JP3808413B2 - Optical communication system - Google Patents

Description

で表される。なお、hはプランク定数である。ここで、(1)式右辺の第１項はそれぞれ増幅された信号光を表し、第２項はSOA変調器で発生する自然放出光を表している。光受信器９４で受信される自然放出光は位相がランダムであるため、信号光と自然放出光が干渉しあい、あるいは自然放出光同士が干渉しあい、ビート雑音として検出される。一般的にビート雑音の影響を抑えるためには、光受信器９４に入射する前に光フィルタ９２を用いて自然放出光を減らせばよい。光受信器９４の帯域をB_e [Hz]、光フィルタ９２の透過スペクトル半値全幅をΔf [Hz]、伝送路９３の区間損失をＬとすると、光受信器９４に入力される平均光子数<n_orin>は、符号がマークおよびスペースの場合、それぞれ
【数２】

と表される。
【００８１】
このような信号光が量子効率ηの光受信器９４に入力された場合、マークおよびスペースにおける光電流の直流成分I_mおよびI_sは、
【数３】

と表される。なお、ｅは電気素量を表す。また、受信された光電流は、各種の雑音によりその強度が揺らいでいる。図１２（ａ）のモデルでは、雑音成分としては(I)ショット雑音、(II)光受信器９４の熱雑音、さらに(III)SOA変調器９１が発生する自然放出光が単一波長の連続光と干渉して発生するビート雑音、(IV)自然放出光自身で干渉して発生するビート雑音が考えられる。これらの雑音電力は、受信された光電流強度の分散として表され、マークおよびスペースにおける分散σ_m ²およびσ_s ²は、
【数４】

と表される。なお、B_e [Hz]は光受信器９４の帯域、R [ohm]は光受信器９４の負荷抵抗、kはボルツマン定数、Ｔは絶対温度である。(4-a)および(4-b)式の右辺第１項はショット雑音、第２項は熱雑音、第３項は単一波長光と自然放出光との干渉によるビート雑音、第４項は自然放出光同士のビート雑音を表している。
【００８２】
上記の式を用いて受信された信号の信号対雑音比SNRを導出する。今、雑音電力は等価的に、(4-a)および(4-b)式で表される雑音の標準偏差σ_mおよびσ_sの平均で表されるとすると、SNRは、
【数５】

と導かれる。
【００８３】
(5)式によると、SOA変調器９１への入力光パワーP_inが小さいときは、自然放出光同士のビート雑音がSNR劣化の支配要因であることが分かる。SNRの劣化を抑えるには、光受信器９４の帯域B_eを小さくしてやればよいことが分かる。これはすなわち、信号が受信可能なビットレートを小さくすることに相当する。そこで、SOA変調器９１への入力光パワーに対する、出力光信号のＳＮＲから類推される伝送可能なビットレートを解析的に計算する。計算の簡略化のため、光受信器９４で発生する雑音（(4-a)および(4-b)式におけるショット雑音、熱雑音）は無視し、かつ量子効率は1、消光比は0として計算した。光受信器９４の帯域B_eは、ビットレートBの0.7倍相当であるとし、SNR=200（ビット誤り率換算で10^-12）を得るために必要なSOA変調器９１の入力光パワーをP_inとすると、(5)式を用いて、
【数６】

と表される。上記計算式の計算例として、利得G=15 [dB]、自然放出光係数n_sp=15、偏波の係数m_p=2、光フィルタ９２の透過スペクトル半値全幅Δf=15 [GHz]、光の周波数ν=200 [THz]として計算した結果を図１２（ｂ）に示す。
【００８４】
入力光パワーが-35 [dBm]以上の場合、ＳＮＲ劣化要因は信号光と自然放出光との干渉によるビート雑音が支配的となるため、入力光パワーにほぼ比例して伝送可能なビットレートは増加する。一方、入力光パワーが-35 [dBm]以下の場合、ＳＮＲ劣化要因は自然放出光同士の干渉によるビート雑音が支配的となり、入力光パワーが-50 [dBm] 以下では伝送可能なビットレートはある一定の値に落ち着く。このようなSOA変調器９１への入力光パワーの低い状態（ここでは-50 [dBm] 以下）では、光信号はスペクトルスライス技術により伝送されていると考えることができる。
【００８５】
なお、(6)式、あるいは図１２（ｂ）で与えられる伝送可能なビットレートは、SOA変調器９１、光受信器９４ならびに入力の光搬送波がすべて理想的な場合であるため、実際にはすべてのＳＮＲ劣化要因を勘案して(4-a)および(4-b)式のような雑音を求め、(6)式の関係を導けばよい。また、光信号の伝送に際して光アンプを用いて信号を増幅した場合は、光アンプによる雑音を別途(4-a)および(4-b)式に加えて計算すればよい。
【００８６】
以上述べてきたとおり、ＳＯＡ変調器による伝送特性は、その入力光レベルに依存することが分かる。すなわち、ＳＯＡ変調器への入力光レベルをモニタすれば、伝送可能なビットレートを類推することができるため、入力光レベルに応じてＳＯＡ変調器のビットレートを変換すればよい、という事実が分かる。
【００８７】
光送受信パッケージ６０ｄ又は６１ｄについて図１１を用いて詳細に説明すると、サーバやクライアント端末等の図示しない通信端末からの信号(例えば1.25Gbps)は、双方向通信インタフェース１１又は２１（例えばギガビットイーサネット）を介して光通信装置に取り込まれ、物理速度下降手段１４における送出光信号用の書込み手段４１を介してメモリ４２に送られる。同時に、伝送速度コントローラ７０は、パワーモニタ８３にて光変調器（ＳＯＡ変調器）８１の入力光レベルP_inをモニタしており、伝送速度決定回路８４にて、入力光レベルP_inに対する伝送可能な送出光信号の物理速度（ビットレート）を(6)式を用いて算出し、その物理速度でメモリ４２から信号を読み出すように、物理速度下降手段１４内にある読出し手段４３に制御信号を与える。あるいは、あらかじめ(6)式を用いて入力光レベルP_inに対する伝送可能な送出光信号の物理速度（ビットレート）を伝送速度決定回路８４に記憶しておき、パワーモニタ８３から入力される光変調器８１への入力光レベルP_inに対応する送出光信号の物理速度（ビットレート）を示す制御信号を、物理速度下降手段１４内にある読出し手段４３に与えるようにしても良い。この制御信号は、例えば、クロック信号である。物理速度下降手段１４内にある読出し手段４３は、伝送速度コントローラ７０から供給されるクロック信号に同期してメモリ４２から信号を読み出す。メモリ４２から読出された信号は光変調器８１を駆動するドライバ回路８２に送られ、光変調器８１にてメモリ４２から読み出された信号が光信号に変換され、光ファイバによって接続されている対向の光通信装置（図示省略）へ送出信号として送出される。
【００８８】
ここで、伝送速度コントローラ７０で決定される送出光信号の物理速度は、以下のような２値のどちらかを取るように設定してもよい。例えばSOA変調器の特性が図１２（ｂ）であった場合、入力光レベルが-35 dBm 以上であれば、ギガビットイーサネットの物理速度である1.25 GbpsでSOA変調器を駆動し、入力光パワーが-35 dBm以下であれば、430Mbpsより低い固定的な伝送速度、例えばファストイーサネットの物理速度である125 Mbps でSOA変調器を駆動してもよい。
【００８９】
一方、光ファイバを介して対向する光通信装置（図示省略）から図１１に示す光送受信パッケージへ入力される受信信号を受信するためには、以下のような構成にすればよい。光受信器７２としては、例えばマルチビットレート対応の３R光受信器（すなわち、Re-shaping，Re-timing，Re-generating機能を有する光受信器）を用いればよい。上記光受信器７２により光信号は電気信号に変換され、かつクロック信号も再生される。このクロック信号は物理速度上昇手段２４内の書込み手段４１に送られ、前記書込み手段４１はクロック信号に同期して光受信器７２から出力された電気信号をメモリ４２に書き込む。物理速度上昇手段２４のメモリ４２からは、読出し手段４３により双方向通信インタフェース１１又は２１の物理速度(1.25Gbps)で信号が読み出され、この双方向通信インタフェースを介して通信端末へ送られる。
【００９０】
本実施形態を用いた光通信システムを構成することにより、光送信器の光源、あるいは光送信器へ光搬送波を供給する光源が故障した場合でも、各光通信装置間で低速で通信を続けることができる。
【００９１】
＜本発明の光通信システムの第６の実施形態＞
図１３は、本発明の光通信システムの第６の実施形態を示す。
【００９２】
下り光信号および上り光信号を伝送させるネットワークの基本的な構成は、第５の実施形態の説明で用いられた図１０と同じである。ただし本実施形態では、センタ装置２００ｅにおいて、センタ装置２００ｅ内およびユーザ装置１００ｅ内の光送受信パッケージ６１ｅ，６０ｅに光搬送波を供給する多波長一括発生光源２８，２１０が配置されており、センタ装置２００ｅと光分岐装置５６ｅの間には、下り光信号および上り光信号が伝送する光ファイバ３２とは異なる光ファイバ２１１が設けられている。また光分岐装置５６ｅには、光搬送波を分波するAWG２１２を備えている。さらに光分岐装置５６ｅと各ユーザ装置１００ｅの間には、下り光信号および上り光信号が伝送する光ファイバ３１とは異なる光搬送波供給用の光ファイバ２１３がそれぞれ備えられている。
【００９３】
このような光通信システムに用いるセンタ装置２００ｅおよびユーザ装置１００ｅにおける光送受信パッケージ６１ｅ，６０ｅとしては、図１４に示す構成にすればよい。図１４の光送受信パッケージは、図１１のそれにほぼ等しいが、光搬送波は該光送受信パッケージの外部に設けられた光源より供給されるため、光搬送波入力ポート２２０を持つ点、光送信器７１は、自発光可能な光変調器２２１と、光変調器２２１を駆動するドライバ回路８２のみにより構成される点、光搬送波を２方向に分岐して光変調器２２１およびパワーモニタ８３に出力する光カプラ２２２を追加した点が図１１の構成と異なる。また、光送受信パッケージ内の信号の流れについては、第５の実施形態で述べたとおりである。
【００９４】
図１３に話しを戻すと、下り信号用の多波長一括発生光源２８から送出された多波長光搬送波は、AWG２７−２により分波された後、センタ装置２００ｅ内にある複数の光送受信パッケージ６１ｅの各光搬送波入力ポート２２０及び光カプラ２２２（図１４）を介して、光変調器２２１に導かれる。一方、上り信号用の多波長一括発生光源２１０から送出された多波長光搬送波は、下り光信号および上り光信号が伝送する光ファイバ３２とは異なる光ファイバ２１１を伝送して光分岐装置５６ｅに到達した後、光分岐装置５６ｅに配備されたAWG２１２にて各波長の光搬送波に分波された後、下り光信号および上り光信号が伝送する光ファイバ３１とは異なる光ファイバ２１３を介して各ユーザ装置１００ｅに送られ、各ユーザ装置１００ｅの光送受信パッケージ６０ｅの光搬送波入力ポート２２０（図１４）を介して光変調器２２１に導かれる。
【００９５】
なお、図１３では、光分岐装置５６ｅに３つのAWGを備えた構成を示したが、光搬送波を分波するAWG２１２は、他のAWGと兼用して２つ、あるいは１つのAWGを備える構成でもよい。
【００９６】
また、図１３では、下り光信号および上り光信号が伝送するセンタ装置２００ｅ−光分岐装置５６ｅ間、ならびに光分岐装置５６ｅ−ユーザ装置１００ｅ間の光ファイバ３２，３１は、波長多重分離フィルタ（WDMフィルタ）２５，５８，６２，１５を用いてそれぞれ1本の光ファイバとしているが、図５と同様に、下り光信号、上り光信号それぞれ1本ずつの光ファイバを用いてもよい。さらに、信号光の光ファイバを上り光信号、下り光信号それぞれ1本ずつ用いた場合、上り光信号用の光搬送波を下り信号が伝送する光ファイバに多重して伝送してもよい。その場合、センタ装置２００ｅ−光分岐装置５６ｅ間の光ファイバ数は2本でよく、光分岐装置５６ｅ−各ユーザ装置１００ｅ間の光ファイバ数は、それぞれ2本でよい。
【００９７】
本実施形態を用いた光通信システムを構成することにより、光送信器の光源、あるいは多波長一括発生光源が故障した場合でも、低速で通信を続けることができる。また、光送信器の光源、あるいは多波長一括発生光源の波長がずれた場合でも、センタ装置２００ｅ−各ユーザ装置１００ｅ間で低速で通信を続けることができる。
【００９８】
＜本発明の光通信システムの第７の実施形態＞
図１５は、光通信の光送信システムの第７の実施形態を示す。
【００９９】
本実施形態では、第６の実施形態の説明で用いられた図１３に比べて、多波長一括発生光源の代わりに、以下で説明する波長可変多波長光源を用いた点が異なっている。センタ装置２００ｆ、およびユーザ装置１００ｅにおける光送受信パッケージおよびAWG、光ファイバは、第６の実施形態で用いた構成と同じ構成（図１３）にすればよい。
【０１００】
センタ装置２００ｆには、下り信号用の波長可変多波長光源２３０および上り信号用の波長可変多波長光源２３１が備えられる。波長可変多波長光源２３０，２３１の各々は、本実施形態の光通信システムに接続されているユーザ装置１００の数よりも少ない、１つないし複数の波長可変レーザ光源２３２と、それらの波長可変レーザ光源２３２より出力されるレーザ光を合波して出力する合波器２３３により構成される。合波器２３３は、例えば光カプラなどを用いればよい。
【０１０１】
波長可変多波長光源２３０，２３１に内蔵されている波長可変レーザ光源２３２は、制御装置２３４によりそれぞれ光出力の入／断が制御されると共に、光出力が“入”のときには発振波長が制御される。また発振波長は動的に変化させることもできる。すべての波長可変レーザ光源２３２の光出力を“入”にすることにより、波長可変多波長光源２３０，２３１は、最大で内蔵している波長可変レーザ光源２３２と同じ数の光キャリアを発生させることができる。
【０１０２】
下り信号用の波長可変多波長光源２３０から出力される多波長光搬送波は、センタ装置２００ｆに備えられたAWG２７−２により各波長に分波され、その波長に応じた出力ポートを介して、センタ装置２００内の光送受信パッケージ６１ｅの光搬送波入力ポート２２０（図１４）より光変調器２２１へ導かれ、光変調器２２１で変調されて、合波用のAWG２７−３へ送出される。ただし、光送受信パッケージ６１ｅへ分配される光キャリアの数は、センタ装置２００ｆにインストールされた光送受信パッケージ６１ｅの数より少ないため、すべての光送受信パッケージ６１ｅに光キャリアが分配されるわけではない。また、波長可変多波長光源２３２から送出される光キャリアの波長は時々刻々と変化する場合もあるため、ある光送受信パッケージ６１ｅへの光キャリアの供給が途絶えることもある。このような光キャリアが供給されていない光送受信パッケージ６１ｅでは、光送受信パッケージ６１ｅに備えられた伝送速度コントローラ７０が伝送速度を下降させ、広帯域変調光を出力する。このように各光送受信パッケージ６１ｅからは、単一波長の光キャリアを高速で変調した下り信号、あるいは広帯域光を低速で変調した下り信号が、センタ装置２００ｆに備えられた合波用のAWG２７−３に送られ、該AWG２７−３により波長多重され、光ファイバ３２を介して光分岐装置５６ｅへ送られる。光分岐装置５６ｅでは、波長多重された下りの光信号を分波し、光ファイバ３１を介して各ユーザ装置１００ｅへ下り光信号を送出し、この下り光信号がユーザ装置１００ｅの光受信器７２にて受信される。受信された電気信号は、ユーザ装置１００ｅの物理速度上昇手段２４を介して双方向通信インタフェース１１へ送られる。
【０１０３】
一方、上り信号用の波長可変多波長光源２３１から出力される多波長光搬送波は、変調信号が伝送する光ファイバ３２および３１とは異なる光ファイバ２１１および２１３を伝搬して、センタ装置１００ｆから光分岐装置５６ｅを介して各ユーザ装置１００ｅへ分配される。ただし下り信号と同様、すべてのユーザ装置１００ｅの光送受信パッケージ６０ｅに光キャリアが分配されるわけではないので、光キャリアが供給されている光送受信パッケージ６０ｅでは、該光キャリアを光送信器７１ｅ内の光変調器２２１（図１４）が変調し、光キャリアが供給されていない光送受信パッケージ６０ｅでは、光送受信パッケージ６０ｅに備えられた伝送速度コントローラ７０が伝送速度を下降させ、広帯域変調光を出力する。このように各光送受信パッケージからは、単一波長の光キャリアを高速で変調した上り信号、あるいは広帯域光を低速で変調した上り信号が送出され、光ファイバ３１を介して光分岐装置５６ｅに備えられた合波用のAWG５７−１に送られ、該AWG５７−１にて各ユーザ装置１００ｅからの上り信号が波長多重された後、光ファイバ３２を介してセンタ装置２００ｆへ送られ、センタ装置２００ｆに備えられた分波用のAWG２７−１により各波長に分波された後、光送受信パッケージ６１ｅの光受信器７２にて受信される。受信された電気信号は、各光送受信パッケージ６１ｅの物理速度上昇手段２４を介して双方向通信インタフェース２１に送られる。
【０１０４】
なお、図１５では、光分岐装置５６ｅに３つのAWGを備えた構成を示したが、光搬送波を分波するAWG２１２は、他のAWGと兼用して２つ、あるいは１つのＡＷＧを備える構成でもよい。
【０１０５】
また、図１５においては、下り光信号および上り光信号が伝送するセンタ装置２００ｆ−光分岐装置５６ｅ間、ならびに光分岐装置５６ｅ−ユーザ装置１００ｅ間の光ファイバは、波長多重分離フィルタ（WDMフィルタ）２５，５８，６２，１５を用いてそれぞれ1本の光ファイバとしているが、図５のように、下り光信号、上り光信号それぞれ1本ずつの光ファイバを用いてもよい。さらに、信号光の光ファイバを上り光信号、下り光信号それぞれ1本ずつ用いた場合、上り光信号用の光搬送波を下り信号が伝送する光ファイバに多重して伝送してもよい。その場合、センタ装置２００ｆ−光分岐装置５６ｅ間の光ファイバ数は2本でよく、光分岐装置５６ｅ−各ユーザ装置１００ｅ間の光ファイバ数は、それぞれ2本でよい。
【０１０６】
また、下り信号用，上り信号用のそれぞれの波長可変多波長光源２３０，２３１に用いられる波長可変レーザ光源２３２の数は同一である必要はない（すなわち、図１５に示すｊの値とｋの値は異なっていても良い）。また、図１５ではセンタ装置２００ｆ内に下り光信号用および上り光信号用の２つの波長可変多波長光源２３０，２３１を備えたが、どちらか一方のみが波長可変多波長光源であってもよい。
【０１０７】
ここで、波長可変多波長光源２３０，２３１は、例えば以下のような手順により光搬送波の波長を動的に変化させられる構成にすればよい。
【０１０８】
波長可変多波長光源２３０，２３１と制御装置２３４は、ケーブルを用いて直接、あるいはネットワークを介して接続されている。制御装置２３４は、波長可変多波長光源２３０，２３１に内蔵されている個々の波長可変レーザ光源２３２の状態（光出力の入／断、および光出力が入の場合は発振波長）を示す監視信号を波長可変多波長光源２３０，２３１から受け取ることにより、波長可変多波長光源２３０，２３１が送出している光搬送波の波長を知ることができる。また、制御装置２３４は、各波長可変レーザ光源２３２の光出力の入／断および発振波長を個別に、かつ遠隔で制御しうる制御信号を送出することにより、波長可変多波長光源２３０，２３１の発振波長を遠隔で制御することができる。
【０１０９】
制御装置２３４からの制御信号は、例えば以下のような手順により送出される。
【０１１０】
制御装置２３４にはオペレータ端末（図示されていない）が接続されており、オペレータ端末を介して制御装置２３４に「あるユーザに、通信に用いる光搬送波を与えなさい」というような命令が入力されると、制御装置２３４は波長可変多波長光源２３０，２３１からの監視信号を取り寄せ、光出力が断となっている波長可変レーザ光源２３２を探す。次に、制御装置２３４に記憶されている各ユーザ装置１００ｅと、そのユーザ装置１００ｅが用いる光搬送波の波長の対応表から、該当するユーザ装置１００ｅが通信に用いる光搬送波の波長を決定し、先の波長可変レーザ光源２３２にその波長で発振するよう、制御信号を送出する。
【０１１１】
上記の例で、もし光出力が断となっている波長可変レーザ光源２３２がない場合、内蔵されている波長可変レーザ光源２３２からランダムに１つの波長可変レーザ光源を選んで、波長を切り替えてもよい。また、通信サービスを提供するときに、あらかじめ各ユーザ装置１００ｅに優先順位をつけておき、優先順位の低いユーザのユーザ装置１００ｅが通信に用いている波長可変レーザ光源２３２の波長を切り替えてもよい。また、各ユーザ装置１００ｅが通信しているデータトラヒックを双方向通信インタフェース２１においてモニタしておき、データトラヒックが低いユーザ装置１００ｅが通信に用いている波長可変レーザ光源２３２の波長を切り替えてもよい。
【０１１２】
上記のような制御信号の送出手順は、例えば、現在低速な通信サービスを使っているユーザから、通信キャリアに対してより高速な通信サービス開通の要求があった場合などが該当する。この場合、該当ユーザのユーザ装置１００ｅの通信速度を、光通信装置の構成を変えることなく、また通信が途絶えることなく切り換えて、ユーザにサービスを提供することができる。
【０１１３】
制御装置２３４からの制御信号は、例えば以下のような別の手順により送出されるようにしても良い。
【０１１４】
制御装置２３４にはあらかじめ、各ユーザ装置１００ｅが光搬送波を必要とする時間が記憶されており、その時間がくると、制御装置２３４は自動的に波長可変多波長光源２３０，２３１からの監視信号を取り寄せ、光出力が断となっている波長可変レーザ光源２３２を探す。次に、制御装置２３４に記憶されている各ユーザ装置１００ｅと、そのユーザ装置１００ｅが用いる光搬送波の波長の対応表から、該当するユーザ装置１００ｅが通信に用いる光搬送波の波長を決定し、探し出した波長可変レーザ光源２３２にその波長で発振するよう、制御信号を送出する。
【０１１５】
上記の例で、もし光出力が断となっている波長可変レーザ光源２３２がない場合は、先の例と同様の手順で、使われている波長可変レーザ光源２３２の波長を強制的に切り替えてもよい。
【０１１６】
上記のような制御信号の送出手順を用いれば、ユーザごとに時間限定で高速な通信サービスを提供することができる。例えばあるユーザには、1日のうち9時から17時までは高速な通信サービスを使い、それ以外の時間では低速なサービスに切り替える場合などである。
【０１１７】
さらに別の例として、制御装置２３４からの制御信号を例えば以下のような手順により送出されるようにしても良い。
【０１１８】
各ユーザ装置１００ｅの通信トラヒックは、双方向通信インタフェース２１にて、あるいは双方向通信インタフェース２１に接続された通信ノード（スイッチングハブ等）にてモニタし、その情報を制御装置２３４へ送出できるように構成する（図示されていない）。なお、こうした構成は既存の技術を用いて容易に実現することができる。制御装置２３４にはあらかじめ、各ユーザ装置１００ｅが光搬送波を必要とする通信トラヒックの閾値が記憶されており、その閾値を越えると、制御装置２３４は自動的に波長可変多波長光源２３０，２３１からの監視信号を取り寄せ、光出力が断となっている波長可変レーザ光源２３２を探す。次に、制御装置２３４に記憶されている各ユーザ装置１００ｅと、そのユーザ装置１００ｅが用いる光搬送波の波長の対応表から、該当するユーザ装置１００ｅが通信に用いる光搬送波の波長を決定し、探し出した波長可変レーザ光源にその波長で発振するよう、制御信号を送出する。
【０１１９】
上記の例で、もし光出力が断となっている波長可変レーザ光源がない場合は、先の例と同様の手順で、使われている波長可変レーザ光源２３２の波長を強制的に切り替えてもよい。なお、上記とは逆に、通信トラヒックが閾値以下となった場合には、上記波長の割り当てを解除して、通信トラヒックが閾値を超えた別のユーザ装置１００ｅに対してこの波長を割り当てれば良い。
【０１２０】
上記のような制御信号の送出手順を用いれば、帯域オンデマンドと呼ばれる、通信トラヒックに応じた高速な通信サービスを提供できる。
【０１２１】
以上のように本実施形態を用いた光通信システムを構成することにより、ユーザ装置と同じ台数の光源をセンタ装置に用意する必要がなくなるため、システム全体が所有するレーザ光源の数を減らしつつ、ユーザや通信キャリアの要求に応じて高速のビットレートでの通信を提供することができるとともに、安価に高速なアクセスネットワークを提供することができる。また、波長可変多波長光源が故障した場合でも、低速で通信を続けることができる。
【０１２２】
なお、以上示した各実施形態では、通信インタフェースをギガビットイーサネットとし、下降させた物理速度をファストイーサネットの物理速度とした例を示したが、通信インタフェースとして例えば10ギガビットイーサネットを用い、下降させた物理速度として例えばギガビットイーサネットや10メガビットイーサネットを用いてもよい。
【０１２３】
【発明の効果】
以上説明したように、本発明によれば、送信信号と受信信号の物理速度が等しい双方向通信インタフェースを備えた光通信装置間で、一方向の光信号の物理速度を他方向に比べて減少させることができるので、一方の伝送帯域が他方と同程度に確保できない場合でも光通信装置間の双方向通信が可能となる。
【０１２４】
また、本発明を波長多重アクセスネットワークに用いた場合に、広く利用されている双方向通信インタフェースであるギガビットイーサネット等、送出信号／受信信号の物理速度が等速度のインタフェースを用いて、上り信号伝送にスペクトルスライス技術を利用して光通信装置のコスト低減を可能にするとともに、下り信号伝送はユーザの要求に応えるべくギガビットクラスの速度を提供する波長多重アクセスネットワークを実現することができる。
【０１２６】
また、本発明によれば、波長多重アクセスネットワークに用いた場合、広く利用されている双方向通信インタフェースであるギガビットイーサネット等、上り／下りの物理速度が等速度のインタフェースを用いて、上り／下りの物理速度がギガビットクラスの速度を安価に提供できる波長多重アクセスネットワークを実現することができるとともに、光源装置の故障時にも低速で通信ができるため、信頼性の高い波長多重アクセスネットワークを実現できる。
【図面の簡単な説明】
【図１】 本発明の光通信システムの第１の実施形態を示すブロック図である。
【図２】 本発明の光通信システムの第２の実施形態を示すブロック図である。
【図３】 （ａ）は物理速度下降手段１４および物理速度上昇手段２４の構成例を示すブロック図、（ｂ）は伝送する情報をビット単位で見た場合における物理速度下降手段１４の動作例を示す図、（ｃ）は伝送する情報をパケット単位で見た場合における物理速度下降手段１４の動作例を示す図である。
【図４】 本発明の光通信システムの第３の実施形態を示すブロック図である。
【図５】 本発明の光通信システムの第３の実施形態において光送受信パッケージを採用した場合の構成例を示すブロック図である。
【図６】 本発明の光通信システムの第４の実施形態を示すブロック図である。
【図７】 本発明の光通信システムの第４の実施形態における波長合分波フィルタ（ＡＷＧ）のフィルタ特性を示す図である。
【図８】 （ａ）及び（ｂ）は本発明の光通信システムの第４の実施形態における波長多重分離フィルタ（ＷＤＭフィルタ）１５のフィルタ特性を示す図、（ｃ）及び（ｄ）は本発明の光通信システムの第４の実施形態における波長多重分離フィルタ（ＷＤＭフィルタ）２５，５８のフィルタ特性を示す図である。
【図９】 本発明の光通信システムの第４の実施形態において光送受信パッケージを採用した場合の構成例を示すブロック図である。
【図１０】 本発明の光通信システムの第５の実施形態を示すブロック図である。
【図１１】 第５の実施形態における光送受信パッケージの構成例を示すブロック図である。
【図１２】 （ａ）は半導体光増幅器を変調器として用いた場合における伝送系の一モデルを示すブロック図、（ｂ）は半導体光増幅器における入力光パワーと伝送可能な最大ビットレートとの関係を示す図である。
【図１３】 本発明の光通信システムの第６の実施形態を示すブロック図である。
【図１４】 第６の実施形態における光送受信パッケージの構成例を示す図である。
【図１５】 本発明の光通信システムの第７の実施形態を示すブロック図である。
【図１６】 イーサネットアクセスシステムの構成例を示すブロック図である。
【図１７】 波長多重アクセスネットワークの構成例を示すブロック図である。
【図１８】 スペクトルスライス光を用いる波長多重アクセスネットワークの構成例を示すブロック図である。
【図１９】 広帯域変調光と波長多重されたスペクトルスライス光の関係を示す図である。
【図２０】 スペクトルスライスを用いる場合におけるビート雑音の影響を説明する図である。
【図２１】 キャリア供給型波長多重アクセスネットワークの構成例を示すブロック図である。
【符号の説明】
１０ 光通信装置
１１ 双方向通信インタフェース
１２，２２ 光送信器
１３，２３ 光受信器
１４ 物理速度下降手段
１５ 波長多重分離フィルタ
２０ 光通信装置
２１ 双方向通信インタフェース
２４ 物理速度上昇手段
２５ 波長多重分離フィルタ
２６ 光変調器
２７−１〜２７−３ 波長合分波フィルタ
２８ 多波長一括発生光源
３１，３２ 光ファイバ
５６，５６ｂ〜５６ｃ，５６ｅ 光分岐装置
５７，５７−１〜５７−２ 波長合分波フィルタ
５８ 波長多重分離フィルタ
６０，６０ｄ，６０ｅ，６１，６１ｄ，６１ｅ 光送受信パッケージ
６２ 波長多重分離フィルタ
７０ 伝送速度コントローラ
７１，７１ｅ 光送信器
７２ 光受信器
８０ レーザ光源
８１ 光変調器
８２ ドライバ回路
８３ パワーモニタ
８４ 伝送速度決定回路
９０ レーザ
９１ 半導体光増幅器
９２ 光フィルタ
９３ 伝送路
９４ 光受信器
１００，１００ａ〜１００ｅ ユーザ装置
２００，２００ａ〜２００ｆ センタ装置
２１０ 多波長一括発生光源
２１１ 光ファイバ
２１２ ＡＷＧ
２１３ 光ファイバ
２２０ 光搬送波入力ポート
２２１ 光変調器
２２２ 光カプラ
２３０，２３１ 波長可変多波長光源
２３２ 波長可変レーザ光源
２３３ 合波器
２３４ 制御装置[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical access network, and more particularly to optical communication constituting a wavelength division multiplexing access network.To the systemRelated.
[0002]
[Prior art]
FIG. 16 shows a configuration example of an Ethernet (registered trademark) access system. In FIG. 16, switches or routers 1053 arranged in a plurality of user apparatuses 1051 and a center apparatus 1052 are connected via one or two optical fibers 1031 respectively, and bidirectional communication is performed. Here, it is assumed that Fast Ethernet with a physical speed of 125 Mbps and a data transfer speed of up to 100 Mbps, Gigabit Ethernet with a physical speed of 1.25 Gbps and a data transfer speed of up to 1 Gbps, and the like. The physical speed means a speed at which an electrical signal or an optical signal is physically turned on / off regardless of an actual data transfer speed.
[0003]
FIG. 17 shows a configuration example of a wavelength division multiplexing access network. In FIG. 17, a plurality of user apparatuses 1051 and a center apparatus 1052 are connected via an optical fiber 1031, an optical branching apparatus 1056, and an optical fiber 1032. The wavelength multiplexing / demultiplexing filter (AWG) 1057 of the optical branching device 1056 multiplexes the upstream optical signal from each user device 1051 and sends it to the center device 1052, and the downstream wavelength multiplexed optical signal transmitted from the center device 1052. Is demultiplexed for each wavelength and transmitted to each user apparatus 1051. The wavelength multiplexing / demultiplexing filter (AWG) 1054 of the center apparatus 1052 demultiplexes the upstream wavelength multiplexed optical signal multiplexed by the optical branching apparatus 1056 for each wavelength, and sends the demultiplexed optical signal to the switch or router 1053. In this configuration, the downstream optical signal addressed to each user apparatus 1051 is wavelength-multiplexed and transmitted to the optical branching apparatus 1056.
[0004]
Note that the configuration of FIG. 17 is an example, and the upstream and downstream of the optical transmission line are separated and two optical fibers are used, and the upstream and downstream signals are multiplexed / demultiplexed by separate wavelength multiplexing / demultiplexing filters. It is good.
[0005]
By the way, in a wavelength division multiplexing access network, studies have been made on the assumption that each user apparatus transmits an optical signal having a different wavelength. Recently, each user apparatus transmits broadband modulated light, and each optical apparatus uses an optical branching apparatus. A method of slicing a spectrum to a wavelength assigned to a user apparatus, wavelength-multiplexing the spectrum slice light of each wavelength and transmitting it to the center apparatus has been studied (Reference 1 (K. Akimoto, et al., “Spectrum-sliced”). , 25-GHz spaced, 155Mbps × 32 channel WDM access ”, Proc. CLEO / Pacific Rim 2001, ThB1-5, pp.II-556 to II-557, Chiba (Japan), July, 2001)). As a result, each user apparatus can perform wavelength multiplexing access using an optical transmitter having the same specification (wavelength characteristics), thereby reducing the production cost of the optical transmitter and the cost for wavelength control.
[0006]
FIG. 18 shows a configuration example of a wavelength division multiplexing access network using spectrum slice light. The basic configuration is the same as that shown in FIG. 17, but the function in the upstream direction is shown here.
[0007]
Each user device 1051 is provided with a broadband light source (not shown) that generates broadband spontaneous emission light (ASE). The user apparatus is also called an ONU (Optical Network Unit). Examples of the broadband light source include a light emitting diode (LED), a super luminescent diode (SLD), a semiconductor optical amplifier (SOA), and an optical fiber amplifier. Since LEDs, SLDs, and SOAs are semiconductor elements and can be directly modulated, when used as a transmitter, spontaneous emission light can be modulated and output alone, but in the case of an optical fiber amplifier, an external modulator is used. It is necessary to modulate spontaneous emission light using This modulated spontaneous emission light is called “broadband modulated light”. The broadband modulated light output from each user apparatus 1051 is shown in FIG.
[0008]
The wavelength multiplexing / demultiplexing filter 1057 of the optical branching device 1056 receives the broadband modulated light transmitted from each user device 1051 via each optical fiber 1031, and signal light (spectral slice light) obtained by spectrally slicing a predetermined wavelength. Are wavelength-multiplexed and transmitted to the center apparatus 1052 via the optical fiber 1032. In the case of 64 user devices 1051, wavelength-multiplexed spectrum slice light is shown in FIG. The wavelength multiplexing / demultiplexing filter 1054 of the center device 1052 demultiplexes the wavelength multiplexed optical signal transmitted via the optical fiber 1032 for each wavelength assigned to each user device.
[0009]
However, the signal speed that can be transmitted using the spectrum slicing technique is limited by the filter characteristic (transmission spectrum width) of the wavelength multiplexing / demultiplexing filter 1057 of the optical branching device 1056 as described in the above-mentioned document 1. This is because spontaneous emission light is used as a signal carrier instead of laser light.
[0010]
When transmission is performed using spontaneously emitted light, beat noise caused by interference between the spectral components of spontaneously emitted light reduces the signal-to-noise ratio. 20 (a) to 20 (d) show the results of numerical calculations for explaining the influence of beat noise when using spectrum slices. FIG. 20 (a) shows the light spectrum when the spontaneous emission light having a flat spectrum with respect to the wavelength is simulated on the computer, and FIG. 20 (b) shows that the spontaneous emission light is received by the optical receiver having a bandwidth of 200 GHz. The time waveform after having been shown is shown. FIG. 20 (c) shows an optical spectrum when spontaneous emission light having a spectrum flat with respect to the wavelength is sliced by a wavelength multiplexing / demultiplexing filter with a full width at half maximum of 25 GHz, and FIG. 20 (d) shows optical reception in a band of 200 GHz. The time waveform after receiving a spectrum slice light with the instrument is shown.
[0011]
Beat noise generated by spontaneously emitted light having a flat spectrum with respect to wavelength (FIG. 20 (a)) is widely distributed from a low frequency to a high frequency equivalent to the optical spectrum width (band). Indicates. However, since the electrical band of the optical receiver generally has a very small band with respect to the optical spectrum band, most of the beat noise is removed by this optical receiver. As a result, as shown in FIG. A low-noise time waveform can be obtained.
[0012]
On the other hand, beat noise generated by light (FIG. 20 (c)) obtained by slicing spontaneously emitted light having a flat spectrum with respect to the wavelength by the wavelength multiplexing / demultiplexing filter is from the low frequency to the bandwidth of the wavelength multiplexing / demultiplexing filter. The frequency characteristics are distributed up to the same frequency. When the band of the wavelength multiplexing / demultiplexing filter is equal to or less than that of the optical receiver, the beat noise is hardly removed by this optical receiver, and as a result, the intensity as shown in FIG. A time waveform with many noise components can be obtained.
[0013]
In a wavelength division multiplexing access system, in order to increase the number of user apparatuses that can be multiplexed simultaneously, it is necessary to narrow the wavelength interval (referred to as channel interval) between wavelength multiplexed optical signals (or spectrum slice lights). For this purpose, the spectrum width occupied by each channel has to be narrowed, and as a result, the speed at which each user can transmit is reduced.
[0014]
Quantitative analysis of the above characteristics is given in Reference 2 (JSLee, et al., “Spectrum-sliced fiber amplifier light source for multichannel WDM applications”, IEEE Photonics Technologies Letters, vol.5, pp.1458-1461, 1993). The signal-to-noise ratio can be determined by Bo / Be using the full width at half maximum Bo of the wavelength multiplexing / demultiplexing filter and the electrical bandwidth Be of the optical receiver. A signal-to-noise ratio of approximately 144 or more indicates a code error rate of 10 as a measure of transmission quality.^-9It corresponds to the following. Since the bandwidth of the optical receiver is required to be about 0.7 times the transmission speed, for example, in a wavelength division multiplexing system with a 25 GHz interval, the transmission speed in the spectrum slice is 0.7% of the full width at half maximum of the wavelength multiplexing / demultiplexing filter. Doubled is limited to about 170 Mbps or less. Further, considering leakage light from other channels in the wavelength multiplexing / demultiplexing filter, it is described in the above-mentioned document 1 that the rate at which the spectrum slice can be transmitted in the wavelength division multiplexing system at 25 GHz intervals is about 125 to 155 Mbps. .
[0015]
Here, if a 1.25 Gbps signal is transmitted in a spectrum slice wavelength division multiplexing system with a 25 GHz interval, the full width at half maximum of the wavelength multiplexing / demultiplexing filter 1057 will be about 0.7 times the wavelength interval, and the signal-to-noise ratio will be about 16. It becomes. As a result, the code error rate becomes 0.01 or more, and for example, a packet signal of 16 bytes or more is almost 100% lost and cannot be transmitted at all.
[0016]
On the other hand, for downstream optical signal transmission, the center device 1052 performs multi-wavelength (multi-channel) collective wavelength management and multi-wavelength collective light source (Japanese Patent Laid-Open No. 2002-82323, Reference 3 (M. Fujiwara et al., “ Flattened optical multicarrier generation of 12.5 GHz spaced 256 channels based on sinusoidal amplitude and phase hybrid modulation ”, Electronics Letters, Vol. 37, No. 15, pp. 967-968, July, 2001) The necessity of applying spectrum slices is not so high as compared with upstream optical signal transmission, where the multi-wavelength light sources disclosed in Japanese Patent Application Laid-Open No. 2002-82323 and Document 3 generate light having different single center wavelengths. The input light from the 2n light sources is divided into two, and two systems are combined and modulated, and each modulation result is polarized and synthesized, and the result is separated into a plurality of carriers having different wavelengths to obtain a final output. It is a configuration to get. In addition, the multi-wavelength collective light source disclosed in Japanese Patent Laid-Open No. 2002-82323 and Document 3 performs phase modulation and amplitude modulation of light having a single central wavelength using an electrical signal (for example, a sine wave) having a specific repetition period. This is a configuration in which multi-wavelength light having a plurality of center wavelengths is collectively generated by generating sideband waves.
[0017]
Regarding the transmission speed, it is possible to transmit a signal at a speed of at least about 1.25 Gbps per channel (wavelength) using the multi-wavelength light source disclosed in Japanese Patent Laid-Open No. 2002-82323, Reference 3, and Reference 4 (N. Takachio, et al., "Wide area gigabit access network based on 12.5GHz spaced 256 channel super-dense WDM technologies", Electronics Letters, vol.37, pp.309-310, March, 2001).
[0018]
Therefore, for example, as a method of constructing a wavelength division multiplexing access network at 25 GHz intervals at low cost, if a spectrum slicing technique is used for upstream signal transmission and a multi-wavelength collective light source is applied for downstream signal generation, the upstream transmission rate is 155. While it is limited to about Mbps or less, the downlink transmission speed can provide a gigabit-class speed, and a system suitable for downloading various content files can be realized.
[0019]
In addition, as another approach in cost reduction technology for upstream optical signal transmission, an optical carrier wave for upstream optical signal is supplied from the center device to each user device, and each user device modulates and transmits the given optical carrier wave. In addition, a carrier-supplied wavelength division multiplexing access network has been proposed (Japanese Patent Laid-Open No. 2000-196536, Reference 5 (Takuya Nakamura, et al., “Examination of Transmission Characteristics at Reflective WDM-PON Transmission System at Optical Transmission / Reception Level”) , IEICE Technical Report OCS2000-50, pp.13-18, September 2000)). FIG. 21 shows a configuration example of a carrier supply type wavelength division multiplexing access network.
[0020]
In FIG. 21, the center device 1152 includes a transmission unit 1160 and a reception unit 1161. The transmission unit 1160 includes a multi-wavelength batch generation / modulation unit 1162 that generates a downstream optical signal, a multi-wavelength batch generation unit 1163 that generates an optical carrier wave of the upstream optical signal, the multi-wavelength batch generation / modulation unit 1162, and the multi-wavelength It comprises a wavelength demultiplexing filter (WDM filter) 1164 that multiplexes the multi-wavelength light output from the collective generator 1163.
[0021]
The downstream optical signal from the center device 1152 is sent to the optical branching device 1156 connected via the optical fiber 1132, and the downstream optical signal is demultiplexed for each wavelength by the AWG 1157 in the optical branching device 1156. To each user device 1151 and received by a receiver 1170 in the user device 1151.
[0022]
The optical carrier wave for the upstream optical signal generated by the multi-wavelength collective generation unit 1163 is sent to the AWG 1157 of the optical branching device 1156 through the same path as the downstream optical signal sent from the center device 1152 to the user device 1151. The AWG 1157 demultiplexes each of the downstream optical signal and the optical carrier wave for each wavelength and sends the demultiplexed optical signal and the optical carrier wave to the user apparatus 1151. In the user apparatus 1151, the downstream optical signal and the optical carrier wave are separated by the WDM filter 1171, and the optical carrier wave is input to the optical modulator 1172. The optical modulator 1172 modulates the optical carrier wave, generates an upstream optical signal, and sends it to the AWG 1157 connected via the optical fiber 1141. The AWG 1157 wavelength-multiplexes the upstream optical signal from each user apparatus 1151 and sends it to the center apparatus 1152 via the optical fiber 1142, and the upstream optical signal is received by the receiving unit 1161 of the center apparatus 1152.
[0023]
Here, the wavelength λ of the downstream optical signal₁, λ₂, ..., λ_N(Downlink modulated light) and wavelength λ of optical carrier wave for upstream optical signal₁’, Λ₂', ..., λ_NThe wavelength arrangement uses a wavelength band different from '(unmodulated light, upstream modulated light) (N is the number of user apparatuses 1151).
[0024]
As an advantage of such a carrier supply type WDM access network, there is no need to have a laser light source in the user apparatus, and there is no need for wavelength control in the user apparatus, so the transmitter configuration of the user apparatus is simple. Therefore, the cost reduction of the wavelength division multiplexing access system can be expected.
[0025]
[Problems to be solved by the invention]
In the above-mentioned Fast Ethernet and Gigabit Ethernet, which are two-way optical communication interfaces that are widely used at present, the physical speed of uplink / downlink is equal.
[0026]
Therefore, a wavelength division multiplexing access network that uses a low-cost spectrum slicing technique for upstream signal transmission to limit the transmission speed to about 155 Mbps or less and that can provide a gigabit-class speed in response to the user's request. Fast Ethernet and Gigabit Ethernet signals cannot be transmitted as they are. This is because when using Fast Ethernet, the downlink speed cannot be set to the gigabit class, and when using Gigabit Ethernet, the uplink signal speed is high and the bandwidth is wide, so that spectrum slice light cannot be transmitted at all.
[0027]
On the other hand, when a multi-wavelength collective light source is used as the light source of the upstream optical signal and downstream optical signal, there is a high possibility that the optical carrier wave of all wavelengths stops when the light source device fails. In that case, there is a problem in that communication with all user apparatuses connected to the wavelength division multiplexing access network is interrupted and the damage is serious.
[0028]
The present invention uses, for example, Gigabit Ethernet having a uniform uplink / downlink physical speed as a widely used bidirectional optical communication interface, and uses wideband modulated light or spectrum slice technology for uplink signal transmission. An object of the present invention is to provide an optical communication system, an optical communication apparatus, and an optical transceiver for providing a gigabit class speed in response to a user request in order to reduce the cost of the apparatus.
[0029]
In addition, the present invention uses gigabit Ethernet or the like having a uniform uplink / downlink physical speed as a widely used bidirectional optical communication interface, and concentrates on a center apparatus as a light source for uplink signal transmission and downlink signal transmission. By using deployed multi-wavelength collective light source, cost reduction of optical communication equipment that can provide high-speed communication service of gigabit class, and when optical carrier supply is cut off due to failure of light source equipment etc. Another object of the present invention is to provide an optical communication system, an optical communication apparatus, and an optical transceiver that can communicate at low speed.
[0030]
[Means for Solving the Problems]
    The optical communication system according to claim 1 is a user-side bidirectional communication interface, a user-side optical transmitter, a user-side optical receiver, and the user-side bidirectional communication interface having the same physical speed of a transmission signal and a reception signal. A plurality of user-side physical speed lowering means each for writing the transmission signal input from the memory into the memory and reading out at a lower speed than the writing speed to lower the physical speed of the transmission signal and output it to the user-side optical transmitter. A user-side optical communication device, a center-side bidirectional communication interface having the same physical speed of a transmission signal and a reception signal, a plurality of center-side optical transmitters and a plurality of center sides respectively corresponding to the plurality of user-side optical communication devices Optical signals output from the optical receiver and the plurality of center-side optical transmitters are wavelength-multiplexed and transmitted as downlink wavelength-multiplexed optical signals. Both wavelength multiplexing / demultiplexing means for demultiplexing an input upstream wavelength multiplexed optical signal into each wavelength and receiving it by the plurality of center side optical receivers, and a memory for receiving signals received by the center side optical receivers A center-side optical communication device having center-side physical speed increasing means for increasing the physical speed of the received signal by reading at a higher speed than the writing speed and outputting to the center-side bidirectional communication interface;The center-side optical communication device and each of the plurality of user-side optical communication devicesThe optical signals from the plurality of user-side optical communication devices are connected via at least one optical fiber and transmitted to the center-side optical communication device as the upstream wavelength multiplexed optical signal. An optical branching device for demultiplexing the downstream wavelength-multiplexed optical signal from the optical communication device for each wavelength and transmitting the demultiplexed optical signal to the plurality of user-side optical communication devices;The center-side optical communication device includes multi-wavelength light batch generation means for outputting optical carriers having different wavelengths, and the user-side optical communication device and the center-side optical communication device receive the optical carrier. An input port, wherein the user side optical transmitter and the center side optical transmitter each include a user side optical modulator and a center side optical modulator, and each of the user side optical modulator and the center side optical modulator is When the optical carrier input from the multi-wavelength light batch generation means is received via the input port, the optical carrier is modulated and an optical signal is transmitted, and the optical carrier supply is interrupted. The user side optical modulator and the center side optical modulator itself emit light to transmit an optical signal.
[0046]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment of Optical Communication System of the Present Invention>
FIG. 1 shows a first embodiment of the optical communication system of the present invention. As shown in FIG. 1, the optical communication system according to the present embodiment has a configuration in which a pair of optical communication devices 10 and 20 are connected via two optical fibers 31 to perform bidirectional communication. Each of the optical communication apparatuses 10 and 20 includes bidirectional communication interfaces 11 and 21, optical transmitters 12 and 22, and optical receivers 13 and 23 having the same physical speed (in this case, 1.25 Gbps) of the transmission signal and the reception signal. One optical communication apparatus 10 is provided with a physical speed lowering means 14 for reducing the physical speed from 1.25 Gbps to a low physical speed (125 Mbps in this case) between the bidirectional communication interface 11 and the optical transmitter 12. The optical communication apparatus 20 includes a physical speed increasing means 24 between the optical receiver 23 and the bidirectional communication interface 21 for increasing the physical speed from 125 Mbps to 1.25 Gbps.
[0047]
Here, in the transmission from the optical communication device 10 to the optical communication device 20, the transmission signal (physical speed 1.25 Gbps) from the bidirectional communication interface 11 is converted into a transmission signal having a physical speed of 125 Mbps by the physical speed lowering means 14, The optical transmitter 12 converts a transmission signal with a physical speed of 125 Mbps into an optical signal and transmits it. The optical receiver 23 of the optical communication apparatus 20 converts the received optical signal into an electrical signal (physical speed 125 Mbps), and further converts the physical speed 125 Mbps signal into a physical speed 1.25 Gbps signal by the physical speed increasing means 24. The received signal of the bidirectional communication interface 21.
[0048]
On the other hand, in transmission from the optical communication device 20 to the optical communication device 10, the transmission signal (physical speed 1.25 Gbps) from the bidirectional communication interface 21 is converted into an optical signal by the optical transmitter 22 and transmitted. In the optical receiver 13 of the optical communication device 10, the received optical signal is converted into an electric signal and used as a received signal of the bidirectional communication interface 11.
[0049]
As described above, the optical signal (physical speed 125 Mbps) transmitted from the optical communication apparatus 10 to the optical communication apparatus 20 has a lower physical speed than the optical signal (physical speed 1.25 Gbps) transmitted in the reverse direction. It will be a thing. Thereby, even if one transmission capacity cannot be ensured to the same extent as the other due to some cause, bidirectional communication between optical communication devices is possible.
[0050]
<Second Embodiment of Optical Communication System of the Present Invention>
In the first embodiment, the configuration in which two-way communication is performed using two optical fibers is shown. However, the wavelength of the optical signal is set to be different depending on the direction, and the light of each wavelength is set in each of the optical communication devices 10 and 20. By providing a wavelength demultiplexing filter (WDM filter) that demultiplexes signals, bidirectional communication is possible using a single optical fiber. The configuration is shown in FIG. In FIG. 2, the wavelength division multiplexing filter (WDM filter) 15 of the optical communication apparatus 10 and the wavelength division multiplexing filter (WDM filter) 25 of the optical communication apparatus 20 both have filter characteristics for separating optical signals in respective directions.
[0051]
<Configuration Examples of Physical Speed Lowering Unit 14 and Physical Speed Increasing Unit 24>
The physical speed lowering means 14 and the physical speed increasing means 24 in the first embodiment and the second embodiment described above use, for example, a writing means 41, a memory 42, and a reading means 43 as shown in FIG. Thus, the writing means 41 writes the input signal into the memory 42, temporarily holds it in the memory 42, and the reading means 43 reads the input signal held in the memory 42 at different speeds.
[0052]
Here, an operation example of the physical speed lowering means 14 will be described with reference to FIGS. 3 (b) and 3 (c). When the information to be transmitted is viewed in bit units, the physical speed lowering unit 14 outputs a data string in which the bit widths of the input continuous bit strings are each multiplied as shown in FIG. However, since all of the input information cannot be output as it is, the memory 42 is provided as a buffer so that the information is not lost up to the capacity range of the memory 42.
[0053]
FIG. 3C shows an operation example when the information to be transmitted is viewed in units of packets. The input data packet is written into the memory 42, and the physical speed lowering means 14 outputs a packet that has been scaled in proportion to the bit width of the buffered packet being scaled. When the memory 42 is filled, it is discarded as data packets 4 and 5 in FIG. However, when the widely used TCP / IP (Transmission Control Protocol / Internet Protocol) is used as the upper level protocol, the throughput of data to be sent out is adjusted so that no packet loss occurs in the TCP layer. There is no problem in communication even if is used.
[0054]
The physical speed increasing means 24 performs the reverse operation to the above, and since the output speed is faster, there is no packet loss if there is a memory that can hold one packet of the maximum length.
[0055]
<Third Embodiment of Optical Communication System of the Present Invention>
FIG. 4 shows a third embodiment of the optical communication system of the present invention. Here, in a wavelength division multiplexing access network in which a plurality of user apparatuses 100 and a center apparatus 200 are connected via an optical branching apparatus 56, spectrum slicing technology is used for uplink signal transmission from each user apparatus 100 to the center apparatus 200, and the center A configuration example in which a multi-wavelength collective light source is used to generate a downstream signal from the apparatus 200 to each user apparatus 100 is shown.
[0056]
In FIG. 4, a plurality of user devices 100 and a center device 200 are connected via an optical fiber 31, an optical branching device 56, and an optical fiber 32. Each user apparatus 100 includes a bidirectional communication interface 11, an optical transmitter 12, and an optical receiver 13 that have the same physical speed (in this case, 1.25 Gbps) between the transmission signal and the reception signal. A physical speed lowering means 14 is provided between the transmitter 12 and the physical speed to lower the physical speed from 1.25 Gbps to 125 Mbps. The optical transmitter 12 outputs broadband modulated light obtained by modulating spontaneous emission light with a transmission signal whose physical speed is reduced to 125 Mbps.
[0057]
The center apparatus 200 includes a bidirectional communication interface 21, an optical receiver 23, an optical modulator (M) 26, and a wavelength multiplexing / demultiplexing filter (AWG) that have the same physical speed (here, 1.25 Gbps) between the transmission signal and the reception signal. ) 27-1, 27-2, 27-3 and a multi-wavelength collective light source 28, and further increase the physical speed from 125 Mbps to 1.25 Gbps between the optical receiver 23 and the bidirectional communication interface 21. Means 24 are provided. The wavelength multiplexing / demultiplexing filter 27-1 receives an upstream wavelength multiplexed optical signal that is wavelength-multiplexed after the broadband modulated light transmitted from each user apparatus 100 is spectrally sliced by the optical branching device 56, and this wavelength multiplexed optical signal Are demultiplexed to the optical receiver 23 corresponding to each user apparatus 100. The wavelength multiplexing / demultiplexing filter 27-2 demultiplexes the multi-wavelength light output from the multi-wavelength collective light source 28 into continuous light of each wavelength, and gives it to the optical modulator 26 corresponding to each user device 100. The wavelength multiplexing / demultiplexing filter 27-3 multiplexes the optical signal addressed to each user apparatus 100 modulated by the optical modulator 26, and sends it to the optical branching device 56 as a downstream wavelength multiplexed optical signal.
[0058]
The optical branching device 56 includes wavelength multiplexing / demultiplexing filters (AWGs) 57-1 and 57-2. The wavelength multiplexing / demultiplexing filter 57-1 spectrally slices the broadband modulated light transmitted from each user apparatus 100 at the wavelength assigned to each user apparatus 100, and wavelength-multiplexes the spectrum slice light of each wavelength to the center apparatus 200. Send it out. The wavelength multiplexing / demultiplexing filter 57-2 demultiplexes the downstream wavelength multiplexed optical signal from the center device 200 for each wavelength and sends it to each user device 100.
[0059]
Here, in transmission from the user apparatus 100 to the center apparatus 200, a transmission signal (physical speed 1.25 Gbps) from the bidirectional communication interface 11 is converted into a transmission signal having a physical speed 125 Mbps by the physical speed lowering means 14, and optical transmission is performed. The device 12 converts it into an optical signal and transmits it. For example, a transmission signal (physical speed 1.25 Gbps) from the Gigabit Ethernet interface in the user apparatus 100 is converted into a signal of 125 Mbps which is the physical speed of Fast Ethernet by the physical speed lowering means 14, and the upstream light of 125 Mbps is transmitted from the optical transmitter 12. It is transmitted as a signal (broadband modulated light). In the center apparatus 200, the optical receiver 23 converts the received optical signal into an electrical signal (physical speed 125 Mbps), and the physical speed increasing means 24 converts the received optical signal into a physical speed 1.25 Gbps signal to convert it into a bidirectional communication interface (Gigabit Ethernet interface) ) 21 received signals.
[0060]
On the other hand, in transmission from the center apparatus 200 to the user apparatus 100, a transmission signal (physical speed 1.25 Gbps) from the bidirectional communication interface 21 is input to the optical modulator 26, and output from the multi-wavelength collective light source 28 to be transmitted to the wavelength. Each wavelength light (optical carrier) demultiplexed by the multiplexing / demultiplexing filter 27-2 is modulated and transmitted. In the optical receiver 13 of the user apparatus 100, the received optical signal is converted into an electric signal and used as a received signal of the bidirectional communication interface 11.
[0061]
As described above, the upstream optical signal (physical speed 125 Mbps) transmitted from the user apparatus 100 to the center apparatus 200 has its physical speed reduced compared to the downstream optical signal (physical speed 1.25 Gbps) transmitted in the reverse direction. Therefore, spectral slice optical transmission in which broadband modulated light is sliced as an upstream optical signal is possible.
[0062]
In the user apparatus 100 according to the present embodiment, the bidirectional communication interface 11 is premised on electrical signal connection, but an optical interface may be used. In this case, a separate photoelectric converter may be provided, or the downstream optical signal may be directly connected to the bidirectional communication interface without using the optical receiver 13.
[0063]
Here, for example, if the center apparatus 200 is configured with a HiPAS rack, each component such as an optical transceiver and an AWG is collected in a package and accommodated in the apparatus (frame). Further, in the user apparatus 100, each component may be integrated and mounted on a board in order to reduce the size of the housing. Therefore, the bidirectional communication interface 21, the optical receiver 23, the physical speed increasing unit 24, the optical modulator 26 in the center device 200, or the bidirectional communication interface 11, the optical transmitter 12, the optical receiver 13 in the user device 100, FIG. 4 can also be drawn as shown in FIG. 5 by treating the physical speed lowering means 14 as one package or board and calling them the optical transmission / reception package 61 and the optical transmission / reception package 60, respectively. Note that the structure in which the constituent elements are combined is not limited to the package or board as described above, but encompasses all equivalents (for example, cards and modules). Moreover, you may call a transceiver and an optical transmitter / receiver as a function name.
[0064]
<Fourth Embodiment of Optical Communication System of the Present Invention>
In the third embodiment, the configuration in which the optical fiber is arranged in each of the upstream direction and the downstream direction to perform bidirectional communication is shown. However, the wavelength of the optical signal is set to be different depending on the direction, and the optical signal of each wavelength is set. By using a wavelength demultiplexing filter (WDM filter) that performs demultiplexing, bidirectional communication can be performed with a single optical fiber. A configuration example in this case is shown in FIG. Here, the use band of the upstream optical signal and downstream optical signal is divided into two, and the long wavelength side is used for the downstream optical signal and the short wavelength side is used for the upstream optical signal.
[0065]
In FIG. 6, a wavelength demultiplexing filter (WDM filter) 15 provided in the user apparatus 100 b is a filter that separates broadband modulated light transmitted as an upstream optical signal and a downstream optical signal having a wavelength assigned to each user apparatus 100. It has characteristics (FIG. 8A). The broadband modulated light (λu) transmitted from the optical transmitter 12 is transmitted to the optical fiber 31 via the wavelength demultiplexing filter 15, and the downstream optical signal (λdi (i = 1 to n)) from the optical fiber 31. ) Is received by the optical receiver 13 via the wavelength demultiplexing filter 15 (the wavelength arrangement of the broadband modulated light and the downstream signal light is shown in FIG. 8B).
[0066]
The wavelength demultiplexing filter (WDM filter) 58 provided in the optical branching device 56b and the wavelength demultiplexing filter (WDM filter) 25 provided in the center device 200b are wavelength-multiplexed on the short wavelength side transmitted as an upstream optical signal. It has a filter characteristic (FIG. 8C) for demultiplexing the optical signal (λu1 to λun) and the wavelength multiplexed optical signal (λd1 to λdn) on the long wavelength side transmitted as the downstream optical signal. The upstream wavelength multiplexed optical signal from the optical branching device 56b to the center device 200b is transmitted via the wavelength demultiplexing filter 58 and the optical fiber 32, and is separated from the downstream wavelength multiplexed optical signal by the wavelength demultiplexing filter 25 (upstream signal). The wavelength arrangement of light and downstream signal light is shown in FIG. 8 (d)). The downstream wavelength multiplexed optical signal from the center device 200b to the optical branching device 56b is transmitted through the wavelength demultiplexing filter 25 and the optical fiber 32, and is separated from the upstream wavelength multiplexed optical signal by the wavelength demultiplexing filter 58.
[0067]
In the optical branching device 56 of the third embodiment, the uplink signal and the downlink signal are combined / demultiplexed by the separate wavelength multiplexing / demultiplexing filters 57-1 and 57-2. One wavelength multiplexing / demultiplexing filter 57 combined with the wavelength demultiplexing filter (WDM filter) 58 can cope with this. 7A and 7B show the filter characteristics of the wavelength multiplexing / demultiplexing filter 57 in the upstream direction and the downstream direction.
[0068]
In the center devices of the third embodiment and the fourth embodiment, the uplink signal and the downlink signal are combined / demultiplexed by separate wavelength multiplexing / demultiplexing filters, but the wavelength demultiplexing filter (WDM filter) ) And a single wavelength multiplexing / demultiplexing filter.
[0069]
6 shows the optical modulator 26, the optical transmitter 12, the optical receivers 23 and 13, the bidirectional communication interfaces 21 and 11, the physical speed increasing means 24, and the physical speed decreasing means 14 in the center apparatus 200b and the user apparatus 100b. 9 can be drawn as shown in FIG. Here, in FIG. 9, the upstream signal and the downstream signal are multiplexed / demultiplexed by separate wavelength multiplexing / demultiplexing filters 57-1 and 57-2, and therefore have a filter characteristic that separates the optical signal for each direction. One wavelength demultiplexing filter (WDM filter) 62 is provided between the wavelength multiplexing / demultiplexing filters 57-1 and 57-2 and each user apparatus 100c.
[0070]
<Fifth Embodiment of Optical Communication System of the Present Invention>
FIG. 10 shows a fifth embodiment of the optical communication system of the present invention.
[0071]
In FIG. 10, in the optical communication system of the present embodiment, one center device 200d and a plurality of user devices 100d are connected by one optical fiber 31 and 32 through an optical branching device 56c, respectively, and bidirectional communication is performed. It is the structure to perform. Note that the basic configuration of the network for transmitting downstream optical signals and upstream optical signals is the same as that in FIG. 9 used in the description of the fourth embodiment. However, in this embodiment, in addition to the physical speed increasing means 24 of the center apparatus 200c and the physical speed decreasing means 14 of the user apparatus 100c in FIG. 9, the physical speed decreasing means 14 and the transmission speed controller 70 are provided in the center apparatus 200d. In addition, the physical speed increasing means 24 and the transmission speed controller 70 are provided in the user apparatus 100d. Further, the optical transmitter 71 of each of the center device 200d and the user device 100d is configured to include a semiconductor optical amplifier as an optical modulator.
[0072]
The flow of signals inside each optical communication device (center device 200d or user device 100d) is as follows. The signal (physical speed 1.25 Gbps) taken into each optical communication device via the bidirectional communication interface 11 or 21 is kept at 1.25 Gbps or lowered to 125 Mbps by the physical speed lowering means 14 to the optical transmitter 71. And is converted into an optical signal by the optical transmitter 71 and transmitted to the other optical communication apparatus. At this time, the transmission rate of the signal sent to the optical transmitter 71 is determined by the transmission rate controller 70 based on the physical quantity monitored by the optical transmitter 71. In addition, the physical quantity said here is the power of the optical carrier wave in the optical transmitter 71, for example.
[0073]
On the other hand, the optical signal input to each optical communication device is received as an electrical signal by the broadband optical receiver 72 that can receive signals of a wide range of bit rates. The physical speed at this time is 1.25 Gbps or 125 Mbps, but is converted to 1.25 Gbps by the physical speed increasing means 24 and used as a reception signal of the bidirectional communication interface 11 or 21.
[0074]
As described above, the optical signal transmitted between the optical communication devices can be transmitted at the physical speed of high speed (1.25 Gbps) or low speed (125 Mbps) by the physical speed lowering means 14 or the physical speed increasing means 24. Thereby, even when a high-speed optical signal band cannot be ensured due to some cause, bidirectional communication between optical communication apparatuses is possible.
[0075]
Although the configuration in which bidirectional communication is performed using one optical fiber is shown here, the upstream optical signal and the downstream optical signal may be separated and bidirectional communication may be performed using two optical fibers.
[0076]
The optical transmission / reception packages 60d and 61d of the center device 200d and the user device 100d in FIG. 10 can have the same configuration, and can be realized by, for example, the configuration shown in FIG.
[0077]
The optical transmitter 71 includes a laser light source 80, a light modulator 81 that can emit light, and a driver circuit 82 that drives the light modulator 81. In order to realize a self-luminous optical modulator, for example, a semiconductor optical amplifier may be used. The transmission speed controller 70 includes a power monitor 83 that measures the output power of the laser light source 80 in the optical transmitter 71, and a transmission speed determination circuit 84 that receives the output power measurement signal from the power monitor 83 and determines the transmission speed. Is done. The physical speed lowering means 14 and the physical speed increasing means 24 can be realized by the same configuration (FIG. 3A) as described in the description of the first embodiment.
[0078]
In FIG. 11, the laser light source 80 is incorporated in the optical transmission / reception package 60d (61d), but the laser light source 80 may be disposed outside the optical transmission / reception package.
[0079]
<Operating characteristics when a semiconductor optical amplifier is used as an optical modulator>
Here, operation characteristics when the semiconductor optical amplifier is used as an optical modulator will be described. When a semiconductor optical amplifier is used as an optical modulator, it exhibits different characteristics from other optical modulators. Since the semiconductor optical amplifier is an optical amplifier, 1. 1. having an amplification effect; Noise due to spontaneous emission is generated. For this reason, when the input optical power to the semiconductor optical amplifier is large to some extent, the noise due to spontaneous emission has little effect on the signal transmission characteristics, but when the input optical power decreases, this noise causes signal-to-noise. The ratio (SNR) is degraded. Details of this characteristic will be described quantitatively with reference to FIGS. 12 (a) and 12 (b). In the case where a semiconductor optical amplifier is used as a modulator, it is hereinafter referred to as an SOA modulator.
[0080]
As a transmission system using the SOA modulator, a model including a laser 90, a semiconductor optical amplifier (SOA modulator) 91, an optical filter 92, a transmission path 93, and an optical receiver 94 as shown in FIG. The gain of the SOA modulator 91 is G, and the spontaneous emission coefficient is n_sp, The coefficient of polarization m_pAnd Note that the polarization coefficient is the total number of transverse modes that are guided, and is m for a polarization-dependent SOA modulator that amplifies only the TE polarization component._p = 1, m for polarization independent type_p = 2. Now, assume that such an SOA modulator 91 is driven at a bit rate B [bps] and an extinction ratio ε. Where the optical frequency ν [Hz], optical power P_in It is assumed that continuous light having a single wavelength [W] is incident on the SOA modulator 91 from the laser 90 as an optical carrier wave. At this time, the average number of photons output from the SOA modulator 91 <n_out> If the sign is a mark and a space, respectively
[Expression 1]

It is represented by Note that h is a Planck constant. Here, the first term on the right side of equation (1) represents the amplified signal light, and the second term represents the spontaneous emission light generated by the SOA modulator. Since spontaneous emission light received by the optical receiver 94 has a random phase, the signal light and the spontaneous emission light interfere with each other, or the spontaneous emission lights interfere with each other, and are detected as beat noise. In general, in order to suppress the influence of beat noise, the spontaneous emission light may be reduced using the optical filter 92 before entering the optical receiver 94. The bandwidth of the optical receiver 94 is B_e [Hz], where the full width at half maximum of the transmission spectrum of the optical filter 92 is Δf [Hz], and the section loss of the transmission line 93 is L, the average number of photons input to the optical receiver 94 <n_orin> If the sign is a mark and a space, respectively
[Expression 2]

It is expressed.
[0081]
When such signal light is input to the optical receiver 94 having a quantum efficiency η, the direct current component I of the photocurrent in the mark and space_mAnd I_sIs
[Equation 3]

It is expressed. Note that e represents the elementary amount of electricity. Further, the intensity of the received photocurrent fluctuates due to various noises. In the model of FIG. 12A, as noise components, (I) shot noise, (II) thermal noise of the optical receiver 94, and (III) spontaneous emission light generated by the SOA modulator 91 is a continuous single wavelength. Beat noise generated by interference with light and (IV) beat noise generated by interference with spontaneously emitted light itself can be considered. These noise powers are expressed as the variance of the received photocurrent intensity, and the variance σ in marks and spaces_m ²And σ_s ²Is
[Expression 4]

It is expressed. B_e [Hz] is the bandwidth of the optical receiver 94, R [ohm] is the load resistance of the optical receiver 94, k is the Boltzmann constant, and T is the absolute temperature. The first term on the right side of equations (4-a) and (4-b) is shot noise, the second term is thermal noise, the third term is beat noise due to interference between single-wavelength light and spontaneous emission light, and the fourth term Represents the beat noise between spontaneously emitted lights.
[0082]
The signal-to-noise ratio SNR of the received signal is derived using the above equation. Now, the noise power is equivalent to the noise standard deviation σ expressed by the equations (4-a) and (4-b)._mAnd σ_sSNR is expressed as the average of
[Equation 5]

It is guided.
[0083]
According to the equation (5), the input optical power P to the SOA modulator 91_inWhen is small, it can be seen that beat noise between spontaneously emitted lights is the dominant factor of SNR degradation. In order to suppress the degradation of the SNR, the bandwidth B of the optical receiver 94_eIt can be seen that it should be reduced. This is equivalent to reducing the bit rate at which a signal can be received. Therefore, the transmittable bit rate inferred from the SNR of the output optical signal with respect to the input optical power to the SOA modulator 91 is analytically calculated. To simplify the calculation, the noise generated by the optical receiver 94 (shot noise and thermal noise in equations (4-a) and (4-b)) is ignored, the quantum efficiency is 1, and the extinction ratio is 0. Calculated. Band B of optical receiver 94_eIs equivalent to 0.7 times the bit rate B, and SNR = 200 (10 bit error rate conversion)^-12The input optical power of the SOA modulator 91 necessary to obtain_inThen, using equation (5),
[Formula 6]

It is expressed. As an example of the above formula, gain G = 15 [dB], spontaneous emission coefficient n_sp= 15, polarization coefficient m_pFIG. 12 (b) shows the result of calculation assuming that the transmission spectrum full width at half maximum Δf = 15 [GHz] and the light frequency ν = 200 [THz].
[0084]
When the input optical power is -35 [dBm] or more, the SNR degradation factor is dominated by beat noise due to interference between the signal light and the spontaneous emission light. Therefore, the bit rate that can be transmitted almost in proportion to the input optical power is To increase. On the other hand, when the input optical power is -35 [dBm] or less, the SNR degradation factor is dominated by beat noise due to interference between spontaneously emitted lights. When the input optical power is -50 [dBm] or less, the bit rate that can be transmitted is It settles to a certain value. In such a state where the input optical power to the SOA modulator 91 is low (here, -50 [dBm] or less), it can be considered that the optical signal is transmitted by the spectrum slice technique.
[0085]
Note that the transmittable bit rate given by equation (6) or FIG. 12B is an ideal case where the SOA modulator 91, the optical receiver 94, and the input optical carrier are all ideal. In consideration of all the SNR degradation factors, the noise as in equations (4-a) and (4-b) is obtained, and the relationship of equation (6) may be derived. In addition, when an optical amplifier is used to amplify a signal during transmission of an optical signal, the noise due to the optical amplifier may be calculated in addition to equations (4-a) and (4-b).
[0086]
As described above, it can be seen that the transmission characteristics of the SOA modulator depend on the input light level. That is, if the input optical level to the SOA modulator is monitored, the bit rate that can be transmitted can be inferred, so that the fact that the bit rate of the SOA modulator may be converted according to the input optical level is understood. .
[0087]
The optical transmission / reception package 60d or 61d will be described in detail with reference to FIG. 11. A signal (for example, 1.25 Gbps) from a communication terminal (not shown) such as a server or a client terminal is transmitted to the bidirectional communication interface 11 or 21 (for example, Gigabit Ethernet). And is sent to the memory 42 via the writing means 41 for the transmitted optical signal in the physical speed lowering means 14. At the same time, the transmission speed controller 70 receives the input light level P of the optical modulator (SOA modulator) 81 by the power monitor 83._inThe transmission speed decision circuit 84 monitors the input light level P._inThe physical speed (bit rate) of the transmission optical signal that can be transmitted with respect to is calculated using the equation (6), and the reading means 43 in the physical speed lowering means 14 reads the signal from the memory 42 at the physical speed. Give a control signal. Alternatively, the input light level P using Equation (6) in advance_inThe physical speed (bit rate) of the transmitted optical signal that can be transmitted to the optical modulator 81 is stored in the transmission speed determination circuit 84, and the input optical level P to the optical modulator 81 input from the power monitor 83 is stored._inA control signal indicating the physical speed (bit rate) of the transmitted optical signal corresponding to the above may be given to the reading means 43 in the physical speed lowering means 14. This control signal is, for example, a clock signal. The reading means 43 in the physical speed lowering means 14 reads a signal from the memory 42 in synchronization with the clock signal supplied from the transmission speed controller 70. The signal read from the memory 42 is sent to a driver circuit 82 that drives the optical modulator 81, and the signal read from the memory 42 is converted into an optical signal by the optical modulator 81 and connected by an optical fiber. It is transmitted as a transmission signal to the opposite optical communication device (not shown).
[0088]
Here, the physical speed of the transmitted optical signal determined by the transmission speed controller 70 may be set to take one of the following two values. For example, if the characteristics of the SOA modulator are as shown in FIG. 12B, if the input optical level is −35 dBm or more, the SOA modulator is driven at 1.25 Gbps, which is the physical speed of Gigabit Ethernet, and the input optical power is If it is −35 dBm or less, the SOA modulator may be driven at a fixed transmission speed lower than 430 Mbps, for example, 125 Mbps, which is the physical speed of Fast Ethernet.
[0089]
On the other hand, in order to receive a reception signal input to the optical transmission / reception package shown in FIG. 11 from an optical communication device (not shown) opposed via an optical fiber, the following configuration may be used. As the optical receiver 72, for example, a 3R optical receiver compatible with a multi-bit rate (that is, an optical receiver having Re-shaping, Re-timing, and Re-generating functions) may be used. The optical receiver 72 converts the optical signal into an electrical signal, and also regenerates the clock signal. This clock signal is sent to the writing means 41 in the physical speed increasing means 24, and the writing means 41 writes the electric signal output from the optical receiver 72 in the memory 42 in synchronization with the clock signal. A signal is read from the memory 42 of the physical speed increasing means 24 at the physical speed (1.25 Gbps) of the bidirectional communication interface 11 or 21 by the reading means 43, and sent to the communication terminal via this bidirectional communication interface.
[0090]
By configuring the optical communication system using this embodiment, even if the light source of the optical transmitter or the light source that supplies the optical carrier to the optical transmitter fails, communication between the optical communication devices is continued at a low speed. Can do.
[0091]
<Sixth Embodiment of Optical Communication System of the Present Invention>
FIG. 13 shows a sixth embodiment of the optical communication system of the present invention.
[0092]
The basic configuration of the network for transmitting downstream optical signals and upstream optical signals is the same as that in FIG. 10 used in the description of the fifth embodiment. However, in the present embodiment, in the center apparatus 200e, the multi-wavelength collective light sources 28 and 210 that supply optical carriers to the optical transmission / reception packages 61e and 60e in the center apparatus 200e and the user apparatus 100e are arranged. And an optical branching device 56e, an optical fiber 211 different from the optical fiber 32 through which the downstream optical signal and upstream optical signal are transmitted is provided. The optical branching device 56e includes an AWG 212 that demultiplexes the optical carrier wave. Further, an optical fiber 213 for supplying an optical carrier different from the optical fiber 31 through which the downstream optical signal and upstream optical signal are transmitted is provided between the optical branching device 56e and each user device 100e.
[0093]
The optical transmission / reception packages 61e and 60e in the center apparatus 200e and the user apparatus 100e used in such an optical communication system may be configured as shown in FIG. The optical transmission / reception package of FIG. 14 is substantially the same as that of FIG. 11, but the optical carrier is supplied from a light source provided outside the optical transmission / reception package. The optical coupler 221 is configured by only a self-luminous optical modulator 221 and a driver circuit 82 that drives the optical modulator 221, and an optical coupler that branches an optical carrier wave in two directions and outputs the optical carrier to the optical modulator 221 and the power monitor 83. 11 is different from the configuration of FIG. The signal flow in the optical transmission / reception package is as described in the fifth embodiment.
[0094]
Returning to FIG. 13, the multi-wavelength optical carrier wave transmitted from the multi-wavelength collective light source 28 for downstream signals is demultiplexed by the AWG 27-2, and then a plurality of optical transmission / reception packages 61e in the center device 200e. Are guided to the optical modulator 221 via each optical carrier input port 220 and the optical coupler 222 (FIG. 14). On the other hand, the multi-wavelength optical carrier wave transmitted from the multi-wavelength collective light source 210 for the upstream signal is transmitted to the optical branching device 56e through the optical fiber 211 different from the optical fiber 32 through which the downstream optical signal and upstream optical signal are transmitted. After arriving, the optical signal is demultiplexed into optical carriers of each wavelength by the AWG 212 provided in the optical branching device 56e, and then transmitted through the optical fiber 213 different from the optical fiber 31 through which the downstream optical signal and the upstream optical signal are transmitted. It is sent to the user apparatus 100e and guided to the optical modulator 221 via the optical carrier input port 220 (FIG. 14) of the optical transmission / reception package 60e of each user apparatus 100e.
[0095]
Although FIG. 13 shows a configuration in which the optical branching device 56e includes three AWGs, the AWG 212 that demultiplexes the optical carrier wave may be configured to include two or one AWG that is also used as another AWG. Good.
[0096]
In FIG. 13, the optical fibers 32 and 31 between the center device 200e and the optical branching device 56e for transmitting the downstream optical signal and the upstream optical signal and between the optical branching device 56e and the user device 100e are wavelength division multiplexing filters (WDM). Filter) 25, 58, 62, and 15 are used as one optical fiber, but one optical fiber may be used for each downstream optical signal and upstream optical signal as in FIG. Furthermore, when one optical fiber for signal light is used for each of the upstream optical signal and the downstream optical signal, the optical carrier for the upstream optical signal may be multiplexed and transmitted on the optical fiber for transmitting the downstream signal. In that case, the number of optical fibers between the center device 200e and the optical branching device 56e may be two, and the number of optical fibers between the optical branching device 56e and each user device 100e may be two.
[0097]
By configuring the optical communication system using this embodiment, communication can be continued at a low speed even when the light source of the optical transmitter or the multi-wavelength collective light source fails. Further, even when the light source of the optical transmitter or the wavelength of the multi-wavelength collective light source is shifted, communication can be continued between the center device 200e and each user device 100e at a low speed.
[0098]
<Seventh Embodiment of Optical Communication System of the Present Invention>
FIG. 15 shows a seventh embodiment of an optical transmission system for optical communication.
[0099]
This embodiment is different from FIG. 13 used in the description of the sixth embodiment in that a wavelength variable multi-wavelength light source described below is used instead of the multi-wavelength collective light source. The optical transmission / reception package, the AWG, and the optical fiber in the center device 200f and the user device 100e may have the same configuration (FIG. 13) as that used in the sixth embodiment.
[0100]
The center device 200f includes a wavelength tunable multi-wavelength light source 230 for downstream signals and a wavelength tunable multi-wavelength light source 231 for upstream signals. Each of the wavelength tunable multi-wavelength light sources 230 and 231 includes one or a plurality of wavelength tunable laser light sources 232 that are fewer than the number of user apparatuses 100 connected to the optical communication system of the present embodiment, and their wavelength tunable lasers. It is constituted by a multiplexer 233 that multiplexes and outputs laser beams output from the light source 232. As the multiplexer 233, for example, an optical coupler or the like may be used.
[0101]
The wavelength tunable laser light source 232 incorporated in the wavelength tunable multi-wavelength light sources 230 and 231 is controlled to turn on / off the light output by the control device 234, and the oscillation wavelength is controlled when the light output is "on". The The oscillation wavelength can also be changed dynamically. By setting the optical output of all the wavelength tunable laser light sources 232 to “On”, the wavelength tunable multi-wavelength light sources 230 and 231 generate the same number of optical carriers as the wavelength tunable laser light sources 232 incorporated therein at maximum. Can do.
[0102]
The multi-wavelength optical carrier wave output from the tunable multi-wavelength light source 230 for the downstream signal is demultiplexed into each wavelength by the AWG 27-2 provided in the center device 200f, and the center is output via the output port corresponding to the wavelength. It is guided to the optical modulator 221 from the optical carrier input port 220 (FIG. 14) of the optical transmission / reception package 61e in the device 200, modulated by the optical modulator 221, and sent to the AWG 27-3 for multiplexing. However, since the number of optical carriers distributed to the optical transmission / reception package 61e is smaller than the number of optical transmission / reception packages 61e installed in the center device 200f, the optical carriers are not distributed to all the optical transmission / reception packages 61e. In addition, since the wavelength of the optical carrier transmitted from the wavelength variable multi-wavelength light source 232 may change every moment, the supply of the optical carrier to a certain optical transmission / reception package 61e may be interrupted. In such an optical transmission / reception package 61e to which no optical carrier is supplied, the transmission speed controller 70 provided in the optical transmission / reception package 61e decreases the transmission speed and outputs broadband modulated light. As described above, from each optical transmission / reception package 61e, a downlink signal obtained by modulating a single wavelength optical carrier at a high speed or a downlink signal obtained by modulating a broadband light at a low speed is an AWG27− for multiplexing provided in the center device 200f. 3 is wavelength-multiplexed by the AWG 27-3 and sent to the optical branching device 56e via the optical fiber 32. The optical branching device 56e demultiplexes the wavelength-multiplexed downstream optical signal and sends the downstream optical signal to each user device 100e via the optical fiber 31, and this downstream optical signal is transmitted to the optical receiver 72 of the user device 100e. Received at. The received electrical signal is sent to the bidirectional communication interface 11 via the physical speed increasing means 24 of the user device 100e.
[0103]
On the other hand, the multi-wavelength optical carrier wave output from the wavelength variable multi-wavelength light source 231 for the upstream signal propagates through the optical fibers 211 and 213 different from the optical fibers 32 and 31 through which the modulated signal is transmitted, It is distributed to each user device 100e via the branch device 56e. However, since the optical carrier is not distributed to the optical transmission / reception packages 60e of all the user apparatuses 100e as in the case of the downlink signal, the optical transmission / reception package 60e supplied with the optical carriers transmits the optical carrier to the optical transmitter 71e. In the optical transmission / reception package 60e that is modulated by the optical modulator 221 (FIG. 14) and no optical carrier is supplied, the transmission rate controller 70 provided in the optical transmission / reception package 60e decreases the transmission rate and outputs broadband modulated light. To do. As described above, each optical transmission / reception package transmits an upstream signal obtained by modulating a single wavelength optical carrier at a high speed or an upstream signal obtained by modulating broadband light at a low speed, and is provided in the optical branching device 56e via the optical fiber 31. Is sent to the combined AWG 57-1, and after the upstream signal from each user apparatus 100e is wavelength-multiplexed by the AWG 57-1, it is sent to the center apparatus 200f via the optical fiber 32, and the center apparatus 200f After being demultiplexed to each wavelength by the demultiplexing AWG 27-1, the optical receiver 72 of the optical transmission / reception package 61e receives the signal. The received electrical signal is sent to the bidirectional communication interface 21 via the physical speed increasing means 24 of each optical transmission / reception package 61e.
[0104]
Although FIG. 15 shows a configuration in which the optical branching device 56e includes three AWGs, the AWG 212 that demultiplexes the optical carrier wave may be configured to include two or one AWG that is also used as another AWG. Good.
[0105]
In FIG. 15, the optical fibers between the center device 200f and the optical branching device 56e for transmitting the downstream optical signal and the upstream optical signal and between the optical branching device 56e and the user device 100e are wavelength division multiplexing filters (WDM filters). 25, 58, 62, and 15 are each used as one optical fiber. However, as shown in FIG. 5, one optical fiber may be used for each of the downstream optical signal and the upstream optical signal. Furthermore, when one optical fiber for signal light is used for each of the upstream optical signal and the downstream optical signal, the optical carrier for the upstream optical signal may be multiplexed and transmitted on the optical fiber for transmitting the downstream signal. In that case, the number of optical fibers between the center device 200f and the optical branching device 56e may be two, and the number of optical fibers between the optical branching device 56e and each user device 100e may be two.
[0106]
Further, the number of wavelength tunable laser light sources 232 used in each of the wavelength tunable multi-wavelength light sources 230 and 231 for downstream signals and upstream signals does not need to be the same (that is, the value of j shown in FIG. Value may be different). In FIG. 15, the center apparatus 200f includes the two wavelength variable multi-wavelength light sources 230 and 231 for the downstream optical signal and the upstream optical signal, but only one of them may be the wavelength variable multi-wavelength light source. .
[0107]
Here, the wavelength tunable multi-wavelength light sources 230 and 231 may be configured to dynamically change the wavelength of the optical carrier by the following procedure, for example.
[0108]
The wavelength variable multi-wavelength light sources 230 and 231 and the control device 234 are connected directly using a cable or via a network. The control device 234 is a monitoring signal indicating the state of each of the wavelength tunable laser light sources 232 incorporated in the wavelength tunable multi-wavelength light sources 230 and 231 (light output on / off and oscillation wavelength when the light output is on). Is received from the wavelength variable multi-wavelength light sources 230 and 231, the wavelength of the optical carrier wave transmitted from the wavelength variable multi-wavelength light sources 230 and 231 can be known. Further, the control device 234 sends / receives the optical output of each wavelength tunable laser light source 232 and sends a control signal that can individually and remotely control the oscillation wavelength, so that the wavelength tunable multi-wavelength light sources 230 and 231 are controlled. The oscillation wavelength can be controlled remotely.
[0109]
The control signal from the control device 234 is sent out by the following procedure, for example.
[0110]
An operator terminal (not shown) is connected to the control device 234, and a command such as “give a certain user an optical carrier wave for communication” is input to the control device 234 via the operator terminal. Then, the control device 234 obtains monitoring signals from the wavelength tunable multi-wavelength light sources 230 and 231 and searches for the wavelength tunable laser light source 232 whose light output is cut off. Next, from the correspondence table of each user apparatus 100e stored in the control apparatus 234 and the wavelength of the optical carrier used by the user apparatus 100e, the wavelength of the optical carrier used for communication by the corresponding user apparatus 100e is determined. A control signal is transmitted to the wavelength tunable laser light source 232 so as to oscillate at the wavelength.
[0111]
In the above example, if there is no wavelength tunable laser light source 232 whose light output is cut off, even if one wavelength tunable laser light source is selected at random from the built-in wavelength tunable laser light source 232 and the wavelength is switched, Good. Further, when providing a communication service, priorities may be set in advance for each user apparatus 100e, and the wavelength of the wavelength tunable laser light source 232 used for communication by the user apparatus 100e of the user with a lower priority may be switched. . Further, the data traffic with which each user apparatus 100e is communicating may be monitored in the bidirectional communication interface 21, and the wavelength of the tunable laser light source 232 used for communication by the user apparatus 100e with low data traffic may be switched. .
[0112]
The control signal transmission procedure described above corresponds to, for example, a case where a user who is currently using a low-speed communication service requests a communication carrier to open a higher-speed communication service. In this case, it is possible to provide a service to the user by switching the communication speed of the user device 100e of the corresponding user without changing the configuration of the optical communication device and without interrupting communication.
[0113]
The control signal from the control device 234 may be sent out by another procedure as follows, for example.
[0114]
The control device 234 stores in advance the time that each user device 100e requires an optical carrier wave, and when that time comes, the control device 234 automatically monitors signals from the wavelength tunable multi-wavelength light sources 230 and 231. And search for a tunable laser light source 232 whose optical output is cut off. Next, from the correspondence table of each user device 100e stored in the control device 234 and the wavelength of the optical carrier used by the user device 100e, the wavelength of the optical carrier used by the corresponding user device 100e is determined and searched. A control signal is sent to the tunable laser light source 232 so as to oscillate at that wavelength.
[0115]
In the above example, if there is no tunable laser light source 232 whose light output is cut off, the wavelength of the tunable laser light source 232 being used is forcibly switched in the same procedure as in the previous example. Also good.
[0116]
By using the control signal transmission procedure as described above, a high-speed communication service can be provided for each user for a limited time. For example, a user may use a high-speed communication service from 9:00 to 17:00 of the day and switch to a low-speed service at other times.
[0117]
As yet another example, a control signal from the control device 234 may be transmitted by the following procedure, for example.
[0118]
The communication traffic of each user apparatus 100e is monitored by the bidirectional communication interface 21 or a communication node (such as a switching hub) connected to the bidirectional communication interface 21 so that the information can be sent to the control apparatus 234. Configure (not shown). Such a configuration can be easily realized by using existing technology. The control device 234 stores in advance a threshold for communication traffic that each user device 100e requires an optical carrier wave. When the threshold is exceeded, the control device 234 automatically starts from the wavelength variable multi-wavelength light sources 230 and 231. Are searched for a tunable laser light source 232 whose optical output is cut off. Next, from the correspondence table of each user device 100e stored in the control device 234 and the wavelength of the optical carrier used by the user device 100e, the wavelength of the optical carrier used by the corresponding user device 100e is determined and searched. A control signal is transmitted to the tunable laser light source so as to oscillate at the wavelength.
[0119]
In the above example, if there is no wavelength tunable laser light source whose light output is cut off, the wavelength tunable laser light source 232 being used can be forcibly switched using the same procedure as in the previous example. Good. Contrary to the above, when the communication traffic is equal to or lower than the threshold, the wavelength allocation is canceled and this wavelength is allocated to another user apparatus 100e whose communication traffic exceeds the threshold. good.
[0120]
By using the control signal transmission procedure as described above, it is possible to provide a high-speed communication service according to communication traffic, which is called bandwidth on demand.
[0121]
By configuring the optical communication system using this embodiment as described above, it is not necessary to prepare the same number of light sources as the user apparatus in the center apparatus, so while reducing the number of laser light sources owned by the entire system, It is possible to provide communication at a high bit rate according to the demands of users and communication carriers, and it is possible to provide a high-speed access network at a low cost. Further, even when the wavelength variable multi-wavelength light source fails, communication can be continued at a low speed.
[0122]
In each of the above-described embodiments, an example in which the communication interface is Gigabit Ethernet and the lowered physical speed is the Fast Ethernet physical speed has been described. For example, Gigabit Ethernet or 10 megabit Ethernet may be used as the speed.
[0123]
【The invention's effect】
As described above, according to the present invention, the physical speed of an optical signal in one direction is reduced compared to the other direction between optical communication apparatuses having a bidirectional communication interface in which the physical speeds of a transmission signal and a reception signal are equal. Therefore, bidirectional communication between optical communication devices is possible even when one transmission band cannot be secured to the same extent as the other.
[0124]
In addition, when the present invention is used in a wavelength division multiplexing access network, uplink signal transmission is performed using an interface having a constant physical speed of a transmission signal / reception signal such as Gigabit Ethernet which is a widely used bidirectional communication interface. In addition, the spectrum slicing technique can be used to reduce the cost of the optical communication apparatus, and the downstream signal transmission can realize a wavelength division multiplexing access network that provides a gigabit class speed to meet the user's request.
[0126]
  Further, according to the present invention, when used in a wavelength division multiplexing access network, an uplink / downlink interface is used by using an interface having a constant uplink / downlink physical speed, such as Gigabit Ethernet, which is a widely used bidirectional communication interface. As a result, it is possible to realize a wavelength multiplex access network that can provide a gigabit-class speed at a low cost, and to perform communication at a low speed even when a light source device fails, so that a highly reliable wavelength multiplex access network can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of an optical communication system of the present invention.
FIG. 2 is a block diagram showing a second embodiment of the optical communication system of the present invention.
3A is a block diagram showing a configuration example of the physical speed lowering means 14 and the physical speed increasing means 24, and FIG. 3B is an operation example of the physical speed lowering means 14 when the information to be transmitted is viewed in bits. FIG. 8C is a diagram illustrating an operation example of the physical speed lowering unit 14 when the information to be transmitted is viewed in units of packets.
FIG. 4 is a block diagram showing a third embodiment of the optical communication system of the present invention.
FIG. 5 is a block diagram illustrating a configuration example when an optical transmission / reception package is employed in the third embodiment of the optical communication system of the present invention.
FIG. 6 is a block diagram showing a fourth embodiment of the optical communication system of the present invention.
FIG. 7 is a diagram showing filter characteristics of a wavelength multiplexing / demultiplexing filter (AWG) in the fourth embodiment of the optical communication system of the present invention.
FIGS. 8A and 8B are diagrams showing filter characteristics of a wavelength demultiplexing filter (WDM filter) 15 in the fourth embodiment of the optical communication system of the present invention, and FIGS. It is a figure which shows the filter characteristic of the wavelength demultiplexing filter (WDM filter) 25 and 58 in 4th Embodiment of the optical communication system of invention.
FIG. 9 is a block diagram showing a configuration example when an optical transmission / reception package is employed in the fourth embodiment of the optical communication system of the present invention;
FIG. 10 is a block diagram showing a fifth embodiment of the optical communication system of the present invention.
FIG. 11 is a block diagram illustrating a configuration example of an optical transmission / reception package according to a fifth embodiment.
12A is a block diagram showing a model of a transmission system when a semiconductor optical amplifier is used as a modulator, and FIG. 12B is a relationship between input optical power and the maximum bit rate that can be transmitted in the semiconductor optical amplifier. FIG.
FIG. 13 is a block diagram showing a sixth embodiment of the optical communication system of the present invention.
FIG. 14 is a diagram illustrating a configuration example of an optical transmission / reception package according to a sixth embodiment.
FIG. 15 is a block diagram showing a seventh embodiment of the optical communication system of the present invention.
FIG. 16 is a block diagram illustrating a configuration example of an Ethernet access system.
FIG. 17 is a block diagram illustrating a configuration example of a wavelength division multiplexing access network.
FIG. 18 is a block diagram illustrating a configuration example of a wavelength division multiplexing access network using spectrum slice light.
FIG. 19 is a diagram showing the relationship between broadband modulated light and wavelength-multiplexed spectrum slice light.
FIG. 20 is a diagram for explaining the influence of beat noise in the case of using spectrum slices.
FIG. 21 is a block diagram showing a configuration example of a carrier-supplied wavelength division multiplexing access network.
[Explanation of symbols]
10 Optical communication equipment
11 Bidirectional communication interface
12, 22 Optical transmitter
13, 23 Optical receiver
14 Physical speed lowering means
15 Wavelength demultiplexing filter
20 Optical communication device
21 Two-way communication interface
24 Physical speed increasing means
25 wavelength demultiplexing filter
26 Light modulator
27-1 to 27-3 wavelength multiplexing / demultiplexing filter
28 Multi-wavelength light source
31, 32 Optical fiber
56, 56b-56c, 56e Optical branching device
57, 57-1 to 57-2 wavelength multiplexing / demultiplexing filter
58 wavelength demultiplexing filter
60, 60d, 60e, 61, 61d, 61e optical transmission / reception package
62 Wavelength demultiplexing filter
70 Transmission speed controller
71, 71e Optical transmitter
72 Optical receiver
80 Laser light source
81 Optical modulator
82 Driver circuit
83 Power monitor
84 Transmission rate decision circuit
90 laser
91 Semiconductor optical amplifier
92 Optical filter
93 Transmission path
94 Optical receiver
100, 100a to 100e User device
200, 200a to 200f Center device
210 Multi-wavelength light source
211 optical fiber
212 AWG
213 optical fiber
220 optical carrier input port
221 Optical modulator
222 Optical coupler
230, 231 Tunable multi-wavelength light source
232 Tunable laser light source
233 multiplexer
234 control device

Claims (1)

A user side bidirectional communication interface having the same physical speed of the transmission signal and the reception signal, a user side optical transmitter, a user side optical receiver, and a transmission signal input from the user side bidirectional communication interface are written in a memory, A plurality of user-side optical communication devices each having user-side physical speed lowering means for lowering the physical speed of the transmission signal by reading at a lower speed than the writing speed and outputting it to the user-side optical transmitter;
A center-side bidirectional communication interface having the same physical speed of the transmission signal and the reception signal, a plurality of center-side optical transmitters and a plurality of center-side optical receivers respectively corresponding to the plurality of user-side optical communication devices, A plurality of center-side optical receivers that wavelength-multiplex the optical signal output from the center-side optical transmitter and transmit it as a downstream wavelength-multiplexed optical signal and demultiplex the input upstream wavelength-multiplexed optical signal into each wavelength. Wavelength multiplexing / demultiplexing means to be received by the center side optical receiver, and the received signal received by the center side optical receiver is written into the memory and read out at a higher speed than the writing speed to increase the physical speed of the received signal, thereby causing the center side bidirectional A center side optical communication device having a center side physical speed increasing means for outputting to the communication interface;
The center-side optical communication device and each of the plurality of user-side optical communication devices are connected via at least one optical fiber, and combine the optical signals from the plurality of user-side optical communication devices to Light that is transmitted to the center-side optical communication device as a wavelength-multiplexed optical signal and that is transmitted to the plurality of user-side optical communication devices by demultiplexing the downstream wavelength-multiplexed optical signal from the center-side optical communication device for each wavelength. A branching device;
Comprising
The center-side optical communication device includes multi-wavelength light batch generation means for outputting optical carriers having different wavelengths, and the user-side optical communication device and the center-side optical communication device include an input port to which the optical carrier is input. The user-side optical transmitter and the center-side optical transmitter each include a user-side optical modulator and a center-side optical modulator, and each of the user-side optical modulator and the center-side optical modulator has the multi-wavelength When receiving the optical carrier input from the optical batch generation means through the input port, the optical carrier is modulated to transmit an optical signal, and when the optical carrier supply is interrupted, the user side An optical communication system, wherein the optical modulator and the center side optical modulator itself emit light to transmit an optical signal .

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