JP2015078859A - Branched optical fiber characteristic analyzer and analysis method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow individual measurement of branch optical fiber characteristics with only an extra-facility in PON (Passive Optical Network) type optical branch lines, and to allow the measurement even if a branch optical fiber length difference is shorter than 1 m.SOLUTION: A branch optical fiber characteristic analyzer pulses and multiplexes first and second test light different in a sign and a wavelength and makes it incident on a measured optical fiber, extracts return light by reflection of branch light fibers inside the measured optical fiber, extracts the first test light from the return light, detects the extracted first test light nu local light to acquire an optical beat signal, and receives the optical beat signal to measure stimulated Brillouin backscattering light generated in the first test light. In the measurement, when a minimum difference between respective lengths of N-core branch optical fibers from a branch point to the termination of the measured optical fiber is longer than branch optical fiber identification resolution ΔL, the branch optical fiber characteristic analyzer measures the stimulated Brillouin backscattering light while changing the signs of the first and second test light and the local light to analyze characteristics of the branch optical fibers.

Description

  The present invention relates to a branched optical fiber characteristic analysis apparatus and an analysis method for individually measuring and analyzing the characteristics of each branched optical fiber branched by an optical splitter in, for example, a PON (Passive Optical Network) type optical line.

  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. The optical pulse line monitoring device utilizes the fact that backscattered light having the same wavelength as the light is generated and propagates in the reverse direction as the light propagates in the optical line. That is, when an optical pulse is incident on the optical line as test light, backscattered light continues to be generated until the optical pulse reaches the breaking point, and the end face of the optical line on which the return light having the same wavelength as the test light is incident. It is emitted from. By measuring the duration of the backscattered light, it is possible to specify the break position of the optical line. A typical monitoring device based on this principle is an OTDR (Optical Time Domain Reflectometer).

  However, in a conventional optical pulse line monitoring apparatus, for a PON (Passive Optical Network) type optical branch line, a branch optical fiber located on the user apparatus side from the optical splitter, or an optical device (for example, a reflection type filter), splitter It is difficult to individually identify the status of optical devices connected to the optical line, such as optical fiber components and fiber connection components. That is, because the trunk optical fiber laid from the telecommunications carrier equipment building is branched into a plurality of optical fibers by the optical splitter, the test light is also branched into the plurality of optical fibers by the optical splitter. The optical fiber (hereinafter referred to as “branch lower optical fiber”) is uniformly distributed. Then, when the return light from each optical fiber core wire returns to the incident end, it overlaps with the optical splitter. For this reason, it becomes impossible to identify which branch optical fiber has a failure from the OTDR waveform observed at the incident end. As described above, the existing optical pulse line monitoring device is basically effective only for one optical line, and cannot be applied to an optical branch line as it is.

Therefore, a technique for enabling application of an optical pulse line monitoring device to an optical branch line has been proposed. (See Non-Patent Document 1, Patent Document 1, and Non-Patent Document 2)
In Non-Patent Document 1, an optical filter that reflects test light is installed in front of a user device as a termination filter, and the intensity of reflected light from each user is measured by a high-resolution OTDR device. According to this measurement, it has been reported that the accuracy of 2 m can be obtained as the distance resolution in the branched optical fiber downstream from the optical splitter. However, with this technology, it is only possible to identify the fault core and to identify the fault location such as whether the user device or the optical line is faulty, and at which position of the lower branch optical fiber the fault occurs. I can't identify what it is.

  In Patent Document 1, a diffraction grating type wavelength multiplexer / demultiplexer using an arrayed waveguide that utilizes multi-beam interference of light is used as an optical splitter, and a test optical line is selected by switching the wavelength of the test light with a wavelength variable light source. Proposals have been made. According to this proposed method, the wavelength of the tunable light source is swept, the wavelength of the reflected light is detected by the light reflection processing unit, and the wavelength of the test light is set on the basis of the wavelength, thereby obtaining the wavelength of the test light. Correspondingly, individual monitoring of each optical line can be realized. However, an optical branching device having a wavelength routing function, represented by a diffraction grating type wavelength multiplexer / demultiplexer using an arrayed waveguide, is generally expensive and used for an access optical system that accommodates many subscribers. Is difficult in terms of cost. Furthermore, such optical components are highly temperature dependent and need to be added with a temperature adjustment function, which is not preferable because the cost required for constructing the system increases.

  According to Non-Patent Document 2, two test light pulses, a pump light pulse and a probe light pulse, are incident and a Brillouin gain at the collision position of both test lights is analyzed to obtain individual loss distributions of the lower core of the splitter. Proposals have been made. However, in the Brillouin gain analysis using the pulse method, the branch fiber identification resolution is longer than 1 m. This is because, in the pulse method, the sensitivity is significantly deteriorated when the pulse width is narrower than the phonon lifetime (˜1 m) of Brillouin scattering. The method described in Patent Document 2 cannot be measured unless there is a difference in the length of the branched optical fiber that is longer than the pulse width of the test light. Therefore, it is not possible to measure when the neighbors such as apartment houses are close to each other and the difference in length of the branched fibers is shorter than 1 m.

JP-A-7-87017

Y. Enomoto et al., "Over 31.5dB dynamic range optical fiber line testing system with optical fiber fault isolation function 32dB-branched PON", OFC2003 Technical Digest, paper ThAA3 (2003), pp. 608-610 H. takahashi et al., "Individual fault location in PON using pulsed pump-probe Brillouin analysis", Electronics letters, vol.47, pp.1384-1385 (2011). Yasuaki Sugawara “Bragg Wavelength Distribution Measurement System for Long Fiber Bragg Grating by Synthesis of Lightwave Coherence Function” http://repository.dl.itc.u-tokyo.ac.jp/dspace/bitstream/2261/29062/1 /37066461.pdf

  Therefore, in the PON type optical branching line, when monitoring the optical device device such as the optical fiber splitter and the branching lower optical fiber on the user equipment side from the optical splitter, the optical device and the optical line configuration are not newly changed (existing). Branching optical fiber characteristics can be measured individually by using existing off-the-shelf equipment (branching optical fiber of the same characteristics and the same wavelength light reflection filter) without changing the cost. There is a need for a technique that can measure even when the optical fiber length difference is shorter than 1 m.

  The present invention has been made paying attention to the above circumstances, and in the PON type optical branch line, the optical fiber characteristics of the existing equipment in the site and the optical line configuration are not changed, and the branch optical fiber characteristics are individually determined only by the outside equipment. It is an object of the present invention to provide a branching optical fiber characteristic analysis apparatus and an analysis method thereof that can measure even when the difference in length of the branching optical fiber is shorter than 1 m.

The branched optical fiber characteristic analyzer according to the present invention has the following configuration.
(1) One end of the backbone optical fiber is branched into N (N is a natural number of 2 or more) system by an optical splitter, and one end of the branched optical fiber is optically coupled to each branch end of the optical splitter, and each measured object A branched optical fiber characteristic analyzing apparatus for analyzing branched optical fiber characteristics of an optical fiber, wherein the light source module encodes and outputs continuous light from a laser into waveforms of a first test light, a second test light, and a local light, and Optical frequency changing means for changing the optical frequency of the first test light and the local light; branching means for branching the first test light and the local light from the output light of the optical frequency changing means; First pulsed means for pulsing the changed first test light, second optical pulsed means for pulsing the second test light, and the encoded and pulsed first test, respectively. And a multiplexing element that multiplexes the second test light and the other end of each of the plurality of branch optical fibers of the optical fiber to be measured, and reflects the wavelength of the first and second test lights, A plurality of light reflection filters that transmit light of a wavelength and the test light combined by the multiplexing element are incident on the backbone optical fiber of the optical fiber to be measured and returned from the incident end of the backbone optical fiber An optical circulator for extracting light, an optical delay means for matching the incident timing of the first test light and the second test light to the optical fiber to be measured, and a local branching of the first test light by the branching means Detection means for detecting an optical beat signal of the first test light and the local light by detecting with light; an optical receiver for receiving the optical beat signal and converting it into an electrical signal; and Generated in test light An arithmetic processing unit for measuring the guided Brillouin backscattered light and analyzing the characteristics of the optical fiber under test. The arithmetic processing unit is configured to branch N cores from a branch point by the optical splitter to the light reflection filter. For the optical fiber, when the minimum difference between the respective lengths is longer than the branching optical fiber identification resolution ΔL, the guiding is performed while changing the signs of the first and second test lights and the local light generated by the light source module. By measuring Brillouin backscattered light, the characteristics of the branched optical fiber are analyzed.

  (2) In (1), in the optical frequency changing means, the frequency difference between the first test light and the second test light corresponds to a Brillouin frequency shift amount in which stimulated Brillouin backscattered light is generated in the measured optical fiber. It is set as the aspect changed so that it may.

  (3) In (1), the light source module generates a laser beam of the continuous light based on an injection current, modulates the continuous light into an arbitrary waveform by the injection current, and an injection current to the light source Is continuously changed according to the modulation waveform of each of the first test light, the second test light, and the local light, and the first and second optical pulsing means perform time division to encode the first The second test light and the local light are generated.

  (4) In (1), the arithmetic processing unit measures stimulated Brillouin scattering by the first and second test lights, measures Brillouin scattered light distribution with respect to each distance of the plurality of branched optical fibers, and measures the measurement An individual loss distribution in the plurality of branched optical fibers is analyzed from each result.

  (5) In (1), the arithmetic processing unit designates the stimulated Brillouin scattering position from the end of the branched optical fiber in the optical fiber under test by designating the signs of the first and second test lights. By specifying the signs of the first test light and the local light, it is possible to identify and obtain an electrical signal corresponding to the first test light reflected from which branch optical fiber of the optical fiber under test. After analyzing the stimulated Brillouin scattered light from the measured electrical signal, an analysis process for outputting the analysis result is executed until the first test light from the longest branched optical fiber among the N-system branched optical fibers arrives After waiting, the signs of the first and second test lights and the local light are changed and the analysis process is repeated to obtain the loss distribution of each of the branched optical fibers.

Moreover, the optical line characteristic analysis method according to the present invention has the following configuration.
(6) One end of the backbone optical fiber is branched into N (N is a natural number of 2 or more) system by an optical splitter, and one end of the branched optical fiber is optically coupled to each of the branch end portions of the optical splitter. A branched optical fiber characteristic analysis method for analyzing a branched optical fiber characteristic of an optical fiber, wherein continuous light from a laser is encoded into waveforms of a first test light, a second test light, and a local light, and the first test light and the The optical frequency of the local light is changed by a predetermined frequency, the first test light and the local light are branched from the optical frequency change output light, the first test light subjected to the change of the optical frequency is pulsed, Two test lights are pulsed, and the encoded and pulsed first test light and second test light are combined, and the first end of each of the plurality of branched optical fibers of the optical fiber to be measured is connected to the first end. as well as A plurality of light reflection filters that reflect the wavelength of the second test light and transmit light of other wavelengths, and the combined test light is incident on the backbone optical fiber of the optical fiber to be measured; The return light emitted from the incident end of the optical fiber is extracted, the incident timings of the first test light and the second test light to the measured optical fiber are matched, and the first test light is split into the branched local light An optical beat signal of the first test light and the local light is obtained by light detection, the optical beat signal is received and converted into an electrical signal, and an induction generated from the electrical signal to the first test light The Brillouin backscattered light is measured to analyze the characteristics of the optical fiber under test, and the minimum difference between the lengths of the N-core branched optical fibers from the branch point by the optical splitter to the light reflection filter is measured. The characteristics of the branched optical fiber are analyzed by measuring the stimulated Brillouin backscattered light while changing the signs of the first and second test lights and the local light when the resolution is longer than the branched optical fiber identification resolution ΔL. Let it be an aspect.

  (7) In (6), the frequency difference between the first and second test lights is made to correspond to a Brillouin frequency shift amount in which stimulated Brillouin backscattered light is generated in the measured optical fiber.

  As described above, according to the present invention, in order to obtain the characteristic distribution of the individual branched optical fibers on the lower side of the optical splitter, the length of each branched optical fiber is different, and the test light wavelength is set at the end of each branched optical fiber. Because it is only necessary to have a light reflection filter that reflects light, it can be measured accurately at low cost without replacing any current PON type optical line, even if the required branch optical fiber length is shorter than 1 m A measurable branch optical fiber characteristic analyzer and an analysis method thereof can be provided.

It is a block diagram which shows the structure of the branch optical fiber characteristic analyzer based on one Embodiment of this invention. The wave form diagram which shows the arbitrary waveforms which each encode a 1st test light, a 2nd test light, and a local light in the optical encoder of the analyzer shown in FIG. It is a characteristic view which shows the example of the distance-loss distribution analyzed with the analyzer shown in FIG. The wave form diagram which shows the change of the correlation peak of the Brillouin gain which arises between the 1st test light of the analyzer shown in FIG. 1, and a 2nd test light.

Embodiments of the present invention will be described with reference to the 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.
FIG. 1 is a diagram showing a configuration of a branched optical fiber characteristic analyzing apparatus according to an embodiment of the present invention. The analysis apparatus shown in FIG. 1 can determine the characteristic distribution of the Brillouin gain received by the first test light in the measured fiber.

  The continuous light from the laser output from the light source 11 is branched by the branch element 12. One of the branched lights is a first test light (probe light) and the other is a second test light (pump light). Here, the light source 11 outputs local light following the first test light and the second test light. The light source 11 appropriately encodes the output light based on the waveform signal from the optical encoder 13. Specifically, the optical encoder 13 is configured to modulate the laser injection current of the light source 11 with an arbitrary waveform, and encodes an arbitrary waveform for encoding the first test light, the second test light, and the local light, respectively. As shown in FIG. 2, it outputs continuously in time. At this time, the first test light, the second test light, and the local light are sequentially and sequentially output from the light source 11.

The optical frequency of the first test light is changed by the optical frequency changer 14 by f _B. The optical frequency changer 14 may be an external modulator having a function of changing the frequency of the modulation sideband in accordance with the signal frequency from the sine wave generator 15 to be driven, and LiNbO ₃ is used. A phase modulator, amplitude modulator or SSB modulator may be used.

  The output light of the optical frequency changer 14 is branched into two systems by the branching element 16, and one of the branched lights is pulsed by extracting the first test light portion shown in FIG. . The second test light is delayed for a predetermined time by the optical delay device 18, then the second test light portion shown in FIG. 2 is extracted and pulsed by the optical pulse generator 19, and amplified by the optical amplifier 20. After that, the multiplexing element 21 combines the pulsed first test light.

  That is, the output light of the light source 11 is pulsed only to the encoded first test light by the optical pulse generator 17 and is pulsed only to the encoded second test light by the pulse generator 19. At this time, the optical delay device 18 adjusts the incident time difference between the first test light and the second test light, combines the first test light encoded by the multiplexing element 21 and the encoded second test light, and circulators. The light passes through 22 and enters the optical fiber 23 to be measured. Here, the optical delay unit 18 only needs to make the time difference between the first test light and the second test light incident on the optical fiber under test zero, and the length of the optical delay unit 18 may be adjusted by the optical fiber itself.

  The optical fiber 23 to be measured is constituted by a backbone optical fiber 230, an optical splitter 231, a branched optical fiber 2321 to 232N (N is a natural number of 2 or more), and light reflection filters 2331 to 233N installed at the end of the branched optical fiber. . The first test light and the second test light that have been N-branched by the optical splitter 231 interact in each of the branched optical fibers 2321 to 232N, and the first test light undergoes Brillouin amplification. The first test light and the second test light that have undergone this Brillouin amplification reach the optical circulator 22, and only the first test light reaches the optical heterodyne receiver 25 by the optical filter 24. After being combined with the local light branched from, the light is 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 arithmetic processing unit 28. The arithmetic processing unit 28 performs arithmetic processing of a branched fiber information separation method, a Brillouin gain analysis method, and a distribution measurement method, which will be described below, on the input current value, for example, as shown in FIGS. Find the loss distribution for the distance as shown.

Next, the operation of the above-described branching optical fiber characteristic analyzer of this embodiment will be described.
First, the optical encoder 13, the optical frequency changer 14, the measured optical fiber 23, and the optical receiver 26 must satisfy the following conditions.
(Condition 1) In the optical encoder 13, the code φ _n (t) for encoding the first test light and the code Ψ _n (t) for encoding the second test light always have a frequency at a desired time difference t. The difference f ₁ (f ₁ is an arbitrary number including 0) is constant, and the frequency difference is not constant in other time differences.
(Condition 2) The frequency shift by the optical frequency changer 14 is equal to the difference frequency between the Brillouin frequency shift f _B and the intersymbol frequency difference f ₁ described in Condition 1.
(Condition 3) The code φ _n (t) of the optical encoding means for encoding the first test light and the code θ _n (t) of the optical encoder 13 for encoding the local light are correlated at a desired time difference t. Is 1, and the correlation is 0 at other time differences.
(Condition 4) The minimum fiber length difference between the branched optical fibers 2321 to 232N is longer than the branched optical fiber identification resolution ΔL.
(Condition 5) band of the optical receiver 26, it is band available receive frequency difference f ₁ (Condition 1).

Here, the conditions 1 to 5 have the following meanings.
Condition 1 is a condition for acquiring Brillouin gain information only at a desired position z.
When the code characteristic of the optical encoder 13 is as described above, the frequency difference between the first test light and the second test light is always shifted by the Brillouin frequency shift by matching with the condition 2 at the desired position z in the measured optical fiber 23. So that it undergoes Brillouin amplification over the code length. At other positions, the frequency difference between the first test light and the second test light fluctuates, so that the Brillouin amplification is not always performed over the code length. Therefore, the Brillouin gain at the desired position z can be acquired by integrating over the code length of the first test light.

Condition 2 is a condition necessary for the first test light to undergo Brillouin amplification by the second test light. Conditions 3 and 4 are conditions necessary for acquiring individual loss information of the branched optical fibers 2321 to 232N.
When the code characteristics of the optical encoder 13 are as described above, the first test light reflected and returned by the light reflection filters 2331 to 233N at the end of the branch optical fiber is modulated with the code θ _n (t) and the local light and code By taking the correlation over the length, it is possible to obtain the intensity of the first test light returned from any of the branched optical fibers 2321 to 232N.
Condition 5 requires that the band of the optical receiver 26 and the band of the A / D converter 27 be wider than the frequency difference f _{1 of} Condition 1 in order to accurately measure the optical code.

A method for analyzing characteristics of a branched optical fiber using the present invention when the above conditions 1 to 5 are satisfied will be described.
Two test lights having different wavelengths (first test light and second test light) are used. The first test light is probe light and has an optical frequency f ₀ -f _B. The second test light is pump light and has an optical frequency f ₀ . Here, f ₀ is the optical frequency of the pump light, and f _B is the optical frequency shift amount due to Brillouin backscattering.
The encoded first test light and the encoded second test light are incident on the optical fiber 23 to be measured.
The first test light and the second test light are N-branched by the optical splitter 231.

(i) Brillouin gain analysis method
When the frequency of the first test light (probe light) and the second test light (pump light) is different by f _B , when the first test light and the second test light propagate in opposite directions, Brillouin scattering occurs. The test light is amplified by the equation (1).

Here, α _B is the Brillouin gain, g _B is the Brillouin scattering coefficient, z _c is the distance from the incident end of the branched optical fiber to the position where the first test light and the second test light interact, and I _pump (z) is the branched light The intensity of the second test light (pump light) at a position away from the fiber incident end by a distance z, t _c is the code length, and v is the speed of light in the optical fiber.

If the loss coefficient of the core wire #i of the i (N = i) -th branch optical fiber 232i is α _i , and the total loss when reciprocating through the core wire #i of the branch optical fiber 232i is 1−D _i , The intensity I _probe (2L _i ) of the first test light that is reflected by the light reflection filter 233i and then enters the incident end of the branch optical fiber 232i is expressed by Expression (2).

From Expression (2), the intensity I _probe (2L _i ) of the first test light at the incident end of the branch fiber is a function of only I _pump (z).
Here, I _pump (z) is expressed by Equation (3).

Therefore, Expression (2) is expressed as Expression (4) when Expression (3) is used.

By analyzing the Brillouin gain using the above equation (4), the loss up to the location where the interaction occurred can be obtained. The return light I _probe (2L _i ) from each branch optical fiber 232 _i is subjected to the same loss by the optical fiber from the optical splitter 231 to the optical receiver 26. Therefore, line loss can be measured by analyzing the Brillouin gain.

(ii) Distribution measurement method
Assuming that the encoding of the first test light is φ _n (t) and the encoding of the second test light is ψ _n (t), φ _n (t) and ψ _n (t) are frequencies only at a certain time difference t. The difference is constant at f _B , and the frequency difference is not constant at other time differences.
The length from the incident end of the optical fiber under test 23 to the end of the branch lower optical fiber #a (integer of 1 ≦ a ≦ N) and L _a. The encoded first test light is reflected by a light reflection filter installed at the end of the branched lower optical fiber #a. The first test light and the second test light that have returned after reflection propagate in opposite directions and interact in the measured fiber 23. Here, the sign of the first test light is changed from phi ₁ to [phi] _n, changing the sign of the second test light to ψ ₁ ~ψ _n.

For example, consider the case of frequency modulation as follows.
Δf is the modulation amplitude of encoding, f _mn is the nth modulation frequency, and Θ is the initial phase. At this time, when the first test light and the second test light encoded by φ _n and ψ _n are incident on the optical fiber 23 to be measured, the position where the frequency difference is constant as shown in FIG. Appears periodically. If this interval is d _mn ,

It becomes. At this position z (correlation peak position), as shown in FIGS. 4A to 4D, the first test light and the second test light have the same frequency difference as the Brillouin frequency shift. Received Brillouin amplification. Here, from the equation (6), the interval d _mn is changed by changing the modulation frequency f _mn , and the correlation peak position can be changed. Alternatively, the correlation peak position can also be changed by changing the initial phase Θ of ψ _n in equation (5). Therefore, it is possible to obtain Brillouin gain distribution information by repeating measurement while changing the modulation frequency f _mn or the initial phase Θ.

(iii) Branch fiber separation method
The first test light sign φ _n (t) and the local light sign θ _n (t) is the correlation only when it is convenient time difference t ₁ is 1, in code correlation becomes 0 in the time difference t ₂ else is there.

However, the operator · represents the inner product of the vectors.
If the time for the first test light to be reflected by the light reflection filter at the end of the branched optical fiber #a and reach the optical receiver 26 is t _da , it is expressed by equation (8).

Here, L _a is the distance from the incident end to the light reflection filter at the end of the branch lower fiber #a.
The time t _{db for} the first test light returned from the other branch optical fiber #b (an integer satisfying 1 ≦ b ≦ N) to reach the optical receiver 26 is expressed by Expression (9).

Therefore, the time difference of the first test light returning from #a and #b to the optical receiver 26 is expressed by Expression (10).

When L _a ≠ L _b, the time for the first test light reflected and returned from the different branch optical fibers to reach the optical receiver 26 is different. Here, the encoded first test light returned from the different branch optical fibers is multiplexed by the optical splitter 231. When the first test light returned from the different branch optical fibers is multiplexed by the optical splitter 231, the signs are out of phase. The first test light returned to the optical receiver 26 side is given by the following equation.

Therefore, the code θ _N (t) of the local light is generated in accordance with the first test light returned from the branch #N.

At this time, _a Brillouin gain at the position z of the branch #a is obtained by correlating θ _a (t) with the received signal. Further, by obtaining a correlation between θ _b (t) and the received signal, the Brillouin gain at the position z of the branch #b can be obtained. That is, by obtaining the correlation between the first test light I _d that has returned to the light receiving side and the sign θ _N (t), it is possible to separate and acquire information on the branched lower optical fiber.

  Here, according to Non-Patent Document 3 (Equation (3.28) in Section 3.3), the resolution for separating and identifying the branched optical fiber is determined by the code characteristics of the encoded first test light. The encoded first test light is decoded by the correlation between the codes. The resolution (branch optical fiber identification resolution) ΔL for identifying the branched optical fiber when encoded by equation (5) is

It becomes. For this reason, the branching optical fiber identification resolution is determined not by the pulse width but by the code characteristics, so that the branching optical fiber identification resolution can be made shorter than the phonon lifetime. From equation (13), by modulating Δf at 50 MHz or more, the branch optical fiber identification resolution can be made shorter than 1 m.

  That is, the first test light obtained on the optical receiving side can be separated into information for each branch by decoding with the initial phase changed. In addition, when sine wave modulation is used, the branching fiber identification resolution can be made shorter than 1 m by modulating Δf at 50 MHz or more. By setting Δf to 5 GHz, branching optical fiber identification of about 1 cm can be performed. Resolution can be realized.

  As described above, according to the present embodiment, when the measurement results (i) to (iii) and the conditions (1) to (5) are satisfied, the individual branch lower optical fibers of the PON type optical branch line are individually Loss distribution measurement can be performed only with the configuration of existing off-site equipment (optical splitter, branch optical fiber, and light reflection filter installed at the end of the branch optical fiber), and the branch optical fiber identification resolution should be shorter than 1 m. Can do.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. 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 ... Light source, 12 ... Branch element, 13 ... Optical encoder, 14 ... Optical frequency changer, 15 ... Sine wave generator, 16 ... Branch element, 17 ... Optical pulse generator, 18 ... Optical delay device, 19 ... Optical pulse generator, 20 ... optical amplifier, 21 ... multiplexing element, 23 ... optical fiber to be measured, 230 ... backbone optical fiber, 231 ... N branch optical splitter, 2321 to 232N ... branch optical fiber, 2331 to 233N ... light reflection Filter, 24 ... Optical filter, 25 ... Optical heterodyne receiver, 26 ... Optical receiver, 27 ... A / D converter, 28 ... Arithmetic processing device.

Claims (7)

One end of the backbone optical fiber is branched into N (N is a natural number of 2 or more) system by an optical splitter, one end of the branched optical fiber is optically coupled to each branch end of the optical splitter, and each optical fiber to be measured is A branched optical fiber characteristic analyzer for analyzing branched optical fiber characteristics,
A light source module that encodes and outputs continuous light from a laser into waveforms of a first test light, a second test light, and a local light;
Optical frequency changing means for changing the optical frequency of the first test light and the local light;
Branching means for branching the first test light and the local light from the output light of the optical frequency changing means;
First pulsing means for pulsing the first test light subjected to the change of the optical frequency;
Second optical pulse forming means for pulsing the second test light;
A multiplexing element for multiplexing the encoded and pulsed first test light and second test light, and
A plurality of light reflection filters that are disposed at the other ends of the plurality of branch optical fibers of the optical fiber to be measured, reflect the wavelengths of the first and second test lights, and transmit light of other wavelengths;
An optical circulator that makes the test light multiplexed by the multiplexing element incident on the trunk optical fiber of the optical fiber to be measured, and extracts return light emitted from the incident end of the trunk optical fiber;
Optical delay means for matching the incident timing of the first test light and the second test light to the optical fiber to be measured;
Detecting means for detecting an optical beat signal between the first test light and the local light by detecting the first test light with the local light branched by the branching means;
An optical receiver that receives the optical beat signal and converts it into an electrical signal;
An arithmetic processing unit that measures the stimulated Brillouin backscattered light generated in the first test light from the electrical signal and analyzes the characteristics of the optical fiber under test, and
When the minimum difference between the lengths of the N-core branched optical fibers from the branch point by the optical splitter to the light reflection filter is longer than the branched optical fiber identification resolution ΔL, the arithmetic processing unit The branched optical fiber is characterized in that the characteristics of the branched optical fiber are analyzed by measuring the stimulated Brillouin backscattered light while changing the sign of the first and second test lights and the local light generated by Characteristic analysis device.   The optical frequency changing means changes the frequency difference between the first test light and the second test light so as to correspond to a Brillouin frequency shift amount in which stimulated Brillouin backscattered light is generated in the measured optical fiber. The branching optical fiber characteristic analysis apparatus according to claim 1.   The light source module generates a laser of the continuous light based on an injection current, a light source that modulates the continuous light into an arbitrary waveform by the injection current, an injection current to the light source as the first test light, a second The encoded first and second test light and local light are continuously changed in accordance with the modulation waveforms of the test light and the local light, and time-divided by the first and second optical pulsing means. The branching optical fiber characteristic analyzing apparatus according to claim 1, wherein the branching optical fiber characteristic analyzing apparatus is generated. The arithmetic processing unit includes:
Measuring stimulated Brillouin scattering by the first and second test lights;
Measuring the Brillouin scattered light distribution with respect to the distance of each of the plurality of branched optical fibers;
2. The branched optical fiber characteristic analyzer according to claim 1, wherein individual loss distributions in the plurality of branched optical fibers are analyzed from each of the measurement results. The arithmetic processing unit includes:
By designating the signs of the first and second test lights, the stimulated Brillouin scattering position from the end of the branched optical fiber in the optical fiber under test is designated,
By specifying the signs of the first test light and the local light, it is possible to identify which branch optical fiber of the optical fiber under test is the electric signal corresponding to the first test light and to obtain the obtained electric signal. After analyzing the stimulated Brillouin scattered light from the signal, execute the analysis process to output the analysis result,
After waiting until the first test light from the longest branch optical fiber of the N systems of branched optical fibers arrives, the signs of the first and second test lights and local light are changed and the analysis process is performed. 2. The branched optical fiber characteristic analyzing apparatus according to claim 1, wherein the loss distribution of each of the branched optical fibers is repeatedly acquired. One end of the backbone optical fiber is branched into N (N is a natural number of 2 or more) system by an optical splitter, one end of the branched optical fiber is optically coupled to each branch end of the optical splitter, and each optical fiber to be measured is A branching optical fiber characteristic analysis method for analyzing branching optical fiber characteristics,
Encode the continuous light from the laser into the waveform of the first test light, second test light, local light,
Changing the optical frequencies of the first test light and the local light by a predetermined frequency;
Branching the first test light and the local light from the optical frequency change output light,
Pulse the first test light that has undergone the change in the optical frequency,
Pulsing the second test light;
Respectively combining the encoded and pulsed first and second test lights;
A plurality of light reflection filters that reflect the wavelengths of the first and second test lights and transmit light of other wavelengths are disposed at the other ends of the plurality of branched optical fibers of the optical fiber to be measured,
The combined test light is incident on the trunk optical fiber of the optical fiber to be measured, and the return light emitted from the incident end of the trunk optical fiber is extracted.
Match the incident timing of the first test light and the second test light to the measured optical fiber,
Extracting the first test light from the return light;
Detecting the first test light extracted from the return light with the branched local light to obtain an optical beat signal between the first test light and the local light;
Receives the optical beat signal and converts it into an electrical signal,
Analyzing the characteristics of the optical fiber under test by measuring the stimulated Brillouin backscattered light generated in the first test light from the electrical signal,
When the minimum difference between the lengths of the N-core branched optical fibers from the branch point by the optical splitter to the light reflection filter is longer than the branched optical fiber identification resolution ΔL, the first and second test lights A branched optical fiber characteristic analyzing method, wherein the characteristic of the branched optical fiber is analyzed by measuring the stimulated Brillouin backscattered light while changing the sign of local light.   7. The branched optical fiber characteristic analysis method according to claim 6, wherein the frequency difference between the first and second test lights corresponds to a Brillouin frequency shift amount in which stimulated Brillouin backscattered light is generated in the optical fiber to be measured. .