JPH0443935A - Measuring method for laying length of optical fiber cable - Google Patents

Abstract

PURPOSE:To accurately measure the laying length of the optical fiber cable from length information on the cable itself by generating a temperature difference at a known position of the fiber cable and measuring the laying length while setting the position as a measurement reference point. CONSTITUTION:While the temperature difference is generated at the start part A of a laying route, an OTDR device 3 makes a light pulse incident on an optical fiber of the optical fiber cable 2 from one end and when backward RAMAN scattered light which is generated in the optical fiber is photodetected, the intensity levels of Stokes light and anti-Stokes light which are two components of the Raman scattered light are detected as a function of the distance from the optical fiber incidence end to calculate their intensity ratio. Then the distance from the point (start part A) where temperature is maximum or minimum in this temperature distribution to the tip of the optical fiber cable 2 is found to obtain the wiring length l.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the installation length of an optical fiber cable.

[Prior Art] Generally, when an optical fiber cable is installed, it is necessary to specifically know the length of the installation. Conventionally, a method is known in which a marking indicating the length is attached to the optical fiber cable in advance at the time of manufacturing the cable, the marking is read at the time of installation, and the installation length is determined from the read value.

[Problems to be Solved by the Invention] However, optical fiber cables inevitably elongate due to tension applied during installation. For this reason, in the method of measuring the installation length using markings as described above, the reading value of the markings is distorted due to the elongation of the cable, making it difficult to accurately measure the installation length. Of course, it is also possible to actually measure using a measuring tape or the like, but this method requires a lot of effort.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for accurately and easily measuring the length of a laid optical fiber cable by using an OTDR technique, which eliminates the drawbacks of the prior art described above.

[Means for Solving the Problems 1] In order to achieve the above-mentioned object, the present invention provides an optical fiber cable with a temperature difference applied to a known position of the installed optical fiber cable.
The installation length of the optical fiber cable is measured using the OTDR device using the position I where the temperature difference is given as a measurement reference point.

[Operation] By applying a temperature difference to a known position of a laid optical fiber cable, the known position can be used as a measurement reference point, and the length of the laid optical fiber cable can be measured by the OTDR method. According to the OTDR method, the installed length of an optical fiber cable can be measured using the length information of the optical fiber cable itself, and even if the cable expands or contracts, it can be measured with high accuracy, including the amount of expansion or contraction. In addition, the optical fiber cable itself
Since it can be used as a length measurement sensor, there is no need to separately prepare a measurement device such as a tape measure, and the installation length can be easily determined.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In Fig. 1, 1 is a support structure such as a steel tower or telephone pole that is erected above the ground surface, 2 is an optical fiber cable that is supported by the structure 1, and 3 is the cable 2
4 is an OTDR device that measures the temperature distribution along the optical fiber cable 2 by injecting a light pulse into the optical fiber and using the backscattered light generated therein, 4 heating or cooling the optical fiber cable 2 from its outer circumference; This is a temperature difference providing device that provides a temperature difference with respect to the outside air temperature.

The optical fiber cable 2 is wound on a drum or the like in advance, and one end side is sent out in sequence from the winding part 2a, and a hook is passed between the support structures 1.1 and 1.1 along the installation route. Therefore, the actual installation length of the optical fiber cable 2 to be measured is from the cable 2 delivery part from the winding fi section 2a, that is, the starting point A of the installation route, to the tip of the installed optical fiber cable 2.

In this embodiment, in order to measure the installation length of this optical fiber cable 2 on the scale of the cable 2 itself, O
The TDR method is adopted. However, the distance information obtained by the OTDR method is expressed with the end of the optical fiber cable 2 as a reference, and for some reason this distance information cannot be correlated with the starting point A above. ,
It is not possible to distinguish between the optical fiber cable 2 that is still in the winding section 2a and the optical fiber cable 2 that has already been laid, and the laying length cannot be measured.Therefore, in the present invention, the starting point A of the laying route is By providing a temperature difference applying device 4 at a known position (in this embodiment, on the starting point A) and applying a temperature difference to the cable 2, the distance information and the starting point 2a are associated with each other. , creates a measurement reference point when measuring the installation length using the OTDR method.

Now, with a temperature difference being applied to the starting point A of the installation route,
When the OTDR device 3 inputs a light pulse into the optical fiber of the optical fiber cable 2 from one end and receives the backward Raman scattered light generated therein, the two components of the Raman scattered light, Stokes light and anti- The intensity level of each Stokes beam is detected as a function of the distance from the input end of the optical fiber, and the intensity ratio of these is calculated.Normally, the intensity ratio of the Stokes beam and the anti-Stokes beam is determined purely by temperature. Since it is a function, then
Based on this intensity ratio, the temperature distribution along the optical fiber cable 2 is determined. At this time, since a temperature difference is applied to the cable 2 at the starting point A as described above,
The temperature distribution obtained by the OTDR device 3 is as shown in FIG. 2(b). That is, the temperature of the cable 2 at the starting point A appears to change more or less than the temperature in other areas. Therefore, in this temperature distribution, the distance from the position where the temperature is maximum or minimum (starting point A) to the end of the optical fiber cable #it is determined, and the installation length Δj is obtained. A temperature difference is given to the starting point A, which is the starting point of the fiber cable 2, to create a measurement reference point there, and the temperature distribution along the optical fiber cable 2 is determined by the OTDR method, and from that distribution, the laying length Δ is determined. Since the distance is measured, the installation length Δj can be determined from the distance information of the optical fiber pull 2 itself. Therefore, even if the optical fiber cable 2 is stretched during or after installation, the length Δj of the cloth 8 can be measured in a manner that includes the stretch, and high accuracy of measurement can be achieved.

Moreover, the measurement of the installation length Δj as described above is performed using the OTDR device 3 at the winding part 2a (tl end) of the optical fiber cable 2.
This can be done by simply installing the temperature difference imparting devices 4 at the starting point A of the installation route, so there is no need to measure the part of the optical fiber cable 2 that has already been installed using a separate measurement device, and it is possible to Only by acting on the cable 2, the installation length Δ1 can be easily determined. Moreover, the installation length ΔJ of the optical fiber cable 2 installed along any route can be easily measured.

The measurement of the installation length may be carried out at the time when the installation work of the optical fiber cable 2 is completed, or may be carried out at an appropriate time as the installation work progresses.

FIG. 2 shows a second diagram showing how the temperature distribution of the optical fiber cable 2 changes over time as the optical fiber cable 2 is laid.
Figure (a) is a temperature distribution diagram just before laying the cable 2. When the installation of the optical fiber group 2 is started from this state, the location where the temperature difference is applied by the device 4 moves to the inside of the cable 2. , changes as shown in FIG. 2(b).

In the above embodiment, the temperature difference imparting device 4 was provided at the starting point A of the installation route, but it may be provided at any position. In short, it suffices if the position to which the temperature difference is applied is known with respect to the starting point A of the installation route so that it can be used as a measurement reference point during OTDR measurement.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects are achieved.

By applying a temperature difference to a known position on the optical fiber cable and measuring the installation length using the OTDR method using that position as the measurement reference point, it is possible to accurately determine the installation length of the optical fiber couple from the length information of the cable itself. Not only can it be measured, but it can also be easily measured using the cable itself as a sensor.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a measurement system for implementing the optical fiber cable installation length measurement method of the present invention, and FIG. 2 is a diagram showing the temperature distribution characteristics of an optical fiber cable obtained by an OTDR device. A) shows the image immediately before the optical fiber cable is laid, and (b) shows the image after the optical fiber cable is laid. In the figure, 1 is a support structure, 2 is an optical fiber cable, 3 is an OTDR device, 4 is a temperature difference imparting device, A is the starting point of the installation route, and Δj is the installation length. Patent applicant: Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani (Q) (b) Figure 2

Claims (1)

[Claims] 1. With a temperature difference applied to a known position of the installed optical fiber cable, the installed length of the optical fiber cable is measured using the OTDR device using the position where the temperature difference is applied as a measurement reference point. A method for measuring the installation length of optical fiber cables.