JP4054078B2 - Acousto-optic device, light beam scanning apparatus, and acousto-optic device attitude adjustment method - Google Patents

Description

【００３４】
また、入射光進行方向の軸回りの回転角θ_Z を、図４から得られる回折効率がピークとなる角度、例えばθ_Z ＝７０°に固定し、あおり角θ_A を変化させた場合の回折効率特性を図７に示す。
【００３５】
図７から理解されるように、入射光進行方向の軸回りの回転角θ_Z を固定し、あおり角θ_A のみを変化させる場合にも、あおり角θ_A を例えばθ_A ≒１．５°以上に調節することで、回折効率を従来より向上させることができ、回折効率はθ_A ≒９°で略９５％、θ_A ≒４．５°以上で略８０〜９５％、θ_A ≒３°以上で略７０〜９５％、になる。
【００３６】
従って、入射光進行方向の軸回りの回転角θ_Z 及びあおり角θ_A を調整する場合において、最大の回折効率が得られる状態から、入射光進行方向の軸回りの回転角θ_Z を固定してあおり角θ_A を変化させた場合には、あおり角θ_A を略１．５°以上にすると回折効率を従来より向上することができ、あおり角θ_A が略３°以上で略７０〜９５％の回折効率が得られ、あおり角θ_A が略４．５°以上で略８０〜９５％の回折効率が得られることになる。
【００３７】
上記は、中心周波数における結果であるが、所定の周波数帯域においても従来より回折効率は向上する。図８に、表１の回折効率がピークになる条件の１つである、θ_Z ＝７０°、かつθ_A ＝９°における回折効率の周波数特性、入射光進行方向の軸回りの回転角θ_Z を９０°（θ_A ＝９°）にしたときの回折効率の周波数特性、及び従来の回折効率の周波数特性（θ_Z ＝θ_A ＝±０°）を示す。本実施の形態では、所定の周波数帯域において回折効率が従来より向上している。
【００３８】
以上より、異方ブラッグ回折が利用できるように配置すると共に、異方性結晶の光学軸が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならないように配置することで、回折効率を向上することができる。
【００３９】
すなわち、異方ブラッグ回折が利用できるように配置すると共に、異方性結晶の光学軸が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならず、かつ入射光の偏光面が入射光の進行方向と超音波の進行方向とを含む面に対して平行となるようにするか、異方性結晶の光学軸が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならず、かつ入射光の偏光面が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならないようにすることで回折効率を向上することができる。
【００４０】
なお、上記では、音響光学媒体としてＴｅＯ₂ の単結晶を用いた例について説明したが、本発明はＰｂＭｏＯ₄ その他の一軸結晶や二軸結晶を使用することもできる。また、上記では、ＡＯＤについて説明したが、本発明はＡＯＭにも適用できる。
【００４１】
次に、上記ＡＯＤを光ビーム走査装置に利用した円筒内面走査型画像記録装置の実施の形態を図面を参照して説明する。この円筒内面走査型画像記録装置は、所定方向に並列させた複数本のレーザビームを発生するレーザビーム発生手段と、各レーザビームの光路中に配置され、かつレーザビームをレーザビームの並列方向と直交する方向に偏向する複数の偏向器と、円筒の中心軸に対して傾斜した反射面を備え、かつ円筒の中心軸を中心に回転されることによりレーザビームを円筒の内面に沿って走査する走査手段と、偏向器で偏向された複数のレーザビームを走査手段の反射面に入射させる光学系と、を含んで構成されている。
【００４２】
図９に示すように、本実施の形態の画像記録装置は、レーザビームＬを発生するレーザビーム発生器１４と、レーザビーム発生器１４から発生されたレーザビームを所定方向に並列させた３本のレーザビームＬ₁ ，Ｌ₂ ，Ｌ₃ に分割するレーザビームスプリッタ１６とを備えている。レーザビームＬ₁ の射出側には、レーザビームＬ₁ をレーザビームの並列方向と直交する方向、すなわち図９のｙ軸方向（記録シートＳ上ではレーザビームの並列方向と直交する方向）に偏向すると共に、画像情報に応じてレーザビームを強度変調（オンオフ変調）するＡＯＤ１８ｘが配置され、レーザビームＬ₂ の射出側には、レーザビームＬ₂ を偏向することなく画像情報に応じてレーザビームをオンオフ変調するＡＯＤ２０が配置され、レーザビームＬ₃ の射出側には、レーザビームＬ₃ をＡＯＤ１８ｘと同様にｙ軸方向に偏向すると共に、画像情報に応じてレーザビームをオンオフ変調するＡＯＤ２２ｘが配置されている。
【００４３】
ＡＯＤ１８ｘ、２０、２２ｘは、上記で説明したように、異方性結晶の光学軸が、入射光の進行方向と超音波の進行方向とを含む面に対して平行にならないように配置されている。なお、本実施の形態ではθ_B ≒４°、θ_Z ≒７０°、θ_A ≒９°に調整するのが好ましいが、θ_Z ≒０°としてθ_B とθ_A とを調整するようにしてもよい。
【００４４】
ＡＯＤ１８ｘ、２０、２２ｘのレーザビーム射出側には、各々レーザビームをｘ軸の負の方向に反射するミラー２４、２６、２８が配置され、ミラーのレーザビーム反射側には、これらのミラーから反射されたレーザビームを集光する集光レンズ３０、軸に対して４５°傾斜した反射面を備えかつモータ３４により軸を中心として回転される円柱状の回転鏡３２が配置されている。なお、記録シートＳは、展開して図示した円筒状のドラム３６の内周面に保持されており、回転鏡３２は軸がドラム３６の中心軸と一致するように配置されている。
【００４５】
上記の画像記録装置では、レーザビームによって記録されるドットが記録シートＳ上でｘ軸方向に配列された状態（図９の状態）から回転鏡３２を９０°回転させると、図１３（１）に示されるように回転鏡３２の回転に伴ってドット配列が９０°回転されことになる。すなわち、ドット配列が回転鏡３２の回転に伴って回転され、回転鏡３２の反射面の中心に入射されないレーザビームＬ₁ ，Ｌ₃ によって記録されるドットが単振動し、レーザビームＬ₁ ，Ｌ₃ によって記録されるドットの軌跡Ｒ₁ ，Ｒ₃ が正弦波状になる。この場合、レーザビームＬ₁ によって記録されるドットの軌跡は、レーザビームＬ₃ によって記録されるドットの軌跡に対して位相が１８０°ずれている。なお、レーザビームＬ₂ は、回転鏡３２の反射面の中心に入射されるため、レーザビームＬ₂ によって記録されるドットは単振動することはなく、レーザビームＬ₂ によって記録されるドットの軌跡Ｒ₂ は直線になる。本実施の形態では、このドット配列の回転を補正して各走査線を平行にするために、図１０に示す制御装置が設けられている。
【００４６】
図１０に示すように、制御装置３８は、各ＡＯＤのトランスデューサに接続されている。制御装置３８は、モータ３４に取り付けられた図示しないロータリエンコーダからのモータの回転に同期した回転位置信号Ｐ、及び主走査開始位置で出力される主走査開始信号ＬＳＹＮＣに基づいて基本クロック信号及び制御クロック信号を生成する制御回路４０と、基本クロック信号に従って余弦波電圧信号（ｘ＝−ａ・ｃｏｓωｔ，ただし、ａは定数、ωは基本クロック信号によって定まるモータの角速度、ｔは経過時間である）を生成する余弦波電圧信号生成回路４２ａと、基本クロック信号に従って上記とは位相が１８０°ずれた余弦波電圧信号（ｘ＝ａ・ｃｏｓωｔ）を生成する余弦波電圧信号生成回路４２ｃと、定電圧信号を生成する定電圧信号生成回路４２ｂとを備えている。
【００４７】
電圧信号生成回路４２ａ，４２ｂ，４２ｃは、電圧信号から周波数変調信号を生成する電圧制御発振器（ＶＣＯ）４４ａ，４４ｂ，４４ｃに接続されている。
【００４８】
また、制御回路４０には、２値画像信号を生成する２値画像信号生成回路４８が接続されており、ＶＣＯ４４ａ，４４ｂ，４４ｃから出力された周波数変調信号は、変調器４６ａ，４６ｂ，４６ｃにより、２値画像信号生成回路４８からの２値画像信号によってオンオフ変調され、増幅回路５０ａ，５０ｂ，５０ｃによって増幅された後、各ＡＯＤのトランスデューサに入力される。
【００４９】
上記のように、余弦波電圧信号（ｘ＝−ａ・ｃｏｓωｔ，ａ・ｃｏｓωｔ）によって変調された電圧信号をＡＯＤ１８ｘ，２２ｘのトランスデューサに印加することにより、ＡＯＤ１８ｘ、２２ｘを通過するレーザビームが図９の状態（図１３（１）の０°の位置）からｙ軸方向に偏向される。このとき、記録シートＳ上では、ＡＯＤ１８ｘを通過したレーザビームによるドットはドットの配列方向と直交する方向に移動することによってｘ軸の正方向に移動し、ＡＯＤ２２ｘを通過したレーザビームはによるドットはドットの配列方向と直交する方向でかつＡＯＤ１８ｘを通過したレーザビームによるドットと逆方向に移動することによってｘ軸の負方向に移動し、この偏向によって正弦波状の単振動を相殺し走査線を図１３（２）に示すように平行な直線にすることができる。
【００５０】
しかしながら、各レーザビームによる軌跡の長さが異なるため、本実施の形態のように、−９０°〜＋９０°の範囲で走査する場合には、図１３（２）に示すように、１ラインの走査開始端側でレーザビームＬ₃ によって記録されるドットの軌跡Ｒ₃ は、レーザビームＬ₁ ，Ｌ₂ によって記録されるドットの軌跡Ｒ₁ ，Ｒ₂ に対して各々Ｔｄ１，Ｔｄ２ずれており、１ラインの走査終了端側では各々Ｔｄ３，Ｔｄ２ずれている。従って、軌跡は、レーザビームＬ₁ によって記録されるドットの軌跡Ｒ₁ 、レーザビームＬ₂ によって記録されるドットの軌跡Ｒ₂ 、レーザビームＬ₃ によって記録されるドットの軌跡Ｒ₃ の順に短くなるので、走査長が異なることになる。本実施の形態では、この走査長の相違を補正するために、制御回路４０内に図１１に示す制御クロック信号生成回路５２が設けられている。
【００５１】
制御クロック信号生成回路５２は、上記の回転位置信号Ｐから位相同期信号を生成するＰＬＬ回路５４、上記の主走査開始信号ＬＳＹＮＣ及びＰＬＬ回路５４出力に従って基本クロック信号Ｂを生成する基本クロック信号生成回路５６、基本クロック信号をカウントするカウンタ５８、カウンタ５８からのカウント値に従って遅延量を設定するための遅延量設定信号を出力するルックアップテーブル６０、遅延量設定信号に従って基本クロック信号生成回路５６からの基本クロック信号を遅延させて制御クロック信号ＣＬ１，ＣＬ２，ＣＬ３として出力する遅延回路６２ａ，６２ｂ，６２ｃから構成されている。この制御クロック信号ＣＬ１，ＣＬ２，ＣＬ３は、上記の２値画像信号生成回路４８に供給される。
【００５２】
なお、図１３（２）に示すずれ量を補正して、レーザビームによって記録されるドットを記録シート上でｘ軸方向に配列させるための遅延量は、主走査位置によって異なる。このため、ルックアップテーブル６０の遅延量は、レーザビーム毎に、主走査方向の走査位置に応じて、すなわち基本クロック信号の各パルス毎に予め定められている。
【００５３】
次に、上記実施の形態の画像記録装置の動作について説明する。モータ３４に設けられている図示しないエンコーダからの回転位置信号Ｐは、ＰＬＬ回路５４に入力されて位相制御され、位相同期信号が生成される。位相同期信号は基本クロック信号生成回路５６に入力され、主走査開始信号ＬＳＹＮＣの発生タイミングで図１２に示す基本クロック信号Ｂが出力される。基本クロック信号はカウンタ５８によってカウントされると共に、遅延回路６２ａ，６２ｂ，６２ｃに入力される。
【００５４】
カウンタ５８によってカウントされた基本クロック信号のカウント値は、ルックアップテーブル６０に供給される。ルックアップテーブル６０は、カウント値に応じて、すなわち、記録シートの主走査方向における記録位置に応じて各レーザビームＬ₁ ，Ｌ₂ ，Ｌ₃ 毎に予め定められている遅延量に基づいて遅延量設定信号を遅延回路６２ａ，６２ｂ，６２ｃの各々に入力する。遅延回路６２ａ，６２ｂ，６２ｃは、入力された遅延量設定信号に応じて基本クロック信号を遅延させて制御クロック信号ＣＬ１，ＣＬ２，ＣＬ３として出力する。
【００５５】
制御クロック信号ＣＬ１は、レーザビームＬ₁ により記録される２値画像信号の出力タイミングを制御する信号であり、遅延回路６２ａは、遅延量設定信号に基づき、図１２に示すように、レーザビームＬ₁ により記録される２値画像信号による画像の記録開始時期を基本クロック信号の発生タイミング、すなわち主走査開始信号ＬＳＹＮＣの発生タイミングよりＴｄ１だけ遅延させ、かつ記録終了時期を基本クロック信号の主走査終了タイミング（ｍ番目のクロック）に一致させた制御クロック信号ＣＬ１を出力する。
【００５６】
制御クロック信号ＣＬ２は、レーザビームＬ₂ により記録される２値画像信号の出力タイミングを制御する信号であり、遅延回路６２ｂは、遅延量設定信号に基づき、図１２に示すように、レーザビームＬ₂ により記録される２値画像信号による画像の記録開始時期を主走査開始信号ＬＳＹＮＣの発生タイミングよりＴｄ２だけ遅延させ、かつ記録終了時期を基本クロック信号の主走査終了タイミングよりもＴｄ２だけ遅延させた制御クロック信号ＣＬ２を出力する。
【００５７】
制御クロック信号ＣＬ３は、レーザビームＬ₃ により記録される２値画像信号の出力タイミングを制御する信号であり、遅延回路６２ｃは、遅延量設定信号に基づき、図１２に示すように、レーザビームＬ₃ により記録される２値画像信号による画像の記録開始時期を主走査開始信号ＬＳＹＮＣの発生タイミングと同じになり、かつ記録終了時期を基本クロック信号の主走査終了タイミングよりもＴｄ３だけ遅延させた制御クロック信号ＣＬ３を出力する。
【００５８】
なお、ルックアップテーブルの遅延量は、各制御クロック信号のパルス間隔ができるだけ等間隔になるように各主走査位置に応じて設定されている。また、隣合う走査線間の遅延位置が重なると、網点の周期との間にビートが発生して画像のムラになる虞れがあるので、ルックアップテーブルの遅延量は各走査線間でランダムとなるように設定するのが好ましい。
【００５９】
上記のように出力された制御クロック信号ＣＬ１，ＣＬ２，ＣＬ３は、２値画像信号生成回路４８に供給され、２値画像信号生成回路４８は図１２に示すタイミングで２値画像信号を各変調器４６ａ，４６ｂ，４６ｃに出力する。
【００６０】
一方、電圧信号生成回路４２ａ，４２ｃは、入力された基本クロック信号に基づいて余弦波電圧信号（ｘ＝−ａ・ｃｏｓωｔ，ａ・ｃｏｓωｔ）を生成し、ＶＣＯ４４ａ，４４ｃを介して周波数変調信号を変調器４６ａ，４６ｃに入力し、定電圧信号生成回路４２ｂは、ＶＣＯ４４を介して周波数変調信号を変調器４６ｂに入力する。これにより、電圧信号生成回路４８ａ，４８ｂ，４８ｃから出力された周波数変調信号は、変調器４６ａ，４６ｂ，４６ｃにおいて、２値画像信号生成回路４８からの２値画像信号によってオンオフ変調され、増幅回路５０ａ，５０ｂ，５０ｃで増幅された後、各ＡＯＤのトランスデューサに入力される。
【００６１】
レーザビーム発生器１４から発生され、ビームスプリッタ１６によって分割されたレーザビームＬ₁ ，Ｌ₃ は、ＡＯＤ１８ｘ，２２ｘによってｙ軸方向に偏向されると共に、２値画像信号に応じてオンオフ変調され、ミラー２４，２８で反射され、集光レンズ２２を介して回転鏡３２に入射される。また、レーザビームＬ₂ は、ＡＯＤ２０によって偏向されることなく、２値画像信号に応じてオンオフ変調され、ミラー２６で反射され、集光レンズ２２を介して回転鏡３２に入射される。
【００６２】
回転鏡３２は、ｘ軸を中心に回転しているため、反射によってレーザビームを記録シート上に走査させる。この場合、２値画像信号でオンオフ変調されたレーザビームＬ₁ ，Ｌ₂ は、レーザビームＬ₃ と同一の記録範囲内（図１３（３））において画像を記録シートに記録することになる。従って、主走査方向の記録範囲が同一で、かつ歪みのない高精度の画像を記録することができる。
【００６３】
以上説明したように本実施の形態によれば、異方性結晶の光学軸が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならないようにＡＯＤを配置したので、回折効率を向上した低コストの円筒内面走査型画像記録装置を提供することできる。
【００６４】
なお、上記では本発明を円筒内面走査型画像記録装置に適用した実施の形態について説明したが、本発明は、記録シートを副走査方向に搬送しながらレーザビームを主走査方向に走査して記録を行う平面走査型画像記録装置や、ドラムの外周面に記録シートを支持し、ドラムを回転させながらレーザビームを主走査方向に走査して記録を行う円筒外面走査型画像記録装置の光ビーム走査装置にも適用することができる。また、本発明は、レーザビームを走査して読取を行う各種読取装置にも適用することができる。
【００６５】
【発明の効果】
以上説明したように、本発明の音響光学機器及び音響光学素子の姿勢調整方法によれば、異方性結晶の光学軸が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならず、かつ入射光の偏光面が入射光の進行方向と超音波の進行方向とを含む面に対して平行にならないように音響光学素子を配置したので、異方性結晶を大きくすることなく直線偏光を用いて回折効率を更に向上した低コストの音響光学機器を提供することができる、という効果が得られる。
【００６６】
また、本発明の光ビーム走査装置は、上記のように音響光学素子が配置された音響光学機器を利用しているので、回折効率を更に向上した低コストの光ビーム走査装置を提供することができる、という効果が得られる。
【図面の簡単な説明】
【図１】本発明の実施の形態のＡＯＤの概略図である。
【図２】本発明の実施の形態においてＡＯＤを回転させる軸を説明するためのＡＯＤの斜視図である。
【図３】本発明の実施の形態のあおり角θ_A のみの変化に対する回折効率の変化を示す線図である。
【図４】本発明の実施の形態の入射光進行方向の軸回りの回転角θ_Z の変化に対する回折効率の変化（回折効率の周波数特性の形状がフラットの場合）を示す線図である。
【図５】図４の回折効率を得るための入射光進行方向の軸回りの回転角θ_Z とあおり角θ_A との関係を示す線図である。
【図６】入射光進行方向の軸回りの回転角θ_Z の変化に対する回折効率の変化（回折効率の周波数特性の形状がピーク状の場合）を示す線図である。
【図７】入射光進行方向の軸回りの回転角θ_Z が７０°のときのあおり角θ_A の変化に対する回折効率の変化を示す線図である。
【図８】本発明の実施の形態のある周波数帯域における回折効率を示す線図である。
【図９】本発明の実施の形態の画像記録装置の概略図である。
【図１０】本発明の実施の形態の画像記録装置の制御装置のブロック図である。
【図１１】本発明の実施の形態の画像記録装置の制御回路のブロック図である。
【図１２】本発明の実施の形態の画像記録装置の制御クロック信号のタイミングを示す線図である。
【図１３】（１）は回転鏡による像の回転を補正しない場合の走査線を示し、（２）は回転鏡による像の回転を補正した場合の走査線を示し、（３）は走査長の相違を補正した場合の走査線を示す線図である。
【符号の説明】
１０ ＴｅＯ₂ の単結晶
１２ トランスデューサ[0001]
BACKGROUND OF THE INVENTION
  This inventionAcousto-optic device, light beam scanning apparatus, and acousto-optic device attitude adjustment methodIn particular, an acoustooptic device such as an acoustooptic modulator (AOM) or an acoustooptic deflector (AOD) that utilizes an acoustooptic effect.Acousto-optic equipment including,thisAcousto-optic equipmentUsed for image recording and image readingAnd attitude adjustment method of acoustooptic deviceAbout.
[0002]
[Prior art]
A conventional AOD that is a kind of acoustooptic device using anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in an anisotropic crystal is tellurium dioxide as an acoustooptic medium. (TeO₂) TeO₂TeO is generated by transverse wave ultrasonic waves traveling in the [110] direction of the crystal and displaced in the [1′10] (where 1 ′ means −1 direction) direction.₂The light wave incident on the crystal is diffracted (on [110] type deflector). This TeO₂AOD using crystals can provide a large acoustooptic figure of merit and high diffraction efficiency compared to AOD using lithium niobate or quartz as the acoustooptic medium.
[0003]
However, flat diffraction efficiency cannot be obtained over a wide frequency band, and the efficiency drops near the center frequency, so that there is a problem that the used frequency band is limited. In addition, circularly polarized light is necessary to obtain high diffraction efficiency, and it is necessary to insert a λ / 4 plate into the optical path of linearly polarized laser light to convert it into circularly polarized light, which is expensive. was there.
[0004]
As an AOD that solves the above problems, an off- [110] type deflector in which the traveling direction of ultrasonic waves is greatly inclined from the [110] direction of the crystal is known (Japanese Patent Laid-Open No. 51-99039). According to this off [110] type deflector, the drop in efficiency near the center frequency, which was a problem of the above on [110] type deflector, is eliminated, and the incident laser light may be linearly polarized light, A λ / 4 plate becomes unnecessary.
[0005]
Conventionally, the diffraction efficiency is increased by adjusting only the Bragg angle so that the Bragg condition is satisfied in a plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and is orthogonal to the traveling direction of the incident light. Although the adjustment for translating the AOD in the direction in which the AOD is performed is made, the adjustment for rotating the other AOD is not made.
[0006]
[Problems to be solved by the invention]
However, the conventional off [110] deflector has a problem in that it requires a large crystal to increase the cost because the traveling direction of the ultrasonic wave needs to be greatly inclined from the [110] direction.
[0007]
  The present invention has been made to solve the above-mentioned problems, and is a low-cost acousto-optic device that uses linearly polarized light and can obtain high diffraction efficiency over a wide frequency band.machine,This acousto-opticmachineLight beam scanning device usingAnd attitude adjustment method of acoustooptic deviceThe purpose is to provide.
[0008]
[Means for Solving the Problems]
  To achieve the above objective,An acousto-optic device according to claim 1 is:An acoustooptic device using anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in the anisotropic crystal;An acoustooptic device comprising a light source that causes linearly polarized light to be incident on the acoustooptic device, and performing acoustooptic deflection or modulation, by adjusting the posture of the acoustooptic device,The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. To satisfy the condition of not parallel to the plane containingThe acoustooptic device is arranged.
[0009]
  The present inventionWhen anisotropic Bragg diffraction is availableboth,The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. Not parallel to the plane containingThe conditionsAn acousto-optic element is arranged so as to satisfy.
[0010]
The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. The optical axis of the anisotropic crystal is inclined at a predetermined angle with respect to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave.
[0011]
  On the other hand, as in the present invention,The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. The optical axis of the anisotropic crystal is inclined at a predetermined angle with respect to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the incident light is arranged so as not to be parallel to the plane including the incident light. The polarization plane is inclined at a predetermined angle with respect to a plane including the traveling direction of incident light and the traveling direction of ultrasonic waves.
[0012]
To arrange the acoustooptic device as described above, the incident light may be fixed to adjust the attitude of the acoustooptic device, or the acoustooptic device may be fixed to adjust the traveling direction of the incident light. Alternatively, both the attitude of the acoustooptic device and the traveling direction of the incident light may be adjusted.
[0013]
The inventors adjust the attitude of the acoustooptic device in a direction other than the Bragg angle that has not been adjusted conventionally, and the optical axis of the anisotropic crystal includes the traveling direction of incident light and the traveling direction of ultrasonic waves. It has been found by experiments that the diffraction efficiency increases when the acoustooptic element is arranged so as not to be parallel to the surface, and the present invention has been conceived.
[0014]
By disposing the acoustooptic device as described above, it is possible to increase the diffraction efficiency compared to the prior art using linearly polarized light without increasing the anisotropic crystal.
[0015]
  The acoustooptic device is arranged so that the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of incident light and the traveling direction of ultrasonic waves.And differentThe optical axis of the isotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light determines the traveling direction of the incident light and the traveling direction of the ultrasonic wave. Not parallel to the containing surfaceThe condition may be satisfied.
[0016]
  The acoustooptic device according to claim 2 defines an xyz coordinate system in which the traveling direction of incident light is the z-axis and the polarization direction of incident light is the x-axis, and the traveling direction of ultrasonic waves traveling in the anisotropic crystal and x Assuming that the state in which the axis is parallel and the optical axis of the anisotropic crystal coincides with the z-axis is the initial state, the predetermined state around the axis perpendicular to the plane including the z-axis and the traveling direction of the ultrasonic wave from the initial state An acoustooptic device that utilizes anisotropic Bragg diffraction that occurs between an ultrasonic wave that rotates through an angle and a light wave that travels in the anisotropic crystal, and linearly polarized light is incident on the acoustooptic device. An acousto-optic device that performs acousto-optic deflection or modulation, and rotates the acousto-optic element about an axis in the same direction as the traveling direction of the incident light (z-axis), By rotating around the axis in the same direction as the traveling direction of the ultrasonic wave (x-axis) The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light (z-axis) and the traveling direction of the ultrasonic wave (x-axis), and the polarization plane of the incident light is The acoustooptic device is arranged so as to satisfy a condition that the traveling direction (z axis) and the traveling direction of ultrasonic waves (x axis) are not parallel to a plane.
[0017]
That is, when the initial state is the state in which the [110] direction of the anisotropic crystal and the x-axis are parallel and the [001] direction coincides with the z-axis, the initial crystal is rotated around the axis in the [110] direction. Or rotated about both the axis in the [110] direction and the z axis and rotated by a predetermined angle around an axis perpendicular to the plane including the z axis and the traveling direction of the ultrasonic wave. .
[0018]
From the initial state, the angle around the axis perpendicular to the plane including the z axis and the traveling direction of the ultrasonic wave is the first predetermined angle, the angle around the axis in the [110] direction is the second predetermined angle, and the angle around the z axis. When the first predetermined angle and the second predetermined angle are adjusted when the angle is the third predetermined angle, the first predetermined angle is a Bragg angle (for example, approximately 4 °), and the second predetermined angle. Can be set to approximately 3 ° or more, preferably approximately 9 °. When these angles are set within this range, the diffraction efficiency can be set to a preferable value.
[0019]
When adjusting the first to third predetermined angles together, the first predetermined angle is a Bragg angle (for example, approximately 4 °), the second predetermined angle is approximately 3 ° or more, and a third predetermined angle. The angle can be about 30 ° to about 90 °, and when these angles are set within this range, the diffraction efficiency can be set to a preferable value. Further, the first predetermined angle is a Bragg angle (for example, approximately 4 °), the second predetermined angle is approximately 5 ° to approximately 10 °, and the third predetermined angle is approximately 30 ° to approximately 90 °, preferably The predetermined angle of 1 is a Bragg angle (for example, approximately 4 °), the second predetermined angle is approximately 7 ° to approximately 10 °, the third predetermined angle is approximately 45 ° to approximately 90 °, more preferably the first The predetermined angle may be a Bragg angle (for example, approximately 4 °), the second predetermined angle may be approximately 9 ° to approximately 10 °, and the third predetermined angle may be approximately 70 ° to approximately 75 °. When the first to third predetermined angles are adjusted to the above preferable values, the highest and flat diffraction efficiency can be obtained over a wide frequency band.
[0020]
  As the anisotropic crystal, a uniaxial crystal or a biaxial crystal can be used.₂The acoustooptic device of the present invention is preferably an acoustooptic deflector.The acousto-optic device described above can be applied to an image recording apparatus that records an image by scanning a light beam, or a light beam scanning apparatus of an image reading apparatus that scans an optical beam and reads an image.
  The light beam scanning apparatus according to claim 9 is a light including an acoustooptic device that utilizes anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in the anisotropic crystal. In the beam scanning device, by adjusting the posture of the acoustooptic device, when linearly polarized incident light is incident, the optical axis of the anisotropic crystal is changed between the traveling direction of the incident light and the traveling direction of the ultrasonic wave. The acoustooptic device so as to satisfy the condition that the plane of polarization of the incident light is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave. Is arranged.
[0021]
  According to a tenth aspect of the present invention, there is provided an acoustooptic device attitude adjusting method that uses an anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in the anisotropic crystal. In the attitude adjustment method, the acoustooptic device is rotated about an axis in the same direction as the traveling direction of incident light, and is rotated about an axis in the same direction as the traveling direction of the ultrasonic wave, thereby When incident light is incident, the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light. The posture of the acoustooptic device is adjusted so as to satisfy a condition that the direction is not parallel to the plane including the direction and the traveling direction of the ultrasonic wave.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the present invention is TeO₂A case where the present invention is applied to an on [110] deflector (AOD) using a single crystal will be described. As shown in FIG. 1, this AOD has TeO whose head is cut obliquely.₂Single crystal 10 and TeO₂The transducer 12 is attached to the bottom surface of the single crystal 10 and travels in the [110] direction of the crystal and generates a transverse wave ultrasonic wave that is displaced in the [1′10] direction. TeO₂A sound absorbing material (not shown) may be attached to the head of the single crystal 10.
[0023]
As shown in FIGS. 1 and 2, the z-axis coincides with the traveling direction of the incident light, the x-axis coincides with the polarization direction of the incident light, and the y-axis is determined by the right hand system from the z-axis and the x-axis. Define the xyz coordinate system.
[0024]
In addition, as shown in FIG.₂The initial state is a state in which the traveling direction of the ultrasonic wave traveling in the single crystal 10, that is, the [110] direction of the crystal is parallel to the x axis and the [001] direction that is the optical axis is coincident with the z axis direction. To do. Then, from this initial state, rotation angles around three axes for adjusting the attitude of the AOD, that is, the Bragg angle θ_B, Tilt angle θ_A, Rotation angle θ around the axis of the incident light traveling direction_ZAre determined as follows as shown in FIG.
[0025]
Bragg angle θ_BIs rotation of the AOD in a plane including the traveling direction (z-axis) of the incident light and the ultrasonic traveling direction, that is, rotation about the axis B perpendicular to the plane formed by the z-axis and the ultrasonic traveling direction. It is. This Bragg angle θ_BIs positive when rotated from the positive side of the z-axis in the positive direction of the ultrasonic traveling direction, that is, when rotated in the right-handed direction toward the positive direction of the axis B, and the ultrasonic traveling direction is changed to the z-axis. Θ for vertical_B= 0.
[0026]
Tilt angle θ_A Is rotation about the axis in the ultrasonic traveling direction, that is, rotation about the axis A in the [110] direction. This tilt angle θ_A Is positive when rotated in the direction of the right-handed screw toward the ultrasonic traveling direction, and the optical axis [001] of the crystal indicates the traveling direction of the incident light and the traveling direction of the ultrasonic wave.Including planeWhen parallel to θ_A = 0.
[0027]
Rotation angle θ around the axis of incident light traveling direction_ZIs rotation around the z-axis, and is positive when rotated in the right-handed direction toward the positive direction in the z-axis direction, and the ultrasonic wave traveling direction is parallel to the x-axis (the incident light polarization plane is incident When parallel to a plane including the traveling direction of light and the traveling direction of ultrasonic waves), θ_Z= 0.
[0028]
A high-frequency signal having a power of 0.25 W is applied to the transducer 12 to advance ultrasonic waves, and a laser beam whose polarization direction is in the x-axis direction is incident from the z-axis direction._AThe Bragg angle θ_BFIG. 3 shows the diffraction efficiency characteristics when the angle is adjusted so as to satisfy the Bragg condition, and the rotation angle θ about the axis in the incident light traveling direction is shown in FIG._Z, And rotation angle θ about the axis of each incident light traveling direction_ZSo that the diffraction efficiency is maximized at_AAdjust the Bragg angle θ_BFIG. 4 shows the diffraction efficiency characteristics at the center frequencies of 76, 80, and 84 MHz when is adjusted to satisfy the Bragg condition. In addition, the rotation angle θ around the axis of the incident light traveling direction at this time_ZAnd tilt angle θ_AFIG. 5 shows the relationship.
[0029]
The same rotation angle θ_ZTilt angle θ_AIt has been confirmed by the present inventors that two characteristics can be obtained by adjusting the above, and FIG. 4 is a case where the shape of the frequency characteristic of the diffraction efficiency is flat (the diffraction efficiency is substantially constant regardless of the frequency). However, FIG. 6 shows a case where the shape of the frequency characteristic of the diffraction efficiency is a peak shape (the diffraction efficiency is high at the center frequency and low at the periphery).
[0030]
As can be seen from FIG. 3, the Bragg angle θ_BOnly when (θ_B≒ 4 °, θ_Z= Θ_A= 0 °) compared to the diffraction efficiency (approximately 58% at 80 MHz), the Bragg angle θ_BAnd tilt angle θ_AThe diffraction efficiency is improved by adjusting both the angles. In particular, θ_AThe diffraction efficiency η is η≈95% at ≈ ± 9 °. And θ_A≒ ± 6 ° ~ ± 9 °, the diffraction efficiency η will be η ≒ 80 ~ 95%, θ_A≈ ± 4 ° to ± 9 °, the diffraction efficiency η is η≈70 to 95%. When the diffraction efficiency η is higher than the conventional diffraction efficiency by about 10% or more, the tilt angle θ_AShould be approximately 3 ° or more.
[0031]
Also, as can be seen from FIG. 4, the Bragg angle θ is compared with the diffraction efficiency when adjusted as in the prior art._BAnd the rotation angle θ about the axis of the incident light traveling direction_ZAnd tilt angle θ_AThe diffraction efficiency is improved by adjusting in the positive or negative direction. In particular, θ_Z≒ ± (70 ° ~ 75 °), θ_A≈ ± (9 ° to 10 °), and the diffraction efficiency η is η≈95%. And θ_Z≒ ± (45 ° ~ 90 °), θ_A≈ ± (7 ° to 10 °), the diffraction efficiency η becomes η≈80 to 95%, θ_Z≒ ± (30 ° ~ 90 °), θ_AThe diffraction efficiency η is η≈70 to 95% at approximately ± (5 ° to 10 °).
[0032]
Above is the Bragg angle θ_BIs positive, but the Bragg angle θ_BIs negative (θ_BThe same applies to the case of ≈−4 °, and the cases where the diffraction efficiency η reaches a peak (about 95%) are summarized in Table 1 below.
[0033]
[Table 1]

[0034]
In addition, the rotation angle θ about the axis of the incident light traveling direction_ZIs the angle at which the diffraction efficiency obtained from FIG._Z= 70 ° fixed, tilt angle θ_AFIG. 7 shows the diffraction efficiency characteristics when V is changed.
[0035]
As understood from FIG. 7, the rotation angle θ about the axis of the incident light traveling direction_ZThe tilt angle θ_AWhen changing only the tilt angle θ_AFor example, θ_ABy adjusting to ≒ 1.5 ° or more, the diffraction efficiency can be improved compared to the conventional case, the diffraction efficiency is θ_A≒ 9 °, about 95%, θ_A≒ Approximately 80-95% over 4.5 °, θ_AApprox. 70 to 95% at 3 ° or more.
[0036]
Therefore, the rotation angle θ around the axis of the incident light traveling direction_ZAnd tilt angle θ_AWhen adjusting the rotation angle θ around the axis of the incident light traveling direction from the state where the maximum diffraction efficiency is obtained_ZTilt angle θ_AIs changed, the tilt angle θ_AIs approximately 1.5 ° or more, the diffraction efficiency can be improved compared to the conventional case, and the tilt angle θ_AIs approximately 3 ° or more, a diffraction efficiency of approximately 70 to 95% is obtained, and the tilt angle θ_AIs about 4.5 ° or more, a diffraction efficiency of about 80 to 95% can be obtained.
[0037]
The above is the result at the center frequency, but the diffraction efficiency is improved even in a predetermined frequency band. FIG. 8 shows one of the conditions for achieving the peak diffraction efficiency in Table 1, θ_Z= 70 ° and θ_A= Frequency characteristics of diffraction efficiency at 9 °, rotation angle θ around the axis of the incident light traveling direction_Z90 ° (θ_A= 9 °), and the frequency characteristic of the conventional diffraction efficiency (θ_Z= Θ_A= ± 0 °). In the present embodiment, the diffraction efficiency is improved over the conventional frequency band.
[0038]
From the above, it is arranged so that anisotropic Bragg diffraction can be used, and the optical axis of the anisotropic crystal is arranged not to be parallel to the plane including the traveling direction of incident light and the traveling direction of ultrasonic waves. Thus, the diffraction efficiency can be improved.
[0039]
That is, the anisotropic Bragg diffraction is arranged so that it can be used, and the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave. The polarization plane is made parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, or the optical axis of the anisotropic crystal determines the traveling direction of the incident light and the traveling direction of the ultrasonic wave. The diffraction efficiency can be improved by preventing the plane of polarization of incident light from being parallel to the plane including the incident light and the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave. it can.
[0040]
In the above, TeO is used as the acousto-optic medium.₂An example using a single crystal of PbMoO has been described._FourOther uniaxial crystals and biaxial crystals can also be used. In the above description, AOD has been described. However, the present invention can also be applied to AOM.
[0041]
Next, an embodiment of a cylindrical inner surface scanning type image recording apparatus using the AOD for a light beam scanning apparatus will be described with reference to the drawings. This cylindrical inner surface scanning type image recording apparatus includes a laser beam generating means for generating a plurality of laser beams arranged in parallel in a predetermined direction, a laser beam arranged in the optical path of each laser beam, and the laser beam in a parallel direction of the laser beam. A plurality of deflectors deflecting in an orthogonal direction and a reflecting surface inclined with respect to the central axis of the cylinder, and rotated about the central axis of the cylinder to scan the laser beam along the inner surface of the cylinder The scanning unit and an optical system that causes a plurality of laser beams deflected by the deflector to enter the reflecting surface of the scanning unit.
[0042]
As shown in FIG. 9, the image recording apparatus according to the present embodiment includes a laser beam generator 14 that generates a laser beam L and three laser beams generated in parallel in a predetermined direction. Laser beam L₁, L₂, L_ThreeAnd a laser beam splitter 16 that divides the laser beam. Laser beam L₁On the exit side of the laser beam L₁Is deflected in the direction orthogonal to the parallel direction of the laser beam, that is, the y-axis direction in FIG. 9 (direction orthogonal to the parallel direction of the laser beam on the recording sheet S), and the intensity of the laser beam is modulated according to image information ( AOD18x for on-off modulation) is arranged and the laser beam L₂On the exit side of the laser beam L₂An AOD 20 for on / off-modulating the laser beam according to the image information without deflecting the laser beam is arranged, and the laser beam L_ThreeOn the exit side of the laser beam L_ThreeIs arranged in the y-axis direction in the same manner as the AOD 18x, and an AOD 22x for on / off-modulating the laser beam according to the image information is arranged.
[0043]
As described above, the AODs 18x, 20, and 22x are arranged so that the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of incident light and the traveling direction of ultrasonic waves. . In this embodiment, θ_B≒ 4 °, θ_Z≒ 70 °, θ_AIt is preferable to adjust to ≈ 9 °, but θ_Z≒ 0 ° as θ_BAnd θ_AAnd may be adjusted.
[0044]
Mirrors 24, 26, and 28 that reflect the laser beam in the negative x-axis direction are arranged on the laser beam emission side of the AODs 18x, 20, and 22x, respectively, and are reflected from these mirrors on the laser beam reflection side of the mirror. A condensing lens 30 for condensing the laser beam and a cylindrical rotating mirror 32 having a reflecting surface inclined by 45 ° with respect to the axis and rotated about the axis by a motor 34 are arranged. The recording sheet S is held on the inner peripheral surface of the cylindrical drum 36 that is developed and illustrated, and the rotary mirror 32 is arranged so that its axis coincides with the central axis of the drum 36.
[0045]
In the image recording apparatus described above, when the rotating mirror 32 is rotated by 90 ° from the state where the dots recorded by the laser beam are arranged on the recording sheet S in the x-axis direction (state shown in FIG. 9), FIG. As shown in FIG. 4, the dot array is rotated by 90 ° as the rotary mirror 32 rotates. In other words, the dot array is rotated in accordance with the rotation of the rotary mirror 32 and is not incident on the center of the reflecting surface of the rotary mirror 32.₁, L_ThreeThe dots recorded by the laser beam vibrate and the laser beam L₁, L_ThreeThe dot trajectory R recorded by₁, R_ThreeBecomes sinusoidal. In this case, the laser beam L₁The locus of the dots recorded by the laser beam L_ThreeIs 180 degrees out of phase with respect to the locus of the dots recorded. Laser beam L₂Is incident on the center of the reflecting surface of the rotary mirror 32, so that the laser beam L₂The dots recorded by the laser beam L do not vibrate simply.₂The dot trajectory R recorded by₂Becomes a straight line. In the present embodiment, a control device shown in FIG. 10 is provided in order to correct the rotation of the dot arrangement and make the scanning lines parallel.
[0046]
As shown in FIG. 10, the control device 38 is connected to the transducer of each AOD. The control device 38 controls the basic clock signal and the control based on the rotation position signal P synchronized with the rotation of the motor from a rotary encoder (not shown) attached to the motor 34 and the main scanning start signal LSYNC output at the main scanning start position. A cosine wave voltage signal (x = −a · cos ωt, where a is a constant, ω is an angular velocity of the motor determined by the basic clock signal, and t is an elapsed time) according to the control circuit 40 that generates the clock signal and the basic clock signal A cosine wave voltage signal generation circuit 42a for generating a cosine wave voltage signal (x = a · cosωt) whose phase is shifted by 180 ° in accordance with the basic clock signal, and a constant voltage And a constant voltage signal generation circuit 42b for generating a signal.
[0047]
The voltage signal generation circuits 42a, 42b, and 42c are connected to voltage controlled oscillators (VCO) 44a, 44b, and 44c that generate a frequency modulation signal from the voltage signal.
[0048]
The control circuit 40 is connected to a binary image signal generation circuit 48 that generates a binary image signal. The frequency modulation signals output from the VCOs 44a, 44b, and 44c are output by the modulators 46a, 46b, and 46c. The binary image signal from the binary image signal generation circuit 48 is on / off modulated, amplified by the amplifier circuits 50a, 50b, and 50c, and then input to the transducer of each AOD.
[0049]
As described above, the voltage signal modulated by the cosine wave voltage signal (x = −a · cos ωt, a · cos ωt) is applied to the transducers of the AODs 18x and 22x, so that the laser beam passing through the AODs 18x and 22x is changed to FIG. From the state (0 ° position in FIG. 13A) is deflected in the y-axis direction. At this time, on the recording sheet S, the dot by the laser beam that has passed through the AOD 18x moves in the positive direction of the x-axis by moving in the direction orthogonal to the dot arrangement direction, and the dot by the laser beam that has passed through the AOD 22x is By moving in the negative direction of the x-axis by moving in the direction orthogonal to the dot arrangement direction and in the direction opposite to the dot by the laser beam that has passed through the AOD 18x, this deflection cancels the sinusoidal single vibration and the scanning line is shown. As shown in 13 (2), it can be a parallel straight line.
[0050]
However, since the length of the trajectory by each laser beam is different, when scanning in the range of −90 ° to + 90 ° as in the present embodiment, as shown in FIG. Laser beam L at the scanning start side_ThreeThe dot trajectory R recorded by_ThreeIs the laser beam L₁, L₂The dot trajectory R recorded by₁, R₂Are shifted by Td1 and Td2, respectively, and are shifted by Td3 and Td2 on the scanning end end side of one line. Therefore, the locus is the laser beam L₁The dot trajectory R recorded by₁, Laser beam L₂The dot trajectory R recorded by₂, Laser beam L_ThreeThe dot trajectory R recorded by_ThreeTherefore, the scanning length is different. In the present embodiment, a control clock signal generation circuit 52 shown in FIG. 11 is provided in the control circuit 40 in order to correct this difference in scanning length.
[0051]
The control clock signal generation circuit 52 generates a basic clock signal B in accordance with the PLL circuit 54 that generates a phase synchronization signal from the rotational position signal P, the main scanning start signal LSYNC, and the PLL circuit 54 output. 56, a counter 58 that counts the basic clock signal, a lookup table 60 that outputs a delay amount setting signal for setting a delay amount according to the count value from the counter 58, and a basic clock signal generation circuit 56 according to the delay amount setting signal. It is composed of delay circuits 62a, 62b and 62c which delay the basic clock signal and output it as control clock signals CL1, CL2 and CL3. The control clock signals CL1, CL2, CL3 are supplied to the binary image signal generation circuit 48 described above.
[0052]
Note that the delay amount for correcting the shift amount shown in FIG. 13B and arranging the dots recorded by the laser beam in the x-axis direction on the recording sheet differs depending on the main scanning position. Therefore, the delay amount of the lookup table 60 is determined in advance for each laser beam, according to the scanning position in the main scanning direction, that is, for each pulse of the basic clock signal.
[0053]
Next, the operation of the image recording apparatus of the above embodiment will be described. A rotational position signal P from an encoder (not shown) provided in the motor 34 is input to the PLL circuit 54 and subjected to phase control to generate a phase synchronization signal. The phase synchronization signal is input to the basic clock signal generation circuit 56, and the basic clock signal B shown in FIG. 12 is output at the generation timing of the main scanning start signal LSYNC. The basic clock signal is counted by the counter 58 and input to the delay circuits 62a, 62b, and 62c.
[0054]
The count value of the basic clock signal counted by the counter 58 is supplied to the lookup table 60. The look-up table 60 indicates that each laser beam L is in accordance with the count value, that is, in accordance with the recording position in the main scanning direction of the recording sheet.₁, L₂, L_ThreeA delay amount setting signal is input to each of the delay circuits 62a, 62b, 62c based on a predetermined delay amount for each time. The delay circuits 62a, 62b, and 62c delay the basic clock signal according to the input delay amount setting signal and output the delayed signals as control clock signals CL1, CL2, and CL3.
[0055]
The control clock signal CL1 is the laser beam L₁The delay circuit 62a controls the output timing of the binary image signal recorded by the laser beam L as shown in FIG. 12 based on the delay amount setting signal.₁Is delayed by Td1 from the generation timing of the basic clock signal, that is, the generation timing of the main scanning start signal LSYNC, and the recording end timing is the main scanning end timing of the basic clock signal. A control clock signal CL1 matched with (m-th clock) is output.
[0056]
The control clock signal CL2 is the laser beam L₂The delay circuit 62b controls the output timing of the binary image signal recorded by the laser beam L as shown in FIG. 12 based on the delay amount setting signal.₂The recording start time of the image by the binary image signal recorded by the above is delayed by Td2 from the generation timing of the main scanning start signal LSYNC, and the recording end time is delayed by Td2 from the main scanning end timing of the basic clock signal. The clock signal CL2 is output.
[0057]
The control clock signal CL3 is the laser beam L_ThreeThe delay circuit 62c controls the output timing of the binary image signal recorded by the laser beam L as shown in FIG. 12 based on the delay amount setting signal._ThreeThe control clock in which the recording start time of the image by the binary image signal recorded by the above is the same as the generation timing of the main scanning start signal LSYNC and the recording end time is delayed by Td3 from the main scanning end timing of the basic clock signal. The signal CL3 is output.
[0058]
Note that the delay amount of the lookup table is set according to each main scanning position so that the pulse intervals of the respective control clock signals are as equal as possible. In addition, if the delay positions between adjacent scanning lines overlap, a beat may occur between halftone dots and the image may become uneven, so the delay amount of the lookup table is between each scanning line. It is preferable to set it to be random.
[0059]
The control clock signals CL1, CL2, and CL3 output as described above are supplied to the binary image signal generation circuit 48. The binary image signal generation circuit 48 converts the binary image signal to each modulator at the timing shown in FIG. It outputs to 46a, 46b, 46c.
[0060]
On the other hand, the voltage signal generation circuits 42a and 42c generate cosine wave voltage signals (x = −a · cos ωt, a · cos ωt) based on the input basic clock signal, and generate frequency modulation signals via the VCOs 44a and 44c. The constant voltage signal generation circuit 42b inputs the signals to the modulators 46a and 46c, and inputs the frequency modulation signal to the modulator 46b via the VCO 44. Thus, the frequency modulation signals output from the voltage signal generation circuits 48a, 48b, and 48c are on / off modulated by the binary image signal from the binary image signal generation circuit 48 in the modulators 46a, 46b, and 46c, and the amplification circuit After being amplified by 50a, 50b and 50c, it is input to the transducer of each AOD.
[0061]
Laser beam L generated from the laser beam generator 14 and split by the beam splitter 16₁, L_ThreeAre deflected in the y-axis direction by the AODs 18x and 22x, modulated on and off according to the binary image signal, reflected by the mirrors 24 and 28, and incident on the rotary mirror 32 via the condenser lens 22. Laser beam L₂Without being deflected by the AOD 20, is on / off modulated in accordance with the binary image signal, is reflected by the mirror 26, and is incident on the rotary mirror 32 via the condenser lens 22.
[0062]
Since the rotary mirror 32 rotates about the x-axis, the laser beam is scanned on the recording sheet by reflection. In this case, the laser beam L modulated on and off with a binary image signal.₁, L₂Is the laser beam L_ThreeThe image is recorded on the recording sheet within the same recording range (FIG. 13 (3)). Therefore, it is possible to record a highly accurate image with the same recording range in the main scanning direction and without distortion.
[0063]
As described above, according to the present embodiment, the AOD is arranged so that the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of incident light and the traveling direction of ultrasonic waves. A low-cost cylindrical inner surface scanning type image recording apparatus with improved diffraction efficiency can be provided.
[0064]
In the above, the embodiment in which the present invention is applied to the cylindrical inner surface scanning image recording apparatus has been described. However, the present invention scans and records a laser beam in the main scanning direction while conveying the recording sheet in the sub scanning direction. Light beam scanning of a planar scanning image recording apparatus that performs recording and a cylindrical outer surface scanning image recording apparatus that records by supporting a recording sheet on the outer peripheral surface of the drum and scanning the laser beam in the main scanning direction while rotating the drum It can also be applied to devices. The present invention can also be applied to various reading devices that perform reading by scanning a laser beam.
[0065]
【The invention's effect】
  As explained above,The present inventionAcoustooptic device and attitude adjustment method of acoustooptic deviceAccording toThe optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. Not parallel to the plane containingThe low-cost acousto-optic device uses a linearly polarized light to further improve the diffraction efficiency without increasing the size of the anisotropic crystal.machineCan be provided.
[0066]
  Also,The light beam scanning apparatus of the present invention is an acoustooptic device in which an acoustooptic element is arranged as described above.As a result, it is possible to provide a low-cost light beam scanning apparatus with further improved diffraction efficiency.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an AOD according to an embodiment of the present invention.
FIG. 2 is a perspective view of an AOD for explaining an axis for rotating the AOD in the embodiment of the present invention.
FIG. 3 shows a tilt angle θ according to the embodiment of the present invention._AIt is a diagram which shows the change of the diffraction efficiency with respect to the change of only.
FIG. 4 is a rotation angle θ about an axis in the direction of travel of incident light according to the embodiment of the present invention._ZIt is a diagram which shows the change of the diffraction efficiency with respect to the change of (when the shape of the frequency characteristic of a diffraction efficiency is flat).
5 is a rotation angle θ about the axis of the incident light traveling direction to obtain the diffraction efficiency of FIG._ZAnd tilt angle θ_AFIG.
FIG. 6 shows a rotation angle θ about the axis of incident light traveling direction._ZIt is a diagram which shows the change of the diffraction efficiency with respect to the change of (when the shape of the frequency characteristic of a diffraction efficiency is peak shape).
FIG. 7 shows a rotation angle θ about an axis in the direction of incident light travel._ZTilt angle θ when is 70 °_AIt is a diagram which shows the change of the diffraction efficiency with respect to the change of.
FIG. 8 is a diagram showing diffraction efficiency in a certain frequency band according to the embodiment of the present invention.
FIG. 9 is a schematic diagram of an image recording apparatus according to an embodiment of the present invention.
FIG. 10 is a block diagram of a control device of the image recording apparatus according to the embodiment of the present invention.
FIG. 11 is a block diagram of a control circuit of the image recording apparatus according to the embodiment of the present invention.
FIG. 12 is a diagram showing the timing of a control clock signal in the image recording apparatus according to the embodiment of the present invention.
FIGS. 13A and 13B show scanning lines when the rotation of the image by the rotating mirror is not corrected, FIG. 13B shows scanning lines when the rotation of the image by the rotating mirror is corrected, and FIG. 13C shows the scanning length. It is a diagram which shows the scanning line at the time of correct | amending the difference.
[Explanation of symbols]
10 TeO₂Single crystal
12 Transducer

Claims (11)

An acoustooptic device using anisotropic Bragg diffraction generated between an ultrasonic wave traveling in the anisotropic crystal and a light wave traveling in the anisotropic crystal, and a light source for causing linearly polarized light to enter the acoustooptic device, An acousto-optic device that performs acousto-optic deflection or modulation,
By adjusting the attitude of the acousto-optic element,
The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is the traveling direction of the incident light and the traveling direction of the ultrasonic wave. An acoustooptic device, characterized in that the acoustooptic device is arranged so as to satisfy a condition that it is not parallel to a plane including the . An xyz coordinate system is defined in which the traveling direction of incident light is the z-axis and the polarization direction of incident light is the x-axis. The traveling direction of the ultrasonic wave traveling in the anisotropic crystal is parallel to the x-axis and is anisotropic. Assuming that the optical axis of the crystal coincides with the z-axis as an initial state, the crystal is rotated by a predetermined angle around an axis perpendicular to the plane including the z-axis and the traveling direction of the ultrasonic wave from the initial state, An acoustooptic device using anisotropic Bragg diffraction generated between a traveling ultrasonic wave and a light wave traveling in an anisotropic crystal, and a light source for causing linearly polarized light to enter the acoustooptic device, An acousto-optic device that deflects or modulates,
By rotating the acoustooptic element about an axis in the same direction as the traveling direction of the incident light (z axis), and rotating about the same direction as the traveling direction of the ultrasonic wave (x axis),
The optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light (z-axis) and the traveling direction of the ultrasonic wave (x-axis) , and the polarization plane of the incident light travels the incident light. An acoustooptic device, wherein the acoustooptic device is arranged so as to satisfy a condition that the direction (z axis) and the ultrasonic traveling direction (x axis) are not parallel to a plane . The acousto-optic device according to claim 2, wherein a rotation angle about an axis in the same direction as the traveling direction of the ultrasonic wave is approximately 3 ° or more . A predetermined angle around an axis perpendicular to the plane including the z-axis and the traveling direction of the ultrasonic wave is a Bragg angle, and a rotational angle around the same axis as the traveling direction of the ultrasonic wave is about 3 ° or more, around the z-axis. The acousto-optic device according to claim 2 or 3, wherein the rotation angle of said is approximately 30 ° to approximately 90 ° . The acoustooptic device according to claim 1 , wherein the anisotropic crystal is a uniaxial crystal . The acoustooptic device according to claim 1 , wherein the anisotropic crystal is TeO ₂ . The acoustooptic device according to any one of claims 1 to 6, wherein the acoustooptic element is an acoustooptic deflection element . A light beam scanning device comprising the acousto-optic device according to claim 1. A light beam scanning device including an acoustooptic device using anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in the anisotropic crystal ,
By adjusting the attitude of the acousto-optic element,
When linearly polarized incident light is incident, the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is incident A light beam scanning device, wherein the acoustooptic device is arranged so as to satisfy a condition that the light traveling direction and the ultrasonic traveling direction are not parallel to a plane . Anisotropic braces between ultrasonic waves traveling in anisotropic crystals and light waves traveling in anisotropic crystals A method for adjusting the attitude of an acousto-optic device using diffraction of diffraction,
By rotating the acousto-optic element about an axis in the same direction as the traveling direction of incident light, and rotating about the axis in the same direction as the traveling direction of the ultrasonic wave,
When linearly polarized incident light is incident, the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light and the traveling direction of the ultrasonic wave, and the polarization plane of the incident light is incident A method of adjusting an attitude of an acoustooptic device, wherein the orientation of the acoustooptic device is adjusted so as to satisfy a condition not parallel to a plane including a traveling direction of light and a traveling direction of ultrasonic waves. For a linearly polarized incident light, an xyz coordinate system is defined in which the traveling direction of the incident light is the z axis and the polarization direction of the incident light is the x axis, and the traveling direction of the ultrasonic wave traveling in the anisotropic crystal and the x axis Is assumed to be the initial state when the optical axis of the anisotropic crystal coincides with the z-axis, and is rotated from the initial state by a predetermined angle around an axis perpendicular to the plane including the z-axis and the traveling direction of the ultrasonic wave. A method of adjusting the attitude of an acoustooptic device using anisotropic Bragg diffraction generated between an ultrasonic wave traveling in an anisotropic crystal and a light wave traveling in the anisotropic crystal ,
By rotating the acoustooptic element about an axis in the same direction as the traveling direction of the incident light (z axis), and rotating about the same direction as the traveling direction of the ultrasonic wave (x axis),
When linearly polarized incident light is incident, the optical axis of the anisotropic crystal is not parallel to the plane including the traveling direction of the incident light (z axis) and the traveling direction of the ultrasonic wave (x axis), In addition, the acousto-optic device is positioned so that the plane of polarization of the incident light is not parallel to the plane including the traveling direction of the incident light (z-axis) and the traveling direction of the ultrasonic wave (x-axis). A method of adjusting the attitude of an acousto-optic device, characterized by adjusting.

Images