JP3647656B2 - Optical functional element and optical communication device - Google Patents

Description

ここで、回折格子は導波路の座標のｘ＝０からｘ＝ｇまで存在すると仮定する。（１）式のａ（ｘ）は回折格子領域の下端（ｘ＝０）から下向きに放射される放射モードの振幅を表し、（２）式のｂ（ｘ）は回折格子領域の上端（ｘ＝ｇ）から上向きに放射される放射モードのｘにおける振幅を表す。Ｔ（ｘ）は回折格子のフーリエ（Fourier）係数と導波モードのフィールド（field：界）で決まる関数である。
【００６８】
定数Ｃ_a、Ｃ_bは境界条件で決まる定数である。導波路の上下に放出された放射モードがそれぞれ反射機構により反射されるという境界条件で、この定数を求める。導波路の上の反射率をｒ_g、導波路の下の振幅反射率をｒ₀とする。なお、これらの反射率は位相も含んでいる。放射モードが回折格子から放射されたあと反射機構までの層構造の影響もこの反射率に含め、回折格子領域境界に反射機構があると仮定して求める。すなわち、ａ_n（ｇ）＝ｒ_gｂ_n（ｇ）、ｂ_n（０）＝ｒ₀ｂ_n（０）とする。
【００６９】
すると、定数Ｃ_a、Ｃ_bは、それぞれ次式により表すことができる。
【００７０】
【数２】

但し、次式を定義した。
【００７１】
【数３】

ここで、重要なのは式（３）の分母である。すなわち、
【００７２】
【数４】

なる関係が成立すれば、式（３）の分母がゼロとなり、定数Ｃ_a、Ｃ_bは無限大となる。つまり、式（１）、（２）から分かるように、「放射モード共振器」として発振する。つまり、反射率が大きく、ゲインがあり、位相条件が満たされれば発振することが分かる。
【００７３】
また、導波路側からみると、従来は損失となっていた放射モードが、本発明においては増幅されて戻ってくるので利得になる。ゆえに、ＤＦＢレーザの解析に用いられる結合波方程式における放射モード損が利得項に置き換わる。放射モード共振器が発振条件に至らなくても、ＤＦＢレーザとしても低しきい値での発振が可能になる。
【００７４】
本願の請求項において、放射モードに対する増幅機構、反射機構、位相制御機構の３つの要素が請求されていることは、この説明から理解しやすい。
【００７５】
以上説明した第１〜第３実施形態の構成は、本発明の基本である。しかし、本発明においては、前述した増幅機構、反射機構、位相制御機構などの要素が互いに独立に存在している必要はない。例えば、次に説明する第４実施形態の如く、２つ以上の機構が１つの構成要素の中に共通して含まれていても良い。
【００７６】
図４は、本発明の第４の実施の形態にかかる光機能素子の構成を例示する概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。同図の光機能素子においては、ゲインを有する媒質３がない。その代わりに、導波路１の近傍にゲインを有する活性層６が設けられている。また、反射機構４’もゲインを有する。すなわち、これらの活性層６や反射機構４’が増幅機構として作用する。
【００７７】
反射機構がゲインを有する例としては、面方向に積層された半導体の多層膜によるＤＢＲ（分布ブラッグ反射：Distributed Bragg Reflector）鏡にｐｎ接合を形成して電流注入によりゲインを持たせることもできるし、導波路１に対して垂直に別の導波路を設け、その中にＤＢＲ鏡を設けても良い。
【００７８】
次に、本発明の第５の実施の形態について説明する。
【００７９】
図５は、本発明の第５の実施の形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。同図の例では、２次以上の回折格子２は、位相シフト２０、すなわち位相の不連続を有する。位相シフト２０は、導波路に平行な方向の放射モードの強度分布の制御に有効である。すなわち、導波路から放射モードが発生する場合、導波路は、進行方向の逆な２つの波を許容する。放射モードの軸方向すなわち導波路方向の強度分布は、この２つの導波モードによって発生するそれぞれの放射モードの干渉によって強めあったり弱めあったりすることに大きく影響される。この干渉の状態は、位相シフトによって変化する。したがって、適当な位相シフトを設けることは、大きなメリットがある。また、位相シフトは導波モードそのものの軸方向の強度にも影響を与えるため本発明の重要な構成要素となりうる。
【００８０】
すなわち、位相シフトがないと、導波路の中央部で放射モード強度が小さい縦モードが発振する。これに対して、例えば、導波路の両端面の反射を低く抑え、導波路中央にλ／４相当の位相シフトを設け、この導波路をＤＦＢ（distributed feedback：分布帰還）発振させると、位相シフト位置において導波モードと放射モードの強度が大きい縦モードが発振する。
【００８１】
つまり、利得を受けて帰還される放射モードの軸方向の強度分布と導波モードの強度が一致する。位相シフト位置で空間的に強く同期するため、光帰還、すなわち共振器の効率が極めて大きくなるという効果が得られる。
【００８２】
なお、このような位相シフトの代わりに、導波路の実効屈折率を変化させる構造を採用しても同様の効果を得ることができる。つまり、回折格子の周期が一様でも、導波構造の幅、厚さ、或いは屈折率を変化させた実効位相シフト領域（図示せず）を設けることにより代替できる。また、位相シフトは、導波路内波長λの整数倍から１／８倍以上３／８倍以下の範囲内の位相のずれ量を有することが望ましい。前述した１／４は、この範囲の中心値に相当する。
【００８３】
次に、本発明の第６の実施の形態について説明する。
図６は、本発明の第６の実施の形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態においては、回折格子２の断面形状が非対称となる、いわゆるブレーズ角（blaze angle）をもつ。ブレーズのない対称な断面形状の回折格子では、所定の方向に進む導波モードによって発生する放射モードは上下２方向にほぼ同様に放射されることが多い。しかし、ブレーズがあると上下に放射される放射モードに選択性を持たせることができる。例えば、図６において、導波路を左から右へ通る光波は、図面の上方に放射される割合が大きく、逆向きの場合は下方に放射される割合が大きい。
【００８４】
このようなブレーズ角を導入することにより、次のようなメリットが得られる。つまり、導波路に対して常に一方向に信号光が伝搬している場合に、ブレーズの角度によって導波路の上下のいずれかの側に放射される放射モードを大きくすることができる。そして、その大きい側の反射率を大きくしたり、増幅機構のゲインを大きくすることにより片側の機構を増強すると、効率よく機能を強化できる。また、逆方向に伝搬する信号に対して増幅効果が小さくなるようにすれば、光アイソレータ（isolator）や方向性結合器の機能を持たせることができる。
【００８５】
次に、本発明の第７の実施の形態について説明する。
本実施形態の光機能素子は、図１〜図６に例示した構成を用いて説明することができる。すなわち、本実施形態においては、導波機構、増幅機構、反射機構をそれぞれ独立に変調制御する。これらは、第３実施形態において前述した位相制御機構とあわせて、光信号を扱う光機能デバイスにおける基本的な要請である。例えば、増幅機構を変調制御することで前述した式（５）の条件が満足され、導波路に対して垂直な共振器の発振を電流注入で制御できるようになる。他の機構すなわち導波機構や反射機構のパラメータも同様に変調制御することができる。
【００８６】
次に、本発明の第８の実施の形態について説明する。
図７は、本実施形態に係る光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態においては、放射モードを利用した別の共振構造を導波路に沿って形成する。導波路に沿って形成するということは、長い導波路の全長を利用できることを意味する。したがって、導波路に沿って共振器構造を変化のあるものとすることが可能である。また、導波路に沿って多数の共振器構造を形成することも可能である。
【００８７】
図７に表した例においては、導波路構造１の回折格子２の周期が導波路に沿って変化している。この例では、回折格子の周期はΛ１、Λ２、及びΛ３の３種類である。そして、それぞれの周期の回折格子に対応して、反射機構４、位相変調機構５、増幅機構３が設けられている。
【００８８】
この光機能素子の動作について説明すると以下の如くである。すわわち、導波路１を励起しておき、自然放出光を発生させる。その中の回折格子周期Λ１、Λ２、及びΛ３に対応して垂直に放射される波長成分の放射モードが、それぞれの放射モード共振器において増幅される。増幅の程度は、ゲインや反射率や、位相等を独立に制御することにより、特定の波長を自由に増幅できる。反射機構そのものも、ＤＢＲなどの構成を採用することにより、波長の選択性を強化できる。また、ゲインスペクトラムのピークをその特定波長に合わせることも可能である。増幅が強ければ発振させることもできる。このような増幅光をそれぞれの共振器から取り出すことも可能である。また、導波路１に戻してその端面から取り出すこともできる。また、それぞれの共振器で特定の波長を変調した信号として取り出すこともできる。
【００８９】
このような構成は、合波器や分波器の機能も兼ね備えているため、光回路を省スペースにレイアウトできる。したがって、モノリシック（monolithic）な集積に向く。図７の例では、導波路機構及びもその他の機構をＩｎＰなどの基板上にモノリシックに集積することができる。しかし、その他にも、例えば導波路をファイバとし、回折格子をファイバグレーティングとしても良い。
【００９０】
また、回折格子の周期を変化させる代わりに、導波路１の実効屈折率を局所的に変化させることによって波長選択機能を持たせることもできる。その他、回折格子の周期を段階的に変化させるのではなく、連続的に変化させる応用例も考えられる。
【００９１】
次に、本発明の第９の実施の形態について説明する。
【００９２】
図８は、本発明の第９の実施の形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。その構成は、前述した第８実施形態と類似している。主な相違点は、応用の仕方である。つまり、本実施形態においては、導波路１を、信号、とりわけ波長の異なる複数の信号が伝搬している伝送線路と位置づけている。第８実施形態と同様の構成により、その信号をチューニング（tuning）して別々に増幅して取り出す機能を実現することができる。すなわち、本実施形態は、チューナアンプに相当する。
【００９３】
同時に、本実施形態の伝送系は、リングネットワークでもある。つまり、導波路の左端から入力された信号は、右端からも出力され、また別のターミナル（terminal）でも検出される。この場合には、放射モードの共振器構造の増幅機能は中継器の役目も果たし信号の減衰を防ぐ。
【００９４】
本実施形態の素子の動作は、前述した第８実施形態の考え方を基本としている。つまり、周期の異なる回折格子からそれぞれ垂直放射される放射モードを波長選択性のある共振器で増幅し、その出力を検出する。図８では、各共振器を出力ポート（port）と見なし、波長の異なる信号を各ポート毎に図面の下向きに出力して、図示しない検出器で受ける。
【００９５】
回折格子の周期により決定される波長の間隔（図８の例では、Λ１とΛ２とΛ３との波長間隔）が広い場合は、それぞれの波長に対応する周期の回折格子部分以外では、導波路に対して垂直からずれた方向に放射される。したがって、共振器の配置のみで、チューニングされる。また、導波路の屈折率を変調することでもチューニングされる。
【００９６】
波長間隔が狭い場合は、位相制御機構５による変調や、ＤＢＲ反射機構の屈折率を変化させてチューニングすることができる。
【００９７】
次に、本発明の第１０の実施の形態ついて説明する。
【００９８】
図９は、本実施形態の光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態は、レーザ発振する機能を備えた光機能素子を中心とする。本発明の著しい特徴として、通常の導波路型レーザの導波路共振器の他に、放射モードの共振器を備える点を挙げることができる。したがって、どちらを主要な共振器とし、どちらを補助的な共振器とするかというバリエーション（variation）が発生する。もちろん、両方とも発振させるという組み合わせもある。また、出力をどこから取り出すかというバリエーション（variation）もある。
【００９９】
図９においては、導波路機構１は回折格子のみでも光フィードバックを起こすことができるが、さらにフィードバックを強めるための反射構造３０を両端面に備えた場合を例示した。
【０１００】
従来のレーザのように導波路機構を主要共振器とした場合は、放射モードの共振器は主要共振器に対する光ポンピング機構と解釈することもできる。このポンピング機構は導波路１に沿って密に構成することも可能なため、非常に効率の良い励起が可能となる。導波路のみに電流を注入する従来の半導体レーザでは、狭い導波路への電流密度が高くなり、活性層６の劣化や局所的な熱の発生が問題となる。これに対して、本発明によれば、電流の注入は補助共振器の方に分散されるため、熱の影響を小さくし、信頼性も向上させることができる。主要共振器に対して電流励起と光励起の両方をバランスさせることができることも本発明による新しいメリットの一つである。
【０１０１】
光出力は、従来のように端面から取り出す場合（出力１００）と、放射モード共振器から増幅された放射モードとして導波路に沿う形で取り出す場合（出力２００）の両方を実施できる。どちらか都合の良い出力形態を選択できる。
【０１０２】
また、主要共振器を放射モード共振器とした場合は、導波路機構１を光ポンピング機構と考えることができる。上述の例と同様に、光出力を端面から取り出す場合（出力１００）と、放射モード共振器から導波路に沿う形で取り出す場合（出力２００）の両方を実施できる。もちろん、どちらか都合の良い出力形態を選択できる。
【０１０３】
また、本実施形態も、発明に共通に付加される機構としての受光機構４０を有する。この場合は、受光機構４０によって出力光をモニタ（monitor）し、図示しない外部回路を用いてレーザの出力を制御することができる。例えば、レーザの出力を一定に維持するためのＡＰＣ（Automatic power control）をかけることができる。
光ポンピングされる導波路機構１には、材料として電流励起できない媒質、特に光励起でのみ利得を持つ媒質を配することができる。たとえば、Ｅｒ（エルビウム）やＰｒ（プラセオジム）をドープした石英系の導波路である。これらはいわゆるファイバアンプと同様のものである。導波路１に沿った放射モードの共振器はこの導波路アンプに対して強力な光励起効果をもつ。励起だけが目的であれば、放射モードに対する反射率はほぼ１００％とし、出力２００を無視することもできる。
【０１０４】
この光励起と電流励起の使い分けはその逆で放射モード共振器側の方でも良い。ただし、一般的には長い導波路に沿って励起する上記の例の方が効率が良い。また、導波路機構１を電流を流せないパッシブ（passive）な材料で構成することも製作上に大きなメリットをもたらす。つまり、ｐｎ接合をもつ半導体で適当な屈折率差をもつ導波路をつくりにくい場合である。このとき、導波路を半導体ではない材料で形成しても良い。これは、例えば、石英（ＳｉＯ₂）クラッドとＳｉＮのコアをもつような構成である。
【０１０５】
図１０は、石英クラッドを採用した素子の断面構造を例示する概念図である。すなわち、同図（ａ）は、その導波路の中心軸に沿った断面図であり、同図（ｂ）は、導波路に対して垂直に切断した断面図である。
【０１０６】
その構成を製造工程に沿って説明すれば、以下の如くである。まず、半導体基板５０上にＤＢＲ反射鏡４’とｐｎ接合で利得をもつ活性層３を成長する。面倒な結晶成長はこれのみで良く成長回数を低減できる。電極はＩＴＯ（indium tin oxide：酸化インジウム・錫）などの透明電極５５とする。この上に石英（ＳｉＯ₂）クラッド１ｂとＳｉＮのコア１ａよりなる導波路構造１を形成する。ＳＩＮの導波路コア１ａには２次の回折格子２を形成する。この導波路構造１の上にさらにＳｉＯ₂とＳｉ（シリコン）からなる誘電体高反射多層膜４’を形成する。基板５０の裏面には、電極７０が形成されている。また、透明電極５５には、ワイア６０がボンディングされている。透明電極５５を介して注入された電流は、図１０（ｂ）に矢印で示したように、電流ブロック領域５３により導波路構造１の下部の活性層３に流入する。
【０１０７】
本変形例によれば、通電領域と導波路領域を全く異なる材料系で分離できるので製作が容易である。例えば、導波路領域は、上述したようなＳｉＯ₂クラッド／ＳｉＮコアの組み合わせの他にも、回折格子が形成された光ファイバとしても良く、または、ＩＴＯなどの透明電極に回折格子を形成し、ＳｉＯ₂などの材料からなるクラッドを積層しても良い。
【０１０８】
このように、導波路領域を通電領域とは異なる材料系により構成すれば、導波路部分の製作に失敗しても高価な半導体成長ウェーハに損傷を与えないように、導波路部を形成する工程をやり直すことができる。また、半導体より小さい屈折率で導波路をつくれるため、そのサイズも２倍程度大きくできるために加工がしやすいという利点も有する。
【０１０９】
また、発振波長を決める回折格子２と導波路部１の屈折率の温度変化が半導体材料よりも小さいので、温度に対して波長の安定したレーザが実現できる。これは光通信のうちＷＤＭ（wavelength division multiplexing：波長多重）用光源に適する。また、導波路部１が石英系ファイバと類似であるので、ファイバとの結合が容易になる。
【０１１０】
前述のように、利得領域では半導体を導波路上に加工する必要がない。活性層ストライプの外側に光のモードの滲みだし領域を設ける必要がないため、半導体部の製作が格段に楽になる。
【０１１１】
一方、導波路をパッシブな半導体材料により形成しても大きな効果が得られる。導波路がパッシブであれば、導波路自体がキャリア密度の影響を受けない。そのため、キャリア密度の空間的不均一により屈折率の不均一が発生して横モードや縦モードが不安定となる「ホールバーニング」という現象が防げる。ゆえに、高出力になってもモードが安定で、電流−光出力特性に「キンク（kink）」と呼ばれる折れ曲がりが発生しない。
【０１１２】
さらに、導波路１を逆バイアスで動作させる方式がある。
図１１は、導波路を逆バイアスで動作される素子の断面構造を例示する概念図である。同図に関しては、前述した各具体例と同一の部分には同一の符号を付して詳細な説明は省略する。
【０１１３】
この素子においては、導波路構造１と利得領域３との間の層をｎ型ＩｎＰのグラウンド（ground）とし、その上下がｐ層になるようにする。ここで、導波路１ａ（コア）を、電界で屈折率の実数部が変化するような結晶組成の材料により形成すると、電界によって発振波長を調整することができる。つまり、同調範囲の広い波長可変型レーザ（tunable laser）を実現することができる。
【０１１４】
または、導波路１ａ（コア）を電界で屈折率の虚数部が変化するような結晶組成の材料により形成すると、電界によって損失が変化する。これは電界吸収型外部変調器と同じ作用である。この電界による変化を出力光の変調に利用できる。この場合には、電流による直接変調と異なり、光学的損失の電界による変調である。順方向の注入キャリア密度を変調させる場合と比べると、本具体例の場合には高速で緩和振動の影響の少ないきれいな出力波形が得られる。これは、出力波形を観察した時に、いわゆる「アイが開く状態」が得られることに対応し、ビット・エラー・レートが極めて低い高速光伝送が可能となる。
さらに、レーザと変調器とを集積することもできる。
【０１１５】
図１２は、レーザと光変調器とを集積した光機能素子の断面構造を例示する概念図である。レーザに注入する電流を変化させるいわゆる直接変調方式では、屈折率の変化によりチャープ（chirp）も起こってしまう。これに対して、本具体例においては、電界吸収型の変調器であるＥＡＭを分離させて集積することにより、さらに高速で安定した光伝送が可能となる。
【０１１６】
すなわち、導波路１のコア部１ａが電界で屈折率の虚数部が変化するような結晶組成とする。例えば、ＩｎＧａＡｓＰを用いる。すると電界の印加によって光の損失が変化する。これは電界吸収型外部変調器と同じ作用である。この電界による変化を光変調に利用できる。
【０１１７】
レーザとして作用する本発明の主要構造部分の他に、回折格子つき導波路の延長部分（この部分においては回折格子を除去してレーザ機能をなくする）を電界吸収型外部変調器（ＥＡＭ：Electro-Absorption Modulator）として利用する。この場合、活性（gain）領域から導波路まで一回の結晶成長で形成可能である。本発明の導波路は活性領域やＤＢＲから離れており、導波モードの伝搬に影響を与えないようにできるため、このように一回で成長できる。ＥＡＭ部では、活性領域には電流を注入せず、励起させない。活性領域を励起させないと吸収率が高くなるが、本発明においては、別に導波路１を設けてあるので、光はこの導波路１を介して伝搬し変調することができる。
【０１１８】
回折格子のある活性領域の導波路部分は、吸収をあまり増加させない範囲で波長可変（tunable）型のレーザとすることもできる。
【０１１９】
ＥＡＭは、電流によるレーザの直接変調と異なり、光学的損失の電界による変調である。順方向の注入キャリア密度の変調に比べると、高速で緩和振動の影響の少ないきれいな出力波形が得られるというメリットを有する。
次に、本発明の第１１の実施の形態について説明する。
図１３は、本実施形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態においては、長い導波路１に沿って複数の放射モード共振器を配置し、それぞれ独立に制御変調する。この構成により、導波路１を主要発振器とした場合に、そのポンピングを導波路軸方向で変化させることができる。これにより発振波長のチューニングもできる。また、導波路軸方向の光強度が平坦になり、空間ホールバーニング等の不均一性に依存する発振不安定性を補償することができる。
【０１２０】
また、複数の放射モード共振器を主要発振器とした場合、それぞれを独立に変調することもできる。さらに、それぞれの発振波長を異なるように制御して、導波路１へ出力する波長多重通信（ＷＤＭ：wavelength division multiplexing）用の光源にも応用できる。
【０１２１】
前述した第９実施形態のチューナアンプは光信号を分波して受信する光機能素子であったが、本実施形態においては、このように放射モード共振器を波長多重レーザ発振器として、合波して導波路に送信する光機能素子とすることができる。本実施形態の送信器と第９実施形態の受信器とは構成が類似するので、生産性の点もで優れる。
【０１２２】
次に、本発明の第１２の実施形態について説明する。
【０１２３】
図１４は、本実施形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態は、放射モード共振器の変形例であり、この放射モード共振器自体にも導波機能を持たせるものである。すなわち、図１４の光機能素子は、放射モードを増幅するための共振器を、導波路型の活性ＤＢＲ構造７により実現した構成例である。ここで、「活性ＤＢＲ」とは、ゲインを有する波長選択性のある分布反射鏡のことである。本実施形態においては、増幅機構、反射機構、及び位相制御機構をまとめて活性ＤＢＲ導波路７に集約している。
【０１２４】
これは、通常のＤＦＢレーザと部分的に類似した構成を有する。すなわち、導波路に回折格子を有し、活性層があって、電流を供給することにより利得が得られれば増幅機能がある。逆バイアスの電界により屈折率を変化させれば、位相制御機能が得られる。勿論、回折格子によって入力に対して反射して戻す反射機能も有することは言うまでもない。
【０１２５】
また、放射モードを受け入れるテーパ領域８を介して放射モードをＤＢＲ導波路７に導くように形成する。ＤＢＲ導波路７の方向は放射モードの方向を考慮して、導波路１に対して垂直とした。
【０１２６】
次に、本発明の第１３の実施の形態について説明する。
【０１２７】
図１５は、本実施形態にかかる光機能素子を表す概念図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態は、前述した第１２実施形態と関連する。すなわち、放射モードを増幅する共振器のうちの上側を、もとの導波路１と平行な導波路１’として構成する。導波路１’には活性領域６’が形成されておりゲインすなわち増幅作用を有する。反射膜３０’は端面に形成されている。放射モードの導波路１’への結合は、導波路１に形成された２次の回折格子２と同様の回折格子２’とにより行う。本実施形態は、別の見方をすると、導波路１の構造体が複数であり、回折格子同士により結合しているとも言える。従って、本実施形態の変形例として、導波路１’の上側にさらに図示しない垂直方向の共振器が設けられていても良い。
【０１２８】
次に、本発明の第１４の実施の形態について説明する。
【０１２９】
図１６は、本実施形態にかかる光機能素子を表す一部切断斜視図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。本実施形態の光機能素子の構成を、その製造工程に沿って説明すると以下の如くである。
【０１３０】
まず、同一のｎ型ＩｎＰ基板５０１上に、同じｎ型ＩｎＰの緩衝層（図示せず）を成長させた後、ＩｎＧａＡｓＰで構成される活性層兼導波層（１＋６）を成長する。これをパターニングして、その側面に２次の回折格子２を形成する。このとき残りの部分としてゲイン領域３も形成する。
【０１３１】
この上に、ｐ型ＩｎＰクラッド層５０２、ｐ型ＩｎＧａＡｓＰコンタクト層５０３を成長する。次に、活性導波路（１＋６）とゲイン領域３とを独立に励起するため、絶縁（isolation）のためのプロトン照射領域５０４を形成する。さらに、ｐ側電極５０５、５０６を形成し、基板の裏面側にはｎ側電極５０７を形成する。最後に、高反射膜４をゲイン領域３の外側の劈開面に堆積させる。
【０１３２】
このように、ＩｎＰ基板上にモノリシック（monolithic）に本発明の構成を集積できる。この例は基板の面に対して水平な方向に各機能を集積した例である。また、図示した例は、単純な基本素子であるが、アレイ（array）のように複数の素子を集積することも可能である。
【０１３３】
次に、本発明の第１５の実施の形態について説明する。
【０１３４】
図１７は、本実施形態にかかる光機能素子を表す概略斜視図である。同図についても、前述した各実施形態と同様の部分は、同一の符号を付して詳細な説明は省略する。図１７に表した例は、ＧａＡｌＡｓ／ＧａＡｓ系材料を用いた場合にの実施例であり、その構成を製造工程に沿って説明すると以下の如くである。
【０１３５】
まず、半絶縁性ＧａＡｓ基板６０１上に、下側の高反射多層膜４を成長する。この多層膜４は、例えば、ＡｌＡｓ層とＧａＡｓ層との多層構造とすることができる。また、このようにして成長させた多層膜４について、後に、ＡｌＡｓ層を選択酸化法でＡｌの酸化物に変えて、さらに反射率を大きくすることもできる。この上に、ゲインを有するＧａＡｓの増幅層３を成長し、さらに、ｎ型のＡｌＡｓ層６０２、ＧａＡｌＡｓ（Ａｌ組成比：０．３）クラッド層６０３を成長する。活性層６を続いて成長した後、ＧａＡｌＡｓ（Ａｌ組成比：０．１５）の導波路層１を成長する。いったん成長炉から取り出した後、２次の回折格子２を形成する。次に、再び結晶成長工程でＧａＡｌＡｓクラッド層６０３を成長する。さらに、連続して、ＧａＡｓコンタクト層６０４を成長する。
【０１３６】
ｐｎ接合は、Ｚｎ（亜鉛）を拡散した拡散領域６１０により形成される。これは、いわゆる横方向接合ストライプ（ＴＪＳ：Transverse junction stripe）構造である。積層されて集積された増幅機構３の層構造と活性層６の層構造に対し、ｐｎ接合を同時に形成できる。このＴＪＳ構造では、光が接合付近に閉込められて導波するという特徴がある。さらに、上側に高反射膜５として誘電体多層膜を形成する。
【０１３７】
このようにして、基板面に対して垂直な方向に各機構を積層した集積素子ができる。加えて、横方向から水蒸気による選択酸化法でＡｌＡｓ層６０２の一部をＡｌ酸化膜６５０に変えて、活性層６とゲイン層３との絶縁と電流狭窄の効果を持たせることができる。
【０１３８】
さらに、ｐ側電極５０５、ｎ側電極（導波路用）５０７、及びｎ側電極（増幅層用）５０８を形成して光機能素子が完成する。
【０１３９】
本実施形態の光機能素子は、面型の垂直集積デバイスと言える。第１４実施形態と同様に複数の素子を有するアレイにも応用できる。
【０１４０】
次に、本発明の第１６の実施の形態について説明する。
図１８は、実施形態にかかる光通信装置を表す概念図である。すなわち、同図の光通信装置は、本発明による光機能素子７００を応用したものである。光機能素子７００の周辺には、ＬＤ（laser diode）の駆動回路、ＰＤ（photo diode）からの光電流を計測する回路、ＡＰＣ回路、信号発生器等の電子回路部９００が接続されている。光機能素子において発生した光信号は、光ファイバ８００を通って伝送される。もちろんファイバを使わない空間伝送により伝送しても良い。
【０１４１】
本発明によれば、種々の機能が集積化されるため、送受信装置を非常に小型化できる。また、送受信装置の製造の際にアセンブリが簡単になるので、コストを大幅に低減できる。さらに、光ファイバとの接続が容易になる。また、温度の変化の少ない導波路を、温度の変化の大きい利得領域から分離できるため、波長の安定性を維持できる。
【０１４２】
以上、具体例を参照しつつ本発明の実施の形態について説明した。しかし、本発明は、これらの具体例に限定されるものではない。
【０１４３】
例えば、上述した具体例においては、ＩｎＧａＡｓＰ／ＩｎＰ系やＧａＡｌＡｓ／ＧａＡｓ系について説明したが、本発明は、これら以外にも、種々の材料系を用いて同様に適用することができる。このような材料系としては、例えば、ＩｎＧａＡｌＰ系、ＢＩｎＧａＡｌＮ系などの種々のIII−Ｖ族化合物半導体、ＺｎＳｅ系、ＺｎＳ系などのII−IV族化合物半導体、ＳｉＣなどのIV族半導体などの材料を挙げることができる。
【０１４４】
また、本発明において用いる導波機構、増幅機構、反射機構、位相制御機構などの具体的な構成についても、当業者が適宜選択した構成を同様に用いて上述した具体例と同様の効果を得ることができる。
【０１４５】
さらに、これらの機構の数や具体的な配置関係についても、当業者が適宜決定してし同様の効果を得ることができる。
【０１４６】
すなわち、本発明は、その主旨を逸脱しない範囲において種々に応用あるいは拡張が可能である。
【０１４７】
【発明の効果】
本発明によれば、新しい概念の放射モード共振器構造を種々の導波路構造に沿って適用することで、さまざまな機能の新規な光デバイスを実現できる。
【０１４８】
以上の説明においては、具体例の数が多く、その効果は各具体例の中でも個別に説明したので、ここでは、一般的な効果に関して言及する。
【０１４９】
本発明によれば、増幅機構や反射機構などの要素を導波路に沿った形で配列するので、導波路に対して効率的な相互作用が可能である。その一例としては、効率的な光励起を挙げることができる。また、導波路に沿って設けることにより効率的な配置が可能であり、大きな面積を必要としない。このことはまた、モノリシックな集積化にも向いている。また、回折格子自体に波長選択性や回折格子結合器の作用があるので、分波器や合波器の機能が実現され、波長多重用光デバイスとして用いた場合に、コンパクトで低コストの光機能素子が実現できる。
【０１５０】
また、上述したような低価格で高性能の光機能素子を用いれば、高性能の光通信装置を安価に提供することができるようになる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態にかかる光機能素子を表す概念図である。
【図２】本発明の第２の実施の形態にかかる光機能素子を表す概念図である。
【図３】本発明の第３の実施の形態にかかる光機能素子を表す概念図である。
【図４】本発明の第４の実施の形態にかかる光機能素子の構成を例示する概念図である。
【図５】本発明の第５の実施の形態にかかる光機能素子を表す概念図である。
【図６】本発明の第６の実施の形態にかかる光機能素子を表す概念図である。
【図７】本発明の第７の実施の形態に係る光機能素子を表す概念図である。
【図８】本発明の第９の実施の形態にかかる光機能素子を表す概念図である。
【図９】本発明の第１０の実施の形態にかかる光機能素子を表す概念図である。
【図１０】石英クラッドを採用した素子の断面構造を例示する概念図である。
【図１１】導波路を逆バイアスで動作される素子の断面構造を例示する概念図である。
【図１２】レーザと光変調器とを集積した素子の断面構造を表す概念図である。
【図１３】本発明の第１１の実施の形態にかかる光機能素子を表す概念図である。
【図１４】本発明の第１２の実施の形態にかかる光機能素子を表す概念図である。
【図１５】本発明の第１３の実施の形態にかかる光機能素子を表す概念図である。
【図１６】本発明の第１４の実施の形態にかかる光機能素子を表す一部切断斜視図である。
【図１７】本発明の第１５の実施の形態にかかる光機能素子を表す概略斜視図である。
【図１８】本発明の実施の形態にかかる光通信装置を表す概念図である。
【符号の説明】
１，１’導波機構
２，２’２次以の回折格子
３ 増幅機構
４ 反射機構
５ 位相制御（変調）機構
６，６’活性層（導波路機構のゲイン部分）
７ 導波路型活性ＤＢＲ
８ 導波路型活性ＤＢＲの放射モード入力テーパ部
１１ 位相シフト
２０ 高反射構造
２１ 端面高反射構造
３０、３０’ 導波路端面の反射鏡
４０ 受光機構
５０ 基板
５３ 電流ブロック領域
５５ 透明電極
６０ ワイア
７０ 電極
１００ 垂直出力
２００ 導波路端出力
５０１ ｎ型ＩｎＰ
５０２ ｐ型ＩｎＰ
５０３ ＩｎＧａＡｓＰコンタクト層
５０４ プロトン照射領域
５０５ ｐ側電極（導波路）
５０６ ｐ側電極（増幅領域）
５０７ ｎ側電極
５０８ ｎ側電極（導波路）
６０１ ＳＩ（半絶縁性）ＧａＡｓ
６０２ ＧａＡｌＡｓクラッド層
６０３ ＡｌＡｓ
６０４ ＧａＡｓコンタクト層
６１０ Ｚｎ拡散領域
６５０ ＡｌＡｓ６０３の選択酸化膜
７００ 本発明の光機能素子
８００ 光ファイバ
９００ 外部回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical functional element and an optical communication device. More specifically, the present invention is based on a waveguide mechanism having a second-order or higher diffraction grating, and an optical amplifier having a resonator structure for amplifying a radiation mode radiated from this waveguide mechanism with high efficiency, The present invention relates to optical functional elements such as a modulator and a laser oscillator, and an optical communication device using them.
[0002]
[Prior art]
As an optical functional element including a waveguide for guiding a light wave, for example, a semiconductor laser can be cited. A normal semiconductor laser forms a resonator with a single waveguide structure. Similarly, a semiconductor optical amplifier (SOA) includes a single waveguide structure. In other words, in the conventional optical functional element, the concept of “one resonator” was assumed.
[0003]
[Problems to be solved by the invention]
Since this concept is common sense, the description of the configuration of the conventional optical functional element will be omitted with reference to the drawings. There are no major problems with these conventional concepts and specific structures. The disadvantage of the prior art is that it has a single resonator structure and thus lacks expandability and flexibility.
[0004]
[Means for Solving the Problems]
The present invention greatly advances such a conventional concept. That is, the concept is that another resonator structure is formed in another direction along one resonator structure or waveguide structure. In particular, it is based on the concept of constructing a radiation mode resonator structure radiated from a waveguide with a hologram. Here, “hologram” is defined as “a fine structure of complex refractive index or complex reflectance (imaginary part represents loss / gain) capable of generating a spatially controlled radiation mode”. The “second-order or higher diffraction grating” employed in the specific example described in detail below is merely one form of the “hologram”. This is because the diffraction grating has a structure based on a uniform periodic structure mainly of the real part of the most simplified refractive index. Since it is easy to understand in this way, the following description will be given with a specific example using a diffraction grating.
[0005]
On the other hand, as will be described later in detail, it is also an important embodiment of the present invention that the period of the diffraction grating is slightly changed in the waveguide direction or that a phase shift is provided. When these modified examples are collectively, the “hologram” is as defined above.
[0006]
Next, the novel resonator structure of the present invention will be described in a little more detail. Conventionally, it has been common knowledge that if a waveguide is formed, the resonator structure of the waveguide is unidirectional. When this waveguide has a second-order or higher diffraction grating, the radiation mode is radiated from the entire waveguide as a narrow beam extending in a predetermined direction. Focusing on this radiation mode with uniform characteristics, what constitutes a new radiation mode resonator is constructed and entangled with the original waveguide resonator is the remarkable novelty of the present invention.
[0007]
That is, the present invention opens up entirely new functions rather than improving the drawbacks of the prior art.
[0008]
Specifically, the optical functional device of the present invention is a waveguide mechanism that guides light waves and has gain or loss, and has a hologram that can generate radiation mode light by combining with the guided light waves. 1 waveguide mechanism, an amplification mechanism for amplifying and emitting the radiation mode light emitted from the first waveguide mechanism, and the radiation mode light emitted from the amplification mechanism for the first waveguide. A first reflection mechanism that reflects toward the mechanism, and the radiation mode light generated from the first waveguide mechanism is amplified by the amplification mechanism and reflected by the first reflection mechanism. By returning to the first waveguide mechanism, the light wave guided through the first waveguide mechanism is amplified and can be extracted from the end face of the first waveguide mechanism.
[0009]
Here, the amplifying mechanism is provided apart from the first waveguide mechanism so that a guided mode of the guided light wave is a single transverse mode. That is, by maintaining the single transverse mode in the waveguide mechanism, the radiation mode is stabilized, and it is possible to ensure coupling when light is extracted from the end face of the waveguide mechanism.
[0010]
Further, the amplification mechanism may give not only a gain action but also a loss action to the radiation mode light.
[0011]
The optical functional element of the present invention further includes a phase control mechanism for controlling the phase of the radiation mode light reflected by the first reflection mechanism. With such a phase control mechanism, the reflected light from the reflection mechanism can be coupled to the first waveguide mechanism via the diffraction grating with high efficiency.
[0012]
Here, the phase control mechanism is also provided apart from the first waveguide mechanism so that the guided mode of the guided light wave is a single transverse mode, thereby providing a single transverse mode in the waveguide mechanism. It is possible to maintain the radiation mode to be stable and to secure the coupling when the light is extracted from the end face of the waveguide mechanism.
[0013]
Further, at least two of the waveguide mechanism, the amplification mechanism, the first reflection mechanism, and the phase control mechanism may be realized by a common structure. For example, by providing an active layer having a gain as a part of the waveguide mechanism, it is possible to serve as both the waveguide mechanism and the amplification mechanism.
[0014]
Also, a second waveguide mechanism provided substantially parallel to the first waveguide mechanism, having a second hologram, and optically coupled to the first waveguide mechanism via the second hologram Is further provided.
[0015]
Here, as a preferred embodiment of the present invention, the hologram is a second-order or higher diffraction grating.
[0016]
The diffraction grating may have a blaze angle. That is, if the cross-sectional shape of the diffraction grating is asymmetrical, selectivity can be generated in the direction of the light wave, and an optical isolator or a directional coupler can be formed.
[0017]
Further, by providing a phase discontinuity, that is, a phase shift in the diffraction grating, it is possible to adjust the distribution of the waveguide mode and the radiation mode in the waveguide structure.
Yes.
[0018]
Also, the resonance conditions of the resonator formed perpendicular to the waveguide mechanism should be optimized by modulating the amplification factor of the amplification mechanism, the refractive index of the waveguide mechanism, and the reflectance or refractive index of the reflection mechanism. Can do.
[0019]
Further, by changing the period of the diffraction grating along the waveguide direction of the waveguide mechanism, it becomes possible to resonate and amplify light having a plurality of wavelengths. Then, functions such as a light-emitting element, a multiplexer, or a demultiplexer for wavelength multiplexing communication can be realized.
[0020]
Similar effects can be realized by changing the amplification factor of the amplification mechanism, the refractive index of the waveguide mechanism, the reflectance of the reflection mechanism, and the like along the waveguide direction.
[0021]
The same effect can also be realized by providing a plurality of the phase control mechanisms for adjusting the relative phase along the direction of the waveguide, and allowing each to modulate independently.
[0022]
Alternatively, a plurality of amplification mechanisms may exist along the waveguide direction, and each of them may be independently modulated.
[0023]
Alternatively, it can be realized by providing a plurality of mechanisms for modulating the refractive index of the waveguide mechanism along the direction of the waveguide and independently modulating them.
[0024]
Alternatively, it can be realized by providing a plurality of mechanisms for modulating the reflectance of the first reflecting mechanism along the direction of the waveguide and independently modulating them.
On the other hand, the optical functional element of the present invention can be regarded as having a transmission line through which an optical signal propagates in the waveguide mechanism. Specifically, a tuner amplifier can be mentioned.
[0025]
That is, the optical signal propagating to the waveguide mechanism of such an optical functional element includes optical signals having a plurality of wavelengths that are independently modulated.
[0026]
Furthermore, in the present invention, the optical signal can be converted into the radiation mode light and output.
[0027]
Further, the radiation mode output with respect to the signal intensity input to the waveguide mechanism
It can also be amplified.
[0028]
Further, the radiation mode output can be divided into a plurality of output ports for output.
[0029]
In addition, the optical signals of the plurality of wavelengths can be selectively tuned according to the wavelength and taken out as a radiation mode output.
[0030]
The optical functional element of the present invention described above can be configured to perform a laser oscillation operation in the waveguide mechanism.
[0031]
In this case, the laser oscillation characteristic can be improved by providing the second reflection mechanism at at least one end of the waveguide mechanism.
[0032]
Further, such laser output may be extracted from at least one end of the waveguide mechanism.
[0033]
Alternatively, the laser output may be taken out from the resonator formed by the first reflection mechanism as the radiation mode light.
[0034]
Furthermore, the resonator formed by the first reflection mechanism may be configured to perform a laser oscillation operation.
[0035]
In addition, the input of light from the outside or the output of light to the outside is performed by either one of a waveguide mode from at least one end face of the first waveguide mechanism and a radiation mode from the first waveguide mechanism. Or by both the waveguide mode and the radiation mode.
[0036]
In addition, the light input unit from the outside or the light output unit from the outside is provided with a light collecting function for optically coupling to another optical element. Further, at least one of the waveguide mechanism and the amplification mechanism includes a medium that generates a gain by optical excitation.
[0037]
Specifically, the medium that generates gain by optical excitation is a medium containing at least one of erbium (Er), Pr (praseodymium), and other rare earth elements.
[0038]
In addition, a translucent electrode for supplying a current or applying an electric field is provided between the waveguide mechanism and the amplification mechanism.
[0039]
Further, the present invention is characterized in that the real part or the imaginary part of the refractive index of the waveguide mechanism can be changed by applying an electric field.
[0040]
On the other hand, by providing a plurality of resonators formed by the first reflecting mechanism along the waveguide mechanism, pumping in the waveguide mechanism can be changed along the waveguide direction. Thereby, the oscillation wavelength can be tuned. Further, the light intensity in the waveguide direction becomes flat, and oscillation instability that depends on nonuniformity such as spatial hole burning can be compensated.
[0041]
Further, such a plurality of resonators may be independently controlled and modulated.
[0042]
Further, the oscillation wavelengths of the laser beams of the plurality of resonators may be different from each other.
[0043]
Alternatively, the oscillation wavelengths of the laser beams of the plurality of resonators are controlled to have different wavelengths according to the reflection characteristics of the first reflection mechanism, the phase control mechanism, the wavelength characteristics of the amplification mechanism, or the control mechanism thereof. You may do it.
[0044]
Further, the output of the laser beam from the resonator formed by the first reflection mechanism may be taken out from at least one end of the first waveguide mechanism.
[0045]
Alternatively, the output of the laser beam from the resonator formed by the first reflecting mechanism may be taken out from at least one of the reflecting mirrors of the resonator as the radiation mode light.
[0046]
On the other hand, in the optical functional element described above, a light receiving mechanism for the output light may be further provided.
[0047]
Further, at least one of the amplification mechanism, the phase control mechanism, and the reflection mechanism may constitute a waveguide mechanism independent of the waveguide mechanism. A specific example is an active DBR structure.
[0048]
Further, such an independent waveguide mechanism can be formed perpendicular to the first waveguide mechanism.
[0049]
Alternatively, such an independent waveguide mechanism is formed in parallel to the first waveguide mechanism, and has a diffraction grating, and is optically coupled to the first waveguide structure via the diffraction grating. It may be made to be.
[0050]
The optical functional element described above can be formed by monolithically integrating at least two of the mechanisms.
[0051]
Further, such a monolithic integration state can be a state in which they are stacked in a direction perpendicular to the substrate surface.
[0052]
Furthermore, a portion having a pn junction among a plurality of mechanisms stacked in a direction perpendicular to the substrate surface may have a lateral junction stripe (TJS) structure.
[0053]
Furthermore, an insulating or semi-insulating layer may be inserted between the plurality of lateral junction stripe structures.
[0054]
On the other hand, the optical communication apparatus of the present invention is characterized by including any one of the optical functional elements described above.
[0055]
DETAILED DESCRIPTION OF THE INVENTION
In a hologram capable of generating radiation mode light, for example, a waveguide having a diffraction grating of second or higher order, a part of the guided light is emitted as radiation mode light perpendicular to the waveguide direction. In the present invention, this radiation mode light is amplified by another amplification mechanism, and then returned to the waveguide again using a reflection mechanism. Since radiation mode light is emitted to both sides of the waveguide, it is desirable to provide a reflection mechanism on both. The present invention encompasses many application inventions based on this unique resonator configuration. One of them is an amplifier. The present invention further includes an optical modulator, a laser oscillator, a coupler, and an optical communication device using them.
[0056]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0057]
FIG. 1 is a conceptual diagram showing an optical functional element according to the first embodiment of the present invention. The basic principle of the optical functional element of the present invention will be described with reference to FIG. First, the optical functional element according to the present invention has a waveguide mechanism for guiding light. In the illustrated example, the optical waveguide 1 is provided as a waveguide mechanism. A secondary diffraction grating 2 is formed on the optical waveguide 1. The waveguide 1 may be an optical fiber, a general dielectric waveguide, or a semiconductor waveguide. For example, an InGaAsP / InP waveguide can be used. This is a laminated structure (slab waveguide) in which an InGaAsP quaternary mixed crystal having a high refractive index is used as a core of a waveguide, and InP having a low refractive index is sandwiched from above and below by a clad. Although this is a one-dimensional cross section, it may be a two-dimensional buried waveguide buried with InP from the lateral direction.
[0058]
As shown in FIG. 1, a part of the light guided in the waveguide 1 having the secondary diffraction grating 2 is radiated in both the upper and lower directions substantially perpendicular to the waveguide direction. This is so-called radiation mode light.
[0059]
In the present invention, the radiation mode light is configured to pass through the amplification mechanism 3. The amplification mechanism 3 has an effect of amplifying light. The amplification mechanism 3 may be an EDFA (Erbium Doped Fiber Amplifier), an SOA (Semiconductor Optical Amplifier), or an optically pumped gain medium. For example, a pn junction having an InGaAsP / InP stacked structure that is energized can be used.
[0060]
However, it is desirable that the amplifying mechanism 3 be disposed at a sufficient distance so as not to directly interfere with the waveguide mode waveguide of the waveguide 1. This is based on the gist of the present invention in which a resonator structure is formed for a light wave converted from a waveguide mode to a radiation mode.
[0061]
A reflection mechanism 4 having a higher reflectivity is disposed at the tip of the amplification mechanism 3. The reflection mechanism 4 has a function of reflecting the radiation mode light with a high reflectance, and can be configured by a dielectric multilayer film, for example. The radiation mode light reflected by the reflection mechanism 4 is amplified again by the amplification mechanism 3 and returns to the waveguide 1 through the diffraction grating 2. By repeating such amplification / reflection / amplification cycle, a unique resonator structure is realized. A more specific configuration example of the optical functional element will be described in detail later.
[0062]
Next, a second embodiment of the present invention will be described.
FIG. 2 is a conceptual diagram showing an optical functional element according to the second embodiment of the present invention. That is, in the element shown in the figure, a stronger resonator mechanism is realized by providing the above-described resonator structure both above and below the waveguide 1. That is, each of the radiation mode light emitted upward and downward in the waveguide 1 repeats the cycle of amplification / reflection / amplification.
[0063]
A feature of the radiation mode is that it can be output with a very sharp beam over the entire region where the diffraction grating exists. Therefore, the radiation mode light has the flexibility to configure various optical functions along the waveguide, unlike the output of the waveguide end face regarded as a point light source. For example, there is an input / output condensing function for coupling with another optical element. Specific examples include a lens function, another hologram, and an optical isolator.
[0064]
Next, a third embodiment of the present invention will be described.
FIG. 3 is a conceptual diagram showing an optical functional element according to the third embodiment of the present invention. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, a phase control mechanism 5 is added to the configuration of the second embodiment described above. The phase control mechanism 5 has an action of controlling the phase of light, and adjusts the phase of the reflected light so that the reflected light from the reflection mechanism 4 can be efficiently coupled to the waveguide 1 through the diffraction grating 2. is there. Thereby, the coupling efficiency of the reflected light with respect to the waveguide 1 can be improved, and resonance can be performed with higher efficiency.
[0065]
A specific example of the phase control mechanism 5 is an InGaAsP / InP slab type waveguide structure having a pn junction. When the pn junction of such a waveguide is energized or an electric field is applied with a reverse bias, the refractive index changes and the light phase can be controlled. The phase control mechanism 5 may be provided between the amplification mechanism 3 and the reflection mechanism 4, or may be provided between the waveguide 1 and the amplification mechanism 3. In the amplifying mechanism 3, the carrier density can be changed by energization to change the refractive index. An application in which it is canceled by the phase control mechanism 5 is also conceivable.
[0066]
The basic configuration of the optical functional element of the present invention has been described above as the first to third embodiments.
Next, the theoretical background of the resonator structure in the present invention will be described.
First, a situation is assumed in which a waveguide having a second or higher order diffraction grating oscillates by distributed feedback. In the analysis method proposed by the present inventor, the amplitude of the radiation mode in the diffraction grating is approximately expressed by the following equation.
[0067]
[Expression 1]

Here, it is assumed that the diffraction grating exists from x = 0 to x = g of the coordinates of the waveguide. In the equation (1), a (x) represents the amplitude of the radiation mode radiated downward from the lower end (x = 0) of the diffraction grating region, and b (x) in the equation (2) represents the upper end (x = Represents the amplitude at x of the radiation mode emitted upward from g). T (x) is a function determined by the Fourier coefficient of the diffraction grating and the field of the waveguide mode.
[0068]
Constant C _a , C _b Is a constant determined by boundary conditions. This constant is obtained under the boundary condition that the radiation modes emitted above and below the waveguide are reflected by the reflection mechanism. The reflectance on the waveguide is r _g , The amplitude reflectivity under the waveguide r ₀ And These reflectances include the phase. The influence of the layer structure up to the reflection mechanism after the radiation mode is radiated from the diffraction grating is also included in this reflectance, and it is obtained on the assumption that there is a reflection mechanism at the diffraction grating region boundary. That is, a _n (G) = r _g b _n (G), b _n (0) = r ₀ b _n (0).
[0069]
Then the constant C _a , C _b Can be represented by the following equations, respectively.
[0070]
[Expression 2]

However, the following equation was defined.
[0071]
[Equation 3]

Here, what is important is the denominator of Equation (3). That is,
[0072]
[Expression 4]

Is established, the denominator of equation (3) becomes zero, and the constant C _a , C _b Becomes infinite. That is, as can be seen from the equations (1) and (2), it oscillates as a “radiation mode resonator”. That is, it can be seen that oscillation occurs when the reflectivity is large, the gain is provided, and the phase condition is satisfied.
[0073]
Further, when viewed from the waveguide side, a radiation mode that has been a loss in the past is amplified and returned in the present invention, which is a gain. Therefore, the radiation mode loss in the coupled wave equation used for the analysis of the DFB laser replaces the gain term. Even if the radiation mode resonator does not reach the oscillation condition, the DFB laser can oscillate at a low threshold.
[0074]
In the claims of the present application, it is easy to understand from this explanation that three elements of the amplification mechanism, the reflection mechanism, and the phase control mechanism for the radiation mode are claimed.
[0075]
The configurations of the first to third embodiments described above are the basis of the present invention. However, in the present invention, the elements such as the amplification mechanism, the reflection mechanism, and the phase control mechanism described above do not have to exist independently of each other. For example, as in a fourth embodiment described below, two or more mechanisms may be included in one component in common.
[0076]
FIG. 4 is a conceptual diagram illustrating the configuration of the optical functional device according to the fourth embodiment of the invention. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In the optical functional element of the same figure, there is no medium 3 having a gain. Instead, an active layer 6 having a gain is provided in the vicinity of the waveguide 1. The reflection mechanism 4 ′ also has a gain. That is, the active layer 6 and the reflection mechanism 4 ′ function as an amplification mechanism.
[0077]
As an example in which the reflection mechanism has a gain, a pn junction can be formed in a DBR (Distributed Bragg Reflector) mirror made of a semiconductor multilayer film laminated in the plane direction, and gain can be given by current injection. Alternatively, another waveguide may be provided perpendicular to the waveguide 1, and a DBR mirror may be provided therein.
[0078]
Next, a fifth embodiment of the present invention will be described.
[0079]
FIG. 5 is a conceptual diagram showing an optical functional element according to the fifth embodiment of the present invention. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In the example shown in the figure, the second-order or higher diffraction grating 2 has a phase shift 20, that is, a phase discontinuity. The phase shift 20 is effective for controlling the intensity distribution of the radiation mode in the direction parallel to the waveguide. That is, when a radiation mode is generated from the waveguide, the waveguide allows two waves having opposite directions of travel. The intensity distribution in the axial direction of the radiation mode, that is, in the waveguide direction, is greatly influenced by being strengthened or weakened by the interference of the respective radiation modes generated by the two waveguide modes. This state of interference changes with the phase shift. Therefore, providing an appropriate phase shift has a great merit. Further, since the phase shift also affects the intensity in the axial direction of the waveguide mode itself, it can be an important component of the present invention.
[0080]
That is, if there is no phase shift, a longitudinal mode having a small radiation mode intensity oscillates at the center of the waveguide. On the other hand, for example, when reflection at both end faces of the waveguide is kept low, a phase shift equivalent to λ / 4 is provided in the center of the waveguide, and this waveguide is oscillated by DFB (distributed feedback), the phase shift A longitudinal mode in which the intensity of the waveguide mode and the radiation mode is large oscillates at the position.
[0081]
That is, the intensity distribution in the axial direction of the radiation mode fed back by receiving the gain matches the intensity of the waveguide mode. Since it is strongly synchronized spatially at the phase shift position, the optical feedback, that is, the effect that the efficiency of the resonator becomes extremely large is obtained.
[0082]
Note that the same effect can be obtained by adopting a structure that changes the effective refractive index of the waveguide instead of such a phase shift. That is, even if the period of the diffraction grating is uniform, it can be replaced by providing an effective phase shift region (not shown) in which the width, thickness, or refractive index of the waveguide structure is changed. Further, it is desirable that the phase shift has a phase shift amount in a range from an integral multiple of the in-waveguide wavelength λ to 1/8 to 3/8. The above-mentioned 1/4 corresponds to the center value of this range.
[0083]
Next, a sixth embodiment of the present invention will be described.
FIG. 6 is a conceptual diagram showing an optical functional element according to a sixth embodiment of the present invention. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, the diffraction grating 2 has a so-called blaze angle in which the cross-sectional shape is asymmetric. In a diffraction grating having a symmetrical cross-sectional shape without a blaze, the radiation mode generated by the guided mode traveling in a predetermined direction is often radiated in substantially the same manner in the two upper and lower directions. However, if there is a blaze, the radiation mode radiated up and down can be made selective. For example, in FIG. 6, the light wave passing through the waveguide from left to right has a high ratio of being emitted upward in the drawing, and in the reverse direction, the ratio of being emitted downward is large.
[0084]
By introducing such a blaze angle, the following advantages can be obtained. That is, when the signal light always propagates in one direction with respect to the waveguide, the radiation mode radiated to either the upper or lower side of the waveguide can be increased depending on the blaze angle. When the reflectance on the large side is increased or the gain on the amplification mechanism is increased to enhance the one-side mechanism, the function can be efficiently enhanced. Further, if the amplification effect is reduced with respect to the signal propagating in the reverse direction, the function of an optical isolator or a directional coupler can be provided.
[0085]
Next, a seventh embodiment of the present invention will be described.
The optical functional element of this embodiment can be described using the configuration illustrated in FIGS. That is, in this embodiment, the waveguide mechanism, the amplification mechanism, and the reflection mechanism are independently modulated and controlled. These are basic requirements for an optical functional device that handles an optical signal, together with the phase control mechanism described above in the third embodiment. For example, by controlling the amplification mechanism, the condition of the above-described equation (5) is satisfied, and the oscillation of the resonator perpendicular to the waveguide can be controlled by current injection. The parameters of other mechanisms, that is, the waveguide mechanism and the reflection mechanism can be similarly controlled.
[0086]
Next, an eighth embodiment of the present invention will be described.
FIG. 7 is a conceptual diagram showing the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In this embodiment, another resonance structure using a radiation mode is formed along the waveguide. Forming along the waveguide means that the full length of the long waveguide can be utilized. Therefore, it is possible to change the resonator structure along the waveguide. It is also possible to form a large number of resonator structures along the waveguide.
[0087]
In the example shown in FIG. 7, the period of the diffraction grating 2 of the waveguide structure 1 changes along the waveguide. In this example, the diffraction grating has three types of periods of Λ1, Λ2, and Λ3. A reflection mechanism 4, a phase modulation mechanism 5, and an amplification mechanism 3 are provided corresponding to the diffraction gratings of each period.
[0088]
The operation of this optical functional element will be described as follows. In other words, the waveguide 1 is excited to generate spontaneous emission light. The radiation modes of the wavelength components emitted vertically corresponding to the diffraction grating periods Λ1, Λ2, and Λ3 therein are amplified in the respective radiation mode resonators. The degree of amplification can freely amplify a specific wavelength by independently controlling the gain, reflectance, phase, and the like. The reflection mechanism itself can also enhance the wavelength selectivity by adopting a configuration such as DBR. It is also possible to adjust the peak of the gain spectrum to the specific wavelength. If the amplification is strong, it can be oscillated. Such amplified light can be extracted from each resonator. Moreover, it can also return to the waveguide 1 and can take out from the end surface. Moreover, it can also be taken out as a signal in which a specific wavelength is modulated by each resonator.
[0089]
Such a configuration also has functions of a multiplexer and a duplexer, so that the optical circuit can be laid out in a space-saving manner. Therefore, it is suitable for monolithic integration. In the example of FIG. 7, the waveguide mechanism and other mechanisms can be monolithically integrated on a substrate such as InP. However, for example, the waveguide may be a fiber and the diffraction grating may be a fiber grating.
[0090]
Further, a wavelength selection function can be provided by locally changing the effective refractive index of the waveguide 1 instead of changing the period of the diffraction grating. In addition, an application example in which the period of the diffraction grating is not changed stepwise but continuously is conceivable.
[0091]
Next, a ninth embodiment of the present invention will be described.
[0092]
FIG. 8 is a conceptual diagram showing an optical functional element according to the ninth embodiment of the present invention. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The configuration is similar to that of the eighth embodiment described above. The main difference is how it is applied. That is, in the present embodiment, the waveguide 1 is positioned as a transmission line through which signals, particularly a plurality of signals having different wavelengths, propagate. With the same configuration as that of the eighth embodiment, it is possible to realize a function of tuning the signal and amplifying and extracting the signal separately. That is, this embodiment corresponds to a tuner amplifier.
[0093]
At the same time, the transmission system of this embodiment is also a ring network. That is, a signal input from the left end of the waveguide is also output from the right end, and is also detected at another terminal. In this case, the amplification function of the radiation mode resonator structure also serves as a repeater to prevent signal attenuation.
[0094]
The operation of the element of this embodiment is based on the concept of the eighth embodiment described above. That is, the radiation modes vertically radiated from the diffraction gratings having different periods are amplified by the wavelength selective resonator, and the output is detected. In FIG. 8, each resonator is regarded as an output port, and a signal having a different wavelength is output downward for each port and received by a detector (not shown).
[0095]
When the wavelength interval determined by the period of the diffraction grating (the wavelength interval between Λ1, Λ2, and Λ3 in the example of FIG. 8) is wide, the waveguide is used except for the diffraction grating part having the period corresponding to each wavelength. On the other hand, it is emitted in a direction deviating from the vertical direction. Therefore, tuning is performed only by the arrangement of the resonators. Tuning is also possible by modulating the refractive index of the waveguide.
[0096]
When the wavelength interval is narrow, tuning can be performed by changing the refractive index of the modulation by the phase control mechanism 5 or the DBR reflection mechanism.
[0097]
Next, a tenth embodiment of the present invention will be described.
[0098]
FIG. 9 is a conceptual diagram showing the optical functional element of the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The present embodiment is centered on an optical functional element having a function of laser oscillation. A significant feature of the present invention is that a radiation mode resonator is provided in addition to a waveguide resonator of a normal waveguide laser. Therefore, a variation occurs, which is the main resonator and which is the auxiliary resonator. Of course, there is also a combination of causing both to oscillate. There is also a variation of where the output is taken from.
[0099]
In FIG. 9, the waveguide mechanism 1 can generate optical feedback only with the diffraction grating, but the case where the reflection structures 30 for further enhancing the feedback are provided on both end faces is illustrated.
[0100]
When the waveguide mechanism is a main resonator as in a conventional laser, the radiation mode resonator can be interpreted as an optical pumping mechanism for the main resonator. Since this pumping mechanism can be densely configured along the waveguide 1, very efficient excitation is possible. In the conventional semiconductor laser in which current is injected only into the waveguide, the current density into the narrow waveguide becomes high, and degradation of the active layer 6 and generation of local heat become a problem. On the other hand, according to the present invention, since the current injection is distributed toward the auxiliary resonator, the influence of heat can be reduced and the reliability can be improved. One of the new advantages of the present invention is that both current excitation and optical excitation can be balanced with respect to the main resonator.
[0101]
Both the case where the optical output is extracted from the end face (output 100) as in the conventional case and the case where the optical output is extracted along the waveguide as the radiation mode amplified from the radiation mode resonator (output 200) can be implemented. Either convenient output form can be selected.
[0102]
When the main resonator is a radiation mode resonator, the waveguide mechanism 1 can be considered as an optical pumping mechanism. Similar to the above example, both the case where the optical output is extracted from the end face (output 100) and the case where the optical output is extracted from the radiation mode resonator along the waveguide (output 200) can be implemented. Of course, either convenient output form can be selected.
[0103]
The present embodiment also has a light receiving mechanism 40 as a mechanism commonly added to the invention. In this case, the output light can be monitored by the light receiving mechanism 40, and the output of the laser can be controlled using an external circuit (not shown). For example, APC (Automatic power control) for maintaining the laser output constant can be applied.
The optically pumped waveguide mechanism 1 can be provided with a medium that cannot be excited by current as a material, particularly a medium that has gain only by optical excitation. For example, a quartz-based waveguide doped with Er (erbium) or Pr (praseodymium). These are the same as so-called fiber amplifiers. The radiation mode resonator along the waveguide 1 has a strong optical excitation effect for this waveguide amplifier. If the purpose is excitation only, the reflectivity for the radiation mode can be almost 100% and the output 200 can be ignored.
[0104]
The optical pumping and current pumping can be used in the opposite manner, and may be on the radiation mode resonator side. However, in general, the above example that excites along a long waveguide is more efficient. In addition, the waveguide mechanism 1 made of a passive material that does not allow a current to flow also has a great merit in manufacturing. That is, it is a case where it is difficult to produce a waveguide having an appropriate refractive index difference with a semiconductor having a pn junction. At this time, the waveguide may be formed of a material that is not a semiconductor. For example, quartz (SiO ₂ ) The structure has a clad and a SiN core.
[0105]
FIG. 10 is a conceptual diagram illustrating the cross-sectional structure of an element employing a quartz cladding. That is, FIG. 4A is a cross-sectional view taken along the central axis of the waveguide, and FIG. 4B is a cross-sectional view cut perpendicularly to the waveguide.
[0106]
The configuration will be described along the manufacturing process as follows. First, the active layer 3 having a gain at the pn junction with the DBR reflecting mirror 4 ′ is grown on the semiconductor substrate 50. This is sufficient for troublesome crystal growth, and the number of growth can be reduced. The electrode is a transparent electrode 55 such as ITO (indium tin oxide). On top of this, quartz (SiO ₂ ) A waveguide structure 1 comprising a clad 1b and a SiN core 1a is formed. A secondary diffraction grating 2 is formed in the waveguide core 1a of the SIN. On top of this waveguide structure 1 further SiO ₂ And a dielectric highly reflective multilayer film 4 'made of Si (silicon). An electrode 70 is formed on the back surface of the substrate 50. A wire 60 is bonded to the transparent electrode 55. The current injected through the transparent electrode 55 flows into the active layer 3 below the waveguide structure 1 through the current blocking region 53 as indicated by an arrow in FIG.
[0107]
According to this modification, the current-carrying region and the waveguide region can be separated by a completely different material system, so that the manufacture is easy. For example, the waveguide region may be SiO as described above. ₂ In addition to the clad / SiN core combination, an optical fiber with a diffraction grating may be formed, or a diffraction grating may be formed on a transparent electrode such as ITO, and SiO 2 ₂ A clad made of such a material may be laminated.
[0108]
As described above, if the waveguide region is made of a material system different from the energized region, the step of forming the waveguide portion so as not to damage the expensive semiconductor growth wafer even if the production of the waveguide portion fails. Can be redone. In addition, since a waveguide can be formed with a refractive index smaller than that of a semiconductor, the size can be increased by a factor of about two, so that there is an advantage that processing is easy.
[0109]
Further, since the temperature change of the refractive index of the diffraction grating 2 and the waveguide portion 1 that determines the oscillation wavelength is smaller than that of the semiconductor material, a laser having a stable wavelength with respect to the temperature can be realized. This is suitable for a WDM (wavelength division multiplexing) light source in optical communication. Further, since the waveguide portion 1 is similar to a silica-based fiber, coupling with the fiber is facilitated.
[0110]
As described above, it is not necessary to process the semiconductor on the waveguide in the gain region. Since there is no need to provide a light mode bleed area outside the active layer stripe, the manufacture of the semiconductor portion becomes much easier.
[0111]
On the other hand, a great effect can be obtained even if the waveguide is formed of a passive semiconductor material. If the waveguide is passive, the waveguide itself is not affected by the carrier density. Therefore, the phenomenon of “hole burning” in which the transverse mode and the longitudinal mode become unstable due to the nonuniformity of the refractive index due to the spatial nonuniformity of the carrier density can be prevented. Therefore, the mode is stable even when the output is high, and no bending called “kink” occurs in the current-light output characteristics.
[0112]
Furthermore, there is a method of operating the waveguide 1 with a reverse bias.
FIG. 11 is a conceptual diagram illustrating the cross-sectional structure of an element that operates with a reverse bias in the waveguide. With respect to this figure, the same parts as those in the specific examples described above are denoted by the same reference numerals, and detailed description thereof is omitted.
[0113]
In this element, the layer between the waveguide structure 1 and the gain region 3 is the n-type InP ground, and the upper and lower layers are p layers. Here, when the waveguide 1a (core) is formed of a material having a crystal composition in which the real part of the refractive index is changed by an electric field, the oscillation wavelength can be adjusted by the electric field. That is, a tunable laser with a wide tuning range can be realized.
[0114]
Alternatively, when the waveguide 1a (core) is formed of a material having a crystal composition in which the imaginary part of the refractive index is changed by an electric field, the loss is changed by the electric field. This is the same operation as the electroabsorption external modulator. Changes due to this electric field can be used for modulation of output light. In this case, unlike the direct modulation by the current, the optical loss is modulated by the electric field. Compared with the case where the injected carrier density in the forward direction is modulated, in the case of this specific example, a clean output waveform can be obtained at a high speed and less affected by the relaxation oscillation. This corresponds to the fact that when the output waveform is observed, a so-called “eye open state” is obtained, and high-speed optical transmission with a very low bit error rate becomes possible.
Furthermore, the laser and the modulator can be integrated.
[0115]
FIG. 12 is a conceptual diagram illustrating a cross-sectional structure of an optical functional element in which a laser and an optical modulator are integrated. In the so-called direct modulation method in which the current injected into the laser is changed, chirp also occurs due to a change in the refractive index. On the other hand, in this example, EAM, which is an electroabsorption modulator, is separated and integrated, so that it is possible to transmit light more stably at a higher speed.
[0116]
That is, the core 1a of the waveguide 1 has a crystal composition in which the imaginary part of the refractive index changes with an electric field. For example, InGaAsP is used. Then, the loss of light changes due to the application of an electric field. This is the same operation as the electroabsorption external modulator. Changes due to this electric field can be used for light modulation.
[0117]
In addition to the main structure portion of the present invention that acts as a laser, an extended portion of a waveguide with a diffraction grating (in this portion, the diffraction grating is removed to eliminate the laser function) is used as an electroabsorption external modulator (EAM: Electro -Absorption Modulator) In this case, it can be formed by a single crystal growth from the active (gain) region to the waveguide. Since the waveguide of the present invention is away from the active region and the DBR and can prevent the propagation of the waveguide mode, it can be grown at once. In the EAM portion, no current is injected into the active region and it is not excited. If the active region is not excited, the absorptance increases. However, in the present invention, since the waveguide 1 is provided separately, the light can propagate through the waveguide 1 and be modulated.
[0118]
The waveguide portion of the active region with the diffraction grating may be a tunable laser as long as the absorption is not increased so much.
[0119]
EAM is modulation of an optical loss by an electric field, unlike direct modulation of a laser by current. Compared to the modulation of injected carrier density in the forward direction, there is an advantage that a clean output waveform can be obtained at a high speed and less affected by relaxation oscillation.
Next, an eleventh embodiment of the present invention will be described.
FIG. 13 is a conceptual diagram illustrating the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, a plurality of radiation mode resonators are arranged along the long waveguide 1 and controlled and modulated independently of each other. With this configuration, when the waveguide 1 is a main oscillator, the pumping can be changed in the waveguide axis direction. Thus, the oscillation wavelength can be tuned. Further, the light intensity in the waveguide axis direction becomes flat, and oscillation instability that depends on nonuniformity such as spatial hole burning can be compensated.
[0120]
Further, when a plurality of radiation mode resonators are used as the main oscillator, each of them can be modulated independently. Further, the present invention can be applied to a light source for wavelength division multiplexing (WDM) that is output to the waveguide 1 by controlling each oscillation wavelength to be different.
[0121]
The above-described tuner amplifier of the ninth embodiment is an optical functional element that demultiplexes and receives an optical signal. However, in this embodiment, the radiation mode resonator is combined as a wavelength multiplexing laser oscillator in this way. Thus, an optical functional element that transmits to the waveguide can be obtained. Since the transmitter of the present embodiment and the receiver of the ninth embodiment are similar in configuration, the productivity is also excellent.
[0122]
Next, a twelfth embodiment of the present invention will be described.
[0123]
FIG. 14 is a conceptual diagram illustrating the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The present embodiment is a modification of the radiation mode resonator, and the radiation mode resonator itself has a waveguide function. That is, the optical functional element of FIG. 14 is a configuration example in which a resonator for amplifying a radiation mode is realized by a waveguide type active DBR structure 7. Here, “active DBR” refers to a distributed reflector having a wavelength selectivity and having a gain. In the present embodiment, the amplification mechanism, the reflection mechanism, and the phase control mechanism are integrated into the active DBR waveguide 7.
[0124]
This has a configuration that is partially similar to a normal DFB laser. That is, if a waveguide has a diffraction grating, an active layer, and a gain is obtained by supplying a current, there is an amplification function. If the refractive index is changed by a reverse bias electric field, a phase control function can be obtained. Of course, it goes without saying that it also has a reflection function of reflecting the light back to the input by the diffraction grating.
[0125]
Further, the radiation mode is formed so as to be guided to the DBR waveguide 7 through the tapered region 8 that accepts the radiation mode. The direction of the DBR waveguide 7 is perpendicular to the waveguide 1 in consideration of the direction of the radiation mode.
[0126]
Next, a thirteenth embodiment of the present invention will be described.
[0127]
FIG. 15 is a conceptual diagram showing the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. This embodiment is related to the twelfth embodiment described above. That is, the upper side of the resonator that amplifies the radiation mode is configured as a waveguide 1 ′ parallel to the original waveguide 1. An active region 6 'is formed in the waveguide 1' and has a gain, that is, an amplification action. The reflective film 30 ′ is formed on the end face. The coupling of the radiation mode to the waveguide 1 ′ is performed by a diffraction grating 2 ′ similar to the secondary diffraction grating 2 formed in the waveguide 1. From another viewpoint, it can be said that this embodiment includes a plurality of structures of the waveguide 1 and is coupled by diffraction gratings. Therefore, as a modification of the present embodiment, a vertical resonator (not shown) may be provided above the waveguide 1 ′.
[0128]
Next, a fourteenth embodiment of the present invention will be described.
[0129]
FIG. 16 is a partially cut perspective view showing the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The configuration of the optical functional element of the present embodiment will be described as follows along the manufacturing process.
[0130]
First, after growing a buffer layer (not shown) of the same n-type InP on the same n-type InP substrate 501, an active layer / waveguide layer (1 + 6) made of InGaAsP is grown. This is patterned to form a secondary diffraction grating 2 on the side surface. At this time, the gain region 3 is also formed as the remaining portion.
[0131]
On top of this, a p-type InP cladding layer 502 and a p-type InGaAsP contact layer 503 are grown. Next, in order to independently excite the active waveguide (1 + 6) and the gain region 3, a proton irradiation region 504 for isolation is formed. Further, p-side electrodes 505 and 506 are formed, and an n-side electrode 507 is formed on the back side of the substrate. Finally, the highly reflective film 4 is deposited on the cleavage surface outside the gain region 3.
[0132]
In this way, the configuration of the present invention can be monolithically integrated on the InP substrate. In this example, each function is integrated in a direction horizontal to the surface of the substrate. The illustrated example is a simple basic element, but it is also possible to integrate a plurality of elements like an array.
[0133]
Next, a fifteenth embodiment of the present invention is described.
[0134]
FIG. 17 is a schematic perspective view showing the optical functional element according to the present embodiment. Also in the figure, the same parts as those of the above-described embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The example shown in FIG. 17 is an example in the case of using a GaAlAs / GaAs-based material, and its configuration will be described along the manufacturing process as follows.
[0135]
First, the lower highly reflective multilayer film 4 is grown on the semi-insulating GaAs substrate 601. For example, the multilayer film 4 can have a multilayer structure of an AlAs layer and a GaAs layer. Further, the multilayer film 4 grown in this manner can be further increased in reflectance by changing the AlAs layer to an Al oxide by a selective oxidation method later. A GaAs amplification layer 3 having a gain is grown thereon, and an n-type AlAs layer 602 and a GaAlAs (Al composition ratio: 0.3) cladding layer 603 are further grown. After the active layer 6 is subsequently grown, the waveguide layer 1 of GaAlAs (Al composition ratio: 0.15) is grown. After taking out from the growth furnace once, the secondary diffraction grating 2 is formed. Next, the GaAlAs cladding layer 603 is grown again in the crystal growth process. Further, a GaAs contact layer 604 is continuously grown.
[0136]
The pn junction is formed by a diffusion region 610 in which Zn (zinc) is diffused. This is a so-called transverse junction stripe (TJS) structure. A pn junction can be formed simultaneously for the layer structure of the amplification mechanism 3 and the layer structure of the active layer 6 that are stacked and integrated. This TJS structure is characterized in that light is confined near the junction and guided. Further, a dielectric multilayer film is formed on the upper side as the highly reflective film 5.
[0137]
In this way, an integrated device in which the mechanisms are stacked in a direction perpendicular to the substrate surface can be obtained. In addition, a part of the AlAs layer 602 can be changed to the Al oxide film 650 by the selective oxidation method using water vapor from the lateral direction, so that the effect of the insulation between the active layer 6 and the gain layer 3 and the current confinement can be obtained.
[0138]
Further, a p-side electrode 505, an n-side electrode (for a waveguide) 507, and an n-side electrode (for an amplification layer) 508 are formed to complete an optical functional element.
[0139]
It can be said that the optical functional element of the present embodiment is a planar vertical integrated device. Similar to the fourteenth embodiment, the present invention can be applied to an array having a plurality of elements.
[0140]
Next, a sixteenth embodiment of the present invention will be described.
FIG. 18 is a conceptual diagram illustrating the optical communication device according to the embodiment. That is, the optical communication apparatus shown in the figure applies the optical functional element 700 according to the present invention. Around the optical functional element 700, an LD (laser diode) drive circuit, a circuit for measuring a photocurrent from a PD (photo diode), an APC circuit, a signal generator, and other electronic circuit units 900 are connected. An optical signal generated in the optical functional element is transmitted through the optical fiber 800. Of course, you may transmit by the spatial transmission which does not use a fiber.
[0141]
According to the present invention, since various functions are integrated, the transmission / reception apparatus can be very miniaturized. Further, since the assembly becomes simple when manufacturing the transmission / reception device, the cost can be greatly reduced. Furthermore, connection with an optical fiber becomes easy. Further, since the waveguide having a small temperature change can be separated from the gain region having a large temperature change, the wavelength stability can be maintained.
[0142]
The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.
[0143]
For example, although the InGaAsP / InP system and the GaAlAs / GaAs system have been described in the specific examples described above, the present invention can be similarly applied using various material systems in addition to these. Examples of such materials include various III-V compound semiconductors such as InGaAlP and BInGaAlN, II-IV compound semiconductors such as ZnSe and ZnS, and IV group semiconductors such as SiC. Can be mentioned.
[0144]
In addition, with respect to specific configurations such as a waveguide mechanism, an amplification mechanism, a reflection mechanism, and a phase control mechanism used in the present invention, the same effects as those of the specific examples described above can be obtained by using the configurations appropriately selected by those skilled in the art. be able to.
[0145]
Furthermore, the number of these mechanisms and the specific arrangement relationship can be determined as appropriate by those skilled in the art, and similar effects can be obtained.
[0146]
That is, the present invention can be applied or expanded in various ways without departing from the spirit of the present invention.
[0147]
【The invention's effect】
According to the present invention, a novel optical device having various functions can be realized by applying a new concept radiation mode resonator structure along various waveguide structures.
[0148]
In the above description, the number of specific examples is large, and the effects thereof have been described individually in each specific example. Therefore, here, general effects will be referred to.
[0149]
According to the present invention, since elements such as an amplification mechanism and a reflection mechanism are arranged along the waveguide, efficient interaction with the waveguide is possible. One example is efficient photoexcitation. Moreover, by providing along a waveguide, efficient arrangement | positioning is possible and a big area is not required. This is also suitable for monolithic integration. In addition, because the diffraction grating itself has the function of wavelength selectivity and a diffraction grating coupler, the functions of a demultiplexer and a multiplexer are realized, and when used as an optical device for wavelength multiplexing, a compact and low-cost optical device is used. A functional element can be realized.
[0150]
Further, if a low-cost and high-performance optical functional element as described above is used, a high-performance optical communication device can be provided at a low cost.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an optical functional element according to a first embodiment of the present invention.
FIG. 2 is a conceptual diagram illustrating an optical functional element according to a second embodiment of the present invention.
FIG. 3 is a conceptual diagram showing an optical functional element according to a third embodiment of the present invention.
FIG. 4 is a conceptual diagram illustrating the configuration of an optical functional device according to a fourth embodiment of the invention.
FIG. 5 is a conceptual diagram showing an optical functional element according to a fifth embodiment of the present invention.
FIG. 6 is a conceptual diagram showing an optical functional element according to a sixth embodiment of the present invention.
FIG. 7 is a conceptual diagram showing an optical functional element according to a seventh embodiment of the present invention.
FIG. 8 is a conceptual diagram illustrating an optical functional element according to a ninth embodiment of the present invention.
FIG. 9 is a conceptual diagram showing an optical functional element according to a tenth embodiment of the present invention.
FIG. 10 is a conceptual diagram illustrating the cross-sectional structure of an element employing a quartz cladding.
FIG. 11 is a conceptual diagram exemplifying a cross-sectional structure of an element operated with a reverse bias in a waveguide.
FIG. 12 is a conceptual diagram showing a cross-sectional structure of an element in which a laser and an optical modulator are integrated.
FIG. 13 is a conceptual diagram showing an optical functional element according to an eleventh embodiment of the present invention.
FIG. 14 is a conceptual diagram showing an optical functional element according to a twelfth embodiment of the present invention.
FIG. 15 is a conceptual diagram showing an optical functional element according to a thirteenth embodiment of the present invention.
FIG. 16 is a partially cut perspective view showing an optical functional element according to a fourteenth embodiment of the present invention.
FIG. 17 is a schematic perspective view showing an optical functional element according to a fifteenth embodiment of the present invention.
FIG. 18 is a conceptual diagram illustrating an optical communication device according to an embodiment of the present invention.
[Explanation of symbols]
1,1 'waveguide mechanism
2,2'2nd or higher diffraction grating
3 Amplification mechanism
4 reflection mechanism
5 Phase control (modulation) mechanism
6,6 'active layer (gain part of waveguide mechanism)
7 Waveguide type active DBR
8 Radiation mode input taper part of waveguide type active DBR
11 Phase shift
20 High reflection structure
21 End face reflection structure
30, 30 'Waveguide end face reflector
40 Light receiving mechanism
50 substrates
53 Current block area
55 Transparent electrode
60 Wire
70 electrodes
100 Vertical output
200 Waveguide end output
501 n-type InP
502 p-type InP
503 InGaAsP contact layer
504 Proton irradiation area
505 p-side electrode (waveguide)
506 p-side electrode (amplification region)
507 n-side electrode
508 n-side electrode (waveguide)
601 SI (semi-insulating) GaAs
602 GaAlAs cladding layer
603 AlAs
604 GaAs contact layer
610 Zn diffusion region
650 Selective oxide film of AlAs603
700 Optical Functional Element of the Present Invention
800 optical fiber
900 External circuit

Claims (14)

A first waveguide mechanism having a hologram capable of generating a radiation mode light by being coupled with the guided light wave;
An amplification mechanism for amplifying and emitting the radiation mode light emitted from the first waveguide mechanism;
A first reflection mechanism that reflects the radiation mode light emitted from the amplification mechanism toward the first waveguide mechanism;
With
The radiation mode light generated from the first waveguide mechanism is amplified by the amplification mechanism, reflected by the first reflection mechanism, and returned to the first waveguide mechanism, thereby returning the first waveguide mechanism. An optical functional element characterized in that the light wave guided through the substrate can be amplified and extracted from the end face of the first waveguide mechanism.   2. The optical functional element according to claim 1, wherein the amplification mechanism is provided apart from the first waveguide mechanism so that a waveguide mode of the guided light wave is a single transverse mode. .   The optical functional element according to claim 1, further comprising a phase control mechanism that controls a phase of the radiation mode light reflected by the first reflection mechanism.   A second waveguide mechanism provided substantially parallel to the first waveguide mechanism, having a second hologram, and optically coupled to the first waveguide mechanism via the second hologram; The optical functional element according to claim 1, wherein the optical functional element is provided.   The optical functional element according to claim 1, wherein the hologram is a second-order or higher diffraction grating.   The at least one of the amplification mechanism and the first reflection mechanism is provided in plural along the waveguide direction of the first waveguide mechanism. The optical functional element according to one.   The optical functional element according to claim 1, further comprising a second reflection mechanism provided at at least one end of the first waveguide mechanism.   An input of light from the outside or an output of light to the outside is performed by either a guided mode from at least one end face of the first waveguide mechanism or a radiation mode from the first waveguide mechanism The optical functional element according to claim 1, wherein the optical functional element is performed in both the waveguide mode and the radiation mode.   The optical functional element according to any one of 1 to 8, wherein at least one of the waveguide mechanism and the amplification mechanism includes a medium that generates a gain by optical excitation.   The optical functional element according to claim 1, wherein a translucent electrode for supplying a current or applying an electric field is provided between the waveguide mechanism and the amplification mechanism.   The optical functional element according to claim 1, wherein a real part or an imaginary part of a refractive index of the waveguide mechanism can be changed by applying an electric field. .   The optical functional element according to claim 1, further comprising a light receiving mechanism for the radiation mode light. The first waveguide mechanism has a modulation unit not provided with the hologram,
The structure according to claim 1, wherein an electric field is applied to the modulation unit to change a real part or an imaginary part of a refractive index thereof, and light propagating through the modulation unit can be modulated. The optical functional element as described in any one.   An optical communication device comprising the optical functional element according to claim 1.

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