JP2004289287A

JP2004289287A - Optical carrier generator, optical modulator, optical signal transmitter/receiver, and optical communication system

Info

Publication number: JP2004289287A
Application number: JP2003076267A
Authority: JP
Inventors: Hiroki Takei; 弘樹武居; Naoto Yoshimoto; 直人吉本
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2003-03-19
Filing date: 2003-03-19
Publication date: 2004-10-14
Anticipated expiration: 2023-03-19
Also published as: JP3987447B2

Abstract

<P>PROBLEM TO BE SOLVED: To generate an optical carrier for avoiding the occurrence of crosstalk having the same wavelength in a node generating the optical carrier for transmission from signal light inputted from the outside. <P>SOLUTION: There are a light intensity saturating means having I/O characteristics, where output light intensity is saturated to the input light intensity set to the minimum saturated input intensity or more and the maximum one or less; and a wavelength conversion means for converting the wavelength of input light. A light signal is subjected to intensity modulation so that the minimum value of the light intensity is the minimum saturated input intensity or more and the maximum value is the maximum saturated input intensity or less and is inputted to the light intensity saturating means for generating continuous light whose light intensity is saturated. The continuous light is inputted to the wavelength conversion means for outputting continuous light with a new wavelength having a specific wavelength difference to the signal light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、外部から入力される強度変調された信号光から所定の波長の連続光（光キャリア）を発生する光キャリア発生装置に関する。また、この光キャリア発生装置から出力される光キャリアを変調し、入力信号光と異なる波長の信号光を出力する光変調装置に関する。また、光キャリア発生装置に入力する信号光を受信し、光キャリア発生装置から出力される光キャリアを変調して入力信号光と異なる波長の信号光を出力する光信号送受信装置、さらにこの光信号送受信装置を用いた光通信システムに関する。
【０００２】
【従来の技術】
図１６は、センタノードに光源を集中的に配置する従来の光通信システムの構成例を示す（非特許文献１、特願２００２−１４７２５０号）。
【０００３】
図において、光通信システムは、センタノード５０と複数のリモートノード５１−１〜５１−ｎが、光ファイバ伝送路５２および１：ｎ波長ルータ５３を介してスター状に接続された構成である。各リモートノード５１−１〜５１−ｎは、光双方向結合素子５５を介して光ファイバ伝送路５２から入力する信号光を光信号送受信装置６０に入力し、光信号送受信装置６０から出力される信号光を光ファイバ伝送路５２に接続する。光信号送受信装置６０は、入力する信号光を２分岐する光分岐素子６１、分岐された一方の信号光を受信する光受信器６２、他方の信号光を入力する光強度飽和素子６３および光強度変調器６４から構成される。
【０００４】
センタノード５０は、消光比をやや低く設定した複数の波長チャネルの下り信号光を波長多重し、光ファイバ伝送路５２を介して１：ｎ波長ルータ５３に送出する。１：ｎ波長ルータ５３は、センタノード５０から送信された波長多重信号光を各波長の信号光に分波し、それぞれ対応するリモートノード５１−１〜５１−ｎへ送信する。各リモートノードには、それぞれ割り当てられた波長の下り信号光が入力され、光双方向結合素子５５を介して光信号送受信装置６０に入力される。光信号送受信装置６０では、下り信号光の一部を光分岐素子６１で分岐して受信処理するとともに、光強度飽和素子６３で下り信号光の強度変調成分を抑圧し、これにより得られた下り信号光と同一波長の光キャリアを光強度変調器６４に入力し、送信信号により強度変調して出力する。新たに生成された信号光は、光双方向結合素子５５を介して１：ｎ波長ルータ５３へ送信され、他のリモートノードから送信された各波長の信号光と合波してセンタノード５０へ送信される。
【０００５】
このように、センタノード５０に集中的に光源を配置することにより、各リモートノード５１−１〜５１−ｎに光源を配置することなく、それぞれ１つの波長を用いてセンタノード５０と各リモートノード５１−１〜５１−ｎとの間の双方向通信が可能になる。よって、各リモートノードにそれぞれ個別の波長の光源を配置する波長多重光通信システムに比べて、保守が容易な波長多重光通信システムを構築することができる。
【０００６】
図１７は、従来の光通信システムの他の構成例を示す（特願２００２−１４７２５０号）。本構成例は、光強度飽和素子６３を用いた光信号送受信装置６０を含むリモートノードをリング型に接続したものである。
【０００７】
図において、光通信システムは、センタノード５０および複数のリモートノード５１−１〜５１−３を光ファイバ伝送路５２を介してリング状に接続した構成である。リモートノード５１−２は、図１６と同様の光信号送受信装置６０と、リモートノード５１−１からリモートノード５１−２，５１−３に伝送される波長多重信号光に対して、リモートノード５１−２に割り当てた波長の信号光を分岐・挿入する波長分岐挿入素子５６を備える。他のリモートノードも同様である。
【０００８】
センタノード５０は、消光比をやや低く設定した複数の波長チャネルの下り信号光を波長多重し、光ファイバ伝送路５２を介して各リモートノードへ送出する。各リモートノードでは、センタノード５０から送信された波長多重信号光からそれぞれ割り当てられた波長の下り信号光を分波し、光信号送受信装置６０に入力する。光信号送受信装置６０では、下り信号光の一部を光分岐素子６１で分岐して受信処理するとともに、光強度飽和素子６３で下り信号光の強度変調成分を抑圧し、これにより得られた下り信号光と同一波長の光キャリアを光強度変調器６４に入力し、送信信号により強度変調して出力する。新たに生成された信号光は、波長分岐挿入素子５６を介して他の信号光と合波して光ファイバ伝送路５２へ再入力され、センタノード５０へ送信される。
【０００９】
これにより、各リモートノード５１−１〜５１−３に光源を配置することなく、それぞれ１つの波長を用いてセンタノード５０と各リモートノード５１−１〜５１−３との間の双方向通信が可能になる。
【００１０】
【非特許文献１】
Ｈ．ＴａｋｅｓｕｅａｎｄＴ．Ｓｕｇｉｅ，”ＤａｔａｒｅｗｒｉｔｅｏｆｗａｖｅｌｅｎｇｔｈｃｈａｎｎｅｌｕｓｉｎｇｓａｔｕｒａｔｅｄＳＯＡｍｏｄｕｌａｔｏｒｆｏｒＷＤＭｍｅｔｒｏ／ａｃｃｅｓｓｎｅｔｗｏｒｋｓｗｉｔｈｃｅｎｔｒａｌｉｚｅｄｌｉｇｈｔｓｏｕｒｃｅｓ”，ｉｎＰｒｏｃｅｅｄｉｎｇｓｏｆ２８ｔｈＥｕｒｏｐｅａｎｃｏｎｆｅｒｅｎｃｅｏｎｏｐｔｉｃａｌｃｏｍｍｕｎｉｃａｔｉｏｎ，ＥＣＯＣ２００２，Ｃｏｐｅｎｈａｇｅｎ，Ｐａｐｅｒ８．５．６，２００２年９月８日
【００１１】
【発明が解決しようとする課題】
図１６に示す光通信システムにおいて、光ファイバ伝送路５２の利用効率を上げるには、センタノード５０と１：ｎ波長ルータ５３とを双方向接続する光ファイバ伝送路５２、さらに１：ｎ波長ルータ５３と各リモートノード５１−１〜５１−ｎとを双方向接続する光ファイバ伝送路５２として、それぞれ１本の光ファイバで構成されることが望ましい。しかし、このような１心双方向伝送において、同一波長の光が双方向に伝搬する構成では、例えば下り信号光が光ファイバケーブルの接続点などで反射すると、その反射戻り光が上り信号光に対するクロストーク光となる。このクロストーク光は上り信号光と同一波長であるため、異波長のクロストーク光によりも大きなパワーペナルティを生じさせる問題がある。
【００１２】
一方、図１７の光通信システムでは、リング状に接続された光ファイバ伝送路５２中の光の伝送方向は一方向であるので、図１６の光通信システムのような双方向伝送におけるクロストーク問題は発生しない。しかし、波長分岐挿入素子５６の遮断特性が不十分であると、波長分岐挿入素子５６を通過する光キャリア成分が、光信号送受信装置６０から出力される上り信号光に対する同一波長のクロストーク光となる。そのため、波長分岐挿入素子５６の遮断特性に対する要求条件が厳しくなる問題がある。
【００１３】
本発明は、外部から入力する信号光から送信用の光キャリアを発生させるノードにおいて、同一波長クロストークの発生を回避するための光キャリアを発生する光キャリア発生装置を提供することを目的とする。また、この光キャリア発生装置から出力される光キャリアを変調して出力する光変調装置、この光変調装置を用いた光信号送受信装置、さらにこの光信号送受信装置を用いた光通信システムを提供することを目的とする。
【００１４】
【課題を解決するための手段】
（光キャリア発生装置：請求項１〜４）
請求項１の光キャリア発生装置は、最小飽和入力強度以上かつ最大飽和入力強度以下の入力光強度に対して出力光強度が飽和する入出力特性を有する光強度飽和手段と、入力光の波長を変換する波長変換手段とを備え、光強度の最小値が最小飽和入力強度以上であり、光強度の最大値が最大飽和入力強度以下であるように強度変調された信号光を光強度飽和手段に入力して光強度が飽和した連続光を生成し、その連続光を波長変換手段に入力し、信号光に対して所定の波長差をもつ新たな波長の連続光を出力する構成である。
【００１５】
請求項２の光キャリア発生装置は、最小飽和入力強度以上かつ最大飽和入力強度以下の入力光強度に対して出力光強度が飽和する入出力特性を有する光強度飽和手段と、入力光の波長を変換する波長変換手段とを備え、波長変換手段を通過して光強度飽和手段に入力する光強度の最小値が最小飽和入力強度以上であり、波長変換手段を通過して光強度飽和手段に入力する光強度の最大値が最大飽和入力強度以下であるように強度変調された信号光を波長変換手段に入力し、その波長変換光を光強度飽和手段に入力して光強度が飽和した連続光を生成し、信号光に対して所定の波長差をもつ新たな波長の連続光を出力する構成である。
【００１６】
ここで、光強度飽和手段に入力される信号光の光強度の最小値が最小飽和入力強度以上であり、その最大値が最大飽和入力強度以下になるように調整する光強度調整手段を備えてもよい（請求項３）。
【００１７】
また、光強度飽和手段および波長変換手段は、非線形光学媒質に強度変調された信号光および所定の波長の励起光を入力し、非線形光学効果により発生する信号光に対して所定の波長差をもつ連続光を出力する構成としてもよい（請求項４）。
【００１８】
（光変調装置：請求項５）
請求項５の光変調装置は、請求項１〜４のいずれかに記載の光キャリア発生装置と、光キャリア発生装置から出力される連続光を送信信号により強度変調して出力する光強度変調手段とを備え、光キャリア発生装置に入力する信号光に対して所定の波長差をもつ信号光を出力する構成である。
【００１９】
（光信号送受信装置：請求項６）
請求項６の光信号送受信装置は、請求項５に記載の光変調装置と、光強度飽和手段に入力する信号光の一部を分岐する光分岐手段と、光分岐手段で分岐された信号光を受信処理する光受信手段とを備え、信号光を受信するとともに、信号光に対して所定の波長差をもつ信号光を光変調装置から出力する構成である。
【００２０】
（光通信システム：請求項７〜１４）
請求項７の発明は、複数のノードが光ファイバ伝送路を介して接続され、各ノードでは、他のノードから送信された所定の波長の信号光を受信するとともに、他のノードへ所定の波長の信号光を送信する光通信システムにおいて、各ノードは、請求項６に記載の光信号送受信装置と、光ファイバ伝送路からそのノードに割り当てた波長の信号光を分岐して光信号送受信装置に入力し、かつ光信号送受信装置から出力された信号光に対して所定の波長差をもつ信号光を光ファイバ伝送路に挿入する波長分岐挿入手段とを備える。
【００２１】
請求項８の発明は、センタノードと複数のリモートノードが、波長ルータおよび光ファイバ伝送路を介してスター状に接続され、各リモートノードでは、センタノードから送信された所定の波長の下り信号光を受信するとともに、センタノードへ所定の波長の上り信号光を送信する光通信システムにおいて、各リモートノードは、請求項６に記載の光信号送受信装置と、光ファイバ伝送路から入力する下り信号光を光信号送受信装置に入力し、光信号送受信装置から出力された下り信号光に対して所定の波長差をもつ上り信号光を光ファイバ伝送路に接続する光双方向結合手段とを備える。
【００２２】
請求項９の発明は、センタノードと複数のリモートノードが、光スターカプラおよび光ファイバ伝送路を介してスター状に接続され、各リモートノードでは、センタノードから送信された所定の波長の下り信号光を受信するとともに、センタノードへ所定の波長の上り信号光を送信する光通信システムにおいて、各リモートノードは、請求項６に記載の光信号送受信装置と、光ファイバ伝送路からそのリモートノードに割り当てた波長の下り信号光を分波して光信号送受信装置に入力し、光信号送受信装置から出力された下り信号光に対して所定の波長差をもつ上り信号光を光ファイバ伝送路に接続する光フィルタおよび光双方向結合手段とを備える。
【００２３】
ここで、各リモートノードの光フィルタは、分波する波長が可変である波長可変フィルタとしてもよい（請求項１０）。
【００２４】
請求項１１の発明は、センタノードと複数のリモートノードが光ファイバ伝送路を介してリング状に接続され、各リモートノードでは、センタノードから送信された所定の波長の下り信号光を受信するとともに、センタノードへ所定の波長の上り信号光を送信する光通信システムにおいて、各リモートノードは、請求項６に記載の光信号送受信装置と、光ファイバ伝送路からそのリモートノードに割り当てた波長の下り信号光を分岐して光信号送受信装置に入力し、光信号送受信装置から出力された下り信号光に対して所定の波長差をもつ上り信号光を光ファイバ伝送路に挿入する波長分岐挿入手段とを備える。
【００２５】
ここで、各リモートノードの波長分岐挿入手段は、分岐・挿入する波長が可変である構成としてもよい（請求項１２）。
【００２６】
請求項１３の発明は、請求項７〜１２のいずれかに記載の光通信システムにおいて、請求項６に記載の光信号送受信装置に用いる請求項５に記載の光変調装置に請求項４に記載の光キャリア発生装置を用い、光通信システム中のノードまたはリモートノードは、所定の波長の励起光を出力する励起光源を備え、その励起光を光キャリア発生装置の非線形光学媒質に入力する構成である。
【００２７】
請求項１４の発明は、請求項７〜１２のいずれかに記載の光通信システムにおいて、請求項６に記載の光信号送受信装置に用いる請求項５に記載の光変調装置に請求項４に記載の光キャリア発生装置を用い、光通信システム中の特定のノードから、光ファイバ伝送路を介して信号光とともに信号光と異なる波長の励起光を送信し、他のノードでその励起光を光キャリア発生装置の非線形光学媒質に入力する構成である。
【００２８】
【発明の実施の形態】
（光キャリア発生装置の第１の実施形態）
図１は、本発明の光キャリア発生装置の第１の実施形態を示す。図において、本実施形態の光変調装置は、光強度飽和素子１と波長変換素子２により構成される。入力信号光は強度変調された信号光であり、その光強度の最大値をＰ_Ｍ、最小値をＰ_Ｓとする。
【００２９】
光強度飽和素子１の光入出力特性は、図２に示すように、入力光強度が小さい領域では出力光強度が入力光強度にほぼ比例し、入力光強度が所定値以上になると出力光強度が飽和し、入力光強度の変化に対する出力光強度の変化が抑圧される。この所定値を「最小飽和入力強度」とする。光強度飽和素子１の性質によっては、最小飽和入力強度を越えて入力光強度をさらに増大してゆき、入力光強度が所定値以上になると入力光強度の変化に対する出力光強度の変化が再び大きくなる場合がある。この所定値を「最大飽和入力強度」とする。出力光強度が飽和する最小飽和入力強度以上最大飽和入力強度以下の入力光強度の領域を「飽和入力領域」と定義する。
【００３０】
ここで、光強度の最小値Ｐ_Ｓおよび最大値Ｐ_Ｍが飽和入力領域にあるように強度変調された信号光（波長λ）を光強度飽和素子１に入力すると、強度変調成分（光強度の最大値と最小値の差）が抑圧された信号光（連続光）が出力される。この連続光（波長λ）を波長変換素子２に入力して別波長に変換することにより、入力信号光の波長に対して所定の波長差をもつ新たな光キャリア（波長λ′）を発生することができる。
【００３１】
なお、光強度飽和素子１と波長変換素子２の接続の順序を入れ換えてもよい。この場合には、入力信号光の光強度の最大値Ｐ_Ｍおよび最小値Ｐ_Ｓが、波長変換素子２を通過して光強度飽和素子１に入力される時点で飽和入力領域にあるように強度変調される。
【００３２】
（光キャリア発生装置の第２の実施形態）
図３は、本発明の光キャリア発生装置の第２の実施形態を示す。本実施形態は、第１の実施形態の光強度飽和素子１の前段に光増幅器３を配置した構成である。
【００３３】
第１の実施形態では、入力信号光の光強度の最小値Ｐ_Ｓおよび最大値Ｐ_Ｍが光強度飽和素子１の飽和入力領域にあるとしたが、これらが最小飽和入力強度に満たない場合には光増幅器３を用い、光強度の最小値Ｐ_Ｓおよび最大値Ｐ_Ｍが飽和入力領域にあるように増幅して光強度飽和素子１に入力する。これにより、入力光強度が小さい場合でも動作可能な光キャリア発生装置を実現することができる。
【００３４】
一方、入力信号光の光強度の最大値Ｐ_Ｍが最大飽和入力強度を越える場合には、光増幅器３の代わりに光減衰器を用い、入力信号光の光強度の最小値Ｐ_Ｓおよび最大値Ｐ_Ｍが光強度飽和素子１の飽和入力領域にあるように調整することにより、入力光強度が大きい場合でも動作可能な光キャリア発生装置を実現することができる。
【００３５】
以上示した実施形態において、波長変換素子２には、音響光学周波数シフタまたは光ＳＳＢ（ｓｉｎｇｌｅｓｉｄｅｂａｎｄ）変調器を用いることができる。音響光学周波数シフタでは、音響光学効果により入力する信号光（連続光）に対して所定の波長差をもつ信号光（連続光）が出力される。光ＳＳＢ変調器では、電気光学効果により入力する信号光（連続光）に対して所定の波長差をもつ信号光（連続光）が出力される（Ｍ．Ｉｚｕｔｓｕ，Ｓ．ＳｈｉｋａｍａａｎｄＴ．Ｓｕｅｔａ，”ＩｎｔｅｇｒａｔｅｄｏｐｔｉｃａｌＳＳＢｍｏｄｕｌａｔｏｒ／ｆｒｅｑｕｅｎｃｙｓｈｉｆｔｅｒ”，ＩＥＥＥＪ．ＱｕａｎｔｕｍＥｌｅｃｔｒｏｎ．，Ｖｏｌ．ＱＥ−１７，Ｎｏ．１１，ｐｐ．２２２５−２２２７，１９８１）。
【００３６】
また、波長変換素子２は、非線形光学媒質に信号光（連続光）と所定の波長の励起光を入力することにより、非線形光学効果により信号光（連続光）に対して所定の波長差をもつ信号光（連続光）を生成する構成としてもよい。例えば、２次の非線形光学媒質であるＰＰＬＮでは、信号光と励起光の和（差）周波数の信号光が生成される。また、高非線形光ファイバや半導体光増幅器では、信号光と励起光の四光波混合光が生成される。波長変換素子２としては、非線形光学媒質の出力光からこれらの波長変換光を光フィルタで選択出力する。
【００３７】
（光キャリア発生装置の第３の実施形態）
図４は、本発明の光キャリア発生装置の第３の実施形態を示す。本実施形態は、第１の実施形態および第２の実施形態における光強度飽和素子１と波長変換素子２を兼ねるものとして、非線形光学媒質１１における入力信号光と励起光との間の非線形光学効果（ここでは縮退四光波混合）を利用する構成である。非線形光学媒質１１に、入力信号光（光周波数ｆ_Ｓ）と励起光レーザ１２から出力される励起光（光周波数ｆ_Ｐ）を光合波器１３で合波して入力すると、新たに四光波混合光（光周波数２ｆ_Ｐ−ｆ_Ｓ）が発生する。非線形光学媒質１１から出力される信号光、励起光、四光波混合光を光バンドパスフィルタ１４に入力し、四光波混合光のみを入力信号光に対して波長変換された光キャリアとして出力する。
【００３８】
ここで、非線形光学媒質１１の分散、非線形利得係数等のパラメータや、励起光および信号光のパワーを適切に調整することにより、入力する信号光の光強度と出力される四光波混合光（波長変換光）の光強度との間に、図５に示すような光入出力特性を実現することができる。すなわち、光強度の最小値Ｐ_Ｓおよび最大値Ｐ_Ｍが飽和入力領域にある信号光を非線形光学媒質１１に入力すると、その飽和特性により変調パターンが除去された四光波混合光（波長変換光）が出力される。このような機能を有する非線形光学媒質１１としては、高非線形光ファイバや半導体光増幅器などを用いることができる。
【００３９】
（光キャリア発生装置の第４の実施形態）
図６は、本発明の光キャリア発生装置の第４の実施形態を示す。本実施形態は、第３の実施形態における励起光レーザ１２を用いず、外部から波長多重された信号光と励起光を入力する構成である。信号光と励起光は光分波器１５で分波し、分波した励起光を光増幅器１６で増幅する。増幅された励起光は、光合波器１３で再度信号光と合波され、非線形光学媒質１１に入力される。なお、光分波器１５および光増幅器１６は、ここでは光キャリア発生装置の外部に配置した例を示したが、光キャリア発生装置の内部にあってもよい。
【００４０】
（光キャリア発生装置の第５の実施形態）
図７は、本発明の光キャリア発生装置の第５の実施形態を示す。本実施形態は、複数の非線形光学媒質を用いて複数の光周波数の光キャリアを一括発生させる構成である。
【００４１】
光周波数ｆ_Ｓ１，ｆ_Ｓ２，…，ｆ_Ｓｍの波長多重信号光は、光分波器１７で各光周波数の信号光に分波される。励起光レーザ１２から出力される光周波数ｆ_Ｐの励起光は光分岐器１８でｍ分岐され、光合波器１３−１〜１３−ｍで光周波数ｆ_Ｓ１，ｆ_Ｓ２，…，ｆ_Ｓｍの信号光とそれぞれ合波され、非線形光学媒質１１−１〜１１−ｍに入力される。各非線形光学媒質１１−１〜１１−ｍは、それぞれ光周波数２ｆ_Ｐ−ｆ_Ｓ１，２ｆ_Ｐ−ｆ_Ｓ２，…，２ｆ_Ｐ−ｆ_Ｓｍの四光波混合光を発生する。各非線形光学媒質１１−１〜１１−ｍから出力される信号光、励起光、四光波混合光は、それぞれ対応する光バンドパスフィルタ１４−１〜１４−ｍに入力され、四光波混合光のみが入力信号光に対して波長変換された光キャリアとして出力される。
【００４２】
本実施形態では、１つの励起光レーザ１２を備えるだけで、波長多重信号光の各光周波数に応じた複数の光周波数の光キャリアを一括して発生させることができる。なお、図６の第４の実施形態のように、波長多重信号光に波長多重された励起光を分波、増幅して入力するようにしてもよい。
【００４３】
（光キャリア発生装置の第６の実施形態）
図８は、本発明の光キャリア発生装置の第６の実施形態を示す。本実施形態は、１つの非線形光学媒質を用いて複数の光周波数の光キャリアを一括発生させる構成である。
【００４４】
光周波数ｆ_Ｓ１，ｆ_Ｓ２，…，ｆ_Ｓｍの波長多重信号光と、励起光レーザ１２から出力される光周波数ｆ_Ｐの励起光は光合波器１３で合波され、非線形光学媒質１１に入力される。非線形光学媒質１１は、それぞれ光周波数２ｆ_Ｐ−ｆ_Ｓ１，２ｆ_Ｐ−ｆ_Ｓ２，…，２ｆ_Ｐ−ｆ_Ｓｍの四光波混合光を発生し、光分波器１７を介して各光周波数の四光波混合光のみが入力信号光に対して波長変換された光キャリアとして出力される。本実施形態では、１つの励起光レーザ１２と１つの非線形光学媒質１１を備えるだけで、波長多重信号光の各光周波数に応じた複数の光周波数の光キャリアを一括して発生させることができる。
【００４５】
なお、図７および図８の構成において、図６の第４の実施形態のように、波長多重信号光に波長多重された励起光を分波、増幅して入力するようにしてもよい。
【００４６】
（光変調装置の第１の実施形態）
図９は、本発明の光変調装置の第１の実施形態を示す。図において、本実施形態の光変調装置は、本発明の光キャリア発生装置の波長変換素子２の後段に光強度変調器４を接続した構成である。ここでは、図１に示す光キャリア発生装置の第１の実施形態に適用した例を示すが、図３の第２の実施形態の構成、図４の第３の実施形態、図６の第４の実施形態の構成にも同様に適用できる。
【００４７】
光キャリア発生装置の波長変換素子２は、入力信号光の波長λに対して所定の波長差をもつ波長λ′の光キャリアを出力する。この光キャリアを光強度変調器４に入力し、送信信号で強度変調することにより、入力信号光の波長λに対して所定の波長差をもつ新たな波長λ′の信号光を出力することができる。
【００４８】
（光変調装置の第２の実施形態）
図１０は、本発明の光変調装置の第２の実施形態を示す。図において、本実施形態の光変調装置は、図７に示す第５の実施形態の光キャリア発生装置の各光バンドパスフィルタ１４−１〜１４−ｍの後段に光強度変調器４−１〜４−ｍを接続し、各光周波数２ｆ_Ｐ−ｆ_Ｓ１，２ｆ_Ｐ−ｆ_Ｓ２，…，２ｆ_Ｐ−ｆ_Ｓｍの光キャリアを強度変調した信号光を光合波器１９で合波して出力する構成である。
【００４９】
なお、図８に示す第６の実施形態の光キャリア発生装置の光分波器１７の後段に光強度変調器４−１〜４−ｍを接続し、各光周波数の光キャリアを強度変調した信号光を光合波器１９で合波して出力する構成としてもよい。
【００５０】
（光信号送受信装置の実施形態）
図１１は、本発明の光信号送受信装置の実施形態を示す。図において、本実施形態の光信号送受信装置１０は、本発明の光キャリア発生装置の波長変換素子２の後段に光強度変調器４を接続した光変調装置に加え、光キャリア発生装置の光強度飽和素子１に入力する信号光を２分岐する光分岐素子５と、分岐された信号光を受信する光受信器６により構成される。ここでは、図１に示す光キャリア発生装置の第１の実施形態に適用した例を示すが、図３の第２の実施形態の構成、図４の第３の実施形態の構成、図６の第４の実施形態の構成にも同様に適用できる。
【００５１】
光信号送受信装置１０に入力される信号光（波長λ）は、光分岐素子５を介して光受信器６に受信されるとともに、光強度飽和素子１で強度変調成分が抑圧された光キャリア（波長λ）に変換される。この光キャリアは波長変換素子２に入力され、入力信号光の波長λに対して所定の波長差をもつ波長λ′の光キャリアに波長変換され、光強度変調器４で送信信号により変調することにより、入力信号光の波長λに対して所定の波長差をもつ新たな波長λ′の信号光を出力することができる。
【００５２】
また、図１０に示す光変調装置を用いて光信号送受信装置を構成する場合には、光合波器１３−１〜１３−ｍの前段に、各光周波数の信号光を２分岐する光分岐素子と、分岐された信号光を受信する光受信器を備えることにより、複数の信号光の送受信に対応することができる。さらに、図８に示す光キャリア発生装置を用いる場合には、波長多重信号光を光分岐素子で分岐した後に光分波器で各波長の信号光に分波し、それぞれ対応する光受信器で波長チャネルごとに受信する構成とする。
【００５３】
（光通信システムの第１の実施形態）
図１２は、本発明の光通信システムの第１の実施形態を示す。図において、本実施形態の光通信システムは、複数のノード２１−１〜２１−３を光通信網２２を介して接続した構成である。各ノード２１−１〜２１−３は、図１１に示す本発明の光信号送受信装置１０と、それぞれ割り当てられ波長の信号光を分岐し、分岐する波長と異なる波長の信号光を挿入する波長分岐挿入素子２３を備える。ここで、ノード２１−２で分岐する波長をλ_１、挿入する波長をλ_２とする。
【００５４】
ノード２１−１から送信された波長多重信号光は、光通信網２２を介してノード２１−２の波長分岐挿入素子２３に入力され、波長λ_１の信号光が分岐して光信号送受信装置１０に入力される。光信号送受信装置１０では、波長λ_１の信号光を受信処理するとともに、信号光波長λ_１に対して所定の波長差をもつ波長λ_２の信号光を生成して出力する。新たに生成された波長λ_２の信号光は、波長分岐挿入素子２３を介して波長多重信号光に多重され、光通信網２２を介してノード２１−３へ送信される。これにより、ノード２１−１からノード２１−２への信号光伝送と、ノード２１−２からノード２１−３への信号光伝送が可能になる。また、同一波長クロストーク抑圧のために波長分岐挿入素子２３に要求される遮断特性に対する条件を緩和することができる。
【００５５】
なお、本実施形態では、波長分岐挿入素子２３はノード内に配置されているが、光通信網２２中に配置してもよい。また、光通信網２２としては、光ファイバ通信網の他に、空間伝送を用いた光通信網であってもよい。
【００５６】
（光通信システムの第２の実施形態）
図１３は、本発明の光通信システムの第２の実施形態を示す。図において、本実施形態の光通信システムは、センタノード３０と複数のリモートノード３１−１〜３１−ｎが、光ファイバ伝送路３２および１：ｎ波長ルータ３３を介してスター状に接続された構成である。１：ｎ波長ルータ３３は、センタノード３０から送信された波長多重信号光を各波長の信号光に分波し、それぞれ対応するリモートノードに送信し、各リモートノードから送信された各波長の信号光を合波してセンタノード３０に送信する。ここで、各リモートノードは、図１１に示す本発明の光信号送受信装置１０と、１：ｎ波長ルータ３３との間でそれぞれ所定の波長の信号光を双方向接続する光双方向結合素子３４を備える。光双方向結合素子３４としては、光サーキュレータ、光カプラ、ＷＤＭカプラ等を用いることができる。
【００５７】
センタノード３０から送信された波長多重信号光は光ファイバ伝送路３２を介して１：ｎ波長ルータ３３に入力され、各波長の信号光に分波してそれぞれ対応するリモートノード３１−１〜３１−ｎに伝送される。各リモートノードには、それぞれ割り当てられた波長の信号光が入力され、その信号光が光双方向結合素子３４を介して光信号送受信装置１０に入力される。光信号送受信装置１０では、入力信号光を受信処理するとともに、入力信号光に対して所定の波長差をもつ信号光を生成して出力する。新たに生成された信号光は、光双方向結合素子３４を介して１：ｎ波長ルータ３３に送信され、他のリモートノードからの信号光と波長多重されてセンタノード３０へ送信される。これにより、センタノード３０と各リモートノード３１−１〜３１−ｎとの間で、異なる波長を用いた双方向伝送が可能になる。
【００５８】
本実施形態では、センタノード３０から各リモートノード３１−１〜３１−ｎへ伝送される下り信号光の波長と、各リモートノード３１−１〜３１−ｎからセンタノード３０へ伝送される上り信号光の波長が異なっているため、光ファイバ伝送路３２の接続点における反射等により発生するクロストーク光は、同一方向の信号光に対して異なる波長となる。したがって、同一波長のクロストーク光による信号品質の劣化を回避することができる。
【００５９】
なお、１：ｎ波長ルータ３３としてルーティング特性に周期性のあるアレイ導波路回折格子（ＡＷＧ）などを用いた場合に、各リモートノードの光信号送受信装置１０に入力する信号光の波長と、光信号送受信装置１０から送信される信号光の波長との間に、１：ｎ波長ルータ３３のフリースペクトルレンジ（ＦＳＲ）の整数倍の関係があれば、図１３に示すようにセンタノード３０と１：ｎ波長ルータ３３との間を１本の光ファイバ伝送路３２で接続することができる。
【００６０】
（光通信システムの第３の実施形態）
図１４は、本発明の光通信システムの第３の実施形態を示す。図において、本実施形態の光通信システムは、センタノード３０と複数のリモートノード３１−１〜３１−ｎが、光ファイバ伝送路３２および光スターカプラ３５を介してスター状に接続された構成である。ここで、各リモートノードは、図１１に示す本発明の光信号送受信装置１０と、それぞれ割り当てられた波長の信号光を通過する光フィルタ３６および光双方向結合素子３４を備える。
【００６１】
センタノード３０から送信された波長多重信号光は光ファイバ伝送路３２を介して光スターカプラ３５に入力され、リモートノード３１−１〜３１−ｎに伝送される。各リモートノードでは、波長多重信号光が光双方向結合素子３４を介して光フィルタ３６に入力され、それぞれ割り当てられた波長の信号光を分波して光信号送受信装置１０に入力される。光信号送受信装置１０では、入力信号光を受信処理するとともに、入力信号光に対して所定の波長差をもつ信号光を生成して出力する。新たに生成された信号光は、光双方向結合素子３４を介して光スターカプラ３５に送信され、他のリモートノードからの信号光と波長多重されてセンタノード３０へ送信される。これにより、センタノード３０と各リモートノード３１−１〜３１−ｎとの間で、異なる波長を用いた双方向伝送が可能になる。
【００６２】
なお、各リモートノードの光フィルタ３６として波長可変フィルタを用いることにより、各リモートノードの送受信波長を可変させることができ、波長可変のスター型ＷＤＭシステムを構成することができる。
【００６３】
（光通信システムの第４の実施形態）
図１５は、本発明の光通信システムの第４の実施形態を示す。図において、本実施形態の光通信システムは、センタノード３０と複数のリモートノード３１−１〜３１−３を光ファイバ伝送路３２を介してリング状に接続した構成である。各リモートノード３１−１〜３１−３は、図１１に示す本発明の光信号送受信装置１０と、それぞれ割り当てられ波長の信号光を分岐し、分岐する波長と異なる波長の信号光を挿入する波長分岐挿入素子３７を備える。
【００６４】
センタノード３０から送信された波長多重信号光は、光ファイバ伝送路３２を介してリモートノード３１−２の波長分岐挿入素子３７に入力され、リモートノード３１−２に割り当てられた波長の信号光が分岐して光信号送受信装置１０に入力される。光信号送受信装置１０では、入力信号光を受信処理するとともに、入力信号光に対して所定の波長差をもつ信号光を生成して出力する。新たに生成された信号光は、波長分岐挿入素子３７を介して波長多重信号光に多重され、光ファイバ伝送路３２を介してセンタノード３０へ送信される。これにより、センタノード３０と各リモートノード３１−１〜３１−ｎとの間で、異なる波長を用いた双方向伝送が可能になる。また、同一波長クロストーク抑圧のために波長分岐挿入素子３７に要求される遮断特性に対する条件を緩和することができる。
【００６５】
なお、各リモートノードの波長分岐挿入素子３７として、分岐挿入波長が可変である素子を用いることにより、各リモートノードの送受信波長を可変させることができ、波長可変のリング型ＷＤＭシステムを構成することができる。
【００６６】
（光通信システムの第５の実施形態）
以上示した光通信システムにおいて、各リモートノードの光信号送受信装置１０の光キャリア発生装置として、図４に示す非線形光学媒質１１を用いる構成では、各リモートノードに励起光レーザ１２を配置することになる。この場合は、各リモートノードの励起光波長は共通でも、それぞれに割り当てられた下り信号光の波長に応じて、上り信号光となる光キャリアの波長は個別に設定されることになる。すなわち、各リモートノードに個別の波長の上り信号光用の光源を配置する場合と異なり、共通波長の励起光光源で対応することができる利点がある。
【００６７】
また、以上示した光通信システムにおいて、各リモートノードの光信号送受信装置１０の光キャリア発生装置として、図６に示す外部入力の励起光を用いる構成では、センタノードまたは他のリモートノードから励起光を供給することになる。図１２または図１５に示す光通信システムでは、各ノードにそれぞれ割り当てられた波長の信号光を分波するとともに、所定の波長の励起光を分波し、増幅して光信号送受信装置１０の非線形光学媒質に入力する。図１３に示す光通信システムでは、１：ｎ波長ルータ３３に所定の波長の励起光をｎ分配する機能を付加し、各リモートノードにそれぞれ割り当てられた波長の信号光とともに励起光を分配し、さらに各リモートノードで所定の波長の励起光を分波し、増幅して光信号送受信装置１０の非線形光学媒質に入力する。図１４に示す光通信システムでは、各リモートノードの光フィルタ３６でそれぞれ割り当てられた波長の信号光を分波する前に光分波器を用いて励起光を分波し、その励起光を増幅して光信号送受信装置１０の非線形光学媒質に入力する。これらの構成では、各ノードに共通波長の励起光を供給しながら、それぞれ個別の波長の上り信号光用の光キャリアを生成することができる。
【００６８】
また、各ノードにおいて、図１０に示す光変調装置を用いて複数の波長の信号光を受信する光信号送受信装置を構成した場合には、異なる波長の信号光を新たに生成し波長多重して送信することができる。
【００６９】
【発明の効果】
以上説明したように、本発明の光キャリア発生装置は、外部から入力する強度変調された信号光と異なる波長の光キャリアを発生させることができる。本発明の光変調装置は、外部から入力する強度変調された信号光と異なる波長および信号成分を有する新たな信号光を発生させることができる。この光変調装置を用いた光信号送受信装置は、入力する信号光を受信するとともに、その信号光と異なる波長および信号成分を有する新たな信号光を発生させ、送信することができる。
【００７０】
さらに、波長多重光通信システムのノードにおいて、この光信号送受信装置を用いることにより、波長資源を有効に活用しつつ上り信号と下り信号の伝送容量に対する制限を緩和し、かつ同一波長クロストークの影響を低減することができる。
【図面の簡単な説明】
【図１】本発明の光キャリア発生装置の第１の実施形態を示す図。
【図２】光強度飽和素子１の光入出力特性を示す図。
【図３】本発明の光キャリア発生装置の第２の実施形態を示す図。
【図４】本発明の光キャリア発生装置の第３の実施形態を示す図。
【図５】非線形光学媒質１１の光入出力特性を示す図。
【図６】本発明の光キャリア発生装置の第４の実施形態を示す図。
【図７】本発明の光キャリア発生装置の第５の実施形態を示す図。
【図８】本発明の光キャリア発生装置の第６の実施形態を示す図。
【図９】本発明の光変調装置の第１の実施形態を示す図。
【図１０】本発明の光変調装置の第２の実施形態を示す図。
【図１１】本発明の光信号送受信装置の実施形態を示す図。
【図１２】本発明の光通信システムの第１の実施形態を示す図。
【図１３】本発明の光通信システムの第２の実施形態を示す図。
【図１４】本発明の光通信システムの第３の実施形態を示す図。
【図１５】本発明の光通信システムの第４の実施形態を示す図。
【図１６】従来の光通信システムの構成例を示す図。
【図１７】従来の光通信システムの他の構成例を示す図。
【符号の説明】
１光強度飽和素子
２波長変換素子
３光増幅器
４光強度変調器
５光分岐素子
６光受信器
１０光信号送受信装置
１１非線形光学媒質
１２励起光レーザ
１３光合波器
１４光バンドパスフィルタ
１５光分波器
１６光増幅器
１７光分波器
１８光分岐器
１９光合波器
２１ノード
２２、３２光ファイバ伝送路
２３、３７波長分岐挿入素子
３０センタノード
３１リモートノード
３３１：ｎ波長ルータ
３４光双方向結合素子
３５光スターカプラ（ＳＣ）
３６光フィルタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical carrier generator that generates continuous light (optical carrier) of a predetermined wavelength from intensity-modulated signal light input from the outside. The present invention also relates to an optical modulation device that modulates an optical carrier output from the optical carrier generation device and outputs a signal light having a different wavelength from the input signal light. An optical signal transmitting / receiving device that receives a signal light input to the optical carrier generation device, modulates an optical carrier output from the optical carrier generation device, and outputs a signal light having a different wavelength from the input signal light; The present invention relates to an optical communication system using a transmission / reception device.
[0002]
[Prior art]
FIG. 16 shows a configuration example of a conventional optical communication system in which light sources are centrally arranged at a center node (Non-Patent Document 1, Japanese Patent Application No. 2002-147250).
[0003]
In the figure, the optical communication system has a configuration in which a center node 50 and a plurality of remote nodes 51-1 to 51-n are connected in a star shape via an optical fiber transmission line 52 and a 1: n wavelength router 53. Each of the remote nodes 51-1 to 51-n inputs the signal light input from the optical fiber transmission line 52 via the optical bidirectional coupling element 55 to the optical signal transmitting / receiving device 60, and outputs the signal light from the optical signal transmitting / receiving device 60. The signal light is connected to the optical fiber transmission line 52. The optical signal transmitting / receiving device 60 includes an optical branching element 61 that branches the input signal light into two, an optical receiver 62 that receives one of the branched signal lights, a light intensity saturation element 63 that receives the other signal light, and a light intensity. It comprises a modulator 64.
[0004]
The center node 50 wavelength-multiplexes downstream signal lights of a plurality of wavelength channels whose extinction ratios are set to be slightly lower, and sends them to the 1: n wavelength router 53 via the optical fiber transmission line 52. The 1: n wavelength router 53 demultiplexes the wavelength multiplexed signal light transmitted from the center node 50 into signal lights of each wavelength, and transmits them to the corresponding remote nodes 51-1 to 51-n. Downlink signal light of the assigned wavelength is input to each remote node, and is input to the optical signal transmitting / receiving device 60 via the optical bidirectional coupling element 55. In the optical signal transmitting / receiving device 60, a part of the downstream signal light is branched by the optical branching element 61 to perform reception processing, and the intensity modulation component of the downstream signal light is suppressed by the light intensity saturating element 63. An optical carrier having the same wavelength as the signal light is input to the optical intensity modulator 64, intensity-modulated by a transmission signal, and output. The newly generated signal light is transmitted to the 1: n wavelength router 53 via the optical two-way coupling element 55, multiplexed with the signal light of each wavelength transmitted from another remote node, and transmitted to the center node 50. Sent.
[0005]
In this way, by arranging the light sources intensively in the center node 50, the center node 50 and each of the remote nodes 5 are respectively used by using one wavelength without arranging the light sources in the remote nodes 51-1 to 51-n. Two-way communication with 51-1 to 51-n becomes possible. Therefore, it is possible to construct a wavelength-division multiplexed optical communication system that is easier to maintain than a wavelength-division multiplexed optical communication system in which a light source having an individual wavelength is arranged in each remote node.
[0006]
FIG. 17 shows another configuration example of a conventional optical communication system (Japanese Patent Application No. 2002-147250). In this configuration example, a remote node including an optical signal transmitting / receiving device 60 using a light intensity saturation element 63 is connected in a ring shape.
[0007]
In the figure, the optical communication system has a configuration in which a center node 50 and a plurality of remote nodes 51-1 to 51-3 are connected in a ring shape via an optical fiber transmission line 52. The remote node 51-2 transmits the wavelength division multiplexed signal light transmitted from the remote node 51-1 to the remote nodes 51-2 and 51-3 to the remote node 51-1. 2 is provided with a wavelength dropping / adding element 56 for dropping / adding the signal light of the wavelength assigned to 2. The same applies to other remote nodes.
[0008]
The center node 50 wavelength-multiplexes downstream signal lights of a plurality of wavelength channels whose extinction ratios are set a little lower, and sends them to each remote node via the optical fiber transmission line 52. In each remote node, the downstream signal light of the assigned wavelength is demultiplexed from the wavelength multiplexed signal light transmitted from the center node 50 and input to the optical signal transmitting / receiving device 60. In the optical signal transmitting / receiving device 60, a part of the downstream signal light is branched by the optical branching element 61 to perform reception processing, and the intensity modulation component of the downstream signal light is suppressed by the light intensity saturating element 63. An optical carrier having the same wavelength as the signal light is input to the optical intensity modulator 64, intensity-modulated by a transmission signal, and output. The newly generated signal light is multiplexed with another signal light via the wavelength add / drop element 56, re-input to the optical fiber transmission line 52, and transmitted to the center node 50.
[0009]
Thereby, bidirectional communication between the center node 50 and each of the remote nodes 51-1 to 51-3 can be performed using one wavelength, without arranging a light source in each of the remote nodes 51-1 to 51-3. Will be possible.
[0010]
[Non-patent document 1]
H. Takesue and T.S. Sugie, "Data rewrite of wavelength channel using saturated SOA modulator for WDM metro / access networks with centralized light sources", in Proceedings of 28th European conference on optical communication, ECOC 2002, Copenhagen, Paper8.5.6, 9 May 2002 8 Day
[0011]
[Problems to be solved by the invention]
In the optical communication system shown in FIG. 16, in order to increase the utilization efficiency of the optical fiber transmission line 52, an optical fiber transmission line 52 that bidirectionally connects the center node 50 and the 1: n wavelength router 53, and further a 1: n wavelength router It is desirable that each optical fiber transmission line 52 that bidirectionally connects the remote node 53 to each of the remote nodes 51-1 to 51-n is composed of one optical fiber. However, in such a single-fiber bidirectional transmission, in a configuration in which light of the same wavelength propagates in both directions, for example, when a downstream signal light is reflected at a connection point of an optical fiber cable or the like, the reflected return light returns to the upstream signal light. It becomes crosstalk light. Since the crosstalk light has the same wavelength as the upstream signal light, there is a problem that a greater power penalty is caused by crosstalk light of a different wavelength.
[0012]
On the other hand, in the optical communication system of FIG. 17, since the light is transmitted in one direction in the optical fiber transmission line 52 connected in a ring shape, the crosstalk problem in bidirectional transmission as in the optical communication system of FIG. Does not occur. However, if the cut-off characteristics of the wavelength add / drop multiplexer 56 are insufficient, the optical carrier component passing through the wavelength add / drop multiplexer 56 becomes crosstalk light of the same wavelength with respect to the upstream signal light output from the optical signal transmitting / receiving device 60. Become. Therefore, there is a problem that the requirements for the cutoff characteristics of the wavelength add / drop multiplexer 56 become strict.
[0013]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical carrier generation device that generates an optical carrier for avoiding the occurrence of crosstalk of the same wavelength in a node that generates an optical carrier for transmission from signal light input from the outside. . Further, the present invention provides an optical modulation device that modulates and outputs an optical carrier output from the optical carrier generation device, an optical signal transmission / reception device using the optical modulation device, and an optical communication system using the optical signal transmission / reception device. The purpose is to:
[0014]
[Means for Solving the Problems]
(Optical carrier generator: Claims 1 to 4)
The optical carrier generation device according to claim 1 is a light intensity saturation means having an input / output characteristic in which an output light intensity is saturated with respect to an input light intensity equal to or more than a minimum saturation input intensity and equal to or less than a maximum saturation input intensity; Wavelength conversion means for converting, the minimum value of the light intensity is not less than the minimum saturation input intensity, the signal light intensity modulated so that the maximum value of the light intensity is less than the maximum saturation input intensity to the light intensity saturation means In this configuration, continuous light having a saturated light intensity is generated, the continuous light is input to the wavelength conversion means, and continuous light having a new wavelength having a predetermined wavelength difference from the signal light is output.
[0015]
The optical carrier generation device according to claim 2 is a light intensity saturation means having an input / output characteristic in which an output light intensity is saturated with respect to an input light intensity equal to or more than a minimum saturation input intensity and equal to or less than a maximum saturation input intensity; Wavelength conversion means for converting, the minimum value of the light intensity that passes through the wavelength conversion means and is input to the light intensity saturation means is equal to or greater than the minimum saturation input intensity, and passes through the wavelength conversion means and is input to the light intensity saturation means. The signal light intensity-modulated so that the maximum value of the light intensity to be emitted is equal to or less than the maximum saturation input intensity is input to the wavelength conversion means, and the wavelength-converted light is input to the light intensity saturation means, and the continuous light whose light intensity is saturated is output. And outputs continuous light of a new wavelength having a predetermined wavelength difference with respect to the signal light.
[0016]
Here, light intensity adjusting means for adjusting the minimum value of the light intensity of the signal light input to the light intensity saturation means to be equal to or greater than the minimum saturation input intensity and to adjust the maximum value to be equal to or less than the maximum saturation input intensity is provided. (Claim 3).
[0017]
Further, the light intensity saturation means and the wavelength conversion means input the intensity-modulated signal light and the excitation light having a predetermined wavelength into the nonlinear optical medium and have a predetermined wavelength difference with respect to the signal light generated by the nonlinear optical effect. It may be configured to output continuous light (claim 4).
[0018]
(Light modulator: Claim 5)
An optical modulation device according to claim 5, wherein the optical carrier generation device according to any one of claims 1 to 4, and an optical intensity modulation unit that intensity-modulates and outputs continuous light output from the optical carrier generation device by a transmission signal. And outputting a signal light having a predetermined wavelength difference with respect to the signal light input to the optical carrier generation device.
[0019]
(Optical signal transmitting / receiving device: Claim 6)
According to a sixth aspect of the present invention, there is provided an optical signal transmitting and receiving apparatus, wherein the optical modulator according to the fifth aspect, an optical branching unit for branching a part of the signal light input to the light intensity saturation unit, and a signal light branched by the optical branching unit. And a light receiving means for receiving the signal light, receiving the signal light and outputting the signal light having a predetermined wavelength difference from the signal light from the optical modulation device.
[0020]
(Optical communication system: Claims 7 to 14)
According to a seventh aspect of the present invention, a plurality of nodes are connected via an optical fiber transmission line, and each node receives a signal light of a predetermined wavelength transmitted from another node and transmits a predetermined wavelength to another node. In the optical communication system for transmitting the signal light of the above, each node splits the signal light of the wavelength allocated to the node from the optical signal transmitting and receiving device according to claim 6 and the optical signal transmitting and receiving device to the optical signal transmitting and receiving device. A wavelength dropping / inserting unit for inserting a signal light having a predetermined wavelength difference with respect to the signal light inputted and outputted from the optical signal transmitting / receiving apparatus into the optical fiber transmission line.
[0021]
According to the invention of claim 8, the center node and the plurality of remote nodes are connected in a star through a wavelength router and an optical fiber transmission line, and each remote node transmits a downstream signal light of a predetermined wavelength transmitted from the center node. 7. In an optical communication system for receiving an optical signal and transmitting an upstream signal light of a predetermined wavelength to a center node, each remote node comprises: an optical signal transmitting / receiving device according to claim 6; and a downstream signal light input from an optical fiber transmission line. To an optical signal transmitting / receiving apparatus, and an optical bidirectional coupling unit for connecting an upstream signal light having a predetermined wavelength difference to a downstream signal light output from the optical signal transmitting / receiving apparatus to an optical fiber transmission line.
[0022]
According to a ninth aspect of the present invention, a center node and a plurality of remote nodes are connected in a star through an optical star coupler and an optical fiber transmission line, and each remote node transmits a downstream signal of a predetermined wavelength transmitted from the center node. In an optical communication system that receives light and transmits an upstream signal light of a predetermined wavelength to a center node, each remote node transmits an optical signal transmitting / receiving device according to claim 6 and an optical fiber transmission line to the remote node. The downstream signal light of the assigned wavelength is demultiplexed and input to the optical signal transmitting / receiving device, and the upstream signal light having a predetermined wavelength difference from the downstream signal light output from the optical signal transmitting / receiving device is connected to the optical fiber transmission line. Optical filter and optical bidirectional coupling means.
[0023]
Here, the optical filter of each remote node may be a wavelength variable filter in which the wavelength to be demultiplexed is variable (claim 10).
[0024]
According to the eleventh aspect of the present invention, the center node and the plurality of remote nodes are connected in a ring via an optical fiber transmission line, and each remote node receives the downstream signal light of a predetermined wavelength transmitted from the center node. In an optical communication system for transmitting an upstream signal light of a predetermined wavelength to a center node, each remote node includes an optical signal transmitting / receiving device according to claim 6 and a downstream of a wavelength allocated to the remote node from an optical fiber transmission line. Wavelength-branching / inserting means for branching the signal light and inputting the signal light to the optical signal transmitting / receiving device, and inserting an upstream signal light having a predetermined wavelength difference with respect to the downstream signal light output from the optical signal transmitting / receiving device into the optical fiber transmission line; Is provided.
[0025]
Here, the wavelength dropping / adding means of each remote node may be configured such that the wavelength to be dropped / added is variable (claim 12).
[0026]
According to a thirteenth aspect of the present invention, in the optical communication system according to any one of the seventh to twelfth aspects, the optical modulator according to the fifth aspect is used in the optical signal transmitting / receiving apparatus according to the sixth aspect. A node or a remote node in an optical communication system includes an excitation light source that outputs excitation light having a predetermined wavelength, and the excitation light is input to a nonlinear optical medium of the optical carrier generation device. is there.
[0027]
According to a fourteenth aspect of the present invention, in the optical communication system according to any one of the seventh to twelfth aspects, the optical modulator according to the fifth aspect is used in the optical signal transmitting and receiving apparatus according to the sixth aspect. A specific node in the optical communication system transmits pump light having a wavelength different from that of the signal light together with the signal light through an optical fiber transmission line using the optical carrier generator of the optical communication system. This is a configuration for inputting to the nonlinear optical medium of the generator.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment of Optical Carrier Generator)
FIG. 1 shows a first embodiment of the optical carrier generation device of the present invention. In the figure, the light modulation device of the present embodiment includes a light intensity saturation element 1 and a wavelength conversion element 2. The input signal light is intensity-modulated signal light, and the maximum value of the light intensity is P _M , The minimum value is P _S And
[0029]
As shown in FIG. 2, the light input / output characteristic of the light intensity saturating element 1 is such that the output light intensity is almost proportional to the input light intensity in a region where the input light intensity is small, and the output light intensity becomes equal to or more than a predetermined value. Is saturated, and the change in the output light intensity with respect to the change in the input light intensity is suppressed. This predetermined value is referred to as “minimum saturation input intensity”. Depending on the properties of the light intensity saturation element 1, the input light intensity is further increased beyond the minimum saturation input intensity, and when the input light intensity exceeds a predetermined value, the change of the output light intensity with respect to the change of the input light intensity becomes large again. May be. This predetermined value is referred to as “maximum saturation input intensity”. The region of the input light intensity where the output light intensity is saturated and is equal to or higher than the minimum saturation input intensity and equal to or lower than the maximum saturation input intensity is defined as a “saturation input region”.
[0030]
Here, the minimum value P of the light intensity _S And the maximum value P _M When the signal light (wavelength λ) intensity-modulated so that is in the saturation input region is input to the light intensity saturation element 1, the signal light (the difference between the maximum value and the minimum value of the light intensity) of the signal light ( Continuous light) is output. The continuous light (wavelength λ) is input to the wavelength conversion element 2 and converted into another wavelength, thereby generating a new optical carrier (wavelength λ ′) having a predetermined wavelength difference from the wavelength of the input signal light. be able to.
[0031]
The order of connection between the light intensity saturation element 1 and the wavelength conversion element 2 may be changed. In this case, the maximum value P of the light intensity of the input signal light _M And the minimum value P _S Is input to the light intensity saturation element 1 after passing through the wavelength conversion element 2, and is intensity-modulated so as to be in the saturation input region.
[0032]
(Second Embodiment of Optical Carrier Generator)
FIG. 3 shows a second embodiment of the optical carrier generator of the present invention. The present embodiment has a configuration in which an optical amplifier 3 is arranged in a stage preceding the light intensity saturation element 1 of the first embodiment.
[0033]
In the first embodiment, the minimum value P of the light intensity of the input signal light is _S And the maximum value P _M Are in the saturation input region of the light intensity saturation element 1, but when these are less than the minimum saturation input intensity, the optical amplifier 3 is used to reduce the minimum value P of the light intensity. _S And the maximum value P _M Is input to the light intensity saturating element 1 so as to be in the saturation input region. This makes it possible to realize an optical carrier generation device that can operate even when the input light intensity is low.
[0034]
On the other hand, the maximum value P of the light intensity of the input signal light is _M Exceeds the maximum saturation input intensity, an optical attenuator is used instead of the optical amplifier 3, and the minimum value P of the light intensity of the input signal light is used. _S And the maximum value P _M Is adjusted to be in the saturation input region of the light intensity saturation element 1, it is possible to realize an optical carrier generator that can operate even when the input light intensity is high.
[0035]
In the embodiment described above, an acousto-optic frequency shifter or an optical SSB (single side band) modulator can be used as the wavelength conversion element 2. The acousto-optic frequency shifter outputs a signal light (continuous light) having a predetermined wavelength difference with respect to the input signal light (continuous light) due to the acousto-optic effect. In the optical SSB modulator, signal light (continuous light) having a predetermined wavelength difference with respect to input signal light (continuous light) due to the electro-optic effect is output (M. Izutsu, S. Shikama and T. Sueta, "Integrated optical SSB modulator / frequency shifter", IEEE J. Quantum Electron., Vol. QE-17, No. 11, pp. 2225-2227, 1981).
[0036]
The wavelength conversion element 2 has a predetermined wavelength difference from the signal light (continuous light) due to the nonlinear optical effect by inputting the signal light (continuous light) and the excitation light having a predetermined wavelength into the nonlinear optical medium. It may be configured to generate signal light (continuous light). For example, in a PPLN that is a second-order nonlinear optical medium, signal light having a sum (difference) frequency of signal light and pump light is generated. In a highly nonlinear optical fiber or a semiconductor optical amplifier, four-wave mixing light of signal light and pump light is generated. The wavelength conversion element 2 selectively outputs these wavelength-converted lights from the output light of the nonlinear optical medium using an optical filter.
[0037]
(Third Embodiment of Optical Carrier Generator)
FIG. 4 shows a third embodiment of the optical carrier generation device of the present invention. In the present embodiment, the optical intensity saturation element 1 and the wavelength conversion element 2 in the first and second embodiments are combined, and the nonlinear optical effect between the input signal light and the pump light in the nonlinear optical medium 11 is used. (Here, degenerate four-wave mixing) is used. An input signal light (optical frequency f) is applied to the nonlinear optical medium 11. _S ) And the excitation light (optical frequency f) output from the excitation light laser 12. _P ) Are multiplexed by the optical multiplexer 13 and input, when a new four-wave mixing light (optical frequency 2f) is input. _P −f _S ) Occurs. The signal light, the excitation light, and the four-wave mixing light output from the nonlinear optical medium 11 are input to the optical bandpass filter 14, and only the four-wave mixing light is output as an optical carrier wavelength-converted with respect to the input signal light.
[0038]
Here, by appropriately adjusting parameters such as dispersion and nonlinear gain coefficient of the nonlinear optical medium 11 and the powers of the pump light and the signal light, the light intensity of the input signal light and the four-wave mixing light (wavelength Light input / output characteristics as shown in FIG. 5 can be realized between the light intensity of the converted light. That is, the minimum value P of the light intensity _S And the maximum value P _M Is input to the nonlinear optical medium 11, the four-wave mixing light (wavelength-converted light) from which the modulation pattern has been removed due to its saturation characteristics is output. As the nonlinear optical medium 11 having such a function, a highly nonlinear optical fiber, a semiconductor optical amplifier, or the like can be used.
[0039]
(Fourth Embodiment of Optical Carrier Generator)
FIG. 6 shows a fourth embodiment of the optical carrier generator of the present invention. The present embodiment has a configuration in which signal light and wavelength-multiplexed signal light and pump light are input from outside without using the pump light laser 12 in the third embodiment. The signal light and the pump light are split by the optical splitter 15, and the split pump light is amplified by the optical amplifier 16. The amplified pump light is multiplexed with the signal light again by the optical multiplexer 13 and input to the nonlinear optical medium 11. Although the optical splitter 15 and the optical amplifier 16 are shown here as being arranged outside the optical carrier generator, they may be arranged inside the optical carrier generator.
[0040]
(Fifth Embodiment of Optical Carrier Generator)
FIG. 7 shows a fifth embodiment of the optical carrier generator of the present invention. The present embodiment is configured to collectively generate optical carriers of a plurality of optical frequencies using a plurality of nonlinear optical media.
[0041]
Light frequency f _S1 , F _S2 , ..., f _Sm Is split by the optical demultiplexer 17 into signal light of each optical frequency. Optical frequency f output from pump light laser 12 _P Is split by the optical splitter 18 into m, and the optical frequency f is output from the optical multiplexers 13-1 to 13-m. _S1 , F _S2 , ..., f _Sm , And are input to the nonlinear optical media 11-1 to 11-m. Each of the nonlinear optical media 11-1 to 11-m has an optical frequency of 2f. _P −f _S1 , 2f _P −f _S2 , ..., 2f _P −f _Sm To generate four-wave mixing light. The signal light, the pump light, and the four-wave mixing light output from each of the nonlinear optical media 11-1 to 11-m are input to the corresponding optical bandpass filters 14-1 to 14-m, and only the four-wave mixing light is output. Is output as an optical carrier wavelength-converted with respect to the input signal light.
[0042]
In the present embodiment, the optical carrier having a plurality of optical frequencies corresponding to each optical frequency of the wavelength-division multiplexed signal light can be generated collectively by only providing one pumping light laser 12. As in the fourth embodiment shown in FIG. 6, the pump light wavelength-multiplexed to the wavelength-division multiplexed signal light may be split, amplified, and input.
[0043]
(Sixth Embodiment of Optical Carrier Generator)
FIG. 8 shows a sixth embodiment of the optical carrier generator of the present invention. The present embodiment has a configuration in which optical carriers of a plurality of optical frequencies are collectively generated using one nonlinear optical medium.
[0044]
Light frequency f _S1 , F _S2 , ..., f _Sm And the optical frequency f output from the pumping light laser 12 _P Are coupled by the optical multiplexer 13 and input to the nonlinear optical medium 11. Each of the nonlinear optical media 11 has an optical frequency of 2f _P −f _S1 , 2f _P −f _S2 , ..., 2f _P −f _Sm , And only the four-wave mixed light of each optical frequency is output as an optical carrier whose wavelength has been converted with respect to the input signal light via the optical demultiplexer 17. In the present embodiment, it is possible to collectively generate optical carriers of a plurality of optical frequencies corresponding to the respective optical frequencies of the wavelength-division multiplexed signal light only by providing one pumping light laser 12 and one nonlinear optical medium 11. .
[0045]
In the configuration of FIGS. 7 and 8, as in the fourth embodiment of FIG. 6, the pump light multiplexed with the wavelength multiplexed signal light may be split, amplified, and input.
[0046]
(First Embodiment of Light Modulator)
FIG. 9 shows a first embodiment of the light modulation device of the present invention. In the figure, the light modulation device of the present embodiment has a configuration in which a light intensity modulator 4 is connected to the subsequent stage of the wavelength conversion element 2 of the optical carrier generation device of the present invention. Here, an example in which the optical carrier generation device shown in FIG. 1 is applied to the first embodiment is shown, but the configuration of the second embodiment in FIG. 3, the third embodiment in FIG. 4, and the fourth embodiment in FIG. The same can be applied to the configuration of the embodiment.
[0047]
The wavelength conversion element 2 of the optical carrier generator outputs an optical carrier having a wavelength λ ′ having a predetermined wavelength difference from the wavelength λ of the input signal light. This optical carrier is input to the optical intensity modulator 4 and intensity-modulated by a transmission signal, so that a signal light of a new wavelength λ ′ having a predetermined wavelength difference from the wavelength λ of the input signal light can be output. it can.
[0048]
(Second embodiment of light modulation device)
FIG. 10 shows a second embodiment of the light modulation device of the present invention. In the figure, the optical modulation device of the present embodiment is different from the optical carrier generation device of the fifth embodiment shown in FIG. 4-m, each optical frequency 2f _P −f _S1 , 2f _P −f _S2 , ..., 2f _P −f _Sm The signal light obtained by intensity-modulating the optical carrier is multiplexed by the optical multiplexer 19 and output.
[0049]
The optical intensity modulators 4-1 to 4-m are connected to the subsequent stage of the optical demultiplexer 17 of the optical carrier generator according to the sixth embodiment shown in FIG. 8, and the optical carriers of each optical frequency are intensity-modulated. The signal light may be multiplexed by the optical multiplexer 19 and output.
[0050]
(Embodiment of optical signal transmitting / receiving apparatus)
FIG. 11 shows an embodiment of the optical signal transmitting / receiving device of the present invention. In the figure, an optical signal transmitting and receiving apparatus 10 of the present embodiment includes an optical modulation apparatus in which an optical intensity modulator 4 is connected downstream of a wavelength conversion element 2 of the optical carrier generation apparatus of the present invention, and an optical intensity of the optical carrier generation apparatus. The saturating device 1 includes an optical splitter 5 for splitting the signal light input to the saturator 1 into two, and an optical receiver 6 for receiving the split signal light. Here, an example in which the optical carrier generation device shown in FIG. 1 is applied to the first embodiment is shown, but the configuration of the second embodiment of FIG. 3, the configuration of the third embodiment of FIG. The same can be applied to the configuration of the fourth embodiment.
[0051]
The signal light (wavelength λ) input to the optical signal transmission / reception device 10 is received by the optical receiver 6 via the optical branching element 5 and the optical carrier (the intensity modulation component of which is suppressed by the optical intensity saturation element 1). Wavelength λ). This optical carrier is input to the wavelength conversion element 2 and wavelength-converted to an optical carrier having a wavelength λ ′ having a predetermined wavelength difference with respect to the wavelength λ of the input signal light. Accordingly, it is possible to output a signal light of a new wavelength λ ′ having a predetermined wavelength difference with respect to the wavelength λ of the input signal light.
[0052]
When an optical signal transmitting / receiving device is configured using the optical modulation device shown in FIG. 10, an optical branching element that splits signal light of each optical frequency into two is provided in front of the optical multiplexers 13-1 to 13-m. And an optical receiver that receives the split signal light, so that transmission and reception of a plurality of signal lights can be supported. Further, when the optical carrier generator shown in FIG. 8 is used, the wavelength-division multiplexed signal light is split by an optical splitter, then split into signal lights of each wavelength by an optical splitter, and the corresponding optical receivers respectively. It is configured to receive for each wavelength channel.
[0053]
(First Embodiment of Optical Communication System)
FIG. 12 shows a first embodiment of the optical communication system of the present invention. In the figure, the optical communication system of the present embodiment has a configuration in which a plurality of nodes 21-1 to 21-3 are connected via an optical communication network 22. Each of the nodes 21-1 to 21-3 is different from the optical signal transmitting and receiving apparatus 10 of the present invention shown in FIG. An insertion element 23 is provided. Here, the wavelength branched at the node 21-2 is λ ₁ , The wavelength to insert is λ ₂ And
[0054]
The wavelength multiplexed signal light transmitted from the node 21-1 is input to the wavelength add / drop element 23 of the node 21-2 via the optical communication network 22, and the wavelength λ ₁ Is branched and input to the optical signal transmitting / receiving device 10. In the optical signal transmitting / receiving device 10, the wavelength λ ₁ Of the signal light and the signal light wavelength λ ₁ Wavelength λ having a predetermined wavelength difference with respect to ₂ And outputs the signal light. Newly generated wavelength λ ₂ Is multiplexed with the wavelength multiplexed signal light via the wavelength add / drop element 23 and transmitted to the node 21-3 via the optical communication network 22. This enables signal light transmission from the node 21-1 to the node 21-2 and signal light transmission from the node 21-2 to the node 21-3. In addition, it is possible to relax the condition for the cutoff characteristic required for the wavelength add / drop element 23 for suppressing the same wavelength crosstalk.
[0055]
In the present embodiment, the wavelength add / drop element 23 is arranged in the node, but may be arranged in the optical communication network 22. Further, the optical communication network 22 may be an optical communication network using spatial transmission in addition to the optical fiber communication network.
[0056]
(Second Embodiment of Optical Communication System)
FIG. 13 shows a second embodiment of the optical communication system of the present invention. In the figure, in the optical communication system of the present embodiment, a center node 30 and a plurality of remote nodes 31-1 to 31-n are connected in a star via an optical fiber transmission line 32 and a 1: n wavelength router 33. Configuration. The 1: n wavelength router 33 demultiplexes the wavelength multiplexed signal light transmitted from the center node 30 into signal light of each wavelength, transmits the signal light to each corresponding remote node, and transmits the signal of each wavelength transmitted from each remote node. The light is multiplexed and transmitted to the center node 30. Here, each remote node is an optical bidirectional coupling element 34 for bidirectionally connecting signal light of a predetermined wavelength between the optical signal transmitting / receiving apparatus 10 of the present invention shown in FIG. Is provided. As the optical bidirectional coupling element 34, an optical circulator, an optical coupler, a WDM coupler, or the like can be used.
[0057]
The wavelength multiplexed signal light transmitted from the center node 30 is input to the 1: n wavelength router 33 via the optical fiber transmission line 32, demultiplexed into signal light of each wavelength, and corresponding to the remote nodes 31-1 to 31 respectively. -N. The signal light of the assigned wavelength is input to each remote node, and the signal light is input to the optical signal transmitting / receiving device 10 via the optical bidirectional coupling element 34. The optical signal transmitting / receiving device 10 receives and processes the input signal light, and generates and outputs a signal light having a predetermined wavelength difference from the input signal light. The newly generated signal light is transmitted to the 1: n wavelength router 33 via the optical bidirectional coupling element 34, wavelength-multiplexed with the signal light from another remote node, and transmitted to the center node 30. This enables bidirectional transmission using different wavelengths between the center node 30 and each of the remote nodes 31-1 to 31-n.
[0058]
In the present embodiment, the wavelength of the downstream signal light transmitted from the center node 30 to each of the remote nodes 31-1 to 31-n and the upstream signal transmitted from each of the remote nodes 31-1 to 31-n to the center node 30 Since the wavelengths of the light are different, the crosstalk light generated by reflection at the connection point of the optical fiber transmission line 32 has a different wavelength with respect to the signal light in the same direction. Therefore, it is possible to avoid deterioration of signal quality due to crosstalk light having the same wavelength.
[0059]
When an array waveguide grating (AWG) having a periodic routing characteristic is used as the 1: n wavelength router 33, the wavelength of the signal light input to the optical signal transmitting / receiving device 10 of each remote node and the light If there is an integer multiple of the free spectrum range (FSR) of the 1: n wavelength router 33 between the wavelength of the signal light transmitted from the signal transmitting / receiving device 10 and the center nodes 30 and 1 as shown in FIG. : It can be connected to the n-wavelength router 33 by one optical fiber transmission line 32.
[0060]
(Third Embodiment of Optical Communication System)
FIG. 14 shows a third embodiment of the optical communication system of the present invention. In the figure, the optical communication system of the present embodiment has a configuration in which a center node 30 and a plurality of remote nodes 31-1 to 31-n are connected in a star shape via an optical fiber transmission line 32 and an optical star coupler 35. is there. Here, each remote node includes the optical signal transmitting and receiving apparatus 10 of the present invention shown in FIG. 11, an optical filter 36 and an optical bidirectional coupling element 34 that pass the signal light of the assigned wavelength.
[0061]
The wavelength multiplexed signal light transmitted from the center node 30 is input to the optical star coupler 35 via the optical fiber transmission line 32 and transmitted to the remote nodes 31-1 to 31-n. In each remote node, the wavelength multiplexed signal light is input to the optical filter 36 via the optical bidirectional coupling element 34, and the signal light having the assigned wavelength is demultiplexed and input to the optical signal transmitting / receiving device 10. The optical signal transmitting / receiving device 10 receives and processes the input signal light, and generates and outputs a signal light having a predetermined wavelength difference from the input signal light. The newly generated signal light is transmitted to the optical star coupler 35 via the optical two-way coupling element 34, wavelength-multiplexed with signal light from another remote node, and transmitted to the center node 30. This enables bidirectional transmission using different wavelengths between the center node 30 and each of the remote nodes 31-1 to 31-n.
[0062]
By using a wavelength tunable filter as the optical filter 36 of each remote node, the transmission / reception wavelength of each remote node can be varied, and a tunable star WDM system can be configured.
[0063]
(Fourth Embodiment of Optical Communication System)
FIG. 15 shows a fourth embodiment of the optical communication system of the present invention. In the figure, the optical communication system of the present embodiment has a configuration in which a center node 30 and a plurality of remote nodes 31-1 to 31-3 are connected in a ring shape via an optical fiber transmission line 32. Each of the remote nodes 31-1 to 31-3 has the optical signal transmitting and receiving device 10 of the present invention shown in FIG. 11 and a wavelength for splitting the signal light of the assigned wavelength and inserting the signal light of a wavelength different from the split wavelength. It has a drop-and-insert element 37.
[0064]
The wavelength multiplexed signal light transmitted from the center node 30 is input to the wavelength add / drop element 37 of the remote node 31-2 via the optical fiber transmission line 32, and the signal light of the wavelength allocated to the remote node 31-2 is The signal is branched and input to the optical signal transmitting / receiving device 10. The optical signal transmitting / receiving device 10 receives and processes the input signal light, and generates and outputs a signal light having a predetermined wavelength difference from the input signal light. The newly generated signal light is multiplexed with the wavelength multiplexed signal light via the wavelength add / drop element 37 and transmitted to the center node 30 via the optical fiber transmission line 32. This enables bidirectional transmission using different wavelengths between the center node 30 and each of the remote nodes 31-1 to 31-n. In addition, the condition for the cutoff characteristics required for the wavelength add / drop element 37 for suppressing the same wavelength crosstalk can be relaxed.
[0065]
In addition, by using an element having a variable add / drop wavelength as the wavelength add / drop element 37 of each remote node, the transmission / reception wavelength of each remote node can be changed, thereby configuring a wavelength-tunable ring-type WDM system. Can be.
[0066]
(Fifth Embodiment of Optical Communication System)
In the optical communication system described above, in the configuration using the nonlinear optical medium 11 shown in FIG. 4 as the optical carrier generator of the optical signal transmitting / receiving device 10 of each remote node, the pumping light laser 12 is arranged at each remote node. Become. In this case, even if the pumping light wavelength of each remote node is common, the wavelength of the optical carrier that becomes the upstream signal light is individually set according to the wavelength of the downstream signal light assigned to each remote node. That is, unlike the case where the light source for the upstream signal light of the individual wavelength is arranged in each remote node, there is an advantage that the pumping light source of the common wavelength can cope with it.
[0067]
Further, in the optical communication system described above, in the configuration using the pump light of the external input shown in FIG. 6 as the optical carrier generator of the optical signal transmitting and receiving device 10 of each remote node, the pump light is transmitted from the center node or another remote node. Will be supplied. In the optical communication system shown in FIG. 12 or FIG. 15, the signal light of the wavelength assigned to each node is demultiplexed, and the pump light of a predetermined wavelength is demultiplexed and amplified, and the nonlinearity of the optical signal transmitting and receiving device 10 is increased. Input to the optical medium. In the optical communication system shown in FIG. 13, a function of distributing pump light of a predetermined wavelength to n is added to the 1: n wavelength router 33, and the pump light is distributed together with the signal light of the wavelength assigned to each remote node. Further, each remote node demultiplexes the pump light of a predetermined wavelength, amplifies it, and inputs the same to the nonlinear optical medium of the optical signal transmitting / receiving device 10. In the optical communication system shown in FIG. 14, before demultiplexing the signal light having the wavelength assigned by the optical filter 36 of each remote node, the pump light is demultiplexed using an optical demultiplexer, and the pump light is amplified. Then, the signal is input to the nonlinear optical medium of the optical signal transmitting / receiving device 10. In these configurations, it is possible to generate an optical carrier for an upstream signal light having an individual wavelength while supplying pump light having a common wavelength to each node.
[0068]
In each node, when an optical signal transmitting and receiving device configured to receive signal light of a plurality of wavelengths is configured using the optical modulation device illustrated in FIG. 10, signal light of a different wavelength is newly generated and wavelength-multiplexed. Can be sent.
[0069]
【The invention's effect】
As described above, the optical carrier generation device of the present invention can generate an optical carrier having a different wavelength from the intensity-modulated signal light input from the outside. The light modulation device of the present invention can generate a new signal light having a wavelength and a signal component different from the intensity-modulated signal light input from the outside. An optical signal transmitting / receiving device using this optical modulation device can receive an input signal light, and generate and transmit a new signal light having a wavelength and a signal component different from the signal light.
[0070]
Furthermore, by using this optical signal transmitting / receiving device in a node of a wavelength division multiplexing optical communication system, the restrictions on the transmission capacity of upstream and downstream signals are relaxed while effectively utilizing wavelength resources, and the influence of the same wavelength crosstalk is reduced. Can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of an optical carrier generation device according to the present invention.
FIG. 2 is a view showing light input / output characteristics of the light intensity saturation element 1;
FIG. 3 is a diagram showing a second embodiment of the optical carrier generation device of the present invention.
FIG. 4 is a diagram showing a third embodiment of the optical carrier generation device of the present invention.
FIG. 5 is a view showing light input / output characteristics of a nonlinear optical medium 11;
FIG. 6 is a diagram showing a fourth embodiment of the optical carrier generation device of the present invention.
FIG. 7 is a diagram showing a fifth embodiment of the optical carrier generation device of the present invention.
FIG. 8 is a diagram showing a sixth embodiment of the optical carrier generation device of the present invention.
FIG. 9 is a diagram showing a first embodiment of the light modulation device of the present invention.
FIG. 10 is a diagram showing a second embodiment of the light modulation device of the present invention.
FIG. 11 is a diagram showing an embodiment of the optical signal transmitting / receiving device of the present invention.
FIG. 12 is a diagram showing a first embodiment of the optical communication system of the present invention.
FIG. 13 is a diagram showing a second embodiment of the optical communication system of the present invention.
FIG. 14 is a diagram showing a third embodiment of the optical communication system of the present invention.
FIG. 15 is a diagram showing a fourth embodiment of the optical communication system according to the present invention.
FIG. 16 is a diagram showing a configuration example of a conventional optical communication system.
FIG. 17 is a diagram showing another configuration example of a conventional optical communication system.
[Explanation of symbols]
1 Light intensity saturation element
2 Wavelength conversion element
3 Optical amplifier
4 Light intensity modulator
5 Optical branching element
6 Optical receiver
10 Optical signal transceiver
11 Nonlinear optical medium
12 Excitation light laser
13 Optical multiplexer
14. Optical bandpass filter
15 Optical splitter
16 Optical amplifier
17 Optical splitter
18 Optical branching device
19 Optical multiplexer
21 nodes
22, 32 Optical fiber transmission line
23, 37 wavelength add / drop elements
30 center node
31 Remote node
33 1: n-wavelength router
34 Optical bidirectional coupling device
35 Optical Star Coupler (SC)
36 Optical Filter

Claims

Light intensity saturation means having an input / output characteristic in which output light intensity is saturated with respect to input light intensity equal to or greater than the minimum saturation input intensity and equal to or less than the maximum saturation input intensity,
Wavelength conversion means for converting the wavelength of the input light,
The minimum value of the light intensity is equal to or higher than the minimum saturation input intensity, and the signal light intensity-modulated so that the maximum value of the light intensity is equal to or lower than the maximum saturation input intensity is input to the light intensity saturation unit, and the light intensity is increased. A light having a configuration in which a saturated continuous light is generated, the continuous light is input to the wavelength conversion means, and a continuous light of a new wavelength having a predetermined wavelength difference with respect to the signal light is output. Carrier generator.

Light intensity saturation means having an input / output characteristic in which output light intensity is saturated with respect to input light intensity equal to or greater than the minimum saturation input intensity and equal to or less than the maximum saturation input intensity,
Wavelength conversion means for converting the wavelength of the input light,
The minimum value of the light intensity input to the light intensity saturation means passing through the wavelength conversion means is equal to or greater than the minimum saturation input intensity, and the minimum value of the light intensity input to the light intensity saturation means through the wavelength conversion means A signal light intensity-modulated so that the maximum value is equal to or less than the maximum saturation input intensity is input to the wavelength conversion means, and the wavelength-converted light is input to the light intensity saturation means to output a continuous light having a saturated light intensity. An optical carrier generation device configured to generate and output continuous light of a new wavelength having a predetermined wavelength difference with respect to the signal light.

The optical carrier generator according to claim 1 or 2,
Light intensity adjusting means for adjusting the minimum value of the light intensity of the signal light input to the light intensity saturation means to be equal to or greater than the minimum saturation input intensity, and to adjust the maximum value to be equal to or less than the maximum saturation input intensity. An optical carrier generator characterized by the above-mentioned.

The optical carrier generator according to any one of claims 1 to 3,
The light intensity saturation means and the wavelength conversion means input the intensity-modulated signal light and the excitation light having a predetermined wavelength to a nonlinear optical medium, and have a predetermined wavelength difference with respect to the signal light generated by the nonlinear optical effect. An optical carrier generation device configured to output continuous light having

An optical carrier generator according to any one of claims 1 to 4,
Light intensity modulation means for intensity-modulating and outputting continuous light output from the optical carrier generation device by a transmission signal,
An optical modulation device having a configuration in which signal light having a predetermined wavelength difference with respect to signal light input to the optical carrier generation device is output.

An optical modulation device according to claim 5,
An optical branching unit that branches a part of the signal light input to the light intensity saturation unit,
Light receiving means for receiving and processing the signal light branched by the optical branching means,
An optical signal transmitting and receiving device, wherein the optical signal transmitting and receiving device receives the signal light and outputs a signal light having a predetermined wavelength difference from the signal light from the optical modulation device.

A plurality of nodes are connected via an optical fiber transmission line, and each node receives a signal light of a predetermined wavelength transmitted from another node and transmits a signal light of a predetermined wavelength to another node. In communication systems,
7. The optical signal transmitting / receiving apparatus according to claim 6, wherein each of the nodes branches the signal light having the wavelength allocated to the node from the optical fiber transmission line, inputs the branched signal light to the optical signal transmitting / receiving apparatus, and transmits and receives the optical signal. An optical communication system comprising: a wavelength dropping / inserting unit that inserts a signal light having a predetermined wavelength difference from the signal light output from the device into the optical fiber transmission line.

A center node and a plurality of remote nodes are connected in a star configuration via a wavelength router and an optical fiber transmission line. Each remote node receives a downstream signal light of a predetermined wavelength transmitted from the center node, and In an optical communication system that transmits upstream signal light of a predetermined wavelength to
The respective remote nodes, the optical signal transmitting and receiving apparatus according to claim 6, and the downstream signal light input from the optical fiber transmission line is input to the optical signal transmitting and receiving apparatus, and the downstream output from the optical signal transmitting and receiving apparatus is output. An optical communication system comprising: optical bidirectional coupling means for connecting upstream signal light having a predetermined wavelength difference to signal light to the optical fiber transmission line.

A center node and a plurality of remote nodes are connected in a star through an optical star coupler and an optical fiber transmission line. Each remote node receives a downstream signal light of a predetermined wavelength transmitted from the center node, and In an optical communication system that transmits upstream signal light of a predetermined wavelength to a node,
Each of the remote nodes, the optical signal transmitting and receiving apparatus according to claim 6, and the downstream signal light of the wavelength allocated to the remote node from the optical fiber transmission line is demultiplexed and input to the optical signal transmitting and receiving apparatus, An optical filter and an optical bidirectional coupling means for connecting an upstream signal light having a predetermined wavelength difference to the downstream signal light output from the optical signal transmitting / receiving device to the optical fiber transmission line. Optical communication system.

The optical communication system according to claim 9,
The optical communication system according to claim 1, wherein the optical filter of each of the remote nodes is a wavelength tunable filter whose wavelength to be demultiplexed is variable.

A center node and a plurality of remote nodes are connected in a ring via an optical fiber transmission line. Each remote node receives a downstream signal light of a predetermined wavelength transmitted from the center node, and transmits a predetermined wavelength to the center node. In an optical communication system for transmitting the upstream signal light,
7. The optical signal transmitting / receiving apparatus according to claim 6, wherein each of the remote nodes branches a downstream signal light having a wavelength allocated to the remote node from the optical fiber transmission line and inputs the branched signal light to the optical signal transmitting / receiving apparatus. An optical communication system comprising: a wavelength dropping / inserting unit that inserts an upstream signal light having a predetermined wavelength difference from the downstream signal light output from a signal transmitting / receiving apparatus into the optical fiber transmission line.

The optical communication system according to claim 11,
An optical communication system, wherein the wavelength dropping / adding means of each of the remote nodes has a configuration in which the wavelength to be dropped / added is variable.

The optical communication system according to any one of claims 7 to 12,
The optical modulation apparatus according to claim 5, which is used in the optical signal transmitting / receiving apparatus according to claim 6, uses the optical carrier generation apparatus according to claim 4,
A node or a remote node in the optical communication system includes an excitation light source that outputs an excitation light having a predetermined wavelength, and the excitation light is input to a nonlinear optical medium of the optical carrier generator. Optical communication system.

The optical communication system according to any one of claims 7 to 12,
The optical modulation apparatus according to claim 5, which is used in the optical signal transmitting / receiving apparatus according to claim 6, uses the optical carrier generation apparatus according to claim 4,
From a specific node in the optical communication system, a pump light having a wavelength different from that of the signal light is transmitted together with the signal light via the optical fiber transmission line, and the pump light is transmitted to the other nodes by the nonlinear optics of the optical carrier generator. An optical communication system having a configuration for inputting to a medium.