JP2004333980A

JP2004333980A - Wdm signal controller

Info

Publication number: JP2004333980A
Application number: JP2003131253A
Authority: JP
Inventors: Takashi Kotanigawa; 喬小谷川; Toshiya Matsuda; 俊哉松田; Tomoyoshi Kataoka; 智由片岡
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2003-05-09
Filing date: 2003-05-09
Publication date: 2004-11-25
Anticipated expiration: 2023-05-09
Also published as: JP4216638B2

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate unevenness of OSNR and path average light power of an optical wavelength multiplex transmission system which uses Raman amplification or Raman amplification and EDFA in combination. <P>SOLUTION: Denoting signal light loss and Raman stimulating light loss obtained from a previously measured transmission-loss wavelength dependence characteristic α(λ) as α(λs) and α(λp) and arbitrary transmission light power as P0, the optical signal-to-noise ratio OSNR and path average power Pave of one relay section are calculated and when a signal wavelength λs1 and an OSNR allowed deviation M1 giving a specified reference for OSNR, and a signal wavelength λs2 and a path average power allowed deviation M2 giving a specified reference for path average power are set, a range satisfying a transmission optical power relative value ΔP(λs) of signal light of each wavelength is found; and the transmission optical power relative value ΔP(λs) of signal light of each wavelength is controlled within the range of the transmission optical power relative value ΔP(λs). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、長距離大容量伝送を行う光波長多重伝送システムにおいて、波長多重信号光の伝送特性を均一にするＷＤＭ信号制御装置に関する。
【０００２】
【従来の技術】
数千ｋｍ以上の長距離光伝送実験の主な報告では、信号帯域として信号光の低損失波長領域であるＣ帯（１５３０ｎｍ〜１５６５ｎｍ）、Ｌ帯（１５６５ｎｍ〜１６２５ｎｍ）でのラマン増幅中継が用いられている（非特許文献１）。さらに、伝送容量を増大させるために、Ｕ帯（１６２５ｎｍ〜１６７５ｎｍ）を用いた伝送実験も報告されている（非特許文献２）。
【０００３】
ラマン増幅は、励起光の波長よりも約１００ｎｍ長波長側に利得のピークが現れる。したがって、波長の異なる複数の励起光を用いると各励起光波長に対してそれぞれ利得ピークが現れるので、励起光波長に応じた任意の波長帯で利得帯域幅を拡大することができる。
【０００４】
ところで、広帯域な波長多重信号光を同時に伝送した場合、各波長の信号光に重畳される光雑音特性や非線形効果などによる波形劣化の波長依存性に起因して、各波長の信号光が不均一な伝送特性になることが知られている。この不均一性を解消するために、受信側で伝送された波長多重信号光の光信号対雑音比（ＯＳＮＲ）を測定し、これが均一になるように送信側で送信光パワーを調整するプリエンファシス技術が提案されている。
【０００５】
図７は、プリエンファシス技術を用いた従来の光波長多重伝送システムの構成例を示す（特許文献１）。図において、波長多重送信端局５０の光送信器５１−１〜５１−ｎから出力される波長λ１〜λｎの信号光は、光合波器５２で波長多重して出力される。この波長多重信号光は、光ファイバ伝送路５３および光増幅中継器５４を介して波長多重受信端局５５に伝送される。波長多重受信端局５５では、波長多重信号光を光分波器５６で各波長の信号光に分波し、それぞれ対応する光受信器５７−１〜５７−ｎで受信する。また、ＯＳＮＲ測定装置５８で各信号チャネルのＯＳＮＲを測定し、波長多重送信端局５０のプリエンファシス制御装置５９にフィードバック伝送する。
【０００６】
プリエンファシス制御装置５９は、各信号チャネルのＯＳＮＲが均一になるように光送信器５１−１〜５１−ｎの各送信光パワーを制御する。例えば、ＯＳＮＲが悪い信号チャネルほど送信光パワーが高くなるように制御する。
【０００７】
【非特許文献１】
Ｔ．Ｍａｔｓｕｄａｅｔａｌ．，”６２×４２．７Ｇｂｉｔ／ｓ（２．５Ｔｂｉｔ／ｓ）ＷＤＭｓｉｇｎａｌｔｒａｎｓｍｉｓｓｉｏｎｏｖｅｒ２２００ｋｍｗｉｔｈｂｒｏａｄｂａｎｄｄｉｓｔｒｉｂｕｔｅｄＲａｍａｎａｍｐｌｉｆｉｃａｔｉｏｎ”，Ｅｌｅｃｔｒｏｎ．Ｌｅｔｔ．，ｖｏｌ．３８，ｎｏ．１５，ｐｐ．８１８−８１９，２００２
【非特許文献２】
Ｔ．Ｔａｎａｋａｅｔａｌ．，”２００−ｎｍＢａｎｄｗｉｄｔｈＷＤＭＴｒａｎｓｍｉｓｓｉｏｎａｒｏｕｎｄ１．５５μｍｕｓｉｎｇＤｉｓｔｒｉｂｕｔｅｄＲａｍａｎＡｍｐｌｉｆｉｅｒ”，ＥＣＯＣ２００２，ＰＤ４．６，２００２
【特許文献１】
特開平８−３２１８２４号公報
【０００８】
【発明が解決しようとする課題】
プリエンファシス技術を用いた従来の光波長多重伝送システムは、各信号チャネルのＯＳＮＲの不均一性を解消するために、各送信光パワーを制御する構成であり、ＯＳＮＲの悪い信号チャネルの送信光パワーが高くなりすぎることがある。その場合には、新たに非線形効果の影響による波形劣化が顕著になることがある。すなわち、従来の構成では、受信端におけるＯＳＮＲのみを考慮しており、非線形効果による波形劣化量に関係する経路平均パワー値の不均一性の解消については検討されていない。
【０００９】
また、従来の構成では、経時劣化などを考慮して送信光パワーを所定の値に制御するためには、受信端でＯＳＮＲを常時モニタする必要があり、図７のようにフィードバック制御系が不可欠であった。
【００１０】
また、図７に示す光増幅中継器５４は、エルビウム添加光ファイバ増幅器（ＥＤＦＡ）や、低雑音性および広帯域性に優れるラマン増幅や、ラマン増幅とＥＤＦＡを組み合わせた構成である。
【００１１】
本発明は、ラマン増幅またはラマン増幅とＥＤＦＡを併用した光波長多重伝送システムにおいて、信号光損失および励起光損失の波長依存性を考慮し、ＯＳＮＲと経路平均光パワーの不均一性を解消し、さらに送信光パワーが経時変化した場合でもモニタリングなしにＯＳＮＲと経路平均光パワーが許容値から大きくずれないように制御できるＷＤＭ信号制御装置を提供することを目的とする。
【００１２】
【課題を解決するための手段】
（請求項１）
本発明のＷＤＭ信号制御装置は、ラマン増幅またはラマン増幅と光ファイバ増幅器を併用した光波長多重伝送システムにおいて、あらかじめ測定した伝送損失波長依存特性α（λ）から得られる信号光損失およびラマン励起光損失をα（λｓ）およびα（λｐ）とし（ただしλｐ＝λｓ−１００）、任意の送信光パワーをＰ０としたときに、１中継区間の光信号対雑音比ＯＳＮＲ［α（λｓ），α（λｐ），Ｐ０］および経路平均パワーＰａｖｅ［α（λｓ），α（λｐ），Ｐ０］を計算する手段と、所定のＯＳＮＲの基準を与える信号波長λｓ１およびＯＳＮＲ許容偏差Ｍ１と、所定の経路平均パワーの基準を与える信号波長λｓ２および経路平均パワー許容偏差Ｍ２を設定したときに、各波長の信号光の送信光パワー相対値ΔＰ（λｓ）について

を満たす範囲を求め、その送信光パワー相対値ΔＰ（λｓ）の範囲内で各波長の信号光の送信光パワー相対値ΔＰ（λｓ）を制御する手段とを備える。
【００１３】
（請求項２）
また、各波長の信号光の送信光パワー相対値ΔＰ（λｓ）について

を満たす値を求め、その送信光パワー相対値ΔＰ（λｓ）に応じて各波長の信号光の送信光パワー相対値ΔＰ（λｓ）を制御する手段を用いてもよい。
【００１４】
（請求項３）
本発明のＷＤＭ信号制御装置は、ラマン増幅と光ファイバ増幅器を併用し、ラマン増幅と光ファイバ増幅器の利得比率をｒとする光波長多重伝送システムにおいて、あらかじめ測定した伝送損失波長依存特性α（λ）から得られる信号光損失およびラマン励起光損失をα（λｓ）およびα（λｐ）とし（ただしλｐ＝λｓ−１００）、任意の送信光パワーをＰ０としたときに、１中継区間の光信号対雑音比ＯＳＮＲ［α（λｓ），α（λｐ），Ｐ０，ｒ］および経路平均パワーＰａｖｅ［α（λｓ），α（λｐ），Ｐ０，ｒ］を計算する手段と、所定のＯＳＮＲの基準を与える信号波長λｓ１およびＯＳＮＲ許容偏差Ｍ１と、所定の経路平均パワーの基準を与える信号波長λｓ２および経路平均パワー許容偏差Ｍ２を設定したときに、各波長の信号光に対するラマン増幅と光ファイバ増幅器の相対利得比率Δｒ（λｓ）について

を満たす範囲を求め、その相対利得比率Δｒ（λｓ）の範囲内で各波長の信号光の相対利得比率Δｒ（λｓ）を制御する手段とを備える。
【００１５】
（請求項４）
また、各波長の信号光に対するラマン増幅と光ファイバ増幅器の相対利得比率Δｒ（λｓ）について

満たす値を求め、その相対利得比率Δｒ（λｓ）に応じて各波長の信号光の相対利得比率Δｒ（λｓ）を制御する手段を用いてもよい。
【００１６】
【発明の実施の形態】
（第１の実施形態）
図１は、本発明のＷＤＭ信号制御装置を用いた光波長多重伝送システムの第１の実施形態を示す。
【００１７】
図において、光波長多重伝送システムは、波長多重送信端局１０の光送信器１１−１〜１１−ｎから出力される波長λ１〜λｎの信号光を光合波器１２で波長多重し、光ファイバ伝送路１３および光増幅中継器１４を介して波長多重受信端局１５に伝送する構成である。
【００１８】
光増幅中継器１４は、波長が異なる複数のラマン励起光源２１−１〜２１−ｍと、各波長のラマン励起光を合波する光合波器２２−１と、合波された各ラマン励起光を光ファイバ伝送路１３に入力する光合波器２２−２と、光ファイバ伝送路１３に挿入されるＥＤＦＡ２３により構成される。なお、全ラマン増幅を行う場合にはＥＤＦＡ２３は省略される。
【００１９】
本発明のＷＤＭ信号制御装置３０は、本実施形態では光送信器１１−１〜１１−ｎから出力される各送信光パワーを制御する構成であり、入力部３１、計算部３２および送信光パワー制御部３３から構成される。
【００２０】
入力部３１は、あらかじめ測定した伝送損失波長依存特性α（λ）と、所定のＯＳＮＲの基準を与える信号波長λｓ１およびＯＳＮＲ許容偏差Ｍ１と、所定の経路平均パワーの基準を与える信号波長λｓ２および経路平均パワー許容偏差Ｍ２を入力し、各入力値を保持している。
【００２１】
計算部３２は、この入力値をもとに、信号光損失をα（λｓ）、ラマン励起光損失をα（λｐ）、任意の送信光パワーをＰ０としたときに、１中継区間のＯＳＮＲ［α（λｓ）， α（λｐ），Ｐ０］および経路平均パワーＰａｖｅ［α（λｓ）， α（λｐ），Ｐ０］について計算し、さらに各波長の信号光の送信光パワー相対値ΔＰ（λｓ）について

を満たす範囲を求める。なお、λｐ＝λｓ −１００である。
【００２２】
送信光パワー制御部３３は、得られた送信光パワー相対値ΔＰ（λｓ）の範囲内で、各光送信器１１−１〜１１−ｎにおける送信光パワー相対値ΔＰ（λｓ）を制御する。例えば、各光送信器１１−１〜１１−ｎの送信光パワーを、得られた送信光パワー相対値ΔＰ（λｓ）の範囲内で極力均一になるように制御する。なお、送信光パワー相対値の制御は、光送信器１１−１〜１１−ｎに配置される可変減衰器の減衰量を制御するか、光源の出力パワーを直接制御する構成とする。
【００２３】
ここで、後方励起による全ラマン増幅を用い、一様の光ファイバ（中継区間Ｌ＝１００ｋｍ）の伝送損失を補償する光増幅中継系における具体的な計算例について説明する。図２は、分散シフトファイバの伝送損失波長依存特性の測定結果を示す。
【００２４】
この測定結果から伝送損失波長依存特性を簡単化するために、Ｃ帯とＬ帯の損失は０．２３ｄＢ／ｋｍで一定とする。１４３０ｎｍから１５３０ｎｍまでの損失は、［１４３０ｎｍ，０．３５ｄＢ／ｋｍ］、［１５３０ｎｍ，０．２３ｄＢ／ｋｍ］を結ぶ直線近似で
α（λ）＝−１．２×１０^−３（λ−１４３０）＋０．３５
とする。Ｕ帯の損失は、［１６２５ｎｍ，０．２３ｄＢ／ｋｍ］、［１６７５ｎｍ，０．２９ｄＢ／ｋｍ］を結ぶ直線近似で
α（λ）＝１．２×１０^−３（λ−１６２５）＋０．２３
とする。
【００２５】
波長多重信号光の波長範囲として１５３０ｎｍ〜１６５０ｎｍまでのＣ帯、Ｌ帯およびＵ帯を適用すると、励起光波長は信号光波長に対して１００ｎｍ短波長であり、λｓ１＝１５３０ｎｍ、λｓ２＝１６２５ｎｍとし、Ｍ１＝０ｄＢ、Ｍ２＝０．５ｄＢと設定すると、式（１−１），（１−２）は

と表される。これを満たす送信光パワー相対値ΔＰ（λｓ）の領域を図３に示す。
【００２６】
送信光パワー制御部３３は、送信光パワー相対値ΔＰ（λｓ）が図３の斜線部の範囲内になるように、各波長の送信光パワーを制御する。これにより、各波長の信号光のＯＳＮＲは、１５３０ｎｍにおけるＯＳＮＲに比べてＭ１（０ｄＢ）小さい許容値以上の範囲内に収まり、かつ各波長の信号光の経路平均パワーＰａｖｅは、１６２５ｎｍにおけるＰａｖｅに比べてＭ２（０．５ｄＢ）大きい許容値以下の範囲内に収まることになる。
【００２７】
（第２の実施形態）
第１の実施形態と同様の構成において、計算部３２は、１中継区間のＯＳＮＲ［α（λｓ），α（λｐ），Ｐ０］および経路平均パワーＰａｖｅ［α（λｓ），α（λｐ），Ｐ０］について計算し、さらに各波長の信号光の送信光パワー相対値ΔＰ（λｓ）について、

を満たす値を求める。なお、λｐ＝λｓ −１００である。
【００２８】
送信光パワー制御部３３は、得られた送信光パワー相対値ΔＰ（λｓ）の値に応じて、各光送信器１１−１〜１１−ｎにおける送信光パワー相対値ΔＰ（λｓ）を制御する。なお、送信光パワー相対値の制御は、光送信器に配置される可変減衰器の減衰量を制御するか、光源の出力を直接制御する構成とする。
【００２９】
第１の実施形態と同様に、波長多重信号光の波長範囲として１５３０ｎｍ〜１６５０ｎｍまでのＣ帯、Ｌ帯およびＵ帯を適用すると、励起光波長は信号光波長に対して１００ｎｍ短波長であり、λｓ１＝１５３０ｎｍ、λｓ２＝１６２５ｎｍとし、Ｍ１＝０ｄＢ、Ｍ２＝０．５ｄＢと設定すると、式（２−１）〜（２−３）は

と表される。これを満たす送信光パワー相対値ΔＰ（λｓ）を図３に破線で示す。
【００３０】
送信光パワー制御部３３は、送信光パワー相対値ΔＰ（λｓ）が図３の破線の値になるように各波長の送信光パワーを制御する。これにより、各波長の信号光のＯＳＮＲおよび経路平均パワーＰａｖｅを上記の許容範囲内に納めることができる。なお、この場合には、各波長の送信光パワーが経時変化などによりずれたとしても、図３の斜線部の範囲内に維持しやすくなる。
【００３１】
（第３の実施形態）
図４は、本発明のＷＤＭ信号制御装置を用いた光波長多重伝送システムの第３の実施形態を示す。
【００３２】
図において、光波長多重伝送システムは、波長多重送信端局１０の光送信器１１−１〜１１−ｎから出力される波長λ１〜λｎの信号光を光合波器１２で波長多重し、光ファイバ伝送路１３および光増幅中継器１４を介して波長多重受信端局１５に伝送する構成である。
【００３３】
光増幅中継器１４は、波長が異なる複数のラマン励起光源２１−１〜２１−ｍと、各波長のラマン励起光を合波する光合波器２２−１と、合波された各ラマン励起光を光ファイバ伝送路１３に入力する光合波器２２−２と、光ファイバ伝送路１３に挿入されるＥＤＦＡ２３により構成される。
【００３４】
本発明のＷＤＭ信号制御装置４０は、本実施形態では各波長の信号光に対するラマン増幅とＥＤＦＡの利得比率ｒを制御することにより、ＯＳＮＲおよびＰａｖｅを変化させる構成であり、入力部４１、計算部４２および利得制御部４３から構成される。
【００３５】
入力部４１は、あらかじめ測定した伝送損失波長依存特性α（λ）と、所定のＯＳＮＲの基準を与える信号波長λｓ１およびＯＳＮＲ許容偏差Ｍ１と、所定の経路平均パワーの基準を与える信号波長λｓ２および経路平均パワー許容偏差Ｍ２を入力し、各入力値を保持している。
【００３６】
計算部４２は、この入力値をもとに、信号光損失をα（λｓ）、ラマン励起光損失をα（λｐ）、任意の送信光パワーをＰ０としたときに、１中継区間のＯＳＮＲ［α（λｓ），α（λｐ），Ｐ０，ｒ］および経路平均パワーＰａｖｅ［α（λｓ），α（λｐ），Ｐ０，ｒ］について計算し、さらに各波長の信号光に対するラマン増幅とＥＤＦＡの利得比率ｒの相対利得比率Δｒ（λｓ）について

たす範囲を求める。なお、λｐ＝λｓ −１００である。
【００３７】
利得制御部４３は、得られた相対利得比率Δｒ（λｓ）の範囲内で、各ラマン励起光源２１−１〜２１−ｍおよびＥＤＦＡ２３における相対利得比率Δｒ（λｓ）を制御する。例えば、各ラマン励起光源２１−１〜２１−ｍおよびＥＤＦＡ２３における相対利得比率Δｒ（λｓ）が、得られた相対利得比率Δｒ（λｓ）の範囲内で極力均一になるように制御する。なお、相対利得比率の制御は、ラマン励起光源およびＥＤＦＡにおける励起光源の出力を直接制御する構成とする。
【００３８】
図５（ａ），（ｂ）は、１５８０ｎｍにおける利得比率ｒとＯＳＮＲの関係および利得比率ｒと経路平均パワーＰａｖｅの関係を示す。この関係に基づく信号光損失および励起光損失の波長依存性から、λｓ１＝１５３０ｎｍ、λｓ２＝１６２５ｎｍとし、Ｍ１＝０ｄＢ、Ｍ２＝０ｄＢと設定すると、式（３−１），（３−２）は

と表される。これを満たす相対利得比率Δｒ（λｓ）の領域を図６に示す。
【００３９】
光パワー制御部４３は、相対利得比率Δｒ（λｓ）が図６の斜線部の範囲内になるように、ラマン励起光源２１−１〜２１−ｍおよびＥＤＦＡ２３を制御する。これにより、各波長の信号光のＯＳＮＲは、１５３０ｎｍにおけるＯＳＮＲに比べてＭ１（０ｄＢ）小さい許容値以上の範囲内に収まり、かつ各波長の信号光の経路平均パワーＰａｖｅは、１６２５ｎｍにおけるＰａｖｅに比べてＭ２（０ｄＢ）大きい許容値以下の範囲内に収まることになる。
【００４０】
（第４の実施形態）
第３の実施形態と同様の構成において、計算部４２は、１中継区間のＯＳＮＲ［α（λｓ），α（λｐ），Ｐ０，ｒ］および経路平均パワーＰａｖｅ［α（λｓ），α（λｐ），Ｐ０，ｒ］について計算し、さらに各波長の信号光に対するラマン増幅とＥＤＦＡの利得比率ｒの相対利得比率Δｒ（λｓ）について

を満たす値を求める。なお、λｐ＝λｓ −１００である。
【００４１】
利得制御部４３は、得られた相対利得比率Δｒ（λｓ）の値に応じて、ラマン励起光源２１−１〜２１−ｍおよびＥＤＦＡ２３における相対利得比率Δｒ（λｓ）を制御する。なお、相対利得比率の制御は、ラマン励起光源およびＥＤＦＡにおける励起光源の出力を直接制御する構成とする。
【００４２】
第３の実施形態と同様に、波長多重信号光の波長範囲として１５３０ｎｍ〜１６５０ｎｍまでのＣ帯、Ｌ帯およびＵ帯を適用すると、励起光波長は信号光波長に対して１００ｎｍ短波長であり、λｓ１＝１５３０ｎｍ、λｓ２＝１６２５ｎｍとし、Ｍ１＝０ｄＢ、Ｍ２＝０ｄＢと設定すると、式（４−１）〜（４−３）は

と表される。これを満たす相対利得比率Δｒ（λｓ）を図６に破線で示す。
【００４３】
利得制御部４３は、相対利得比率Δｒ（λｓ）が図６の破線の利得になるようにラマン励起光源２１−１〜２１−ｍおよびＥＤＦＡ２３を制御する。これにより、各波長の信号光のＯＳＮＲおよび経路平均パワーＰａｖｅを上記の許容範囲内に納めることができる。なお、この場合には、各波長の利得比率が経時変化などによりずれたとしても、図６の斜線部の範囲内に維持しやすくなる。
【００４４】
ところで、特定の波長のラマン励起光源を制御すれば、それに応じてラマン利得プロファイルの波長依存性も変化する一方で、ＥＤＦＡの利得プロファイルの形状はほぼ一定であるので、全信号波長において任意に利得比率を変化させることが困難な場合がある。これを克服するには、ＥＤＦＡに代えて集中増幅型のラマン増幅を併用する構成とすればよい。
【００４５】
また、Ｕ帯においてＥＤＦＡを用いない場合に、全信号波長で任意に利得比率を変化させるには、同様に分布増幅型のラマン増幅と集中増幅型のラマン増幅を併用する構成とすればよい。
【００４６】
【発明の効果】
以上説明したように、本発明のＷＤＭ信号制御装置を用いることにより、広帯域のＷＤＭ信号の伝送特性（光信号対雑音比ＯＳＮＲおよび経路平均パワーＰａｖｅ）をほぼ均一にすることができる。また、各波長の信号光の送信光パワーが経時変化などによりずれたとしても、所定のＯＳＮＲ許容値および経路平均パワー許容値内に保持することが容易になる。
【図面の簡単な説明】
【図１】本発明のＷＤＭ信号制御装置を用いた光波長多重伝送システムの第１の実施形態を示す図。
【図２】分散シフトファイバの伝送損失波長依存特性の測定結果を示す図。
【図３】各波長の信号光における送信光パワー相対値ΔＰ（λｓ）を示す図。
【図４】本発明のＷＤＭ信号制御装置を用いた光波長多重伝送システムの第３の実施形態を示す図。
【図５】１５８０ｎｍにおける利得比率ｒとＯＳＮＲおよびＰａｖｅの関係を示す図。
【図６】各波長の信号光における相対利得比率Δｒ（λｓ）を示す図。
【図７】プリエンファシス技術を用いた従来の光波長多重伝送システムの構成例を示す図。
【符号の説明】
１０波長多重送信端局
１１光送信器
１２光合波器
１３光ファイバ伝送路
１４光増幅中継器
１５波長多重受信端局
２１ラマン励起光源
２２光合波器
２３ＥＤＦＡ
３０ＷＤＭ信号制御装置
３１入力部
３２計算部
３３送信光パワー制御部
４０ＷＤＭ信号制御装置
４１入力部
４２計算部
４３利得制御部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a WDM signal control device for making transmission characteristics of wavelength multiplexed signal light uniform in an optical wavelength multiplex transmission system for performing long-distance large-capacity transmission.
[0002]
[Prior art]
In main reports of long-distance optical transmission experiments of several thousand km or more, Raman amplification relay in the C band (1530 nm to 1565 nm) and the L band (1565 nm to 1625 nm), which are low-loss wavelength regions of signal light, is used as a signal band. (Non-Patent Document 1). Furthermore, in order to increase the transmission capacity, a transmission experiment using the U band (1625 nm to 1675 nm) has been reported (Non-Patent Document 2).
[0003]
In Raman amplification, a gain peak appears on the longer wavelength side by about 100 nm than the wavelength of the pump light. Therefore, when a plurality of pump lights having different wavelengths are used, a gain peak appears for each pump light wavelength, so that the gain bandwidth can be expanded in an arbitrary wavelength band corresponding to the pump light wavelength.
[0004]
By the way, when simultaneously transmitting a wideband wavelength multiplexed signal light, the signal light of each wavelength becomes non-uniform due to the wavelength dependency of waveform deterioration due to optical noise characteristics and nonlinear effects superimposed on the signal light of each wavelength. It has been known that the transmission characteristics are excellent. In order to eliminate the non-uniformity, pre-emphasis measures the optical signal-to-noise ratio (OSNR) of the wavelength-division multiplexed signal light transmitted on the receiving side, and adjusts the transmission optical power on the transmitting side so that this becomes uniform. Technology has been proposed.
[0005]
FIG. 7 shows a configuration example of a conventional optical wavelength division multiplexing transmission system using a pre-emphasis technique (Patent Document 1). In the figure, signal lights of wavelengths λ1 to λn output from the optical transmitters 51-1 to 51-n of the wavelength multiplexing transmitting terminal 50 are wavelength-multiplexed by the optical multiplexer 52 and output. This wavelength multiplexed signal light is transmitted to the wavelength multiplexing receiving terminal 55 via the optical fiber transmission line 53 and the optical amplifier repeater 54. In the wavelength division multiplexing receiving terminal 55, the wavelength division multiplexed signal light is demultiplexed into signal lights of each wavelength by the optical demultiplexer 56, and received by the corresponding optical receivers 57-1 to 57-n. Further, the OSNR measuring device 58 measures the OSNR of each signal channel, and feeds it back to the pre-emphasis control device 59 of the wavelength division multiplexing transmitting terminal 50.
[0006]
The pre-emphasis control device 59 controls each transmission light power of the optical transmitters 51-1 to 51-n so that the OSNR of each signal channel becomes uniform. For example, control is performed such that the transmission optical power becomes higher as the signal channel has a lower OSNR.
[0007]
[Non-patent document 1]
T. Matsuda et al. , “62 × 42.7 Gbit / s (2.5 Tbit / s) WDM signal transmission over 2200 km with broadband distributed Raman amplification”, Electron. Lett. , Vol. 38, no. 15, pp. 818-819, 2002
[Non-patent document 2]
T. Tanaka et al. , "200-nm Bandwidth WDM Transmission around 1.55 μm using Distributed Distributed Raman Amplifier", ECOC2002, PD4.6, 2002.
[Patent Document 1]
JP-A-8-321824
[Problems to be solved by the invention]
The conventional optical wavelength division multiplexing transmission system using the pre-emphasis technique controls each transmission light power in order to eliminate the non-uniformity of the OSNR of each signal channel. May be too high. In such a case, waveform deterioration due to the effect of the nonlinear effect may become remarkable. That is, in the conventional configuration, only the OSNR at the receiving end is considered, and no consideration is given to eliminating the non-uniformity of the path average power value related to the waveform deterioration amount due to the nonlinear effect.
[0009]
Further, in the conventional configuration, it is necessary to constantly monitor the OSNR at the receiving end in order to control the transmission light power to a predetermined value in consideration of deterioration with time, and a feedback control system is indispensable as shown in FIG. Met.
[0010]
The optical amplifying repeater 54 shown in FIG. 7 has a configuration in which an erbium-doped optical fiber amplifier (EDFA), Raman amplification having excellent low-noise and wideband characteristics, and a combination of Raman amplification and EDFA are used.
[0011]
The present invention, in an optical wavelength division multiplexing transmission system using Raman amplification or Raman amplification and EDFA in combination, considers the wavelength dependence of signal light loss and pump light loss, and eliminates non-uniformity of OSNR and path average optical power. It is still another object of the present invention to provide a WDM signal control apparatus capable of controlling the OSNR and the path average optical power so as not to largely deviate from the allowable values without monitoring even if the transmission optical power changes with time.
[0012]
[Means for Solving the Problems]
(Claim 1)
A WDM signal control apparatus according to the present invention provides a signal light loss and Raman pump light obtained from a transmission loss wavelength dependent characteristic α (λ) measured in advance in an optical wavelength division multiplexing transmission system using Raman amplification or a combination of Raman amplification and an optical fiber amplifier. When the loss is α (λs) and α (λp) (where λp = λs−100) and the arbitrary transmission light power is P0, the optical signal to noise ratio OSNR [α (λs), α (Λp), P0] and means for calculating the path average power Pave [α (λs), α (λp), P0], the signal wavelength λs1 and the OSNR allowable deviation M1 that provide a predetermined OSNR reference, and a predetermined path. When the signal wavelength λs2 giving the reference of the average power and the path average power allowable deviation M2 are set, the transmission light power relative value ΔP (λs) of the signal light of each wavelength is

And a means for controlling the transmission light power relative value ΔP (λs) of the signal light of each wavelength within the range of the transmission light power relative value ΔP (λs).
[0013]
(Claim 2)
Further, regarding the transmission light power relative value ΔP (λs) of the signal light of each wavelength,

It is also possible to use means for determining a value that satisfies the following condition, and controlling the transmission light power relative value ΔP (λs) of the signal light of each wavelength according to the transmission light power relative value ΔP (λs).
[0014]
(Claim 3)
The WDM signal control device of the present invention uses a Raman amplification and an optical fiber amplifier together, and in a WDM transmission system in which the gain ratio of the Raman amplification and the optical fiber amplifier is r, the transmission loss wavelength dependence α (λ) measured in advance. ), Α (λs) and α (λp) (where λp = λs-100), and an arbitrary transmission light power P0, the optical signal of one relay section Means for calculating an OSNR [α (λs), α (λp), P0, r] and a path average power Pave [α (λs), α (λp), P0, r], and a predetermined OSNR reference When the signal wavelength λs1 and the OSNR allowable deviation M1 that provide the reference and the signal wavelength λs2 and the path average power allowable deviation M2 that provide a predetermined path average power reference are set, the signal of each wavelength is set. The relative gain ratio Δr Raman amplification optical fiber amplifier for ([lambda] s)

And a means for controlling the relative gain ratio Δr (λs) of the signal light of each wavelength within the range of the relative gain ratio Δr (λs).
[0015]
(Claim 4)
Further, the relative gain ratio Δr (λs) between Raman amplification and optical fiber amplifier for signal light of each wavelength

Means for determining a value to be satisfied and controlling the relative gain ratio Δr (λs) of the signal light of each wavelength according to the relative gain ratio Δr (λs) may be used.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 shows a first embodiment of an optical wavelength division multiplexing transmission system using the WDM signal control device of the present invention.
[0017]
In the figure, an optical wavelength division multiplexing transmission system uses an optical multiplexer 12 to wavelength multiplex signal lights of wavelengths λ1 to λn output from optical transmitters 11-1 to 11-n of a wavelength division multiplexing transmission terminal 10, and In this configuration, the signal is transmitted to the wavelength division multiplexing receiving terminal 15 via the transmission line 13 and the optical amplification repeater 14.
[0018]
The optical amplification repeater 14 includes a plurality of Raman pump light sources 21-1 to 21-m having different wavelengths, an optical multiplexer 22-1 for multiplexing Raman pump light of each wavelength, and each multiplexed Raman pump light. And an EDFA 23 inserted into the optical fiber transmission line 13. The EDFA 23 is omitted when performing all Raman amplification.
[0019]
In the present embodiment, the WDM signal control device 30 of the present invention is configured to control each transmission light power output from the optical transmitters 11-1 to 11-n, and includes an input unit 31, a calculation unit 32, and a transmission light power It is composed of a control unit 33.
[0020]
The input unit 31 includes a transmission loss wavelength dependence characteristic α (λ) measured in advance, a signal wavelength λs1 and an OSNR allowable deviation M1 for giving a predetermined OSNR reference, a signal wavelength λs2 and a path for giving a predetermined path average power reference. The average power allowable deviation M2 is input and each input value is held.
[0021]
Based on the input values, the calculation unit 32 calculates the OSNR of one relay section when the signal light loss is α (λs), the Raman pumping light loss is α (λp), and the arbitrary transmission light power is P0. α (λs), α (λp), P0] and the average path power Pave [α (λs), α (λp), P0], and further, the transmission light power relative value ΔP (λs) of the signal light of each wavelength. about

Find the range that satisfies Note that λp = λs−100.
[0022]
The transmission light power controller 33 controls the transmission light power relative value ΔP (λs) in each of the optical transmitters 11-1 to 11-n within the range of the obtained transmission light power relative value ΔP (λs). For example, the transmission light power of each of the optical transmitters 11-1 to 11-n is controlled to be as uniform as possible within the range of the obtained transmission light power relative value ΔP (λs). The transmission light power relative value is controlled by controlling the attenuation of variable attenuators arranged in the optical transmitters 11-1 to 11-n or by directly controlling the output power of the light source.
[0023]
Here, a specific calculation example in an optical amplification repeater system that compensates for transmission loss of a uniform optical fiber (relay section L = 100 km) using all Raman amplification by backward pumping will be described. FIG. 2 shows a measurement result of the transmission loss wavelength dependence of the dispersion shifted fiber.
[0024]
From this measurement result, the loss in the C band and the L band is fixed at 0.23 dB / km in order to simplify the transmission loss wavelength dependence. The loss from 1430 nm to 1530 nm is represented by a linear approximation connecting [1430 nm, 0.35 dB / km] and [1530 nm, 0.23 dB / km] to α (λ) = − 1.2 × 10 ⁻³ (λ-1430). +0.35
And The loss in the U band is α (λ) = 1.2 × 10 ⁻³ (λ-1625) +0.23 by a linear approximation connecting [1625 nm, 0.23 dB / km] and [1675 nm, 0.29 dB / km].
And
[0025]
When the C band, L band and U band from 1530 nm to 1650 nm are applied as the wavelength range of the wavelength multiplexed signal light, the excitation light wavelength is 100 nm shorter than the signal light wavelength, and λs1 = 1530 nm and λs2 = 1625 nm, When M1 = 0 dB and M2 = 0.5 dB, the equations (1-1) and (1-2) are

It is expressed as FIG. 3 shows a region of the transmission light power relative value ΔP (λs) satisfying this.
[0026]
The transmission light power controller 33 controls the transmission light power of each wavelength so that the transmission light power relative value ΔP (λs) falls within the range of the hatched portion in FIG. As a result, the OSNR of the signal light of each wavelength falls within a range equal to or more than the allowable value smaller by M1 (0 dB) than the OSNR at 1530 nm, and the path average power Pave of the signal light of each wavelength is smaller than Pave at 1625 nm. Therefore, it falls within the range of M2 (0.5 dB) or more, which is larger than the allowable value.
[0027]
(Second embodiment)
In the same configuration as the first embodiment, the calculation unit 32 calculates the OSNR [α (λs), α (λp), P0] and the average path power Pave [α (λs), α (λp), P0], and a relative value ΔP (λs) of the transmission light power of the signal light of each wavelength,

Find a value that satisfies Note that λp = λs−100.
[0028]
The transmission light power controller 33 controls the transmission light power relative value ΔP (λs) in each of the optical transmitters 11-1 to 11-n according to the obtained transmission light power relative value ΔP (λs). . The transmission light power relative value is controlled by controlling the attenuation of a variable attenuator disposed in the optical transmitter or by directly controlling the output of the light source.
[0029]
As in the first embodiment, when the C band, L band, and U band from 1530 nm to 1650 nm are applied as the wavelength range of the wavelength multiplexed signal light, the excitation light wavelength is 100 nm shorter than the signal light wavelength, When λs1 = 1530 nm, λs2 = 1625 nm, and M1 = 0 dB and M2 = 0.5 dB, the expressions (2-1) to (2-3) are obtained.

It is expressed as The transmission light power relative value ΔP (λs) that satisfies this is shown by a broken line in FIG.
[0030]
The transmission light power controller 33 controls the transmission light power of each wavelength such that the transmission light power relative value ΔP (λs) becomes the value indicated by the broken line in FIG. Thus, the OSNR and the path average power Pave of the signal light of each wavelength can be kept within the above-mentioned allowable range. Note that, in this case, even if the transmission light power of each wavelength shifts due to a change with time or the like, it becomes easy to maintain the transmission light power within the range of the hatched portion in FIG.
[0031]
(Third embodiment)
FIG. 4 shows a third embodiment of the optical wavelength division multiplexing transmission system using the WDM signal control device of the present invention.
[0032]
In the figure, an optical wavelength division multiplexing transmission system uses an optical multiplexer 12 to wavelength multiplex signal lights of wavelengths λ1 to λn output from optical transmitters 11-1 to 11-n of a wavelength division multiplexing transmission terminal 10, and In this configuration, the signal is transmitted to the wavelength division multiplexing receiving terminal 15 via the transmission line 13 and the optical amplification repeater 14.
[0033]
The optical amplification repeater 14 includes a plurality of Raman pump light sources 21-1 to 21-m having different wavelengths, an optical multiplexer 22-1 for multiplexing Raman pump light of each wavelength, and each multiplexed Raman pump light. And an EDFA 23 inserted into the optical fiber transmission line 13.
[0034]
In the present embodiment, the WDM signal control device 40 of the present invention has a configuration in which the OSNR and the Pave are changed by controlling the gain ratio r of the Raman amplification and the EDFA with respect to the signal light of each wavelength. 42 and a gain control unit 43.
[0035]
The input unit 41 includes a transmission loss wavelength dependence characteristic α (λ) measured in advance, a signal wavelength λs1 and OSNR allowable deviation M1 for giving a predetermined OSNR reference, a signal wavelength λs2 and a path for giving a predetermined path average power reference. The average power allowable deviation M2 is input and each input value is held.
[0036]
Based on the input values, the calculation unit 42 calculates the OSNR of one relay section when the signal light loss is α (λs), the Raman pumping light loss is α (λp), and an arbitrary transmission light power is P0. α (λs), α (λp), P0, r] and average path power Pave [α (λs), α (λp), P0, r], and further calculate Raman amplification and EDFA of signal light of each wavelength. Relative gain ratio Δr (λs) of gain ratio r

Find the range to add. Note that λp = λs−100.
[0037]
The gain control unit 43 controls the relative gain ratio Δr (λs) in each of the Raman excitation light sources 21-1 to 21-m and the EDFA 23 within the range of the obtained relative gain ratio Δr (λs). For example, control is performed so that the relative gain ratio Δr (λs) in each of the Raman pumping light sources 21-1 to 21-m and the EDFA 23 becomes as uniform as possible within the range of the obtained relative gain ratio Δr (λs). The relative gain ratio is controlled by directly controlling the outputs of the Raman pump light source and the pump light source in the EDFA.
[0038]
5A and 5B show the relationship between the gain ratio r and the OSNR at 1580 nm, and the relationship between the gain ratio r and the path average power Pave. From the wavelength dependence of the signal light loss and the pumping light loss based on this relationship, when λs1 = 1530 nm, λs2 = 1625 nm, and M1 = 0 dB and M2 = 0 dB, the equations (3-1) and (3-2) are obtained.

It is expressed as FIG. 6 shows a region of the relative gain ratio Δr (λs) satisfying this.
[0039]
The optical power control unit 43 controls the Raman pump light sources 21-1 to 21-m and the EDFA 23 such that the relative gain ratio Δr (λs) falls within the range of the hatched portion in FIG. As a result, the OSNR of the signal light of each wavelength falls within a range equal to or more than the allowable value smaller by M1 (0 dB) than the OSNR at 1530 nm, and the path average power Pave of the signal light of each wavelength is smaller than Pave at 1625 nm. Therefore, it falls within a range of M2 (0 dB) or more, which is larger than the allowable value.
[0040]
(Fourth embodiment)
In a configuration similar to that of the third embodiment, the calculation unit 42 determines the OSNR [α (λs), α (λp), P0, r] and the average path power Pave [α (λs), α (λp , P0, r], and further, the relative gain ratio Δr (λs) of the Raman amplification and the EDFA gain ratio r for the signal light of each wavelength.

Find a value that satisfies Note that λp = λs−100.
[0041]
The gain control unit 43 controls the relative gain ratio Δr (λs) in the Raman pump light sources 21-1 to 21-m and the EDFA 23 according to the obtained value of the relative gain ratio Δr (λs). The relative gain ratio is controlled by directly controlling the outputs of the Raman pump light source and the pump light source in the EDFA.
[0042]
As in the third embodiment, when the C band, L band and U band from 1530 nm to 1650 nm are applied as the wavelength range of the wavelength multiplexed signal light, the excitation light wavelength is 100 nm shorter than the signal light wavelength, When λs1 = 1530 nm, λs2 = 1625 nm, and M1 = 0 dB and M2 = 0 dB, the equations (4-1) to (4-3) are obtained.

It is expressed as The relative gain ratio Δr (λs) satisfying this is shown by a broken line in FIG.
[0043]
The gain control unit 43 controls the Raman pump light sources 21-1 to 21-m and the EDFA 23 such that the relative gain ratio Δr (λs) becomes the gain indicated by the broken line in FIG. Thus, the OSNR and the path average power Pave of the signal light of each wavelength can be kept within the above-mentioned allowable range. Note that, in this case, even if the gain ratio of each wavelength shifts due to a change over time or the like, it is easy to maintain the gain ratio within the range of the hatched portion in FIG.
[0044]
By the way, if the Raman pump light source of a specific wavelength is controlled, the wavelength dependence of the Raman gain profile changes accordingly, but the shape of the gain profile of the EDFA is almost constant. It may be difficult to change the ratio. To overcome this, a configuration may be adopted in which lumped amplification type Raman amplification is used in place of the EDFA.
[0045]
In addition, when the EDFA is not used in the U band, the gain ratio can be arbitrarily changed at all signal wavelengths by using a combination of the distributed amplification type Raman amplification and the centralized amplification type Raman amplification.
[0046]
【The invention's effect】
As described above, by using the WDM signal control device of the present invention, the transmission characteristics (optical signal-to-noise ratio OSNR and path average power Pave) of a wideband WDM signal can be made substantially uniform. Further, even if the transmission light power of the signal light of each wavelength is shifted due to a change with time, it becomes easy to maintain the transmission light power within the predetermined allowable OSNR value and the allowable path average power value.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of an optical wavelength division multiplexing transmission system using a WDM signal control device of the present invention.
FIG. 2 is a diagram showing a measurement result of a transmission loss wavelength dependence characteristic of a dispersion-shifted fiber.
FIG. 3 is a diagram showing a transmission light power relative value ΔP (λs) in signal light of each wavelength.
FIG. 4 is a diagram showing a third embodiment of the optical wavelength division multiplexing transmission system using the WDM signal control device of the present invention.
FIG. 5 is a diagram showing a relationship between a gain ratio r at 1580 nm and OSNR and Pave.
FIG. 6 is a diagram showing a relative gain ratio Δr (λs) in signal light of each wavelength.
FIG. 7 is a diagram showing a configuration example of a conventional optical wavelength division multiplexing transmission system using a pre-emphasis technique.
[Explanation of symbols]
Reference Signs List 10 wavelength multiplexing transmitting terminal 11 optical transmitter 12 optical multiplexer 13 optical fiber transmission line 14 optical amplification repeater 15 wavelength multiplexing receiving terminal 21 Raman pumping light source 22 optical multiplexer 23 EDFA
Reference Signs List 30 WDM signal control device 31 Input unit 32 Calculation unit 33 Transmission light power control unit 40 WDM signal control device 41 Input unit 42 Calculation unit 43 Gain control unit

Claims

In an optical wavelength division multiplexing transmission system using Raman amplification or Raman amplification and an optical fiber amplifier together,
The signal light loss and the Raman pumping light loss obtained from the transmission loss wavelength dependence characteristic α (λ) measured in advance are α (λs) and α (λp) (where λp = λs-100), and an arbitrary transmission light power is P0. Means for calculating the optical signal-to-noise ratio OSNR [α (λs), α (λp), P0] and the average path power Pave [α (λs), α (λp), P0] in one relay section. When,
When a signal wavelength λs1 and an OSNR allowable deviation M1 that provide a predetermined OSNR reference and a signal wavelength λs2 and a path average power allowable deviation M2 that provide a predetermined path average power reference are set, the transmission light of the signal light of each wavelength is set. Power relative value ΔP (λs)

And a means for controlling the relative transmission light power ΔP (λs) of the signal light of each wavelength within the range of the relative transmission light power ΔP (λs). Control device.

Means for obtaining a value that satisfies the following condition, and for controlling the transmission light power relative value ΔP (λs) of the signal light of each wavelength in accordance with the transmission light power relative value ΔP (λs). apparatus.

In an optical wavelength division multiplexing transmission system in which Raman amplification and an optical fiber amplifier are used together and the gain ratio between the Raman amplification and the optical fiber amplifier is r,
The signal light loss and the Raman pumping light loss obtained from the transmission loss wavelength dependence characteristic α (λ) measured in advance are α (λs) and α (λp) (where λp = λs-100), and an arbitrary transmission light power is P0. , The optical signal-to-noise ratio OSNR [α (λs), α (λp), P0, r] and the average path power Pave [α (λs), α (λp), P0, r] Means for calculating
When a signal wavelength λs1 and an OSNR allowable deviation M1 that provide a predetermined OSNR reference and a signal wavelength λs2 and a path average power allowable deviation M2 that provide a predetermined path average power reference are set, Raman amplification of the signal light of each wavelength is performed. And the relative gain ratio Δr (λs) of the optical fiber amplifier

Means for obtaining a range that satisfies the following condition, and for controlling the relative gain ratio Δr (λs) of the signal light of each wavelength within the range of the relative gain ratio Δr (λs).

Means for determining a value to be satisfied and controlling the relative gain ratio Δr (λs) of the signal light of each wavelength according to the relative gain ratio Δr (λs).