JP5000443B2

JP5000443B2 - Method and apparatus for measuring backward Brillouin scattered light of optical fiber

Info

Publication number: JP5000443B2
Application number: JP2007250211A
Authority: JP
Inventors: 大輔飯田; 文彦伊藤
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2007-09-26
Filing date: 2007-09-26
Publication date: 2012-08-15
Anticipated expiration: 2027-09-26
Also published as: JP2009080048A

Description

本発明は、基準光ファイバからの後方ブリルアン散乱光と被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波・処理することにより、被測定光ファイバの後方ブリルアン散乱光周波数スペクトルを測定する方法及び装置に関するものである。 The present invention combines the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured to detect and process the beat signal, and thereby the rear Brillouin scattered light frequency spectrum of the optical fiber to be measured. The present invention relates to a method and apparatus for measuring

光ファイバ線路において、歪や温度の異常を検出する測定方法として、ＢＯＴＤＲ（ＢｒｉｌｌｏｕｉｎＯｐｔｉｃａｌＴｉｍｅＤｏｍａｉｎＲｅｆｌｅｃｔｏｍｅｔｒｙ）の方法があり、特許文献１に示されている。 BOTDR (Brillouin Optical Time Domain Reflectometry) is a measuring method for detecting anomalies in strain and temperature in an optical fiber line, and is disclosed in Patent Document 1.

光パルスを、光カプラで被測定光ファイバへ入射する試験光と参照光に分岐して、試験光を光ファイバ線路に入射し、発生した後方ブリルアン散乱光を、先の分岐した参照光と合波し、受光素子でビート信号を受光する。 The optical pulse is split by an optical coupler into test light and reference light incident on the optical fiber to be measured, the test light is incident on the optical fiber line, and the generated Brillouin scattered light is combined with the previously branched reference light. Wave is received and the beat signal is received by the light receiving element.

ビート信号は、１０ＧＨｚほどの参照光と後方ブリルアン散乱光の周波数の差であるブリルアン周波数シフトを示す。 The beat signal indicates a Brillouin frequency shift that is a difference in frequency between the reference light of about 10 GHz and the backward Brillouin scattered light.

光パルスの入射から受光までの時間により、光ファイバ線路内の各点でのブリルアン周波数シフトを測定できる。このブリルアン周波数シフトは、歪分布、温度分布により変化するため、ブリルアン周波数シフトを測定することで、光ファイバ中の歪分布、温度分布を測定できる。 The Brillouin frequency shift at each point in the optical fiber line can be measured according to the time from the incidence of the light pulse to the light reception. Since this Brillouin frequency shift changes depending on the strain distribution and temperature distribution, the strain distribution and temperature distribution in the optical fiber can be measured by measuring the Brillouin frequency shift.

現在、通常用いられている後方ブリルアン散乱光測定においては、直接光源からの参照光と、被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波している。 Currently, in the backward Brillouin scattered light measurement that is usually used, the reference signal from the direct light source and the backward Brillouin scattered light from the optical fiber to be measured are combined to detect the beat signal.

このため、ビート信号を検波するのに必要な受光部、信号処理系の周波数帯域幅は、参照光の周波数と後方ブリルアン散乱光の周波数の差程度になるため、被測定光ファイバのブリルアン周波数シフトと同程度の周波数帯域幅が必要になる。通常のシングルモード光ファイバで、ブリルアン周波数シフトは約１０．８ＧＨｚと広い周波数帯域幅になっている。 For this reason, the frequency bandwidth of the light receiving unit and signal processing system necessary for detecting the beat signal is about the difference between the frequency of the reference light and the frequency of the back Brillouin scattered light, so the Brillouin frequency shift of the optical fiber to be measured The same frequency bandwidth is required. In a normal single mode optical fiber, the Brillouin frequency shift is a wide frequency bandwidth of about 10.8 GHz.

前記ブリルアン周波数シフトを受光するため、受光部に必要な周波数帯域幅は１０ＧＨｚ以上必要であり、また、受光部からの電気信号を後方ブリルアン散乱光周波数スペクトル表示するための電気的な信号処理系においても、受光部と同程度の周波数帯域幅を持ったものが必要となる。 In order to receive the Brillouin frequency shift, a frequency bandwidth necessary for the light receiving unit is required to be 10 GHz or more, and in an electrical signal processing system for displaying an electrical signal from the light receiving unit in the backward Brillouin scattered light frequency spectrum However, the one having the same frequency bandwidth as that of the light receiving unit is required.

上記の事情から、一般的に、後方ブリルアン散乱光測定を行うための測定方法や測定機は、複雑で高価な機器によって構成される。 In view of the above circumstances, in general, a measurement method and a measuring machine for performing backward Brillouin scattered light measurement are configured by complicated and expensive equipment.

また、この広帯域受光・処理系を避けるためには、精密に周波数制御させた２つの光源や、１０ＧＨｚの周波数シフタが必要で、いずれにしても、非常に高価で複雑な測定系となる。 Further, in order to avoid this broadband light receiving / processing system, two light sources with precise frequency control and a frequency shifter of 10 GHz are required, and in any case, it becomes a very expensive and complicated measurement system.

特開平３-１２０４３７号公報Japanese Patent Laid-Open No. 3-120437 特許第３３８６９４８号公報Japanese Patent No. 3386948 “ＤｅｖｅｌｏｐｍｅｎｔｏｆａＤｉｓｔｒｉｂｕｔｅｄＳｅｎｓｉｎｇＴｅｃｈｎｉｑｕｅＵｓｉｎｇＢｒｉｌｌｏｕｉｎＳｃａｔｔｅｒｉｎｇ，”Ｔ．Ｈｏｒｉｇｕｃｈｉ，Ｋ．Ｓｈｉｍｉｚｕ，Ｔ．Ｋｕｒａｓｈｉｍａ，Ｍ．Ｔａｔｅｄａ，Ｙ．Ｋｏｙａｍａｄａ，ＪｏｕｒｎａｌｏｆＬｉｇｈｔｗａｖｅＴｅｃｈｎｏｌｏｇｙ，ｖｏｌ．１３，Ｎｏ．７，１９９５"Development of a Distributed Sensing Technique Using Brillouin Scattering," T. Horiguchi, K .; Shimizu, T .; Kurashima, M .; Tateda, Y .; Koyamada, Journal of Lightwave Technology, vol. 13, no. 7, 1995

本発明は上記の事情に鑑みてなされたもので、基準光ファイバからの後方ブリルアン散乱光と被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波・処理することにより、被測定光ファイバからの後方ブリルアン散乱光を測定するのに必要な周波数帯域幅を狭くでき、受光・処理系の周波数帯域幅を狭くできる光ファイバの後方ブリルアン散乱光周波数スペクトル分布測定方法及び装置、並びに光ファイバの歪分布及び温度分布測定方法及び装置を提供することを目的とする。 The present invention has been made in view of the above circumstances, and by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured, the beat signal is detected and processed. A method and apparatus for measuring the rear Brillouin scattered light frequency spectrum distribution of an optical fiber capable of narrowing the frequency bandwidth necessary for measuring the back Brillouin scattered light from the measurement optical fiber and reducing the frequency bandwidth of the light receiving / processing system, and An object of the present invention is to provide a method and apparatus for measuring strain distribution and temperature distribution of an optical fiber.

上記目的を達成するために本発明の光ファイバの後方ブリルアン散乱光測定方法は、光源からの試験光を２分岐した一方をパルス変調して被測定光ファイバに入射する第１のステップと、前記光源からの試験光を２分岐した他方を基準光ファイバに入射する第２のステップと、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波する第３のステップと、前記第３のステップで検波された時間によって後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された位置を特定して、後方ブリルアン散乱光周波数スペクトル分布を測定する第４のステップとを有し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とする。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In order to achieve the above object, a method for measuring backward Brillouin scattered light of an optical fiber according to the present invention includes a first step of pulse-modulating one of two branched test lights from a light source and entering the measured optical fiber, A second step in which the other of the two test lights from the light source is incident on the reference optical fiber; and the rear Brillouin scattered light from the reference optical fiber and the rear Brillouin scattered light from the measured optical fiber are combined. A third step of detecting a beat signal, and a position of the back Brillouin scattered light scattered in the measured optical fiber according to the time detected in the third step, and a rear Brillouin scattered light frequency spectrum distribution And the kind or concentration of the substance added to the core as the reference optical fiber is the optical fiber to be measured. Characterized by using the type or concentration different from the optical fiber of the material being added in the core of the bar.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定方法は、光源からの試験光を２分岐し、一方を被測定光ファイバに入射し、他方を基準光ファイバに入射する第１のステップと、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波する第２のステップと、前記第２のステップで検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する第３のステップとを有し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とする。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 Further, the method for measuring the backward Brillouin scattered light of the optical fiber according to the present invention includes a first step in which the test light from the light source is branched into two, one is incident on the measured optical fiber, and the other is incident on the reference optical fiber; A second step of detecting the beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured; and the backward Brillouin scattering detected in the second step A third step of measuring a backward Brillouin scattered light frequency spectrum of light scattered in the measured optical fiber, and the kind or concentration of a substance added into the core as the reference optical fiber is: An optical fiber different from the kind or concentration of the substance added to the core of the optical fiber to be measured is used.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定方法は、光源からの試験光を直列接続された基準光ファイバ及び被測定光ファイバに入射する第１のステップと、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光とが合波されたビート光を受光し検波する第２のステップと、前記第２のステップで検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する第３のステップとを有し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とする。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 According to the optical fiber backward Brillouin scattered light measurement method of the present invention, the test light from the light source enters the reference optical fiber and the optical fiber to be measured connected in series, and the rear from the reference optical fiber. A second step of receiving and detecting beat light obtained by combining Brillouin scattered light and backward Brillouin scattered light from the optical fiber to be measured; and the subject of the backward Brillouin scattered light detected in the second step. A third step of measuring a backward Brillouin scattered light frequency spectrum scattered in the measurement optical fiber, and the kind or concentration of a substance added in the core as the reference optical fiber is the light to be measured An optical fiber having a different kind or concentration of a substance added to the core of the fiber is used.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定方法は、光源からの試験光を２分岐した一方をパルス変調して被測定光ファイバに入射する第１のステップと、前記光源からの試験光を２分岐した他方を基準光ファイバに入射する第２のステップと、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波する第３のステップと、前記第３のステップで検波された時間によって後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された位置を特定して、後方ブリルアン散乱光周波数スペクトル分布を測定し、前記被測定光ファイバの後方ブリルアン散乱光の周波数の変化によって前記被測定光ファイバの長手方向の歪分布もしくは温度分布を測定する第４のステップとを有し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とする。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In addition, the method for measuring the backward Brillouin scattered light of the optical fiber according to the present invention includes a first step of pulse-modulating one of the two branched test lights from the light source and entering the measured optical fiber, and the test light from the light source. A second step in which the other is split into the reference optical fiber, and the beat signal is detected by combining the back Brillouin scattered light from the reference optical fiber and the back Brillouin scattered light from the optical fiber to be measured. Determining the position of the back Brillouin scattered light scattered in the measured optical fiber according to the time detected in the third step and the third step, measuring the back Brillouin scattered light frequency spectrum distribution, A strain distribution or a temperature distribution in the longitudinal direction of the optical fiber to be measured is measured by a change in the frequency of the back Brillouin scattered light of the optical fiber to be measured. An optical fiber in which the kind or concentration of the substance added in the core is different from the kind or concentration of the substance added in the core of the optical fiber to be measured. It is characterized by that.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定方法は、光源からの試験光を２分岐し、一方を被測定光ファイバに入射し、他方を基準光ファイバに入射する第１のステップと、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波する第２のステップと、前記第２のステップで検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定し、前記被測定光ファイバの後方ブリルアン散乱光の周波数の変化によって前記被測定光ファイバの歪もしくは温度を測定する第３のステップとを有し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とする。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 Further, the method for measuring the backward Brillouin scattered light of the optical fiber according to the present invention includes a first step in which the test light from the light source is branched into two, one is incident on the measured optical fiber, and the other is incident on the reference optical fiber; A second step of detecting the beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured; and the backward Brillouin scattering detected in the second step A back Brillouin scattered light frequency spectrum of light scattered in the measured optical fiber is measured, and strain or temperature of the measured optical fiber is measured by a change in the frequency of the backward Brillouin scattered light of the measured optical fiber. And the type or concentration of the substance added in the core as the reference optical fiber is the optical fiber to be measured. Characterized by using an optical fiber different from the type or concentration of a substance that is added in the core.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定装置は、試験光を２分岐し、一方を光変調器でパルス変調して被測定光ファイバに入射すると共に他方を基準光ファイバに入射する光源と、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波する光カプラと、前記光カプラで合波したビート信号を検波する受光部と、前記受光部で検波された時間によって後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された位置を特定して、後方ブリルアン散乱光周波数スペクトル分布を測定する信号処理系とを具備し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とするものである。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In addition, the optical fiber rear Brillouin scattered light measuring apparatus of the present invention splits the test light into two light sources, one of which is pulse-modulated by an optical modulator and incident on the optical fiber to be measured, and the other is incident on the reference optical fiber. An optical coupler that combines backward Brillouin scattered light from the reference optical fiber and backward Brillouin scattered light from the optical fiber to be measured, a light receiving unit that detects a beat signal combined by the optical coupler, and the light receiving device A signal processing system for measuring the position of the back Brillouin scattered light frequency spectrum by specifying the position of the back Brillouin scattered light scattered in the measured optical fiber according to the time detected by the unit, and the reference optical fiber. The kind or concentration of the substance added to the core is different from the kind or concentration of the substance added to the core of the optical fiber to be measured. And it is characterized in that an optical fiber is used.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定装置は、試験光を２分岐し、一方を被測定光ファイバに入射すると共に他方を基準光ファイバに入射する光源と、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波する光カプラと、前記光カプラで合波したビート信号を検波する受光部と、前記受光部で検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する信号処理系とを具備し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とするものである。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In addition, the optical fiber rear Brillouin scattered light measuring device according to the present invention splits the test light into two branches, one of which is incident on the optical fiber to be measured and the other of which is incident on the reference optical fiber, and the reference optical fiber. An optical coupler that combines backward Brillouin scattered light and backward Brillouin scattered light from the optical fiber to be measured, a light receiving unit that detects a beat signal combined by the optical coupler, and a back Brillouin scattering detected by the light receiving unit A signal processing system for measuring a back Brillouin scattered light frequency spectrum scattered in the optical fiber to be measured, and the kind or concentration of a substance added in the core as the reference optical fiber is An optical fiber having a different type or concentration of a substance added to the core of the optical fiber to be measured is used.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定装置は、試験光を直列接続された基準光ファイバ及び被測定光ファイバに入射する光源と、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光とが合波されたビート光を受光し検波する受光部と、前記受光部で検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する信号処理系とを具備し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とするものである。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 The optical fiber rear Brillouin scattered light measuring apparatus according to the present invention includes a reference optical fiber in which test light is connected in series, a light source incident on the optical fiber to be measured, rear Brillouin scattered light from the reference optical fiber, and the target optical fiber. A light receiving unit that receives and detects beat light combined with backward Brillouin scattered light from the measurement optical fiber, and a rear Brillouin scattered in the measured optical fiber of the backward Brillouin scattered light detected by the light receiving unit. A signal processing system for measuring a scattered light frequency spectrum, and the kind or concentration of the substance added in the core as the reference optical fiber is the same as that of the substance added in the core of the optical fiber to be measured. An optical fiber having a different type or concentration is used.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定装置は、試験光を２分岐し、一方を光変調器でパルス変調して被測定光ファイバに入射すると共に他方を基準光ファイバに入射する光源と、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波する光カプラと、前記光カプラで合波したビート信号を検波する受光部と、前記受光部で検波された時間によって後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された位置を特定して、後方ブリルアン散乱光周波数スペクトル分布を測定し、前記被測定光ファイバの後方ブリルアン散乱光の周波数の変化によって前記被測定光ファイバの長手方向の歪分布もしくは温度分布を測定する信号処理系とを具備し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とするものである。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In addition, the optical fiber rear Brillouin scattered light measuring apparatus of the present invention splits the test light into two light sources, one of which is pulse-modulated by an optical modulator and incident on the optical fiber to be measured, and the other is incident on the reference optical fiber. An optical coupler that combines backward Brillouin scattered light from the reference optical fiber and backward Brillouin scattered light from the optical fiber to be measured, a light receiving unit that detects a beat signal combined by the optical coupler, and the light receiving device The position of the back Brillouin scattered light scattered in the measured optical fiber is determined according to the time detected by the unit, the back Brillouin scattered light frequency spectrum distribution is measured, and the back Brillouin scattered light of the measured optical fiber is measured. A signal processing system for measuring strain distribution or temperature distribution in the longitudinal direction of the optical fiber to be measured according to a change in frequency, and the reference optical fiber To, the type or concentration of a substance that is added to the core, the is characterized in the use of the type or concentration of a substance that is added in the core of the optical fiber to be measured different optical fibers.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

また、本発明の光ファイバの後方ブリルアン散乱光測定装置は、試験光を２分岐し、一方を被測定光ファイバに入射すると共に他方を基準光ファイバに入射する光源と、前記基準光ファイバからの後方ブリルアン散乱光と前記被測定光ファイバからの後方ブリルアン散乱光を合波する光カプラと、前記光カプラで合波したビート信号を検波する受光部と、前記受光部で検波された後方ブリルアン散乱光の前記被測定光ファイバ内で散乱された後方ブリルアン散乱光周波数スペクトルを測定し、前記被測定光ファイバの後方ブリルアン散乱光の周波数の変化によって前記被測定光ファイバの歪もしくは温度を測定する信号処理系とを具備し、前記基準光ファイバとして、コア中に添加されている物質の種類もしくは濃度が、前記被測定光ファイバのコア中に添加されている物質の種類もしくは濃度と異なる光ファイバを用いることを特徴とするものである。
例えば、前記被測定光ファイバとして、シングルモード光ファイバを用い、前記基準光ファイバとして、コア中に何も添加していない光ファイバを用いればよい。 In addition, the optical fiber rear Brillouin scattered light measuring device according to the present invention splits the test light into two branches, one of which is incident on the optical fiber to be measured and the other of which is incident on the reference optical fiber, and the reference optical fiber. An optical coupler that combines backward Brillouin scattered light and backward Brillouin scattered light from the optical fiber to be measured, a light receiving unit that detects a beat signal combined by the optical coupler, and a back Brillouin scattering detected by the light receiving unit A signal for measuring a back Brillouin scattered light frequency spectrum of light scattered in the measured optical fiber and measuring strain or temperature of the measured optical fiber according to a change in frequency of the backward Brillouin scattered light of the measured optical fiber And the type or concentration of a substance added to the core as the reference optical fiber is the optical fiber to be measured. And is characterized in that using the type or concentration of a substance that is added in the core is different from the optical fiber.
For example, a single mode optical fiber may be used as the optical fiber to be measured, and an optical fiber with nothing added in the core may be used as the reference optical fiber.

本発明の光ファイバの後方ブリルアン散乱光測定方法は、基準光ファイバからの後方ブリルアン散乱光と被測定光ファイバからの後方ブリルアン散乱光を合波してビート信号を検波・処理することにより、被測定光ファイバからの後方ブリルアン散乱光を測定するのに必要な周波数帯域幅を、前記被測定光ファイバからの後方ブリルアン散乱光の周波数と、前記基準光ファイバからの後方ブリルアン散乱光の周波数の差に狭くでき、受光・処理系の周波数帯域幅を狭くできるため、例えば１ＧＨｚ以下の狭い周波数帯域幅の受光・処理系で測定することができる。 The optical fiber backward Brillouin scattered light measurement method of the present invention combines the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured, and detects and processes the beat signal, thereby The frequency bandwidth required to measure the backward Brillouin scattered light from the measurement optical fiber is the difference between the frequency of the backward Brillouin scattered light from the measured optical fiber and the frequency of the backward Brillouin scattered light from the reference optical fiber. Since the frequency bandwidth of the light receiving / processing system can be narrowed, for example, measurement can be performed with a light receiving / processing system having a narrow frequency bandwidth of 1 GHz or less.

しかも、測定に必要な物品は、例えば光カプラや基準光ファイバなど、受動的で、低価格の物品で構成することができるため、非常に廉価で簡易に行うことができ、また測定器を構成することができる。 In addition, the articles required for measurement can be made of passive and low-priced articles such as optical couplers and reference optical fibers, so that they can be made very inexpensively and easily, and the measuring instrument is configured. can do.

このため、光ファイバ線路の歪分布及び温度分布の測定などのブリルアン散乱光測定の応用技術をより容易に行うことができる。 For this reason, it is possible to more easily perform application techniques of Brillouin scattered light measurement such as measurement of strain distribution and temperature distribution of the optical fiber line.

また、ブリルアン周波数シフトを用いた光ファイバ線路保守試験などのその他のブリルアン散乱光測定の応用に対しても利便性の向上を図ることができる。 In addition, it is possible to improve convenience for other Brillouin scattered light measurement applications such as an optical fiber line maintenance test using the Brillouin frequency shift.

以下図面を参照して本発明の実施の形態を詳細に説明する。
図１は本発明の第１の実施形態を示す構成説明図である。図１において、１は例えばレーザ光発生手段等の光源、２は光変調器、３は被測定光ファイバ、４は受光部、５，６は光カプラ、７，８は光サーキュレータ、９は基準後方ブリルアン散乱光を発生させる基準光ファイバ、１０は電気的な信号処理系である。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram showing the configuration of the first embodiment of the present invention. In FIG. 1, 1 is a light source such as laser light generating means, 2 is an optical modulator, 3 is an optical fiber to be measured, 4 is a light receiving unit, 5 and 6 are optical couplers, 7 and 8 are optical circulators, and 9 is a reference. Reference optical fiber 10 for generating back Brillouin scattered light is an electrical signal processing system.

図１に示すように、光源１から発せられた試験光は光カプラ５で２方向に分岐され、一方の試験光は光変調器２でパルス変調されてパルス化され、光サーキュレータ７を通して被測定光ファイバ３に入射される。前記被測定光ファイバ３は長手方向の各点で後方ブリルアン散乱光が発生し、該後方ブリルアン散乱光は光サーキュレータ７を通り、光カプラ６を通過する。 As shown in FIG. 1, test light emitted from a light source 1 is branched in two directions by an optical coupler 5, and one test light is pulse-modulated and pulsed by an optical modulator 2 and is measured through an optical circulator 7. The light enters the optical fiber 3. The measured optical fiber 3 generates backward Brillouin scattered light at each point in the longitudinal direction, and the backward Brillouin scattered light passes through the optical circulator 7 and passes through the optical coupler 6.

前記光カプラ５で２分岐された他方の試験光は、光サーキュレータ８を通して基準光ファイバ９に入射され、後方ブリルアン散乱を起こす。前記基準光ファイバ９に入射される試験光はパルス変調されていないので、基準光ファイバ９からの後方ブリルアン散乱光は、基準光ファイバ９の各点で発生した後方ブリルアン散乱光が重なった連続光となる。基準光ファイバ９からの後方ブリルアン散乱光は、光サーキュレータ８を通り、光カプラ６を通過する。 The other test light branched into two by the optical coupler 5 enters the reference optical fiber 9 through the optical circulator 8 and causes backward Brillouin scattering. Since the test light incident on the reference optical fiber 9 is not pulse-modulated, the backward Brillouin scattered light from the reference optical fiber 9 is a continuous light in which the backward Brillouin scattered light generated at each point of the reference optical fiber 9 is overlapped. It becomes. Back Brillouin scattered light from the reference optical fiber 9 passes through the optical circulator 8 and passes through the optical coupler 6.

前記光カプラ６では、被測定光ファイバ３からの後方ブリルアン散乱光と基準光ファイバ９からの後方ブリルアン散乱光が合波され、受光部４で２つ後方ブリルアン散乱光のビート光として受光されると共にヘテロダイン検波され、前記基準光ファイバ９からの後方ブリルアン散乱光と前記被測定光ファイバ３からの後方ブリルアン散乱光のビート信号を測定して信号処理系１０へ入力する。 In the optical coupler 6, the backward Brillouin scattered light from the measured optical fiber 3 and the backward Brillouin scattered light from the reference optical fiber 9 are combined and received by the light receiving unit 4 as beat light of two backward Brillouin scattered lights. The beat signal of the back Brillouin scattered light from the reference optical fiber 9 and the back Brillouin scattered light from the measured optical fiber 3 is measured and input to the signal processing system 10.

前記信号処理系１０では、前記ビート信号から、前記被測定光ファイバ３からの後方ブリルアン散乱光の周波数と、前記基準光ファイバ９からの後方ブリルアン散乱光の周波数の差を測定し、前記受光部４で受光して検波された時間によって後方ブリルアン散乱光の前記被測定光ファイバ３内で散乱された位置を特定して、後方ブリルアン散乱光周波数スペクトル分布を測定する。 The signal processing system 10 measures the difference between the frequency of the back Brillouin scattered light from the measured optical fiber 3 and the frequency of the back Brillouin scattered light from the reference optical fiber 9 from the beat signal, and the light receiving unit The position where the back Brillouin scattered light is scattered in the measured optical fiber 3 is specified according to the time detected and detected at 4, and the back Brillouin scattered light frequency spectrum distribution is measured.

図２は本発明の第１の実施形態に係る被測定光ファイバの後方ブリルアン散乱光周波数スペクトル分布を示す特性図である。図２に示すように、被測定光ファイバ３内のある点で、温度もしくは歪の異常があると、後方ブリルアン散乱光の周波数が変化し、測定される後方ブリルアン散乱光周波数スペクトル分布が矢印方向に変化する。 FIG. 2 is a characteristic diagram showing the rear Brillouin scattered light frequency spectrum distribution of the optical fiber under measurement according to the first embodiment of the present invention. As shown in FIG. 2, when there is a temperature or distortion abnormality at a certain point in the optical fiber 3 to be measured, the frequency of the backward Brillouin scattered light changes, and the measured rear Brillouin scattered light frequency spectrum distribution is in the direction of the arrow. To change.

したがって、被測定光ファイバ３の後方ブリルアン散乱光の周波数の変化によって、被測定光ファイバ３の長手方向の歪分布及び温度分布を測定することができる。 Therefore, the strain distribution and temperature distribution in the longitudinal direction of the measured optical fiber 3 can be measured by the change in the frequency of the backward Brillouin scattered light of the measured optical fiber 3.

すなわち、本発明の第１の実施形態で受光して検波すべきビート信号の周波数帯域幅は、基準光ファイバ９からの後方ブリルアン散乱光の周波数（光源周波数−基準光ファイバのブリルアン周波数シフト）と、被測定光ファイバ３からの後方ブリルアン散乱光の周波数（光源周波数−被測定光ファイバのブリルアン周波数シフト）の差、つまり、基準光ファイバ９と被測定光ファイバ３のブリルアン周波数シフト差（基準光ファイバ９のブリルアン周波数シフト−被測定光ファイバ３のブリルアン周波数シフト）程度となる。 That is, the frequency bandwidth of the beat signal to be received and detected in the first embodiment of the present invention is the frequency of the back Brillouin scattered light from the reference optical fiber 9 (light source frequency—Brillouin frequency shift of the reference optical fiber). The difference between the frequencies of the backward Brillouin scattered light from the optical fiber 3 to be measured (light source frequency-Brillouin frequency shift of the optical fiber to be measured), that is, the Brillouin frequency shift difference between the reference optical fiber 9 and the optical fiber 3 to be measured (reference light) Brillouin frequency shift of the fiber 9-Brillouin frequency shift of the optical fiber 3 to be measured).

したがって、基準光ファイバ９の温度と歪が変化して基準光ファイバ９からの後方ブリルアン散乱光の周波数が変化しないように密封し、基準光ファイバ９のブリルアン周波数シフトと被測定光ファイバ３のブリルアン周波数シフトの差を所定の値に設計すれば、従来の測定法よりもはるかに受光部４、信号処理系１０の周波数帯域幅を狭くすることができる。 Accordingly, the temperature and strain of the reference optical fiber 9 are changed so that the frequency of the backward Brillouin scattered light from the reference optical fiber 9 is not changed, and the Brillouin frequency shift of the reference optical fiber 9 and the Brillouin of the measured optical fiber 3 are changed. If the difference in frequency shift is designed to a predetermined value, the frequency bandwidth of the light receiving unit 4 and the signal processing system 10 can be made much narrower than in the conventional measurement method.

一般的に、非特許文献１より、光ファイバの温度変化によるブリルアン周波数シフトの変化は約１ＭＨｚ／℃、歪によるブリルアン周波数シフトの変化は１００ＭＨｚ／％程度であるので、現実的な環境変化で最大の温度変化として数十℃の温度変化、光ファイバ破断限界に近い０．２〜０．４％程度の歪を考慮すると、温度や歪による光ファイバのブリルアン周波数シフトの変化量は、最大でも１００〜２００ＭＨｚ程度と見積もられる。 Generally, from Non-Patent Document 1, since the change in the Brillouin frequency shift due to the temperature change of the optical fiber is about 1 MHz / ° C. and the change in the Brillouin frequency shift due to the distortion is about 100 MHz /%, Considering a temperature change of several tens of degrees Celsius as a temperature change and a strain of about 0.2 to 0.4% close to the optical fiber breaking limit, the change amount of the Brillouin frequency shift of the optical fiber due to the temperature and the strain is 100 at the maximum. It is estimated to be about ~ 200 MHz.

したがって、基準光ファイバ９と被測定光ファイバ３のブリルアン周波数シフトの差を２００ＭＨｚ以上とすれば、１ＧＨｚ以下の周波数帯域幅で十分に後方ブリルアン散乱光周波数スペクトル分布を測定することができ、歪分布、温度分布を測定できる。 Therefore, if the difference in Brillouin frequency shift between the reference optical fiber 9 and the optical fiber 3 to be measured is 200 MHz or more, the rear Brillouin scattered light frequency spectrum distribution can be measured sufficiently with a frequency bandwidth of 1 GHz or less, and the distortion distribution Temperature distribution can be measured.

基準光ファイバ９の一例を説明すると、特許文献２に示されているように、光ファイバのブリルアン周波数シフトは一般的にコア中に添加されている物質の種類と濃度に依存する。 An example of the reference optical fiber 9 will be described. As shown in Patent Document 2, the Brillouin frequency shift of the optical fiber generally depends on the kind and concentration of the substance added to the core.

通常使われる光ファイバでは、コアに何も添加せず、クラッドにフッ素を添加した光ファイバが最も大きいブリルアン周波数シフトを示す（約１１．１ＧＨｚ）ので、このような光ファイバを基準光ファイバ９に用いれば、最も測定される頻度が高い、シングルモード光ファイバ（ブリルアン周波数シフトが約１０．８ＧＨｚ）との差が約３００ＭＨｚであり、およそ５００ＭＨｚ以下の周波数帯域幅で測定することができる。 In an optical fiber normally used, an optical fiber in which nothing is added to the core and fluorine is added to the cladding exhibits the largest Brillouin frequency shift (about 11.1 GHz). Therefore, such an optical fiber is used as the reference optical fiber 9. If used, the difference from a single-mode optical fiber (Brillouin frequency shift is about 10.8 GHz), which is the most frequently measured, is about 300 MHz, and can be measured with a frequency bandwidth of about 500 MHz or less.

図３は本発明の第２の実施形態を示す構成説明図である。図３において、２１は例えばレーザ光発生手段等の光源、２２は光カプラ、２３は被測定光ファイバ、２４は基準後方ブリルアン散乱光を発生させる基準光ファイバ、２５は受光部、２６は電気的な信号処理系である。 FIG. 3 is an explanatory diagram showing the configuration of the second embodiment of the present invention. In FIG. 3, 21 is a light source such as a laser beam generating means, 22 is an optical coupler, 23 is an optical fiber to be measured, 24 is a reference optical fiber for generating reference back Brillouin scattered light, 25 is a light receiving unit, and 26 is an electrical unit. It is a simple signal processing system.

図３に示すように、光源２１から発せられた試験光は光カプラ２２で２方向に分岐され、一方の試験光は被測定光ファイバ２３に入射される。前記被測定光ファイバ２３は長手方向の各点で後方ブリルアン散乱光が発生し、該後方ブリルアン散乱光は光カプラ２２を通過する。 As shown in FIG. 3, the test light emitted from the light source 21 is branched in two directions by the optical coupler 22, and one test light is incident on the measured optical fiber 23. The measured optical fiber 23 generates backward Brillouin scattered light at each point in the longitudinal direction, and the backward Brillouin scattered light passes through the optical coupler 22.

前記光カプラ２２で２分岐された他方の試験光は、基準光ファイバ２４に入射され、後方ブリルアン散乱を起こす。基準光ファイバ２４からの後方ブリルアン散乱光は、光カプラ２２を通過する。 The other test light branched into two by the optical coupler 22 enters the reference optical fiber 24 and causes backward Brillouin scattering. Back Brillouin scattered light from the reference optical fiber 24 passes through the optical coupler 22.

前記光カプラ２２では、被測定光ファイバ２３からの後方ブリルアン散乱光と基準光ファイバ２４からの後方ブリルアン散乱光が合波され、受光部２５で２つ後方ブリルアン散乱光のビート光として受光されると共にヘテロダイン検波され、前記基準光ファイバ２４からの後方ブリルアン散乱光と前記被測定光ファイバ２３からの後方ブリルアン散乱光のビート信号を測定して信号処理系２６へ入力する。 In the optical coupler 22, the backward Brillouin scattered light from the measured optical fiber 23 and the backward Brillouin scattered light from the reference optical fiber 24 are combined and received by the light receiving unit 25 as beat light of two backward Brillouin scattered lights. The beat signal of the back Brillouin scattered light from the reference optical fiber 24 and the back Brillouin scattered light from the measured optical fiber 23 is measured and input to the signal processing system 26.

前記信号処理系２６では、前記ビート信号から、前記被測定光ファイバ２３からの後方ブリルアン散乱光の周波数と、前記基準光ファイバ２４からの後方ブリルアン散乱光の周波数の差を測定し、前記受光部２５で受光して検波された後方ブリルアン散乱光の前記被測定光ファイバ２３内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する。 The signal processing system 26 measures the difference between the frequency of the back Brillouin scattered light from the measured optical fiber 23 and the frequency of the back Brillouin scattered light from the reference optical fiber 24 from the beat signal, and the light receiving unit The back Brillouin scattered light frequency spectrum of the back Brillouin scattered light received and detected at 25 and scattered in the measured optical fiber 23 is measured.

前記被測定光ファイバ２３で、温度もしくは歪の異常があると、後方ブリルアン散乱光の周波数が変化し、測定される後方ブリルアン散乱光周波数スペクトルが変化する。 If there is an abnormality in temperature or strain in the measured optical fiber 23, the frequency of the backward Brillouin scattered light changes, and the measured backward Brillouin scattered light frequency spectrum changes.

したがって、被測定光ファイバ２３の後方ブリルアン散乱光の周波数の変化によって、被測定光ファイバ２３の歪及び温度を測定することができる。 Therefore, the strain and temperature of the measured optical fiber 23 can be measured by the change in the frequency of the backward Brillouin scattered light of the measured optical fiber 23.

すなわち、本発明の第２の実施形態で受光して検波すべきビート信号の周波数帯域幅は、基準光ファイバ２４からの後方ブリルアン散乱光の周波数（光源周波数−基準光ファイバのブリルアン周波数シフト）と、被測定光ファイバ２３からの後方ブリルアン散乱光の周波数（光源周波数−被測定光ファイバのブリルアン周波数シフト）の差、つまり、基準光ファイバ２４と被測定光ファイバ２３のブリルアン周波数シフト差（基準光ファイバ２４のブリルアン周波数シフト−被測定光ファイバ２３のブリルアン周波数シフト）程度となる。 That is, the frequency bandwidth of the beat signal to be received and detected in the second embodiment of the present invention is the frequency of the backward Brillouin scattered light from the reference optical fiber 24 (light source frequency—Brillouin frequency shift of the reference optical fiber). The difference between the frequencies of the backward Brillouin scattered light from the optical fiber to be measured 23 (light source frequency—Brillouin frequency shift of the optical fiber to be measured), that is, the Brillouin frequency shift difference between the reference optical fiber 24 and the optical fiber to be measured (reference light) Brillouin frequency shift of the fiber 24-Brillouin frequency shift of the optical fiber 23 to be measured).

したがって、基準光ファイバ２４の温度と歪が変化して基準光ファイバ２４からの後方ブリルアン散乱光の周波数が変化しないように密封し、基準光ファイバ２４のブリルアン周波数シフトと被測定光ファイバ２３のブリルアン周波数シフトの差を所定の値に設計すれば、従来の測定法よりもはるかに受光部２５、信号処理系２６の周波数帯域幅を狭くすることができる。 Therefore, the reference optical fiber 24 is hermetically sealed so that the temperature and strain of the reference optical fiber 24 change and the frequency of the backward Brillouin scattered light from the reference optical fiber 24 does not change, and the Brillouin frequency shift of the reference optical fiber 24 and the Brillouin of the optical fiber 23 to be measured. If the difference in frequency shift is designed to a predetermined value, the frequency bandwidth of the light receiving unit 25 and the signal processing system 26 can be made much narrower than in the conventional measurement method.

図４は本発明の第３の実施形態を示す構成説明図である。図４において、３１は例えばレーザ光発生手段等の光源、３２は光カプラ、３３は被測定光ファイバ、３４は基準後方ブリルアン散乱光を発生させる基準光ファイバ、３５は受光部、３６は電気的な信号処理系である。前記被測定光ファイバ３３と前記基準光ファイバ３４は直列に接続される。 FIG. 4 is an explanatory diagram showing the configuration of the third embodiment of the present invention. In FIG. 4, 31 is a light source such as a laser beam generating means, 32 is an optical coupler, 33 is an optical fiber to be measured, 34 is a reference optical fiber for generating reference back Brillouin scattered light, 35 is a light receiving unit, and 36 is an electrical device. It is a simple signal processing system. The measured optical fiber 33 and the reference optical fiber 34 are connected in series.

図４に示すように、光源３１から発せられた試験光は光カプラ３２を通して後、直列接続された基準光ファイバ３４及び被測定光ファイバ３３に入射される。前記被測定光ファイバ３３は長手方向の各点で後方ブリルアン散乱光が発生し、該後方ブリルアン散乱光は光カプラ３２を通過すると共に、前記基準光ファイバ３４は長手方向の各点で後方ブリルアン散乱光が発生し、該後方ブリルアン散乱光は光カプラ３２を通過する。 As shown in FIG. 4, the test light emitted from the light source 31 passes through the optical coupler 32 and then enters the reference optical fiber 34 and the measured optical fiber 33 that are connected in series. The optical fiber 33 to be measured generates backward Brillouin scattered light at each point in the longitudinal direction, the backward Brillouin scattered light passes through the optical coupler 32, and the reference optical fiber 34 is backward Brillouin scattered at each point in the longitudinal direction. Light is generated, and the backward Brillouin scattered light passes through the optical coupler 32.

前記光カプラ３２では、被測定光ファイバ３３からの後方ブリルアン散乱光と基準光ファイバ３４からの後方ブリルアン散乱光が合波され、受光部３５で２つ後方ブリルアン散乱光のビート光として受光されると共にヘテロダイン検波され、前記基準光ファイバ３４からの後方ブリルアン散乱光と前記被測定光ファイバ３３からの後方ブリルアン散乱光のビート信号を測定して信号処理系３６へ入力する。 In the optical coupler 32, the backward Brillouin scattered light from the optical fiber to be measured 33 and the backward Brillouin scattered light from the reference optical fiber 34 are combined and received by the light receiving unit 35 as beat light of two backward Brillouin scattered lights. The beat signal of the back Brillouin scattered light from the reference optical fiber 34 and the back Brillouin scattered light from the measured optical fiber 33 is measured and input to the signal processing system 36.

前記信号処理系３６では、前記ビート信号から、前記被測定光ファイバ３３からの後方ブリルアン散乱光の周波数と、前記基準光ファイバ３４からの後方ブリルアン散乱光の周波数の差を測定し、前記受光部３５で受光して検波された後方ブリルアン散乱光の前記被測定光ファイバ３３内で散乱された後方ブリルアン散乱光周波数スペクトルを測定する。 The signal processing system 36 measures the difference between the frequency of the back Brillouin scattered light from the measured optical fiber 33 and the frequency of the back Brillouin scattered light from the reference optical fiber 34 from the beat signal, and the light receiving unit The back Brillouin scattered light frequency spectrum of the back Brillouin scattered light received and detected at 35 and scattered in the measured optical fiber 33 is measured.

前記被測定光ファイバ３３内のある点で、温度もしくは歪の異常があると、後方ブリルアン散乱光の周波数が変化し、測定される後方ブリルアン散乱光周波数スペクトルが変化する。 If there is a temperature or distortion abnormality at a certain point in the measured optical fiber 33, the frequency of the backward Brillouin scattered light changes, and the measured backward Brillouin scattered light frequency spectrum changes.

したがって、被測定光ファイバ３３の後方ブリルアン散乱光の周波数の変化によって、被測定光ファイバ３３の歪及び温度を測定することができる。 Therefore, the strain and temperature of the measured optical fiber 33 can be measured by the change in the frequency of the backward Brillouin scattered light of the measured optical fiber 33.

すなわち、本発明の第３の実施形態で受光して検波すべきビート信号の周波数帯域幅は、基準光ファイバ３４からの後方ブリルアン散乱光の周波数（光源周波数−基準光ファイバのブリルアン周波数シフト）と、被測定光ファイバ３３からの後方ブリルアン散乱光の周波数（光源周波数−被測定光ファイバのブリルアン周波数シフト）の差、つまり、基準光ファイバ３４と被測定光ファイバ３３のブリルアン周波数シフト差（基準光ファイバ２４のブリルアン周波数シフト−被測定光ファイバ２３のブリルアン周波数シフト）程度となる。 That is, the frequency bandwidth of the beat signal to be received and detected in the third embodiment of the present invention is the frequency of the back Brillouin scattered light from the reference optical fiber 34 (light source frequency—Brillouin frequency shift of the reference optical fiber). The difference between the frequencies of the backward Brillouin scattered light from the optical fiber to be measured 33 (light source frequency—Brillouin frequency shift of the optical fiber to be measured), that is, the Brillouin frequency shift difference between the reference optical fiber 34 and the optical fiber to be measured 33 (reference light) Brillouin frequency shift of the fiber 24-Brillouin frequency shift of the optical fiber 23 to be measured).

したがって、基準光ファイバ３４の温度と歪が変化して基準光ファイバ３４からの後方ブリルアン散乱光の周波数が変化しないように密封し、基準光ファイバ３４のブリルアン周波数シフトと被測定光ファイバ３３のブリルアン周波数シフトの差を所定の値に設計すれば、従来の測定法よりもはるかに受光部３５、信号処理系３６の周波数帯域幅を狭くすることができる。 Therefore, the reference optical fiber 34 is hermetically sealed so that the frequency and strain of the reference optical fiber 34 change and the frequency of the backward Brillouin scattered light from the reference optical fiber 34 does not change, and the Brillouin frequency shift of the reference optical fiber 34 and the Brillouin of the measured optical fiber 33 are reduced. If the difference in frequency shift is designed to a predetermined value, the frequency bandwidth of the light receiving unit 35 and the signal processing system 36 can be made much narrower than in the conventional measurement method.

なお、本発明は、上記実施形態そのままに限定されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合せにより種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。更に、異なる実施形態に亘る構成要素を適宜組み合せてもよい。 Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

本発明の第１の実施形態を示す構成説明図である。1 is a configuration explanatory diagram illustrating a first embodiment of the present invention. FIG. 本発明の第１の実施形態に係る被測定光ファイバの後方ブリルアン散乱光周波数スペクトル分布を示す特性図である。It is a characteristic view which shows back Brillouin scattered light frequency spectrum distribution of the to-be-measured optical fiber which concerns on the 1st Embodiment of this invention. 本発明の第２の実施形態を示す構成説明図である。It is composition explanatory drawing which shows the 2nd Embodiment of this invention. 本発明の第３の実施形態を示す構成説明図である。It is composition explanatory drawing which shows the 3rd Embodiment of this invention.

Explanation of symbols

１…光源、２…光変調器、３…被測定光ファイバ、４…受光部、５…光カプラ、６…光カプラ、７…光サーキュレータ、８…光サーキュレータ、９…基準光ファイバ、１０…信号処理系。 DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Optical modulator, 3 ... Optical fiber to be measured, 4 ... Light receiving part, 5 ... Optical coupler, 6 ... Optical coupler, 7 ... Optical circulator, 8 ... Optical circulator, 9 ... Reference optical fiber, 10 ... Signal processing system.

Claims

A first step of pulse-modulating one of the two branches of the test light from the light source and entering the optical fiber to be measured;
A second step of entering the other of the test light from the light source into the reference optical fiber,
A third step of detecting a beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured;
The third time is detected at step by to identify the location scattered in the measured optical fiber backward Brillouin scattered light, it has a fourth step of measuring a backward Brillouin scattered light frequency spectrum distribution ,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Method for measuring backward Brillouin scattered light of a fiber.

A first step of splitting the test light from the light source into two branches, one incident on the optical fiber to be measured and the other incident on the reference optical fiber;
A second step of detecting a beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured;
Have a third step of measuring said second backward Brillouin scattered light frequency spectrum the scattered in the measured optical fiber-detected backward Brillouin scattered light in step,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Method for measuring backward Brillouin scattered light of a fiber.

A first step of entering test light from a light source into a reference optical fiber and a measured optical fiber connected in series;
A second step of receiving the beat light and a backward Brillouin scattered light are multiplexed from the optical fiber to be measured and backward Brillouin scattered light from front Kimoto quasi optical fiber detection,
Have a third step of measuring said second backward Brillouin scattered light frequency spectrum the scattered in the measured optical fiber-detected backward Brillouin scattered light in step,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Method for measuring backward Brillouin scattered light of a fiber.

A first step of pulse-modulating one of the two branches of the test light from the light source and entering the optical fiber to be measured;
A second step of entering the other of the test light from the light source into the reference optical fiber,
A third step of detecting a beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured;
The position of the back Brillouin scattered light scattered in the measured optical fiber is determined according to the time detected in the third step, the backward Brillouin scattered light frequency spectrum distribution is measured, and the back of the measured optical fiber have a fourth step of measuring a strain distribution or a temperature distribution in the longitudinal direction of the optical fiber to be measured by the change in frequency of the Brillouin scattered light,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Method for measuring backward Brillouin scattered light of a fiber.

A first step of splitting the test light from the light source into two branches, one incident on the optical fiber to be measured and the other incident on the reference optical fiber;
A second step of detecting a beat signal by combining the backward Brillouin scattered light from the reference optical fiber and the backward Brillouin scattered light from the optical fiber to be measured;
The back Brillouin scattered light frequency spectrum scattered in the measured optical fiber of the backward Brillouin scattered light detected in the second step is measured, and the change in the frequency of the backward Brillouin scattered light of the measured optical fiber is performed as described above. have a third step of measuring the strain or temperature of the optical fiber to be measured,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Method for measuring backward Brillouin scattered light of a fiber.

As the optical fiber to be measured , a single mode optical fiber is used ,
The optical fiber backward Brillouin scattered light measurement method according to any one of claims 1 to 5, wherein an optical fiber in which nothing is added to the core is used as the reference optical fiber.

A light source that divides the test light into two, one is pulse-modulated by an optical modulator and is incident on the optical fiber to be measured, and the other is incident on the reference optical fiber;
An optical coupler for combining the back Brillouin scattered light from the reference optical fiber and the back Brillouin scattered light from the measured optical fiber;
A light receiving unit for detecting a beat signal combined by the optical coupler;
A signal processing system for identifying a position of the back Brillouin scattered light scattered in the measured optical fiber according to a time detected by the light receiving unit, and measuring a back Brillouin scattered light frequency spectrum distribution ; and
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Fiber Brillouin scattered light measurement device.

A light source that divides the test light into two, one incident on the optical fiber to be measured and the other incident on the reference optical fiber;
An optical coupler for combining the back Brillouin scattered light from the reference optical fiber and the back Brillouin scattered light from the measured optical fiber;
A light receiving unit for detecting a beat signal combined by the optical coupler;
A signal processing system for measuring a back Brillouin scattered light frequency spectrum scattered in the measured optical fiber of the back Brillouin scattered light detected by the light receiving unit, and
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Fiber Brillouin scattered light measurement device.

A light source incident on a reference optical fiber and a measured optical fiber connected in series with test light;
A photodetection unit for receiving the beat light and a backward Brillouin scattered light are multiplexed from the optical fiber to be measured and backward Brillouin scattered light from front Kimoto quasi optical fiber detection,
A signal processing system for measuring a back Brillouin scattered light frequency spectrum scattered in the measured optical fiber of the back Brillouin scattered light detected by the light receiving unit, and
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Fiber Brillouin scattered light measurement device.

A light source that divides the test light into two, one is pulse-modulated by an optical modulator and is incident on the optical fiber to be measured, and the other is incident on the reference optical fiber;
An optical coupler for combining the back Brillouin scattered light from the reference optical fiber and the back Brillouin scattered light from the measured optical fiber;
A light receiving unit for detecting a beat signal combined by the optical coupler;
The position of the back Brillouin scattered light scattered in the measured optical fiber is determined according to the time detected by the light receiving unit, the back Brillouin scattered light frequency spectrum distribution is measured, and the back Brillouin scattering of the measured optical fiber A signal processing system for measuring the strain distribution or temperature distribution in the longitudinal direction of the optical fiber to be measured by changing the frequency of light , and
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Fiber Brillouin scattered light measurement device.

A light source that divides the test light into two, one incident on the optical fiber to be measured and the other incident on the reference optical fiber;
An optical coupler for combining the back Brillouin scattered light from the reference optical fiber and the back Brillouin scattered light from the measured optical fiber;
A light receiving unit for detecting a beat signal combined by the optical coupler;
A back Brillouin scattered light frequency spectrum of the back Brillouin scattered light detected by the light receiving unit scattered in the optical fiber to be measured is measured, and the measurement target is measured by a change in the frequency of the back Brillouin scattered light of the optical fiber to be measured. A signal processing system for measuring strain or temperature of the optical fiber ,
An optical fiber in which the type or concentration of a substance added to the core is different from the type or concentration of the substance added to the core of the optical fiber to be measured as the reference optical fiber. Fiber Brillouin scattered light measurement device.

As the optical fiber to be measured , a single mode optical fiber is used ,
The optical fiber rear Brillouin scattered light measurement device according to any one of claims 7 to 11, wherein an optical fiber not added to the core is used as the reference optical fiber.