JP4211226B2

JP4211226B2 - Multiplex light separation device

Info

Publication number: JP4211226B2
Application number: JP2001059632A
Authority: JP
Inventors: 慎荒平
Original assignee: Oki Electric Industry Co Ltd
Current assignee: Oki Electric Industry Co Ltd
Priority date: 2001-03-05
Filing date: 2001-03-05
Publication date: 2009-01-21
Anticipated expiration: 2021-03-05
Also published as: JP2002258338A

Description

【０００１】
【発明の属する技術分野】
本発明は、複数の光信号列が時分割により多重化されてなる多重光から１つの光信号列を分離するための多重光分離装置に関する。
【０００２】
【従来の技術】
多重光の分離装置の１つに、例えば、S. Kawanishi、その他により、「100Gbit/s all-optical demultiplex using four-wave mixing in a travelling wave laser diode amplifier」、Electron Letter 、第３０巻、第９８１−９８２頁（１９９４年発行）で開示されているような分離装置がある。
この従来の分離装置によれば、波長が相等しい光から成り相互に同一周期の光パルスを含む複数の光信号列を時分割により多重化してなる多重光と、この多重光の波長と異なる波長を有しかつ前記周期と同一周期の励起光を４波混合素子に導き、励起光の周期パルスと前記多重光のいずれかの光信号列の周期パルスとを相互干渉させることにより、前記励起パルス光に重なり合う一つの前記光信号列に対応して前記励起パルス光の波長および前記多重光の波長と異なる波長の波長変換パルス光を生成させることができる。前記多重光および励起パルス光と共に前記４波混合素子から出力される波長変換パルス光は、フィルタを用いて前記励起光および前記多重光から抽出され、これにより、前記多重光の前記一つの光信号列が、これに対応した前記波長変換光として、分離される。
【０００３】
本発明者は、特願平１１−３５１６０１号において、前記４波混合素子として、モード同期半導体レーザを用いることを提案した。このモード同期半導体レーザは、その内部に、複数の光信号列の波長と異なる波長の励起パルス光を前記光信号列の周期と同一周期で生成することができる。また、前記同期半導体レーザは、前記４波混合素子の機能と、前記励起光発生源の機能とを兼ね備えることから、多重光分離装置の構成の簡素化および小型化を図ることができる。
【０００４】
【発明が解決しようとする課題】
ところで、前記したモード同期半導体を用いた多重光分離装置では、前記モード同期半導体レーザは、これに入射する多重光の偏光状態に比較的強い依存性を示すことから、多重光の偏光状態の変化に応じて前記波長変換光の強度が変化する。前記モード同期半導体に案内される多重光は、例えば光通信状況の変化により、光の進行方向を回転軸としてその回りに偏波方向を回転させるが、この偏波方向の回転に応じて、分離された前記波長変換光の強度に変化が見られた。
【０００５】
そこで、本発明の目的は、多重光の偏波方向の変化に拘わらず、分離された光信号列のパルス強度に大きな変化を生じることのない多重光分離装置を提供することにある。
【０００６】
【課題を解決するための手段】
本発明は、以上の点を解決するために、次の構成を採用する。
〈構成〉
本発明は、波長及び周期が同一の複数の光信号列を時分割して多重化して成る多重光から１つの前記光信号列を分離するための多重光分離装置において、前記波長と異なる波長及び前記周期と同一の周期を有する励起パルス光を生成する半導体レーザと、前記多重光を互いに異なる二つの偏光成分に分離する分離手段と、一方の偏光成分を前記半導体レーザの一端に案内入力すると共に他方の偏光成分を前記半導体レーザの他端に前記一方の偏光成分と偏光方向を一致させて案内入力する案内手段と、前記光信号列と前記半導体レーザ内を周回する前記励起パルス光との位相を時間的に一致させるべく該半導体レーザを同期制御し、かつ前記励起パルス光が前記半導体レーザ内を周回して両端に位置するとき前記各偏光成分を混合させるべく各端から入力するタイミングを前記半導体レーザに対して設定する同期設定手段とを含み、前記半導体レーザは、前記周回する励起パルス光に前記両偏光成分が混合されると４波混合して波長変換光を生成して出力する波長変換機能を更に備える多重光分離装置であって、前記案内手段は、光の偏光方向を保持した状態で前記分離手段からの前記光を前記半導体レーザの一方の端面に案内する偏波面保持光ファイバと、該ファイバに設けられ該ファイバ内を案内される一方の前記偏光成分に、前記半導体レーザの他方の端面に案内される他方の前記偏光成分に関して、前記励起パルス光の前記半導体レーザ内の周回周期の半値の遅延を与える光遅延回路と、前記光ファイバから前記半導体レーザの前記一方の端面に向けられる前記一方の偏光成分を前記半導体レーザの前記他方の端面に向けられる前記偏光成分の偏光方向に一致させるためのファラデー回転子とを備え、更に、前記半導体レーザの両端から出力される前記波長変換光の偏光成分を含む両偏光成分を合成する光合成手段と、該光合成手段を経た光から前記波長変換光を抽出するフィルタとを含むことを特徴とする。
【０００７】
〈作用〉
本発明に係る前記分離装置では、前記半導体レーザに案内される前記多重光は、前記分離手段により、２つの偏光成分に分けられ、それぞれが前記半導体レーザ内の前記励起パルス光に同期して前記半導体レーザ内にその両端から入力される。このとき、前記両偏光成分は、相互に偏光方向を一致させた状態で、前記半導体レーザに案内される。
前記半導体レーザは、その両端から案内されたそれぞれの偏光成分と、半導体レーザ内を周回する前記励起パルス光との相互作用により、前記各偏光成分の入力端部と反対側の端部から、それぞれの偏光成分の強度に応じた波長変換パルス光を生成する。各偏光成分に応じて前記半導体レーザの両端から出力された各波長変換パルス光は、前記光合成手段により合成された後、前記フィルタを経ることにより、抽出され、これにより、抽出された波長変換光が、前記多重光からその一つの光信号列として分離される。
【０００８】
本発明に係る前記分離装置によれば、前記したように、前記多重光は２つの偏波光成分に分けられて前記半導体レーザに案内されることから、前記多重光が、その進行方向を回転軸として、その回りに偏光方向を回転させることにより、例えば一方の前記偏光成分が減少しても、この減少分を補償すべく他方の前記偏光成分が増大することから、前記多重光の偏光方向の回転に拘わらず、前記半導体レーザ内に案内される両偏光成分の強度の和は、ほぼ一定の強度に保持される。
従って、前記多重光の偏光方向の回転に拘わらず、両偏光成分と前記励起パルス光との相互作用により生成される波長変換光の強度の変化を抑制することができ、これにより、前記多重光の偏光方向の回転に拘わらず、ほぼ一定強度の波長変換パルス光を抽出することができることから、前記多重光の偏光方向の回転に伴って生じる分離信号列のパルス強度の変化を抑制することが可能となる。
【０００９】
前記半導体レーザの光の入出力端となる前記両端には、該半導体レーザの内部に案内された前記光パルスが反射して外部のそれに重複することを防止するための反射防止処理が施される。
【００１０】
前記案内手段は、光の偏光方向を保持した状態で前記分離手段からの前記光を前記半導体レーザの一方の端面に案内する偏波面保持光ファイバと、該ファイバに設けられ該ファイバ内を案内される一方の前記偏光成分に、前記半導体レーザの他方の端面に案内される他方の前記偏光成分に関して、前記励起パルス光の前記半導体レーザ内における周回周期の半値の遅延を与える光遅延回路と、前記光ファイバから前記半導体の前記一方の端面に向けられる前記一方の偏光成分を前記半導体レーザの前記他方の端面に向けられる前記偏光成分の偏光方向に一致させるためのファラデー回転子とで構成することができる。
【００１１】
前記分離手段は、例えば偏光ビームスプリッタで構成することができる。
【００１２】
前記半導体レーザは、その内部における励起パルス光の発生周期が周回周期の１／偶数を示す偶数次の高調波モード動作で動作する半導体レーザを用いることができる。
この場合、前記半導体レーザの両端に同期的に励起パルス光が存在し得ることから、前記した励起パルス光の周回を待つことなく前記半導体レーザの両端から同期的に前記両偏光成分を入力することができる。従って、前記遅延回路が不要となることから、前記案内手段は、光の偏光面を保持した状態で該光を前記半導体レーザの一方の前記端面に案内する偏波面保持光ファイバと、前記光ファイバから前記半導体の前記一方の端面に向けられる前記偏光成分を前記半導体レーザの他方の端面に向けられる前記偏光成分の偏光面に一致させるためのファラデー回転子とで構成することができる。
【００１３】
また、前記半導体レーザは、同期的に該半導体レーザの両端から互いに反対側の端部に向けての励起パルス光を生成する衝突パルスモードで動作する半導体レーザを用いることができる。
この場合、前記半導体レーザの両端から互いに反対側の端部に向けて同期的に周回する励起パルス光が生成されることから、高調波モード動作の半導体レーザにおけると同様に、前記した励起パルス光の周回を待つことなく前記半導体レーザの両端から同期的に前記両偏光成分を入力することができる。従って、前記遅延回路が不要となることから、前記案内手段は、光の偏光面を保持した状態で該光を前記半導体レーザの一方の前記端面に案内する偏波面保持光ファイバと、前記光ファイバから前記半導体の前記一方の端面に向けられる前記偏光成分を前記半導体レーザの他方の端面に向けられる前記偏光成分の偏光面に一致させるためのファラデー回転子とで構成することができる。
【００１４】
【発明の実施の形態】
以下、本発明を図示の実施の形態について詳細に説明する。
〈具体例１〉
本発明に係る多重光分離装置１０は、図１に示されているように、光時分割多重光１１の分離に用いられる。前記多重光１１は、それぞれが互いに等しい波長λ１を有しかつ相互に等しい繰り返しパルス周期ｆを有する光信号が時分割多重を受けることにより、形成される。図１に示す例では、前記多重光１１の光パルスａ，ｃ，ｅ，ｇおよびｉが１つのチャンネルのパルス信号であり、光パルスｂ，ｄ，ｆおよびｈが他のチャンネルのパルス信号であり、この２つのチャンネルのパルス信号が時間的に交互に挿入されることにより、前記多重光１１が形成されている。
【００１５】
前記多重光分離装置１０は、前記多重光１１に関連した波長変換パルス光を生成するための半導体レーザ１２を含む。
具体例１に示す前記半導体レーザ１２は、受動モード同期機能および能動モード同期機能を兼ね備えた、いわゆるハイブリッドモード同期半導体レーザであり、後述する励起光の反射にブラッグ反射を利用したＤＢＲ（分布反射型：distributed Bragg reflector）半導体レーザである。
【００１６】
前記半導体レーザ１２は、従来よく知られているように、半導体材料から成るｎ型クラッド層１３、ｐ型クラッド層１４および両クラッド層１３および１４間の活性層１５とからなる積層構造を有し、活性層１５には、一対の相等しい回折格子１５ａおよび１５ａ′を間に、一方の回折格子１５ａから他方の回折格子１５ａ′に向けて受動導波路領域１５ｂ、利得領域１５ｃおよび可飽和吸収領域１５ｄが形成されている。
【００１７】
前記ｎ型クラッド層１３の裏面には、接地される共通電極１６が設けられ、また、前記ｐ型クラッド層１４には、各回折格子１５ａ、１５ａ′および各領域１５ｂ〜１５ｄに対応してそれぞれの電極１７ａ、１７ａ、１７ｂ、１７ｃ、１７ｄが形成されている。
両回折格子１５ａおよび１５ａ′に対応する両電極１７ａおよび１７ａには、前記積層構造に順方向電圧を印加するための直流電源１８ａが接続され、また、前記受動導波路領域１５ｂおよび利得領域１５ｃに対応する電極１７ｂおよび１７ｃのそれぞれには、対応するそれぞれの領域１５ｂおよび１５ｃに、順方向電圧を印加するための直流電源１８ｂおよび１８ｃが接続されている。
さらに、可飽和吸収領域１５ｄに対応する電極１７ｄには、前記多重光１１の繰り返しパルス周期ｆに等しい周期を有する交流電源１８ｄと、逆バイアス電源１８ｅとが接続されている。
【００１８】
前記半導体レーザ１２では、従来よく知られているように、順方向電圧が印加される利得領域１５ｃで、前記多重光１１の波長λ１と異なる波長λ２を有する誘導放出光が発生すると、逆バイアスが周期ｆで変化する可飽和吸収領域１５ｄを経ることにより、誘導放出光が部分的に吸収される。また、各回折格子１５ａの格子周期により規定される前記波長λ２の誘導放出光が、活性層１５の両端で選択的に反射されることから、所定の励起パルス光１９が、前記活性層１５内における回折格子１５ａおよび１５ａ′間での周回に伴い、順次、成長する。この波長λ２の励起パルス光１９は、両回折格子１５ａおよび１５ａ′により規定される共振器長（Ｌ）の２倍（２Ｌ）の値で決まる周期であって前記パルス周期ｆにほぼ等しい周期を有する。
前記半導体レーザ１２内を周回する励起パルス光１９の一部は、その両端１２ａおよび１２ｂから、レーザ光として外部に放出される。
【００１９】
各回折格子１５ａおよび１５ａ′に関連して設けられる前記直流電源１８ａの電圧を調整することにより、従来よく知られているように、前記回折格子１５ａおよび１５ａ′の屈折率を変えることができ、これにより、励起パルス光１９の波長λ２を微調整することができる。
また、可飽和吸収領域１５ｄに関連して設けられる周期ｆの交流電源１８ｄにより、周期ｆで繰り返される励起パルス光１９の安定化を図ることができ、また、その位相を調整することにより、前記励起パルス光列の位相を調整することができる。すなわち、交流電源１８ｄの位相の調整により、前記励起パルス光１９の列を時間軸上で全体的にシフトさせることができる。前記導波路領域１５ｂに関連して設けられた直流電源１８ｂの電圧の調整によっても、前記励起パルス光列の位相を調整することができる。
【００２０】
前記多重光１１は、図示の例では、３つの入出力端を有するいわゆる３ポート光サーキュレータ２０を経て、分離手段２１に案内され、該分離手段により、２つの偏光成分に分けられた後、案内手段２２により、それぞれの偏光成分が前記半導体レーザ１２の両端１２ａおよび１２ｂから、該レーザの内部に案内される。
【００２１】
分離手段２１は、例えば偏光ビームスプリッタからなり、図示の例では、光に対する可逆作用により、後述する合波手段の機能を兼ね備える。前記多重光１１のうち、前記スプリッタ２１により分離された一方の偏光成分は、図２に示されているように、例えば垂直面に沿った偏光面を有するＳ偏光成分であり、この一方の偏光成分であるＳ偏光成分は、その偏光面を保持する導波路として機能する偏波面保持光ファイバ２２ａ経て、前記半導体レーザ１２の前記一端１２ａに案内される。
【００２２】
偏波面保持光ファイバ２２ａには、該ファイバを経る前記Ｓ偏光成分に所定の時間遅延を与えるための光遅延回路２２ｂおよび前記Ｓ偏光成分の偏光面を光の進行方向の回りに９０度回転させるためのファラデー回転子２２ｃが設けられている。前記Ｓ偏光成分は、光遅延回路２２ｂを経ることにより、所定の時間遅れを与えられた後、ファラデー回転子２２ｃを経ることにより、偏光面を９０度回転させ、その後、光結合レンズ２２ｄを経ることにより、効率的に、前記半導体レーザ１２内に照射される。
【００２３】
前記多重光１１のうち、前記スプリッタ２１により分離された他方の偏光成分は、図３に示されているように、例えばＳ偏光成分の偏光面と直角な偏光面を有するＰ偏光成分であり、該Ｐ偏光成分は、偏光面を維持した状態で光結合レンズ２２ｅを経ることにより、効率的に、前記半導体レーザ１２の他端１２ｂからその内部に照射される。
前記前記半導体レーザ１２の両端１２ａおよび１２ｂから内部に入射する両偏光成分の内部反射を防止するための反射防止膜２３がその両端１２ａおよび１２ｂに設けられている。反射防止膜２３からなる反射防止処理により、光信号の無信号部分への転移による信号化け、すなわち「０」信号が「１」信号に化けることを確実に防止することができる。
【００２４】
前記スプリッタ２１からの前記Ｐ偏光成分が前記半導体レーザ１２にその前記他端から入射するとき、前記光ファイバ２２ａおよびファラデー回転子２２ｃを含む前記案内手段２２を経る前記Ｓ偏光成分は、その偏波面を前記ファラデー回転子２２ｃによる回転により前記Ｐ偏光成分のそれに一致させかつ前記光遅延回路２２ｂにより、前記Ｐ偏光成分に関して、前記励起パルス光１９の前記周回周期の半値の時間遅延を以て、前記半導体レーザ１２の前記一端に入射される。
【００２５】
従って、例えば前記多重光１１のうち、光パルスａ，ｃ，ｅ，ｇおよびｉを含むチャンネルの光パルス信号列１１ａと前記半導体レーザ１２内を周回する前記励起パルス光との位相が時間的に一致するように前記半導体レーザ１２が動作されている場合、符号１９で示されているように、前記励起パルス光が前記半導体レーザ１２の前記他端にあるとき、前記多重光１１の前記光パルスの前記Ｐ偏光成分が前記他端に入力され、前記所定の時間遅れを以て、この励起パルス光が図１に符号１９′を付して示されているように、前記半導体レーザ１２の前記一端に位置するとき、前記Ｐ偏光成分に偏波面を一致させた前記Ｓ偏光成分が前記半導体レーザ１２の前記一端からその内部に入射する。
【００２６】
従って、前記多重光１１の前記Ｓ偏光成分およびＰ偏光成分は、その偏光面を一致させた状態で、前記半導体レーザ１２内を周回する前記励起パルス光（１９および１９′）に同期して前記半導体レーザ１２の両端１２ａおよび１２ｂからその内部に照射される。
【００２７】
波長λ２を有する励起パルス光（１９および１９′）を周回させる前記半導体レーザ１２内に、波長λ１を有する前記両偏光成分が入射すると、いわゆる４波混合作用により、前記両波長λ１およびλ２と波長を異にする波長変換光が生じる。
この波長変換光のうち、Ｐ偏光波と前記励起パルス光１９との相互作用により起生する波長変換光は、前記半導体レーザ１２の前記一端から前記光結合レンズ２２ｄ、前記ファラデー回転子２２ｃおよび前記光遅延回路２２ｂを有する前記案内手段２２を経て、前記スプリッタ２１に案内される。このとき、前記波長変換光は、前記ファラデー回転子２２ｃにより、その偏光面を９０度回転させられる。
【００２８】
他方、Ｓ偏光波と前記励起パルス光１９′との相互作用により起生する波長変換光は、前記半導体レーザ１２の前記他端から前記光結合レンズ２２ｅを経て、前記スプリッタ２１に案内される。
前記スプリッタ２１は、光の可逆作用により、それぞれの偏光成分に基づく両波長変換光を合成して前記サーキュレータ２０に返す。前記スプリッタ２１により合成されて前記サーキュレータ２０に案内される光には、前記した波長変換光に加えて、前記半導体レーザ１２から放射される波長λ２を有する前記励起パルス光および前記半導体レーザ１２を透過する波長λ１を有する前記多重光１１が含まれる。しかしながら、波長λ３を有する波長変換光の通過を許す波長フィルタ２４により、所定のチャンネルの光パルス信号列１１ａ（例えばａ、ｃ、ｅ、ｇおよびｉ）に同期的に生成される波長変換光が分離されることから、実質的に、前記多重光１１から所定のチャンネルの光パルスを分離することができる。
【００２９】
例えば、前記サーキュレータ２０から前記スプリッタ２１に至る前記多重光１１に時間遅延を与え、あるいは前記したように交流電源１８ｄの位相を変化させることにより、前記半導体レーザ１２内の前記励起パルス光１９に同期する前記多重光１１のチャンネルを選択することができ、これにより、分離すべき光信号のチャンネルの切り換えを実現することができる。
【００３０】
本発明に係る前記多重光分離装置では、前記したように、前記半導体レーザ１２内の前記励起パルス光１９に相互作用させる前記多重光１１は、Ｓ偏光成分およびＰ偏光成分に分離された後、前記案内手段２２により、相互に偏光面を一致させて前記半導体レーザ１２内にその両端から照射され、前記励起パルス光１９都の相互作用により生成されるそれぞれの偏光成分による前記波長変換光は、前記スプリッタ２１により合成された後、前記波長フィルタ２４により、他の波長を有する光信号から分離される。
【００３１】
従って、前記多重光１１がその偏波面を回転させることにより、前記Ｓ偏光成分およびＰ偏光成分のそれぞれに強度変化が生じても、それぞれの偏波成分が前記励起パルス光１９との相互作用に寄与しており、両偏光成分強度の和に対応した強度の波長変換光が得られることから、前記多重光１１の偏波面の回転によっても、波長変換光の強度に従来のような大きな変化は生じることなく、安定した強度の波長変換光を得ることができる。
【００３２】
図１の具体例１に沿って説明したところでは、前記スプリッタ２１が前記多重光１１をそれぞれの偏光成分に分離し、また波長変換光のそれぞれの偏光成分を合成する例を示した。この例に代えて、前記半導体レーザ１２を間に、前記スプリッタ２１と反対の側で波長変換光の偏光成分を合成するための光合成手段を前記スプリッタ２１とは別に設けることができる。
【００３３】
また、前記交流電源１８ｄが前記多重光１１の各チャンネルの光パルスの繰り返し周期ｆにほぼ等しい周期ｆを有する例を示したが、これに代えて、前記半導体レーザ１２を高調波モードで動作させることができる。この高調波モードでは、前記交流電源１８ｄは前記光パルスの繰り返し周期ｆの１／偶数倍２ｎｆ（ｎは、正の整数）に設定されることから、図１に示したように、前記半導体レーザ１２の前記他端１２ｂに前記励起パルス光１９が存在するとき、この励起パルス光の周回を待つことなく、前記一端１２ａに前記励起パルス光１９′を存在させることができる。
【００３４】
従って、前記半導体レーザ１２を高調波モードで動作させることにより、前記光ファイバ２２ａを経て前記一端１２ａに案内される前記Ｓ偏光成分に前記した時間遅延を与えることなく、該Ｓ偏光成分および前記Ｐ偏光成分のそれぞれを前記励起パルス光１９′および前記励起パルス光１９に同時的に作用させることができることから、前記案内手段２２に前記光遅延回路２２ｂを設けることなく、前記Ｓ偏光成分および前記Ｐ偏光成分のそれぞれを前記励起パルス光に効果的に作用させることができ、これにより、前記したと同様に、安定した強度の波長変換光を得ることができることに加えて、構成の一層の簡素化を図ることが可能となる。
【００３５】
〈具体例２〉
図４に示す多重光分離装置１０では、半導体レーザとして、衝突パルスモードで動作する半導体レーザ５２が用いられている。図４に示された前記多重光分離装置１０の具体例１におけると同様な機能部分には、これと同一の参照符号が付されている。
衝突パルスモード動作の半導体レーザ５２は、従来よく知られているように、活性層１５の中央部には、可飽和吸収領域１５ｄが設けられ、該可飽和吸収領域に関して対称的となるように、前記半導体レーザ５２の両端１２ａおよび１２ｂへ向けて、利得領域１５ｃ、受動導波路領域１５ｂおよび回折格子１５ａ、１５ａ′がそれぞれ配置されている。前記ｎ型クラッド層１３には、前記したと同様な共通電極１６が設けられ、また前記ｐ型クラッド層１４には、各領域１５ａ、１５ａ′、１５ｂ、１５ｂ、１５ｃ、１５ｃおよび１５ｄに対応して、それぞれ前記した各電源に接続される電極１７ａ、１７ａ、１７ｂ、１７ｂ、１７ｃ、１７ｃおよび１７ｄが設けられている。
【００３６】
前記半導体レーザ５２では、従来よく知られているように、活性層１５の中央部の可飽和吸収領域１５ｄを間に、各利得領域１５ｃ、受動導波路領域１５ｂおよび回折格子１５ａ、１５ａ′がそれぞれ対称的に配置されていることから、前記半導体レーザの両端から互いに反対側の端部に向けて同期的に周回する励起パルス光１９および１９′が生成される。
半導体レーザ５２の両端には、内部反射を防止するための前記したと同様な反射防止膜２３が設けられている。
【００３７】
前記半導体レーザ５２を含む多重光分離装置１０によれば、前記半導体レーザの両端から互いに反対側の端部に向けて同期的に周回する励起パルス光１９および１９′が生成されることから、具体例１の変形例として説明した高調波モード動作の半導体レーザにおけると同様に、前記した励起パルス光の周回を待つことなく前記半導体レーザの両端から同期的に前記両偏光成分を入力することができる。従って、前記遅延回路が不要となり、前記案内手段２２に前記光遅延回路２２ｂを設けることなく、前記Ｓ偏光成分および前記Ｐ偏光成分のそれぞれを前記励起パルス光１９および励起パルス光１９′に効果的に作用させることができ、これにより、前記したと同様に、安定した強度の波長変換光を得ることができることに加えて、構成の一層の簡素化を図ることが可能となる。
【００３８】
前記した前記半導体レーザとして、前記したハイブリッドモード同期ＤＢＲレーザに拘わらず、能動モード同期レーザあるいは受動モード同期レーザ等の種々のモード同期レーザを適用することができる。
【００３９】
【発明の効果】
本発明に係る前記多重光分離装置では、前記したように、２つの偏波光成分に分けられた前記多重光がそれぞれの偏波方向を一致させて前記半導体レーザに案内されることから、たとえ前記多重光がその進行方向を回転軸として、その回りに偏光方向を回転させても、前記半導体レーザ内に案内される多重光の強度すなわち両偏光成分の強度の和は、ほぼ一定の強度に保持される。
【００４０】
従って、本発明によれば、両偏光成分と前記励起パルス光との相互作用により生成される波長変換光の強度の変化を抑制することができることから、前記多重光の偏光方向の回転に拘わらず、ほぼ一定強度の波長変換パルス光を抽出することができ、これにより、前記多重光の偏光方向の回転に伴って生じる分離信号列のパルス強度の変化を抑制することが可能となる。
【図面の簡単な説明】
【図１】本発明に係る多重光分離装置の具体例１を概略的に示す図面である。
【図２】図１に示した線II−IIに沿って得られた一方の偏光成分の偏波状態を示す断面図である。
【図３】図１に示した線III−IIIに沿って得られた他方の偏光成分の偏波状態を示す断面図である。
【図４】本発明に係る多重光分離装置の具体例２を概略的に示す図面である。
【符号の説明】
１０多重光分離装置
１１多重光
１１ａ波長変換パルス光
１２、５２半導体レーザ
１９、１９′ 励起パルス光
２１（分離手段および合成手段）偏光ビームスプリッタ
２２（２２ａ、２２ｂ、２２ｃ）案内手段
２４フィルタ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multiplexed optical demultiplexing device for separating one optical signal sequence from multiplexed light obtained by multiplexing a plurality of optical signal sequences by time division.
[0002]
[Prior art]
For example, S. Kawanishi et al., "100 Gbit / s all-optical demultiplex using four-wave mixing in a traveling wave laser diode amplifier", Electron Letter, Vol. 30, Vol. 981 There are separation devices as disclosed on page -982 (issued in 1994).
According to this conventional separation device, a multiplexed light obtained by multiplexing a plurality of optical signal sequences composed of light having the same wavelength and containing optical pulses having the same period, and a wavelength different from the wavelength of the multiplexed light. And pumping the pumping light having the same cycle as the cycle to the four-wave mixing element, and causing the periodic pulse of the pumping light and the periodic pulse of one of the optical signal trains of the multiplexed light to interfere with each other. Corresponding to one optical signal train overlapping with light, wavelength-converted pulse light having a wavelength different from the wavelength of the excitation pulse light and the wavelength of the multiplexed light can be generated. The wavelength-converted pulse light output from the four-wave mixing element together with the multiplexed light and the pump pulse light is extracted from the pump light and the multiplexed light using a filter, whereby the one optical signal of the multiplexed light is extracted. The columns are separated as the corresponding wavelength converted light.
[0003]
The present inventor proposed in Japanese Patent Application No. 11-351601 to use a mode-locked semiconductor laser as the four-wave mixing element. This mode-locked semiconductor laser can generate pumping pulse light having a wavelength different from the wavelengths of the plurality of optical signal trains in the same period as that of the optical signal trains. Further, since the synchronous semiconductor laser has both the function of the four-wave mixing element and the function of the pumping light generation source, the configuration of the demultiplexing device can be simplified and downsized.
[0004]
[Problems to be solved by the invention]
By the way, in the demultiplexing device using the mode-locked semiconductor described above, the mode-locked semiconductor laser exhibits a relatively strong dependence on the polarization state of the multiplexed light incident thereon, and therefore the change in the polarization state of the multiplexed light. The intensity of the wavelength-converted light changes according to. The multiplexed light guided to the mode-locked semiconductor rotates the polarization direction around the light traveling direction as a rotation axis due to, for example, a change in the optical communication status, and is separated according to the rotation of the polarization direction. A change was observed in the intensity of the converted wavelength light.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a multiplexed optical demultiplexing device that does not cause a large change in the pulse intensity of a separated optical signal train regardless of the change in the polarization direction of the multiplexed light.
[0006]
[Means for Solving the Problems]
The present invention adopts the following configuration in order to solve the above points.
<Constitution>
The present invention relates to a multiplex optical demultiplexer for separating one optical signal sequence from multiplexed light obtained by time-division multiplexing a plurality of optical signal sequences having the same wavelength and period, and a wavelength different from the wavelength, A semiconductor laser that generates pumping pulse light having the same period as the period, a separating unit that separates the multiplexed light into two different polarization components, and one polarization component is guided and input to one end of the semiconductor laser. Guiding means for guiding and inputting the other polarization component to the other end of the semiconductor laser so that the polarization direction of the one polarization component coincides The semiconductor laser is synchronously controlled so as to temporally match the phases of the optical signal train and the excitation pulse light circulating in the semiconductor laser, and When the excitation pulse light circulates in the semiconductor laser and is positioned at both ends, the polarization components should be mixed. Each The timing to input from the end For the semiconductor laser The semiconductor laser further includes a wavelength conversion function for generating and outputting wavelength-converted light by mixing four waves when the two polarized components are mixed with the circulating excitation pulse light. In the multiple light separating device, the guiding means guides the light from the separating means to one end face of the semiconductor laser while maintaining the polarization direction of the light, and a polarization plane holding optical fiber, The one of the polarization components provided in the fiber and guided in the other end surface of the semiconductor laser with respect to the other polarization component guided in the fiber has a cycle period of the pump pulse light in the semiconductor laser. Half An optical delay circuit for delaying the value, and the optical fiber to the semiconductor laser A Faraday rotator for causing the one polarization component directed to the one end face of the semiconductor laser to coincide with the polarization direction of the polarization component directed to the other end face of the semiconductor laser. And a light combining unit that combines both polarization components including the polarization component of the wavelength converted light output from both ends of the semiconductor laser, and a filter that extracts the wavelength converted light from the light that has passed through the light combining unit. It is characterized by that.
[0007]
<Action>
In the separation device according to the present invention, the multiplexed light guided to the semiconductor laser is divided into two polarization components by the separation means, each of which is synchronized with the excitation pulse light in the semiconductor laser. Input from both ends of the semiconductor laser. At this time, the two polarization components are guided to the semiconductor laser in a state in which the polarization directions coincide with each other.
The semiconductor laser has an interaction between each polarization component guided from both ends thereof and the excitation pulsed light that circulates in the semiconductor laser, respectively, from the end opposite to the input end of each polarization component, respectively. Wavelength-converted pulsed light corresponding to the intensity of the polarized light component is generated. Each wavelength conversion pulse light outputted from both ends of the semiconductor laser in accordance with each polarization component is extracted by passing through the filter after being synthesized by the light synthesizing means, and thereby extracted wavelength converted light. Are separated from the multiplexed light as one optical signal train.
[0008]
According to the separation device of the present invention, as described above, since the multiplexed light is divided into two polarized light components and guided to the semiconductor laser, the traveling direction of the multiplexed light is a rotation axis. By rotating the polarization direction around it, for example, even if one of the polarization components decreases, the other polarization component increases to compensate for this decrease, so that the polarization direction of the multiplexed light Regardless of the rotation, the sum of the intensities of both polarization components guided into the semiconductor laser is maintained at a substantially constant intensity.
Therefore, regardless of the rotation of the polarization direction of the multiplexed light, it is possible to suppress a change in the intensity of the wavelength-converted light generated by the interaction between both polarization components and the excitation pulse light. Since the wavelength-converted pulsed light having a substantially constant intensity can be extracted regardless of the rotation of the polarization direction, it is possible to suppress the change in the pulse intensity of the separated signal sequence caused by the rotation of the polarization direction of the multiplexed light. It becomes possible.
[0009]
Antireflection treatment is performed on the both ends, which are the input / output ends of the light of the semiconductor laser, to prevent the light pulse guided inside the semiconductor laser from being reflected and overlapping with the outside. .
[0010]
The guide means is a polarization-maintaining optical fiber that guides the light from the separation means to one end face of the semiconductor laser while maintaining the polarization direction of light, and is guided in the fiber. The other one polarization component guided to the other end surface of the semiconductor laser is related to the other one polarization component of the excitation pulse light in the cycle period in the semiconductor laser. Half An optical delay circuit for delaying the value, and the one polarization component directed from the optical fiber toward the one end surface of the semiconductor is made to coincide with the polarization direction of the polarization component directed toward the other end surface of the semiconductor laser For the Faraday rotator.
[0011]
The separating means can be constituted by a polarizing beam splitter, for example. Ru .
[0012]
In the semiconductor laser, the generation period of the excitation pulse light in the semiconductor laser is Lap Periodic 1 / Even Number Show Even order A semiconductor laser operating in harmonic mode operation can be used.
In this case, since the excitation pulse light can exist synchronously at both ends of the semiconductor laser, both the polarization components are input synchronously from both ends of the semiconductor laser without waiting for the circulation of the excitation pulse light. Can do. Accordingly, since the delay circuit is unnecessary, the guide means maintains the polarization plane of light and guides the light to one of the end faces of the semiconductor laser, and the optical fiber. To a Faraday rotator for matching the polarization component directed to the one end face of the semiconductor with the polarization plane of the polarization component directed to the other end face of the semiconductor laser.
[0013]
Further, as the semiconductor laser, a semiconductor laser that operates in a collision pulse mode that generates excitation pulse light from both ends of the semiconductor laser toward opposite ends can be used.
In this case, pumping pulse light that circulates synchronously from both ends of the semiconductor laser toward opposite ends is generated. Therefore, as in the semiconductor laser operating in the harmonic mode, the pumping pulse light described above is used. Both polarization components can be input synchronously from both ends of the semiconductor laser without waiting for the rotation of the semiconductor laser. Accordingly, since the delay circuit is unnecessary, the guide means maintains the polarization plane of light and guides the light to one of the end faces of the semiconductor laser, and the optical fiber. To a Faraday rotator for matching the polarization component directed to the one end face of the semiconductor with the polarization plane of the polarization component directed to the other end face of the semiconductor laser.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
<Specific example 1>
The demultiplexing device 10 according to the present invention is used for demultiplexing the optical time-division multiplexed light 11 as shown in FIG. The multiplexed light 11 is formed by time-division multiplexing of optical signals each having the same wavelength λ1 and having the same repetitive pulse period f. In the example shown in FIG. 1, the optical pulses a, c, e, g and i of the multiplexed light 11 are pulse signals of one channel, and the optical pulses b, d, f and h are pulse signals of other channels. Yes, the multiplexed light 11 is formed by alternately inserting the pulse signals of these two channels in terms of time.
[0015]
The demultiplexing device 10 includes a semiconductor laser 12 for generating wavelength-converted pulse light related to the demultiplexed light 11.
The semiconductor laser 12 shown in the first specific example is a so-called hybrid mode-locked semiconductor laser that has both a passive mode-locking function and an active mode-locking function, and is a DBR (distributed reflection type) that uses Bragg reflection to reflect excitation light to be described later. : Distributed Bragg reflector) semiconductor laser.
[0016]
As is well known, the semiconductor laser 12 has a laminated structure including an n-type cladding layer 13 made of a semiconductor material, a p-type cladding layer 14 and an active layer 15 between the cladding layers 13 and 14. In the active layer 15, a passive waveguide region 15b, a gain region 15c, and a saturable absorption region are provided with a pair of identical diffraction gratings 15a and 15a 'interposed therebetween and from one diffraction grating 15a to the other diffraction grating 15a'. 15d is formed.
[0017]
A common electrode 16 that is grounded is provided on the back surface of the n-type clad layer 13, and the p-type clad layer 14 corresponds to the diffraction gratings 15 a and 15 a ′ and the regions 15 b to 15 d, respectively. Electrodes 17a, 17a, 17b, 17c, and 17d are formed.
Both electrodes 17a and 17a corresponding to both diffraction gratings 15a and 15a 'are connected to a DC power source 18a for applying a forward voltage to the laminated structure, and to the passive waveguide region 15b and the gain region 15c. DC power supplies 18b and 18c for applying a forward voltage are connected to the corresponding regions 15b and 15c, respectively, to the corresponding electrodes 17b and 17c.
Further, an AC power source 18d having a period equal to the repetitive pulse period f of the multiplexed light 11 and a reverse bias power source 18e are connected to the electrode 17d corresponding to the saturable absorption region 15d.
[0018]
In the semiconductor laser 12, as is well known in the art, when stimulated emission light having a wavelength λ2 different from the wavelength λ1 of the multiplexed light 11 is generated in the gain region 15c to which a forward voltage is applied, a reverse bias is generated. Stimulated emission light is partially absorbed by passing through the saturable absorption region 15d that changes in the period f. Further, since the stimulated emission light having the wavelength λ 2 defined by the grating period of each diffraction grating 15 a is selectively reflected at both ends of the active layer 15, a predetermined excitation pulse light 19 is generated in the active layer 15. In turn, the crystal grows sequentially with the rotation between the diffraction gratings 15a and 15a '. The excitation pulsed light 19 having the wavelength λ2 has a period determined by a value twice (2L) the resonator length (L) defined by both diffraction gratings 15a and 15a ′, and has a period substantially equal to the pulse period f. Have.
A part of the excitation pulse light 19 that circulates in the semiconductor laser 12 is emitted to the outside as laser light from both ends 12a and 12b.
[0019]
By adjusting the voltage of the DC power supply 18a provided in association with each of the diffraction gratings 15a and 15a ', the refractive index of the diffraction gratings 15a and 15a' can be changed, as is well known in the art. Thereby, the wavelength λ2 of the excitation pulse light 19 can be finely adjusted.
Further, the AC power source 18d having a period f provided in association with the saturable absorption region 15d can stabilize the excitation pulsed light 19 repeated in the period f, and by adjusting the phase thereof, The phase of the excitation pulse beam can be adjusted. That is, by adjusting the phase of the AC power supply 18d, the column of the excitation pulsed light 19 can be entirely shifted on the time axis. The phase of the excitation pulse light train can also be adjusted by adjusting the voltage of the DC power supply 18b provided in association with the waveguide region 15b.
[0020]
In the illustrated example, the multiplexed light 11 is guided to a separation means 21 through a so-called three-port optical circulator 20 having three input / output terminals, and is divided into two polarization components by the separation means, and then guided. By means 22, the respective polarization components are guided from both ends 12 a and 12 b of the semiconductor laser 12 into the laser.
[0021]
The separating means 21 is composed of, for example, a polarization beam splitter. In the illustrated example, the separating means 21 also has a function of a multiplexing means described later by a reversible action on light. Of the multiplexed light 11, one polarization component separated by the splitter 21 is, for example, an S polarization component having a polarization plane along a vertical plane, as shown in FIG. The S-polarized component, which is a component, is guided to the one end 12a of the semiconductor laser 12 through the polarization-maintaining optical fiber 22a that functions as a waveguide that retains the polarization plane.
[0022]
In the polarization-maintaining optical fiber 22a, the optical delay circuit 22b for giving a predetermined time delay to the S-polarized component passing through the fiber and the polarization plane of the S-polarized component are rotated 90 degrees around the light traveling direction. A Faraday rotator 22c is provided. The S-polarized component is given a predetermined time delay by passing through the optical delay circuit 22b, and then passes through the Faraday rotator 22c to rotate the polarization plane by 90 degrees, and then passes through the optical coupling lens 22d. As a result, the semiconductor laser 12 is efficiently irradiated.
[0023]
Of the multiplexed light 11, the other polarization component separated by the splitter 21 is, for example, a P polarization component having a polarization plane perpendicular to the polarization plane of the S polarization component, as shown in FIG. The P-polarized component is efficiently irradiated from the other end 12b of the semiconductor laser 12 to the inside through the optical coupling lens 22e while maintaining the polarization plane.
Antireflection films 23 are provided at both ends 12a and 12b for preventing internal reflection of both polarization components incident on both ends 12a and 12b of the semiconductor laser 12. By the antireflection process comprising the antireflection film 23, it is possible to reliably prevent the signal from being changed due to the transition of the optical signal to the non-signal portion, that is, the “0” signal being changed to the “1” signal.
[0024]
When the P-polarized component from the splitter 21 enters the semiconductor laser 12 from the other end, the S-polarized component passing through the guiding means 22 including the optical fiber 22a and the Faraday rotator 22c has its polarization plane. By the rotation by the Faraday rotator 22c, and the optical delay circuit 22b causes the semiconductor laser to have a time delay of half the rotation period of the pump pulse light 19 with respect to the P-polarized component by the optical delay circuit 22b. 12 is incident on the one end.
[0025]
Therefore, for example, the phase of the optical pulse signal sequence 11a of the channel including the optical pulses a, c, e, g and i in the multiplexed light 11 and the pumping pulse light circulating in the semiconductor laser 12 is temporally changed. When the semiconductor laser 12 is operated so as to coincide, when the pump pulse light is at the other end of the semiconductor laser 12, as shown by reference numeral 19, the optical pulse of the multiplexed light 11 The P-polarized component is input to the other end, and with the predetermined time delay, the excitation pulse light is applied to the one end of the semiconductor laser 12 as shown by reference numeral 19 'in FIG. When positioned, the S-polarized component whose plane of polarization coincides with the P-polarized component enters the semiconductor laser 12 from the one end thereof.
[0026]
Therefore, the S-polarized component and the P-polarized component of the multiplexed light 11 are synchronized with the excitation pulse light (19 and 19 ') that circulates in the semiconductor laser 12 with their polarization planes matched. The inside of the semiconductor laser 12 is irradiated from both ends 12a and 12b.
[0027]
When the two polarized components having the wavelength λ1 are incident on the semiconductor laser 12 that circulates the pump pulse light (19 and 19 ′) having the wavelength λ2, the both wavelengths λ1 and λ2 and the wavelength are combined by a so-called four-wave mixing action. Wavelength converted light having different values is generated.
Among the wavelength-converted lights, the wavelength-converted light generated by the interaction between the P-polarized wave and the excitation pulse light 19 is transmitted from the one end of the semiconductor laser 12 to the optical coupling lens 22d, the Faraday rotator 22c, and the The light is guided to the splitter 21 through the guide means 22 having an optical delay circuit 22b. At this time, the plane of polarization of the wavelength-converted light is rotated by 90 degrees by the Faraday rotator 22c.
[0028]
On the other hand, the wavelength-converted light generated by the interaction between the S-polarized wave and the excitation pulse light 19 ′ is guided to the splitter 21 from the other end of the semiconductor laser 12 through the optical coupling lens 22 e.
The splitter 21 synthesizes both wavelength-converted lights based on the respective polarization components and returns them to the circulator 20 by the reversible action of light. The light synthesized by the splitter 21 and guided to the circulator 20 is transmitted through the pump pulse light having the wavelength λ2 emitted from the semiconductor laser 12 and the semiconductor laser 12 in addition to the wavelength converted light described above. The multiplexed light 11 having the wavelength λ1 is included. However, the wavelength-converted light that is generated synchronously with the optical pulse signal train 11a (for example, a, c, e, g, and i) of a predetermined channel by the wavelength filter 24 that allows passage of the wavelength-converted light having the wavelength λ3. As a result, the optical pulses of a predetermined channel can be substantially separated from the multiplexed light 11.
[0029]
For example, a time delay is given to the multiplexed light 11 from the circulator 20 to the splitter 21 or the phase of the AC power supply 18d is changed as described above to synchronize with the pump pulse light 19 in the semiconductor laser 12. The channel of the multiplexed light 11 to be selected can be selected, whereby the switching of the channel of the optical signal to be separated can be realized.
[0030]
In the demultiplexing device according to the present invention, as described above, after the demultiplexing light 11 that interacts with the pump pulse light 19 in the semiconductor laser 12 is separated into an S-polarized component and a P-polarized component, The guide means 22 makes the polarization planes coincide with each other and irradiates the semiconductor laser 12 from both ends thereof, and the wavelength converted light by the respective polarization components generated by the interaction of the excitation pulse light 19 After being synthesized by the splitter 21, the wavelength filter 24 separates the optical signal having another wavelength.
[0031]
Therefore, even if intensity changes occur in each of the S-polarized component and the P-polarized component by rotating the plane of polarization of the multiplexed light 11, each polarized component interacts with the excitation pulsed light 19. The wavelength-converted light having an intensity corresponding to the sum of both polarization component intensities is obtained, and therefore, the conventional large change in the intensity of the wavelength-converted light is also caused by the rotation of the polarization plane of the multiplexed light 11. A stable wavelength-converted light can be obtained without being generated.
[0032]
As described in the specific example 1 of FIG. 1, the example in which the splitter 21 separates the multiplexed light 11 into respective polarization components and synthesizes the respective polarization components of the wavelength converted light has been shown. Instead of this example, a light combining means for combining the polarization components of the wavelength-converted light on the side opposite to the splitter 21 with the semiconductor laser 12 in between can be provided separately from the splitter 21.
[0033]
In addition, the AC power supply 18d has an example having a period f substantially equal to the repetition period f of the optical pulse of each channel of the multiplexed light 11. Instead, the semiconductor laser 12 is operated in the harmonic mode. be able to. In this harmonic mode, the AC power supply 18d has a repetition period f of the optical pulse. 1 / Since it is set to an even multiple 2nf (n is a positive integer), when the pump pulse light 19 is present at the other end 12b of the semiconductor laser 12, as shown in FIG. It is possible to allow the excitation pulse light 19 'to exist at the one end 12a without waiting for the rotation.
[0034]
Accordingly, by operating the semiconductor laser 12 in the harmonic mode, the S-polarized component and the P are not given to the S-polarized component guided to the one end 12a through the optical fiber 22a without the time delay described above. Since each of the polarization components can simultaneously act on the excitation pulse light 19 ′ and the excitation pulse light 19, the S polarization component and the P light can be provided without providing the optical delay circuit 22b in the guide means 22. Each of the polarization components can be effectively acted on the excitation pulse light, and, as described above, in addition to obtaining wavelength-converted light having a stable intensity, further simplification of the configuration. Can be achieved.
[0035]
<Specific example 2>
In the demultiplexing device 10 shown in FIG. 4, a semiconductor laser 52 operating in a collision pulse mode is used as a semiconductor laser. The same functional parts as those in the first specific example of the demultiplexing device 10 shown in FIG. 4 are denoted by the same reference numerals.
As is well known in the art, the semiconductor laser 52 in the collision pulse mode operation is provided with a saturable absorption region 15d at the center of the active layer 15, and is symmetrical with respect to the saturable absorption region. A gain region 15c, a passive waveguide region 15b, and diffraction gratings 15a and 15a 'are arranged toward both ends 12a and 12b of the semiconductor laser 52, respectively. The n-type cladding layer 13 is provided with a common electrode 16 similar to that described above, and the p-type cladding layer 14 corresponds to the regions 15a, 15a ', 15b, 15b, 15c, 15c and 15d. Electrodes 17a, 17a, 17b, 17b, 17c, 17c, and 17d, which are connected to the respective power sources described above, are provided.
[0036]
In the semiconductor laser 52, as is well known in the art, each gain region 15c, passive waveguide region 15b, and diffraction gratings 15a and 15a 'are provided with a saturable absorption region 15d at the center of the active layer 15 therebetween. Since they are arranged symmetrically, pumping pulse lights 19 and 19 'that circulate synchronously from both ends of the semiconductor laser toward opposite ends are generated.
At both ends of the semiconductor laser 52 , Inside An antireflection film 23 similar to that described above for preventing partial reflection is provided.
[0037]
According to the demultiplexing device 10 including the semiconductor laser 52, the excitation pulse lights 19 and 19 'that circulate synchronously from both ends of the semiconductor laser toward the opposite ends are generated. Similarly to the semiconductor laser operating in the harmonic mode described as a modification of Example 1, the both polarization components can be input synchronously from both ends of the semiconductor laser without waiting for the circulation of the excitation pulse light. . Accordingly, the delay circuit is not required, and the S polarization component and the P polarization component are effectively applied to the excitation pulse light 19 and the excitation pulse light 19 ′ without providing the optical delay circuit 22b in the guide means 22, respectively. This makes it possible to obtain wavelength-converted light having a stable intensity as described above, and to further simplify the configuration.
[0038]
As the semiconductor laser, various mode-locked lasers such as an active mode-locked laser and a passive mode-locked laser can be applied regardless of the hybrid mode-locked DBR laser.
[0039]
【The invention's effect】
In the demultiplexing device according to the present invention, as described above, since the demultiplexed light divided into two polarized light components is guided to the semiconductor laser with their respective polarization directions being matched, Even if the traveling direction of the multiplexed light is the rotation axis and the polarization direction is rotated around it, the intensity of the multiplexed light guided into the semiconductor laser, that is, the sum of the intensities of both polarization components, is maintained at a substantially constant intensity Is done.
[0040]
Therefore, according to the present invention, it is possible to suppress a change in the intensity of the wavelength-converted light generated by the interaction between both polarization components and the excitation pulsed light, so that regardless of the rotation of the polarization direction of the multiplexed light. Therefore, it is possible to extract the wavelength-converted pulsed light having a substantially constant intensity, and thereby it is possible to suppress the change in the pulse intensity of the separated signal sequence that occurs with the rotation of the polarization direction of the multiplexed light.
[Brief description of the drawings]
FIG. 1 is a drawing schematically showing a specific example 1 of a demultiplexing device according to the present invention.
2 is a cross-sectional view showing a polarization state of one polarization component obtained along line II-II shown in FIG. 1. FIG.
3 is a cross-sectional view showing the polarization state of the other polarization component obtained along line III-III shown in FIG.
FIG. 4 is a drawing schematically showing a specific example 2 of the demultiplexing device according to the present invention;
[Explanation of symbols]
10 Multiplexed light separation device
11 Multiplexed light
11a Wavelength converted pulsed light
12, 52 Semiconductor laser
19, 19 'Excitation pulse light
21 (Separating means and combining means) Polarizing beam splitter
22 (22a, 22b, 22c) Guide means
24 filters

Claims

In a demultiplexing device for separating one optical signal sequence from multiplexed light obtained by time-division multiplexing a plurality of optical signal sequences having the same wavelength and period,
A semiconductor laser that generates excitation pulsed light having a wavelength different from the wavelength and the same period as the period;
Separating means for separating the multiplexed light into two different polarization components;
Guidance means for guiding and inputting one polarization component to one end of the semiconductor laser and guiding and inputting the other polarization component to the other end of the semiconductor laser so that the polarization direction of the one polarization component coincides with the polarization direction ;
The semiconductor laser is synchronously controlled so that the phase of the optical signal train and the pumping pulse light that circulates in the semiconductor laser is temporally matched, and the pumping pulse light circulates in the semiconductor laser and is connected to both ends. the timing of inputting the base Ku each end to mix the respective polarization components when located and a synchronous setting unit for setting to said semiconductor laser,
The semiconductor laser is a demultiplexing device that further includes a wavelength conversion function for generating and outputting wavelength-converted light by mixing four waves when the two polarized components are mixed with the circulating excitation pulse light,
The guide means is a polarization-maintaining optical fiber that guides the light from the separation means to one end face of the semiconductor laser while maintaining the polarization direction of light, and is guided in the fiber. that the one polarization component with respect to the semiconductor laser other other of the polarization components is guided to the end face of the optical delay circuit for delaying the half value of a recirculation period of said semiconductor laser of the excitation pulse light, and a Faraday rotator for matching the one polarized light component directed from the optical fiber to said one end face of the semiconductor laser to the polarization direction of the polarized light component directed to the other end face of said semiconductor laser,
Furthermore, a light synthesizing means for synthesizing both polarization components including polarization components of the wavelength-converted light output from both ends of the semiconductor laser,
A filter that extracts the wavelength-converted light from the light that has passed through the photosynthesis means;
Multiple beam splitter which comprises a.

In a demultiplexing device for separating one optical signal sequence from multiplexed light obtained by time-division multiplexing a plurality of optical signal sequences having the same wavelength and period,
A semiconductor laser that generates excitation pulsed light having a wavelength different from the wavelength and the same period as the period;
Separating means for separating the multiplexed light into two different polarization components;
Guidance means for guiding and inputting one polarization component to one end of the semiconductor laser and guiding and inputting the other polarization component to the other end of the semiconductor laser so that the polarization direction of the one polarization component coincides with the polarization direction ;
The semiconductor laser is synchronously controlled so that the phase of the optical signal train and the pumping pulse light that circulates in the semiconductor laser is temporally matched, and the pumping pulse light circulates in the semiconductor laser and is connected to both ends. the timing of inputting the base Ku each end to mix the respective polarization components when located and a synchronous setting unit for setting to said semiconductor laser,
The semiconductor laser is a demultiplexing device that further includes a wavelength conversion function for generating and outputting wavelength-converted light by mixing four waves when the two polarized components are mixed with the circulating excitation pulse light,
The semiconductor laser operates in an even-order harmonic mode operation in which the generation period of the excitation pulse light in the inside thereof is 1 / even of the circulation period, and the guide means holds the light in a state of holding the polarization plane of light. A polarization-maintaining optical fiber guiding the one end face of the semiconductor laser to the one end face, and the polarization component directed from the optical fiber to the one end face of the semiconductor laser to the other end face of the semiconductor laser. With a Faraday rotator to match the polarization plane of the component ,
Furthermore, a light synthesizing means for synthesizing both polarization components including polarization components of the wavelength-converted light output from both ends of the semiconductor laser,
A filter that extracts the wavelength-converted light from the light that has passed through the photosynthesis means;
Multiple beam splitter which comprises a.