JP3364899B2 - Optical cable abnormality monitoring method and monitoring system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring method and a monitoring system for optical fiber cables for communication.

When an abnormality occurs in an optical fiber cable for communication, as a technique for detecting the abnormality at a stage before the loss of the optical fiber increases and communication cannot be performed, and for use in preventive maintenance, there is a rear Brillouin. There is a method to measure the distribution of the scattering gain spectrum in the longitudinal direction of the optical fiber. However, this method requires a long time for measurement and analysis of the measured data and judgment of whether there is any abnormality. It is only used for the purpose of detecting a static strain abnormality that occurs later. There is a demand for an optical fiber cable monitoring system that can monitor an accident of the optical fiber cable that leads to a disconnection failure in a short time.
Until now, such a system did not exist.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to detect this abnormality and give an alarm at the stage before the communication is lost due to an increase in the loss of the optical fiber when the optical fiber cable is broken. It is to provide a monitoring method and a monitoring system capable of issuing

[0004]

In order to achieve the above object, an optical cable abnormality monitoring method of the present invention is an optical cable abnormality monitoring method for monitoring an abnormality occurring in an optical fiber cable. The step of injecting light of a predetermined polarization state from one end of the fiber, the step of detecting the total light intensity of the light emitted from the other end of the optical fiber, and the specific polarization of the light emitted from the other end of the optical fiber A step of detecting the light intensity of the component, a step of detecting the difference between the total light intensity and the light intensity of the specific polarization component as a time series, and a step of obtaining the fluctuation speed of the difference from the time series of the detected difference. And a step of performing statistical processing on the variation speed of the obtained difference and determining whether or not an abnormality has occurred in the optical fiber based on the result of the statistical processing. According to the present invention as described above, by measuring the fluctuation speed of the polarization state of the light propagating in the optical fiber, the statistical property of the fluctuation speed is used to cause an accident such as disconnection. At times, it is possible to easily detect an abnormality that the optical fiber covers before cutting or the like.

The optical cable abnormality monitoring system of the present invention also monitors a light source for generating light in a predetermined polarization state, a means for causing the light in the predetermined polarization state to enter an optical fiber to be monitored, and monitoring. Means for detecting the total light intensity of the light emitted from the optical fiber, a means for detecting the light intensity of a specific polarization component of the light emitted from the optical fiber, and the detected total light intensity and the specific polarization component The difference with the intensity of the difference is detected as a time series, the fluctuation speed of the difference is obtained, statistical processing is executed for the fluctuation speed of the difference, and whether an abnormality occurs in the optical fiber based on the result of the statistical processing. And data processing means for determining whether or not.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an embodiment of a monitoring system of the present invention, 1 is a laser light source, 2 is a polarizer, 3 is an optical output port, 4 is an optical input port, 5 is an optical coupler, and 6
Is a polarizer, 7 and 8 are light intensity measuring devices, 9 is a data processing unit, 10 is an alarm signal output port, and 11 is an optical cable to be measured.

In such a system according to the present invention, only the linearly polarized component of the laser light output from the light source 1 is cut out by the polarizer 2 of the transmitting section, output from the optical output port 3, and the measured light is output. Input to the fiber 11. The monitoring light propagating through the optical fiber 11 to be measured is guided from the optical input port 4 of the receiving section to the inside of the receiving section.

The monitoring light guided into the receiving section is branched by the optical coupler 5. One of the branched monitoring lights is directly guided to the light intensity measuring device 8 and the total light intensity Po is measured. Only the linearly polarized component in one arbitrary direction of the other branching supervisory light is cut out by the polarizer 6 and then guided to the light intensity measuring device 7 to measure the light intensity PL. FIG. 2 shows an example of the time series of the difference P0-PL between the total light intensity Po and the light intensity PL in the normal state, and FIG. 3 shows an example in the abnormal state (when the optical fiber is buried).

The optical cable abnormality monitoring system according to the present invention can detect an abnormality in the cable when the total light intensity P0 is stable and no abnormality appears in optical communication as shown in FIG. This is because when the degree of strain applied to the optical fiber in the cable changes due to the disturbance such as vibration applied to the optical cable 11 to be measured, the birefringence of the optical fiber also changes and the propagation in the optical fiber is monitored. Since the polarization of light rotates according to the amount of birefringence fluctuation, the total light intensity P0
And the change in the difference P0-PL between the light intensity PL of the linearly polarized wave component in any one direction of the monitoring light corresponds to the state of rotation of the polarization of the monitoring light.

In a disconnection accident or the like, a disturbance is applied to the optical cable and the optical fiber.
It is reflected in 0-PL. However, the optical fiber actually laid is placed in an environment where various disturbances as well as the disturbance applied at the time of the cutting accident are added, and therefore the cutting accident is detected from the fluctuation of the difference P0-PL in the light intensity due to various causes. It is necessary to extract and detect only the disturbance added at the time. In the present invention, this is realized by the method described below.

That is, as shown in FIGS. 2 and 3, the total light intensity P0 is extremely stable both in the normal state and in the abnormal state, but the difference P0- PL
Shows a slow and smooth fluctuation in the normal range, but a chaotic fast fluctuation in the abnormal case. FIGS. 4 and 5 show histograms relating to the magnitude of the fluctuation speed created from the time series of the fluctuation speed of the difference P0-PL of the light intensities under normal and abnormal conditions, respectively. According to this, it can be seen that the magnitude of the fluctuating speed has a normal distribution in the normal state, but it greatly deviates from the normal distribution of the fluctuating speed in the abnormal case. This means that at the time of abnormality, the fluctuation speed is statistically abnormal with reference to the normal time. In the present invention, such a change is detected.

In the data processing unit 9 in the embodiment of the monitoring system according to the present invention shown in FIG.
-The magnitude of the fluctuation speed of PL is obtained for each measurement, and it is statistically judged whether or not there is an abnormality. If judged as abnormal, an alarm signal output port 10 outputs an alarm signal.

For example, in the example shown in FIG. 4, since the variation speed of the light intensity difference P 0 -PL has a normal distribution with a standard deviation of 0.07 in a normal state, a series of 10 variation speed data is obtained. The probability that there are three or more data in which the magnitude of the fluctuation speed of the light intensity difference P0-PL is 0.2 dB / min or more is statistically determined to be 0.00075%, and this low probability Nevertheless, if such a situation actually occurs, it can be statistically judged to be abnormal. By applying such a criterion to the data processing unit 9, it is possible to quickly and easily detect the presence or absence of an abnormality.

[0014]

As described above in detail, according to the present invention, when an accident such as cutting of the optical fiber cable for communication occurs, the cable is lost at a stage where the loss of the optical fiber in the cable is not increased. It is possible to quickly detect the abnormal condition in a short time of about several minutes.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of a monitoring system of the present invention.

FIG. 2 is a diagram showing an example of a time series of a difference P0-PL between a total light intensity Po and a light intensity PL in a normal state.

FIG. 3 is a diagram showing an example of a time series of the difference P0-PL between the total light intensity Po and the light intensity PL at the time of abnormality.

FIG. 4 is a histogram relating to the magnitude of fluctuation speed created from a time series of fluctuation speeds of the light intensity difference P0-PL in a normal state.

FIG. 5 is a histogram relating to the magnitude of the fluctuation speed created from the time series of the fluctuation speed of the difference P0-PL of the light intensity at the time of abnormality.

[Explanation of symbols]

1 laser light source 2 Polarizer 3 optical output ports 4 optical input ports 5 Optical coupler 6 Polarizer 7,8 Light intensity measuring instrument 9 Data processing unit 10 Alarm signal output port 11 Optical cable to be measured

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Yoshida 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Junichi Masuda 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Nihon Telegraph and Telephone Corporation (56) Reference JP-A-7-83792 (JP, A) Special Table H4-503997 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) G01M 11/00-11/08

Claims (4)

(57) [Claims] 1. A method of monitoring an abnormality of an optical fiber cable, the method including: a step of injecting light having a predetermined polarization state from one end side of the optical fiber to be monitored; and the other end of the optical fiber. The total light intensity of the light emitted from the optical fiber, the step of detecting the light intensity of a specific polarization component of the light emitted from the other end of the optical fiber, and the total light intensity and the light intensity of the specific polarization component. Of the difference as a time series, a step of obtaining the fluctuation speed of the difference from the time series of the detected difference, statistical processing is performed on the fluctuation speed of the obtained difference, and the optical speed is calculated based on the result of the statistical processing. And a step of judging whether or not an abnormality has occurred in the fiber. 2. The method of monitoring an abnormality of an optical cable according to claim 1, wherein, as the statistical processing, a relationship between a variation speed of the difference and a frequency is obtained, and the occurrence of abnormality is determined based on the result. Optical cable abnormality monitoring method. 3. A light source for generating light of a predetermined polarization state, means for causing the light of the predetermined polarization state to enter an optical fiber to be monitored, and all light emitted from the optical fiber to be monitored. A means for detecting the intensity, a means for detecting the light intensity of a specific polarization component of the light emitted from the optical fiber, and a time series difference between the total intensity of the detected light and the intensity of the specific polarization component. , And obtain the fluctuation speed of the difference,
An optical cable abnormality monitoring system, comprising: data processing means for performing statistical processing on the variation speed of the difference and determining whether or not an abnormality has occurred in the optical fiber based on the result of the statistical processing. 4. The optical cable abnormality monitoring system according to claim 3, wherein the data processing means obtains a relationship between the variation speed and frequency of the difference as statistical processing, and determines the occurrence of abnormality based on the result. An optical cable abnormality monitoring system characterized by: