JP2004072062A - Optical amplifier and control method thereof - Google Patents

Abstract

When performing automatic gain control and automatic level control, an optical amplifier applicable to wavelength division multiplexing that does not easily cause a control error, does not require a complicated configuration, and can easily cope with an increase or decrease in the number of wavelengths. And a method for controlling an optical amplifier.
A first light amplifying unit, a variable light attenuator optically connected between the first and second light amplifying units, and a first light amplifying unit. A first control unit 36 for controlling the gains of the first and second optical amplification units 16 and 20 based on the input of the amplification unit 16 and the output of the second optical amplification unit 20; The above object is achieved by providing a second control unit that controls the attenuation of the variable optical attenuator based on the input and output and the input and output of the second optical amplification unit.
[Selection diagram] FIG.

Description

なお、上記式のＩＮ１ＭＯＮ、ＯＵＴ１ＭＯＮ、ＩＮ２ＭＯＮ及びＯＵＴ２ＭＯＮは、それぞれフォトディテクタ３２，３４，５０及び５２による光パワーのモニタリング値である。
【００５９】
そして、ＥＤＦ＿Ｇ′とＥＤＦ＿Ｇ′の目標値であるＥＤＦ＿Ｇとの比較が行われ、ＥＤＦ＿Ｇ′とＥＤＦ＿Ｇとの差分が零になるように次式に従って可変光減衰器１８の減衰が制御される。
【００６０】

なお、上記式のＡＭＰ＿Ｇは光増幅器全体の利得である。また、ＶＯＡ＿Ｌは可変光減衰器１８の減衰である。したがって、ＶＯＡ＿Ｌ＝ＥＤＦ＿Ｇ′−ＡＭＰ＿Ｇにより求まる値となるように可変光減衰器１８の減衰を制御すれば、光増幅器全体での利得が一定に保たれるように、容易に制御できる。
【００６１】
図６は、本発明による光増幅器の第２実施例のブロック図である。この光増幅器は、入力端８２及び出力端８４の間に第１の光増幅ユニット８６、第１の可変光減衰器（ＶＯＡ）８８と、第２の光増幅ユニット９２とを光学的にカスケード接続するように構成されている。
【００６２】
入力端８２に供給された増幅されるべき信号光は、第１の光増幅ユニット８６において、光カプラ９４及びＷＤＭカプラ９６をこの順に通ってＥＤＦ１００に供給される。レーザダイオード１０４からのポンプ光は、ＷＤＭカプラ９６を通ってＥＤＦ１００に供給される。これにより、ポンプ光のパワーに応じた利得が得られるようになっている。ＥＤＦ１００内において増幅された信号光は、光カプラ１０２を通って第１の光増幅ユニット８６から出力される。また、光カプラ９４で分岐された信号光は光カプラ９８を通って第１の光増幅ユニット８６から出力される。
【００６３】
第１の光増幅ユニット８６の入力及び出力をモニタリングするために、光増幅器は、それぞれフォトディテクタ１０６及び１０８が設けられている。フォトディテクタ１０６は光カプラ９８で分岐された信号光を電気信号に変換する。フォトディテクタ１０８は、光カプラ１０２で分岐された信号光を電気信号に変換する。フォトディテクタ１０６及び１０８からの電気信号は、第２の制御ユニットとしてのＡＧＣ回路１１２に供給される。
【００６４】
第１の光増幅ユニット８６により増幅された信号光は第１の可変光減衰器８８によって減衰されたあと、第２の光増幅ユニット９２に供給される。また、光カプラ９４で分岐された信号光は光カプラ９８を通って第２の可変光減衰器（ＶＯＡ）９０に供給され、減衰される。第２の可変光減衰器９０で減衰された信号光をモニタリングするために、光増幅器はフォトディテクタ１２４が設けられている。
【００６５】
フォトディテクタ１２４は第２の可変光減衰器９０で減衰された信号光を電気信号に変換する。フォトディテクタ１２４からの電気信号は、ＡＧＣ回路１１０に供給される。
【００６６】
また、第２の光増幅ユニット９２に供給された信号光は、光カプラ１１４およびＷＤＭカプラ１１６をこの順に通ってＥＤＦ１１８に供給される。レーザダイオード１２２からのポンプ光は、ＷＤＭカプラ１１６を介してＥＤＦ１１８に供給される。これによりポンプ光のパワーに応じた利得が得られている。ＥＤＦ１１８において増幅された信号光は、光カプラ１２０及び出力端８４を通って出力される。
【００６７】
第２の光増幅ユニット９２の入力及び出力をモニタリングするために、光増幅器は、それぞれフォトディテクタ１２６及び１２８が設けられている。フォトディテクタ１２６は光カプラ１１４で分岐された信号光を電気信号に変換する。フォトディテクタ１２８は、光カプラ１２０で分岐された信号光を電気信号に変換する。フォトディテクタ１２６からの電気信号は、ＡＧＣ回路１１２に供給される。また、フォトディテクタ１２８からの電気信号はＡＧＣ回路１１０及び１１２に供給される。
【００６８】
ＡＧＣ回路１１０からの制御信号は、ポンプ光源としてのレーザダイオード１０４及びレーザダイオード１２２に供給される。これにより、入力端８２から出力端８４に至るトータル部分における総利得が目標値に制御される。
【００６９】
また、ＡＧＣ回路１１２は第１の光増幅ユニット８６における利得と第２の光増幅ユニット９２における利得の和が一定になるように第１の可変光減衰器８８の減衰を制御する。なお、光増幅器は、ＡＧＣ回路１１０および１１２からなる制御回路部と、制御回路部以外の光回路部とに大別される。
【００７０】
図６の光増幅器では、フォトディテクタ１０６からの電気信号（以下、ＰＤ１モニタ値という）と，フォトディテクタ１０８からの電気信号（以下、ＰＤ２モニタ値という）と，フォトディテクタ１２４からの電気信号（以下、ＰＤ３モニタ値という）と，フォトディテクタ１２６からの電気信号（以下、ＰＤ４モニタ値という）と，フォトディテクタ１２８からの電気信号（以下、ＰＤ５モニタ値という）とを用いて、光増幅器全体利得（Ａｍｐ＿Ｇａｉｎ），ＥＤＦ利得（ＥＤＦ＿ｔｏｔａｌ＿Ｇａｉｎ），ＶＯＡ１減衰量（ＶＯＡ１＿Ｌｏｓｓ），ＶＯＡ２減衰量（ＶＯＡ２＿Ｌｏｓｓ）の制御を行う。
【００７１】
なお、ＰＤ１モニタ値は入力光信号のモニタ値である。ＰＤ２モニタ値は、第１の光増幅ユニット８６により増幅された光信号のモニタ値である。ＰＤ３モニタ値は、第２の可変光減衰器９０により減衰された光信号のモニタ値である。ＰＤ４モニタ値は、第１の可変光減衰器８８により減衰された光信号のモニタ値である。ＰＤ５モニタ値は、第２の光増幅ユニット９２により増幅された光信号のモニタ値である。
【００７２】
光増幅器全体利得は、光増幅器全体の利得である。ＥＤＦ利得は、光増幅ユニット８６及び９２の利得和である。ＶＯＡ１減衰量は、第１の可変光減衰器８８の減衰である。ＶＯＡ２減衰量は、第２の可変光減衰器９０の減衰である。
【００７３】
光増幅器全体利得，ＥＤＦ利得，ＶＯＡ１減衰量，ＶＯＡ２減衰量は、ＰＤ１モニタ値〜ＰＤ５モニタ値を用いて以下のように求めることができる。
【００７４】

上記の関係により、図６の光増幅器では通常動作（ＡＧＣ状態）においてＶＯＡ１減衰量および光増幅器全体利得を制御している。
【００７５】
次に、ＡＧＣ回路１１０の構成例について説明する。ＡＧＣ回路１１０は、光増幅器全体利得が所望の値となるようにレーザダイオード１０４および１２２を駆動するため、光増幅器全体利得一定制御を行う。
【００７６】
図７は、光増幅ユニット８６及び９２の利得を制御するＡＧＣ回路の第２実施例の構成図である。フォトディテクタ１２４及び抵抗Ｒ３は、電源線Ｖｃｃとグランドとの間に直列に接続されている。フォトディテクタ１２４には逆バイアスが与えられ、可変光減衰器９０の出力に応じた光電流がフォトディテクタ１２４及び抵抗Ｒ３を流れる。
【００７７】
したがって、フォトディテクタ１２４及び抵抗Ｒ３の接続点の電位を可変光減衰器９０の出力に応じた電圧信号として取り出すことができる。信号成分をカットして可変光減衰器９０の出力の平均レベルを得るために、抵抗Ｒ３には並列にキャパシタＣ３が接続されている。
【００７８】
同じように、フォトディテクタ１２８及び抵抗Ｒ５は、電源線Ｖｃｃとグランドとの間に直列に接続されている。フォトディテクタ１２８には逆バイアスが与えられ、光増幅ユニット９２の出力に応じた光電流がフォトディテクタ１２８及び抵抗Ｒ５を流れる。
【００７９】
したがって、フォトディテクタ１２８及び抵抗Ｒ５の接続点の電位を光増幅ユニット９２の出力に応じた電圧信号として取り出すことができる。信号成分をカットして光増幅ユニット９２の出力の平均レベルを得るために、抵抗Ｒ５には並列にキャパシタＣ５が接続されている。
【００８０】
フォトディテクタ１２４による電圧信号は、利得が固定されている増幅器１３０によりインピーダンス変換および増幅されて差動増幅器１３４の一方の入力ポートに供給される。また、フォトディテクタ１２８による電圧信号は利得が固定されている増幅器１３２によりインピーダンス変換および増幅されて差動増幅器１３４の他方の入力ポートに供給される。
【００８１】
光増幅器は、ポンプ光源としてのレーザダイオード１０４を駆動するための増幅器１３６、トランジスタ１３８および抵抗Ｒ１が設けられている。また、光増幅器はレーザダイオード１２２を駆動するための増幅器１４０，トランジスタ１４２および抵抗Ｒ２が設けられている。そして、レーザダイオード１０４及び１２２は差動増幅器１３４の出力に基づいて駆動制御される。
【００８２】
増幅器１３０及び１３２の出力レベルをそれぞれＡｍｐ３＿ＯＵＴおよびＡｍｐ５＿ＯＵＴとすると、次の関係が満足されるように抵抗Ｒ３及びＲ５の値ならびに増幅器１３０および１３２の利得が設定される。
【００８３】
即ち、ＰＤ３モニタ値，ＰＤ５モニタ値がそれぞれｘ［ｄＢｍ］、ｘ＋Ａｍｐ＿Ｇａｉｎ基準値［ｄＢｍ］のときに、Ａｍｐ３＿ＯＵＴおよびＡｍｐ５＿ＯＵＴが同じｙ［Ｖ］で一致するようにフォトディテクタ１２４および１２８にそれぞれ関連するモニタ回路の受光感度［Ｖ／Ｗ］を設定する。これは、フォトディテクタ１２４および１２８にそれぞれ関連するモニタ回路の受光感度［Ｖ／Ｗ］に１０^{（ＡＭＰ＿Ｇ／１０）}の比を持たせることを意味している。ここで、ＡＭＰ＿Ｇは光増幅器全体の利得である。
【００８４】
そして、差動増幅器１３４の出力は入力ポートに供給される電圧の差分が０になるようにレーザダイオード１０４及び１２２が駆動制御される。したがって、図６の光増幅器では波長数変化時であっても光増幅器全体利得を一定に保持することができる。
【００８５】
しかし、上記の関係では光増幅器全体利得基準値（ＡＭＰ＿Ｇａｉｎ基準値）が一定であるので、一波当たりの入力信号光パワーが変動した場合に、これに連動して出力信号光パワーも変動してしまう。そこで、図６の光増幅器では出力信号光パワーが制御目標値で一定になるように、後述するＡＬＣを用いて入力信号光の変動を補償する制御を行う。
【００８６】
光増幅器では、伝送路損失のバラツキや光ファイバ伝送路の経年劣化などに起因した入力ダイナミックレンジを吸収する必要があり、この制御をＡＬＣにより実現している。ＡＬＣ状態では、光増幅器に対して上流側に設けられている監視制御装置から波長数情報が通知され、この波長数情報を用いることで光増幅器の出力目標値が決定される。
【００８７】
従来の光増幅器では、中段のＡＬＣユニット８の信号出力が制御目標値になるように可変光減衰器を駆動させ、ＶＯＡ減衰量の制御を実施していた。この制御目標値は、以下のように算出される。
【００８８】
ＡＬＣユニット制御目標値［ｄＢｍ］＝ＡＬＣユニット出力基準値［ｄＢｍ／ｃｈ］＋１０Ｌｏｇ（波長数）−Ｇｃ［ｄＢ］
なお、Ｇｃは前段のＡＧＣユニット６の不足利得であり、以下のように算出される。
【００８９】
Ｇｃ［ｄＢ］＝ＡＧＣユニット利得目標値［ｄＢ］−ＡＧＣユニット利得［ｄＢ］
したがって、後段のＡＧＣユニット１０の利得目標値はＧｃ［ｄＢ］だけ増加させる必要があった。なお、可変光減衰器は光増幅器全体におけるＮＦおよび励起効率の観点から光増幅器の中段に構成されている。
【００９０】
一方、本発明では一波当たりの入力信号の変動をＶＯＡ１減衰量の制御により行わない。前述したように光増幅器全体利得一定制御では入力信号が変動した分、出力信号を変化させるように制御し、後述するＡＧＣ回路１１２の制御でＶＯＡ１減衰量が一定値に保持されるためである。
【００９１】
また、１つのＡＧＣ回路１１０で光増幅ユニット８６及び９２の利得を制御する光増幅器では、一波当たりの入力信号の変動が発生すると出力信号も連動して変動してしまうために、一波当たりの入力信号の変動を補償する回路またはマイクロコントローラなどによる制御を設ける必要がある。この結果、入力信号変動を補償する回路またはマイクロコントローラなどの雑音および応答速度が制御回路部に影響を与え、光増幅器の特性を劣化させる可能性がある。
【００９２】
本願発明による光増幅器では、入力信号の変動を光回路部で補償するため、以下の処理方法１及び２に示すように、制御回路部での補償を必要としない構成である。
［処理方法１］
処理方法１では、ＰＤ１モニタ値から入力信号が入力ダイナミックレンジ内の何処にいるのかを認識する。その認識した情報に基づき、ＶＯＡ２減衰量が制御され、出力信号レベルが一定に制御される。なお、光増幅器は上流側に設けられている監視制御装置から通知される波長数情報を用いて、制御に必要な以下の値を算出する。
【００９３】
ＰＤ１モニタ値：ｚ１［ｄＢｍ］
ＰＤ３モニタ値：ｚ３［ｄＢｍ］
入力信号波長数情報：Ｎ
入力信号光ハ゜ワー：ｚ１−１０Ｌｏｇ（Ｎ）［ｄＢｍ／ｃｈ］
一波当たりの入力信号光ハ゜ワー上限値：ｕ［ｄＢｍ／ｃｈ］
入力タ゛イナミックレンシ゛での位置付け：Ｌ０＝ｕ−｛ｚ１−１０Ｌｏｇ（Ｎ）｝
ＶＯＡ２減衰量：Ｌ＝ｚ１−ｚ３−Ｌｄ［ｄＢ］
なお、入力信号光パワー，入力ダイナミックレンジでの位置付け，ＶＯＡ２減衰量は、例えばマイクロコントローラなどで計算される。また、一波当たりの入力信号光パワー上限値は例えばＲＯＭに格納されている。
【００９４】
ここでＬｄは、一波当たりの入力信号光パワーがｕ［ｄＢｍ／ｃｈ］のときのＶＯＡ２減衰量（デッドロス）である。本発明の光増幅器では、一波当たりの入力光信号の変動（Ｌ０に相当）を算出してＬ＝Ｌ０となる様にＶＯＡ２減衰量Ｌを制御する。この処理により、一波当たりの入力信号光パワーが変化した場合でも増幅器１３０の出力値は変化しない。
【００９５】
この結果、増幅器１３２の出力値もＡＧＣ回路１１０により変化しないように制御されているため、光増幅器からの出力信号光パワーが一定に制御されてＡＬＣ動作が実現できる。
［処理方法２］
処理方法２では、ＰＤ５モニタ値と出力信号基準値とを比較し、この差分が０となるようにＶＯＡ２減衰量を制御する。なお、光増幅器は上流側に設けられている監視制御装置から光増幅器に通知される波長数情報を用いて、制御に必要な以下の値を算出する。
【００９６】
ＰＤ５モニタ値：ｚ５［ｄＢｍ］
入力信号波長数情報：Ｎ
一波当たりの出力基準値：Ａ０［ｄＢｍ／ｃｈ］
一波当たりの出力信号光ハ゜ワー：Ａ［ｄＢｍ／ｃｈ］　＝ｚ５−１０Ｌｏｇ（Ｎ）
なお、一波当たりの出力信号ハ゜ワーは、例えばマイクロコントローラなどで計算される。また、一波当たりの出力基準値は例えばＲＯＭに格納されている。本発明の光増幅器では、ＶＯＡ２減衰量Ｌにより、一波当たりの出力信号光パワーＡを制御できる。したがって、Ａ＝Ａ０となる様にＶＯＡ２減衰量Ｌを制御すればＡＬＣ動作が実現できる。なお、ＶＯＡ２減衰量Ｌは処理方法１と同様にＬ＝Ｌ０となる。
【００９７】
前述した光増幅器全体利得一定制御およびＡＬＣ動作のみでは、入力ダイナミックレンジを考慮すると、ＥＤＦ利得偏差の影響により信号光波長帯域における信号利得の特性を一定に保つことができない。このため、本発明の光増幅器では利得偏差の特性を一定に保つために、ＥＤＦ利得一定制御を行う。
【００９８】
図８は、可変光減衰器８８及び９０の減衰を制御するＡＧＣ回路の第２実施例の構成図である。第１の光増幅ユニット８６の入力および出力をモニタリングするために、フォトディテクタ１０６及び１０８による電圧信号は利得が固定されている増幅器１５０または１５２により増幅されて、それぞれＡＤＣ１５８及び１６０に供給される。ＡＤＣ１５８及び１６０は、フォトディテクタ１０６及び１０８による電圧信号をデジタル信号に変換してマイクロコントローラ１６６に供給する。
【００９９】
第２の光増幅ユニット９２の入力および出力をモニタリングするために、フォトディテクタ１２６及び１２８による電圧信号は利得が固定されている増幅器１５４または１５６により増幅されて、それぞれＡＤＣ１６２及び１６４に供給される。ＡＤＣ１６２及び１６４は、フォトディテクタ１２６及び１２８による電圧信号をデジタル信号に変換してマイクロコントローラ１６６に供給する。
【０１００】
マイクロコントローラ１６６では、前述したように、光増幅器全体利得とＶＯＡ１減衰量とを加算してＥＤＦ利得を算出できる。そのため、ＶＯＡ１減衰量が以下のようなＶＯＡ１減衰量の目標値（ＶＯＡ１＿Ｌｏｓｓ目標値）となるように可変光減衰器８８を駆動することで、マイクロコントローラ１６６はＥＤＦ利得一定制御を実現する。
【０１０１】
ＶＯＡ１減衰量目標値＝光増幅器全体利得−ＥＤＦ利得目標値
マイクロコントローラ１６６はＶＯＡ１減衰量目標値を算出し、そのＶＯＡ１減衰量目標値となるように可変光減衰器８８を制御する。可変光減衰器８８を制御するためにマイクロコントローラ１６６から出力された制御信号は、ＤＡＣ１６８により電圧信号に変換されて、増幅器１７０、トランジスタ１７２及び抵抗Ｒ６からなる可変光減衰器８８の駆動回路に供給される。
【０１０２】
次に、図６の光増幅器の動作について図９を参照しつつ説明する。図９は、光増幅器の動作について説明するための模式図である。また、図１０は、光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【０１０３】
グラフ１８０は、入力上限時（入力上限以外でもよい）にＰＤ１モニタ値およびＰＤ３モニタ値が同じ値を持つように初期値が設定された初期設定制御状態を表すものである。ＶＯＡ１減衰量は、例えばＲＯＭなどに格納されている初期値となっている。
【０１０４】
グラフ１８２は、入力信号に変動が発生した入力変動制御状態を表すものである。グラフ１８２は、グラフ１８０に比べて信号パワーが小さくなるように変動している。
【０１０５】
グラフ１８４は、入力信号の変動量を算出し、その変動量を補正するようにＶＯＡ２減衰量を制御する変動補正制御状態を表すものである。ＶＯＡ２減衰量の制御により、一波当たりの入力信号の変動量が補正される。また、グラフ１８６はＰＤ３モニタ値およびＰＤ５モニタ値を用いたＡＧＣにより光増幅器全体利得一定制御が行われ、ＥＤＦ利得目標値を保持するようにＶＯＡ１減衰量が制御される。
【０１０６】
なお、図１０の表に含まれる「Ｘ」は、入力信号パワーを表す。「α」は、変動量を表す。「Ｌ１」は、ＶＯＡ１減衰量を表す。「Ｌ２」は、ＶＯＡ２減衰量を表す。「Ａ」は、光増幅器全体利得を表す。
【０１０７】
本実施例では、可変光減衰器８８及び９０を独立に制御しているが、一波当たりの入力レベルがＸ［ｄＢ］変動したとき、可変光減衰器８８及び９０の減衰量の変化が同じくＸ［ｄＢ］となる。そこで、２つの可変光減衰器を有する第２実施例の光増幅器と同様な処理を、１つの可変光減衰器を有する光増幅器で行う例について説明する。
【０１０８】
図１１は、本発明による光増幅器の第３実施例のブロック図である。この光増幅器は、入力端１９２及び出力端１９４の間に第１の光増幅ユニット１９６、可変光減衰器（ＶＯＡ）１９８および第２の光増幅ユニット２００を光学的にカスケード接続するように構成されている。
【０１０９】
入力端１９２に供給された増幅されるべき信号光は、第１の光増幅ユニット１９６において、光カプラ２０２及びＷＤＭカプラ２０４をこの順に通ってＥＤＦ２０６に供給される。レーザダイオード２１２からのポンプ光は、ＷＤＭカプラ２０４を通ってＥＤＦ２０６に供給される。これにより、ポンプ光のパワーに応じた利得が得られるようになっている。ＥＤＦ２０６内において増幅された信号光は、アイソレータ２０８及び光カプラ２１０をこの順に通って第１の光増幅ユニット１９６から出力される。また、光カプラ２０２で分岐された第１の分岐信号光は第１の光増幅ユニット１９６からそのまま出力される。
【０１１０】
第１の光増幅ユニット１９６により増幅された信号光は可変光減衰器１９８によって減衰されたあと、第２の光増幅ユニット２００に供給される。第２の光増幅ユニット２００に供給された信号光は、光カプラ２２０，アイソレータ２２２およびＷＤＭカプラ２２４をこの順に通ってＥＤＦ２２６に供給される。レーザダイオード２３２からのポンプ光は、ＷＤＭカプラ２２４を介してＥＤＦ２２６に供給される。これによりポンプ光のパワーに応じた利得が得られている。ＥＤＦ２２６において増幅された信号光は、光カプラ２２８及び出力端１９４を通って出力される。
【０１１１】
第１の光増幅ユニット１９６から出力された第１の分岐信号光は、第２の光増幅ユニット２００の光カプラ２２０に供給され、第２の分岐信号光および第３の分岐信号光に分岐される。また、第３の分岐信号光は可変光減衰器１９８によって減衰されたあと、光カプラ２１０に供給される。光カプラ２１０に供給された第３の分岐信号光は、第４の分岐信号光に分岐される。
【０１１２】
第１の光増幅ユニット１９６の入力をモニタリングするために、光増幅器はフォトディテクタ２３０が設けられている。フォトディテクタ２３０は光カプラ２２０で分岐された第２の分岐信号光を電気信号に変換する。
【０１１３】
第１の光増幅ユニット１９６の入力に可変光減衰器１９８の減衰を反映させた信号光をモニタリングするために、光増幅器はフォトディテクタ２１４が設けられている。フォトディテクタ２１４は光カプラ２１０で分岐された第４の分岐信号光を電気信号に変換する。
【０１１４】
また、第２の光増幅ユニット２００の出力をモニタリングするために、光増幅器はフォトディテクタ２３４が設けられている。フォトディテクタ２３４は光カプラ２２８で分岐された第５の分岐信号光を電気信号に変換する。
【０１１５】
フォトディテクタ２３０からの電気信号は、第２の制御ユニットとしてのＡＧＣ回路２１８に供給される。また、フォトディテクタ２１４及び２３４からの電気信号はＡＧＣ回路２１８及び第１の制御ユニットとしてのＡＧＣ回路２１６に供給される。
【０１１６】
ＡＧＣ回路２１６からの制御信号は、ポンプ光源としてのレーザダイオード２１２及びレーザダイオード２３２に供給される。これにより、入力端１９２から出力端１９４に至るトータル部分における総利得が目標値に制御される。
【０１１７】
また、ＡＧＣ回路２１８は第１の光増幅ユニット１９６における利得と第２の光増幅ユニット２００における利得の和が一定になるように可変光減衰器１９８の減衰を制御する。なお、光増幅器は、ＡＧＣ回路２１６および２１８からなる制御回路部と、制御回路部以外の光回路部とに大別される。
【０１１８】
図１１の光増幅器では、フォトディテクタ２１４からの電気信号（以下、ＰＤ１モニタ値という）と，フォトディテクタ２３０からの電気信号（以下、ＰＤ２モニタ値という）と，フォトディテクタ２３４からの電気信号（以下、ＰＤ３モニタ値という）とを用いて、光増幅器全体利得，ＥＤＦ利得，ＶＯＡ減衰量の制御を行う。
【０１１９】
なお、アイソレータ２０８は第４の分岐信号光がＥＤＦ２０６に入るのを防いでいる。アイソレータ２２２はＥＤＦ２２６のＢａｃｋ＿ＡＳＥがフォトディテクタ２１４および２３０に入るのを防いでいる。
【０１２０】
光増幅器全体利得，ＥＤＦ利得，ＶＯＡ減衰量は、ＰＤ１モニタ値〜ＰＤ３モニタ値を用いて以下のように求めることができる。
【０１２１】

上記の関係により、図１１の光増幅器では通常動作（ＡＧＣ状態）において光増幅器全体利得およびＶＯＡ減衰量を制御している。
【０１２２】
次に、ＡＧＣ回路２１６の処理について説明する。ＡＧＣ２１６は、光増幅器全体利得が所望の値となるようにレーザダイオード２１２および２３２を駆動するため、光増幅器全体利得一定制御を行う。なお、ＡＧＣ回路２１６の構成は前述したＡＧＣ回路１１０の構成と同様でよい。
【０１２３】
光増幅器全体利得一定制御は、第２実施例と同様に、ＰＤ１モニタ値およびＰＤ３モニタ値より算出される光増幅器全体利得が所定の値となるようにレーザダイオード２１２および２３２の出力を制御する。なお、実際の光増幅器全体利得一定制御はＰＤ１モニタ値およびＰＤ３モニタ値において以下の設定条件が満足されるように実施される。
【０１２４】
即ち、ＰＤ１モニタ値，ＰＤ３モニタ値がそれぞれｘ［ｄＢｍ］、ｘ＋Ａｍｐ＿Ｇａｉｎ基準値［ｄＢｍ］のときに、図７の増幅器１３０及び１３２の出力が同じｙ［Ｖ］で一致するようにフォトディテクタ２１４および２３４にそれぞれ関連するモニタ回路の受光感度［Ｖ／Ｗ］を設定する。
【０１２５】
そして、差動増幅１３４の出力は入力ポートに供給される電圧の差分が０になるようにレーザダイオード２１２及び２３２が駆動制御される。したがって、図１１の光増幅器では波長数変化時であっても光増幅器全体利得を一定に保持することができる。
【０１２６】
また、図１１の光増幅器においても、一波当たりの入力信号光パワーの変動に対応するため、ＡＬＣを用いて入力信号光の変動を補償する制御を行う。ＡＬＣ状態では、光増幅器に対して上流側に設けられている監視制御装置から波長数情報が通知され、この波長数情報を用いることで光増幅器の出力目標値が第２実施例と同様に決定される。
［処理方法１］
処理方法１では、ＰＤ２モニタ値から入力信号が入力ダイナミックレンジ内の何処にいるのかを認識する。その認識した情報に基づき、ＶＯＡ減衰量が制御され、出力信号レベルが一定に制御される。なお、光増幅器は上流側に設けられている監視制御装置から通知される波長数情報を用いて、制御に必要な以下の値を算出する。
【０１２７】
ＰＤ１モニタ値：ｚ１［ｄＢｍ］
ＰＤ２モニタ値：ｚ２［ｄＢｍ］
入力信号波長数情報：Ｎ
入力信号光ハ゜ワー：ｚ２−１０Ｌｏｇ（Ｎ）［ｄＢｍ／ｃｈ］
一波当たりの入力信号光ハ゜ワー上限値：ｕ［ｄＢｍ／ｃｈ］
入力タ゛イナミックレンシ゛での位置付け：Ｌ０＝ｕ−｛ｚ２−１０Ｌｏｇ（Ｎ）｝
ＶＯＡ減衰量：Ｌ＝ｚ２−ｚ１−Ｌｄ［ｄＢ］
なお、入力信号光パワー，入力ダイナミックレンジでの位置付け，ＶＯＡ減衰量は、例えばマイクロコントローラなどで計算される。また、一波当たりの入力信号光パワー上限値は例えばＲＯＭに格納されている。
【０１２８】
ここでＬｄは、一波当たりの入力信号光パワーがｕ［ｄＢｍ／ｃｈ］のときのＶＯＡ減衰量（デッドロス）である。本発明の光増幅器では、第２実施例と同様に、一波当たりの入力光信号の変動（Ｌ０に相当）を算出してＬ＝Ｌ０となる様にＶＯＡ減衰量Ｌを制御する。この結果、一波当たりの入力信号光パワーが変化した場合であっても、ＰＤ１モニタ値およびＰＤ３モニタ値を用いたＡＧＣ動作を行うことで、光増幅器の出力信号光パワーは目標値（ＰＤ１モニタ値＋光増幅器全体利得目標値）となる。
［処理方法２］
処理方法２では、ＰＤ３モニタ値と出力信号基準値とを比較し、この差分が０となるようにＶＯＡ減衰量を制御する。なお、光増幅器は上流側に設けられている監視制御装置から光増幅器に通知される波長数情報を用いて、制御に必要な以下の値を算出する。
【０１２９】
ＰＤ３モニタ値：ｚ３［ｄＢｍ］
入力信号波長数情報：Ｎ
一波当たりの出力基準値：Ａ０［ｄＢｍ／ｃｈ］
一波当たりの出力信号光ハ゜ワー：Ａ［ｄＢｍ／ｃｈ］　＝ｚ３−１０Ｌｏｇ（Ｎ）
なお、一波当たりの出力信号ハ゜ワーは、例えばマイクロコントローラなどで計算される。また、一波当たりの出力基準値は例えばＲＯＭに格納されている。本発明の光増幅器では、ＶＯＡ減衰量Ｌにより、一波当たりの出力信号光パワーＡを制御できる。したがって、Ａ＝Ａ０となる様にＶＯＡ減衰量Ｌを制御すればＡＬＣ動作が実現できる。なお、ＶＯＡ減衰量Ｌは処理方法１と同様にＬ＝Ｌ０となる。
【０１３０】
前述したＡＬＣ動作は、処理方法１又は２の目標値を満足させるようにＶＯＡ減衰量を制御すればよい。なお、ＡＬＣ動作中のＶＯＡ減衰量が変化する速度とＰＤ１モニタ値が補正される速度とが同じになるため、ＥＤＦ利得はＡＬＣ動作中であっても常に一定値をとる。つまり、ＡＬＣ動作中は利得偏差が発生することがない。
【０１３１】
第２実施例のＥＤＦ利得一定制御で説明したように、光増幅器においてはＶＯＡ減衰量を目標値に制御することにより、ＥＤＦ利得一定制御を実現する。
【０１３２】
図１２は、可変光減衰器１９８の減衰を制御するＡＧＣ回路の第３実施例の構成図である。ＰＤ１モニタ値〜ＰＤ３モニタ値は、利得が固定されている増幅器２４０，２４２又は２４４により増幅されて、それぞれＡＤＣ２４６，２４８又は２５０に供給される。ＡＤＣ２４６，２４８又は２５０は、ＰＤ１モニタ値〜ＰＤ３モニタ値をデジタル信号に変換してマイクロコントローラ２５２に供給される。
【０１３３】
マイクロコントローラ２５２では、前述したように、光増幅器全体利得とＶＯＡ減衰量とを加算してＥＤＦ利得を算出できる。そのため、ＶＯＡ減衰量が以下のようなＶＯＡ減衰量の目標値（ＶＯＡ＿Ｌｏｓｓ目標値）となるように可変光減衰器１９８を駆動することで、マイクロコントローラ２５２はＥＤＦ利得一定制御を実現する。
【０１３４】
ＶＯＡ減衰量目標値＝光増幅器全体利得−ＥＤＦ利得目標値
マイクロコントローラ２５２はＶＯＡ減衰量目標値を算出し、そのＶＯＡ減衰量目標値となるように可変光減衰器１９８を制御する。可変光減衰器１９８を制御するためにマイクロコントローラ２５２から出力された制御信号は、ＤＡＣ２５４により電圧信号に変換されて、増幅器２５６、トランジスタ２５８及び抵抗Ｒ５からなる可変光減衰器１９８の駆動回路に供給される。なお、第３実施例においては、ＡＬＣ動作を行うと同時にＥＤＦ利得が目標値となるため、ＶＯＡ減衰量を一定値に制御させるだけでよい。
【０１３５】
次に、図１１の光増幅器の動作について図１３を参照しつつ説明する。図１３は、光増幅器の動作について説明するための模式図である。また、図１４は、光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【０１３６】
グラフ２６０は、入力上限時（入力上限以外でもよい）にＰＤ１モニタ値およびＰＤ２モニタ値が同じ値を持つように初期値が設定された初期設定制御状態を表すものである。ＶＯＡ減衰量は、光増幅器全体利得基準値からＥＤＦ利得目標値を減算した値となるように設定される。
【０１３７】
グラフ２６２は、入力信号に変動が発生した入力変動制御状態を表すものである。グラフ２６２は、グラフ２６０に比べて信号パワーが小さくなるように変動している。
【０１３８】
グラフ２６４は、変動補正制御状態および光増幅器全体利得一定制御状態を表すものである。光増幅器は入力信号の変動量を算出し、その変動量を補正するようにＶＯＡ減衰量を制御する。ＡＬＣ動作によりＶＯＡ減衰量を制御すると、ＥＤＦ利得が目標値となる。ＶＯＡ減衰量の制御により、一波当たりの入力信号の変動量が補正される。また、ＰＤ１モニタ値およびＰＤ３モニタ値を用いたＡＧＣにより光増幅器全体利得一定制御が行われる。
【０１３９】
なお、図１４の表に含まれる「Ｘ」は、入力信号パワーを表す。「α」は、変動量を表す。「Ｌ」は、ＶＯＡ減衰量を表す。「Ａ」は、光増幅器全体利得を表す。第３実施例の光増幅器は、第２実施例の光増幅器に比べて制御シーケンスが簡略化されている。
【０１４０】
前述した第２及び第３実施例の光増幅器では、部品のバラツキおよび温度特性などにより「可変光減衰器の減衰量」対「駆動電流（又は電圧）」の関係が変化してしまうため、図１５のように各モニタ値により減衰量をモニタリングしながら可変光減衰器の制御を実施していた。図１５は、部品のバラツキおよび温度特性などにより可変光減衰器の減衰量対駆動電流（又は電圧）の関係が変化することを説明するための図である。
【０１４１】
しかしながら、可変光減衰器の特性を光増幅器内で持つようにすれば、可変光減衰器の駆動電流を制御することでＶＯＡ減衰量を制御できる。そこで、第２および第３実施例において可変光減衰器の減衰量と駆動電流（又は電圧）の関係が既知であるとき、光増幅器を図１６および図１９のような構成にすることで光回路部品を削減することができる。
【０１４２】
図１６は、本発明による光増幅器の第４実施例のブロック図である。図１６の光増幅器は、フォトディテクタ１０６，１０８及び１２６が削減されている点が図６の光増幅器の構成と異なっている。そこで、図１６では図６と同一部分に同一符号を付して説明を省略する。なお、図１６の光増幅器は可変光減衰器の特性をテーブルまたは関数として持ち、例えばマイクロコントローラで処理した値で可変光減衰器を駆動する。
【０１４３】
光増幅器全体利得，ＥＤＦ利得，ＶＯＡ１減衰量，ＶＯＡ２減衰量は、ＰＤ３モニタ値，ＰＤ５モニタ値を用いて以下のように求めることができる。なお、ＰＤ３モニタ値とＶＯＡ２減衰量との加算値は入力信号パワーに相当する。
【０１４４】
Ａｍｐ＿Ｇａｉｎ＝ＰＤ５モニタ値−（ＰＤ３モニタ値＋ＶＯＡ２＿Ｌｏｓｓ）
ＥＤＦ＿ｔｏｔａｌ＿Ｇａｉｎ＝Ａｍｐ＿Ｇａｉｎ＋ＶＯＡ１＿Ｌｏｓｓ
光増幅器全体利得一定制御は、ＰＤ３モニタ値およびＰＤ５モニタ値により算出される光増幅器全体利得が、所望の値となる様にレーザダイオード１０４及び１２２を駆動する。なお、ＡＧＣ回路１１０の構成は図７と同様であるので説明を省略する。
【０１４５】
また、ＡＬＣ動作は第２実施例の光増幅器と同様に、入力信号または出力信号のモニタ値から一波当たりの入力信号の変動を算出し、算出した値を目標値として可変光減衰器８８および９０を駆動する。
【０１４６】
さらに、図１６の光増幅器は図１７のようなＡＧＣ回路１１２を用いてＥＤＦ利得一定制御を行う。図１７は、可変光減衰器８８及び９０の減衰を制御するＡＧＣ回路の第４実施例の構成図である。
【０１４７】
フォトディテクタ１２４及び１２８による電圧信号は、利得が固定されている増幅器２７０または２７２により増幅されて、それぞれＡＤＣ２７４及び２７６に供給される。ＡＤＣ２７４及び２７６は、フォトディテクタ１２４及び１２８による電圧信号をデジタル信号に変換してマイクロコントローラ２７８に供給する。
【０１４８】
マイクロコントローラ２７８では、前述したように、光増幅器全体利得とＶＯＡ１減衰量とを加算してＥＤＦ利得を算出できる。そのため、ＶＯＡ１減衰量が以下のようなＶＯＡ１減衰量の目標値（ＶＯＡ１＿Ｌｏｓｓ目標値）となるように可変光減衰器８８を駆動することで、マイクロコントローラ２７８はＥＤＦ利得一定制御を実現する。
【０１４９】
ＶＯＡ１減衰量目標値＝光増幅器全体利得−ＥＤＦ利得目標値
マイクロコントローラ２７８はＶＯＡ１減衰量目標値を算出し、そのＶＯＡ１減衰量目標値となるように可変光減衰器８８を制御する。可変光減衰器８８を制御するためにマイクロコントローラ２７８から出力された制御信号は、ＤＡＣ２８０により電圧信号に変換されて、増幅器２８２、トランジスタ２８４及び抵抗Ｒ５からなる可変光減衰器８８の駆動回路に供給される。
【０１５０】
次に、図１６の光増幅器の動作について説明する。図１８は、光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【０１５１】
図１６の光増幅器は、入力上限時（入力上限以外でもよい）のＶＯＡ２減衰量およびＰＤ１モニタ値を設定する。なお、ＶＯＡ１減衰量は、例えばＲＯＭなどに格納されている初期値となっている。
【０１５２】
光増幅器は、入力信号に変動が発生しているとき、その入力信号の変動量を算出し、その変動量を補正するようにＶＯＡ２減衰量を制御する。ＶＯＡ２減衰量の制御により、一波当たりの入力信号の変動量が補正される。また、ＰＤ３モニタ値およびＰＤ５モニタ値を用いたＡＧＣにより光増幅器全体利得一定制御が行われ、ＥＤＦ利得目標値を保持するようにＶＯＡ１減衰量が制御される。
【０１５３】
なお、図１８の表に含まれる「Ｘ」は、入力信号パワーを表す。「α」は、変動量を表す。「Ｌ１」は、ＶＯＡ１減衰量を表す。「Ｌ２」は、ＶＯＡ２減衰量を表す。「Ａ」は、光増幅器全体利得を表す。
【０１５４】
図１９は、本発明による光増幅器の第５実施例のブロック図である。図１９の光増幅器は、フォトディテクタ２３０が削減されている点が図１１の光増幅器の構成と異なっている。そこで、図１９では図１１と同一部分に同一符号を付して説明を省略する。なお、図１９の光増幅器は可変光減衰器の特性をテーブルまたは関数として持ち、例えばマイクロコントローラで処理した値で可変光減衰器を駆動する。
【０１５５】
光増幅器全体利得，ＥＤＦ利得，ＶＯＡ減衰量は、ＰＤ１モニタ値，ＰＤ３モニタ値を用いて以下のように求めることができる。なお、ＰＤ１モニタ値とＶＯＡ減衰量との加算値は入力信号パワーに相当する。
【０１５６】
Ａｍｐ＿Ｇａｉｎ＝ＰＤ３モニタ値−（ＰＤ１モニタ値＋ＶＯＡ＿Ｌｏｓｓ）
ＥＤＦ＿ｔｏｔａｌ＿Ｇａｉｎ＝Ａｍｐ＿Ｇａｉｎ＋ＶＯＡ＿Ｌｏｓｓ
光増幅器全体利得一定制御は、ＰＤ１モニタ値およびＰＤ３モニタ値により算出される光増幅器全体利得が、所望の値となる様にレーザダイオード２１２及び２３２を駆動する。なお、ＡＧＣ回路２１６の構成は図７と同様であるので説明を省略する。
【０１５７】
また、ＡＬＣ動作は第２実施例の光増幅器と同様に、入力信号または出力信号のモニタ値から一波当たりの入力信号の変動を算出し、算出した値を目標値として可変光減衰器１９８を駆動する。
【０１５８】
さらに、図１９の光増幅器は前述したようなＡＧＣ回路２１８を用いてＥＤＦ利得一定制御を行う。フォトディテクタ２１４及び２３４による電圧信号は、利得が固定されている増幅器により増幅されて、それぞれＡＤＣ２７４に供給される。ＡＤＣは、フォトディテクタ２１４及び２３４による電圧信号をデジタル信号に変換してマイクロコントローラに供給する。
【０１５９】
マイクロコントローラでは、前述したように、光増幅器全体利得とＶＯＡ減衰量とを加算してＥＤＦ利得を算出できる。そのため、ＶＯＡ減衰量が以下のようなＶＯＡ減衰量の目標値（ＶＯＡ１＿Ｌｏｓｓ目標値）となるように可変光減衰器１９８を駆動することで、マイクロコントローラはＥＤＦ利得一定制御を実現する。
【０１６０】
ＶＯＡ減衰量目標値＝光増幅器全体利得−ＥＤＦ利得目標値
マイクロコントローラはＶＯＡ減衰量目標値を算出し、そのＶＯＡ減衰量目標値となるように可変光減衰器１９８を制御する。可変光減衰器１９８を制御するためにマイクロコントローラから出力された制御信号は、ＤＡＣにより電圧信号に変換されて、増幅器、トランジスタ及び抵抗からなる可変光減衰器１９８の駆動回路に供給される。
【０１６１】
次に、図１９の光増幅器の動作について説明する。図２０は、光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【０１６２】
図１９の光増幅器は、入力上限時（入力上限以外でもよい）のＶＯＡ減衰量およびＰＤ１モニタ値を設定する。なお、ＶＯＡ減衰量は、例えばＲＯＭなどに格納されている初期値となっている。
【０１６３】
光増幅器は、入力信号に変動が発生しているとき、その入力信号の変動量を算出し、その変動量を補正するようにＶＯＡ減衰量を制御する。ＶＯＡ減衰量の制御により、一波当たりの入力信号の変動量が補正される。また、ＰＤ１モニタ値およびＰＤ３モニタ値を用いたＡＧＣにより光増幅器全体利得一定制御が行われ、ＥＤＦ利得目標値を保持するようにＶＯＡ減衰量が制御される。
【０１６４】
なお、図２０の表に含まれる「Ｘ」は、入力信号パワーを表す。「α」は、変動量を表す。「Ｌ」は、ＶＯＡ減衰量を表す。「Ａ」は、光増幅器全体利得を表す。
【０１６５】
このように、本実施形態では、可変光減衰器の制御により光増幅器全体としての利得の波長特性が一定に保たれるようにしている。従って、従来のように複数の光増幅ユニットのそれぞれに関してＡＧＣを行って利得の波長特性を一定に保つ場合と比較して、光増幅器の制御構成を簡単にすることができるため高速ＡＧＣに対応が可能となる。
【０１６６】
また、光増幅器の制御構成を簡単にすることができるため、必要な部品点数を削減できる。この結果、本発明の光増幅器は大幅なコストの削減と部品点数の削減に伴う実装面積の縮小とを実現できる。
【０１６７】
本発明は、以下の付記を含むものである。
（付記１）　第１及び第２の光増幅ユニットと、
前記第１及び第２の光増幅ユニットの間に光学的に接続された可変光減衰器と、
前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１の制御ユニットと、
前記第１の光増幅ユニットの入力及び出力並びに前記第２の光増幅ユニットの入力及び出力に基き前記可変光減衰器の減衰を制御する第２の制御ユニットとを備えた光増幅器。
（付記２）　前記第１の光増幅ユニットの入力及び出力をそれぞれ電気信号に変換する第１及び第２のフォトディテクタと、前記第２の光増幅ユニットの入力及び出力をそれぞれ電気信号に変換する第３及び第４のフォトディテクタとを更に備え、
前記第１及び第４のフォトディテクタからの電気信号が前記第１の制御ユニットに供給され、
前記第１乃至第４のフォトディテクタからの電気信号が前記第２の制御ユニットに供給される付記１記載の光増幅器。
（付記３）　前記第１の制御ユニットは、前記第１及び第４のフォトディテクタからの電気信号のレベル差が設定値に一致するように前記第１及び第２の光増幅ユニットを制御する手段を含む付記２記載の光増幅器。
（付記４）　前記第２の制御ユニットは、前記第１及び第２のフォトディテクタからの電気信号のレベル差と前記第３及び第４のフォトディテクタからの電気信号のレベル差の和が一定になるように前記可変光減衰器の減衰を制御する手段を含む付記２記載の光増幅器。
（付記５）　第１及び第２の光増幅ユニットと、
前記第１の光増幅ユニットの出力を減衰する第１の可変光減衰器と、
前記第１の光増幅ユニットの入力を減衰する第２の可変光減衰器と、
前記第２の可変光減衰器の出力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１の制御ユニットと、
前記第１の光増幅ユニットの入力及び出力並びに前記第２の光増幅ユニットの入力及び出力に基き前記第１及び第２の可変光減衰器の減衰を制御する第２の制御ユニットとを備えた光増幅器。
（付記６）　前記第１の光増幅ユニットの入力及び出力をそれぞれ電気信号に変換する第１及び第２のフォトディテクタと、前記第２の可変光減衰器の出力を電気信号に変換する第３のフォトディテクタと、前記第２の光増幅ユニットの入力及び出力をそれぞれ電気信号に変換する第４及び第５のフォトディテクタとを更に備え、
前記第３及び第５のフォトディテクタからの電気信号が前記第１の制御ユニットに供給され、
前記第１，２，４及び５のフォトディテクタからの電気信号が前記第２の制御ユニットに供給される付記５記載の光増幅器。
（付記７）　第１及び第２の光増幅ユニットと、
前記第１の光増幅ユニットの入力及び出力を減衰する可変光減衰器と、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１の制御ユニットと、
前記第１の光増幅ユニットの入力，前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記可変光減衰器の減衰を制御する第２の制御ユニットとを備えた光増幅器。
（付記８）　前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力を電気信号に変換する第１のフォトディテクタと、前記第１の光増幅ユニットの入力を電気信号に変換する第２のフォトディテクタと、前記第２の光増幅ユニットの出力を電気信号に変換する第３のフォトディテクタとを更に備え、
前記第１及び第３のフォトディテクタからの電気信号が前記第１の制御ユニットに供給され、
前記第１〜３のフォトディテクタからの電気信号が前記第２の制御ユニットに供給される付記７記載の光増幅器。
（付記９）　第１及び第２の光増幅ユニットと、
前記第１の光増幅ユニットの出力を減衰する第１の可変光減衰器と、
前記第１の光増幅ユニットの入力を減衰する第２の可変光減衰器と、
前記第２の可変光減衰器の出力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１の制御ユニットと、
前記第２の可変光減衰器の出力，前記第２の光増幅ユニットの出力及び前記第１及び第２の可変光減衰器の特性に基き前記第１及び第２の可変光減衰器の減衰を制御する第２の制御ユニットとを備えた光増幅器。
（付記１０）　前記第２の可変光減衰器の出力を電気信号に変換する第１のフォトディテクタと、前記第２の光増幅ユニットの出力を電気信号に変換する第２のフォトディテクタとを更に備え、
前記第１及び第２のフォトディテクタからの電気信号が前記第１の制御ユニットに供給され、
前記第１及び２のフォトディテクタからの電気信号が前記第２の制御ユニットに供給される付記９記載の光増幅器。
（付記１１）　第１及び第２の光増幅ユニットと、
前記第１の光増幅ユニットの入力及び出力を減衰する可変光減衰器と、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１の制御ユニットと、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力，前記第２の光増幅ユニットの出力及び前記可変光減衰器の特性に基き前記可変光減衰器の減衰を制御する第２の制御ユニットとを備えた光増幅器。
（付記１２）　前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力を電気信号に変換する第１のフォトディテクタと、前記第２の光増幅ユニットの出力を電気信号に変換する第２のフォトディテクタとを更に備え、
前記第１及び第２のフォトディテクタからの電気信号が前記第１の制御ユニットに供給され、
前記第１及び２のフォトディテクタからの電気信号が前記第２の制御ユニットに供給される付記１１記載の光増幅器。
（付記１３）　前記第１の制御ユニットは前記光増幅器の出力パワーが一定になるように前記第１及び第２の光増幅ユニットの利得を制御し、
前記第２の制御ユニットは前記第１及び第２の光増幅ユニットの利得の和が一定になるように前記可変光減衰器の減衰を制御する付記１乃至１２何れか一項記載の光増幅器。
（付記１４）　前記第１及び第２の光増幅ユニットの各々は、光増幅媒体と、前記光増幅媒体にポンプ光を供給するポンプ光源とを備えており、
前記第１及び第２の光増幅ユニットの各利得は前記ポンプ光源から出力されるポンプ光のパワーにより制御される付記１乃至１３何れか一項記載の光増幅器。
（付記１５）　第１及び第２の光増幅ユニットと、前記第１及び第２の光増幅ユニットの間に光学的に接続された可変光減衰器とを備えた光増幅器の制御方法であって、
前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１のステップと、
前記第１の光増幅ユニットの入力及び出力並びに前記第２の光増幅ユニットの入力及び出力に基き前記可変光減衰器の減衰を制御する第２のステップとを備えた制御方法。
（付記１６）　前記第１のステップは前記光増幅器の出力パワーが一定になるように前記第１及び第２の光増幅ユニットの利得を制御するステップを含み、
前記第２のステップは前記第１及び第２の光増幅ユニットの利得の和が一定になるように前記可変光減衰器の減衰を制御するステップを含む付記１５記載の制御方法。
（付記１７）　前記第１及び第２の光増幅ユニットの各々は、光増幅媒体と、前記光増幅媒体にポンプ光を供給するポンプ光源とを備えており、
前記第１及び第２の光増幅ユニットの各利得は前記ポンプ光源から出力されるポンプ光のパワーにより制御される付記１６記載の制御方法。
（付記１８）　前記第１の光増幅ユニットの入力及び出力をそれぞれ第１及び第２の電気信号に変換するステップと、前記第２の光増幅ユニットの入力及び出力をそれぞれ第２及び第３の電気信号に変換するステップとを更に備え、
前記第１のステップは前記第１及び第４の電気信号を供給されることを含み、前記第２のステップは前記第１乃至第４の電気信号を供給されることを含む付記１５記載の制御方法。
（付記１９）　前記第１のステップは、前記第１及び第４の電気信号のレベル差が設定値に一致するように前記第１及び第２の光増幅ユニットを制御するステップを含む付記１８記載の制御方法。
（付記２０）　前記第２のステップは、前記第１及び第２の電気信号のレベル差と前記第３及び第４の電気信号のレベル差の和が一定になるように前記可変光減衰器の減衰を制御するステップを含む付記１８記載の制御方法。
（付記２１）　第１及び第２の光増幅ユニットと、前記第１の光増幅ユニットの出力を減衰する第１の可変光減衰器とを備えた光増幅器の制御方法であって、
前記第２の可変光減衰器の出力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１のステップと、
前記第１の光増幅ユニットの入力及び出力並びに前記第２の光増幅ユニットの入力及び出力に基き前記第１及び第２の可変光減衰器の減衰を制御する第２のステップとを備えた制御方法。
（付記２２）　第１及び第２の光増幅ユニットと、前記第１の光増幅ユニットの入力及び出力を減衰する可変光減衰器とを備えた光増幅器の制御方法であって、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１のステップと、
前記第１の光増幅ユニットの入力，前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記可変光減衰器の減衰を制御する第２のステップとを備えた制御方法。
（付記２３）　第１及び第２の光増幅ユニットと、前記第１の光増幅ユニットの出力を減衰する第１の可変光減衰器と、前記第１の光増幅ユニットの入力を減衰する第２の可変光減衰器とを備えた光増幅器の制御方法であって、
前記第２の可変光減衰器の出力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１のステップと、
前記第２の可変光減衰器の出力，前記第２の光増幅ユニットの出力及び前記第１及び第２の可変光減衰器の特性に基き前記第１及び第２の可変光減衰器の減衰を制御する第２のステップとを備えた制御方法。
（付記２４）第１及び第２の光増幅ユニットと、前記第１の光増幅ユニットの入力及び出力を減衰する可変光減衰器とを備えた光増幅器の制御方法であって、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力及び前記第２の光増幅ユニットの出力に基き前記第１及び第２の光増幅ユニットの利得を制御する第１のステップと、
前記可変光減衰器により減衰された前記第１の光増幅ユニットの入力，前記第２の光増幅ユニットの出力及び前記可変光減衰器の特性に基き前記可変光減衰器の減衰を制御する第２のステップとを備えた制御方法。
【０１６８】
【発明の効果】
以上説明したように、本発明によると、ＷＤＭに適用可能な光増幅器においてＡＧＣ及びＡＬＣを実施する場合に、制御誤差が生じにくく、複雑な構成を必要とせず、且つ、波長数増減に容易に対応可能な光増幅器及び光増幅器の制御方法を提供できる。
【０１６９】
【図面の簡単な説明】
【図１】光増幅器においてＡＧＣ及びＡＬＣの両方を行うのに最適な構成を示すブロック図である。
【図２】光増幅器の動作の一例について説明するための模式図である。
【図３】本発明による光増幅器の第１実施例のブロック図である。
【図４】光増幅ユニットの利得を制御するＡＧＣ回路の第１実施例の構成図である。
【図５】可変光減衰器１８の減衰を制御するＡＧＣ回路の第１実施例の構成図である。
【図６】本発明による光増幅器の第２実施例のブロック図である。
【図７】光増幅ユニットの利得を制御するＡＧＣ回路の第２実施例の構成図である。
【図８】可変光減衰器の減衰を制御するＡＧＣ回路の第２実施例の構成図である。
【図９】光増幅器の動作について説明するための模式図である。
【図１０】光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【図１１】本発明による光増幅器の第３実施例のブロック図である。
【図１２】可変光減衰器の減衰を制御するＡＧＣ回路の第３実施例の構成図である。
【図１３】光増幅器の動作について説明するための模式図である。
【図１４】光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【図１５】部品のバラツキおよび温度特性などにより可変光減衰器の減衰量対駆動電流の関係が変化することを説明するための図である。
【図１６】本発明による光増幅器の第４実施例のブロック図である。
【図１７】可変光減衰器の減衰を制御するＡＧＣ回路の第４実施例の構成図である。
【図１８】光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【図１９】本発明による光増幅器の第５実施例のブロック図である。
【図２０】光増幅器の各モニタ値およびＶＯＡ減衰量の変化を示した表である。
【符号の説明】
１６，８６，１９６　　第１の光増幅ユニット
１８，１９８　　可変光減衰器
２０，９２，２００　　第２の光増幅ユニット
２６，４４，１００，１１８，２０６，２２６　　ＥＤＦ
２８，４６，１０４，１２２，２１２，２３２　　レーザダイオード
３２，３４，５０，５４，１０６，１０８，１２４，１２６，１２８，２１４，２３０，２３４　　フォトディテクタ
３６，３８，１１０，１１２，２１６，２１８　　ＡＧＣ回路
８８　　第１の可変光減衰器
９０　　第２の可変光減衰器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplifier and a method for controlling the optical amplifier.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the establishment of a technique for manufacturing and using a silica-based optical fiber having a low loss (for example, 0.2 dB / km), an optical communication system using an optical fiber as a transmission line has been put to practical use. In such an optical communication system, an optical amplifier for amplifying an optical signal or signal light has been put to practical use in order to compensate for loss in an optical fiber and enable long-distance transmission.
[0003]
Conventionally known optical amplifiers pump an optical amplifying medium such that the optical amplifying medium to which the signal light to be amplified is supplied and a gain band including the wavelength of the signal light are provided. And a pumping unit.
[0004]
For example, an erbium-doped fiber amplifier (hereinafter, referred to as EDFA) has been developed as an example of an optical amplifier for amplifying signal light in the 1.55 μm band with a small loss in a silica-based fiber.
[0005]
The EDFA includes an erbium-doped fiber (hereinafter, referred to as EDF) as an optical amplification medium, and a pump light source for supplying pump light having a predetermined wavelength to the EDF. The EDFA can obtain a gain band including a wavelength of 1.55 μm by using pump light having a wavelength in the 0.98 μm band or the 1.48 μm band.
[0006]
As a technique for increasing the transmission capacity of an optical fiber, there is wavelength division multiplexing (WDM). In an optical communication system to which WDM is applied, a plurality of optical carriers having different wavelengths are used (for example, see Patent Document 1).
[0007]
In an optical communication system to which WDM is applied, a plurality of optical signals obtained by independently modulating each optical carrier are wavelength division multiplexed by an optical multiplexer, and the resulting WDM signal light is transmitted to an optical fiber transmission line. Sent out. On the receiving side, the received WDM signal light is separated into individual optical signals by an optical demultiplexer, and transmission data is reproduced based on each optical signal. Therefore, in an optical communication system to which WDM is applied, the transmission capacity of one optical fiber is increased according to the number of multiplexed optical signals.
[0008]
As described above, in an optical communication system to which WDM is applied, by using an optical amplifier as a linear repeater, the number of components in the repeater is reduced and reliability is reduced as compared with the case where a conventional regenerative repeater is used. In addition to securing them, the cost was reduced.
[0009]
[Patent Document]
JP-A-11-122192
[0010]
[Problems to be solved by the invention]
When an optical amplifier is incorporated into an optical communication system to which WDM is applied, various controls on the optical amplifier are required due to the necessity of keeping the wavelength characteristic of the gain constant and the requirement to prevent waveform deterioration due to the nonlinear effect of the optical fiber transmission line. Is required.
[0011]
For example, in the EDFA, since the wavelength characteristic of the gain changes according to the gain determined by the pumping condition, AGC (automatic gain control) is performed so as to apply a constant gain to the input and output the input. In this case, when the input changes under a constant gain, the output changes accordingly.
[0012]
On the other hand, in an optical amplifier, the higher the signal output is, the better from the viewpoint of S / N. However, considering the waveform degradation due to the non-linear effect of the optical fiber transmission line and the input dynamic range at the receiving end, it can be generally said that. Absent. That is, there is a demand for performing ALC (automatic level control) so that the output of the optical amplifier becomes constant within a predetermined range.
[0013]
As an optimal configuration for performing both AGC and ALC, an optical amplifier including first and second optical amplification units and a variable optical attenuator connected therebetween has been proposed. In the optical amplifier having such a configuration, AGC is performed in each of the first and second optical amplification units, and ALC is performed by the variable optical attenuator.
[0014]
First, such a configuration is proposed because it is disadvantageous to provide a variable optical attenuator for ALC in a preceding stage from the viewpoint of optimizing NF (Noise @ Figure) of the entire optical amplifier. Sometimes. Second, from the viewpoint of securing a predetermined signal output power as an optical amplifier, if a variable optical attenuator for ALC is provided at the subsequent stage, a higher signal output power can be obtained in the optical amplification unit for AGC immediately before the ALC. This is disadvantageous from the viewpoint of reducing the power consumption of the laser diode as the pump light source.
[0015]
By the way, in the configuration of the optical amplification suitable for performing both the AGC and the ALC described above, the configuration of the optical amplifier is complicated because the first and second optical amplification units need to perform the AGC independently. Problem.
[0016]
Further, when this optical amplifier is used in an optical communication system to which WDM is applied, there is a problem that control of a variable optical attenuator for ALC is complicated when the number of WDM channels changes. More specifically, when performing ALC when amplifying WDM signal light in an optical amplifier, control is performed so that the total power of the output of the variable optical attenuator becomes constant. When the number of channels of the signal light changes, the target value of the control of the variable optical attenuator becomes different.
[0017]
Since the target value of this control of the variable optical attenuator is generally transmitted from a monitoring control device provided on the upstream side, complicated monitoring work is required when increasing or decreasing the number of wavelengths of the optical communication system. In the optical amplifier, the attenuation of the variable optical attenuator is temporarily fixed when the number of wavelengths is increased or decreased. However, with the ALC loop open, the control value is updated to the target value according to the change in the number of wavelengths, and the ALC loop is again updated. Is required, there is a risk that the attenuation of the variable optical attenuator fluctuates during a series of operations.
[0018]
Here, since the AGC is continuously performed in the first and second optical amplifying units, there is a risk that the output power per one wavelength channel fluctuates when the target value of the control of the variable optical attenuator is switched. is there.
[0019]
The present invention has been made in view of the above points, and when performing automatic gain control and automatic level control, a control error hardly occurs, a complicated configuration is not required, and the number of wavelengths can be easily increased and decreased. It is an object of the present invention to provide an optical amplifier applicable to wavelength division multiplexing and a control method of the optical amplifier. Other objects of the present invention will become clear from the following description.
[0020]
[Means for Solving the Problems]
According to the present invention, the first and second optical amplification units, the variable optical attenuator optically connected between the first and second optical amplification units, the input of the first optical amplification unit and the A first control unit for controlling gains of the first and second optical amplification units based on an output of the second optical amplification unit, an input and an output of the first optical amplification unit, and an input of the second optical amplification unit And a second control unit for controlling the attenuation of the variable optical attenuator based on the output.
[0021]
For example, the first control unit controls the gains of the first and second optical amplification units so that the output power of the optical amplifier becomes constant, and the second control unit controls the gains of the first and second optical amplification units. The attenuation of the variable optical attenuator is controlled so that the sum of the gains becomes constant.
[0022]
According to this configuration, without performing ALC on the variable optical attenuator as in the related art, based on an appropriate combination of AGC, it becomes substantially equivalent to ALC being performed on the optical amplifier as a whole. The object of the invention is achieved.
[0023]
According to another aspect of the present invention, control of an optical amplifier including first and second optical amplification units and a variable optical attenuator optically connected between the first and second optical amplification units. A method is provided. The method includes controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, and inputting and outputting the first optical amplification unit. And controlling the attenuation of the variable optical attenuator based on the input and output of the second optical amplification unit.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0025]
FIG. 1 is a block diagram showing an optimal configuration for performing both AGC and ALC in an optical amplifier. An AGC unit 6, an ALC unit 8, and an AGC unit 10 are optically connected between the input terminal 2 and the output terminal 4 in this order. For example, AGC units 6 and 10 are provided by EDFA. The ALC unit 8 is provided by a variable optical attenuator.
[0026]
In the preceding AGC unit 6, even when the power fluctuation of the input signal light occurs, the optical amplification by the AGC is performed including the power fluctuation. In the ALC unit 8, since control is performed so that the output signal light power is constant, even when power fluctuation of the input signal light occurs, control is performed in a direction to suppress the power fluctuation. Therefore, in the case of power fluctuation at a speed sufficiently slower than the control time constant of the ALC unit 8, the power fluctuation of the input signal light can be completely suppressed in the ALC unit 8. Further, in the ALC unit 8, by setting the following value as the control target value, the output signal light power at the output terminal 4 can be indirectly controlled to a desired value.
[0027]
P_ALC[DBm] = P_SIGOUT-G_B
Where P_SIGOUTIs a target power [dBm] of the output signal light at the output terminal 4. G_BIs a gain [dB] set in the AGC unit 10 at the subsequent stage. In the latter AGC unit 10, since the power fluctuation is suppressed by the ALC unit 8, the input signal power is constant. Therefore, the output signal light power of the AGC unit 10 becomes constant according to the operation of the AGC unit 10, and the value of the output signal light power becomes the target power at the output terminal 4.
[0028]
FIG. 2 is a schematic diagram for explaining an example of the operation of the optical amplifier. Referring to FIG. 2, the operation in the configuration of the optical amplifier shown in FIG. 1 is schematically shown.
[0029]
In FIG. 2, a graph A represents a change in signal light power at the input terminal 2. A graph B shows a change in signal light power at the input of the ALC unit 8. A graph C represents a change in the signal light power at the input of the AGC unit 10 at the subsequent stage. A graph D represents a change in the signal light power at the output terminal 4.
[0030]
The change in the signal light power at the input terminal 2 is reflected on the output of the preceding AGC unit 6. The change in the signal light power at the input terminal 2 is suppressed according to the operation of the ALC unit 8. Then, the signal light power whose change has been suppressed is amplified by the subsequent AGC unit 10 according to a certain gain.
[0031]
As described above, in the configuration of the optical amplifier shown in FIG. 1, since the ALC unit 8 is provided independently, there is a problem that it is not possible to easily cope with a change in the number of WDM channels. In the present invention, by combining an AGC unit with a master, the function of ALC is substantially provided, and the above-described problem is solved.
[0032]
FIG. 3 is a block diagram of a first embodiment of the optical amplifier according to the present invention. This optical amplifier is configured to optically cascade a first optical amplification unit 16, a variable optical attenuator (VOA) 18, and a second optical amplification unit 20 between an input terminal 12 and an output terminal 14. ing.
[0033]
The signal light to be amplified supplied to the input terminal 12 is supplied to the EDF 26 in the first optical amplification unit 16 through the optical coupler 22 and the WDM coupler 24 in this order. The pump light from the laser diode 28 is supplied to the EDF 26 through the WDM coupler 24. Thereby, a gain according to the power of the pump light can be obtained. The signal light amplified in the EDF 26 is output from the first optical amplification unit 16 through the optical coupler 30.
[0034]
In order to monitor the input and output of the first optical amplification unit 16, the optical amplifier is provided with photodetectors 32 and 34, respectively. The photodetector 32 converts the signal light split by the optical coupler 22 into an electric signal. The photo detector 34 converts the signal light branched by the optical coupler 30 into an electric signal. An electric signal from the photodetector 32 is supplied to an AGC circuit 36 as a first control unit. The electric signals from the photodetectors 32 and 34 are supplied to an AGC circuit 38 as a second control unit.
[0035]
The signal light amplified by the first optical amplification unit 16 is supplied to the second optical amplification unit 20 after being attenuated by the variable optical attenuator 18. The signal light supplied to the second optical amplification unit 20 is supplied to the EDF 44 through the optical coupler 40 and the WDM coupler 42 in this order. The pump light from the laser diode 46 is supplied to the EDF 44 via the WDM coupler 42. As a result, a gain corresponding to the power of the pump light is obtained. The signal light amplified by the EDF 44 is output through the optical coupler 48 and the output terminal 14.
[0036]
In order to monitor the input and output of the second optical amplification unit 20, the optical amplifier is provided with photodetectors 50 and 52, respectively. The photodetector 50 converts the signal light split by the optical coupler 40 into an electric signal. The photodetector 52 converts the signal light split by the optical coupler 48 into an electric signal. The electric signal from the photo detector 52 is supplied to the AGC circuit 36. The electric signals from the photo detectors 50 and 52 are supplied to the AGC circuit 38.
[0037]
The control signal from the AGC circuit 36 is supplied to a laser diode 28 and a laser diode 46 as pump light sources. Thereby, the total gain in the total portion from the input terminal 12 to the output terminal 14 is controlled to the target value. The AGC circuit 38 controls the attenuation of the variable optical attenuator 18 so that the sum of the gain in the first optical amplification unit 16 and the gain in the second optical amplification unit 20 is constant.
[0038]
Here, a configuration example of the AGC circuit 36 will be described. FIG. 4 is a block diagram of the first embodiment of the AGC circuit for controlling the gains of the optical amplification units 16 and 20. The photodetector 32 and the resistor R1 are connected in series between the power supply line Vcc and the ground. A reverse bias is applied to the photodetector 32, and a photocurrent according to the input of the optical amplification unit 16 flows through the photodetector 32 and the resistor R1.
[0039]
Therefore, the potential at the connection point between the photodetector 32 and the resistor R1 can be extracted as a voltage signal corresponding to the input of the optical amplification unit 16. A capacitor C1 is connected in parallel with the resistor R1 in order to cut the signal component and obtain the average level of the input of the optical amplification unit 16.
[0040]
Similarly, the photodetector 52 and the resistor R2 are connected in series between the power supply line Vcc and the ground. A reverse bias is applied to the photodetector 52, and a photocurrent according to the output of the optical amplification unit 20 flows through the photodetector 52 and the resistor R2.
[0041]
Therefore, the potential at the connection point between the photodetector 52 and the resistor R2 can be extracted as a voltage signal corresponding to the output of the optical amplification unit 20. A capacitor C2 is connected in parallel with the resistor R2 in order to cut the signal component and obtain the average level of the output of the optical amplification unit 20.
[0042]
The gain of the voltage signal from the photodetector 32 is amplified by a voltage control amplifier (hereinafter, referred to as VCA) 54 and supplied to one input port of a differential amplifier 66. The voltage signal from the photodetector 52 is amplified by the amplifier 56 having a fixed gain and supplied to the other input port of the differential amplifier 66.
[0043]
Outputs of the VCA 54 and the amplifier 56 are converted into digital signals by analog / digital converters (hereinafter, referred to as ADCs) 58 and 60, respectively, and supplied to the CPU 64. Further, a digital signal obtained by an operation in the CPU 64 is converted into a voltage signal by a digital / analog converter (hereinafter, referred to as DAC) 62, and the gain of the VCA 54 is adjusted based on the voltage signal.
[0044]
An amplifier 68, a transistor 70, and a resistor R3 are provided to drive the laser diode 28 as a pump light source. Further, an amplifier 72, a transistor 74, and a resistor R4 are provided to drive the laser diode 46. The driving of the laser diodes 28 and 46 is controlled based on the output of the differential amplifier 66.
[0045]
Assuming that the output levels of the amplifier 56 and the VCA 54 are V_AMP1OUT and V_VCA1OUT, respectively, the values of the resistors R1 and R2 and the gains of the VCA 54 and the amplifier 56 are set so as to satisfy the following relationship.
[0046]
That is, when the input signal light power, the output signal light power, and the gain of the optical amplifier are x [dB], x + A [dB], and A [dB], V_AMP1OUT and V_VCA1OUT match at the same y [V]. Is done. This is 10% less than the light receiving sensitivity [V / W] of the monitor circuits associated with the photodetectors 32 and 52, respectively.^{(AMP_G / 10)}Means to have a ratio of Here, AMP_G is the gain of the optical amplifier.
[0047]
Since A is constant in the above relationship, when the input signal light power per wave fluctuates, the output signal light power also fluctuates in conjunction therewith. Therefore, the CPU 64 performs an operation so that the output signal light power becomes constant at the target value, and the gain of the VCA 54 is adjusted according to the result.
[0048]
Thus, in this embodiment, ALC can be performed substantially by controlling the gains of the optical amplification units 16 and 20. Therefore, compared to the case where ALC is performed using a variable optical attenuator as in the related art, a complicated switching operation is not required when the number of operating channels is changed.
[0049]
Here, a configuration example of the AGC circuit 38 will be described. FIG. 5 is a configuration diagram of an AGC circuit for controlling the attenuation of the variable optical attenuator 18 according to a first embodiment. To monitor the input and output of the first optical amplification unit 16, the voltage signals from the photodetectors 32 and 34 are amplified by amplifiers 54 or 56 having a fixed gain and supplied to ADCs 62 and 64, respectively. The ADCs 62 and 64 convert the voltage signals from the photodetectors 32 and 34 into digital signals and supply the digital signals to the CPU 70.
[0050]
To monitor the input and output of the second optical amplification unit 20, the voltage signals from the photodetectors 50 and 52 are amplified by amplifiers 58 or 60 having a fixed gain and supplied to ADCs 66 and 68, respectively. The ADCs 66 and 68 convert the voltage signals from the photodetectors 50 and 52 into digital signals and supply the digital signals to the CPU 70.
[0051]
The CPU 70 calculates a condition (specifically, the attenuation of the variable optical attenuator 18) that makes the sum of the gain generated in the first optical amplification unit 16 and the gain generated in the second optical amplification unit 20 constant. You. The result of the calculation is converted into a voltage signal by the DAC 74 and supplied to the drive circuit of the variable optical attenuator 18 including the amplifier 76, the transistor 78, and the resistor R7.
[0052]
Next, a more specific description of the control of the variable optical attenuator 18 and a technical effect obtained thereby will be described.
[0053]
If only the control by the AGC circuit 36 shown in FIG. 4 is used, the wavelength characteristics of the gain in the wavelength band of the WDM signal light cannot be kept constant. There is. In a configuration in which a plurality of optical amplifiers are cascaded, in order to keep the wavelength characteristic of the gain constant, it is sufficient to control the gain of each optical amplifier to be constant. Control may be performed so that the sum is constant.
[0054]
The actual gain of the first optical amplifier unit 16 is G_A '[dB], the actual gain of the second optical amplifier unit 20 is G_B' [dB], the target gain of the first optical amplifier unit 16 is G_A [dB], and If the target gain of the second optical amplifier unit is G_B [dB], the basic control is to set G_A ′ = G_A and G_B ′ = G_B.
[0055]
For example, when the gain of the first optical amplification unit 16 decreases by ΔG [dB], in the related art, control is performed so that the gain of the second optical amplification unit 20 increases by ΔG [dB]. Thereby, G_A '+ G_B' = G_A + G_B is substantially satisfied, and the wavelength characteristic of the gain of the entire optical amplifier is kept constant.
[0056]
However, the AGC circuit 36 is required in each of the first optical amplification unit 16 and the second optical amplification unit 20, and a function of transferring ΔG between the two optical amplification units 16 and 20 is required. It is difficult to apply a proper AGC.
[0057]
In this embodiment, the variable optical attenuator 18 controls the sum of the gains to be constant, thereby addressing this problem. First, the CPU 70 calculates the gain sum EDF_G 'of the optical amplification units 16 and 20 according to the following equation.
[0058]

Note that IN1MON, OUT1MON, IN2MON, and OUT2MON in the above equation are monitoring values of the optical power by the photodetectors 32, 34, 50, and 52, respectively.
[0059]
Then, a comparison is made between EDF_G 'and EDF_G, which is the target value of EDF_G', and the attenuation of the variable optical attenuator 18 is controlled according to the following equation so that the difference between EDF_G 'and EDF_G becomes zero.
[0060]

Note that AMP_G in the above equation is the gain of the entire optical amplifier. VOA_L is the attenuation of the variable optical attenuator 18. Therefore, if the attenuation of the variable optical attenuator 18 is controlled so that VOA_L = the value obtained by EDF_G'-AMP_G, the control can be easily performed so that the gain of the entire optical amplifier is kept constant.
[0061]
FIG. 6 is a block diagram of a second embodiment of the optical amplifier according to the present invention. This optical amplifier optically cascade-connects a first optical amplification unit 86, a first variable optical attenuator (VOA) 88, and a second optical amplification unit 92 between an input terminal 82 and an output terminal 84. It is configured to
[0062]
The signal light to be amplified supplied to the input terminal 82 is supplied to the EDF 100 in the first optical amplification unit 86 through the optical coupler 94 and the WDM coupler 96 in this order. The pump light from the laser diode 104 is supplied to the EDF 100 through the WDM coupler 96. Thereby, a gain according to the power of the pump light can be obtained. The signal light amplified in the EDF 100 is output from the first optical amplification unit 86 through the optical coupler 102. The signal light split by the optical coupler 94 is output from the first optical amplification unit 86 through the optical coupler 98.
[0063]
In order to monitor the input and output of the first optical amplification unit 86, the optical amplifier is provided with photodetectors 106 and 108, respectively. The photodetector 106 converts the signal light split by the optical coupler 98 into an electric signal. The photodetector 108 converts the signal light split by the optical coupler 102 into an electric signal. The electric signals from the photodetectors 106 and 108 are supplied to an AGC circuit 112 as a second control unit.
[0064]
The signal light amplified by the first optical amplification unit 86 is supplied to the second optical amplification unit 92 after being attenuated by the first variable optical attenuator 88. The signal light split by the optical coupler 94 is supplied to a second variable optical attenuator (VOA) 90 through an optical coupler 98 and is attenuated. In order to monitor the signal light attenuated by the second variable optical attenuator 90, the optical amplifier is provided with a photodetector 124.
[0065]
The photodetector 124 converts the signal light attenuated by the second variable optical attenuator 90 into an electric signal. The electric signal from the photo detector 124 is supplied to the AGC circuit 110.
[0066]
The signal light supplied to the second optical amplification unit 92 is supplied to the EDF 118 through the optical coupler 114 and the WDM coupler 116 in this order. The pump light from the laser diode 122 is supplied to the EDF 118 via the WDM coupler 116. As a result, a gain corresponding to the power of the pump light is obtained. The signal light amplified by the EDF 118 is output through the optical coupler 120 and the output terminal 84.
[0067]
In order to monitor the input and output of the second optical amplification unit 92, the optical amplifier is provided with photodetectors 126 and 128, respectively. The photodetector 126 converts the signal light split by the optical coupler 114 into an electric signal. The photodetector 128 converts the signal light split by the optical coupler 120 into an electric signal. The electric signal from the photo detector 126 is supplied to the AGC circuit 112. The electric signal from the photodetector 128 is supplied to AGC circuits 110 and 112.
[0068]
A control signal from the AGC circuit 110 is supplied to a laser diode 104 and a laser diode 122 as pump light sources. Thereby, the total gain in the total portion from the input terminal 82 to the output terminal 84 is controlled to the target value.
[0069]
The AGC circuit 112 controls the attenuation of the first variable optical attenuator 88 so that the sum of the gain in the first optical amplification unit 86 and the gain in the second optical amplification unit 92 becomes constant. The optical amplifier is roughly divided into a control circuit unit including the AGC circuits 110 and 112 and an optical circuit unit other than the control circuit unit.
[0070]
In the optical amplifier of FIG. 6, an electric signal from the photodetector 106 (hereinafter referred to as a PD1 monitor value), an electric signal from the photodetector 108 (hereinafter referred to as a PD2 monitor value), and an electric signal from the photodetector 124 (hereinafter referred to as a PD3 monitor value). Value, an electric signal from the photodetector 126 (hereinafter, referred to as a PD4 monitor value), and an electric signal from the photodetector 128 (hereinafter, referred to as a PD5 monitor value), and the overall gain (Amp_Gain) and the EDF gain of the optical amplifier. (EDF_total_Gain), VOA1 attenuation (VOA1_Loss), and VOA2 attenuation (VOA2_Loss) are controlled.
[0071]
The PD1 monitor value is a monitor value of the input optical signal. The PD2 monitor value is a monitor value of the optical signal amplified by the first optical amplification unit 86. The PD3 monitor value is a monitor value of the optical signal attenuated by the second variable optical attenuator 90. The PD4 monitor value is a monitor value of the optical signal attenuated by the first variable optical attenuator 88. The PD5 monitor value is a monitor value of the optical signal amplified by the second optical amplification unit 92.
[0072]
The optical amplifier overall gain is the gain of the entire optical amplifier. The EDF gain is the sum of the gains of the optical amplification units 86 and 92. The VOA1 attenuation is the attenuation of the first variable optical attenuator 88. The VOA2 attenuation is the attenuation of the second variable optical attenuator 90.
[0073]
The overall gain of the optical amplifier, the EDF gain, the VOA1 attenuation, and the VOA2 attenuation can be obtained as follows using the PD1 monitor value to the PD5 monitor value.
[0074]

According to the above relationship, the VOA1 attenuation and the overall gain of the optical amplifier are controlled in the normal operation (AGC state) in the optical amplifier of FIG.
[0075]
Next, a configuration example of the AGC circuit 110 will be described. The AGC circuit 110 controls the entire gain of the optical amplifier to drive the laser diodes 104 and 122 so that the overall gain of the optical amplifier becomes a desired value.
[0076]
FIG. 7 is a configuration diagram of an AGC circuit for controlling the gains of the optical amplification units 86 and 92 according to a second embodiment. The photodetector 124 and the resistor R3 are connected in series between the power supply line Vcc and the ground. A reverse bias is applied to the photodetector 124, and a photocurrent according to the output of the variable optical attenuator 90 flows through the photodetector 124 and the resistor R3.
[0077]
Therefore, the potential at the connection point between the photodetector 124 and the resistor R3 can be extracted as a voltage signal corresponding to the output of the variable optical attenuator 90. A capacitor C3 is connected in parallel with the resistor R3 in order to cut the signal component and obtain the average level of the output of the variable optical attenuator 90.
[0078]
Similarly, the photodetector 128 and the resistor R5 are connected in series between the power supply line Vcc and the ground. A reverse bias is applied to the photodetector 128, and a photocurrent according to the output of the optical amplification unit 92 flows through the photodetector 128 and the resistor R5.
[0079]
Therefore, the potential at the connection point between the photodetector 128 and the resistor R5 can be extracted as a voltage signal corresponding to the output of the optical amplification unit 92. A capacitor C5 is connected in parallel with the resistor R5 in order to cut the signal component and obtain the average level of the output of the optical amplification unit 92.
[0080]
The voltage signal from the photodetector 124 is subjected to impedance conversion and amplification by an amplifier 130 having a fixed gain, and is supplied to one input port of a differential amplifier 134. The voltage signal from the photodetector 128 is impedance-converted and amplified by an amplifier 132 having a fixed gain, and is supplied to the other input port of the differential amplifier 134.
[0081]
The optical amplifier includes an amplifier 136 for driving the laser diode 104 as a pump light source, a transistor 138, and a resistor R1. The optical amplifier includes an amplifier 140 for driving the laser diode 122, a transistor 142, and a resistor R2. The driving of the laser diodes 104 and 122 is controlled based on the output of the differential amplifier 134.
[0082]
When the output levels of the amplifiers 130 and 132 are Amp3_OUT and Amp5_OUT, respectively, the values of the resistors R3 and R5 and the gains of the amplifiers 130 and 132 are set so as to satisfy the following relationship.
[0083]
That is, when the PD3 monitor value and the PD5 monitor value are x [dBm] and x + Amp_Gain reference value [dBm], respectively, the monitor circuits associated with the photodetectors 124 and 128 so that Amp3_OUT and Amp5_OUT match at the same y [V]. The light receiving sensitivity [V / W] is set. This is a factor of 10 for the photosensitivity [V / W] of the monitor circuits associated with photodetectors 124 and 128, respectively.^{(AMP_G / 10)}Means to have a ratio of Here, AMP_G is the gain of the entire optical amplifier.
[0084]
Then, the laser diodes 104 and 122 are driven and controlled so that the output of the differential amplifier 134 has a voltage difference of 0 supplied to the input port. Therefore, in the optical amplifier of FIG. 6, the gain of the entire optical amplifier can be kept constant even when the number of wavelengths changes.
[0085]
However, in the above relationship, since the overall gain reference value of the optical amplifier (AMP_Gain reference value) is constant, when the input signal light power per wave fluctuates, the output signal light power also fluctuates in conjunction with this. I will. Therefore, the optical amplifier shown in FIG. 6 performs control for compensating for fluctuations in the input signal light using ALC described later so that the output signal light power becomes constant at the control target value.
[0086]
In an optical amplifier, it is necessary to absorb an input dynamic range caused by variations in transmission line loss and aging of an optical fiber transmission line, and this control is realized by ALC. In the ALC state, the number of wavelengths is notified from the monitoring and control device provided on the upstream side of the optical amplifier, and the output target value of the optical amplifier is determined by using the wavelength number information.
[0087]
In the conventional optical amplifier, the variable optical attenuator is driven so that the signal output of the middle ALC unit 8 becomes the control target value, and the VOA attenuation is controlled. This control target value is calculated as follows.
[0088]
ALC unit control target value [dBm] = ALC unit output reference value [dBm / ch] + 10 Log (number of wavelengths)-Gc [dB]
Gc is the deficiency gain of the preceding AGC unit 6, and is calculated as follows.
[0089]
Gc [dB] = AGC unit gain target value [dB]-AGC unit gain [dB]
Therefore, the gain target value of the latter AGC unit 10 needs to be increased by Gc [dB]. The variable optical attenuator is arranged at the middle stage of the optical amplifier from the viewpoint of NF and pumping efficiency in the entire optical amplifier.
[0090]
On the other hand, in the present invention, the fluctuation of the input signal per wave is not performed by controlling the VOA1 attenuation. This is because, as described above, in the optical amplifier overall gain constant control, the output signal is changed by an amount corresponding to the change in the input signal, and the VOA1 attenuation is held at a constant value by the control of the AGC circuit 112 described later.
[0091]
Further, in the optical amplifier in which the gain of the optical amplification units 86 and 92 is controlled by one AGC circuit 110, the output signal fluctuates in conjunction with the fluctuation of the input signal per wave. It is necessary to provide control by a circuit or a microcontroller for compensating the fluctuation of the input signal. As a result, noise and response speed of a circuit or a microcontroller or the like that compensates for fluctuations in the input signal may affect the control circuit unit and degrade the characteristics of the optical amplifier.
[0092]
The optical amplifier according to the present invention has a configuration that does not require compensation in the control circuit unit as shown in the following processing methods 1 and 2 in order to compensate for the fluctuation of the input signal in the optical circuit unit.
[Processing method 1]
In the processing method 1, it is recognized from the PD1 monitor value where the input signal is within the input dynamic range. Based on the recognized information, the VOA2 attenuation is controlled, and the output signal level is controlled to be constant. The optical amplifier calculates the following values required for control using the wavelength number information notified from the monitoring control device provided on the upstream side.
[0093]
PD1 monitor value: z1 [dBm]
PD3 monitor value: z3 [dBm]
Input signal wavelength number information: N
Input signal light power: z1-10 Log (N) [dBm / ch]
Upper limit of input signal light power per wave: u [dBm / ch]
Positioning in the input dynamic range: L0 = u- {z1-10Log (N)}
VOA2 attenuation: L = z1-z3-Ld [dB]
The input signal light power, the position in the input dynamic range, and the VOA2 attenuation are calculated by, for example, a microcontroller. The input signal light power upper limit per wave is stored in, for example, a ROM.
[0094]
Here, Ld is the VOA2 attenuation (dead loss) when the input signal light power per wave is u [dBm / ch]. In the optical amplifier of the present invention, the variation of the input optical signal per one wave (corresponding to L0) is calculated, and the VOA2 attenuation amount L is controlled so that L = L0. By this processing, the output value of the amplifier 130 does not change even when the input signal light power per wave changes.
[0095]
As a result, the output value of the amplifier 132 is also controlled by the AGC circuit 110 so as not to change, so that the output signal light power from the optical amplifier is controlled to be constant and the ALC operation can be realized.
[Processing method 2]
In the processing method 2, the PD5 monitor value is compared with the output signal reference value, and the VOA2 attenuation is controlled so that the difference becomes zero. The optical amplifier calculates the following values required for control using the wavelength number information notified to the optical amplifier from the monitoring and control device provided on the upstream side.
[0096]
PD5 monitor value: z5 [dBm]
Input signal wavelength number information: N
Output reference value per wave: A0 [dBm / ch]
Output signal light power per one wave: A [dBm / ch] = z5-10 Log (N)
Note that the output signal power per wave is calculated by, for example, a microcontroller or the like. The output reference value per wave is stored in, for example, a ROM. In the optical amplifier of the present invention, the output signal light power A per wave can be controlled by the VOA2 attenuation amount L. Therefore, the ALC operation can be realized by controlling the VOA2 attenuation amount L so that A = A0. Note that the VOA2 attenuation amount L is L = L0 as in the processing method 1.
[0097]
With the above-described optical amplifier overall gain constant control and ALC operation alone, considering the input dynamic range, the signal gain characteristics in the signal light wavelength band cannot be kept constant due to the influence of the EDF gain deviation. Therefore, in the optical amplifier of the present invention, the EDF gain constant control is performed in order to keep the characteristic of the gain deviation constant.
[0098]
FIG. 8 is a configuration diagram of an AGC circuit for controlling the attenuation of the variable optical attenuators 88 and 90 according to a second embodiment. To monitor the input and output of the first optical amplification unit 86, the voltage signals from the photodetectors 106 and 108 are amplified by amplifiers 150 or 152 having a fixed gain and supplied to ADCs 158 and 160, respectively. The ADCs 158 and 160 convert the voltage signals from the photodetectors 106 and 108 into digital signals and supply the digital signals to the microcontroller 166.
[0099]
To monitor the input and output of the second optical amplification unit 92, the voltage signals from the photodetectors 126 and 128 are amplified by fixed gain amplifiers 154 or 156 and supplied to ADCs 162 and 164, respectively. The ADCs 162 and 164 convert the voltage signals from the photodetectors 126 and 128 into digital signals and supply the digital signals to the microcontroller 166.
[0100]
As described above, the microcontroller 166 can calculate the EDF gain by adding the overall gain of the optical amplifier and the VOA1 attenuation. Therefore, the microcontroller 166 realizes the EDF gain constant control by driving the variable optical attenuator 88 so that the VOA1 attenuation amount becomes the following VOA1 attenuation amount target value (VOA1_Loss target value).
[0101]
VOA1 attenuation target value = optical amplifier overall gain−EDF gain target value
The microcontroller 166 calculates the VOA1 attenuation target value, and controls the variable optical attenuator 88 so as to reach the VOA1 attenuation target value. A control signal output from the microcontroller 166 for controlling the variable optical attenuator 88 is converted into a voltage signal by the DAC 168 and supplied to a drive circuit of the variable optical attenuator 88 including the amplifier 170, the transistor 172, and the resistor R6. Is done.
[0102]
Next, the operation of the optical amplifier of FIG. 6 will be described with reference to FIG. FIG. 9 is a schematic diagram for explaining the operation of the optical amplifier. FIG. 10 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
[0103]
A graph 180 represents an initial setting control state in which an initial value is set so that the PD1 monitor value and the PD3 monitor value have the same value at the time of the input upper limit (other than the input upper limit). The VOA1 attenuation amount is an initial value stored in, for example, a ROM.
[0104]
A graph 182 represents an input fluctuation control state in which a fluctuation has occurred in the input signal. The graph 182 fluctuates so that the signal power is smaller than that of the graph 180.
[0105]
A graph 184 indicates a fluctuation correction control state in which the fluctuation amount of the input signal is calculated, and the VOA2 attenuation amount is controlled so as to correct the fluctuation amount. By controlling the VOA2 attenuation amount, the fluctuation amount of the input signal per wave is corrected. In the graph 186, the optical amplifier overall gain constant control is performed by the AGC using the PD3 monitor value and the PD5 monitor value, and the VOA1 attenuation is controlled so as to maintain the EDF gain target value.
[0106]
Note that “X” included in the table of FIG. 10 represents the input signal power. “Α” represents a variation. “L1” represents the VOA1 attenuation. “L2” represents the VOA2 attenuation. “A” represents the overall gain of the optical amplifier.
[0107]
In the present embodiment, the variable optical attenuators 88 and 90 are independently controlled. However, when the input level per wave fluctuates by X [dB], the attenuation of the variable optical attenuators 88 and 90 is similarly changed. X [dB]. Therefore, an example in which the same processing as that of the optical amplifier of the second embodiment having two variable optical attenuators is performed by an optical amplifier having one variable optical attenuator will be described.
[0108]
FIG. 11 is a block diagram of a third embodiment of the optical amplifier according to the present invention. This optical amplifier is configured to optically cascade a first optical amplification unit 196, a variable optical attenuator (VOA) 198, and a second optical amplification unit 200 between an input terminal 192 and an output terminal 194. ing.
[0109]
The signal light to be amplified supplied to the input terminal 192 is supplied to the EDF 206 in the first optical amplification unit 196 through the optical coupler 202 and the WDM coupler 204 in this order. The pump light from the laser diode 212 is supplied to the EDF 206 through the WDM coupler 204. Thereby, a gain according to the power of the pump light can be obtained. The signal light amplified in the EDF 206 passes through the isolator 208 and the optical coupler 210 in this order, and is output from the first optical amplification unit 196. Further, the first branched signal light branched by the optical coupler 202 is output from the first optical amplification unit 196 as it is.
[0110]
The signal light amplified by the first optical amplifying unit 196 is supplied to the second optical amplifying unit 200 after being attenuated by the variable optical attenuator 198. The signal light supplied to the second optical amplification unit 200 is supplied to the EDF 226 through the optical coupler 220, the isolator 222, and the WDM coupler 224 in this order. The pump light from the laser diode 232 is supplied to the EDF 226 via the WDM coupler 224. As a result, a gain corresponding to the power of the pump light is obtained. The signal light amplified by the EDF 226 is output through the optical coupler 228 and the output terminal 194.
[0111]
The first split signal light output from the first optical amplification unit 196 is supplied to the optical coupler 220 of the second optical amplification unit 200, and is split into a second split signal light and a third split signal light. You. The third split signal light is supplied to the optical coupler 210 after being attenuated by the variable optical attenuator 198. The third split signal light supplied to the optical coupler 210 is split into a fourth split signal light.
[0112]
To monitor the input of the first optical amplification unit 196, the optical amplifier is provided with a photodetector 230. The photodetector 230 converts the second branched signal light branched by the optical coupler 220 into an electric signal.
[0113]
The optical amplifier is provided with a photodetector 214 in order to monitor the signal light reflecting the attenuation of the variable optical attenuator 198 at the input of the first optical amplification unit 196. The photodetector 214 converts the fourth branched signal light branched by the optical coupler 210 into an electric signal.
[0114]
In order to monitor the output of the second optical amplification unit 200, the optical amplifier is provided with a photodetector 234. The photodetector 234 converts the fifth branched signal light branched by the optical coupler 228 into an electric signal.
[0115]
The electric signal from the photo detector 230 is supplied to an AGC circuit 218 as a second control unit. The electric signals from the photo detectors 214 and 234 are supplied to the AGC circuit 218 and the AGC circuit 216 as a first control unit.
[0116]
The control signal from the AGC circuit 216 is supplied to a laser diode 212 and a laser diode 232 as pump light sources. Thereby, the total gain in the total portion from the input terminal 192 to the output terminal 194 is controlled to the target value.
[0117]
The AGC circuit 218 controls the attenuation of the variable optical attenuator 198 so that the sum of the gain in the first optical amplification unit 196 and the gain in the second optical amplification unit 200 becomes constant. The optical amplifier is roughly classified into a control circuit section including AGC circuits 216 and 218 and an optical circuit section other than the control circuit section.
[0118]
In the optical amplifier shown in FIG. 11, an electric signal from the photodetector 214 (hereinafter, referred to as a PD1 monitor value), an electric signal from the photodetector 230 (hereinafter, referred to as a PD2 monitor value), and an electric signal from the photodetector 234 (hereinafter, a PD3 monitor value) , The gain of the optical amplifier, the EDF gain, and the amount of VOA attenuation are controlled.
[0119]
The isolator 208 prevents the fourth branched signal light from entering the EDF 206. Isolator 222 prevents Back_ASE of EDF 226 from entering photodetectors 214 and 230.
[0120]
The overall gain of the optical amplifier, the EDF gain, and the amount of VOA attenuation can be obtained as follows using the monitored values of PD1 to PD3.
[0121]

From the above relationship, the optical amplifier of FIG. 11 controls the overall gain and VOA attenuation of the optical amplifier in the normal operation (AGC state).
[0122]
Next, the processing of the AGC circuit 216 will be described. The AGC 216 controls the entire gain of the optical amplifier to drive the laser diodes 212 and 232 so that the overall gain of the optical amplifier becomes a desired value. Note that the configuration of the AGC circuit 216 may be the same as the configuration of the AGC circuit 110 described above.
[0123]
In the optical amplifier overall gain constant control, as in the second embodiment, the outputs of the laser diodes 212 and 232 are controlled such that the optical amplifier overall gain calculated from the PD1 monitor value and the PD3 monitor value becomes a predetermined value. The actual optical amplifier overall gain constant control is performed so that the following setting conditions are satisfied in the PD1 monitor value and the PD3 monitor value.
[0124]
That is, when the PD1 monitor value and the PD3 monitor value are x [dBm] and x + Amp_Gain reference value [dBm], respectively, the photodetectors 214 and 234 such that the outputs of the amplifiers 130 and 132 in FIG. The light receiving sensitivity [V / W] of the monitor circuit related to each is set.
[0125]
Then, the laser diodes 212 and 232 are driven and controlled so that the output of the differential amplifier 134 has a voltage difference of 0 supplied to the input port. Therefore, in the optical amplifier of FIG. 11, the overall gain of the optical amplifier can be kept constant even when the number of wavelengths changes.
[0126]
Also, in the optical amplifier of FIG. 11, in order to cope with the fluctuation of the input signal light power per one wave, the control for compensating the fluctuation of the input signal light using the ALC is performed. In the ALC state, the number-of-wavelength information is notified from the monitoring control device provided on the upstream side to the optical amplifier, and the output target value of the optical amplifier is determined in the same manner as in the second embodiment by using this wavelength-number information. Is done.
[Processing method 1]
In the processing method 1, it is recognized from the PD2 monitor value where the input signal is within the input dynamic range. Based on the recognized information, the VOA attenuation is controlled, and the output signal level is controlled to be constant. The optical amplifier calculates the following values required for control using the wavelength number information notified from the monitoring control device provided on the upstream side.
[0127]
PD1 monitor value: z1 [dBm]
PD2 monitor value: z2 [dBm]
Input signal wavelength number information: N
Input signal light power: z2-10 Log (N) [dBm / ch]
Upper limit of input signal light power per wave: u [dBm / ch]
Positioning in input dynamics: L0 = u- {z2-10Log (N)}
VOA attenuation: L = z2-z1-Ld [dB]
The input signal light power, the positioning in the input dynamic range, and the VOA attenuation are calculated by, for example, a microcontroller. The input signal light power upper limit per wave is stored in, for example, a ROM.
[0128]
Here, Ld is the VOA attenuation (dead loss) when the input signal light power per wave is u [dBm / ch]. In the optical amplifier of the present invention, as in the second embodiment, the variation of the input optical signal per wave (corresponding to L0) is calculated, and the VOA attenuation L is controlled so that L = L0. As a result, even if the input signal light power per one wave changes, the AGC operation using the PD1 monitor value and the PD3 monitor value allows the output signal light power of the optical amplifier to reach the target value (PD1 monitor value). (Value + target gain of the optical amplifier).
[Processing method 2]
In the processing method 2, the PD3 monitor value is compared with the output signal reference value, and the VOA attenuation is controlled so that the difference becomes zero. The optical amplifier calculates the following values required for control using the wavelength number information notified to the optical amplifier from the monitoring and control device provided on the upstream side.
[0129]
PD3 monitor value: z3 [dBm]
Input signal wavelength number information: N
Output reference value per wave: A0 [dBm / ch]
Output signal light power per wave: A [dBm / ch] = z3-10 Log (N)
Note that the output signal power per wave is calculated by, for example, a microcontroller or the like. The output reference value per wave is stored in, for example, a ROM. In the optical amplifier of the present invention, the output signal light power A per wave can be controlled by the VOA attenuation L. Therefore, the ALC operation can be realized by controlling the VOA attenuation amount L so that A = A0. Note that the VOA attenuation amount L is L = L0 as in the processing method 1.
[0130]
In the above-described ALC operation, the VOA attenuation may be controlled so as to satisfy the target value of the processing method 1 or 2. Since the speed at which the VOA attenuation changes during the ALC operation is the same as the speed at which the PD1 monitor value is corrected, the EDF gain always takes a constant value even during the ALC operation. That is, no gain deviation occurs during the ALC operation.
[0131]
As described in the EDF gain constant control of the second embodiment, the EDF gain constant control is realized in the optical amplifier by controlling the VOA attenuation to the target value.
[0132]
FIG. 12 is a configuration diagram of a third embodiment of the AGC circuit for controlling the attenuation of the variable optical attenuator 198. The PD1 monitor value to the PD3 monitor value are amplified by the amplifiers 240, 242 or 244 having a fixed gain, and supplied to the ADCs 246, 248 or 250, respectively. The ADC 246, 248, or 250 converts the PD1 monitor value to the PD3 monitor value into a digital signal and supplies the digital signal to the microcontroller 252.
[0133]
As described above, the microcontroller 252 can calculate the EDF gain by adding the overall gain of the optical amplifier and the VOA attenuation. Therefore, by driving the variable optical attenuator 198 so that the VOA attenuation becomes the following VOA attenuation target value (VOA_Loss target value), the microcontroller 252 realizes constant EDF gain control.
[0134]
VOA attenuation target value = optical amplifier overall gain−EDF gain target value
The microcontroller 252 calculates the VOA attenuation target value, and controls the variable optical attenuator 198 so as to reach the VOA attenuation target value. A control signal output from the microcontroller 252 to control the variable optical attenuator 198 is converted into a voltage signal by the DAC 254 and supplied to a drive circuit of the variable optical attenuator 198 including the amplifier 256, the transistor 258, and the resistor R5. Is done. In the third embodiment, since the EDF gain becomes the target value at the same time as the ALC operation is performed, it is only necessary to control the VOA attenuation to a constant value.
[0135]
Next, the operation of the optical amplifier of FIG. 11 will be described with reference to FIG. FIG. 13 is a schematic diagram for explaining the operation of the optical amplifier. FIG. 14 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
[0136]
The graph 260 represents the initial setting control state in which the initial value is set so that the PD1 monitor value and the PD2 monitor value have the same value at the time of the input upper limit (other than the input upper limit). The VOA attenuation is set to a value obtained by subtracting the EDF gain target value from the optical amplifier overall gain reference value.
[0137]
A graph 262 represents an input fluctuation control state in which a fluctuation has occurred in the input signal. The graph 262 fluctuates so that the signal power is smaller than that of the graph 260.
[0138]
A graph 264 shows the fluctuation correction control state and the optical amplifier overall gain constant control state. The optical amplifier calculates the fluctuation amount of the input signal and controls the VOA attenuation amount so as to correct the fluctuation amount. When the VOA attenuation is controlled by the ALC operation, the EDF gain becomes a target value. By controlling the VOA attenuation, the fluctuation amount of the input signal per wave is corrected. In addition, the AGC using the PD1 monitor value and the PD3 monitor value performs overall gain constant control of the optical amplifier.
[0139]
Note that “X” included in the table of FIG. 14 represents the input signal power. “Α” represents a variation. “L” represents the VOA attenuation. “A” represents the overall gain of the optical amplifier. The control sequence of the optical amplifier of the third embodiment is simplified as compared with the optical amplifier of the second embodiment.
[0140]
In the optical amplifiers of the second and third embodiments described above, the relationship between “attenuation amount of the variable optical attenuator” and “drive current (or voltage)” changes due to variations in parts and temperature characteristics. As shown in FIG. 15, the variable optical attenuator is controlled while monitoring the amount of attenuation by each monitor value. FIG. 15 is a diagram for explaining that the relationship between the amount of attenuation of the variable optical attenuator and the drive current (or voltage) changes due to variations in components, temperature characteristics, and the like.
[0141]
However, if the characteristics of the variable optical attenuator are provided in the optical amplifier, the VOA attenuation can be controlled by controlling the drive current of the variable optical attenuator. Therefore, in the second and third embodiments, when the relationship between the attenuation of the variable optical attenuator and the drive current (or voltage) is known, the optical amplifier is configured as shown in FIGS. Parts can be reduced.
[0142]
FIG. 16 is a block diagram of a fourth embodiment of the optical amplifier according to the present invention. The optical amplifier in FIG. 16 differs from the optical amplifier in FIG. 6 in that the photodetectors 106, 108, and 126 are eliminated. Therefore, in FIG. 16, the same parts as those in FIG. The optical amplifier in FIG. 16 has the characteristics of the variable optical attenuator as a table or function, and drives the variable optical attenuator with a value processed by a microcontroller, for example.
[0143]
The overall gain of the optical amplifier, the EDF gain, the VOA1 attenuation, and the VOA2 attenuation can be obtained as follows using the PD3 monitor value and the PD5 monitor value. Note that the sum of the PD3 monitor value and the VOA2 attenuation amount corresponds to the input signal power.
[0144]
Amp_Gain = PD5 monitor value− (PD3 monitor value + VOA2_Loss)
EDF_total_Gain = Amp_Gain + VOA1_Loss
The optical amplifier overall gain constant control drives the laser diodes 104 and 122 such that the optical amplifier overall gain calculated from the PD3 monitor value and the PD5 monitor value becomes a desired value. The configuration of the AGC circuit 110 is the same as that of FIG.
[0145]
In the ALC operation, similarly to the optical amplifier of the second embodiment, the fluctuation of the input signal per wave is calculated from the monitored value of the input signal or the output signal, and the calculated value is set as the target value, and the variable optical attenuator 88 and 90 is driven.
[0146]
Further, the optical amplifier of FIG. 16 performs EDF gain constant control using the AGC circuit 112 as shown in FIG. FIG. 17 is a block diagram of the fourth embodiment of the AGC circuit for controlling the attenuation of the variable optical attenuators 88 and 90.
[0147]
The voltage signals from the photodetectors 124 and 128 are amplified by amplifiers 270 or 272 having a fixed gain, and supplied to ADCs 274 and 276, respectively. The ADCs 274 and 276 convert the voltage signals from the photodetectors 124 and 128 into digital signals and supply the digital signals to the microcontroller 278.
[0148]
As described above, the microcontroller 278 can calculate the EDF gain by adding the overall gain of the optical amplifier and the VOA1 attenuation. Therefore, the microcontroller 278 realizes the EDF gain constant control by driving the variable optical attenuator 88 so that the VOA1 attenuation amount becomes the following target value of the VOA1 attenuation amount (VOA1_Loss target value).
[0149]
VOA1 attenuation target value = optical amplifier overall gain−EDF gain target value
The microcontroller 278 calculates the VOA1 attenuation target value, and controls the variable optical attenuator 88 so as to reach the VOA1 attenuation target value. A control signal output from the microcontroller 278 for controlling the variable optical attenuator 88 is converted into a voltage signal by the DAC 280 and supplied to a drive circuit of the variable optical attenuator 88 including an amplifier 282, a transistor 284, and a resistor R5. Is done.
[0150]
Next, the operation of the optical amplifier of FIG. 16 will be described. FIG. 18 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
[0151]
The optical amplifier of FIG. 16 sets the VOA2 attenuation and the PD1 monitor value at the time of the input upper limit (other than the input upper limit). Note that the VOA1 attenuation amount is an initial value stored in, for example, a ROM or the like.
[0152]
When a fluctuation occurs in the input signal, the optical amplifier calculates the fluctuation amount of the input signal and controls the VOA2 attenuation so as to correct the fluctuation amount. By controlling the VOA2 attenuation amount, the fluctuation amount of the input signal per wave is corrected. In addition, the AGC using the PD3 monitor value and the PD5 monitor value performs constant control of the overall gain of the optical amplifier, and controls the VOA1 attenuation so as to maintain the EDF gain target value.
[0153]
Note that “X” included in the table of FIG. 18 represents the input signal power. “Α” represents a variation. “L1” represents the VOA1 attenuation. “L2” represents the VOA2 attenuation. “A” represents the overall gain of the optical amplifier.
[0154]
FIG. 19 is a block diagram of a fifth embodiment of the optical amplifier according to the present invention. The optical amplifier in FIG. 19 differs from the optical amplifier in FIG. 11 in that the photodetector 230 is eliminated. Therefore, in FIG. 19, the same parts as those in FIG. The optical amplifier in FIG. 19 has the characteristics of the variable optical attenuator as a table or function, and drives the variable optical attenuator with a value processed by, for example, a microcontroller.
[0155]
The overall gain of the optical amplifier, the EDF gain, and the VOA attenuation can be obtained as follows using the monitor values of PD1 and PD3. The sum of the PD1 monitor value and the VOA attenuation corresponds to the input signal power.
[0156]
Amp_Gain = PD3 monitor value− (PD1 monitor value + VOA_Loss)
EDF_total_Gain = Amp_Gain + VOA_Loss
The optical amplifier overall gain constant control drives the laser diodes 212 and 232 such that the optical amplifier overall gain calculated based on the PD1 monitor value and the PD3 monitor value becomes a desired value. The configuration of the AGC circuit 216 is the same as that of FIG.
[0157]
In the ALC operation, similarly to the optical amplifier of the second embodiment, the fluctuation of the input signal per one wave is calculated from the monitor value of the input signal or the output signal, and the calculated value is used as a target value to control the variable optical attenuator 198 Drive.
[0158]
Further, the optical amplifier of FIG. 19 performs the EDF gain constant control using the AGC circuit 218 as described above. The voltage signals from the photodetectors 214 and 234 are amplified by an amplifier having a fixed gain and supplied to the ADC 274, respectively. The ADC converts the voltage signals from the photodetectors 214 and 234 into digital signals and supplies the digital signals to the microcontroller.
[0159]
As described above, the microcontroller can calculate the EDF gain by adding the overall gain of the optical amplifier and the VOA attenuation. Therefore, the microcontroller realizes constant EDF gain control by driving the variable optical attenuator 198 such that the VOA attenuation amount becomes the following VOA attenuation amount target value (VOA1_Loss target value).
[0160]
VOA attenuation target value = optical amplifier overall gain−EDF gain target value
The microcontroller calculates a VOA attenuation target value, and controls the variable optical attenuator 198 so as to reach the VOA attenuation target value. A control signal output from the microcontroller for controlling the variable optical attenuator 198 is converted into a voltage signal by a DAC and supplied to a drive circuit of the variable optical attenuator 198 including an amplifier, a transistor, and a resistor.
[0161]
Next, the operation of the optical amplifier in FIG. 19 will be described. FIG. 20 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
[0162]
The optical amplifier of FIG. 19 sets the VOA attenuation and the PD1 monitor value at the time of the input upper limit (other than the input upper limit). The VOA attenuation is an initial value stored in, for example, a ROM.
[0163]
When a fluctuation occurs in the input signal, the optical amplifier calculates the fluctuation amount of the input signal and controls the VOA attenuation so as to correct the fluctuation amount. By controlling the VOA attenuation, the fluctuation amount of the input signal per wave is corrected. In addition, the AGC using the PD1 monitor value and the PD3 monitor value performs overall gain constant control of the optical amplifier, and controls the VOA attenuation so as to maintain the EDF gain target value.
[0164]
Note that “X” included in the table of FIG. 20 represents the input signal power. “Α” represents a variation. “L” represents the VOA attenuation. “A” represents the overall gain of the optical amplifier.
[0165]
As described above, in the present embodiment, the wavelength characteristic of the gain of the optical amplifier as a whole is kept constant by controlling the variable optical attenuator. Therefore, the control configuration of the optical amplifier can be simplified as compared with the conventional case where the AGC is performed for each of the plurality of optical amplification units to keep the wavelength characteristic of the gain constant. It becomes possible.
[0166]
Further, since the control configuration of the optical amplifier can be simplified, the required number of components can be reduced. As a result, the optical amplifier of the present invention can achieve a significant reduction in cost and a reduction in mounting area due to a reduction in the number of components.
[0167]
The present invention includes the following supplementary notes.
(Supplementary Note 1) First and second optical amplification units;
A variable optical attenuator optically connected between the first and second optical amplification units;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit;
An optical amplifier comprising: a second control unit that controls attenuation of the variable optical attenuator based on an input and an output of the first optical amplifying unit and an input and an output of the second optical amplifying unit.
(Supplementary Note 2) First and second photodetectors for converting the input and output of the first optical amplifying unit into electric signals, respectively, and a second photodetector for converting the input and output of the second optical amplifying unit into electric signals, respectively. Further comprising third and fourth photodetectors,
Electrical signals from the first and fourth photodetectors are provided to the first control unit;
2. The optical amplifier according to claim 1, wherein electric signals from the first to fourth photodetectors are supplied to the second control unit.
(Supplementary Note 3) The first control unit controls the first and second optical amplification units so that a level difference between electric signals from the first and fourth photodetectors matches a set value. 3. The optical amplifier according to claim 2, including:
(Supplementary Note 4) The second control unit makes the sum of the level difference between the electric signals from the first and second photodetectors and the level difference between the electric signals from the third and fourth photodetectors constant. 3. The optical amplifier according to claim 2, further comprising means for controlling attenuation of the variable optical attenuator.
(Supplementary Note 5) First and second optical amplification units;
A first variable optical attenuator for attenuating an output of the first optical amplification unit;
A second variable optical attenuator for attenuating an input of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
A second control unit that controls the attenuation of the first and second variable optical attenuators based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit. Optical amplifier.
(Supplementary Note 6) First and second photodetectors for converting the input and output of the first optical amplification unit into electric signals, respectively, and a third for converting the output of the second variable optical attenuator into electric signals. A photodetector; and fourth and fifth photodetectors for converting an input and an output of the second optical amplification unit into an electric signal, respectively.
Electrical signals from the third and fifth photodetectors are supplied to the first control unit;
6. The optical amplifier according to claim 5, wherein electric signals from the first, second, fourth and fifth photodetectors are supplied to the second control unit.
(Supplementary Note 7) First and second optical amplification units,
A variable optical attenuator for attenuating an input and an output of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; When,
The attenuation of the variable optical attenuator is controlled based on the input of the first optical amplification unit, the input of the first optical amplification unit attenuated by the variable optical attenuator, and the output of the second optical amplification unit. An optical amplifier comprising a second control unit.
(Supplementary Note 8) A first photodetector that converts the input of the first optical amplification unit attenuated by the variable optical attenuator into an electric signal, and a second photodetector that converts the input of the first optical amplification unit into an electric signal. Further comprising: a second photodetector; and a third photodetector that converts an output of the second optical amplification unit into an electric signal.
Electrical signals from the first and third photodetectors are provided to the first control unit;
8. The optical amplifier according to claim 7, wherein electric signals from the first to third photodetectors are supplied to the second control unit.
(Supplementary Note 9) First and second optical amplification units,
A first variable optical attenuator for attenuating an output of the first optical amplification unit;
A second variable optical attenuator for attenuating an input of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
The attenuation of the first and second variable optical attenuators is determined based on the output of the second variable optical attenuator, the output of the second optical amplifying unit, and the characteristics of the first and second variable optical attenuators. An optical amplifier comprising a second control unit for controlling the optical amplifier.
(Supplementary Note 10) Further provided are a first photodetector that converts an output of the second variable optical attenuator into an electric signal, and a second photodetector that converts an output of the second optical amplifying unit into an electric signal,
Electrical signals from the first and second photodetectors are provided to the first control unit;
The optical amplifier according to claim 9, wherein electric signals from the first and second photodetectors are supplied to the second control unit.
(Supplementary Note 11) {First and Second Optical Amplifying Units,
A variable optical attenuator for attenuating an input and an output of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; When,
A second control unit that controls the attenuation of the variable optical attenuator based on the input of the first optical amplification unit, the output of the second optical amplification unit, and the characteristics of the variable optical attenuator, which are attenuated by the variable optical attenuator. An optical amplifier comprising: a control unit;
(Supplementary Note 12) A first photodetector that converts an input of the first optical amplification unit attenuated by the variable optical attenuator into an electric signal, and a second photodetector that converts an output of the second optical amplification unit into an electric signal. And two photodetectors,
Electrical signals from the first and second photodetectors are provided to the first control unit;
The optical amplifier according to claim 11, wherein electric signals from the first and second photodetectors are supplied to the second control unit.
(Supplementary Note 13) The first control unit controls the gains of the first and second optical amplifying units so that the output power of the optical amplifier becomes constant,
13. The optical amplifier according to claim 1, wherein the second control unit controls the attenuation of the variable optical attenuator so that the sum of the gains of the first and second optical amplification units is constant.
(Supplementary Note 14) Each of the first and second optical amplification units includes an optical amplification medium, and a pump light source that supplies pump light to the optical amplification medium.
14. The optical amplifier according to any one of supplementary notes 1 to 13, wherein each gain of the first and second optical amplification units is controlled by power of pump light output from the pump light source.
(Supplementary Note 15) A method of controlling an optical amplifier including first and second optical amplifying units and a variable optical attenuator optically connected between the first and second optical amplifying units. ,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit;
Controlling the attenuation of the variable optical attenuator based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit.
(Supplementary Note 16) The first step includes a step of controlling gains of the first and second optical amplifying units so that an output power of the optical amplifier becomes constant,
16. The control method according to claim 15, wherein the second step includes a step of controlling the attenuation of the variable optical attenuator so that the sum of the gains of the first and second optical amplification units becomes constant.
(Supplementary Note 17) Each of the first and second optical amplification units includes an optical amplification medium, and a pump light source that supplies pump light to the optical amplification medium.
17. The control method according to claim 16, wherein each gain of the first and second optical amplification units is controlled by power of pump light output from the pump light source.
(Supplementary note 18) {Converting the input and output of the first optical amplifying unit into first and second electrical signals, respectively; and converting the input and output of the second optical amplifying unit into second and third electrical signals, respectively. Converting to an electrical signal,
The control according to claim 15, wherein the first step includes supplying the first and fourth electric signals, and the second step includes supplying the first to fourth electric signals. Method.
(Supplementary note 19) The supplementary note 18, wherein the first step includes a step of controlling the first and second optical amplification units such that a level difference between the first and fourth electric signals matches a set value. Control method.
(Supplementary Note 20) The second step is to adjust the variable optical attenuator so that the sum of the level difference between the first and second electric signals and the level difference between the third and fourth electric signals becomes constant. 19. The control method according to claim 18, comprising the step of controlling the attenuation.
(Supplementary Note 21) A method for controlling an optical amplifier including: first and second optical amplification units; and a first variable optical attenuator for attenuating an output of the first optical amplification unit,
A first step of controlling gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
Controlling the attenuation of the first and second variable optical attenuators based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit. Method.
(Supplementary Note 22) A method of controlling an optical amplifier including: first and second optical amplification units; and a variable optical attenuator that attenuates an input and an output of the first optical amplification unit,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; ,
The attenuation of the variable optical attenuator is controlled based on the input of the first optical amplification unit, the input of the first optical amplification unit attenuated by the variable optical attenuator, and the output of the second optical amplification unit. A control method comprising: a second step.
(Supplementary Note 23) First and second optical amplification units, a first variable optical attenuator that attenuates the output of the first optical amplification unit, and a second variable attenuator that attenuates the input of the first optical amplification unit A method for controlling an optical amplifier comprising a variable optical attenuator of
A first step of controlling gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
The attenuation of the first and second variable optical attenuators is determined based on the output of the second variable optical attenuator, the output of the second optical amplifying unit, and the characteristics of the first and second variable optical attenuators. And a second step of controlling.
(Supplementary Note 24) A method for controlling an optical amplifier, comprising: first and second optical amplifying units; and a variable optical attenuator for attenuating an input and an output of the first optical amplifying unit,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; ,
A second control unit that controls the attenuation of the variable optical attenuator based on the input of the first optical amplification unit, the output of the second optical amplification unit, and the characteristics of the variable optical attenuator, which are attenuated by the variable optical attenuator. Control method comprising the steps of:
[0168]
【The invention's effect】
As described above, according to the present invention, when AGC and ALC are performed in an optical amplifier applicable to WDM, a control error hardly occurs, a complicated configuration is not required, and the number of wavelengths can be easily increased or decreased. A compatible optical amplifier and a control method of the optical amplifier can be provided.
[0169]
[Brief description of the drawings]
FIG. 1 is a block diagram showing an optimal configuration for performing both AGC and ALC in an optical amplifier.
FIG. 2 is a schematic diagram for explaining an example of the operation of the optical amplifier.
FIG. 3 is a block diagram of a first embodiment of the optical amplifier according to the present invention.
FIG. 4 is a configuration diagram of a first embodiment of an AGC circuit for controlling a gain of an optical amplification unit.
5 is a configuration diagram of a first embodiment of an AGC circuit for controlling attenuation of a variable optical attenuator 18. FIG.
FIG. 6 is a block diagram of a second embodiment of the optical amplifier according to the present invention.
FIG. 7 is a configuration diagram of a second embodiment of the AGC circuit for controlling the gain of the optical amplification unit.
FIG. 8 is a configuration diagram of an AGC circuit for controlling attenuation of a variable optical attenuator according to a second embodiment.
FIG. 9 is a schematic diagram for explaining an operation of the optical amplifier.
FIG. 10 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
FIG. 11 is a block diagram of a third embodiment of the optical amplifier according to the present invention.
FIG. 12 is a configuration diagram of a third embodiment of the AGC circuit for controlling the attenuation of the variable optical attenuator.
FIG. 13 is a schematic diagram for explaining the operation of the optical amplifier.
FIG. 14 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
FIG. 15 is a diagram for explaining that the relationship between the amount of attenuation of the variable optical attenuator and the drive current changes due to variations in components, temperature characteristics, and the like.
FIG. 16 is a block diagram of a fourth embodiment of the optical amplifier according to the present invention.
FIG. 17 is a configuration diagram of a fourth embodiment of the AGC circuit that controls the attenuation of the variable optical attenuator.
FIG. 18 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
FIG. 19 is a block diagram of a fifth embodiment of the optical amplifier according to the present invention.
FIG. 20 is a table showing changes in monitor values and VOA attenuation of the optical amplifier.
[Explanation of symbols]
16, 86, 196 First optical amplification unit
18,198 variable optical attenuator
20, 92, 200 ° second optical amplification unit
26,44,100,118,206,226 EDF
28, 46, 104, 122, 212, 232 laser diode
32, 34, 50, 54, 106, 108, 124, 126, 128, 214, 230, 234} photodetector
36, 38, 110, 112, 216, 218 AGC circuit
88 ° first variable optical attenuator
90 ° second variable optical attenuator

Claims (10)

First and second optical amplification units;
A variable optical attenuator optically connected between the first and second optical amplification units;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit;
An optical amplifier comprising: a second control unit that controls attenuation of the variable optical attenuator based on an input and an output of the first optical amplifying unit and an input and an output of the second optical amplifying unit. First and second optical amplification units;
A first variable optical attenuator for attenuating an output of the first optical amplification unit;
A second variable optical attenuator for attenuating an input of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
A second control unit that controls the attenuation of the first and second variable optical attenuators based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit. Optical amplifier. First and second optical amplification units;
A variable optical attenuator for attenuating an input and an output of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; When,
The attenuation of the variable optical attenuator is controlled based on the input of the first optical amplification unit, the input of the first optical amplification unit attenuated by the variable optical attenuator, and the output of the second optical amplification unit. An optical amplifier comprising a second control unit. First and second optical amplification units;
A first variable optical attenuator for attenuating an output of the first optical amplification unit;
A second variable optical attenuator for attenuating an input of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
The attenuation of the first and second variable optical attenuators is determined based on the output of the second variable optical attenuator, the output of the second optical amplifying unit, and the characteristics of the first and second variable optical attenuators. An optical amplifier comprising a second control unit for controlling the optical amplifier. First and second optical amplification units;
A variable optical attenuator for attenuating an input and an output of the first optical amplification unit;
A first control unit that controls gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; When,
A second control unit that controls the attenuation of the variable optical attenuator based on the input of the first optical amplification unit, the output of the second optical amplification unit, and the characteristics of the variable optical attenuator, which are attenuated by the variable optical attenuator. An optical amplifier comprising: a control unit; A method for controlling an optical amplifier comprising: first and second optical amplification units; and a variable optical attenuator optically connected between the first and second optical amplification units,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit;
Controlling the attenuation of the variable optical attenuator based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit. A method for controlling an optical amplifier, comprising: first and second optical amplification units; and a first variable optical attenuator for attenuating an output of the first optical amplification unit,
A first step of controlling gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
Controlling the attenuation of the first and second variable optical attenuators based on the input and output of the first optical amplification unit and the input and output of the second optical amplification unit. Method. A method for controlling an optical amplifier comprising: first and second optical amplification units; and a variable optical attenuator for attenuating an input and an output of the first optical amplification unit,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; ,
The attenuation of the variable optical attenuator is controlled based on the input of the first optical amplification unit, the input of the first optical amplification unit attenuated by the variable optical attenuator, and the output of the second optical amplification unit. A control method comprising: a second step. A first and a second optical amplifying unit, a first variable optical attenuator for attenuating an output of the first optical amplifying unit, and a second variable optical attenuator for attenuating an input of the first optical amplifying unit A method for controlling an optical amplifier comprising a device and
A first step of controlling gains of the first and second optical amplification units based on an output of the second variable optical attenuator and an output of the second optical amplification unit;
The attenuation of the first and second variable optical attenuators is determined based on the output of the second variable optical attenuator, the output of the second optical amplifying unit, and the characteristics of the first and second variable optical attenuators. And a second step of controlling. A method for controlling an optical amplifier comprising: first and second optical amplification units; and a variable optical attenuator for attenuating an input and an output of the first optical amplification unit,
A first step of controlling gains of the first and second optical amplification units based on an input of the first optical amplification unit and an output of the second optical amplification unit, which are attenuated by the variable optical attenuator; ,
A second control unit that controls the attenuation of the variable optical attenuator based on the input of the first optical amplification unit, the output of the second optical amplification unit, and the characteristics of the variable optical attenuator, which are attenuated by the variable optical attenuator. Control method comprising the steps of:

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