JP6429325B2 - Brillouin scattering measuring apparatus and Brillouin scattering measuring method - Google Patents

Description

  The present invention relates to a measuring apparatus for measuring Brillouin scattering of an optical fiber and a measuring method thereof.

  B-OTDA (Brillouin Optical Time Domain Analysis) and B-OTDR (Brillouin Optical Time Domain Reflexometry) have been developed as measurement / evaluation means for strain distribution and loss distribution in the longitudinal direction of optical fibers (for example, non-patent literature). 1 and 2). These are based on the Brillouin scattering phenomenon that occurs in optical fibers as the measurement principle.

  In B-OTDA described in Non-Patent Document 1, a pump pulse light source and a probe (continuous light) light source are arranged at both ends of an optical fiber to be measured, and light emitted from both light sources is opposed to the optical fiber to be measured. It becomes the structure to propagate. At this time, the probe light is Brillouin amplified in the optical fiber to be measured by the photoelectric conversion process from the pump pulse to the probe light. For example, the amount of distortion applied to the optical fiber to be measured can be evaluated by monitoring the change in the frequency shift amount of Brillouin amplification, and the position of the distortion can be identified from the time difference when the probe light reaches the photodetector. can do. Such a method can generate Brillouin amplification efficiently, and thus has an excellent dynamic range. However, it is necessary to connect devices to both ends of the measured fiber.

  On the other hand, the B-OTDR described in Non-Patent Document 2 has a configuration in which pulse light is incident from one end of the optical fiber to be measured, and backscattered light of natural Brillouin scattering generated in the optical fiber to be measured is also detected from the incident end side. Become. Such a method can evaluate the amount of distortion and specify the position by measurement using only one end, but has a problem that the dynamic range is small because of the use of natural Brillouin scattering.

T.A. Horiguchi and M.H. Tateda, “BOTDA-Nonstructural measurement of single-mode optical fiber attraction charac- teristics using Brillouin interaction: Theory,” Lighttw. Technol. , Vol. 7, no. 8, pp. 1170-1176, 1989. T.A. Horiguchi, K. et al. Shimizu, T .; Kurashima, M .; Tateda, and Y.T. Koyamada, “Development of a distributed sensing technique, Brillouin Scattering,” J. Am. Lighttw. Technol. , Vol. 13, no. 7, pp. 1296-1302. 1995.

  In view of the above problems, an object of the present invention is to provide an optical fiber Brillouin scattering measuring apparatus and method for measuring Brillouin scattering with high sensitivity using only one end of the optical fiber to be measured.

The Brillouin scattering measurement apparatus according to the present invention is
Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement An optical pulse generator for generating a pulse train;
An optical circulator that enters the optical pulse train into the optical fiber to be measured and separates backscattered light of the optical pulse train in the optical fiber to be measured;
An arithmetic processing unit that measures Brillouin scattering in the optical fiber to be measured using a waveform of backscattered light separated by the optical circulator;
Is provided.

In the Brillouin scattering measurement apparatus according to the present invention,
The optical pulse generator generates only the first optical pulse,
The optical circulator enters only the first optical pulse into the optical fiber to be measured, and separates backscattered light of only the first optical pulse in the optical fiber to be measured,
The arithmetic processing unit uses the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse, to measure the measured light. Brillouin scattering in the fiber may be measured.

The Brillouin scattering measurement method according to the present invention is:
Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement A waveform measurement procedure for generating a pulse train, entering the optical pulse train into the optical fiber to be measured, and measuring a waveform of backscattered light of the optical pulse train in the optical fiber to be measured;
Brillouin scattering measurement procedure for measuring Brillouin scattering in the optical fiber to be measured using the waveform of backscattered light of the optical pulse train;
In order.

In the Brillouin scattering measurement method according to the present invention,
In the waveform measurement procedure, only the first optical pulse is generated, only the first optical pulse is incident on the measured optical fiber, and only the first optical pulse in the measured optical fiber is used. Measure the backscattered light waveform of
In the Brillouin scattering measurement procedure, the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse is used. Brillouin scattering in the optical fiber may be measured.

  According to the present invention, it is possible to provide an optical fiber Brillouin scattering measurement apparatus and method for measuring Brillouin scattering with high sensitivity using only one end of the optical fiber to be measured.

The structural example of the Brillouin scattering measuring apparatus which concerns on this embodiment is shown. An example of the generation principle of Brillouin scattered light in this embodiment will be shown. It is an example of wavelength arrangement in the present embodiment, (a) shows the probe light generation pulse P1 and the probe light R1 that is the backscattered light thereof, (b) shows the pump pulse P2 and its Brillouin gain spectrum R2, (C) shows the Brillouin gain spectrum R23 and the probe light R13 amplified by Brillouin. It is an example of the waveform obtained in the present embodiment, (a) shows the first probe light waveform F ^R (z), (b) shows the second probe light waveform F ^P (z), (c ) Shows an example of a Brillouin gain waveform. An image of a Brillouin gain spectrum over the longitudinal direction of the optical fiber 2 to be measured is shown. It is a flowchart explaining an example of the waveform analysis procedure in this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

  In FIG. 1, the structural example of the Brillouin scattering measuring apparatus which concerns on this embodiment is shown. The Brillouin scattering measurement apparatus according to the present embodiment includes a light source 11, an optical pulse generator 12, an electric pulse generator 13, an optical circulator 14, an optical bandpass filter 15, an optical detector 16, and an A / D. A conversion unit 17, an arithmetic processing unit 18, an optical frequency modulation unit 19, and a frequency signal generation unit 20 are provided. The light source 11, the optical frequency modulation unit 19, the frequency signal generation unit 20, the optical pulse generation unit 12, and the electric pulse generation unit 13 function as an optical pulse generation unit.

  The light source 11 oscillates continuous light having an optical frequency ν1. The frequency signal generator 20 generates an electrical signal having a frequency ν1 and an electrical signal having a frequency ν1 + Δν. The optical frequency modulation unit 19 modulates the continuous light emitted from the light source 11 with the frequency ν1, and modulates the continuous light emitted from the light source 11 with the frequency ν1 + Δν. The optical pulsing unit 12 intensity-modulates the continuous light from the frequency-modulated optical frequency modulation unit 19 to generate the first optical pulse (probe light generation pulse P1) and the second optical pulse (pump pulse P2). Generate. As a result, an optical pulse train in which the pump pulse P2 follows the probe light generation pulse P1 is generated. The electric pulse generator 13 generates an electric pulse for modulation by the optical pulse generator 12.

  The optical circulator 14 is connected to the incident end of the optical fiber 2 to be measured. The optical circulator 14 causes the optical pulse train generated by the optical pulse unit 12 to enter the optical fiber 2 to be measured. The probe light generation pulse P1 is backscattered by the optical fiber 2 to be measured, and the backscattered light enters the optical circulator 14. The optical circulator 14 separates the backscattered light returning from the measured optical fiber 2 to the incident end side and outputs it to the optical bandpass filter 15. The optical bandpass filter 15 extracts the backscattered light (probe light R1) of the first light pulse (probe light generation pulse P1) from the backscattered light.

  Hereinafter, it will be theoretically explained that the Brillouin gain waveform of the optical fiber 2 to be measured can be measured with the configuration of FIG.

  The continuous light having the optical frequency ν oscillated from the light source 11 is frequency-modulated by the optical frequency modulator 19 controlled by the frequency signal generator 20. It is assumed that the first optical signal having the frequency ν1 generated first in time is used for probe light generation, and the second optical signal having the frequency ν1 + Δν that is generated next is used for the pump light.

  The pump light and the probe light are modulated and pulsed by the optical pulse unit 12 by an electric signal from the electric pulse generator 13. At this time, the optical pulse having the frequency ν1 generated earlier in time is set as the first optical pulse (probe light generation pulse P1), and the second optical pulse having the frequency ν1 + Δν generated next is the pump pulse. Let P2. A set of optical pulse trains generated in this way is input from one end of the optical fiber 2 to be measured.

  The optical frequency modulator 19 is intended to change the frequency of the pump pulse P2 by Δν with respect to the frequency of the probe pulse P1, and the specific configuration method is not limited as long as this purpose is achieved. The optical pulse unit 12 is for cutting out the pump light and the probe light to a constant pulse width, and a method for setting the pulse width will be described later.

  When the optical pulse train is incident on the optical fiber 2 to be measured, backward Brillouin scattered light is first generated by the probe light generation pulse P1 previously incident. The backward Brillouin scattered light generated by the probe light generation pulse P1 is referred to as probe light R1.

  Subsequently, the pump pulse P2 is input to the measured fiber 2 in such a manner as to follow the probe light generation pulse P1. When the pump pulse P2 and the probe light R1 meet, the probe light R1 is Brillouin amplified by the optical power conversion process (stimulated Brillouin scattering) from the pump pulse P2 to the probe light R1.

The probe light R1 that has been amplified and returned to the incident end of the optical fiber 2 to be measured passes through the optical band pulse filter 15, is converted into an electric signal by the light detection unit 16, and is digitized by the A / D conversion unit 17. And analyzed by the arithmetic processing unit 18. The center frequency of the optical bandpass filter 15 is matched with the optical frequency ν ₁ of the probe light R 1 (probe light generation pulse). As a result, the optical bandpass filter 15 separates and removes the backward Rayleigh scattered light generated by the probe light generation pulse P1 and the pump pulse P2.

When the input end of the optical fiber 2 to be measured is set to z = 0, the backward generated by the first optical pulse (probe light generation pulse P1) at a point where the distance from the input end of the optical fiber 2 to be measured is z. The power P (z) of Brillouin scattered light (probe light R1) is expressed by the following equation.

Here, P ₀ is the peak power of the probe light generating pulse P1, α is the transmission loss of the optical fiber 2 to be measured, R _BR is the backward Brillouin scattering generation efficiency, and the pulse width ΔT of the probe light generating pulse P1 There is a proportional relationship with _probe as follows.

Thus, the power of the probe light R1 depends on the pulse width ΔT _probe of the probe light generating pulse P1, while the distance resolution is determined by the pulse width ΔT _pump of the pump pulse P2, as will be described later. Therefore, in this measurement, it is desirable to use the probe light generation pulse P1 having a pulse width as long as possible.

ここで、Ｐ_ｂ（ｚ，Δν）がブリルアン利得成分であり、演算処理部１８が最終的に解析したい信号である。 The probe light power P _probe observed at the receiving unit (z = 0) of this apparatus is expressed as follows.

Here, P _b (z, Δν) is a Brillouin gain component, and is a signal that the arithmetic processing unit 18 wants to finally analyze.

  FIG. 2 shows the interaction between the backward Brillouin scattered light (probe light R1) generated in the first optical pulse (probe light generation pulse P1) and the second optical pulse (pump pulse P2) in the optical fiber 2 to be measured. It is an image figure shown.

  Back Brillouin scattered light of the first light pulse (probe light generation pulse P1) incident on the optical fiber 2 to be measured first in time becomes the probe light R1. When this probe light R1 encounters the second incident light pulse (pump pulse P2) that subsequently enters, it is Brillouin amplified by interaction to become R13 and returns to the incident end side of the optical fiber 2 to be measured. .

FIG. 3 schematically shows an arrangement relationship of the optical frequencies of the probe light generation pulse P1, the pump pulse P2, and the probe lights R1 and R13. The backward Brillouin scattered light generated by the probe light generation pulse P1, that is, the probe light R1, has an optical frequency ν ₁ −ν _b that is downshifted by the Brillouin frequency shift ν _b of the optical fiber 2 to be measured. Similarly, the Brillouin gain spectrum of the pump pulse P2 having the optical frequency ν ₁ + Δν is also about several tens of MHz centering on ν ₁ −ν _b + Δν downshifted by the Brillouin frequency shift ν _b of the optical fiber 2 to be measured. With a gain range of Therefore, when the probe light R1 having the optical frequency ν ₁ −ν _b collides with the pump pulse P2, the probe light R1 is Brillouin amplified in the optical fiber 2 to be measured to become the probe light R13. The invention according to this embodiment uses the probe light R13 as an analysis signal. In the figure, the case of Δν = 0 is shown for easy understanding.

  When the frequency difference Δν is changed, the Brillouin gain spectrum R2 changes like R23. In order to obtain the Brillouin gain spectrum of the optical fiber 2 to be measured, the change width of the frequency difference Δν is preferably equal to or greater than the frequency width of the Brillouin gain spectrum of the optical fiber 2 to be measured. For example, when the frequency width of the Brillouin gain spectrum of the optical fiber 2 to be measured is about several tens of MHz, the change width of the frequency difference Δν is preferably about several tens of MHz or more.

FIG. 4 schematically shows a time waveform of the probe light observed by this apparatus. L41 shown in (a) is a waveform F ^R (z) of the probe light R1 acquired in a state where the pump pulse P2 is not input. This is the reference waveform. L42 shown in (b) is a waveform F ^P (z) of the probe light R13 acquired in a state where the pump pulse P2 is inputted and the probe light R1 is Brillouin amplified. L43 shown in (c) is a Brillouin gain waveform F ^G (z) calculated by subtracting F ^R (z) from the waveform F ^P (z).

The waveform F ^G (z), that is, P _b (z, Δν) in the above equation (3) is expressed as follows.

  The distribution over the longitudinal direction of the Brillouin gain at a specific optical frequency can be known from Equation (4).

By sequentially measuring the Brillouin gain while changing Δν by the optical frequency modulator 19, a Brillouin gain spectrum over the longitudinal direction of the optical fiber to be measured can be obtained as follows.

  FIG. 5 shows an example of the Brillouin gain spectrum according to the present embodiment. The Brillouin gain spectrum shown in FIG. 6 is a Brillouin gain spectrum obtained when the time interval ΔT between the probe light generation pulse P1 and the pump pulse P2 is kept constant and Δν is changed. L61 to L64 indicate Brillouin gain spectra at respective points of distances z1, z2, z3, and z4 shown in FIG.

When the time interval between the probe light generation pulse P1 and the pump pulse P2 is ΔT, the distance z1 at which the probe light R1 is Brillouin amplified by the pump pulse P2 is obtained by the following equation.

Here, ν _probe represents the group velocity of the probe light generation pulse P1 and the probe light R1 in the optical fiber 2 to be measured. As described above, the probe light R1 can be amplified from an arbitrary distance by controlling the time interval ΔT between the probe light generation pulse P1 and the pump pulse P2.

FIG. 6 is a flowchart for explaining a waveform analysis procedure in the arithmetic processing unit 18. The Brillouin scattering measurement method according to this embodiment includes a waveform measurement procedure and a Brillouin scattering measurement procedure in this order.
In the waveform measurement procedure, the Brillouin scattering measurement apparatus according to the present embodiment executes steps S101 to S102.
In the Brillouin scattering measurement procedure, the Brillouin scattering measurement apparatus according to this embodiment executes step S103.

First, only the probe generation pulse P1 is generated without inputting the pump pulse P2, only the probe generation pulse P1 is incident on the optical fiber 2 to be measured, and the Brillouin scattered light ( The waveform F ^R (z) of the probe light R1) is acquired (S101).
Then, the probe light R1 enter the pump pulse P2 to obtain the waveform ^F P of the probe light R13 (z) while being Brillouin amplification (S102).
Finally, the Brillouin gain waveform F ^G (z) is obtained by taking the difference between these waveforms (S103). Thereby, the magnitude (gain) of Brillouin amplification in the measured optical fiber 2 can be calculated.

  By repeating steps S102 and S103 while changing Δν, that is, changing the frequency of the pump pulse P2, the gain spectrum of Brillouin scattering in the optical fiber 2 to be measured can be measured. For this reason, the invention according to the present embodiment can analyze Brillouin scattering in the optical fiber 2 to be measured.

  As described above, in the invention according to the present embodiment, the probe light generation pulse P1 having the optical frequency ν1 is incident on the optical fiber 2 to be measured, and then the pump pulse P2 having the optical frequency ν1 + Δν is incident. By observing a change in Δν of stimulated Brillouin scattering generated by the interaction between the backward Brillouin scattered light (probe light R1) of the light generation pulse P1 and the pump pulse P2, it is possible to extend over the length direction z of the optical fiber 2 to be measured. Brillouin gain spectrum distribution can be obtained.

In order to accurately calculate the waveform F ^G (z), Brillouin scattering is preferably stable during measurement of the waveform F ^P (z) from the waveform F ^R (z). It is preferable that the applied distortion or the like does not change.

ここで、ν_ｐｕｍｐは被測定光ファイバ２中におけるポンプパルスＰ２の群速度を表す。 The distance resolution Δz of this method is determined as follows according to the pulse width ΔT _pump of the pump pulse.

Here, ν _pump represents the group velocity of the pump pulse P2 in the optical fiber 2 to be measured.

  The present invention can be applied to the information communication industry.

11: Light source 12: Optical pulse generator 13: Electric pulse generator 14: Optical circulator 15: Optical band pal filter 16: Optical detector 17: A / D converter 18: Arithmetic processor 19: Optical frequency modulator 20: Frequency signal generator

Claims (4)

Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement An optical pulse generator for generating a pulse train;
An optical frequency modulation unit that varies a frequency difference between the first optical pulse and the second optical pulse to be equal to or greater than a frequency width of a Brillouin gain spectrum of the optical fiber to be measured;
An optical circulator that enters the optical pulse train into the optical fiber to be measured and separates backscattered light of the optical pulse train in the optical fiber to be measured;
An arithmetic processing unit that measures Brillouin scattering in the optical fiber to be measured using a waveform of backscattered light separated by the optical circulator;
Equipped with a,
The optical pulse generator further generates only the first optical pulse,
The optical circulator further enters only the first optical pulse into the optical fiber to be measured, and separates backscattered light of only the first optical pulse in the optical fiber to be measured,
The arithmetic processing unit uses the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse, to measure the measured light. Measuring Brillouin scattering in the fiber,
Brillouin scattering measurement device. Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement An optical pulse generator for generating a pulse train;
An optical circulator that enters the optical pulse train into the optical fiber to be measured and separates backscattered light of the optical pulse train in the optical fiber to be measured;
An arithmetic processing unit that measures Brillouin scattering in the optical fiber to be measured using a waveform of backscattered light separated by the optical circulator;
With
The optical pulse generator further generates only the first optical pulse,
The optical circulator further enters only the first optical pulse into the optical fiber to be measured, and separates backscattered light of only the first optical pulse in the optical fiber to be measured,
The arithmetic processing unit uses the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse, to measure the measured light. Measuring Brillouin scattering in the fiber,
Brillouin scattering measurement device. Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement A waveform measurement procedure for generating a pulse train, entering the optical pulse train into the optical fiber to be measured, and measuring a waveform of backscattered light of the optical pulse train in the optical fiber to be measured;
Brillouin scattering measurement procedure for measuring Brillouin scattering in the optical fiber to be measured using the waveform of backscattered light of the optical pulse train;
In order,
In the waveform measurement procedure, only the first optical pulse is generated, only the first optical pulse is incident on the measured optical fiber, and only the first optical pulse in the measured optical fiber is used. Measure the backscattered light waveform of
In the Brillouin scattering measurement procedure, the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse is used. Measure Brillouin scattering in optical fiber,
Repeating the waveform measurement procedure and the Brillouin scattering measurement procedure while changing the frequency difference between the first optical pulse and the second optical pulse to a frequency width of the Brillouin gain spectrum of the optical fiber to be measured.
Brillouin scattering measurement method. Light following the first light pulse for generating backscattered light in the optical fiber under measurement, followed by a second optical pulse for Brillouin amplification of the Brillouin backscattered light of the first optical pulse in the optical fiber under measurement A waveform measurement procedure for generating a pulse train, entering the optical pulse train into the optical fiber to be measured, and measuring a waveform of backscattered light of the optical pulse train in the optical fiber to be measured;
Brillouin scattering measurement procedure for measuring Brillouin scattering in the optical fiber to be measured using the waveform of backscattered light of the optical pulse train;
In order,
In the waveform measurement procedure, only the first optical pulse is generated, only the first optical pulse is incident on the measured optical fiber, and only the first optical pulse in the measured optical fiber is used. Measure the backscattered light waveform of
In the Brillouin scattering measurement procedure, the difference between the first waveform obtained from the backscattered light of the optical pulse train and the second waveform obtained from the backscattered light of only the first light pulse is used. Measuring Brillouin scattering in optical fibers,
Brillouin scattering measurement method.

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