JP2004198926A

JP2004198926A - Multi-channel batch optical waveform shaping circuit

Info

Publication number: JP2004198926A
Application number: JP2002370046A
Authority: JP
Inventors: Hidehiko Takara; 秀彦高良; Takuya Ohara; 拓也大原
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2002-12-20
Filing date: 2002-12-20
Publication date: 2004-07-15

Abstract

【課題】ＤＷＤＭシステムにおいて、波長多重信号光の伝送中に発生する各チャネルの強度雑音成分を一括して抑圧する。
【解決手段】チャネル間隔ｆの波長多重信号光を増幅する光増幅器と、チャネル間隔２ｆの奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号光に分離する光分離器と、奇数チャネルおよび偶数チャネルの波長多重信号光をそれぞれ入力する第１の非線形光ファイバおよび第２の非線形光ファイバと、奇数チャネルおよび偶数チャネルの波長多重信号光を各チャネルの光パルス信号に分波して再度合波する第１の分波フィルタおよび第１の合波フィルタ、および第２の分波フィルタおよび第２の合波フィルタと、第１の合波フィルタから出力される奇数チャネルの波長多重信号光と、第２の合波フィルタから出力される偶数チャネルの波長多重信号光とを多重して出力する光多重器とを備える。
【選択図】図１In a DWDM system, an intensity noise component of each channel generated during transmission of wavelength multiplexed signal light is suppressed collectively.
An optical amplifier for amplifying a wavelength-division multiplexed signal light with a channel interval of f, an optical separator for separating the wavelength-division multiplexed signal light of an odd-numbered channel and the wavelength-division multiplexed signal light of an even-numbered channel with a channel interval of 2f, an odd channel and an even number A first nonlinear optical fiber and a second nonlinear optical fiber for inputting the wavelength multiplexed signal light of the channel, and the wavelength multiplexed signal light of the odd channel and the even channel are demultiplexed into the optical pulse signal of each channel and multiplexed again. A first demultiplexing filter and a first multiplexing filter, a second demultiplexing filter and a second multiplexing filter, and a wavelength-division multiplexed signal light of an odd channel output from the first multiplexing filter; An optical multiplexer that multiplexes and outputs the wavelength-multiplexed signal light of the even-numbered channel output from the second multiplexing filter.
[Selection diagram] Fig. 1

Description

【０００１】
【発明の属する技術分野】
本発明は、波長多重された複数チャネルの光パルス信号を一括して波形整形する多チャネル一括光波形整形回路に関する。
【０００２】
【従来の技術】
光伝送システムでは、光ファイバ伝送路における減衰、光増幅器における自然放出光雑音の付加、光ファイバ伝送路の分散や光非線形効果による符号間干渉などの様々な要因により、伝送される光信号に波形劣化が生じる。そのため、光ファイバ伝送路には、光増幅器や波形再生を行う識別再生中継器が適当な間隔で配置される。
【０００３】
一方、伝送容量増大の要求に応えるために、１本の光ファイバ伝送路で異なる波長を有する複数の光信号を伝送する波長分割多重（ＷＤＭ）が積極的に利用されている。このような波長多重伝送システムにおいても、同様に光増幅器や識別再生中継器などが必要になっている。
【０００４】
図１１は、波長多重伝送システムにおける従来の識別再生中継器の構成例を示す。図において、波長多重信号光は、光ファイバ伝送路５１および光増幅器５２を介して識別再生中継器５３に入力される。識別再生中継器５３は、光分波器５４、複数の識別再生回路５５、光合波器５６により構成される。識別再生中継器５３に入力する波長多重信号光は、光分波器５４で各チャネルの信号光に分波され、それぞれ対応する識別再生回路５５で識別再生され、さらに光合波器５６で合波して波長多重信号光として出力される。
【０００５】
この識別再生回路５５としては、光信号を電気信号に変換した後に電子回路により識別再生し、再度光信号に変換する方法が実用化されている。また、光信号を光信号のままで識別再生する方法が研究されており、例えば半導体光増幅器を組み込んだマッハツェンダ干渉計や、非線形ループミラーなどの光制御スイッチを用いる方法が知られている。
【０００６】
一方、光信号の強度揺らぎを低減する波形整形技術が提案されている（特許文献１）。この技術は、リタイミング機能は含まれていないが、簡単な構成で光信号の強度雑音を抑圧できる特徴を有している。さらに、この強度雑音抑圧技術を多チャネルに適用する一括光波形整形技術が提案されている（特願２００１−１９７４７８）。この原理について、図１２を参照して説明する。
【０００７】
図１２において、従来の多チャネル一括光波形整形回路は、光増幅器１１、非線形光ファイバ１２、分波フィルタ１３、合波フィルタ１４を縦続に接続した構成である。光増幅器１１は、波長多重信号光の全チャネルを一括増幅する利得帯域を有する。非線形光ファイバ１２は、ファイバ長がソリトン周期より長く、平均の波長分散が異常分散になる特性を有する。分波フィルタ１３および合波フィルタ１４は、各チャネルの光パルス信号の中心波長を含む離散的（周期的）な透過帯域を有し、１対で用いることにより、透過帯域が各チャネルの中心波長に対応するバンドパスフィルタを集合したものと等価な機能を果たす。
【０００８】
ここで、符号１〜４は波長多重信号光の時間波形、符号５〜７は波長多重信号光２〜４に対応するスペクトル波形を示す。ただし、時間波形１〜４は、波長多重信号光のうちのある１チャネルの波形のみを示す。その他のチャネルの波形も１〜４と同様に変化する。
【０００９】
波長多重信号光１は、光増幅器１１により各チャネルの光パルス信号のピークパワーが基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように増幅される。増幅された波長多重信号光２（スペクトル波形５）は、ソリトン周期よりも長い非線形光ファイバ１２に入射されると、各チャネルの光パルス信号の強度揺らぎは、自己位相変調によりスペクトル幅の揺らぎに変換される。ただし、入射ピークパワーが基本ソリトンパワーに近いために、スペクトルの中心部分は基本ソリトンに近い形に収束し、波長多重信号光３（スペクトル波形６）となって分波フィルタ１３に入力する。
【００１０】
分波フィルタ１３は、各チャネルの光パルス信号の中心波長が透過帯域になっているので、波長多重信号光３（スペクトル波形６）のスペクトル幅の揺らぎを切り落とすことにより、各光パルス信号が当初持っていた強度揺らぎ（雑音）を取り除くことができる。強度雑音が除去された各チャネルの光パルス信号は、分波フィルタ１３と同様の合波フィルタ１４で合波することにより、波長多重信号光４（スペクトル波形７）に変換される。
【００１１】
【特許文献１】
特開平１１−２８４２６１号公報
【００１２】
【発明が解決しようとする課題】
ところで、従来技術ではチャネル間隔を狭くすると、非線形光ファイバ内での相互位相変調や四光波混合等の非線形光学効果によるチャネル間の相互作用の影響が大きくなり、光信号波形の劣化が生じる問題があった。この光信号波形の整形状態を計算した例を図１０(a) 〜(c) に示す。
【００１３】
図１０(a) は、非線形光ファイバに入射する前の波長多重信号光のある１チャネルの光波形を示す（パルス幅８ｐｓ、ビットレート40Ｇbit/s ）。図１０(b),(c) は、それぞれチャネル間隔を 400ＧHzおよび 200ＧHzに設定したときの光波形整形回路通過後の光波形を示す。チャネル間隔が 400ＧHzと広いとき（図１０(b))は良好な光波形整形効果がみられるが、チャネル間隔が 200ＧHzに狭くなると（図１０(c))、むしろ入射光波形（図１０(a))よりも劣化する。したがって、従来技術ではチャネル間隔をある程度以下に設定することができず、光周波数（波長）領域で高密度にチャネルをつめるＤＷＤＭ（Dence ＷＤＭ）システムへの適用が困難であった。
【００１４】
本発明は、ＤＷＤＭシステムにおいて、波長多重信号光の伝送中に発生する各チャネルの強度雑音成分を一括して抑圧することができる多チャネル一括光波形整形回路を提供することを目的とする。
【００１５】
【課題を解決するための手段】
請求項１に記載の発明は、チャネル間隔ｆの複数チャネルの光パルス信号を波長多重した波長多重信号光を増幅する光増幅器と、増幅された波長多重信号光を入力し、チャネル間隔２ｆの奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号光に分離する光分離器と、奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ入力する第１の非線形光ファイバおよび第２の非線形光ファイバと、第１の非線形光ファイバを通過した奇数チャネルの波長多重信号光を各チャネルの光パルス信号に分波して再度合波する第１の分波フィルタおよび第１の合波フィルタと、第２の非線形光ファイバを通過した偶数チャネルの波長多重信号光を各チャネルの光パルス信号に分波して再度合波する第２の分波フィルタおよび第２の合波フィルタと、第１の合波フィルタから出力される強度雑音が除去された奇数チャネルの波長多重信号光と、第２の合波フィルタから出力される強度雑音が除去された偶数チャネルの波長多重信号光とを多重して出力する光多重器とを備える。
【００１６】
請求項２に記載の発明は、チャネル間隔ｆの複数チャネルの光パルス信号を波長多重した波長多重信号光を入力し、チャネル間隔２ｆの奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号光に分離する光分離器と、奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ増幅する第１の光増幅器および第２の光増幅器と、増幅された奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ入力する第１の非線形光ファイバおよび第２の非線形光ファイバと、第１の非線形光ファイバを通過した奇数チャネルの波長多重信号光を各チャネルの光パルス信号に分波して再度合波する第１の分波フィルタおよび第１の合波フィルタと、第２の非線形光ファイバを通過した偶数チャネルの波長多重信号光を各チャネルの光パルス信号に分波して再度合波する第２の分波フィルタおよび第２の合波フィルタと、第１の合波フィルタから出力される強度雑音が除去された奇数チャネルの波長多重信号光と、第２の合波フィルタから出力される強度雑音が除去された偶数チャネルの波長多重信号光とを多重して出力する光多重器とを備える。
【００１７】
請求項３に記載の発明は、チャネル間隔ｆの複数チャネルの光パルス信号を波長多重した波長多重信号光を増幅する光増幅器と、増幅された波長多重信号光を入力し、チャネル間隔２ｆの奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号光に分離する光分離器と、奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ入力する第１の非線形光ファイバおよび第２の非線形光ファイバと、第１の非線形光ファイバを通過した奇数チャネルの波長多重信号光および第２の非線形光ファイバを通過した偶数チャネルの波長多重信号光を入力し、各チャネルの光パルス信号に分波して再度合波し、強度雑音が除去された波長多重信号光を出力する分波フィルタおよび合波フィルタとを備える。
【００１８】
請求項４に記載の発明は、チャネル間隔ｆの複数チャネルの光パルス信号を波長多重した波長多重信号光を入力し、チャネル間隔２ｆの奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号光に分離する光分離器と、奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ増幅する第１の光増幅器および第２の光増幅器と、増幅された奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光をそれぞれ入力する第１の非線形光ファイバおよび第２の非線形光ファイバと、チャネル間隔ｆの各チャネルの光パルス信号の中心波長を含む所定の透過帯域を有し、第１の非線形光ファイバを通過した奇数チャネルの波長多重信号光および第２の非線形光ファイバを通過した偶数チャネルの波長多重信号光を入力し、各チャネルの光パルス信号に分波して再度合波し、強度雑音が除去された波長多重信号光を出力する分波フィルタおよび合波フィルタとを備える。
【００１９】
また、請求項１〜４のいずれかに記載の多チャネル一括光波形整形回路において、各チャネルの光パルス信号のパワーをモニタし、各非線形光ファイバに入射する奇数チャネルおよび偶数チャネルの光パルス信号のピークパワーが、基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように制御する光パワー制御手段を備えてもよい（請求項５）。
【００２０】
また、請求項１〜４のいずれかに記載の多チャネル一括光波形整形回路において、非線形光ファイバの入力、または非線形光ファイバの出力、または合波フィルタの出力の波長多重信号光を入力して各チャネルの光パルス信号のパワーを検出する光スペクトラムアナライザを用い、各非線形光ファイバに入射する奇数チャネルおよび偶数チャネルの光パルス信号のピークパワーが、基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように制御する光パワー制御手段を備えてもよい（請求項６）。
【００２１】
【発明の実施の形態】
＜第１の実施形態：請求項１＞
図１は、本発明の多チャネル一括光波形整形回路の第１の実施形態を示す。なお、ここでは波長多重信号光の多重チャネル数を２ｍ、チャネル間隔をｆとする。
【００２２】
図において、チャネル間隔ｆの複数チャネルの光パルス信号を波長多重した波長多重信号光は光増幅器１１で増幅され、増幅された波長多重信号光が光分離器１５でチャネル間隔２ｆの奇数チャネルと偶数チャネルに分離され、ファイバ長がソリトン周期より長く、平均の波長分散が異常分散になる特性を有する非線形光ファイバ１２−１，１２−２にそれぞれ入力される。
【００２３】
光増幅器１１では、分離後の奇数チャネルと偶数チャネルの各光パルス信号のピークパワーが基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように増幅する。非線形光ファイバ１２−１，１２−２では、光パルス信号の強度揺らぎが自己位相変調によりスペクトル広がりの揺らぎに変換されるが、入射ピークパワーが基本ソリトンパワーに近いためにスペクトルの中心部分は基本ソリトンに近い形に収束する。このとき、チャネル間隔がもとの波長多重信号光の２倍の２ｆになっているので、相互位相変調や四光波混合等の非線形光学効果によるチャネル間の干渉が低減できる。
【００２４】
非線形光ファイバ１２−１から出力される奇数チャネルの波長多重信号光は、奇数チャネルの光パルス信号の中心波長を含む所定の透過帯域（チャネル間隔２ｆ）を有する分波フィルタ１３−１に入力される。分波フィルタ１３−１では、奇数チャネルのスペクトル広がりの揺らぎを切り落とすことにより、当初の光パスがもっていた強度揺らぎ（雑音）を取り除くことができる。雑音が取り除かれた奇数チャネルの光パルス信号は、分波フィルタ１３−１と同様の透過帯域（チャネル間隔２ｆ）を有する合波フィルタ１４−１で合波され、奇数チャネルの波長多重信号光として出力される。
【００２５】
非線形光ファイバ１２−２から出力される偶数チャネルの波長多重信号光も同様に、分波フィルタ１３−２および合波フィルタ１４−２（図面では見えない）により雑音が取り除かれて出力される。
【００２６】
合波フィルタ１４−１，１４−２から出力される奇数チャネルの波長多重信号光および偶数チャネルの波長多重信号光は光多重器１６で多重され、チャネル間隔ｆの波長多重信号光として出力される。
【００２７】
図１０(d) は、チャネル間隔 200ＧHzの波長多重信号光に対して、本発明の構成により波形整形した出力光波形を示す。従来構成では、チャネル間隔 200ＧHzの場合には図１０(c) に示すように波形劣化が生じていたが、本発明により波形整形できることがわかる。
【００２８】
なお、光分離器１５としては、例えばインタリーブフィルタやマッハツェンダ型光フィルタを用いることができる。分波フィルタ１３および合波フィルタ１４としては、例えばアレイ導波路回折格子（ＡＷＧ）フィルタを用いることができる。光多重器１６としては、例えばインタリーブフィルタやマッハツェンダ型光フィルタの他に光カプラを用いることができる。
【００２９】
＜第２の実施形態：請求項１，５＞
図２は、本発明の多チャネル一括光波形整形回路の第２の実施形態を示す。本実施形態は、第１の実施形態の構成に加えて、各チャネルの光パルス信号のパワーをモニタし、非線形光ファイバ１２−１，１２−２に入射する奇数チャネルおよび偶数チャネルの各光パルス信号のピークパワーが、基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように制御する光パワー制御手段を備えるものである。
【００３０】
光パワー制御手段は、次のような構成により実現される。光増幅器１１は、エルビウム添加光ファイバ２１と、励起光を発生する励起光源２２と、波長多重信号光と励起光を合波してエルビウム添加光ファイバ２１に入射する光合波器２３と、入出力端に配置される光アイソレータ２４−１，２４−２とにより構成される。さらに、光増幅器１１の出力段に配置される等化器３１と、分波フィルタ１３−１と合波フィルタ１４−１との間に配置される光カプラ３２−１〜３２−ｍと、光カプラで分岐された奇数チャネルの各光パワーを検出する光検出器３３−１〜３３−ｍとを備える。図示しない偶数チャネルに対する分波フィルタ１３−２と合波フィルタ１４−２との間にも同様に光カプラを配置し、光検出器を備える。制御回路３４は、各光検出器の検出結果に応じて励起光源２２または等化器３１、またはその両方を制御し、非線形光ファイバ１２−１，１２−２に入力する各チャネルの光パルス信号のピークパワーを基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように設定する。
【００３１】
＜第３の実施形態：請求項１，６＞
図３は、本発明の多チャネル一括光波形整形回路の第３の実施形態を示す。本実施形態の特徴は、第２の実施形態において各チャネルに対応する光検出器に代えて光スペクトラムアナライザを用いるところにある。その他の構成は、第２の実施形態と同様である。
【００３２】
ここでは、非線形光ファイバ１２−１の入力、または非線形光ファイバ１２−１の出力、または合波フィルタ１４−１の出力の波長多重信号光を分岐する光カプラ３５と、光カプラで分岐された奇数チャネルの各光パワーを検出する光スペクトラムアナライザ３６−１を用いる。偶数チャネル側の構成も同様である。制御回路３４は、各光スペクトラムアナライザ３６−１，３６−２の検出結果に応じて、励起光源２２または等化器３１、またはその両方を制御し、非線形光ファイバ１２−１，１２−２に入力する各チャネルの光パルス信号のピークパワーを基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように設定する。
【００３３】
また、光多重器１６の出力側をモニタしてもよく、その場合には１つの光スペクトラムアナライザ３６で各チャネルの光パワーを検出して制御回路３４に通知する構成となる。
【００３４】
＜第４の実施形態：請求項２，５＞
図４は、本発明の多チャネル一括光波形整形回路の第４の実施形態を示す。本実施形態の特徴は、第２の実施形態において、チャネル間隔ｆの波長多重信号光をまず光分離器１５でチャネル間隔２ｆの奇数チャネルおよび偶数チャネルの波長多重信号光に分離するところにある。
【００３５】
すなわち、チャネル間隔ｆの波長多重信号光は、光分離器１５でチャネル間隔２ｆの奇数チャネルと偶数チャネルに分離され、奇数チャネルの波長多重信号光は光増幅器１１−１で増幅され、さらに等化器３１−１を介して、ファイバ長がソリトン周期より長く、平均の波長分散が異常分散になる特性を有する非線形光ファイバ１２−１に入力される。偶数チャネルの波長多重信号光も同様に、図示しない光増幅器（１１−２）、光等化器（３１−２）を介して非線形光ファイバ（１２−２）に入力される。その他の構成および動作は第２の実施形態と同様である。
【００３６】
＜第５の実施形態：請求項２，６＞
図５は、本発明の多チャネル一括光波形整形回路の第５の実施形態を示す。本実施形態の特徴は、第４の実施形態において各チャネルに対応する光検出器に代えて光スペクトラムアナライザを用いるところにある。その他の構成は、第４の実施形態と同様である。
【００３７】
ここでは、非線形光ファイバ１２−１の入力、または非線形光ファイバ１２−１の出力、または合波フィルタ１４−１の出力の波長多重信号光を分岐する光カプラ３５と、光カプラで分岐された奇数チャネルの各光パワーを検出する光スペクトラムアナライザ３６−１を用いる。制御回路３４−１は、光スペクトラムアナライザ３６−１の検出結果に応じて、光増幅器１１−１の励起光源２２または等化器３１−１、またはその両方を制御し、非線形光ファイバ１２−１に入力する奇数チャネルの光パルス信号のピークパワーを基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように設定する。偶数チャネル側の構成も同様である。
【００３８】
また、光多重器１６の出力側をモニタしてもよく、その場合には１つの光スペクトラムアナライザ３６で各チャネルの光パワーを検出し、奇数チャネルの制御回路３４−１および偶数チャネルの制御回路（３４−２）に通知する構成となる。
【００３９】
＜第６の実施形態：請求項３，５＞
図６は、本発明の多チャネル一括光波形整形回路の第６の実施形態を示す。
第２の実施形態では、奇数チャネルに対する分波フィルタ１３−１および合波フィルタ１４−１と、偶数チャネルに対する分波フィルタ（１３−２）および合波フィルタ（１４−２）を個別に備え、奇数チャネルの波長多重信号光と偶数チャネルの波長多重信号を光多重器１６で多重する構成であった。本実施形態の特徴は、奇数チャネルおよび偶数チャネルに対応する２組の分波フィルタおよび合波フィルタと光多重器に代えて、１組の分波フィルタ１３および合波フィルタ１４を用いるところにある。
【００４０】
分波フィルタ１３は例えば２入力のＡＷＧフィルタを用い、非線形光ファイバ１２−１から出力される奇数チャネルの波長多重信号光をポート1-1 ，1-2 ，…，1-m に分波し、非線形光ファイバ１２−２から出力される偶数チャネルの波長多重信号光をポート2-1 ，2-2 ，…，2-m に分波する。合波フィルタ１４は例えばＡＷＧフィルタを用い、分波フィルタ１３のポート1-1 ，2-1 ，1-2 ，2-2 ，…，1-m ，2-m の順に接続することにより、奇数チャネルおよび偶数チャネルの光パルス信号を多重することができる。その他の構成および動作は第２の実施形態と同様である。
【００４１】
＜第７の実施形態：請求項３，６＞
図７は、本発明の多チャネル一括光波形整形回路の第７の実施形態を示す。本実施形態の特徴は、第６の実施形態において各チャネルに対応する光検出器に代えて光スペクトラムアナライザを用いるところにある。その他の構成は、第６の実施形態と同様である。
【００４２】
ここでは、非線形光ファイバ１２−１の入力、または非線形光ファイバ１２−１の出力の波長多重信号光を分岐する光カプラ３５と、光カプラで分岐された奇数チャネルの各光パワーを検出する光スペクトラムアナライザ３６−１を用いる。偶数チャネル側の構成も同様である。制御回路３４は、光スペクトラムアナライザ３６−１，３６−２の検出結果に応じて、励起光源２２または等化器３１、またはその両方を制御し、非線形光ファイバ１２−１，１２−２に入力する各チャネルの光パルス信号のピークパワーを基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように設定する。
【００４３】
また、合波フィルタ１４の出力側をモニタしてもよく、その場合には１つの光スペクトラムアナライザ３６で各チャネルの光パワーを検出し、制御回路３４に通知する構成となる。
【００４４】
＜第８の実施形態：請求項４，５＞
図８は、本発明の多チャネル一括光波形整形回路の第８の実施形態を示す。本実施形態の特徴は、第６の実施形態において、チャネル間隔ｆの波長多重信号光をまず光分離器１５でチャネル間隔２ｆの奇数チャネルおよび偶数チャネルの波長多重信号光に分離するところにある。
【００４５】
すなわち、チャネル間隔ｆの波長多重信号光は、光分離器１５でチャネル間隔２ｆの奇数チャネルと偶数チャネルに分離され、奇数チャネルの波長多重信号光は光増幅器１１−１で増幅され、さらに等化器３１−１を介して、ファイバ長がソリトン周期より長く、平均の波長分散が異常分散になる特性を有する非線形光ファイバ１２−１に入力される。偶数チャネルの波長多重信号光も同様に、図示しない光増幅器（１１−２）、光等化器（３１−２）を介して非線形光ファイバ（１２−２）に入力される。その他の構成および動作は第６の実施形態と同様である。
【００４６】
＜第９の実施形態：請求項４，６＞
図９は、本発明の多チャネル一括光波形整形回路の第９の実施形態を示す。本実施形態の特徴は、第８の実施形態において各チャネルに対応する光検出器に代えて光スペクトラムアナライザを用いるところにある。その他の構成は、第８の実施形態と同様である。
【００４７】
ここでは、非線形光ファイバ１２−１の入力、または非線形光ファイバ１２−１の出力の波長多重信号光を分岐する光カプラ３５と、光カプラで分岐された奇数チャネルの各光パワーを検出する光スペクトラムアナライザ３６−１を用いる。制御回路３４−１は、光スペクトラムアナライザ３６−１の検出結果に応じて、光増幅器１１−１の励起光源２２または等化器３１−１、またはその両方を制御し、非線形光ファイバ１２−１に入力する奇数チャネルの光パルス信号のピークパワーを基本ソリトンパワーより大きく、かつ基本ソリトンパワーの２倍以下になるように設定する。偶数チャネル側の構成も同様である。
【００４８】
また、合波フィルタ１４の出力側をモニタしてもよく、その場合には１つの光スペクトラムアナライザ３６で各チャネルの光パワーを検出し、奇数チャネルの制御回路３４−１および偶数チャネルの制御回路（３４−２）に通知する構成となる。
【００４９】
【発明の効果】
以上説明したように、本発明の多チャネル一括光波形整形回路は、識別再生回路を含まない簡単な構成で、波長多重信号光に重畳された強度雑音を、各チャネルごとにスペクトル幅の揺らぎに変換してフィルタリングすることにより、波長多重信号光の強度雑音を一括して除去することができる。特に、奇数チャネルと偶数チャネルに分割して上記の処理を行うことにより、高密度に波長多重された波長多重信号光の強度雑音を一括して除去することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態を示すブロック図。
【図２】本発明の第２の実施形態を示すブロック図。
【図３】本発明の第３の実施形態を示すブロック図。
【図４】本発明の第４の実施形態を示すブロック図。
【図５】本発明の第５の実施形態を示すブロック図。
【図６】本発明の第６の実施形態を示すブロック図。
【図７】本発明の第７の実施形態を示すブロック図。
【図８】本発明の第８の実施形態を示すブロック図。
【図９】本発明の第９の実施形態を示すブロック図。
【図１０】従来構成と本発明構成の実験結果を示す図。
【図１１】波長多重伝送システムにおける従来の識別再生中継器の構成例を示す図。
【図１２】波長多重信号光の強度揺らぎを低減する従来の光波形整形技術を説明する図。
【符号の説明】
１１光増幅器
１２非線形光ファイバ
１３分波フィルタ
１４合波フィルタ
１５光分離器
１６光多重器
２１エルビウム添加光ファイバ
２２励起光源
２３光合波器
２４光アイソレータ
３１等化器
３２光カプラ
３３光検出器
３４制御回路
３５光カプラ
３６光スペクトラムアナライザ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-channel collective optical waveform shaping circuit for collectively shaping waveforms of wavelength-multiplexed optical pulse signals of a plurality of channels.
[0002]
[Prior art]
In an optical transmission system, the waveform of an optical signal to be transmitted is affected by various factors such as attenuation in an optical fiber transmission line, addition of spontaneous emission noise in an optical amplifier, dispersion between optical fiber transmission lines, and intersymbol interference due to optical nonlinear effects. Deterioration occurs. Therefore, in the optical fiber transmission line, an optical amplifier and an identification regeneration repeater for performing waveform regeneration are arranged at appropriate intervals.
[0003]
On the other hand, wavelength division multiplexing (WDM), which transmits a plurality of optical signals having different wavelengths through one optical fiber transmission line, has been actively used in order to meet the demand for increased transmission capacity. Such a wavelength division multiplexing transmission system also requires an optical amplifier, an identification regenerative repeater, and the like.
[0004]
FIG. 11 shows a configuration example of a conventional identification regenerative repeater in a wavelength division multiplexing transmission system. In the figure, a wavelength division multiplexed signal light is input to an identification regeneration repeater 53 via an optical fiber transmission line 51 and an optical amplifier 52. The identification reproduction repeater 53 includes an optical demultiplexer 54, a plurality of identification reproduction circuits 55, and an optical multiplexer 56. The wavelength-division multiplexed signal light input to the discriminating / reproducing repeater 53 is split into signal lights of respective channels by the optical demultiplexer 54, discriminated and reproduced by the corresponding discriminating / regenerating circuits 55, and further multiplexed by the optical multiplexer 56. Then, it is output as a wavelength multiplexed signal light.
[0005]
As the identification and reproduction circuit 55, a method of converting an optical signal into an electric signal, performing identification and reproduction by an electronic circuit, and converting the optical signal into an optical signal again has been put to practical use. Also, a method of discriminating and reproducing an optical signal as it is has been studied. For example, a method using an optical control switch such as a Mach-Zehnder interferometer incorporating a semiconductor optical amplifier or a nonlinear loop mirror is known.
[0006]
On the other hand, a waveform shaping technique for reducing the intensity fluctuation of an optical signal has been proposed (Patent Document 1). Although this technique does not include a retiming function, it has a feature that the intensity noise of an optical signal can be suppressed with a simple configuration. Furthermore, a collective optical waveform shaping technique that applies this intensity noise suppression technique to multiple channels has been proposed (Japanese Patent Application No. 2001-197478). This principle will be described with reference to FIG.
[0007]
In FIG. 12, the conventional multi-channel collective optical waveform shaping circuit has a configuration in which an optical amplifier 11, a nonlinear optical fiber 12, a demultiplexing filter 13, and a multiplexing filter 14 are connected in cascade. The optical amplifier 11 has a gain band for collectively amplifying all channels of the wavelength multiplexed signal light. The nonlinear optical fiber 12 has a characteristic that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion. Each of the demultiplexing filter 13 and the multiplexing filter 14 has a discrete (periodic) transmission band including the center wavelength of the optical pulse signal of each channel. Performs a function equivalent to a set of bandpass filters corresponding to.
[0008]
Here, reference numerals 1 to 4 denote time waveforms of the wavelength multiplexed signal light, and reference numerals 5 to 7 denote spectrum waveforms corresponding to the wavelength multiplexed signal light 2 to 4. However, the time waveforms 1 to 4 show only the waveform of one channel of the wavelength multiplexed signal light. The waveforms of the other channels also change in the same manner as 1-4.
[0009]
The wavelength multiplexed signal light 1 is amplified by the optical amplifier 11 so that the peak power of the optical pulse signal of each channel is larger than the basic soliton power and equal to or less than twice the basic soliton power. When the amplified wavelength-division multiplexed signal light 2 (spectral waveform 5) is incident on the nonlinear optical fiber 12 longer than the soliton cycle, the intensity fluctuation of the optical pulse signal of each channel is changed to the fluctuation of the spectrum width by self-phase modulation. Is converted. However, since the incident peak power is close to the basic soliton power, the central part of the spectrum converges to a shape close to the basic soliton, and is input to the demultiplexing filter 13 as the wavelength multiplexed signal light 3 (spectral waveform 6).
[0010]
Since the center wavelength of the optical pulse signal of each channel is in the transmission band, the demultiplexing filter 13 cuts off the fluctuation of the spectral width of the wavelength-division multiplexed signal light 3 (spectral waveform 6) so that each optical pulse signal is initially It can remove the intensity fluctuations (noise) it had. The optical pulse signal of each channel from which the intensity noise has been removed is multiplexed by a multiplexing filter 14 similar to the demultiplexing filter 13 to be converted into a wavelength multiplexed signal light 4 (spectral waveform 7).
[0011]
[Patent Document 1]
JP-A-11-284261
[0012]
[Problems to be solved by the invention]
By the way, in the related art, when the channel spacing is narrowed, the influence of the interaction between channels due to the nonlinear optical effect such as the cross-phase modulation and the four-wave mixing in the nonlinear optical fiber becomes large, and the problem that the optical signal waveform is deteriorated occurs. there were. FIGS. 10A to 10C show examples of calculating the shaping state of the optical signal waveform.
[0013]
FIG. 10A shows an optical waveform of one channel of the wavelength multiplexed signal light before entering the nonlinear optical fiber (pulse width: 8 ps, bit rate: 40 Gbit / s). FIGS. 10B and 10C show the optical waveforms after passing through the optical waveform shaping circuit when the channel interval is set to 400 GHz and 200 GHz, respectively. When the channel interval is as wide as 400 GHz (FIG. 10 (b)), a good optical waveform shaping effect is observed. However, when the channel interval is reduced to 200 GHz (FIG. 10 (c)), the incident optical waveform (FIG. )). Therefore, in the related art, the channel interval cannot be set to a certain value or less, and it has been difficult to apply to a DWDM (Dence WDM) system in which channels are densely packed in an optical frequency (wavelength) region.
[0014]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-channel collective optical waveform shaping circuit that can collectively suppress the intensity noise component of each channel generated during transmission of wavelength multiplexed signal light in a DWDM system.
[0015]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an optical amplifier for amplifying a wavelength-division multiplexed signal light obtained by wavelength-divisionally multiplexing optical pulse signals of a plurality of channels with a channel interval of f, and an input of the amplified wavelength-division multiplexed signal light and an odd number of a channel interval of 2f. An optical splitter for separating a channel wavelength multiplexed signal light and an even channel wavelength multiplexed signal light, a first nonlinear optical fiber for inputting the odd channel wavelength multiplexed signal light and the even channel wavelength multiplexed signal light, and a second A first demultiplexing filter and a first demultiplexing filter for demultiplexing the wavelength-multiplexed signal light of the odd-numbered channels passed through the first non-linear optical fiber into optical pulse signals of the respective channels and re-multiplexing them. A filter, a second demultiplexing filter for demultiplexing the wavelength-multiplexed signal light of the even-numbered channels that has passed through the second nonlinear optical fiber into optical pulse signals of the respective channels, and re-multiplexing them. A second multiplexing filter, an odd channel wavelength multiplexed signal light from which the intensity noise output from the first multiplexing filter has been removed, and an even number from which the intensity noise output from the second multiplexing filter has been removed An optical multiplexer for multiplexing and outputting the wavelength-multiplexed signal light of the channel.
[0016]
According to a second aspect of the present invention, a wavelength-division multiplexed signal light obtained by wavelength-multiplexing optical pulse signals of a plurality of channels having a channel interval of f is input, and an odd-numbered wavelength-division multiplexed signal light and an even-numbered wavelength-division multiplexed signal light having a channel interval of 2f are input. , A first optical amplifier and a second optical amplifier for respectively amplifying the odd-numbered wavelength multiplexed signal light and the even-numbered wavelength multiplexed signal light, and the amplified odd-numbered wavelength multiplexed signal light A first nonlinear optical fiber and a second nonlinear optical fiber for inputting the wavelength-multiplexed signal light of the even-numbered channel, and a wavelength-multiplexed signal light of the odd-numbered channel that has passed through the first nonlinear optical fiber. A first demultiplexing filter and a first demultiplexing filter for demultiplexing and remultiplexing, and an even-numbered channel that has passed through a second nonlinear optical fiber. A second demultiplexing filter and a second demultiplexing filter for demultiplexing the multiplexed signal light into an optical pulse signal of each channel and re-demultiplexing, and an intensity noise output from the first demultiplexing filter are removed. An optical multiplexer is provided for multiplexing and outputting the wavelength-multiplexed signal light of the odd-numbered channel and the wavelength-multiplexed signal light of the even-numbered channel from which the intensity noise output from the second multiplexing filter has been removed.
[0017]
According to a third aspect of the present invention, there is provided an optical amplifier for amplifying a wavelength-division multiplexed signal light obtained by wavelength-divisionally multiplexing optical pulse signals of a plurality of channels with a channel interval of f, and an input of the amplified wavelength-division multiplexed signal light and an odd number of a channel interval of 2f. An optical splitter for separating a channel wavelength multiplexed signal light and an even channel wavelength multiplexed signal light, a first nonlinear optical fiber for inputting the odd channel wavelength multiplexed signal light and the even channel wavelength multiplexed signal light, and a second And the odd channel wavelength multiplexed signal light passing through the first nonlinear optical fiber and the even channel wavelength multiplexed signal light passing through the second nonlinear optical fiber are input to the optical pulse signal of each channel. A demultiplexing filter and a multiplexing filter for demultiplexing and multiplexing and outputting wavelength-division multiplexed signal light from which intensity noise has been removed are provided.
[0018]
According to a fourth aspect of the present invention, a wavelength-division multiplexed signal light obtained by wavelength-divisionally multiplexing optical pulse signals of a plurality of channels with a channel interval of f is input, and a wavelength-division multiplexed signal light of an odd-numbered channel and a wavelength-division multiplexed signal light of an even-numbered channel with a channel interval of 2f. , A first optical amplifier and a second optical amplifier for respectively amplifying the odd-numbered wavelength multiplexed signal light and the even-numbered wavelength multiplexed signal light, and the amplified odd-numbered wavelength multiplexed signal light A first non-linear optical fiber and a second non-linear optical fiber for inputting the wavelength-multiplexed signal light of the even-numbered channels, and a predetermined transmission band including the center wavelength of the optical pulse signal of each channel at a channel interval f; Wavelength multiplexed signal light of odd channels passed through the first nonlinear optical fiber and wavelength multiplexed signal light of even channels passed through the second nonlinear optical fiber Enter a, it comprises the channels again multiplexes with demultiplexed into optical pulse signal, and demultiplexing filter and multiplexing filter outputs a wavelength-multiplexed signal light intensity noise has been removed.
[0019]
Further, in the multi-channel collective optical waveform shaping circuit according to any one of claims 1 to 4, the power of the optical pulse signal of each channel is monitored, and the optical pulse signal of the odd channel and the even channel incident on each nonlinear optical fiber. May be provided with an optical power control means for controlling the peak power to be larger than the basic soliton power and not more than twice the basic soliton power.
[0020]
Further, in the multi-channel collective optical waveform shaping circuit according to any one of claims 1 to 4, the wavelength multiplexed signal light of the input of the nonlinear optical fiber, the output of the nonlinear optical fiber, or the output of the multiplexing filter is input. Using an optical spectrum analyzer that detects the power of the optical pulse signal of each channel, the peak power of the optical pulse signals of the odd and even channels incident on each nonlinear optical fiber is larger than the basic soliton power, and the peak power of the basic soliton power is 2 An optical power control means for controlling the power to be twice or less may be provided (claim 6).
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
<First Embodiment: Claim 1>
FIG. 1 shows a multi-channel collective optical waveform shaping circuit according to a first embodiment of the present invention. Here, it is assumed that the number of multiplexed channels of the wavelength multiplexed signal light is 2 m and the channel interval is f.
[0022]
In the figure, wavelength multiplexed signal light obtained by wavelength multiplexing optical pulse signals of a plurality of channels with a channel interval f is amplified by an optical amplifier 11, and the amplified wavelength multiplexed signal light is split by an optical demultiplexer 15 into an odd channel and an even channel with a channel interval 2f. The optical signals are separated into channels, and are input to nonlinear optical fibers 12-1 and 12-2 having a characteristic that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion.
[0023]
The optical amplifier 11 amplifies the separated optical pulse signals of the odd-numbered and even-numbered channels so that the peak power is greater than the basic soliton power and equal to or less than twice the basic soliton power. In the nonlinear optical fibers 12-1 and 12-2, the intensity fluctuation of the optical pulse signal is converted into the fluctuation of the spectrum spread by the self-phase modulation. However, since the incident peak power is close to the basic soliton power, the central part of the spectrum is basically changed. It converges to a shape close to solitons. At this time, since the channel interval is 2f, which is twice the original wavelength multiplexed signal light, interference between channels due to nonlinear optical effects such as cross-phase modulation and four-wave mixing can be reduced.
[0024]
The wavelength-multiplexed signal light of the odd channel output from the nonlinear optical fiber 12-1 is input to the demultiplexing filter 13-1 having a predetermined transmission band (channel interval 2f) including the center wavelength of the optical pulse signal of the odd channel. You. The splitter filter 13-1 can remove the intensity fluctuation (noise) of the original optical path by cutting off the fluctuation of the spectrum spread of the odd channel. The odd-numbered channel optical pulse signal from which the noise has been removed is multiplexed by the multiplexing filter 14-1 having the same transmission band (channel interval 2f) as the demultiplexing filter 13-1, and becomes a wavelength-multiplexed signal light of the odd-numbered channel. Is output.
[0025]
Similarly, the wavelength multiplexed signal light of the even-numbered channels output from the nonlinear optical fiber 12-2 is output after the noise is removed by the demultiplexing filter 13-2 and the multiplexing filter 14-2 (not shown in the drawing).
[0026]
The wavelength-multiplexed signal light of the odd-numbered channel and the wavelength-multiplexed signal light of the even-numbered channel output from the multiplexing filters 14-1 and 14-2 are multiplexed by the optical multiplexer 16, and output as the wavelength-multiplexed signal light having the channel interval f. .
[0027]
FIG. 10D shows an output optical waveform obtained by shaping the waveform of the wavelength multiplexed signal light having a channel interval of 200 GHz by the configuration of the present invention. In the conventional configuration, when the channel interval is 200 GHz, the waveform is deteriorated as shown in FIG. 10C, but it can be seen that the waveform can be shaped by the present invention.
[0028]
In addition, as the optical separator 15, for example, an interleave filter or a Mach-Zehnder optical filter can be used. As the demultiplexing filter 13 and the multiplexing filter 14, for example, an arrayed waveguide diffraction grating (AWG) filter can be used. As the optical multiplexer 16, for example, an optical coupler can be used in addition to an interleave filter and a Mach-Zehnder optical filter.
[0029]
<Second embodiment: Claims 1 and 5>
FIG. 2 shows a second embodiment of the multi-channel collective optical waveform shaping circuit of the present invention. In the present embodiment, in addition to the configuration of the first embodiment, the power of the optical pulse signal of each channel is monitored, and the optical pulses of the odd channel and the even channel incident on the nonlinear optical fibers 12-1 and 12-2. Optical power control means for controlling the peak power of the signal so as to be higher than the basic soliton power and not more than twice the basic soliton power is provided.
[0030]
The optical power control means is realized by the following configuration. The optical amplifier 11 includes an erbium-doped optical fiber 21, a pump light source 22 for generating pump light, an optical multiplexer 23 for multiplexing the wavelength multiplexed signal light and the pump light and entering the erbium-doped optical fiber 21, It is composed of optical isolators 24-1 and 24-2 arranged at the ends. Further, an equalizer 31 disposed at the output stage of the optical amplifier 11, an optical coupler 32-1 to 32-m disposed between the demultiplexing filter 13-1 and the multiplexing filter 14-1, Photodetectors 33-1 to 33-m for detecting optical powers of odd channels branched by the coupler are provided. An optical coupler is similarly arranged between the demultiplexing filter 13-2 and the multiplexing filter 14-2 for an even-numbered channel (not shown), and a photodetector is provided. The control circuit 34 controls the excitation light source 22 and / or the equalizer 31 according to the detection result of each photodetector, and outputs the optical pulse signal of each channel to be input to the nonlinear optical fibers 12-1 and 12-2. Is set to be larger than the basic soliton power and equal to or less than twice the basic soliton power.
[0031]
<Third Embodiment: Claims 1 and 6>
FIG. 3 shows a third embodiment of the multi-channel collective optical waveform shaping circuit of the present invention. The feature of the present embodiment resides in that an optical spectrum analyzer is used instead of the photodetector corresponding to each channel in the second embodiment. Other configurations are the same as those of the second embodiment.
[0032]
Here, an optical coupler 35 for splitting the wavelength-multiplexed signal light at the input of the nonlinear optical fiber 12-1, the output of the nonlinear optical fiber 12-1, or the output of the multiplexing filter 14-1, and the optical coupler. An optical spectrum analyzer 36-1 for detecting each optical power of an odd channel is used. The same applies to the configuration on the even channel side. The control circuit 34 controls the pumping light source 22 and / or the equalizer 31 according to the detection results of the optical spectrum analyzers 36-1 and 36-2, and controls the nonlinear optical fibers 12-1 and 12-2. The peak power of the input optical pulse signal of each channel is set to be larger than the basic soliton power and equal to or less than twice the basic soliton power.
[0033]
Further, the output side of the optical multiplexer 16 may be monitored. In this case, the optical power of each channel is detected by one optical spectrum analyzer 36 and notified to the control circuit 34.
[0034]
<Fourth embodiment: Claims 2 and 5>
FIG. 4 shows a multi-channel collective optical waveform shaping circuit according to a fourth embodiment of the present invention. The feature of this embodiment lies in that, in the second embodiment, the wavelength division multiplexed signal light having the channel interval f is first separated by the optical separator 15 into the wavelength multiplexed signal light of the odd channel and the even channel having the channel interval 2f.
[0035]
That is, the wavelength-division multiplexed signal light having the channel interval f is separated by the optical separator 15 into odd and even channels having the channel interval 2f, and the wavelength-division multiplexed signal light having the odd channel is amplified by the optical amplifier 11-1 and further equalized. The signal is input to the nonlinear optical fiber 12-1 having a property that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion via the optical device 31-1. Similarly, the wavelength multiplexed signal light of the even-numbered channel is input to the nonlinear optical fiber (12-2) via the optical amplifier (11-2) and the optical equalizer (31-2) not shown. Other configurations and operations are the same as those of the second embodiment.
[0036]
<Fifth embodiment: Claims 2 and 6>
FIG. 5 shows a fifth embodiment of the multi-channel collective optical waveform shaping circuit of the present invention. The feature of this embodiment lies in that an optical spectrum analyzer is used instead of the photodetector corresponding to each channel in the fourth embodiment. Other configurations are the same as those of the fourth embodiment.
[0037]
Here, an optical coupler 35 for splitting the wavelength-multiplexed signal light at the input of the nonlinear optical fiber 12-1, the output of the nonlinear optical fiber 12-1, or the output of the multiplexing filter 14-1, and the optical coupler. An optical spectrum analyzer 36-1 for detecting each optical power of an odd channel is used. The control circuit 34-1 controls the pumping light source 22 and / or the equalizer 31-1 of the optical amplifier 11-1 or both according to the detection result of the optical spectrum analyzer 36-1, and controls the nonlinear optical fiber 12-1. Is set so that the peak power of the optical pulse signal of the odd-numbered channel to be input is larger than the basic soliton power and equal to or less than twice the basic soliton power. The same applies to the configuration on the even channel side.
[0038]
The output side of the optical multiplexer 16 may be monitored. In this case, the optical power of each channel is detected by one optical spectrum analyzer 36, and the control circuit 34-1 for the odd channel and the control circuit for the even channel are used. (34-2).
[0039]
<Sixth embodiment: Claims 3 and 5>
FIG. 6 shows a sixth embodiment of the multi-channel collective optical waveform shaping circuit according to the present invention.
In the second embodiment, a demultiplexing filter 13-1 and a multiplexing filter 14-1 for odd channels and a demultiplexing filter (13-2) and a multiplexing filter (14-2) for even channels are individually provided. The wavelength multiplexed signal light of the odd channel and the wavelength multiplexed signal of the even channel are multiplexed by the optical multiplexer 16. A feature of the present embodiment resides in that one set of the demultiplexing filter 13 and the multiplexing filter 14 is used instead of the two sets of the demultiplexing filters and the multiplexing filters and the optical multiplexers corresponding to the odd and even channels. .
[0040]
The demultiplexing filter 13 uses, for example, a two-input AWG filter, and demultiplexes the odd-numbered channel wavelength multiplexed signal light output from the nonlinear optical fiber 12-1 to the ports 1-1, 1-2,..., 1-m. , 2-m wavelength-multiplexed signal light output from the nonlinear optical fiber 12-2 to the ports 2-1, 2-2,..., 2-m. The multiplexing filter 14 uses, for example, an AWG filter, and is connected to the ports 1-1, 2-1, 1-2, 2-2,... The optical pulse signals of the channels and the even channels can be multiplexed. Other configurations and operations are the same as those of the second embodiment.
[0041]
<Seventh Embodiment: Claims 3 and 6>
FIG. 7 shows a multi-channel collective optical waveform shaping circuit according to a seventh embodiment of the present invention. The feature of this embodiment lies in that an optical spectrum analyzer is used instead of the photodetector corresponding to each channel in the sixth embodiment. Other configurations are the same as in the sixth embodiment.
[0042]
Here, an optical coupler 35 for splitting the wavelength multiplexed signal light at the input of the nonlinear optical fiber 12-1 or the output of the nonlinear optical fiber 12-1, and a light for detecting each optical power of the odd channel split by the optical coupler. The spectrum analyzer 36-1 is used. The same applies to the configuration on the even channel side. The control circuit 34 controls the pump light source 22 and / or the equalizer 31 according to the detection results of the optical spectrum analyzers 36-1 and 36-2, and inputs the same to the nonlinear optical fibers 12-1 and 12-2. The peak power of the optical pulse signal of each channel is set to be larger than the basic soliton power and equal to or less than twice the basic soliton power.
[0043]
Further, the output side of the multiplexing filter 14 may be monitored. In that case, the optical power of each channel is detected by one optical spectrum analyzer 36 and notified to the control circuit 34.
[0044]
<Eighth Embodiment: Claims 4 and 5>
FIG. 8 shows an eighth embodiment of the multi-channel collective optical waveform shaping circuit of the present invention. The feature of this embodiment is that, in the sixth embodiment, first, the wavelength division multiplexed signal light having the channel interval f is separated by the optical separator 15 into the wavelength multiplexed signal light of the odd channel and the even channel having the channel interval 2f.
[0045]
That is, the wavelength-division multiplexed signal light having the channel interval f is separated by the optical separator 15 into odd and even channels having the channel interval 2f, and the wavelength-division multiplexed signal light having the odd channel is amplified by the optical amplifier 11-1 and further equalized. The signal is input to the nonlinear optical fiber 12-1 having a property that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion via the optical device 31-1. Similarly, the wavelength multiplexed signal light of the even-numbered channel is input to the nonlinear optical fiber (12-2) via the optical amplifier (11-2) and the optical equalizer (31-2) not shown. Other configurations and operations are the same as in the sixth embodiment.
[0046]
<Ninth embodiment: Claims 4 and 6>
FIG. 9 shows a ninth embodiment of the multi-channel collective optical waveform shaping circuit of the present invention. The feature of this embodiment resides in that an optical spectrum analyzer is used instead of the photodetector corresponding to each channel in the eighth embodiment. Other configurations are the same as those of the eighth embodiment.
[0047]
Here, an optical coupler 35 for splitting the wavelength-multiplexed signal light input to the nonlinear optical fiber 12-1 or the output of the nonlinear optical fiber 12-1 and a light for detecting each optical power of the odd channel split by the optical coupler. The spectrum analyzer 36-1 is used. The control circuit 34-1 controls the pumping light source 22 and / or the equalizer 31-1 of the optical amplifier 11-1 according to the detection result of the optical spectrum analyzer 36-1, and controls the nonlinear optical fiber 12-1. Is set so that the peak power of the optical pulse signal of the odd-numbered channel to be input is larger than the basic soliton power and equal to or less than twice the basic soliton power. The same applies to the configuration on the even channel side.
[0048]
In addition, the output side of the multiplexing filter 14 may be monitored. In this case, the optical power of each channel is detected by one optical spectrum analyzer 36, and the control circuit 34-1 for the odd channel and the control circuit for the even channel are used. (34-2).
[0049]
【The invention's effect】
As described above, the multi-channel collective optical waveform shaping circuit of the present invention has a simple configuration that does not include the identification and reproduction circuit, and converts the intensity noise superimposed on the wavelength multiplexed signal light into the fluctuation of the spectral width for each channel. By converting and filtering, the intensity noise of the wavelength multiplexed signal light can be removed at once. In particular, by dividing the signal into odd channels and even channels and performing the above processing, it is possible to collectively remove the intensity noise of the wavelength multiplexed signal light that has been wavelength multiplexed at high density.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 2 is a block diagram showing a second embodiment of the present invention.
FIG. 3 is a block diagram showing a third embodiment of the present invention.
FIG. 4 is a block diagram showing a fourth embodiment of the present invention.
FIG. 5 is a block diagram showing a fifth embodiment of the present invention.
FIG. 6 is a block diagram showing a sixth embodiment of the present invention.
FIG. 7 is a block diagram showing a seventh embodiment of the present invention.
FIG. 8 is a block diagram showing an eighth embodiment of the present invention.
FIG. 9 is a block diagram showing a ninth embodiment of the present invention.
FIG. 10 is a diagram showing experimental results of a conventional configuration and a configuration of the present invention.
FIG. 11 is a diagram showing a configuration example of a conventional identification regeneration repeater in a wavelength division multiplexing transmission system.
FIG. 12 is a diagram illustrating a conventional optical waveform shaping technique for reducing the intensity fluctuation of the wavelength multiplexed signal light.
[Explanation of symbols]
11 Optical amplifier
12 Nonlinear optical fiber
13 Demultiplexing filter
14 Combining filter
15 Optical separator
16 Optical multiplexer
21 Erbium-doped optical fiber
22 Excitation light source
23 Optical multiplexer
24 Optical Isolator
31 Equalizer
32 optical coupler
33 Photodetector
34 control circuit
35 Optical coupler
36 Optical Spectrum Analyzer

Claims

An optical amplifier for amplifying a wavelength-multiplexed signal light obtained by wavelength-multiplexing optical pulse signals of a plurality of channels at a channel interval f;
An optical separator that receives the wavelength-multiplexed signal light amplified by the optical amplifier and separates the wavelength-multiplexed signal light into odd-numbered channel light and even-numbered channel wavelength-multiplexed signal light with a channel interval of 2f;
A first nonlinear optical fiber having a characteristic that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion, and the wavelength-multiplexed signal light of the odd-numbered channel and the wavelength-multiplexed signal light of the even-numbered channel are input; Two nonlinear optical fibers,
It has a predetermined transmission band including the center wavelength of the optical pulse signal of the odd-numbered channel, and wavelength-division multiplexed signal light of the odd-numbered channel that has passed through the first nonlinear optical fiber is demultiplexed into an optical pulse signal of each channel and re-divided. A first demultiplexing filter and a first multiplexing filter that multiplex;
It has a predetermined transmission band including the center wavelength of the optical pulse signal of the even-numbered channel, and the wavelength-multiplexed signal light of the even-numbered channel that has passed through the second nonlinear optical fiber is demultiplexed into an optical pulse signal of each channel and re-divided. A second demultiplexing filter and a second multiplexing filter for multiplexing,
Odd-numbered channel wavelength multiplexed signal light output from the first multiplexing filter from which intensity noise has been removed, and even-numbered channel wavelength multiplexed signal light output from the second multiplexing filter from which intensity noise has been removed. And an optical multiplexer for multiplexing and outputting the signals.

An optical separator for inputting wavelength multiplexed signal light obtained by wavelength multiplexing optical pulse signals of a plurality of channels at a channel interval f, and separating the wavelength multiplexed signal light of odd channels and the wavelength multiplexed signal light of even channels at a channel interval of 2f;
A first optical amplifier and a second optical amplifier for amplifying the odd-numbered channel wavelength multiplexed signal light and the even-numbered channel wavelength multiplexed signal light, respectively;
The fiber length is longer than the soliton period, the average chromatic dispersion has a characteristic of anomalous dispersion, and the wavelength multiplexed signal light of the odd channel amplified by the first optical amplifier and amplified by the second optical amplifier. A first nonlinear optical fiber and a second nonlinear optical fiber for inputting the wavelength-multiplexed signal lights of the even channels, respectively;
It has a predetermined transmission band including the center wavelength of the optical pulse signal of the odd-numbered channel, and wavelength-division multiplexed signal light of the odd-numbered channel that has passed through the first nonlinear optical fiber is demultiplexed into an optical pulse signal of each channel and re-divided. A first demultiplexing filter and a first multiplexing filter that multiplex;
It has a predetermined transmission band including the center wavelength of the optical pulse signal of the even-numbered channel, and the wavelength-multiplexed signal light of the even-numbered channel that has passed through the second nonlinear optical fiber is demultiplexed into an optical pulse signal of each channel and re-divided. A second demultiplexing filter and a second multiplexing filter for multiplexing,
Odd-numbered channel wavelength multiplexed signal light output from the first multiplexing filter from which intensity noise has been removed, and even-numbered channel wavelength multiplexed signal light output from the second multiplexing filter from which intensity noise has been removed. And an optical multiplexer for multiplexing and outputting the signals.

An optical amplifier for amplifying a wavelength-multiplexed signal light obtained by wavelength-multiplexing optical pulse signals of a plurality of channels at a channel interval f;
An optical separator that receives the wavelength-multiplexed signal light amplified by the optical amplifier and separates the wavelength-multiplexed signal light into odd-numbered channel light and even-numbered channel wavelength-multiplexed signal light with a channel interval of 2f;
A first nonlinear optical fiber having a characteristic that the fiber length is longer than the soliton period and the average chromatic dispersion becomes anomalous dispersion, and the wavelength-multiplexed signal light of the odd-numbered channel and the wavelength-multiplexed signal light of the even-numbered channel are input; Two nonlinear optical fibers,
It has a predetermined transmission band including the center wavelength of the optical pulse signal of each channel at the channel interval f, and the wavelength-division multiplexed signal light of the odd channel and the second nonlinear optical fiber that have passed through the first nonlinear optical fiber. A wavelength division multiplexing signal light of the even-numbered channel that has passed is input, demultiplexed into an optical pulse signal of each channel and multiplexed again, and a demultiplexing filter and a multiplexing filter for outputting the wavelength multiplexing signal light from which the intensity noise has been removed are provided. A multi-channel collective optical waveform shaping circuit comprising:

An optical separator for inputting wavelength multiplexed signal light obtained by wavelength multiplexing optical pulse signals of a plurality of channels at a channel interval f, and separating the wavelength multiplexed signal light of odd channels and the wavelength multiplexed signal light of even channels at a channel interval of 2f;
A first optical amplifier and a second optical amplifier for amplifying the odd-numbered channel wavelength multiplexed signal light and the even-numbered channel wavelength multiplexed signal light, respectively;
The fiber length is longer than the soliton period, the average chromatic dispersion has a characteristic of anomalous dispersion, and the wavelength multiplexed signal light of the odd channel amplified by the first optical amplifier and amplified by the second optical amplifier. A first nonlinear optical fiber and a second nonlinear optical fiber for inputting the wavelength-multiplexed signal lights of the even channels, respectively;
It has a predetermined transmission band including the center wavelength of the optical pulse signal of each channel at the channel interval f, and the wavelength-division multiplexed signal light of the odd channel and the second nonlinear optical fiber that have passed through the first nonlinear optical fiber. A wavelength division multiplexing signal light of the even-numbered channel that has passed is input, demultiplexed into an optical pulse signal of each channel and multiplexed again, and a demultiplexing filter and a multiplexing filter for outputting the wavelength multiplexing signal light from which the intensity noise has been removed are provided. A multi-channel collective optical waveform shaping circuit comprising:

The multi-channel collective optical waveform shaping circuit according to claim 1,
The power of the optical pulse signal of each channel is monitored, and the peak powers of the optical pulse signals of the odd-numbered and even-numbered channels incident on each of the nonlinear optical fibers are larger than the basic soliton power and less than twice the basic soliton power. 1. A multi-channel collective optical waveform shaping circuit, comprising: an optical power control means for controlling the optical waveform shaping.

The multi-channel collective optical waveform shaping circuit according to claim 1,
The input of the nonlinear optical fiber, or the output of the nonlinear optical fiber, or the input of the wavelength multiplexed signal light of the output of the multiplexing filter, using an optical spectrum analyzer to detect the power of the optical pulse signal of each channel, Optical power control means for controlling the peak power of the optical pulse signals of the odd and even channels incident on the nonlinear optical fiber to be higher than the basic soliton power and equal to or less than twice the basic soliton power. Multi-channel collective optical waveform shaping circuit.