JP3224762B2 - Fiber optic cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable, and more particularly to an optical fiber cable in which cable abnormality detecting means is integrally provided.

[0002]

2. Description of the Related Art In an optical fiber cable, when an external force such as lateral pressure is applied to an optical fiber core, if the external force is large, a slight bending (microbending) occurs in the optical fiber, and the transmission loss increases and the performance is reduced. Consideration is given to cable construction and manufacturing. For example, there is a cable buried in the ground where the cable body of an optical fiber cable is provided with a flexible spiral metal tube as an exterior. In addition, a spiral metal pipe may be applied to an optical fiber cable laid particularly in a place where lateral pressure is likely to be applied.

Japanese Utility Model Application Laid-Open No. 60-107804 discloses a method for detecting a damage caused by excavation of an underground cable, a gas pipe, a water pipe and the like, or for monitoring an abnormality due to land subsidence. Discloses an "underground buried object abnormality monitoring system". That is, according to this publication, a structure in which a line sensor provided with an optical fiber is attached to the outer surface of a spiral metal tube into which an underground object such as an underground cable is inserted is shown. I have. When an underground cable or the like is buried in the ground and the line sensor receives an external force such as lateral pressure, the light emitted from the light emitting element disposed at one end of the optical fiber is changed to the light receiving element disposed at the other end of the optical fiber. Abnormalities can be easily detected by capturing the transmission loss.

[0004]

However, when the present inventors applied the above-mentioned system to the above-mentioned optical fiber cable, in this system, an external force such as lateral pressure extends to the cable body inside the spiral metal tube. It was found that it was not possible to judge whether the size was large, or whether the external force was detected but was absorbed by the outer surface of the spiral metal tube and did not reach the cable body. In other words, the effect of external force is extremely large in optical fiber cables, unlike gas pipes, etc., so it is important to accurately observe and understand the current situation due to this external force and to predict future effects, but the above system is important. It was impossible to fulfill such a request. Further, in the configuration of the above system, a coating layer as a jacket is provided on the outer surface of the optical fiber serving as a line sensor. However, the transmission loss of the optical fiber is increased at the time of manufacturing the coating layer, so that accurate detection of the external pressure cannot be performed. Make it possible,
Alternatively, it was considered that detection could not be performed at all.
The present invention has been made in view of the above circumstances, and provides an optical fiber cable that can easily detect an abnormality in a cable laid by detecting a change in transmission loss due to an external force such as lateral pressure, and can also eliminate inconvenience in manufacturing. It is another object of the present invention to enable quick determination and response to the influence on the transmission characteristics of an optical fiber cable.

[0005]

In order to achieve the above object, an optical fiber cable according to the present invention has a spiral metal tube fitted on a cable body and a coating layer formed on the outer peripheral surface of the spiral metal tube. In the laminated optical fiber cable,
An abnormality detecting optical fiber in which transmission loss increases due to external pressure is provided between the cable main body and the spiral metal tube.

[0006] When an external force such as lateral pressure acts on the optical fiber cable and its size reaches the cable body via the coating layer and the helical metal tube, the inner wall surface of the valley portion of the helical metal tube is formed. And the outer peripheral surface of the cable body presses the optical fiber. As a result, the transmission loss of the optical fiber for abnormality detection increases. By measuring the transmission loss, the external pressure applied to the optical fiber cable is detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical fiber cable according to the present invention will be described below with reference to the drawings.
FIG. 1 is an end perspective view of an optical fiber cable according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part of the cable. As shown in FIGS. 1 and 2, the optical fiber cable 1 has a helical metal tube 4 fitted on a cable main body 2 and a coating layer 6 serving as an outer sheath on the outer peripheral surface of the helical metal tube 4. And is mainly applied for underground burial. The cable body 2
Although not shown in detail, has a structure in which a tension member is provided at the center, a multi-core optical fiber is twisted around the tension member, and this is covered with a cushioning material to form an inner sheath.

[0008] Between the cable body 2 and the spiral metal tube 4,
That is, inside the helical metal tube 4, an abnormality detecting optical fiber (hereinafter, simply referred to as an optical fiber) 8, which is a characteristic constituent member of the present invention and acts as a line sensor, is disposed in the longitudinal direction of the cable main body 2. It is arranged in a state of being vertically attached linearly along the direction. That is, this optical fiber 8
The transmission loss increases due to external force such as lateral pressure acting on the optical fiber cable 1. In addition, between the cable main body 2 and the helical metal tube 4, processing can be performed without applying a load to the optical fiber 8 at the time of forming the helical metal tube 4. A plurality of (two in this embodiment) vinyl strings 10 that can be regulated are arranged in a straight line like the optical fiber 8.

The helical metal tube 4 is formed of an aluminum material, and the coating layer 6 has excellent mechanical properties. However, when an external force is generated, the external force is transmitted through the helical metal tube 4 to the inner side. It is formed of a material that is flexible enough to transmit to an optical fiber.

The optical fiber cable 1 having the above configuration is
The optical fiber 8 is attached to the long cable body 2.
After arranging the vinyl string 10 vertically, the spiral metal tube 4 is provided so as to be covered, and the outer peripheral surface of the spiral metal tube 4 is further provided with a coating layer 6. Unlike the prior art, the optical fiber cable 1 manufactured in this way can be manufactured without applying a side pressure to the optical fiber 8, so that the transmission loss of the optical fiber 8 does not increase.
Therefore, a suitable optical fiber cable with cable abnormality detecting means can be realized.

The optical fiber cable 1 thus manufactured is buried underground for installation. However, when an abnormal force is applied to the spiral metal tube 4 from the outside of the spiral metal tube 4 via the coating layer 6 by laying, the inner wall surface 4a of the valley portion of the spiral metal tube 4 causes the optical fiber 8 to move. It is pressed onto the outer peripheral surface of the cable body 2. As a result, the transmission loss of the optical fiber 8 increases due to the external pressure. The external pressure is detected by measuring the transmission loss.

Although various measurement methods are well-known for measuring the transmission loss, in the present embodiment, when light is incident on the optical fiber 8, Rayleigh scattered light generated by minute fluctuations in the refractive index of the core glass is measured. Of these, by detecting the backscattered light component propagating in the core and returning to the incident end side, the backscattered light that can measure the longitudinal homogeneity of the optical fiber loss, the position of the break point, the value of the transmission loss, etc. Perform by the method. Commercially available OT as a test device for measuring transmission loss by the backscattered light method
A DR (Optical Time Domain Reflectometer) can be used.

The OTDR 20, as shown in FIG.
Generally, from a detector 25 including a light source 21 and a light receiver 23, a signal processing device 27 or a display or recording device 2
9 are all built-in. Therefore, in practice, simple measurement can be performed simply by connecting the measured optical fiber 8 to the measuring device 20 via an appropriate excitation system as required. In addition, since the measurement by the OTDR 20 can be performed almost non-destructively from one end of the optical fiber 8, it is suitable for the test after the installation of the optical fiber cable on site.

The waveform observed by the backscattered light method is as follows:
OTD in which the power of the detected backscattered light is shown on the vertical axis and the time until the light pulse returns to the incident end is shown on the horizontal axis.
It is shown as a substantially straight line on the display of R20. Then, the transmission loss of the optical fiber 8 is measured as the inclination of this straight line. Accordingly, when a uniform external pressure acts on the entire area of the optical fiber 8, the inclination of the straight line increases, and when the optical fiber 8 receives local external pressure and the transmission loss changes, the change in the inclination of the straight line at that point. Observed as the resulting waveform. By measuring these inclinations, the magnitude of the external pressure can be known.

FIGS. 3 and 4 show modifications of the above embodiment. That is, in the configuration shown in FIG. 3, the optical fiber 8 and the vinyl string 10 are spirally wound around the outer peripheral surface of the cable main body 2 at a predetermined pitch. In FIG. 4, the optical fiber 8 is attached along the longitudinal direction on the outer peripheral surface of the cable body 2 with a constant sinusoidal curve. In addition, the vinyl string 10 is disposed linearly. In these modified examples, the radius of curvature of the optical fiber is specified to be 3 cm or more, so that unnecessary transmission loss is not reduced.

By configuring the optical fiber cable as in each of the above modifications, the amount of change in external force such as lateral pressure received from all directions of the optical fiber cable or the position of the change point can be measured on the entire peripheral surface of the fiber cable. can do.

[0017]

As described above, in the optical fiber cable according to the present invention, since the cable abnormality detecting means is integrally provided, the cable is laid by observing the transmission loss measured by the abnormality detecting means. Abnormality such as cable damage or ground subsidence that occurs at the time of or after installation can be easily detected. Further, by detecting the influence on the transmission characteristics of the optical fiber cable while the influence is small, and responding to the influence, it is possible to eliminate the occurrence of a serious situation. In particular, by arranging the optical fiber inside the spiral metal tube, it is possible to accurately determine the magnitude of the external pressure. Moreover, the optical fiber cable can be favorably manufactured without causing a reduction in transmission loss in the manufacturing process.

[Brief description of the drawings]

FIG. 1 is an end perspective view of an optical fiber cable showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the optical fiber cable of FIG.

FIG. 3 is an end perspective view showing another embodiment of the optical fiber cable of the present invention.

FIG. 4 is an end perspective view showing still another embodiment of the optical fiber cable of the present invention.

FIG. 5 is a configuration diagram of a transmission loss measurement test device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber cable 2 Cable main body 4 Spiral metal tube 6 Coating layer 8 Optical fiber for abnormality detection 10 Vinyl string 20 Transmission loss test device (OTDR)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-196685 (JP, A) JP-A-4-249207 (JP, A) JP-A 5-73549 (JP, U) JP-A-60- 107804 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/00 G02B 6/44

Claims (5)

(57) [Claims] 1. An optical fiber cable in which a spiral metal tube is fitted on a cable main body and a coating layer is laminated on an outer peripheral surface of the spiral metal tube, wherein between the cable main body and the spiral metal tube. An optical fiber cable having an abnormality detecting optical fiber in which transmission loss increases due to external pressure. 2. The optical fiber cable according to claim 1, wherein the abnormality detecting optical fiber is vertically attached along a longitudinal direction of the cable main body. 3. The optical fiber cable according to claim 1, wherein the abnormality detecting optical fiber is spirally wound around the outer peripheral surface of the cable body at a predetermined pitch. 4. The optical fiber cable according to claim 1, wherein the optical fiber for abnormality detection is provided along a longitudinal direction on the outer peripheral surface of the cable body with a constant sine wave curve. 5. The transmission loss test device (OTDR) is connected to one end of the optical fiber for abnormality detection, and transmission loss is measured by a backscattered light method.
Optical fiber cable as described.