JP2004163154A - Wavelength-measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength-measuring apparatus, where linearity in wavelength measurement output to the reflection center wavelength of FBG is improved and measurement resolution and/or detection precision can be increased as compared with before. <P>SOLUTION: In the wavelength-measuring apparatus, a coefficient is obtained in advance by using a measurement value to the reflection light from an FBG 4 and a monitor value to light for monitoring as preparation processing before the wavelength measurement of reflection light from the FBG 4, and the coefficient is used for obtaining first and second true values, where an error component is removed by using coefficients and the wavelength of the reflection light is measured, based on the logarithm of ratio of the first true value to the second one as the wavelength measurement processing of a specific FBG 4. <P>COPYRIGHT: (C)2004,JPO

Description

【０００５】
ここで、Ｉ_１，Ｉ_２は各ダイオードＡ_１Ｃ，Ａ_２Ｃによる光電流、Ｓ_１（λ），Ｓ_２（λ）は各ダイオードＡ_１Ｃ，Ａ_２Ｃの波長依存感度、φ（λ）は照射光の波長依存強度分布、Δλは照射光波長の半値全幅である。
すなわち、φ（λ）の波長依存強度分布を持つ照射光がＳ_１（λ），Ｓ_２（λ）の波長依存感度を持つフォトダイオードＡ_１Ｃ，Ａ_２Ｃに入射した場合、光センサの出力Ｗは、各ダイオードＡ_１Ｃ，Ａ_２Ｃについての積φ（λ）Ｓ_１（λ），φ（λ）Ｓ_２（λ）を半値全幅Δλにわたって積分した値（つまり光電流Ｉ_１，Ｉ_２）の比のｌｏｇを取ることで求められる。
そして、照射光の出力が所定の範囲内では、照射光の波長ごとに、ｌｏｇ（Ｉ_１／Ｉ_２）がほぼ一定になり、そのときの照射光波長は数式２で表されることが記載されている。
【０００６】
【数２】

【０００７】
なお、図４は上記原理に基づく波長測定システムの構成図であり、３１はレーザ光源、３２は回転式偏光プリズム、３３はビームスプリッタ、３４は前述の一対のフォトダイオードＡ_１Ｃ，Ａ_２Ｃからなるダイオード装置、３５は光出力測定器、３６は上記数式１、数式２を演算する演算器である。
【０００８】
更に、上記文献によれば、各ダイオードの波長感度がほぼ直線的であるような波長範囲（例えば、図３における約６００〜約９００ｎｍ間の３００ｎｍの範囲）では、０．１ｎｍ以下の間隔で波長測定が可能である。つまり、分解能としては１／３０００となる。
【０００９】
従来技術として挙げた前記物理量測定システムでは、前述した数式１、数式２による波長測定原理を基本としたうえ、この測定原理を微小な波長範囲（例えば３ｎｍ以下の範囲）について適用するために、アレイ導波路格子（ＡＷＧ）を使用している。
このＡＷＧは、論文「Ｗａｖｅｌｅｎｇｔｈ Ｍｕｌｔｉｐｌｅｘｅｒ Ｂａｓｅｄ ｏｎ ＳｉＯ２−Ｔａ２０５ Ａｒｒａｙｅｄ−Ｗａｖｅｇｕｉｄｅ Ｇｒａｔｉｎｇ （Ｔａｋａｈａｓｉ， ｅｔ．ａｌ， Ｊｏｕｒｎａｌ ｏｆ Ｌｉｇｈｔｗａｖｅ Ｔｅｃｈｎｏｌｏｇｙ Ｖｏｌ．１２， Ｎｏ．６， １９９４）」等に記載されているように、所定の曲率半径のアレイ導波路と、その入力側、出力側にそれぞれ形成されたスラブ導波路と、これらのスラブ導波路にそれぞれ連続する複数チャンネルの入力導波路及び出力導波路とを有する構造であり、入力光を１ｎｍ以下の分解能で弁別可能な素子である。
【００１０】
従来技術では、図５に示すごとく、光ファイバ３の長手方向に形成された複数のＦＢＧ４に対し、それぞれ重複しないように微小な反射光波長範囲を割り当てておき（一例として、第１のＦＢＧには１５００〜１５０３ｎｍ、第２のＦＢＧには１５０３ｎｍ〜１５０６ｎｍ、第３のＦＢＧには１５０６〜１５０９ｎｍ、・・・等）、光源１から光分岐器２、光コネクタ５を経た出射光のＦＢＧ４からの反射光をＡＷＧ６に入力することにより、中心波長が例えば１ｎｍ以下の間隔の複数の波長に分離する。
そして、ＡＷＧ６の隣接する二つの出力導波路（計測用出力チャンネル）から一対のプリアンプ付きフォトダイオード７に光を入射させることにより、微小な波長範囲について前述した数式１、数式２を適用し、高分解能で波長を検出可能としている。
【００１１】
すなわち、従来技術によれば、各ＦＢＧ４の位置における温度や歪み等の物理量に対応する波長を検出することができ、これによって温度分布や圧力分布を計測することが可能になっている。
なお、図５において８は一対のフォトダイオード７の光電流（前述のＩ_１，Ｉ_２に相当）を除算する割算器、９’は波長検出器、１０は波長計測のための演算を行うマイクロコンピュータである。割算器８からの出力は、数式２のＩ_１／Ｉ_２に相当する。さらに、マイクロコンピュータ１０で数式２の演算を行って、波長を算出し、その波長からどの位置にあるＦＢＧにおいて物理量が変化したか、つまり物理量の変化位置を測定する。
【００１２】
【発明が解決しようとする課題】
図６は、上記従来技術におけるＦＢＧ４の反射率及びＡＷＧ６の透過率のスペクトルを示す図である。従来技術では、一対のプリアンプ付きフォトダイオード７ごとに割算器８により光電流の比演算を行い、その出力の対数を計算して波長測定出力ρ（λ_ｂｊ）を求めていた。ここで、ｊ＝１，２，３，・・・，Ｎであり、ＮはＦＢＧの数である。
【００１３】
すなわち、各ＦＢＧには前述のごとくその反射波長を測定するためのＡＷＧの出力チャンネル対（プリアンプ付きフォトダイオード７の対）を予め定めてあり、他のＦＢＧの反射帯域の影響を受けないように設計されている。例えば、図６に示すようにＦＢＧ_ｊの反射帯域はＡＷＧのチャンネルｉ及びチャンネル（ｉ＋１）の透過帯域のみにラップしてチャンネル（ｉ＋２）の透過帯域にはラップせず、また、ＦＢＧ_ｊ＋１の反射帯域はＡＷＧのチャンネル（ｉ＋２）及びチャンネル（ｉ＋３）の透過帯域のみにラップしてチャンネル（ｉ＋１）の透過帯域にはラップしないようになっている。
【００１４】
このような条件で、ｊ番目のＦＢＧの波長測定出力ρ（λ_ｂｊ）を以下に求めてみる。光ファイバの光損失及び後方散乱は無視できるものとすると、一対のプリアンプ付きフォトダイオード７のうち一方のフォトダイオードの出力Ｐ（λ_ｂｊ）は、数式３によって表される。
【００１５】
【数３】

【００１６】
また、他方のフォトダイオードの出力Ｐ（λ_ｂｊ）は、数式３におけるｉをｉ＋１に変えた式となる。
従って、これらの式の比の対数をとると、数式４を得る。
【００１７】
【数４】

【００１８】
ただし、数式３，数式４におけるεは、数式５の通りである。
【００１９】
【数５】

【００２０】
また、数式３〜数式５における各値は以下の通りである。このうちの一部は図６にも示してある。
Ｋ：定数
ａ：ＡＷＧのピーク透過率
ｂ：ＦＢＧのピーク反射率
ａ_０：ＡＷＧの不要なノイズ光となるバイアス透過率
ｂ_０：ＦＢＧの不要なノイズ光となるバイアス反射率
Δλ_ａ：ＡＷＧの半値全幅
Δλ_ｂ：ＦＢＧの半値全幅
Δλ_ｓ：光源の半値全幅
λ_ｂｊ：ＦＢＧの反射中心波長
λ_ｊ：ＡＷＧのチャンネルｉの透過中心波長
λ_ｊ＋１：ＡＷＧのチャンネル（ｉ＋１）の透過中心波長
【００２１】
前述した数式４の特性を図示すると図７のようになる。つまり、ＦＢＧの反射中心波長λ_ｂｊに対する波長測定出力ρ（λ_ｂｊ）の特性が一部非直線状になっていて測定分解能が悪く、波長検出精度を低下させる原因となっていた。
これは、数式４において、ＡＷＧの不要なノイズ光となるバイアス透過ａ_ｏやＦＢＧの不要なノイズ光となるバイアス反射率ｂ_ｏ等により、εがゼロにならず誤差成分として作用するためである。
そこで本発明は、上記誤差成分εに起因する波長測定出力ρ（λ_ｂｊ）の非直線性を改善し、測定分解能及び検出精度を向上させるようにした波長計測装置を提供しようとするものである。
【００２２】
【課題を解決するための手段】
上記問題を解決するため、請求項１記載の発明に係る波長計測装置によれば、測定光が入射される光ファイバに一以上のＦＢＧが形成され、各ＦＢＧからの反射光の波長を検出して各ＦＢＧの位置における物理量を測定するシステムであって、ＦＢＧからの反射光を、中心波長が微小な間隔の複数波長に分離可能なＡＷＧに入射させるとともに、このＡＷＧの複数の計測用出力チャンネルにそれぞれ接続された計測用受光素子を一対ごとにＦＢＧに対応させて、一対の計測用受光素子の計測値を用いて反射光の波長を計測するようにした波長計測装置において、
前記ＡＷＧの複数対の計測用出力チャンネルとは別個に設けられた一対のモニタ用出力チャンネルにそれぞれ接続され、モニタ値を出力する一対のモニタ用受光素子を備え、
ＦＢＧからの反射光の波長計測前の準備処理として、
あるＦＢＧからの反射光に対する計測値、および、モニタ用の光に対するモニタ値を用いて係数を予め求めておき、
所定のＦＢＧの波長計測処理として、
係数を用いて誤差成分を除去した第１，第２の真値を求め、これら第１の真値と第２の真値とによる比の対数に基づいて反射光の波長を測定することを特徴とする。
【００２３】
また、請求項２記載の発明に係る波長計測装置によれば、
請求項１記載の波長計測装置において、
一対の計測用出力チャンネルは第１，第２の計測値を出力するものと、また、一対のモニタ用出力チャンネルは第１，第２のモニタ値を出力値として出力するものとし、
ＦＢＧからの反射光の波長計測前の準備処理として、
第１の計測値と第１のモニタ値との差分値（以下、第１の補正用差分値という。）、第２の計測値と第１のモニタ値との差分値（以下、第２の補正用差分値という。）第１，第２のモニタ値の差分値（以下、第３の補正用差分値という。）を求め、
第１の補正用差分値を第３の補正用差分値で除した比（以下、単に第１係数という）、および、
第２の補正用差分値を第３の補正用差分値で除した比（以下、単に第２係数という）を予め登録しておき、
所定のＦＢＧの波長計測処理として、
第１の計測値と第１のモニタ値との差分値（以下、第１の差分値という。）、第２の計測値と第１のモニタ値との差分値（以下、第２の差分値という。）、および、第１，第２のモニタ値の差分値（以下、第３の差分値という。）を求め、第３の差分値と第１係数との積を、第１の差分値から減じて、第１の真値を求め、
第３の差分値と第２係数との積を、第２の差分値から減じて、第２の真値を求め、
第１（第２）の真値と第２（第１）の真値との比の対数に基づいて反射光の波長を計測することを特徴とする。
【００２４】
また、請求項３記載の発明に係る波長計測装置によれば、
請求項２記載の波長計測装置において、
光源と、
光源に接続される光分岐器と、
光分岐器に接続され、複数のＦＢＧが設けられた光ファイバと、
光分岐器に接続され、光ファイバからの光のみを入射するＡＷＧと、
ＡＷＧから出力される計測用出力チャンネルからの光を光電流信号に変換して出力する計測用受光素子と、
ＡＷＧから出力されるモニタ用出力チャンネルからの光を光電流信号に変換して出力するモニタ用受光素子と、
これら計測用受光素子およびモニタ用受光素子からの光電流信号が入力されるマイクロコンピュータと、
を備え、
前記マイクロコンピュータは、計測用受光素子からの第１，第２の計測値およびモニタ用受光素子からの第１，第２のモニタ値に相当する光電流信号をデジタルデータに変換して入力し、前記ＦＢＧからの反射光の波長計測前の準備処理、および、所定のＦＢＧの波長計測処理を行って、波長を算出することを特徴とする。
【００２５】
【発明の実施の形態】
以下、本発明の波長測定装置の実施形態について図を参照しつつ説明する。
図１は本発明の実施形態を示すシステム構成図あり、図５と同一の構成要素には同一の参照符号を付してある。光源１、光分岐器２、光ファイバ３、ＦＢＧ４、光コネクタ５の構成及び動作と、波長検出器９内のＡＷＧ６、計測用受光素子の一具体例であるプリアンプ付きフォトダイオード７の構成及び動作は図５と同様である。
【００２６】
本実施形態では、ＡＷＧ６にさらにモニタ用出力チャンネル一対を設け、この一対のモニタ用出力チャンネルにモニタ用受光素子の一具体例であるプリアンプ付きフォトダイオード１１が一対接続されている。この一対のプリアンプ付きフォトダイオード１１の出力信号はマイクロコンピュータ１０に入力されている。これらのモニタ用出力チャンネル及びプリアンプ付きフォトダイオード１１は、前述の数式５におけるａ，ｂ，ｃ，ａ_０，ｂ_０ や半値全幅を検出するためのものである。
【００２７】
続いてマイクロコンピュータ１０による計測処理について説明する。
まず、計測原理について解析的に説明する。
本実施形態では、まずＦＢＧからの反射光の波長計測前の準備処理を予め行っておき、そのうえで、所定のＦＢＧの波長計測処理を行うものである。
【００２８】
まず、ＦＢＧからの反射光の波長計測前の準備処理について説明する。
一対の計測用出力チャンネルのプリアンプ付きフォトダイオード７は、第１，第２の計測値を出力するものと、また、一対のモニタ用出力チャンネルのプリアンプ付きフォトダイオード１１は、第１，第２のモニタ値を出力値を出力するものとする。
【００２９】
一対の計測用出力チャンネルのうちの一方に接続されたプリアンプ付きフォトダイオード７の第１の計測値Ｐ（λ_ｉ，λ_ｂｊ）から、一対のモニタ用出力チャンネルのうちの一方に接続されたプリアンプ付きフォトダイオード１１の第１のモニタ値Ｐ（λ_ｍ１，λ_ｂｊ）を差し引いた差分値Ｅ（λ_ｉ，λ_ｍ１）＝Ｐ（λ_ｉ，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）を算出する（以下、第１の補正用差分値という）。
この第１の補正用差分値Ｐ（λ_ｉ，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）は詳しくは次の式で表される。
【００３０】
【数６】

【００３１】
ここで、λ_ｍ１は一対のモニタ用出力チャンネルのうちの一方のチャンネルの中心波長、Ｃ_ｉは光分岐器２の透過率、Ｉ_ｓは光源１のピークパワー、ｄはフォトダイオード７，１１の光電変換効率、Δλ_ｆはＡＷＧ６のフリースペクトルレンジ、λ_ｓは光源１の中心波長、Ｎ_ｒは光源１のフリースペクトルレンジで表されるＡＷＧ６の透過率の繰り返し特性をガウス分布の繰り返し関数で近似した場合の繰り返し回数、ｒはこの繰り返し特性をシグマ記号で表した場合の繰り返しのためのパラメータである。
【００３２】
また、一対の計測用出力チャンネルのうちの他方に接続されたプリアンプ付きフォトダイオード７の第２の計測値Ｐ（λ_ｉ＋１，λ_ｂｊ）から、一対のモニタ用出力チャンネルのうちの一方のチャンネルに接続されたプリアンプ付きフォトダイオード１１の第１のモニタ値Ｐ（λ_ｍ１，λ_ｂｊ）を差し引いた差分値Ｅ（λ_ｉ＋１，λ_ｍ１）＝Ｐ（λ_ｉ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）を算出する（以下、第２の補正用差分値という）。この第２の補正用差分値は、上記の数式６のｉに代えてｉ＋１を挿入したものである。
【００３３】
そして、第１のモニタ値と第２のモニタ値との差分値Ｅ（λ_ｍ２，λ_ｍ１）を算出する（以下、第３の補正用差分値という）。この第３の補正用差分値Ｅ（λ_ｍ２，λ_ｍ１）は次の式で示される。
【００３４】
【数７】

【００３５】
ここでλ_ｍ２は、一対のモニタ用出力チャンネルのうちの一方のチャンネルの中心波長λ_ｍ１とは別のチャンネルの中心波長である。
【００３６】
続いて、第１の補正用差分値を第３の補正用差分値で除した比であるＲ（λ_ｉ，λ_ｍ１，λ_ｍ２）を算出する（以下Ｒ（λ_ｉ，λ_ｍ１，λ_ｍ２）を第１係数という）。
この第１係数Ｒ（λ_ｉ，λ_ｍ１，λ_ｍ２）は次式で示される。
【００３７】
【数８】

【００３８】
そして同様に、第２の補正用差分値を第３の補正用差分値で除した比であるＲ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２）を算出する（以下Ｒ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２）を第２係数という）。
この第２係数Ｒ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２）は数式８のｉの代わりにｉ＋１を代入した式で示される。
【００３９】
この第１係数Ｒ（λ_ｉ，λ_ｍ１，λ_ｍ２）および第２係数Ｒ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２）はマイクロコンピュータ１０の図示しないメモリ部に登録される。
【００４０】
上記したような、ＦＢＧからの反射光の波長計測前の準備処理を予め行っておき、続いて、所定のＦＢＧの波長計測処理の解析的な説明を行う。
計測処理時には、再度数式６の差分値Ｐ（λ_ｉ，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）＝Ｅ（λ_ｉ，λ_ｍ１）（以下、第１の差分値という）、および、数式７の差分値Ｅ（λ_ｍ２，λ_ｍ１）（以下、第３の差分値という）が算出される。そして、マイクロコンピュータ１０に登録された数式８の第１係数Ｒ（λ_ｉ，λ_ｍ１，λ_ｍ２）とを用いて次式のような第１の真値が算出される。
【００４１】
【数９】

【００４２】
第２の真数も同様にして求める。
差分値Ｅ（λ_ｉ，λ_ｍ１）＝Ｐ（λ_ｉ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）（以下、第２の差分値という）、および、数式７の第３の差分値Ｅ（λ_ｍ２，λ_ｍ１）が算出される。そして、マイクロコンピュータに登録された数式８の第２係数Ｒ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２）とを用いて第２の真値が算出される。
これら、第１の真数と第２の真数の比の対数をとれば次式を得る。
【００４３】
【数１０】

【００４４】
第１の差分値だけでは数式６の第１項（誤差要因）が残ってしまうが、数式９の演算を行うことによりλ_ｂｊを含むガウス分布だけとなるので、第１の真数、第２の真数の比の対数演算で数式１０に示すようにλ_ｂｊの１次関数ρ（λ_ｂｊ）を得ることができる。即ちＦＢＧの反射中心波長λ_ｂｊに対する波長測定出力ρ（λ_ｂｊ）は図２に示すように直線性が改善されることになる。
【００４５】
続いて、上記原理に基づくマイクロコンピュータ１０による処理に重点をおいて具体的に説明する。
まず、マイクロコンピュータ１０は、ＦＢＧからの反射光の波長計測前の準備処理を行う。この準備処理では、プリアンプ付きフォトダイオード１１から第１のモニタ値（Ｐ（λ_ｍ１，λ_ｂｊ）に相当）および第２のモニタ値（Ｐ（λ_ｍ２，λ_ｂｊ）に相当）を入力し、また、あるＦＢＧを計測する一対のチャンネルであるプリアンプ付きフォトダイオード７からの第１の計測値（Ｐ（λ_ｉ，λ_ｂｊ）に相当）および第２の計測値（Ｐ（λ_ｉ＋１，λ_ｂｊ）に相当）を入力する。
【００４６】
そして、マイクロコンピュータ１０は、第１の計測値と第１のモニタ値との差である第１の補正用差分値（Ｅ（λ_ｉ，λ_ｍ１）＝Ｐ（λ_ｉ，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）に相当）、第２の計測値と第１のモニタ値との差である第２の補正用差分値（Ｅ（λ_ｉ＋１，λ_ｍ１）＝Ｐ（λ_ｉ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）に相当）、および、第１のモニタ値と第２のモニタ値との差である第３の補正用差分値（Ｅ（λ_ｍ２，λ_ｍ１）＝Ｐ（λ_ｍ２，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）に相当）を求める。
【００４７】
そして、第１の補正用差分値を第３の補正用差分値で除した比である第１係数（Ｒ（λ_ｉ，λ_ｍ１，λ_ｍ２））と、第２の補正用差分値を第３の補正用差分値で除した比である第２係数（Ｒ（λ_ｉ＋１，λ_ｍ１，λ_ｍ２））とを予め求め、マイクロコンピュータ１０の図示しないメモリ部等に登録しておく。
【００４８】
続いて、通常のＦＢＧの波長計測処理を行う。この場合、マイクロコンピュータ１０は、第１の計測値から第１のモニタ値を差し引いた第１の差分値（Ｐ（λ_ｉ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ）に相当する。）、第２の計測値から第１のモニタ値を差し引いた第２の差分値（Ｐ（λ_ｉ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ））に相当する。）、および、第１，第２のモニタ値の第３の差分値（Ｅ（λ_ｍ２，λ_ｍ１）＝Ｐ（λ_ｍ＋１，λ_ｂｊ）−Ｐ（λ_ｍ１，λ_ｂｊ））に相当する。）を求める。
【００４９】
そして第３の差分値と前記の第１係数との積を、第１の差分値から減じて第１の真値を求め、また、第３の差分値と前記の第２係数との積を、第２の差分値から減じて第２の真値を求める。
そして、第１の真値と第２の真値との比の対数（数式１０参照）に基づいて反射光の波長を計測する。
【００５０】
マイクロコンピュータ１０が、このような、▲１▼ＦＢＧからの反射光の波長計測前の準備処理、および、▲２▼所定のＦＢＧの波長計測処理を行って、波長を計測するようにしたため、誤差成分εによる影響が完全に除去され、ＦＢＧの反射中心波長λ_ｂｊ に対する波長測定出力ρ（λ_ｂｊ ）は図２のように直線性が改善されるため、検出能力を高めることができる。
【００５１】
【発明の効果】
以上のように本発明によれば、ＦＢＧの反射中心波長に対する波長測定出力の直線性が改善され、従来よりも測定分解能ならびに検出精度を向上させることができる。
【図面の簡単な説明】
【図１】本発明の実施形態を示すシステム構成図である。
【図２】本発明の実施形態におけるＦＢＧの反射中心波長に対する波長測定出力の特性図である。
【図３】従来技術における波長測定原理の説明図である。
【図４】公知の波長測定システムの構成図である。
【図５】従来技術を示す構成図である。
【図６】従来技術におけるＦＢＧの反射率及びＡＷＧの透過率を示す図である。
【図７】従来技術におけるＦＢＧの反射中心波長に対する波長測定出力の特性図である。
【符号の説明】
１ 光源
２ 光分岐器
３ 光ファイバ
４ ＦＢＧ（ブラッグ回折格子）
５ 光コネクタ
６ ＡＷＧ（アレイ導波路格子）
７，１１ プリアンプ付きフォトダイオード
８ 割算器
９ 波長検出器
１０ マイクロコンピュータ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring a physical quantity such as temperature or strain (pressure) at a measurement point from a Bragg diffraction grating of an optical fiber formed at the measurement point (hereinafter, referred to as FBG for Fiber Bragg Grating). The present invention relates to a wavelength measuring device that measures the wavelength of reflected light.
[0002]
[Prior art]
As this kind of invention, there is known a physical quantity measurement system (hereinafter, referred to as a prior art) described in Japanese Patent Application Laid-Open No. 2000-180270 by the present applicant.
The above-mentioned prior art is a system in which one or more FBGs are formed on an optical fiber on which measurement light is incident, and a wavelength of reflected light from each FBG is detected to measure a physical quantity such as a temperature at a position of each FBG. The reflected light from the FBG is made incident on an arrayed waveguide diffraction grating (hereinafter abbreviated as AWG, acronym for Arrayed Wave Guide) capable of separating the center wavelength into a plurality of wavelengths having minute intervals. The wavelength of the reflected light is measured based on the logarithm of the ratio of the photocurrent by a pair of light receiving elements provided in each channel.
[0003]
In this prior art, the principle described in the paper "Wavelength determination of semiconductor lasers: precision but inexpensive" (Jan Christian Braash et al., Optical Engineering 1995) is described.
According to the above literature, form a diode formed between the wavelength sensitivity different pair of photodiodes (electrodes A ₁ -C shown in the graph of FIG. 3 diode A _{1 C,} across the electrodes A ₂ -C When a monochromatic light is applied to a sensor including a diode A ₂ C) and a high-precision long amplifier, the output W of the sensor is expressed by Expression 1.
[0004]
(Equation 1)

[0005]
Here, I ₁ and I ₂ are photocurrents generated by the diodes A ₁ C and A ₂ C, S ₁ (λ) and S ₂ (λ) are wavelength-dependent sensitivities of the diodes A ₁ C and A ₂ C, and φ ( λ) is the wavelength-dependent intensity distribution of the irradiation light, and Δλ is the full width at half maximum of the irradiation light wavelength.
That, φ (λ) illuminating light S ₁ having a wavelength dependent intensity distribution _(lambda), the photodiode A _{1 C} having a wavelength-dependent sensitivity of the S 2 _(λ), when entering the A 2 _C, the optical sensor The output W is a value obtained by integrating the products φ (λ) S ₁ (λ) and φ (λ) S ₂ (λ) of the diodes A ₁ C and A ₂ C over the full width at half maximum Δλ (that is, the photocurrent I ₁ , It is determined by taking the log of the ratio of I ₂ ).
Then, when the output of the irradiation light is within a predetermined range, log (I ₁ / I ₂ ) becomes substantially constant for each wavelength of the irradiation light, and the irradiation light wavelength at that time is expressed by Expression 2. Have been.
[0006]
(Equation 2)

[0007]
FIG. 4 is a configuration diagram of a wavelength measurement system based on the above principle. Reference numeral 31 denotes a laser light source, 32 denotes a rotating polarizing prism, 33 denotes a beam splitter, and 34 denotes the pair of photodiodes A ₁ C and A ₂ C described above. , 35 is an optical output measuring device, and 36 is a calculator for calculating the above-described equations (1) and (2).
[0008]
Further, according to the above-mentioned document, in a wavelength range where the wavelength sensitivity of each diode is almost linear (for example, a range of 300 nm between about 600 to about 900 nm in FIG. 3), the wavelength is not more than 0.1 nm. Measurement is possible. That is, the resolution is 1/3000.
[0009]
In the physical quantity measurement system described as a conventional technique, based on the wavelength measurement principle based on the above-described equations 1 and 2, the array is used to apply the measurement principle to a minute wavelength range (for example, a range of 3 nm or less). A waveguide grating (AWG) is used.
This AWG is described in the paper "Wavelength Multiplexer Based on SiO2-Ta205 Arrayed-Waveguide Grating" (Takahashi, et.al, Journal of Lightwave, etc., and described in Vol. An array waveguide having a radius of curvature, a slab waveguide formed on each of the input side and the output side thereof, and a structure having an input waveguide and an output waveguide of a plurality of channels respectively continuous with these slab waveguides, It is an element that can discriminate input light with a resolution of 1 nm or less.
[0010]
In the prior art, as shown in FIG. 5, a small reflected light wavelength range is allocated to a plurality of FBGs 4 formed in the longitudinal direction of the optical fiber 3 so as not to overlap (for example, the first FBG is assigned to the first FBG). Are 1500 to 1503 nm, 1503 nm to 1506 nm for the second FBG, 1506 to 1509 nm for the third FBG, etc.), and the light emitted from the light source 1 through the optical splitter 2 and the optical connector 5 from the FBG 4. By inputting the reflected light to the AWG 6, the central wavelength is separated into a plurality of wavelengths at intervals of, for example, 1 nm or less.
Then, by letting light from two adjacent output waveguides (measurement output channels) of the AWG 6 into a pair of photodiodes with a preamplifier 7, the above-described equations 1 and 2 are applied to a minute wavelength range, and The wavelength can be detected with the resolution.
[0011]
That is, according to the related art, it is possible to detect a wavelength corresponding to a physical quantity such as a temperature and a strain at the position of each FBG 4, and thereby it is possible to measure a temperature distribution and a pressure distribution.
In FIG. 5, reference numeral 8 denotes a divider for dividing the photocurrent of the pair of photodiodes 7 (corresponding to the above-described I ₁ and I ₂ ), reference numeral 9 ′ denotes a wavelength detector, and reference numeral 10 denotes an operation for wavelength measurement. It is a microcomputer. The output from the divider 8 corresponds to I ₁ / I ₂ in Equation 2. Further, the microcomputer 10 calculates the wavelength by calculating Equation 2, and measures the position of the FBG at which the physical quantity changes from the wavelength, that is, the change position of the physical quantity.
[0012]
[Problems to be solved by the invention]
FIG. 6 is a diagram showing spectra of the reflectance of the FBG 4 and the transmittance of the AWG 6 in the above-described conventional technique. In the prior art, the ratio calculation of the photocurrent is performed by the divider 8 for each pair of the photodiodes 7 with a preamplifier, and the logarithm of the output is calculated to obtain the wavelength measurement output ρ (λ _bj ). Here, j = 1, 2, 3,..., N, where N is the number of FBGs.
[0013]
That is, as described above, an AWG output channel pair (a pair of photodiodes 7 with a preamplifier) for measuring the reflection wavelength is predetermined for each FBG, so that the FBG is not affected by the reflection band of another FBG. Designed. For example, as shown in FIG. 6, the reflection band of FBG _j wraps only in the transmission band of AWG channel i and channel (i + 1), does not wrap in the transmission band of channel (i + 2), and the reflection band of FBG _{j + 1} The band is wrapped only in the transmission band of the channel (i + 2) and the channel (i + 3) of the AWG, and is not wrapped in the transmission band of the channel (i + 1).
[0014]
Under such conditions, the wavelength measurement output ρ (λ _bj ) of the j-th FBG will be obtained below. Assuming that the optical loss and the backscatter of the optical fiber are negligible, the output P (λ _bj ) of one of the pair of photodiodes with a preamplifier 7 is expressed by Expression 3.
[0015]
[Equation 3]

[0016]
Further, the output P (λ _bj ) of the other photodiode is an expression obtained by changing i in Expression 3 to i + 1.
Therefore, taking the logarithm of the ratio of these equations, Equation 4 is obtained.
[0017]
(Equation 4)

[0018]
However, ε in Equations 3 and 4 is as shown in Equation 5.
[0019]
(Equation 5)

[0020]
In addition, each value in Expressions 3 to 5 is as follows. Some of them are also shown in FIG.
K: constant a: peak transmittance of AWG b: peak reflectance of FBG a ₀ : bias transmittance b ₀ which becomes unnecessary noise light of AWG b ₀ : bias reflectance Δλ _a which becomes unnecessary noise light of FBG Full width at half maximum Δλ _b : Full width at half maximum of FBG Δλ _s : Full width at half maximum of light source λ _bj : Reflection center wavelength of FBG λ _j : Transmission center wavelength of AWG channel i λ _{j + 1} : Transmission center wavelength of AWG channel (i + 1) ]
FIG. 7 shows the characteristics of the above-described equation (4). In other words, the characteristics of the wavelength measurement output ρ (λ _bj ) with respect to the reflection center wavelength λ _bj of the FBG are partially non-linear, and the measurement resolution is poor, causing a decrease in wavelength detection accuracy.
This is because the in Equation 4, the bias reflectance b _o, etc. becomes unnecessary noise light bias transmitting a _o and FBG becomes unnecessary noise light AWG, epsilon acts as an error component does not become zero .
Therefore, the present invention aims to provide a wavelength measurement device that improves the non-linearity of the wavelength measurement output ρ (λ _bj ) due to the error component ε, thereby improving the measurement resolution and detection accuracy. .
[0022]
[Means for Solving the Problems]
In order to solve the above problem, according to the wavelength measuring apparatus according to the first aspect of the present invention, one or more FBGs are formed in the optical fiber on which the measuring light is incident, and the wavelength of the reflected light from each FBG is detected. A system for measuring a physical quantity at the position of each FBG by making reflected light from the FBG incident on an AWG that can be separated into a plurality of wavelengths whose center wavelengths are minutely spaced, and a plurality of measurement output channels of the AWG. In a wavelength measuring device, the measuring light receiving elements respectively connected to the FBG are associated with each pair, and the wavelength of the reflected light is measured using the measured value of the pair of measuring light receiving elements.
The AWG includes a pair of monitoring light output elements connected to a pair of monitoring output channels provided separately from the plurality of pairs of measurement output channels of the AWG, and outputting a monitoring value,
As preparation processing before measuring the wavelength of the reflected light from the FBG,
A coefficient is obtained in advance by using a measurement value for reflected light from a certain FBG and a monitor value for light for monitoring,
As a predetermined FBG wavelength measurement process,
First and second true values from which error components have been removed using coefficients are obtained, and the wavelength of the reflected light is measured based on the logarithm of the ratio between the first true value and the second true value. And
[0023]
According to the wavelength measuring apparatus of the invention described in claim 2,
The wavelength measuring device according to claim 1,
A pair of output channels for measurement output the first and second measurement values, and a pair of output channels for monitoring output the first and second monitor values as output values,
As preparation processing before measuring the wavelength of the reflected light from the FBG,
A difference value between the first measurement value and the first monitor value (hereinafter, referred to as a first correction difference value), and a difference value between the second measurement value and the first monitor value (hereinafter, a second correction value). A difference value between the first and second monitor values (hereinafter, referred to as a third difference value for correction) is obtained.
A ratio obtained by dividing the first correction difference value by the third correction difference value (hereinafter, simply referred to as a first coefficient), and
A ratio obtained by dividing the second correction difference value by the third correction difference value (hereinafter simply referred to as a second coefficient) is registered in advance,
As a predetermined FBG wavelength measurement process,
A difference value between the first measurement value and the first monitor value (hereinafter, referred to as a first difference value), and a difference value between the second measurement value and the first monitor value (hereinafter, a second difference value) And a difference value between the first and second monitor values (hereinafter, referred to as a third difference value) is obtained, and the product of the third difference value and the first coefficient is calculated as the first difference value. To obtain a first true value,
Subtracting the product of the third difference value and the second coefficient from the second difference value to obtain a second true value;
The wavelength of the reflected light is measured based on the logarithm of the ratio between the first (second) true value and the second (first) true value.
[0024]
According to the wavelength measuring device of the invention described in claim 3,
The wavelength measuring device according to claim 2,
A light source,
An optical splitter connected to the light source,
An optical fiber connected to the optical branching device and provided with a plurality of FBGs;
An AWG connected to the optical branching device and receiving only light from an optical fiber;
A light receiving element for measurement that converts light from the output channel for measurement output from the AWG into a photocurrent signal and outputs the photoelectric current signal;
A monitor light receiving element for converting light from the monitor output channel output from the AWG into a photocurrent signal and outputting the photocurrent signal;
A microcomputer to which photocurrent signals from the measurement light receiving element and the monitoring light receiving element are input;
With
The microcomputer converts the photocurrent signal corresponding to the first and second measurement values from the measurement light-receiving element and the first and second monitor values from the monitoring light-receiving element into digital data and inputs them. The wavelength is calculated by performing a preparation process before measuring the wavelength of the reflected light from the FBG and a predetermined FBG wavelength measurement process.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a wavelength measuring device of the present invention will be described with reference to the drawings.
FIG. 1 is a system configuration diagram showing an embodiment of the present invention, and the same components as those in FIG. 5 are denoted by the same reference numerals. The configuration and operation of the light source 1, the optical splitter 2, the optical fiber 3, the FBG 4, and the optical connector 5, and the configuration and operation of the AWG 6 in the wavelength detector 9 and the photodiode 7 with a preamplifier which is a specific example of the light receiving element for measurement. Is similar to FIG.
[0026]
In this embodiment, the AWG 6 is further provided with a pair of monitor output channels, and a pair of photodiodes 11 with a preamplifier, which is a specific example of a monitor light receiving element, are connected to the pair of monitor output channels. Output signals of the pair of photodiodes with preamplifier 11 are input to the microcomputer 10. The monitor output channel and the photodiode 11 with a preamplifier are for detecting a, b, c, a ₀ , b ₀ and the full width at half maximum in the above-described equation (5).
[0027]
Subsequently, the measurement processing by the microcomputer 10 will be described.
First, the measurement principle will be analytically described.
In the present embodiment, first, preparation processing before measuring the wavelength of the reflected light from the FBG is performed in advance, and then a predetermined FBG wavelength measurement processing is performed.
[0028]
First, a preparation process before measuring the wavelength of the reflected light from the FBG will be described.
The pair of photodiodes with a preamplifier 7 of output channels for measurement output the first and second measured values, and the pair of photodiodes 11 with a preamplifier of the output channels for monitoring correspond to the first and second photodiodes. It is assumed that the monitor value outputs the output value.
[0029]
From the first measured value P (λ _i , λ _bj ) of the photodiode 7 with a preamplifier connected to one of the pair of measurement output channels, the preamplifier connected to one of the pair of monitor output channels A difference value E (λ _i , λ _m1 ) = P (λ _i , λ _bj ) −P (λ _m1 , λ _bj ) obtained by subtracting the first monitor value P (λ _m1 , λ _bj ) of the attached photodiode 11 is obtained. It is calculated (hereinafter, referred to as a first correction difference value).
This first correction difference value P (λ _i , λ _bj ) −P (λ _m1 , λ _bj ) is expressed in detail by the following equation.
[0030]
(Equation 6)

[0031]
Here, lambda _m1 One channel center wavelength of the of the output channel for a pair of monitors, C _i transmittance of the optical divider 2, I _s is the peak power of the light source 1, d is the photodiode 7,11 The photoelectric conversion efficiency, Δλ _f is the free spectral range of the AWG 6, λ _s is the center wavelength of the light source 1, and N _r is the repetition characteristic of the transmittance of the AWG 6 represented by the free spectral range of the light source 1 by a Gaussian repetition function. The number of repetitions, r, is a parameter for repetition when this repetition characteristic is represented by a sigma symbol.
[0032]
Further, from the second measurement value P (λ _{i + 1} , λ _bj ) of the photodiode 7 with a preamplifier connected to the other of the pair of measurement output channels, the signal is transferred to one of the pair of monitoring output channels. A difference value E (λ _{i + 1} , λ _m1 ) obtained by subtracting the first monitor value P (λ _m1 , λ _bj ) of the connected photodiode 11 with a preamplifier = P (λ _{i + 1} , λ _bj ) −P (λ _m1 , λ _bj ) is calculated (hereinafter, referred to as a second correction difference value). The second correction difference value is obtained by inserting i + 1 in place of i in Expression 6 above.
[0033]
Then, a difference value E (λ _m2 , λ _m1 ) between the first monitor value and the second monitor value is calculated (hereinafter, referred to as a third correction difference value). The third correction difference value E (λ _m2 , λ _m1 ) is expressed by the following equation.
[0034]
(Equation 7)

[0035]
Here, λ _m2 is the center wavelength of a channel different from the center wavelength λ _m1 of one of the pair of monitor output channels.
[0036]
Subsequently, R (λ _i , λ _m1 , λ _m2 ), which is a ratio of the first correction difference value divided by the third correction difference value, is calculated (hereinafter, R (λ _i , λ _m1 , λ _m2). ) Is referred to as a first coefficient).
The first coefficient R (λ _i , λ _m1 , λ _m2 ) is represented by the following equation.
[0037]
(Equation 8)

[0038]
Similarly, a ratio R (λ _{i + 1} , λ _m1 , λ _m2 ) obtained by dividing the second correction difference value by the third correction difference value is calculated (hereinafter, R (λ _{i + 1} , λ _m1 , λ _m2 ) is referred to as a second coefficient).
The second coefficient R (λ _{i + 1} , λ _m1 , λ _m2 ) is represented by an equation obtained by substituting i + 1 for i in Equation 8.
[0039]
The first coefficient _{R (λ i, λ m1,} λ m2) and a second coefficient _{R (λ i + 1, λ} m1, λ m2) is registered in the memory unit (not shown) of the microcomputer 10.
[0040]
The above-described preparation process before measuring the wavelength of the reflected light from the FBG is performed in advance, and then, an analytical description of the predetermined FBG wavelength measurement process will be given.
At the time of the measurement processing, the difference value P (λ _i , λ _bj ) −P (λ _m1 , λ _bj ) = E (λ _i , λ _m1 ) (hereinafter, referred to as a first difference value) in Expression 6 and the expression 7 is calculated (hereinafter, referred to as a third difference value) E (λ _m2 , λ _m1 ). Then, using the first coefficient R (λ _i , λ _m1 , λ _m2 ) of Equation 8 registered in the microcomputer 10, a first true value such as the following equation is calculated.
[0041]
(Equation 9)

[0042]
The second antilog is similarly obtained.
Difference value E (λ _i , λ _m1 ) = P (λ _{i + 1} , λ _bj ) −P (λ _m1 , λ _bj ) (hereinafter, referred to as a second difference value) and a third difference value E (Λ _m2 , λ _m1 ) is calculated. Then, a second true value is calculated using the second coefficient R (λ _{i + 1} , λ _m1 , λ _m2 ) of Equation 8 registered in the microcomputer.
Taking the logarithm of the ratio of these first and second antilogs gives the following equation.
[0043]
(Equation 10)

[0044]
The first term (error factor) in Equation 6 remains with only the first difference value. However, by performing the operation in Equation 9, only the Gaussian distribution including λ _bj is obtained. in logarithmic operation of antilogarithm ratio can be obtained a linear function of the lambda _bj as shown in equation 10 ρ (λ _bj) of. That is, the linearity of the wavelength measurement output ρ (λ _bj ) with respect to the reflection center wavelength λ _bj of the FBG is improved as shown in FIG.
[0045]
Next, a specific description will be given focusing on processing by the microcomputer 10 based on the above principle.
First, the microcomputer 10 performs a preparation process before measuring the wavelength of the reflected light from the FBG. In this preparation processing, a first monitor value (corresponding to P (λ _m1 , λ _bj )) and a second monitor value (corresponding to P (λ _m2 , λ _bj )) are input from the photodiode 11 with a preamplifier. Also, a first measurement value (corresponding to P (λ _i , λ _bj )) and a second measurement value (P (λ _{i + 1} , λ _bj ) from a photodiode 7 with a preamplifier, which is a pair of channels for measuring a certain FBG. )).
[0046]
Then, the microcomputer 10 calculates a first correction difference value (E (λ _i , λ _m1 ) = P (λ _i , λ _bj ) −P which is a difference between the first measurement value and the first monitor value. (Equivalent to (λ _m1 , λ _bj )), a second correction difference value (E (λ _{i + 1} , λ _m1 ) = P (λ _{i + 1} , λ) which is a difference between the second measurement value and the first monitor value. _bj ) -P (equivalent to [lambda] _m1 , [lambda] _bj )) and a third correction difference value (E ([lambda] _m2 , [lambda] _m1 )), which is the difference between the first monitor value and the second monitor value. P ( _λm2 , _λbj ) −P (equivalent to _λm1 , _λbj ) is obtained.
[0047]
Then, a first coefficient (R (λ _i , λ _m1 , λ _m2 )), which is a ratio obtained by dividing the first correction difference value by the third correction difference value, and the second correction difference value A second coefficient (R (λ _{i + 1} , λ _m1 , λ _m2 )) which is a ratio divided by the correction difference value of 3 is obtained in advance and registered in a memory unit (not shown) of the microcomputer 10.
[0048]
Subsequently, a normal FBG wavelength measurement process is performed. In this case, the microcomputer 10 subtracts the first monitor value from the first measurement value and corresponds to a first difference value (P (λ _{i + 1} , λ _bj ) −P (λ _m1 , λ _bj )). , And a second difference value (P (λi _{+ 1} , _λbj ) −P ( _λm1 , _λbj )) obtained by subtracting the first monitor value from the second measurement value. ) And a third difference value between the first and second monitor values (E (λ _m2 , λ _m1 ) = P (λ _{m + 1} , λ _bj ) −P (λ _m1 , λ _bj )). ).
[0049]
Then, the product of the third difference value and the first coefficient is subtracted from the first difference value to obtain a first true value. Further, the product of the third difference value and the second coefficient is calculated. , The second true value is obtained by subtracting the second true value from the second difference value.
Then, the wavelength of the reflected light is measured based on the logarithm of the ratio between the first true value and the second true value (see Equation 10).
[0050]
The microcomputer 10 measures the wavelength by performing (1) the preparation process before the wavelength measurement of the reflected light from the FBG and (2) the wavelength measurement process of the predetermined FBG as described above. Since the influence of the component ε is completely removed, and the linearity of the wavelength measurement output ρ (λ _bj ) with respect to the reflection center wavelength λ _bj of the FBG is improved as shown in FIG. 2, the detection capability can be improved.
[0051]
【The invention's effect】
As described above, according to the present invention, the linearity of the wavelength measurement output with respect to the reflection center wavelength of the FBG is improved, and the measurement resolution and detection accuracy can be improved as compared with the related art.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram of a wavelength measurement output with respect to a reflection center wavelength of the FBG according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram of a wavelength measurement principle in the related art.
FIG. 4 is a configuration diagram of a known wavelength measurement system.
FIG. 5 is a configuration diagram showing a conventional technique.
FIG. 6 is a diagram showing the reflectance of an FBG and the transmittance of an AWG according to the related art.
FIG. 7 is a characteristic diagram of a wavelength measurement output with respect to a reflection center wavelength of an FBG in the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Optical splitter 3 Optical fiber 4 FBG (Bragg diffraction grating)
5 Optical connector 6 AWG (Array waveguide grating)
7,11 Photodiode with preamplifier 8 Divider 9 Wavelength detector 10 Microcomputer

Claims (3)

One or more Bragg diffraction gratings (hereinafter, referred to as FBGs) are formed in an optical fiber into which measurement light is incident, and a system for detecting a wavelength of light reflected from each FBG and measuring a physical quantity at a position of each FBG is provided. , The reflected light from the FBG is made incident on an arrayed waveguide grating (hereinafter, referred to as AWG) capable of separating the center wavelength into a plurality of wavelengths having minute intervals, and connected to a plurality of measurement output channels of the AWG. In a wavelength measuring device, the measuring light receiving elements are made to correspond to the FBG for each pair, and the wavelength of the reflected light is measured using the measured value of the pair of measuring light receiving elements.
The AWG includes a pair of monitoring light output elements connected to a pair of monitoring output channels provided separately from the plurality of pairs of measurement output channels of the AWG, and outputting a monitoring value,
As preparation processing before measuring the wavelength of the reflected light from the FBG,
A coefficient is obtained in advance using a measurement value for reflected light from a certain FBG and a monitor value for light for monitoring,
As a predetermined FBG wavelength measurement process,
First and second true values from which error components have been removed using coefficients are obtained, and the wavelength of the reflected light is measured based on the logarithm of the ratio between the first true value and the second true value. Wavelength measuring device. The wavelength measuring device according to claim 1,
A pair of output channels for measurement output the first and second measurement values, and a pair of output channels for monitoring output the first and second monitor values as output values,
As preparation processing before measuring the wavelength of the reflected light from the FBG,
A difference value between the first measurement value and the first monitor value (hereinafter, referred to as a first correction difference value), and a difference value between the second measurement value and the first monitor value (hereinafter, a second correction value). A difference value between the first and second monitor values (hereinafter, referred to as a third difference value for correction) is obtained.
A ratio obtained by dividing the first correction difference value by the third correction difference value (hereinafter, simply referred to as a first coefficient), and
A ratio obtained by dividing the second correction difference value by the third correction difference value (hereinafter simply referred to as a second coefficient) is registered in advance, and
As a predetermined FBG wavelength measurement process,
A difference value between the first measurement value and the first monitor value (hereinafter, referred to as a first difference value), and a difference value between the second measurement value and the first monitor value (hereinafter, a second difference value) And a difference value between the first and second monitor values (hereinafter, referred to as a third difference value) is obtained, and the product of the third difference value and the first coefficient is calculated as the first difference value. To obtain a first true value,
Subtracting the product of the third difference value and the second coefficient from the second difference value to obtain a second true value;
A wavelength measuring apparatus for measuring a wavelength of reflected light based on a logarithm of a ratio between a first (second) true value and a second (first) true value. The wavelength measuring device according to claim 2,
A light source,
An optical splitter connected to the light source,
An optical fiber connected to the optical branching device and provided with a plurality of FBGs;
An AWG connected to the optical branching device and receiving only light from an optical fiber;
A light receiving element for measurement that converts light from the output channel for measurement output from the AWG into a photocurrent signal and outputs the photoelectric current signal;
A monitor light receiving element for converting light from the monitor output channel output from the AWG into a photocurrent signal and outputting the photocurrent signal;
A microcomputer to which photocurrent signals from the measurement light receiving element and the monitoring light receiving element are input;
With
The microcomputer converts the photocurrent signal corresponding to the first and second measurement values from the measurement light-receiving element and the first and second monitor values from the monitoring light-receiving element into digital data and inputs them. A wavelength measurement apparatus that performs a preparation process before measuring the wavelength of the reflected light from the FBG and a wavelength measurement process of a predetermined FBG to calculate a wavelength.

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