JP4460194B2

JP4460194B2 - Variable optical attenuator

Info

Publication number: JP4460194B2
Application number: JP2001171477A
Authority: JP
Inventors: 順吉城野; 博長谷川
Original assignee: Anritsu Corp
Current assignee: Anritsu Corp
Priority date: 2001-06-06
Filing date: 2001-06-06
Publication date: 2010-05-12
Anticipated expiration: 2021-06-06
Also published as: JP2002365563A

Description

【０００１】
【発明の属する技術分野】
本発明は、光ファイバから入射される光を所定量減衰させ、光の強さを調整して出力する可変光減衰器に関し、特にハイパワーの光入力に対しても常に安定した減衰特性が得られる可変光減衰器に関する。
【０００２】
【従来の技術】
従来、光ファイバから入射される光の強さを調整する可変光減衰器として、回転式の減衰板が知られている。この回転式の減衰板は、回転可能に支持された円板の表面に金属膜が施されたものである。金属膜は、光が入射される円板の表面に対し、回転方向である円周方向に徐々に濃度が変化するように蒸着により薄膜形成されている。
【０００３】
上記構成による回転式の減衰板では、光ファイバの光の出射位置に対し、所望の減衰量が得られる金属膜の位置まで円板を一方向に回転させる。これにより、光ファイバから入射された光は円板上の金属膜により減衰され、この減衰された光が円板を透過して出射される。
【０００４】
しかしながら、上述した従来の回転式の減衰板は、光ファイバから入射される光がハイパワーのものには対応することができなかった。すなわち、上記減衰板に対してハイパワーの光が入射されると、その光の一部が金属膜に吸収される。ところが、金属膜が蒸着による薄膜で形成されているので、吸収した熱を放熱することができず、その熱によって金属膜の一部が蒸発してしまう。しかも、金属膜が熱を吸収するだけでなく、常に外気に晒された状態なので、金属膜の表面が酸化してしまう。その結果、光ファイバから入射される光の減衰量が変化してしまい、所望の減衰量を得ることができなかった。
【０００５】
そこで、上述した従来の回転式の減衰板のように発熱によって減衰性能が変わることがなく、ハイパワーの光入力にも対応できる可変光減衰器として、図９に示すものが提案されている。
【０００６】
図９に示す可変光減衰器５１は、光ファイバから入射される光を物理的に遮断するものである。可変減衰器５１は、矩形状の本体５２の対向する側面５２ａと側面５２ｂとの間に直線状の貫通穴５３が形成されている。本体５２の両側面５２ａ，５２ｂには、貫通穴５３に臨むようにして一対の光ファイバ５４（５４ａ，５４ｂ）が取り付けられる。貫通穴５３は、一対の光ファイバ５４ａ，５４ｂの光路を形成している。本体５２の上面５２ｃには、貫通穴５３と直交する方向に貫通穴５３に連通してネジ穴５５が形成されている。ネジ穴５５には、貫通穴５３に対して先端部が進退移動するようにネジ５６が取り付けられている。
【０００７】
上記構成による可変光減衰器５１では、ネジ５６を所定量回転させてネジ５６の先端部を貫通穴５３（光路）に進入させる。この貫通穴５３に対するネジ５６の先端部の進入量によって光ファイバ５４ａから入射される光の減衰量が決定される。そして、ネジ５６の調整により光の減衰量が決定されると、光ファイバ５４ａから入射された光は、貫通穴５３に突出するネジ５６の先端部により遮られて減衰し、この減衰した光が光ファイバ５４ｂから出射される。
【０００８】
【発明が解決しようとする課題】
図９に示す従来の可変光減衰器５１では、貫通穴５３が光ファイバ５４ａからの入射光の光路を形成しており、この貫通穴５３に対してネジ５６が進退するようにネジ５６が回転移動する。このため、ネジ５６とネジ穴５５との間に所定量の遊びを持っている。従って、ネジ５６自身にガタつきがあり、ネジ５６の回転移動に伴い、ネジ５６自身が偏心してブレが生じる。その結果、入射光の減衰量が安定せずに変化し、損失変動が生じるという問題があった。
【０００９】
しかも、図９の可変光減衰器５１では、ネジ５６の回転量に対してネジ５６の移動量がリニアに変化する。これに対し、光ファイバ５４ａから入射される光は、中央部分の光量が強く、外側に向かうに従って光量が弱くなるガウスビーム光である。一般に、この種の可変光減衰器５１に入射される半導体レーザの光強度分布は、図１０に示すようなガウシアン分布になっている。そして、減衰量をデシベル［ｄＢ］で表すと、ネジ５６の移動量が一定の場合、減衰量が大きくなるに従い、ネジ５６の回転量に対する減衰変化率が大きくなる。このため、減衰量が大きく場合には高い分解能が必要になり、ネジ５６による一定量の移動では例えば０．０１ｄＢ毎の微量な減衰量設定を行うことができない。
【００１０】
このように、図９の可変光減衰器５１では、ネジ５６を少し回転移動させただけでも入射光の減衰量が大きく変化してしまい、ネジ５６を回転させた時のネジ１回転当たりの入射光の減衰量が異なる。その結果、所望の減衰量が得られにくく、再現性がとれないという問題があった。
【００１１】
さらに、図９の可変光減衰器５１では、減衰量を調整するためのネジ５６自身が周囲温度により歪みを起こして変形することがある。このため、常に安定した減衰量を得ることができず、再現性も悪くなるという問題があった。
【００１２】
そこで、本発明は、上記問題点に鑑みてなされたものであり、ハイパワーの入射光に対しても安定した減衰性能を得ることができる可変光減衰器を提供することを目的としている。
【００１３】
【課題を解決するための手段】
上記目的を達成するため、請求項１の発明は、入射光を所定量減衰させ、光の強さを調整して出力する可変光減衰器１において、
少なくとも一端が軸受部材５によって回転可能に支持されて入射光の光路にほぼ直角に配置されており、円柱棒状の部分と、自身の回転に応じて前記入射光のビームの通過量を連続的に可変する遮蔽部３とを有する軸部材２と、
前記軸部材の回転移動量を制御する駆動制御手段６，７と、
板部と該板部から該板部の面と平行に突出した突出部８ａとで成り、前記軸部材に付された遮蔽板８とを備え、
前記遮蔽部は、前記軸部材の前記円柱棒状の一部が断面扇状に３／４だけ欠切されて前記円柱棒状の部分と一体形成されており、前記欠切された箇所は２つの平面を成し、該２つの平面の交わる稜線は前記軸部材の中心軸と合致しており、
前記遮蔽板は、前記入射光の光路上で前記稜線から前記軸部材の半径方向外向きに所定量突出するように前記２つの平面の一方の平面３ｃ上に付されており、
前記軸部材が所定量回転したときに、前記突出部が前記入射光の光強度の強いビームの中心部を遮蔽するとともに、前記軸部材の回転に伴う光減衰量変化が小さくなるように成したことを特徴とする。
【００１４】
請求項２の発明は、請求項１の可変光減衰器において、
前記突出部８ａの形状は、二等辺三角形状であることを特徴とすることを特徴とする。
【００１５】
請求項３の発明は、請求項１の可変光減衰器において、
前記突出部８ａの形状は、半円状の曲面形状であることを特徴とする。
【００１６】
【発明の実施の形態】
図１は本発明による可変光減衰器の第１実施の形態の概略構成を示す図、図２は図１における可変光減衰器の遮蔽部の部分拡大図であり、入射光と遮蔽部の位置関係を示す図である。
【００１７】
以下に説明する本発明の可変光減衰器は、例えば一対の光ファイバの間に配設され、入力側の光ファイバから入射される光を所望の値に減衰させて調整し、この調整された光を出力側の光ファイバから出力するものである。
【００１８】
第１実施の形態の可変光減衰器１（１Ａ）は、図１に示すように、円柱棒状の軸部材２を有している。軸部材２は、光ファイバからの入射光（例えばビーム径が１ｍｍ程度のレーザ光による平行光）の光路にほぼ直角に配置されており、入射光の光軸Ｌ１−Ｌ１と同一平面上で直交する方向に回転可能とされている。
【００１９】
軸部材２の中途位置には、入射光の光路上に遮蔽部３が一体形成されている。図１における遮蔽部３は、入射光が軸部材２の回転軸Ｌ２−Ｌ２近傍を通るように、軸部材２の中央部の円柱部分が断面扇状に３／４だけ欠切されて一体形成される。この遮蔽部３は、入射光の光軸Ｌ１−Ｌ１と直交し、かつ軸部材２の回転軸Ｌ２−Ｌ２と平行をなす平坦なエッジ（稜線）３ａを有する。遮蔽部３は、軸部材２が図１の矢印Ａ方向に回転したときに、エッジ３ａを含む平面３ｂにより、軸部材２の回転に伴って入射光を所定量ずつ遮蔽している。
【００２０】
遮蔽部３は、軸部材２が初期位置にある状態（図１の状態）で、光ファイバからの入射光がエッジ３ａを含む平面３ｂによって減衰されることなく全て通過させる。そして、遮蔽部３のエッジ３ａを含む平面３ｂにより、軸部材２の回転に伴って入射光を所定量ずつ遮光し、入射光を所定量ずつ減衰させる。このように、遮蔽部３は、軸部材２の回転に応じて入射光のビームの通過量を連続的に可変している。
【００２１】
軸部材２は、回転時の軸振れによる機械的誤差（ガタツキ）を減少させるため、コ字状の支持部材４に対し、両端が例えばベアリング等の軸受部材５により回転可能に支持されている。軸部材２は、一端が軸受部材５を介して駆動手段としてのサーボモータ６に連動連結されている。サーボモータ６には、軸部材２の回転量に応じた電気信号を出力するポテンショメータ（不図示）が設けられている。サーボモータ６は、制御回路７によって回転量が制御される。制御回路７は、ポテンショメータからの電気信号によって軸部材２が所定回転角度まで回転駆動されたか否かを判別し、この判別結果に応じて制御信号（回転角度量に相当する信号）をサーボモータ６に入力し、所望の減衰量が得られる位置まで軸部材２を回転させるべく、サーボモータ６を駆動制御している。
【００２２】
軸部材２は、光ファイバからの入射光が遮蔽部３によって遮蔽されることなく全て通過する状態（図１に示す状態）を初期位置としている。また、軸部材２の回転軸Ｌ２−Ｌ２は、この回転軸Ｌ２−Ｌ２と入射光の光軸Ｌ１−Ｌ１の両方の軸に直交する方向であって、入射光の光軸Ｌ１−Ｌ１から所定量ずれた位置にある。図１の例における軸部材２の回転軸Ｌ２−Ｌ２は、光軸Ｌ１−Ｌ１と同一平面上で直交し、光軸Ｌ１−Ｌ１から所定量下方にずれた位置にある。このように回転可能に支持された軸部材２は、制御回路７からの制御信号で駆動制御されるサーボモータ６により、所定回転角度位置まで回転駆動される。
【００２３】
なお、本例では、サーボモータ６及び制御回路７（不図示のポテンショモータを含む）により、軸部材２の回転移動量を制御する駆動制御手段を構成している。
【００２４】
上記構成による可変光減衰器１では、光ファイバからの入射光を減衰させて出力する際、軸部材２がサーボモータ６の駆動により所望の減衰量が得られる位置まで一方向に所定回転角度だけ回転して停止する。これにより、光ファイバからの光が軸部材２の回転軸Ｌ２−Ｌ２近傍に入射されると、この入射光は、軸部材２の遮蔽部３のエッジ３ａを含む平面３ｂによって遮られ、所望の減衰量だけ減衰して出力される。
【００２５】
ここで、軸部材２の遮蔽部３のエッジ３ａの形状を平坦にした場合の軸部材２の軸回転角度に対する減衰量変化シミュレーションの結果を図３に示す。なお、図３では、軸部材２の回転角度に対する減衰量変化を実線で示し、軸部材２の回転角度に対する減衰量変化率を破線で示している。
【００２６】
図３からも明らかなように、第１実施の形態の可変光減衰器１Ａでは、例えば軸部材２の回転角度が４５°を超えると、回転角度５°に対し減衰量が２ｄＢの割合で変化している。そして、軸部材２の回転量が一定の場合、減衰量が大きくなるに従って、軸部材２の回転角度に対する減衰量変化率が大きくなっているのが判る。
【００２７】
従って、上記第１実施の形態の可変光減衰器１Ａでは、特に、高い分解能を必要としない減衰量で入射光を減衰する場合に有効である。
【００２８】
ところで、上記第１実施の形態の可変光減衰器１Ａでは、入射光を遮蔽する遮蔽部３のエッジ３ａの形状が平坦なので、軸部材２の回転量が一定の場合、減衰量が大きくなるに従って、軸部材２の回転角度に対する減衰量変化率が大きくなる。このため、減衰量が大きくなると、高い分解能が必要になるが、減衰量によってはサーボモータ６の分解能が不足し、例えば０．０１ｄＢ毎の微量な減衰量設定が行えないおそれがある。
【００２９】
そこで、上記第１実施の形態の可変光減衰器１Ａによる問題を解消した本発明による第２実施の形態の可変光減衰器１Ｂ（１）を以下に説明する。
【００３０】
図４は本発明による可変光減衰器の第２実施の形態の概略構成を示す図、図５（ａ），（ｂ）は図４における可変光減衰器の遮蔽部の側面図及び断面図、図６は入射光と遮蔽部の位置関係を示す部分拡大図である。
【００３１】
第２実施の形態の可変光減衰器１Ｂは、可変光減衰器１Ａと比較して、遮蔽部３のエッジ３ａの形状が異なる他は同一構成である。従って、可変光減衰器１Ｂにおいて、可変光減衰器１Ａと同一構成要素には同一番号を付し、その詳細な説明については省略する。
【００３２】
第２実施の形態の可変光減衰器１Ｂは、図５（ｂ）に示すように、遮蔽部３の平面３ｃ（平面３ｂと直角をなす平面）に遮蔽板８が設けられている。遮蔽板８の中央部分には、三角形状に突出したエッジ８ａを有している。図４及び図５では二等辺三角形によるエッジ８ａの例を示し、図６では直角二等辺三角形によるエッジ８ａの例を示している。この遮蔽板８は、エッジ８ａが遮蔽部３の平面３ｂから所定量突出するように、光ファイバからの入射光の光路上に位置して設けられる。本例における遮蔽板８は、軸部材２が図４に示す状態から矢印Ａ方向に９０°回転したときに、図６に示すように、三角形状の突出したエッジ８ａが入射光のビーム断面の下半部の中心部分を覆うように遮蔽部３の平面３ｃに設けられる。
【００３３】
そして、光ファイバからの入射光を減衰させて出力する場合、高い分解能を必要としない低い減衰量のときは、軸部材２を図６に示す状態まで図４及び図５（ｂ）の矢印Ａ方向に回転させ、遮蔽板８の三角形状のエッジ８ａの先端部で光強度の強い中心部を最初に遮蔽する。そして、高い分解能が要求される減衰量が大きい領域では、入射光の光強度分布の低い部分をエッジ８ａを含む遮蔽部３の平面３ｂで遮蔽する。これにより、軸部材２の回転に伴う遮蔽板８による減衰量変化率を低く抑えることができる。
【００３４】
また、遮蔽板８が設けられる遮蔽部３は、軸部材２の一部を切欠し、遮蔽板８のエッジ８ａを軸部材２の回転軸Ｌ２−Ｌ２に近づけ、回転半径を小さくしている。これにより、サーボモータ６の回転角度に対するエッジ８ａの変位を減少させて分解能を向上させることができる。
【００３５】
ここで、軸部材２の遮蔽部３に設けられる遮蔽板８のエッジ８ａの形状を三角形状にした場合の軸部材２の軸回転角度に対する減衰量変化シミュレーションの結果を図７に示す。なお、図７では、軸部材２の回転角度に対する減衰量変化を実線で示し、軸部材２の回転角度に対する減衰量変化率を破線で示している。
【００３６】
図７からも明らかなように、第２実施の形態の可変光減衰器１Ｂでは、例えば軸部材２の回転角度が４５°を超えると、回転角度５°に対して減衰量が１ｄＢ前後の割合で変化している。そして、軸部材２の回転角度が約６０°を超えた時点から減衰量変化率が一定しており、軸部材２の回転角度に対する減衰量変化が小さくなっているのが判る。すなわち、第２実施の形態の可変光減衰器１Ｂでは、前述した第１実施の形態の可変光減衰器１Ａと比較した場合、軸部材２の回転角度に対する減衰量変化が小さくなっている。
【００３７】
従って、第２実施の形態の可変光減衰器１Ｂは、特に、高い分解能が要求される減衰量で入射光を減衰する場合に有効である。
【００３８】
なお、第２実施の形態の可変光減衰器１Ｂでは、構成上、三角形状に突出したエッジ８ａを有する遮蔽板８を遮蔽部３とは別体にしているが、遮蔽板８を用いず、三角形状に突出したエッジを有する遮蔽部３としても良い。
【００３９】
このように、上述した各実施の形態の可変光減衰器１（１Ａ，１Ｂ）では、入射光の光路上に遮蔽部３（及び遮蔽板８）を有する軸部材２を設け、この軸部材２をサーボモータ６で回転させる。これにより、軸部材２の回転に応じて遮蔽部３近傍を通過する入射光が遮られ、入射光のビームの通過量が連続的に可変し、入射光が所定量減衰して出力される。これにより、従来の金属を蒸着した減衰板のように、ハイパワー入力による熱の影響で化学変化を起こすことがないので、損失変動が少なく、ハイパワー入力の入射光に対応することができる。
【００４０】
また、軸部材２の回転運動によって入射光を減衰させるので、従来の図９に示すような直線運動による可変光減衰器５１とは異なり、サーボモータ６の動作を変換することなく直接利用できる。これにより、装置の部品点数の削減、簡略化を図ることができる。
【００４１】
さらに、サーボモータ６によって回転駆動される軸部材２を用いて装置の簡略化がされたことに加え、軸部材２を軸受部材５によって支持している。これにより、装置の機械的誤差（ガタツキ）を減少させ、損失変動が少なく、再現性、耐久性の向上を図ることができる。
【００４２】
特に、第２実施の形態の可変光減衰器１Ｂによれば、三角形状のエッジ８ａを有する遮蔽板８を遮蔽部３の平面３ｃに設けた構成なので、高い分解能を必要としない低い減衰量のときは、遮蔽板８の三角形状のエッジ８ａの先端部で光強度の強い中心部を最初に遮蔽する。そして、高い分解能が要求される減衰量が大きい領域では、入射光の光強度分布の低い部分をエッジ８ａを含む遮蔽部３の平面３ｂで遮蔽する。これにより、軸部材２の回転に伴う遮蔽板８による減衰量変化率を低く抑えることができる。その際、入射光と軸部材との位置関係がずれることなく、軸部材２の回転とともに光を遮る量を変化させることができる。
【００４３】
ところで、第２実施の形態の可変光減衰器１Ｂにおいて、遮蔽部３の平面３ｃに設けられる遮蔽板８のエッジ８ａの形状を三角形状以外の形状、例えば半円状等の曲面形状とすることもできる。
【００４４】
また、上述した各実施の形態の可変光減衰器１Ａ，１Ｂは、軸部材２の両側が支持部材４に対して軸受部材５で支持された構成としているが、軸部材２の片側のみを支持部材４に対して軸受部材５で支持する構成としてもよい。例えば図８に示すように、軸部材２の片側のみを支持部材４に対して軸受部材５で支持し、軸受部材５を介して軸部材２をサーボモータ６に連動連結する構成としてもよい。なお、図８において、遮蔽板８が無い構成とすることもできる。
【００４５】
さらに、各実施の形態の可変光減衰器１Ａ，１Ｂの軸部材２は、自身の回転に伴って入射光を徐々に減衰することができれば、特に円柱状に限定されるものではない。
【００４６】
【発明の効果】
以上の説明で明らかなように、本発明の可変光減衰器によれば、軸部材が所定量回転したときに、突出部が入射光の光強度の強いビームの中心部を遮蔽するとともに、軸部材の回転に伴う光減衰量変化が小さくなるように成すので、高い分解能を必要としない低い減衰量のときは、遮蔽部の突出部の先端部で光強度の強い中心部を最初に遮蔽し、高い分解能が要求される減衰量が大きい領域では、入射光の光強度分布の低い部分を遮蔽する。これにより、軸部材の回転に伴う遮蔽部による減衰量変化率を低く抑えることができる。その際、入射光と軸部材との位置関係がずれることなく、軸部材の回転とともに光を遮る量を変化させることができる。
【図面の簡単な説明】
【図１】本発明による可変光減衰器の第１実施の形態の概略構成を示す図
【図２】図１における可変光減衰器の遮蔽部の部分拡大図であり、入射光と遮蔽部の位置関係を示す図
【図３】図１の可変光減衰器において、遮蔽部のエッジ形状を平坦にした場合の軸部材の軸回転角度に対する減衰量変化シミュレーションの結果を示す図
【図４】本発明による可変光減衰器の第２実施の形態の概略構成を示す図
【図５】（ａ），（ｂ）図４における可変光減衰器の遮蔽部の側面図及び断面図
【図６】図４の可変光減衰器において入射光と遮蔽部の位置関係を示す部分拡大図
【図７】図４の可変光減衰器において、遮蔽部のエッジ形状を三角形状にした場合の軸部材の軸回転角度に対する減衰量変化シミュレーションの結果を示す図
【図８】本発明による可変光減衰器の変形例を示す図
【図９】従来の可変光減衰器の概略構成を示す断面図
【図１０】半導体レーザの光強度分布を示す図
【符号の説明】
１（１Ａ，１Ｂ）…可変光減衰器、２…軸部材、３…遮蔽部、３ａ…エッジ、５…軸受部材、６…サーボモータ、７…制御回路、８…遮蔽板、８ａ…エッジ、Ｌ１−Ｌ１…光軸、Ｌ２−Ｌ２…回転軸。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable optical attenuator that attenuates a predetermined amount of light incident from an optical fiber and adjusts and outputs the light intensity. In particular, the present invention can always provide stable attenuation characteristics even for high-power optical input. The present invention relates to a variable optical attenuator.
[0002]
[Prior art]
Conventionally, a rotary attenuator is known as a variable optical attenuator that adjusts the intensity of light incident from an optical fiber. This rotary type attenuation plate is a plate in which a metal film is applied to the surface of a disk that is rotatably supported. The metal film is formed into a thin film by vapor deposition so that the concentration gradually changes in the circumferential direction that is the rotation direction with respect to the surface of the disk on which light is incident.
[0003]
In the rotary attenuation plate having the above-described configuration, the disk is rotated in one direction with respect to the light emission position of the optical fiber to the position of the metal film where a desired attenuation is obtained. Thereby, the light incident from the optical fiber is attenuated by the metal film on the disk, and the attenuated light is transmitted through the disk and emitted.
[0004]
However, the above-described conventional rotary attenuation plate cannot cope with light incident from an optical fiber having high power. That is, when high power light is incident on the attenuation plate, a part of the light is absorbed by the metal film. However, since the metal film is formed as a thin film by vapor deposition, the absorbed heat cannot be dissipated, and a part of the metal film evaporates due to the heat. Moreover, since the metal film not only absorbs heat but is always exposed to the outside air, the surface of the metal film is oxidized. As a result, the amount of attenuation of light incident from the optical fiber changes, and a desired amount of attenuation cannot be obtained.
[0005]
Therefore, a variable optical attenuator as shown in FIG. 9 has been proposed as a variable optical attenuator that does not change the attenuation performance due to heat generation as in the conventional rotary attenuation plate described above and can cope with high-power optical input.
[0006]
A variable optical attenuator 51 shown in FIG. 9 physically blocks light incident from an optical fiber. In the variable attenuator 51, a linear through hole 53 is formed between a side surface 52a and a side surface 52b of the rectangular main body 52 facing each other. A pair of optical fibers 54 (54 a, 54 b) are attached to both side surfaces 52 a, 52 b of the main body 52 so as to face the through hole 53. The through hole 53 forms an optical path of the pair of optical fibers 54a and 54b. A screw hole 55 is formed on the upper surface 52 c of the main body 52 so as to communicate with the through hole 53 in a direction orthogonal to the through hole 53. A screw 56 is attached to the screw hole 55 so that the tip part moves forward and backward with respect to the through hole 53.
[0007]
In the variable optical attenuator 51 having the above-described configuration, the screw 56 is rotated by a predetermined amount so that the tip of the screw 56 enters the through hole 53 (optical path). The amount of attenuation of light incident from the optical fiber 54 a is determined by the amount of penetration of the tip of the screw 56 into the through hole 53. When the amount of attenuation of light is determined by adjusting the screw 56, the light incident from the optical fiber 54 a is blocked by the tip of the screw 56 protruding into the through hole 53 and attenuated, and this attenuated light is The light is emitted from the optical fiber 54b.
[0008]
[Problems to be solved by the invention]
In the conventional variable optical attenuator 51 shown in FIG. 9, the through hole 53 forms an optical path of incident light from the optical fiber 54 a, and the screw 56 rotates so that the screw 56 advances and retreats with respect to the through hole 53. Moving. For this reason, there is a predetermined amount of play between the screw 56 and the screw hole 55. Therefore, the screw 56 itself is rattled, and the screw 56 itself is eccentric as the screw 56 rotates, causing blurring. As a result, there has been a problem that the attenuation amount of incident light changes unstably and a loss fluctuation occurs.
[0009]
In addition, in the variable optical attenuator 51 of FIG. 9, the movement amount of the screw 56 changes linearly with respect to the rotation amount of the screw 56. On the other hand, the light incident from the optical fiber 54a is Gaussian beam light that has a strong light quantity at the center and becomes weaker toward the outside. In general, the light intensity distribution of a semiconductor laser incident on this type of variable optical attenuator 51 is a Gaussian distribution as shown in FIG. When the amount of attenuation is expressed in decibel [dB], when the amount of movement of the screw 56 is constant, the rate of change in attenuation with respect to the amount of rotation of the screw 56 increases as the amount of attenuation increases. For this reason, when the amount of attenuation is large, a high resolution is required. With a certain amount of movement by the screw 56, it is not possible to set a small amount of attenuation, for example, every 0.01 dB.
[0010]
As described above, in the variable optical attenuator 51 of FIG. 9, even if the screw 56 is slightly rotated, the amount of attenuation of incident light changes greatly, and the incident per rotation of the screw when the screw 56 is rotated. Light attenuation is different. As a result, there is a problem that it is difficult to obtain a desired attenuation and reproducibility cannot be obtained.
[0011]
Furthermore, in the variable optical attenuator 51 of FIG. 9, the screw 56 itself for adjusting the attenuation may be distorted due to the ambient temperature. For this reason, there has been a problem that a stable attenuation cannot always be obtained and the reproducibility is deteriorated.
[0012]
Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a variable optical attenuator that can obtain a stable attenuation performance with respect to high-power incident light.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 is directed to a variable optical attenuator 1 for attenuating incident light by a predetermined amount and adjusting and outputting the intensity of light.
At least one end is arranged substantially perpendicular to the optical path of the rotatably supported by the incident light by the bearing member 5, the portion of the cylindrical rod-like, continuous passage of the beam of the incident light according to the rotation of its the shaft member 2 having a shielding portion 3 variable for,
Drive control means 6 and 7 for controlling the rotational movement amount of the shaft member ;
A plate portion and a protruding portion 8a protruding in parallel with the surface of the plate portion from the plate portion, and comprising a shielding plate 8 attached to the shaft member ,
The shielding portion is formed by integrally forming the cylindrical rod-shaped portion by partially cutting the cylindrical rod-shaped portion of the shaft member by 3/4 in a sectional fan shape, and the notched portion has two planes. And the ridgeline where the two planes intersect is coincident with the central axis of the shaft member,
The shielding plate is attached on one plane 3c of the two planes so as to project a predetermined amount outwardly in the radial direction of the shaft member from the ridge line on the optical path of the incident light,
When the shaft member rotates by a predetermined amount, the projecting portion shields the central portion of the beam having a high light intensity of the incident light, and the change in light attenuation accompanying the rotation of the shaft member is reduced. It is characterized by that.
[0014]
The invention of claim 2 provides the variable optical attenuator of claim 1,
The protruding portion 8a has an isosceles triangular shape .
[0015]
The invention of claim 3 is the variable optical attenuator of claim 1 ,
The shape of the protrusion 8a is a semicircular curved surface .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a variable optical attenuator according to the present invention, and FIG. 2 is a partially enlarged view of a shielding portion of the variable optical attenuator in FIG. It is a figure which shows a relationship.
[0017]
The variable optical attenuator of the present invention described below is disposed between a pair of optical fibers, for example, and adjusts the light incident from the optical fiber on the input side by attenuating to a desired value. Light is output from the optical fiber on the output side.
[0018]
The variable optical attenuator 1 (1A) of 1st Embodiment has the cylindrical rod-shaped shaft member 2, as shown in FIG. The shaft member 2 is disposed substantially perpendicular to the optical path of incident light from the optical fiber (for example, parallel light by laser light having a beam diameter of about 1 mm), and is orthogonal to the optical axis L1-L1 of the incident light on the same plane. It is possible to rotate in the direction to do.
[0019]
A shield 3 is integrally formed on the optical path of the incident light at a midway position of the shaft member 2. The shielding part 3 in FIG. 1 is integrally formed with the cylindrical part of the central part of the shaft member 2 being cut out by 3/4 in a sectional fan shape so that incident light passes through the vicinity of the rotation axis L2-L2 of the shaft member 2. The The shielding portion 3 has a flat edge (ridge line) 3a that is orthogonal to the optical axis L1-L1 of incident light and is parallel to the rotation axis L2-L2 of the shaft member 2. When the shaft member 2 rotates in the direction of arrow A in FIG. 1, the shielding unit 3 shields incident light by a predetermined amount along with the rotation of the shaft member 2 by the plane 3 b including the edge 3 a.
[0020]
The shielding unit 3 allows all incident light from the optical fiber to pass through without being attenuated by the plane 3b including the edge 3a in a state where the shaft member 2 is in the initial position (the state of FIG. 1). Then, by the plane 3b including the edge 3a of the shielding part 3, incident light is blocked by a predetermined amount as the shaft member 2 rotates, and the incident light is attenuated by a predetermined amount. As described above, the shielding unit 3 continuously varies the amount of incident light passing through the shaft member 2 according to the rotation of the shaft member 2.
[0021]
The shaft member 2 is rotatably supported at both ends by a bearing member 5 such as a bearing with respect to the U-shaped support member 4 in order to reduce mechanical errors (backlash) due to shaft runout during rotation. One end of the shaft member 2 is linked to a servo motor 6 as a driving means via a bearing member 5. The servo motor 6 is provided with a potentiometer (not shown) that outputs an electrical signal corresponding to the amount of rotation of the shaft member 2. The amount of rotation of the servo motor 6 is controlled by the control circuit 7. The control circuit 7 determines whether or not the shaft member 2 has been rotationally driven to a predetermined rotation angle based on an electric signal from the potentiometer, and sends a control signal (a signal corresponding to the rotation angle amount) to the servo motor 6 according to the determination result. The servo motor 6 is driven and controlled to rotate the shaft member 2 to a position where a desired attenuation is obtained.
[0022]
The shaft member 2 has an initial position in which all incident light from the optical fiber passes without being shielded by the shield 3 (the state shown in FIG. 1). The rotation axis L2-L2 of the shaft member 2 is a direction orthogonal to both the rotation axis L2-L2 and the optical axis L1-L1 of the incident light, and is away from the optical axis L1-L1 of the incident light. It is in a position shifted by a fixed amount. The rotation axis L2-L2 of the shaft member 2 in the example of FIG. 1 is at a position that is orthogonal to the optical axis L1-L1 on the same plane and is shifted downward by a predetermined amount from the optical axis L1-L1. The shaft member 2 rotatably supported in this way is rotationally driven to a predetermined rotational angle position by a servo motor 6 that is driven and controlled by a control signal from the control circuit 7.
[0023]
In this example, the servo motor 6 and the control circuit 7 (including a potentiometer (not shown)) constitute drive control means for controlling the rotational movement amount of the shaft member 2.
[0024]
In the variable optical attenuator 1 configured as described above, when the incident light from the optical fiber is attenuated and output, the shaft member 2 is driven at a predetermined rotation angle in one direction until a desired attenuation is obtained by driving the servo motor 6. Rotate to stop. Thereby, when the light from the optical fiber is incident in the vicinity of the rotation axis L2-L2 of the shaft member 2, the incident light is blocked by the plane 3b including the edge 3a of the shielding portion 3 of the shaft member 2, Attenuation is attenuated and output.
[0025]
Here, FIG. 3 shows a result of the attenuation amount change simulation with respect to the shaft rotation angle of the shaft member 2 when the shape of the edge 3a of the shielding portion 3 of the shaft member 2 is flattened. In FIG. 3, the change in attenuation with respect to the rotation angle of the shaft member 2 is indicated by a solid line, and the rate of change in attenuation with respect to the rotation angle of the shaft member 2 is indicated by a broken line.
[0026]
As is apparent from FIG. 3, in the variable optical attenuator 1A of the first embodiment, for example, when the rotation angle of the shaft member 2 exceeds 45 °, the attenuation changes at a rate of 2 dB with respect to the rotation angle 5 °. is doing. When the rotation amount of the shaft member 2 is constant, it can be seen that the rate of change of the attenuation amount with respect to the rotation angle of the shaft member 2 increases as the attenuation amount increases.
[0027]
Therefore, the variable optical attenuator 1A of the first embodiment is effective particularly when the incident light is attenuated by an attenuation amount that does not require high resolution.
[0028]
By the way, in the variable optical attenuator 1A of the first embodiment, since the shape of the edge 3a of the shielding portion 3 that shields incident light is flat, when the rotation amount of the shaft member 2 is constant, the attenuation amount increases. The rate of change in attenuation with respect to the rotation angle of the shaft member 2 increases. For this reason, when the amount of attenuation increases, a high resolution is required. However, depending on the amount of attenuation, the resolution of the servo motor 6 may be insufficient, and for example, a small amount of attenuation may not be set every 0.01 dB.
[0029]
Therefore, a variable optical attenuator 1B (1) according to the second embodiment of the present invention that solves the problems caused by the variable optical attenuator 1A according to the first embodiment will be described below.
[0030]
FIG. 4 is a diagram showing a schematic configuration of a second embodiment of a variable optical attenuator according to the present invention, and FIGS. 5A and 5B are a side view and a sectional view of a shielding portion of the variable optical attenuator in FIG. FIG. 6 is a partially enlarged view showing the positional relationship between the incident light and the shielding part.
[0031]
The variable optical attenuator 1B of the second embodiment has the same configuration as the variable optical attenuator 1A except that the shape of the edge 3a of the shielding part 3 is different. Therefore, in the variable optical attenuator 1B, the same components as those in the variable optical attenuator 1A are denoted by the same reference numerals, and detailed description thereof is omitted.
[0032]
As shown in FIG. 5B, the variable optical attenuator 1B of the second embodiment is provided with a shielding plate 8 on a plane 3c of the shielding unit 3 (a plane perpendicular to the plane 3b). The central portion of the shielding plate 8 has an edge 8a protruding in a triangular shape. 4 and 5 show an example of the edge 8a by an isosceles triangle, and FIG. 6 shows an example of the edge 8a by a right isosceles triangle. The shielding plate 8 is provided on the optical path of incident light from the optical fiber so that the edge 8a protrudes from the flat surface 3b of the shielding part 3 by a predetermined amount. In the shielding plate 8 in this example, when the shaft member 2 is rotated by 90 ° in the direction of arrow A from the state shown in FIG. 4, the triangular protruding edge 8a has a beam cross section of incident light as shown in FIG. It is provided on the flat surface 3c of the shielding part 3 so as to cover the central part of the lower half part.
[0033]
When the incident light from the optical fiber is attenuated and output, when the attenuation is low and does not require high resolution, the shaft member 2 is moved to the state shown in FIG. 6 and the arrow A in FIGS. 4 and 5B. The central portion having a high light intensity is shielded first by the tip of the triangular edge 8a of the shielding plate 8. And in the area | region where the attenuation amount with which high resolution is requested | required is large, the part with low light intensity distribution of incident light is shielded by the plane 3b of the shielding part 3 including the edge 8a. Thereby, the rate of change in attenuation by the shielding plate 8 accompanying the rotation of the shaft member 2 can be kept low.
[0034]
Moreover, the shielding part 3 provided with the shielding plate 8 has a part of the shaft member 2 cut away, the edge 8a of the shielding plate 8 is brought close to the rotation axis L2-L2 of the shaft member 2, and the rotation radius is reduced. Thereby, the displacement of the edge 8a with respect to the rotation angle of the servo motor 6 can be reduced to improve the resolution.
[0035]
Here, FIG. 7 shows the result of the attenuation amount change simulation with respect to the shaft rotation angle of the shaft member 2 when the shape of the edge 8a of the shielding plate 8 provided in the shielding portion 3 of the shaft member 2 is triangular. In FIG. 7, the change in attenuation with respect to the rotation angle of the shaft member 2 is indicated by a solid line, and the rate of change in attenuation with respect to the rotation angle of the shaft member 2 is indicated by a broken line.
[0036]
As is apparent from FIG. 7, in the variable optical attenuator 1B of the second embodiment, for example, when the rotation angle of the shaft member 2 exceeds 45 °, the ratio of the attenuation around 1 dB with respect to the rotation angle of 5 °. Has changed. It can be seen that the rate of change in attenuation is constant from the time when the rotation angle of the shaft member 2 exceeds about 60 °, and the change in attenuation with respect to the rotation angle of the shaft member 2 is small. That is, in the variable optical attenuator 1B of the second embodiment, the amount of attenuation change with respect to the rotation angle of the shaft member 2 is smaller than that of the variable optical attenuator 1A of the first embodiment described above.
[0037]
Therefore, the variable optical attenuator 1B of the second embodiment is particularly effective when attenuating incident light with an attenuation amount that requires high resolution.
[0038]
In addition, in the variable optical attenuator 1B of the second embodiment, the shielding plate 8 having the edge 8a protruding in a triangular shape is separated from the shielding portion 3 in terms of configuration, but the shielding plate 8 is not used. It is good also as the shielding part 3 which has the edge protruded in the triangle shape.
[0039]
Thus, in the variable optical attenuator 1 (1A, 1B) of each embodiment described above, the shaft member 2 having the shielding portion 3 (and the shielding plate 8) is provided on the optical path of the incident light. Is rotated by the servo motor 6. As a result, incident light passing through the vicinity of the shielding portion 3 is blocked according to the rotation of the shaft member 2, the amount of incident light passing through the beam is continuously varied, and the incident light is attenuated by a predetermined amount and output. Thus, unlike a conventional metal-deposited attenuation plate, there is no chemical change due to the influence of heat due to high power input, so there is little loss variation and it is possible to deal with incident light with high power input.
[0040]
Further, since the incident light is attenuated by the rotational movement of the shaft member 2, unlike the conventional variable optical attenuator 51 by linear movement as shown in FIG. 9, the operation of the servo motor 6 can be directly used without conversion. Thereby, the number of parts of the apparatus can be reduced and simplified.
[0041]
Furthermore, the shaft member 2 is supported by the bearing member 5 in addition to the simplification of the apparatus using the shaft member 2 that is rotationally driven by the servo motor 6. As a result, the mechanical error (backlash) of the apparatus can be reduced, loss fluctuation is small, and reproducibility and durability can be improved.
[0042]
In particular, according to the variable optical attenuator 1B of the second embodiment, since the shielding plate 8 having the triangular edge 8a is provided on the plane 3c of the shielding part 3, a low attenuation amount that does not require high resolution. In some cases, the central portion where the light intensity is strong is shielded first at the tip of the triangular edge 8a of the shielding plate 8. And in the area | region where the attenuation amount with which high resolution is requested | required is large, the part with low light intensity distribution of incident light is shielded by the plane 3b of the shielding part 3 including the edge 8a. Thereby, the rate of change in attenuation by the shielding plate 8 accompanying the rotation of the shaft member 2 can be kept low. At this time, the amount of light to be blocked can be changed with the rotation of the shaft member 2 without shifting the positional relationship between the incident light and the shaft member.
[0043]
By the way, in the variable optical attenuator 1B of the second embodiment, the shape of the edge 8a of the shielding plate 8 provided on the flat surface 3c of the shielding portion 3 is a shape other than a triangular shape, for example, a curved shape such as a semicircular shape. You can also.
[0044]
Moreover, although variable optical attenuator 1A, 1B of each embodiment mentioned above is set as the structure by which the both sides of the shaft member 2 were supported by the bearing member 5 with respect to the support member 4, only the one side of the shaft member 2 is supported. The member 4 may be supported by the bearing member 5. For example, as shown in FIG. 8, only one side of the shaft member 2 may be supported by the bearing member 5 with respect to the support member 4, and the shaft member 2 may be linked to the servo motor 6 via the bearing member 5. In addition, in FIG. 8, it can also be set as the structure without the shielding board 8. FIG.
[0045]
Furthermore, the shaft member 2 of the variable optical attenuators 1A and 1B of each embodiment is not particularly limited to a cylindrical shape as long as incident light can be gradually attenuated with its rotation.
[0046]
【The invention's effect】
As apparent from the above description, according to the variable optical attenuator of the present invention, when the shaft member rotates by a predetermined amount, the projecting portion shields the central portion of the beam having a high light intensity of the incident light, and the shaft Since the change in light attenuation associated with the rotation of the member is small , when the attenuation is low and high resolution is not required, the central part where the light intensity is strong is shielded first at the tip of the protruding part of the shielding part. In a region where the amount of attenuation requiring a high resolution is large, the low light intensity distribution portion of the incident light is shielded. Thereby, the attenuation change rate by the shielding part accompanying rotation of a shaft member can be suppressed low. At that time, the amount of light to be blocked can be changed with the rotation of the shaft member without shifting the positional relationship between the incident light and the shaft member.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a variable optical attenuator according to a first embodiment of the present invention. FIG. 2 is a partial enlarged view of a shielding part of the variable optical attenuator in FIG. FIG. 3 is a diagram showing the positional relationship. FIG. 3 is a diagram showing a simulation result of attenuation change with respect to the shaft rotation angle of the shaft member when the edge shape of the shielding portion is flattened in the variable optical attenuator of FIG. The figure which shows schematic structure of 2nd Embodiment of the variable optical attenuator by invention FIG. 5: (a), (b) The side view and sectional drawing of the shielding part of the variable optical attenuator in FIG. FIG. 7 is a partially enlarged view showing the positional relationship between incident light and the shielding portion in the variable optical attenuator 4. FIG. 7 shows the axial rotation of the shaft member when the edge shape of the shielding portion is triangular in the variable optical attenuator in FIG. The figure which shows the result of the attenuation amount change simulation with respect to an angle. Figure 9 [EXPLANATION OF SYMBOLS] illustrates the light intensity distribution of the conventional variable optical attenuator sectional view schematically showing the structure of Figure 10. The semiconductor laser shown a modification of that variable optical attenuator
DESCRIPTION OF SYMBOLS 1 (1A, 1B) ... Variable optical attenuator, 2 ... Shaft member, 3 ... Shielding part, 3a ... Edge, 5 ... Bearing member, 6 ... Servo motor, 7 ... Control circuit, 8 ... Shielding plate, 8a ... Edge, L1-L1 ... optical axis, L2-L2 ... rotation axis.

Claims

In a variable optical attenuator (1) that attenuates incident light by a predetermined amount and adjusts and outputs the intensity of light,
At least one end is rotatably supported by the bearing member (5) and is arranged substantially perpendicular to the optical path of the incident light. The cylindrical bar-shaped portion and the amount of the incident light beam that pass through the rotation of the cylindrical bar are continuous. variable shielding portion (3) and the shaft member (2) having a basis,
Drive control means (6, 7) for controlling the rotational movement amount of the shaft member ;
A plate portion and a protruding portion (8a) protruding in parallel with the surface of the plate portion from the plate portion, comprising a shielding plate (8) attached to the shaft member ;
The shielding portion is formed by integrally forming the cylindrical rod-shaped portion by partially cutting the cylindrical rod-shaped portion of the shaft member by 3/4 in a cross-sectional fan shape, and the notched portion has two planes. And the ridgeline where the two planes intersect is coincident with the central axis of the shaft member,
The shielding plate is attached on one plane (3c) of the two planes so as to project a predetermined amount outward from the ridge line in the radial direction of the shaft member on the optical path of the incident light,
When the shaft member rotates by a predetermined amount, the projecting portion shields the central portion of the beam having a high light intensity of the incident light, and the change in light attenuation accompanying the rotation of the shaft member is reduced. A variable optical attenuator characterized by that.

The variable optical attenuator according to claim 1, wherein the shape of the projecting portion (8a) is an isosceles triangle .

The shape of the protruding portion (8a) is variable optical attenuator of claim 1 Symbol mounting characterized in that it is a semi-circular curved shape.