JP3727520B2

JP3727520B2 - WDM transmission system

Info

Publication number: JP3727520B2
Application number: JP2000240058A
Authority: JP
Inventors: 章平野; 明秀佐野; 宮本　　裕; 一茂米永
Original assignee: Nippon Telegraph and Telephone Corp; NTT Inc USA
Current assignee: NTT Inc; NTT Inc USA
Priority date: 2000-08-08
Filing date: 2000-08-08
Publication date: 2005-12-14
Anticipated expiration: 2020-08-08
Also published as: JP2002057623A

Description

【０００１】
【発明の属する技術分野】
本発明は、光波長多重伝送における広い帯域を有する光ファイバ等の伝送路の持つ群速度分散および分散スロープあるいはこれと非線形光学効果との相互作用による伝送品質の劣化を抑圧する群速度分散および分散スロープ補償技術に関する。
【０００２】
【従来の技術】
光伝送システムでは、その伝送媒体である光ファイバの持つ波長分散あるいはこれと光ファイバの持つ非線形光学効果の相互作用による波形劣化に起因する伝送品質の劣化が問題となる。これは光ファイバの持つ群速度分散が光信号の持つ帯域幅に作用することによりその光パルスの形が崩れ、隣接タイムスロットとの間で干渉することにより起こる。これを防ぐために種々の分散補償技術が提案されている。
【０００３】
特に、広い波長帯域を使用する波長多重伝送システムでは、ある波長に対して群速度分散を補償しても光ファイバ自身が持つ群速度分散の波長に対する依存性、つまり分散スロープの影響で、異なる波長の信号に対しては群速度分散が残存する。このため、波長によって群速度分散が十分補償されないチャネルが発生し、伝送品質の劣化あるいは伝送不可となる。
【０００４】
この問題を解消するために、ＡＷＧ(Arrayed-Waveguide-Grating)分波器で各チャネルを分波し、それぞれのチャネルに波長に依存したスロープ分の補正を加えた分散補償ファイバを挿入することで各チャネルを均等に分散補償し、再びＡＷＧ合波器で合波する方式の分散および分散スロープ補償回路が提案されている「Long-distance WDM transmission experiment using the dispersion slope compensator;H.Taga etal,;IEEE JLT,Vol.34,No.11,1998」。
【０００５】
【発明が解決しようとする課題】
しかし、この方式では分散および分散スロープを補償する度に、波長多重化した光信号を一度分波し、それぞれのチャネルを補償した後、再度合波するプロセスが加わる。この合分波の際に用いられるＡＷＧ合分波器は、その通過の際に各波長の光信号に対してガウシアンあるいはその組み合わせの透過プロファイルの帯域制限が加わる。この帯域制限を受けた光信号は、その信号成分の一部を切り取られるためにその光波形が劣化する。
【０００６】
波長多重伝送システムでは、光合波器および光分波器を少なくとも２回（送信および受信側）通過するがこの劣化が十分小さなものとなるよう設計されている。ところが、従来は、波長分散および分散スロープの補償を行う度にＡＷＧ合分波器を通過することになり、これによる帯域制限がさらに２回分加わる。多中継の光波長多重システムでは、この補償回路の数がさらに増加する。この帯域制限が多数回加わると、それらの効果は積算されるために深刻な伝送品質の劣化を引き起こす。また、従来は、分散補償ファイバモジュールが合分波数分だけ必要となるためにコストや所用スペースが増加し、システム構築上の大きなデメリットとなる。
【０００７】
本発明は、このような背景に行われたものであって、光合分波手段による帯域制限に起因する光信号の品質劣化が起こり難く、また構成品点数も低減でき、低コストで高品質な波長多重伝送システムを提供することを目的とする。本発明は、光ファイバ中の非線形光学効果の累積と波長分散の相互作用による伝送品質の劣化に対しても強い特徴を持つ波長多重伝送システムを提供することを目的とする。本発明は、従来の群遅延が補償される波長多重伝送システムに比較し、より長距離かつ大容量な光伝送システムを高信頼に構築することができる波長多重伝送システムを提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明の波長多重伝送システムは、上記問題点を解決するために、伝送路である光ファイバ中の群速度分散および分散スロープを波長多重光信号を分波することなしに補償する群速度分散および分散スロープ補償回路を構成することを特徴とする。
【０００９】
すなわち、本発明は、それぞれ波長の異なる光信号を送信するＮ個の光送信器と、このＮ個の光送信器の光信号を合波する手段と、この合波する手段によって合波された波長多重光信号を伝送する光伝送媒体と、この光伝送媒体によって伝送された波長多重光信号を分波する手段と、この分波する手段によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器とを備えた波長多重伝送システムである。
【００１０】
ここで、本発明の特徴とするところは、前記光伝送媒体と前記分波する手段との間には、前記波長多重光信号が前記光伝送媒体の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散補償手段と、前記波長多重光信号が前記光伝送媒体の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する分散スロープ補償手段とを備えたところにある。
【００１１】
あるいは、前記光伝送媒体と前記分波する手段との間には、前記波長多重光信号が前記光伝送媒体の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散および分散スロープ補償手段を備えた構成とすることもできる。
【００１２】
これにより、従来は補償の度毎にＡＷＧ合分波器を通過することによる帯域制限の効果で引き起こされていた光信号の品質劣化を大きく低減することができる。
【００１３】
さらに、従来は多品種必要であった分散補償ファイバが不要もしくは１本となり、光伝送システムの簡易化および低コスト化を実現できる。
【００１４】
また、本発明の別の構成は、それぞれ波長の異なる光信号を送信するＮ個の光送信器と、このＮ個の光送信器の光信号を合波する手段と、この合波する手段によって合波された波長多重光信号を伝送する第一および第二の光伝送媒体と、この第一および第二の光伝送媒体の間に介挿された光増幅手段と、この第一および第二の光伝送媒体によって伝送された波長多重光信号を分波する手段と、この分波する手段によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器とを備えた波長多重伝送システムである。
【００１５】
ここで、本発明の特徴とするところは、前記第一の光伝送媒体と前記光増幅手段との間には、前記波長多重光信号が前記第一の光伝送媒体の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第一の波長分散補償手段と、前記波長多重光信号が前記第一の光伝送媒体の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第一の分散スロープ補償手段とを備え、前記第二の光伝送媒体と前記分波する手段との間には、前記波長多重光信号が前記第二の光伝送媒体の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第二の波長分散補償手段と、前記波長多重光信号が前記第二の光伝送媒体の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第二の分散スロープ補償手段とを備えたところにある。
【００１６】
この構成では、前記波長分散補償手段およびまたは前記分散スロープ補償手段には、前記波長多重光信号が前記光伝送媒体の群遅延特性により生じるチャネル間の相対遅延であるウォークオフについてはこれを無補償とする手段を備えることが望ましい。
【００１７】
あるいは、前記第一の光伝送媒体と前記光増幅手段との間には、前記波長多重光信号が前記第一の光伝送媒体の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第一の波長分散および分散スロープ補償手段を備え、前記第二の光伝送媒体と前記分波する手段との間には、前記波長多重光信号が前記第二の光伝送媒体の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する第二の波長分散および分散スロープ補償手段を備えた構成とすることもできる。
【００１８】
この構成では、前記波長分散および分散スロープ補償手段には、前記波長多重光信号が前記光伝送媒体の群遅延特性により生じるチャネル間の相対遅延であるウォークオフについてはこれを無補償とする手段を備えることが望ましい。
【００１９】
このように、各波長間での群遅延に伴うウォークオフを補償しないために波長多重信号の多中継伝送において特に問題となる群速度分散および分散スロープと光非線形光学効果の相互作用の累積が緩和される。すなわち、ウォークオフを補償する場合に比べて伝送品質および距離を大きく向上させることが出来る。
【００２０】
例えば、前記波長分散補償手段は、分散補償ファイバを備え、前記分散スロープ補償手段は、時空間光処理型分散スロープ補償回路を備えることにより実現できる。また、前記波長分散および分散スロープ補償手段は、時空間光処理型分散スロープ補償回路を備えることにより実現できる。
【００２１】
【発明の実施の形態】
本発明実施例の波長多重伝送システムの構成を図１、図３、図４、図６、図７を参照して説明する。図１は本発明第一実施例の波長多重伝送システムの全体構成図である。図３は本発明第二実施例の波長多重伝送システムの全体構成図である。図４は本発明第三実施例の波長多重伝送システムの全体構成図である。図６は本発明第四実施例の波長多重伝送システムの全体構成図である。図７は本発明第五実施例の波長多重伝送システムの全体構成図である。
【００２２】
本発明第一実施例は、図１に示すように、それぞれ波長の異なる光信号を送信するＮ個の光送信器１−１〜１−Ｎと、このＮ個の光送信器１−１〜１−Ｎの光信号を合波する光合波器２と、この光合波器２によって合波された波長多重光信号を伝送する光伝送媒体３と、この光伝送媒体３によって伝送された波長多重光信号を分波する光分波器４と、この光分波器４によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器５−１〜５−Ｎとを備えた波長多重伝送システムである。
【００２３】
ここで、本発明の特徴とするところは、光伝送媒体３と光分波器４との間には、前記波長多重光信号が光伝送媒体３の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散補償器６と、前記波長多重光信号が光伝送媒体３の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する分散スロープ補償器７とを備えたところにある。
【００２４】
本発明第二実施例は、図３に示すように、それぞれ波長の異なる光信号を送信するＮ個の光送信器１−１〜１−Ｎと、このＮ個の光送信器１−１〜１−Ｎの光信号を合波する光合波器２と、この光合波器２によって合波された波長多重光信号を伝送する光伝送媒体３と、この光伝送媒体３によって伝送された波長多重光信号を分波する光分波器４と、この光分波器４によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器５−１〜５−Ｎとを備えた波長多重伝送システムである。
【００２５】
ここで、本発明の特徴とするところは、光伝送媒体３と光分波器４との間には、前記波長多重光信号が光伝送媒体３の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散および分散スロープ補償器８を備えたところにある。
【００２６】
本発明第三実施例は、図４に示すように、それぞれ波長の異なる光信号を送信するＮ個の光送信器１−１〜１−Ｎと、このＮ個の光送信器１−１〜１−Ｎの光信号を合波する光合波器２と、この光合波器２によって合波された波長多重光信号を伝送する光伝送媒体３−１および３−２と、この光伝送媒体３−１および３−２の間に介挿された光増幅器９と、この光伝送媒体３−１および３−２によって伝送された波長多重光信号を分波する光分波器４と、この光分波器４によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器５−１〜５−Ｎとを備えた波長多重伝送システムである。
【００２７】
ここで、本発明の特徴とするところは、光伝送媒体３−１と光増幅器９との間には、前記波長多重光信号が光伝送媒体３−１の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散補償器６−１と、前記波長多重光信号が光伝送媒体３−１の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する群遅延無補償型分散スロープ補償器１０−１とを備え、光伝送媒体３−２と光分波器４との間には、前記波長多重光信号が光伝送媒体３−２の群速度分散特性により受ける影響を前記波長多重光信号単位で補償する特性を有する波長分散補償器６−２と、前記波長多重光信号が光伝送媒体３−２の分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する群遅延無補償型分散スロープ補償器１０−２とを備えたところにある。
【００２８】
群遅延無補償型分散スロープ補償器１０−１、１０−２は、前記波長多重光信号が光伝送媒体３−１、３−２の群遅延特性により生じるチャネル間の相対遅延であるウォークオフについてはこれを無補償とする。
【００２９】
また、図６に示すように、本発明第四実施例では、本発明第三実施例の波長分散補償器６−１、６−２、群遅延無補償型分散スロープ補償器１０−１、１０−２の代わりに群遅延無補償型波長分散補償器１１−１、１１−２、分散スロープ補償器７−１、７−２を用い、群遅延無補償型波長分散補償器１１−１、１１−２は、前記波長多重光信号が光伝送媒体３−１、３−２の群遅延特性により受けるウォークオフについてはこれを無補償とする。
【００３０】
本発明第五実施例は、図７に示すように、それぞれ波長の異なる光信号を送信するＮ個の光送信器１−１〜１−Ｎと、このＮ個の光送信器１−１〜１−Ｎの光信号を合波する光合波器２と、この光合波器２によって合波された波長多重光信号を伝送する光伝送媒体３−１および３−２と、この光伝送媒体３−１および３−２の間に介挿された光増幅器９と、この光伝送媒体３−１および３−２によって伝送された波長多重光信号を分波する光分波器４と、この光分波器４によって分波されたそれぞれ波長の異なるＮ個の光信号を受信するＮ個の光受信器５−１〜５−Ｎとを備えた波長多重伝送システムである。
【００３１】
ここで、本発明の特徴とするところは、光伝送媒体３−１と光増幅器９との間には、前記波長多重光信号が光伝送媒体３−１の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する群遅延無補償型波長分散および分散スロープ補償器１２−１を備え、光伝送媒体３−２と光分波器４との間には、前記波長多重光信号が光伝送媒体３−２の群速度分散特性および分散スロープ特性により受ける影響を前記波長多重光信号単位で補償する特性を有する群遅延無補償型波長分散および分散スロープ補償器１２−２を備えたところにある。
【００３２】
群遅延無補償型波長分散および分散スロープ補償器１２−１および１２−２は、前記波長多重光信号が光伝送媒体３−１および３−２の群遅延特性により生じるチャネル間の相対遅延であるウォークオフについてはこれを無補償とする。
【００３３】
本発明第一、第三、第四実施例の波長分散補償器６、６−１、６−２、群遅延無補償型波長分散補償器１１−１、１１−２は、分散補償ファイバを備え、分散スロープ補償器７、７−１、７−２、群遅延無補償型分散スロープ補償器１０−１、１０−２は、時空間光処理型分散スロープ補償回路を備える。
【００３４】
本発明第二、第五実施例の波長分散および分散スロープ補償器８、群遅延無補償型波長分散および分散スロープ補償器１２−１、１２−２は、時空間光処理型分散スロープ補償回路を備える。
【００３５】
以下では、本発明実施例をさらに詳細に説明する。
【００３６】
（第一実施例）
本発明第一実施例の波長多重伝送システムは、波長＃１の光送信器１−１から波長＃Ｎの光送信者器１−Ｎまで、合計Ｎ個の光送信器１−１〜１−Ｎと、これらＮ種の光波長を持つ光信号を波長多重化する光合波器２と、波長多重化された光信号を伝送する光伝送媒体３と、光伝送媒体３の持つ群速度分散を補償する波長分散補償器６と、光伝送媒体３の持つ分散スロープを補償する分散スロープ補償器７と、波長多重化された光信号から多重化前の各波長の光信号を分離する光分波器４と、波長＃１から波長＃Ｎに対応するＮ個の光受信器５−１〜５−Ｎとにより構成される。波長＃ｉ（ｉ＝１〜Ｎ）の光送信器１−ｉは、それぞれ異なる波長の光信号を生成するもので、ＤＦＢ(分布帰還型:distributed feedback)レーザと外部変調器や半導体レーザの直接駆動あるいはＤＦＢ−ＥＡ変調器集積化光源をデータ信号で駆動する等の方法で実現される。
【００３７】
光合波器２は、アレイ導波路型回折格子等の光回路を用いることができる。光伝送媒体３は、１．３μｍ零分散の標準シングルモードファイバ、１．５μｍ零分散の分散シフトファイバ、あるいはＮＺ−ＤＳＦ(NonZero-Dispersion-Shifted-Fiber)等である。
【００３８】
波長分散補償器６は、ＤＣＦ(Dispersion-Compensation-Fiber)等の分散補償ファイバである。分散スロープ補償器７は、光伝送媒体３の持つ分散スロープと符号が反対で値がほぼ等しく、したがって光伝送媒体３の持つ分散スロープを補償可能な値を持つ時空間光処理型分散スロープ補償回路(H.Tsuda etal.,ECOC’98,Vol.1,PP.533-534)である。
【００３９】
光分波器４は、光合波器２と同様である。波長＃ｉ（ｉ＝１〜Ｎ）の光受信器５−ｉは、フォトダイオード等の光電変換手段で電気信号に変換し、識別回路等の電気処理回路によりデータを復調するものである。
【００４０】
本発明第一実施例の波長多重伝送システムの動作を図１および図２を参照して説明する。第一実施例では、分散シフト光ファイバ（ＤＳＦ：Dispersion-Shifted-Fiber）のＬ−ｂａｎｄにおいて波長多重光信号を伝送するものとする。波長＃１〜＃Ｎの光送信器１−１〜１−Ｎより生成された各波長の光信号は、光合波器２に入力される。ここで、波長多重化された波長多重光信号は、伝送路である光伝送媒体３へと入射される。この光伝送媒体３を伝搬した波長多重光信号は、まず波長分散補償器６に入射される。ここで、波長分散補償器６には市販の分散補償光ファイバ（ＤＣＦ）を使用する。
【００４１】
図２を参照すると、実線で示されたＤＳＦ１００ｋｍが光伝送媒体３が持つ群速度分散を表す。そして破線で示されたＤＣＦ１０ｋｍが波長分散補償器６の補償特性であり、波長分散補償器６を通過後は一点鎖線で示したように、その零分散波長がＤＳＦのＬ−ｂａｎｄのほぼ中央の波長である１５８０ｎｍ近傍へシフトする。これによりこの波長、つまり１５８０ｎｍ近傍においては分散が補償されるために良好に伝送される。図２中の波長分散が０ｐｓ／ｎｍの近傍に示した幅７０ｐｓ／ｎｍの点線で囲まれた領域は、４０Ｇｂｉｔ／ｓ／ｃｈＮＲＺ(non-return to zero)の光信号の群速度分散に対する許容範囲（分散耐力）を示す。このように、波長分散補償器６のみを使用した際には、図２中の波長１５８０ｎｍの１０ｎｍの幅の領域内でしか伝送できないことがわかる。
【００４２】
ここで、さらに図１にある分散スロープ補償器７に入力することで、図２内の一点鎖線で示す「ＤＳＦ＋ＤＣＦ」と点線で示す「ｃｏｍｐｅｎｓａｔｏｒ」の和になり、つまり群速度分散が０ｐｓ／ｎｍ近傍の二点鎖線で示したように、広い波長範囲で残留分散が７０ｐｓ／ｎｍの幅の中に収まり伝送可能となる。
【００４３】
その後、光分波器４により各チャネルの光信号が分離され、それぞれが波長＃１〜＃Ｎの光受信器５−１〜５−Ｎにより受信される。
【００４４】
（第二実施例）
本発明第二実施例の波長多重伝送システムは、図３に示すように、波長＃１の光送信器１−１から波長＃Ｎの光送信器１−Ｎまでの合計Ｎ個の光送信器１−１〜１−Ｎと、これらＮ種の光波長を持つ光信号を波長多重化する光合波器２と、波長多重化された光信号を伝送する光伝送媒体３と、光伝送媒体３の持つ群速度分散および分散スロープを補償する波長分散および分散スロープ補償器８と、波長多重化された光信号から多重化前の各波長の光信号を分離する光分波器４と、波長＃１から波長＃Ｎに対応するＮ個の光受信器５−１〜５−Ｎとにより構成される。
【００４５】
本発明第二実施例の波長多重伝送システムの動作の基本は第一実施例に準ずる。第二実施例の動作における特徴は、第一実施例において個別に補償していた群速度分散と分散スロープを一括して一つの波長分散および分散スロープ補償器８により補償するところにある。本構成により、第一実施例よりも簡易で安価なシステムを実現することができる。
【００４６】
（第三実施例）
本発明第三実施例の波長多重伝送システムは、図４に示すように、波長＃１の光送信器１−１から波長＃Ｎの光送信器１−Ｎまで合計Ｎ個の光送信器１−１〜１−Ｎと、これらＮ種の光波長を持つ光信号を波長多重化する光合波器２と、波長多重化された光信号を伝送する光伝送媒体３−１と、光伝送媒体３−１の持つ群速度分散を補償する波長分散補償器６−１と、光伝送媒体３−１の持つ分散スロープをチャネル間の相対遅延を補償せずに補償する群遅延無補償型分散スロープ補償器１０−１と、光伝送媒体３−１、波長分散補償器６−１および群遅延無補償型分散スロープ補償器１０−１による光損失を補償する光増幅器９と、光伝送媒体３−２と、波長分散補償器６−２と、群遅延無補償型分散スロープ補償器１０−２と、波長多重化された光信号から多重化前の各波長の光信号を分離する光分波器４と、波長＃１から波長＃Ｎに対応するＮ個の光受信器５−１〜５−Ｎとにより構成される。
【００４７】
ここで新たに記述される群遅延無補償型分散スロープ補償器１０−１、１０−２は、分散スロープを補償する際に、光伝送媒体３−１、３−２を伝搬する間に生じたチャネル間の相対遅延、つまりウォークオフを補償しない分散スロープ補償手段である。また、光伝送媒体３−２は光伝送媒体３−１と同等である。波長分散補償器６−２は波長分散補償器６−１に準ずるがその補償量は光伝送媒体３−２の持つ群速度分散を補償するものである。また、群遅延補償型分散スロープ補償器１０−２は、同様に光伝送媒体３−２の持つ分散スロープを補償する値を持つ。
【００４８】
本発明第三実施例の波長多重伝送システムの動作の基本は第一実施例に準ずる。第三実施例の動作における特徴は、波長多重信号を伝送路の途中で少なくとも１回以上、光増幅器９により中継すること、および分散スロープを補償する際に群遅延を補償しない群遅延無補償型分散スロープ補償器１０−１、１０−２を用いることである。
【００４９】
本特徴について図５を参照して説明する。図５の１）および２）には、それぞれ群遅延を補償する場合の分散スロープ補償の際の遅延の波長依存性と、群遅延を補償しない場合の依存性を示した。図中の実線は光伝送媒体３−１である光ファイバの群速度分散を補償した後の各チャネルの光信号の遅延を示す。残留する分散スロープに起因する遅延により、光信号の相対位置は図のようにばらつく。これに対して図中の一点鎖線の遅延特性を持つ、つまり遅延補償を行う分散スロープ補償を施すと、全てのチャネル（ここでは８チャネル）の光信号は分散スロープ補償後には、１）の破線で示したように相対遅延が補償される。
【００５０】
一方、チャネル毎の遅延補償を行わない場合には、２）に示したように、分散スロープに伴う光信号の相対的遅延がそのまま残存する。もし１）の分散スロープ補償方法を適用し、次段の光伝送媒体３−２へ波長多重信号を入力した場合には、その各チャネルの光信号の相対位置は、最初に光伝送媒体に入力した際と同じになる。そうすると、光信号の波形劣化をもたらす光非線形効果が最初に入射した際と同じ量だけ、同じ光信号パターンの位置に加わり累積されてしまう。これに対して遅延補償を行わない分散スロープ補償を適用した場合には、２）に示されるように各光信号間の相対位置は、最初の入射のときからシフトしていく。したがって、光非線形効果の累積の局在が緩和され、最大許容光入射パワが改善されることにより伝送距離の伸長が実現される。
【００５１】
（第四実施例）
本発明第四実施例の波長多重伝送システムは、図６に示すように、波長＃１の光送信器１−１から波長＃Ｎの光送信器１−Ｎまで合計Ｎ個の光送信器１−１〜１−Ｎと、これらＮ種の光波長を持つ光信号を波長多重化する光合波器２と、波長多重化された光信号を伝送する光伝送媒体３−１と、光伝送媒体３−１の持つ群速度分散をチャネル間の相対遅延を補償せずに補償する群遅延無補償型波長分散補償器１１−１と、光伝送媒体３−１の持つ分散スロープを補償する分散スロープ補償器７−１と、光伝送媒体３−１、群遅延無補償型波長分散補償器１１−１および分散スロープ補償器７−１による光損失を補償する光増幅器９と、光伝送媒体３−２と、群遅延無補償型波長分散補償器１１−２と、分散スロープ補償器７−２と、波長多重化された光信号から多重化前の各波長の光信号を分離する光分波器４と、波長＃１から波長＃Ｎに対応するＮ個の光受信器５−１〜５−Ｎとにより構成される。
【００５２】
ここで新たに記述される群遅延無補償型波長分散補償器１１−１、１１−２は、群速度分散を補償する際に、光伝送媒体３−１、３−２を伝搬する間に生じたチャネル間の相対遅延、つまりウォークオフを補償しない分散補償手段である。
【００５３】
本発明第四実施例の波長多重伝送システムの動作の基本は第三実施例に準ずる。第四実施例の動作における特徴は、波長分散補償手段に対して群遅延無補償とし、分散スロープ補償手段に対しては群遅延を補償する構成としたものである。本構成においても各光信号間の相対位置が最初の入射のときからシフトしていく。したがって、光非線形効果の累積の局在が緩和され、最大許容光入射パワが改善されることにより伝送距離の伸長が実現される。
【００５４】
（第五実施例）
本発明第五実施例の波長多重伝送システムは、図７に示すように、波長＃１の光送信器１−１から波長＃Ｎの光送信器１−Ｎまでの合計Ｎ個の光送信器１−１〜１−Ｎと、これらＮ種の光波長を持つ光信号を波長多重化する光合波器２と、波長多重化された光信号を伝送する光伝送媒体３−１と、光伝送媒体３−１の持つ群速度分散および分散スロープをチャネル間の相対遅延を補償せずに補償する群遅延無補償型波長分散および分散スロープ補償器１２−１と、光伝送媒体３−１、群遅延無補償型波長分散および分散スロープ補償器１２−１による光損失を補償する光増幅器９と、光伝送媒体３−２と、群遅延無補償型波長分散および分散スロープ補償器１２−２と、波長多重化された光信号から多重化前の各波長の光信号を分離する光分波器４と、波長＃１から波長＃Ｎに対応するＮ個の光受信器５−１〜５−Ｎとにより構成される。
【００５５】
ここで新たに記述される群遅延無補償型波長分散および分散スロープ補償器１２−１、１２−２は、群速度分散および分散スロープを補償する際に、光伝送媒体３−１、３−２を伝搬する間に生じたチャネル間の相対遅延、つまりウォークオフを補償しない波長分散および分散スロープ補償手段である。
【００５６】
本発明第五実施例の波長多重伝送システムの動作の基本は第三および第四実施例に準ずる。第五実施例の動作における特徴は、第三および第四実施例においては、波長分散補償手段あるいは分散スロープ補償手段に対してウォークオフ無補償としていたところを波長分散および分散スロープ補償手段に対してウォークオフ無補償としたものである。本構成においても各光信号間の相対位置が最初の入射のときからシフトしていく。したがって、光非線形効果の累積の局在が緩和され、最大許容光入射パワが改善されることにより伝送距離の伸長が実現される。
【００５７】
なお、第三および第四実施例では、波長分散補償手段あるいは分散スロープ補償手段に対してウォークオフ無補償としていたが波長分散補償手段と分散スロープ補償手段の両方に対してウォークオフ無補償としてもよい。
【００５８】
また、以上の全ての実施例において、光合波器２および光分波器４は送信側と受信側にそれぞれ一つでよいために従来例のような帯域制限の影響も低減される。
【００５９】
【発明の効果】
以上説明したように、本発明の波長多重伝送システムは、光合分波手段による帯域制限に起因する光信号の品質劣化が起こり難く、また構成品点数も低減でき、低コストで高品質な波長多重伝送システムを実現できる。また、光ファイバ中の非線形光学効果の累積と波長分散の相互作用による伝送品質の劣化に対しても強い特徴を持つ。この特徴により、本発明の波長多重伝送システムは、従来の群遅延が補償される波長多重伝送システムに比較し、より長距離かつ大容量な光伝送システムを高信頼に構築することができる。
【図面の簡単な説明】
【図１】本発明第一実施例の波長多重伝送システムの構成図。
【図２】本発明第一実施例の波長多重伝送システムの動作を説明するための図。
【図３】本発明第二実施例の波長多重伝送システムの構成図。
【図４】本発明第三実施例の波長多重伝送システムの構成図。
【図５】本発明第三実施例の波長多重伝送システムの動作を説明するための図。
【図６】本発明第四実施例の波長多重伝送システムの構成図。
【図７】本発明第五実施例の波長多重伝送システムの構成図。
【符号の説明】
１−１〜１−Ｎ光送信器
２光合波器
３、３−１、３−２光伝送媒体
４光分波器
５−１〜５−Ｎ光受信器
６、６−１、６−２波長分散補償器
７、７−１、７−２分散スロープ補償器
８波長分散および分散スロープ補償器
９光増幅器
１０−１、１０−２群遅延無補償型分散スロープ補償器
１１−１、１１−２群遅延無補償型波長分散補償器
１２−１、１２−２群遅延無補償型波長分散および分散スロープ補償器[0001]
BACKGROUND OF THE INVENTION
The present invention provides group velocity dispersion and dispersion for suppressing degradation of transmission quality due to interaction between the group velocity dispersion and dispersion slope or the nonlinear optical effect of a transmission line such as an optical fiber having a wide band in optical wavelength division multiplexing transmission. It relates to slope compensation technology.
[0002]
[Prior art]
In an optical transmission system, there is a problem of transmission quality deterioration due to chromatic dispersion of an optical fiber that is a transmission medium or waveform deterioration due to the interaction between this and the nonlinear optical effect of the optical fiber. This occurs when the group velocity dispersion of the optical fiber acts on the bandwidth of the optical signal, causing the shape of the optical pulse to collapse and interfering with adjacent time slots. In order to prevent this, various dispersion compensation techniques have been proposed.
[0003]
In particular, in a wavelength division multiplexing transmission system using a wide wavelength band, even if the group velocity dispersion is compensated for a certain wavelength, the wavelength depends on the dependency of the group velocity dispersion on the optical fiber itself, that is, the influence of the dispersion slope. The group velocity dispersion remains for these signals. For this reason, a channel is generated in which the group velocity dispersion is not sufficiently compensated for by the wavelength, and transmission quality is deteriorated or transmission is impossible.
[0004]
In order to solve this problem, each channel is demultiplexed with an AWG (Arrayed-Waveguide-Grating) demultiplexer, and a dispersion compensation fiber with a slope-dependent correction depending on the wavelength is inserted into each channel. A dispersion-and-dispersion slope compensation circuit of a type in which each channel is uniformly compensated for dispersion and multiplexed again by an AWG multiplexer is proposed as “Long-distance WDM transmission experiment using the dispersion slope compensator; H. Taga etal ,; IEEE JLT, Vol. 34, No. 11, 1998 ”.
[0005]
[Problems to be solved by the invention]
However, in this method, every time the dispersion and the dispersion slope are compensated, a process of demultiplexing the wavelength-multiplexed optical signal once, compensating each channel, and recombining is added. In the AWG multiplexer / demultiplexer used for this multiplexing / demultiplexing, the band limitation of the transmission profile of Gaussian or a combination thereof is added to the optical signal of each wavelength when passing. The optical signal subjected to the band limitation has its optical waveform deteriorated because a part of the signal component is cut off.
[0006]
The wavelength division multiplexing transmission system is designed so that this deterioration is sufficiently small although it passes through the optical multiplexer and the optical demultiplexer at least twice (on the transmission and reception sides). However, conventionally, each time chromatic dispersion and dispersion slope are compensated, the light passes through the AWG multiplexer / demultiplexer, and this further limits the bandwidth twice. In a multi-relay optical wavelength division multiplexing system, the number of compensation circuits further increases. If this band limitation is applied many times, these effects are integrated, causing a serious deterioration in transmission quality. Conventionally, since dispersion compensation fiber modules are required for the number of multiplexed / demultiplexed parts, the cost and required space increase, which is a major demerit in system construction.
[0007]
The present invention has been made in such a background, and it is difficult for optical signal quality degradation due to band limitation by the optical multiplexing / demultiplexing means, and the number of components can be reduced, and the cost is high and the quality is high. An object is to provide a wavelength division multiplexing transmission system. SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength division multiplexing transmission system having a strong characteristic against degradation of transmission quality due to the interaction between accumulation of nonlinear optical effects in an optical fiber and wavelength dispersion. An object of the present invention is to provide a wavelength division multiplexing transmission system capable of constructing a longer-distance and large-capacity optical transmission system with higher reliability than a conventional wavelength division multiplexing transmission system in which group delay is compensated. To do.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the wavelength multiplexing transmission system of the present invention compensates for group velocity dispersion and dispersion slope in an optical fiber as a transmission line without demultiplexing the wavelength multiplexed optical signal, and A dispersion slope compensation circuit is configured.
[0009]
That is, the present invention is combined by N optical transmitters that transmit optical signals having different wavelengths, means for combining the optical signals of the N optical transmitters, and means for combining the optical signals. Optical transmission medium for transmitting wavelength-multiplexed optical signal, means for demultiplexing wavelength-multiplexed optical signal transmitted by this optical transmission medium, and N optical signals having different wavelengths demultiplexed by the means for demultiplexing Is a wavelength division multiplexing transmission system including N optical receivers.
[0010]
Here, a feature of the present invention is that, between the optical transmission medium and the means for demultiplexing, the wavelength multiplexed optical signal is affected by the group velocity dispersion characteristic of the optical transmission medium. Chromatic dispersion compensation means having a characteristic to compensate in units of optical signals; and dispersion slope compensation means having characteristics to compensate for the influence of the wavelength multiplexed optical signal on the dispersion slope characteristics of the optical transmission medium in units of wavelength multiplexed optical signals. It is in the place with.
[0011]
Alternatively, between the optical transmission medium and the means for demultiplexing, the influence of the wavelength multiplexed optical signal due to the group velocity dispersion characteristic and the dispersion slope characteristic of the optical transmission medium is compensated in units of the wavelength multiplexed optical signal. A configuration including chromatic dispersion and dispersion slope compensating means having characteristics can also be adopted.
[0012]
As a result, it is possible to greatly reduce the deterioration of the quality of the optical signal that has been caused by the band limitation effect caused by passing through the AWG multiplexer / demultiplexer for each compensation.
[0013]
In addition, the dispersion compensation fiber, which has conventionally been required for many types, is no longer necessary or only one, so that the optical transmission system can be simplified and the cost can be reduced.
[0014]
Another configuration of the present invention includes N optical transmitters that transmit optical signals having different wavelengths, a unit that combines the optical signals of the N optical transmitters, and a unit that combines the optical signals. First and second optical transmission media for transmitting the combined wavelength multiplexed optical signal, optical amplification means interposed between the first and second optical transmission media, and the first and second optical transmission media Means for demultiplexing the wavelength multiplexed optical signal transmitted by the optical transmission medium, and N optical receivers for receiving N optical signals of different wavelengths demultiplexed by the demultiplexing means. Wavelength multiplex transmission system.
[0015]
The feature of the present invention is that the wavelength-multiplexed optical signal is received by the group velocity dispersion characteristic of the first optical transmission medium between the first optical transmission medium and the optical amplification means. A first chromatic dispersion compensation means having a characteristic for compensating the influence in units of the wavelength multiplexed optical signal; and the wavelength multiplexed optical signal unit affected by the dispersion slope characteristic of the first optical transmission medium. A first dispersion slope compensating means having a characteristic to be compensated for at a time between the second optical transmission medium and the demultiplexing means. A second chromatic dispersion compensator having a characteristic for compensating the influence of the group velocity dispersion characteristic by the wavelength multiplexed optical signal unit; and the influence of the wavelength multiplexed optical signal affected by the dispersion slope characteristic of the second optical transmission medium. Wavelength multiplexing It is in place and a second dispersion slope compensating means having a characteristic which compensates the signal units.
[0016]
In this configuration, the chromatic dispersion compensation means and / or the dispersion slope compensation means do not compensate for the walk-off in which the wavelength-multiplexed optical signal is a relative delay between channels caused by the group delay characteristic of the optical transmission medium. It is desirable to provide means for
[0017]
Alternatively, between the first optical transmission medium and the optical amplifying means, the wavelength multiplexed optical signal is affected by the group velocity dispersion characteristic and the dispersion slope characteristic of the first optical transmission medium. A first chromatic dispersion and dispersion slope compensating means having a characteristic to be compensated in signal units, and the wavelength-multiplexed optical signal is between the second optical transmission medium and the demultiplexing means. It is also possible to employ a configuration including second chromatic dispersion and dispersion slope compensation means having a characteristic of compensating the influence of the group velocity dispersion characteristic and dispersion slope characteristic of the optical transmission medium in units of the wavelength multiplexed optical signal.
[0018]
In this configuration, the chromatic dispersion and dispersion slope compensating means includes means for making no compensation for walk-off in which the wavelength-multiplexed optical signal is a relative delay between channels caused by group delay characteristics of the optical transmission medium. It is desirable to provide.
[0019]
In this way, since the walk-off due to the group delay between wavelengths is not compensated, the accumulation of the interaction between the group velocity dispersion and dispersion slope and the optical nonlinear optical effect, which is particularly problematic in multi-relay transmission of wavelength multiplexed signals, is mitigated. Is done. That is, transmission quality and distance can be greatly improved as compared with the case where walk-off is compensated.
[0020]
For example, the chromatic dispersion compensating means can be realized by including a dispersion compensating fiber, and the dispersion slope compensating means can be realized by including a spatiotemporal light processing type dispersion slope compensating circuit. The chromatic dispersion and dispersion slope compensation means can be realized by providing a spatio-temporal light processing type dispersion slope compensation circuit.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the wavelength division multiplexing transmission system according to the embodiment of the present invention will be described with reference to FIG. 1, FIG. 3, FIG. 4, FIG. FIG. 1 is an overall configuration diagram of a wavelength division multiplexing transmission system according to a first embodiment of the present invention. FIG. 3 is an overall configuration diagram of the wavelength division multiplexing transmission system according to the second embodiment of the present invention. FIG. 4 is an overall configuration diagram of the wavelength division multiplexing transmission system according to the third embodiment of the present invention. FIG. 6 is an overall configuration diagram of a wavelength division multiplexing transmission system according to a fourth embodiment of the present invention. FIG. 7 is an overall configuration diagram of a wavelength division multiplexing transmission system according to a fifth embodiment of the present invention.
[0022]
As shown in FIG. 1, the first embodiment of the present invention includes N optical transmitters 1-1 to 1 -N that transmit optical signals having different wavelengths and N optical transmitters 1-1 to 1-1. An optical multiplexer 2 for multiplexing 1-N optical signals, an optical transmission medium 3 for transmitting a wavelength-multiplexed optical signal multiplexed by the optical multiplexer 2, and a wavelength multiplexing transmitted by the optical transmission medium 3 An optical demultiplexer 4 for demultiplexing an optical signal, and N optical receivers 5-1 to 5 -N for receiving N optical signals having different wavelengths respectively demultiplexed by the optical demultiplexer 4; Is a wavelength division multiplexing transmission system.
[0023]
Here, the present invention is characterized in that the wavelength multiplexed optical signal is affected by the group velocity dispersion characteristic of the optical transmission medium 3 between the optical transmission medium 3 and the optical demultiplexer 4. A chromatic dispersion compensator 6 having a characteristic of compensating in units of optical signals, and a dispersion slope compensator having a characteristic of compensating the influence of the wavelength multiplexed optical signal by the dispersion slope characteristics of the optical transmission medium 3 in units of wavelength multiplexed optical signals. 7 and with.
[0024]
As shown in FIG. 3, the second embodiment of the present invention includes N optical transmitters 1-1 to 1-N that transmit optical signals having different wavelengths and N optical transmitters 1-1 to 1-1. An optical multiplexer 2 for multiplexing 1-N optical signals, an optical transmission medium 3 for transmitting a wavelength-multiplexed optical signal multiplexed by the optical multiplexer 2, and a wavelength multiplexing transmitted by the optical transmission medium 3 An optical demultiplexer 4 for demultiplexing an optical signal, and N optical receivers 5-1 to 5 -N for receiving N optical signals having different wavelengths respectively demultiplexed by the optical demultiplexer 4; Is a wavelength division multiplexing transmission system.
[0025]
Here, the present invention is characterized in that the wavelength-multiplexed optical signal is affected by the group velocity dispersion characteristic and the dispersion slope characteristic of the optical transmission medium 3 between the optical transmission medium 3 and the optical demultiplexer 4. Is provided with a chromatic dispersion and dispersion slope compensator 8 having a characteristic of compensating for each wavelength multiplexed optical signal.
[0026]
As shown in FIG. 4, the third embodiment of the present invention includes N optical transmitters 1-1 to 1-N that transmit optical signals having different wavelengths, and N optical transmitters 1-1 to 1-1. An optical multiplexer 2 for multiplexing 1-N optical signals, optical transmission media 3-1 and 3-2 for transmitting wavelength-multiplexed optical signals multiplexed by the optical multiplexer 2, and the optical transmission medium 3 -1 and 3-2, an optical demultiplexer 4 for demultiplexing the wavelength multiplexed optical signal transmitted by the optical transmission media 3-1 and 3-2, and the optical amplifier 9 This is a wavelength division multiplexing transmission system including N optical receivers 5-1 to 5-N that receive N optical signals with different wavelengths, which are demultiplexed by the demultiplexer 4.
[0027]
The feature of the present invention is that the wavelength-multiplexed optical signal is affected by the group velocity dispersion characteristic of the optical transmission medium 3-1 between the optical transmission medium 3-1 and the optical amplifier 9. A chromatic dispersion compensator 6-1 having a characteristic of compensating in units of wavelength-multiplexed optical signals, and a characteristic of compensating the influence of the wavelength-multiplexed optical signals on the dispersion slope characteristics of the optical transmission medium 3-1 in units of wavelength-multiplexed optical signals. A non-compensation type dispersion slope compensator 10-1 having a wavelength delay, and between the optical transmission medium 3-2 and the optical demultiplexer 4, the wavelength multiplexed optical signal is a group of the optical transmission medium 3-2. A chromatic dispersion compensator 6-2 having a characteristic of compensating the influence of velocity dispersion characteristics in units of the wavelength-multiplexed optical signal; and the influence of the wavelength-multiplexed optical signal affected by the dispersion slope characteristic of the optical transmission medium 3-2 on the wavelength. Compensation characteristics in units of multiple optical signals It is in place and a group delay uncompensated type dispersion slope compensator 10-2 having.
[0028]
The group delay non-compensation type dispersion slope compensators 10-1 and 10-2 perform walk-off in which the wavelength-multiplexed optical signal is a relative delay between channels caused by the group delay characteristics of the optical transmission media 3-1, 3-2. Makes this uncompensated.
[0029]
As shown in FIG. 6, in the fourth embodiment of the present invention, the chromatic dispersion compensators 6-1 and 6-2 and the non-group delay non-compensation type dispersion slope compensators 10-1 and 10 of the third embodiment of the present invention are shown. Group delay uncompensated chromatic dispersion compensators 11-1 and 11-2 and dispersion slope compensators 7-1 and 7-2 instead of -2, and group delay uncompensated chromatic dispersion compensators 11-1 and 11 -2 does not compensate for the walk-off that the wavelength-multiplexed optical signal receives due to the group delay characteristics of the optical transmission media 3-1 and 3-2.
[0030]
As shown in FIG. 7, the fifth embodiment of the present invention includes N optical transmitters 1-1 to 1-N that transmit optical signals having different wavelengths and N optical transmitters 1-1 to 1-1. An optical multiplexer 2 for multiplexing 1-N optical signals, optical transmission media 3-1 and 3-2 for transmitting wavelength-multiplexed optical signals multiplexed by the optical multiplexer 2, and the optical transmission medium 3 -1 and 3-2, an optical demultiplexer 4 for demultiplexing the wavelength multiplexed optical signal transmitted by the optical transmission media 3-1 and 3-2, and the optical amplifier 9 This is a wavelength division multiplexing transmission system including N optical receivers 5-1 to 5-N that receive N optical signals with different wavelengths, which are demultiplexed by the demultiplexer 4.
[0031]
The feature of the present invention is that the wavelength-multiplexed optical signal is transmitted between the optical transmission medium 3-1 and the optical amplifier 9 by the group velocity dispersion characteristic and the dispersion slope characteristic of the optical transmission medium 3-1. A group delay non-compensation type chromatic dispersion and dispersion slope compensator 12-1 having the characteristic of compensating the influence received in units of the wavelength multiplexed optical signal is provided, and between the optical transmission medium 3-2 and the optical demultiplexer 4 is provided. A group delay non-compensation type chromatic dispersion and dispersion slope compensator having a characteristic for compensating the influence of the wavelength multiplexed optical signal by the group velocity dispersion characteristic and the dispersion slope characteristic of the optical transmission medium 3-2 in units of the wavelength multiplexed optical signal. It is in the place with 12-2.
[0032]
The group delay non-compensation type chromatic dispersion and dispersion slope compensators 12-1 and 12-2 are relative delays between channels caused by the group delay characteristics of the optical transmission media 3-1 and 3-2. This is uncompensated for walk-off.
[0033]
The chromatic dispersion compensators 6, 6-1, and 6-2 and the group delay non-compensation type chromatic dispersion compensators 11-1 and 11-2 according to the first, third, and fourth embodiments of the present invention each include a dispersion compensating fiber. The dispersion slope compensators 7, 7-1 and 7-2, and the group delay non-compensation type dispersion slope compensators 10-1 and 10-2 each include a spatio-temporal light processing type dispersion slope compensation circuit.
[0034]
The chromatic dispersion and dispersion slope compensator 8 and the group delay non-compensation type chromatic dispersion and dispersion slope compensators 12-1 and 12-2 according to the second and fifth embodiments of the present invention are spatiotemporal light processing type dispersion slope compensation circuits. Prepare.
[0035]
In the following, embodiments of the present invention will be described in more detail.
[0036]
(First Example)
The wavelength division multiplexing transmission system according to the first embodiment of the present invention includes a total of N optical transmitters 1-1 to 1- 1 from an optical transmitter 1-1 having a wavelength # 1 to an optical transmitter 1-N having a wavelength #N. N, an optical multiplexer 2 that multiplexes optical signals having these N types of optical wavelengths, an optical transmission medium 3 that transmits the wavelength-multiplexed optical signal, and a group velocity dispersion of the optical transmission medium 3 A chromatic dispersion compensator 6 for compensation, a dispersion slope compensator 7 for compensating for the dispersion slope of the optical transmission medium 3, and an optical demultiplexer for separating optical signals of respective wavelengths before multiplexing from the wavelength multiplexed optical signal. And N optical receivers 5-1 to 5-N corresponding to wavelengths # 1 to #N. The optical transmitters 1-i having wavelengths #i (i = 1 to N) generate optical signals having different wavelengths, and are directly connected to a DFB (distributed feedback) laser and an external modulator or semiconductor laser. This is realized by a method such as driving or driving a DFB-EA modulator integrated light source with a data signal.
[0037]
The optical multiplexer 2 can use an optical circuit such as an arrayed waveguide type diffraction grating. The optical transmission medium 3 is a 1.3 μm zero dispersion standard single mode fiber, a 1.5 μm zero dispersion dispersion shifted fiber, or a NZ-DSF (NonZero-Dispersion-Shifted-Fiber).
[0038]
The chromatic dispersion compensator 6 is a dispersion compensating fiber such as DCF (Dispersion-Compensation-Fiber). The dispersion slope compensator 7 is a spatio-temporal light processing type dispersion slope compensation circuit having a value that is opposite in sign to that of the dispersion slope of the optical transmission medium 3 and has a value that can compensate for the dispersion slope of the optical transmission medium 3. (H. Tsuda et al., ECOC '98, Vol. 1, PP. 533-534).
[0039]
The optical demultiplexer 4 is the same as the optical multiplexer 2. The optical receiver 5-i having the wavelength #i (i = 1 to N) converts the signal into an electric signal by a photoelectric conversion means such as a photodiode, and demodulates data by an electric processing circuit such as an identification circuit.
[0040]
The operation of the wavelength division multiplexing transmission system according to the first embodiment of the present invention will be described with reference to FIGS. In the first embodiment, it is assumed that a wavelength multiplexed optical signal is transmitted in an L-band of a dispersion-shifted fiber (DSF). The optical signals of the respective wavelengths generated from the optical transmitters 1-1 to 1-N having the wavelengths # 1 to #N are input to the optical multiplexer 2. Here, the wavelength-multiplexed wavelength-multiplexed optical signal is incident on the optical transmission medium 3 that is a transmission path. The wavelength multiplexed optical signal propagated through the optical transmission medium 3 is first incident on the chromatic dispersion compensator 6. Here, a commercially available dispersion compensating optical fiber (DCF) is used for the chromatic dispersion compensator 6.
[0041]
Referring to FIG. 2, the DSF 100 km indicated by the solid line represents the group velocity dispersion of the optical transmission medium 3. The DCF 10 km indicated by the broken line is the compensation characteristic of the chromatic dispersion compensator 6. After passing through the chromatic dispersion compensator 6, the zero dispersion wavelength is approximately at the center of the L-band of the DSF, as indicated by the one-dot chain line. The wavelength shifts to around 1580 nm. As a result, the dispersion is compensated in the vicinity of this wavelength, that is, in the vicinity of 1580 nm, so that transmission is performed satisfactorily. A region surrounded by a dotted line having a wavelength dispersion of 70 ps / nm in the vicinity of 0 ps / nm in FIG. 2 indicates an allowance for group velocity dispersion of a 40 Gbit / s / ch NRZ (non-return to zero) optical signal. The range (dispersion resistance) is shown. Thus, it can be seen that when only the chromatic dispersion compensator 6 is used, transmission is possible only within the 10 nm width region of the wavelength 1580 nm in FIG.
[0042]
Here, by further inputting to the dispersion slope compensator 7 in FIG. 1, it becomes the sum of “DSF + DCF” indicated by the one-dot chain line in FIG. 2 and “compensator” indicated by the dotted line, that is, the group velocity dispersion is 0 ps / nm. As indicated by the two-dot chain line in the vicinity, the residual dispersion is within a width of 70 ps / nm over a wide wavelength range and can be transmitted.
[0043]
Thereafter, the optical signals of the respective channels are separated by the optical demultiplexer 4 and received by the optical receivers 5-1 to 5-N having the wavelengths # 1 to #N, respectively.
[0044]
(Second embodiment)
As shown in FIG. 3, the wavelength division multiplexing transmission system according to the second embodiment of the present invention includes a total of N optical transmitters from the optical transmitter 1-1 having the wavelength # 1 to the optical transmitter 1-N having the wavelength #N. 1-1 to 1-N, an optical multiplexer 2 that multiplexes optical signals having these N optical wavelengths, an optical transmission medium 3 that transmits the wavelength-multiplexed optical signal, and an optical transmission medium 3 Chromatic dispersion and dispersion slope compensator 8 for compensating the group velocity dispersion and dispersion slope of the optical signal, an optical demultiplexer 4 for separating the optical signal of each wavelength before multiplexing from the wavelength multiplexed optical signal, and wavelength # 1 to N optical receivers 5-1 to 5-N corresponding to the wavelength #N.
[0045]
The basic operation of the wavelength division multiplexing transmission system of the second embodiment of the present invention is the same as that of the first embodiment. The feature of the operation of the second embodiment is that the group velocity dispersion and dispersion slope individually compensated in the first embodiment are collectively compensated by one chromatic dispersion and dispersion slope compensator 8. With this configuration, a simpler and cheaper system than the first embodiment can be realized.
[0046]
(Third embodiment)
As shown in FIG. 4, the wavelength division multiplexing transmission system according to the third embodiment of the present invention includes a total of N optical transmitters 1 from an optical transmitter 1-1 having a wavelength # 1 to an optical transmitter 1-N having a wavelength #N. -1 to 1-N, an optical multiplexer 2 that multiplexes optical signals having these N optical wavelengths, an optical transmission medium 3-1 that transmits the wavelength-multiplexed optical signal, and an optical transmission medium 3-1. A chromatic dispersion compensator 6-1 for compensating for the group velocity dispersion of 3-1 and a group delay non-compensation type dispersion slope for compensating the dispersion slope of the optical transmission medium 3-1 without compensating for the relative delay between channels. A compensator 10-1, an optical transmission medium 3-1, an optical amplifier 9 that compensates for optical loss caused by the chromatic dispersion compensator 6-1 and the group delay non-compensation type dispersion slope compensator 10-1, and an optical transmission medium 3- 2, chromatic dispersion compensator 6-2, non-group delay non-compensation type dispersion slope compensator 10-2, wavelength multiplexing The optical demultiplexer 4 separates the optical signal of each wavelength before multiplexing from the multiplexed optical signal, and N optical receivers 5-1 to 5-N corresponding to the wavelength # 1 to the wavelength #N. Is done.
[0047]
The group delay non-compensation type dispersion slope compensators 10-1 and 10-2 newly described here are generated during propagation through the optical transmission media 3-1 and 3-2 when compensating for the dispersion slope. This is a dispersion slope compensation means that does not compensate for the relative delay between channels, that is, the walk-off. The optical transmission medium 3-2 is equivalent to the optical transmission medium 3-1. The chromatic dispersion compensator 6-2 conforms to the chromatic dispersion compensator 6-1, but the compensation amount compensates for the group velocity dispersion of the optical transmission medium 3-2. Similarly, the group delay compensation type dispersion slope compensator 10-2 has a value for compensating for the dispersion slope of the optical transmission medium 3-2.
[0048]
The basic operation of the wavelength division multiplexing transmission system of the third embodiment of the present invention is the same as that of the first embodiment. The feature of the operation of the third embodiment is that the wavelength multiplexed signal is relayed by the optical amplifier 9 at least once in the middle of the transmission line, and the group delay non-compensation type that does not compensate the group delay when compensating the dispersion slope. Dispersion slope compensators 10-1 and 10-2 are used.
[0049]
This feature will be described with reference to FIG. 1) and 2) of FIG. 5 show the wavelength dependence of the delay when compensating for the dispersion slope when compensating for the group delay and the dependence when not compensating for the group delay. The solid line in the figure indicates the delay of the optical signal of each channel after compensating for the group velocity dispersion of the optical fiber that is the optical transmission medium 3-1. Due to the delay caused by the remaining dispersion slope, the relative position of the optical signal varies as shown in the figure. On the other hand, when the dispersion slope compensation having the delay characteristic of the one-dot chain line in the figure, that is, the delay compensation is performed, the optical signals of all the channels (here, 8 channels) are broken lines of 1) after the dispersion slope compensation. The relative delay is compensated as shown in FIG.
[0050]
On the other hand, when the delay compensation for each channel is not performed, as shown in 2), the relative delay of the optical signal accompanying the dispersion slope remains as it is. If the dispersion slope compensation method of 1) is applied and a wavelength multiplexed signal is input to the next optical transmission medium 3-2, the relative position of the optical signal of each channel is first input to the optical transmission medium. It will be the same as when As a result, the optical nonlinear effect that causes the waveform degradation of the optical signal is added to the position of the same optical signal pattern and accumulated by the same amount as when it first entered. On the other hand, when dispersion slope compensation without delay compensation is applied, the relative position between the optical signals is shifted from the time of the first incidence as shown in 2). Therefore, the cumulative localization of the optical nonlinear effect is relaxed, and the maximum allowable light incident power is improved, thereby extending the transmission distance.
[0051]
(Fourth embodiment)
As shown in FIG. 6, the wavelength division multiplexing transmission system according to the fourth embodiment of the present invention includes a total of N optical transmitters 1 from an optical transmitter 1-1 having a wavelength # 1 to an optical transmitter 1-N having a wavelength #N. -1 to 1-N, an optical multiplexer 2 that multiplexes optical signals having these N optical wavelengths, an optical transmission medium 3-1 that transmits the wavelength-multiplexed optical signal, and an optical transmission medium 3-1. A group delay non-compensation type chromatic dispersion compensator 11-1 that compensates the group velocity dispersion of 3-1 without compensating the relative delay between channels; and a dispersion slope that compensates for the dispersion slope of the optical transmission medium 3-1. A compensator 7-1, an optical transmission medium 3-1, an optical amplifier 9 that compensates for optical loss due to the group delay non-compensation type chromatic dispersion compensator 11-1, and a dispersion slope compensator 7-1; 2, a group delay non-compensation type chromatic dispersion compensator 11-2, a dispersion slope compensator 7-2, wavelength multiplexing The optical demultiplexer 4 separates the optical signal of each wavelength before multiplexing from the multiplexed optical signal, and N optical receivers 5-1 to 5-N corresponding to the wavelength # 1 to the wavelength #N. Is done.
[0052]
The newly described group delay non-compensation type chromatic dispersion compensators 11-1 and 11-2 are generated during propagation through the optical transmission media 3-1 and 3-2 when compensating for the group velocity dispersion. This is dispersion compensation means that does not compensate for the relative delay between channels, that is, walk-off.
[0053]
The basic operation of the wavelength division multiplexing transmission system of the fourth embodiment of the present invention is the same as that of the third embodiment. The feature of the operation of the fourth embodiment is that the chromatic dispersion compensation means is not subjected to group delay compensation and the dispersion slope compensation means is compensated for group delay. Also in this configuration, the relative position between the optical signals is shifted from the time of the first incidence. Therefore, the cumulative localization of the optical nonlinear effect is relaxed, and the maximum allowable light incident power is improved, thereby extending the transmission distance.
[0054]
(Fifth embodiment)
As shown in FIG. 7, the wavelength division multiplexing transmission system according to the fifth embodiment of the present invention includes a total of N optical transmitters from the optical transmitter 1-1 having the wavelength # 1 to the optical transmitter 1-N having the wavelength #N. 1-1 to 1-N, an optical multiplexer 2 that multiplexes optical signals having these N types of optical wavelengths, an optical transmission medium 3-1 that transmits the wavelength-multiplexed optical signals, and optical transmission A group delay non-compensation type chromatic dispersion and dispersion slope compensator 12-1 for compensating the group velocity dispersion and dispersion slope of the medium 3-1 without compensating for the relative delay between channels, and the optical transmission medium 3-1, group An optical amplifier 9 that compensates for optical loss caused by the delay-uncompensated chromatic dispersion and dispersion slope compensator 12-1, an optical transmission medium 3-2, a group-delay uncompensated chromatic dispersion and dispersion slope compensator 12-2, Optical component that separates optical signals of each wavelength before multiplexing from optical signals that have been multiplexed A vessel 4, constituted by the N optical receivers 5-1 to 5-N corresponding to the wavelength #N wavelength # 1.
[0055]
The group delay non-compensation type chromatic dispersion and dispersion slope compensators 12-1 and 12-2 newly described here are optical transmission media 3-1 and 3-2 when compensating for group velocity dispersion and dispersion slope. Is a chromatic dispersion and dispersion slope compensation means that does not compensate for the relative delay between channels, i.e., walk-off, that occurs during propagation through the channel.
[0056]
The basic operation of the wavelength division multiplexing transmission system according to the fifth embodiment of the present invention is in accordance with the third and fourth embodiments. The feature of the operation of the fifth embodiment is that, in the third and fourth embodiments, the chromatic dispersion compensation means or the dispersion slope compensation means is not subjected to walk-off compensation but the chromatic dispersion and dispersion slope compensation means. No compensation for walk-off. Also in this configuration, the relative position between the optical signals is shifted from the time of the first incidence. Therefore, the cumulative localization of the optical nonlinear effect is relaxed, and the maximum allowable light incident power is improved, thereby extending the transmission distance.
[0057]
In the third and fourth embodiments, there is no walk-off compensation for the chromatic dispersion compensation means or the dispersion slope compensation means. However, there is no walk-off compensation for both the chromatic dispersion compensation means and the dispersion slope compensation means. Good.
[0058]
In all the embodiments described above, the optical multiplexer 2 and the optical demultiplexer 4 may be provided for each of the transmission side and the reception side, so that the influence of band limitation as in the conventional example is reduced.
[0059]
【The invention's effect】
As described above, the wavelength division multiplexing transmission system of the present invention is less susceptible to optical signal quality degradation due to band limitation by the optical multiplexing / demultiplexing means, can reduce the number of components, and is low-cost and high-quality wavelength multiplexing. A transmission system can be realized. It also has strong characteristics against transmission quality degradation due to the interaction between the accumulation of nonlinear optical effects in an optical fiber and wavelength dispersion. Due to this feature, the wavelength division multiplexing transmission system of the present invention can construct a long-distance and large capacity optical transmission system with higher reliability than the conventional wavelength division multiplexing transmission system in which the group delay is compensated.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wavelength division multiplexing transmission system according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the wavelength division multiplexing transmission system according to the first embodiment of the present invention.
FIG. 3 is a configuration diagram of a wavelength division multiplexing transmission system according to a second embodiment of the present invention.
FIG. 4 is a configuration diagram of a wavelength division multiplexing transmission system according to a third embodiment of the present invention.
FIG. 5 is a diagram for explaining the operation of the wavelength division multiplexing transmission system according to the third embodiment of the present invention.
FIG. 6 is a configuration diagram of a wavelength division multiplexing transmission system according to a fourth embodiment of the present invention.
FIG. 7 is a configuration diagram of a wavelength division multiplexing transmission system according to a fifth embodiment of the present invention.
[Explanation of symbols]
1-1 to 1-N optical transmitter
2 Optical multiplexer
3, 3-1, 3-2 Optical transmission medium
4 Optical demultiplexer
5-1-5-N optical receiver
6, 6-1 and 6-2 chromatic dispersion compensator
7, 7-1, 7-2 Dispersion slope compensator
8 Chromatic dispersion and dispersion slope compensator
9 Optical amplifier
10-1, 10-2 Dispersion compensator without group delay compensation
11-1, 11-2 Non-compensation type chromatic dispersion compensator
12-1, 12-2 Non-compensation type chromatic dispersion and dispersion slope compensator

Claims

N optical transmitters for transmitting optical signals of different wavelengths, means for combining the optical signals of the N optical transmitters, and wavelength multiplexed optical signals combined by the means for combining are transmitted. First and second optical transmission media, optical amplification means interposed between the first and second optical transmission media, and wavelength multiplexing transmitted by the first and second optical transmission media In a wavelength division multiplexing transmission system comprising: a means for demultiplexing an optical signal; and N optical receivers for receiving N optical signals having different wavelengths, which are demultiplexed by the demultiplexing means,
Between the first optical transmission medium and the optical amplifying means, a characteristic for compensating the wavelength multiplexed optical signal affected by the group velocity dispersion characteristic of the first optical transmission medium in units of the wavelength multiplexed optical signal a first wavelength dispersion compensation unit having the first dispersion slope compensation having characteristics of compensating the effect of the wavelength-multiplexed optical signal is subjected by the dispersion slope characteristic of said first optical transmission medium in the wavelength-multiplexed optical signal unit Means and
Between the second optical transmission medium and the means for demultiplexing, the influence of the wavelength multiplexed optical signal on the group velocity dispersion characteristic of the second optical transmission medium is compensated in units of the wavelength multiplexed optical signal. A second chromatic dispersion compensation means having a characteristic, and a second dispersion slope having a characteristic for compensating the influence of the WDM optical signal by the dispersion slope characteristic of the second optical transmission medium in units of the WDM optical signal. Compensation means,
The chromatic dispersion compensation means and / or the dispersion slope compensation means include means for making no compensation for a walk-off in which the wavelength multiplexed optical signal is a relative delay between channels caused by a group delay characteristic of the optical transmission medium. the wavelength multiplexing transmission system characterized by comprising.

N optical transmitters for transmitting optical signals of different wavelengths, means for combining the optical signals of the N optical transmitters, and wavelength multiplexed optical signals combined by the means for combining are transmitted. First and second optical transmission media, optical amplification means interposed between the first and second optical transmission media, and wavelength multiplexing transmitted by the first and second optical transmission media In a wavelength division multiplexing transmission system comprising: a means for demultiplexing an optical signal; and N optical receivers for receiving N optical signals having different wavelengths, which are demultiplexed by the demultiplexing means,
Between the first optical transmission medium and the optical amplification means, the wavelength-multiplexed optical signal unit is affected by the wavelength-multiplexed optical signal due to the group velocity dispersion characteristic and the dispersion slope characteristic of the first optical transmission medium. in comprising a first wavelength dispersion and dispersion slope compensating means having a compensation characteristic,
Between the second optical transmission medium and the means for demultiplexing, the wavelength multiplexed optical signal is affected by the group velocity dispersion characteristic and the dispersion slope characteristic of the second optical transmission medium. A second chromatic dispersion and dispersion slope compensation means having a characteristic to compensate in units;
The chromatic dispersion and dispersion slope compensating means includes means for making no compensation for walk-off, which is a relative delay between channels caused by the group delay characteristic of the optical transmission medium. Characteristic wavelength division multiplexing transmission system.