JP5489047B2 - OTDR device - Google Patents

Description

  The present invention relates to an OTDR (Optical Time Domain Reflectometry) apparatus, and more particularly, to an OTDR apparatus that automatically and accurately installs a distance reference point at the end position of a dummy fiber.

An OTDR device, which is one of optical pulse testers, sends an optical pulse to a test optical fiber line (optical fiber to be measured), and the intensity of return light such as backscattered light returning from the optical fiber line. This is a device that detects a failure point existing in an optical fiber line and measures a loss distribution and a connection loss by detecting a change in time.

Here, when the OTDR device is connected to the optical fiber to be measured, it is connected via an optical fiber called a dummy fiber. This is because when the OTDR device is connected to the optical fiber to be measured without going through the dummy fiber, the backscattered light in the vicinity of the connection portion (near end) cannot be measured accurately. Prior art documents of such an OTDR device using a dummy fiber include the following.

Japanese Patent Laid-Open No. 11-284573

Hereinafter, a conventional OTDR apparatus will be described. FIG. 5 is a block diagram showing a configuration of a conventional OTDR apparatus. According to the figure, the drive circuit 2 drives the light source 3 in accordance with the timing signal output from the timing generator 1, whereby the light source 3 emits a light pulse. This light pulse propagates in order through the optical fiber 4, the optical directional coupler 5, the dummy fiber 20, and the optical connector 7 and enters the measured optical fiber 8.

On the other hand, the return light from the optical fiber to be measured 8 propagates in the opposite direction to the incident direction and enters the light receiver 12 from the optical directional coupler 5 through the optical fiber 11. As a result, the return light is received by the light receiver 12 and converted into an electrical signal, and the amplifier 13 amplifies the output of the light receiver 12 and outputs the amplified signal to the digital processing unit 14. The digital processing unit 14 performs an averaging process on the output of the amplifier 13 while following the timing signal sent from the timing generation unit 1, and logarithmically converts the obtained result to obtain a distribution waveform of the return light such as backscattered light. It is displayed on the screen of the display unit 15.

Here, the return light distribution waveform measured by the OTDR apparatus will be described with reference to FIG. This figure shows an example of a waveform when the dummy fiber 20 and the optical fiber 8 to be measured are connected as shown in FIG. 5, where the horizontal axis represents the distance and the vertical axis represents the received light level. . Note that the distance on the horizontal axis means the distance corresponding to the time after the light pulse emitted from the light source 3 is guided to the dummy fiber 20 and the optical fiber 8 to be measured.

Then, by performing logarithmic conversion in the digital processing unit 14 as described above, as shown in FIG. 6A, the backscattered light from the dummy fiber 20 and the optical fiber to be measured becomes a straight line to the right. Appear. In addition, the reflection at the optical connector 7 or the terminal point (so-called Fresnel reflection) is observed as a large upward discontinuous waveform (see reference signs W1 and W2).

By the way, as shown in FIG. 6B, in order to accurately measure the backscattered light of the optical fiber 8 to be measured, a “distance reference point” R that defines that the point is a measurement start point (0 km). Setting is required. Here, as is apparent from FIG. 6B, the distance reference point is normally set at the end position of the dummy fiber.

However, in the conventional OTDR device, when using a built-in dummy fiber, there is an exception that a fixed value (for example, 100 m as a distance reference point) is set in advance as a distance reference point. A distance reference point must be set. In addition, when using an external dummy fiber, the user needs to manually set the distance reference point.

Among these, when the built-in dummy fiber is used, the method of setting the distance reference point as a fixed value in advance has a certain degree of effectiveness because it is not necessary to set the distance reference point for each measurement. However, a manufacturing error may occur in the length of the dummy fiber in the dummy fiber manufacturing stage. On the other hand, if the user sets the distance reference point for each measurement in order to avoid such a problem, the operation is complicated and the measurement efficiency decreases.

The present invention has been made in view of these problems, and does not allow the user to set the measurement conditions for matching the wavelength, modulation mode, or the like of the light to be measured, but automatically sets the OTDR. An object is to provide an apparatus.

In order to solve such a problem, the invention of claim 1
In an OTDR apparatus that emits an optical pulse to a measured optical fiber through a dummy fiber, receives return light obtained from the measured optical fiber in response to the optical pulse, and obtains a temporal change in the intensity of the return light.
A waveform acquisition unit for receiving return light obtained from the optical fiber to be measured;
A search range setting unit that accepts input of information regarding the dummy fiber length, and sets a vicinity of the fiber length of the dummy fiber as a search range;
Search the search range among the waveforms acquired by this waveform acquisition unit, search execution unit for detecting Fresnel reflection ,
A reference position setting unit that sets a distance reference point of the measured fiber as the end position of the dummy fiber at the position of the Fresnel reflection detected by the search execution unit;

The invention according to claim 2 is the OTDR device according to claim 1,
The search range setting unit sets the search range based on a user instruction.

As described above, the distance reference point search range is determined based on the built-in dummy fiber length information, and the position of the event occurring in this range is determined as the distance reference point. An OTDR device installed with high accuracy can be provided.

Hereinafter, a configuration example of the OTDR apparatus of the present invention will be described with reference to FIG. However, the same components as those in FIG. The waveform acquisition unit 141 performs A / D conversion on the waveform input via the amplification unit 13 and stores the waveform. The search range setting unit 142 is not necessarily required in the case of an OTDR device using a built-in dummy fiber, but is used when an external dummy fiber is used. If the length of the dummy fiber is 100 m, for example, 99 m The search range is set to ˜101 m.

The search execution unit 143 searches for a position where an event (Fresnel reflection) occurs in the search range set by the search range setting unit 142, or in the case where a built-in dummy fiber is used. Here, the position where the event is detected is referred to as a distance reference point candidate. This distance reference point candidate is a connection location of the optical connector 7. The reference position setting unit 144 sets a distance reference point at the event position detected by the search execution unit 143.

  Next, the operation of FIG. 1 will be described with reference to FIGS. 2 is a flowchart for explaining the operation of FIG. 1, and FIG. 3 is a conceptual diagram of the measurement operation of FIG. The user gives an instruction to start measurement using an operation unit (not shown), measures the optical fiber 8 to be measured, and obtains a waveform (step 1 in FIG. 2, FIG. 3A).

In the case of the OTDR apparatus using the built-in dummy fiber 20, the search range of the distance reference point is determined based on the pre-recorded built-in dummy fiber length information (step 2, FIG. 3B). When an external dummy fiber is used, information regarding the dummy fiber length is input via the search range setting unit 142. In addition, the search range may be determined uniformly such as 1 m before and after the dummy fiber length, but may be determined by the search range setting unit 12 each time by the user.

Here, the search range of the distance reference point is obtained in accordance with a predetermined algorithm based on the pulse width and sampling resolution of the measurement waveform in addition to information on the dummy fiber length.

Any algorithm can be used as long as it can search the event occurrence position. For example, when the pulse width to be used is wide, the search range is set according to the distance resolution of the OTDR device. Similarly, if the sampling resolution is low and the event occurrence position cannot be accurately grasped, measures such as widening the search range so that the event occurrence position does not deviate from the search range are required. Become.

The search execution unit 143 searches the search range of the distance reference point and performs event detection (step 3, FIG. 3C). The position of the distance reference point candidate can be obtained by using an algorithm similar to the algorithm for obtaining the reflection event and the fusion event normally performed in the OTDR apparatus. Any algorithm can be used as long as an event can be detected. However, for example, as shown in FIG. 4, each measurement point is differentiated, and the inclination at each measurement point is obtained to determine that Fresnel reflection has occurred. .

The reference position setting unit 144 sets a distance reference point to the distance reference point candidate obtained by the search execution unit 143 (step 4, FIG. 3D).

Thus, the search range of the distance reference point is determined based on the dummy fiber length information, and the position of the event occurring in this range is determined as the distance reference point. Therefore, the distance reference point is automatically set as the end position of the dummy fiber 20. And it can set with high precision.

It is a structural example of the OTDR apparatus by this invention. 3 is a flowchart of an OTDR device according to the present invention. It is a conceptual diagram of operation | movement of the OTDR apparatus by this invention. It is a conceptual diagram of event detection. It is a structural example of the OTDR apparatus by a prior art. It is a conceptual diagram of the setting method of a distance reference point.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Timing generation part 2 Drive circuit 3 Light source 4 Optical fiber 5 Directional coupler 7 Dummy fiber 8 Optical fiber 11 to be measured 11 Optical fiber 12 Light receiving part 13 Amplifying part 15 Display part 20 Dummy fiber 140 Digital processing part 141 Waveform acquisition part 142 Search Range setting unit 143 Search execution unit 144 Reference position setting unit

Claims (2)

In an OTDR apparatus that emits an optical pulse to a measured optical fiber through a dummy fiber, receives return light obtained from the measured optical fiber in response to the optical pulse, and obtains a temporal change in the intensity of the return light.
A waveform acquisition unit for receiving return light obtained from the optical fiber to be measured;
A search range setting unit that accepts input of information regarding the dummy fiber length, and sets a vicinity of the fiber length of the dummy fiber as a search range;
Search the search range among the waveforms acquired by this waveform acquisition unit, search execution unit for detecting Fresnel reflection ,
An OTDR apparatus comprising: a reference position setting unit that sets a distance reference point of the fiber to be measured as a termination position of the dummy fiber at the position of the Fresnel reflection detected by the search execution unit. The OTDR apparatus according to claim 1, wherein the search range setting unit sets the search range based on a user instruction .

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