JPH02251729A - Backward-scattering-light measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to detect a broken point at high resolution without deterioration in S/N of backward Rayleigh scattering light by adjusting each pattern of optical pulses and exciting optical pulses into a desired pattern. CONSTITUTION:Optical pulses and exciting optical pulses generated in a laser light source 1a are adjusted with a light pulse adjuster 3a and emitted so that the difference in optical frequencies is made to agree with the shifting amount of the optical frequency of a Brilluoin light that is generated in an optical fiber to be measured FB. The optical pulses and the exciting optical pulses are inputted into one end surface of the optical fiber to be measured, and backward Rayleigh scattering light is generated. At the approximately same time, a Brilluoin light amplified state is induced in the optical fiber to be measured by the exciting pulses. Thus, the backward Rayleigh scattering light is emitted from one end surface of the optical fiber to be measured. Then, the backward Rayleigh scattering light is split with an optical coupler 7 and inputted into a photodetector 8. The intensity of the backward Rayleigh scattering light is detected. The detected signal is inputted into a signal processor 9, and the intensity of the backward Rayleigh scattering light is computed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention generates a Brillouin (Br111ouin) light/amplification state in a specific optical frequency region in an optical fiber or bar to generate weak backward Rayleigh scattered light. This invention relates to a backscattered light measuring device for detecting.

(Prior art) As a method of detecting the optical loss distribution of a single mode optical fiber transmission line and the break point in the optical fiber, light from a light source is incident on the optical fiber under test, and backward Rayleigh generated in the optical fiber is detected. There are four ways to detect scattered light (e.g.
M, to BarnO8k1. +3t8. .

optical N5edosaln reference
ctometer, Appl, Opt, , vol.
, 1B (1977) I), 2395-2379). In this method, the accuracy of determining the break point position depends on the width of the light pulse emitted from the light source. Therefore, when the optical pulse width is narrowed, under conditions where the peak value of the optical pulse is constant, the intensity of backscattered light that can be received will decrease in proportion to the optical pulse width, leading to a decrease in the received light level and reducing the S/N. deteriorate,
Good signal detection becomes difficult.

Therefore, by making the optical fiber under test capable of Brillouin light amplification, the back Rayleigh scattered light component, which was determined only by optical loss, has an amplification component, improving the light reception level and achieving high resolution. A method of making measurements has been proposed.

Figure 2: The first example of a backscattered light measurement device applying this method.
FIG. 2 is a configuration diagram showing a conventional example. In FIG. 2, 1 is a first laser light source that emits a probe light (pulsed light) P for generating backward Rayleigh scattered light. 2 is a second laser light source that connects the optical fiber to be measured F.
Pumping light (CW
emits light) P. 3 is an optical frequency adjustment device that adjusts the optical frequency difference between the respective output lights from the first and second laser light sources 1 and 2 to match the optical frequency shift amount of the Brillouin light generated in the optical fiber FB to be measured. Adjust to. 4.5 is an optical isolator, and 6 is a multiplexer, which combines the probe light P 1 and the excitation light P 2 from the first and second laser light sources 1 and 2 that have passed through the optical isolators 4 and 5. Reference numeral 7 denotes an optical coupler such as an optical coupler, which inputs the multiplexed light from the multiplexer 6 into the optical fiber to be measured FB, and transmits the backward Rayleigh scattered light that has been Brillouin light amplified in the optical fiber to be measured FB to the photodetector 8. Inject it into the A signal processing device 9 inputs an electric signal corresponding to the backward Rayleigh scattered light received and detected by the photodetector 8, and calculates and processes the intensity of the backward Rayleigh scattered light based on this.

In such a configuration, the first and second laser light sources 1 are adjusted by the optical frequency adjustment device 3 so that their optical frequency difference matches the optical frequency shift amount of the Brillouin light.
The probe light P 1 and the excitation light P 2 from 2 and 2 enter the multiplexer 6 via the optical isolators 4 and 5r layers and are multiplexed. This combined light passes through the optical coupler 7 and enters the optical fiber FB to be measured. Along with this, the optical fiber to be measured FB is affected by the pumping light P and enters a Brillouin light amplification state.

Thereby, the backward Rayleigh scattered light generated in the optical fiber to be measured FB is amplified and output from the combined light input end of the optical fiber to be measured FB. This backward Rayleigh scattered light is received by a photodetector 8 via an optical coupler 7 and converted into an electrical signal, and a signal processing device 9 calculates the intensity of the backward Rayleigh scattered light. In this manner, the apparatus shown in FIG. 2 improves the S/H and performs good signal detection.

Further, FIG. 3 is a configuration diagram showing a second conventional example of a backscattered light measuring device. In the conventional example described in Section 2, the probe light P from the first laser light source is made incident from one end face of the optical fiber to be measured FB to generate backward Rayleigh scattered light having a Brillouin-shifted frequency, while the optical frequency is adjusted. The device 3 transmits the pump light P from the second laser light source 2 that matches this optical frequency to the optical fiber FB to be measured.
The backward Rayleigh scattered light is amplified by Brillouin light by entering from the other end face, and the backward Rayleigh scattered light is detected.

(Problem to be Solved by the Invention) However, in the former device, two laser light sources 1.2 for back Rayleigh scattering light generation and Brillouin light amplification are used.
, and probe light P and excitation light P from these laser light sources 1.2 and ``
A multiplexer 6 for multiplexing I is indispensable.

Therefore, in order to set the laser oscillation frequency, a complicated device is required to monitor each oscillation light and adjust the optical frequency.
There is a problem in that reflected light is generated, making it impossible to detect a break point with high resolution and measure optical loss with high precision. moreover,
In order to suppress the light returning to the laser light source 1.2, an optical isolator is required for each laser light source, resulting in an increase in the number of parts.

In addition, in the latter device, since the probe light P and the excitation r light P are made to be incident on both end faces of the optical fiber FB to be measured so as to face each other, for example, the characteristics of the optical fiber cable installed in a conduit or on the seabed can be evaluated. For evaluation, there is a drawback that measurements must be taken simultaneously from both ends, which are far apart (for example, 1001O1). Furthermore, if the optical fiber FB to be measured is broken in the middle, it is theoretically impossible to perform Brillouin optical amplification, and there is a drawback that applicable measurements are limited.

The present invention has been made in view of the above circumstances.
The purpose of this is to be able to induce the generation of backward Rayleigh scattered light and the Brillouin optical amplification state of the optical fiber with a light pulse from a single light source, and to perform high-resolution fracture inspection without causing S/N deterioration of the detected backward Rayleigh scattered light. It is an object of the present invention to provide a backscattered light measuring device capable of measuring light loss with high accuracy.

(Means for Solving the Problem) In order to achieve the above object, claim (1) provides an optical pulse for generating backward Rayleigh scattered light in an optical fiber to be measured and a Brillouin beam in the optical fiber to be measured. A light source that generates an excitation light pulse for inducing an amplification state; and an optical frequency difference between the optical pulse and the excitation light pulse generated by the light source causes an optical frequency shift of the Brillouin light generated in the optical fiber under test. a light pulse adjusting means for adjusting the backward Rayleigh scattered light generated in the optical fiber to be measured and emitted from the optical fiber to be measured in a direction different from the incident direction of the light pulse emitted by the light source; a detector for detecting the intensity of the backward Rayleigh scattered light separated by the optical separating means; and a detector for calculating the intensity of the backward Rayleigh scattered light based on a detection signal from the first detecting means. - No. processing means.

Moreover, in claim (2), the optical amplification means is provided to amplify the emitted light pulse from the light source and make it enter the optical fiber to be measured.

Moreover, in claim (3), a light amplification means for amplifying backward Rayleigh scattered light is disposed between the light separation means and the detection means.

(Function) According to claim (1), the light pulse generated by the light source and the excitation light pulse are adjusted by the light pulse adjusting means so that the difference in their optical frequency is adjusted to the Brillouin light generated in the optical fiber to be measured. It is adjusted to match the frequency shift amount and is emitted. The light pulse and excitation light pulse emitted from these light sources are incident on one end surface of the optical fiber to be measured. Along with this, the optical pulse propagates through the optical fiber to be measured, and backward Rayleigh scattered light is generated.

Almost at the same time, the constant optical fiber 111j is induced into the Brillouin optical amplification state by the excitation light pulse. Thereby, the backward Rayleigh scattered light generated in the optical fiber to be measured is subjected to the Brillouin light amplification effect in the optical fiber to be measured, and is emitted from one end surface of the optical fiber to be measured.

The backward Rayleigh scattered light emitted from the target alJ constant optical fiber is separated by the light separating means in a direction different from the incident direction of each emitted light pulse from the light source, and is incident on the detecting means. As a result, the intensity of the backward Rayleigh scattered light is detected by the detection means, and this detection signal is input to the signal processing means. The signal processing means calculates the intensity of the backward Rayleigh scattered light based on the input detection signal.

According to claim (2), the optical pulses and excitation light pulses adjusted by the optical pulse adjustment means and emitted from the light source are amplified by the optical amplification means, and then are inputted into the optical fiber to be measured. Ru.

Furthermore, according to claim (3), the light is generated in the optical fiber to be measured and subjected to the Brillouin light amplification effect, as described above.
The backward illy scattered light that is emitted to the optical fiber to be measured and separated by the optical separation means is amplified by the optical amplification means and then enters the detection means.

(Embodiment) FIG. 1 is a block diagram showing a first embodiment of a backscattered light DJ fixing device according to the present invention, and the same components as those in FIG. 2 showing a conventional example are denoted by the same reference numerals.

That is, FB is the optical fiber to be measured, 1a is the laser light source,
For example, it is made of a semiconductor laser (for example, DFB-LD) with a narrow spectral linewidth that oscillates in a single mode, and is inserted into the optical fiber FB to be measured based on the injection current adjusted by the optical pulse adjustment device 3a described later. Optical pulse PR and optical fiber to be measured FB for generating Rayleigh scattered light
An excitation light pulse PM for inducing a Brillouin optical amplification state is generated in the laser beam. Reference numeral 3a denotes an optical pulse adjustment device that adjusts the optical frequency difference between the optical pulse PR and the excitation optical pulse PM generated by the laser light source 1a to match the optical frequency shift amount of the Brillouin light generated in the optical fiber FB to be measured. The current value of the pulse applied to the laser light source 1a is adjusted to adjust the pulse pattern generated by the laser light [1a, the optical frequency of the pulse, the pulse repetition conditions, etc.

4 is an optical isolator, 7 is an optical coupler (optical separation means),
A light pulse (PR1PM) from the laser light source 1a is made incident on the optical fiber to be measured FB, and the backward Rayleigh scattered light amplified by Brillouin light in the optical fiber to be measured FB is separated. A photodetector 8 receives the backward Rayleigh scattered light separated by the optical coupler 7 and converts it into a detection signal DT which is an electric signal corresponding to the intensity thereof. A signal processing device 9 calculates the intensity of the backward Rayleigh scattered light based on the detection signal DT from the photodetector 8. Note that the optical pulse adjustment device 3a operates in synchronization with the signal processing device 9.

Next, the operation of the above configuration will be explained step by step based on the optical pulse pattern diagrams of FIGS. 4 and 5.

First, the optical pulse adjustment device 3a modulates the laser light source 1a so that each optical pulse of the optical pulse P and the excitation optical pulse PM generates an optical pulse pattern having a unique optical frequency.

For example, as shown in FIG. 4, the optical pulse PR and the excitation optical pulse PM are generated and emitted with optical pulse widths Wl and W2 and optical frequencies ν and ν2, respectively.

The light pulse PR and the excitation light pulse P set in this way
M is input into the optical fiber FB to be measured via the optical isolator 4 and the optical coupler 7. Along with this, the optical pulse PR propagates through the optical fiber to be measured FB and generates backward Rayleigh scattered light.

The generated backward Rayleigh scattered light is subjected to the Brillouin light amplification effect described later and exits from the optical fiber FB to be measured, and is separated by the optical coupler 7 in a direction different from the incident direction of the optical pulse PR and the pumping optical pulse PM. , is emitted to the photodetector 8.

At this time, the power PBS of the backward Rayleigh scattered light detected is expressed as follows, as shown in the following equation (1). However, Pi is the peak value of optical pulse PR, Vq
is the group velocity of light in the optical fiber FB to be measured, α7 is the Rayleigh scattering coefficient, S is the proportion of the amount of light scattered backwards among the total amount of Rayleigh scattering, α is the loss of the optical fiber FB to be measured, 2
indicates the distance from the input end of the optical fiber FB to be measured to the position where backward Rayleigh scattering occurs.

On the other hand, when a laser beam that oscillates in a single longitudinal mode and has a narrow oscillation spectrum line width is incident, backward Brillouin amplified light is easily generated with a power of several mW of incident pumping light. In that case, the gain G due to Brillouin optical amplification is expressed by the following formula % (2). However, g is the Brillouin gain coefficient, and Ze is the effective length for the waveguide mode, which is expressed by the following equation 2% (3). Further, backward Brillouin scattering occurs in a frequency shifted region to the lower frequency side with respect to the excitation light frequency. If this Brie-Roouin shift amount is νB, then the wavelength λ
-0, 8, 1, 3, 1, 85p m for each wavelength ν
o -2-1, 13, 11Gjlz.

From this, the Brillouin optical amplification gain G due to the pumping light pulse PM is generally calculated by dividing Wl and W2 by the optical pulse P
As shown in the following formula, where G −exp(g ZeP2 °W2 , 1
,,,(4°Wl +W2 A, f.

It is expressed as However, P2 indicates the peak value of the excitation light pulse PM.

Here, the optical frequency ν of the optical pulse PR and the excitation optical pulse PM
and ν2 are set to be shi2-shi1-shiB,
The backward Rayleigh scattered light of the light pulse PR is the excitation light pulse P.
Brillouin light is amplified by R in the optical fiber FB to be measured. This Brillouin light amplified backward Rayleigh scattered light bar exp(g Ze −P2 °W2
1) Wl +W2 A,.

...(5) It is expressed as

For example, the Brillouin shift amount νB is the wavelength λ-1, 55μ
Since the optical frequency of the optical pulse PR is about 11 GHz with respect to m, the optical frequency of the optical pulse PR is set to a lower frequency side of 11 GHz than that of the excitation optical pulse PM. The Brillouin gain width ΔνB is usually about 1
00 Mllz (N, 5h1bata, et al,
Opt, Lett, vol, f3. p, 595.198
8) Therefore, in order to perform Brillouin optical amplification, it is necessary to set the optical frequency with accuracy within −100 Mtlz.

As the laser light source 1a, as described above, a semiconductor laser with a narrow spectral linewidth that oscillates in a single mode (for example, a DPB) is used.
-LD, etc.), by setting the current difference between the pulses applied to the laser to be about 11 mA based on the FM modulation characteristics of the laser, it is possible to easily generate an optical pulse with an optical frequency shifted by 11 GHz for each optical pulse.

In this way, the backward Rayleigh scattered light generated in the optical fiber FB to be measured and subjected to the Brillouin optical amplification effect is received by the photodetector 8, and is converted into a detection signal DT, which is an electric signal according to its intensity. converted. This detection signal DT is input to the signal processing device 9, where the intensity of the backward Rayleigh scattered light is calculated.

Next, detection of the break point position will be explained. When the length of the fiber under test FB is L, the width W2 of the excitation light pulse PM is calculated from the time it takes for the backward Rayleigh scattered light of the light pulse PR to return from the length to the input end, as shown in the following equation: It can be expressed as W2≧znL/C-(6). However, n is the refractive index of the optical fiber,
C indicates the speed of light. For example, for a 300 km optical fiber FB to be measured, W2≧3×1O−3(S),
For a 500kl optical fiber under test FB, Wl≧
5xlO-3(S). Usually, the optical pulse width is Wl-4 μs as the optical pulse PR for generating backward Rayleigh scattered light.
That's about it. Therefore, the light pulse PR and the excitation light pulse PM emitted from the laser light source 1a are Wl-4 μs, W
2m3g+s, (Lm300km), Wl-4μs, W
A fixed pattern of 2 m5■s (L-500km) is repeated. At this time, the repetition frequency is approximately 3
Corresponds to 00Hz and 200Hz. In this way, by setting the pulse interval for both optical pulses of optical frequencies ν 1 and ν 2 , it is possible to measure the position of the break point based on the waveform of the backward Rayleigh scattered light of the Brillouin optically amplified optical pulse PR.

At this time, the backward Rayleigh scattered light of the optical pulse PR starts from the time when the excitation optical pulse PM enters the fiber under test FB.
Since the backward Rayleigh scattered light at the far end of the optical pulse PR is constantly Brillouin optically amplified until it returns to the input end, the Brillouin optically amplified backward Rayleigh scattered light power P
BS and Br can be expressed as in the following equations.

exp (gZeP2/A)
-(7)rr This means that it is almost equivalent to the case where the optical fiber FB to be measured is excited to the Brillouin optical amplification state with CW light, and the optical pulse (PM) is used for Brillouin optical amplification. Using. This means that no deterioration will occur.

Next, the measurement of the optical loss value α will be explained. In the configuration of FIG. 1, if a pulse pattern in which the optical frequency of a part of the pumping light pulse PM is shifted is used, the backward Rayleigh scattered light of the optical pulse PR will not undergo Brillouin optical amplification in the frequency-shifted part.

Therefore, as shown in FIG. 5, the excitation light pulse PM is divided into small pulses P and P of optical frequencies ν and ν.
For example, if M2 and M3 pulse patterns are generated alternately, the Brillouin amplified backward Rayleigh scattered light power cxp(g Ze −P2 meeting W2°
1) W2°+W3 A, r.

... (8) Represented by: Here, excitation light pulse P with optical frequency ν2
The total pulse width of W2' is the excitation light pulse P of optical frequency ν3.
Let the total pulse width of W3 be W21111W2'+W3
Suppose there is a relationship like this. From equation (8), it can be seen that the waveform of the backward Rayleigh scattered light powers PBS and Br does not simply exhibit exponential attenuation.

If w2° −X, then the index interval W2° + in equation (8)
W3 The numerical argument φ is φ−−2az + gZeP2 X 1...(9
) err. For two different Xi and X2, if the longitudinal positions of the optical fiber FB to be measured that satisfy the extreme value condition for the distance Z of the argument φ are Zl and Z2, respectively, the optical loss α is as follows. As such, (1-1j2n(X2) -(10)Z2-ZI
It is expressed as Xi.

Therefore, by finding the positions Z1 and Z2 that give the extreme values from the backward Rayleigh scattered light waveform obtained from equation (10), the ratios Xi' and Therefore, the optical loss value α can be evaluated. At this time, in order to prevent the backward Rayleigh scattered light of the optical pulse PR from being amplified, the optical frequency ν3 of the excitation optical pulse P must be shifted by more than ±100H11z by the optical frequency P2 of the excitation optical pulse PM2. Also,
It is also effective to use a pattern in which the optical output is zero in the portion of the optical pulse width W3. In this manner, in this configuration, optical loss can be measured by using a pulse pattern in which the excitation light pulse PM is further decomposed into small pulses PM2 and 1M3.

In addition to this evaluation method, it is also possible to perform least square approximation of the obtained waveform using equation (7) to calculate the optical loss value α.

Furthermore, the optical pulse adjustment device 3a generates from the laser light source an optical pulse pattern having a code suitable for correlation processing such as an M sequence of optical frequencies ν, ν2 (C2-S1-B). By using the pulse pattern of the backward Rayleigh scattered light amplified by Brillouin light and a part of the pulse pattern applied to the laser light source 1a as reference codes, the signal processing device 9 delays bits and measures the correlation value at each distance. , the amount of backscatter can be determined. The position of the break point and the loss value of the optical fiber can be measured from the distribution of this backward Rayleigh scattered light.

Next, measurement of characteristics of optical fibers when optical fibers are connected in cascade in multiple stages will be explained. In an optical fiber, the shape and distribution of the Brillouin shift value νB and the Brillouin gain value Δν8 vary depending on the structure of the optical fiber, the material of the core, and the like. Furthermore, even for fibers with the same structural parameters, these values differ depending on the manufacturing conditions (N, 5h1ba
ta et al, 0PTIcS LCTTER, pp.
, 595-597.1988. reference). In particular, S i
In a silica-based optical fiber with G e O2-S h02 as the core material, the Brillouin gain is one, but in a dispersion-shifted fiber with G e O2-S h02 as the core material, multiple acoustic wave modes guided in the core and HE A plurality of gain peaks (for example, about 3) are generated due to the interaction with the 11 mode.

Therefore, in a transmission line in which these optical fibers are connected in a long length, the set frequencies of the optical pulse P and the pumping optical pulse PM in the configuration shown in FIG. 1 are changed to reduce the optical frequency difference (
By adjusting νB), only the desired optical fiber is brought into a Brillouin light amplification state, and by detecting the backward Rayleigh scattered light there, it is possible to not only determine the type and structure of the optical fiber, but also to detect a break in the desired optical fiber. This has the great advantage of making it possible to measure loss values.

FIG. 6 is a characteristic diagram showing the relationship between the backscattered light waveform obtained by the backscattered light measuring device according to the present invention and the distance from the optical fiber input end. -0.18 dB/km, optical pulse width W1-4 μs, W2-3 ms, the back Rayleigh scattered light waveform is calculated for parameter X.

Here, X-1 is a Brillouin optically amplified back Rayleigh scattered light waveform corresponding to a pumping light pulse input PM-10 mW, and hereinafter, each optical pulse width W with an optical frequency ν is
This is a waveform corresponding to changing the ratio of 2' to W2. X-0 is a backward Rayleigh scattered light waveform that is not caused by Brillouin optical amplification.

In the present invention, since the Brillouin optical amplification effect is utilized, as can be seen from FIG. 6, there is no simple exponential attenuation with respect to distance 2. For example, X-O, S and 0,
The difference in distance from the maximum value in the backward Rayleigh scattered light waveform for ZIZ2-7.08kl for ZIZ2-7.08kl. By substituting this value into equation (lO), the optical loss value α of the optical fiber can be evaluated as α-0.18 dI3/km.

FIG. 7 is a configuration diagram showing an embodiment of m2 of the backscattered light measuring device according to the present invention. The difference between this second embodiment and the first embodiment is that an optical amplifier 10 consisting of a semiconductor laser or an optical fiber is provided between the optical isolator 4 and the optical coupler 7 and between the optical coupler 7 and the photodetector 8. This is due to the fact that 11 are arranged respectively.

In the present second embodiment, by adopting such a configuration, in addition to the effects of the first embodiment, the emitted light from the laser light source 1a, pulses P and P, or backward Rayleigh scattered light, Alternatively, by amplifying them at the same time using optical amplifiers 10 and 11, the backward Rayleigh scattered light incident on the photodetector 8 can be amplified, and it can also be used to detect high-resolution break points in long optical fiber transmission lines and to detect high-precision optical fibers. This has the effect of making it possible to measure loss.

(Effects of the Invention) As explained above, according to claim (1), an optical pulse for generating backward Rayleigh scattered light in the optical fiber to be measured and a Brillouin optical amplification state in the optical fiber to be measured are provided. A light source that generates an excitation light pulse for inducing the light, and an optical frequency difference between the light pulse generated by the light source and the excitation light pulse, which is the optical frequency shift amount of the Brillouin light generated in the optical target fiber 21-1. an optical pulse adjusting means for adjusting backward Rayleigh scattered light generated in the optical fiber under test and emitted from the optical fiber under test in a direction different from the incident direction of the optical pulse emitted by the light source; A light separating means for separating, a detecting means for detecting the intensity of the backward Rayleigh scattered light separated by the light separating means, and a signal processing means for calculating the intensity of the backward Rayleigh scattered light based on a detection signal by the detecting means. , it is possible to detect backward Rayleigh scattered light with high resolution and high sensitivity without causing S/N deterioration.

In addition, by adjusting each pulse pattern of the light pulse and excitation light pulse generated by the light source to a desired pattern by the light pulse adjustment means, it is possible to measure the optical loss distribution of the optical fiber transmission line, and to detect the break points and connection points. There is an advantage in that it is possible to detect the position, and also to determine the type and structure of the optical fiber, and to detect the position of the break point with high accuracy.

Further, according to claim (2), the emitted light pulse from the light source can be amplified by the optical amplification means and then input to the optical fiber to be measured, so in addition to the effect of claim (1), High-resolution break point detection and high-precision optical loss measurement in long-distance optical fiber transmission lines can be performed.

Furthermore, according to claim (3), the backward Rayleigh scattered light can be detected by the detection means after being amplified by the optical amplification means, so that the effect of claim (1) or claim (2) is achieved. In addition, it is possible to detect break points with higher resolution and measure optical loss with higher precision.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the backscattered light measuring device according to the present invention, and FIG. 2 is a first embodiment of the backscattered light measuring device.
A configuration diagram showing a conventional example, Figure 3 shows backscattered light! 1-1 A configuration diagram showing a second conventional example of the fixed device, FIGS. 4 and 5 are optical pulse pattern diagrams according to the present invention, and FIG. 6 is a diagram showing the backscattered light measurement device according to the present invention. FIG. 7 is a characteristic diagram showing the relationship between the Rayleigh scattered light waveform and the distance from the optical fiber input end, and FIG. 7 is a configuration diagram showing a second embodiment of the backscattered light measuring device according to the present invention. In the figure, 1a... Laser light source, 3a... Optical pulse adjustment device, 4... Optical isolator, 7... Optical coupler (light separation means), 8... Photodetector (detection means) ,9...
Signal processing device, 10.11... optical amplifier. Patent Applicant Nippon Telegraph and Telephone Co., Ltd. Agent Patent Attorney Yoshi 1) Takashi Seiji Diagram 5 Seats 1 Rusumeji U3 Relaxation Diagram of Light Belsuno Chart According to the Present Invention Diagram of Light Belsuno Chart According to the Present Invention

Claims (3)

[Claims] (1) A light source that generates a light pulse for generating backward Rayleigh scattered light in the optical fiber to be measured and an excitation light pulse for inducing a Brillouin optical amplification state in the optical fiber to be measured; and the light source. an optical pulse adjusting means for adjusting the optical frequency difference between the generated optical pulse and the excitation optical pulse to match the optical frequency shift amount of the Brillouin light generated in the optical fiber to be measured; a light separating means for separating the backward Rayleigh scattered light generated by the optical fiber and emitted from the optical fiber to be measured in a direction different from the incident direction of the emitted light pulse from the light source; and the backward Rayleigh scattered light separated by the light separating means. What is claimed is: 1. A backscattered light measuring device comprising: a detection means for detecting the intensity of the backscattered light; and a signal processing means for calculating the intensity of the backward Rayleigh scattered light based on a detection signal from the detection means. (2) Claim comprising an optical amplifying means for amplifying the emitted light pulse from the light source and making it enter the optical fiber to be measured (
1) Backscattered light measuring device described. (3) A light amplifying means for amplifying backward Rayleigh scattered light is disposed between the light separating means and the detecting means (1).
) or the backscattered light measuring device according to claim (2).