JP3775664B2

JP3775664B2 - Optical fiber contrast device

Info

Publication number: JP3775664B2
Application number: JP2002055443A
Authority: JP
Inventors: 郁昭田中; 正裕在間; 正男立蔵
Original assignee: Nippon Telegraph and Telephone Corp; NTT Inc USA
Current assignee: NTT Inc; NTT Inc USA
Priority date: 2002-03-01
Filing date: 2002-03-01
Publication date: 2006-05-17
Anticipated expiration: 2022-03-01
Also published as: JP2003254857A

Description

【０００１】
【発明の属する技術分野】
本発明は光ファイバケーブル網の建設・保守に使用される光心線対照器に関するものである。
【０００２】
【従来の技術】
光ファイバ通信網を建設・保守するにあたり、マンホール内（クロージャ）や構内（キャビネット）の光ファイバを作業現場で特定する必要性がある。即ち、光ファイバ通信網の建設・保守を行なう際には、複数の光ファイバの中から作業を行なう１本の光ファイバを選択して特定する必要がある。この作業を心線対照とよび、通常は図３に示すような方法で実施している。即ち、対照を必要とする光ファイバ６の上部側に設置した心線対照光源７から光カプラやビームスプリッタ等の光分岐結合器８を介して心線対照光（以後、対照光とよぶ）を入射する。光ファイバ６の下部側では、曲げ部１”を用いて光ファイバ６に曲げを加えながら対照光を光ファイバ６の側面から放射させ、これを受光器２で検出する。なお曲げ部１”は、図４に示すように、凸部材１ａ”、凹部材１ｂ”、受光器２により構成されている。
【０００３】
この方法をサービス心線に適用する場合、通信品質を劣化させずに対照しなければならないため、長波長側の光ほど漏洩しやすいという特徴を利用して、現在は通信波長１．３１／１．５５μｍに対して、それらより長波長側の１．６μｍ帯を対照光として使用している。このような技術の詳細は「特開平６−２２１９５８」にも開示されている。
【０００４】
今日、中継系は元よりアクセス系においてもまた、サービスの高度化に伴って大容量の情報を安価に提供するため、１本の光ファイバに数十波を波長多重した光通信方式が検討されている。この方式では通常Ｌバンド（１．５６５〜１．６２５μｍ）が通信波長として用いられているため、曲率半径が小さく（１０ｍｍ）、曲げ長も長い従来の心線対照器（曲げ部１”）や、前述した特開平６−２２１９５８の心線対照器では、通信波長が１．６μｍ帯になると大きな曲げ損失を引き起こす欠点があり、ひいては伝送特性を劣化させる恐れがあった。
【０００５】
また、この欠点を補うため、従来の心線対照器（曲げ部１”）の曲率半径を大きくしたり、曲げ長を短くして曲げ損失を低減することも考えられるが、一方で対照光の放射パワーも弱くしてしまうため、心線対照光源７から遠く離れた作業現場では確実に心線対照ができないという問題があった。
【０００６】
【発明が解決しようとする課題】
上述したように、Ｌバンドを用いた通信サービスに従来の心線対照器（曲げ部１”）を用いると曲げ損失が大きくなり、ひいては伝送品質を劣化させる恐れがあるため、サービス心線の心線対照ができないという問題があった。
【０００７】
本発明の目的は、光ファイバ曲げ部分からの対照光を効率よく放射させ、受光器への対照光パワーを増加させることによって、曲げ部の曲率半径を大きくしたり、あるいは曲げ長を短くしてＬバンド通信光の曲げ損失を小さくする心線対照器を提供することにある。これによって、Ｌバンド通信光を用いたサービスにおいても伝送品質を劣化させることなく心線対照が可能となる。
【０００８】
【課題を解決するための手段】
前記の目的を達成する本発明の構成は、心線対照光を送信する光源と、光ファイバを曲げる曲げ部と、前記曲げ部より漏れた光を受光する受光器より構成され、光ファイバの片端から前記心線対照光を入射し、前記曲げ部によって曲げられた光ファイバの側面から放射される心線対照光を前記受光器で検知することにより心線を特定する光心線対照器において、
前記曲げ部は、光ファイバを弧状に曲げるための凸部材と、前記凸部材に沿って曲げられた光ファイバを前記凸部材との間で挟んで保持するための凹部材とから構成されるものであって、
前記凹部材には、前記光ファイバの被覆と同程度の屈折率を有するゲル状の屈折率整合剤を、前記光ファイバの側面から放射されて前記受光器に向かう心線対照光の光経路の中に塊として前記受光器に接触させることなく位置させるように前記光ファイバの被覆に塗布するための注入器および注入管を有すると共に、
前記注入管の出口付近には、塗布された前記屈折率整合剤がその粘性により塊をもつ程度の隙間を備えたことを特徴とする。
【０００９】
また本発明の構成は、心線対照光を送信する光源と、光ファイバを曲げる曲げ部と、前記曲げ部より漏れた光を受光する受光器より構成され、光ファイバの片端から前記心線対照光を入射し、前記曲げ部によって曲げられた光ファイバの側面から放射される心線対照光を前記受光器で検知することにより心線を特定する光心線対照器において、
前記曲げ部は、光ファイバを弧状に曲げるための凸部材と、前記凸部材に沿って曲げられた光ファイバを前記凸部材との間で挟んで保持するための凹部材とから構成されるものであって、
前記凹部材は、その全体もしくは前記受光器近くの一部が光ファイバの被覆と同程度の屈折率を有する前記被覆に密着する弾力性のあるプラスチックや合成樹脂であり、前記凹部材の受光器側の端面は凹凸がなく、かつ、その端面付近で曲げられた光ファイバの接線に対して７４°〜７６°の角度を有することを特徴とする。
【００１０】
＜発明の原理説明＞
以下に、本発明において、請求項２の曲げ部１’に記載する数値（７４°〜７６°）の根拠について説明する。
【００１１】
図５は、光ファイバを伝搬する対照光が曲げにより各層の境界面で透過と反射される様子を幾何光学的に示したものである。直線領域のコア内を伝搬モード（反射角θ₀）で反射してきた対照光は、曲げによりコア、クラッド、被覆及び空気層で形成される各境界面（点Ａ、点Ｂ、点Ｃ）で臨界角を超えるとその一部がコアからクラッドへ、クラッドから被覆へ、被覆から空気層へと透過され最終的に受光器で検出される。
【００１２】
いま、光ファイバのコア、クラッド、被覆および空気の屈折率を各々ｎ₁，ｎ₂，ｎ₃，ｎ₄、コア、クラッド、被覆の外径を２ｘ₁，２ｘ₂，２ｘ₃、曲げ半径をρ、また、点Ａ〜Ｃでの入射角、屈折率を各々φ₁，φ₂，φ₃、ξ₁，ξ₂，ξ₃、曲がり始めてから点Ａまで、点Ａから点Ｂまで、点Ｂから点Ｃまでの各方向変化をδ₁，δ₂，δ₃とすると、曲げ半径ρに対する各点での透過率Ｔ_iと反射率Ｒ_iは式（１）〜（２）で表わすことができる（詳細は、例えば小嶋著：光波光学、コロナ社、Ｐ２９〜４２を参照されたい）。但し、対照光の電界が入射面に垂直であると仮定する。
【００１３】
【数１】

【００１４】
ここで、幾何学的な計算からφ₁＝（π／２−θ₀）−δ₁、φ_i＝ξ_i−１−δ_i（ｉ＝２，３）であり、δ₁，δ_i（ｉ＝２，３）は曲げ半径ρの関数として式（３）と式（４）で表される。
【００１５】
【数２】

【００１６】
また、屈折の法則よりξ_iは式（５）で与えられる。
【００１７】
【数３】

【００１８】
ここで、添字ｉ（１〜３）は点Ａ〜Ｃに対応しており、式（１）〜（５）を用いてクラッドと被覆（ｉ＝２）、及び被覆と空気層（ｉ＝３）における曲げ半径ρに対する透過率Ｔ_iと反射率Ｒ_iとの計算例を図９に示す。破線は点Ｂ、実線は点Ｃでの透過率Ｔ_iと反射率Ｒ_iであり、コア内の対照光パワーで規格化されている。計算ではθ₀＝４．３１°、ｎ₁＝１．４６５、ｎ₂＝１．４６、ｎ₃＝１．５、ｎ₄＝１．０、また、２ｘ₁＝７．５μｍ、２ｘ₂＝１２５μｍ、２ｘ₃＝４００μｍとした。
【００１９】
図９より半径１０ｍｍの曲げの場合、対照光は被覆側へ数％程度透過しているが（破線）、点Ｃでは全反射となるため空気層には放射されない（実線）ことが分かる。対照光が空気層へ放射するのは、３００μｍより小さな曲げの場合であるが、実際にはそのような曲げ半径は困難であることから、曲げ部で検出する放射光は被覆表面の粗さ（小さな凹凸）やミクロンオーダの局所的な曲げにより臨界角を超えて放射されていると考えられる。
【００２０】
そこで対照光の放射パワーを増加させるには、被覆と空気層の境界面での入射角φ₃を臨界角以下にして透過させることが有効である。そのためには、まず被覆と同じ屈折率（ｎ₃＝１．５）をもつ放射補助部材１１を被覆に密着させ反射を低減させながら対照光を放射補助部材１１側に透過させる。この時、この透過光は放射補助部材１１側へ直進することから（φ₃＝ξ₃）、密着させた曲げ部分の接線に対してφ₃だけ放射補助部材１１の端面を傾けることで空気層に対して直角に出射できる。例えば、曲げ半径ρが１３ｍｍの場合、式（４）と（５）よりφ₃が約７４°となる。このようにφ₃が約７４°となることと、曲げ半径は一般には６ｍｍ〜１３ｍｍ程度であることを併せて考慮すると、放射補助部材１１の端面を曲げ半径に応じて７４°〜７６°の間の任意の角度に傾けると最適である。
【００２１】
【作用】
本願の請求項１の発明によれば、凹部材の受光器付近に、光ファイバの被覆と同程度の屈折率を有するゲル状の屈折率整合剤を、受光器に接触させることなく塊として塗布することにより、光ファイバから漏れる対照光を効率よく放射させ、受光器への対照光パワーを増加させられるため、光ファイバ曲げ部における凸部材の曲率半径を従来より拡大したり、あるいは曲げ長を従来より短くすることができる。その結果、Ｌバンド通信光の曲げ損失を従来より小さくすることができる。
【００２２】
本願の請求項２の発明によれば、凹部材の全体もしくは受光器近くの一部が光ファイバの被覆と同程度の屈折率を有し、前記被覆に密着するように弾力性のあるプラスチックや合成樹脂を用い、かつ、前記凹部材の受光器側の端面は凹凸がなく、かつ、その端面付近で曲げられた光ファイバの接線に対して７４°〜７６°の角度をもたせることによって光ファイバから漏れる対照光を効率よく放射させ、受光器への対照光パワーを増加させられる。その結果、請求項１と同様に光ファイバ曲げ部における凸部材の曲率半径を従来より拡大したり、あるいは曲げ長を従来より短くすることができるため、Ｌバンド通信光の曲げ損失を従来より小さくすることができる。
【００２３】
以上のように、対照光パワーの増加によりＬバンド通信光に対する曲げ損失の低減化が可能となるため、Ｌバンドを用いる波長多重通信などの伝送品質を劣化させることなく心線対照作業が遂行できる。
【００２４】
【発明の実施の形態】
以下に本発明の実施の形態を図面に基づき詳細に説明する。
【００２５】
＜第１の実施の形態＞
本発明の第１の実施の形態にかかる光心線対照器を図１により説明する。図１は本発明における光心線対照器の曲げ部全体の正面図であって、１は曲げ部、１ａは凸部材、１ｂは凹部材、２は受光器、３は注入管、４は注入器、５は屈折率整合剤、６は光ファイバを示す。
【００２６】
曲げ部１は上下動自在の凸部材１ａと、この凸部材１ａの凸面に合致するように固定された凹部材１ｂと、凹部材１ｂの底部近傍に配置されて対照光を検出する受光器２と、孔穴である注入管３と、屈折率整合剤５を塗布する注入器４から構成されている。
【００２７】
凸部材１ａは、例えば、曲げ半径が１３ｍｍ、曲げ長が予備曲げを含めて２０．４ｍｍ（一様な曲げの角度に換算すると９０°）であり、光ファイバ６をガイドするための溝がある。凹部材１ｂは凸部材１ａとほぼ合致する形状であり、注入管３の出口付近は屈折率整合剤５を塗布し、その粘性により塊を形成させるために１〜２ｍｍ程度の隙間（凹部材１ｂと光ファイバ６との間の隙間）を備えている。
【００２８】
屈折率整合剤５は、光ファイバ６の被覆の屈折率（１．５）と同一の屈折率乃至同程度の屈折率（１．４〜１．６）を持つゲル状部材である。そして屈折率整合剤５は受光器２の付近で、しかも、光ファイバ６の側面から放射されて受光器２に向かう対照光の経路の中に位置するように光ファイバ６の被覆に塗布するのが効果的である。そのため、凹部材１ｂのエッジＤ，Ｅに約１ｍｍの注入管３の出口を設けている。尚、屈折率整合剤５を塗布するための注入器４は市販されている注射器タイプのものを用いると便利である。受光器２はその受光面が光ファイバ６の接線方向とほぼ平行になる角度で凸部材１ａの底部近傍に設置している。
【００２９】
次に、上述した曲げ部１の動作について説明する。ｘ軸の正方向（紙面の左から右）へ対照光が送信されている光ファイバ６をｙ軸方向に上下動自在の凸部材１ａで凹部材１ｂ側に押し付けて所定量の曲げを形成する。そして、注入器４から注入管３を介して屈折率整合剤５を送り出し、屈折率整合剤５を光ファイバ６の被覆に少量（米粒の半分程度）塗布する。これによって、光ファイバ６の被覆表面に漏洩している対照光が、屈折率整合剤５の表面を介して空気中に放射しやすくなり、結果として受光器２への対照光パワーが増加することになる。
【００３０】
本発明の第１の実施の形態である曲げ部１と従来の曲げ部１”との性能を比較するため、曲げ損失と結合損失とをそれらの等価モデルを用いて各々測定した。図６は曲げ部１を等価的に再現するため、半径１３ｍｍの円筒９に曲げ長が２０．４ｍｍ（一様な曲げの角度に換算すると９０°）になるように光ファイバ６を固定し、受光器２を円筒９の中心に光ファイバ６の接線方向とほぼ平行になるように設置した。また、屈折率整合剤５は受光器２付近に米粒の半分ほどを塗布した。尚、塗布した屈折率整合剤５と受光器２との間隔は約９ｍｍである。
【００３１】
一方、図８は従来の曲げ部１”を等価的に再現したものであり、半径１０ｍｍの円筒９’に曲げ長が３．１ｍｍ（一様な曲げ角度に換算すると１８０°）になるように光ファイバ６を固定し、受光器２を円筒９’の中心に光ファイバ６の接線方向とほぼ平行になるように設置した。測定波長には１．６５μｍの光を用い、常温においてモードフィールド径が約９．２μｍ、被覆の外径が０．４ｍｍ程度のＳＭファイバを用いた。
【００３２】
曲げ損失は、光ファイバ６が直線状態での受光パワー（Ｐ１）から曲げ部１もしくは曲げ部１”で光ファイバ６を曲げた時の受光パワー（Ｐ２）を差し引いて求められる（Ｐ１−Ｐ２）。インサービスの心線対照では、この曲げ損失（Ｐ１−Ｐ２）が小さければ小さいほど好ましいが、一般的にコネクタ接続程度の損失（約０．５ｄＢ以下）であれば伝送品質の低下にはならないと考えられる。
【００３３】
一方、結合損失は、光ファイバ６が直線状態での受光パワー（Ｐ１）から曲げ部１もしくは曲げ部１”で光ファイバ６を曲げ、受光器２で検出される放射光パワー（Ｐ３）を差し引いて求められる（Ｐ１−Ｐ３）。この結合損失は光ファイバ内から放射される対照光が受光器２で検出される効率を表わしている。
【００３４】
図６と図８に示す測定系を用いて、曲げ部１と曲げ部１”における曲げ損失、および結合損失の測定結果を表１に示す。尚、表１においては曲げ半径が１３ｍｍの場合の屈折率整合剤５の効果を明らかにするため、屈折率整合剤５がある場合とない場合との改善量についても示している。曲げ部１、及び曲げ部１”と等価的な曲げ形状を用いて１０回の測定を行った結果、曲げ部１、及び曲げ部１”の曲げ損失においては、平均で各々約０．１６ｄＢ、及び約０．３５ｄＢであった。また、結合損失は平均で各々３５．１ｄＢ、及び４３．９ｄＢであり、９ｄＢ程度の改善がみられた。尚、屈折率整合剤５の効果としては、平均で８．９ｄＢもある。
【００３５】
【表１】

【００３６】
以上のように、本発明の第１の実施の形態である曲げ部１を用いることによって、Ｌバンドで通信している光ファイバに対して、従来の曲げ部１”より伝送品質に影響を与えず、かつ、確実に心線対照を行えることが分かる。
【００３７】
＜第２の実施の形態＞
次に、第２の実施の形態にかかる光心線対照器を図２より説明する。第２の実施の形態では、以下に述べる点の他は、第１の実施の形態と同様の構成、動作、作用、および効果を有する。
【００３８】
図２は本発明における第２の実施の形態であって、１’は曲げ部、１ａ’は凸部材、１ｂ’は凹部材、２は受光器、６は光ファイバを示す。
【００３９】
曲げ部１’は上下動自在の凸部材１ａ’と、この凸部材１ａ’の凸面に合致するように固定された凹部材１ｂ’と、凹部材１ｂ’の底部近傍に対照光を検出する受光器２とから構成されている。凸部材１ａ’の底部として、例えば、曲げ半径が１３ｍｍ、曲げ長が２０．４ｍｍ（一様な曲げ角度に換算すると９０°）であり、光ファイバ６をガイドするための溝がある。凹部材１ｂ’は凸部材１ａ’とほぼ合致する形状であり、その全体が光ファイバ６の被覆の屈折率（１．５）と同一の屈折率乃至同程度の屈折率（１．４〜１．６）で、その被覆に密着し弾力性のある合成樹脂である。
【００４０】
また、凹部材１ｂ’における受光器２側の端面は凹凸がなく、その端面付近で曲げられた光ファイバ６の接線に対して７５°程度の角度を有している。受光器２はその受光面が光ファイバ６の接線方向とほぼ平行になる角度で凸部材１ａ’の底部近傍に設置している。
【００４１】
次に、上述した曲げ部１’の動作について説明する。ｘ軸の正の方向（紙面の左から右）へ対照光が送信されている光ファイバ６をｙ軸方向に上下動自在の凸部材１ａ’を凹部材１ｂ’側に押し付け、所定量の曲げを形成する。曲げられた光ファイバ６は凹部材１ｂ’と密着状態にあり、光ファイバ６の被覆表面に漏洩している対照光は、凹部材１ｂ’を介して空気中に放射しやすくなり、結果として受光器２に対する対照光量を増やすことになる。その理由は［課題を解決するための手段］の中で述べた通りである。
【００４２】
本発明の第２の実施の形態である曲げ部１’と従来の曲げ部１”との性能を比較するため、曲げ損失と結合損失とをそれらの等価モデルを用いて各々測定した。図７は曲げ部１’を等価的に再現するため、半径１３ｍｍの円筒９に、曲げ長を２０．４ｍｍ（一様な曲げ角度に換算すると９０°）になるように光ファイバ６を固定し、受光器２を円筒９の中心に光ファイバ６の接線方向とほぼ平行になるように設置した。尚、図７については本発明の第１の実施の形態で説明した通りである。また、測定についても本発明における第１の実施の形態と同様に波長１．６５μｍの光を用い、常温において同じＳＭファイバを使用した。
【００４３】
図７と図８に示す測定系と、第１の実施の形態で定義した曲げ損失と結合損失との算出方法とを用いて、曲げ部１’と曲げ部１”との曲げ損失と結合損失とを各々評価し、その結果を表２に示す。本測定では、図７と図８に示す測定系を用いて１０回の測定を行った。その結果、曲げ部１’、及び曲げ部１”の曲げ損失においては、平均で各々約０．１６ｄＢ、及び約０．３５ｄＢであった。また、結合損失は平均で各々３５．１ｄＢ、及び４２．２ｄＢであった。尚、屈折率整合剤５の効果としては、平均で８．６ｄＢもある。
【００４４】
【表２】

【００４５】
以上のように、本発明の第２の実施の形態である曲げ部１’を用いることによって、Ｌバンドで通信している光ファイバに対して、従来の曲げ部１”より伝送品質に影響を与えず、かつ、確実に心線対照を行えることが分かる。また、第２の実施の形態では、凹部材１ｂ’自体が第１の実施の形態でいうところの屈折率整合剤５の役割を果たしており、構造が簡単で屈折率整合剤５を注入する行程も必要ないため心線対照作業の効率がよい。また、凹部材１ｂ’と光ファイバ６との接触している面が屈折率整合剤５を注入する方法より広いことから、より多くの対照光を受光器２へ放射できるという点で有利である。
【００４６】
【発明の効果】
以上説明したように、本発明により、従来の心線対照器より曲げ損失を低減しながら光ファイバから漏れる対照光を効率よく放射させ、受光器への光量を増加させることができるため、Ｌバンドの通信サービスにおいても、伝送品質に影響のない心線対照作業が実現できる。また、本発明はＬバンドに止まらず一般的に従来の心線対照器より対照光の受光効率を向上させ、曲げ損失を小さくしているためサービス提供中の心線対照作業の信頼性も向上することが期待できる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態にかかる光心線対照器を示す正面図。
【図２】本発明の第２の実施の形態にかかる光心線対照器を示す正面図。
【図３】心線対照方法の一例を示す構成図。
【図４】従来の曲げ部の構造を示す正面図。
【図５】心線対照光の放射モデルを示す説明図。
【図６】本発明の第１の実施の形態の等価測定系を示す構成図。
【図７】本発明の第２の実施の形態の等価測定系を示す構成図。
【図８】従来における心線対照の等価測定系を示す構成図。
【図９】曲げ半径ρに対する透過率Ｔ_iと反射率Ｒ_iとの計算例を示す特性図。
【符号の説明】
１，１’，１” 曲げ部
１ａ，１ａ’，１ａ” 凸部材
１ｂ，１ｂ’，１ｂ” 凹部材
２受光器
３注入管
４注入器
５屈折率整合剤
６光ファイバ
７心線対照光源
８光分岐結合器
９，９’ 円筒
１０光パワーメーター
１１放射補助部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber core contrast device used for construction and maintenance of an optical fiber cable network.
[0002]
[Prior art]
In constructing and maintaining an optical fiber communication network, it is necessary to identify optical fibers in manholes (closures) and campuses (cabinets) at work sites. That is, when constructing and maintaining an optical fiber communication network, it is necessary to select and specify one optical fiber to be operated from a plurality of optical fibers. This operation is called cord contrast, and is usually performed by the method shown in FIG. That is, the control light (hereinafter referred to as control light) is supplied from the control light source 7 installed on the upper side of the optical fiber 6 requiring control through the optical branching coupler 8 such as an optical coupler or a beam splitter. Incident. On the lower side of the optical fiber 6, while bending the optical fiber 6 using the bent portion 1 ", the control light is radiated from the side surface of the optical fiber 6, and this is detected by the light receiver 2. The bent portion 1" 4, a convex member 1 a ″, a concave member 1 b ″, and a light receiver 2 are included.
[0003]
When this method is applied to a service core, the communication quality must be compared without degrading the communication quality. Therefore, using the feature that light on the longer wavelength side is more likely to leak, the communication wavelength is currently 1.31 / 1. For .55 μm, the 1.6 μm band on the longer wavelength side is used as the control light. Details of such a technique are also disclosed in Japanese Patent Laid-Open No. Hei 6-221958.
[0004]
Today, in order to provide high-capacity information at a low cost with the advancement of services in the relay system as well as in the access system, an optical communication system in which several tens of waves are wavelength-multiplexed on one optical fiber has been studied. ing. In this method, since the L band (1.565 to 1.625 μm) is usually used as a communication wavelength, a conventional cord contrast device (bending portion 1 ″) having a small radius of curvature (10 mm) and a long bending length is used. However, the above-mentioned core line contrast device disclosed in Japanese Patent Laid-Open No. 6-221958 has a drawback of causing a large bending loss when the communication wavelength is in the 1.6 μm band, and there is a risk of degrading the transmission characteristics.
[0005]
In order to compensate for this drawback, it is conceivable to increase the radius of curvature of the conventional optical fiber contrast device (bending portion 1 ″) or shorten the bending length to reduce bending loss. Since the radiant power is also weakened, there is a problem in that the contrast control cannot be performed reliably at the work site far from the contrast control light source 7.
[0006]
[Problems to be solved by the invention]
As described above, if a conventional cord contrast device (bending portion 1 ″) is used for a communication service using the L band, the bending loss increases and, as a result, the transmission quality may be deteriorated. There was a problem that line contrast was not possible.
[0007]
The object of the present invention is to increase the radius of curvature of the bent portion or shorten the bending length by efficiently radiating the reference light from the bent portion of the optical fiber and increasing the reference light power to the receiver. An object of the present invention is to provide a cord contrast device that reduces the bending loss of L-band communication light. As a result, even in a service using the L-band communication light, it is possible to perform the contrast control without degrading the transmission quality.
[0008]
[Means for Solving the Problems]
The configuration of the present invention that achieves the above-described object includes a light source that transmits a core-line contrast light, a bending portion that bends the optical fiber, and a light receiver that receives light leaking from the bending portion, and is provided at one end of the optical fiber. In the optical fiber core contrast device, the optical fiber core light is incident from the optical fiber, and the optical fiber core light is identified by detecting the optical fiber core light emitted from the side surface of the optical fiber bent by the bending portion with the light receiver.
The bent portion is composed of a convex member for bending the optical fiber in an arc shape and a concave member for holding the optical fiber bent along the convex member between the convex member. Because
A gel-like refractive index matching agent having a refractive index similar to that of the coating of the optical fiber is applied to the concave member, and the optical path of the optical fiber for the core-line contrast light emitted from the side surface of the optical fiber and directed to the light receiver. which has an injection and infusion tubes for applying the coating of the optical fiber so that is positioned without contact with the light receiver as a mass in,
In the vicinity of the outlet of the injection tube, a gap is formed so that the applied refractive index matching agent has a lump due to its viscosity.
[0009]
Further, the configuration of the present invention includes a light source that transmits a core contrast light, a bending portion that bends the optical fiber, and a light receiver that receives light leaking from the bending portion, and the core contrast is received from one end of the optical fiber. In an optical core contrast device for identifying a core wire by detecting light from the side surface of an optical fiber bent by the bending portion and detecting the core wire contrast light with the light receiver,
The bent portion is composed of a convex member for bending the optical fiber in an arc shape and a concave member for holding the optical fiber bent along the convex member between the convex member. Because
The recess material is an elastic plastic or synthetic resin that is in close contact with the coating having the same refractive index as that of the coating of the optical fiber, or a portion near the receiver. The end face on the side has no irregularities and has an angle of 74 ° to 76 ° with respect to the tangent line of the optical fiber bent in the vicinity of the end face.
[0010]
<Description of Principle of Invention>
Below, in this invention, the basis of the numerical value (74 degrees-76 degrees) described in bending part 1 'of Claim 2 is demonstrated.
[0011]
FIG. 5 shows geometrically the state in which the reference light propagating through the optical fiber is transmitted and reflected at the boundary surface of each layer by bending. The contrast light reflected in the propagation mode (reflection angle θ ₀ ) in the core in the straight region is bent at each boundary surface (point A, point B, point C) formed by the core, cladding, coating, and air layer. When the critical angle is exceeded, a part of the light is transmitted from the core to the clad, from the clad to the clad, and from the clad to the air layer, and finally detected by the light receiver.
[0012]
Now, the refractive indexes of the core, clad, coating and air of the optical fiber are n ₁ , n ₂ , n ₃ and n ₄ , the outer diameters of the core, clad and coating are 2x ₁ , 2x ₂ and 2x ₃ , and the bending radius is ρ, and incident angles and refractive indexes at points A to C are φ ₁ , φ ₂ , φ ₃ , ξ ₁ , ξ ₂ , ξ ₃ , from the start of bending to point A, from point A to point B, If each direction change from B to point C is δ ₁ , δ ₂ , and δ ₃ , the transmittance T _i and the reflectance R _i at each point with respect to the bending radius ρ are expressed by equations (1) to (2). (For details, see, for example, Kojima: Lightwave Optics, Corona, P29-42). However, it is assumed that the electric field of the reference light is perpendicular to the incident surface.
[0013]
[Expression 1]

[0014]
Here, from the geometric calculation, φ ₁ = (π / 2−θ ₀ ) −δ ₁ , φ _i = ξ _i −1−δ _i (i = 2, 3), and δ ₁ , δ _i ( i = 2, 3) is expressed by equations (3) and (4) as a function of the bending radius ρ.
[0015]
[Expression 2]

[0016]
Further, ξ _i is given by equation (5) from the law of refraction.
[0017]
[Equation 3]

[0018]
Here, the suffix i (1-3) corresponds to the points A to C, and using the equations (1) to (5), the cladding and coating (i = 2), and the coating and air layer (i = 3). FIG. 9 shows a calculation example of the transmittance T _i and the reflectance R _i with respect to the bending radius ρ in FIG. The broken line is the point B, and the solid line is the transmittance T _i and the reflectance R _i at the point C, which are normalized by the reference light power in the core. In the calculation, θ ₀ = 4.31 °, n ₁ = 1.465, n ₂ = 1.46, n ₃ = 1.5, n ₄ = 1.0, and 2x ₁ = 7.5 μm, 2x ₂ = 125 μm, 2 × ₃ = 400 μm.
[0019]
From FIG. 9, it can be seen that in the case of bending with a radius of 10 mm, the reference light is transmitted to the coating side by about several percent (broken line), but is totally radiated at point C and is not radiated to the air layer (solid line). The control light radiates to the air layer in the case of a bend smaller than 300 μm. However, since such a bend radius is difficult in practice, the radiated light detected at the bend is not suitable for the roughness of the coating surface ( It is considered that the radiation is beyond the critical angle due to local bending of small irregularities) and micron order.
[0020]
Therefore, in order to increase the radiant power of the control light, it is effective to transmit the incident angle φ ₃ at the boundary surface between the coating and the air layer at a critical angle or less. For this purpose, first, the radiation auxiliary member 11 having the same refractive index (n ₃ = 1.5) as that of the coating is brought into close contact with the coating, and the reference light is transmitted to the radiation auxiliary member 11 side while reducing reflection. At this time, since the transmitted light travels straight toward the radiation assisting member 11 (φ ₃ = ξ ₃ ), the air layer is inclined by tilting the end surface of the radiation assisting member 11 by φ _{3 with} respect to the tangent of the bent portion that is in close contact. Can be emitted at right angles to the angle. For example, when the bending radius ρ is 13 mm, φ ₃ is about 74 ° from the equations (4) and (5). Thus, considering that φ ₃ is about 74 ° and that the bending radius is generally about 6 mm to 13 mm, the end surface of the radiation assisting member 11 is 74 ° to 76 ° according to the bending radius. It is best to tilt to any angle between.
[0021]
[Action]
According to the invention of claim 1 of the present application, a gel-like refractive index matching agent having a refractive index comparable to that of the coating of the optical fiber is applied as a lump in the vicinity of the light receiver of the concave member without contacting the light receiver. Therefore, the reference light leaking from the optical fiber can be efficiently radiated and the reference light power to the optical receiver can be increased, so that the radius of curvature of the convex member in the optical fiber bending portion can be increased or the bending length can be increased. It can be made shorter than before. As a result, the bending loss of L-band communication light can be made smaller than before.
[0022]
According to the invention of claim 2 of the present application, the whole of the recess material or a part near the light receiver has a refractive index comparable to the coating of the optical fiber, and is made of an elastic plastic so as to be in close contact with the coating. An optical fiber is formed by using a synthetic resin, and having an end surface on the light receiver side of the concave portion that is not uneven and has an angle of 74 ° to 76 ° with respect to a tangent line of the optical fiber bent near the end surface. The control light leaking from the light can be efficiently emitted, and the control light power to the light receiver can be increased. As a result, the curvature radius of the convex member in the optical fiber bending portion can be increased as compared with the conventional case or the bending length can be shortened as compared with the conventional case, so that the bending loss of the L-band communication light can be reduced. can do.
[0023]
As described above, since the bending loss with respect to the L-band communication light can be reduced by increasing the reference optical power, it is possible to perform the core-line contrast work without degrading the transmission quality of the wavelength division multiplexing communication using the L band. .
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0025]
<First Embodiment>
An optical fiber core contrast device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a front view of the entire bent portion of the optical fiber core contrast device according to the present invention, wherein 1 is a bent portion, 1a is a convex member, 1b is a concave member, 2 is a light receiver, 3 is an injection tube, and 4 is an injection. 5 represents a refractive index matching agent, and 6 represents an optical fiber.
[0026]
The bending portion 1 is a convex member 1a that can move up and down, a concave member 1b that is fixed so as to match the convex surface of the convex member 1a, and a light receiver 2 that is disposed near the bottom of the concave member 1b and detects contrast light. And an injection tube 3 that is a hole and an injector 4 that applies a refractive index matching agent 5.
[0027]
The convex member 1a has, for example, a bending radius of 13 mm, a bending length of 20.4 mm including preliminary bending (90 ° when converted to a uniform bending angle), and a groove for guiding the optical fiber 6. . The concave member 1b has a shape that substantially matches the convex member 1a, and a refractive index matching agent 5 is applied to the vicinity of the outlet of the injection tube 3, and a gap of about 1 to 2 mm (the concave member 1b is formed to form a lump by its viscosity. And a gap between the optical fiber 6 and the optical fiber 6.
[0028]
The refractive index matching agent 5 is a gel-like member having the same or similar refractive index (1.4 to 1.6) as the refractive index (1.5) of the coating of the optical fiber 6. Then, the refractive index matching agent 5 is applied to the coating of the optical fiber 6 so as to be positioned in the vicinity of the light receiver 2 and in the path of the reference light emitted from the side surface of the optical fiber 6 toward the light receiver 2. Is effective. Therefore, the outlet of the injection tube 3 of about 1 mm is provided at the edges D and E of the recess 1b. The injector 4 for applying the refractive index matching agent 5 is conveniently a commercially available syringe type. The light receiver 2 is installed in the vicinity of the bottom portion of the convex member 1 a at an angle at which the light receiving surface is substantially parallel to the tangential direction of the optical fiber 6.
[0029]
Next, operation | movement of the bending part 1 mentioned above is demonstrated. A predetermined amount of bending is formed by pressing the optical fiber 6 in which the reference light is transmitted in the positive direction of the x-axis (from the left to the right of the page) toward the concave member 1b with the convex member 1a that is movable up and down in the y-axis direction. . Then, the refractive index matching agent 5 is sent out from the injector 4 through the injection tube 3, and the refractive index matching agent 5 is applied to the coating of the optical fiber 6 in a small amount (about half of rice grains). As a result, the reference light leaking to the coating surface of the optical fiber 6 is likely to be emitted into the air through the surface of the refractive index matching agent 5, and as a result, the control light power to the light receiver 2 is increased. become.
[0030]
In order to compare the performance of the bending portion 1 according to the first embodiment of the present invention and the conventional bending portion 1 ″, bending loss and coupling loss were measured using their equivalent models, respectively. In order to reproduce the bending portion 1 equivalently, the optical fiber 6 is fixed to a cylinder 9 having a radius of 13 mm so that the bending length is 20.4 mm (90 ° in terms of a uniform bending angle). Was placed in the center of the cylinder 9 so as to be substantially parallel to the tangential direction of the optical fiber 6. Also, the refractive index matching agent 5 was applied about half of the rice grains in the vicinity of the light receiver 2. The applied refractive index matching was applied. The distance between the agent 5 and the light receiver 2 is about 9 mm.
[0031]
On the other hand, FIG. 8 is an equivalent reproduction of the conventional bending portion 1 ″ so that the bending length is 3.1 mm (180 ° in terms of a uniform bending angle) in a cylinder 9 ′ having a radius of 10 mm. The optical fiber 6 was fixed, and the optical receiver 2 was installed at the center of the cylinder 9 'so as to be substantially parallel to the tangential direction of the optical fiber 6. The measurement wavelength was 1.65 μm, and the mode field diameter at room temperature. Was an SM fiber having a diameter of about 9.2 μm and a coating outer diameter of about 0.4 mm.
[0032]
The bending loss is obtained by subtracting the light receiving power (P2) when the optical fiber 6 is bent at the bent portion 1 or the bent portion 1 ″ from the light receiving power (P1) when the optical fiber 6 is in a straight state (P1-P2). In in-service cord contrast, the smaller the bending loss (P1-P2), the better, but generally a loss equivalent to a connector connection (about 0.5 dB or less) does not cause a decrease in transmission quality. it is conceivable that.
[0033]
On the other hand, the coupling loss is obtained by subtracting the radiated light power (P3) detected by the light receiver 2 by bending the optical fiber 6 at the bent portion 1 or the bent portion 1 ″ from the received light power (P1) when the optical fiber 6 is in a straight state. (P1-P3) This coupling loss represents the efficiency with which the reference light emitted from within the optical fiber is detected by the optical receiver 2.
[0034]
The measurement results of the bending loss and the coupling loss at the bending portion 1 and the bending portion 1 ″ using the measurement system shown in FIGS. 6 and 8 are shown in Table 1. In Table 1, the bending radius is 13 mm. In order to clarify the effect of the refractive index matching agent 5, the amount of improvement with and without the refractive index matching agent 5 is also shown. The bending shape equivalent to the bending portion 1 and the bending portion 1 ″ is shown. As a result of performing the measurement 10 times, the bending loss of the bent portion 1 and the bent portion 1 ″ was about 0.16 dB and about 0.35 dB on average, respectively, and the coupling loss was average. These were 35.1 dB and 43.9 dB, respectively, and an improvement of about 9 dB was observed, and the effect of the refractive index matching agent 5 was an average of 8.9 dB.
[0035]
[Table 1]

[0036]
As described above, by using the bent portion 1 according to the first embodiment of the present invention, the transmission quality is more affected than the conventional bent portion 1 ″ for the optical fiber communicating in the L band. It can be seen that the cords can be reliably controlled.
[0037]
<Second Embodiment>
Next, the optical fiber core contrast device according to the second embodiment will be described with reference to FIG. The second embodiment has the same configuration, operation, action, and effect as those of the first embodiment except for the points described below.
[0038]
FIG. 2 shows a second embodiment of the present invention, in which 1 ′ is a bent portion, 1a ′ is a convex member, 1b ′ is a concave member, 2 is a light receiver, and 6 is an optical fiber.
[0039]
The bent portion 1 ′ is a convex member 1a ′ that is movable up and down, a concave member 1b ′ that is fixed so as to match the convex surface of the convex member 1a ′, and a light receiving unit that detects contrast light near the bottom of the concave member 1b ′. And the container 2. As the bottom of the convex member 1a ′, for example, a bending radius is 13 mm, a bending length is 20.4 mm (90 ° in terms of a uniform bending angle), and there is a groove for guiding the optical fiber 6. The concave member 1b ′ has a shape that substantially matches the convex member 1a ′, and the entirety thereof has the same or similar refractive index (1.4 to 1) as the refractive index (1.5) of the coating of the optical fiber 6. .6) is an elastic synthetic resin which is in close contact with the coating.
[0040]
Further, the end face of the concave member 1b ′ on the side of the light receiver 2 is not uneven, and has an angle of about 75 ° with respect to the tangent line of the optical fiber 6 bent in the vicinity of the end face. The light receiver 2 is installed in the vicinity of the bottom of the convex member 1 a ′ at an angle at which the light receiving surface is substantially parallel to the tangential direction of the optical fiber 6.
[0041]
Next, the operation of the bending portion 1 ′ described above will be described. A convex member 1a 'that can move up and down in the y-axis direction is pressed against the concave member 1b' side by pressing the optical fiber 6 in which the reference light is transmitted in the positive direction of the x-axis (from left to right in the drawing), and a predetermined amount of bending is performed. Form. The bent optical fiber 6 is in close contact with the concave portion 1b ′, and the reference light leaking to the coating surface of the optical fiber 6 is likely to be radiated into the air through the concave portion 1b ′. This will increase the amount of contrast for the device 2. The reason is as described in [Means for Solving the Problems].
[0042]
In order to compare the performance of the bending portion 1 ′ according to the second embodiment of the present invention and the conventional bending portion 1 ″, bending loss and coupling loss were measured using their equivalent models, respectively. In order to reproduce the bending portion 1 'equivalently, an optical fiber 6 is fixed to a cylinder 9 having a radius of 13 mm so that the bending length is 20.4 mm (90 ° in terms of a uniform bending angle). The vessel 2 was installed at the center of the cylinder 9 so as to be substantially parallel to the tangential direction of the optical fiber 6. Note that Fig. 7 is as described in the first embodiment of the present invention. Similarly to the first embodiment of the present invention, light having a wavelength of 1.65 μm was used and the same SM fiber was used at room temperature.
[0043]
Using the measurement system shown in FIGS. 7 and 8 and the calculation method of the bending loss and the coupling loss defined in the first embodiment, the bending loss and the coupling loss of the bending portion 1 ′ and the bending portion 1 ″ are calculated. And the results are shown in Table 2. In this measurement, ten measurements were performed using the measurement system shown in Fig. 7 and Fig. 8. As a result, the bent portion 1 'and the bent portion 1 were measured. "Bending loss" was about 0.16 dB and about 0.35 dB on average, respectively. The average coupling loss was 35.1 dB and 42.2 dB, respectively. In addition, as an effect of the refractive index matching agent 5, there is an average of 8.6 dB.
[0044]
[Table 2]

[0045]
As described above, by using the bent portion 1 ′ according to the second embodiment of the present invention, the transmission quality of the optical fiber communicating in the L band is more affected than the conventional bent portion 1 ″. In the second embodiment, the concave member 1b ′ itself plays the role of the refractive index matching agent 5 in the first embodiment. Therefore, since the structure is simple and the process of injecting the refractive index matching agent 5 is not required, the efficiency of the contrast control work is good, and the surface where the concave portion 1b ′ and the optical fiber 6 are in contact is refractive index matching. Since it is wider than the method of injecting the agent 5, it is advantageous in that more control light can be emitted to the light receiver 2.
[0046]
【The invention's effect】
As described above, according to the present invention, it is possible to efficiently emit the reference light leaking from the optical fiber while reducing the bending loss as compared with the conventional optical fiber contrast device, and to increase the light quantity to the light receiver. Even in this communication service, it is possible to realize a core-line contrast work that does not affect the transmission quality. In addition, the present invention is not limited to the L band, and generally improves the light receiving efficiency of the reference light compared to the conventional core wire contrast device and reduces the bending loss, so that the reliability of the core wire comparison work during service provision is also improved. Can be expected to do.
[Brief description of the drawings]
FIG. 1 is a front view showing an optical fiber core contrast device according to a first embodiment of the present invention.
FIG. 2 is a front view showing an optical fiber core contrast device according to a second embodiment of the present invention.
FIG. 3 is a configuration diagram showing an example of a method of contrasting core wires.
FIG. 4 is a front view showing a structure of a conventional bending portion.
FIG. 5 is an explanatory diagram showing a radiation model of core wire contrast light.
FIG. 6 is a configuration diagram showing an equivalent measurement system according to the first embodiment of the present invention.
FIG. 7 is a configuration diagram showing an equivalent measurement system according to a second embodiment of the present invention.
FIG. 8 is a configuration diagram showing a conventional equivalent measurement system for core wire contrast.
FIG. 9 is a characteristic diagram showing a calculation example of transmittance T _i and reflectance R _i with respect to a bending radius ρ.
[Explanation of symbols]
1, 1 ', 1 "Bending

portions

1a, 1a', 1a"

Convex members

1b, 1b ', 1b "Concavity material 2 Light receiver 3 Injection tube 4 Injector 5 Refractive index matching agent 6 Optical fiber 7 Core wire contrast light source 8 Optical branch coupler 9, 9 'Cylinder 10 Optical power meter 11 Radiation auxiliary member

Claims

A light source that transmits a core-line contrast light, a bending portion that bends the optical fiber, and a light receiver that receives light leaking from the bending portion, the core-line contrast light is incident from one end of the optical fiber, and the bending In an optical fiber core contrast device that identifies a core wire by detecting the core wire contrast light emitted from the side surface of the optical fiber bent by the section with the light receiver,
The bent portion is composed of a convex member for bending the optical fiber in an arc shape and a concave member for holding the optical fiber bent along the convex member between the convex member. Because
A gel-like refractive index matching agent having a refractive index similar to that of the coating of the optical fiber is applied to the concave member, and the optical path of the optical fiber for the core-line contrast light emitted from the side surface of the optical fiber and directed to the light receiver. which has an injection and infusion tubes for applying the coating of the optical fiber so that is positioned without contact with the light receiver as a mass in,
In the vicinity of the outlet of the injection tube, there is provided a gap of the coated refractive index matching agent having a mass due to its viscosity.

A light source that transmits a core-line contrast light, a bending portion that bends the optical fiber, and a light receiver that receives light leaking from the bending portion, the core-line contrast light is incident from one end of the optical fiber, and the bending In an optical fiber core contrast device that identifies a core wire by detecting the core wire contrast light emitted from the side surface of the optical fiber bent by the section with the light receiver,
The bent portion is composed of a convex member for bending the optical fiber in an arc shape and a concave member for holding the optical fiber bent along the convex member between the convex member. Because
The recess material is an elastic plastic or synthetic resin that is in close contact with the coating having the same refractive index as that of the coating of the optical fiber, or a portion near the receiver. An optical core contrast device characterized in that the end face on the side has no irregularities and has an angle of 74 ° to 76 ° with respect to the tangent of the optical fiber bent near the end face.