JP3573332B2

JP3573332B2 - Interferometric thermo-optical components

Info

Publication number: JP3573332B2
Application number: JP2000032964A
Authority: JP
Inventors: 亮一笠原; 隆司郷
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2000-02-10
Filing date: 2000-02-10
Publication date: 2004-10-06
Anticipated expiration: 2020-02-10
Also published as: JP2001222034A

Description

【０００１】
【発明の属する技術分野】
本発明は、光導波路で構成されたマッハ・ツェンダ干渉計と薄膜ヒータからなる干渉型熱光学光部品に関するものである。
更に詳しくは、特性制御に必要な電力を低減し、且つ、回路作製後の特性ずれ補正を可能にして、生産性が高く、省電力で特性が優れた干渉型熱光学光部品を提供するための回路構成法に関するものである。
【０００２】
【従来の技術】
近年、コンピュータの急激な普及が大きな牽引力となって取り扱われる情報量が急速に増大しており、大容量光ネットワークの実現が強く望まれている。
それに伴って、さまざまな通信用光部品の研究開発が盛んに行われているが、平面光波回路（ＰＬＣ）は微細加工技術により高精度に作製でき、また、生産性が高く低価格で作製できるため、次世代光機能部品の実現手段として大きな期待を集めている。
【０００３】
既に、各種光機能部品が実現されているが、その中でも、干渉型熱光学光部品は光空間スイッチや光周波数フィルタ等で用いられる最も重要な要素回路の一つである。
この回路は、図７（ａ）（ｂ）に示すように、２つの合分波器３２ａ，３２ｂを光導波路３３ａ，３３ｂで接続したマッハ・ツェンダ干渉計と、２本の光導波路３３ａ，３３ｂの上部に装荷された薄膜ヒータ４ａ，４ｂから構成される。
【０００４】
この回路では、薄膜ヒータ４ａ，４ｂのいずれかに電流を流して２本の光導波路３３ａ，３３ｂに温度差を与え光路長差を変化させることで、入力光導波路３１ａ，３１ｂから出力光導波路３４ａ，３４ｂへの透過特性を制御することができる。
例えば、導波路材料として石英系ガラスを使用して光空間スイッチを構成した場合、石英ガラスの温度変化に対する屈折率変化率ｄｎ／ｄＴは約１０^−５［１／℃］であり、薄膜ヒータの長さを５［ｍｍ］、使用波長を１．５［μｍ］と仮定すると、約２０℃の温度変化で光路切替え動作に必要な１／２波長の光路長変化を与えることができる。
【０００５】
この干渉型熱光学光部品は複数個組み合わせて大規模熱光学光部品を作製することができ、既に、Ｍ×Ｎマトリックス熱光学光スイッチや多並列２×２熱光学光スイッチなどが実現されている。
これらの大規模熱光学光部品では、数十〜数百個の干渉型熱光学光部品が集積されて消費電力が増大するため、消費電力の低減が強く求められている。
これら大規模熱光学光部品の消費電力は、駆動しない干渉型熱光学光部品で消費するバイアス電力と、駆動する干渉型熱光学光部品で消費するドライブ電力からなる。
【０００６】
前者のバイアス電力は、作製時に生じた２本の光導波路の光路長誤差を補正するために薄膜ヒータに印加する電力であり、作製誤差に起因する特性劣化を抑制する役目を果たす。
作製時に生じる２本の光導波路の光路長誤差は、例えば、光空間スイッチで考えた場合には、光路切替えに要する１／２波長の１／１０以下と小さく、バイアス電力はドライブ電力の１／１０以下であるが、大規模熱光学光部品では集積される干渉型熱光学光部品の個数が非常に多いため、バイアス電力の低減は非常に重要である。
【０００７】
バイアス電力を抑制する方法として、局所加熱による光路長誤差補正技術が既に実現されている。
干渉型熱光学光部品では、２本の光導波路の一方に局所的な温度変化を与えて個々の光に位相変調を与えるために熱伝導率の高い基板、例えばシリコン基板を用いている。
【０００８】
このため、光導波路部にはシリコンと石英系ガラスの熱膨張係数差によって生じる応力が加わっている。
このような光導波路に、局所的に数百度の熱を加えると、光導波路部に加わっている応力が不可逆的に変化し、それに伴って屈折率変化を残留させることができる。
【０００９】
この残留屈折率変化を用いて、作製後に光路長誤差を補正することができる。この局所加熱による光路長誤差補正技術は既に確立しており、バイアス電力を与えることなく設計に合致した良好な特性の干渉型熱光学光部品を実現できることが既に確認されている。
一方、後者のドライブ電力は、特性制御を行うために導波路に温度変化を与えるのに必要な電力である。
【００１０】
前述の通り、干渉型熱光学光部品では局所的な温度変化を与えるために熱伝導率の高い基板を用いているが、熱が基板へ逃げてしまうため導波路に所望の温度変化を与えるために必要なドライブ電力は増大する。
このドライブ電力を低減する方法として、図８に示すように、薄膜ヒータの両脇に導波路材料を除去した溝を形成する方法が既に提案されている。
この方法では、溝の形成により薄膜ヒータで発生した熱が基板へ伝導する際の断面積が減少し、熱の拡散が抑制されるため所望の温度変化を少ない電力で得ることができる。
【００１１】
【発明が解決しようとする課題】
しかしながら、前述の両脇の導波路材料を除去するドライブ電力抑制法と局所加熱により光路長誤差を補正するバイアス電力抑制法の両方を適用することは原理的に困難であった。
前述のバイアス電力抑制法では、局所加熱によって光導波路部に加わる応力に不可逆的な変化を与えるため、あらかじめ光導波路部にある程度の応力が加わっている必要がある。
【００１２】
しかし、前述のドライブ電力抑制法では、導波路材料を除去することでもともと光導波路が持っている応力が開放されてほぼゼロとなるため、局所加熱を行っても光導波路部の応力はほとんど変化せず、光路長誤差を補正することはできない。
この問題の解決法として、片側の光導波路だけに両側の導波路材料を除去した溝を形成し、溝を形成した領域の光導波路上に薄膜ヒータを装荷して特性制御用ヒータとして使用し、もう一方の光導波路は応力開放の影響がないように十分に離して光導波路上に形成した薄膜ヒータを光路長誤差補正用ヒータとして使用する方法が考えられるが、２本の光導波路を離すと回路寸法が増大することや２つの光導波路に構造的な差異を与えると特性劣化が生じたり、設計が困難になったりすることを考慮すると実用的ではない。
【００１３】
本発明は、上記従来技術に鑑みてなされたものであり、干渉型熱光学光部品の２つの合分波器に挟まれた２つの光導波路の一部分の両脇に導波路材料を除去した溝を形成し、一方の光導波路には溝が形成された領域に薄膜ヒータを形成して特性制御用ヒータとして使用し、もう一方の光導波路には溝が形成されていない領域に薄膜ヒータを形成して光路長誤差補正用ヒータとして使用することによって、回路寸法の増大や特性劣化を伴わずに省電力で特性が優れた干渉型熱光学光部品を安定に提供することを目的とする。
【００１４】
【課題を解決するための手段】
上記目的を達成する本発明の請求項１に記載した干渉型熱光学光部品は、２つの合分波器を２つの光導波路で接続したマッハ・ツェンダ干渉計を構成し、前記光導波路の上部に薄膜ヒータを装荷した干渉型熱光学光部品において、２つの光導波路の一部分に両脇の導波路材料を除去した溝が形成され、一方の光導波路上には溝が形成されている領域に薄膜ヒータが装荷され、もう一方の光導波路上には溝が形成されていない領域に薄膜ヒータが装荷されていることを特徴とする。
【００１５】
また、上記目的を達成する本発明の請求項２に記載した干渉型熱光学光部品は、請求項１に記載された干渉型熱光学光部品において、両脇の導波路材料を除去した溝が前記光導波路の中央部分に配置されており、一方の光導波路上には溝が形成されている中央部分に薄膜ヒータが装荷され、もう一方の光導波路上には溝が形成されていない溝の両側に薄膜ヒータが装荷されていることを特徴とする。
【００１６】
また、上記目的を達成する本発明の請求項３に記載した干渉型熱光学光部品は、請求項１若しくは請求項２のいずれかに記載された干渉型熱光学光部品において、溝が形成された領域に薄膜ヒータが形成される光導波路側には、溝が形成されない領域の光導波路上に薄膜ヒータに接続された電気配線が形成され、且つ、溝が形成されない領域に薄膜ヒータが形成される光導波路側には、溝が形成される領域の光導波路上に薄膜ヒータに接続された電気配線が形成されていることを特徴とする。
【００１７】
また、上記目的を達成する本発明の請求項４に記載した干渉型熱光学光部品は、請求項３に記載された干渉型熱光学光部品において、電気配線が薄膜ヒータ材料の上部に薄膜ヒータ材料に比べて電気伝導率が大きい材料が積層された構造であることを特徴とする。
【００１８】
また、上記目的を達成する本発明の請求項５に記載した干渉型熱光学光部品は、請求項１から請求項４のいずれかに記載された干渉型熱光学光部品において、導波路材料が石英を主成分とするガラス材料であり、基板材料がシリコンであることを特徴とする。
【００１９】
【作用】
本発明の請求項１に記載した干渉型熱光学光部品は、２つの合分波器を接続する２つの光導波路の一部分に両脇の導波路材料を除去した溝が形成され、一方の光導波路上には溝が形成された領域に薄膜ヒータが装荷され、もう一方の光導波路上には溝が形成されない領域に薄膜ヒータが装荷されているため、溝が形成された領域に装荷された薄膜ヒータを特性制御用ヒータとして使用することで効率的に光導波路を加熱して少ない電力で特性制御を行うことができ、更に、溝が形成されない領域に装荷された薄膜ヒータを光路長誤差補正用ヒータとして使用することで局所加熱による光路長誤差補正をすることができるため、省電力で特性が優れた干渉型熱光学光部品を安定に提供することができる。
【００２０】
本発明の請求項２に記載した干渉型熱光学光部品は、請求項１に記載した干渉型熱光学光部品において、特に、両脇の導波路材料を除去した溝が前記光導波路の中央部分に配置されており、一方の光導波路上には溝が形成されている中央部分に薄膜ヒータが装荷され、もう一方の光導波路上には溝が形成されていない溝の両側に薄膜ヒータが装荷されているため、回路寸法の増大を伴わずに両脇の導波路材料を除去した溝を２つの合分波器から遠ざけて、溝で生じる応力変化による合分波器の特性劣化を防ぐことができ、省電力で特性が優れ、且つ、より小型な干渉型熱光学光部品を安定に提供することができる。
【００２１】
本発明の請求項３に記載した干渉型熱光学光部品は、請求項１若しくは請求項２に記載した干渉型熱光学光部品において、特に、溝が形成された領域に薄膜ヒータが形成される光導波路側には、溝が形成されない領域の光導波路上に薄膜ヒータに接続された電気配線が形成され、且つ、溝が形成されない領域に薄膜ヒータが形成される光導波路側には、溝が形成される領域の光導波路上に薄膜ヒータに接続された電気配線が形成されているため、薄膜ヒータに給電するための電気配線を整然と配置することができ、小型で大規模化に適し、且つ省電力で特性が優れた干渉型熱光学光部品を安定に提供することができる。
【００２２】
本発明の請求項４に記載した干渉型熱光学光部品は、請求項３に記載した干渉型熱光学光部品において、特に、電気配線が薄膜ヒータ材料の上部に薄膜ヒータ材料に比べて電気伝導率が大きい材料が積層された構造であるため、２つの光導波路上に形状の異なる薄膜ヒータ及び電気配線を形成しても光導波路に加わる応力の差異を小さく抑えることができ、小型で大規模化に適し、且つ省電力で特性が優れた干渉型熱光学光部品をより安定に提供することができる。
【００２３】
本発明の請求項５に記載した干渉型熱光学光部品は、請求項１から４のいずれかに記載した干渉型熱光学光部品において、特に、導波路材料として石英を主成分とするガラス材料を使用し、基板としてシリコン基板を使用することで、特に低損失で温度安定性に優れ、且つ省電力で特性が優れた干渉型熱光学光部品を提供することができる。
【００２４】
【発明の実施の形態】
〔実施例１〕
本発明の第１の実施例に係る干渉型熱光学光部品を図１に示す。
図１（ａ）は上面図、図１（ｂ）はＡ−Ａ’線断面図、図１（ｃ）はＢ−Ｂ’線断面図である。
なお、本実施例、及び以下の実施例では、導波路型熱光学光スイッチの場合について記載する。
【００２５】
同図に示すように、本実施例は、２つの３ｄＢ合分波器３２ａ，３２ｂを２本の光導波路３３ａ，３３ｂで接続してマッハ・ツェンダ干渉計を構成し、光導波路３３ａ，３３ｂの一部に両脇の導波路材料を除去した溝５を形成し、更に、光導波路３３ａ上には溝５が形成された領域に薄膜ヒータ（以下、特性制御用ヒータと言う）４ａを形成し、光導波路３３ｂ上には溝５が形成されない領域に薄膜ヒータ（以下、光路長誤差補正用ヒータという）４ｂを形成している。
また、特性制御用ヒータ４ａ，光路長誤差補正用ヒータ４ｂの両端には給電用電気配線６を接続した。
【００２６】
本実施例では、基板としてシリコン基板１を使用し、全ての光導波路は石英を主成分とするガラス材料で形成した。
コア寸法を７［μｍ］×７［μｍ］、比屈折率差を０．７５［％］、クラッド２の厚さを６０［μｍ］とした。
また回路の概略寸法は、光導波路３３ａの長さを５［ｍｍ］、光導波路３３ｂの長さを（５＋０．０００５）［ｍｍ］、光導波路３３ａ，３３ｂの距離を０．２［ｍｍ］、特性制御用ヒータ４ａの寸法を幅３０［μｍ］、長さ３［ｍｍ］、光路長誤差補正用ヒータ４ｂの寸法を幅３０［μｍ］、長さ２［ｍｍ］、溝５の寸法を幅０．１５［ｍｍ］、長さ３［ｍｍ］とした。
【００２７】
光導波路３３ａの長さは、無電力印加の状態で入力光導波路３１ａに入射した光が出力光導波路３４ａに出射するように、石英ガラス中における１／２波長（λ＝１．５５［μｍ］）に相当する０．０００５［ｍｍ］だけ光導波路３３ｂよりも長くした。
本実施例は、図６に示す工程により作製した。
まず、図６（ａ）に示すように、シリコン基板１上に火炎堆積法（ＦＨＤ法）を用いてクラッド層２とコア層３を堆積した。
【００２８】
次いで、図６（ｂ）に示すように、堆積したコア層３をフォトリソグラフィ技術と反応性ドライエッチング技術（ＲＩＥ）を用いて導波路形状に加工し、図６（ｃ）に示すように、その上にクラッド層２を堆積して埋め込み型石英系光導波路を形成した。
その後、図６（ｄ）に示すように、作製した光導波路のクラッド層２の上にＣｒ膜からなる薄膜ヒータ４とＡｕ膜からなる電気配線６を形成し、最後に図６（ｅ）に示すように、ＲＩＥを用いて溝５を形成した。
なお、本実施例及び以降の実施例では、光導波路の作製に火炎堆積法を用いているが、これに何ら縛られるものではなく、気相法やゾルゲル法といったあらゆる方法を用いることが可能である。
【００２９】
また、本実施例及び以降の実施例では、薄膜ヒータと電気配線の材料として、それぞれＣｒ膜とＡｕ膜を用いているが、これに何ら縛られるものではなく、電気特性の類似したあらゆる材料の組み合わせを用いることが可能である。
前述の作製工程を用いて導波路型熱光学光スイッチを作製し特性評価を行った。
特性評価は、局所加熱による光路長誤差補正工程の前後での消光比とドライブ電力、及び光路長誤差について行った。
詳細には、消光比は電力を印加しない状態で入力光導波路３１ａに光を入射し、出力光導波路３４ｂに出射する光強度を測定して求めた。
【００３０】
ドライブ電力は入力光導波路３１ａに光を入射して出力光導波路３４ｂに出射する光強度を測定しながら、特性制御用ヒータ４ａに印加する電力を最も消光する点が２点観測されるまで増加させ、その２点での電力値の差を測定して求めた（ドライブ電力［Ｗ］＝（２点の電力値の差）÷２）。
また、光路長誤差は、入力光導波路３１ａに光を入射して出力光導波路３４ｂに出射する光強度を測定しながら特性制御用ヒータ４ａに電力を印加して、設計上は無電力印加状態で得られるはずの最も消光する点が無電力印加状態からどの程度ずれているか測定し、前述のドライブ電力と比較して求めた（光路長誤差［％］＝（最も消光する点と無電力状態とのずれ）／（ドライブ電力）×１００）。
【００３１】
測定の結果、光路長誤差補正前の特性は、消光比１６［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差１０．０［％］であった。
また、光路長誤差補正後の特性は、消光比３０［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差０．５［％］以下であった。
ここで、図８に示す従来の省電力構造の導波路型光スイッチは、光路長誤差を補正することができないため、消光比２０［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差６．５［％］であり、従って、本構造によってドライブ電力を従来の省電力構造の導波路型光スイッチと同等まで低減しつつ、局所加熱による光路長誤差補正によって消光比を１０［ｄＢ］改善することができた。
【００３２】
本実施例では、光路長誤差補正前の消光比が１６［ｄＢ］であり、光路長誤差が１０．０［％］であったが、これは光導波路３３ａ，３３ｂの上に形成される薄膜ヒータの形状が異なり、光導波路３３ａ，３３ｂに加わる応力に差異があったためである。
理論上は、光路長差を０．５［％］以下に抑えると４５［ｄＢ］以上の消光比が得られるが、本実施例では、溝５の形成による応力変化の影響が合分波器３２ｂに加わり、分岐比が設計値である５０［％］からずれたため、３０［ｄＢ］の消光比しか得られなかった。
【００３３】
本実施例では、導波路材料として石英を主成分としたガラス材料を用いたが、本技術はこれに制限されるものでなく、使用する基板と導波路材料の熱膨張係数長になどに起因する応力が光導波路部に加わっていれば無機誘電体材料や有機誘電体材料を導波路材料とした場合にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
また、本実施例では、導波路型熱光学光スイッチの場合について記述したが、本技術はこれに制限されるものでなく、光周波数フィルタや光可変減衰器等のあらゆる干渉型熱光学光部品にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
【００３４】
〔実施例２〕
本発明の第２の実施例に係る干渉型熱光学光部品を図２に示す。
図２（ａ）は上面図、図２（ｂ）はＣ−Ｃ’線断面図、図２（ｃ）はＤ−Ｄ’線断面図である。
なお、本実施例は、合分波器の分岐比を３［ｄＢ］（５０％）とし、導波路型熱光学光スイッチを作製した一例である。
【００３５】
同図に示すように、本実施例の導波路型熱光学光スイッチは、実施例１の導波路型熱光学光スイッチにおいて、特性制御用ヒータ４ａ及び溝５を光導波路３３ａ，３３ｂの中央に配置し、光路長誤差補正用ヒータを４ｂ，４ｃの２つに分割して光導波路３３ａ，３３ｂの両脇に配置したものである。
光路長誤差補正用ヒータ４ｂ，４ｃの長さが１［ｍｍ］であることを除き、その他の概略構成、作製手順は実施例１の導波路型熱光学光スイッチと同様であるので詳細な説明は省略する。
【００３６】
本実施例においても実施例１と同様に、局所加熱による光路長誤差補正工程の前後での消光比とドライブ電力、及び光路長誤差について測定を行った。
測定の結果、光路長誤差補正前の特性は、消光比１６［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差１０．０［％］であった。
また、光路長誤差補正後の特性は、消光比３５［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差０．５［％］以下であった。
【００３７】
本実施例でも、実施例１と同様に、ドライブ電力を図８に示す従来の省電力構造の導波路型熱光学光スイッチと同等の０．１７［Ｗ］まで低減しつつ、局所加熱による光路長誤差補正によって消光比を１５［ｄＢ］改善することができた。また、本実施例では、溝５を２つの合分波器３２ａ，３２ｂから離して配置したため、応力変化による合分波器３２ａ，３２ｂの特性劣化を低く抑えることができ、実施例１と比較して、消光比を更に５［ｄＢ］改善することができた。
【００３８】
本実施例では、光路長誤差補正前の消光比が１６［ｄＢ］であり、光路長誤差が１０．０［％］であったが、これは光導波路３３ａ，３３ｂの上に形成される薄膜ヒータの形状が異なり、光導波路３３ａ，３３ｂに加わる応力に差異があったためである。
本実施例では、導波路材料として石英を主成分としたガラス材料を用いたが、本技術はこれに制限されるものでなく、使用する基板と導波路材料の熱膨張係数差になどに起因する応力が光導波路部に加わっていれば無機誘電体材料や有機誘電体材料を導波路材料とした場合にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な導波路型熱光学光スイッチを良好な特性で生産性良く低価格に実現することができる。
【００３９】
また、本実施例では、導波路型熱光学光スイッチの場合について記述したが、本技術はこれに制限されるものでなく、光周波数フィルタや光可変減衰器等のあらゆる干渉型熱光学光部品にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
【００４０】
〔実施例３〕
本発明の第３の実施例に係る干渉型熱光学光部品を図３に示す。
図３（ａ）は上面図、図３（ｂ）はＥ−Ｅ’線断面図、図３（ｃ）はＦ−Ｆ’線断面図である。
なお、本実施例は、合分波器の分岐比を３［ｄＢ］（５０％）とし、導波路型熱光学光スイッチを作製した一例である。
【００４１】
同図に示すように、本実施例の導波路型熱光学光スイッチは、実施例１の導波路型熱光学光スイッチにおいて、特性制御用ヒータ４ａに給電するための電気配線６ａを溝５が形成されていない領域の光導波路３３ａ上に形成し、光路長誤差補正用ヒータ４ｂに給電するための電気配線６ｂを溝５が形成されている領域の光導波路３３ｂ上に形成したものである。
電気配線は薄膜ヒータ膜として使用しているＣｒ膜上にＡｕ膜を積層した構造とした。
その他の概略構成、作製手順は実施例１の導波路型熱光学光スイッチと同様であるので詳細な説明は省略する。
【００４２】
本実施例においても実施例１と同様に、局所加熱による光路長誤差補正工程の前後での消光比とドライブ電力、及び光路長誤差について測定を行った。
測定の結果、光路長誤差補正前の特性は、消光比２０［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差６．４［％］であった。
また、光路長誤差補正後の特性は、消光比３０［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差０．５［％］以下であった。
本実施例でも、実施例１と同様に、ドライブ電力を図８に示す従来の省電力構造の導波路型熱光学光スイッチと同等の０．１７［Ｗ］まで低減しつつ、局所加熱による光路長誤差補正によって消光比を１０［ｄＢ］改善することができた。
【００４３】
本実施例でも実施例１と同様に、２つの合分波器の分岐比が設計値である５０［％］からずれたため、３０［ｄＢ］程度の消光比しか得られなかった。
また、本実施例では、光導波路３３ａ，３３ｂに形成される電気配線と薄膜ヒータの形状が異なっているが、電気配線をＣｒ膜とＡｕ膜の積層構造とし、薄膜ヒータをＣｒ膜の単層構造としたため、光導波路３３ａ，３３ｂに加わる応力の差異が低く抑えられ、補正前の消光比が実施例１よりも４［ｄＢ］改善した。
【００４４】
本実施例では、導波路材料として石英を主成分としたガラス材料を用いたが、本技術はこれに制限されるものでなく、使用する基板と導波路材料の熱膨張係数差になどに起因する応力が光導波路部に加わっていれば無機誘電体材料や有機誘電体材料を導波路材料とした場合にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な導波路型熱光学光スイッチを良好な特性で生産性良く低価格に実現することができる。
また、本実施例では、導波路型熱光学光スイッチの場合について記述したが、本技術はこれに制限されるものでなく、光周波数フィルタや光可変減衰器等のあらゆる干渉型熱光学光部品にも適用することができ、本実施例と同様に光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
【００４５】
〔実施例４〕
本発明の第４の実施例に係る干渉型熱光学光部品を図４に示す。
図４（ａ）は上面図、図４（ｂ）はＧ−Ｇ’線断面図、図４（ｃ）はＨ−Ｈ’線断面図である。
なお、本実施例は、合分波器の分岐比を３［ｄＢ］（５０％）とし、導波路型熱光学光スイッチを作製した一例である。
【００４６】
同図に示すように、本実施例の導波路型熱光学光スイッチは、実施例２の導波路型熱光学光スイッチにおいて、特性制御用ヒータ４ａに給電するための電気配線６ａを溝５が形成されていない領域の光導波路３３ａ上に形成し、光路長誤差補正用ヒータ４ｂに給電するための電気配線６ｂを溝５が形成されている領域の光導波路３３ｂ上に形成したものである。
その他の概略構成、作製手順は実施例２の導波路型熱光学光スイッチと同様であるので詳細な説明は省略する。
【００４７】
本実施例においても実施例１と同様に、局所加熱による光路長誤差補正工程の前後での消光比とドライブ電力、及び光路長誤差について測定を行った。
測定の結果、光路長誤差補正前の特性は、消光比２０［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差６．４［％］であった。
また、光路長誤差補正後の特性は、消光比３５［ｄＢ］、ドライブ電力０．１７［Ｗ］、光路長誤差０．５［％］以下であった。
【００４８】
本実施例でも、実施例１と同様に、ドライブ電力を図５に示す従来の省電力構造の導波路型熱光学光スイッチと同等の０．１７［Ｗ］まで低減しつつ、局所加熱による光路長誤差補正によって消光比を１５［ｄＢ］改善することができた。また、本実施例でも実施例２と同様に、溝５を２つの合分波器３２ａ，３２ｂから離して配置したため、応力変化による合分波器３２ａ，３２ｂの特性劣化を防ぐことができ、実施例１と比較して、消光比を更に５［ｄＢ］改善することができた。
【００４９】
また、本実施例では、光導波路３３ａ，３３ｂに形成される電気配線と薄膜ヒータの形状が異なっているが、電気配線をＣｒ膜とＡｕ膜の積層構造とし、薄膜ヒータをＣｒ膜の単層構造としたため、光導波路３３ａ，３３ｂに加わる応力の差異が低く抑えられ、補正前の消光比が実施例１よりも４［ｄＢ］改善した。
また、本実施例では、特に、２つの光路長誤差補正用ヒータ４ｂ，４ｃに給電するための電気配線６ｂを共通にすることで、電気配線６ｂを整然と配置することができ、小型化、大規模化に適した構成にすることができた。
【００５０】
本実施例では、導波路材料として石英を主成分としたガラス材料を用いたが、本技術はこれに制限されるものでなく、使用する基板と導波路材料の熱膨張係数差になどに起因する応力が光導波路部に加わっている場合には、例えば無機誘電体材料や有機誘電体材料を導波路材料とした場合にも適用することができ、本実施例と同様に作製時の光路長誤差を作製工程後に補正して、省電力な導波路型熱光学光スイッチを良好な特性で生産性良く低価格に実現することができる。
また、本実施例では、導波路型熱光学光スイッチの場合について記述したが、本技術はこれに制限されるものでなく、光周波数フィルタや光可変減衰器等のあらゆる干渉型熱光学光部品にも適用することができ、本実施例と同様に作製時の光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
【００５１】
〔実施例５〕
本発明の第５の実施例に係る干渉型熱光学光部品を図５に示す。
図５（ａ）は上面図、図５（ｂ）はＩ−Ｉ’線断面図、図５（ｃ）はＪ−Ｊ’線断面図である。
なお、本実施例は、合分波器の分岐比を３［ｄＢ］（５０％）として導波路型熱光学光スイッチを作製し、更に溝を形成する領域の光導波路の直下に、シリコン基板上に凹形形状を形成してその内部にクラッド材料を充填したトレンチを形成した一例である。
【００５２】
同図に示すように、本実施例の導波路型熱光学光スイッチは、実施例４の導波路型熱光学光スイッチにおいて、光導波路３３ａ，３３ｂの溝５を形成する領域の直下に、シリコン基板１上に凹形形状を形成してその内部にクラッド材料を充填したトレンチ１１を形成したものである。
トレンチの寸法は幅１５０［μｍ］、長さ２［ｍｍ］、深さ５０［μｍ］とした。
その他の概略構成は実施例４の導波路型熱光学光スイッチと同様であるので詳細な説明は省略する。
【００５３】
本実施例の作製手順は、まずシリコン基板１に凹形形状を形成してその上にクラッド材料を堆積した。
その後クラッド材料が凹形形状の内部にのみ残るように表面を機械研磨で平坦化し、その上に図６に示す工程で前述の実施例と同様に光導波路と薄膜ヒータと電気配線と溝を形成した。
本実施例においても実施例１と同様に、局所加熱による光路長誤差補正工程の前後での消光比とドライブ電力、及び光路長誤差について測定を行った。
【００５４】
測定の結果、光路長誤差補正前の特性は、消光比２０［ｄＢ］、ドライブ電力０．１２［Ｗ］、光路長誤差６．５［％］であった。
また、光路長誤差補正後の特性は、消光比３５［ｄＢ］、ドライブ電力０．１２〔Ｗ］、光路長誤差０．５［％］以下であった。
本実施例では、トレンチ１１を形成することにより、ドライブ電力を図５に示す従来の省電力構造の導波路型熱光学光スイッチの０．１７［Ｗ］よりも３０［％］低減することができ、また、局所加熱による光路長誤差補正によって消光比を１５［ｄＢ］改善することができた。
【００５５】
また、本実施例でも実施例４と同様に、溝５を２つの合分波器３２ａ，３２ｂから離して配置したため、応力変化による合分波器３２ａ，３２ｂの特性劣化を防ぐことができ、実施例１と比較して、消光比を更に５［ｄＢ］改善することができた。
また、本実施例では、光導波路３３ａ，３３ｂに形成される電気配線と薄膜ヒータの形状が異なっているが、電気配線をＣｒ膜とＡｕ膜の積層構造とし、薄膜ヒータをＣｒ膜の単層構造としたため、光導波路３３ａ，３３ｂに加わる応力の差異が低く抑えられ、補正前の消光比が実施例１よりも４［ｄＢ］改善した。
【００５６】
本実施例では、光導波路３３ａ，３３ｂの下部にトレンチ１１を形成したが、光導波路３３ａ，３３ｂの下部のトレンチは同一の構造であるため、消光比等の劣化は見られなかった。
また、本実施例でも実施例４と同様に、特に２つの光路長誤差補正用ヒータ４ｂ，４ｃに給電するための電気配線６ｂを共通にすることで、電気配線６ｂを整然と配置することができ、小型化、大規模化に適した構成にすることができた。
【００５７】
本実施例では、導波路材料として石英を主成分としたガラス材料を用いたが、本技術はこれに制限されるものでなく、使用する基板と導波路材料の熱膨張係数差になどに起因する応力が光導波路部に加わっている場合には、例えば無機誘電体材料や有機誘電体材料を導波路材料とした場合にも適用することができ、本実施例と同様に作製時の光路長誤差を作製工程後に補正して、省電力な導波路型熱光学光スイッチを良好な特性で生産性良く低価格に実現することができる。
また、本実施例では、導波路型熱光学光スイッチの場合について記述したが、本技術はこれに制限されるものでなく、光周波数フィルタや光可変減衰器等のあらゆる干渉型熱光学光部品にも適用することができ、本実施例と同様に作製時の光路長誤差を作製工程後に補正して、省電力な干渉型熱光学光部品を良好な特性で生産性良く低価格に実現することができる。
【００５８】
【発明の効果】
以上、実施例に基づいて具体的に説明したように、本発明では、マッハ・ツェンダ干渉計の２つの合分波器を接続する２本の光導波路の一部に、両側の導波路材料を除去した溝を形成し、一方の光導波路上には溝が形成された領域に薄膜ヒータを形成して特性制御用ヒータとして使用し、もう一方の光導波路上には溝が形成されない領域に薄膜ヒータを形成して光路誤差補正用ヒータとして使用することで、回路寸法を増大させることなく、特性制御に必要なドライブ電力を低減し、且つ作製時の光路長誤差を局所加熱によって補正することができるため、生産性が高く、低価格で、且つ省電力で特性が優れた干渉型熱光学光部品を提供することができる。
従って、本発明は、省電力で特性が優れた干渉型熱光学光部品を実用する上で極めて効果的である。
【図面の簡単な説明】
【図１】図１（ａ）は本発明の第１の実施例に係る干渉型熱光学光部品の概略構成を示す上面図、図１（ｂ）は図１（ａ）中のＡ−Ａ’線断面図、図１（ｃ）は図１（ａ）中のＢ−Ｂ’線断面図である。
【図２】図２（ａ）は本発明の第２の実施例に係る干渉型熱光学光部品の概略構成を示す上面図、図２（ｂ）は図２（ａ）中のＣ−Ｃ’線断面図、図２（ｃ）は図２（ａ）中のＤ−Ｄ’線断面図である。
【図３】図３（ａ）は本発明の第３の実施例に係る干渉型熱光学光部品の概略構成を示す上面図、図３（ｂ）は図３（ａ）中のＥ−Ｅ’線断面図、図３（ｃ）は図３（ａ）中のＦ−Ｆ’線断面図である。
【図４】図４（ａ）は本発明の第４の実施例に係る干渉型熱光学光部品の概略構成を示す上面図、図４（ｂ）は図４（ａ）中のＧ−Ｇ’線断面図、図４（ｃ）は図４（ａ）中のＨ−Ｈ’線断面図である。
【図５】図５（ａ）は本発明の第５の実施例に係る干渉型熱光学光部品の概略構成を示す上面図、図５（ｂ）は図５（ａ）中のＩ−Ｉ’線断面図、図５（ｃ）は図５（ａ）中のＪ−Ｊ’線断面図である。
【図６】図６（ａ）〜（ｅ）は、石英系平面光波回路技術を用いて作製される干渉型熱光学光部品の作製手順を示す工程図である。
【図７】図７（ａ）は従来の干渉型熱光学光部品の概略構成を示す上面図、図７（ｂ）は図７（ａ）中のＫ−Ｋ’線断面図である。
【図８】図８（ａ）は従来の干渉型熱光学光部品の概略構成を示す上面図、図８（ｂ）は図８（ａ）中のＬ−Ｌ’線断面図である。
【符号の説明】
１シリコン基板
２クラッド層
３コア
４薄膜ヒータ
４ａ特性制御用ヒータ
４ｂ，４ｃ光路長誤差補正用ヒータ
５溝
６給電用電気配線
６ａ特性制御用ヒータ給電用電気配線
６ｂ光路長誤差補正用ヒータ給電用電気配線
１１トレンチ
３１ａ，３１ｂ入力光導波路
３２ａ，３２ｂ合分波器
３３ａ，３３ｂ光導波路
３４ａ，３４ｂ出力光導波路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an interferometric thermo-optic optical component comprising a Mach-Zehnder interferometer composed of an optical waveguide and a thin film heater.
More specifically, in order to provide an interference-type thermo-optic optical component having high productivity, low power consumption, and excellent characteristics, by reducing the power required for characteristic control and enabling correction of characteristic deviation after circuit fabrication. Circuit configuration method.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the amount of information handled has been rapidly increasing due to the rapid spread of computers as a major driving force, and the realization of large-capacity optical networks has been strongly desired.
Along with this, research and development of various optical components for communication have been actively conducted, but a planar lightwave circuit (PLC) can be manufactured with high precision by fine processing technology, and can be manufactured with high productivity and at a low price. Therefore, it is attracting great expectations as a means for realizing next-generation optical functional components.
[0003]
Various optical functional components have already been realized, and among them, the interferometric thermo-optical optical component is one of the most important element circuits used in optical space switches, optical frequency filters, and the like.
As shown in FIGS. 7A and 7B, this circuit includes a Mach-Zehnder interferometer in which two multiplexers / demultiplexers 32a and 32b are connected by optical waveguides 33a and 33b, and two optical waveguides 33a and 33b. Is composed of thin film heaters 4a and 4b loaded on the upper part.
[0004]
In this circuit, a current is applied to one of the thin film heaters 4a and 4b to give a temperature difference to the two optical waveguides 33a and 33b to change the optical path length difference, thereby changing the input optical waveguides 31a and 31b to the output optical waveguide 34a. , 34b.
For example, when an optical space switch is configured using silica-based glass as a waveguide material, the refractive index change rate dn / dT with respect to a temperature change of silica glass is approximately 10%. ^-5 [1 / ° C.], assuming that the length of the thin-film heater is 5 [mm] and the wavelength used is 1.5 [μm], the half wavelength required for the optical path switching operation at a temperature change of about 20 ° C. An optical path length change can be provided.
[0005]
A large-scale thermo-optical component can be manufactured by combining a plurality of the interference-type thermo-optical components, and an M × N matrix thermo-optical switch and a multi-parallel 2 × 2 thermo-optical switch have already been realized. I have.
In these large-scale thermo-optical components, tens to hundreds of interference-type thermo-optical components are integrated to increase power consumption. Therefore, reduction in power consumption is strongly demanded.
The power consumption of these large-scale thermo-optical components consists of bias power consumed by the non-driven interferometric thermo-optical components and drive power consumed by the driven interferometric thermo-optical components.
[0006]
The former bias power is power applied to the thin-film heater for correcting an optical path length error between two optical waveguides generated at the time of fabrication, and has a role of suppressing characteristic deterioration due to fabrication error.
The optical path length error of the two optical waveguides that occurs at the time of fabrication is as small as 1/10 or less of 1/2 wavelength required for optical path switching when considering an optical space switch, and the bias power is 1/100 of the drive power. Although it is 10 or less, the reduction of the bias power is very important in a large-scale thermo-optical component because the number of interferometric thermo-optical components integrated is very large.
[0007]
As a method of suppressing the bias power, an optical path length error correction technique by local heating has already been realized.
In the interference-type thermo-optical component, a substrate having a high thermal conductivity, for example, a silicon substrate, is used to apply a local temperature change to one of the two optical waveguides to apply phase modulation to each light.
[0008]
For this reason, a stress generated due to a difference in thermal expansion coefficient between silicon and quartz glass is applied to the optical waveguide portion.
When heat of several hundred degrees is locally applied to such an optical waveguide, the stress applied to the optical waveguide portion changes irreversibly, and the refractive index can be changed with the change.
[0009]
Using this change in residual refractive index, an optical path length error can be corrected after fabrication. The technology of correcting the optical path length error by the local heating has already been established, and it has been already confirmed that an interference-type thermo-optic optical component having good characteristics conforming to the design can be realized without applying bias power.
On the other hand, the latter drive power is power required to give a temperature change to the waveguide in order to control the characteristics.
[0010]
As described above, in the interference-type thermo-optic optical component, a substrate having a high thermal conductivity is used to give a local temperature change. However, since the heat escapes to the substrate, a desired temperature change is given to the waveguide. The required drive power increases.
As a method of reducing the drive power, as shown in FIG. 8, a method of forming a groove from which a waveguide material is removed on both sides of a thin film heater has already been proposed.
According to this method, the cross-sectional area when heat generated by the thin film heater is conducted to the substrate is reduced by the formation of the groove, and the diffusion of heat is suppressed, so that a desired temperature change can be obtained with a small amount of power.
[0011]
[Problems to be solved by the invention]
However, it has been difficult in principle to apply both the drive power suppression method for removing the waveguide material on both sides and the bias power suppression method for correcting an optical path length error by local heating.
In the above-described bias power suppression method, a certain amount of stress needs to be applied to the optical waveguide portion in advance in order to give an irreversible change to the stress applied to the optical waveguide portion by local heating.
[0012]
However, in the above-described drive power suppression method, the stress of the optical waveguide is originally reduced to almost zero by removing the waveguide material, so that even when local heating is performed, the stress in the optical waveguide portion hardly changes. Without this, the optical path length error cannot be corrected.
As a solution to this problem, a groove formed by removing the waveguide material on both sides is formed only on one side of the optical waveguide, and a thin film heater is loaded on the optical waveguide in the region where the groove is formed, and used as a characteristic control heater, A method of using the thin film heater formed on the optical waveguide as a heater for correcting an optical path length error by sufficiently separating the other optical waveguide so as not to be affected by the stress release can be considered. However, if the two optical waveguides are separated, It is not practical in view of an increase in circuit size or a structural difference between the two optical waveguides, which may cause characteristic degradation or make design difficult.
[0013]
The present invention has been made in view of the above prior art, and has a groove formed by removing a waveguide material on both sides of a part of two optical waveguides sandwiched between two multiplexers / demultiplexers of an interference-type thermo-optic optical component. A thin film heater is formed in a region where a groove is formed in one optical waveguide and used as a characteristic control heater, and a thin film heater is formed in a region where a groove is not formed in the other optical waveguide. It is another object of the present invention to stably provide an interference-type thermo-optic optical component having excellent power saving characteristics without increasing the circuit size or deteriorating characteristics by using the heater as an optical path length error correcting heater.
[0014]
[Means for Solving the Problems]
An interference-type thermo-optical component according to claim 1 of the present invention, which achieves the above object, constitutes a Mach-Zehnder interferometer in which two multiplexers / demultiplexers are connected by two optical waveguides, and an upper part of the optical waveguide. In the interference-type thermo-optical component in which a thin film heater is loaded, a groove formed by removing the waveguide material on both sides is formed in a part of the two optical waveguides, and a groove is formed on one of the optical waveguides. A thin film heater is loaded, and the thin film heater is loaded in a region where a groove is not formed on the other optical waveguide.
[0015]
According to a second aspect of the present invention, there is provided an interference-type thermo-optical component according to the first aspect of the present invention, wherein the groove formed by removing the waveguide material on both sides is provided. A thin film heater is loaded on a central portion where a groove is formed on one optical waveguide, and a thin film heater is loaded on a central portion where a groove is formed on the other optical waveguide. A thin film heater is loaded on both sides.
[0016]
According to a third aspect of the present invention, there is provided an interference-type thermo-optical component, wherein the groove is formed in the interference-type thermo-optical component. On the optical waveguide side where the thin film heater is formed in the region where the thin film heater is formed, the electric wiring connected to the thin film heater is formed on the optical waveguide in the region where the groove is not formed, and the thin film heater is formed in the region where the groove is not formed. On the optical waveguide side, electrical wiring connected to the thin film heater is formed on the optical waveguide in the region where the groove is formed.
[0017]
According to a fourth aspect of the present invention, there is provided an interference-type thermo-optical component according to the third aspect of the present invention, wherein the electric wiring is provided on the thin-film heater material above the thin-film heater material. It is characterized by a structure in which materials having higher electric conductivity than materials are stacked.
[0018]
According to a fifth aspect of the present invention, there is provided an interference-type thermo-optical component according to any one of the first to fourth aspects, wherein the waveguide material is selected from the group consisting of: A glass material mainly composed of quartz, and the substrate material is silicon.
[0019]
[Action]
In the interference type thermo-optic optical component according to the first aspect of the present invention, a groove formed by removing the waveguide material on both sides is formed in a part of the two optical waveguides connecting the two multiplexers / demultiplexers. The thin film heater is loaded on the region where the groove is formed on the waveguide, and the thin film heater is loaded on the region where the groove is not formed on the other optical waveguide, so that the thin film heater is loaded on the region where the groove is formed. By using the thin-film heater as a heater for controlling the characteristics, the optical waveguide can be efficiently heated to control the characteristics with a small amount of electric power. In addition, the thin-film heater loaded in the area where the groove is not formed can be corrected for the optical path length error. Since the optical path length error can be corrected by local heating by using the heater as a heater, it is possible to stably provide an interference-type thermo-optical component having excellent power saving characteristics.
[0020]
According to a second aspect of the present invention, there is provided the interferometric thermo-optic optical component according to the first aspect, wherein the groove formed by removing the waveguide material on both sides is formed at a central portion of the optical waveguide. The thin film heater is loaded on the central portion where a groove is formed on one optical waveguide, and the thin film heater is loaded on both sides of the groove where no groove is formed on the other optical waveguide. Therefore, the groove from which the waveguide material has been removed on both sides is kept away from the two multiplexers / demultiplexers without increasing the circuit size to prevent the deterioration of the characteristics of the multiplexer / demultiplexer due to the stress change generated in the grooves. Thus, it is possible to stably provide a smaller interference-type thermo-optic optical component which is power saving, has excellent characteristics, and is small.
[0021]
According to a third aspect of the present invention, there is provided an interference-type thermo-optic optical component according to the first or second aspect, wherein a thin film heater is formed in a region where a groove is formed. On the optical waveguide side, electrical wiring connected to the thin film heater is formed on the optical waveguide in the region where the groove is not formed, and on the optical waveguide side where the thin film heater is formed in the region where the groove is not formed, a groove is formed. Since the electric wiring connected to the thin-film heater is formed on the optical waveguide in the region where the thin-film heater is formed, the electric wiring for supplying power to the thin-film heater can be arranged neatly, and is small, suitable for large-scale, and It is possible to stably provide an interference-type thermo-optical component having excellent power saving characteristics.
[0022]
According to a fourth aspect of the present invention, there is provided an interference-type thermo-optic optical component according to the third aspect, wherein the electric wiring is provided above the thin-film heater material as compared with the thin-film heater material. Due to the structure in which materials having a high ratio are laminated, even if thin film heaters and electric wirings having different shapes are formed on the two optical waveguides, the difference in stress applied to the optical waveguides can be suppressed to be small, and a small and large scale Therefore, it is possible to more stably provide an interference-type thermo-optic optical component that is suitable for power saving, and has excellent characteristics with low power consumption.
[0023]
According to a fifth aspect of the present invention, there is provided an interference-type thermo-optical component according to any one of the first to fourth aspects, particularly, a glass material mainly composed of quartz as a waveguide material. By using a silicon substrate as the substrate, it is possible to provide an interference-type thermo-optical component that is particularly low in loss, has excellent temperature stability, and is power saving and has excellent characteristics.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
[Example 1]
FIG. 1 shows an interference-type thermo-optical component according to a first embodiment of the present invention.
1A is a top view, FIG. 1B is a cross-sectional view taken along line AA ′, and FIG. 1C is a cross-sectional view taken along line BB ′.
In this embodiment and the following embodiments, the case of a waveguide type thermo-optical switch will be described.
[0025]
As shown in the figure, in this embodiment, two 3 dB multiplexers / demultiplexers 32a and 32b are connected by two optical waveguides 33a and 33b to constitute a Mach-Zehnder interferometer, and the optical waveguides 33a and 33b A groove 5 from which the waveguide material on both sides is removed is partially formed, and a thin film heater (hereinafter referred to as a characteristic control heater) 4a is formed on the optical waveguide 33a in a region where the groove 5 is formed. On the optical waveguide 33b, a thin film heater (hereinafter referred to as an optical path length error correction heater) 4b is formed in a region where the groove 5 is not formed.
Electric wires 6 for power supply were connected to both ends of the heater 4a for controlling the characteristic and the heater 4b for correcting the optical path length error.
[0026]
In this embodiment, a silicon substrate 1 was used as a substrate, and all the optical waveguides were formed of a glass material mainly composed of quartz.
The core dimensions were 7 μm × 7 μm, the relative refractive index difference was 0.75%, and the thickness of the cladding 2 was 60 μm.
The schematic dimensions of the circuit are as follows: the length of the optical waveguide 33a is 5 [mm], the length of the optical waveguide 33b is (5 + 0.0005) [mm], the distance between the optical waveguides 33a and 33b is 0.2 [mm], The characteristic control heater 4a has a width of 30 [μm] and a length of 3 [mm], the optical path length error correction heater 4b has a width of 30 [μm], a length of 2 [mm], and the groove 5 has a width of [mm]. 0.15 [mm] and length 3 [mm].
[0027]
The length of the optical waveguide 33a is set to a half wavelength (λ = 1.55 [μm]) in the quartz glass so that the light incident on the input optical waveguide 31a with no power applied is emitted to the output optical waveguide 34a. ), Which is longer than the optical waveguide 33b by 0.0005 [mm].
This example was manufactured by the steps shown in FIG.
First, as shown in FIG. 6A, a clad layer 2 and a core layer 3 were deposited on a silicon substrate 1 by using a flame deposition method (FHD method).
[0028]
Next, as shown in FIG. 6B, the deposited core layer 3 is processed into a waveguide shape using a photolithography technique and a reactive dry etching technique (RIE), and as shown in FIG. A cladding layer 2 was deposited thereon to form a buried quartz optical waveguide.
Thereafter, as shown in FIG. 6D, a thin film heater 4 made of a Cr film and an electric wiring 6 made of an Au film are formed on the clad layer 2 of the manufactured optical waveguide, and finally, as shown in FIG. As shown, the groove 5 was formed using RIE.
In the present embodiment and the following embodiments, a flame deposition method is used for manufacturing an optical waveguide.However, the present invention is not limited to this, and any method such as a gas phase method or a sol-gel method can be used. is there.
[0029]
Further, in the present embodiment and the following embodiments, the Cr film and the Au film are used as the materials of the thin film heater and the electric wiring, respectively. However, the present invention is not limited thereto, and any material having similar electric characteristics may be used. Combinations can be used.
A waveguide-type thermo-optical switch was manufactured using the above-described manufacturing process, and its characteristics were evaluated.
The characteristic evaluation was performed on the extinction ratio, the drive power, and the optical path length error before and after the optical path length error correction step due to local heating.
More specifically, the extinction ratio was obtained by measuring the intensity of light that enters light into the input optical waveguide 31a and emits light to the output optical waveguide 34b without applying power.
[0030]
The drive power is increased while the light applied to the input optical waveguide 31a and the light intensity emitted to the output optical waveguide 34b are measured, and the power applied to the characteristic control heater 4a is increased until two points where the extinction is most observed are observed. The difference between the power values at the two points was measured and determined (drive power [W] = (difference between the power values at the two points) / 2).
Further, the optical path length error is measured by applying power to the characteristic control heater 4a while measuring the intensity of light incident on the input optical waveguide 31a and emitted from the output optical waveguide 34b. The degree of deviation of the most extinction point that should be obtained from the no-power application state was measured and compared with the drive power described above. (Optical path length error [%] = (the most extinction point and the no-power state Deviation) / (drive power) × 100).
[0031]
As a result of the measurement, the characteristics before correction of the optical path length error were an extinction ratio of 16 [dB], drive power of 0.17 [W], and an optical path length error of 10.0 [%].
The characteristics after the correction of the optical path length error were as follows: the extinction ratio was 30 [dB], the drive power was 0.17 [W], and the optical path length error was 0.5 [%] or less.
Here, the conventional optical switch of the power saving structure shown in FIG. 8 cannot correct the optical path length error, so that the extinction ratio is 20 [dB], the drive power is 0.17 [W], and the optical path length error is Therefore, the drive power is reduced to the same level as that of the conventional waveguide-type optical switch having a power-saving structure, and the extinction ratio is reduced to 10 [dB] by correcting the optical path length error by local heating. Could be improved.
[0032]
In the present embodiment, the extinction ratio before the correction of the optical path length error was 16 [dB] and the optical path length error was 10.0 [%]. This is because the thin film formed on the optical waveguides 33a and 33b This is because the shapes of the heaters are different and the stresses applied to the optical waveguides 33a and 33b are different.
Theoretically, an extinction ratio of 45 [dB] or more can be obtained if the optical path length difference is suppressed to 0.5 [%] or less. In addition to 32b, the branching ratio deviated from the design value of 50 [%], so that only an extinction ratio of 30 [dB] was obtained.
[0033]
In the present embodiment, a glass material mainly composed of quartz was used as the waveguide material. However, the present technology is not limited to this, and may be caused by the substrate used and the thermal expansion coefficient length of the waveguide material. As long as the applied stress is applied to the optical waveguide portion, the method can be applied to a case where an inorganic dielectric material or an organic dielectric material is used as the waveguide material, and the optical path length error is corrected after the manufacturing process as in the present embodiment. As a result, it is possible to realize a power-saving interference-type thermo-optical component with good characteristics and high productivity at a low price.
Further, in the present embodiment, the case of the waveguide type thermo-optical switch has been described. However, the present technology is not limited to this, and any interference type thermo-optical component such as an optical frequency filter and an optical variable attenuator. The optical path length error can be corrected after the manufacturing process in the same manner as in the present embodiment, and a power-saving interference-type thermo-optical component can be realized with good characteristics and high productivity at a low price. .
[0034]
[Example 2]
FIG. 2 shows an interference-type thermo-optical component according to a second embodiment of the present invention.
2A is a top view, FIG. 2B is a cross-sectional view taken along line CC ′, and FIG. 2C is a cross-sectional view taken along line DD ′.
This embodiment is an example in which the branching ratio of the multiplexer / demultiplexer is set to 3 [dB] (50%), and a waveguide-type thermo-optical switch is manufactured.
[0035]
As shown in the drawing, the waveguide thermo-optical switch of the present embodiment is different from the waveguide thermo-optical switch of Embodiment 1 in that the characteristic control heater 4a and the groove 5 are provided at the center of the optical waveguides 33a and 33b. The heater for correcting the optical path length error is divided into two parts, 4b and 4c, and placed on both sides of the optical waveguides 33a and 33b.
Except that the length of the optical path length error correcting heaters 4b and 4c is 1 [mm], the other schematic configuration and the manufacturing procedure are the same as those of the waveguide type thermo-optic switch of the first embodiment, so that the detailed description will be made. Is omitted.
[0036]
In this embodiment, as in the first embodiment, the extinction ratio, the drive power, and the optical path length error were measured before and after the optical path length error correction step due to local heating.
As a result of the measurement, the characteristics before correction of the optical path length error were an extinction ratio of 16 [dB], drive power of 0.17 [W], and an optical path length error of 10.0 [%].
The characteristics after the correction of the optical path length error were as follows: extinction ratio 35 [dB], drive power 0.17 [W], and optical path length error 0.5 [%] or less.
[0037]
In this embodiment, as in the first embodiment, the drive power is reduced to 0.17 [W] equivalent to that of the conventional waveguide-type thermo-optical switch having the power saving structure shown in FIG. The extinction ratio could be improved by 15 [dB] by the long error correction. Further, in the present embodiment, since the groove 5 is disposed apart from the two multiplexers / demultiplexers 32a and 32b, the deterioration of the characteristics of the multiplexers / demultiplexers 32a and 32b due to the stress change can be suppressed to a low level. As a result, the extinction ratio could be further improved by 5 [dB].
[0038]
In the present embodiment, the extinction ratio before the correction of the optical path length error was 16 [dB] and the optical path length error was 10.0 [%]. This is because the thin film formed on the optical waveguides 33a and 33b This is because the shapes of the heaters are different and the stresses applied to the optical waveguides 33a and 33b are different.
In the present embodiment, a glass material mainly composed of quartz was used as the waveguide material. However, the present technology is not limited to this, and is caused by a difference in thermal expansion coefficient between the substrate used and the waveguide material. As long as the applied stress is applied to the optical waveguide portion, the method can be applied to a case where an inorganic dielectric material or an organic dielectric material is used as the waveguide material, and the optical path length error is corrected after the manufacturing process as in the present embodiment. Thus, a power-saving waveguide-type thermo-optical switch can be realized with good characteristics and high productivity at low cost.
[0039]
Further, in the present embodiment, the case of the waveguide type thermo-optical switch has been described. However, the present technology is not limited to this, and any interference type thermo-optical component such as an optical frequency filter and an optical variable attenuator. The optical path length error can be corrected after the manufacturing process in the same manner as in the present embodiment, and a power-saving interference-type thermo-optical component can be realized with good characteristics and high productivity at a low price. .
[0040]
[Example 3]
FIG. 3 shows an interference-type thermo-optical component according to a third embodiment of the present invention.
3A is a top view, FIG. 3B is a cross-sectional view taken along line EE ′, and FIG. 3C is a cross-sectional view taken along line FF ′.
This embodiment is an example in which the branching ratio of the multiplexer / demultiplexer is set to 3 [dB] (50%), and a waveguide-type thermo-optical switch is manufactured.
[0041]
As shown in the drawing, the waveguide type thermo-optical switch of the present embodiment is different from the waveguide type thermo-optical switch of Embodiment 1 in that the electrical wiring 6a for supplying power to the characteristic control heater 4a is formed by the groove 5. This is formed on the optical waveguide 33a in a region where the groove 5 is not formed, and an electric wiring 6b for supplying power to the heater 4b for correcting an optical path length error is formed on the optical waveguide 33b in a region where the groove 5 is formed.
The electric wiring had a structure in which an Au film was laminated on a Cr film used as a thin film heater film.
Other schematic configurations and manufacturing procedures are the same as those of the waveguide-type thermo-optical switch of the first embodiment, and thus detailed description is omitted.
[0042]
In this embodiment, as in the first embodiment, the extinction ratio, the drive power, and the optical path length error were measured before and after the optical path length error correction step due to local heating.
As a result of the measurement, the characteristics before the correction of the optical path length error were an extinction ratio of 20 [dB], a drive power of 0.17 [W], and an optical path length error of 6.4 [%].
The characteristics after the correction of the optical path length error were as follows: the extinction ratio was 30 [dB], the drive power was 0.17 [W], and the optical path length error was 0.5 [%] or less.
In this embodiment, as in the first embodiment, the drive power is reduced to 0.17 [W] equivalent to that of the conventional waveguide-type thermo-optical switch having the power saving structure shown in FIG. The extinction ratio could be improved by 10 [dB] by the long error correction.
[0043]
In this embodiment, as in the first embodiment, the extinction ratio of only about 30 [dB] was obtained because the branching ratio of the two multiplexers / demultiplexers deviated from the design value of 50 [%].
Further, in this embodiment, the shape of the electric wiring formed in the optical waveguides 33a and 33b and the thin film heater are different. However, the electric wiring has a laminated structure of a Cr film and an Au film, and the thin film heater is a single layer of a Cr film. Due to the structure, the difference in stress applied to the optical waveguides 33a and 33b was suppressed low, and the extinction ratio before correction was improved by 4 [dB] as compared with the first embodiment.
[0044]
In the present embodiment, a glass material mainly composed of quartz was used as the waveguide material. However, the present technology is not limited to this, and is caused by a difference in thermal expansion coefficient between the substrate used and the waveguide material. As long as the applied stress is applied to the optical waveguide portion, the method can be applied to a case where an inorganic dielectric material or an organic dielectric material is used as the waveguide material, and the optical path length error is corrected after the manufacturing process as in the present embodiment. Thus, a power-saving waveguide-type thermo-optical switch can be realized with good characteristics and high productivity at low cost.
Further, in the present embodiment, the case of the waveguide type thermo-optical switch has been described. However, the present technology is not limited to this, and any interference type thermo-optical component such as an optical frequency filter and an optical variable attenuator. The optical path length error can be corrected after the manufacturing process in the same manner as in the present embodiment, and a power-saving interference-type thermo-optical component can be realized with good characteristics and high productivity at a low price. .
[0045]
[Example 4]
FIG. 4 shows an interference-type thermo-optical component according to a fourth embodiment of the present invention.
4A is a top view, FIG. 4B is a sectional view taken along line GG ′, and FIG. 4C is a sectional view taken along line HH ′.
This embodiment is an example in which the branching ratio of the multiplexer / demultiplexer is set to 3 [dB] (50%), and a waveguide-type thermo-optical switch is manufactured.
[0046]
As shown in the figure, the waveguide type thermo-optical switch of the present embodiment is different from the waveguide type thermo-optical switch of Example 2 in that the electric wire 6a for supplying power to the characteristic control heater 4a is formed by the groove 5. This is formed on the optical waveguide 33a in a region where the groove 5 is not formed, and an electric wiring 6b for supplying power to the heater 4b for correcting an optical path length error is formed on the optical waveguide 33b in a region where the groove 5 is formed.
Other schematic configurations and manufacturing procedures are the same as those of the waveguide-type thermo-optical switch according to the second embodiment, and thus detailed description is omitted.
[0047]
In this embodiment, as in the first embodiment, the extinction ratio, the drive power, and the optical path length error were measured before and after the optical path length error correction step due to local heating.
As a result of the measurement, the characteristics before the correction of the optical path length error were an extinction ratio of 20 [dB], a drive power of 0.17 [W], and an optical path length error of 6.4 [%].
The characteristics after the correction of the optical path length error were as follows: extinction ratio 35 [dB], drive power 0.17 [W], and optical path length error 0.5 [%] or less.
[0048]
In this embodiment, as in the first embodiment, the drive power is reduced to 0.17 [W] equivalent to that of the conventional waveguide-type thermo-optical switch having the power saving structure shown in FIG. The extinction ratio could be improved by 15 [dB] by the long error correction. Also, in the present embodiment, as in the second embodiment, the groove 5 is arranged apart from the two multiplexers / demultiplexers 32a and 32b. Therefore, it is possible to prevent the characteristics of the multiplexers / demultiplexers 32a and 32b from being deteriorated due to a stress change. As compared with Example 1, the extinction ratio could be further improved by 5 [dB].
[0049]
Further, in this embodiment, the shape of the electric wiring formed in the optical waveguides 33a and 33b and the thin film heater are different. However, the electric wiring has a laminated structure of a Cr film and an Au film, and the thin film heater is a single layer of a Cr film. Due to the structure, the difference in stress applied to the optical waveguides 33a and 33b was suppressed low, and the extinction ratio before correction was improved by 4 [dB] as compared with the first embodiment.
Further, in the present embodiment, the electric wiring 6b for supplying power to the two optical path length error correcting heaters 4b and 4c is commonly used. The configuration was suitable for scaling up.
[0050]
In the present embodiment, a glass material mainly composed of quartz was used as the waveguide material. However, the present technology is not limited to this, and is caused by a difference in thermal expansion coefficient between the substrate used and the waveguide material. When a stress is applied to the optical waveguide portion, the present invention can be applied to a case where an inorganic dielectric material or an organic dielectric material is used as the waveguide material, for example. The error can be corrected after the manufacturing process, and a power-saving waveguide-type thermo-optical switch can be realized with good characteristics and high productivity at a low price.
Further, in the present embodiment, the case of the waveguide type thermo-optical switch has been described. However, the present technology is not limited to this, and any interference type thermo-optical component such as an optical frequency filter and an optical variable attenuator. The optical path length error at the time of fabrication is corrected after the fabrication process in the same manner as in the present embodiment, thereby realizing a low power interference type thermo-optic optical component with good characteristics at good productivity and low cost. be able to.
[0051]
[Example 5]
FIG. 5 shows an interference-type thermo-optical component according to a fifth embodiment of the present invention.
5A is a top view, FIG. 5B is a cross-sectional view taken along line II ′, and FIG. 5C is a cross-sectional view taken along line JJ ′.
In this embodiment, a waveguide-type thermo-optical switch is manufactured by setting the branching ratio of the multiplexer / demultiplexer to 3 [dB] (50%), and a silicon substrate is formed immediately below the optical waveguide in a region where a groove is formed. It is an example in which a concave shape is formed thereon and a trench filled with a clad material is formed therein.
[0052]
As shown in the figure, the waveguide type thermo-optical switch according to the present embodiment is different from the waveguide type thermo-optical switch according to the fourth embodiment in that the silicon is provided immediately below the regions where the grooves 5 of the optical waveguides 33a and 33b are formed. A trench 11 is formed in a concave shape on a substrate 1 and the inside thereof is filled with a cladding material.
The dimensions of the trench were 150 [μm] in width, 2 [mm] in length, and 50 [μm] in depth.
The rest of the schematic configuration is the same as that of the waveguide-type thermo-optical switch according to the fourth embodiment, and a detailed description thereof will be omitted.
[0053]
In the manufacturing procedure of this example, first, a concave shape was formed on the silicon substrate 1 and a clad material was deposited thereon.
Thereafter, the surface is flattened by mechanical polishing so that the clad material remains only inside the concave shape, and the optical waveguide, the thin film heater, the electric wiring, and the groove are formed thereon in the process shown in FIG. did.
In this embodiment, as in the first embodiment, the extinction ratio, the drive power, and the optical path length error were measured before and after the optical path length error correction step due to local heating.
[0054]
As a result of the measurement, the characteristics before correction of the optical path length error were an extinction ratio of 20 [dB], drive power of 0.12 [W], and an optical path length error of 6.5 [%].
The characteristics after correction of the optical path length error were an extinction ratio of 35 [dB], a drive power of 0.12 [W], and an optical path length error of 0.5 [%] or less.
In the present embodiment, by forming the trench 11, the drive power can be reduced by 30% from 0.17 [W] of the waveguide type thermo-optical switch of the conventional power saving structure shown in FIG. The extinction ratio could be improved by 15 [dB] by correcting the optical path length error due to local heating.
[0055]
Also, in the present embodiment, as in the fourth embodiment, the groove 5 is arranged apart from the two multiplexers / demultiplexers 32a and 32b, so that deterioration of the characteristics of the multiplexers / demultiplexers 32a and 32b due to a change in stress can be prevented. As compared with Example 1, the extinction ratio could be further improved by 5 [dB].
Further, in this embodiment, the shape of the electric wiring formed in the optical waveguides 33a and 33b and the thin film heater are different. However, the electric wiring has a laminated structure of a Cr film and an Au film, and the thin film heater is a single layer of a Cr film. Due to the structure, the difference in stress applied to the optical waveguides 33a and 33b was suppressed low, and the extinction ratio before correction was improved by 4 [dB] as compared with the first embodiment.
[0056]
In this embodiment, the trench 11 is formed below the optical waveguides 33a and 33b. However, since the trenches below the optical waveguides 33a and 33b have the same structure, no deterioration in the extinction ratio or the like is observed.
Also, in this embodiment, similarly to the fourth embodiment, the electric wiring 6b for supplying power to the two optical path length error correction heaters 4b and 4c is commonly used, so that the electric wiring 6b can be arranged neatly. It was possible to make the configuration suitable for miniaturization and large scale.
[0057]
In the present embodiment, a glass material mainly composed of quartz was used as the waveguide material. However, the present technology is not limited to this, and is caused by a difference in thermal expansion coefficient between the substrate used and the waveguide material. When a stress is applied to the optical waveguide portion, the present invention can be applied to a case where an inorganic dielectric material or an organic dielectric material is used as the waveguide material, for example. The error can be corrected after the manufacturing process, and a power-saving waveguide-type thermo-optical switch can be realized with good characteristics and high productivity at a low price.
Further, in the present embodiment, the case of the waveguide type thermo-optical switch has been described. However, the present technology is not limited to this, and any interference type thermo-optical component such as an optical frequency filter and an optical variable attenuator. The optical path length error at the time of fabrication is corrected after the fabrication process in the same manner as in the present embodiment, thereby realizing a low power interference type thermo-optic optical component with good characteristics at good productivity and low cost. be able to.
[0058]
【The invention's effect】
As described above in detail based on the embodiments, according to the present invention, the waveguide material on both sides is added to a part of two optical waveguides connecting two multiplexers / demultiplexers of the Mach-Zehnder interferometer. A removed groove is formed, and a thin film heater is formed in a region where the groove is formed on one optical waveguide to be used as a heater for controlling characteristics, and a thin film is formed in a region where no groove is formed on the other optical waveguide. By forming a heater and using it as an optical path error correction heater, it is possible to reduce the drive power required for characteristic control without increasing the circuit size and to correct the optical path length error during manufacturing by local heating. Therefore, it is possible to provide an interference-type thermo-optical component having high productivity, low cost, low power consumption, and excellent characteristics.
Therefore, the present invention is extremely effective for practical use of an interference-type thermo-optical component that is excellent in power saving and characteristics.
[Brief description of the drawings]
FIG. 1A is a top view showing a schematic configuration of an interference-type thermo-optical component according to a first embodiment of the present invention, and FIG. 1B is an AA in FIG. 1A. 1 (c) is a sectional view taken along the line BB 'in FIG. 1 (a).
FIG. 2A is a top view showing a schematic configuration of an interference-type thermo-optical component according to a second embodiment of the present invention, and FIG. 2B is a sectional view taken along line CC in FIG. 2A. FIG. 2C is a cross-sectional view taken along a line DD ′ in FIG. 2A.
FIG. 3A is a top view showing a schematic configuration of an interference-type thermo-optical component according to a third embodiment of the present invention, and FIG. 3B is an EE in FIG. 3A. FIG. 3C is a sectional view taken along line FF ′ in FIG. 3A.
FIG. 4A is a top view showing a schematic configuration of an interference-type thermo-optical component according to a fourth embodiment of the present invention, and FIG. 4B is a GG in FIG. 4A. FIG. 4C is a sectional view taken along line HH ′ in FIG. 4A.
FIG. 5A is a top view showing a schematic configuration of an interference-type thermo-optical component according to a fifth embodiment of the present invention, and FIG. 5B is a sectional view taken along a line II in FIG. 5A. FIG. 5C is a sectional view taken along line JJ ′ in FIG. 5A.
FIGS. 6 (a) to 6 (e) are process diagrams showing a procedure for manufacturing an interference-type thermo-optical component manufactured using a quartz-based planar lightwave circuit technique.
7A is a top view showing a schematic configuration of a conventional interference-type thermo-optical component, and FIG. 7B is a cross-sectional view taken along the line KK 'in FIG. 7A.
8A is a top view showing a schematic configuration of a conventional interference-type thermo-optical component, and FIG. 8B is a sectional view taken along line LL 'in FIG. 8A.
[Explanation of symbols]
1 Silicon substrate
2 Cladding layer
3 core
4 Thin film heater
4a Characteristic control heater
4b, 4c Heater for optical path length error correction
5 grooves
6 Electrical wiring for power supply
6a Electrical wiring for heater power supply for characteristic control
6b Electric wiring for heater power supply for optical path length error correction
11 trench
31a, 31b Input optical waveguide
32a, 32b multiplexer / demultiplexer
33a, 33b Optical waveguide
34a, 34b Output optical waveguide

Claims

A Mach-Zehnder interferometer comprising a buried optical waveguide in which a core is buried with a clad layer having a sufficient thickness and two multiplexers / demultiplexers connected by two optical waveguides, and loaded on top of the optical waveguide In an interference type thermo-optic optical component comprising a thin film heater, a region where a waveguide material is removed is formed on both sides of a part of the two optical waveguides, and a groove is formed on one of the optical waveguides A thin film heater is loaded on the other optical waveguide, and a thin film heater is loaded on a region where no groove is formed on the other optical waveguide.

The interference-type thermo-optical component according to claim 1, wherein the groove is disposed at a central portion of the optical waveguide, and a thin film heater is loaded on a central portion of the optical waveguide where the groove is formed, An interference-type thermo-optical component, wherein thin-film heaters are loaded on both sides of a groove where no groove is formed on the other optical waveguide.

3. The optical waveguide device according to claim 1, wherein a thin-film heater is formed in a region where the groove is formed, and an optical waveguide in a region where no groove is formed is formed on a side of the optical waveguide where a thin-film heater is formed. An electric wiring connected to the thin film heater is formed on the road, and the thin film heater is formed in a region where the groove is not formed. On the optical waveguide side, a thin film heater is connected on the optical waveguide in the region where the groove is formed. An interferometric thermo-optical component, wherein an electrical wiring is formed.

4. The interference type thermo-optical component according to claim 3, wherein the electric wiring has a structure in which a material having higher electric conductivity than the thin film heater material is laminated on the thin film heater material. Type thermo-optical parts.

5. The interferometric thermo-optical component according to claim 1, wherein the waveguide material is a glass material containing quartz as a main component, and the substrate material is silicon. Optical components.