JPH1022948A - Faulty point detector for optical transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the positions of all the faulty points in transmission lines plurally divided by an optical branch circuit in a passive optical network(PON) in which the optical branch circuit is arranged in the middle of a transmission line and which executs one-to-multiple communication between a single station side and plural subscribers' houses. SOLUTION: This detector is provided with optical filters 20-1 to 20-n just behind n-number of output ports of the optical branching circuit arranged in the middle of the transmission line. The optical filters transmit only signal light (wavelength λs) and the test light of test light (λn). λn is the transmitting wavelength of each of the optical filters and they are different from each other. The detector 7 output pulse light whose wavelength is λn being one of the transmitting wavelengths of the optical filters 20-1 to 20-n as test light and receives rear scattered light and reflected light from a transmission line of the wavelength λn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the detection of a failure point in a transmission line of an optical transmission system, and more particularly, to a passive optical branching circuit arranged in the middle of a transmission line to communicate between one optical transmission device and a plurality of optical transmission devices. Passive optical network (Pa
sive Optical Network: PO
The present invention relates to an apparatus for measuring a loss in a transmission line and detecting a failure point.

[0002]

2. Description of the Related Art In a PON system, an optical pulse test apparatus, an optical multiplexer / demultiplexer, and an optical filter are used to detect a failure point in an optical transmission line as a detection apparatus.
No. 1,177,354 are known.

FIG. 8 shows US Pat.
7 shows a configuration diagram of an apparatus described in US Pat.

The signal light (wavelength λ) output from the optical transmitter 1
S) is multiplexed by the WDM coupler 11 with the test light (wavelength λOTDR), which is pulsed light output from the transmission path fault point detection device 7, transmitted through the optical fiber 2, and n (an integer of 2 or more) ) Output optical ports.

[0005] In the optical branching circuit 6, the signal light and the test light are branched into n, and transmitted through transmission paths 4-1 to 4-n, respectively. At the receiving end, the signal light and the test light transmitted through the transmission paths 4-1 to 4-n are input to the optical filters 12-1 to 12-n. The signal light passes through these optical filters and is input to the optical receivers 5-1 to 5-n. On the other hand, the test light is reflected by the optical filter, is again input to the transmission lines 4-1 to 4-n, is multiplexed by the optical branching circuit 6, is transmitted again to the optical fiber 2, and is transmitted by forming the WDM coupler 11. It is returned to the road fault point detection device.

Next, the operation of the transmission path fault point detecting device will be described with reference to FIG. The test light input to the transmission path fault point detection device is the backscattered light (Rayleigh scattered light) from the transmission path and the reflected light from the optical filters 12-1 to 12-n. By measuring the time from the output time of the pulse light output from the transmission path fault point detection device to the time until the backscattered light and the reflected light are received, and the optical power of the backscattered light and the reflected light, FIG. The characteristics shown are obtained.

In FIG. 9, distances from the optical transmitter 1 to the optical branching circuit 6 and the optical receivers 5-1, 5-2, 5-n are represented by L1, L4, L5, L6 (L1 <L4 <L
5 <L6). In the figure, solid lines indicate transmission paths 4-1 to 4
-N is a characteristic obtained when there is no failure, and the broken line indicates a case where the transmission line 4-2 has one break point as a failure. The detection of the fault point is performed by comparing the solid line and the broken line. Specifically, since the reflection point at the transmission distance L5 has disappeared, it is known that a failure has occurred somewhere in the optical fiber 4-2, and the broken line indicates that the transmission distances L1 and L4 are different. A bright line indicating a decrease in transmission loss, which was not seen in the solid line, appears, indicating that the optical fiber 4-2 is broken at the position of the bright line.

[0008]

A problem with the above-mentioned conventional technique is that it is difficult to specify a plurality of fault points when there are a plurality of fault points.

The reason will be described with reference to FIG. FIG. 7 shows a case where there is one break point between each of the transmission distances L1 and L4 of the optical fibers 4-1 and 4-2 from the optical transmitter. In this case, when there is no obstacle in the transmission line, the transmission distance L is compared with the solid line obtained.
It can be understood that the optical fibers 4-1 and 4-2 have an obstacle due to the disappearance of the reflected light at 4 and L5.

At this time, a bright line indicating the break of the transmission path is obtained at the position of the transmission distance L2, L3. However, at these two break points, it is not known whether the break point of the transmission distance L2 is the optical fiber 4-1 or the optical fiber 4-2, and similarly, the break point of the transmission distance L3 is the optical fiber 4 −
It cannot be determined which of 1, 4-2. In the related art, it is impossible to detect a plurality of fault points in a PON system having an optical branch circuit in a transmission path.

[0011] It is an object of the present invention to improve the performance of determining the position of which transmission path when a plurality of failure points are present in a PON system.
It is to improve the maintainability to enable any failure point detection.

[0012]

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, an optical transmission line fault point detecting device according to the present invention comprises an optical transmitter for transmitting signal light and a test light having a wavelength different from that of the signal light. , A test optical transmitter that multiplexes the signal light and the test light, and outputs a multiplexed light, and a first optical transmission line that transmits the multiplexed light. Further, the multiplexed light transmitted through the first optical transmission line is branched into n signal lights and test light (n is 2
An optical splitter that outputs a split light with the above natural numbers, and a signal light that passes through the split light, and selectively passes only a signal light of a predetermined wavelength out of the signal light and the test light. And n first optical filters that output light. Further, n second optical transmission paths for transmitting the selection light, and only the signal light are respectively selected from the selection lights transmitted through the second optical transmission path, each being connected to the second optical transmission path. It is characterized by comprising: n second optical filters that selectively pass the selected signal light and output the selected signal light; and n optical receivers that respectively receive the selected signal light and convert the selected signal light into an electric signal.

Here, the predetermined wavelengths are different from each other.

Further, in the optical transmission line fault point detecting apparatus according to the present invention, the n first optical filters respectively separate the signal light and the test light and output the separated signal light and the separated test light, respectively. A demultiplexer, a third optical filter that passes test light of only a predetermined wavelength out of the separation test light and outputs a selective separation test light, and multiplexes the separation signal light and the selective separation test light to form a second And an optical wavelength multi-wave device for outputting to an optical transmission line.

On the other hand, the test light transmitter includes a pulse generator for outputting pulse light, and a photodetector for receiving the return light of the pulse light from the first optical transmission line and the second optical transmission line. , And further, the pulsed light is transmitted to the optical multiplexer,
An optical multiplexer / demultiplexer that couples return light from the first optical transmission line and the second optical transmission line to the light detection means, and a relationship between an elapsed time and a light reception level of the return light based on a transmission time of the pulse light And an arithmetic unit for detecting

The optical transmission line fault point detecting device according to the present invention has a configuration similar to the above configuration, wherein an optical transmitter for transmitting signal light and a test light for transmitting test light having a wavelength different from that of the signal light. A transmitter, an optical multiplexer / demultiplexer that multiplexes the signal light and the test light, and outputs n-branch (n is a natural number of 2 or more) and outputs a multiplexed / branched light; And n first optical filters for selectively passing only the test light having a predetermined wavelength out of the signal light and the test light and outputting the selected light, and the n selected light Each of the second optical transmission lines for transmitting the signal and the n second optical transmission lines is connected to each of the n second optical transmission lines, and the n second second optical transmission lines transmit only the signal light from the selected light transmitted through the second optical transmission line. An optical filter and n optical receivers each receiving the selected signal light and converting it to an electric signal It is equipped with a.

The optical transmission line fault point detection system of the present invention has the following features. That is, immediately after the n output ports of the optical branch circuit arranged in the transmission path, the optical filter (FIG. 1)
20-1 to 20-n). This optical filter passes only the signal light (wavelength λs) and the test light (λn). λn is the passing wavelength of each of the optical filters, which are different from each other.

In addition, as a test light, a pulse light having a wavelength of λn, which is one of the passing wavelengths of the optical filter, is output, and an optical transmission for receiving backscattered light and reflected light from the transmission line having the wavelength λn It has a road fault point detection device (7 in FIG. 1).

By arranging the optical filter and the optical transmission line fault point detecting device in a PON system, the pass path of the test light wavelength λn is branched into a plurality of transmission lines by an optical branch circuit arranged in the middle of the transmission line. , But is limited to any one of the plurality of transmission paths. Thereby, the backscattered light and the reflected light of the test light received by the optical transmission line fault point detection device are limited to any one of the transmission lines branched by the optical branching circuit. By measuring the time until the backscattered light and the reflected light from the test light output are received and the power thereof, a fault point can be detected. By setting the wavelength of the test light to λ1 to λn, it is possible to independently detect faults in a plurality of branched transmission paths, so that even when there are a plurality of fault points, the transmission path and position of the fault point are determined. Can be specified.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical transmission line fault point detecting apparatus according to the present invention will be described in detail in the order of configuration and operation with reference to the drawings.

First, the configuration of the present invention will be described with reference to FIG.

The signal light (wavelength:
λS) is a test light (wavelength λ1, λ2,...) which is a pulsed light output from the transmission path fault point detection device 7.
.lambda.n (.lambda.1 {.lambda.2}... {.lambda.n) and transmitted by the WDM coupler 11, transmitted through the optical fiber 2, and input to the optical branch circuit 6 having n output optical ports. In the optical branch circuit 6, the signal light and the test light are n-branched and input to the optical filters 20-1 to 20-n, respectively.

The pass wavelength of the optical filters 20-1 to 20-n is a signal light wavelength λ as a pass wavelength common to all filters.
Sμm and the test light wavelengths λ1, λ2,..., Λn as the transmission wavelengths of the respective optical filters. Specifically, the passing wavelength of the optical filter 20-1 is the signal light wavelength λS and the test light wavelength λ1, the passing wavelength of the optical filter 20-n is the signal light wavelength λS and the test light wavelength λn,
Other test light wavelengths are blocked by this optical filter 20-n.

Output lights from the optical filters 20-1 to 20-n are input to optical fibers 4-1 to 4-n, respectively.
At the receiving end, the signal light and the test light transmitted through the optical fibers 4-1 to 4-n are input to the optical filters 13-1 to 13-n. The signal light (wavelength: λS) passes through these optical filters and is input to the optical receivers 5-1 to 5-n. On the other hand, test light (wavelength: λ1, λ2,..., Λ
n) is blocked by the optical filter.

FIG. 2 shows the configuration of the optical filters 20-1 to 20-n, and FIG. 3 shows the wavelength passing characteristics. Signal light (wavelength λS)
And the test light (wavelength λn) are fused WDM coupler 21-1
And separated into two output ports of the WDM coupler 21-1 and output. The test light (wavelength λn) output from one output port of the WDM coupler 21-1 is input to an interference film type optical bandpass filter 22-n in which an oxide film whose transmission center wavelength is λn is stacked in multiple layers. You.

In the optical bandpass filter 22-n, only the wavelength λn is transmitted, and the other wavelengths are blocked. Therefore, the test light wavelength is changed to other λ1, λ2,.
In the case of 1, it is cut off by this optical bandpass filter 22-n.

The signal light (wavelength λS) output from another output port of the WDM coupler 21-1 and the test light output from the optical bandpass filter 22-n are combined with a fusion type WDM coupler 21-2. Are multiplexed and output to the optical fiber 4-n. Backscattered light and reflected light of the test light (wavelength λn) are transmitted from the optical fiber 4-n to the WDM coupler 21-n.
2. Optical bandpass filter 22-n, WDM coupler 21
The signal is input to the optical branch circuit through the path of -1. As shown in FIG. 3, the wavelength passing characteristics of this optical filter allow the signal light wavelength λS and the test light wavelength λn to pass.

The configuration of the transmission path fault point detecting device 7 will be described below. A pulse light source 71 that outputs pulse light by driving the semiconductor laser in pulse outputs test light,
The wavelength of the light source can be set to λ1, λ2,..., Λn. The output light of the pulse light source 71 is input to the fusion type optical coupler 74. The output light of the optical coupler 74 is output to the transmission path via the WDM coupler 11. The backscattered light and reflected light in the transmission path of the output test light (section between the optical fiber 2 and the optical filters 13-1 to 13-n) are input from the optical fiber 2 to the WDM coupler 11, and the optical transmission path failure Input to the point detection device 7. This light is input to the photodetector 72 via the optical coupler 74 and received. The pulse light source 71 and the photodetector 72 are
3 and detects a failure point of the transmission path.

Next, the operation of the transmission path fault point detecting device will be described with reference to FIGS.

FIGS. 4 and 5 show an optical transmission line fault point detecting device 7.
This is an example of a case where the transmission line loss is measured using λ1 as the test light wavelength from the optical transmission line. In this case, the transmission line for which the transmission line loss is measured is from the optical fiber 2 to the optical filter 13-1 because the optical filter 20-1 for passing the test light wavelength λ1 is disposed in the optical fiber 4-1. It is a section of.

The power of the test light (wavelength: λ1) output from the optical transmission line fault point detection device 7 is attenuated by the loss of the transmission line and the optical branch circuit 6, and at the same time, a part of the power of the test light is Due to backscattering (Rayleigh scattering) or reflection (when there is a failure point due to transmission line breakage) on the transmission line, the light is returned in the direction opposite to the traveling direction. The backscattered light and the light reflected by the fault point are input to the optical transmission line fault point detecting device 7.

The transmission path fault point detector 7 measures the time from the output time of the output pulse light to the reception of the backscattered light and the reflected light, and the optical power of the backscattered light and the reflected light. As a result, the characteristics shown in FIG. 4 are obtained.

In FIG. 4, the distances to the optical branch circuit 6, the break point, and the optical receiver 5-1 are L1, L2, and L3 (L1 <L2 <L3) based on the position of the optical transmitter 1. . In the figure, the solid line shows the characteristics obtained when there is no failure in the transmission line, and the broken line shows the case where the optical fiber 4-1 has one break point as a failure. The increase in transmission loss at the transmission distance L1 is due to the branch loss of the optical branch circuit 6. The detection of the fault point is performed by comparing the solid line and the broken line. Specifically, a bright line that cannot be seen with the solid line appears at the position of L2, and the transmission loss increases after L2. Therefore, at the point of the distance L2 of the optical fiber 4-1 from the optical transmitter 1, It can be seen that a failure has occurred.

In FIG. 5, the break point, the distance to the optical branching circuit 6, and the distance to the optical receiver 5-1 are L2, L1, and L3 (L2 <L1 <L3) based on the position of the optical transmitter 1. . As in FIG. 4, the solid line shows the characteristics obtained when there is no failure in the transmission line, and the broken line shows the case where the optical fiber 2 has one break point as a failure. The detection of the fault point is performed by comparing the solid line and the broken line. Specifically, a bright line that cannot be seen with a solid line appears at the position of L2, and the transmission loss increases after L2. Therefore, a failure occurs at a point at a distance L2 of the optical fiber 2 from the optical transmitter 1. It can be seen that this has occurred.

As shown in FIGS. 4 and 5, a fault point of the optical fiber 2 and the optical fiber 4-1 is detected by using λ1 as a test light wavelength from the optical transmission line fault point detecting device 7. Further, by using λ2 as the test light wavelength, the fault point of the optical fiber 2 can be detected at the same time as when λ1 is used, and at the same time, the fault point of the optical fiber 4-2 is detected. Further, by using λn as the test light wavelength, the optical fiber 2 can be used in the same manner as when λ1 and λ2 are used.
Can be detected, and at the same time, the fault point of the optical fiber 4-n is detected.

As described above, the test light wavelengths λ1 to λ
By using the n wavelengths, the fault points of the optical fiber 2 and all the optical fibers 4-1 to 4-n provided with the optical filter that passes the predetermined test light wavelength are detected.

EXAMPLES Specific configurations of each element of the above embodiment,
The specific configuration of another embodiment is shown below.

As the signal light wavelength, here, λS = 1.3.
Although μm is used, other wavelengths such as the 1.5 μm band can be used as long as transmission is not hindered. The modulation method and modulation code are not particularly limited.

As the test light wavelength, λ1 = 1.640 μm
m, λ2 = 1.642 μm,..., λn = 1.6
40 + 0.002 × (n−1) μm. Different from the signal wavelength, the optical filters 20-1 to 20-n and W
As long as the wavelength characteristics of the DM coupler 11 are satisfied, other wavelength bands may be used, and the wavelength interval is not limited to 2 nm, but may be longer or shorter.

The WDM coupler 11 is composed of a fusion type coupler, but may also be composed of a mirror type coupler or a waveguide type coupler having wavelength characteristics.

The optical fibers 2, 4-1 to 4-n are single-mode fibers having a zero-dispersion wavelength in the 1.3 μm band, but optical fibers having a zero-dispersion wavelength in the 1.5 μm band may also be used. , And other multimode fibers.

The optical branching circuit 6 is composed of optical couplers in which fused optical couplers are cascaded in multiple stages, but may be composed of cascaded mirror type optical couplers. Further, it may be constituted by an optical coupler using a waveguide formed on a semiconductor or quartz substrate.

As an example, the number of branches is 16,
It can be configured with more or less branches.

The optical filters 20-1 to 20-n are composed of fused optical couplers as the WDM couplers 21-1 and 21-2, but may be composed of mirror type optical couplers. The optical bandpass filter 22-n is formed of an interference film filter in which an oxide film is stacked in multiple layers. It is also implemented with Fabry-Perot type filters.

As the optical filters 20-1 to 20-n, a waveguide type filter formed on a semiconductor or a quartz substrate having the above-mentioned functions may be used.

Each of the optical filters 13-1 to 13-n is constituted by an interference film filter in which an oxide film is laminated in a multilayer, but is also constituted by a Fabry-Perot type filter or a fusion type optical coupler having a WDM function. You.

In the optical transmission line fault point detecting device 7, the pulse light source 71 is a pulsed drive of a semiconductor laser.
The pulse width is 1 ns, and the repetition period is 10 ms. A solid-state laser may be used instead of a semiconductor laser. The pulse width may be set to 1 ns or more or less depending on the resolution of the fault point. The repetition period may be longer or shorter depending on the distance of the transmission path.

The photodetector 72 comprises a PIN photodiode and an amplifier. It is also constituted by a device having a photoelectric conversion function such as a photomultiplier tube. The computer 73 is realized by a device having a function of acquiring the light emission time of the pulse light source 71, the light reception time of the photodetector 72, and its power, and calculating the transmission loss of the transmission path. The optical coupler 74 is constituted by a fusion type optical coupler. It is also composed of a mirror type optical coupler.

The optical transmission line fault point detecting device of the present invention will be described in detail in the order of configuration and operation with reference to the drawings.

First, the configuration will be described with reference to FIG.

The test is a signal light (wavelength: λS) output from the optical transmitter 1 and transmitted through the optical fiber 2, and a pulsed light output from the transmission path fault point detecting device 7 and transmitted through the optical fiber 3. Light (wavelengths λ1, λ2,..., Λn:
.lambda.1 {.lambda.2} (.lambda.n) is input to an optical branch circuit 6 having two input ports and n output optical ports. After the signal light and the test light are multiplexed by the optical branching circuit 6,
The light is branched into n and input to the optical filters 20-1 to 20-n, respectively.

The passing wavelength of the optical filters 20-1 to 20-n is a signal light wavelength λ as a passing wavelength common to all filters.
Sμm and the test light wavelengths λ1, λ2,..., Λn as the transmission wavelengths of the respective optical filters. Specifically, the passing wavelength of the optical filter 20-1 is the signal light wavelength λS and the test light wavelength λ1, the passing wavelength of the optical filter 20-n is the signal light wavelength λS and the test light wavelength λn,
Other test light wavelengths are blocked by this optical filter 20-n.

Output lights from the optical filters 20-1 to 20-n are input to optical fibers 4-1 to 4-n, respectively.
At the receiving end, the signal light and the test light transmitted through the optical fibers 4-1 to 4-n are input to the optical filters 13-1 to 13-n. The signal light (wavelength: λS) passes through these optical filters and is input to the optical receivers 5-1 to 5-n. On the other hand, test light (wavelength: λ1, λ2,..., Λ
n) is blocked by the optical filter.

FIG. 2 shows the configuration of the optical filters 20-1 to 20-n, and FIG. 3 shows the wavelength passing characteristics. Signal light (wavelength λS)
And the test light (wavelength λn) are fused WDM coupler 21-1
And separated into two output ports of the WDM coupler 21-1 and output. The test light (wavelength λn) output from one output port of the WDM coupler 21-1 is input to an interference film type optical bandpass filter 22-n in which an oxide film whose transmission center wavelength is λn is stacked in multiple layers. You. In this optical bandpass filter 22-n, only the wavelength λn is transmitted, and the other wavelengths are blocked. Therefore, when the test light wavelength is another λ1, λ2,..., Λn−1, the test light wavelength is cut off by the optical bandpass filter 22-n.

The signal light (wavelength λS) output from another output port of the WDM coupler 21-1 and the test light output from the optical bandpass filter 22-n are combined with the fusion type WDM coupler 21-2. Are multiplexed and output to the optical fiber 4-n. Backscattered light and reflected light of the test light (wavelength λn) are transmitted from the optical fiber 4-n to the WDM coupler 21-n.
2. Optical bandpass filter 22-n, WDM coupler 21
The signal is input to the optical branch circuit through the path of -1. As shown in FIG. 3, the wavelength passing characteristic of this optical filter is a signal light wavelength λS
And the test light wavelength λn.

The configuration of the transmission path fault point detecting device 7 will be described below. A pulse light source 71 that outputs pulse light by driving the semiconductor laser in pulse outputs test light,
The wavelength of the light source can be set to λ1, λ2,..., Λn. The output light of the pulse light source 71 is input to the fusion type optical coupler 74. The output light of the optical coupler 74 is output to the transmission path via the WDM coupler 11. The backscattered light and reflected light in the transmission path of the output test light (section between the optical fiber 2 and the optical filters 13-1 to 13-n) are input from the optical fiber 2 to the WDM coupler 11, and the optical transmission path failure Input to the point detection device 7. This light is input to the photodetector 72 via the optical coupler 74 and received. The pulse light source 71 and the photodetector 72 are
3 and detects a failure point of the transmission path.

Next, the operation of the transmission path fault point detecting device will be described.

The power of the test light (wavelength: λ1) output from the optical transmission line fault point detection device 7 is attenuated by the loss of the transmission line and the optical branching circuit 6, and at the same time, a part of the power of the test light is Due to backscattering (Rayleigh scattering) or reflection (when there is a failure point due to transmission line breakage) on the transmission line, the light is returned in the direction opposite to the traveling direction. The backscattered light and the light reflected by the fault point are input to the optical transmission line fault point detecting device 7.

The transmission path fault point detecting device 7 measures the time from the output time of the output pulse light to the reception of the backscattered light and the reflected light, and the optical power of the backscattered light and the reflected light. As a result, the loss of the transmission path with respect to the transmission distance is obtained.

In FIG. 4, if the reference position of the transmission distance is set to the position of the optical transmission line fault point detecting device 7 from the position of the optical transmitter 1, exactly the same characteristics as in FIG. 4 can be obtained. The distance to the optical branch circuit 6, the break point, and the distance to the optical receiver 5-1 are each L.
1, L2, L3 (L1 <L2 <L3). In the figure, the solid line shows the characteristics obtained when there is no failure in the transmission line, and the broken line shows the case where the optical fiber 4-1 has one break point as a failure. The increase in transmission loss at the transmission distance L1 is due to the branch loss of the optical branch circuit 6. The detection of the fault point is performed by comparing the solid line and the broken line. Specifically, a bright line that cannot be seen with the solid line appears at the position of L2, and the transmission loss increases after L2. Therefore, at the point of the distance L2 of the optical fiber 4-1 from the optical transmitter 1, It can be seen that a failure has occurred.

As shown in FIG. 4, a fault point of the optical fiber 4-1 is detected by using λ1 as the test light wavelength from the optical transmission line fault point detecting device 7. Further, by using λ2 as the test light wavelength, the fault point of the optical fiber 4-2 is detected in the same manner as when λ1 is used.
Furthermore, by using λn as the test light wavelength,
As in the case where λ1 and λ2 are used, a fault point of the optical fiber 4-n is detected.

As described above, the test light wavelengths λ1 to λ
By using the n wavelengths, an optical fiber 4 having an optical filter for passing a predetermined test light wavelength is provided.
Detect all fault points 1 to 4-n.

[0062]

The advantages of the present invention are as follows. In a PON system in which a plurality of transmission paths are divided by an optical branching circuit in the middle of a transmission path, even if there are a plurality of failure points in a plurality of transmission paths, the failure point can be reduced. Can be detected 100%.

The reason for this is that an optical filter that allows signal light and test light of a specific wavelength to pass is arranged in a plurality of transmission paths divided by an optical branching circuit, and that an optical filter that is arranged near an optical transmitter is arranged. This is because the output wavelength of the transmission path fault point detection device is set to a wavelength corresponding to the passing wavelength of the optical filter arranged in one of the plurality of transmission paths to be subjected to the fault test. In other words, the test light of a certain wavelength
By transmitting only one transmission line out of the branched transmission lines, it is possible to perform a failure test without being affected by other transmission lines, and by setting the wavelength to the passing wavelength of other transmission lines, This is because a failure test can be performed on all transmission paths.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a detailed embodiment of an optical filter 20-n.

FIG. 3 is a diagram illustrating a wavelength passing characteristic of an optical filter 20-n.

FIG. 4 is a diagram showing a first example of a result obtained by the measurement according to the first invention of the present invention.

FIG. 5 is a diagram showing a second example of the result obtained by the measurement according to the first invention of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 is an explanatory view of a problem of the conventional invention.

FIG. 8 is a block diagram showing a configuration of a conventional invention.

FIG. 9 is a diagram showing an example of a result obtained by measurement according to a conventional invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical transmitter 2, 3, 4-1 to 4-n Optical fiber 5-1 to 5-n Optical receiver 6 Optical branch circuit 7 Optical transmission path fault point detection device 71 Pulse light source 72 Photodetector 73 Computer 74 Light Couplers 11-1 to 11-n WDM couplers 12-1 to 12-n, 13-1 to 13-n, 20-1
Reference Signs List 20-n optical filter 21-1, 21-2 WDM coupler 22-n optical bandpass filter

Claims (8)

[Claims] An optical transmitter for transmitting a signal light; a test light transmitter for transmitting a test light having a wavelength different from that of the signal light; and a multiplexed light by multiplexing the signal light and the test light. An optical multiplexing means for outputting, a first optical transmission line for transmitting the multiplexed light, and n-branch of the multiplexed light transmitted through the first optical transmission line into the signal light and the test light (where n is 2 or more) An optical branching means for outputting a branched light by dividing the signal light from the branched light, and selectively passing only a signal light having a predetermined wavelength among the signal light and the test light. N first optical filters that output the selected light, n second optical transmission lines that transmit the selected light, and the second optical transmission line that are connected to the second optical transmission line, respectively. Of the selected light transmitted through the optical transmission line, only the signal light is selected. N second optical filters for selectively passing the selected signal light and outputting the selected signal light, and n optical receivers for respectively receiving the selected signal light and converting the selected signal light into an electric signal. Optical transmission line fault point detection device. 2. The optical transmission line fault point detecting device according to claim 1, wherein the predetermined wavelengths are different from each other. 3. The n number of first optical filters, each of which separates the signal light and the test light to output a separated signal light and a separated test light, respectively; A third optical filter that passes test light having only a predetermined wavelength and outputs selective separation test light, multiplexes the separation signal light and the selective separation test light, and transmits the multiplexed light to the second optical transmission line. 3. The optical transmission line fault point detecting device according to claim 1, further comprising an optical wavelength multiplexing means for outputting. 4. A test light transmitting means, comprising: pulse generating means for outputting pulse light; and light detection for receiving return light of the pulse light from the first optical transmission path and the second optical transmission path. Means, and an optical multiplexing / demultiplexing means for sending the pulsed light to the optical multiplexing means and coupling the return light from the first optical transmission path and the second optical transmission path to the light detection means. 4. The apparatus according to claim 1, further comprising: an arithmetic unit configured to detect a relationship between an elapsed time and a light receiving level of the return light based on a transmission time of the pulse light. 5. Optical transmission line fault point detection device. 5. An optical transmitting means for transmitting a signal light, a test light transmitting means for transmitting a test light having a different wavelength from the signal light, and a multiplexing of the signal light and the test light, and n-branch. (N is a natural number of 2 or more) to output multiplexed / branched light; and n optical outputs of the multiplex / branch means, each being connected to the n outputs of the multiplex / branch means, and being predetermined among the signal light and the test light. N first optical filters that selectively pass only the test light having the selected wavelength and output the selected light; second optical transmission paths that respectively transmit the n pieces of the selected light; N second optical filters that are connected to each of the second optical transmission lines and pass only the signal light from the selected light transmitted through the second optical transmission line, And n optical receivers for receiving and converting the signals into electric signals. An optical transmission line fault point detection device, characterized in that: 6. The optical transmission line fault point detecting device according to claim 5, wherein the predetermined wavelengths are different from each other. 7. The n first optical filters each include: an optical wavelength separating unit that separates the signal light and the test light to output a separated signal light and a separated test light, respectively; A third optical filter that passes test light having only a predetermined wavelength and outputs selective separation test light, multiplexes the separation signal light and the selective separation test light, and transmits the multiplexed light to the second optical transmission line. 7. The optical transmission line fault point detecting device according to claim 5, further comprising an optical wavelength multiplexing means for outputting. 8. A test light transmitting means, comprising: pulse generating means for outputting pulse light; and light detection for receiving return light of the pulse light from the first optical transmission path and the second optical transmission path. Means for transmitting the pulse light to the optical multiplexing means, and coupling and returning the return light from the second optical transmission line to the light detecting means; and a transmitting time of the pulse light. 8. The optical transmission line fault point detecting device according to claim 5, further comprising a calculating means for detecting a relationship between an elapsed time and a light receiving level of the return light based on a reference.