JP2015021748A - Characteristic analyzer for optical fiber line and characteristic analysis method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the reduction of measurement time about an optical fiber strain variation of an optical fiber line in a lengthwise direction of the optical fiber line.SOLUTION: Measurement in a short time can be achieved by allowing a Brillouin gain spectrum at a point on an optical fiber line to be obtained in a single measurement. Concretely, the Brillouin gain spectrum is obtained by counter propagation of a probe light pulse train including X probe light beams different by frequencies and a pump light pulse train including X pump light beams different by frequencies, which pair with the probe light beams. A frequency difference of an i-th probe-pump pair (pair of a probe light beam and a pump light beam) is changed from that of an (i-1)th probe-pump pair by Δf, and the Brillouin gain spectrum is obtained from Brillouin gains of respective probe light beams obtained by this change of frequency differences.

Description

  The present invention relates to an optical line characteristic analyzer for measuring characteristics of an optical line to be measured and an analysis method therefor.

  In an optical communication system using an optical line such as an optical fiber, an optical pulse line monitoring device is used to detect a failure of the optical line or to specify a failure position. A typical optical pulse line monitoring device is an OTDR (Optical Time Domain Reflectometer).

  By the way, in the optical line monitoring of the PDS (Passive Double Star) type optical line structure, the light reflection filter on the subscriber side is used, the probe light pulse and the pump light pulse are incident with a time difference, and the two pulses collide. A method (Non-Patent Document 1) for grasping the optical line characteristics by analyzing the Brillouin gain associated with is proposed. Conventionally, in this method, repeated measurement is performed for averaging processing, and a long measurement time has been a problem. Recently, however, a method of obtaining a light loss distribution in the longitudinal direction of an optical line in a short time (non- Patent Document 2) has been proposed.

  However, in addition to those specified by the optical loss distribution, such as the optical attenuation with respect to the distance, the position of the bending obstacle, the degree of bending, the position of the disconnection obstacle, etc. Some are specified by the change in the Brillouin frequency shift amount of the optical fiber, such as the amount of change in the optical fiber strain in the longitudinal direction of the path, and the latter measurement has not solved the problem that the measurement time is long.

  By the way, a technique for obtaining one Brillouin gain spectrum by limiting the form of the optical line to be measured to a single line and repeatedly measuring while shifting the center frequency of the optical comb by the required frequency resolution has been proposed. (Non-Patent Document 3). However, this method has a trade-off relationship between the spatial resolution of the optical line characteristics and the frequency resolution of the Brillouin gain spectrum to be measured, and the spatial resolution and the frequency resolution of the Brillouin gain spectrum cannot be arbitrarily determined. For this reason, there is a concern that when the frequency resolution is increased, the sampling rate deteriorates and it becomes impossible to cope with a dynamic characteristic change.

H. Takahashi, et al., "Individual loss distribution measurement in 32-branched PON using pulsed pump-probe Brillouin Gain Analysis," Opt. Express, 21, No. 6, 6739-6748, (2013). Hiroshi Takahashi, Kunihiro Toge, Fumihiko Ito, Chihiro Kito, “Branching monitoring technology by Brillouin gain analysis of far-end reflection,” Proceedings of 51th Meeting on Lightwave Sensing Technology, LST51-18, (2013). P. Chaube, et al., “Distributed Fiber-Optic Sensor for Dynamic Strain Measurement,” IEEE Sens. J., 8, No. 7, (2008). Tatsuya Kumagai and Shinobu Sato, “Development of Sagnac Interferometric Optical Fiber Sensor for Physical Security,” IEEJ Transactions E (Sensor Micromachine Division), 132, No. 11, (2012).

  As described above, when monitoring the optical device in the optical line, the light reflection filter on the subscriber side is used, the probe light pulse and the pump light pulse are incident with a time difference, and the Brillouin accompanying the collision of the two pulses is used. In the method of grasping the optical line characteristic by analyzing the gain, the measurement is repeatedly performed for the averaging process, and the measurement time is long.

  Recently, a method for obtaining the optical loss distribution in the longitudinal direction of the optical line in a short time has been proposed, but the characteristic items indicating the optical line characteristics include the optical attenuation with respect to the distance, the position of the bending obstacle, the degree of bending, and the disconnection. In addition to what is specified by the optical loss distribution such as the position of the fault, there are those specified by the Brillouin frequency shift amount change of the optical fiber, such as the temperature change with respect to the distance and the optical fiber strain change in the longitudinal direction of the optical line. In the measurement of, the problem of long measurement time has not been solved.

  The present invention has been made by paying attention to the above circumstances, and can measure the Brillouin gain spectrum distribution with an arbitrary frequency resolution in a single trial, and measure the amount of change in optical fiber strain in the longitudinal direction of the optical line. An object of the present invention is to provide an optical line characteristic analysis apparatus and its characteristic analysis method capable of reducing time.

The optical line characteristic analyzing apparatus according to the present invention has the following configuration.
(1) An optical line characteristic analyzing apparatus for analyzing the characteristics of an optical line to be measured, wherein the first test light and the second test light having different wavelengths are temporally controlled to obtain X pieces (X is a natural number). Test light frequency modulating means for modulating the frequency, and test light pulse forming means for synchronizing X probe light and X pump light having different frequencies with an arbitrary time difference in synchronization with the test light modulating means And means for combining the pulsed probe light pulse train of the X first test lights and the pump light pulse train of the X second test lights, and the combined probe light pulse train and the pump light A pulse train is sequentially incident on the optical path to be measured, and a circulator for extracting the test light returned from the optical path to be measured, and a frequency component of X first test lights from the test light extracted by the circulator. Means for extracting the first test light extracted by the filter means and converting it into a current, and an analog for converting the first test light converted into the current into a digital signal -Digital conversion means, decoding the digital signal, specifying which digital signal of the first test light is incident on the branched lower optical fiber from the control information at the time of generation and the light receiving timing, and specifying the specified digital Frequency separation means for separating the signal for each of X frequency components from the signal, Brillouin gain of each of the X frequency components is analyzed, and the above measurement is repeated while changing the incident time difference between the probe light pulse train and the pump light pulse train And an arithmetic processing means for obtaining a Brillouin gain characteristic distribution of the optical line to be measured from measurement results repeatedly measured, and the test The frequency modulation means is means for frequency-modulating the first test light and the second test light at predetermined time intervals, and causes the Brillouin interaction only between the specific first test light and the second test light. The first and second test lights are subjected to frequency modulation, and the arithmetic processing means changes the frequency interval between the first test light and the second test light at predetermined time intervals, and the frequency interval and the Brillouin frequency are changed. A Brillouin gain spectrum at a measurement point is acquired from the scattered intensity, and Brillouin gain spectrum distribution information is formed by repeatedly performing the above measurement while changing the difference in incident time between the probe light pulse train and the pump light pulse train. It is set as the aspect which analyzes the optical line characteristic of the longitudinal direction of a measurement optical line.

(2) In (1), in the optical line under measurement, one end of the backbone optical fiber is branched into a plurality of systems by an optical branching device, and one end of the branching optical fiber is optically connected to each branching end portion of the optical branching device. It is set as the aspect formed by couple | bonding.
(3) In (1), the optical line characteristics include optical attenuation with respect to the distance of the optical line to be measured, position of bending failure, degree of bending, position of disconnection failure, temperature change amount with respect to distance, optical line longitudinal direction The optical fiber strain change amount is at least one of the aspects.

(4) In (1), the frequency modulation means is realized by a modulated electric signal of a single sideband modulator or a low noise phase modulator and an arbitrary waveform signal generator.
The optical line characteristic analysis method according to the present invention has the following configuration.
(5) A method for analyzing characteristics of an optical line for analyzing characteristics of an optical line to be measured, wherein the first test light and the second test light having different wavelengths are temporally controlled to obtain X pieces (X is a natural number). Modulating to frequency, synchronizing with the modulation, pulsing X probe light and X pump light having different frequencies with an arbitrary time difference, and probe by the pulsed X first test lights The optical pulse train and the pump optical pulse train of the X second test lights are combined, and the combined probe optical pulse train and pump optical pulse train are sequentially incident on the optical path to be measured and returned from the optical path to be measured. The test light is extracted, frequency components of X first test lights are extracted from the extracted test light, and the extracted first test light is received and converted into current, which is converted into the current. The first test light The digital signal is decoded, and it is determined whether it is a digital signal of the first test light incident on the optical path to be measured from the control information at the time of generation and the light reception timing, and X signals are identified from the specified digital signal. The signal is separated for each frequency component, the Brillouin gain of each of the X frequency components is analyzed, the above measurement is repeated while changing the incident time difference between the probe light pulse train and the pump light pulse train, An arithmetic process for obtaining a Brillouin gain characteristic distribution of the optical line to be measured is executed, and when the first test light and the second test light are frequency-modulated at each predetermined time interval, a specific first test light and The first test light and the second test light are frequency-modulated so as to cause a Brillouin interaction only between the second test lights, and the arithmetic processing includes the first test light and the second test light. The frequency interval between the test light and the second test light is changed at predetermined time intervals, the Brillouin gain spectrum at the measurement point is obtained from the frequency interval and the Brillouin scattering intensity, and the difference in incident time between the probe light pulse train and the pump light pulse train is obtained. The Brillouin gain spectrum distribution information is formed by repeatedly performing the above measurement while changing, and the optical line characteristic in the longitudinal direction of the measured optical line is analyzed from the distribution information.

(6) In (5), in the optical line under test, one end of the trunk optical fiber is branched into a plurality of systems by an optical branching device, and one end of the branching optical fiber is optically connected to each branching end portion of the optical branching device. It is set as the aspect formed by couple | bonding.
(7) In (5), the optical line characteristics are: optical attenuation with respect to the distance of the optical line to be measured, position of bending failure, degree of bending, position of disconnection failure, temperature change amount with respect to distance, optical line longitudinal direction The optical fiber strain change amount is at least one of the aspects.

  (8) In (5), the frequency modulation means is realized by a modulated electric signal of a single sideband modulator or a low noise phase modulator and an arbitrary waveform signal generator.

  As described above, according to the present invention, the Brillouin gain spectrum distribution can be measured with a single trial at an arbitrary frequency resolution, and the measurement time of the optical fiber strain variation in the longitudinal direction of the optical line can be shortened. It is possible to provide an optical line characteristic analyzing apparatus and a characteristic analyzing method thereof.

It is a block diagram which shows the structure of the characteristic analyzer of the optical line which concerns on the 1st Embodiment of this invention. In a 1st embodiment, it is a key map showing change of Brillouin gain which probe light included in a Brillouin gain spectrum (BGS) which a pump light pulse train comprises and a probe light pulse train. It is a flowchart which shows the flow of the characteristic analysis process in 1st Embodiment. It is a block diagram which shows the structure of the characteristic analyzer of the optical line which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the flow of the characteristic analysis process in 2nd Embodiment.

Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment.
First, to outline the present invention, an optical line characteristic analyzing apparatus according to the present invention is configured in the following manner.

(Conditions for optical line under measurement)
An optical line to be measured to which the present invention is applied includes a test light reflection filter at the far end of a single optical fiber, or each branched lower part obtained by branching a single optical fiber from a first optical fiber to an Nth optical fiber by an optical splitter. A test light reflection filter is provided at the far end of the optical fiber, and the minimum difference in length of the N branched lower optical fibers from the branch point to the optical filter by the optical splitter is greater than or equal to the optical fiber identification resolution of the device of the present invention. An optical branch line having

(Outline of device configuration)
The test light of the present invention generates a pair of first test light (probe light) and second test light (pump light) having a frequency difference that causes Brillouin interaction. It is modulated to X different frequencies (X is a natural number) by a frequency modulator that operates in response to the signal.

Here, if the i-th frequency included in the first test light is f _1i , and the i-th frequency f _2i included in the second test light (i is a natural number), the first test light and the second test light Performs frequency modulation so as to satisfy the following four expressions with respect to the initial value f _B of the Brillouin frequency shift amount assumed in the optical line to be measured.

Frequency difference between the first test light and the second test light that make a pair: f _2i -f _1i = f _B + iΔf
Frequency difference between the first test light and the second test light that do not form a pair: f _2i -f _1j = f _B + (ij) Δf + kΔf _B
Frequency difference of probe light included in first test light: | f _1i -f _1j | ≧ Δf + kΔf _B
Frequency difference of pump light contained in second test light: | f _2i -f _2j | ≧ Δf + kΔf _B
However, 0 <iΔf ≦ Δf _B , Δf _B is the Brillouin spectrum width, n is a natural number, Δf is the plot interval (frequency resolution) on the frequency axis of the Brillouin gain spectrum to be measured, i and j are natural numbers less than X, i ≠ j and k are constants of 1 or more, and kΔf _B is set to be sufficiently larger than the larger of the Brillouin frequency shift amount assumed for the optical line to be measured or Δf _B ) The modulation frequency of the probe light or pump light is controlled. Δf can be set arbitrarily and is not limited by the required spatial resolution.

  The frequency-modulated electrical signal is a frequency-modulated electrical signal pre-programmed in the arbitrary waveform generator. The arbitrary waveform generator operates by being controlled in time by a trigger signal from a pulse pattern generator (PPG) or a function generator (FG).

As the frequency modulator, a single sideband modulator or an LN phase modulator can be used. The trigger signal of the PPG or FG can be shared with the trigger signal for reception signal recording, so that the transmission side and the reception side of the modulation frequency can be synchronized.
X probe lights and X pump lights having different frequencies are pulsed with a relatively arbitrary time difference by a synchronized pulse generator based on a PPG or FG trigger signal shared with the frequency modulator, It becomes a probe light pulse train and a pump light pulse train.

Here, an acousto-optic modulator, an LN intensity modulator, and an optical switch can be used as the pulsing device.
The test optical pulse train is transmitted after the previously transmitted test optical pulse train is discharged from the optical line to be measured.
With the above configuration, the first test light and the second test light incident on the measured optical line change at a predetermined frequency interval every predetermined time interval and coincide with f _2i -f _1i = f _B + iΔf The test light pulse trains are paired with a frequency difference, and the frequencies of X probe light and X pump light do not match.

Also, since the frequency modulation electrical signal, pulsing device, and reception signal recording start operation share one trigger signal, the receiving side characteristic analysis device sets the transmission side output state (frequency, presence / absence of output) at an arbitrary time. I can grasp it.
The probe light pulse train and the pump light pulse train are combined by a multiplexing element and sequentially enter the optical path to be measured. The X probe lights reflected by the test light reflection filter at the far end of the optical path to be measured are only the pump light paired with the frequency difference of f _2i -f _1i = f _B + iΔf and in the optical path to be measured. Generates Brillouin interaction and receives Brillouin gain. On the other hand, the frequency difference between the unpaired probe light and the pump light pulse is f _2i -f _1j = f _B + (ij) Δf + kΔf _B , which is sufficiently large (or sufficient) compared to f _B + Δf _B Therefore, the Brillouin interaction does not occur, and the same probe light does not receive multiple Brillouin gains in the measured optical line.

The returned test light is extracted by an optical circulator, and only the frequency components of X probe lights are extracted by an optical filter.
The probe light extracted by the optical filter is received by a photodetector and converted into a current, and the probe light converted into a current is converted into a digital signal by analog / digital conversion, the digital signal is decoded, and the measured optical line is If it is a branch line, specify which digital signal of the probe light is incident on the lower branch optical fiber from the control information and the light reception timing at the time of test light generation, and the specified digital signal is Fourier transform etc. It is separated into X frequency components by calculation processing, Brillouin gain of each frequency component is analyzed, and line characteristic information up to the collision point of probe light and pump light is output.

  Furthermore, the Brillouin gain characteristic of each of the lower branch fibers of the optical splitter is determined by repeating the above measurement while changing the collision point of the probe light and the pump light by changing the incident time difference between the probe light and the pump light. Output the distribution.

(Characteristic items to be measured)
The optical line characteristics include at least one of the optical attenuation with respect to the distance of the optical line to be measured, the position of the bending failure, the degree of bending, the position of the disconnection failure, the temperature change with respect to the distance, and the optical fiber strain change in the longitudinal direction of the optical line. It is.
(Calculation processing)
The arithmetic processing means has the probe light pulse train incident in advance under the condition that the pump light pulse train is not incident, and has the return time t _{1 at} the head of the probe pulse train from _one optical fiber to be measured, or N branch lower optical fibers respectively measuring the head of the return time t ₁ ~t _N probe pulse train from the measured light path, from the information of the frequency modulation time by the head of the return time and the frequency modulating means of the probe optical pulse train, it is included in the probe optical pulse train The return time of each of the X probe optical frequencies is specified, the modulation frequency to be received from the return time of each of the X probe optical frequencies included in the probe optical pulse train to the frequency modulation time is specified, and the probe optical pulse train Frequency is obtained by Fourier-transforming the time variation of received signal strength within the frequency modulation time from the return time of each X probe optical frequencies included. It performed away, to extract the probe light frequency component to be received in the time, and the reference probe light power of the frequency signal components.

  Subsequently, the probe light pulse train and the pump light pulse train are incident at a predetermined time difference, and the probe light signal power subjected to the Brillouin gain by the pump light is measured in the same manner as the measurement of the reference probe light power. Then, the Brillouin gain obtained by the probe light frequency component is independently analyzed from the ratio of the intensity of the frequency component of the probe signal power and the reference probe light power.

At this time, since the frequency difference between the paired probe light and pump light differs depending on the pair, the amount of Brillouin gain from which the probe light is obtained also differs. Since the Brillouin frequency shift amount ν _B made by the pump light in the band (100 GHz or less) used in this method can be regarded as unchanged, the Brillouin gain of each probe light included in the same probe light pulse train is By plotting the frequency difference f _2i -f _1i = f _B + iΔf of the pump light with respect to the horizontal axis, the Brillouin gain spectrum at the collision point can be obtained by one measurement. The frequency difference taking the maximum value is the measured value ν _B of the Brillouin frequency shift. By sequentially changing the incident time difference between the probe light pulse train and the pump light pulse train, the Brillouin gain spectrum distribution in the longitudinal direction of the measured optical line can be formed. By obtaining the Brillouin frequency shift ν _B distribution from these Brillouin gain spectrum distributions, the strain distribution and temperature distribution can be measured. Alternatively, the loss distribution can be measured by obtaining the maximum value or area of the Brillouin gain spectrum.

  The sampling rate for acquiring the optical line characteristic data described above is based on the length of the optical line to be measured when the signal-to-noise ratio is 1 or more in one trial (measured with one set of probe optical pulse train and pump optical pulse train). It is determined only by the reciprocal of the round trip time of the test light. When the signal-to-noise ratio is less than 1 in one trial, the value obtained by dividing the reciprocal of the round-trip time of the test light with respect to the measured optical line length by the average number of times until the signal-to-noise ratio becomes 1 or more This is the sampling rate of this method. In particular, under the measurement conditions in which the signal-to-noise ratio is 1 or more at a time, the present technique can measure the strain fluctuation information at one point at the optical sampling rate for the optical line to be measured whose strain changes dynamically.

  As described above, in the optical line characteristic analysis technique using the Brillouin gain analysis, when the Brillouin frequency shift amount changes in the longitudinal direction in the optical line to be measured having a single core or a branch line, the test optical pulse pairs having different frequency differences are used. The Brillouin gain spectrum at one point can be acquired by a single measurement by the collective parallel measurement by, so that the Brillouin frequency shift change can be measured at a high sampling rate, and repeated trials are repeated. The Brillouin gain spectrum distribution in the longitudinal direction of the measurement optical line can be measured, and the above measurement results can be obtained without degrading the branch optical fiber identification resolution, characteristic distribution resolution, and Brillouin gain spectrum resolution compared to the conventional technology. It is possible to provide a characteristic analysis device for a simple optical line and a branched optical line.

(First embodiment)
FIG. 1 is a block diagram illustrating the configuration of the optical branch line characteristic analyzer according to the first embodiment. The apparatus shown in FIG. 1 (all other components excluding the optical fiber to be measured surrounded by a dotted line) is opposed to X pump lights having different frequencies, each paired with X probe lights having different frequencies. The characteristic distribution of the Brillouin gain received in the measured fiber 23 by propagation can be obtained.

In the first embodiment shown in FIG. 1, the continuous light output from the laser light source 11 is branched into two systems by the branch element 12.
One of the lights branched by the branch element 12 is a first test light (probe light) and the other is a second test light (pump light). The first test light is shifted in frequency by the Brillouin frequency shift amount ν _B by the optical frequency shifter 13. Specifically, the optical frequency shifter 13 may be any external modulator having a function of frequency of the modulation sidebands is changed according to the signal frequency from the sine wave generator (not shown), a LiNbO ₃ The used phase modulator (LN phase modulator), amplitude intensity modulator, or SSB modulator can be used.

  The first test light frequency-shifted by the optical frequency shifter 13 is branched into two systems by the branch element 14, one being probe light and the other being local light. The probe light is incident on the optical frequency modulation device 15 and becomes light whose frequency is modulated in the X stage controlled temporally. Further, the probe light becomes a probe light pulse train arranged in time with different frequencies of the X wave by pulsed modulation by the optical pulse device 16.

On the other hand, the second test light branched by the branching element 12 is similarly frequency-modulated by the optical frequency modulation device 17 and further arranged temporally with different X-wave frequencies by pulsed modulation by the optical pulse device 18. The pump light pulse train thus obtained is obtained. Of the X probe lights and pump lights, the first wave probe light and pump light, the second wave probe light and pump light, ... the X wave probe light and pump light have a frequency difference of ν _B. A probe-pump pair. Only the probe-pump pair satisfies the condition for causing the Brillouin interaction, and both the probe light and the pump light have different frequencies.

Here, when f ₀ is an unmodulated optical frequency of the laser light source 11, ν _B is an optical frequency shift amount due to Brillouin backscattering, Δν _B is a half-value width of the Brillouin gain band, and A is a constant, the laser light source (frequency f ₀ ) The gain coefficient g _B of stimulated Brillouin scattering given by 11 is expressed by the following equation.

（1）式によれば、本実施形態の手法においてポンプ光パルス列に内包されるi番目のポンプ光の光周波数f_2i = f₀ -iΔf -ikΔf_Bとし、プローブ光パルス列に内包されるi番目のプローブ光の周波数f_1iはプローブ−ポンプ対において互いにν_Bの周波数差を持つようなf_1i = f₀ -iΔf -ikΔf_B -ν_B に一致する場合、プローブ光はポンプ光から最大の利得を得る。

According to the equation (1), the optical frequency f _2i = f ₀ -iΔf -ikΔf _{B of the} i-th pump light included in the pump light pulse train in the method of the present embodiment, and the i-th included in the probe light pulse train. If the frequency f _1i of the probe light coincides with f _1i = f ₀ -iΔf -ikΔf _B -ν _B , which has a frequency difference of ν _B in the probe-pump pair, the probe light has the maximum gain from the pump light. Get.

In order to obtain the Brillouin gain spectrum at the point of one measurement, which is the purpose of this method, the initial value of the frequency difference between the probe light and the pump light with respect to ν _B assumed for a single measured optical line was a f _B, i th ₀ optical frequency f _2i = f of the pump light -iΔf-ikΔf _B which is contained in the pump optical pulse train, the i th probe light to be encapsulated in the probe optical pulse train frequency f _1i = f ₀ -iΔf -ikΔf _B Set to -f _B. However, although it is desirable for efficient measurement to set to about f _B = ν _B -Δf _B / 2, f _B <ν _B -Δf _B / 2 and a pair of test lights forming a pair If the number is X, set X and Delta] f such that XΔf> Δf _B. This makes it possible to measure the Brillouin gain spectrum.

In addition, for each frequency component included in the probe light pulse train and the pump light pulse train, adjacent components in the frequency space are the larger of the change amount of the Brillouin frequency shift assumed in the optical line to be measured or Δf _B Place them far enough apart. Thereby, generation | occurrence | production of the Brillouin interaction except between pairs can be avoided.

FIG. 2 shows a conceptual diagram of the Brillouin gain spectrum (BGS) formed by the pump light pulse train of this method and the Brillouin gain obtained by the probe light included in the probe light pulse train. As shown in FIG. 2A, Brillouin gain spectra BGS1, BGS2, BGS3, and BGS4 are formed on the low frequency side by the Brillouin frequency shift amount ν _B by the pump light powers P ₂₁ , P ₂₂ , P ₂₃ , and P ₂₄ , respectively. To do. The probe light (frequency f ₁₁ , f ₁₂ , f ₁₃ , f ₁₄ ) included in the probe light pulse train obtains a Brillouin gain indicated by a round dot in each BGS.

Here, as shown in FIG. 2B, the Brillouin frequency shift amount ν _B can be regarded as unchanged in the frequency band of pump light (here, f ₂₄ -f ₂₁ ), and the frequencies f ₁₁ , f ₁₂ , f ₁₃ , f ₁₄ is to have Δf, 2Δf, 3Δf, the frequency difference 4Δf the initial setting Brillouin frequency shift amount, the probe light component would get different Brillouin gain. A Brillouin gain spectrum can be obtained by plotting the Brillouin gain obtained by each probe light with the horizontal axis representing the frequency difference between the probe light and the pump light forming a pair.

As the optical pulse device 16 and the optical pulse device 18, specifically, an amplitude modulator or an acousto-optic modulator using LiNbO ₃ driven with an arbitrary waveform can be used. Here, optical pulsing means intensity-modulating the continuous probe light and pump light to temporally separate the m-th (m is a natural number) test light and the (m-1) -th test light. That is. The order of the optical frequency modulation by the optical frequency modulators 15 and 17 and the optical pulse modulation by the optical pulse generators 16 and 18 are arbitrary.

  However, the analog frequency connected to the modulation frequency controller 19 for controlling the modulation frequency of the optical frequency modulators 15 and 17, the optical pulse controller 20 for controlling the optical pulse generators 16 and 18, and the signal processor (PC) 28. The digital / digital (A / D) converter 27 operates in synchronization with a trigger signal of a pulse pattern generator (PPG) or a function generator (FG).

  A probe light pulse train using probe lights having different X frequencies (wavelengths) and a pump light pulse train using pump lights having different X frequencies (wavelengths) are combined by a multiplexing element 21 and pass through a circulator 22 to be measured. The light is sequentially incident on the optical line (optical fiber) 23. The measured optical line 23 includes an optical fiber 23a and a test light reflection filter 23b installed at the end of the optical fiber.

  The probe light pulse train and the pump light pulse train incident on the measured optical line 23 cause Brillouin interaction only by the probe-pump pair during propagation in the measured optical line 23, and the probe light propagates back and forth along the measured optical line 23. Receive Brillouin amplification only once. Each probe light included in the probe light pulse train subjected to the Brillouin amplification reaches the optical circulator 22 and is guided to the optical filter 24 by the optical circulator 22. Similarly, the pump light pulse train is guided to the optical filter 24. The optical filter 24 transmits only the probe light pulse train, and the probe light pulse train transmitted here is received by the optical receiver 26. Note that heterodyne detection may be performed by combining with unmodulated local light branched by the branch element 14 by the multiplexer 25.

The output current from the optical receiver 26 is converted into a digital signal by the A / D converter 27 and then input to the signal processing device (PC) 28. The signal processing device 28 performs arithmetic processing described later on the input current value.
When the signal-to-noise ratio is 1 or more in one trial (measurement with one set of probe light pulse train and pump light pulse train), the sampling rate of the above optical line characteristic data is the light beam of the measured optical line 23. It is determined only by the reciprocal of the round trip time of the test light with respect to the path length. When the signal-to-noise ratio is less than 1 in one trial, the value obtained by dividing the reciprocal of the round-trip time of the test light with respect to the measured optical line length by the average number of times until the signal-to-noise ratio becomes 1 or more This is the sampling rate of this method.

  For example, if the signal-to-noise ratio exceeds a single trial (theoretically, if the required spatial resolution is 10 m, the one-way line loss is about 18 dB or less), the one-way optical path 23 to be measured is 1 km. It can be measured at a sampling rate of 100 kHz, and the distortion changes by several tens to several hundreds of Hz by shaking with natural wind (Non-Patent Document 4). realizable.

Next, the operation of the above-described optical line characteristic analyzing apparatus of the present embodiment will be described. The optical frequency modulation devices 15 and 17, the optical pulse devices 16 and 18, the optical receiver 26, and the measured optical line 23 need to satisfy the following conditions.
(Condition 1) The frequency f _1i of the i-th probe light and the frequency f _2i of the i-th pump light included in the probe light pulse train and the pump light pulse train are the initial values of the Brillouin frequency shift assumed in the measured optical line 23. The optical frequency modulators 15 and 17 operate so as to form a probe-pump pair having a frequency difference of f _2i -f _1i = f _B + iΔf with respect to the value f _B , and the probe light and pump light that make a pair are arbitrary The optical pulse generators 16 and 18 operate so as to be incident on the measured optical line with a time difference of.

(Condition 2) When a test light pulse train composed of a probe light pulse train and a pump light pulse train is sequentially incident on the optical path under measurement 23, the second group of test optical pulse trains are ejected from the optical path under measurement 23 after being discharged from the optical path under measurement 23. The test optical pulse trains are incident on the optical line to be measured 23, and all the test optical pulses included in the test optical pulse trains have frequencies different from each other by kΔf _B. However, k is set so that kΔf _B is sufficiently larger than the larger one of the change amount of the Brillouin frequency shift assumed in the optical line to be measured 23 or Δf _B.

Here, conditions 1 and 2 have the following meanings.
Condition 1 is a condition for the probe light to undergo Brillouin amplification by the pump light.
Condition 2 is a condition for acquiring Brillouin gain information only at an arbitrary position z.
When the conditions 1 and 2 are satisfied, the Brillouin gain spectrum, which fluctuates at one point, can be measured at a sampling rate determined only by the length of the optical line to be measured for a single optical line to be measured according to the present embodiment, and the trial is performed. By repeating, it is possible to measure the Brillouin gain spectrum distribution of the entire measured optical line. Therefore, the measurement time can be shortened without degrading the branch optical fiber identification resolution and the spatial resolution and frequency resolution of the Brillouin gain spectrum distribution as compared with the prior art.

The arithmetic processing unit 28 performs arithmetic processing according to the flowchart shown in FIG. 3 based on the above measurement. All of this arithmetic processing can be controlled by a computer.
Only the probe light pulse train from the measured optical line 23 is incident, and the return time t _d at the head of the probe light pulse train is recorded (step S11). From the return time t _d at the beginning and the probe light pulse width recorded as the reference probe light intensity, the probe light amplitude intensity included in the probe light pulse train under the condition that Brillouin gain is not received (no pump light is incident) The reference probe light intensity of the probe light is linked (step S12). Also, from the return time t _d at the beginning and the probe light pulse width recorded and recorded as the probe light amplitude intensity included in the probe light pulse train under the condition of receiving the Brillouin gain (entering the pump light), Which probe light is the reference probe light intensity is linked (step S13). Subsequently, the reference probe light intensity is compared with the signal probe light intensity to obtain bullian gain information (step S14). Finally, the horizontal axis indicates the frequency difference between the paired probe light and pump light, the Brillouin gain is plotted to obtain the Brillouin gain spectrum at the point (step S15), and the series of processes is terminated.

(Second Embodiment)
In the second embodiment, an optical line having a branch is a measured optical line.
FIG. 4 is a block diagram showing the configuration of the optical line characteristic analyzing apparatus according to the second embodiment. The apparatus shown in FIG. 4 (all other components excluding the optical line to be measured surrounded by a dotted line) is opposed to X pump lights having different frequencies, each paired with X probe lights having different frequencies. The characteristic distribution of the Brillouin gain received in the measured optical line by propagation can be obtained.

In the second embodiment shown in FIG. 4, the continuous light output from the laser light source 11 is branched into two systems by the branch element 12.
One of the lights branched by the branch element 12 is referred to as a first test light, and the other is referred to as a second test light. The first test light is shifted by the optical frequency shifter 13 by an initial set value f _B of the Brillouin frequency shift amount assumed in the optical line 23 to be measured. Specifically, the optical frequency shifter 13 may be any external modulator having a function of frequency of the modulation sidebands is changed according to the signal frequency from the sine wave generator (not shown), a LiNbO ₃ The used phase modulator (LN phase modulator) and SSB modulator can be used.

The first test light frequency-shifted by the optical frequency shifter 13 is branched into two systems by the branch element 2, one being probe light and the other being local light. The probe light is incident on the optical frequency modulation device 15 and becomes light whose frequency is modulated in the X stage controlled temporally.
Further, the probe light becomes a probe light pulse train arranged in time with different frequencies of the X wave by pulsed modulation by the optical pulse device 16.

On the other hand, the second test light branched by the branching element 12 is similarly frequency-modulated by the optical frequency modulation device 17 and further arranged temporally with different X-wave frequencies by pulsed modulation by the optical pulse device 18. The pump light pulse train thus obtained is obtained. Of the X probe lights and pump lights, the first wave probe light and pump light, the second wave probe light and pump light, ... the X wave probe light and pump light are f _2i -f _1i = f _It has a frequency difference of _B + iΔf and forms a probe-pump pair. Only the probe-pump pair satisfies the condition for causing Brillouin interaction, and any probe light and pump light have different frequencies.

  The conditions for the frequency difference between the probe light and the pump light and the conditions for the frequency interval between the probe light and the pump light included in the probe light pulse train and the pump light pulse train are the same as those in the first embodiment. In addition, the Brillouin gain spectrum (BGS) formed by the pump light pulse train described with reference to FIG. 2 in the first embodiment and the Brillouin gain obtained by the probe light included in the probe light pulse train are the same in the second embodiment. The frequency interval between the paired probe light and pump light differs between the pairs, so that each probe light component obtains a Brillouin gain of a different magnitude. Therefore, similarly to the first embodiment, the Brillouin gain spectrum can be obtained by plotting the Brillouin gain obtained by each probe light by taking the frequency difference between the paired probe light and pump light on the horizontal axis. .

As the optical pulse device 16 and the optical pulse device 18, specifically, an amplitude modulator or an acousto-optic modulator using LiNbO ₃ driven with an arbitrary waveform can be used. Here, optical pulsing means intensity-modulating the continuous probe light and pump light to temporally separate the m-th (m is a natural number) test light and the (m-1) -th test light. That is.
The order of the optical frequency modulation by the optical frequency modulators 15 and 17 and the optical pulse modulation by the optical pulse generators 16 and 18 are arbitrary.

  However, an analog connected to a modulation frequency controller 19 for controlling the modulation frequency of the optical frequency modulators 15 and 17, an optical pulse controller 20 for controlling the optical pulse generators 16 and 18, and a signal processor (PC) 28. The digital / digital (A / D) converter 27 operates in synchronization with a trigger signal of a pulse pattern generator (PPG) or a function generator (FG), and the optical frequency modulators 15 and 17 and the optical pulse converters 16 and 18 are operated. The temporal frequency arrangement of the pulsed test light that has passed through is ascertained by the signal processing device (PC) 28.

  A probe light pulse train using probe lights having different X frequencies (wavelengths) and a pump light pulse train using pump lights having different X frequencies (wavelengths) are combined by a multiplexer 21 and pass through an optical circulator 22 to be measured. The light is sequentially incident on the optical line 23. The measured optical line 23 includes an optical splitter 231, a lower branch optical fiber 232 i (i is 1 to N), and a test light reflection filter 233 i installed at the end of the lower branch optical fiber. The probe optical pulse train and the pump optical pulse train that are N-branched by the optical splitter 231 cause a Brillouin interaction only in the probe-pump pair during propagation in the optical line 23 to be measured. Receive Brillouin amplification only once. Each probe light included in the probe light pulse train subjected to the Brillouin amplification reaches the optical circulator 22 and is guided to the optical filter 24 by the optical circulator 22. Similarly, the pump optical pulse train is guided to the optical filter 24. The optical filter 24 transmits only the probe optical pulse train, and the probe optical pulse train transmitted here is an unmodulated local light branched by the branch element 14. Heterodyne detection is performed by the light and multiplexing element 25 and received by the optical receiver 26.

The output current from the optical receiver 26 is converted into a digital signal by the A / D converter 27 and then input to the signal processing device 28. The signal processing device 28 performs arithmetic processing described later on the input current value.
The sampling rate of the above optical line characteristic data is the same as in the first embodiment, and the signal-to-noise ratio is 1 or more in one trial (measurement with one set of probe light pulse train and pump light pulse train) Is determined only by the reciprocal of the round trip time of the test light with respect to the length of the optical line to be measured. When the signal-to-noise ratio is less than 1 in one trial, the value obtained by dividing the reciprocal of the round-trip time of the test light with respect to the measured optical line length by the average number of times until the signal-to-noise ratio becomes 1 or more This is the sampling rate of this method.

Next, the operation of the optical line characteristic analyzing apparatus of the second embodiment will be described. The optical frequency modulators 15 and 17, the optical pulse generators 16 and 18, the optical receiver 26, and the measured optical line 23 need to satisfy the following conditions.
(Condition 1) The frequency f _1i of the i-th probe light and the frequency f _2i of the i-th pump light included in the probe light pulse train and the pump light pulse train are the initial values of the Brillouin frequency shift assumed in the measured optical line 23 to f _B, the frequency difference _{f 2i -f 1i = f B +} iΔf probe - operating optical frequency modulation apparatus 15 and 17 to form a pump pair, and probe light and the pumping light in a pair of arbitrary The optical pulse generators 16 and 18 operate so as to be incident on the measured optical line 23 with a time difference.

(Condition 2) When a test light pulse train composed of a probe light pulse train and a pump light pulse train is sequentially incident on the optical path under measurement 23, the second group of test optical pulse trains are ejected from the optical path under measurement 23 after being discharged from the optical path under measurement 23. The test optical pulse trains are incident on the optical line to be measured 23, and all the test optical pulses included in the test optical pulse trains have frequencies different from each other by kΔf _B. However, k is set so that kΔf _B is sufficiently larger than the larger one of the change amount of the Brillouin frequency shift assumed in the optical line to be measured 23 or Δf _B.

(Condition 3) The signal processing device (PC) 28 for the received signal includes the frequency of the probe light pulse train and the pump light pulse train that are incident on the measured optical line 23 at an arbitrary time (temporal arrangement of frequencies), You know the time delay.
Here, Conditions 1 to 3 have the following meanings.
Condition 1 is a condition for the probe light to undergo Brillouin amplification by the pump light.
Condition 2 is a condition for acquiring Brillouin gain information only at an arbitrary position z.
Condition 3 is a condition necessary for separating and identifying the signals collectively received by the optical receiver 26 as signals having the characteristic information of each branch lower optical fiber 232i depending on the frequency.

An optical line characteristic analysis method using the second embodiment when these conditions are satisfied will be described.
FIG. 3 shows the relationship between the branched lower optical fibers F _{1 to} F _{N of the} measured optical line 23 and the time required for the probe light to reach the optical receiver. Here, a case where the branch optical fiber has three cores (three systems) is shown. Assume that the length of the three-branch optical fibers has the relationship of equation (1).

すると、プローブ光の光受信器２６に到達する時間は、式(2)の関係が成り立つ。

Then, the time for the probe light to reach the optical receiver 26 satisfies the relationship of the expression (2).

周波数変調時間tとすると、

If the frequency modulation time t is

のとき、各分岐下部光ファイバ２３２ｉから戻ったプローブ光は光受信器２６への到達時間に差が生じるため、どの心線から戻ったプローブ光であるかを時間的に切り分けることができる。つまり、周波数の異なるX個のプローブパルス列を順次入射した場合にも、光受信器に同一周波数のプローブ光が到達することはない。

At this time, since the probe light returned from each branch lower optical fiber 232i has a difference in arrival time to the optical receiver 26, it can be determined in time from which core line the probe light has returned. That is, even when X probe pulse trains having different frequencies are sequentially incident, probe light having the same frequency does not reach the optical receiver.

Subsequently, a method for separating gain information when X probe light pulse trains having different frequencies are used as test light and sequentially incident on the optical line to be measured 23 will be described first. .
The time width of a probe light pulse train composed of X probe lights having different pulse time widths (= frequency modulation time) τ is Xτ. In FIG. 4, a probe optical pulse train having a time width of 4τ composed of four types of probe lights having a pulse time width τ, frequencies ν ₁ , ν ₂ , ν ₃ , and ν ₄ is measured with an optical line to be measured 23 having a three-branch splitter 231. ₂ shows how the probe pulse train reaches the optical receiver 26 at times t _d1 , t _d2 , and t _d3 .
Here, the optical receiver arrival times t _d1 , t _d2 and t _d3 of the probe optical pulse train have been measured and are known amounts. In addition, the probe lights included in the probe light pulse train from the core wire # 1 are named # 1-1, # 1-2,. Similarly, probe light from core wire # 2 is # 2-1, # 2-2, ... # 2-4, probe light from core wire # 3 is # 3-1, # 3-2, ... # 3 Set to -4.
Each probe light pulse train is Fourier-transformed in each grid (Fourier window) divided in time for each frequency modulation time t according to the number of probe lights contained with reference to arrival times t _d1 , t _d2 , t _d3 Then, the light receiving power of the probe light having the frequency to be extracted is detected.

In FIG. 4, t _d1 −t _d2 > 4τ, and the optical receiver does not receive the probe light from the other cores simultaneously while receiving the probe pulse train from the core line # 1. On the other hand, t _d2 −t _d3 <4τ, and the optical receiver 26 simultaneously receives a part of the probe pulse train from the core wire # 2 and a part of the probe pulse train from the core wire # 3.

In this case, the reception method of # 2-3 is described. The frequency component ν ₁ of # 3-1 also exists in the grid to receive the frequency component ν ₃ of # 2-3. Since the arithmetic processing unit 28 receives a trigger signal that synchronizes the frequency modulators 15 and 17 and the pulse generators 16 and 18, a temporal arrangement of the frequencies included in the transmission probe optical pulse train (pulse width, modulation frequency) ). Therefore, the arithmetic processing unit 28 uses the optical receiver arrival times t _d1 , t _d2 , and t _d3 of the probe light pulse train as a reference, and the start time of each probe light grid and the frequency of the probe light to be analyzed contained in the grid. know.

(Start time of the nth probe light grid)
= (Optical receiver arrival time of probe optical pulse train) + (n-1) × (frequency modulation time τ)
For example, for the probe light pulse train from the core line # 1, the start time of the nth grid is represented by t _d1 + (n−1) τ.

Using this grid as a Fourier window, Fourier transform is performed, and the probe light power of the frequency component to be analyzed (here, ν ₃ ) from the power spectrum obtained by overlapping the frequency component ν _{3 of} # 2-3 and the frequency component ν _{1 of} # 3-1 Get. Thus, signal components can be separated even when probe light from other branched lower optical fibers is simultaneously received.

  The above processing can be performed by the arithmetic processing unit 28 grasping the frequency transmitted at an arbitrary time and its time arrangement, and measuring the arrival time of the probe light pulse train in advance. Paradoxically speaking, if the arithmetic processing unit 28 does not grasp the time sequence of the frequencies at the time of transmission, the frequency components to be extracted cannot be determined by the Fourier window setting and the Fourier transform. Processing becomes impossible.

  When the above frequency signal separation procedure is followed and conditions 1 to 3 are satisfied, according to this embodiment, individual loss distribution measurements in the N branched lower optical fibers 232i can be performed in parallel by using test optical pulse pairs having different frequencies. Compared with the prior art, it is possible to perform high-speed measurement that can shorten the measurement time without degrading the branching optical fiber identification resolution and the characteristic distribution resolution.

The arithmetic processing unit 28 performs arithmetic processing according to the flowchart shown in FIG. All of this arithmetic processing can be controlled by a computer.
The temporal frequency arrangement (frequency, frequency modulation time) of the probe light pulse train is recorded in advance in the arithmetic processing unit 28 (step S21). Thereby, the arithmetic processing unit 28 is in a state in which the probe light frequency at an arbitrary time is known. Only the probe light pulse train is incident, and the head return times t _d1 , t _d2 , t _d3 ,..., T _dN of the probe light pulse train are recorded for each branch core (step S22).

  Next, a Fourier window in which each probe light included in the probe light pulse train is extracted is determined from the head return time td and the frequency modulation time τ of the probe pulse train, and the start time of the nth Fourier window is set to td + (n−1 ) τ, and the frequency component to be extracted from the nth Fourier window is determined from the frequency array (step S23).

The frequency component to be extracted from the i-th Fourier window can be determined from the temporal frequency arrangement of the probe light pulse train recorded in the arithmetic processing device 28 in advance.
Next, the amplitude intensity of each frequency component of the probe light is recorded as the reference probe light intensity under the condition that the Brillouin gain is not received (no pump light is incident) (step S24), and the Brillouin gain is received (the pump light is incident). The amplitude intensity of each frequency component of the probe light is recorded as the signal probe light intensity (step S25). Brillouin gain information is obtained by comparing the thus recorded reference probe light intensity and signal probe light intensity (step S26).

Finally, taking the frequency difference between the probe light and the pump light on the horizontal axis, the Brillouin gain is plotted by plotting the Brillouin gain (step S27), and the series of processing is terminated.
As described above, according to the first and second embodiments, a plurality of probe-pump light pulse pairs paired at different frequency numbers are arranged in time with different frequencies of the included test light, respectively. An optical pulse train and a pump optical pulse train are used. These test optical pulse trains are incident on a measured optical line (single-core or branched optical line) with an arbitrary incident time difference, and the reflected light of the probe pulse train incident earlier and the pump incident later Stimulated Brillouin scattered light is generated by the opposite propagation of the optical pulse train. Then, the scattered light is received by the optical receiver 26, and the output current of the optical receiver 26 is measured in advance for the return time of the test light, whereby the stimulated Brillouin scattering from any of the first to N-th branched optical fibers. The Brillouin gain analysis is performed by performing Fourier transform in the Fourier window provided with the head of the pulse train as a reference to extract the amplitude intensity of the predetermined frequency component, and the frequency difference between the probe light and the pump light is measured laterally. By plotting the Brillouin gain for the axis, the Brillouin gain spectrum at the point corresponding to the incident time difference can be obtained, and the sampling rate can be determined by the length of the optical line to be measured. Furthermore, the Brillouin gain spectrum distribution for the entire core or for each branch optical fiber can be obtained by repeating trials by continuously changing the difference in the incident time between the probe light pulse train and the pump light pulse train. Distribution is required.

  Therefore, according to the above-described embodiment, it is possible to measure the Brillouin gain spectrum with an arbitrary frequency resolution in one measurement, and the optical fiber identification resolution and the characteristic distribution measurement resolution compared with the existing technology. This makes it possible to measure the loss, distortion, and temperature characteristics of the optical line individually for each branch line without deterioration.

The stimulated Brillouin scattering can measure distortion due to optical attenuation, temperature, bending, etc. in the optical medium. The optical line characteristics here are the optical attenuation with respect to the distance, the position of the reflection peak, and the bending obstacle. It is the amount of temperature change with respect to position, degree of bending, and distance.
The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some configurations may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different example embodiments may be combined as appropriate.

  DESCRIPTION OF SYMBOLS 11 ... Laser light source, 12 ... Branch element, 13 ... Optical frequency shifter, 14 ... Branch element, 15, 17 ... Optical frequency converter, 16, 18 ... Optical pulse device, 19 ... Modulation frequency controller, 20 ... PPG or FG, 21 ... Multiplexing element, 22 ... Optical circulator, 23 ... Optical fiber to be measured, 23a ... Optical fiber, 23b ... Light reflection filter, 230 ... Main optical fiber, 231 ... N-branch optical splitter, 2321 to 232N ... Lower branch Fibers, 2331-233N: light reflection filters, 24: optical filters, 25: multiplexing elements, 26: optical receivers, 27: A / D converters, 28: arithmetic processing units.

Claims (8)

An optical line characteristic analysis device for analyzing the characteristics of an optical line to be measured,
Test optical frequency modulation means for temporally controlling the first test light and the second test light having different wavelengths and modulating them to X (X is a natural number) frequencies;
Synchronizing with the test light modulation means, test light pulsing means for pulsing X probe lights and X pump lights having different frequencies with an arbitrary time difference;
Combining means for combining the pulsed probe light pulse train of X first test lights and the pump light pulse train of X second test lights;
A circulator for sequentially injecting the combined probe light pulse train and pump light pulse train into the measured optical line, and extracting test light returned from the measured optical line;
Filter means for extracting frequency components of X first test lights from the test light extracted by the circulator;
Photoelectric conversion means for receiving the first test light extracted by the filter means and converting it into current;
Analog-to-digital conversion means for converting the first test light converted into the current into a digital signal;
The digital signal is decoded, the control information at the time of generation and the light reception timing are used to identify which digital optical signal of the first test light is incident on the lower branch optical fiber, and X frequencies are identified from the identified digital signal. Frequency separation means for separating signals for each component;
Analyzing the Brillouin gain of each of the X frequency components, repeating the above measurement while changing the incident time difference between the probe light pulse train and the pump light pulse train, and from the measurement result repeatedly measured, the Brillouin gain characteristic distribution of the measured optical line And an arithmetic processing means for obtaining
The test light frequency modulation means is a means for frequency-modulating the first test light and the second test light at predetermined time intervals, and the Brillouin interaction is performed only between the specific first test light and the second test light. Performing frequency modulation on the first test light and the second test light so as to generate
The arithmetic processing means changes a frequency interval between the first test light and the second test light every predetermined time interval, acquires a Brillouin gain spectrum at a measurement point from the frequency interval and the Brillouin scattering intensity, and transmits the probe light. The Brillouin gain spectrum distribution information is formed by repeatedly performing the above measurement while changing the difference in incident time between the pulse train and the pump light pulse train, and the optical line characteristics in the longitudinal direction of the measured optical line are analyzed from the distribution information. Characteristic analysis device.   The measured optical line is an optical line formed by branching one end of a backbone optical fiber into a plurality of systems by an optical branching device, and optically coupling one end of the branching optical fiber to each branching end portion of the optical branching device. The apparatus for analyzing characteristics of an optical line according to claim 1.   The optical line characteristics include at least the amount of optical attenuation with respect to the distance of the optical line to be measured, the position of the bending failure, the degree of bending, the position of the disconnection failure, the temperature change amount with respect to the distance, and the optical fiber strain change amount in the longitudinal direction of the optical line. The optical line characteristic analysis apparatus according to claim 1, wherein the optical line characteristic analysis apparatus is any one of the above.   2. The optical line characteristic analyzing apparatus according to claim 1, wherein the frequency modulation means is realized by a modulated electric signal of a single sideband modulator or a low noise phase modulator and an arbitrary waveform signal generator. An optical line characteristic analysis method for analyzing characteristics of an optical line to be measured,
The first test light and the second test light having different wavelengths are temporally controlled to be modulated to X frequencies (X is a natural number),
In synchronization with the modulation, X probe lights and X pump lights having different frequencies are pulsed with an arbitrary time difference from each other,
Combining the pulsed probe light pulse train by the X first test lights and the pump light pulse train by the X second test lights,
The combined probe light pulse train and pump light pulse train are sequentially incident on the measured optical line, and the test light returned from the measured optical line is extracted,
Extracting frequency components of X first test lights from the extracted test light;
Receiving the extracted first test light and converting it into a current;
Converting the first test light converted into the current into a digital signal;
Decode the digital signal, specify whether it is a digital signal of the first test light incident on the optical path to be measured from the control information at the time of generation and the light reception timing, and every X frequency components from the specified digital signal To separate the signal,
Analyzing the Brillouin gain of each of the X frequency components, repeating the above measurement while changing the incident time difference between the probe light pulse train and the pump light pulse train, and from the measurement result repeatedly measured, the Brillouin gain characteristic distribution of the measured optical line Execute the calculation process to obtain
When frequency-modulating the first test light and the second test light at the predetermined time intervals, the first test light and the first test light and the second test light are caused to cause a Brillouin interaction only between the specific first test light and the second test light. Apply frequency modulation to the second test light,
In the calculation process, the frequency interval between the first test light and the second test light is changed every predetermined time interval, a Brillouin gain spectrum at a measurement point is obtained from the frequency interval and the Brillouin scattering intensity, and the probe light pulse train The Brillouin gain spectrum distribution information is formed by repeating the above measurement while changing the incident time difference of the pump light pulse train, and the optical line characteristics in the longitudinal direction of the measured optical line are analyzed from the distribution information analysis method.   The measured optical line is an optical line formed by branching one end of a backbone optical fiber into a plurality of systems by an optical branching device, and optically coupling one end of the branching optical fiber to each branching end portion of the optical branching device. The method for analyzing characteristics of an optical line according to claim 5.   The optical line characteristics include at least the amount of optical attenuation with respect to the distance of the optical line to be measured, the position of the bending failure, the degree of bending, the position of the disconnection failure, the temperature change amount with respect to the distance, and the optical fiber strain change amount in the longitudinal direction of the optical line. 6. The optical line characteristic analysis method according to claim 5, wherein the optical line characteristic analysis method is any one of the above.   6. The optical line characteristic analysis method according to claim 5, wherein the frequency modulation means is realized by a modulated electric signal of a single sideband modulator or a low noise phase modulator and an arbitrary waveform signal generator.

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