JP3663966B2

JP3663966B2 - Wavelength measuring device

Info

Publication number: JP3663966B2
Application number: JP09253999A
Authority: JP
Inventors: 紀友平山; 安一佐野
Original assignee: Fuji Electric Systems Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 1999-03-31
Filing date: 1999-03-31
Publication date: 2005-06-22
Anticipated expiration: 2019-03-31
Also published as: JP2000283846A

Description

【０００１】
【発明の属する技術分野】
本発明は、温度や歪み（圧力）等の物理量を、光ファイバのブラッグ回折格子（Fiber Bragg Grating、以下ＦＢＧと略す）からの反射光の波長によって測定する物理量測定システムに適用可能な波長計測装置に関する。
【０００２】
【従来の技術】
図９は、従来技術としての、光ファイバ上の温度分布を測定する温度分布測定システムの全体構成図である。
図９において、１は後述する波長検出部及び演算部を有する温度分布測定部、１１，１２，１３，１４は測定光及び反射光が通過する光ファイバ、１５，１６，１７は測定点に対応する位置に形成されたセンサ用のブラッグ回折格子、２は光分岐器、３は接続用光ファイバ、４は広帯域光源である。
【０００３】
光ファイバのブラッグ回折格子は、周知のようにコアの屈折率が光軸に沿って周期的に変化しており、屈折率に応じて特定波長を中心とした狭帯域の光を反射する。
例えば、測定対象である物理量が温度である場合、図９のあるブラッグ回折格子の位置（測定点）で温度変化が生じると、ブラッグ回折格子のコアの平均屈折率が変化するため反射光の波長も変化する。従って、広帯域光源４から照射された光の各ブラッグ回折格子からの反射波長の変化と温度変化との関係を予め測定しておけば、温度分布測定部１により検出される反射光の波長から各測定点の温度を測定することができ、光ファイバの長手方向の温度分布を得ることができる。
ここで、図９におけるブラッグ回折格子１５，１６，１７には、所定の温度範囲に対応する固有の反射波長範囲が、互いに重複しないように予め割り当てられている。
【０００４】
図１０は、温度分布測定部１に使用される波長検出部の一例を示す図である。図１０において、２１は各ブラッグ回折格子からの反射光が入射する入力光ファイバ、２２は出力光ファイバ、２３，２４はコリメータレンズ、２５，２６はハーフミラー、２７，２８はハーフミラー２５，２６の間に密接して配置された圧電素子、２９は圧電素子駆動回路である。
【０００５】
この波長検出部は、ハーフミラー２５，２６間のギャップ長ｇが入射光の波長に対して一定の関係にある場合に入射光が強められ、または弱められて出射することを利用したもので、圧電素子駆動回路２９から圧電素子２７，２８に電圧を印加してギャップ長ｇを調節しながら出射光強度を観察し、そのときのギャップ長ｇから入射光の波長を検出するものである。
【０００６】
【発明が解決しようとする課題】
図１０に示したような波長検出部はメカニカルな構成であるため、耐振性に課題があった。つまり、外部から振動を受けても高い機械精度を保たなければならないからである。
また、ハーフミラー２５，２６同士の平行性や、ハーフミラー２５，２６に対するコリメータレンズ２３，２４の光軸の直交性を維持することも構造上、難しく、これらが製造コストの上昇や歩留まり低下の原因となっていた。
【０００７】
そこで本発明は、従来のように可動部品を使用せずに反射光の波長を検出する波長計測装置を提供しようとするものである。
【０００８】
【課題を解決するための手段】
上記課題を解決するため、請求項１記載の発明は、測定光が入射される光ファイバに一以上のセンサ用ブラッグ回折格子が形成され、前記センサ用ブラッグ回折格子からの反射光の波長を検出して前記センサ用ブラッグ回折格子の位置における物理量を測定する物理量測定システムにおいて、前記センサ用ブラッグ回折格子からの反射光を、特定の波長範囲で直線状に反射率が変化するリニア減衰型ブラッグ回折格子に入射させ、このリニア減衰型ブラッグ回折格子による反射光を受光素子に入射させてその光電流の変化に基づいて前記センサ用ブラッグ回折格子による反射光の波長を測定するものである。
【０００９】
請求項２記載の発明は、センサ用ブラッグ回折格子からの反射光を、特定の波長範囲で直線状に反射率が変化するリニア減衰型ブラッグ回折格子に入射させ、このリニア減衰型ブラッグ回折格子による反射光を第１の受光素子に入射させ、かつ、リニア減衰型ブラッグ回折格子による透過光を第２の受光素子に入射させ、第１、第２の受光素子の光電流の比の対数に基づいてセンサ用ブラッグ回折格子による反射光の波長を測定するものである。
ここで、「光電流の比の対数」を実現するに当たっては、二つの受光素子（フォトダイオード）の電流出力（Ｉ₁，Ｉ₂）から換算された二つの電圧出力（Ｖ₁，Ｖ₂）を対数増幅器にて対数出力（logＶ₁，logＶ₂）に換算した後、それらの差分出力（logＶ₁−logＶ₂）をとることにより、「光電流の比の対数」に相当するlog（Ｖ₁／Ｖ₂）の出力が得られる。
【００１０】
請求項３記載の発明は、請求項１記載の波長計測装置において、複数のセンサ用ブラッグ回折格子の波長変化範囲に対応した同数のリニア減衰型ブラッグ回折格子を備え、各リニア減衰型ブラッグ回折格子による複数の反射光をそれぞれ同数の受光素子に入射させ、各受光素子の光電流の変化に基づいて各センサ用ブラッグ回折格子による複数の反射光の波長を同時に測定するものである。
【００１１】
請求項４記載の発明は、請求項１記載の波長計測装置において、複数のセンサ用ブラッグ回折格子の波長変化範囲に対応した同数のリニア減衰型ブラッグ回折格子を備え、各リニア減衰型ブラッグ回折格子による複数の反射光を光スイッチの切り替えにより単一の受光素子に入射させ、この受光素子の光電流の変化に基づいて各センサ用ブラッグ回折格子による複数の反射光の波長を順次測定するものである。
【００１２】
請求項５記載の発明は、請求項１〜４の何れか１項に記載した波長計測装置において、リニア減衰型ブラッグ回折格子の温度検出信号に基づき温度制御素子を動作させてリニア減衰型ブラッグ回折格子の温度を一定に保つことにより、波長測定精度を向上させるものである。
【００１３】
【発明の実施の形態】
以下、図に沿って本発明の実施形態を説明する。まず、図１は本発明の第１実施形態であり、請求項１に記載した発明の実施形態に相当する。
図１において、３１は中心波長が１．５５〔μｍ〕の光を照射する１．５５μｍ光源であり、光ファイバ３８には光分岐器３２を介してセンサ用ブラッグ回折格子Ｓ−ＦＢＧが形成されている。
ブラッグ回折格子Ｓ−ＦＢＧによって反射された光源３１の光は、光分岐器３２を経て波長計測装置５１に入射する。
【００１４】
波長計測装置５１は、光ファイバ３９により前記光分岐器３２に接続される光分岐器３３と、光ファイバ３９の端部に形成されたリニア減衰型ブラッグ回折格子Ｌ−ＦＢＧと、このブラッグ回折格子Ｌ−ＦＢＧによる反射光が光分岐器３３及び光ファイバ４０を介して入射するフォトダイオード（ＰＤ）３４とを備えている。
【００１５】
ここで、図２に示すように中心波長がほぼ１．５５〔μｍ〕であるセンサ用ブラッグ回折格子Ｓ−ＦＢＧの反射波形がリニア減衰型ブラッグ回折格子Ｌ−ＦＢＧに入射すると、リニア減衰型ブラッグ回折格子Ｌ−ＦＢＧは図３に示すような特性（実際に販売されている加Innovative Fibers社製の「リニア分別器ファイバーブラッググレーティング」の特性を基に中心波長だけ変更したもの）を持っているので、センサ用ブラッグ回折格子Ｓ−ＦＢＧの中心波長の変化と、リニア減衰型ブラッグ回折格子Ｌ−ＦＢＧにより反射してフォトダイオード３４により測定される反射受光光量との関係は、図４のようになる。
この図４の特性は完全な直線ではないが、この特性を利用すれば、センサ用ブラッグ回折格子Ｓ−ＦＢＧによる反射波長をフォトダイオード３４の光電流出力から測定することができる。
【００１６】
なお、上記実施形態において、センサ用ブラッグ回折格子Ｓ−ＦＢＧの特性は、グレーティング長さ１０〔ｍｍ〕、屈折率変調０．００００６、屈折率１．４５８として論文「ファイバーグレーティングとその応用」（応用物理、Ｖｏｌ．６６，Ｎｏ．１）を参考に計算したものである。
【００１７】
本実施形態は基本的に可動部分がなく、光ファイバと光分岐器との接続だけによって構成されているので、耐震性に強く、構成が簡単なため低コストであると共に、高速応答性を有することが明らかである。
また、リニア減衰型ブラッグ回折格子Ｌ−ＦＢＧは、その減衰範囲、中心波長等を通常のブラッグ回折格子と同様な範囲で製作可能である。
【００１８】
上述した第１実施形態においては、光源３１の光量が変動すると、この影響を受けて図４の波長と受光光量との関係が変化してしまう。また、波長と受光光量との関係は厳密には直線関係でないことから、図４の特性をパソコン等に記憶させてその都度、参照しなくてはならない。
【００１９】
図５に示す第２実施形態は上記の点を改良したもので、リニア減衰型ブラッグ回折格子Ｌ−ＦＢＧの透過光と反射光を検出する二つのフォトダイオードの受光出力の比の対数をとるようにした。この実施形態は請求項２の発明の実施形態に相当する。
すなわち、図５の構成が図１と異なるのは、波長計測装置５２において、リニア減衰型ブラッグ回折格子Ｌ−ＦＢＧの透過光を検出するフォトダイオード３５が追加された点である。
【００２０】
この実施形態によれば、図６に示すように、センサ用ブラッグ回折格子Ｓ−ＦＢＧの中心波長とフォトダイオード３４，３５の受光出力の比の対数（図６の縦軸ではLOG(PD2/PD1)として示してある）との関係が直線になる。このように受光出力の比をとっているので、光源３１に光量変動があったとしても両方のフォトダイオード３４，３５の出力が同様に変化することになり、影響を受けにくくなる。
【００２１】
次に、図７は本発明の第３実施形態であり、請求項３に記載した発明の実施形態に相当する。この実施形態は、第１実施形態（図１）に対して、センサ用ブラッグ回折格子を複数備え、更に、リニア減衰型ブラッグ回折格子、光分岐器及びフォトダイオードの組を複数、縦続接続して多点計測システムとしたものである。
図７において、Ｓ−ＦＢＧ１〜Ｓ−ＦＢＧｎは光ファイバ３８上のセンサ用ブラッグ回折格子、波長計測装置５３内のＬ−ＦＢＧ１〜Ｌ−ＦＢＧｎは光ファイバ３９上のリニア減衰型ブラッグ回折格子、３３１，３３２，……，３３ｎは光分岐器、３４１，３４２，……，３４ｎはフォトダイオードである。
【００２２】
この実施形態では、各センサ用ブラッグ回折格子Ｓ−ＦＢＧ１〜Ｓ−ＦＢＧｎの波長変化範囲に対して、それぞれの変化範囲で反射特性が直線状に変化する同数のリニア減衰型ブラッグ回折格子Ｌ−ＦＢＧ１〜Ｌ−ＦＢＧｎを用意しておき、それぞれの検出波長範囲が重ならないようにしておく。これにより、波長多重化による多点計測が可能となり、各センサ用ブラッグ回折格子Ｓ−ＦＢＧ１〜Ｓ−ＦＢＧｎの位置における温度等の物理量の同時測定が可能になる。
【００２３】
図８は本発明の第４実施形態であり、請求項４に記載した発明の実施形態に相当する。この実施形態は、第３実施形態のフォトダイオード３４１，３４２，……，３４ｎの特性上のバラツキによる影響を取り除くために、光スイッチを用いた例である。
図８において、波長計測装置５４内の光分岐器３３１，３３２，……，３３ｎには光スイッチ３７を介して単一のフォトダイオード３４が接続されており、光スイッチ３７を切り替えることで所望のリニア減衰型ブラッグ回折格子からの反射光（すなわち、対応するセンサ用ブラッグ回折格子からの反射光）をフォトダイオード３４が受光する。
このように構成すると、第３実施形態に見られるフォトダイオード間の特性のバラツキがなくなり、波長測定精度を高めることができる。
【００２４】
上記各実施形態において、リニア減衰型ブラッグ回折格子の温度を検出し、その温度検出信号に基づきペルチェ素子等の温度制御素子によりリニア減衰型ブラッグ回折格子の温度を一定に保って光フィルタリング特性の変動を少なくすれば、波長測定精度が一層向上する。これは、請求項５に記載した発明の実施形態に相当する。
【００２５】
なお、本発明に適用される波長検出方法は、光ファイバを用いた波長多重通信にも適用できることは明らかである。
【００２６】
【発明の効果】
以上のように請求項１記載の発明によれば、従来のようにギャップ長の微小変位を得るために機械的可動部分を有する波長検出部を用いるのではなく、リニア減衰型ブラッグ回折格子の反射光量を受光素子により計測するようにしたので、耐震性に強く、低コストで製品の歩留まりも高いとともに、高速応答性を有する波長計測装置を実現することができる。
請求項２記載の発明によれば、センサ用ブラッグ回折格子の中心波長と二つの受光素子の光電流出力の比の対数値とが直線関係となり、光源の光量変動を受けにくいシステムを構成することができる。
請求項３記載の発明によれば、中心波長とリニア減衰範囲とが異なるリニア減衰型ブラッグ回折格子をセンサ用ブラッグ回折格子と同数用意することで多点計測が可能となり、また、請求項４記載の発明によれば、多点計測時に問題となる受光素子間の特性上のバラツキを低減できるという効果がある。
更に、請求項５に記載したごとく、リニア減衰型ブラッグ回折格子の温度を一定に保つようにすれば、光フィルタリング特性の変動が少なくなって波長測定精度が一層向上する。
【図面の簡単な説明】
【図１】本発明の第１実施形態を示す構成図である。
【図２】図１のセンサ用ブラッグ回折格子の反射波長と光量との関係を示す図である。
【図３】図１のリニア減衰型ブラッグ回折格子の波長と透過率との関係を示す図である。
【図４】図１のセンサ用ブラッグ回折格子の中心波長とフォトダイオードにより測定される反射受光光量との関係を示す図である。
【図５】本発明の第２実施形態を示す構成図である。
【図６】図５のセンサ用ブラッグ回折格子の中心波長と二つのフォトダイオードの受光出力の比の対数との関係を示す図である。
【図７】本発明の第３実施形態を示す構成図である。
【図８】本発明の第４実施形態を示す構成図である。
【図９】従来技術としての温度分布測定システムの全体構成図である。
【図１０】従来技術における温度検出部の構成図である。
【符号の説明】
Ｓ−ＦＢＧ，Ｓ−ＦＢＧ１〜Ｓ−ＦＢＧｎセンサ用ブラッグ回折格子
Ｌ−ＦＢＧ，Ｌ−ＦＢＧ１〜Ｌ−ＦＢＧｎリニア減衰型ブラッグ回折格子
３１１．５５μｍ光源
３２，３３，３３１，３３２，……，３３ｎ光分岐器
３４，３５，３４１，３４２，……，３４ｎフォトダイオード（ＰＤ）
３６光スイッチ
３８，３９，４０光ファイバ
５１，５２，５３，５４波長計測装置[0001]
BACKGROUND OF THE INVENTION
The present invention is a wavelength measuring device applicable to a physical quantity measuring system that measures physical quantities such as temperature and strain (pressure) by the wavelength of reflected light from an optical fiber Bragg grating (hereinafter referred to as FBG). About.
[0002]
[Prior art]
FIG. 9 is an overall configuration diagram of a temperature distribution measuring system for measuring a temperature distribution on an optical fiber as a conventional technique.
In FIG. 9, 1 is a temperature distribution measurement unit having a wavelength detection unit and a calculation unit to be described later, 11, 12, 13, and 14 are optical fibers through which measurement light and reflected light pass, and 15, 16, and 17 correspond to measurement points. A Bragg diffraction grating for a sensor formed at a position where 2 is an optical branching device, 3 is an optical fiber for connection, and 4 is a broadband light source.
[0003]
As is well known, the Bragg diffraction grating of an optical fiber has a refractive index of the core that periodically changes along the optical axis, and reflects light in a narrow band centered on a specific wavelength according to the refractive index.
For example, when the physical quantity to be measured is temperature, and the temperature changes at the position (measurement point) of a Bragg diffraction grating in FIG. 9, the average refractive index of the core of the Bragg diffraction grating changes, so the wavelength of the reflected light Also changes. Accordingly, if the relationship between the change in the reflection wavelength of the light emitted from the broadband light source 4 from each Bragg diffraction grating and the change in temperature is measured in advance, the wavelength of the reflected light detected by the temperature distribution measuring unit 1 is measured. The temperature at the measurement point can be measured, and the temperature distribution in the longitudinal direction of the optical fiber can be obtained.
Here, specific reflection wavelength ranges corresponding to a predetermined temperature range are assigned in advance to the Bragg diffraction gratings 15, 16, and 17 in FIG. 9 so as not to overlap each other.
[0004]
FIG. 10 is a diagram illustrating an example of a wavelength detection unit used in the temperature distribution measurement unit 1. In FIG. 10, 21 is an input optical fiber into which reflected light from each Bragg diffraction grating is incident, 22 is an output optical fiber, 23 and 24 are collimator lenses, 25 and 26 are half mirrors, and 27 and 28 are half mirrors 25 and 26. Reference numeral 29 denotes a piezoelectric element drive circuit disposed in close contact with the piezoelectric element drive circuit.
[0005]
This wavelength detection unit utilizes the fact that the incident light is strengthened or weakened and emitted when the gap length g between the half mirrors 25 and 26 has a certain relationship with the wavelength of the incident light. A voltage is applied from the piezoelectric element driving circuit 29 to the piezoelectric elements 27 and 28 to observe the emitted light intensity while adjusting the gap length g, and the wavelength of the incident light is detected from the gap length g at that time.
[0006]
[Problems to be solved by the invention]
Since the wavelength detection unit as shown in FIG. 10 has a mechanical configuration, there is a problem in vibration resistance. That is, high mechanical accuracy must be maintained even when subjected to vibration from the outside.
In addition, it is structurally difficult to maintain the parallelism between the half mirrors 25 and 26 and the orthogonality of the optical axes of the collimator lenses 23 and 24 with respect to the half mirrors 25 and 26, which increases the manufacturing cost and decreases the yield. It was the cause.
[0007]
Therefore, the present invention intends to provide a wavelength measuring device that detects the wavelength of reflected light without using a movable part as in the prior art.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 is characterized in that one or more Bragg diffraction gratings for sensors are formed in an optical fiber into which measurement light is incident, and the wavelength of reflected light from the Bragg diffraction grating for sensors is detected. In the physical quantity measurement system that measures the physical quantity at the position of the sensor Bragg diffraction grating, the linear attenuation Bragg diffraction in which the reflectance of the reflected light from the sensor Bragg diffraction grating changes linearly in a specific wavelength range The light is incident on the grating, and the light reflected by the linear attenuation Bragg diffraction grating is incident on the light receiving element, and the wavelength of the light reflected by the Bragg diffraction grating for sensor is measured based on the change in the photocurrent.
[0009]
According to the second aspect of the present invention, the reflected light from the Bragg diffraction grating for sensor is incident on the linear attenuation Bragg diffraction grating whose reflectance changes linearly in a specific wavelength range, and the linear attenuation Bragg diffraction grating is used. Based on the logarithm of the ratio of the photocurrents of the first and second light receiving elements, the reflected light is incident on the first light receiving element and the light transmitted by the linear attenuating Bragg diffraction grating is incident on the second light receiving element. The wavelength of the reflected light by the Bragg diffraction grating for the sensor is measured.
Here, in realizing the “logarithm of the ratio of photocurrents”, two voltage outputs (V ₁ , V ₂ ) converted from the current outputs (I ₁ , I ₂ ) of the two light receiving elements (photodiodes). Is converted into a logarithmic output (logV ₁ , logV ₂ ) by a logarithmic amplifier, and then a differential output (logV ₁ -logV ₂ ) is taken to obtain log (V ₁₎ corresponding to the “logarithm of the photocurrent ratio”. / V ₂ ) is obtained.
[0010]
According to a third aspect of the present invention, in the wavelength measuring device according to the first aspect, the linear attenuation type Bragg diffraction gratings having the same number of linear attenuation type Bragg diffraction gratings corresponding to the wavelength change ranges of the plurality of Bragg diffraction gratings for sensors are provided. Are incident on the same number of light receiving elements, and the wavelengths of the plurality of reflected lights by the Bragg diffraction gratings for each sensor are simultaneously measured based on the change in the photocurrent of each light receiving element.
[0011]
According to a fourth aspect of the present invention, in the wavelength measuring device according to the first aspect, the linear attenuation type Bragg diffraction grating having the same number of linear attenuation type Bragg diffraction gratings corresponding to the wavelength change ranges of the plurality of Bragg diffraction gratings for sensors is provided. Is used to measure the wavelength of the reflected light from each Bragg diffraction grating for each sensor based on the change in the photocurrent of the light receiving element. is there.
[0012]
According to a fifth aspect of the present invention, in the wavelength measuring apparatus according to any one of the first to fourth aspects, the linear attenuation Bragg diffraction is performed by operating the temperature control element based on the temperature detection signal of the linear attenuation Bragg diffraction grating. By keeping the temperature of the grating constant, the wavelength measurement accuracy is improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 shows a first embodiment of the present invention, which corresponds to the embodiment of the invention described in claim 1.
In FIG. 1, reference numeral 31 denotes a 1.55 μm light source that emits light having a center wavelength of 1.55 μm, and a Bragg diffraction grating S-FBG for a sensor is formed on an optical fiber 38 via an optical splitter 32. ing.
The light of the light source 31 reflected by the Bragg diffraction grating S-FBG enters the wavelength measuring device 51 via the optical branching device 32.
[0014]
The wavelength measuring device 51 includes an optical branching device 33 connected to the optical branching device 32 by an optical fiber 39, a linear attenuating Bragg diffraction grating L-FBG formed at the end of the optical fiber 39, and the Bragg diffraction grating. A reflected light from the L-FBG is provided with a light splitter 33 and a photodiode (PD) 34 that enters through the optical fiber 40.
[0015]
As shown in FIG. 2, when the reflected waveform of the sensor Bragg diffraction grating S-FBG having a center wavelength of approximately 1.55 [μm] is incident on the linear attenuation Bragg diffraction grating L-FBG, the linear attenuation Bragg The diffraction grating L-FBG has the characteristics shown in FIG. 3 (changed only at the center wavelength based on the characteristics of “linear linearizer fiber Bragg grating” manufactured by Innovative Fibers, Inc., which is actually sold). Therefore, the relationship between the change in the center wavelength of the sensor Bragg diffraction grating S-FBG and the amount of reflected light received by the photodiode 34 after being reflected by the linear attenuation type Bragg diffraction grating L-FBG is as shown in FIG. Become.
Although the characteristic of FIG. 4 is not a perfect straight line, if this characteristic is used, the reflection wavelength by the Bragg diffraction grating S-FBG for sensor can be measured from the photocurrent output of the photodiode 34.
[0016]
In the above embodiment, the characteristics of the sensor Bragg diffraction grating S-FBG are as follows: the grating length is 10 [mm], the refractive index modulation is 0.00006, and the refractive index is 1.458. Physics, Vol. 66, No. 1).
[0017]
Since this embodiment basically has no moving parts and is configured only by connection between an optical fiber and an optical branching device, it is strong in earthquake resistance, has a simple structure, is low in cost, and has high-speed response. It is clear.
The linear attenuation type Bragg diffraction grating L-FBG can be manufactured in the same range as the normal Bragg diffraction grating in the attenuation range, the center wavelength, and the like.
[0018]
In the first embodiment described above, when the light amount of the light source 31 varies, the relationship between the wavelength and the received light amount in FIG. 4 changes due to this influence. Further, since the relationship between the wavelength and the amount of received light is not strictly a linear relationship, the characteristics shown in FIG. 4 must be stored in a personal computer or the like and referenced each time.
[0019]
The second embodiment shown in FIG. 5 is an improvement of the above point, and takes the logarithm of the ratio of the received light output of two photodiodes that detect the transmitted light and reflected light of the linear attenuation type Bragg diffraction grating L-FBG. I made it. This embodiment corresponds to an embodiment of the invention of claim 2.
That is, the configuration of FIG. 5 is different from that of FIG. 1 in that a photodiode 35 for detecting light transmitted through the linear attenuation type Bragg diffraction grating L-FBG is added to the wavelength measuring device 52.
[0020]
According to this embodiment, as shown in FIG. 6, the logarithm of the ratio of the center wavelength of the Bragg diffraction grating S-FBG for sensor and the light receiving output of the photodiodes 34 and 35 (LOG (PD2 / PD1 on the vertical axis in FIG. 6). ) Is a straight line. Since the ratio of the received light output is taken in this way, even if there is a fluctuation in the amount of light in the light source 31, the outputs of both the photodiodes 34 and 35 change in the same manner, and are less susceptible to influence.
[0021]
Next, FIG. 7 shows a third embodiment of the present invention, which corresponds to the embodiment of the invention described in claim 3. This embodiment includes a plurality of Bragg diffraction gratings for sensors and a plurality of pairs of linear attenuating Bragg diffraction gratings, optical splitters and photodiodes in cascade with respect to the first embodiment (FIG. 1). This is a multipoint measurement system.
In FIG. 7, S-FBG 1 to S-FBGn are sensor Bragg diffraction gratings on the optical fiber 38, and L-FBG 1 to L-FBGn in the wavelength measuring device 53 are linear attenuating Bragg diffraction gratings on the optical fiber 39, 331. , 332,..., 33n are optical splitters, and 341, 342,.
[0022]
In this embodiment, the same number of linear attenuating Bragg diffraction gratings L-FBG1 whose reflection characteristics change linearly in the respective change ranges with respect to the wavelength change ranges of the Bragg diffraction gratings S-FBG1 to S-FBGn for each sensor. ~ L-FBGn is prepared so that the respective detection wavelength ranges do not overlap. Thereby, multipoint measurement by wavelength multiplexing becomes possible, and simultaneous measurement of physical quantities such as temperature at the positions of the Bragg diffraction gratings S-FBG1 to S-FBGn for each sensor becomes possible.
[0023]
FIG. 8 shows a fourth embodiment of the present invention, which corresponds to the embodiment of the invention described in claim 4. This embodiment is an example in which an optical switch is used in order to remove the influence of variations in characteristics of the photodiodes 341, 342,..., 34n of the third embodiment.
In FIG. 8, a single photodiode 34 is connected to the optical branching devices 331, 332,..., 33n in the wavelength measuring device 54 via an optical switch 37. The photodiode 34 receives the reflected light from the linear attenuation type Bragg diffraction grating (that is, the reflected light from the corresponding Bragg diffraction grating for sensor).
With this configuration, there is no variation in characteristics between the photodiodes seen in the third embodiment, and the wavelength measurement accuracy can be improved.
[0024]
In each of the above embodiments, the temperature of the linear attenuating Bragg diffraction grating is detected, and the temperature of the linear attenuating Bragg diffraction grating is kept constant by a temperature control element such as a Peltier element based on the temperature detection signal. If the number is reduced, the wavelength measurement accuracy is further improved. This corresponds to the embodiment of the invention described in claim 5.
[0025]
It is obvious that the wavelength detection method applied to the present invention can also be applied to wavelength multiplexing communication using an optical fiber.
[0026]
【The invention's effect】
As described above, according to the first aspect of the present invention, instead of using a wavelength detecting unit having a mechanically movable portion to obtain a minute displacement of the gap length as in the prior art, the reflection of the linear attenuation type Bragg diffraction grating is used. Since the amount of light is measured by the light receiving element, it is possible to realize a wavelength measuring device that is strong in earthquake resistance, low in cost, high in product yield, and has high-speed response.
According to the second aspect of the present invention, the center wavelength of the sensor Bragg diffraction grating and the logarithmic value of the ratio of the photocurrent outputs of the two light receiving elements are linearly related, and the system is less susceptible to light quantity fluctuations of the light source. Can do.
According to the third aspect of the present invention, it is possible to perform multipoint measurement by preparing the same number of linear attenuation type Bragg diffraction gratings having different center wavelengths and linear attenuation ranges as the Bragg diffraction gratings for sensors. According to this invention, there is an effect that it is possible to reduce the variation in characteristics between the light receiving elements which becomes a problem at the time of multipoint measurement.
Further, as described in claim 5, if the temperature of the linear attenuation type Bragg diffraction grating is kept constant, the fluctuation of the optical filtering characteristic is reduced and the wavelength measurement accuracy is further improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of the present invention.
2 is a diagram showing a relationship between a reflection wavelength and a light amount of the Bragg diffraction grating for sensor in FIG. 1. FIG.
FIG. 3 is a diagram showing the relationship between the wavelength and the transmittance of the linear attenuation type Bragg diffraction grating of FIG. 1;
4 is a diagram showing the relationship between the center wavelength of the Bragg diffraction grating for sensors in FIG. 1 and the amount of reflected light received by a photodiode. FIG.
FIG. 5 is a configuration diagram showing a second embodiment of the present invention.
6 is a graph showing the relationship between the center wavelength of the sensor Bragg diffraction grating of FIG. 5 and the logarithm of the ratio of the light receiving outputs of two photodiodes. FIG.
FIG. 7 is a configuration diagram showing a third embodiment of the present invention.
FIG. 8 is a configuration diagram showing a fourth embodiment of the present invention.
FIG. 9 is an overall configuration diagram of a temperature distribution measuring system as a prior art.
FIG. 10 is a configuration diagram of a temperature detection unit in the prior art.
[Explanation of symbols]
S-FBG, S-FBG1 to S-FBGn Bragg diffraction grating for sensor L-FBG, L-FBG1 to L-FBGn Linear attenuation Bragg diffraction grating 31 1.55 μm Light source 32, 33, 331, 332,. Optical splitters 34, 35, 341, 342, ..., 34n Photodiode (PD)
36 Optical switch 38, 39, 40 Optical fiber 51, 52, 53, 54 Wavelength measuring device

Claims

One or more sensor Bragg diffraction gratings are formed in the optical fiber into which the measurement light is incident, and the physical quantity at the position of the sensor Bragg diffraction grating is measured by detecting the wavelength of the reflected light from the sensor Bragg diffraction grating. In the physical quantity measurement system,
Reflected light from the Bragg diffraction grating for the sensor is incident on a linear attenuation type Bragg diffraction grating whose reflectance changes linearly in a specific wavelength range, and the reflected light from the linear attenuation type Bragg diffraction grating enters the light receiving element. And measuring the wavelength of the reflected light by the Bragg diffraction grating for sensors based on the change in the photocurrent.

One or more sensor Bragg diffraction gratings are formed in the optical fiber into which the measurement light is incident, and the physical quantity at the position of the sensor Bragg diffraction grating is measured by detecting the wavelength of the reflected light from the sensor Bragg diffraction grating. In the physical quantity measurement system,
The reflected light from the sensor Bragg diffraction grating is incident on a linear attenuation type Bragg diffraction grating whose reflectance changes linearly in a specific wavelength range, and the reflected light from the linear attenuation type Bragg diffraction grating is received as a first light. The incident light is incident on the element, and the light transmitted by the linear attenuation Bragg diffraction grating is incident on the second light receiving element. Based on the logarithm of the ratio of the photocurrent of the first and second light receiving elements, the Bragg diffraction for sensor A wavelength measuring device for measuring the wavelength of reflected light from a grating.

In the wavelength measuring device according to claim 1,
Equipped with the same number of linear attenuation type Bragg diffraction gratings corresponding to the wavelength change range of the plurality of Bragg diffraction gratings for sensors. A wavelength measuring device that simultaneously measures the wavelengths of a plurality of reflected lights by the Bragg diffraction gratings for each sensor based on a change in the photocurrent.

In the wavelength measuring device according to claim 1,
Equipped with the same number of linear attenuating Bragg diffraction gratings corresponding to the wavelength change range of multiple Bragg diffraction gratings for sensors. Multiple reflected lights from each linear attenuating Bragg diffraction grating are incident on a single light-receiving element by switching the optical switch. And a wavelength measuring device that sequentially measures wavelengths of a plurality of reflected lights by the Bragg diffraction gratings for each sensor based on a change in photocurrent of the light receiving element.

In the wavelength measuring device according to any one of claims 1 to 4,
A wavelength measurement apparatus characterized in that a temperature control element is operated based on a temperature detection signal of a linear attenuation type Bragg diffraction grating to keep the temperature of the linear attenuation type Bragg diffraction grating constant.