JP2009063377A - Optical line test system and optical line test method - Google Patents

Abstract

An optical line test system and an optical line test method capable of individually measuring the state of a branched fiber downstream of an optical splitter are provided at low cost.
In an optical branch line system including an optical splitter for branching an optical line into, for example, four systems, an FBG filter is connected to each branch fiber. The FBG filter 20 reflects light having a specific wavelength and sets the reflection wavelength to λ1 to λ4. An OTDR 18 is connected to the optical line 13 and an OTDR waveform is obtained individually by test optical pulses having wavelengths λ1 to λ4. In this OTDR waveform, the waveform indicating the backscattered light of the test light reflected by the FBG filter 20 specifies the wavelength indicating the specific shape. For example, if the OTDR waveform does not have a waveform indicating the backscattered light of the test light reflected by the FBG filter 20, it is concluded that the branch fiber 15 connected to the FBG filter 20 that reflects the corresponding wavelength is broken. .
[Selection] Figure 2

Description

  The present invention relates to a technique for testing characteristics of an optical line such as an optical fiber.

  In recent years, it is common to construct an optical subscriber network between a user's house and a station building with an optical branch line (PDS) system. The line configuration of the optical branch line system is a form in which one optical fiber is branched into a plurality of lines at a station building, and each of the plurality of optical fibers is further branched into a plurality of lines outdoors. As a result, a plurality of external devices can be integrated into a single in-house device, the equipment cost of the transmission device can be reduced, and the optical line equipment can also be shared. That is, it is possible to distribute signal light to many user devices with a small number of optical lines, and thus the cost of the entire communication facility can be greatly reduced.

  In the optical branch line system, a double star topology is formed by using a plurality of optical branch portions. By configuring the optical branching unit (optical splitter) closer to the user side with only passive optical components, the reliability of the system can be improved. This type of optical branch line system is sometimes referred to as a PON (Passive Optical Network).

  By the way, in an optical communication system using an optical line such as an optical fiber, an optical pulse line monitoring device is used in order to detect the breakage of the optical line and to determine the breakage 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 a light pulse (test light) enters the optical line, backscattered light continues to be generated until the light pulse reaches the breaking point, and return light having the same wavelength as the test light is emitted from the input end face. The breaking point of the optical line can be determined by measuring the duration of the backscattered light. A typical measurement apparatus based on this principle is an OTDR (Optical Time Domain Reflectometer).

  However, when testing and monitoring a PDS type optical branch line system with an optical pulse line monitoring device, it is difficult to individually identify the branch fiber on the user device side or the state of the device from the optical splitter. That is, since the trunk fiber extending from the office building is branched into a plurality of branch fibers by the optical splitter, the test light is also uniformly distributed from the optical splitter to each core wire. The return light from each core wire is overlapped by the optical splitter when returning to the incident end, and therefore, it is impossible to identify which branch fiber is broken from the OTDR waveform observed at the incident end. As described above, in the existing technology, the optical pulse line monitoring device is basically effective only for one optical line, and cannot be applied to an optical branch line system as it is.

  Non-Patent Document 1 and Patent Document 1 propose techniques for solving the above-described problem. The proposal of Non-Patent Document 1 is to install an optical filter that reflects test light highly as a termination filter in front of the user device, and measure the intensity of reflected light from each user with a high-resolution OTDR device. In this document, it is reported that this method can obtain an accuracy of 2 m as a distance resolution in the branch fiber downstream from the optical splitter. However, with this accuracy, the fault location cannot be specified. In the technique of this document, it is only possible to specify the fault line number and to determine whether the device or the optical line is faulty.

  In Patent Literature 1, an arrayed waveguide grating type wavelength multiplexer / demultiplexer that uses multi-beam interference of light is used as an optical splitter, and the wavelength of the test light is switched by a wavelength tunable light source to select the optical line to be tested. Proposals have been made. By sweeping the wavelength of the tunable light source, detecting the wavelength of the reflected light with the light reflection processing unit, and setting the wavelength of the test light based on that wavelength, each optical line is individually associated with the wavelength of the test light. Monitoring can be realized.

However, an optical branching device having a wavelength routing function represented by an arrayed waveguide grating type wavelength multiplexer / demultiplexer is generally expensive and difficult to use in an access optical system accommodating many subscribers. . Furthermore, such an optical component has a large temperature dependency, and it is necessary to add a temperature adjustment function. For this reason, it is inevitable that the cost of the entire system will jump.
Y. Enomoto et al., "Over 31.5 dB dynamic range optical fiber line testing system with optical fiber fault isolation function 32-branched PON", OFC2003 Technical Digest, paper ThAA3 (2003), pp. 608-610. JP-A-7-87017

As described above, in the PDS type optical line, individual orientation is difficult to monitor the branch fiber and the device on the user device side from the optical splitter, and some technical development is awaited.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical line test system and an optical line test method capable of individually measuring the state of the branch fiber downstream of the optical splitter at a low cost.

  In order to achieve the above object, according to one aspect of the present invention, an optical line used in an optical branch line system including an optical splitter for branching an optical fiber into first to n-th branch fibers connectable to user terminals. In the test system, an optical line test in which test lights having different wavelengths λ1, λ2,..., Λn are individually incident on the optical fiber, and an intensity distribution waveform with respect to the distance of the backscattered light of the test light is obtained for each wavelength. A device and a first to n-th branch fiber, each of which individually reflects light having a wavelength of λm (m = 1, 2,..., N) and transmits light of other wavelengths. 1 to nth reflection type optical filters, and a measurement unit that acquires an intensity distribution waveform for each wavelength from the optical line test apparatus, and the measurement unit determines whether there is a fault in the m-th branch fiber. An optical line test system for determining based on a state of a waveform obtained by measuring backscattered light of test light reflected by the reflective optical filter in an intensity distribution waveform using test light having a wavelength λm Is provided.

  By taking such means, if the wavelength of the test light is λ1, the test light is reflected by the reflection type optical filter that reflects only the wavelength λ1. At this time, the return light of the reflected light is generated and observed in the intensity distribution waveform. On the other hand, if the branch fiber connected to the reflection filter of λ1 is broken, the test light of wavelength λ1 is not reflected by the reflection optical filter, and therefore no generation of return light of reflected light is observed in the intensity distribution waveform. . That is, it can be concluded that the branch fiber is broken at a wavelength at which the return light of the reflected light does not appear in the intensity distribution waveform. The position can be accurately obtained by observing Fresnel reflection due to breakage. By such means, it becomes possible to individually monitor the branch fibers.

  According to the present invention, it is possible to provide an optical line test system and an optical line test method capable of individually measuring the state of the branch fiber downstream of the optical splitter at a low cost.

  FIG. 1 is a diagram showing an example of an optical branch line (PDS) system to which the present invention is applied. In FIG. 1, an optical signal transmission unit 11 of an optical signal transmission station 10 is connected to an optical branching unit 12. N (1 ≦ N) optical lines 13 are extended in a star shape from the optical branching section 12. An optical splitter 14 is connected to each optical line 13, and M branch fibers 15 are further extended in a star shape downstream thereof. A user terminal 16 is connected to the end of each branch fiber 15. Thus, the communication light incident on the optical line 13 from the optical signal transmission unit 11 via the optical branching unit 12 further reaches a plurality of user terminals 16 via the optical splitter 14 and the branching fiber 15.

  In the above configuration, a system in which the optical splitter 14 is composed of only passive optical components is particularly referred to as a passive double star PON. In FIG. 1, only one system downstream from the optical splitter 14 is displayed. If the optical branching unit 12 is an N branch and the optical splitter 14 is an M branch, signal light can be distributed to N × M user terminals 16 with a small number of optical lines.

  In the system configuration of FIG. 1, since the return light from each branch fiber 15 overlaps with the optical splitter 14, it is difficult to evaluate the location of the failure from the OTDR waveform observed at the optical signal transmission station 10. Hereinafter, two embodiments will be described as an example for a technique that can easily solve this difficulty.

[First Embodiment]
FIG. 2 is a system diagram showing a first embodiment of an optical line test system according to the present invention. The number of the branch fibers 15 downstream of the splitter 14 is 4 (M = 4), and the same reference numerals are given to the portions common in FIG. In the optical signal transmission station 10, an optical line monitoring and testing apparatus (OTDR) 18 is connected to one of the optical lines 13 from the optical branching unit 12 via an optical coupler 19. According to the OTDR 18, it is possible to obtain an intensity distribution waveform with respect to the distance (propagation direction) of the backscattered light of the test light incident on the optical fiber line. The OTDR 18 has a function capable of switching the wavelength of the test light. In this embodiment, test light having wavelengths of λ1, λ2,. That is, the OTDR 18 can output test light having a wavelength of λm (m = 1, 2,..., N) using m as an index.

  The processing apparatus 100 is connected to the OTDR 18 via a LAN (Local Area Network) cable or the like. The processing apparatus 100 is a personal computer or the like equipped with dedicated processing software, and acquires measurement data of the OTDR 18 via a LAN. Based on the acquired data, the processing apparatus 100 determines the state of the branch fiber 15 on the downstream side of the splitter 14.

  As shown in FIG. 3, the installation sections of the branch fibers 15 on the downstream side of the optical splitter 14 are distinguished as sections A, B, C, and D, respectively. In each section, an FBG (Fiber Bragg Grating) filter 20 is installed immediately before the user terminal 16 in each branch fiber 14.

  FIG. 4 is a diagram for explaining the characteristics of the FBG filter 20. Each of the FBG filters 20 includes an FBG 21 that reflects a specific wavelength, whereby the FBG filter 20 reflects light of a specific wavelength and transmits light of other wavelengths. In this embodiment, each FBG filter 20 is individually provided with a characteristic of reflecting the test light wavelengths λ1, λ2,. That is, one FBG filter 20 reflects only the test light wavelength λ1, the other FBG filter 20 reflects only the test light wavelength λ2, and so on, so that the characteristics of each FBG filter 20 are selected. The dotted line (reference numeral 22) in the figure is the backscattered light of the light reflected by the FBG filter 20, and its reflection characteristics are important in this embodiment. FIG. 4 shows a state in which the wavelength λn is reflected.

  FIG. 5 is a diagram showing an example of optical characteristics of the FBG 21 shown in FIG. The FBG 21 has the same center wavelength as the wavelength output from the OTDR device 18, and the reflection wavelength width at −3 dB is 1.0 nm. In this embodiment, four wavelengths λ1 to λ4 are used with N = 4, that is, n = 4. For example, 1630, 1640, 1650, and 1660 (nm) are set as λ1 to λ4, respectively. Next, the operation of the above configuration will be described.

  FIG. 6 is a diagram showing an example of an OTDR measurement waveform when measurement by the OTDR 18 is performed in the system of FIG. The following processing is mainly performed by the processing apparatus 100. FIG. 6 shows a state in which the branch fiber 15 has no obstacle such as breakage or bending. The length of each section is set to 500 m for section A, 800 m for section B, 1400 m for section C, and 1900 m for section D.

  FIG. 6 shows the result when the wavelength of the test light from the OTDR 18 is λ1. Assume that an FBG filter having a reflection wavelength λ1 is provided in the section A, which is denoted by reference numeral 20 ′ and is referred to as a termination filter 20 ′. If the branch fiber 15 is not broken, the waveforms of the sections A and A 'and the sections a and a' centering on the termination filter 20 'appear in the OTDR waveform. The waveforms in the sections a and A are waveforms in which the backscattered light of the optical pulse (test light) transmitted from the OTDR and the reflection at the termination filter 20 ′ are measured.

  The measurement waveforms in the sections A ′ and a ′ are measured when the Rayleigh backscattered light of the test light once reflected by the termination filter 20 ′ is reflected again by the termination filter 20 ′ and reaches the OTDR 18. Since this re-reflected light reaches the OTDR 18 with a shift of the length of the section A on the time axis, the fiber is folded back at the end of the branch fiber 15 (the connection end of the FBG filter 20) as shown in FIG. A waveform appears. That is, the lengths of the sections A and A ′ are the same on the measurement waveform, and the lengths of the sections a and a ′ are also the same. Since the length of the section A is 500 m, when the position of the optical splitter 14 is used as a reference of the OTDR waveform, the received light intensity peaks are shown around 500 m and 1000 m in the test light λ1.

  Note that the test light incident on the other sections B to D that are not assigned to λ1 is also slightly reflected by the FBG filter 20, but from the filter characteristics shown in FIG. 5, the intensity is reflected from the termination filter 20 ′. Small enough compared to the strength level. Therefore, it can be ignored in the OTDR waveform. If the user-side termination state of the FBG filter 20 is an open end, it is possible to further reduce the influence of reflection that occurs after transmission through another FBG by taking measures such as installing a non-reflection termination at the end. .

  By the way, the OTDR waveform in the section A is obtained by multiplexing the backscattered light from the sections A, B, C, and D of each branch fiber 15, and it is difficult to evaluate individual core wires. On the other hand, the section A ′ of the OTDR waveform shows the backscattered light of the test light generated only by the termination filter 20 ′ of the section A that reflects the wavelength λ 1 with high reflectivity. Based on this, the branch fibers can be individually identified, and the line characteristics in the section A can be correctly evaluated.

  That is, in this embodiment, each branch fiber is specified using the folded waveform of backscattered light. Even when test lights having other wavelengths λ2 to λ4 are used, OTDR waveforms showing peaks of the light reception intensity are observed in the vicinity of 800 m and 1600 m, 1400 m and 2800 m, 1900 m and 3800 m, respectively. By observing the folded waveform in the OTDR measurement result in this way, it is possible to evaluate line characteristics such as the section loss of the branch fiber assigned with each wavelength. This will be described in detail below.

  FIG. 7 is a diagram illustrating an example of an OTDR measurement waveform when a fracture failure occurs. Suppose that in the section A, a break occurs at a position 300 m downstream of the splitter 14 (point P). When the break occurs, Fresnel reflection and Fresnel loss occur at the break point. Since this Fresnel reflection and loss appear in all the test lights λ1 to λ4, when comparing the OTDR waveforms for the respective test light wavelengths, the received light peaks overlap. Therefore, the information obtained by observing the Fresnel reflection alone cannot be separated from the reflection information generated elsewhere in the branch line 15, and it is specified that the line break occurs at the point P in the section A. Can not. In other words, it cannot be specified in which branch fiber the break occurs.

  Therefore, in this embodiment, not only the Fresnel reflection information but also the reflection characteristics of the backscattered light 22 of the light reflected by the FBG filter 20 are evaluated. That is, since light is blocked by the break, test light of any wavelength does not reach the FBG filter 20 only in the section where the break occurs. Therefore, the folding around the FBG filter 20 does not appear in the OTDR waveform.

In FIG. 7, since the light is blocked at the point P, the test light pulse of λ1 does not reach the termination filter 20 ′. Therefore, backscattered light once reflected by the termination filter 20 ′ is not generated, and the OTDR waveform has the shape shown in FIG. As can be seen from comparison with FIG. 6, the waveform of FIG. 7 does not show a waveform showing central symmetry as if the fiber was folded at the end of the branch fiber.
On the other hand, in the measurement using the test light of wavelengths other than λ1, that is, λ2-λ4, each test light is reflected by the FBG filter 20 for each wavelength, and the reflected light generates backscattered light. Therefore, an OTDR waveform having central symmetry as shown in FIG. 6 is always observed.

  From the above, it can be seen that the presence or absence of breakage can be determined by switching the test light wavelength and measuring the OTDR waveform for each wavelength and associating whether or not central symmetry is observed in the waveform. That is, whether or not the breakage has occurred is determined by whether or not the Rayleigh backscattered light of the test light pulse reflected by the FBG filter 20 is reflected again by the termination filter 20 and measured by OTDR. That is, it can be concluded that a break has occurred in the section corresponding to the wavelength at which the OTDR waveform having no central symmetry is obtained.

  Furthermore, the Fresnel loss generated at the break is about -14 dB. This value is larger than the light intensity level of the light reflected by the FBG filter 20 having a return loss of -35 dB at other wavelengths shown in FIG. Therefore, by comparing the received light levels of the OTDR waveform, it is possible to specify that a break has occurred at the position of the break point P, that is, at a position 300 m from the splitter 14. Next, observation of a bending failure will be described as another example of the failure apart from the fracture.

  FIG. 8 is a diagram illustrating an example of an OTDR measurement waveform when a bending failure occurs. It is assumed that a line failure due to bending occurs at a position P in the section A in FIG. The loss due to this bending is 3 dB. Since all wavelengths are multiplexed in the section A of the OTDR waveform, even if the loss due to bending is 3 dB, the fluctuation of the backscattered light level changes only about 0.58 dB. Therefore, when there is a lot of noise, it is difficult to determine that a failure has occurred at this position. Further, if the number of branch fibers under the splitter 14 is unknown, an accurate loss value at the point P cannot be calculated from the OTDR waveform in the section A.

  However, as in the case of the breakage, it is possible to distinguish the branch fiber where the bending failure has occurred and specify the position of the failure based on the state of the folded section A ′. That is, at the position P ′ of the turn-back section A ′, an OTDR waveform is obtained only by the backscattered light of the test light pulse reflected by the terminal FBG filter 20. As shown in FIG. 8, it can be considered that a loss has occurred at a wavelength where the degree of loss in the section A ′ is significantly large. At wavelengths λ2 to λ4 where there is no loss due to bending, an OTDR waveform having such a step does not appear, and therefore it is possible to identify a branched fiber in which a bending failure has occurred in association with a wavelength exhibiting a specific waveform shape. Become.

  Depending on the place where bending occurs, it is also possible to observe the value of bending loss. For example, the position of the point P is 300 m from the splitter 14. Then, since the section A is 500 m on the OTDR waveform, the distance from the splitter 14 to the point P ′ is 700 m. Since the position of the P ′ point is closer to any of the length of the section B of 800 m, the length of the section C of 1400 m, and the length of the section D of 1900 m, the back scattered light in the sections B, C, and D is superimposed. Will be. In such a case, it is difficult to read the accurate value of the loss from the peak value of the OTDR waveform.

  In contrast, for example, it is assumed that a bending failure occurs in any position of the section D. On the other hand, the folded region on the waveform by OTDR performed at the wavelength λ4 is farther from any of the other sections A to C. Therefore, backscattered light from the sections A, B, and C is not superimposed, and an accurate loss value can be read from the peak value of the OTDR waveform. As described above, even when it is difficult to determine a fault in the evaluation of the section A on the OTDR waveform, it is possible to accurately measure the loss fluctuation in the turn-back section A ′, and each time the loss fluctuation is evaluated, the fault position P is determined. It becomes possible to judge.

  Using this fact, the following procedure can be considered at the actual work site. That is, when laying the sections A to D downstream of the splitter 14, the construction is performed in order from the section with the shortest length of the branch fiber. In other words, the shortest section A is laid first, the test by OTDR is performed on this section to confirm that there is no bending loss, and then the next short section B is laid. In this way, the system can be laid after always knowing accurately the value of the loss due to bending.

  As described above, in this embodiment, the FBG filter 20 is connected to each branch fiber 15 in the optical branch line (PDS) system including the optical splitter 14 that branches the optical line 13 into a plurality of (for example, four systems). The FBG filter 20 reflects light having a specific wavelength, and the reflection wavelengths are λ1 to λ4. Further, an OTDR 18 is connected to the optical line 13, and an OTDR waveform is obtained individually by test light pulses having wavelengths λ1 to λ4. In this OTDR waveform, the waveform indicating the backscattered light of the test light reflected by the FBG filter 20 specifies the wavelength indicating the specific shape.

  For example, if the OTDR waveform does not have a waveform indicating the backscattered light of the test light reflected by the FBG filter 20, it is concluded that the branch fiber 15 connected to the FBG filter 20 that reflects the corresponding wavelength is broken. I did it. Thus, by analyzing the center symmetry of the OTDR waveform with respect to the test light wavelength and the light reception level, it becomes possible to identify the line fault point downstream of the splitter 14. Therefore, according to the first embodiment, it is possible to individually identify the failure location of the branch fiber downstream of the optical splitter in the optical line under test by the optical pulse test only from one end of the optical fiber. Moreover, the above configuration does not require an expensive optical device such as an arrayed waveguide grating type wavelength multiplexer / demultiplexer. Therefore, it is possible to provide an optical line test method and an optical line test system that can individually measure the state of the branch fiber downstream of the optical splitter at a low cost.

[Second Embodiment]
In the first embodiment, all the test light pulses incident from the OTDR 18 reach the user terminal 16 except for the wavelengths reflected by the FBG filter 20. Therefore, since unnecessary light for communication is mixed in the user terminal 16, the communication service must be stopped during the optical line monitoring test. In order to solve this problem, in the second embodiment, a broadband optical filter that transmits light in a band used for information transmission and has a cutoff characteristic over the entire test light wavelength range is provided between at least the FBG filter 20 and the user terminal 16. Connect between.

  More preferably, a broadband optical filter having the same characteristics is also provided between the optical branching unit 12 and the optical coupler 19 in FIG. 2 or between the optical branching unit 12 and the optical signal transmission unit 11. That is, on the transmission side, a broadband optical filter is connected to the light propagation path from the optical coupler 19 to the optical signal transmitter 11. The form of the connection is in series with the propagation path.

  For example, a dielectric multilayer film can be used as the broadband optical filter. The dielectric multilayer film has a multilayer film structure in which several tens to several hundreds of thin films having different refractive indexes are laminated on quartz glass or the like. By inserting this into the optical fiber, optical waveguide, or optical connector portion at a specific angle, only a specific wavelength is reflected on the clad, and the transmission / cutoff wavelength band and the reflection amount of the cutoff wavelength can be adjusted.

  FIG. 9 is a diagram showing optical characteristics of the dielectric multilayer filter used in the second embodiment. The band settings of the test light wavelengths λ1 to λ4 are the same as those in FIG. 5, and the wavelength of communication light used for information transmission is 1.49 μm. As shown in FIG. 9, the transmission loss in the band of 1.26 μm to 1.58 μm is 1.0 dB or less, and the transmission loss is gradually increased from this to the band of 1.58 to 1.61 μm, and the wavelength is 1.625 μm. The above test light has a blocking amount of about 40 dB. The return loss of the test light can be set to 40 dB or more by adjusting the insertion angle of the dielectric multilayer filter.

  If the broadband optical filter has such characteristics, the input of unnecessary test light other than the communication wavelength to the user terminal 16 can be blocked, and information transmission by communication light is normally performed. The OTDR test can be performed correctly. That is, it becomes possible to perform in-service the identification of the branch fiber 15 as shown in the first embodiment, the identification of the broken portion, and the determination of the bending loss.

  As described above, in the second embodiment, a broadband optical filter is added between the user terminal 16 and the FBG filter 20 to block all test light, thereby preventing unnecessary light components from entering the user terminal 16. I try to prevent it. Therefore, it is possible to individually identify the failure point of the branch fiber downstream of the optical splitter 14 by the optical pulse test only from one end of the optical fiber without affecting the communication.

  The present invention is not limited to the above embodiment. For example, the number of branches in the optical splitter 14 is not limited to four. In addition, various modifications can be made without departing from the gist of the present specification, such as a broadband filter format and a termination filter format.

The figure which shows an example of the optical branch line (PDS) system to which this invention is applied. 1 is a system diagram showing a first embodiment of an optical line testing system according to the present invention. The figure which shows the sections A, B, C, D of the downstream of the optical splitter 14. FIG. The figure for demonstrating the characteristic of the FBG filter. The figure which shows an example of the optical characteristic of FBG21 of FIG. The figure which shows an example of the OTDR measurement waveform at the time of implementing the measurement by OTDR18 in the system of FIG. The figure which shows an example of the OTDR measurement waveform at the time of producing a fracture | rupture disorder | damage | failure. The figure which shows an example of the OTDR measurement waveform at the time of producing a bending disorder. The figure which shows the optical characteristic of the dielectric multilayer filter used for the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical signal transmission station, 11 ... Optical signal transmission part, 12 ... Optical branch part, 13 ... Optical line, 14 ... Optical splitter, 15 ... Branch fiber, 16 ... User terminal, 18 ... Optical line monitoring and testing apparatus (OTDR) , 19 ... optical coupler, 20 ... FBG filter, 21 ... FBG, 22 ... backscattered light of light reflected by the FBG filter 20, 100 ... processing device

Claims (10)

In an optical line test system used for an optical branch line system including an optical splitter that branches optical fibers into first to n-th branch fibers connectable to user terminals, respectively.
An optical line test apparatus that individually enters test light having different wavelengths λ1, λ2,..., Λn into the optical fiber, and obtains an intensity distribution waveform with respect to the distance of the backscattered light of the test light for each wavelength;
The first to nth optical fibers are individually connected to the first to nth branch fibers and individually reflect light having wavelengths λm (m = 1, 2,..., N) and transmit light having other wavelengths. n reflective optical filters;
A measurement unit that obtains an intensity distribution waveform for each wavelength from the optical line testing device,
This measuring part is
Based on the state of the waveform obtained by measuring the backscattered light of the test light reflected by the reflective optical filter in the intensity distribution waveform using the test light having the wavelength λm, the presence or absence of a failure in the m-th branch fiber. An optical line test system characterized by determining. The measurement unit breaks into the m-th branch fiber when the waveform indicating the backscattered light of the test light reflected by the reflective optical filter does not appear in the intensity distribution waveform using the test light having the wavelength λm. The optical line test system according to claim 1, wherein the optical line test system is determined to have occurred. The measurement unit measures the position of the break in the m-th branch fiber determined to have caused the break based on a peak position corresponding to Fresnel reflection of an intensity distribution waveform using the test light having the wavelength λm. The optical line test system according to claim 2. The measurement unit bends to the m-th branch fiber when a loss occurs in a section indicating the backscattered light of the test light reflected by the reflective optical filter in the intensity distribution waveform using the test light having the wavelength λm. 2. The optical line test system according to claim 1, wherein it is determined that a failure has occurred. In the case where the optical branch line system includes an optical signal transmitter that enters communication light used for information transmission into the optical fiber,
A first optical filter connected to a propagation path for the test light from an incident end to the optical fiber to the optical signal transmitter;
A second optical filter connected between the reflective optical filter and the user terminal;
The said 1st and 2nd optical filter permeate | transmits the said communication light, and has a cutoff characteristic over the whole range of the wavelength of (lambda) m (m = 1, 2, ..., n). Optical line test system. In an optical line test method used for an optical branch line system including an optical splitter for branching an optical fiber into first to n-th branch fibers each connectable to a user terminal,
First to nth reflective optical filters that individually reflect light of different wavelengths λ1, λ2,..., Λn and transmit light of other wavelengths are individually connected to the first to nth branch fibers. And
A test light having a wavelength of λm (m = 1, 2,..., n) is individually incident on the optical fiber, and an intensity distribution waveform with respect to the distance of the backscattered light of the test light is measured for each wavelength.
Based on the state of the waveform obtained by measuring the backscattered light of the test light reflected by the reflective optical filter in the intensity distribution waveform using the test light having the wavelength λm, the presence or absence of a failure in the m-th branch fiber. An optical line test method characterized by determining. When the waveform indicating the backscattered light of the test light reflected by the reflective optical filter does not appear in the intensity distribution waveform using the test light having the wavelength λm, it is determined that the mth branch fiber is broken. The optical line testing method according to claim 6. The position of the break in the m-th branch fiber determined to have caused the break is measured based on a peak position corresponding to Fresnel reflection of an intensity distribution waveform using the test light having the wavelength λm. Item 8. The optical line testing method according to Item 7. It is determined that a bending failure has occurred in the m-th branch fiber when a loss occurs in a section indicating the backscattered light of the test light reflected by the reflective optical filter in the intensity distribution waveform using the test light having the wavelength λm. The optical line testing method according to claim 6, wherein: In the case where the optical branch line system includes an optical signal transmitter that enters communication light used for information transmission into the optical fiber,
A first optical filter that transmits the communication light and has a cutoff characteristic over the entire wavelength range of λm (m = 1, 2,..., N) is transmitted from the incident end of the test light to the optical fiber. Connected to the propagation path leading to
A second optical filter that transmits the communication light and has a cutoff characteristic over the entire wavelength range of λm (m = 1, 2,..., N) is connected between the reflective optical filter and the user terminal. The optical line testing method according to claim 6.

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