JP2004304369A - Optical transmission system using raman amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission system using a Raman amplifier in which the optical power balance of WDM light and the optical power of entire WDM light are accurately managed. <P>SOLUTION: The optical communication system in which WDM light is transmitted from a transmitter station 10 to a receiver station 20 comprises a plurality of relay stations 30. The WDM light contains signal light fs1-fsn and reference light fr1-fr3. Excitation light fp1-fp3 generated by an excitation light source 2 is supplied to a transmission-path optical fiber 1. A control circuit 33 controls the excitation light fp1-fp3 based on the optical power of each reference light fr1-fr3. The reference light fr1-fr3 is arranged on the frequency in which the gain of Raman amplification caused by the excitation light fp1-fp3 gets to peak. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３１】
この関係式において、「Ｐｒ１」〜「Ｐｒ３」は、光スペクトラムアナライザ３２により検出された参照光ｆｒ１〜ｆｒ３の光パワー値を表す。また、「Ｐｓｒｅｆ」は、目標とする出力レベル（目標光パワー）を表す。なお、「Ｐｓｒｅｆ」は、予め決められた固定値である。さらに、マトリクスＡ（Ａ１１〜Ａ３３）の各要素は、シミュレーション等により予め算出された利得係数である。そして、「ΔＰｐ１」〜「ΔＰｐ３」は、励起光ｆｐ１〜ｆｐ３の変動量を表す。
【００３２】
ＤＳＰ４２は、この関係式を用いて励起光ｆｐ１〜ｆｐ３についてフィードバック制御を行う。そして、「Ｐｒ１」〜「Ｐｒ３」がそれぞれ「Ｐｓｒｅｆ」に対して所定の誤差範囲内に収まったときに、制御ループが収束したものとみなされる。
【００３３】
ＤＳＰ４２は、上述の関係式に従って変動量「ΔＰｐ１」〜「ΔＰｐ３」を求めると、その変動量を用いて励起光ｆｐ１〜ｆｐ３の光パワーを設定する設定値を算出する。すなわち、下記の演算を行う。なお、「Ｐｐ１（ｎ）」〜「Ｐｐ３（ｎ）」は、前回の設定値であり、「Ｐｐ１（ｎ＋１）」〜「Ｐｐ３（ｎ＋１）」は、新たな設定値である。
Ｐｐ１（ｎ＋１）＝Ｐｐ１（ｎ）＋ΔＰｐ１
Ｐｐ２（ｎ＋１）＝Ｐｐ２（ｎ）＋ΔＰｐ２
Ｐｐ３（ｎ＋１）＝Ｐｐ３（ｎ）＋ΔＰｐ３
Ｄ／Ａ変換器４３は、ＤＳＰ４２により算出された設定値（励起光ｆｐ１〜ｆｐ３の光パワーを指示する設定値）をそれぞれアナログ値に変換し、対応する増幅器４４−１〜４４−３に与える。増幅器４４−１〜４４−３は、それぞれ、ＤＳＰ４２から与えられたアナログ値を増幅する。そして、パワートランジスタ４５−１〜４５−３は、それぞれ、増幅器４４−１〜４４−３の出力に対応する電流を生成する。
【００３４】
励起光源２は、増幅器４４−１〜４４−３が生成する電流により駆動される。すなわち、励起光ｆｐ１を生成するためのレーザダイオードは、増幅器４４−１が生成する電流により駆動される。同様に、励起光ｆｐ２、ｆｐ３を生成するためのレーザダイオードは、それぞれ、増幅器４４−２、４４−３が生成する電流により駆動される。
【００３５】
このように、制御回路３３は、参照光ｆｒ１〜ｆｒ３を利用して励起光ｆｐ１〜ｆｐ３の光パワーを制御する。このとき、各励起光ｆｐ１〜ｆｐ３の光パワーは、例えば、参照光ｆｒ１〜ｆｒ３の光パワーが等化されるように調整される。したがって、実施形態の光伝送システムでは、信号光ｆｓ１〜ｆｓｎの配置にかかわらず、常に、適切なラマン増幅が行われる。
【００３６】
なお、ラマン増幅を利用する光伝送システムにおいて広い信号帯域を効率的に得るためには、一般に、複数の励起光ｐ１〜ｆｐ３が、適切な周波数間隔または波長間隔で配置される。このため、これらの励起光ｐ１〜ｆｐ３に起因するラマン利得がピークとなる波長に複数の参照光ｆｒ１〜ｆｒ３を配置すると、図６に示すように、それらの参照光ｆｒ１〜ｆｒ３は、結果的に、ＷＤＭ光の信号帯域のほぼ全域に渡って適切な周波数間隔または波長間隔で配置されることになる。そして、実施形態の光伝送システムでは、これらの参照光ｆｒ１〜ｆｒ３を利用してラマン増幅が制御される。したがって、ＷＤＭ光に含まれる信号光の数が少ない場合（図６では、４つの信号光ｆｓ１〜ｆｓ４のみが使用されている）、あるいは、ＷＤＭ光に含まれる信号光の配置が偏っている場合（図６では、信号帯域の中の短い波長領域にのみ信号光が配置されている）であっても、好適なラマン増幅が得られる。すなわち、全信号帯域に渡って、利得を等化することができる。
【００３７】
また、実施形態のシステムでは、励起光ｐ１〜ｆｐ３に起因するラマン利得がピークとなる波長に参照光ｆｒ１〜ｆｒ３が配置されているので、励起光ｐ１〜ｆｐ３を調整することによって比較的容易に所望の利得チルトを得ることができる。
【００３８】
さらに、上述の実施例では、参照光ｆｒ１〜ｆｒ３を利用してＷＤＭ光の信号帯域の利得を等化する制御を行っているが、この参照光は、ＷＤＭ光の全出力パワーを制御するために用いられてもよい。この場合、制御回路３３は、例えば、図７に示すように、等化制御部５１およびＡＬＣ（Ａｕｔｏｍａｔｉｃ Ｌｅｖｅｌ Ｃｏｎｔｒｏｌ）部５２を備える。ここで、等化制御部５１は、上述のようにして励起光源２が生成する励起光ｆｐ１〜ｆｐ３を制御する。一方、ＡＬＣ部５２は、光スペクトラムアナライザ３２により検出された参照光ｆｒ１〜ｆｒ３の各光パワーの平均値を算出する。
【００３９】
そして、ＡＬＣ部５２は、例えば、その平均値に基づいて等価制御部５１の計算結果を補正するようにしてもよい。この場合、制御回路３３は、参照光ｆｒ１〜ｆｒ３の各光パワーだけでなく、それらの平均値にも基づいて励起光ｐ１〜ｆｐ３を制御することになる。この結果、ラマン増幅の利得が等化されると同時に、ＷＤＭ光の出力パワーが所望のレベルに保持されるようになる。
【００４０】
なお、ＡＬＣ制御部５２は、例えば、参照光ｆｒ１〜ｆｒ３の各光パワーの平均値が、予め決められている１チャネル当たりの目標出力パワーに一致するように、光減衰器（ＡＴＴ）５３における減衰量を制御するようにしてもよい。
【００４１】
このように、ＷＤＭ光から参照光ｆｒ１〜ｆｒ３のみを抽出し、それらの参照光を利用してＷＤＭ光の全出力パワー（または、ＷＤＭ光に含まれている各信号光の光パワー）を推定する方式によれば、ＷＤＭ光に含まれている信号光の数が少ない場合であっても、ＷＤＭ光の光パワーを精度よくモニタできる。
【００４２】
すなわち、従来のシステムのように、１つのフォトダイオードを用いてＷＤＭ光の光パワーを検出しようとすると、信号光の光パワーだけでなく、ＡＳＥ等の雑音に起因する光パワーも全帯域に渡って検出してしまう。例えば、図８（ａ）に示す例では、信号光が１つだけ存在する場合であっても、斜線領域すべての光パワーを検出してしまうので、信号光の光パワーを正しく検出することができない。
【００４３】
一方、実施形態の方式では、各参照光を含む狭い帯域の光パワーが検出されるので、雑音の影響を受けにくい。すなわち、実施形態の方式では、図８（ｂ）に示す斜線領域の光パワーのみが検出されるので、参照光の光パワーを正確に検出でき、これによってＷＤＭ光（または、ＷＤＭ光に含まれる各信号光）の光パワーを正確に検出できる。
【００４４】
図９は、他の実施形態の光伝送システムの中継局の構成図である。ここで、この中継局は、信号帯域を増幅するためのエルビウム添加ファイバ光増幅器（ＥＤＦＡ）６１を備えている。すなわち、このシステムでは、ラマン増幅器およびエルビウム添加ファイバ光増幅器が混在する。そして、ラマン増幅器およびエルビウム添加ファイバ光増幅器６１の関係は、図１０に示すようになっているものとする。
【００４５】
エルビウム添加ファイバ光増幅器６１およびラマン増幅器は、図１０に示すように、信号帯域を増幅するように設計される。ここで、ラマン増幅器による利得は、励起光ｆｐ１〜ｆｐ３により得られている。そして、信号帯域全体に渡ってフラットなラマン利得を得ようとすると、しばしば、複数の励起光の中の一部の励起光に起因するラマン利得がピークとなる周波数が信号帯域の外に位置することがある。図１０に示す例では、励起光ｆｐ１に起因するラマン利得がピークとなる周波数が信号帯域の外に位置している。
【００４６】
ところが、実施形態の光伝送システムでは、各励起光ｆｐ１〜ｆｐ３に起因するラマン利得がピークとなる周波数にそれぞれ参照光ｆｒ１〜ｆｒ３が設定される。すなわち、図１０に示す例においては、参照光ｆｒ１は、信号帯域の外に位置することになり、エルビウム添加ファイバ光増幅器６１によっては増幅されない、あるいは増幅量が不十分となることになる。したがって、このままでは、参照光ｆｒ１は、他の参照光ｆｒ２、ｆｒ３と比較して光パワーが弱くなってしまう
このため、この実施形態のシステムでは、各中継局（または、全中継局の中のいくつかの中継局）に、参照光ｆｒ１と同じ周波数の補助光を生成するための補助光源（ＬＤ）６２、およびその補助光源６２により生成される補助光をＷＤＭ光に合波するＷＤＭカプラ６３が設けられている。そして、このようにして参照光ｆｒ１と同じ周波数の補助光が供給されることにより、エルビウム添加ファイバ光増幅器６１によって増幅されない参照光ｆｒ１の光パワーが、他の参照光ｆｒ２、ｆｒ３と同じレベルになるように調整される。
【００４７】
また、さらに光スペクトラムアナライザ３２と光分岐カプラ３１との間にＷＤＭカプラ７１を設置し、これにより信号帯域外の参照光ｆｐ１のパワーの一部を選択してフォトダイオード７２に導き、監視信号中継器７３によって中継増幅される際に補助光源６２で監視信号データを載せてＷＤＭカプラ６３を通して合波することで信号帯域外参照光に監視信号光を載せることも可能である。
【００４８】
なお、図１または図９に示す例では、各参照光ｆｒ１〜ｆｒ３の光パワーを検出するための回路（検出手段）として、光スペクトラムアナライザ３２が用いられているが、本発明はこれに限定されるものではない。
【００４９】
図１１は、参照光の光パワーを検出するための回路の実施例である。ここで、この検出回路７０は、図１または図９に示した光スペクトラムアナライザ３２の代わりの設けられる。すなわち、検出回路７０は、分岐カプラ３１により分岐されたＷＤＭ光が与えられ、そのＷＤＭ光に含まれている参照光ｆｒ１〜ｆｒ３の光パワーを検出して制御回路３３に通知する。
【００５０】
検出回路７０は、参照光ｆｒ１〜ｆｒ３を選択的に反射する反射素子７１−１〜７１−３を備える。ここで、反射素子７１−１〜７１−３は、それぞれ、例えば、ファイバブラッググレーティングにより実現される。そして、反射素子７１−１は、参照光ｆｒ１が設定されている周波数の光のみを反射する。同様に、反射素子７１−２、７１−３は、それぞれ、参照光ｆｒ２、ｆｒ３が設定されている周波数の光のみを反射する。なお、検出回路７０は、無反射終端部７４により終端されている。
【００５１】
反射素子７１−１により反射された光（すなわち、参照光ｆｒ１）は、光デバイス７２−１によりフォトダイオード７３−１に導かれる。ここで、この光デバイス７２−１は、例えば、光分岐カプラまたは光サーキュレータ等により実現することができる。そして、フォトダイオード７３−１によって参照光ｆｒ１の光パワーが検出される。同様に、反射素子７１−２、７１−３によって反射された参照光ｆｒ２、ｆｒ３は、光デバイス７２−２、７２−３によってフォトダイオード７３−２、７３−３に導かれる。そして、フォトダイオード７３−２、７３−３により参照光ｆｒ２、ｆｒ３の光パワーが検出される。
【００５２】
このように、図１１に示す検出回路は、シンプルな光部品を組み合わせることにより実現されるので、光スペクトラムアナライザ３２を利用する構成と比較して低コスト化が図れる。
【００５３】
図１２は、図１１に示す検出回路の変形例である。この検出回路は、予め決められた波長のみを選択的に通過させる波長分離フィルタ７５を備える。この例では、波長分離フィルタ７５は、参照光ｆｒ１〜ｆｒ３のみを通過させる。そして、これらの参照光ｆｒ１〜ｆｒ３は、それぞれ、対応するフォトダイオード７３−１〜７３−３に導かれる。
【００５４】
なお、図１〜図１２に示した実施例では、３波の励起光ｆｐ１〜ｆｐ３によってラマン増幅を実現しているが、本発明はこれに限定されるものではなく、互いに波長の異なる複数の励起光を利用するシステムであれば適用可能である。
【００５５】
（付記１）ラマン増幅器を利用して送信局から受信局へＷＤＭ光を伝送する光伝送システムであって、
上記ラマン増幅器は、
光増幅媒体と、
互いに波長の異なる複数の励起光を生成する励起光源と、
上記複数の励起光を上記光増幅媒体に導く光デバイスと、
上記励起光源を制御する制御手段を備え、
上記送信局は、上記複数の励起光により得られる各ラマン利得がそれぞれピークとなる波長またはその近傍の波長を持った複数の参照光を送出し、
上記制御手段は、上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する
ことを特徴とする光伝送システム。
【００５６】
（付記２）ラマン増幅器を利用して送信局から受信局へＷＤＭ光を伝送する光伝送システムであって、
上記ラマン増幅器は、
光増幅媒体と、
互いに波長の異なる複数の励起光を生成する励起光源と、
上記複数の励起光を上記光増幅媒体に導く光デバイスと、
上記励起光源を制御する制御手段を備え、
上記送信局は、上記複数の励起光に対してそれぞれラマンシフト周波数だけシフトした周波数またはその近傍の周波数で対応する複数の参照光を送出し、
上記制御手段は、上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する
ことを特徴とする光伝送システム。
【００５７】
（付記３）付記１または２に記載の光伝送システムであって、
上記送信局は、上記複数の参照光の中の少なくとも一部を利用して上記受信局へ情報を送信する。
【００５８】
（付記４）付記１に記載の光伝送システムであって、
上記ＷＤＭ光が予め決められた周波数間隔が定義されている周波数グリッド上に配置される場合に、上記複数の参照光は、それぞれ、上記励起光に基づいて決められる波長に対応する周波数に最も近接するグリッド上に配置される。
【００５９】
（付記５）付記２に記載の光伝送システムであって、
上記ＷＤＭ光が予め決められた周波数間隔が定義されている周波数グリッド上に配置される場合に、上記複数の参照光は、それぞれ、上記励起光に基づいて決められる周波数に最も近接するグリッド上に配置される。
【００６０】
（付記６）付記１または２に記載の光伝送システムであって、
上記ＷＤＭ光に含まれている上記複数の参照光の光パワーを検出する検出手段をさらに有し、
上記制御手段は、上記検出手段により検出される複数の参照光の光パワーが等化されるように上記複数の励起光の光パワーを制御する。
【００６１】
（付記７）付記６に記載の光伝送システムであって、
上記検出手段は、光スペクトラムアナライザである。
（付記８）付記６に記載の光伝送システムであって、
上記検出手段は、
上記複数の参照光を選択的に反射する反射手段と、
上記反射手段により反射された参照光を電気信号に変換する受光手段、
を備える。
【００６２】
（付記９）付記１または２に記載の光伝送システムであって、
上記制御手段は、上記複数の参照光の各光パワーの平均値に基づいて上記複数の励起光を制御する。
【００６３】
（付記１０）付記１または２に記載の光伝送システムであって、
上記制御手段は、上記複数の参照光の各光パワーの平均値に基づいて上記ＷＤＭ光の出力パワーを制御する。
【００６４】
（付記１１）ラマン増幅を利用して送信局から中継局を介して受信局へＷＤＭ光を伝送する光伝送システムであって、
上記中継局は、
互いに波長の異なる複数の励起光を生成する励起光源と、
上記複数の励起光を光増幅媒体に導く光デバイスと、
上記励起光源を制御する制御手段、を備え、
上記送信局は、上記複数の励起光により得られる各ラマン利得がそれぞれピークとなる波長またはその近傍の波長を持った複数の参照光を生成する参照光生成手段を有し、
上記中継局は、さらに、
上記ＷＤＭ光を増幅する集中型光増幅器と、
上記複数の参照光の中で上記集中型光増幅器の利得帯域の外に位置する参照光と同じ波長の補助光を上記ＷＤＭ光に合波する補助光供給手段、を備え
上記制御手段は、上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する
ことを特徴とする光伝送システム。
【００６５】
（付記１２）ラマン増幅を利用して送信局から中継局を介して受信局へＷＤＭ光を伝送する光伝送システムであって、
上記中継局は、
互いに波長の異なる複数の励起光を生成する励起光源と、
上記複数の励起光を光増幅媒体に導く光デバイスと、
上記励起光源を制御する制御手段、を備え、
上記送信局は、上記複数の励起光により得られる各ラマン利得がそれぞれピークとなる波長またはその近傍の波長を持った複数の参照光を生成する参照光生成手段を有し、
上記制御手段は、上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する
ことを特徴とする光伝送システム。
【００６６】
（付記１３）送信局から受信局へ複数の信号光および複数の参照光を含むＷＤＭ光を伝送する光伝送システムにおいて上記ＷＤＭ光を増幅するラマン増幅器であって、
光増幅媒体と、
互いに波長の異なる複数の励起光を生成する励起光源と、
上記複数の励起光を上記光増幅媒体に導く光デバイスと、
上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する制御手段を備え、
上記複数の参照光が、上記複数の励起光により得られる各ラマン利得がそれぞれピークとなる波長またはその近傍の波長に配置されることを特徴とするラマン増幅器。
【００６７】
（付記１４）互いに波長の異なる複数の励起光を用いるラマン増幅器を利用して送信局から受信局へＷＤＭ光を伝送する光伝送方法であって、
上記送信局は、上記複数の励起光により得られる各ラマン利得がそれぞれピークとなる波長またはその近傍の波長を持った複数の参照光を上記ＷＤＭ光の一部として送出し、
上記ラマン増幅器は、上記複数の参照光の光パワーに基づいて上記複数の励起光を制御する
ことを特徴とする光伝送方法。
【００６８】
（付記１５）付記１１に記載の光伝送システムであって、
上記中継局は、
上記複数の参照光のうち上記集中型光増幅器の利得帯域の外に位置する帯域外参照光に監視情報を載せ、中継局でこの参照光を電気信号に変換し、さらに光信号に変換して上記ＷＤＭ光に合波する補助光供給手段、を備え、
上記制御手段は、上記帯域外参照光を含む上記複数の参照光の光パワーに基づいて上記複数の励起光を制御し、さらに、上記帯域外参照光を用いて中継局を遠隔制御して状態を監視する情報を中継伝送する
ことを特徴とする光伝送システム。
【００６９】
【発明の効果】
本発明によれば、ラマン増幅を利用する光伝送システムにおいて、ＷＤＭ光の中に含まれる信号光の数や配置が変化した場合であっても、常に、利得の波長特性を精度よく制御できる。また、ＷＤＭ光の中に含まれる信号光の数が少ない場合であっても、ＡＳＥ等の雑音累積の影響を抑えながらＷＤＭ光の出力パワーを正確にモニタできる。さらに、ラマン増幅器の動作の管理が簡単になる。
【図面の簡単な説明】
【図１】本発明の実施形態の光伝送システムの構成図である。
【図２】参照光の配置方法について説明する図である。
【図３】送信局の構成図である。
【図４】参照光を利用してデータを伝送する場合の送信回路の例である。
【図５】各中継局が備える制御回路の構成図である。
【図６】実施形態の光伝送システムの効果を説明する図である。
【図７】ＷＤＭ光の光パワーに基づいて動作する中継局の実施例である。
【図８】（ａ）は従来技術における光検出、（ｂ）は実施形態の光検出について説明する図である。
【図９】他の実施形態の光伝送システムの中継局の構成図である。
【図１０】ラマン増幅器とエルビウム添加ファイバ光増幅器との関係を説明するための図である。
【図１１】参照光の光パワーを検出するための装置の実施例である。
【図１２】図１１に示す検出回路の変形例である。
【図１３】一般的なラマン増幅器を用いた光伝送システムの構成図である。
【符号の説明】
１ 伝送路光ファイバ（光増幅媒体）
２ 励起光源
３ ＷＤＭカプラ
１０ 送信局
２０ 受信局
３０ 中継局
３２ 光スペクトラムアナライザ
３３ 制御回路
４２ ＤＳＰ
６１ エルビウム添加ファイバ光増幅器（ＥＤＡ）
６２ 補助光源
７０ 検出回路
７１−１〜７１−３ 反射素子
７３−１〜７３−３ フォトダイオード
７５ 波長分離フィルタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical transmission system for amplifying and relaying WDM light using a Raman amplifier.
[0002]
[Prior art]
2. Description of the Related Art In recent years, wavelength-division multiplexing (WDM: Wavelength Division Multiplex) technology has been introduced in trunk optical transmission systems in order to increase capacity or speed. As a core technology of the WDM transmission technology, a Raman optical amplification technology has been put to practical use.
[0003]
FIG. 13 is a configuration diagram of an optical transmission system using a general Raman amplifier. Here, in this system, a plurality of relay stations are provided between the transmitting station (Tx) 101 and the receiving station (Rx) 102, and WDM light is transmitted via these relay stations. Then, Raman amplification is performed in each relay station. Each relay station is provided with a centralized optical amplifier such as an erbium-doped fiber optical amplifier.
[0004]
The transmission line fiber 1 is an optical transmission medium for propagating WDM light, but also acts as an optical amplification medium when supplied with pump light. The pumping light source (LD) 2 is, for example, a laser diode or a combination of light emitted from a plurality of laser diodes by a multiplexer or the like, and generates pumping light for amplifying WDM light. Here, the excitation light generated by the excitation light source 2 includes a plurality of lights having different wavelengths. The WDM coupler 3 guides the pump light generated by the pump light source 2 to the transmission line optical fiber 1.
In the optical transmission system, the WDM light transmitted from the transmitting station 101 is transmitted to the receiving station 102 while being amplified by the transmission line fiber 1. At this time, in each relay station, the output power of the entire WDM light is managed, and the optical power balance of a plurality of signal lights included in the WDM light is managed. That is, for example, in each relay station, the optical power of a plurality of signal lights included in the WDM light is equalized so that the output power of the entire WDM light is maintained at a predetermined value. Thus, the excitation light source 2 is controlled (for example, see Patent Documents 1 to 3).
[0005]
[Patent Document 1]
JP-A-2002-72262 (FIGS. 3, 3 to 5)
[Patent Document 2]
JP-A-2000-98433 (FIG. 1, paragraphs 0070 to 0072)
[Patent Document 3]
JP-A-2002-76482 (FIG. 10, paragraphs 0162 to 0177)
[0006]
[Problems to be solved by the invention]
However, the existing optical transmission systems as described above have the following problems.
1. It is difficult to accurately monitor the balance (optical power tilt) of the output power of a plurality of signal lights included in the WDM light. For example, in Patent Document 1 described above, the signal light band is divided into a plurality of blocks, and the optical power tilt is controlled using the optical power detected for each block. However, in this case, when the signal light is not uniformly arranged in each block, the optical power tilt cannot be accurately detected, and the WDM light cannot be equalized. Note that this problem does not occur only in the system described in Patent Document 1 described above. Even when the optical power of a plurality of signal lights included in the WDM light is individually detected, the signal light Occurs in a specific wavelength region within the signal light band.
[0007]
2. When the output power of the entire WDM light is detected using a photodiode or the like, the photodiode receives light over a wide band. Therefore, when the number of signal lights included in the WDM light is small, ASE is used. (Amplified Spontaneous Emission) becomes dominant (that is, the ratio of the noise light power to the total light power becomes relatively high). For this reason, the optical power of the main signal light (that is, the WDM light to transmit the signal) cannot be accurately detected.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to accurately manage the optical power balance of WDM light and the overall optical power of WDM light in an optical transmission system using a Raman amplifier.
[0009]
[Means for Solving the Problems]
The optical transmission system of the present invention is a system for transmitting WDM light from a transmitting station to a receiving station using a Raman amplifier. The Raman amplifier includes an optical amplification medium, an excitation light source that generates a plurality of excitation lights having different wavelengths, an optical device that guides the plurality of excitation lights to the optical amplification medium, and a control unit that controls the excitation light source. The transmitting station transmits a plurality of reference lights having a wavelength at which each Raman gain obtained by the plurality of pump lights reaches a peak or a wavelength near the peak. Then, the control means controls the plurality of excitation lights based on the optical powers of the plurality of reference lights.
[0010]
In the above optical transmission system, since the pump light is controlled based on the reference light, the optical power of the pump light can always be appropriately controlled regardless of the number or arrangement of the signal lights included in the WDM light, and the Raman gain can be controlled. Management of tilt and output power becomes easier.
[0011]
In the optical transmission system, the transmitting station may transmit information to the receiving station using at least a part of the plurality of reference lights. In this case, since information is transmitted using the reference light, communication resources (particularly, wavelength or band) are effectively used.
[0012]
Further, in the optical transmission system, a detection unit for detecting the optical power of the plurality of reference lights included in the WDM light is further provided, and the control unit includes a light source for the plurality of reference lights detected by the detection unit. The optical power of the plurality of excitation lights may be controlled so that the powers are equalized. Here, the detection means may be constituted by, for example, a reflection means for selectively reflecting the plurality of reference lights, and a light receiving means for converting the reference light reflected by the reflection means into an electric signal. Good.
[0013]
Further, in the optical transmission system, the control means may control the plurality of pump lights based on an average value of each optical power of the plurality of reference lights. In this case, since the influence of the noise light is suppressed, the optical power of the WDM light can be accurately monitored.
[0014]
Further, when the optical transmission system includes a centralized optical amplifier for amplifying the WDM light, and a part of the plurality of reference lights is located outside the gain band of the centralized optical amplifier. Alternatively, the auxiliary light having the same wavelength as the reference light located outside the gain band of the centralized optical amplifier may be combined with the WDM light. In this configuration, the optical power of the reference light that is not amplified by the centralized optical amplifier is lower than the optical power of the reference light that is amplified by the centralized optical amplifier. The optical power of the reference light located outside the gain band of the amplifier is compensated.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an optical transmission system according to an embodiment of the present invention. Here, in this system, a plurality of relay stations 30 are provided between the transmitting station 10 and the receiving station 20, and the WDM light is transmitted via these relay stations 30. Further, Raman amplification is performed in each relay station 30.
[0016]
The transmitting station 10 generates and transmits WDM light including signal light and reference light. Here, this signal light is composed of a plurality of signal lights fs1 to fsn having different wavelengths. The reference light is composed of a plurality of reference lights fr1 to fr3 having different wavelengths. Note that the wavelengths or frequencies of the reference lights fr1 to fr3 are respectively determined based on the wavelengths or frequencies of the excitation lights fp1 to fp3 described later.
[0017]
The transmission line fiber 1 connects between the transmitting station 10 and the first-stage relay station 30, between the relay stations 30, and between the last-stage relay station 30 and the receiving station 20, respectively. . Here, each transmission line fiber 1 is an optical transmission medium for propagating WDM light, but also acts as an optical amplification medium by being supplied with pump light.
[0018]
Each relay station 30 includes an excitation light source (LD) 2, a WDM coupler 3, a branch coupler 31, an optical spectrum analyzer 32, and a control circuit 33. Here, the pump light source 2 includes a plurality of laser diodes and generates a plurality of pump lights having different wavelengths. Here, it is assumed that three excitation lights fp1 to fp3 are generated. Then, the WDM coupler 3 guides the pump light fp1 to fp3 generated by the pump light source 2 to the transmission line optical fiber 1. As a result, the transmission line optical fiber 1 is supplied with the pump lights fp1 to fp3 and functions as an optical amplification medium for Raman amplification. That is, the transmission line optical fiber 1, the pump light source 2, and the WDM coupler 3 function as a Raman amplifier that amplifies WDM light.
[0019]
The branch coupler 31 branches a part of the WDM light amplified in the transmission path optical fiber 1 and guides the branched WDM light to the optical spectrum analyzer 32. The optical spectrum analyzer 32 monitors the optical power of each wavelength included in the WDM light. Then, the optical power of the reference lights fr1 to fr3 included in the WDM light is detected.
[0020]
The control circuit 33 drives the excitation light source 2 based on the optical power of the reference lights fr1 to fr3 detected by the optical spectrum analyzer 32. That is, the control circuit 33 adjusts the optical power of the pump light fp1 to fp3 based on the optical power of the reference light fr1 to fr3. Specifically, for example, the light of each of the excitation lights fp1 to fp3 is set such that the average light power of the reference lights fr1 to fr3 is maintained at a predetermined value and the light powers of the reference lights fr1 to fr3 are equalized. Power is adjusted.
[0021]
FIG. 2 is a diagram illustrating a method of arranging the reference light. The frequencies (or wavelengths) of the reference lights fr1 to fr3 are determined based on the frequencies (or wavelengths) of the corresponding pump lights fp1 to fp3, respectively. For example, a frequency shifted from the pump light fp1 by the Raman shift frequency is assigned to the reference light fr1. Here, the "Raman shift frequency" is not unique, but means "the difference between the frequency of a given pump light and the frequency at which the Raman gain obtained due to the pump light has a peak". Shall be. The Raman shift frequency is about 13.2 THz when a quartz optical fiber is used as the transmission line optical fiber 1. Also, when this Raman shift frequency is converted into a wavelength, it corresponds to about 100 nm in the 1.3 to 1.55 μm band. That is, the reference light fr1 is arranged at a wavelength at which the Raman gain due to the pump light fp1 has a peak. In other words, a frequency lower than the frequency of the pump light fp1 by about 13.2 THz is assigned to the reference light fr1. In other words, a wavelength longer by about 100 nm than the wavelength of the excitation light fp1 is assigned to the reference light fr1.
[0022]
Similarly, the reference light fr2 is arranged at a wavelength at which the Raman gain due to the pump light fp2 has a peak. The reference light fr3 is arranged at a wavelength where the Raman gain due to the pump light fp3 has a peak.
[0023]
As described above, the reference lights fr1 to fr3 are arranged at wavelengths at which the Raman gains caused by the corresponding pump lights fp1 to fp3 become peaks. However, the reference lights fr1 to fr3 do not necessarily have to be accurately arranged at the wavelength where the Raman gain caused by the corresponding pump lights fp1 to fp3 peaks, and the Raman gain caused by the corresponding pump lights fp1 to fp3 does not necessarily have to be arranged. It may be arranged at a wavelength close to the peak wavelength.
[0024]
When the signal lights fs1 to fsn are arranged and transmitted on a predetermined frequency grid, the reference lights fr1 to fr3 are also arranged and transmitted on the frequency grid. At this time, the reference lights fr1 to fr3 are respectively arranged on the frequency grid closest to the frequency at which the Raman gain caused by the pump lights fp1 to fp3 becomes a peak. In addition, such a frequency grid is prescribed | regulated in ITU-T, for example. In the ITU-T regulations, recommended values of a reference frequency (anchor frequency) and frequency intervals (50 GHz, 100 GHz) are indicated.
[0025]
FIG. 3 is a configuration diagram of the transmitting station 10. Here, only the functions necessary for generating the WDM light are illustrated.
The transmitting station 10 includes light sources (LD) 11-1 to 11-n for generating signal lights fs1 to fsn, light sources (LD) 12-1 to 12-3 for generating reference lights fr1 to fr3, and a signal. A multiplexer 13 that combines the light fs1 to fsn and the reference light fr1 to fr3 to generate WDM light is provided. Here, the frequencies (or wavelengths) of the reference lights fr1 to fr3 are determined as described above.
[0026]
The light sources 11-1 to 11-n are driven when transmitting data (or information) to the receiving station 20. For example, the light source 11-1 is driven when transmitting data generated by the data source 14-1 to the receiving station 20. On the other hand, the light sources 12-1 to 12-3 basically always generate and output the reference lights fr1 to fr3. Here, the light sources 12-1 to 12-3 may output continuous (CW) light, or may transmit a signal of a predetermined pattern.
[0027]
The signal lights fs1 to fsn are used for transmitting data (or information), whereas the reference lights fr1 to fr3 are originally used for controlling the Raman amplification operation in each relay station 30. Used for However, in the optical transmission system of the embodiment, data (or information) may be transmitted using the reference lights fr1 to fr3. However, since the reference lights fr1 to fr3 are used for controlling the Raman amplification operation in each relay station 30, it is basically not allowed to stop. For this reason, in a system that allows transmission of data (or information) using the reference lights fr1 to fr3, for example, as shown in FIG. A function to select “fixed pattern data” is provided. Although FIG. 4 shows a case where direct modulation is performed by an LD, it is necessary to enable selection including the presence or absence of data and the presence or absence of modulation as described above even in the case of external modulation by an optical modulator. Suppose. Then, in this case, the light source 12 (12-1 to 12-3) transmits the data when the data to be transmitted is provided, and transmits the fixed pattern data (or when the data to be transmitted is not provided). Unmodulated).
[0028]
FIG. 5 is a configuration diagram of a control circuit included in each relay station 30. The control circuit 33 includes an A / D converter 41, a DSP 42, a D / A converter 43, amplifiers 44-1 to 44-3, and power transistors 45-1 to 45-3. The A / D converter 41 converts the optical power values of the reference lights fr1 to fr3 detected by the optical spectrum analyzer 32 into digital data and passes the digital data to the DSP. When the optical spectrum analyzer 32 has a digital output interface, the A / D converter 41 is unnecessary, and the optical power values of the reference lights fr1 to fr3 detected by the optical spectrum analyzer 32 are passed to the DSP 42 as they are. It is.
[0029]
The DSP 42 calculates a command value necessary for controlling the excitation light source 2 according to a predetermined algorithm. Here, assuming that the algorithm executed by the DSP 42 forms a control loop using the three excitation lights fp1 to fp3 and the three reference lights fr1 to fr3, for example, the following equation is used.
[0030]
(Equation 1)

[0031]
In this relational expression, “Pr1” to “Pr3” represent the optical power values of the reference lights fr1 to fr3 detected by the optical spectrum analyzer 32. “Psref” represents a target output level (target light power). “Psref” is a predetermined fixed value. Further, each element of the matrix A (A11 to A33) is a gain coefficient calculated in advance by simulation or the like. “ΔPp1” to “ΔPp3” represent the amounts of fluctuation of the excitation lights fp1 to fp3.
[0032]
The DSP 42 performs feedback control on the pump lights fp1 to fp3 using this relational expression. Then, when each of “Pr1” to “Pr3” falls within a predetermined error range with respect to “Psref”, it is considered that the control loop has converged.
[0033]
When the DSP 42 obtains the fluctuation amounts “ΔPp1” to “ΔPp3” according to the above relational expression, the DSP 42 calculates a set value for setting the optical power of the pump light fp1 to fp3 using the fluctuation amounts. That is, the following calculation is performed. “Pp1 (n)” to “Pp3 (n)” are previous set values, and “Pp1 (n + 1)” to “Pp3 (n + 1)” are new set values.
Pp1 (n + 1) = Pp1 (n) + ΔPp1
Pp2 (n + 1) = Pp2 (n) + ΔPp2
Pp3 (n + 1) = Pp3 (n) + ΔPp3
The D / A converter 43 converts the set values (set values indicating the optical power of the pump light fp1 to fp3) calculated by the DSP 42 into analog values, respectively, and supplies the analog values to the corresponding amplifiers 44-1 to 44-3. . The amplifiers 44-1 to 44-3 amplify the analog values provided from the DSP 42, respectively. Then, power transistors 45-1 to 45-3 generate currents corresponding to the outputs of amplifiers 44-1 to 44-3, respectively.
[0034]
The excitation light source 2 is driven by the current generated by the amplifiers 44-1 to 44-3. That is, the laser diode for generating the pump light fp1 is driven by the current generated by the amplifier 44-1. Similarly, the laser diodes for generating the pump lights fp2 and fp3 are driven by the currents generated by the amplifiers 44-2 and 44-3, respectively.
[0035]
Thus, the control circuit 33 controls the optical power of the pump light fp1 to fp3 using the reference light fr1 to fr3. At this time, the optical power of each of the excitation lights fp1 to fp3 is adjusted so that, for example, the optical powers of the reference lights fr1 to fr3 are equalized. Therefore, in the optical transmission system of the embodiment, appropriate Raman amplification is always performed regardless of the arrangement of the signal lights fs1 to fsn.
[0036]
In order to efficiently obtain a wide signal band in an optical transmission system using Raman amplification, a plurality of pump lights p1 to fp3 are generally arranged at appropriate frequency intervals or wavelength intervals. For this reason, if a plurality of reference lights fr1 to fr3 are arranged at wavelengths at which Raman gains caused by these pump lights p1 to fp3 become peaks, as shown in FIG. In addition, the WDM light is arranged at an appropriate frequency interval or wavelength interval over almost the entire signal band. Then, in the optical transmission system of the embodiment, Raman amplification is controlled using these reference lights fr1 to fr3. Therefore, when the number of signal lights included in the WDM light is small (only four signal lights fs1 to fs4 are used in FIG. 6), or when the arrangement of the signal lights included in the WDM light is biased (In FIG. 6, the signal light is arranged only in a short wavelength region in the signal band.), A suitable Raman amplification can be obtained. That is, the gain can be equalized over the entire signal band.
[0037]
Further, in the system of the embodiment, since the reference lights fr1 to fr3 are arranged at wavelengths at which the Raman gains caused by the pump lights p1 to fp3 are at a peak, it is relatively easy to adjust the pump lights p1 to fp3. A desired gain tilt can be obtained.
[0038]
Further, in the above-described embodiment, the control for equalizing the gain of the signal band of the WDM light using the reference lights fr1 to fr3 is performed. However, the reference light controls the total output power of the WDM light. May be used. In this case, the control circuit 33 includes, for example, an equalization control unit 51 and an ALC (Automatic Level Control) unit 52, as shown in FIG. Here, the equalization control unit 51 controls the excitation lights fp1 to fp3 generated by the excitation light source 2 as described above. On the other hand, the ALC unit 52 calculates an average value of each optical power of the reference lights fr1 to fr3 detected by the optical spectrum analyzer 32.
[0039]
Then, the ALC unit 52 may correct the calculation result of the equivalent control unit 51 based on the average value, for example. In this case, the control circuit 33 controls the pump lights p1 to fp3 based on not only the respective optical powers of the reference lights fr1 to fr3, but also their average values. As a result, the gain of the Raman amplification is equalized, and the output power of the WDM light is maintained at a desired level.
[0040]
The ALC control unit 52 controls the optical attenuator (ATT) 53 so that, for example, the average value of each optical power of the reference lights fr1 to fr3 matches a predetermined target output power per one channel. The amount of attenuation may be controlled.
[0041]
As described above, only the reference lights fr1 to fr3 are extracted from the WDM light, and the total output power of the WDM light (or the optical power of each signal light included in the WDM light) is estimated using the reference lights. According to this method, the optical power of the WDM light can be accurately monitored even when the number of signal lights included in the WDM light is small.
[0042]
That is, as in the conventional system, when trying to detect the optical power of the WDM light using one photodiode, not only the optical power of the signal light but also the optical power caused by noise such as ASE over the entire band. And detect it. For example, in the example shown in FIG. 8A, even if only one signal light exists, the optical power of all the shaded areas is detected, so that the optical power of the signal light can be correctly detected. Can not.
[0043]
On the other hand, in the method of the embodiment, since the optical power in a narrow band including each reference light is detected, it is hardly affected by noise. That is, in the method according to the embodiment, only the optical power in the hatched area shown in FIG. 8B is detected, so that the optical power of the reference light can be accurately detected, whereby the WDM light (or WDM light is included). The optical power of each signal light can be accurately detected.
[0044]
FIG. 9 is a configuration diagram of a relay station of the optical transmission system according to another embodiment. Here, the relay station includes an erbium-doped fiber optical amplifier (EDFA) 61 for amplifying a signal band. That is, in this system, a Raman amplifier and an erbium-doped fiber optical amplifier are mixed. The relationship between the Raman amplifier and the erbium-doped fiber optical amplifier 61 is as shown in FIG.
[0045]
The erbium-doped fiber optical amplifier 61 and the Raman amplifier are designed to amplify the signal band as shown in FIG. Here, the gain by the Raman amplifier is obtained by the pump light fp1 to fp3. Then, when trying to obtain a flat Raman gain over the entire signal band, the frequency at which the Raman gain caused by a part of the plurality of pump lights becomes a peak is often located outside the signal band. Sometimes. In the example shown in FIG. 10, the frequency at which the Raman gain due to the pump light fp1 reaches a peak is located outside the signal band.
[0046]
However, in the optical transmission system of the embodiment, the reference lights fr1 to fr3 are set to the frequencies at which the Raman gains caused by the pump lights fp1 to fp3 peak. That is, in the example shown in FIG. 10, the reference light fr1 is located outside the signal band, and is not amplified by the erbium-doped fiber optical amplifier 61, or the amplification amount is insufficient. Therefore, in this state, the optical power of the reference light fr1 becomes weaker than that of the other reference lights fr2 and fr3.
For this reason, in the system of this embodiment, an auxiliary light source (LD) 62 for generating an auxiliary light having the same frequency as the reference light fr1 at each relay station (or some of the relay stations). And a WDM coupler 63 for multiplexing the auxiliary light generated by the auxiliary light source 62 with the WDM light. When the auxiliary light having the same frequency as the reference light fr1 is supplied in this manner, the optical power of the reference light fr1 that is not amplified by the erbium-doped fiber optical amplifier 61 becomes the same level as the other reference lights fr2 and fr3. It is adjusted to become.
[0047]
Further, a WDM coupler 71 is further provided between the optical spectrum analyzer 32 and the optical branching coupler 31, thereby selecting a part of the power of the reference light fp1 outside the signal band, guiding the selected power to the photodiode 72, and relaying the monitoring signal. When the monitoring signal data is loaded by the auxiliary light source 62 and multiplexed through the WDM coupler 63 when the signal is relay-amplified by the device 73, the monitoring signal light can be loaded on the reference light outside the signal band.
[0048]
In the example shown in FIG. 1 or FIG. 9, the optical spectrum analyzer 32 is used as a circuit (detection means) for detecting the optical power of each of the reference lights fr1 to fr3, but the present invention is not limited to this. It is not done.
[0049]
FIG. 11 is an embodiment of a circuit for detecting the optical power of the reference light. Here, the detection circuit 70 is provided instead of the optical spectrum analyzer 32 shown in FIG. 1 or FIG. That is, the detection circuit 70 is provided with the WDM light branched by the branch coupler 31, detects the optical power of the reference lights fr1 to fr3 included in the WDM light, and notifies the control circuit 33 of the detected light power.
[0050]
The detection circuit 70 includes reflection elements 71-1 to 71-3 that selectively reflect the reference lights fr1 to fr3. Here, each of the reflection elements 71-1 to 71-3 is realized by, for example, a fiber Bragg grating. Then, the reflection element 71-1 reflects only the light of the frequency for which the reference light fr1 is set. Similarly, the reflection elements 71-2 and 71-3 reflect only the light of the frequency for which the reference lights fr2 and fr3 are set, respectively. Note that the detection circuit 70 is terminated by a non-reflection termination unit 74.
[0051]
The light reflected by the reflection element 71-1 (that is, the reference light fr1) is guided to the photodiode 73-1 by the optical device 72-1. Here, the optical device 72-1 can be realized by, for example, an optical branching coupler or an optical circulator. Then, the light power of the reference light fr1 is detected by the photodiode 73-1. Similarly, the reference lights fr2 and fr3 reflected by the reflection elements 71-2 and 71-3 are guided to the photodiodes 73-2 and 73-3 by the optical devices 72-2 and 72-3. Then, the optical powers of the reference lights fr2 and fr3 are detected by the photodiodes 73-2 and 73-3.
[0052]
As described above, since the detection circuit shown in FIG. 11 is realized by combining simple optical components, the cost can be reduced as compared with the configuration using the optical spectrum analyzer 32.
[0053]
FIG. 12 is a modification of the detection circuit shown in FIG. This detection circuit includes a wavelength separation filter 75 that selectively allows only a predetermined wavelength to pass. In this example, the wavelength separation filter 75 passes only the reference lights fr1 to fr3. Then, these reference lights fr1 to fr3 are guided to the corresponding photodiodes 73-1 to 73-3, respectively.
[0054]
In the embodiment shown in FIGS. 1 to 12, Raman amplification is realized by three pumping lights fp1 to fp3. However, the present invention is not limited to this. Any system using excitation light is applicable.
[0055]
(Supplementary Note 1) An optical transmission system for transmitting WDM light from a transmitting station to a receiving station using a Raman amplifier,
The Raman amplifier is
An optical amplification medium;
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to the optical amplification medium,
Comprising control means for controlling the excitation light source,
The transmitting station transmits a plurality of reference lights having a wavelength at or near the wavelength at which each Raman gain obtained by the plurality of pump lights is a peak,
The control unit controls the plurality of excitation lights based on optical powers of the plurality of reference lights.
An optical transmission system, characterized in that:
[0056]
(Supplementary Note 2) An optical transmission system for transmitting WDM light from a transmitting station to a receiving station using a Raman amplifier,
The Raman amplifier is
An optical amplification medium;
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to the optical amplification medium,
Comprising control means for controlling the excitation light source,
The transmitting station transmits a plurality of reference lights corresponding to a frequency shifted by the Raman shift frequency with respect to the plurality of pump lights or a frequency in the vicinity thereof,
The control unit controls the plurality of excitation lights based on optical powers of the plurality of reference lights.
An optical transmission system, characterized in that:
[0057]
(Supplementary note 3) The optical transmission system according to supplementary note 1 or 2, wherein
The transmitting station transmits information to the receiving station using at least a part of the plurality of reference lights.
[0058]
(Supplementary note 4) The optical transmission system according to supplementary note 1, wherein
When the WDM light is arranged on a frequency grid in which a predetermined frequency interval is defined, each of the plurality of reference lights is closest to a frequency corresponding to a wavelength determined based on the pump light. Placed on a grid.
[0059]
(Supplementary note 5) The optical transmission system according to supplementary note 2, wherein
When the WDM light is arranged on a frequency grid in which a predetermined frequency interval is defined, each of the plurality of reference lights is placed on a grid closest to a frequency determined based on the excitation light. Be placed.
[0060]
(Supplementary note 6) The optical transmission system according to supplementary note 1 or 2, wherein
Further comprising a detecting means for detecting the optical power of the plurality of reference lights included in the WDM light,
The control means controls the optical power of the plurality of excitation lights so that the optical powers of the plurality of reference lights detected by the detection means are equalized.
[0061]
(Supplementary note 7) The optical transmission system according to supplementary note 6, wherein
The detection means is an optical spectrum analyzer.
(Supplementary note 8) The optical transmission system according to supplementary note 6, wherein
The detecting means includes:
Reflection means for selectively reflecting the plurality of reference lights,
Light receiving means for converting the reference light reflected by the reflecting means into an electric signal,
Is provided.
[0062]
(Supplementary note 9) The optical transmission system according to supplementary note 1 or 2, wherein
The control unit controls the plurality of excitation lights based on an average value of each optical power of the plurality of reference lights.
[0063]
(Supplementary note 10) The optical transmission system according to supplementary note 1 or 2, wherein
The control means controls the output power of the WDM light based on an average value of each light power of the plurality of reference lights.
[0064]
(Supplementary Note 11) An optical transmission system that transmits WDM light from a transmitting station to a receiving station via a relay station using Raman amplification,
The relay station,
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to an optical amplification medium,
Control means for controlling the excitation light source,
The transmitting station has reference light generating means for generating a plurality of reference lights having a wavelength at or near the wavelength at which each Raman gain obtained by the plurality of pump lights is a peak,
The relay station further comprises:
A centralized optical amplifier for amplifying the WDM light,
Auxiliary light supply means for multiplexing auxiliary light having the same wavelength as the reference light located outside the gain band of the centralized optical amplifier with the WDM light in the plurality of reference lights.
The control unit controls the plurality of excitation lights based on optical powers of the plurality of reference lights.
An optical transmission system, characterized in that:
[0065]
(Supplementary Note 12) An optical transmission system for transmitting WDM light from a transmitting station to a receiving station via a relay station using Raman amplification,
The relay station,
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to an optical amplification medium,
Control means for controlling the excitation light source,
The transmitting station has reference light generating means for generating a plurality of reference lights having a wavelength at or near the wavelength at which each Raman gain obtained by the plurality of pump lights is a peak,
The control unit controls the plurality of excitation lights based on optical powers of the plurality of reference lights.
An optical transmission system, characterized in that:
[0066]
(Supplementary Note 13) A Raman amplifier that amplifies the WDM light in an optical transmission system that transmits WDM light including a plurality of signal lights and a plurality of reference lights from a transmitting station to a receiving station,
An optical amplification medium;
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to the optical amplification medium,
Control means for controlling the plurality of excitation lights based on the optical power of the plurality of reference lights,
A Raman amplifier, wherein the plurality of reference lights are arranged at a wavelength at which each Raman gain obtained by the plurality of pump lights becomes a peak or at a wavelength near the peak.
[0067]
(Supplementary Note 14) An optical transmission method for transmitting WDM light from a transmitting station to a receiving station using a Raman amplifier using a plurality of pump lights having different wavelengths,
The transmitting station transmits a plurality of reference lights each having a wavelength at or near a wavelength at which each Raman gain obtained by the plurality of pump lights has a peak, as a part of the WDM light,
The Raman amplifier controls the plurality of pump lights based on the optical powers of the plurality of reference lights.
An optical transmission method, comprising:
[0068]
(Supplementary note 15) The optical transmission system according to supplementary note 11, wherein
The relay station,
Of the plurality of reference lights, the monitoring information is placed on the out-of-band reference light located outside the gain band of the centralized optical amplifier, the reference light is converted into an electric signal by a relay station, and further converted into an optical signal. Auxiliary light supply means for multiplexing with the WDM light,
The control means controls the plurality of excitation lights based on the optical powers of the plurality of reference lights including the out-of-band reference light, and further remotely controls a relay station using the out-of-band reference light to control a state. Relays information for monitoring
An optical transmission system, characterized in that:
[0069]
【The invention's effect】
According to the present invention, in an optical transmission system using Raman amplification, even if the number or arrangement of signal lights included in WDM light changes, the wavelength characteristic of gain can always be controlled accurately. Further, even when the number of signal lights included in the WDM light is small, the output power of the WDM light can be accurately monitored while suppressing the influence of noise accumulation such as ASE. Further, management of the operation of the Raman amplifier is simplified.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical transmission system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a method of arranging reference light.
FIG. 3 is a configuration diagram of a transmitting station.
FIG. 4 is an example of a transmission circuit when data is transmitted using a reference light.
FIG. 5 is a configuration diagram of a control circuit provided in each relay station.
FIG. 6 is a diagram illustrating effects of the optical transmission system according to the embodiment.
FIG. 7 is an embodiment of a relay station that operates based on the optical power of WDM light.
FIG. 8A is a diagram illustrating light detection in the related art, and FIG. 8B is a diagram illustrating light detection in the embodiment.
FIG. 9 is a configuration diagram of a relay station of an optical transmission system according to another embodiment.
FIG. 10 is a diagram for explaining a relationship between a Raman amplifier and an erbium-doped fiber optical amplifier.
FIG. 11 is an embodiment of an apparatus for detecting the optical power of reference light.
FIG. 12 is a modification example of the detection circuit shown in FIG. 11;
FIG. 13 is a configuration diagram of an optical transmission system using a general Raman amplifier.
[Explanation of symbols]
1 Transmission line optical fiber (optical amplification medium)
2 Excitation light source
3 WDM coupler
10 transmitting station
20 receiving stations
30 relay station
32 Optical Spectrum Analyzer
33 control circuit
42 DSP
61 Erbium-doped fiber optical amplifier (EDA)
62 auxiliary light source
70 Detection circuit
71-1 to 71-3 Reflecting element
73-1 to 73-3 Photodiode
75 Wavelength separation filter

Claims (5)

An optical transmission system for transmitting WDM light from a transmitting station to a receiving station using a Raman amplifier,
The Raman amplifier is
An optical amplification medium;
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to the optical amplification medium,
Comprising control means for controlling the excitation light source,
The transmitting station transmits a plurality of reference lights having a wavelength at or near the wavelength at which each Raman gain obtained by the plurality of pump lights is a peak,
The optical transmission system, wherein the control means controls the plurality of pump lights based on optical powers of the plurality of reference lights. The optical transmission system according to claim 1, wherein
The transmitting station transmits information to the receiving station using at least a part of the plurality of reference lights. The optical transmission system according to claim 1, wherein
Further comprising a detecting means for detecting the optical power of the plurality of reference lights included in the WDM light,
The control means controls the optical power of the plurality of excitation lights so that the optical powers of the plurality of reference lights detected by the detection means are equalized. The optical transmission system according to claim 1, wherein
The control unit controls the plurality of excitation lights based on an average value of each optical power of the plurality of reference lights. An optical transmission system for transmitting WDM light from a transmitting station to a receiving station via a relay station using Raman amplification,
The relay station,
An excitation light source that generates a plurality of excitation lights having different wavelengths from each other;
An optical device for guiding the plurality of excitation lights to an optical amplification medium,
Control means for controlling the excitation light source,
The transmitting station has reference light generating means for generating a plurality of reference lights having a wavelength at or near the wavelength at which each Raman gain obtained by the plurality of pump lights is a peak,
The relay station further comprises:
A centralized optical amplifier for amplifying the WDM light,
Auxiliary light supply means for multiplexing the WDM light with auxiliary light having the same wavelength as the reference light located outside the gain band of the centralized optical amplifier among the plurality of reference lights, the control means comprising: An optical transmission system, wherein the plurality of excitation lights are controlled based on the optical powers of a plurality of reference lights.

Images