JP3924182B2 - Variable dispersion compensator - Google Patents

Description

なお、ｃ₁およびｃ₂は、分散特性が式（１），（２）が示す群遅延特性に近くなる値を選ぶ。
【００３９】
上述したように全反射膜１３，１６のエネルギー反射率は１００％であり、部分反射膜１１，１４のエネルギー反射率をそれぞれＲ₁，Ｒ₂とし、光学厚みをｄ₁，ｄ₂とすると、伝達関数Ｈ_ri（λ）は、次式（３）に示すようになる。なお、ｉは１または２であり、ｊは虚数単位である。また、記号「＾」は、べき乗を示す。

なお、伝達関数の絶対値の二乗が、エネルギー反射率であり、伝達関数の複素平面上の偏角が、位相応答であり、位相応答の周波数微分の符号を逆にしたものが、群遅延特性である。また、光学厚みｄ₁，ｄ₂は、波長λ₀で群遅延特性が極値をもつ値とした。
【００４０】
ここで、周波数周期間隔ＦＳＲと光学厚みｄとの関係は次式（４）で示される。
ｄ＝ｃ／（２×ＦＳＲ） （４）
なお、波長λ₀で群遅延特性が極値をもつためには、光学厚みｄがエタロンＥ１ではλ₀／４の偶数倍であって、エタロンＥ２ではλ₀／４の奇数倍である必要があるため、光学厚みｄは、式（４）の計算値の近傍の値とした。
【００４１】
この実施の形態１では、波長λ₀を１５５０ｎｍとし、この波長λ₀を中心として±０．１９ｎｍを使用波長帯域とした。また、エタロンＥ１の波長シフトは、−０．１７５〜＋０．１７５ｎｍと設定した場合に、使用波長帯域内で−３０〜＋３０ｐｓ／ｎｍの群遅延分散量を有し、周波数周期間隔ＦＳＲが１００ＧＨｚとした可変分散補償器を実現する。その計算結果は、図３および図４に示すプロットとして表現している。
【００４２】
また、エタロンＥ１，Ｅ２の部分反射膜１１，１４の各エネルギー反射率は、群遅延特性が、式（１），（２）に示した群遅延特性との二乗誤差が最小となるように非線形フィッティングによって求めた。エタロンＥ１の光学厚みｄ₁＝９６７．５０λ₀、エタロンＥ２の光学厚みｄ₂＝９６７．７５λ₀として計算すると、エタロンＥ１の部分反射膜１１のエネルギー反射率Ｒ₁＝７．０７％であり、エタロンＥ２の部分反射膜１４のエネルギー反射率Ｒ₂＝１．５３％となる。なお、エタロン板１２，１５は、ガラス板で構成できる。ここで、エタロン板１２，１５をＢＫ７で構成した場合、波長λ₀＝１５５０ｎｍにおける屈折率は、１．５０１４であるから、エタロン板１２，１５の物理厚みは、それぞれ９９８．８２μｍ、９９９．０８μｍとなる。
【００４３】
図３および図４は、それぞれエタロン板１２，１５の光学厚みｄ₁，ｄ₂を９６７．５０λ₀、９６７．７５λ₀とした場合であって、波長シフトさせない場合における、波長に対する群遅延特性を示す図である。図３および図４において、図３に示したエタロンＥ１の群遅延特性と図４に示したエタロンＥ２の群遅延特性とは、波長λ₀において、π位相ずれしており、しかも使用波長帯域において互いに相反する二次関数の群遅延特性を呈している。
【００４４】
図５は、図３に示した群遅延特性を波長シフトさせ、図４に示した各群遅延特性を合成した場合における群遅延特性を示す図である。すなわち、波長シフトを行った場合であって、光信号がエタロンＥ１およびエタロンＥ２を経由した場合における、波長シフト毎の各群遅延特性を示している。図５では、エタロンＥ２を波長に対して固定し、エタロンＥ１の群遅延特性を波長方向に、−０．１７５ｎｍ、−０．０７０ｎｍ、０．０００ｎｍ、＋０．０７０ｎｍ、＋０．１７５ｎｍシフトさせた場合における各エタロンＥ１，Ｅ２の合成群遅延特性を示している。
【００４５】
図６は、図５に示した使用波長帯域における各シフト毎の合成群遅延特性の拡大図である。図６において、波長を−０．１７５ｎｍ、−０．０７０ｎｍ、０．０００ｎｍ、＋０．０７０ｎｍ、＋０．１７５ｎｍシフトさせた場合、それぞれ線Ｌ１１、Ｌ１２、Ｌ１３、Ｌ１４、Ｌ１５を示し、それぞれ＋３０ｐｓ／ｎｍ、＋１２ｐｓ／ｎｍ、０ｐｓ／ｎｍ、−１２ｐｓ／ｎｍ、−３０ｐｓ／ｎｍの群遅延分散量を与えている。これらの線Ｌ１１〜Ｌ１５は、波長に対して、ほぼ直線的な群遅延変化を示している。これは、エタロンＥ１，Ｅ２の使用波長帯域における群遅延特性が互いに相反する二次関数として表されるからである。すなわち、エタロンＥ１は、下に凸の二次関数として示され、エタロンＥ２は、上に凸の二次関数として示され、各二次関数を合成した場合に１次関数となるからである。ただし、図３および図４に示した群遅延特性は、理想的な二次関数でないため、合成した群遅延特性は、図６に示すように、やや揺らいだ線Ｌ１１〜Ｌ１５となる。
【００４６】
なお、エタロンＥ１，Ｅ２は、光サーキュレータ５などの部品によって相互干渉しないように結合される。また、この実施の形態１では、エタロンＥ１の群遅延特性を波長シフトして最終的な分散補償量を可変しているが、これに限らず、エタロンＥ１の群遅延特性を波長に対して固定し、エタロンＥ２の群遅延特性を波長シフトさせるようにしてもよい。さらに、エタロンＥ１，Ｅ２のうちのいずれか一方のみの群遅延特性を波長シフトさせるのではなく、エタロンＥ１，Ｅ２の双方を異なる方向にそれぞれ同量または異なる量、波長シフトさせるようにしてもよし、同じ方向に異なる量、波長シフトさせるようにしてもよい。
【００４７】
また、エタロンＥ１，Ｅ２の個数は、２つに限らず、３つ以上の組合せによって所望の群遅延特性を得るようにしてもよい。ただし、互いに相反する群遅延特性をもつことが必要である。
【００４８】
さらに、上述したエタロンＥ１の全反射膜１３にはペルチェ素子６が結合されていたが、これに限らず、たとえばヒーターを用いるようにしてもよい。なお、エタロン板１２は、線膨張の温度係数が大きいものを使用し、ヒーターに電流をを流して発熱量を温度制御部８によって制御し、エタロン板１２の光学厚みを制御する。エタロン板１２がＢＫ７を使用する場合、ＢＫ７の線膨張係数による波長シフト量は約１０ｐｍ／Ｋであるので、上述した−０．１７５ｎｍ〜＋０．１７５ｎｍの波長シフトは、３５Ｋの温度範囲を変化させることによって実現できる。もちろん、ペルチェ素子６を用いた場合も同様である。
【００４９】
なお、図１に示した光サーキュレータ５は、４ポート型の光サーキュレータを用いているが、これに限らず、３ポート型の光サーキュレータを用いてもよい。たとえば、図７は、３ポート型の光サーキュレータを用いて光可変分散補償器を実現している。図７において、４ポート型の光サーキュレータ５に代えて３ポート型の光サーキュレータ５ａ，５ｂを設け、光サーキュレータ５ａの出力用のポートＰ１３と光サーキュレータ５ｂの入力用のポートＰ２１との間を光ファイバ９で接続している。光サーキュレータ５ａの入力用のポートＰ１１には光ファイバ１が接続され、入出力用のポートＰ１２にはエタロンＥ１が接続される。また、光サーキュレータ５ｂの入出力用のポートＰ２２にはエタロンＥ２が接続され、出力用のポートＰ２３には光ファイバ４が接続される。このような構成によって、入力端子Ｔ１から入力された光信号は、光サーキュレータ５ａを介してエタロンＥ１による群遅延が与えられ、その後光サーキュレータ５ｂを介してエタロンＥ２による群遅延が与えられ、出力端子Ｔ２から出力される光信号は、エタロンＥ１，Ｅ２の合成群遅延が付与され、分散補償されることになる。
【００５０】
この実施の形態１では、オール・パス・フィルタとしての機能を有したエタロンＥ１，Ｅ２を用いて分散補償するようにしているので、減衰が少ない可変分散補償器を実現することができる。なお、各エタロンＥ１，Ｅ２の減衰量は、０．１ｄＢ程度であり、光サーキュレータ５による光入出力の３ｄＢ減衰に比較するとほとんど無視できる減衰量である。
【００５１】
また、この実施の形態１では、それぞれ二次関数型の群遅延特性であって、互いに相反する群遅延特性をもったエタロンＥ１，Ｅ２を用いて可変分散補償を行っているので、使用波長帯域における群遅延特性の波長依存性をリニアにすることができ、群遅延の二次特性、すなわち三次分散などの発生を抑止した分散補償を行うことができる。
【００５２】
なお、上述したエタロンＥ１，Ｅ２は、それぞれ相互に相反する二次関数型の群遅延特性を持たせるようにしたが、この場合、二次関数の二次項の定数は、絶対値が同じで符号が異なることが好ましい。エタロンＥ１，Ｅ２の各群遅延特性を合成した場合に、１次項以下の群遅延特性を呈するからである。この場合における一次関数が使用波長帯域における群遅延特性となる。また、各エタロンＥ１，Ｅ２の群遅延特性は、二次関数型に限らず、３次以上の高次の関数であってもよい。この場合、二次関数型と同様に、各エタロンＥ１，Ｅ２における２次項以上の定数が合成時に相殺されるようにする。
【００５３】
また、上述したエタロンＥ１，Ｅ２に入射される光信号は、エタロン板１２，１５が形成する平面に垂直に入射されるものとしたが、数度程度の入射角であれば、オール・パス・フィルタとしての機能をほぼ発揮するので実用に値する。ただし、この場合、入射角に対応した光学厚みに設定する必要がある。
【００５４】
（実施の形態２）
つぎに、この発明の実施の形態２について説明する。上述した実施の形態１では、光サーキュレータ５を介して各エタロンＥ１，Ｅ２に光信号が入出射されるようにしていたが、この実施の形態２では、光サーキュレータ５あるいは光サーキュレータ５ａ，５ｂを用いずに群遅延補償できるようにしている。
【００５５】
図８は、この発明の実施の形態２である可変分散補償器の構成を示す図である。図８において、この可変分散補償器は、実施の形態１に示したエタロンＥ１，Ｅ２がそれぞれ含まれるエタロンモジュールＭ１，Ｍ２を有し、入力端子Ｔ１とエタロンモジュールＭ１との間は、光ファイバ１で接続され、エタロンモジュールＭ１，Ｍ２間は、光ファイバ９で接続され、エタロンモジュールＭ２と出力端子Ｔ２との間は、光ファイバ４で接続される。
【００５６】
エタロンモジュールＭ１，Ｍ２は、それぞれフェルール１７ａ，１７ｂと、レンズ１８ａ，１８ｂと、エタロンＥ１，Ｅ２を有する。レンズ１８ａ，１８ｂは、たとえば焦点距離が１．８〜４．０ｍｍ程度、好ましくは３．０ｍｍの非球面レンズである。フェルール１７ａ，１７ｂは、光ファイバ１，９あるいは光ファイバ９，４とする２本の光ファイバが取り付けられた２芯フェルールである。このフェルール１７ａ，１７ｂは、合成樹脂、ガラスあるいはジルコニアなどの材質によって形成される。ここで、光ファイバ１，９あるいは光ファイバ９，４は、それぞれエタロンＥ１，Ｅ２への入射角が０度に近づくように、１２７μｍのピッチで配置される。
【００５７】
フェルール１７ａ，１７ｂは、図９に示すように円柱形の本体に長手方向に形成された２つのファイバ孔１９ａ，１９ｂを有する。フェルール１７ａ，１７ｂは、レンズ１８ａ，１８ｂ側に配置される面において、光ファイバ１，９あるいは光ファイバ９，４からの光信号が入射され、出射されるようになっていればよく、他方の面（光ファイバ１，９あるいは光ファイバ９，４側）は、光ファイバ１，９あるいは光ファイバ９，４を挿入するためのガイド孔などが形成されていてもよい。
【００５８】
なお、実施の形態１で示したように、エタロンＥ１にはペルチェ素子６が設けられ、このペルチェ素子６は、温度制御部８による制御のもとに電源７が制御され、ペルチェ素子６への通電方向および通電量が制御される。これによって、エタロンＥ１の群遅延特性が可変制御される。
【００５９】
ここで、入力端子Ｔ１および光ファイバ１を介して光信号がエタロンモジュールＭ１に入射されると、光信号はフェルール１７ａの一方のファイバ孔１９ａを介してレンズ１８ａに入射され、レンズ１８ａは、この信号光を集光してエタロンＥ１に入射する。レンズ１８ａは、エタロンＥ１から反射した光信号を再びフェルール１７ａのファイバ孔１９ｂに集光し、この光信号を光ファイバ９を介してエタロンモジュールＭ２側に出射する。
【００６０】
エタロンモジュールＭ２側では、エタロンモジュールＭ１側と同様に、光ファイバ９を介して入射された光信号を、フェルール１７ｂの一方のファイバ孔１９ａを介してレンズ１８ｂに入射し、レンズ１８ｂは、この信号光を集光してエタロンＥ２に入射する。レンズ１８ｂは、エタロンＥ２から反射した光信号を再びフェルール１７ｂのファイバ孔１９ｂに集光し、この光信号を光ファイバ４を介して出力端子Ｔ２に出射する。
【００６１】
この実施の形態２では、図１０に示しように、出射用のファイバ孔１９ｂがフェルール１７ａの中心に位置し、入射用のファイバ孔１９ａがファイバ孔１９ｂからオフセット量ｗ分、ずれているが、図１１に示すように、フェルール１７ａの断面の中心から対称に同量のオフセットを持たせ、ファイバ孔１９ａ，１９ｂ間がオフセット量ｗ分、離隔させるようにしてもよい。あるいは、図１２に示すように、各ファイバ孔１９ａ，１９ｂをそれぞれ断面の中心から非対称にオフセット量ｗ１，ｗ２分ずらし、結果的にファイバ孔１９ａ，１９ｂ間がオフセット量ｗをもつようにしてもよい。なお、ファイバ孔１９ａに、光信号が入射する光ファイバが取り付けられ、ファイバ孔１９ｂに、エタロンＥ１，Ｅ２からの反射光が入射する光ファイバが取り付けられるようにしたが、これに限らず、入出射する光ファイバを逆にしてもよい。さらに、各エタロンモジュールＭ１，Ｍ２毎に、入出射する光ファイバが取り付けられるファイバ孔１９ａ，１９ｂの選択は任意である。
【００６２】
この実施の形態２によれば、光サーキュレータ５あるいは光サーキュレータ５ａ，５ｂを用いずに可変分散補償することができ、分散補償対象の光信号が減衰しないので、低損失の可変分散補償器を実現できる。
【００６３】
（実施の形態３）
つぎに、この発明の実施の形態３について説明する。上述した実施の形態１では、光サーキュレータ５を介して各エタロンＥ１，Ｅ２に光信号が入出射されるようにしていたが、この実施の形態３では、光サーキュレータ５あるいは光サーキュレータ５ａ，５ｂを用いず、エタロンＥ１，Ｅ２と同じ２つのエタロンによって直接、群遅延補償できるようにしている。
【００６４】
図１３は、この発明の実施の形態３である可変分散補償器の構成を示す図である。図１３において、この可変分散補償器は、実施の形態１におけるエタロンＥ１，Ｅ２、エタロンＥ１に結合したペルチェ素子６、このペルチェ素子６に電流を通電する電源７、およびペルチェ素子６に対する電流量と通電方向とを制御する温度制御部８を有する。ただし、エタロンＥ１，Ｅ２は、光サーキュレータ５に接続されるのではなく、エタロンＥ１とエタロンＥ２とが対向配置される。すなわち、エタロンＥ１の部分反射膜１１とエタロンＥ２の部分反射膜１４とが向き合うように配置される。また、エタロンＥ１，Ｅ２は、光入出力の関係上、ずらして配置される。
【００６５】
図１３において、光ファイバ２１から入力された光信号は、光入力部２２からエタロンＥ１に対して入射角θをもって入射される。この入射角θは、４°以内に収めるようにするとよい。実施の形態１でも述べたように、このエタロンＥ１をオール・パス・フィルタとして機能させるためには、光信号をエタロン板１２に対して垂直に入射させる必要があるが、エタロンＥ１，Ｅ２を鏡のように配置すると、光の入出力を行うことができないため、エタロンＥ１への入射角θを０°から４°以内に若干ずらしている。この結果、エタロンＥ１は完全なオール・パス・フィルタとして機能しないが、オール・パス・フィルタとほぼ同様な機能をもつことになる。また、この場合、エタロンＥ１に対して光信号が斜めに入射されるため、実施の形態１におけるエタロン板１２の光学厚みによる干渉と同じ効果を得るためには、入射角θに応じてエタロン板１２の物理的厚みを大きくする必要がある。
【００６６】
エタロンＥ２は、エタロンＥ１から出力された光信号が、エタロンＥ１と同様に入射角θが４°以内で入射される位置に配置される。そして、エタロンＥ２から反射される光信号が光出力部２３に入射され、分散補償された光信号が光ファイバ２４に出力される。エタロン板１５の物理厚みは、この実施の形態２におけるエタロン板１２と同様に、入射角に応じて大きくする必要がある。
【００６７】
このような構成において、光信号は、エタロンＥ１に入射され、エタロンＥ１による群遅延特性による群遅延が与えられ、この群遅延が与えられた光信号は、さらにエタロンＥ２に入射され、エタロンＥ２による群遅延特性による群遅延が与えられ、このエタロンＥ１，Ｅ２による合成群遅延が与えられた光信号が光出力部２３を介して光ファイバ２４に出力される。
【００６８】
この実施の形態３では、エタロンＥ１，Ｅ２に入出力される光信号が斜めに入出力されるため、光出力がやや減衰するものの、光サーキュレータ５あるいは光サーキュレータ５ａ，５ｂを用いていないため、全体的な光出力の減衰が少なくて済むとともに、簡易な構成で実現できる。
【００６９】
（実施の形態４）
つぎに、この発明の実施の形態４について説明する。上述した実施の形態１〜３ではいずれもペルチェ素子６を用いてエタロンＥ１のエタロン板１２の光学厚みを調整するようにしていたが、この実施の形態４では、ピエゾ素子を用いてエタロン板１２の光学厚みを調整するようにしている。
【００７０】
図１４は、この発明の実施の形態４である可変分散補償器に用いられるエタロンの構成を示す図である。図１４に示したエタロン３０は、エタロン板１２に代えて空気層であるエアギャップ３４を用いて光信号の多重反射を行うようにしている。このエタロン３０は、エアギャップ３４を平行に挟む形態で、光信号入射側に部分反射膜３３と設け、光信号反射側に全反射膜３５を設けている。この部分反射膜３３、エアギャップ３４および全反射膜３５によってエタロンＥ１と同様に、オール・パス・フィルタとしての機能を発揮することになる。このエタロン３０と、電源７および温度制御部８とを除いた構成は、実施の形態１〜３と同じである。
【００７１】
部分反射膜３３は、基板３２によって固定され、この基板３２の光信号入射側には反射防止膜３１がコーティングされる。基板３２は、部分反射膜３３を固定し、光信号を透過させる。反射防止膜３１は、部分反射膜３３や全反射膜３５との多重反射による干渉を防止するためにコーティングされる。一方、全反射膜３５は、基板３６によって固定され、基板３６の他面には、ピエゾ素子３７が貼着される。
【００７２】
ピエゾ素子３７には、電圧付加部３８が接続され、この電圧付加部３８には電圧制御部３９が接続される。電圧制御部３９の制御のもとに、電圧付加部３８はピエゾ素子３７に電圧を印加し、ピエゾ素子３７は、圧電効果によって印加された電圧に応じて、光信号の入出射方向、すなわち矢印Ａ方向に変位する。この結果、基板３６と全反射膜３５とが矢印Ａ方向に移動し、エアギャップ３４の間隔が調整され、図３に示すような群遅延特性が設定される。
【００７３】
この実施の形態３では、ペルチェ素子６に代えてピエゾ素子３７を用いて多重反射の間隔、すなわち光学厚みを変化させるようにしているので、群遅延特性の設定時に、加熱に伴う他の光学素子への影響をなくすことができる。
【００７４】
（実施の形態５）
つぎに、この発明の実施の形態５について説明する。上述した実施の形態１〜４では、いずれも電源を用い、ペルチェ素子６あるいはピエゾ素子３７に通電し続けることによって光学厚みを設定するようにしていたが、この実施の形態５では光学厚みを機械的に設定するようにしている。
【００７５】
図１５は、この発明の実施の形態５である可変分散補償器に用いられるエタロンの構成を示す図である。図１５に示したエタロン４０は、実施の形態３に示したエタロンと同じである。ただし、ピエゾ素子３７を取り除き、エアギャップ３４間に平行平板４１を挿入され、この平行平板４１を回転駆動される回転駆動部４８および回転駆動部４８の制御を行う回転制御部４９を有している。この平行平板４１の両面には、部分反射膜３３や全反射膜３５との多重反射による干渉を防止するために、反射防止処理が施されている。エタロン４０は、この平行平板４１の光学厚みを考慮して、部分反射膜３３と全反射膜３５との間の物理的厚みが決定され、それぞれ固定配置される。ここで、平行平板４１は、矢印Ｂ方向に回転可能であり、平行平板４１の回転によって光信号の入出射方向に対する光路長が変化し、部分反射膜３３と全反射膜３５との間の光学厚みが変化する。これによって、所望の群遅延特性を設定することができる。
【００７６】
この実施の形態５では、ペルチェ素子６やピエゾ素子３７のように電流あるいは電圧を常時印加する必要がなく、一度、光学厚みを設定した後は、大きな経時変化を伴わずに、設定した光学厚みを安定して維持することができる。
【００７７】
【発明の効果】
以上説明したように、請求項１の発明によれば、所定波長範囲内の波長に対する群遅延特性が２次関数で近似できる第１光学部品と、前記所定波長範囲内の波長に対する群遅延特性が２次関数で近似でき、かつ前記第１光学部品が有する群遅延特性と相反する群遅延特性を有する第２光学部品と、前記第１光学部品および前記第２光学部品に対して群遅延補償対象の光信号をそれぞれ入出力接続する第１および第２の入出力ポートと群遅延補償対象の光信号を入力する入力ポートと群遅延補償後の光信号を出力する出力ポートとを有したサーキュレータとを設け、波長シフト手段が、前記第１光学部品あるいは前記第２光学部品の少なくとも一方の群遅延特性を波長に対してシフトさせ、前記群遅延補償対象の光信号が、前記入力ポート、前記第１の入出力ポート、第１光学部品、前記第１の入出力ポート、前記第２の入出力ポート、前記第２光学部品、前記第２の入出力ポート、および前記出力ポートを介して形成された光路を経由し、前記波長シフト手段による波長シフトによって設定された前記第１光学部品および前記第２光学部品が有する各群遅延特性が合成されることによって前記光信号の群遅延分散を可変に補償するようにしているので、柔軟かつ細かな分散補償を可変に行うことができるとともに、２次分散の少ない所望の群遅延特性を簡易な構成によって実現することができるという効果を奏する。
【００７８】
また、請求項２の発明によれば、第１分散補償モジュールが、所定波長範囲内の波長に対する群遅延特性が２次関数で近似できる第１光学部品と、群遅延補償対象の光信号を導波する第１光ファイバおよび前記第１光学部品から反射した光信号を導波する第２光ファイバを取り付ける第１フェルールと、前記第１フェルールと前記第１光学部品との間に設けられ、前記第１光ファイバおよび前記第２光ファイバから入出射される光信号の光学的結合を行う第１集光レンズとを有し、第２分散補償モジュールが、前記所定波長範囲内の波長に対する群遅延特性が２次関数で近似でき、かつ前記第１光学部品が有する群遅延特性と相反する群遅延特性を有する第２光学部品と、前記第１分散補償モジュールから出射された光信号を導波する前記第２光ファイバおよび前記第２光学部品から反射した光信号を導波する第３光ファイバを取り付ける第２フェルールと、前記第２フェルールと前記第２光学部品との間に設けられ、前記第２光ファイバおよび前記第３光ファイバから入出射される光信号の光学的結合を行う第２集光レンズと有し、波長シフト手段が、前記第１光学部品あるいは前記第２光学部品の少なくとも一方の群遅延特性を波長に対してシフトさせ、前記群遅延補償対象の光信号が、前記第１光ファイバ、前記第１分散補償モジュール、前記第２光ファイバ、前記第２分散補償モジュール、および前記第３光ファイバを介して形成された光路を経由し、前記波長シフト手段による波長シフトによって設定された前記第１光学部品および前記第２光学部品が有する各群遅延特性が合成されることによって前記光信号の群遅延分散を可変に補償するようにしているので、柔軟かつ細かな分散補償を可変に行うことができるとともに、光サーキュレータを用いないため、低損失の群遅延分散補償を行うことができ、しかも２次分散の少ない所望の群遅延特性を簡易な構成によって実現することができるという効果を奏する。
【００７９】
また、請求項３の発明によれば、所定波長範囲内の波長に対する群遅延特性が２次関数で近似できる第１光学部品と、前記所定波長範囲内の波長に対する群遅延特性が２次関数で近似でき、かつ前記第１光学部品が有する群遅延特性と相反する群遅延特性を有し、前記第１光学部品から反射された光信号が当該第２光学部品に直接入射されるように前記第１光学部品に対して略対向配置された第２光学部品と、前記第１光学部品に対して略対向配置され、前記第１光学部品に群遅延補償対象の光信号を直接入射する光入力手段と、前記第２光学部品に対して略対向配置され、前記第２光学部品から出力される光信号を直接受光して出力する光出力手段とを設け、波長シフト手段が、前記第１光学部品あるいは前記第２光学部品の少なくとも一方の群遅延特性を波長に対してシフトさせ、前記群遅延補償対象の光信号が、前記光入力手段、前記第１光学部品、前記第２光学部品、および前記光出力手段を介して形成された光路を経由し、前記波長シフト手段による波長シフトによって設定された前記第１光学部品および前記第２光学部品が有する各群遅延特性が合成されることによって前記光信号の群遅延分散を可変に補償するようにしているので、柔軟かつ細かな分散補償を可変に行うことができるとともに、光サーキュレータを用いないため、低損失の群遅延補償を行うことができ、しかも２次分散の少ない所望の群遅延特性を一層簡易な構成によって実現することができるという効果を奏する。
【００８０】
また、請求項４の発明によれば、前記第１光学部品および前記第２光学部品を、オールパスフィルタ機能を有するエタロンによって実現しているので、柔軟かつ細かな分散補償を可変に行うことができるとともに、挿入損失が小さく使用帯域の透過特性が平坦な分散補償を可変に行うことができるという効果を奏する。
【００８１】
また、請求項５の発明によれば、前記エタロンの他方の面への入射角度は、４°以内に抑えられ、前記エタロンの他方の面から入射された光信号は、前記エタロンの一方の面における９８％以上の反射率で反射し、前記エタロンの一方の面から出射され、これによって光信号に群遅延特性が付与されるようにしているので、オール・パス・フィルタとしての機能をほぼ十分に発揮し、損失が小さく透過特性が平坦な群遅延を付与することができるという効果を奏する。
【００８２】
また、請求項６の発明によれば、前記エタロンの他方の面において前記エタロンの他方の面から反射された光信号を反射する反射率を変化させ、該エタロンの周期的な群遅延特性を設定し、所定周波数帯域における群遅延特性の２次関数型形状を任意に設定できるようにしているので、所望の群遅延特性を柔軟かつ細かに得ることができるという効果を奏する。
【００８３】
また、請求項７の発明によれば、前記第１光学部品および前記第２光学部品の各群遅延特性の２次関数は、該２次関数の２次項の係数の絶対値をほぼ同じにし、かつ符号が異なるようにし、これによって２次関数が合成された群遅延特性が１次関数型になるようにしているので、群遅延の二次特性、すなわち三次分散がが小さい良好な群遅延分散補償を可変に行うことができるという効果を奏する。
【００８４】
また、請求項８の発明によれば、前記波長シフト手段の制御手段が、ヒーターからの加熱によって前記エタロンの間隙を変化させ、該エタロンの群遅延特性を波長シフトさせるようにしているので、簡易な構成で精度の高い分散補償を可変して行うことができるという効果を奏する。
【００８５】
また、請求項９の発明によれば、前記波長シフト手段は、前記エタロンに結合されたペルチェ素子と、前記ペルチェ素子の通電量と通電方向を制御する制御手段と、波長シフト手段の制御手段が、ペルチェ素子から加熱あるいは冷却によって前記エタロンの間隙を変化させ、該エタロンの群遅延特性を波長シフトさせるようにしているので、簡易な構成で精度の高い分散補償を可変して行うことができるという効果を奏する。
【００８６】
また、請求項１０の発明によれば、波長シフト手段の制御手段が、圧電素子の物理的変化によって前記エタロンの間隙を変化させ、該エタロンの群遅延特性を波長シフトさせるようにしているので、熱の発生を抑えた簡易な構成で精度の高い分散補償を可変して行うことができるという効果を奏する。
【００８７】
また、請求項１１の発明によれば、波長シフト手段の制御手段が、前記平行平板の傾斜によって前記エタロンの間隙の光路差を変化させ、該エタロンの群遅延特性を波長シフトさせるようにしているので、設定された波長シフトの状態を電源を用いず、機械的設定のみによって維持し、経時変化の少ない可変分散補償器を実現することができるという効果を奏する。
【図面の簡単な説明】
【図１】この発明の実施の形態１である可変分散補償器の構成を示す図である。
【図２】図１に示したエタロンの動作を示す説明図である。
【図３】図１に示したエタロンの群遅延特性を示す図である。
【図４】図１に示した他のエタロンの群遅延特性を示す図である。
【図５】図３および図４に示した各エタロンの可変合成群遅延特性を示す図である。
【図６】図５に示した使用波長帯域における可変群遅延特性の拡大図である。
【図７】この発明の実施の形態１である可変分散補償器の変形例の構成を示す図である。
【図８】この発明の実施の形態２である可変分散補償器の構成を示す図である。
【図９】図８に示したフェルールの構成を示す斜視図である。
【図１０】図８に示したフェルールの一対のファイバ孔の位置関係を示す断面図である。
【図１１】図８に示したフェルールの一対のファイバ孔の位置関係の第１変形例を示す断面図である。
【図１２】図８に示したフェルールの一対のファイバ孔の位置関係の第２変形例を示す断面図である。
【図１３】この発明の実施の形態３である可変分散補償器の構成を示す図である。
【図１４】この発明の実施の形態４である可変分散補償器に用いられるエタロンの構成を示す図である。
【図１５】この発明の実施の形態５である可変分散補償器に用いられるエタロンの構成を示す図である。
【図１６】従来の固定型の分散補償器に用いられるファイバの群遅延特性を示す図である。
【図１７】従来のＶＩＰＡ板を用いた可変分散補償器の構成を示す図である。
【符号の説明】
Ｅ１，Ｅ１，３０，４０ エタロン
Ｍ１，Ｍ２ エタロンモジュール
１，４，９，２１，２４ 光ファイバ
２，３ 光路
５，５ａ，５ｂ 光サーキュレータ
６ ペルチェ素子
７ 電源
８ 温度制御部
１１，１４，３３ 部分反射膜
１２，１５ エタロン板
１３，１６，３５ 全反射膜
１７ａ，１７ｂ フェルール
１８ａ，１８ｂ レンズ
１９ａ，１９ｂ ファイバ孔
２２ 光入力部
２３ 光出力部
３１ 反射防止膜
３２，３６ 基板
３４ エアギャップ
３７ ピエゾ素子
３８ 電圧付加部
３９ 電圧制御部
４１ 平行平板
４８ 回転駆動部
４９ 回転制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable dispersion compensator capable of variably compensating for dispersion characteristics of group delay.
[0002]
[Prior art]
With the recent spread of the Internet, optical communication systems are required to have a large capacity and high speed, and the large capacity and high speed are realized by wavelength multiplexing using a wavelength division multiplexing communication system. On the other hand, the communication speed is currently achieved at 10 Gbps, but development is progressing toward the realization of 40 Gbps in the next generation optical communication system.
[0003]
When the communication speed is 40 Gbps, dispersion transmitted in the optical fiber cannot be ignored, and this dispersion causes inter-signal interference, leading to an increase in errors. Here, conventionally, a fiber-type fixed dispersion compensator has been used to compensate for the dispersion characteristics of the group delay.
[0004]
In this fiber type fixed dispersion compensator, the dispersion compensating fiber (DCF) 102 and the dispersion shifted fiber (DSF) 103 shown in FIG. 16 are inserted between the single mode fibers (SMF) 101, and the dispersion generated or generated in the SMF 101 is obtained. Had to compensate.
[0005]
On the other hand, in recent years, a tunable dispersion compensator using a multiple reflection (VIPA: Virtually Imaged Phased Array) plate has been proposed. This variable dispersion compensator uses the interference effect of the VIPA plate and attempts to perform dispersion compensation using a physical optical path difference depending on the wavelength.
[0006]
FIG. 17 is a diagram illustrating a configuration of a tunable dispersion compensator using a VIPA plate. In FIG. 17, the optical signal to be dispersion compensated enters the condenser lens system 111 via the optical circulator 110 and is input to the VIPA plate 112. The optical signal is multiple-reflected by the VIPA plate 112 but is emitted from the VIPA plate 112 so that the reflection direction for each wavelength is different. The emitted optical signal is reflected by the reflecting mirror 113 and is incident on the VIPA plate 112 again. The VIPA plate 112 has a different number of multiple reflections depending on the incident position of the reflected optical signal. Are made different so that they are returned to the condenser lens system. As a result, a desired group delay characteristic can be obtained by changing the reflection characteristic of the reflection mirror 113.
[0007]
[Problems to be solved by the invention]
However, in the above-described fiber type fixed dispersion compensator, it is necessary to prepare a plurality of dispersion compensators of different sizes and to reconnect each time in order to obtain an optimum dispersion amount, and to perform fine dispersion compensation. There was a problem that could not.
[0008]
On the other hand, a tunable dispersion compensator using a VIPA plate has many components, has a complicated structure, has a large insertion loss, and has different transmission characteristics for each wavelength within the use band. was there.
[0009]
In order to eliminate the above-mentioned problems caused by the prior art, the present invention can variably perform flexible and fine dispersion compensation, and performs dispersion compensation that has a small insertion loss and does not change the transmission characteristics of the used band. An object of the present invention is to provide a tunable dispersion compensator that can be variably performed.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, a tunable dispersion compensator according to claim 1 includes a first optical component capable of approximating a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function, and the predetermined wavelength. A second optical component having a group delay characteristic that can be approximated by a quadratic function with respect to a wavelength within the range and having a group delay characteristic opposite to that of the first optical component, the first optical component, and the second optical component. First and second input / output ports for inputting / outputting optical signals subject to group delay compensation to / from optical components, input ports for inputting optical signals subject to group delay compensation, and optical signals after group delay compensation are output. A circulator having an output port, and wavelength shift means for shifting a group delay characteristic of at least one of the first optical component or the second optical component with respect to the wavelength, and the group delay compensation pair Optical signals of the input port, the first input / output port, the first optical component, the first input / output port, the second input / output port, the second optical component, and the second input / output. Each group delay characteristic of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means is synthesized through the optical path formed through the port and the output port. Thus, the group delay dispersion of the optical signal is variably compensated.
[0011]
According to the first aspect of the invention, the first optical component capable of approximating the group delay characteristic with respect to the wavelength within the predetermined wavelength range by a quadratic function and the group delay characteristic with respect to the wavelength within the predetermined wavelength range can be approximated by the quadratic function. And a second optical component having a group delay characteristic opposite to the group delay characteristic of the first optical component, and an optical signal to be compensated for group delay with respect to the first optical component and the second optical component, respectively. Wavelength shift means provided with first and second input / output ports for output connection, an input port for inputting an optical signal to be subjected to group delay compensation, and an output port for outputting an optical signal after group delay compensation, Shifts the group delay characteristic of at least one of the first optical component or the second optical component with respect to the wavelength, and the optical signal to be compensated for the group delay includes the input port and the first input / output port. Via an optical path formed through the first optical component, the first input / output port, the second input / output port, the second optical component, the second input / output port, and the output port; The group delay dispersion of the optical signal is variably compensated by synthesizing the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means. .
[0012]
The tunable dispersion compensator according to claim 2 includes a first optical component that can approximate a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function, and a first light that guides an optical signal to be compensated for group delay. A first ferrule to which a second optical fiber for guiding an optical signal reflected from the fiber and the first optical component is attached; and provided between the first ferrule and the first optical component; A first dispersion compensation module having a first condenser lens for optically coupling an optical signal incident / exited from the second optical fiber, and a group delay characteristic with respect to a wavelength within the predetermined wavelength range is a quadratic function; A second optical component that can be approximated and has a group delay characteristic opposite to that of the first optical component, and the second optical fiber that guides the optical signal emitted from the first dispersion compensation module. Yo A second ferrule for attaching a third optical fiber for guiding an optical signal reflected from the second optical component; and a second ferrule provided between the second ferrule and the second optical component; A second dispersion compensation module having a second condenser lens for optically coupling optical signals incident and output from the three optical fibers, and a group delay characteristic of at least one of the first optical component and the second optical component; Wavelength shift means for shifting the wavelength relative to the wavelength, and the optical signal subject to group delay compensation is the first optical fiber, the first dispersion compensation module, the second optical fiber, the second dispersion compensation module, And the first optical component and the second optical component set by wavelength shift by the wavelength shift means via an optical path formed through the third optical fiber Characterized by variably compensate for the group delay dispersion of the optical signal by the group delay characteristics are synthesized to have.
[0013]
According to the second aspect of the invention, the first dispersion compensation module guides the optical signal to be compensated for the group delay and the first optical component whose group delay characteristic with respect to the wavelength within the predetermined wavelength range can be approximated by a quadratic function. A first ferrule for attaching a first optical fiber and a second optical fiber for guiding an optical signal reflected from the first optical component; and a first ferrule between the first ferrule and the first optical component. An optical fiber and a first condensing lens that optically couples optical signals incident and output from the second optical fiber, and the second dispersion compensation module has a group delay characteristic with respect to a wavelength within the predetermined wavelength range. A second optical component that can be approximated by a quadratic function and has a group delay characteristic opposite to that of the first optical component; and the first optical component that guides the optical signal emitted from the first dispersion compensation module. 2 light A second ferrule for attaching a third optical fiber for guiding an optical signal reflected from the optical fiber and the second optical component, and provided between the second ferrule and the second optical component, A second condensing lens that optically couples an optical signal incident / exited from the third optical fiber, and the wavelength shift means has at least one group delay characteristic of the first optical component or the second optical component. Are shifted with respect to the wavelength, and the optical signal to be compensated for the group delay includes the first optical fiber, the first dispersion compensation module, the second optical fiber, the second dispersion compensation module, and the third optical fiber. The group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path formed via And so as to variably compensate for the group delay dispersion of the optical signal by being.
[0014]
According to a third aspect of the present invention, the variable dispersion compensator includes a first optical component that can approximate a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function, and a group delay characteristic with respect to a wavelength within the predetermined wavelength range. A group delay characteristic that can be approximated by a function and that is contrary to the group delay characteristic of the first optical component, so that the optical signal reflected from the first optical component is directly incident on the second optical component. A second optical component disposed substantially opposite to the first optical component, and a light disposed substantially opposite to the first optical component and directly incident on the first optical component with a group delay compensation target optical signal An input means, a light output means that is disposed substantially opposite to the second optical component, directly receives and outputs an optical signal output from the second optical component, and the first optical component or the second optical component. Group delay characteristics of at least one of the parts Wavelength shift means for shifting relative to the wavelength, and the optical signal to be compensated for group delay is formed via the light input means, the first optical component, the second optical component, and the light output means. The group delay dispersion of the optical signal is made variable by synthesizing the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path. It is characterized by compensating.
[0015]
According to the third aspect of the present invention, the first optical component that can approximate the group delay characteristic with respect to the wavelength within the predetermined wavelength range by a quadratic function and the group delay characteristic with respect to the wavelength within the predetermined wavelength range can be approximated by the quadratic function. And the first optical component has a group delay property that is opposite to the group delay property of the first optical component, and the optical signal reflected from the first optical component is directly incident on the second optical component. A second optical component disposed substantially opposite to the component, a light input means disposed substantially opposite to the first optical component, and directly entering a group delay compensation target optical signal into the first optical component; A light output means that is disposed substantially opposite to the second optical component and that directly receives and outputs an optical signal output from the second optical component, and the wavelength shift means includes the first optical component or the optical component. At least one group of second optical components The optical characteristics of the group delay compensation target optical path formed through the optical input means, the first optical component, the second optical component, and the optical output means. The group delay dispersion of the optical signal is variably compensated by synthesizing the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means. I have to.
[0016]
A variable dispersion compensator according to a fourth aspect of the present invention is characterized in that, in the above invention, the first optical component and the second optical component are etalons having an all-pass filter function.
[0017]
According to the invention of claim 4, the first optical component and the second optical component are realized by an etalon having an all-pass filter function.
[0018]
The variable dispersion compensator according to claim 5 is the above invention, wherein one surface of the etalon has a reflectance of 98% or more to reflect the optical signal, and the other surface of the etalon is The surface on which the optical signal enters and exits, and the incident angle of the etalon on the other surface is within 4 °.
[0019]
According to the invention of claim 5, the incident angle of the etalon on the other surface is suppressed within 4 °, and an optical signal incident from the other surface of the etalon is 98 on one surface of the etalon. The light is reflected at a reflectance of at least% and emitted from one surface of the etalon so that a group delay characteristic is imparted to the optical signal.
[0020]
According to a sixth aspect of the present invention, in the tunable dispersion compensator according to the above invention, the reflectance of the optical signal reflected from the other surface of the etalon is changed on the other surface of the etalon, and the period of the etalon is changed. A characteristic group delay characteristic is set.
[0021]
According to the invention of claim 6, the reflectance of reflecting the optical signal reflected from the other surface of the etalon is changed on the other surface of the etalon, and the periodic group delay characteristic of the etalon is set. The quadratic function shape of the group delay characteristic in a predetermined frequency band can be arbitrarily set.
[0022]
According to a seventh aspect of the present invention, in the variable dispersion compensator according to the present invention, the group delay characteristics of the first optical component and the second optical component have substantially the same absolute value of the coefficient of the quadratic term of the quadratic function. Thus, the signs are different.
[0023]
According to the invention of claim 7, the quadratic function of each group delay characteristic of the first optical component and the second optical component has the same absolute value of the coefficient of the quadratic term of the quadratic function, and the sign Thus, the group delay characteristic obtained by synthesizing the quadratic function becomes a linear function type.
[0024]
The variable dispersion compensator according to claim 8 is the above invention, wherein the wavelength shift means includes a heater coupled to the etalon, and a control means for controlling an energization amount to the heater. The gap of the etalon is changed by heating from the etalon, and the group delay characteristic of the etalon is wavelength-shifted.
[0025]
According to the invention of claim 8, the control means of the wavelength shift means changes the gap of the etalon by heating from a heater, and shifts the group delay characteristic of the etalon.
[0026]
According to a ninth aspect of the present invention, in the tunable dispersion compensator according to the above invention, the wavelength shift unit includes: a Peltier element coupled to the etalon; and a control unit that controls an energization amount and an energization direction of the Peltier element. The etalon gap is changed by heating or cooling from the Peltier device, and the group delay characteristic of the etalon is wavelength-shifted.
[0027]
According to a ninth aspect of the present invention, the wavelength shift means includes: a Peltier element coupled to the etalon; a control means for controlling an energization amount and an energization direction of the Peltier element; and a control means for the wavelength shift means. The gap of the etalon is changed by heating or cooling from the element, and the group delay characteristic of the etalon is shifted in wavelength.
[0028]
The variable dispersion compensator according to claim 10 is the above invention, wherein the wavelength shift means includes a piezoelectric element coupled to the etalon and a control means for controlling a voltage applied to the piezoelectric element. The gap of the etalon is changed by a physical change of the piezoelectric element, and the group delay characteristic of the etalon is wavelength-shifted.
[0029]
According to the invention of claim 10, the control means of the wavelength shift means changes the gap of the etalon by a physical change of the piezoelectric element so as to shift the wavelength of the group delay characteristic of the etalon.
[0030]
The variable dispersion compensator according to claim 11 is the above invention, wherein the wavelength shift means includes a parallel plate inserted in a gap of the etalon, and a control means for controlling an inclination amount of the parallel plate. The optical path difference of the etalon gap is changed by the inclination of the parallel plate, and the group delay characteristic of the etalon is wavelength-shifted.
[0031]
According to the invention of claim 11, the control means of the wavelength shift means changes the optical path difference of the gap of the etalon by the inclination of the parallel plate, and shifts the wavelength of the group delay characteristic of the etalon.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
A variable dispersion compensator according to the present invention will be described below with reference to the accompanying drawings.
[0033]
(Embodiment 1)
First, a first embodiment of the present invention will be described. FIG. 1 is a diagram showing a configuration of a tunable dispersion compensator according to Embodiment 1 of the present invention. In FIG. 1, this tunable dispersion compensator includes an optical circulator 5, two etalons E1, E2 connected to the optical circulator, a Peltier element 6 coupled to the etalon E1, and a current to the Peltier element 6. It has a power supply 7 and a temperature control unit 8 that controls the amount of current and the direction of current flow to the Peltier element 6.
[0034]
In FIG. 1, an optical signal input from the input terminal T1 is input to the port P1 of the optical circulator 5 through the optical fiber 1, and is output from the port P2 to the etalon E1 through the optical path 2. The optical signal group-delayed by the group delay characteristic of the etalon E1 returns to the port P2 again via the optical path 2, and is output from the port P3 to the etalon E2 via the optical path 3. The optical signal group-delayed by the group delay characteristic of the etalon E2 returns to the port P3 again through the optical path 3, and is output to the output terminal T2 through the port P4 and the optical fiber 4.
[0035]
Here, the etalons E1 and E2 have a structure in which parallel etalon plates 12 and 15 are sandwiched between the partial reflection films 11 and 14 and the total reflection films 13 and 16, respectively. The optical signal input between the reflective films 13 and 16 is subjected to multiple reflection. The energy reflectance of the total reflection films 13 and 16 is 100%, and the energy reflectance R of the partial reflection films 11 and 14 is 100%. ₁ , R ₂ Are different and are about several percent to several tens of percent.
[0036]
As shown in FIG. 2, the optical signal is incident on the partial reflection film 11 perpendicularly from the partial reflection film 11 side, is totally reflected by the total reflection film 13, and a part of the reflected light is an energy reflectance R. ₁ Accordingly, the light is transmitted to the outside and the remaining optical signal is further totally reflected by the total reflection film 13. However, since the input optical signal is always totally reflected by the total reflection film 13, all energy of the optical signal is returned to the input side. However, the optical signal has a periodic phase delay with respect to the wavelength period determined by the optical thickness d of the etalon plate 12, that is, a group delay characteristic with respect to the wavelength. In other words, the etalon E1 functions as an all-pass filter that reflects all optical signals and changes only the phase. Note that the etalon E2 also has a function as an all-pass filter like the etalon E1.
[0037]
Here, the etalon E1 has a downwardly convex quadratic function type group delay characteristic, and the etalon E2 has an upwardly convex quadratic function type group delay characteristic. Then, the optical signals are given the respective group delay characteristics by the etalon E1 and the etalon E2, and finally output as an optical signal to which the combined group delay characteristics of the etalons E1 and E2 are given. In this case, the temperature control unit 8 controls the power supply 7 to control the amount of current and the energization direction for the Peltier element 6. Thereby, the etalon plate 12 is heated or cooled, the optical thickness d of the etalon plate 12 is changed, and the group delay characteristic of the etalon E1 is shifted in the wavelength direction. As a result, the combined group delay characteristics of the etalons E1 and E2 change, and a variable dispersion compensator capable of varying the group delay with respect to the optical signal is realized.
[0038]
Here, a change in the combined group delay characteristic using the two etalons E1 and E2 described above will be described in detail. First, the wavelength band of the optical signal that produces the desired group delay characteristic is changed to the wavelength λ. ₀ It is assumed that the wavelength band is ± a centering on. In addition, a tunable dispersion compensator having a group delay dispersion amount of −b to + b within the wavelength band to be used is realized. The wavelength shift of the group delay characteristic is performed only for the etalon E1, and is performed only in one direction with respect to the wavelength, and the wavelength variable amount is set to −s to + s. In this case, the group delay characteristic f required for the etalons E1 and E2 ₁ (x), f ₂ Each of (x) is represented by the following equations (1) and (2), where λ is the wavelength of the incident signal light.

C ₁ And c ₂ Select a value whose dispersion characteristic is close to the group delay characteristic indicated by the equations (1) and (2).
[0039]
As described above, the energy reflectivity of the total reflection films 13 and 16 is 100%, and the energy reflectivity of the partial reflection films 11 and 14 is R, respectively. ₁ , R ₂ And the optical thickness is d ₁ , D ₂ Then, transfer function H _ri (Λ) is expressed by the following equation (3). Note that i is 1 or 2, and j is an imaginary unit. The symbol “^” indicates a power.

The square of the absolute value of the transfer function is the energy reflectivity, the declination on the complex plane of the transfer function is the phase response, and the reverse of the sign of the frequency derivative of the phase response is the group delay characteristic. It is. Also, the optical thickness d ₁ , D ₂ Is the wavelength λ ₀ Thus, the group delay characteristic has an extreme value.
[0040]
Here, the relationship between the frequency period interval FSR and the optical thickness d is expressed by the following equation (4).
d = c / (2 × FSR) (4)
The wavelength λ ₀ In order for the group delay characteristic to have an extreme value, when the optical thickness d is etalon E1, λ ₀ / 4 is an even multiple of λ for etalon E2. ₀ Since it is necessary to be an odd multiple of / 4, the optical thickness d is set to a value in the vicinity of the calculated value of Expression (4).
[0041]
In the first embodiment, the wavelength λ ₀ Is 1550 nm, and this wavelength λ ₀ ± 0.19 nm was used as the wavelength band. Further, when the wavelength shift of the etalon E1 is set to −0.175 to +0.175 nm, it has a group delay dispersion amount of −30 to +30 ps / nm within the used wavelength band, and the frequency period interval FSR is 100 GHz. The tunable dispersion compensator is realized. The calculation results are expressed as plots shown in FIGS.
[0042]
Further, the energy reflectivities of the partial reflection films 11 and 14 of the etalons E1 and E2 are nonlinear so that the group delay characteristic has a minimum square error with the group delay characteristic shown in the equations (1) and (2). Obtained by fitting. Optical thickness d of etalon E1 ₁ = 967.50λ ₀ , Optical thickness d of etalon E2 ₂ = 967.75λ ₀ , The energy reflectance R of the partial reflection film 11 of the etalon E1 ₁ = 7.07%, and the energy reflectance R of the partial reflection film 14 of the etalon E2 ₂ = 1.53%. The etalon plates 12 and 15 can be made of glass plates. Here, when the etalon plates 12 and 15 are made of BK7, the wavelength λ ₀ Since the refractive index at = 1550 nm is 1.5014, the physical thicknesses of the etalon plates 12 and 15 are 998.82 μm and 999.08 μm, respectively.
[0043]
3 and 4 show the optical thickness d of the etalon plates 12 and 15, respectively. ₁ , D ₂ 967.50λ ₀ , 967.75λ ₀ FIG. 6 is a diagram illustrating group delay characteristics with respect to wavelength when the wavelength is not shifted. 3 and 4, the group delay characteristic of the etalon E1 shown in FIG. 3 and the group delay characteristic of the etalon E2 shown in FIG. ₀ In FIG. 2, the phase delay is π phase and exhibits a group delay characteristic of a quadratic function that is mutually opposite in the used wavelength band.
[0044]
FIG. 5 is a diagram showing the group delay characteristics when the group delay characteristics shown in FIG. 3 are wavelength-shifted and the group delay characteristics shown in FIG. 4 are combined. That is, each group delay characteristic for each wavelength shift is shown when the wavelength shift is performed and the optical signal passes through the etalon E1 and the etalon E2. In FIG. 5, when the etalon E2 is fixed with respect to the wavelength, the group delay characteristic of the etalon E1 is shifted in the wavelength direction by −0.175 nm, −0.070 nm, 0.000 nm, +0.070 nm, and +0.175 nm. The combined group delay characteristics of each etalon E1, E2 in FIG.
[0045]
FIG. 6 is an enlarged view of a combined group delay characteristic for each shift in the used wavelength band shown in FIG. In FIG. 6, when the wavelength is shifted by −0.175 nm, −0.070 nm, 0.000 nm, +0.070 nm, and +0.175 nm, lines L11, L12, L13, L14, and L15 are shown, respectively, and +30 ps / nm, respectively. , +12 ps / nm, 0 ps / nm, −12 ps / nm, and −30 ps / nm. These lines L11 to L15 show a substantially linear group delay change with respect to the wavelength. This is because the group delay characteristics in the used wavelength band of the etalons E1 and E2 are expressed as quadratic functions that are opposite to each other. That is, the etalon E1 is shown as a downward convex quadratic function, and the etalon E2 is shown as an upward convex quadratic function, and becomes a linear function when the respective quadratic functions are combined. However, since the group delay characteristics shown in FIGS. 3 and 4 are not ideal quadratic functions, the synthesized group delay characteristics are slightly fluctuating lines L11 to L15 as shown in FIG.
[0046]
The etalons E1 and E2 are coupled by components such as the optical circulator 5 so as not to interfere with each other. In the first embodiment, the final dispersion compensation amount is varied by shifting the wavelength of the group delay characteristic of the etalon E1. However, the present invention is not limited to this, and the group delay characteristic of the etalon E1 is fixed with respect to the wavelength. However, the group delay characteristic of the etalon E2 may be shifted in wavelength. Further, the group delay characteristic of only one of the etalons E1 and E2 may not be wavelength-shifted, but both the etalons E1 and E2 may be wavelength-shifted by the same or different amounts in different directions. The wavelength may be shifted by different amounts in the same direction.
[0047]
The number of etalons E1 and E2 is not limited to two, and a desired group delay characteristic may be obtained by a combination of three or more. However, it is necessary to have group delay characteristics that are opposite to each other.
[0048]
Further, the Peltier element 6 is coupled to the total reflection film 13 of the etalon E1 described above. However, the present invention is not limited thereto, and for example, a heater may be used. The etalon plate 12 uses a material having a large linear expansion temperature coefficient, and controls the optical thickness of the etalon plate 12 by passing a current through the heater and controlling the amount of heat generated by the temperature control unit 8. When the etalon plate 12 uses BK7, the wavelength shift amount due to the linear expansion coefficient of BK7 is about 10 pm / K. Therefore, the above-described wavelength shift of −0.175 nm to +0.175 nm changes the temperature range of 35K. Can be realized. Of course, the same applies when the Peltier element 6 is used.
[0049]
The optical circulator 5 shown in FIG. 1 uses a four-port optical circulator, but is not limited thereto, and a three-port optical circulator may be used. For example, in FIG. 7, an optical variable dispersion compensator is realized using a three-port optical circulator. In FIG. 7, three-port optical circulators 5a and 5b are provided in place of the four-port optical circulator 5, and light is transmitted between the output port P13 of the optical circulator 5a and the input port P21 of the optical circulator 5b. They are connected by a fiber 9. The optical fiber 1 is connected to the input port P11 of the optical circulator 5a, and the etalon E1 is connected to the input / output port P12. The etalon E2 is connected to the input / output port P22 of the optical circulator 5b, and the optical fiber 4 is connected to the output port P23. With such a configuration, the optical signal input from the input terminal T1 is given a group delay due to the etalon E1 via the optical circulator 5a, and then given a group delay due to the etalon E2 via the optical circulator 5b. The optical signal output from T2 is given a combined group delay of etalons E1 and E2, and is compensated for dispersion.
[0050]
In the first embodiment, since dispersion compensation is performed using the etalons E1 and E2 having a function as an all-pass filter, a variable dispersion compensator with little attenuation can be realized. The attenuation amount of each etalon E1 and E2 is about 0.1 dB, which is almost negligible compared to the 3 dB attenuation of light input / output by the optical circulator 5.
[0051]
In the first embodiment, the variable dispersion compensation is performed using the etalons E1 and E2 each having a group delay characteristic of a quadratic function type and having mutually opposite group delay characteristics. The wavelength dependency of the group delay characteristic in can be made linear, and dispersion compensation can be performed while suppressing the occurrence of secondary characteristics of the group delay, that is, third-order dispersion.
[0052]
Note that the etalons E1 and E2 described above have a quadratic function type group delay characteristic that is mutually opposite, but in this case, the constant of the quadratic term of the quadratic function has the same absolute value and the sign Are preferably different. This is because, when the group delay characteristics of the etalons E1 and E2 are combined, the group delay characteristics of the first order term or less are exhibited. The linear function in this case is the group delay characteristic in the used wavelength band. Further, the group delay characteristics of the etalons E1 and E2 are not limited to the quadratic function type, but may be a higher order function of the third order or higher. In this case, as in the quadratic function type, constants of quadratic terms or more in each etalon E1, E2 are canceled at the time of synthesis.
[0053]
In addition, the optical signal incident on the etalons E1 and E2 is incident perpendicularly to the plane formed by the etalon plates 12 and 15, but if the incident angle is about several degrees, the all-pass It is practical because it almost functions as a filter. However, in this case, it is necessary to set the optical thickness corresponding to the incident angle.
[0054]
(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the first embodiment described above, the optical signals are inputted to and outputted from the etalons E1 and E2 via the optical circulator 5. However, in the second embodiment, the optical circulator 5 or the optical circulators 5a and 5b are provided. Group delay compensation can be performed without using it.
[0055]
FIG. 8 is a diagram showing a configuration of a tunable dispersion compensator according to Embodiment 2 of the present invention. In FIG. 8, this tunable dispersion compensator has etalon modules M1 and M2 each including the etalons E1 and E2 shown in the first embodiment, and an optical fiber 1 is provided between the input terminal T1 and the etalon module M1. The etalon modules M1 and M2 are connected by an optical fiber 9, and the etalon module M2 and the output terminal T2 are connected by an optical fiber 4.
[0056]
The etalon modules M1 and M2 include ferrules 17a and 17b, lenses 18a and 18b, and etalons E1 and E2, respectively. The lenses 18a and 18b are aspherical lenses having a focal length of about 1.8 to 4.0 mm, preferably 3.0 mm, for example. The ferrules 17a and 17b are two-core ferrules to which two optical fibers that are the optical fibers 1 and 9 or the optical fibers 9 and 4 are attached. The ferrules 17a and 17b are formed of a material such as synthetic resin, glass or zirconia. Here, the optical fibers 1 and 9 or the optical fibers 9 and 4 are arranged at a pitch of 127 μm so that the incident angles to the etalons E1 and E2 approach 0 degrees, respectively.
[0057]
The ferrules 17a and 17b have two fiber holes 19a and 19b formed in a longitudinal direction in a cylindrical main body as shown in FIG. The ferrules 17a and 17b may be configured so that the optical signals from the optical fibers 1 and 9 or the optical fibers 9 and 4 are incident on and emitted from the surfaces disposed on the lenses 18a and 18b side. A guide hole or the like for inserting the optical fibers 1 and 9 or the optical fibers 9 and 4 may be formed on the surface (the optical fibers 1 and 9 or the optical fibers 9 and 4 side).
[0058]
As shown in the first embodiment, the etalon E1 is provided with the Peltier element 6, and the Peltier element 6 is controlled by the temperature control unit 8 so that the power source 7 is controlled. The energization direction and energization amount are controlled. As a result, the group delay characteristic of the etalon E1 is variably controlled.
[0059]
Here, when an optical signal is incident on the etalon module M1 via the input terminal T1 and the optical fiber 1, the optical signal is incident on the lens 18a via one fiber hole 19a of the ferrule 17a. The signal light is collected and incident on the etalon E1. The lens 18a condenses the optical signal reflected from the etalon E1 again in the fiber hole 19b of the ferrule 17a, and emits this optical signal to the etalon module M2 side through the optical fiber 9.
[0060]
On the etalon module M2 side, similarly to the etalon module M1 side, an optical signal incident through the optical fiber 9 enters the lens 18b through one fiber hole 19a of the ferrule 17b, and the lens 18b The light is collected and incident on the etalon E2. The lens 18b condenses the optical signal reflected from the etalon E2 again in the fiber hole 19b of the ferrule 17b, and emits the optical signal to the output terminal T2 through the optical fiber 4.
[0061]
In the second embodiment, as shown in FIG. 10, the outgoing fiber hole 19b is located at the center of the ferrule 17a, and the incident fiber hole 19a is displaced from the fiber hole 19b by an offset amount w. As shown in FIG. 11, the same amount of offset may be provided symmetrically from the center of the cross section of the ferrule 17a, and the fiber holes 19a and 19b may be separated by an offset amount w. Alternatively, as shown in FIG. 12, the fiber holes 19a and 19b are shifted asymmetrically from the center of the cross section by the offset amounts w1 and w2, respectively, so that the fiber holes 19a and 19b have an offset amount w. Good. Although an optical fiber for receiving an optical signal is attached to the fiber hole 19a, and an optical fiber for receiving reflected light from the etalons E1 and E2 is attached to the fiber hole 19b, the present invention is not limited to this. The outgoing optical fiber may be reversed. Furthermore, the selection of the fiber holes 19a and 19b to which the incoming and outgoing optical fibers are attached is arbitrary for each etalon module M1 and M2.
[0062]
According to the second embodiment, the variable dispersion compensation can be performed without using the optical circulator 5 or the optical circulators 5a and 5b, and the optical signal to be compensated for dispersion is not attenuated, thereby realizing a low loss variable dispersion compensator. it can.
[0063]
(Embodiment 3)
Next, a third embodiment of the present invention will be described. In the first embodiment described above, the optical signals are inputted to and outputted from the etalons E1 and E2 via the optical circulator 5, but in the third embodiment, the optical circulator 5 or the optical circulators 5a and 5b are provided. Without using it, group delay compensation can be performed directly by the same two etalons as the etalons E1 and E2.
[0064]
FIG. 13 is a diagram showing a configuration of a tunable dispersion compensator according to Embodiment 3 of the present invention. In FIG. 13, this tunable dispersion compensator includes the etalons E1 and E2, the Peltier element 6 coupled to the etalon E1, the power source 7 that supplies current to the Peltier element 6, and the amount of current for the Peltier element 6. A temperature control unit 8 that controls the energization direction is provided. However, the etalons E1 and E2 are not connected to the optical circulator 5, but the etalon E1 and the etalon E2 are arranged to face each other. That is, the partial reflection film 11 of the etalon E1 and the partial reflection film 14 of the etalon E2 are disposed so as to face each other. Further, the etalons E1 and E2 are shifted from each other because of optical input / output.
[0065]
In FIG. 13, the optical signal input from the optical fiber 21 is incident on the etalon E1 from the optical input unit 22 with an incident angle θ. The incident angle θ should be within 4 °. As described in the first embodiment, in order for this etalon E1 to function as an all-pass filter, it is necessary to make an optical signal incident perpendicularly to the etalon plate 12, but the etalons E1 and E2 are mirrors. Since the light input / output cannot be performed, the incident angle θ to the etalon E1 is slightly shifted from 0 ° to within 4 °. As a result, the etalon E1 does not function as a complete all-pass filter, but has almost the same function as the all-pass filter. Further, in this case, since the optical signal is incident obliquely on the etalon E1, in order to obtain the same effect as the interference due to the optical thickness of the etalon plate 12 in the first embodiment, the etalon plate according to the incident angle θ. The physical thickness of 12 needs to be increased.
[0066]
The etalon E2 is disposed at a position where the optical signal output from the etalon E1 is incident within an incident angle θ of 4 ° as in the etalon E1. Then, the optical signal reflected from the etalon E <b> 2 enters the optical output unit 23, and the dispersion-compensated optical signal is output to the optical fiber 24. Similar to the etalon plate 12 in the second embodiment, the physical thickness of the etalon plate 15 needs to be increased according to the incident angle.
[0067]
In such a configuration, the optical signal is incident on the etalon E1, is given a group delay due to the group delay characteristic by the etalon E1, and the optical signal to which this group delay is given is further incident on the etalon E2, and is caused by the etalon E2. A group delay due to the group delay characteristic is given, and an optical signal given a combined group delay by the etalons E1 and E2 is output to the optical fiber 24 via the optical output unit 23.
[0068]
In the third embodiment, since the optical signals input to and output from the etalons E1 and E2 are input and output obliquely, the optical output is slightly attenuated, but the optical circulator 5 or the optical circulators 5a and 5b are not used. The overall light output attenuation is small and can be realized with a simple configuration.
[0069]
(Embodiment 4)
Next, a fourth embodiment of the present invention will be described. In any of the first to third embodiments described above, the optical thickness of the etalon plate 12 of the etalon E1 is adjusted using the Peltier element 6, but in the fourth embodiment, the etalon plate 12 is formed using a piezo element. The optical thickness is adjusted.
[0070]
FIG. 14 is a diagram showing a configuration of an etalon used in the variable dispersion compensator according to the fourth embodiment of the present invention. The etalon 30 shown in FIG. 14 performs multiple reflection of an optical signal using an air gap 34 that is an air layer instead of the etalon plate 12. The etalon 30 is provided with a partial reflection film 33 on the optical signal incident side and a total reflection film 35 on the optical signal reflection side, with the air gap 34 sandwiched in parallel. The partial reflection film 33, the air gap 34, and the total reflection film 35 exhibit a function as an all-pass filter in the same manner as the etalon E1. The configuration excluding etalon 30, power supply 7 and temperature control unit 8 is the same as in the first to third embodiments.
[0071]
The partial reflection film 33 is fixed by the substrate 32, and the antireflection film 31 is coated on the optical signal incident side of the substrate 32. The substrate 32 fixes the partial reflection film 33 and transmits the optical signal. The antireflection film 31 is coated to prevent interference due to multiple reflection with the partial reflection film 33 and the total reflection film 35. On the other hand, the total reflection film 35 is fixed by the substrate 36, and a piezo element 37 is attached to the other surface of the substrate 36.
[0072]
A voltage adding unit 38 is connected to the piezo element 37, and a voltage control unit 39 is connected to the voltage adding unit 38. Under the control of the voltage control unit 39, the voltage adding unit 38 applies a voltage to the piezo element 37, and the piezo element 37 has an optical signal incident / exit direction, that is, an arrow, according to the voltage applied by the piezoelectric effect. Displaces in the A direction. As a result, the substrate 36 and the total reflection film 35 move in the direction of arrow A, the interval of the air gap 34 is adjusted, and the group delay characteristic as shown in FIG. 3 is set.
[0073]
In this third embodiment, the piezo element 37 is used in place of the Peltier element 6 to change the interval between multiple reflections, that is, the optical thickness. Therefore, when setting the group delay characteristic, other optical elements accompanying heating are used. The influence on can be eliminated.
[0074]
(Embodiment 5)
Next, a fifth embodiment of the present invention will be described. In the first to fourth embodiments described above, the optical thickness is set by using the power source and continuously energizing the Peltier element 6 or the piezo element 37. However, in the fifth embodiment, the optical thickness is set to the mechanical thickness. I am trying to set it.
[0075]
FIG. 15 is a diagram showing a configuration of an etalon used in the variable dispersion compensator according to the fifth embodiment of the present invention. The etalon 40 shown in FIG. 15 is the same as the etalon shown in the third embodiment. However, the piezoelectric element 37 is removed, a parallel plate 41 is inserted between the air gaps 34, a rotation drive unit 48 that rotates the parallel plate 41, and a rotation control unit 49 that controls the rotation drive unit 48 are provided. Yes. In order to prevent interference due to multiple reflection with the partial reflection film 33 and the total reflection film 35, both surfaces of the parallel plate 41 are subjected to antireflection treatment. In consideration of the optical thickness of the parallel plate 41, the etalon 40 has a physical thickness between the partial reflection film 33 and the total reflection film 35 determined and fixedly arranged. Here, the parallel plate 41 is rotatable in the direction of arrow B, and the optical path length with respect to the light incident / exit direction of the optical signal is changed by the rotation of the parallel plate 41, so The thickness changes. Thereby, a desired group delay characteristic can be set.
[0076]
In the fifth embodiment, unlike the Peltier element 6 and the piezo element 37, it is not necessary to always apply a current or a voltage, and once the optical thickness is set, the set optical thickness is not accompanied by a large change with time. Can be maintained stably.
[0077]
【The invention's effect】
As described above, according to the first aspect of the present invention, the first optical component whose group delay characteristic with respect to the wavelength within the predetermined wavelength range can be approximated by a quadratic function, and the group delay characteristic with respect to the wavelength within the predetermined wavelength range. A second optical component that can be approximated by a quadratic function and has a group delay characteristic that is opposite to the group delay characteristic of the first optical component; and a group delay compensation target for the first optical component and the second optical component A circulator having first and second input / output ports for input / output connection of the respective optical signals, an input port for inputting an optical signal subject to group delay compensation, and an output port for outputting the optical signal after group delay compensation; And a wavelength shift means shifts at least one group delay characteristic of the first optical component or the second optical component with respect to the wavelength, and the optical signal to be compensated for the group delay is transmitted to the input port Formed via a first input / output port, a first optical component, the first input / output port, the second input / output port, the second optical component, the second input / output port, and the output port The group delay dispersion of the optical signal is made variable by combining the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path. Therefore, flexible and fine dispersion compensation can be variably performed, and a desired group delay characteristic with little secondary dispersion can be realized with a simple configuration.
[0078]
According to the invention of claim 2, the first dispersion compensation module introduces the first optical component whose group delay characteristic with respect to the wavelength within the predetermined wavelength range can be approximated by a quadratic function and the optical signal to be subjected to group delay compensation. A first ferrule for attaching a first optical fiber to be waved and a second optical fiber for guiding an optical signal reflected from the first optical component; and provided between the first ferrule and the first optical component, A first condensing lens for optically coupling optical signals incident and output from the first optical fiber and the second optical fiber, wherein the second dispersion compensation module has a group delay with respect to a wavelength within the predetermined wavelength range. A second optical component whose characteristics can be approximated by a quadratic function and having a group delay characteristic opposite to that of the first optical component, and an optical signal emitted from the first dispersion compensation module are guided. Said A second ferrule for mounting an optical fiber and a third optical fiber for guiding an optical signal reflected from the second optical component; and the second optical fiber provided between the second ferrule and the second optical component. And a second condensing lens that optically couples an optical signal incident / exited from the third optical fiber, and the wavelength shift means has a group delay of at least one of the first optical component or the second optical component A characteristic is shifted with respect to the wavelength, and the optical signal to be compensated for the group delay includes the first optical fiber, the first dispersion compensation module, the second optical fiber, the second dispersion compensation module, and the third light. Each group delay characteristic of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via an optical path formed through the fiber. Since the group delay dispersion of the optical signal is variably compensated by combining the optical signals, flexible and fine dispersion compensation can be variably performed, and the optical circulator is not used, so that the low loss group Delay dispersion compensation can be performed, and desired group delay characteristics with little second order dispersion can be realized with a simple configuration.
[0079]
According to the invention of claim 3, the first optical component capable of approximating the group delay characteristic with respect to the wavelength within the predetermined wavelength range by a quadratic function, and the group delay characteristic with respect to the wavelength within the predetermined wavelength range are expressed by the quadratic function. The first optical component has a group delay characteristic that can be approximated and contradicts the group delay characteristic of the first optical component, and the optical signal reflected from the first optical component is directly incident on the second optical component. A second optical component disposed substantially opposite to one optical component; and an optical input means disposed substantially opposite to the first optical component and directly entering an optical signal subject to group delay compensation into the first optical component. And a light output means that is disposed substantially opposite to the second optical component and directly receives and outputs an optical signal output from the second optical component, and a wavelength shift means is provided for the first optical component. Alternatively, at least one of the second optical components The group delay characteristic is shifted with respect to the wavelength, and the optical signal to be compensated for group delay is formed via the light input means, the first optical component, the second optical component, and the light output means. The group delay dispersion of the optical signal is variably compensated by synthesizing the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path. Therefore, flexible and fine dispersion compensation can be variably performed, and since an optical circulator is not used, low-loss group delay compensation can be performed, and a desired group with little second order dispersion can be obtained. There is an effect that the delay characteristic can be realized by a simpler configuration.
[0080]
According to the invention of claim 4, since the first optical component and the second optical component are realized by an etalon having an all-pass filter function, flexible and fine dispersion compensation can be variably performed. In addition, there is an effect that dispersion compensation with a small insertion loss and a flat transmission characteristic in the use band can be variably performed.
[0081]
According to the invention of claim 5, the incident angle of the etalon on the other surface is suppressed within 4 °, and an optical signal incident from the other surface of the etalon is transmitted to the one surface of the etalon. Is reflected at a reflectance of 98% or more and is emitted from one surface of the etalon, thereby giving a group delay characteristic to the optical signal, so that the function as an all-pass filter is almost sufficient. The effect is that it is possible to provide a group delay with a small loss and a flat transmission characteristic.
[0082]
According to the invention of claim 6, the reflectance of reflecting the optical signal reflected from the other surface of the etalon is changed on the other surface of the etalon, and the periodic group delay characteristic of the etalon is set. In addition, since the quadratic function shape of the group delay characteristic in the predetermined frequency band can be arbitrarily set, the desired group delay characteristic can be obtained flexibly and finely.
[0083]
According to the invention of claim 7, the quadratic function of each group delay characteristic of the first optical component and the second optical component has substantially the same absolute value of the coefficient of the quadratic term of the quadratic function, Also, since the signs are different so that the group delay characteristic obtained by synthesizing the quadratic function becomes a linear function type, the group delay secondary characteristic, that is, a good group delay dispersion with a small third order dispersion is obtained. There is an effect that the compensation can be variably performed.
[0084]
According to the invention of claim 8, since the control means of the wavelength shift means changes the gap of the etalon by heating from the heater and shifts the group delay characteristic of the etalon, the wavelength shift means is simplified. With such a configuration, there is an effect that highly accurate dispersion compensation can be varied.
[0085]
According to a ninth aspect of the present invention, the wavelength shift means includes: a Peltier element coupled to the etalon; a control means for controlling an energization amount and an energization direction of the Peltier element; and a control means for the wavelength shift means. Since the etalon gap is changed by heating or cooling from the Peltier element and the group delay characteristic of the etalon is shifted in wavelength, highly accurate dispersion compensation can be varied with a simple configuration. There is an effect.
[0086]
According to the invention of claim 10, the control means of the wavelength shift means changes the gap of the etalon by a physical change of the piezoelectric element, and shifts the wavelength of the group delay characteristic of the etalon. There is an effect that dispersion compensation with high accuracy can be variably performed with a simple configuration in which generation of heat is suppressed.
[0087]
According to the invention of claim 11, the control means of the wavelength shift means changes the optical path difference of the gap of the etalon by the inclination of the parallel plate, and shifts the group delay characteristic of the etalon by wavelength. Therefore, the set wavelength shift state is maintained only by the mechanical setting without using the power source, and it is possible to realize a variable dispersion compensator with little change with time.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a tunable dispersion compensator according to a first embodiment of the present invention.
2 is an explanatory diagram showing an operation of the etalon shown in FIG. 1. FIG.
3 is a diagram showing group delay characteristics of the etalon shown in FIG. 1. FIG.
4 is a diagram showing group delay characteristics of another etalon shown in FIG. 1. FIG.
5 is a diagram showing variable synthesis group delay characteristics of each etalon shown in FIGS. 3 and 4. FIG.
6 is an enlarged view of a variable group delay characteristic in the used wavelength band shown in FIG.
FIG. 7 is a diagram showing a configuration of a modification of the tunable dispersion compensator that is Embodiment 1 of the present invention;
FIG. 8 is a diagram showing a configuration of a tunable dispersion compensator that is Embodiment 2 of the present invention;
9 is a perspective view showing a configuration of the ferrule shown in FIG. 8. FIG.
10 is a cross-sectional view showing the positional relationship between a pair of fiber holes of the ferrule shown in FIG.
11 is a cross-sectional view showing a first modification of the positional relationship between a pair of fiber holes of the ferrule shown in FIG. 8. FIG.
12 is a cross-sectional view showing a second modification of the positional relationship between a pair of fiber holes of the ferrule shown in FIG. 8. FIG.
FIG. 13 is a diagram showing a configuration of a tunable dispersion compensator according to a third embodiment of the present invention.
FIG. 14 is a diagram showing a configuration of an etalon used in a tunable dispersion compensator that is Embodiment 4 of the present invention.
FIG. 15 is a diagram showing a configuration of an etalon used in a tunable dispersion compensator that is Embodiment 5 of the present invention.
FIG. 16 is a diagram showing a group delay characteristic of a fiber used in a conventional fixed dispersion compensator.
FIG. 17 is a diagram showing a configuration of a tunable dispersion compensator using a conventional VIPA plate.
[Explanation of symbols]
E1, E1, 30, 40 Etalon
M1, M2 etalon module
1, 4, 9, 21, 24 Optical fiber
A few light paths
5,5a, 5b Optical circulator
6 Peltier elements
7 Power supply
8 Temperature controller
11, 14, 33 Partial reflection film
12,15 Etalon plate
13, 16, 35 Total reflection film
17a, 17b Ferrule
18a, 18b lens
19a, 19b Fiber hole
22 Light input section
23 Light output section
31 Antireflection film
32, 36 substrates
34 Air gap
37 Piezo elements
38 Voltage adding section
39 Voltage controller
41 Parallel plate
48 Rotation drive
49 Rotation controller

Claims (11)

A first optical component capable of approximating a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function;
A group delay characteristic with respect to a wavelength within the predetermined wavelength range can be approximated by a quadratic function, and the first optical component has a group delay characteristic having a sign of a coefficient of a quadratic term of the quadratic function different from the group delay characteristic of the first optical component. Two optical components,
First and second input / output ports for input / output connection of optical signals subject to group delay compensation to the first optical component and the second optical component, and input ports for inputting optical signals subject to group delay compensation, respectively A circulator having an output port for outputting an optical signal after group delay compensation;
Wavelength shifting means for shifting the group delay characteristic of at least one of the first optical component or the second optical component with respect to the wavelength;
And the optical signal to be compensated for group delay includes the input port, the first input / output port, the first optical component, the first input / output port, the second input / output port, and the second optical Each of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path formed through the component, the second input / output port, and the output port A variable dispersion compensator characterized in that group delay dispersion of the optical signal is variably compensated by combining group delay characteristics. A first optical component capable of approximating a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function;
A first ferrule for mounting a first optical fiber for guiding an optical signal to be compensated for group delay and a second optical fiber for guiding an optical signal reflected from the first optical component;
A first condenser lens that is provided between the first ferrule and the first optical component and optically couples an optical signal that enters and exits the first optical fiber and the second optical fiber;
A first dispersion compensation module having
A group delay characteristic with respect to a wavelength within the predetermined wavelength range can be approximated by a quadratic function, and the first optical component has a group delay characteristic having a sign of a coefficient of a quadratic term of the quadratic function different from the group delay characteristic of the first optical component. Two optical components,
A second ferrule for attaching the second optical fiber that guides the optical signal emitted from the first dispersion compensation module and the third optical fiber that guides the optical signal reflected from the second optical component;
A second condenser lens that is provided between the second ferrule and the second optical component and optically couples optical signals incident and output from the second optical fiber and the third optical fiber;
A second dispersion compensation module having
Wavelength shifting means for shifting the group delay characteristic of at least one of the first optical component or the second optical component with respect to the wavelength;
The optical signal to be compensated for group delay is formed through the first optical fiber, the first dispersion compensation module, the second optical fiber, the second dispersion compensation module, and the third optical fiber. The group delay dispersion of the optical signal is made variable by synthesizing the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by the wavelength shift means via the optical path. A variable dispersion compensator characterized by compensating. A first optical component capable of approximating a group delay characteristic with respect to a wavelength within a predetermined wavelength range by a quadratic function;
The group delay characteristic for a wavelength within the predetermined wavelength range can be approximated by a quadratic function, and the first optical component has a group delay characteristic in which the sign of the coefficient of the quadratic term of the quadratic function is different. A second optical component disposed substantially opposite to the first optical component so that an optical signal reflected from the first optical component is directly incident on the second optical component;
A light input means that is disposed substantially opposite to the first optical component and directly enters an optical signal subject to group delay compensation into the first optical component;
A light output means that is disposed substantially opposite to the second optical component and directly receives and outputs an optical signal output from the second optical component;
Wavelength shifting means for shifting the group delay characteristic of at least one of the first optical component or the second optical component with respect to the wavelength;
And the wavelength shift means passes through an optical path formed through the optical input means, the first optical component, the second optical component, and the optical output means. Variable dispersion compensation, wherein the group delay dispersion of the optical signal is variably compensated by combining the group delay characteristics of the first optical component and the second optical component set by the wavelength shift by vessel. The group delay characteristics of the first optical component and the second optical component have substantially the same absolute value of a coefficient of a quadratic term of a quadratic function. The variable dispersion compensator as described. The first optical component and the second optical component are:
The tunable dispersion compensator according to any one of claims 1 to 4 , wherein the tunable dispersion compensator is an etalon having an all-pass filter function. One surface of the etalon reflects the optical signal with a reflectance of 98% or more,
The other surface of the etalon is a surface on which the optical signal enters and exits,
6. The variable dispersion compensator according to claim 5 , wherein an incident angle of the etalon on the other surface is within 4 [deg.]. By changing the reflectivity for reflecting the optical signal reflected from the other surface of the etalon on the other surface of the etalon, according to claim 5 or 6, characterized in that setting the periodic group delay characteristic of the etalon A variable dispersion compensator as described in 1. The wavelength shift means includes
A heater coupled to the etalon;
Control means for controlling the energization amount to the heater;
A variable dispersion compensator according to any one of claims 5 to 7, wherein the optical thickness of the etalon is changed by heating from the heater to shift the wavelength of the group delay characteristic of the etalon. . The wavelength shift means includes
A Peltier element coupled to the etalon;
Control means for controlling the energization amount and energization direction of the Peltier element;
The optical dispersion of the etalon is changed by heating or cooling from the Peltier element, and the group delay characteristic of the etalon is wavelength-shifted, The variable dispersion according to any one of claims 5 to 7 Compensator. The wavelength shift means includes
A piezoelectric element coupled to the etalon;
Control means for controlling the voltage applied to the piezoelectric element;
8. The variable dispersion according to claim 5 , wherein the optical thickness of the etalon is changed by a physical change of the piezoelectric element, and the group delay characteristic of the etalon is shifted in wavelength. Compensator. The wavelength shift means includes
A parallel plate inserted in the gap of the etalon;
Control means for controlling the amount of inclination of the parallel plate;
The variable dispersion according to any one of claims 5 to 7, wherein an optical path difference of the gap of the etalon is changed by the inclination of the parallel plate, and a group delay characteristic of the etalon is shifted in wavelength. Compensator.

Images