JP3591174B2 - Nonlinear optical element and method of manufacturing the same - Google Patents

Description

【００３２】
【化２】

【００３３】
ところでＧｅＥ´センタの生成に関しては、前述のＮＯＶによる構造変化だけでなく、高光子密度の紫外光によって４配位Ｇｅの電子捕獲中心（ＧＥＣ）への変化を経て、さらにその一部がＧｅＥ´センタに構造変化するという過程や、＝Ｇｅ: の構造をもつＧＬＰＣと水素分子Ｈ_２との反応によって、ＮＯＶへの構造変化を経由してＧｅＥ´センタが生成するという過程も存在すると考えられる。ＧｅＥ´センタは６．３ｅＶ帯に吸収ピークをもち、吸収帯の変化に従って屈折率が増加する。このＧｅＥ´センタが生成される現象は、現在光誘起により光ファイバ等にグレーティングを書き込むことに広く利用されている。
【００３４】
本発明はＧｅＥ´センタの存在よりも、むしろ同時に生成される電気双極子の生成に着目しこれを利用するものである。
【００３５】
しかしながらＧｅＥ´センタ生成過程において、ＧｅＥ´センタと電気双極子とは対をなして生成されるので、結果として誘起される非線形光学効果はＧｅＥ´センタの濃度に比例することになる。
【００３６】
本発明は、以上のような電気双極子生成のメカニズムを利用し、最も効率よく非線形光学効果を誘起するものである。そのための着眼のポイントを以下に述べる。
【００３７】
まず、ＮＯＶやＧＬＰＣの酸素欠乏欠陥そのものの絶対量を増加させる必要がある。次にＧｅＥ´センタへの構造変化を促進し電気双極子の生成効率を高めなければならない。そして電気双極子の生成と同時に強力な外部電場により規則的な電気双極子の配向性により光学的異方性を誘起させることが重要である。
【００３８】
このような観点から本発明が提案されたのである。
【００３９】
酸素欠乏欠陥の絶対量はＧｅの濃度だけでなく、ガラスの製法によっても大きく異なる。ＧｅＯ_２を含有したＳｉＯ_２をターゲットとした高周波スパッタリング法によって形成したＧｅドープＳｉＯ_２ガラス膜は、電子ビーム蒸着やガラスの微粒子を溶融させて形成する方法よりも酸素欠乏欠陥が多く含まれていることが分かった。また波長５５０ｎｍ以下の励起光をＧｅドープＳｉＯ_２ガラス膜の近傍から照射したり、導波構造をとるコア領域内を伝搬させることにより高エネルギー密度を実現し、電気双極子の発生効率を高めることができる。また前述のようにＧＬＰＣとＨ_２との反応によってもＧｅＥ´センタと電気双極子とが生成されるので、この反応を促進させるために高温或いは高圧水素雰囲気中に光導波路を一定時間保持する工程、或いは光導波路の少なくとも一部を酸水素バーナで炙る工程を経て、直流高電圧の電場を印加すると同時にコア領域に励起光を照射するか或いはコア領域内に伝搬させてもよい。
【００４０】
電気双極子の規則的な配向性を高めるため、本発明では光導波路に印加する直流高電圧の電場の方向とコア領域に照射されるか或いはコア領域内を伝搬する励起光の電界の偏光方向が略平行になるようにした。また直流高電圧の電場の印加及び励起光の照射と同時に、基板を高温状態に保持し、これにより電気双極子の配向を促進させている。
【００４１】
【発明の実施の形態】
以下、本発明の実施の形態を添付図面に基づいて詳述する。
【００４２】
図１は本発明の非線形光学素子の製造方法の一実施の形態を示す概念図である。
【００４３】
非線形光学素子としての光導波路１１は、石英基板１２の上に形成されＧｅがドープされたＳｉＯ_２ガラスからなるコア領域１３と、コア領域１３より低い屈折率を有しコア領域１３を囲むクラッド領域１４とで構成されている。
【００４４】
コア領域１３は、ＧｅＯ_２を含有したＳｉＯ_２をターゲットとして高周波スパッタリング法によって石英基板１２上に形成されたコア膜がホトリソグラフィ法によって導波路のパターニングが行われ、ＣＨＦ_３ガスを用いた反応性イオンエッチング法により矩形断面形状に形成されたものである。
【００４５】
クラッド領域１４は、火炎堆積法でコア領域１３が形成された後、石英基板１２の上全体に火炎加水分解反応によりＳｉＯ_２にＰ（リン）とＢ（ホウ素）とを添加したガラス微粒子が堆積され、石英基板１２ごと１３００℃の高温で焼結されて、微粒子が透明ガラス化されたものである。
【００４６】
ＰをＳｉＯ_２に添加するとＳｉＯ_２の屈折率が高くなり、ＢをＳｉＯ_２へ添加すると逆にＳｉＯ_２の屈折率が低くなる。ＰとＢとの量を調整することによりクラッド領域１４の屈折率は石英基板１２の屈折率と略等しくなる。本実施の形態においては、コア領域１３の断面寸法を約５×５μｍとし、コア領域１３とクラッド領域１４との比屈折率差を０．８％とした。
【００４７】
このようにして形成されたクラッド領域１４の表面にコア領域１３を挟むように両側に一対の電極１５，１６を形成した。
【００４８】
これら二つの電極１５，１６を直流高電圧電源１７に接続すると、電場が光導波路１１のコア領域１３に対して横方向に発生する。電場の発生と同時にコア領域１３及び電場に対し交差する方向（図では上方から）に励起光を矢印Ａ方向に照射することにより、光導波路１１のコア領域１３に光学的異方性領域が形成される。
【００４９】
励起光は、図示しないシリンドリカルレンズにより線状に集光されコア領域１３の長手方向にわたって照射される。尚、励起光をレンズによって集光し得られた円形ビームを、コア領域１３の長手方向に走査させながら照射しても特定の長さの光学的異方性領域がコア領域１３の内部に形成される。本実施の形態では電極１５，１６によってコア領域１３に印加される電場の強さを約１０^６〜１０^７Ｖ／ｃｍとした。
【００５０】
直流高電圧の印加と同時にコア領域１３に照射される励起光には、１００〜２００ｍＪ、１０ｐｐｓのＫｒＦエキシマレーザが用いられ、その照射時間は２０〜３０分間とした。尚、励起光は、これに限定されず、波長５５０ｎｍ以下のＨｇランプ光、Ａｒレーザ、ＡｒＦエキシマレーザ、Ａｒレーザ、色素レーザの第二高調波或いはＮｄ3⁺：ＹＬＦレーザの第四高調波によっても同様な非線形光学効果が得られる。
【００５１】
ここで、低エネルギーのＨｇランプ励起の場合は、１光子吸収過程により酸素欠乏欠陥ＮＯＶがＧｅＥ´に構造変化し、Ａｒレーザ励起の場合は同様の構造変化が２光子吸収過程によって行われると考えられる。また、エキシマレーザ等の高エネルギー密度の紫外励起光照射の場合には、２光子吸収過程による無欠陥構造のＧＥＣへの変化と、さらにその一部がＧｅＥ´センタに変化する２段階反応も寄与していると考えられる。
【００５２】
また、この励起光照射のときの電気双極子の配向性を高めるために、励起光の電界の偏光方向が直流高電圧電場の電気力線と略平行になるようにした。さらにポーリング処理時、すなわち直流高電圧の印加と同時に行われる励起光照射の間（２０〜３０分間）は、石英基板１２全体を約３００℃に保持することによってもコア領域１３に誘起される光学的異方性が増強される傾向が見られ、ポーリング処理時の高温保持も有効である。
【００５３】
また電気双極子の生成過程の効率を高めるために、直流高電圧電場を発生させると同時に光導波路１１内のコア領域１３に励起光を照射する工程の前処理として、高温或いは高圧水素雰囲気に光導波路１１を石英基板１２ごと一定時間保持する工程、或いは光導波路１１の少なくとも一部を酸水素バーナによって炙る工程を経ても光学的異方性が増強される効果がみられる。これは前述のようにＧＬＰＣと水素分子との反応によってＧｅＥ´センタが生成するという過程が促進されるためと考えられる。
【００５４】
尚、本実施の形態ではコア領域１３が前述のようにＧｅＯ_２をターゲットとした高周波スパッタリング法により形成されている。コア領域１３を形成するためのＧｅドープＳｉＯ_２層は、本実施の形態のようなスパッタリング法だけでなく、電子ビーム蒸着法や火炎堆積法を用いて形成してもよい。しかし、コア領域１３内の欠陥の量はコア層の形成方法に大きく依存するので、検討の結果、本実施の形態で採用した高周波スパッタリング法が最も有効であることが分かった。
【００５５】
図１に示した実施の形態では励起光としてエネルギー密度の高いＫｒＦエキシマレーザを用いた。レーザ光は主にコア領域に照射されるが、その一部は電極１５，１６にも照射されるので、電極１５，１６が熱的な損傷を受けるおそれがある。この熱的な損傷を防止するため電極の材料としてアルミニウムを採用した。エキシマレーザの波長帯での金属の反射率は、例えば金を材料とした場合では約３２．９％であるのに対し、アルミニウムを材料とした場合では約９２．４％と非常に高く、金属材料の中ではアルミニウムが吸収による熱的損傷が最も起こりにくい。尚、電極１５，１６の材料としては、アルミニウムのように反射によって熱的損傷を防止する以外に、ＩＴＯ(indium-tin-oxide)等の透明電極材料を用いても励起光照射による電極１５，１６の損傷を防止するのに有効である。
【００５６】
図１に示した電極１５，１６は、コア領域１３に光学的異方性領域を形成するために使用した高電圧印加用の電極であるが、これはそのまま直流高電圧電源１７を適当な制御用電源に取り替えれば、光導波路１１のコア領域１３を伝搬する導波光を高速で制御する駆動電極として使用することができる。
【００５７】
図２は、本発明の非線形光学素子の製造方法の他の実施の形態を示す概念図である。
【００５８】
図１に示した実施の形態との相違点は、クラッド領域２２の形状が台形断面形状となっており、クラッド領域２２の両斜面上に電極２３，２４が形成されている点であり、非線形光学効果の誘起効率、或いは導波光を制御するための駆動電圧印加効率をさらに向上させることを目的としたものである。
【００５９】
光導波路２１は、図１に示した光導波路１１と同様に、屈折率の高いＧｅドープのＳｉＯ_２ガラスからなるコア領域１３と、このコア領域１３を囲む屈折率の低いクラッド領域２２とで構成されている。コア領域１３を囲む周辺のクラッド領域２２の断面形状は側面が傾斜をもった台形形状をなし、この傾斜した側面上に非線形光学効果を誘起させるための高電圧印加用の電極２３，２４が形成されている。
【００６０】
ポーリング処理時の励起光の照射方法等は図１に示した場合と同様に、電極２３，２４間に直流高電圧を印加すると同時に矢印Ｂ方向に励起光を照射することである。コア領域１３を囲む周辺のクラッド領域２２の断面形状を側面が傾斜をもった台形状にするためには、図１に示した実施の形態と同様に火炎堆積法により平坦なクラッド層を形成した後、コア領域１３の上部をマスクし、例えば反応性イオンエッチング等を用いることにより形成できる。コア領域１３を囲むクラッド領域２２の側面の傾斜角度はマスクのサイドエッチングによって異なるが、マスクの材料或いはエッチング条件によって決定される。台形断面形状のクラッド領域２２の形成方法は、平坦化に適した火炎堆積法及びエッチング加工を用いる以外にも、例えばバイアススパッタリング法を用いても可能である。バイアススパッタリングは火炎堆積法よりも平坦化作用は小さく、ＳｉＯ_２をコア上部に堆積させるだけで直接図２に示したような形状を形成することができる。同図に示したような構造は、ポーリング処理時に非線形光学効果の誘起効率を高めるだけでなく、高電圧印加用の電極２３，２４をそのまま導波光を制御するための駆動電極として使用すれば、より小さな電圧で導波光を制御することができる。
【００６１】
図１及び図２に示した実施の形態では、直流高電圧の電場が印加され、同時に励起光が光導波路１１（２１）のコア領域１３に対して交差する方向（図では上部方向）から照射する場合で説明したが、これに限定されず励起光をコア領域１３内に伝搬させてもよい。
【００６２】
尚、励起光としてエキシマレーザを用いたが、これに限定されず、波長約４８８ｎｍのＡｒレーザを導波路に入射してもよい。図１或いは図２に示したように励起光を導波路と交差する方向に照射する方法では、Ａｒレーザの方がより高光エネルギーを有するエキシマレーザよりも非線形光学効果を誘起する効率は小さい。
【００６３】
しかし、光導波路１１（２１）のコア領域１３内を励起光が伝搬すれば、その光エネルギー密度は数ＭＷ／ｃｍ^２にも達するため、２光子吸収過程によって高い効率で光学的異方性領域を誘起できる。但し、この場合も光導波路１１（２１）のコア領域１３に伝搬される励起光の電界の偏光方向が、直流高電圧の電場の方向と平行になるようにした方が非線形光学効果の誘起効率を高めることができる。
【００６４】
図３は本発明の非線形光学素子の製造方法の他の実施の形態を示す概念図である。
【００６５】
図１に示した実施の形態との相違点は、直流高電圧が石英基板１２の厚さ方向に印加され、直流高電圧電場と交差する方向の励起光がコア領域１３に照射される点である。
【００６６】
石英基板１２、コア領域１３及びクラッド領域３１からなる光導波路３２の石英基板１２の上部及び下部に電極３３，３４が形成され、石英基板１２の厚さ方向（図では上下方向）に直流高電圧を印加すると同時にコア領域１３へコア領域１３の長手方向と交差する方向（図では矢印Ｃ方向）に励起光が照射される。このような構造のため光導波路３２に電極を形成するのが容易となる。尚、一般に、二つの電極間に直流高電圧を印加してポーリング処理する場合、陽極側の方が光学的異方性領域を形成しやすいことが知られている。そのため図３に示す実施の形態ではコア領域１３の真上にある電極３３が陽極側になるように設定されている。照射される励起光の電界の方向は、前述と同様に印加される直流高電圧電場の電気力線の方向と平行になるように設定されている。電極３３，３４の材料としてはアルミニウムが用いられる。
【００６７】
この光導波路３２の場合、図１に示した実施の形態のように励起光をコア領域１３の上方から照射することはできない。そのため図３に示すようにコア領域１３の側面から励起光を照射しているが、光導波路３２の側面とコア領域１３との間の距離Ｌが長いと、励起光が側面からコア領域に達するまでにビーム径が拡がってしまい高いエネルギー密度で照射できないことがある。
【００６８】
そこで、光導波路を細長く切断し、側面からの照射でも十分コア領域１３に励起光が照射されるようにしているが、回路構成によっては側面からの効率よい照射は難しい場合がある。このような場合には電極３３，３４としてＩＴＯ等の透明電極を用いることにより、励起光を透明電極を透過してコア領域１３の上方から効率よく照射することができる。
【００６９】
尚、励起光をコア領域１３の側面から照射する代わりに、コア領域１３に直接入射して長手方向に伝搬させてもよい。
【００７０】
また、基板として石英基板を用いたが、これに限定されず低抵抗半導体基板を用いてもよい。低抵抗半導体基板を用いる場合には、電極を光導波路の表裏に形成し、厚さ方向に直流高電圧電場を印加すればよい。この場合、半導体基板は低抵抗であるため陰極として機能し、図３に示すような電極３４を基板裏面にわざわざ設ける必要はない。
【００７１】
さらに基板に低抵抗Ｓｉ基板を用いた場合には、Ｓｉ基板上に熱酸化或いはスパッタリングによってＳｉＯ_２膜をバッファ層（下部クラッド層）として形成するのが好ましい。コア領域１３はバッファ層の上に形成され、それ以外の構造は図３と同様である。Ｓｉ基板による導波光の吸収が無視できるように、バッファ層の厚さは約２０μｍが好ましい。励起光は図３と同様コア領域の側面から照射する。或いはコア領域の上側の電極に透明電極を用いれば、コア上部からも励起光を照射することができる。図３に示した実施の形態では石英基板を用いているため、電極３３と電極３４との間隔は大きい。そのためコア領域１３内に大きな電場を印加するには、両電極３３，３４間に非常に高い直流電圧を印加しなければならない。これに対し、低抵抗半導体基板を陰極として用いれば、コア領域１３の上側の電極と陰極（低抵抗基板）との間隔は数十μｍ程度に接近するので、より低い電圧の電源を用いてもコア領域１３に大きな電場を印加することができる。基板に低抵抗半導体基板を用い、この低抵抗半導体基板を陰極とすることは、コア領域１３に光学的異方性領域を誘起するポーリング処理の時だけでなく、導波光を制御する場合にも低い駆動電圧で動作するので有利である。
【００７２】
図４は本発明の非線形光学素子の一例を示す概念図であり、電気光学効果を用いたＭａｃｈ−Ｚｅｈｎｄｅｒ型の光変調器４１を示したものである。
【００７３】
光変調器４１は、石英基板４２上にコア領域４３が形成され、コア領域４３を囲むようにクラッド領域４４が形成されている。導波光の入力側及び出力側にそれぞれＹ分岐４５，４６が形成されている。矢印Ｄ方向に入射する導波光は入力側のＹ分岐４５で２等分され、同じ長さの２本の導波路アーム４７，４８を伝搬するようになっている。
【００７４】
クラッド領域４４上の一方の導波路アーム４７の両側にはこの導波路アーム４７を挟んで二つの電極４９，５０が形成され、交流電源５１と接続されている。導波路アーム４７内を伝搬する導波光は交流電圧の電場によって位相変化を受ける。この導波光を出力側のＹ分岐４６で他方の導波路アーム４８を伝搬してきた参照導波光と合波・干渉させることにより、両導波光の位相差に対応して出力強度が変化して矢印Ｅ方向に出射する。
【００７５】
ここで光変調器４１に入射する導波光の偏光は、交流電場の方向と平行になるようにする。尚、位相変化を生じさせるための電極４９，５０は、両電極４９，５０で挟まれた導波路アーム４７のコア内に光学的異方性領域を誘起させるポーリング処理時に使用した電極をそのまま使用することができる。ポーリング処理時には電極４９，５０間に図には示されない直流高電圧電源が接続され、数百〜数ＫＶの高電圧が印加される。これに対し導波光の伝搬を制御し変調器として動作させるには、数Ｖの交流電源を接続すれば十分である。
【００７６】
以上において本発明によれば、従来微弱な非線形光学効果しか実現されていなかったＧｅドープのＳｉＯ_２ガラスにおいて、非常に大きな光学的異方性領域を効率的に誘起できる。これにより、電気光学効果や第２高調波発生等の非線形光学効果を利用した光のスイッチング、変調、波長変換等の各種機能を石英系の平面光回路内部に集積できる。その結果、低損失で信頼性が高く小型で駆動エネルギーの小さい機能性光素子が実現できる。
【００７７】
【発明の効果】
以上要するに本発明によれば、次のような優れた効果を発揮する。
【００７８】
光導波路と交差するように外部から直流高電圧の電場を印加すると同時に電場及び光導波路と交差するように波長５５０ｎｍ以下の励起光を照射することにより、光導波路のコア領域に光学的異方性領域が形成され、低損失で信頼性が高く小型で駆動エネルギーの小さい非線形光学素子及びその製造方法の実現を提供することができる。
【図面の簡単な説明】
【図１】本発明の非線形光学素子の製造方法の一実施の形態を示す概念図である。
【図２】本発明の非線形光学素子の製造方法の他の実施の形態を示す概念図である。
【図３】本発明の非線形光学素子の製造方法の他の実施の形態を示す概念図である。
【図４】本発明の非線形光学素子の一例を示す概念図である。
【符号の説明】
１１ 光導波路
１２ 基板（石英基板）
１３ コア領域
１４ クラッド領域
１５，１６ 電極
１７ 直流高電圧電源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nonlinear optical element and a method for manufacturing the same.
[0002]
[Prior art]
With the development of the fields of communication, measurement and information processing using light, highly functional and highly reliable SiO₂-GeO₂There is a demand for the development of an optical element using glass and an optical element having nonlinear characteristics such as an electro-optic effect and second harmonic generation. In particular, a waveguide-type optical element using a quartz-based material has received the most attention because it has the possibility of forming a complicated circuit on a flat substrate in addition to its low loss.
[0003]
In these waveguide type optical elements, a light propagation region called a core having a relatively high refractive index is formed on a Si substrate having a low refractive index layer called a buffer layer (lower cladding layer) or a quartz substrate. In general, the core portion is further covered with a low refractive index cladding layer. In particular, the material composition of the core portion is SiO 2 which has been proven as a low-loss core material for optical fibers.₂-GeO₂Composition glass is considered to be effective.
[0004]
By the way, in general, inorganic glass such as silica glass is an optically isotropic substance, and originally considered to have no nonlinear optical characteristics such as an electro-optic effect and second harmonic generation due to its inversion symmetry. I have been.
[0005]
However, recently, it has been revealed that even in such an optically isotropic glass material, a second-order optical nonlinearity is induced by performing the poling process.
[0006]
Here, the poling process is a process of applying a DC electric field to a sample, that is, a glass material in a high temperature state, keeping the electric field applied for a certain period of time, radiating heat, and releasing the DC electric field after the optical waveguide has dropped to room temperature. It is. The nonlinear optical effect of such a glass material has been confirmed in various glasses such as tellurite glass and phosphate glass in addition to silica glass.
[0007]
However, the mechanism of inducing the nonlinear optical effect by the poling process has not been elucidated in detail, and it is considered that there are some factors relating to the origin of the nonlinear optical effect. That is, it is considered that there are several different types of electric dipoles induced in the glass by the poling treatment depending on the structure, composition, poling treatment conditions and the like of the glass as follows.
[0008]
First, mobile proton ions (Na⁺), A cation-deficient region (space charge layer) near the anode is formed during the poling process, and this cation-deficient region may cause electric dipole orientation. In this case, only the surface layer several tens of μm on the anode side mainly becomes the optically anisotropic region.
[0009]
In contrast, electric dipoles generated by factors related to the presence of point defects, OH groups, non-crosslinking oxygen, and the like, if these factors are present in the entire optical waveguide, the electric dipole is applied to the entire optical waveguide by the poling process. Optical anisotropy is observed.
[0010]
New attempts to incorporate anisotropic features in such optically isotropic glass materials have attracted increasing academic and practical interest. Especially SiO₂Is a material that plays a central role in the current optoelectronics in terms of low loss and reliability, and the production technology for optical fibers and planar optical waveguides has already been established. In addition, silica glass has a particularly wide band gap and is a material that can be greatly expected in the future as an element in the ultraviolet region and the far ultraviolet region even in fields other than the communication field.
[0011]
[Problems to be solved by the invention]
However, in order to realize a practical optical device such as an optical modulator, an optical switch, or a wavelength conversion device, the nonlinear optical effect in glass materials reported so far is still weak. At the current level, for example, in order to perform an optical switching operation using the electro-optic effect, an element length (the length of the core region of the optical waveguide) is required to be several tens of cm, and a driving voltage for controlling the guided light is required. However, it is not practical because several hundred volts are required. LiNbO at least already in practical use as a nonlinear optical element₃It is desired to realize a nonlinear optical effect comparable to a ferroelectric material such as described above and to develop an optimum element.
[0012]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a small-sized nonlinear optical element having low loss, high reliability, small driving energy, and a method of manufacturing the same.
[0013]
[Means for Solving the Problems]
In order to solve the above-described problems, it is necessary to find optimal conditions from all viewpoints such as the composition of the glass material, the production method, the poling method, and the structure of the optical element.
[0014]
In view of this, the present invention provides a Ge-doped SiO.₂I focused on glass. As described above, this material has many excellent characteristics such as low loss, high reliability, and workability for element formation, and has already been put into practical use as a passive element for communication. If a nonlinear optical effect can be induced with high efficiency by using such a material, it can be applied to even more optical functional elements. Moreover, considering the mechanism of the nonlinear optical effect due to the poling process, it is found that Ge-doped SiO₂It has been found that glass has a larger nonlinear optical effect than other glass materials.
[0015]
That is, in order to achieve the above object, a method for manufacturing a nonlinear optical element according to the present invention uses a Ge-doped SiO 2 having a high refractive index on a substrate.₂Forming a core region made of glass,TheSurround the core region with a low refractive index cladding regionIsOptical waveguideOptical anisotropic regionFormationdidIn a method for manufacturing a nonlinear optical element,the aboveAn optically anisotropic region is formed in the core region by applying a DC high voltage electric field from the outside so as to cross the optical waveguide and irradiating excitation light having a wavelength of 550 nm or less so as to cross the electric field and the optical waveguide.At this time, the direction of deflection of the electric field of the excitation light was made substantially parallel to the direction of the electric field of the DC high voltage.Things.
[0016]
The method for manufacturing a nonlinear optical element according to the present invention includes the steps of:₂Forming a core region made of glass,TheSurround the core region with a low refractive index cladding regionIsOptical waveguideOptical anisotropic regionFormationdidIn a method for manufacturing a nonlinear optical element,the aboveAt the same time as applying a DC high voltage electric field from outside so as to cross the optical waveguideCore areaForming an optically anisotropic region in the core region by propagating excitation light having a wavelength of 550 nm or less withinAt this time, the direction of deflection of the electric field of the excitation light was made substantially parallel to the direction of the electric field of the DC high voltage.Things.
[0017]
The method for manufacturing a nonlinear optical element according to the present invention includes the steps of: ₂ A DC high voltage electric field is externally applied to an optical waveguide in which a core region made of glass is formed and the core region is surrounded by a cladding region having a low refractive index so as to intersect the optical waveguide. In a method for manufacturing a nonlinear optical element in which an optically anisotropic region is formed by irradiating the core region with light or by propagating the core region, the core region is formed by a high-frequency sputtering method.
[0018]
The method for manufacturing a nonlinear optical element according to the present invention includes the steps of: ₂ A DC high voltage electric field is externally applied to an optical waveguide in which a core region made of glass is formed and the core region is surrounded by a cladding region having a low refractive index so as to intersect the optical waveguide. In the method for manufacturing a nonlinear optical element in which an optically anisotropic region is formed by irradiating the core region with light or by propagating the core region, the substrate on which the optical waveguide is formed is heated in a high-temperature hydrogen atmosphere or a high-pressure hydrogen atmosphere. After maintaining in an atmosphere for a certain period of time or burning at least a part of the optical waveguide with an oxyhydrogen burner, applying an external electric field of DC high voltage and simultaneously irradiating the core region inside the optical waveguide with excitation light, or It is formed by propagating inside.
[0019]
In addition to the above structure, the method for manufacturing a nonlinear optical element according to the present invention includes locally heating the core region at a high temperature, applying an external electric field of a DC high voltage in a high temperature state, and simultaneously irradiating the core region with excitation light, or After a certain period of time, the heat is released, and after the temperature of the optical waveguide has dropped to room temperature, the electric field of DC high voltage is released and the irradiation of the excitation light is stopped, so that the optically anisotropic region is formed in the core region. Is preferably formed.
[0020]
In addition to the above structure, the method of manufacturing a nonlinear optical element according to the present invention is characterized in that the excitation light having a wavelength of 550 nm or less which is irradiated to the core region simultaneously with the application of the high-voltage DC electric field to the optical waveguide or propagates in the core region is Hg. Lamp light, Ar laser, ArF excimer laser, KrF excimer laser, second harmonic of Ar laser or dye laser or Nd^{3 +}: Preferably one of the fourth harmonics of a YLF laser.
[0021]
In addition to the above configuration, in the method for manufacturing a nonlinear optical element of the present invention, it is preferable that an electrode closer to the core region among the electrodes for applying a high DC voltage is used as the anode.
[0022]
In the above configurationIn addition, in the method for manufacturing a nonlinear optical element of the present invention, it is preferable to use aluminum or a transparent conductor as the material of the high voltage application electrode.
[0023]
In addition to the above configuration, the method for manufacturing a nonlinear optical element according to the present invention is configured such that at least one of the electrodes for applying a high voltage is a transparent electrode. Irradiation with excitation light is preferred.
[0024]
The present inventionIs a high refractive index Ge-doped SiO.₂A core region made of glass;TheWith a low refractive index cladding region surrounding the core regionOptically anisotropic region formed in optical waveguideIn a nonlinear optical element, at least one pairUsing aluminum or transparent conductorThe drive electrodes are formed on the same surface, and the drive electrodesDepartmentA field is applied in a direction crossing the optical waveguide to control the propagation of the guided light.
[0025]
The nonlinear optical element of the present invention has a high refractive index of Ge-doped SiO.₂A core region made of glass;TheWith a low refractive index cladding region surrounding the core regionOptically anisotropic region formed in optical waveguideIn nonlinear optical elements,the aboveThe cross-sectional shape of the peripheral cladding region surrounding the core region has a trapezoidal shape with inclined side surfaces, and at least a pair of drive electrodes are formed on the inclined side surfaces and intersect the optical waveguide by the drive electrodes. An external electric field is applied in the direction to control the propagation of the guided light.
[0026]
The nonlinear optical element of the present invention has a high refractive index of Ge-doped SiO.₂A core region made of glass;TheWith a low refractive index cladding region surrounding the core regionOptically anisotropic region formed in optical waveguideIn nonlinear optical elements,the aboveLow resistance semiconductor under the core areaLayerA transparent electrode or a metal electrode is formed above the core region, and an external electric field for controlling propagation of guided light is applied to the optical waveguide in the thickness direction.
[0027]
According to the present invention, it is possible to realize an optically anisotropic region having a large nonlinear optical coefficient in a glass waveguide. The mechanism is presumed as follows.
[0028]
As described above, a nonlinear optical effect is induced in various glass materials by performing poling. It is considered that the formation of different types of electric dipoles, such as mobile proton ions, point defects, OH groups, and non-crosslinked oxygen, is involved as the cause.
[0029]
SiO of the present invention₂-GeO₂The nonlinear optical effect in glass is mainly due to SiO₂-GeO₂It utilizes oxygen deficiency defects in glass.
[0030]
GeO₂Doped SiO₂Glass has two types of NOV (neutral oxygen vacancies) having absorption in the 5 eV band and oxygen deficiency defects called GLPCs (lone electron pairs of Ge). Among them, NOV is a defect having a structure represented by the following formula (1). When irradiated with ultraviolet light such as an excimer laser or blue-green light such as an Ar laser, a photochemical reaction represented by the following formula (2) proceeds and GeE A paramagnetic center called an 'center' and an electric dipole are simultaneously generated.
[0031]
Embedded image

[0032]
Embedded image

[0033]
Incidentally, regarding the formation of the GeE 'center, not only the above-mentioned structural change due to NOV, but also the change of the tetracoordinate Ge to an electron trapping center (GEC) due to the high photon density ultraviolet light, and a part of the GeE' center is further changed to GeE '. The process of structural change to the center, the GLPC having the structure of = Ge: and the hydrogen molecule H₂It is thought that there is also a process in which a GeE 'center is generated via a structural change to NOV by the reaction with The GeE 'center has an absorption peak in the 6.3 eV band, and the refractive index increases as the absorption band changes. The phenomenon that this GeE 'center is generated is now widely used for writing a grating in an optical fiber or the like by photo-induced light.
[0034]
The present invention focuses on the generation of an electric dipole generated at the same time, rather than the existence of a GeE 'center, and utilizes this.
[0035]
However, during the GeE 'center generation process, the GeE' center and the electric dipole are generated in pairs, so that the resulting nonlinear optical effect is proportional to the concentration of the GeE 'center.
[0036]
The present invention utilizes the mechanism of electric dipole generation as described above to induce the nonlinear optical effect most efficiently. The points of interest for that purpose are described below.
[0037]
First, it is necessary to increase the absolute amount of the oxygen deficiency defect itself of NOV or GLPC. Next, it is necessary to promote the structural change to the GeE 'center and increase the generation efficiency of the electric dipole. At the same time as the generation of the electric dipole, it is important to induce optical anisotropy by regular electric dipole orientation by a strong external electric field.
[0038]
The present invention has been proposed from such a viewpoint.
[0039]
The absolute amount of oxygen deficiency defects greatly varies not only with the Ge concentration but also with the glass manufacturing method. GeO₂Containing SiO₂Doped SiO formed by a high frequency sputtering method with a target of₂It was found that the glass film contains more oxygen deficiency defects than the method of forming by melting electron beam evaporation or glass fine particles. In addition, excitation light having a wavelength of 550 nm or less is₂Irradiation from the vicinity of the glass film or propagation in a core region having a waveguide structure realizes a high energy density and can increase the generation efficiency of electric dipoles. Also, as described above, GLPC and H₂A GeE ′ center and an electric dipole are also generated by the reaction with, and in order to promote this reaction, a step of holding the optical waveguide in a high-temperature or high-pressure hydrogen atmosphere for a certain time, or at least a part of the optical waveguide is performed. After the step of burning with an oxyhydrogen burner, a DC high-voltage electric field may be applied, and at the same time, the core region may be irradiated with excitation light or propagated in the core region.
[0040]
In order to enhance the regular orientation of the electric dipole, in the present invention, the direction of the DC high voltage electric field applied to the optical waveguide and the polarization direction of the electric field of the excitation light irradiated to the core region or propagated in the core region Were made substantially parallel. At the same time as applying a DC high-voltage electric field and irradiating the excitation light, the substrate is kept at a high temperature, thereby promoting the orientation of the electric dipole.
[0041]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0042]
FIG. 1 is a conceptual diagram showing one embodiment of a method for manufacturing a nonlinear optical element of the present invention.
[0043]
The optical waveguide 11 as a nonlinear optical element is formed on a quartz substrate 12 and doped with Ge.₂It comprises a core region 13 made of glass and a cladding region 14 having a lower refractive index than the core region 13 and surrounding the core region 13.
[0044]
The core region 13 is made of GeO₂Containing SiO₂The core film formed on the quartz substrate 12 by the high-frequency sputtering method is patterned by photolithography to form a waveguide.₃It is formed in a rectangular cross-sectional shape by a reactive ion etching method using a gas.
[0045]
After the core region 13 is formed by the flame deposition method, the clad region 14 is formed on the entire surface of the quartz substrate 12 by a flame hydrolysis reaction.₂Glass particles obtained by adding P (phosphorus) and B (boron) are deposited on the substrate and sintered together with the quartz substrate 12 at a high temperature of 1300 ° C., and the fine particles are turned into a transparent glass.
[0046]
P for SiO₂When added to₂Has a high refractive index, and B is converted to SiO₂When added to SiO₂Has a low refractive index. By adjusting the amounts of P and B, the refractive index of the cladding region 14 becomes substantially equal to the refractive index of the quartz substrate 12. In the present embodiment, the sectional size of the core region 13 is about 5 × 5 μm, and the relative refractive index difference between the core region 13 and the cladding region 14 is 0.8%.
[0047]
A pair of electrodes 15 and 16 were formed on both sides of the clad region 14 thus formed with the core region 13 interposed therebetween.
[0048]
When these two electrodes 15, 16 are connected to a DC high voltage power supply 17, an electric field is generated in a direction transverse to the core region 13 of the optical waveguide 11. An optically anisotropic region is formed in the core region 13 of the optical waveguide 11 by irradiating the core region 13 and the core region 13 of the optical waveguide 11 with excitation light in the direction intersecting the electric field (from above in the figure) at the same time as the generation of the electric field. Is done.
[0049]
The excitation light is condensed linearly by a cylindrical lens (not shown) and is irradiated over the longitudinal direction of the core region 13. Even if a circular beam obtained by condensing the excitation light by a lens is irradiated while scanning in the longitudinal direction of the core region 13, an optically anisotropic region having a specific length is formed inside the core region 13. Is done. In this embodiment, the intensity of the electric field applied to the core region 13 by the electrodes 15 and 16 is about 10⁶-10⁷V / cm.
[0050]
A KrF excimer laser of 100 to 200 mJ and 10 pps was used as the excitation light applied to the core region 13 simultaneously with the application of the high DC voltage, and the irradiation time was set to 20 to 30 minutes. The excitation light is not limited to this, but is a Hg lamp light having a wavelength of 550 nm or less, an Ar laser, an ArF excimer laser, an Ar laser, a second harmonic of a dye laser, or Nd3.⁺: A similar nonlinear optical effect can be obtained by the fourth harmonic of the YLF laser.
[0051]
Here, in the case of low-energy Hg lamp excitation, the oxygen-deficient defect NOV undergoes a structural change to GeE 'by a one-photon absorption process, and in the case of Ar laser excitation, a similar structural change is performed by a two-photon absorption process. Can be In addition, in the case of irradiation with high-energy-density ultraviolet excitation light such as an excimer laser, a two-step reaction in which the defect-free structure changes to GEC by the two-photon absorption process and a part of the structure changes to the GeE 'center also contributes. it seems to do.
[0052]
In addition, in order to enhance the orientation of the electric dipole at the time of irradiation with the excitation light, the polarization direction of the electric field of the excitation light was set to be substantially parallel to the lines of electric force of the DC high-voltage electric field. Further, during the poling process, that is, during the excitation light irradiation (20 to 30 minutes) performed simultaneously with the application of the DC high voltage, the optical material induced in the core region 13 also by maintaining the entire quartz substrate 12 at about 300 ° C. There is a tendency that the thermal anisotropy is enhanced, and holding at a high temperature during the poling treatment is also effective.
[0053]
Further, in order to enhance the efficiency of the electric dipole generation process, as a pretreatment of the step of generating a DC high voltage electric field and simultaneously irradiating the core region 13 in the optical waveguide 11 with the excitation light, the photoconductor was introduced into a high-temperature or high-pressure hydrogen atmosphere. The effect of enhancing the optical anisotropy is obtained even after the step of holding the waveguide 11 together with the quartz substrate 12 for a certain time or the step of burning at least a part of the optical waveguide 11 with an oxyhydrogen burner. This is considered to be because the process of generating a GeE ′ center by the reaction between GLPC and hydrogen molecules is promoted as described above.
[0054]
In this embodiment, the core region 13 is made of GeO as described above.₂Is formed by a high-frequency sputtering method targeting. Ge-doped SiO for forming the core region 13₂The layer may be formed not only by the sputtering method in this embodiment mode but also by an electron beam evaporation method or a flame deposition method. However, the amount of defects in the core region 13 greatly depends on the method of forming the core layer. As a result of examination, it has been found that the high frequency sputtering method employed in the present embodiment is the most effective.
[0055]
In the embodiment shown in FIG. 1, a KrF excimer laser having a high energy density is used as the excitation light. Although the laser light is mainly applied to the core region, a part of the laser light is also applied to the electrodes 15 and 16, so that the electrodes 15 and 16 may be thermally damaged. In order to prevent this thermal damage, aluminum was adopted as the material of the electrode. The reflectivity of a metal in the wavelength band of an excimer laser is, for example, about 32.9% in the case of using gold as a material, whereas it is as high as about 92.4% in the case of using aluminum as a material. Of the materials, aluminum is least likely to cause thermal damage due to absorption. As a material of the electrodes 15 and 16, besides preventing thermal damage by reflection like aluminum, a transparent electrode material such as ITO (indium-tin-oxide) can be used to form the electrodes 15 and 16 by irradiation with excitation light. 16 is effective to prevent damage.
[0056]
The electrodes 15 and 16 shown in FIG. 1 are electrodes for applying a high voltage used for forming an optically anisotropic region in the core region 13, and are directly controlled by the DC high voltage power supply 17. If the power supply is replaced with a power supply, it can be used as a drive electrode for controlling the guided light propagating through the core region 13 of the optical waveguide 11 at high speed.
[0057]
FIG. 2 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.
[0058]
The difference from the embodiment shown in FIG. 1 is that the shape of the cladding region 22 has a trapezoidal cross-sectional shape, and electrodes 23 and 24 are formed on both slopes of the cladding region 22. An object of the present invention is to further improve the efficiency of inducing an optical effect or the efficiency of applying a driving voltage for controlling guided light.
[0059]
The optical waveguide 21 is, like the optical waveguide 11 shown in FIG.₂It comprises a core region 13 made of glass and a cladding region 22 having a low refractive index surrounding the core region 13. The cross-sectional shape of the peripheral cladding region 22 surrounding the core region 13 has a trapezoidal shape with an inclined side surface, and electrodes 23 and 24 for applying a high voltage for inducing a nonlinear optical effect are formed on the inclined side surface. Have been.
[0060]
The method of irradiating the excitation light at the time of the poling process is to apply a high DC voltage between the electrodes 23 and 24 and irradiate the excitation light in the direction of arrow B at the same time as in the case shown in FIG. In order to make the cross-sectional shape of the peripheral cladding region 22 surrounding the core region 13 into a trapezoidal shape with inclined side surfaces, a flat cladding layer was formed by the flame deposition method as in the embodiment shown in FIG. After that, it can be formed by masking the upper part of the core region 13 and using, for example, reactive ion etching. The inclination angle of the side surface of the cladding region 22 surrounding the core region 13 varies depending on the side etching of the mask, but is determined by the material of the mask or the etching conditions. The cladding region 22 having a trapezoidal cross section can be formed by using, for example, a bias sputtering method in addition to the flame deposition method and the etching process suitable for flattening. Bias sputtering has less planarizing effect than flame deposition, and SiO₂The shape as shown in FIG. 2 can be formed directly only by depositing on the upper part of the core. The structure as shown in the figure not only increases the efficiency of inducing the nonlinear optical effect during the poling process but also uses the electrodes 23 and 24 for applying a high voltage as drive electrodes for controlling the guided light as they are. The guided light can be controlled with a smaller voltage.
[0061]
In the embodiment shown in FIGS. 1 and 2, an electric field of a DC high voltage is applied, and at the same time, the excitation light is irradiated from a direction (upward direction in the figure) crossing the core region 13 of the optical waveguide 11 (21). However, the present invention is not limited to this, and the pumping light may be propagated in the core region 13.
[0062]
Although an excimer laser is used as the excitation light, the present invention is not limited to this, and an Ar laser having a wavelength of about 488 nm may be incident on the waveguide. In the method of irradiating the excitation light in a direction intersecting with the waveguide as shown in FIG. 1 or FIG. 2, the efficiency of inducing the nonlinear optical effect of the Ar laser is smaller than that of the excimer laser having higher light energy.
[0063]
However, if the excitation light propagates in the core region 13 of the optical waveguide 11 (21), the light energy density becomes several MW / cm.², An optically anisotropic region can be induced with high efficiency by the two-photon absorption process. However, also in this case, it is better to make the polarization direction of the electric field of the excitation light propagated to the core region 13 of the optical waveguide 11 (21) parallel to the direction of the electric field of the DC high voltage to induce the nonlinear optical effect. Can be increased.
[0064]
FIG. 3 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.
[0065]
The difference from the embodiment shown in FIG. 1 is that a DC high voltage is applied in the thickness direction of the quartz substrate 12, and the excitation light in a direction crossing the DC high voltage electric field is irradiated on the core region 13. is there.
[0066]
Electrodes 33 and 34 are formed on the upper and lower portions of the quartz substrate 12 of the optical waveguide 32 including the quartz substrate 12, the core region 13 and the cladding region 31, and a DC high voltage is applied in the thickness direction of the quartz substrate 12 (vertical direction in the figure). Is applied, the core region 13 is irradiated with the excitation light in a direction intersecting the longitudinal direction of the core region 13 (the direction of arrow C in the figure). With such a structure, it is easy to form an electrode on the optical waveguide 32. In general, it is known that when poling is performed by applying a DC high voltage between two electrodes, an optically anisotropic region is more easily formed on the anode side. Therefore, in the embodiment shown in FIG. 3, the electrode 33 immediately above the core region 13 is set to be on the anode side. The direction of the electric field of the irradiated excitation light is set to be parallel to the direction of the electric lines of force of the applied DC high-voltage electric field in the same manner as described above. Aluminum is used as a material of the electrodes 33 and 34.
[0067]
In the case of the optical waveguide 32, the excitation light cannot be irradiated from above the core region 13 as in the embodiment shown in FIG. Therefore, as shown in FIG. 3, the excitation light is irradiated from the side surface of the core region 13. However, if the distance L between the side surface of the optical waveguide 32 and the core region 13 is long, the excitation light reaches the core region from the side surface. By this time, the beam diameter may expand so that irradiation with high energy density may not be possible.
[0068]
Therefore, the optical waveguide is cut into a long and narrow shape so that the core region 13 is sufficiently irradiated with the excitation light even when irradiated from the side. However, depending on the circuit configuration, efficient irradiation from the side may be difficult. In such a case, by using transparent electrodes such as ITO as the electrodes 33 and 34, the excitation light can be efficiently transmitted from above the core region 13 through the transparent electrodes.
[0069]
Instead of irradiating the excitation light from the side surface of the core region 13, the excitation light may be directly incident on the core region 13 and propagated in the longitudinal direction.
[0070]
Although a quartz substrate is used as the substrate, the present invention is not limited to this, and a low-resistance semiconductor substrate may be used. When a low-resistance semiconductor substrate is used, electrodes may be formed on the front and back of the optical waveguide, and a DC high-voltage electric field may be applied in the thickness direction. In this case, since the semiconductor substrate has low resistance, it functions as a cathode, and it is not necessary to provide the electrode 34 as shown in FIG. 3 on the back surface of the substrate.
[0071]
Further, when a low-resistance Si substrate is used as the substrate, SiO 2 is formed on the Si substrate by thermal oxidation or sputtering.₂Preferably, the film is formed as a buffer layer (lower cladding layer). The core region 13 is formed on the buffer layer, and the other structure is the same as that of FIG. The thickness of the buffer layer is preferably about 20 μm so that the absorption of the guided light by the Si substrate can be ignored. The excitation light is applied from the side of the core region as in FIG. Alternatively, if a transparent electrode is used as the upper electrode of the core region, the excitation light can be irradiated from above the core. In the embodiment shown in FIG. 3, since the quartz substrate is used, the distance between the electrode 33 and the electrode 34 is large. Therefore, to apply a large electric field in the core region 13, a very high DC voltage must be applied between the electrodes 33 and 34. On the other hand, if a low-resistance semiconductor substrate is used as the cathode, the distance between the upper electrode of the core region 13 and the cathode (low-resistance substrate) is close to several tens of μm, so that a lower voltage power supply can be used. A large electric field can be applied to the core region 13. Using a low-resistance semiconductor substrate as a substrate and using the low-resistance semiconductor substrate as a cathode is not only at the time of poling processing for inducing an optically anisotropic region in the core region 13 but also when controlling guided light. This is advantageous because it operates at a low drive voltage.
[0072]
FIG. 4 is a conceptual diagram showing an example of the nonlinear optical element of the present invention, and shows a Mach-Zehnder type optical modulator 41 using the electro-optic effect.
[0073]
In the optical modulator 41, a core region 43 is formed on a quartz substrate 42, and a cladding region 44 is formed so as to surround the core region 43. Y branches 45 and 46 are formed on the input side and the output side of the guided light, respectively. The guided light incident in the direction of arrow D is divided into two equal parts by the Y branch 45 on the input side, and propagates through two waveguide arms 47 and 48 having the same length.
[0074]
Two electrodes 49 and 50 are formed on both sides of one waveguide arm 47 on the cladding region 44 with the waveguide arm 47 interposed therebetween, and are connected to an AC power supply 51. The guided light propagating in the waveguide arm 47 undergoes a phase change due to the electric field of the AC voltage. This waveguide light is multiplexed and interfered with the reference waveguide light propagating through the other waveguide arm 48 by the Y branch 46 on the output side, so that the output intensity changes in accordance with the phase difference between the two waveguide lights and the arrow. Emitted in the E direction.
[0075]
Here, the polarization of the guided light incident on the optical modulator 41 is made parallel to the direction of the AC electric field. As the electrodes 49 and 50 for causing a phase change, the electrodes used at the time of the poling process for inducing an optically anisotropic region in the core of the waveguide arm 47 sandwiched between the electrodes 49 and 50 are used as they are. can do. During the polling process, a DC high-voltage power supply (not shown) is connected between the electrodes 49 and 50, and a high voltage of several hundreds to several KV is applied. On the other hand, in order to control the propagation of the guided light and operate as a modulator, it is sufficient to connect an AC power supply of several volts.
[0076]
As described above, according to the present invention, Ge-doped SiO 2 which has conventionally only realized a weak nonlinear optical effect has been realized.₂In glass, a very large optically anisotropic region can be efficiently induced. This makes it possible to integrate various functions such as light switching, modulation, wavelength conversion and the like utilizing the non-linear optical effect such as the electro-optical effect and the second harmonic generation in the quartz-based planar optical circuit. As a result, a functional optical device having low loss, high reliability, small size, and low driving energy can be realized.
[0077]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0078]
An optical anisotropy is applied to the core region of the optical waveguide by applying a DC high voltage electric field from the outside so as to intersect the optical waveguide and irradiating excitation light having a wavelength of 550 nm or less so as to intersect the electric field and the optical waveguide. It is possible to provide a non-linear optical element in which a region is formed, which has a small loss, high reliability, small size, and small driving energy, and a method of manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing one embodiment of a method for manufacturing a nonlinear optical element of the present invention.
FIG. 2 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.
FIG. 3 is a conceptual diagram showing another embodiment of the method for manufacturing a nonlinear optical element of the present invention.
FIG. 4 is a conceptual diagram showing an example of the nonlinear optical element of the present invention.
[Explanation of symbols]
11 Optical waveguide
12 Substrate (quartz substrate)
13 core area
14 Cladding area
15, 16 electrodes
17 DC high voltage power supply

Claims (12)

A nonlinear optical element having a core region made of Ge-doped SiO ₂ glass having a high refractive index formed on a substrate and an optically anisotropic region formed in an optical waveguide in which the core region is surrounded by a clad region having a low refractive index. In the manufacturing method, the core region is optically anisotropic by applying a DC high voltage electric field from the outside so as to intersect with the optical waveguide and irradiating excitation light having a wavelength of 550 nm or less so as to intersect with the electric field and the optical waveguide. in forming the sexual region, the polarization direction of the electric field of the excitation light, a manufacturing method of the non-linear optical element characterized in that set to be substantially parallel to the direction of the electric field of the DC high voltage. A nonlinear optical element having a core region made of Ge-doped SiO ₂ glass having a high refractive index formed on a substrate and an optically anisotropic region formed in an optical waveguide in which the core region is surrounded by a clad region having a low refractive index. In the manufacturing method, an optically anisotropic region is formed in the core region by applying an electric field of DC high voltage from the outside so as to intersect with the optical waveguide and simultaneously transmitting excitation light having a wavelength of 550 nm or less into the core region. when the polarization direction of the electric field of the excitation light, a manufacturing method of the non-linear optical element characterized in that set to be substantially parallel to the direction of the electric field of the DC high voltage. A core region made of Ge-doped SiO ₂ glass having a high refractive index is formed on a substrate, and a DC high voltage is applied from outside to an optical waveguide in which the core region is surrounded by a clad region having a low refractive index so as to intersect the optical waveguide. In the method for manufacturing a nonlinear optical element, which forms an optically anisotropic region by irradiating the core region with excitation light having a wavelength of 550 nm or less at the same time as applying a voltage electric field, or forming the core region, Is formed by a high frequency sputtering method. A core region made of Ge-doped SiO ₂ glass having a high refractive index is formed on a substrate, and a DC high voltage is applied from outside to an optical waveguide in which the core region is surrounded by a clad region having a low refractive index so as to intersect the optical waveguide. In the method for manufacturing a nonlinear optical element, which forms an optically anisotropic region by irradiating the core region with excitation light having a wavelength of 550 nm or less at the same time as applying a voltage electric field, or forming the optical waveguide, After the substrate on which is formed is kept in a high-temperature hydrogen atmosphere or a high-pressure hydrogen atmosphere for a certain period of time, or after at least a part of the optical waveguide is burned by an oxyhydrogen burner, an external electric field of DC high voltage is applied and simultaneously the inside of the optical waveguide is A method for manufacturing a nonlinear optical element, comprising irradiating a core region with excitation light or propagating the excitation light into the core region . The core region is locally heated to a high temperature, and in a high temperature state, an external electric field of DC high voltage is applied, and at the same time, the core region is irradiated with excitation light or propagated in the core region, and after a certain period of time, heat is released, and the optical waveguide is emitted. The nonlinear optics according to any one of claims 1 to 4, wherein the optical anisotropic region is formed in the core region by releasing the electric field of the DC high voltage and stopping the irradiation of the excitation light after the temperature of the substrate has dropped to room temperature. Device manufacturing method. Excitation light having a wavelength of 550 nm or less that is applied to the core region at the same time as the application of the DC high voltage electric field to the optical waveguide or propagates in the core region is Hg lamp light, Ar laser, ArF excimer laser, KrF excimer laser, The method for manufacturing a nonlinear optical element according to claim 1 , wherein the nonlinear optical element is any one of a second harmonic of an Ar laser or a dye laser or a fourth harmonic of an Nd ^{3 +} : YLF laser . The electrode closer to the core region among the electrodes for applying a DC high voltage is used as the anode. Item 5. The method for manufacturing a nonlinear optical element according to any one of Items 1 to 4. 5. The method for manufacturing a nonlinear optical element according to claim 1, wherein aluminum or a transparent conductor is used as a material of the high voltage application electrode . 5. The method according to claim 1, wherein at least one of the high voltage applying electrodes is a transparent electrode, and the excitation light is irradiated from a direction crossing the optical waveguide through the transparent electrode at the same time as applying a high DC voltage. A manufacturing method of the nonlinear optical element according to the above. In a nonlinear optical element in which an optically anisotropic region is formed in an optical waveguide including a core region made of Ge-doped SiO ₂ glass having a high refractive index and a clad region having a low refractive index surrounding the core region, at least one pair is provided. A drive electrode using aluminum or a transparent conductor is formed on the same surface, and an external electric field is applied by the drive electrode in a direction intersecting the optical waveguide to control propagation of the guided light. nonlinear optical element to. A core region made of SiO ₂ glass having a high refractive index Ge-doped, in the nonlinear optical element formed of the optical anisotropic region in the optical waveguide having a lower cladding region enclose refractive index of the core region, the The cross-sectional shape of the peripheral cladding region surrounding the core region has a trapezoidal shape with inclined side surfaces, and at least a pair of drive electrodes are formed on the inclined side surfaces and intersect the optical waveguide by the drive electrodes. A nonlinear optical element wherein an external electric field is applied in a direction to control propagation of guided light . A core region made of SiO ₂ glass having a high refractive index Ge-doped, in the nonlinear optical element formed of the optical anisotropic region in the optical waveguide having a lower cladding region refractive index surrounding the core region, the core A low-resistance semiconductor layer is formed below the region, and a transparent electrode or a metal electrode is formed above the core region. An external electric field for controlling propagation of guided light is applied to the optical waveguide in the thickness direction. A non-linear optical element characterized in that:

Images