electrically shift the light emitted from the light emitter 101 in the direction in which the light emitters 101 are arranged. Then, the optical writing device of the present embodiment shifts the light emitted from the light emitting body 101 by controlling the drive of the optical path shift means 301, and thereby applies the light irradiation in which the pixel pitch is complemented to the recording body 201. Do it for.
[0055]
Here, the optical path shift means 301 is provided on a pair of transparent substrates 303 which are arranged on the optical path from the luminous body array 102 to the recording medium 201 and whose facing distance is regulated by the spacer 302, and on the inner surface side of these substrates 303. A vertical alignment film 304 provided and a liquid crystal layer 305 formed of a chiral smectic C phase filled between the substrates 303 via the vertical alignment film 304 and having homeotropic alignment by the vertical alignment film 304 are provided. The optical path shifting means 301 also has an electric field generating means 306 in addition to those components. The electric field generating means 306 applies a voltage to the electrode pair 307 arranged along both side edges of the liquid crystal layer 305, and thereby the electric field generating means 306 is substantially in the liquid crystal layer 305 in the direction normal to the substrate surface and the arrangement direction of the luminous bodies 101. An electric field is generated in an orthogonal direction.
[0056]
In such an optical writing device according to the present embodiment, the light emitters 101 arranged at a predetermined pitch in the light emitter array 102 are driven in accordance with an image signal, and light is emitted from the light emitter 101. The light emitted from each light emitting body 101 passes through a lens (not shown) and an optical path shift unit 301 and is focused on the recording body 201, thereby exposing the pixels on the recording body 201. Therefore, the two-dimensional image information is exposed on the recording body 201 by moving the recording body 201 relative to the light emitting array 102.
[0057]
At this time, the optical path shifting means 301 shifts the optical path in the direction in which the light emitting bodies 101 are arranged. Therefore, assuming that the arrangement pitch of the light emitters 101 is P μm, the optical path is shifted by P / 2 μm at a high speed in the arrangement direction of the light emitters 101 by the optical path shift means 301, so that the pixel density of the interpolated pixel is doubled. Exposure becomes possible.
[0058]
Hereinafter, each part will be described in detail.
[0059]
As the light emitting body 101, an LED (light emitting diode), a laser diode (semiconductor laser), a combination of a light source and a liquid crystal shutter, a combination of a light source and a micromirror, or the like can be used. In order to perform high-definition pixel exposure on the recording body 201, it is preferable that the area of the light emitting body 101 is small and the directivity of light emitted from the light emitting body 101 is high. The wavelength of the light emitted from the light emitting body 101 can be designed based on the characteristics of the light emitting material and the filter, and is appropriately set according to the spectral sensitivity of the recording body 201 to be exposed. A plurality of these luminous bodies 101 are arranged one-dimensionally or two-dimensionally to form a luminous body array 102.
[0060]
Further, the light emitted from each light emitter 101 is condensed to change the luminance distribution of the light emission spot, and a microlens array for controlling the shape of the exposure spot on the recording medium 201 is brought close to the light emitter array 102. It may be provided. Further, a liquid crystal microlens array may be used as the microlens array, and the exposure spot size on the recording medium 201 may be made variable by a variable focus function using an electric field.
[0061]
A spherical lens, an aspherical lens, a gradient index lens array, or the like can be used as a lens for focusing the light emitted by the light emitting body 101 on the recording medium 201. A gradient index lens array (Selfoc lens array) that can shorten the distance between image planes is preferable. Further, a liquid crystal layer may be provided on a part of this lens to form a liquid crystal lens, and the exposure spot size on the recording medium 201 may be made variable by a variable focus function using an electric field.
[0062]
Next, the optical path shift means 301 will be described.
[0063]
Glass, quartz, plastic, or the like can be used for the pair of transparent substrates 303 that are opposed to each other. Among them, a transparent material having no birefringence is preferable. Further, the thickness of the substrate 303 is preferably several tens μm to several mm.
[0064]
Further, the thickness of the pair of substrates 303 may be set such that one is thin and the other is thick. For example, the optical path shifting means 301 is arranged close to the light emitting array 102, only the substrate on the light emitting array 102 side has a thickness of about several tens μm to several hundred μm, and the other substrate is several millimeters for securing rigidity. When the thickness is about the same, the distance from the light emitting body 101 to the liquid crystal layer 305 can be set at a position of about several tens μm to several hundred μm. At this position, since the spread range of the radiated light from the luminous body 101 is relatively small, the area of the optical path passing through the liquid crystal layer 305 can be reduced. Therefore, the effective area of the optical path shift means 301 can be reduced. it can. The same effect can be obtained by disposing the optical path shifting means 301 close to the recording medium 201 and setting only the substrate on the recording medium 201 side to be thin.
[0065]
The vertical alignment film 304 formed on the inner surface of the substrate 303 is not particularly limited as long as it is a material that vertically aligns (homeotropically aligns) liquid crystal molecules with respect to the surface of the substrate 303. Coupling agent, SiO ₂ It can be formed using an evaporation film or the like. The vertical alignment (homeotropic alignment) here includes not only a state where liquid crystal molecules are vertically aligned with respect to the plate surface of the substrate 303 but also an alignment state where the liquid crystal molecules are tilted to about several tens degrees.
[0066]
Then, a spacer 302 is sandwiched between the two substrates 303, thereby defining the distance between the two substrates 303, a liquid crystal layer 305 is formed between the two substrates 303, and the electrode pair 307 is located at a position sandwiching the liquid crystal layer 305 in the horizontal direction. Is installed. As the spacer 302, a sheet member having a thickness of about several μm to several mm or particles having a similar particle diameter are used. Such a spacer 302 is preferably provided outside the effective area of the light transmitting portion of the element. As the electrode pair 307, a metal such as aluminum, copper, and chromium, and a transparent electrode such as ITO are used. In FIG. 2, the electrode pair 307 is formed on the side surface of the transparent substrate 303; however, the arrangement is not limited as long as an electric field can be applied in the horizontal direction of the liquid crystal layer 305. In order to apply a uniform horizontal electric field to the liquid crystal layer 305, it is preferable to use a metal layer having a width equal to or greater than the thickness of the liquid crystal layer 305. Further, in order to reduce the number of components, a member forming the spacer 302 and a metal sheet member forming the electrode pair 307 are formed by a common member, and the thickness of the liquid crystal layer 305 is determined by the thickness of the metal sheet member. You may do it.
[0067]
As the liquid crystal layer 305, liquid crystal capable of forming a smectic C phase in a use temperature range is used. Accordingly, an electric field is applied in the horizontal direction of the liquid crystal layer 305 by applying a voltage between the electrode pair 307.
[0068]
Here, the liquid crystal layer 305 capable of forming a smectic C phase will be described in detail. “Smectic liquid crystal” is a liquid crystal layer 305 in which the major axis directions of liquid crystal molecules are arranged in layers (smectic layer). With respect to such a liquid crystal, a liquid crystal in which the normal direction of the layer (the layer normal direction) coincides with the major axis direction of the liquid crystal molecules is referred to as a “smectic A phase”, and a liquid crystal that is not coincident with the normal direction is referred to as a “smectic A phase”. It is called "Smectic C phase". A ferroelectric liquid crystal composed of a smectic C phase generally has a so-called helical structure in which the liquid crystal director direction is helically rotated for each smectic layer in a state where an external electric field does not work, and is called a “chiral smectic C phase”. The chiral smectic C reciprocal ferroelectric liquid crystal is oriented in a direction in which the liquid crystal directors face each other. Since the liquid crystal composed of these chiral smectic C phases has an asymmetric carbon in the molecular structure and is spontaneously polarized, the liquid crystal molecules are rearranged in a direction determined by the spontaneous polarization Ps and the external electric field E. Optical properties are controlled. In the present embodiment, the optical path shift unit 301 will be described by taking a ferroelectric liquid crystal as an example of the liquid crystal layer 305, but an antiferroelectric liquid crystal can be used similarly.
[0069]
The chiral smectic C phase has an extremely high response speed as compared with the smectic A phase and the nematic liquid crystal, and is characterized by being capable of switching in sub-ms. In particular, since the direction of the liquid crystal director is uniquely determined with respect to the direction of the electric field, the direction of the director is easier to control and easier to handle than a liquid crystal having a smectic A phase.
[0070]
The liquid crystal layer 305 composed of the smectic C phase forming the homeotopic alignment has a substrate 303 for the operation of the liquid crystal director as compared with a case where the liquid crystal layer has a homogeneous alignment (a state in which the liquid crystal director is oriented parallel to the plate surface of the substrate 303). This is advantageous in that it is difficult to receive the regulating force from the optical path, the optical path deflection direction can be easily controlled by adjusting the direction of the external electric field, and the required electric field is low. Further, when the liquid crystal director is homogeneously aligned, the liquid crystal director strongly depends not only on the direction of the electric field but also on the surface of the substrate 303, so that the position accuracy of the optical path shift means 301 is required more. Conversely, in the case of homeotopic alignment as in the present embodiment, the setting margin of the optical path shift means 301 with respect to light deflection increases. In order to take advantage of these features, it is not necessary to strictly make the spiral axis perpendicular to the surface of the substrate 303, and the spiral axis may be inclined to some extent. It is sufficient if the liquid crystal director can face two directions without receiving the restricting force from the substrate 303.
[0071]
In such a configuration, the operation of the optical writing device according to the present embodiment will be described focusing on the operation principle of the optical path shift unit 301.
[0072]
FIG. 3 is a schematic view showing the direction of an electric field generated in the liquid crystal layer 305 of the optical path shifting means 301 and the tilt direction of the liquid crystal molecules. FIG. 4 shows the liquid crystal layer 305 of the optical path shifting means 301 when the electric field direction is reversed. FIG. 5 is a schematic diagram showing the direction of the electric field and the tilt direction of the liquid crystal molecules. FIG. 5 is a schematic diagram showing the orientation state of the liquid crystal molecules in the liquid crystal layer 305. FIG. FIG. 3 is a schematic diagram showing an alignment state of the liquid crystal.
[0073]
In FIGS. 3 and 4, for convenience, the length of the element is expressed as being shorter than the width between the electrodes of the element. However, the width and length of the operable element correspond to the effective area of the light emitting array 102. It may be elongated.
[0074]
FIGS. 3A and 4A are views of the optical path shifting means 301 as viewed from the emission surface side. The side where the width of the liquid crystal molecules is drawn wide is on the front side of the drawing, and the side where the width is drawn is narrow. This shows a state in which the liquid crystal director is inclined toward the back of the paper. The direction of the spontaneous polarization Ps of the liquid crystal is indicated by an arrow. As shown in FIG. 4A, when the direction of the electric field is reversed, the direction of the tilt angle of the substantially vertically aligned liquid crystal molecules is reversed. Here, the relationship between the direction in which an electric field is applied and the tilt direction of liquid crystal molecules is shown for a case where the spontaneous polarization of the liquid crystal is positive. Here, when the direction of the tilt angle is reversed, it is considered that the liquid crystal molecules in the smectic layer rotate in a virtual cone-shaped plane as shown in FIGS. 3B and 4B.
[0075]
5 and 6, the vertical alignment film 304, the spacer 302, and the electrode pair 307 are omitted. 5 and 6, for convenience, a voltage is shown to be applied to the front and back of the paper, and the electric field acts in the front and back of the paper. The direction of the electric field is switched by a voltage applying means (not shown) in accordance with the target light deflection direction, whereby the state shown in FIG. 5 and the state shown in FIG. 6 are switched.
[0076]
As shown in FIG. 5, when an electric field is applied to the near side of the drawing, if the spontaneous polarization of the liquid crystal molecules is positive, the number of molecules tilted to the upper right in FIG. The optical axis also tilts in the upper right direction in FIG. 5 and functions as a birefringent plate. Above the threshold electric field at which the helical structure of the chiral smectic C phase can be solved, all the liquid crystal directors exhibit a tilt angle θ, and the birefringent plate has an optical axis inclined upward at an angle θ. The linearly polarized light incident from the left as extraordinary light is shifted upward in parallel. Here, assuming that the refractive index in the major axis direction of the liquid crystal molecules is ne, the refractive index in the minor axis direction is no, and the thickness (gap) of the liquid crystal layer 4 is d, the shift amount S is expressed by the following equation 1. (See “Crystal Optics” Japan Society of Applied Physics, edited by Optical Society, p. 198).
[0077]

Similarly, when the voltage applied to the electrode pair 307 is inverted and an electric field is applied to the far side of the drawing, as shown in FIG. 6, if the spontaneous polarization of the liquid crystal molecules is positive, the liquid crystal director moves to the lower right in FIG. Function as a birefringent plate whose optical axis is inclined downward at an angle θ. The linearly polarized light incident from the left side as extraordinary light is shifted parallel to the lower side in FIG. Therefore, an optical path deflection amount of 2S is obtained by reversing the direction of the electric field.
[0078]
Therefore, the liquid crystal layer 305 exhibits an optical path shift function by performing a switching operation of the polarity of the electric field applied to the liquid crystal layer 305 via the electrode pair 307. This makes it possible to irradiate the recording medium 201 with light irradiation in which the pixel pitch is complemented, so that high-resolution image exposure can be performed even when the light-emitting array 102 having a low resolution is used.
[0079]
Here, as is clear from FIGS. 5 and 6, the optical path of the light emitted by the light emitter array 102 shifts symmetrically. Therefore, the optical path shift unit 301 has an advantage that the optical path length does not change when shifting the optical path.
[0080]
Further, even when the electric field is equal to or less than the threshold electric field at which the spiral structure of the chiral smectic C phase can be solved in the liquid crystal layer 305, the threshold electric field at which the spiral structure of the chiral smectic C phase can be solved by treating the average direction of the liquid crystal director as the optical axis of the liquid crystal layer 305. It can be handled in the same way as the above case. Even in a region where the helical structure of the chiral smectic C phase can be solved or less than the threshold electric field, the tilt direction of the optical axis changes with respect to the electric field intensity, so that the shift amount can be controlled.
[0081]
Further, the shift amount 2S at the time of the electric field inversion depends on the optical characteristics of the liquid crystal material of the liquid crystal layer 305 and the thickness of the liquid crystal layer 305. For example, when the thickness of the liquid crystal layer 305 is about several tens μm to about 100 μm, a shift amount of several μm to several tens μm is possible. Thus, the optical path shifting means 301 of the present embodiment is suitable as a structure corresponding to several hundreds to several thousand dpi.
[0082]
Further, in the present embodiment, in order to apply a horizontal electric field, there is no need to provide a transparent electrode in the optical path as in the optical writing device illustrated in FIG. There is a structural advantage.
[0083]
In addition, the switching time of the optical axis in the optical path shift unit 301 varies depending on the spontaneous polarization, tilt angle, helical pitch, viscoelasticity, electric field strength, temperature, etc. of the liquid crystal material in the liquid crystal layer 305, but is several hundred V / mm. A high-speed response of about several hundred μsec with an electric field strength of several hundred μsec and several tens μsec with an electric field strength of several thousand V / mm (several V / μm) is possible.
[0084]
FIG. 7 is a schematic diagram illustrating the relationship between the pitch of the light emitting body 101, the amount of optical path shift by the optical path shift unit 301, the pixel pitch, and the resolution.
[0085]
Here, the relationship between the pitch of the luminous bodies 101, the amount of optical path shift by the optical path shifting means 301, the pixel pitch, and the resolution will be described with a specific example.
[0086]
For example, as shown in FIG. 7, using a one-dimensional light emitter array 102 of 600 dpi (light emitter pitch of 42.3 μm), a resolution of 1200 dpi (pixel pitch of 21.1 μm), and a recording medium moving speed of 20 mm / sec. When writing an image, the required shift amount is 21.1 μm, and the above-described optical path shift means can be used. The writing time for one line is about 1060 μsec. Since printing at two shift positions is required during that time, the time at one place is about 530 μsec, which is a half, and a sufficient exposure time can be secured even with an optical path switching time of several hundred μsec. When the movement of the recording body 201 is constant, the recording body 201 slightly advances during exposure at the shift position, and thus the trajectory of the exposure unit by one light emitting body 101 has a zigzag shape as illustrated in FIG. . The data of the image to be written may be processed corresponding to such alternately arranged pixel positions. Alternatively, the movement of the recording medium 201 may be performed stepwise using a stepping motor or the like, and the movement of the recording medium 201 may be stopped during the optical path shift, and the pixels at the time of the shift may be exposed on the same line.
[0087]
[Second Embodiment of Optical Writing Device]
A second embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted.
[0088]
FIG. 8A is a vertical side view of the optical writing device, and FIG. 8B is a vertical front view thereof.
[0089]
In the present embodiment, a plurality of (two in this embodiment) optical path shift means 301 are arranged in series with respect to the optical paths such that the directions of light movement by the respective optical path shift means 301 are substantially parallel. In addition, a power source 308 is provided so that a voltage can be independently applied to each optical path shift unit 301. In the present embodiment, a first power supply 308a for applying a voltage to one optical path shift means 301 and a second power supply 308b for applying a voltage to the other optical path shift means 301 are provided.
[0090]
The shift amount of the light path shift means 301 in the light emitting element array 102 is P / 2, and the shift amount of the light path shift means 301 in the light emitting element array 102 is P / 2. The shift amount of the optical path shift means 301 is set to P / 4.
[0091]
In such a configuration, by controlling the operations of the first and second power supplies 308a and 308b, optical writing can be performed with a pixel density of 2 × 2 × 4 times. Therefore, the pixel density can be increased twice or more. Moreover, such an increase in pixel density can be realized by simply stacking the optical path shift means 301 in multiple stages. This is because the linear polarization plane of the optical path shift means 301 is constant.
[0092]
The number of the optical path shift units 301 and the shift amount of the optical path in each optical path shift unit 301 are not limited to the above examples.
[0093]
[Third Embodiment of Optical Writing Device]
A third embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted.
[0094]
FIG. 9 is a vertical sectional front view of the optical writing device.
[0095]
When using an inexpensive luminous body array 102 in which the distance between the luminous bodies 101 is relatively large, it is necessary to set a large optical path shift amount. Therefore, when the thickness of the liquid crystal layer 305 is set to be large, an alignment defect in which the vertical alignment state is broken may occur in the liquid crystal layer 305. This alignment defect is more likely to occur as the thickness of the liquid crystal layer 305 increases. Then, when such an alignment defect occurs, the liquid crystal layer 305 becomes cloudy and causes light scattering and a decrease in transmittance.
[0096]
Therefore, in the present embodiment, in order to prevent the occurrence of such alignment defects, as shown in FIG. 9, the liquid crystal layer 305 of one optical path shift unit 301 is divided in the thickness direction by an intermediate layer 309, and A vertical alignment film 304 similar to that formed on the substrate 303 is formed on at least one surface of the layer 309. Then, the electrode pair 307 is arranged so as to be uniformly applied inside the divided liquid crystal layers 305. In the example shown in FIG. 9, the electrode pair 307 is arranged so as to sandwich the entire part of the liquid crystal layer 305. Alternatively, the spacer 302 of each liquid crystal layer 305 may be formed of a metal electrode and also serve as an electrode pair.
[0097]
As the intermediate layer 309, a transparent film-like or plate-like material having a small refractive index anisotropy can be used. However, it is preferable that the intermediate layer 309 has resistance to the use of a temperature or a solvent in the vertical alignment film forming process, A glass plate having a thickness of about several tens μm to several hundred μm is particularly preferable.
[0098]
In such a configuration, the intermediate layer 309 generates an alignment regulating force at the center of the liquid crystal layer 305 where the alignment regulating force of the smectic layer becomes weak. Therefore, the amount of optical path shift by the optical path shift unit 301 increases without setting the thickness of each liquid crystal layer 305 to be large. Accordingly, the thickness of each layer of the liquid crystal layer 305 can be set relatively small, thereby preventing the occurrence of alignment defects and setting the thickness of the entire liquid crystal to be large. Becomes possible.
[0099]
[Fourth Embodiment of Optical Writing Device]
A fourth embodiment of the optical writing device according to the present invention will be described with reference to FIG.
[0100]
FIG. 10 is a longitudinal sectional front view of one embodiment of the optical writing device, and FIG. 11 is a longitudinal sectional front view of another embodiment of the optical writing device.
[0101]
In the first to third embodiments described above, the thickness of the liquid crystal layer 305 is regulated by the spacer 302, and the electrode pair 307 is provided on the side surface of the optical path shift unit 301. In this configuration, since the liquid crystal layer 305 and the spacer 302 are interposed between the electrode pair 307, when an electric field is generated inside the liquid crystal layer 305, it is necessary to apply an extra voltage corresponding to the width of the spacer 302. There is.
[0102]
Therefore, in the present embodiment, as illustrated in FIG. 10 or FIG. 11, a sheet-like electrode pair 307 is provided inside the spacer 302 so that the electrode pair 307 is positioned between the liquid crystal layer 305 and the spacer 302. Was. Therefore, the distance between the electrode pairs 307 is equal to the thickness of the liquid crystal layer 305.
[0103]
Although a sheet-like electrode is provided on the inner side surface of the spacer 302 in the drawing, a metal material may be attached to the side surface of the spacer 302 by a sputtering method, or a metal layer may be formed on one surface of the spacer material mass. After bonding, the spacer material can be sliced so that the metal layer is on the side surface. Further, the spacer itself may be made of a metal material, and may serve as both the spacer and the electrode.
[0104]
With such a configuration, a horizontal electric field can be efficiently generated inside the liquid crystal layer 305, and thus, the value of the voltage applied to the liquid crystal layer 305 can be reduced.
[0105]
In addition, since the electrode pair 307 also serves as the spacer 302, the number of components can be reduced, and the thickness of the liquid crystal layer 305 can be reliably made uniform.
[0106]
The optical writing device illustrated in FIG. 10 is based on the configuration of the optical writing device according to the second embodiment illustrated in FIG. Therefore, the same parts as those in the second embodiment are denoted by the same reference numerals, and description thereof is omitted. The optical writing device illustrated in FIG. 11 is based on the configuration of the optical writing device according to the third embodiment illustrated in FIG. Therefore, the same portions as those of the third embodiment are denoted by the same reference numerals, and the description is omitted.
[0107]
[Fifth Embodiment of Optical Writing Device]
A fifth embodiment of the optical writing apparatus according to the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted.
[0108]
FIG. 12 is a vertical side view of the optical writing device for explaining a phenomenon that occurs in the optical writing device according to the first embodiment. FIG. 13 is an optical diagram illustrating one aspect of the optical writing device according to the present embodiment. FIG. 14 is a longitudinal side view of an optical writing device illustrating another aspect of the optical writing device of the present embodiment.
[0109]
In each of the first to fourth embodiments described above, the operation has been described on the assumption that the radiated light from the light emitter array 102 is linearly polarized light parallel to the optical path shift direction. However, actually, the light emitted from the light emitter array 102 is not always the desired linearly polarized light. Therefore, the linearly polarized light component parallel to the optical path shift direction, that is, parallel to the tilt direction of the liquid crystal director is shifted as illustrated in FIGS. 5A and 5B, but the other light is shifted. Instead, the light becomes noise light as illustrated in FIG. Such noise light reduces the resolution and the contrast ratio.
[0110]
Therefore, in this embodiment, the linear polarizing plate 401 that transmits only light having a polarization plane parallel to the moving direction of the optical path is provided so that only the desired shifted light is exposed on the recording medium 201. . The installation position of such a linear polarizing plate 401 may be on either the entrance side or the exit side of the optical path shift unit 301. 13 illustrates an example in which a linear polarizing plate 401 is disposed on the incident side of the optical path shifting unit 301. In another embodiment illustrated in FIG. 14, a linear polarizing plate is disposed on the emitting side of the optical path shifting unit 301. An example where 401 is arranged is shown.
[0111]
In such a configuration, the light to be exposed on the recording body 201 is only linearly polarized light parallel to the moving direction of the optical path by the linear polarizing plate 401, so that unnecessary light is exposed to the recording body 201. Thus, high-definition and high-contrast optical writing can be performed.
[0112]
[Sixth Embodiment of Optical Writing Device]
A sixth embodiment of the optical writing device according to the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted.
[0113]
FIG. 15 is a vertical side view of the optical writing device, and FIG. 16 is a schematic diagram for explaining the operation of the optical writing device of the present embodiment.
[0114]
In the above-described first to fifth embodiments, since only the linearly polarized light component in the optical path shift direction is exposed on the recording medium 201, the extra polarized light component is reflected unless the light emitting body 101 itself emits linearly polarized light. Alternatively, it is transmitted and not used for exposure. Accordingly, the light use efficiency from the light emitting body 101 to the exposure of the recording body 201 is reduced.
[0115]
Therefore, in the present embodiment, as illustrated in FIG. 15, two optical path shift units 301 having substantially the same thickness of the liquid crystal layer 305 are placed in the optical path in such a manner that their light shift directions are substantially parallel. A polarization plane rotation element 501 that is arranged in series and rotates the linear polarization plane by approximately 90 degrees between both optical path shift means 301 is arranged. FIGS. 15 and 16 show a state in which liquid crystal molecules are inclined in one direction due to an electric field in one direction.
[0116]
As shown in FIG. 15, when the unpolarized radiation light from the light emitting body 101 passes through the first optical path shift means 301, the polarization component parallel to the optical path shift direction corresponds to the thickness d of the liquid crystal layer 305 in FIG. The polarized light component shifted to the right and perpendicular to the plane of the paper travels straight without being deflected. When these emitted lights pass through the polarization plane rotation element 501 and the respective polarization planes are rotated by about 90 degrees, in the succeeding optical path shift means 301, the polarized light components that have been shifted earlier travel straight, and the polarized light components that have traveled straight ahead pass through the liquid crystal layer. 15 is shifted to the right in FIG. FIG. 16 schematically shows such a light shift state in relation to the direction of an electric field generated in each liquid crystal layer 305.
[0117]
At this time, if the liquid crystal material and the liquid crystal thickness of the two liquid crystal layers 305 and the applied electric field applied to such liquid crystal layers 305 are set to be equal, the shift amounts of the polarization components generated in the respective liquid crystal layers 305 match. become. Accordingly, all the polarization components of the light emitted from the light emitting body 101 can be used, and the light use efficiency is approximately doubled compared to the case of using linear polarization in one direction.
[0118]
Here, as the polarization plane rotation element 501, a half-wave plate, a twisted nematic liquid crystal cell, a twisted nematic liquid crystal film, or the like can be used.
[0119]
[Seventh Embodiment of Optical Writing Device]
A seventh embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same parts as those of the third embodiment described with reference to FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted.
[0120]
FIG. 17 is a vertical sectional side view of the optical writing device.
[0121]
In the present embodiment, a member corresponding to the above-mentioned intermediate layer 309 includes a polarization plane rotation element 501 for rotating the linear polarization plane by approximately 90 degrees, and the upstream side and the downstream side of the optical path with respect to the position of the polarization plane rotation element 501. The thicknesses of the liquid crystal layers 305 located on the sides are set substantially equal to each other.
[0122]
Thus, since the intermediate layer 309 also serves as the polarization plane rotation element 501, the number of substrates forming the optical path shift unit 301 can be reduced.
[0123]
Further, since the influence of interface reflection can be reduced, the transmittance of the entire optical path shift unit 301 is improved.
[0124]
Further, the orientation of the liquid crystal layer 305 is improved, and the light of all the polarization components incident on the optical path shifting means 301 can be shifted, so that the light use efficiency is improved.
[0125]
Here, as the polarization plane rotation element 501, a half-wave plate, a twisted nematic liquid crystal cell, a twisted nematic liquid crystal film, or the like can be used.
[0126]
Further, in practice, an intermediate layer 309 may be further provided in the liquid crystal layers 305 on the upstream side and the downstream side. In this case, the thickness of each liquid crystal layer 305 may be set so that the total thickness of the liquid crystal layer 305 divided by the intermediate layer 309 becomes substantially equal.
[0127]
[Eighth Embodiment of Optical Writing Device]
An eighth embodiment of the optical writing apparatus according to the present invention will be described with reference to FIGS. The same parts as those in the first to seventh embodiments are denoted by the same reference numerals, and description thereof is omitted.
[0128]
FIG. 18 is a longitudinal sectional front view of an optical writing device showing an example of the arrangement of the optical path shifting means, and FIG. 19 is a longitudinal sectional front view of the optical writing apparatus showing an example of the arrangement of the optical path shifting means of the present embodiment.
[0129]
Light emitted from the light emitting body 101 passes through the optical path shift unit 301, enters the lens 510, and is collected on the recording body 201. The luminous bodies 101 are arranged in an array arranged in a direction perpendicular to the plane of the drawing. FIG. 18 shows a type in which the thickness of the pair of substrates 303 of the optical path shift means 301 is substantially equal, and the metal electrode pair 207 also serves as a spacer. In addition, the angle actually changes at the interface according to the refractive index difference of the medium through which light passes, but here, for simplicity of illustration, the angle change in each medium due to the refractive index difference is not shown. (The same shall apply hereinafter). Here, assuming that the distance from the luminous body 101 to the liquid crystal layer 305 is T, the area of the optical path passing through the liquid crystal layer 305 increases as the distance T increases. Therefore, when the electrode pair 207 is provided so as not to lower the light use efficiency, the electrode interval d must be relatively large. If the electrode spacing is widened, it is necessary to apply a high voltage in order to apply a high electric field. Therefore, it is preferable to set T to be small, but T is limited by the thickness of the substrate.
[0130]
Therefore, in the present embodiment, as shown in FIG. 19, the luminous body array 102 and the optical path shift means 301 are arranged close to each other, and the thickness of the substrate 303 on the luminous body array 102 side of the pair of substrates 303 The thickness is set smaller than the thickness of the substrate 303 on the 510 side. For example, the optical path shifting means 301 is arranged close to the light emitter array 102, only the substrate 303 on the light emitter array 102 side has a thickness of about several tens μm to several hundred μm, and the other substrate 303 is provided for securing rigidity. When the thickness is about several millimeters, the distance from the light emitting body 101 to the liquid crystal layer 305 can be set at a position of several tens μm to several hundred μm. Therefore, the liquid crystal layer 305 of the optical path shift means 301 can be arranged in a region where the spread of the radiated light emitted from the light emitter array 102 is small, so that the effective area of the liquid crystal layer 305 required for the optical path shift can be reduced. When the effective area of the liquid crystal layer 305 is small, the distance d between the electrodes can be set small, so that a high electric field can be applied even at a relatively low voltage. By applying a high electric field, a high-speed optical path deflection operation becomes possible, and a high-speed optical writing device can be obtained. In addition, cost can be reduced because the amount of liquid crystal material used is reduced.
[0131]
[Ninth Embodiment of Optical Writing Device]
A ninth embodiment of the optical writing apparatus according to the present invention will be described with reference to FIG. The same parts as those in the eighth embodiment described with reference to FIGS. 18 and 19 are denoted by the same reference numerals, and description thereof will be omitted.
[0132]
FIG. 20 is a vertical sectional front view of an optical writing device showing an example of the arrangement of the optical path shift means of the present embodiment.
[0133]
In this embodiment, as shown in FIG. 20, the optical path shift means 301 and the recording medium 201 are arranged close to each other, and the thickness of the substrate 303 on the recording medium 201 side is set to the thickness of the substrate on the lens 510 side. The thickness is set to be smaller than the thickness of 303.
[0134]
According to such a configuration, the liquid crystal layer 305 of the optical path shift means 301 can be arranged in a region where the spread of the light immediately before the emitted light is converged on the recording medium 201 is small. The effective area of the liquid crystal layer 305 can be reduced. When the effective area of the liquid crystal layer 305 is small, the distance between the electrodes can be set small, so that a high electric field can be applied even at a relatively low voltage. Therefore, a high-speed optical path deflection operation can be performed by applying a high electric field, and a high-speed optical writing device can be obtained. In addition, cost can be reduced because the amount of liquid crystal material used is reduced.
[0135]
[Tenth Embodiment of Optical Writing Device]
A tenth embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same parts as those in the eighth and ninth embodiments described with reference to FIGS. 18 to 20 are denoted by the same reference numerals, and description thereof will be omitted.
[0136]
In the present embodiment, when considering the optical system configuration as shown in FIGS. 18 to 20, the numerical aperture (NA) of the lens 510 is A, the refractive index of the substrate 303 of the optical path shift means 301 is n, and the lens 510 The distance d between the electrode pair 307 and the maximum distance from the focal position to the liquid crystal layer 305 in the optical path shift means 301 is represented by the following relational expression.
2T × A / n ≦ d ≦ 2T × A
Set to satisfy.
[0137]
FIG. 21 shows the relationship between the light take-in angle θ of the lens 510, the distance T from the focal position, and the diameter d of the optical path. Here, assuming that the focal length of the lens 510 is f and the aperture is D, the numerical aperture (NA value) of the lens 510 is
NA = n × sin θ = n × 2f / D
Can be expressed as Here, n represents the refractive index between the lens 510 and the focal point. In order to set the electrode interval to be narrow in a range where the optical path spread range is not blocked by the electrode pair 307 of the optical path shift means 301, the relationship between the aperture width d of the electrode interval and the distance from the focal length to the liquid crystal layer 305 is determined by the numerical aperture. (NA). That is, it is sufficient that NA = n × 2T / d from the similarity relationship in FIG. Actually, the substrate 303 and the liquid crystal layer 305 having a relatively large refractive index exist between the lens 510 and the focal position or between the liquid crystal layer 305 and the focal position. If the thickness of the glass substrate is zero, the refractive index n = 1 between the liquid crystal layer 305 and the focal position with air, and d = 2T × A. Conversely, when the entire area between the liquid crystal layer 305 and the focal position is filled with a substrate having a refractive index of n, d = 2T × A / n.
[0138]
Therefore, by setting the electrode interval d between them, it is possible to make an optimal setting that achieves both light use efficiency and electric field application efficiency. As a result, a relatively high electric field can be applied even at the same applied voltage without lowering the light use efficiency of the optical system, and a high-speed optical writing operation can be performed.
[0139]
[Eleventh Embodiment of Optical Writing Device]
An eleventh embodiment of the optical writing apparatus according to the present invention will be described with reference to FIG. The same parts as those in the eighth embodiment described with reference to FIG. 19 are denoted by the same reference numerals, and description thereof will be omitted.
[0140]
FIG. 22 is a vertical sectional front view of the optical writing device of the present embodiment.
[0141]
In the present embodiment, a microlens array 520 is provided near the light emitter 101 of the light emitter array 102 as shown in FIG. In FIG. 22, the light emitters 101 and the microlenses 521 are arranged in an array in a direction perpendicular to the paper surface, and the pitches and positions of the individual light emitters 101 and the microlenses 521 correspond to each other.
[0142]
According to such a configuration, the radiated light from the light emitting body 101 is once condensed by the corresponding microlens 521 of the microlens array 520, and the condensed point is projected on the recording body 201, thereby obtaining the recording spot size. Can be reduced, and an increase in recording density due to an optical path shift becomes effective.
[0143]
[Twelfth Embodiment of Optical Writing Device]
A twelfth embodiment of the optical writing apparatus according to the present invention will be described with reference to FIG. The same portions as those of the eleventh embodiment described with reference to FIG. 22 are denoted by the same reference numerals, and description thereof will be omitted.
[0144]
FIG. 23 is a cross-sectional view showing a microlens of the microlens array of the present embodiment.
[0145]
The microlens 521 includes at least a liquid crystal layer 522 and an electrode capable of applying an electric field to the liquid crystal layer 522, and changes the focal length of the microlens 521 for light in a specific polarization direction according to the electric field strength. Have been. In the example shown in FIG. 23, a liquid crystal layer 522 is provided between a lens substrate 523 having a microlens-shaped concave portion and a parallel substrate 524. A transparent electrode layer (not shown) and an alignment film (not shown) are provided at the interface between the substrates 523 and 524 and the liquid crystal layer 522. An ITO electrode or the like can be used as the transparent electrode layer, and is formed in an effective area on the substrate surface. As the alignment film, for example, a film for horizontal alignment is used, and an alignment process such as rubbing is performed in the vertical direction on the paper surface.
[0146]
Therefore, as shown in FIG. 23A, when no electric field is applied, the liquid crystal molecules are oriented vertically in the plane of the drawing. Here, by selecting a material that makes the refractive index in the long axis direction of the liquid crystal molecules (the extraordinary light refractive index) sufficiently larger than the refractive index of each of the substrates 523 and 524, the incident light of linearly polarized light in FIG. Generates a large lens effect.
[0147]
On the other hand, when an electric field is applied between the transparent electrodes, for example, when the liquid crystal molecules have a positive dielectric anisotropy, the liquid crystal molecules are vertically aligned with respect to the substrates 523 and 524 as shown in FIG. . Here, the difference between the refractive index of each of the substrates 523 and 524 and the ordinary refractive index of the liquid crystal molecules becomes relatively small, so that the lens effect is reduced.
[0148]
Therefore, it is possible to control the presence or absence or the size of the light collecting function of the microlens array 520. In the case of performing high-density writing by an optical path shift operation, the pixel size can be set small by generating a condensing function of the microlens array 520 to reduce the light emitting spot. On the other hand, when the optical path shift operation is not required, the pixel size corresponding to the low-density writing can be set by eliminating the light-collecting function of the microlens array 520 and enlarging the light emitting spot.
[0149]
The sign of the dielectric anisotropy of the liquid crystal molecules, the direction of the alignment treatment, the relationship between the presence / absence of an electric field, and the magnitude of the lens effect are not limited to the above examples, but may be any combination that achieves the same effect.
[0150]
[Thirteenth Embodiment of Optical Writing Device]
A thirteenth embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same portions as those of the twelfth embodiment described with reference to FIG. 23 are denoted by the same reference numerals, and description thereof will be omitted.
[0151]
The twelfth embodiment described above can cope only with the case where the incident light is linearly polarized light, and when the light from the luminous body 101 is unpolarized light, it is necessary to use it in combination with a linearly polarizing plate. Usage efficiency is reduced.
[0152]
Therefore, in the present embodiment, the microlens array is composed of two liquid crystal microlens arrays 520 arranged in series in the optical axis direction as shown in FIG. The alignment processing direction or the electric field application direction is set so that the alignment directions of the liquid crystal molecules in 520 are orthogonal to each other. The configuration of each liquid crystal microlens 521 is similar to that of the twelfth embodiment.
[0153]
In FIG. 24A, the liquid crystal alignment direction in the left liquid crystal microlens 521 is set in the vertical direction in the plane of the paper, and the liquid crystal alignment direction in the right liquid crystal microlens 521 is set in a direction perpendicular to the paper. When non-polarized light is incident without an electric field, in the left liquid crystal microlens 521, the vertical polarization component in the plane of the paper is affected by the extraordinary light refractive index of the liquid crystal layer 522 and undergoes a lens effect. The component permeates the liquid crystal layer 522 almost as it is, feeling the ordinary light refractive index. However, in the liquid crystal microlens 521 on the right side thereafter, the polarization component in the vertical direction in the paper senses the ordinary light refractive index of the liquid crystal layer 522 and is transmitted almost as it is, and the polarization component in the direction perpendicular to the paper is extraordinary light refraction of the liquid crystal layer 522. Feel the rate and receive the lens effect to collect light. By optimizing the lens shape and the liquid crystal material so that the focal positions of the two liquid crystal microlens arrays 520 coincide, a variable focus function can be realized for non-polarized incident light, and an optical path shift corresponding to non-polarized light In combination with the means 301, the writing density can be switched with high light use efficiency.
[0154]
As an example of the liquid crystal microlens, the substrate has a lens shape and the lens effect is generated by the thickness distribution of the liquid crystal layer. However, the substrate is parallel, the thickness of the liquid crystal layer is constant, and the electric field distribution is formed in the liquid crystal layer. By giving the refractive index distribution spatially, a lens effect may be generated. In this case, the electrode may be divided into a plurality of parts and the voltage value of each electrode may be changed, or the electric field distribution may be formed by forming a potential distribution in the electrode using a high-resistance electrode material. . The electrode shape may be a stripe shape or a ring shape, and is appropriately designed according to a desired electric field intensity distribution shape.
[0155]
[Fourteenth Embodiment of Optical Writing Device]
A fourteenth embodiment of the optical writing device according to the present invention will be described.
[0156]
In the above-described example, the liquid crystal microlens array 520 is provided close to the light emitting body 101 to provide a variable focus and the exposure spot size on the recording body 201 is variable. However, in the present embodiment, although not particularly shown, The lens 510 itself that focuses the light emitted by the light emitting body 101 on the recording medium 201 has at least a liquid crystal layer and an electrode capable of applying an electric field to the liquid crystal layer, and has a specific polarization direction according to the electric field intensity. It is configured to change the focal length of the lens with respect to light.
[0157]
The principle and basic configuration of the variable focus by the liquid crystal micro lens are the same as those of the liquid crystal micro lens 521 in FIG. The design of the varifocal lens portion made of liquid crystal is optimized according to the design of the fixed portion spherical or aspherical lens or the gradient index lens.
[0158]
When performing high-density writing by an optical path shift operation, the pixel size can be set small by controlling the focal length of the lens 510 to reduce the size of the condensed spot on the recording medium 201. On the other hand, when the optical path shift operation is not required, if the focal length of the lens 510 is controlled to increase the size of the condensed spot on the recording medium 201, a pixel size corresponding to low-density writing can be set. .
[0159]
[Fifteenth Embodiment of Optical Writing Device]
A fifteenth embodiment of the optical writing device according to the present invention will be described.
[0160]
The fourteenth embodiment described above can cope only with the case where the incident light is linearly polarized light, and when the light from the luminous body 101 is unpolarized light, it is necessary to use it in combination with a linearly polarizing plate. Usage efficiency is reduced.
[0161]
Therefore, in this embodiment, the lens 510 that focuses the light emitted from the light emitting body 101 on the recording medium 201 has at least two liquid crystal layers and electrodes capable of applying an electric field to each liquid crystal layer. The configuration is such that the alignment processing direction or the electric field application direction is set such that the alignment directions of the liquid crystal molecules of each liquid crystal layer at the time of application or no electric field are orthogonal to each other.
[0162]
The principle and basic configuration of variable focus by two liquid crystal microlenses whose orientation directions are orthogonal to each other are the same as those of the liquid crystal microlens 521 shown in FIG. The design of the varifocal lens portion made of liquid crystal is optimized according to the design of the fixed portion spherical or aspherical lens or the gradient index lens.
[0163]
Therefore, a variable focus function can be realized for non-polarized incident light, and the writing density can be switched with high light use efficiency by combining with the optical path shift unit 301 corresponding to non-polarized light.
[0164]
[16th Embodiment of Optical Writing Device]
A sixteenth embodiment of the optical writing device according to the present invention will be described with reference to FIG. The same parts as those in the first to fifteenth embodiments are denoted by the same reference numerals, and description thereof is omitted.
[0165]
FIG. 25 is a vertical sectional side view of the light emitting array 102.
[0166]
In the first to fifteenth embodiments, the type of the light emitting array 102 is not particularly specified.
[0167]
On the other hand, for example, when a light source and a nematic liquid crystal light valve array are used as the light emitting array 102, the response of the liquid crystal light valve is relatively slow. Can not. However, in a system in which a light source and a ferroelectric liquid crystal light valve are combined, one dot can be written at a high speed of about several tens of microseconds, which is preferable as a light emitting array for high-speed recording. However, since the light switched by the liquid crystal needs to be linearly polarized light, there is a problem that the use efficiency of light is reduced by half when a non-polarized light source is used.
[0168]
Therefore, in the present embodiment, an LED array is used as the light emitter array 102. For example, as illustrated in FIG. 25, a diffusion prevention film 112 of aluminum oxide or the like is formed by a photolithography process on a wafer 111 of gallium, aluminum, and arsenic, which is a base material of an LED array. In this case, let P be the pitch at the portion where the diffusion prevention film 112 is not provided, that is, the center of the light emitting body 101, and L be the width between the diffusion prevention films 112. Next, the wafer 111 is placed in a zinc atmosphere, and phosphorus is selectively diffused into the opening of the diffusion preventing film 112 to form the light emitting portion 113. At this time, in order to maximize the light emission output of the light emitting unit 113, the formation depth D of the light emitting unit 113 is set to about 10 μm. Thus, the width W of the light emitting unit 113 that actually emits light is L + 2D. Here, if the width of the diffusion preventing film is 5 μm and the width L between the diffusion preventing films 112 is 2 μm or more from the accuracy of the photolithography process, the width W of the light emitting unit 113 needs to be about 22 μm or more and the pitch of the light emitting unit needs to be 27 μm or more. Become.
[0169]
For this reason, it is difficult to realize a 21 μm pitch required for writing at 1200 dpi with a single-row light-emitting array 102, whereas a 600-dpi light-emitting array 102 that is easy to produce is created and By combining with the optical path shift means 301 in the first to seventh embodiments described above, it is possible to realize high-definition writing equivalent to 1200 dpi.
[0170]
Here, as illustrated in FIG. 25, the LED array has the light-emitting unit 113 formed directly on the wafer 111 as a substrate, so that the size can be reduced.
[0171]
At the time of implementation, a microlens array (not shown) may be provided near the light emitting unit 113 in order to enhance the directivity of light emitted from the LED.
[0172]
[Seventeenth Embodiment of Optical Writing Device]
A seventeenth embodiment of the optical writing device according to the present invention will be described.
[0173]
In the present embodiment, although not shown, a laser diode array is used as the light emitter array 102. The laser diode is capable of high output with high efficiency. By narrowing down the pixels in the exposed area, even if the recording medium 201 is a heat mode optical recording medium, it can sufficiently heat and record the recording medium. .
[0174]
At the time of implementation, a microlens array (not shown) may be provided near the light emitting body 101 in order to enhance the directivity of light emitted from the laser diode.
[0175]
[First Embodiment of Image Forming Apparatus]
A first embodiment of the image forming apparatus of the present invention will be described with reference to FIG. The same portions as those of the first to seventeenth embodiments of the optical writing device are denoted by the same reference numerals, and the description is omitted.
[0176]
The optical writing device of the present invention can be applied to the recording body 201 as long as a latent image or a visible image can be formed by exposure. Therefore, here, an example of an image forming apparatus having the light emitting array 102 and the optical path shift unit 301 using the electrophotographic photosensitive member 601 as the recording body 201 will be described with reference to FIG.
[0177]
Around the drum-shaped or belt-shaped photoconductor 601, a charging device 602, an optical writing device 603 including the luminous body array 102 and the optical path shift unit 301, a developing device 604, a transfer device 605, and a cleaning device 606 are arranged. I have. A transfer paper transport path 608 for guiding and transporting the transfer paper 607 is formed between the photoconductor 601 and the transfer device 605. In the transfer paper transport path 608, the transfer paper 608 is positioned upstream of the photoconductor 601 and supplied. A paper device 609 is disposed, and a fixing device 610 is disposed downstream of the photoconductor 601.
[0178]
Here, a photosensitive layer (not shown) made of an inorganic material or an organic material is formed on the surface of the photoconductor 601. The photoconductor 601 on which the photosensitive layer made of an inorganic material is formed is called an inorganic photoconductor, and the photoconductor 601 on which the photosensitive layer made of an organic material is formed is called an organic photoconductor.
[0179]
As the inorganic photoreceptor, an amorphous selenium-based or amorphous silicon-based material is used.
[0180]
The organic photoreceptor is preferably of a function separation type of a charge generation layer and a charge transport layer (neither is shown). The electric field generating layer has a thickness of about several μm, and is formed as a resin-dispersed film in which the pigment is dispersed in a binder resin such as a polycarbonate or a deposited resin of a charge generating agent such as a phthalocyanine-based pigment, a bisazo-based pigment, or a perylene-based pigment. Is done. The charge transport layer has a thickness of about several tens of μm and is formed as a film in which a donor material having a hole transport ability or an acceptor material having an electron transport ability is dispersed in a binder resin such as polycarbonate. In a general function-separated type organic photoreceptor, a base layer, an electric field generating layer, and a charge transport layer are sequentially formed on a photoreceptor substrate.
[0181]
In addition, a surface protective layer (not shown) having excellent mechanical strength may be provided if necessary, whether the photosensitive member is an inorganic photosensitive member or an organic photosensitive member. Generally, since the surface of the photoconductor is negatively charged, a donor material for transporting a positive charge is dispersed in the charge transport layer. As the donor material, triphenylmethane, triphenylamine dimer, hydrazone, pyrazoline and the like are used.
[0182]
As the charging device 602, a contact charging type charging roller is used. By applying a negative voltage to the charging roller, the surface of the photoconductor 601 is negatively charged. In order to form the charging device 602, not only the charging roller but also a corona charger or a brush member can be used. When the photoconductor 601 charged to about minus several hundred volts by the charging device 602 is exposed using the above-described optical writing device 603, the negative potential of the exposed portion becomes small, and an electrostatic latent image is formed. In this case, it is preferable that the wavelength of the light emitted from the light emitting body 101 is adjusted to the wavelength at which the spectral sensitivity of the photosensitive body 601 is large.
[0183]
The developing device 604 selectively attaches the toner to the electrostatic latent image and visualizes the electrostatic latent image as a toner image. In other words, the developing device 604 has a developing roller (not shown), and by applying a developing bias potential of minus several hundred volts to the developing roller, a negative polarity toner is applied to a low potential portion which is an exposed portion on the photoconductor 601. The particles are allowed to adhere, thereby rendering the electrostatic latent image visible as a toner image.
[0184]
As a developing method of such a developing device 604, either a one-component developing method using a one-component developer or a two-component developing method using a two-component developer can be used. It is preferable that
[0185]
Further, as the transfer device 605, a roller member, a belt member, a corona charger, or the like can be used. Such a transfer device 605 generates an electric field between the transfer device 605 and the photoconductor 601.
[0186]
In the image forming apparatus having such a configuration, conveyance of the transfer sheet 607 is started by a sheet feeding device (not shown) at a timing when a toner image is formed on the photoconductor 601. Then, when the toner image on the photoconductor 601 and the printing start position of the transfer paper 607 contact in synchronization with each other, the toner image is sucked by the transfer device 605 that generates an electric field between the photoconductor 601 and the toner image. The transferred toner image is electrostatically transferred onto the transfer paper 607. Then, the transfer paper 607 with the toner image attached thereto is conveyed to the fixing device 610, where the toner image is heated and fused to the transfer paper 607. On the other hand, the toner particles remaining on the surface of the photoconductor 601 after the transfer process are removed by the cleaning device 606.
[0187]
Thus, image formation using the electrophotographic process is performed. In an image forming operation using such an electrophotographic process, an electrostatic latent image can be formed on the photoconductor 601 even if exposure energy is relatively small, so that high-speed, high-definition optical writing is possible. It is.
[0188]
[Second Embodiment of Image Forming Apparatus]
A second embodiment of the image forming apparatus according to the present invention will be described. The same portions as those of the first to seventeenth embodiments of the optical writing device are denoted by the same reference numerals, and the description is omitted.
[0189]
As another example of the recording body 201, a material on which an image is formed by applying external energy, for example, a recording body 201 formed of a photosensitive image forming material or a heat-sensitive image forming material is used. Can be.
[0190]
As the photosensitive image forming material, diazo, photochromic material, and the like can be used. In this case, the recording body 201 directly develops color. Therefore, there is an advantage that the size of the image forming apparatus itself can be reduced. Moreover, by using the optical writing device exemplified in the first to ninth embodiments, high-definition recording is possible.
[0191]
As the heat-sensitive coloring material, a conventional leuco dye-based material or the like can be used. In this case, it is preferable to use a material that absorbs light and converts it into heat. In order to convert light into heat for recording, it is preferable to use high-output light such as laser light. However, in order to perform high-speed and high-density recording, it is necessary to array laser light sources. As in the case of the above-mentioned LED, it is difficult to form a high-density array even in the case of a laser diode, but by using the optical writing device exemplified in the first to ninth embodiments, a high-definition Image recording becomes possible.
[0192]
【Example】
[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
[0193]
[Creation of optical path shifting means]
FIGS. 27A and 27B are optical path shift means 1001 created by the inventor of the present invention. FIG. 27A is a plan view and FIG. 27B is a side view.
[0194]
A commercially available vertical (homeotropic) alignment film 1003 having a thickness of 0.06 μm was formed on a surface of a glass substrate 1002 having a width of 10 mm, a length of 100 mm, and a thickness of 1 mm. An aluminum electrode sheet 1004 having a thickness of 100 μm, a width of 2 mm, and a length of 110 mm is used as a spacer and an electrode, and two glass substrates 1002 having an alignment film 1003 inside so that the width of the effective area is 1 mm. The electrode sheet 1004 was arranged in parallel. A cell 1006 was formed by fixing the periphery except a part with an ultraviolet curing adhesive 1005. In a state where the cell 1006 is heated to about 90 degrees, a ferroelectric liquid crystal (CS1029 manufactured by Chisso: birefringence Δn = 0.16, a tilt angle θ = 25 degrees, a liquid crystal layer 1007) is provided in a space between the glass substrates 1002. Spontaneous polarization Ps = -40 nC / cm ² ) Was injected by the capillary method. After cooling, the injection port was also sealed with an adhesive to form a liquid crystal layer 1007 having a thickness of 100 μm, an effective width of 1 mm, and a length of about 95 mm. Then, a power supply 1008 composed of a pulse generator and a high-speed amplifier was connected to the electrode sheet 1004 to be each electrode pair, and thereby an optical path shifting means 1001 as shown in FIG. 27 was created.
[0195]
The optical path shifting means 1001 thus produced exhibited a high transmittance of 85% or more.
[0196]
[Observation of optical axis]
When a conoscopic image of the liquid crystal layer 1007 in the effective area of the created optical path shifting means 1001 was observed in the absence of an electric field, cross-shaped and annular images were observed at the center. Therefore, it was confirmed that the optic axis was perpendicular to the liquid crystal layer 1007 under no electric field. In this state, the liquid crystal molecules have a spiral structure in which the tilt direction rotates with respect to the direction perpendicular to the surface of the glass substrate 1002, and the average optical axis is the direction perpendicular to the surface of the glass substrate 1002, which is the direction of the spiral axis. Is observed as Next, when a rectangular wave voltage of ± 150 V and 1 Hz was applied from the power supply 1008 to the electrode sheet 1004 forming an electrode pair, the position of the cross and the ring of the conoscopic image was reciprocated vertically at 1 Hz. When the tilt angle of the optical axis was calculated from the NA value of the objective lens of the microscope, the refractive index of the liquid crystal, and the shift amount of the cross position, it was about 25 degrees, which confirmed that the tilt angle was unique to the liquid crystal material. . At an electric field intensity of about 150 V / mm, the helical structure was melted and the liquid crystal molecules were oriented in a uniform direction, and the direction of the optical axis of the liquid crystal layer 1007 could be switched at ± 25 degrees.
[0197]
[Electric field dependence of optical path shift amount]
The electric field dependence of the optical path shift amount was confirmed. This will be described with reference to FIG.
[0198]
FIG. 28 is a graph showing the relationship between the applied electric field and the amount of optical path shift.
[0199]
In the experiment, the mask pattern having an opening of 4 μm square was illuminated with linearly polarized light from the back surface, and the transmitted light was observed through the optical path shifting means 1001. That is, the manner in which the position of the mask pattern was shifted by operating the optical path shifting means 1001 was observed with a video camera equipped with a microscope, and the optical path shift amount at this time was measured. The temperature of the optical path shifting means 1001 was about 30 ° C. In addition, a rectangular wave voltage of 0 to ± 175 V and 1 Hz was applied from a power source 1008 to an electrode sheet 1004 forming an electrode pair. As a result, when the polarization plane of the incident light was perpendicular to the electric field direction, that is, parallel to the optical path shift direction, the characteristics of the optical path shift amount as shown in FIG. 28 were obtained.
[0200]
As shown in FIG. 28, at an electric field strength of about ± 125 V / mm, the shift amount was about 21 μm, and the value was saturated at this value. Similarly, measurements were made at several locations in the longitudinal direction of the optical path shifting means 1001, and similar shift characteristics were obtained in each case. No out-of-focus was observed at both shift positions.
[0201]
Further, the degree of degradation of the resolution (contrast transfer function: CTF) was examined from the change in the luminance distribution of the aperture when the optical path shifting means 1001 was not provided and the luminance distribution of the aperture during the optical path shift. Was 80% or more, and it was judged that there was no practical problem.
[0202]
In addition, when the plane of polarization of the incident light was horizontal to the direction of the electric field, no optical path shift was observed.
[0203]
[Measurement of optical path shift response time]
The measurement of the response time of the optical path shift was confirmed. This will be described with reference to FIG.
[0204]
FIG. 29 is a graph showing the relationship between the applied electric field and the response time.
[0205]
By observing the state of the shift in the same manner as when confirming the electric field dependence of the optical path shift amount with a high-speed camera equipped with a microscope, the optical path shift amount and the time required for its movement, that is, the response time of the optical path shift, were measured. At this time, the temperature of the optical path shift means 1001 was set to about 30 ° C.
[0206]
In the experiment, a rectangular wave voltage of ± 100 V to ± 400 V, 100 Hz was applied from a power source 1008 to an electrode sheet 1004 forming an electrode pair, and observation with a high-speed camera (time resolution: 40,500 frames / sec) was performed. As a result, a response time characteristic as shown in FIG. 29 was obtained. At ± 400 V / mm, the response time was 0.5 msec or less.
[0207]
[Second embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIG.
[0208]
FIGS. 30A and 30B show the optical path shifting means created by the inventor of the present invention. FIG. 30A is a plan view thereof, and FIG. 30B is a side view thereof.
[0209]
A commercially available vertical (homeotropic) orientation having a thickness of 0.06 μm on the surface of a thin glass substrate 1002 having a width of 10 mm, a length of 100 mm and a thickness of 0.15 mm and a thick glass substrate 1002 having a width of 10 mm, a length of 100 mm and a thickness of 2 mm. A film 1003 was formed. An aluminum electrode sheet 1004 having a thickness of 100 μm, a width of 2 mm, and a length of 110 mm is used as a spacer and an electrode, so that the effective region has a width of 0.15 mm between two glass substrates 1002 with an alignment film 1003 inside. Two electrode sheets 1004 were arranged in parallel. A cell 1006 in which the thickness of the substrate 1002 was asymmetric was formed by fixing the periphery except for a part with the ultraviolet curing adhesive 1005. The same liquid crystal material as in the first embodiment was sealed in the cell 1006 to form a liquid crystal layer having a thickness of 100 μm, an effective width of 0.15 mm, and a length of about 95 mm. Then, a power supply 1008 composed of a pulse generator and a high-speed amplifier was connected to the electrode sheet 1004 to be each electrode pair, thereby forming an optical path shifting means 1001 as shown in FIG.
[0210]
The optical path shifting means 1001 thus produced exhibited a high transmittance of 85% or more. As in the first embodiment, when a voltage of 400 V was applied between the electrode sheets 1004 to be each electrode pair and the response time was measured by a high-speed camera, the response time was as high as 30 μsec, showing a very high-speed response.
[0211]
【The invention's effect】
The invention according to claim 1 is a light-emitting array in which a plurality of light-emitting units are arranged at a predetermined pixel pitch, a lens that focuses light emitted by the light-emitting units on a recording medium, and light emitted from the light-emitting unit. Optical path shifting means capable of electrically shifting the light emitted in the arrangement direction of the light emitting section, and light emitted from the light emitting section is shifted by driving and controlling the optical path shifting means, whereby the light In an optical writing apparatus in which light irradiation in which pixel pitches are complemented is performed on the recording medium, the optical path shift means is disposed on an optical path from the light emitting element array to the recording medium and is opposed by a spacer. A pair of transparent substrates whose spacing is regulated, a vertical alignment film provided on the inner surface side of the substrate, and a space between the substrates filled with a vertical alignment film interposed therebetween, and the vertical alignment film By applying a voltage to a liquid crystal layer composed of a chiral smectic C phase forming a pick alignment and an electrode pair disposed at a position sandwiching the optical path, a normal direction of the substrate surface and a light emitting portion of the light emitting portion are formed in the liquid crystal layer. Electric field generating means for generating an electric field in a direction substantially orthogonal to the arrangement direction,
(1) High-speed response by spontaneous polarization of liquid crystal is possible,
(2) Since there is no transparent electrode in the optical path, the light use efficiency is high,
(3) The shift amount can be adjusted according to the electric field strength.
(4) there is no change in the optical path length during shifting;
High-speed, high-definition optical writing can be performed while having such an excellent effect.
[0212]
According to a second aspect of the present invention, in the optical writing apparatus according to the first aspect, the optical path shifting means is stacked in a plurality of layers so that the optical path shift direction is parallel, and the electric field generating means sets each of the optical path shifting means. Since the pixel positions are independently driven, the pixel position can be multiplied to, for example, four times.
[0213]
According to a third aspect of the present invention, in the optical writing device according to the first or second aspect, an intermediate layer that divides the liquid crystal layer in a thickness direction is provided, and a vertical alignment film is formed on at least one surface of the intermediate layer. Since the amount of optical path shift increases due to the presence of the intermediate layer, it is possible to set the amount of optical path shift large while setting the thickness of the liquid crystal layer thin, thereby improving the vertical alignment of the liquid crystal layer, A decrease in transmittance due to poor vertical alignment can be prevented.
[0214]
According to a fourth aspect of the present invention, in the optical writing device according to any one of the first to third aspects, since the electrode pair is provided inside the spacer, the electrode pair also serves as the spacer, As a result, the number of components can be reduced, and the thickness of the liquid crystal layer can be reliably made uniform, so that a uniform horizontal electric field can be applied in the liquid crystal layer. Therefore, it is possible to obtain an optical writing device having a relatively simple configuration and high optical path shift position accuracy.
[0215]
According to a fifth aspect of the present invention, in the optical writing apparatus according to any one of the first to fourth aspects, an optical path parallel to a shift direction of the optical path by the optical path shift means is provided on an optical path from the luminous body array to the recording medium. Since a linear polarizer that transmits only the light on the polarization plane is interposed, when light incident on the optical path shifting means is mixed with light on an unnecessary polarization plane, light components that are not optical path shifted are unnecessary on the recording medium. In the present invention, the light is incident on the optical path shift means only by the linearly polarized light parallel to the moving direction of the optical path due to the action of the linear polarizing plate. Therefore, generation of unnecessary light can be prevented, and a high-definition and high-contrast optical writing device can be obtained.
[0216]
According to a sixth aspect of the present invention, in the optical writing device according to any one of the first to fourth aspects, at least two light shifting directions are parallel to each other on an optical path from the luminous body array to the recording medium. Since the optical path shifting means is arranged, and a polarization plane rotating element for rotating the linear polarization plane by approximately 90 degrees is arranged between these optical path shifting means, the shift amounts of both optical path shifting means are set to be the same. If so, all the polarization components can be shifted in the same direction, and therefore, the light use efficiency can be approximately doubled as compared with the case where linear polarization in one direction is used.
[0219]
According to a seventh aspect of the present invention, in the optical writing device according to any one of the first to fourth aspects, the liquid crystal layer is divided into substantially uniform thicknesses in a thickness direction thereof, and a linear polarization plane is rotated by approximately 90 degrees. Since an intermediate layer composed of a rotating element is provided, and a vertical alignment film is formed on at least one surface of the intermediate layer, even when the thickness of the liquid crystal layer portion is increased in order to set a large optical path shift amount, the intermediate layer Can improve the alignment stability near the center of the liquid crystal layer, and can prevent a decrease in transmittance due to poor vertical alignment. Moreover, since the polarization plane rotation element is provided in the intermediate layer in the liquid crystal layer, the number of substrates constituting the optical path shift means can be reduced, and the influence of interface reflection is reduced by the polarization plane rotation element. In addition, the transmittance of the entire device can be improved.
[0218]
According to an eighth aspect of the present invention, in the optical writing device according to any one of the first to seventh aspects, the thickness of the substrate on the light emitting array side of the pair of transparent substrates is greater than the thickness of the substrate on the lens side. Since it is thin, the light path shifting means can be arranged close to the light emitting array, that is, the liquid crystal layer of the light path shifting means can be arranged in a region where the spread of radiated light emitted from the light emitting array is small. The required effective area of the liquid crystal layer can be reduced. Also, if the effective area of the liquid crystal layer is small, the electrode spacing can be set small, so that a high electric field can be applied even at a relatively low voltage, and a high-speed optical path deflection operation is possible by applying such a high electric field. As a result, a high-speed optical writing device can be obtained, and the cost can be reduced because the amount of the liquid crystal material used is reduced.
[0219]
According to a ninth aspect of the present invention, in the optical writing device according to any one of the first to seventh aspects, the thickness of the recording body-side substrate is smaller than the thickness of the lens-side substrate among the pair of transparent substrates. Arranging the optical path shifting means close to the recording medium, that is, the liquid crystal layer of the optical path shifting means can be arranged in an area where the spread of the light immediately before the radiated light converges on the recording medium is small; The effective area of the liquid crystal layer required for the shift can be reduced. Also, if the effective area of the liquid crystal layer is small, the electrode spacing can be set small, so that a high electric field can be applied even at a relatively low voltage, and a high-speed optical path deflection operation is possible by applying such a high electric field. As a result, a high-speed optical writing device can be obtained, and the cost can be reduced because the amount of the liquid crystal material used is reduced.
[0220]
According to a tenth aspect of the present invention, in the optical writing apparatus according to any one of the first to ninth aspects, the numerical aperture (NA) of the lens is A, the refractive index of the substrate of the optical path shifting means is n, and the refractive index of the lens is n. When the maximum distance from the focal position to the liquid crystal layer of the optical path shifting means is T, the distance d between the electrode pairs is expressed by the following relational expression.
2T × A / n ≦ d ≦ 2T × A
So that the relationship among the numerical aperture A representing the light taking-in angle of the lens, the refractive index n of the substrate, the maximum distance T from the focal position to the liquid crystal layer, and the distance d between the electrode pairs is within a certain range. As a result, the distance between the electrodes can be set narrower within the range in which the optical path spread range is not obstructed by the electrode spacing of the optical path shift means, making it possible to achieve optimal settings that balance light use efficiency and electric field application efficiency. Therefore, a relatively high electric field can be applied even at the same applied voltage without lowering the light use efficiency of the optical system, and a high-speed optical writing operation can be performed.
[0221]
According to an eleventh aspect of the present invention, in the optical writing device according to any one of the first to tenth aspects, a microlens array having microlenses corresponding to individual light emitters is provided near the light emitter of the light emitter array. Therefore, even if the optical path is shifted in a state where the recording spot size is large, the exposed pixels overlap, but the emitted light from each illuminant is once condensed by the microlens array, and the condensing point is recorded on the recording medium. By projecting upward, the recording spot size can be reduced, and the recording density can be effectively increased by an optical path shift.
[0222]
According to a twelfth aspect of the present invention, in the optical writing apparatus according to the eleventh aspect, the microlens array includes at least a liquid crystal layer and an electrode capable of applying an electric field to the liquid crystal layer, and the microlens array has a specific function according to the electric field intensity. By changing the focal length of the microlens with respect to the light in the polarization direction, the liquid crystal layer capable of applying an electric field is provided in the microlens array for collecting the radiated light from the illuminant array. It is possible to control the presence / absence of the function, and therefore, when performing high-density writing by an optical path shift operation, the pixel size is set small by generating the condensing function of the microlens array to reduce the luminous spot. On the other hand, when the optical path shift operation is not required, the light-spot The By increasing, it is possible to set the pixel size corresponding to the low density writing, it is possible to switch the writing density.
[0223]
According to a thirteenth aspect of the present invention, in the optical writing device according to the twelfth aspect, the two liquid crystal microlens arrays are arranged in series in an optical axis direction, and each liquid crystal microlens array is provided when an electric field is applied or when no electric field is applied. Since the alignment direction or electric field application direction was set so that the alignment directions of the liquid crystal molecules are orthogonal to each other, the liquid crystal alignment directions of the two liquid crystal microlens arrays having a variable focus function were arranged orthogonally. One liquid crystal microlens array functions as a variable lens for incident light components in a specific polarization direction, and the other liquid crystal microlens array functions as a variable lens for incident light components in orthogonal polarization directions. As a result, a variable focus function can be realized for unpolarized incident light, and it is combined with an optical path shift means corresponding to non-polarized light. By combining, in a high light utilization efficiency, it is possible to switch the writing density.
[0224]
According to a fourteenth aspect of the present invention, in the optical writing device according to any one of the first to tenth aspects, the lens that focuses the light emitted by the light emitting unit on the recording medium includes at least a liquid crystal layer and a liquid crystal. An electrode capable of applying an electric field to the layer, and by changing the focal length of the lens with respect to light in a specific polarization direction in accordance with the electric field intensity, radiated light from the light emitting array is condensed on a recording medium By having a liquid crystal layer to which an electric field can be applied in a lens to be controlled, the focal length of the lens can be controlled. Therefore, when performing high-density writing by an optical path shift operation, the focal length of the lens is controlled to control the recording medium. The pixel size can be set small by reducing the size of the focused light spot above, but if the optical path shift operation is not required, the focal length of the lens is controlled to By increasing the light spot size, it is possible to set the pixel size corresponding to the low density writing, it is possible to switch the writing density.
[0225]
According to a fifteenth aspect of the present invention, in the optical writing device according to the fourteenth aspect, the lens that focuses the light emitted by the light emitting unit on the recording medium includes at least two liquid crystal layers and an electric field applied to each liquid crystal layer. An electrode capable of applying an electric field, and by setting the alignment direction or the electric field application direction such that the liquid crystal molecules of each liquid crystal layer are perpendicular to each other when an electric field is applied or when no electric field is applied, the two electrodes in the lens are set. By arranging the liquid crystal orientation directions of the two liquid crystal layers at right angles, one liquid crystal layer functions as a varifocal lens for the incident light component of a specific polarization direction, and In addition, the other liquid crystal layer can function as a varifocal lens, so that a varifocal function can be realized for non-polarized incident light, and it is combined with an optical path shift means corresponding to non-polarized light. By combining, in a high light utilization efficiency, it is possible to switch the writing density.
[0226]
According to a sixteenth aspect of the present invention, in the optical writing device according to any one of the first to fifteenth aspects, since the light-emitting body array is an LED array, the size of the light source unit can be reduced.
[0227]
According to a seventeenth aspect of the present invention, in the optical writing device according to any one of the first to fifteenth aspects, since the light-emitting body array is a laser diode array, high efficiency and small size of the light source unit are realized. Can be.
[0228]
The invention of an image forming apparatus according to claim 18, wherein the photosensitive member on which the electrophotographic process is performed as the recording member, a charging device for uniformly charging the photosensitive member, and the photosensitive member uniformly charged by light irradiation 18. The optical writing device according to claim 1, which forms an electrostatic latent image on a body, a developing device for developing the electrostatic latent image, and transferring a developed image on the photoconductor to a transfer paper. And a transfer device, which has the effect of the optical writing device according to any one of claims 1 to 17, and can form an image with high contrast even when writing with a relatively low light intensity.
[0229]
According to a nineteenth aspect of the present invention, there is provided an image forming apparatus using the optical writing device according to any one of the first to seventeenth aspects, wherein the recording medium is made of a material on which an image is formed by applying external energy. Since the image is formed directly, the effect of the optical writing device according to any one of claims 1 to 17 is obtained, and the size of the image forming device can be reduced because the image is formed directly on the recording medium.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional side view of an optical writing device showing a first embodiment of the optical writing device of the present invention.
FIG. 2 is a longitudinal sectional front view thereof.
FIG. 3 is a schematic diagram showing a direction of an electric field generated in a liquid crystal layer of the optical path shifting means and a tilt direction of liquid crystal molecules.
FIG. 4 is a schematic diagram showing a direction of an electric field generated in a liquid crystal layer of the optical path shifting means and a tilt direction of liquid crystal molecules when the direction of the electric field is reversed.
FIG. 5 is a schematic view showing an alignment state of liquid crystal molecules in a liquid crystal layer.
FIG. 6 is a schematic diagram showing an alignment state of liquid crystal molecules in a liquid crystal layer when the direction of an electric field is reversed from that shown in FIG.
FIG. 7 is a schematic view illustrating the relationship between the pitch of the luminous body, the amount of optical path shift by the optical path shifting means, the pixel pitch, and the resolution.
8A and 8B show a second embodiment of the optical writing apparatus according to the present invention, wherein FIG. 8A is a vertical sectional side view of the optical writing apparatus, and FIG. 8B is a vertical sectional front view thereof.
FIG. 9 is a longitudinal sectional front view of an optical writing device showing a third embodiment of the optical writing device of the present invention.
FIG. 10 is a vertical sectional front view showing one mode of an optical writing device as a fourth embodiment of the optical writing device of the present invention.
FIG. 11 is a vertical sectional front view showing another aspect of the optical writing device as a fourth embodiment of the optical writing device of the present invention.
FIG. 12 is a vertical side view of the optical writing device for describing a phenomenon occurring in the optical writing device according to the first embodiment.
FIG. 13 is a longitudinal sectional side view showing one mode of an optical writing device as a fifth embodiment of the optical writing device of the present invention.
FIG. 14 is a vertical sectional side view showing another aspect of the optical writing apparatus as a fifth embodiment of the optical writing apparatus of the present invention.
FIG. 15 is a longitudinal sectional side view of an optical writing device showing a sixth embodiment of the optical writing device of the present invention.
FIG. 16 is a schematic diagram for explaining the operation.
FIG. 17 is a longitudinal sectional side view of an optical writing device showing a seventh embodiment of the optical writing device of the present invention.
FIG. 18 is a longitudinal sectional front view of an optical writing device showing an example of arrangement of optical path shifting means.
FIG. 19 is a vertical sectional front view of an example of arrangement of optical path shift means showing an eighth embodiment of the optical writing apparatus of the present invention.
FIG. 20 is a vertical sectional front view of an arrangement example of optical path shift means showing a ninth embodiment of the optical writing device of the present invention.
FIG. 21 is an explanatory diagram showing a relationship between a light taking-in angle of a lens, a distance from a focal position, and a diameter of an optical path, showing a tenth embodiment of the optical writing apparatus of the present invention.
FIG. 22 is a longitudinal sectional front view of the optical writing device showing an eleventh embodiment of the optical writing device of the present invention.
FIG. 23 is a sectional view showing a microlens of a microlens array showing a twelfth embodiment of the optical writing device of the present invention.
FIG. 24 is a sectional view showing a microlens of a microlens array showing a thirteenth embodiment of the optical writing device of the present invention.
FIG. 25 is a longitudinal sectional side view of a light emitting array showing a sixteenth embodiment of the optical writing device of the present invention.
FIG. 26 is a schematic diagram illustrating a first embodiment of the image forming apparatus of the present invention.
FIGS. 27A and 27B are examples of the optical path shifting means of the first embodiment created by the inventor of the present invention for an experiment, wherein FIG. 27A is a plan view and FIG. 27B is a side view.
FIG. 28 is a graph showing a relationship between an applied electric field and an optical path shift amount.
FIG. 29 is a graph showing a relationship between an applied electric field and a response time.
FIGS. 30A and 30B show an example of an optical path shifting means according to a second embodiment prepared by the inventor of the present invention for an experiment, wherein FIG. 30A is a plan view and FIG.
FIG. 31 is a longitudinal sectional side view showing an example of a conventional optical writing device using a liquid crystal layer.
[Explanation of symbols]
101 Light emitting unit
102 Light-emitting body array
113 Light emitting unit
201 Recorded body
301 Optical path shift means
302 spacer
303 substrate
304 vertical alignment film
305 liquid crystal layer
306 Electric field generating means
307 electrode pairs
309 Middle class
401 linear polarizing plate
501 Polarization plane rotation element
510 lens
520 micro lens array
521 micro lens
522 liquid crystal layer
601 photoconductor
602 charging device
603 Optical writing device
604 developing device
605 Transfer device

Claims (19)

A light emitting array in which a plurality of light emitting units are arranged at a predetermined pixel pitch, a lens for focusing light emitted by the light emitting unit on a recording medium, and light emitted from the light emitting unit to the light emitting unit An optical path shifter electrically shiftable in the arrangement direction, wherein the light emitted from the light emitting unit is shifted by controlling the driving of the optical path shifter, whereby the light between the pixel pitches is complemented. In an optical writing device configured to perform irradiation on the recording medium,
The optical path shifting means,
A pair of transparent substrates that are arranged on an optical path from the light emitting body array toward the recording medium and whose facing distance is regulated by a spacer;
A vertical alignment film provided on the inner surface side of the substrate,
A liquid crystal layer composed of a chiral smectic C phase filled with a vertical alignment film between the substrates and forming a homeotropic alignment by the vertical alignment film,
Electric field generation that generates an electric field in the liquid crystal layer in a direction substantially normal to the substrate surface normal direction and the arrangement direction of the light emitting portions by applying a voltage to an electrode pair disposed at a position sandwiching the optical path. Means,
An optical writing device comprising: 2. The optical writing apparatus according to claim 1, wherein the optical path shifting means is stacked in a plurality of layers so that the optical path shifting directions are parallel, and the electric field generating means drives each of the optical path shifting means independently. . 3. The optical writing device according to claim 1, wherein an intermediate layer is provided to divide the liquid crystal layer in the thickness direction, and a vertical alignment film is formed on at least one surface of the intermediate layer. The optical writing device according to claim 1, wherein the electrode pair is provided inside the spacer. 4. A linear polarizing plate which transmits only light having a polarization plane parallel to a light path shifting direction by said light path shifting means on an optical path from said luminous body array to said recording medium. 5. The optical writing device according to any one of 4. At least two light path shift means are arranged so that light shift directions are parallel on a light path from the light emitter array to the recording medium, and a linear polarization plane is rotated by approximately 90 degrees between these light path shift means. 5. The optical writing device according to claim 1, further comprising a polarization plane rotating element for causing the rotation. The liquid crystal layer is divided into substantially uniform thicknesses in the thickness direction, and an intermediate layer including a polarization plane rotating element that rotates the linear polarization plane by about 90 degrees is provided. At least one surface of the intermediate layer has a vertical alignment film formed thereon. 4. The optical writing device according to claim 1, wherein: The optical writing device according to claim 1, wherein a thickness of the substrate on the light emitting array side is smaller than a thickness of the substrate on the lens side among the pair of transparent substrates. 8. The optical writing device according to claim 1, wherein a thickness of a substrate on a recording medium side of the pair of transparent substrates is smaller than a thickness of a substrate on a lens side. When the numerical aperture (NA) of the lens is A, the refractive index of the substrate of the optical path shifting means is n, and the maximum distance from the focal position of the lens to the liquid crystal layer of the optical path shifting means is T, The distance d between the electrode pairs is represented by the following relational expression: 2T × A / n ≦ d ≦ 2T × A
10. The optical writing device according to claim 1, wherein the optical writing device satisfies the following. The optical writing device according to any one of claims 1 to 10, wherein a microlens array having microlenses corresponding to individual light emitting units is provided near a light emitting unit of the light emitting body array. The microlens array includes a liquid crystal microlens array having at least a liquid crystal layer and an electrode capable of applying an electric field to the liquid crystal layer, and has a focal length of the microlens with respect to light having a specific polarization direction according to the electric field intensity. 12. The optical writing device according to claim 11, wherein: The two liquid crystal microlens arrays are arranged in series in the optical axis direction, and the alignment processing direction or the electric field direction is set such that the liquid crystal molecules in each liquid crystal microlens array are perpendicular to each other when an electric field is applied or when no electric field is applied. 13. The optical writing device according to claim 12, wherein an application direction is set. The lens that focuses the light emitted by the light emitting unit on the recording medium has at least a liquid crystal layer and an electrode that can apply an electric field to the liquid crystal layer, and has a specific polarization direction according to the electric field intensity. The optical writing apparatus according to claim 1, wherein a focal length of the lens with respect to the distance is changed. The lens that focuses the light emitted by the light emitting unit on the recording medium has at least two liquid crystal layers and electrodes capable of applying an electric field to each liquid crystal layer. 15. The optical writing device according to claim 14, wherein the alignment direction or the electric field application direction is set so that the alignment directions of the liquid crystal molecules of the liquid crystal layer are orthogonal to each other. The optical writing device according to any one of claims 1 to 15, wherein the illuminant array is an LED array. 16. The optical writing device according to claim 1, wherein the light emitting array is a laser diode array. A photoconductor on which an electrophotographic process is performed as the recording medium,
A charging device for uniformly charging the photoconductor,
The optical writing device according to any one of claims 1 to 17, wherein an electrostatic latent image is formed on the photosensitive member uniformly charged by light irradiation.
A developing device for developing the electrostatic latent image;
A transfer device for transferring the developed image on the photoconductor to transfer paper,
An image forming apparatus comprising: An image forming apparatus using the optical writing device according to any one of claims 1 to 17, wherein an image is formed directly on the recording body made of a material on which an image is formed by applying external energy.

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