JP3753674B2 - Optical amplifier - Google Patents

Description

【００６０】
なお、制御パラメータ２５としては、励起光源１１及び２２に与える電流値を記述したものを用いてもよい。
【００６１】
また、制御パラメータ２５は出力光のパワ−の組み合わせ毎に設けておき、制御部２６が外部より通知された所望の出力光のパワ−の組み合わせに応じて選択するようにしてもよい。
【００６２】
表２に、出力光のパワ−の組み合わせ毎に設けた制御パラメータ２５の例を示す。
【００６３】
表２に示す制御パラメ−タ２５によれば、任意の出力波長間偏差毎、出力光パワ−を得ることができる。本実施例における光送信器１の光増幅装置への入力パワーはλ１、λ２、λ３共に−２ｄＢｍに精度良く制御され、入力パワーの変動や入力波長間偏差がほとんどない。このような条件において、信号光を１２０ｋｍ伝送した後の光パワーを、各波長共−２５ｄＢｍ一定にするためには、伝送中の減衰の波長間偏差が相殺されるように、制御部２６によって例えば表２の網掛のパラメータ２５ａを選択すればよい。各波長の光出力パワ−は、伝送距離や伝送ファイバ３の損失に応じて最適な状態を求めるようにする。
【００６４】
【表２】

【００６５】
この場合も、制御パラメータ２５としては、励起光源１１及び２２に与える電流値を用いてもよい。また、出力パワーではなく、換算利得を制御するように設定してもよい。
【００６６】
ところで、光パワー調節部８は、図７に示すように構成しても良い。
【００６７】
図７に示した構成と、先に図３に示した構成との相違は、λ１、λ２、λ３全ての波長に対して光利得調節器１７ａ，１７ｂ，１７ｃを設けた点である。このように構成すれば、全く独立に各波長の光パワーを調節可能であり、調節精度も向上する。この場合、制御部１４において記憶する制御パラメータ２５には、λ１、の光利得調節器１７ａの励起光源２２ａの励起光パワ−も記述するようにする。なお、この構成は、同様に光利得調節器１７の数を増やすことにより、波長の多重数をλ１、λ２、λ３、λ４‥‥‥‥λＮのように増えた場合にも対応できる。
【００６８】
なお、この場合も、光利得調節器１７ａ，１７ｂ，１７ｃとして、半導体増幅装置を用いるようにしてもよい。
【００６９】
光パワー調節部８は、また、図８のように構成するようにしてもよい。
【００７０】
図８に示した構成によれば、前記光パワー調節部８は、光アイソレータ２７と希土類添加光ファイバ２８と、制御部１４によって制御される励起光源２９と光合波器３０と、外部から制御部１４によって制御される１種以上の相異なるλ１、λ２、λ３の波長の光源３１ａ，３１ｂ，３１ｃと該光源からの光を信号光とは逆方向に合波する１×４光スターカップラ３２とで構成される。
【００７１】
光源３１ａ，３１ｂ，３１ｃの光はそれぞれ多重した信号光の波長帯と一致している。このような構成により、例えば或る波長の信号光の光パワーが大きいときにはそれと同じ波長帯の光源３１の光出力を大きくすることにより、希土類添加光ファイバ２８内の増幅エネルギーを消費させ、その波長の信号光の増幅率を下げることができる。逆に或る波長の信号光の光パワーが小さいときにはそれと同じ波長帯の光源３１の光出力を小さくすることにより、希土類添加光ファイバ２８内の増幅エネルギーを保ち、その波長の信号光の増幅率を上げることができる。
【００７２】
図８の構成では、光源３１からの光を信号光とは逆方向に入射することにより、これらの光が信号光に混在することを防止している。また、希土類添加光ファイバ２８の前段に光アイソレータ２７によって、希土類添加光ファイバ２８内において増幅されて逆方向に進む光源３１からの光を遮断し、光パワー調節部８前段に配置される部品への影響を防止している。ここで、図８の構成でも、希土類添加光ファイバ２８にはエルビウム添加光ファイバを、励起光源２９には８３０ｎｍの半導体レーザーを用いた。そして、光出力を各波長とも＋１０ｄＢｍ、波長間偏差を０ｄＢに設定する為に、制御部２６によって表３のような制御パラメータ２５を選択した。
【００７３】
【表３】

【００７４】
なお、この構成においても、制御パラメータ２５は、励起光源１１及び２２や光源３１の電流値を用いてもよい。また光合波器３０、エルビウム添加光ファイバ２８、励起光源２９の部分を半導体増幅装置に置き換えてもよい。
【００７５】
以下、本発明に係る光増幅装置の第２の実施例について説明する。
【００７６】
図９に、本第２実施例に係る光増幅装置の構成を示す。
【００７７】
本第２実施例に係る光増幅装置の構成が、光ブ−スタアンプ２として適用した第１実施例に係る光増幅装置（図２参照）と異なる点は、光出力の一部を分岐する光分岐部３３、光分岐部３３によって分岐された光中に含まれるλ１、λ２、λ３の波長の光各々のパワ−もしくは波長間偏差を検知する出力モニタ部３４、入力光の一部を分岐する光分岐部３５、光分岐部３５によって分岐された光に含まれるλ１、λ２、λ３の波長の光の各々のパワ−もしくは波長間偏差を検知する入力モニタ部３６を備えた点である。また、本第２実施例においては、制御装置１４は、出力モニタ部３４と入力モニタ部３６との少なくとも一方により検出された各波長の光のパワーもしくは波長間偏差に応じて、出力光に含まれる各波長の光のパワ−あるいは波長間偏差が予め定められた値になるよう、前記光パワー調節器８内の各光利得調節器１７と、光増幅部９の励起光源１１を自動制御する。
【００７８】
このような構成によれば、光増幅装置への入力パワーや出力パワーや換算利得に変動があった場合でも、各波長の光出力パワ−や波長間偏差を予め定められた値に自動制御することができる。また何れかの波長の光のみに変動があった場合も、他の波長の出力パワ−に影響を与えることなく、この変動があった波長の光の出力パワ−を予め定められた値に制御することが可能となる。また、光増幅部９の励起光源１１などの経年劣化が生じた場合でも、常に各波長の光出力パワ−及び波長間偏差を予め定められた値に維持することができ、光増幅装置全体としての安定性と信頼性を向上させることが可能となる。
【００７９】
ただし、本第２実施例において新たに設けた光分岐部３３、出力モニタ部３４、光分岐部３５、入力モニタ部３６のうち、光分岐部３３と出力モニタ部３４のみ、もしくは、光分岐部３５と入力モニタ部３６のみを設けるようにしてもよい。
【００８０】
以下では、本第２実施例において新たに設けた光分岐部３３、出力モニタ部３４、光分岐部３５、入力モニタ部３６のうち、光分岐部３３、出力モニタ部３４のみを設けた場合について説明する。
【００８１】
図１０に、この場合の光増幅装置の、より詳細な構成を示す。
【００８２】
図中において、出力モニタ部３４は、１×３光スターカップラ３７、光カップラ３８ａ，３８ｂ，３８ｃ、光フィルタ２０ａ，２０ｂ，２０ｃを通過して再び光カップラ３９ａ，３９ｂ，３９ｃ、光検出器４０ａ，４０ｂ，４０ｃによって構成される。ここで、光フィルタ２０ａ，２０ｂ，２０ｃは、図３に示した光フィルタ２０ａ，２０ｂ，２０ｃである。すなわち、本第２実施例では、光フィルタ２０ａ，２０ｂ，２０ｃは、出力モニタ部３４の一部としても用いられる。また、他の部位は、図３に同符号で示した部位と同じものである。
【００８３】
さて、このような構成において、出力の一部から光カップラを用いた光分岐部３３によって分岐されたモニタ光は、１×３光スターカップラ３７によって再分岐し、それぞれ光パワー調節器８内部において、光カップラ３８ａ，３８ｂ，３８ｃにより、信号光とは逆方向に入射する。入射した光は各波長に対応する光フィルタ２０ａ，２０ｂ，２０ｃによって各々の波長の光が取り出された後に、さらに光カップラ３９ａ，３９ｂ，３９ｃにより一部が分岐される。分岐した各波長の光のパワ−は光検出器４０ａ，４０ｂ，４０ｃによって検出され、制御装置１４に通知される。
【００８４】
このように、図１０に示した構成では、光フィルタ２０ａ，２０ｂ，２０ｃは、モニタ光のうち必要な波長成分を抽出する機能と、前記第１実施例において果たした入力光を波長毎に分光する機能を共に果たしている。このような構成によれば、出力モニタ部３４のために新たに光フィルタを設ける必要が無いので、構成が簡略化させる。
【００８５】
また、本構成によれば、出力光から分岐したモニタ光は、光利得調節器１７ａ，１７ｂ，１７ｃの前段において光フィルタ２０ａ，２０ｂ，２０ｃに接続する光ファイバに入力するため、モニタ光が、光利得調節器１７ａ，１７ｂ，１７ｃの影響を被ることはない。逆に、モニタ光は、光利得調節器１７ａ，１７ｂ，１７ｃへの入力光とは逆方向に入射するため、入力光と同一の光ファイバを通過するにも関わらず、入力光自体に悪影響を与えない。また、本構成では、光カップラ３３を光アイソレータ１３の後段に配置することによって、光パワー調節部８から分岐された信号光が、光カップラ３３によってエルビウム添加光ファイバ１０に逆流せぬようになっている。
【００８６】
このように図１０に示した構成によれば、簡略な構成で出力モニタ部３４を実現することができる。なお、本構成は、波長の多重数をλ１、λ２、λ３、λ４‥‥‥‥のように増やしても１×３光スターカップラ３７の分岐数を増やすことにより拡張可能である。
【００８７】
次に、図１１に、制御装置１４の詳細な構成を示す。
【００８８】
図中、４０ａ，４０ｂ，４０ｃは光検出器、４１は比較回路、４２は所定の基準値を与える回路、４３は最大誤差判定回路、４４は選択回路、１１は励起光源、１７ａ，１７ｂ，１７ｃは光利得調節器である。
【００８９】
このような構成において、比較回路４１は、光検出器４０ａ，４０ｂ，４０ｃにより検出された各波長の光のパワーと、回路４２が与える基準値とを比較し、その誤差を出力する。最大誤差判定回路４３は誤差が最大である波長を求め、選択回路４４が、誤差が最大である波長の誤差を励起光源１１に伝達し、それ以外の波長の誤差を各波長に対応する光利得調節器（図では１７ｂ，１７ｃ）に伝達するよう制御する。これにより、検出した各波長の光のパワーのうち、誤差が最大である波長の光パワーが予め定められた値になるよう励起光源１１を制御し、同時にそれ以外の波長の光パワーが予め定められた値になるよう各波長に対応した光利得調節器（図では１７ｂ，１７ｃ）を制御することができる。また、誤差が与えられない光利得調節器（図では１７ａ）は、常に光損失が最小になるような利得を対応する波長の光に与える。ここで、回路４２は、誤差が、励起パワーの不足を示す基準値を与えるように予め設定する。
【００９０】
このような構成によれば、光利得調節器１７による光損失を最小にしても予め定められた値に到達しない波長が存在する時のみ、光増幅部９の励起光源１１のパワーが加増されるため、励起パワーの過剰な入力を防止することが可能となる。また、併せて光利得調節器（図では１７ｂ，１７ｃ）を制御することにより励起パワーがどの波長に対しても不足せぬようにすることができる。
【００９１】
従って光増幅装置全体の消費電力を低減でき、信頼性を向上させる。
【００９２】
ところで、図１０に示した光分岐部３３、出力モニタ部３４は、図１２に示すように構成するようにしてもよい。
【００９３】
図１２に示した構成では、光カップラ３９ａ，３９ｂ，３９ｃ、光受光器４０ａ，４０ｂ，４０ｃ、光カップラ４５、光合分波部１６によって出力モニタ部３４を構成している。図中の光合分波部１５および光合分波部１６は、それぞれ図４に示した構成を備えている。ただし、本第２実施例における光合分波部１５および光合分波部１６は、図４中の光フィルタ２０ａ，２０ｂ，２０ｃを共有しておらず、光合分波部１５と光合分波部１６のそれぞれに、光フィルタ２０ａ，２０ｂ，２０ｃの組を備えている。
【００９４】
このような構成において、光出力の一部を光分岐部である光カップラ３３によって分岐し、エルビウム添加光ファイバ１０の前段において、光カップラ４５によって入力光とは逆方向に入力する。ただし、本構成では、前記光パワー調節部８内部の合分波部１６を、光利得調節器１７ａ，１７ｂ，１７ｃによって調節した各波長の光を合波すると共に、信号光とは逆方向に入射した光をλ１、λ２、λ３の各波長に分波するように構成している。
【００９５】
合分波部１６によって、各波長毎に分波された各波長の光は、それぞれ光カップラ３９ａ，３９ｂ，３９ｃによって分岐し、光受光器４０ａ，４０ｂ，４０ｃにて、そのパワ−が検出される。
【００９６】
このような構成によれば、光合分波器１６を光パワー調節部８用と出力モニタ部３４用とで共有させたため、少ない構成要素で出力モニタ部３４を実現することが可能となる。また、モニタ光は信号光とは逆方向に入射するため、信号光と同一の光ファイバを通過するにも関わらず、信号光自体に悪影響を与えない。また、光カップラ３３を光アイソレータ１３の後段に配置することによって、光パワー調節部８から分岐された光が、光カップラ３３によってエルビウム添加光ファイバ１０に逆流せぬようにしている。なお、同様の構成によって、波長の多重数をλ１、λ２、λ３、λ４‥‥‥‥のように拡張することができる。
【００９７】
なお、図３に示したように任意の一つの波長の光に対する部の光利得調節器１７を設けない場合には、図１２に光増幅装置は図１３に示すように構成する。
【００９８】
図１３に示した構成が、図１２と異なる点は、光パワー調節部８内部の光利得調節器１７を一つ削減した点である。このような構成において、制御装置１４は、光利得調節器１７が設けられていない波長の光のモニタ光の検出パワーにより、光増幅部９に励起光源１１を制御するようにする。また、他の波長の光は、光利得調節器１７ｂ，１７ｃの調節により制御するようにする。
【００９９】
このように構成すれば、構成要素を減らすことが化できる。また制御装置による制御も簡易となる。
【０１００】
図１４に、図１３に示すように光増幅装置を構成した場合の制御装置１４の構成を示す。
【０１０１】
図１４中、４０ａ，４０ｂ，４０ｃは光検出器、４１は比較回路、４２は所定の基準値を与える回路、１１は励起光源、１７ｂ，１７ｃは光利得調節器である。回路４２が与える基準値は、比較回路４１が出力する光増幅部９の励起光源１１に対する制御量が、光利得調節器１７を設けなかった波長の光を光増幅部９が予め定められたパワ−にするような制御量となるように定めている。また、回路４２が与える基準値は、残りの波長の光のパワ−が予め定めたパワ−になるような制御量が比較回路４２より光利得調節器１７ｂ，１７ｃに対して出力するように定めている。つまり、光利得調節器１７を設けない波長に対しては励起光源１１の増減によって調節を行い、この光に対する光利得調節器１７を設ける波長の光の調節は光利得調節器１７ｂ，１７ｃの調節量の増減によって調節を行うようにしている。
【０１０２】
以下、本発明の第３の実施例について説明する。
【０１０３】
本第３実施例は、図１に示した光中継器４として適用する光増幅装置についてのものである。
【０１０４】
図１５に、本第３実施例に係る光増幅装置の構成を示す。
【０１０５】
図示するように、本第３実施例に係る光増幅装置が前記第２の実施例に係る光増幅装置と異なる点は、光パワー調節器８の前段にも光前置増幅部４６を設けた点である。
【０１０６】
本第３実施例では、このような構成によって、光増幅装置全体としてのＳ／Ｎ比劣化を防止すると共に、光伝送システム全体のＳ／Ｎ比劣化を防止する。
【０１０７】
図１６に、本第３実施例に係る光増幅装置の、より詳細な構成を示す。
【０１０８】
図中、出力モニタ部３４、光パワー調節部８の構成は、先に図１３に示した光増幅装置の構成と同じである。
【０１０９】
光前置増幅部４６はエルビウム添加光ファイバ４７と光合波器４８とで構成される。光カップラ４９は、励起光源１１からの励起光を分岐し、光増幅部９内部のエルビウム添加光ファイバ１１へ入力し励起する働きと、光前置増幅部４６内部のエルビウム添加光ファイバ４７へ入力し励起する働きを果たしている。
【０１１０】
本構成では光カップラ４９の分岐比を２０：８０としており、２０側を光前置増幅部４６へ、８０側を光増幅部９へ分岐している。例えば光パワー調節部８においてλ１の波長の光が−５ｄＢｍの損失を受ける場合、光前置増幅部４６において約１８ｄＢの増幅を行うことによって、光増幅装置全体のＳ／Ｎ比劣化を約６０％低減することができる。また、本構成における光前置増幅部４６はλ１、λ２、λ３の波長の光を同時に増幅するため、同時にλ２の波長の光もＳ／Ｎ比劣化を約６２％低減、λ３の波長の光もＳ／Ｎ比劣化を約６５％低減する
ところで、光増幅器では、一般に信号光の増幅と同時に、信号波長外に自然放出光と呼ばれる光の雑音成分が発生する。この自然放出光は光増幅器全体のＳ／Ｎ比を劣化させる要因となる。しかし、光フルタ２０によって信号光の波長近傍のみを抽出しているため、前記光パワー調節部８の前段からλ１、λ２、λ３と同時に入射する自然放出光成分は除去される。このため、この構成によれば、この意味においても光増幅装置全体としてのＳ／Ｎ比劣化を抑圧できる。
【０１１１】
以下、本発明の第４の実施例について説明する。
【０１１２】
本第４実施例は、図１に示した光プリアンプ５として適用する光増幅装置についてのものである。
【０１１３】
図１７に本第４実施例に係る光増幅装置の構成を示す。
【０１１４】
図示するように、本第４実施例が第１、第２、第３の実施例と異なる点は、光パワー調節部８と光増幅部９の前後を入れ替えた点である。一般に、光プリアンプ５では過大な光出力を必要としないため、このように光増幅部９の後段で、光パワー調節器８により出力パワ−や波長間偏差を調節してもよい。このように構成すれば、光増幅部９の前段における光損失を防止できるため、光増幅装置全体としてのＳ／Ｎ比劣化を抑圧できる光プリアンプ５を、簡単な構成で提供可能である。なお、図中光パワー調節部８と光アイソレータ１３の位置は入れ換えてもよい。
【０１１５】
以上、本発明の実施例について説明した。
【０１１６】
なお、以上の各実施例では、光増幅装置８において、各光利得調節器１７の前段に各光フィルタ２０を設けた。しかし、図１０に示した光増幅装置を除く他の光増幅装置においては、各光利得調節器１７の前段に各光フィルタ２０を設けず、各光利得調節器１７の後段に光フィルタ２０を設けるようにしてもよい。
【０１１７】
すなわち、図３の光増幅装置８において、光フィルタ２０ｂを光合波器２３ｂと光スタ−カプラ１９の間に配置し、光フィルタ２０ｃを、光合波器２３ｃと光スタ−カプラ１９の間に配置するように変更してもよい。また、同様に、図７の光増幅装置８において、光フィルタ２０ａを光合波器２３ａと光スタ−カプラ１９の間に配置し、光フィルタ２０ｂを光合波器２３ｂと光スタ−カプラ１９の間に配置し、光フィルタ２０ｃを光合波器２３ｃと光スタ−カプラ１９の間に配置するように変更してもよい。また、図１２、図１３、図１６の光増幅装置においては、光分波部１５内に光フィルタ２０を設けず、光分波部１５を光スタ−カプラ１８のみで構成するようにしてもよい。
【０１１８】
このようにしても、各光利得調節器１７の後段に設けた光フィルタ２０によって、各光利得調節器１７で増幅された光のうちから、各光フィルタを各光利得調節器１７の前段に設けた場合と同じ各波長の光のみが取り出され、光スタ−カプラ１９に入力するので、前述した各実施例と同様に、各光利得調節器１７で、それぞれ調節された各波長の光が光スタ−カプラ１９で合波されることになる。
【０１１９】
【発明の効果】
以上のように、本発明によれば各波長の光出力パワ−と波長間偏差を任意に調節することができる光増幅装置を提供することができる。
【図面の簡単な説明】
【図１】 本発明の第１実施例に係る光伝送システムの構成を示すブロック図である例を示す構成図である。
【図２】 本発明の第一の実施例に係る光増幅装置の構成を示すブロック図である。
【図３】 本発明の第一の実施例に係る光パワー調節部の第１の構成例を示すブロック図である。
【図４】 本発明の第一の実施例に係る光合分波器の構成を示すブロック図である。
【図５】 本発明の第一の実施例に係る光利得調節器の構成を示すブロック図である。
【図６】 本発明の第一の実施例に係る制御装置の構成を示すブロック図である。
【図７】 本発明の第一の実施例に係る光パワー調節部の第２の構成例を示すブロック図である。
【図８】 本発明の第一の実施例に係る光パワー調節部の第３の構成例を示すブロック図である。
【図９】 本発明の第二の実施例に係る光増幅装置の概略構成を示すブロック図である。
【図１０】 本発明の第二の実施例に係る光増幅装置の第１の構成例を示すブロック図である。
【図１１】 本発明の第二の実施例に係る光増幅装置の第１の構成例における制御装置の構成を示す図である。
【図１２】 本発明の第二の実施例に係る光増幅装置の第２の構成例を示すブロック図である。
【図１３】 本発明の第二の実施例に係る光増幅装置の第３の構成例を示すブロック図である。
【図１４】 本発明の第三の実施例に係る光増幅装置の第１の構成例における制御装置の構成を示すブロック図である。
【図１５】 本発明の第三の実施例に係る光増幅装置の構成を示すブロック図である。
【図１６】 本発明の第三の実施例に係る光増幅装置の詳細な構成を示すブロック図である。
【図１７】 本発明の第四の実施例に係る光増幅装置の構成を示すブロック図である。
【図１８】 従来の光増幅装置の構成を示すブロック図である。
【符号の説明】
１…光送信器、２…光ブースタアンプ、３…伝送ファイバ、４…光中継器、５…光プリアンプ、６…光受信器、７、１３、２７、５１、５２…光アイソレータ、９…光増幅部、１２、１６、２３、３０、４８、５３…光合波器、１０、２１、２８、４７、５０…希土類添加光ファイバ、１１、２２、２９、５４…励起光源、８…光パワー調節部、１４…制御装置、１５、３２…光分波部、１６…光合波部、１７…光利得調節器、１８、１９、３３、３５、３７、３８、３９、４５、４９、５６…光カップラ、２４…記憶部、２５…制御パラメータ、２６…制御部、３１…光源、３４…出力モニタ部、３６…入力モニタ部、４０、５７…光検出器、４２…基準値、４１…比較器、４３…最大誤差判定器、４４…選択器、４６…光前置増幅部、５５…光減衰器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical amplifying device used in an optical transmission system or the like.
[0002]
[Prior art]
In response to a demand for cost reduction of an optical communication system, wavelength division multiplexing optical transmission in which one or more types of signal light having different wavelengths are multiplexed and transmitted on a single transmission fiber is being studied. Further, as an amplifier used for such wavelength division multiplexing optical transmission, it is considered that an optical amplifying apparatus having a wide amplification wavelength band and capable of performing amplification with low noise is suitable.
[0003]
However, it is known that the rare earth-doped optical fiber and the semiconductor optical amplifier constituting this optical amplifying device have wavelength dependency of gain and cause an inter-wavelength deviation in optical output or gain of each wavelength after amplification. For this reason, a deviation between wavelengths occurs in the optical power after transmission. In particular, when performing multi-stage relaying using an optical amplifier, the inter-wavelength deviations of the optical power after transmission increase because the inter-wavelength deviations of the optical amplifying devices at each relay stage are integrated.
[0004]
Here, since the wavelength signal with the lowest power among the multiplexed wavelengths must be considered as the lower limit value of the received power after transmission, the maximum transmission distance in wavelength multiplexing transmission is limited by the wavelength signal with the lowest power. . Therefore, reducing the deviation between the output wavelengths of the optical amplifying device is important in extending the maximum repeater transmission distance.
[0005]
Therefore, for example, in the IEICE Technical Society OCS94-66, OPE94-88 (1994-11) “Flatening of multi-wavelength amplification characteristics of an optical fiber amplifier using fiber gain control”, the following technique is used. Proposed.
[0006]
FIG. 18 shows a configuration of an optical amplifying device according to this technique. In FIG. 18, 50 is an erbium-doped optical fiber, 51 and 52 are optical isolators, 53 is an optical multiplexer, 54 is an excitation light source, and 55 is an optical attenuator. Reference numeral 56 denotes an optical coupler that branches the output of the optical attenuator 55, and reference numeral 57 denotes a photodetector 57 that detects the branched light.
[0007]
In this technique, the deviation between each wavelength is minimized by controlling the fiber gain to be constant at 12 dB by an auto fiber gain controller (AFGC) with such an optical amplifying device. Further, an auto power controller (APC) by the optical attenuator 55 prevents the gain spectrum from being affected even if the repeater amplification factor changes.
[0008]
According to the theoretical calculation, according to such an optical amplifier, when the inter-wavelength deviation of the input light is assumed to be 0 dB, the gain deviation between the wavelengths when the length of the erbium-doped optical fiber 50 is 11 m. Has been reported to be minimum and below 0.12 dB. In addition, it has also been reported that the gain deviation after relaying light multiplexed with four wavelengths 60 times using such an optical amplifier is 1.5 dB or less.
[0009]
[Problems to be solved by the invention]
By the way, the optical loss of each wavelength during transmission differs depending on the difference in fiber loss in the relay section, the difference in optical power between adjacent wavelengths, and the like. Further, in the actual use state, the relay interval and the fiber loss in the section are not necessarily constant. For this reason, it is difficult to predict the inter-wavelength deviation and the optical power of each wavelength in the actual use state. Therefore, the optical amplifier shown in FIG. 18 has the following problems in actual use. That is, when the input level changes or an input wavelength deviation occurs, the output wavelength deviation cannot be set to 0 dB.
[0010]
Further, when the optical amplifier shown in FIG. 18 is used, for example, when an independent variation caused in one wavelength is to be suppressed due to an external factor, stable output power of other wavelengths is also suppressed at the same time. Therefore, the stability of the signal light wavelength output power is adversely affected.
[0011]
Further, in the optical amplifier shown in FIG. 18, since the optimum condition for eliminating the deviation between wavelengths depends on the gain of the optical amplifier, the output of the signal light cannot be freely set. That is, since the repeat interval is limited by the optical amplifier, the degree of freedom in system construction is limited. There is also a problem in that it is necessary to perform optimization for eliminating the inter-wavelength deviation for each relay section.
[0012]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical amplifying device capable of arbitrarily adjusting the wavelength-multiplexed optical output power of each wavelength and the inter-wavelength deviation of the light power of each wavelength. .
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a light having a plurality of signal lights of different wavelengths multiplexed before or after the optical amplifying means for amplifying the light multiplexed with a plurality of input signal lights of different wavelengths. Optical power adjusting means for receiving and amplifying or attenuating light of at least one wavelength included in the received light independently of light having a wavelength different from the wavelength of the light is provided. Further, there is provided control means for controlling the gain of amplification or attenuation performed by the optical power adjusting means and the gain of amplification performed by the optical amplification means.
[0014]
Here, in the rare earth-doped optical fiber and the semiconductor amplifier that are generally used as the optical amplifying means, the output power depends on the input power under a constant pumping power condition. The same applies to the case where multiplexed light obtained by multiplexing light of wavelengths λ1, λ2, λ3,. Therefore, it is possible to obtain an output depending on the increase or decrease of the input power by increasing or decreasing the input power of the optical amplifier for the light of each wavelength.
[0015]
Therefore, in the present invention, light multiplexed with a plurality of wavelengths is received before the optical amplification means, and at least one wavelength of light included in the received light is changed to light having a wavelength different from the wavelength of the light. Are provided with optical power adjusting means for independently amplifying or attenuating, and the optical power adjusting means adjusts the inter-wavelength deviation of the light of each wavelength input to the optical amplifying means, and thereafter, the optical amplifying means adjusts the wavelength of each wavelength. By simultaneously amplifying the multiplexed light, the power of each wavelength and the deviation between wavelengths are adjusted to desired values.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the optical amplifying device according to the present invention will be described below.
[0017]
First, the first embodiment will be described.
[0018]
FIG. 1 shows the configuration of the optical transmission system according to the first embodiment.
[0019]
In the figure, 1 is an optical transmitter for transmitting signal light, 2 is an optical booster amplifier for amplifying the power of the transmitted signal light, 3 is a transmission fiber for transmitting signal light, and 4 is for amplifying and relaying signal light. An optical repeater 5 is an optical preamplifier for amplifying the transmitted signal light, and 6 is an optical receiver for inputting the signal light amplified by the optical preamplifier.
[0020]
The optical amplifying apparatus according to the first embodiment can be used as the optical booster amplifier 2, the optical repeater 4, and the optical preamplifier 5 in such an optical transmission system.
[0021]
In the first embodiment, a case where the optical booster amplifier 2 is constituted by the optical amplifying apparatus according to the first embodiment will be described as a representative.
[0022]
Next, FIG. 2 shows a configuration of the optical booster amplifier 2.
[0023]
In the first embodiment, an input signal light Pin obtained by wavelength-multiplexing light of three types of wavelengths of λ1 = 1547 nm, λ2 = 1552 nm, and λ3 = 1557 nm is input from the optical transmitter 1 to the optical booster amplifier 2. .
[0024]
As shown in FIG. 2, the optical booster amplifier 2 includes an optical isolator 7, an optical power adjustment unit 8, an optical amplification unit 9, an optical isolator 13, and a control device 14.
[0025]
The optical amplifying unit 9 includes a rare earth-doped optical fiber 10, a pumping light source 11, and an optical multiplexer 12. In the first embodiment, an erbium-doped optical fiber is used as the rare earth-doped optical fiber 10. As the excitation light source 11, a 1480 nm semiconductor laser is used.
[0026]
In such an optical booster amplifier 2, the input signal light Pin is supplied to the optical power adjustment unit 8 via the optical isolator 7.
[0027]
The optical power adjusting unit 8 adjusts the optical power of the supplied light of each wavelength and the inter-wavelength deviation of the optical power. Then, the adjusted signal light is output to the optical amplifying unit 9.
[0028]
In the optical amplifying unit 9, the excitation light from the excitation light source 11 flows into the erbium-doped optical fiber 10 through the optical multiplexer 12 and excites the erbium-doped optical fiber 10. Therefore, the signal light input from the optical power adjusting unit 8 to the erbium-doped optical fiber 10 is amplified and output to the optical isolator 13 via the optical multiplexer 12. Then, the optical isolator 13 outputs the output signal light Pout in which lights having wavelengths of λ1, λ2, and λ3 are multiplexed. Here, the control of the excitation light quantity of the excitation light source 11 is performed by the control device 14.
[0029]
The pumping light in the optical amplifying unit 9 may be input from the front stage of the erbium-doped optical fiber 10. As the optical amplifying unit 9, a semiconductor amplifier may be used.
[0030]
The control device 14 adjusts the optical output and the inter-wavelength deviation for each wavelength by controlling the optical amplifying unit 9 and the optical power adjusting unit 8. Details thereof will be described later.
[0031]
Next, the optical power adjustment unit 8 will be described.
[0032]
FIG. 3 shows an internal configuration of the optical power adjustment unit 8.
[0033]
As shown in the figure, the optical power adjustment unit 8 includes optical multiplexing / demultiplexing units 15 and 16 that demultiplex the signal light for each wavelength of λ1, λ2, and λ3, and light that adjusts the optical power of the light having the wavelengths of λ1 and λ2. Gain adjusters 17b and 17c are provided. The optical multiplexing / demultiplexing units 15 and 16 are configured by combining two 1 × 3 optical star couplers 18 and 19 and optical filters 20a, 20b, and 20c. The optical gain adjusters 17b and 17c include rare-earth doped optical fibers 21b and 21c, pumping light sources 22b and 22c, and optical multiplexers 23b and 23c. In the first embodiment, light emitting diodes having a wavelength of 820 nm are used as the excitation light sources 22b and 22c, and erbium-doped optical fibers are used as the rare earth-doped optical fibers 21b and 21c.
[0034]
The inter-wavelength deviation can be set relatively with reference to light of one wavelength. For example, the gain of the optical amplifying unit 9 is determined by setting the pumping light quantity of the pumping light source 11 so that the light output power of the wavelength of λ1 becomes +10 dBm, and the wavelengths of λ2 and λ3 are set accordingly. If the light gain is adjusted to the excitation light amounts of the excitation light sources 22b and 22cc of the optical gain adjusters 17b and 17, the output power and inter-wavelength deviation of the light of each wavelength can be arbitrarily adjusted. Here, the control of the adjustment output from the excitation light sources 22b and 22c is performed by the control device 14.
[0035]
Although FIG. 3 shows the case where the optical gain adjuster for the light of the wavelength λ1 is not provided, an optical gain adjuster for the light of the wavelength λ1 is provided, and instead, the light of the wavelength λ2 or the light gain adjuster of the wavelength λ3 is provided. An optical gain adjuster for light of a wavelength may not be provided. Further, according to the characteristics of the erbium-doped optical fiber 10 used in the first embodiment, there is almost no deviation between wavelengths of 1544 nm and 1565 nm. Therefore, when the wavelength of 1544 nm and 1565 nm is used as one of the wavelengths to be multiplexed, the optical gain adjuster for only the other wavelengths without adjusting the gain by the optical multiplexing / demultiplexing of 1544 nm and 1565 nm or the optical gain adjuster 17. The adjustment by 17 may be performed. With this configuration, a simplified optical power adjustment unit 8 can be configured.
[0036]
Here, the operation of the optical multiplexing / demultiplexing units 15 and 16 of the optical power adjusting unit 8 will be described with reference to FIG. In FIG. 4, the optical gain adjusters 17b and 17c are not shown for clarity.
[0037]
Now, the light is divided into three equal parts by the 1 × 3 light star coupler 18 in the figure. Then, light of wavelengths λ1, λ2, and λ3 is output from the three optical filters 20a to 20c that respectively input the light equally divided into three. That is, the optical filter 20a having a passband of 1547 nm ± 1 nm passes only light having a wavelength of λ1 = 1547 nm, and the optical filter 20b having a passband of 1552 nm ± 1 nm passes only light having a wavelength of λ2 = 1552 nm, and has a wavelength of 1557 nm ± 1 nm. The optical filter 20c having a pass band passes only light of λ3 = 1557 nm.
[0038]
Among these lights, the lights having the wavelengths λ 2 and λ 3 are adjusted in gain by the optical gain adjusters 17 b and 17 c, respectively, and multiplexed by the 1 × 3 optical star coupler 19 with the light having the wavelength λ 1 output from the optical filter 20 a. Let
[0039]
As long as the optical filter 20a does not pass the wavelengths of λ2 and λ3, for example, a low-pass filter having a pass wavelength band of about 1548 nm or less may be used. Similarly, the optical filter 20c has λ1, λ2 For example, a high-pass filter having a pass wavelength band of about 1564 nm or more may be used.
[0040]
Here, each of the three wavelengths receives a substantially equal loss of −5 dB by the 1 × 3 optical star coupler 18, and each of the optical filters 20a, 20b, and 20c receives a substantially equal loss of −1 dB. With the optical star coupler 19, each of the three wavelengths suffers an approximately equal loss of -5 dB. Therefore, the optical loss of each wavelength due to the optical component is almost uniformly -11 dB. This indicates that the optical gain adjuster 17 is the only factor causing the inter-wavelength deviation in the optical power adjusting unit 8 and is not based on other optical components. When the number of multiplexed wavelengths is increased to λ1, λ2, λ3, λ4,..., ΛN, the number of branches of the star couplers 18 and 19, the number of optical filters 20, and the number of optical gain adjusters 17 are the same. Increase to.
[0041]
Next, the operation of the optical gain adjuster 17 will be described in detail with reference to FIG.
[0042]
In the first embodiment, since the same optical gain adjusters 17b and 17c are used, the optical gain adjuster 17b will be described here.
[0043]
Excitation light from the excitation light source 22b in the figure flows from the rear end of the erbium-doped optical fiber 21b by the optical multiplexer 23b and excites it. Light having a wavelength of λ2 is input from the front end of the erbium-doped optical fiber 21b, and is amplified or attenuated in the erbium-doped optical fiber 21b and then output. The excitation light source 22b is controlled by the control device 14. Here, the excitation light may be input from the front stage of the erbium-doped optical fiber 21. The optical gain adjuster 17b may use a semiconductor amplifier. In this case, the pumping current is controlled by the control device 14.
[0044]
In general, an optical amplifying medium used in an optical amplifier functions as a medium for amplifying light when pumping power is flowing in, but functions as a medium for attenuating light when the inflow amount is small or zero. Since the optical gain adjuster 17 according to the first embodiment is composed of the rare earth-doped optical fiber 21, the pumping light source 22, and the optical multiplexer 23, the optical gain adjuster having a negative gain when the pumping power is low. 17 and functions as an optical gain adjuster 17 having a positive gain when the pumping power is high.
[0045]
The conventional optical attenuator requires a control by an electric motor or the like from the outside, so that the configuration scale is large and the control speed is slow. On the other hand, in the present optical gain adjuster 17, the optical output power is increased only by increasing or decreasing the pumping power. Therefore, it is possible to easily and instantaneously adjust the light gain including the attenuation direction. Furthermore, since the amplification wavelength band has a width that sufficiently covers the band of signals to be multiplexed, the optical gain controller 17 having the same configuration can be used for each wavelength.
[0046]
In the first embodiment, the erbium-doped optical fiber 21b made of the same material as the erbium-doped optical fiber 10 of the optical amplifier 9 in the subsequent stage is used for the optical gain adjuster 17b for the following reason.
[0047]
That is, as described above, the control speed (about 1 to 5 mS) controlled by the control unit 14 by the pumping light source 11 of the optical amplifier 9 is substantially excited by the pumping light of the erbium-doped optical fiber 10 of the optical amplifier 9. It depends on the relaxation life time when Similarly, the adjustment speed of the optical gain adjuster 17b is determined by the relaxation lifetime when the erbium-doped optical fiber 21b is pumped by the pumping light, so that the speed is almost the same as the control speed of the optical amplifier 9. Therefore, it is possible to adjust at a high speed equivalent to the control speed by the excitation light quantity of the excitation light source 11 of the optical amplifier 9 controlled by the control unit 14 and to adversely affect the signal modulation waveform at the time of adjustment. Do not adjust too quickly. Further, the amplification wavelength band of the erbium-doped optical fiber 10 of the optical amplifier 9 and the adjustment wavelength band of the optical gain adjuster 17b can be made exactly the same.
[0048]
For the above reasons, the inventors consider that it is better to make the materials of the rare earth doped optical fiber 21b in the optical gain controller 17b and the rare earth doped optical fiber 10 of the optical amplifier 9 in the subsequent stage identical. However, another rare earth-doped optical fiber may be used instead of the erbium-doped optical fiber 21b.
[0049]
The length of the erbium-doped optical fiber 21b does not need excessive amplification characteristics, and may be about 3 m, which is about 1/10 of the length of the erbium-doped optical fiber 10 used for the optical amplifier 9. Just do it.
[0050]
Next, the output of the light emitting diode 22b having a wavelength of 830 nm used for the excitation light source 22b may be 20 mW or less. In general, when a rare earth-doped optical fiber is used as an amplifying medium, a high-power semiconductor laser having a wavelength band of 980 nm or 1480 nm, which can obtain high gain efficiency, is effective, but the pumping light source 22b used for the optical gain controller 17b is effective. Is sufficiently applicable to light sources having a wavelength band with low gain efficiency and light sources having low output. Therefore, the applicable range of the excitation light source 22b that can be used for the optical gain adjuster 17b is wide. For example, a low-power light source having a wavelength band in the vicinity of 520 nm, 660 nm, 820 nm, 980 nm, or 1480 nm can be used. In particular, since the light emitting diode 22b in the vicinity of 830 nm is available at a low price, according to the first embodiment using this, the optical gain controller 17b can be configured at a low cost.
[0051]
Next, the control device 14 will be described.
[0052]
As described above, the control device 14 controls the excitation light amount of the excitation light source 11 of the optical amplifier 9 and the excitation light amounts of the excitation light sources 22b and 22c of the optical gain adjusters 17b and 17c of the optical power adjustment unit 8 for each wavelength. Adjust optical output and inter-wavelength deviation.
[0053]
FIG. 6 shows the internal configuration of the control device 14.
[0054]
In the figure, the memory unit 24 stores several control parameters 25 in advance. For example, the parameter 25 is a set of the pumping light amount of the 1480 nm semiconductor laser 11 that is the pumping light source 11 of the optical amplifier 9 and the pumping light amounts of the light emitting diodes 22b and 22c of 820 nm that are the pumping light sources 22b and 22c in each optical gain controller 17 Are stored, and one of them is selected by the control unit 26 according to input information from the outside.
[0055]
The control unit 26 determines the excitation light amount of the 1480 nm semiconductor laser 11 that is the excitation light source 11 of the optical amplifier 9 and the excitation light amounts of the 820 nm light emitting diodes 22b and 22c that are the excitation light sources 22b and 22c in each optical gain adjuster 17. Control according to the selected parameter 25.
[0056]
Here, the control parameter 25 is provided for each combination of power of each wavelength of the input light, and the control unit 26 selects according to the actual input light power notified from the outside.
[0057]
Table 1 shows control parameters 25 provided for each combination of input light power of each wavelength.
[0058]
According to this control parameter 25, the optical output power can be set to +10 dBm for each wavelength and the inter-wavelength deviation can be set to 0 dB regardless of the combination of the power of each wavelength of the input light shown in Table 1. . In the first embodiment, the input power to the optical booster amplifier 2 of the optical transmitter 1 is accurately controlled to -2 dBm for λ1, λ2, and λ3, and there is almost no fluctuation in input power or deviation between input wavelengths. The parameter 26 in the shaded part of Table 1 below is selected by the part 26.
[0059]
[Table 1]

[0060]
As the control parameter 25, a value describing a current value given to the excitation light sources 11 and 22 may be used.
[0061]
The control parameter 25 may be provided for each output light power combination, and the control unit 26 may select the output light power according to the desired output light power combination notified from the outside.
[0062]
Table 2 shows an example of the control parameter 25 provided for each combination of output light power.
[0063]
According to the control parameter 25 shown in Table 2, output light power can be obtained for each output wavelength deviation. In this embodiment, the input power to the optical amplifying device of the optical transmitter 1 is accurately controlled to −2 dBm for all of λ1, λ2, and λ3, and there is almost no fluctuation in input power or deviation between input wavelengths. Under such conditions, in order to make the optical power after transmission of the signal light 120 km constant at each wavelength of −25 dBm, the control unit 26, for example, cancels the inter-wavelength deviation of attenuation during transmission. The shaded parameter 25a in Table 2 may be selected. The optical output power of each wavelength is obtained in an optimum state according to the transmission distance and the loss of the transmission fiber 3.
[0064]
[Table 2]

[0065]
Also in this case, as the control parameter 25, a current value given to the excitation light sources 11 and 22 may be used. Moreover, you may set so that not a output power but a conversion gain may be controlled.
[0066]
By the way, the optical power adjusting unit 8 may be configured as shown in FIG.
[0067]
The difference between the configuration shown in FIG. 7 and the configuration shown in FIG. 3 is that optical gain adjusters 17a, 17b, and 17c are provided for all wavelengths λ1, λ2, and λ3. If comprised in this way, the optical power of each wavelength can be adjusted completely independently, and adjustment precision will also improve. In this case, the control parameter 25 stored in the control unit 14 also describes the pumping light power of the pumping light source 22a of the optical gain adjuster 17a of λ1. This configuration can also be applied to the case where the number of multiplexed wavelengths is increased to λ1, λ2, λ3, λ4,..., ΛN by increasing the number of optical gain adjusters 17 in the same manner.
[0068]
In this case as well, a semiconductor amplifier may be used as the optical gain adjusters 17a, 17b, and 17c.
[0069]
The optical power adjustment unit 8 may be configured as shown in FIG.
[0070]
According to the configuration shown in FIG. 8, the optical power adjusting unit 8 includes an optical isolator 27, a rare earth-doped optical fiber 28, a pumping light source 29 and an optical multiplexer 30 controlled by the control unit 14, and a control unit from the outside. A light source 31a, 31b, 31c having different wavelengths of λ1, λ2, and λ3 controlled by 14 and a 1 × 4 optical star coupler 32 that multiplexes light from the light source in the opposite direction to the signal light, and Consists of.
[0071]
The light from the light sources 31a, 31b, and 31c coincides with the wavelength band of the multiplexed signal light. With such a configuration, for example, when the optical power of signal light having a certain wavelength is large, the optical output of the light source 31 having the same wavelength band is increased, thereby consuming the amplification energy in the rare earth-doped optical fiber 28 and its wavelength. The signal light gain can be reduced. Conversely, when the optical power of signal light of a certain wavelength is low, the optical output of the light source 31 of the same wavelength band is reduced, thereby maintaining the amplification energy in the rare earth-doped optical fiber 28 and the amplification factor of the signal light of that wavelength. Can be raised.
[0072]
In the configuration of FIG. 8, the light from the light source 31 is incident in the opposite direction to the signal light, thereby preventing the light from being mixed in the signal light. In addition, the optical isolator 27 in front of the rare earth-doped optical fiber 28 blocks light from the light source 31 that is amplified in the rare earth doped optical fiber 28 and travels in the reverse direction, to a component arranged in the previous stage of the optical power adjusting unit 8. To prevent the effects of Here, also in the configuration of FIG. 8, an erbium-doped optical fiber is used for the rare earth-doped optical fiber 28, and a 830 nm semiconductor laser is used for the excitation light source 29. Then, in order to set the optical output to +10 dBm for each wavelength and the inter-wavelength deviation to 0 dB, the control parameter 25 as shown in Table 3 was selected by the control unit 26.
[0073]
[Table 3]

[0074]
Also in this configuration, the control parameter 25 may use the current values of the excitation light sources 11 and 22 and the light source 31. Further, the optical multiplexer 30, the erbium-doped optical fiber 28, and the pumping light source 29 may be replaced with a semiconductor amplifier.
[0075]
A second embodiment of the optical amplifying device according to the present invention will be described below.
[0076]
FIG. 9 shows the configuration of the optical amplifying device according to the second embodiment.
[0077]
The configuration of the optical amplifying apparatus according to the second embodiment is different from the optical amplifying apparatus according to the first embodiment applied as the optical booster amplifier 2 (see FIG. 2). A branching unit 33, an output monitoring unit 34 for detecting the power or wavelength deviation of each of the light beams having the wavelengths λ1, λ2, and λ3 included in the light branched by the light branching unit 33, and a part of the input light are branched. The optical branching unit 35 is provided with an input monitoring unit 36 that detects the power or wavelength deviation of light having wavelengths λ1, λ2, and λ3 included in the light branched by the optical branching unit 35. Further, in the second embodiment, the control device 14 is included in the output light according to the power or inter-wavelength deviation of the light of each wavelength detected by at least one of the output monitor unit 34 and the input monitor unit 36. Each optical gain adjuster 17 in the optical power adjuster 8 and the pumping light source 11 of the optical amplifying unit 9 are automatically controlled so that the power of each wavelength or the deviation between wavelengths becomes a predetermined value. .
[0078]
According to such a configuration, even when there is a change in input power, output power, or conversion gain to the optical amplifying device, the optical output power and inter-wavelength deviation of each wavelength are automatically controlled to predetermined values. be able to. Also, even if there is a change in the light of any wavelength, the output power of the light having the changed wavelength is controlled to a predetermined value without affecting the output power of the other wavelengths. It becomes possible to do. Further, even when the pump light source 11 or the like of the optical amplifying unit 9 deteriorates over time, the optical output power of each wavelength and the wavelength deviation can always be maintained at predetermined values, so that the entire optical amplifying device can be maintained. It is possible to improve the stability and reliability.
[0079]
However, among the optical branching unit 33, the output monitoring unit 34, the optical branching unit 35, and the input monitoring unit 36 newly provided in the second embodiment, only the optical branching unit 33 and the output monitoring unit 34, or the optical branching unit. Only 35 and the input monitor unit 36 may be provided.
[0080]
Hereinafter, among the optical branching unit 33, the output monitoring unit 34, the optical branching unit 35, and the input monitoring unit 36 newly provided in the second embodiment, only the optical branching unit 33 and the output monitoring unit 34 are provided. explain.
[0081]
FIG. 10 shows a more detailed configuration of the optical amplification device in this case.
[0082]
In the figure, the output monitor unit 34 passes through the 1 × 3 optical star coupler 37, the optical couplers 38a, 38b, 38c, the optical filters 20a, 20b, 20c, and again, the optical couplers 39a, 39b, 39c, and the photodetector 40a. , 40b, 40c. Here, the optical filters 20a, 20b, and 20c are the optical filters 20a, 20b, and 20c shown in FIG. That is, in the second embodiment, the optical filters 20a, 20b, and 20c are also used as a part of the output monitor unit 34. Other parts are the same as the parts indicated by the same reference numerals in FIG.
[0083]
Now, in such a configuration, the monitor light branched by the optical branching unit 33 using the optical coupler from a part of the output is re-branched by the 1 × 3 optical star coupler 37, and each inside the optical power adjuster 8. The optical couplers 38a, 38b, and 38c enter the signal light in the opposite direction. After the incident light is extracted by the optical filters 20a, 20b, and 20c corresponding to the respective wavelengths, a part of the incident light is further branched by the optical couplers 39a, 39b, and 39c. The power of the branched light of each wavelength is detected by the photodetectors 40a, 40b, and 40c and notified to the control device 14.
[0084]
As described above, in the configuration shown in FIG. 10, the optical filters 20a, 20b, and 20c extract the necessary wavelength components from the monitor light and split the input light performed in the first embodiment for each wavelength. It plays the function to do together. According to such a configuration, it is not necessary to newly provide an optical filter for the output monitor unit 34, so the configuration is simplified.
[0085]
Further, according to this configuration, the monitor light branched from the output light is input to the optical fiber connected to the optical filters 20a, 20b, and 20c in the previous stage of the optical gain adjusters 17a, 17b, and 17c. The optical gain adjusters 17a, 17b, and 17c are not affected. On the contrary, the monitor light is incident in the opposite direction to the input light to the optical gain adjusters 17a, 17b, and 17c. Therefore, the monitor light has an adverse effect on the input light itself despite passing through the same optical fiber as the input light. Don't give. Further, in this configuration, the optical coupler 33 is disposed at the subsequent stage of the optical isolator 13, so that the signal light branched from the optical power adjusting unit 8 does not flow backward to the erbium-doped optical fiber 10 by the optical coupler 33. ing.
[0086]
As described above, according to the configuration shown in FIG. 10, the output monitor unit 34 can be realized with a simple configuration. Note that this configuration can be expanded by increasing the number of branches of the 1 × 3 optical star coupler 37 even if the number of multiplexed wavelengths is increased to λ1, λ2, λ3, λ4,.
[0087]
Next, FIG. 11 shows a detailed configuration of the control device 14.
[0088]
In the figure, 40a, 40b and 40c are photodetectors, 41 is a comparison circuit, 42 is a circuit which gives a predetermined reference value, 43 is a maximum error determination circuit, 44 is a selection circuit, 11 is an excitation light source, 17a, 17b and 17c. Is an optical gain controller.
[0089]
In such a configuration, the comparison circuit 41 compares the light power of each wavelength detected by the photodetectors 40a, 40b, and 40c with the reference value given by the circuit 42, and outputs an error. The maximum error determination circuit 43 obtains the wavelength with the maximum error, the selection circuit 44 transmits the error of the wavelength with the maximum error to the pumping light source 11, and the optical gain corresponding to each wavelength with the error of the other wavelengths. Control is performed so as to transmit to the regulator (17b, 17c in the figure). As a result, the pumping light source 11 is controlled so that the optical power of the wavelength with the largest error among the detected optical powers of the respective wavelengths becomes a predetermined value, and at the same time, the optical powers of the other wavelengths are predetermined. The optical gain adjusters (in the figure, 17b and 17c) corresponding to each wavelength can be controlled so that the obtained values are obtained. Further, the optical gain adjuster (17a in the figure) to which no error is given always gives the light of the corresponding wavelength such that the optical loss is minimized. Here, the circuit 42 is preset so that the error gives a reference value indicating a lack of excitation power.
[0090]
According to such a configuration, the power of the pumping light source 11 of the optical amplifying unit 9 is increased only when there is a wavelength that does not reach a predetermined value even if the optical loss by the optical gain adjuster 17 is minimized. Therefore, it is possible to prevent an excessive input of excitation power. In addition, by controlling the optical gain adjuster (in the figure, 17b and 17c), it is possible to prevent the pump power from becoming insufficient for any wavelength.
[0091]
Therefore, the power consumption of the entire optical amplifying device can be reduced and the reliability is improved.
[0092]
Incidentally, the optical branching unit 33 and the output monitoring unit 34 shown in FIG. 10 may be configured as shown in FIG.
[0093]
In the configuration illustrated in FIG. 12, the output monitor unit 34 is configured by the optical couplers 39 a, 39 b, 39 c, the optical receivers 40 a, 40 b, 40 c, the optical coupler 45, and the optical multiplexing / demultiplexing unit 16. The optical multiplexing / demultiplexing unit 15 and the optical multiplexing / demultiplexing unit 16 in the figure each have the configuration shown in FIG. However, the optical multiplexing / demultiplexing unit 15 and the optical multiplexing / demultiplexing unit 16 in the second embodiment do not share the optical filters 20a, 20b, and 20c in FIG. Each includes a set of optical filters 20a, 20b, and 20c.
[0094]
In such a configuration, a part of the optical output is branched by the optical coupler 33 which is an optical branching unit, and is input in the opposite direction to the input light by the optical coupler 45 in the previous stage of the erbium-doped optical fiber 10. However, in this configuration, the multiplexing / demultiplexing unit 16 in the optical power adjusting unit 8 combines the light of each wavelength adjusted by the optical gain adjusters 17a, 17b, and 17c, and in the opposite direction to the signal light. The incident light is demultiplexed into wavelengths of λ1, λ2, and λ3.
[0095]
The light of each wavelength demultiplexed for each wavelength by the multiplexing / demultiplexing unit 16 is branched by the optical couplers 39a, 39b, 39c, and the power is detected by the optical receivers 40a, 40b, 40c. The
[0096]
According to such a configuration, since the optical multiplexer / demultiplexer 16 is shared by the optical power adjustment unit 8 and the output monitor unit 34, the output monitor unit 34 can be realized with a small number of components. Further, since the monitor light is incident in the opposite direction to the signal light, it does not adversely affect the signal light itself even though it passes through the same optical fiber as the signal light. Further, by arranging the optical coupler 33 at the subsequent stage of the optical isolator 13, the light branched from the optical power adjusting unit 8 is prevented from flowing back to the erbium-doped optical fiber 10 by the optical coupler 33. Note that the number of multiplexed wavelengths can be expanded to λ1, λ2, λ3, λ4,.
[0097]
If the optical gain adjuster 17 is not provided for the light of any one wavelength as shown in FIG. 3, the optical amplifying device shown in FIG. 12 is configured as shown in FIG.
[0098]
The configuration shown in FIG. 13 is different from FIG. 12 in that the optical gain adjuster 17 in the optical power adjuster 8 is reduced by one. In such a configuration, the control device 14 causes the optical amplification unit 9 to control the pumping light source 11 with the detection power of the monitor light having the wavelength for which the optical gain adjuster 17 is not provided. Further, light of other wavelengths is controlled by adjusting the optical gain adjusters 17b and 17c.
[0099]
If comprised in this way, a component can be reduced. Also, control by the control device is simplified.
[0100]
FIG. 14 shows the configuration of the control device 14 when the optical amplification device is configured as shown in FIG.
[0101]
In FIG. 14, 40a, 40b, and 40c are photodetectors, 41 is a comparison circuit, 42 is a circuit that gives a predetermined reference value, 11 is an excitation light source, and 17b and 17c are optical gain adjusters. The reference value given by the circuit 42 is such that the control amount for the pumping light source 11 of the optical amplifying unit 9 output from the comparing circuit 41 is a predetermined power for the light having the wavelength for which the optical gain adjuster 17 is not provided. The control amount is set to be −. The reference value given by the circuit 42 is determined such that a control amount is output from the comparison circuit 42 to the optical gain adjusters 17b and 17c so that the power of light of the remaining wavelengths becomes a predetermined power. ing. In other words, the wavelength at which the optical gain adjuster 17 is not provided is adjusted by increasing or decreasing the pumping light source 11, and the adjustment of the light having the wavelength at which the optical gain adjuster 17 is provided is adjusted by the optical gain adjusters 17b and 17c. Adjustments are made by increasing or decreasing the amount.
[0102]
The third embodiment of the present invention will be described below.
[0103]
The third embodiment relates to an optical amplifying device applied as the optical repeater 4 shown in FIG.
[0104]
FIG. 15 shows the configuration of the optical amplifying device according to the third embodiment.
[0105]
As shown in the figure, the optical amplifying device according to the third embodiment is different from the optical amplifying device according to the second embodiment in that an optical preamplifier 46 is also provided at the front stage of the optical power adjuster 8. Is a point.
[0106]
In the third embodiment, with such a configuration, the S / N ratio deterioration of the entire optical amplifying apparatus is prevented, and the S / N ratio deterioration of the entire optical transmission system is prevented.
[0107]
FIG. 16 shows a more detailed configuration of the optical amplifying device according to the third embodiment.
[0108]
In the figure, the configurations of the output monitor unit 34 and the optical power adjustment unit 8 are the same as the configurations of the optical amplifying device shown in FIG.
[0109]
The optical preamplifier 46 includes an erbium-doped optical fiber 47 and an optical multiplexer 48. The optical coupler 49 branches the pumping light from the pumping light source 11 and inputs it to the erbium-doped optical fiber 11 in the optical amplifying unit 9 and pumps it, and inputs it to the erbium-doped optical fiber 47 in the optical preamplifier 46. It plays an exciting role.
[0110]
In this configuration, the branching ratio of the optical coupler 49 is 20:80, and the 20 side is branched to the optical preamplifier 46 and the 80 side is branched to the optical amplifier 9. For example, when light having a wavelength of λ1 receives a loss of −5 dBm in the optical power adjustment unit 8, the optical preamplification unit 46 amplifies about 18 dB, thereby reducing the S / N ratio degradation of the entire optical amplification device by about 60. % Can be reduced. In addition, since the optical preamplifier 46 in this configuration simultaneously amplifies the light with the wavelengths λ1, λ2, and λ3, the light with the wavelength λ2 also reduces the S / N ratio deterioration by about 62%, and the light with the wavelength λ3. Reduces S / N ratio degradation by about 65%
By the way, in an optical amplifier, in general, a noise component of light called spontaneous emission is generated outside a signal wavelength simultaneously with amplification of signal light. This spontaneously emitted light becomes a factor that degrades the S / N ratio of the entire optical amplifier. However, since only the vicinity of the wavelength of the signal light is extracted by the optical filter 20, the spontaneously emitted light components incident simultaneously with λ1, λ2, and λ3 from the preceding stage of the optical power adjusting unit 8 are removed. For this reason, according to this configuration, the S / N ratio deterioration of the entire optical amplifying apparatus can be suppressed also in this sense.
[0111]
The fourth embodiment of the present invention will be described below.
[0112]
The fourth embodiment relates to an optical amplifying apparatus applied as the optical preamplifier 5 shown in FIG.
[0113]
FIG. 17 shows the configuration of the optical amplifying device according to the fourth embodiment.
[0114]
As shown in the figure, the fourth embodiment is different from the first, second, and third embodiments in that the front and rear of the optical power adjusting unit 8 and the optical amplifying unit 9 are interchanged. In general, since the optical preamplifier 5 does not require an excessive optical output, the output power and the wavelength deviation may be adjusted by the optical power adjuster 8 after the optical amplifying unit 9 in this way. With this configuration, optical loss in the previous stage of the optical amplifying unit 9 can be prevented, so that the optical preamplifier 5 capable of suppressing the S / N ratio deterioration of the entire optical amplifying device can be provided with a simple configuration. In the figure, the positions of the optical power adjusting unit 8 and the optical isolator 13 may be interchanged.
[0115]
The embodiment of the present invention has been described above.
[0116]
In each of the above-described embodiments, each optical filter 20 is provided in the preceding stage of each optical gain adjuster 17 in the optical amplifying device 8. However, in other optical amplifying devices other than the optical amplifying device shown in FIG. 10, each optical filter 20 is not provided before each optical gain adjuster 17, and the optical filter 20 is provided after each optical gain adjuster 17. You may make it provide.
[0117]
That is, in the optical amplifying apparatus 8 of FIG. 3, the optical filter 20b is disposed between the optical multiplexer 23b and the optical star coupler 19, and the optical filter 20c is disposed between the optical multiplexer 23c and the optical star coupler 19. You may change so that it does. Similarly, in the optical amplifying device 8 of FIG. 7, the optical filter 20a is disposed between the optical multiplexer 23a and the optical star coupler 19, and the optical filter 20b is disposed between the optical multiplexer 23b and the optical star coupler 19. The optical filter 20c may be changed to be disposed between the optical multiplexer 23c and the optical star coupler 19. 12, 13, and 16, the optical demultiplexing unit 15 may be configured only by the optical star coupler 18 without providing the optical filter 20 in the optical demultiplexing unit 15. Good.
[0118]
Even in this case, each optical filter is placed in front of each optical gain adjuster 17 out of the light amplified by each optical gain adjuster 17 by the optical filter 20 provided in the subsequent stage of each optical gain adjuster 17. Since only the light having the same wavelength as that provided is taken out and inputted to the optical star coupler 19, the light of each wavelength adjusted by the optical gain adjuster 17 is obtained in the same manner as in the above-described embodiments. It is multiplexed by the optical star coupler 19.
[0119]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical amplifying device capable of arbitrarily adjusting the optical output power of each wavelength and the deviation between wavelengths.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an example that is a block diagram illustrating a configuration of an optical transmission system according to a first embodiment of the present invention;
FIG. 2 is a block diagram illustrating a configuration of an optical amplifying device according to a first embodiment of the present invention.
FIG. 3 is a block diagram showing a first configuration example of an optical power adjustment unit according to the first embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of an optical multiplexer / demultiplexer according to the first embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of an optical gain adjuster according to the first embodiment of the present invention.
FIG. 6 is a block diagram showing a configuration of a control device according to the first embodiment of the present invention.
FIG. 7 is a block diagram illustrating a second configuration example of the optical power adjustment unit according to the first embodiment of the present invention.
FIG. 8 is a block diagram showing a third configuration example of the optical power adjustment unit according to the first example of the present invention.
FIG. 9 is a block diagram showing a schematic configuration of an optical amplifying device according to a second embodiment of the present invention.
FIG. 10 is a block diagram illustrating a first configuration example of an optical amplifying device according to a second embodiment of the present invention.
FIG. 11 is a diagram illustrating a configuration of a control device in a first configuration example of an optical amplifying device according to a second embodiment of the present invention.
FIG. 12 is a block diagram showing a second configuration example of the optical amplifying apparatus according to the second embodiment of the present invention.
FIG. 13 is a block diagram showing a third configuration example of the optical amplifying apparatus according to the second embodiment of the present invention.
FIG. 14 is a block diagram showing a configuration of a control device in a first configuration example of an optical amplifying device according to a third embodiment of the present invention.
FIG. 15 is a block diagram showing a configuration of an optical amplifying device according to a third embodiment of the present invention.
FIG. 16 is a block diagram showing a detailed configuration of an optical amplifying device according to a third embodiment of the present invention.
FIG. 17 is a block diagram showing a configuration of an optical amplifying device according to a fourth example of the present invention.
FIG. 18 is a block diagram showing a configuration of a conventional optical amplifying device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical transmitter, 2 ... Optical booster amplifier, 3 ... Transmission fiber, 4 ... Optical repeater, 5 ... Optical preamplifier, 6 ... Optical receiver, 7, 13, 27, 51, 52 ... Optical isolator, 9 ... Optical Amplifying unit 12, 16, 23, 30, 48, 53 ... optical multiplexer, 10, 21, 28, 47, 50 ... rare earth doped optical fiber, 11, 22, 29, 54 ... pumping light source, 8 ... optical power adjustment , 14 ... control device, 15, 32 ... optical demultiplexing unit, 16 ... optical multiplexing unit, 17 ... optical gain adjuster, 18, 19, 33, 35, 37, 38, 39, 45, 49, 56 ... light Coupler 24... Storage unit 25. Control parameter 26. Control unit 31. Light source 34. Output monitor unit 36 Input monitor unit 40. 57 Photodetector 42 Reference value 41 Comparator 43 ... Maximum error determination unit 44 ... Selector 46 ... Optical preamplifier 5 ... optical attenuator

Claims (5)

An optical amplifying apparatus that amplifies and outputs light multiplexed with a plurality of input signal lights having different wavelengths,
Optical power adjusting means for receiving the input light and amplifying or attenuating light of at least one wavelength included in the received light independently of light having a wavelength different from the wavelength of the light;
A light amplifying means for amplifying light obtained by amplifying or attenuating light of the at least one wavelength by the light power adjusting means;
Control means for controlling the gain of amplification or attenuation performed by the optical power adjustment means and the gain of amplification performed by the optical amplification means,
The optical power adjusting means is
A plurality of paths for propagating light;
An optical demultiplexing unit that demultiplexes the received light into light of each wavelength included in the light and propagates the light to each of the plurality of paths;
An optical multiplexing unit for wavelength-multiplexing light of each wavelength propagated through the plurality of paths;
An optical gain adjuster that is provided in at least one of the plurality of paths and amplifies or attenuates light having a wavelength propagating through the path according to control of the control unit;
The optical demultiplexing unit is
A first optical coupler for branching the received light;
An optical filter provided in correspondence with the light branched by the optical coupler between the optical coupler and the plurality of paths, each transmitting only light of a specific wavelength in both directions;
The optical multiplexing unit includes an optical star coupler that combines light of each wavelength propagated through the plurality of paths,
Furthermore, the optical amplification device
Means for branching a part of the light amplified by the light amplification means as monitor light;
An optical coupler for monitoring light that guides the branched monitor light to the optical star coupler from a direction opposite to the propagation direction of the light combined with the respective wavelengths, and the optical coupler each of the plurality of optical filters. A plurality of light detecting means for detecting the power of light of each wavelength included in the monitor light respectively transmitted in the direction opposite to the branched light,
The control means, depending on the power of light of each wavelength detected by each light detection means, the gain of amplification or attenuation performed by the optical power adjustment means, and the gain of amplification performed by the light amplification means, respectively An optical amplifying device characterized by controlling. An optical amplifying apparatus that amplifies and outputs light multiplexed with a plurality of input signal lights having different wavelengths,
A light amplifying means for amplifying the input light;
Optical power adjusting means for receiving the light amplified by the light amplifying means and amplifying or attenuating light of at least one wavelength included in the received light independently of light having a wavelength different from the wavelength of the light;
Control means for controlling the gain of amplification performed by the optical amplification means and the gain of amplification or attenuation performed by the optical power adjustment means,
The optical power adjusting means is
A plurality of paths for propagating light;
An optical demultiplexing unit that demultiplexes the received light into light of each wavelength included in the light and propagates the light to each of the plurality of paths;
An optical multiplexing unit for wavelength-multiplexing light of each wavelength propagated through the plurality of paths;
An optical gain adjuster that is provided in at least one of the plurality of paths and amplifies or attenuates light having a wavelength propagating through the path according to control of the control unit;
The optical demultiplexing unit is
A first optical coupler for branching the received light;
An optical filter provided in correspondence with the light branched by the optical coupler between the optical coupler and the plurality of paths, each transmitting only light of a specific wavelength in both directions;
The optical multiplexing unit includes an optical star coupler that combines light of each wavelength propagated through the plurality of paths,
Furthermore, the optical amplification device
Means for branching a part of the light amplified by the light amplification means as monitor light;
An optical coupler for monitoring light that guides the branched monitor light to the optical star coupler from a direction opposite to the propagation direction of the light combined with the respective wavelengths, and the optical coupler each of the plurality of optical filters. A plurality of light detecting means for detecting the power of light of each wavelength included in the monitor light respectively transmitted in the direction opposite to the branched light,
The control means, depending on the power of light of each wavelength detected by each light detection means, the gain of amplification or attenuation performed by the optical power adjustment means, and the gain of amplification performed by the light amplification means, respectively An optical amplifying device characterized by controlling. An optical amplifying apparatus that amplifies and outputs light multiplexed with a plurality of input signal lights having different wavelengths,
Optical power adjusting means for receiving the input light and amplifying or attenuating light of at least one wavelength included in the received light independently of light having a wavelength different from the wavelength of the light;
A light amplifying means for amplifying light obtained by amplifying or attenuating light of the at least one wavelength by the light power adjusting means;
Control means for controlling the gain of amplification or attenuation performed by the optical power adjustment means and the gain of amplification performed by the optical amplification means,
The optical power adjusting means is
A plurality of paths for propagating light;
An optical branching section for each propagated to each of the plurality of paths of the light received, branching off,
Out of each light propagated through the plurality of paths, for each path, extract a light of a specific wavelength, respectively, and an optical multiplexing unit that wavelength-multiplexes the extracted light of each wavelength,
An optical gain adjuster provided in at least one of the plurality of paths and amplifying or attenuating light propagating through the path according to control of the control means;
The optical multiplexing unit is
A plurality of optical filters that are provided corresponding to the plurality of paths, and that bidirectionally transmit only light of a specific wavelength,
An optical star coupler that multiplexes light of each wavelength transmitted through each of the plurality of optical filters,
Furthermore, the optical amplification device
Means for branching a part of the light amplified by the light amplification means as monitor light;
Monitoring light optical multiplexing means for guiding the branched monitor light to the optical star coupler from a direction opposite to the propagation direction of the combined light of each wavelength;
A plurality of light detection means for detecting the power of light of each wavelength included in the monitor light respectively transmitted in the opposite direction to the light demultiplexed by the light demultiplexing unit through each of the plurality of optical filters; Have
The control means includes
Amplifying or attenuating gain performed by the optical power adjusting unit and an amplifying gain performed by the optical amplifying unit are controlled according to the power of light of each wavelength detected by each photodetecting unit. An optical amplification device. An optical amplifying apparatus that amplifies and outputs light multiplexed with a plurality of input signal lights having different wavelengths,
A light amplifying means for amplifying the input light;
Optical power adjusting means for receiving the light amplified by the light amplifying means and amplifying or attenuating light of at least one wavelength included in the received light independently of light having a wavelength different from the wavelength of the light;
Control means for controlling the gain of amplification performed by the optical amplification means and the gain of amplification or attenuation performed by the optical power adjustment means,
The optical power adjusting means is
A plurality of paths for propagating light;
An optical demultiplexing unit for branching and propagating the received light to each of the plurality of paths;
Out of each light propagated through the plurality of paths, for each path, extract a light of a specific wavelength, respectively, and an optical multiplexing unit that wavelength-multiplexes the extracted light of each wavelength,
An optical gain adjuster provided in at least one of the plurality of paths and amplifying or attenuating light propagating through the path according to control of the control means;
The optical multiplexing unit is
A plurality of optical filters that are provided corresponding to the plurality of paths, and that bidirectionally transmit only light of a specific wavelength,
An optical star coupler that multiplexes light of each wavelength transmitted through each of the plurality of optical filters,
Furthermore, the optical amplification device
Means for branching a part of the light amplified by the light amplification means as monitor light;
Monitoring light optical multiplexing means for guiding the branched monitor light to the optical star coupler from a direction opposite to the propagation direction of the combined light of each wavelength;
A plurality of light detection means for detecting the power of light of each wavelength included in the monitor light respectively transmitted in the opposite direction to the light demultiplexed by the light demultiplexing unit through each of the plurality of optical filters; Have
The control means includes
Amplifying or attenuating gain performed by the optical power adjusting unit and an amplifying gain performed by the optical amplifying unit are controlled according to the power of light of each wavelength detected by each photodetecting unit. An optical amplification device. The optical amplifying device according to claim 1,
The control means includes
A comparator for comparing each light power of each wavelength detected by each of the light detection means with a predetermined reference value;
An optical amplifying apparatus comprising: means for controlling a gain of amplification performed by the optical amplifying means according to a maximum value of a difference from a reference value.

Images