JP2004138680A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an optical device so as to have desired temperature characteristics by compensating effective optical length of a part determining wavelength characteristics and phase characteristics in the optical device. <P>SOLUTION: The optical device for controlling characteristic change due to a temperature change of an optical system 31 operated at a single wavelength is joined to one end on an optical axis of the optical system 31, and provided with a chirped grating 10 in which an effective refractive index periodically changes toward an advancing direction of light. A case that a short period side of the grating is joined to the optical system 31 to make a temperature compensating module, and another case that a long period side of the grating is joined to the optical system 31 to make a temperature sensitizing module exist. Furthermore, the optical device is joined to one end on the optical axis of the optical system, and provided with the chirped grating 10 in which the effective refractive index periodically changes toward the advancing direction of the light. In order to control the characteristic change due temperature change of the optical system, the optical device controlled so as to have the desired temperature characteristics can be obtained by compensating the effective optical length of the part determining the wavelength characteristics and the phase characteristics in the optical device. <P>COPYRIGHT: (C)2004,JPO

Description

【００６６】
但し、代表的な光学系材料の典型的な値を示すものであって、本発明の適用範囲を示すものではない。表１より、材料種別により異なるが、１℃当たり１０^−５〜１０^−８の桁で屈折率や物理的長さが変化しており、大きいものでは±３０℃の温度変化に対して０．５％にも及ぶ。
【００６７】
石英ガラスや高分子材料を用いる光ファイバ中に、チャープト・グレーティングを作製する方法として、紫外線照射による方法が一般的である。干渉縞やマスクを通して作られた紫外線の縞を、紫外線により屈折率が変化しやすい組成を有する光ファイバに照射して、光ファイバのコアおよび／またはクラッドに屈折率大小の縞を作りつける。また、石英ガラス、光学ガラス、高分子材料等を用いた導波路の場合には、材料特性や所望精度に応じて、紫外線照射の外に、電子ビーム露光とエッチングによるグレーティング形成法も使われる。
【００６８】
半導体光デバイスの場合には、電子ビーム露光とエッチングとにより導波路組成や導波路形状を変化させて、周期的な実効屈折率変化や形状変化を作り込むことが行われる。これらの作製方法は、半導体製造技術、ナノテクノロジー技術とも密接に関係しており、製造技術の進歩により、作製精度も向上している。
【００６９】
（基本原理）
本発明の基本原理について説明する。最初に、チャープト・グレーティング（以下、ＣＧという）の温度変化に対する特性変化について、直感的な説明を行っておく。本発明は、これまで認識されていなかった温度変化に対するＣＧの振る舞いに関する新たな知見に基づくものである。
【００７０】
図１に、チャープト・グレーティングの温度変化に対する特性変化を示す。基準温度におけるＣＧ１０を模式的に示す。縦の短い線による区切りは、グレーティング１周期を示しており、左端の最初の１周期１２を基準として、順次１０％ずつ周期が長くなる。実際の光ファイバや光導波路におけるＣＧは、図１に比べてごく僅かな周期変化しかなく、グレーティング周期の数は遙かに多い。
【００７１】
次に、温度変化によりＣＧ１０が一様に伸びて、ＣＧ２０に変化したとする。一様な伸びを作図で求めるために、ＣＧ１０の最初の１周期１２を中心とし、右端の最後の１周期１３を回転しつつ垂直方向に伸ばす。これによりＣＧ２０の最初の１周期２２と最後の１周期２３との間に新たなＣＧ２０が得られる。ＣＧ２０における温度変化後のグレーティング周期は、最後の１周期２３を求めたのと同様にして求めることができる。図１においては、ＣＧ２０は、約１８％伸びている。
【００７２】
ＣＧ１０におけるグレーティング周期１４に着目する。温度変化後において、グレーティング周期１４と同じ長さのグレーティング周期を有する位置を、ＣＧ２０において求めると、グレーティング周期２４が求まる。最初の１周期２２ととグレーティング周期２４との距離を、ＣＧ１０に移すと、グレーティング周期１５を得る。ここで、グレーティング周期１４〜１５の距離は、最初の１周期１２〜グレーティング周期１４の約２２％に相当し、温度変化による伸びの割合よりも大きい「収縮」が生じている。
【００７３】
このことから、
（１）グレーティング周期１４の位置は、温度変化によってグレーティング周期１５の位置まで移動する。その収縮移動量は、温度変化によるＣＧの伸張移動量よりも一般に大きい。
（２）最初の１周期１２から見ると、ＣＧ全体が温度変化で伸びたにも拘わらず、グレーティング周期１４と同じ周期を有するグレーティング周期２４またはグレーティング周期１５は、最初の１周期１２に近付く。
（３）最後の１周期１３から見ると、グレーティング周期２４またはグレーティング周期１５は、最後の１周期２３または最後の１周期１３から遠ざかる。遠ざかる距離は、温度変化による伸びよりも一般に大きい。
【００７４】
グレーティング周期１４またはグレーティング周期２４は、対応する同一波長を反射する位置を表していることを考慮すると、この原理を用いて光ファイバまたは光導波路の温度補償または温度増感を行うことができる。
【００７５】
図２に、光ファイバまたは光導波路におけるチャープト・グレーティングの特性変化を示す。図２（ａ）は、基準温度Ｔ_０におけるＣＧであり、図２（ｂ）は、温度Ｔ_０＋ΔＴにおけるＣＧである。以下の説明において、ＣＧは、光ファイバや光導波路のような光導波構造またはその周辺に作りつけられているとするが、実効的には光導波構造を有しない一様なバルク材料に作りつけられていても、光の回折による光の広がりの影響を無視できれば以下の議論は同様に成立する。簡単のために屈折率の大小が順次縞状に配置された屈折率グレーティングとし、グレーティング周期は、左端から順次一定値ａずつ広くなるとする。光は、左端から入射して、同じく左端から反射光が出射する。光ファイバまたは光導波路媒質の実効屈折率をｎ_ｅｆｆとする。
【００７６】
温度Ｔ_０においてｋ番目の局所的グレーティング周期ｄ_ｋを、
ｄ_ｋ＝ｄ_１＋（ｋ−１）ａ　　　　　（式１）
とすると、最初の１周期１２からｋ番目の周期１６までの長さは、
ｘ_ｋ＝Σ_ｊ＝１ ^ｋｄ_ｉ＝ｄ_１ｋ＋ａｋ（ｋ−１）／２　　　　　（式２）
周期ｄ_ｋの縞を中心としたＣＧの部分において、
λ＝２ｎ_ｅｆｆｄ_ｋ　　　　　（式３）
の光が反射され、最初の１周期１２から反射点までの距離がｘ_ｋで与えられることを意味している。なお、全長Ｌに含まれる全周期の数ｎ_Ｔは、
Ｌ＝ｄ_１ｎ_Ｔ＋ａｎ_Ｔ（ｎ_Ｔ−１）／２　　　　　（式４）
より得られる。
【００７７】
次に、温度Ｔ_０における長さＬが、温度Ｔ_０＋ΔＴにおいてＬ［１＋αΔＴ］に伸びたとする。この変化は、熱膨張と屈折率変化の両方の温度変化を含んでいる。ｋ’　番目の周期１６は、
ｄ’_ｋ’＝［ｄ_１＋（ｋ’−１）ａ］（１＋αΔＴ）　　　　　（式５）
左端からｋ’　番目の周期１６までの長さは、
ｘ’_ｋ’＝Σ_ｊ＝１ ^ｋ’ｄ’_ｊ　　　　　（式６）
＝ｄ_１（１＋αΔＴ）ｋ’＋ａ（１＋αΔＴ）ｋ’（１−ｋ’）／２
温度Ｔ_０において、ｋ番目の周期１６の幅ｄ_ｋと、その位置ｘ_ｋに着目し、温度Ｔ_０＋ΔＴにおいて、ｄ_ｋと等しい値ｄ’_ｋ’＝ｄ_ｋを有する周期の位置ｘ’_ｋ’を求める。次に、温度変化の前後における反射点の変化ｘ’_ｋ’−ｘ_ｋを求める。ここで、温度変化後の反射点ｘ’_ｋ’が、元の反射点ｘ_ｋよりも入射端に近付くか遠ざかるかに注目する。
【００７８】
上述したように、温度変化によって、熱膨張と屈折率温度変化の両方が影響を受ける。従って、
光学長Ｌ＝（実効屈折率ｎ_ｅｆｆ）×（幾何学長Ｌ_ｇ）　　　　　（式７）
の変化を扱う必要がある。ここで、実効屈折率ｎ_ｅｆｆは、光学材料自体の屈折率と導波構造に基づく屈折率の両方を含む。光学長Ｌの温度変化は、
Ｌ（Ｔ_０＋ΔＴ）＝Ｌ（Ｔ_０）＋（ｄＬ／ｄＴ）ΔＴ　　　　　（式８）
＝Ｌ（Ｔ_０）＋［ｎ_ｅｆｆ（ｄＬ_ｇ／ｄＴ）＋Ｌ_ｇ（ｄ_ｎｅｆｆ／ｄＴ）
］ΔＴ
係数αを、
α＝［ｎ_ｅｆｆ（ｄＬ_ｇ／ｄＴ）＋Ｌ_ｇ（ｄｎ_ｅｆｆ／ｄＴ）］　　　　（式９）
とおくと、
Ｌ（Ｔ_０＋ΔＴ）＝Ｌ（Ｔ_０）［１＋αΔＴ］　　　　　（式１０）
となる。
【００７９】
導波路構造に基づく屈折率は、材料の屈折率より一般的に小さいことから無視することができ、ここでは説明を簡略化している。導波路構造と使用波長とに依存する導波路構造に基づく屈折率も考慮して詳細な設計を行えば、さらに精度を向上することができる。
【００８０】
さらに、光デバイスの作製・実装においては、光学系部分を基板上に製作したり、クラッディングで覆ったり、外部の影響を排除するためにパッケージに実装したりする。このとき、基板・クラッディング・パッケージ等に用いられる材料は光学系部分とは異なることが多く、製作時や使用時の温度変化に伴い光学系に対して内部歪みを与える。光学材料に歪みが加わると、歪み光学効果を通じて屈折率やその温度変化が変化するので、この変化分も取り込む必要がある。本実施形態における温度補償および温度増感は、光学系に加わる歪みが均一であると見なされる場合に適用する。
【００８１】
ＣＧの温度変化数値例として、Ｌ＝５ｍｍ、ｄ_１＝４９０ｎｍ、ａ＝０．００４７９ｎｍ、ｎ_ｅｆｆ＝１．５、αΔＴ＝１×１０^−４とすると、波長λ＝１５５０ｎｍに対して、

長さＬ＝５ｍｍ、チャーピング量ａ＝０．００４７９ｎｍのＣＧに、短周期グレーティング側から光が入射した場合には、基準温度において波長１５５０ｎｍの光は、ｋ＝５５６６番目の周期を中心として反射される。温度変化αΔＴ＝１×１０^−４後の反射は、長さの温度変化が＋２８０ｎｍであるのに対して、反射中心点の位置変化が−５３００ｎｍとなる。すなわち、長さの温度変化とは逆方向であり、光の入射端に近付く方向に大きくシフトすることがわかる。このシフト量は、チャープ量ａの値によって変化し、上述した数値例では、長さの温度変化の約２０倍にも及んでいる。
【００８２】
短周期グレーティング側から光が入射した場合には、熱膨張に伴ってＣＧ内の反射中心点が短周期側入射端に近付くことを示した。一方、ＣＧの長周期グレーティング側から光を入射すると、熱膨張に伴って反射中心点が長周期側入射端から遠ざかることがわかる。すなわち、光学長の温度変化が強調されて、はるかに大きな反射点シフトが生じる。
【００８３】
このようなＣＧの温度変化による反射点シフトの性質を用いて、光ファイバや光導波路の温度変化を補償することができる。図３（ａ）に、チャープト・グレーティングによる温度補償を示す。ＣＧ１０の短周期グレーティング側、すなわち最初の１周期１２に光ファイバや光導波路などの光学系３１を接続する。光学系３１は、光ファイバや光導波路のような光導波構造を有していてもよいし、バルク光学系のように光導波構造を有していなくてもよい。
【００８４】
ここで、ＣＧ１０を用いて、長さＬ_０の光学系３１の温度変化を補償することを考える。簡単のために、ＣＧと補償対象光学系は同じ材料であり、熱膨張係数と屈折率温度変化率が等しいとする。基準温度におけるＬ_０とｘ_ｋとの和が、温度変化後のＬ_０（１＋αΔＴ）とｘ’_ｋ’との和に等しいという温度補償条件により、
Ｌ_０＝（ｘ_ｋ−ｘ’_ｋ’）／αΔＴ　　　　　（式１２）
となる光学系の温度変化を補償することができる。
【００８５】
ここでは、ＣＧ１１と制御対象となる光学系３１とは、同じ屈折率、熱膨張係数、屈折率温度変化を示す同一材料であると想定している。光デバイスの温度補償技術にあっては、制御対象と制御手段が同一材料からなることは必ずしも自明のことではなく、むしろ異なる特性を示す異種材料を組み合わせることによって温度補償が行われる場合が一般的である。本実施形態によれば、特別な材料の組み合わせを選ぶことなく、両者を同一の材料により、温度補償または温度増感を行うことができる。もちろん、互いに特性の異なる異種材料の組み合わせに、拡張することも容易にできる。
【００８６】
温度補償の数値例を示す。上述した数値例に対して、温度補償ができる光学長Ｌ_０は、（式１２）よりＬ_０＝５２．９ｍｍとなる。すなわち、長さ約５０ｍｍの光学系の温度変化を、長さ５ｍｍのＣＧで補償することができる。なお、上述した数値例は、１４７０ｎｍ〜１６１０ｎｍに至る広範な波長帯域を対象としたものであり、必ずしも特定の波長帯域に最適化したものではない。波長１５５０ｎｍ帯域のみの補償に限定すれば、ＣＧの所要波長帯域は、約１／１０となり、所要長さは０．５ｍｍ程度となる。
【００８７】
波長帯域１４７０ｎｍ〜１６１０ｎｍをカバーするＣＧを想定した場合、グレーティング長Ｌによって、チャーピング量ａ、中心反射点の位置変化、および補償対象光学系の長さＬ_０がどの様に変化するかを知ることは有益である。波長１５５０ｎｍにおいて、温度変化αΔＴ＝１０^−４を補償するという条件から求めた数値を表２に示す。
【００８８】
【表２】

【００８９】
この例では、波長１５５０ｎｍの中心反射点が、チャープト・グレーティングのほぼ中央にあることを考えると、長さＬ_０の光学系を補償するために要するＣＧ長Ｌ／２は、およそＬ_０／２０である。
【００９０】
図３（ｂ）に、チャープト・グレーティングによる温度増感を示す。ＣＧ１０の長周期グレーティング側、すなわち最後の１周期１３に、光ファイバまたは光導波路などの光学系３１を接続する。この構成によれば、光学系３１の温度変化を増感することができる。このとき、ＣＧ１０内の温度変化が大きいことから、接続する光ファイバまたは光導波路がなくても、大きな温度変化が得られることを指摘しておく。
【００９１】
図３（ａ）に示したＣＧ１０に対して、複数波長の光が入射した場合を考える。入射波長として表３に示す８チャンネルの波長を定義する。
【００９２】
【表３】

【００９３】
なお、表３に示した光波長配置は、周波数間隔が比較的大きい、ＣＷＤＭ（ｃｏａｒｓｅ　ｗａｖｅｌｅｎｇｔｈ　ｄｉｖｉｓｉｏｎ　ｍｕｌｔｉｐｌｅｘｉｎｇ）を想定したもので、本発明の性能限界を示すものではない。実際に、光波長間隔が一層狭く光チャンネル数がさらに多いＤＷＤＭ（ｄｅｎｓｅ　ｗａｖｅｌｅｎｇｔｈ　ｄｉｖｉｓｉｏｎ　ｍｕｌｔｉｐｌｅｘｉｎｇ）に対しても、本発明を適用することができる。
【００９４】
ＣＧの最短周期をΛ_１、最長周期をΛ_８とし、波長λ_５に対して温度補償をした場合に、他の波長における補償誤差を求める。上述したように、表２において、波長１５５０ｎｍで補償できる光学長Ｌ_０（λ＝１５５０ｎｍ）を求めた。このときの波長は、表３におけるλ_５に相当している。同様にして、他の波長λ_１〜λ_４、λ_６〜λ_８において補償できる光学長Ｌ_０（λ＝λ_１）、Ｌ_０（λ＝λ_２）、・・・を求め、Ｌ_０（λ＝λ_５）との相違を求めた結果を表４に示す。
【００９５】
【表４】

【００９６】
この結果により、Ｌ＝２．５ｍｍの場合に、波長範囲±１５ｎｍの範囲において、補償誤差１％以下が得られること、および波長１４７０〜１６１０ｎｍにわたる幅±７０ｎｍの範囲において、補償誤差５％以下が得られることがわかる。しかしながら、１つのＣＧを用いて、２つ以上の波長において厳密な温度補償はできないことを示している。
【００９７】
波長多重光ファイバ通信のように複数波長の光を同時に扱う光デバイスにおいては、全波長に対して等しく高い精度を有する光デバイスが所望される。図４（ａ）に、１つの波長に対して温度補償を行う８波長分のＣＧを示す。各波長ごとのＣＧが重なり合わないようにずらして配置し、各々の波長において、ＣＧに接続する光ファイバまたは光導波路の温度変化を補償する。図４（ｂ）に、温度補償を行う場合を示す。温度補償された８本の光ファイバまたは光導波路を、図４（ｂ）に示すように重畳し、集積化することができる。
【００９８】
この集積化されたグレーティングを総体的に見ると、各チャンネルの波長λ_ｉに対応する周期Λ_ｉと、正確な温度補償をするために求められるチャープ量ａ_ｉを有するチャープト・グレーティングを、光軸方向に鎖状に縦続接続したものとなっている。この複合デバイスを縦続型チャープト・グレーティング（以下、ＣＣＧ：Ｃｏｎｃａｔｅｎａｔｅｄ　ｃｈｉｒｐｅｄ　ｇｒａｔｉｎｇという）という。但し、各チャンネルのＣＧを設計するにあたっては、集積化するために各チャンネルのＣＧをシフトさせた量だけ、制御対象となる光ファイバまたは光導波路として、繰り入れて設計を行う必要がある。
【００９９】
波長λ_５＝１５５０ｎｍに対して温度補償された光学系と、ＣＣＧとに対して、他の波長においても温度補償を実現するために要するａ_ｉの値を表５に示す。
【０１００】
【表５】

【０１０１】
この結果により、ＣＣＧにおいてチャンネルごとのチャープ量ａ_ｉを最適に選択することによって、αΔＴ＝１０^−４に対して全チャンネルの反射位置シフト量を等しくすることができ、全波長チャンネルで同時に温度補償を実現することができる。
【０１０２】
図４（ｂ）に示したＣＣＧの構成では、光ファイバまたは光導波路の光軸に沿って、光チャンネル中心波長の増加方向と、各チャンネル内のグレーティング周期の増加方向とが一致している。図５に、単一のＣＧにおいて短周期側から測った位置とグレーティング周期との関係を示す。短周期側から測った位置に対して、チャーピングが線形で変化する。図６に、ＣＣＧにおいて短周期側からはかった位置とグレーティング周期との関係を示す。図６（ａ）は、個別のチャンネルに対して温度補償を最適化したＣＣＧである。図６（ｂ）は、光ファイバまたは光導波路の光軸に沿って、光チャンネル中心波長の増加方向と各チャンネル内のグレーティング周期の増加方向とが互いに逆方向になるように配置したＣＣＧを示す。
【０１０３】
図４（ｃ）に、温度増感を行う場合を示す。温度増感された８本の光ファイバまたは光導波路を、図４（ｃ）に示すように重畳し、集積化することができる。上述したＣＣＧによる温度補償の詳細な説明からも明らかである。このとき、ＣＣＧ内の温度変化が大きいことから、接続する光ファイバまたは光導波路などの光学系３１がなくても、大きな温度変化が得られることを指摘しておく。
【０１０４】
（チャープト・グレーティング内蔵光方向性結合器）
平行配置された光ファイバ・コアまたは導波路コア間の光波結合を利用して、光パワーを分配または移行する光ファイバまたは光導波路方向性結合器が知られている。例えば、Ｐ．Ｙｅｈ　ａｎｄ　Ｈ．Ｆ．Ｔａｙｌｏｒ，　”Ｃｏｎｔｒａｄｉｒｅｃｔｉｏｎａｌ　ｆｒｅｑｕｅｎｃｙ−ｓｅｌｅｃｔｉｖｅ　ｃｏｕｐｌｅｒｓ　ｆｏｒ　ｇｕｉｄｅｄ　ｗａｖｅ　ｏｐｔｉｃｓ”，　Ａｐｐｌｉｅｄ　Ｏｐｔｉｃｓ，　ｖｏｌ．７，　ｐ．２８４８，　１９８０には、ブラッグ・グレーティングを内蔵した方向性結合器が記載されている。方向性結合器のコア部および／または隣接クラッディング部内に、屈折率、利得若しくは損失が周期的に変化するグレーティング構造を作りつける。このようにして光波の結合を制御する光デバイスを、グレーティング内蔵方向性結合器という。本実施形態では、さらにＣＧを採用したものをチャープト・グレーティング内蔵光方向性結合器（以下、ＣＧＤＣ：Ｃｈｉｒｐｅｄ　ｇｒａｔｉｎｇ　ｃｏｕｐｌｅｄ　ｄｉｒｅｃｔｉｏｎａｌ　ｃｏｕｐｌｅｒという）という。図７に、チャープト・グレーティング内蔵光方向性結合器の構成を示す。
【０１０５】
図７（ａ）に、温度補償を行う場合を示す。ＣＧＤＣの入力ポート６４から入射した光は、結合部グレーティング６１に対応する一定波長成分が選択的に反射され、もう一方の導波路に結合して出力ポート６５より出力される。結合部グレーティング６１のＣＧは、上述したように温度補償の機能を有する。入力ポート６４および出力ポート６５となる光ファイバまたは導波路の長さを勘案して、ＣＧＤＣの設計を行う。
【０１０６】
ここで、ＣＧまたはＣＣＧによる温度補償は、「反射型」であり、温度補償すべき導波路への光入力ポートと光出力ポートとは同一であった。これに対してＣＧＤＣによる温度補償は、光入力ポートと光出力ポートとが異なるために、「透過型」の構成にすることができる。このことは、光デバイスの構成、設計上大きな自由度を与え、本発明の適用領域と有効性が大幅に向上する。
【０１０７】
図７（ｂ）に、温度増感を行う場合を示す。結合部グレーティング６１の長周期側を、入力ポート６４および出力ポート６５となる光ファイバまたは導波路に接続する。このとき、ＣＧＤＣ内の温度による反射点シフトが大きいことから、接続する光ファイバまたは光導波路などの光学系３１がなくても、大きな温度変化が得られることを指摘しておく。
【０１０８】
（温度安定化ファブリ・ペロー干渉計）
図３（ａ）、図４（ｂ）および図７（ａ）にそれぞれ示した温度補償のためのＣＧを、温度補償モジュールという。従来、ファブリ・ペロー干渉計は、対向する１対の反射鏡間で光が共振する。この反射を安定に動作させるためには、反射鏡間の間隔を一定に保つ必要がある。この目的のために、温度補償モジュールが有用である。対向する反射デバイスとして、表６に示した組み合わせがある。ここで○印は、安定化ファブリ・ペロー干渉計として望ましい組み合わせ、×は安定化ができない組み合わせ、−は構成が複雑になる組み合わせを表す。
【０１０９】
【表６】

【０１１０】
図８に、ＣＧによる温度安定化ファブリ・ペロー干渉計の構成を示す。図８（ａ）は、ＣＧ７１とＣＧ７２の組み合わせ、図８（ｂ）は、ＣＧ７１と反射鏡８１の組み合わせ、図８（ｃ）は、ＣＧ７１とブラッグ・グレーティング（Ｇ）８２の組み合わせである。また、ＣＣＧとＣＣＧの組み合わせ、ＣＣＧと反射鏡の組み合わせ、ＣＣＧとＧの組み合わせも有効である。なお、ＣＧＤＣは２つのポート間で「透過型」の性質を有するため、ファブリ・ペロー干渉計を構成するのは困難である。
【０１１１】
図９に、ファブリ・ペロー干渉計型の温度安定化狭帯域フィルタの構成を示す。幅の広いスペクトルを有する光源９２からの光は、次段光学系からの反射光を遮断する光アイソレータ９３を介して、温度安定化ファブリ・ペロー干渉計９１に入力される。温度安定化ファブリ・ペロー干渉計９１には、受光器９４が接続されている。温度安定化狭帯域フィルタは、広帯域の光スペクトル９５の中から所望の狭帯域スペクトル９６を取り出すことができる。このような狭帯域フィルタは、光ファイバ通信において、雑音除去、信号のスペクトル制御、波長多重信号から特定チャンネルの抽出、分光スペクトルの同定などの、多くの適用範囲がある。
【０１１２】
図１０に、ファブリ・ペロー干渉計型の波長レファレンスによる多波長安定化光源を示す。図１０（ａ）は構成図である。ＣＧとＣＧの組み合わせによる温度安定化ファブリ・ペロー干渉計１０１は、検出器１０７に接続され、波長誤差信号が検出される。制御部１０８は、波長誤差信号に基づいて、光源１０２〜１０５をフィードバック制御する。光源１０２〜１０５と温度安定化ファブリ・ペロー干渉計１０１との間には、合波器１０６と光アイソレータ９３とが接続されている。
【０１１３】
図１０（ｂ）に、温度安定化ファブリ・ペロー干渉計１０１において、１対の反射デバイス間で共振する半波長の数の変化に応じた周期的なスペクトルの透過波長１０９を示す。温度安定化ファブリ・ペロー干渉計１０１における周期的透過ピーク波長を用いて、フィードバック制御を行う。図１０（ｂ）における波長１１０を安定化するレファレンスを提供することができる。本実施形態では、４波長に対する波長レファレンスを示すが、波長数はこれに限るものではない。
【０１１４】
図８に示した温度安定化ファブリ・ペロー干渉計において、温度補償の対象とする光ファイバまたは光導波路などの光学系３１をレーザ媒質とし、または光学系３１の一部にレーザ媒質を含む場合には、温度変化に対して安定な波長を与えるレーザ発振が得られる。図８に示したＣＧとの組み合わせのみならず、表６に示したＣＣＧとの組み合わせを用いて、安定な波長を与える多波長のレーザ発振が得られる。
【０１１５】
図８に示した温度安定化ファブリ・ペロー干渉計において、温度補償の対象とする光ファイバまたは光導波路などの光学系３１を非線形光媒質とし、または光学系３１の一部に非線形光媒質を含む場合には、温度変化に対して安定な波長を与える非線形光デバイスが得られる。図８に示したＣＧとの組み合わせのみならず、表６に示したＣＣＧとの組み合わせを用いて、安定な波長を与える多波長の非線形光デバイスが得られる。
【０１１６】
非線形光媒質効果として、光高調波発生、光差周波発生、光混合、縮退４光波混合、光パラメトリック混合、誘導ラマン散乱、誘導ブリルアン散乱、誘導レーリー散乱、光ソリトン発生等による波長変換、光増幅、波形整形などを利用することができる。
【０１１７】
（温度安定化マイケルソン干渉計）
図１１に、ＣＧによるマイケルソン干渉計の構成を示す。図１１（ａ）に、温度安定化マイケルソン干渉計の構成を示す。方向性結合器１３１の２つの出力ポート１３２、１３３となる光ファイバまたは光導波路の各々の温度変化を補償するために、温度補償モジュールを用いて安定化する。
【０１１８】
図１１（ｂ）に、差分安定化マイケルソン干渉計の構成を示す。方向性結合器１３１の２つの出力ポート１３２、１３３となる光ファイバまたは光導波路の長さの差分１３８により生じる温度変化を補償する。長い方の出力ポート１３２に温度補償モジュールを接合し、短い方の出力ポート１３３に反射鏡８１を接合する。１波長または多波長で動作するマイケルソン型干渉計を安定化することができる。なお、長い方の出力ポート１３２に反射鏡８１を接合し、短い方の出力ポート１３３に温度増感モジュールを接合することによっても、安定化することができる。
【０１１９】
図１２に、マイケルソン干渉計型の温度安定化ＰＭ−ＡＭ変換器を示す。図１２（ａ）は構成図である。温度安定化ＰＭ−ＡＭ変換器は、図１１（ａ）に示した温度安定化マイケルソン干渉計の方向性結合器１３１の２つの入力ポート１３４、１３５となる光ファイバまたは光導波路に、位相変調光源１４１と振幅変調受光器１４２とを接続している。温度安定化ＰＭ−ＡＭ変換器は、温度変動の影響を受けることなく、位相変調光を振幅変調光の変換する。図１２（ｂ）に、温度安定化ＰＭ−ＡＭ変換器の振幅位相特性を示す。
【０１２０】
図１３に、マイケルソン干渉計型の波長レファレンスによる多波長安定化光源を示す。図１３（ａ）は構成図である。多波長安定化光源は、図１１（ａ）に示した温度安定化マイケルソン干渉計の方向性結合器１３１の２つの入力ポート１３４、１３５となる光ファイバまたは光導波路に、多波長多重化光源１５１と多波長波長誤差検出器１５２とを接続している。制御回路１５３は、多波長波長誤差検出器１５２により検出された波長誤差によって、多波長多重化光源１５１をフィードバック制御する。このようにして、温度変動の影響を受けることなく、安定した周波数レファレンスを提供する。図１３（ｂ）に、多波長安定化光源の波長透過特性を示す。周期的なスペクトルの透過波長１５５を、波長１５４に安定化する。
【０１２１】
図１４に、マイケルソン干渉計型の歪みセンサを示す。図１４（ａ）は構成図である。歪みセンサは、図１１（ａ）に示した温度安定化マイケルソン干渉計の方向性結合器１３１の２つの入力ポート１３４、１３５となる光ファイバまたは光導波路に、光源１６２と受光器１６３とを接続している。出力ポート１３２となる光ファイバまたは光導波路は、歪み検出部１６１を有している。このようにして、温度変動の影響を受けることなく、歪みを検出する。図１４（ｂ）に、歪み対透過振幅特性を示す。
【０１２２】
（ＡＷＧ）
複数波長の光を合波／分波する光合分波器は、超大容量波長多重光ファイバ通信の光デバイスとして、広く用いられている。代表的な光合分波器として、アレイ導波路グレーティング（以下、ＡＷＧ：Ａｒｒａｙ　Ｗａｖｅｇｕｉｄｅ　Ｇｒａｔｉｎｇという）が知られている（例えば、Ｍ．Ｓｍｉｔ，　”Ｎｅｗ　ｆｏｃｕｓｉｎｇ　ａｎｄ　ｄｉｓｐｅｒｓｉｖｅ　ｐｌａｎａｒ　ｃｏｍｐｏｎｅｎｔ　ｂａｓｅｄ　ｏｎ　ａｎ　ｏｐｔｉｃａｌ　ｐｈａｓｅｄ　ａｒｒａｙ”　Ｅｌｅｃｔｒｏｎ．　Ｌｅｔｔ．　Ｖｏｌ．２４，　ｐｐ．３８５−３８６，　Ｍａｒｃｈ　１９８８、およびＭ．Ｓｍｉｔ，　Ｃ．Ｖａｎｄａｒｎ，　”ＰＨＡＳＡＲ−ｂａｓｅｄ　ＷＤＭ−ｄｅｖｉｃｅｓ，　ｐｒｉｎｃｉｐｌｅｓ，　ｄｅｓｉｇｎ　ａｎｄ　ａｐｐｌｉｃａｔｉｏｎｓ”　ＩＥＥＥ　Ｊ．　Ｓｅｌｅｃｔｅｄ　Ｔｏｐｉｃｓ　ｉｎ　Ｑｕａｎｔｕｍ　Ｅｌｅｃｔｒｏｎ，　Ｖｏｌ．２，　Ｎｏ．２，　ｐｐ．２３６−２５０，　Ｊｕｎｅ　１９９６に詳しい。）。石英導波路等を用いたＡＷＧにより、数百チャンネルに及ぶ合波／分波が可能であり、Ｔｂｉｔ／ｓに及ぶ大容量システムを実現することができる。
【０１２３】
図１５に、ＡＷＧの構成を示す。複数チャンネルの光が入力ポート１７３からスター・カプラ１７１に入射し、アレイ導波路１７５に分配される。複数チャンネルの光は、複数のアレイ導波路間に設けられた長さの違いによって位相差が生じ、スター・カプラ１７２において波長ごとに分波される。複数チャンネルの光は、チャンネルごとに異なる光ファイバ１７４に出力されて分波される。逆の光路を取ると、複数のチャンネルが合波される。
【０１２４】
ＡＷＧは、主として石英導波路を用いて製作されているが、デバイス面積が大きく低コスト化が難しい。また、微妙な位相調整を必要とするため、高精度な温度安定化が必要とされている。ＡＷＧの温度安定化に対しては、高い関心が示されており、例えば、Ｙ．Ｋｏｋｕｂｕｎｎ，　Ｍ．Ｔａｋｉｚａｗａ　ａｎｄ　Ｓ．Ｔａｇａ，　”Ｔｈｒｅｅ−ｄｉｍｅｎｓｉｏｎａｌ　ａｔｈｅｒｍａｌ　ｗａｖｅｇｕｉｄｅｓ　ｆｏｒ　ｔｅｍｐｅｒａｔｕｒｅ　ｉｎｄｅｐｅｎｄｅｎｔ　ｌｉｇｈｔｗａｖｅ　ｄｅｖｉｃｅｓ”，　Ｅｌｅｃｔｒｏｎ．　Ｌｅｔｔ．，　ｖｏｌ．３０，　ｐｐ．１２２３−１２２５，　１９９４には、石英導波路の上部クラッディングとして負の温度係数を持つ高分子材料を装着することが記載されている。この方法は、安定化できる温度範囲が狭く、付加されるストレスによりデバイス性能が劣化する。
【０１２５】
また、Ｙ．Ｉｎｏｕｅ，　Ａ．Ｋａｎｅｔｏ，　Ｆ．Ｈａｎａｗａ，　Ｈ．Ｔａｋａｈａｓｈｉ，　Ｋ．Ｈａｔｔｏｒｉ　ａｎｄ　Ｓ．Ｓｕｍｉｄａ，　”Ａｔｈｅｒｍａｌ　ｓｉｌｉｃａ　ｂａｓｅｄ　ａｒｒａｙｅｄ−ｗａｖｅｇｕｉｄｅ　ｇｒａｔｉｎｇ　ｍｕｌｔｉｐｌｅｘｅｒ”，　Ｅｌｅｃｔｒｏｎ．　Ｌｅｔｔ．，　ｖｏｌ．３３，　ｐｐ．１９４５−１９４７，　１９９７には、アレイ導波路部分の３角形断面の溝を埋めた高分子材料を使用し、０〜８５℃の広温度範囲にわたって波長の温度変化を約１／２０に下げることが記載されている。この方法は、特殊な導波路構造のために光損失が大幅に増加する。
【０１２６】
さらに、Ａ．Ｋａｎｅｔｏ，　Ｓ．Ｋａｍｅｉ，　Ｙ．Ｉｎｏｕｅ，　Ｈ．Ｔａｋａｈａｓｈｉ　ａｎｄ　Ａ．Ｓｕｇｉｔａ，　”Ａｔｈｅｒｍａｌ　ｓｉｌｉｃａ−ｂａｓｅｄ　ａｒｒａｙｅｄ−ｗａｖｅｇｕｉｄｅ　ｇｒａｔｉｎｇ　（ＡＷＧ）　ｍｕｌｔｉｐｌｅｘｅｒｓ　ｗｉｔｈ　ｎｅｗ　ｌｏｗｌｏｓｓ　ｇｒｏｏｖｅ　ｄｅｓｉｇｎ”，　ＯＦＣ’９９，　ｐａｐｅｒ　ＴｕＯ１−１，　１９９９，　Ｓａｎ　Ｄｉｅｇｏ，　ＣＡには、三角形断面の溝を矢印型に変更することにより、低損失を保って温度特性を約１／５０に改善することが記載されている。
【０１２７】
さらにまた、Ｋ．Ｍａｒｕ，　Ｍ．Ｏｈｋａｗａ，　Ｈ．Ｎｏｕｎｅｎ，　Ｓ．Ｔａｋａｓｕｇｉ，　Ｓ．Ｋａｓｈｉｍｕｒａ，　Ｈ．Ｏｋａｎｏ　ａｎｄ　Ｈ．Ｕｅｔｓｕｋａ，　”Ａｔｈｅｒｍａｌ　ａｎｄ　ｃｅｎｔｅｒ　ｗａｖｅｌｅｎｇｔｈ　ａｄｊｕｓｔａｂｌｅ　ａｒｒａｙｅｄ−ｗａｖｅｇｕｉｄｅ　ｇｒａｔｉｎｇ”，　ＯＦＣ’２０００，　ｐａｐｅｒ　ＷＨ３，　２０００，　Ｓａｎ　Ｊｏｓｅ，　ＣＡには、入力スター・カプラに数個の三日月形の溝を作って高分子材料を充填することにより、−０．００１３ｎｍ／℃という高安定度を有することが記載されている。しかしながら、上述した４つの例では、いずれも付加的な位相誤差や偏光依存性を生じており、この補正を行うためにさらに損失が増加している。
【０１２８】
Ｈ．Ｈ．Ｙａｏ，　Ｃ．Ｚａｗａｄｚｋｉ，　Ｎ．Ｋｅｉｌ，　Ｍ．Ｂａｕｅｒ，　Ｃ．Ｄｒｅｙｅｒ　ａｎｄ　Ｊ．Ｓｃｈｎｅｉｄｅｒ　”Ａｔｈｅｒｍａｌ　ａｌｌ−ｐｏｌｙｍｅｒ　ａｒｒａｙｅｄ　ｗａｖｅｇｕｉｄｅ　ｇｒａｔｉｎｇ　ｍｕｌｔｉｐｌｅｘｅｒ”，　ＯＦＣ’２００２　ｉｎｖｉｔｅｄ　ｐａｐｅｒ　ＴｕＣ，　Ｍａｒｃｈ　１７−２２，　Ａｎａｈｅｉｍ，　Ｃａｌｉｆｏｒｎｉａには、適当な熱膨張係数を持つ高分子基板を選び、高分子材料だけを用いて、高分子導波路の温度依存性を補償することが記載されている。
【０１２９】
また、Ｇ．Ｗ．Ｙｏｆｆｅ，　Ｐ．Ａ．Ｋｒｕｇ，　Ｆ．Ｑｕｅｌｌｅｔｔｅ　ａｎｄ　Ｄ．Ｔｏｒｎｃｒａｆｔ，　”Ｔｅｍｐｅｒａｔｕｒｅ−　ｃｏｍｐｅｎｓａｔｅｄ　ｏｐｔｉｃａｌ　ｆｉｂｅｒ　Ｂｒａｇｇ　ｇｒａｔｉｎｇｓ”，　ＯＦＣ’９５，　ｐａｐｅｒ　ＷＩ４，　１９９５，　Ｓａｎ　Ｄｉｅｇｏ，　ＣＡおよび、Ｙ．Ｈｉｂｉｎｏ，　Ｍ．Ａｂｅ，　Ｔ．Ｔａｎａｋａ，　Ａ．Ｈｉｍｅｎｏ，　Ａ．Ｓｕｇｉｔａ，　Ｊ．Ａｌｂｅｒｔ，　Ｄ．Ｃ．Ｊｏｈｎｓｏｎ　ａｎｄ　Ｋ．Ｏ．Ｈｉｌｌ，　”Ｔｅｍｐｅｒａｔｕｒｅ−ｉｎｓｅｎｓｉｔｉｖｅ　ＵＶ−ｉｎｄｕｃｅｄ　Ｂｒａｇｇ　ｇｒａｔｉｎｇｓ　ｉｎ　ｓｉｌｉｃａ−ｂａｓｅｄ　ＰＬＣｓ　ｏｎ　Ｓｉ”，　ＥＣＯＣ’９９，　ｐａｐｅｒ　ＰＤ１−５，　１９９９，　Ｎｉｃｅ，　Ｆｒａｎｃｅに示されているように、負性熱膨張係数のセラミック基板や合成バイメタル／シリコン基板上に石英ガラス導波路を形成するＡＷＧが知られている。これらＡＷＧは、直線性が悪く、製作プロセスが複雑になるという欠点を有する。
【０１３０】
入力スター・カプラに変更を加えることにより、温度特性を保持する方法が、Ｇ．Ｈｅｉｓｅ，　Ｈ．Ｗ．Ｓｃｈｎｅｉｄｅｒ　ａｎｄ　Ｐ．Ｃ．Ｃｌｅｍｅｎｓ，　”Ｏｐｔｉｃａｌ　ｐｈａｓｅｄ　ａｒｒａｙ　ｆｉｌｔｅｒ　ｍｏｄｕｌｅ　ｗｉｔｈ　ｐａｓｓｉｖｅｌｙ　ｃｏｍｐｅｎｓａｔｅｄ　ｔｅｍｐｅｒａｔｕｒｅ　ｄｅｐｅｎｄｅｎｃｅ”，　ＥＣＯＣ’９８，　ｐｐ．３１９−３２０，　１９９８，　Ｍａｄｒｉｄ，　Ｓｐａｉｎに示されている。この方法は、入力ファイバの位置を温度変化に応じて移動させるので、製作工程が複雑になるとともに、長期の安定性に課題が残る。
【０１３１】
本発明にかかるチャープト・グレーティングを適用した合分波器を、反射型アレイ導波路エシュロン（以下、ＡＷＥ：Ａｒｒａｙ　Ｗａｇｅｇｕｉｄｅ　Ｅｃｈｅｌｏｎという）という。図１６に、ＡＷＥの構成を示す。入力ポート１７７からスター・カプラ１７６に入射した複数チャンネルの光は、長さの異なるアレイ導波路１７９に分配される。複数チャンネルの光は、アレイ導波路端面で反射された後、元のスター・カプラ１７６に戻る。複数チャンネルの光は、長さの異なるアレイ導波路で生じた位相差によって、チャンネルごとに分光されて互いに異なる出力ポート１７８より出力され分波される。逆の光路を取ると、複数のチャンネルが合波される。
【０１３２】
ＡＷＥは、図１５に示した破線ａで、ＡＷＧを折り返したものに相当する。また、ＡＷＥは、分光学の分野でエシュロンとして知られている分光デバイスを導波路化し、導波路端面で反射して、折り返したものに相当する。本実施形態によれば、素子自体の小型化が可能であり、複数波長に対して温度補償を行うことができる。
【０１３３】
ＡＷＥの温度安定化機構は、アレイ導波路１７９の各々にＣＧまたはＣＣＧを接続し、それぞれの導波路長の温度変化を全チャンネル波長に対して補償する。これによって、温度変化が生じてもアレイ導波路１７９における隣接導波路間の位相差を一定に保つことができ、温度によって合波／分波性能が変化しない合分波器を提供することができる。なお、上述したように、多波長チャンネルに対してＣＧを用いると補償誤差を生じるが、多少の誤差が許容できる少数チャンネル、狭チャンネル間隔のシステムなどでは、ＣＧによる補償も使用することができる。
【０１３４】
（温度安定化マッハ・ツェンダ干渉計）
図１７に、ＣＧＤＣによるマッハ・ツェンダ干渉計の構成を示す。図１７（ａ）に、温度安定化マッハ・ツェンダを示す。２つの方向性結合器１３１のポート間を接続する２つの光ファイバまたは光導波路の両方または一方に対して、図７（ａ）に示したＣＧＤＣを用いることにより、温度変動に対して安定なマッハ・ツェンダ干渉計を構成することができる。また、図１７（ｂ）に、差分安定化型マッハ・ツェンダ干渉計を示す。干渉計を構成する２つの光ファイバまたは光導波路の長さの差分に対して、ＣＧＤＣを用いることにより、温度安定化を図ることができる。
【０１３５】
図１８に、マッハ・ツェンダ干渉計型の温度安定化ＰＭ−ＡＭ変換器を示す。図１８（ａ）は構成図である。温度安定化ＰＭ−ＡＭ変換器は、図１７（ａ）に示した温度安定化マッハ・ツェンダ干渉計の方向性結合器１３１ａ，１３１ｂのそれぞれの入力ポート１３４、１３５となる光ファイバまたは光導波路に、位相変調光源１４１と振幅変調受光器１４２とを接続している。温度安定化ＰＭ−ＡＭ変換器は、温度変動の影響を受けることなく、位相変調光を振幅変調光の変換する。図１８（ｂ）に、温度安定化ＰＭ−ＡＭ変換器の振幅位相特性を示す。
【０１３６】
図１９に、マッハ・ツェンダ干渉計型の波長レファレンスによる多波長安定化光源を示す。図１９（ａ）は構成図である。多波長安定化光源は、図１７（ａ）に示した温度安定化マッハ・ツェンダ干渉計の方向性結合器１３１ａ，１３１ｂのそれぞれの入力ポート１３４、１３５となる光ファイバまたは光導波路に、多波長多重化光源１５１と多波長波長誤差検出器１５２とを接続している。制御回路１５３は、多波長波長誤差検出器１５２により検出された波長誤差によって、多波長多重化光源１５１をフィードバック制御する。このようにして、温度変動の影響を受けることなく、安定した周波数レファレンスを提供する。図１９（ｂ）に、多波長安定化光源の波長透過特性を示す。周期的なスペクトルの透過波長１５４を、波長１５５に安定化する。
【０１３７】
（温度安定化リング共振器）
図２０に、ＣＧＤＣによる温度安定化リング回路の構成を示す。図７（ａ）に示したＣＧＤＣの２つの出力ポート間を、方向性結合器２１２を介して、光ファイバまたは光導波路２１１によりリング状に接続する。ここで方向性結合器２１２は、入力ポートの一方と出力ポートの一方とを、光ファイバまたは光導波路２１１に接続する。入力ポートの他方と出力ポートの他方とは、リング回路への入出力に用いる。このような構成により、このリングで生じる温度変化をＣＧＤＣ１２１により補償する。
【０１３８】
図２１に、ＣＧＤＣによる温度安定化リング・レーザの構成を示す。上述した温度安定化リング回路において、リング状の光ファイバまたは光導波路２１１をレーザ媒質１１１とするか、またはその一部にレーザ媒質１１１を含める。レーザ媒質１１１を励起する光エネルギー供給するため、およびレーザ出力を取り出すために方向性結合器２１２を接続する。図２１（ａ）に示した温度安定化リング・レーザによれば、安定なレーザ光を得ることができる。
【０１３９】
また、リング状の光ファイバまたは光導波路２１１の中を、一方向のみに進行する発振光を得る場合には、図２１（ｂ）に示すように、アイソレータ２２１を配置する。さらに、図２１（ａ）または図２１（ｂ）に示すレーザ媒質１１１に代えて、非線形光媒質を用いることにより、安定な非線形光デバイスを得ることができる。非線形光媒質効果として、光高調波発生、光差周波発生、光混合、縮退４光波混合、光パラメトリック混合、誘導ラマン散乱、誘導ブリルアン散乱、誘導レーリー散乱、光ソリトン発生等による波長変換、光増幅、波形整形を利用することができる。
【０１４０】
本実施形態によれば、温度補償モジュールによって、光ファイバまたは光導波路の実効長の変化や屈折率変化を補償することにより、１）受動的または能動的な光フィルタの透過／反射スペクトルを、温度に対して一定に保つこと、２）レーザの発振波長を一定に保つこと、３）非線形光デバイスの動作波長を一定に保つこと、および波長多重光合分波器において複数チャンネル光の合波／分波特性を一定に保つこと、４）光ファイバ／光導波路歪みセンサから温度変化の影響を排除すること等ができる。
【０１４１】
（温度増感ファブリ・ペロー干渉計）
図３（ｂ）、図４（ｃ）および図７（ｂ）にそれぞれ示した温度増感のためのＣＧを、温度増感モジュールという。ファブリ・ペロー干渉計において、反射鏡間の光学長を変えることにより、透過する狭帯域光の波長を変えることができる。この目的に温度増感モジュールが有用である。対向する反射デバイスとして、表６に示した組み合わせを適用することができる。その組み合わせの方法は、図８に示した温度安定化ファブリ・ペロー干渉計と同じであり、光学系３１に接続するＣＧ７１の向きが異なる他は、構成も同じである。図２２（ａ）〜（ｃ）に、ＣＧによる温度増感ファブリ・ペロー干渉計の構成を示す。図８と同様に、ＣＧとの組み合わせのみならず、表６に示したＣＣＧとの組み合わせを用いて、温度増感ファブリ・ペロー干渉計を構成することができる。
【０１４２】
式１１を参照して示したように、ＣＧにおける温度変化の数値例からわかるように、温度変化によってＣＧ内部の反射点は大きくシフトする。従って、感度は少し犠牲にしてもコンパクトな光デバイスを実現する場合には、増感対象とする光ファイバまたは光導波路を取り除き、ＣＧのみで温度変化に敏感な光デバイスを構成することができる。図２２（ｄ）〜（ｆ）に、その構成を示す。ＣＣＧとの組み合わせを用いて構成した温度増感ファブリ・ペロー干渉計について同様である。
【０１４３】
図２３に、ファブリ・ペロー干渉計型の波長可変フィルタの構成を示す図である。幅の広いスペクトルを有する光源９２からの光は、次段光学系からの反射光を遮断する光アイソレータ９３を介して、温度増感ファブリ・ペロー干渉計１６１に入力される。温度増感ファブリ・ペロー干渉計１６１には、受光器２６２が接続されている。温度増感ファブリ・ペロー干渉計１６１の温度を掃引することにより、広帯域スペクトル９５から波長掃引スペクトル２６３を作り出すことができる。
【０１４４】
上述した温度増感ファブリ・ペロー干渉計において、制御対象とする光ファイバまたは光導波路などの光学系をレーザ媒質とし、または光学系の一部にレーザ媒質を含む場合には、温度によって波長が変化する波長可変レーザを構成することができる。温度安定化ファブリ・ペロー干渉計の場合と同様に、図８に示したＣＧとの組み合わせのみならず、表６に示したＣＣＧとの組み合わせを用いて、波長可変レーザを構成することができる。
【０１４５】
上述した温度増感ファブリ・ペロー干渉計において、制御対象とする光ファイバまたは光導波路などの光学系を非線形光媒質とし、または光学系の一部に非線形光媒質を含む場合には、温度によって波長が変化する波長可変非線形光デバイスを構成することができる。非線形光媒質効果として、光高調波発生、光差周波発生、光混合、縮退４光波混合、光パラメトリック混合、誘導ラマン散乱、誘導ブリルアン散乱、誘導レーリー散乱、光ソリトン発生等による波長変換、光増幅、波形整形などを利用することができる。
【０１４６】
図２４に、ファブリ・ペロー干渉計型の温度センサの構成を示す。制御対象となる光ファイバまたは光導波路である光学系３１は、温度により実効光学長が大きく変化する材料で構成されることが望ましい。上述したように、多少感度を犠牲にして小型化を希望する場合には、光学系３１を取り除き、図２２（ｂ）に示した構成とすることもできる。
【０１４７】
図２５に、ファブリ・ペロー干渉計型の温度検出回路を示す。図２５（ａ）は、構成図である。温度検出回路は、光源１６２からの光を、反射光遮断のためのアイソレータ９３を介して、温度センサ２９１に入射する。温度センサ２９１の出力は、受光器１６３に入力される。図２５（ｂ）に示すように、温度センサ２９１は、非常に狭帯域であるから、受光量から温度変化を高感度で検出することができる。
【０１４８】
（温度増感マイケルソン干渉計）
図１１（ａ）に示した温度安定化マイケルソン干渉計において、温度補償モジュールであるＣＧ１０を、温度増感モジュールに置き換えることにより、温度増感マイケルソン干渉計が得られる。マイケルソン干渉計の出力が２つ光路の位相差によることに着目すると、より高感度な温度センサを実現することができる。
【０１４９】
図２６に、プッシュ・プル温度増感型マイケルソン干渉計の構成を示す。マイケルソン干渉計の２光路に対して、長い光路３０１に温度増感モジュールを、短い光路３０２に温度補償モジュールを接続する（図２６（ａ））。温度補償モジュールは、ポートの長さを補償する以上に大きく変化することが望ましいので、短い光路３０２に接続する。温度による反射点シフトをプッシュ・プル方式により位相変化に変換し、高感度化することができる。なお、ポートの長さは等しくてもよいし、いずれの長さも０であってもよい（図２６（ｂ））。
【０１５０】
また、図１１（ｂ）に示した差分安定化マイケルソン干渉計において、温度補償モジュールであるＣＧ１０を、温度増感モジュールに置き換えることにより、差分増感マイケルソン干渉計が得られる。すなわち、長い方の出力ポートに温度増感モジュールを接合し、短い方の出力ポートに反射鏡を接合する。また、長い方の出力ポートに反射鏡を接合し、短い方の出力ポートに温度補償モジュールを接合することによっても、差分増感マイケルソン干渉計を構成することができる。さらに、多少感度を犠牲にして小型化を希望する場合には、図２６（ｂ）と同様に、ポートの長さを０とする構成にしてもよい。
【０１５１】
図２７に、マイケルソン干渉計型の温度センサを示す。図２７（ａ）は、構成図である。制御対象となる光ファイバまたは光導波路である光学系３１は、温度により実効光学長が大きく変化する材料で構成されることが望ましい。上述したように、多少感度を犠牲にして小型化を希望する場合には、光路２８１，２８２を取り除くこともできる。
【０１５２】
光源１６２からの光を、プッシュ・プル温度増感型マイケルソン干渉計に入射し、その出力を受光器１６３に入力する。図２７（ｂ）に示すように、温度センサは、受光量から温度変化を高感度で検出することができる。
【０１５３】
（温度増感マッハ・ツェンダ干渉計）
図１７に示した温度安定化マッハ・ツェンダ干渉計において、図７（ｂ）に示した温度増感モジュールであるＣＧＤＣを用いることにより、温度変動によって感度良く出力が変化するマッハ・ツェンダ干渉計を構成することができる。また、長い光路には温度増感モジュールを挿入し、短い光路には温度補償モジュールを挿入することにより、プッシュ・プル型の構成とすることもできる。
【０１５４】
図２８に、マッハ・ツェンダ干渉計型の温度センサを示す図である。図２８（ａ）は構成図である。上述した温度増感マッハ・ツェンダ干渉計の方向性結合器１３１ａ，１３１ｂのそれぞれの入力ポート１３４、１３５となる光ファイバまたは光導波路に、光源１６２と受光器１６３とを接続している。図２８（ｂ）に示すように、温度センサは、受光量から温度変化を高感度で検出することができる。
【０１５５】
（温度増感リング共振器）
図２０に示した温度安定化リング回路において、ＣＧＤＣ１２１を温度増感モジュールとする。このリングで生じる温度変化をＣＧＤＣにより増感する。図２１に示した温度安定化リング・レーザにおいて、ＣＧＤＣ１２１を温度増感モジュールとすることにより、温度による波長可変レーザを構成することができる。さらに、レーザ媒質に代えて、非線形光媒質を用いることにより、温度変化によって感度良く波長が変化する非線形光デバイスを得ることができる。非線形光媒質効果として、光高調波発生、光差周波発生、光混合、縮退４光波混合、光パラメトリック混合、誘導ラマン散乱、誘導ブリルアン散乱、誘導レーリー散乱、光ソリトン発生等による波長変換、光増幅、波形整形を利用することができる。
【０１５６】
本実施形態によれば、温度増感モジュールによって、光ファイバや光導波路の実効長の変化や屈折率変化を増感することにより、１）受動的または能動的光フィルタの透過／反射スペクトルの温度または駆動電力に対する変化を拡大して可変掃引範囲を大きくすること、２）レーザ発振の可変波長範囲ないしは掃引波長範囲を拡大すること、３）非線形光デバイスの波長可変範囲を拡大すること等ができる。
【０１５７】
また、本実施形態によれば、ＣＣＧを用いることにより、複数波長に対して同時に温度補償または温度増感を行うことができる。
【０１５８】
（ＣＧ、ＣＣＧの測定方法）
ＣＧの設計にあたっては、解析的手法が困難であり、現実問題として数値解に頼らざるを得ない部分が多い。光デバイスによっては、複雑な製作プロセスが要求されるので、設計通りのＣＧが構成されたか否かを実際に測定して確認しなければならない。このような目的には、製作された光デバイスと同一の材料、構造、製作プロセスで製作したＣＧまたはＣＣＧを測定して確認する。
【０１５９】
ＣＧまたはＣＣＧの反射波長域、反射率等は、可変波長の光を入射し、反射光の強度を測定することにより求める。本実施形態においては、反射光の波長領域の中心点が温度によってどの様に変化するかが重要である。光軸方向の長さが波長に比べて非常に大きなＣＧにおいて、反射点を同定することは困難であるが、図１１（ｂ）に示した差分安定化マイケルソン干渉計を構成することにより、中心点を求めることができる。
【０１６０】
図２９（ａ）に、マイケルソン干渉計型の温度依存性測定回路を示す。マイケルソン干渉計において、一方のアームには反射鏡を接続し、他方のアームにはＣＧまたはＣＣＧを接続する。全測定系の温度が均一であるとすると、ＣＧまたはＣＣＧが補償する対象は、他方のアーム３７１の長さであり、この長さを既知とする。このとき、温度が変化したときの一定波長の入力光に対するマイケルソン干渉計の出力により、図２９（ｂ）に示すように、ＣＧまたはＣＣＧの反射点の動きを知ることができる。
【０１６１】
（熱光学効果スイッチ・モジュール）
光導波路の熱光学効果を用いた従来の光スイッチは、例えば、Ａ．Ｓｕｇｉｔａ，　Ｋ．Ｊｉｎｇｕｊｉ，　Ｎ．Ｔａｋａｔｏ，　Ｋ．Ｋａｔｏｈ　ａｎｄ　Ｍ．Ｋａｗａｃｈｉ，　”Ｂｒｉｄｇｅ−ｓｕｓｐｅｎｄｅｄ　ｓｉｌｉｃａ−ｗａｖｅｇｕｉｄｅ　ｔｈｅｒｍｏ−ｏｐｔｉｃ　ｐｈａｓｅ　ｓｈｉｆｔｅｒ　ａｎｄ　ｉｔｓ　ａｐｐｌｉｃａｔｉｏｎ　ｔｏ　Ｍａｃｈ−Ｚｅｈｎｄｅｒ　ｔｙｐｅ　ｏｐｔｉｃａｌ　ｓｗｉｔｃｈ”，　Ｔｒａｎｓ．　ＩＥＩＣＥ，　ｖｏｌ．Ｅ７３，　ｎｏ．１，　ｐｐ．１０５−１０９，　１９９０　に記載されている。ここで、上述したＣＧの温度変化による反射点シフトの性質を用いると、小さな温度変化、すなわち少ない電力でスイッチングが可能な熱光学効果スイッチを実現することができる。
【０１６２】
温度補償モジュールにおいて、ＣＧ、ＣＣＧまたはＣＧＤＣに近接し、かつ光学的に損失や歪みによる屈折率変動を与えない距離に、局部的に電気加熱を行うヒータを設置する。グレーティングの温度を変化させることによって、光路長を変更することができる。この光路長変化は、光ファイバや光導波路の温度変化に比べて優に１桁以上大きい。従って、単純に光ファイバや光導波路を加熱する熱効果スイッチに比べて、１桁以上小さい加熱電力と温度変化によりスイッチングを行うことができる。また、温度補償モジュールを局部的に加熱することによって、周囲温度に対しては安定であり、局部加熱に対しては、敏感な熱光学効果スイッチが可能となる。
【０１６３】
図３０に、熱光学効果スイッチ・モジュールの構成を示す。図３０（ａ）にＣＧの場合を、図３０（ｂ）にＣＧＤＣの場合を示す。局部加熱に用いるヒータは、例えばクローム、タングステンのような抵抗材料を薄膜の形で装着することにより得られる。局部加熱による温度上昇は、チャープト・グレーティング部全体にわたって均一であることが必要である。装着形態は、光ファイバまたは光導波路を伝搬する光の電磁界強度が十分に低下した距離に設置するものとし、面内の片側でもよいし、両側でもよい。光ファイバの場合には、光ファイバ・コアを取り巻く形状でもよく、光導波路の場合には、導波路を形成する平面内を含まない平行な平面内に設置する形状でもよい。
【０１６４】
上述のＣＧまたはＣＣＧを用いた熱光学効果スイッチ・モジュールと、方向性結合器１３１とを用いて、マイケルソン型干渉計を構成する。温度安定化を行うとともに、熱光学効果を通じて、高感度に光の強度をスイッチングすることができる。
【０１６５】
図３１に、マイケルソン干渉計型熱光学効果スイッチの構成を示す。図３１（ａ）に示したように、図１１に示した温度安定化モジュールの場合と同様に、マイケルソン干渉計の出力ポート１３２にＣＧの熱光学効果スイッチ・モジュールを接続し、出力ポート１３３にＣＧの温度安定化モジュールを接続する。また、図３１（ｂ）に示したように、出力ポート１３３にＣＧの熱光学効果スイッチ・モジュールを接続し、出力ポート１３３に反射鏡またはブラッグ・グレーティングを接続することができる。
【０１６６】
上述のＣＧＤＣを用いた熱光学効果スイッチ・モジュールと、方向性結合器１３１ａ，１３１ｂとを用いて、マッハ・ツェンダ型干渉計を構成する。温度安定化を行うとともに、熱光学効果を通じて、高感度に光の経路をスイッチングすることができる。
【０１６７】
図３２に、マッハ・ツェンダ型干渉計の熱光学効果スイッチの構成を示す。図３２（ａ）に示したように、図１７の温度安定化モジュールの場合と同様に、２つの方向性結合器１３１のポート間を接続する２つの光ファイバまたは光導波路の両方または一方に対して、ＣＧＤＣの熱光学効果スイッチ・モジュールとＣＧＤＣの温度安定化モジュールとを接続する。また、図３２（ｂ）に示したように、一方にＣＧＤＣの熱光学効果スイッチ・モジュールを、他方に光ファイバまたは光導波路を接続する構成とすることもできる。
【０１６８】
本実施形態によれば、抵抗加熱等の手段によって、少ない電力によりＣＧの温度を変えることにより、温度補償をした状態を保ちながら、光ファイバまたは光導波路を通過する光の強度や経路をスイッチングすることができる。
【０１６９】
【発明の効果】
以上説明したように、本発明によれば、光学系の光軸上の一端に接合され、光の進行方向に向かって実効的屈折率が周期的に変化するチャープト・グレーティングを備え、光学系の温度変化による特性の変化を制御するので、光デバイス中の波長特性、位相特性を決定している部分の実効光学長を補償して、所望の温度特性を有するように制御された光デバイスを提供することができ、周囲温度を一定に維持する温度安定化装置などを不要とし、または簡略化することが可能となる。
【０１７０】
また、本発明によれば、小型高感度の可変光デバイスを実現することができ、光システムの小型化、省電力化、低コスト化に貢献できる光デバイスを提供することが可能となる。
【０１７１】
さらに、本発明によれば、温度補償をした状態を保ちながら、光ファイバまたは光導波路を通過する光の強度や経路をスイッチングすることが可能となる。
【図面の簡単な説明】
【図１】チャープト・グレーティングの温度変化に対する特性変化を示す図である。
【図２】光ファイバまたは光導波路におけるチャープト・グレーティングの特性変化を示す図である。
【図３】チャープト・グレーティングによる温度補償および温度増感を説明するための図である。
【図４】縦続型チャープト・グレーティングによる温度補償および温度増感を説明するための図である。
【図５】単一のＣＧにおいて短周期側から測った位置とグレーティング周期との関係を示す図である。
【図６】ＣＣＧにおいて短周期側から測った位置とグレーティング周期との関係を示す図である。
【図７】チャープト・グレーティング内蔵光方向性結合器の構成を示す図である。
【図８】ＣＧによる温度安定化ファブリ・ペロー干渉計の構成を示す図である。
【図９】ファブリ・ペロー干渉計型の温度安定化狭帯域フィルタの構成を示す図である。
【図１０】ファブリ・ペロー干渉計型の波長レファレンスによる多波長安定化光源の構成を示す図である。
【図１１】ＣＧによるマイケルソン干渉計の構成を示す図である。
【図１２】マイケルソン干渉計型の温度安定化ＰＭ−ＡＭ変換器を示す図である。
【図１３】マイケルソン干渉計型の波長レファレンスによる多波長安定化光源を示す図である。
【図１４】マイケルソン干渉計型の歪みセンサを示す図である。
【図１５】ＡＷＧの構成を示す図である。
【図１６】ＡＷＥの構成を示す図である。
【図１７】ＣＧＤＣによるマッハ・ツェンダ干渉計の構成を示す図である。
【図１８】マッハ・ツェンダ干渉計型の温度安定化ＰＭ−ＡＭ変換器を示す図である。
【図１９】マッハ・ツェンダ干渉計型の波長レファレンスによる多波長安定化光源を示す図である。
【図２０】ＣＧＤＣによる温度安定化リング回路の構成を示す図である。
【図２１】ＣＧＤＣによる温度安定化リング・レーザの構成を示す図である。
【図２２】ＣＧによる温度増感ファブリ・ペロー干渉計の構成を示す図である。
【図２３】ファブリ・ペロー干渉計型の波長可変フィルタの構成を示す図である。
【図２４】ファブリ・ペロー干渉計型の温度センサの構成を示す図である。
【図２５】ファブリ・ペロー干渉計型の温度検出回路を示す図である。
【図２６】プッシュ・プル温度増感型マイケルソン干渉計の構成を示す図である。
【図２７】マイケルソン干渉計型の温度センサを示す図である。
【図２８】マッハ・ツェンダ干渉計型の温度センサを示す図である。
【図２９】マイケルソン干渉計型の温度依存性測定回路を示す図である。
【図３０】熱光学効果スイッチ・モジュールの構成を示す図である。
【図３１】マイケルソン干渉計型の熱光学効果スイッチの構成を示す図である。
【図３２】マッハ・ツェンダ型干渉計の熱光学効果スイッチの構成を示す図である。
【符号の説明】
１０，２０，７１，７２　　チャープト・グレーティング（ＣＧ）
３１　　光学系
６１　　結合部グレーティング
８１　　反射鏡
８２　　ブラッグ・グレーティング（Ｇ）
９１，１０１　　温度安定化ファブリ・ペロー干渉計
１２１　　チャープト・グレーティング内蔵光方向性結合器（ＣＧＤＣ）
１６１　　温度増感ファブリ・ペロー干渉計[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical device, and more particularly, to an optical device in which a temperature characteristic of an optical system is controlled by a chirped grating.
[0002]
[Prior art]
When the length or the refractive index of the optical material constituting the optical device changes, the performance of the optical device changes due to the change of the effective optical length given by the product of the length and the effective refractive index. For example, light output, light receiving sensitivity, light wavelength, and the like change due to a change in the effective optical length due to a temperature change. For example, in a laser light source, when the length of the resonator constituting the laser changes, the wavelength of the output light changes. Therefore, in order to obtain an optical output of a constant wavelength, the optical length between the resonators is kept exactly constant. There must be. On the other hand, when the wavelength of the laser beam is swept by changing the temperature, it is desirable that the wavelength be sensitively changed by the temperature change (hereinafter, referred to as temperature sensitization).
[0003]
2. Description of the Related Art An optical wavelength division multiplexing transmission technique is known in which light having a large number of wavelengths is simultaneously transmitted by a single optical fiber using a slight difference in optical wavelength. In an optical wavelength multiplexing device for multiplexing / demultiplexing light having a slight wavelength difference, when the effective optical length changes, interference occurs between channels having different wavelengths. To prevent this, the oscillation wavelength is fixed by keeping the temperature of the laser light source constant, and the demultiplexing performance is kept by keeping the temperature of the wavelength multiplexing device constant.
[0004]
A direct measure against an optical device that does not like temperature changes is to keep the temperature of the optical device constant by compensating for temperature changes in the external environment. That is, the optical device is heated or cooled in order to keep the temperature of the optical device constant. For example, in optical fiber communication, a stable system operation is realized by keeping the temperature of an optical device constant using a thermoelectric cooling element.
[0005]
In addition, even if a temperature change occurs in the optical device itself, a material having a small temperature change is used for a portion that determines the temperature performance, or a combination with a dissimilar material that causes a temperature change in the opposite direction is compensated so that the performance does not change. Methods are also known. Such a method is adopted at the stage of designing and manufacturing an optical device and eliminates the need for a temperature control device, which is useful for reducing the cost of the system.
[0006]
Here, a grating used in an optical fiber or an optical waveguide and a chirped grating will be described. A grating is a device made for dispersing an optical spectrum in spectroscopy, and is a device in which a number of fine grooves are cut in parallel on a flat or concave reflecting surface. Hereinafter, in the present specification, such a classical grating is not considered as a grating, but an optical fiber grating or an optical waveguide grating.
[0007]
In an optical fiber or an optical waveguide, a grating has a period that is a fraction of the light wavelength in a tube, and has a periodic structure in which large and small stripes of a refractive index, a loss, or a gain are formed. The shape of the periodic structure includes a sine wave shape, a rectangular wave shape, a saw-tooth wave, and a dull shape thereof. In particular, the period is the axial wavelength Λ_gIn this case, the slight light reflected by each of the periodic structures overlaps with the same phase, resulting in a large reflectance. That is, it can be used as a distributed reflector. A distributed feedback laser and a distributed Bragg reflection laser are examples in which this grating is applied. The distributed reflection laser includes a refractive index grating and a gain grating, and the refractive index grating is frequently used. As a grating used in these semiconductor lasers, a uniform grating (hereinafter referred to as a Bragg grating) is used.
[0008]
In a grating built in an optical fiber or optical waveguide, the period of which gradually changes from one end to the other end, that is, the period that gradually expands or contracts is called a chirped grating. . In a semiconductor laser that can be regarded as an optical waveguide in a broad sense, a chirped grating is used as a reflector, and the oscillation wavelength is changed over a wide range by changing the temperature (for example, see Non-Patent Document 1). ). By using a distributed reflection structure in which a plurality of chirped gratings having the same structure are connected in cascade as a laser reflector, a wavelength sweep of about 100 nm is realized in the 1550 nm band.
[0009]
In addition, a chirped grating is used in a semiconductor module to realize a light source having a constant output level and a single spectrum (for example, see Patent Document 1).
[0010]
Furthermore, a chirped grating is known as a means for compensating chromatic dispersion of an optical fiber in ultra-high-speed and long-distance optical fiber communication (for example, see Non-Patent Document 2). A device in which a chirped grating is built in an optical fiber is called a fiber chirped grating. Since the reflection point changes according to the difference in wavelength, it is used for compensating for waveform deterioration due to chromatic dispersion of the long-distance optical fiber using the delay time difference at the time of reflection.
[0011]
[Patent Document 1]
JP-A-2000-257422
[0012]
[Non-patent document 1]
H. Ishii, Y Tohmori, Y. Yoshikuni, T. {Tamamura and and Y. Kondo, “Multiple-phase-shift superstructure grading DBR lasers for broad wavelength tuning”, IEEE Photonics Technology Letter. $ 5, $ no. $ 6, $ pp. 613-615, ｕｎJune 1993
[0013]
[Non-patent document 2]
K. O. Hill and G. {Meltz,} "Fiber \ Bragg \ grading \ technology \ fundamentals \ and \ overview", IEEE / OSA \ J. {Lightwave} Tech. , @Vol. $ 15, $ no. $ 8, $ pp. 1263-1276, Aug. 1997
[0014]
[Problems to be solved by the invention]
Conventionally, chirped gratings of tunable wavelength lasers have been used to widen the wavelength tunable range, and fiber chirped gratings have been used to equalize waveform degradation due to chromatic dispersion during optical fiber transmission. However, sufficient consideration has not been given to the temperature change of the chirped grating itself.
[0015]
In particular, chirped gratings that have been used for tunable wavelength lasers do not always optimize desired effects with respect to changes in refractive index based on changes in drive current and thermal expansion based on changes in temperature. Absent.
[0016]
An object of the present invention is to solve the problem of controlling the optical device performance change due to temperature by compensating for the effective optical length of the portion that determines the wavelength characteristics and phase characteristics in the optical device to obtain a desired temperature characteristic. It is to provide an optical device controlled to have the following.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an optical device for controlling a change in characteristics of an optical system operating at a single wavelength due to a change in temperature, wherein the optical device is an optical device. A chirped grating which is joined to one end on the optical axis of the system and whose effective refractive index periodically changes in the traveling direction of light.
[0018]
According to this configuration, the temperature change of the optical system is emphasized with respect to the temperature change of the optical system. The change can be compensated.
[0019]
The invention according to claim 2 is an optical device that controls a change in characteristics of an optical system operating at a plurality of wavelengths due to a temperature change, wherein the optical device is joined to one end on the optical axis of the optical system, and And a cascaded chirped grating in which a plurality of chirped gratings whose effective refractive indices periodically change at different periods are provided.
[0020]
According to a third aspect of the present invention, there is provided an optical device for controlling a change in characteristics of an optical system operating at a single wavelength due to a temperature change, wherein the optical device is joined to one end of the optical system on an optical axis, and travels light. A directional coupler incorporating a chirped grating whose effective refractive index periodically changes in the direction is provided.
[0021]
According to a fourth aspect of the present invention, a short-period side of the chirped grating of the first to third aspects is joined to the optical system to compensate for a change in characteristics of the optical system due to a temperature change. It is characterized by the following.
[0022]
According to a fifth aspect of the present invention, there is provided an optical device for controlling a change in a characteristic of an optical system due to a temperature change, wherein an effective refractive index periodically changes in a traveling direction of light, and a short period side of the grating. A chirped grating joined to one end of the optical system on the optical axis, and a reflecting device joined to the other end of the optical system on the optical axis.
[0023]
The invention according to claim 6 is characterized in that the reflection device according to claim 5 is any one of the chirped grating, reflecting mirror, and Bragg grating.
[0024]
A seventh aspect of the present invention is characterized in that a heating element that electrically generates heat is mounted near the grating portion of the chirped grating according to the fifth or sixth aspect.
[0025]
The invention according to claim 8 is an optical device for controlling a change in characteristics of an optical system due to a change in temperature, wherein a plurality of optical devices whose effective refractive indices periodically change at different periods in a traveling direction of light. A cascaded chirped grating in which the short-period side of the grating is joined to one end of the optical system on the optical axis, and a reflective device joined to the other end of the optical system on the optical axis. It is characterized by having.
[0026]
According to a ninth aspect of the present invention, the reflective device according to the eighth aspect is any one of the cascaded chirped grating, reflecting mirror, and Bragg grating.
[0027]
According to a tenth aspect of the present invention, a heating element that electrically generates heat is mounted near the grating portion of the cascaded chirped grating according to the eighth or ninth aspect.
[0028]
An eleventh aspect of the present invention is characterized in that the optical system according to any one of the fifth to tenth aspects includes a laser medium.
[0029]
According to a twelfth aspect of the present invention, the optical system according to any one of the fifth to tenth aspects includes a non-linear optical medium.
[0030]
According to a thirteenth aspect of the present invention, there is provided a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and the effective refractive index periodically changes in the traveling direction of light, A chirped grating in which a short-period side of the grating is joined to each of the two output ports.
[0031]
A fourteenth aspect of the present invention is characterized in that a heating element that electrically generates heat is mounted near one of the grating portions of the chirped grating according to the thirteenth aspect.
[0032]
According to a fifteenth aspect of the present invention, there is provided a directional coupler in which the lengths of the optical fibers or the optical waveguides serving as the two output ports are different from each other, and the effective refractive indices in the traveling direction of light have different periods. And a cascaded chirped grating in which a plurality of chirped gratings that change in time are connected, and a short-period side of the grating is joined to each of the two output ports.
[0033]
A sixteenth aspect of the present invention is characterized in that a heating element that electrically generates heat is mounted near one of the grating portions of the cascaded chirped grating according to the fifteenth aspect.
[0034]
According to a seventeenth aspect of the present invention, there is provided a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and an effective refractive index periodically changes in a traveling direction of light, A chirped grating in which the short-period side of the grating is joined to the one output port, and a reflection device joined to the other output port.
[0035]
According to an eighteenth aspect of the present invention, a heating element that electrically generates heat is mounted near the grating portion of the chirped grating according to the seventeenth aspect.
[0036]
The twelfth aspect of the present invention is directed to a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and the effective refractive indices in the traveling direction of light have different periods. A plurality of chirped gratings that change periodically, and a cascaded chirped grating in which the short-period side of the grating is joined to the one output port; and a reflecting device that is joined to the other output port. Features.
[0037]
According to a twentieth aspect of the present invention, a heating element that electrically generates heat is mounted near the grating portion of the cascaded chirped grating according to the nineteenth aspect.
[0038]
According to a twenty-first aspect of the present invention, there is provided a star coupler for distributing light having a plurality of wavelengths input from one input port to a plurality of waveguide ports, and a star coupler connected to the plurality of waveguide ports. A plurality of different waveguide arrays, and an effective refractive index, which is joined to an end of the waveguide array that is not connected to the star coupler, in the light traveling direction, periodically changes at different periods. A plurality of chirped gratings are provided.
[0039]
According to an embodiment of the present invention, a star coupler for distributing light having a plurality of wavelengths input from one input port to a plurality of waveguide ports, and a star coupler connected to the plurality of waveguide ports having a length equal to each other. A plurality of different waveguide arrays, and an effective refractive index, which is joined to an end of the waveguide array that is not connected to the star coupler, in the light traveling direction, periodically changes at different periods. A cascaded chirped grating in which a plurality of chirped gratings are connected.
[0040]
According to a twenty-third aspect of the present invention, in a Mach-Zehnder interferometer having an optical fiber or an optical waveguide having different lengths for connecting between ports of two directional couplers, at least one of the optical fiber and the optical waveguide is provided. A directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light, wherein the short-period side of the grating of the chirped grating is inserted between the ports. It is characterized by.
[0041]
A twenty-fourth aspect of the present invention is characterized in that a heating element that electrically generates heat is mounted near the grating portion of the chirped grating according to the twenty-third aspect.
[0042]
According to a twenty-fifth aspect of the present invention, there is provided a first directional coupler incorporating a chirped grating whose effective refractive index periodically changes in the traveling direction of light; An input port connected to an input port, and a second directional coupler having an output port connected to an output port of the first directional coupler, wherein the short-period side of the chirped grating is It is characterized by being joined to the second directional coupler.
[0043]
According to a twenty-sixth aspect, the optical system that connects the input port of the first directional coupler and the input port of the second directional coupler according to the twenty-fifth aspect includes a laser medium. It is characterized by.
[0044]
According to a twenty-seventh aspect, the optical system that connects the input port of the first directional coupler and the input port of the second directional coupler according to the twenty-fifth aspect includes a nonlinear optical medium. It is characterized by the following.
[0045]
According to a twenty-eighth aspect of the present invention, a long-period side of the chirped grating of the chirped grating according to the first, second, or third aspect is joined to the optical system to sensitize a change in characteristics of the optical system due to a temperature change. It is characterized by doing.
[0046]
The invention according to claim 29 is an optical device for controlling a change in characteristics of an optical system due to a change in temperature, wherein the effective refractive index periodically changes in a traveling direction of light, and the grating has a longer period. A chirped grating joined to one end of the optical system on the optical axis, and a reflecting device joined to the other end of the optical system on the optical axis.
[0047]
The invention according to claim 30 is characterized in that the reflection device according to claim 29 is any one of the chirped grating, reflecting mirror and Bragg grating.
[0048]
The invention according to claim 31 is an optical device for controlling a change in characteristics of an optical system due to a temperature change, wherein a plurality of optical devices whose effective refractive indices periodically change at different periods in a light traveling direction. Tandem-type chirped grating in which the long-period side of the grating is joined to one end on the optical axis of the optical system, and a reflective device joined to the other end of the optical system on the optical axis. It is characterized by having.
[0049]
The invention according to claim 32 is characterized in that the reflection device according to claim 31 is any one of the cascaded chirped grating, reflecting mirror, and Bragg grating.
[0050]
The invention according to claim 33 is characterized in that the optical system according to any one of claims 29 to 32 includes a laser medium.
[0051]
The invention according to claim 34 is characterized in that the optical system according to any one of claims 29 to 32 includes a nonlinear optical medium.
[0052]
The twelfth aspect of the present invention is directed to a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and the effective refractive index periodically changes in the traveling direction of light, A chirped grating in which a long-period side of the grating is joined to each of the two output ports.
[0053]
According to a thirty-sixth aspect of the present invention, there is provided a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and the effective refractive indices in the traveling direction of light have different periods. And a cascaded chirped grating in which a plurality of chirped gratings that change in time are connected, and a long-period side of the grating is joined to each of the two output ports.
[0054]
The invention according to claim 37, wherein the optical fiber or the optical waveguide serving as the two output ports has directional couplers having different lengths, and the effective refractive index periodically changes in the traveling direction of light; A chirped grating having a long-period side of the grating joined to the one output port; and a reflecting device joined to the other output port.
[0055]
The twentieth aspect of the present invention is directed to a directional coupler in which the length of an optical fiber or an optical waveguide serving as two output ports is different from each other, and the effective refractive index in the traveling direction of light is different from each other in a period. A plurality of chirped gratings that change periodically, a cascaded chirped grating in which the long-period side of the grating is joined to the one output port, and a reflection device joined to the other output port. Features.
[0056]
The ninth aspect of the present invention is directed to a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and an effective refractive index periodically changes in a traveling direction of light, A first chirped grating having a short-period side of the grating joined to the one output port; and a second chirped grating having a long-period side of the grating joined to the other output port. I do.
[0057]
According to another aspect of the present invention, there is provided a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, and the effective refractive indices in the traveling direction of light have different periods. The first cascaded chirped grating in which the short-period side of the grating is connected to the one output port and the long-period side of the grating are connected to the other output port And a second cascaded chirped grating.
[0058]
The invention according to claim 41 is a Mach-Zehnder interferometer having optical fibers or optical waveguides having different lengths for connecting ports of two directional couplers, wherein at least one of the optical fibers or optical waveguides is provided. A directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the light traveling direction, wherein a long-period side of the chirped grating is inserted between the ports. It is characterized by.
[0059]
The invention according to claim 42 provides a first directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light; An input port connected to the input port, and a second directional coupler having an output port connected to the output port of the first directional coupler, wherein a long-period side of the chirped grating is a long-period side. It is characterized by being joined to the second directional coupler.
[0060]
The optical system for connecting the input port of the first directional coupler and the input port of the second directional coupler according to the present invention may include a laser medium. It is characterized by.
[0061]
According to a forty-fourth aspect, an optical system connecting the input port of the first directional coupler and the input port of the second directional coupler according to the forty-second aspect includes a non-linear optical medium. It is characterized by the following.
[0062]
The invention according to claim 45 is directed to a directional coupler in which the lengths of optical fibers or optical waveguides serving as two output ports are different from each other, a reflection device joined to the one output port, and a known length. A chirped grating whose effective refractive index is periodically changed in the traveling direction of the light, which is joined to the other output port via an optical fiber or an optical waveguide; and The temperature characteristic of the chirped grating is measured by inputting the signal to a reflector and identifying a reflection point.
[0063]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is to perform appropriate temperature compensation or temperature sensitization of an optical device based on new knowledge on a temperature change of a chirped grating.
[0064]
(Optical materials)
Materials used as a transparent optical system material include a quartz glass material, an optical glass material, a polymer material, and a semiconductor material. Optical characteristics such as a refractive index, a temperature coefficient, and a thermal expansion coefficient are different from each other, and materials having different characteristics in each category have been developed. Representative values are shown in Table 1.
[0065]
[Table 1]

[0066]
However, it shows a typical value of a typical optical system material, and does not indicate the applicable range of the present invention. From Table 1, it depends on the material type,^-5-10^-8The refractive index and the physical length change in the order of の, and as large as 0.5% for a temperature change of ± 30 ° C.
[0067]
As a method for producing a chirped grating in an optical fiber using quartz glass or a polymer material, a method using ultraviolet irradiation is generally used. The optical fiber having a composition whose refractive index is easily changed by ultraviolet light is irradiated with interference fringes or ultraviolet stripes formed through a mask, thereby forming stripes having a large refractive index on the core and / or cladding of the optical fiber. In the case of a waveguide using quartz glass, optical glass, a polymer material, or the like, a grating forming method by electron beam exposure and etching is used in addition to ultraviolet irradiation depending on the material characteristics and desired accuracy.
[0068]
In the case of a semiconductor optical device, the composition of the waveguide and the shape of the waveguide are changed by electron beam exposure and etching to produce a periodic effective refractive index change and a shape change. These manufacturing methods are closely related to the semiconductor manufacturing technology and the nanotechnology, and the manufacturing accuracy has been improved with the progress of the manufacturing technology.
[0069]
(Basic principle)
The basic principle of the present invention will be described. First, an intuitive description will be given of a characteristic change of a chirped grating (hereinafter, referred to as CG) with respect to a temperature change. The present invention is based on new knowledge regarding the behavior of CG with respect to a temperature change that has not been recognized so far.
[0070]
FIG. 1 shows a characteristic change of the chirped grating with respect to a temperature change. CG10 at a reference temperature is schematically shown. The division by a short vertical line indicates one period of the grating, and the period is sequentially increased by 10% with respect to the first period 12 at the left end. The CG of an actual optical fiber or an optical waveguide has a very small period change compared to FIG. 1, and the number of grating periods is much larger.
[0071]
Next, it is assumed that the CG 10 expands uniformly due to the temperature change and changes to the CG 20. In order to obtain uniform elongation by drawing, the CG 10 is extended in the vertical direction while rotating the last one period 13 at the right end with the first period 12 as the center. Thereby, a new CG 20 is obtained between the first cycle 22 and the last cycle 23 of the CG 20. The grating cycle after the temperature change in the CG 20 can be obtained in the same manner as when the last one cycle 23 is obtained. In FIG. 1, the CG 20 has grown by about 18%.
[0072]
Attention is focused on the grating period 14 in the CG 10. After the temperature change, a position having the same grating period as the grating period 14 is obtained in the CG 20, and the grating period 24 is obtained. When the distance between the first cycle 22 and the grating cycle 24 is moved to the CG 10, a grating cycle 15 is obtained. Here, the distance between the grating periods 14 to 15 corresponds to about 22% of the first one period 12 to the grating period 14, and "shrinkage" occurs which is larger than the rate of elongation due to temperature change.
[0073]
From this,
(1) The position of the grating period 14 moves to the position of the grating period 15 due to a temperature change. The contraction movement amount is generally larger than the CG expansion movement amount due to the temperature change.
(2) When viewed from the first cycle 12, the grating cycle 24 or the grating cycle 15 having the same cycle as the grating cycle 14 approaches the first cycle 12, although the entire CG has been extended by the temperature change.
(3) As viewed from the last cycle 13, the grating cycle 24 or the grating cycle 15 is farther from the last cycle 23 or the last cycle 13. The distance away is generally greater than the elongation due to temperature changes.
[0074]
Considering that the grating period 14 or the grating period 24 indicates the corresponding position where the same wavelength is reflected, temperature compensation or temperature sensitization of the optical fiber or the optical waveguide can be performed using this principle.
[0075]
FIG. 2 shows a characteristic change of a chirped grating in an optical fiber or an optical waveguide. FIG. 2A shows the reference temperature T.₀FIG. 2B is a graph showing the temperature T₀CG at + ΔT. In the following description, it is assumed that the CG is formed on or around an optical waveguide structure such as an optical fiber or an optical waveguide. However, if the influence of light spread due to light diffraction can be neglected, the following discussion is similarly established. For the sake of simplicity, it is assumed that the refractive index is a refractive index grating in which the magnitude of the refractive index is sequentially arranged in a stripe pattern, and the grating period is sequentially increased by a constant value a from the left end. Light enters from the left end, and similarly, reflected light exits from the left end. The effective refractive index of the optical fiber or the optical waveguide medium is n_effAnd
[0076]
Temperature T₀At the k-th local grating period d_kTo
d_k= D₁+ (K-1) a (Equation 1)
Then, the length from the first cycle 12 to the k-th cycle 16 is
x_k= Σ_{j = 1} ^kd_i= D₁k + ak (k-1) / 2 (Equation 2)
Period d_kIn the CG part centered on the stripe of
λ = 2n_effd_k(Equation 3)
Is reflected, and the distance from the first cycle 12 to the reflection point is x_kIs given by Note that the number n of all the cycles included in the total length L_TIs
L = d₁n_T+ An_T(N_T-1) / 2} (Equation 4)
Is obtained.
[0077]
Next, the temperature T₀At the temperature T₀At + ΔT, it is assumed to have extended to L [1 + αΔT]. This change includes temperature changes, both thermal expansion and refractive index change. The k ′ th cycle 16 is
d '_{k '}= [D₁+ (K′−1) a] (1 + αΔT) (Equation 5)
The length from the left end to the k ′ th cycle 16 is
x '_{k '}= Σ_{j = 1} ^{k '}d '_j(Equation 6)
= D₁(1 + αΔT) k ′ + a (1 + αΔT) k ′ (1-k ′) / 2
Temperature T₀At the width d of the k-th period 16_kAnd its position x_kAnd the temperature T₀At + ΔT, d_kA value d 'equal to_{k '}= D_kThe position x 'of the cycle having_{k '}Ask for. Next, the change x 'of the reflection point before and after the temperature change_{k '}-X_kAsk for. Here, the reflection point x ′ after the temperature change_{k '}Is the original reflection point x_kAttention is paid more to whether it is closer to or farther from the incident end than to the incident end.
[0078]
As mentioned above, both thermal expansion and refractive index temperature change are affected by temperature changes. Therefore,
Optical length L = (effective refractive index n_eff) × (Chief of geometry L_g) (Equation 7)
Need to deal with the changes. Here, the effective refractive index n_effIncludes both the refractive index of the optical material itself and the refractive index based on the waveguide structure. The temperature change of the optical length L is
L (T₀+ ΔT) = L (T₀) + (DL / dT) ΔT (Equation 8)
= L (T₀) + [N_eff(DL_g/ DT) + L_g(D_neff/ DT)
] ΔT
Coefficient α,
α = [n_eff(DL_g/ DT) + L_g(Dn_eff/ DT)] (Equation 9)
After all,
L (T₀+ ΔT) = L (T₀) [1 + αΔT] (Equation 10)
Becomes
[0079]
The refractive index based on the waveguide structure can be neglected because it is generally smaller than the refractive index of the material, and the description is simplified here. The precision can be further improved by performing a detailed design in consideration of the refractive index based on the waveguide structure which depends on the waveguide structure and the used wavelength.
[0080]
Further, in manufacturing and mounting an optical device, an optical system portion is manufactured on a substrate, covered with cladding, or mounted on a package to eliminate external influences. At this time, the material used for the substrate, cladding, package, and the like is often different from the optical system portion, and gives an internal strain to the optical system due to a temperature change during manufacturing or use. When a strain is applied to the optical material, the refractive index and its temperature change change through the strain optical effect, and it is necessary to capture the change. The temperature compensation and the temperature sensitization in the present embodiment are applied when the distortion applied to the optical system is considered to be uniform.
[0081]
As an example of the temperature change numerical value of CG, L = 5 mm, d₁= 490 nm, a = 0.00479 nm, n_eff= 1.5, αΔT = 1 × 10^-4Then, for a wavelength λ = 1550 nm,

When light is incident on a CG having a length L = 5 mm and a chirping amount a = 0.00479 nm from the side of the short-period grating, the light having a wavelength of 1550 nm is reflected around the k = 5566-th period at the reference temperature. Is done. Temperature change αΔT = 1 × 10^-4In the later reflection, the temperature change of the length is +280 nm, whereas the position change of the reflection center point is -5300 nm. In other words, it can be seen that the length is in the opposite direction to the temperature change and shifts greatly in the direction approaching the light incident end. This shift amount changes depending on the value of the chirp amount a, and in the above-described numerical example, reaches about 20 times the temperature change of the length.
[0082]
It has been shown that when light is incident from the short-period grating side, the reflection center point in the CG approaches the short-period side incident end due to thermal expansion. On the other hand, when light is incident from the long-period grating side of the CG, it can be seen that the reflection center point moves away from the long-period side incident end due to thermal expansion. That is, the temperature change of the optical length is emphasized, and a much larger reflection point shift occurs.
[0083]
By using the nature of the reflection point shift caused by the temperature change of the CG, the temperature change of the optical fiber or the optical waveguide can be compensated. FIG. 3A shows temperature compensation by a chirped grating. An optical system 31 such as an optical fiber or an optical waveguide is connected to the short period grating side of the CG 10, that is, to the first period 12. The optical system 31 may have an optical waveguide structure such as an optical fiber or an optical waveguide, or may not have an optical waveguide structure like a bulk optical system.
[0084]
Here, using CG10, length L₀Compensation for the temperature change of the optical system 31 is considered. For simplicity, it is assumed that the CG and the optical system to be compensated are made of the same material, and the thermal expansion coefficient and the refractive index temperature change rate are equal. L at reference temperature₀And x_kIs the sum of L after temperature change₀(1 + αΔT) and x ′_{k '}Is equal to the sum of
L₀= (X_k-X '_{k '}) / ΑΔT (Equation 12)
Can be compensated for the temperature change of the optical system.
[0085]
Here, it is assumed that the CG 11 and the optical system 31 to be controlled are the same material having the same refractive index, thermal expansion coefficient, and refractive index temperature change. In the temperature compensation technology of an optical device, it is not always obvious that the controlled object and the control means are made of the same material, but rather temperature compensation is generally performed by combining different materials having different characteristics. It is. According to the present embodiment, temperature compensation or temperature sensitization can be performed using the same material without selecting a special combination of materials. Of course, it can be easily extended to a combination of different materials having different characteristics.
[0086]
A numerical example of temperature compensation is shown. For the above numerical example, the optical length L for which temperature compensation can be performed₀Is L from the equation (12).₀= 52.9 mm. That is, the temperature change of the optical system having a length of about 50 mm can be compensated for by the CG having a length of 5 mm. The numerical examples described above cover a wide wavelength band from 1470 nm to 1610 nm, and are not necessarily optimized for a specific wavelength band. If the compensation is limited to only the 1550 nm wavelength band, the required wavelength band of the CG is about 1/10, and the required length is about 0.5 mm.
[0087]
Assuming a CG covering the wavelength band of 1470 nm to 1610 nm, the chirping amount a, the change in the position of the central reflection point, and the length L of the compensation target optical system are determined by the grating length L.₀It is useful to know how changes occur. At a wavelength of 1550 nm, a temperature change αΔT = 10^-4Table 2 shows numerical values obtained from the condition of compensating.
[0088]
[Table 2]

[0089]
In this example, considering that the center reflection point at the wavelength of 1550 nm is almost at the center of the chirped grating, the length L₀The CG length L / 2 required for compensating the optical system is approximately L₀/ 20.
[0090]
FIG. 3B shows temperature sensitization by a chirped grating. An optical system 31 such as an optical fiber or an optical waveguide is connected to the long-period grating side of the CG 10, that is, the last period 13. According to this configuration, the temperature change of the optical system 31 can be sensitized. At this time, it should be pointed out that since the temperature change in the CG 10 is large, a large temperature change can be obtained without an optical fiber or an optical waveguide to be connected.
[0091]
Consider a case where light of a plurality of wavelengths is incident on the CG 10 shown in FIG. Eight channel wavelengths shown in Table 3 are defined as incident wavelengths.
[0092]
[Table 3]

[0093]
Note that the optical wavelength arrangement shown in Table 3 assumes CWDM (coarse / wavelength / division / multiplexing) having a relatively large frequency interval, and does not indicate the performance limit of the present invention. In fact, the present invention can also be applied to DWDM (dense / wavelength / division / multiplexing) in which the optical wavelength interval is narrower and the number of optical channels is even greater.
[0094]
The shortest cycle of CG₁, The longest period Λ₈And the wavelength λ₅When the temperature is compensated for, a compensation error at another wavelength is obtained. As described above, in Table 2, the optical length L that can be compensated at a wavelength of 1550 nm is shown.₀(Λ = 1550 nm) was obtained. The wavelength at this time is λ in Table 3.₅Is equivalent to Similarly, for other wavelengths λ₁~ Λ₄, Λ₆~ Λ₈Optical length L that can be compensated for₀(Λ = λ₁), L₀(Λ = λ₂), ...₀(Λ = λ₅) Are shown in Table 4.
[0095]
[Table 4]

[0096]
According to these results, when L = 2.5 mm, a compensation error of 1% or less is obtained in a wavelength range of ± 15 nm, and a compensation error of 5% or less is obtained in a range of ± 70 nm in a wavelength range of 1470 to 1610 nm. It can be seen that it can be obtained. However, it shows that strict temperature compensation cannot be performed at two or more wavelengths using one CG.
[0097]
In an optical device that handles light of a plurality of wavelengths at the same time, such as wavelength division multiplexed optical fiber communication, an optical device having the same high accuracy for all wavelengths is desired. FIG. 4A shows CGs for eight wavelengths for performing temperature compensation on one wavelength. The CGs of the respective wavelengths are arranged so as to be shifted so as not to overlap with each other, and at each wavelength, a temperature change of an optical fiber or an optical waveguide connected to the CGs is compensated. FIG. 4B shows a case where temperature compensation is performed. As shown in FIG. 4B, eight temperature-compensated optical fibers or optical waveguides can be superposed and integrated.
[0098]
Looking at the integrated grating as a whole, the wavelength λ of each channel_iPeriod corresponding to Λ_iAnd the chirp amount a required for accurate temperature compensation_iAre connected in cascade in the optical axis direction. This composite device is called a cascaded chirped grating (hereinafter referred to as CCG: Concatenated chirped grating). However, when designing the CG of each channel, it is necessary to redesign the optical fiber or optical waveguide to be controlled by the amount of shifting the CG of each channel for integration.
[0099]
Wavelength λ₅A required for realizing temperature compensation at other wavelengths for an optical system temperature compensated for = 1550 nm and CCG_iAre shown in Table 5.
[0100]
[Table 5]

[0101]
According to this result, the chirp amount a for each channel in the CCG_iBy optimally selecting αΔT = 10^-4, The reflection position shift amounts of all the channels can be made equal, and the temperature compensation can be simultaneously realized in all the wavelength channels.
[0102]
In the configuration of the CCG shown in FIG. 4B, along the optical axis of the optical fiber or the optical waveguide, the increasing direction of the central wavelength of the optical channel coincides with the increasing direction of the grating period in each channel. FIG. 5 shows the relationship between the position measured from the short cycle side and the grating cycle in a single CG. Chirping changes linearly with respect to the position measured from the short cycle side. FIG. 6 shows the relationship between the position of the short period side in the CCG and the grating period. FIG. 6A is a CCG in which temperature compensation is optimized for individual channels. FIG. 6B shows CCGs arranged so that the increasing direction of the center wavelength of the optical channel and the increasing direction of the grating period in each channel are opposite to each other along the optical axis of the optical fiber or the optical waveguide. .
[0103]
FIG. 4C shows a case where the temperature sensitization is performed. The eight temperature-sensitized optical fibers or optical waveguides can be superimposed and integrated as shown in FIG. It is clear from the above detailed description of the temperature compensation by the CCG. At this time, since the temperature change in the CCG is large, it is pointed out that a large temperature change can be obtained without the optical system 31 such as an optical fiber or an optical waveguide to be connected.
[0104]
(Optical directional coupler with built-in chirp grating)
2. Description of the Related Art Optical fibers or optical waveguide directional couplers that distribute or transfer optical power using optical wave coupling between optical fiber cores or waveguide cores arranged in parallel are known. For example, Yeh and H. F. Taylor, {"Contradirectional-frequency-selective-couplers-for-guided-wave-optics", "Applied-Optics," vol. 7, @p. 2848 and 1980 describe a directional coupler incorporating a Bragg grating. In the core and / or adjacent cladding of the directional coupler, a grating structure is created in which the refractive index, gain or loss changes periodically. An optical device that controls the coupling of light waves in this manner is called a directional coupler with a built-in grating. In the present embodiment, an optical directional coupler with a built-in chirped grating (hereinafter, referred to as a CGDC: Chirped grating coupled coupled director) is one that further employs CG. FIG. 7 shows the configuration of an optical directional coupler with a built-in chirped grating.
[0105]
FIG. 7A shows a case where temperature compensation is performed. The light incident from the input port 64 of the CGDC has a certain wavelength component corresponding to the coupling portion grating 61 selectively reflected, is coupled to the other waveguide, and is output from the output port 65. The CG of the coupling portion grating 61 has a temperature compensation function as described above. The CGDC is designed in consideration of the length of the optical fiber or the waveguide serving as the input port 64 and the output port 65.
[0106]
Here, the temperature compensation by CG or CCG was of the “reflection type”, and the optical input port and the optical output port to the waveguide to be temperature compensated were the same. On the other hand, the temperature compensation by the CGDC can be of a “transmission type” configuration because the optical input port and the optical output port are different. This gives a great degree of freedom in the configuration and design of the optical device, and greatly improves the application area and effectiveness of the present invention.
[0107]
FIG. 7B shows a case where temperature sensitization is performed. The long period side of the coupling portion grating 61 is connected to an optical fiber or a waveguide serving as the input port 64 and the output port 65. At this time, it should be pointed out that since the reflection point shift due to the temperature in the CGDC is large, a large temperature change can be obtained without the optical system 31 such as an optical fiber or an optical waveguide to be connected.
[0108]
(Temperature stabilized Fabry-Perot interferometer)
The CG for temperature compensation shown in FIGS. 3A, 4B and 7A is called a temperature compensation module. Conventionally, in a Fabry-Perot interferometer, light resonates between a pair of opposing reflecting mirrors. In order to operate this reflection stably, it is necessary to keep the interval between the reflecting mirrors constant. A temperature compensation module is useful for this purpose. There are combinations shown in Table 6 as opposing reflection devices. Here, ○ indicates a desirable combination as a stabilized Fabry-Perot interferometer, X indicates a combination that cannot be stabilized, and − indicates a combination that requires a complicated configuration.
[0109]
[Table 6]

[0110]
FIG. 8 shows the configuration of a temperature stabilized Fabry-Perot interferometer using CG. 8A shows a combination of the CG 71 and the CG 72, FIG. 8B shows a combination of the CG 71 and the reflecting mirror 81, and FIG. 8C shows a combination of the CG 71 and the Bragg grating (G) 82. Also, a combination of CCG and CCG, a combination of CCG and reflector, and a combination of CCG and G are effective. Since the CGDC has the property of “transmission type” between two ports, it is difficult to configure a Fabry-Perot interferometer.
[0111]
FIG. 9 shows the configuration of a Fabry-Perot interferometer type temperature stabilized narrow band filter. Light from a light source 92 having a wide spectrum is input to a temperature-stabilized Fabry-Perot interferometer 91 via an optical isolator 93 that blocks reflected light from the next-stage optical system. A light receiver 94 is connected to the temperature stabilized Fabry-Perot interferometer 91. The temperature-stabilized narrowband filter can extract a desired narrowband spectrum 96 from the broadband optical spectrum 95. Such a narrow band filter has many application ranges in optical fiber communication, such as noise removal, signal spectrum control, extraction of a specific channel from a wavelength multiplexed signal, and identification of a spectral spectrum.
[0112]
FIG. 10 shows a multi-wavelength stabilized light source based on a Fabry-Perot interferometer type wavelength reference. FIG. 10A is a configuration diagram. The temperature stabilized Fabry-Perot interferometer 101 based on a combination of CG and CG is connected to a detector 107 and detects a wavelength error signal. The control unit 108 performs feedback control of the light sources 102 to 105 based on the wavelength error signal. A multiplexer 106 and an optical isolator 93 are connected between the light sources 102 to 105 and the temperature stabilized Fabry-Perot interferometer 101.
[0113]
FIG. 10B shows a transmission wavelength 109 of a periodic spectrum in the temperature-stabilized Fabry-Perot interferometer 101 according to a change in the number of half wavelengths that resonate between a pair of reflecting devices. Feedback control is performed using the periodic transmission peak wavelength in the temperature stabilized Fabry-Perot interferometer 101. A reference for stabilizing the wavelength 110 in FIG. 10B can be provided. In the present embodiment, a wavelength reference for four wavelengths is shown, but the number of wavelengths is not limited to this.
[0114]
In the temperature-stabilized Fabry-Perot interferometer shown in FIG. 8, when the optical system 31 such as an optical fiber or an optical waveguide to be subjected to temperature compensation is used as a laser medium or a part of the optical system 31 includes a laser medium. Can obtain laser oscillation giving a stable wavelength with respect to temperature change. Using not only the combination with the CG shown in FIG. 8 but also the combination with the CCG shown in Table 6, a multi-wavelength laser oscillation giving a stable wavelength can be obtained.
[0115]
In the temperature-stabilized Fabry-Perot interferometer shown in FIG. 8, an optical system 31 such as an optical fiber or an optical waveguide to be subjected to temperature compensation is used as a nonlinear optical medium, or a part of the optical system 31 includes a nonlinear optical medium. In this case, a nonlinear optical device that gives a stable wavelength with respect to a temperature change can be obtained. Using not only the combination with the CG shown in FIG. 8 but also the combination with the CCG shown in Table 6, a multi-wavelength nonlinear optical device giving a stable wavelength can be obtained.
[0116]
Nonlinear optical medium effects include wavelength generation by optical harmonic generation, optical difference frequency generation, optical mixing, degenerate four-wave mixing, optical parametric mixing, stimulated Raman scattering, stimulated Brillouin scattering, stimulated Rayleigh scattering, optical soliton generation, and optical amplification. , Waveform shaping, etc. can be used.
[0117]
(Temperature stabilized Michelson interferometer)
FIG. 11 shows a configuration of a Michelson interferometer using CG. FIG. 11A shows a configuration of a temperature stabilized Michelson interferometer. In order to compensate for the temperature change of each of the optical fibers or optical waveguides serving as the two output ports 132 and 133 of the directional coupler 131, the temperature is stabilized using a temperature compensation module.
[0118]
FIG. 11B shows a configuration of the differential stabilized Michelson interferometer. The temperature change caused by the difference 138 in the length of the optical fiber or the optical waveguide serving as the two output ports 132 and 133 of the directional coupler 131 is compensated. The temperature compensation module is joined to the longer output port 132, and the reflector 81 is joined to the shorter output port 133. A Michelson interferometer operating at one wavelength or multiple wavelengths can be stabilized. The stabilization can also be achieved by joining the reflecting mirror 81 to the longer output port 132 and joining the temperature sensitizing module to the shorter output port 133.
[0119]
FIG. 12 shows a Michelson interferometer type temperature stabilized PM-AM converter. FIG. 12A is a configuration diagram. The temperature-stabilized PM-AM converter is a phase-modulated optical fiber or optical waveguide serving as the two input ports 134 and 135 of the directional coupler 131 of the temperature-stabilized Michelson interferometer shown in FIG. The light source 141 and the amplitude modulation light receiver 142 are connected. The temperature-stabilized PM-AM converter converts phase-modulated light into amplitude-modulated light without being affected by temperature fluctuations. FIG. 12B shows the amplitude-phase characteristics of the temperature-stabilized PM-AM converter.
[0120]
FIG. 13 shows a multi-wavelength stabilized light source based on a Michelson interferometer type wavelength reference. FIG. 13A is a configuration diagram. The multi-wavelength stabilized light source is a multi-wavelength multiplexed light source on an optical fiber or an optical waveguide serving as two input ports 134 and 135 of the directional coupler 131 of the temperature stabilized Michelson interferometer shown in FIG. 151 and the multi-wavelength wavelength error detector 152 are connected. The control circuit 153 performs feedback control of the multi-wavelength multiplexed light source 151 based on the wavelength error detected by the multi-wavelength wavelength error detector 152. In this way, a stable frequency reference is provided without being affected by temperature fluctuations. FIG. 13B shows the wavelength transmission characteristics of the multi-wavelength stabilized light source. The transmission wavelength 155 of the periodic spectrum is stabilized at the wavelength 154.
[0121]
FIG. 14 shows a distortion sensor of the Michelson interferometer type. FIG. 14A is a configuration diagram. The strain sensor includes a light source 162 and a light receiver 163 on an optical fiber or an optical waveguide serving as the two input ports 134 and 135 of the directional coupler 131 of the temperature stabilized Michelson interferometer shown in FIG. Connected. The optical fiber or the optical waveguide serving as the output port 132 has a distortion detection unit 161. In this way, the distortion is detected without being affected by the temperature fluctuation. FIG. 14B shows distortion versus transmission amplitude characteristics.
[0122]
(AWG)
An optical multiplexer / demultiplexer that multiplexes / demultiplexes light of a plurality of wavelengths is widely used as an optical device for ultra-large-capacity wavelength multiplexing optical fiber communication. As a typical optical multiplexer / demultiplexer, an array waveguide grating (hereinafter, referred to as AWG: Array Waveguide Grating) is known (for example, M. Smit, "New Focusing and Dispersive Planar Component on Electronic Components"). 24, pp. 385-386, March 1988, and M. Smit, C. Vandarn, "PHASAR-based WDM-devices, principles, design and application of electronic equipment, IEEE Electronics. ron, Vol.2, No.2, pp.236-250, detailed in June 1996.). AWG using a quartz waveguide or the like enables multiplexing / demultiplexing over several hundred channels and realizes a large-capacity system up to Tbit / s.
[0123]
FIG. 15 shows the configuration of the AWG. Light of a plurality of channels enters the star coupler 171 from the input port 173 and is distributed to the array waveguide 175. The light of the plurality of channels has a phase difference due to the difference in length provided between the plurality of arrayed waveguides, and is split by the star coupler 172 for each wavelength. The light of a plurality of channels is output to a different optical fiber 174 for each channel and split. By taking the opposite optical path, a plurality of channels are multiplexed.
[0124]
AWGs are mainly manufactured using quartz waveguides, but have a large device area and are difficult to reduce cost. Further, since fine phase adjustment is required, high-precision temperature stabilization is required. High interest has been shown in temperature stabilization of AWGs. Kokubunn, {M. Takezawa {and} S. Taga, "Three-dimensions, thermal, waveguides, for, temperature, independent, lightwave, devices", Electron. {Lett. , @Vol. 30, @pp. 1223-1225, # 1994, describe mounting a polymeric material having a negative temperature coefficient as the upper cladding of a quartz waveguide. In this method, the temperature range that can be stabilized is narrow, and the device performance is degraded by the applied stress.
[0125]
In addition, Y. Inoue, @A. Kaneto, @F. Hanawa, H. Takahashi, @K. Hattori and S. Sumida, {"Thermal \ silica \ based \ arrayed-waveguide \ grading \ multiplexer", \ Electron. {Lett. , @Vol. 33, @pp. 1945-1947, 1997 uses a polymer material in which grooves of a triangular cross section of an arrayed waveguide portion are filled, and can reduce the temperature change of wavelength to about 1/20 over a wide temperature range of 0 to 85 ° C. Has been described. This method greatly increases light loss due to the special waveguide structure.
[0126]
Further, A.I. Kaneto, S. Kamei, @Y. Inoue, @H. Takahashi and A. Sugita, {"Thermal-silica-based {arranged-waveguide | grating} (AWG)"} Multiplexers @ with @ new | lowloss @ groove-design, "OFC'99, @ paper-gau", "OFC'99, @ paper-gau", and "Op'-Gu" on the cross section. It is described that the temperature characteristic is improved to about 1/50 while maintaining low loss.
[0127]
Furthermore, K. Maru, @M. Ohkawa, H. Nounen, S. Takagi, {S. Kashimura, @H. Okano and H. Uetsuka, "" Thermal and center, "wavelength", "adjustable," arrayed-waveguide, "grading", "OFC'2000," paper, "WH3," "2000," "San, Jose," and "CA" are used to fill the polymer with several days and three months in the input star coupler. By doing so, it describes that it has a high stability of -0.0013 nm / ° C. However, in each of the four examples described above, additional phase errors and polarization dependence are caused, and the loss is further increased due to the correction.
[0128]
H. H. Yao, @C. Zawadzki, {N. Keil, @M. Bauer, C. Dreyer @ and @ J. Schneider “Atomic all-polymer arrayed waveguide grading multiplexer”, OFC'2002 invited paper TuC, March 17-22, Anaheim, California It describes that the temperature dependence of a polymer waveguide is compensated.
[0129]
Also, G. W. Yoffe, @P. A. Krug, @F. Quellette and and D. Torncraft, "Temperature-Compensated Optical Fiber Bragg Gratings," OFC 95, Paper WI4, 1995, San Diego, CA, and Y. Torncraft. Hibino, @M. Abe, @T. Tanaka, {A. Himeno, @A. Sugita, @J. Albert, D. C. Johnson @ and @ K. O. Hill, ”Temperature-insensitive UV-inducedｉｎBragg grading in silica-based PLCs on Si”, ECOC'99, paper PD1-5, 1999, Nice, France, as indicated by the coefficient of thermal expansion as shown in the ceramics And AWGs that form a quartz glass waveguide on a synthetic bimetal / silicon substrate are known. These AWGs have the disadvantage of poor linearity and complicating the fabrication process.
[0130]
A method of maintaining a temperature characteristic by making a change to an input star coupler is described in G. Heise, H. W. Schneider @ and @ P. C. Clemens, "Optical phased array filter, module with, passive, compensated, temperature, dependence," ECOC'98, @pp. 319-320, @ 1998, @Madrid, @Spain. In this method, the position of the input fiber is moved in accordance with a change in temperature, so that the manufacturing process becomes complicated and there remains a problem in long-term stability.
[0131]
The multiplexer / demultiplexer to which the chirped grating according to the present invention is applied is referred to as a reflection type array waveguide Echelon (hereinafter, referred to as AWE: Array \ Wageguide \ Echelon). FIG. 16 shows the configuration of the AWE. The light of a plurality of channels incident on the star coupler 176 from the input port 177 is distributed to array waveguides 179 having different lengths. The multi-channel light returns to the original star coupler 176 after being reflected at the end face of the array waveguide. The light of a plurality of channels is separated for each channel by the phase difference generated in the arrayed waveguides having different lengths, outputted from different output ports 178, and demultiplexed. By taking the opposite optical path, a plurality of channels are multiplexed.
[0132]
AWE is equivalent to a broken line of AWG indicated by a broken line a shown in FIG. AWE is equivalent to a spectroscopic device known as Echelon in the field of spectroscopy that is formed into a waveguide, reflected at the end face of the waveguide, and folded. According to the present embodiment, the element itself can be reduced in size, and temperature compensation can be performed for a plurality of wavelengths.
[0133]
The AWE temperature stabilization mechanism connects a CG or CCG to each of the arrayed waveguides 179, and compensates for temperature changes in the respective waveguide lengths for all channel wavelengths. Thus, even if a temperature change occurs, the phase difference between adjacent waveguides in the arrayed waveguide 179 can be kept constant, and a multiplexer / demultiplexer whose multiplexing / demultiplexing performance does not change depending on temperature can be provided. . As described above, when CG is used for a multi-wavelength channel, a compensation error occurs. However, in a system with a small number of channels and a narrow channel interval where some error can be tolerated, CG compensation can also be used.
[0134]
(Temperature stabilized Mach-Zehnder interferometer)
FIG. 17 shows a configuration of a Mach-Zehnder interferometer using CGDC. FIG. 17A shows a temperature-stabilized Mach-Zehnder. By using the CGDC shown in FIG. 7A for both or one of two optical fibers or optical waveguides connecting between the ports of the two directional couplers 131, a Mach that is stable against temperature fluctuations -A Zehnder interferometer can be configured. FIG. 17B shows a differential stabilized Mach-Zehnder interferometer. By using CGDC for the difference between the lengths of two optical fibers or optical waveguides constituting the interferometer, the temperature can be stabilized.
[0135]
FIG. 18 shows a Mach-Zehnder interferometer type temperature stabilized PM-AM converter. FIG. 18A is a configuration diagram. The temperature-stabilized PM-AM converter is connected to an optical fiber or an optical waveguide serving as input ports 134 and 135 of the directional couplers 131a and 131b of the temperature-stabilized Mach-Zehnder interferometer shown in FIG. , The phase modulation light source 141 and the amplitude modulation light receiver 142 are connected. The temperature-stabilized PM-AM converter converts phase-modulated light into amplitude-modulated light without being affected by temperature fluctuations. FIG. 18B shows the amplitude / phase characteristics of the temperature stabilized PM-AM converter.
[0136]
FIG. 19 shows a multi-wavelength stabilized light source based on a Mach-Zehnder interferometer type wavelength reference. FIG. 19A is a configuration diagram. The multi-wavelength stabilized light source is connected to an optical fiber or an optical waveguide serving as input ports 134 and 135 of the directional couplers 131a and 131b of the temperature-stabilized Mach-Zehnder interferometer shown in FIG. The multiplexed light source 151 and the multi-wavelength wavelength error detector 152 are connected. The control circuit 153 performs feedback control of the multi-wavelength multiplexed light source 151 based on the wavelength error detected by the multi-wavelength wavelength error detector 152. In this way, a stable frequency reference is provided without being affected by temperature fluctuations. FIG. 19B shows the wavelength transmission characteristics of the multi-wavelength stabilized light source. The transmission wavelength 154 of the periodic spectrum is stabilized at the wavelength 155.
[0137]
(Temperature stabilized ring resonator)
FIG. 20 shows a configuration of a temperature stabilizing ring circuit using CGDC. The two output ports of the CGDC shown in FIG. 7A are connected in a ring shape by an optical fiber or an optical waveguide 211 via a directional coupler 212. Here, the directional coupler 212 connects one of the input ports and one of the output ports to the optical fiber or the optical waveguide 211. The other of the input ports and the other of the output ports are used for input and output to and from the ring circuit. With such a configuration, the CGDC 121 compensates for a temperature change occurring in the ring.
[0138]
FIG. 21 shows the configuration of a temperature stabilized ring laser using CGDC. In the above-mentioned temperature stabilizing ring circuit, the ring-shaped optical fiber or the optical waveguide 211 is used as the laser medium 111, or the laser medium 111 is included in a part thereof. A directional coupler 212 is connected to supply optical energy for exciting the laser medium 111 and to extract laser output. According to the temperature stabilized ring laser shown in FIG. 21A, a stable laser beam can be obtained.
[0139]
When obtaining an oscillating light traveling in only one direction in the ring-shaped optical fiber or the optical waveguide 211, an isolator 221 is arranged as shown in FIG. Furthermore, by using a nonlinear optical medium instead of the laser medium 111 shown in FIG. 21A or 21B, a stable nonlinear optical device can be obtained. Nonlinear optical medium effects include optical harmonic generation, optical difference frequency generation, optical mixing, degenerate four-wave mixing, optical parametric mixing, stimulated Raman scattering, stimulated Brillouin scattering, stimulated Rayleigh scattering, wavelength conversion by optical soliton generation, and optical amplification. , Waveform shaping can be used.
[0140]
According to the present embodiment, the temperature compensation module compensates for the change in the effective length or the change in the refractive index of the optical fiber or the optical waveguide, so that 1) the transmission / reflection spectrum of the passive or active optical filter is converted to the temperature. 2) keeping the oscillation wavelength of the laser constant, 3) keeping the operating wavelength of the nonlinear optical device constant, and combining / demultiplexing the multi-channel light in the wavelength division multiplexing / demultiplexing device. It is possible to keep the wave characteristics constant, and 4) to eliminate the influence of temperature change from the optical fiber / optical waveguide strain sensor.
[0141]
(Temperature sensitized Fabry-Perot interferometer)
The CG for temperature sensitization shown in FIGS. 3B, 4C and 7B is called a temperature sensitization module. In the Fabry-Perot interferometer, the wavelength of the transmitted narrowband light can be changed by changing the optical length between the reflecting mirrors. A temperature sensitizing module is useful for this purpose. The combinations shown in Table 6 can be applied as the opposing reflection devices. The method of the combination is the same as that of the temperature stabilized Fabry-Perot interferometer shown in FIG. 8, and the configuration is the same except that the direction of the CG 71 connected to the optical system 31 is different. FIGS. 22A to 22C show the configuration of a temperature-sensitized Fabry-Perot interferometer using CG. As in FIG. 8, the temperature-sensitized Fabry-Perot interferometer can be configured using not only the combination with CG but also the combination with CCG shown in Table 6.
[0142]
As can be seen from the numerical example of the temperature change in the CG as shown with reference to Expression 11, the reflection point inside the CG is greatly shifted by the temperature change. Therefore, when realizing a compact optical device even if the sensitivity is slightly sacrificed, the optical fiber or the optical waveguide to be sensitized can be removed, and the optical device sensitive to the temperature change can be constituted only by CG. FIGS. 22D to 22F show the configuration. The same applies to a temperature-sensitized Fabry-Perot interferometer configured using a combination with CCG.
[0143]
FIG. 23 is a diagram showing a configuration of a Fabry-Perot interferometer type tunable filter. Light from a light source 92 having a wide spectrum is input to a temperature-sensitized Fabry-Perot interferometer 161 via an optical isolator 93 that blocks reflected light from the next-stage optical system. The light receiver 262 is connected to the temperature-sensitized Fabry-Perot interferometer 161. By sweeping the temperature of the temperature sensitized Fabry-Perot interferometer 161, a wavelength sweep spectrum 263 can be created from the broadband spectrum 95.
[0144]
In the above-mentioned temperature-sensitized Fabry-Perot interferometer, when the optical system such as an optical fiber or an optical waveguide to be controlled is used as a laser medium, or when a part of the optical system includes a laser medium, the wavelength changes depending on the temperature. Wavelength tunable laser can be configured. As in the case of the temperature-stabilized Fabry-Perot interferometer, a tunable laser can be formed using not only the combination with the CG shown in FIG. 8 but also the combination with the CCG shown in Table 6.
[0145]
In the above-described temperature-sensitized Fabry-Perot interferometer, when an optical system such as an optical fiber or an optical waveguide to be controlled is a nonlinear optical medium, or when a part of the optical system includes a nonlinear optical medium, the wavelength depends on the temperature. Can be constructed. Nonlinear optical medium effects include wavelength generation by optical harmonic generation, optical difference frequency generation, optical mixing, degenerate four-wave mixing, optical parametric mixing, stimulated Raman scattering, stimulated Brillouin scattering, stimulated Rayleigh scattering, optical soliton generation, and optical amplification. , Waveform shaping, etc. can be used.
[0146]
FIG. 24 shows a configuration of a Fabry-Perot interferometer type temperature sensor. The optical system 31 which is an optical fiber or an optical waveguide to be controlled is desirably made of a material whose effective optical length changes greatly with temperature. As described above, when miniaturization is desired at the expense of some sensitivity, the optical system 31 can be removed and the configuration shown in FIG. 22B can be adopted.
[0147]
FIG. 25 shows a Fabry-Perot interferometer type temperature detecting circuit. FIG. 25A is a configuration diagram. The temperature detection circuit makes the light from the light source 162 enter the temperature sensor 291 via the isolator 93 for blocking the reflected light. The output of the temperature sensor 291 is input to the light receiver 163. As shown in FIG. 25B, since the temperature sensor 291 has a very narrow band, it can detect a temperature change from the amount of received light with high sensitivity.
[0148]
(Temperature-sensitized Michelson interferometer)
In the temperature-stabilized Michelson interferometer shown in FIG. 11A, a temperature-sensitized Michelson interferometer can be obtained by replacing the temperature compensation module CG10 with a temperature-sensitized module. Focusing on the fact that the output of the Michelson interferometer depends on the phase difference between the two optical paths, it is possible to realize a more sensitive temperature sensor.
[0149]
FIG. 26 shows the configuration of a push-pull temperature-sensitized Michelson interferometer. For the two optical paths of the Michelson interferometer, the temperature sensitizing module is connected to the long optical path 301, and the temperature compensation module is connected to the short optical path 302 (FIG. 26A). The temperature compensating module is preferably connected to the short optical path 302 because it is desirable that the temperature compensating module changes more than compensating for the length of the port. The reflection point shift due to the temperature can be converted into a phase change by the push-pull method, and the sensitivity can be increased. Incidentally, the lengths of the ports may be equal, or all the lengths may be 0 (FIG. 26B).
[0150]
Also, in the differential stabilized Michelson interferometer shown in FIG. 11B, a differentially sensitized Michelson interferometer can be obtained by replacing the temperature compensation module CG10 with a temperature sensitizing module. That is, the temperature sensitizing module is joined to the longer output port, and the reflector is joined to the shorter output port. Also, a differential sensitized Michelson interferometer can be configured by joining a reflecting mirror to the longer output port and joining a temperature compensation module to the shorter output port. Further, when miniaturization is desired at the expense of some sensitivity, the length of the port may be set to 0 as in FIG.
[0151]
FIG. 27 shows a Michelson interferometer-type temperature sensor. FIG. 27A is a configuration diagram. The optical system 31 which is an optical fiber or an optical waveguide to be controlled is desirably made of a material whose effective optical length changes greatly with temperature. As described above, the optical paths 281 and 282 can be eliminated when miniaturization is desired at the expense of some sensitivity.
[0152]
Light from the light source 162 enters the push-pull temperature-sensitized Michelson interferometer, and its output is input to the light receiver 163. As shown in FIG. 27B, the temperature sensor can detect a change in temperature from the amount of received light with high sensitivity.
[0153]
(Temperature-sensitized Mach-Zehnder interferometer)
In the temperature-stabilized Mach-Zehnder interferometer shown in FIG. 17, by using the CGDC which is the temperature sensitizing module shown in FIG. Can be configured. Further, by inserting a temperature sensitizing module in a long optical path and inserting a temperature compensating module in a short optical path, a push-pull type configuration can be obtained.
[0154]
FIG. 28 is a diagram showing a Mach-Zehnder interferometer type temperature sensor. FIG. 28A is a configuration diagram. A light source 162 and a photodetector 163 are connected to optical fibers or optical waveguides serving as input ports 134 and 135 of the directional couplers 131a and 131b of the temperature-sensitized Mach-Zehnder interferometer described above. As shown in FIG. 28B, the temperature sensor can detect a change in temperature from the amount of received light with high sensitivity.
[0155]
(Temperature sensitizing ring resonator)
In the temperature stabilizing ring circuit shown in FIG. 20, the CGDC 121 is a temperature sensitizing module. The temperature change occurring in this ring is sensitized by CGDC. In the temperature-stabilized ring laser shown in FIG. 21, by using the CGDC 121 as a temperature sensitizing module, a wavelength tunable laser can be formed by temperature. Further, by using a non-linear optical medium instead of the laser medium, a non-linear optical device whose wavelength changes with high sensitivity can be obtained. Nonlinear optical medium effects include optical harmonic generation, optical difference frequency generation, optical mixing, degenerate four-wave mixing, optical parametric mixing, stimulated Raman scattering, stimulated Brillouin scattering, stimulated Rayleigh scattering, wavelength conversion by optical soliton generation, and optical amplification. , Waveform shaping can be used.
[0156]
According to the present embodiment, the temperature sensitizing module sensitizes the change of the effective length or the change of the refractive index of the optical fiber or the optical waveguide, thereby 1) the temperature of the transmission / reflection spectrum of the passive or active optical filter. Alternatively, it is possible to increase the variable sweep range by enlarging the change with respect to the driving power, 2) expand the variable wavelength range of laser oscillation or the sweep wavelength range, and 3) expand the wavelength variable range of the nonlinear optical device. .
[0157]
Further, according to the present embodiment, by using CCG, it is possible to simultaneously perform temperature compensation or temperature sensitization on a plurality of wavelengths.
[0158]
(Method of measuring CG and CCG)
In designing a CG, an analytical method is difficult, and in many cases, it is necessary to rely on a numerical solution as a real problem. Depending on the optical device, a complicated fabrication process is required, and it is necessary to actually measure and confirm whether a CG as designed is configured. For this purpose, CG or CCG manufactured by the same material, structure and manufacturing process as the manufactured optical device is measured and confirmed.
[0159]
The reflection wavelength range, reflectance, and the like of CG or CCG are obtained by inputting light of a variable wavelength and measuring the intensity of the reflected light. In the present embodiment, it is important how the center point of the wavelength region of the reflected light changes with temperature. Although it is difficult to identify the reflection point in a CG whose length in the optical axis direction is much larger than the wavelength, by configuring the differential stabilized Michelson interferometer shown in FIG. The center point can be determined.
[0160]
FIG. 29A shows a Michelson interferometer type temperature dependency measuring circuit. In a Michelson interferometer, a reflector is connected to one arm, and CG or CCG is connected to the other arm. Assuming that the temperatures of all the measurement systems are uniform, the object to be compensated by the CG or the CCG is the length of the other arm 371, and this length is known. At this time, as shown in FIG. 29B, the movement of the reflection point of the CG or the CCG can be known from the output of the Michelson interferometer with respect to the input light having a constant wavelength when the temperature changes.
[0161]
(Thermo-optic effect switch module)
A conventional optical switch using the thermo-optic effect of an optical waveguide is described in, for example, A.I. Sugita, @K. Jinguji, @N. Takato, @K. Katoh and M. Kawachi, {"Bridge-suspended \ silica-waveguide \ thermo-optic \ phase \ shifter \ and \ its \ applications \ to \ Mach-Zehnder \ typical \ switch". IEICE, vol. E73, @no. 1, @ pp. 105-109, {1990}. Here, if the above-described property of the reflection point shift due to the temperature change of the CG is used, it is possible to realize a thermo-optic effect switch capable of switching with a small temperature change, that is, with small power.
[0162]
In the temperature compensation module, a heater that locally performs electric heating is installed at a distance close to CG, CCG, or CGDC, and at a distance that does not optically cause a change in refractive index due to loss or distortion. By changing the temperature of the grating, the optical path length can be changed. The change in the optical path length is significantly larger by one digit or more than the change in the temperature of the optical fiber or the optical waveguide. Therefore, the switching can be performed with a heating power and a temperature change smaller by one digit or more than a heat effect switch that simply heats an optical fiber or an optical waveguide. Also, by locally heating the temperature compensation module, a thermo-optic effect switch that is stable to ambient temperature and sensitive to local heating is possible.
[0163]
FIG. 30 shows the configuration of the thermo-optic effect switch module. FIG. 30A shows the case of CG, and FIG. 30B shows the case of CGDC. A heater used for local heating is obtained by mounting a resistive material such as chrome or tungsten in the form of a thin film. The temperature rise due to local heating needs to be uniform throughout the chirped grating section. The mounting form is set at a distance where the electromagnetic field intensity of the light propagating through the optical fiber or the optical waveguide is sufficiently reduced, and may be one side in the plane or both sides. In the case of an optical fiber, the shape surrounding the optical fiber core may be used, and in the case of an optical waveguide, the shape may be installed in a parallel plane not including the plane forming the waveguide.
[0164]
A Michelson-type interferometer is configured by using the CG or the thermo-optic effect switch module using the CCG and the directional coupler 131. While stabilizing the temperature, the light intensity can be switched with high sensitivity through the thermo-optic effect.
[0165]
FIG. 31 shows the configuration of a Michelson interferometer type thermo-optic effect switch. As shown in FIG. 31A, as in the case of the temperature stabilization module shown in FIG. 11, a thermo-optic effect switch module of CG is connected to the output port 132 of the Michelson interferometer, and the output port 133 is output. To the CG temperature stabilization module. Further, as shown in FIG. 31B, a thermo-optic effect switch module of CG can be connected to the output port 133, and a reflecting mirror or a Bragg grating can be connected to the output port 133.
[0166]
A Mach-Zehnder interferometer is configured using the thermo-optic effect switch module using the CGDC and the directional couplers 131a and 131b. In addition to stabilizing the temperature, the light path can be switched with high sensitivity through the thermo-optic effect.
[0167]
FIG. 32 shows a configuration of a thermo-optic effect switch of the Mach-Zehnder interferometer. As shown in FIG. 32 (a), as in the case of the temperature stabilizing module of FIG. 17, both or one of two optical fibers or optical waveguides connecting between the ports of the two directional couplers 131 are connected. Then, the thermo-optic effect switch module of CGDC and the temperature stabilization module of CGDC are connected. Further, as shown in FIG. 32 (b), a configuration may be adopted in which one side is connected to a thermo-optic effect switch module of CGDC and the other side is connected to an optical fiber or an optical waveguide.
[0168]
According to the present embodiment, the intensity and path of light passing through the optical fiber or the optical waveguide are switched while maintaining the temperature compensated state by changing the temperature of the CG with a small amount of electric power by means such as resistance heating. be able to.
[0169]
【The invention's effect】
As described above, according to the present invention, a chirped grating that is joined to one end on the optical axis of an optical system and has an effective refractive index that periodically changes in the traveling direction of light is provided. Since the change in characteristics due to temperature changes is controlled, the optical device is controlled to have a desired temperature characteristic by compensating for the effective optical length of the portion of the optical device that determines the wavelength characteristics and phase characteristics. This eliminates or simplifies the need for a temperature stabilizing device or the like that maintains a constant ambient temperature.
[0170]
Further, according to the present invention, it is possible to realize a small and highly sensitive variable optical device, and to provide an optical device that can contribute to downsizing, power saving, and cost reduction of an optical system.
[0171]
Further, according to the present invention, it is possible to switch the intensity and path of light passing through an optical fiber or an optical waveguide while maintaining a temperature-compensated state.
[Brief description of the drawings]
FIG. 1 is a diagram showing a change in characteristics of a chirped grating with a change in temperature.
FIG. 2 is a diagram showing a change in characteristics of a chirped grating in an optical fiber or an optical waveguide.
FIG. 3 is a diagram for explaining temperature compensation and temperature sensitization by a chirped grating.
FIG. 4 is a diagram for explaining temperature compensation and temperature sensitization by a cascaded chirped grating.
FIG. 5 is a diagram illustrating a relationship between a position measured from a short cycle side and a grating cycle in a single CG.
FIG. 6 is a diagram showing a relationship between a position measured from a short cycle side and a grating cycle in CCG.
FIG. 7 is a diagram showing a configuration of an optical directional coupler with a built-in chirped grating.
FIG. 8 is a diagram showing a configuration of a temperature stabilized Fabry-Perot interferometer using CG.
FIG. 9 is a diagram showing a configuration of a Fabry-Perot interferometer type temperature stabilized narrow band filter.
FIG. 10 is a diagram showing a configuration of a multi-wavelength stabilized light source based on a Fabry-Perot interferometer type wavelength reference.
FIG. 11 is a diagram showing a configuration of a Michelson interferometer using CG.
FIG. 12 is a diagram showing a temperature stabilized PM-AM converter of the Michelson interferometer type.
FIG. 13 is a diagram showing a multi-wavelength stabilized light source based on a Michelson interferometer type wavelength reference.
FIG. 14 is a diagram showing a Michelson interferometer type strain sensor.
FIG. 15 is a diagram showing a configuration of an AWG.
FIG. 16 is a diagram showing a configuration of an AWE.
FIG. 17 is a diagram showing a configuration of a Mach-Zehnder interferometer using CGDC.
FIG. 18 shows a Mach-Zehnder interferometer type temperature stabilized PM-AM converter.
FIG. 19 is a diagram showing a multi-wavelength stabilized light source based on a Mach-Zehnder interferometer type wavelength reference.
FIG. 20 is a diagram showing a configuration of a temperature stabilizing ring circuit using CGDC.
FIG. 21 is a diagram showing a configuration of a temperature stabilized ring laser using CGDC.
FIG. 22 is a diagram showing a configuration of a temperature-sensitized Fabry-Perot interferometer using CG.
FIG. 23 is a diagram showing the configuration of a Fabry-Perot interferometer type tunable filter.
FIG. 24 is a diagram showing a configuration of a Fabry-Perot interferometer type temperature sensor.
FIG. 25 is a diagram showing a temperature detection circuit of the Fabry-Perot interferometer type.
FIG. 26 is a diagram showing a configuration of a push-pull temperature-sensitized Michelson interferometer.
FIG. 27 is a diagram showing a temperature sensor of the Michelson interferometer type.
FIG. 28 is a diagram showing a Mach-Zehnder interferometer type temperature sensor.
FIG. 29 is a diagram showing a Michelson interferometer-type temperature dependency measurement circuit.
FIG. 30 is a diagram showing a configuration of a thermo-optic effect switch module.
FIG. 31 is a diagram showing a configuration of a Michelson interferometer type thermo-optic effect switch.
FIG. 32 is a diagram showing a configuration of a thermo-optic effect switch of a Mach-Zehnder interferometer.
[Explanation of symbols]
10, 20, 71, 72 Chirped grating (CG)
31 ° optical system
61 joint grating
81 ° reflector
82 Bragg grating (G)
91,101 ° temperature stabilized Fabry-Perot interferometer
121 Optical Directional Coupler with Built-in Chirped Grating (CGDC)
161 temperature-sensitized Fabry-Perot interferometer

Claims (45)

An optical device that controls a change in characteristics due to a change in temperature of an optical system that operates at a single wavelength,
An optical device, comprising: a chirped grating that is joined to one end of the optical system on the optical axis and has an effective refractive index that periodically changes in a traveling direction of light. An optical device that controls a change in characteristics due to a temperature change of an optical system operating at a plurality of wavelengths,
A cascaded chirped grating connected to a plurality of chirped gratings that are joined to one end on the optical axis of the optical system and that have an effective refractive index in the traveling direction of light and that periodically change at different periods. An optical device, characterized in that: An optical device that controls a change in characteristics due to a change in temperature of an optical system that operates at a single wavelength,
An optical device, comprising: a directional coupler having a built-in chirped grating that is joined to one end on the optical axis of the optical system and has an effective refractive index that periodically changes in a traveling direction of light. . 4. The optical device according to claim 1, wherein a short-period side of the chirped grating is joined to the optical system to compensate for a change in characteristics of the optical system due to a temperature change. An optical device that controls a change in characteristics due to a change in temperature of an optical system,
A chirped grating in which the effective refractive index periodically changes in the light traveling direction, and the short-period side of the grating is joined to one end on the optical axis of the optical system;
An optical device, comprising: a reflection device joined to the other end of the optical system on the optical axis. The optical device according to claim 5, wherein the reflection device is any one of the chirped grating, the reflecting mirror, and the Bragg grating. 7. The optical device according to claim 5, wherein a heating element that electrically generates heat is mounted near the grating portion of the chirped grating. An optical device that controls a change in characteristics due to a change in temperature of an optical system,
A cascade in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and the short-period side of the grating is joined to one end on the optical axis of the optical system. Type chirp grating,
An optical device, comprising: a reflection device joined to the other end of the optical system on the optical axis. 9. The optical device according to claim 8, wherein the reflection device is one of the cascaded chirped grating, a reflector, and a Bragg grating. The optical device according to claim 8, wherein a heating element that electrically generates heat is mounted near the grating portion of the cascaded chirped grating. The optical device according to any one of claims 5 to 10, wherein the optical system includes a laser medium. The optical device according to claim 5, wherein the optical system includes a nonlinear optical medium. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
An optical device comprising: a chirped grating in which an effective refractive index periodically changes in a traveling direction of light and a short-period side of the grating is joined to each of the two output ports. 14. The optical device according to claim 13, wherein a heating element that electrically generates heat is mounted near one of the grating portions of the chirped grating. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A cascaded chirp in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and a short-period side of the grating is connected to each of the two output ports. -An optical device comprising a grating. The optical device according to claim 15, wherein a heating element that electrically generates heat is mounted near one of the grating portions of the cascaded chirped grating. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A chirped grating in which the effective refractive index periodically changes in the light traveling direction, and the short-period side of the grating is joined to the one output port;
An optical device, comprising: a reflection device joined to the other output port. 18. The optical device according to claim 17, wherein a heating element that electrically generates heat is mounted near the grating portion of the chirped grating. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A cascaded chirped grating in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and a short-period side of the grating is connected to the one output port. An optical device comprising: a reflection device joined to the other output port. 20. The optical device according to claim 19, wherein a heating element that electrically generates heat is mounted near the grating portion of the cascaded chirped grating. A star coupler for distributing light having a plurality of wavelengths input from one input port to a plurality of waveguide ports;
A plurality of waveguide arrays of different lengths connected to the plurality of waveguide ports,
A plurality of chirped gratings, each of which has an effective refractive index that is periodically changed at a different period in a traveling direction of light, which is joined to an end of the waveguide array that is not connected to the star coupler. An optical device, characterized in that: A star coupler for distributing light having a plurality of wavelengths input from one input port to a plurality of waveguide ports;
A plurality of waveguide arrays of different lengths connected to the plurality of waveguide ports,
A plurality of chirped gratings, each of which has an effective index of refraction in the traveling direction of light and is periodically changed at a different period, are connected to an end of the waveguide array that is not connected to the star coupler. An optical device comprising a cascaded chirped grating. In a Mach-Zehnder interferometer having optical fibers or optical waveguides of different lengths connecting between ports of two directional couplers,
At least one of the optical fiber or the optical waveguide, a directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light,
A Mach-Zehnder interferometer, wherein a short cycle side of the chirped grating is inserted between the ports. 24. The Mach-Zehnder interferometer according to claim 23, wherein a heating element that electrically generates heat is mounted near the grating portion of the chirped grating. A first directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light;
A second directional coupler having an input port connected to the input port of the first directional coupler and an output port connected to the output port of the first directional coupler;
An optical device, wherein a short-period side of the chirped grating is joined to the second directional coupler. 26. The optical device according to claim 25, wherein the optical system connecting the input port of the first directional coupler and the input port of the second directional coupler includes a laser medium. 26. The optical device according to claim 25, wherein the optical system connecting the input port of the first directional coupler and the input port of the second directional coupler includes a nonlinear optical medium. 4. The optical device according to claim 1, wherein a long-period side of the chirped grating is joined to the optical system to sensitize a change in characteristics of the optical system due to a temperature change. An optical device that controls a change in characteristics due to a change in temperature of an optical system,
A chirped grating in which the effective refractive index periodically changes toward the traveling direction of light, and a long-period side of the grating is joined to one end on the optical axis of the optical system;
An optical device, comprising: a reflection device joined to the other end of the optical system on the optical axis. 30. The optical device according to claim 29, wherein the reflection device is any one of the chirped grating, reflecting mirror, and Bragg grating. An optical device that controls a change in characteristics due to a change in temperature of an optical system,
A cascade in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and a long-period side of the grating is joined to one end on the optical axis of the optical system. Type chirp grating,
An optical device, comprising: a reflection device joined to the other end of the optical system on the optical axis. 32. The optical device according to claim 31, wherein the reflection device is one of the cascaded chirped grating, a reflector, and a Bragg grating. 33. The optical device according to claim 29, wherein the optical system includes a laser medium. 33. The optical device according to claim 29, wherein the optical system includes a non-linear optical medium. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
An optical device, comprising: a chirped grating whose effective refractive index periodically changes in a light traveling direction, and a long-period side of the grating is joined to each of the two output ports. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A cascaded chirp in which a plurality of chirped gratings whose effective refractive indices periodically change at different periods in the light traveling direction are connected, and a long-period side of the grating is connected to each of the two output ports. -An optical device comprising a grating. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A chirped grating in which the effective refractive index periodically changes in the light traveling direction, and a long-period side of the grating is joined to the one output port;
An optical device, comprising: a reflection device joined to the other output port. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A cascaded chirped grating in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and a long-period side of the grating is connected to the one output port. An optical device comprising: a reflection device joined to the other output port. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A first chirped grating in which the effective refractive index changes periodically in the light traveling direction, and the short-period side of the grating is joined to the one output port;
An optical device comprising: a second chirped grating in which a long-period side of the grating is joined to the other output port. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A first cascaded type in which a plurality of chirped gratings whose effective refractive indices are periodically changed at different periods in the traveling direction of light are connected, and the short-period side of the grating is connected to the one output port. An optical device comprising: a chirped grating; and a second cascaded chirped grating having a long-period side of the grating joined to the other output port. In a Mach-Zehnder interferometer having optical fibers or optical waveguides of different lengths connecting between ports of two directional couplers,
At least one of the optical fiber or the optical waveguide, a directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light,
A Mach-Zehnder interferometer, wherein a long-period side of the chirped grating is inserted between the ports. A first directional coupler having a built-in chirped grating whose effective refractive index periodically changes in the traveling direction of light;
A second directional coupler having an input port connected to the input port of the first directional coupler and an output port connected to the output port of the first directional coupler;
An optical device, wherein a long-period side of the chirped grating is joined to the second directional coupler. 43. The optical device according to claim 42, wherein the optical system connecting the input port of the first directional coupler and the input port of the second directional coupler includes a laser medium. 43. The optical device according to claim 42, wherein the optical system connecting the input port of the first directional coupler and the input port of the second directional coupler includes a nonlinear optical medium. Directional couplers having different lengths of optical fibers or optical waveguides serving as two output ports,
A reflective device joined to the one output port;
A chirped grating whose effective refractive index periodically changes in the traveling direction of light, which is joined to the other output port via an optical fiber or optical waveguide of a known length,
A measuring device for measuring the temperature characteristic of the chirped grating by inputting light of a variable wavelength to the directional coupler and identifying a reflection point.

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