JP2001021445A - Multiple branching optical path test apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a line and a distance of fault points. SOLUTION: Each of optical fibers of a multiple branching optical path is made different in length (S1). A test light is inputted to the multiple branching optical path in an initial state without a fault, an OTDR (optical time region back scattering measurement method) waveform is measured from a time series change of the returning light, and event information composed of a distance and a level difference of Fresnel reflection points is obtained (S2). Fresh event information is obtained from the OTDR waveform for every constant time afterwards (S3) until a fault takes place (S5). The obtained two event informations are compared with each other and, the optical fiber in the initial state corresponding to the reflection points where distances do not agree is set as a fault line. Then, when the number of reflection points is smaller than in the initial state, a difference of the level differences of both event informations is obtained for each set of reflection points. A distance of the set of reflection points closest to the level difference of the reflection points present only in the initial state is set as a distance of the fault. On the other hand, when the number of the reflection points is equal, a distance of the reflection points not present in the initial state is set as the distance of the fault (S4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-branch optical line test apparatus for measuring a position of a fault point in addition to an optical line having a fault point when a fault occurs in the multi-branch optical line.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing a conventional multi-branch optical line test apparatus and the configuration of a test object thereof. The apparatus is provided in a 1.31 / 1.55 wavelength multiplex transmission system. This is to perform a fault isolation test of the branch optical line. In FIG. 1, a 1.6 μm band test light (light pulse) emitted from an OTDR (optical time domain backscattering measurement method) measuring device 1 is incident on an optical line 3 via an optical coupler 2. The light propagates through the path 3 and enters the star coupler 5 from the connector 4. The star coupler 5 splits the incident test light in eight directions and distributes it to optical fibers 7-1 to 7-8 via connectors 6-1 to 6-8, respectively. The test light propagating through these optical fibers is incident on filters 9-1 to 9-8 installed before ONUs (Optical Network Units) 8-1 to 8-8, respectively.

Here, filters 9-1 to 9-8 are O
It has a pass band characteristic of passing only optical signals output to the NUs 8-1 to 8-8 (that is, communication light transmitted from the OSU (transmission device) 10) and reflecting test light. Therefore,
The propagating test light is reflected by the filters 9-1 to 9-8, respectively, and returns to the optical fibers 7-1 to 7-8 toward the connectors 6-1 to 6-8, respectively. After being multiplexed, the light passes through the connector 4 and the optical line 3 and enters the optical coupler 2, and returns from the optical coupler 2 to the OTDR measuring device 1 as response light. Therefore, the OTDR measuring instrument 1 analyzes the response light returned from the multi-branch optical line and observes the waveform (OTDR).
Various processes such as display of waveforms are performed.

[0004] FIG. 10 is a graph showing an example of the waveform of the response light observed by the OTDR measuring instrument 1. The waveform shown in the figure shows the time-series change of the response light. In the figure, the horizontal axis represents the value obtained by multiplying the propagation time of the response light by the transmission speed of the light (that is, the value that is incident on the multi-branch optical line). The distance of the optical fiber through which the test light propagated), and the vertical axis represents the relative intensity of the response light observed. As described above, the response light is obtained by multiplexing the Fresnel reflected lights reflected by the filters 9-1 to 9-8.
Reference numerals 9-8 are provided at positions different from each other in distance from the OTDR measuring instrument 1. Therefore, the reflected lights from the filters 9-1 to 9-8 are separately observed on the OTDR waveform without overlapping on the time axis.

In the case of FIG. 10, for example, the leftmost waveforms W _R shown in corresponds to light reflected by the star coupler 5, thereafter, sequentially the optical fiber 7-1 toward the right side in FIG.
Waveforms W _{1 to} W _{8 of} reflected light reflected by filters 9-1 to 9-8 via 7-8 are shown. FIG. 11 corresponds to FIG.
5A is an enlarged view of the vicinity of the waveforms W _{6 to} W _{8 in} the observation waveforms shown in FIG.
FIG. 7B shows a case where a failure is simulated by giving a bending loss of 3 dB to the optical fiber 7-7 when there is no failure in any of 7-8. As can be seen by comparing these two observation waveforms, if there is a fault in the optical fiber, the intensity of the reflected light will decrease.Therefore, a fault occurring in the optical line will be detected by analyzing the intensity of the reflected light included in the response light. it can. Such a technique is disclosed in, for example, "" 1.6 μm Band Fault Isolation Test Technique for Branched Optical Line ", IEICE Autumn Meeting 1994, Paper B-846".

[0006]

The multi-branch optical line test apparatus described above can detect a line of a failed optical line, but cannot determine the distance of a fault point on the line. Further, it is necessary to install each filter so that the distances from the star coupler 5 to the filters 9-1 to 9-8 are different from each other, but if it is considered that these filters are installed in the immediate vicinity of the subscriber, However, arranging the filters so as to satisfy the above-described conditions is not practical in view of the cost required.

The present invention has been made in view of the above points, and an object of the present invention is to provide a multi-branch optical line test apparatus capable of measuring not only a line having a failure point but also the distance of the failure point on the line. It is in.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention according to claim 1 provides an optical pulse to a multi-branch optical line which branches light into a plurality of optical lines having different lengths. In the multi-branch optical line test apparatus for obtaining a measurement waveform that is a time-series change of response light that is incident and returns from the multi-branch optical line, a reflection point and a connection point existing on each of the optical lines are determined from the measurement waveform. An event detecting means for detecting and calculating a distance and a loss for each of the reflection point and the connection point; and instructing the event detecting means to perform an initial state and a fault search time when there is no obstacle in the multi-branch optical line. Control means for determining the distance and the loss, and comparing the distance and the loss determined for each of the initial state and the fault detection time to determine the optical path and the position where the fault point exists. It is characterized by comprising a failure information obtaining means.

According to a second aspect of the present invention, in the first aspect of the present invention, the fault information calculating means exists in the distance obtained at the time of the fault search among the distances obtained for the initial state. Determine the optical path corresponding to the reflection point or the connection point having a distance not to the optical path where the fault point is present, if the total number of the reflection points and the connection points detected at the time of the fault search is less than the initial state, The difference between the loss at each of the reflection point and the connection point where the distances match at the initial state and at the time of the fault detection is determined, and the difference corresponds to the difference closest to the level difference of the reflection point or the connection point detected only in the initial state. Determined the distance of the reflection point or the connection point to the distance of the obstacle point, if the total number of the detected reflection points and connection points is the same at the initial state and at the time of the obstacle detection, at the time of the obstacle search Among the distances calculated for, it is characterized by determining the distance that is not in the distances calculated for the initial state distance of the fault point.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the control means instructs the event detection means to repeat the distance and the loss with respect to the fault search time. The fault information calculating means includes fault detecting means for detecting the occurrence of a fault from the distance and the loss obtained for the initial state and the fault search time, respectively, and the fault point is conditioned on the condition that the fault occurs. Is determined by determining the optical path and the position of the optical path. The invention according to claim 4 is the invention according to claim 3, wherein:
And a failure occurrence time determining means for obtaining a time from the clock means under the condition of the occurrence of the failure and determining the time as a failure occurrence time. The invention according to claim 5 is the invention according to claim 3 or 4,
The fault detecting means determines that the fault has occurred if there is a mismatch between the distance obtained for the initial state and the fault search time, or a mismatch between the total number of detected reflection points and connection points. It is characterized by judging.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a multi-branch optical line test apparatus according to the present embodiment and a test object thereof. The same components as those shown in FIG. 11 are denoted by the same reference numerals. In this embodiment, a multi-branch optical line provided with four optical fibers is a test object for convenience of explanation.

In FIG. 1, an OTDR measuring device 11 is provided with a timer (not shown) for performing an OTDR waveform analysis process peculiar to the present embodiment, which will be described in detail below, and for knowing the current time. Except for this, it has the same function as the OTDR measuring instrument 1 shown in FIG. The storage device 12 is composed of a large-capacity hard disk or the like.
This is for storing the measurement result by the TDR measuring device 11. Each of the terminators 13-1 to 13-4 is an optical fiber 7
-1 to 7-4 are terminated. The connector 14 connects between the OTDR measuring instrument 11 and the star coupler 15, and the star coupler 15 has the same function as the star coupler 5 shown in FIG. 11 except that the test light is branched in four directions instead of eight directions. have. The connector 14, the star coupler 15, the connectors 6-1 to 6-4, and the optical fibers 7-1 to 7-4
And terminators 13-1 to 13-4 constitute a test object,
The OTDR measuring device 11 and the storage device 12 constitute a multi-branch optical line test device.

FIG. 2 shows an example of an OTDR waveform obtained when there is no failure in any of the optical fibers 7-1 to 7-4, and returns from the optical fibers 7-1 to 7-4. Incoming reflected light and backscattered light (hereinafter collectively referred to as “return light”) are formed to overlap. In the figure, the horizontal axis indicates the reciprocating distance from the OTDR measuring instrument 11 to each observation point, and the vertical axis indicates the optical power level of the return light from the multi-branch optical line. In the figure, the OTD is closer to the left end.
It is closer to the R measuring device 11 and closer to the subscriber side as it goes to the right end. Each data of the OTDR waveform is collected at an interval of 0.5 m. For example, if the number of data is 20,000 points, it is converted into a distance to 0.5 mx 20,000 = 10 km.
Is the observation target.

The Fresnel reflection point CP is connected to the connector 6-1 for connecting the star coupler 15 and the optical fibers 7-1 to 7-4.
~ 6-4 corresponds to the peak waveform of Fresnel reflected light,
The Fresnel reflection points ED1 to ED4 are respectively terminators 13-1.
13-4 corresponds to the peak waveform of Fresnel reflected light. Here, the star coupler 15 is connected to the optical fiber 7-1.
7-4 have the characteristic of 4 equal branches for splitting light having the same optical power. Therefore, the power of the return light from the optical fibers 7-1 to 7-4 is P1 to P1, respectively.
If P4 is satisfied, the following equation is established. P1 = P2 = P3 = P4 (1)

If it is assumed that the dispersion of the loss of the optical fibers 7-1 to 7-4 is small, the loss before and after the Fresnel reflection points ED1 to ED4 corresponds to the case where no failure exists in any of the optical fibers. Level differences ΔED1 to ΔED4
(See FIG. 2) are as follows. First, at the Fresnel reflection point ED1 corresponding to the distance of the far end (termination device 13-1) of the optical fiber 7-1, immediately before this reflection point, the power of the backscattered light from the optical fibers 7-1 to 7-4. P1 to P
4 is observed, and immediately after the reflection point, the sum of the backscattered light from the optical fibers 7-2 to 7-4 is observed. Then, from the difference between these two optical powers, the Fresnel reflection point E
A step waveform at D1 is formed. Therefore,
The level difference ΔED1 at the Fresnel reflection point ED1 is calculated by the following equation from the ratio of these two optical powers. ΔED1 = 5 · log ｛(P1 + P2 + P3 + P4) / (P2 + P3 + P4)｝ (2) Accordingly, the following equation is derived from this equation and the above-described equation (1). ΔED1 = 5 · log (4/3) ≒ 0.62 dB (3)

Similarly, Fresnel reflection points ED2, ED
3, the level differences ΔED2 and ED3 are calculated as follows. ΔED2 = 5 · log ｛(P2 + P3 + P4) / (P3 + P4)｝ = 5 · log (3/2) ≒ 0.88 dB (4) ΔED3 = 5 · log ｛(P3 + P4) / P4｝ = 5 · log ( 2) ≒ 1.51 dB (5) Also, the level difference ΔED at the Fresnel reflection point ED4 corresponding to the distance at the far end (termination device 13-4) of the optical fiber 7-4.
4 is equal to the dynamic range at this far end,
It is calculated as the ratio between the optical power level at the far end and the optical power level of the noise. Therefore, the value of the level difference ΔED4 is determined depending on the performance of the OTDR measuring instrument 11.

On the other hand, if a fault point exists in any one of the optical fibers and the distance of the fault point coincides with the end of an optical fiber other than the optical fiber having the fault point, the Fresnel reflection caused by the fault point and the end point may occur. Since the Fresnel reflection by the installed terminator overlaps, the loss is as follows. If the optical fiber 7-2 has a failure point, the Fresnel reflection points ED1 and ED2 overlap with each other.
Since the length of -1 is equivalent to the length of the optical fiber 7-2 being equal, the loss at the fault point is as follows. ΔED1 + △ ED2 ≒ 1.50 dB (6) If there is a failure point in the optical fiber 7-3, it is equal to the overlapping of the Fresnel reflection points ED2 and ED3.
Since the length of -2 is equivalent to the length of the optical fiber 7-3 being equal, the loss at the fault point is as follows. ΔED2 + ΔED3 ≒ 2.39 dB (7) If there is a failure point in the optical fiber 7-4, it is equal to the overlapping of the Fresnel reflection points ED3 and ED4.
Since the length of the optical fiber 7-4 is equal to the length of the optical fiber 7-4, the loss at the fault point is as follows. ΔED3 + ΔED4 ≒ dynamic range at the terminal point of the optical fiber 7-4 + 1.51 dB (8)

Next, a procedure for obtaining the distance between the optical fiber line where the fault exists and the fault using the above configuration will be described with reference to the flowchart shown in FIG. First, the optical fibers 7-1 to 7-4 are laid so that the fiber lengths thereof are different from each other, and their installation locations are checked in advance (step S1). Next, in an initial state where there is no failure in any of the optical fibers, the OTDR measuring device 11 detects the Fresnel reflection points and calculates the level difference between the reflection points from the OTDR waveform obtained by measuring the multi-branch optical line. Then, these are stored in the storage device 12 as “event information” in the initial state. The event information in the initial state is, for example, as shown in FIG. 4, and the distance and the level difference are recorded for each Fresnel reflection point. The OTDR measuring device 11 measures the event information in the initial state only once for the first time.
Incidentally, the procedure for detecting the Fresnel reflection points from the OTDR waveform and calculating the level difference between them is a well-known technique that is also implemented in a conventional OTDR measuring instrument, and thus the details thereof will not be described here. Step S
2).

Next, the OTDR measuring device 11 measures the multi-branch optical line, calculates the event information from the obtained OTDR waveform in the same manner as in the case where the event information in the initial state is obtained, and stores it in the storage device. 12 (step S
3). Next, the OTDR measuring device 11 determines whether or not a failure has occurred according to a procedure described in detail below, and if a failure has occurred, calculates the distance between the line having the failure point and the failure point. In the present embodiment, it is assumed that there is only one failure point such as a disconnection. Therefore, two types of cases A and B described below are assumed as patterns of event information when a failure occurs. Only. In the following, description will be made by taking an example in which a failure occurs in the optical fiber 7-4.

Case A In this case, for example, the position P on the optical fiber 7-4
₁ (see FIG. 1) when a fault occurs, that is, when a fault point exists at the same distance as the distance at which the terminator 13-3 is installed. At this time, the event information obtained from the OTDR waveform is as shown in FIG. 5, and the observed OTDR waveform is as shown in FIG. In other words, three Fresnel reflection points to be detected are ED1, ED2, and ED3A, and the distances and level differences at the Fresnel reflection points ED1 and ED2 are the same as those in the initial state shown in FIG. On the other hand, only the distance of the Fresnel reflection point ED3A is the same as that of the Fresnel reflection point ED3 shown in FIG. Thus, in case A, fewer Fresnel reflection points are detected than in the initial state,
Each distance between the detected Fresnel reflection points matches one of the distances between the Fresnel reflection points detected in the initial state.

Case B In this case, for example, the position P on the optical fiber 7-4
₂ (see FIG. 1) when a fault occurs, that is, when a fault point exists between the installation position of the terminator 13-2 and the installation position of the terminator 13-3. At this time, the event information obtained from the OTDR waveform is as shown in FIG.
The observed OTDR waveform is as shown in FIG. That is, the detected Fresnel reflection points are ED1, ED2, ED
3B, ED4B, Fresnel reflection point ED
Both the distance and the level difference between ED1 and ED2 are the same as in the initial state shown in FIG. On the other hand, the Fresnel reflection point corresponding to the Fresnel reflection point ED3B is not shown in FIG.
Further, only the distance of the Fresnel reflection point ED4B is the same as that of the Fresnel reflection point ED3 shown in FIG. As described above, in case B, the same number of Fresnel reflection points as those detected in the initial state are detected, but any of the detected Fresnel reflection points is detected in the initial state. Different from any of the Fresnel reflection points.

As can be seen from the description of each of these cases, the OTDR measuring instrument 11 compares the event information in the initial state (step S2) with the event information collected in step S3, and determines that the distance between the Fresnel reflection points is small. If there is a mismatch, or if the number of detected Fresnel reflection points differs from each other, it is determined that a failure has occurred.

Next, when it is determined that a fault has occurred, the OTDR measuring device 11 determines the distance between the line of the optical fiber where the fault point exists and the fault point according to a procedure described in detail below. Case A The OTDR measurement device 11 extracts the event information in the initial state shown in FIG. 4 and the newly detected event information in FIG. 5 from the storage device 12 and compares these two pieces of event information to determine a failure point. Now, Fresnel reflection points ED1, ED2
Since the distance and the level difference are the same for both event information, the OTDR measuring instrument 11 determines that there is no fault point in the optical fiber 7-1 and the optical fiber 7-2. The Fresnel reflection point ED3 and the Fresnel reflection point E
Since the distances of D3A are the same, the OTDR measuring instrument 11 determines that there is no fault point in the optical fiber 7-3.

Next, the OTDR measuring device 11 adds the Fresnel reflection points ED1, ED2, ED to the event information shown in FIG.
Since there is no Fresnel reflection point other than 3A, it is estimated that a failure has occurred at a distance that coincides with any one of the ends of the Fresnel reflection points ED1 to ED3 in the initial state. In addition, the OTDR measuring device 11 determines, among the Fresnel reflection points ED1 to ED4 in the initial state, the Fresnel reflection points ED1, ED2, whose distances are detected in step S3.
The Fresnel reflection point ED4 is found as a Fresnel reflection point that does not correspond to the ED 3A, and it is estimated that a fault point exists on the optical fiber 7-4 corresponding to the Fresnel reflection point.

Next, the OTDR measuring device 11 determines which of the optical fibers 7-1 to 7-3 has the distance of the fault point on the optical fiber 7-4 coincident with the end distance of the optical fiber. presume. For this purpose, the OTDR measuring device 11 calculates the difference between the level differences of the Fresnel reflection points having the same distance in the initial state and the obstacle state, and finds the difference between the level difference of the Fresnel reflection point ED4 in the initial state. A closer one is searched for, and a distance corresponding to the searched set of Fresnel reflection points is estimated as a distance of the obstacle point.

In this case, the Fresnel reflection points ED1, ED
Since the level difference of 2 is the same between the event information in the initial state and the event information in the failure state, the difference between the two level differences for the two Fresnel reflection points is 0 dB. On the other hand, the difference in the level difference between the Fresnel reflection point ED3 and the Fresnel reflection point ED3A is 9.2-1.5 = 7.7 dB. Therefore, it is understood that the pair having the level difference closest to the level difference 7.4 dB of the Fresnel reflection point ED4 is the pair of the Fresnel reflection points ED3 and ED3A,
The OTDR measuring instrument 11 estimates that the fault point is disconnected at a distance of 4.185 km on the optical fiber 7-4.

Case B As in the case A, the OTDR measuring device 11 extracts the event information in the initial state shown in FIG. 4 and the newly detected event information in FIG. 7 from the storage device 12 and extracts these two event information. The failure point is determined by comparison. Since the distance and the level difference are the same for the Fresnel reflection points ED1 and ED2, the OTDR measuring device 11 determines that there is no fault point in the optical fibers 7-1 and 7-2. Further, since the distance of the Fresnel reflection point ED4B is the same as the distance of the Fresnel reflection point ED3, the OTD
The R measuring device 11 determines that no fault point exists in the optical fiber 7-3. On the other hand, the Fresnel reflection point ED3B
Are the Fresnel reflection points ED1 to ED in the initial state.
4, the OTDR measuring device 11 estimates that a fault has occurred in the optical fiber 7-4 and the distance between the fault point is 3.912 km from the Fresnel reflection point ED3B. , Step S4).

Next, the OTDR measuring device 11 executes step S4
If no failure is detected in step S5 (the determination result in step S5 is "NO"), the process returns to step S3, and after a predetermined time has elapsed, the processes in steps S3 to S4 are performed again. Thus, the OTDR measuring device 11 repeatedly executes the processing of steps S3 to S5 until a failure occurs. Thereafter, when a failure occurs in the multi-branch optical line and the result of the determination in step S5 becomes "YES", the OTDR measuring instrument 11 obtains the current time from an internal timer and determines this as the failure occurrence time. In addition to the above, the OTDR measuring device 11 performs various processes to be performed when a failure occurs (for example, notification that a failure has occurred) (step S6).

In the above description, when the distance included in the event information in the initial state is compared with the distance of the event information collected in step S3, it is determined whether or not these distances completely match. I was However, in practice, if the distance between them is within a certain allowable range (for example, ± 0.5 m), they may be treated as being considered to be the same. In the above description, the Fresnel reflection point is described as an example of the failure point, but the failure may be caused by a loss abnormality other than the disconnection. May be detected as a “connection point”, and the connection point detected together with the Fresnel reflection point may be used to obtain the line where the fault point exists and the distance between the line and the line.

[0030]

As described above, according to the present invention, the time series change of the response light returning from the multi-branch optical line in each of the initial state in which the multi-branch optical line does not have a fault and the time of searching for a fault. A reflection point and a connection point existing on each optical line are detected from the measured waveform to determine respective distances and losses, and the comparison is made to determine an optical line and a position where a fault point exists. As a result, it is possible to obtain information on the distance to the fault point, which has not been obtained conventionally. In addition, since the optical path and position where the point of failure exists can be automatically measured,
There is no need to install each filter so that the distance between the star coupler and the filter differs for each optical line as in the past,
The measurement operation can be performed efficiently. In addition, since the same measurement operation is performed, more reliable measurement can be performed as compared with a case where a human performs measurement.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a multi-branch optical line test apparatus and a test object according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of an OTDR waveform when no failure occurs in any of the optical fibers in the embodiment.

FIG. 3 is a flowchart showing a procedure for obtaining a line where a fault point exists in the multi-branch optical line and a distance thereof in the same embodiment.

FIG. 4 is a table showing event information obtained in an initial state in which no optical fiber has a failure in the embodiment.

FIG. 5 is a table showing event information obtained in a first case in which a failure has occurred in the optical fiber 7-4 in the embodiment.

FIG. 6 shows OT observed in the case shown in FIG.
FIG. 4 is an explanatory diagram showing an example of a DR waveform.

FIG. 7 is a table showing event information obtained in a second case in which a failure has occurred in the optical fiber 7-4 in the embodiment.

8 is an OT observed in the case shown in FIG.
FIG. 4 is an explanatory diagram showing an example of a DR waveform.

FIG. 9 is a block diagram illustrating a configuration of a conventional multi-branch optical line test apparatus and a test target thereof.

FIG. 10 is an explanatory diagram showing an example of a response light waveform observed by the OTDR measuring device 1 in the same device.

11 is a waveform W ₆ of the observed waveforms shown in FIG.
An explanatory view enlarging the vicinity of the to _W-8, it is (a) if there is no failure in any of the optical fiber, (b) if there is a fault in the optical fiber 7-7.

[Description of References] 6-1 to 6-4, 14: Connector, 7-1 to 7-4: Optical fiber, 11: OTDR measuring instrument, 12: Storage device, 13-1 to
13-4: Terminator, 15: Star coupler

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keiichi Shimizu 3-3-22 Nakanoshima, Kita-ku, Osaka-shi, Osaka F-term within Kansai Electric Power Company (Reference) 2F065 AA01 AA18 BB12 CC00 FF31 FF58 GG08 LL00 LL03 QQ13 QQ23 QQ25 QQ26 QQ27 2G086 CC03 KK02 KK05 5K002 BA21 DA12 EA05 FA01

Claims (5)

[Claims] 1. A time-series change of a response light that is incident on a multi-branch optical line that branches light into a plurality of optical lines having different lengths from each other and returns from the multi-branch optical line. In a multi-branch optical line test apparatus for obtaining a measurement waveform, an event detecting means for detecting a reflection point and a connection point existing on each of the optical lines from the measurement waveform, and obtaining a distance and a loss for each of the reflection point and the connection point Control means for instructing the event detection means to obtain the distance and the loss for each of the initial state and the fault search time point where the multi-branch optical line has no fault, and the initial state and the fault search time point. A multi-branch optical line test device, comprising: a fault information calculating means for comparing the distance and the loss obtained for each of them to determine an optical line at which a fault point exists and a position thereof. . 2. The method according to claim 1, wherein, among the distances obtained for the initial state, the optical path corresponding to a reflection point or a connection point having a distance that does not exist in the distance obtained at the time of the fault search is used. Determined in the optical path where the fault point exists, if the total number of reflection points and connection points detected at the time of the fault search is less than the initial state, the reflection point and the distance match at the initial state and the fault search time and The difference between the losses is determined for each connection point, and the distance between the reflection point or the connection point corresponding to the difference closest to the level difference of the reflection point or the connection point detected only in the initial state is determined as the distance between the failure points. If the total number of detected reflection points and connection points is the same at the initial state and at the time of the fault search, the distance obtained at the time of the fault search was determined for the initial state. Multi-branch optical testing apparatus according to claim 1, wherein the determining the distance that is not in the release of the distance of the fault point. 3. The control means instructs the event detection means to repeatedly determine the distance and the loss with respect to the fault search time, and the fault information calculation means determines the initial state and the fault search time. 2. The apparatus according to claim 1, further comprising: a fault detecting unit configured to detect a fault from the distance and the loss obtained, and determining an optical path and a position where the fault point exists on condition that the fault occurs. Or the multi-branch optical line test apparatus according to 2. 4. A time measuring means for measuring time, and a fault occurrence time determining means for obtaining a time from the time counting means on condition that the fault occurs and determining the time as a fault occurrence time. The multi-branch optical line test device according to claim 3. 5. The apparatus according to claim 1, wherein the fault detecting means determines whether there is a mismatch between the initial state and the distance obtained at the time of the fault search.
5. The multi-branch optical line test device according to claim 3, wherein if there is a mismatch in the total number of the detected reflection points and the connection points, it is determined that the failure has occurred.