JP4595210B2

JP4595210B2 - Configuration and control method of optical amplifier or add / drop multiplexer in wavelength division multiplexing optical network

Info

Publication number: JP4595210B2
Application number: JP2001036307A
Authority: JP
Inventors: 伸治坂野; 博行中野
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2001-02-14
Filing date: 2001-02-14
Publication date: 2010-12-08
Anticipated expiration: 2021-02-14
Also published as: JP2002246986A

Description

【０００１】
【発明の属する技術分野】
本発明は波長多重光ネットワークに係り、特に光増幅器を有する構成において光レベル制御機能と波長平坦性を合わせて持ち、より安定した伝送品質を提供する光増幅器と分岐挿入器の構成と制御方法に関係する。
【０００２】
【従来の技術】
光ファイバ増幅器を用いた波長多重光ネットワークでは光ファイバ増幅器が複数の波長の光信号を容易に一括して増幅できることから、低コストな損失補償技術として長距離伝送や波長多重の合波損失補償に光ファイバ増幅器を利用する。しかし、光ファイバ増幅器の利得は波長依存性があるため、複数の波長の光信号を増幅する場合には波長の平坦化技術が必要となる。光ファイバ増幅器の波長依存性は利得に強く依存するため、波長平坦化は特定の利得条件で波長依存性を補償するための平坦化フィルタを用いて実現する。
【０００３】
光ファイバ増幅器の特定の利得条件を得るためには、利得一定制御を行えばよいのであるが、光伝送では光レベルが伝送路損失に依存するため、利得一定制御のみでは光出力値が一定にならない。伝送路損失の如何によらず光出力を一定に保つには出力一定制御を行えばよいのであるが、それでは、伝送路損失によって光入力が変わるため、光入力と光出力である利得が変化する。この両者を満足するためにの一手法として光ファイバ増幅器は利得一定制御を行い、光減衰器と組み合わせる事で光レベルを調整する手法がとられた。光増幅器と異なり、光減衰器は減衰量が変わっても波長依存性が変わらないため、光ファイバ増幅器の利得が一定制御下で光出力一定になるように光減衰器で光入力が一定になるように光のレベル調節を行うものである。
【０００４】
上記光出力は通常波長多重化された状態で光モニタを行うために多重化された波長数にとチャネル（波長）毎の光出力の総和値をモニタする。実際求められる制御は光信号の品質を保つために光チャネル当たりの光出力レベルが常に設定値になることである。総和の光出力レベルをモニタする手法は簡単で低コストであるが、制御では光チャネルでの光出力レベルを得るために波長数情報が必要になる。波長数情報を与えて総和出力モニタ値を割り、チャネル当たりの光出力が一定になるように負帰還制御を行った。
【０００５】
ところが実際の波長数が波長多重に挿入される前の光入力が断線などで急に減少し、制御に使われる波長数情報と実際の波長数に差を生じると光チャネル当たりのレベルが求められる値からずれるという現象があった。例えば、ある一つの波長の光チャネルが分岐挿入ノードで挿入されるケースで挿入前に１５波長多重されている状態でその１チャネルを挿入し１６波長になる場合を例にとる。その１５波長の光入力が断すると当初１６波長多重されていた状態から挿入された１波長に減る。このとき総和モニタ出力が１６波長分の設定になっていると、残された１波長の光出力が１６波長総和と光出力と同じになるように制御をかける。その結果、残された光チャネルの光出力は求められる値の１６倍の光出力なるように制御される。このように出力一定制御では場合によっては受信器を破壊危険性があった。
また、波長多重光ネットワークにおける分岐挿入部においては限られた波長の分岐挿入を行う装置において任意の波長を組み合わせて分岐挿入を行う場合には分岐挿入される光チャネル信号と通過光チャネルの光レベルを合わせるためには必要なときに任意の波長の分岐挿入フィルタを挿入するできる機構が必要である。このときに追加フィルタにより通過波長信号のレベルが変化し、現地で調節する必要があった。
さらに、挿入光チャネルにおいては、波長依存性がないように波長依存性のない合波器を使用すると、波長分岐からの分岐光の漏れが挿入部では遮断されないため、漏れ光と挿入光でコヒーレントクロストークを生じ、伝送品質が劣化した。
【０００６】
【発明が解決しようとする課題】
本発明の課題は波長数が変化した場合には残された光チャネルの光出力が異常に大きくなることを回避しながら、光チャネル当たりの光出力レベルが損失変動に対してはその変動を吸収するように安定した光チャネル出力レベルを提供することである。また、分岐挿入する波長数の増設もしくは減設に対して高い品質で安定して揃った光チャネル毎の光出力を有する分岐挿入器を提供することである。されに、分岐挿入の構成を変更した場合に自動的にその損失変動を吸収することにある。
【０００７】
【課題を解決するための手段】
光伝送システムネットワーク内の波長多重光を増幅する光増幅器は利得一定制御を行うとともに、いつもは波長多重信号のレベル調節用の光減衰器の減衰量を固定する。いつもは利得一定制御と光減衰器の減衰量が固定されているため、例え光チャネル数が変化しても総和光レベルを制御に利用しないため、光チャネル当りのレベルダイヤは変動しない。
確実な波長数情報が得られたときにのみ、可変光減衰器からの波長多重光のモニタ値がその波長数情報の波長時の所定のモニタ値になるようにその光減衰器の減衰量を調節する。そうすることで光ファイバ伝送路などで生じる光損失変動等により引き起こされる光レベル変動を吸収する。その後再び光減衰器の減衰量を固定するのであるがその固定値は光レベル変動を吸収したときの値とする。そのようにすることで再び光減衰器の値が一定となるので波長数が変化しても光チャネル当たりのレベルが変化することはなくなる。
【０００８】
波長数変動に伴う光チャネルレベルの変動はモニタ値負帰還制御を行っているときに波長数情報と実際の波長数に差を生じた時に生じるのであるが、本手法によればモニタ負帰還制御の頻度を少なく、かつ制御そのものの時間も短かくするので波長数情報と実際の波長数が異なる状態でモニタ負帰還制御を行う危険度が大幅に減少する。また、損失変動は季節の変化に伴う温度変化に起因したり、光部品や光コネクタの接合や光伝送路の経時変化というように非常に緩やかなものであり、モニタ負帰還の頻度は秒オーダで充分である。
【０００９】
光ネットワークの伝送路にノードを追加したり、あるいは光チャネルの追加のための変更を加えるなどして損失が変化した時には、波長数情報を与えて一度モニタ負帰還を行うことで、損失変動の補正ができる。
分岐挿入の波長組み合わせてを行うにあたり、分岐側には任意の波長の分岐フィルタを挿入できるようにして、通過信号光に対しては分岐挿入器の光チャネルの光レベルが所望の値になるように可変光減衰器で調節し、挿入信号に対しては波長依存性をもたず光減衰器または光増幅器で所望の光レベルになるように制御する挿入部と波長依存性のない合波器で挿入信号光と通過波長信号を合波する。挿入信号には任意波長信号を接続することができる。
【００１０】
【発明の実施の形態】
図１は本発明を波長平坦化波長多重光増幅器構成への適用した例を示したものである。構成に合わせて、各部の機能を説明する。入力側接続光ファイバ１−１からの波長多重光入力１−２は、光入力モニタ用タップカプラ１−４で一部の光が分岐され、光入力モニタ１−５に達する。メインの光信号は前段光増幅部１−３０の中心の機能である光増幅を行う前段光ファイバ増幅器１−６で増幅され、波長平坦化フィルタ１−９で前段光ファイバ増幅器１−６で生じる利得の波長依存性を補正し、前段光ファイバ増幅器光出力用モニタカプラ１−１０で一部のモニタ光が分岐され、残りの主な増幅信号光は可変減衰器型光レベル調節部に結合する。前段光ファイバ増幅器光出力用モニタカプラ１−１０で一部のモニタ光は光出力モニタ１−１１に達して出力レベルがモニタされる。前段光増幅部１−３０では光入力の如何によらず波長依存性を一定に保つため、利得一定制御を行う。光利得制御では光入力モニタ１−５の光レベルと光出力モニタ１−１１の光レベルから利得検出一定制御回路１−８で両者の相対的な比をである利得の検出演算を行い、これが常時一定になるように励起ＬＤ制御回路１−７へ制御信号を流し、前段光ファイバ増幅器１−６の増幅率を決める励起ＬＤの出力を制御する。
また、後段光増幅部１−３２においても前段光増幅部１−３０と同様に利得一定制御を行う。可変減衰器型光レベル調節部１−３１からの波長多重光入力は、後段光ファイバ増幅器光入力モニタ用タップカプラ１−１７で一部の光が分岐され、光入力モニタ１−１８に達する。メインの光信号は後段光増幅部１−３２の中心の機能である光増幅を行う後段光ファイバ増幅器１−１９で増幅され、波長平坦化フィルタ１−２２で後段光ファイバ増幅器１−１９で生じる利得の波長依存性を補正し、後段光ファイバ増幅器光出力用モニタカプラ１−２３で一部のモニタ光が分岐され、残りの主な増幅信号光は波長多重光出力１−２５として出力される。光出力用モニタカプラ１−２３で一部のモニタ光は光出力モニタ１−２４に達して出力レベルがモニタされる。後段光増幅部１−３２では光入力の如何によらず波長依存性を一定に保つため、利得一定制御を行う。光利得制御では光入力モニタ１−１８の光レベルと光出力モニタ１−２４の光レベルから利得検出一定制御回路１−２１で両者の相対的な比をである利得の検出演算を行い、これが常時一定になるように励起ＬＤ制御回路１−２０へ制御信号を流し、後段光ファイバ増幅器１−１９の増幅率を決める励起ＬＤの出力を制御する。
【００１１】
上記のようにして、前段と後段の光増幅部で利得一定制御を行うことにより、波長平坦化した状態で光増幅を行う。ところが光伝送では伝送路区間損失は必ずしも一定でなく光入力変動１−３を生じる。入力変動１−３に対しても光伝送特性上は波長多重光出力１−２５の光チャネル当りの光出力を一定に保ことが望ましい。このため、前段後段の光増腹部の間に可変減衰器型光レベル調節部１−３１を挿入する。前段光増幅部１−３０からの波長多重光信号は可変減衰器１−１２で光レベルを調節する。可変光減衰器１−１２は光減衰量に依らず波長依存性は一定であるため、光レベルを変えても波長平坦性が変化することがない。この光減衰器と利得一定制御の光増幅部を組み合わせることにより、波長平坦性を保ちながら光チャネル当りの光出力を一定に制御できる。
可変減衰器１−１２の制御においていつもは減衰量一定制御・現推量変更回路１−１４から減衰量を一定に保つように中間光減衰器制御回路１−１３に指示される。この状態では、波長多重光増幅器全体で光入出力の利得関係は一定に保たれるため、仮に波長数が変動しても個々の光チャネルの利得は変わらない。
【００１２】
図２に波長数をトリガにした自動光出力制御方式の相関を示す。温度環境変化やファイバ伝送路劣化やあるいは光コネクタ接続状態の変化に伴う光入力変動１−３を損失変動として一例を示しす。また、実チャネル数とは入力される波長多重信号の前段までの光チャネルの増設や減設、何かの事故による波長数変動として初期が５チャネル、一時的に４チャネル、一気に２チャネル増えて６チャネルに変化を想定した場合を示す。光チャネル情報１−１５が入力されないときには減衰量一定制御・減衰量変更回路１−１４では自動比光出力一定制御がoffで、光減衰器１−１２は一定の減衰量を保持する。この状態で▲１▼のように波長数が減少しても波長多重信号のトータル光出力を示す、光モニタ出力値は波長数減少分減るが、平均光チャネル光出力は保持される。このように、光減衰器１−１２の減衰量を保持すると波長数変動耐力が得られるが、▲２▼光入力変動１−３に対応した平均光チャネル光出力の減少が生じる。
【００１３】
光チャネル数情報１−１５は前段中継までの波長数情報あるいはNE-OpS（網装置管理操作システム）からシステム全体の光チャネル情報を集計して監視制御系１−１６から入力するか、場合よっては自ノードに波長数測定系がありその情報を監視制御系１−１６から入力することを示す。この情報は波長数が変化して即座に通知できるものではないのが、特にこだわる必要はなく、その時点の光チャネル情報１−１５を正確にその光増幅器に入力される実光チャネル数に合わせることが重要となる。波長数情報の検出から通知までの時間を短くすることにより、波長数情報１−１５を得て減衰量一定制御・減衰量変更回路１−１４で減衰量変更を行う時点での実光チャネル数と波長数情報のミスマッチによる制御誤りの発生を極力減らすことができる。波長数情報１−１５が入力されると、減衰量一定制御・減衰量変更回路１−１４は減衰量の変更を行う。即ち、光入力変動１−３に伴う、光レベルの変化の補正を行うために、▲３▼波長数に応じた出力値に一致するように自動光出力一定制御（ＡＬＣ）をonして光出力モニタ１−２４の出力が所定の値になるように光減衰器制御回路を調整して、可変減衰器１−１２の減衰量を調整する。このとき、光入力変動に伴う平均光チャネル光出力の減少が補正される。その後即座に自動光出力一定制御をoffして、補正で得た光減衰器１−１２減衰量を保持する。平均光チャネル光出力の破線は補正を行わない場合であるが、このときには光入力変動１−３が平均光チャネル光出力１−２５に反映され、伝送品質を劣化させることになるが、波長数情報１−１５トリガによる補正を行うことで改善される。
補正後に再び、▲４▼光減衰器１−１２の減衰量を固定すると▲１▼と同じように実光波長数が突然４から６に変化しても、平均光チャネル光出力はほぼ一定に保たれる。
【００１４】
図３は本発明をチャネル単位分岐挿入構成への適用した例を示したものである。構成に合わせて、各部の機能を説明する。入力側接続光ファイバ２−１からの波長多重光入力２−２は、受信用光増幅器２−３で例えば最初の実施例の光増幅器制御により、光出力を補正した光出力を得られる。10 Gbit/sのような高速変調信号を波長多重信号が含む場合には受信側光増幅器２−３には分散補償光部品２−４が結合される。受信光増幅部２−３１で伝送ろ損失や分散の補償を受けた波長多重信号は光チャネル単位分岐部２−３２で特定の波長の光信号例えば波長λj分岐フィルタ２−５により被分岐波長λj光信号２−６のみが分岐され、通過信号光は残りは通過する。このとき、10 G bit/sのような高速では分岐時の波形劣化を防止するためには集中的数μmで光分離する誘電体多層膜フィルタを分岐に使用するとよい。また、後段では分岐光信号と同じ波長の光信号を挿入するのであるが、後述するように、挿入部は波長依存性を持たないため分岐光の漏れ光との干渉によるコヒーレントクロストークを生じる危険性がある。このため、分岐フィルタからの漏れ40dB程度遮断するために、通過側にファイバブラググレーティングを挿入すとよい。
【００１５】
光チャネル単位分岐部２−３２からの通過波長多重光信号は通過信号レベル調節部２−３３に結合する。通過信号は可変光減衰器２−１０により所望の光レベルに減衰を受けるのであるが、通常は減衰量は一定制御される。監視制御系２−１４から波長数情報２−１３が入力された時にのみ、可変光減衰器の出力し通過光チャネル波長波長多重光出力モニタ用タップカプラ２−１５で分岐された光信号の一部を光出力モニタ２−１６でモニタし、その検出レベルが減衰量一定制御・減衰量変更回路２−１２に入力されて、入力された波長数情報２−１３から波長数に応じた設定レベルにモニタがなるように光減衰器制御回路２−１１を制御して、可変光減衰器２−１０の設定を変更する。その後、再び減衰量を固定する。本機能の利用方法は、初期には波長λj分岐フィルタ２−５のみを挿入して被分岐波ｈ項λj光信号を得るが、その後、波長λi分岐フィルタ２−７を挿入して被分岐波長λi光信号を得る。この時、通過光信号は分岐フィルタの挿入による損失変動を受け光レベル変化２−９を生じる。波長多重光伝送では各波長の光レベルを揃えることが重要であり、先の波長数情報２−１３を通過信号レベル調節部２−３３の制御部に通知することで、光出力モニタ２−１６のレベルが一定になるように可変光減衰器２−１０の減衰量を下げる。
再び減衰量を固定（自動光出力一定制御off）することにより、先の例と同様に実波長数が変化しても、平均光チャネル光レベルが保たれ、変化しない。
【００１６】
通過信号レベル調節部２−３３からの光信号は光チャネル単位挿入部２−３４に結合する。挿入光として例えば波長λj挿入用光信号が入射すると光信号レベル調節用可変光減衰器２−１９からの信号光の一部が挿入光信号出力モニタ用タップカカプラ２−１８で分岐され、光出力モニタ２−２７でモニタされ、これが一定になるように可変減衰器２−１９を制御する。この出力一定制御は挿入する波長を問わないため、現地での調整が不要である。別の挿入用ポートからも波長λi挿入用光信号が入射し、やはり、光信号レベル調節用光減衰器２−２９と挿入光信号出力モニタ用タップカプラ２−２３、光出力モニタ２−２８により、光出力を所望の値に制御する。本実施例では可変光減衰器を用いる例を示しtが、光増幅器を用いてその励起系に出力モニタのレベルを負帰還させれる制御でも同様に波長依存性のない、自動レベル調整器を持つ挿入部が構成できる。その後、２つの挿入光は波長依存性のない挿入光信号合波カプラで合波され、さらに、通過光信号と挿入光信号合波器２−２２で合波される。挿入光まで波長多重された光信号は送信用光増幅部２−３５に結合し、送信用光増幅器２−２６で所望に値に増幅されて光出力レベルの揃った波長多重光出力２−３０として光伝送路へ送出される。
【００１７】
【発明の効果】
本発明によれば、波長多重時の波長数変化に伴う光チャネル毎のレベルの変動を抑えると共に光入力レベルの変動に対して、その変動を補正した光出力が得られるので光サージを防止してかつ高い伝送品質を安定に提供する波長多重ネットワークシステムが構成できる。また、任意の波長の光チャネル増減設が容易に可能となり、波長多重リソースの有効利用ができる。
【図面の簡単な説明】
【図１】波長平坦化波長多重光増幅器構成への適用
【図２】波長数トリガ自動光出力制御方式の相関図
【図３】チャネル単位分岐挿入構成への適用
【符号の説明】
１−１：入力側接続光ファイバ伝送路、１−２：波長多重光入力、１−３：光入力変動、１−４：光入力モニタ用タップカプラ、１−５：光入力モニタ、１−６：前段光ファイバ増幅器、１−７：励起LD制御回路、１−８：利得検出一定制御回路、１−９：波長平坦化フィルタ、１−１０：前段光ファイバ増幅器光出力モニタ用タップカプラ、１−１１：光出力モニタ、１−１２：可変光減衰器、１−１３：中間光減衰器制御回路、１−１４：減衰量一定制御・減衰量変更回路、１−１５：波長数情報、１−１６：監視制御系、１−１７：後段光ファイバ増幅器光入力モニタ用タップカプラ、１−１８：光入力モニタ、１−１９：後段光ファイバ増幅器、１−２０：励起LD制御回路、１−２１：利得検出一定制御回路、１−２２：波長平坦化フィルタ、１−２３：光出力モニタ用タップカプラ、１−２４：光出力モニタ、１−２５：波長多重光出力、１−３０：前段光増幅部、１−３１：可変減衰器型光レベル調節部、１−３２：後段光増幅部、２−１：入力側接続光ファイバ伝送路、２−２：波長多重光入力、２−３：受信用光増幅器、２−４：分散補償光部品、２−５：波長λj分岐フィルタ、２−６：被分岐波長λj光信号、２−７：波長λi分岐フィルタ、２−８：被分岐波長λi光信号、２−９：光レベル変化、２−１０：可変光減衰器、２−１１：光減衰器制御回路、２−１２：減衰量一定制御・減衰量変更回路、２−１３：波長数情報、２−１４：監視制御系、２−１５：通過光チャネル波長多重光出力モニタ用タップカプラ、２−１６：光出力モニタ、２−１７：挿入光信号合波カプラ、２−１８：波長λj挿入光信号出力モニタ用タップカプラ、２−１９：波長λj光信号レベル調節用可変光減衰器、２−２０：波長λj挿入用光信号、２−２１：レベ制御回路、２−２２：通過光信号と挿入光信号合波器、２−２３：波長λi挿入光信号出力モニタ用タップカプラ、２−２４：波長λi挿入用光信号、２−２５：レベル制御回路、２−２６：送信用光増幅器、２−２７：光出力モニタ、２−２８：光出力モニタ、２−１９：波長λi光信号レベル調節用可変光減衰器、２−３０：波長多重光出力、２−３１：受信用光増幅部、２−３２：光チャネル単位分岐部、２−３３：通過信号レベル調節部、２−３４：光チャネル単位挿入部、２−３５：送信用光増幅部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength division multiplexing optical network, and more particularly, to a configuration and control method of an optical amplifier and an add / drop multiplexer that have both optical level control function and wavelength flatness in a configuration having an optical amplifier and provide more stable transmission quality. Involved.
[0002]
[Prior art]
In a wavelength division multiplexing optical network using optical fiber amplifiers, optical fiber amplifiers can easily amplify optical signals of multiple wavelengths at once, making low-cost loss compensation technology suitable for long-distance transmission and wavelength division multiplexing loss compensation. An optical fiber amplifier is used. However, since the gain of the optical fiber amplifier is wavelength-dependent, a wavelength flattening technique is required when amplifying optical signals having a plurality of wavelengths. Since the wavelength dependency of the optical fiber amplifier strongly depends on the gain, the wavelength flattening is realized by using a flattening filter for compensating the wavelength dependency under a specific gain condition.
[0003]
In order to obtain a specific gain condition for an optical fiber amplifier, constant gain control may be performed. However, in optical transmission, the optical level depends on the transmission line loss. Don't be. In order to keep the optical output constant regardless of the transmission line loss, it is sufficient to perform constant output control. However, since the optical input changes depending on the transmission line loss, the gain of the optical input and the optical output changes. . As a technique for satisfying both, an optical fiber amplifier performs a constant gain control and adjusts the light level by combining with an optical attenuator. Unlike the optical amplifier, the optical attenuator does not change the wavelength dependency even if the attenuation is changed, so that the optical input is constant in the optical attenuator so that the gain of the optical fiber amplifier becomes constant under constant control. In this way, the light level is adjusted.
[0004]
In order to perform optical monitoring in the state where the optical output is usually wavelength-multiplexed, the total number of optical outputs for each channel (wavelength) and the number of multiplexed wavelengths are monitored. The control required in practice is that the optical output level per optical channel always becomes a set value in order to maintain the quality of the optical signal. The method of monitoring the total optical output level is simple and low-cost, but control requires wavelength number information to obtain the optical output level in the optical channel. Given the number of wavelengths information, the total output monitor value was divided, and negative feedback control was performed so that the optical output per channel was constant.
[0005]
However, if the optical input before the actual number of wavelengths is inserted into the wavelength multiplex is suddenly decreased due to disconnection or the like, and there is a difference between the number of wavelengths used for control and the actual number of wavelengths, the level per optical channel is required. There was a phenomenon of deviation from the value. For example, in the case where an optical channel of a certain wavelength is inserted at a branch / insert node, a case where the one channel is inserted and becomes 16 wavelengths in a state where 15 wavelengths are multiplexed before insertion is taken as an example. When the 15-wavelength light input is cut off, the 16-wavelength multiplexed state is reduced to the inserted one wavelength. At this time, if the total monitor output is set to 16 wavelengths, control is performed so that the remaining one-wavelength optical output is the same as the 16-wavelength total and the optical output. As a result, the optical output of the remaining optical channel is controlled to be 16 times the required value. As described above, there is a risk of destroying the receiver in some cases in the constant output control.
In addition, in an optical add / drop unit in a wavelength division multiplexing optical network, when performing optical add / drop by combining arbitrary wavelengths in an optical add / drop unit with a limited wavelength, the optical level of the optical channel signal to be added / dropped and the optical level of the passing optical channel In order to match, a mechanism capable of inserting an add / drop filter of an arbitrary wavelength is required when necessary. At this time, the level of the passing wavelength signal was changed by the additional filter, and it was necessary to adjust the level locally.
Furthermore, in the insertion optical channel, if a wavelength independent multiplexer is used so that there is no wavelength dependence, the leakage of the branched light from the wavelength branch is not blocked by the insertion section, so the leakage light and the insertion light are coherent. Crosstalk occurred and transmission quality deteriorated.
[0006]
[Problems to be solved by the invention]
It is an object of the present invention to avoid the optical output of the remaining optical channel from becoming abnormally large when the number of wavelengths is changed, while the optical output level per optical channel absorbs the fluctuation with respect to the loss fluctuation. It is to provide a stable optical channel output level. It is another object of the present invention to provide a branching / inserting device having an optical output for each optical channel that is stably provided with high quality with respect to the increase or decrease of the number of wavelengths to be added / dropped. In addition, when the branch / insert configuration is changed, the loss variation is automatically absorbed.
[0007]
[Means for Solving the Problems]
The optical amplifier that amplifies the wavelength multiplexed light in the optical transmission system network performs constant gain control and always fixes the attenuation amount of the optical attenuator for adjusting the level of the wavelength multiplexed signal. Since the constant gain control and the attenuation amount of the optical attenuator are always fixed, even if the number of optical channels changes, the total light level is not used for control, and the level diagram per optical channel does not change.
Only when reliable wavelength number information is obtained, the attenuation amount of the optical attenuator is set so that the monitored value of the wavelength multiplexed light from the variable optical attenuator becomes the predetermined monitor value at the wavelength of the wavelength number information. Adjust. By doing so, fluctuations in light level caused by fluctuations in optical loss that occur in the optical fiber transmission line and the like are absorbed. Thereafter, the attenuation amount of the optical attenuator is fixed again, and the fixed value is a value when the light level fluctuation is absorbed. By doing so, the value of the optical attenuator becomes constant again, so that the level per optical channel does not change even if the number of wavelengths changes.
[0008]
The fluctuation of the optical channel level due to the fluctuation of the number of wavelengths occurs when there is a difference between the wavelength number information and the actual number of wavelengths when the monitor value negative feedback control is performed. Therefore, the risk of performing the monitor negative feedback control in a state where the wavelength number information is different from the actual wavelength number is greatly reduced. Loss fluctuations are caused by temperature changes accompanying seasonal changes, and are very gradual, such as optical component and optical connector joining and optical transmission path changes over time. The frequency of monitor negative feedback is on the order of seconds. Is enough.
[0009]
When the loss changes due to the addition of a node to the transmission line of the optical network or the change for adding the optical channel, etc. Can be corrected.
When combining the wavelength of branching and inserting, it is possible to insert a branching filter of any wavelength on the branching side so that the optical level of the optical channel of the branching / inserting device becomes a desired value for the passing signal light. The insertion unit and the wavelength-independent multiplexer are controlled by a variable optical attenuator and controlled so as to have a desired optical level with an optical attenuator or optical amplifier without having wavelength dependency with respect to the insertion signal. Then, the insertion signal light and the passing wavelength signal are combined. An arbitrary wavelength signal can be connected to the insertion signal.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example in which the present invention is applied to a wavelength flattened wavelength division multiplexing optical amplifier configuration. The function of each part will be described according to the configuration. A part of the light from the wavelength-division multiplexed optical input 1-2 from the input side connecting optical fiber 1-1 is branched by the optical input monitor tap coupler 1-4 and reaches the optical input monitor 1-5. The main optical signal is amplified by the pre-stage optical fiber amplifier 1-6 that performs optical amplification, which is the central function of the pre-stage optical amplification unit 1-30, and is generated by the wavelength flattening filter 1-9 in the pre-stage optical fiber amplifier 1-6. The wavelength dependence of the gain is corrected, a part of the monitor light is branched by the optical fiber amplifier optical output monitor coupler 1-10, and the remaining main amplified signal light is coupled to the variable attenuator type optical level adjuster. . A part of the monitor light reaches the optical output monitor 1-11 by the upstream optical fiber amplifier optical output monitor coupler 1-10, and the output level is monitored. The pre-stage optical amplifying unit 1-30 performs constant gain control in order to keep the wavelength dependence constant regardless of the optical input. In the optical gain control, the gain detection constant control circuit 1-8 performs a gain detection calculation which is a relative ratio between the optical level of the optical input monitor 1-5 and the optical level of the optical output monitor 1-11. A control signal is sent to the pumping LD control circuit 1-7 so as to be always constant, and the output of the pumping LD that determines the amplification factor of the preceding optical fiber amplifier 1-6 is controlled.
The rear stage optical amplifying unit 1-32 also performs constant gain control as in the former stage optical amplifying unit 1-30. A part of the wavelength multiplexed light input from the variable attenuator type optical level adjusting unit 1-31 is branched by the post-stage optical fiber amplifier optical input monitor tap coupler 1-17, and reaches the optical input monitor 1-18. The main optical signal is amplified by a post-stage optical fiber amplifier 1-19 that performs optical amplification, which is a central function of the post-stage optical amplification unit 1-32, and is generated by the wavelength flattening filter 1-22 in the post-stage optical fiber amplifier 1-19. The wavelength dependence of the gain is corrected, a part of the monitor light is branched by the post-stage optical fiber amplifier light output monitor coupler 1-23, and the remaining main amplified signal light is output as the wavelength multiplexed light output 1-25. . A part of the monitor light reaches the optical output monitor 1-24 by the optical output monitor coupler 1-23, and the output level is monitored. The post-stage optical amplifying unit 1-32 performs constant gain control in order to keep the wavelength dependency constant regardless of the optical input. In the optical gain control, a gain detection constant control circuit 1-21 performs a gain detection calculation which is a relative ratio between the optical level of the optical input monitor 1-18 and the optical level of the optical output monitor 1-24. A control signal is sent to the pumping LD control circuit 1-20 so as to be always constant, and the output of the pumping LD that determines the amplification factor of the post-stage optical fiber amplifier 1-19 is controlled.
[0011]
As described above, the optical amplification is performed in a state in which the wavelength is flattened by performing the constant gain control in the optical amplifying units at the front stage and the rear stage. However, in optical transmission, the transmission line section loss is not always constant, and optical input fluctuation 1-3 occurs. Even for the input fluctuation 1-3, it is desirable to keep the optical output per optical channel of the wavelength multiplexed optical output 1-25 constant in terms of optical transmission characteristics. For this reason, the variable attenuator type light level adjusting unit 1-31 is inserted between the light abdominal parts at the front stage and the rear stage. The optical level of the wavelength multiplexed optical signal from the pre-stage optical amplifying unit 1-30 is adjusted by the variable attenuator 1-12. Since the wavelength dependency of the variable optical attenuator 1-12 is constant regardless of the optical attenuation, the wavelength flatness does not change even if the optical level is changed. By combining this optical attenuator and an optical amplifying unit with constant gain control, the optical output per optical channel can be controlled to be constant while maintaining wavelength flatness.
In the control of the variable attenuator 1-12, the intermediate optical attenuator control circuit 1-13 is always instructed by the constant attenuation amount control / current estimation amount changing circuit 1-14 to keep the attenuation amount constant. In this state, since the gain relationship between the optical input and output is kept constant throughout the wavelength division multiplexing optical amplifier, even if the number of wavelengths fluctuates, the gain of each optical channel does not change.
[0012]
FIG. 2 shows the correlation of the automatic light output control method using the number of wavelengths as a trigger. An example will be shown in which the optical input fluctuation 1-3 due to temperature environment change, fiber transmission line deterioration, or optical connector connection state change is loss fluctuation. Also, the actual number of channels means that the number of optical channels up to the previous stage of the input wavelength multiplexed signal is increased or decreased, and the number of wavelengths due to some accidents is initially 5 channels, temporarily 4 channels, or 2 channels at a time. The case where a change is assumed to 6 channels is shown. When the optical channel information 1-15 is not inputted, the automatic constant light output constant control is off in the constant attenuation control / attenuation change circuit 1-14, and the optical attenuator 1-12 holds a constant attenuation. In this state, even if the number of wavelengths is reduced as in (1), the optical monitor output value indicating the total optical output of the wavelength multiplexed signal is reduced by the decrease in the number of wavelengths, but the average optical channel light output is maintained. As described above, when the attenuation amount of the optical attenuator 1-12 is maintained, the resistance to fluctuation in the number of wavelengths can be obtained, but (2) the average optical channel optical output corresponding to the optical input fluctuation 1-3 is reduced.
[0013]
The optical channel number information 1-15 may be input from the supervisory control system 1-16 by summing up the optical channel information of the entire system from the information on the number of wavelengths up to the preceding stage relay or NE-OpS (network device management operation system). Indicates that there is a wavelength number measurement system in its own node and that information is input from the monitoring control system 1-16. Although this information is not something that can be notified immediately as the number of wavelengths changes, there is no need to be particularly concerned, and the optical channel information 1-15 at that time is accurately matched to the number of actual optical channels input to the optical amplifier. It becomes important. The number of actual optical channels at the time when the wavelength number information 1-15 is obtained and the attenuation amount is changed by the constant attenuation amount control / attenuation amount changing circuit 1-14 by shortening the time from the detection of the wavelength number information to the notification. And the occurrence of control errors due to mismatch of wavelength information can be reduced as much as possible. When the wavelength number information 1-15 is input, the constant attenuation control / attenuation change circuit 1-14 changes the attenuation. That is, in order to correct the change in the light level due to the light input fluctuation 1-3, (3) the automatic light output constant control (ALC) is turned on so as to match the output value according to the number of wavelengths. The optical attenuator control circuit is adjusted so that the output of the output monitor 1-24 becomes a predetermined value, and the attenuation amount of the variable attenuator 1-12 is adjusted. At this time, the decrease in the average optical channel light output accompanying the optical input fluctuation is corrected. Thereafter, the automatic light output constant control is turned off immediately, and the attenuation amount of the optical attenuator 1-12 obtained by the correction is held. The broken line of the average optical channel light output is a case where correction is not performed. At this time, the optical input fluctuation 1-3 is reflected in the average optical channel light output 1-25, which degrades the transmission quality. Information 1-15 It can be improved by performing correction by trigger.
After the correction, if the attenuation amount of (4) optical attenuator 1-12 is fixed again, the average optical channel light output is almost constant even if the actual optical wavelength number suddenly changes from 4 to 6 as in (1). Kept.
[0014]
FIG. 3 shows an example in which the present invention is applied to a channel-by-channel branch / insert configuration. The function of each part will be described according to the configuration. The wavelength multiplexed optical input 2-2 from the input side connecting optical fiber 2-1 can obtain an optical output whose optical output is corrected by the optical amplifier control of the first embodiment in the receiving optical amplifier 2-3. When the wavelength multiplexed signal includes a high-speed modulation signal such as 10 Gbit / s, the dispersion compensating optical component 2-4 is coupled to the reception side optical amplifier 2-3. The wavelength multiplexed signal that has been compensated for transmission filter loss and dispersion by the reception optical amplifying unit 2-31 is optical signal of a specific wavelength by the optical channel unit branching unit 2-32, for example, a wavelength λj branching filter λj by a wavelength λj branching filter 2-5. Only the optical signal 2-6 is branched, and the remaining signal light passes. At this time, in order to prevent waveform degradation at the time of branching at a high speed such as 10 Gbit / s, it is preferable to use a dielectric multilayer filter that performs light separation at a concentrated several μm for branching. In the latter stage, an optical signal having the same wavelength as that of the branched optical signal is inserted. However, as will be described later, since the insertion section has no wavelength dependence, there is a risk of causing coherent crosstalk due to interference with the leakage light of the branched light. There is sex. For this reason, in order to cut off about 40 dB of leakage from the branching filter, a fiber Bragg grating may be inserted on the passing side.
[0015]
The passing wavelength multiplexed optical signal from the optical channel unit branching unit 2-32 is coupled to the passing signal level adjusting unit 2-33. The passing signal is attenuated to a desired light level by the variable optical attenuator 2-10. Normally, the attenuation amount is controlled to be constant. Only when the wavelength number information 2-13 is input from the supervisory control system 2-14, one of the optical signals output from the variable optical attenuator and branched by the pass coupler 2-15 for monitoring the wavelength-wavelength-multiplexed-wavelength optical output monitor. Is monitored by the optical output monitor 2-16, and the detected level is input to the constant attenuation control / attenuation change circuit 2-12, and the set level corresponding to the number of wavelengths from the input wavelength number information 2-13. Then, the optical attenuator control circuit 2-11 is controlled so that monitoring is performed, and the setting of the variable optical attenuator 2-10 is changed. Thereafter, the attenuation is fixed again. The method of using this function initially inserts only the wavelength λj branching filter 2-5 to obtain the branched wave h-term λj optical signal, but then inserts the wavelength λi branching filter 2-7 to add the branched wavelength. A λi optical signal is obtained. At this time, the passing optical signal undergoes loss fluctuation due to the insertion of the branching filter, and causes an optical level change 2-9. In wavelength division multiplexing optical transmission, it is important to align the optical levels of the respective wavelengths, and the optical output monitor 2-16 can be obtained by notifying the control unit of the passing signal level adjusting unit 2-33 of the previous wavelength number information 2-13. The amount of attenuation of the variable optical attenuator 2-10 is lowered so that the level of is constant.
By fixing the attenuation amount again (automatic optical output constant control off), the average optical channel light level is maintained and does not change even if the actual number of wavelengths changes as in the previous example.
[0016]
The optical signal from the passing signal level adjusting unit 2-33 is coupled to the optical channel unit inserting unit 2-34. For example, when an optical signal for inserting a wavelength λj is incident as insertion light, a part of the signal light from the optical signal level adjusting variable optical attenuator 2-19 is branched by the insertion optical signal output monitor tap coupler 2-18, and the optical output monitor The variable attenuator 2-19 is controlled so as to be constant and monitored at 2-27. This constant output control does not require any wavelength to be inserted, so no local adjustment is required. An optical signal for inserting a wavelength λi is also incident from another insertion port, and again, an optical signal level adjusting optical attenuator 2-29, an inserted optical signal output monitor tap coupler 2-23, and an optical output monitor 2-28. The light output is controlled to a desired value. In this embodiment, an example using a variable optical attenuator is shown, but t has an automatic level adjuster that does not depend on wavelength even in the control in which the level of the output monitor is negatively fed back to the pumping system using an optical amplifier. The insertion part can be configured. Thereafter, the two insertion lights are combined by an insertion optical signal multiplexing coupler having no wavelength dependency, and further combined by a passing optical signal and an insertion optical signal multiplexer 2-22. The optical signal wavelength-multiplexed up to the inserted light is coupled to the transmission optical amplifier 2-35, amplified to a desired value by the transmission optical amplifier 2-26, and the wavelength-multiplexed optical output 2-30 having the same optical output level. To the optical transmission line.
[0017]
【The invention's effect】
According to the present invention, the fluctuation of the level for each optical channel due to the change in the number of wavelengths at the time of wavelength multiplexing is suppressed, and an optical output in which the fluctuation is corrected with respect to the fluctuation of the optical input level can be obtained, thereby preventing an optical surge. In addition, a wavelength division multiplexing network system that stably provides high transmission quality can be configured. In addition, it is possible to easily increase / decrease an optical channel of an arbitrary wavelength, and to effectively use wavelength multiplexing resources.
[Brief description of the drawings]
Fig. 1 Application to wavelength flattened wavelength division multiplexing optical amplifier configuration Fig. 2 Correlation diagram of wavelength-triggered automatic optical output control system Fig. 3 Application to channel-by-channel branching and insertion configuration
1-1: input side connection optical fiber transmission line, 1-2: wavelength multiplexed optical input, 1-3: optical input fluctuation, 1-4: optical input monitor tap coupler, 1-5: optical input monitor, 1- 6: front-stage optical fiber amplifier, 1-7: pumping LD control circuit, 1-8: constant gain detection control circuit, 1-9: wavelength flattening filter, 1-10: front-stage optical fiber amplifier optical output monitor tap coupler, 1-11: Optical output monitor, 1-12: Variable optical attenuator, 1-13: Intermediate optical attenuator control circuit, 1-14: Attenuation constant control / attenuation change circuit, 1-15: Wavelength number information, 1-16: Monitoring control system, 1-17: Tap coupler for optical input monitor of rear stage optical fiber amplifier, 1-18: Optical input monitor, 1-19: Optical fiber amplifier of rear stage, 1-20: Pumping LD control circuit, 1 -21: Gain detection constant control circuit, 1-22: Wavelength flattening circuit Filter, 1-23: Tap coupler for optical output monitor, 1-24: Optical output monitor, 1-25: Wavelength multiplexed optical output, 1-30: Pre-stage optical amplifier, 1-31: Variable attenuator type optical level adjustment Section, 1-32: rear-stage optical amplification section, 2-1: input side connection optical fiber transmission line, 2-2: wavelength division multiplexed optical input, 2-3: reception optical amplifier, 2-4: dispersion compensation optical component, 2-5: Wavelength λj branching filter, 2-6: Branched wavelength λj optical signal, 2-7: Wavelength λi branching filter, 2-8: Branched wavelength λi optical signal, 2-9: Optical level change, 2- 10: Variable optical attenuator, 2-11: Optical attenuator control circuit, 2-12: Attenuation constant control / attenuation amount changing circuit, 2-13: Wavelength number information, 2-14: Monitoring control system, 2-15 : Tap coupler for passing optical channel wavelength division multiplexing optical output monitor, 2-16: Optical output monitor, 2-17: Inserted optical signal Wave coupler, 2-18: Wavelength λj insertion optical signal output monitoring tap coupler, 2-19: Wavelength λj optical signal level adjusting variable optical attenuator, 2-20: Wavelength λj insertion optical signal, 2-21: Level Control circuit, 2-22: passing optical signal and insertion optical signal multiplexer, 2-23: tap coupler for monitoring output of wavelength λi optical signal, 2-24: optical signal for insertion of wavelength λi, 2-25: level control Circuit, 2-26: optical amplifier for transmission, 2-27: optical output monitor, 2-28: optical output monitor, 2-19: variable optical attenuator for adjusting wavelength λi optical signal level, 2-30: wavelength multiplexed light Output, 2-31: reception optical amplification unit, 2-32: optical channel unit branching unit, 2-33: passing signal level adjustment unit, 2-34: optical channel unit insertion unit, 2-35: transmission optical amplification unit Part

Claims

An optical amplifier having an optical amplification unit, an optical adjustment unit including an optical attenuator and an attenuator control circuit, and an optical output monitor installed at a stage subsequent to the optical adjustment unit ,
The optical amplification unit performs a constant gain control so that the optical gain of the input light to the optical amplification unit and the output light from the optical amplification unit is constant ,
The attenuator control circuit usually performs a control for setting to a fixed value attenuation of the optical attenuator, wherein the number of wavelengths output value of the optical output monitor only when the wavelength number information is input as the control information An optical amplifier comprising: adjusting an attenuation amount of the attenuator so as to obtain an output according to information; and thereafter controlling to maintain the adjusted attenuation amount.

An optical amplifying unit, an optical branching unit installed downstream from the optical amplification unit, an optical attenuator installed downstream from the optical branching unit, an attenuator control circuit for controlling the attenuator, and the attenuator A branching and inserting device having an optical output monitor installed at a later stage and an optical insertion unit installed at a stage after the attenuator,
The optical amplification unit performs a constant gain control so that the optical gain of the input light to the optical amplification unit and the output light from the optical amplification unit is constant,
The attenuator control circuit normally performs control to set the attenuation amount of the attenuator to a fixed value, and the output value of the optical output monitor is set to the wavelength number information only when wavelength number information is input as control information. An add / drop device characterized in that the attenuation amount of the attenuator is adjusted so as to obtain an output according to the control, and thereafter, the adjusted attenuation amount is controlled to be maintained.