JP2004364033A

JP2004364033A - System and apparatus for optical multiplex transmission and optical multiplex reception apparatus

Info

Publication number: JP2004364033A
Application number: JP2003161040A
Authority: JP
Inventors: Aritomo Kamimura; 有朋上村
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2003-06-05
Filing date: 2003-06-05
Publication date: 2004-12-24
Anticipated expiration: 2023-06-05
Also published as: JP4145726B2

Abstract

<P>PROBLEM TO BE SOLVED: To detect deviation between a transmission wavelength in a wavelength multiplexer, a wavelength demultiplexer, etc. and the output wavelength of a light source by a simple structure. <P>SOLUTION: The optical multiplex transmission system includes a modulation waveform generator for generating a modulation waveform having a periodic waveform with a non-similar pattern when reversing the the waveform in positive and negative sides; a wavelength modulator for modulating an optical signal wavelength according to the modulation waveform; a mean processor for extracting an intensity variation component from an electric signal converted in a photodetector, using a synchronizing signal used for reference timing for data acquisition, and outputting as time waveform; a synchronization detector for detecting a repetition period of the time waveform, generating a synchronizing signal having the detected period, and supplying the generated synchronizing signal to the mean processor; and a waveform evaluation portion for calculating the deviation direction and the deviation amount of the optical wavelength generated by the transmission from the transmission side to the reception side based on the time waveform, and outputting a wavelength error signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明は、波長多重信号を伝送する光ネットワークにおいて、波長多重部や波長分離部などの透過波長と光源の出力波長間の波長ずれを検出し制御管理する光多重伝送システム、光多重送信装置および光多重受信装置に関するものである。
【０００２】
【従来の技術】
光ネットワークを介して通信を行う光多重伝送システムでは、波長多重伝送を行う場合、送信側の光源、波長多重部および受信側の波長分離部における各波長が一致していなくてはならない。そのため、光送信部に含まれる波長制御部により発信波長の絶対値を制御していた（例えば、特許文献１、特許文献２参照）。また、複数の波長を多重する波長多重部および分離する波長分離部は、温度などで中心波長がシフトする場合が多い。そのため、温度制御などを行う波長制御部を設けて絶対波長を制御していた。また、波長多重信号を伝送する光伝送路では、伝送されている波長がずれたり、無くなったりした時に警報を出すように送信波長および受信波長を光スペアナによって監視するようにしてきた。
【０００３】
【特許文献１】
特開２０００−１２９４９号公報
【特許文献２】
特開平７−２０２３１１号公報
【０００４】
【発明が解決しようとする課題】
従来の波長制御方法は、以上のように構成されているので、光送信器、波長多重部、波長分離部などの各部位が独立に規定された絶対波長へ合わせることを目的としており、許容される誤差範囲が狭く、高い制御精度が求められるためにコストが高くなる。また、従来の光送信部の波長制御は、出力波長を絶対波長に正確に合わせるために、光送信器それぞれの内部に絶対波長基準を持つ必要があり、システム全体でコストが高くなる。また、光送信部から出力された光信号の波長監視を行う場合、光強度変化を用いるのではなく光スペクトル自体を光領域で観測する必要があったため、光スペアナなどの高価な光学測定機材が必要となり、コストが高くなるなどの問題があった。
【０００５】
また、特許文献１では、光源の出力波長を光フィルタなどの周波数弁別素子の波長に一致させる技術を用いており、光源の波長を変調信号で微小変調し、周波数弁別素子を透過した後にロックインアンプで変動成分を抽出するようにしている。この技術では、光送信部の変調信号をリファレンスとして光受信部にも供給する必要がある。したがって、光伝送路を経由した光受信端で光波長の誤差を検出するためには、変調信号を別途伝送する必要があり、実現が難しいという問題があった。また、波長多重数が増大し波長間隔が高密度になってきたときには、各光部品に求められる波長精度が厳しくなり、波長ロッカーや光スペアナなどの絶対波長の基準精度を上げるとコストが非常に高くなり、基準精度を甘くしてコストを下げると波長ずれが増大し性能が劣化するという問題があった。
【０００６】
この発明は上記のような課題を解決するためになされたもので、光源の出力波長を微小に周期的に変化させて伝送路を隔てた受光側で光強度変化を検出することにより、波長多重部や波長分離部などの透過波長と光源の出力波長との波長ずれ検出を簡易な構成で行えるようにした光多重伝送システム、光多重送信装置および光多重受信装置を得ることを目的とする。
【０００７】
【課題を解決するための手段】
この発明に係る光多重伝送システムは、送信側で複数の光源から光強度変調したそれぞれの波長の光信号を生成し、波長多重部により各光信号を波長多重して光伝送路を介して他地点の受信側に伝送し、受信側で波長分離部により波長多重された光信号から各波長を分離し、分離された各波長の光信号をそれぞれの受光器で電気信号に変換し再生処理する光多重伝送システムにおいて、送信側は、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生する変調波形発生器と、変調波形に応じて光源から出力する光信号の波長を変調させる波長変調部を備え、受信側は、データ取得のタイミング基準とする同期信号を用いて受光器で変換された電気信号から強度変化成分を抽出して時間波形として出力する平均化処理部と、時間波形の繰返し周期を検出し、検出した周期を持つ同期信号を生成して平均化処理部に与える同期検出部と、時間波形に基づいて、送信側から受信側の伝送により生じた光波長のずれ方向とずれ量を算出し、波長誤差信号として出力する波形評価部を備えたものである。
【０００８】
この発明に係る光多重送信装置は、複数の光源から光強度変調したそれぞれの波長の光信号を生成し、波長多重部により各光信号を波長多重して光伝送路を介して他地点の光多重受信装置に伝送する光多重送信装置において、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生する変調波形発生器と、変調波形に応じて光源から出力する光信号の波長を変調させる波長変調部を備えたものである。
【０００９】
この発明に係る光多重受信装置は、他地点の光多重送信装置から伝送されてきた波長多重された光信号を波長分離部により各波長に分離し、分離された各波長の光信号をそれぞれの受光器で電気信号に変換し再生処理する光多重受信装置において、光多重送信装置で波長多重される前の光信号は、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形により波長が変調されており、受光器で変換された電気信号強度の時間変化を時間波形として出力する信号抽出部と、時間波形に基づいて、相手方の光多重送信装置からの伝送により生じた光波長のずれ方向とずれ量を算出し、波長誤差信号として出力する波形評価部を備えたものである。
【００１０】
【発明の実施の形態】
以下、この発明の各実施の形態を説明する。
実施の形態１．
図１はこの発明の実施の形態１による光多重伝送システムの構成を示すブロック回路図である。なお、この図では説明を簡略化するために、光波長多重伝送システムとして送信側（光多重送装置）と受信側（光多重受信装置）に分けた構成で示しているが、実際の光波長多重伝送システムでは、光伝送路を介して送受信の両機能（図１で光伝送路４を挟んだ左右の回路）を持つ同種光多重送受信装置が配置される場合が一般的と考える。
図１において、送信側は複数の光送信部１、波長多重部２および波長制御部３ａで構成されている。それぞれの光送信部１は、光源７、波長変調部９および変調波形発生器１０から構成されている。光源７は、主信号源８から入力される信号で光強度変調を行い、光信号を出力する手段である。変調波形発生器１０は、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生する手段である。波長変調部９は、変調波形発生器１０の変調波形に応じて、例えば光源７の温度を変化させ、光源７から出力する光信号の波長を変調させる手段である。波長多重部２は、複数の光送信部１から送出される光信号を波長多重する手段である。波長制御部３ａは、波長多重部２の透過波長の温度による影響に対して安定化を図る手段である。光伝送路４は、波長多重部２の波長多重された光信号を光ファイバに結合し受信側に伝送する手段である。
【００１１】
受信側は、波長分離部５、複数の光受信部６および波長制御部３ｂで構成されている。波長分離部５は、波長多重された光信号から各光波長の信号を分離する手段である。波長制御部３ｂは、波長分離部５の透過波長の温度による影響に対して安定化を図る手段である。それぞれの光受信部６は、受光器１１、主信号再生部１２、信号抽出部１７および波形評価部１４から構成されている。受光器１１は、波長分離部５で分離された波長の光信号を電気信号に変換する手段である。主信号再生部１２は、変換された電気信号を増幅およびリタイミングなどの信号再生処理を行い主信号を再生する手段である。信号抽出部１７は、平均化処理部１６および同期検出部１５から構成されている。平均化処理部１６は、データ取得のタイミング基準とする同期信号を用いて受光器１１で変換された電気信号から強度変化成分を抽出し、この強度変化成分を時間波形として出力する手段である。同期検出部１５は、時間波形の繰返し周期を検出し、検出した周期の同期信号を生成して平均化処理部１６に与える手段である。波形評価部１４は、平均化処理部１６で出力された時間波形に基づいて、送信側から受信側の伝送により生じた光信号の波長がずれた方向と量を算出し、波長誤差信号として出力する手段である。
【００１２】
図１の光多重伝送システムの概略動作について説明する。
光送信部１の光源７から出力される光信号が波長多重部２に与えられる。波長多重部２では、他の波長の光信号が同様に入力され、複数の波長の光信号が波長多重され、光ファイバからなる光伝送路４に結合される。波長多重された光信号は、光伝送路４を伝播した後、受信側の波長分離部５により波長ごとの光信号に分離される。波長多重部２および波長分離部５は、温度安定化などを行う波長制御部３ａ，３ｂによって、その透過波長の安定化が図られている。波長分離部５で分波された光信号は、光受信部６の受光器１１で電気信号に変換され、主信号再生部１２で増幅やリタイミングなどの信号再生処理を受けて主信号として光受信部６から取り出される。
【００１３】
次に、この発明が対象とする部分の動作について説明する。
光送信部１の光源７は、主信号源８から入力される信号で光強度変調を行い、光信号を出力する。この光強度変調には、例えばレーザダイオード（以下、ＬＤとする。）の変調電流を変化させる方法、あるいはマッハツェンダ干渉計型の外部光変調器を用いる方法などが適用される。
【００１４】
光源７が出力する光信号の波長は、例えば光源がＬＤの場合には、温度を変化させることによって微調整することが可能である。この発明では、光源７の出力波長は、ＬＤの温度をおおよそ一定に保つことにより波長多重の周波数グリッド近辺に安定化させておく。この状態で、光源７が出力する光信号の波長を変調する。この場合の変調は、波長変調部９が変調波形発生器１０からの変調波形に応じて、例えば光源７の温度を変化させることにより行われ、光源７から出力する光信号の波長は変調される。変調波形発生器１０が出力する変調波形としては、例えば鋸波形などのように、周期的に繰り返され、かつ正負を反転した場合にパターンが相似にならない波形（非相似波形）を用いる。このような特徴を持つ変調波形を使用することによって、波長多重部２や波長分離部５などの光フィルタを透過して波長が強度変化されるときに、光波長がフィルタの中心波長に対してどちら側にずれたのかを判定することが可能となる。光受信部６における波長変化の検出は、信号抽出部１７と波形評価部１４により行われる。
【００１５】
光送信部１で微小に波長変調された光信号が光フィルタ特性を持つ伝送媒体を透過すると光強度変化が発生するが、その変動量はわずかであるため、再生される主信号中の同一周波数成分および光伝送に伴うノイズなどに埋もれてしまう。信号抽出部１７において、平均化処理部１６は、このわずかな光強度の変動量を周期的に平均化処理し、ランダムな成分を打ち消すことで微小な強度変化成分を抽出し、その変化を時間波形として出力する。また同期検出部１５は、平均化処理部１６で抽出増幅された強度変化成分を表す時間波形から、送信側での変調波形の繰返し周期を検出し、検出した周期の同期信号を生成する。この同期信号は、平均化処理の感度を向上させるために、データ取得のタイミング基準として平均化処理部１６へ供給される。
【００１６】
平均化処理部１６から出力される強度変化成分を表す時間波形は、その形状から後述するように、光波長が光フィルタの中心波長に対し、どちら側へどの程度ずれているかの情報を持っている。波形評価部１４は、入力される強度変化成分を表す時間波形を評価し、波形形状と波長ずれの関係から、光波長のずれ方向とずれの量を算出して波長誤差信号として外部へ出力する。外部へ出力された波長誤差信号は、波長異常警報などのオペレーションシステムに対しての通知に使用される。
【００１７】
次に、光源の波長の微小変調とフィルタ透過後の光強度変化の関係について、図２〜図５を用いて説明する。なお、この場合の微小変調の「微小」とは、波長多重された隣接するチャネルとの間隔に対して十分に小さいという意味である。
図２は、光送信部１から光受信部６までの間に含まれる波長多重部２、波長分離部５などの光部品を合計したシステム全体の波長透過特性を示す説明図である。図中、点線は波長多重部２の波長特性の一例を、一点鎖線は波長分離部５の波長特性の一例を、また実線はそれらを合計した全体の波長特性を示している。波長多重部２および波長分離部５の透過波長は、それぞれの波長制御部３ａ，３ｂにより波長制御されている。しかし、制御誤差があったり、入射光の偏波の回転によって若干波長特性がシフトしたりするので、それらの透過波長には若干のずれが発生する。このため全体の波長特性では、中心波長が波長多重の規定グリッドに必ずしも一致するとは限らない。上記システムを伝播する光信号の波長は、全体の波長特性（図２の実線）の中心波長と一致していた方がグリッドに正確に一致させるよりも、伝播後に光受信部６で波長ずれを検出して光源７の波長を調整するための特性として好ましい。
【００１８】
図３は、光源７の出力光波長の変調波形を鋸波とした場合の透過光の強度変化を示す説明図である。光送信部１からの出力光波長が図のように鋸波形状に変動したとき、光受信部６で検出される強度変化成分は、システム全体の波長透過特性を写し取るような形状で時間的に変化し、変調波形発生器１０の鋸波形の繰返し周期で、周期的に同じ時間波形として得られる。同期検出部１５により強度変化成分の時間波形の繰り返しの同期タイミングを検出し、その時間波形を波形評価部１４で処理することによって、光送信部１からの光波長がシステム全体の波長透過特性のどの位置にあるかを求める。
【００１９】
光受信部６の受光器１１で検出される平均光パワーの強度変化成分はごくわずかな変化成分のため、平均化処理部１６は、同期信号を用いて繰返し周期で平均化を行い、主信号やノイズに含まれるランダムな変化成分を打ち消すことで、ノイズの少ない強度変化成分を表す時間波形を得る。同期検出部１５が繰り返しタイミングを抽出できるまでの期間、あるいは同期がはずれた過渡状態においては、周波数安定度がある程度確保された発振器などを用いて繰返し周期に近い周期で平均化処理を行うことで、ノイズの少ない時間波形を抽出する。その抽出した時間波形を用いて同期検出部１５はさらに正確な同期信号を生成する。
なお、上記の平均化処理部１６および波形評価部１４における波形処理は、アナログ回路で実現してもよいが、アナログ／デジタル変換を施してデジタル処理で実現した方が少ない部品点数で簡易に実現することができる。
【００２０】
図４は、光源７の出力光波長の変調波形を３値デジタル信号とした場合の透過光の強度変化を示す説明図である。変調波形発生器１０の出力波形として、３値のデジタル波形を用いると、変調波形の生成が鋸波形より簡易にできる。また、受信側の強度変化成分を表す時間波形も３値もしくは２値の波形となり、信号処理を簡易にすることができる。図に示したように、受信側の強度変化成分を表す時間波形を評価することによって、光波長がシステム全体の透過特性に対してどちら側へどの程度ずれているかを判断することができる。
【００２１】
図５は、光源の出力光波長の変調波形を正弦波とした場合の透過光の強度変化を示す説明図である。この例では、正弦波を使用したときには、光波長がシステム全体の透過特性に対してずれた方向を検出できないことを示している。波長変調が正弦波の場合は、光波長が中心波長からずれたときに強度変化成分を表す時間波形が生成されるが、このケースでは波長がどちら側へ変化しても図５（ｂ），（ｃ）に示すように生成された両時間波形は相似の波形となってしまう。そのため、ずれの方向は波形のみでは判断できず、特許文献２のように、波長微小変調の位相と時間波形の位相を比較する必要がある。特許文献２では、光送信部の内部で波長制御を行っているため、微小変調位相と時間波形の位相比較はロックインアンプなどで容易に実現することができるが、光伝送路を経由した受信側では微小変調の位相情報が無いため、時間波形から波長ずれの方向を判別することができない。
【００２２】
光波長の変化は、光波長が波長透過特性の右肩にある場合と左肩にある場合とで、正負が反転した強度変化となって現れる。光波長のずれの方向を判断するためには、光波長が右肩にある場合と左肩にある場合を、強度変化成分を表す時間波形で判別することが必要である。よって、受信側で検出した強度変化成分の時間波形から波長ずれの方向を検出するためには、微小変調信号の正負を反転した波形が非相似となることが必要条件となる。なお、ずれ量については、時間波形の振幅の大きさとその形状から算出する。
【００２３】
図６は、正負を反転した場合、相似、非相似となる各種波形の一覧を示す説明図である。正弦波形は、正負を反転すると位相は１８０度変化するが、波形は相似形であり、波長ずれの方向を検出することができない。一方、鋸波形および３値デジタル波形は、正負を反転すると非相似形となるため、強度変化成分を表す時間波形を観測することで波長ずれの方向を検出できるので、変調波形として適している。同様に、図６（ｄ）のＰＮランダム信号（擬似ランダム信号）などのような２値デジタル波形も、正負を反転したときに非相似形となるため、変調波形として用いれば受信側で波長ずれの方向を検出できる。また、ＳＤＨフレーム信号などのようなフレーム同期信号を持った信号の場合も、正負反転するとフレーム同期ができない非相似形になるため、同様に波長ずれの方向を検出することが可能となる。フレーム信号の場合は、フレーム中の一部のみを波長検出のために使用し、他の部分を制御信号などの転送に使用してもよい。
【００２４】
以上のように、この実施の形態１によれば、送信側の変調波形発生器１０により周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生させ、その変調波形に応じて波長変調部９により光源７の温度を変化させ、光源７から出力する光信号の波長を微小変調し、受信側の平均化処理部１６により、データ取得のタイミング基準とする同期信号を用いて受光器１１で変換された電気信号から強度変化成分を抽出して時間波形として出力させ、、同期検出部１５により時間波形の繰返し周期を検出し、検出した周期を持つ同期信号を生成して平均化処理部に与え、波形評価部で、時間波形に基づいて送信側から受信側の伝送により生じた光波長のずれ方向とずれ量を算出し、波長誤差信号として出力するようにしている。したがって、光送信部１から光受信部６までの波長透過特性と光源の出力光波長のずれ検出を、特に高価な光部品を使用することなく簡易な構成で行うことができる効果が得られる。特に、波長ずれ検出のために必要な光源７の波長の微小変調は温度変調により行い、光受信部６での強度変化成分を表す時間波形の抽出および波形処理はデジタル処理を適用することで非常に簡易な構成で実現できる効果が得られる。なお、この実施の形態１では、光源７の波長の微小変調には温度変調を用いているが、この発明は、温度変調以外の他の変調方法を適用することでも実現できることは言うまでもない。
【００２５】
実施の形態２．
図７はこの発明の実施の形態２による光多重伝送システムの構成を示すブロック回路図である。図において、図１と同じ部分には同一符号を付し、原則としてその説明は省略する。実施の形態２では、新たに、受信側が監視制御部１８および制御信号送信手段１９を備え、送信側が制御信号受信手段２０を備えている。監視制御部１８は、波形評価部１４により算出された光波長のずれ方向とずれの量を表す波長誤差信号の適正を監視し、適正でない場合には異常警報などでシステムの管理者に知らせる。また、適正でない場合には、その波長誤差信号を制御信号送信手段１９に入力する。制御信号送信手段１９は、波長誤差信号を制御信号として対向する送信側へ転送する手段である。制御信号受信手段２０は、転送された波長誤差信号を受信して波長変調部９へ与える手段である。
【００２６】
次に、動作について説明する。
波形評価部１４により算出された光波長のずれ方向とずれの量を表す波長誤差信号は、監視制御部１８に通知され、波長異常が監視される。また、波長誤差信号は制御信号送信手段１９により受信側の制御信号受信手段２０へ転送される。転送された波長誤差信号は、光送信部１の波長変調部９に与えられる。波長変調部９は、受信した波長誤差信号が示す光波長のずれ方向とずれ量を小さくし、光送信部１の出力光波長が光ネットワークの波長透過特性の最適位置に来るように当該波長誤差信号に応答して光源７の温度を制御する。このように、光受信部６で検出した波長のずれを補正する光送信部１へのフィードバック構成を持つ。
なお、制御信号送信手段１９から制御信号受信手段２０への波長誤差信号の伝達は、例えば主信号とは異なるＳＶ光（スーパバイザリ光）を用いる方法、あるいは主信号に適用された誤り訂正フレームの監視領域を用いる方法により行われる。また、この場合の波長の変動は非常に緩慢であるので、高速の信号伝達は必要無く、インターネットなどの別ネットワークを経由して伝達するようにしてもよい。
【００２７】
以上のように、この実施の形態２によれば、波形評価部１４で算出された光波長のずれ方向とずれ量を示す波長誤差信号を制御信号送信手段１９により対向する送信側へ転送し、送信側の制御信号受信手段２０は、この転送された波長誤差信号を受信して波長変調部９へ与え、波長変調部９が、受信した波長誤差信号に応答して光波長のずれ方向とずれ量を小さくするように光源の温度を制御するようにしている。したがって、光送信部１から光受信部６までの波長透過特性と光源の出力波長を一致させる機能を、特に高価な光波長モニタのための光部品などを使用することなく、簡単な構成で安価に実現きる効果が得られる。また、波長多重部、波長分離部および光伝送路中の光部品類の波長特性が絶対波長において基準値からずれてしまったときに、従来のように光源の波長を絶対波長で制御すると最適な伝送特性が得られないが、この発明によれば光源の波長を光伝送路状態に合わせた最適な波長に合わせこむことでき、伝送特性などの性能を向上させる効果が得られる。
【００２８】
【発明の効果】
以上のように、この発明によれば、送信側で複数の光源から光強度変調したそれぞれの波長の光信号を生成し、波長多重部により各光信号を波長多重して光伝送路を介して他地点の受信側に伝送し、受信側で波長分離部により波長多重された光信号から各波長を分離し、分離された各波長の光信号をそれぞれの受光器で電気信号に変換し再生処理する光多重伝送システムにおいて、送信側は、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生する変調波形発生器と、変調波形に応じて光源から出力する光信号の波長を変調させる波長変調部を備え、受信側は、データ取得のタイミング基準とする同期信号を用いて受光器で変換された電気信号から強度変化成分を抽出して時間波形として出力する平均化処理部と、時間波形の繰返し周期を検出し、検出した周期を持つ同期信号を生成して平均化処理部に与える同期検出部と、時間波形に基づいて、送信側から受信側の伝送により生じた光波長のずれ方向とずれ量を算出し、波長誤差信号として出力する波形評価部を備えるように構成したので、光送信部から光受信部までの波長透過特性と光源の出力光波長のずれ検出を簡易な構成で行うことができる効果がある。特に、波長ずれ検出のために必要な光源の波長微小変調は温度変調により実現でき、光受信部での強度変化成分を表す時間信号の抽出および波形処理はデジタル処理を適用することで非常に簡易な構成で実現できる効果がある。
【００２９】
また、この発明によれば、複数の光源から光強度変調したそれぞれの波長の光信号を生成し、波長多重部により各光信号を波長多重して光伝送路を介して他地点の光多重受信装置に伝送する光多重送信装置において、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形を発生する変調波形発生器と、変調波形に応じて光源から出力する光信号の波長を変調させる波長変調部を備えるように構成したので、対応する受信装置との間で、光送信部から光受信部までの波長透過特性と光源の出力光波長のずれ検出を簡易な構成で実現できる効果がある。特に、波長ずれ検出のために必要な光源の波長微小変調は温度変調により実現でき、光受信部での強度変化成分を表す時間信号の抽出および波形処理はデジタル処理を適用することで非常に簡易な構成で実現できる効果がある。
【００３０】
さらに、この発明によれば、他地点の光多重送信装置から伝送されてきた波長多重された光信号を波長分離部により各波長に分離し、分離された各波長の光信号をそれぞれの受光器で電気信号に変換し再生処理する光多重受信装置において、光多重送信装置で波長多重される前の光信号は、周期的でかつ正負を反転させた場合にパターンが非相似となる波形を持つ変調波形により波長が変調されており、受光器で変換された電気信号強度の時間変化を時間波形として出力する信号抽出部と、時間波形に基づいて、相手方の光多重送信装置からの伝送により生じた光波長のずれ方向とずれ量を算出し、波長誤差信号として出力する波形評価部を備えるように構成したので、対応する送信装置との間で、光送信部から光受信部までの波長透過特性と光源の出力光波長のずれ検出を簡易な構成で実現できる効果がある。特に、波長ずれ検出のために必要な光源の波長微小変調は温度変調により実現でき、光受信部での強度変化成分を表す時間信号の抽出および波形処理はデジタル処理を適用することで非常に簡易な構成で実現できる効果がある。
【図面の簡単な説明】
【図１】この発明の実施の形態１による光多重伝送システムの構成を示すブロック回路図である。
【図２】システム全体の波長透過特性を示す説明図である。
【図３】光源の出力光波長の変調波形を鋸波とした場合の透過光の強度変化を示す説明図である。
【図４】光源の出力光波長の変調波形を３値ディジタル信号とした場合の透過光の強度変化を示す説明図である。
【図５】光源の出力光波長の微小変調波形を正弦波とした場合の透過光の強度変化の関係を示す説明図である。
【図６】正負反転して相似、非相似となる各種波形の一覧を示す説明図である。
【図７】この発明の実施の形態２による光多重伝送システムの構成を示すブロック回路図である。
【符号の説明】
１光送信部、２波長多重部、３ａ，３ｂ波長制御部、４光伝送路、５波長分離部、６光受信部、７光源、８主信号原、９波長変調部、１０変調波形発生器、１１受光器、１２主信号再生部、１４波形評価部、１５同期検出部、１６平均化処理部、１７信号抽出部、１８監視制御部、１９制御信号送信手段、２０制御信号受信手段。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical multiplex transmission system, an optical multiplex transmitter, and an optical network for transmitting a wavelength multiplex signal, which detects and controls and manages a wavelength shift between a transmission wavelength of a wavelength multiplexing unit and a wavelength separation unit and an output wavelength of a light source. The present invention relates to an optical multiplex receiving device.
[0002]
[Prior art]
In an optical multiplex transmission system that performs communication via an optical network, when performing wavelength multiplex transmission, the wavelengths of a light source on the transmitting side, a wavelength multiplexing unit, and a wavelength separating unit on the receiving side must match. Therefore, the absolute value of the emission wavelength is controlled by a wavelength control unit included in the optical transmission unit (for example, see Patent Documents 1 and 2). Also, the wavelength multiplexing unit that multiplexes a plurality of wavelengths and the wavelength separation unit that separates a plurality of wavelengths often shift the center wavelength due to temperature or the like. Therefore, an absolute wavelength is controlled by providing a wavelength controller for performing temperature control or the like. In an optical transmission line for transmitting a wavelength-division multiplexed signal, an optical spectrum analyzer has been used to monitor a transmission wavelength and a reception wavelength so that an alarm is issued when the transmitted wavelength shifts or disappears.
[0003]
[Patent Document 1]
JP-A-2000-12949
[Patent Document 2]
JP-A-7-202311
[0004]
[Problems to be solved by the invention]
Since the conventional wavelength control method is configured as described above, the purpose of each part such as the optical transmitter, the wavelength multiplexing unit, and the wavelength demultiplexing unit is to adjust to the absolute wavelength defined independently, and it is allowed. The error range is narrow, and high control accuracy is required, which increases the cost. Further, in the conventional wavelength control of the optical transmitter, it is necessary to have an absolute wavelength reference inside each optical transmitter in order to accurately adjust the output wavelength to the absolute wavelength, which increases the cost of the entire system. Also, when monitoring the wavelength of the optical signal output from the optical transmission unit, it was necessary to observe the optical spectrum itself in the optical region instead of using the light intensity change, so expensive optical measuring equipment such as an optical spectrumr was used. However, there is a problem that the cost becomes high.
[0005]
Further, Patent Document 1 uses a technique for matching the output wavelength of a light source to the wavelength of a frequency discriminating element such as an optical filter. The wavelength of the light source is minutely modulated by a modulation signal, and the light is locked in after passing through the frequency discriminating element. The fluctuation component is extracted by the amplifier. In this technique, it is necessary to supply the modulated signal of the optical transmitter to the optical receiver as a reference. Therefore, in order to detect an error in the optical wavelength at the optical receiving end via the optical transmission line, it is necessary to separately transmit a modulation signal, and there has been a problem that implementation is difficult. In addition, when the number of wavelength multiplexes increases and the wavelength interval becomes higher, the wavelength accuracy required for each optical component becomes stricter. If the reference accuracy of the absolute wavelength such as a wavelength locker or an optical spectrumr is increased, the cost becomes extremely high. If the standard accuracy is reduced and the cost is reduced, the wavelength shift increases and the performance deteriorates.
[0006]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and wavelength multiplexing is performed by detecting a change in light intensity on a light receiving side across a transmission line by periodically and minutely changing the output wavelength of a light source. It is an object of the present invention to provide an optical multiplex transmission system, an optical multiplex transmission device, and an optical multiplex reception device that can detect a wavelength shift between a transmission wavelength of a light source and a wavelength separation unit and an output wavelength of a light source with a simple configuration.
[0007]
[Means for Solving the Problems]
An optical multiplexing transmission system according to the present invention generates optical signals of respective wavelengths that are light intensity modulated from a plurality of light sources on a transmitting side, wavelength-multiplexes each optical signal by a wavelength multiplexing unit, and performs other wavelength multiplexing via an optical transmission path. Transmitted to the receiving side at the point, the receiving side separates each wavelength from the wavelength multiplexed optical signal by the wavelength demultiplexing unit, and converts the separated optical signal of each wavelength into an electric signal with each optical receiver and performs the reproduction processing. In an optical multiplex transmission system, a transmitting side outputs a modulation waveform generator that generates a modulation waveform having a waveform that is periodic and whose pattern becomes non-similar when the sign is inverted, and outputs the light from a light source according to the modulation waveform. A wavelength modulation unit for modulating the wavelength of the optical signal is provided, and the receiving side extracts an intensity change component from the electric signal converted by the light receiver using a synchronization signal as a timing reference for data acquisition, and outputs the extracted signal as a time waveform. flat A synchronization processing unit, a synchronization detection unit that detects a repetition period of the time waveform, generates a synchronization signal having the detected period, and provides the synchronization signal to the averaging processing unit, and performs transmission from the transmission side to the reception side based on the time waveform. The apparatus is provided with a waveform evaluation unit that calculates the direction and amount of shift of the generated light wavelength and outputs the result as a wavelength error signal.
[0008]
An optical multiplex transmission apparatus according to the present invention generates optical signals of respective wavelengths, which are light intensity modulated, from a plurality of light sources, wavelength-multiplexes each optical signal by a wavelength multiplexing unit, and transmits the optical signal at another point via an optical transmission line. In an optical multiplex transmitting apparatus for transmitting to a multiplex receiving apparatus, a modulation waveform generator that generates a modulation waveform having a waveform that is non-similar when it is periodic and the sign is inverted, and a light source according to the modulation waveform. It has a wavelength modulator for modulating the wavelength of an optical signal to be output.
[0009]
An optical multiplex receiving apparatus according to the present invention separates a wavelength-multiplexed optical signal transmitted from an optical multiplex transmitting apparatus at another point into respective wavelengths by a wavelength demultiplexer, and separates the separated optical signals of respective wavelengths into respective wavelengths. In an optical multiplexing receiver that converts an electric signal into an electrical signal with a light receiver and reproduces the signal, the optical signal before being wavelength-multiplexed by the optical multiplexing transmitter has a waveform that is periodic and has a pattern that is not similar when inverted. The wavelength is modulated by a modulation waveform having a signal extractor that outputs a time change of the electric signal intensity converted by the light receiver as a time waveform, and transmission from the optical multiplex transmission device of the other party based on the time waveform. And a waveform evaluation unit that calculates the shift direction and shift amount of the light wavelength caused by the above and outputs the calculated wavelength error signal.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
Embodiment 1 FIG.
FIG. 1 is a block circuit diagram showing a configuration of an optical multiplex transmission system according to Embodiment 1 of the present invention. In this figure, for the sake of simplicity, the optical wavelength division multiplexing transmission system is shown as being divided into a transmission side (optical multiplex transmission apparatus) and a reception side (optical multiplex reception apparatus). In a multiplex transmission system, it is generally considered that the same type of optical multiplex transmission / reception apparatus having both functions of transmission and reception (left and right circuits sandwiching the optical transmission path 4 in FIG. 1) is arranged via the optical transmission path.
In FIG. 1, the transmission side includes a plurality of optical transmission units 1, a wavelength multiplexing unit 2, and a wavelength control unit 3a. Each optical transmission unit 1 includes a light source 7, a wavelength modulation unit 9, and a modulation waveform generator 10. The light source 7 is a unit that performs light intensity modulation with a signal input from the main signal source 8 and outputs an optical signal. The modulation waveform generator 10 is means for generating a modulation waveform having a waveform which is periodic and whose pattern becomes non-similar when the sign is inverted. The wavelength modulation unit 9 is a unit that changes, for example, the temperature of the light source 7 according to the modulation waveform of the modulation waveform generator 10 and modulates the wavelength of the optical signal output from the light source 7. The wavelength multiplexing unit 2 is means for wavelength multiplexing the optical signals transmitted from the plurality of optical transmission units 1. The wavelength control section 3a is a means for stabilizing the transmission wavelength of the wavelength multiplexing section 2 against the influence of the temperature. The optical transmission line 4 is means for coupling the wavelength-multiplexed optical signal of the wavelength multiplexing unit 2 to an optical fiber and transmitting the optical signal to the receiving side.
[0011]
The receiving side includes a wavelength separation unit 5, a plurality of optical reception units 6, and a wavelength control unit 3b. The wavelength separation unit 5 is a unit that separates a signal of each optical wavelength from the wavelength-multiplexed optical signal. The wavelength control section 3b is a means for stabilizing the transmission wavelength of the wavelength separation section 5 against the influence of temperature. Each of the optical receiving units 6 includes a light receiver 11, a main signal reproducing unit 12, a signal extracting unit 17, and a waveform evaluating unit 14. The light receiver 11 is a unit that converts an optical signal having a wavelength separated by the wavelength separation unit 5 into an electric signal. The main signal reproducing unit 12 is means for reproducing the main signal by performing signal reproduction processing such as amplification and retiming on the converted electric signal. The signal extraction unit 17 includes an averaging processing unit 16 and a synchronization detection unit 15. The averaging section 16 is a means for extracting an intensity change component from the electric signal converted by the light receiver 11 using a synchronization signal as a timing reference for data acquisition, and outputting the intensity change component as a time waveform. The synchronization detection unit 15 is a unit that detects a repetition period of the time waveform, generates a synchronization signal of the detected period, and provides the synchronization signal to the averaging processing unit 16. The waveform evaluation unit 14 calculates, based on the time waveform output by the averaging processing unit 16, the direction and amount of the wavelength shift of the optical signal generated by transmission from the transmission side to the reception side, and outputs it as a wavelength error signal. It is a means to do.
[0012]
A schematic operation of the optical multiplex transmission system of FIG. 1 will be described.
An optical signal output from the light source 7 of the optical transmission unit 1 is provided to the wavelength multiplexing unit 2. In the wavelength multiplexing unit 2, optical signals of other wavelengths are similarly input, and optical signals of a plurality of wavelengths are multiplexed and coupled to an optical transmission line 4 composed of an optical fiber. The wavelength-multiplexed optical signal propagates through the optical transmission path 4 and is separated into an optical signal for each wavelength by a wavelength separator 5 on the receiving side. The wavelength multiplexing unit 2 and the wavelength demultiplexing unit 5 stabilize their transmission wavelengths by the wavelength control units 3a and 3b that stabilize the temperature. The optical signal demultiplexed by the wavelength separation unit 5 is converted into an electric signal by the optical receiver 11 of the optical reception unit 6, subjected to signal reproduction processing such as amplification and retiming by the main signal reproduction unit 12, and converted into an optical signal as a main signal. It is taken out from the receiving unit 6.
[0013]
Next, the operation of the part targeted by the present invention will be described.
The light source 7 of the optical transmission unit 1 performs light intensity modulation with a signal input from the main signal source 8 and outputs an optical signal. For this light intensity modulation, for example, a method of changing a modulation current of a laser diode (hereinafter, referred to as an LD), a method using a Mach-Zehnder interferometer type external light modulator, and the like are applied.
[0014]
For example, when the light source is an LD, the wavelength of the optical signal output from the light source 7 can be finely adjusted by changing the temperature. In the present invention, the output wavelength of the light source 7 is stabilized near the wavelength multiplexed frequency grid by keeping the temperature of the LD approximately constant. In this state, the wavelength of the optical signal output from the light source 7 is modulated. The modulation in this case is performed, for example, by changing the temperature of the light source 7 according to the modulation waveform from the modulation waveform generator 10 by the wavelength modulation unit 9, and the wavelength of the optical signal output from the light source 7 is modulated. . As a modulation waveform output from the modulation waveform generator 10, a waveform (a non-similar waveform) such as a sawtooth waveform, which is periodically repeated and whose pattern does not become similar when the sign is inverted, is used. By using a modulated waveform having such characteristics, when the intensity of the wavelength is changed by passing through an optical filter such as the wavelength multiplexing unit 2 or the wavelength demultiplexing unit 5, the light wavelength is changed with respect to the center wavelength of the filter. It is possible to determine on which side the displacement has occurred. The detection of the wavelength change in the optical receiving unit 6 is performed by the signal extracting unit 17 and the waveform evaluating unit 14.
[0015]
When an optical signal whose wavelength is slightly modulated by the optical transmission unit 1 passes through a transmission medium having an optical filter characteristic, a change in light intensity occurs. However, since the change amount is small, the same frequency in the reproduced main signal is used. It is buried in components and noise accompanying optical transmission. In the signal extraction unit 17, the averaging processing unit 16 periodically averages the slight variation in light intensity, cancels out random components, extracts a minute intensity change component, and compares the change with time. Output as a waveform. The synchronization detection unit 15 detects a repetition period of the modulation waveform on the transmission side from a time waveform representing the intensity change component extracted and amplified by the averaging processing unit 16, and generates a synchronization signal of the detected period. This synchronization signal is supplied to the averaging unit 16 as a timing reference for data acquisition in order to improve the sensitivity of the averaging process.
[0016]
The time waveform representing the intensity change component output from the averaging processing unit 16 has information on which side and how much the optical wavelength is shifted from the center wavelength of the optical filter due to its shape, as described later. I have. The waveform evaluation unit 14 evaluates the time waveform representing the input intensity change component, calculates the shift direction and the shift amount of the optical wavelength from the relationship between the waveform shape and the wavelength shift, and outputs the calculated wavelength error signal to the outside. . The wavelength error signal output to the outside is used for notification to an operation system such as a wavelength abnormality alarm.
[0017]
Next, the relationship between the minute modulation of the wavelength of the light source and the change in light intensity after passing through the filter will be described with reference to FIGS. In this case, "small" of the minute modulation means that the distance between the adjacent channels that are wavelength-multiplexed is sufficiently small.
FIG. 2 is an explanatory diagram showing the wavelength transmission characteristics of the entire system in which optical components such as the wavelength multiplexing unit 2 and the wavelength demultiplexing unit 5 included between the optical transmitting unit 1 and the optical receiving unit 6 are combined. In the figure, a dotted line shows an example of the wavelength characteristic of the wavelength multiplexing unit 2, an alternate long and short dash line shows an example of the wavelength characteristic of the wavelength demultiplexing unit 5, and a solid line shows the total wavelength characteristic obtained by adding them. The transmission wavelengths of the wavelength multiplexing unit 2 and the wavelength separation unit 5 are wavelength-controlled by the respective wavelength control units 3a and 3b. However, since there is a control error or the wavelength characteristic slightly shifts due to the rotation of the polarization of the incident light, a slight shift occurs between the transmission wavelengths. For this reason, in the entire wavelength characteristics, the center wavelength does not always coincide with the specified grid of wavelength multiplexing. When the wavelength of an optical signal propagating through the above system coincides with the center wavelength of the entire wavelength characteristic (solid line in FIG. 2), the wavelength shift in the optical receiving unit 6 after propagation is more accurate than when the wavelength coincides with the grid. This is preferable as a characteristic for detecting and adjusting the wavelength of the light source 7.
[0018]
FIG. 3 is an explanatory diagram showing a change in intensity of transmitted light when the modulation waveform of the output light wavelength of the light source 7 is a sawtooth wave. When the wavelength of the output light from the optical transmitter 1 fluctuates in a sawtooth shape as shown in the figure, the intensity change component detected by the optical receiver 6 is temporally changed to a shape that reflects the wavelength transmission characteristics of the entire system. It changes and is obtained as the same time waveform periodically at the repetition period of the sawtooth waveform of the modulation waveform generator 10. The synchronization detection unit 15 detects the synchronization timing of the repetition of the time waveform of the intensity change component, and the time waveform is processed by the waveform evaluation unit 14 so that the light wavelength from the optical transmission unit 1 can be used as the wavelength transmission characteristic of the entire system. Find out where it is.
[0019]
Since the intensity change component of the average light power detected by the light receiver 11 of the light receiving unit 6 is a very small change component, the averaging processing unit 16 performs averaging in a repetitive cycle using a synchronization signal, and outputs the main signal. By canceling random change components included in the noise and the noise, a time waveform representing an intensity change component with less noise is obtained. In the period until the synchronization detection unit 15 can repeatedly extract the timing, or in a transient state in which synchronization is lost, the averaging process is performed at a cycle close to the repetition cycle using an oscillator or the like having a certain degree of frequency stability. , A time waveform with less noise is extracted. Using the extracted time waveform, the synchronization detector 15 generates a more accurate synchronization signal.
The waveform processing in the averaging processing unit 16 and the waveform evaluation unit 14 may be realized by an analog circuit. However, it is easier to perform analog / digital conversion and to realize the processing by digital processing with a smaller number of parts. can do.
[0020]
FIG. 4 is an explanatory diagram showing the intensity change of transmitted light when the modulation waveform of the output light wavelength of the light source 7 is a ternary digital signal. When a ternary digital waveform is used as the output waveform of the modulation waveform generator 10, the generation of the modulation waveform can be made easier than the sawtooth waveform. Further, the time waveform representing the intensity change component on the receiving side is also a ternary or binary waveform, and signal processing can be simplified. As shown in the figure, by evaluating the time waveform representing the intensity change component on the receiving side, it is possible to determine which side and how much the optical wavelength is shifted with respect to the transmission characteristics of the entire system.
[0021]
FIG. 5 is an explanatory diagram illustrating a change in the intensity of transmitted light when the modulation waveform of the output light wavelength of the light source is a sine wave. This example shows that when a sine wave is used, it is not possible to detect a direction in which the light wavelength is deviated from the transmission characteristics of the entire system. When the wavelength modulation is a sine wave, a time waveform representing an intensity change component is generated when the light wavelength deviates from the center wavelength. In this case, no matter which side the wavelength changes, the waveform shown in FIG. The two time waveforms generated as shown in (c) are similar waveforms. For this reason, the direction of the shift cannot be determined only by the waveform, and it is necessary to compare the phase of the minute wavelength modulation with the phase of the time waveform as in Patent Document 2. In Patent Literature 2, since the wavelength control is performed inside the optical transmission unit, the phase comparison between the minute modulation phase and the time waveform can be easily realized by a lock-in amplifier or the like. Since there is no phase information of the minute modulation on the side, the direction of the wavelength shift cannot be determined from the time waveform.
[0022]
The change in the light wavelength appears as a change in the intensity where the sign is reversed between the case where the light wavelength is on the right shoulder and the case where the light wavelength is on the left shoulder of the wavelength transmission characteristic. In order to determine the direction of the shift of the light wavelength, it is necessary to determine the case where the light wavelength is on the right shoulder and the case where the light wavelength is on the left shoulder using a time waveform representing an intensity change component. Therefore, in order to detect the direction of the wavelength shift from the time waveform of the intensity change component detected on the receiving side, a necessary condition is that the waveform obtained by inverting the sign of the minute modulation signal is not similar. Note that the shift amount is calculated from the magnitude and shape of the amplitude of the time waveform.
[0023]
FIG. 6 is an explanatory diagram showing a list of various waveforms that are similar and non-similar when the sign is inverted. The phase of the sine waveform changes by 180 degrees when the sign is inverted, but the waveform is similar and the direction of the wavelength shift cannot be detected. On the other hand, the sawtooth waveform and the ternary digital waveform become non-similar when inverted, so that the direction of the wavelength shift can be detected by observing the time waveform representing the intensity change component, and thus is suitable as the modulation waveform. Similarly, a binary digital waveform such as a PN random signal (pseudo-random signal) shown in FIG. 6D has a non-similar shape when the sign is inverted. Direction can be detected. Also, in the case of a signal having a frame synchronization signal such as an SDH frame signal or the like, a non-similar shape in which frame synchronization is not possible if the sign is reversed, it is possible to detect the direction of the wavelength shift in the same manner. In the case of a frame signal, only a part of the frame may be used for wavelength detection, and the other part may be used for transmitting a control signal or the like.
[0024]
As described above, according to the first embodiment, the modulation waveform generator 10 on the transmission side generates a modulation waveform having a waveform which is periodic and whose pattern becomes non-similar when the sign is inverted. The temperature of the light source 7 is changed by the wavelength modulation unit 9 according to the modulation waveform, the wavelength of the optical signal output from the light source 7 is minutely modulated, and the averaging processing unit 16 on the receiving side is used as a synchronization reference for timing of data acquisition. The intensity change component is extracted from the electric signal converted by the light receiver 11 using the signal, and is output as a time waveform. The repetition period of the time waveform is detected by the synchronization detection unit 15, and the synchronization signal having the detected period is detected. Generated and provided to the averaging processing unit, and the waveform evaluation unit calculates the shift direction and the shift amount of the optical wavelength caused by the transmission from the transmission side to the reception side based on the time waveform, and outputs it as a wavelength error signal. There. Therefore, an effect is obtained that the shift between the wavelength transmission characteristics from the optical transmitter 1 to the optical receiver 6 and the output light wavelength of the light source can be detected with a simple configuration without using particularly expensive optical components. In particular, the minute modulation of the wavelength of the light source 7 necessary for detecting the wavelength shift is performed by temperature modulation, and the extraction of the time waveform representing the intensity change component and the waveform processing in the light receiving unit 6 are performed by applying digital processing. Thus, an effect that can be realized with a simple configuration can be obtained. In the first embodiment, the temperature modulation is used for the minute modulation of the wavelength of the light source 7. However, it goes without saying that the present invention can be realized by applying a modulation method other than the temperature modulation.
[0025]
Embodiment 2 FIG.
FIG. 7 is a block circuit diagram showing a configuration of an optical multiplex transmission system according to Embodiment 2 of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted in principle. In the second embodiment, the receiving side newly includes the monitoring control unit 18 and the control signal transmitting unit 19, and the transmitting side includes the control signal receiving unit 20. The monitoring control unit 18 monitors the appropriateness of the wavelength error signal indicating the shift direction and the amount of shift of the optical wavelength calculated by the waveform evaluation unit 14, and notifies the system administrator by an abnormality alarm or the like if the wavelength error signal is not appropriate. If the wavelength error signal is not appropriate, the wavelength error signal is input to the control signal transmitting means 19. The control signal transmitting means 19 is a means for transferring the wavelength error signal as a control signal to the opposite transmitting side. The control signal receiving means 20 is a means for receiving the transferred wavelength error signal and providing it to the wavelength modulation unit 9.
[0026]
Next, the operation will be described.
The wavelength error signal indicating the shift direction and the shift amount of the optical wavelength calculated by the waveform evaluation unit 14 is notified to the monitoring control unit 18 and the wavelength abnormality is monitored. The wavelength error signal is transferred by the control signal transmitting means 19 to the control signal receiving means 20 on the receiving side. The transferred wavelength error signal is provided to the wavelength modulator 9 of the optical transmitter 1. The wavelength modulation unit 9 reduces the shift direction and the shift amount of the optical wavelength indicated by the received wavelength error signal, and adjusts the wavelength error so that the output light wavelength of the optical transmission unit 1 comes to the optimum position of the wavelength transmission characteristic of the optical network. The temperature of the light source 7 is controlled in response to the signal. As described above, a feedback configuration to the optical transmitter 1 for correcting the wavelength shift detected by the optical receiver 6 is provided.
The transmission of the wavelength error signal from the control signal transmitting means 19 to the control signal receiving means 20 may be performed, for example, by using an SV light (supervisory light) different from the main signal, or by transmitting an error correction frame applied to the main signal. This is performed by a method using a monitoring area. In this case, since the fluctuation of the wavelength is very slow, high-speed signal transmission is not required, and the signal may be transmitted via another network such as the Internet.
[0027]
As described above, according to the second embodiment, the wavelength error signal indicating the shift direction and the shift amount of the optical wavelength calculated by the waveform evaluation unit 14 is transferred to the opposite transmitting side by the control signal transmitting unit 19, The control signal receiving means 20 on the transmission side receives the transferred wavelength error signal and provides it to the wavelength modulation unit 9. The wavelength modulation unit 9 responds to the received wavelength error signal and shifts and shifts the optical wavelength. The temperature of the light source is controlled so as to reduce the amount. Therefore, the function of matching the wavelength transmission characteristics from the light transmitting unit 1 to the light receiving unit 6 to the output wavelength of the light source can be achieved with a simple configuration and at low cost without using an optical component for an expensive optical wavelength monitor. The effect that can be realized is obtained. Further, when the wavelength characteristics of the wavelength division multiplexing unit, the wavelength demultiplexing unit and the optical components in the optical transmission line deviate from the reference value in the absolute wavelength, it is optimal to control the wavelength of the light source with the absolute wavelength as in the related art. Although transmission characteristics cannot be obtained, according to the present invention, the wavelength of the light source can be adjusted to an optimum wavelength according to the state of the optical transmission line, and an effect of improving performance such as transmission characteristics can be obtained.
[0028]
【The invention's effect】
As described above, according to the present invention, the transmission side generates optical signals of each wavelength subjected to optical intensity modulation from a plurality of light sources, wavelength-multiplexes each optical signal by the wavelength multiplexing unit, and transmits the optical signal via the optical transmission line. Transmitted to the receiving side at another point, the receiving side separates each wavelength from the wavelength multiplexed optical signal by the wavelength demultiplexing unit, and converts the separated optical signal of each wavelength into an electric signal by each photodetector and reproduces it. In an optical multiplexing transmission system, a transmitting side generates a modulation waveform generator that generates a modulation waveform having a waveform that is periodic and whose pattern becomes non-similar when the sign is inverted, and outputs from a light source according to the modulation waveform. The receiver has a wavelength modulator that modulates the wavelength of the optical signal to be received, and the receiving side extracts the intensity change component from the electrical signal converted by the photodetector using a synchronization signal as a timing reference for data acquisition and outputs it as a time waveform Averaging And a synchronization detection unit that detects a repetition period of the time waveform, generates a synchronization signal having the detected period, and provides the synchronization signal to the averaging processing unit, and generates a synchronization signal from the transmission side to the reception side based on the time waveform. It is configured to include a waveform evaluation unit that calculates the shift direction and shift amount of the optical wavelength and outputs the result as a wavelength error signal, so that the wavelength transmission characteristics from the optical transmitter to the optical receiver and the shift of the output light wavelength of the light source are different. There is an effect that detection can be performed with a simple configuration. In particular, the wavelength modulation of the light source required for wavelength shift detection can be realized by temperature modulation, and the extraction of the time signal representing the intensity change component and the waveform processing at the optical receiver are very simple by applying digital processing. There is an effect that can be realized with a simple configuration.
[0029]
Further, according to the present invention, a plurality of light sources generate optical signals of respective wavelengths subjected to light intensity modulation, wavelength-multiplexing each optical signal by a wavelength multiplexing unit, and optical multiplex reception at another point via an optical transmission line. In an optical multiplex transmission apparatus for transmitting to a device, a modulation waveform generator that generates a modulation waveform having a waveform that is periodic and has a pattern that is non-similar when the sign is inverted, and output from a light source according to the modulation waveform A wavelength modulator that modulates the wavelength of the optical signal is provided, so it is easy to detect the wavelength transmission characteristics from the optical transmitter to the optical receiver and the deviation of the output light wavelength of the light source between the corresponding receiver. There is an effect that can be realized with a simple configuration. In particular, the wavelength modulation of the light source required for wavelength shift detection can be realized by temperature modulation, and the extraction of the time signal representing the intensity change component and the waveform processing at the optical receiver are very simple by applying digital processing. There is an effect that can be realized with a simple configuration.
[0030]
Further, according to the present invention, the wavelength multiplexed optical signal transmitted from the optical multiplex transmission device at another point is separated into each wavelength by the wavelength separation unit, and the separated optical signal of each wavelength is received by the respective light receiver. In an optical multiplex receiving apparatus that converts an electric signal into an electric signal and performs reproduction processing, the optical signal before being wavelength-multiplexed by the optical multiplex transmitting apparatus has a waveform that is periodic and whose pattern becomes non-similar when the sign is inverted. The wavelength is modulated by the modulation waveform, and the signal extractor outputs the time change of the electric signal strength converted by the light receiver as a time waveform, and is generated by transmission from the optical multiplex transmission device of the other party based on the time waveform. It is configured to include a waveform evaluation unit that calculates the shift direction and the shift amount of the optical wavelength and outputs the result as a wavelength error signal, so that the wavelength transmission from the optical transmitting unit to the optical receiving unit between the corresponding transmitting device. Characteristic There is an effect that can realize the shift detection of the output light wavelength of the light source with a simple structure. In particular, the wavelength modulation of the light source required for wavelength shift detection can be realized by temperature modulation, and the extraction of the time signal representing the intensity change component and the waveform processing at the optical receiver are very simple by applying digital processing. There is an effect that can be realized with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram showing a configuration of an optical multiplex transmission system according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory diagram showing wavelength transmission characteristics of the entire system.
FIG. 3 is an explanatory diagram showing a change in intensity of transmitted light when a modulation waveform of an output light wavelength of a light source is a sawtooth wave.
FIG. 4 is an explanatory diagram showing a change in intensity of transmitted light when a modulation waveform of an output light wavelength of a light source is a ternary digital signal.
FIG. 5 is an explanatory diagram showing a relationship of a change in intensity of transmitted light when a minute modulation waveform of an output light wavelength of a light source is a sine wave.
FIG. 6 is an explanatory diagram showing a list of various waveforms that are similar and dissimilar by reversing the sign.
FIG. 7 is a block circuit diagram showing a configuration of an optical multiplex transmission system according to a second embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1 optical transmission section, 2 wavelength multiplexing section, 3a, 3b wavelength control section, 4 optical transmission line, 5 wavelength separation section, 6 optical reception section, 7 light source, 8 main signal source, 9 wavelength modulation section, 10 modulation waveform generator , 11 light receiver, 12 main signal reproducing section, 14 waveform evaluation section, 15 synchronization detecting section, 16 averaging processing section, 17 signal extracting section, 18 monitoring control section, 19 control signal transmitting section, 20 control signal receiving section.

Claims

The transmitting side generates optical signals of respective wavelengths modulated with light intensity from a plurality of light sources, wavelength-multiplexes each optical signal by a wavelength multiplexing unit, and transmits the multiplexed optical signal to a receiving side at another point via an optical transmission line. In an optical multiplexing transmission system in which each wavelength is separated from an optical signal wavelength-multiplexed by a wavelength demultiplexing unit, and the separated optical signal of each wavelength is converted into an electric signal by each optical receiver and reproduced,
The transmission side is a modulation waveform generator that generates a modulation waveform having a waveform that is periodic and the pattern becomes non-similar when the polarity is reversed, and an optical signal output from the light source according to the modulation waveform. It has a wavelength modulation unit that modulates the wavelength,
The receiving side is a signal extraction unit that outputs a time change of the electric signal strength converted by the light receiver as a time waveform, and a shift of an optical wavelength caused by transmission from the transmitting side to the receiving side based on the time waveform. An optical multiplex transmission system comprising a waveform evaluation unit that calculates a direction and a shift amount and outputs the calculated wavelength and an error signal.

A signal extraction unit that extracts an intensity change component from the electric signal converted by the light receiver using a synchronization signal that is a timing reference for data acquisition, and outputs an intensity change component as a time waveform; and a repetition of the time waveform. 2. The optical multiplex transmission system according to claim 1, further comprising: a synchronization detection unit that detects a period, generates the synchronization signal having the detected period, and supplies the synchronization signal to the averaging unit.

The receiving side includes a control signal transmitting unit that transfers the wavelength error signal indicating the shift direction and the shift amount of the optical wavelength calculated by the waveform evaluation unit to the opposed transmitting side,
The transmitting side includes a control signal receiving unit that receives the transferred wavelength error signal and provides the received wavelength error signal to the wavelength modulation unit.
2. The apparatus according to claim 1, wherein the wavelength modulator controls a wavelength of the optical signal output from the light source so as to reduce a shift direction and a shift amount of the optical wavelength in response to the received wavelength error signal. Or an optical multiplex transmission system according to claim 2.

The optical multiplex transmission system according to any one of claims 1 to 3, wherein the modulation waveform having a waveform whose pattern is dissimilar is a sawtooth waveform.

The optical multiplex transmission system according to any one of claims 1 to 3, wherein a modulation waveform having a waveform whose pattern is dissimilar is a ternary digital waveform.

The optical multiplex transmission system according to any one of claims 1 to 3, wherein the modulation waveform having a waveform whose pattern is non-similar is a binary digital waveform of a pseudo random signal.

An optical multiplex transmission device that generates optical signals of respective wavelengths that are light intensity modulated from a plurality of light sources, wavelength multiplexes each optical signal by a wavelength multiplexing unit, and transmits the multiplexed optical signal to an optical multiplex receiving device at another point via an optical transmission line. At
A modulated waveform generator that generates a modulated waveform having a waveform that is periodic and has a pattern that is non-similar when inverted in polarity;
An optical multiplex transmission device, comprising: a wavelength modulation unit that modulates a wavelength of an optical signal output from the light source according to the modulation waveform.

The wavelength modulating unit receives a wavelength error signal indicating a shift direction and a shift amount of the optical wavelength caused by transmission from a partner optical multiplex receiving apparatus, and responds to the error signal to shift the shift direction and the shift amount of the optical wavelength. 8. The optical multiplex transmitting apparatus according to claim 7, wherein the wavelength of the optical signal output from the light source is controlled so as to reduce the wavelength.

The wavelength multiplexed optical signal transmitted from the optical multiplex transmission device at another point is separated into each wavelength by the wavelength separation unit, and the separated optical signal of each wavelength is converted into an electric signal by each optical receiver and reproduced. Optical multiplex receiving device,
The optical signal before being wavelength-division multiplexed by the optical multiplex transmission device, the wavelength is modulated by a modulation waveform having a waveform that is non-similar when the pattern is inverted periodically and positive and negative,
A signal extraction unit that outputs a time change of the electric signal strength converted by the light receiver as a time waveform,
An optical multiplexing apparatus comprising: a waveform evaluation unit that calculates a shift direction and a shift amount of an optical wavelength caused by transmission from a partner optical multiplex transmission apparatus based on the time waveform and outputs the calculated wavelength error signal. Receiver.