JP3589056B2

JP3589056B2 - Optical repeater monitoring system and method

Info

Publication number: JP3589056B2
Application number: JP35442398A
Authority: JP
Inventors: 幸夫堀内; 正敏鈴木; 周山本; 重幸秋葉
Original assignee: KDDI Corp
Current assignee: KDDI Corp
Priority date: 1998-12-14
Filing date: 1998-12-14
Publication date: 2004-11-17
Anticipated expiration: 2018-12-14
Also published as: JP2000183820A

Description

【０００１】
【発明の属する技術分野】
本発明は、光中継器監視システム及び方法に関し、より具体的には、光伝送システムにおいて中継器などの監視情報を端局に転送するシステム及び方法に関する。
【０００２】
【従来の技術】
光伝送システム、特に、光信号を光増幅中継する１以上の光中継器を具備する光中継伝送システムでは、その光中継器の動作状態等を遠隔監視したり、遠隔制御したりする必要がある。光中継器の動作状態等を端局に送信する構成として、従来、各光中継器に固有の周波数又は同じ周波数の局部発振信号源を設け、その出力を中継器監視情報データで変調して端局に送信していた。
【０００３】
【発明が解決しようとする課題】
しかし、局部発振信号源は、温度変動及びエージングによってその発振周波数が変動するので、端局では、この周波数変動を見込んで受信帯域を広くとっておく必要があった。即ち、従来例では、必要以上に帯域を広くすることによって、信号電力対雑音電力比（ＳＮＲ）を劣化させていた。
【０００４】
本発明は、このような問題点を解決し、高いＳＮＲで監視信号を受信できる光中継器監視システム及び方法を提示することを目的とする。
【０００５】
【課題を解決するための手段】
本発明に係る光中継器監視システムは、発振源と、当該発振源の出力から生成される所定周波数の基準信号を第１の光ファイバに送出する基準信号送出手段と、当該第１の光ファイバからの光を電気信号に変換する受光器、当該受光器から当該基準信号成分を抽出する基準信号抽出手段、当該基準信号抽出手段の出力から搬送波を生成する搬送波生成手段、当該光中継器の動作状態を示す監視信号で当該搬送波生成手段により生成された搬送波を変調する監視信号変調手段、及び、当該監視信号変調手段の出力を第２の光ファイバ上に送出する送出手段を具備する光中継器と、当該発振源の出力及び当該基準信号の一方から当該監視信号の搬送波と同じ周波数の復調用信号を生成する復調用信号生成手段と、当該第２の光ファイバを伝送した光を受光する受光器と、当該受光器の出力と、当該検復調用信号生成手段の出力とから当該監視信号を復調する監視信号復調手段とからなることを特徴とする。
【０００６】
この構成により、光中継器の動作状態などを示す監視信号を端局に送信するための搬送波を、同じ端局又は別の端局からの基準信号を元に光中継器内で生成するので、光中継器内に局部発振器を設ける必要がなくなる。その結果、監視信号を受信する側で監視信号を搬送する搬送波の周波数変動を考慮する必要が無くなり、監視信号を受信するために不必要に広い帯域の受信装置を設けなくて良くなる。監視信号変調信号を復調するのに同期検波を使用できるので、高いＳ／Ｎ比で監視信号を復調できる。監視信号は、基準信号を送出する端局又は別の端局の何れでの受信できる。
【０００７】
基準信号を伝送信号光に重畳すれば、光ファイバ伝送路を有効活用できる。監視信号を搬送する専用光を使用すれば、信号光への悪影響を軽減できる。
【０００８】
本発明に係る光中継器監視方法は、基準信号送出装置から光ファイバ線路を介して光中継器に所定周波数の基準信号を送出する基準信号送信ステップと、当該光中継器において、当該基準信号から、当該光中継器の監視信号を搬送する、当該基準信号の周波数とは異なる周波数の搬送波を生成する搬送波生成ステップと、当該光中継器において、当該監視信号で当該搬送波を変調する監視信号変調ステップと、当該光中継器において、当該監視信号変調ステップによる監視信号の変調波を監視信号受信装置に向けて送信する監視信号送信ステップと、当該監視信号受信装置において、当該搬送波と同じ周波数の復調用信号を生成する復調用信号生成ステップと、当該監視信号受信装置において、当該光中継器から送られた監視信号変調信号を当該復調用信号により復調する監視信号復調ステップとからなることを特徴とする。
【０００９】
このような構成により、本発明に係る光中継器監視システムの場合と同様の利点が得られる。
【００１０】
【実施例】
以下、図面を参照して、本発明の実施例を詳細に説明する。
【００１１】
図１は、本発明の一実施例の概略構成ブロック図を示す。端局１０，１２間に、端局１０から端局１２に信号光を伝送する光ファイバ線路１４と、端局１２から端局１０に信号光を伝送する光ファイバ線路１６を敷設してある。そして、光ファイバ線路１４，１６の中間に光中継器１８が配置されている。説明の都合上、光ファイバ線路１４で、端局１０と光中継器１８との間の光ファイバを符号１４ａで特定し、光中継器１８と端局１２との間の光ファイバを符号１４ｂで特定する。同様に、光ファイバ線路１６で、端局１２と光中継器１８との間の光ファイバを符号１６ａで特定し、光中継器１８と端局１０との間の光ファイバを符号１６ｂで特定する。
【００１２】
端局１０の構成と動作を説明する。基準発振器２０は、光中継器１８が中継器データを含む監視信号を端局１０（又は端局１２）に向け送信する際に使用する搬送波を作成するのに使用する周波数信号（例えば、６．３７ＭＨｚ）を発生する。基準発振器２０の出力は分周器２２により分周（例えば、１／１４）されて、制御信号変調器２４に印加される。制御・処理回路２６は光中継器１８を制御する制御信号を発生し、その制御信号を制御信号変調器２４に印加する。本実施例では、端局１０は、制御信号と基準信号を時分割で光中継器１８に送信する。制御信号変調器２４は、制御信号を光中継器１８に送信すべき期間、制御・処理回路２６からの制御信号で分周器２２からの周波数信号（光中継器１８に送信する基準信号）を変調し、それ以外の期間、即ち、基準信号を光中継器１８に送信すべき期間では、分周器２２の出力をそのまま出力する。基準信号は、好ましくは、単一周波数のトーン信号である。
【００１３】
レーザ光源２７は、端局１２に送信すべき信号（例えば、１０Ｇｂｉｔ／ｓ）を搬送するレーザ光を発生し、光変調器２８は、レーザ光源２７の出力レーザ光を伝送信号で強度変調し、ＲＺ光パルス列又はＮＲＺ光パルス列を出力する。重畳器３０は、光変調器２８から出力される信号光に制御信号変調器２４の出力を重畳する。重畳方法として、具体的には、制御信号（及び基準信号）を搬送する専用波長光を使用する方法と、光変調器２８から出力される信号光の振幅を、制御信号変調器２４の出力で変調する方法があるが、これらの詳細は後述する。重畳器３０の出力光は光ファイバ線路１４の光ファイバ１４ａに入射し、これを伝送して光中継器１８に入射する。
【００１４】
他方、受光器３２は、光ファイバ線路１６から入力する光を電気信号に変換する。受光器３２に入力する信号光は、後述するように、光中継器１８の中継器データ等を含む監視信号をも搬送している。受信装置３４は、光ファイバ線路１６からの入力光を電気信号に変換し、端局１２からの信号を受信処理する。受光器３２の出力は監視信号復調器３６に入力する。分周器３８は、光中継器１８が監視信号を端局１０に伝送するのに使用する搬送波の周波数（例えば、４３．０４１ｋＨｚ）を得るような分周比（例えば、１／１４８）で、基準発振器２０の出力を分周し、監視信号復調器３６に印加する。監視信号復調器３６は、分周器３８の出力を使って受光器３２の出力から監視信号を復調する。復調された監視信号は制御・処理回路２６に供給される。
【００１５】
光中継器１８の構成と動作を説明する。光アンプ（例えば、エルビウム添加光ファイバを使用する光増幅器）４０，４２は、励起回路４４からの励起光により励起されて、それぞれ、光ファイバ１４ａ，１６ａからの信号光を光増幅する。光分岐器４６，４８は、それぞれ、光アンプ４０，４２の出力のほとんどを後段の光ファイバ１４ｂ，１６ｂに出力すると共に、一部を分岐して受光器５０，５２に供給する。受光器５０，５２は、それぞれ、光分岐器４６，４８からの光を電気信号に変換する。受光器５０，５２は、端局１０からの制御信号及び基準信号を検出できればよいので、低速のものでよい。
【００１６】
受光器５０，５２の出力はワイヤード・オアにより合成され、バンドパス・フィルタ（ＢＰＦ）５４に印加される。２つの受光器５０，５２を使用する代わりに、光分岐器４６，４８の出力光を光合波してから受光器により電気信号に変換しても良い。これにより、単一の中継器監視回路で端局１０，１２のどちらからも光中継器１８を監視できる。即ち、低コストで両方の端局１０，１２から光中継器１８を監視できる。。
【００１７】
ＢＰＦ５４は、受光器５０，５２の出力から、端局１０からの制御信号及び基準信号の周波数成分を抽出して、基準再生回路５６及び制御信号復調器５８に供給する。基準再生回路５６は、ＢＰＦ５４の出力に含まれる基準信号成分をＰＬＬにより逓倍し、その後、分周器６０が、基準再生回路５６の出力を分周して、監視信号を搬送する搬送波を作成する。即ち、基準再生回路５６及び分周器６０が搬送波生成回路となる。このような逓倍と分周により、安定した周波数の搬送波を得ることができる。勿論、基準再生回路５６は端局１０から送出される基準信号の周波数成分を抽出する狭帯域フィルタであってもよい。本実施例では、例えば、基準再生回路５６は、ＢＰＦ５４の出力の基準周波数（４５５ｋＨｚ）成分を７倍し、分周器６０は、基準再生回路５６の出力を１／７４分周する。分周器６０の出力周波数は４３．０４ｋＨｚとなる。
【００１８】
制御信号復調器５８は、ＢＰＦ５４の出力から制御信号を復調して、制御回路６２に供給する。制御回路６２は、制御信号復調器５８からの制御信号に従って、各部を制御又は監視し、監視結果を示す監視信号を監視信号変調器６４に出力する。監視信号変調器６４には分周器６０の出力が印加されている。監視信号変調器６４は、分周器６０の出力を制御回路６２からの監視信号で変調する。変調方式は、例えば、ＡＳＫ、ＦＳＫ又はＰＳＫ方式が好ましい。
【００１９】
監視信号変調器６４の出力は励起回路４４に印加される。励起回路４４は、監視信号変調器６４の出力に従って、光アンプ４０及び／又は同４２への励起光を浅く強度変調する。この結果、光ファイバ線路１６を端局１２から端局１０に向けて伝搬する信号光に監視信号変調信号が重畳されて、端局１０に伝送される。本実施例では、監視信号を端局１０に伝送するために、光アンプ４２のゲインを監視信号変調器６４の出力で変調したが、光ファイバ線路１６上でラマン増幅を発生させ、その利得を監視信号変調器６４の出力に応じて変動させる方法を使用しても良い。即ち、光ファイバ線路１６上の信号光の波長帯でラマン増幅を起こさせるポンプ光を光ファイバ線路１６に供給し、そのポンプ光の強度を、監視信号変調器６４の出力で変調する。すると、光ファイバ線路１６上を伝送する信号光のゲインが、監視信号変調器６４の出力に応じて変動することになり、光アンプ４２のゲインを変動させるのと同じ作用になる。
【００２０】
図２（Ａ）は、端局１０から光中継器への信号伝送のタイミングを示し、図２（Ｂ）は、光中継器１８から端局１０への監視信号の伝送タイミングを示す。光中継器１８は、端局１０から基準信号を受信している間に、監視信号の搬送波を生成し、監視信号を端局１０に送信する。
【００２１】
端局１０が光中継器１８に光中継器１８の動作状態を示す監視信号を端局１０に送信させるためのプロセスを説明する。
【００２２】
図２（Ａ）に図示したように、端局１０は先ず、光中継器１８に中継器制御信号を送る。中継器制御信号は、例えば、光中継器１８の動作状態を遠隔制御する信号、及び、光中継器１８の動作状態を問い合わせる信号等である。制御・処理回路２６は、所望の内容（ここでは、光中継器１８の動作状態を問い合わせる信号であるとする。）の制御信号を制御信号変調器２４に出力する。制御信号変調器２４には他に、基準発振器２０の出力を分周器２２で分周した基準信号が印加されている。制御信号変調器２４は、その基準信号を制御・処理回路２６からの制御信号で変調する。変調結果は重畳器３０に印加される。重畳器３０は、レーザ光源２７及び光変調器２８により生成される信号光に、制御信号変調器２４の出力を重畳し、光ファイバ１４ａに出力する。
【００２３】
光ファイバ１４ａを伝搬する光は、光中継器１８の光アンプ４０に入射して、光増幅され、光分岐器４６により２つに分割され、一方が後段の光ファイバ１６ｂに、他方が受光器５０に入射する。受光器５０は入射光強度を電気信号に変換し、その出力はＢＰＦ５４に印加される。ＢＰＦ５４は、受光器５０の出力から分周器２２の出力周波数の成分を抽出して、基準再生回路５６及び制御信号復調器５８に印加する。この段階では、制御信号復調器５８は、ＢＰＦ５４の出力を、制御信号変調器２４の変調方式に対応する復調方式で復調し、得られた制御信号を制御回路６２に印加する。制御回路６２は、入力する制御信号に従って各部を制御し、各部の動作状態を示すデータを収集する。
【００２４】
端局１０は、一定期間、制御信号を光中継器１８に向けて送信した後、制御信号を制御信号変調器２４に供給するのを止めて、制御信号変調器２４を無変調動作状態にする。これにより、分周器２２の出力が制御信号変調器２４を素通りして、重畳器３０に印加される。重畳器３０は、制御信号を送信する場合と同様に、レーザ光源２７及び光変調器２８により生成される信号光に、制御信号変調器２４の出力を重畳し、光ファイバ１４ａに出力する。これにより、光中継器１８が監視信号を端局１０（又は１２）に送信するための搬送波周波数を規定する基準信号が、端局１０から光中継器１８に向けて送信される。
【００２５】
制御信号の場合と同様に、光中継器１８では、ＢＰＦ５４が、受光器５０の出力から分周器２２の出力周波数の成分を抽出して、基準再生回路５６及び制御信号復調器５８に印加する。基準再生回路５６は、ＢＰＦ５４の出力（基準信号）の周波数を逓倍し、分周器６０が基準再生回路５６の出力を分周する。これにより、監視信号を端局１０（又は１２）に向けて送信するための搬送波が形成され、監視信号変調器６４に印加される。制御回路６２は、先に収集した中継器データを示す監視信号を監視信号変調器６４に印加する。監視信号変調器６４は、ＡＳＫ、ＦＳＫ又はＰＳＫ等のディジタル変調方式により、制御回路６２からの監視信号で分周器６０の出力を変調する。監視信号変調器６４の出力は励起回路４４に印加される。励起回路４４は、先に説明したように、監視信号変調器６４の出力に従って、光アンプ４０及び／又は同４２への励起光を浅く強度変調して、監視信号変調信号を光ファイバ線路１６上で端局１２から端局１０に向かう信号光に重畳し、この信号光と一緒に端局１０に送信する。
【００２６】
端局１０では、受光器３２が、光ファイバ線路１６から入力する光を電気信号に変換する。受光器３２の出力は受信装置３４と監視信号復調器３６に入力する。分周器３８は、光中継器１８が監視信号を端局１０に伝送するのに使用する搬送波の周波数（例えば、４３．０４１ｋＨｚ）を得るような分周比（例えば、１／１４８）で、基準発振器２０の出力を分周し、監視信号復調器３６に印加する。監視信号復調器３６は、分周器３８の出力を使って受光器３２の出力から監視信号を復調する。復調された監視信号は制御・処理回路２６に供給される。これにより、端局１０は、遠隔にある光中継器１８の詳細な動作状態を知ることができる。
【００２７】
ここで、分周器２２，６０，３８における分周比の関係を簡単に説明する。監視信号の搬送波としては、太平洋横断長とされる１０，０００ｋｍ長の中継伝送システムでは、光増幅器の変調特性及びこれらの多段接続による周波数特性から見て、４３ｋＨｚ帯が最良である。光中継器１８内での処理の容易さを考慮し、端局１０から光中継器１８に送信する基準信号の周波数を４５５ｋＨｚとする。基準再生回路５６は、受信した基準信号を奇数倍（具体的には、７倍）して、３．１８５ＭＨｚを生成し、分周器６０が基準再生回路５６の出力を７４分周して、４３．０４ｋＨｚを生成する。端局１０では、基準発振器２０の発振周波数を３．１８５ＭＨｚとすると、分周器２２の分周比が１／７になり、デューティ比が５０％でなくなる。デューティ比は５０％であるのが好ましいので、分周器２２の分周比１／ｎのｎを整数にする必要がある。従って、基準発振器２０の発振周波数を、４５５ｋＨｚの１４倍（＝２×７）の６．３７ＭＨｚとした。基準発振器２０の発振周波数はまた、４５５ｋＨｚの２１倍（＝３×７）の９．５５５ＭＨｚでもよい。光中継器１８の分周器６０から出力される搬送波の周波数と分周器３８の出力の周波数とを一致させるためには、分周器３８の分周比を１／１４８にすればよい。但し、基準発振器２０の発振周波数が９．５５５ＭＨｚである場合には、分周器３８の分周比を１／２２２とする。分周器３８の出力の周波数を監視信号の搬送波の周波数と一致させることにより、監視信号復調器３６で同期検波が可能になり、監視信号を容易に復調できるようになる。
【００２８】
監視信号はまた、端局１２で受信しても良い。端局１２において監視信号を復調するための構成例を、図３に示す。この場合、光中継器１８の励起回路４４は、監視信号変調器６４の出力に従って、光アンプ４０への励起光を強度変調する。
【００２９】
受光器７０は、光ファイバ１４ｂから入力する光を電気信号に変換する。受光器７０の出力は、ＢＰＦ７２及びＢＰＦ７４に印加される。ＢＰＦ７２は、端局１０から光ファイバ線路１４上に送出される基準信号成分を抽出する。ＢＰＦ７４は、光アンプ４０の利得の変調により光ファイバ線路１４に光中継器１８から送出される監視信号変調信号の周波数成分を抽出する。ＢＰＦ７２の出力は基準再生回路７６に印加される。基準再生回路７６は、光中継器１８の基準再生回路５６と同様の回路であり、ＢＰＦ７２の出力周波数をＰＬＬにより逓倍し、分周器７８が基準再生回路７６の出力を分周して、監視信号変調信号を同期検波するための周波数信号を生成する。基準再生回路７６及び分周器７８はそれぞれ、光中継器１８の基準再生回路５６及び分周器６０と同じであり、同様に機能する。即ち、分周器７８の出力周波数は、分周器６０の出力周波数と同じである。監視信号復調器８０は、分周器７８の出力をＢＰＦ７４の出力に乗算して、監視信号を同期検波する。
【００３０】
本実施例では、端局１０から光ファイバ線路１４に送出される基準信号の周波数（４５５ｋＨｚ）と、光中継器１８から端局１２に監視信号を伝送するのに使用するキャリアの周波数（４３．０４１ｋＨｚ）を上述のように異なる値にしているので、端局１２は、基準信号と監視信号搬送波とを容易に識別できる。
【００３１】
重畳器３０における信号光と基準信号（又は制御信号の変調信号）の重畳方法を簡単に説明する。図４は、伝送信号光の振幅を基準信号（又は制御信号の変調信号）で変調して伝送する構成例を示し、図５は、基準信号（又は制御信号の変調信号）を送信する専用波長を設ける構成例を示す。
【００３２】
図４を説明する。レーザ光源８２−１〜８２−ｎはそれぞれ異なる波長λ１〜λｎでレーザ発振し、光変調器８４−１〜８４−ｎは、各レーザ光源８２−１〜８２−ｎの出力光を伝送信号＃１〜＃ｎで強度変調する。合波器８６は、光変調器８４−１〜８４−ｎの出力光を合波する。光変調器８８は、合波器８６の出力を制御信号変調器２４の出力（即ち、基準信号又は制御信号変調信号）で、浅く強度変調する。光変調器８８の出力は光ファイバ線路１４に出力される。この例では、光変調器８８が、重畳器３０となる。図１に示す実施例の光中継器１８の構成は、図５に示す重畳方式に対応するものである。
【００３３】
図５を説明する。レーザ光源９０−１〜９０−ｎはそれぞれ異なる波長λ１〜λｎでレーザ発振し、光変調器９２−１〜９２−ｎは、各レーザ光源９０−１〜９０−ｎの出力光を伝送信号＃１〜＃ｎで強度変調する。また、レーザ光源９４は、信号光の波長λ１〜λｎのどれとも異なる波長λａでレーザ発振し、光変調器９６が、レーザ光源９４の出力光を、制御信号変調器２４の出力（即ち、基準信号又は制御信号変調信号）で強度変調する。合波器９８は、光変調器９２−１〜９２−ｎ及び光変調器９６の出力光を合波して、光ファイバ線路１４に出力する。この例では、レーザ光源９４、光変調器９６及び合波器９８が、重畳器３０を構成する。光中継器１８では、波長λａを分離する光フィルタが光段に必要になる。
【００３４】
【発明の効果】
以上の説明から容易に理解できるように、本発明によれば、光中継器の動作状態などを示す監視信号を端局に送信するための搬送波を、同じ端局又は別の端局からの基準信号を元に光中継器内で生成するので、光中継器内に局部発振器を設ける必要がなくなる。その結果、監視信号受信側で監視信号を搬送する搬送波の周波数変動を考慮する必要が無くなり、監視信号を受信するために不必要に広い帯域の受信装置を設けなくて良くなる。端局で監視信号変調信号を復調するのに同期検波を使用できるので、高いＳ／Ｎ比で監視信号を復調できる。
【図面の簡単な説明】
【図１】本発明の一実施例の概略構成ブロック図である。
【図２】本実施例における制御信号、基準信号及び監視信号のタイミング・チャートであり、（Ａ）は、制御信号及び基準信号の送信シーケンスを示し、（Ｂ）は、監視信号の送信タイミングを示す。
【図３】端局１２における監視信号受信系の概略構成ブロック図である。
【図４】重畳器３０の一例の概略構成ブロック図である。
【図５】重畳器３０の別の例の概略構成ブロック図である。
【符号の説明】
１０，１２：端局
１４，１６：光ファイバ線路
１４ａ，１４ｂ，１６ａ，１６ｂ：光ファイバ
１８：光中継器
２０：基準発振器
２２：分周器
２４：制御信号変調器
２６：制御・処理回路
２７：レーザ光源
２８：光変調器
３０：重畳器
３２：受光器
３４：受信装置
３６：監視信号復調器
３８：分周器
４０，４２：光アンプ
４４：励起回路
４６，４８：光分岐器
５０，５２：受光器
５４：バンドパス・フィルタ（ＢＰＦ）
５６：基準再生回路
５８：制御信号復調器
６０：分周器
６２：制御回路
６４：監視信号変調器
７０：受光器
７２，７４：ＢＰＦ
７６：基準再生回路
７８：分周器
８０：監視信号復調器
８２−１〜８２−ｎ：レーザ光源
８４−１〜８４−ｎ：光変調器
８６：合波器
８８：光変調器
９０−１〜９０−ｎ：レーザ光源
９２−１〜９２−ｎ：光変調器
９４：レーザ光源
９６：光変調器
９８：合波器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical repeater monitoring system and method, and more particularly, to a system and method for transferring monitoring information of a repeater or the like to a terminal station in an optical transmission system.
[0002]
[Prior art]
2. Description of the Related Art In an optical transmission system, particularly an optical repeater transmission system including one or more optical repeaters for optically amplifying and repeating an optical signal, it is necessary to remotely monitor and remotely control an operation state and the like of the optical repeater. . Conventionally, a local oscillation signal source having a unique frequency or the same frequency is provided for each optical repeater, and the output is modulated by the repeater monitoring information data. Was sending to the station.
[0003]
[Problems to be solved by the invention]
However, since the oscillation frequency of the local oscillation signal source fluctuates due to temperature fluctuation and aging, it is necessary for the terminal station to widen the reception band in consideration of the frequency fluctuation. That is, in the conventional example, the signal power to noise power ratio (SNR) is deteriorated by making the band wider than necessary.
[0004]
An object of the present invention is to solve such a problem and to provide an optical repeater monitoring system and method capable of receiving a monitoring signal with a high SNR.
[0005]
[Means for Solving the Problems]
An optical repeater monitoring system according to the present invention includes: an oscillation source; a reference signal sending unit that sends a reference signal of a predetermined frequency generated from an output of the oscillation source to a first optical fiber; Receiver for converting light from the optical signal into an electric signal, reference signal extraction means for extracting the reference signal component from the light receiver, carrier generation means for generating a carrier from the output of the reference signal extraction means, operation of the optical repeater An optical repeater comprising: a monitor signal modulator for modulating a carrier generated by the carrier generator with a monitor signal indicating a state; and a transmitter for transmitting an output of the monitor signal modulator onto a second optical fiber. And a demodulation signal generating means for generating a demodulation signal having the same frequency as the carrier of the monitor signal from one of the output of the oscillation source and the reference signal, and the second optical fiber is transmitted. A photodetector receiving the, characterized by comprising the output of the photodetector, and an output of the detection demodulation signal generating means and the monitoring signal demodulating means for demodulating the monitoring signal.
[0006]
With this configuration, a carrier wave for transmitting a monitoring signal indicating an operation state of the optical repeater to the terminal station is generated in the optical repeater based on a reference signal from the same terminal station or another terminal station. There is no need to provide a local oscillator in the optical repeater. As a result, it is not necessary for the receiving side of the monitoring signal to consider the frequency fluctuation of the carrier that carries the monitoring signal, and it is not necessary to provide a receiving device having an unnecessarily wide band for receiving the monitoring signal. Since synchronous detection can be used to demodulate the monitor signal modulation signal, the monitor signal can be demodulated with a high S / N ratio. The monitoring signal can be received at either the terminal transmitting the reference signal or another terminal.
[0007]
If the reference signal is superimposed on the transmission signal light, the optical fiber transmission line can be used effectively. If the dedicated light for carrying the monitoring signal is used, the adverse effect on the signal light can be reduced.
[0008]
An optical repeater monitoring method according to the present invention includes a reference signal transmitting step of transmitting a reference signal of a predetermined frequency from a reference signal transmitting device to an optical repeater via an optical fiber line, and in the optical repeater, Carrying a monitoring signal of the optical repeater, a carrier generation step of generating a carrier having a frequency different from the frequency of the reference signal, and a monitoring signal modulation step of modulating the carrier with the monitoring signal in the optical repeater A monitoring signal transmitting step of transmitting a modulated wave of the monitoring signal by the monitoring signal modulation step to the monitoring signal receiving device in the optical repeater; and a demodulating device for demodulating the same frequency as the carrier wave in the monitoring signal receiving device. A demodulation signal generation step of generating a signal, and the monitoring signal receiving device, wherein the monitoring signal modulation signal sent from the optical repeater is Characterized by comprising the monitoring signal demodulating step of demodulating the demodulated signal.
[0009]
With such a configuration, the same advantages as those of the optical repeater monitoring system according to the present invention can be obtained.
[0010]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 shows a schematic block diagram of an embodiment of the present invention. An optical fiber line 14 for transmitting signal light from the terminal station 10 to the terminal station 12 and an optical fiber line 16 for transmitting signal light from the terminal station 12 to the terminal station 10 are laid between the terminal stations 10 and 12. An optical repeater 18 is arranged between the optical fiber lines 14 and 16. For convenience of explanation, an optical fiber between the terminal station 10 and the optical repeater 18 is specified by reference numeral 14a on the optical fiber line 14, and an optical fiber between the optical repeater 18 and the terminal station 12 is indicated by reference numeral 14b. Identify. Similarly, on the optical fiber line 16, the optical fiber between the terminal station 12 and the optical repeater 18 is specified by reference numeral 16a, and the optical fiber between the optical repeater 18 and the terminal station 10 is specified by reference numeral 16b. .
[0012]
The configuration and operation of the terminal station 10 will be described. The reference oscillator 20 is a frequency signal (for example, 6.x) used to generate a carrier wave used when the optical repeater 18 transmits a monitoring signal including repeater data to the terminal station 10 (or the terminal station 12). 37 MHz). The output of the reference oscillator 20 is frequency-divided (for example, 1/14) by the frequency divider 22 and applied to the control signal modulator 24. The control / processing circuit 26 generates a control signal for controlling the optical repeater 18, and applies the control signal to the control signal modulator 24. In this embodiment, the terminal station 10 transmits the control signal and the reference signal to the optical repeater 18 in a time-division manner. The control signal modulator 24 converts the frequency signal from the frequency divider 22 (the reference signal to be transmitted to the optical repeater 18) with the control signal from the control / processing circuit 26 during the period when the control signal is to be transmitted to the optical repeater 18. During the period other than the modulation, that is, the period when the reference signal is to be transmitted to the optical repeater 18, the output of the frequency divider 22 is output as it is. The reference signal is preferably a single frequency tone signal.
[0013]
The laser light source 27 generates a laser beam that carries a signal to be transmitted to the terminal station 12 (for example, 10 Gbit / s), and the optical modulator 28 modulates the intensity of the output laser light of the laser light source 27 with a transmission signal. An RZ optical pulse train or an NRZ optical pulse train is output. The superimposer 30 superimposes the output of the control signal modulator 24 on the signal light output from the optical modulator 28. As a superposition method, specifically, a method using a dedicated wavelength light that carries a control signal (and a reference signal), and an amplitude of the signal light output from the optical modulator 28 are determined by the output of the control signal modulator 24. There is a modulation method, and details thereof will be described later. The output light of the superimposer 30 enters the optical fiber 14 a of the optical fiber line 14, transmits this, and enters the optical repeater 18.
[0014]
On the other hand, the light receiver 32 converts the light input from the optical fiber line 16 into an electric signal. The signal light input to the light receiver 32 also carries a monitoring signal including the repeater data of the optical repeater 18 as described later. The receiving device 34 converts the input light from the optical fiber line 16 into an electric signal, and receives and processes the signal from the terminal station 12. The output of the light receiver 32 is input to the monitor signal demodulator 36. The frequency divider 38 has a frequency division ratio (for example, 1/148) that obtains a frequency (for example, 43.041 kHz) of a carrier used by the optical repeater 18 to transmit the monitoring signal to the terminal station 10. The output of the reference oscillator 20 is frequency-divided and applied to the monitor signal demodulator 36. The monitor signal demodulator 36 demodulates the monitor signal from the output of the light receiver 32 using the output of the frequency divider 38. The demodulated monitoring signal is supplied to the control / processing circuit 26.
[0015]
The configuration and operation of the optical repeater 18 will be described. The optical amplifiers (for example, optical amplifiers using erbium-doped optical fibers) 40 and 42 are excited by the excitation light from the excitation circuit 44 and optically amplify the signal light from the optical fibers 14a and 16a, respectively. The optical splitters 46 and 48 output most of the outputs of the optical amplifiers 40 and 42 to the optical fibers 14b and 16b at the subsequent stage, respectively, and partially split and supply the split light to the optical receivers 50 and 52. The light receivers 50 and 52 convert the light from the optical splitters 46 and 48 into electric signals, respectively. The light receivers 50 and 52 need only be able to detect the control signal and the reference signal from the terminal station 10, and therefore may be low-speed ones.
[0016]
The outputs of the light receivers 50 and 52 are combined by wired OR, and applied to a band pass filter (BPF) 54. Instead of using two photodetectors 50 and 52, the output light of the optical divider 46, 48 from the Hikarigo waves may be converted into an electric signal by the photo detector. Thus, the optical repeater 18 can be monitored from both the terminal stations 10 and 12 by a single repeater monitoring circuit. That is, the optical repeater 18 can be monitored from both the terminal stations 10 and 12 at low cost. .
[0017]
The BPF 54 extracts the frequency components of the control signal and the reference signal from the terminal station 10 from the outputs of the light receivers 50 and 52, and supplies them to the reference reproduction circuit 56 and the control signal demodulator 58. The reference reproduction circuit 56 multiplies the reference signal component included in the output of the BPF 54 by the PLL, and then the frequency divider 60 divides the output of the reference reproduction circuit 56 to create a carrier for carrying the monitoring signal. . That is, the reference reproduction circuit 56 and the frequency divider 60 serve as a carrier generation circuit. By such multiplication and frequency division, a carrier wave having a stable frequency can be obtained. Of course, the reference reproduction circuit 56 may be a narrow band filter that extracts the frequency component of the reference signal transmitted from the terminal station 10. In the present embodiment, for example, the reference reproduction circuit 56 multiplies the reference frequency (455 kHz) component of the output of the BPF 54 by 7, and the frequency divider 60 divides the output of the reference reproduction circuit 56 by 1/74. The output frequency of the frequency divider 60 is 43.04 kHz.
[0018]
The control signal demodulator 58 demodulates a control signal from the output of the BPF 54 and supplies the control signal to the control circuit 62. The control circuit 62 controls or monitors each unit according to the control signal from the control signal demodulator 58 and outputs a monitoring signal indicating a monitoring result to the monitoring signal modulator 64. The output of the frequency divider 60 is applied to the monitor signal modulator 64. The monitoring signal modulator 64 modulates the output of the frequency divider 60 with the monitoring signal from the control circuit 62. The modulation scheme is preferably, for example, ASK, FSK or PSK scheme.
[0019]
The output of the monitor signal modulator 64 is applied to the excitation circuit 44. The excitation circuit 44 shallowly modulates the intensity of the excitation light to the optical amplifier 40 and / or 42 according to the output of the monitor signal modulator 64. As a result, the monitor signal modulation signal is superimposed on the signal light propagating from the terminal station 12 to the terminal station 10 on the optical fiber line 16 and transmitted to the terminal station 10. In this embodiment, the gain of the optical amplifier 42 is modulated by the output of the monitor signal modulator 64 in order to transmit the monitor signal to the terminal station 10. However, Raman amplification is generated on the optical fiber line 16, and the gain is reduced. A method of changing the output according to the output of the monitor signal modulator 64 may be used. That is, pump light for causing Raman amplification in the wavelength band of the signal light on the optical fiber line 16 is supplied to the optical fiber line 16, and the intensity of the pump light is modulated by the output of the monitor signal modulator 64. Then, the gain of the signal light transmitted on the optical fiber line 16 changes in accordance with the output of the monitor signal modulator 64, which has the same effect as changing the gain of the optical amplifier 42.
[0020]
FIG. 2A shows the timing of signal transmission from the terminal station 10 to the optical repeater, and FIG. 2B shows the timing of transmission of a monitoring signal from the optical repeater 18 to the terminal station 10. The optical repeater 18 generates a carrier of the monitor signal while receiving the reference signal from the terminal station 10, and transmits the monitor signal to the terminal station 10.
[0021]
A process in which the terminal station 10 causes the optical repeater 18 to transmit a monitoring signal indicating the operation state of the optical repeater 18 to the terminal station 10 will be described.
[0022]
As shown in FIG. 2A, the terminal station 10 first sends a repeater control signal to the optical repeater 18. The repeater control signal is, for example, a signal for remotely controlling the operation state of the optical repeater 18 and a signal for inquiring about the operation state of the optical repeater 18. The control / processing circuit 26 outputs a control signal having desired contents (in this case, a signal for inquiring about the operation state of the optical repeater 18) to the control signal modulator 24. In addition to the control signal modulator 24, a reference signal obtained by dividing the output of the reference oscillator 20 by the divider 22 is applied. The control signal modulator 24 modulates the reference signal with a control signal from the control / processing circuit 26. The modulation result is applied to superimposer 30. The superimposer 30 superimposes the output of the control signal modulator 24 on the signal light generated by the laser light source 27 and the optical modulator 28, and outputs the signal light to the optical fiber 14a.
[0023]
The light propagating through the optical fiber 14a enters the optical amplifier 40 of the optical repeater 18, is optically amplified, is split into two by an optical splitter 46, and one of the light is divided into a subsequent optical fiber 16b and the other is a photodetector. It is incident on 50. The light receiver 50 converts the intensity of the incident light into an electric signal, and the output is applied to the BPF 54. The BPF 54 extracts the component of the output frequency of the frequency divider 22 from the output of the light receiver 50 and applies it to the reference reproduction circuit 56 and the control signal demodulator 58. At this stage, the control signal demodulator 58 demodulates the output of the BPF 54 by a demodulation method corresponding to the modulation method of the control signal modulator 24, and applies the obtained control signal to the control circuit 62. The control circuit 62 controls each unit according to the input control signal, and collects data indicating the operation state of each unit.
[0024]
After transmitting the control signal to the optical repeater 18 for a certain period, the terminal station 10 stops supplying the control signal to the control signal modulator 24 and sets the control signal modulator 24 to the non-modulation operation state. . Thus, the output of the frequency divider 22 passes through the control signal modulator 24 and is applied to the superimposer 30. The superimposer 30 superimposes the output of the control signal modulator 24 on the signal light generated by the laser light source 27 and the optical modulator 28 and outputs the same to the optical fiber 14a, as in the case of transmitting the control signal. Thereby, the reference signal that defines the carrier frequency for the optical repeater 18 to transmit the monitoring signal to the terminal station 10 (or 12) is transmitted from the terminal station 10 to the optical repeater 18.
[0025]
As in the case of the control signal, in the optical repeater 18, the BPF 54 extracts the component of the output frequency of the frequency divider 22 from the output of the light receiver 50 and applies it to the reference reproduction circuit 56 and the control signal demodulator 58. . The reference reproduction circuit 56 multiplies the frequency of the output (reference signal) of the BPF 54, and the frequency divider 60 divides the output of the reference reproduction circuit 56. As a result, a carrier for transmitting the supervisory signal toward the terminal station 10 (or 12) is formed and applied to the supervisory signal modulator 64. The control circuit 62 applies a monitoring signal indicating the previously collected repeater data to the monitoring signal modulator 64. The monitoring signal modulator 64 modulates the output of the frequency divider 60 with the monitoring signal from the control circuit 62 by a digital modulation method such as ASK, FSK, or PSK. The output of the monitor signal modulator 64 is applied to the excitation circuit 44. The pumping circuit 44 shallowly modulates the pumping light to the optical amplifier 40 and / or 42 according to the output of the monitor signal modulator 64 to lightly modulate the monitor signal modulated signal on the optical fiber line 16 as described above. The signal is superimposed on the signal light traveling from the terminal station 12 to the terminal station 10 and transmitted to the terminal station 10 together with the signal light.
[0026]
In the terminal station 10, the light receiver 32 converts the light input from the optical fiber line 16 into an electric signal. The output of the light receiver 32 is input to a receiver 34 and a monitor signal demodulator 36. The frequency divider 38 has a frequency division ratio (for example, 1/148) that obtains a frequency (for example, 43.041 kHz) of a carrier used by the optical repeater 18 to transmit the monitoring signal to the terminal station 10. The output of the reference oscillator 20 is frequency-divided and applied to the monitor signal demodulator 36. The monitor signal demodulator 36 demodulates the monitor signal from the output of the light receiver 32 using the output of the frequency divider 38. The demodulated monitoring signal is supplied to the control / processing circuit 26. Thus, the end station 10 can know the detailed operation state of Ru Ah remote optical repeater 18.
[0027]
Here, the relationship between the frequency division ratios in the frequency dividers 22, 60, and 38 will be briefly described. In a relay transmission system having a length of 10,000 km, which is the trans-Pacific length, the 43 kHz band is the best as the carrier of the monitoring signal, in view of the modulation characteristics of the optical amplifier and the frequency characteristics of these multistage connections. Considering the easiness of processing in the optical repeater 18, the frequency of the reference signal transmitted from the terminal station 10 to the optical repeater 18 is 455 kHz. The reference reproduction circuit 56 generates an odd multiple (specifically, 7 times) of the received reference signal to generate 3.185 MHz, and the frequency divider 60 divides the output of the reference reproduction circuit 56 by 74. Generate 43.04 kHz. In the terminal station 10, when the oscillation frequency of the reference oscillator 20 is 3.185 MHz, the frequency division ratio of the frequency divider 22 becomes 1/7, and the duty ratio is not 50%. Since the duty ratio is preferably 50%, it is necessary to make n of the frequency division ratio 1 / n of the frequency divider 22 an integer. Therefore, the oscillation frequency of the reference oscillator 20 is set to 6.37 MHz, which is 14 times (= 2 × 7) 455 kHz. The oscillation frequency of the reference oscillator 20 may be 9.555 MHz, which is 21 times 455 kHz (= 3 × 7). In order to make the frequency of the carrier outputted from the frequency divider 60 of the optical repeater 18 coincide with the frequency of the output of the frequency divider 38, the frequency division ratio of the frequency divider 38 may be set to 1/148. However, when the oscillation frequency of the reference oscillator 20 is 9.555 MHz, the frequency division ratio of the frequency divider 38 is set to 1/222. By making the frequency of the output of the frequency divider 38 coincide with the frequency of the carrier of the monitoring signal, synchronous detection can be performed by the monitoring signal demodulator 36, and the monitoring signal can be easily demodulated.
[0028]
The monitoring signal may also be received at the terminal 12. FIG. 3 shows an example of a configuration for demodulating a monitoring signal in the terminal station 12. In this case, the excitation circuit 44 of the optical repeater 18 modulates the intensity of the excitation light to the optical amplifier 40 according to the output of the monitor signal modulator 64.
[0029]
The light receiver 70 converts light input from the optical fiber 14b into an electric signal. The output of the light receiver 70 is applied to the BPF 72 and the BPF 74. The BPF 72 extracts a reference signal component transmitted from the terminal station 10 onto the optical fiber line 14. The BPF 74 extracts the frequency component of the monitoring signal modulation signal transmitted from the optical repeater 18 to the optical fiber line 14 by modulating the gain of the optical amplifier 40. The output of the BPF 72 is applied to the reference reproduction circuit 76. The reference reproduction circuit 76 is a circuit similar to the reference reproduction circuit 56 of the optical repeater 18, multiplies the output frequency of the BPF 72 by PLL, and the frequency divider 78 divides the output of the reference reproduction circuit 76 to monitor. A frequency signal for synchronous detection of the signal modulation signal is generated. The reference reproduction circuit 76 and the frequency divider 78 are the same as the reference reproduction circuit 56 and the frequency divider 60 of the optical repeater 18, and function similarly. That is, the output frequency of the frequency divider 78 is the same as the output frequency of the frequency divider 60. The monitoring signal demodulator 80 multiplies the output of the frequency divider 78 by the output of the BPF 74, and synchronously detects the monitoring signal.
[0030]
In the present embodiment, the frequency of the reference signal (455 kHz) transmitted from the terminal station 10 to the optical fiber line 14 and the frequency of the carrier (43.3) used to transmit the monitoring signal from the optical repeater 18 to the terminal station 12 are used. 041 kHz) are different values as described above, so that the terminal station 12 can easily identify the reference signal and the monitor signal carrier.
[0031]
A method of superposing the signal light and the reference signal (or the modulation signal of the control signal) in the superimposer 30 will be briefly described. FIG. 4 shows a configuration example in which the amplitude of a transmission signal light is modulated by a reference signal (or a modulation signal of a control signal) and transmitted. FIG. 5 is a diagram showing a dedicated wavelength for transmitting the reference signal (or a modulation signal of the control signal). An example of a configuration in which is provided.
[0032]
Referring to FIG. The laser light sources 82-1 to 82-n oscillate at different wavelengths λ1 to λn, and the optical modulators 84-1 to 84-n transmit the output light of each of the laser light sources 82-1 to 82-n to a transmission signal #. The intensity is modulated by 1 to #n. The multiplexer 86 multiplexes the output lights of the optical modulators 84-1 to 84-n. The optical modulator 88 shallowly modulates the output of the multiplexer 86 with the output of the control signal modulator 24 (that is, the reference signal or the control signal modulation signal). The output of the optical modulator 88 is output to the optical fiber line 14. In this example, the optical modulator 88 is the superimposing device 30. The configuration of the optical repeater 18 of the embodiment shown in FIG. 1 corresponds to the superposition method shown in FIG.
[0033]
Referring to FIG. The laser light sources 90-1 to 90-n oscillate at different wavelengths [lambda] 1 to [lambda] n, and the optical modulators 92-1 to 92-n transmit the output light of each of the laser light sources 90-1 to 90-n to a transmission signal #. The intensity is modulated by 1 to #n. The laser light source 94 oscillates at a wavelength λa different from any of the signal light wavelengths λ1 to λn, and the optical modulator 96 outputs the output light of the laser light source 94 to the output of the control signal modulator 24 (that is, the reference Signal or control signal modulation signal). The multiplexer 98 multiplexes the output lights of the optical modulators 92-1 to 92-n and the optical modulator 96 and outputs the multiplexed light to the optical fiber line 14. In this example, the laser light source 94, the optical modulator 96, and the multiplexer 98 constitute the superimposer 30. In the optical repeater 18, an optical filter for separating the wavelength λa is required in the optical stage.
[0034]
【The invention's effect】
As can be easily understood from the above description, according to the present invention, the carrier for transmitting the monitoring signal indicating the operation state of the optical repeater or the like to the terminal station is determined by the reference from the same terminal or another terminal. Since the signal is generated in the optical repeater based on the signal, it is not necessary to provide a local oscillator in the optical repeater. As a result, there is no need to consider the frequency fluctuation of the carrier that carries the supervisory signal on the supervisory signal receiving side, and it is not necessary to provide a receiving device with an unnecessarily wide band for receiving the supervisory signal. Since synchronous detection can be used to demodulate the monitor signal modulation signal at the terminal station, the monitor signal can be demodulated with a high S / N ratio.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an embodiment of the present invention.
FIGS. 2A and 2B are timing charts of a control signal, a reference signal, and a monitoring signal in the present embodiment, wherein FIG. 2A shows a transmission sequence of the control signal and the reference signal, and FIG. Show.
FIG. 3 is a schematic configuration block diagram of a monitoring signal receiving system in the terminal station 12;
FIG. 4 is a schematic configuration block diagram of an example of a superimposer 30;
FIG. 5 is a schematic block diagram of another example of the superimposer 30.
[Explanation of symbols]
10, 12: terminal stations 14, 16: optical fiber lines 14a, 14b, 16a, 16b: optical fiber 18: optical repeater 20: reference oscillator 22: frequency divider 24: control signal modulator 26: control / processing circuit 27 : Laser light source 28: optical modulator 30: superimposing device 32: light receiving device 34: receiving device 36: monitoring signal demodulator 38: frequency divider 40, 42: optical amplifier 44: excitation circuit 46, 48: optical splitter 50, 52: light receiver 54: band pass filter (BPF)
56: reference reproduction circuit 58: control signal demodulator 60: frequency divider 62: control circuit 64: monitor signal modulator 70: photodetectors 72, 74: BPF
76: reference reproduction circuit 78: frequency divider 80: monitor signal demodulators 82-1 to 82-n: laser light sources 84-1 to 84-n: optical modulator 86: multiplexer 88: optical modulator 90-1 90-n: laser light sources 92-1 to 92-n: optical modulator 94: laser light source 96: optical modulator 98: multiplexer

Claims

An oscillation source;
Reference signal sending means for sending a reference signal of a predetermined frequency generated from the output of the oscillation source to the first optical fiber;
A light receiver for converting light from the first optical fiber into an electric signal, a reference signal extracting means for extracting the reference signal component from an output of the light receiver, a carrier generation for generating a carrier from an output of the reference signal extracting means Means, monitoring signal modulation means for modulating a carrier generated by the carrier generation means with a monitoring signal indicating an operation state of the optical repeater, and output of the monitoring signal modulation means on a second optical fiber. An optical repeater having a sending unit;
Demodulation signal generation means for generating a demodulation signal having the same frequency as the carrier of the monitoring signal from one of the output of the oscillation source and the reference signal,
A light receiver for receiving the light transmitted through the second optical fiber,
An optical repeater monitoring system, comprising: a monitoring signal demodulating unit that demodulates the monitoring signal from an output of the photodetector and an output of the detection / demodulation signal generation unit.

The oscillation source, the reference signal transmitting unit, the demodulation signal generation unit, and the monitoring signal demodulation unit are arranged at the same terminal, and the demodulation signal generation unit generates the demodulation signal from the output of the oscillation source. The optical repeater monitoring system according to claim 1.

The oscillation source and the reference signal transmitting means are arranged at the first terminal station, and the demodulation signal generating means and the monitoring signal demodulating means are arranged at the second terminal station;
The optical repeater sends light from the first optical fiber to the second optical fiber,
2. The optical repeater monitoring system according to claim 1, wherein the demodulation signal generation unit generates the demodulation signal from the reference signal transmitted through the first optical fiber and the second optical fiber.

The optical repeater monitoring system according to claim 1, wherein the reference signal transmitting unit includes a superimposing unit that superimposes the reference signal on a transmission signal light.

5. The optical repeater monitoring system according to claim 4, wherein the superimposing means comprises optical multiplexing means for multiplexing the light carrying the monitoring signal having a different wavelength from the transmission signal light with the transmission signal light.

5. The optical repeater monitoring system according to claim 4, wherein said superimposing means comprises optical modulation means for intensity-modulating said transmission signal light according to said reference signal.

The optical repeater monitoring system according to claim 1, wherein the reference signal is a single-frequency tone signal.

2. The optical repeater monitoring system according to claim 1, wherein the monitoring signal modulation unit is any one of an amplitude shift keying system, a phase shift keying system, and a frequency shift keying system.

2. The optical repeater monitoring system according to claim 1, wherein the transmission unit is an optical modulation unit that intensity-modulates the signal light output to the second optical fiber according to an output of the monitoring signal modulation unit. 3.

10. The optical repeater monitoring system according to claim 9, wherein the optical modulation means is means for changing a gain of a signal output to the second optical fiber according to an output of the monitoring signal modulation means.

A reference signal transmitting step of transmitting a reference signal of a predetermined frequency from the reference signal transmitting device to the optical repeater via the optical fiber line,
In the optical repeater, which carries a monitoring signal of the optical repeater, a carrier generation step of generating a carrier having a frequency different from the frequency of the reference signal from the reference signal,
In the optical repeater, a monitor signal modulation step of modulating the carrier with the monitor signal,
In the optical repeater, a monitoring signal transmitting step of transmitting a modulated wave of the monitoring signal by the monitoring signal modulation step toward a monitoring signal receiving device,
In the monitoring signal receiving device, a demodulation signal generation step of generating a demodulation signal having the same frequency as the carrier wave,
A monitoring signal demodulation step of demodulating the monitoring signal modulation signal sent from the optical repeater with the demodulation signal in the monitoring signal receiving apparatus.

12. The optical repeater monitoring method according to claim 11, wherein the demodulation signal generating step generates the demodulation signal from one of the reference signal and an output of a signal source from which the reference signal is generated.

The optical repeater monitoring method according to claim 11, wherein the reference signal transmitting step is a superimposing step of superimposing the reference signal on a transmission signal light.

14. The optical repeater monitoring method according to claim 13, wherein the superimposing step includes an optical multiplexing step of multiplexing the light carrying the monitoring signal having a different wavelength from the transmission signal light with the transmission signal light.

14. The optical repeater monitoring method according to claim 13, wherein the superimposing step includes an optical modulation step of intensity-modulating the transmission signal light according to the reference signal.

The optical repeater monitoring method according to claim 11, wherein the monitoring signal modulation step is any one of an amplitude shift keying method, a phase shift keying method, and a frequency shift keying method.

12. The optical repeater monitoring method according to claim 11, wherein the monitoring signal transmitting step is an optical modulation step of intensity-modulating a transmission signal light according to an output of the monitoring signal modulation step.